Garlic Compounds Research Articles

Garlic arrests MDA-MB-435 cancer cells in mitosis, phosphorylates the proapoptotic BH3-only protein BimEL and induces apoptosis

Components of garlic (Allium sativum) can cause disruption of microtubules, cell cycle arrest, and apoptosis in cancer cells. We show here that a water-soluble extract of garlic arrested MDA-MB-435 cancer cells in mitosis and caused apoptosis. The proapoptotic BH3-only, bcl-2 family protein BimEL, which in healthy cells can be tightly sequestered to the microtubule-associated dynein motor complex, was modified after garlic treatment. The main effect of garlic on BimEL was a considerable increase in a phosphorylated form of the protein. This phosphorylation(s), probably partly dependent on c-jun N-terminal kinase activity, promoted mitochondrial localisation of BimEL. Furthermore, inhibition of extracellular signal-regulated kinases 1/2 increased the amount of another form of BimEL present in the mitochondrial cellular fraction. Treatment of cells with the garlic compound diallyl disulphide had similar effects on BimEL. The results indicate that the apoptotic effect of garlic and a combination of garlic and the inhibitor of extracellular signal-regulated kinases 1/2 in MDA-MB-435 cells partly is due to modifications that are necessary for translocation of the proapoptotic protein BimEL to mitochondria where it executes its proapoptotic function.

Modulation of Cytokine Secretion by Garlic Oil Derivatives Is Associated with Suppressed Nitric Oxide Production in Stimulated Macrophages

We previously described that garlic oil derivatives differentially suppress the production of nitric oxide (NO) and prostaglandin E(2) (PGE(2)) in activated macrophages. In the present study, we investigated the effects of the garlic derivatives, diallyl sulfide (DAS), diallyl disulfide (DADS), and allyl methyl sulfide (AMS), on cytokine production in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells, and the association between modulation of cytokines and inhibition of NO production was also assessed. The results indicated that these garlic compounds had different effects on the secretion of activated cytokines, including proinflammatory tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, and IL-6, as well as the antiinflammatory, IL-10. DAS inhibited the production of all stimulated cytokines in a concentration-dependent manner, and the inhibition was closely associated with the suppression of NO and PGE(2) production. DADS repressed the production of stimulated TNF-alpha and IL-10 and increased the production of activated IL-1beta and, to a lesser extent, IL-6; but only the decreased IL-10 production was associated with DADS-induced NO inhibition. Yet, the DAS- and DADS-suppressed NO production was independent of TNF-alpha. AMS, on the other hand, slightly suppressed the stimulated TNF-alpha but enhanced IL-10 production, and such modulation was closely associated with the decrease in NO production.

Allicin and Allicin-Derived Garlic Compounds Increase Breath Acetone through Allyl Methyl Sulfide: Use in Measuring Allicin Bioavailability

Progress in establishing systemic pharmacological effects for fresh, crushed garlic (Allium sativum L) in humans has been hindered by (1) the inability to measure allicin bioavailability, (2) lack of direct evidence that allicin has significant systemic activity at doses of garlic normally consumed, and (3) lack of a model for an acute effect. We have addressed these problems by quantifying the increases in breath acetone and breath allyl methyl sulfide (AMS). The area under the 48 h curve was measured in humans after consumption of standardized garlic preparations, allicin, and allicin-derived compounds, at the equivalent of 7 g of crushed garlic. It was shown that the allyl thiosulfinates (mainly allicin) are solely responsible for breath AMS and increased breath acetone. Diallyl trisulfide, diallyl disulfide, ajoene, and S-allylmercaptocysteine, at isomolar dithioallyl, showed the same quantitative effects as allicin. Consumption of AMS at isomolar allyl also gave the same effects as allicin, indicating that AMS is the main metabolite of allicin and is an active metabolite. In conclusion, allicin and allicin-derived compounds are rapidly metabolized to AMS, a compound which stimulates the production of acetone and which can be used to measure the bioavailability of allicin and, hence, the ability of garlic supplements to represent fresh garlic.

