Role of Garlic (Allium. Sativum L.) in Human and Plant Diseases
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Indian Journal of Experim cntal Biology Vol. 39. Apri l 200 1. pp. 310-322 Review Article Role of garlic (Allium. sativum L.) in human and plant diseases UP Singh ', B Prilhiviraj ', B K Sarma ', Mandavi Singh2 & A B Rai 'Departmen t of Mycology and Pl ant Pathology. Institutc of Agri cultural Scienccs. Banaras Hindu Universit y, Varan as i 221005, India Fax: 9 1-542-3 17074. E mail: ups @ banaras. crn et.in !Dcpart mcnt of Anatomy. In sti tute of Mcdical Scicnces, I3anaras Hindu Uni ve rsity, Va r3nasi 22 1005. India, JDepartment of Mcd icinal Chemistry, In stitutc of Medical Scienccs. Banaras Hindu Univcrsity, Varanasi 221005. India A n:surgcncc of intcrest in garlic due to recent rcvelations of its bcneficial cffec ts in th c treatmcnt of various hum an and plan t diseascs and also due to validation of claims made in traditional systems of medici nc has resulted a plcth ora of publi ca ti ons on diffcrcnt a pects of garlic in reCC I1l years. Chcmical constituents of garlic and their variati ons on the mcth ods of isolation havc been discussed in the prcsent rev iew. Effect of garlic and it s constituents aga inst various human anel plant pathogenic and sap roph yt ic mi croorganisms has also been reviewcd. Garlic (A lliulIl sativulII L.) is used worldwide as a view of the variety of bioactivities th at garlic and its l food additive, spi ce and medicine. In Ayurveda , it various preparations exhibit, it is considered has been described as a gastric sti mu lant. It aids appropriate to comp il e the various findings in a digesti on and is given in tlatulence. It has special systematic manner and an attempt in this direction has influence over the bronchi al and pulmonary secreti ons been made in this bri ef review. and in promotion of fl ow of menses. Garlic is used as ClJell/ica l constituents of garlic - Garli c is a rich a tonic, carminati ve and stimulant. In large doses, it is source of organosulphur compounds showing a an irritant and produces flatulence, headache, nau sea va ri ety of bi ological activi ti es. The chemical and even diarrhoea. As a local stimul ant and ilTitant, it constituents from garlic cl oves (b ul bs) vary with the causes red ness of th e skin and vesication. It is appli ed isolation procedure and obviously many of the to the nose of hysterical patients when in a state of compounds report ed from thi s source have been swooning. Gi ven wi th common salt , it rel ieves colic proved to be artifacts. Thus, while ga rlic oil obtained pain and nervous headache. It is used as a vermi fu ge by steam disti ll ation of garlic cloves was proved to be to ex pel round worms. It causes diuresis and hence essentially cl iall yl di sulphide (1) accompanied by 26 used in dropsy . In cold catarrh of chi ldren, brui sed lesser amounts of diallyl tri-and tetra-sulphides . garlic is applied to the chest as a poulti ce or lini ment. Ext rac ti on of garli c with eth yl alcohol at room It is also used as a remedy to bites of venomous temperature yield s ox ide of diallyl disulphide (2) reptil es. The rubificent action of garlic is enh anced by call ed all ici n27. Extraction of garlic with ethanol at addition of mu stard powder. It is rubbed over subzero temperature yields28 an adourl ess am ino acid, ringworm for reli ef. Garli c juice boiled wi th salad oil (+)-S-allyl-L-cystein e sul foxide (3) whi ch is named gives reli ef from earache. It is beneficial in several alli in (Fi g. I). Odourl ess alliin has been proved to be forms of atonic dy spepsia and is effecti ve in the th e precursor of alli ci n, the main odorous principl e of treatment of tuberculosis. garlic and conversion of the forme r to latter takes Many of these effects have been substantiated by place under th e influence of an enzy me, allinase modern research and garli c has been proved to eli cit whi ch comes in contact wi th alli in on ly when garlic 2 5 6 antimicrobiaI . , antihypertensive , hypol ipidemic 7-'J, bul bs arc CLl t or crushed. It is for this reason that the Il epatoprotectlve. 