Effects of an Angiotensin IV Analog on 3-Nitropropionic Acid-Induced Huntington's Disease-Like Symptoms in Rats.

Background: Huntington's disease (HD) is a neurodegenerative disorder characterized by motor, cognitive, and psychiatric dysfunction caused by a mutant huntingtin protein. Compromised metabolic activity resulting from systemic administration of the mitochondrial toxin, 3-nitropropionic acid (3-NP), is known to mimic the pathology of HD and induce HD-like symptoms in rats. N-hexanoic-Tyr-Ile-(6)-amino hexanoic amide (PNB-0408), also known as Dihexa, has been shown to have neuroprotective and procognitive properties in animal models of Alzheimer's and Parkinson's diseases. Given the mechanism of action and success in other neurodegenerative diseases, we felt it an appropriate compound to investigate further for HD. Objective: The present study was designed to test if PNB-0408, an angiotensin IV analog, could attenuate 3-NP-induced HD-like symptoms in rats and serve as a potential therapeutic agent. Methods: Forty male Wistar rats were randomized into three groups consisting of a "vehicle" group, a "3-NP" group, and a "3-NP + PNB-0408" group. PNB-0408 was administered along with chronic exposure to 3-NP. Animal body weight, motor function, and cognitive abilities were measured for five weeks, before euthanasia and histopathological analysis. Results: Exposure to 3-NP decreased the amount of weight rats gained, impaired spatial learning and memory consolidation, and led to marked motor dysfunction. From our observations and analysis, PNB-0408 did not protect rats from the deficits induced by 3-NP neurotoxicity. Conclusions: Our findings suggest that PNB-0408 may not be an efficacious treatment strategy for preventing 3-NP-induced HD-like symptoms in a preclinical model. These data highlight the need for further research of this compound in alternate models and/or alternative approaches to managing this disorder.

Intrathecal injections of angiotensin IV and oxytocin conjugates induce antihyperalgesia and antiallodynia in both sexes of rats.

Our previous studies have established that intrathecal oxytocin (OT) and angiotensin IV (Ang IV) injections induce antihyperalgesia and antiallodynia in rodents. Ang IV, a renin-angiotensin system hexapeptide, acts as an endogenous inhibitor that inhibits the oxytocin-degrading enzyme insulin-regulated aminopeptidase (IRAP). The pain inhibitory effects by Ang IV were found to be through its inhibition on IRAP to potentiate the effect of OT. However, these effects were found to be with a significant sex difference, which could be partially due to the higher expression of IRAP at the spinal cords of female. Therefore, we synthesized Ang IV and OT conjugates connected with a peptide bond and tested for their effects on hyperalgesia and allodynia. Carrageenan-induced hyperalgesia and partial sciatic nerve ligation (PSNL) were performed using rat models. Conjugates Ang IV-OT (Ang IV at the N-terminal) and OT-Ang IV (OT at the N-terminal) were synthesized and intrathecally injected into male and female rats. Our results showed that Ang IV-OT exhibited prominent antihyperalgesia in male rats, particularly during hyperalgesia recovery, whereas OT-Ang IV was more effective during development stage. Ang IV-OT showed clear antihyperalgesia in female rats, but OT-Ang IV had no significant effect. Notably, both conjugates alleviated neuropathic allodynia in male rats; however, OT-Ang IV had no effect in female rats, whereas Ang IV-OT induced significant antiallodynia. In conclusion, Ang IV-OT has greater therapeutic potential for treating hyperalgesia and allodynia than OT-Ang IV. Its effects were not affected by sex, unlike those of OT and OT-Ang IV, extending its possible clinical applications.

Interaction of Angiotensin-(1-7) with kinins in the kidney circulation: Role of B1 receptors.

Changes in renal hemodynamics impact renal function during physiological and pathological conditions. In this context, renal vascular resistance (RVR) is regulated by components of the Renin-Angiotensin System (RAS) and the Kallikrein-Kinin System (KKS). However, the interaction between these vasoactive peptides on RVR is still poorly understood. Here, we studied the crosstalk between angiotensin-(1-7) and kinins on RVR. The right kidneys of Wistar rats were isolated and perfused in a closed-circuit system. The perfusion pressure and renal perfusate flow were continuously monitored. Ang-(1-7) (1.0-25.0 nM) caused a sustained, dose-dependent reduction of relative RVR (rRVR). This phenomenon was sensitive to 10 nM A-779, a specific Mas receptor (MasR) antagonist. Bradykinin (BK) promoted a sustained and transient reduction in rRVR at 1.25 nM and 125 nM, respectively. The transient effect was abolished by 4 µM des-Arg9-Leu8-bradykinin (DALBK), a specific kinin B1 receptor (B1R) antagonist. Accordingly, des-Arg9-bradykinin (DABK) 1 µM (a B1R agonist) increased rRVR. Interestingly, pre-perfusion of Ang-(1-7) changed the sustained reduction of rRVR triggered by 1.25 nM BK into a transient effect. On the other hand, pre-perfusion of Ang-(1-7) primed and potentiated the DABK response, this mechanism being sensitive to A-779 and DALBK. Binding studies performed with CHO cells stably transfected with MasR, B1R, and kinin B2 receptor (B2R) showed no direct interaction between Ang-(1-7) with B1R or B2R. In conclusion, our findings suggest that Ang-(1-7) differentially modulates kinin's effect on RVR in isolated rat kidneys. These results help to expand the current knowledge regarding the crosstalk between the RAS and KKS complex network in RVR.

