Effects of calcium channel blockade on angiotensin II-induced peritubular ischemia in rats

Mucin-fused myeloid-derived growth factor (MYDGF164) exhibits a prolonged half-life and alleviates fibrosis in CKD

BACKGROUND AND PURPOSE

Currently, no effective therapy is available to completely stop or reverse CKD progression targeting its key feature, loss of peritubular capillaries (PTCs) leading to interstitial fibrosis, while Myeloid-derived growth factor (MYDGF) with tissue-repairing activities enlightened its therapeutic potential. However, the extremely short circulatory lifetime (15 minutes) restricts its applications.

EXPERIMENTAL APPROACH

We selected a tandem repeated (TR) region of human CD164 as a carrier to fuse with MYDGF and investigated the biophysical and pharmacokinetic changes. The MYDGF164 bioactivities were validated in HUVECs and assessed in HK-2 cells. Then, we investigated its efficacy in unilateral ureteral obstruction (UUO)-treated mice and adenine-induced CKD rats.

KEY RESULTS

MYDGF164 was intensively modified with sialoglycans, improving its resistance to serum proteases and increasing hydrodynamic radius. The half-life of MYDGF164 was significantly prolonged. MYDGF164 retained the original cell proliferation, anti-apoptosis, and tubulogenesis activities. It selectively stimulated the proliferation in endothelial and epithelial cells through phosphorylating MAPK1/3. MYDGF164 alleviated capillary rarefaction, hypoxia, renal fibrosis, and tubular atrophy in the UUO mice and adenine-induced CKD rats. Moreover, MYDGF164 restored renal function with normalized creatinine and urea levels in adenine-induced CKD rats. Histopathology and immunohistochemistry results revealed that the protection of MYDGF164 was related to its cell-proliferative, anti-apoptosis, and angiogenesis activities.

CONCLUSIONS AND IMPLICATIONS

This study is the first successful example of using a tandem repeated region of hCD164 as a cargo protein for the pharmacokinetic improvement of therapeutic proteins. Our findings also suggest the potential of MYDGF164 in alleviating renal fibrosis in CKD.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Angiotensin II-induced hypertension in rats is only transiently accompanied by lower renal oxygenation

Activation of the renin-angiotensin system may initiate chronic kidney disease. We hypothesised that renal hypoxia is a consequence of hemodynamic changes induced by angiotensin II and occurs prior to development of severe renal damage. Male Sprague-Dawley rats were infused continuously with angiotensin II (350 ng/kg/min) for 8 days. Mean arterial pressure (n = 5), cortical (n = 6) and medullary (n = 7) oxygenation (pO₂) were continuously recorded by telemetry and renal tissue injury was scored. Angiotensin II increased arterial pressure gradually to 150 ± 18 mmHg. This was associated with transient reduction of oxygen levels in renal cortex (by 18 ± 2%) and medulla (by 17 ± 6%) at 10 ± 2 and 6 ± 1 hours, respectively after starting infusion. Thereafter oxygen levels normalised to pre-infusion levels and were maintained during the remainder of the infusion period. In rats receiving angiotensin II, adding losartan to drinking water (300 mg/L) only induced transient increase in renal oxygenation, despite normalisation of arterial pressure. In rats, renal hypoxia is only a transient phenomenon during initiation of angiotensin II-induced hypertension.

Hypertension: a problem of organ blood flow supply-demand mismatch

This review introduces a new hypothesis that sympathetically mediated hypertensive diseases are caused, in the most part, by the activation of visceral afferent systems that are connected to neural circuits generating sympathetic activity. We consider how organ hypoperfusion and blood flow supply–demand mismatch might lead to both sensory hyper-reflexia and aberrant afferent tonicity. We discuss how this may drive sympatho-excitatory-positive feedback and extend across multiple organs initiating, or at least amplifying, sympathetic hyperactivity. The latter, in turn, compounds the challenge to sufficient organ blood flow through heightened vasoconstriction that both maintains and exacerbates hypertension.

