Effects of polaprezinc on morphological change of the tongue in zinc-deficient rats.

OBJECTIVE: To examine the effects of polaprezinc on morphologic change of the tongue epithelium and on cell cycle regulation of taste bud cells by using zinc-deficient rats, an animal model of taste disturbance. METHODS: After 28 days of feeding with zinc-sufficient or -deficient diet, the rats fed a zinc-deficient diet were divided into four groups in which 0, 1, 3 and 10 mg/kg of polaprezinc were administered for 28 days with continuation of diet. Histopathological and morphological examinations of the tongue were carried out. RESULTS: Parakeratosis was observed in all rats receiving the zinc-deficient diet and 1 mg/kg polaprezinc but not in rats receiving 3 and 10 mg/kg polaprezinc. The ratio of keratinizing epithelium in the outer and inner circumference were significantly increased from 9.6% and 11.3%, respectively, in zinc-sufficient rats to 36.9% and 32.9%, respectively, in zinc-deficient rats (P<0.001 and <0.01). This increase was reversed to 13.7% and 12.3% in rats that received 3 and 10 mg/kg polaprezinc in the outer circumference, respectively. Same phenomenon was seen in the inner circumference part, 13.0% and 10.8% (P<0.01), respectively. In addition, proliferating cell nuclear antigen-positive cells in the taste bud were significantly decreased from 75.5% in zinc-sufficient rats to 32.2% in zinc-deficient rats (P<0.001). This decrease was reversed to 70.3%, 83.1% and 81.2% in rats that received 1, 3 and 10 mg/kg polaprezinc, respectively. CONCLUSION: Polaprezinc improves parakeratosis and decreases taste bud cell proliferation caused by zinc deficiency. These effects may be involved in mechanisms underlying improvement of taste disorders in animal models.

Effect of polaprezinc on taste disorders in zinc-deficient rats.

The effect of polaprezinc, a chelate compound consisting of zinc ion and L-carnosine, on abnormalities of taste sensation induced by feeding a zinc-deficient diet to rats was examined by using the two-bottle preference test (quinine hydrochloride as a bitter taste and sodium chloride as a salty taste). Rats were fed either a zinc-deficient or a zinc-sufficient diet. The zinc-deficient diet increased the preference for both taste solutions, while polaprezinc (at doses of 3 and 10 mg/kg) restored the altered taste preferences. We also evaluated the proliferation of taste bud cells using 5-bromo-2'-deoxyuridine (BrdU). The BrdU incorporation into taste bud cells was significantly reduced in rats fed a zinc-deficient diet compared with rats fed a zinc-sufficient diet (from 50.8% to 45.0%, p<0.05) and this reduction was reversed by polaprezinc at doses of 1, 3, and 10 mg/kg, increasing to 50.2%, 53.5%, and 52.5%, respectively. These findings indicate that zinc deficiency induces the delayed of proliferation of taste bud cells, while polaprezinc improves cell proliferation. In conclusion, polaprezinc had a therapeutic effect in a rat model of abnormal taste sensation. Its mechanism of action was suggested to involve improvement of the decrease in taste bud cell proliferation caused by zinc deficiency.