Role of Leptin in the Digestive System

Long Noncoding RNAs in Diet-Induced Metabolic Diseases

The prevalence of metabolic diseases, including type 2 diabetes and metabolic dysfunction-associated steatotic liver disease (MASLD), is steadily increasing. Although many risk factors, such as obesity, insulin resistance, or hyperlipidemia, as well as several metabolic gene programs that contribute to the development of metabolic diseases are known, the underlying molecular mechanisms of these processes are still not fully understood. In recent years, it has become evident that not only protein-coding genes, but also noncoding genes, including a class of noncoding transcripts referred to as long noncoding RNAs (lncRNAs), play key roles in diet-induced metabolic disorders. Here, we provide an overview of selected lncRNA genes whose direct involvement in the development of diet-induced metabolic dysfunctions has been experimentally demonstrated in suitable in vivo mouse models. We further summarize and discuss the associated molecular modes of action for each lncRNA in the respective metabolic disease context. This overview provides examples of lncRNAs with well-established functions in diet-induced metabolic diseases, highlighting the need for appropriate in vivo models and rigorous molecular analyses to assign clear biological functions to lncRNAs.

Leptin- and cytokine-like unpaired signaling in Drosophila

Animals have evolved a multitude of signaling pathways that enable them to orchestrate diverse physiological processes to tightly regulate systemic homeostasis. This signaling is mediated by various families of peptide hormones and cytokines that are conserved across the animal kingdom. In this review, we primarily focus on the unpaired (Upd) family of proteins in Drosophila which are evolutionarily related to mammalian leptin and the cytokine interleukin 6. We summarize expression patterns of Upd in Drosophila and discuss the parallels in structure, signaling pathway, and functions between Upd and their mammalian counterparts. In particular, we focus on the roles of Upd in governing metabolic homeostasis, growth and development, and immune responses. We aim to stimulate future studies on leptin-like signaling in other phyla which can help bridge the evolutionary gap between insect Upd and vertebrate leptin and cytokines like interleukin 6.

Association of the Human Leptin Receptor Gene (rs1137101; Gln223Arg) Polymorphism and Circulating Leptin in Patients with Metabolic Syndrome in the Indian Population

Phenotypic expression of metabolic syndrome is precipitated by environmental variables along with the individual genetic susceptibility to the obesogenic environment and growing body of evidence suggest a paramount role of adipocytokines. Therefore, identifying the genetic influence on circulation leptin levels and clarifying genotype-phenotype correlation of rs1137101 {Leptin receptor gene (LEPR) Gln223Arg (Q223R; A668G)} in metabolic syndrome were the primary objective of this study. A total of 447 adult participants, including 214 metabolic syndrome patients and 233 healthy controls, were genotyped using polymerase chain reaction-restriction fragment length polymorphism method to unravel the effects of genetic risk loci {Leptin receptor gene; Gln223Arg (Q223R; A668G); rs1137101} on the occurrence of metabolic syndrome in consort with circulation leptin levels. Suitable descriptive statistics was used for different variables. The genotype frequencies were found to be in Hardy-Weinberg equilibrium for both cases (p > 0.2722) as well as in controls (p > 0.2331). However, genotype (x2: 11.26, 2 d.f. p = 0.0036) and allele distribution (x2: 10.51, 2 d.f. p: 0.0012) of the LEPR Gln223Arg (Q223R; A668G) differed significantly between cases and controls. Gln/Arg genotype (OR = 1.6099; 95% CI = 1.0847-2.3893; p value = 0.0181), Arg/Arg genotype (OR = 2.8121; 95% CI = 1.4103-5.6074; p value = 0.0033) and R allele (OR = 1.5875; 95% CI = 1.1996-2.1008; p value = 0.0012) were significantly associated with increased risk of metabolic syndrome in univariate analysis. Further a multivariate logistic regression adjusted for potential confounders showed that Arg/Arg genotype (OR = 1.9; 95% CI = 1.271-2.639; p-value < 0.05) and Gln/Arg (OR: 1.3; 95% CI = 0.873-2.034; p value < 0.05) have a significant risk for the occurrence of the metabolic syndrome. A progressive increase in the serum leptin levels from major homozygous alleles to minor homozygous alleles were observed indicating that rs1137101 modify the serum leptin concentrations in patients with metabolic syndrome. These findings provide enough evidence of a significant association of LEPR Gln223Arg (Q223R; A668G) polymorphism in the LepR gene in Indian patients with increased risk of metabolic syndrome for R allele and Arg/Arg homozygote. Thus, rs1137101 might be a pleiotropic locus for metabolic syndrome and its components in studied population.

