Urotensin-II is a nitric oxide-dependent vasodilator in the pial arteries of the newborn pig

Transient Opening of the Blood-Brain Barrier by Vasoactive Peptides to Increase CNS Drug Delivery: Reality Versus Wishful Thinking?

BACKGROUND

The blood-brain barrier inhibits the central nervous system penetration of 98% of small molecule drugs and virtually all biologic agents, which has limited progress in treating neurologic disease. Vasoactive peptides have been shown in animal studies to transiently disrupt the blood-brain barrier and regadenoson is currently being studied in humans to determine if it can improve drug delivery to the brain. However, many other vasoactive peptides could potentially be used for this purpose.

METHODS

We performed a review of the literature evaluating the physiologic effects of vasoactive peptides on the vasculature of the brain and systemic organs. To assess the likelihood that a vasoactive peptide might transiently disrupt the blood-brain barrier, we devised a four-tier classification system to organize the available evidence.

RESULTS

We identified 32 vasoactive peptides with potential blood-brain barrier permeabilityaltering properties. To date, none of these are shown to open the blood-brain barrier in humans. Twelve vasoactive peptides increased blood-brain barrier permeability in rodents. The remaining 20 had favorable physiologic effects on blood vessels but lacked specific information on permeability changes to the blood-brain barrier.

CONCLUSION

Vasoactive peptides remain an understudied class of drugs with the potential to increase drug delivery and improve treatment in patients with brain tumors and other neurologic diseases. Dozens of vasoactive peptides have yet to be formally evaluated for this important clinical effect. This narrative review summarizes the available data on vasoactive peptides, highlighting agents that deserve further in vitro and in vivo investigations.

Urotensin II: an inflammatory cytokine

Urotensin II (UII) is a polypeptide molecule with neurohormone-like activity. It has been confirmed that UII is widely distributed in numerous organs of different animal species from fish to mammals, including humans. The UII receptor is orphan G-protein coupled receptor 14, also known as UT. The tissue distribution of UII and UT is highly consistent, and their expression may be regulated by autocrine and paracrine mechanisms. In the body, UII has many physiological and pathophysiological activities, such as vasoconstrictor and vasodilatory actions, cell proliferation, pro-fibrosis, neuroendocrine activity, insulin resistance, and carcinogenic and inflammatory effects, which have been recognized only in recent years. In fact, UII is involved in the process of inflammatory injury and plays a key role in the onset and development of inflammatory diseases. In this paper, we will review the roles UII plays in inflammatory diseases.

A new therapeutic approach to erectile dysfunction: urotensin-II receptor high affinity agonist ligands

Urotensin-II (U-II) is a cyclic peptide that acts through a G protein-coupled receptor (urotensin-II receptor [UTR]) mainly involved in cardiovascular function in humans. The urotensinergic system is also implicated in the urogenital tract. Indeed, U-II relaxes human corpus cavernosum strips and causes an increase in intracavernous pressure (ICP) in rats. In light of this, the U-II/UTR pathway can be considered a new target for the treatment of erectile dysfunction. On this hypothesis, herein we report on two new UTR high affinity-agonists, P5U (H-Asp-c[Pen-Phe-Trp-Lys-Tyr-Cys]-Val-OH) and UPG84(H-Asp-c[Pen-Phe-DTrp-Orn-(pNH₂) Phe-Cys]-Val-OH). The effects of P5U and UPG84 were each compared separately with U-II by monitoring the ICP in anesthetized rats. Intracavernous injection of U-II (0.03–1 nmol), P5U (0.03–1 nmol) or UPG84 (0.03–1 nmol) caused an increase in ICP. P5U, in particular, elicited a significant increase in ICP as compared to U-II. The observed effect by using P5U at a dose of 0.1 nmol per rat was comparable to the effect elicited by U-II at a dose of 0.3 nmol. Moreover, UPG84 at the lowest dose (0.03 nmol) showed an effect similar to the highest dose of U-II (1 nmol). Furthermore, UPG84 was found to be more effective than P5U. Indeed, while the lowest dose of P5U (0.03 nmol) did not affect the ICP, UPG84, at the same dose, induced a prominent penile erection in rat. These compounds did not modify the blood pressure, which indicates a good safety profile. In conclusion, UPG84 and P5U may open new perspectives for the management of erectile dysfunction.

