Decreased arterial responses in WHHL rabbits, an animal model of spontaneous hypercholesterolemia and atherosclerosis

RhoA and Rac1 changes in the atherosclerotic lesions of WHHLMI rabbits

AIM

The activation of RhoA and Rac1 is crucial for the pathogenesis of atherosclerosis. This study investigated the changes of unprocessed and mature forms of RhoA and Rac1 in the progression of atherosclerosis.

METHODS

Unprocessed and geranylgeranylated forms of RhoA and Rac1 in aortic atherosclerotic lesions were separated by the Triton X-114 partition method using Watanabe heritable hyperlipidemic (WHHLMI) rabbits prone to myocardial infarction. The activation of RhoA and Rac1 was determined by membrane translocation and pull-down assays.

RESULTS

The levels of unprocessed RhoA and Rac1 of the aortas were higher at 7 months than 3 months, accompanied by increased levels of total RhoA and Rac1. Membrane-bound RhoA and Rac1 levels of the aortas at 7 months were significantly increased compared with those at 3 months, consistent with the results of GTP-loading. Unprocessed and activated forms of RhoA and Rac1 had gradually decreas at 15 and 24 months compared to 7 months.

CONCLUSIONS

We show evidence of marked increases in unprocessed RhoA and Rac1 with enhanced activities in the progression of atherosclerosis in WHHLMI rabbits. This is important for better understanding of the pathogenesis of hyperlipidemia-dependent atherosclerosis.

Diabetes impairs the vascular recruitment of normal stem cells by oxidant damage, reversed by increases in pAMPK, heme oxygenase-1, and adiponectin

BACKGROUND

Atherosclerosis progression is accelerated in diabetes mellitus (DM) by either direct endothelial damage or reduced availability and function of endothelial progenitor cells (EPCs). Both alterations are related to increased oxidant damage.

AIM

We examined if DM specifically impairs vascular signaling, thereby reducing the recruitment of normal EPCs, and if increases in antioxidant levels by induction of heme oxygenase-1 (HO-1) can reverse this condition.

METHODS

Control and diabetic rats were treated with the HO-1 inducer cobalt protoporphyrin (CoPP) once a week for 3 weeks. Eight weeks after the development of diabetes, EPCs harvested from the aorta of syngenic inbred normal rats and labeled with technetium-99m-exametazime were infused via the femoral vein to estimate their blood clearance and aortic recruitment. Circulating endothelial cells (CECs) and the aortic expression of thrombomodulin (TM), CD31, and endothelial nitric oxide synthase (eNOS) were used to measure endothelial damage.

RESULTS

DM reduced blood clearance and aortic recruitment of EPCs. Both parameters were returned to control levels by CoPP treatment without affecting EPC kinetics in normal animals. These abnormalities of EPCs in DM were paralleled by reduced serum adiponectin levels, increased numbers of CECs, reduced endothelial expression of phosphorylated eNOS, and reduced levels of TM, CD31, and phosphorylated AMP-activated protein kinase (pAMPK). CoPP treatment restored all of these parameters to normal levels.

CONCLUSION

Type II DM and its related oxidant damage hamper the interaction between the vascular wall and normal EPCs by mechanisms that are, at least partially, reversed by the induction of HO-1 gene expression, adiponectin, and pAMPK levels.

Mild hypertension in young Kurosawa and Kusanagi-hypercholesterolaemic (KHC) rabbits

The coexistence of hypertension and hypercholesterolaemia from youth may increase the prevalence of and mortality from cardiovascular disease and stroke. We thus investigated haemodynamics of mild hypertension in young Kurosawa and Kusanagi-hypercholesterolaemic (KHC) rabbits aged 10-12 months old, as models of heritable hypercholesterolaemia. Pressure and flow waves were simultaneously recorded at the ascending aorta with a catheter-tip micromanometer and ultrasonic flow meter under pentobarbital anaesthesia, respectively. Systolic (119.3 +/- 6.5 and 138.4 +/- 7.4 mmHg (mean +/- SD) for control and KHC rabbit groups; p < 0.001), diastolic (95.7 +/- 6.1 and 109.8 +/- 5.2; p < 0.001), mean (105.8 +/- 6.5 and 122.5 +/- 4.9; p < 0.001) and pulse (23.7 +/- 2.5 and 28.6 +/- 4.0; p < 0.001) pressures as well as total peripheral vascular resistance (0.32 +/- 0.02 and 0.37 +/- 0.03 mmHg/ml/min; p < 0.001) were significantly greater in the KHC rabbit group than those in the age-matched control rabbit group, respectively, while there were no significant differences in the mean aortic flow, heart rate or stroke volume between the two rabbit groups. Aortic input impedance (p < 0.05) and reflection coefficient (p < 0.05) were significantly greater at lower frequency in the KHC rabbit group than in the control rabbit group, whereas there was no significant difference in the characteristic impedance between the two rabbit groups. Plasma angiotensin I (p < 0.01) and II (p < 0.01) levels and serum angiotensin converting enzyme activity (p < 0.05) were significantly greater in the KHC rabbit group than in the age-matched control rabbit group. Atheromatous plaque was in the early stage and composed mainly of abundant foam cells. Neither sclerotic lesions nor stenosis were observed in main peripheral arteries. The mild hypertension in young KHC rabbits was due partly to the increased activity of the renin-angiotensin system. These findings may be thought provoking in elucidating the mechanism and developing preventive and therapeutic strategies in young patients with coexistent hypertension and hypercholesterolaemia.

PROGRESSION OF SEVERE ATHEROSCLEROSIS AND INCREASED ARTERIAL PULSE PRESSURE IN THE NEWLY DEVELOPED HERITABLE MIXED HYPERLIPIDAEMIC RABBITS

We have recently segregated a new line of rabbit, named TGH, with severely high levels of plasma triglyceride and cholesterol. The aim of the present study was to investigate the progression of atherosclerosis and haemodynamic parameters in TGH rabbits. 2. Japanese white (JW) and TGH rabbits (24-27 months old) were anaesthetized with ketamine and xylazine. Plasma concentrations of triglyceride were 63.1 8.0 and 446.0 35.2 mg/dL in JW and TGH rabbits, respectively. Blood pressure was measured by a catheter implanted in the femoral artery. Histological examinations were performed using haematoxylin-eosin and elastica-Masson trichrome staining to detect atherosclerotic lesions. 3. The JW rabbits had no atherosclerotic lesions. In TGH rabbits, severe atherosclerotic lesions were observed throughout the aorta, especially in the aortic arch. Basal femoral arterial pressure was not significantly different between JW and TGH rabbits. However, the basal pulse pressure in TGH rabbits (48.3 4.5 mmHg) was significantly greater than that of JW rabbits (28.0 5.6 mmHg). Intravenous infusion of N(G)-nitro-L-arginine methyl ester (L-NAME; 26.9 mg/kg) increased the blood pressure of TGH and JW rabbits. There was no significant difference in the response to L-NAME between the two rabbit strains. 4. The present study shows that severe atherosclerotic changes develop in TGH rabbits and suggests that the hyperlipidaemia combined with hypercholesterolaemia and hypertriglyceridaemia is an important factor for promoting atherosclerosis in TGH rabbits. The greater pulse pressure in TGH rabbits may be due to the increased vascular stiffness with atherosclerosis. 5. This newly developed TGH rabbit line of heritable hypertriglyceridaemia with hypercholesterolaemia will become a useful animal model for studies on the role of hyperlipidaemia in the progression of atherosclerosis and in many atherosclerosis-related diseases.