Induction of apoptosis in tumor cells by naturally occurring sulfur-containing compounds

Chemoprevention is regarded as one of the most promising and realistic approaches in the prevention of human cancer. Among naturally occurring products, sulfur-containing compounds (OSCs), especially garlic compounds (GCs) and isothiocyanates (ITCs), represent two important and promising chemopreventive families because of their potent chemopreventive effects in various in vivo and in vitro models. In recent years, numerous investigations have shown that sulfur-containing compounds induce apoptosis in multiple cell lines and experimental animals. In the course of apoptosis induction by GCs and ITCs, multiple signal-transduction pathways and apoptosis intermediates are modulated. In particular, modulation of MAPKs and production of reactive oxygen species (ROS) seem to play pivotal roles in apoptosis induction by most GCs and ITCs. However, the role of P53 is still controversial. Based on present knowledge, GCs and ITCs may target not only the metabolism of carcinogens but also apoptosis signaling molecules. The effects of ITCs and GCs at multiple points of cancer development make these compounds highly promising candidates in cancer chemoprevention. However, the mechanisms of their anticancer effects are not fully understood, and further studies are required, especially to elucidate the role of cell-death receptors (the extrinsic pathway) and whether these agents induce apoptotic effects in non-tumor cells.

Diallyl Disulfide-Induced Modulation of a Few Phase I and II Drug Metabolizing Enzymes on Aroclor 1254 Toxicity in Rattus norvegicus Liver and Ventral Prostate

Polychlorinated biphenyls (PCBs) are persistent bioaccumulative toxicants. These synthetic organochlorinated compounds are well documented for their carcinogenic property, reproductive, neuro, hepato and developmental toxicities. Diallyl disulfide (DADS), a garlic organosulfur compound exerts its effect as a chemopreventive agent via the modulation of drug metabolizing enzymes which has led us to hypothesize that DADS could ameliorate the PCB-induced toxicity in liver and ventral prostate of the rats. In the present investigation, experimentally induced PCB toxicity elevated the activities of phase I enzymes and lipid peroxides level, whereas lowered the levels of phase II enzymes. Oral administration of DADS for 7 days modulated the levels of drug metabolizing enzymes and reduced the lipid peroxides level. These results suggest that PCBs can be readily metabolized by DADS administration through enhancing phase II enzymes thereby it reduces the toxic effects.

Growth Suppressing Effect of Garlic Compound Diallyl Disulfide on Prostate Cancer Cell Line (PC-3) in Vitro

Prostate cancer is the most predominant cancer in men and prostate cancer related death increases every year. Till date, there is no effective therapy other than androgen ablation therapy. At this stage, induction of apoptosis is considered as a better strategy to control cancer. Previous studies reported that aged garlic extract suppresses cancer growth and enhances immune system against cancer. In the present study, diallyl disulfide, oil soluble organosulfur compound of garlic, was studied for its antiproliferative effect on prostate cancer cells in vitro. The suppression of cell growth was demonstrated by [(3)H]thymidine incorporation assay. Induction of DNA damage was assessed by agarose gel electrophoresis. The results showed that diallyl disulfide inhibited the growth of prostate cancer cells in a dose dependent manner, compared to the control. At 50 microM and 100 microM concentrations, diallyl disulfide induced DNA damage in PC-3 cells. It is concluded that diallyl disulfide, component of aged garlic extract, inhibits proliferation of prostate cancer cells through the induction of apoptosis.

