Development of original metabolically stable apelin-17 analogs with diuretic and cardiovascular effects

Apelin, a (neuro)vasoactive peptide, plays a prominent role in controlling cardiovascular functions and water balance. Because the in vivo apelin half-life is in the minute range, we aimed to identify metabolically stable apelin-17 (K17F) analogs. We generated P92 by classic chemical substitutions and LIT01-196 by original addition of a fluorocarbon chain to the N terminus of K17F. Both analogs were much more stable in plasma (half-life >24 h for LIT01-196) than K17F (4.6 min). Analogs displayed a subnanomolar affinity for the apelin receptor and behaved as full agonists with regard to cAMP production, ERK phosphorylation, and apelin receptor internalization. Ex vivo, these compounds induced vasorelaxation of rat aortas and glomerular arterioles, respectively, precontracted with norepinephrine and angiotensin II, and increased cardiac contractility. In vivo, after intracerebroventricular administration in water-deprived mice, P92 and LIT01-196 were 6 and 160 times, respectively, more efficient at inhibiting systemic vasopressin release than K17F. Administered intravenously (nmol/kg range) in normotensive rats, these analogs potently increased urine output and induced a profound and sustained decrease in arterial blood pressure. In summary, these new compounds, which favor diuresis and improve cardiac contractility while reducing vascular resistances, represent promising candidates for the treatment of heart failure and water retention/hyponatremic disorders.-Gerbier, R., Alvear-Perez, R., Margathe, J.-F., Flahault, A., Couvineau, P., Gao, J., De Mota, N., Dabire, H., Li, B., Ceraudo, E., Hus-Citharel, A., Esteoulle, L., Bisoo, C., Hibert, M., Berdeaux, A., Iturrioz, X., Bonnet, D., Llorens-Cortes, C. Development of original metabolically stable apelin-17 analogs with diuretic and cardiovascular effects.

Development of an Experimental Model to Study the Relationship Between Day-to-Day Variability in Blood Pressure and Aortic Stiffness

We aimed to develop an animal model of long-term blood pressure variability (BPV) and to investigate its consequences on aortic damage. We hypothesized that day-to-day BPV produced by discontinuous treatment of spontaneously hypertensive rats (SHR) by valsartan may increase arterial stiffness. For that purpose, rats were discontinuously treated, 2 days a week, or continuously treated by valsartan (30 mg/kg/d in chow) or placebo. Telemetered BP was recorded during 2 min every 15 min, 3 days a week during 8 weeks to cover the full BP variations in response to the treatment schedule. Pulse wave velocity (PWV) and aortic structure evaluated by immunohistochemistry were investigated in a second set of rats treated under the same conditions. Continuous treatment with valsartan reduced systolic BP (SBP) and reversed the aortic structural alterations observed in placebo treated SHR (decrease of medial cross-sectional area). Discontinuous treatment with valsartan decreased SBP to a similar extent but increased the day-to-day BPV, short term BPV, diastolic blood pressure (DBP), and PWV as compared with continuous treatment. Despite no modifications in the elastin/collagen ratio and aortic thickness, an increase in PWV was observed following discontinuous treatment and was associated with a specific accumulation of fibronectin and its α_v-integrin receptor compared with both groups of rats. Taken together the present results indicate that a discontinuous treatment with valsartan is able to induce a significant increase in day-to-day BPV coupled to an aortic phenotype close to that observed in hypertension. This experimental model should pave the way for future experimental and clinical studies aimed at assessing how long-term BPV increases aortic stiffness.

Identification and pharmacological properties of E339-3D6, the first nonpeptidic apelin receptor agonist

Apelin plays a prominent role in body fluid and cardiovascular homeostasis. To explore further upstream the role played by this peptide, nonpeptidic agonists and antagonists of the apelin receptor are required. To identify such compounds that do not exist to date, we used an original fluorescence resonance energy transfer-based assay to screen a G-protein-coupled receptor-focused library of fluorescent compounds on the human EGFP-tagged apelin receptor. This led to isolated E339-3D6 that displayed a 90 nM affinity and behaved as a partial agonist with regard to cAMP production and as a full agonist with regard to apelin receptor internalization. Finally, E339-3D6 induced vasorelaxation of rat aorta precontracted with noradrenaline and potently inhibited systemic vasopressin release in water-deprived mice when intracerebroventricularly injected. This compound represents the first nonpeptidic agonist of the apelin receptor, the optimization of which will allow development of a new generation of vasodilator and aquaretic agents.

