Age-related effect of aluminium on the catalase activities of the brains of two species of poikilothermic vertebrates.

BACKGROUND: Although aluminium (Al) has been implicated in various neuropathological states with aging due to its involvement in neurotoxicity, the exact role of the metal ion is still unclear. OBJECTIVE: The aim of the present study is to ascertain whether the antioxidant enzymes of the brain protecting from oxidative damages which accumulate with aging are regulated by Al in an age-dependent manner. METHOD: The inhibitory effect of Al on the catalase activity of brain homogenates of two species of poikilothermic vertebrates was studied in vitro using a spectrophotometric method. RESULTS: At a final concentration of 666 microM, the metal ion inhibited the enzyme activity of the brain in both species. In fish brain the degree of inhibition was not age-dependent. On the other hand, the rate of inhibition increased between young and middle-aged lizards followed by a decline in the old counterparts. CONCLUSION: Al inhibits catalase activity but this effect may not be a major contributing factor in the aging of the brain in the two species capable of maintaining their antioxidant capacity until old age.

Effect of age on lipid peroxides, lipofuscin and ascorbic acid contents of the lungs of male garden lizard.

Oxidative damage was assessed through the estimation of lipid peroxides (LP) in the lungs of an ageing short-lived species of reptile, Calotes versicolor, commonly known as the garden lizard. Attempts were also made to trace its relationship with the age pigment, lipofuscin and the antioxidant ascorbic acid. While LP increased with advancing age the contents of both lipofuscin and ascorbic acid did not show appreciable change during maturation ( < 1-1 year old) but declined during senescence phase (1 to 2-4 year old). While the pattern of age associated changes in LP and ascorbic acid indicate similarity with the pattern observed in most of the mammals, the reduction of lipofuscin in older lizards is a significant departure from the common trend.

Effects of age and manganese (II) chloride on peroxidase activity of brain and liver of the teleost, Channa punctatus.

Fish provide enormous spectrum of longevity and thus present the possibility of multiple mechanisms of senescence. Oxidative stress as a causative agent of senescence and the protective role of antioxidant enzymes were tested in the teleost, Channa punctatus taking peroxidase (POD) (EC 1.1 1.1.7) as the representative enzyme. The activity of POD in brain and liver declined during maturation phase (young vs middle-aged). During senescence phase (middle-aged to old) the enzyme activity increased in liver but remained stabilized in brain. The degree of increase in peroxidase activity following in vitro MnCl2 treatment was always higher in liver than in brain. The rate of MnCl2 induced increase in POD activity of both tissues showed an increasing trend with age. However statistical significance was observed only in brain during senescence phase. No significant loss of enzyme activity in both the tissues and greater degree of increase by MnCl2 in brain suggest that antioxidant capacity is not impaired in old murrels.

Age-related changes in catalase activity and its inhibition by manganese (II) chloride in the brain of two species of poikilothermic vertebrates.

Two species of poikilothermic vertebrates, a teleost fish (Channa punctatus) and the garden lizard (Calotes versicolor) were used to study the effect of age on brain catalase (CT) activity and its inhibition by manganese (II) chloride (MnCl(2)). While in fish the CT activity of brain remained unchanged throughout the lifespan, the enzyme activity decreased during maturation and then showed an increase during aging in the garden lizard. MnCl(2) at a concentration of 333 muM in incubating medium significantly inhibited the CT activity of the brain of both fishes and lizards of all the three age groups (young, middle-aged and old), the degree of inhibition showing a trend of increase with advancing age. However, statistical significance was observed when fishes of the young age group were compared either with those of middle-aged or old counterparts, and between young versus old and middle-aged versus old lizards. Increased susceptibility to Mn(2+) during aging suggests changes in regulation of CT.

Age related modifications of soluble proteins in various organs of male garden lizard, Calotes versicolor.

The oxidative modification of proteins measured as carbonyl derivatives increased with advancing age in the liver of male garden lizard. The same parameter did not show a significant change in other organs (brain, heart and kidney). Based on the observations in both homeotherms (mammals) and poikilotherms (insect and reptile), the in vivo oxidative modification of cellular proteins appears to be the most common mechanism leading to accumulation of altered proteins during aging. However, the degree of modifications may vary among the tissues/organs of a species. On the other hand the variations may also account for the role of modification of proteins in the pattern of aging in different species.

Effect of age on lipid peroxidation in a short-lived species of reptile, Calotes versicolor.

The lipid peroxidation potential, measured as a thiobarbituric acid-reactive substance (TBA-RS) increased with advancing age in liver, brain and kidney of a short-lived species of reptile, Calotes versicolor. The same parameter did not show a significant change in an ageing heart. The pattern of age changes in lipid peroxidation potential in this species shows similarity with the findings in a majority of mammalian species. While suggesting a commonality in a basic mechanism of ageing between reptiles and mammals, the results also partially support the free radical theory of ageing.

