Effects Of G Protein Inhibitory Polypeptide GCIP On Ventricular Remodeling In Spontaneously Hypertensive Rats And Its Pharmacokinetics

BACKGROUND: A major advance in understanding the pathophysiology of heart failure has been gaining an understanding of the process of left ventricular (LV) remodelling. Hypertension is always accompanied with left ventricular hypertrophy, cardiac fibrosis and artery wall thickening. These structural changes in heart and blood vessels are known as cardiovascular remodeling. Cardiovascular remodeling mainly caused by hypertension is the major pathogeny of cardiovascular diseases, and it also increases morbidity and mortality significantly. Left ventricular hypertrophy and remodling is one of the major forms of cardiovascular remodeling, which consists of cardiac cell proliferation, hypertrophy, interstitial fibrosis and necrosis, and then affects ventricle functions. Left ventricular (LV) remodeling , which is characterized by the alteration of LV size, shape, and function, occurs during several clinical conditions, such as hypertension, chronic heart failure, valvular heart disease, and myocardial infarction, etc. Therefore, the aim of treatment hypertension is not only to control the blood pressure effectively, but also to prevent the cardiovascular remodeling, and then to protect target organ.Various factors, including stretch stimulation, AngII, NE, neuropeptide Y and endothelin (ET)-1, among others, can induce ventricular hypertrophy and remodelling through their respective receptor and G-protein signalling pathways. The G-protein is located at the convergent point in the signal transduction pathway that leads to cardiovascular remodelling. It has been shown that the Gα-protein carboxyl terminus imitation polypeptide (GCIP), cloned and expressed in our laboratory, can inhibit cardiomyocyte hypertrophy induced by NE in vitro. GCIP-27, the optimised form of GCIP, has been shown to effectively prevent cardiac hypertrophy in vitro and in vivo.AIM: This study was to explore the effects of G protein inhibitory polypeptide GCIP-27 on the left ventricular remodeling and blood pressure in spontaneous hypertensive rats (SHR), the potential underlying mechanisms and its pharmacokinetics. METHODS:1. In the present study,10, 30 or 90μg/kg, i.p., GCIP-27 was administered for 8 weeks to SHR. In addition, another two groups of SHR were treated with either 6 mg/kg losartan or vehicle (saline). Wistar-Kyoto rats were used as controls. Systolic blood pressure (SBP) was measured using the standard tail-cuff method once every 2 weeks. At the end of the experiment, the LV mass index (LVMI) was evaluated. In addition, LV structure and function, collagen content, microstructure and ultrastructure were examined using echocardiography, the hydroxyproline assay, routine light microscopy and transmission electron microscopy, respectively.2. The expression of ANP, BNP,α-MHC,β-MHC were measured with RT-PCR method. The phosphslipase C activity was determined with radioimmunoassay technique. 3. The pharmacokinetics of GCIP-27 were measured by isotope labeling tracer method.RESULTS:1. In the losartan- and GCIP-27 (10, 30 and 90μg.kg-1)-treated groups, SBP decreased significantly compared with that of the vehicle group. However, even at the highest concentration used, the hypotensive effect of GCIP-27 was weaker than that of losartan.2. GCIP-27 (10, 30 and 90μg.kg-1) significantly reduced LV posterior wall thickness(PWT), the thickness of the interventricular septum(IVST), LVMI, collagen content, collagen areas(CA), and collagen volume fractin(CVF) compared with vehicle group(p<0.01), and Losartan (6 mg.kg-1) also obviously reduced PWT, IVST, collagen content, CA and CVF(p<0.05),and reduced LVMI(p>0.05). And the effects of GCIP-27 at all three concentrations tested being greater than that of losartan.3. GCIP-27 was more obvious in improving myocardial ultrastructure and pathology such as inflammation, hypertrophy, fibrosis, degeneration and necrosis, simultaneously. And the effects of GCIP-27 was superior to Losartan.4. Both GCIP-27 (10, 30 and 90μg.kg-1) and Losartan (6mg.kg-1) significantly inhibited Phospholipase C activity(p<0.01), and ANPmRNA, BNPmRNA,β-MHCmRNA levels expression in SHR(p<0.01), and increasedα-MHCmRNA levels, respectively.5. The plasma concentration-time curves of GCIP-27 in mice conformed to three-compartment open model with first order kinetics pattern.After intravenous injection of 125I GCIP-27 at a dose of 90μg.kg-1, t1/2α, t1/2β, t1/2γdetermined by trichloroacetic acid (TCA) method were 0.009h, 0.245h and 2.054h, respectively, and by SDS-PAGE method were 0.025h, 0.306h and 2.323h, respectively. The time to peak ( Tmax) for both methods was 0.0333h, with mean plasma clearance (CL) of 0.295 L·h -1·kg-1 and 0.322 L·h -1·kg-1, apparent volume of distribution ( Vd) of 0.559 L·kg-1 and 1.29L·kg-1 and mean residence time( MRT) of 2.353 h and 2.515h in mice.6. GCIP-27 was shown to be widely distributed to the various tissues. There was a relatively higher in heart, blood vessel, kidney, stomach, lung, mall intestine,etc, and relatively lower in fat and muscle, and the lowest in brain.7. GCIP-27 excreted in urine, feces and bile within 72h was 26.13% , 0.95% and 4.12% in rats, and urine, feces within 72h was 27.92%, 0.84% in mice respectively.The parent compound of GCIP-27 was mainly excreted by urine. And kidney is main emunctory organ.CONCLUSION:1. GCIP-27 could effectively attenuate left ventricular remodelling and decreases the SBP in SHR, and the effect was dose-dependent.2. GCIP-27 treatment of SHR is superior to treatment with losartan in terms of suppressing the development of LV remodelling, although the hypotensive effect of GCIP-27 is weaker than that of losartan. Therefore, the anti-remodelling effect of GCIP-27 in SHR is not entirely dependent on reductions in BP.3. The potential underlying mechanisms of GCIP-27 is the inhibition of G protein, it could inhibite the decrease of phospholipase C activity and ANPmRNA, BNPmRNA,β-MHC mRNA expression, and increaseα-MHCmRNA levels in SHR, respectively.4. The Plasma concentration-time curves of GCIP-27 in mice conformed to three-compartment open model of first order kinetics.5. GCIP-27 was shown to be widely distributed to the various tissues. There was a relatively higher in heart, blood vessel, kidney, stomach, lung, mall intestine, etc. The parent compound of GCIP-27 was mainly excreted by urine, and, kidney is major emunctory organ.