Antioxidant capacity and oxidative stress in the freeze-tolerant woolly bear caterpillar, Pyrrharctia isabella

Reactive oxygen species (ROS) are normal byproducts of aerobic metabolism. However, increased production of these molecules may overwhelm antioxidant systems resulting in oxidative damage to cellular membranes, proteins, and nucleic acids. Freeze-tolerant ectotherms may experience such increased production of ROS and oxidative stress during frequent cycles of freeze/thaw and the accompanying tissue ischemia/reperfusion. Therefore, the purpose of this study was to investigate the effects of subfreezing temperature exposures on the metabolic rate, antioxidant capacity, and measures of oxidative stress in freeze-tolerant woolly bear caterpillars, Pyrrharctia isabella. Following freezing, a slight decrease in the rate of oxygen consumption was observed at 1 and 5 h post-thaw, suggesting the organisms may reduce metabolic rate in an attempt to limit ROS production. However, lipid peroxidation was significantly elevated at 4 h post-thaw, demonstrating the caterpillars did still incur an oxidative stress. At 24 and 48 h post-thaw, the rate of oxygen consumption was markedly increased, while lipid peroxidation was significantly lower, perhaps as a result of the activation of cellular repair mechanisms. The total antioxidant capacity of fat body isolated from P. isabella was comparable to that of whole body homogenates of other freeze-tolerant insects, the goldenrod gall fly Eurosta solidaginis and Antarctic midge Belgica antarctica, and significantly higher than that of the freeze-intolerant Drosophila melanogaster. These results provide insight into the nature of freeze/thaw injury and the mechanisms used by naturally freeze-tolerant species to limit and repair oxidative damage.