Effects of garlic extract consumption on plasma and erythrocyte antioxidant parameters in atherosclerotic patients

Pharmacotherapeutic Potential of Garlic in Age-Related Neurological Disorders

Age-related neurological disorders [ANDs] involve neurodegenerative diseases [NDDs] such as Alzheimer's disease [AD], the most frequent kind of dementia in elderly people, and Parkinson's disease [PD], and also other disorders like epilepsy and migraine. Although ANDs are multifactorial, Aging is a principal risk factor for them. The common and most main pathologic features among ANDs are inflammation, oxidative stress, and misfolded proteins accumulation. Since failing brains caused by ANDs impose a notable burden on public health and their incidence is increasing, a lot of works has been done to overcome them. Garlic, Allium sativum, has been used for different medical purposes globally and more than thousands of publications have reported its health benefits. Garlic and aged garlic extract are considered potent anti-inflammatory and antioxidants agents and can have remarkable neuroprotective effects. This review is aimed to summarize knowledge on the pharmacotherapeutic potential of garlic and its components in ANDs.

Wild garlic extract reduces lipid peroxidation in terbuthylazine-treated human erythrocytes

Background: Among other negative effects, herbicides induce oxidative stress, leading to lipid peroxidation and protein oxidation. Therefore, there is a growing need to identify natural compounds with sufficient antioxidant capacity and mitigate the negative effects of herbicides without side effects.Objective: Our study aimed to examine the protective effect of the phenolic extract of wild garlic (WG) leaves on terbuthylazine-treated erythrocytes.Material and methods: In human erythrocytes treated with the herbicide terbuthylazine (4.5 mg/L) alone and a combination of terbuthylazine and WG extract, we measured malondialdehyde (MDA) and haemoglobin (Hb) concentrations and the antioxidant activities of CuZn superoxide dismutase (SOD1; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6) in vitro.Results: In comparison with terbuthylazine, WG extract reduced the concentrations of MDA and Hb from 59.69 to 43.45 nmol/gHb (27%, p < 0.001) and 165.08 to 128.64 g/L (22%, p < 0.05), respectively. Catalase activity was induced for samples treated with both WG extract and terbuthylazine compared with terbuthylazine alone (p < 0.05).Conclusions: The results demonstrated that WG may reduce the toxicity of terbuthylazine, and the erythrocyte membrane may be the primary site of phenolic action. Therefore, the lipid peroxidation intensity could be a biomarker of oxidative damage caused by terbuthylazine and the protective effect of WG.

Effects of garlic supplementation on oxidative stress and antioxidative capacity biomarkers: A systematic review and meta-analysis of randomized controlled trials

Evidence suggests that garlic supplementation may have an effect on oxidative stress by augmenting the rate of enzymatic and non-enzymatic antioxidants and diminishing pro-oxidant enzymes. Given inconsistencies across studies, we aimed to systematically review the current literature and quantify the effects of garlic supplementation on oxidative stress. We conducted a systematic search with multiple databases (Scopus, PubMed, and Web of Science) to find relevant articles published prior to October 2020. Results were reported as bias-corrected standardized mean difference (Hedges' g) with 95% confidence intervals (CI) using random-effects models. Cochrane's Q and I squared (I² ) tests were used to determine heterogeneity among the studies included. Twelve randomized controlled trials (RCTs) were included. Garlic doses ranged from 80 to 4,000 mg/day, and intervention duration varied between 2 and 24 weeks. Garlic supplementation increased serum level of total antioxidant capacity (TAC) (Hedges' g: 2.77, 95% CI: 1.37 to 4.17, p < 0.001) and superoxide dismutase (SOD) (Hedges' g: 13.76, 95% CI: 4.24 to 23.29, p = 0.004), while it reduced the malondialdehyde serum level (MDA) (Hedges' g: -1.94, 95% CI: -3.17 to -0.70, p = 0.002). Due to limited data available, glutathione (GSH) was not considered for the current meta-analysis. The nonlinear dose-response effect of garlic supplementation was not observed with regard to serum TAC and MDA levels (TAC: p-nonlinearity = 0.398; MDA: p-nonlinearity = 0.488). Garlic supplementation appears to improve serum levels of TAC, MDA, and SOD. Garlic supplementation may be useful to reduce oxidative stress and related diseases. Future studies with large sample sizes and longer duration are required to confirm these findings.