Expression of Urotensin II During Focal Cerebral Ischemic in Diabetic Rats

BACKGROUND

The objective of this study was to explore the expression of urotensin II (UII), its receptor (GPR14), and vascular endothelial growth factor (VEGF), as well as their associations in the ischaemic brains of rats with focal cerebral ischaemia, under normal and diabetic conditions.

METHODS

Diabetes mellitus (DM) was induced by injection of streptozotocin (STZ) into Sprague - Dawley rats. Focal cerebral ischaemia was induced by middle cerebral artery occlusion (MCAO) four weeks after DM onset by STZ. Rats (n=80) were divided into four groups: normal control, DM, MCAO, and DM/MCAO. Immunohistochemistry and reverse-transcriptase-polymerase chain reaction (RT-PCR) were used to detect the expression of UII, GPR14 and VEGF in the diabetic and ischaemic brain.

RESULTS

Expression of UII and GPR14 was increased at mRNA and protein levels in the DM and MCAO group compared with controls. In the DM/MCAO group, expression of UII and GPR14 was increased significantly in the ischaemic brain, and was accompanied by a significantly increased VEGF expression.

CONCLUSION

Diabetes mellitus was seen to aggravate brain lesions after ischaemia, and UII may have an important role.

Potential Clinical Implications of the Urotensin II Receptor Antagonists

Urotensin II (UII) binds to its receptor, UT, playing an important role in the heart, kidneys, pancreas, adrenal gland, and central nervous system. In the vasculature, it acts as a potent endothelium-independent vasoconstrictor and endothelium-dependent vasodilator. In disease states, however, this constriction–dilation equilibrium is disrupted. There is an upregulation of the UII system in heart disease, metabolic syndrome, and kidney failure. The increase in UII release and UT expression suggest that UII system may be implicated in the pathology and pathogenesis of these diseases by causing an increase in acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) activity leading to smooth muscle cell proliferation and foam cell infiltration, insulin resistance (DMII), as well as inflammation, high blood pressure, and plaque formation. Recently, UT antagonists such as SB-611812, palosuran, and most recently a piperazino-isoindolinone based antagonist have been developed in the hope of better understanding the UII system and treating its associated diseases.

Urotensin II alters vascular reactivity in animals subjected to volume overload

Congestive heart failure (CHF) alters vascular reactivity and up regulates in urotensin II (UTII), a potent vasoactive peptide. The aim of this study was to investigate the interaction between CHF and UTII in altering vascular reactivity in a rat model of volume overload heart failure. Animals were divided into 4 groups: control, UTII infused (UTII), volume overload only (VO) or volume overload+UTII (VO+UTII). Volume overload was established by the formation of an aortocaval fistula. Following fistula formation animals were administered UTII at a rate of 300 pmol/kg/h for 4 weeks subcutaneously with mini-osmotic pumps. Thoracic aorta rings, with/without endothelium, were subjected to cumulative dose-responses to phenylephrine, sodium nitroprusside (SNP), acetylcholine (ACH), UTII, and the Rho-kinase inhibitor HA-1077. Aortas from VO animals exhibited increased sensitivity to phenylephrine and UTII with a decreased relaxation response to ACH and HA-1077. Aortas from animals subjected to chronic UTII with volume overload (VO + UTII) retained their sensitivity to phenylephrine and UTII while they improved their relaxation to HA-1077 but not ACH. The constrictive response to UTII was dose-dependent and augmented at concentrations <0.01 μM in VO animals. The changes in vascular reactivity paralleled an elevation of both the UTII and α(1A)-adrenergic receptor while the Rho and Rho-kinase signalling proteins were diminished. We found that volume overload increased sensitivity to the vasoconstrictor agents that was inversely related to changes in the Rho-kinase expression. The addition of UTII with VO reversed the constrictive vascular response through alterations in the Rho-kinase signalling pathway.

