Chronic calcitriol supplementation improves the inflammatory profiles of circulating monocytes and the associated intestinal/adipose tissue alteration in a diet-induced steatohepatitis rat model

Vitamin D/vitamin D receptor pathway in non-alcoholic fatty liver disease

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide, but underlying mechanisms are not fully understood. In recent years, a growing body of evidence has emphasized the therapeutic role of vitamin D in NAFLD, but the specific mechanism remains to be investigated.

AREAS COVERED

This review summarized the roles of vitamin D/VDR (vitamin D receptor) pathway in different types of liver cells (such as hepatocytes, hepatic stellate cells, liver macrophages, T lymphocytes, and other hepatic immune cells) in case of NAFLD. Meanwhile, the effects of pathways in the gut-liver axis, adipose tissue-liver axis, and skeletal muscle-liver axis on the development of NAFLD were further reviewed. Relevant literature was searched on PubMed for the writing of this review.

EXPERT OPINION

The precise regulation of regional vitamin D/VDR signaling pathway based on cell-specific or tissue-specific function will help clarify the potential mechanism of vitamin D in NAFLD, which may provide new therapeutic targets to improve the safety and efficacy of vitamin D based drugs.

Vitamin D3 enhances the effects of omega-3 oils against metabolic dysfunction-associated fatty liver disease in rat

This study investigated the effects of omega-3 oils (OM) and/or vitamin D₃ (VD) against metabolic dysfunction-associated fatty liver disease (MAFLD). Forty rats were divided into negative (NC) and positive (PC) controls, OM, VD, and OM + VD groups, and MAFLD was induced by high-fat/high-fructose diet (12 weeks). Oral OM (415 mg/kg/day) and/or intramuscular VD (290 IU/kg/day) were given for 4 weeks (5 times/week). The PC animals were markedly obese and had hyperglycemia, insulin resistance, dyslipidemia, elevated liver enzymes, abnormal hepatic histology, and increased caspase-3 with apoptosis than the NC group. The expression of hepatic peroxisome proliferator-activated receptor-α (PPAR-α; 5.3-fold), insulin induced gene-1 (INSIG1; 7.8-fold), adiponectin receptor-1 (AdipoR1; 4.4-fold), and leptin receptor (LEPR; 6-fold) declined, while PPAR-γ (3.7-fold) and sterol regulatory element-binding protein-1 (SREBP1; 2.4-fold) increased, in the PC than the NC group. Leptin (2.2-fold), malondialdehyde (2.1-fold), protein carbonyl groups (17.3-fold), IL-1β (4.4-fold), IL-6 (2.1-fold), TNF-α (1.8-fold) also increased, whereas adiponectin (2.8-fold) glutathione (2.1-fold), glutathione peroxidase-1 (2.4-fold), glutathione reductase (2.2-fold), catalase (1.4-fold), and IL-10 (2.8-fold) decreased, in the PC livers. Both monotherapies attenuated obesity, metabolic profiles, and PPAR-γ/SREBP1/leptin/Caspase-3/apoptosis, while induced PPAR-α/adiponectin/AdipoR1/LEPR/INSIG1. The monotherapies also reduced the oxidative stress and pro-inflammatory markers and increased the antioxidant and anti-inflammatory molecules. However, the OM effects were better than VD monotherapy. Alternatively, the co-therapy group showed the greatest ameliorations in liver functions, lipid-regulatory molecules, oxidative stress, inflammation, and apoptosis. In conclusion, while OM monotherapy was superior to VD, the co-therapy protocol displayed the best alleviations against MAFLD, possibly by enhanced modulation of metabolic, antioxidant, and anti-inflammatory pathways.

A Lipid-Based Nanocarrier Containing Active Vitamin D3 Ameliorates NASH in Mice via Direct and Intestine-Mediated Effects on Liver Inflammation

The gut-liver axis may be involved in non-alcoholic steatohepatitis (NASH) progression. Pathogen-associated molecular patterns leak through the intestinal barrier to the liver via the portal vein to contribute to NASH development. Active vitamin D₃ (1,25(OH)₂D₃) is a potential therapeutic agent to enhance the intestinal barrier. Active vitamin D₃ also suppresses inflammation and fibrosis in the liver. However, the adverse effects of active vitamin D₃ such as hypercalcemia limit its clinical use. We created a nano-structured lipid carrier (NLC) containing active vitamin D₃ to deliver active vitamin D₃ to the intestine and liver to elicit NASH treatment. We found a suppressive effect of the NLC on the lipopolysaccharide-induced increase in permeability of an epithelial layer in vitro. Using mice in which NASH was induced by a methionine and choline-deficient diet, we discovered that oral application of the NLC ameliorated the permeability increase in the intestinal barrier and attenuated steatosis, inflammation and fibrosis in liver at a safe dose of active vitamin D₃ at which the free form of active vitamin D₃ did not show a therapeutic effect. These data suggest that the NLC is a novel therapeutic agent for NASH.

