Phytochemistry, pharmacology, and medicinal aspects of Allium fistulosum L.: A narrative review

Plants have been employed as traditional remedies for treating several ailments. Allium fistulosum L. is an important plant of the family Amaryllidaceae. In this review, its pharmacology, phytochemical, and medicinal aspects have been discussed in detail. It has been reported to be effective against diverse ailments, such as cold, influenza, abdominal pain, cephalgia, arthritis, etc. Allium fistulosum medicinal potential is attributed to flavonoids, furostanol saponins, cinnamic acid derivatives, thiolane-type sulfide, and several other bioactive compounds. Subsequently, pharmacological shreds of evidence revealed its anti-obesity, anti-viral, antimicrobial, anti-tumor, anti-oxidant, anti-inflammatory, and immunomodulatory activities. Interestingly, some recent studies also showed the immense potential of A. fistulosum to boost immunity against COVID-19. The bioactive composition of this plant should be subjected to clinical trials in the future for paving new aspects to develop a potential plant-based drug to treat human ailments.


ETHNOMEDICINAL IMPORTANCE OF A. fistulosum
Ethnomedicines are the traditional heritage used to treat ailments in diverse ethnic cultures.The ethnic group has transferred this knowledge orally over the years to their future generations.Allium fistulosum is used by different communities in various countries, such as China, Taiwan, Japan, India, etc. for treating diseases related to the respiratory system, gastrointestinal system, cancer, arthritis, skin disorders, and others (Table 1).
In China, A. fistulosum has been extensively employed against various illnesses.In terms of plant parts, whole plant, and roots are recommended for the treatment of the majority of ailments.According to ethnomedicinal records, this plant has been used to treat disorders of the respiratory system, digestive system, arthritis, cephalgia, and other diverse ailments (Table 1).

INCLUSION AND EXCLUSION CRITERIA
In light of existing literature, this study was drafted utilizing various online databases, such as PubMed, Google Scholar, Web of Science, and Science Direct.Different keywords used were A. fistulosum, Welsh onion, bioactive composition, phytochemistry, ethnomedicine, biological potential, clinical trials, mechanistic insights, mechanism of action, and others.Full-length, peer-reviewed, and English-language papers have been included in this study.The replicated records, conference proceedings, editorials, and also papers not indexed in Scopus and WOS were excluded.

Anthelmintic activity
The aqueous and ethanolic extracts (50, 100, and 200 mg/ml) of A. fistulosum leaves showed dose-dependent and significant anthelmintic effect with decreased paralysis and death time of Ascaris lumbricoides when compared with pyrantel pamoate (3 and 6 mg/ml) used as standard drug.It was concluded that both extracts were more efficient than the standard (Husori et al., 2016).

Anti-arthritis activity
The aqueous extract of A. fistulosum with rice porridge revealed significant anti-arthritis activity against monoiodoacetate-induced ovariectomized female rats.The extract increased the body weight, bone mineral density, food intake, lean body mass, and fat mass for 11 weeks and also showed enhancement in collagen deposition score and (Sang et al., 2002), fistulosaponins A-F, and protogracillin (Lai et al., 2010).

PHARMACOLOGICAL PROFILE OF A. fistulosum: MECHANISTIC INSIGHTS
In light of existing literature, several studies were found with the pharmacological properties of A. fistulosum extracts and compounds.These pharmacological studies provided scientific evidence for some ethnomedicinal uses of this plant.A brief overview of the biological activities of A. fistulosum and mechanistic insights into these activities have been depicted in Table 2 and Figure 3, respectively.

Analgesic activity
The ethanol extract (200, 400, and 600 mg/kg) of A. fistulosum demonstrated analgesic activity in the hot plate, tail flick, and acetic acid-induced writhing in adult Albino mice.The administration of extract and standard aspirin (300 mg/kg) led to a significant (p < 0.01) increase in latency time at 4 hours in both the hot plate and tail flick test as compared to the control.Likewise, the writhing response stimulated by acetic acid was found to be remarkably inhibited by the extract (600 mg/kg) and standard diclofenac sodium (5 mg/kg) with 50% and 46% inhibition, respectively (Nazir et al., 2022).as compared with positive control; aminoguanidine at 20 mM (75.9%) when monitored after 2 weeks (Ramkissoon et al., 2013).Thus, the Welsh onion can be employed in the management of diverse complications.