Role of urotensin II in health and disease

Urotensin II (UII) is an 11 amino acid cyclic peptide originally isolated from the goby fish. The amino acid sequence of UII is exceptionally conserved across most vertebrate taxa, sharing structural similarity to somatostatin. UII binds to a class of G protein-coupled receptor known as GPR14 or the urotensin receptor (UT). UII and its receptor, UT, are widely expressed throughout the cardiovascular, pulmonary, central nervous, renal, and metabolic systems. UII is generally agreed to be the most potent endogenous vasoconstrictor discovered to date. Its physiological mechanisms are similar in some ways to other potent mediators, such as endothelin-1. For example, both compounds elicit a strong vascular smooth muscle-dependent vasoconstriction via Ca2+ release. UII also exerts a wide range of actions in other systems, such as proliferation of vascular smooth muscle cells, fibroblasts, and cancer cells. It also 1) enhances foam cell formation, chemotaxis of inflammatory cells, and inotropic and hypertrophic effects on heart muscle; 2) inhibits insulin release, modulates glomerular filtration, and release of catecholamines; and 3) may help regulate food intake and the sleep cycle. Elevated plasma levels of UII and increased levels of UII and UT expression have been demonstrated in numerous diseased conditions, including hypertension, atherosclerosis, heart failure, pulmonary hypertension, diabetes, renal failure, and the metabolic syndrome. Indeed, some of these reports suggest that UII is a marker of disease activity. As such, the UT receptor is emerging as a promising target for therapeutic intervention. Here, a concise review is given on the vast physiologic and pathologic roles of UII.

Norfloxacin treatment for clinically significant portal hypertension: results of a randomised double-blind placebo-controlled crossover trial

BACKGROUND

While selective intestinal decontamination (SID) can alter the hyperdynamic circulatory state of cirrhosis, the impact of SID on portal pressure remains unclear especially in the setting of clinically significant portal hypertension.

AIMS

To examine the impact of SID with norfloxacin on portal pressure in subjects with clinically significant portal hypertension and explore the potential mechanisms by which norfloxacin exerts its haemodynamic effects.

METHODS

Randomised, double blind, placebo-controlled, crossover trial of norfloxacin 400 mg twice daily for 4 weeks. The portal pressure was assessed by hepatic venous pressure gradient (HVPG). Endotoxaemia was assessed by the Limulus amebocyte lysate (LAL) assay. l-arginine (l-Arg) transporter function was assessed in peripheral blood mononuclear cells (PBMCs). Plasma levels of urotensin II (UII) and tumour necrosis factor were measured before and after therapy.

RESULTS

Sixteen subjects with clinically significant portal hypertension (16.5+/-1.1 mmHg) completed the study. Norfloxacin therapy was not superior to placebo in reducing HVPG (13.8+/-1.0 mmHg vs 13.6+/-1.2 mmHg, P=0.3). Furthermore, no alteration in l-Arg transport was detected after 4 weeks of norfloxacin therapy. Plasma UII levels correlated positively with HVPG (P=0.01) and the Child-Pugh score (P<0.05). However, UII levels following therapy did not parallel HVPG changes.

CONCLUSIONS

Norfloxacin is not superior to placebo in reducing HVPG in subjects with clinically significant portal hypertension. Furthermore, norfloxacin does not appear to modulate the l-Arg transporter mechanism in this patient population. Although plasma UII correlates positively with HVPG, UII does not appear to have a direct role in modulating HVPG.

