Aging of the Liver: Age–Associated Mitochondrial Damage in Intact Hepatocytes

Abstract

activated species.3 It is well known that fixed, postmitotic Mitochondrial damage may be a major cause of cellucells accumulate different age pigments, especially lipofuscin. lar aging. So far, this hypothesis had only been tested A considerable amount of this pigment may derive from inusing isolated mitochondria. The aim of this study was jured mitochondria. 4 This led us to propose a hypothesis 5 of to investigate the involvement of mitochondria in aging cell aging, according to which senescence is a by-product of using whole liver cells and not isolated mitochondria oxy-radical attack to the mitochondrial genome. only. Using flow cytometry, we found that age is associRecently, several studies have shown changes in mitochonated with a decrease in mitochondrial membrane potendria on aging. Age-related changes in mitochondrial respiratial (30%), an increase in mitochondrial size, and an intory function and in mitochondrial transport systems have crease in mitochondrial peroxide generation (23%).been reported. [6][7][8] All these changes were found in experiments Intracellular peroxide levels were also increased. The using isolated mitochondria. However, these effects could be number of mitochondria per cell and inner mitochoncaused by altered susceptibility of old mitochondria to the drial membrane mass did not change. Gluconeogenesis stress caused by the isolation procedure. Moreover, because from glycerol or fructose (mitochondrial-independent) intact cells were not used, the mitochondrial-cytosolic interdid not change with age, whereas it did from lactate actions were also ignored. This may lead to errors. The iso-(mitochondrial-dependent). The change in the rate of lated hepatocyte is an excellent model for aging studies. 9 This gluconeogenesis was not accompanied by changes in is especially useful when attempting to study aging at the any of the following parameters: phosphoenolpyruvate cellular level, using whole cells. carboxykinase or pyruvate carboxylase activities or miTo our knowledge, no attempts have been made to correlate tochondrial ATP/ADP or cytosolic NADH/NAD / ratios. age-associated changes in physiological functions of intact This was caused by a decreased rate of malate export cells with specific biochemical or molecular changes in mito-(to 20% of the controls) from mitochondria. The impairchondria. The aim of this study was to test whether mitochonment of the mitochondrial malate transporter is postdrial performance is impaired with aging, using intact liver transcriptional because its expression in Xenopus oocells. To this end, we have measured the rate of biochemical cytes using polyadenylated RNA from livers of young or pathways, gluconeogenesis, and ketogenesis, which critically old animals did not change. Ketogenesis from oleate also depend on mitochondrial function. In addition, we have used fell in hepatocytes from old rats. Our results show, for flow cytometry, which allows a noninvasive analysis of indithe first time in intact cells, a correlation between agevidual cells, to study ...

Acetyl-L-carnitine treatment stimulates oxygen consumption and biosynthetic function in perfused liver of young and old rats

“…Despite the utilisation of different metabolic pathways by the two substrates, gluconeogenesis and oxygen consumption fell in old compared to young rats. The last result is partially in agreement with Sastre et al [1] who found, in isolated hepatocytes, a decrease with age only in gluconeogenesis from lactate + pyruvate. Age-related declines in the activity of phosphoenolpyruvate carboxykinase [30,31], considered the rate-limiting enzyme of gluconeogenesis from lactate [1], are consistent with our results.…”

“…The effect of ALCAR on gluconeogenesis from lactate + pyruvate could be explained as follows. The lower rate of gluconeogenesis from lactate + pyruvate has been reported as due to an impaired transport of malate across the mitochondrial membrane using the dicarboxylate carrier [1] and this impairment is associated with a concomitant decrease in mitochondrial cardiolipin content [25]. Therefore, ALCAR treatment, by increasing the Research Article cardiolipin concentration [25], would positively influence the activity of protein carriers.…”

AZT treatment induces molecular and ultrastructural oxidative damage to muscle mitochondria. Prevention by antioxidant vitamins.

“…Thus, mitochondria will not be properly renewed in the cell, and old mitochondria will remain in the cell. We have found that mitochondria from old animals produce more peroxides than those from young ones and suffer from oxidative stress (28). In any case, oxidative stress directly or indirectly contributes to mtDNA damage caused by AZT, and treatment with antioxidant vitamins prevents such mt damage.…”

“…The mt membrane potential is the driving force for rhodamine 123 uptake by mitochondria (26). This reduced rhodamine has been used to monitor reactive oxygen intermediates in different cellular and subcellular models (27,28).…”

Mitochondria and aging: A role for the mitochondrial transition pore?

“…Several studies have shown that the mitochondrial membrane potential is lower in aged cells (Sastre et al., 1996; Sugrue & Tatton, 2001). This may have consequences on mPTP opening as mPTP is a voltage‐dependent channel which tends to open upon depolarization (Figure 1).…”