Vitamin D up-regulates glucose transporter 4 (GLUT4) translocation and glucose utilization mediated by cystathionine-γ-lyase (CSE) activation and H2S formation in 3T3L1 adipocytes

Advances in biomedical applications of vitamin D for VDR targeted management of obesity and cancer

BACKGROUND

1,25(OH)2D3 is a fat-soluble vitamin, involved in regulating Ca2+ homeostasis in the body. Its storage in adipose tissue depends on the fat content of the body. Obesity is the result of abnormal lipid deposition due to the prolonged positive energy balance and increases the risk of several cancer types. Furthermore, it has been associated with vitamin D deficiency and defined as a low 25(OH)2D3 blood level. In addition, 1,25(OH)2D3 plays vital roles in Ca2+-Pi and glucose metabolism in the adipocytes of obese individuals and regulates the expressions of adipogenesis-associated genes in mature adipocytes.

SCOPE AND APPROACH

The present contribution focused on the VDR mediated mechanisms interconnecting the obese condition and cancer proliferation due to 1,25(OH)2D3-deficiency in humans. This contribution also summarizes the identification and development of molecular targets for VDR-targeted drug discovery.

KEY FINDINGS AND CONCLUSIONS

Several studies have revealed that cancer development in a background of 1,25(OH)2D3 deficient obesity involves the VDR gene. Moreover, 1,25(OH)2D3 is also known to influence several cellular processes, including differentiation, proliferation, and adhesion. The multifaceted physiology of obesity has improved our understanding of the cancer therapeutic targets. However, currently available anti-cancer drugs are notorious for their side effects, which have raised safety issues. Thus, there is interest in developing 1,25(OH)2D3-based therapies without any side effects.

Vitamin D and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): Novel Mechanistic Insights

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an increasingly prevalent condition characterized by abnormal fat accumulation in the liver, often associated with metabolic disorders. Emerging evidence suggests a potential link between vitamin D deficiency and the development and progression of MASLD. The current review provides a concise overview of recent studies uncovering novel mechanistic insights into the interplay between vitamin D and MASLD. Several epidemiological studies have highlighted a significant association between low vitamin D levels and an increased risk of MASLD. Vitamin D, traditionally known for its role in bone health, has now been recognized as a key player in various physiological processes, including immune regulation and inflammation. Experimental studies using animal models have demonstrated that vitamin D deficiency exacerbates liver steatosis and inflammation, suggesting a potential protective role against MASLD. Mechanistically, vitamin D appears to modulate MASLD through multiple pathways. Firstly, the vitamin D receptor (VDR) is abundantly expressed in liver cells, indicating a direct regulatory role in hepatic function. Activation of the VDR has been shown to suppress hepatic lipid accumulation and inflammation, providing a mechanistic basis for the observed protective effects. Additionally, vitamin D influences insulin sensitivity, a critical factor in MASLD pathogenesis. Improved insulin sensitivity may mitigate the excessive accumulation of fat in the liver, thus attenuating MASLD progression. In parallel, vitamin D exhibits anti-inflammatory properties by inhibiting pro-inflammatory cytokines implicated in MASLD pathophysiology. Experimental evidence suggests that the immunomodulatory effects of vitamin D extend to the liver, reducing inflammation and oxidative stress, key drivers of MASLD, and the likelihood of hepatocyte injury and fibrosis. Understanding the complex interplay between vitamin D and MASLD provides a basis for exploring targeted therapeutic strategies and preventive interventions. As vitamin D deficiency is a modifiable risk factor, addressing this nutritional concern may prove beneficial in mitigating the burden of MASLD and associated metabolic disorders.

Cholecalciferol ameliorates insulin signalling and insulin regulation of enzymes involved in glucose metabolism in the rat heart

CONTEXT

The evidence on potential cross-talk of vitamin D and insulin in the regulation of cardiac metabolism is very scanty.

OBJECTIVE

Cholecalciferol was administered to male Wistar rats for six weeks to study its effects on cardiac glucose metabolism regulation.

MATERIALS AND METHODS

An expression, phosphorylation and/or subcellular localisation of insulin signalling molecules, glucose transport and metabolism key proteins were studied.

RESULTS

Circulating non-esterified fatty acids (NEFA) level was lower after cholecalciferol administration. Cholecalciferol decreased cardiac insulin receptor substrate 1 Ser307 phosphorylation, while insulin-stimulated Akt Thr308 phosphorylation was increased. Cardiac 6-phosphofructo-2-kinase protein, hexokinase 2 mRNA level and insulin-stimulated glycogen synthase kinase 3β Ser9 phosphorylation were also increased. Finally, FOXO1 transcription factor cytosolic level was reduced.

CONCLUSION

Vitamin D-related improvement of insulin signalling and insulin regulation of glucose metabolism in the rat heart is accompanied by the decrease of blood NEFA level and dysregulation of cardiac FOXO1 signalling.

Free radical scavenging polyphenols isolated from Phyllanthus niruri L. ameliorates hyperglycemia via SIRT1 induction and GLUT4 translocation in in vitro and in vivo models

Type 2 diabetes milletus (T2DM) is a complex multifaceted disorder characterized by insulin resistance in skeletal muscle. Phyllanthus niruri L. is well reported sub-tropical therapeutically beneficial ayurvedic medicinal plant from Euphorbiaceae family used in various body ailments such as metabolic disorder including diabetes. The present study emphasizes on the therapeutic potential of Phyllanthus niruri L. and its phytochemical(s) against insulin resistance conditions and impaired antioxidant activity thereby aiding as an anti-hyperglycemic agent in targeting T2DM. Three compounds were isolated from the most active ethyl acetate fraction namely compound 1 as 1-O-galloyl-6-O-luteoyl-β-D-glucoside, compound 2 as brevifolincarboxylic acid and compound 3 as ricinoleic acid. Compounds 1 and 2, the two polyphenols enhanced the uptake of glucose and inhibited ROS levels in palmitate induced C2C12 myotubes. PNEAF showed the potent enhancement of glucose uptake in palmitate-induced insulin resistance condition in C2C12 myotubes and significant ROS inhibition was observed in skeletal muscle cell line. PNEAF treated IR C2C12 myotubes and STZ induced Wistar rats elevated SIRT1, PGC1-α signaling cascade through phosphorylation of AMPK and GLUT4 translocation resulting in insulin sensitization. Our study revealed an insight into the efficacy of marker compounds isolated from P. niruri and its enriched ethyl acetate fraction as ROS scavenging agent and helps in attenuating insulin resistance condition in C2C12 myotubes as well as in STZ induced Wistar rat by restoring glucose metabolism. Overall, this study can provide prospects for the marker-assisted development of P. niruri as a phytopharmaceutical drug for the insulin resistance related diabetic complications.

