The Effects Of Catheter-based Radiofrequency Renal Sympathetic Denervation On Left Ventricular Hypertrophy And VEGFR1-PKGI-Calcineurin Pathway In Hypertensive Canine

Objective:To investigate the effect of catheter-based radio frequency renal sympathetic denervation (RDN) on left ventricular hypertrophy in hypertensive canine. Secondarily, we hypothesized that VEGF-mediated angiogenesis might be involved in the regression of left ventricular hypertrophy by RDN. Therefore, we observed the change of Vascular Endothelial Growth Factor (VEGF)-Vascular Endothelial Growth Factor Receptor-1(VEGFR-1)-cGMP-dependent Protein Kinase I (PKG-1)-Calcineurin expression following RDN.Materials and Methods:A total number of28Beagles were included in the study. Hypertension model (n=22) was established by feeding the animals with high fat diet for12weeks, whereas the control group (n=6) was fed only with basal canine diet.After hypertension model was established (n=20), animals were randomized into RDN group (n=10) and SHAM group (n=10). RDN group underwent catheter-based radiofrequency renal sympathetic denervation whereas animals in Sham group underwent only the renal angiography.Blood pressure was measured and trans-thoracic echocardiography was performed in all the animals at several time points as follow: baseline, before procedure (12weeks of feeding), and6months after procedure. Echocardiographic parameters, particularly left ventricular mass index (LVMI) and index of diastolic dysfunction, were calculated. At the end of the experiment, all animals were sacrificed. Left ventricular tissue samples were subjected to morphological study and biochemichal assay. Hematoxylin-eosin (HE) staining and electron microscopic (EM) analysis were performed. Myocardial capillary density was calculated using CD31immuno-staining. Vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor-1(VEGFR-1), cGMP-dependent protein kinase type I (PKG-I), and Calcineurin expression were examined.Results:1. During the study, three animals died (RDN n=1, SHAM n=2) and were therefore excluded from the final analysis. At3months time of feeding, compared to baseline and control group, both RDN (n=9) and SHAM group (n=8) gained significant increase of body weight and blood pressure (p<0.05). In addition, left ventricular mass index significantly increased while E/A ratio remarkedly decreased (all p<0.05). Six months after renal denervation, blood pressure, left ventricular mass index decreased whereas E/A ratio increased significantly (all p<0.05).2.The actual left ventricular mass in SHAM group was significantly higher than control group (p<0.05). Compared to SHAM group, left ventricular mass in RDN group was significantly lower (p<0.05).3. Compared to RDN group, HE in SHAM group showed that the myocardial cross-sectional area was significantly larger (p<0.05); EM revealed that the myocardial filaments were not intact, focal lysis were evident, mitochondrias were disorganized and showed obvious edema; CD31immunostaining showed a significant decrease in myocardial capillary density (p<0.05). In contrast, RDN group had a remarkably smaller myocardial cross-sectional area; myocardial filaments and mitochondria showed focal lysis and edema to a lesser extent than of those in sham group; myocardial capillary density was significantly higher than SHAM group. However, myocardial capillary density in RDN group was still remarkably lower than control group (p<0.05).4. Compared to control and RDN group, cardiac VEGF mRNA expression was found lower in Sham group. However, the difference was not statistically significant (P>0.05). Compared to Sham group, VEGFR-1mRNA expression and PKG-1protein as well as mRNA expression were significantly higher in control and RDN group (P<0.05). VEGFR-1mRNA expression between control and RDN group was not statistically significant (p>0.05). PKG-I expression was found even higher in RDN group than in control group (p<0.05). Calcineurin protein expression was significantly higher in sham operated animals than both RDN and control group (p<0.05). Calcineurin protein expression between control and RDN group was not statistically significant (p>0.05).5. Significant positive correlation was found between LVMI and VEGFR-1as well as PKG-1expression, whereas negative correlation was found between LVMI and Calcineurin expression.Conclusion:Beyond its lowering blood pressure effect, RDN significantly improved left ventricular hypertrophy and improved diastolic function in hypertensive canine model. The improvement of VEGFR1-mediated angiogenesis may be involved in the regression of left ventricular hypertrophy following renal denervation through the upregulation of PKG-I which eventually inhibited the calcineurin/NFAT signaling pathway.