Associations Of Carbon Disulfide Exposure With Oxidative Stress,fasting Plasma Glucose And Risk Of Type 2 Diabetes Among Community Residents

Carbon disulfide（CS₂）is a kind of colorless aromatic liquid with highly fat-solubility and volatility.In addition to being used as an industrial solvent,CS₂mainly comes from the production of viscose fiber,cellophane,rayon,pesticides and so on,and it can release to the atmosphere and contaminate the environment.In our daily life,people are exposed to CS₂ when using pesticides,detergents,degreasing agents,etc.After CS₂ enters the body through inhalation,diet,eyes and skin contact,it can be activated by cytochrome p-450 in the liver and conjugate with reduced glutathione,forming 2-thiothiazolidin-4-carboxylic acid（TTCA）in urine ultimately.Numerous studies have proved that CS₂ exposure was strongly related to the concentrations of urinary TTCA,which indicated urinary TTCA was a reliable biomarker to reflect the levels of CS₂ internal exposure.Previously published literature showed that CS₂ is highly toxic and it can do great harm to nervous system,cardiovascular system,reproductive system and the others.It has been found that CS₂ exposure is closely correlated with impaired glycometabolism among occupational population.However,data on the associations and mechanisms of CS₂ exposure with fasting plasma glucose（FPG）levels and type 2 diabetes mellitus in general population is limited.Oxidative stress was deemed to play an important role in the pathogenesis of CS₂-related diseases.Epidemiological and animal experimental studies have shown that exposure to CS₂ may lead to increased oxidation levels and decreased antioxidant levels.Furthermore,excessive oxygen free radicals can damage pancreatic beta cells and reduce the sensitivity of peripheral tissues to insulin,thus promoting the development of diabetes.Based on these discoveries,we proposed a hypothesis that CS₂ exposure might lead to increased FPG levels or risk of type 2 diabetes partially through oxidative stress.We measured the concentrations of urinary biomarkers of CS₂ exposure（TTCA）,and biomarkers for lipid peroxidation（8-iso-Prostaglandin F2α,8-iso-PGF2α）and DNA oxidative damage（8-oxo-7,8-dihydro-20-deoxyguanosine,8-OHdG）among residents from the Wuhan-Zhuhai cohort.To explore the influence of CS₂on plasma glucose metabolism and the mechanisms involved,we studied the associations between urinary TTCA,oxidative damage markers,FPG levels and type 2 diabetes risk.Mediation analysis was employed to estimate the role of oxidative damage markers in the associations between urinary TTCA,FPG levels,and type 2 diabetes.This study was approved by the ethics committee,and written informed consent was signed for all participants.We have strict quality control system to ensure the accuracy of data collection and detection of biological samples.Part 1.Associations of carbon disulfide exposure with fasting plasma glucose and risk of type 2 diabetes among community populationObjective:We aimed to analyze the factors influencing the concentrations of urinary TTCA and the associations of urinary TTCA with fasting plasma glucose and type 2 diabetes in community population,and to further explore the combined effects of urinary TTCA and obesity on plasma glucose and diabetes.Method:All subjects were originated from the Wuhan-Zhuhai community cohort at baseline.We excluded those with a history of renal disease,failed to provide data on FPG levels and anthropometric indicators,or without sufficient urine samples for TTCA and creatinine（Cr）measurement,and a total of 3281 individuals were included in final analysis.Through structured questionnaires and physical examinations,individual detailed information including demographic characteristics,anthropometric indices,etc.were collected.We measured the concentrations of urinary TTCA and FPG levels via ultra-high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry and fully automated biochemical analyzer RX Daytona with enzymatic colorimetric method,respectively.The diagnosis of type 2 diabetes was based on the recommendations presented by American Diabetes Association,and subgroups of different physical types were defined according to the standards developed by the working group on obesity in China and the WHO[non-overweight:body mass index,BMI<24 kg/m²;overweight:24≤BMI<28 kg/m²;obesity:BMI≥28 kg/m²;central obesity:waist-to-hip ratio,WHR≥0.90（male）and WHR≥0.85（female）].We conducted log10-transformation for urinary TTCA concentrations.The influence factors of urinary CS₂ metabolite,whether demographic characteristics or health-related behaviors,were examined by single factor and multiple regression analysis.General linear regressions and restrictive cubic splines were applied to derive the association between urinary TTCA concentration and FPG levels.Logistic regression models were performed to analyze the relationship between urinary TTCA concentration and type 2 diabetes mellitus.Results:1.The levels and influence factors of urinary CS₂ metabolite:The median level of creatinine-corrected urinary TTCA concentrations was 0.736μg/mmol Cr.Univariate regression analysis results showed that both demographic characteristics（gender,age,BMI）and health-related behaviors（smoking,alcohol consumption and physical exercise）have an effect on the levels of urinary TTCA.The results of multiple regression analysis indicated that TTCA concentrations in urine elevated with increasing age,and the regression coefficient（β）was 0.004（P<0.05）.Smokers and those doing exercise rarely tended to have higher TTCA levels compared with nonsmokers and individuals doing more