Integrated structural and functional analysis of the protective effects of kinetin against oxidative stress in mammalian cellular systems.

Metabolism and signaling of cytokinins was first established in plants, followed by cytokinin discoveries in all kingdoms of life. However, understanding of their role in mammalian cells is still scarce. Kinetin is a cytokinin that mitigates the effects of oxidative stress in mammalian cells. The effective concentrations of exogenously applied kinetin in invoking various cellular responses are not well standardized. Likewise, the metabolism of kinetin and its cellular targets within the mammalian cells are still not well studied. Applying vitality tests as well as comet assays under normal and hyper-oxidative states, our analysis suggests that kinetin concentrations of 500 nM and above cause cytotoxicity as well as genotoxicity in various cell types. However, concentrations below 100 nM do not cause any toxicity, rather in this range kinetin counteracts oxidative burst and cytotoxicity. We focus here on these effects. To get insights into the cellular targets of kinetin mediating these pro-survival functions and protective effects we applied structural and computational approaches on two previously testified targets for these effects. Our analysis deciphers vital residues in adenine phosphoribosyltransferase (APRT) and adenosine receptor (A2A-R) that facilitate the binding of kinetin to these two important human cellular proteins. We finally discuss how the therapeutic potential of kinetin against oxidative stress helps in various pathophysiological conditions.

Influence of bariatric surgery induced weight loss on oxidative DNA damage.

Obesity is associated with elevated cancer risk, which may be represented by elevated genomic damage. Oxidative stress plays a key role in obesity related detrimental health consequences including DNA oxidation damage. The elevated cancer risk in obesity may be a consequence. Weight loss has been shown to reduce genomic damage, but the role of oxidative stress in that has not been clarified. The aim of this study is therefore to investigate the influence of bariatric surgery induced weight loss on DNA oxidation damage in morbidly obese subjects. For this aim, we used cryopreserved peripheral blood mononuclear cells in the FPG comet assay. Advanced protein oxidation products and 3-nitrotyrosine were measured as oxidative and nitrative protein stress markers. Furthermore, expression of oxidative stress related proteins HSP70 and Nrf2 as well as mitochondrial enzyme citrate synthase and NADPH oxidase subunit p22 phox were analysed. Our findings revealed significantly reduced DNA strand breaks, but DNA base oxidation was not reduced. We observed significant reduction in plasma AOPPs and 3-nitrotyrosine, which indicated an improvement in oxidative/nitrative stress. However, expression of HSP70 and Nrf2 were not altered after weight loss. In addition, expression of citrate synthase and p22 phox were also unaltered. Overall, bariatric surgery induced significant reduction in excess body weight and improved the patients' health status, including reduced DNA strand breaks and slightly improved antioxidant status in some of the investigated endpoints, while cellular ROS formation and DNA oxidation damage stayed unaltered. This complex situation may be due to combined beneficial effects of weight loss and burdening of the body with fat breakdown products. In the future, collecting samples two years after surgery, when patients have been in a weight plateau for some time, might be a promising approach.

Overlapping mechanism of the induction of genomic damage by insulin and adrenaline in human promyelocytic HL-60 cells.

Endogenous hormones systemically regulate the growth and metabolism and some prior studies have shown that their imbalance can have a potential to induce genomic damage in in vitro and animal models. Some conditions that are associated with elevated levels of endogenous hormones are hyperinsulinemia and intense exercise-induced stress causing increased adrenaline. In this study we test whether these two hormones, could cause an additive increase in genomic damage and whether they have an overlapping mechanism of action. For this, we use the human promyelocytic HL60 cells, as they express the receptors for both hormones. At doses taken from the saturation level of the individual dose response curves, no additivity in genomic damage was detected through micronucleus induction. This hints towards a common step in the pathway, which is under these conditions fully activated by each of the individual hormone. To investigate this further, individual and common parts in insulin and adrenaline signalling such as their respective hormone receptors, the downstream protein AKT and the involvement of mitochondria and NADPH oxidase (NOX) enzymes were studied. The results indicate no additive effect of high hormone concentrations in genomic damage in the in vitro model, which may be due to exhaustion of the NOX 2-mediated reactive oxygen production. It remains to be determined whether a similar situation may occur in in vivo situations.

A systematic review of the use of the alkaline comet assay for genotoxicity studies in human colon-derived cells.

This review describes the use of the comet assay for assessment of DNA damage in human colon cells. We screened 98 papers, which employed human colon -derived cells to analyse DNA damage induced by different insults with the comet assay. In most cases tumour cell lines were used, and only a few studies were performed with primary colon cells. The comet assay was mostly applied to test chemotherapeutics and natural products. We could not find a clear difference between the susceptibility of cell lines to genotoxic insults and they were all suitable for comet assay experiments. Further comparisons between cell lines, and with primary cells and stem cells would be desirable to understand the relevance of the established cell lines as model for the human target tissue better.

Anti-inflammatory effect of piperine in adjuvant-induced arthritic rats--a biochemical approach.

The present study was undertaken to investigate the anti-inflammatory effect of piperine against adjuvant-induced arthritis in rats, an experimental model for rheumatoid arthritis and compared it with that of the non-steroidal anti-inflammatory drug indomethacin. Administration of heat-killed Mycobacterium tuberculosis (0. 1 ml) intradermally into the right hind paw of rats resulted in increased paw volume, lysosomal enzymes, glycoproteins and tissue marker enzymes and decreased body weight. However, these changes were reverted to near normal levels upon piperine (30 mg/kg body weight, i.p.) treatment. Histopathological analysis of joints also revealed that synovial hyperplasia and mononuclear infiltration observed in arthritic rats were alleviated by piperine. Thus, the present study clearly indicated that piperine possesses promising anti-inflammatory effect against adjuvant-induced arthritis by suppressing inflammation and cartilage destruction.