Ethanol Extract of Fructus ligustri lucidi Increased Circulating 1,25(OH)2D3 Levels, but Did Not Improve Calcium Balance in Mature Ovariectomized Rats

Our previous studies found that different extracts or fractions of Fructus ligustri lucidi (FLL) played different roles in altering the regulation of bone and mineral metabolism in different animal models. The present study was designed to compare the actions of FLL ethanol (EE) and water extracts (WE) on bone and mineral metabolism in a 6-month-old mature ovariectomized (OVX) rat model. Our results showed that FLL extracts did not significantly improve systematic Ca balance in mature OVX rats. However, EE, but not WE treatment, significantly increased serum 1,25(OH)(2)D-3 levels in mature OVX rats. An in vitro study using human proximal tubule (HKC-8) cells showed that EE, but not WE, significantly enhanced renal 25-dihydroxyvitamin D3-1 alpha-hydroxylase (1-OHase) mRNA expressions and simultaneously repressed renal 25-dihydroxyvitamin D-3-24-hydroxylase (24-OHase) mRNA expressions. Further investigation indicated that EE could significantly induce the protein expression of 1-OHase, but did not alter 24-OHase expression in HKC-8 cells. Our results demonstrated that EE increased circulating 1,25(OH)(2)D-3 levels in OVX rats, possibly via upregulation of renal 1-OHase expressions in renal proximal tubule cells. Our study indicates that FLL is a natural oral agent that could directly regulate renal vitamin D metabolism in vivo and in vitro.