Bioleptin as a useful marker of metabolic status in children with diabetes mellitus type 1

Introduction

The purpose of our study was tomeasure the level of leptin and biologically active leptin (bioLEP) in children with type 1 diabetes, depending on the duration of diabetes and its degree of metabolic control.

Methods

The study included 94 children (58 boys and 36 girls). In a group of children with diabetes, 40 patients were newly diagnosed with type 1 diabetes, 40 children who have diabetes for more than a year (20 with good metabolic control and 20 with poor metabolic control). The control group consisted of 14 healthy children. The serum level of leptin and bioLEP was measured using a sandwich enzyme-linked immunosorbent assay. To our knowledge, this is the first study to describe bioLEP levels among diabetic children with different forms of disease control.

Results

Lower levels of leptin were found in children with diabetes compared to healthy children. Furthermore, we found a statistically higher concentration of leptin in the group of children with newly diagnosed diabetes compared to children from the diabetic group with poor metabolic control and lower than healthy children (11.19 vs. 7.84 and 20.94 ng/mL). Moreover, children in the metabolically well-controlled group had statistically lower levels of this hormone (5.11 ng/mL) than healthy children. Leptin concentrations differed significantly between underweight, overweight, and obese children.

Discussion

In our study, the level of bioLEP differed significantly between children in the newly diagnosed diabetes group and children in the long-term, poorly controlled diabetes group and healthy controls. Despite many studies published in recent years, many aspects of leptin secretion, action, and mechanisms of its influence on carbohydrate and fat metabolism are still to be clarified. In our opinion, studies evaluating the status of bioLEP in diabetes can also contribute to a better understanding of the mechanisms regulating metabolism.

Leptin system is not affected by different diets in the abomasum of the sheep reared in semi-natural pastures of the Central Apennines

The growing summer drought stress is affecting the nutritional value of pastures, no longer sufficient to support the nutritional status of sheep in extensive rearing. Adipokines affect organ and tissue functionality can be useful to evaluate animal welfare and prompt an improvement in the management of the grazing animals. Leptin (Lep) is an adipokine mainly produced by adipose tissue that regulates food intake by an anorexigenic action. Lep has also been detected in the human and rat gastrointestinal tract, where it regulates the rate of gastric emptying. In this study, Lep system was evaluated in the abomasum of 15 adult sheep reared on Apennine pastures and subjected to different diets. Until the maximum pasture flowering (MxF group), the sheep fed on fresh forage; from that moment until the maximum pasture dryness (MxD group), the experimental group (Exp group) received a feed supplementation in addition to MxD group feeding. The Lep system was investigated in the abomasum samples by immunohistochemistry (IHC) and RT-qPCR. Double-label localisation of Lep and leptin receptor (LepR) with neuroendocrine hormones was conducted to distinguish the gland cell types. The analysis performed revealed the presence of Lep and LepR in the chief and neuroendocrine cells of the fundic glands of the abomasum. RT-qPCR evidenced the transcript for Lep and LepR also identifying the long isoform (LepRb). No significant differences were observed among the three groups of sheep subjected to different diets. The abundant immunostaining observed in the fundic glands suggests that the Lep intervenes in the regulation of abomasum in sheep with a similar pattern to monogastric species while long term food supplementation seems do not influence the local function of the Lep system. A better understanding of the gastrointestinal system can contribute to improving sheep management and optimising the sustainability of livestock production.

Impact of biliopancreatic diversion with duodenal switch on glucose homeostasis and gut hormones and their correlations with appetite

BACKGROUND

Biliopancreatic diversion with duodenal switch (BPD/DS) results in lifelong changes in gastrointestinal physiology with unclear associations with appetite perception.