Multi-phytochemical determination of polar and non-polar garlic bioactive compounds in different food and nutraceutical preparations

Amongst functional foods, garlic and its by-products stand out given their rich phytochemical profile. A comprehensive analytical approach becomes necessary to fully address garlic preparations health-promoting activities, considering the coexistence of several active ingredients from different chemical families. For this, we developed a multi-phytochemical protocol combining Ultrasound and Dispersive Liquid-Liquid Microextraction, coupled to Liquid Chromatography, for the determination of flavonols, organosulfur compounds, and inulin. Hydrophilic interaction chromatography showed an adequate resolution of flavonols and sugars in a shorter time. The protocol showed a suitable performance and acceptable quantitative yields for garlic powder, cooked garlic, black garlic, and liquid garlic flavouring samples. Additionally, the proposed methodology represented a useful tool to assess how the different garlic products related to functional properties, taking into account the various phytochemical families present in each sample. This is the first time a comprehensive and multi-phytochemical validated analysis of garlic preparations is proposed.

Characteristics, biosynthesis, decomposition, metabolism and functions of the garlic odour precursor, S-allyl-L-cysteine sulfoxide

S-Allyl-L-cysteine sulfoxide (ACSO) is an odour precursor in garlic bulbs. One plausible pathway for the biosynthesis of ACSO involves S-2-carboxypropyl glutathione produced from glutathione and methacrylic acid via valine or from γ-glutamyl cysteine. The elimination of glycine and glutamic acid from S-2-carboxypropyl glutathione produces S-2-carboxypropyl cysteine, which is converted to S-allyl cysteine by decarboxylation and oxidation. S-Allyl cysteine is also biosynthesized via the elimination of glutamic acid from γ-glutamyl S-allyl cysteine by γ-glutamyl transpeptidase. The sulfur oxidation of S-allyl cysteine by flavin-containing monooxygenase forms ACSO. When cells are damaged by slicing or grating, ACSO in the cytoplasm or cytoplasmic vesicle is immediately converted to allylsulfenic acid, pyruvic acid, and ammonia by alliinase (C-S lyase), which is located in the vacuoles of vascular bundle sheath cells. Two molecules of allylsulfenic acid form diallyl thiosulfinate (allicin), which exhibits potent antimicrobial activity. Allicin eventually yields garlic odour compounds, such as diallyl disulfide (DADS) and diallyl trisulfide (DATS). Although these sulfides are known to exert various physiological functions, their strong odour limits their use in foods. On the other hand, ACSO is water-soluble and odourless and enhances sweet, salty, and umami tastes, characteristics of which are desirable for food additives. Upon consumption, ACSO is primarily absorbed from the small intestine in the intact form, but is also partly decomposed to allylsulfenic acid, pyruvic acid and ammonia. Allylsulfenic acid is then further converted to DADS and diallyl monosulfide (DAS). ACSO has numerous in vivo functions, such as the prevention of diabetes, myocardial ischaemia, hepatic injury, platelet aggregation and blood ethanol elevation. Although some of these effects may be attributed to its metabolites, ACSO itself contributes to many of these physiological functions.

Benefits of aged garlic extract on Alzheimer's disease: Possible mechanisms of action

Alzheimer's disease (AD) is the most common form of dementia and has become a growing health concern in aging societies. β-amyloid (Aβ) formation in vulnerable brain regions, such as the hippocampus and cerebral cortex is a major neuropathological feature of the disease. Currently, there is no specific drug available for the treatment of AD. However, due to its high antioxidant activity, aged garlic extract (AGE) has been widely used to prevent chronic diseases, such as cancer and cardiovascular disease. A number of studies on the benefits of AGE against cognitive and memory deficits have also been published. This review aimed to summarize the information related to the effects of AGE on learning memory in order to obtain a better understanding of its mechanisms of action. This review also presents an overview of the pathogenesis of AD, and summarizes the main ingredients and neuroprotective effects of AGE against cognitive and learning memory deficits. The mechanisms of action of AGE are also discussed.