Azelnidipine inhibits cultured rat aortic smooth muscle cell death induced by cyclic mechanical stretch

Acute aortic dissection is the most common life-threatening vascular disease, with sudden onset of severe pain and a high fatality rate. Clarifying the detailed mechanism for aortic dissection is of great significance for establishing effective pharmacotherapy for this high mortality disease. In the present study, we evaluated the influence of biomechanical stretch, which mimics an acute rise in blood pressure using an experimental apparatus of stretching loads in vitro, on rat aortic smooth muscle cell (RASMC) death. Then, we examined the effects of azelnidipine and mitogen-activated protein kinase inhibitors on mechanical stretch-induced RASMC death. The major findings of the present study are as follows: (1) cyclic mechanical stretch on RASMC caused cell death in a time-dependent manner up to 4 h; (2) cyclic mechanical stretch on RASMC induced c-Jun N-terminal kinase (JNK) and p38 activation with peaks at 10 min; (3) azelnidipine inhibited RASMC death in a concentration-dependent manner as well as inhibited JNK and p38 activation by mechanical stretch; and (4) SP600125 (a JNK inhibitor) and SB203580 (a p38 inhibitor) protected against stretch-induced RASMC death; (5) Antioxidants, diphenylene iodonium and tempol failed to inhibit stretch-induced RASMC death. On the basis of the above findings, we propose a possible mechanism where an acute rise in blood pressure increases biomechanical stress on the arterial walls, which induces RASMC death, and thus, may lead to aortic dissection. Azelnidipine may be used as a pharmacotherapeutic agent for prevention of aortic dissection independent of its blood pressure lowering effect.

Calcium channel blocker enhances beneficial effects of an angiotensin II AT1 receptor blocker against cerebrovascular-renal injury in type 2 diabetic mice

Recent clinical trials have demonstrated that combination therapy with renin-angiotensin system inhibitors plus calcium channel blockers (CCBs) elicits beneficial effects on cardiovascular and renal events in hypertensive patients with high cardiovascular risks. In the present study, we hypothesized that CCB enhances the protective effects of an angiotensin II type 1 receptor blocker (ARB) against diabetic cerebrovascular-renal injury. Saline-drinking type 2 diabetic KK-A^y mice developed hypertension and exhibited impaired cognitive function, blood-brain barrier (BBB) disruption, albuminuria, glomerular sclerosis and podocyte injury. These brain and renal injuries were associated with increased gene expression of NADPH oxidase components, NADPH oxidase activity and oxidative stress in brain and kidney tissues as well as systemic oxidative stress. Treatment with the ARB, olmesartan (10 mg/kg/day) reduced blood pressure in saline-drinking KK-A^y mice and attenuated cognitive decline, BBB disruption, glomerular injury and albuminuria, which were associated with a reduction of NADPH oxidase activity and oxidative stress in brain and kidney tissues as well as systemic oxidative stress. Furthermore, a suppressive dose of azelnidipine (3 mg/kg/day) exaggerated these beneficial effects of olmesartan. These data support the hypothesis that a CCB enhances ARB-associated cerebrovascular-renal protective effects through suppression of NADPH oxidase-dependent oxidative stress in type 2 diabetes.

Angiotensin II blockade and renal protection

Current national guidelines have recommended the use of renin-angiotensin system inhibitors, including angiotensin II type 1 receptor blockers (ARBs), in preference to other antihypertensive agents for treating hypertensive patients with chronic kidney disease. However, the mechanisms underlying the renoprotective effects of ARBs are multiple and complex. Blood pressure reduction by systemic vasodilation with an ARB contributes to its beneficial effects in treating kidney disease. Furthermore, ARB-induced renal vasodilation results in an increase in renal blood flow, leading to improvement of renal ischemia and hypoxia. ARBs are also effective in reducing urinary albumin excretion through a reduction in intraglomerular pressure and the protection of glomerular endothelium and/or podocyte injuries. In addition to blocking angiotensin II-induced renal cell and tissue injuries, ARBs can decrease intrarenal angiotensin II levels by reducing proximal tubular angiotensinogen and production of collecting duct renin, as well as angiotensin II accumulation in the kidney. In this review, we will briefly summarize our current understanding of the pharmacological effects of an ARB in the kidney. We will also discuss the possible mechanisms responsible for the renoprotective effects of ARBs on type 2 diabetic nephropathy.

