Reversible renal impairment induced by treatment with the angiotensin II receptor antagonist candesartan in a patient with bilateral renal artery stenosis

Nonatherosclerotic Renovascular Hypertension

Renovascular hypertension (RVH) is a secondary form of high blood pressure resulting from impaired blood flow to the kidneys with subsequent activation of the renin-angiotensin-aldosterone system. Often, this occurs due to abnormally small, narrowed, or blocked blood vessels supplying one or both kidneys (ie: renal artery occlusive disease) and is correctable. Juxtaglomerular cells release renin in response to decreased pressure, which in turn catalyzes the cleavage of circulating angiotensinogen synthesized by the liver to the decapeptide angiotensin I. Angiotensin-converting enzyme then cleaves angiotensin I to form the octapeptide angiotensin II, a potent vasopressor and the primary effector of renin-induced hypertension. The effects of angiotensin II are mediated by signaling downstream of its receptors. Angiotensin receptor type 1 is a G-protein-coupled receptor that activates vasoconstrictor and mitogenic signaling pathways resulting in peripheral arteriolar vasoconstriction and increased renal tubular reabsorption of sodium and water which promotes intravascular volume expansion. Angiotensin II stimulates the adrenal cortical release of aldosterone, which promotes renal tubular sodium reabsorption, resulting in volume expansion. Angiotensin II acts on glial cells and regions of the brain responsible for blood pressure regulation increasing renal sympathetic activation. Angiotensin II simulates the release of vasopressin from the pituitary which stimulates thirst and water reabsorption from the kidney to expand the intravascular volume and cause peripheral vasoconstriction (increased sympathetic tone). All of these mechanisms coalesce to increase arterial pressure by way of arteriolar constriction, enhanced cardiac output, and the retention of sodium and water.

Current and Emerging Classes of Pharmacological Agents for the Management of Hypertension

Cardiovascular disease accounts for more than 17 million deaths globally every year, of which complications of hypertension account for 9.4 million deaths worldwide. Early detection and management of hypertension can prevent costly interventions, including dialysis and cardiac surgery. Non-pharmacological approaches for managing hypertension commonly involve lifestyle modification, including exercise and dietary regulations such as reducing salt and fluid intake; however, a majority of patients will eventually require antihypertensive medications. In 2020, the International Society of Hypertension published worldwide guidelines in its efforts to reduce the global prevalence of raised blood pressure (BP) in adults aged 18 years or over. Currently, several classes of medications are used to control hypertension, either as mono- or combination therapy depending on the disease severity. These drug classes include those that target the renin-angiotensin-aldosterone system (RAAS) and adrenergic receptors, calcium channel blockers, diuretics and vasodilators. While some of these classes of medications have shown significant benefits in controlling BP and reducing cardiovascular mortality, the prevalence of hypertension remains high. Significant efforts have been made in developing new classes of drugs that lower BP; these medications exert their therapeutic benefits through different pathways and mechanism of actions. With several of these emerging classes in phase III clinical trials, it is hoped that the discovery of these novel therapeutic avenues will aid in reducing the global burden of hypertension.

Acute renal injury after partial hepatectomy

Currently, partial hepatectomy is the treatment of choice for a wide variety of liver and biliary conditions. Among the possible complications of partial hepatectomy, acute kidney injury (AKI) should be considered as an important cause of increased morbidity and postoperative mortality. Difficulties in the data analysis related to postoperative AKI after liver resections are mainly due to the multiplicity of factors to be considered in the surgical patients, moreover, there is no consensus of the exact definition of AKI after liver resection in the literature, which hampers comparison and analysis of the scarce data published on the subject. Despite this multiplicity of risk factors for postoperative AKI after partial hepatectomy, there are main factors that clearly contribute to its occurrence. First factor relates to large blood losses with renal hypoperfusion during the operation, second factor relates to the occurrence of post-hepatectomy liver failure with consequent distributive circulatory changes and hepatorenal syndrome. Eventually, patients can have more than one factor contributing to post-operative AKI, and frequently these combinations of acute insults can be aggravated by sepsis or exposure to nephrotoxic drugs.

