Fractionation of Heteromorpha arborescens var abyssinica (Apiaceae) leaf extracts based on polarity leads to a marked change in cytotoxicity that may yield a commercially useful product

•H. arborescens had the best anthelmintic activity of several species previously examined.•The crude extract was too toxic to test in animal experiments.•Solvent–solvent fractionation of the crude extract decreased the cytotoxicity up to 50-fold.•This did not affect the antifungal or anthelmintic activity of the butanol fraction.•The fractionation yielded a potentially useful product with a selectivity index of more than 3.

Parasitic gastroenteritis caused by helminths remains a major cause of mortality and morbidity especially in small ruminants in the tropics. Haemonchus contortus is the major helminth responsible for this disease. Chemical anthelmintics are the most reliable means of treatment. The frequent use of these anthelmintics has led to resistance development. The issue of residues in meat and milk also motivates the use of plants and plant derived products as alternate to chemical anthelmintics. The anthelmintic, antimicrobial activity and cytotoxicity of the fractions of Heteromorpha arborescens var abyssinica were investigated. The egg hatch assay and the larval development test were used to determine the anthelmintic activity. A serial microdilution method with iodo nitrotetrazolium violet as growth indicator was used to determine the antibacterial and antifungal activities. The cellular cytotoxicity of the fractions was determined using the MTT assay. The egg hatch assay led to an EC50 of 0.68, 0.73, 1.58 and 2.88 mg/ml for the butanol, ethyl acetate, chloroform and hexane fractions respectively. The larval development test of the butanol, chloroform, ethyl acetate and hexane fractions led to EC50 values of 0.64, 1.05, 1.05 and 3.28 mg/ml respectively. Because extracts or fractions can be more useful if they have activity against more than one indication the antimicrobial activity of the fractions was also determined. The best antifungal minimum inhibitory concentrations (MICs) of 0.08 mg/ml was against Cryptococcus neoformans and 0.63 mg/ml against Aspergillus fumigatus and Candida albicans. Pseudomonas aeruginosa was most susceptible bacterium in this study. The cytotoxicity LC50 values of the fractions of hexane, ethyl acetate, butanol and chloroform were 1.40, 0.91, 2.06 and 2.04 mg/ml. Fractionation of the acetone extract of H. arborescens var abyssinica led to a remarkable 35 to 50-fold reduction in cytotoxicity of the fractions compared to the original extract.The anthelmintic activities of the crude leaf extract and fractions were not that high, but due to the decreased cytotoxicity the butanol fraction had a three-fold higher efficacy against H. contortus in both assays than toxicity against the cells. This may lead to a product that can be used to treat helminthiasis in animals if animal safety is in line with cellular safety. The results stress the importance of determining the cytotoxicity of plant extracts with a potential to be used in animal studies. The selectivity index may be more important than the activity of an extract against microorganisms or parasites.