The hCOMET project: International database comparison of results with the comet assay in human biomonitoring. Baseline frequency of DNA damage and effect of main confounders

The alkaline comet assay, or single cell gel electrophoresis, is one of the most popular methods for assessing DNA damage in human population. One of the open issues concerning this assay is the identification of those factors that can explain the large inter-individual and inter-laboratory variation. International collaborative initiatives such as the hCOMET project - a COST Action launched in 2016 - represent a valuable tool to meet this challenge. The aims of hCOMET were to establish reference values for the level of DNA damage in humans, to investigate the effect of host factors, lifestyle and exposure to genotoxic agents, and to compare different sources of assay variability. A database of 19,320 subjects was generated, pooling data from 105 studies run by 44 laboratories in 26 countries between 1999 and 2019. A mixed random effect log-linear model, in parallel with a classic meta-analysis, was applied to take into account the extensive heterogeneity of data, due to descriptor, specimen and protocol variability. As a result of this analysis interquartile intervals of DNA strand breaks (which includes alkali-labile sites) were reported for tail intensity, tail length, and tail moment (comet assay descriptors). A small variation by age was reported in some datasets, suggesting higher DNA damage in oldest age-classes, while no effect could be shown for sex or smoking habit, although the lack of data on heavy smokers has still to be considered. Finally, highly significant differences in DNA damage were found for most exposures investigated in specific studies. In conclusion, these data, which confirm that DNA damage measured by the comet assay is an excellent biomarker of exposure in several conditions, may contribute to improving the quality of study design and to the standardization of results of the comet assay in human populations.

Effect of PUFA-rich plant oil on risk factors of STZ-induced diabetes in Wistar rats

OBJECTIVE

This study has been focused on the effect of an n-6 polyunsaturated fatty acid (PUFA) rich plant oil on oxidation and glycooxidation stress markers as well as on antioxidant enzyme activities in male Wistar rats with streptozotocin-induced diabetes.

METHODS

The non-diabetic and diabetic groups of Wistar rats were administered plant oil at concentrations of 100 and 500 mg/kg body weight and controls without plant oil. The parameters of glycaemic control, lipid profile, total antioxidant status, antioxidant enzyme activities, together with oxidative and glycooxidative stress markers were measured in the blood.

RESULTS

The intake of the plant oil did not significantly influence the parameters of glycaemic control and significantly increased the levels of all lipid profile parameters in the diabetic rats. Plant oil administration significantly decreased the total antioxidant status and glutathione peroxidase activity and the activity of Cu/Zn superoxide dismutase was significantly increased. The plant oil also increased the levels of lipoperoxides and advanced the glycation end products.

DISCUSSION

These results suggest that the plant oil with high concentrations of n-6 PUFA - linoleic acid, acts prooxidatively when administered to the rats.

Effect of natural polyphenols, pycnogenol® on superoxide dismutase and nitric oxide synthase in diabetic rats

The work is focused on clarifying the impact of diabetes and natural plant polyphenols contained in Pycnogenol® (PYC) on the activity and synthesis of Cu/Zn-SOD and synthesis of nNOS and eNOS in the cerebellum and cerebral cortex in rats with induced diabetes. Rats included in the study (n=38) were divided into three groups: the controls (C), (n=7), untreated diabetics (D) (n=19) and diabetic rats treated with PYC (DP) (n=12). Diabetes significantly decreased synthesis, as well as the activity of Cu/Zn-SOD in both studied parts of the brain. PYC significantly increased the synthesis of Cu/Zn-SOD but had no effect on its activity. Diabetes also reduced the synthesis of nNOS in cerebral cortex and administered PYC elevated its amount to the level of controls. In the cerebellum, diabetes does not affect the synthesis of nNOS and PYC reduces synthesis of NOS. Diabetes as well as PYC had no influence on the synthesis of eNOS in both, the cerebellum and cerebral cortex. PYC modulated level of Cu/Zn-SOD and nNOS in cerebellum and cerebral cortex of diabetic rats, but in a different way.

How does pycnogenol® influence oxidative damage to DNA and its repair ability in elderly people?

Our purpose in this randomized, double blind, placebo controlled study was to find out the possible effect of a polyphenolic pine bark extract, Pycnogenol® (Pyc) on the level of 8-oxo-7,8-dihydroguanine (8-oxoG) as representative of oxidative damage to DNA and on the DNA repair ability of elderly people. According to our results, three months of Pyc administration had no effect on the level of oxidative damage to DNA or on repair ability, but we found a relationship between the level of 8-oxoG and repair ability of DNA in this group. To conclude, even if the positive effect of Pyc was not confirmed in the case of elderly people it is important to highlight the necessity of further investigations about the mechanisms of Pyc acting on different age groups.

Hypercholesterolemia, oxidative stress and gender dependence in children

Hypercholesterolemia (HCH) is characterized by an increase of the total- and LDL-cholesterol in serum. In hypercholesterolemia, generally recognized as a risk factor of atherogenesis, oxidative stress and oxidatively modified LDL play a crucial role. In our study, children with elevated total cholesterol (above 4.5 mmol/l) were included. Parameters of lipid profile, lipophilic vitamins and antioxidants (retinol, α-tocopherol, γ-tocopherol, xantophyll, lycophen and β-carotene) and markers of oxidative damage to lipids (lipoperoxides and 8-isoprostanes) were evaluated. We found that children with hypercholesterolemia have significantly increased parameters of lipid profile and these are gender dependent only in HDL-cholesterol (1.27 ± 0.10 mmol/l in boys vs. 1.53 ± 0.07 mmol/l in girls; p<0.05) and TAG (1.63 ± 0.31 mmol/l in boys vs. 1.08 ± 0.09 mmol/l in girls; p<0.05). In addition, children with HCH have decreased total antioxidant capacity of serum (TEAC) (about 19.64%, p<0.05) and increased lipoperoxides (LP) (about 45.73%, p<0.001). We have revealed statistically significant correlations between parameters of lipid profile and lipophilic vitamins and antioxidants, as well as between markers of oxidative stress: positive correlation between LP and 8-iso (r=0.353, n=33, p<0.05) and negative correlations between these parameters and TEAC (r= -0.377, n=33, p<0.05 for LP and r= -0.379, n=33, p<0.05 for 8-iso). In conclusion, we confirmed relation between hypercholesterolemia and oxidative stress and effect of gender on these processes already in childhood. Since the atherosclerotic process begins in childhood before clinical symptoms, early detection of hypercholesterolemia and oxidative stress is important in later atherosclerosis prevention.