[Orally active aminopeptidase A inhibitors reduce blood pressure: a new strategy for treating hypertension]

The hyperactivity of the brain renin-angiotensin system (RAS) has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. Among the main bioactive peptides of the brain RAS, angiotensin (Ang) II and Ang III display the same affinity for type 1 and type 2 Ang II receptors. Both peptides, injected intracerebroventricularly, similarly increase arginine vasopressin release and blood pressure (BP); however, because Ang II is converted in vivo to Ang III, the identity of the true effector is unknown. We first identified the enzymes involved in the metabolism of brain angiotensins and developed specific and selective inhibitors. Here we review new insights into the predominant role of brain Ang III in the control of BP, underlining the fact that brain aminopeptidase A (APA), the enzyme generating brain Ang III, may therefore be an interesting candidate target for the treatment of hypertension. This justifies the development of potent systemically active APA inhibitors, such as RB150, as prototypes of a new class of antihypertensive agents for the treatment of certain forms of hypertension.

Central antihypertensive effects of orally active aminopeptidase A inhibitors in spontaneously hypertensive rats

Brain renin-angiotensin system hyperactivity has been implicated in the development and maintenance of hypertension. We reported previously in the brain that aminopeptidase A and aminopeptidase N are involved in the metabolism of angiotensin II and angiotensin III, respectively. By using in vivo specific and selective aminopeptidase A and aminopeptidase N inhibitors, we showed that angiotensin III is one of the main effector peptides of the brain renin-angiotensin system, exerting a tonic stimulatory control more than blood pressure in hypertensive rats. Aminopeptidase A, the enzyme generating brain angiotensin III, thus represents a potential target for the treatment of hypertension. We demonstrated here the antihypertensive effects of RB150, a prodrug of the specific and selective aminopeptidase A inhibitor, EC33, in spontaneously hypertensive rats, a model of human essential hypertension. Oral administration of RB150 in conscious spontaneously hypertensive rats inhibited brain aminopeptidase A activity, demonstrating the central bioavailability of RB150 and its ability to generate EC33 into the brain. Oral RB150 treatment dose-dependently reduced blood pressure in spontaneously hypertensive rats with an ED(50) of 30 mg/kg, lasting for several hours. This decrease in blood pressure is partly attributed to a decrease in sympathetic tone, reducing vascular resistance. This treatment did not modify systemic renin-angiotensin system activity. Concomitant oral administration of RB150 with a systemic renin-angiotensin system blocker, enalapril, potentiated the RB150-induced blood pressure decrease achieved in <2 hours. Thus, RB150 may be the prototype of a new class of centrally active antihypertensive agents that might be used in combination with classic systemic renin-angiotensin system blockers to improve blood pressure control.

The role of the brain renin-angiotensin system in hypertension: implications for new treatment

Hypertension affects 26% of adults and is in constant progress related to increased incidence of obesity and diabetes. One-third of hypertensive patients may be successfully treated with one antihypertensive agent, one-third may require two agents and in the remaining patients will need three agents for effective blood pressure (BP) control. The development of new classes of antihypertensive agents with different mechanisms of action therefore remains an important goal. Brain renin-angiotensin system (RAS) hyperactivity has been implicated in hypertension development and maintenance in several types of experimental and genetic hypertension animal models. Among the main bioactive peptides of the brain RAS, angiotensin (Ang) II and Ang III have similar affinities for type 1 (AT1) and type 2 (AT2) Ang II receptors. Following intracerebroventricular (i.c.v.) injection, Ang II and Ang III similarly increase arginine-vasopressin (AVP) release and BP. Blocking the brain RAS may be advantageous as it simultaneously (1) decreases sympathetic tone and consequently vascular resistance, (2) decreases AVP release, reducing blood volume and vascular resistance and (3) blocks angiotensin-induced baroreflex inhibition, decreasing both vascular resistance and cardiac output. However, as Ang II is converted to Ang III in vivo, the exact nature of the active peptide is not precisely determined. We summarize here the main findings identifying AngIII as one of the major effector peptides of the brain RAS in the control of AVP release and BP. Brain AngIII exerts a tonic stimulatory effect on BP in hypertensive rats, identifying brain aminopeptidase A (APA), the enzyme generating brain Ang III, as a potentially candidate target for hypertension treatment. This has led to the development of potent orally active APA inhibitors, such as RB150--the prototype of a new class of centrally acting antihypertensive agents.