Comparative study on the composition of four different varieties of garlic

Garlic is used as a medicinal seasoning worldwide. The aim of this work was to compare four varieties of garlic: ‘Taicangbaipi’, ‘Ershuizao’, ‘Hongqixing’, and ‘Single-clove’; among them, ‘Ershuizao’ and ‘Hongqixing’ are unique to the Sichuan Province of China. Firstly, soluble sugar, starch, and the protein content of the garlic were analysed. There was more soluble sugar in ‘Single-clove’, total starch in ‘Hongqixing’, and protein content in ‘Ershuizao’ relative to the other three varieties, respectively. Gas chromatography–mass spectrometry analysis showed that ‘Ershuizao’ and ‘Hongqixing’ contained high levels of 5-hydroxymethylfurfural, which has antitumor, antioxidant, and cytoprotective effects. Indeed, the extracts from these two types of garlic were more effective at inhibiting tumour growth than that from the others. Moreover, the sulphide content and antimicrobial effects of ‘Ershuizao’ and ‘Hongqixing’ garlic were also higher than those of the other two types of garlic. In addition, changes observed in the membrane permeability and protein leakage suggest that the antimicrobial activity of the ‘Ershuizao’ and ‘Hongqixing’ extracts may be due to the destruction of the structural integrity of the cell membranes, leading to cell death.

The effects of garlic extract upon endothelial function, vascular inflammation, oxidative stress and insulin resistance in adults with type 2 diabetes at high cardiovascular risk. A pilot double blind randomized placebo controlled trial

BACKGROUND AND AIMS

Endothelial dysfunction, vascular inflammation and oxidative stress have been integrally linked to the pathogenesis of both type 2 diabetes and cardiovascular disease. Aged Garlic Extract (AGE), a potent antioxidant, has been shown in previous studies to attenuate these novel risk factors in a non-diabetic population.

AIMS

This study tested the hypothesis that AGE may improve endothelial function, oxidative stress, vascular inflammation and insulin resistance in high risk cardiovascular subjects with type 2 diabetes.

METHODS

A double blind, placebo controlled crossover pilot study was performed in 26 subjects with type 2 diabetes who received 1200 mg of AGE or placebo daily for 4 weeks with a 4 week washout period. Plasma HsCRP was measured as a marker of inflammation. Plasma TAOS, blood GSH/GSSG and plasma LHP were measured as markers of oxidative stress/anti-oxidant defense. Insulin resistance was measured using the HOMA-IR method. Endothelial function was measured using change in the reflective index (RI) post-salbutamol using digital photoplethysmography and urinary albumin/creatinine ratio was measured as a biochemical surrogate. Measurements were taken at baseline and after intervention with AGE or placebo.

RESULTS

Of the 26 patients studied (male 17, female 9), age was 61 ± 8 years (mean ± 1 SD), HbA1c 7.2 ± 1.1%, BP 130/75 ± 15.9/9.8 mmHg, total cholesterol 4.2 ± 0.81 mmol/l, triglyceride 2.11 ± 1.51 mmol/l, and HDL cholesterol 1.04 ± 0.29 mmol/l. The majority of patients were being treated with metformin (59%), aspirin (50%) and statin (96%) therapy. 36% were treated with an ACEI. There were no changes in these therapies throughout the study. Treatment with AGE had no significant effect upon the above metabolic parameters including insulin resistance. Treatment with AGE also had no significant effect on markers of endothelial function (plethysmography), oxidative stress (TAOS, GSH/GSSG, LHP) or inflammation (HsCRP).

CONCLUSION

In this group of type 2 diabetic patients at high cardiovascular risk, 4 weeks treatment with AGE did not significantly improve endothelial function, vascular inflammation, oxidative stress or insulin resistance.

