Jean-Claude Dussaule

Angiotensin II Activates Collagen I Gene Through a Mechanism Involving the MAP/ER Kinase Pathway

Vascular remodeling and rearrangement of the extracellular matrix formation are among the major adaptive mechanisms to chronic increase in blood pressure. In previous studies we have found that angiotensin II (Ang II) participates in the hypertension-associated aortic and renal vascular fibrosis by stimulating collagen type I formation. The purpose of the present study was to gain insight into the molecular events that lead from the Ang II receptor to collagen I gene activation. To this end, we used a novel strain of transgenic mice harboring the luciferase gene under the control of the collagen I-&agr;2 chain promoter [procol&agr;2(I)]. Ang II produced an early (1 hour) 2- to 3-fold stimulation of procol&agr;2(I) activity in freshly isolated aortas and renal cortical slices (P <0.01) followed by similar increase in procol&agr;2(I) mRNA aortic levels. This effect of Ang II was inhibited by AT1-receptor antagonism (candesartan) and blockade of the MAPK/ERK cascade (PD98059); in contrast, inhibition of the P38 kinase pathway (SB202190) and blockade of the release of the transcription factor NF&kgr;B (PDTC) did not have any effect in the Ang II–induced activation of the collagen I gene. In addition, Ang II induced a rapid (5 minutes) increase of the MAPK/ERK activity that was accompanied by increased expression (3-fold) of the c-fos proto-oncogene. This increase of c-fos mRNA expression was blocked by PD98059; in addition, curcumin, a blocker of the transcriptional factor AP-1, canceled the effect of Ang II on the collagen I gene. Decorin, a scavenger of the active form of transforming growth factor-&bgr; (TGF-&bgr;), canceled the Ang II effect on collagen I gene, whereas inhibition of the MAPK/ERK pathway had no effect on the TGF-&bgr;–induced activation of procol&agr;2(I). These data indicate that the cellular events after AT1 receptor stimulation and leading to activation of collagen I gene expression require activation of both the MAPK/ERK and TGF-&bgr; signaling pathways.

Angiotensin II Activates Collagen Type I Gene in the Renal Vasculature of Transgenic Mice During Inhibition of Nitric Oxide Synthesis Evidence for an Endothelin-Mediated Mechanism

BACKGROUNDnHypertension is frequently associated with renal vascular fibrosis. The purpose of this study was to investigate whether angiotensin II (Ang II) is involved in this fibrogenic process.nnnMETHODS AND RESULTSnExperiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Hypertension was induced by chronic inhibition of NO synthesis (N(G)-nitro-L-arginine methyl ester, L-NAME). Procolalpha(2)(I) activity started to increase in the renal vasculature after 4 weeks of L-NAME treatment (P<0.01) and at 14 weeks reached 3- and 8-fold increases over control in afferent arterioles and glomeruli, respectively (P<0.001). Losartan, an AT(1) receptor antagonist, given simultaneously with L-NAME prevented the increase of procolalpha(2)(I) levels and attenuated the development of renal vascular fibrosis without normalizing systolic pressure increase. Because we found previously that endothelin mediated renal vascular fibrosis in the L-NAME model, the interaction between Ang II, endothelin, and procolalpha(2)(I) was investigated in ex vivo and short-term in vivo experiments. In both conditions, the Ang II-induced activation of procolalpha(2)(I) in renal cortex was blocked by an endothelin receptor antagonist.nnnCONCLUSIONSnDuring chronic inhibition of NO, the collagen I gene becomes activated, leading to the development of renal vascular fibrosis. Ang II is a major player in this fibrogenic process, and its effect on collagen I gene is independent of systemic hemodynamics and is at least partly mediated by the profibrogenic action of endothelin.

Notch-3 receptor activation drives inflammation and fibrosis following tubulointerstitial kidney injury.

