Post-Graduate Program in Biological Sciences: Biochemistry, Institute of Basic Health Sciences (ICBS), Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil; Department of Biochemistry, ICBS, UFRGS, Porto Alegre, Rio Grande do Sul, Brazil.
Department of Biochemistry, ICBS, UFRGS, Porto Alegre, Rio Grande do Sul, Brazil.
Free Radic Biol Med. 2019 Dec;145:87-102. doi: 10.1016/j.freeradbiomed.2019.08.033. Epub 2019 Sep 7.
Skeletal muscle disuse results in myofibrillar atrophy and protein degradation, via inflammatory and oxidative stress-mediated NF-kB signaling pathway activation. Nutritional interventions, such as l-glutamine (GLN) supplementation have shown antioxidant properties and cytoprotective effects through the modulation on the 70-kDa heat shock protein (HSP70) expression. However, these GLN-mediated effects on cell signaling pathways and biochemical mechanisms that control the myofibrillar protein content degradation in muscle disuse situations are poorly known yet. This study investigated the effects of oral GLN plus l-alanine (ALA; GLN + ALA-solution) supplementation, either in their free or dipeptide (L-alanyl-l-glutamine-DIP) form, on GLN-glutathione (GSH) axis and cytoprotection mediated by HSP70 protein expression in the slow-twitch soleus and fast-twitch gastrocnemius skeletal muscle of rats submitted to 14-days of hindlimb immobilization-induced disuse muscle atrophy. Forty-eight Wistar rats were distributed into 6 groups: hindlimb immobilized (IMOB group) and hindlimb immobilized orally supplemented with either GLN (1 g kg) plus ALA (0.61 g kg) (GLN + ALA-IMOB group) or 1.49 g kg of DIP (DIP-IMOB group) and; no-immobilized (CTRL) and no-immobilized supplemented GLN + ALA and DIP baselines groups. All animals, including CTRL and IMOB rats (water), were supplemented via intragastric gavage for 14 days, concomitantly to immobilization period. Plasma and muscle GLN levels, lipid (thiobarbituric acid reactive substances-TBARS) and protein (carbonyl) peroxidation, erythrocyte concentration of reduced GSH and GSH disulfide (GSSG), plasma and muscle pro-inflammatory TNF-α levels, muscle IKKα/β-NF-kB signaling pathway and, the myofibrillar protein content (MPC) were measured. The MPC was significantly lower in IMOB rats, compared to CTRL, GLN + ALA, and DIP animals (p < 0.05). This finding was associated with reduced plasma and muscle GLN concentration, equally in IMOB animals. Conversely, both GLN + ALA and DIP supplementation restored plasma and muscle GLN levels, which equilibrated GSH and intracellular redox status (GSSG/GSH ratio) in erythrocytes and skeletal muscle even as, increased muscle HSP70 protein expression; attenuating oxidative stress and TNF-α-mediated NF-kB pathway activation, fact that reverberated on reduction of MPC degradation in GLN + ALA-IMOB and DIP-IMOB animals (p < 0.05). In conclusion, the findings shown herein support the oral GLN + ALA and DIP supplementations as a therapeutic and effective nutritional alternative to attenuate the deleterious effects of the skeletal muscle protein degradation induced by muscle disuse.
骨骼肌废用导致肌原纤维萎缩和蛋白质降解,通过炎症和氧化应激介导的 NF-κB 信号通路激活。营养干预,如 l-谷氨酰胺(GLN)补充剂,通过调节 70kDa 热休克蛋白(HSP70)的表达,显示出抗氧化和细胞保护作用。然而,这些 GLN 对细胞信号通路的影响以及控制肌肉废用情况下肌原纤维蛋白含量降解的生化机制尚不清楚。本研究探讨了口服 GLN 加 l-丙氨酸(ALA;GLN+ALA 溶液)补充剂,无论是游离形式还是二肽(L-丙氨酰-L-谷氨酰胺-DIP)形式,对 GLN-谷胱甘肽(GSH)轴和 HSP70 蛋白表达介导的细胞保护作用,在接受 14 天下肢固定诱导废用性肌肉萎缩的大鼠的慢收缩比目鱼肌和快收缩腓肠肌中。将 48 只 Wistar 大鼠分为 6 组:下肢固定(IMOB 组)和下肢固定口服补充 GLN(1g/kg)加 ALA(0.61g/kg)(GLN+ALA-IMOB 组)或 1.49g/kg 的 DIP(DIP-IMOB 组)和;非固定(CTRL)和非固定补充 GLN+ALA 和 DIP 基线组。所有动物,包括 CTRL 和 IMOB 大鼠(水),通过胃内灌胃在 14 天内同时进行补充,同时进行固定期。测量血浆和肌肉 GLN 水平、脂质(硫代巴比妥酸反应物质-TBARS)和蛋白质(羰基)过氧化、红细胞还原型 GSH 和 GSH 二硫化物(GSSG)浓度、血浆和肌肉促炎 TNF-α水平、肌肉 IKKα/β-NF-κB 信号通路和肌原纤维蛋白含量(MPC)。与 CTRL、GLN+ALA 和 DIP 动物相比,IMOB 大鼠的 MPC 明显降低(p<0.05)。这一发现与 IMOB 动物中血浆和肌肉 GLN 浓度降低有关。相反,GLN+ALA 和 DIP 补充剂均恢复了血浆和肌肉 GLN 水平,使红细胞和骨骼肌中的 GSH 和细胞内氧化还原状态(GSSG/GSH 比值)平衡,同时增加了肌肉 HSP70 蛋白表达;减轻氧化应激和 TNF-α 介导的 NF-κB 通路激活,这一事实反映在 GLN+ALA-IMOB 和 DIP-IMOB 动物中减少了 MPC 降解(p<0.05)。总之,这些发现支持口服 GLN+ALA 和 DIP 补充剂作为一种治疗和有效的营养替代物,可减轻肌肉废用引起的骨骼肌蛋白降解的有害影响。