Oxidative Stress and the ER Stress Response in a Murine Model for Early-Stage Alcoholic Liver Disease

Abstract

Alcoholic liver disease (ALD) is a primary cause of morbidity and mortality in the United States and constitutes a significant socioeconomic burden. Previous work has implicated oxidative stress and endoplasmic reticulum (ER) stress in the etiology of ALD; however, the complex and interrelated nature of these cellular responses presently confounds our understanding of ethanol-induced hepatopathy. In this paper, we assessed the pathological contribution of oxidative stress and ER stress in a time-course mouse model of early-stage ALD. Ethanol-treated mice exhibited significant hepatic panlobular steatosis and elevated plasma ALT values compared to isocaloric controls. Oxidative stress was observed in the ethanol-treated animals through a significant increase in hepatic TBARS and immunohistochemical staining of 4-HNE-modified proteins. Hepatic glutathione (GSH) levels were significantly decreased as a consequence of decreased CBS activity, increased GSH utilization, and increased protein glutathionylation. At the same time, immunoblot analysis of the PERK, IRE1α, ATF6, and SREBP pathways reveals no significant role for these UPR pathways in the etiology of hepatic steatosis associated with early-stage ALD. Collectively, our results indicate a primary pathogenic role for oxidative stress in the early initiating stages of ALD that precedes the involvement of the ER stress response.

Pathogenesis of alcoholic liver disease: Role of oxidative metabolism

“…acetaldehyde produced from ethanol metabolism enhances the levels of SREBP-1 in hepatoma cells [66] and SREBP-1 protein levels are increased in animal models of alcohol-induce hepatic fat accumulation [66,67] . The role of SREBP-1 in alcoholic steatosis has been confirmed by several studies that couple the levels of this transcription factor with the ability to promote alcoholic fat accumulation by tumor necrosis factor (TNF)-α [68] , circadian gene Per-1 [69] , early growth response (Egr)-1 [70] , epinephrine [71] and ER stress response [72] . In response to acute and chronic ethanol exposure, mitogen-activated protein kinase family members, including c-Jun N-terminal protein kinase (JNK), are activated and JNK inhibitors blunt steatosis, reducing oxidative stress and blocking SREBP-1 expression in hepatoma cells [73] .…”

Susceptibility of L-FABP−/− mice to oxidative stress in early-stage alcoholic liver

“…] mice were fed a modifi ed 45% fat-containing Lieber-DeCarli liquid diet (11)(12)(13). In the present study, mice were euthanized in the morning immediately following ad libitum feeding the previous night in order to circumvent any metabolic changes induced by fasting.…”

“…Blood ethanol concentration (BEC) was measured via head-space gas chromatography as previously described ( 12,14 ), utilizing propionaldehyde as the internal standard. Neutral lipids were extracted from whole tissue using a modifi ed 2:1 chloroform:methanol Folch extraction.…”

“…Thiobarbituric acid reactive substances (TBARS) were measured in whole-liver homogenates (200 µg) according to Hartley et al ( 15 ). GSH and GSSG were measured from whole tissue by HPLC following derivatization with 2,4-dinitrobenzene as previously described ( 12 ). Pan-GST activity was measured in whole liver homogenates according to Rinaldi et al ( 16 ).…”

PI3K-Akt-mTOR signal inhibition affects expression of genes related to endoplasmic reticulum stress

“…It provides a site for protein modification and folding as well as functions as an intracellular Ca 2+ store that plays a central role in signal transduction (Galligan et al, 2012;Pagliassotti, 2012). However, when oxidative stress, chemical toxicity, hepatic viral infections, metabolic disorders, and abuse of alcohol or drugs cause accumulation of unfolded proteins in the ER lumen and disrupt the intracellular Ca 2+ homeostasis (Lai et al, 2003;Rao et al, 2004;Schröder and Kaufman, 2005b), ER stress occurs.…”