Kidney diseases impart a vast burden on affected individuals and the overall health care system. Progressive loss of renal parenchymal cells and functional decline following injury are often observed. Notch‐1 and ‐2 receptors are crucially involved in nephron development and contribute to inflammatory kidney diseases. We specifically determined the participation of receptor Notch‐3 following tubulointerstitial injury and in inflammatory responses. Here we show by heat map analyses that Notch‐3 transcripts are up‐regulated in human kidney diseases. A similar response was corroborated with kidney cells following TGF‐β exposure in vitro. The murine unilateral ureteral obstruction (UUO) model mirrors hallmarks of tubulointerstitial injury and damage. A subset of tubular and interstitial cells demonstrated up‐regulated Notch‐3 receptor expression in diseased animals. We hypothesized a relevance of Notch‐3 receptors for the chemotactic response. To address this question, animals with genetic ablation of receptor Notch‐3 were analysed following UUO. As a result, we found that Notch‐3‐deficient animals are protected from tubular injury and cell loss with significantly reduced interstitial collagen deposition. Monocytic cell infiltration was significantly reduced and retarded, likely due to abrogated chemokine synthesis. A cell model was set up that mimics enhanced receptor Notch‐3 expression and activation. Here a pro‐mitogenic response was seen with activated signalling in tubular cells and fibroblasts. In conclusion, Notch‐3 receptor fulfils non‐redundant roles in the inflamed kidney that may not be replaced by other Notch receptor family members. Thus, specific blockade of this receptor may be suitable as therapeutic option to delay progression of kidney disease. Copyright

Plasma atrial natriuretic factor and cyclic GMP in mitral stenosis treated by balloon valvulotomy. Effect of atrial fibrillation.

To study the relation between plasma atrial natriuretic factor (ANF) and cardiac pressures, we measured plasma ANF in 24 patients with mitral stenosis 30 minutes before and 20 minutes after balloon mitral valvulotomy. All patients were without physical signs of congestive heart failure. Normal sinus rhythm was present in 15 (group 1), whereas the other nine (group 2) had permanent atrial fibrillation. There were no significant differences between groups for basal mean pressures in right atrium (RA), left atrium (LA), and pulmonary artery (PA). Valvulotomy resulted in a fall in both groups (p less than 0.001) in LA and PA mean pressures, whereas heart rate, cardiac index, and RA and aorta (AO) pressures did not change significantly. Basal ANF was not different in either group in RA (240 +/- 43 vs. 266 +/- 35 pg/ml) or AO (441 +/- 92 vs. 643 +/- 70 pg/ml) but tended to be higher in group 2 in LA (428 +/- 88 vs. 682 +/- 84 pg/ml; p = 0.059) and PA (488 +/- 93 vs. 759 +/- 92 pg/ml; p = 0.057). Plasma ANF was the highest in PA, and about 50% ANF was extracted in the systemic circulation. After valvulotomy, plasma ANF was greater (p less than 0.05) in group 2 (372 +/- 90, 755 +/- 152, 805 +/- 134, and 707 +/- 144 pg/ml) than in group 1 (206 +/- 36, 386 +/- 47, 429 +/- 66, and 421 +/- 49 pg/ml), regardless of the site of blood collection (RA, LA, PA, and AO, respectively). PA ANF was correlated with LA pressure (p less than 0.05) in group 1 before as well as after valvulotomy, whereas there was no such correlation in group 2. Cyclic GMP (cGMP) in LA was correlated (p less than 0.01) with PA ANF in group 1, and LA cGMP (10.0 +/- 1.2 and 9.1 +/- 1.8 pmol/ml in groups 1 and 2, respectively) was higher (p less than 0.05) than PA cGMP (9.1 +/- 1.0 and 8.0 +/- 1.5 pmol/ml in groups 1 and 2, respectively) before valvulotomy, which suggests the presence of ANF receptors in the pulmonary circulation. Taken together, these results indicate that in patients in sinus rhythm with mitral stenosis, there is an increase in ANF secretion depending on LA pressure. ANF secretion is also high in patients with mitral stenosis and atrial fibrillation but does not respond appropriately to changes in LA pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Progression and regression in renal vascular and glomerular fibrosis

End‐stage renal disease (ESRD) is characterized by the development of fibrotic lesions in the glomerular, interstitial and vascular compartments. Renal fibrogenesis, a common complication of diabetes and hypertension, is a complex dynamic process involving several players such as inflammatory agents, cytokines, vasoactive agents and enzymes participating in extracellular matrix assembly, anchoring or degradation. The only available treatment today against chronic renal failure is dialysis or kidney transplantation, making thus ESRD one of the most expensive diseases to treat on a per‐patient basis. An emerging challenge for clinicians, maybe the nephrologists Holy Grail in the 21st century, is to stop definitively the decline of renal function and, if possible, to achieve regression of renal fibrosis and restoration of renal structure. Over the last 5 years, different approaches have been tested in experimental models of nephropathy with variable degree of success. In this review, we will focus on the mechanisms of the hypertension‐associated fibrosis and the few recent studies that gave promising results for a therapeutic intervention.

