Lasun (Allium sativum)

Latin Name Allium sativum
Sanskrit Name Lashuna, Rasona, Ugragandha, Yavaneshta
English Name Garlic, Poor man's treacle, Churl's treacle
Common Name Lahasun, Lasan, Balluci, Vellulli, Tellapya, Saum, Seer

Ayurvedic Properties and Action:1

 

Rasa

Katu, Madura, Tikta, Kasaya, Lavana

Guna

Guru, Sara, Snigdha, Tikshna, Pichchila

Virya

Ushna

Vipaka

Katu

Karma

Raktotkleshaka, Medhya, Deepana, Pachana, Hridayottejaka, Rasayana, Amapachana, etc.


Phytochemistry:

The most important chemical constituents reported from Garlic are the sulfur compounds. It has been estimated that cysteine sulfoxides (e.g. alliin [1]) and the non-volatile γ-glutamylcysteine peptides make up more than 82% of the total sulfur content of garlic. The thiosulfinates (e.g. allicin [2]), ajoenes (e.g. E-ajoene [3], Z-ajoene [4]), vinyldithiins (e.g. 2-vinyl-(4H)-1,3-dithiin [5], 3-vinyl-(4H)-1,2-dithiin [6]), and sulfides (e.g. diallyl disulfide [7], diallyl trisulfide [8]), however, are not naturally occurring compounds. Rather, they are degradation products from the naturally occurring cysteine sulfoxide, alliin [1]. Allicin itself is an unstable product and will undergo additional reactions to form other derivatives (e.g. products [3]–[8]), depending on environmental and processing conditions. Extraction of garlic cloves with ethanol at _0°C gave alliin [1]; extraction with ethanol and water at 25 °C led to allicin [2] and no alliin; and steam distillation (100 °C) converted the alliin totally to diallyl sulfides [7], [8]. Gamma-glutamylcysteine peptides are not acted on by alliinase. On prolonged storage or during germination, these peptides are acted on by γ-glutamyl transpeptidase to form thiosulfinates67.

 


Pharmacological Actions:

It is thermogenic, alexeteric, tonic, antibacterial, antifungal, antiinflammatory, hypolipidaemic, hypocholesteremic, hypotensive, antioxidant, antiaging, cardioprotective and antiperoxidase1.


Medicinal Use:

It is useful in cardiac diseases1.
In modern medicine, garlic and its preparations have been widely recognized as agents for prevention and treatment of cardiovascular and other metabolic diseases, atherosclerosis, hyperlipidemia, thrombosis, hypertension and diabetes. These biological responses have been largely attributed to the ability of garlic to reduce risk factors for cardiovascular diseases and cancer, stimulate immune function, and enhance detoxification of foreign compounds. It also has hepatoprotective, antimicrobial and antioxidant effect3,8.


Clinical / experimental study:

Garlic showed marked improvement in systolic and diastolic arterial tension in 144 hypertensive and atherosclerotic patients with significantly decrease in blood cholesterol level. Experimental studies of garlic with fatty meals in healthy volunteers revealed that it might prevent the harmful effect of fat in diet1.
It has Hypocholesterolaemic property and useful as a supportive to dietary measures for elevated levels of lipids in blood; as a preventive measure for age-dependent vascular changes. Diallyltetra, penta-, hexa- and heptasulphides are potential antioxidants. It has hypotensive actions2.
The studies have demonstrated that garlic has a significant antiarrhythmic effect in both ventricular & supraventricular arrhythmias,3,4 especially its free radical scavenging activity which reduces the incidence of VT and VF induced by myocardial ischemic-reperfusion injury5,8.
In human studies, many clinical trials studying cardiovascular effects of garlic used dried garlic powder that contains approximately 1.3% alliin (precursor of allicin) at a dosage of 300 to 900 mg/day (5-15 mg/kg), corresponding to 0.9 to 2.7 g of fresh garlic daily6. For example, in a prospective, 4-year clinical trial of patients treated with 900 mg daily of standardized garlic powder, there was a 9-18% reduction in plaque volume, a 4% decrease in low-density lipoprotein (LDL) levels, an 8% increase in high-density lipoprotein (HDL) concentrations, and a 7% decrease in blood pressure7,8.


