Calcineurin inhibitor effects on kidney electrolyte handling and blood pressure: tacrolimus versus voclosporin

BACKGROUND AND HYPOTHESIS

Calcineurin inhibitors affect kidney electrolyte handling and blood pressure through an effect on the distal tubule. The second generation calcineurin inhibitor voclosporin causes hypomagnesemia and hypercalciuria less often than tacrolimus. This suggests different effects on the distal tubule, but this has not yet been investigated experimentally.

METHODS

Rats were treated with voclosporin, tacrolimus or vehicle for 28 days. Dosing was based on a pilot experiment to achieve clinically therapeutic concentrations. Drug effects were assessed by electrolyte handling at day 18 and 28, thiazide testing at day 20, telemetric blood pressure recordings, and analysis of mRNA and protein levels of distal tubular transporters at day 28.

RESULTS

Compared to vehicle, tacrolimus but not voclosporin significantly increased the fractional excretions of calcium (>4-fold), magnesium and chloride (both 1.5-fold) and caused hypomagnesemia. Tacrolimus but not voclosporin significantly reduced distal tubular transporters at mRNA and/or protein level, including the sodium-chloride cotransporter, transient receptor melastatin 6, transient receptor potential vanilloid 5, cyclin M2, sodium-calcium exchanger and calbindin-D28K. Tacrolimus but not voclosporin reduced the mRNA level and urinary excretion of epidermal growth factor. The saluretic response to hydrochlorothiazide at day 20 was similar in the voclosporin and vehicle groups, whereas it was lower in the tacrolimus group. The phosphorylated form of the sodium-chloride cotransporter was significantly higher at day 28 in rats treated with voclosporin than in those treated with tacrolimus. Tacrolimus transiently increased blood pressure, whereas voclosporin caused a gradual but persistent increase in blood pressure which was further characterized by high renin, normal aldosterone, and low endothelin-1.

CONCLUSIONS

In contrast to tacrolimus, voclosporin does not cause hypercalciuria and hypomagnesemia, but similarly causes hypertension. Our data reveal differences between the distal tubular effects of tacrolimus and voclosporin and provide a pathophysiological basis for the clinically observed differences between the two calcineurin inhibitors.

Counteracting Angiotensinogen Small-Interfering RNA-Mediated Antihypertensive Effects With REVERSIR

BACKGROUND

Ssmall-interfering RNA (siRNA) targeting hepatic AGT (angiotensinogen) mRNA depletes AGT, lowering blood pressure for up to 6 months. However, certain situations may require a rapid angiotensin increase. The reverse siRNA silencing, RVR technology is a potential approach to counteract siRNA effects.

METHODS

Spontaneously hypertensive rats received 10 mg/kg AGT siRNA, and 3 weeks later were given AGT-RVR (1, 10, or 20 mg/kg). One week after AGT-RVR dosing, a redose of AGT siRNA assessed its post-AGT-RVR effectiveness for 2 weeks. Additionally, the impact of AGT-RVR after an equihypotensive dose of valsartan (4 mg/kg per day) was examined.

RESULTS

Baseline mean arterial pressure (MAP) was 144±1 mm Hg. AGT siRNA reduced MAP by ≈16 mm Hg and AGT by >95%, while renin increased 25-fold. All AGT-RVR doses restored MAP to baseline within 4 to 7 days. Notably, 10 and 20 mg/kg restored AGT and renin to baseline, while 1 mg/kg allowed ≈50% AGT restoration, with renin remaining above baseline. A second AGT siRNA treatment, following 1-mg/kg AGT-RVR, reduced MAP to the same degree as the initial dose, while following 10 mg/kg AGT-RVR, it resulted in ≈50% of the first dose's MAP effect at 2 weeks. The valsartan-induced MAP reduction was unaffected by AGT-RVR.

CONCLUSIONS

In spontaneously hypertensive rats, angiotensinogen-RVR dose-dependently reversed AGT siRNA-induced AGT reduction, normalizing MAP. MAP normalization persisted even with 50% recovered AGT levels, likely due to upregulated renin maintaining adequate angiotensin generation. Post-AGT-RVR dosing, a second AGT siRNA dose lowered MAP again.

Combining renin-angiotensin system blockade and sodium-glucose cotransporter-2 inhibition in experimental diabetes results in synergistic beneficial effects

BACKGROUND

Sodium-glucose cotransporter-2 (SGLT2) inhibition exerts cardioprotective and renoprotective effects, often on top of renin-angiotensin system (RAS) blockade. We investigated this in diabetic hypertensive (mREN2)27 rats.

METHODS

Rats were made diabetic with streptozotocin and treated with vehicle, the angiotensin receptor blocker valsartan, the SGLT2 inhibitor empagliflozin, or their combination. Blood pressure (BP) was measured by telemetry.

RESULTS

Diabetes resulted in albuminuria, accompanied by glomerulosclerosis, without a change in glomerular filtration rate. Empagliflozin did not lower BP, while valsartan did, and when combined the BP drop was largest. Only dual blockade reduced cardiac hypertrophy and prevented left ventricular dilatation. Valsartan, but not empagliflozin, increased renin, and the largest renin rise occurred during dual blockade, resulting in plasma angiotensin II [but not angiotensin-(1-7)] upregulation. In contrast, in the kidney, valsartan lowered angiotensin II and angiotensin-(1-7), and empagliflozin did not alter this. Although both valsartan and empagliflozin alone tended to diminish albuminuria, the reduction was significant only when both drugs were combined. This was accompanied by reduced glomerulosclerosis, no change in glomerular filtration rate, and a favorable expression pattern of fibrosis and inflammatory markers (including SGLT2) in the kidney.

CONCLUSION

RAS blockade and SGLT2 inhibition display synergistic beneficial effects on BP, kidney injury and cardiac hypertrophy in a rat with hypertension and diabetes. The synergy does not involve upregulation of angiotensin-(1-7), but may relate to direct RAS-independent effects of empagliflozin in the heart and kidney.

Cyclooxygenase-2 inhibition prevents renal toxicity but not hypertension during sunitinib treatment

BACKGROUND

Anticancer angiogenesis inhibitors cause hypertension and renal injury. Previously we observed in rats that high-dose aspirin (capable of blocking cyclooxygenase (COX)-1 and-2) was superior to low-dose aspirin (blocking COX-1 only) to prevent these side-effects during treatment with the angiogenesis inhibitor sunitinib, suggesting a role for COX-2. High-dose aspirin additionally prevented the rise in COX-derived prostacyclin (PGI2). Therefore, we studied the preventive effects of selective COX-2 inhibition and the hypothesized contributing role of PGI2 during angiogenesis inhibition.

METHODS

Male WKY rats received vehicle, sunitinib ((SU), 14 mg/kg/day) alone or combined with COX-2 inhibition (celecoxib, 10 mg/kg/day) or a PGI2 analogue (iloprost, 100 μg/kg/day) for 8 days (n = 8-9 per group). Mean arterial pressure (MAP) was measured via radiotelemetry, biochemical measurements were performed via ELISA and vascular function was assessed via wire myography.

RESULTS

SU increased MAP (17±1mmHg versus 3±1mmHg after vehicle on day 4, P < 0.002), which could not be significantly blunted by celecoxib (+12±3mmHg on day 4, P = 0.247), but was temporarily attenuated by iloprost (treatment days 1 + 2 only). Urinary PGI2 (996 ± 112 versus 51 ± 11ng/24h after vehicle, P < 0.001), but not circulating PGI2 increased during SU, which remained unaffected by celecoxib and iloprost. Celecoxib reduced sunitinib-induced albuminuria (0.36 ± 0.05 versus 0.58 ± 0.05mg/24h after SU, P = 0.005). Wire myography demonstrated increased vasoconstriction to endothelin-1 after SU (Emax P = 0.005 versus vehicle), which remained unaffected by celecoxib or iloprost.

CONCLUSION

Selective COX-2 inhibition ameliorates albuminuria during angiogenesis inhibition with sunitinib, which most likely acts independently of PGI2. To combat angiogenesis inhibitor-induced hypertension, dual rather than selective COX-1/2 blockade seems preferential.

