Leptin decreases de novo lipogenesis in patients with lipodystrophy

Leptin acutely increases hepatic triglyceride secretion in patients with lipodystrophy

BACKGROUND AND AIMS

Metreleptin ameliorates hepatic steatosis partially independent of its anorexic action. We previously showed that metreleptin increases hepatic very low-density lipoprotein triglycerides (VLDL1-TG) export in rodents and healthy humans requiring intact hepatic autonomic innervation. The primary aim of this study was to investigate whether metreleptin has anti-steatotic properties in patients with lipodystrophy by increasing VLDL1-TG export. In addition, we present a case of generalized lipodystrophy undergoing metreleptin treatment after liver transplantation, a model for hepatic autonomic denervation.

METHODS

In this randomized, placebo-controlled, crossover trial (EudraCT 2017-003014-22) we assessed the acute effects of a single metreleptin injection in 10 patients (8 females, 2 males; mean age ± SD: 49 ± 14 yrs; 9 familial partial and 1 generalized lipodystrophy) on hepatic VLDL1-TG secretion and hepatocellular lipid content (HCL) measured via an intravenous fat emulsion test and 1H-magnetic resonance spectroscopy, respectively.

RESULTS

We found that a single injection of metreleptin increased hepatic VLDL1-TG secretion by 75 % (mean difference ± SD: +219 ± 149 mg/h metreleptin vs. placebo; p = 0.001), without significant changes in HCL within 3 h (mean difference ± SD: -8 ± 14 % metreleptin vs. placebo, p = 0.14). Metreleptin therapy in a patient with generalized lipodystrophy following liver transplantation failed to ameliorate hepatic steatosis despite improving glucose and lipid metabolism.

CONCLUSIONS

Leptin acutely increases hepatic VLDL1-TG secretion in patients with lipodystrophy, likely contributing to metreleptin's body weight-independent anti-steatotic effects. The case report suggests that intact autonomic liver innervation may be required for this action, warranting further research.

Leptin limits hepatic lipid accumulation and inflammation via vagal activation of the JAK2-STAT3/AMPK pathway

Non-Alcoholic Fatty Liver Disease (NAFLD) begins with hepatic lipid accumulation, and leptin has antisteatosis properties. In this study, we investigated the effects of leptin on hepatic steatosis and inflammation through the vagal pathway independently of the inhibitory effect of food intake. Male Sprague-Dawley rats were matched for food intake after the high-fat diet (HFD)-induced obesity model and were injected intraperitoneally with leptin or leptin + lidocaine for 6 weeks. Control rats received equal volumes of saline. Adipose tissue mass, NAFLD activity scores (NAS), hepatic inflammatory factors, hepatic triglyceride content and hepatic lipid metabolism-related protein levels were evaluated. Leptin ameliorated HFD-induced hepatic lipid accumulation, improved NAS, and decreased tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and monocyte chemotactic protein-1 (MCP-1) levels in the presence of matched intake. Lidocaine decreased the phosphorylation of signal transducer and activator of transcription 3 (p-STAT3) expression in the nucleus tractus solitarius (NTS) and abrogated the leptin-mediated improvement. Leptin increased hypothalamic phosphorylated Janus kinase 2 (p-JAK2) and p-STAT3 expression, as well as the expression of mitochondrial respiratory chain-related genes. Leptin also increased hepatic phosphorylated adenosine 5'-monophosphate-activated protein kinase (p-AMPK) expression and phosphorylation of its downstream target acetyl Co A carboxylase 1 (ACC1), reducing de novo lipogenesis. Our results suggest that leptin ameliorated hepatic lipid accumulation and inflammation by activating the JAK2-STAT3/AMPK pathway through the vagal pathway independently of the inhibitory effect of ingestion. Leptin has the potential to be a drug for early NAFLD treatment.

Influence of diet and body weight in treatment-resistant acquired partial lipodystrophy after hematopoietic stem cell transplantation and its potential for metabolic improvement

Lipodystrophy is a rare disease characterized by various metabolic complications resulting from the complete or partial loss of adipose tissues and abnormal fat accumulation. Acquired lipodystrophy may occur due to certain drugs, autoimmunity or for unknown reasons. Recently, cases of acquired lipodystrophy after hematopoietic stem cell transplantation (HSCT) have been reported. Leptin administration, used recently to treat generalized lipodystrophy, effectively controlled metabolic complications; however, few reports demonstrated the effectiveness of leptin for acquired partial lipodystrophy. In this report, we present the case of a 17-year-old woman who developed insulin resistance, hypertriglyceridemia, and fatty liver after HSCT. Due to her thin gluteal fat and low blood adiponectin levels, her metabolic abnormalities were attributed to partial lipodystrophy. While both leptin and pemafibrate administration partially attenuated metabolic abnormalities, its effects were relatively limited, probably because the serum leptin levels were maintained, which is not likely in generalized lipodystrophy. Nevertheless, after she developed adjustment disorder and experienced weight loss, along with decreased food intake, her metabolic markers significantly improved. This case suggests the modest effect of leptin and permafibrate in partial lipodystrophy after HSCT, highlighting the importance of diet therapy in metreleptin treatment for acquired partial lipodystrophy.

