Anti-caries activity of selected Sudanese medicinal plants with emphasis on Terminalia laxiflora

In Sudan, some medicinal plants, such as Acacia seyal, Calotropisprocera and Balanites aegyptiaca have been used to prevent or treat oral health problems. The stem and stem bark of Terminalia laxiflora Engl., Combretaceae, are used as antiseptics for mouthwash to prevent gingivitis and thrush in Africa. Methanol and 50% hydroethanolic extracts of 25 plants that are used in traditional Sudanese medicine for several diseases and cavity disorders were screened for anti-cavity activities. T. laxiflora methanolic wood extracts, which exhibited such activity, were investigated. The crude extracts were assayed for their antimicrobial activities against Streptococcus sobrinus in terms of minimum inhibitory concentration and glucosyltransferase inhibition. The active extract of T. laxiflora wood was subsequently fractionated by different chromatographic techniques. Isolated compounds were identified by spectroscopic methods and assessed for S. sobrinus and glucosyltransferase inhibitory effects. Methanolic extracts of Terminalia brownii (bark), T. laxiflora (wood), A. seyal (bark), Persicaria glabra (leaves) and Tamarix nilotica (stem) showed good activities against both S. sobrinus and glucosyltransferase (MIC ≤ 1 mg/ml, IC50 values <50 μg/ml). Over all plant extracts, T. laxiflora demonstrated the good combined activities (MIC 0.5 mg/ml, glucosyltransferase, IC50 10.3 μg/ml); therefore, its methanolic wood extracts were selected for further phytochemical studies. Four constituents were isolated by chromatographic techniques and identified by spectroscopic techniques. Pharmacological evaluation of the obtained compounds showed that flavogallonic acid dilactone had comparatively good antibacterial activity. In the glucosyltransferase inhibitory test, terchebulin displayed potent activity with an IC50 of 7.5 μM. The screening presented in this study showed that methanol extracts of T. laxiflora wood possessed promising anti-cavity effects.