10 , anti'd 'la be tl. c 11 -15 ,and' In secliclc.. I a 116 bul bs are odourless unless cut or bruised. properties. Immunomod ulati on and antitumor All in<lse, a pyricloxal-phosphate-depclldent enzy activities of garlic have also been reponed 17. Garlic me, which is responsible for conversion or alliin (3) to ex trac t has also been shown to reduce serum allicin (2) has becn isolated in a fai rl y pure state from l R I 29 cholesterol levels . ') and increase blood coagul ati on AI/it/Ill tt/bCroSIIJ1/ and thc mechani sm or thi s 3 2XJo t.t me ' 8 '-'0. A ntlun. f ga l aCli"v lty 0 f' gar I'Ie bit'u )s- ,.'- an d transformation has been establi shed . Allinasc aqueous extract 0 f· ·It s Ieaves- ,~ '-'5 are a Iso on recorcI . I n breaks down alliin to 2-propcnesulphenic acid (-t ). SINGH et al.: ROLE OF GARLIC IN HUMAN & PLANT DISEASES 3 11 ,..--"'-U<.W.!................... ""-!.!..n .. CH2 = CH - CH2 -S - S - CH2 - CH = CH2 1 Allium sativum_!---"E1"-'=<!H-'-'r..... .t~. -- .. CH2 = CH - CH2 i S - S - C1-I2 - CH = CH2 2 0 ElOH<OOC ~=-=-~'---. CH2 = CH - CH2 - S - C1-I2 - CH - COOH ~ I 3 0 NH2 Fig. I-Variation in chemical constituents of garlic due to change in isolat ion procedure CH2 = CH - CH2 - S - Cl-i2 - CH - COOH ~ I 3 0 NH2 CH2=CH-CH2-S-0H /k:'NH3 CH3-CO-COOH 4 -H20 2 x CH2 = CH - CH2 - S - OH • CH2 = CH - CH2 - S - S - CH2 - CH = CH2 J. 4 2 0 Scheme I ammonia and pyruvic acid . Two molecules of o f /N~ sulphenic acid then react together to give alli ci n by ~C /S~ C0 2 H loss of a molecule of water (Scheme I). Subsequent research has revealed that cysteine 6 sulfoxide fraction of garlic consists of 85% alliin (3) o along with 2% S-propylcysteine sulfoxide (5) and f H 3 C / S ,S/ C~ 13% S-methyl cysteine su lfox ide (6). Action of allinase on this mixture affords, besides alli cin, 8 allylmethanethi osulfinate (7), methyl methanethio sulfinate (8) and other mixed or symmetrical thi osu lfinates of th e general structure, R-S(O)-S-R' where Rand R' represent anyone of methyl, propyl or all yl groups. Obviously all these thiosul finates are 3t found to be present in garl ic extract . Lawson & 9 coworkers.l2 have shown that in addition to endogenous allii n (3), a reserve for alli in ex ists in the C6H IOS20 ~ C(, HgS2 + H20 precursor compound, y-glutamyl-S-allyl cystei ne (9) Mechanistically speaking, allicin first breaks down and is present in a significant quantity in freshly into 2-propene sulfenic ac id (4) and thioacrolein (12). picked garl ic cloves. While two molecul es of sulfenic acid regenerate a Analysis of garli c extracts)) using GC-MS revealed molecule of allicin by loss of a molecule of water, two the presence of mixture (2.4 : I) of two compounds molecul es of thi oacrolein undergo Di els-Alder (79%) which have been proved to be 3-vi nyl-[4H]- cyclisation to give cyclic 1,2 dithiins (Scheme II ). 1,2-dithiin (10) and 3-vinyl-[6H]- I,2-dithiin (11) Thioacroleins may also cycl ise in a different (Scheme II ), on the bas is of comprehensive spectral manner to give 2-vinyl-[4H]-I,3-dithiin (13; Scheme analysis. Compounds (10) and (11) are regarded as II ) which is al so found to be present in the fracti on. dehydration products of all icin (2) and th eir formation Other volati le components of garli c ex tract detected is considered to take place during gas chromatography by GC-MS analysi s have been proved to be allyl according to the equati on: alcohol (5.4%), methyl all yl disulphide (1.2%), diallyl 312 INDIAN J EXP. BIOL., APRIL 2001 disulphide (5.7%), dimethyl trisulphide (2.4%), allyl aqueous acetone for 4 hr gives a mixture containing methyl trisulphide (1.5 %), diallyl trisulphide (1.0%) ajoenes. Removal of nonpolar fraction by washing of JJ and sulfur dioxide . Volatiles identified in garlic oils this mixture with pentane and subsequent extraction are suprisingly few and it has been considered that with CHzClz yields mixture (4:1) of Z-ajoene (18a) investigation of volatiles using modern techniques and E-ajoene (18b). The synthetic material is such as HPLC or capillary GC-MS would indistinguishable from ajoene obtained from garlic. considerably extend the list of components. In fact, a When an ether-soluble fraction of methanolic temperature-programmed GC-MS analysis of garlic extract of garlic is stored in aqueous methanol for 4 essential oil has revealed a group of previously days at 25°C and then successively extracted with unknown cyclic and acyclic organo-sulphur hexane and methylene chloride, ajoene has been compounds of which the compounds 14 - 17 are found to be present in the latter fraction. Hexane particularly important because of their Jipo-oxyginase soluble fraction contains several divalent sulfur inhibitory activity.