MC903, an analogue of 1,25-dihydroxyvitamin D3, increases the synthesis of nerve growth factor

An update on vitamin D and B deficiency in the pathogenesis and treatment of diabetic neuropathy: a narrative review

Diabetic peripheral neuropathy (DPN) is highly prevalent and affects up to 50% of patients with diabetes. Painful neuropathic symptoms may occur in a third of patients with diabetes and is a major cause of sleep disturbance, morbidity and poor quality of life. Effective treatment of DPN remains a major challenge as current therapeutic options have a number of undesirable side effects and only provide a partial response to neuropathic pain. Furthermore, there are a lack of treatments that modulate the natural history of DPN. A growing body of evidence suggests that vitamin B and vitamin D may have analgesic effects and neuroprotective benefits in DPN. This narrative review explores the role of these vitamins in DPN. Given their limited side effects, further mechanistic studies and good quality randomized controlled trials of their putative analgesic ability are required to define the role of vitamin B and D in DPN.

Vitamin D and Diabetic Complications: True or False Prophet?

Vitamin D deficiency is now recognized as a condition of increasing prevalence worldwide. Vitamin D has an established role in calcium and bone metabolism; however, more recently associations with vitamin D deficiency and risk of developing diabetes, diabetes complications, and cardiovascular disease have all been acknowledged. The vitamin D receptor is ubiquitously expressed, and experimental, in vitro, and in vivo studies strongly suggest a role in regulating the transcription of multiple genes beyond calcium homeostasis. These include antiproliferative, immunomodulatory, angiogenic, inhibition of the renin-angiotensin-aldosterone system, and neurotrophic factor expression. Observational studies report a strong association between vitamin D deficiency and cardiovascular and metabolic disorders; however, there remains a paucity of large long-term randomized clinical trials showing a benefit with treatment. An increasing body of literature suggests a possible pathogenetic role of vitamin D in the long-term complications of diabetes and vitamin D deficiency may also exacerbate symptoms of painful diabetic peripheral neuropathy. It remains unknown if supplementation of vitamin D to normal or non-deficient levels alters pathogenetic processes related to diabetic microvascular complications. With the high prevalence of vitamin D deficiency in patients with diabetes and putative mechanisms linking vitamin D deficiency to diabetic complications, there is a compelling argument for undertaking large well-designed randomized controlled trials of vitamin D supplementation.

Pharmacological modulation of nerve growth factor synthesis: a mechanistic comparison of vitamin D receptor and beta(2)-adrenoceptor agonists

Increasing nerve growth factor (NGF) in the PNS is a rational strategy for treating certain neurodegenerative disorders. The present studies were undertaken to compare two compounds, a vitamin D(3) analogue (CB1093) with minimal calcaemic effects, and clenbuterol, a long-acting beta(2)-adrenoceptor agonist, both of which induce NGF synthesis in vivo. Clenbuterol caused significant increases in both NGF mRNA and protein in 3T3 cells; with maxima at 10 nM and at 8-12 h exposure. Effects of clenbuterol on NGF mRNA were antagonized by propranolol. Mobility shift assays on whole cell extracts showed that clenbuterol increased AP1 binding in 3T3 cells prior to increasing NGF synthesis. Clenbuterol was without effect on NGF mRNA levels in L929 cells, whereas CB1093 caused significant increases in both NGF mRNA and protein levels in both 3T3 and L929 cells. Stimulation was almost maximal at 24 h exposure and was sustained for at least 72 h. The magnitude of the increase was much greater in L929 (700% increase) than in 3T3 cells (80%). Binding to the vitamin D nuclear receptor (VDR), which acts as a transcription factor itself, was increased as early as 30 min after exposure to of CB1093 and maintained up to 24 h. Increased VDR binding preceded increased NGF mRNA. A 150% increase in AP-1 binding was also evident. This study demonstrates that CB1093 and clenbuterol stimulate NGF levels in vitro and that AP-1 binding could be a commonality between the mechanism of NGF induction of these two compounds.

Regulation of a novel immediate early response gene, IEX-1, in keratinocytes by 1alpha,25-dihydroxyvitamin D3

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3] regulates cellular growth and differentiation. We show that in keratinocytes, 1alpha, 25(OH)2D3 reduces concentrations of the messenger RNA of IEX-1, the product of which blocks Fas- or tumor necrosis factor type alpha-induced apoptosis in various cells. In sub-confluent keratinocyte cultures, the addition of 1alpha,25(OH)2D3, in amounts that induce growth arrest, reduces IEX-1 mRNA concentrations. In confluent cells, 1alpha,25(OH)2D3 initially reduces and then increases IEX-1 mRNA concentrations. IEX-1 protein is localized in the nucleus and perinuclear region of keratinocytes. In sub-confluent cells, 1alpha,25(OH)2D3 translocates IEX-1 protein from the nucleus to the perinuclear region and cytoplasm. Since IEX-1 has recently been shown to regulate cell survival and number, we suggest that IEX-1 may play a role in keratinocyte growth and differentiation and that 1alpha,25(OH)2D3 may reduce keratinocyte growth via a reduction in IEX-1 mRNA and a change in the intracellular distribution of IEX-1 protein.