Arterial stiffness and the autonomic nervous system during the development of Zucker diabetic fatty rats

AIM

This study aimed to investigate the role played by sympathovagal balance in arterial stiffness, a common feature of insulin resistance and type 2 diabetes.

METHODS

We investigated the relationship between autonomic nervous system activity and arterial stiffness in Zucker diabetic fatty rats (ZDF: Gmi-fa/fa) and their age-matched controls (lean: ?/fa). Using simultaneous catheterization of the proximal and distal aorta, we measured intra-arterial blood pressure (BP), heart rate (HR), their variability (spectral analysis) and aortic pulse wave velocity (PWV) in a series of at least six conscious rats aged 6, 12, 18 and 24 weeks.

RESULTS

BP and PWV increased with age (P<0.001) in both strains with no differences between strains, despite the insulin resistance already present at 6 weeks in ZDF rats. HR was significantly lower (P<0.001) in ZDF than in lean rats. In ZDF compared with lean rats, the low-frequency (LF) component of the systolic BP variations and the LF/high-frequency (HF) component of the pulse interval (PI) variation ratio were reduced (P<0.01 and P<0.05, respectively), while the HF component of the PI (HF-PI) variation was raised (P<0.05). PWV was negatively correlated with HF-PI (r=-0.37, P<0.01), but not with biochemical parameters. HF-PI was an independent variable explaining the variation in PWV.

CONCLUSION

During the development of disease of ZDF rats, sympathovagal balance might account for the lack of increase in PWV.

Aortic stiffness and pulse pressure amplification in Wistar-Kyoto and spontaneously hypertensive rats

In humans, increased body weight and arterial stiffness are significantly associated, independently of blood pressure (BP) level. The finding was never investigated in rodents devoid of metabolic disorders as spontaneously hypertensive rats (SHR). Using simultaneous catheterization of proximal and distal aorta, we measured body weight, intra-arterial BP, heart rate and their variability (spectral analysis), aortic pulse wave velocity (PWV), and systolic and pulse pressure (PP) amplifications in unrestrained conscious Wistar-Kyoto (WKY) rats and SHR between 6 and 24 wk of age. Aortic proximal systolic and diastolic pressure, PP, and mean BP were significantly higher in SHR than in WKY rats and increased significantly with age (with the exception of PP). PP amplification increased with age but did not differ between strains. PWV was significantly associated with heart rate variability. PWV was significantly higher (via two-way variance analysis) in SHR than in WKY rats (strain effect) and increased markedly with age in both strains (age effect). Adjustment of PWV to mean BP attenuated markedly both the age and the strain effects. After adjustment for body weight, either alone or associated with mean BP, the age effect was not more significant, but the strain effect was markedly enhanced. In conscious unanesthetized SHR and WKY rats, aortic stiffness is consistently associated with body weight independent of age and mean BP. An intervention study should consider in the objectives systolic BP and PP amplifications measured in conscious animals, central control of body weight, and autonomic nervous system.

Angiotensinogen gene M235T polymorphism and reduction in wall thickness in response to antihypertensive treatment

The angiotensinogen M235T polymorphism has been linked to hypertension and cardiovascular disease. Carotid intima-media thickness (IMT) is an early marker of atherosclerosis. The objectives of the present study were to determine in previously untreated essential hypertensive patients whether carotid IMT was associated with the M235T polymorphism, and to determine whether the M235T polymorphism could influence the reduction of carotid IMT by antihypertensive treatment. Common carotid artery IMT was determined with a high-definition echotracking system in 98 previously untreated hypertensive patients in a cross-sectional study. A subgroup of 56 patients was included in a randomized double-blind parallel group study comparing the effect of the angiotensin-converting-enzyme-inhibitor enalapril with that of the beta-blocker celiprolol during a 5 month period. In the cross-sectional study, a multivariate analysis showed that the M235T genotype was a significant independent determinant of carotid IMT, explaining 7% of the variance. Carotid IMT was higher in patients homozygous for the T allele than in MM patients. In the longitudinal study, the reduction in carotid IMT after antihypertensive treatment was significantly ( P <0.01) higher in patients carrying the TT genotype than in patients carrying the MM genotype, despite similar reductions in blood pressure and independently of drug type. In conclusion, these data suggest that the angiotensinogen TT genotype at position 235 is a genetic marker for early carotid atherosclerosis in a hypertensive population and its regression under antihypertensive treatment.