Induction of detoxifying enzymes by garlic organosulfur compounds through transcription factor Nrf2: effect of chemical structure and stress signals

Garlic organosulfur compounds (OSCs) are recognized as a group of potential chemopreventive compounds. It is known that garlic OSCs can modulate drug metabolism systems, especially various phase II detoxifying enzymes, though the mechanism underlying their inductive effect on these enzymes remains largely unknown. In the present study, we investigated the transcriptional levels of NAD(P)H:quinone oxidoreductase 1 (NQO1) and heme oxygenase 1 (HO1) genes, the reporter activity mediated by antioxidant response element (ARE), and the protein level of transcription factor nuclear factor E2-related factor 2 (Nrf2), after administration of three major garlic OSCs—diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS)—in human hepatoma HepG2 cells. Our results showed that ARE activation and Nrf2 protein accumulation were well correlated with phase II gene expression induction. The structure–activity relationship study indicated that the third sulfur in the structure of OSCs contributed substantially to their bioactivities, and that allyl-containing OSCs were more potent than propyl-containing OSCs. To better understand the signaling events involved in the upregulation of detoxifying enzymes by DATS, ARE activity and Nrf2 protein levels were examined after transient transfection of HepG2 cells with mutant Nrf2, cotreatment with antioxidants, and pretreatment with protein kinase inhibitors. DATS-induced ARE activity was inhibited by dominant-negative Nrf2 Kelch-like ECH-associating protein 1 and constructs. Cotreatment with thiol antioxidants decreased the ARE activity and Nrf2 protein level induced by DATS. Three major mitogen-activated protein kinases (MAPKs)—extracellular signal-regulated protein kinase, c-Jun N-terminal kinase, and p38-were activated by DATS treatment. However, the inhibition of these MAPKs did not affect DATS-induced ARE activity. Pretreatment with various upstream protein kinase inhibitors showed that the protein kinase C pathway was not directly involved in DATS-induced ARE activity, but instead the calcium-dependent signaling pathway appeared to play a role in the DATS-induced cytoprotective effect.

Ajoene (natural garlic compound): a new anti-leukaemia agent for AML therapy

Ajoene (natural garlic compound): a new anti-leukaemia agent for AML therapy

Anti-atherogenic effects of an egg yolk-enriched garlic supplement

It has been suggested that oxidation of low-density lipoprotein (LDL) plays an important role in the initiation and progression of atherosclerosis. In the present study, we determined the anti-atherogenic effects of egg yolk-enriched garlic powder (EGP), which has been used as a traditional health-promoting food in southern Japan since ancient times, on LDL oxidation and oxidant stress-induced cell injury models. We confirmed that EGP inhibits copper-induced LDL oxidation in a dose-dependent manner. We also observed that pretreatment of EGP significantly suppressed the production of peroxides in HL60 cells and protected endothelial cells from hydrogen peroxide-induced cell injury. These findings might, in part, be ascribed to the biodistribution of garlic compounds and egg yolk interaction, and suggest that EGP might be useful in the prevention of atherosclerosis.

Ajoene (natural garlic compound): a new anti-leukaemia agent for AML therapy

The reputation of garlic ( Allium sativum) as an effective remedy for tumours extends back to the Egyptian Codex Ebers of 1550 b.c. Several garlic compounds including allicin and its corresponding sulfide inhibit the proliferation and induce apoptosis of several human non-leukaemia malignant cells including breast, bladder, colorectal, hepatic, prostate cancer, lymphoma and skin tumour cell lines. Ajoene (4,5,9-trithiadodeca-1,6,11-triene-9-oxide) is a garlic-derived compound produced most efficiently from pure allicin and has the advantage of a greater chemical stability than allicin. Several clinical trials and in vitro studies of ajoene have demonstrated its best-known anti-thrombosis, anti-microbial and cholesterol lowering activities. Recently, topic application of ajoene has produced significant clinical response in patients with skin basal cell carcinoma. Ajoene was shown to inhibit proliferation and induce apoptosis of several human leukaemia CD34-negative cells including HL-60, U937, HEL and OCIM-1. Also, ajoene induces 30% apoptosis in myeloblasts from chronic myeloid leukaemia patient in blast crisis. More significantly, ajoene profoundly enhanced the apoptotic effect of the two chemotherapeutic drugs: cytarabine and fludarabine in human CD34-positive resistant myeloid leukaemia cells through enhancing their bcl-2 inhibitory and caspase-3 activation activities. The two key anti-leukaemia biological actions of ajoene were the inhibition of proliferation and the induction of apoptosis. Studies have shown the anti-proliferation activity of ajoene to be associated with a block in the G2/M phase of cell cycle in human myeloid leukaemia cells. The apoptosis inducing activity of ajoene is via the mitochondria-dependent caspase cascade through a significant reduction of the anti-apoptotic bcl-2 that results in release of cytochrome c and the activation of caspase-3. Since acute myeloid leukaemia (AML) is a heterogeneous malignant disease in which disease progression at the level of CD34-positive cells has a major impact on resistance to chemotherapy and relapse and the inability to undergo apoptosis is a crucial mechanism of multi-drug resistance in AML patients. The recent findings of the potent enhancing activity of ajoene on chemotherapy-induced apoptosis in CD34-positive resistant human myeloid leukaemia cells suggest a novel promising role for the treatment of refractory and/or relapsed AML patients as well as elderly AML patients. Further studies are warranted to evaluate similar enhancing effect for ajoene in blast cells from AML patients in primary cultures before its introduction in pilot clinical study.

