sexta-feira, 30 de março de 2012

Anti IL-17 inibe psoriase. New England Journal of Medicine

Anti–Interleukin-17 Monoclonal Antibody Ixekizumab in Chronic Plaque Psoriasis

Craig Leonardi, M.D., Robert Matheson, M.D., Claus Zachariae, M.D., D.M.Sci., Gregory Cameron, Ph.D., Linda Li, M.S., Emily Edson-Heredia, M.P.H., Daniel Braun, M.D., Ph.D., and Subhashis Banerjee, M.D.
N Engl J Med 2012; 366:1190-1199March 29, 2012

Psoriasis vulgaris (plaque psoriasis) is a chronic, frequently painful, and often debilitating skin disorder. The estimated prevalence of diagnosed psoriasis in the United States is 3%, with approximately 17% of these patients having moderate-to-severe plaque psoriasis.1 Psoriasis is characterized by inflammation and keratinocyte hyperproliferation2 thought to be the pathological consequence of a T-cell–mediated immune response to an as-yet unidentified autoantigen. Studies have shown that a subgroup of CD4+ T cells, type 17 helper T (Th17) cells, may play a specific pathological role in psoriasis.3 Type 17 helper T cells secrete a number of proinflammatory cytokines, including interleukin-17A, a member of the proinflammatory interleukin-17 cytokine family.4,5 Specific inhibition of interleukin-17A represents a novel, targeted approach to psoriasis treatment. Ixekizumab (LY2439821) is a humanized IgG4 monoclonal antibody that neutralizes interleukin-17A (also known as interleukin-17). In a phase 2 study, we evaluated the safety and efficacy of ixekizumab administered subcutaneously in patients with chronic moderate-to-severe plaque psoriasis.

Methods

Study Design

This double-blind, multicenter, randomized, dose-ranging study was designed to evaluate the safety and efficacy of multiple subcutaneous doses of ixekizumab in patients with chronic moderate-to-severe plaque psoriasis, as defined in the study protocol (available with the full text of this article at NEJM.org). The protocol was approved by the investigational review board at each site. All patients provided written informed consent. The first patient visit occurred on April 19, 2010; the last, on March 17, 2011. The study was designed jointly by consultant experts in psoriasis and representatives of the sponsor, Eli Lilly. Data were collected by the investigators, gathered by Parexel International, and analyzed by the sponsor. All authors contributed to the interpretation of and vouch for the accuracy and completeness of the data. The principal investigator and coauthors from the sponsor wrote the manuscript, with medical writing support paid for by the sponsor. All authors made the decision to submit the manuscript for publication. The investigators, participating institutions, and sponsor agreed to maintain confidentiality of the data.

Study Patients

Eligibility criteria were an age of 18 years or older, chronic moderate-to-severe plaque psoriasis for at least 6 months before randomization, scores of at least 12 on the psoriasis area-and-severity index (PASI, on which scores range from 0 to 72, with higher scores indicating more severe disease)6 and at least 3 on the static physician's global assessment (on which scores range from 0 [clear of disease] to 5 [severe disease]) at the screening and baseline visits, and psoriasis involving at least 10% of body-surface area at the screening and baseline visits. Exclusion criteria were the presence of nonplaque psoriasis, a clinically significant flare of psoriasis during the 12 weeks before randomization, an active infection within 5 days before administration of study drug, a recent serious systemic or local infection requiring hospitalization or antibiotic therapy, receipt of conventional systemic psoriasis therapy or phototherapy within the previous 4 weeks, receipt of topical psoriasis treatment within 2 weeks before randomization, or use of any biologic agent recently or concurrently with the study drug. Patients were randomly assigned to receive subcutaneous injections of placebo or 10 mg, 25 mg, 75 mg, or 150 mg of ixekizumab at 0, 2, 4, 8, 12, and 16 weeks. Patients were permitted to use topical moisturizers or emollients, bath oils, oatmeal bath preparations, or topical salicylic acid preparations for skin conditions during the study, as needed. Other medications could be used as medically necessary. Weak topical steroids (class VI or VII only) were permitted for use limited to the face, axillae, or genitalia as required. Topical medications were to be discontinued approximately 24 hours before visits requiring PASI assessments. No other topical preparations were allowed in the 2 weeks before randomization or during the study unless medically required to treat an adverse event.

End Points

The primary objective was to test whether ixekizumab treatment was superior to placebo, as measured by the proportion of patients who achieved a reduction in the PASI score by at least 75% over baseline at 12 weeks, and to estimate the percentage of reduction in the PASI score in each treatment group, by means of regression techniques. The PASI score combines assessments of the extent of involvement of body-surface area in psoriasis on four anatomical regions (head, trunk, arms, and legs) and the severity of desquamation, erythema, and plaque induration or infiltration (thickness) in each region, yielding an overall score of 0 for no psoriasis to 72 for the worst possible psoriasis.6 Secondary end points included reduction in the PASI score by at least 90% or by 100% over baseline; the score on the static physician's global assessment, which is used to grade psoriasis lesions at a given time point (with 0 for clear of disease and 5 for severe disease); the joint-pain visual-analogue scale (VAS), which assesses joint pain from psoriatic arthritis reported by the patient (score range, 0 [no pain] to 100 [severe pain]); the Nail Psoriasis Severity Index (NAPSI), which scores the nail matrix and nail bed of each finger and toe (score range, 0 [no nail psoriasis] to 160 [worst possible nail psoriasis]); and the Psoriasis Scalp Severity Index (PSSI), which yields a composite score of erythema, induration, and desquamation of scalp lesions and the extent of the scalp area involved (range, 0 [no psoriasis] to 72 [worst possible scalp psoriasis]). These end points were ascertained at baseline and at 1, 2, 4, 6, 8, 12, 16, and 20 weeks. Two additional secondary end points (both patient-reported) were collected only at weeks 0, 8, and 16: an itch VAS (on which scores range from 0 [no itching] to 100 [severe itching]) and the Dermatology Life Quality Index (DLQI, on which scores ranging from 0 to 30, with higher scores indicating worse health-related quality of life).7 A 5-point change from baseline in the DLQI score is considered clinically relevant.8 Adverse events were defined as those that first occurred or worsened after randomization. Adverse events and routine laboratory values were monitored and evaluated through 20 weeks. Adverse events of special interest included allergic reactions or hypersensitivities, injection-site reactions, and infections. Laboratory abnormalities of special interest included cytopenias (leukopenia, neutropenia, and thrombocytopenia) and liver biochemical-test elevations (of alanine aminotransferase, aspartate aminotransferase, bilirubin, and alkaline phosphatase).