Renal oxygen content is increased in healthy subjects after angiotensin-converting enzyme inhibition

OBJECTIVE

The association between renal hypoxia and the development of renal injury is well established. However, no adequate method currently exists to non-invasively measure functional changes in renal oxygenation in normal and injured patients.

METHOD

R2* quantification was performed using renal blood oxygen level-dependent properties. Five healthy normotensive women (50 ± 5.3 years) underwent magnetic resonance imaging in a 1.5T Signa Excite HDx scanner (GE Healthcare, Waukesha, WI). A multiple fast gradient-echo sequence was used to acquire R2*/T2* images (sixteen echoes from 2.1 ms/slice to 49.6 ms/slice in a single breath hold per location). The images were post-processed to generate R2* maps for quantification. Data were recorded before and at 30 minutes after the oral administration of an angiotensin II-converting enzyme inhibitor (captopril, 25 mg). The results were compared using an ANOVA for repeated measurements (mean + standard deviation) followed by the Tukey test. ClinicalTrials.gov: NCT01545479.

RESULTS

A significant difference (p<0.001) in renal oxygenation (R2*) was observed in the cortex and medulla before and after captopril administration: right kidney, cortex = 11.08 ± 0.56 ms, medulla = 17.21 ± 1.47 ms and cortex = 10.30 ± 0.44 ms, medulla = 16.06 ± 1.74 ms, respectively; and left kidney, cortex= 11.79 ± 1.85 ms, medulla = 17.03 ± 0.88 ms and cortex = 10.89 ± 0.91 ms, medulla = 16.43 ± 1.49 ms, respectively.

CONCLUSIONS

This result suggests that the technique efficiently measured alterations in renal blood oxygenation after angiotensin II-converting enzyme inhibition and that it may provide a new strategy for identifying the early stages of renal disease and perhaps new therapeutic targets.

Additive antioxidative effects of azelnidipine on angiotensin receptor blocker olmesartan treatment for type 2 diabetic patients with albuminuria

The present study aimed to determine whether either of two calcium channel blockers affected urinary albumin excretion or urinary levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) and liver-type fatty acid-binding protein (L-FABP) in hypertensive diabetic patients with chronic kidney disease (CKD) who were already being treated with maximum doses of the angiotensin II receptor blocker olmesartan. We conducted an open-label, randomized, parallel-controlled study on type 2 diabetic patients with stable glycemic control who were receiving fixed doses of antidiabetic agents. The patients received either 8 mg per day azelnidipine, which was increased up to 16 mg per day (azelnidipine group; n=34), or 2.5 mg per day amlodipine, which was increased up to 5 mg per day (amlodipine group; n=33), over a 24-week period. Mean systolic and diastolic blood pressure decreased significantly in both groups, but there was no significant difference between the two groups at the end of the study. Serum creatinine levels and estimated glomerular filtration rate did not differ significantly between the two groups, whereas the urinary albumin/creatinine ratio and 8-OHdG and L-FABP levels decreased significantly in the azelnidipine group compared with the amlodipine group. Plasma aldosterone level was significantly decreased in the azelnidipine group, and its changes correlated significantly with those of urinary 8-OHdG and L-FABP. Our results suggest that the addition of azelnidipine to the maximal recommended dose of olmesartan was more effective in reducing albuminuria and oxidant stress in hypertensive diabetic patients with CKD than the addition of amlodipine.