Alleviation of Diabetic Retinopathy by Glucose-Triggered Delivery of Vitamin D via Dextran-Gated Functionalized Mesoporous Silica Nanoparticles

Diabetic retinopathy (DR) is the most common retinal disorder, developed in 35% of patients with diabetes mellitus. Lower serum levels of 25-hydroxyvitamin D are associated with the increased risk of developing DR. High doses of the active form of vitamin D (VD), on the contrary, for a long period of time may lead to hypercalcemia and an imbalance in the regulation of bone metabolism. Herein, we studied the efficacy of dextran-gated carboxyphenylboronic acid (CPBA)-functionalized mesoporous silica nanoparticles (MSNs) for glucose-sensitive delivery of 1,25-dihydroxyvitamin D3 to modulate cellular oxidative stress and inflammation for managing DR. The physical adsorption technique was employed to load VD onto nanoparticles (263.63 μg/mg (w/w)). In the presence of glucose, the dextran molecules detach from pores, allowing VD to release since glucose has 1,2-cis diol groups which have very high affinity to CPBA. Approximately 75% of VD was released upon exposure to 25 mM glucose at a time point of 10 h, demonstrating glucose-responsive delivery. Furthermore, MSN-CPBA was able to deliver VD in a glucose-dependent manner and improve the bioavailability of VD. In high-glucose-supplemented human retinal cells, MSN-CPBA increased the bioavailability of VD and reduced cellular oxidative stress and inflammation. The results suggested that the VD-loaded nanocarrier exerted remarkable therapeutic capacity in reducing the risk of developing DR. By using MSN-CPBA as a delivery platform with dextran gating, the research proposes an effective treatment approach for improving the bioavailability and effectiveness of a hydrophobic molecule in the treatment of DR.

Molecular Mechanisms in the Etiology of Polycystic Ovary Syndrome (PCOS): A Multifaceted Hypothesis Towards the Disease with Potential Therapeutics

Among the premenopausal women, Polycystic Ovary Syndrome (PCOS) is the most prevalent endocrinopathy affecting the reproductive system and metabolic rhythms leading to disrupted menstrual cycle. Being heterogeneous in nature it is characterized by complex symptomology of oligomennorhoea, excess of androgens triggering masculine phenotypic appearance and/or multiple follicular ovaries. The etiology of this complex disorder remains somewhat doubtful and the researchers hypothesize multisystem links in the pathogenesis of this disease. In this review, we attempt to present several hypotheses that tend to contribute to the etiology of PCOS. Metabolic inflexibility, aberrant pattern of gonadotropin signaling along with the evolutionary, genetic and environmental factors have been discussed. Considered a lifelong endocrinological implication, no universal treatment is available for PCOS so far however; multiple drug therapy is often advised along with simple life style intervention is mainly advised to manage its cardinal symptoms. Here we aimed to present a summarized view of pathophysiological links of PCOS with potential therapeutic strategies.

Vitamin D status and supplementation before and after Bariatric Surgery: Recommendations based on a systematic review and meta-analysis

Bariatric surgery is associated with a postoperative reduction of 25(OH) vitamin D levels (25(OH)D) and with skeletal complications. Currently, guidelines for 25(OH)D assessment and vitamin D supplementation in bariatric patients, pre- and post-surgery, are still lacking. The aim of this work is to analyse systematically the published experience on 25(OH)D status and vitamin D supplementation, pre- and post-surgery, and to propose, on this basis, recommendations for management. Preoperatively, 18 studies including 2,869 patients were evaluated. Prevalence of vitamin D insufficiency as defined by 25(OH)D < 30 ng/mL (75 nmol/L) was 85%, whereas when defined by 25(OH)D < 20 ng/mL (50 nmol/L) was 57%. The median preoperative 25(OH)D level was 19.75 ng/mL. After surgery, 39 studies including 5,296 patients were analysed and among those undergoing either malabsorptive or restrictive procedures, a lower rate of vitamin D insufficiency and higher 25(OH)D levels postoperatively were observed in patients treated with high-dose oral vitamin D supplementation, defined as ≥ 2,000 IU/daily (mostly D3-formulation), compared with low-doses (< 2,000 IU/daily). Our recommendations based on this systematic review and meta-analysis should help clinical practice in the assessment and management of vitamin D status before and after bariatric surgery. Assessment of vitamin D should be performed pre- and postoperatively in all patients undergoing bariatric surgery. Regardless of the type of procedure, high-dose supplementation is recommended in patients after bariatric surgery.

Interplay between Vitamin D and Adipose Tissue: Implications for Adipogenesis and Adipose Tissue Function

Adipose tissue encompasses various types, including White Adipose Tissue (WAT), Brown Adipose Tissue (BAT), and beige adipose tissue, each having distinct roles in energy storage and thermogenesis. Vitamin D (VD), a fat-soluble vitamin, maintains a complex interplay with adipose tissue, exerting significant effects through its receptor (VDR) on the normal development and functioning of adipocytes. The VDR and associated metabolic enzymes are widely expressed in the adipocytes of both rodents and humans, and they partake in the regulation of fat metabolism and functionality through various pathways. These encompass adipocyte differentiation, adipogenesis, inflammatory responses, and adipokine synthesis and secretion. This review primarily appraises the role and mechanisms of VD in different adipocyte differentiation, lipid formation, and inflammatory responses, concentrating on the pivotal role of the VD/VDR pathway in adipogenesis. This insight furnishes new perspectives for the development of micronutrient-related intervention strategies in the prevention and treatment of obesity.

Effects of Endurance Exercise and Vitamin D Supplementation on Insulin Resistance and Plasma Lipidome in Middle-Aged Adults with Type 2 Diabetes

(1) Background: We investigated the effects of a 12-week exercise intervention with or without vitamin D supplementation on insulin resistance and the plasma lipidome of participants with type 2 diabetes. We further explored whether the effects of the intervention on glycemic parameters could be associated with the baseline lipidome. (2) Methods: Sixty-one participants were randomly allocated to control (Con), exercise (EX), vitamin D (VD), and EX + VD groups. Multiple glycemic and anthropometric parameters were evaluated before and after intervention. The homeostasis model assessment of insulin resistance (HOMA-IR) was the primary outcome. The plasma lipidome was analyzed before, after, and at an additional 12-week follow-up. Machine learning was applied to establish prediction models for responsiveness of glycemic control. (3) Results: Our interventions failed to improve the HOMA-IR index while fasting glucose was reduced in the EX + VD group (change%, -11.9%; effect size, 0.65; p < 0.05). Both EX and VD interventions altered the plasma lipidome, with EX + VD intervention considerably affecting levels of lyso-phosphatidylcholines and triglycerols containing long-chain unsaturated fatty acids. Such effects could last until 12 weeks after intervention. Notably, there was high inter-individual variability in glycemic parameters including HOMA-IR in response to the interventions, which could be predicted with great accuracy using an optimal panel of baseline lipid predictors alone or in combination with clinical indices, as assessed by an area under the receiver operating characteristic curve value of over 0.9. (4) Conclusions: Although substantial alterations were observed in the plasma lipidome related to glycemic control, our intervention failed to improve HOMA-IR scores, which may have been predominately due to the large inter-individual variability in responses. Basal plasma lipid levels could potentially predict an individual's response to intervention, highlighting the necessity of personalized nutrition.

Clarifying the Heterogeneity in Response to Vitamin D in the Development, Prevention, and Treatment of Type 2 Diabetes Mellitus: A Narrative Review

In this review, we explore the potential drivers of heterogeneity in response to Vitamin D (VitD) therapy, such as bioavailability, sex-specific response, and autoimmune pathology, in those at risk for and diagnosed with T2DM. In addition, we propose distinct populations for future interventions with VitD. The literature concerning VitD supplementation in the prevention, treatment, and remission of type 2 diabetes mellitus (T2DM) spans decades, is complex, and is often contradictory with mixed findings upon intervention. By association, VitD status is powerfully predictive with deficient subjects reporting greater risk for T2DM, conversion to T2DM from prediabetes, and enhanced response to VitD therapy. Preclinical models strongly favor intervention with VitD owing to the pleiotropic influence of VitD on multiple systems. Additional research is crucial as there remain many questions unanswered that are related to VitD status and conditions such as T2DM. Future research must be conducted to better understand the potentially spurious relationships between VitD status, supplementation, sun exposure, health behaviors, and the diagnosis and management of T2DM. Public health practice can greatly benefit from a better understanding of the mechanisms by which we can reliably increase VitD status and how this can be used to develop education and improve health behaviors.

