Is Transcatheter Closure Better than Medical Therapy for Cryptogenic Stroke with Patent Foramen Ovale? A Meta-analysis of Randomised Trials

Secondary prevention of cryptogenic stroke in patients with patent foramen ovale: a systematic review and meta-analysis

The aim of our study is to compare patent foramen ovale (PFO) closure versus medical treatment and antiplatelet versus anticoagulant therapy in patients with cryptogenic stroke (CS) and PFO. We conducted a systematic review and meta-analysis with trial sequential analysis (TSA) of randomized trials. Primary outcomes are stroke or transient ischemic attack (TIA) and all-cause mortality. Secondary outcomes are peripheral embolism, bleeding, serious adverse events, myocardial infarction and atrial dysrhythmias. We performed an intention to treat meta-analysis with a random-effects model. We include six trials (3677 patients, mean age 47.3 years, 55.8% men). PFO closure is associated with a lower recurrence of stroke or TIA at a mean follow-up of 3.88 years compared to medical therapy [risk ratio (RR) 0.55, 95% CI 0.38-0.81; I² = 40%]. The TSA confirms this result. No difference is found in mortality (RR 0.74, 95% CI 0.35-1.60; I² = 0%), while PFO closure is associated with a higher incidence of atrial dysrhythmias (RR 4.55, 95% CI 2.16-9.60; I² = 25%). The rate of the other outcomes is not different among the two groups. The comparison between anticoagulant and antiplatelet therapy shows no difference in terms of stroke recurrence, mortality and bleeding. There is conclusive evidence that PFO closure reduces the recurrence of stroke or TIA in patients younger than 60 years of age with CS. More data are warranted to assess the consequences of the increase in atrial dysrhythmias and the advantage of PFO closure over anticoagulants.

Transcatheter closure of patent foramen ovale following cryptogenic stroke: An updated meta-analysis of randomized controlled trials

BACKGROUND

Transcatheter closure of patent foramen ovale (PFO) after cryptogenic stroke has long been a contentious issue. Herein, we pool aggregate data examining safety and efficacy of transcatheter closure of PFO compared with medical therapy following initial cryptogenic stroke.

METHODS

We searched for randomized clinical trials (RCT) that compared device closure with medical management and reported on subsequent stroke and adverse events. Stroke was considered as the primary efficacy endpoint, whereas bleeding and atrial fibrillation were considered primary safety endpoints. Data were pooled by the random effects model and I2 was used to assess heterogeneity.

RESULTS

A total of 5 RCT investigating 3630 patients met inclusion criteria. Pooled analysis revealed that device closure compared to medical management was associated with a significant reduction in stroke (RR=0.3, 95% CI=0.02-0.57). There was, however, a significant increase in atrial arrhythmias with device therapy (RR=4.8, 95% CI=2.2-10.7). We found no increase in bleeding (RR=0.80, 95% CI=0.5-1.4), death (RR=0.76, 95% CI=0.3-1.99) or "any adverse events" (RR=1.02, 95% CI=0.85-1.23) with device therapy. Sub-group analysis revealed that device closure significantly reduced the incidence of the composite primary endpoint among patients who had moderate to large shunt sizes (RR=0.22, 95% CI=0.02-0.42).

CONCLUSIONS

Transcatheter closure is associated with a significant reduction in the risk of stroke compared to medical management at the expense of an increased risk of atrial arrhythmias.

Reduced Stroke After Transcatheter Patent Foramen Ovale Closure: A Systematic Review and Meta-analysis

BACKGROUND

Recent randomized control trials (RCTs) have suggested benefit with transcatheter patent foramen ovale (PFO) closure plus antiplatelet therapy over medical treatment alone for secondary stroke prevention.

MATERIAL AND METHODS

Data sources: we searched PubMed and Ovid MEDLINE from the inception until November 10, 2017 for RCTs comparing TPFO closure to medical therapy in patients with a PFO and a history of cryptogenic stroke.

