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.

Mild hyperbilirubinaemia as an endogenous mitigator of overweight and obesity: Implications for improved metabolic health

BACKGROUND AND AIMS

Mild endogenous elevation of unconjugated bilirubin (UCB) as seen in Gilbert's syndrome (GS), might mitigate cardiovascular disease (CVD) risk factors including overweight/obesity. This study aimed to determine whether hyperbilirubinaemia is linked to improved anthropometric data and lipid profile.

METHODS

Our study considered GS and age-/gender-matched healthy controls (n = 248). Additionally, obese female type 2 diabetic patients (DM2) (n = 26) were included as a "disease control group".

RESULTS

BMI, hip circumference (HC), and lipid profile were significantly lower in GS. UCB was inversely correlated with BMI (p <0 .001), HC as well as with fat mass (FM) and lipid variables (p < 0.05). Moreover, DM2 patients had significantly lower UCB compared to GS and healthy controls. Older GS subjects (≥35 years) had significantly reduced anthropometric data and improved lipid profile.

CONCLUSIONS

Our results propose that the health promoting potential of mild hyperbilirubinaemia may extend to protection from age-related weight gain and dyslipidaemia.

Association of Genomic Instability with HbA1c levels and Medication in Diabetic Patients

Diabetes Mellitus type 2 (DM2) is associated with increased cancer risk. Instability of the genetic material plays a key role in the aetiology of human cancer. This study aimed to analyse genomic instability with the micronucleus cytome assay in exfoliated buccal cells depending on glycated haemoglobin (HbA1c) levels and medication in 146 female DM2 patients. The occurrence of micronuclei was significantly increased in DM2 patients compared to healthy controls. Furthermore, it was doubled in DM2 patients with HbA1c > 7.5% compared to subjects with HbA1c ≤ 7.5%. Positive correlations were found between micronuclei frequencies and HbA1c as well as fasting plasma glucose. Patients under insulin treatment showed a two-fold increase in micronuclei frequencies compared to subjects under first-line medication (no drugs or monotherapy with non-insulin medication). However, after separation of HbA1c (cut-off 7.5%) only patients with severe DM2 characterised by high HbA1c and insulin treatment showed higher micronuclei frequencies but not patients with insulin treatment and low HbA1c. We demonstrated that the severity of DM2 accompanied by elevated micronuclei frequencies predict a possible enhanced cancer risk among female DM2 patients. Therapy, therefore, should focus on a strict HbA1c control and personalised medical treatments.

Oxidative Stress, DNA Damage and DNA Repair in Female Patients with Diabetes Mellitus Type 2

BACKGROUND

Diabetes mellitus type 2 (T2DM) is associated with oxidative stress which in turn can lead to DNA damage. The aim of the present study was to analyze oxidative stress, DNA damage and DNA repair in regard to hyperglycemic state and diabetes duration.

METHODS

Female T2DM patients (n = 146) were enrolled in the MIKRODIAB study and allocated in two groups regarding their glycated hemoglobin (HbA1c) level (HbA1c≤7.5%, n = 74; HbA1c>7.5%, n = 72). In addition, tertiles according to diabetes duration (DD) were created (DDI = 6.94±3.1 y, n = 49; DDII = 13.35±1.1 y, n = 48; DDIII = 22.90±7.3 y, n = 49). Oxidative stress parameters, including ferric reducing ability potential, malondialdehyde, oxidized and reduced glutathione, reduced thiols, oxidized LDL and F2-Isoprostane as well as the activity of antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase were measured. Damage to DNA was analyzed in peripheral blood mononuclear cells and whole blood with single cell gel electrophoresis. DNA base excision repair capacity was tested with the modified comet repair assay. Additionally, mRNA expressions of nine genes related to base excision repair were analyzed in a subset of 46 matched individuals.

RESULTS

No significant differences in oxidative stress parameters, antioxidant enzyme activities, damage to DNA and base excision repair capacity, neither between a HbA1c cut off />7.5%, nor between diabetes duration was found. A significant up-regulation in mRNA expression was found for APEX1, LIG3 and XRCC1 in patients with >7.5% HbA1c. Additionally, we observed higher total cholesterol, LDL-cholesterol, LDL/HDL-cholesterol, triglycerides, Framingham risk score, systolic blood pressure, BMI and lower HDL-cholesterol in the hyperglycemic group.