Statistical Analysis

Analyses of baseline characteristics included all randomly assigned patients. Efficacy analyses included patients who received at least one dose of the study drug and had at least one postbaseline efficacy assessment. Safety analyses were conducted on data from all patients who received the study drug. Missing data for the primary end point at 12 weeks were imputed by means of the last-observation-carried-forward method, whereby missing data points are replaced by the last available observation; in a separate analysis, missing data were imputed with the use of nonresponse imputation, in which patients who discontinued early, regardless of the status of response at the time of discontinuation, or who had a missing value at any time point had data imputed as a nonresponse at that time point. For the primary analysis, we expected to observe a reduction in the PASI score by at least 75% over a 12-week period in at least 70% of patients receiving the optimal ixekizumab dose and in 10% of patients receiving placebo. On this basis, we estimated that pairwise comparison of an ixekizumab group and the placebo group would have more than 99% power, with the use of a two-sided Fisher's exact test at the 0.05 significance level. The rates of reduction in the PASI score by at least 75% or 90% or by 100% and the scores on the static physician's global assessment were summarized for each group and compared between each study group and the placebo group. Numerical data, other than in the primary analysis, were analyzed by means of analysis of variance or covariance, and categorical data were analyzed with the use of the chi-square or Fisher's exact test.

Results

Study Patients

For the 142 patients, baseline characteristics for the dosing groups were similar (Table 1Table 1Baseline Characteristics of the Patients, According to Study Group.). By 20 weeks, 13 patients (9%) had discontinued treatment; the most common reason for discontinuation (in 4 [3%]) was development of an adverse event (Figure 1Figure 1Enrollment and Follow-up of the Study Patients through 12 Weeks.). Concomitant topical glucocorticoids were used before the primary end point (at 12 weeks) in 1 patient in the 150-mg ixekizumab group, who used desoximetasone ointment from 8 to 10 weeks for an adverse event of contact dermatitis, as permitted in the protocol.

Efficacy

At 12 weeks, reduction in the PASI score by at least 75% (the primary outcome) or 90% occurred in significantly more patients in the 25-mg, 75-mg, and 150-mg ixekizumab groups (P<0.001 for each vs. placebo) (Table 2Table 2Study End Points at 12 Weeks, According to Study Group. and Figure 2Figure 2Time Course of Clinical Responses as Measured by the Psoriasis Area-and-Severity Index (PASI) and Static Physician's Global Assessment (sPGA) through 20 Weeks, According to Study Group.). In addition, significantly more patients in the 75-mg and 150-mg groups had a reduction in the PASI score by 100% (complete skin clearance) (P<0.001 for each vs. placebo) (Table 2 and Figure 2). When the data were analyzed with the use of nonresponse imputation, the results were identical to the results obtained by means of the last-observation-carried-forward method. In addition, significantly higher percentages of patients in the three highest ixekizumab dose groups had a static physician's global assessment score of 0 (clear of disease) or of 0 or 1 (minimal disease) (P<0.05 for each dose and score group vs. placebo) (Table 2 and Figure 2; and Figure 1 in the Supplementary Appendix, available at NEJM.org). Significant differences between the two highest-dose groups and the placebo group were seen as early as 1 week in PASI scores, and significant differences between the 150-mg group and the placebo group were seen as early as 2 weeks in reduction in the PASI score by at least 75% and static physician's global assessment scores of 0 or 1. Differences with the placebo group were sustained through 20 weeks for all clinical measures (Figure 2). Among patients with scalp psoriasis, significant reductions in the PSSI score were observed in the 25-mg, 75-mg, and 150-mg ixekizumab groups versus placebo at 12 weeks (Table 2 and Figure 3Figure 3Percent Change in Nail Psoriasis Severity Index (NAPSI) and Psoriasis Scalp Severity Index (PSSI) Scores through 20 Weeks, According to Study Group.) and were sustained through 20 weeks. Among patients with nail psoriasis, significant reductions in the NAPSI scores were observed as early as 2 weeks in the 75-mg ixekizumab group versus placebo, and these effects were also sustained through 20 weeks (Figure 3). Among patients who reported having psoriatic arthritis, significant reductions from baseline were observed in the 150-mg ixekizumab group at 12 weeks (Table 2), as measured on the joint-pain VAS, and this reduction was sustained through 20 weeks (not shown). Significant reductions in the mean (±SD) DLQI scores were detected at 8 weeks in the 150-mg ixekizumab group (−7.8±5.7), the 75-mg ixekizumab group (−8.5±5.1), and the 25-mg ixekizumab group (−7.1±6.5) as compared with placebo (−2.4±4.4) (P<0.001 for all comparisons). These significant reductions were sustained through 16 weeks (P<0.001 for all comparisons). In addition, at 16 weeks, significantly more patients had a DLQI score of 0 in the 150-mg, 75-mg, and 25-mg ixekizumab groups (39.3%, 37.9%, and 31.0%, respectively) as compared with placebo (0%, P<0.05 for all comparisons). The 25-mg, 75-mg, and 150-mg treatment groups also had significant reductions in itch severity (VAS scores) as compared with the placebo group from 8 through 16 weeks (P<0.001) (data not shown).

Safety

There were no reported serious adverse events, including deaths, in any group. The frequency of adverse events was similar between the combined ixekizumab groups and the placebo group (Table 3Table 3Adverse Events during the Study Period (through 20 Weeks), According to Study Group.). The most common adverse events were nasopharyngitis, upper respiratory infection, injection-site reaction, and headache. A total of four patients discontinued the study because of the following adverse events: hypertriglyceridemia (one patient receiving placebo), peripheral edema (one patient receiving 10 mg of ixekizumab), hypersensitivity (one patient receiving 10 mg of ixekizumab), and urticaria (one patient receiving 25 mg of ixekizumab). Across all four ixekizumab groups, six patients reported injection-site reactions; none were severe, and no patients discontinued treatment because of these reactions. There were no instances of anaphylactic reaction, angioedema, or major cardiovascular events (e.g., cardiovascular death, nonfatal myocardial infarction, or stroke). No serious infections, including mycobacterial or systemic fungal infections, were reported. There were no significant changes in mean absolute neutrophil counts with ixekizumab treatment. Neutropenia with a Common Terminology Criteria for Adverse Events (CTCAE)9 grade of 2 (i.e., 1000 to <1500 cells per cubic millimeter) was observed in two patients (receiving either 75 mg or 150 mg of ixekizumab) with no reported symptoms; the lowest neutrophil count observed was 1350 per cubic millimeter (Table 1 in the Supplementary Appendix). No obvious dose-related trend in infections or other adverse events was observed. In one patient in the ixekizumab 150-mg group with a history of treated basal-cell carcinoma, two new basal-cell carcinomas were detected during the treatment period. No other cancer was reported. Mean values for the serum transaminases alanine aminotransferase and aspartate aminotransferase and total and direct bilirubin showed no significant changes from baseline in any ixekizumab group, as compared with the placebo group, from 1 through 20 weeks. Two patients in the 25-mg ixekizumab group had grade 3 or higher elevations of creatine kinase and aspartate aminotransferase (one also had a grade 3 elevation of alanine aminotransferase) that increased from the time of the screening visit or baseline without associated symptoms. These elevated enzyme levels decreased over time, and both patients continued ixekizumab treatment, while total and direct bilirubin and alkaline phosphatase levels remained normal throughout.

