Leptin-replacement therapy for lipodystrophy

Novel perspectives on leptin in osteoarthritis: Focus on aging

Osteoarthritis (OA) is a common chronic joint disease characterized by articular cartilage degeneration, subchondral sclerosis, synovitis, and osteophyte formation. OA is associated with disability and impaired quality of life, particularly among the elderly. Leptin, a 16-kD non-glycosylated protein encoded by the obese gene, is produced on a systemic and local basis in adipose tissue and the infrapatellar fat pad located in the knee. The metabolic mechanisms employed by leptin in OA development have been widely studied, with attention being paid to aging as a corroborative risk factor for OA. Hence, in this review, we have attempted to establish a potential link between leptin and OA, by focusing on aging-associated mechanisms and proposing leptin as a potential diagnostic and therapeutic target in aging-related mechanisms of OA that may provide fruitful guidance and emphasis for future research.

Development of an adipose-tropic AAV capsid ablating liver tropism

AAV vectors are mainstream delivery platforms in gene therapy, yet AAV-mediated gene transfer to adipose tissue is underdeveloped due to low efficiency of natural AAVs. We previously demonstrated that an engineered capsid Rec2 displayed improved adipo-tropism but with the caveat of liver transduction. To generate highly adipo-tropic capsid, we modified Rec2 capsid by site-specific mutagenesis and found the variant V7 with F503Y, Y708D and K709I substitution to harbor highly selective adipo-tropism while diminishing liver transduction. Intraperitoneal injection favored transduction to visceral fat while intravenous administration favored subcutaneous fat. Intraperitoneal administration of V7 vector harboring human leptin and adiponectin as single transcript normalized the metabolic dysfunction of ob/ob mice at a low dose. Moreover, introducing the same mutagenesis to AAV8 capsid diminished liver transduction suggesting F503, Y708 and K709 critical for liver transduction. The Rec2.V7 vector may provide a powerful tool for basic research and potent vehicle for adipose-targeting gene therapy.

Longitudinal proteomics of leptin treatment in humans with acute and chronic energy deficiency-induced hypoleptinemia reveal novel, mainly immune-related, pleiotropic effects

BACKGROUND

Leptin is known for its metabolic, immunomodulatory and neuroendocrine properties, but the full spectrum of molecules downstream of leptin and relevant underlying mechanisms remain to be fully clarified. Our objective was to identify proteins and pathways influenced by leptin through untargeted proteomics in two clinical trials involving leptin administration in lean individuals.

METHODS

We performed untargeted liquid chromatography-tandem mass spectrometry serum proteomics across two studies a) Short-term randomized controlled crossover study of lean male and female humans undergoing a 72-h fast with concurrent administration of either placebo or high-dose leptin; b) Long-term (36-week) randomized controlled trial of leptin replacement therapy in human females with acquired relative energy deficiency and hypoleptinemia. We explored longitudinal proteomic changes and run adjusted mixed models followed by post-hoc tests. We further attempted to identify ontological pathways modulated during each experimental condition and/or comparison, through integrated qualitative pathway and enrichment analyses. We also explored dynamic longitudinal relationships between the circulating proteome with clinical and hormonal outcomes.

RESULTS

289 and 357 unique proteins were identified per each respective study. Short-term leptin administration during fasting markedly upregulated several proinflammatory molecules, notably C-reactive protein (CRP) and cluster of differentiation (CD) 14, and downregulated lecithin cholesterol acyltransferase and several immunoglobulin variable chains, in contrast with placebo, which produced minimal changes. Quantitative pathway enrichment further indicated an upregulation of the acute phase response and downregulation of immunoglobulin- and B cell-mediated immunity by leptin. These changes were independent of participants' biological sex. In the long term study, leptin likewise robustly and persistently upregulated proteins of the acute phase response, and downregulated immunoglobulin-mediated immunity. Leptin also significantly and differentially affected a wide array of proteins related to immune function, defense response, coagulation, and inflammation compared with placebo. These changes were more notable at the 24-week visit, coinciding with the highest measured levels of serum leptin. We further identified distinct co-regulated clusters of proteins and clinical features during leptin administration indicating robust longitudinal correlations between the regulation of immunoglobulins, immune-related molecules, serpins (including cortisol and thyroxine-binding globulins), lipid transport molecules and growth factors, in contrast with placebo, which did not produce similar associations.

CONCLUSIONS

These high-throughput longitudinal results provide unique functional insights into leptin physiology, and pave the way for affinity-based proteomic analyses measuring several thousands of molecules, that will confirm these data and may fully delineate underlying mechanisms.

History and future of leptin: Discovery, regulation and signaling

The cloning of leptin 30 years ago in 1994 was an important milestone in obesity research. Prior to the discovery of leptin, obesity was stigmatized as a condition caused by lack of character and self-control. Mutations in either leptin or its receptor were the first single gene mutations found to cause severe obesity, and it is now recognized that obesity is caused mostly by a dysregulation of central neuronal circuits. Since the discovery of the leptin-deficient obese mouse (ob/ob) the cloning of leptin (ob aka lep) and leptin receptor (db aka lepr) genes, we have learned much about leptin and its action in the central nervous system. The first hope that leptin would cure obesity was quickly dampened because humans with obesity have increased leptin levels and develop leptin resistance. Nevertheless, leptin target sites in the brain represent an excellent blueprint to understand how neuronal circuits control energy homeostasis. Our expanding understanding of leptin function, interconnection of leptin signaling with other systems and impact on distinct physiological functions continues to guide and improve the development of safe and effective interventions to treat metabolic illnesses. This review highlights past concepts and current emerging concepts of the hormone leptin, leptin receptor signaling pathways and central targets to mediate distinct physiological functions.

Preclinical evaluation of tissue-selective gene therapies for congenital generalised lipodystrophy

Lipodystrophy is a rare disorder which can be life-threatening. Here individuals fail to develop or maintain appropriate adipose tissue stores. This typically causes severe metabolic complications, including hepatic steatosis and lipoatrophic diabetes. There is no cure for lipodystrophy, and treatment options remain very limited. Here we evaluate whether tissue-selective adeno-associated virus (AAV) vectors can provide a targeted form of gene therapy for lipodystrophy, using a preclinical lipodystrophic mouse model of Bscl2 deficiency. We designed AAV vectors containing the mini/aP2 or thyroxine-binding globulin promoter to selectively target adipose or liver respectively. The AAV-aP2 vectors also contained the liver-specific microRNA-122 target sequence, restricting hepatic transgene expression. Systemic delivery of AAV-aP2 vectors overexpressing human BSCL2 restored adipose tissue development and metabolic health in lipodystrophic mice without detectable expression in the liver. High doses (1 × 1012 GCs) of liver-selective vectors led to off target expression and adipose tissue development, whilst low doses (1 × 1010 GCs) expressed selectively and robustly in the liver but did not improve metabolic health. This reveals that adipose tissue-selective, but not liver directed, AAV-mediated gene therapy is sufficient to substantially recover metabolic health in generalised lipodystrophy. This provides an exciting potential new avenue for an effective, targeted, and thereby safer therapeutic intervention.

Navigating Lipodystrophy: Insights from Laminopathies and Beyond

Recent research into laminopathic lipodystrophies-rare genetic disorders caused by mutations in the LMNA gene-has greatly expanded our knowledge of their complex pathology and metabolic implications. These disorders, including Hutchinson-Gilford progeria syndrome (HGPS), Mandibuloacral Dysplasia (MAD), and Familial Partial Lipodystrophy (FPLD), serve as crucial models for studying accelerated aging and metabolic dysfunction, enhancing our understanding of the cellular and molecular mechanisms involved. Research on laminopathies has highlighted how LMNA mutations disrupt adipose tissue function and metabolic regulation, leading to altered fat distribution and metabolic pathway dysfunctions. Such insights improve our understanding of the pathophysiological interactions between genetic anomalies and metabolic processes. This review merges current knowledge on the phenotypic classifications of these diseases and their associated metabolic complications, such as insulin resistance, hypertriglyceridemia, hepatic steatosis, and metabolic syndrome, all of which elevate the risk of cardiovascular disease, stroke, and diabetes. Additionally, a range of published therapeutic strategies, including gene editing, antisense oligonucleotides, and novel pharmacological interventions aimed at addressing defective adipocyte differentiation and lipid metabolism, will be explored. These therapies target the core dysfunctional lamin A protein, aiming to mitigate symptoms and provide a foundation for addressing similar metabolic and genetic disorders.

