Leptin replacement therapy for the treatment of non-HAART associated lipodystrophy syndromes: a meta-analysis into the effects of leptin on metabolic and hepatic endpoints

Detangling the interrelations between MAFLD, insulin resistance, and key hormones

Metabolic dysfunction-associated fatty liver disease (MAFLD) has increasingly become a significant and highly prevalent cause of chronic liver disease, displaying a wide array of risk factors and pathophysiologic mechanisms of which only a few have so far been clearly elucidated. A bidirectional interaction between hormonal discrepancies and metabolic-related disorders, including obesity, type 2 diabetes mellitus (T2DM), and polycystic ovarian syndrome (PCOS) has been described. Since the change in nomenclature from non-alcoholic fatty liver disease (NAFLD) to MAFLD is based on the clear impact of metabolic elements on the disease, the reciprocal interactions of hormones such as insulin, adipokines (leptin and adiponectin), and estrogens have strongly pointed to the intrinsic links that lead to the heterogeneous epidemiology, clinical presentations, and risk factors involved in MAFLD in different populations. The objective of this work is twofold. Firstly, there is a brief discussion regarding the change in nomenclature as well as epidemiology, risk factors, and pathophysiologic mechanisms other than hormonal effects, which include nutrition and the gut microbiome, as well as genetic and epigenetic influences. Secondly, we review the basis of the most important hormonal factors involved in the development and progression of MAFLD that act both independently and in an interrelated manner.

Treatment Options for Lipodystrophy in Children

Lipodystrophy includes a heterogeneous group of rare diseases characterized by different amounts of adipose tissue loss and several metabolic complications, including hypertriglyceridemia, steatohepatitis and particularly insulin resistance, that may lead to severe morbidity and, sometimes, mortality. Therefore, therapy for lipodystrophy primarily consists of a conventional approach that involves standard treatments of metabolic abnormalities. Given the evidence of leptin deficiency in lipodystrophy syndromes, leptin replacement therapy has been considered as a treatment option. Long-term studies on the use of therapy with a methionylated analog of human leptin, metreleptin, first on animals and subsequently on human patients, demonstrated enormous improvements of patients' clinical features and metabolic conditions. Recently, metreleptin was approved by Food and Drug Administration (FDA) for the treatment of generalized lipodystrophy and by European Medicines Agency (EMA) for the treatment of both generalized and partial lipodystrophy. However, further research is being conducted for new and different therapeutic agents, especially helpful for the treatment of patients with partial lipodystrophy, as some of them do not have access to metreleptin therapy or show poor response.

Metreleptin treatment of non-HIV lipodystrophy syndromes

Lipodystrophy syndromes (LS) constitute a group of rare diseases of the adipose tissue, characterized by a complete or selective deficiency of the fat mass. These disorders are associated with important insulin resistance, cardiovascular and metabolic comorbidities that impact patient's survival and quality of life. Management is challenging and includes diet, physical activity, and specific pharmacological treatment of LS-associated comorbidities. Because of a common pathophysiology involving decreased concentration of the adipokine leptin, efforts have been made to develop therapeutic strategies with leptin replacement therapy. Metreleptin, a recombinant human leptin analogue, has been proposed in hypoleptinemic patients since the beginning of 2000's. The treatment leads to an improvement in metabolic parameters, more important in generalized than in partial LS forms. In this review, the current knowledge about the development of the drug, its outcomes in the treatment of lipodystrophic patients as well as the peculiarities of its use will be presented.

Fatty liver in lipodystrophy: A review with a focus on therapeutic perspectives of adiponectin and/or leptin replacement

Lipodystrophy is a group of clinically heterogeneous, inherited or acquired, disorders characterized by complete or partial absence of subcutaneous adipose tissue that may occur simultaneously with the pathological, ectopic, accumulation of fat in other regions of the body, including the liver. Fatty liver adds significantly to hepatic and extra-hepatic morbidity in patients with lipodystrophy. Lipodystrophy is strongly associated with severe insulin resistance and related comorbidities, such as hyperglycemia, hyperlipidemia and nonalcoholic fatty liver disease (NAFLD), but other hepatic diseases may co-exist in some types of lipodystrophy, including autoimmune hepatitis in acquired lipodystrophies, or viral hepatitis in human immunodeficiency virus (HIV)-associated lipodystrophy. The aim of this review is to summarize evidence linking lipodystrophy with hepatic disease and to provide a special focus on potential therapeutic perspectives of leptin replacement therapy and adiponectin upregulation in lipodystrophy.

