Mast cell chymase in the ischemic kidney of severe unilateral renovascular hypertension

A case of primary aldosteronism with excessive secretion of renin that was unmasked by kidney transplantation

A 42-year-old man showed marked hypokalemia after kidney transplantation. He was diagnosed with hypertension and suffered from acute myocardial infarction at 33 and 38 years of age. At 40 years of age, hemodialysis was introduced. A left adrenal tumor was noted and suspected as a non-functional adrenal adenoma at that time. Therefore, he received a living-donor kidney transplant at 42 years of age. After kidney transplantation, the serum creatinine level dropped. His blood pressure remained high, and the serum potassium level decreased. The PRA and PAC were elevated, and ARR was not elevated. Based on the results of various confirmatory tests and vein sampling, he was diagnosed with excessive secretion of renin from the native kidneys that was complicated by primary aldosteronism (PA), and left nephrectomy and adrenalectomy were performed. The overproduction of aldosterone in the resected adrenal adenoma and over secretion of renin in the kidney with arteriolosclerosis were immunohistologically confirmed. After surgery, the PAC decreased, but the PRA did not decrease. The postoperative serum potassium level improved, and the blood pressure was well controlled with a small dose of medication. This is the first reported case of PA with hyperreninemia after kidney transplantation. It should be noted that PA in dialysis patients and kidney transplant recipients may not fulfill the usual diagnostic criteria of an elevated ARR. In such patients, PA should be suspected based on the absolute value of the PAC and responsiveness to ACTH stimulation, and adrenal and renal vein sampling is required for a definitive diagnosis.

PTRA is useful for renal artery angina by atherosclerotic plaque rupture with unilateral functioning kidney

We report a case of acute ischemic nephropathy in a patient with severe renal artery stenosis and bradycardia due to sick sinus syndrome. An 83-year-old Japanese woman with a history of hypertension was diagnosed with sick sinus syndrome and scheduled for pacemaker implantation. Four days prior to admission for the procedure, she experienced sudden-onset severe right flank pain that persisted for 1 day. On the day of admission, her serum creatinine level increased from 1.35 mg/dL, measured 2 weeks earlier, to 7.04 mg/dL. Laboratory examinations showed elevated C-reactive protein and lactate dehydrogenase levels. A computed tomography scan showed a severely atrophied left kidney, suggesting that it was non-functioning. Doppler ultrasonography of the right renal artery showed an extended acceleration time, suggesting proximal stenosis. Magnetic resonance imaging showed no enhancement in the proximal portions of the right renal artery, consistent with severe stenosis or occlusion. The patient developed severe bradycardia with lightheadedness; as a result, pacemaker implantation was performed on post-admission day 7. On day 10, digital subtraction angiography revealed diffuse severe stenosis of the right renal artery; intravascular ultrasonography suggested plaque rupture. Percutaneous transluminal renal angioplasty (PTRA) was performed and a drug-eluting stent was placed. On day 11, hemodialysis was performed owing to deteriorating renal function. The patient's renal function dramatically improved shortly thereafter. This case highlights the importance of PTRA for select patients, as it can potentially save some patients from chronic dialysis, and outlines the possible implications of bradycardia in the pathogenesis of ischemic nephropathy.

Chymase Dependent Pathway of Angiotensin II Generation and Rapeseed Derived Peptides for Antihypertensive Treatment of Spontaneously Hypertensive Rats

The contribution of chymase, one of the enzymes responsible for angiotensin II generation in non-ACE pathway, remains unclear in the development of hypertension. The aim of the study was to investigate chymase inhibition as potential antihypertensive therapy in spontaneously hypertensive rats (SHR). To block chymase we employed chymostatin, a commercial inhibitor, and new analogues of rapeseed-derived peptides, VWIS and RIY. These simple and easy to obtain peptides not only block chymase, but also possess weak activity to inhibit ACE. This is a first attempt to evaluate the impact of chronic administration of selected inhibitors on blood pressure of SHR in two phases of hypertension. Male SHR (6 or 16 weeks old) were treated daily for two weeks with chymostatin (CH; 2 mg/kg/day), the peptides VWIS (12.5 mg/kg/day) or RIY (7.5 mg/kg/day); control groups received chymostatin solvent (0.15% DMSO in saline) or peptide solvent (saline). The substances were administered intravenously to conscious animals via a chronically cannulated femoral vein. Systolic blood pressure (SBP) was measured by telemetry. Metabolic parameters were measured weekly, and tissue samples were harvested after two weeks of treatment. None of the administered chymase inhibitors affected the development of hypertension in young rats. Only RIY exhibited beneficial properties when administered in the established phase of hypertension: SBP decreased from 165 ± 10 to 157 ± 7 mmHg while the excretion of nitric oxide metabolites increased significantly. The glomerulosclerosis index was lower after RIY treatment in both age groups (significant only in young rats 0.29 ± 0.05 vs 0.48 ± 0.04 in the control group; p < 0.05). Hence, it seems that peptide RIY exhibits some positive effect on renal morphology. The results obtained suggest that the peptide RIY may be a useful tool in the treatment of hypertension, especially in cases when ACE inhibitors are not effective.

