Volume 8, Number 2, June 2007

PAPERThe blockade of the renin-angiotensin system reverses tacrolimus related cardiovascular toxicity at the histopathological level
Mehmet Agirbasli, Nurdan Papila-Topal, Betul Ogutmen, Hicran Deniz, Fulya Cakalagaoglu, Serhan Tuglular, Emel Akoglu

Introduction: In this study, we investigate the toxic effects of tacrolimus (FK506) on the cardiovascular system at the histopathological level in a rat model and whether these effects can be reversed by the blockade of the renin-angiotensin system (RAS) by either an angiotensin-converting enzyme inhibitor (ACE-inhibitors) or an angiotensin receptor antagonist (ARB).
Methods and results: Thirty-one Wistar rats were divided into four groups. FK506 group was treated with FK506 intraperitoneally (i.p.), FK506+ACE-inhibitors and FK506+ARB groups were treated with either quinapril or valsartan orally in addition to FK506. Control group was treated with saline i.p. Histological and immunohistochemical staining of cardiovascular tissue in the FK506 group showed increased vacuolar degeneration (11.2 vs. 5.8, p=0.008), arterial hyalinosis (10.7 vs. 6.3, p=0.036), transforming growth factor-beta (TGF-β) (12.2 vs. 4.8, p=0.001) and vascular endothelial growth factor expression (VEGF) (10.7 vs. 6.3, p=0.036), elastic van Gieson (11.5 vs. 5.5, p=0.004), and periodic acid Schiff stain scores (12.5 vs. 4.5, p<0.001) compared to the control group. Immunohistochemical scores showed that expression of TGF-β is up-regulated, and bone morphogenic protein (BMP-7) is down-regulated with FK506 toxicity. Adding RAS blockade with either an ACE-inhibitor or an ARB could reverse FK506 induced changes. Both FK506+ACE-inhibitors and FK506+ARB groups demonstrated decrease in arterial hyalinosis (22.1 vs. 14.4 (FK506+ACE-inhibitor) and 13.6 (FK506+ARB), p=0.09) and vacuolar degeneration (23.1 vs. 16.1 (FK506+ACE-inhibitor) and 12.4 (FK506+ARB), p=0.006) scores compared to the FK506 group.
Conclusion: Blockade of RAS could reverse the histopathological signs of FK506 induced cardiac toxicity in a rat model.

JRAAS 2007;8:54-58.

PAPERCross-talk related to insulin and angiotensin II binding on myocardial remodelling in diabetic rat hearts
Wael M Maharsy, Lina N Kadi, Nahla G Issa, Khalil M Bitar, Asdghig H Der-Boghossian, Roy Abrahamian, Anwar B Bikhazi

This study focused on the regulation and affinity modulation of angiotensin II (Ang II) binding to its receptor subtypes (AT₁- and AT₂-receptor) in the coronary endothelium (CE) and cardiomyocytes (CM) of Sprague-Dawley male rats in normal (N), normal treated with losartan (NL), streptozotocin-induced diabetic (D), insulin-treated diabetic (DI), losartan-treated diabetic (DL), and diabetic co-treated with insulin and losartan (DIL). Heart perfusion was used to estimate Ang II binding affinity (τ=1/k_-n) to its receptor subtypes on CE and CM. Diabetes decreased τ value on CE and increased it on CM as compared to normal. In DL group, the τ value decreased on CE but was normalised on CM. Insulin treatment alone (DI) or with losartan (DIL) restored t to normal on both CE and CM. Western blot results for AT₁-receptor density showed an increase in diabetics compared to normal with no normalising effect with insulin treatment. The AT₁-receptor density was normalised in the diabetic groups treated with losartan +/- insulin. Results for AT₂-receptor regulation revealed a significant difference between untreated (D) and losartan-treated (DL, DIL) diabetic groups. All of these data show the interrelated pathway and cross-talk between insulin and Ang II system indicating potentially negative effects on the diabetic heart.

JRAAS 2007;8:59-65.

