The ascorbyl/ascorbate ratio as index of oxidative stress in aquatic organisms

MALANGA G.; AGUIAR M.B.; PUNTARULO S.

Oxidative Stress in Aquatic Ecosystems

Wiley-Blackwell

Año: 2012; p. 458 - 464

Aquatic organisms, as all biological systems, contain many antioxidants; including water-soluble compounds, such as ascorbic acid. The one-electron oxidation of ascorbate (AH-) produces the ascorbyl radical (A·) which is easily detectable by electron paramagnetic resonance (EPR) even in aqueous solution at room-temperature. The A· has a relatively long lifetime compared to other species, such as hydroxyl radical, peroxyl, alkoxyl, and carbon-centered lipid free radicals. A· has been proposed as a marker of oxidative stress either in vitro, or in vivo in numerous systems, such as plasma, lyophilized tissue, ischemic-reperfused organs, photosynthetic organisms and even clams. In previous reports it has been demonstrated that when the reaction variables  such as pH, catalytic metal concentration, and AH- levels) are controlled, the intensity of the steady-state A·-EPR signal can serve as an indicator of oxidative processes taking place in the organisms. However, when total ascorbate content is changed by oxidative conditions, the A· radical content/ascorbate content ratio could be successfully used to estimate early oxidative stress. We studied the A· content by EPR spectroscopy, AH- content by HPLC, to evaluate by the value of the A·/AH- ratio, the oxidative stress in the hydrophilic mileiu, in algae cultures, invertebrates (limpet, sea urchins and bivalves) and fish. In all tested situations, the A·/AH- ratio, reflects the actual state of one part of the oxidative defense system and provides an early and simple diagnosis of environmental stressing conditions.