Effects of Aliskiren on Stroke in Rats Expressing Human Renin and Angiotensinogen Genes

OBJECTIVE: Pre-treatment with angiotensin receptor blockers is known to improve neurological outcome after stroke. This study investigated for the first time, whether the renin inhibitor aliskiren has similar neuroprotective effects. METHODS: Since aliskiren specifically blocks human renin, double transgenic rats expressing human renin and angiotensinogen genes were used. To achieve a systolic blood pressure of 150 or 130 mmHg animals were treated with aliskiren (7.5 or 12.5 mg/kg*d) or candesartan (1.5 or 10 mg/kg*d) via osmotic minipump starting five days before middle cerebral artery occlusion with reperfusion. Infarct size was determined by magnetic resonance imaging. mRNA of inflammatory marker genes was studied in different brain regions. RESULTS: The mortality of 33.3% (7 of 21 animals) in the vehicle group was reduced to below 10% by treatment with candesartan or aliskiren (p<0.05). Aliskiren-treated animals had a better neurological outcome 7 days post-ischemia, compared to candesartan (Garcia scale: 9.9±0.7 vs. 7.3±0.7; p<0.05). The reduction of infarct size in the aliskiren group did not reach statistical significance compared to candesartan and vehicle (24 h post-ischemia: 314±81 vs. 377±70 and 403±70 mm(3) respectively). Only aliskiren was able to significantly reduce stroke-induced gene expression of CXC chemokine ligand 1, interleukin-6 and tumor necrosis factor-alpha in the ischemic core. CONCLUSIONS: Head-to-head comparison suggests that treatment with aliskiren before and during cerebral ischemia is at least as effective as candesartan in double transgenic rats. The improved neurological outcome in the aliskiren group was blood pressure independent. Whether this effect is due to primary anti-inflammatory mechanisms has to be investigated further

Prevention and Intervention Studies with Telmisartan, Ramipril and Their Combination in Different Rat Stroke Models

The effects of AT1 receptor blocker, telmisartan, and the ACE inhibitor, ramipril, were tested head-to head and in combination on stroke prevention in hypertensive rats and on potential neuroprotection in acute cerebral ischemia in normotensive rats. Normotensive Wistar rats were treated s.c. 5 days prior to middle cerebral artery occlusion (MCAO) for 90 min with reperfusion. Groups (n = 10 each): (1) sham, (2) vehicle (V; 0,9% NaCl), (3) T (0,5 mg/kg once daily), (4) R (0,01 mg/kg twice daily), (5) R (0,1 mg/kg twice daily) or (6) T (0,5 mg/kg once daily) plus R (0,01 mg/kg twice daily). Twenty-four and 48 h after MCAO, neurological outcome (NO) was determined. Forty-eight h after MCAO, infarct volume by MRI, neuronal survival, inflammation factors and neurotrophin receptor (TrkB) were analysed.Stroke incidence was reduced, survival was prolonged and neurological outcome was improved in all treated SHR-SP with no differences between treated groups. In the acute intervention study, T and T+R, but not R alone, improved NO, reduced infarct volume, inflammation (TNFα), and induced TrkB receptor and neuronal survival in comparison to V.T, R or T+R had similar beneficial effects on stroke incidence and NO in hypertensive rats, confirming BP reduction as determinant factor in stroke prevention. In contrast, T and T+R provided superior neuroprotection in comparison to R alone in normotensive rats with induced cerebral ischemia

Renal Outcome in Equipotent Antihypertensive Treatment with Telmisartan, Ramipril and in Combination in SHR-SP Rats

