Lisinopril reduces left ventricular hypertrophy and cardiac polyamine concentrations without a reduction in left ventricular wall stress in transgenic Tsukuba hypertensive mice

Angiotensin-converting-enzyme inhibitor prevents skeletal muscle fibrosis in myocardial infarction mice

BACKGROUND

Transforming growth factor beta (TGF-β)-Smad2/3 is the major signaling pathway of fibrosis, which is characterized by the excessive production and accumulation of extracellular matrix (ECM) components, including collagen. Although the ECM is an essential component of skeletal muscle, fibrosis may be harmful to muscle function. On the other hand, our previous studies have shown that levels of angiotensin II, which acts upstream of TGF-β-Smad2/3 signaling, is increased in mice with myocardial infarction (MI). In this study, we found higher skeletal muscle fibrosis in MI mice compared with control mice, and we investigated the mechanisms involved therein. Moreover, we administered an inhibitor based on the above mechanism and investigated its preventive effects on skeletal muscle fibrosis.

METHODS

Male C57BL/6 J mice with MI were created, and sham-operated mice were used as controls. The time course of skeletal muscle fibrosis post-MI was analyzed by picrosirius-red staining (days 1, 3, 7, and 14). Mice were then divided into 3 groups: sham + vehicle (Sham + Veh), MI + Veh, and MI + lisinopril (an angiotensin-converting enzyme [ACE] inhibitor, 20 mg/kg body weight/day in drinking water; MI + Lis). Lis or Veh was administered from immediately after the surgery to 14 days postsurgery.

RESULTS

Skeletal muscle fibrosis was significantly increased in MI mice compared with sham mice from 3 to 14 days postsurgery. Although mortality was lower in the MI + Lis mice than the MI + Veh mice, there was no difference in cardiac function between the 2 groups at 14 days. Skeletal muscle fibrosis and hydroxyproline (a key marker of collagen content) were significantly increased in MI + Veh mice compared with the Sham + Veh mice. Consistent with these results, protein expression of TGF-β and phosphorylated Smad2/3 in the skeletal muscle during the early time points after surgery (days 1-7 postsurgery) and blood angiotensin II at 14 days postsurgery was increased in MI mice compared with sham mice. These impairments were improved in MI + Lis mice, without any effects on spontaneous physical activity, muscle strength, muscle weight, and blood pressure.

CONCLUSIONS

ACE inhibitor administration prevents increased skeletal muscle fibrosis during the early phase after MI. Our findings indicate a new therapeutic target for ameliorating skeletal muscle abnormalities in heart diseases.

Activation of the renin-angiotensin system in mice aggravates mechanical loading-induced knee osteoarthritis

Epidemiological studies have shown an association between hypertension and knee osteoarthritis (OA). The purpose of this study was to investigate whether activation of the renin–angiotensin system (RAS) can aggravate mechanical loading-induced knee OA in mice. Eight-week-old male Tsukuba hypertensive mice (THM) and C57BL/6 mice were divided into four groups: i) running THM group, ii) running C57BL/6 mice group, iii) non-running THM group, and iv) non-running C57BL/6 mice group. Mice in the running group were forced to run (25 m/min, 30 min/day, 5 days/week) on a treadmill. All mice in the four groups (n=10 in each group) were euthanized after 0, 2, 4, 6, or 8 weeks of running or natural breeding. Cartilage degeneration in the left knees was histologically evaluated using the modified Mankin score. Expression of Col X, MMP-13, angiotensin type 1 receptor (AT1R), and AT2R was examined immunohistochemically. To study the effects of stimulation of the AT1R in chondrocytes by mechanical loading and/or Angiotensin II (AngII) on transduction of intracellular signals, phosphorylation levels of JNK and Src were measured in bovine articular chondrocytes cultured in three-dimensional agarose scaffolds. After 4 weeks, the mean Mankin score for the lateral femoral condylar cartilage was significantly higher in the THM running group than in the C57BL/6 running group and non-running groups. AT1R and AT2R expression was not detected at 0 weeks in any group but was noted after 4 weeks in the THM running group. AT1R expression was also noted at 8 weeks in the C57BL/6 running group. The expression levels of AT1R, COL X, and MMP-13 in chondrocytes were significantly higher in the THM running group than in the control groups. Positive significant correlations were noted between the Mankin score and the rate of AT1R-immunopositive cells, between the rates of AT1R- and Col X-positive cells, and between the rates of AT1Rand AT2R-positive cells. The phosphorylation level of JNK was increased by cyclic compression loading or addition of AngII to the cultured chondrocytes and was reversed by pretreatment with an AT1R blocker. A synergistic effect on JNK phosphorylation was observed between compression loading and AngII addition. Transgene activation of renin and angiotensinogen aggravated mechanical load-induced knee OA in mice. These findings suggest that AT1R expression in chondrocytes is associated with early knee OA and plays a role in the progression of cartilage degeneration. The RAS may be a common molecular mechanism involved in the pathogenesis of hypertension and knee OA.