Urotensin II in cardiovascular regulation

Cardiovascular function is modulated by neuronal transmitters, circulating hormones, and factors that are released locally from tissues. Urotensin II (UII) is an 11 amino acid peptide that stimulates its' obligatory G protein coupled urotensin II receptors (UT) to modulate cardiovascular function in humans and in other animal species, and has been implicated in both vasculoprotective and vasculopathic effects. For example, tissue and circulating concentrations of UII have been reported to increase in some studies involving patients with atherosclerosis, heart failure, hypertension, preeclampsia, diabetes, renal disease and liver disease, raising the possibility that the UT receptor system is involved in the development and/or progression of these conditions. Consistent with this hypothesis, administration of UT receptor antagonists to animal models of cardiovascular disease have revealed improvements in cardiovascular remodelling and hemodynamics. However, recent studies have questioned this contributory role of UII in disease, and have instead postulated a protective effect on the cardiovascular system. For example, high concentrations of circulating UII correlated with improved clinical outcomes in patients with renal disease or myocardial infarction. The purpose of this review is to consider the regulation of the cardiovascular system by UII, giving consideration to methodologies for measurement of plasma concentrations, sites of synthesis and triggers for release.

Biological properties and functional determinants of the urotensin II receptor

The urotensin II receptor (UT) is a member of the G protein-coupled receptor (GPCR) family and binds the cyclic undecapeptide urotensin II (U-II) as well as the octapeptide urotensin II-related peptide (URP). The active UT mediates pleiotropic effects through various signal transduction pathways, including coupling to G proteins and activating the mitogen-activated protein kinase pathway. Several highly conserved residues and motifs of class A GPCRs that are important for activity are found in UT. This review highlights some of the putative roles of these motifs in the binding, activation and desensitization of UT.

Cardiorenovascular effects of urotensin II and the relevance of the UT receptor

Urotensin II (U-II) is a vasoactive peptide with many potent effects in the cardiorenovascular system. U-II activates a G-protein-coupled receptor termed UT. UT and U-II are highly expressed in the cardiovascular and renal system. Patients with various cardiovascular diseases show high U-II plasma levels. It was demonstrated that elevated U-II plasma levels and increased UT expression seem to play a role in heart failure, end-stage renal disease and atherosclerosis. U-II induces potent changes in vascular tone regulation. In addition, U-II stimulates vascular smooth muscle cell proliferation and cardiomyocyte hypertrophy. Currently several pharmaceutical companies are developing compounds to control the U-II/UT system. There are preclinical and some clinical studies showing potential benefits of inhibiting U-II function in renal disease, heart failure, and diabetes. This article will review both pre- and clinical data concerning cardiorenovascular effects of U-II.

Urotensin II in chronic liver disease: in vivo effect on vascular tone

OBJECTIVE

Urotensin II (UII) is now recognized as the most potent human vasoconstrictor. Although its role in human pathophysiology is unknown, vasoactive mediators are known to be important in the pathogenesis of portal hypertension complicating chronic liver disease. The objective of this study was to investigate the role of UII in liver cirrhosis via examination of the in vivo effect of UII in this patient group.

MATERIAL AND METHODS

The vasoactive effects of UII were measured using Laser Doppler velocimetry on cirrhotic patients (n = 14) and age-matched healthy controls (n = 14) after UII administration by iontophoresis to the cutaneous microcirculation of the forearm.

RESULTS

In vivo administration of UII produced vasoconstriction of the cutaneous microcirculation in the cirrhotic group and vasodilatation in the controls, with values differing significantly at the two highest doses of UII: 10(-9) mol (p = 0.01) and 10(-7) mol (p = 0.004).

CONCLUSIONS

UII mediates vasoconstriction of the microcirculation of cirrhotics but not of controls. This suggests that UII has pathophysiological relevance in the portal hypertensive population through its vasoactive properties. Further studies of UII and UII-antagonists are warranted in this patient population.