A reduced protein diet modulates enzymes of vitamin D and cholesterol metabolism in young ruminants

• Published in: The Journal of steroid biochemistry and molecular biology 2019-02, Vol.186, p.196-202
• Main Authors: Wilkens, Mirja R., Firmenich, Caroline S., Schnepel, Nadine, Muscher-Banse, Alexandra S.
• Format: Article
• Language: English
• Subjects: Calcitriol; Calcium; Caprinae; Cholesterol; Cytochrome P450 2J2; Dietary intake; Enzymes; Excretion; Gene expression; Goat; Hydroxylase; Investigations; Lipid metabolism; Low protein diet; Metabolism; Nitrogen; Nutrient deficiency; Plasma; Proteins; Sterol 27-hydroxylase; Urea; Vitamin D; Vitamin D receptors; Vitamin D-binding protein; Vitamin D3
• ISSN: 0960-0760; 1879-1220
• DOI: 10.1016/j.jsbmb.2018.10.014

•Blood 25OHD3 and total cholesterol concentrations were elevated during a protein reduction while 1,25(OH)2D3 was decreased.•A protein reduction stimulated hepatic CYP2R1 expression while CYP27A1 and CYP2J2 expression was diminished.•A protein reduced diet modulated vitamin D and cholesterol metabolism. Besides other adverse effects, a low protein diet has been shown to modulate cholesterol and vitamin D metabolism in monogastric species like rats and humans. As ruminants can increase the efficiency of the rumino-hepatic circulation of urea, it is assumed that goats should be able to compensate for a low dietary protein intake better. After a dietary protein restriction (9% vs. 20%) for six weeks, plasma concentrations of urea, albumin, 1,25-dihydroxyvitamin D3 and calcium were decreased, while plasma 25-hydroxyvitamin D3 (25−OHD3), and total cholesterol were significantly increased in young goats. Because this was not accompanied by any decrease in expression of CYP24A1 mRNA, we investigated mRNA expression of additional enzymes with known 24- and/or 25-hydroxylase activities (CYP2R1, CYP2J2, CYP3 A24, CYP27A1), receptors involved in their regulation (VDR, PXR, RXRα) and vitamin D binding protein (VDBP). CYP2R1expression was stimulated with the low dietary protein intake, negatively correlated with plasma urea and positively associated with serum 25−OHD3. The greater plasma concentrations of total cholesterol could be explained with the reduction of CYP2J2 and CYP27A1 expression. None of the receptors investigated were affected by the dietary protein restriction but mRNA expression of VDBP was slightly reduced. Taken together our results show that dietary protein restriction has an impact on vitamin D and cholesterol metabolism in ruminants, too. Therefore, further investigations are needed before dietary interventions aiming at diminishing nitrogen excretion can be implemented.