key: cord-0940637-j28yhb5u
authors: Rouf, Razina; Uddin, Shaikh Jamal; Sarker, Dipto Kumer; Islam, Muhammad Torequl; Ali, Eunus S.; Shilpi, Jamil A.; Nahar, Lutfun; Tiralongo, Evelin; Sarker, Satyajit D.
title: Anti-viral potential of garlic (Allium sativum) and it's organosulfur compounds: A systematic update of pre-clinical and clinical data
date: 2020-08-19
journal: Trends Food Sci Technol
DOI: 10.1016/j.tifs.2020.08.006
sha: 4b823ad742a102c175893bd0db4b9896e6afbb77
doc_id: 940637
cord_uid: j28yhb5u

BACKGROUND: Garlic (Allium sativum L.) is a common herb consumed worldwide as functional food and traditional remedy for the prevention of infectious diseases since ancient time. Garlic and its active organosulfur compounds (OSCs) have been reported to alleviate a number of viral infections in pre-clinical and clinical investigations. However, so far no systematic review on its anti-viral effects and the underlying molecular mechanisms exists. SCOPE AND APPROACH: The aim of this review is to systematically summarize pre-clinical and clinical investigations on antiviral effects of garlic and its OSCs as well as to further analyse recent findings on the mechanisms that underpin these antiviral actions. PubMed, Cochrane library, Google Scholar and Science Direct databases were searched and articles up to June 2020 were included in this review. KEY FINDINGS AND CONCLUSIONS: Pre-clinical data demonstrated that garlic and its OSCs have potential antiviral activity against different human, animal and plant pathogenic viruses through blocking viral entry into host cells, inhibiting viral RNA polymerase, reverse transcriptase, DNA synthesis and immediate-early gene 1(IEG1) transcription, as well as through downregulating the extracellular-signal-regulated kinase (ERK)/mitogen activated protein kinase (MAPK) signaling pathway. The alleviation of viral infection was also shown to link with immunomodulatory effects of garlic and its OSCs. Clinical studies further demonstrated a prophylactic effect of garlic in the prevention of widespread viral infections in humans through enhancing the immune response. This review highlights that garlic possesses significant antiviral activity and can be used prophylactically in the prevention of viral infections.

