Well-characterized garlic-derived materials are not hypolipidemic in APOE*3-Leiden transgenic mice

Diallyl disulfide alleviates hypercholesterolemia induced by a western diet by suppressing endoplasmic reticulum stress in apolipoprotein E-deficient mice

BACKGROUND

The endoplasmic reticulum (ER) plays a pivotal role in maintaining cellular metabolic homeostasis. ER stress refers to the accumulation of misfolded proteins, which can trigger an unfolded protein response for survival or death in the cells. Diallyl disulfide (DADS), a major active compound in garlic, has many health benefits for patients with metabolic diseases, especially cardiovascular or fatty liver diseases. However, its role in attenuating hypercholesterolemia by suppressing ER stress remains unknown. Therefore, in this study, we determined whether DADS supplementation could reduce ER stress in apolipoprotein E-deficient (ApoE^-/-) mice fed a Western-type diet (WD).

METHODS

ApoE^-/- mice were fed either a WD alone or a WD supplemented with 0.1% DADS for 12 weeks (n = 10). Levels of plasma total cholesterol, triglyceride, leptin, and insulin were determined. Western blotting was performed to measure protein levels involved in ER stress markers. Histology and Immunostaining were performed on aortic root sections to confirm the effect of DADS on histology and expression of ER chaperone protein GRP78.

RESULTS

The metabolic parameters showed that increases in fat weight, leptin resistance, and hypercholesterolemia were reversed in DADS-supplemented mice (p < 0.05). In addition, DADS ameliorated not only the protein of ER stress markers, phospho-eukaryotic initiation factor 2 subunit alpha and C/EBP homologous protein in the liver (p < 0.05) but also glucose-related protein 78 localization in the aorta.

CONCLUSIONS

This indicates that DADS inhibits diet-induced hypercholesterolemia, at least in parts by regulating ER stress markers. DADS may be a good candidate for treating individuals with diet-induced hypercholesterolemia.

Current studies and potential future research directions on biological effects and related mechanisms of allicin

Allicin, a thiosulfonate extract from freshly minced garlic, has been reported to have various biological effects on different organs and systems of animals and human. It can reduce oxidative stress, inhibit inflammatory response, resist pathogen infection and regulate intestinal flora. In addition, dozens of studies also demonstrated allicin could reduce blood glucose level, protect cardiovascular system and nervous system, and fight against cancers. Allicin was widely used in disease prevention and health care. However, more investigations on human cohort study are needed to verify the biological or clinical effects of allicin in the future. In this review, we summarized the biological effects of allicin from previous outstanding and valuable studies and provided useful information for future studies on the health effects of allicin.

Cholesterol-lowering effect of allicin on hypercholesterolemic ICR mice

Allicin was discussed as an active compound with regard to the beneficial effects of garlic in atherosclerosis. The aim of this study was to investigate the cholesterol-lowering properties of allicin. In order to examine its effects on hypercholesterolemia in male ICR mice, this compound with doses of 5, 10, or 20 mg/kg body weight was given orally daily for 12 weeks. Changes in body weight and daily food intake were measured regularly during the experimental period. Final contents of serum cholesterol, triglyceride, glucose, and hepatic cholesterol storage were determined. Following a 12-week experimental period, the body weights of allicin-fed mice were less than those of control mice on a high-cholesterol diet by 38.24 ± 7.94% (P < 0.0001) with 5 mg/kg allicin, 39.28 ± 5.03% (P < 0.0001) with 10 mg/kg allicin, and 41.18 ± 5.00% (P < 0.0001) with 20 mg/kg allicin, respectively. A decrease in daily food consumption was also noted in most of the treated animals. Meanwhile, allicin showed a favorable effect in reducing blood cholesterol, triglycerides, and glucose levels and caused a significant decrease in lowering the hepatic cholesterol storage. Accordingly, both in vivo and in vitro results demonstrated a potential value of allicin as a pronounced cholesterol-lowering candidate, providing protection against the onset of atherosclerosis.