A review on the effects of Allium sativum (Garlic) in metabolic syndrome

The metabolic syndrome is a common problem world-wide and includes abdominal obesity, hypertension, dyslipidemia, and hyperglycemia disorders. It leads to insulin resistance and the development of diabetes mellitus or cardiovascular disease. Allium sativum (garlic) has been documented to exhibit anti-diabetic, hypotensive, and hypolipidemic properties. This suggests a potential role of A. sativum in the management of metabolic syndrome; however, more studies should be conducted to evaluate its effectiveness. In this review, we discussed the most relevant articles to find out the role of A. sativum in different components of metabolic syndrome and cardiovascular disease risk factors. Because human reports are rare, further studies are required to establish the clinical value of A. sativum in metabolic syndrome.

Salivary antioxidants of male athletes after aerobic exercise and garlic supplementation on: A randomized, double blind, placebo-controlled study

PURPOSE

Production of reactive oxygen species and reactive nitrogen species is a natural biological event in metabolism. However, the presence of antioxidants can highly reduce the negative effect of free radicals. Thus, the efficiency of antioxidant system in the physiology of exercise is very important.

DESIGN

Considering the known antioxidant capacity of garlic, the purpose of this study was to evaluate the effect on combining 14 days aerobic exercise till exhaustion with garlic extract supplementation on the antioxidant capacity of saliva.

METHODS

Sixteen young men volunteered to participate in this randomized, double blind, placebo-controlled study and were randomly placed into two groups, placebo (Group I) and garlic extract (Group II). The participants performed exhaustive aerobic exercise on a treadmill before and after supplementation. Their unstimulated salivary samples were collected before, immediately after, and 1 h after the activity. The antioxidant activity in terms of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) was then measured in the collected samples using their specific substrates.

RESULTS

A significant increase in salivary antioxidant activity of SOD, POD, and CAT was observed in saliva of the supplement group compared to the placebo group (P ≤ 0.05).

CONCLUSION

The findings from this study suggest that increased activity of antioxidant enzymes could possibly decrease exercise-induced oxidative damage in male athletes.

Antioxidant effect of garlic (Allium sativum) and black seeds (Nigella sativa) in healthy postmenopausal women

Objectives:

The objective of this study is to investigate the antioxidant effects of garlic extract and crude black seeds’ consumption on blood oxidant/antioxidant levels in healthy postmenopausal women.

Methods:

In total, 30 healthy postmenopausal women (mean age = 50.31 ± 4.23 years) participated. They ingested two garlic soft gels per day (each is equivalent to 1000 mg of fresh garlic bulb) and crude black seed grounded to powder in a dose of 3 g/day for 8 weeks. Oxidant (malondialdehyde) activity in plasma and antioxidants superoxide dismutase and glutathione peroxidase activities in erythrocytes were studied.

Results:

Significant low levels of plasma malondialdehyde with increased erythrocyte glutathione peroxidase and superoxide dismutase activities.

Discussion:

Menopause is associated with an increase in oxidative stress and a decrease in some antioxidant parameters. Consumption of garlic extracts and crude black seeds may have a beneficial effect on improved balance between blood oxidants and antioxidants in healthy postmenopausal women.

The antioxidant mechanisms underlying the aged garlic extract- and S-allylcysteine-induced protection

Aged garlic extract (AGE) is an odorless garlic preparation containing S-allylcysteine (SAC) as its most abundant compound. A large number of studies have demonstrated the antioxidant activity of AGE and SAC in both in vivo--in diverse experimental animal models associated to oxidative stress--and in vitro conditions--using several methods to scavenge reactive oxygen species or to induce oxidative damage. Derived from these experiments, the protective effects of AGE and SAC have been associated with the prevention or amelioration of oxidative stress. In this work, we reviewed different antioxidant mechanisms (scavenging of free radicals and prooxidant species, induction of antioxidant enzymes, activation of Nrf2 factor, inhibition of prooxidant enzymes, and chelating effects) involved in the protective actions of AGE and SAC, thereby emphasizing their potential use as therapeutic agents. In addition, we highlight the ability of SAC to activate Nrf2 factor--a master regulator of the cellular redox state. Here, we include original data showing the ability of SAC to activate Nrf2 factor in cerebral cortex. Therefore, we conclude that the therapeutic properties of these molecules comprise cellular and molecular mechanisms at different levels.