could play an essential role in a pandemic response as is the case in the current COVID-19 23 pandemic. which might be linked to their many multifunctional components (Tolo et al., 2006) . The 32 J o u r n a l P r e -p r o o f mechanism by which these extracts, or their purified constituents, display their antiviral action 1 may vary depending on the virus strains and viral life cycle including viral entry, fusion, 2 replication, assembly and virus-host-specific interactions (Lin, L. T. et al., 3 2014) . Immunomodulatory properties are one the potential activity of herbal medicine products 4 that can fight viral infections. Several plants have shown to enhance the immune system of the 5 host to boost it's antiviral defence (Raza et al., 2015) . Therefore, plants might be an exciting 6 source for the development of new antiviral drugs 7 Garlic (Allium sativum L.) is an annual bulbous herb of the Alliaceae family that are 8 native to Central and South Asia. It has been used for culinary and spiritual purposes for many 9 years. Now-a-days garlic is cultivated all over the world mainly in dry and hot climate. China, 10 India, South Korea, Egypt and USA have been reported as the countries with the highest garlic 11 production country in the world (Medina & Garcia, 2007; Rehman et al., 2019) . For thousands of 12 years garlic has been used as a functional food, spice and seasoning herb, as well as an effective, 13 traditional medicine against different ailments including viral diseases (Ayaz & Alpsoy, 2007; 14 Rehman et al., 2019; Tsai et al., 1985) . In 1720 garlic was successfully used to save the Marseille 15 population from the plague (Petrovska & Cekovska, 2010) . The consumption of fresh and 16 cooked, as well supplementation with garlic are well tolerated at a reasonable level in or with a 17 meal and regarded as "generally safe (GRAS)" by the American Food Drug Administration 18 (FDA) (Holub et al., 2016) . Garlic has been used for centuries as an ethnomedicinal plant to treat 19 infectious diseases. It has been reported that fresh garlic ingestion or intravenous preparation of 20 its extracts is used to treat various viral infections or cryptococcal meningitis patients, 21 respectively, in China (Tsai et al., 1985) . In Asia and Europe, garlic is used to treat the common 22 cold, fever, coughs, asthma and wounds (Rehman et al., 2019) . Garlic oil has also been used to 23 relieve pain due to ear infections (Al Abbasi, 2008) . Garlic has been used in African traditional (Table 1) . 28 Although garlic has been used since ancient time for its medicinal purposes, the 29 exploration of its active constituents began only recently. The OSCs of garlic are to be the main 30 bioactive constituents, and are also responsible for its pungent odor (Omar & Al-Wabel, 2010) . 31 J o u r n a l P r e -p r o o f More than thirty sulfur containing compounds belonging to two main chemical classes, L-1 cysteine sulfoxides and γ-glutamyl-L-cysteine peptides, are presents in garlic ( Fig. 1A) 2 (Yamaguchi & Kumagai, 2020) . Alliin (S-allyl-L-cysteine sulfoxide) is the most abundant sulfur 3 compound present in fresh and dry garlic (10-30 mg/g) (Lawson, 1998) . Alliin can quickly 4 convert into allicin (diallyl thiosulfinate) via alliinase enzymes upon chopping, mincing, 5 crushing or chewing of fresh garlic (Fig. 1B) (Borlinghaus et al., 2014; Lawson, 1998) . Allicin (Table 2) (Amagase, 2006; Ginter & Simko, 2010; Higdon, 2016; Staba et al., 2001) . Garlic also 19 contains non-sulfur constituents including lectins, flavonoids (kaempferol, quercetin and 20 myricetin), polysaccharides (fructan), steroids, saponins, fatty acids (lauric and linoleic acid), 21 several enzymes, vitamins (A, B 1 and C), allixin, minerals (Ca, Cu, Fe, K, Mg, Zn and Se) and 22 amino acids which are likely having additive or synergistic effects with OSCs (Amagase, 2006; 23 Josling, P. A., 2005; Keyaerts et al., 2007; Li, M. et al., 2017; Sharma, 2019) . Allicin was 24 reported as one of the main OSCs that was considered one of the principle compounds 25 responsible for antiviral activity (Wang, L. et al., 2017; Weber et al., 1992) , immunomodulatory 26 (Arreola et al., 2015) , anti-inflammatory (Metwally et al., 2018 ), antioxidant (Prasad et al., 1995 27 and other pharmacological properties (Borlinghaus et al., 2014) . Pre-clinical studies, both in- 28 vitro and in-vivo, showed that allicin-derived OSCs such as ajoene, allitridin, garlicin and DAS 29 also possess potential antiviral (Fang et al., 1999; Keyaerts et al., 2007; Liu, Z. F. et al., 2004; 30 Terrasson et al., 2007; Walder et al., 1997) , immune enhancing (Hall et al., 2017; Li, Y. N. et al., infections (Chavan et al., 2016; Chen et al., 2011; Choi, 2018; Liu, Y. et al., 2013; Mehmood et 5 al., 2018; Mehrbod et al., 2009; Mehrbod et al., 2013; Mohajer Shojai et al., 2016; Rasool et al., 6 2017; Tsai et al., 1985; Weber et al., 1992) , immunosuppression ("Garlic extract for HIV?," 7 1998; Kun Silprasit et al., 2011; Shoji et al., 1993; Tatarintsev et al., 1992; Walder et al., 1997), 8 genital herpes (Romeilah et al., 2010; Weber et al., 1992) , neurological infections (Luo et al., Wang, X. Y. et al., 2020) and others (Liu, Y. et al., 2013; Seo et al., 2017; Wang, L. et al., 12 2017; Weber et al., 1992) (Table 3 and 4) . Further, randomized clinical trials on different 13 commercial garlic preparations also showed that garlic plays a significant therapeutic role in 14 various viral infections such as cold and flu, viral-induced hepatitis, viral-associated warts, as 15 well as immune enhancing activity in viral infected patients (Table 5 ). The proposed mechanism 16 of their antiviral activity was reported to be the inhibition of the viral cell cycle, enhancing host 17 immune response or reduction of cellular oxidative stress. However, there is no systematic 18 review to-date that covers the antiviral activity of garlic and its OSCs in pre-clinical and clinical 19 studies in detail. The aim of this review is to summarize and highlighted the potential antiviral 20 effects of garlic and its OSCs with focus on underlying mechanisms of action by compiling both 21 preclinical and clinical published data using afore-mentioned databases. Direct were used to search literature on garlic and its OSCs for this review. A complete literature 25 search was conducted using the above databases with the term 'Garlic' or 'Allium sativum' along 26 with 'antiviral activity', 'viral infections', 'antimicrobial activity', 'viral replication' 27 'immunomodulatory' and 'immune enhancing activity'. Only reports that were in English were 28 considered in this review. Antiviral studies of garlic and its OSCs were included in this 29 systematic review if they covered the following information: (i) in-vivo studies, (ii) in-vitro 30 studies, (iii) studies indicating the dose, EC 50 or viral selectivity index (SI) (iv) clinical trials of 31 J o u r n a l P r e -p r o o f garlic in viral infections specifying dose, intervention, placebo, parallel group and duration of 1 treatment (v) studies that include garlic extracts or its isolated OSCs and (vi) studies that 2 incorporated the mechanisms of actions of garlic and its OSCs. Garlic has been used traditionally as an herbal medicine to treat various infectious 7 diseases including cold/flu and other viral infections (Kun Silprasit et al., 2011; Lissiman et al., 8 2014; Tsai et al., 1985) . Contemporary in-vitro and in-vivo pharmacological investigations of 9 different garlic extracts and its isolated OSCs have confirmed the reasons for garlic's 10 ethnomedicinal use in various viral infections. (De Clercq, 2002) . Sometimes host cellular enzymes (such as inosine 5′-26 monophosphate dehydrogenase and S-adenosylhomocysteine hydrolase) that have an effect on 27 viral assembly or replication can also be targeted by antiviral agents (Story et al., 2005) .