Angiotensin inhibition in renovascular disease: a population-based cohort study

BACKGROUND

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers effectively reduce blood pressure in patients with renovascular disease (RVD); yet, randomized cardiovascular prevention trials of these drugs typically exclude individuals with this condition.

PATIENTS AND METHODS

We studied the association of renin-angiotensin system inhibition with prognosis in a population-based cohort comprising 3,570 patients with RVD in Ontario, Canada; slightly more than half (n = 1,857, 53%) were prescribed angiotensin inhibitors. The primary outcome was the composite of death, myocardial infarction, or stroke. Secondary outcomes included individual cardiovascular and renal events.

RESULTS

Patients receiving angiotensin inhibitors had a significantly lower risk for the primary outcome during follow-up (10.0 vs 13.0 events per 100 patient-years at risk, multivariable adjusted hazard ratio [HR] 0.70, 95% CI 0.59-0.82). In addition, hospitalization for congestive heart failure (HR 0.69, 95% CI 0.53-0.90), chronic dialysis initiation (HR 0.62, 95% CI 0.42-0.92), and mortality (HR 0.56, 95% CI 0.47-0.68) was lower in treated patients. Conversely, patients receiving angiotensin inhibitors were significantly more likely to be hospitalized for acute renal failure during follow-up (HR 1.87, 95% CI 1.05-3.33; 1.2 vs 0.6 events per 100 patient-years at risk).

CONCLUSIONS

These data emphasize the high vascular risk of RVD and suggest that angiotensin inhibitors may improve prognosis in this setting at the expense of acute renal toxicity. If the latter are selected in the management of RVD, renal function parameters should be assiduously followed.

Orally active aminopeptidase A inhibitors reduce blood pressure: a new strategy for treating hypertension

Overactivity of the brain renin-angiotensin system has been implicated in the development and maintenance of hypertension. We reported previously that angiotensin II is converted to angiotensin III by aminopeptidase A in the mouse brain. We then used specific and selective aminopeptidase A inhibitors to show that angiotensin III is one of the main effector peptides of the brain renin-angiotensin system, exerting tonic stimulatory control over blood pressure in hypertensive rats. Aminopeptidase A, the enzyme generating brain angiotensin III, thus represents a potential candidate central nervous system target for the treatment of hypertension. Given this possible clinical use of aminopeptidase A inhibitors, it was, therefore, important to investigate their pharmacological activity after oral administration. We investigated RB150, a dimer of the selective aminopeptidase A inhibitor, EC33, generated by creating a disulfide bond. This chemical modification allows prodrug to cross the blood-brain barrier when administered by systemic route. Oral administration of RB150 in conscious DOCA-salt rats inhibited brain aminopeptidase A activity, resulting in values similar to those obtained with the brains of normotensive rats, demonstrating the central bioavailability of RB150. Oral RB150 treatment resulted in a marked dose-dependent reduction in blood pressure in DOCA-salt but not in normotensive rats, with an ED(50) in the 1-mg/kg range, achieved in <2 hours and lasting for several hours. This treatment also significantly decreased plasma arginine-vasopressin levels and increased diuresis, which may participate to the blood pressure decrease by reducing the size of fluid compartment. Thus, RB150 may be the prototype of a new class of centrally active antihypertensive agents.

Jacques Benoit lecture: the neuroendocrine view of the angiotensin and apelin systems

The hyperactivity of the brain renin-angiotensin system (RAS) has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. Among the main bioactive peptides of the brain RAS, angiotensin (Ang) II and Ang III display the same affinity for type 1 and type 2 Ang II receptors. Both peptides, injected intracerebroventricularly, similarly increase arginine vasopressin (AVP) release and blood pressure (BP); however, because Ang II is converted in vivo to Ang III, the identity of the true effector is unknown. We review new insights into the predominant role of brain Ang III in the control of BP, underlining the fact that brain aminopeptidase A (APA), the enzyme generating brain Ang III, may therefore be an interesting candidate target for the treatment of hypertension. This justifies the development of potent systemically active APA inhibitors, such as RB150, as prototypes of a new class of antihypertensive agents for the treatment of certain forms of hypertension. We also searched for a putative angiotensin receptor subtype specific for Ang III and isolated a seven transmembrane-domain G protein-coupled receptor corresponding to the receptor for apelin, a newly-discovered peptide isolated from bovine stomach. Apelin and its receptor are expressed in magnocellular vasopressinergic neurones in the hypothalamus. The central injection of apelin in lactating rats decreases the phasic electrical activity of vasopressinergic neurones and the systemic secretion of AVP, inducing water diuresis. Apelin is therefore a natural inhibitor of the antidiuretic effect of AVP. In addition, systemic administration of apelin decreases BP, improves cardiac contractility and reduces cardiac loading. The development of nonpeptide agonists of the apelin receptor may provide new therapeutic tools for treating water retention, hyponatraemia and cardiovascular diseases. Angiotensins and apelin thus exert opposing but complementary effects, and are thereby determinant for the maintenance of body fluid homeostasis and cardiovascular functions.