Discussion

The results of this study demonstrate that neutralization of interleukin-17 with the humanized monoclonal antibody ixekizumab may be an effective treatment for patients with chronic moderate-to-severe plaque psoriasis. At 12 weeks, significant and dose-dependent increases were seen in the proportions of patients receiving ixekizumab who had a reduction in the PASI score by at least 75% or 90% or by 100% as well as in the proportions of patients who had a static physician's global assessment score of 0 or of 0 or 1. These reductions were sustained through 20 weeks. Consistent with these clinical improvements, DLQI scores and itching severity also significantly decreased with ixekizumab treatment. Ixekizumab had a rapid onset of action, as evidenced by significant reductions in PASI scores, as compared with placebo, occurring at as early as week 1 in the two highest-dose groups and by the significantly higher percentage of patients with a reduction in the PASI score by at least 75% or static physician's global assessment score of 0 or 1, as compared with placebo, at as early as week 2 in the highest-dose group. Approximately 40% of patients in the two highest dose groups had complete clearance of psoriasis plaques on the skin, as reflected by a reduction in the PASI score by 100% or a static physician's global assessment score of 0 at 12 weeks. Although it is difficult to draw conclusions from cross-study comparisons, the magnitude and rapidity of the clinical responses compare favorably to responses to other available biologic compounds targeting tumor necrosis factor, T cells, or interleukin-12/23 p40.10-13 Although interleukin-23 can drive the maturation of type 17 helper T cells,2 interleukin-17 and interleukin-23 have many independent effects.14 For difficult-to-treat areas such as the scalp and nails, significant differences from placebo were observed with ixekizumab treatment. Improvements in scalp psoriasis (i.e., reductions in the PSSI score) were notable, because it is difficult to evaluate psoriasis on the scalp and a high rate of response to placebo has been shown in clinical trials.15,16 In our evaluations of nail psoriasis according to the NAPSI, both fingernails and toenails were included. Because toenails grow more slowly than fingernails, a longer treatment duration than that used in this trial may be required to assess greater effects of the treatment on toenails.17 No serious adverse events, including deaths, were observed in any group. Our study was not large enough or of long enough duration to ascertain uncommon adverse events. Although infections were the most common type of adverse event, there were no dose-related trends in the incidence rate or severity of events. As with other subcutaneous biologic therapies, injection-site reactions were more frequent in patients receiving ixekizumab as compared with placebo; none of these reactions were severe or resulted in treatment discontinuation. Two patients in the 25-mg ixekizumab group had grade 3 or greater elevations in creatine kinase, aspartate aminotransferase, or alanine aminotransferase levels that returned to screening or baseline levels over time with continued ixekizumab treatment. No major cardiovascular events, mycobacterial infections, or systemic fungal infections were reported. The only cancers reported were two basal-cell carcinomas in one patient. Two of the 115 patients (1.7%) receiving ixekizumab had CTCAE grade 2 neutropenia (lowest observed level, 1350 per cubic millimeter); neither patient had concurrent infection reported. No CTCAE grade 3 or 4 neutropenia was observed. Although interleukin-17 may have a role in neutrophil mobilization and homeostasis,14 it is not clear whether there is an association between interleukin-17 inhibition and neutropenia in psoriasis. In a previous proof-of-concept study of ixekizumab in patients with moderate-to-severe plaque psoriasis, neutralization of interleukin-17 led to improvements both in clinical measures of disease and in pathologic features of psoriasis in skin-biopsy specimens, including reductions in acanthosis, keratinocyte proliferation, and dermal infiltration of lymphocytes and other inflammatory cells within 2 weeks.18 These changes were accompanied by significant down-modulation of a broad array of genes in the skin from multiple inflammatory pathways. The results from the proof-of-concept and phase 2 studies with ixekizumab add further evidence that interleukin-17 is a central cytokine driving psoriasis pathogenesis. Interleukin-17 levels are known to be increased in psoriatic skin.19 Increased interleukin-17 levels may enhance neutrophil migration and survival in the dermis20,21 and drive angiogenesis.22 In addition, in synergy with tumor necrosis factor α, interleukin-17 causes release of inflammatory cytokines.23-26 Furthermore, in a trial exploring the efficacy of another investigational monoclonal antibody (AIN457) against interleukin-17, reductions in the PASI score were observed after a single dose.27 More recently, it has been shown that neutralization of the interleukin-17 receptor with monoclonal antibody AMG827 resulted in significant clinical improvements, consistent with the results of this study.28 Taken together, these data suggest that inhibition of interleukin-17 may be an effective and targeted therapy for psoriasis. Patients with chronic moderate-to-severe plaque psoriasis treated with ixekizumab had significant improvement in clinical measures during the 12-week treatment period that were rapid and sustained through 20 weeks with continued treatment. Further studies are needed to establish the long-term safety and efficacy of ixekizumab in the treatment of psoriasis.

sexta-feira, 23 de março de 2012

Glomerulonefrite membranosa NEJ of Medicine



Membranoproliferative Glomerulonephritis — A New Look at an Old Entity

Sanjeev Sethi, M.D., Ph.D., and Fernando C. Fervenza, M.D., Ph.D.
N Engl J Med 2012; 366:1119-1131March 22, 2012
Article
References
Membranoproliferative glomerulonephritis (MPGN), also termed mesangiocapillary glomerulonephritis, is diagnosed on the basis of a glomerular-injury pattern that is common to a heterogeneous group of diseases. MPGN accounts for approximately 7 to 10% of all cases of biopsy-confirmed glomerulonephritis1-4 and ranks as the third or fourth leading cause of end-stage renal disease among the primary glomerulonephritides.2,5 Although some diseases associated with MPGN are well known, recent advances have identified additional MPGN-associated conditions.