Stereoselective protection of exogenous and endogenous atrial natriuretic factor by enkephalinase inhibitors in mice and humans.

We compared the relative potencies of sinorphan and retorphan, the S- and R-enantiomers of acetorphan a potent inhibitor of enkephalinase (EC 3.4.34.11), to inhibit membrane metalloendopeptidase in vivo and to protect exogenous and endogenous ANF after oral administration. In mice, sinorphan was 2-3 fold as potent as retorphan in inhibiting the specific in vivo binding of [3H]acetorphan to kidney enkephalinase. The same potency ratio was found for the enhancement of trichloroacetic acid-precipitated radioactivity in kidneys of mice that had received 125I-ANF, which is used as a test for the protection of the hormone against inactivation in vivo. In nine healthy human volunteers who had received a low oral dosage of sinorphan or retorphan in a double-blind, placebo-controlled, randomized trial, sinorphan was also 2-3 fold more potent than retorphan in inhibiting plasma enkephalinase activity. These effects were accompanied by a related rise in plasma ANF immunoreactivity, which also reflected the difference in the effectiveness of the two compounds. Sinorphan was also more potent than retorphan in enhancing urinary cyclic GMP excretion and sodium excretion in five of these subjects. These data indicate that, in humans as in rodents, enkephalinase plays a crucial role in the inactivation of ANF, its partial inhibition in vivo being accompanied by a significant protection of the exogenous or endogenous hormone as well as by typical ANF-like responses. Thus orally administered sinorphan appears to be a promising compound for therapeutic use in cardiovascular and renal diseases in which ANF has been postulated to exert beneficial effects.

Variation in natriuretic peptides and mitral flow indexes during successful ventilatory weaning: a preliminary study

AbstractObjectiveTo assess the cardiac consequences of successful respiratory weaning using the variations of circulating B-type and atrial natriuretic peptides (BNP, ANP) and Doppler mitral flow.DesignAxa0prospective preliminary observational study.SettingAxa014-bed medical ICU in axa0French university hospital.PatientsThirty-one patients undergoing axa0spontaneous breathing trial on axa0T-tube.InterventionsCirculating BNP and ANP levels and Doppler-derived E/A ratio and deceleration time of the Exa0wave were measured before and 1u202fh after disconnection.ResultsBNP levels increased from 299u202fpg/ml (rangen56–1079) to 412u202fpg/ml (147–1324) (pu202f=u202f0.02) in patients with systolic left ventricular dysfunction, decreased from 98u202fpg/ml (25–337) to 45u202fpg/ml (38–180) (pu202f=u202f0.04) in patients with right ventricular dilation and remained unchanged in patients with neither of these cardiac abnormalities. Overall ANP levels increased from 33u202fpg/ml to 67u202fpg/ml (pu202f<u202f0.001) regardless of ventricular function. The E/A ratio increased from 0.91 (0.66–3.56) to 1.17 (0.5–4.76), (pu202f=u202f0.01), after disconnection, whereas deceleration time of Exa0wave decreasedfrom 185u202fms (120–280) to 160u202fms (70–206) (pu202f=u202f0.02).ConclusionDuring successful weaning from mechanical ventilation ANP levels increase in all patients whereas changes in BNP levels depend on underlying cardiac function. Changes in Doppler mitral flow indexes following ventilator disconnection suggest an increase in left-ventricular filling pressure.

Pressure-Heart Rate Responses to α-Adrenergic Stimulation and Hormonal Regulation in Normotensive Patients With Obstructive Sleep Apnea