Inhibits Platelet Aggregation and Antithrombotic Effects

It appears that the method of garlic preparation has a great influence over its antiplatelet activity in humans9,10.
Additionally, antithrombotic activity has been identified under clinical conditions11.


Antiplatelet effects

Antiplatelet effects of garlic are well recognized, but the dose at which this becomes significant remains uncertain. Results from a 2001 double blind study have identified a dose of 7.2 g/day of aged garlic extract as significantly inhibiting platelet aggregation and adhesion12.


Stimulates Fibrinolysis

A significant increase in fibrinolysis has been observed in several clinical tests for both raw and fried garlic13,15.


Reduces Serum Cholesterol Levels

A significant increase in fibrinolysis has been observed in several clinical tests for both raw and fried garlic13-15.


Reduces Serum Cholesterol Levels

A 2000 meta-analysis of 13 clinical trials concluded that garlic is superior to placebo in reducing total cholesterol levels, exerting a modest effect16.
The mechanism of action involves inhibition of cholesterol synthesis by deactivating HMG-CoA reductase via enhanced phosphorylation, but not changing the amount of the enzyme, according to in vitro research17.
The compounds containing an allyl-disulfide or allyl-sulfhydryl group are most likely responsible for the inhibition of cholesterol synthesis by garlic and that this inhibition is likely to be mediated at sterol 4-alpha-methyl oxidase18.
Clinical evidence also suggests it raises HDL levels and reduces triglyceride levels13

Antihypertensive Activity

Numerous clinical studies have identified antihypertensive activity with garlic19,20. Evidence from in vivo research suggests that both the renin–angiotensin system and the NO system are responsible for this activity21.

Hypertension A meta-analysis of seven clinical trials using a garlic preparation, found that three showed a significant reduction in SBP and four in DBP. It was used in these studies in the dosage of 600–900 mg daily. Garlic treatment resulted in a mean reduction in SBP of 7.7 mmHg and 5.0 mmHg in DBP compared with placebo20.

Antiatherosclerotic Activity

Evidence from in vitro, animal and human research has shown that garlic supplementation significantly reduces the atherosclerotic process22-27.
More specifically, garlic significantly decreased aortic tissue cholesterol as determined biochemically, fatty streak formation and the size of atherosclerotic plaque, compared with controls in an animal model. Garlic exerts antiatherogenic effects through inhibition of smooth muscle phenotypic change and proliferation, and by another (unclarified) effect on lipid accumulation in the artery wall22.
Similar results have been obtained using ultrasound techniques in a randomised, double-blind, placebo-controlled clinical trial, involving 152 people. Not only did high-dose garlic powder significantly reduce arteriosclerotic plaque volume, it also induced a slight regression in plaque spread within the 4-year test period25.
Results from several recently published animal studies further confirm antiatherogenic effects and have investigated the mechanisms responsible23,24,26
. One in-vivo study found that garlic activated antioxidant systems and decreased peroxidation in aortic tissue 23 whereas ajoene inhibited smooth muscle cell proliferation in another24.

Enhances Microcirculation

Jung et al (1991)28 found that 5 hours after the administration of garlic powder (total dose 900 mg garlic powder) a significant increase in capillary skin perfusion (55%) occurred in the healthy volunteers, whereas Kiesewetter et al (1993)29 showed a 48% increase with a dose of 800 mg garlic.

Cardiovascular Disease

Epidemiologic studies show an inverse correlation between garlic consumption and progression of CVD in general. This review will consider the evidence for garlic in the management of specific risk factors such as hypertension and hyperlipidaemia. Additionally, investigation into the effects of garlic directly on the atherosclerotic and arteriosclerotic processes is presented30.