Anti-glycation activity
Advanced glycation end products (AGEs) are a complex class of substances that can be exogenously or endogenously in nature and have a pathogenic role in the onset and progression of oxidative stress-mediated diseases, such as atherosclerosis, diabetes, and neurological conditions (Vistoli et al., 2013).The ethanolic extract (100 μl) of Welsh onion exhibited a significant anti-glycation effect by inhibiting the fluorescent AGEs formation with 27.9%,

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subtilisin/kexin type 9 (PCSK9), hepatocyte nuclear factor 1α, sterol regulatory element-binding protein-2 (SREBP-1c) gene expressions, as well as, LDLR protein expressions without affecting the cell viability.Moreover, the extract protected the lysosomal degradation of LDLR protein in the presence of bafilomycin A1 (lysosomal inhibitor) and blocked the protein synthesis of LDLR.Subsequently, all compounds maintained the LDLR level while quercetin, p-coumaric acid, and kaempferol significantly attenuated the PCSK9 level under conditions of lipid depletion.The tested samples can be effective in lowering hypercholesterolemia in humans (Choi et al., 2017).

Anti-ischemia activity
The fistulosaponins (A-F) and protogracillin (0.5-100 μM) of A. fistulosum seeds displayed an antiischemia effect against hypoxia/reoxygenation (H/R)stimulated injury in human umbilical vein endothelial cell (HUVEC).The tested compounds significantly protected HUVEC from injury and increased the survival of H/Rtreated cells, where fistulasaponin A was highly resistant to injury even better than positive control dioscin (Lai et al., 2010).Allium fistulosum aqueous seed extract (15, 150, and 300 mg/kg) exerted a protective effect on acute myocardial ischemia in Sprague Dawley rats.Extract and positive control xingling granules (900 mg/kg) significantly decreased serum creatine kinase levels (p < 0.05), lactate dehydrogenase levels, and infarcted area (p < 0.01) as compared with the saline group (Lai et al., 2023).Thus, the Welsh onion showed a beneficial effect on cardiac function in rat model of acute myocardial ischemia.

Anti-inflammatory activity
The typheramide and alfrutamide compounds of Welsh onion potently inhibited the cyclooxygenases-1 (COX1) and HeLa cell lines.This activity is attributed to the fact that total phenols and flavonoids are significantly affected by N fertilizers (Zhao et al., 2021).The Onionin A 1 of A. fistulosum significantly inhibited the IL-10-induced CD163 expression (M2 macrophage marker), tumor culture supernatant-induced CD163 overexpression, and also, reversed the interleukin-12 (IL-12) downregulation and IL-10 upregulation in ovarian cancer (SKOV3) cell.Moreover, Onionin A 1 inhibited the cellcell interactions between macrophages and suppressed the protumoral macrophage function.Simultaneously, Onionin A 1 significantly suppressed the tumor weight and lung metastasis in osteosarcoma (LM-8) cell-bearing C3H mice along with suppression in tumor progression of SKOV-3-bearing C57B6 mice (Nohara et al., 2017).Likewise, ethanolic and aqueous extracts (cold and hot) of A. fistulosum were investigated for anti-cancer activity against colon carcinoma (CT-26) cells using a mouse model.The hot-aqueous extract significantly inhibited tumor growth and increased the apoptotic index more than other extracts.Moreover, hot-aqueous extract highly suppressed both cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) activities and the levels of IL-6 and TNF-α than other tested extracts.Similarly, hot-aqueous extract displayed a better reduction of cellular markers that were involved in proliferation (cyclin D1 and c-Myc), angiogenesis (vascular endothelial growth factor and hypoxia-inducible factor 1-alpha), and tumor invasion [MMP-9 and intercellular adhesion molecule (ICAM-1)] ( Arulselvan et al., 2012).

Anti-hyperlipidemic activity
The ethanolic extract, p-coumaric acid, quercetin, ferulic acid, and kaempferol from Welsh onion were investigated for anti-hyperlipidemic activity against delipidated serum (DLPS; a mixture of mevalonate and rosuvastatin)-treated HepG2 cells.The extract significantly reduced the lowdensity lipoprotein receptor (LDLR), pro-protein convertase   et al., 2022).These findings suggested that the plant has the potential to be used for inflammatory disease.

