Oxidative denaturation of lens protein: prevention by pyruvate

Quality changes and indicator proteins of Litopenaeus vannamei based on label-free proteomics analysis during partial freezing storage

Litopenaeus vannamei are known to deteriorate in quality during low-temperature storage. This study demonstrated the potential protein indicators of partial freezing of stored shrimp by traditional quality parameters and label-free based proteomic techniques. The carbonyl content and myofibril fragmentation index (MFI) of shrimp increased from 0.56 ± 0.03 to 2.14 ± 0.03 nmol/mg and 13.09 ± 0.14 to 54.93 ± 0.96, respectively. Within the extension of storage, the trichloroacetic acid (TCA), cooking loss and whiteness significantly increased. A total of 240 proteins changed in abundance at 10, 20, and 30 days compared to fresh samples. Projectin, ribosomal protein and histone were potential biomarkers for protein denaturation and oxidation in shrimp muscle. Myosin heavy chain and glyceraldehyde-3-phosphate dehydrogenase corresponded with the degradation of muscle proteins. Myosin light chain, tubulin alpha chain, and heat shock protein correlated with tenderness and water holding capacity; meantime, malate dehydrogenase and hemocyanin can serve as color indicators. Further study of the properties of these indicator proteins can inform their exploitation as quality indicator proteins during partial freezing storage.

High cell density attenuates reactive oxygen species: implications for in vitro assays

In vitro cell-based assays are an essential and universally used step in elucidation of biological processes as well as in drug development. However, results obtained depend on the validity of protocols used. This statement certainly pertains to in vitro assays of oxidative stress. The holy grail of in vitro models is reliability and predictability of outcomes that relate to a single variable like addition of hydrogen peroxide or xanthine oxidase. Without such validated outcomes, comparison of results among different laboratories is not possible. Achieving this goal requires a thorough understanding of the complex interplay between the cells, their environment, and the experimental assays. Furthermore, as this knowledge is attained, it must be disseminated and used to update and standardize existing protocols. Here, we confirm and extend the effect of pyruvate and cell density on in vitro oxidative stress assays. Cell viability was assessed using a colorimetric assay measuring the reduction of a tetrazolium salt (XTT) into a colored formazan dye. Extracellular hydrogen peroxide concentrations were measured using the foxp3 assay. We confirmed a previously reported finding that pyruvate, a common ingredient in cell culture media, acts as an extracellular scavenger of reactive oxygen species. We also demonstrated that cell density directly correlates with resistance to oxidative stress in tissue culture. It is theorized that the protective effect due to cell density predominantly relates to intracellular factors such as reduced glutathione and extracellular factors such as catalase.

Oxidative damage to lens in culture: reversibility by pyruvate and ethyl pyruvate

It is generally believed that prophylactic intake of antioxidants is beneficial in delaying the onset of some aging manifestations such as cataract. However, whether such a supplementation will also be effective if the pathophysiological process has already set in remains a largely open question. We examined this possibility with lens changes leading to cataract formation, since cataract genesis is intimately related to a continued generation of reactive oxygen species (ROS) in the aqueous humor. Since the formation of cataract is a well-defined progressive disease, starting with an early refractive change and leading to gradual enhancement of opacification, we hypothesized that even a belated start with an appropriate anti-oxidant could halt the pathological process and delay cataract maturation and vision impairment. Using lens cultures, we tested this hypothesis with pyruvate, known to be an effective and highly potent ROS scavenger. Adding pyruvate to the culture medium after lenses had sustained a 50% damage was significantly effective in preventing progress. This was apparent by better maintenance of the active rubidium transport activity in these lenses compared to controls without pyruvate treatment. Glutathione levels were also higher in the pyruvate group.

Peroxynitrite-mediated decarboxylation of pyruvate to both carbon dioxide and carbon dioxide radical anion

There has been a recent renewal of interest in the antioxidant properties of pyruvate which are usually attributed to its capacity to undergo oxidative decarboxylation in the presence of hydrogen peroxide. The interaction of pyruvate with other oxidizing biological intermediates, however, has been scarcely considered in the literature. Here we report that peroxynitrite, the oxidant produced by the reaction between superoxide anion and nitric oxide, reacts with pyruvate with an apparent second-order rate constant of 88 +/- 7 M-1 s-1 at pH 7.4 and 37 degrees C. Kinetic studies indicated that pyruvate reacts with peroxynitrite anion (k = 100 +/- 7 M-1 s-1, peroxynitrous acid (k = 49 +/- 7 M-1 s-1, and a highly oxidizing species derived from peroxynitrous acid. Pyruvate decarboxylation was proved by anion exchange chromatography detection of acetate in incubations of peroxynitrite and pyruvate at pH 7.4 and 5.5. Formation of carbon dioxide radical anion was ascertained by EPR spin-trapping studies in the presence of GSH and the spin-trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The use of pyruvate labeled with 13C at the 1-position led to the detection of the labeled DMPO carbon dioxide radical anion adduct. In the absence of GSH, oxygen consumption studies confirmed that peroxynitrite mediates the decarboxylation of pyruvate to free radical intermediates. Comparing the yields of acetate and free radicals estimated from the oxygen uptake studies, it is concluded that pyruvate is oxidized by both one- and two-electron oxidation pathways, the latter being preponderant. Hydrogen peroxide-mediated pyruvate oxidation does not produce detectable levels of carbon dioxide radical anion except in the presence of iron(II)-ethylenediamine-N,N,N',N'-tetraacetate (EDTA). The apparent second-order rate constant of the reaction between pyruvate and hydrogen peroxide was determined to be 1 order of magnitude lower than that of the reaction between pyruvate and peroxynitrite. The latter process may contribute to the antioxidant properties of pyruvate.