Clinical translation and application in orthopaedics

Identification of naturally occurring inhibitors in Xian-Ling-Gu-Bao capsule against the glucuronidation of estrogens

Xian-Ling-Gu-Bao (XLGB) capsule, a well-known traditional Chinese medicine prescription, is widely used for the treatment of osteoporosis. It could significantly increase the levels of estrogen in ovariectomized rats and mice. However, this working mechanism has not been well elucidated. Considering that UDP-glucuronosyltransferase (UGT) enzymes are the important enzymes that inactivate and regulate estrogen activity in vivo, this study aimed to identify the bioactive compounds from XLGB against the glucuronidation of estrogens. First, thirty compounds were considered as candidate bioactive compounds based on our previous studies including pharmacological evaluation, chemical profiles, and metabolic profiles. Second, the characteristics of estrogen glucuronidation by uridine diphosphate glucuronic acid (UDPGA)-supplemented human liver microsomes (HLM), human intestine microsomes (HIM), and expressed UGT enzymes were determined, and the incubation systems of their key UGT enzymes were optimized. Then, inhibitory effects and mechanisms of XLGB and its main compounds toward the key UGT isozymes were further investigated. As a result, estrogen underwent efficient glucuronidation by HLM and HIM. UGT1A10, 1A1, and 2B7 were mainly responsible for the glucuronidation of estrone, β-estradiol, and estriol, respectively. For E1 and E2, UGT1A10 and 1A1 tended to mediate estrogen-3-O-glucuronidation, while UGT2B7 preferred catalyzing estrogen-16-O-glucuronidation. Furthermore, the incubation system for active UGT isoforms was optimized including Tris-HCl buffer, detergents, MgCl2 concentration, β-glucuronidase inhibitors, UDPGA concentration, protein concentration, and incubation time. Based on optimal incubation conditions, eleven, nine, and nine compounds were identified as the potent inhibitors for UGT1A10, 1A1, and 2B7, respectively (IC50 < 4.97 μM and Ki < 3.35 μM). Among them, six compounds (bavachin, isobavachin, isobavachalcone, neobavaisoflavone, corylifol A, and icariside II) simultaneously demonstrated potent inhibitory effects against these three active enzymes. Prenylated flavanols from Epimedium brevicornu Maxim., prenylated flavonoids from Psoralea corylifolia L., and salvianolic acids from Salvia miltiorrhiza Bge. were characterized as the most important and effective compounds. The identification of potent natural inhibitors of XLGB against the glucuronidation of estrogen laid an important foundation for the pharmacodynamic material basis.

Potential metabolism determinants and drug-drug interactions of a natural flavanone bavachinin

Bavachinin, a natural bioactive flavanone, is reported to have many pharmacological proprieties, especially anti-osteoporosis activity. Here we aim to determine the roles of cytochrome P450s (CYP), UDP-glucuronosyltransferases (UGT), and efflux transporters in metabolism and drug–drug interactions (DDI) of bavachinin. Phase I metabolism and glucuronidation were performed by human liver microsomes (HLM) and human intestine microsomes (HIM). Reaction phenotyping was used to identify the main CYPs and UGTs. Gene silencing methods were employed to investigate the roles of breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs) in HeLa1A1 cells. Inhibition mechanisms towards CYPs and UGTs were explored through kinetic modeling. Three phase I metabolites (M1–M3) and one glucuronide (G1) were detected after incubation of bavachinin with HLM and HIM. The intrinsic clearance (CL_int) values of M1 and G1 by HLM were 89.4 and 270.2 μL min⁻¹ mg⁻¹, respectively, while those of M3 and G1 by HIM were 25.8 and 247.1 μL min⁻¹ mg⁻¹, respectively. CYP1A1, 1A2, 1B1, 2C8, 2C19, and UGT1A1, 1A8 participated more in bavachinin metabolism. The metabolism showed marked species difference. BCRP and MRP4 were identified as the main contributors. Bavachinin displayed potent inhibitory effects against several CYP and UGT isozymes (K_i = 0.28–2.53 μM). Bavachinin was subjected to undergo metabolism and disposition by CYPs, UGTs, BCRP, MRP4, and was also a potent non-selective inhibitor against several CYPs and UGTs.

Metabolism, efflux transport and drug–drug interactions of bavachinin.

Serum copper levels are associated with bone mineral density and total fracture

Background

Both copper deficiency and overexposure have been associated with adverse health effects. Evidence linking copper to bone mineral density (BMD) and total fracture, however, is limited.

Methods

This nationally representative cross-sectional study enrolled participants from the National Health and Nutrition Examination Survey (2011–2014) in the United States. Using unadjusted and multivariate adjusted logistic regression analyses and a two-piecewise linear regression model with a smoothing function, we evaluated the associations between serum copper levels, bone mineral density and total fracture in 722 participants.

Results

The study sample (n = 722, mean age: 56.47 ± 11.55 y) represented a population of which 47.2% were men; 43.91% were non-Hispanic white, 18.84% non-Hispanic black and 13.71% Mexican American; 25.9% had total fracture. In the multivariate logistic regression analysis, individuals in the lowest category (<98.5 μg/dL) of serum copper concentration had 0.049 g/cm² lower total femur BMD and 0.045 g/cm² lower femoral neck BMD than those in the second concentration category (98.5–114 μg/dL). Individuals in the highest category (≥134 μg/dL) of serum copper concentration had an approximately 4-fold increase in the risk of total fracture than those in the second concentration category. There were no significant associations between per 10 μg/dL increases in serum copper levels and total fracture in multivariate logistic regression analysis after multivariate adjustment (all p > 0.05). However, a differential association between serum copper levels and total fractures between men and women was observed (odds ratio = 1.81, 95% confidence interval 1.08–3.03, p = 0.026 for men and odds ratio = 1.07, 95% confidence interval 0.86–1.32, p = 0.552 for women).

Conclusion

Moderate serum copper levels are critically important for bone health. Lower serum copper levels are significantly associated with decreased BMD in the total femur and femoral neck. Higher serum copper levels are significantly associated with increased total fracture, especially in men.

The Translational Potential of this Article

The impact of serum copper concentrations on bone mineral density and total fracture can provide insights into clinical application of copper-containing supplements and biomaterials.