Chronic free-choice drinking in crossed HAP (cHAP) mice leads to sustained blood ethanol levels and metabolic tolerance without evidence of liver damage

Abstract

Background: Crossed High Alcohol Preferring (cHAP) mice were selectively bred from a cross of the HAP1xHAP2 replicate lines, and demonstrate blood ethanol concentrations (BECs) during free-choice drinking that are reminiscent of those observed in alcohol-dependent humans. Therefore, this line may provide an unprecedented opportunity to learn about the consequences of excessive voluntary ethanol consumption, including metabolic tolerance and liver pathology. Cytochrome p450 2E1 (CYP 2E1) induction plays a prominent role in driving both metabolic tolerance and ethanol-induced liver injury. In this report, we sought to characterize cHAP drinking by assessing whether pharmacologically relevant BEC levels are sustained throughout the active portion of the light-dark cycle. Given that cHAP intakes and BECs are similar to those observed in mice given an ethanol liquid diet, we assessed whether free-choice exposure results in metabolic tolerance, hepatic enzyme induction, and hepatic steatosis.

Methods: In Experiment 1, blood samples were taken across the dark portion of a 12:12 light-dark cycle to examine the pattern of ethanol accumulation in these mice. In Experiments 1 and 2, mice were injected with ethanol following 3–4 weeks of access to water or 10% ethanol and water, and blood samples were taken to assess metabolic tolerance. In Experiment 3, 24 mice had 4 weeks access to 10% ethanol and water or water alone, followed by necropsy and hepatological assessment.

Results: In experiment 1, cHAP mice mean BEC values exceeded 80 mg/dl at all sampling points, and approached 200 mg/dl during the middle of the dark cycle. In experiments 1 and 2, ethanol-exposed mice metabolized ethanol faster than ethanol-naïve mice, demonstrating metabolic tolerance (p < .05). In experiment 3, ethanol-drinking mice showed greater expression of hepatic CYP 2E1 than water controls, consistent with the development of metabolic tolerance (p < .05). Ethanol access altered neither hepatic histology nor levels of ADH and ALDH.

Conclusions: These results demonstrate that excessive intake by cHAP mice results in sustained BECs throughout the active period, leading to the development of metabolic tolerance and evidence of CYP 2E1 induction. Together these results provide additional support for the cHAP mice as a highly translational rodent model of alcoholism.