Garlic in health and disease

The present article reviews the historical and popular uses of garlic, its antioxidant, haematological, antimicrobial, hepatoprotective and antineoplastic properties and its potential toxicity (from sulfoxide). Garlic has been suggested to affect several cardiovascular risk factors. It has also been shown that garlic and its organic allyl sulfur components are effective inhibitors of the cancer process. Since garlic and its constituents can suppress carcinogen formation, bioactivation and tumour proliferation, it is imperative that biomarkers be established to identify which individuals might benefit most. Garlic powder, aged garlic and garlic oil have demonstrated antiplatelet and anticoagulant effects by interfering with cyclo-oxygenase-mediated thromboxane synthesis. Garlic has also been found to have synergistic effects against Helicobacter pylori with a proton pump inhibitor. The active compound allicin may affect atherosclerosis not only by acting as an antioxidant, but also by other mechanisms, such as lipoprotein modification and inhibition of LDL uptake and degradation by macrophages. Freshly prepared garlic homogenate protects against isoniazid+rifampicin-induced liver injury in experimental animal models. Several mechanisms are likely to account for this protection.

Oxidative insults to neurons and synapse are prevented by aged garlic extract and S-allyl-L-cysteine treatment in the neuronal culture and APP-Tg mouse model

Alzheimer's disease (AD) is one of the most common forms of dementia in the elderly. In AD patients, β-amyloid peptide (Aβ) plaques and neurofibrillary tangles are common features observed in the CNS. Aβ deposition results in the production of reactive oxygen species (ROS) leading to the hyperphosphorylation of tau that are associated with neuronal damage. Cholinesterase inhibitors and a partial NMDA receptor antagonist (memantine) have been identified as potential treatment options for AD. However, clinical studies have found that these drugs fail to prevent the disease progression. From ancient times, garlic (Allium sativum) has been used to treat several diseases. By 'aging' of garlic, some adverse reactions of garlic can be eliminated. Recent findings suggest that 'aged garlic extract' (AGE) may be a therapeutic agent for AD because of its antioxidant and Aβ lowering properties. To date, the molecular properties of AGE have been sparsely studied in vitro or in vivo. The present study tested specific biochemical and molecular effects of AGE in neuronal and AD rodent models. Furthermore, we identified S-allyl-L-cysteine (SAC) as one of the most active chemicals responsible for the AGE-mediated effect(s). We observed significant neuroprotective and neurorescue properties of AGE and one of its ingredients, SAC, from ROS (H(2)O(2))-mediated insults to neuronal cells. Treatment of AGE and SAC were found to protect neuronal cells when they were independently co-treated with ROS. Furthermore, a novel neuropreservation effect of AGE was detected in that pre-treatment with AGE alone protected ∼ 80% neuronal cells from ROS-mediated damage. AGE was also found to preserve pre-synaptic protein synaptosomal associated protein of 25 kDa (SNAP25) from ROS-mediated insult. For example, treatment with 2% AGE containing diet and SAC (20 mg/kg of diet) independently increased (∼70%) levels of SNAP25 and synaptophysin in Alzheimer's amyloid precursor protein-transgenic mice, of which the latter was significantly decreased in AD. Taken together, the neuroprotective, including preservation of pre-synaptic proteins by AGE and SAC can be utilized in future drug development in AD.