Lipodystrophy as a target to delay premature aging

Lipodystrophy syndromes are rare diseases characterized by low levels and an abnormal distribution of adipose tissue, caused by diverse genetic or acquired causes. These conditions commonly exhibit metabolic complications, including insulin resistance, diabetes, hypertriglyceridemia, nonalcoholic fatty liver disease, and adipose tissue dysfunction. Moreover, genetic lipodystrophic laminopathies exhibit a premature aging phenotype, emphasizing the importance of restoring adipose tissue distribution and function. In this opinion, we discuss the relevance of adipose tissue reestablishment as a potential approach to alleviate premature aging and age-related complications in genetic lipodystrophy syndromes.

Lipid Metabolism in Metabolic-Associated Steatotic Liver Disease (MASLD)

Metabolic-associated steatotic liver disease (MASLD) is a cluster of pathological conditions primarily developed due to the accumulation of ectopic fat in the hepatocytes. During the severe form of the disease, i.e., metabolic-associated steatohepatitis (MASH), accumulated lipids promote lipotoxicity, resulting in cellular inflammation, oxidative stress, and hepatocellular ballooning. If left untreated, the advanced form of the disease progresses to fibrosis of the tissue, resulting in irreversible hepatic cirrhosis or the development of hepatocellular carcinoma. Although numerous mechanisms have been identified as significant contributors to the development and advancement of MASLD, altered lipid metabolism continues to stand out as a major factor contributing to the disease. This paper briefly discusses the dysregulation in lipid metabolism during various stages of MASLD.

Leptin Decreases Gluconeogenesis and Gluconeogenic Substrate Availability in Patients With Lipodystrophy

CONTEXT

The effects of leptin, an adipocyte-derived hormone that signals overall energy sufficiency, can only be studied in leptin-deficient conditions. In patients with lipodystrophy, a rare disease and unique model of leptin deficiency, treatment with recombinant leptin (metreleptin) improves glycemia and decreases energy expenditure. We hypothesized that these improvements might be mediated by reduced gluconeogenesis (GNG), an energy-requiring process.

OBJECTIVE

To determine the effects of metreleptin on GNG and GNG substrates.

METHODS

This was a single-arm prospective study of metreleptin administration in 15 patients with lipodystrophy, 9 of whom had data on GNG (NIH, 2013-2018). We analyzed total GNG, insulin-mediated suppression of GNG, glycerol, palmitate, alanine, lactate, peripheral and hepatic insulin sensitivity, and markers of glycemia (eg, HbA1c, glucose, fasting insulin).

RESULTS

Metreleptin administration decreased basal GNG, increased insulin-mediated suppression of GNG, and improved insulin sensitivity and markers of glycemic control. Metreleptin reduced carbon sources for GNG, including plasma alanine and lactate, and rate of appearance (Ra) of glycerol, and decreased Ra of palmitate, a driver of GNG. Glycerol and palmitate Ra correlated with GNG prior to but not during metreleptin administration. Alanine strongly correlated with GNG both before and during metreleptin administration.

CONCLUSIONS

Metreleptin treatment in patients with lipodystrophy reduced GNG likely through decreased availability of carbon sources for gluconeogenesis, such as alanine, lactate, and glycerol. Associations between alanine and GNG persisted after metreleptin treatment while correlations with glycerol and palmitate Ra did not persist, suggesting reduced importance of lipolysis as a driver of GNG in the leptin-replete state.

Isotope Labeling and Biochemical Assessment of Liver-Triacylglycerol in Patients with Different Levels of Histologically-Graded Liver Disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) prevalence is rapidly growing, and fatty liver has been found in a quarter of the US population. Increased liver lipids, particularly those derived from the pathway of de novo lipogenesis (DNL), have been identified as a hallmark feature in individuals with high liver fat. This has led to much activity in basic science and drug development in this area. No studies to date have investigated the contribution of DNL across a spectrum of disease, although it is clear that inhibition of DNL has been shown to reduce liver fat.

OBJECTIVES

The purpose of this study was to determine whether liver lipid synthesis increases across the continuum of liver injury.

METHODS

Individuals (n = 49) consumed deuterated water for 10 d before their scheduled bariatric surgeries to label DNL; blood and liver tissue samples were obtained on the day of the surgery. Liver lipid concentrations were quantitated, and levels of protein and gene expression assessed.

RESULTS

Increased liver DNL, measured isotopically, was significantly associated with liver fatty acid synthase protein content (R = 0.470, P = 0.003), total steatosis assessed by histology (R = 0.526, P = 0.0008), and the fraction of DNL fatty acids in plasma very low-density lipoprotein-triacylglycerol (R = 0.747, P < 0.001). Regression analysis revealed a parabolic relationship between fractional liver DNL (percent) and NAFLD activity score (R = 0.538, P = 0.0004).

CONCLUSION

These data demonstrate that higher DNL is associated with early to mid stages of liver disease, and this pathway may be an effective target for the treatment of NAFLD and nonalcoholic steatohepatitis. This study was registered at clinicaltrials.gov as NCT03683589.