Diagnosis, treatment and management of lipodystrophy: the physician perspective on the patient journey

BACKGROUND

Lipodystrophy syndromes are a heterogeneous group of rare, life-limiting diseases characterized by a selective loss of adipose tissue and severe metabolic complications. There is a paucity of information describing the experiences and challenges faced by physicians who have seen and treated patients with lipodystrophy. This study aimed to provide a better understanding of the physician's perspective regarding the patient journey in lipodystrophy, including diagnosis, the burden of disease, and treatment approaches.

METHODS

Thirty-three physicians from six countries who had seen or treated patients with lipodystrophy were interviewed using a semi-structured questionnaire. Interviews were transcribed, anonymized, and analyzed for themes and trends. Four main themes were developed: (1) the diagnostic journey in lipodystrophy including the disease features or 'triggers' that result in the onward referral of patients to specialist medical centers with experience in managing lipodystrophy; (2) the impact of lipodystrophy on patient quality of life (QoL); (3) the use of standard therapies and leptin replacement therapy (metreleptin) in lipodystrophy, and (4) barriers to metreleptin use.

RESULTS

Participants reported that, due to their rarity and phenotypic heterogeneity, lipodystrophy cases are frequently unrecognized, leading to delays in diagnosis and medical intervention. Early consultation with multidisciplinary specialist medical teams was recommended for suspected lipodystrophy cases. The development and progression of metabolic complications were identified as key triggers for the referral of patients to specialist centers for follow-up care. Participants emphasized the impact of lipodystrophy on patient QoL, including effects on mental health and self-image. Although participants routinely used standard medical therapies to treat specific metabolic complications associated with lipodystrophy, it was acknowledged that metreleptin was typically required in patients with congenital generalized lipodystrophy and in some acquired generalized and partial lipodystrophy cases. A lack of experience among some participants and restrictions to access remained as barriers to metreleptin use.

CONCLUSIONS

To our knowledge, this is one of the first studies describing the qualitative experiences of physicians regarding the diagnosis and management of lipodystrophy. Other physician-centered studies may help increase the awareness of lipodystrophy among the wider medical community and support clinical approaches to this rare disease.

A rapid action plan to improve diagnosis and management of lipodystrophy syndromes

Introduction

Lipodystrophy syndromes are rare diseases that can present with a broad range of symptoms. Delays in diagnosis are common, which in turn, may predispose to the development of severe metabolic complications and end-organ damage. Many patients with lipodystrophy syndromes are only diagnosed after significant metabolic abnormalities arise. Prompt action by clinical teams may improve disease outcomes in lipodystrophy syndromes. The aim of the Rapid Action Plan is to serve as a set of recommendations from experts that can support clinicians with limited experience in lipodystrophy syndromes.

Methods

The Rapid Action Plan was developed using insights gathered through a series of advisory meetings with clinical experts in lipodystrophy syndromes. A skeleton template was used to facilitate interviews. A consensus document was developed, reviewed, and approved by all experts.

Results

Lipodystrophy is a clinical diagnosis. The Rapid Action Plan discusses tools that can help diagnose lipodystrophy syndromes. The roles of clinical and family history, physical exam, patient and family member photos, routine blood tests, leptin levels, skinfold measurements, imaging studies, and genetic testing are explored. Additional topics such as communicating the diagnosis to the patients/families and patient referrals are covered. A set of recommendations regarding screening and monitoring for metabolic diseases and end-organ abnormalities is presented. Finally, the treatment of lipodystrophy syndromes is reviewed.

Discussion

The Rapid Action Plan may assist clinical teams with the prompt diagnosis and holistic work-up and management of patients with lipodystrophy syndromes, which may improve outcomes for patients with this rare disease.

Leptin replacement therapy in the management of lipodystrophy syndromes

Lipodystrophy syndromes are rare diseases of genetic or acquired origin, characterized by quantitative and qualitative defects in adipose tissue. The metabolic consequences of lipodystrophy syndromes, such as insulin resistant diabetes, hypertriglyceridemia and hepatic steatosis, are frequently very difficult to treat, resulting in significant risks of acute and/or chronic complications and of decreased quality of life. The production of leptin by lipodystrophic adipose tissue is decreased, more severely in generalized forms of lipodystrophy, where adipose tissue is absent from almost all body fat depots, than in partial forms of the disease, where lipoatrophy affects only some parts of the body and can be associated with increased body fat in other anatomical regions. Several lines of evidence in preclinical and clinical models have shown that leptin replacement therapy could improve the metabolic complications of lipodystrophy syndromes. Metreleptin, a recombinant leptin analogue, was approved as an orphan drug to treat the metabolic complications of leptin deficiency in patients with generalized lipodystrophy in the USA or with either generalized or partial lipodystrophy in Japan and Europe. In this brief review, we will discuss the benefits and limitations of this therapy, and the new expectations arising from the recent development of a therapeutic monoclonal antibody able to activate the leptin receptor.

Adipose transplantation improves metabolism and atherosclerosis but not perivascular adipose tissue abnormality or vascular dysfunction in lipodystrophic Seipin/Apoe null mice

Adipose dysfunction in lipodystrophic SEIPIN deficiency is associated with multiple metabolic disorders and increased risks of developing cardiovascular diseases, such as atherosclerosis, cardiac hypertrophy, and heart failure. Recently, adipose transplantation has been found to correct adipose dysfunction and metabolic disorders in lipodystrophic Seipin knockout mice; however, whether adipose transplantation could improve lipodystrophy-associated cardiovascular consequences is still unclear. Here, we aimed to explore the effects of adipose transplantation on lipodystrophy-associated metabolic cardiovascular diseases in Seipin knockout mice crossed into atherosclerosis-prone apolipoprotein E (Apoe) knockout background. At 2 months of age, lipodystrophic Seipin/Apoe double knockout mice and nonlipodystrophic Apoe knockout controls were subjected to adipose transplantation or sham operation. Seven months later, mice were euthanized. Our data showed that although adipose transplantation had no significant impact on endogenous adipose atrophy or gene expression, it remarkably increased plasma leptin but not adiponectin concentration in Seipin/Apoe double knockout mice. This led to significantly reduced hyperlipidemia, hepatic steatosis, and insulin resistance in Seipin/Apoe double knockout mice. Consequently, atherosclerosis burden, intraplaque macrophage infiltration, and aortic inflammatory gene expression were all attenuated in Seipin/Apoe double knockout mice with adipose transplantation. However, adipocyte morphology, macrophage infiltration, or fibrosis of the perivascular adipose tissue was not altered in Seipin/Apoe double knockout mice with adipose transplantation, followed by no significant improvement of vasoconstriction or relaxation. In conclusion, we demonstrate that adipose transplantation could alleviate lipodystrophy-associated metabolic disorders and atherosclerosis but has an almost null impact on perivascular adipose abnormality or vascular dysfunction in lipodystrophic Seipin/Apoe double knockout mice.NEW & NOTEWORTHY Adipose transplantation (AT) reverses multiply metabolic derangements in lipodystrophy, but whether it could improve lipodystrophy-related cardiovascular consequences is unknown. Here, using Seipin/Apoe double knockout mice as a lipodystrophy disease model, we showed that AT partially restored adipose functionality, which translated into significantly reduced atherosclerosis. However, AT was incapable of reversing perivascular adipose abnormality or vascular dysfunction. The current study provides preliminary experimental evidence on the therapeutic potential of AT on lipodystrophy-related metabolic cardiovascular diseases.

Hippo-YAP/TAZ signalling coordinates adipose plasticity and energy balance by uncoupling leptin expression from fat mass

Adipose tissues serve as an energy reservoir and endocrine organ, yet the mechanisms that coordinate these functions remain elusive. Here, we show that the transcriptional coregulators, YAP and TAZ, uncouple fat mass from leptin levels and regulate adipocyte plasticity to maintain metabolic homeostasis. Activating YAP/TAZ signalling in adipocytes by deletion of the upstream regulators Lats1 and Lats2 results in a profound reduction in fat mass by converting mature adipocytes into delipidated progenitor-like cells, but does not cause lipodystrophy-related metabolic dysfunction, due to a paradoxical increase in circulating leptin levels. Mechanistically, we demonstrate that YAP/TAZ-TEAD signalling upregulates leptin expression by directly binding to an upstream enhancer site of the leptin gene. We further show that YAP/TAZ activity is associated with, and functionally required for, leptin regulation during fasting and refeeding. These results suggest that adipocyte Hippo-YAP/TAZ signalling constitutes a nexus for coordinating adipose tissue lipid storage capacity and systemic energy balance through the regulation of adipocyte plasticity and leptin gene transcription.

