1α,25-Dihydroxyvitamin D(3) and its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), suppress intraocular pressure in non-human primates.

Ocular hypertension is the greatest known risk factor for glaucoma that affects an estimated 70 million people worldwide. Lowering intraocular pressure (IOP) remains the mainstay of therapy in the management of glaucoma. By means of microarray analysis, we have discovered that 1α,25-dihydroxyvitamin D(3) (1α,25-(OH)(2)D(3)) regulates genes that are known to be involved in the determination of intraocular pressure (IOP). Topical administration of 1α,25-(OH)(2)D(3) or its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), markedly reduces IOP in non-human primates. The reduction in IOP is not the result of reduced aqueous humor formation, while a 35% increase in aqueous humor drainage by 1α,25-(OH)(2)D(3) was found but this increase did not achieve significance. Nevertheless, our results suggest that 1α,25-(OH)(2)D(3), or an analog thereof, may present a new approach to the treatment of glaucoma.

TRPV6 is not required for 1alpha,25-dihydroxyvitamin D3-induced intestinal calcium absorption in vivo.

The requirement for TRPV6 for vitamin D-dependent intestinal calcium absorption in vivo has been examined by using vitamin D-deficient TRPV6 null mice and littermate wild-type mice. Each of the vitamin D-deficient animals received each day for 4 days 50 ng of 1,25-dihydroyvitamin D(3) in 0.1 ml of 95% propylene glycol:5% ethanol vehicle or vehicle only. Both the wild-type and TRPV6 null mice responded equally well to 1,25-dihydroxyvitamin D(3) in increasing intestinal calcium absorption. These results, along with our microarray data, demonstrate that TRPV6 is not required for vitamin D-induced intestinal calcium absorption and may not carry out a significant role in this process. These and previous results using calbindin D9k null mutant mice illustrate that molecular events in the intestinal calcium absorption process in response to the active form of vitamin D remain to be defined.

1,25-Dihydroxyvitamin D3 regulates genes responsible for detoxification in intestine.

1Alpha,25-Dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)), the biologically active form of vitamin D(3), not only plays a major role in mammalian calcium and phosphorous homeostasis but also exerts pleiotropic effects on cell proliferation, differentiation and the immune system. Further, vitamin D is believed to play a significant role in the prevention of colon, prostate, and breast cancer and in reducing the risk of autoimmune diseases. To gain insight into the mechanism whereby vitamin D can have such diverse actions, we have employed microarray technology. We studied the effect of a single dose of 1,25-(OH)(2)D(3) on gene expression in the intestine of vitamin D-deficient rats. Within 6 h, 1,25-(OH)(2)D(3) stimulates the expression of several phase I and phase II biotransformation genes. There is also an increased expression of antioxidant genes. These results support the idea that vitamin D is a significant factor in detoxification and protection against environmental toxins.

Calbindin D9k is not required for 1,25-dihydroxyvitamin D3-mediated Ca2+ absorption in small intestine.

The exact role of calbindin D9k in vitamin D-mediated calcium absorption has been debated but remains unsettled. In 129/OlaHsd mice, calbindin D9k was found highest in duodenum (36-50%) and kidney (24-34%) followed by stomach, lung and uterus. Age does not affect the relative distribution of calbindin D9k but it does decline with age in duodenum of both male and female 129/Ola mice. Recently, we produced a null calbindin D9k mutant 129/OlaHsd mouse; this mouse proved to be indistinguishable from the wild-type in phenotype and in a serum calcium level regardless of age or gender. We have now examined directly whether the mutant mouse can absorb calcium from the intestine in response to the active form of vitamin D. The calbindin D9k null mutant mouse is fully able to absorb calcium from the intestine in response to 1,25-dihydroxyvitamin D3. It is, therefore, clear that calbindin D9k is not required for vitamin D-induced intestinal calcium absorption.

Calbindin D(9k) knockout mice are indistinguishable from wild-type mice in phenotype and serum calcium level.

Since the discovery of calbindin D(9k), its role in intestinal calcium absorption has remained unsettled. Further, a wide distribution of calbindin D(9k) among tissues has argued for its biological importance. We discovered a frameshift deletion in the calbindin D(9k) gene in an ES cell line, E14.1, that originated from 129/OlaHsd mice. We produced mice with the mutant calbindin D(9k) gene by injecting the E14.1 ES cell subline into the C57BL/6 host blastocysts and proved that these mice lack calbindin D(9k) protein. Calbindin D(9k) knockout mice were indistinguishable from wild-type mice in phenotype, were able to reproduce, and had normal serum calcium levels. Thus, calbindin D(9k) is not required for viability, reproduction, or calcium homeostasis.

Gene expression profiles in rat intestine identify pathways for 1,25-dihydroxyvitamin D(3) stimulated calcium absorption and clarify its immunomodulatory properties.

Microarray technology has been used to discover 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) induced gene expression changes in rat small intestine in vivo. Here, we report gene expression changes related to intestinal absorption or transport, the immune system and angiogenesis in response to 1,25-(OH)(2)D(3). Vitamin D deficient rats were intrajugularly given vehicle or vehicle containing 730 ng of 1,25-(OH)(2)D(3)/kg of body weight. Intestinal mRNA was harvested from duodenal mucosa at 15 min, 1, 3, and 6 h post-injection and studied by Affymetrix microarrays. Genes significantly affected by 1,25-(OH)(2)D(3) were confirmed by quantitative RT-PCR with remarkable agreement. The most strongly affected gene in intestine was CYP24 with 97-fold increase at 6 h post-1,25-(OH)(2)D(3) treatment. Intestinal calcium absorption genes: TRPV5, TRPV6, calbindin D(9k), and Ca(2+) dependent ATPase all were up-regulated in response to 1,25-(OH)(2)D(3), supporting the currently accepted mechanism of 1,25-(OH)(2)D(3) induced transcellular calcium transport. However, a 1,25-(OH)(2)D(3) suppression of several intra-/intercellular matrix modeling proteins such as sodium/potassium ATPase, claudin 3, aquaporin 8, cadherin 17, and RhoA suggests a vitamin D regulation of tight junction permeability and paracellular calcium transport. Several other genes related to the immune system and angiogenesis whose expression was changed in response to 1,25-(OH)(2)D(3) provided evidence for an immunomodulatory and anti-angiogenic role of 1,25-(OH)(2)D(3).