High sensitivity of rat hepatic vitamin D₃-25 hydroxylaseCYP27Ato 1,25-dihydroxyvitamin D₃administration

Abstract

High sensitivity of the rat hepatic vitamin D3-25 hydroxylase CYP27A to 1,25-dihydroxyvitamin D 3 administration. Am J Physiol Endocrinol Metab 284: E138-E147, 2003. First published October 1, 2002 10.1152 10. /ajpendo.00303.2002 is considered the main vitamin D3 (D3)-25 hydroxylase in humans. Our purpose was to evaluate the effect of the D3 nutritional and hormonal status on hepatic CYP27A mRNA, cellular distribution, transcription rate, and enzyme activity. Studies were carried out in normal and in D-depleted rats supplemented with D3, 25OHD3, or 1,25(OH)2D3. CYP27A exhibited a significant gender difference and was observed throughout the hepatic acinus not only in hepatocytes but also in sinusoidal endothelial, stellate, and Kupffer cells. Neither D3 nor 25OHD3 influenced CYP27A mRNA levels. However, 1,25(OH)2D3 repletion led to a 60% decrease in CYP27A mRNA, which was accompanied by a 46% decrease in mitochondrial D3-25 hydroxylase activity. The effect of 1,25(OH)2D3 was mediated by a significant decrease in CYP27A transcription, whereas its mRNA half-life remained unchanged. Our data indicate that CYP27A is present in hepatic parenchymal and sinusoidal cells and that the gene transcript is not influenced by the D3 nutritional status but is transcriptionally regulated by 1,25(OH)2D3 exposure.bile acid biosynthesis; Kupffer cells; stellate cells; hepatocytes; sinusoidal endothelial cells THE SECOSTEROID VITAMIN D 3 (D 3 ) of endogenous or exogenous origin has, in its native form, no biological activity. Once in circulation, D 3 is efficiently taken up by the liver (26) and hydroxylated at C-25 by a mitochondrial mixed-function oxidase CYP27A [C 27 sterol hydroxylase (EC 1.14.13.15)] (15). In humans, the enzyme is presumed to be the only D 3 -25 hydroxylase (51). However, a microsomal D 3 -25 hydroxylase has also been reported in rodents (11), chickens (12), and pigs (35), but only the porcine enzyme (which has been termed CYP2D25) has been cloned to date (34,44).CYP27A is a cytochrome P-450 that catalyzes the first step in the oxidation of the cholesterol side chain in the secondary "acidic" bile acid biosynthesis pathway (13). CYP27A is also able to hydroxylate D 3 and D 3 metabolites at position C-25 (51) as well as at other positions on the secosteroid side chain (29, 54). It has also been reported to be able to catalyze the 1␣-hydroxylation of 25-hydroxyvitamin D 3 (25OHD 3 ), albeit at a much lower rate than the transformation of D 3 into 25OHD 3 (3). However, unlike the tight regulation by the D 3 endocrine system associated with the renal 25-hydroxyvitamin D 3 -1␣-hydroxylase, the sensitivity of the gene encoding CYP27A to D 3 or to D 3 metabolites has not been characterized. The presence of regulatory mechanisms related to the D 3 status as a modulator of the 25-hydroxylation of the vitamin is, however, a widely accepted notion, which rests on the studies of DeLuca's group in the early 1970s (Bhattacharyya and DeLuca, Refs. 10, 12). Several laboratories have attempted to evaluate the mechanism(s) inv...

How Much Vitamin D3Do the Elderly Need?

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Regulation of Human Vitamin D325-Hydroxylases in Dermal Fibroblasts and Prostate Cancer LNCaP Cells

“…In this study, we report that phenobarbital and the antiretroviral drug efavirenz, as well as the active hormone 1␣,25-dihydroxyvitamin D 3 (calcitriol), suppress the expression levels also of human 25-hydroxylating enzymes. In humans, several possible candidates for vitamin D 3 or vitamin D 2 25-hydroxylase have been suggested, including CYP27A1 (Theodoropoulos et al, 2003), CYP2R1 (Cheng et al, 2003), CYP2J2 (Aiba et al, 2006), and CYP3A4 (Gupta et al, 2004). In recent years, the bioactivation of vitamin D 3 in extrahepatic cells has been subject to increased interest because of the regulating functions ascribed to 1␣,25-dihydroxyvitamin D 3 (calcitriol) in cell proliferation and differentiation.…”

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“…Injections were performed in nonfasting normal rats 6 hours before they were killed, as already reported. 13 …”

“…In addition, the hormone has been reported as an inhibitor of the D 3 -25 hydroxylase 11,12 and a significant modulator of the gene encoding the mitochondrial D 3 -25/cholesterol/bile acid hydroxylase (CYP27A). 13 However, the hormone mode of action during these experimental paradigms has not been investigated and the presence of the VDR n in liver cells still remains an open question. The absence or extremely low level of VDR n reported to date in liver led us to propose that hepatocytes, which constitute the largest hepatic cell population, were most…”