Clinical Presentation

MPGN most commonly presents in childhood but can occur at any age. The clinical presentation and course are extremely variable — from benign and slowly progressive to rapidly progressive. Thus, patients can present with asymptomatic hematuria and proteinuria, the acute nephritic syndrome, the nephrotic syndrome, chronic kidney disease, or even a rapidly progressive glomerulonephritis. The varied clinical presentation is caused by differences in the pathogenesis of the disorder and in the timing of the diagnostic biopsy relative to the clinical course. The degree of kidney impairment also varies, and hypertension may or may not be present. Patients who present early in the disease process, when the kidney biopsy shows proliferative lesions, are more likely to have a nephritic phenotype, and those with crescentic MPGN may present with a rapidly progressive glomerulonephritis. In contrast, patients with biopsies showing advanced changes that include both repair and sclerosis are more likely to have a nephrotic phenotype. Patients with classic MPGN often have features of both the acute nephritic syndrome and the nephrotic syndrome — termed the nephritic–nephrotic phenotype.

Classification and Pathophysiology

The typical features of MPGN on light microscopy include mesangial hypercellularity, endocapillary proliferation, and capillary-wall remodeling (with the formation of double contours) — all of which result in lobular accentuation of the glomerular tufts. These changes result from the deposition of immunoglobulins, complement factors, or both in the glomerular mesangium and along the glomerular capillary walls. On the basis of the electron-microscopical findings, MPGN is traditionally classified as primary (idiopathic) MPGN type I (MPGN I), type II (MPGN II), or type III (MPGN III) or secondary MPGN. MPGN I, the most common form, is characterized by subendothelial deposits, and MPGN III has both subepithelial and subendothelial deposits.6,7 MPGN II is characterized by dense deposits in the glomerular basement membrane (“dense-deposit disease”). Secondary MPGN, described by Rennke,8 is most often due to hepatitis C and other infections.
As currently classified, MPGN I and MPGN III are likely to include cases of both immune-complex–mediated and complement-mediated MPGN. Given recent advances in our understanding of the role of the alternative pathway of complement in MPGN, a practical approach is to view MPGN as immune-complex–mediated or complement-mediated.9 Thus, immune-complex–mediated MPGN may occur when there are increased levels of circulating immune complexes, and complement-mediated MPGN may occur because of disorders associated with dysregulation of the alternative pathway of complement.

Immune-Complex–Mediated MPGN

Immune-complex–mediated MPGN results from the deposition of immune complexes in the glomeruli owing to persistent antigenemia, with antigen-antibody immune complexes forming as a result of chronic infections, elevated levels of circulating immune complexes due to autoimmune diseases, or paraproteinemias due to monoclonal gammopathies. The immune complexes trigger the activation of the classical pathway of complement and the deposition of complement factors of the classical pathway and terminal complement pathway in the mesangium and along the capillary walls (Figure 1Figure 1Normal Glomerular Capillary Wall and Immune-Complex–Mediated Membranoproliferative Glomerulonephritis (MPGN).; and Fig. 1 in the Supplementary Appendix, available with the full text of this article at NEJM.org). A kidney-biopsy specimen typically shows immunoglobulin and complement on immunofluorescence microscopy.

Hepatitis C and Other Infections

Chronic viral infections such as hepatitis C and hepatitis B, with or without circulating cryoglobulins, are an important cause of MPGN. Hepatitis C, which was recognized as a common cause of immune-complex–mediated MPGN in the 1990s, is now considered to be the main viral infection causing MPGN. 8,10-13 In addition to viral infections, chronic bacterial infections (e.g., endocarditis, shunt nephritis, and abscesses), fungal infections, and parasitic infections are associated with MPGN, particularly in the developing world.14-18 Bacteria associated with MPGN include staphylococcus, Mycobacterium tuberculosis, streptococci, Propionibacterium acnes, Mycoplasma pneumoniae, brucella, Coxiella burnetii, nocardia, and meningococcus. 19-30

Autoimmune Diseases

MPGN occurs in a number of autoimmune diseases. These include systemic lupus erythematosus and, occasionally, Sjögren's syndrome, rheumatoid arthritis, and mixed connective-tissue disorders. 31-35

Monoclonal Gammopathy

Recent studies indicate that glomerular deposition of monoclonal immunoglobulin as a result of monoclonal gammopathy (also called dysproteinemia or plasma-cell dyscrasia), with or without cryoglobulins, is associated with MPGN.36-39– Monoclonal gammopathy is characterized by the proliferation of a single clone of immunoglobulin-producing lymphocytes or plasma cells, resulting in the circulation of monoclonal immunoglobulin. In one single-center study, 41% of the patients who had MPGN without an autoimmune process or chronic infection had evidence of monoclonal gammopathy, as assessed by means of serum electrophoresis, urine electrophoresis, or both.36 Bone marrow biopsies on such patients revealed a variety of conditions: monoclonal gammopathy of undetermined significance (MGUS) (the most common condition), low-grade B-cell lymphoma, lymphoplasmacytic lymphoma, chronic lymphocytic leukemia, and multiple myeloma. The authors suggested that patients with monoclonal gammopathy and MPGN should be classified as having “monoclonal gammopathy–associated MPGN” rather than MGUS.36