Blood pressure-independent renoprotective effects of small interference RNA targeting liver angiotensinogen in experimental diabetes

BACKGROUND AND PURPOSE

Small interfering RNA (siRNA) targeting liver angiotensinogen lowers blood pressure, but its effects in hypertensive diabetes are unknown.

EXPERIMENTAL APPROACH

To address this, TGR (mRen2)27 rats (angiotensin II-dependent hypertension model) were made diabetic with streptozotocin over 18 weeks and treated with either vehicle, angiotensinogen siRNA, the AT₁ antagonist valsartan, the ACE inhibitor captopril, valsartan + siRNA or valsartan + captopril for the final 3 weeks. Mean arterial pressure (MAP) was measured via radiotelemetry.

KEY RESULTS

MAP before treatment was 153 ± 2 mmHg. Diabetes resulted in albuminuria, accompanied by glomerulosclerosis and podocyte effacement, without a change in glomerular filtration rate. All treatments lowered MAP and cardiac hypertrophy, and the largest drop in MAP was observed with siRNA + valsartan. Treatment with siRNA lowered circulating angiotensinogen by >99%, and the lowest circulating angiotensin II and aldosterone levels occurred in the dual treatment groups. Angiotensinogen siRNA did not affect renal angiotensinogen mRNA expression, confirming its liver-specificity. Furthermore, only siRNA with or without valsartan lowered renal angiotensin I. All treatments lowered renal angiotensin II and the reduction was largest (>95%) in the siRNA + valsartan group. All treatments identically lowered albuminuria, whereas only siRNA with or without valsartan restored podocyte foot processes and reduced glomerulosclerosis.

CONCLUSION AND IMPLICATIONS

Angiotensinogen siRNA exerts renoprotection in diabetic TGR (mRen2)27 rats and this relies, at least in part, on the suppression of renal angiotensin II formation from liver-derived angiotensinogen. Clinical trials should now address whether this is also beneficial in human diabetic kidney disease.

Conventional Vasopressor and Vasopressor-Sparing Strategies to Counteract the Blood Pressure-Lowering Effect of Small Interfering RNA Targeting Angiotensinogen

Background

A single dose of small interfering RNA (siRNA) targeting liver angiotensinogen eliminates hepatic angiotensinogen and lowers blood pressure. Angiotensinogen elimination raises concerns for clinical application because an angiotensin rise is needed to maintain perfusion pressure during hypovolemia. Here, we investigated whether conventional vasopressors can raise arterial pressure after angiotensinogen depletion.

Methods and Results

Spontaneously hypertensive rats on a low‐salt diet were treated with siRNA (10 mg/kg fortnightly) for 4 weeks, supplemented during the final 2 weeks with fludrocortisone (6 mg/kg per day), the α‐adrenergic agonist midodrine (4 mg/kg per day), or a high‐salt diet (all groups n=6–7). Pressor responsiveness to angiotensin II and norepinephrine was assessed before and after siRNA administration. Blood pressure was measured via radiotelemetry. Depletion of liver angiotensinogen by siRNA lowered plasma angiotensinogen concentrations by 99.2±0.1% and mean arterial pressure by 19 mm Hg. siRNA‐mediated blood pressure lowering was rapidly reversed by intravenous angiotensin II or norepinephrine, or gradually reversed by fludrocortisone or high salt intake. Midodrine had no effect. Unexpectedly, fludrocortisone partially restored plasma angiotensinogen concentrations in siRNA‐treated rats, and nearly abolished plasma renin concentrations. To investigate whether this angiotensinogen originated from nonhepatic sources, fludrocortisone was administered to mice lacking hepatic angiotensinogen. Fludrocortisone did not increase angiotensinogen in these mice, implying that the rise in angiotensinogen in the siRNA‐treated rats must have depended on the liver, most likely reflecting diminished cleavage by renin.

Conclusions

Intact pressor responsiveness to conventional vasopressors provides pharmacological means to regulate the blood pressure–lowering effect of angiotensinogen siRNA and may support future therapeutic implementation of siRNA.

Abstract 05: Cyclooxygenase-2 Inhibition As A New Tool To Combat Angiogenesis Inhibitor-induced Hypertension And Renal Toxicity

Angiogenesis inhibitors are effective anti-cancer agents, but also cause hypertension and renal injury. Earlier, we observed in rats that high-dose aspirin (capable of blocking cyclooxygenase (COX)-1 and -2) prevented these side effects better than low-dose aspirin (blocking COX-1 only). Therefore, we hypothesized that selective COX-2 inhibition would prevent toxicity during angiogenesis inhibition, and that this toxicity involves a reduced ratio of vasodilator/constrictor COX-derived prostanoids, i.e., prostacyclin (PGI 2 ) and thromboxane (TXA 2 ). Male WKY rats received vehicle, angiogenesis inhibition (sunitinib (SU), 14 mg/kg/day) alone or combined with COX-2 inhibition (celecoxib, 10mg/kg/day), a PGI 2 analogue (iloprost 100 μg/kg/day), or a dual TXA 2 synthase/receptor antagonist (picotamide, 2.5 mg/kg/day) for 8 days (n=7-8/group). Mean arterial pressure (MAP) was measured via radiotelemetry, vascular function was assessed via wire myography, and biochemical measurements were performed by ELISA. SU induced a rapid increase in MAP (16±2 vs. 3±1 mmHg after vehicle on day 6, P<0.001), which was blunted by celecoxib (10±2 mmHg on day 6, P=0.06 versus SU), temporarily attenuated by iloprost (on treatment days 1-2) and unaffected by picotamide. Wire myography demonstrated a trend towards increased vasoconstrictor response to endothelin-1 in iliac arteries after SU, which was prevented by celecoxib (P<0.001). SU increased albuminuria (0.6±0.1 vs. 0.3±0.1 mg/24h after vehicle; P<0.001), and this was prevented by celecoxib only (0.4±0.1 mg/24h, P=0.01 vs. SU). SU increased the PGI 2 /TXA 2 ratio in both plasma (2.7±1.2 vs. 0.6±0.2 after vehicle, P=0.05) and urine (22±2.2 vs. 0.9±0.2 after vehicle, P<0.001). In conclusion, selective COX-2 inhibition combats angiogenesis inhibitor-induced hypertension and renal toxicity. SU paradoxically increases the PGI 2 /TXA 2 ratio, particularly in the kidney. Although this upregulation might initially be protective, it could eventually contribute to renal toxicity, most likely because PGI 2 exerts deleterious effects in excessive concentrations. Targeting excessive renal PGI 2 production might be another promising strategy to prevent renal toxicity during angiogenesis inhibition.

Selective ETA vs. dual ETA/B receptor blockade for the prevention of sunitinib-induced hypertension and albuminuria in WKY rats

AIMS

Although effective in preventing tumour growth, angiogenesis inhibitors cause off-target effects including cardiovascular toxicity and renal injury, most likely via endothelin (ET)-1 up-regulation. ET-1 via stimulation of the ETA receptor has pro-hypertensive actions whereas stimulation of the ETB receptor can elicit both pro- or anti-hypertensive effects. In this study, our aim was to determine the efficacy of selective ETA vs. dual ETA/B receptor blockade for the prevention of angiogenesis inhibitor-induced hypertension and albuminuria.

METHODS AND RESULTS

Male Wistar Kyoto (WKY) rats were treated with vehicle, sunitinib (angiogenesis inhibitor; 14 mg/kg/day) alone or in combination with macitentan (ETA/B receptor antagonist; 30 mg/kg/day) or sitaxentan (selective ETA receptor antagonist; 30 or 100 mg/kg/day) for 8 days. Compared with vehicle, sunitinib treatment caused a rapid and sustained increase in mean arterial pressure of ∼25 mmHg. Co-treatment with macitentan or sitaxentan abolished the pressor response to sunitinib. Sunitinib did not induce endothelial dysfunction. However, it was associated with increased aortic, mesenteric, and renal oxidative stress, an effect that was absent in mesenteric arteries of the macitentan and sitaxentan co-treated groups. Albuminuria was greater in the sunitinib- than vehicle-treated group. Co-treatment with sitaxentan, but not macitentan, prevented this increase in albuminuria. Sunitinib treatment increased circulating and urinary prostacyclin levels and had no effect on thromboxane levels. These increases in prostacyclin were blunted by co-treatment with sitaxentan.