Antimicrobial activity
The N-coumaroyltyramine from the subterranean part of the Welsh onion showed the highest anti-bacterial effect against Staphylococcus aureus and Escherichia coli.Subsequently, N-feruloyltyramine and N-coumaroyltyrosine attained effectiveness only against S. aureus while, 1-O-(4hydroxybenzoyl)-β-D-glucopyranose and isorhamnetin

Anti-obesity activity
Obesity, a metabolic disorder is characterized by an excess accumulation of fats in the body.In this context, several reports revealed the anti-obesity potential of A. fistulosum.The aqueous and ethanolic extracts significantly decreased the lipid accumulation, final body weight, serum level of leptin, weight of adipose tissues, triacylglycerol, alanine transaminase (ALT) levels, and adipocyte area whereas, enhanced the adiponectin level, high-density lipoprotein (HDL)-cholesterol level, adenosine monophosphate-activated protein kinase-α1 and 2 mRNA expressions in liver tissue of high-fat diet (HFD) obese mice.Moreover, ethanolic extract lowered the aspartate transaminase (AST) level, low-density lipoprotein (LDL)-cholesterol, food efficiency ratio, total cholesterol, and peroxisome proliferator-activated receptor gamma (PPAR-γ) mRNA expression, whereas, enhanced uncoupling protein 2 mRNA expression.Thus, extracts can be an ingredient of functional food to control obesity in people (Sung et al., 2018).Similarly, lyophilized whole plant extract (aqueous) significantly reduced the body, liver weight, food efficiency, serum triglyceride, leptin, glucose, total and LDL cholesterol, AST, ALT, creatinine, mRNA uncoupling protein-2 (UCP-2) and adiponectin levels, adipocyte size and fat accumulation while, enhanced the HDL-cholesterol, mRNA PPAR-γ, and leptin levels in HFD obese mice (Sung et al., 2015).Likewise, cereal bars containing A. fistulosum fresh bulbs and roots aqueous extract significantly attenuated the body weight gain, food efficiency ratio, subcutaneous and visceral fats, liver, adipocytes area, and other lipid parameters whereas, increased the β3-adrenoreceptors, UCP-2, and PPAR-γ mRNA expressions in HFD obese mice (Sung et al., 2014).Whole plant ethanolic extract significantly attenuated weight gain, triglycerides, total cholesterol, leptin, adiponectin, white adipose tissue area, mRNA expression of SREBP1c, PPARγ and FAS, LDLcholesterol, and white adipose tissue weight in HFD mice (Sung et al., 2011).In the in vitro study, the extract reduced the intracellular lipid accumulation and free glycerol release by 36.7% and 84%, respectively in 3T3-L1 adipocytes (Park et al., 2013).As a result, the plant might be useful in treating metabolic disorders linked to obesity, such as hyperlipidemia and insulin resistance.

Anti-oxidant activity
Allium fistulosum was reported to be a strong antioxidant evident by various studies.The extracts different parts (root, stem, and leaf) were prepared in rice wine (Michiu Tou; 34% alcohol and Michiu; 19.5% alcohol) and exhibited an anti-oxidant effect with 6.2-15.5 mmol TE/g in Trolox equivalent antioxidant capacity.Further, extracts showed a scavenging effect with IC 50 ranging between 14.6 and 26 μg/ ml in 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay.The effect of alcohol concentrations on the anti-oxidant profile needs further validation (Chang et al., 2016).The ethanolic extract of A. fistulosum showed an anti-oxidant effect with 1.220 and 0.812 mg ascorbic acid/ml using ferric reducing antioxidant power (FRAP) and DPPH assays, respectively (Ramkissoon et al., 2013).Similarly, protein extract from the seeds of this species showed anti-oxidant potential with IC 50 of 1.43, 1.37, 2.17, and 0.006 mg/ml in DPPH, hydroxyl, superoxide radical and chelating assays, respectively as well as, this extract increased the reducing power at 700 nm (Zuo et al., 2018).Additionally, ethanolic extract of the whole plant exhibited an anti-oxidant effect with IC 50 of 0.58 and 0.24 mg/ml in DPPH and metal chelating assays.Whereas, absorbance with 3.38 and 6.35 mg equivalent of ascorbic acid/g at 563 nm was observed during FRAP and total phosphomolybdate assays, respectively (Obuotor et al., 2018).Some compounds N-trans-feruloyl-3′methoxytyramine and N-cis-feruloyl-3′-methoxytyramine from the whole plant showed potent DPPH scavenging activity as compared with N-trans-p-coumaroyltyramine (Seo et al., 2011).The ethanolic extracts of A. fistulosum stem and leaves displayed higher DPPH and 2,2-Azino-bis (3-ethylbenzothiazoline-6sulfonic acid (ABTS) scavenging effects than that of root extract (Chang et al., 2013).Besides, the aqueous ethanol extract of Welsh onion stems with different nitrogen levels (N1 and N2: 0130 and 260 kg/ha) as urea fertilizer showed DPPH and ABTS scavenging effects (Zhao et al., 2021).Thus, A. fistulosum can be used to develop antioxidant-rich food products that will help in the fight against oxidative stress-mediated disorders.