Vitamin D Status Determines Cardiometabolic Effects of Cabergoline in Women with Elevated Prolactin Levels: A Pilot Study

Both hyperprolactinemia and vitamin D deficiency appear to be associated with increased cardiometabolic risk. This study aimed to determine whether vitamin D status influences the cardiometabolic effects of cabergoline. The study included three matched groups of women with mild to moderate hyperprolactinemia: vitamin D-naive subjects with vitamin D insufficiency (group A), women with vitamin D deficiency/insufficiency successfully treated with vitamin D (group B), and vitamin D-naive individuals with normal vitamin D status (group C). Plasma prolactin, 25-hydroxyvitamin D, estradiol, glucose homeostasis markers, lipids, high-sensitivity C-reactive protein (hsCRP), fibrinogen, homocysteine, and uric acid, as well as the urinary albumin-to-creatinine ratio (UACR), were measured at study entry and after four months of cabergoline treatment. Although cabergoline reduced prolactin levels and increased estradiol levels in all study groups, the effect on prolactin was more pronounced in groups B and C compared to group A. In groups B and C, the drug enhanced glucose homeostasis, increased HDL-cholesterol, and decreased triglycerides, hsCRP, fibrinogen, homocysteine, uric acid, and UACR. In group A, only insulin resistance, hsCRP, and homocysteine were reduced by cabergoline. The effects on insulin sensitivity, HDL-cholesterol, triglycerides, hsCRP, fibrinogen, homocysteine, uric acid, and UACR were proportional to the decrease in prolactin and baseline levels of 25-hydroxyvitamin D. The obtained results suggest that vitamin D status determines cabergoline's cardiometabolic effects.

Vitamin D and malabsorptive gastrointestinal conditions: A bidirectional relationship?

This paper is one of the outcomes of the 5th International Conference "Controversies in Vitamin D" held in Stresa, Italy from 15 to 18 September 2021 as part of a series of annual meetings which was started in 2017. The scope of these meetings is to discuss controversial issues about vitamin D. Publication of the outcomes of the meeting in international journals allows a wide sharing of the most recent data with the medical and academic community. Vitamin D and malabsorptive gastrointestinal conditions was one of the topics discussed at the meeting and focus of this paper. Participants to the meeting were invited to review available literature on selected issues related to vitamin D and gastrointestinal system and to present their topic to all participants with the aim to initiate a discussion on the main outcomes of which are reported in this document. The presentations were focused on the possible bidirectional relationship between vitamin D and gastrointestinal malabsorptive conditions such as celiac disease, inflammatory bowel diseases (IBDs) and bariatric surgery. In fact, on one hand the impact of these conditions on vitamin D status was examined and on the other hand the possible role of hypovitaminosis D on pathophysiology and clinical course of these conditions was also evaluated. All examined malabsorptive conditions severely impair vitamin D status. Since vitamin D has known positive effects on bone this in turn may contribute to negative skeletal outcomes including reduced bone mineral density, and increased risk of fracture which may be mitigated by vitamin D supplementation. Due to the immune and metabolic extra-skeletal effects there is the possibility that low levels of vitamin D may negatively impact on the underlying gastrointestinal conditions worsening its clinical course or counteracting the effect of treatment. Therefore, vitamin D status assessment and supplementation should be routinely considered in all patients affected by these conditions. This concept is strengthened by the existence of a possible bidirectional relationship through which poor vitamin D status may negatively impact on clinical course of underlying disease. Sufficient elements are available to estimate the desired threshold vitamin D level above which a favourable impact on the skeleton in these conditions may be obtained. On the other hand, ad hoc controlled clinical trials are needed to better define this threshold for obtaining a positive effect of vitamin D supplementation on occurrence and clinical course of malabsorptive gastrointestinal diseases.

A popular fermented soybean food of Northeast India exerted promising antihyperglycemic potential via stimulating PI3K/AKT/AMPK/GLUT4 signaling pathways and regulating muscle glucose metabolism in type 2 diabetes

This study examined the antidiabetic efficacy of popular fermented soybean foods (FSF) of Northeast (NE) India. Results showed that among different FSF, aqueous extract of Hawaijar (AEH), a traditional FSF of Manipur, NE India, significantly augmented glucose utilization in cultured myotubes treated with high glucose (HG, 25 mM). Furthermore, AEH also upregulated glucose uptake, glucose-6-phosphate level, and phopho-PI3K/phospho-AKT/phospho-AMPK/GLUT4 protein expression in HG-treated myotubes. In vivo studies demonstrated that AEH supplementation (50, 100, or 200 mg/kg body weight/day, oral gavaging, 16 weeks) reduced body weight, fasting blood glucose, glycated hemoglobin, insulin resistance, and glucose intolerance in rats fed with high-fat diet (HFD). AEH supplementation stimulated phopho-PI3K/phospho-AKT/phospho-AMPK/GLUT4 signaling cascades involved in glucose metabolism of muscle tissues in diabetic rats. Chemical profiling of AEH (SDS-PAGE, immunoblotting, and HRMS) suggests the possible role of bioactive proteins/peptides and isoflavones underlying the antihyperglycemic potential AEH. Results from this study will be helpful for developing food-based prophylactics/therapeutics in managing hyperglycemia. PRACTICAL APPLICATIONS: Fermented soybean foods are gaining acceptance due to multiple health benefits. This study for the first time reports the antidiabetic potential of Hawaijar, an indigenous fermented soybean food of North-East India. Higher abundance of bioactive compounds (isoflavones and proteins/peptides) in Hawaijar may be responsible for the alleviation of impaired glucose metabolism associated with diabetes. The findings may be helpful for the development of a novel therapeutic to achieve better control of hyperglycemia and improve the lives of the patient population with diabetes.

Association between serum 25-hydroxy vitamin D concentrations and mortality among individuals with metabolic dysfunction-associated fatty liver disease: a prospective cohort study

BACKGROUND

The association between serum 25-hydroxy vitamin D (25(OH)D) concentrations and mortality remains unclear among patients with metabolic dysfunction-associated fatty liver disease (MAFLD) or non-alcoholic fatty liver disease (NAFLD).

OBJECTIVES

To evaluate the association between serum 25(OH)D concentrations and mortality among individuals with MAFLD/NAFLD.

METHODS

The study included 4651 individuals with fatty liver disease (FLD) (3964 had MAFLD and 3968 had NAFLD) from the Third National Health and Nutrition Examination Survey. Fatty liver disease was identified by ultrasonographic detection of hepatic steatosis. Mortality was ascertained by linkage to the National Death Index up to 31 December 2019. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) with adjustment of potential confounders.