Regulated regeneration of adipose tissue in lipodystrophic Agpat2-null mice partially ameliorates hepatic steatosis

Both humans and mice with congenital generalized lipodystrophy due to AGPAT2 deficiency develop diabetes mellitus, insulin resistance, and hepatic steatosis, which have been attributed to the near total loss of adipose tissue (AT). Here, we show that regulated AT regeneration in doxycycline (dox)-fed Tg-AT-hAGPAT2;mAgpat2-/- mice partially ameliorates hepatic steatosis at 12 weeks of age and causes reduced expression of genes involved in hepatic de novo lipogenesis despite partial (∼30-50%) AT regeneration compared to that in wild-type mice. Compared to chow-fed Tg-AT-hAGPAT2;mAgpat2-/- mice, those fed dox diet had markedly reduced serum insulin levels, suggesting an improvement in insulin resistance. Interestingly, the fasting plasma glucose levels in dox-fed Tg-AT-hAGPAT2;mAgpat2-/- mice were no different than those in chow-fed wild-type mice. Indirect calorimetry revealed normalization in the energy balance of dox-fed Tg-AT-hAGPAT2;mAgpat2-/- mice compared to that in chow-fed mice. This study's findings suggest that partial AT regeneration in lipodystrophic mice can ameliorate metabolic derangements.

Correlation of Leptin in Patients With Type 2 Diabetes Mellitus

The exponential increase in diabetes mellitus (DM) poses serious public health concerns. In this review, we focus on the role of leptin in type 2 DM. The peripheral actions of leptin consist of upregulating proinflammatory cytokines which play an important role in the pathogenesis of type 2 DM and insulin resistance. Moreover, leptin is known to inhibit insulin secretion and plays a significant role in insulin resistance in obesity and type 2 DM. A literature search was conducted on Medline, Cochrane, Embase, and Google Scholar for relevant articles published until December 2023. The following search strings and Medical Subject Headings (MeSH terms) were used: "Diabetes Mellitus," "Leptin," "NPY," and "Biomarker." This article aims to discuss the physiology of leptin in type 2 DM, its glucoregulatory actions, its relationship with appetite, the impact that various lifestyle modifications can have on leptin levels, and, finally, explore leptin as a potential target for various treatment strategies.

Understanding wound healing in obesity

Obesity has become more prevalent in the global population. It is associated with the development of several diseases including diabetes mellitus, coronary heart disease, and metabolic syndrome. There are a multitude of factors impacted by obesity that may contribute to poor wound healing outcomes. With millions worldwide classified as obese, it is imperative to understand wound healing in these patients. Despite advances in the understanding of wound healing in both healthy and diabetic populations, much is unknown about wound healing in obese patients. This review examines the impact of obesity on wound healing and several animal models that may be used to broaden our understanding in this area. As a growing portion of the population identifies as obese, understanding the underlying mechanisms and how to overcome poor wound healing is of the utmost importance.

Deciphering the Clinical Presentations in LMNA-related Lipodystrophy: Report of 115 Cases and a Systematic Review

CONTEXT

Lipodystrophy syndromes are a heterogeneous group of rare genetic or acquired disorders characterized by generalized or partial loss of adipose tissue. LMNA-related lipodystrophy syndromes are classified based on the severity and distribution of adipose tissue loss.

OBJECTIVE

We aimed to annotate all clinical and metabolic features of patients with lipodystrophy syndromes carrying pathogenic LMNA variants and assess potential genotype-phenotype relationships.

METHODS

We retrospectively reviewed and analyzed all our cases (n = 115) and all published cases (n = 379) curated from 94 studies in the literature.

RESULTS

The study included 494 patients. The most common variants in our study, R482Q and R482W, were associated with similar metabolic characteristics and complications though those with the R482W variant were younger (aged 33 [24] years vs 44 [25] years; P < .001), had an earlier diabetes diagnosis (aged 27 [18] vs 40 [17] years; P < .001) and had lower body mass index levels (24 [5] vs 25 [4]; P = .037). Dyslipidemia was the earliest biochemical evidence described in 83% of all patients at a median age of 26 (10) years, while diabetes was reported in 61% of cases. Among 39 patients with an episode of acute pancreatitis, the median age at acute pancreatitis diagnosis was 20 (17) years. Patients who were reported to have diabetes had 3.2 times, while those with hypertriglyceridemia had 12.0 times, the odds of having pancreatitis compared to those who did not.

CONCLUSION

This study reports the largest number of patients with LMNA-related lipodystrophy syndromes to date. Our report helps to quantify the prevalence of the known and rare complications associated with different phenotypes and serves as a comprehensive catalog of all known cases.

Liver transplantation in patient with Berardinelli-Seip syndrome: A literature review and case report

BACKGROUND

Berardinelli-Seip syndrome is an infrequently seen and potentially fatal genetic disorder characterized by the absence of adipose tissue. Herein, we report a first-in-literature liver transplant done on a 7-year-old girl because of liver cirrhosis caused by the Berardinelli-Seip syndrome.

CASE REPORT

Physical examination showed prominent subdermal fat tissue loss and mild muscle hypertrophy, giving her a slim appearance, hirsutism, thick hair, a large head in contrast to the body, low anterior hairline, icterus, prominent facial contours, prominent mandibula, loss of buccal fat, low set ears, and large limbs. After the diagnosis, she admitted to our clinic because of variceal esophageal bleeding and increasing liver enzymes. Transplantation decision was made and orthothopic liver transplantation done by the surgery team.

DISCUSSION

Common causes of death in Berardinelli-Seip syndrome patients are infections and liver cirrhosis. The mean age of the patients was 27.1 at the time of death. There is no any established cure for congenital lipodystrophies so far. However, some symptomatic treatment methods are found to be helpful. The main point of the case report to be discussed is the liver transplantation done by our surgical team. There are no examples of any transplantation in Berardinelli-Seip syndrome patients, but several reports can be found of patients with kidney or liver failure.

CONCLUSION

Berardinelli-Seip syndrome is a rare disorder with no cure but a chance of improving lifestyle and life expectancy. The transplantation option should be considered in young patients after a multidisciplinary review.

Leptin Reduction as a Required Component for Weight Loss

Partial leptin reduction can induce significant weight loss, while weight loss contributes to partial leptin reduction. The cause-and-effect relationship between leptin reduction and weight loss remains to be further elucidated. Here, we show that FGF21 and the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide rapidly induced a reduction in leptin. This leptin reduction contributed to the beneficial effects of GLP-1R agonism in metabolic health, as transgenically maintaining leptin levels during treatment partially curtailed the beneficial effects seen with these agonists. Moreover, a higher degree of leptin reduction during treatment, induced by including a leptin neutralizing antibody with either FGF21 or liraglutide, synergistically induced greater weight loss and better glucose tolerance in diet-induced obese mice. Furthermore, upon cessation of either liraglutide or FGF21 treatment, the expected immediate weight regain was observed, associated with a rapid increase in circulating leptin levels. Prevention of this leptin surge with leptin neutralizing antibodies slowed down weight gain and preserved better glucose tolerance. Mechanistically, a significant reduction in leptin induced a higher degree of leptin sensitivity in hypothalamic neurons. Our observations support a model that postulates that a reduction of leptin levels is a necessary prerequisite for substantial weight loss, and partial leptin reduction is a viable strategy to treat obesity and its associated insulin resistance.

ARTICLE HIGHLIGHTS

Association between plasma leptin/adiponectin ratio and insulin resistance indexes in prepubertal children

Objective

To assess the association between leptin/adiponectin ratio (LAR) and insulin resistance surrogates in prepubertal children.

Materials and methods

Study based on data from the Growth and Obesity Chilean Cohort Study (GOCS) involving 968 Chilean prepubertal children. Plasma insulin, leptin, and adiponectin were determined by immunoassays. Several common insulin resistance surrogates were calculated, including the homeostasis model assessment of insulin resistance (HOMA-IR), triglyceride/HDL cholesterol index, triglyceride-glucose (TyG) index, and the TyG index corrected for body mass index (BMI; TyG-BMI) and waist circumference (WC; TyG-WC). Associations among variables were assessed using multiple linear and logistic regression analysis.

Results

There was a significant direct association between plasma leptin and LAR with BMI z-score but no association between plasma adiponectin and adiposity. After adjustments for sex and age, LAR was significantly associated with all insulin resistance surrogates (which were categorized using the 75th percentile as the cutoff point), with the TyG-WC index emerging as the surrogate with the highest magnitude of association (odds ratio [OR] 2.44, 95% confidence interval [CI] 2.05-2.9). After additional adjustment for BMI z-score, only the association between LAR and TyG-WC remained significant (OR 1.64, 95% CI 1.27-2.12).