Atherosclerosis and arteriosclerosis

Garlic indirectly affects atherosclerosis by reduction of hyperlipidaemia, hypertension, and prevention of thrombus formation. Koscielny et al conducted a randomised, double-blind, placebo-controlled clinical trial involving 152 volunteers to determine whether garlic powder supplements (900 mg daily) directly alter plaque volumes in carotid and/or femoral arteries 25. After 4 years’ treatment, garlic intake significantly reduced the expected increase in arteriosclerotic plaque volume by 5–18%, with a slight regression also observed. A subsequent re-evaluation of the results found that significant effects were limited to women only31

Hyperlipidaemia

In 2000, a meta-analysis of 13 clinical trials concluded that garlic reduces total cholesterol levels significantly more than placebo; however, the effects can only be described as modest16. The same year, a systematic review and meta-analysis were published by the Agency for Health Care Research and Quality, which analysed results from 44 studies with lipid outcomes. Pooled data from the placebo-controlled trials reporting changes in total cholesterol levels found a significant average reduction in total cholesterol levels of 7.2 mg/dL after 4–6 weeks using any form of garlic and a reduction of 17.1 mg/dL at 8–12 weeks32.
According to one review, non-enteric coated tablets containing dehydrated garlic powder (standardised to 1.3% allicin) produce the most consistent results33.

Comparative studies

Two clinical studies have compared different garlic preparations with pharmaceutical cholesterol-lowering medicines. Garlic taken as 300 mg three times daily produced similar lipid-lowering effects to 200 mg bezafibrate (a hypolipidaemic fibrate) three times daily in subjects with primary hyperlipidaemia34 whereas clofibrate 500 mg was more effective than an essential oil extract of 50 g raw garlic35.
Commission E approves the use of garlic as an adjunct to dietary changes in the treatment of hyperlipidaemia36.

Diabetics with hyperlipidaemia

A 12-week placebo-controlled, single-blind, randomised study of 70 patients with type 2 diabetes and newly diagnosed dyslipidaemia found that treatment with a garlic tablet (300 mg, containing 1.3% allicin) twice daily, together with a diet and exercise plan, resulted in a significant reduction in total cholesterol of 28 mg/dL (12.03%) compared to placebo37.

Antimicrobial and Immune-Enhancing Activity

Garlic appears to exert both direct and indirect effects against various pathogens, as it enhances macrophage and T-lymphocyte function and has direct antibacterial, antifungal, antiviral and antiparasitic activity38,39.

Peripheral Arterial Occlusive Disease

In 2000, Mulrow et al reported on two double-blind, placebo-controlled trials in participants with atherosclerotic lower extremity disease32. One study of 64 participants showed that pain-free walking increased by approximately 40 metres with standardised dehydrated garlic (800 mg daily) compared with approximately 30 metres with placebo over 12 weeks. The other study of 100 participants showed that a combination treatment of garlic oil macerate with soya lecithin significantly increased the maximum walking distance (114%) compared to placebo (17%) (P < 0.05).39.

Hypercholesterolemia

Individual randomized controlled trials comparing garlic to placebo have provided disparate results. Some studies have suggested that garlic has no effect in adults with mild to moderate hypercholesterolemia4044. However, other studies looking specifically at moderate hypercholesterolemia in males have demonstrated that garlic has beneficial effects on lipid profiles (reduction in total cholesterol and LDL cholesterol)46,47. Other data have shown that there may be a role for garlic as add-on therapy to traditional medicines (eg, reducing the dose of HMG-CoA reductase inhibitors)48. Additional trials have demonstrated that allicin (the presumed active ingredient of garlic) may reduce total cholesterol and LDL cholesterol in adults with moderate hypercholesterolemia49.
One meta-analysis report on the use of garlic for hypercholesterolemia specifically examined randomized, controlled trials comparing garlic with placebo. The inclusion criteria were patients with a mean total cholesterol level of 5.17 mmol/L (200 mg/dL). Pooling data from 13 trials (including 796 patients) suggested that garlic is superior to placebo in reducing cholesterol levels. However the effect is modest (6% reduction in total cholesterol).50.
Another meta-analysis of 16 randomized, controlled trials (including 1365 patients) also showed a modest reduction in serum lipids. Overall, a 12% greater reduction was observed with garlic therapy compared with placebo. This meta-analysis, however, consisted of small randomized studies of poor quality and not all patients recruited had hyperlipidemia51.