Neurotoxicity induced by amyloid β-peptide and ibotenic acid in organotypic hippocampal cultures: protection by S-allyl- l-cysteine, a garlic compound

We have assessed amyloid-β (Aβ)-induced neurotoxicity, with and without added ibotenic acid (IBO), a potent N-methyl- d-aspartate (NMDA) agonist, in an organotypic hippocampal slice culture (OHC). In the OHC, there was little neurotoxicity after treatment with Aβ 25–35 (25 or 50 μM) alone for 48 h. However, with IBO alone neuronal death was observed in the pyramidal cell layer at low concentrations, and there was dramatic neuronal death at concentrations of 65 μM or more. When Aβ was combined with IBO (Aβ+IBO) there was more intense cell death than with IBO alone. S-Allyl- l-cysteine (SAC), one of the organosulfur compounds having a thioallyl group in aged garlic extract, was shown to protect the hippocampal neurons in the CA3 area and the dentate gyrus (DG) from the cell death induced by Aβ+IBO with no change in the CA1 area. Although l-glutamate (500 μM) potentiated the degree of IBO-induced neuronal death, it attenuated the Aβ+IBO-induced neuronal death in both the CA3 area and the DG with no obvious effect on the CA1 area. These results suggest that Aβ+IBO induces extensive neuronal death, and that SAC and l-glutamate protect cells from death in specific areas of the hippocampus. In addition, inhibition using a pan-caspase inhibitor, z-VAD-fmk, only provided partial protection from Aβ+IBO-induced toxicity for the neurons in the CA3 area. These results suggest that multiple mechanisms may be involved in Aβ+IBO-induced neuronal death in the OHC.

Ajoene inhibits the activation of human endothelial cells induced by porcine cells: implications for xenotransplantation.

Ajoene, is an organosulfur compound derived from garlic that strongly inhibit platelet aggregation, proliferation of human lymphocytes induced by phytohemagglutinin, and in general, blocks membrane-mediated signaling of cell activation. As a thrombotic microangiopathy frequently complicates procedures designed to induce pig-to-baboon chimerism by infusion of large amounts of pig progenitor cells in baboons, it was thought that ajoene might be useful to prevent such complication. For such purpose, we studied the effects of ajoene on the activation of human umbilical vein endothelial cells (HUVEC) induced by pig peripheral blood mononuclear cells (p-PBMC). Co-cultures of p-PBMC with HUVEC results in activation of the HUVEC as shown by over-expression of E-selectin and vascular cells adhesion molecule-1 (VCAM-1). Ajoene (25 microm) strongly inhibits HUVEC activation induced by tumor necrosis factor-alpha (TNF-alpha) or p-PBMC as shown by a down regulation of VCAM-1 and of E-selectin expression. After 5 or 8 h of pre-treatment with Ajoene, HUVEC incubated with TNF and p-PBMC showed an E-selectin or VCAM-1 expression, respectively, at levels similar to the positive control indicating that the inhibitory effect is transient. Ajoene at concentration of 25 microm or lower did not affect HUVEC viability. Based on the finding that Ajoene has a strong, although transient, inhibitory effect on the activation of the endothelium induced by pig cells and its known anti-platelet activity, it is suggested that this garlic compound could be useful to prevent the development of microangiopathy and thrombotic disorders seen in primates infused with pig cells.