Preventive effect of S-allyl cysteine sulfoxide (alliin) on cardiac marker enzymes and lipids in isoproterenol-induced myocardial injury

The present study was designed to evaluate the preventive effect of S-allyl cysteine sulfoxide (SACS) in isoproterenol (ISO)-induced myocardial ischaemia in male Wistar rats. Rats were pretreated with SACS (40 and 80 mg kg(-1) body-weight) for 5 weeks. After the treatment period, ISO (150 mg kg(-1) body-weight) was administered subcutaneously to rats at intervals of 24 h for 2 days. The activities of creatine kinase, creatine kinase-MB, lactate dehydrogenase, aspartate transaminase and alanine transferase were significantly increased in serum and significantly decreased in the hearts of ISO-treated rats. Pretreatment with SACS decreased the activities of these enzymes significantly in serum and significantly increased the activities in heart in ISO-treated rats. The levels of cholesterol, triglycerides and free fatty acids increased in serum and heart, while the levels of phospholipids increased in serum and decreased in heart in ISO-treated rats. SACS pretreatment showed a significant effect on the lipids studied. The activity of 3-hydroxy 3-methyl glutaryl coenzyme A (HMG CoA) reductase was significantly increased and the activity of lecithin cholesterol acyl transferase (LCAT) was significantly reduced in ISO-induced rats. Oral pretreatment with SACS significantly decreased the activity of HMG CoA reductase and significantly increased the activity of LCAT in ISO-induced rats. The levels of plasma thiobarbituric acid reactive substances and hydroperoxides were increased in ISO-treated rats. Pretreatment with SACS significantly decreased the levels of lipidperoxides in ISO-treated rats. The effect at a dose of 80 mg kg(-1) body-weight was more effective than at a dose of 40 mg kg(-1) body-weight and brought back all the biochemical parameters to near normal levels. Thus our study shows that SACS has a lipid-lowering effect in ISO-induced rats. Our study may have clinical relevance.

The antiatherogenic effect of allicin: possible mode of action

OBJECTIVE

Garlic (Allium sativum) has been suggested to affect several cardiovascular risk factors. Its antiatherosclerotic properties are mainly attributed to allicin that is produced upon crushing of the garlic clove. Most previous studies used various garlic preparations in which allicin levels were not well defined. In the present study, we evaluated the effects of pure allicin on atherogenesis in experimental mouse models.

METHODS AND RESULTS

Daily dietary supplement of allicin, 9 mg/kg body weight, reduced the atherosclerotic plaque area by 68.9 and 56.8% in apolipoprotein E-deficient and low-density lipoprotein (LDL) receptor knockout mice, respectively, as compared with control mice. LDL isolated from allicin-treated groups was more resistant to CuSO(4)-induced oxidation ex vivo than LDL isolated from control mice. Incubation of mouse plasma with (3)H-labeled allicin showed binding of allicin to lipoproteins. By using electron spin resonance, we demonstrated reduced Cu(2+) binding to LDL following allicin treatment. LDL treatment with allicin significantly inhibited both native LDL and oxidized LDL degradation by isolated mouse macrophages.

CONCLUSIONS

By using a pure allicin preparation, we were able to show that 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.

Absence of an atheroprotective effect of the garlic powder printanor in APOE*3-Leiden transgenic mice

Numerous animal studies have reported that garlic can protect against atherosclerosis. However, a comparable number of studies do not support this observation. This contradiction may result from differences in study design, use of different animal models, and use of different garlic formulations and preparations. Here, we investigated the effect of the chemically well-characterized and production-controlled garlic powder printanor on atherosclerosis in the APOE*3-Leiden transgenic mouse, a mouse model well suited for evaluating anti-atherosclerotic properties of drugs and food components under human-like conditions. APOE*3-Leiden mice were fed a Western diet supplemented with either 5 or 50 g kg(-1) printanor. As a reference, the commercially available fermented garlic kyolic was included (1.6 g kg(-1) diet). Treatment with printanor demonstrated reduced body weight, coinciding with increased feces production and fecal fatty acids excretion. Printanor and kyolic treatment did not affect plasma lipids, markers of inflammation (serum amyloid A, serum-soluble intercellular adhesion molecule-1, and blood-leukocytes tumor necrosis factor-alpha (TNFalpha) production) and vascular activation (plasma von Willebrand factor (vWF)). As analyzed after 28 weeks of treatment, printanor and kyolic did not affect atherosclerotic lesion type, area or composition. Under conditions relevant to the human situation, the well-characterized and production-controlled garlic powder printanor does not display hypolipidemic, anti-inflammatory or anti-atherosclerotic properties.