Modeling Diet-Induced NAFLD and NASH in Rats: A Comprehensive Review

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, characterized by hepatic steatosis without any alcohol abuse. As the prevalence of NAFLD is rapidly increasing worldwide, important research activity is being dedicated to deciphering the underlying molecular mechanisms in order to define new therapeutic targets. To investigate these pathways and validate preclinical study, reliable, simple and reproducible tools are needed. For that purpose, animal models, more precisely, diet-induced NAFLD and nonalcoholic steatohepatitis (NASH) models, were developed to mimic the human disease. In this review, we focus on rat models, especially in the current investigation of the establishment of the dietary model of NAFLD and NASH in this species, compiling the different dietary compositions and their impact on histological outcomes and metabolic injuries, as well as external factors influencing the course of liver pathogenesis.

The Role of Vitamin D in Adipose Tissue Biology: Adipocyte Differentiation, Energy Metabolism, and Inflammation

Adipose tissue is composed of diverse cell types and plays a major role in energy homeostasis and inflammation at the local and systemic levels. Adipose tissue serves as the main site for vitamin D storage and is among the most important extraskeletal targets of vitamin D which can modulate multiple aspects of adipose tissue biology. Vitamin D may exert inhibitory or stimulatory effects on adipocyte differentiation depending on cell type, stage of differentiation, and the treatment time point. Moreover, vitamin D controls energy metabolism in adipose tissue by affecting fatty acid oxidation, expression of uncoupling proteins, insulin resistance, and adipokine production. Adipose tissue inflammation can have a significant impact on the metabolic disorders often associated with obesity, and vitamin D can modulate the inflammatory response of immune cells and adipocytes within the adipose tissue. This review discusses the role of adipose tissue in vitamin D metabolism, as well as the regulatory role of vitamin D in adipocyte differentiation, adipose tissue energy metabolism, and inflammation, thereby providing insights into the importance of vitamin D in adipose tissue biology.

A role for intestinal alkaline phosphatase in preventing liver fibrosis

Rationale: Liver fibrosis is frequently associated with gut barrier dysfunction, and the lipopolysaccharides (LPS) -TLR4 pathway is common to the development of both. Intestinal alkaline phosphatase (IAP) has the ability to detoxify LPS, as well as maintain intestinal tight junction proteins and gut barrier integrity. Therefore, we hypothesized that IAP may function as a novel therapy to prevent liver fibrosis. Methods: Stool IAP activity from cirrhotic patients were determined. Common bile duct ligation (CBDL) and Carbon Tetrachloride-4 (CCl4)-induced liver fibrosis models were used in WT, IAP knockout (KO), and TLR4 KO mice supplemented with or without exogenous IAP in their drinking water. The gut barrier function and liver fibrosis markers were tested. Results: Human stool IAP activity was decreased in the setting of liver cirrhosis. In mice, IAP activity and genes expression decreased after CBDL and CCl4 exposure. Intestinal tight junction related genes and gut barrier function were impaired in both models of liver fibrosis. Oral IAP supplementation attenuated the decrease in small intestine tight junction protein gene expression and gut barrier function. Liver fibrosis markers were significantly higher in IAP KO compared to WT mice in both models, while oral IAP rescued liver fibrosis in both WT and IAP KO mice. In contrast, IAP supplementation did not attenuate fibrosis in TLR4 KO mice in either model. Conclusions: Endogenous IAP is decreased during liver fibrosis, perhaps contributing to the gut barrier dysfunction and worsening fibrosis. Oral IAP protects the gut barrier and further prevents the development of liver fibrosis via a TLR4-mediated mechanism.