Protective effect of S-allyl- l-cysteine, a garlic compound, on amyloid β-protein-induced cell death in nerve growth factor-differentiated PC12 cells

Aged garlic extract (AGE) contains several neuroactive compounds, including S-allyl- l-cysteine (SAC) and allixin. We characterized cell death induced by amyloid β-protein (Aβ), 4-hydroxynonenal (HNE), tunicamycin, an endoplasmic reticulum (ER) stressor, or trophic factor deprivation, and investigated whether and how SAC could prevent this in nerve growth factor (NGF)-differentiated PC12 cells, a model of neuronal cells. Exposure of the cells to amyloid β-protein 1–40 (Aβ 1–40) decreased the extent of [3-(4,5)-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) reduction activity and loss of neuronal integrity, but these effects were not prevented by Ac-DEVD-CHO, a caspase-3 inhibitor. Simultaneously applied SAC protected the cells against Aβ-induced cell death in a concentration-dependent manner. It also protected them against tunicamycin-induced neuronal death. In contrast, it afforded no protection against cell death induced by HNE and trophic factor deprivation, which is mediated by a caspase-3-dependent pathway. These results suggest that SAC may selectively protect cell death induced by Aβ and tunicamycin, which may be triggered by ER dysfunction in NGF-differentiated PC12 cells.

Ajoene, a garlic compound, inhibits protein prenylation and arterial smooth muscle cell proliferation.

(1) Ajoene is a garlic compound with anti-platelet properties and, in addition, was shown to inhibit cholesterol biosynthesis by affecting 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase and late enzymatic steps of the mevalonate (MVA) pathway. (2) MVA constitutes the precursor not only of cholesterol, but also of a number of non-sterol isoprenoids, such as farnesyl and geranylgeranyl groups. Covalent attachment of these MVA-derived isoprenoid groups (prenylation) is a required function of several proteins that regulate cell proliferation. We investigated the effect of ajoene on rat aortic smooth muscle cell proliferation as related to protein prenylation. (3) Cell counting, DNA synthesis, and cell cycle analysis showed that ajoene (1-50 micro M) interfered with the progression of the G1 phase of the cell cycle, and inhibited rat SMC proliferation. (4) Similar to the HMG-CoA reductase inhibitor simvastatin, ajoene inhibited cholesterol biosynthesis. However, in contrast to simvastatin, the antiproliferative effect of ajoene was not prevented by the addition of MVA, farnesol (FOH), and geranylgeraniol (GGOH). Labelling of smooth muscle cell cellular proteins with [3H]-FOH and [3H]-GGOH was significantly inhibited by ajoene. (5) In vitro assays for protein farnesyltransferase (PFTase) and protein geranylgeranyltransferase type I (PGGTase-I) confirmed that ajoene inhibits protein prenylation. High performance liquid chromatography (HPLC) and mass spectrometry analyses also demonstrated that ajoene causes a covalent modification of the cysteine SH group of a peptide substrate for protein PGGTase-I. (6) Altogether, our results provide evidence that ajoene interferes with the protein prenylation reaction, an effect that may contribute to its inhibition of SMC proliferation.

Antitumor activity of Z-ajoene, a natural compound purified from garlic: antimitotic and microtubule-interaction properties.

