Abstract：
Limonene, a dietary monocyclic monoterpene commonly found in citrus fruits and various aromatic plants, has garnered increasing interest as a gastrointestinal protectant. This study aimed to assess the effects of limonene on intestinal epithelial barrier function and investigate the involvement of cannabinoid receptor type-1 (CB1R) in vitro. Additionally, the study focused on examining the metabolomic changes induced by limonene in the intestinal epithelial cells (Caco-2). Initial analysis of transepithelial electrical resistance (TEER) revealed that both l-limonene and d-limonene, isomers of limonene, led to a dose- and time-dependent increase in TEER in normal cells and those inflamed by pro-inflammatory cytokines mixture (CytoMix). Furthermore, both types of limonene reduced CytoMix-induced paracellular permeability, as demonstrated by a decrease in Lucifer yellow flux. Moreover, d-limonene and l-limonene treatment increased the expression of tight junction molecules (TJs) such as occludin, claudin-1, and ZO-1, at both the transcriptional and translational levels. d-Limonene upregulates E-cadherin, a molecule involved in adherens junctions (AJs). Mechanistic investigations demonstrated that d-limonene and l-limonene treatment significantly inhibited CB1R at the protein, while the mRNA level remained unchanged. Notably, the inhibitory effect of d-limonene on CB1R was remarkably similar to that of pharmacological CB1R antagonists, such as rimonabant and ORG27569. d-limonene also alters Caco-2 cell metabolites. A substantial reduction in β-glucose and 2-succinamate was detected, suggesting limonene may impact intestinal epithelial cells\' glucose uptake and glutamate metabolism. These findings suggest that d-limonene\'s CB1R antagonistic property could effectively aid in the recovery of intestinal barrier damage, marking it a promising gastrointestinal protectant.
摘要：
柠檬烯,一种常见于柑橘类水果和各种芳香植物中的膳食单环单萜，作为胃肠保护剂已经引起了越来越多的兴趣。这项研究旨在评估柠檬烯对肠道上皮屏障功能的影响，并探讨大麻素受体1型（CB1R）在体外的参与。此外,该研究的重点是研究柠檬烯在肠上皮细胞（Caco-2）中引起的代谢组学变化。跨上皮电阻（TEER）的初步分析表明，1-柠檬烯和d-柠檬烯，柠檬烯的异构体，导致正常细胞和由促炎细胞因子混合物（CytoMix）引起的TEER的剂量和时间依赖性增加。此外，两种柠檬烯都能降低CytoMix诱导的细胞旁通透性，路西法黄色通量的减少证明了这一点。此外，d-柠檬烯和l-柠檬烯处理增加了紧密连接分子（TJs）的表达，例如occludin，claudin-1和ZO-1，在转录和翻译水平。d-柠檬烯上调E-钙粘蛋白，参与粘附连接（AJs）的分子。机理研究表明，d-柠檬烯和l-柠檬烯处理显着抑制蛋白的CB1R，而mRNA水平保持不变。值得注意的是,d-柠檬烯对CB1R的抑制作用与药理学CB1R拮抗剂的抑制作用非常相似，如rimonabant和ORG27569。d-柠檬烯还改变Caco-2细胞代谢物。检测到β-葡萄糖和2-琥珀酰胺的大幅减少，提示柠檬烯可能影响肠上皮细胞葡萄糖摄取和谷氨酸代谢。这些发现表明，d-柠檬烯的CB1R拮抗特性可以有效地帮助恢复肠屏障损伤，标志着它是一个有前途的胃肠保护剂。