Complement-Mediated MPGN

The complement cascade plays an important role in innate immunity. Complement factors can induce a potent inflammatory response that results in phagocyte chemotaxis, with opsonization and lysis of cells, including microorganisms. Complement activation occurs through the classical, lectin, or alternative pathways, all of which converge to form C3 convertase, which cleaves C3 into C3a and C3b. C3b, in the presence of factor B and factor D, associates with C3 convertase, generating even more C3 convertase and resulting in a potent amplification loop (Figure 2Figure 2Complement-Mediated MPGN., and Fig. 1 in the Supplementary Appendix). Thus, C3 convertase is a nodal point in the complement cascade. The association of C3b and C3 convertase also results in the formation of C5 convertase, which activates the terminal complement complex pathway and the formation of the membrane-attack complex (C5b–C9) on cell surfaces, thereby resulting in cell lysis.40,41
The alternative pathway is continually active at low levels in the circulation (fluid phase) through spontaneous hydrolysis of the thioester bond of C3 (“tick over” mechanism), which generates C3b; C3b then binds to host cell membranes and extracellular membranes such as the glomerular basement membrane (surface phase) as well as membranes of pathogenic microorganisms.42,43 To prevent self-damage, activation of the alternative pathway occurs in a tightly regulated, sequential manner. Multiple complement-regulating and complement-inhibiting proteins operate at different levels of the cascade, particularly at the C3 and C5 convertase level.41 Such plasma or fluid-phase regulators include factors H and I and factor H–related proteins 1 through 5 and cell-bound and surface regulators such as decay-accelerating factor (CD55), complement receptor 1, CD59, membrane cofactor protein (CD46), and complement receptor of the immunoglobulin superfamily.40-42 Factor H accelerates the breakdown of C3 convertase and is a cofactor for factor I–mediated cleavage and inactivation of C3b,41,42 thereby controlling the alternative pathway in the fluid phase. Fluid-phase regulators of the terminal complement complex include vitronectin and clusterin. Some of the fluid-phase regulators, including factor H and factor H–related protein 1, also attach to cell surfaces and extracellular membranes, adding an extra protective mechanism to prevent the formation of active complement products.41 Surface regulators control C3 convertase through the inactivation of C3b deposited on cell surfaces and basement membranes.44
Dysregulation of the alternative pathway can occur because of mutations in or autoantibodies to complement-regulating proteins (Figure 3Figure 3Acquired and Genetic Abnormalities Associated with Complement-Mediated MPGN.). For example, mutations in proteins that regulate the assembly and activity of C3 convertase and degradation of C3b, such as factors H, I, and B and factor H–related protein 5, result in dysregulation of the alternative pathway.45-53 Heterozygous mutations in C3 itself cause fluid-phase dysregulation of the alternative pathway, because the mutant C3 is resistant to cleavage by C3 convertase. In addition, the generation through the tick-over mechanism of an abnormal C3 convertase, which contains the C3 mutation, renders it resistant to inactivation by factor H. The abnormal C3 convertase then cleaves C3 produced by the normal C3 allele, resulting in increased levels of C3 breakdown products.54 Similarly, antibodies to the complement-regulating proteins (such as factors H and B) and to C3 convertase itself can result in overactivity of the alternative pathway.49,55 Antibodies to C3 convertase (called C3 nephritic factor) stabilize the convertase and prolong its half-life by preventing its inactivation and degradation, thereby activating the alternative pathway.40,45
Certain genetic polymorphisms in factors H and B, membrane cofactor protein, and C3 are also associated with MPGN.56,57 Polymorphisms in the gene encoding factor H, notably Tyr402His allele variants, are the polymorphisms that have been studied most often. As compared with Tyr402, His402 is overrepresented in patients with MPGN and alternative-pathway abnormalities, and functional studies show that His402 impairs factor H–mediated regulation of C3 convertase on cell surfaces.49,58,59
Whatever the mechanism may be, dysregulation of the alternative pathway results in activated complement products, including C3b and terminal complement factors, which are delivered indiscriminately to endothelial surfaces, including glomeruli.41,60 The deposition of these complement products and debris in the mesangium and subendothelial region triggers glomerular inflammation and leads to MPGN. Immunoglobulins are not directly involved; thus, complement-mediated MPGN is typically immunoglobulin-negative but complement-positive on immunofluorescence studies.
Despite multiple genetic risk factors, MPGN due to complement abnormalities often develops relatively late in life, suggesting that additional insults or environmental factors are required. Furthermore, MPGN does not develop in all genetically similar members of high-risk families, again indicating that additional disease-inducing factors are required. We speculate that when MPGN does not occur despite the presence of a mutation or of an allele variant that confers a predisposition to the disease, redundant control mechanisms may be present.43 However, when an additional insult such as a complement-activating infection occurs, it may overwhelm the compensatory regulatory mechanism, triggering glomerular deposition of complement factors.41 This scenario may explain the recurrent episodes of macroscopic hematuria associated with infections (synpharyngitic hematuria) that are noted in many patients with MPGN. Similarly, an additional insult, such as the production of monoclonal proteins that act as autoantibodies to complement-regulating proteins in patients with MGUS, could result in dysregulation of the alternative pathway and the development of MPGN.61,62

Pathological Features

The deposition of immunoglobulin, complement, or both in the mesangium and subendothelial region of the capillary wall triggers an acute injury, which is often followed by an inflammatory (cellular or proliferative) phase, with an influx of inflammatory cells. A subsequent reparative phase occurs, during which new mesangial matrix results in mesangial expansion, along with the generation of new glomerular basement membrane, which looks like a duplicated basement membrane (so-called tram tracks or double contours) (Figure 1 and Figure 2).
Immunofluorescence findings are used to distinguish immune-complex–mediated MPGN from complement-mediated MPGN and can often point to a specific cause. For example, MPGN associated with monoclonal gammopathy shows monotypic immunoglobulin with kappa or lambda light-chain restriction (Figure 4Figure 4Representative Findings on Light, Immunofluorescence, and Electron Microscopy in MPGN.). MPGN associated with hepatitis C infection typically shows IgM, IgG, C3, and kappa and lambda light chains. An MPGN pattern in association with autoimmune diseases often includes multiple immunoglobulins and complement proteins — IgG, IgM, IgA, C1q, C3, and kappa and lambda light chains. MPGN associated with alternative-pathway dysfunction is characterized by bright C3 immunostaining in the mesangium and along the capillary walls (Figure 4). The absence of marked immunoglobulin staining on immunofluorescence microscopy distinguishes MPGN due to alternative-pathway dysfunction from immune-complex–mediated MPGN.
Electron microscopy typically reveals mesangial and subendothelial deposits and, in some cases, intramembranous and subepithelial deposits. During the reparative phase, new basement membrane forms, entrapping capillary-wall deposits, along with cellular elements derived from inflammatory, mesangial, and endothelial cells, within the new basement-membrane material; the result is a thickening of the capillary walls and the formation of double contours along the capillary walls. With the exception of dense-deposit disease, electron microscopy cannot distinguish between immune-complex–mediated MPGN and complement-mediated MPGN.
MPGN due to alternative-pathway dysregulation may be subdivided into dense-deposit disease and C3 glomerulonephritis (C3GN), on the basis of electron-microscopical findings. Dense-deposit disease is characterized by osmiophilic, sausage-shaped, wavy, dense deposits that replace the glomerular basement membrane and also occur in the mesangium, whereas C3GN has mesangial, subendothelial, and sometimes subepithelial and intramembranous deposits (Figure 4). On the basis of the morphologic characteristics of C3GN on electron microscopy, C3GN is most likely to be termed MPGN I or MPGN III according to the older classification. Data from laser microdissection and mass spectrometric analysis of glomeruli obtained from patients with C3GN are consistent with unrestricted activation of the alternative pathway, and the proteomic profile in such patients is similar to that in patients with dense-deposit disease.49,60 The hypothesis that dense-deposit disease and C3GN are part of a continuum is further supported by cases that show features that are intermediate between dense-deposit disease and C3GN, with some capillary loops showing the sausage-shaped intramembranous deposits of dense-deposit disease and other loops showing the subendothelial and subepithelial deposits of C3GN on electron microscopy.
Five cases of immune-complex–mediated or complement-mediated MPGN with a clearly identifiable cause are discussed in the Supplementary Appendix.