Ajoene, a garlic stable oil-soluble sulfur rich compound was generally isolated as a mixture of two isomers [(E, Z)-4,5,9-trithiadodeca-1,6,11-triene-9-oxide]. It has been described essentially as a potent inhibitor of platelet aggregation in vitro and in vivo. The antiproliferative effects of ajoene and experiments using a single isomer had received little attention. The present study aims at defining the antitumor activities of cis-Z-ajoene in vitro and in vivo. Antiproliferative activity of Z-ajoene was demonstrated against a panel of human tumor cell lines with IC(50) values varying from 5.2 mM to 26.1 mM and at a lower extent in normal marsupial kidney cells (PtK2). Meanwhile, Z-ajoene arrested HL60 cells in G(2)/M phase of cell cycle in a dose and time-dependent way. In PtK2 cells, exposure to 20 microM Z-ajoene for 6 h induced a complete disassembly of the microtubule network, that was associated with an increased number of cells blocked in early mitotic stages. An IC(50) for microtubule disassembly of 1 microM was determined by a fully automated microplate-based multi-detection reader. In vitro, a reversible inhibition of the microtubule protein assembly was observed with an IC(50) of 25 microM Z-ajoene. In vivo, Z-ajoene inhibited tumor growth by 38% and 42% in mice grafted with sarcoma 180 and hepatocarcinoma 22, respectively. For the first time, Z-ajoene was shown to be a potent inhibitor of tumor cell growth both in vitro and in vivo. The microtubule cytoskeleton appeared to be one of the Z-ajoene targets, but the mechanisms by which Z-ajoene interacted with microtubule appeared different from those of other microtubule poisons such as those of the Vinca alkaloids family. The ability of Z-ajoene to preferentially suppress the growth of neoplastic cells could provide a new approach in tumor therapy.

Investigation of the volatile aroma components of garlic leaves essential oil. Possibility of utilization to enrich garlic bulb oil

The volatile aroma components of Egyptian green garlic leaves essential oil was investigated for the first time. After the utilization of garlic bulbs to prepare garlic oil or after drying the bulbs to produce garlic powder, garlic leaves are considered to be waste material, which is disposed of without any benefit. In this investigation, green garlic leaves were distilled and the essential oil was subjected to GC and GC-MS identification. The yield of the oil was 0.06% (based on wet weight of the leaves). The most prominent compounds of the essential oil were diallyl trisulfide (32.32%), followed by diallyl disulfide (31.35%) and methyl allyl trisulfide (11.40%); these compounds are the same as those found in garlic bulb oil. This means that garlic leaf oil is a rich, renewable and priceless source of garlic aroma compounds which could be utilized in fortification and enriching of garlic bulb essential oil to increase its quantity without changing the quality. Utilization of green garlic leaves for production of essential oil will also save, to some extent, the costs of disposing of large amounts of leaves in garlic possessing factories, transforming them into profits.

Effects of the garlic compound diallyl disulfide on the metabolism, adherence and cell cycle of HT-29 colon carcinoma cells: evidence of sensitive and resistant sub-populations.

Diallyl disulfide (DADS) is a major organosulphur compound present in garlic with an anti-mitotic potential against colon neoplastic lesions in vivo and colon tumour cell growth in vitro. Using the human colon adenocarcinoma HT-29 Glc(-/+) cell line we identified sub-populations of tumoural cells with markedly different characteristics in terms of metabolic capacities, adhesion properties and distribution in the cell cycle phases. After 1 and 2 days treatment with 100 microM DADS HT-29 cells were largely released into the culture medium. These floating cells accumulated in the G(2)/M phase and were characterized by a 5-fold reduction in cell capacity for de novo protein synthesis. Polyamine metabolism, which is necessary for intestinal epithelial cell attachment and growth, was also severely affected, since 3-fold reductions in polyamine biosynthesis and net accumulation of putrescine were measured after DADS treatment. However, oxidation of L-glutamine, the main precursor of the tricarboxylic acid cycle in these cells, and de novo synthesis of glutathione, a tripeptide involved in tumoural cell chemoresistance, were not affected by DADS treatment. In contrast, the adherent sub-population of HT-29 cells, although partially accumulated in G(2)/M phase, were characterized by unaffected metabolic capacities when compared with control cells except for putrescine accumulation, which was transiently decreased, and L-glutamine oxidation, which was increased 2-fold. DADS-resistant cells selected within 5 days were then able to proliferate at a similar rate to control untreated cells. The DADS-induced changes in HT-29 metabolic capacities, adhesion properties and the cell cycle are discussed from a causal perspective.