Ageing in fishes.

Fishes show three types of senescence. Lampreys, eels and pacific salmon exhibit rapid senescence and sudden death at first spawning. The guppy, red panchax, medaka, platyfish, Indian murrel and many other teleosts undergo gradual senescence, as observed in most of the vertebrates. A number of fishes (e.g. sturgeons, paddlefish, female plaice, flatfish, rockfish) show indeterminate growth, the occurrence of senescence in them is supposed to be very slow or negligible. Neuroendocrine mechanisms are involved in rapid senescence. Most of the evidences in favour of the occurrence of senescence in fishes have been derived from studies in species showing gradual senescence. Age-related increases in mortality rate, accumulation of lipofuscin, lipid peroxidation, collagen cross-linking and decreases in growth rate, reproductive capacity and protein utilisation are clearly marked in such species. Anatomical changes in various organs during ageing also confirm increases in degenerative changes and pathological symptoms. Dietary restriction and lower environmental temperature retard the ageing processes in a few species showing gradual senescence. These results tentatively support the contention of commonality in mechanism of ageing processes in vertebrates. At present, anatomical, cellular, biochemical and genetic evidences in support or against the occurrence of slow senescence or negligible senescence in long-lived fish species are almost nonexistent. Extensive studies on ageing in fishes are needed to explain the multiple mechanisms which are not unexpected considering the number and variety of the existing species.

Ageing in reptiles.

Like in fishes, the reptiles appear to show three types of senescence. The African skink, Mabuya buettneri, shows rapid senescence similar to death at mating observed in Salmon and marsupial mouse. Most of the lizards and snakes undergo gradual senescence comparable to the pattern exhibited by a majority of vertebrates. On the other hand, turtles, tortoises and crocodiles continue to grow throughout life and are thus credited with slow or negligible senescence. Evidences and mechanisms of rapid or negligible senescence in reptiles are still fragmentary and unclear. Findings in a few species of lizards (Calotes versicolor) and snakes (Natrix natrix) showing gradual senescence support the concept of commonalities in ageing phenomena in vertebrates. An age-related increase in the stability of collagen and accumulation of altered enzyme molecules, a decrease in metabolism and response to stress-enhanced anti-oxidative defence mechanisms and the nature of responses to hormones, restricted diet and lower environmental temperature corroborate the concept. On the other hand neither the increase in mortality rate and accumulation of lipofuscin nor the reproductive senility have been shown conclusively in ageing reptile populations. It is likely that there are multiple mechanisms of senescence in reptiles. Further studies on selected species from among the 6,000 living species are necessary to unravel the phenomena.

Effect of partial water deprivation and restricted feeding on age-related changes in two enzymes of energy metabolism in the brain of male garden lizards.

The lactate dehydrogenase (LDH) activity of garden lizard brain did not change with advancing age. On the other hand the succinate dehydrogenase (SDH) activity showed a decline during maturation (young to middle-aged) remaining stabilized thereafter. Seven days of partial water deprivation did not alter the LDH activity of lizards of all three age groups but caused an increase in SDH activity of old lizards only. Restricted feeding led to a decline in the activities of both the enzymes (LDH and SDH) in young lizards and an increase in LDH activity of only the old, the response in middle-aged being insignificant. The protein content of the brain did not change during maturation, but declined in old lizards. Partial water deprivation caused an increase in protein content of the brain of both middle-aged and old lizards but not in young counterparts. Only the young lizards showed an increase in protein content of the brain in response to food restriction.

Age-dependent changes in some aspects of glutamate metabolism in the brain of the teleost, Channa punctatus. I. Ammonia and glutamine contents and glutamate dehydrogenase activity.

Age related changes in some aspects of glutamate metabolism were followed in the brain of a short lived species of tropical murrel, Channa punctatus. Both ammonia and glutamine contents of brain increased with advancing age of the murrel. The glutamate dehydrogenase activity of brain increased during maturation phase (year classes 0(+)-3+) followed by a decline in senescence phase (year classes 3(+)-6+). The pattern of age changes in glutamate metabolism in this species of fish shows similarity with the observations made in a majority of mammalian species, thereby suggesting a commonality in a basic metabolic mechanism during aging process in the central nervous system of vertebrates.

Effect of two inhibitors on succinic dehydrogenase activity in cerebral hemispheres of male garden lizards of three different age groups.

Age changes in the specific activity of cerebral succinic dehydrogenase (SDH) and the effect of two inhibitors (malonate and p-chlorophenoxy acetic acid) on enzyme activity were traced in a short-lived species of reptile, Calotes versicolor, the garden lizard. The enzyme activity reached a peak level in middle-aged lizards followed by a decline in old counterparts. The enzyme inhibitions by both the inhibitors were significantly higher in old than in middle-aged and young lizards suggesting a change in specificity of SDH molecules during ageing.

