Abstract：
Inflammatory cytokine interleukin-6 (IL-6) plays a pivotal role in skeletal muscle degradation after intra-abdominal sepsis (IAS), with mechanism remained to be elucidated. Indoleamine 2,3-dioxygenase 1 (IDO-1), a key enzyme in converting tryptophan into kynurenine, could be activated by IL-6, and kynurenine has been shown to be involved in muscle degradation. We hypothesized that IL-6 could promote muscle degradation via tryptophan-IDO-1-kynurenine pathway in IAS patients.
Serum and rectus abdominis (RA) were obtained from IAS or non-IAS patients. Mouse model of IAS-induced muscle wasting was generated by caecal ligation and puncture (CLP) and lipopolysaccharide (LPS) injection. IL-6 signalling was blocked by anti-mouse IL-6 antibody (IL-6-AB), and the IDO-1 pathway was blocked by navoximod. To elucidate the role of kynurenine in muscle mass and physiology, kynurenine was administered to IAS mice treated with IL-6-AB.
Compared to non-IAS patients, kynurenine levels in serum (+2.30-fold vs. non-IAS, P < 0.001) and RA (+3.11-fold vs. non-IAS, P < 0.001) were elevated, whereas tryptophan levels in serum (-53.65% vs. non-IAS, P < 0.01) and RA (-61.39% vs. non-IAS, P < 0.01) were decreased. Serum IL-6 level of the IAS group was significantly higher compared to non-IAS patients (+5.82-fold vs. non-IAS, P = 0.01), and muscle cross-sectional area (MCSA) was markedly reduced compared to non-IAS patients (-27.73% vs. non-IAS, P < 0.01). In animal experiments, IDO-1 expression was up-regulated in the small intestine, colon and blood for CLP or LPS-treated mice, and there was correlation (R2 = 0.66, P < 0.01) between serum and muscle kynurenine concentrations. Navoximod significantly mitigated IAS-induced skeletal muscle loss according to MCSA analysis (+22.94% vs. CLP, P < 0.05; +23.71% vs. LPS, P < 0.01) and increased the phosphorylated AKT (+2.15-fold vs. CLP, P < 0.01; +3.44-fold vs. LPS, P < 0.01) and myosin heavy chain (+3.64-fold vs. CLP, P < 0.01; +2.13-fold vs. LPS, P < 0.01) protein expression in myocytes. In the presence of anti-IL-6 antibody, a significantly decreased IDO-1 expression was observed in the small intestine, colon and blood in CLP or LPS mice (all P < 0.01), whereas the decrease of MCSA was alleviated (+37.43% vs. CLP + IgG, P < 0.001; +30.72% vs. LPS + IgG, P < 0.001). In contrast, additional supplementation of kynurenine decreased the MCSA in septic mice treated with IL-6-AB (both P < 0.01).
This study provided novel insights into the tryptophan-IDO-1-kynurenine-dependent mechanisms that underlie inflammatory cytokine-induced skeletal muscle catabolism during intra-abdominal sepsis.
Serum and rectus abdominis (RA) were obtained from IAS or non-IAS patients. Mouse model of IAS-induced muscle wasting was generated by caecal ligation and puncture (CLP) and lipopolysaccharide (LPS) injection. IL-6 signalling was blocked by anti-mouse IL-6 antibody (IL-6-AB), and the IDO-1 pathway was blocked by navoximod. To elucidate the role of kynurenine in muscle mass and physiology, kynurenine was administered to IAS mice treated with IL-6-AB.
Compared to non-IAS patients, kynurenine levels in serum (+2.30-fold vs. non-IAS, P < 0.001) and RA (+3.11-fold vs. non-IAS, P < 0.001) were elevated, whereas tryptophan levels in serum (-53.65% vs. non-IAS, P < 0.01) and RA (-61.39% vs. non-IAS, P < 0.01) were decreased. Serum IL-6 level of the IAS group was significantly higher compared to non-IAS patients (+5.82-fold vs. non-IAS, P = 0.01), and muscle cross-sectional area (MCSA) was markedly reduced compared to non-IAS patients (-27.73% vs. non-IAS, P < 0.01). In animal experiments, IDO-1 expression was up-regulated in the small intestine, colon and blood for CLP or LPS-treated mice, and there was correlation (R2 = 0.66, P < 0.01) between serum and muscle kynurenine concentrations. Navoximod significantly mitigated IAS-induced skeletal muscle loss according to MCSA analysis (+22.94% vs. CLP, P < 0.05; +23.71% vs. LPS, P < 0.01) and increased the phosphorylated AKT (+2.15-fold vs. CLP, P < 0.01; +3.44-fold vs. LPS, P < 0.01) and myosin heavy chain (+3.64-fold vs. CLP, P < 0.01; +2.13-fold vs. LPS, P < 0.01) protein expression in myocytes. In the presence of anti-IL-6 antibody, a significantly decreased IDO-1 expression was observed in the small intestine, colon and blood in CLP or LPS mice (all P < 0.01), whereas the decrease of MCSA was alleviated (+37.43% vs. CLP + IgG, P < 0.001; +30.72% vs. LPS + IgG, P < 0.001). In contrast, additional supplementation of kynurenine decreased the MCSA in septic mice treated with IL-6-AB (both P < 0.01).
This study provided novel insights into the tryptophan-IDO-1-kynurenine-dependent mechanisms that underlie inflammatory cytokine-induced skeletal muscle catabolism during intra-abdominal sepsis.