physical activity(β_smoking=0.108,β_{physical inactive}=0.048,P<0.05).2.Association of urinary CS₂ metabolite with FPG levels:Urinary TTCA concentrations were positively related to the levels of FPG（P<0.05）,and the results of restricted cubic spline models indicated a“U-shaped”relationship between them(P _{for nonlinear}=0.04).The FPG levels monotonically increased when urinary TTCA concentration was more than 0.436μg/mmol Cr.The results of stratified analyses by basic characteristics revealed that the association between urinary TTCA and altered FPG levels was stronger among females,individuals who were non-overweight and doing exercise rarely（all P<0.05）.3.Association of urinary CS₂ metabolite with type 2 diabetes:Urinary TTCA concentrations were positively associated with the risk of type 2 diabetes.Each one-unit increase in log-transformed urinary TTCA,there was a 30.6%（95%CI:7.4%,58.8%）increase in the risk of diabetes.Besides,we observed that the risk of diabetes was 1.436times higher in the highest TTCA concentrations group（Q4）than in the lowest TTCA concentrations group（Q1）from categorical analysis,showing a dose-response manner（P trend<0.05）.4.Combined effects of urinary CS₂ metabolite and obesity on FPG levels and type2 diabetes:Compared with people with low CS₂ exposure and non-overweight,those with low CS₂ exposure and obesity,high CS₂ exposure and overweight,high CS₂exposure and obesity have significantly higher FPG levels（P<0.05）.Compared with people with low CS₂ exposure and non-central obesity,people with low CS₂ exposure and central obesity,high CS₂ exposure and central obesity have significantly higher FPG levels（P<0.05）.Compared with subjects with low CS₂ exposure and non-overweight,the risk of diabetes increased by 146.5%among those with high CS₂exposure and obesity（P<0.05）.Compared with subjects with low CS₂ exposure and non-central obesity,the risk of diabetes increased by 158.2%,107.9%,210.0%among those with low CS₂ exposure and central obesity,high CS₂ exposure and non-central obesity,high CS₂ exposure and central obesity,respectively（P<0.05）.Conclusions:The levels of urinary CS₂ metabolite tend to be higher among older adults,smokers,and those doing exercise rarely.There were positive relationships between urinary CS₂ metabolite and FPG levels,risk of type 2 diabetes.In addition,combined exposure to CS₂ and obesity significantly increase FPG levels and risk of diabetes.Part 2.The mediating effect of oxidative damage on the relationships between carbon disulfide exposure and fasting plasma glucose and type 2 diabetes mellitusObjective:We aimed to examine the relationships between urinary CS₂ metabolite and the biomarkers of oxidative damage,as well as the biomarkers of oxidative damage and FPG levels,type 2 diabetes.And to further assess the potential mediating role of oxidative stress among the associations between CS₂ exposure and FPG levels,type 2diabetes in Chinese general adults.Method:Participants in this part were selected in the same way as Part 1.The levels of urinary 8-iso-PGF2αwere detected by commercially available ELISA kits,and the levels of urinary 8-OHdG were detected using solid phase extraction followed by high performance liquid chromatography combined with an electrochemical detector.We conducted log10-transformation for both 8-iso-PGF2αand 8-OHdG concentrations.General linear regressions were applied to derive the associations between urinary TTCA concentrations and biomarkers of oxidative damage（urinary 8-iso-PGF2α、8-OHdG）,as well as biomarkers of oxidative damage（urinary 8-iso-PGF2α、8-OHdG）and FPG levels.Logistic regression models were performed to analyze the relationships between urinary biomarkers of oxidative damage and type 2 diabetes mellitus.Besides,mediation analysis was employed to estimate the role of oxidative damage markers in the associations between urinary TTCA and FPG levels,type 2 diabetes.Results:1.Associations of urinary CS₂ metabolite with oxidative damage markers:There was a significant positive dose-response relationship between urinary TTCA and8-iso-PGF2αlevels(P _trend<0.05).Also,we observed a quite robust correlation between urinary TTCA and 8-iso-PGF2αwhen stratified by gender,age etc.,and age significantly modified such association(P _modification=0.026).Similarly,there was a significant positive dose-response relationship between urinary TTCA and 8-OHdG levels(P _trend<0.05).Such relationship was mainly apparent for females,nonsmokers,nondrinkers,and individuals more than 45 years old,non-overweight or doing regular physical activity（P<0.05）.2.Associations of urinary oxidative damage markers with FPG levels and type 2diabetes:Each one unit increase in log-transformed urinary 8-iso-PGF2αwas associated with a 0.205 mmol/L increase in FPG levels.The results of categorical analysis indicated a dose-response relationship between them(P _trend<0.05).However,no significant relationship was found between urinary 8-OHdG and FPG levels,as well as two kinds of urinary oxidative damage biomarkers（both 8-iso-PGF2αand 8-OHdG）and risk of type 2 diabetes.3.Mediating role of urinary oxidative damage markers in the association between urinary CS₂ metabolite and FPG levels:We found a significant mediating role of urinary8-iso-PGF2αin the relationship between urinary TTCA and FPG levels,and the mediated proportion by urinary 8-iso-PGF2αwas 21.43%.Conclusions:There were significant associations between urinary TTCA concentrations and oxidative damage biomarkers（8-iso-PGF2αand 8-OHdG）,and FPG levels increased with elevated urinary 8-iso-PGF2α.Urinary 8-iso-PGF2αsignificantly mediated CS₂-associated FPG increment.