RESULTS

Of 4651 individuals with FLD, 3427 individuals (69.7%) had both MAFLD and NAFLD. During median follow-ups of 25.8 and 26.1 years, we identified 1809 and 1665 deaths among 3964 participants with MAFLD and 3968 participants with NAFLD, respectively. Compared with participants with serum 25(OH)D concentrations ≤30.0 nmol/L, the multivariable-adjusted HR and 95% CI of all-cause mortality were 0.62 (0.43, 0.89) for participants with MAFLD having serum 25(OH)D >75.0 nmol/L (P-trend = 0.001), and 0.63 (0.42, 0.95) for participants with NAFLD having serum 25(OH)D >75.0 nmol/L (P-trend = 0.002). A nonlinearly inverse association was observed between serum 25(OH)D concentrations and all-cause mortality among participants with MAFLD (Poverall <0.001; Pnonlinear = 0.003) or NAFLD (Poverall <0.001; Pnonlinear = 0.009), with a threshold effect at around 50.0 nmol/L. The inverse association was stronger among participants with MAFLD aged <60 years (P-interaction = 0.001).

CONCLUSIONS

This study suggested a nonlinearly inverse association between serum 25(OH)D concentrations and all-cause mortality among patients with MAFLD/NAFLD, with a threshold effect at around 50.0 nmol/L of serum 25(OH)D.

Vitamin D–VDR Novel Anti-Inflammatory Molecules—New Insights into Their Effects on Liver Diseases

There is consistent evidence that vitamin D deficiency is strongly associated with liver dysfunction, disease severity, and poor prognosis in patients with liver disease. Vitamin D and its receptor (VDR) contribute to the regulation of innate and adaptive immune responses. The presence of genetic variants of vitamin D- and VDR-associated genes has been associated with liver disease progression. In our recent work, we summarized the progress in understanding the molecular mechanisms involved in vitamin D–VDR signaling and discussed the functional significance of VDR signaling in specific cell populations in liver disease. The current review focuses on the complex interaction between immune and liver cells in the maintenance of liver homeostasis and the development of liver injury, the interplay of vitamin D and VDR in the development and outcome of liver disease, the role of vitamin D- and VDR-associated genetic variants in modulating the occurrence and severity of liver disease, and the therapeutic value of vitamin D supplementation in various liver diseases. The association of the vitamin D–VDR complex with liver dysfunction shows great potential for clinical application and supports its use as a prognostic index and diagnostic tool.

The role of adipose tissue-derived hydrogen sulfide in inhibiting atherosclerosis

Hydrogen sulfide (H₂S) is the third gaseous signaling molecule discovered in the body after NO and CO and plays an important organismal protective role in various diseases. Within adipose tissue, related catalytic enzymes (cystathionine-β-synthetase, cystathionine-γ-lyase, and 3-mercaptopyruvate transsulfuration enzyme) can produce and release endogenous H₂S. Atherosclerosis (As) is a pathological change in arterial vessels that is closely related to abnormal glucose and lipid metabolism and a chronic inflammatory response. Previous studies have shown that H₂S can act on the cardiovascular system, exerting effects such as improving disorders of glycolipid metabolism, alleviating insulin resistance, protecting the function of vascular endothelial cells, inhibiting vascular smooth muscle cell proliferation and migration, regulating vascular tone, inhibiting the inflammatory response, and antagonizing the occurrence and development of As.

Vitamin D regulates insulin pathway and glucose metabolism in zebrafish (Danio rerio)

1,25-dihydroxyvitamin D₃ [1,25(OH)₂ D₃ ], the most active vitamin D (VD) metabolite, is a steroid hormone playing an important role in many physiological functions in addition to maintaining mineral homeostasis. In this study, we explored the mechanism that the VD regulated insulin pathway and glucose metabolism in zebrafish in vitro and in vivo. Our results show that 1,25(OH)₂ D₃  significantly enhances the expression of insulin receptor a (insra), insulin receptor substrate 1 (irs1) and glucose transporter 2 (glut2), and promotes glycolysis and glycogenesis, while suppressing gluconeogenesis in zebrafish liver cell line (ZFL) under the condition of high glucose (20 mM), instead of the normal glucose (10 mM). Moreover, consistent results were obtained from the zebrafish fed with VD₃ -deficient diet, as well as the cyp2r1^-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, results from dual-luciferase reporting system exhibited that 1,25(OH)₂ D₃ directly activated the transcription of insra, rather than insrb in zebrafish by binding to vitamin D response element (VDRE) located at -181 to -167 bp in the promoter region of insra. Importantly, the 1,25(OH)₂ D₃ treatment significantly alleviated the symptoms of hyperglycemia in diabetic zebrafish. In conclusion, our study demonstrated that VD activates VDRE located in the promoter area of insra in zebrafish to promote insulin/insra signaling pathway, thereby contributing to the maintenance of glucose homeostasis.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Endogenous hydrogen sulfide promotes human preimplantation embryonic development by regulating metabolism-related gene expression

Hydrogen sulfide (H₂S) as an endogenous gaseous signaling molecule had been proved to play a vital role in gametes physiology, covering meiosis, maturation and aging. However, little is known about H₂S involvement in embryonic development. The present study explored the positive effect of H₂S on human early embryonic development. Results validated that the two H₂S producing enzymes, CBS and CSE mRNA and proteins were identified in donated human cleavage and blastocyst-stage embryos. The l-cysteine incubation produced endogenous H₂S in human blastocysts. NaHS positively affected in vitro blastulation. Single-cell RNA-seq analysis identified 228 differentially expressed genes (DEGs) after NaHS treatment versus the control. The Gene Ontology (GO) enrichment analysis of DEGs showed that genes for protein modification and metabolism were significantly enriched in the NaHS treatment group. For the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, 2-oxocarboxylic acid metabolism, glycosaminoglycan biosynthesis-keratan sulfate, steroid biosynthesis, carbon metabolism, and biosynthesis of amino acids were significantly enriched. Six DEGs, including Neural EGFL like 1 (NELL1), aconitase 1 (ACO1), phosphoglycerate mutase 1 (PGAM1), TP53 induced glycolysis regulatory phosphatase (TIGAR), UDP-GlcNAc:betaGal beta-1,3-N-acetylglucosaminyltransferase 2 (B3GNT2), and carbohydrate Sulfotransferase 4 (CHST4) were validate by real-time RT-PCR. These findings suggest that H₂S is a positive regulator of early embryonic development and may alter the transcription of embryonic genes for protein modification and metabolism in human embryos.

Mechanisms Linking Vitamin D Deficiency to Impaired Metabolism: An Overview

Vitamin D deficiency is a common health problem worldwide. Despite its known skeletal effects, studies have begun to explore its extra-skeletal effects, that is, in preventing metabolic diseases such as obesity, hyperlipidemia, and diabetes mellitus. The mechanisms by which vitamin D deficiency led to these unfavorable metabolic consequences have been explored. Current evidence indicates that the deficiency of vitamin D could impair the pancreatic β-cell functions, thus compromising its insulin secretion. Besides, vitamin D deficiency could also exacerbate inflammation, oxidative stress, and apoptosis in the pancreas and many organs, which leads to insulin resistance. Together, these will contribute to impairment in glucose homeostasis. This review summarizes the reported metabolic effects of vitamin D, in order to identify its potential use to prevent and overcome metabolic diseases.