摘要：
背景：炎症细胞因子白细胞介素-6（IL-6）在腹内脓毒症（IAS）后骨骼肌降解中起关键作用，机制尚待阐明。吲哚胺2,3-双加氧酶1（IDO-1），将色氨酸转化为犬尿氨酸的关键酶，可以被IL-6激活，犬尿氨酸已被证明参与肌肉降解。我们假设IL-6可以通过色氨酸-IDO-1-犬尿氨酸途径促进IAS患者的肌肉降解。
方法：从IAS或非IAS患者获得血清和腹直肌（RA）。通过盲肠结扎和穿刺（CLP）和脂多糖（LPS）注射产生IAS诱导的肌肉消耗的小鼠模型。IL-6信号传导被抗小鼠IL-6抗体（IL-6-AB）阻断，IDO-1通路被纳伏莫德阻断。为了阐明犬尿氨酸在肌肉质量和生理学中的作用，将犬尿氨酸给予用IL-6-AB处理的IAS小鼠。
结果：与非IAS患者相比，血清犬尿氨酸水平（+2.30倍vs.非国际会计准则，P<0.001）和RA（+3.11倍vs.非国际会计准则，P<0.001）升高，而血清中的色氨酸水平(-53.65%vs.非国际会计准则，P<0.01）和RA（-61.39%vs.非国际会计准则，P<0.01)均下降。与非IAS患者相比，IAS组的血清IL-6水平显着升高（+5.82倍vs.非国际会计准则，P=0.01),与非IAS患者相比，肌肉横截面积（-27.73%vs.非国际会计准则，P<0.01)。在动物实验中,IDO-1在小肠中表达上调,CLP或LPS处理小鼠的结肠和血液，血清和肌肉犬尿氨酸浓度之间存在相关性（R2=0.66，P<0.01）。根据MCSA分析，纳伏莫德可显着减轻IAS诱导的骨骼肌损失（+22.94％vs.CLP,P<0.05;+23.71%vs.LPS,P<0.01）并增加磷酸化AKT（2.15倍vs.CLP,P<0.01;+3.44倍vs.LPS,P<0.01）和肌球蛋白重链（+3.64倍vs.CLP,P<0.01;+2.13倍vs.LPS,肌细胞中P<0.01)蛋白表达。在抗IL-6抗体的存在下，在小肠中观察到IDO-1表达显着降低，CLP或LPS小鼠的结肠和血液（均P<0.01），而MCSA的下降得到缓解(+37.43%vs.CLP+IgG,P<0.001;+30.72%vs.LPS+IgG,P<0.001)。相比之下,额外补充犬尿氨酸可降低IL-6-AB治疗的脓毒症小鼠的MCSA（均P<0.01）。
结论：这项研究提供了新的见解，揭示了色氨酸-IDO-1-犬尿氨酸依赖的机制，这些机制是腹腔内脓毒症时炎性细胞因子诱导的骨骼肌分解代谢的基础。
方法：从IAS或非IAS患者获得血清和腹直肌（RA）。通过盲肠结扎和穿刺（CLP）和脂多糖（LPS）注射产生IAS诱导的肌肉消耗的小鼠模型。IL-6信号传导被抗小鼠IL-6抗体（IL-6-AB）阻断，IDO-1通路被纳伏莫德阻断。为了阐明犬尿氨酸在肌肉质量和生理学中的作用，将犬尿氨酸给予用IL-6-AB处理的IAS小鼠。
结果：与非IAS患者相比，血清犬尿氨酸水平（+2.30倍vs.非国际会计准则，P<0.001）和RA（+3.11倍vs.非国际会计准则，P<0.001）升高，而血清中的色氨酸水平(-53.65%vs.非国际会计准则，P<0.01）和RA（-61.39%vs.非国际会计准则，P<0.01)均下降。与非IAS患者相比，IAS组的血清IL-6水平显着升高（+5.82倍vs.非国际会计准则，P=0.01),与非IAS患者相比，肌肉横截面积（-27.73%vs.非国际会计准则，P<0.01)。在动物实验中,IDO-1在小肠中表达上调,CLP或LPS处理小鼠的结肠和血液，血清和肌肉犬尿氨酸浓度之间存在相关性（R2=0.66，P<0.01）。根据MCSA分析，纳伏莫德可显着减轻IAS诱导的骨骼肌损失（+22.94％vs.CLP,P<0.05;+23.71%vs.LPS,P<0.01）并增加磷酸化AKT（2.15倍vs.CLP,P<0.01;+3.44倍vs.LPS,P<0.01）和肌球蛋白重链（+3.64倍vs.CLP,P<0.01;+2.13倍vs.LPS,肌细胞中P<0.01)蛋白表达。在抗IL-6抗体的存在下，在小肠中观察到IDO-1表达显着降低，CLP或LPS小鼠的结肠和血液（均P<0.01），而MCSA的下降得到缓解(+37.43%vs.CLP+IgG,P<0.001;+30.72%vs.LPS+IgG,P<0.001)。相比之下,额外补充犬尿氨酸可降低IL-6-AB治疗的脓毒症小鼠的MCSA（均P<0.01）。
结论：这项研究提供了新的见解，揭示了色氨酸-IDO-1-犬尿氨酸依赖的机制，这些机制是腹腔内脓毒症时炎性细胞因子诱导的骨骼肌分解代谢的基础。
