Development and Age-associated Differences in Electron Transport Potential and Consequences for Oxidant Generation

Abstract

We determined the activities of NADH dehydrogenase (ND), succinate dehydrogenase, and cytochrome c oxidase (COX) in 29 skin fibroblast lines established from donors ranging in age from 12 gestational weeks to 94 years. The results of this study demonstrate that all three of the enzyme activities examined are greater in adult-derived fibroblasts than in the fetal cell lines. The ratio of enzyme activities that control electron entry into and exit from the electron transport chain varied directly with lucigenin-detected chemiluminescence (an indicator of ⅐ O 2 ؊ generation) and inversely with H 2 O 2 generation. These results indicate a clear difference in the predominant oxidant species generated during fetal and adult stages of life. We also examined the mRNA abundances of different components of the electron transport chain complexes. We observed higher abundances of mitochondrial encoded mRNAs (COX 1 and ND 4) in cell lines established from adults than in fetal cells. No differences in the mRNA abundances of the nuclear encoded sequences (COX 4 and ND 51) were observed in fetal and postnatal-derived lines. Succinate dehydrogenase mRNA abundance was greater in cell lines established from postnatal donors than in fetal cell lines. No significant differences between cell lines established from young and old adults were detected in any of the parameters examined.Mitochondria are the primary site of aerobic energy production and are thus the major site of generation of reactive oxygen species (ROS), 1 such as oxygen-centered free radicals and peroxides, which are by-products of metabolism (1-4). Estimates of the rate of ROS generation can differ greatly; however, it has been demonstrated repeatedly that the relative rate of oxidant generation increases with age and that this increase correlates strongly with age-associated changes in the cellular redox state (5-8). For example, the rates of superoxide ( ⅐ O 2 Ϫ ) (8 -14) and H 2 O 2 generation (7, 10, 14 -17) increase in the cells of aging organisms, whereas the glutathione concentration declines progressively with advancing age (5,6,18,19). Differences in ROS metabolism also exist between cells obtained from early developmental stages and from postnatal tissues (for review, see Refs. 20 and 21). The activities of enzymic antioxidant defenses tend to be lower in fetal cells than in cells derived from postnatal tissues (22-24); however, the GSH concentration is frequently greater in fetal cells than in cells from adults (20,24). Whether these observations reflect differences in the steadystate level of ROS in fetal and postnatal cells is not presently known (20, 21).The rate of mitochondrial ROS generation in cells is largely dependent on the amounts of autoxidizable respiratory carriers and the redox state of electron carriers (1,3,25,26). All electron carriers located prior to one of low abundance will exhibit a greater propensity to be chemically reduced because of the slowing of electron flux (electron stacking; 1, 16, 25, 27). Thus, either age or development-a...

Activities of cytochrome c oxidase and citrate synthase in lymphocytes of obese and normal-weight subjects

“…30 Similarly, no significant differences in the COX activity were found in fibroblast cell lines derived from patients of different age. 44 The decrease of the CS activity can reflect a decline of the matrix content of mitochondria with age, which would be consistent with results of Conley et al, 33 who found reduced mitochondrial volume density in skeletal muscle of elderly human subjects compared to adults. Our data clearly showed that the COX=CS ratio is increasing with age, thus supporting the view that the composition of mitochondrial compartments may be changing with age.…”

Gestation linked radical oxygen species fluxes and vitamins and trace mineral deficiencies in the ruminant

“…More sources of ROS have been described, such as the triggering of radical phenomena by changes in oxygen partial pressures [22,24,37,38] or synthesis of hormones [5]. ROS can also be formed after electron escape from the mitochondria of proliferating cells, favored by high rates of multiplication and metabolism and increased activity of mitochondrial superoxide dismutase (Mn-SOD) [39,40] or, in human placental mitochondria, after interaction between NADPH and iron [41].…”

“…Environmental oxygen partial pressure of living organisms is one of the basis of formation of ROS, notably at the level of placental tissue [22,24,37,38]. It has been reported that oxygen partial pressure displays positive effects on embryo development only within a narrow range and that an oxidative stress can occur, with possibly potential lethal effects, below (slowing down of ATP synthesis) or above this range (direct peroxidation of membranes due to an excess of oxygen and radical chain initiation) [37].…”

“…It has been reported that oxygen partial pressure displays positive effects on embryo development only within a narrow range and that an oxidative stress can occur, with possibly potential lethal effects, below (slowing down of ATP synthesis) or above this range (direct peroxidation of membranes due to an excess of oxygen and radical chain initiation) [37]. In vitro, deviation of the oxygen partial pressures from the normal can induce oxidative stress and end embryo-toxicity if antioxidant enzymes (AOE) or antioxidant components are not provided [28,50,51].…”

“…Several features specific to embryogenesis increase mitochondrial production of O −• 2 and H 2 O 2 , since, as opposed to the situation in the adult, an initial imbalance between enzymatic production of electrons (NAD dehydrogenase and succinate deshydrogenase), on the one hand, and the ability of the respiratory chain to use them for ATP synthesis (cytochrome oxidase), on the other hand, are seen in the fetus [37].…”