NLRP3 inflammasome activation in gestational diabetes mellitus placentas is associated with hydrogen sulfide synthetase deficiency

The placenta may play a key role in the activation of inflammation and initiation of insulin resistance (IR) during gestational diabetes mellitus (GDM) pathogenesis. Interleukin (IL)-1β and IL-18, regulated by NLR family pyrin domain containing-3 (NLRP3) inflammasome, are important inflammatory cytokines in the initiation of maternal IR during GDM. However, the mechanism responsible for the regulatory of NLRP3 inflammasome in placenta remains unknown. Hydrogen sulfide (H₂S) exerts anti-inflammatory function partially via suppressing the activation of the NLPR3 inflammasome. The present study aimed to investigate the role of NLRP3 inflammasome, H₂S synthetase cystathionine-γ-lyase (CSE) and cystathionine-β-synthetase (CBS) in placenta in the pathogenesis of GDM. Clinical placenta samples were collected from pregnant women with GDM (n=16) and healthy pregnant women at term (n=16). Western blot analysis was performed to detect the protein expression levels of NLRP3, cleaved caspase-1, CBS and CSE in the placenta samples. Pearson's correlation analysis was performed to assess the correlation between NLRP3 inflammasome and H₂S synthetase. Human placental cells were cultured and treated with different concentrations of NaHS (0, 10, 25 and 50 nmol/l) or L-cysteine (0, 0.25, 0.50 and 1.00 mmol/l). In addition, western blot analysis was performed to detect the protein expression levels of NLRP3 and cleaved caspase-1, while ELISA was performed to measure the production of IL-1β and IL-18 in the culture media. The results demonstrated that the expression levels of NLRP3 and cleaved caspase-1 increased, while the expression levels of CBS and CSE decreased in the placenta samples. In addition, the expression levels of NLRP3 and cleaved caspase-1 were inversely correlated with the expression levels of CBS and CSE. Notably, NaHS and L-cysteine significantly suppressed the expression levels of NLRP3 and cleaved caspase-1, and the production of IL-1 and IL-18 in human placental cells. Taken together, the results of the present study suggest that H₂S synthetase deficiency in placenta may contribute to excessive activation of NLRP3 inflammasome in GDM.

Hydrogen sulfide in ageing, longevity and disease

Hydrogen sulfide (H₂S) modulates many biological processes, including ageing. Initially considered a hazardous toxic gas, it is now recognised that H₂S is produced endogenously across taxa and is a key mediator of processes that promote longevity and improve late-life health. In this review, we consider the key developments in our understanding of this gaseous signalling molecule in the context of health and disease, discuss potential mechanisms through which H₂S can influence processes central to ageing and highlight the emergence of novel H₂S-based therapeutics. We also consider the major challenges that may potentially hinder the development of such therapies.

Vitamin D and COVID-19: A review on the role of vitamin D in preventing and reducing the severity of COVID-19 infection

Severe Acute Respiratory Syndrome Coronavirus‐2 (SARS‐CoV‐2) is a pathogenic coronavirus causing COVID‐19 infection. The interaction between the SARS‐CoV‐2 spike protein and the human receptor angiotensin‐converting enzyme 2, both of which contain several cysteine residues, is impacted by the disulfide‐thiol balance in the host cell. The host cell redox status is affected by oxidative stress due to the imbalance between the reactive oxygen/nitrogen species and antioxidants. Recent studies have shown that Vitamin D supplementation could reduce oxidative stress. It has also been proposed that vitamin D at physiological concentration has preventive effects on many viral infections, including COVID‐19. However, the molecular‐level picture of the interplay of vitamin D deficiency, oxidative stress, and the severity of COVID‐19 has remained unclear. Herein, we present a thorough review focusing on the possible molecular mechanism by which vitamin D could alter host cell redox status and block viral entry, thereby preventing COVID‐19 infection or reducing the severity of the disease.

Regulation of zebrafish fin regeneration by vitamin D signaling

BACKGROUND

Vitamin D is an essential nutrient that has long been known to regulate skeletal growth and integrity. In models of major appendage regeneration, treatment with vitamin D analogs has been reported to improve aspects of zebrafish fin regeneration in specific disease or gene misexpression contexts, but also to disrupt pattern in regenerating salamander limbs. Recently, we reported strong mitogenic roles for vitamin D signaling in several zebrafish tissues throughout life stages, including epidermal cells and osteoblasts of adult fins. To our knowledge, molecular genetic approaches to dissect vitamin D function in appendage regeneration have not been described.

RESULTS

Using a knock-in GFP reporter for the expression of the vitamin D target gene and negative regulator cyp24a1, we identified active vitamin D signaling in adult zebrafish fins during tissue homeostasis and regeneration. Transgenic expression of cyp24a1 or a dominant-negative vitamin D receptor (VDR) inhibited regeneration of amputated fins, whereas global vitamin D treatment accelerated regeneration. Using tissue regeneration enhancer elements, we found that local enhancement of VDR expression could improve regeneration with low doses of a vitamin D analog.

CONCLUSIONS

Vitamin D signaling enhances the efficacy of fin regeneration in zebrafish.

Activation of Endogenous H2S Biosynthesis or Supplementation with Exogenous H2S Enhances Adipose Tissue Adipogenesis and Preserves Adipocyte Physiology in Humans

Aims: To investigate the impact of exogenous hydrogen sulfide (H₂S) and its endogenous biosynthesis on human adipocytes and adipose tissue in the context of obesity and insulin resistance. Results: Experiments in human adipose tissue explants and in isolated preadipocytes demonstrated that exogenous H₂S or the activation of endogenous H₂S biosynthesis resulted in increased adipogenesis, insulin action, sirtuin deacetylase, and PPARγ transcriptional activity, whereas chemical inhibition and gene knockdown of each enzyme generating H₂S (CTH, CBS, MPST) led to altered adipocyte differentiation, cellular senescence, and increased inflammation. In agreement with these experimental data, visceral and subcutaneous adipose tissue expression of H₂S-synthesising enzymes was significantly reduced in morbidly obese subjects in association with attenuated adipogenesis and increased markers of adipose tissue inflammation and senescence. Interestingly, weight-loss interventions (including bariatric surgery or diet/exercise) improved the expression of H₂S biosynthesis-related genes. In human preadipocytes, the expression of CTH, CBS, and MPST genes and H₂S production were dramatically increased during adipocyte differentiation. More importantly, the adipocyte proteome exhibiting persulfidation was characterized, disclosing that different proteins involved in fatty acid and lipid metabolism, the citrate cycle, insulin signaling, several adipokines, and PPAR, experienced the most dramatic persulfidation (85-98%). Innovation: No previous studies investigated the impact of H₂S on human adipose tissue. This study suggests that the potentiation of adipose tissue H₂S biosynthesis is a possible therapeutic approach to improve adipose tissue dysfunction in patients with obesity and insulin resistance. Conclusion: Altogether, these data supported the relevance of H₂S biosynthesis in the modulation of human adipocyte physiology. Antioxid. Redox Signal. 35, 319-340.

Vitamin D and non-alcoholic fatty liver disease: a meta-analysis of randomized controlled trials

The results of randomized controlled trials (RCTs) investigating supplemental vitamin D on aminotransferases and cardio-metabolic risk factors in subjects with non-alcoholic fatty liver disease (NAFLD) have been inconsistent. The present study aimed to quantitatively evaluate whether supplementation with vitamin D has beneficial effects in treatment of NAFLD. A systematical literature search was performed with Cochrane Library, PubMed, Scopus databases and Web of Science up to June 2020. The mean changes in alanine aminotransferase (ALT), aspartate aminotransferase (AST), fasting glucose, insulin, homeostasis model assessment of insulin resistance (HOMA-IR), total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), and triglyceride (TAG) were calculated as standard mean difference (SMD) using a random-effects model. Pre-specified subgroup and univariate meta-regression analyses were performed to identify the sources of heterogeneity. Ten trials with a total of 544 NAFLD subjects were included for data synthesis. The summary estimates indicated that supplemental vitamin D significantly reduced the levels of serum/plasma fasting glucose (-0.22; 95%CI: -0.39, -0.04), insulin (-0.68; 95%CI: -1.22, -0.14) and HOMA-IR (-1.32; 95%CI: -2.30, -0.34), and marginally reduced the ALT (-0.18; 95%CI: -0.39, 0.04) and TAG (-10.38; 95%CI: -21.09, 0.34) levels. However, the pooled effect did not support that supplemental vitamin D was beneficial for concentrations of AST, TC, HDL-C and LDL-C. The present study provides substantial evidence that supplemental vitamin D has favorable effects on glycemic control and insulin sensitivity in NAFLD patients. Vitamin D could be as an adjuvant pharmacotherapy of NAFLD.

