Fleck Rochele M Müller, Rodrigues Junior Valnes, Giacomazzi Juliana, Parissoto Daiana, Dutra-Filho Carlos Severo, de Souza Wyse Angela Terezinha, Wajner Moacir, Wannmacher Clovis Milton Duval
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600 - Anexo, CEP 90.035-003 Porto Alegre, RS, Brazil.
Neurochem Int. 2005 Apr;46(5):391-7. doi: 10.1016/j.neuint.2004.11.008.
Cystinosis is a disorder associated with lysosomal cystine accumulation caused by defective cystine efflux. Cystine accumulation provokes a variable degree of symptoms depending on the involved tissues. Adult patients may present brain cortical atrophy. However, the mechanisms by which cystine is toxic to the tissues are not fully understood. Considering that brain damage may be developed by energy deficiency, creatine kinase is a thiolic enzyme crucial for energy homeostasis, and disulfides like cystine may alter thiolic enzymes by thiol/disulfide exchange, the main objective of the present study was to investigate the effect of cystine on creatine kinase activity in total homogenate, cytosolic and mitochondrial fractions of the brain cortex from 21-day-old Wistar rats. We performed kinetic studies and investigated the effects of GSH, a biologically occurring thiol group protector, and cysteamine, the drug used for cystinosis treatment, to better understand the effect of cystine on creatine kinase activity. Results showed that cystine inhibited the enzyme activity non-competitively in a dose- and time-dependent way. GSH partially prevented and reversed CK inhibition caused by cystine and cysteamine fully prevented and reversed this inhibition, suggesting that cystine inhibits creatine kinase activity by interaction with the sulfhydryl groups of the enzyme. Considering that creatine kinase is a crucial enzyme for brain cortex energy homeostasis, these results provide a possible mechanism for cystine toxicity and also a new possible beneficial effect for the use of cysteamine in cystinotic patients.
胱氨酸病是一种与溶酶体胱氨酸蓄积相关的疾病，由胱氨酸外排缺陷引起。根据受累组织的不同，胱氨酸蓄积会引发不同程度的症状。成年患者可能出现脑皮质萎缩。然而，胱氨酸对组织产生毒性的机制尚未完全明确。鉴于能量缺乏可能导致脑损伤，肌酸激酶是一种对能量稳态至关重要的硫醇酶，而胱氨酸等二硫化物可能通过硫醇/二硫化物交换改变硫醇酶，本研究的主要目的是探讨胱氨酸对21日龄Wistar大鼠大脑皮质总匀浆、胞质和线粒体部分中肌酸激酶活性的影响。我们进行了动力学研究，并研究了生物体内存在的硫醇基团保护剂谷胱甘肽（GSH）以及用于治疗胱氨酸病的药物半胱胺的作用，以更好地了解胱氨酸对肌酸激酶活性的影响。结果表明，胱氨酸以剂量和时间依赖性方式非竞争性抑制该酶活性。谷胱甘肽部分预防并逆转了胱氨酸引起的肌酸激酶抑制，半胱胺则完全预防并逆转了这种抑制，这表明胱氨酸通过与该酶的巯基相互作用来抑制肌酸激酶活性。鉴于肌酸激酶是大脑皮质能量稳态的关键酶，这些结果为胱氨酸毒性提供了一种可能的机制，也为半胱胺在胱氨酸病患者中的使用提供了一种新的可能的有益作用。
