Characterization and Promising in vitro Antiherpetic Effect of Galactomannan from Delonix regia Seeds

Herpes simplex virus (HSV) infections can occur throughout life, thereby allowing transmission to new hosts, with an impact on public health. Acyclovir remains the treatment of choice for these infections; however, an increase in resistant strains in recent years has been observed. In this study, the activity of a native Delonix regia galactomannan (NDr) against HSV-1 was investigated in vitro. NDr was characterized using infrared spectroscopy and NMR. Evaluation of cytotoxicity and the antiviral effect was determined, respectively, by MTT and plaque reduction assays. The NDr concentrations that inhibited cell viability (CC₅₀) and viral infection (IC₅₀) by 50% were above 2000 and 64 μg/mL, respectively. Thus, the polysaccharide showed a high selectivity index (> 31.25). When NDr was added at different stages of HSV-1 replication, a strong inhibitory effect was found by direct interaction with the virus (71–67%, virucidal effect) or previously with the cell, 6 h before infection (99.8–68.4%, prophylactic effect) at concentrations from 200 to 50 μg/mL. NDr showed similar effects in prophylactic 1 h (52%) and adsorption inhibition (55%) assays at 200 μg/mL. A reduction in the antiherpetic effect was observed after infection. These results suggest that NDr is effective in the early stages of HSV-1 infection and is a promising agent for controlling herpetic infections.