Mineralocorticoid receptor blockade and calcium channel blockade have different renoprotective effects on glomerular and interstitial injury in rats

We hypothesized that combination treatment with the mineralocorticoid receptor antagonist eplerenone and the calcium channel blocker amlodipine elicits better renoprotective effects than monotherapy with either drug, via different mechanisms in Dahl salt-sensitive (DS) hypertensive rats. DS rats were fed a high-salt diet (4% NaCl) for 10 wk and were treated with vehicle ( n = 12), eplerenone (50 mg·kg−1·day−1, po, n = 12), amlodipine (3 mg·kg−1·day−1, po, n = 12), or eplerenone plus amlodipine ( n = 12) after 2 wk of salt feeding. Vehicle-treated DS rats developed proteinuria, which was attenuated by eplerenone or amlodipine. Interestingly, eplerenone attenuated the glomerulosclerosis and podocyte injury, but amlodipine did not. Conversely, treatment with amlodipine markedly improved interstitial fibrosis, while the effect of eplerenone was minimal. Combination treatment markedly improved proteinuria, glomerulosclerosis, podocyte injury, and interstitial fibrosis in DS rats. Renal hypoxia estimated by pimonidazole, vascular endothelial growth factor expression, and density of peritubular endothelial cells was exacerbated by salt feeding. Amlodipine, either as monotherapy or in combination, ameliorated the renal hypoxia, whereas eplerenone treatment had no effect. In conclusion, both eplerenone and amlodipine attenuated renal injuries in high salt-fed DS rats, but the targets for renoprotection differed between these two drugs, with eplerenone predominantly acting on glomeruli and amlodipine acting on interstitium. The combination of eplerenone and amlodipine improved renal injury more effectively than either monotherapy in high salt-fed DS rats, presumably by achieving their own renoprotective effects.

Combination therapy with renin-angiotensin system inhibitors and the calcium channel blocker azelnidipine decreases plasma inflammatory markers and urinary oxidative stress markers in patients with diabetic nephropathy

A calcium channel blocker (CCB), azelnidipine (AZ), is reported to inhibit oxidative stresses, particularly when administered under blockade of the renin-angiotensin system (RAS). The purpose of this study was to investigate whether AZ inhibits oxidative stresses more potently than other CCBs under blockade of RAS and exerts renoprotection in type 2 diabetic nephropathy. Subjects were hypertensive type 2 diabetics with nephropathy, taking RAS inhibitors. The patients were randomly assigned to two groups, an AZ group (n=21, 16 mg/d) and a nifedipine-CR (NF) group (n=17, 40 mg/d). The plasma levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), high-sensitive C-reactive protein (hsCRP), adiponectin and tumor necrosis factor-alpha (TNF(alpha)), the urinary excretion of 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)) and 8-hydroxydeoxyguanosine (8-OHdG), and the urinary albumin-to-creatinine ratios (ACR) were determined before and after 16-week treatment. Neither metabolic parameters nor blood pressure levels differed between the two groups not only at baseline but also after the treatment. However, significant decreases in MCP-1, IL-6, hsCRP, TNF(alpha), 8-epi-PGF(2alpha), 8-OHdG and ACR levels, and a significant increase in the plasma adiponectin level were detected in the AZ group, but not in the NF group. The % change in the urinary oxidative stress markers correlated with that in ACR. Our results indicate that, in hypertensive patients with diabetic nephropathy, a combination therapy of RAS inhibitors and AZ is an effective therapeutic modality for decreasing not only blood pressure but also inflammations and oxidative stresses.

Renal ischemia and reperfusion injury: influence of chorpromazine on renal function and lipid peroxidation

PURPOSE: To evaluate the influence of chlorpromazine (CPZ) on renal function and lipid peroxidation in a rat model of kidney ischemia/reperfusion injury. METHODS: Forty eight Wistar rats underwent a laparotomy for hilar clamping of left kidney with a bulldog clamp for 60 minutes followed by organ reperfusion and contralateral nephrectomy. Of these, 26 received 3mg/kg of CPZ intravenously 15 minutes before renal ischemia (G-E) while the remaining 22 were used as ischemic control group (G-C). Eleven rats of G-E and 8 of G-C were followed for blood urea nitrogen and creatinine determinations before renal ischemia and at 1st, 4th and 7th postoperative days. Samplings of left renal tissue were obtained at 5 minutes (5 rats from each group) and 24 hours (9 G-C and 10 of G-E) of reperfusion for malondialdehy (MDA) content determination. Controls of renal MDA content were determined in kidneys harvested from 6 additional normal rats. RESULTS: Acute renal failure occurred in all animals but levels of BUN and creatinine were significantly lower in G-E (p<0.001). MDA content rose strikingly at 5 minutes of reperfusion in both groups (p>0.05) and returned near to normal levels 24 hours later. CONCLUSION: CPZ conferred partial protection of renal function to kidneys submitted to ischemia/reperfusion injury that seems to be not dependent on inhibition of lipid peroxidation.