Associations of fatty acids composition and estimated desaturase activities in erythrocyte phospholipids with biochemical and clinical indicators of cardiometabolic risk in non-diabetic Serbian women: the role of level of adiposity

Introduction

Fatty acids (FAs) composition and desaturase activities can be altered in different metabolic conditions, but the adiposity-independent associations with clinical and biochemical indicators of cardiometabolic risk are still unclear. This study aimed to analyze the associations of FAs composition and estimated desaturase activities with anthropometric, clinical, and biochemical cardiometabolic risk indicators in non-diabetic Serbian women, and to investigate if these associations were independent of the level of adiposity and other confounders.

Methods

In 76 non-diabetic, otherwise healthy Serbian women, aged 24-68 years, with or without metabolic syndrome or obesity (BMI=23.6±5.6 kg/m2), FA composition in erythrocyte phospholipids was measured by gas-liquid chromatography. Desaturase activities were estimated from product/precursor FAs ratios (D9D:16:1n-7/16:0; D6D:20:3n-6/18:2n-6; D5D:20:4n-6/20:3n-6). Correlations were made with anthropometric, biochemical (serum glucose, triacylglycerols, LDL-C, HDL-C, ALT, AST, and their ratios) and clinical (blood pressure) indicators of cardiometabolic risk. Linear regression models were performed to test the independence of these associations.

Results

Estimated desaturase activities and certain FAs were associated with anthropometric, clinical and biochemical indicators of cardiometabolic risk: D9D, D6D, 16:1n-7 and 20:3n-6 were directly associated, while D5D and 18:0 were inversely associated. However, the associations with clinical and biochemical indicators were not independent of the associations with the level of adiposity, since they were lost after controlling for anthropometric indices. After controlling for multiple confounders (age, postmenopausal status, education, smoking, physical activity, dietary macronutrient intakes, use of supplements, alcohol consumption), the level of adiposity was the most significant predictor of desaturase activities and aforementioned FAs levels, and mediated their association with biochemical/clinical indicators. Vice versa, desaturase activities predicted the level of adiposity, but not other components of cardiometabolic risk (if the level of adiposity was accounted). While the associations of anthropometric indices with 16:1n-7, 20:3n-6, 18:0 and D9D and D6D activities were linear, the associations with D5D activity were the inverse U-shaped. The only adiposity-independent association of FAs profiles with the indicators of cardiometabolic risk was a positive association of 20:5n-3 with ALT/AST ratio, which requires further exploration.

Discussion

Additional studies are needed to explore the mechanisms of the observed associations.

Liver insulinization as a driver of triglyceride dysmetabolism

Metabolic dysfunction-associated fatty liver disease (MAFLD) is an increasingly prevalent fellow traveller with the insulin resistance that underlies type 2 diabetes mellitus. However, the mechanistic connection between MAFLD and impaired insulin action remains unclear. In this Perspective, we review data from humans to elucidate insulin's aetiological role in MAFLD. We focus particularly on the relative preservation of insulin's stimulation of triglyceride (TG) biosynthesis despite its waning ability to curb hepatic glucose production (HGP). To explain this apparent 'selective insulin resistance', we propose that hepatocellular processes that lead to TG accumulation require less insulin signal transduction, or 'insulinization,' than do those that regulate HGP. As such, mounting hyperinsulinaemia that barely compensates for aberrant HGP in insulin-resistant states more than suffices to maintain hepatic TG biosynthesis. Thus, even modestly elevated or context-inappropriate insulin levels, when sustained day and night within a heavily pro-lipogenic metabolic milieu, may translate into substantial cumulative TG biosynthesis in the insulin-resistant state.

Non-Alcoholic Fatty Liver Disease: Translating Disease Mechanisms into Therapeutics Using Animal Models

Nonalcoholic fatty liver disease (NAFLD) is a range of pathologies arising from fat accumulation in the liver in the absence of excess alcohol use or other causes of liver disease. Its complications include cirrhosis and liver failure, hepatocellular carcinoma, and eventual death. NAFLD is the most common cause of liver disease globally and is estimated to affect nearly one-third of individuals in the United States. Despite knowledge that the incidence and prevalence of NAFLD are increasing, the pathophysiology of the disease and its progression to cirrhosis remain insufficiently understood. The molecular pathogenesis of NAFLD involves insulin resistance, inflammation, oxidative stress, and endoplasmic reticulum stress. Better insight into these molecular pathways would allow for therapies that target specific stages of NAFLD. Preclinical animal models have aided in defining these mechanisms and have served as platforms for screening and testing of potential therapeutic approaches. In this review, we will discuss the cellular and molecular mechanisms thought to contribute to NAFLD, with a focus on the role of animal models in elucidating these mechanisms and in developing therapies.