Serum zinc-α2-glycoprotein levels are elevated and correlated with thyroid hormone in newly diagnosed hyperthyroidism

BACKGROUND

Zinc-α2-glycoprotein (ZAG) is a recently novel lipolytic adipokine implicated in regulation of glucose and lipid metabolism in many metabolic disorders. In vitro and animal studies suggest that thyroid hormones (TH) up-regulates ZAG production in hepatocytes. However, there is no data evaluating the possible relationship between ZAG and TH in a human model of hyperthyroidism. The objective of the present study is to assess the association of serum ZAG levels with TH and lipid profile in patients with hyperthyroidism before and after methimazole treatment.

METHODS

A total of 120 newly diagnosed overt hyperthyroidism and 122 healthy control subjects were recruited. Of them, 39 hyperthyroidism patients were assigned to receive methimazole treatment as follow-up study for 2 months.

RESULTS

The clinical consequence showed that serum ZAG levels were elevated in patients with hyperthyroidism (P < 0.01). Adjust for age, gender and BMI, serum ZAG levels were positively related with serum free T3 (FT3), free T4 (FT4) levels and negatively correlated with serum total cholesterol (TC), low density lipoprotein cholesterol (LDLC) levels in hyperthyroidism subjects (all P < 0.01). After methimazole treatment, serum ZAG levels were decreased and the decline was associated with decreased FT3, FT4 and increased TC levels (all P < 0.001).

CONCLUSION

We conclude that ZAG may be involved in the pathogenesis of lipid metabolism disorder in patients with hyperthyroidism.

TRIAL REGISTRATION

ChiCTR-ROC-17012943 . Registered 11 October 2017, retrospectively registered.

Evaluation of the hypothalamic-pituitary-adrenal axis in a case series of familial partial lipodystrophy

BACKGROUND

Familial partial lipodystrophy (FPL) is a rare genetic disease characterized by body fat abnormalities that lead to insulin resistance (IR). Clinical conditions linked to milder IR, such as type 2 diabetes (T2D) and metabolic syndrome, are associated with abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis, but little is known about its activity in FPL.

METHODS

Patients meeting the clinical criteria for FPL were subjected to anthropometric, biochemical and hormone analyses. A genetic study to identify mutations in the genes encoding peroxisome proliferator-activated receptor gamma (PPARγ) was performed. Polycystic ovary syndrome and hepatic steatosis were investigated, and the patient body compositions were analyzed via dual X-ray energy absorptiometry (DXA). The HPA axis was assessed via basal [cortisol, adrenocorticotrophic hormone (ACTH), cortisol binding globulin, nocturnal salivary cortisol and urinary free cortisol (UFC)] as well as dynamic suppression tests (cortisol post 0.5 mg and post 1 mg dexamethasone).

RESULTS

Six patients (five female and one male) aged 17 to 42 years were included. In DXA analyses, the fat mass ratio between the trunk and lower limbs (FMR) was > 1.2 in all phenotypes. One patient had a confirmed mutation in the PPARγ gene: a novel heterozygous substitution of p. Arg 212 Trp (c.634C>T) at exon 5. HPA sensitivity to glucocorticoid feedback was preserved in all six patients, and a trend towards lower basal serum cortisol, serum ACTH and UFC values was observed.

CONCLUSIONS

Our findings suggest that FPL is not associated with overt abnormalities in the HPA axis, despite a trend towards low-normal basal cortisol and ACTH values and lower UFC levels. These findings suggest that the extreme insulin resistance occurring in FPL may lead to a decrease in HPA axis activity without changing its sensitivity to glucocorticoid feedback, in contrast to the abnormalities in HPA axis function in T2D and common metabolic syndrome.