Garlic and Garlic-Derived Compounds Inhibit Human Squalene Monooxygenase

Although extracts of garlic inhibit cholesterol biosynthesis in cultured hepatocytes, the inhibitory components of garlic and the site or sites of inhibition in the cholesterol biosynthetic pathway have not been established. To elucidate potential mechanisms of inhibition, we examined the effect of fresh garlic extract and 16 water- or lipid-soluble compounds derived from garlic on purified recombinant human squalene monooxygenase. Squalene monooxygenase catalyzes the second and likely rate-limiting step in the downstream pathway for cholesterol biosynthesis. A 50% inhibitory concentration (IC(50)) of squalene epoxidation was achieved with 1 g/L of fresh garlic extract; of the 16 garlic compounds tested, only selenocystine (IC(50) = 65 micromol/L), S-allylcysteine (IC(50) = 110 micromol/L), alliin (IC(50) = 120 micromol/L), diallyl trisulfide (IC(50) = 195 micromol/L), and diallyl disulfide (IC(50) = 400 micromol/L) substantially inhibited the enzyme. Kinetic analysis showed that the inhibition by garlic and by these compounds was slow and irreversible, suggestive of covalent binding to the enzyme; the ability of thiol-containing compounds such as glutathione and 2,3-dimercaptopropanol to prevent and reverse the inhibition indicated that the garlic compounds were reacting with sulfhydryl groups on the protein. Dithiols were better reversal agents than monothiols, further suggesting that these inhibitors bind to the proposed vicinal sulfhydryls present on this enzyme. These results indicate that squalene monooxygenase may be one of the target enzymes through which garlic inhibits cholesterol biosynthesis.

Suppression of LDL Oxidation by Garlic

It has been known for several decades that hypercholesterolemia is a major risk factor for atherosclerosis and that lowering of cholesterol can significantly reduce risk for cardiovascular diseases. More recently, oxidation of LDL has been recognized as playing an important role in the initiation and progression of atherosclerosis. Oxidized LDL, but not native LDL, promotes vascular dysfunction by exerting direct cytotoxicity toward endothelial cells, by increasing chemotactic properties for monocytes, by transforming macrophages to foam cells via scavenger-receptors and by enhancing the proliferation of various cell types, e.g., endothelial cells, monocytes and smooth muscle cells; all of these events are recognized as contributing to atherogenesis. In this paper, experimental evidence is presented that shows that several garlic compounds can effectively suppress LDL oxidation in vitro. Short-term supplementation of garlic in human subjects has demonstrated an increased resistance of LDL to oxidation. These data suggest that suppressed LDL oxidation may be one of the powerful mechanisms accounting for the antiatherosclerotic properties of garlic.

The Influence of Heating on the Anticancer Properties of Garlic

Allyl sulfur compounds are the major active constituents found in crushed garlic. Research has revealed that garlic and its lipid- or water-soluble components have many pharmacologic properties; however, studies also demonstrate that heating has a negative influence on these beneficial effects. We recently conducted several studies to investigate the influence of microwave or oven heating on the anticarcinogenesis property of garlic. Our studies showed that as little as 60 s of microwave heating or 45 min of oven heating can block garlic's ability to inhibit in vivo binding of mammary carcinogen [7,12-dimethylbenzene(a)anthracene (DMBA)] metabolites to rat mammary epithelial cell DNA. Allowing crushed garlic to "stand" for 10 min before microwave heating for 60 s prevented the total loss of anticarcinogenic activity. Our studies demonstrated that this blocking of the ability of garlic was consistent with inactivation of alliinase. These studies suggest that heating destroyed garlic's active allyl sulfur compound formation, which may relate to its anticancer properties.