OBJECTIVE

To explore mixed meal-induced changes in glucose homeostasis and gut hormones and their correlations with appetite perception.

SETTING

University hospital.

METHODS

Of 28 patients studied preoperatively (age: 38.4 ± 11.3 years; body mass index [BMI]: 56.5 ± 5.1 kg/m²; 14 women), 19 (68%) returned for postoperative follow-up. Plasma was sampled for 180 minutes during a 260-kcal standardized mixed meal. Concentrations of leptin, glucose, insulin, triglycerides, active acyl-ghrelin, motilin, total glucose-dependent insulinotropic polypeptide (GIP), active glucagon-like peptide 1 (GLP-1), and total peptide YY (PYY) were measured. Subjective appetite sensations were scored.

RESULTS

BPD/DS resulted in 66.1% ± 23.3% excess BMI loss. Leptin was halved. Glucose and insulin levels were reduced, blunting a preoperative peak at 30 minutes, giving a lower homeostasis model assessment for insulin resistance (HOMA-IR; 13.9 versus 4.8). In contrast, reduced ghrelin and motilin concentrations were accompanied by pronounced peaks 20-30 minutes prior to meal responses. GIP was reduced, whereas GLP-1 and PYY responses were markedly increased, with an early postprandial peak (P < .05, for all). HOMA-IR correlated with insulin (r = .72) and GIP (r = .57). Postoperatively, satiety correlated with GLP-1 (r = .56), whereas the gastric motility index correlated with the desire to eat (r = .60), percentage excess BMI loss (r = -.55), and percentage total weight loss (r = -.49). Delta insulin, GLP-1, and leptin correlated positively with percentage total weight loss (r = .51, r = .48, and r = .58, respectively).

CONCLUSIONS

BPD/DS reduces leptin, HOMA-IR, and GIP while markedly increasing GLP-1 and PYY. This study marks the magnitude change in GLP-1 with additional effects of PYY as important factors for weight loss.

The Circadian Axis and Cardiometabolic Syndrome

Circadian rhythm refers to the daily physiologically fluctuating patterns of systemic processes that occur within a circa 24-hour timeframe, independently of external factors. There is evidence that in time, external and internal cycle misalignment leads to severe health consequences, resulting in the development of cardiometabolic disturbances. Desynchronized hormonal fluctuations along with daily specific macronutrient utilization patterns are also discussed, which by consequence, are all predictors of metabolic syndrome. The aim of this paper is to provide insight on the circadian clock’s organization throughout the human body and to explain the underlying genetic background. By understanding these well-established molecular mechanisms and processes, we believe this paper will provide accuracy regarding the importance of the circadian clock’s integrity and will highlight its role in the etiopathology of cardiometabolic syndrome.

The role of hypoleptinemia in the psychological and behavioral adaptation to starvation: implications for anorexia nervosa

This narrative review aims to pinpoint mental and behavioral effects of starvation, which may be triggered by hypoleptinemia and as such may be amenable to treatment with leptin receptor agonists. The reduced leptin secretion results from the continuous loss of fat mass, thus initiating a graded triggering of diverse starvation related adaptive functions. In light of leptin receptors located in several peripheral tissues and many brain regions adaptations may extend beyond those of the hypothalamus-pituitary-end organ-axes. We focus on gastrointestinal tract and reward system as relevant examples of peripheral and central effects of leptin. Despite its association with extreme obesity, congenital leptin deficiency with its many parallels to a state of starvation allows the elucidation of mental symptoms amenable to treatment with exogenous leptin in both ob/ob mice and humans with this autosomal recessive disorder. For starvation induced behavioral changes with an intact leptin signaling we particularly focus on rodent models for which proof of concept has been provided for the causative role of hypoleptinemia. For humans, we highlight the major cognitive, emotional and behavioral findings of the Minnesota Starvation Experiment to contrast them with results obtained upon a lesser degree of caloric restriction. Evidence for hypoleptinemia induced mental changes also stems from findings obtained in lipodystrophies. In light of the recently reported beneficial cognitive, emotional and behavioral effects of metreleptin-administration in anorexia nervosa we discuss potential implications for the treatment of this eating disorder. We postulate that leptin has profound psychopharmacological effects in the state of starvation.

