Modern views on the metabolism and biological effects of vitamin D

Vitamin D is a steroid hormone that plays a crucial role in maintaining normal bone condition and calcium homeostasis. In recent years, vitamin D has become a hot topic of endocrino-logical research, largely Due to the COVID-19 pandemic and the likely correlation between hypovitaminosis D and a high risk of chronic lung disease and associated mortality. Recent studies have shown that vitamin D exhibits a complex multistage metabolism and acts as a hormone on many extracellular targets. This review examines some new intriguing and as yet unclear aspects of vitamin D metabolism, such as new concepts of enzyme regulation, new pleiotropic effects of vitamin D receptor activation (VDR), and epigenetic effects. The mechanisms of vitamin D synthesis in the skin, its metabolism in the hepatic cytochrome P450 system, catabolism, metabolites and transport, gene control and epigenetic modulation are considered in Detail. In addition to the well-known role of vitamin D in calcium and bone metabolism, it has many pleiotropic extraskeletal effects, including potent effects on the immune system, cardiovascular system, adipose tissue and glucose/ lipid metabolism, muscle and more. Experimental studies have shown that VDRs are expressed by cancer cell lines. Recent studies have shown a link between low levels of vitamin D and almost all aspects of the metabolic syndrome, such as type 2 diabetes, fasting blood glucose, hypertension, dyslipidemia, obesity and insulin re-sistance. Several studies have focused on the role of vitamin D in adipose tissue biology. In particular, a negative correlation between vitamin D and leptin or resistin is shown, as well as an inverse correlation with adiponectin. Recent studies in vitamin D-deficient mice have shown impaired secretion of glucose-stimulated insulin by pancreatic islets. Vitamin D is thought to play a role in the pathogenesis and progression of cancer, and vitamin D analogues can slow cancer progression and metastasis. It is concluded that vitamin D is a molecule with several endocrine, paracrine and auto-crine effects on many tissues and organs, in addition to maintaining skeletal homeostasis. Research in this area, which aims to clarify the pleiotropy of many effects of vitamin D and its metabolites, continues. © 2022, Zaslavsky Publishing House. All rights reserved.

To the question of classification of intestinal post-COVID lesions. Review

Pandemic of COVID-19 has brought significant changes not only to the daily life of mankind, but also to the course of many chronic diseases. In addition to lung damage, extrapulmonary manifestations may develop against the background of coronavirus disease progression. These changes often have multi-organ nature, espe cially against the background of existing chronic diseases. Literature describes cardiac, neurologic, renal extrapulmonary SARS-CoV-2 lesions as well as eye damage. Gastrointestinal tract is one of the areas affected by SARS-CoV-2 virus. This impact is stipulated by the significant effects of virus on the microbiota and permeability of mucosal barriers, as well as important role of changes in the intestinal barrier function in the development of local and systemic immune response. Working group of the Ukrainian Gastroenterological Association (UGA) worked out a classification of intestinal post-covid lesions, which was presented at the UGA congress in September 2021. The following types of damage have been outlined: COVID-19 induced bacterial overgrowth syndrome, functional diarrhea after previous COVID-19 infection, infection-induced irritable bowel syndrome (post-infectious IBS), antibiotic-associated diarrhea (without Clostridium difficile and pseudomembranous colitis with confirmed Clostridium difficile), exacerbation of inflammatory bowel disease (ulcerative colitis, Crohn's disease), newly diagnosed (COVID-induced) inflammatory bowel disease. The course of functional and inflammatory diseases can be modified by COVID-19, affecting the gut microbiome. It is necessary to conduct a thorough differential diagnosis of exacerbation of functional, inflammatory and post-covid lesions of the intestine. Complex therapy including agents to correct dysbiosis should be used to treat this group of patients. © Modern gastroenterology, 2022.