Potential mechanisms of action of pesticides on factors related to type 2 diabetes

Abstract

In most agriculturally based economies around the world, large scale industrial agriculture entails the use of modern agricultural machinery, herbicides and pesticides. Meanwhile there are recent debates around agroecology/organic agriculture in which less pesticides are used, the use of pesticide and herbicide in agriculture remain a dominant feature even among small scale farmers. Moreover, pesticides are used by public health experts for the control of vectors of infectious diseases. Therefore, pest control is largely dependent on pesticides some of which include: Imidacloprid, Chlorpyrifos, Lambda cyhalothrin and Oxamyl, belonging to the neonicotinoids, organophosphate, pyrethroids and carbamate classes respectively. In addition to their primary mode of action and their specific targets such as insects, recent studies show that they affect metabolic parameters in primates. The present study inscribes itself in these body of recent research and specifically sought to investigate the effects of gestational exposure to the above mentioned four pesticides on oxidative stress and metabolic parameters in female Wistar rats and their offspring. This study was divided into 3 parts with a preliminary section carried out to determine the lethal dose 50 (LD50) of the four studied pesticides. For LD50, each pesticide was administered to female nulliparous Wistar rats (age: 10 - 12 weeks, weight: 180g - 200g) in increasing dose by oral gavage until death was recorded. The pesticide was diluted in distilled water with the volume being 10mL/kg rat. "The highest dose with no mortality and the lowest with mortality were used to calculate the LD50". In the 1st part, thirty-female nulliparous Wistar rats (age: 12 - 14 weeks, weight: 200g - 220g) were divided into 5 equal groups matched by weight and fasting blood glucose levels. Each rat in group 2, group 3, group 4 and group 5 received 44 mg Imidacloprid, 13.5 mg Chlorpyrifos, 5.6 mg Imidacloprid + 5.6 mg Lambda cyhalothrin, and 0.4 mg Oxamyl per kg body weight/ day respectively. All pesticides were administered using a gastro-oesophageal probe throughout gestation. Each rat from the Control Group (group 1) received distilled water (10mL/kg rat). At birth, pesticide administration was discontinued, and the female rats were followed up for 4 weeks. They were fasted overnight and sacrificed upon local anaesthesia and blood samples, liver, kidney, pancreas and muscles collected. Part of the liver and kidney were used to quantify antioxidants and lipid peroxidation markers while serum was used to measure alanine transaminase and aspartate transaminase. In the 2nd part, all offspring were followed up by weekly measuring of body weight. At weaning (4 weeks), 8 offspring were randomly selected from each group, fasted overnight and sacrifice upon local anaesthesia. The remaining offspring were followed up until adult age (12 weeks), 8 randomly selected and sacrificed upon local anaesthesia after an overnight fast. After sacrifice in each case (4 week and 12 week), blood samples, liver and kidney were collected. Part of the liver and kidney were used to quantify antioxidants and lipid peroxidation markers while serum was used to measure alanine transaminase and aspartate transaminase. In the 3rd part, samples were collected from parent rats, their offspring at weaning and at adult age. Blood samples were collected, and serum prepared for lipid profile and insulin quantification. Muscles samples were collected from the biceps femoris for glucose transporter-4 and nuclear factor kappa beta protein expression. Liver, kidney, and pancreas were collected for histological studies. Statistical analyses were performed using the GraphPad Prism software. The LD50 values obtained were "440 mg/kg" for Imidacloprid, "135 mg/kg" for Chlorpyrifos, "56 mg/kg" for the formulation containing Lambda cyhalothrin+Imidacloprid and "4 mg/kg" for Oxamyl. Antioxidant enzyme levels (super oxide dismutase, catalase, glutathione peroxidase, glutathione reductase), reduced glutathione and malondialdehyde were altered in at-least one of the pesticide-exposed groups compared to the control group. These alterations observed in parents were also observed in offspring sacrificed at weaning as well as those sacrificed at adult age. Fasting Blood glucose, lipid profile (total cholesterol, triglycerides and low-density lipoprotein cholesterol), insulin and homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly higher in the pesticide-exposed groups compared to the control group. Similar results were observed in offspring sacrificed at weaning and those sacrificed at adult age. Moreover, Imidacloprid and Chlorpyrifos significantly reduced glucose transporter-4 (GLUT4) and significantly increased nuclear factor kappa beta (NFkβ) expression in muscles of parents and offspring explored at adult age. According to this study, pesticides induced oxidative stress, lipid peroxidation, insulin resistance and dyslipidemia in female Wistar rats during gestation and their offspring. The effect on offspring persisted until adult age, suggesting epigenetic mechanisms. These findings suggest that exposure to pesticides could contribute to an increase in the incidence of diabetes worldwide. Therefore, future studies are needed to elucidate the current findings in humans. Such studies might inform public health and agricultural policy makers on the need to regulate the use of pesticides especially in a country like Cameroon where the drive to a second-generation agriculture has paved the way for an increase in the use of pesticides sometimes by farmers not wearing any form of protection nor respecting prescribed doses.