Anti-platelet aggregation activity
The raw and boiled A. fistulosum green leaf and white sheath extracts were evaluated against adenosine diphosphate (ADP)-stimulated platelet aggregation where green extracts significantly and potently suppressed the platelet aggregation and adhesion more than white extracts.In addition, green extracts significantly affected the thromboxane release from platelets and also stimulated the cyclic adenosine monophosphate (cAMP) level.Moreover, ADP stimulation of platelets caused their [Ca 2+ ] elevation, which was suppressed by the green extract (raw) while increased by green extract (boiled).Furthermore, the raw extract also stimulated cAMP levels (Chen et al., 2000).Thus, results revealed that raw extracts inhibited platelet function while boiled extracts activate platelets.

Anti-viral activity
Welsh onion was reported to be broad spectrum antiviral agent.For instance, A. fistulosum congee (40-80 g with 50 g rice/400 ml water) was evaluated against SARS-COV-2.Administration with congee on day 1 in male patient resulted in sweating, phlegm release, and a decrease from 38.5°C to 37.3°C in body temperature after 2-3 hours.Subsequently next day, more phlegm was discharged and the temperature declined to 36.7°C.Interestingly, only one patient completely recovered in 11 days, while other patients were recovered usually within 3-4 days after consuming congee (Hsu et al., 2020).The hot aqueous extract along with its compound, fructan from leaves showed an effect on influenza A virus (IFV-As)-infected mice, with a significant decrease in virus replication (titer) in bronchoalveolar lavage fluid (BALF) and lung, followed by increased production of neutralizing antibodies in BALFs.Whereas, only fructan enhanced neutralizing antibodies production in sera of mice.Additionally, from day 3 to day 7, extract and compound both showed a consistent drop in body weight which was recovered after day 9 (Lee et al., 2012).cells in rats (Lee et al., 2018).Thus, the extensive property of this plant is mediated by normalizing hormonal levels that were altered by PCOS.

Hepatoprotective activity
The ethanolic extract of A. fistulosum significantly reduced the lipid accumulation, mRNA expression of SREBP1c, and fatty acid synthase (FASN) in oleic acid (OA)induced non-alcoholic fatty liver disease model using HepG2 cells, without affecting the cell viability.Moreover, the extract significantly attenuated body, liver, and epididymal fat weight, food efficiency ratio, and plasma levels of ALP, ALT, and AST in the western diet-fed obese mice (Hwang et al., 2018).

Vasorelaxant activity
The raw and boiled A. fistulosum green leaf and sheath extracts-induced vasodilatation in norepinephrine (NE)precontracted aortae of rats, where green extract (<5 × 10 −4 g/ ml) stimulated vasorelaxation that was completely inhibited in the presence of indomethacin (inhibitor of prostanoid synthesis).Moreover, boiled green and white extracts evoked the vasocontractile responses in NE-precontracted or resting vessel rings, which was abolished by thromboxane A 2 (TXA 2 )-receptor antagonist, SQ29548 as well as, the release of endothelium-derived contracting factor, TXA 2 was also stimulated by white extract (Chen et al., 1999).

CLINICAL EVIDENCE OF A. fistulosum's BIOLOGICAL POTENTIAL
Welsh onion has been proclaimed to have health benefits, several formulations reported the efficacy of its formulations against different diseases but effective targeted constituents have not been focused on a large scale.In this context, some studies highlighted the medicinal efficacy of individual or herbal formulations containing A. fistulosum has been included here.A 29-year-old male patient was diagnosed with wind-cold joined by dampness, characterized by an impaired flow of Lung-Qi.He was given a detoxifying powder formulation (Jing Fang Bai Du San) consisting of A. fistulosum (three pieces), Citrus tangerina (6 g), Schizonepeta (5 g) along with other ingredients.It was observed that after one dose, the patient sweated and recovered from cold and fever with improvement in headache and body pain along with pulse stabilization (Li, 2006).The children (3rd and 25th percentiles in height, aged between 5 and 12 years) had significant enhancement in height after treatment with A. fistulosum root extract (5 g) in a double-blind and placebo-controlled trial (Shim et al., 2021).The clinical studies of the bioactive components of the plant should be futuristic work for researchers to develop novel efficacious remedies which are safe and cost-effective.