The Impact of H2S on Obesity-Associated Metabolic Disturbances

Over the last several decades, hydrogen sulfide (H₂S) has gained attention as a new signaling molecule, with extensive physiological and pathophysiological roles in human disorders affecting vascular biology, immune functions, cellular survival, metabolism, longevity, development, and stress resistance. Apart from its known functions in oxidative stress and inflammation, new evidence has emerged revealing that H₂S carries out physiological functions by targeting proteins, enzymes, and transcription factors through a post-translational modification known as persulfidation. This review article provides a critical overview of the current state of the literature addressing the role of H₂S in obesity-associated metabolic disturbances, with particular emphasis on its mechanisms of action in obesity, diabetes, non-alcoholic fatty liver disease (NAFLD), and cardiovascular diseases.

Vitamin D Supplementation and Impact on Skeletal Muscle Function in Cell and Animal Models and an Aging Population: What Do We Know So Far?

Aging is associated with impairment in skeletal muscle mass and contractile function, predisposing to fat mass gain, insulin resistance and diabetes. The impact of Vitamin D (VitD) supplementation on skeletal muscle mass and function in older adults is still controversial. The aim of this review was to summarize data from randomized clinical trials, animal dietary intervention and cell studies in order to clarify current knowledge on the effects of VitD on skeletal muscle as reported for these three types of experiments. A structured research of the literature in Medline via PubMed was conducted and a total of 43 articles were analysed (cells n = 18, animals n = 13 and humans n = 13). The results as described by these key studies demonstrate, overall, at cell and animal levels, that VitD treatments had positive effects on the development of muscle fibres in cells in culture, skeletal muscle force and hypertrophy. Vitamin D supplementation appears to regulate not only lipid and mitochondrial muscle metabolism but also to have a direct effect on glucose metabolism and insulin driven signalling. However, considering the human perspective, results revealed a predominance of null effects of the vitamin on muscle in the ageing population, but experimental design may have influenced the study outcome in humans. Well-designed long duration double-blinded trials, standardised VitD dosing regimen, larger sample sized studies and standardised measurements may be helpful tools to accurately determine results and compare to those observed in cells and animal dietary intervention models.

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.

Molecular mechanisms from insulin-mimetic effect of vitamin D: treatment alternative in Type 2 diabetes mellitus

Diabetes mellitus is a complex and multifactorial disease with a global prevalence that exceeds 425 million people. Type 2 diabetes mellitus (T2DM) is characterized by a state of insulin resistance, which leads to metabolic alterations that aggravate the state of health of people. Vitamin D deficiency appears to play an important role in the triggering mechanisms of insulin resistance. In this review, an analysis is made of the biochemical mechanisms associated with the insulin-mimetic effect of vitamin D, its supplementation being a possible nutritional strategy for the T2DM treatment. The current scientific evidence is extensive regarding the dose of vitamin D used for an insulin-mimetic effect. However, clinical trials and systematic reviews show statistical differences on glucose, insulin, and glycated hemoglobin levels of patients with T2DM, associated with activation mechanisms of transcription factors related to genes of the glucide metabolism and the insulin receptor, and the regulation of intracellular Ca2+ insulin concentrations. Likewise, an indirect mechanism associated with antioxidant and anti-inflammatory effects has been shown that also leads to sensitivity to the insulin receptor. The use of a specific dose of vitamin D could be an effective alternative in the T2DM treatment, which would reduce the risk of complications derived from hyperglycemia.

The Role of H2S in the Metabolism of Glucose and Lipids

Glucose and lipids are essential elements for maintaining the body's homeostasis, and their dysfunction may participate in the pathologies of various diseases, particularly diabetes, obesity, metabolic syndrome, cardiovascular ailments, and cancers. Among numerous endogenous mediators, the gasotransmitter hydrogen sulfide (H₂S) plays a central role in the maintenance of glucose and lipid homeostasis. Current evidence from both pharmacological studies and transgenic animal models suggest a complex relationship between H₂S and metabolic dysregulation, especially in diabetes and obesity. This notion is achieved through tissue-specific expressions and actions of H₂S on target metabolic and hormone organs including the pancreas, skeletal muscle, livers, and adipose. In this chapter, we will summarize the roles and mechanisms of H₂S in several metabolic organs/tissues that are necessary for glucose and lipid metabolic homeostasis. In addition, future research directions and valuable therapeutic avenues around the pharmacological regulation of H₂S in glycolipid metabolism disorder will be also discussed.

Update on the Crosstalk Between Adipose Tissue and Mineral Balance in General Population and Chronic Kidney Disease

Adipose tissue is nowadays considered as a major endocrine organ, which apart from controlling lipid metabolism, displays a significant role in energy expenditure, food intake and in the regulation of various systemic physiological processes. Adipose derived pro-inflammatory cytokines and adipokines, particularly leptin and adiponectin, provide inter-communication of adipose tissue with various metabolic pathways, ultimately resulting in a complex network of interconnected organ systems. Recent clinical and experimental research has been focused on exploring the direct interaction between adipokine profile and elements of mineral metabolism, including parathormone (PTH), fibroblast growth factor-23 (FGF23) and calcitriol. The emerging crosstalk between adipose tissue and calcium and phosphorus homeostasis suggests that metabolic disorders from one system may directly affect the other and vice versa. It is current knowledge that fat metabolism disturbance, commonly encountered in obese individuals, influences the expression of calciotriopic hormones in general population, while various clinical trials attempting to successfully achieve body fat loss by modulating mineral profile have been published. In chronic kidney disease (CKD) state, there is an increasing evidence suggesting that mineral disorders, influence adipose tissue and linked endocrine function. On the contrary, the impact of disturbed fat metabolism on CKD related mineral disorders has been also evocated in clinical studies. Recognizing the pathogenetic mechanisms of communication between adipose tissue and mineral balance is critical for understanding the effects of metabolic perturbations from the one system to the other and for identifying possible therapeutic targets in case of disrupted homeostasis in one of the two connected systems. To that end, this review aims to enlighten the recent advances regarding the interplay between mineral metabolism, fat mass and adipokine profile, based on in vitro, in vivo and clinical studies, in general population and in the course of CKD.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Pharmacological modulation of the hydrogen sulfide (H2 S) system by dietary H2 S-donors: A novel promising strategy in the prevention and treatment of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) represents the most common age-related metabolic disorder, and its management is becoming both a health and economic issue worldwide. Moreover, chronic hyperglycemia represents one of the main risk factors for cardiovascular complications. In the last years, the emerging evidence about the role of the endogenous gasotransmitter hydrogen sulfide (H₂ S) in the pathogenesis and progression of T2DM led to increasing interest in the pharmacological modulation of endogenous "H₂ S-system". Indeed, H₂ S directly contributes to the homeostatic maintenance of blood glucose levels; moreover, it improves impaired angiogenesis and endothelial dysfunction under hyperglycemic conditions. Moreover, H₂ S promotes significant antioxidant, anti-inflammatory, and antiapoptotic effects, thus preventing hyperglycemia-induced vascular damage, diabetic nephropathy, and cardiomyopathy. Therefore, H₂ S-releasing molecules represent a promising strategy in both clinical management of T2DM and prevention of macro- and micro-vascular complications associated to hyperglycemia. Recently, growing attention has been focused on dietary organosulfur compounds. Among them, garlic polysulfides and isothiocyanates deriving from Brassicaceae have been recognized as H₂ S-donors of great pharmacological and nutraceutical interest. Therefore, a better understanding of the therapeutic potential of naturally occurring H₂ S-donors may pave the way to a more rational use of these nutraceuticals in the modulation of H₂ S homeostasis in T2DM.