RESULTS

Five RCTs with 3,627 patients (TPFO closure = 1,829 versus medical therapy =1,798) were included. There was a decreased number of post-TPFO closure strokes compared to the medical therapy arm; 53 versus 80 strokes (odds ratio [OR] = 0.61, CI: 0.39-0.94, P = 0.03, I² = 17%). Transient ischemic attacks occurred in 43 patients after TPFO closure versus 60 patients in the medical therapy group (OR = 0.80, CI: 0.53-1.19, P = 0.26, I² = 0%). There was a higher incidence of atrial fibrillation in the TPFO closure group, which occurred in 75 patients, compared to 12 patients in the medical therapy group (OR = 5.23, CI: 2.17-12.59, P = 0.0002, I² = 43%). There was a trend toward a decreased number of neuropsychiatric events in the TPFO closure closure group compared to the medical therapy group; 42 versus 67 neuropsychiatric events (OR = 0.71, CI: 0.48-1.06, P = 0.09, I² = 0%).

CONCLUSIONS

TPFO closure plus antiplatelet therapy is superior to medical therapy in patients with a PFO and cryptogenic stroke. PFO closure is associated with new-onset atrial fibrillation and a trend toward reduced neuropsychiatric events.

Meta-Analysis Comparing Patent Foramen Ovale Closure Versus Medical Therapy to Prevent Recurrent Cryptogenic Stroke

New evidence suggests that closure of a patent foramen ovale (PFO) plus medical therapy (MT; antiplatelet or anticoagulation) is superior to MT alone to prevent recurrent cryptogenic stroke. We performed a meta-analysis of randomized controlled trials that compared PFO closure plus MT with MT alone in patients with cryptogenic stroke. The efficacy end points were recurrent stroke, transient ischemia attack, and death. The safety end points were major bleeding and newly detected atrial fibrillation. Trials were pooled using random effects and fixed effects models. A trial sequential analysis was performed to assess if the current evidence is sufficient. Risk ratios (RR) were calculated for pooled estimates of risk. Five randomized controlled trials (3,440 patients) were included. Mean follow-up was 4.1 years. PFO closure reduced the risk of recurrent stroke by 58% (RR 0.42, 95% CI 0.20 to 0.91, p = 0.03). The number needed to treat was 38. The cumulative Z-line crossed the trial sequential boundary, suggesting there is adequate evidence to conclude that PFO closure reduces the risk of recurrent stroke by 60%. PFO closure did not reduce the risk of transient ischemia attack (RR 0.78, 95% CI 0.53 to 1.15, p = 0.21), mortality (RR 0.74, 95% CI 0.35 to 1.60, p = 0.45), or major bleeding (RR 0.96, 95% CI 0.42 to 2.20, p = 0.93); it did increase the risk of atrial fibrillation (RR 4.69, 95% CI 2.17 to 10.12, p <0.0001).

Patent foramen ovale closure to prevent secondary neurologic events

In October of 2016 the United States Food and Drug Administration approved the Amplatzer Patent Foramen Ovale (PFO) occluder device for use in patients with cryptogenic stroke, to reduce the risk of recurrent stroke. This event followed 15years of off-label use of atrial septal occluder devices, 3 randomized trials, and enormous controversy over the efficacy of this procedure. While none of the trials reached the primary endpoint needed to prove the efficacy of PFO closure in preventing recurrent stroke, meta-analyses and 5-year follow-up of 1 trial suggest that PFO closure decreases the risk of recurrent stroke, especially in sub-groups with large shunts and atrial septal aneurysms, and especially when the Amplatzer device (rather than other devices) is used. While the relative reduction in stroke associated with PFO closure is large (about 50%), the absolute reduction is low (1-2%) and must be balanced against complications of the procedure (about 3%). Thus, PFO closure is restricted to patients with cryptogenic stroke, and depends heavily on patients' personal preferences. Uncertainties about the etiology of stroke in patients with PFO and the efficacy of PFO closure cause a difficult problem for the internal medicine specialist. At one extreme the internist may wonder if every patient with a documented PFO should be referred to a cardiologist. At the other extreme, supported by specialty society guidelines, internists may conclude that PFO closure is rarely necessary. In this paper we review the current status of PFO closure and suggest a rational strategy for this procedure.

