Mucosal associated invariant T-cells (MAIT cells) are activated following recognition of bacterial antigens (riboflavin intermediates) presented on major histocompatibility complex class I-related molecule (MR1). Our previous study showed that MR1^−/− knock-out (KO) mice (lacking MAIT cells) harbor a unique microbiota that is resistant to antibiotic disruption and Clostridioides difficile colonization. While we have characterized the microbiota of this mouse strain, changes in global metabolic activity in these KO mice have not been assessed. Here, LC/MS-based untargeted metabolomics was applied to investigate the differences in the metabolome, specifically in the bile acid (BA) profile of wild-type (WT) and MR1^−/− KO mice, as well as how antibiotics change these profiles. BA changes were evaluated in the intestinal content, cecum content, and stool samples from MR1^−/− mice and WT mice treated with cefoperazone (Cef). Fecal pellets were collected daily and both intestinal and cecal contents were harvested at predetermined endpoints on day 0 (D0), day 1 (D1), day 3 (D3), and day 5 (D5). KO mice exhibited no changes in 6-hydroxymethyl-8-D-ribityllumazine (rRL-6-CH₂OH; an MR1-restricted riboflavin derivative) in the stool samples at either time point vs. D0, while WT mice showed significant decreases in rRL-6-CH₂OH in the stool samples on all treatment days vs. D0. Metabolomics analysis from cecal and stool samples showed that KO mice had more total BA intensity (KO/WT = ~1.7 and ~3.3 fold higher) than that from WT mice prior to Cef treatment, while the fold change difference (KO/WT = ~4.5 and ~4.4 fold) increased after five days of Cef treatment. Both KO and WT mice showed decreases in total BA intensity in response to Cef treatment, however, less dramatic decreases were present in KO vs. WT mice. Increases in taurocholic acid (TCA) intensity and decreases in deoxycholic acid (DCA) intensity in the stool samples from WT mice were associated with the depletion of certain gut bacteria, which was consistent with the previously reported microbiome data. Furthermore, the non-detected TCA and relatively higher DCA intensity in the KO mice might be related to Clostridioides difficile infection resistance, although this needs further investigation.

中文翻译：

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MR1缺陷小鼠胆汁酸谱及其对头孢哌酮治疗反应的变化。

识别存在于主要组织相容性复合物I类相关分子（MR1）上的细菌抗原（核黄素中间体）后，激活与粘膜相关的恒定T细胞（MAIT细胞）。我们以前的研究表明，MR1 ^-/-敲除（KO）小鼠（缺少MAIT细胞）具有独特的微生物群，可抵抗抗生素的破坏和艰难梭菌的定殖。虽然我们已经表征了该小鼠品系的微生物群，但尚未评估这些KO小鼠中整体代谢活性的变化。在这里，基于LC / MS的非靶向代谢组学被用于研究代谢组的差异，特别是野生型（WT）和MR1 ^-/-的胆汁酸（BA）谱KO小鼠，以及抗生素如何改变这些特征。在用头孢哌酮（Cef）处理的MR1 ^-/-小鼠和WT小鼠的肠含量，盲肠含量和粪便样本中评估BA变化。每天收集粪便颗粒，并在第0天（D0），第1天（D1），第3天（D3）和第5天（D5）的预定终点收集肠道和盲肠内容物。与D0相比，KO小鼠在任何时间点的粪便样品中6-羟甲基-8-D-ribityllumazine（rRL-6-CH ₂ OH； MR1限制的核黄素衍生物）均无变化，而WT小鼠在D0时显着降低。 rRL-6-CH ₂与D0相比，所有治疗日粪便样品中的OH均高。盲肠和粪便样品的代谢组学分析表明，KO小鼠的总BA强度（KO / WT =〜1.7和〜3.3倍）比Cef治疗前的WT小鼠更高，而倍数变化差异（KO / WT =〜 Cef治疗5天后增加了4.5倍和〜4.4倍）。KO和WT小鼠均显示出响应Cef治疗的总BA强度降低，但是KO与WT小鼠相比，KO的降低幅度较小。WT小鼠粪便中牛磺胆酸（TCA）强度的增加和脱氧胆酸（DCA）强度的减少与某些肠道细菌的消耗有关，这与先前报道的微生物组数据一致。此外，KO小鼠中未检测到的TCA和相对较高的DCA强度可能与艰难梭菌对感染的抵抗力，尽管这需要进一步研究。