Conclusion

Plasma leptin and LAR were strongly associated with several common insulin resistance surrogates in prepubertal children, most notably with the TyG-WC index. Associations between LAR and insulin resistance indexes were mainly driven by the effect of plasma leptin, which is also directly associated with increased adiposity.

Across-species benefits of adrenalectomy on congenital generalized lipoatrophic diabetes: a review

Two adrenalectomies py -45erformed fourteen years apart notoriously alleviated insulin resistance in a female teenager with Congenital Generalized Lipoatrophy (CGL, 1988) and in a murine model of CGL (2002). Following a successful therapeutic trial with anti-glucocorticoids, we performed the first surgical procedure on an 18-year-old girl. Before surgery, the anti-glucocorticoid therapy produced a rapid and striking drop in fasting serum insulin levels (from over 400 to 7.0 mU/L) and a slower -but impressive- fall in fasting serum triglycerides from 7,400 to 220-230 mg/dL. In contrast, fasting serum glucose levels dropped more slowly, from 225-290 to 121-138 mg/dL. Two weeks following total adrenalectomy, the fasting serum glucose level was 98 mg/dL, with a corresponding serum insulin level of 10 mU/L. During an Oral Glucose Tolerance Test, the 2-hour serum glucose was 210 mg/dL, and serum insulin values during the test did not exceed 53 mU/L. In 2002, the A-ZIP/F1 hypoleptinemic mouse had its adrenal glands removed. Even though this CGL model does not respond well to leptin replacement, an infusion of recombinant leptin reduced the characteristic hypercorticosteronemia of this murine model of CGL. Adrenalectomy in this transgenic mouse improved insulin sensitivity in the liver and muscle. In summary, adrenalectomy -in both a human and a mouse case of CGL- limited adipose tissue exposure to corticosteroid action and led to a notorious metabolic improvement. On a broader scenario, given that leptin restrains the adrenal axis, the reduced leptin activity of the leptin resistance displayed by obese subjects should lead to adrenal axis overactivity. This overactivity should result in elevated serum levels of free cortisol, free fatty acids, and glycerol. In this manner, leptin resistance should lead to peripheral (adipose tissue, liver, and muscle) insulin resistance and islet beta-cell apoptosis, paving the way to Type 2 diabetes.

Body Fat Distribution Contributes to Defining the Relationship between Insulin Resistance and Obesity in Human Diseases

The risk for metabolic and cardiovascular complications of obesity is defined by body fat distribution rather than global adiposity. Unlike subcutaneous fat, visceral fat (including hepatic steatosis) reflects insulin resistance and predicts type 2 diabetes and cardiovascular disease. In humans, available evidence indicates that the ability to store triglycerides in the subcutaneous adipose tissue reflects enhanced insulin sensitivity. Prospective studies document an association between larger subcutaneous fat mass at baseline and reduced incidence of impaired glucose tolerance. Case-control studies reveal an association between genetic predisposition to insulin resistance and a lower amount of subcutaneous adipose tissue. Human peroxisome proliferator-activated receptorgamma (PPAR-γ) promotes subcutaneous adipocyte differentiation and subcutaneous fat deposition, improving insulin resistance and reducing visceral fat. Thiazolidinediones reproduce the effects of PPAR-γ activation and therefore increase the amount of subcutaneous fat while enhancing insulin sensitivity and reducing visceral fat. Partial or virtually complete lack of adipose tissue (lipodystrophy) is associated with insulin resistance and its clinical manifestations, including essential hypertension, hypertriglyceridemia, reduced HDL-c, type 2 diabetes, cardiovascular disease, and kidney disease. Patients with Prader Willi syndrome manifest severe subcutaneous obesity without insulin resistance. The impaired ability to accumulate fat in the subcutaneous adipose tissue may be due to deficient triglyceride synthesis, inadequate formation of lipid droplets, or defective adipocyte differentiation. Lean and obese humans develop insulin resistance when the capacity to store fat in the subcutaneous adipose tissue is exhausted and deposition of triglycerides is no longer attainable at that location. Existing adipocytes become large and reflect the presence of insulin resistance.

From scarcity to solutions: Therapeutic strategies to restore adipose tissue functionality in rare disorders of lipodystrophy

AIMS

Lipodystrophy is a rare disorder characterised by abnormal or deficient adipose tissue formation and distribution. It poses significant challenges to affected individuals, including the development of severe metabolic complications like diabetes and fatty liver disease. These conditions are often chronic, debilitating and life-threatening, with limited treatment options and a lack of specialised expertise. This review aims to raise awareness of lipodystrophy disorders and highlights therapeutic strategies to restore adipose tissue functionality.

METHODS

Extensive research has been conducted, including both historical and recent advances. We have examined and summarised the literature to provide an overview of potential strategies to restore adipose tissue functionality and treat/reverse metabolic complications in lipodystrophy disorders.

RESULTS

A wealth of basic and clinical research has investigated various therapeutic approaches for lipodystrophy. These include ground-breaking methods such as adipose tissue transplantation, innovative leptin replacement therapy, targeted inhibition of lipolysis and cutting-edge gene and cell therapies. Each approach shows great potential in addressing the complex challenges posed by lipodystrophy.

CONCLUSIONS

Lipodystrophy disorders require urgent attention and innovative treatments. Through rigorous basic and clinical research, several promising therapeutic strategies have emerged that could restore adipose tissue functionality and reverse the severe metabolic complications associated with this condition. However, further research and collaboration between academics, clinicians, patient advocacy groups and pharmaceutical companies will be crucial in transforming these scientific breakthroughs into effective and viable treatment options for individuals and families affected by lipodystrophy. Fostering such interdisciplinary partnerships could pave the way for a brighter future for those battling this debilitating disorder.

Management of Monogenic and Syndromic Obesity

Similar to the general population, lifestyle interventions focused on nutrition and physical activity form the foundation for treating obesity caused by rare genetic disorders. Additional therapies, including metreleptin and setmelanotide, that target defects within the leptin signaling pathway can effectively synergize with lifestyle efforts to treat monogenic disorders of leptin, leptin receptor, proopiomelanocortin (POMC), and proprotein convertase subtilisin/kexin type 1 (PCSK1) and syndromic conditions, such as the ciliopathies Bardet-Biedl and Alström syndromes, whose pathophysiological mechanisms also converge on the leptin pathway. Investigational treatments for Prader-Willi syndrome target specific defects caused by reduced expression of paternally derived genes within the chromosome 15q region.

Seeking satiety: From signals to solutions

Remedies for the treatment of obesity date to Hippocrates, when patients with obesity were directed to "reduce food and avoid drinking to fullness" and begin "running during the night." Similar recommendations have been repeated ever since, despite the fact that they are largely ineffective. Recently, highly effective therapeutics were developed that may soon enable physicians to manage body weight in patients with obesity in a manner similar to the way that blood pressure is controlled in patients with hypertension. These medicines have grown out of a revolution in our understanding of the molecular and neural control of appetite and body weight, reviewed here.

Preclinical, randomized phase 1, and compassionate use evaluation of REGN4461, a leptin receptor agonist antibody for leptin deficiency

Deficiency in the adipose-derived hormone leptin or leptin receptor signaling causes class 3 obesity in individuals with genetic loss-of-function mutations in leptin or its receptor LEPR and metabolic and liver disease in individuals with hypoleptinemia secondary to lipoatrophy such as in individuals with generalized lipodystrophy. Therapies that restore leptin-LEPR signaling may resolve these metabolic sequelae. We developed a fully human monoclonal antibody (mAb), REGN4461 (mibavademab), that activates the human LEPR in the absence or presence of leptin. In obese leptin knockout mice, REGN4461 normalized body weight, food intake, blood glucose, and insulin sensitivity. In a mouse model of generalized lipodystrophy, REGN4461 alleviated hyperphagia, hyperglycemia, insulin resistance, dyslipidemia, and hepatic steatosis. In a phase 1, randomized, double-blind, placebo-controlled two-part study, REGN4461 was well tolerated with an acceptable safety profile. Treatment of individuals with overweight or obesity with REGN4461 decreased body weight over 12 weeks in those with low circulating leptin concentrations (<8 ng/ml) but had no effect on body weight in individuals with higher baseline leptin. Furthermore, compassionate-use treatment of a single patient with atypical partial lipodystrophy and a history of undetectable leptin concentrations associated with neutralizing antibodies to metreleptin was associated with noteable improvements in circulating triglycerides and hepatic steatosis. Collectively, these translational data unveil an agonist LEPR mAb that may provide clinical benefit in disorders associated with relatively low leptin concentrations.

