Analyses of Cytotoxic and Genotoxic Potentials of Loranthus micranthus using the Allium cepa Test

Loranthus micranthus (LM) is one of the Nigerian folk medicinal plants used chronically for the management of immuno-depressive illnesses such as diabetes mellitus, cancer and hypertension. There has not been report on the cytotoxic and genotoxic effects of the plant. This study was conducted to investigate the cytotoxic, mitodepressive and genotoxic effects of LM against Allium cepa root cells. The roots of Allium cepa (onion bulb) were exposed to different concentrations (2.5-40 mg/mL) of L. micranthus aqueous leaf extract (LMAE) using NaN3 (100 ug/mL) and distilled water as positive and negative controls and examined macroscopically and microscopically for toxic effects. Phytochemical screening of the plant was also carried out using conventional methods. LMEA was found to significantly (p<0.05) inhibit root growth of Allium cepa with an EC50 of 28.2 mg/mL and elicit a strong negative association (r = -0.97; p<0.05) in concentration with the bulb root length, suggesting a dose-dependent root growth inhibition. In comparison with the negative control, sodium azide used at 100 :g/mL as a positive control decreased mitotic index by 50%, while LMAE dose-dependently decreased MI by 2.4-27.4% at 5-40 mg/mL concentration range except at 2.5 mg/mL in which 11.9% increase in MI was observed. The observed dose-dependent alterations in cell division by LMAE was also not significant (p>0.05) at 5 mg/mL compared to the control and did not display significant variation in activity between 20 and 40 mg/mL concentrations respectively (p>0.05). Furthermore, LMAE at 10 mg/mL was found to produce the highest number of aberrant cells but failed to elicit c-mitosis found only at 40 mg/mL. LMAE at 5 mg/mL produced the least number of aberrant cells and also failed to induce micronucleus and binucleated cell formation found mostly at 40 mg/mL. Chromosomal aberrations including stickiness, multipolar anaphase and lagging chromosomes, breaks and bridges were induced by all the extract concentrations tested but not dose-dependently. Tannins, alkaloids, saponins and flavonoids were also present in the extract. Our findings indicate that LM is cytotoxic, mitodepressive and genotoxic to Allium cepa especially at doses beyond pharmacological range in vitro and suggest for safety reasons, the continuous use of this plant at lower concentrations for human phytomedicine coupled with a need to conduct further in vivo genotoxic tests.