PerspectivesAre you interested in submitting a Perspective Article? Be sure to read The Science Advisory Board's Editorial Guides for Perspective Articles. Click here. Importance of Garlic in Health and Diseases by Tahira Farooqui Garlic, Allium sativum L. is a species in the onion family Alliaceae. Garlic has long been used around the world in cooking as well as in medicine. The objective of this commentary is to briefly examine medical uses of garlic throughout the ages. The complex chemistry of garlic makes it plausible that variations in processing can yield quite different preparations. Highly unstable thiosulfinates, such as allicin (2-propene-1-sulfinothioic acid S-2-propenyl ester), disappear during processing and are quickly transformed into a variety of organosulfur components [1]. Garlic contains sulfur compounds (allicin, alliin and agoene), volatile oils, enzymes (allinase, peroxidase and miracynase), carbohydrates (sucrose and glucose), minerals (selenium), and amino acids such as cysteine, glutamine, isoleucine and methionine, which protect cells from free radical-mediated damage. Furthermore, bioflavonoids (quercetin and cyanidin, allistatin I and allistatin II) and vitamins (C, E and A) in garlic also protect from oxidation agents and free radicals. Therefore, it is possible that health benefits of garlic likely arise from a wide variety of components, possibly working synergistically. We still do not fully understand the chemistry of garlic because each tiny clove contains the potential for almost 200 chemicals that can be generated and interact with each other in a number of ways. Commercially available garlic supplements mainly fall into one of four categories: (1) dehydrated garlic powder, (2) garlic oil, (3) garlic oil macerate and (4) aged garlic extract (AGE) [2]. Biblical references to garlic, its medical applications in ancient medical texts and historical perspective have been reported in literature [3]. Table 1 shows beliefs in ancient cultures about the use of garlic. Table 1. Beliefs of ancients cultures regarding garlic
Based on modern science, garlic exerts several therapeutic effects as shown in Table II. It has anti-platelet activity in humans. Its lower dose in long-term administration is considered more effective in inhibiting platelet aggregation than 2-3 fold higher dose, when administered at once [4]. Anti-atherosclerotic effects of dietary supplementations of garlic have been observed in rats [5]. Short-term supplementation of garlic in human subjects increases resistance of low density lipoprotein (LDL) to oxidation suggesting that suppressed LDL oxidation may be responsible for its anti-atherosclerotic effect [6]. Garlic seems to detoxify chemical carcinogens and prevent carcinogenesis. It can also directly inhibit the growth of cancer cells. Garlic stimulates immunity, including macrophage activity, natural killer and killer cells, and LAK cells, and increases production of IL-2, TNF, and interferon-gamma. These cytokines are associated with the beneficial Th1 antitumor response, which is characteristic of effective cancer immunotherapies [7-9]. Its broad range of beneficial effects are worthy of serious consideration in clinical trials for the prevention and treatment of cancer. In addition to its hypolipidemic, antiplatelet and procirculatory effects, some preparations of garlic such as AGE have antioxidant effects, which may be due to formation of S-allylcysteine, S-allylmercaptocysteine, and N(alpha)-fructosyl arginine during the extraction process [1]. Reactive oxygen species (ROS)-mediated oxidative stress causes modification in DNA, proteins and lipids that results in oxidative damage in tissue. Oxidative stress tends to increase with aging and diseases including cardiovascular, neurodegenerative and inflammatory diseases and cancer. AGE contains antioxidant phytochemicals (unique water-soluble organosulfur compounds, lipid-soluble organosulfur components and flavonoids, notably allixin and selenium), which help in preventing oxidative damage. AGE protects by scavenging ROS, enhancing the cellular antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, and increasing glutathione in the cells [10]. AGE reduces cholesterol synthesis by inhibiting 3-hydroxy-3-methylglutaryl-CoA reductase [11]. AGE lowers homocysteine, decreases blood pressure, and increases microcirculation. AGE exerts selective inhibition on platelet aggregation and adhesion, platelet functions suggesting that it is an important modulator of cardiovascular risk factors [12]. AGE has hepatoprotective effects on liver injury in experimental animal models [13]. The antibiotic activity of garlic has mostly been associated with the thiosulfinate allicin [14-16]. Wild garlic (high in allicin) has demonstrated a greater effect on reducing systolic blood pressure than cultivated garlic (low in allicin) preparation in hypertensive rats [17]. The circulating angiotensin II levels have been significantly lowered in garlic-eating subjects. Furthermore, the renin-angiotensin system is less active and the nitric oxide system more active in garlic-consuming hypertensive subjects. This supports involvement of renin-angiotensin and nitric oxide systems in the anti-hypertensive effects of garlic [17]. Anti-thrombotic effects of odorless garlic powder have been demonstrated in vitro and in vivo [18]. Odorless garlic activates fibrinolytic activity by accelerating tissue-type plasminogen activator-mediated