Baviera Amanda Martins, Zanon Neusa Maria, Carvalho Navegantes Luiz Carlos, Migliorini Renato Hélios, do Carmo Kettelhut Isis
Department of Biochemistry and Immunology, School of Medicine, USP, 14049-900 Ribeirão Preto, São Paulo, Brazil.
Am J Physiol Endocrinol Metab. 2007 Mar;292(3):E702-8. doi: 10.1152/ajpendo.00147.2006. Epub 2006 Oct 31.
Previous studies from this laboratory have shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cAMP cascade. The present work investigated the systemic effect of pentoxifylline (PTX; cAMP-phosphodiesterase inhibitor) treatment on the rate of overall proteolysis, the activity of proteolytic systems, and the process of protein synthesis in extensor digitorum longus muscles from normal and acutely diabetic rats. The direct in vitro effect of this drug on the rates of muscle protein degradation was also investigated. Muscles from diabetic rats treated with PTX showed an increase (22%) in the cAMP content and reduction in total rates of protein breakdown and in activity of Ca2+-dependent (47%) and ATP proteasome-dependent (23%) proteolytic pathways. The high content of m-calpain observed in muscles from diabetic rats was abolished by PTX treatment. The addition of PTX (10(-3) M) to the incubation medium increased the cAMP content in muscles from normal (22%) and diabetic (51%) rats and induced a reduction in the rates of overall proteolysis that was accompanied by decreased activity of the Ca2+-dependent and ATP proteasome-dependent proteolytic systems, in both groups. The in vitro addition of H-89, an inhibitor of protein kinase A (PKA), completely blocked the effect of PTX on the reduction of proteolysis in muscles from normal and diabetic rats. The present data suggest that PTX exerts a direct inhibitory effect on protein degradative systems in muscles from acutely diabetic rats, probably involving the participation of cAMP intracellular pathways and activation of PKA, independently of tumor necrosis factor-alpha inhibition.
本实验室先前的研究表明，儿茶酚胺通过涉及环磷酸腺苷（cAMP）级联反应的途径对肌肉蛋白质降解发挥抑制作用。本研究调查了己酮可可碱（PTX；一种cAMP磷酸二酯酶抑制剂）处理对正常和急性糖尿病大鼠趾长伸肌中整体蛋白水解速率、蛋白水解系统活性及蛋白质合成过程的全身影响。还研究了该药物对肌肉蛋白质降解速率的直接体外作用。用PTX处理的糖尿病大鼠的肌肉，其cAMP含量增加（22%），蛋白质分解总速率以及钙离子依赖性（47%）和ATP蛋白酶体依赖性（23%）蛋白水解途径的活性降低。PTX处理消除了糖尿病大鼠肌肉中观察到的高含量m-钙蛋白酶。向孵育培养基中添加PTX（10⁻³ M）可增加正常（22%）和糖尿病（51%）大鼠肌肉中的cAMP含量，并导致两组整体蛋白水解速率降低，同时伴随着钙离子依赖性和ATP蛋白酶体依赖性蛋白水解系统活性下降。在体外添加蛋白激酶A（PKA）抑制剂H-89可完全阻断PTX对正常和糖尿病大鼠肌肉中蛋白水解减少的作用。目前的数据表明，PTX对急性糖尿病大鼠肌肉中的蛋白质降解系统具有直接抑制作用，可能涉及cAMP细胞内途径的参与和PKA的激活，与肿瘤坏死因子-α抑制无关。