Decreased ornithine decarboxylase activity in the kidneys of Dahl salt-sensitive rats

To assess the roles of polyamines (putrescine, spermidine, and spermine) and ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine synthesis, in the development of salt-sensitive hypertension, we evaluated activity and expression of ODC, urinary polyamine excretion, and antizyme (endogenous ODC inhibitor protein) expression in Dahl salt-sensitive (SS) and salt-resistant (SR) rats after they were fed on a low (0.3%) or high (4%) salt diet for 4 weeks. We also examined the effects of spermidine and difluoromethylornithine (DFMO: a specific inhibitor of ODC) on the systolic blood pressure and ODC protein expression in SS rats fed a high salt diet. Renal ODC activity and urinary polyamine excretion in SS rats were lower than those in SR rats after 4 weeks treatment with a low or high salt diet. The renal ODC protein expression of SS rats was paradoxically increased as compared to the SR group. A high salt diet did not alter ODC activity but increased ODC protein only in SS rats. ODC mRNA and antizyme protein expressions were not significantly different among the four groups. Spermidine supplementation attenuated and DFMO exaggerated hypertension in SS rats fed a high salt diet. Spermidine down-regulated and DFMO up-regulated renal ODC protein in SS rats on a high salt diet. ODC activity was decreased but protein was paradoxically increased in kidneys of SS rats. ODC protein was suggested to increase in compensation for the inhibition of its activity. Impaired ODC activity and polyamine production in the kidney may exaggerate salt-sensitive hypertension in SS rats.

Perindopril reverses myocyte remodeling in the hypertensive heart

Studies have shown that the renin-angiotensin system (RAS) plays an important role in cardiac remodeling induced by hypertension. However, the role of this system on myocyte remodeling remains unclear. In the present study, we have assessed the effect of perindopril, an angiotensin converting enzyme (ACE) inhibitor, in spontaneously hypertensive rats (SHRs) as a means to evaluate the role of RAS in myocyte remodeling. We also investigated the effect of beta blockade on myocyte remodeling. We used female SHRs at 12 weeks of age. They were divided into four experimental groups: a control group, group C; low dose perindopril group (0.3 mg/kg/day, p.o.), group PL; high dose perindopril group (3 mg/kg/day, p.o.), group PH; and bisoprolol group (60 mg/kg/day, p.o.), group B. We isolated myocytes from these rats after 4 weeks. LV myocyte volume and cross-sectional area decreased in groups PL and PH compared to group C. LV myocyte length decreased in group PH compared to group C. However, there was no morphological change in LV myocytes in group B compared to group C. In summary, ACE inhibitors reversed cardiac hypertrophy mainly by a reduction in LV myocyte volume; however, beta blockade did not reverse myocyte remodeling. These results suggest that RAS plays an important role in myocyte remodeling in the hypertensive heart.

Continuous blockade of L-type Ca2+ channels suppresses activation of calcineurin and development of cardiac hypertrophy in spontaneously hypertensive rats

We examined whether Ca2+ channel blockers inhibit the activation of the Ca2+-dependent phosphatase calcineurin and the development of cardiac hypertrophy in spontaneously hypertensive rats (SHR). We randomly divided 12-week-old SHR into three groups, one each receiving vehicle, bolus injection or continuous infusion of nifedipine (10 mg/kg/day) from 12 to 24 weeks of age. Systolic blood pressure (BP) and heart rate were measured every week after the treatment using the tail-cuff plethysmography method. After 4, 8 and 12 weeks of treatment, 6 rats of each group were subjected to examinations that included an assay for calcineurin activity in the heart, magnetic resonance imaging (MRI), histology and Northern blot analysis. Continuous infusion of nifedipine consistently reduced BP, whereas bolus injection resulted in a fluctuation of BP. Continuous infusion of nifedipine not only reduced left ventricular mass but also decreased the transverse diameter of cardiomyocytes, interstitial fibrosis and the expression of the atrial natriuretic peptide and brain natriuretic peptide genes in the heart, while bolus injection of nifedipine did not significantly attenuate any of these hypertrophic responses in SHR. The activity of calcineurin in the heart was strongly suppressed by continuous but not bolus infusion of nifedipine in SHR. The results indicate that continuous blockade of Ca2+ channels with nifedipine effectively suppresses the development of cardiac hypertrophy in SHR, possibly through inhibition of the calcineurin activity.

Hypertension does not account for the accelerated atherosclerosis and development of aneurysms in male apolipoprotein e/endothelial nitric oxide synthase double knockout mice

BACKGROUND

Apolipoprotein E (apoE)/endothelial nitric oxide synthase (eNOS) double knockout (DKO) mice demonstrate accelerated atherosclerosis and develop abdominal aortic aneurysms and aortic dissection, suggesting a role for eNOS in suppressing atherogenesis. To test whether accelerated atherosclerosis and aortic aneurysms were due to hypertension, we administered hydralazine to male apoE/eNOS DKO mice to reduce blood pressure.

METHODS AND RESULTS

Male apoE/eNOS DKO mice were treated with hydralazine in their drinking water (250 mg/L) using a dose that lowers the blood pressure to levels seen in apoE KO mice. The mice were fed a Western-type diet for 16 weeks, and lesion formation was assessed by inspection of the vessel and staining with Sudan IV. Hydralazine-treated, normotensive male apoE/eNOS DKO mice developed increased aortic lesion areas (30.0+/-2.8%, n=11) compared with male apoE KO mice (14.6+/-0.8%, n=7). The extent of lesion formation was not significantly different from male apoE/eNOS DKO mice that were not given hydralazine (28.3+/-3.1%, n=9). Four of 11 hydralazine-treated male apoE/eNOS DKO mice developed abdominal aortic aneurysms.

CONCLUSIONS

Hypertension is not required for the accelerated atherosclerosis seen in apoE/eNOS DKO animals, and control of hypertension during a 16-week period does not prevent aortic aneurysm formation.