Antiviral activity of natural humic substances and shilajit materials against HIV-1: Relation to structure

Natural products, such as humic substances (HS) and shilajit, are known to possess antiviral activity. Humic-like components are often called as carriers of biological activity of shilajit. The goal of this study was to evaluate anti-HIV activity of well characterized HS isolated from coal, peat, and peloids, and compare it to that of water-soluble organic matter (OM) isolated from different samples of Shilajit. The set of humic materials included 16 samples of different fractional composition: humic acid (HA), hymatomelanic acid (HMA), fulvic acid (FA). The set of shilajit OM included 19 samples of different geographic origin and level of alteration. The HIV-1 p24 antigen assay and cell viability test were used for assessment of antiviral activity. The HIV-1 Bru strain was used to infect CEM-SS cells. The obtained EC50 values varied from 0.37 to 1.4 mg·L-1 for the humic materials, and from 14 to 142 mg·L-1 for the shilajit OM. Hence, all humic materials used in this study outcompeted largely the shilajit materials with respect to anti-HIV activity: For the humic materials, the structure-activity relationships revealed strong correlation between the EC50 values and the content of aromatic carbon indicating the most important role of aromatic structures. For shilajit OM, the reverse relationship was obtained indicating the different mechanism of shilajit activity. The FTICRMS molecular assignments were used for ChEMBL data mining in search of the active humic molecules. As potential carriers of antiviral activity were identified aromatic structures with alkyl substituents, terpenoids, N-containing analogs of typical flavonoids, and aza-podophyllotoxins. The conclusion was made that the typical humic materials and Shilajit differ greatly in molecular composition, and the humic materials have substantial preferences as a natural source of antiviral agents as compared to shilajit.
Highlights • Comparison of anti-HIV activity measured for the two large sets of humic materials and Shilajit water extracts demonstrated much higher activity of the humic materials. • Structure-activity relationships revealed leading role of aromatic structures in anti-HIV activity of humic substances, and the opposite trend was observed for shilajit. • 13C NMR and FTICR MS studies revealed structural similarity of shilajit extract to fulvic acid. • Different mode of antiviral action is suggested for aromatics-rich humic materials (humic acids, hymatomelanic acids) and N-rich shilajit. • This work was partially supported by the Russian Science Foundation: project 20-63-47070 in the part of structural characterization of the humic materials used in this study, and project 19-75-00092 in the part of FTICR MS data-mining and chemometrics.