Potential role of hydrogen sulfide in diabetes-impaired angiogenesis and ischemic tissue repair

Diabetes is one of the most prevalent metabolic disorders and is estimated to affect 400 million of 4.4% of population worldwide in the next 20 year. In diabetes, risk to develop vascular diseases is two-to four-fold increased. Ischemic tissue injury, such as refractory wounds and critical ischemic limb (CLI) are major ischemic vascular complications in diabetic patients where oxygen supplement is insufficient due to impaired angiogenesis/neovascularization. In spite of intensive studies, the underlying mechanisms of diabetes-impaired ischemic tissue injury remain incompletely understood. Hydrogen sulfide (H₂S) has been considered as a third gasotransmitter regulating angiogenesis under physiological and ischemic conditions. Here, the underlying mechanisms of insufficient H₂S-impaired angiogenesis and ischemic tissue repair in diabetes are discussed. We will primarily focuses on the signaling pathways of H₂S in controlling endothelial function/biology, angiogenesis and ischemic tissue repair in diabetic animal models. We summarized that H₂S plays an important role in maintaining endothelial function/biology and angiogenic property in diabetes. We demonstrated that exogenous H₂S may be a theraputic agent for endothelial dysfunction and impaired ischemic tissue repair in diabetes.

C2C12 cell model: its role in understanding of insulin resistance at the molecular level and pharmaceutical development at the preclinical stage

OBJECTIVES

The myoblast cell line, C2C12, has been utilised extensively in vitro as an examination model in understanding metabolic disease progression. Although it is indispensable in both preclinical and pharmaceutical research, a comprehensive review of its use in the investigation of insulin resistance progression and pharmaceutical development is not available.

KEY FINDINGS

C2C12 is a well-documented model, which can facilitate our understanding in glucose metabolism, insulin signalling mechanism, insulin resistance, oxidative stress, reactive oxygen species and glucose transporters at cellular and molecular levels. With the aid of the C2C12 model, recent studies revealed that insulin resistance has close relationship with various metabolic diseases in terms of disease progression, pathogenesis and therapeutic management. A holistic, safe and effective disease management is highly of interest. Therefore, significant efforts have been paid to explore novel drug compounds and natural herbs that can elicit therapeutic effects in the targeted sites at both cellular (e.g. mitochondria, glucose transporter) and molecular level (e.g. genes, signalling pathway).

SUMMARY

The use of C2C12 myoblast cell line is meaningful in pharmaceutical and biomedical research due to their expression of GLUT-4 and other features that are representative to human skeletal muscle cells. With the use of the C2C12 cell model, the impact of drug delivery systems (nanoparticles and quantum dots) on skeletal muscle, as well as the relationship between exercise, pancreatic β-cells and endothelial cells, was discovered.

Vitamin D regulation of adipogenesis and adipose tissue functions

Vitamin D insufficiency is associated with obesity and its related metabolic diseases. Adipose tissues store and metabolize vitamin D and expression levels of vitamin D metabolizing enzymes are known to be altered in obesity. Sequestration of vitamin D in large amount of adipose tissues and low vitamin D metabolism may contribute to the vitamin D inadequacy in obesity. Vitamin D receptor is expressed in adipose tissues and vitamin D regulates multiple aspects of adipose biology including adipogenesis as well as metabolic and endocrine function of adipose tissues that can contribute to the high risk of metabolic diseases in vitamin D insufficiency. We will review current understanding of vitamin D regulation of adipose biology focusing on vitamin D modulation of adiposity and adipose tissue functions as well as the molecular mechanisms through which vitamin D regulates adipose biology. The effects of supplementation or maintenance of vitamin D on obesity and metabolic diseases are also discussed.

The livestock growth-promoter zeranol facilitates GLUT4 translocation in 3T3 L1 adipocytes

Zeranol is an approved but controversial growth-promoting agent for livestock in North America. It is a mycotoxin metabolite secreted by the Fusarium family fungi. The regulatory bodies in this region have established the acceptable daily intake and exposure below the level would not significantly increase the health risk for humans. However, their European counterparts have yet to establish an acceptable level and do not permit the use of this agent in farm animals. Given the growth-promoting ability of zeranol, its effect on energy metabolism was investigated in the current study. Our results indicated that zeranol could induce glucose transporter type 4 (GLUT4) expression in 3T3 L1 cells at 10 μM and initiate the translocation of the glucose transporter to the membrane as assayed by confocal microscopy. The translocation was likely triggered by the increase of GLUT4 and p-Akt. The insulin signal transduction pathway of glucose translocation was analyzed by Western blot analysis. Since no increase in the phosphorylated insulin receptor substrate in zeranol-treated cells was evidenced, the increased p-Akt and GLUT4 amount should be the mechanism dictating the GLUT4 translocation. In summary, this study showed that zeranol could perturb glucose metabolism in differentiated 3T3 L1 adipocytes. Determining the growth-promoting mechanism is crucial to uncover an accepted alternative to the general public.

Hydrogen sulfide regulates insulin secretion and insulin resistance in diabetes mellitus, a new promising target for diabetes mellitus treatment? A review

Background

Insulin resistance and impaired insulin secretion lead to disorders of glucose metabolism, which contributes to the development of diabetes. Hydrogen sulfide (H2S), a novel gasotransmitter, is found to play important roles in regulation of glucose metabolism homeostasis.

Aim of Review

This study aimed to summarize and discuss current data about the function of H2S in insulin secretion and insulin resistance regulation as well as the underlying mechanisms.

