Maria Susana Estevez

Effects of seasonal and latitudinal cold on oxidative stress parameters and activation of hypoxia inducible factor (HIF-1) in zoarcid fish

Acute, short term cooling of North Sea eelpout Zoarces viviparus is associated with a reduction of tissue redox state and activation of hypoxia inducible factor (HIF-1) in the liver. The present study explores the response of HIF-1 to seasonal cold in Zoarces viviparus, and to latitudinal cold by comparing the eurythermal North Sea fish to stenothermal Antarctic eelpout (Pachycara brachycephalum). Hypoxic signalling (HIF-1 DNA binding activity) was studied in liver of summer and winter North Sea eelpout as well as of Antarctic eelpout at habitat temperature of 0°C and after long-term warming to 5°C. Biochemical parameters like tissue iron content, glutathione redox ratio, and oxidative stress indicators were analyzed to see whether the cellular redox state or reactive oxygen species formation and HIF activation in the fish correlate. HIF-1 DNA binding activity was significantly higher at cold temperature, both in the interspecific comparison, polar vs. temperate species, and when comparing winter and summer North Sea eelpout. Compared at the low acclimation temperatures (0°C for the polar and 6°C for the temperate eelpout) the polar fish showed lower levels of lipid peroxidation although the liver microsomal fraction turned out to be more susceptible to lipid radical formation. The level of radical scavenger, glutathione, was twofold higher in polar than in North Sea eelpout and also oxidised to over 50%. Under both conditions of cold exposure, latitudinal cold in the Antarctic and seasonal cold in the North Sea eelpout, the glutathione redox ratio was more oxidised when compared to the warmer condition. However, oxidative damage parameters (protein carbonyls and thiobarbituric acid reactive substances (TBARS) were elevated only during seasonal cold exposure in Z. viviparus. Obviously, Antarctic eelpout are keeping oxidative defence mechanisms high enough to avoid accumulation of oxidative damage products at low habitat temperature. The paper discusses how HIF could be instrumental in cold adaptation in fish.

Iron-dependent oxidative stress in Chlorella vulgaris

Abstract The role of iron as catalyst for oxidative stress was studied during the development of Chlorella vulgaris cells. Increases on iron availability beyond 200 μM led to a decrease in the growth rate of the cultures of C. vulgaris. Quantification of the EPR signals of POBN/lipid radicals adducts indicated that iron addition increased lipid radical content in the membranes (more than three-fold at 500 μM Fe). The ratio of ascorbyl radical content/ascorbate content was increased in cells exposed to 500 μM iron as compared to standard conditions (90 μM Fe). β-Carotene content was not affected by iron addition, however, α-tocopherol, ascorbate and total thiol content in C. vulgaris cells was increased when iron supply was higher than 90 μM. The morphology of the cells developed under 500 μM iron showed a decreased number of ribosomes and alterations in the cellular starch deposits as compared to the cells grown at 90 μM iron. Exposure to UV-B increased the content of lipid radicals and affected cellular internal structure as compared to non-irradiated cells developed at 500 μM iron. Even though results from model systems cannot be directly used to predict ecological effects, these data suggest that oxidative stress triggered by an excess of iron could affect cellular growth and have a negative impact to phytoplankton.

Lipid radical generation in polar (Laternula elliptica) and temperate (Mya arenaria) bivalves

Lipid peroxidation in Laternula elliptica was assessed by detecting lipid radicals by electronic paramagnetic resonance. The values were compared with data from the temperate mud clam Mya arenaria. Lipid radical content was higher in the Antarctic bivalve than in the temperate mud clam, even within the range of its habitat temperature. The rate of generation of lipid radicals was affected by the iron content in the samples. The iron content in individual samples of digestive glands in L. elliptica ranged from 3 to 6 nmol g(-1) fresh weight (fwt) and in M. arenaria from 0.6 to 2.7 nmol g(-1) fwt. Arrhenius plots, developed from the rates obtained in the presence of 25 microM iron, showed no significant differences between the activation energy calculated for digestive glands of L. elliptica and M. arenaria. The Fe3+ reduction rate in L. elliptica was higher than in M. arenaria (4.7 +/- 0.9 vs. 1.8 +/- 0.4 nmol mg(-1) protein min(-1), respectively). L. elliptica had a higher content of alpha-tocopherol and beta-carotene than M. arenaria. Our data suggest that increased lipid radical content in the membranes of cold-adapted organisms could be related to iron content.

UV-B effects on Antarctic Chlorella sp cells

Growth of Antarctic Chlorella sp cells was measured in cultures irradiated with 30 kJ m(-2) UV-B (280-320 nm). The specific growth rate immediately after the lag phase was 0.36+/-0.06 and 0.26+/-0.03 day(-1) for unirradiated cultures and cultures irradiated with UV-B, respectively, UV-B irradiation significantly decreased ascorbate content by 54.5%, and increased the ascorbyl radical content/ascorbate content ratio by 2.25-fold in algae cultures in log phase. UV-B exposure significantly decreased by 95, 62 and 71% the content of alpha-tocopherol, beta-carotene and total thiols, respectively, in cells in log phase of development. The cellular content of alpha-tocopherol, beta-carotene and total thiols was reduced by 78, 43 and 44%, respectively in stationary phase, as compared to the antioxidant content in the cells during log phase of development. UV-B exposure reduced the content of alpha-tocopherol and total thiols in stationary phase of development by 64 and 91%, respectively, as compared to unirradiated cells. The content of beta-carotene in stationary phase was not affected by UV-B exposure. The results presented here suggest that increased UV-B radiation was responsible for the development of oxidative stress conditions, assessed as the ascorbyl radical content/ascorbate content ratio, in Antarctic Chlorella sp cells. Moreover, a significant decrease in the content of both lipid and water soluble antioxidants might contribute to establish oxidative stress in the cells.