The health risk of acetochlor metabolite CMEPA is associated with lipid accumulation induced liver injury

Liver injury may cause many diseases, such as non-alcoholic fatty liver disease (NAFLD). Acetochlor is one of the representative chloroacetamide herbicides, and its metabolite 2-chloro-N-(2-ethyl-6-methyl phenyl) acetamide (CMEPA) is the main form of exposure in the environment. It has been shown that acetochlor can cause mitochondrial damage of HepG2 cells and induce apoptosis by activating Bcl/Bax pathway (Wang et al., 2021). But there has been less research on CMEPA. we explored the possibility of CMEPA and liver injury through biological experiments. In vivo, CMEPA (0-16 mg/L) induced liver damage in zebrafish larvae, including increased lipid droplets, changes in liver morphology (>1.3-fold) and increased TC/TG content (>2.5-fold). In vitro, we selected L02 (human normal liver cells) as the model, and explored its molecular mechanism. We found that CMEPA (0-160 mg/L) induced apoptosis (similar to 40%), mitochondrial damage and oxidative stress in L02 cells. CMEPA induced intracellular lipid accumulation by inhibiting AMPK/ACC/CPT-1A signaling pathway and activating SREBP-1c/FAS signaling pathway. Our study provides evidence of a link between CMEPA and liver injury. This raises concerns regarding the health risks of pesticide metabolites to liver health.

An adipocentric perspective on the development and progression of non-alcoholic fatty liver disease

Alongside the liver, white adipose tissue (WAT) is critical in regulating systemic energy homeostasis. Although each organ has its specialised functions, they must work coordinately to regulate whole-body metabolism. Adipose tissues and the liver are relatively resilient and can adapt to an energy surplus by facilitating triglyceride (TG) storage up to a certain threshold level without significant metabolic disturbances. However, lipid storage in WAT beyond a "personalised" adiposity threshold becomes dysfunctional, leading to metabolic inflexibility, progressive inflammation, and aberrant adipokine secretion. Moreover, the failure of adipose tissue to store and mobilise lipids results in systemic knock-on lipid overload, particularly in the liver. Factors contributing to hepatic lipid overload include lipids released from WAT, dietary fat intake, and enhanced de novo lipogenesis. In contrast, extrahepatic mechanisms counteracting toxic hepatic lipid overload entail coordinated compensation through oxidation of surplus fatty acids in brown adipose tissue and storage of fatty acids as TGs in WAT. Failure of these integrated homeostatic mechanisms leads to quantitative increases and qualitative alterations to the lipidome of the liver. Initially, hepatocytes preferentially accumulate TG species leading to a relatively "benign" non-alcoholic fatty liver. However, with time, inflammatory responses ensue, progressing into more severe conditions such as non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma, in some individuals (often without an early prognostic clue). Herein, we highlight the pathogenic importance of obesity-induced "adipose tissue failure", resulting in decreased adipose tissue functionality (i.e. fat storage capacity and metabolic flexibility), in the development and progression of NAFL/NASH.

Targeting adipokines in polycystic ovary syndrome and related metabolic disorders: from experimental insights to clinical studies

Polycystic ovary syndrome (PCOS) affects approximately 15% of women of reproductive age worldwide. It is the most prevalent endocrine disorder with marked risks for female infertility, type 2 diabetes mellitus (T2DM), psychiatric disorders and gynecological cancers. Although the pathophysiology of PCOS remains largely elusive, growing evidence suggests a close link with obesity and its related metabolic disorders. As a highly active endocrine cell population, hypertrophic adipocytes in obesity have disturbed production of a vast array of adipokines, biologically active peptides that exert pleiotropic effects on homeostatic regulation of glucose and lipid metabolism. In parallel with their crucial roles in the pathophysiology of obesity-induced metabolic diseases, adipokines have recently been identified as promising targets for novel therapeutic strategies for multiple diseases. Current treatments for PCOS are suboptimal with insufficient alleviation of all symptoms. Novel findings in adipokine-targeted agents may provide important insight into the development of new drugs for PCOS. This Review presents an overview of the current understanding of mechanisms that link PCOS to obesity and highlights emerging evidence of adipose-ovary crosstalk as a pivotal mediator of PCOS pathogenesis. We summarize recent findings of preclinical and clinical studies that reveal the therapeutic potential of adipokine-targeted novel approaches to PCOS and its related metabolic disorders. We also discuss the critical gaps in knowledge that need to be addressed to guide the development of adipokine-based novel therapies for PCOS.

Leptin increases hepatic triglyceride export via a vagal mechanism in humans

Recombinant human leptin (metreleptin) reduces hepatic lipid content in patients with lipodystrophy and overweight patients with non-alcoholic fatty liver disease and relative hypoleptinemia independent of its anorexic action. In rodents, leptin signaling in the brain increases very-low-density lipoprotein triglyceride (VLDL-TG) secretion and reduces hepatic lipid content via the vagus nerve. In this randomized, placebo-controlled crossover trial (EudraCT Nr. 2017-003014-22), we tested whether a comparable mechanism regulates hepatic lipid metabolism in humans. A single metreleptin injection stimulated hepatic VLDL-TG secretion (primary outcome) and reduced hepatic lipid content in fasted, lean men (n = 13, age range 20-38 years) but failed to do so in metabolically healthy liver transplant recipients (n = 9, age range 26-62 years) who represent a model for hepatic denervation. In an independent cohort of lean men (n = 10, age range 23-31 years), vagal stimulation by modified sham feeding replicated the effects of metreleptin on VLDL-TG secretion. Therefore, we propose that leptin has anti-steatotic properties that are independent of food intake by stimulating hepatic VLDL-TG export via a brain-vagus-liver axis.

