Anti-Herpes Simplex virus and antibacterial activities of Graptopetalum paraguayense E. Walther leaf extract: a pilot study

Graptopetalum paraguayense E. Walther (GP) belongs to the Crassulaceae family and has several health benefits. In the present study we evaluated the cytotoxic, anti-Herpes Simplex virus (HSV) and antibacterial activities of a total methanol/water GP extract. The results from the cytotoxicity investigation of the tested extract showed a high cell tolerable concentration range. The GP extract demonstrated a significant inhibitory effect on the wild-type HSV-1 strain Victoria in a concentration of 0.0001 mg/mL equal to the maximal nontoxic concentration (with 97.5% protection of the cells). Regarding the acyclovir-resistant mutant HSV-2 strain PU and wild-type HSV-2 strain Bja, the antiviral activity and selectivity of the extract were very low, with EC50 values from 0.1 to 0.01 mg/mL, and the selectivity index ranging from 25 to 250, respectively. The GP extract exhibited selective inhibitory activity also on the growth of Gram-positive bacterial pathogens, with Staphylococcus aureus being most sensitive. It also prevented the formation of MRSA biofilm up to 50% at a concentration of 1.6 mg/mL and up to 90% at a concentration of 2.5 mg/mL. The anti-herpetic and antibacterial activities demonstrated in our investigation are probably related to the presence of phenols, and in particular gallic acid. The antimicrobial activity of the GP extract holds a promise for the future development of nutrition supplements based on G. paraguayense and therefore warrants further studies aimed at isolating biologically active compounds or mixtures thereof with subsequent in-depth investigation of their anti-HSV and antibacterial mechanisms of action.