Effect of Antioxidants on Minocycline Discoloration in a Rat Model

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Minocycline is the treatment of choice for acne vulgaris and has been shown to cause discoloration of the natural tooth in adults. Discoloration has been reported to be the product of an oxidation reaction. Laboratory studies have shown that discoloration can be induced by exposure to light, and that an antioxidant can block its formation. Objectives: The purpose of this study was to evaluate the discoloration of minocycline in vivo and to determine subsequent changes with the intervention of antioxidants. Methods: Four groups of five Male Sprague-Dawley rats (150-200 gm) each were fed Harlan 7013 (negative control), or one containing either Vitamin E, Vitamin C, or Epigallocatechin gallate (EGCG) for 3 months. Four other groups received the same diets, plus minocycline 0.5mg/kg calculated therapeutic dose (positive controls). Digital images of rat incisors were recorded every 2 weeks to monitor color change (Fig 1). At 3 months, the forty rats were sacrificed and the thyroid glands, femurs, mandibles and incisors were harvested. The hard tissues were scanned under UV light and confocal microscopy. The body weights (424-461gm) were recorded for each group to verify no change in eating habit. Results: No significant change was observed from the digital images of incisors. Visible discoloration was observed in the thyroid (Fig 2) and femurs of the minocycline diet groups. The color difference is further enhanced by observation under short wave UV light (Fig 3). Confocal microscopy of surface bone did not reveal major differences. (Fig 4). Conclusion: EGCG, Vitamin C and Vitamin E did not appear to be effective in preventing discoloration of the thyroid glands and bones caused by minocycline. Hard tissue, thyroid and salivary glands are planned for further histological analysis. Funded by a fellowship grant from the Academy of Operative Dentistry.