A nexus of lipid and O-Glcnac metabolism in physiology and disease

Although traditionally considered a glucose metabolism-associated modification, the O-linked β-N-Acetylglucosamine (O-GlcNAc) regulatory system interacts extensively with lipids and is required to maintain lipid homeostasis. The enzymes of O-GlcNAc cycling have molecular properties consistent with those expected of broad-spectrum environmental sensors. By direct protein-protein interactions and catalytic modification, O-GlcNAc cycling enzymes may provide both acute and long-term adaptation to stress and other environmental stimuli such as nutrient availability. Depending on the cell type, hyperlipidemia potentiates or depresses O-GlcNAc levels, sometimes biphasically, through a diversity of unique mechanisms that target UDP-GlcNAc synthesis and the availability, activity and substrate selectivity of the glycosylation enzymes, O-GlcNAc Transferase (OGT) and O-GlcNAcase (OGA). At the same time, OGT activity in multiple tissues has been implicated in the homeostatic regulation of systemic lipid uptake, storage and release. Hyperlipidemic patterns of O-GlcNAcylation in these cells are consistent with both transient physiological adaptation and feedback uninhibited obesogenic and metabolic dysregulation. In this review, we summarize the numerous interconnections between lipid and O-GlcNAc metabolism. These links provide insights into how the O-GlcNAc regulatory system may contribute to lipid-associated diseases including obesity and metabolic syndrome.

Health benefits of dietary chronobiotics: beyond resynchronizing internal clocks

The internal circadian clock in mammals drives whole-body biological activity rhythms. The clock reflects changes in external signals by controlling enzyme functions and the release of hormones involved in metabolic processes. Thus, misalignments between the circadian clock and an individual's daily schedule are recognized to be related to various metabolic diseases, such as obesity and diabetes. Although evidence has shown the existence of a complex relationship between circadian clock regulation and daily food intake, the regulatory effects of phytochemicals on the circadian clock remain unclarified. To better elucidate these relationships/effects, the circadian system components in mammals, circadian misalignment-related metabolic diseases, circadian rhythm-adjusting phytochemicals (including the heterocycles, acids, flavonoids and others) and the potential mechanisms (including the regulation of clock genes/proteins, metabolites of gut microbiota and secondary metabolites) are reviewed here. The bioactive components of functional foods discussed in this review could be considered potentially effective factors for the prevention and treatment of metabolic disorders related to circadian misalignment.

The Leptin System and Diet: A Mini Review of the Current Evidence

Leptin promotes satiety and modulates energy balance and weight. Diet-induced obesity leads to leptin resistance, exacerbating overeating. We reviewed the literature on the relationship between diet and leptin, which suggests that addressing leptin resistance through dietary interventions can contribute counteracting obesity. Albeit some limitations (e.g., limited rigor, small samples sizes), studies in animals and humans show that diets high in fat, carbohydrates, fructose, and sucrose, and low in protein are drivers of leptin resistance. Despite methodological heterogeneity pertaining to this body of literature, experimental studies show that energy-restricted diets can reduce leptinemia both in the short and long term and potentially reverse leptin resistance in humans. We also discuss limitations of this evidence, future lines of research, and implications for clinical and public health translations. Main limitations include the lack of a single universally-accepted definition of leptin resistance, and of adequate ways to accurately measure it in humans. The use of leptin sensitizers (drugs) and genetically individualized diets are alternatives against leptin resistance that should be further researched in humans. The tested very-low-energy intervention diets are challenging to translate into wide clinical or population recommendations. In conclusion, the link between nutritional components and leptin resistance, as well as research indicating that this condition is reversible, emphasizes the potential of diet to recover sensitivity to this hormone. A harmonized definition of leptin resistance, reliable methods to measure it, and large-scale, translational, clinical, and precision nutrition research involving rigorous methods are needed to benefit populations through these approaches.