Alternative-Pathway Dysregulation and Disease Subtype

Dysregulation of the alternative pathway results in dense-deposit disease in some patients and C3GN in others, most likely because of differences in the degree or site (or both) of the dysregulation. In addition, certain allele variations of complement-regulating proteins may be associated with dense-deposit disease, and others may be associated with C3GN.57

Other Patterns of Immune-Complex–Mediated and Complement-Mediated Glomerular Injury

Other patterns of glomerular injury besides MPGN may result from the deposition of immunoglobulin, complement, or both. For example, mesangial proliferative glomerulonephritis, diffuse proliferative glomerulonephritis, crescentic glomerulonephritis, and a sclerosing glomerulopathy can be present in both C3GN and dense-deposit disease.63,64 The umbrella term “C3 glomerulopathy” describes the various patterns of injury,65 which probably depend on multiple factors, including the severity of injury and the phase of the disease process (acute or chronic) at the time the biopsy is performed. Prior treatment may also affect the biopsy findings.

MPGN without Immune Complexes or Complement

A pattern of injury consistent with MPGN is also noted in thrombotic microangiopathies resulting from injury to the endothelial cells. In the acute phase, mesangiolysis, endothelial swelling, and fibrin thrombi are present in the glomerular capillaries. As the process evolves into a reparative and chronic phase, mesangial expansion and remodeling of the glomerular capillary walls, including double-contour formation, take place. Thus, the healing phase of thrombotic thrombocytopenic purpura or hemolytic–uremic syndrome, atypical hemolytic–uremic syndrome associated with complement abnormalities, the antiphospholipid antibody syndrome, drug-induced thrombotic microangiopathies, nephropathy associated with bone marrow transplantation, radiation nephritis, malignant hypertension, and connective-tissue disorders can all present with an MPGN pattern of injury on biopsy.66,67 In thrombotic microangiopathies, immunoglobulin and complement are typically absent on immunofluorescence, and electron-dense deposits are not present in the mesangium or along the capillary walls on electron microscopy.

Evaluation

Persistently decreased serum levels of complement C3, C4, or both are commonly seen in patients with MPGN. Low C3 and low C4 complement levels are more common in immune-complex–mediated MPGN, whereas low C3 and normal C4 levels are more common in alternative-pathway dysfunction, particularly in the acute phase. A normal C3 level does not rule out alternative-pathway dysfunction.
When a kidney-biopsy specimen from a patient with MPGN shows immunoglobulins, an evaluation for infections, autoimmune diseases, and monoclonal gammopathies is indicated (Figure 5Figure 5Pathophysiology of MPGN.). Relevant tests for the detection of infections include blood cultures and polymerase-chain-reaction and serologic tests for viral, bacterial, and fungal infections. Cryoglobulins may be present. Tests for the detection of monoclonal gammopathy include serum and urine electrophoresis, immunofixation studies, and free light-chain assays; positive results necessitate bone marrow studies for a more precise diagnosis. Positive screening tests for an autoimmune disease should be followed by specific tests for the autoimmune disease.
If the biopsy specimen from a patient with MPGN shows bright C3 immunostaining (with minimal or no immunoglobulin staining), an evaluation to detect abnormalities of the alternative pathway is indicated regardless of whether an electron microscopic examination shows dense-deposit disease or C3GN (Figure 5). The initial evaluation of the alternative pathway should include measurement of serum complement levels and serum levels of the membrane-attack complex, an alternative pathway functional assay, and hemolytic complement assays, followed by genetic analysis for mutations and allele variants of complement factors and assays for the presence of autoantibodies to complement-regulating proteins, including tests for the detection of C3 nephritic factor (Fig. 7 in the Supplementary Appendix).
Even after extensive evaluation, the cause may remain enigmatic in a few cases of immune-complex–mediated or complement-mediated MPGN. In some patients, immune-complex–mediated MPGN may be initiated by immunoglobulin deposition, but the disease may be accelerated by alternative-pathway abnormalities.68 Over time, new methods will probably be developed that can further separate specific causes of MPGN from idiopathic cases.

Therapy

Early reports on the treatment of “idiopathic” MPGN should be interpreted with caution. In many instances, historical controls were used, the statistical significance was marginal, or the power to detect substantial differences was small.69,70 Most early studies antedated the use of angiotensin-converting–enzyme (ACE) inhibitors and angiotensin II–receptor blockers, and the protean pathogenic processes that lead to MPGN were as yet unknown. Thus, most studies on MPGN conflated various types of MPGN in unknown proportions.71
The benefit of long-term alternate-day glucocorticoid therapy for idiopathic MPGN in children was suggested by a few uncontrolled studies72-74 and one randomized, controlled trial.75 However, these studies included a mix of patients with MPGN I, MPGN III, and dense-deposit disease, limiting the conclusions that could be reached. There has been no systematic evaluation of glucocorticoid therapy for idiopathic MPGN in adults. Retrospective studies showed no clear benefit from glucocorticoid therapy, but treatment was not as prolonged in adults as it was in children.70,76
Early claims of the beneficial effects of anticoagulants (i.e., heparin and warfarin), frequently combined with glucocorticoids and cytotoxic agents, have not been confirmed in a prospective study.77 Similarly, an early randomized, controlled trial showed that the combination of aspirin and dipyridamole slowed the decline in the glomerular filtration rate in adults with idiopathic MPGN,78 but there was no long-term benefit, suggesting that prolonged antiplatelet therapy is required for a sustained benefit.70 Limited uncontrolled data suggest that calcineurin inhibitors may reduce proteinuria in some patients with MPGN.79-82 In patients with a rapidly progressive course and crescents on renal biopsy, a few small, uncontrolled studies have suggested a benefit with high-dose “pulse” glucocorticoids, either as monotherapy83-85 or in combination with azathioprine,86 cyclophosphamide,87 or mycophenolate mofetil.88-90
The lack of randomized, controlled trials and the current understanding that multiple pathogenic processes lead to MPGN make it impossible to give strong treatment recommendations in this patient population. Pragmatic considerations would suggest that patients with MPGN due to chronic infections should undergo treatment of the infection, and those with MPGN due to an autoimmune disease should undergo treatment of the autoimmune disease. Similarly, patients with MPGN due to a monoclonal gammopathy should undergo treatment aimed at attaining remission of the hematologic dyscrasia. A recent study involving patients with MPGN associated with monoclonal immunoglobulin deposits and no overt hematologic cancer showed that patients had a good response to rituximab.91 Patients with normal kidney function, no active urinary sediment, and non–nephrotic-range proteinuria can be treated conservatively with angiotensin II blockade to control blood pressure and reduce proteinuria, since the long-term outcome is relatively benign in this context.92,93, Follow-up is required to detect early deterioration in kidney function.
A better understanding of the causes and pathogenesis of complement-mediated MPGN would logically set the stage for the possible use of newer drugs, including anticomplement drugs. However, current recommendations are based on theory, not studies. For example, patients with MPGN due to autoantibodies to complement-regulating proteins may benefit from immunosuppressive therapy (e.g., glucocorticoids and rituximab), whereas those with MPGN due to a genetic mutation in complement-regulating proteins may benefit from treatment with drugs that inhibit formation of the membrane-attack complex (e.g., eculizumab).
Eculizumab, an anti-C5 monoclonal antibody that inhibits C5 activation, has been used successfully in patients with atypical hemolytic–uremic syndrome due to complement abnormalities in the alternative pathway.94-96 The role of such anticomplement agents in MPGN is not delineated but offers exciting possibilities for the future. It is also conceivable that patients with elevated serum levels of the membrane-attack complex may be more likely than those with normal levels to have a response to treatment with eculizumab. Patients with MPGN due to a deficiency of factor H might benefit from plasma infusion97 or infusion of factor H. Patients who present with advanced renal insufficiency and severe tubulointerstitial fibrosis on renal biopsy are unlikely to benefit from immunosuppressive therapy.

