[Cholecalciferol hydroxylation in rat hepatocytes under the influence of prednisolone]

The impact of vitamin D(3) on bone remodeling in different types of experimental pathology

Osteoporosis is a progressive systemic skeletal disease characterized by a decrease in bone density, impairment of its microarchitectonics, and an increased risk of fractures that occur under minimal or no mechanical stress. One of the main causes of osteoporosis is vitamin D deficiency, which leads to disruption of normal bone remodeling. The aim of our study was to analyze the features of the process of bone tissue remodeling by measuring the key biochemical markers of bone formation/resorption in primary and secondary osteoporosis, as well as to investigate the potential corrective effect of vitamin D3 supplementation. The work was conducted on rats with different osteoporosis models: alimentary, dysfunctional and secondary osteoporosis associated with diabetes mellitus. We used ELISA to measure 25(OH)D content in blood serum. Blood serum and bone tissue calcium, and alkaline phosphatase activity were determined with bioassay kits. The content of inorganic phosphate in blood serum and ash was assayed by the Dyce method. It was shown that all the studied pathological conditions were accompanied by vitamin D deficiency, which led to impaired absorption of calcium in the intestine and reabsorption of inorganic phosphates by the kidneys, reducing, as a result, their concentration in the blood serum. Hypocalcemia and hypophosphatemia contributed to the disruption of normal bone remodeling, excessive activation of alkaline phosphatase, and a decrease in the content of calcium and phosphate in bone tissue. Thus, sufficient vitamin D bioavailability was confirmed to be critical for effective bone remodeling in primary and secondary osteoporosis. Keywords: bone remodelin, osteoporosis, type 1 diabetes mellitus, vitamin D

Oral Calcidiol Is More Effective Than Cholecalciferol Supplementation to Reach Adequate 25(OH)D Levels in Patients with Autoimmune Diseases Chronically Treated with Low Doses of Glucocorticoids: A "Real-Life" Study

Glucocorticoids (GCs) are the cornerstone of the therapy in many autoimmune and inflammatory diseases. However, it is well known that their use is a double edged sword, as their beneficial effects are associated almost universally with unwanted effects, as, for example glucocorticoid-induced osteoporosis (GIO). Over the last years, several clinical practice guidelines emphasize the need of preventing bone mass loss and reduce the incidence of fractures associated with GC use. Calcium and vitamin D supplementation, as adjunctive therapy, are included in all the practice guidelines. However, no standard vitamin D dose has been established. Several studies with postmenopausal women show that maintaining the levels above 30-33 ng/mL help improve the response to bisphosphonates. It is unknown if the response is the same in GIO, but in the clinical practice the levels are maintained at around the same values. In this study we demonstrate that patients with autoimmune diseases, undergoing glucocorticoid therapy, often present suboptimal 25(OH)D levels. Patients with higher body mass index and those receiving higher doses of glucocorticoids are at increased risk of having lower levels of 25(OH)D. In these patients, calcidiol supplementations are more effective than cholecalciferol to reach adequate 25(OH)D levels.