Influence of gastric acidity on fluoride absorption in rats

Modulation of the Nrf-2 and HO-1 signalling axis is associated with Betaine's abatement of fluoride-induced hepatorenal toxicities in rats

Sodium fluoride (NaF) ingestion has several detrimental effects in humans and rodents. NaF mechanisms of toxicity include perturbation of intracellular redox homeostasis and apoptosis. Betaine (BET) is a modified amino acid with anti-inflammatory, antioxidant, and anti-apoptotic properties. This study investigates BET's effect on NaF-induced hepatorenal toxicities in rats. Experimental rats (n = 30) were randomly assigned to groups (n = 6) and treated by gavage for 28 days. Group I (2 mL of distilled water), Group II (NaF: 9 mg/kg) alone, Group III: (BET: 100 mg/kg), Group IV: (NaF: 9 mg/kg and BET 1: 50 mg/kg), and Group V: (NaF: 9 mg/kg and BET 2: 100 mg/kg). Our findings revealed significantly (p < 0.05) increased hepatic transaminase activities alongside creatinine and urea levels following NaF-alone treatment in addition to increased oxidative status, lipid peroxidation, reactive oxygen and nitrogen species, decreased superoxide dismutase, catalase, glutathione-s-transferase, glutathione peroxidase, glutathione, and total sulfhydryl groups. The reduced levels of nuclear factor erythroid 2-related factor-2 and the activities of heme oxygenase-1, thioredoxin, and thioredoxin reductase in NaF-alone treated rats equally compromised cellular molecular responses to oxidative stress. Also, NaF increased (p < 0.05) hepatorenal inflammatory biomarkers-nitric oxide, interleukin-10, myeloperoxidase, and xanthine oxidase. Furthermore, caspase-3 and caspase-9 were increased (p < 0.05) in rats treated with NaF alone. Contrastingly, BET was observed to alleviate the harmful effects of NaF. Treatment with BET mitigated NaF-induced oxido-inflammatory responses and apoptosis in the experimental rat's hepatorenal system. The study demonstrates the potential of BET to abate NaF-induced hepatorenal toxicity.

Assessment of water contribution on total fluoride intake of various age groups of people in fluoride endemic and non-endemic areas of Dindigul District, Tamil Nadu, South India

The prevalence of fluorosis is mainly due to the intake of large quantities of fluoride through water. It is necessary to determine the contribution of water used for drinking and food processing and other diet sources on daily fluoride intake for finding the ways to reduce the excess fluoride intake than the minimum safe level intake of 0.05 mg/kg/day. The main objectives of this study are to determine the quantitative impact of water through drinking and cooking of food and beverages on total fluoride intake as well as to estimate the contribution of commonly consumed diet sources on total fluoride intake. Contribution of water on daily fluoride intake and estimation of total fluoride intake through the diet sources were accomplished through analysis of fluoride in drinking water, solid and liquid food items, Infant formulae, tea and coffee infusions using fluoride ion selective electrode. Determination of incidence of fluorosis in different fluoride endemic areas in Dindigul District of Tamil Nadu, South India is achieved through clinical survey. The percentage of daily fluoride intake through water is significantly higher for infants than children, adults and old age groups of people. The percentile scores of fluoride intake through water from drinking and cooking increases with increase of water fluoride level. The rate of prevalence of fluorosis is higher in adolescent girls and females than adolescent boys and males residing in high fluoride endemic areas. More than 60% of the total fluoride intake per day derived from water used for drinking and food processing. Hence the people residing in the fluoride endemic areas in Dindigul District of Tamil Nadu, South India are advised to take serious concern about the fluoride level of water used for drinking and cooking to avoid further fluorosis risks.

pH-dependent fluoride transport in intestinal brush border membrane vesicles

Fluoride (F) absorption from the rat stomach and urinary bladder, hamster cheek pouch, and the renal tubules of several species are pH gradient-dependent. These observations led to the hypothesis that F crosses these epithelia in the form of the undissociated acid, HF. Several recent reports, however, have provided evidence that F absorption from the rat small intestine is insensitive to the lumenal pH. We report here our evidence that F uptake by rabbit intestinal brush border membrane vesicles (BBMV) occurred rapidly and with an overshoot only in the presence of an inward-directed proton gradient. In the absence of a proton gradient or in the presence of an outward-directed gradient, F uptake was slow and without an overshoot. In the presence of an inward-directed proton gradient, F uptake was partially inhibited by DIDS and DEP but not by diBAC. PCMBS inhibited F uptake by up to 83% in a dose-response manner. DiBAC appeared to reduce intravesicular pH slightly but the other reagents had no effect. When the uptake buffer contained chloride or nitrate, F uptake was partially inhibited compared to the mannitol or gluconate controls. It was concluded that F transport across the rabbit intestinal BBMV occurs via a carrier-mediated process which may involve cotransport of F with H+ or exchange of F with OH-. The inhibitory effects of DIDS, DEP and PCMBS may occur by affecting this carrier-mediated transport.