Transcatheter closure of PFO as secondary prevention of cryptogenic stroke

This article covers the main unsolved issues regarding the potential role that the patent foramen ovale (PFO) plays in the genesis of so-called cryptogenic stroke. Some brief notions of the anatomy and epidemiology of the PFO are outlined. Subsequently, the results of the three trials on secondary prevention (medical therapy vs. transcatheter closure) in patients with PFO and a history of cryptogenic stroke are presented. The conflicting results of numerous meta-analyses derived from the three randomized controlled trials are discussed. Official scientific guidelines dispute an alleged superior efficacy of transcatheter PFO occlusion in comparison with antithrombotic therapy alone (anticoagulants or antiplatelet agents), except for selected cases of patients with documented PFO and a concomitant clinical-instrumental picture of deep venous thrombosis. Nevertheless, considering recent doubts about the presumptive thrombogenic and arrhythmogenic potential of PFO occlusion, which concerns only one of the septal occluders previously used, further in-depth investigations are warranted, centered on the use of newer dedicated devices to be tested in comparison with antithrombotic regimens alone.

Unresolved or Contradictory Issues About Management of Patients With Patent Foramen Ovale and Previous Cryptogenic Stroke: Additional Randomized Controlled Trials Are Eagerly Awaited

Stating a well-codified and widely accepted therapeutic conduct for patients with patent foramen ovale (PFO) and previous cryptogenic stroke is made difficult and somewhat controversial by several issues remained unresolved so far. In this short review, some aspects of the possible role played by the PFO in the pathogenesis of cryptogenic stroke are succinctly analyzed. First, some aspects of cardiovascular anatomy of the human fetus and the adult are outlined. Subsequently, the three randomized controlled trials (RCTs) that have been accomplished so far to compare the implant of a transeptal occluding device with a simple medical therapy in patients with PFO and history of cryptogenic stroke are briefly examined. These RCTs, when assessed using the “intention to treat” method, do not show a greater protective effect of therapy with transeptal device as regards the recurrences of stroke. Afterwards, there is a brief presentation of the findings of several meta-analyses that have been derived from the three above mentioned RCTs, whose results are strikingly discordant with each other. In fact, some of them come to the conclusion that the transcatheter closure of PFO does not offer significant advantages compared to antithrombotic therapy for the secondary prevention of cryptogenic stroke, while others based on subgroup analyses argue that the transcatheter closure of PFO with Amplatzer device, differently from the one performed using the STARFlex device, would be associated with significantly lower incidence of cerebrovascular events compared with medical therapy alone. Finally, the authors argue the need to adhere to the current scientific guidelines. They substantially deny an alleged superior efficacy of transcatheter PFO occlusion compared to medical therapy with antithrombotic agents (anticoagulants or antiplatelet agents), except for selected cases of patients with documented PFO and concomitant clinical-instrumental picture of deep venous thrombosis.

Disorganized Systematic Reviews and Meta-analyses: Time to Systematize the Conduct and Publication of These Study Overviews?

The number of meta-analyses published annually has increased more than 20-fold between 1994 (n = 386) and 2014 (n = 8203). In examining how much of this increase in meta-analysis publication has genuinely represented novel contributions to clinical medicine and public health, it became clear that there was an abundance of redundant and disorganized meta-analyses, creating confusion and generating considerable debate. Ironically, meta-analyses, which should prevent redundant research, have become a victim of it. Recently, 17 meta-analyses were published based on the results of only 3 randomized controlled trials that studied the role of transcatheter closure of patent foramen ovale for prevention of cryptogenic stroke. In our search of the published literature, we identified at least 10 topics that were the subject of 10 meta-analyses. In the context of overlapping meta-analyses, one questions what needs to be done to put this "runaway train" back on track. In this review we examine the practice of redundant meta-analyses and the reasons for its disturbing "popularity." The registration of systematic reviews should be mandatory in prospective registries, such as PROSPERO, and the PRISMA checklist should be updated to incorporate new evidence and mandate the reference of previously published reviews and rationale for any new study.

A time-series study of percutaneous closure of patent foramen ovale: premature adoption?

Objectives

To evaluate the impact of National Institute for Health and Care Excellence (NICE) guidance in January 2005 and subsequent trial evidence on the adoption of percutaneous closure of patent foramen ovale (PCPFO).

Methods

A retrospective time series study was conducted using the Inpatient Hospital Episode Statistics (HES) England. A total of 3801 patients, aged ≥18 and ≤60 years, who had PCPFO from 1 April 2006 to 31 March 2012 in England. Percentage change annualised (PCA) in PCPFO procedure rates between initial NICE guidance and publication of trial results was analysed.

