The Free Radical Theory of Ageing: Does it apply to Antarctic and Temperate Sea Urchins?

Abstract

Sea urchins were used as a model organism to investigate oxidative damage with age as they are readily available in both temperate and Antarctic environments and growth data is known. The free radical theory of aging was first proposed in the 1950’s by Denham Harman and is one of the most popular explanations for how ageing occurs at the molecular level. Oxidative damage is believed to be due to an imbalance between oxidants and antioxidants, in favour of the oxidants, resulting in a progressive loss of functional cellular processes. Environmental conditions such as a decrease in sea temperature causes an increase in oxygen solubility, which is expected to cause an increase in oxidative stress, suggesting latitude may influence levels of oxidative stress experienced by an organism. The common Antarctic sea urchin Sterechinus neumayeri was collected from Cape Evans, Ross Island, Antarctica (77°38'5.15"S, 166°24'37.21"E) and the common New Zealand sea urchin Evechinus chloroticus from Blanket Bay, Fiordland (45°18'3.35"S, 166°58'43.73"E). To assess oxidative stress with age, assays of common antioxidants, lipid peroxides and protein carbonyls were carried out of the gut and gonad tissues. Upon analysing the results of S. neumayeri it was discovered that sex was potentially a key variable and therefore was included as a factor in the analysis of E. chloroticus. Results showed that oxidative stress is increasing with age in the gonad tissue but not the gut. Interestingly, the glutathione metabolism in the gonad decreased once a certain size/age had been reached, consistent with a decrease in reproductive potential. Greater levels of antioxidants and oxidative stress measures were observed in female gonad tissue suggesting that females may have a higher metabolic rate within the gonads. The results found suggest that the accumulation of oxidative damage is tissue specific, the first such example from within a single organism.