CONCLUSIONS

Our results demonstrate that both selective ETA and dual ETA/B receptor antagonism prevents sunitinib-induced hypertension, whereas sunitinib-induced albuminuria was only prevented by selective ETA receptor antagonism. In addition, our results uncover a role for prostacyclin in the development of these effects. In conclusion, selective ETA receptor antagonism is sufficient for the prevention of sunitinib-induced hypertension and renal injury.

Renoprotective Effects of Small Interfering RNA Targeting Liver Angiotensinogen in Experimental Chronic Kidney Disease

[Figure: see text].

Dietary salt modifies the blood pressure response to renin-angiotensin inhibition in experimental chronic kidney disease

Chronic kidney disease contributes to hypertension, but the mechanisms are incompletely understood. To address this, we applied the 5/6th nephrectomy rat model to characterize hypertension and the response to dietary salt and renin-angiotensin inhibition. 5/6th nephrectomy caused low-renin, salt-sensitive hypertension with hyperkalemia and unsuppressed aldosterone. Compared with sham rats, 5/6th nephrectomized rats had lower Na⁺/H⁺ exchanger isoform 3, Na⁺-K⁺-2Cl^- cotransporter, Na⁺-Cl^- cotransporter, α-epithelial Na⁺ channel (ENaC), and Kir4.1 levels but higher serum and glucocorticoid-regulated kinase 1, prostasin, γ-ENaC, and Kir5.1 levels. These differences correlated with plasma renin, aldosterone, and/or K⁺. On a normal-salt diet, adrenalectomy (0 ± 9 mmHg) and spironolactone (-11 ± 10 mmHg) prevented a progressive rise in blood pressure (10 ± 8 mmHg), and this was enhanced in combination with losartan (-41 ± 12 and -43 ± 9 mmHg). A high-salt diet caused skin Na⁺ and water accumulation and aggravated hypertension that could only be attenuated by spironolactone (-16 ± 7 mmHg) and in which the additive effect of losartan was lost. Spironolactone also increased natriuresis, reduced skin water accumulation, and restored vasorelaxation. In summary, in the 5/6th nephrectomy rat chronic kidney disease model, salt-sensitive hypertension develops with a selective increase in γ-ENaC and despite appropriate transporter adaptations to low renin and hyperkalemia. With a normal-salt diet, hypertension in 5/6th nephrectomy depends on angiotensin II and aldosterone, whereas a high-salt diet causes more severe hypertension mediated through the mineralocorticoid receptor.NEW & NOTEWORTHY Chronic kidney disease (CKD) causes salt-sensitive hypertension, but the interactions between dietary salt and the renin-angiotensin system are incompletely understood. In rats with CKD on a normal-salt diet targeting aldosterone, the mineralocorticoid receptor (MR) and especially angiotensin II reduced blood pressure. On a high-salt diet, however, only MR blockade attenuated hypertension. These results reiterate the importance of dietary salt restriction to maintain renin-angiotensin system inhibitor efficacy and specify the MR as a target in CKD.

No evidence for brain renin-angiotensin system activation during DOCA-salt hypertension

Brain renin-angiotensin system (RAS) activation is thought to mediate deoxycorticosterone acetate (DOCA)-salt hypertension, an animal model for human primary hyperaldosteronism. Here, we determined whether brainstem angiotensin II is generated from locally synthesized angiotensinogen and mediates DOCA-salt hypertension. To this end, chronic DOCA-salt-hypertensive rats were treated with liver-directed siRNA targeted to angiotensinogen, the angiotensin II type 1 receptor antagonist valsartan, or the mineralocorticoid receptor antagonist spironolactone (n = 6-8/group). We quantified circulating angiotensinogen and renin by enzyme-kinetic assay, tissue angiotensinogen by Western blotting, and angiotensin metabolites by LC-MS/MS. In rats without DOCA-salt, circulating angiotensin II was detected in all rats, whereas brainstem angiotensin II was detected in 5 out of 7 rats. DOCA-salt increased mean arterial pressure by 19 ± 1 mmHg and suppressed circulating renin and angiotensin II by >90%, while brainstem angiotensin II became undetectable in 5 out of 7 rats (<6 fmol/g). Gene silencing of liver angiotensinogen using siRNA lowered circulating angiotensinogen by 97 ± 0.3%, and made brainstem angiotensin II undetectable in all rats (P<0.05 vs. non-DOCA-salt), although brainstem angiotensinogen remained intact. As expected for this model, neither siRNA nor valsartan attenuated the hypertensive response to DOCA-salt, whereas spironolactone normalized blood pressure and restored brain angiotensin II together with circulating renin and angiotensin II. In conclusion, despite local synthesis of angiotensinogen in the brain, brain angiotensin II depended on circulating angiotensinogen. That DOCA-salt suppressed circulating and brain angiotensin II in parallel, while spironolactone simultaneously increased brain angiotensin II and lowered blood pressure, indicates that DOCA-salt hypertension is not mediated by brain RAS activation.

Abstract P110: Renal Angiotensin Generation Depends on Hepatic Angiotensinogen: Evidence From a Preclinical Study With RNAi Therapeutics Targeting Liver Angiotensinogen

Angiotensinogen (AGT) synthesis is proposed to occur not only in the liver, but also in kidney, brain and adipocytes. Selectively deleting hepatic AGT might therefore not affect renal angiotensin (Ang) levels. Here we investigated whether arterial pressure lowering with liver-targeted AGT siRNA versus renin-Ang system (RAS) blockers affects renal function and Ang levels. Arterial pressure was measured via radiotelemetry in spontaneously hypertensive rats during vehicle, valsartan, captopril (both p.o.), siRNA (s.c. fortnightly injection), siRNA+valsartan or captopril+valsartan treatment for 4 weeks. Transcutaneous measurement of glomerular filtration rate (GFR) and 24h urinary excretory function was assessed at 2 and 4 weeks. Renal Ang levels were measured by mass spectrometry. Dual RAS blockade synergistically lowered arterial pressure compared to monotherapy. Valsartan and captopril increased AngI (1096±205 and 939±128 fmol/g, respectively versus 413±46 fmol/g in vehicle-treated; both P<0.01 vs. vehicle), while captopril+valsartan did not affect AngI (260±42 fmol/g). siRNA and siRNA+valsartan lowered AngI (59±6 and 12±3 fmol/g, respectively; P<0.0001 versus vehicle). Conversely, neither siRNA nor valsartan lowered AngII (228±15 and 338±39 fmol/g versus 431±48 fmol/g in vehicle-treated). Captopril modestly lowered AngII while dual RAS blockade with siRNA+valsartan or captopril+valsartan greatly reduced AngII (115±20, 15±5 and 9±3 fmol/g, respectively; all P<0.0001). The renal AngII/I ratio was increased 4-fold after siRNA (P<0.001), reduced by >70% after valsartan, captopril and captopril+valsartan (all P<0.001) and unaltered after siRNA+valsartan. No treatment affected GFR, natriuresis or albuminuria. In conclusion, the lowering of renal AngI after liver-targeted AGT siRNA suggests that hepatic rather than renal AGT determines renal Ang generation. Upregulation of ACE and/or AT 1 R may allow renal AngII to remain intact after AGT siRNA, and only dual RAS blockade significantly reduces renal AngII. AGT siRNA synergistically lowers arterial pressure when combined with existing RAS blockers and may be a novel treatment for hypertension without apparent negative effects on renal function.

Abstract P149: VEGF Inhibitor-Induced Hypertension and Renal Injury: Prevention by Aspirin?