Vitamin D and Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD): An Update

Non-alcoholic fatty liver disease (NAFLD) is the first cause of chronic liver disease worldwide; it ranges from simple steatosis to steatohepatitis (NASH) and, potentially, cirrhosis and hepatocarcinoma. NAFLD is also an independent risk factor for type 2 diabetes, cardiovascular diseases, and mortality. As it is largely associated with insulin resistance and related disorders, NAFLD has been recently re-named as Metabolic dysfunction-Associated Fatty Liver Disease (MAFLD). At present, there are no approved pharmacological treatments for this condition. Vitamin D is a molecule with extensive anti-fibrotic, anti-inflammatory, and insulin-sensitizing properties, which have been proven also in hepatic cells and is involved in immune-metabolic pathways within the gut–adipose tissue–liver axis. Epidemiological data support a relationship hypovitaminosis D and the presence of NAFLD and steatohepatitis (NASH); however, results from vitamin D supplementation trials on liver outcomes are controversial. This narrative review provides an overview of the latest evidence on pathophysiological pathways connecting vitamin D to NAFLD, with emphasis on the effects of vitamin D treatment in MAFLD by a nonsystematic literature review of PubMed published clinical trials. This article conforms to the Scale for Assessment of Narrative Review Articles (SANRA) guidelines. Evidence so far available supports the hypothesis of potential benefits of vitamin D supplementation in selected populations of NAFLD patients, as those with shorter disease duration and mild to moderate liver damage.

Active vitamin D impedes the progression of non-alcoholic fatty liver disease by inhibiting cell senescence in a rat model

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) refers to an accumulation of excess fat in liver due to causes other than alcohol use. The relationship between vitamin D (VD) and NAFLD has been previously studied. Therefore, we aimed to explore the mechanism involved active VD regulating the progression of NAFLD by inhibiting cell senescence and to provide a potential approach for further nutritional treatment of NAFLD.

METHODS

Following the induction with high-fat diet and intraperitoneal injection of corn oil, the successfully established NAFLD rat models were treated with 1,25(OH)₂D₃ at 1μg/kg, 5μg/kg or 10μg/kg. Meanwhile, the levels of factors related to oxidative stress, cell senescence, the p53-p21 signaling pathway and inflammation in liver were determined. Then, cell senescence was also measured by using senescence-associated β-galactosidase (SAβ-gal) staining.

RESULTS

It was also found that active VD increased the concentration of VD in serum and VDR in liver of NAFLD rats, and alleviated hepatic fibrosis. Besides, treatment of 1,25(OH)₂D₃ at 1μg/kg, 5μg/kg or 10μg/kg reduced oxidative stress and inflammation, inhibited the p53-p21 signaling pathway and consequent cell senescence. Furthermore, treatment of 1,25(OH)₂D₃ at a dosage of 5μg/kg made the most impact on these factors.

CONCLUSION

Collectively, the evidences from this study demonstrated that active VD could alleviate the development of NAFLD through blocking the p53-p21 signaling pathway, which provided a novel nutritional therapeutic insight for NAFLD.

Calcitriol Attenuates Doxorubicin-Induced Cardiac Dysfunction and Inhibits Endothelial-to-Mesenchymal Transition in Mice

Doxorubicin (Dox) is an effective anti-neoplasm drug, but its cardiac toxicity limits its clinical use. Endothelial-to-mesenchymal transition (EndMT) has been found to be involved in the process of heart failure. It is unclear whether EndMT contributes to Dox-induced cardiomyopathy (DoIC). Calcitriol, an active form Vitamin D3, blocks the growth of cancer cells by inhibiting the Smad pathway. To investigate the effect of calcitriol via inhibiting EndMT in DoIC, C57BL/6 mice and endothelial-specific labeled mice were intraperitoneally administered Dox twice weekly for 4 weeks (32 mg/kg cumulative dose) and were subsequently treated with or without calcitriol for 12 weeks. Echocardiography revealed diastolic dysfunction at 13 weeks following the first Dox treatment, accompanied by increased myocardial fibrosis and up-regulated pro-fibrotic proteins. Calcitriol attenuated Dox-induced myocardial fibrosis, down-regulated pro-fibrotic proteins and improved diastolic function. Endothelial fate tracing revealed that EndMT-derived cells contributed to Dox-induced cardiac fibrosis. In vitro, human umbilical vein endothelial cells and mouse cardiac fibroblasts were treated with Transforming growth factor (TGF)-β with or without calcitriol. Morphological, immunofluorescence staining, and Western blot analyses revealed that TGF-β-induced EndMT and fibroblast-to-myofibroblast transition (FMT) were attenuated by calcitriol by the inhibition of the Smad2 pathway. Collectively, calcitriol attenuated DoIC through the inhibition of the EndMT and FMT processes.