Mast cell proteases as pharmacological targets

Mast cells are rich in proteases, which are the major proteins of intracellular granules and are released with histamine and heparin by activated cells. Most of these proteases are active in the granule as well as outside of the mast cell when secreted, and can cleave targets near degranulating mast cells and in adjoining tissue compartments. Some proteases released from mast cells reach the bloodstream and may have far-reaching actions. In terms of relative amounts, the major mast cell proteases include the tryptases, chymases, cathepsin G, carboxypeptidase A3, dipeptidylpeptidase I/cathepsin C, and cathepsins L and S. Some mast cells also produce granzyme B, plasminogen activators, and matrix metalloproteinases. Tryptases and chymases are almost entirely mast cell-specific, whereas other proteases, such as cathepsins G, C, and L are expressed by a variety of inflammatory cells. Carboxypeptidase A3 expression is a property shared by basophils and mast cells. Other proteases, such as mastins, are largely basophil-specific, although human basophils are protease-deficient compared with their murine counterparts. The major classes of mast cell proteases have been targeted for development of therapeutic inhibitors. Also, a human β-tryptase has been proposed as a potential drug itself, to inactivate of snake venins. Diseases linked to mast cell proteases include allergic diseases, such as asthma, eczema, and anaphylaxis, but also include non-allergic diseases such as inflammatory bowel disease, autoimmune arthritis, atherosclerosis, aortic aneurysms, hypertension, myocardial infarction, heart failure, pulmonary hypertension and scarring diseases of lungs and other organs. In some cases, studies performed in mouse models suggest protective or homeostatic roles for specific proteases (or groups of proteases) in infections by bacteria, worms and other parasites, and even in allergic inflammation. At the same time, a clearer picture has emerged of differences in the properties and patterns of expression of proteases expressed in human mast cell subsets, and in humans versus other mammals. These considerations are influencing prioritization of specific protease targets for therapeutic inhibition, as well as options of pre-clinical models, disease indications, and choice of topical versus systemic routes of inhibitor administration.

Targets of chymase inhibitors

INTRODUCTION

Chymase converts angiotensin I to angiotensin II and it can also convert precursors of TGF-β and MMP-9 to their active forms. Therefore, diseases related to angiotensin II TGF-β, and MMP-9 could potentially be treated with chymase inhibitors.

AREAS COVERED

This review discusses the appropriate targets and safety of chymase inhibitors. Six diseases with notable mortality or morbidity as targets of chymase inhibitors are focused on; abdominal aortic aneurysms (AAAs), nephropathy and retinopathy, cardiomyopathy, nonalcoholic steatohepatitis (NASH), organ fibrosis and intestinal diseases.

EXPERT OPINION

If chymase inhibition proves to be a useful strategy for the attenuation of angiotensin II, TGF-β and MMP-9 in vivo, the application of chymase inhibitors is likely to become widespread in various diseases in the clinical setting. Chymase inhibitors are anticipated not to interfere with the homeostasis of resting tissues, that is, those not affected by injury or inflammation.

