S-1-propenylcysteine improves TNF-α-induced vascular endothelial barrier dysfunction by suppressing the GEF-H1/RhoA/Rac pathway

Background

Vascular endothelial barrier function is maintained by cell-to-cell junctional proteins and contributes to vascular homeostasis. Various risk factors such as inflammation disrupt barrier function through down-regulation of these proteins and promote vascular diseases such as atherosclerosis. Previous studies have demonstrated that aged garlic extract (AGE) and its sulfur-containing constituents exert the protective effects against several vascular diseases such as atherosclerosis. In this study, we examined whether AGE and its sulfur-containing constituents improve the endothelial barrier dysfunction elicited by a pro-inflammatory cytokine, Tumor-necrosis factor-α (TNF-α), and explored their mode of action on TNF-α signaling pathway.

Methods

Human umbilical vein endothelial cells (HUVECs) were treated with test substances in the presence of TNF-α for various time periods. The endothelial permeability was measured by using a transwell permeability assay. The localization of cell-to-cell junctional proteins and actin cytoskeletons were visualized by immunostaining. RhoA and Rac activities were assessed by using GTP-binding protein pulldown assay. Gene and protein expression levels of signaling molecules were analyzed by real-time PCR and western blotting, respectively.

Results

We found that AGE and its major sulfur-containing constituent, S-1-propenylcysteine (S1PC), reduced hyperpermeability elicited by TNF-α in HUVECs. In addition, S1PC inhibited TNF-α-induced production of myosin light chain (MLC) kinase and inactivation of MLC phosphatase through the suppression of the Rac and RhoA signaling pathways, respectively, which resulted in the dephosphorylation of MLC2, a key factor of actin remodeling. Moreover, S1PC inhibited the phosphorylation and activation of guanine nucleotide exchange factor-H1 (GEF-H1), a common upstream key molecule and activator of Rac and RhoA. These effects of S1PC were accompanied by its ability to prevent the disruption of junctional proteins on the cell–cell contact regions and the increase of actin stress fibers induced by TNF-α.

Conclusions

The present study suggested that AGE and its major constituent, S1PC, improve endothelial barrier disruption through the protection of junctional proteins on plasma membrane.

-1-Propenylcysteine, a sulfur compound in aged garlic extract, alleviates cold-induced reduction in peripheral blood flow in rat via activation of the AMPK/eNOS/NO pathway

Aged garlic extract (AGE) has been shown to improve peripheral circulatory disturbances in both clinical trials and experimental animal models. To investigate the effect of S-1-propenylcysteine (S1PC), a characteristic sulfur compound in AGE, on cold-induced reduction in tail blood flow of rat, Wistar rats were individually placed in a restraint cage and given the treatment with cold water (15˚C) after the oral administration of AGE or its constituents S1PC, S-allylcysteine (SAC) and S-allylmercaptocysteine (SAMC). After the cold-treatment the tail blood flow of rats was measured at the indicated times. The pretreatment with AGE (2 g/kg BW) and S1PC (6.5 mg/kg BW) significantly alleviated the reduction of rat tail blood flow induced by cold treatment. The effect of S1PC was dose-dependent and maximal at the dose of 6.5 mg/kg BW, whereas SAC and SAMC were ineffective. To gain insight into the mechanism of S1PC action, the concentration of nitrogen oxide metabolites (NOx) in the plasma and the levels of phosphorylated endothelial nitric oxide synthase (eNOS) and 5'-AMP-activated protein kinase (AMPK) in the aorta were measured. The pretreatment with S1PC significantly increased the plasma concentration of NOx as well as the level of phosphorylated form of AMPK and eNOS in the aorta after cold-treatment. The present findings suggest that S1PC is a major constituent responsible for the effect of AGE to alleviate the cold-induced reduction of peripheral blood flow in rat by acting on the AMPK/eNOS/NO pathway in the aorta.

Antimicrobial properties of hydrophobic compounds in garlic: Allicin, vinyldithiin, ajoene and diallyl polysulfides

Allium plants, such as garlic, onion and leek have long been known to be effective in the therapy of infectious diseases. In particular, garlic has a greater antimicrobial activity than other Allium plants as it contains several hydrophobic antimicrobial compounds, such as allicin, vinyldithiins, ajoenes and diallyl polysulfides. Allicin is a characteristic sulfur-containing compound found in raw garlic produced from alliin and exhibits antimicrobial activity against both Gram-positive and Gram-negative bacteria. In addition, allicin has been reported to inhibit the biofilm formation of bacteria, which is a major cause of bacterial resistance to the antibiotic treatment of infections, by regulating quorum sensing in microorganisms. Other hydrophobic compounds also have similar inhibitory effects on bacteria as allicin. These biological properties of garlic-derived hydrophobic compounds can be used to enhance the effects of existing drugs and may thus be used in the treatment of infections, such as by preventing drug resistance through the inhibition of biofilm formation. In this review, we summarize the effects of hydrophobic compounds of garlic on bacteria.

Mechanisms underlying the attenuation of chronic inflammatory diseases by aged garlic extract: Involvement of the activation of AMP-activated protein kinase

AMP-activated protein kinase (AMPK) is an ubiquitously expressed serine/threonine kinase and an important regulator of energy metabolism. The decreased activity of AMPK induced by low-grade chronic inflammation has been implicated in several diseases, including type 2 diabetes and atherosclerosis. However, the activation of AMPK by natural and synthetic products can ameliorate these diseases through the inhibition of inflammation. For example, aged garlic extract (AGE) has been shown to enhance the phosphorylation of Thr172 of the α-subunit of AMPK in several tissues of disease model animals. In addition, AGE has been reported to suppress the progression of atherosclerotic plaque formation in an animal model of atherosclerosis. Moreover, AGE has been found to decrease the level of plasma glycated albumin and to improve hyperglycemia in an animal model of type 2 diabetes. These inhibitory effects of AGE are induced by the suppression of the inflammatory response. In the present review, we discuss the mechanisms through which AGE activates AMPK, as well as the mechanisms through which the activation of AMPK by AGE modulates the inflammatory response in disease models.

Effects of S-1-propenylcysteine, a sulfur compound in aged garlic extract, on blood pressure and peripheral circulation in spontaneously hypertensive rats

OBJECTIVES

This study was designed to investigate the antihypertensive effect of S-1-propenylcysteine, a characteristic sulfur compound in aged garlic extract, using a hypertensive rat model.

METHODS

The blood pressure and tail blood flow of both spontaneously hypertensive rats and control Wistar Kyoto rats were measured by the tail-cuff method and the noncontact laser Doppler method, respectively, at various times after single oral administration of a test compound for 24 h.

KEY FINDINGS

Treatment with S-1-propenylcysteine (6.5 mg/kg BW) significantly decreased the systolic blood pressure of spontaneously hypertensive rat approximately 10% at 3 h after administration, and thereafter, the systolic blood pressure gradually returned to the baseline level in 24 h. The effect of S-1-propenylcysteine was dose-dependent and was maximal at the dose of 6.5 mg/kg BW at 3 h. However, the other compounds such as S-allylcysteine and S-allylmercaptocysteine in aged garlic extract were ineffective. In addition, S-1-propenylcysteine had no effect on systolic blood pressure of control Wistar Kyoto rats. Furthermore, S-1-propenylcysteine significantly increased the blood flow at 3 h after administration at the dose of 6.5 mg/kg BW.

CONCLUSIONS

S-1-propenylcysteine is a key constituent of aged garlic extract responsible for its antihypertensive effect, and the effect of S-1-propenylcysteine involves the improvement in peripheral circulation.