Han Derick, Matsumaru Katsu, Rettori Daniel, Kaplowitz Neil
USC-UCLA Research Center for Alcoholic and Pancreatic Disease and University of Southern California Research Center for Liver Diseases, Keck School of Medicine, University of Southern California, 2011 Zonal Avenue, HMR 101, Los Angeles, CA 90089-9121, USA.
Biochem Pharmacol. 2004 Feb 1;67(3):439-51. doi: 10.1016/j.bcp.2003.09.032.
Usnic acid, a lichen acid, is a compound found in crude medicines and dietary supplements, including Lipokinetix, a supplement marketed as a weight loss agent that caused hepatotoxicity and acute liver failure in patients. In this study, we examined the toxicity of usnic acid and assessed whether usnic acid may be contributing to hepatotoxicity caused by Lipokinetix. In primary cultured murine hepatocytes, usnic acid treatment (5 microM) resulted in 98% necrosis within 16 hr (no apoptosis was detected). Usnic acid treatment was associated with early inhibition and uncoupling of the electron transport chain in mitochondria of cultured hepatocytes. This inhibition of mitochondria by usnic acid corresponded with a fall in ATP levels in hepatocytes. In isolated liver mitochondria, usnic acid was observed to directly inhibit and uncouple oxidative phosphorylation. Oxidative stress appears to be central in usnic acid-induced hepatotoxicity based on the following findings: (1) pretreatment with antioxidants (butylated hydroxytoluene+Vitamin E) decreased usnic acid-induced necrosis by nearly 70%; (2) depletion of mitochondrial GSH with diethylmaleate increased susceptibility of hepatocytes to usnic acid; (3) usnic acid treatment was associated with increase free radical generation, measured using the fluorescent probe, dichlorodihydrofluorescin. The source of reactive oxygen species after usnic acid treatment include autoxidation of usnic acid and increased hydrogen peroxide generation by mitochondria caused by usnic acid inhibition of the respiratory chain, with the latter playing a more prominent role. Taken together, our results suggest that usnic acid is a strong hepatotoxic agent that triggers oxidative stress and disrupts the normal metabolic processes of cells. Usnic acid therefore may contribute to the hepatotoxic effects of Lipokinetix and its use in any supplement must come into question.
松萝酸是一种地衣酸，是一种存在于草药和膳食补充剂中的化合物，包括Lipokinetix，一种作为减肥剂销售的补充剂，曾导致患者肝毒性和急性肝衰竭。在本研究中，我们检测了松萝酸的毒性，并评估松萝酸是否可能导致Lipokinetix引起的肝毒性。在原代培养的小鼠肝细胞中，松萝酸处理（5微摩尔）在16小时内导致98%的坏死（未检测到凋亡）。松萝酸处理与培养肝细胞线粒体中电子传递链的早期抑制和解偶联有关。松萝酸对线粒体的这种抑制与肝细胞中ATP水平的下降相对应。在分离的肝线粒体中，观察到松萝酸直接抑制并解偶联氧化磷酸化。基于以下发现，氧化应激似乎是松萝酸诱导肝毒性的核心：（1）用抗氧化剂（丁基羟基甲苯+维生素E）预处理可使松萝酸诱导的坏死减少近70%；（2）用马来酸二乙酯消耗线粒体谷胱甘肽会增加肝细胞对松萝酸的敏感性；（3）松萝酸处理与使用荧光探针二氯二氢荧光素测量的自由基生成增加有关。松萝酸处理后活性氧的来源包括松萝酸的自氧化以及松萝酸抑制呼吸链导致线粒体产生过氧化氢增加，后者起更突出的作用。综上所述，我们的结果表明松萝酸是一种强效肝毒性剂，可引发氧化应激并破坏细胞的正常代谢过程。因此，松萝酸可能导致Lipokinetix的肝毒性作用，其在任何补充剂中的使用都必须受到质疑。
