Supplemental Ascorbate Diminishes DNA Damage Yet Depletes Glutathione and Increases Acute Liver Failure in a Mouse Model of Hepatic Antioxidant System Disruption.

Colin G Miller,David J Orlicky,Julie A Amato,Jean A Kundert,Edward E Schmidt,Gabrielle N Rizzo,Colin T Shearn,Allison E Perez,Lucia Coppo,Justin R Prigge,Michael P Kavanaugh

doi:10.3390/antiox10030359

Abstract

Cellular oxidants are primarily managed by the thioredoxin reductase-1 (TrxR1)- and glutathione reductase (Gsr)-driven antioxidant systems. In mice having hepatocyte-specific co-disruption of TrxR1 and Gsr (TrxR1/Gsr-null livers), methionine catabolism sustains hepatic levels of reduced glutathione (GSH). Although most mice with TrxR1/Gsr-null livers exhibit long-term survival, ~25% die from spontaneous liver failure between 4- and 7-weeks of age. Here we tested whether liver failure was ameliorated by ascorbate supplementation. Following ascorbate, dehydroascorbate, or mock treatment, we assessed survival, liver histology, or hepatic redox markers including GSH and GSSG, redox enzyme activities, and oxidative damage markers. Unexpectedly, rather than providing protection, ascorbate (5 mg/mL, drinking water) increased the death-rate to 43%. In adults, ascorbate (4 mg/g × 3 days i.p.) caused hepatocyte necrosis and loss of hepatic GSH in TrxR1/Gsr-null livers but not in wildtype controls. Dehydroascorbate (0.3 mg/g i.p.) also depleted hepatic GSH in TrxR1/Gsr-null livers, whereas GSH levels were not significantly affected by either treatment in wildtype livers. Curiously, however, despite depleting GSH, ascorbate treatment diminished basal DNA damage and oxidative stress markers in TrxR1/Gsr-null livers. This suggests that, although ascorbate supplementation can prevent oxidative damage, it also can deplete GSH and compromise already stressed livers.

Highlights

Mice with thioredoxin reductase-1 (TrxR1)/Gsr-null livers are born at expected Mendelian frequencies; a portion of the animals of both sexes die of spontaneous acute liver failure between postnatal
Mice with TrxR1/Gsr-null livers are born at expected Mendelian frequencies; a portion of the animals of both sexes die of spontaneous acute liver failure between postnatal days 28–49 (P28–49), and animals surviving to P50 thereafter exhibit survival curves past days 28–49 (P28–49), and animals surviving to P50 thereafter exhibit survival curves past
Adult TrxR1/Gsrnull livers exhibit accumulation of damaged protein and DNA, high hepatocyte death innull livers exhibit accumulation of damaged protein and DNA, high hepatocyte death dexes, and hyperproliferation [23,24]. It is not yet clear why liver failure is reindexes, and hyperproliferation [23,24]. It is not yet clear why liver failure is stricted to the three-week window of age from P28–49, the association with oxidative restricted to the three-week window of age from P28–49, the association with oxidative damage led us to hypothesize that liver failure results when individuals exceed a threshdamage led us to hypothesize that liver failure results when individuals exceed a threshold old of hepatocyte oxidative stress-induced cell death that becomes incompatible with liver of hepatocyte oxidative stress-induced cell death that becomes incompatible with liver survival and function

Summary

Introduction

Oxidative stress is defined as a substantial deviation from normal cellular redox steady state [1]. Cells generate reactive oxygen species (ROS) as a byproduct of cellular respiration and metabolism or in response to external factors such as xenobiotic exposure, radiation, or environmental pollution [2]. Inflammation exposes surrounding cells and tissues to high levels of ROS. Hydrogen peroxide (H2 O2 ), the major cellular oxidant, is generated from superoxide (O2 − ) both spontaneously and catalytically by superoxide dismutases [3]. Superoxide is produced primarily by the mitochondria as a byproduct of cellular respiration

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