Seven normotensive untreated patients with obstructive sleep apnea (OSA) and five control subjects without OSA were compared. Patients with cardiac dilation, chronic airflow limitation, liver and kidney disease, or diabetes mellitus were excluded. Change in pressure-heart rate relation to alpha-adrenergic stimulation (P-HRR), extracellular volume (ECV), and plasma volume (Vp) were measured during daytime. Plasma atrial natriuretic peptide (ANP), plasma renin and aldosterone concentrations were obtained at 1 hour intervals during the night. A mean apnea/hypopnea index (AHI) of 52.2 +/- 23.9/h and a mean lowest arterial oxygen saturation (SaO2) of 61.2 +/- 19.3% (mean +/- SD) were determined from polysomnographic monitoring in the patient group. Release of ANP was significantly higher during sleep in OSA patients than in control subjects (P < .01), with a maximum concentration between 4 and 6 AM in the former. Daytime ECV was significantly higher (P < .05) and Vp significantly lower (P < .05) in OSA patients. Night maximum concentration of ANP (max ANP) was negatively related to AHI (P < .05). P-HRR was negatively related to AHI (P < .05) and positively related to max ANP (P < .05). In conclusion, OSA syndrome alters hormonal system control of body fluid compartment regulation. The decreased response in night max ANP secretion in the most severe OSA patients could be explained by the smaller Vp observed in these patients, decreasing atrial and ventricular pressure loading. Furthermore, alteration of P-HRR, correlated to AHI and max ANP, strengthens the hypothesis that patients who develop hypertension are those in whom the protective mechanism of ANP release failed.

Renal Effects of Omapatrilat and Captopril in Salt-Loaded, Nitric Oxide-Deficient Rats

Abstract—Inhibition of nitric oxide synthases causes systemic hypertension and renal injury in rats. Our objective was to examine whether omapatrilat, a vasopeptidase inhibitor that inhibits both angiotensin-converting enzyme (ACE) and neutral endopeptidase, could induce better regression of renal injury than ACE inhibitor alone. Ten groups of rats were studied. They were fed either a normal (0.8% NaCl) or a high (4% NaCl) sodium diet. Eight of these groups received NG-nitro-l-arginine methyl ester (l-NAME, 20 mg · kg−1 · d−1) in their drinking water. After 4 weeks, 1 group on each diet was killed and considered the l-NAME group, whereas the others received l-NAME alone, captopril (200 mg · kg−1 · d−1) plus l-NAME, or omapatrilat (80 mg · kg−1 · d−1) plus l-NAME for 4 additional weeks. In rats receiving l-NAME alone for 8 weeks, the mortality rate was ≈90%, irrespective of the diet. In contrast, all rats survived in the captopril and the omapatrilat groups. In rats fed a normal-sodium diet, captopril and omapatrilat normalized systolic blood pressure and induced a complete regression of renal injury. Creatinine clearance and proteinuria were also normalized. In the high-sodium-diet groups, both treatments were less efficient: blood pressure remained elevated, and the regression of renal fibrosis was only partial. Although proteinuria decreased significantly with captopril or omapatrilat, creatinine clearance remained lower than in the controls. These results demonstrate that, in nitric oxide–deficient rats fed a normal-sodium diet, ACE and vasopeptidase inhibitors exhibit a marked renoprotective effect, whereas these treatments are less efficient in rats fed a high-sodium diet.

Effects of bradykinin on prostaglandin synthesis and cytosolic calcium in rabbit subcultured renal cortical smooth muscle cells

Smooth muscle cells were cultured from an arteriole-rich fraction of the rabbit renal cortex and characterized by their ultrastructural and immunohistochemical features, their high content in creatine kinase (60-times that of the initial preparation) and their ability to synthesize renin. Cells, studied between passages 2 and 5, produced mainly PGE2 and, to a lesser extent, PGF2 alpha. Bradykinin (BK) (0.1 nM-1 microM) induced a concentration-dependent increase in PGE2 (28-40-times basal value at 1 microM after a 5 min incubation period) and stimulated also the free cytosolic calcium concentration [( Ca2+]i) with a 2-fold maximal rise to its basal value. Both effects, inhibited by the anti-B2 receptor [Thi5.8D-Phe7] BK, were not reproduced by DesArg9 BK. A decrease in the extracellular calcium concentration and incubation in the presence of a calcium-channel blocker (lanthanum chloride) inhibited the BK-dependent rise of [Ca2+]i but not that of PGE2. Preincubation with phorbol myristate acetate increased basal and BK-induced PGE2 synthesis but prevented the effect of BK on [Ca2+]i. These results demonstrate the ability of BK to increase [Ca2+]i and PGE2 production in cultured vascular cells from the rabbit renal cortex and suggest that kinins might act on the cortical microcirculation via their direct effects on arteriolar smooth muscle cells.