Anti-protozoal effects of the tomato tetrasaccharide glycoalkaloid tomatine and the aglycone tomatidine on mucosal trichomonads

Authors: LIU, JENY - University Of The Pacific; KANETAKE, SIERRA - University Of The Pacific; WU, YUN-HSUAN - University Of The Pacific; Tam, Christina; Cheng, Luisa; LAND, KIRKWOOD - University Of The Pacific; Friedman, Mendel

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2016
Publication Date: 11/11/2016
Citation: Liu, J., Kanetake, S., Wu, Y., Tam, C.C., Cheng, L.W., Land, K.M., Friedman, M. 2016. Anti-protozoal effects of the tomato tetrasaccharide glycoalkaloid tomatine and the aglycone tomatidine on mucosal trichomonads. Journal of Agricultural and Food Chemistry. 64:8806-8810. doi: 10.1021/acs.jafc.6b04030.

Interpretive Summary: Trichomoniasis is an infection of the vagina or male genital tract with the protozoan organism Trichomonas vaginalis and is usually treated with single 2 g dose of the drug metronidazole. Trichomoniasis is reported to be the most common non-viral sexually transmitted infection (STI) in the world, an important source of reproductive morbidity, as well as a facilitator of human immunodeficiency virus (HIV) transmission and acquisitio. The organism is reported to annually infect an estimated 3.7 million women and men in the United States. About 348 million new infections are estimated to occur annually. Different protozoa strains also infect food animals (cattle, pigs) and domestic animals (cats). In a collaborative study with the Department of Biological Sciences, University of the Pacific identified tomatine, a natural glycoalkaloid found in tomatoes, to have potent antimicrobial activity against pathogenic protozoa that infect both humans and animals. Tomatine showed great inhibitory effects on both Trichomonas vaginalis and Tritrichomonas foetus strains, suggesting its potential value for developing alternative therapy toward trichomoniasis in humans, bovines, and felines.

Technical Abstract: The present study investigated the inhibitory effects of the commercial tetrasaccharide tomato glycoalkaloid tomatine and the aglycone tomatidine on three mucosal pathogenic protozoa that are reported to infect humans, cattle, and cats, respectively: Trichomonas vaginalis Strain G3, Tritrichomonas foetus Strain D1, and Tritrichomonas foetus Strain C1. A preliminary screen showed that tomatine at 100 µM concentration completely inhibited the growth of all three trichomonads. In contrast, the inhibition of all three pathogens by tomatidine was much lower, suggesting the involvement of the lycotetraose carbohydrate side chain in the mechanism of inhibition. Midpoints of concentration-response sigmoid plots of tomatine on the three strains correspond to IC50 values, the concentration that inhibits 50% of growth of the pathogenic protozoa. The concentration data were used to calculate the following IC50 values (in µM) for G3, D1, and C1 of 7.9, 1.9, and 2.2, respectively. The results show an approximately 4-fold variation from the lowest to the highest value (lowest activity). Although the inhibitory effects of tomatine was not as effective as that of the medicinal drug metronidazole, the relatively low IC50 values for both T. vaginalis and T. foetus indicated tomatine as a possible natural alternative therapeutic for trichomoniasis in humans and food-producing (cattle, pigs) and domestic (cats) animals. Because tomatine has the potential to serve as a new antiprotozoan functional (medical) food, the distribution of this glycoalkaloid in tomatoes and suggestions for further research are discussed.