Vascular endothelial growth factor inhibitor (VEGFi)-induced hypertension and renal injury in cancer patients mimic the clinical phenotype of preeclampsia. ET-1 has been implicated to be involved. Since aspirin can prevent the onset of preeclampsia, we hypothesized that co-treatment of the VEGFi sunitinib (SU) with aspirin might be beneficial and may improve ET-1 status. Male WKY rats were treated with vehicle, 14 mg/kg/day SU, or SU + low or high dose aspirin (5 or 100 mg/kg/day) for 8 days. Mean arterial pressure (MAP) was measured via radiotelemetry. On day 8, 24h urine was collected to determine albuminuria and prostanoid (PGF2α and TxB2) levels. Plasma endothelin-1 (ET-1) was measured via ELISA. Endothelial dysfunction was assessed in iliac vessels and reactive oxygen species (ROS) was measured via aortic superoxide anion production. Renal cyclooxygenase (COX)-1, COX-2 and ET-1 mRNA expression were determined via PCR. SU induced a rapid and sustained increase in MAP (24±2 versus 1±1 mmHg in vehicle on day 6; P<0.001), which was blunted by both low and high aspirin doses (18±3 and 13±4 mmHg respectively on day 6; P<0.05 versus SU). Plasma ET-1 was increased by SU (2.2±0.3 versus 1.4±0.1 pg/ml in vehicle; P<0.05) and this was not affected by aspirin. SU increased albuminuria (1.2±0.2 versus 0.3±0.1 mg/24h in vehicle; P<0.05) which was prevented by high, but not low dose aspirin (0.5±0.1 and 1.3±0.1 mg/24h, respectively), suggesting that this effect is COX-2 dependent. Although renal mRNA expression levels were unchanged, renal COX-2 and ET-1 mRNA expression correlated positively, suggesting that ET-1 upregulates COX-2. SU increased ROS production 2.5-fold (P<0.05 versus vehicle) and this was prevented by both aspirin doses. SU did not induce endothelial dysfunction, nor did it alter prostanoid levels. However, both aspirin doses reduced TxB2 (P<0.05 versus vehicle). In conclusion, high rather than low dose aspirin was more efficacious for the prevention of VEGFi-induced hypertension and renal injury, suggesting that its beneficial effects largely involve COX-2 inhibition. Aspirin may be a novel intervention to allow cancer patients to gain the full benefit of VEGFi without deleterious cardiovascular and renal side effects.

Abstract 079: Long-Lasting RNAi Therapeutics Targeting Angiotensinogen Induces a Robust and Durable Antihypertensive Effect

All angiotensin stems from angiotensinogen (AGT). A single dose of small interfering ribonucleic acids (siRNA) targeting AGT may provide long-lasting blood pressure reductions, as it would abolish angiotensin generation. Here we assessed efficacy of AGT siRNA in spontaneously hypertensive rats (SHRs). SHRs were treated for 4 weeks with vehicle, siRNA (10 mg/kg; s.c. every 2 weeks), valsartan (31 mg/kg/day; oral), captopril (100 mg/kg/day; oral), valsartan+siRNA, or captopril+valsartan (all groups n=8). Mean arterial pressure (MAP) was measured via radiotelemetry. Baseline MAP was 137±2 mmHg. ΔMAP was largest after valsartan+siRNA (-67±3 mmHg; P<0.01 vs. captopril+valsartan), followed by captopril+valsartan, captopril, siRNA and valsartan (-55±4, -24±2, -14±1, and -9±2 mmHg, respectively). Valsartan+siRNA reduced cardiac hypertrophy the most (P<0.05 vs. captopril+valsartan). After 4 weeks, siRNA lowered AGT by 98.6%, which increased to 99.9% in combination with valsartan. All treatments increased renin, the highest rise occurring after valsartan+siRNA. Yet, only valsartan+siRNA lowered angiotensin II. No treatment altered aldosterone. Plasma K + tended to increase in all groups, significance being reached only in the valsartan+siRNA group. Both types of dual blockade attenuated normal growth from the second week of treatment onwards. In conclusion, due to renin upregulation, circulating angiotensin II remained intact even with only 1.4% of AGT left, relative to pretreatment. Consequently, AGT siRNA caused a similar antihypertensive effect as valsartan and captopril. Importantly, when combining siRNA+valsartan, angiotensin II collapsed, and blood pressure decreased synergistically. Given the potential for low dosing frequency suggested by this study, this novel treatment may address medication adherence problems in patients with resistant hypertension and further development is warranted.

Abstract P186: Selective ET A Receptor Antagonism versus Dual ET A /ET B Receptor Blockade for Preventing Angiogenesis Inhibitor-induced Hypertension

Angiogenesis inhibitors are a mainstay treatment for cancer. While effective in preventing tumor growth, angiogenesis inhibitors cause off-target effects including cardiovascular toxicity and renal injury, most likely via endothelin-1 (ET-1) upregulation. ET-1 via stimulation of the ET A receptor causes pro-hypertensive effects whereas stimulation of the ET B receptor can elicit both pro- or anti-hypertensive effects. In the present study, we hypothesized that selective ET A receptor blockade versus dual ET A /ET B blockade provides better cardiovascular protection from angiogenesis inhibitor-induced hypertension. Male WKY rats were treated with vehicle, sunitinib (VEGF inhibitor; 14 mg/kg/day) alone or in combination with macitentan (ET A/B receptor antagonist; 30 mg/kg/day) or sitaxentan (ET A receptor antagonist; 30 or 100 mg/kg/day) for 8 days. Mean arterial pressure (MAP) was measured via radiotelemetry at baseline and days 1-6 of treatment. Vasoreactivity to acetylcholine (ACh) and ET-1 was assessed in iliac vessels. Compared to vehicle treatment, sunitinib treatment caused a rapid and sustained increase in MAP (1±1 versus 23±2 mmHg on day 6 of treatment, respectively, P<0.001). Co-treatment with macitentan blunted the pressor response to sunitinib, such that on day 6 of treatment the increase in MAP was 7±4 mmHg (P<0.01 versus sunitinib-treated). Similar results were observed for co-treatment with 30 mg/kg/day of sitaxentan. Conversely, co-treatment with 100 mg/kg/day sitaxentan, which has been shown to induce a depressor response in normotensive Wistar rats, completely abolished sunitinib-induced hypertension, with MAP actually decreasing before returning to near baseline level (-1±1 mmHg on day 6 of treatment, P<0.001 versus sunitinib-treated). Compared to vehicle treatment, ET B receptor stimulation yielded a constrictor response after 8 days of sunitinib treatment, while the response to ACh was unaltered. Both macitentan and sitaxentan reversed the constrictor ET B receptor response. Our results support a key role for the ET-1 system in the development of sunitinib-induced hypertension and suggest that selective ET A receptor blockade is sufficient to block this effect.

Angiotensin II type 2 receptor- and acetylcholine-mediated relaxation: essential contribution of female sex hormones and chromosomes

Angiotensin-induced vasodilation, involving type 2 receptor (AT2R)-induced generation of nitric oxide (NO; by endothelial NO synthase) and endothelium-derived hyperpolarizing factors, may be limited to women. To distinguish the contribution of female sex hormones and chromosomes to AT2R function and endothelium-derived hyperpolarizing factor-mediated vasodilation, we made use of the four-core genotype model, where the testis-determining Sry gene has been deleted (Y(-)) from the Y chromosome, allowing XY(-) mice to develop a female gonadal phenotype. Simultaneously, by incorporating the Sry gene onto an autosome, XY(-)Sry and XXSry transgenic mice develop into gonadal male mice. Four-core genotype mice underwent a sham or gonadectomy (GDX) operation, and after 8 weeks, iliac arteries were collected to assess vascular function. XY(-)Sry male mice responded more strongly to angiotensin than XX female mice, and the AT2R antagonist PD123319 revealed that this was because of a dilator AT2R-mediated effect occurring exclusively in XX female mice. The latter could not be demonstrated in XXSry male and XY(-) female mice nor in XX female mice after GDX, suggesting that it depends on both sex hormones and chromosomes. Indeed, treating C57bl/6 GDX male mice with estrogen could not restore angiotensin-mediated, AT2R-dependent relaxation. To block acetylcholine-induced relaxation of iliac arteries obtained from four-core genotype XX mice, both endothelial NO synthase and endothelium-derived hyperpolarizing factor inhibition were required, whereas in four-core genotype XY animals, endothelial NO synthase inhibition alone was sufficient. These findings were independent of gonadal sex and unaltered after GDX. In conclusion, AT2R-induced relaxation requires both estrogen and the XX chromosome sex complement, whereas only the latter is required for endothelium-derived hyperpolarizing factors.