Targeting the entry or adsorption of virus to host cells by an effective entry-blocking or 29 entry-inhibiting agent would be a potential strategy for therapeutic intervention because of easy crude GE and its OSCs exert their antiviral activity through interaction with the viral cell surface 10 charge molecule and subsequently block or inhibit viral entry into host cells (Table 3 and 4) . results demonstrated that thiosulfinate constituents were more active (allicin; EC 50 0.15-3.4 µM 4 > allyl methyl thiosulfinate; EC 50 0.37-2.9 µM > methyl allyl thiosulfinate) with lower EC 50 than 5 fresh GE (EC 50 8-1000 mg/ml) (Weber et al., 1992) . Both the crude extract and thiosulfinate 6 compounds were more active against enveloped viruses (herpes simplex virus-1 and 2, 7 parainfluenza-3, vaccinia virus, vesicular stomatitis virus) than non-enveloped virus (human 8 rhinovirus-2) and their direct viricidal properties were due to the disruption of viral envelope and 9 cell membrane rather than any intracellular antiviral mechanism ( Fig. 2) (Weber et al., 1992) . It 10 is well stablished that OSCs, and allicin and its derivatives contribute significantly to garlics 11 antiviral properties (Bayan et al., 2014; Sharma, 2019; Wang, L. et al., 2017) . The OSCs are 12 highly reactive to the thiol group present in various active viral proteins or enzymes that are 13 crucial for microbial surveillance and fusion (Ankri & Mirelman, 1999; Jain et al., 2007) . During 14 exposure to allicin or its derivatives many enzymes that contain catalytically important thiol-15 groups are oxidized and inhibited (Leontiev et al., 2018; Wills, 1956 ) which support the Weber Another study demonstrated that a non-organosulfur proteinous compound, a lectin, derived 28 from garlic, showed antiviral activity against severe acute respiratory syndrome-coronavirus 29 (SARS-CoV) via inhibition of early viral attachment and inhibitory activity at the end of the acetyl-L-cysteine and 2,3-dimercapto-1-propanol) (Kubota et al., 1990; Roederer et al., 1990; 22 Shoji et al., 1993) . There was no report found on allicin ability to inhibit HIV, but a recent study 23 reported that allicin can inhibit replication of reticuloendotheliosis virus (REV) and alleviates the (Table 5) . (Table 5 ). At the end of the trial, including an extra 2 week of follow up, the active group showed significantly fewer and shorter incidences of the 3 cold than the placebo group. Viral re-infection was also higher in the placebo group than active 4 group (Josling, P., 2001).. The results of this study suggest that the reduction of viral infection 5 and reinfection can be decreased through daily garlic supplementation. This may be due to 6 garlic's, specifically allicin's, r immunomodulating effects which have been shown in preclinical 7 studies ("Garlic extract for HIV?," 1998; Li, M. et al., 2017; Walder et al., 1997) . This research did not receive any specific grant from funding agencies in the public, 10 commercial, or not-for-profit sectors. LGE (n= 25) and placebo (n = 25)

Size of warts and photographic comparison. The response was considered complete (complete disappearance), partial (reduced size in 25% -100%) and no response (0-25% decrease in size) as well as also examined serum TNF-α (0 and 4 th week) and adverse effect up to 6 months Five point scale to examine health and number of infections, day of recovery start and day of fully recovery, variety of symptoms in their daily diary (Hiltune n et al., 2007) 

Adenovirus-3 (AdV-3)

Adenovirus-41(AdV-41)

Cold and respiratory tract illness 

Fresh garlic clove Slice of fresh raw garlic Alliin and γ-Glutamyl-L-cysteine peptides and different percentage of allicin and its derivatives