Effect of cold stress and starvation on the cerebral glucose-6-phosphate dehydrogenase activity of male garden lizards of three different age groups.

In the present study we observed that the cerebral glucose-6-phosphate dehydrogenase activity of male garden lizards did not change appreciably during maturation but showed a significant rise between middle-aged and old-aged groups. Whereas cold stress (1 h at 0-4 degrees C) induced a significant increase in G6PDH activity of young animals, it caused a decrease in both middle-aged and old lizards. This decrease was more severe in the old group than in the middle-aged group. Another form of stress, 72 hours of starvation, led to a significant increase in enzyme activity in young and in middle-aged lizards with young animals showing the greater effect. The old counter-parts showed a decrease in enzyme activity after starvation stress.

Effect of thermal inactivation and ATP on age related changes in hepatic glutamate dehydrogenase activity of male garden lizard.

The total glutamate dehydrogenase (GDH) activity of the liver of the male garden lizard did not change during maturation (young to middle-aged) but showed a decline in later phase of the life span (middle-aged to old). On the other hand, the heat stable GDH activity increase during maturation and declined thereafter. The degree of thermal inactivation of the total GDH activity at 45 degrees +/- 1 degree C was not age-dependent. ATP stimulation of total GDH activity was about three times higher in old than in middle-aged lizards.

Changes in catalase activity and its thermolability in liver and kidneys of ageing male garden lizard.

Catalase activity in liver and kidneys of male garden lizards remained unchanged during maturation, but showed an increase during ageing. Instead of inactivating catalase, thermal treatment at 60 +/- 1 degree C caused a marginal increase in enzyme activity in the liver of middle-aged and kidneys of young lizards with no significant effect in old counterparts. Increase in basal enzyme activity during ageing and the maintenance of resistance against thermal inactivation of the enzyme throughout the life-span support the contention that catalase molecules in lizard tissues are not altered as a function of age, a deviation from the predictions of Orgel's error catastrophe hypothesis.

Age-related changes in glucose uptake of cerebral hemisphere slices of male garden lizards in response to starvation stress.

In the male garden lizard, the glucose uptake of cerebral hemisphere slices did not change during maturation (young to middle-aged) but declined during ageing (middle-aged to old). Short-term starvation (3 days) did not cause a significant change in glucose uptake of cerebral hemisphere of young lizards but led to an increase in the parameter in both the middle-aged and old.

Age-related changes in brain and spinal cord lipids of the male garden lizard.

The lipid composition (cholesterol, phospholipid triglyceride and fatty acids) of brain and spinal cord of the male garden lizard was traced during maturation and ageing. The total brain cholesterol content of both the tissues showed a significant rise during maturation, remaining almost constant thereafter. The free cholesterol content of the brain increased between middle and old age and that of the spinal cord increased during maturation. The esterified cholesterol content of the brain increased during maturation, the same parameter being not age-dependent in the spinal cord. While in the brain the phospholipid content increased during maturation followed by a decrease in old age, it showed a reverse trend in the spinal cord. The level of triglyceride in the brain declined during maturation followed by an increase in old age with no appreciable age change in the spinal cord. A comparison between young and old age-groups revealed a decrease in fatty acid content of the brain. A similar trend of decline was observed during maturation in the spinal cord. The pattern of age changes in the lipid profile of nervous tissue of the lizard, a non-mammalian vertebrate, almost conform to the pattern observed in a majority of mammals.

Effect of age on thermal inactivation of glucose-6-phosphate dehydrogenase in liver and kidney of the male garden lizard.

A comparison between middle-aged and old lizards revealed no significant age change in glucose-6-phosphate dehydrogenase activity of liver and kidney. Thermal inactivation at 51 +/- 1 degree C induced a significantly higher degree of decline in enzyme activity of tissues of old than that of middle-aged lizards. The increase in thermolability of enzyme in liver and kidney of ageing lizards suggests an accumulation of altered enzyme molecules.

Effect of malonate and p-chlorophenoxy acetic acid on hepatic succinic dehydrogenase activity of ageing lizards.

The degree of inhibition of hepatic succinic dehydrogenase activity by malonate, a competitive inhibitor, did not differ between young and middle-aged lizards. On the other hand, the same parameter increased significantly between middle-aged and old lizards. The percent inhibition of enzyme activity by p-chlorophenoxy acetic acid was also age-dependent, being higher in middle-aged and old than in young lizards.

Age-related responses of hepatic glucose uptake to starvation and cold stress in male garden lizards.

The hepatic glucose uptake of male garden lizards did not change during maturation but showed a decline between middle-aged and old age groups. The decline in glucose uptake following starvation and cold stress was age-dependent, the young and middle-aged lizards being more responsive than the old counterparts.