Azelnidipine reduces urinary protein excretion and urinary liver-type fatty acid binding protein in patients with hypertensive chronic kidney disease

BACKGROUND

Hypoxia plays a significant role in the pathogenesis and progression of chronic renal disease. Urinary liver-type fatty acid binding protein (L-FABP) levels reflect the clinical prognosis of chronic renal disease. The calcium channel blocker azelnidipine has anti-oxidative properties and these may contribute to the beneficial effects of this drug. The aim of the present study was to determine whether azelnidipine and/or amlodipine affected urinary protein excretion or the urinary levels of 8-OHdG and L-FABP in hypertensive patients with mild chronic kidney disease (CKD).

METHODS

Thirty moderately hypertensive chronic kidney disease patients were randomly assigned to 2 treatment groups: azelnidipine 16 mg once daily or amlodipine 5 mg once daily. Treatment was continued for 6 months. Urinary protein excretion and urinary levels of 8-OHdG and urinary L-FABP were measured before 3 and 6 months after the treatment period.

RESULTS

Both drugs exhibited comparable and significant effects on the systolic and diastolic blood pressure. Azelnidipine decreased heart rate significantly after 3 and 6 months whereas amlodipine increased it significantly after 3 and 6 months. Urinary protein excretion, urinary 8-OHdG and urinary L-FABP levels decreased significantly after 3 months (p < 0.05) and 6 months (p < 0.05) in the azelnidipine group. In contrast, amlodipine showed little effect on urinary protein excretion or the urinary levels of 8-OHdG and L-FABP throughout the experimental period.

CONCLUSIONS

Azelnidipine is renoprotective in hypertensive patients with mild CKD and this action is, at least in part, due to the anti-oxidative effect.

Angiotensin-induced hypoxia in the kidney: functional and structural changes of the renal circulation

Recent studies emphasize the role of chronic hypoxia in the kidney as a final common pathway to end-stage renal disease (ESRD). Hypoxia of tubular cells leads to apoptosis or epithelial-mesenchymal transdifferentiation. This in turn exacerbates fibrosis of the kidney with loss of peritubular capillaries and subsequent chronic hypoxia, setting in train a vicious cycle whose end point is ESRD. To support this notion, our studies utilizing various techniques such as hypoxia-sensing transgenic rats revealed hypoxia of the kidney in various disease models. While fibrotic kidneys with advanced renal disease are devoid of peritubular capillary blood supply and oxygenation to the corresponding region, imbalances in vasoactive substances and associated intrarenal vasoconstriction can cause chronic hypoxia even at the early phase of kidney disease. Among various vasoactive substances, local activation of RAS is especially important because it can lead to constriction of efferent arterioles, hypoperfusion of postglomerular peritubular capillaries, and subsequent hypoxia of the tubulointerstitium in the downstream compartment. Recent studies using BOLD-MRI showed an immediate decrease of oxygen tension in the kidney after angiotensin II infusion. In addition, angiotensin II induces oxidative stress via activation of NADPH oxidase. Oxidative stress damages endothelial cells directly, causing the loss of peritubular capillaries. Oxidative stress also results in relative hypoxia due to inefficient cellular respiration. Thus, angiotensin II induces renal hypoxia via both hemodynamic and nonhemodynamic mechanisms. While the beneficial effects of blockade of RAS in kidney disease are, at least in part, mediated by amelioration of hypoxia, recent studies have also elucidated the mechanism of hypoxia-induced gene regulation via the HIF-HRE system. This has given hope for the development of novel therapeutic approaches against hypoxia in the kidney.