A Study Of Genistein's Role In Regulating Angiotensin-converting Enzyme In Rats

Systemic hypertension is a complex pathophysiological state that isprimarily manifested as chronic high blood pressure and is a major riskfactor for stroke, ischemic heart disease, peripheral vascular disease, andprogressive renal damage. It is well established that a hyperactiverenin-angiotensin system (RAS) plays a key role in the development andmaintenance of human primary hypertension and, by some estimates,contributes to at least 10% to 30% of all cases of hypertension. It is notsurprising that tremendous efforts have been directed toward the under-standing of the RAS and its involvement in the control of blood pressure.The interruption of the RAS attenuates high blood pressure and manypathophysiological aspects of hypertension. Also, some genes encodingmembers of the RAS are associated with hypertension. Thus, it is rea-sonable to conclude that the RAS is essential in the normal regulation ofblood pressure and pathophysiology of systemic hypertension.Genistein is a principal isoflavone found in soy phytoestrogen, and ithas structural similarity with 17β-estradiol. It is a naturally occurringplant estrogen with selective estrogen receptor modulator properties. Genistein has received a great deal of attention over the last few yearsbecause of its potentially preventive roles against cardiovascular diseases.It decreases cholesterol concentration, lowers blood pressure and in-creases HDL cholesterol. Genistein inhibits vascular smooth muscle cellproliferation, improves arterial compliance and it has an antioxidant ac-tion. Therefore, dietary phytoestrogen may contribute to a low incidenceof heart disease through these actions.Angiotensin-converting enzyme (ACE) is a carboxyl-terminaldipeptidyl exopeptidase that plays a pivotal role in the RAS. ACE is anecto-enzyme anchored in plasma membrane of endothelial cells control-ling vascular tone and permeability by converting angiotensinⅠ(AngⅠ)into angiotensinⅡ(AngⅡ) and by degrading bradykinin (BK). Angio-tensin-converting enzyme inhibitors (ACEI) have been an increasinglyand impressively successful approach for a wide range of patients withvascular disease.The objective of present study is to investigate the relationship be-tween genistein and ACE in rats.Present study can be divided into two parts, in vitro and in vivo.PartⅠEffects of genistein on ACE activity and ACE expression inrat aortic endothelial cells (RAECs)RAECs were randomly divided and subjected to different treatmentsfor 48 h as follows: (1) control; (2) genistein at four concentrations (10 μM, 50μM, 100μM and 200μM); (3) 17β-estradiol 100μM; (4) capto-pril 1 mM; (5) tamoxifen 100μM; (6) genistein 100μM + tamoxifen 100μM; (7) 17β-estradiol 100μM + tamoxifen 100μM; (8) PD98059 10μM;and (9) genistein 100μM + PD98059 10μM. In relevant groups above (6,7, 9), cells were pretreated with tamoxifen or PD98059 for 60 min beforegenistein or 17β-estradiol treatment. ACE expression was assessed by theimmunofluorescence and the reverse transcriptase-polymerase chain re-action (RT-PCR) assay.Genistein decreased ACE activity on RAECs in a concentra-tion-dependent manner. The effects of genistein on ACE mRNA expres-sion in RAECs were highly consistent with the data in the immunofluo-rescence analysis. Furthermore, our data showed that genistein exertedthe effect on ACE activity and ACE expression by activating the estrogenreceptor and extracellular signal-regulated kinase 1/2 (ERK1/2) pathway.PartⅡEffects of genistein on ACE activity and ACE expression inSprague-Dawley (SD) ratsSD rats were randomly divided into the following groups: (1) control;(2) genistein at four concentrations (2.5 mg/kg/day, 10 mg/kg/day, 25mg/kg/day, and 50 mg/kg/day); (3) 17β-estradiol (0.5 mg/kg/day); (4)captopril (8 mg/kg/day); (5) tamoxifen (5 mg/kg/day); (6) genistein (25mg/kg/day) + tamoxifen (5 mg/kg/day); (7) 17β-estradiol (0.5 mg/kg/day)+ tamoxifen (5 mg/kg/day); (8) PD98059 (4 mg/kg/day); (9) genistein (25 mg/kg/day) + PD98059 (4 mg/kg/day); (10) 17β-estradiol (0.5 mg/kg/day)+ PD98059 (4 mg/kg/day). In relevant groups above, genistein or17β-estradiol was administered 10min after pretreatment with tamoxifenor PD98059. All drugs were administered intravenously via tail vein bybolus. One hour after the administration on day two, blood samples wereobtained from the thoracic aortas for the determination of serum ACE ac-tivity. Meanwhile, thoracic aortas were harvested to analyze tissue ACEactivity and tissue ACE mRNA expression.Administration of genistein induced a dose-related decrease in serumACE activity. Similar dose-related decreases were detected in ACE activ-ity in the aorta and tissue ACE mRNA expression with genistein. Our re-sults also proved that genistein functioned via activation of estrogen re-ceptor and ERK1/2 pathway.In conclusion, results of the present study indicated that genisteindose-dependently decreased ACE levels in rats both in vivo and in vitro.The effect was mediated by the estrogen receptor and subsequent activa-tion of the ERK1/2 pathway. This finding expands our knowledge of themechanisms of genistein and may further support the potential use ofgenistein as a therapeutic agent in cardiovascular events. It may provide apromising approach in women with contraindications to the use of con-ventional estrogen replacement or those wanting a natural alternative aswell.