Gut microbiota tryptophan metabolite indole-3-propionic acid alleviates inflammatory bowel disease-related osteoporosis in a mouse model

doi:10.12307/2026.615

Abstract

Abstract: BACKGROUND: The gut-bone axis refers to the interaction network through which gut microbiota and its metabolites influence bone development, metabolism, and health by regulating host immune, endocrine, and metabolic pathways. Previous studies have demonstrated that disturbances in gut microbiota have been shown to interact with inflammatory bowel disease-associated osteoporosis.
OBJECTIVE: To investigate the protective effects and potential mechanisms of the gut microbiota tryptophan metabolite, indole-3-propionic acid, in inflammatory bowel disease combined with osteoporosis.
METHODS: Male Balb/c mice, aged 6-8 weeks, were randomly divided into three groups: control, model, and indole-3-propionic acid groups. In the latter two groups, 1.5% sodium dextran sulfate was added to the drinking water for 12 weeks to induce chronic enteritis, and then in the indole-3-propionic acid group, intraperitoneal injections of indole-3-propionic acid at a dose of 20 mg/kg were administered three times per week, for 4 weeks. Severity of colon inflammation was assessed by hematoxylin-eosin staining, colon length measurement, and ELISA detection of intestinal inflammatory cytokine levels. Bone mass and structure of the femur were analyzed by Micro-CT scanning. Viability of osteoblasts and osteoclasts and bone metabolism were assessed using tartrate-resistant acid phosphatase staining, hematoxylin-eosin staining, calcein double labeling and immunofluorescence staining.
RESULTS AND CONCLUSION: (1) The colon length in the model group was shorter than that in the control group, while indole-3-propionic acid treatment improved the colon length. Hematoxylin-eosin staining of the colon showed that the model group exhibited disrupted colon structure, disordered crypt arrangement, and extensive infiltration of inflammatory cells. After the administration of indole-3-propionic acid, the infiltration of inflammatory cells was significantly reduced, and the colon structure was restored. (2) ELISA results indicated that the levels of intestinal inflammatory cytokines were significantly elevated in the model group compared with the control group (P < 0.000 1). After treatment with indole-3-propionic acid, the levels of intestinal inflammatory cytokines were significantly reduced (P < 0.001). (3) Micro-CT scanning and three-dimensional reconstruction showed that indole-3-propionic acid significantly alleviated bone loss in the mouse model of chronic enteritis. (4) Tartrate-resistant acid phosphatase staining and hematoxylin-eosin staining revealed that indole-3-propionic acid reduced the number of osteoclasts and increased the number of trabeculae. Calcein double labeling experiments showed that indole-3-propionic acid treatment improved bone formation capacity. Immunofluorescence analysis indicated that indole-3-propionic acid promoted the expression of SP7. These findings suggest that indole-3-propionic acid improves bone metabolism by reducing intestinal inflammation, inhibiting osteoclast activity, and upregulating osteoblast function, highlighting its potential application in the treatment of osteoporosis associated with inflammatory bowel disease.

Key words: gut microbiota, tryptophan metabolites, indole-3-propionic acid, inflammatory bowel disease, osteoporosis, gut-bone axis, bone metabolism

CLC Number:

Qiu Xueli, Cui Hao, Wu Chenyang, Tao Lide, Yao Yuqian, Tian Bo, Bai Jinyu, Zhang Yingzi. Gut microbiota tryptophan metabolite indole-3-propionic acid alleviates inflammatory bowel disease-related osteoporosis in a mouse model [J]. Chinese Journal of Tissue Engineering Research, 2026, 30(10): 2413-2421.