Determinants and mechanisms of enamel fluorosis

Enamel fluorosis occurs when fluoride concentrations in or in the vicinity of the forming enamel are excessive during its pre-eruptive development. Fluoride concentrations in plasma, enamel and other tissues reflect the difference between intake and excretion, i.e. fluoride balance. In addition to the diet, modern sources of ingested fluoride include a variety of dental products, some of which have been identified as risk factors for fluorosis. Fluoride absorption is inversely related to dietary calcium which, at high concentrations, may cause net fluoride secretion into the gastrointestinal tract. The excretion of absorbed fluoride occurs almost exclusively via the kidneys, a process which is directly related to urinary pH. Thus, fluoride balance and tissue concentrations and the risk of fluorosis are increased by factors such as high protein diets, residence at high altitude, and certain metabolic and respiratory disorders that decrease pH. Factors that increase urinary pH and decrease the balance of fluoride include vegetarian diets, certain drugs and some other medical conditions. Although several other fluoride-induced effects might be involved in the aetiology of fluorosis, it now appears that inhibition of enzymatic degradation of amelogenins, which may delay their removal from the developing enamel and impair crystal growth, may be of critical importance. In addition to the effects of fluoride, disturbances in enamel formation that can be confused with fluorosis are caused by chronic acidosis and hypoxia independently of the level of fluoride exposure.

Lack of significant effect of coffee and caffeine on fluoride metabolism in rats

It has been reported that rat plasma fluoride (F) concentrations are higher by up to 100% when F is administered ig in coffee or a caffeine solution compared with when it is administered in water. It was hypothesized that the consumption of caffeinated beverages has contributed to the prevalence of dental fluorosis. The present studies were done to determine the physiological mechanisms for these effects. For approximately 2 h after F was administered in coffee, plasma F concentrations were higher than when administered in water, decaffeinated coffee, or a caffeine solution (3 mg/kg), but the intergroup differences were small and generally not statistically significant. The 4-hour plasma AUC values did not differ with statistical significance. There were no differences among the groups in the renal or extrarenal (skeletal) clearances of F, which suggested that the higher plasma F concentrations in the coffee groups may have been due to a slight and transient increase in absorption rate. The possibility that caffeine per se might elevate endogenous plasma F and calcium concentrations was excluded after caffeine (25 mg/kg) ig without F was given. In addition, the renal excretion, clearance, and fractional renal clearance of calcium did not differ among the groups. The results indicated that decaffeinated coffee and caffeine had no effect on F metabolism, whereas caffeinated coffee appeared to increase the initial absorption rate but not the 4-hour bio-availability.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of plasma fluoride and dietary calcium concentrations on GI absorption and secretion of fluoride in the rat

This 30-day balance study with weanling rats was designed to determine the effects of plasma fluoride and dietary calcium concentration and their interaction on the absorption, balance, and tissue concentrations of fluoride. The three major groups differed according to the total exposure and plasma concentrations of fluoride. One group received fluoride only in the diet and the other two received additional fluoride by continuous infusion from miniosmotic pumps implanted S.C. Each group was divided into two subgroups with dietary calcium concentrations of 0.4% or 1.4%. Fluoride intake with the diet did not differ among the groups. Fecal fluoride excretion was directly related to plasma fluoride concentration. The absorption and balance of dietary fluoride were inversely related to plasma fluoride concentration. These effects were greatest in the groups fed the 1.4% calcium diet. The interactions of plasma fluoride and dietary calcium on these variables were highly significant (P < 0.0001). The balance of dietary fluoride was negative in the four groups that received additional fluoride by infusion. In the two groups that received fluoride only in the diet, the plasma and bone fluoride concentrations were 41% and 59% lower, respectively, in the 1.4% dietary calcium group. The findings indicate that net fluoride secretion into the GI tract can occur when plasma fluoride concentrations and calcium intake are elevated. They suggest that elevated plasma fluoride levels and calcium intake are factors that may diminish the effect of oral fluoride treatment in osteoporotic patients.

Effects of chronic fluoride exposure on morphometric parameters defining the stages of amelogenesis and ameloblast modulation in rat incisors

The response of ameloblasts to long-term (6 weeks) exposure to 100 ppm fluoride was examined in continuously erupting mandibular incisors of female Sprague-Dawley rats as compared to control rats receiving a similar diet (Teklad L-356) but no sodium fluoride in their drinking water. After treatment, animals from both groups were perfused intravascularly with glutaraldehyde, and the incisors were removed and processed for light microscope morphometric analyses directly from 1 microns thick Epon sections. Other animals were injected intravenously with calcein (green fluorescence) followed 4 hours later by xylenol orange (red fluorescence) in order to reveal smooth-ended ameloblast modulation bands and thereby allow quantification of parameters related to the creation and movement of modulation waves within the maturation zone of these teeth. The results indicated that rat incisors expressed four major changes in normal amelogenesis which could be attributed to the chronic fluoride treatment. First, ameloblasts produced a thinner than normal enamel layer by the time they completed the secretory stage and entered the maturation stage of amelogenesis. Second, enamel organ cells within the maturation zone, especially those from the papillary layer, were shorter in height than normal. Third, ameloblasts related to maturing enamel in areas where it was partially soluble and/or fully soluble in EDTA modulated at a rate that was much slower than normal. In some locations ameloblasts remained ruffle-ended for as much as 30% longer than normal per cycle. This upset the usual pattern such that fewer total modulation cycles were completed per unit time by these ameloblasts. Fourth, enamel proteins were lost from the maturing enamel layer at a rate that was about 40% slower than normal. The data suggested that ameloblasts detected the delay in the extracellular breakdown and/or loss of enamel proteins and they responded by remaining ruffle-ended for longer intervals than usual (positive feedback).