The Effect And A Mechanistic Evaluation Of Polystyrene Nanoplastics On Type 2 Diabetes

Plastic pollution in the environment is growing at a staggering rate and has attracted worldwide attention.Plastic waste will be decomposed into microplastics(MPs)and nanoplastics(NPs)through physical,chemical or biological processes,which are widely distributed in water,soil and air,and may pose a serious threat to human health.Compared with MPs,NPs has higher surface area and volume ratio,and is easier to enter into cells or tissues,so it has greater potential toxicity.Presently,there are few evidences on the biotoxicological effects of NPs on mammals,especially the effects of NPs exposure on blood glucose in mammals and its mechanism.Polystyrene plastic is the most common plastic material in the environment,which is widely used in the manufacture of thermal insulation materials,disposable tableware,foam boxes and cleaning products.It is of great significance to evaluate the effects of polystyrene nano-plastics(Polystyrene nano-plastics,PS-NPs)on human health.Oral exposure is the main way of exposure to plastic particles,in this study,mice were exposed to 80 nm PS-NPs by intragastric administration.One hundred C57 BL/6 mice were randomly divided into 10 groups:(1)normal saline group;(2)PS-NPs 1 mg/kg/day;(3)PS-NPs 10 mg/kg/day;(4)PS-NPs 30 mg/kg/day;(5)saline + high fat diet;(6)PS-NPs1 mg/kg/day + high fat diet;(7)PS-NPs 10 mg/kg/day + high fat diet;(8)PS-NPs 30mg/kg/day + high fat diet.(9)PS-NPs 10 mg/kg/day + high fat diet + SC79;(10)normal saline + high fat diet + SC79.Injecting mice with a low dose of STZ(Streptozocin)(40mg/kg)and giving them a high fat diet which allowed researchers to create a model of type2 diabetes(T2DM).The mice were exposed to PS-NPs or saline respectively for 8 weeks.SC79,a specific activator of AKT,was injected to evaluate the mechanism of AKT.The mice showed hyperglycemia after 8-12 injections of STZ.Every week,a blood glucose meter was used to test fasting blood glucose.A few days before the exposure ended,it was used to measure oral glucose tolerance(OGTT)and insulin tolerance(ITT).After exposure,mice were anesthetized to take heart blood and liver and pancreas tissues,serum insulin was measured to evaluate HOMA-IR.Organs were weighed and then organ coefficients were calculated.In this study,the levels of reactive oxygen species(ROS),malondialdehyde(MDA)and glutathione(GSH)related to oxidative stress in liver and pancreas of mice were measured to evaluate the oxidative damage of liver and pancreas exposed to PS-NPs,and the serum levels of liver function enzymes and blood lipids were detected by kit to evaluate the metabolic disorder of mice exposed to PS-NPs.The changes of inflammation in mice exposed to PS-NPs were evaluated by identifying variations in the blood levels of the important inflammatory markers TNF-α,IL-6,and IL-27.Pathological abnormalities and glycogen accumulation of related organs in mice exposed to PS-NPs were evaluated by H&E staining and PAS staining.The expression of PAKTser473 and P-GSK3βser9 in the liver tissue of the mice was detected by immunohistochemistry to evaluate the changes of key signaling pathways of insulin metabolism after exposure to PS-NPs.The results showed that:(1)PS-NPs exposure alone had a slight effect on the body weight and drinking water of mice;In the diabetic model group,PS-NPs exposure led to weight loss and a significant increase in drinking water.(2)In the liver tissue of 30 mg/kg/day PS-NPs exposure group and PS-NPs exposure plus diabetes model group,obvious inflammatory cell infiltration and tissue damage were observed,and obvious pathological damage was also observed in pancreatic tissue,such as irregular outline and shape of islets,unclear cell structure and so on.(3)After 8 weeks of PS-NPs exposure alone,the fasting blood glucose of mice increased slightly;And in the diabetic model group,the exposure of PS-NPs at 30mg/kg/day caused a significant increase in fasting blood glucose in mice in a dosedependent manner.(4)PS-NPs exposure to 30 mg/kg/day significantly increased the levels of OGTT,ITT and HOMA-IR,but had no significant effect on insulin secretion;while in the diabetic model group,PSNPs exposure to 30 mg/kg/day caused a significant increase in OGTT and HOMA-IR,and increased ITT to some extent,but had no significant effect on insulin secretion.(5)In the 30 mg/kg/day PS-NPs exposure group,the levels of ROS and MDA increased significantly;while the level of GSH decreased significantly,while in the diabetic model group,the levels of ROS and MDA in liver and pancreas increased significantly and the level of GSH decreased significantly in the diabetic model group.(6)PS-NPs exposure caused the accumulation of glycogen in liver tissue,caused the disorder of blood lipid metabolism,increased the levels of T-CHO,TG and LDL-C,decreased the level of HDL-C,and increased the activities of ALT,AKP and AST in mice exposed to PS-NPs.PS-NPs exposure significantly decreased the content of IL-27 in serum,but had no significant effect on TNF-α and IL-6.(7)Phosphorylation of AKT and GSK3β in mice was significantly decreased by exposure to PS-NPs alone in a dose-dependent manner;while in the diabetic model group,30 mg/kg/day PS-NPs exposure further decreased the phosphorylation levels of AKT and GSK3β in mice.(8)Injection of SC79 could partially alleviate the aggravating effect of PS-NPs exposure on diabetic mice,such as increasing the phosphorylation levels of AKT and GSK3β,effectively alleviating the increase of ROS level in liver or pancreas,and slightly attenuating the increase of fasting blood glucose and insulin resistance induced by PS-NPs exposure.In summary,30 mg/kg/day PS-NPs exposure can lead to a significant increase in blood glucose,oxidative stress,glucose tolerance and insulin resistance.In the diabetic model group,PS-NPs exposure significantly aggravated oxidative stress,glucose tolerance,insulin tolerance and insulin resistance,and induced pathological changes in the liver and pancreas.PS-NPs exposure decreased the phosphorylation levels of AKT and GSK3β,and AKT activator SC79 increased the phosphorylation levels of AKT and GSK3β,effectively alleviated the increase of ROS levels in liver or pancreas,and alleviated the increase of fasting blood glucose and insulin resistance induced by PS-NPs exposure.This suggests that exposure to PS-NPs aggravates type 2 diabetes,and its underlying mechanism involves inhibition of AKT/GSK3β phosphorylation.