Elsevier

Experimental Gerontology

Volume 37, Issue 12, December 2002, Pages 1481-1487
Experimental Gerontology

Short Communication
Effect of age and hypoxia/reoxygenation on mRNA expression of antioxidative enzymes in rat liver and kidneys

https://doi.org/10.1016/S0531-5565(02)00168-7Get rights and content

Abstract

The influence of a short-time isobaric hypoxia as well as reoxygenation on markers of oxidative stress (MDA, total SOD, GSH) and on the mRNA expression of the antioxidative enzymes (Cu/Zn-and Mn-SOD, catalase, GSH reductase and GSH peroxidase) has been studied in liver and kidneys of young (6 months) and old (22–25 months) Wistar rats.

In livers of old animals, the concentration of GSH, the activity of SOD, and the mRNA expression of the antioxidative enzymes (except Mn-SOD) points to a restricted protection against oxidative stress or a lower production of ROS compared to young animals. Hypoxia resulted in a significant decrease of enzyme gene expression in both age groups. Reoxygenation caused an increase in mRNA of Cu/Zn-SOD and GPX in livers of young and of Mn-SOD in livers of old animals.

In kidneys, gene expression of Cu/Zn-SOD, GSH reductase, and GPX was significantly higher in old animals compared to young animals. Whereas hypoxia caused a decrease of gene expression in the livers, it lead to a significant increase of Cu/Zn-SOD, catalase, and GSH reductase mRNA in kidneys of young rats. A reduced gene expression was observed after reoxygenation. In old kidneys, the expression of all enzymes except for catalase progressively declined in the hypoxic and reoxygenation groups. These data show that gene expression of antioxidative enzymes is affected by age and significantly differs between liver and kidney.

Introduction

During lifetime the organism encounters a series of damages including those caused by radicals or reactive oxygen species (ROS: H2O2, O2radical dot, OHradical dot,NOradical dot).

In the ‘Free Radical Theory of Aging’, the increased production of superoxide radicals and H2O2 as major causes of aging has been discussed in addition to changes in the defense mechanisms and decreased formation of ATP (Harman, 1994).

Hitherto, reports concerning age-dependent changes of parameters of oxidative stress are partly divergent due to different methodology, species, organs, and parameters studied (Amicarelli et al., 1997, Azhar et al., 1995, De and Darad, 1991, De la Asuncion et al., 1996, Dogru-Abbasoglu et al., 1997, Ji, 1993, Rao et al., 1990, Rikans et al., 1992, Sanz et al., 1997, Sohal et al., 1995, Tian et al., 1998).

There are also conflicting data with respect to the influence of hypoxia on these parameters and on radical release, due to different hypoxia times and varying O2 pressures applied. Few publications can be found on the effect of age on mRNA expression of antioxidative enzymes and particularly the effect of hypoxia and reoxygenation on the expression of these genes (Amicarelli et al., 1997, Azhar et al., 1995, Dobashi et al., 2000, Gasbarrini et al., 1998, Rao et al., 1990, Rikans et al., 1992).

The aim of the present work was therefore to study the effect of age and of a short-time isobaric hypoxia and reoxygenation on MDA as an indicator for lipid peroxidation and on two antioxidative markers (total SOD activity and GSH) in rat livers and kidneys. In addition, we have investigated the cellular response on the gene level by determining mRNA expression of different antioxidative enzymes.

Section snippets

Treatment of animals

Male Wistar rats of two age groups (6 and 22–25 months) were maintained under standard conditions (a daily schedule of 12 h light and 12 h darkness, food and water ad libitum). Hypoxia was induced by down regulating the environmental O2 pressure to 5–6 vol.% within 25 min before sacrificing. Reoxygenation with atmospheric O2 pressure was performed within 4.5 h. Animals were treated according to the national standards for humane care of animals and the study was approved by the Regierungspräsidium

Parameters of oxidative stress

Table 1 presents the results of parameters of oxidative stress in liver and kidneys. The activity of total SOD and the GSH content were significantly higher in the liver of young rats than in old ones. Unexpectedly, the concentration of MDA was significantly increased in the liver of the young control group compared to the old one.

Hypoxia resulted in a significant rise of MDA in young hypoxic livers and in a decrease of SOD in young hypoxic and reoxygenation groups, whereas SOD showed a rise in

Discussion

In general, a higher oxidative stress caused by either increased ROS generation or restricted antioxidative defense mechanisms is discussed in aging (Harman, 1994). The significantly lower SOD activity and GSH content in livers as well as kidneys of old animals and the significantly higher MDA concentration in kidneys of old rats (Table 1) confirm this assumption and are in agreement with other authors (Azhar et al., 1995, De and Darad, 1991, De la Asuncion et al., 1996, Rao et al., 1990, Tian

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