CONCLUSION

BMI, blood pressure and blood lipid status were worse in hyperglycemic individuals. However, no major disparities regarding oxidative stress, damage to DNA and DNA repair were present which might be due to good medical treatment with regular health checks in T2DM patients in Austria.

Cheek cell fatty acids reflect n-3 PUFA in blood fractions during linseed oil supplementation: a controlled human intervention study

Background

Adequate biomarkers for the dietary supply of fatty acids (FA) are FA of adipose tissue and blood fractions. In human studies, invasive sample collection is unpleasant for subjects. In contrast, cheek cell sampling can be considered as a non-invasive alternative to investigate FA status.

The aim of this study was to analyze whether cheek cell FA composition reflect the supplementation of alpha-linolenic acid (ALA) using a linseed oil mixture compared to olive oil supplementation. Additionally, it was investigated if cheek cell FA composition correlates with the FA composition of plasma, red blood cells (RBC) and peripheral blood mononuclear cells (PBMC) before and during both interventions.

Methods

During a 10-week randomized, controlled, double-blind human intervention study, 38 subjects provided cheek cell and blood samples. After a two-week run-in period, the test group (n = 23) received 17 g/d of an ALA-rich linseed oil mixture, while the control group (n = 15) received 17 g/d of an omega-3 (n-3) polyunsaturated FA (PUFA)-free olive oil. Cheek cells and blood were collected on days 0, 7 and 56 of the 8-week intervention period.

Results

Compared to olive oil, the linseed oil intervention increased ALA and also the endogenously converted long-chain n-3 metabolites eicosatetraenoic-, eicosapentaenoic- and docosapentaenoic acid in cheek cells (P ≤ 0.05). Docosahexaenoic acid remained unchanged. Reflecting the treatment, the n-6/n-3 ratio decreased in the test group. In general, cheek cell FA reflected the changes of FA in blood fractions. Independent of treatment, significant correlations (P ≤ 0.05) of n-6 PUFA and n-3 PUFA between cheek cells and plasma, RBC and PBMC were found, except for linoleic acid and ALA.

Conclusions

The changes in FA composition of cheek cells confirmed that ALA from linseed oil increased endogenously derived n-3 PUFA in cheek cell lipids. These changes in cheek cells and their correlation to the respective FA in blood fractions indicate the cheek cell FA profile as an adequate non-invasive biomarker for short-term n-3 PUFA intake and metabolism. Therefore, cheek cell FA can be used in human intervention studies or large-scale epidemiological studies, especially for assessment of the n-3 PUFA status.

Trial registration

ClinicalTrials.gov, IDNCT01317290

Aryl hydrocarbon receptor signaling regulates NF-κB RelB activation during dendritic-cell differentiation

How the aryl hydrocarbon receptor (AhR) regulates dendritic-cell (DC) differentiation is unknown. We show that activation of AhR by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) caused enhanced differentiation from immature DCs (IDCs) to mature DCs (MDCs) in the bone-marrow-derived DCs (BMDC) from B6 wild-type mice but not in the BMDCs from AhR-null mice as indicated by the expression of CD11c and class II major histocompatibility complex (MHC). Enhanced maturation of BMDCs was associated with elevated levels of CD86 and an increased AhR-dependent nuclear accumulation of nuclear factor-kappa-light-chain enhancer of activated B cell (NF-κB) member RelB in BMDCs. The expression of interleukin (IL) 10 and chemokine DC-CK1 was suppressed, whereas that of CXCL2, CXCL3 and IL-22 was significantly increased in AhR-activated BMDCs. Furthermore, TCDD induced expression of the regulatory enzymes indoleamine 2,3-dioxygenase (IDO1) and indoleamine 2,3-dioxygenase-like 1 (IDO2). Increased expression of IDO2 was associated with coexpression of the cell-surface marker CCR6. Interestingly, mRNA expression of the chemokine receptor CCR6 was drastically decreased in AhR-null IDCs and MDCs. Overall, these data demonstrate that AhR modifies the maturation of BMDCs associated with the induction of the regulatory enzyme IDO and altered expression of cytokine, chemokines and DC-specific surface markers and receptors.