Hypercholesterolemia

Individual randomized controlled trials comparing garlic to placebo have provided disparate results. Some studies have suggested that garlic has no effect in adults with mild to moderate hypercholesterolemia4044. However, other studies looking specifically at moderate hypercholesterolemia in males have demonstrated that garlic has beneficial effects on lipid profiles (reduction in total cholesterol and LDL cholesterol)46,47. Other data have shown that there may be a role for garlic as add-on therapy to traditional medicines (eg, reducing the dose of HMG-CoA reductase inhibitors)48. Additional trials have demonstrated that allicin (the presumed active ingredient of garlic) may reduce total cholesterol and LDL cholesterol in adults with moderate hypercholesterolemia49.
One meta-analysis report on the use of garlic for hypercholesterolemia specifically examined randomized, controlled trials comparing garlic with placebo. The inclusion criteria were patients with a mean total cholesterol level of 5.17 mmol/L (200 mg/dL). Pooling data from 13 trials (including 796 patients) suggested that garlic is superior to placebo in reducing cholesterol levels. However the effect is modest (6% reduction in total cholesterol).50.
Another meta-analysis of 16 randomized, controlled trials (including 1365 patients) also showed a modest reduction in serum lipids. Overall, a 12% greater reduction was observed with garlic therapy compared with placebo. This meta-analysis, however, consisted of small randomized studies of poor quality and not all patients recruited had hyperlipidemia51.

Antithrombotic effects

Studies on the effects of platelet aggregation have produced inconsistent results, possibly related to variations in study design and in the garlic preparation used. The proposed mechanism for garlic oil inhibition of platelet function is by interfering with thromboxane synthesis52.Researchers isolated a component of garlic oil that inhibits platelet aggregation and identified it as methylallyltrisulphide (MATS). MATS is present in natural oil in a concentration of 4% to 10%. The purified compound inhibits ADP-induced platelet aggregation in plasma53.
Further studies indicated that the most potent antithrombotic compound in garlic is 4,5,9, trithiadodeca-1,6,11-triene 9-oxide, also known as ajoene. This compound is formed by an acid-catalyzed reaction of 2 allicin molecules followed by rearrangement; the compound can be synthesized commercially. Unlike other antithrombotics now under investigation, ajoene appears to inhibit platelet aggregation regardless of the mechanism of induction54.

Animal data

Scientists demonstrated the effect of ajoene in preventing clot formation caused by vascular damage. The experiment was designed to mimic the conditions of blood flow in small- and medium-sized arteries by varying the velocity of the blood; the compound proved to be effective in both conditions. The authors suggested that the compound may be useful in situations where emergency treatment is needed to prevent clot formation produced by vascular damage55.

Clinical data

Clinical studies have demonstrated that inhibition of platelet aggregation is also observed in vivo after ingestion of fresh garlic. In 1 study, the platelets from healthy subjects who had eaten garlic cloves (100 to 150 mg/kg) showed complete inhibition to aggregation induced by 5-hydroxytryptamine56. Other studies have shown that ingestion of “aged” garlic extract can produce an inhibition of some of the platelet functions important for initiating thromboembolic events in the arterial circulation57. The effects of garlic on platelet aggregation may be dependent on the garlic preparation used. Differences appear to be mostly dependent on their content of organo-sulfur compounds, many of which are unstable or capable of interconversion during processing58.

Blood pressure

Strong evidence for the effect of garlic on blood pressure is lacking. The results of a meta-analysis suggest that garlic supplements of 600 to 900 mg/day for 1 to 3 months are associated with a clinically important reduction in blood pressure59. Their meta-analysis included 8 trials consisting of 415 patients. However, the trials were of generally moderate to poor quality and not all patients were hypertensive. A review of the literature suggested that the effects of garlic on blood pressure were insignificant45.

The objective of this review is to update and assess the clinical evidence based on rigorous trials of the effectiveness of garlic (A. sativum). The literature searches identified six relevant systematic reviews and meta-analysis and double-blind randomized trials (RCT) that were published subsequently. These relate to cancer, common cold, hypercholesterolemia, hypertension, peripheral arterial disease and pre-eclampsia. The evidence based on rigorous clinical trials of garlic is not convincing. For hypercholesterolemia, the reported effects are small and may therefore not be of clinical relevance. For reducing blood pressure, few studies are available and the reported effects are too small to be clinically meaningful. For all other conditions not enough data are available for clinical recommendations61.