Background: The ONTARGET trial revealed an association of ACEI/ARB combination treatment (telmisartan and ramipril) with adverse renal outcome versus respective monotherapy; preclinical evidence regarding renal outcome in ACEI/ARB combination treatment is scarce.Methods: Spontaneously hypertensive stroke prone rats (SHR-SP) rats on a salt-rich diet were randomly allocated to 4 groups: SHR (untreated, n = 24), SHR + telmisartan (SHR-T, 2.39 +/- 0.69 mg/kg bw; n = 27), SHR + ramipril (SHR-R, 6.28 +/- 3.48 mg/kg bw; n = 27) and combination treatment (SHR-TR, 0.51 +/- 0.14 mg/kg bw; same dose for telmisartan and ramipril; n = 26). Study duration was 12 weeks, blood pressure was assessed weekly and doses were adjusted to maintain equal blood pressure. Finally, blood and urine samples were obtained and kidneys were harvested for histological studies.Results: Blood pressure in untreated rats rose to a maximum of 239 mmHg, whereas in all treatment groups it remained stable betvveen 140 and 150 mmHg. Mortality was 50% in the untreated group, whereas all treatment groups survived completely. Renal function - as indicated by plasma urea and cystatin c - was significantly worse in SHR-TR animals compared to all other groups. With plasma creatinine a similar trend was observed. All treatment options significantly decreased albuminuria. Renal glomerulosclerosis was decreased by monotherapy, whereas combination therapy failed to have a significant effect. Interstitial fibrosis was decreased to a similar extent by all treatment options.Conclusions: ACEI/ARB combination treatment failed to render significant additional benefits on renal outcome in hypertensive rats when compared to monotherapy. Instead our data indicate that dual RAAS blockade might have an adverse effect on kidney function and histology when compared to monotherapy in salt-loaded SHR-SP. (Clin. Lab. 2012;58:625-633. DOI: 10.7754/Clin.Lab.2011.110622

Moderate Correlations of in vitro versus in vivo Pharmacokinetics Questioning the Need of Early Microsomal Stability Testing

Putative in vitro-in vivo correlations of pharmacokinetic (PK) parameters are regarded as a prerequisite to filter hits derived from high-throughput screening (HTS) approaches for subsequent murine in vivo PK studies.In this study, we assessed stabilities in rat and human microsomes of 121 compounds from an early, academic drug discovery programme targeting the (pro)renin receptor and correlated the respective data with single-dose, in vivo PK parameters of 22 hits administered intravenously in rats.After transformation of in vitro half-lives to predicted in vivo hepatic clearances, r(2) regarding in vitro-in vivo clearance correlations were 0.31 and 0.27 for the rat and human species, respectively.Our data concerning structurally diverse real-world compounds indicate that microsomal stability testing is not a tool to triage early compounds for in vivo PK testing

Mortality of double transgenic rats after middle cerebral artery occlusion with reperfusion.

<p>Groups according to treatment (Veh, vehicle, Cand, candesartan, Alis, aliskiren), systolic blood pressure and duration of follow-up. There was no mortality in the groups with sham intervention. Absolute numbers are given at the bottom of the columns. Mortality rates were compared by log-rank test. *p<0.05 vs. treated animals.</p

Systolic blood pressure (SBP), body weight, brain weight and neurological score of double transgenic rats before and after middle cerebral artery occlusion with reperfusion or sham intervention; protocol 1 with blood pressure target of 150 mmHg and 24 h of follow-up.

<p>Data are means ± standard error of the mean.</p><p>The Mann-Whitney-U test was used for comparisons.</p><p>*p<0.05, **p<0.01, ***p<0.001, vs. same group before intervention.</p>#<p>p<0.05, ^##p<0.01, ^###p<0.001, vs. respective vehicle group.</p

Representative T2-weighted, axial magnetic resonance image 24 h after middle cerebral artery occlusion with reperfusion.

<p>The hyperintensity corresponds to the ischemic area. Tissue was obtained from the ischemic core (black circles), the border of the ischemic lesion (black squares) and areas corresponding to the ischemic core (white circles) and its border (white squares) in the contralateral, non-ischemic hemisphere.</p

Relative expression of inflammatory genes in brain tissue of double transgenic rats 24 h after middle cerebral artery occlusion with reperfusion.

<p>Tissue was obtained from the ischemic core, the border of the ischemic lesion and corresponding areas in the contralateral, non-ischemic hemisphere (“core” and “border”). Animals were pre-treated to a systolic blood pressure of 150 mmHg or received vehicle. Data are means ± standard error of the mean. n = 11-14 per group. The Mann-Whitney-U test was used for comparisons. *p<0.05, **p<0.01, vs. vehicle, ^#p<0.05 vs. vehicle and candesartan.</p

Infarct size determined by magnetic resonance imaging in double transgenic rats after middle cerebral artery occlusion with reperfusion.

<p>Groups according to treatment (Veh, vehicle, Cand, candesartan, Alis, aliskiren), systolic blood pressure and duration of follow-up. Differences between the treatment groups were not statistically significant. Data are means ± standard error of the mean. n = 11-14 per group.</p