Genotype-stratified treatment for monogenic insulin resistance: a systematic review

BACKGROUND

Monogenic insulin resistance (IR) includes lipodystrophy and disorders of insulin signalling. We sought to assess the effects of interventions in monogenic IR, stratified by genetic aetiology.

METHODS

Systematic review using PubMed, MEDLINE and Embase (1 January 1987 to 23 June 2021). Studies reporting individual-level effects of pharmacologic and/or surgical interventions in monogenic IR were eligible. Individual data were extracted and duplicates were removed. Outcomes were analysed for each gene and intervention, and in aggregate for partial, generalised and all lipodystrophy.

RESULTS

10 non-randomised experimental studies, 8 case series, and 23 case reports meet inclusion criteria, all rated as having moderate or serious risk of bias. Metreleptin use is associated with the lowering of triglycerides and haemoglobin A1c (HbA1c) in all lipodystrophy (n = 111), partial (n = 71) and generalised lipodystrophy (n = 41), and in LMNA, PPARG, AGPAT2 or BSCL2 subgroups (n = 72,13,21 and 21 respectively). Body Mass Index (BMI) is lowered in partial and generalised lipodystrophy, and in LMNA or BSCL2, but not PPARG or AGPAT2 subgroups. Thiazolidinediones are associated with improved HbA1c and triglycerides in all lipodystrophy (n = 13), improved HbA1c in PPARG (n = 5), and improved triglycerides in LMNA (n = 7). In INSR-related IR, rhIGF-1, alone or with IGFBP3, is associated with improved HbA1c (n = 17). The small size or absence of other genotype-treatment combinations preclude firm conclusions.

CONCLUSIONS

The evidence guiding genotype-specific treatment of monogenic IR is of low to very low quality. Metreleptin and Thiazolidinediones appear to improve metabolic markers in lipodystrophy, and rhIGF-1 appears to lower HbA1c in INSR-related IR. For other interventions, there is insufficient evidence to assess efficacy and risks in aggregated lipodystrophy or genetic subgroups.

Senescence-associated inflammation and inhibition of adipogenesis in subcutaneous fat in Werner syndrome

Werner syndrome (WS) is a hereditary premature aging disorder characterized by visceral fat accumulation and subcutaneous lipoatrophy, resulting in severe insulin resistance. However, its underlying mechanism remains unclear. In this study, we show that senescence-associated inflammation and suppressed adipogenesis play a role in subcutaneous adipose tissue reduction and dysfunction in WS. Clinical data from four Japanese patients with WS revealed significant associations between the decrease of areas of subcutaneous fat and increased insulin resistance measured by the glucose clamp. Adipose-derived stem cells from the stromal vascular fraction derived from WS subcutaneous adipose tissues (WSVF) showed early replicative senescence and a significant increase in the expression of senescence-associated secretory phenotype (SASP) markers. Additionally, adipogenesis and insulin signaling were suppressed in WSVF, and the expression of adipogenesis suppressor genes and SASP-related genes was increased. Rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), alleviated premature cellular senescence, rescued the decrease in insulin signaling, and extended the lifespan of WS model of C. elegans. To the best of our knowledge, this study is the first to reveal the critical role of cellular senescence in subcutaneous lipoatrophy and severe insulin resistance in WS, highlighting the therapeutic potential of rapamycin for this disease.

Mice lacking triglyceride synthesis enzymes in adipose tissue are resistant to diet-induced obesity

Triglycerides (TGs) in adipocytes provide the major stores of metabolic energy in the body. Optimal amounts of TG stores are desirable as insufficient capacity to store TG, as in lipodystrophy, or exceeding the capacity for storage, as in obesity, results in metabolic disease. We hypothesized that mice lacking TG storage in adipocytes would result in excess TG storage in cell types other than adipocytes and severe lipotoxicity accompanied by metabolic disease. To test this hypothesis, we selectively deleted both TG synthesis enzymes, DGAT1 and DGAT2, in adipocytes (ADGAT DKO mice). As expected with depleted energy stores, ADGAT DKO mice did not tolerate fasting well and, with prolonged fasting, entered torpor. However, ADGAT DKO mice were unexpectedly otherwise metabolically healthy and did not accumulate TGs ectopically or develop associated metabolic perturbations, even when fed a high-fat diet. The favorable metabolic phenotype resulted from activation of energy expenditure, in part via BAT (brown adipose tissue) activation and beiging of white adipose tissue. Thus, the ADGAT DKO mice provide a fascinating new model to study the coupling of metabolic energy storage to energy expenditure.

Incident low muscle mass is associated with greater lung disease and lower circulating leptin in a tobacco-exposed longitudinal cohort

BACKGROUND

Muscle loss is prevalent in chronic obstructive pulmonary disease (COPD). Prior studies evaluating musculoskeletal dysfunction in COPD have focused on individuals with baseline low muscle mass. Currently, there is limited data evaluating clinical characteristics and outcomes associated with progression to incident low muscle mass in a tobacco-exposed cohort of individuals with baseline normal muscle mass.

METHODS

We evaluated 246 participants from a single-center longitudinal tobacco-exposed cohort with serial spirometry, thoracic imaging, dual energy x-ray absorptiometry (DXA) measurements, walk testing, and plasma adipokine measurements. DXA-derived fat free mass index (FFMI) and appendicular skeletal mass index (ASMI) were used as surrogates for muscle mass. Participants with incident low muscle mass (LM) at follow-up were characterized by FFMI < 18.4 kg/m2 in males and < 15.4 kg/m2 in females and/or ASMI < 7.25 kg/m2 in males and < 5.67 kg/m2 in females.

RESULTS

Twenty-five (10%) participants progressed to incident low muscle mass at follow-up. At baseline, the LM subgroup had greater active smoking prevalence (60% v. 38%, p = 0.04), lower FFMI (17.8 ± 1.7 kg/m2 v. 19.7 ± 2.9 kg/m2, p = 0.002), lower ASMI (7.3 ± 0.9 kg/m2 v. 8.2 ± 1.2 kg/m2, p = 0.0003), and lower plasma leptin (14.9 ± 10.1 ng/mL v. 24.0 ± 20.9 ng/mL, p = 0.04). At follow-up, the LM subgroup had higher COPD prevalence (68% v. 43%, p = 0.02), lower FEV1/FVC (0.63 ± 0.12 v. 0.69 ± 0.12, p = 0.02), lower %DLco (66.5 ± 15.9% v. 73.9 ± 16.8%, p = 0.03), and higher annual rate of FFMI decline (-0.17 kg/m2/year v. -0.04 kg/m2/year, p = 0.006). There were no differences in age, gender distribution, pack years smoking history, or walk distance.

CONCLUSIONS

We identified a subgroup of tobacco-exposed individuals with normal baseline muscle mass who progressed to incident DXA-derived low muscle mass. This subgroup demonstrated synchronous lung disease and persistently low circulating leptin levels. Our study suggests the importance of assessing for muscle loss in conjunction with lung function decline when evaluating individuals with tobacco exposure.

Breaking down silos: the multifaceted nature of obesity and the future of weight management

The continued global increase in the prevalence of obesity prompted a meeting at the Royal Society of London investigating causal mechanisms of the disease, 'Causes of obesity: theories, conjectures, and evidence' in October 2022. Evidence presented indicates areas of obesity science where there have been advancements, including an increased understanding of biological and physiological processes of weight gain and maintenance, yet it is clear there is still debate on the relative contribution of plausible causes of the modern obesity epidemic. Consensus was reached that obesity is not a reflection of diminished willpower, but rather the confluence of multiple, complex factors. As such, addressing obesity requires multifactorial prevention and treatment strategies. The accumulated evidence suggests that a continued focus primarily on individual-level contributors will be suboptimal in promoting weight management at the population level. Here, we consider individual biological and physiological processes within the broader context of sociodemographic and sociocultural exposures as well as environmental changes to optimize research priorities and public health efforts. This requires a consideration of a systems-level approach that efficiently addresses both systemic and group-specific environmental determinants, including psychosocial factors, that often serve as a barrier to otherwise efficacious prevention and treatment options. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part I)'.