Abstract 507: Dual AT1 Receptor/Neprilysin (NEP) Inhibition (ARNI) vs. AT1 Receptor Blockade in TGR(mRen2)27 Rats: The More NEP Inhibition The Better?

Objective: Neprilysin inhibitors (NEPi) prevent the breakdown of natriuretic peptides, promoting vasodilation and natriuresis. However, they also increase angiotensin and endothelin-1 (ET1). This study compared the combination of an AT1 receptor antagonist (irbesartan, IRB) ± a low or a high dose of the NEPi thiorphan in renin-overexpressing, hypertensive TGR(mREN2)27 rats.

Methods: TGR(mREN2)27 rats were treated for three weeks with vehicle, IRB (15 mg/kg.day) or IRB + thiorphan (0.1 or 1.0 mg/kg.day; TH0.1 and TH1.0). Hemodynamics were evaluated by telemetry, and vascular reactivity was determined in isolated mesenteric arteries (Mulvany myograph).

Results: Baseline mean arterial blood pressure (MAP) was 168±3 mmHg. All treatments lowered MAP by ≈50 mmHg around day 4. After 7 days, MAP started to increase during treatment with IRB or IRB+TH1.0 (to 141±10 mmHg and 133±10 mmHg, respectively, on day 21), while MAP in rats treated with IRB+TH0.1 remained low at 104±5 mmHg on day 21. Heart weight/body weight ratio, cardiac ANP expression and myocyte size decreased only in the IRB+TH0.1 group. Plasma ET1 was increased only by TH1.0 versus IRB alone, and this increase was accompanied by an increase in renal sodium-hydrogen exchanger 3 (NHE3) protein

expression: ET1-induced constriction was reduced by IRB+TH0.1 only. Vascular ET B R expression levels and studies with the ET1 type B receptor (ET B R) antagonist BQ788 revealed that this reduction was most likely due to ET B R upregulation.

Conclusion: TH0.1 enhanced the blood pressure-lowering effects of irbesartan and diminished cardiac hypertrophy. Higher doses of thiorphan resulted in significant ET1 rises and renal NHE3 upregulation, thereby increasing blood pressure and sodium reabsorption. The simultaneously occurring upregulation of vasodilatory ET B R was insufficient to overcome this effect. Clearly therefore, too much NEPi on top of AT1 receptor antagonism might be harmful.

Combined renin inhibition/(pro)renin receptor blockade in diabetic retinopathy--a study in transgenic (mREN2)27 rats

Dysfunction of renin-angiotensin system (RAS) contributes to the pathogenesis of diabetic retinopathy (DR). Prorenin, the precursor of renin is highly elevated in ocular fluid of diabetic patients with proliferative retinopathy. Prorenin may exert local effects in the eye by binding to the so-called (pro)renin receptor ((P)RR). Here we investigated the combined effects of the renin inhibitor aliskiren and the putative (P)RR blocker handle-region peptide (HRP) on diabetic retinopathy in streptozotocin (STZ)-induced diabetic transgenic (mRen2)27 rats (a model with high plasma prorenin levels) as well as prorenin stimulated cytokine expression in cultured Müller cells. Adult (mRen2)27 rats were randomly divided into the following groups: (1) non-diabetic; (2) diabetic treated with vehicle; (3) diabetic treated with aliskiren (10 mg/kg per day); and (4) diabetic treated with aliskiren+HRP (1 mg/kg per day). Age-matched non-diabetic wildtype Sprague-Dawley rats were used as control. Drugs were administered by osmotic minipumps for three weeks. Transgenic (mRen2)27 rat retinas showed increased apoptotic cell death of both inner retinal neurons and photoreceptors, increased loss of capillaries, as well as increased expression of inflammatory cytokines. These pathological changes were further exacerbated by diabetes. Aliskiren treatment of diabetic (mRen2)27 rats prevented retinal gliosis, and reduced retinal apoptotic cell death, acellular capillaries and the expression of inflammatory cytokines. HRP on top of aliskiren did not provide additional protection. In cultured Müller cells, prorenin significantly increased the expression levels of IL-1α and TNF-α, and this was completely blocked by aliskiren or HRP, their combination, (P)RR siRNA and the AT1R blocker losartan, suggesting that these effects entirely depended on Ang II generation by (P)RR-bound prorenin. In conclusion, the lack of effect of HRP on top of aliskiren, and the Ang II-dependency of the ocular effects of prorenin in vitro, argue against the combined application of (P)RR blockade and renin inhibition in diabetic retinopathy.

Deterioration of kidney function by the (pro)renin receptor blocker handle region peptide in aliskiren-treated diabetic transgenic (mRen2)27 rats

Dual renin-angiotensin system (RAS) blockade in diabetic nephropathy is no longer feasible because of the profit/side effect imbalance. (Pro)renin receptor [(P)RR] blockade with handle region peptide (HRP) has been reported to exert beneficial effects in various diabetic models in a RAS-independent manner. To what degree (P)RR blockade adds benefits on top of RAS blockade is still unknown. In the present study, we treated diabetic TGR(mREN2)27 rats, a well-established nephropathy model with high prorenin levels [allowing continuous (P)RR stimulation in vivo], with HRP on top of renin inhibition with aliskiren. Aliskiren alone lowered blood pressure and exerted renoprotective effects, as evidenced by reduced glomerulosclerosis, diuresis, proteinuria, albuminuria, and urinary aldosterone levels as well as diminished renal (P)RR and ANG II type 1 receptor expression. It also suppressed plasma and tissue RAS activity and suppressed cardiac atrial natriuretic peptide and brain natriuretic peptide expression. HRP, when given on top of aliskiren, did not alter the effects of renin inhibition on blood pressure, RAS activity, or aldosterone. However, it counteracted the beneficial effects of aliskiren in the kidney, induced hyperkalemia, and increased plasma plasminogen activator-inhibitor 1, renal cyclooxygenase-2, and cardiac collagen content. All these effects have been linked to (P)RR stimulation, suggesting that HRP might, in fact, act as a partial agonist. Therefore, the use of HRP on top of RAS blockade in diabetic nephropathy is not advisable.

Abstract 184: Deterioration of Kidney Function by the (Pro)renin Receptor Blocker Handle Region Peptide in Aliskiren-treated Diabetic Transgenic (mRen2)27 Rats

Objective Renal function in patients with diabetes mellitus (DM) might be influenced by the level of prorenin due to its binding to the (pro)renin receptor ((P)RR) and the subsequently occurring angiotensin production and/or the direct agonistic effects of prorenin mediated via this receptor. Indeed, in DM elevated prorenin levels are correlated with the development of microvascular complications such as nephropathy.

Design and Methods In this study we evaluated renal function in diabetic TGR(mREN2)27 rats (a high prorenin hypertensive model), treated with vehicle, the renin inhibitor aliskiren, or aliskiren plus the putative (P)RR antagonist HRP for 3 weeks. 24-hour urine was collected, and blood and kidney were evaluated for renin-angiotensin system components and pathology.

Results Increased diuresis and proteinuria due to DM were prevented by aliskiren, but not aliskiren+HRP. Aliskiren+HRP additionally decreased creatinine clearance, and increased the plasma levels of the profibrotic marker plasminogen-activator inhibitor-1. The increased natriuresis and renal collagen-1 expression in this model were unaffected by aliskiren±HRP. Aliskiren increased rat renin expression in the renal cortex. This was associated with a decline in (P)RR and AT 1 receptor mRNA expression, and these changes were unaffected by HRP. Glomerular volume and interlobar arterial lumen diameter modestly increased in the aliskiren+HRP group, and were unaffected by aliskiren alone.

