Chronic fluoride intake: effect in parameters related to insulin resistance in mice with different susceptibilities to dental fluorosis

Abstract

Fluoride (F) derives from fluorine, one of the most widespread elements in the earth's crust. Its absorption is inversely related to pH and occurs rapidly from the gastrointestinal trait, initially in the stomach and then in the small intestine. After its absorption, F is distributed to the tissues by the blood circulation and stored in the hard and soft tissues. Its excretion occurs essentially via the kidney system. It is an extremely relevant element in Public Health due to its properties to prevent or reverse carious lesions in individuals from all ages. However, excessive ingestion can affect bone metabolism, as well as the development of dental enamel. Some studies suggest that F can interfere in metabolic pathways, inhibiting the action of different enzymes and acting on the glycolytic pathway. Studies conducted with animals have investigated the relationship between fluoride intake and insulin resistance. It has been demonstrated that after administration of single dose of 40 µmol F/100 g body weitght to Sprague dawley female rats, an immediate fall of plasma insulin is detected, leading to an increase in glycemia. Plasma insulin and glycemia returned to normal baseline levels in 4-5 hours, together with the removal of F from plasma and soft tissues. On the other hand, in a study with rats from a different strain (Wistar) submitted to chronic F intake in the drinking water (5 or 50 ppm F), alterations in plasma insulin an glycemia were not observed. These conflicting results can be maybe explained by the genetic difference between the strains employed in the distinct studies. It is recognized that A/J mice are extremely sensitive to the treatment with F, while 129P3/J mice are remarkably resistant. Based on this, the present study aims to investigate if these animals that present differential protein expression when exposed to F due to their genetic background also have distinct responses in the parameters related with peripheral insulin resistance. For this, after approval of the ethical Committee, 96 animals (48 from A/J strain and 48 from 129P3/J strain) will be obtained after weaning, divided into 3 groups for each strain and treated for 42 days with water containing 0, 15 or 50 ppm F, under light, temperature and humidity controlled conditions. The animals will have access to low-F diet. After the treatment, animals will be submitted to euthanasia in order to get samples. The following analyses will be performed: glycemia, plasma insulin, plasma F, urine F. HOMA2-IR index and insulin tolerance test (ITT) will be also calculated. After checking normality and homogeneity, data will be analyzed by appropriate tests (p<0.05).