The positive influences of commercial garlic on plasma lipids, proteins, antioxidant activity, and some indices of blood coagulation are dose-dependent. Therefore, commercial garlic (Elena, Zelazków, Poland) could be a valuable component of atherosclerosis-preventing diets only in optimal doses62.

Increased platelet aggregation plays a significant role in the aetiology of cardiovascular disease, and is complex involving multiple mechanisms. On platelet activation, there is a transient increase in free cytoplasmic calcium (Ca(2+)), thromboxane A2 generation, and the activation of the fibrinogen receptor GPIIb/IIIa. Other modulators are also involved in platelet aggregation and include lipoxygenase metabolites, protein kinase C, cyclic adenosine monophosphate (cAMP), cyclic guanine monophosphate (cGMP) and nitric oxide (NO). Garlic is reported to prevent cardiovascular disease by multiple effects, one of which is the inhibition of platelet aggregation and its ability to do this has been extensively investigated in vitro, however, in vivo studies are limited. In vitro studies indicate that garlic prevents inhibition of platelet aggregation by inhibiting cyclooxygenase activity and thus thromboxane A2 formation, by suppressing mobilization of intraplatelet Ca2+, and by increasing levels of cAMP and cGMP. Garlic also displays strong antioxidant properties and activates nitric oxide synthase (NOS), leading to an increase in platelet-derived NO. It can also interact directly with the GPIIb/IIIa receptors, thus reducing the ability of platelets to bind to fibrinogen. It is concluded that garlic inhibits platelet aggregation by multiple mechanisms and may have a role in preventing cardiovascular disease63.

More than three thousand publications in the past have confirmed the efficacy of garlic for the prevention and treatment of a variety of diseases, acknowledging and validating its traditional uses. Garlic is also used for the treatment of fatigue, although the mechanism involved remain unclear. The anti-fatigue function of garlic may be closely related to its many favorable biological and pharmacological effects. In animal studies, garlic has been shown to promote exercise endurance. Differences in the methods of processing garlic result in differences in the intensity of its anti-fatigue effect, and the most favorable form of processing has been shown to be extraction of raw garlic followed by its natural aging for a long period in a water-ethanol mixture. In human studies, it has been confirmed that garlic produces symptomatic improvement in persons with physical fatigue, systemic fatigue due to cold, or lassitude of indefinite cause, suggesting that garlic can resolve fatigue through a variety of actions. Recently, primarily in Japan, attempts have been made to measure the intensity of fatigue objectively and quantitatively using biomarkers. Currently available data strongly suggest that garlic may be a promising anti-fatigue agent, and that further studies to elucidate its application are warranted64.

Raw and boiled garlic improved plasma lipid metabolism and plasma antioxidant activity in an experiment on rats. Thus, dietary hypolipidemic garlic was effective in reducing the oxidant stress, which was indicated by an increase of antioxidant activity and a decrease of lipids in the rats' blood. It was found that garlic boiled for 20 min has the same bioactivity as raw garlic in its antioxidant and protein spectra. Therefore it should be added at this time to foods. The selenium and copper content of raw garlic is not altered by boiling. The protein electrophoretic pattern of raw garlic is altered by boiling65.

Garlic in different forms has antioxidant properties. These properties are shown to be due to the existence of compounds such as water soluble organosulfur compounds, S-allylcysteine and lipid soluble compounds like diallyl sulfide. The in vivo and in vitro ischemia reperfusion studies showed that prophylactic administration of aqueous garlic prior to ischemia reperfusion inhibit lipid peroxidation and prevent depletion in glutathione through its compounds that led to functional recovery. Its ability to inhibit neutrophil migration could suppress fibrosis formation. These preventive effects are seen in models that studied organs such as kidney and liver with functional recovery. Organ system specific activity such as angiotensin converting enzyme-inhibiting activity contributes to a cardioprotective and blood pressure lowering effect. Future studies should focus on post ischemia reperfusion administration of garlic to explore its rescue potential rather than prophylactic impact. Bench research findings should be translated into clinical use through human studies66

The ethanol extract of garlic bulb exhibited anti-inflammatory properties in rheumatic conditions68,69.


Reference:

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