Key Scientific Concepts of Review

H₂S could be endogenously produced in islet β cells, liver, adipose, skeletal muscles, and the hypothalamus, and regulates local and systemic glucose metabolism. It is reported that H₂S suppresses insulin secretion, promotes or reduces the apoptosis of islet β cells. It plays important roles in the regulation of insulin sensitivity in insulin responsive tissues. H₂S inhibits glucose uptake and glycogen storage, and promotes or inhibits gluconeogenesis, mitochondrial biogenesis and mitochondrial bioenergetics in the liver. In adipose tissue, several investigators indicated that H2S promoted glucose uptake in adipocytes, while other studies reported that H₂S inhibits this process. H₂S has also been shown to promote adipogenesis, inhibit lipolysis, and regulate adiponectin and MCP-1 secretion from adipocytes. In skeletal muscle, H₂S increases glucose uptake and improves insulin sensitivity. It is also observed that H₂S modulates circadian-clock genes in muscle. Hypothalamic CBS/H₂S pathway reduces obesity and improves insulin sensitivity via the brain-adipose interaction. Most studies indicated plasma H₂S levels decreased in diabetic patients. However, the mechanisms by which H₂S regulates systemic glucose metabolism remain unclear. Whether H₂S acts as a new promising target for diabetes mellitus treatment merits further studies.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Dietary methionine restriction improves glucose metabolism in the skeletal muscle of obese mice

Dietary methionine restriction (MR) has many positive effects on metabolic health. Recent studies have indicated that overall insulin sensitivity is improved by dietary MR. This study aimed to determine the effects of MR on insulin signalling and glucose utilisation in the skeletal muscle of obese mice. First, male C57BL/6J mice in the CON group were fed a control diet (0.86% methionine + 4% fat) for 34 weeks, and others were fed a high-fat (HF) diet (0.86% methionine + 20% fat) for 10 weeks to induce obesity. Then, the mice were divided into four dietary groups: the HF group (maintained on the HF diet), HF + MR group (0.17% methionine + 20% fat), C* group (changed to a control diet, 0.86% methionine + 4% fat), and C* + MR group (0.17% methionine + 4% fat) for 24 weeks. Mice were euthanised at 8, 16 or 24 weeks. The results indicated that MR ameliorated obesity-induced hyperglycaemia and hyperinsulinemia. Moreover, MR up-regulated the gene expression of disulfide-bond A oxidoreductase-like protein and cystathionine-γ-lyase and promoted adiponectin and H2S production in inguinal white adipose tissue. Furthermore, MR activated AMP-activated protein kinase and inhibited its downstream signalling and up-regulated insulin signalling-related molecules in gastrocnemius muscle. Overall, MR improved glucose metabolism via increasing glycogen synthesis, glycolysis, and aerobic oxidation. Interestingly, most parameters were equivalent between the HF + MR group and C* + MR group. These findings suggest that dietary MR can improve glucose metabolism in obese mice.

Hydrogen Sulfide, Adipose Tissue and Diabetes Mellitus

Hydrogen sulfide (H₂S) is now increasingly considered to be the third gasotransmitter alongside other gaseous signaling molecules, nitric oxide (NO) and carbon monoxide (CO). H₂S is produced by a variety of endogenous enzymatic and non-enzymatic pathways and acts as a modulator of the physiological and pathological events of the body. Adipocytes express the cystathionine γ lyase (CSE)/H₂S system, which modulates a variety of biological activities in adipose tissue (AT), including inflammation, apoptosis, insulin resistance, adipokine secretion and adipocyte differentiation. Abnormalities in the physiological functions of AT play an important role in the process of diabetes mellitus. Therefore, this review provides an overview of the general aspects of H₂S biochemistry, the effect of H₂S on AT function and diabetes mellitus and its molecular signalling mechanisms as well as the potential application of H₂S in pharmacotherapy.

Nutritional interventions for autism spectrum disorder

Autism spectrum disorder (ASD) is an increasingly prevalent neurodevelopmental disorder with considerable clinical heterogeneity. With no cure for the disorder, treatments commonly center around speech and behavioral therapies to improve the characteristic social, behavioral, and communicative symptoms of ASD. Gastrointestinal disturbances are commonly encountered comorbidities that are thought to be not only another symptom of ASD but to also play an active role in modulating the expression of social and behavioral symptoms. Therefore, nutritional interventions are used by a majority of those with ASD both with and without clinical supervision to alleviate gastrointestinal and behavioral symptoms. Despite a considerable interest in dietary interventions, no consensus exists regarding optimal nutritional therapy. Thus, patients and physicians are left to choose from a myriad of dietary protocols. This review, summarizes the state of the current clinical and experimental literature on nutritional interventions for ASD, including gluten-free and casein-free, ketogenic, and specific carbohydrate diets, as well as probiotics, polyunsaturated fatty acids, and dietary supplements (vitamins A, C, B6, and B12; magnesium and folate).

Vitamins D and E Stimulate the PI3K-AKT Signalling Pathway in Insulin-Resistant SK-N-SH Neuronal Cells

This study investigated the effects of vitamins D and E on an insulin-resistant model and hypothesized that this treatment would reverse the effects of Alzheimer’s disease (AD) and improves insulin signalling. An insulin-resistant model was induced in SK-N-SH neuronal cells with a treatment of 250 nM insulin and re-challenged with 100 nM at two different incubation time (16 h and 24 h). The effects of vitamin D (10 and 20 ng/mL), vitamin E in the form of tocotrienol-rich fraction (TRF) (200 ng/mL) and the combination of vitamins D and E on insulin signalling markers (IR, PI3K, GLUT3, GLUT4, and p-AKT), glucose uptake and AD markers (GSK3β and TAU) were determined using quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). The results demonstrated an improvement of the insulin signalling pathway upon treatment with vitamin D alone, with significant increases in IR, PI3K, GLUT3, GLUT4 expression levels, as well as AKT phosphorylation and glucose uptake, while GSK3β and TAU expression levels was decreased significantly. On the contrary, vitamin E alone, increased p-AKT, reduced the ROS as well as GSK3β and TAU but had no effect on the insulin signalling expression levels. The combination of vitamins D and E only showed significant increase in GLUT4, p-AKT, reduced ROS as well as GSK3β and TAU. Thus, the universal role of vitamin D, E alone and in combinations could be the potential nutritional agents in restoring the sensitivity of neuronal cells towards insulin and delaying the pathophysiological progression of AD.

Sodium hydrosulphide restores tumour necrosis factor-α-induced mitochondrial dysfunction and metabolic dysregulation in HL-1 cells

Tumour necrosis factor (TNF)‐α induces cardiac metabolic disorder and mitochondrial dysfunction. Hydrogen sulphide (H₂S) contains anti‐inflammatory and biological effects in cardiomyocytes. This study investigated whether H₂S modulates TNF‐α‐dysregulated mitochondrial function and metabolism in cardiomyocytes. HL‐1 cells were incubated with TNF‐α (25 ng/mL) with or without sodium hydrosulphide (NaHS, 0.1 mmol/L) for 24 hours. Cardiac peroxisome proliferator‐activated receptor (PPAR) isoforms, pro‐inflammatory cytokines, receptor for advanced glycation end products (RAGE) and fatty acid metabolism were evaluated through Western blotting. The mitochondrial oxygen consumption rate and adenosine triphosphate (ATP) production were investigated using Seahorse XF24 extracellular flux analyzer and bioluminescence assay. Fluorescence intensity using 2′, 7′‐dichlorodihydrofluorescein diacetate was used to evaluate mitochondrial oxidative stress. NaHS attenuated the impaired basal and maximal respiration, ATP production and ATP synthesis and enhanced mitochondrial oxidative stress in TNF‐α‐treated HL‐1 cells. TNF‐α‐treated HL‐1 cells exhibited lower expression of PPAR‐α, PPAR‐δ, phosphorylated 5′ adenosine monophosphate‐activated protein kinase‐α2, phosphorylated acetyl CoA carboxylase, carnitine palmitoyltransferase‐1, PPAR‐γ coactivator 1‐α and diacylglycerol acyltransferase 1 protein, but higher expression of PPAR‐γ, interleukin‐6 and RAGE protein than control or combined NaHS and TNF‐α‐treated HL‐1 cells. NaHS modulates the effects of TNF‐α on mitochondria and the cardiometabolic system, suggesting its therapeutic potential for inflammation‐induced cardiac dysfunction.