LBODP016 Lithocholic Acid Induced 25-hydroxyvitamin D-1alpha Hydroxylase (cyp27b1) Expression And Activities In Vitro And In Vivo

Our previous study reported that oleanolic acid, a natural agonist for bile acid membrane receptor Takeda G protein coupled receptor 5 (TGR5), could exert bone protective effects, increase circulating 1, 25(OH)2D3 level and induce renal CYP27B1 expression and activities. However, it is unclear if bile acids, as the endogenous agonist of bile acid receptors, could regulate CYP27B1 expression and activities in kidney and bone tissues. The present study aimed to characterize the effects of lithocholic acid (LCA), a secondary bile acid, on CYP27B1 expression and activities in vitro using human proximal tubule (HKC-8) and osteosarcoma (MG-63) and in vivo using mature (6-month-old) male C57BL/6 mice. HKC-8 and MG-63 cells were treated with either LCA (10-10 to 10-5 M), PTH (10-7M), or its vehicle for 4 hours. For MG-63 cells, LCA significantly induced CYP27B1 protein expression at 10-10 and 10-9M (P<0. 001) and CYP27B1 mRNA expression at 10-9M (P<0. 001). For HKC-8 cells, LCA significantly induced CYP27B1 protein expression at 10-10 to 10-6M (P<0. 01) and CYP27B1 mRNA expression at 10-10M (P<0. 001). In addition, LCA significantly induced CYP27B1 activity in MG-63 cells (10-10M) (P<0. 05) and in HKC-8 cells (10-6M) (P<0. 01). For the in vivo study, male C57BL/6 mice were fed with 25mg/kg LCA or its vehicle for three consecutive days and sacrificed 5 hours after the last gavage. Serum, kidney, and iliac crests were collected for subsequent analysis. LCA significantly induced circulating 1,25(OH)2D3 levels (P<0. 01) and CYP27B1 protein expression in both kidney and iliac crests in mice (P <0. 05). In addition, the time-dependent change (2, 5, 8 hours) in serum 1,25(OH)2D3 levels were determined upon feeding the male mice with a single dose of 25mg/kg LCA. LCA significantly increased serum 1,25(OH)2D3 levels in male mice at 2 and 5 hours (P <0. 01 and P <0. 05, respectively), and serum 1,25(OH)2D3 levels returned to basal level by 8 hours. LCA significantly increased CYP27B1 protein expression in kidney in mice at 8 hours after treatment (vs. control group, P<0. 05). In summary, our results showed that LCA significantly induced circulating 1,25(OH)2D3 levels, possibly by its actions to induce CYP27B1 expressions and activities in renal and extra-renal (bone) tissues. The study indicated that bile acids and other TGR5 ligands might play an important role in the regulation of vitamin D metabolism. Presentation: No date and time listed