Recurrence after Kidney Transplantation

MPGN often recurs in kidney-transplant recipients. Recurrence rates range from 27 to 65%, depending on the study.98-100 One recent study, which excluded from the analysis patients with dense-deposit disease, showed a recurrence rate of 41%; of patients with a recurrence, 36% had a monoclonal gammopathy. The study showed that recurrent MPGN due to deposition of monoclonal immunoglobulin was associated with early recurrence and a more aggressive course.100 Low complement levels were shown to be an early marker for recurrent MPGN.100 Few data exist on the recurrence of C3GN. In patients with dense-deposit disease, there is almost universal recurrence of disease, with a 5-year rate of allograft failure of 50%.40,45

Conclusions

Two major pathophysiological factors — the deposition of immunoglobulin and the deposition of complement in the glomerular mesangium and capillary walls — may lead to MPGN. The presence of immune-complex–mediated MPGN necessitates evaluation for infections, autoimmune diseases, and monoclonal gammopathy. Complement-mediated MPGN is further subdivided into dense-deposit disease and C3GN, depending on the electron-microscopical findings; the presence of complement-mediated MPGN necessitates evaluation of the alternative pathway. Evaluation of MPGN according to the underlying pathophysiological processes may facilitate proper treatment.

sábado, 17 de março de 2012

Droga anti HIV também pode curar malária


SEATTLE, WASHINGTON—Bed nets and insecticides form the cornerstone of malaria prevention, with antimalarial drugs being used mainly to treat people who become ill with the disease. The drugs do have some protective effect, but it quickly wanes. Now a study in Uganda suggests that an antiretroviral drug given to HIV-infected children can boost the preventive power of a key malaria drug.

Researchers have long known that in test-tube studies, a class of anti-HIV drugs known as protease inhibitors also cripples the parasites that cause malaria. So a team led by clinicians Diane Havlir of the University of California, San Francisco (UCSF), and Moses Kamya of Makerere University College of Health Sciences in Uganda decided to compare two different cocktails of anti-HIV drugs, only one of which contained protease inhibitors, in HIV-infected children who live in a malarial area of that eastern African country. The results, presented here last week by Makerere University's Jane Achan at the 19th Conference on Retroviruses and Opportunistic Infections, show that one protease inhibitor indeed helped stave off malaria, and it worked by a surprising mechanism.

As Achan explained, the trial in Tororo, Uganda, involved 170 children under 5 who were randomized to receive one of the two combinations of antiretroviral drugs. The group that received a drug cocktail containing the co-formulated protease inhibitors lopinavir and ritonavir had a 41% drop in malaria cases over 2 years compared with the group that received the other antiretroviral cocktail. Further studies showed that the HIV drugs containing protease inhibitors had only a modest direct impact on the malaria parasites. Rather, the success primarily occurred because ritonavir extended the preventive effects of a widely used antimalarial drug, lumefantrine.

"The 41% reduction in clinical malaria episodes is both statistically and clinically significant," says Paula Brentlinger, a clinician at the University of Washington, Seattle, who studies both malaria and HIV in Mozambique. "The fact that it was achieved in one of the most malaria-vulnerable populations in the world is especially heartening." (Other than in pregnancy, research has not shown a convincing link between HIV and malaria susceptibility or severity of disease.)

The researchers teased out the effects of ritonavir by separately analyzing first episodes of malaria and recurrent cases. Children with first episodes were unlikely to have any antimalarial drugs in their bodies at the time of analysis, whereas those who had recurrent cases during the study received an artemether-lumefantrine combination as treatment. When it came to first episodes, the group taking ritonavir had a 29% reduction in malaria cases, which hinted at some effect but was not statistically significant. Recurrent cases in the ritonavir group plummeted by a highly significant 59%. "This is where we really found the dramatic findings," Achan said.

Lumefantrine, unlike artemether, stays in the body for weeks, which provides some protection against malaria. Given that ritonavir blocks cytochrome p450, a liver enzyme that plays a key role in metabolizing drugs, the researchers wondered whether the drug might have extended lumefantrine's preventive effects. Blood samples from the children showed that those receiving ritonavir had nearly fivefold higher levels of lumefantrine 7 days after receiving the antimalarial. "We think that these higher lumefantrine exposures were really what was driving the protection against recurrent episodes of malaria," Achan said.

Carlos "Kent" Campbell, who heads the Malaria Control Program at PATH, a nonprofit organization in Seattle, says bed nets remain the most critical prevention strategy. He also notes that most children who are vulnerable to malaria are not infected with HIV and have no need for antiretrovirals. Yet Campbell says in HIV-infected children, the "unanticipated positive consequences" of ritonavir could have the added benefit of reducing persistent parasitemia caused by malaria, a leading cause of anemia in young children in many African countries. "It's a very interesting finding and could help decide which antiretroviral regimen to use in areas where there's an increased malarial burden," says Campbell, who previously headed the malaria branch at the U.S. Centers for Disease Control and Prevention (CDC).

The current director of CDC's malaria program, S. Patrick Kachur, points out that there have been attempts to use long-acting antimalarials as preventives in specific populations such as pregnant women or people who live in the Sahel and suffer from the disease only during a few months of the year. If ritonavir "potentiates the long tail of lumefantrine," he says, "we certainly want to know."