The Clinical Characteristics and Potential Molecular Mechanism of LMNA Mutation-Related Lipodystrophy

This study aimed to enhance understanding of LMNA mutation-related lipodystrophy by elucidating genotype-phenotype correlations and potential molecular mechanisms. Clinical data from six patients with LMNA mutation-related lipodystrophy are analyzed, and four distinct LMNA mutations are identified. Associations between mutations and lipodystrophy phenotypes are assessed. Three LMNA mutation plasmids are constructed and transfected into HEK293 cells. Protein stability, degradation pathways, and binding proteins of mutant Lamin A/C are examined using Western blotting, co-immunoprecipitation, and mass spectrometry. Confocal microscopy is employed to observe nuclear structure. Four different LMNA mutations are identified in the six patients, all exhibiting lipodystrophy and metabolic disorders. Cardiac dysfunction is observed in two out of six patients. Metformin and pioglitazone are the primary treatments for glucose control. Confocal microscopy revealed nuclear blebbing and irregular cell membranes. Mutant Lamin A/C stability is significantly decreased, and degradation occurred primarily via the ubiquitin-proteasome system (UPS). Potential binding ubiquitination-related proteins of mutant Lamin A/C are identified. This study investigated LMNA mutation-related lipodystrophy, identifying four unique mutations and their connections to specific phenotypes. It is found to decreased mutant Lamin A/C stability and degradation primarily through the UPS, offering new insights into molecular mechanisms and potential therapeutic targets.

Metreleptin Treatment in a Boy with Congenital Generalized Lipodystrophy due to Homozygous c.465_468delGACT (p.T156Rfs*8) Mutation in the BSCL2 Gene: Results From the First-year

Congenital generalized lipodystrophy (CGL) is a rare, autosomal recessive disorder characterized by an almost complete absence of body fat. In CGL, patients may have hyperphagia due to leptin deficiency. Recombinant human leptin (metreleptin) has been suggested as an effective treatment option. We present successful treatment with metreleptin in a boy with CGL and results from the first year of follow-up. An eight-month-old boy presented with excessive hair growth and a muscular appearance. On examination he had hypertrichosis, decreased subcutaneous adipose tissue over the whole body and hepatomegaly. Laboratory investigations revealed hypertriglyceridemia, hyperinsulinemia, elevated liver transaminases and low leptin levels. Molecular genetic analysis detected a homozygous, c.465_468delGACT (p.T156Rfs*8) mutation in the BSCL2 gene. A diagnosis of CGL type 2 was considered. Despite dietary intervention, exercise, and treatment with additional omega-3 and metformin, the hypertriglyceridemia, hyperinsulinemia, and elevated liver transaminase levels worsened. Metreleptin treatment was started and after one year hyperphagia had disappeared, and there was dramatic improvement in levels of insulin, hemoglobin A1c, triglycerides and liver transaminases. Hepatosteatosis was lessened and hepatosplenomegaly was much improved. Metreleptin appears to be an effective treatment option in children with CGL that remarkably improved metabolic complications in the presented case. Initiation of metreleptin treatment in the early period may decrease mortality and morbidity, and increase the quality of life in children with CGL.

Clinical features of generalized lipodystrophy in Turkey: A cohort analysis

AIM

To describe the Turkish generalized lipodystrophy (GL) cohort with the frequency of each complication and the death rate during the period of the follow-up.

METHODS

This study reports on 72 patients with GL (47 families) registered at different centres in Turkey that cover all regions of the country. The mean ± SD follow-up was 86 ± 78 months.

RESULTS

The Kaplan-Meier estimate of the median time to diagnosis of diabetes and/or prediabetes was 16 years. Hyperglycaemia was not controlled in 37 of 45 patients (82.2%) with diabetes. Hypertriglyceridaemia developed in 65 patients (90.3%). The Kaplan-Meier estimate of the median time to diagnosis of hypertriglyceridaemia was 14 years. Hypertriglyceridaemia was severe (≥ 500 mg/dl) in 38 patients (52.8%). Seven (9.7%) patients suffered from pancreatitis. The Kaplan-Meier estimate of the median time to diagnosis of hepatic steatosis was 15 years. Liver disease progressed to cirrhosis in nine patients (12.5%). Liver disease was more severe in congenital lipodystrophy type 2 (CGL2). Proteinuric chronic kidney disease (CKD) developed in 32 patients (44.4%) and cardiac disease in 23 patients (31.9%). Kaplan-Meier estimates of the median time to diagnosis of CKD and cardiac disease were 25 and 45 years, respectively. Females appeared to have a more severe metabolic disease, with an earlier onset of metabolic abnormalities. Ten patients died during the follow-up period. Causes of death were end-stage renal disease, sepsis (because of recurrent intestinal perforations, coronavirus disease, diabetic foot infection and following coronary artery bypass graft surgery), myocardial infarction, heart failure because of dilated cardiomyopathy, stroke, liver complications and angiosarcoma.

CONCLUSIONS

Standard treatment approaches have only a limited impact and do not prevent the development of severe metabolic abnormalities and early onset of organ complications in GL.

What is Obesity?: Definition as a Disease, with Implications for Care

Advances in the understanding of weight regulation provide the framework for the recognition of obesity as a chronic disease. Lifestyle approaches are foundational in the prevention of obesity and should be continued while weight management interventions, including antiobesity medications and metabolic-bariatric procedures, are offered to eligible patients. Clinical challenges remain, however, including overcoming obesity stigma and bias within the medical community toward medical and surgical approaches, ensuring insurance coverage for obesity management (including medications and surgery), and promoting policies that reverse the upward worldwide trend in obesity and adiposity complications in populations.

Familial partial lipodystrophy type 2 and obesity, two adipose tissue pathologies with different inflammatory profiles

INTRODUCTION

The transition to metabolically unhealthy obesity (MUO) is driven by the limited expandability of adipose tissue (AT). Familial Partial Lipodystrophy type 2 (FPLD2) is an alternative model for AT dysfunction that is suitable for comparison with obesity. While MUO is associated with low-grade systemic inflammation, studies of inflammation in FPLD2 have yielded inconsistent results. Consequently, comparison of inflammation markers between FPLD2 and obesity is of great interest to better understand the pathophysiological defects of FPLD2.

OBJECTIVE

To compare the levels of inflammatory biomarkers between a population of patients with FPLD2 due to the same 'Reunionese' LMNA variant and a population of patients with obesity (OB group).

METHODS

Adiponectin, leptin, IL-6, TNF-α and MCP-1 plasma levels were measured by enzyme-linked immuno assays for 60 subjects with FPLD2 and for 60 subjects with obesity. The populations were closely matched for age, sex, and diabetic status.

RESULTS

Metabolic outcomes were similar between the two populations. Adiponectinemia and leptinemia were lower in the FPLD2 group than in the OB group (p < 0.01 for both), while MCP-1 levels were higher in the FPLD2 than in the OB group (p < 0.01). Levels of other inflammatory markers were not significantly different.

CONCLUSIONS

Insulin-resistant patients with FPLD2 and obesity share common complications related to AT dysfunction. Inflammatory biomarker analyses demonstrated that MCP-1 levels and adiponectin levels differ between patients with FPLD2 and patients with obesity. These two AT pathologies thus appear to have different inflammatory profiles.

Hepatokines and Adipokines in Metabolic Syndrome

Hepatokines and adipokines are secretory proteins derived from hepatocytes and adipocytes, respectively. These proteins play a main role in the pathogenesis of metabolic syndrome (MetS), characterized by obesity, dysglycemia, insulin resistance, dyslipidemia, and hypertension. Adipose tissue and liver are important endocrine organs because they regulate metabolic homeostasis as well as inflammation because they secrete adipokines and hepatokines, respectively. These adipokines and hepatokines communicate their action through different autocrine, paracrine and endocrine pathways. Liver regulates systemic homeostasis and also glucose and lipid metabolism through hepatokines. Dysregulation of hepatokines can lead to progression toward MetS, type 2 diabetes (T2D), inflammation, hypertension, and other diseases. Obesity is now a worldwide epidemic. Increasing cases of obesity and obesity-associated metabolic syndrome has brought the focus on understanding the biology of adipocytes and the mechanisms occurring in adipose tissue of obese individuals. A lot of facts are now available on adipose tissue as well. Adipose tissue is now given the status of an endocrine organ. Recent evidence indicates that obesity contributes to systemic metabolic dysfunction. Adipose tissue plays a significant role in systemic metabolism by communicating with other central and peripheral organs via the production and secretion of a group of proteins known as adipokines. Adipokine levels regulate metabolic state of our body and are potent enough to have a direct impact upon energy homeostasis and systemic metabolism. Dysregulation of adipokines contribute to obesity, T2D, hypertension and several other pathological changes in various organs. This makes characterization of hepatokines and adipokines extremely important to understand the pathogenesis of MetS. Hepatokines such as fetuin-A and leukocyte cell-derived chemotaxin 2, and adipokines such as resistin, leptin, TNF-α, and adiponectin are some of the most studied proteins and they can modulate the manifestations of MetS. Detailed insight into the function and mechanism of these adipokines and hepatokines in the pathogenesis of MetS can show the path for devising better preventative and therapeutic strategies against this present-day pandemic.