POPULAR
TOPICPAPERActivation of protective and damaging components of the cardiac renin-angiotensin system after myocardial infarction in experimental diabetes
Tom Bäcklund, Päivi Lakkisto, Eeva Palojoki, Tina Grönholm, Antti Saraste, Piet Finckenberg, Eero Mervaala, Ilkka Tikkanen, Mika Laine

Introduction:Diabetes is associated with prolonged apoptotic cell death of cardiac myocytes and adverse remodelling after myocardial infarction (MI). Because the renin-angiotensin system (RAS) has a major role in the remodelling, we studied whether diabetes is associated with altered regulation of RAS after MI in rats.
Methods: Male Wistar rats were randomised to receive either streptozotocin (diabetic group) or citrate buffer (control group) intravenously. MI was produced four weeks later by ligating the left descending coronary artery. The rats were sacrificed 1, 4 and 12 weeks after the operation. Angiotensin-converting enzyme (ACE) and angiotensin-converting enzyme 2 (ACE 2), angiotensin type 1 and 2 receptors (AT₁-receptor, AT₂-receptor), and connective tissue growth factor (CTGF) mRNA expression were determined.
Results: The expression of both protective and damaging components of RAS increased after MI. However, myocardial ACE 2 and AT₂-receptor messenger ribonucleic acid (mRNA) expression levels were significantly lower in diabetic compared to non-diabetic rats 1 week after MI. In contrast, AT₁-receptor, ACE and CTGF mRNA levels were up-regulated in diabetic as compared with non-diabetic rats 12 weeks after MI.
Conclusion: The activation of the protective components of RAS (ACE 2 and AT₂-receptor) was blunted early after MI in diabetic rats, whereas the levels of ACE, AT₁-receptor and CTGF mRNA leading to adverse effects on myocardium, were elevated in diabetic as compared with non-diabetic rats. This unbalanced activation of the RAS may influence the pathophysiology of myocardial injury in diabetes after MI.

JRAAS 2007;8:66-73.

PAPERBeneficial versus harmful effects of Angiotensin (1-7) on impulse propagation and cardiac arrhythmias in the failing heart
Walmor C De Mello, Carlos M Ferrario, Jewell A Jessup

Introduction: The presence of Angiotensin (1-7) (Ang 1-7) and ACE 2 in the ventricle of cardiomyopathic hamsters as well as the influence of Ang (1-7) on membrane potential, impulse propagation and cardiac excitability were investigated.
Methods: Histology and immunochemistry were used to demonstrate the presence of Ang (1-7) and ACE 2 in the ventricle of cardiomyopathic hamsters. Measurements of transmembrane potentials, conduction velocity and refractoriness were made using conventional intracellular microelectrodes. The influence of Ang (1-7) on sodium pump current was investigated in voltage-clamped myocytes isolated from the ventricle.
Results: The results indicated the presence of Ang (1-7) and ACE 2 in myocytes of cardiomyopathic hamsters. Moreover, Ang (1-7) (10^-8 M) hyperpolarised the heart cell, increased the conduction velocity, and reduced transiently the action potential duration. The cardiac refractoriness was also increased by the heptapeptide, an effect in part reduced by an inhibitor of mas receptor. These findings indicate that Ang (1-7) has important antiarrhythmic properties. However, the beneficial effects of Ang (1-7) are dose-dependent because at higher concentration (10^-7 M) the heptapeptide elicited an appreciable increase of action potential duration and early-after depolarisations. Since losartan (10^-7 M) did not counteract this effect of the high dose of the heptapeptide, it is possible to conclude that activation of AT₁-receptors is not involved in this effect of Ang (1-7). To investigate the mechanism of the hyperpolarising action of Ang (1-7) the influence of the heptapeptide on the sodium potassium pump current was studied in myocytes isolated from the ventricle of cardiomyopathic hamsters. The peak pump current density was measured under voltage clamp using the whole cell configuration. The results indicated that Ang (1-7) (10^-8 M) enhanced the electrogenic sodium pump, an effect suppressed by ouabain (10^-7 M).
Conclusions: Ang (1-7) has beneficial effects on the failing heart by activating the sodium pump, hyperpolarising the cell membrane and increasing the conduction velocity. These effects as well as the increment of refractoriness indicate that Ang (1-7) has antiarrhythmic properties. At higher concentrations (10^-7 M), however, the heptapeptide induced early-after depolarisations which leads to the conclusion that an optimal generation of Ang (1-7) must be achieved to permit a protective role of Ang (1-7) on cardiac arrhythmias.

JRAAS 2007;8:74-80.