An emerging role of mast cells in cerebral ischemia and hemorrhage

Mast cells (MCs) are perivascularly located resident cells of hematopoietic origin, recognized as effectors in inflammation and immunity. Their subendothelial location at the boundary between the intravascular and extravascular milieus, and their ability to rapidly respond to blood- and tissue-borne stimuli via release of potent vasodilatatory, proteolytic, fibrinolytic, and proinflammatory mediators, render MCs with a unique status to act in the first-line defense in various pathologies. We review experimental evidence suggesting a role for MCs in the pathophysiology of brain ischemia and hemorrhage. In new-born rats, MCs contributed to brain damage in hypoxic-ischemic insults. In experimental cerebral ischemia/reperfusion, MCs regulated permeability of the blood-brain barrier, brain edema formation, and the intensity of local neutrophil infiltration. MCs were reported to play a role in the tissue plasminogen activator-mediated cerebral hemorrhages after experimental ischemic stroke, and to be involved in the expansion of hematoma and edema following intracerebral hemorrhage. Importantly, the MC-stabilizing drug cromoglycate inhibited MC-mediated adverse effects on brain pathology and improved survival of experimental animals. This brings us to a position to consider MC stabilization as a novel initial adjuvant therapy in the prevention of brain injuries in hypoxia-ischemia in new-borns, as well as in ischemic stroke and intracerebral hemorrhage in adults.

Effect of acetaldehyde upon cathepsin G and chymase. NRAS implications

Hypertension is commonly observed in alcoholics. Both the renin-angiotensin system (RAS) and the non-renin-angiotensin system (NRAS) have been implicated in the dynamics of blood pressure maintenance. In bilaterally nephrectomized rats, acetaldehyde has been reported to enhance the generation of the rate-limiting angiotensin I (ANG I) in the plasma, and in humans it inhibits the activity of several angiotensinases (A, B, and M) in the serum, thereby promoting a hypertensive set of reactions. We report here the results of a study on the effect of acetaldehyde upon cathepsin G and mast cell chymase. Acetaldehyde enhanced cathepsin G activity at all of the concentrations tested between 11.2 and 223.5 mM in a statistically significant manner. Since cathepsin G is one of several enzymes transforming ANG I into ANG II and is also capable of cleaving ANG II directly from angiotensinogen, we suggest that alcoholism, which will generate exogenous acetaldehyde from ingested alcohol, may be a contributory factor for an elevated cathepsin G activity and, consequently, hypertension via the NRAS. Chymase activity also is elevated in the presence of 440 mM acetaldehyde and diminished in the presence of 27 mM acetaldehyde. Since both enzymes also degrade ANG II, the degradative effects of each enzyme on ANG II may neutralize one another.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Inflammatory cells in renal injury and repair

Renal inflammation may result from a myriad of insults and often is characterized by the presence of infiltrating inflammatory leukocytes within the glomerulus or tubulointerstitium. Accumulating evidence indicates that infiltrating leukocytes are key players in the induction of renal injury. Although renal inflammation often is followed by the development of fibrosis with loss of renal function, it can resolve. Resolution may be spontaneous as in poststreptococcal glomerulonephritis or after the administration of effective treatment such as immunosuppressive agents. The mechanisms and cells underlying the resolution process and the exact temporal sequence remains uncertain at present but likely involves the removal of injurious leukocytes, the down-regulation of immune responses, and the alteration of the phenotype of infiltrating macrophages from proinflammatory to prorepair. In this review we examine the role of leukocytes in both renal inflammation and repair.

Renal Protective Effects of the Renin-Angiotensin-Aldosterone System Blockade: From Evidence-Based Approach to Perspectives

The renin-angiotensin-aldosterone system (RAAS) blockade is currently the best-documented treatment strategy to delay the progression of chronic nephropathies. Angiotensin-converting enzyme inhibitors (CEIs) or angiotensin II type 1 receptor antagonists (ARBs) should be used in every normotensive and hypertensive patient with chronic proteinuric nephropathy of both diabetic and non-diabetic origin. The therapy should be initiated as early as possible, bearing in mind that the renoprotection is more effective if used before overt proteinuria or a reduction in kidney function is present. The therapy should be offered to all patients, regardless of renal function, as well as to subjects with severely impaired glomerular filtration. CEIs and ARBs should be administered in therapeutic doses as high as possible to achieve maximal possible proteinuria reduction and systemic blood pressure target <130/80 mm Hg, and 125/75 mm Hg in those subjects with renal insufficiency who present with proteinuria above 1 g/24 h. The combined therapy with the concomitant use of CEIs and ARBs should be offered to all patients with proteinuric non-diabetic chronic nephropathies who do not achieve full and persistent remission of proteinuria with CEI or ARB alone. The article reviews an evidence-based approach on the use of RAAS-inhibiting agents in kidney diseases, considers treatment strategies in different clinical situations and discusses some perspectives related to the implementation of the RAAS blockade in renal protection.