Lactation alters the relationship between liver lipid synthesis and hepatic fat stores in the postpartum period

In mothers who are nursing their infants, increased clearance of plasma metabolites into the mammary gland may reduce ectopic lipid in the liver. No study to date has investigated the role of lactation on liver lipid synthesis in humans, and we hypothesized that lactation would modify fatty acid and glucose handling to support liver metabolism in a manner synchronized with the demands of milk production. Lactating (n = 18) and formula-feeding women (n = 10) underwent metabolic testing at 6-week postpartum to determine whether lactation modified intrahepatic triacylglycerols (IHTGs), measured by proton magnetic resonance spectroscopy. Subjects ingested oral deuterated water to measure fractional de novo lipogenesis (DNL) in VLDL-TG during fasting and during an isotope-labeled clamp at an insulin infusion rate of 10 mU/m²/min. Compared with formula-feeding women, we found that lactating women exhibited lower plasma VLDL-TG concentrations, similar IHTG content and similar contribution of DNL to total VLDL-TG production. These findings suggest that lactation lowers plasma VLDL-TG concentrations for reasons that are unrelated to IHTG and DNL. Surprisingly, we determined that the rate of appearance of nonesterified fatty acids was not related to IHTG in either group, and the expected positive association between DNL and IHTG was only significant in formula-feeding women. Further, in lactating women only, the higher the prolactin concentration, the lower the IHTG, while greater DNL strongly associated with elevations in VLDL-TG. In conclusion, we suggest that future studies should investigate the role of lactation and prolactin in liver lipid secretion and metabolism.

Excess 11-Oxygenated Androgens in Women With Severe Insulin Resistance Are Mediated by Adrenal Insulin Receptor Signaling

CONTEXT

Syndromes of severe insulin resistance (SIR) include insulin receptoropathy, in which all signaling downstream of the insulin receptor is lost, and lipodystrophy, in which some signaling pathways are impaired and others preserved. Women with SIR commonly have ovarian hyperandrogenemia; adrenal-derived 11-oxygenated androgens, produced by CYP11B1, have not been studied.

OBJECTIVE

We aimed to evaluate classic pathway androgens (androstenedione, testosterone) and 11-oxygenated androgens in women with SIR and hyperandrogenemia, and to elucidate the role of insulin receptor signaling for 11-oxygenated androgen production by comparing lipodystrophy and receptoropathy.

METHODS

Steroid hormones were quantified using LC-MS/MS in a cross-sectional study of 18 women with hyperandrogenemia and SIR (11 lipodystrophy, 7 receptoropathy) and 23 controls. To assess ovarian vs adrenal origin, steroids were compared in receptoropathy patients with (Ovary+) vs without (Ovary-) ovarian function.

RESULTS

Compared with controls, classic androgens were elevated in both lipodystrophy and receptoropathy, and 11-oxygenated androgens were increased in lipodystrophy (2.9-fold higher 11β-hydroxyandrostenedione (11OHA4), 2.4-fold higher 11-ketoandrostenedione (11KA4), 3.6-fold higher 11-ketotestosterone (11KT); P < 0.01), but not receptoropathy. Product-to-precursor ratios for CYP11B1 conversion of androstenedione to 11OHA4 were similar in lipodystrophy and controls but decreased in receptoropathy (6.5-fold lower than control; P = 0.001). Classic androgens were elevated in Ovary + but not Ovary- patients.

CONCLUSIONS

11-Oxygenated androgens are elevated in lipodystrophy but not receptoropathy. In SIR, insulin receptor signaling is necessary for adrenal hyperandrogenemia but not ovarian hyperandrogenemia; excess classic androgens are derived from the ovaries. Insulin receptor signaling increases adrenal 19-carbon steroid production, which may have implications for more common disorders of mild IR.

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.

Abnormal transaminase and lipid profiles in coexisting diseases in patients with fatty liver: a population study in Sichuan

Among chronic liver diseases, fatty liver has the highest incidence worldwide. Coexistence of fatty liver and other chronic diseases, such as diabetes, hepatitis B virus (HBV) and Helicobacter pylori (Hp) infection, is common in clinical practice. The present study was conducted to analyze the prevalence and association of coexisting diseases in patients with fatty liver and to investigate how coexisting diseases contribute to abnormal transaminase and lipid profiles. We enrolled participants who were diagnosed with fatty liver via ultrasound in the physical examination center of West China Hospital. Multivariable logistic regression was used to determine the adjusted odds ratios (ORs). We found that 23.6% of patients who underwent physical examinations were diagnosed with fatty liver. These patients had higher risks of metabolic syndrome (MetS), type 2 diabetes mellitus (T2DM), and hypertension and a lower risk of HBV infection. The risks of Hp infection and hyperthyroidism did not statistically differ. When fatty liver coexisted with T2DM, MetS and thyroid dysfunction, it conferred a higher risk of elevated transaminase. Fatty liver was positively correlated with triglycerides, cholesterol and low-density lipoprotein cholesterol (LDL-C) and negatively correlated with HBV; thus, HBV had a neutralizing effect on lipid metabolism when coexisting with fatty liver. In conclusion, patients with fatty liver that coexists with T2DM, MetS and thyroid dysfunction are more prone to elevated transaminase levels. Patients with both fatty liver and HBV may experience a neutralizing effect on their lipid metabolism. Thus, lipid alterations should be monitored in these patients during antiviral treatment for HBV.

