Date Published: January 19, 2017
Publisher: Public Library of Science
Author(s): Wanxia Gao, Jie Zhao, Zhonghong Gao, Hailing Li, Jia Luo.
It is well known that iron overload promotes alcoholic liver injury, but the doses of iron or alcohol used in studies are usually able to induce liver injury independently. Little attention has been paid to the coexistence of low alcohol consumption and mild iron overload when either of them is insufficient to cause obvious liver damage, although this situation is very common among some people. We studied the interactive effects and the underlining mechanism of mild doses of iron and alcohol on liver injury in a mouse model. Forty eight male Kunming mice were randomly divided into four groups: control, iron (300 mg/kg iron dextran, i.p.), alcohol (2 g/kg/day ethanol for four weeks i.g.), and iron plus alcohol group. After 4 weeks of treatment, mice were sacrificed and blood and livers were collected for biochemical analysis. Protein nitration level in liver tissue was determined by immunoprecipitation and Western blot analysis. Although neither iron overload nor alcohol consumption at our tested doses can cause severe liver injury, it was found that co-administration of the same doses of alcohol and iron resulted in liver injury and hepatic dysfunction, accompanied with elevated ratio of NADH/NAD+, reduced antioxidant ability, increased oxidative stress, and subsequent elevated protein nitration level. Further study revealed that triosephosphate isomerase, an important glycolytic enzyme, was one of the targets to be oxidized and nitrated, which was responsible for its inactivation. These data indicate that even under low alcohol intake, a certain amount of iron overload can cause significant liver oxidative damage, and the modification of triosephosphate isomerasemight be the important underlining mechanism of hepatic dysfunction.
Alcohol consumption is prevalent in societies and long-term alcohol consumption leads to alcoholic liver disease ranging from initial steatosis to cirrhosis. The pathogenesis of alcoholic liver disease is a sophisticated process and iron is thought to play a key role in the progression of alcoholic liver disease . Iron is an essential trace element, which is very important in living body. However, excessive iron and alcohol are associated with higher risk of liver disease and hepatocellular carcinoma . Interactions between moderate levels of alcohol and iron are of great medical importance. With the improvement of living standards, alcohol consumption often accompanies with iron overload in modern life. Firstly, alcohol is one of the most frequently abused substances by humans, and age-associated iron accumulation was found in various tissues . Secondly, the process of alcohol consumption is always accompaniedwith eating lots of red meat, which contains large amount of easily absorbed form of iron, leading to higher risk of iron overload.
There are many animal models to study the synergistic effect of iron and alcohol. Simultaneous administration of iron and large dosage ethanol to establish rat models of hepatic fibrosis or cirrhosis has been reported [27, 28]. Tan et al. found mild iron overload could enhance alcoholand obesityinduced liver injury in mice . In this study, we established the animal model specifically using mild levels of iron and alcohol: one is for avoiding the additive effect of individual toxicity at high doses, and the other is for closely mimicking the physiological conditions commonly seen in some people’s daily life. Under such circumstance, we could find out whether a combination of the two safe-seeming doses is harmful. Administrating alcohol with different doses, duration and times to mice would cause different degrees of liver injury. Low dose of alcohol (2 g/kg/day) showed no histopathological difference compared with control rats . In our previous studies, we found different amount of iron (150, 300, 500 mg/kg) caused slight-to-severe rat liver injury . To embody the interaction of iron and alcohol, we specially chose 300 mg/kg iron and 2 g/kg/day alcohol to establish the animal model in the present study. Histopathology examination showed that only co-exposure group led to liver steatosis and necrosis, suggesting the liver injury is intensified by the combination use of alcohol and iron, even each separateseems to be safe.Usually, researchers used higher doses of iron or alcohol to investigate the synergic toxicities [27–29]. Our established animal model is a complement to the previous studies on the synergistic effect of iron and alcohol.