Conclusions HRP, when given on top of aliskiren in DM TGR(mREN2)27 rats worsens kidney damage and counteracts the beneficial effects of aliskiren. (P)RR blockade is therefore contraindicated in DM.

Abstract 197: Effects of a Stabile Angiotensin-(1-7) Analogue, Cyclic Angiotensin-(1-7), on Progenitor Cell Recruitment and Cardiac Remodeling

Objectives: In animal models, angiotensin-(1-7) treatment has beneficial effects improving cardiac function and remodeling after myocardial infarction (MI). Angiotensin-(1-7) might have a beneficial angiogenic effect after MI, since infusion increases the number of progenitor and VEGF+ cells in the heart. Angiotensin-(1-7) also promotes the in vitro differentiation of endothelial progenitor cells (EPC), and tube formation. For optimal clinical use, metabolically stable 4-Ser,7-Cys-thioether-bridged angiotensin-(1-7), called cyclic angiotensin-(1-7) (cAng-(1-7)), has been developed. We studied the effect of cAng-(1-7) treatment on progenitor cells recruitment and early cardiac remodeling after MI, with an emphasis on angiogenic properties.

Design and Methods: Angiogenic progenitor cell recruitment was measured 24 h after a bolus injection of 50 ug/kg cAng-(1-7) in healthy mice by flow cytometric counting of ckit+, sca-1+ and flk1+ cells in blood and bone marrow. In addition, mice underwent coronary ligation or sham surgery and either saline or 2.4 ug/kg/h cAng-(1-7). After 3 weeks of treatment, cardiac function was measured by intraluminal pressure catheter. Cardiac vascular density, fibrosis and myocyte dimensions were assessed. Furthermore, we studied the dose-related effects of normal and cAng-(1-7) on tube formation by HUVEC.

Results: cAng-(1-7) increased blood ckit+, sca-1+ and flk1+ cells, which tended to decrease in bone marrow. cAng-(1-7) reduced cardiomyocyte hypertrophy (476±99μm 2 vs 292±78μm 2 /cell) compared to saline, but showed no effect on heart weight, infarct size, fibrosis and vascular density. Cardiac contractile function was not improved by cAng-(1-7). Tube formation by HUVEC was reduced by cAng-(1-7) as well as by native Ang-(1-7).

Conclusions: Our results suggest that cAng-(1-7) given early after MI might not lead to improved angiogenesis, despite an increased recruitment of hematopoietic and endothelial-like cells from the bone marrow. This might explain why there is no swift beneficial effect of cAng-(1-7) on cardiac performance despite a reduction of myocyte hypertrophy. Further optimization of cAng-(1-7) treatment and evaluation of treatment lasting longer than 3 weeks will be necessary.

Compound 21 Induces Vasorelaxation via an Endothelium- and Angiotensin II Type 2 Receptor-Independent Mechanism

Angiotensin II type 2 (AT 2 ) receptor stimulation has been linked to vasodilation. Yet, AT 2 receptor-independent hypertension and hypotension (or no effect on blood pressure) have been observed in vivo after application of the AT 2 receptor agonist compound 21 (C21). We, therefore, studied its effects in vitro, using preparations known to display AT 2 receptor-mediated responses. Hearts of Wistar rats, spontaneously hypertensive rats (SHRs), C57Bl/6 mice, and AT 2 receptor knockout mice were perfused according to Langendorff. Mesenteric and iliac arteries of these animals, as well as coronary microarteries from human donor hearts, were mounted in Mulvany myographs. In the coronary vascular bed of Wistar rats, C57Bl/6 mice, and AT 2 receptor knockout mice, C21 induced constriction followed by dilation. SHR hearts displayed enhanced constriction and no dilation. Irbesartan (angiotensin II type 1 receptor blocker) abolished the constriction and enhanced or (in SHRs) reintroduced dilation, and PD123319 (AT 2 receptor blocker) did not block the latter. C21 relaxed preconstricted vessels of all species, and this did not depend on angiotensin II receptors, the endothelium, or the NO-guanylyl cyclase-cGMP pathway. C21 constricted SHR iliac arteries but none of the other vessels, and irbesartan prevented this. C21 shifted the concentration-response curves to U46619 (thromboxane A 2 analog) and phenylephrine (α-adrenoceptor agonist) but not ionomycine (calcium ionophore) to the right. In conclusion, C21 did not cause AT 2 receptor-mediated vasodilation. Yet, it did induce vasodilation by blocking calcium transport into the cell and constriction via angiotensin II type 1 receptor stimulation. The latter effect is enhanced in SHRs. These data may explain the varying effects of C21 on blood pressure in vivo.

Nucleotide excision DNA repair is associated with age-related vascular dysfunction

BACKGROUND

Vascular dysfunction in atherosclerosis and diabetes mellitus, as observed in the aging population of developed societies, is associated with vascular DNA damage and cell senescence. We hypothesized that cumulative DNA damage during aging contributes to vascular dysfunction.

METHODS AND RESULTS

In mice with genomic instability resulting from the defective nucleotide excision repair genes ERCC1 and XPD (Ercc1(d/-) and Xpd(TTD) mice), we explored age-dependent vascular function compared with that in wild-type mice. Ercc1(d/-) mice showed increased vascular cell senescence, accelerated development of vasodilator dysfunction, increased vascular stiffness, and elevated blood pressure at a very young age. The vasodilator dysfunction was due to decreased endothelial nitric oxide synthase levels and impaired smooth muscle cell function, which involved phosphodiesterase activity. Similar to Ercc1(d/-) mice, age-related endothelium-dependent vasodilator dysfunction in Xpd(TTD) animals was increased. To investigate the implications for human vascular disease, we explored associations between single-nucleotide polymorphisms of selected nucleotide excision repair genes and arterial stiffness within the AortaGen Consortium and found a significant association of a single-nucleotide polymorphism (rs2029298) in the putative promoter region of DDB2 gene with carotid-femoral pulse wave velocity.

CONCLUSIONS

Mice with genomic instability recapitulate age-dependent vascular dysfunction as observed in animal models and in humans but with an accelerated progression compared with wild-type mice. In addition, we found associations between variations in human DNA repair genes and markers for vascular stiffness, which is associated with aging. Our study supports the concept that genomic instability contributes importantly to the development of cardiovascular disease.

Aldosterone does not require angiotensin II to activate NCC through a WNK4-SPAK-dependent pathway

We and others have recently shown that angiotensin II can activate the sodium chloride cotransporter (NCC) through a WNK4–SPAK-dependent pathway. Because WNK4 was previously shown to be a negative regulator of NCC, it has been postulated that angiotensin II converts WNK4 to a positive regulator. Here, we ask whether aldosterone requires angiotensin II to activate NCC and if their effects are additive. To do so, we infused vehicle or aldosterone in adrenalectomized rats that also received the angiotensin receptor blocker losartan. In the presence of losartan, aldosterone was still capable of increasing total and phosphorylated NCC twofold to threefold. The kinases WNK4 and SPAK also increased with aldosterone and losartan. A dose-dependent relationship between aldosterone and NCC, SPAK, and WNK4 was identified, suggesting that these are aldosterone-sensitive proteins. As more functional evidence of increased NCC activity, we showed that rats receiving aldosterone and losartan had a significantly greater natriuretic response to hydrochlorothiazide than rats receiving losartan only. To study whether angiotensin II could have an additive effect, rats receiving aldosterone with losartan were compared with rats receiving aldosterone only. Rats receiving aldosterone only retained more sodium and had twofold to fourfold increase in phosphorylated NCC. Together, our results demonstrate that aldosterone does not require angiotensin II to activate NCC and that WNK4 appears to act as a positive regulator in this pathway. The additive effect of angiotensin II may favor electroneutral sodium reabsorption during hypovolemia and may contribute to hypertension in diseases with an activated renin–angiotensin–aldosterone system.

