H-Leu-Leu-OMe . HBr (Leu-Leu methyl ester hydrobromide) is a dipeptide generated by human monocytes or polymorphonuclear leukocytes. H-Leu-Leu-OMe . HBr selectively eliminates lymphocytes, especially natural killer cells with cytotoxic potential, and induces endolysosomal pathway stress[1]. The sensitivity of cytotoxic lymphocytes to H-Leu-Leu-OMe . HBr depends upon the production of membranolytic metabolites of the structure (Leu-Leu)n-OMe by dipeptidyl peptidase I[2]. Such membranolytic metabolites are present at far higher levels in cytotoxic lymphocytes than in cells without cytolytic potential or not of bone marrow origin[2].
In vitro, H-Leu-Leu-OMe . HBr may act as an inflammasome activator on RPE cells (primary human fetal RPE cells; 1mM; 3h), leading to caspase-1 cleavage, cytokine secretion, and X-linked inhibitor of apoptosis protein (XIAP) reduction[3]. H-Leu-Leu-OMe . HBr activates NLRP3 inflammasome that promotes IL-6 and IL-8 production (human umbilical vein endothelial cells, 20μM; 19h) in primed human umbilical vein endothelial cells[4]. Moreover, H-Leu-Leu-OMe . HBr may act as an apoptosis inducer (U937 cells; 0.5mM; 30min) in natural killer cells and macrophages[5].
In vivo, H-Leu-Leu-OMe . HBr shows toxicity to lymphocytes (adult (CBA x BALB/c) F1 mice, H-Leu-Leu-OMe . HBr-treated CBA spleen cells(0.15M; 15min; room temperature; i.p) that suppressing lymphocyte function[6]. H-Leu-Leu-OMe . HBr can also mimic alum-mediated necrosis that specifically kills myeloid leukocytes in 8-week-old female C57BL/6 mice (1mg; once; i.v)[7].
References:
[1] Thiele, D L, and P E Lipsky. “The immunosuppressive activity of L-leucyl-L-leucine methyl ester: selective ablation of cytotoxic lymphocytes and monocytes.” *Journal of immunology (Baltimore, Md. : 1950)* vol. 136,3 (1986): 1038-48.
[2] Thiele, D L, and P E Lipsky. “Mechanism of L-leucyl-L-leucine methyl ester-mediated killing of cytotoxic lymphocytes: dependence on a lysosomal thiol protease, dipeptidyl peptidase I, that is enriched in these cells.” *Proceedings of the National Academy of Sciences of the United States of America* vol. 87,1 (1990): 83-7. doi:10.1073/pnas.87.1.83
[3] Gao, Jiangyuan et al. “The reduction of XIAP is associated with inflammasome activation in RPE: implications for AMD pathogenesis.” Journal of neuroinflammation vol. 16,1 171. 22 Aug. 2019, doi:10.1186/s12974-019-1558-5
[4] Kinnunen, K et al. “Lysosomal destabilization activates the NLRP3 inflammasome in human umbilical vein endothelial cells (HUVECs).” *Journal of cell communication and signaling* vol. 11,3 (2017): 275-279. doi:10.1007/s12079-017-0396-4
[5] Odaka, M et al. “Synthesis, photoreactivity and cytotoxic activity of caged compounds of L-leucyl-L-leucine methyl ester, an apoptosis inducer.” *Photochemistry and photobiology* vol. 63,6 (1996): 800-6. doi:10.1111/j.1751-1097.1996.tb09633.x
[6] Mowat, A M, and P A Leck. “Generalized toxicity of L-leucyl-leucine-methyl ester for lymphocyte functions.” *Immunology* vol. 69,4 (1990): 564-9.
[7]Jacobson, Lee S et al. “Cathepsin-mediated necrosis controls the adaptive immune response by Th2 (T helper type 2)-associated adjuvants.” *The Journal of biological chemistry* vol. 288,11 (2013): 7481-7491. doi:10.1074/jbc.M112.400655
H-Leu-Leu-OMe . HBr（亮氨酸-亮氨酸甲酯氢溴化物）是由人类单核细胞或多形核白细胞产生的二肽。H-Leu-Leu-OMe . HBr选择性地清除淋巴细胞，特别是具有细胞毒性的自然杀伤细胞，并诱导内溶酶体途径应激[1]。淋巴细胞对H-Leu-Leu-OMe . HBr细胞毒性的敏感性取决于二肽基肽酶产生的结构(Leu-Leu)n-OMe的膜分解代谢产物[2]。这种膜分解代谢物在细胞毒性淋巴细胞中的含量远高于无细胞分解潜能或非骨髓来源的细胞[2]。
在体外，H-Leu-Leu-OMe . HBr可能作为炎性体激活剂作用于RPE细胞（原代人胎RPE细胞; 1mM; 3h），导致caspase-1裂解、细胞因子分泌和X-linked inhibitor of apoptosis protein （XIAP）减少[3]。激活NLRP3炎性小体，促进IL-6和IL-8的产生（人脐静脉内皮细胞; 20μM; 19h）在原生的人脐静脉内皮细胞中[4]。H-Leu-Leu-OMe . HBr在自然杀伤细胞和巨噬细胞中作为凋亡诱导剂（U937细胞; 0.5mM; 30min）[5]。
在体内，H-Leu-Leu-OMe . HBr显示出对淋巴细胞（成年（CBA × BALB/c） F1小鼠，H-Leu-Leu-OMe . HBr处理的CBA脾细胞（0.15M; 15min; 室温），i.p）的毒性，抑制淋巴细胞功能[6]。H-Leu-Leu-OMe . HBr还可以模拟铝介导的坏死，特异性杀死8周龄雌性C57BL/6小鼠的髓系白细胞（1mg; 1次; 静脉注射）[7]。