Ugandan medicinal plants used traditonally for oral care : investigation of extracts for anti-bacterial, cytotoxic and anti-inflammatory effects

The use of traditional medicine for treating human diseases remain widespread in low-resource settings. Medicinal plants form the backbone for traditional medicine systems in many parts of the world. In Uganda, most communities rely on medicinal plants to prevent and treat oral diseases. Despite the long history and widespread use of these plants in oral health care, there is limited scientific evidence on the efficacy and safety of these plants. The aim of this thesis was to investigate various extracts from the medicinal plants for anti-bacterial, cytotoxic and potential anti-inflammatory effects.

The thesis is based on three studies. Study 1 investigated 16 commonly used plant species from different parts of Uganda. Pulp juice from fresh plant materials and solvent extracts (hexane, methanol and water) from dry plant materials were obtained and tested for their anti-bacterial effects on periodontopathic bacteria Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis, Tannerella forsythia and cariogenic bacteria Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus. Study II assessed the essential oil extracts from ten Ugandan aromatic medicinal plants for growth inhibitory effects on periodontopathic bacteria A. actinomycetemcomitans, P. gingivalis, and cariogenic bacteria S. mutans and L. acidophilus. Chemical compositions of the oils were explored by gas chromatography–mass spectrometry. Study III investigated the cytotoxicity of essential oils from four promising plants (Bidens pilosa, Ocimum gratissimum, Cymbopogon nardus, Zanthoxylum chalybeum) that had shown strong anti-bacterial effects on Gram-negative periodontopathic bacteria A. actinomycetemcomitans, P. gingivalis in Study II. Potential effects of the oils on the production of pro-inflammatory cytokines (IL-6, IL-8 and prostaglandin E2) by human gingival fibroblasts induced by IL-1β were also investigated.

In study I, the major findings were that fresh pulp juice prepared from Zanthoxylum chalybeum and Euclea latidens showed activity against all the bacterial species tested and at all strengths. Hexane extract from the aerial part of Helichrysum odoratissimum exhibited the best activity with MIC ranging from 0.0125 to 0.5mg/ml on all the bacterial species tested except A. actinomycetemcomitans. Methanol extract from Lantana trifolia was active on all the bacteria tested with MIC ranging 0.25 to 1mg/ml. In study II, the major findings were that essential oil from Cymbopogon nardus exhibited the highest activity with complete growth inhibition of A. actinomycetemcomitans, P. gingivalis at all the three concentrations tested, the major constituents in the oil being mainly oxygenated sesquiterpenes. Essential oils extracted from Teclea nobilis. Hoslundia opposita, Ocimum gratissimum and Bidens pilosa were also considered promising because they showed marked growth inhibitory effects on least 2 bacterial species. In study III, essential oil from Z. chalybeum was the most cytotoxic while the oil from C. nardus the least cytotoxic. Essential oil from O. gratissimum significantly decreased baseline and induced secretion of Prostaglandin E2.

We conclude that fresh extracts from the roots of Z. chalybeum and E. latidens had anti-bacterial effects on the cariogenic and periodontopathic bacteria, confirming the use of chewing sticks prepared from these plants as a tool for brushing teeth. The hexane extract from the aerial part of H. odoratissimum had strong anti-bacterial effects on cariogenic and periodontopathic bacteria, suggesting the potential use of this extract, or isolated active principles, in the treatment or prevention of dental caries and periodontal diseases. The marked inhibitory effects of the essential oils on periodontopathic bacteria A. actinomycetemcomitans and P. gingivalis suggest these oils could be avenues to explore for possible application in treatment of periodontal diseases. The essential oil extracted from O. gratissimum demonstrated both anti-bacterial and anti-inflammatory effects suggesting the oil could be worth exploring for possible application in treatment of periodontitis.

List of scientific papers

I. Francis Ocheng, Freddie Bwanga, Moses Joloba, Ann-Karin Borg-Karlson, Anders Gustafsson, Celestino Obua. Anti-bacterial activities of extracts from Ugandan medicinal plants used for oral care. Journal of Ethnopharmacology, 2014, 155, Pages 852–85.
https://doi.org/10.1016/j.jep.2014.06.027

II. Francis Ocheng, Freddie Bwanga, Moses Joloba, Abier Softrata, Muhammad Azeem, Katrin Pütsep Anna-Karin Borg-Karlson, Celestino Obua, Anders Gustafsson. Essential oils from Ugandan aromatic medicinal plants: Chemical composition and growth inhibitory effects on oral pathogen. Evidence-Based Complementary and Alternative Medicine 2015;2015:230832
https://doi.org/10.1155/2015/230832

III. Francis Ocheng, Freddie Bwanga, Elisabeth Almer Boström, Moses Joloba, Ann-Karin Borg-Karlson, Tülay Yucel-Lindberg, Celestino Obua, Anders Gustafsson. Essential oils from Ugandan medicinal plants: in vitro cytotoxicity and effects on IL-1-β induced pro-inflammatory cytokines and chemokine by human gingival fibroblasts [Manuscript]