Mechanisms underlying erythrocyte and endothelial nitrite reduction to nitric oxide in hypoxia: role for xanthine oxidoreductase and endothelial nitric oxide synthase

Reduction of nitrite (NO(2)(-)) provides a major source of nitric oxide (NO) in the circulation, especially in hypoxemic conditions. Our previous studies suggest that xanthine oxidoreductase (XOR) is an important nitrite reductase in the heart and kidney. Herein, we have demonstrated that conversion of nitrite to NO by blood vessels and RBCs was enhanced in the presence of the XOR substrate xanthine (10 micromol/L) and attenuated by the XOR inhibitor allopurinol (100 micromol/L) in acidic and hypoxic conditions only. Whereas endothelial nitric oxide synthase (eNOS) inhibition had no effect on vascular nitrite reductase activity, in RBCs L-NAME, L-NMMA, and L-arginine inhibited nitrite-derived NO production by >50% (P<0.01) at pH 7.4 and 6.8 under hypoxic conditions. Western blot and immunohistochemical analysis of RBC membranes confirmed the presence of eNOS and abundant XOR on whole RBCs. Thus, XOR and eNOS are ideally situated on the membranes of RBCs and blood vessels to generate intravascular vasodilator NO from nitrite during ischemic episodes. In addition to the proposed role of deoxyhemoglobin, our findings suggest that the nitrite reductase activity within the circulation, under hypoxic conditions (at physiological pH), is mediated by eNOS; however, as acidosis develops, a substantial role for XOR becomes evident.

Neuroprotective effects of garlic a review

Garlic has been investigated extensively for health benefits, resulting in more than one thousand publications over the last decade alone. It is considered one of the best disease preventive foods, based on its potent and varied effects. Midlife risk factors for cardiovascular diseases, such as high serum total cholesterol, raised LDL, increased LDL oxidation, increased platelet aggregation, impaired fibrinolysis, hypertension and homocystinemia are important risk factors for dementia in later years. These risk factors play a major role in the genesis of atherosclerosis of vital arteries causing both cardiovascular and cerebrovascular disease. Garlic is best known for its lipid lowering and anti-atherogenic effects. Possible mechanisms of action include inhibition of the hepatic activities of lipogenic and cholesterogenic enzymes that are thought to be the genesis for dyslipidemias, increased excretion of cholesterol and suppression of LDL-oxidation. Oxidative stress caused by increased accumulation of reactive oxygen species (ROS) in cells has been implicated in the pathophysiology of several neurodegenerative diseases including Alzheimer's disease (AD). Several studies have demonstrated the antioxidant properties of garlic and its different preparations including Aged Garlic Extract (AGE). AGE and S-allyl-cysteines (SAC), a bioactive and bioavailable component in garlic preparations have been shown in a number of in vitro studies to protect neuronal cells against beta-amyloid (A) toxicity and apoptosis. Thus the broad range of anti-atherogenic, antioxidant and anti-apoptotic protection afforded by garlic may be extended to its neuroprotective action, helping to reduce the risk of dementia, including vascular dementia and AD.

Garlic and cardiovascular disease: a critical review

Epidemiologic studies show an inverse correlation between garlic consumption and progression of cardiovascular disease. Cardiovascular disease is associated with multiple factors such as raised serum total cholesterol, raised LDL and an increase in LDL oxidation, increased platelet aggregation, hypertension, and smoking. Numerous in vitro studies have confirmed the ability of garlic to reduce these parameters. Thus, garlic has been shown to inhibit enzymes involved in lipid synthesis, decrease platelet aggregation, prevent lipid peroxidation of oxidized erythrocytes and LDL, increase antioxidant status, and inhibit angiotension-converting enzyme. These findings have also been addressed in clinical trials. The studies point to the fact that garlic reduces cholesterol, inhibits platelet aggregation, reduces blood pressure, and increases antioxidant status. Since 1993, 44% of clinical trials have indicated a reduction in total cholesterol, and the most profound effect has been observed in garlic's ability to reduce the ability of platelets to aggregate. Mixed results have been obtained in the area of blood pressure and oxidative-stress reduction. The findings are limited because very few trials have addressed these issues. The negative results obtained in some clinical trials may also have resulted from usage of different garlic preparations, unknown active constituents and their bioavalability, inadequate randomization, selection of inappropriate subjects, and short duration of trials. This review analyzes in vitro and in vivo studies published since 1993 and concludes that although garlic appears to hold promise in reducing parameters associated with cardiovascular disease, more in-depth and appropriate studies are required.