[Relationship between vasosympathetic activity and insulin resistance in normotensive and mildly hypertensive obese patients]

Several studies have well demonstrated that obesity is associated with changes in cardiovascular vagosympathetic activity. The aim of the present work was to evaluate this activity in normotensive and in mildly hypertensive obese patients, and to correlate this activity with clinical and biological indexes of insulin resistance. Heart rate (HR) and systolic blood pressure (sBP) were examined by spectral analysis in 70 normotensive obese patients (group 1), 32 mildly hypertensive obese patients (group 2), and 21 controls. The high frequency peak of HR variations at a controlled breathing rate (vagal activity) was significantly reduced in both groups (p < 0.001). The mid frequency peak of sBP in the standing position (sympathetic activity) was similar in both groups and in the control group. In groups 1 and 2, the high frequency peak correlated negatively with age (p = 0.005 and 0.034 respectively). In group 1, the mid frequency peak correlated positively with fat mass, fasting plasma insulin and triglyceride levels, and insulin resistance index (p < or = 0.03). In group 2, the mid frequency peak correlated positively with fasting insulin and insulin resistance index (p = 0.006 and 0.007 respectively). This study shows that, in obese patients: 1. cardiac vagal activity is reduced in normotensive and mildly hypertensive subjects; 2. vascular sympathetic activity is unchanged in means but may be increased as a consequence of adiposity, hyperinsulinemia and insulin resistance, and this increase is likely to be involved in the increase of blood pressure.

[Arterial rigidity and cardiovascular vagosympathetic activity in normotensive and hypertensive obese patients and type 2 diabetics]

An increase in arterial rigidity is associated with a poor cardiovascular prognosis. Several studies have suggested that an increase in sympathetic activity may be involved in essential hypertension. We have recently shown that vagal control of heart rate (HR) variations during standardised tests is altered in normotensive obese and diabetic patients. The aim of the present study was to compare cardiovascular vagosympathetic activity in obese and type 2 diabetic patients, either normotensive or hypertensive, and to investigate the relationship between pulse pressure (an index of arterial rigidity) and sympathetic activity in this population. Seventy normotensive obese and 32 mildly hypertensive obese patients, 18 normotensive type 2 diabetic patients and 14 mildly hypertensive type 2 diabetic patients were compared with 21 control subjects. Finapres studied HR and blood pressure variations. In the four groups, during a 6-min period at a controlled breathing rate, the high frequency peak of HR variations was significantly reduced (p < 0.001). The mid-frequency peak of systolic BP variations in the standing position, which depends on sympathetic activity, did not differ significantly between the four groups and control subjects. In obese and diabetic hypertensive patients, this peak correlated significantly with pulse pressure measured in the lying position (r = 0.379; p = 0.043 and r = 0.81; p < 0.0001, respectively). This study 1, confirms that vagal control of HR variations is reduced to a similar extent in obese and diabetic patients; and 2, suggests that cardiovascular sympathetic activity is relatively increased in these patients without significant difference between normotensive and hypertensive patients, but interestingly that the increase in arterial rigidity is associated with a higher sympathetic activity.

Long-term cardiovascular effects of high "osteoprotective" dose levels of 17 beta-estradiol in spontaneously hypertensive rats

The effects of estrogen replacement therapy in menopausal women are more obvious on bones than on the cardiovascular system. The optimal estrogen dosage may differ in these different parts of the body. In hypertensive rats, low doses have been shown to reduce arterial collagen and stiffness, whereas higher dosages are required for osteoprotection. From 4 to 20 weeks of age, female spontaneously hypertensive rats (SHRs) were divided into four groups: without ovariectomy, under placebo or 17 beta-estradiol (10 micrograms/kg/day), and with ovariectomy under either placebo or 17 beta-estradiol (same dosage). Serial tail systolic blood pressure measurements were performed, and histomorphometry of the thoracic aorta was determined at the end of the study. Under estrogen, blood pressure was unchanged, whereas the aortic wall-to-lumen ratio was increased, particularly in the presence of ovariectomy. The elastin to collagen ratio was significantly decreased, due both to a decrease in elastin and an increase in collagen density, with no change in media thickness. The latter findings were not observed when ovariectomy was performed. Independent of changes in wall stress, high-dose estrogen increases the aortic extracellular matrix in female SHRs. This increase may be reversed in the presence of ovariectomy, suggesting that estrogen was not the only gonadal factor responsible for altered vascular structure and function.