Figures/Tables 4

2.1 实验动物数量分析 15只Balb/c小鼠全部纳入结果分析。 2.2 IPA缓解炎症性肠病小鼠的肠道炎症大体观察显示，与对照组相比，模型组小鼠体型明显减小，而IPA组小鼠体型接近对照组小鼠(图1A)。实验过程中严密观察各组小鼠的体质量变化，结果显示：在前12周，模型组及IPA组小鼠体质量增长明显慢于对照组小鼠，而在IPA干预后小鼠体质量增长显著快于模型组小鼠(图1B)。解剖小鼠取结肠进行长度测量，结果显示：与对照组相比，模型组小鼠结肠显著缩短，而IPA组小鼠结肠长度部分恢复(图1C，D)。各组小鼠结肠行苏木精-伊红染色，结果显示：对照组小鼠结肠组织结构完整，隐窝排列紧密、腺体结构清晰，未见炎症细胞浸润，表明肠道健康无损伤；模型组小鼠结肠组织表现出隐窝结构紊乱、腺体萎缩且伴有大量炎症细胞浸润等显著的炎症特征；与模型组相比，IPA组小鼠结肠组织结构部分恢复，隐窝结构较为清晰，炎症细胞浸润显著减少(图1E)。 ELISA检测各组小鼠结肠组织炎症因子水平，结果显示：与对照组相比，模型组白细胞介素1β、肿瘤坏死因子α和白细胞介素6水平显著上升(P < 0.000 1)，提示炎症性肠病伴随着显著的促炎因子升高。与模型组相比，IPA组白细胞介素1β、肿瘤坏死因子α和白细胞介素6水平明显降低(白细胞介素1β、白细胞介素6：P < 0.000 1，肿瘤坏死因子α：P < 0.001)，表明IPA能够有效减轻炎症性肠病诱导的肠道炎症因子表达，发挥抗炎保护作用(图1F-H)。 2.3 IPA对炎症性肠病小鼠骨结构的保护作用取各组小鼠股骨进行Micro-CT扫描并通过软件三维重建以分析骨微结构(骨小梁及皮质骨)。图2A为各组小鼠股骨纵向切片的Micro-CT图像。对照组小鼠股骨表现出完整的骨小梁结构和正常的骨量；模型组小鼠股骨骨量显著下降，骨小梁结构严重破坏，表现出典型的骨质疏松特征；IPA组小鼠股骨骨量部分恢复，骨小梁结构较模型组更为完整。图2B为各组小鼠股骨横截面Micro-CT重建图像，包含二维横截面图和三维重建图。二维横截面图显示各组小鼠皮质骨厚度几乎不变；而在三维重建图像中，模型组小鼠骨小梁密度与对照组相比显著稀疏，结构显著破坏，整体骨量下降；而IPA组三维图像显示骨小梁密度恢复，结构改善，接近对照组水平。图2C为Micro-CT图像定量分析骨结构参数，结果显示：与模型组相比，IPA组骨矿物质密度、骨体积分数、骨小梁数目和骨小梁厚度显著增加；3组之间皮质骨厚度没有显著差异。 2.4 IPA调控骨代谢缓解炎症性肠病介导的骨量下降小鼠股骨远端抗酒石酸酸性磷酸酶染色分析显示，对照组破骨细胞数量较少，骨吸收活性正常；模型组破骨细胞数量显著增加(P < 0.000 1)，提示骨吸收活性增强；IPA组破骨细胞数量显著减少(P < 0.001)，提示IPA可通过下调破骨功能缓解骨吸收异常(图3A，B)。苏木精-伊红染色结果显示：对照组骨小梁结构完整且骨质致密；模型组小鼠的骨小梁数量显著减少(P < 0.000 1)，结构严重破坏，表现出典型的骨质疏松特征；而IPA组骨小梁数目与结构部分恢复(P < 0.01)(图3C，D)。钙黄绿素双标荧光染色结果显示，与对照组相比，模型组矿化沉积率显著下降，提示骨形成能力受损(P < 0.000 1)；IPA组较模型组明显改善(P < 0.001)，提示IPA能够通过调控骨形成部分恢复骨代谢平衡(图3E，F)。免疫荧光染色结果显示，对照组SP7表达较高，反映出活跃的成骨细胞功能；而模型组SP7表达显著降低(P < 0.001)，成骨细胞活性受损；IPA组SP7表达有所恢复(P < 0.05)，提示IPA在促进成骨细胞功能方面具有积极作用(图3G，H)。血清学分析进一步支持了上述组织学发现，模型组小鼠P1NP水平显著降低而CTX-1水平显著升高，表明模型组小鼠骨形成能力降低而骨吸收能力增加；与模型组相比，IPA组小鼠P1NP水平增加而CTX-1水平降低，提示IPA调控骨代谢的双重功能从而缓解炎症性肠病小鼠骨量丢失(图3I，J)。"

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