Handle region peptide counteracts the beneficial effects of the Renin inhibitor aliskiren in spontaneously hypertensive rats

To investigate whether the putative (pro)renin receptor blocker, the handle region peptide (HRP), exerts effects on top of the blood pressure-lowering and cardioprotective effects of the renin inhibitor aliskiren, spontaneously hypertensive rats were implanted with telemetry transmitters to monitor heart rate and mean arterial pressure (MAP). After a 2-week recovery period, vehicle, aliskiren, HRP (100 and 1 mg/kg per day, respectively), and HRP+aliskiren were infused for 3 weeks using osmotic minipumps. Subsequently, the heart was removed to study coronary function according to Langendorff. Baseline MAP and heart rate in vehicle-treated rats were 146±3 mm Hg and 326±4 bpm. HRP did not affect MAP, whereas aliskiren and HRP+aliskiren lowered MAP (by maximally 29±2 and 20±1 mm Hg, respectively) without affecting heart rate. Aliskiren significantly reduced MAP throughout the 3-week infusion period, whereas the blood pressure-lowering effect of HRP+aliskiren returned to baseline within 2 weeks of treatment. In comparison with vehicle, aliskiren increased the endothelium-dependent response to bradykinin and decreased the response to angiotensin II in the coronary circulation, whereas these responses were not altered after treatment with HRP or HRP+aliskiren. HRP did not alter plasma renin activity, plasma angiotensin levels, or the renal angiotensin content, either alone or on top of aliskiren, nor did it alter the aliskiren-induced decrease in renal Ang II type 1 receptor expression. Yet, it did reverse the aliskiren-induced reduction in cardiomyocyte area, without affecting this area when given alone. In conclusion, HRP counteracts the beneficial effects of aliskiren on blood pressure, coronary function, and cardiac hypertrophy in an angiotensin-independent manner.

Cardiac Renin levels are not influenced by the amount of resident mast cells

To investigate whether mast cells release renin in the heart, we studied renin and prorenin synthesis by such cells, using the human mast cell lines human mastocytoma 1 and LAD2, as well as fresh mast cells from mastocytosis patients. We also quantified the contribution of mast cells to cardiac renin levels in control and infarcted rat hearts. Human mastocytoma 1 cells contained and released angiotensin I-generating activity, and the inhibition of this activity by the renin inhibitor aliskiren was comparable to that of recombinant human renin. Prorenin activation with trypsin increased angiotensin I-generating activity in the medium only, suggesting release but not storage of prorenin. The adenylyl cyclase activator forskolin, the cAMP analogue 8-db-cAMP, and the degranulator compound 48/80 increased renin release without affecting prorenin. Angiotensin II blocked the forskolin-induced renin release. Angiotensin I-generating activity was undetectable in LAD2 cells and fresh mast cells. Nonperfused rat hearts contained angiotensin I-generating activity, and aliskiren blocked approximately 70% of this activity. A 30-minute buffer perfusion washed away >70% of the aliskiren-inhibitable angiotensin I-generating activity. Prolonged buffer perfusion or compound 48/80 did not decrease cardiac angiotensin I-generating activity further or induce angiotensin I-generating activity release in the perfusion buffer. Results in infarcted hearts were identical, despite the increased mast cell number in such hearts. In conclusion, human mastocytoma 1 cells release renin and prorenin, and the regulation of this release resembles that of renal renin. However, this is not a uniform property of all mast cells. Mast cells appear an unlikely source of renin in the heart, both under normal and pathophysiological conditions.

Cardiovascular phenotype of mice lacking all three subtypes of angiotensin II receptors

Angiotensin II activates two distinct receptors, the angiotensin II receptors type 1 (AT(1)) and type 2 (AT(2)). In rodents, two AT(1) subtypes were identified (AT(1a) and AT(1b)). To determine receptor-specific functions and possible angiotensin II effects independent of its three known receptors we generated mice deficient in either one of the angiotensin II receptors, in two, or in all three (triple knockouts). Triple knockouts were vital and fertile, but survival was impaired. Hypotension and renal histological abnormalities in triple knockouts were comparable to those in mice lacking both AT(1) subtypes. All combinations lacking AT(1a) were distinguished by reduced heart rate. AT(1a) deletion impaired the in vivo pressor response to angiotensin II bolus injection, whereas deficiency for AT(1b) and/or AT(2) had no effect. However, the additional lack of AT(1b) in AT(1a)-deficient mice further impaired the vasoconstrictive capacity of angiotensin II. Although general vasoconstrictor properties were not changed, angiotensin II failed to alter blood pressure in triple knockouts, indicating that there are no other receptors involved in direct angiotensin II pressor effects. Our data identify mice deficient in all three angiotensin II receptors as an ideal tool to better understand the structure and function of the renin-angiotensin system and to search for angiotensin II effects independent of AT(1) and AT(2).

Treprostinil in advanced experimental pulmonary hypertension: beneficial outcome without reversed pulmonary vascular remodeling

INTRODUCTION

Beneficial effects of treprostinil, a stable prostacyclin analogue, were demonstrated in patients with pulmonary arterial hypertension (PAH). Although regression of pulmonary vascular remodeling has been suggested as therapeutic mechanism, its mode of action remains unknown.

METHODS

Flow-associated PAH was created in rats by injection of monocrotaline (60 mg/kg) combined with an abdominal aortocaval shunt. Subsequently, rats were treated with subcutaneous treprostinil (50 ng/kg/min, treated; n = 8) or saline (untreated; n = 9). A control group underwent sham-surgery (n = 8). Animals were sacrificed at symptoms of cardiac failure, together with their matched controls.

RESULTS

Dyspnea and weight loss determined the moment of sacrifice in 8/9 untreated animals (89%) versus in one of eight treated animals (13%; log-rank test survival curves; P = 0.02). Mean pulmonary arterial pressure increased in the model (42 +/- 2 mm Hg in untreated vs. 18 +/- 1 in controls; P < 0.01) and decreased by 8 mm Hg after therapy (34 +/- 3 mm Hg, P = 0.04 vs. untreated). No effects of treatment on right ventricular hypertrophy could be demonstrated. Quantitative morphometry of pre- and intra-acinar pulmonary arteries revealed no effects of treatment on vessel histopathology.

CONCLUSIONS

Treprostinil treatment improved clinical course and ameliorated symptoms of heart failure in a model of advanced PAH. However, beneficial effects were not associated with reversed structural remodelling of the pulmonary vasculature.

Prostacyclin therapy increases right ventricular capillarisation in a model for flow-associated pulmonary hypertension

Pulmonary hypertension, and consequently right ventricular failure, complicates several congenital heart defects. Although intervention in the prostacyclin-thromboxane ratio is known to improve outcome, the underlying mechanism is not clear. Therefore, effects of acetyl salicylic acid and iloprost are studied in an animal model for flow-associated pulmonary hypertension. Male Wistar rats with flow-associated pulmonary hypertension, an aortocaval shunt in addition to monocrotaline induced pulmonary hypertension, were treated with low-dose aspirin (25 mg/kg/day) or iloprost (72 microg/kg/day). Effects on pulmonary hemodynamics and pulmonary vascular remodeling as well as right ventricular hemodynamics and remodeling were evaluated. Ninety percent (n=7/8) of the untreated pulmonary hypertensive rats developed dyspnea and pleural fluid, whereas this was seen in 50% (n=4/8, ns) and 10% (n=1/8, P<0.05 vs. untreated animals) of the aspirin and iloprost-treated rats, respectively. This could not be attributed to changes in pulmonary artery pressure, wall-lumen ratio of the pulmonary vasculature or right ventricular hypertrophy. However, both therapies restored reduced right ventricular capillary to myocyte ratio in pulmonary hypertensive rats (0.95+/-0.10 in untreated rats vs. 1.38+/-0.18 in control animals; P<0.05, and 1.32+/-0.11 in aspirin-treated and 1.29+/-0.9 in iloprost-treated rats; both P<0.05 vs. non-treated animals), which was associated with improved right ventricular contractility (iloprost). Thus, interventions in the prostacyclin-thromboxane metabolism improve outcome in rats with flow-associated pulmonary hypertension. However, these effects may be attributed to effects on cardiac rather than on pulmonary vascular remodeling.