Soy Protein Isolate Suppresses Lipodystrophy-induced Hepatic Lipid Accumulation in Model Mice

Lipodystrophies are acquired and genetic disorders characterized by the complete or partial absence of body fat with a line of metabolic disorders, including hepatic steatosis. Because soy protein isolate (SPI) has been reported to reduce cholesterol and triglyceride levels in animals and humans, we explored the effect of SPI on the pathophysiology of hepatic lipid accumutaion in a diet-induced lipodystrophy model mice. Four weeks of the lipodystrophy model diet induced hepatic lipid accumulation concomitant with marked deficiencies of adipose tissue and serum adipocytokines in mice. However, supplementing the lipodystrophy model diet with SPI could alleviate the hepatic lipid acculation without affecting the lipoatrophic effect of the diet. Enhanced lipogenesis is the principal mechanism of hepatic steatosis in this model, but SPI supplementation significantly attenuated the increase in enzyme activity and/or mRNA expression. Additionally, SPI supplementation upregulated the hepatic mRNA expression of an enzyme involved in cholesterol catabolism. In conclusion, our results indicate the possibility of dietary SPI to attenuate lipodystorophy-induced hepatic steatosis through the direct reduction of hepatic lipogenesis without affecting adipocytokine production.

Non-alcoholic fatty liver disease and dyslipidemia: An update

Non-alcoholic fatty liver (NAFLD) is the most common liver disease worldwide, progressing from simple steatosis to necroinflammation and fibrosis (leading to non-alcoholic steatohepatitis, NASH), and in some cases to cirrhosis and hepatocellular carcinoma. Inflammation, oxidative stress and insulin resistance are involved in NAFLD development and progression. NAFLD has been associated with several cardiovascular (CV) risk factors including obesity, dyslipidemia, hyperglycemia, hypertension and smoking. NAFLD is also characterized by atherogenic dyslipidemia, postprandial lipemia and high-density lipoprotein (HDL) dysfunction. Most importantly, NAFLD patients have an increased risk for both liver and CV disease (CVD) morbidity and mortality. In this narrative review, the associations between NAFLD, dyslipidemia and vascular disease in NAFLD patients are discussed. NAFLD treatment is also reviewed with a focus on lipid-lowering drugs. Finally, future perspectives in terms of both NAFLD diagnostic biomarkers and therapeutic targets are considered.

Metreleptin and generalized lipodystrophy and evolving therapeutic perspectives

INTRODUCTION

Metreleptin was recently approved by the Food and Drug Administration for the treatment of generalized lipodystrophy, a condition characterized by leptin deficiency. Its efficacy as hormone replacement therapy suggests broader applications in diseases also characterized by leptin abnormalities, such as familial partial lipodystrophy (FPLD), non-alcoholic fatty liver disease (NAFLD), and common obesity. Metreleptin, in conjunction with other pharmacologic interventions, has the potential to address one of the most widespread epidemics of our time, obesity.

AREAS COVERED

This review covers the physiology of leptin, the pharmacologic properties of recombinant methionyl human leptin (R-metHu-Leptin, metreleptin), evidence for metreleptin's efficacy in the treatment of generalized lipodystrophy from both completed and ongoing clinical trials, safety concerns, and future directions in metreleptin research.

EXPERT OPINION

Metreleptin's approval for generalized lipodystrophy is the first step in defining and expanding its role to other metabolic diseases. Clinical trials are underway to delineate its efficacy in FPLD, human immunodeficiency virus/highly active anti-retroviral therapy-associated acquired lipodystrophy (HAL), and NAFLD. Additionally, there is growing data that support a therapeutic role in obesity. One of the barriers to development, however, is metreleptin's safety and immunogenicity. Further advances in biologic compatibility are required before metreleptin can be approved for additional indications.

