State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan, China.
James L. Winkle College of Pharmacy University of Cincinnati, Cincinnati, OH, United States.
Front Immunol. 2021 May 17;12:670427. doi: 10.3389/fimmu.2021.670427. eCollection 2021.
Endocannabinoids are endogenous ligands of cannabinoid receptors and activation of these receptors has strong physiological and pathological significance. Structurally, endocannabinoids are esters (e.g., 2-arachidonoylglycerol, 2-AG) or amides (e.g., N-arachidonoylethanolamine, AEA). Hydrolysis of these compounds yields arachidonic acid (AA), a major precursor of proinflammatory mediators such as prostaglandin E. Carboxylesterases are known to hydrolyze esters and amides with high efficiency. CES1, a human arboxylterase, has been shown to hydrolyze 2-AG, and shares a high sequence identity with pig carboxylesterases: PLE1 and PLE6 (ig iver sterase). The present study was designed to test the hypothesis that PLE1 and PLE6 hydrolyze endocannabinoids and promote inflammatory response. Consistent with the hypothesis, purified PLE1 and PLE6 efficaciously hydrolyzed 2-AG and AEA. PLE6 was 40-fold and 3-fold as active as PLE1 towards 2-AG and AEA, respectively. In addition, both PLE1 and PLE6 were highly sensitive to bis(4-nitrophenyl) phosphate (BNPP), an aryl phosphodiester known to predominately inhibit carboxylesterases. Based on the study with BNPP, PLEs contributed to the hydrolysis of 2-AG by 53.4 to 88.4% among various organs and cells. Critically, exogenous addition or transfection of PLE6 increased the expression and secretion of proinflammatory cytokines in response to the immunostimulant lipopolysaccharide (LPS). This increase was recapitulated in cocultured alveolar macrophages and PLE6 transfected cells in transwells. Finally, BNPP reduced inflammation trigged by LPS accompanied by reduced formation of AA and proinflammatory mediators. These findings define an innovative connection: PLE-endocannabinoid-inflammation. This mechanistic connection signifies critical roles of carboxylesterases in pathophysiological processes related to the metabolism of endocannabinoids.
内源性大麻素是大麻素受体的内源性配体，这些受体的激活具有很强的生理和病理意义。从结构上讲，内源性大麻素是酯类（如 2-花生四烯酸甘油，2-AG）或酰胺类（如 N-花生四烯酸乙醇胺，AEA）。这些化合物的水解产物是花生四烯酸（AA），它是促炎介质如前列腺素 E 的主要前体。羧基酯酶已知能够高效水解酯类和酰胺类。人类羧基酯酶 CES1 已被证明能够水解 2-AG，并且与猪羧基酯酶：PLE1 和 PLE6（酰基水解酶）具有很高的序列同一性。本研究旨在检验 PLE1 和 PLE6 是否水解内源性大麻素并促进炎症反应的假设。与假设一致，纯化的 PLE1 和 PLE6 有效地水解 2-AG 和 AEA。PLE6 对 2-AG 和 AEA 的活性分别比 PLE1 高 40 倍和 3 倍。此外，PLE1 和 PLE6 对双（4-硝基苯基）磷酸酯（BNPP）均高度敏感，BNPP 是一种已知主要抑制羧基酯酶的芳基磷酸二酯。基于 BNPP 的研究，PLE 在各种器官和细胞中对 2-AG 的水解贡献了 53.4%至 88.4%。至关重要的是，外源性添加或转染 PLE6 增加了对免疫刺激物脂多糖（LPS）的反应中促炎细胞因子的表达和分泌。这种增加在共培养的肺泡巨噬细胞和转染 PLE6 的细胞中转录中得到了重现。最后，BNPP 减少了 LPS 触发的炎症，同时减少了 AA 和促炎介质的形成。这些发现定义了一个创新的联系：PLE-内源性大麻素-炎症。这种机制联系表明羧基酯酶在与内源性大麻素代谢相关的病理生理过程中起着关键作用。
