Abstract
A number of secondary plant metabolites (e.g., flavonoids) possess antiviral/antimicrobial activity. Most flavonoids, however, are difficult to study, as they are immiscible in water-based systems. The relatively new semisynthetic α-glucosyl hesperitin (GH), and the natural plant product epigallocatechin gallate (EGCG) are unique among most flavonoids, as these flavonoids are highly soluble. The antiviral activity of these plant metabolites were investigated using the rotavirus as a model enteric virus system. Direct loss of virus structural integrity in cell-free suspension and titration of amplified RTV in host cell cultures was measured by a quantitative enzyme-linked immunosorbent assay (qEIA). After 30 min. 100 × 103 μg/ml GH reduced RTV antigen levels by ca. 90%. The same compound reduced infectivity (replication in cell culture) by a similar order of magnitude 3 to 4 days post inoculation. After 3 days in culture, EGCG concentrations of 80, 160, and 320 μg/ml reduced RTV infectivity titer levels to ca. 50, 20, and 15% of the control, respectively. Loss of RTV infectivity titers occurred following viral treatment by parallel testing of both GH and EGCG, with the latter, markedly more effective. Cytotoxicity testing showed no adverse effects by the phenolic concentrations used in this study. The unique chemical structure of each flavonoid rather than each phenolic’s inherent solubility may be ascribed to those marked differences between each molecule’s antiviral (anti-RTV) effects. The solubility of EGCG and GH obviated our need to use potentially confounding or obfuscating carrier molecules (e.g., methanol, ethanol, DMSO) denoting our use of a pure system environ. Our work further denotes the need to address the unique chemical nature of secondary plant metabolites before any broad generalizations in flavonoid (antiviral) activity may be proposed.
Highlights
IntroductionReports have linked the consumption of selected plant juices (e.g., cranberry, grape) and green tea to numerous broad-based health benefits
Reports have linked the consumption of selected plant juices and green tea to numerous broad-based health benefits
We suggest that no one secondary plant metabolite nor virus per se, may serve as an indicator or model system to the myriad of infectious agents circulating ad perpetuity throughout the world’s populations
Summary
Reports have linked the consumption of selected plant juices (e.g., cranberry, grape) and green tea to numerous broad-based health benefits Such health-promoting effects have been traced to certain secondary plant metabolites within these plant species, including proanthocyanidins of berries and grapes, and epigallocatechin gallate (EGCG) of green tea Flavonoids and rotavirus activity (Higdon and Frei, 2003; Aron and Kennedy, 2008; Bose et al, 2008; Xiao et al, 2011). Among those numerous health promoting effects proposed from the consumption of comestible plant products, antimicrobial activity has been the subject of an increasing number of substantive reports over the last one or two decades. In complement with this work, the anti-rotavirus activity of GH was compared where appropriate, to the well-studied and characterized EGCG of green tea, through the determination of changes in RTV infectivity titers in African Green monkey kidney epithelial (MA-104) host cell cultures
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