Results

Between Quarter 2, 2006 and Quarter 4, 2009, 2163 PCPFO procedures were performed, with an increasing PCA of 48.4%. The procedure rate peaked before the presentation of equivocal results from the first randomised controlled trial (RCT) in late 2010, and declined between Quarter 4, 2009 and Quarter 4, 2011 (PCA=−15.3%). Of more than 2300 patients recruited to three RCTs, only 71 were recruited in English hospitals.

Conclusions

PCPFO was rapidly adopted after the publication of initial NICE guidance despite the absence of RCT evidence of efficacy. Very few English patients participated in international RCTs of PCPFO, suggesting that NICE recommendations also failed to encourage the generation of RCT evidence.

Patent foramen ovale: Unanswered questions

The foramen ovale is a remnant of the fetal circulation that remains patent in 20-25% of the adult population. Although long overlooked as a potential pathway that could produce pathologic conditions, the presence of a patent foramen ovale (PFO) has been associated with a higher than expected frequency in a variety of clinical syndromes including cryptogenic stroke, migraines, sleep apnea, platypnea-orthodeoxia, deep sea diving associated decompression illness, and high altitude pulmonary edema. A unifying hypothesis is that a chemical or particulate matter from the venous circulation crosses the PFO conduit between the right and left atria to produce a variety of clinical syndromes. Although observational studies suggest a therapeutic benefit of PFO closure compared to medical therapy alone in patients with cryptogenic stroke, 3 randomized controlled trials (RCTs) did not confirm the superiority of PFO closure for the secondary prevention of stroke. However, meta-analyses of these RCTs demonstrate a significant benefit of PFO closure over medical therapy alone. Similarly, observational studies provide support for PFO closure for symptomatic relief of migraines. But one controversial randomized study failed to replicate the results of the observational studies while another two demonstrated a partial benefit. The goal of this review is to discuss the clinical conditions associated with PFO and provide internists and primary care physicians with current data on PFO trials, and clinical insight to help guide their patients who are found to have a PFO on echocardiographic testing.

Closure versus medical therapy for preventing recurrent stroke in patients with patent foramen ovale and a history of cryptogenic stroke or transient ischemic attack

BACKGROUND

The optimal therapy for preventing recurrent stroke in people with cryptogenic stroke and patent foramen ovale (PFO) has not been defined. The choice between medical therapy (antithrombotic treatment with antiplatelet agents or anticoagulants) and transcatheter device closure has been the subject of intense debate over the past several years. Despite the lack of scientific evidence, a substantial number of people undergo transcatheter device closure (TDC) for secondary stroke prevention.

OBJECTIVES

To: 1) compare the safety and efficacy of TDC with best medical therapy alone for preventing recurrent stroke (fatal or non-fatal) or transient ischemic attacks (TIAs) in people with PFO and a history of cryptogenic stroke or TIA; 2) identify specific subgroups of people most likely to benefit from closure for secondary prevention; and 3) assess the cost-effectiveness of this strategy, if possible.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (July 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 2, 2014), MEDLINE (1950 to July 2014) and EMBASE (1980 to July 2014). In an effort to identify unpublished and ongoing trials we searched seven trials registers and checked reference lists.

SELECTION CRITERIA

We included randomized controlled trials (RCTs), irrespective of blinding, publication status, and language, comparing the safety and efficacy of device closure with medical therapy for preventing recurrent stroke or TIA in people with PFO and a history of cryptogenic stroke or TIA.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, assessed quality and risk of bias, and extracted data. The primary outcome measures of this analysis were the composite endpoint of ischemic stroke or TIA events as well as recurrent fatal or non-fatal ischemic stroke. Secondary endpoints included all-cause mortality, serious adverse events (atrial fibrillation, myocardial infarction, bleeding) and procedural success and effective closure. We used the Mantel-Haenszel method to obtain pooled risk ratios (RRs) using the random-effects model regardless of the level of heterogeneity. We pooled data for the primary outcome measure with the generic inverse variance method using the random-effects model, yielding risk estimates as pooled hazard ratio (HR), which accounts for time-to-event outcomes.

