In vitro cytotoxicity of Carica papaya crude leaf extract

Abstract

Plant-based compounds are an option for the development of new antiviral drugs. Asians commonly use papaya (Carica papaya) leaves to treat dengue without an understanding of its toxicity, if any. The objective of the study was to screen in vitro cytotoxicity of C. papaya leaf extract against normal African green monkey kidney epithelial cell line (Vero) cells. CytoTox 96® Non-Radioactive Cytotoxicity Assay (Promega, USA) is a colourimetric assay, which quantitatively measures lactate dehydrogenase (LDH) released upon cell lysis. Carica papaya leaf extract was prepared in a two-fold dilution series. Two, 96 well assay plates, were prepared with Vero cells and, the assay was set up with an analytical system based (i) Negative control - without Vero cells, (ii) Vehicle control - untreated cells, (iii) Positive control - lysis solution with four replicates. Carica papaya extract was added to the test wells at different concentrations and, one set of plates was incubated for 5 h at 37 °C and the other set for 24 h at 37 °C. The absorbance data were measured using a standard 96-well plate reader (Labtech LT4500, Singapore) and the percentage cytotoxicity was calculated for each concentration tested. Colour intensity and the absorbance values decreased with the decrease of concentration of leaf extract. The percentage cytotoxicity for dilutions, 1/4, 1/8, 1/16, 1/32, 1/64, 1/128, 1/256, 1/512, 1/1024 was 95.60, 71.53, 74.77, 82.16, 79.91, 40.25, 7.37, 0.16, -1.24, respectively, for the 5 h and 141.61, 133.24, 127.78, 121.88, 109.79, 106.67, 30.64, 22.67, 25.39, respectively for 24 h. Higher concentrations of the extract caused higher cell lysis showing cytotoxic effects Vero cells at dilutions < 1/256. The information about the cytotoxicity levels helps select the minimum toxic concentrations of C. papaya leaf extract against the antiviral activity of the dengue virus.