The Possible Mechanisms Responsible For The Protective Effect Of Insulin Like Growth Factor-1(IGF-1) On Vascular Endothelium

The increased level of angiotensinâ…¡(Angâ…¡) is an important riskfactor in endothelial injury, which has been considered to play a key rolein the initiation and development of atherosclerosis. Recently, it has beendemonstrated that insulin like growth factor-1(IGF-1) possesses variouskinds of metabolism and vascular protection. IGF-1 induces endothelium-dependent vasodilation via activation of NOS and increase in NOproduction. IGF-1 possesses antioxidant, anti-inflammatory andanti-platelet actions and prevented blood lipid metabolism fromimbalance. it has been demonstrated IGF-1 is a protective factor tocardiovascular system. Deficiency of IGF-1 was related with earlyatherosclerosis and increasing morbidity of cardiovascular diseases. LowIGF-1 was a independent risk factor of cardiovascular diseases.Tongxinluo capsule possessed vasodilation, activation of fibrinolysis,anti-platelet, antioxidant, anti- inflammatory actions and beneficialeffects on endothelial function. In the present study, we examined thebenefical effects of IGF-1 on endothelium and its action mechanisms inpatients with hypercholesterolemia and in cultured human umbilical veinendothelial cells(HUVECs). We also investigated the new mechanism oftongxinluo in protecting endothelium.This examination included three steps. 40 patients withhypercholesterolemia and 35 healthy controls were recruited to observeendothelium -dependent vasodilation, serum concentrations of IGF-1,Angâ…¡, NO, soluble E-selectin and plasma concentration of Tissue Factor(TF). Pearson relations between Angâ…¡and IGF-1, NO and IGF-1, NOand Angâ…¡were examined in 40 patients with hypercholesterolemia. Forthe studies on the effect of tongxinluo, the 40 cases were divided into twogroups by random, double-blind ways. The tongxinluo group had 20 casesand the patients accepted tongxinluo (4capsule once, 3 times/d)for8weeks at the base of diet control. The placebo group had 20 cases and thepatients accepted placebo for 8weeks at the base of diet control.In the next step, endothelial injury was induced by incubation withAngâ…¡(1μM) for 24 h in cultured HUVECs, and cell viability, cell cycle, cell apoptosis, Angiotensinâ…¡type 1 receptor mRNA(AT1-RmRNA), CyclinE, the content of TF, the activity of NOS, and the levels ofNO and soluble E-selectin in the conditioned medium weremeasured. For the studies on the effect of IGF-1, cells were treatedwith IGF-1 with/without L-NAME(100μM) for 30 minutes, and thenexposed to Angâ…¡. In the third step, endothelial injury was induced byincubation with Angâ…¡(1μM) for 24 h in cultured HUVECs, and cellviability, cell cycle, cell apoptosis, Angiotensinâ…¡type 1 receptormRNA(AT1-RmRNA), the content of TF, the activity of NOS, and thelevels of NO and soluble E-selectin in the conditioned medium weremeasured. For the studies on the effect of tongxinluo, cells weretreated with tongxinluo drug containing plasma with /without IGF-1receptor mono-colony antibodyα-IR3 for 30 minutes, and thenexposed to Angâ…¡. Compared with healthy control, serum concentrationsof IGF-1 and NO were markedly decreased, serum concentrations of Angâ…¡, soluble E-selectin and plasma concentration of TF wereincreased, and flow-mediated vasodilation was impaired in patients withhypercholesterolemia. Angâ…¡was obviously negatively related withIGF-1, NO was obviously positively related with IGF-1, and NO wasobviously negatively related with Angâ…¡in patients withhypercholesterolemia. After 8-week treatment with tongxinluocapsule, the decreased concentrations of IGF-1 and NO and the increasedconcentrations of Angâ…¡, soluble E-selectin and TF were significantlyattenuated and flow-mediated vasodilation was significantly improved.Incubation of endothelial cells with Angâ…¡(1μM) for 24h markedlyinduced a cell cycle arrest of HUVECs at G₀/G₁ phase and cell apoptosis,a decrease in cell viability and in the activity of NOS and content ofNO, an upregulation of AT₁-R mRNA, a downregulation of Cyclin E, aincrease in the content of TF antigen and soluble E-selectin. Pretreatmentwith IGF-1 significantly inhibited cell cycle arrest of HUVECs at G₀/G₁phase, cell apoptosis, upregulation of AT₁-R mRNA and alsoinhibited the increased content of TF and soluble E-selectin,attenuated downregulation of Cyclin E, the decreased activity of NOS andthe content of NO and the decreased cell viability. However, the benefical effects of IGF-1 on cultured endothelial cells were obviously abolishedby L-NAME, a specific NOS inhibitor. Incubation of endothelial cellswith Angâ…¡(1μM) for 24h markedly induced a cell cycle arrest ofHUVECs at G₀/G₁ phase and cell apoptosis, a decrease in cell viabilityand in the activity of NOS and content of NO, an upregulation of AT₁-RmRNA, a increase in the content of TF antigen and solubleE-selectin. Pretreatment with tongxinluo drug containing plasmasignificantly inhibited cell cycle arrest of HUVECs at G₀/G₁ phase, cellapoptosis, upregulation of AT₁-R mRNA and also inhibited theincreased content of TF and soluble E-selectin, attenuated thedecreased activity of NOS and the content of NO and the decreased cellviability. However, the benefical effects of tongxinluo drug containingplasma on cultured endothelial cells were obviously abolished by IGF-1receptor mono-colony antibodyα-IR3.Conclusion: The present findings suggest that: Endothelialdysfunction may be related with the decreased level of IGF-1 in patientswith hypercholesterolemia. The benefical effects of tongxinluo onendothelium may be related to elevation of IGF-1. Incubation with Angâ…¡induced a significant endothelial injury, concomitantly with a markeddecrease in the activity of NOS, the content of NO, and a significantupregulation of AT₁-R mRNA. Pretreatment with IGF-1 inhibited Angâ…¡-induced endothelial injury by increasing NOS activity and NOcontent, and downregulation of AT₁-R, and the protective effects of IGF-1on endothelial cells may be related to activation NOS-NO signalingwhich inhibited AT₁-R. Pretreatment with tongxinluo drug containingplasma inhibited Angâ…¡-induced endothelial injury by increasing NOSactivity, NO content, and downregnlation of AT₁-R, and the protectiveeffects of tongxinluo on endothelial cells may be related to activationIGF-1R-NOS-NO signaling.