The Effects of Leptin Replacement on Neural Plasticity

Leptin, an adipokine synthesized and secreted mainly by the adipose tissue, has multiple effects on the regulation of food intake, energy expenditure, and metabolism. Its recently-approved analogue, metreleptin, has been evaluated in clinical trials for the treatment of patients with leptin deficiency due to mutations in the leptin gene, lipodystrophy syndromes, and hypothalamic amenorrhea. In such patients, leptin replacement therapy has led to changes in brain structure and function in intra- and extrahypothalamic areas, including the hippocampus. Furthermore, in one of those patients, improvements in neurocognitive development have been observed. In addition to this evidence linking leptin to neural plasticity and function, observational studies evaluating leptin-sufficient humans have also demonstrated direct correlation between blood leptin levels and brain volume and inverse associations between circulating leptin and risk for the development of dementia. This review summarizes the evidence in the literature on the role of leptin in neural plasticity (in leptin-deficient and in leptin-sufficient individuals) and its effects on synaptic activity, glutamate receptor trafficking, neuronal morphology, neuronal development and survival, and microglial function.

Metreleptin for injection to treat the complications of leptin deficiency in patients with congenital or acquired generalized lipodystrophy

The lipodystrophies represent a class of diseases characterized by leptin deficiency. Leptin deficiency is associated with a severe form of the metabolic syndrome characterized by dyslipidemia, insulin resistance, diabetes, and ovarian dysfunction. Metreleptin is the pharmaceutical derived product that has been approved by the Food and Drug Administration (FDA) to treat the severe metabolic abnormalities of the generalized forms of lipodystrophy. Herein we describe the properties of metreleptin, its use in patients, which includes the administration of the drug and how it may be acquired by medical professionals as well as its safety, tolerability, and properties. Finally, we speculate on future uses and development of metreleptin.

Leptin applications in 2015: what have we learned about leptin and obesity?

PURPOSE OF REVIEW

To summarize previous and current advancements for leptin therapeutics, we described how leptin may be useful in leptin deficient states such as lipodystrophy, for which leptin was recently approved, and how it may be useful in the future for typical obesity.

RECENT FINDINGS

The discovery of leptin in 1994 built the foundation for understanding the pathophysiology and treatment of obesity. Leptin therapy reverses morbid obesity related to congenital leptin deficiency and appears to possibly treat lipodystrophy, a finding which has led to the approval of leptin for the treatment of lipodystrophy in the USA and Japan. Typical obesity, on the other hand, is characterized by hyperleptinemia and leptin tolerance. Thus, leptin administration has proven ineffective for inducing weight loss on its own but could possibly be useful in combination with other therapies or for weight loss maintenance.

SUMMARY

Leptin is not able to treat typical obesity; however, it is effective for reversing leptin deficiency-induced obesity and is possibly useful in lipodystrophy. New mechanisms and pathways involved in leptin resistance are continuously discovered, whereas the development of new techniques and drug combinations which may improve leptin's efficacy and safety regenerate the hope for its use as an effective treatment for typical obesity.

New advances in the treatment of generalized lipodystrophy: role of metreleptin

Recombinant methionyl human leptin or metreleptin is a synthetic leptin analog that has been trialed in patients with leptin-deficient conditions, such as leptin deficiency due to mutations in the leptin gene, hypothalamic amenorrhea, and lipodystrophy syndromes. These syndromes are characterized by partial or complete absence of adipose tissue and hormones derived from adipose tissue, most importantly leptin. Patients deficient in leptin exhibit a number of severe metabolic abnormalities such as hyperglycemia, hypertriglyceridemia, and hepatic steatosis, which can progress to diabetes mellitus, acute pancreatitis, and hepatic cirrhosis, respectively. For the management of these abnormalities, multiple therapies are usually required, and advanced stages may be progressively difficult to treat. Following many successful trials, the US Food and Drug Administration approved metreleptin for the treatment of non-HIV-related forms of generalized lipodystrophy. Leptin replacement therapy with metreleptin has, in many cases, reversed these metabolic complications, with improvements in glucose-insulin-lipid homeostasis, and regression of fatty liver disease. Besides being effective, a daily subcutaneous administration of metreleptin is generally safe, but the causal association between metreleptin and immune complications (such as lymphoma) is still unclear. Moreover, further investigation is needed to elucidate mechanisms by which metreleptin leads to the development of anti-leptin antibodies. Herein, we review clinical aspects of generalized lipodystrophy and the pharmacological profile of metreleptin. Further, we examine studies that assessed the safety and efficacy of metreleptin, and outline some clinical perspectives on the drug.