Selective targeting of angiopoietin-like 3 (ANGPTL3) with vupanorsen for the treatment of patients with familial partial lipodystrophy (FPLD): results of a proof-of-concept study

BACKGROUND

Familial partial lipodystrophy (FPLD) is a rare disease characterized by selective loss of peripheral subcutaneous fat, associated with dyslipidemia and diabetes mellitus. Reductions in circulating levels of ANGPTL3 are associated with lower triglyceride and other atherogenic lipids, making it an attractive target for treatment of FPLD patients. This proof-of-concept study was conducted to assess the efficacy and safety of targeting ANGPTL3 with vupanorsen in patients with FPLD.

METHODS

This was an open-label study. Four patients with FPLD (two with pathogenic variants in LMNA gene, and two with no causative genetic variant), diabetes (HbA1c ≥ 7.0 % and ≤ 12 %), hypertriglyceridemia (≥ 500 mg/dL), and hepatic steatosis (hepatic fat fraction, HFF ≥ 6.4 %) were included. Patients received vupanorsen subcutaneously at a dose of 20 mg weekly for 26 weeks. The primary endpoint was the percent change from baseline in fasting triglycerides at Week 27. Other endpoints analyzed at the same time point included changes in ANGPTL3, fasting lipids and lipoproteins, insulin secretion/sensitivity, postprandial lipids, and glycemic changes in response to a mixed meal test, HFF measured by MRI, and body composition measured by dual-energy absorptiometry (DEXA).

RESULTS

Baseline mean ± SD fasting triglyceride level was 9.24 ± 4.9 mmol/L (817.8 ± 431.9 mg/dL). Treatment resulted in reduction in fasting levels of triglycerides by 59.9 %, ANGPTL3 by 54.7 %, and in several other lipoproteins/lipids, including very low-density lipoprotein cholesterol by 53.5 %, non-high-density lipoprotein cholesterol by 20.9 %, and free fatty acids (FFA) by 41.7 %. The area under the curve for postprandial triglycerides, FFA, and glucose was reduced by 60 %, 32 %, and 14 %, respectively. Treatment with vupanorsen also resulted in 55 % reduction in adipose tissue insulin resistance index, while other insulin sensitivity indices and HbA1c levels were not changed. Additional investigations into HFF and DEXA parameters suggested dynamic changes in fat partitioning during treatment. Adverse events observed were related to common serious complications associated with diabetes and FPLD. Vupanorsen was well tolerated, and there was no effect on platelet count.

CONCLUSIONS

Although limited, these results suggest that targeting ANGPTL3 with vupanorsen could address several metabolic abnormalities in patients with FPLD.

Complications of lipodystrophy syndromes

Lipodystrophy syndromes are rare complex multisystem disorders caused by generalized or partial lack of adipose tissue. Adipose tissue dysfunction in lipodystrophy is associated with leptin deficiency. Lipodystrophy leads to severe metabolic problems. These abnormalities include, but are not limited to, insulin-resistant diabetes, severe hypertriglyceridemia, and lipid accumulation in ectopic organs such as the liver, and are associated with end-organ complications. Metabolic abnormalities can be present at the time of diagnosis or may develop over time as the disease progresses. In addition to metabolic abnormalities, subtype-specific presentations due to underlying molecular etiology in genetic forms and autoimmunity in acquired forms contribute to severe morbidity in lipodystrophy.

Leptin Decreases Energy Expenditure Despite Increased Thyroid Hormone in Patients With Lipodystrophy

CONTEXT

Leptin is an adipokine that signals energy sufficiency. In rodents, leptin deficiency decreases energy expenditure (EE), which is corrected following leptin replacement. In humans, data are mixed regarding leptin-mediated effects on EE.

OBJECTIVE

To determine the effects of metreleptin on EE in patients with lipodystrophy.

DESIGN, SETTING, AND PATIENTS

Nonrandomized crossover study of 25 patients with lipodystrophy (National Institutes of Health, 2013-2018).

INTERVENTION

The initiation cohort consisted of 17 patients without prior exposure to metreleptin, studied before and after 14 days of metreleptin. The withdrawal cohort consisted of 8 previously metreleptin-treated patients, studied before and after 14 days of metreleptin withdrawal.

MAIN OUTCOMES

24-h total energy expenditure (TEE), resting energy expenditure (REE), autonomic nervous system activity [heart rate variability (HrV)], plasma-free triiodothyronine (T3), free thyroxine (T4), epinephrine, norepinephrine, and dopamine.

RESULTS

In the initiation cohort, TEE and REE decreased by 5.0% (121 ± 152 kcal/day; P = 0.006) and 5.9% (120 ± 175 kcal/day; P = 0.02). Free T3 increased by 19.4% (40 ± 49 pg/dL; P = 0.01). No changes in catecholamines or HrV were observed. In the withdrawal cohort, free T3 decreased by 8.0% (P = 0.04), free T4 decreased by 11.9% (P = 0.002), and norepinephrine decreased by 34.2% (P = 0.03), but no changes in EE, epinephrine, dopamine, or HrV were observed.