Carotid arterial changes produced by a centrally mediated antihypertensive agent in hypertensive rats

We studied the effects of centrally mediated reduction of sympathetic outflow on the mechanical properties of the carotid arterial wall in spontaneously hypertensive rats (SHR) as compared with matched Wistar-Kyoto rats (WKY). Ascending aortic pressure and flow were recorded in open-chest anesthetized rats, and the systemic arterial compliance (SAC) was calculated. Intravenous injection of rilmenidine induced a transient increase in blood pressure (BP) in WKY and SHR, followed by a long-lasting reduction in SHR, together with a decrease in cardiac output (CO) and heart (HR) and a significant increase in SAC. Serial measurements of internal carotid artery diameter made with a newly described echo-tracking technique showed a significant, rapid, and long-lasting constriction in both strains. In this set of experiments, the carotid compliance was determined from the arterial volume-pressure relation under control conditions and after administration of intravenous (i.v.) rilmenidine. In both WKY and SHR, carotid compliance increased, but the increase was observed only at the higher transmural pressure ranges and not at the operating systemic BP of the corresponding animals. Simultaneous recordings of the carotid arterial diameter made with the echo-tracking technique indicated that these compliance changes occurred in the presence of carotid arterial constriction at any given value of transmural pressure. Distensibility was increased in a higher pressure range: from 100 to 200 mm Hg transmural pressure. The centrally mediated antihypertensive agent rilmenidine produced carotid arterial constriction independent of BP changes and, in in vivo in situ carotid preparations, arterial constriction was associated with a decrease in the stiffness of the arterial wall.

[Hemodynamic profile of 8-OH-DPAT and 5-HT1 agonists in the anesthetized dog]

In anaesthetized dogs, intravenous administration of 8-OH-DPAT (1-300 micrograms/kg i.v.) induced dose-dependent decrease in blood pressure (BP) and total peripheral resistance (TPR). Heart rate (HR) and cardiac output (CO) changed little. 5-Carboxamidotryptamine (5-CT) (0.3-3 micrograms/kg i.v.) dose-dependently decreased BP and TPR but increased HR, CO, myocardial contractility and pulmonary arterial pressure (PAP). 5-MeODMT and RU 24969 decreased BP only after the highest dose used (300 micrograms/kg i.v. and 1 mg/kg i.v. respectively) but significantly increased PAP at all doses used. These results indicated that in dogs as in other animal species, 8-OH-DPAT decreases BP by systemic vasodilatation without a reflex activation of the myocardium. This lack of a reflex tachycardia suggests a centrally-mediated effects of 8-OH-DPAT. In contrast to 8-OH-DPAT, the vasodilatation induced by 5-CT triggers a reflex tachycardia. The increase in PAP induced by 5-MeODMT, RU 24969 and--to a lesser extent--5-CT, may be due to a direct stimulation of 5-HT2 receptors. However, a 5-HT1 component could not be ruled out.

Cardiovascular properties of a 5-HT1-like receptor agonist, 5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) in normotensive anaesthetized rats

Intravenous administration of the putative 5-HT1-like receptor agonist RU 24969 (10-1000 micrograms/kg) in anaesthetized rats induced a decrease in heart rate and blood pressure. The bradycardia was reduced, but not suppressed, by tertatolol, bilateral vagotomy or the combination of both treatments. The alpha 1-adrenoceptor blocking agent, AR-C 239, decreased the bradycardia induced by high doses of RU 24969. After treatment with hexamethonium, RU 24969 induced an increase in arterial blood pressure. The hypotensive response induced by RU 24969 was not altered by atropine. The hypotensive and bradycardic effects of RU 24969 were antagonized by methysergide (5-HT1-like receptor antagonist) and in part by spiroxatrine (5-HT1A receptor antagonist). Ketanserin (5-HT2 receptor antagonist) potentiated the effects of low doses of RU 24969. The cardiovascular effects of RU 24969 were antagonized neither by MDL 72222 nor by ICS 205-930 (5-HT3 receptor antagonists). The present results suggest that the cardiovascular effects of RU 24969 seem to be due to the stimulation of 5-HT1-like receptors. The participation of both 5-HT1A and 5-HT1B receptors subtypes has been considered. The results suggest a centrally-mediated inhibition of sympathetic tone and increase in vagal tone in the cardiovascular effects of RU 24969.