Aminopeptidase A inhibitors as centrally acting antihypertensive agents

Among the main bioactive peptides of the brain renin-angiotensin system, angiotensin (Ang) II and AngIII exhibit the same affinity for the type 1 and type 2 Ang receptors. Both peptides, injected intracerebroventricularly, cause similar increase in blood pressure (BP). Because AngII is converted in vivo to AngIII, the identity of the true effector is unknown. This review summarized recent insights into the predominant role of brain AngIII in the central control of BP underlining the fact that brain aminopeptidase A (APA), the enzyme forming central AngIII, could constitute a putative central therapeutic target for the treatment of hypertension. This led to the development of potent, systematically active APA inhibitors, such as RB150, as a prototype of a new class of centrally acting antihypertensive agents for the treatment of certain forms of hypertension.

Brain renin-angiotensin system blockade by systemically active aminopeptidase A inhibitors: a potential treatment of salt-dependent hypertension

The hyperactivity of the brain renin-angiotensin system (RAS) has been implicated in the development and maintenance of hypertension in several types of experimental and genetic hypertension animal models. We previously reported that in the murine brain, aminopeptidase A (APA) is involved in the conversion of angiotensin II (AngII) to AngIII and that AngIII is one of the main effector peptides of the brain RAS in the control of vasopressin release. Here we report that brain AngIII exerts a tonic stimulatory effect on blood pressure in a model of salt-dependent hypertension, the DOCA-salt rat, characterized by a depressed systemic but a hyperactive brain RAS. Similar high blood pressure accompanied by a low systemic renin state was described in some patients, especially in hypertensive African Americans who are resistant to treatment by blockers of the systemic RAS. We developed RB150, a prodrug of the specific and selective APA inhibitor, EC33. RB150 given i.v. is able to cross the blood-brain barrier, to inhibit brain APA, and to block the formation of central AngIII. A single dose of systemic RB150 (15 mg/kg, i.v.) in conscious DOCA-salt rats inhibited brain APA activity and markedly reduced blood pressure for up to 24 h. These results demonstrate the crucial role of brain APA as a candidate target for the treatment of hypertension and suggest that RB150, a potent systemically active APA inhibitor, could be the prototype of a new class of antihypertensive agents for the treatment of certain forms of hypertension.

Acute Renal Failure Secondary to Angiotensin II Receptor Blockade in a Patient with Bilateral Renal Artery Stenosis

A 54-year-old man with diabetes mellitus, peripheral vascular disease, and hypertension was admitted to the hospital for an acute exacerbation of chronic heart failure. Therapy with intravenous furosemide and oral losartan 100 mg twice/day was begun. Ten days later, the patient's blood urea nitrogen and serum creatinine levels rose and peaked at 110 and 6.0 mg/dl, respectively. His serum potassium level increased to 5.7 mg/dl, urine output dropped to 400 ml over 24 hours, and mental status changes occurred. Magnetic resonance angiography revealed bilateral renal artery stenosis. After losartan was discontinued and hemodialysis was performed for 3 consecutive days, the patient's renal function returned to his baseline level. Reports in the medical literature reinforce the importance of recognizing that angiotensin-converting enzyme inhibitors should be used with caution in patients with bilateral renal artery stenosis. However, the literature is not as definitive about using of angiotensin II receptor blockers (ARBs) in these patients. Our patient's experience suggests that ARBs should be used with caution in patients with bilateral renal artery stenosis. Clinicians should be aware that renal failure might occur when using ARBs in these patients.

Urological manifestations of vascular disease

We have detailed several of the urological manifestations of vascular disease. With the aging of the North American population, urologists will encounter the urological complications of vascular disease with ever-increasing frequency.