氧化应激是绝经后骨质疏松（OS）的重要诱因。研究显示黄烷醇抗氧化活性很好。然而黄烷醇体内吸收率却很低，大部分以肠道菌群代谢产物（FMGM）形式被吸收，且FMGM较膳食原体含量更高，半衰期更久。然而我们及他人的既往研究多以膳食摄入量或膳食原体内暴露水平评价黄烷醇与OS的关系，未考虑肠道菌群代谢的影响。我们推测黄烷醇可抗氧化进而改善OS效应主要依赖于FMGM。为验证此假设，本项目拟首先利用病例对照研究，以女性骨质疏松性髋骨骨折为结局，检测血尿FMGM含量，测定氧化应激指标，分析不同FMGM及氧化应激与髋骨骨折的关联；其次通过黄烷醇单独或联合抗生素/益生菌干预去卵巢OS小鼠，验证FMGM是否介导黄烷醇在体内调节骨代谢及抗氧化的效应及其作用大小；最后借助成骨细胞氧化应激模型，探讨FMGM通过抗氧化影响骨形成的具体机制。研究结果可用于指导人群通过合理运用黄烷醇预防OS并为骨健康功能产品开发提供线索。

Oxidative stress has been identified as a pivotal pathogenic factor of postmenopausal osteoporosis. Flavan-3-ols are found to exhibit high antioxidant capacity both in vivo and in vitro. Paradoxically, despite the high biological properties, they were found in low circulating concentration after oral administration. A major fraction of the flavan-3-ols present in the plasma and excreted in urine of rat or human fed with flavan-3-ols enriched food comprises phenyl-γ-valerolactones and phenyl-valeric acids formed in the colon. Most of the previous studies including ours using dietary intakes or circulating parent compounds to evaluate the relationship between flavan-3-ols and osteoporosis could not estimate the potential impacts of gut micriobime-derived metabolites on OS. We hypothesized that those flavan-3-ols metabolites derived from microbiome (FMGM) might exert important impacts on antioxidant capacity and in turn on bone health in vivo. To test the hypothesis, we firstly proposed a 1:1 case-control study, including 420 pairs of new cases of osteoporotic hip fractures and community-derived controls among postmenopausal women, to collect blood and 24-h urine samples. Targeted metabolomics via using high performance liquid chromatography-tandem mass spectrometry will be applied to determine the FMGM. Measurement of oxidative damage markers will be performed. Univariate and multivariate conditional logistic regression analysis will be applied to test the relationship between different kinds of FMGM and the risk of hip fractures. Path analysis will be used to determine the role of oxidative damage in the causal chain between FMGM and the risk of hip fractures. Secondly, in ovariectomized mice model of osteoporosis, we will give the mice with flavan-3-ols, or flavan-3-ols in combination with broad-spectrum antibiotics or probiotics by gavage and determine the parameters of bone remodeling, the FMGM in urine and blood, and gut microbiome composition, and to analyze whether or not FMGM mediate the effects of flavan-3-ols on oxidant stress and bone health. Thirdly, based on a H2O2 induced oxidative damage model of osteoblast cell line in vitro, we will apply siRNA to silence Sirt1/Sirt3/FOXO3 gene expression and incubate cells with selected FMGM, and to investigate the potential mechanisms by which FMGM modulate bone remodeling as antioxidant. Those results will explore the role of microbiome-derived metabolites of flavan-3-ols on bone health, and also be used for dietary guidance of people to prevent osteoporosis or the development of new nutritional products for promoting bone health.