CONCLUSIONS

Metreleptin initiation decreased EE in patients with lipodystrophy, but no changes were observed after metreleptin withdrawal. Thyroid hormone was higher on metreleptin in both initiation and withdrawal cohorts. Decreased EE after metreleptin in lipodystrophy may result from reductions in energy-requiring metabolic processes that counteract increases in EE via adipose tissue-specific neuroendocrine and adrenergic signaling.

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.

Rapid response to leptin therapy in a FPLD patient with a novel PPARG missense variant

SUMMARY

Familial partial lipodystrophy (FPLD) syndromes are rare heterogeneous disorders especially in women characterized by selective loss of adipose tissue, reduced leptin levels and severe metabolic abnormalities. Here we report a 34-year-old female with a novel heterozygotic c.485 thymine>guanine (T>G) missense variant (p.phenylalanine162cysteine; (Phe162Cys)) in exon 4 of the peroxisome proliferator-activated receptor gamma (PPARG) gene, developing a non-ketotic diabetes and severe hypertriglyceridemia with triglyceride concentrations >50 mmol/L. In this case, a particular interesting feature in comparison to other known PPARG mutations in FPLD is that while glycaemic control could be achieved through standard anti-diabetic medication, hypertriglyceridemia did neither respond to fibrate nor to omega-3-fatty acid therapy. This might suggest a lipid metabolism driven phenotype of the novel PPARG c.485T>G missense variant. Notably, recombinant leptin replacement therapy (metreleptin (Myalepta®)) was initiated showing a rapid and profound effect on triglyceride levels as well as on liver function tests and satiety feeling. Unfortunately, severe allergic skin reactions developed at the side of injection which could be covered by anti-histaminc treatment. We conclude that the heterozygous PPARG c.485T>G variant is a yet undescribed molecular basis underlying FPLD with difficulties predominantly to control hypertriglyceridemia and that recombinant leptin therapy may be effective in affected subjects.

LEARNING POINTS

Heterozygous c.485T>G variant in PPARG is most likely a cause for FPLD in humans. This variant results in a special metabolic phenotype with a predominant dysregulation of triglyceride metabolism not responding to standard lipid lowering therapy. Recombinant leptin therapy is effective in rapidly improving hypertriglyceridemia.

Neuropeptide Y and Metabolism Syndrome: An Update on Perspectives of Clinical Therapeutic Intervention Strategies

Through the past decade of research, the pathogenic mechanisms underlying metabolic syndrome have been suggested to involve not only the peripheral tissues, but also central metabolic regulation imbalances. The hypothalamus, and the arcuate nucleus in particular, is the control center for metabolic homeostasis and energy balance. Neuropeptide Y neurons are particularly abundantly expressed in the arcuate of the hypothalamus, where the blood-brain barrier is weak, such as to critically integrate peripheral metabolic signals with the brain center. Herein, focusing on metabolic syndrome, this manuscript aims to provide an overview of the regulatory effects of Neuropeptide Y on metabolic syndrome and discuss clinical intervention strategy perspectives for neurometabolic disease.

From leptin to lasers: the past and present of mouse models of obesity

Introduction: Obesity is a prevalent condition that accounts for significant morbidity and mortality across the globe. Despite substantial effort, most obesity pharmacotherapies have proven unsafe or ineffective. The use of obese mouse models provides unique insight into the hormones and mechanisms that regulate appetite and metabolism. Paramount among these models are the 'obese' and 'diabetic' mice that revealed the powerful satiety hormone leptin, revolutionizing obesity research.Areas Covered: In this article, the authors discuss work on leptin therapy, and the clinical response to leptin in humans. The authors describe the use of modern mouse genetics to study targetable mechanisms for genetic forms of human obesity. Additionally, they describe mouse models of neuromodulation and their utility in unraveling neural circuits that govern appetite and metabolism.Expert opinion: Combining past and present models of obesity is required for the development of safe, effective, and impactful obesity therapy. Current research in obesity can benefit from repositories of genetically engineered mouse models to discover interactions between appetitive systems and circuits. Combining leptin therapy with other satiety signals comprising the gut-brain axis is a promising approach to induce significant enduring weight loss.

Role of Leptin in the Digestive System

Leptin is a pluripotent peptide hormone produced mainly by adipocytes, as well as by other tissues such as the stomach. Leptin primarily acts on the central nervous system, particularly the hypothalamus, where this hormone regulates energy homeostasis and neuroendocrine function. Owing to this, disruption of leptin signaling has been linked with numerous pathological conditions. Recent studies have also highlighted the diverse roles of leptin in the digestive system including immune regulation, cell proliferation, tissue healing, and glucose metabolism. Of note, leptin acts differently under physiological and pathological conditions. Here, we review the current knowledge on the functions of leptin and its downstream signaling in the gastrointestinal tract and accessory digestive organs, with an emphasis on its physiological and pathological implications. We also discuss the current therapeutic uses of recombinant leptin, as well as its limitations.

