Tyrosinase modulation by five Rwandese herbal medicines traditionally used for skin treatment

Ethnopharmacological relevance: Traditional herbal medicines provide an interesting, largely unexplored source for the development of potential new drugs and skin-care cosmetics. Some herbal extracts are known to be inhibitors of melanin formation, sometimes more potent than the classical inhibitors, hydroquinone/arbutin or kojic acid, and are not associated with melanocytes cytotoxicity or mutagenicity. Such plants are used in traditional medicine in many countries, particularly in Africa, for skin lightening. Aim of the study: To evaluate in vitro the ability of Rwandese medicinal plants, traditionally used for the treatment of skin (discoloration and attenuation of discolored spots), to modulate pigmentation and tyrosinase activity. Materials and methods: Based on an ethnopharmacological survey, five herbs [Brillantaisia cicatricosa Lindau (Acanthaceae), Chenopodium ugandae (Aellen) Aellen (Chenopodiaceae), Dolichopentas longiflora Oliv. (Rubiaceae), Protea madiensis Oliv. (Proteaceae) and Sesamum angolense Welw. (Pedaliaceae)] were selected. Twenty-seven extracts, obtained by treating the herbs with increasing polarities solvents, were investigated for their effects on cell viability (MTT test) and on pigmentation: inhibition of the enzyme tyrosinase (colorimetry of reaction products, measurement of enzyme activity, TLC-autography; studies on crude cellular extracts obtained from normal melanocytes and on a mushroom tyrosinase) and measurement of melanogenesis by human melanoma cells. Results: None of the tested plant extracts were cytotoxic on tested human melanoma cell lines, except for Dolichopentas longiflora (IC50 of leaves n-hexane extract, 4 μg/ml for MM028 and 4.5 μg/ml for MM001; IC50 of roots ethyl acetate extract, 0.8 μg/ml for MM028 and 3.9 μg/ml for MM001). Almost all extracts inhibited melanogenesis in a melanoma whole cells overall pigmentation assay, a model reflecting the entire cycle of melanogenesis. All the Protea madiensis extracts quite strongly inhibited melanogenesis and, surprisingly, one of the Dolichopentas longiflora leaves extracts was found to increase melanogenesis. These results were confirmed by the modulation of pigmentation reactions by crude cellular extracts obtained from normal melanocytes; interestingly, one of the extracts (Dolichopentas longiflora ethyl acetate extract) is even more active (61% at 500 μg/ml) than kojic acid (<3% at 142 μg/ml and 68% at 1421 μg/ml). In a mushroom tyrosinase inhibition assay, data obtained on some extracts fairly agree with pigmentation inhibition measured on melanocytes proteins as, for example, the methanol extract of Protea madiensis. While a few others extract display discording data, this probably reflects either differences between human and mushroom tyrosinase, interference with melanocytes enzymes at later steps than tyrosinase or the simultaneous presence of compounds with conflicting activities in a given extract. Conclusions: Ethnopharmacological data represent an efficient approach to discover active herbs. Some of the selected medicinal plants clearly show potent tyrosinase inhibitions while one extract significantly increases cell pigmentation; one extract contains potent growth melanocytes inhibitors. © 2013 Elsevier Ireland Ltd.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Processes and partnerships for effective regional surveillance of banana diseases

Crop diseases do not respect country borders and yet preventive measures to curtail the introduction, establishment and spread of diseases are often coordinated on a country-by-country basis. This is because each country has its own mandate to safeguard food security and trade relations. However, knowledge held by researchers and regulatory officials within each country for any given disease can benefit those in neighbouring countries, and this can be reciprocated for other diseases, depending on aggregated disease distribution and experience of methods for effective diagnosis and management. Based on an appreciation of this common goal, national research and regulatory officials from seven countries networked to prioritize which diseases of banana (Musa spp.) were of critical importance and where to undertake spatially designed surveillance exercises around the Great Lakes region of sub-Saharan Africa. Surveys for banana Xanthomonas wilt and banana bunchy top disease were targeted to zones where outbreaks had been reported but not confirmed, and where invasion risk was high as a consequence of proximity to areas or countries known to contain either disease. To ensure that disease diagnoses were precise, field based visual assessments of symptoms were supported by molecular based diagnostics performed under laboratory conditions. Samples were transferred from plants in the field to the laboratory using pathogen DNA capture kits that could be swiftly and safely moved across country borders for analysis at a centralized laboratory to ensure that results from different surveys could be compared. The accuracy of global positioning system (GPS) coordinates recorded as the origin of samples from surveys was validated by comparing the altitude given by the GPS with altitude data provided by digital elevation models. Geographical information system (GIS) maps could then be generated to clearly show the prevalence of banana Xanthomonas wilt and banana bunchy top disease for the zones surveyed. Furthermore, the GIS maps can be used to interpolate different GPS-linked data sets to highlight factors driving disease establishment and spread, such as conducive environmental conditions, and to determine where to prioritize management strategies based on food insecurity measures. The need to prioritize investments across a region is of particular importance in developing countries where capacities for disease surveillance and diagnostics are limited, resulting in inaccurate pest lists and, as a consequence, limited prospects for sustained agricultural trade. If there is political will for regional communication, harmonized diagnostics and reporting mechanisms, the current scenario of fighting fully blown epidemics with exorbitant funds can be averted by coordinated, pre-emptive and thus cost efficient management interventions