O-acetylation of cryptococcal capsular glucuronoxylomannan is essential for interference with neutrophil migration

The capsular polysaccharide glucuronoxylomannan (GXM) of Cryptococcus neoformans has been shown to interfere with neutrophil migration. Although several receptors have been implied to mediate this process, the structural perspectives are unknown. Here, we assess the contribution of 6-O-acetylation and xylose substitution of the (1-->3)-alpha-d-mannan backbone of GXM, the variable structural features of GXM, to the interference with neutrophil migration. We compare chemically deacetylated GXM and acetyl- or xylose-deficient GXM from genetically modified strains with wild-type GXM in their ability to inhibit the different phases of neutrophil migration. Additionally, we verify the effects of de-O-acetylation on neutrophil migration in vivo. De-O-acetylation caused a dramatic reduction of the inhibitory capacity of GXM in the in vitro assays for neutrophil chemokinesis, rolling on E-selectin and firm adhesion to endothelium. Genetic removal of xylose only marginally reduced the ability of GXM to reduce firm adhesion. In vivo, chemical deacetylation of GXM significantly reduced its ability to interfere with neutrophil recruitment in a model of myocardial ischemia (65% reduction vs a nonsignificant reduction in tissue myeloperoxidase, respectively). Our findings indicate that 6-O-acetylated mannose of GXM is a crucial motive for the inhibition of neutrophil recruitment.

Pharmacological therapy can increase capillary density in post-infarction remodeled rat hearts

OBJECTIVE

Postinfarction hypertrophied hearts have been shown to display a lower capillary density and reduced mechanical efficiency amplified by tachycardia. We investigated whether pharmacological reduction of postinfarction tachycardia would induce capillary growth by treating myocardial infarcted (MI) rats with aspirin, methylprednisolone, moxonidine or captopril, during the first 3 weeks after infarction.

METHODS AND RESULTS

Effects on in vivo heart rate were measured in conscious unrestrained rats, while in vitro heart rate effects were evaluated in isolated perfused hearts. Compared to sham-rats, MI-rats manifested a significant in vivo as well as in vitro tachycardia (increase 9% and 20% vs. sham, respectively). Whereas aspirin, methylprednisolone and moxonidine significantly reduced postinfarction in vivo tachycardia, captopril rather increased in vivo heart rate. In vitro tachycardia of MI-hearts was reduced to sham-values with aspirin and methylprednisolone (P<0.05), but not with moxonidine and captopril. Capillary density defined as the number of Lectin stained capillaries per tissue area, which significantly decreased in MI-hearts (decrease 42% vs. sham), was restored by all treatments (P<0.05). Concentric left ventricular hypertrophy after MI, defined as increased cross-sectional area of transversally cut Gomori stained myocytes, was indicated by almost double myocyte size (P<0.05), while capillary to myocyte ratio remained unchanged. Methylprednisolone, moxonidine and captopril, but not aspirin, prevented hypertrophy (P<0.05). However, treatment with aspirin and methylprednisolone, but not moxonidine and captopril, increased capillary to myocyte ratio (P<0.05) up to twice the values of non-treated MI hearts, indicating newly formed capillaries.

CONCLUSIONS

The above findings confirm that post-MI pharmacological treatment can increase capillary density in the remodeled left ventricle. Whereas prevention of left ventricular hypertrophy normalizes capillary density without actually affecting capillary number, increased capillary to myocyte ratio (at preserved hypertrophic response) indicates actual capillary growth.

Chronic vasopressin V(1A) but not V(2) receptor antagonism prevents heart failure in chronically infarcted rats

Evidence is increasing that therapeutic modulation of neurohormonal activation with vasopressin receptor antagonists via V(1A) and V(2) receptors may favourably affect prognosis of heart failure. This study was designed to compare in vivo hemodynamic effects of early treatment (1-21 days after infarction) with a V(1A) (SR-49059 or ((2S)1-[(2R3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide); 0.3 mg/kg/day) and a V(2) (SR-121463B or (1-[4-(N-tert-Butylcarbamoyl)-2-methoxybenzene sulfonyl]-5-ethoxy-3-spiro-[4-(2-morpholinoethyoxy)-cyclo-hexane]indol-2one,furmate; 0.5 mg/kg/day) receptor antagonist in myocardial infarcted rats, chronically instrumented for hemodynamic measurements. Left ventricular dysfunction in conscious myocardial infarcted rats, which was evidenced by a significantly decreased cardiac output (myocardial infarction: 70+/-3 vs. sham: 81 +/- 3 ml/min) and stroke volume (myocardial infarction: 190 +/- 10 vs. sham: 221 +/- 7 microl), was restored by the vasopressin V(1A) (81+/-2 ml and 224 +/- 5 microl, respectively) but not V(2) receptor antagonist. Improved cardiac output with the vasopressin V(1A) receptor antagonist resulted from an increased stroke volume at a reduced myocardial infarction induced tachycardia. In addition to the hemodynamic measurements, left ventricular hypertrophy and capillary density were determined, histologically measured as the cross-sectional area of Gomori-stained myocytes and Lectin-stained capillaries per tissue area, respectively. The observed left ventricular concentric hypertrophy (myocardial infarction: 525 +/- 38 vs. sham: 347 +/- 28 microm(2); P < 0.05) and reduced capillary density (myocardial infarction: 2068 +/- 162 vs. sham: 2800 +/- 250 number/mm(2); P<0.05) in the spared myocardium of myocardial infarcted rats, remained unaffected by the vasopressin V(1A) or V(2) receptor antagonist. Thus, chronic vasopressin V(1A) but not V(2) receptor blockade prevents heart failure in 3-week-old infarcted rats. Moreover, the improved cardiac function could not attributed to changes in left ventricular hypertrophy and/or capillary density.

At 2 Receptor-Mediated Vasodilation in the Heart: Effect of Myocardial Infarction

P64

To investigate the functional consequences of the changes in AT 2 receptor density that have been reported following myocardial infarction (MI; Matsubara, Circ Res, 1998), three consecutive 10 min intravenous infusions of angiotensin (Ang) II (100, 300 and 1000 ng/kg/min) were given to 19 sham-operated and 16 coronary artery-ligated rats, at four weeks after surgery, pretreated with either saline, the AT 1 receptor antagonist irbesartan (100 μg/kg/min for 30 min), or the AT 2 receptor antagonist PD123319 (20 μg/kg/min for 30 min, followed by continuous infusion). Systemic and regional hemodynamic effects were studied using the radioactive microsphere method. Ang II induced comparable changes in sham and MI rats in mean arterial pressure (MAP; maximally +30±10% and +30±8%, resp., mean±SEM) and systemic vascular conductance (cardiac output/MAP, -27±8% and -32±5%, resp.). Cardiac output decreased in MI (-20±5%) but not in sham rats. Irbesartan decreased MAP by 34% (sham) and 22% (MI), increased SVC by 41% (sham) and 24% (MI), and blocked the Ang II-mediated systemic hemodynamic effects in both sham and MI rats, while PD123319 did not affect these parameters. Myocardial conductance at baseline was diminished in MI vs. sham rats (41±3 vs. 55±6 μl/min/mmHg, resp.), while renal conductance was comparable in both groups (168±9 vs. 156±18 μl/min/mmHg, resp.). Ang II increased myocardial conductance maximally to 56±3 (MI) and 72±3 (sham) μl/min/mmHg, and decreased renal conductance to 67±4 (MI) and 74±8 (sham) μl/min/mmHg. Irbesartan increased renal, but not myocardial, conductance in both groups and blocked the Ang II-mediated renal vasoconstriction. PD123319 did not affect renal or myocardial conductance and blocked the Ang II-mediated myocardial vasodilation in sham but not in MI rats. PD123319 did not affect the Ang II-mediated renal responses. In conclusion, Ang II increases myocardial, but not renal, conductance (i.e., induces vasodilation) via AT 2 receptor stimulation. The inability of PD123319 to block this response in MI rats suggests either an upregulation of AT 2 receptors or a role for non-AT 1 , non-AT 2 receptors in the infarcted heart.