Lipodystrophies in non-insulin-dependent children: Treatment options and results from recombinant human leptin therapy

Lipodystrophy is a general definition containing different pathologies which, except for those observed in insulin-treated subjects falling outside the scope of this paper, are characterized by total or partial lack of body fat, that, according to the amount of missing adipose tissue, are divided in generalized or partial lipodystrophy. These diseases are characterized by leptin deficiency, which often leads to metabolic derangement, causing insulin resistance, dyslipidemia, and increasing cardiovascular risk. In this narrative review, we presentend the clinical presentation of different types of lipodystrophies and metabolic unbalances related to disease in children and adolescents, focusing on the main treatment options and the novel results from recombinant human leptin (metreleptin) therapy. Milestones in the management of lipodystrophy include lifestyle modification as diet and physical activity, paired with hypoglycemic drugs, insulin, hypolipidemic drugs, and other drugs with the aim of treating lipodystrophy complications. Metreleptin has been recently approved for pediatric patients with general lipodystrophy (GL)> 2 years of age and for children with partial lipodystrophy (PL)> 12 years of age not controlled with conventional therapies. New therapeutic strategies are currently being investigated, especially for patients with PL forms, specifically, liver-targeted therapies. Further studies are needed to achieve the most specific and precise treatment possible.

Adipokines from white adipose tissue in regulation of whole body energy homeostasis

Diseases originating from altered energy homeostasis including obesity, and type 2 diabetes are rapidly increasing worldwide. Research in the last few decades on animal models and humans demonstrates that the white adipose tissue (WAT) is critical for energy balance and more than just an energy storage site. WAT orchestrates the whole-body metabolism through inter-organ crosstalk primarily mediated by cytokines named "Adipokines". The adipokines influence metabolism and fuel selection of the skeletal muscle and liver thereby fine-tuning the load on WAT itself in physiological conditions like starvation, exercise and cold. In addition, adipokine secretion is influenced by various pathological conditions like obesity, inflammation and diabetes. In this review, we have surveyed the current state of knowledge on important adipokines and their significance in regulating energy balance and metabolic diseases. Furthermore, we have summarized the interplay of pro-inflammatory and anti-inflammatory adipokines in the modulation of pathological conditions.

Insulin and body mass index decrease serum soluble leptin receptor levels in humans

PURPOSE

Test how serum soluble leptin receptor (sOb-R) is influenced by glucose, insulin, body fat, body mass index (BMI), food intake and physical activity.

METHODS

We performed an epidemiological triangulation combining cross-sectional, interventional and Mendelian randomization study designs. In five independent clinical studies (n = 24-823), sOb-R was quantified in serum or plasma by commercial ELISA kits using monoclonal antibodies. We performed mixed models regression and two-sample Mendelian randomization.

RESULTS

In pooled, cross-sectional data, levelling on study, sOb-R associated inversely with body mass index (BMI) (beta [95% CI] -0.19 [-0.21 to -0.17]), body fat (-0.12 [-0.14 to -0.10) and fasting C-peptide (-2.04 [-2.46 to -1.62]). sOb-R decreased in response to acute hyperinsulinaemia during euglycaemic glucose clamp in two independent clinical studies (-0.5 [-0.7 to -0.4] and -0.5 [-0.6 to -0.3]), and immediately increased in response to intensive exercise (0.18 [0.04 to 0.31]) and food intake (0.20 [0.06 to 0.34]). In two-sample Mendelian randomization, higher fasting insulin and higher BMI were causally linked to lower sOb-R levels (inverse variance weighted, -1.72 [-2.86 to -0.58], and -0.20 [-0.36 to -0.04], respectively). The relationship between hyperglycaemia and sOb-R were inconsistent in cross-sectional studies, non-significant in intervention studies, and two-sample Mendelian randomization suggested no causal effect of fasting glucose on sOb-R.

MAIN CONCLUSION

Both BMI and insulin causally decreased serum sOb-R levels. Conversely, intensive exercise and food intake acutely increased sOb-R. Our results suggest that sOb-R is involved in short-term regulation of leptin signalling, either directly or indirectly, and that hyperinsulinaemia may reduce leptin signalling.

Adipokines: Deciphering the cardiovascular signature of adipose tissue

Obesity and hypertension are intimately linked due to the various ways that the important cell types such as vascular smooth muscle cells (VSMC), endothelial cells (EC), immune cells, and adipocytes, communicate with one another to contribute to these two pathologies. Adipose tissue is a very dynamic organ comprised primarily of adipocytes, which are well known for their role in energy storage. More recently adipose tissue has been recognized as the largest endocrine organ because of its ability to produce a vast number of signaling molecules called adipokines. These signaling molecules stimulate specific types of cells or tissues with many adipokines acting as indicators of adipocyte healthy function, such as adiponectin, omentin, and FGF21, which show anti-inflammatory or cardioprotective effects, acting as regulators of healthy physiological function. Others, like visfatin, chemerin, resistin, and leptin are often altered during pathophysiological circumstances like obesity and lipodystrophy, demonstrating negative cardiovascular outcomes when produced in excess. This review aims to explore the role of adipocytes and their derived products as well as the impacts of these adipokines on blood pressure regulation and cardiovascular homeostasis.

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.

Achievements, prospects and challenges in precision care for monogenic insulin-deficient and insulin-resistant diabetes

Integration of genomic and other data has begun to stratify type 2 diabetes in prognostically meaningful ways, but this has yet to impact on mainstream diabetes practice. The subgroup of diabetes caused by single gene defects thus provides the best example to date of the vision of 'precision diabetes'. Monogenic diabetes may be divided into primary pancreatic beta cell failure, and primary insulin resistance. In both groups, clear examples of genotype-selective responses to therapy have been advanced. The benign trajectory of diabetes due to pathogenic GCK mutations, and the sulfonylurea-hyperresponsiveness conferred by activating KCNJ11 or ABCC8 mutations, or loss-of-function HNF1A or HNF4A mutations, often decisively guide clinical management. In monogenic insulin-resistant diabetes, subcutaneous leptin therapy is beneficial in some severe lipodystrophy. Increasing evidence also supports use of 'obesity therapies' in lipodystrophic people even without obesity. In beta cell diabetes the main challenge is now implementation of the precision diabetes vision at scale. In monogenic insulin-resistant diabetes genotype-specific benefits are proven in far fewer patients to date, although further genotype-targeted therapies are being evaluated. The conceptual paradigm established by the insulin-resistant subgroup with 'adipose failure' may have a wider influence on precision therapy for common type 2 diabetes, however. For all forms of monogenic diabetes, population-wide genome sequencing is currently forcing reappraisal of the importance assigned to pathogenic mutations when gene sequencing is uncoupled from prior suspicion of monogenic diabetes.

The acromegaly lipodystrophy

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Lipodystrophy for the Diabetologist-What to Look For

PURPOSE OF REVIEW

Genetic or acquired lipodystrophies are characterized by selective loss of body fat along with predisposition towards metabolic complications of insulin resistance, such as diabetes mellitus, hypertriglyceridemia, hepatic steatosis, polycystic ovarian syndrome, and acanthosis nigricans. In this review, we discuss the various subtypes and when to suspect and how to diagnose lipodystrophy.

RECENT FINDINGS

The four major subtypes are autosomal recessive, congenital generalized lipodystrophy (CGL); acquired generalized lipodystrophy (AGL), mostly an autoimmune disorder; autosomal dominant or recessive familial partial lipodystrophy (FPLD); and acquired partial lipodystrophy (APL), an autoimmune disorder. Diagnosis of lipodystrophy is mainly based upon physical examination findings of loss of body fat and can be supported by body composition analysis by skinfold measurements, dual-energy x-ray absorptiometry, and whole-body magnetic resonance imaging. Confirmatory genetic testing is helpful in the proband and at-risk family members with suspected genetic lipodystrophies. The treatment is directed towards the specific comorbidities and metabolic complications, and there is no treatment to reverse body fat loss. Metreleptin should be considered as the first-line therapy for metabolic complications in patients with generalized lipodystrophy and for prevention of comorbidities in children. Metformin and insulin therapy are the best options for treating hyperglycemia and fibrates and/or fish oil for hypertriglyceridemia. Lipodystrophy should be suspected in lean and muscular subjects presenting with diabetes mellitus, hypertriglyceridemia, non-alcoholic fatty liver disease, polycystic ovarian syndrome, or amenorrhea. Diabetologists should be aware of lipodystrophies and consider genetic varieties as an important subtype of monogenic diabetes.