Tissue-Specific Effects of Leptin on Glucose and Lipid Metabolism

The discovery of leptin was intrinsically associated with its ability to regulate body weight. However, the effects of leptin are more far-reaching and include profound glucose-lowering and anti-lipogenic effects, independent of leptin's regulation of body weight. Regulation of glucose metabolism by leptin is mediated both centrally and via peripheral tissues and is influenced by the activation status of insulin signaling pathways. Ectopic fat accumulation is diminished by both central and peripheral leptin, an effect that is beneficial in obesity-associated disorders. The magnitude of leptin action depends upon the tissue, sex, and context being examined. Peripheral tissues that are of particular relevance include the endocrine pancreas, liver, skeletal muscle, adipose tissues, immune cells, and the cardiovascular system. As a result of its potent metabolic activity, leptin is used to control hyperglycemia in patients with lipodystrophy and is being explored as an adjunct to insulin in patients with type 1 diabetes. To fully understand the role of leptin in physiology and to maximize its therapeutic potential, the mechanisms of leptin action in these tissues needs to be further explored.

Molecular and Cellular Bases of Lipodystrophy Syndromes

Lipodystrophy syndromes are rare diseases originating from a generalized or partial loss of adipose tissue. Adipose tissue dysfunction results from heterogeneous genetic or acquired causes, but leads to similar metabolic complications with insulin resistance, diabetes, hypertriglyceridemia, nonalcoholic fatty liver disease, dysfunctions of the gonadotropic axis and endocrine defects of adipose tissue with leptin and adiponectin deficiency. Diagnosis, based on clinical and metabolic investigations, and on genetic analyses, is of major importance to adapt medical care and genetic counseling. Molecular and cellular bases of these syndromes involve, among others, altered adipocyte differentiation, structure and/or regulation of the adipocyte lipid droplet, and/or premature cellular senescence. Lipodystrophy syndromes frequently present as systemic diseases with multi-tissue involvement. After an update on the main molecular bases and clinical forms of lipodystrophy, we will focus on topics that have recently emerged in the field. We will discuss the links between lipodystrophy and premature ageing and/or immuno-inflammatory aggressions of adipose tissue, as well as the relationships between lipomatosis and lipodystrophy. Finally, the indications of substitutive therapy with metreleptin, an analog of leptin, which is approved in Europe and USA, will be discussed.

Unraveling the Role of Leptin in Liver Function and Its Relationship with Liver Diseases

Since its discovery twenty-five years ago, the fat-derived hormone leptin has provided a revolutionary framework for studying the physiological role of adipose tissue as an endocrine organ. Leptin exerts pleiotropic effects on many metabolic pathways and is tightly connected with the liver, the major player in systemic metabolism. As a consequence, understanding the metabolic and hormonal interplay between the liver and adipose tissue could provide us with new therapeutic targets for some chronic liver diseases, an increasing problem worldwide. In this review, we assess relevant literature regarding the main metabolic effects of leptin on the liver, by direct regulation or through the central nervous system (CNS). We draw special attention to the contribution of leptin to the non-alcoholic fatty liver disease (NAFLD) pathogenesis and its progression to more advanced stages of the disease as non-alcoholic steatohepatitis (NASH). Likewise, we describe the contribution of leptin to the liver regeneration process after partial hepatectomy, the mainstay of treatment for certain hepatic malignant tumors.

Apolipoprotein CIII and Angiopoietin-like Protein 8 are Elevated in Lipodystrophy and Decrease after Metreleptin

Context

Lipodystrophy syndromes cause hypertriglyceridemia that improves with leptin treatment using metreleptin. Mechanisms causing hypertriglyceridemia and improvements after metreleptin are incompletely understood.

Objective

Determine relationship of circulating lipoprotein lipase (LPL) modulators with hypertriglyceridemia in healthy controls and in patients with lipodystrophy before and after metreleptin.

Methods

Cross-sectional comparison of patients with lipodystrophy (generalized lipodystrophy n = 3; partial lipodystrophy n = 11) vs age/sex-matched healthy controls (n = 28), and longitudinal analyses in patients before and after 2 weeks and 6 months of metreleptin. The study was carried out at the National Institutes of Health, Bethesda, Maryland. Outcomes were LPL stimulators apolipoprotein (apo) C-II and apoA-V and inhibitors apoC-III and angiopoietin-like proteins (ANGPTLs) 3, 4, and 8; ex vivo activation of LPL by plasma.

Results

Patients with lipodystrophy were hypertriglyceridemic and had higher levels of all LPL stimulators and inhibitors vs controls except for ANGPTL4, with >300-fold higher ANGPTL8, 4-fold higher apoC-III, 3.5-fold higher apoC-II, 1.9-fold higher apoA-V, 1.6-fold higher ANGPTL3 (P < .05 for all). At baseline, all LPL modulators except ANGPLT4 positively correlated with triglycerides. Metreleptin decreased apoC-II and apoC-III after 2 weeks and 6 months, and decreased ANGPTL8 after 6 months (P < 0.05 for all). Plasma from patients with lipodystrophy caused higher ex vivo LPL activation vs hypertriglyceridemic control plasma (P < .0001), which did not change after metreleptin.

Conclusion

Elevations in LPL inhibitors apoC-III and ANGPTL8 may contribute to hypertriglyceridemia in lipodystrophy, and may mediate reductions in circulating and hepatic triglycerides after metreleptin. These therefore are strong candidates for therapies to lower triglycerides in these patients.