Increase of cortical cerebral blood flow and further cerebral microcirculatory effects of Serelaxin in a sheep model

Abstract

Serelaxin, recombinant human relaxin-2, modulates endothelial vasodilatory functionality and is under evaluation for treatment of acute heart failure. Little is known about acute effects on cerebral perfusion. We tested the hypothesis that Serelaxin might also have effects on the cerebral microcirculation in a sheep model, which resembles human brain structure quite well. We used laser Doppler flowmetry and sidestream dark-field (SDF) imaging techniques, which are reliable tools to continuously assess dynamic changes in cerebral perfusion. Laser Doppler flowmetry shows that bolus injection of 30 g Serelaxin/kg body wt induces an increase (P ϭ 0.006) to roughly 150% of cortical cerebral blood flow (CBF), whereas subcortical CBF remains unchanged (P ϭ 0.688). The effects on area-dependent CBF were significantly different after the bolus injection (P ϭ 0.042). Effects on cortical CBF were further confirmed by SDF imaging. The bolus injection of Serelaxin increased total vessel density to 127% (P ϭ 0.00046), perfused vessel density to 145% (P ϭ 0.024), and perfused capillary density to 153% (P ϭ 0.024). Western blotting confirmed the expression of relaxin receptors RXFP1 and truncated RXFP2-variants in the respective brain regions, suggesting a possible contribution of RXFP1 on the effects of Serelaxin. In conclusion, the injection of a high dose of Serelaxin exerts quick effects on the cerebral microcirculation. Therefore, Serelaxin might be suitable to improve cortical microcirculation and exert neuroprotective effects in clinically relevant scenarios that involve cortical hypoperfusion. These findings need to be confirmed in relevant experimental settings involving cerebral cortical hypoperfusion and can possibly be translated into clinical practice. RELAXIN-2 IS A HUMAN HORMONE that mediates cardiovascular adaptations during pregnancy and particularly systemic and renal vasodilatation (7). Moreover, these effects are observed in nonpregnant animals and in ex vivo studies following the artificial administration of the substance as well (33). An intravenous bolus injection of a recombinant form of human relaxin-2, Serelaxin (Novartis Pharma, Basel, Switzerland), modulates a sustained endothelial vasodilatory function. Serelaxin mediates systemic hemodynamic changes and increases renal blood flow through a fall in systemic intravascular resistance with a concomitant increase in arterial compliance (15,22,31,38,39). In the RELAX-AHF study, cardiovascular and all-cause mortality was reduced 37% in patients treated with Serelaxin (42). Furthermore, initial positive studies on the cerebral effects of this peptide hormone in a stroke model (47) and in a high blood pressure situation (6) have already been published. Serelaxin induces a nitric oxide-mediated vasodilatation (40) and can particularly reduce the infarction size of the cerebral cortex, suggesting a neuroprotective effect (47).Nonetheless, studies on the influence of Serelaxin on the cerebral blood flow (CBF) have not been performed to this day. Moreover, desp...

Altered Cerebral Blood Flow and Potential Neuroprotective Effect of Human Relaxin-2 (Serelaxin) During Hypoxia or Severe Hypovolemia in a Sheep Model

“…A molecular weight of approximately 85 kDa for the higher molecular weight band detected by the anti-human RXFP1-antibody corresponds to the full-length receptor. An additional band of approximately 65 kDa was detected with the anti-RXFP1 antibody, which was not seen in a previous study using brain samples not enriched for blood vessels [11]. For RXFP2, only bands with lower molecular masses (70 and 55 kDa) than the expected 85 kDa were detectable, which is consistent with the findings of the aforementioned study [11].…”

“…An additional band of approximately 65 kDa was detected with the anti-RXFP1 antibody, which was not seen in a previous study using brain samples not enriched for blood vessels [11]. For RXFP2, only bands with lower molecular masses (70 and 55 kDa) than the expected 85 kDa were detectable, which is consistent with the findings of the aforementioned study [11]. For all RXFP variants, significantly higher amounts were detected in brain vessel samples from the subcortex as compared with the cortex (Figure 9B).…”

“…Moreover, serelaxin induces nitric-oxide-mediated vasodilatation [7] and can particularly reduce the infarction size in the cerebral cortex [8][9][10]. Furthermore, an intravenous bolus injection of serelaxin modulates sustained endothelial vasodilatory function and increases cerebral blood flow (CBF) in sheep [11]. All of the above-mentioned findings suggest a neuroprotective effect of relaxin-2/serelaxin.…”

Redistribution of Cerebral Blood Flow during Severe Hypovolemia and Reperfusion in a Sheep Model: Critical Role of α1-Adrenergic Signaling

“…Therefore, we used it in the sheep model, which provides more similarities to the human situation than small animals like rodents do [30]. Obviously, studies with a design similar to that which we used, i.e., massive blood removal, cannot be done in human subjects for ethical reasons.…”

“…3rd branches of region specific arterioles were snap frozen in liquid nitrogen. Sample preparation and Western blotting protocol were described previously [30]. Briefly, an affinity-purified antibody raised against a peptide conserved in all human and sheep α1-adrenergic receptors (α1-ARs) was used for detection of proteins (rabbit anti-pan-α1-AR; 1:1000; Acris Antibodies, Herford, Germany).…”