Molecular mechanisms involved in the enhancement of mitochondrial malate dehydrogenase activity by calcitriol in chick intestine

Role of mitochondria in the differential action of sodium deoxycholate and ursodeoxycholic acid on rat duodenum

Sodium deoxycholate (NaDOC) inhibits the intestinal Ca²⁺ absorption and ursodeoxycholic acid (UDCA) stimulates it. The aim of this study was to determine whether NaDOC and UDCA produce differential effects on the redox state of duodenal mitochondria altering the Krebs cycle and the electron transport chain (ETC) functioning, which could lead to perturbations in the mitochondrial dynamics and biogenesis. Rat intestinal mitochondria were isolated from untreated and treated animals with either NaDOC, UDCA, or both. Krebs cycle enzymes, ETC components, ATP synthase, and mitochondrial dynamics and biogenesis markers were determined. NaDOC decreased isocitrate dehydrogenase (ICDH) and malate dehydrogenase activities affecting the ETC and ATP synthesis. NaDOC also induced oxidative stress and increased the superoxide dismutase activity and impaired the mitochondrial biogenesis and functionality. UDCA increased the activities of ICDH and complex II of ETC. The combination of both bile acids conserved the functional activities of Krebs cycle enzymes, ETC components, oxidative phosphorylation, and mitochondrial biogenesis. In conclusion, the inhibitory effect of NaDOC on intestinal Ca²⁺ absorption is mediated by mitochondrial dysfunction, which is avoided by UDCA. The stimulatory effect of UDCA alone is associated with amelioration of mitochondrial functioning. This knowledge could improve treatment of diseases that affect the intestinal Ca²⁺ absorption.

Vitamin D and diabetes: its importance for beta cell and immune function

Experimental evidence indicates that vitamin D may play a role in the defense against type 1 diabetes (T1D) as well as type 2 diabetes (T2D). Epidemiological data have established a link between vitamin D deficiency and an increased incidence of both T1D and T2D, whereas early and long-term vitamin D supplementation may decrease the risk of these disorders. The protective effects of vitamin D are mediated through the regulation of several components such as the immune system and calcium homeostasis. However, an increasing amount of evidence suggests that vitamin D also affects beta cells directly thereby rendering them more resistant to the types of cellular stress encountered during T1D and T2D. This review evaluates the role of vitamin D signaling in the pathogenesis of T1D and T2D with a special emphasis on the direct effects of vitamin D on pancreatic beta cells.