Aside from the potential impact of these findings in countries double punched by malaria and HIV, the study encourages researchers and clinicians to take a broader view about the effects one drug can have on another. "We always think of drug-drug interactions as something to be avoided, but HIV has taught us the opposite," says Paul Volberding, an HIV/AIDS clinician at UCSF, who did not participate in this study but saw its presentation at the conference. "This is an intriguing first glimpse at one of these interactions."

domingo, 11 de março de 2012

Sirtuinas pode prolongar a vida? - Naature news

Esse grupo de proteinas para estar associada ao prolongamento da vida, pelo menos em fungos e camundongos. Veja a matéria da Nature

Ageing: Sorting out the sirtuins


Debates over the role of sirtuin proteins in ageing are maturing into functional assessments of the individual proteins. It seems that overexpression of a specific sirtuin can extend lifespan in male mice.


Abraham Lincoln once said that God must have loved the common people because he made so many of them. Nature must feel the same way about the sirtuins, a large family of proteins that achieved celebrity status when one member was found to increase lifespan in yeast1. But are the mammalian sirtuins the rock stars of an ensemble of anti-ageing proteins, or merely members of the entourage? The original model, proposed in about 2005, that sirtuins have broadly evolutionarily conserved roles in promoting longevity per se is now being refined through more detailed functional investigations of each sirtuin2. In a paper published on Nature's website today, Kanfi et al.3 follow this trend by reporting that overexpression of a sirtuin called SIRT6 leads to a modest extension of lifespan in male, but not female, mice.

Does an extension of lifespan imply an effect on ageing? Not necessarily: interventions unrelated to ageing, such as giving insulin to a person with type I diabetes, can increase mean and maximal lifespan. The lifespan extension observed by Kanfi and colleagues in SIRT6-overexpressing male mice could be explained, at least partially, by SIRT6 acting as a tumour suppressor. Because male mice have a higher incidence of spontaneous cancer than female mice (incidences of 81% and 50%, respectively, were observed in this study), an anticancer protein (perhaps SIRT6?) would have a larger effect on lifespan in males than in females.
Proving that a lifespan-increasing intervention indeed acts by delaying ageing processes is not a simple matter. For example, acceptance of the idea that lifespan extension by caloric restriction (a diet with reduced calorie intake) reflects a genuine deceleration of ageing emerged gradually from evidence4 that restriction slows age-related changes in the properties of proliferative and non-proliferative cells in many tissues, and does so in multiple organ systems. Similar cases are being constructed by researchers proposing that dwarf mice could act as models for slowed ageing5.
Reports of lifespan increases in mutant or drug-treated mice, particularly studies in which the observed effects are modest, often prove difficult for other laboratories to repeat. This is presumably due to subtle but crucial variations in the animals' diet or genetic background, or in husbandry practices6. Moreover, the preference for publication of positive over negative findings inevitably inserts a smattering of false positive results into the literature, and these can be identified only by attempts to replicate experiments. One strength of Kanfi and colleagues' paper3 is that SIRT6 overexpression increased male lifespan in each of two groups of mice, which were derived from two different founder animals. However, the test for maximal lifespan — usually taken as stronger evidence than an effect on median longevity alone — reached statistical significance in only one of the two mouse groups. If the longevity effect seen by the authors proves robust, determining whether SIRT6 overexpression does indeed slow ageing will still require follow-up studies analysing a wide range of age-sensitive endpoints.
In their article, Kanfi and colleagues include some observations hinting at potential mechanisms by which SIRT6 overexpression might affect the lifespan of male mice. Compared with their normal counterparts, SIRT6-overexpressing males had modestly reduced serum levels of the hormone IGF-1, and the signalling activity of IGF-1 receptors was weaker in peri-gonadal fat tissue in males but not in females. Previous reports have found that SIRT6 attenuates intracellular signalling initiated by IGF-1 and insulin7. Furthermore, dramatic deficits in IGF-1 and/or growth hormone (GH, which stimulates IGF-1 secretion) lead to slower ageing and increased lifespan in at least four varieties of mutant mouse6. And mutations in the gene encoding the GH receptor in humans are associated with strong protection against diabetes and cancer8. So, it is plausible that SIRT6 overexpression in mice might work through blunting of the GH/IGF-1 pathway. Evidence9 that rat longevity can be augmented by surgical removal of intra-abdominal — but not subcutaneous — fat has begun to focus attention on metabolic and hormonal effects on specific fat depots as potential levers for pharmacological control of ageing.
It is noteworthy that the effects of SIRT6 overexpression reported by Kanfi et al.3 are seen only in male mice. Previous results6, by contrast, indicate that mutations in components of the GH/IGF-1 pathway usually have greater effects on longevity in female mice. This apparent discrepancy might be explained by differences between the mice in terms of underlying disease proclivities, levels of sex-specific hormones, inter-animal conflict or fat-tissue biology, leading to gender-specific responses to mutations, drugs and nutritional interventions. Working out the basis for these sex-specific interactions should provide clues to the mechanisms involved in these anti-ageing manipulations, and perhaps even help to answer the vexing question of why women tend to live longer than men.
SIRT6 has other roles that could foster longer lifespan (Fig. 1). It promotes chromosomal stability by several mechanisms, and above-normal SIRT6 expression increases the efficiency of DNA repair10. SIRT6 also reduces the expression of genes regulated by the NF-κB and HIF-1α proteins, which have roles in inflammation, cancer and, potentially, longevity11, 12. It will be of interest to assess these aspects of SIRT6's function in mice overexpressing the protein, and to test more definitively whether they contribute to protection against cancer and promotion of longevity.

Figure 1: Potential mechanisms of action of SIRT6 on longevity.
Potential mechanisms of action of SIRT6 on longevity.
Several reports7, 10, 11, 12 have demonstrated effects of the sirtuin protein SIRT6 on the activities of the hormones insulin and IGF-1, as well as on inflammation and DNA repair. These effects, together with a possible delay in cancer progression, could contribute to the increased lifespan in SIRT6-overexpressing male mice reported by Kanfi and colleagues3.
The recent spate of activity in sirtuin research, now supplemented by the present work, supports the case for placing the sirtuins on the front line of ageing research, sitting cheek by jowl with other promising contestants, such as the proteins TOR, FoxO, AMPK, NRF2 and ATF4. To paraphrase Winston Churchill, the discoveries of Kanfi et al. do not by any means represent the end of sirtuin research, nor even the beginning of the end. But they are, perhaps, the end of the beginning.