Bioactive essential oils from the Cameroonian rain forest: A review - Part I

Forty traditional medicinal plants from the Cameroonian rain forest belonging to twelve families are reviewed related to botanical description, taxonomy, common names, traditional use, essential oil composition as well as bioactivity and toxicity of their essential oils. A correlation is drawn between traditional use and bioactivity in vitro/in vivo, and structures of seventy-three main oil ingredients are given. Collected data indicate that plant essential oils unfold their biological activity related to functional groups of major and minor compounds, in a complex, fine-tuned interaction, modulated by environmental factors like the vegetation cycle of the plant, the altitude and the presence or absence of plant pathogen microbes, certain crop weevils as well as nematodes, varying with climatic seasons. Comparison of traditional use with laboratory results indicates effectivity of a good number of essential oils received from various plant parts, like leaves, bark, fruit, roots and rhizomes against Plasmodium falciparum, food borne microbes, dermatophytes, the malaria vector Anopheles gambiae, cancer cell lines, river blindness as well as plant pathogen weevils and fungi. However, toxicological studies are needed before any recommendation for application can be given. Importantly, leaf and fruit oil of Cupressus lusitanica (Cupressaceae) displayed strong acute toxicity in animal model, and the bark oil of Cinnamomum verum (Lauraceae) showed high toxicity in a normal cell line, so that preparations should be applied with care. Preformulation and formulation studies will be needed to develop a range of suitable dosage forms to introduce optimized pharmaceuticals (high active, low toxic) as replacement of current crude plant essential oil preparations in Cameroon and other Subsaharan countries.