Time to transition from a negative nomenclature describing what NAFLD is not, to a novel, pathophysiology-based, umbrella classification of fatty liver disease (FLD)

Non-alcoholic fatty liver disease (NAFLD) is a definition of a prevalent condition that has been given a name describing what the disease is not, mainly due to gaps in the physiopathological understanding of NAFLD when the name was given to it. NAFLD still remains an unmet clinical need to a large extent due to the heterogenicity of the disease and the lack of a more accurate physiology-based classification. In essence, fatty liver disease (FLD) has a multifactorial etiology, including metabolic abnormalities, environmental influences, genetic disorders, and/or their overlap which makes it difficult to diagnose, design appropriate trials for it and treat this disease. Therefore, we propose herein that as our knowledge about this disease continues to grow exponentially, it is time to consider ending this unspecific, negative and broad classification of NAFLD, and turn it into a positive and targeted one describing what the disease is and not what it is not. Thus, we propose the novel FLD "Mantzoros classification". This innovative classification proposes to classify the heterogeneous causes of FLD under one umbrella and eventually lead to a better nomenclature and classification system reflecting pathophysiology. This in turn could lead to both better clinical trials and more personalized care. An additional aim is to generate a dialogue among the experts in this field to eventually reach the right nomenclature for an appropriate disease classification that would facilitate our understanding, approach, diagnosis, and management of this epidemic of FLD. Overall, a novel classification, based on phenotypic manifestations, leading risk factors and probable causes of FLD, could help our understanding and clinically would be accurately defining and differentiating the disease, leading to a more accurate design and execution of clinical trials. This would in turn lead to tangible benefits for all patients suffering from FLD through targeted and more effective personalized treatments.

Face-sparing Congenital Generalized Lipodystrophy Type 1 Associated With Nonclassical Congenital Adrenal Hyperplasia

CONTEXT

Congenital generalized lipodystrophy, type 1 (CGL1), due to biallelic pathogenic variants in AGPAT2, is characterized by the near total loss of body fat from the face, trunk, and extremities. Patients develop premature diabetes, hypertriglyceridemia, hepatic steatosis, and polycystic ovary syndrome. However, sparing of the facial fat and precocious pubertal development has not been previously reported in CGL1.

CASE DESCRIPTION

We report a 21-year-old woman of European descent with CGL1 who had sparing of the facial fat and premature thelarche at birth with premature pubarche and menstrual bleeding at age 3 years. Her serum 17-OH progesterone level rose to 1000 ng/dL (30.26 nmol/L) after cosyntropin stimulation test, suggestive of nonclassical congenital adrenal hyperplasia (NCAH) due to 21-hydroxylase deficiency. Hydrocortisone replacement therapy from age 3.5 to 10 years resulted in cessation of menstruation and growth of pubic hair, and a reduction of breast size. Sanger and whole-exome sequencing revealed compound heterozygous variants c.493-1G>C; p.(Leu165_Gln196del), and c.del366_588+534; p.(Leu123Cysfs*55) in AGPAT2 plus c.806G>C; p.(Ser269Thr) and c.844G>T; p.(Val282Leu) in CYP21A2. She developed diabetes at age 13 requiring high-dose insulin and had 7 episodes of acute pancreatitis due to extreme hypertriglyceridemia in the next 5 years. Metreleptin therapy was initiated at age 18 and after 3 years, she had remission of diabetes and hypertriglyceridemia; however, menstrual irregularity and severe hirsutism did not improve.

CONCLUSION

Concomitant NCAH in this CGL1 patient was associated with precocious pubertal development and sparing of facial fat. Metreleptin therapy drastically improved her hyperglycemia and hyperlipidemia but not menstrual irregularity and hirsutism.

Pancreatic Islets as a Target of Adipokines

Rising rates of obesity are intricately tied to the type 2 diabetes epidemic. The adipose tissues can play a central role in protection against or triggering metabolic diseases through the secretion of adipokines. Many adipokines may improve peripheral insulin sensitivity through a variety of mechanisms, thereby indirectly reducing the strain on beta cells and thus improving their viability and functionality. Such effects will not be the focus of this article. Rather, we will focus on adipocyte-secreted molecules that have a direct effect on pancreatic islets. By their nature, adipokines represent potential druggable targets that can reach the islets and improve beta-cell function or preserve beta cells in the face of metabolic stress. © 2022 American Physiological Society. Compr Physiol 12:1-27, 2022.

Therapeutic indications and metabolic effects of metreleptin in patients with lipodystrophy syndromes: Real-life experience from a national reference network

AIM

To describe baseline characteristics and follow-up data in patients with lipodystrophy syndromes treated with metreleptin in a national reference network, in a real-life setting.

PATIENTS AND METHODS

Clinical and metabolic data from patients receiving metreleptin in France were retrospectively collected, at baseline, at 1 year and at the latest follow-up during treatment.

RESULTS

Forty-seven patients with lipodystrophy including generalized lipodystrophy (GLD; n = 28) and partial lipodystrophy (PLD; n = 19) received metreleptin over the last decade. At baseline, the median (interquartile range [IQR]) patient age was 29.3 (16.6-47.6) years, body mass index was 23.8 (21.2-25.7) kg/m² and serum leptin was 3.2 (1.0-4.9) ng/mL, 94% of patients had diabetes (66% insulin-treated), 53% had hypertension and 87% had dyslipidaemia. Metreleptin therapy, administered for a median (IQR) of 31.7 (14.2-76.0) months, was ongoing in 77% of patients at the latest follow-up. In patients with GLD, glycated haemoglobin (HbA1c) and fasting triglyceride levels significantly decreased from baseline to 1 year of metreleptin treatment, from 8.4 (6.5-9.9)% [68 (48-85) mmol/mol] to 6.8 (5.6-7.4)% [51(38-57) mmol/mol], and 3.6 (1.7-8.5) mmol/L to 2.2 (1.1-3.7) mmol/L, respectively (P < 0.001), with sustained efficacy thereafter. In patients with PLD, HbA1c was not significantly modified (7.7 [7.1-9.1]% [61 (54-76) mmol/mol] at baseline vs. 7.7 [7.4-9.5]% [61(57-80) mmol/mol] at 1 year), and the decrease in fasting triglycerides (from 3.3 [1.9-9.9] mmol/L to 2.5 [1.6-5.3] mmol/L; P < 0.01) was not confirmed at the latest assessment (5.2 [2.2-11.3] mmol/L). However, among PLD patients, at 1 year, 61% were responders regarding glucose homeostasis, with lower baseline leptin levels compared to nonresponders, and 61% were responders regarding triglyceridaemia. Liver enzymes significantly decreased only in the GLD group.

CONCLUSIONS

In this real-life setting study, metabolic outcomes are improved by metreleptin therapy in patients with GLD. The therapeutic indication for metreleptin needs to be clarified in patients with PLD.

The genetic elucidation of monogenic obesity in the Arab world: a systematic review

BACKGROUND

Investigation of monogenic obesity (MO), a rare condition caused by a single gene variant(s), especially in consanguineous populations, is a powerful approach for obtaining novel insights into the genetic alterations involved. Here, we present a systematic review of the genetics of MO in the 22 Arab countries and apply protein modeling in silico to the missense variants reported.

METHODS

We searched four literature databases (PubMed, Web of Science, Science Direct and Scopus) from the time of their first creation until December 2020, utilizing broad search terms to capture all genetic studies related to MO in the Arab countries. Only articles published in peer-reviewed journals involving subjects from at least one of the 22 Arab countries and dealing with genetic variants related to MO were included. Protein modelling of the variants identified was performed using PyMOL.

RESULTS

The 30 cases with severe early-onset obesity identified in 13 studies carried 14 variants in five genes (LEP, LEPR, POMC, MC4R and CPE). All of these variants were pathogenic, homozygous and carried by members of consanguineous families.

CONCLUSION

Despite the elevated presence of consanguinity in the Arab countries, the genetic origins of MO remain largely unexplained and require additional studies, both of a genetic and functional character.