Mechanism of cadmium induced crystal defects in developing rat tooth enamel

Abstract

It is well known that exposure to environmental cadmium causes itai-itai (ouch-ouch) disease. However, the exact mechanism underlying this bone disease remains unresolved. By focusing on the calcification mechanism, we examined developing tooth enamel in rats exposed to cadmium to test the hypothesis that cadmium exposure may cause defects in crystal formation. Electron microscopy revealed the presence of perforated crystals in developing tooth enamel, indicating that the process of crystal nucleation may have been interrupted by cadmium exposure. Furthermore, biochemical analyses revealed that the catalytic activity of carbonic anhydrase in the immature enamel matrix declined remarkably despite the fact that quantitative reduction of this enzyme was insignificant, suggesting that the decline of catalytic activity may have resulted from the replacement of zinc with cadmium ions. Therefore, we concluded that the poor catalytic activity of cadmium-binding carbonic anhydrase might hinder the nucleation process, leading to an impairment in mineralization that causes itai-itai disease.

Fluoride Exposure May Accelerate the Osteoporotic Change in Postmenopausal Women: Animal Model of Fluoride-induced Osteoporosis

“…This might be fatal to cellular metabolism and eventually lead to pathological calcification, which might be similar to the vascular calcification accompanying cellular degeneration [43]. On the other hand, the increase of osteoid caused by the relatively low dose of F treatment may be interpreted as an increase of amorphous minerals due to the failure of crystal nucleation observed in the present and the previous studies [13,14,43].…”

“…The scientific justification for F therapy for osteoporosis, which induced irregular periosteal bone formation, ligament calcification, abnormal mineralization, and an increase of osteoid formation [29][30][31][32][33][34][35][36], is as follows: Concerning the high dose of F treatment, the increase of bone mineral density might be attributed to the pathological mineralization seen by an abnormal calcification and the presence of large crystals located outside the collagen fibrils [16,17,35,37]. This occurs because a high content of F ions absolutely inhibits the synthesis or activity of certain enzymes such as enolase and carbonic anhydrase [13,14,[38][39][40][41][42]. This might be fatal to cellular metabolism and eventually lead to pathological calcification, which might be similar to the vascular calcification accompanying cellular degeneration [43].…”

“…Further, the combined effects of Es deficiency and Cd exposure were responsible for greatly increasing amorphous minerals and deceasing trabecular architecture in the bone, resulting in the development of "itai-itai disease" [13]. In the case of fluoride (F) exposure, the detrimental effect of F ions on the crystal nucleation process far exceeded that of Cd ions [14,15]. This led to the assumption that F schemes for caries prevention might leave postmenopausal women exposed to a high risk of developing osteoporosis without any beneficial effects.…”

Bhopal Gas tragedy- An experience of the medical and dental practitioners of this Unfinished Story 1984

“…Biochemical analyses revealed that the catalytic activity of carbonic anhydrase in the immature enamel matrix declined remarkably [23]. The poor catalytic activity of cadmium-binding carbonic anhydrase might hinder the nucleation process, leading to impairment in mineralization [23]. The dental defects and its possible mechanism in Bhopal gas tragedy affected individuals and their preceding generations should be evaluated on a larger scale .The present study conducted had limitations that the findings were solely dependent on the opinion given by the practitioners.…”

“…Also, increased levels of cadmium could affect the crystal formation in the enamel. Biochemical analyses revealed that the catalytic activity of carbonic anhydrase in the immature enamel matrix declined remarkably [23]. The poor catalytic activity of cadmium-binding carbonic anhydrase might hinder the nucleation process, leading to impairment in mineralization [23].…”