POPULAR
TOPICPAPERLow-dose renin inhibitor and low-dose AT₁-receptor blocker therapy ameliorate target-organ damage in rats harbouring human renin and angiotensinogen genes
Ralf Dechend, Erdenechimeg Shagdarsuren, Petra Gratze, Anette Fiebeler, Bernhard Pilz, Silke Meiners, Wolfgang Derer, David L Feldman, Randy Webb, Dominik N Muller

We studied the effects of extremely low-dose human renin inhibition (aliskiren) with low angiotensin II receptor blockade (losartan) in a novel double-transgenic rat model harbouring both human renin and angiotensinogen genes. We found that low-dose aliskiren and low-dose losartan effectively reduced mortality and target-organ damage with minimal, non-significant, effects on blood pressure (BP). Our data suggest that renin-angiotensin system (RAS) inhibition ameliorates target-organ damage in an Ang II-driven model of hypertension. Direct renin inhibition is equally efficacious in this regard. Our study does not fully answer the question of BP-lowering versus RAS inhibition. This question is important and was at least partially addressed with our low-dose model.

JRAAS 2007;8:81-84.

POPULAR
TOPICPAPERShort- and long-term glycaemic control and the state of the renin system in type 1 diabetes mellitus
Radomir D Stevanovic, Naomi DL Fisher, Cecilia M Lansang, Katherine D Freeman, Norman K Hollenberg

Renin system blockade in diabetes exerts a strong positive influence on complications, especially nephropathy. In hyperglycaemic diabetic subjects, however, blockade of the renin-angiotensin system with angiotensin-converting enzyme inhibitors results in a marked rise in plasma renin. We investigated whether glycaemic fluctuations measured in hours, or those measured in weeks by Haemoglobin A_1C (HbA_1C) , influenced the plasma renin response to captopril. Fifty-four type 1 diabetic subjects were studied in high-salt balance. After an all night fast and in the supine position, baseline serum glucose level was drawn. Iv. glucose and insulin were then administered to keep serum glucose between 100 and 150 mg/dL (target). When target was reached, captopril 25 mg pre os was administered and plasma renin activity (PRA) and finger stick glucose were drawn, then serially every 45 minutes for 225 minutes. Baseline glucose and baseline PRA were drawn hours apart. Peak PRA corresponded to the renin level at peak captopril effect, 90’ after administration. Renin response (RR) = peak PRA – baseline PRA.
Correlation of baseline glucose with baseline PRA was weak (r=0.3, p=0.02), but strong with peak PRA (r=0.65; p=0.002). Drop in glucose had a weak, negative correlation with baseline PRA (r=-0.3, p=0.03) but a much stronger one with peak PRA (r=-0.7, p<0.0001). After adjustment for baseline PRA and baseline glucose, mean RR correlated strongly with mean drop in glucose (r=-0.72; p=0.008). Conversely, HbA1C correlated with none of the measures of renin system activation (r=0.05;p=0.7). In type 1 diabetic subjects, short-term hyperglycaemia, but not long-term glycaemic control, enhanced the RR to captopril.

JRAAS 2007;8:85-92.

POPULAR
TOPICPAPERRenoprotective effects of telmisartan in the 5/6 nephrectomised rats
Ichiro Tsunenari, Tsuyoshi Ohmura, Randolph Seidler, Motohiko Chachin, Toshihiro Hayashi, Ayako Konomi, Takehisa Matsumaru, Toshiyuki Sumida, Naoyuki Hayashi, Yoshiharu Horie

The purpose of this study was to investigate the renoprotective effect of telmisartan on the advanced stages of nephropathy in rats with 5/6 nephrectomy (5/6 Nx). Telmisartan was orally administered for 12 weeks to rats that previously underwent 5/6 Nx or sham operations. After completion of the administration period, the degree of renal injury was examined histopathologically using indices of glomerulosclerosis and lesions of the renal tubule and interstitium. An immunohistochemical staining for transforming growth factor–beta (TGF-β1) was also performed.
The suppression of urinary protein was statistically significant in surviving animals dosed with telmisartan. The enalapril group’s urinary protein was also significantly suppressed for these same parameters in surviving animals. Histopathologically, telmisartan significantly decreased the progression of glomerulosclerosis and the interstitial cell infiltration at all doses tested. As assessed by immunohistochemical staining the TGF-β1 reactivity in the glomerular tissue tended to decrease in the telmisartan group when compared to the vehicle group. Thus, telmisartan ameliorates the progressive nephropathy in the remaining kidney after 5/6 Nx by non-haemodynamic as well as antihypertensive actions of the drug.

JRAAS 2007;8:93-100.

COMMENTARYA brief response to Sealey and Laragh
Norman K Hollenberg

JRAAS 2007;8:53.

RENIN REPORTSpotlight on Renin: Nonproteolytic activation of prorenin by the (pro)renin receptor is blocked by decoy peptide
Fumiaki Suzuki

JRAAS 2007;8:101-103.