Abstract
Antiviral treatments inhibiting Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication may represent a strategy complementary to vaccination to fight the ongoing Coronavirus disease 19 (COVID-19) pandemic. Molecules or extracts inhibiting the SARS-CoV-2 chymotripsin-like protease (3CLPro) could contribute to reducing or suppressing SARS-CoV-2 replication. Using a targeted approach, we identified 17 plant products that are included in current and traditional cuisines as promising inhibitors of SARS-CoV-2 3CLPro activity. Methanolic extracts were evaluated in vitro for inhibition of SARS-CoV-2 3CLPro activity using a quenched fluorescence resonance energy transfer (FRET) assay. Extracts from turmeric (Curcuma longa) rhizomes, mustard (Brassica nigra) seeds, and wall rocket (Diplotaxis erucoides subsp. erucoides) at 500 µg mL−1 displayed significant inhibition of the 3CLPro activity, resulting in residual protease activities of 0.0%, 9.4%, and 14.9%, respectively. Using different extract concentrations, an IC50 value of 15.74 µg mL−1 was calculated for turmeric extract. Commercial curcumin inhibited the 3CLPro activity, but did not fully account for the inhibitory effect of turmeric rhizomes extracts, suggesting that other components of the turmeric extract must also play a main role in inhibiting the 3CLPro activity. Sinigrin, a major glucosinolate present in mustard seeds and wall rocket, did not have relevant 3CLPro inhibitory activity; however, its hydrolysis product allyl isothiocyanate had an IC50 value of 41.43 µg mL−1. The current study identifies plant extracts and molecules that can be of interest in the search for treatments against COVID-19, acting as a basis for future chemical, in vivo, and clinical trials.
Highlights
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a predominantly airborne transmitted coronavirus first identified in December 2019, which is the causal agent of Coronavirus disease 19 (COVID-19) [1]
The materials were identified by the authors and acquired in a local market at Valencia (Spain) and included citrus fruit peels (sweet orange (Citrus sinensis), lemon (C. limon), lime (C. aurantiifolia), and grapefruit (Citrus paradisi)), seasoning and aromatic herbs (celery leaves and celery stalks (Apium graveolens var. dulce), parsley (Petroselinum crispum), dill (Anethum graveolens), sweet chamomile (Marticaria chamomilla), and dried oregano (Origanum vulgare)), bulbs and rhizomes (red onion (Allium cepa) and turmeric (Curcuma longa)), a succulent plant (aloe vera (Aloe barbadensis)), and cruciferous condiments (brown mustard seeds (Brassica nigra), horseradish (Armoracia rusticana), and commercial wasabi powder (Tokyo-Ya, S.A., Japan))
fluorescence resonance energy transfer (FRET) Assay for the Inhibition of the 3CL Protease Activity (SARS-CoV-2 3CLPro )
Summary
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a predominantly airborne transmitted coronavirus first identified in December 2019, which is the causal agent of Coronavirus disease 19 (COVID-19) [1]. RNA, the chymotrypsin-like protease (3CLPro ), known as main protease (MPro ), is required for the proteolytic processing of the viral polyproteins during the maturation step, becoming an essential tool for the successful replication of the virus [12] In this sense, the fundamental role of the 3CLPro in viral replication makes this enzyme an attractive target for the development of drugs inhibiting the virus replication. Some compounds found in edible and/or medicinal plant products were identified in these studies as potential natural compounds targeting the SARS-CoV-2 3CLPro , including glucosinolates, flavonoids, and other phenolic compounds. The evaluation of the antiviral capacity of these groups of natural compounds is more limited Based on this consideration, the current work aimed at the targeted testing for inhibitory capacity against the 3CLPro activity of plant extracts selected for being rich in one or more of the aforementioned chemical families. Given the proven safety for human consumption of the plants from which extracts are obtained, their potential use against COVID-19 might be immediate and accessible
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