plasminogen activation. It also suppresses the coagulation system by downregulating thrombin formation. These findings support a beneficial role of odorless garlic in inhibiting thrombus formation. In addition to these properties, garlic possesses anti-fungal activity against Cryptococcus neoformans [19-20]. The adverse effects of garlic include: (a) garlic breath and body odor, heartburn, upset stomach, and allergic reactions, (b) anticoagulant effects of garlic may be a problem during or after surgery. Garlic interacts and interferes with the operation of many anticoagulants, and (c) it interferes with the effectiveness of saquinavir, a drug used for the treatment of AIDS infection. One should consult doctors before entering a hospital, and its use should be stopped at least 1 week before surgery. Table 2. Therapeutic effects of garlic
In summary, garlic and its supplements have long been consumed in many cultures as a natural remedy against a range of human illnesses, including various bacterial, viral and fungal infections, hypolipidemic, antiplatelet, antitumoral, regulating blood pressure, lowering blood sugar and cholesterol levels and providing procirculatory effects. It is fascinating to observe how ancient cultures came to the same conclusion about garlic’s action and efficacy as confirmed from results of modern science. Recent literature has pointed towards a significant biological activity of trisulfides and tetrasulfides found in various Allium species suggesting that a wide range of effects are caused by polysulfides [18]. The biological activity of these polysulfides may include combinations of several different cellular signaling pathways. Therefore, further research is required to understand the mechanism of action of polysulfides. Due to anti-oxidative effects, AGE may help in preventing cognitive decline by protecting neurons from neurotoxicity, apoptosis and thus it may be beneficial in preventing ischemia/reperfusion-related neuronal death and improve learning and memory. The possibility of herb-drug interactions, safety and efficacy should be discussed with healthcare professionals, because slight negligence in this regard can cause serious clinical consequences. References: 1. Amagase, H. (2006) Clarifying the real bioactive constituents of garlic. J. Nutr. 136 (3 Suppl): 716S-725S. 2. Amagase H, Petesch BL, Matsuura H, Kasuga S, Itakura Y. (2001) Intake of garlic and its bioactive components. J. Nutr. 131 (3S):955S-62S. 3. Rivlin R.S. (2001) Historical perspective on the use of garlic. J. Nutr. 131(3S):951S- 954S. 4. Bordia A, Verma SK, Srivastava KC. (1996) Effect of garlic on platelet aggregation in humans: a study in healthy subjects and patients with coronary artery disease. Prostaglandins Lekot Essent Fatty Acids. 55: 201-205. 5. Zahid Ashraf M, Hussain ME, Fahim M. (2005) Antiatherosclerotic effects of dietary supplementations of garlic and turmeric: Restoration of endothelial function in rats. Life Sci. 77:837-857. 6. Lau BH. (2001) Suppression of LDL oxidation by garlic. J. Nutr. 131 (3S) 985S-988S. 7. Lamm DL, Riggs DR. (2000) The potential application of Allium sativum (garlic) for the treatment of bladder cancer. Urol. Clin. North Am. 27:157-162. 8. Fleischauer AT, Poole C, Arab L (2000) Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am. J. Clin. Nutr. 72:1047-1052. 9. Fleischauer AT, Arab L. (2001) Garlic and cancer: a critical review of the epidemiologic literature. J. Nutr. 131 (3S):1032S-40S. 10. Borek C. (2001) Antioxidant health effects of aged garlic extract. J.Nutr. 131(3S):1010S-1015S. 11. Borek C. (2006) Garlic reduces dementia and heart-disease risk. J. Nutr. 136(3Suppl):810S-812S. 12. Steiner M, Li W. (2001) Aged garlic extract, a modulator of cardiovascular risk factors: a dose-finding study on the effects of AGE on platelet functions. J. Nutr. 131 (3S):980S-984S. 13. Park EY, Ki SH, Ko MS, Kim CW, Lee MH, Lee YS, Kim SG. (2005) Garlic oil and DDB, comprised in a pharmaceutical composition for the treatment of patients with viral hepatitis, prevents acute liver injuries potentiated by glutathione deficiency in rats. Chem. Biol. Interact. 155:82-96. 14. Tessema B, Mulu A, Kassu A, Yismaw G. (2006) An in vitro assessment of the antibacterial effect of garlic (Allium sativum) on bacterial isolates from wound infections. Ethiop. Med. J. 44:385-389. 15. Dikasso D, Lemma H, Urga K, Debella A, Addis G, Tadele A, Yirsaw K. (2002) Investigation on the antibacterial properties of garlic (Allium sativum) on pneumonia causing bacteria. Ethiop. Med. J. 40:241-249. 16. Bakri IM, Douglas CW. (2005) Inhibitory effect of garlic extract on oral bacteria. Arch. Oral Biol. 50:645-651. 17. Mohamadi A, Jarrell ST, Shi SJ, Andrawis NS, Myers A, Clouatre D, Preuss HG. (2000) Effects of wild versus cultivated garlic on blood pressure and other parameters in hypertensive rats. Heart Dis. 2:3-9. 18. Fukao H, Yoshida H, Tazawa Y, Hada T. (2007) Antithrombotic effects of odorless garlic powder both in vitro and in vivo. Biosci. Biotechnol. Biochem. 71:84-90. 19. Davis LE, Shen J, Royer RE (1994) In vitro synergism of concentrated Allium sativum extract and amphotericin B against Cryptococcus neoformans. Planta. Med. 60:546-549. 20. Münchberg U, Anwar A, Mecklenburg S, Jacob C. (2007) Polysulfides as biologically active ingredients of garlic. Org. Biomol. Chem. 5:1505-1518. ### << Previous [ View All Perspectives ] |
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