Caracterización de un modelo de diabetes tipo 2 en ratas y evaluación del papel de la angiotensina II y las especies reactivas de oxígeno en la resistencia neuronal a la insulina / Characterization of a type 2 diabetes model in rats and evaluation of the role of angiotensin II and reactive oxygen species in neuronal insulin resistance

La regulación ejercida por la insulina central en individuos diabéticos ha sido muy poco estudiada. La angiotensina II promueve el estrés oxidativo y la resistencia a la insulina. Dada la co-localización del receptor AT1 de la angiotensina II y el RI a nivel hipotalámico, en este trabajo, decidimos evaluar el efecto de la angiotensina II sobre las acciones centrales de la insulina en condiciones diabéticas, a través de un modelo animal de DM2 en ratas Sprague-Dawley, así como el posible efecto protector del tratamiento crónico con Valsartán. El modelo fue caracterizado y validado a través de la medición de diversos parámetros metabólicos, usando técnicas enzimáticas e inmunoenzimáticas. Los efectos de la angiotensina II sobre la señalización y acciones biológicas de la insulina a nivel hipotalámico fueron evaluadas in vivo e in vitro, mediante western blot, así como los cambios en los niveles de glicemia en las ratas tratadas ICV con ANG II y/o insulina. Fue evaluado además, el estado oxidativo a nivel hipotalámico, mediante la determinación de enzimas antioxidantes, así como el estado inflamatorio sistémico, mediante la determinación fluorométrica de citoquinas plasmáticas. El modelo experimental desarrollado mimetizó las características fenotípicas de la DM2. El valsartán previno parcialmente la resistencia a la insulina. En condiciones normales, se demostró que la angiotensina es capaz de inhibir la señalización de la insulina a nivel hipotalámico por un mecanismo dependiente de ERO. En condiciones diabéticas, hay una disminución basal de la activación de las proteínas de señalización de la insulina, la cual fue prevenida por el tratamiento con valsartán. El efecto hipoglicemiante inducido por la insulina central fue significativamente reducido en condiciones diabéticas. El tratamiento ICV con angiotensina II antagonizó los efectos hipoglicemiantes de la insulina central y este efecto fue potenciado en condiciones diabéticas. El valsartán bloquea la acción inducida por la ANG II ICV en todos los grupos. Los resultados demuestran que existe un estado de resistencia a la insulina en nuestro modelo de DM2, evidente tanto a nivel molecular como fisiológico, el cual es potenciado por la angiotensina y prevenido parcialmente por el tratamiento crónico con valsartán.

Conformationally restricted analogs of angiotensin II: titration and biological activity

1. Six conformationally restricted analogues of angiotension II containing one disulfide bridge were synthesized by the solid-phase method. 2. These cyclic analogues were tirated electrometically and spectrophotometrically and their biological activites were assayed on the isolated guinea pig ileum and rat blood pressure. 3. The conformation restrictions led to significant differnces in the pKa values of a the titratable groups in al six analogs. 4. The comparison of tiration data between the cyclic and linear analogs of angiotension II indicates that in the pH range 4 to 9, angiotension II has a preferential folded conformation. An expanded conformation is assumed to occur at pH below 4 and above 9. 5. The biological activites of all cyclic analogs were less than 0.2% of the activity of angiotension II in toth bioassays

1-Sarcosine - Angiotensin II tachyphylaxis in helical strips and everted rings of rabbit aorta

The development of tachyphylaxis to [1-sarcosine]-angiotensin II was studied in helical strips and everted rings of rabbit aorta. Strips, but not everted rings, developed marked (>50%) tachyphylaxis to the peptide, when challenged repeatedly at 1-h intervals. Measurements of the membrane potential showed no difference between the two preparations, but strips were more sensitive to KC1 than everted rings. These results suggest that the strips are more depolarized than the everted rings due to lesions caused by the spiral cutting. This partial depolarization may underlie the tachyphylactic phenomenon

Effects of intracerebroventricular infusion of angiotensin II and related peptides on water and sodium ingestion and excretion

The objetive of the present study was to investigate the effects of an angiotensin II (AII) analogue, Des-Asp1-AII and of two competitive blockers, [Leu8]-AII and [octanoyl-Leu8]-AII, infused intracerebroventriculary on the ingestion of water and of a 3% NaCl solution, as well as on diuresis and natriuresis in normal rats and in adrenalectomized and deoxycorticosterone (DOCA)-treated rats. Both AII and Des-Asp1-AII increased water and 3% NaCl intake and increased urine and Na+ excretion, the effect of AII being more intense. Except for 3% NaCl, the responses of all other parameters were totally or partially reduced by previous treatment with [Leu8]-AII or [octanoyl-Leu8]-AII. Subcytaneous DOCA injection caused water ingestion. Previous treatment with DOCA increased the response to AII for the ingestion of 3% NaCl and inhibited sodium excretion. The results obtained for adrenalectomized rats treated with DOCA, AII and analogous agonists did not differ from those observed in normal rats. These data suggest a possible synergism between the cerebral and renal renin-angiotensin systems in the regulation of the physiological parameters studied