Effect of sodium fluoride-induced toxicity on the renal cortex of lactating mice and their offspring: a light and electron microscopic study

ABSTRACT

Fluoride is commonly added to drinking water for its clarification and to reduce tooth decay. However, fluoride was shown to have cumulative toxic effects on various organs, including the kidneys. To investigate the impact of sodium fluoride toxicity of drinking water on the histological structure of the renal cortex of lactating mice and their suckling offspring. Forty mice [20 mothers and 20 of their offspring] were used in this study and divided equally into four groups group I [control mothers] allowed ad libitum access to tap water without any added sodium fluoride during pregnancy and lactation, group II [treated mothers] drinking tap water containing NaF [0.5 g/L] from day 15 of pregnancy until day 14 after parturition, group III [suckling offspring of control mothers] and group IV [suckling offspring of treated mothers]. All mice were killed on postnatal day 14. Specimens were prepared for light microscope examination [hematoxylene and eosin and periodic acid-Schiff] and electron microscope examination. In addition, tubular epithelial height and tubular diameter were measured morphometrically and analyzed statistically. Examination of the renal cortex of treated mothers [group II] showed atrophic glomeruli with widened glomerular spaces. Tubules appeared dilated with decreased epithelial height as proved morphometrically. Tubular cells had a vacuolated cytoplasm and pyknotic nuclei. The apical brush border of many proximal tubules showed a weak and disrupted periodic acid-Schiff reaction. Ultrastructurally, some proximal lining cells showed heterochromatic nuclei, numerous cytoplasmic vacuolation of variable sizes and small scattered rounded mitochondria associated with loss of basal infoldings. However, the distal tubules maintained their basal infoldings and organized mitochondria. Podocyte foot processes were distorted and rested on a thickened glomerular basement membrane. The suckling offspring of the treated mothers showed less severe tubular injury than observed in their mothers as the tubular dilatation and the epithelial height were not affected significantly. Sodium fluoride induced various degrees of damage to the structure of renal cortex. The lactating mice renal cortices were severely affected compared to those of their suckling offspring. Thus, it is recommended to adjust the fluoride content in the municipal water supply and to avoid excess fluoride intake especially for lactating mothers