Cao Luchuan, Leers-Sucheta Susan, Azhar Salman
Geriatric Research, Education and Clinical Center (GRECC-182 B), Department of Veterans Affairs Palo Alto Health Care System, and Department of Medicine, Stanford University School of Medicine, CA, USA.
J Steroid Biochem Mol Biol. 2004 Jan;88(1):61-7. doi: 10.1016/j.jsbmb.2003.10.007.
In aged rats, trophic hormone-stimulated testosterone secretion by isolated Leydig cells is greatly reduced. The current studies were initiated to establish a functional link between excess oxidative stress and the age-related decline in steroidogenesis. Highly purified Leydig cell preparations obtained from 5-month (young mature) and 24-month (old) Sprague-Dawley rats were employed to measure and compare levels of lipid peroxidation, non-enzymatic (alpha-tocopherol, ascorbic acid, and reduced/oxidized glutathione) and enzymatic (Cu, Zn-superoxide dismutase, Cu, Zn-SOD; Mn-superoxide dismutase, Mn-SOD; glutathione peroxidase-1, GPX-1, and catalase, CAT) anti-oxidants. The extent of lipid peroxidation (oxidative damage) in isolated membrane fractions was quantified by measuring the content of thiobarbituric acid-reactive substances (TBARS) under basal conditions, or in the presence of non-enzymatic or enzymatic pro-oxidants. Membrane preparations isolated from Leydig cells from old rats exhibited two- to three-fold enhancement of basal TBARS formation. However, aging had no significant effect on TBARS formation in response to either non-enzymatic or enzymatic pro-oxidants. Among the non-enzymatic anti-oxidants, the levels of reduced glutathione were drastically reduced during aging, while levels of alpha-tocopherol and ascorbic acid remained unchanged. Both steady-state mRNA levels and catalytic activities of Cu, Zn-SOD, Mn-SOD, and GPX-1 were also significantly lower in Leydig cells from 24-month-old rats as compared with 5-month-old control rats. In contrast, neither mRNA levels nor enzyme activity of catalase was sensitive to aging. From these data we conclude that aging is accompanied by reduced expression of key enzymatic and non-enzymatic anti-oxidants in Leydig cells leading to excessive oxidative stress and enhanced oxidative damage (lipid peroxidation). It is postulated that such excessive oxidative insult may contribute to the observed age-related decline in testosterone secretion by testicular Leydig cells.
在老年大鼠中，促性腺激素刺激下分离的睾丸间质细胞分泌睾酮的能力大幅下降。开展当前这些研究是为了在过量氧化应激与年龄相关的类固醇生成下降之间建立功能联系。使用从5个月大（年轻成熟）和24个月大（老年）的斯普拉格-道利大鼠中获得的高度纯化的睾丸间质细胞制剂，来测量和比较脂质过氧化水平、非酶抗氧化剂（α-生育酚、抗坏血酸以及还原型/氧化型谷胱甘肽）和酶抗氧化剂（铜锌超氧化物歧化酶、Cu, Zn-SOD；锰超氧化物歧化酶、Mn-SOD；谷胱甘肽过氧化物酶-1、GPX-1和过氧化氢酶、CAT）的水平。通过测量基础条件下或存在非酶或酶促促氧化剂时硫代巴比妥酸反应性物质（TBARS）的含量，来量化分离的膜组分中的脂质过氧化程度（氧化损伤）。从老年大鼠睾丸间质细胞分离得到的膜制剂显示基础TBARS形成增加了两到三倍。然而，衰老对非酶或酶促促氧化剂诱导的TBARS形成没有显著影响。在非酶抗氧化剂中，衰老过程中还原型谷胱甘肽水平急剧下降，而α-生育酚和抗坏血酸水平保持不变。与5个月大的对照大鼠相比，24个月大的大鼠睾丸间质细胞中Cu, Zn-SOD、Mn-SOD和GPX-1的稳态mRNA水平和催化活性也显著降低。相比之下，过氧化氢酶的mRNA水平和酶活性对衰老均不敏感。从这些数据我们得出结论，衰老伴随着睾丸间质细胞中关键酶抗氧化剂和非酶抗氧化剂表达的降低，导致过度的氧化应激和增强的氧化损伤（脂质过氧化）。据推测，这种过度的氧化损伤可能导致观察到的睾丸间质细胞睾酮分泌随年龄下降。