Comparison of effects of some 5-HT1 agonists on blood pressure and heart rate of normotensive anaesthetized rats

The present experiments served to compare the effects of the 3 5-HT1 agonists, 8-OH-DPAT, 5-MeODMT and TFMPP on the blood pressure and heart rate of normotensive anaesthetized rats. All the agonists induced, after i.v. injection, a decrease in blood pressure and heart rate. The hypotensive effects of 5-MeODMT and TFMPP were preceded by an increase, suppressed by both ketanserin and methysergide. The decrease in blood pressure induced by 5-MeODMT and 8-OH-DPAT was not antagonized by ketanserin, cocaine (and methysergide for 8-OH-DPAT) but was antagonized by methysergide (for 5-MeODMT) and spiroxatrine (for both). Bradycardia was not susceptible to ketanserin and cocaine (for 5-MeODMT) or to ketanserin and methysergide (for 8-OH-DPAT) but to methysergide and spiroxatrine (for 5-MeODMT) and cocaine and spiroxatrine (for 8-OH-DPAT). These results suggested that the hypotension and bradycardia induced by 5-MeODMT and 8-OH-DPAT are due to the stimulation of '5-HT1-like' receptors and probably to the 5-HT1A subtype; the 5-MeODMT-induced hypertension being ascribed to the stimulation of 5-HT2 receptors.

Pharmacological properties of the enantiomers of idazoxan: possible separation between their alpha-adrenoceptor blocking effects

The alpha-adrenoceptor blocking properties of the two enantiomers of idazoxan have been investigated in rats, dogs and chicks, as well as their agonistic effects in pithed rats. At peripheral sites, (+) idazoxan was equipotent for blocking both postsynaptic alpha-1 and alpha-2 adrenoceptors of the rat and revealed to be a potent antagonist at presynaptic sites of rats and dogs. (-) Idazoxan revealed to be selective for postsynaptic alpha-2 adrenoceptors with an apparent selectivity ratio of about 10. This selectivity of (-) idazoxan was greater in vitro. (-) Idazoxan also antagonized presynaptic alpha-2 adrenoceptors of rats and dogs. At central sites, (+) and (-) idazoxan antagonized the hypotension, bradycardia, inhibition of sympathetic nerve activity induced by clonidine in rats and dogs and sedation induced by clonidine and azepexole in chicks. Although (+) idazoxan was more potent than (-) idazoxan, binding studies revealed (-) idazoxan to be more selective than (+) idazoxan at central sites. It is concluded that (+) idazoxan antagonizes both alpha-1 and alpha-2 adrenoceptors and (-) idazoxan is selective for alpha-2 adrenoceptors. In the pithed rat, only (-) idazoxan possesses both alpha-1 and alpha-2 agonistic effects. These results show little differences between the two enantiomers of idazoxan as for those of imidazoline derivatives.

Pharmacological properties of (N-dicyclopropylmethyl) amino-2-oxazoline (S 3341), an alpha-2 adrenoceptor agonist

Pharmacological actions of (N-dicyclopropylmethyl)-amino-2-oxazoline (S 3341), an agonist of alpha-2 adrenoceptors, were examined in acute animal studies. In the normotensive anaesthetized dog S 3341 (0.3 mg/kg, i.v.) produced an initial transient increase followed by a marked, prolonged fall in mean arterial pressure (MAP) of 20 mmHg. Central actions of S 3341 were demonstrated by administration of low doses into the vertebral artery of the anaesthetized dog. A rapid and marked fall in MAP resulted which was antagonised by piperoxan. Splanchnic discharges were strongly decreased following S 3341 i.v. administration, suggesting a centrally mediated diminution of sympathetic tone. Peripheral actions of S 3341 were observed in the pithed rat where a dose-dependent increase in MAP was noted which was somewhat antagonised by prazosin and largely by prazosin plus yohimbine. S 3341 reduced hypertension and tachycardia due to stimulation of the sympathetic outflow in the pithed rat, an effect also antagonised by piperoxan. These effects were more marked and prolonged than those of clonidine. S 3341 reduced the tachycardia resulting from stimulation of the cardioaccelerator nerve in the anaesthetized, spinalised and bilateraly vagotomised dog, this effect was reversed by piperoxan. S 3341 did no change the tachycardia induced by noradrenaline or tyramine. Plasma renin activity was significantly decreased after S 3341 treatment in dogs on low normal or high sodium diets. In rats S 3341 decreased the rate of discharge of noradrenergic cells located in the locus coeruleus which are believed to be involved in wake/sleep mechanisms. This depression was 63 times less than that of clonidine. At effective hypotensive doses S 3341 produced no sedation (i.e. loss of righting reflex) in 2 day old chicks. In addition the sedative action of clonidine was inhibited by S 3341 pretreatment. In the mouse tail flick model, the antinociceptive effects of S 3341 were 45 times less than those of clonidine. S 3341, an oxazoline derivative, appears to have haemodynamic effects similar to those of other agonists of central alpha-2 adrenoceptors but with fewer side-effects, and therefore could be of interest an as antihypertensive agent.