MAIN RESULTS

We included three RCTs involving a total of 2303 participants: 1150 participants were randomized to receive TDC and 1153 participants were randomized to receive medical therapy. Overall, the risk of bias was regarded as high. The mean follow-up period of all three included trials was less than five years. Baseline characteristics (age, sex, and vascular risk factors) were similar across trials. Intention-to-treat analyses did not show a statistically significant risk reduction in the composite endpoint of recurrent stroke or TIA in the TDC group when compared with medical therapy (RR 0.73, 95% CI 0.45 to 1.17). A time-to-event analysis combining the results of two RCTs also failed to show a significant risk reduction with TDC (HR 0.69, 95% CI 0.43 to 1.13). When assessing stroke prevention alone, TDC still did not show a statistically significant benefit (RR 0.61, 95% CI 0.29 to 1.27) (HR 0.55, 95% CI 0.26 to 1.18). In a sensitivity analysis including the two studies using the Amplatzer PFO occluder, TDC showed a possible protective effect on recurrent stroke compared with medical therapy (HR 0.38, 95% CI 0.14 to 1.02); however, it did not reach statistical significance. Safety analysis found that the overall risks for all-cause mortality and adverse events were similar in both the TDC and medical therapy groups. However, TDC increased the risk of new-onset atrial fibrillation (RR 3.50, 95% CI 1.47 to 8.35) and may be associated with the type of device used.

AUTHORS' CONCLUSIONS

The combined data from recent RCTs have shown no statistically significant differences between TDC and medical therapy in the prevention of recurrent ischemic stroke. TDC closure was associated with an increased risk of atrial fibrillation but not with serious adverse events.

Prevention of recurrent stroke in patients with patent foramen ovale

Patent foramen ovale (PFO) is common and only rarely related to stroke. The high PFO prevalence in healthy individuals makes for difficult decision making when a PFO is found in the setting of a cryptogenic stroke, because the PFO may be an incidental finding. Recent clinical trials of device-based PFO closure have had negative overall summary results; these trials have been limited by low recurrence rates. The optimal antithrombotic strategy for these patients is also unknown. Recent work has identified a risk score that estimates PFO-attributable fractions based on individual patient characteristics, although whether this score can help direct therapy is unclear.

How to Understand Patent Foramen Ovale Clinical Significance - Part II: Therapeutic Strategies in Cryptogenic Stroke

In the first part of this review, we reminded that patent foramen ovale (PFO) is a slit or tunnel-like passage in the interatrial septum occurring in approximately 25% of the population and that a number of conditions have been linked to its presence, the most important being cryptogenic stroke (CS) and migraine. We have also shown how, in the setting of neurological events, it is not often clear whether the PFO is pathogenically-related to the index event or an incidental finding, and therefore we thought to provide some useful key points for understanding PFO clinical significance in a case by case evaluation. The controversy about PFO pathogenicity has consequently prompted a paradigm shift of research interest from medical therapy with antiplatelets or anticoagulants to percutaneous transcatheter closure, in secondary prevention. Observational data and meta-analysis of observational studies previously suggested that PFO closure with a device was a safe procedure with a low recurrence rate of stroke, as compared to medical therapy. However, so far, published randomized controlled trials (CLOSURE I^®, RESPECT^® and PC Trial^®) have not shown the superiority of PFO closure over medical therapy. Thus, the optimal strategy for secondary prevention of paradoxical embolism in patients with a PFO remains unclear. Moreover, the latest guidelines for the prevention on stroke restricted indications for PFO closure to patients with deep vein thrombosis and high-risk of its recurrence. Given these recent data, in the second part of the present review, we aim to discuss today treatment options in patients with PFO and CS, providing an updating on patients’ management.

Role of occlusive devices to prevent thromboembolism among persons with a patent foramen ovale and prior stroke