CONCLUSION AND FUTURE PERSPECTIVES
In conclusion, the information about medicinal uses, chemical constituents, and pharmacological profile of A. fistulosum is documented in this study.Traditionally, this plant has been used for treating cold, influenza, abdominal pain, cephalgia, ulcers, parasitic infestations, arthritis, and cardiac disorders in several countries.Fistuloimidates, onionins A1, Whole plant aqueous extract attained an effective response on adenovirus (ADV41 and ADV3)-infected human lung carcinoma (A549) cells that exhibited an anti-viral effect closer to its cytotoxic concentration at EC 50 value >960 μg/ml (Chen et al., 2011).In contrast, whole plant methyl alcoholic extract significantly reduced the hepatitis A virus titer by 2.07 log after co-treatment at 50 μg/ml (Seo et al., 2017).

Effects on bone growth
The Welsh onion roots aqueous extract increased the longitudinal bone growth by promoting insulin-like growth factor-1 and transforming growth factor signaling, with a significant decrease in body weight gain, retroperitoneal, visceral fat, serum osteocalcin, and total area under the curve, along with a notable increase in fasting serum glucose, insulin, HOMA-IR, serum ALP, femur, tibia bones length, and hypertrophic growth in weanling rats.In addition, the extract markedly improved the survival, alkaline phosphatase (ALP) activity, and mRNA gene expressions of bone morphogenetic protein-2 and Smad4 while, decreased the dickkopf-related protein-1, phosphorylation of insulin receptor substrate-2 and Akt in MG-63 osteoblast cell (Ko et al., 2019).Hence, the longitudinal bone growth of children and adolescents can be achieved by utilizing Welsh onion.Allium fistulosum extracts (aqueous and 30% ethanolic) demonstrated facilitation of bone growth in vitamin D and calcium deficient C57BL/6 mice.Both extracts (150 and 450 mg/kg) significantly increased bone mineral density (BMD), bone mineral content, and growth in a way that encouraged the development of the osteogenic markers (calcium, collagen type 1, ALP, and osteocalcin) in the bone.Additionally, both extracts also displayed significant alkaline phosphate activities.Thus, A. fistulosum can be used to develop functional foods that will promote bone formation and raise BMD (Ryuk et al., 2021).

Effects on immune response enhancement
The mucus extract from green leaves of A. fistulosum showed significant enhancement of TNF-α and monocyte chemotactic protein-1 (MCP-1) in leukemic monocytes (RAW 264) and IL-12 in macrophage-like J774.1 cells in vitro and also increased the TNF-α, IL-12 and phagocytotic activity in peritoneal cells, LPS-interferon-γ (IFN-γ) production in spleen cells and the activity of natural killer cells of mice in vivo (Ueda et al., 2012).These findings revealed that A. fistulosum can enhance natural immunity and can be used as a major defense against various diseases.

Effects on polycystic ovary syndrome (PCOS)
Allium fistulosum's roots extract (aqueous) significantly decreased the blood triacylglycerol, luteinizing hormone, number of follicular cysts, and relative mRNA expressions of luteinizing hormone receptor whereas, increased the blood glucose, relative mRNA expressions of Kitl, bone morphogenetic protein, progesterone receptor, estrogen receptor 1, Cyp19a1, restoration of estrogen and plasma testosterone levels in letrozole-induced PCOS female Sprague Dawley rats.Additionally, the extract normalized the estrus cycle as indicated by the presence of epithelial nucleated and cornified cinnamic acid amides, flavonoids, and fistulosaponins constitute the bioactive composition of A. fistulosum which are reported to be anti-obesity, anti-cancer, anti-oxidant, antimicrobial as well as anti-viral agents.Several pharmacological actions were reported using different plant parts but the active phytochemicals and their mechanistic insights are still obscure.A few clinical trials of A. fistulosum were reported with the plant alone or as an ingredient of herbal formulations.Allium fistulosum as well as its bioactive composition could be developed as a drugdeveloping candidate after detailed follow-up studies.

Table 1 .
Ethnomedicinal uses of A. fistulosum across the globe.

Table 2 .
Pharmacological profile of A. fistulosum extracts and compounds.