Green seaweed Enteromorpha compressa (Chlorophyta, Ulvaceae) derived sulphated polysaccharides inhibit herpes simplex virus

The herpes simplex virus (HSV) diseases represent a relevant medical and social problem due to their communicability and recurrence following latency. The green algae are rich source of polysaccharides referred to as ulvans, reported as being biologically and pharmacologically active. In this work, we analyzed the activity of seven chemically modified polysaccharides from Enteromorpha compressa (Chlorophyta, Ulvaceae), against HSV. Only the derivative named SU1F1 showed satisfactory viral inhibition activity, with a high selectivity index, and, therefore, it was submitted to analysis of the probable mechanism of action and structure. SU1F1 is a sulphated (22% w/w) heteroglycuronan with an apparent molecular mass of 34 kDa. The antiviral activity was assayed by plaque reduction assay under the protocols of the time-of-addition (from 3 h before infection to 16 h after infection), the inhibition of virus adsorption and penetration, and the virucidal effects. SU1F1 showed a high viral activity at the time 0 h. We demonstrated that its inhibitory effect was maintained until 4 h post-treatment with 100% of viral inhibition at 100 μg/ml. No effect was observed in additional protocols (the pre-treatment, the inhibition of adsorption and penetration and virucidal assays). Reverse Transcriptase associated PCR (RT-PCR) results were in accordance with plaque reduction assay and demonstrated the activity of SU1F1 at the initial stages of HSV replication.