OPINION STATEMENT

Patent foramen ovale (PFO) has been linked to stroke, presumably through the mechanism of paradoxical embolism; however, data is confusing regarding the causal relationship between PFO and embolic stroke. What has come to light in the past decade of research is that PFO closure with devices that achieve a high rate of closure may reduce the risk of recurrent stroke compared with medical therapy, but this benefit has not been shown in the general population with a PFO and cryptogenic stroke. The important question now is which patient will benefit from PFO closure for stroke risk reduction. A validated risk prediction tool is needed to help physicians determine those patients who will derive benefit from closure of PFO to prevent recurrent stroke. It is clear that even in studies with a small number of individuals and a very small number of events, there is some benefit to closure. Furthermore, improvements in closure devices and techniques have made percutaneous device closure both safe and efficacious. As such, it is not necessary to wait for a patient to have two strokes prior to serious consideration of PFO closure. We would advocate that the decision to close a PFO in the setting of a cryptogenic stroke be made at an individual level, on a case-by-case basis. Patients with high-risk features may be more likely to benefit, though who exactly comprises this population is still being elucidated. The most difficult aspect of managing this disease is the substantial number of individuals with incidental PFOs, as well as the prevalence of stroke due to other etiologies. When treating this disease, the physician must be able to weigh the likelihood of benefit versus the risk of the procedure, as well as patient preference.

Percutaneous closure versus medical therapy alone for cryptogenic stroke patients with a patent foramen ovale: meta-analysis of randomized controlled trials

Of cryptogenic stroke patients younger than 55 years of age, up to 61% have had a patent foramen ovale (PFO). Observational studies have revealed reductions in recurrent neurologic events through PFO closure versus medical therapy, and randomized controlled trials have shown nonsignificant trends toward benefit. We systematically searched for randomized controlled trials of percutaneous PFO closure with medical therapy versus medical therapy alone in patients with cryptogenic stroke and performed a meta-analysis of treatment outcomes. The primary endpoint was combined death, stroke, and transient ischemic attack. We included 3 trials. Of 2,303 total patients, 1,150 underwent PFO closure and 1,153 received medical therapy (median follow-up period, 2.6 yr). The pooled incidence of the primary endpoint was 1.2 events per 100 patient-years in the closure group (95% confidence interval [CI], 0.2-2.3) and 1.8 in the therapy group (95% CI, 0.7-2.9) (P=0.32); the number needed to treat was 167 (range, 100-500). The corresponding pooled hazard ratio was 0.67 (95% CI, 0.44-1.01; P=0.054) in favor of closure. Closure was associated with an increased risk of atrial fibrillation: relative risk=3.51 (95% CI, 1.44-8.55; P=0.006). When stratified by device, use of the Amplatzer™ PFO Occluder resulted in significant stroke-prevention benefit over medical therapy alone: hazard ratio=0.44 (95% CI, 0.21-0.95; P=0.037). When compared with medical therapy alone, PFO closure with medical therapy showed a trend toward a decreased hazard of combined events, although the absolute event reduction was small and the number needed to treat was high.

Amplatzer PFO occluder device may prevent recurrent stroke in patients with patent foramen ovale and cryptogenic stroke: a meta-analysis of randomised trials

OBJECTIVE

To review efficacy of percutaneous closure of patent foramen ovale compared with medical therapy in prevention of recurrent strokes in patients with cryptogenic stroke.

METHODS AND RESULTS

Electronic databases; PUBMED, EMBASE, Cochrane registry and web of knowledge were searched for relevant studies. In three randomised clinical trials involving 2303 participants, risk of the recurrent strokes (pooled HR 0.62, 95% CI=0.36-1.07, P=0.09, I(2) =10%) did not show benefit with device closure when compared with medical therapy group on meta-analysis of all three trials. However, on sensitivity analysis in trials using Amplatzer PFO occluder device, the closure of PFO was associated with significantly lower recurrent strokes (pooled HR=0.44, 95% CI=0.21-0.94, P=0.03, I(2)=0%) compared with medical therapy.

CONCLUSION

The closure of PFO with Amplatzer PFO occluder device was associated with significant reduction in recurrent strokes in patients with cryptogenic stroke and patent foramen ovale. The better outcome in prevention of secondary stroke in patients with cryptogenic stroke and PFO may be associated with type of closure device used.

Leptin receptor action and mechanisms of leptin resistance

The adipose tissue-derived hormone leptin regulates energy balance and neuroendocrine function. Resistance to the appetite-suppressing effects of leptin is associated with common forms of obesity. Here, we review the mechanisms by which leptin activates intracellular signals and the roles that these signals play in leptin action in vivo. Furthermore, we discuss potential mechanisms of leptin resistance, specifically focusing on data regarding the neuroanatomical locus of leptin resistance and potential mechanisms by which expression of the suppressor of cytokine signaling-3 may impair leptin action.