Alamandine injection in the periaqueductal gray and rostral ventromedial medulla attenuates allodynia induced by sciatic nerve ligation in rats.

Alamandine, a peptide known to interact with Mas-related G protein-coupled receptor subtype D (MrgD), has been implicated in moderating inflammatory signals. MrgD receptors are abundantly found in pain transmission pathways, but the role of alamandine/MrgD in pain modulation has not been thoroughly explored. This study aimed to investigate the effects of alamandine (10, 40, and 100 pmol) in a rat model of allodynia induced by sciatic nerve ligation, with a specific focus on examining the involvement of MrgD receptors, NMDAR1, and serotonin transporter (SERT) in the ventrolateral periaqueductal gray (vlPAG) and rostral ventromedial medulla (RVM). Microinjection of alamandine into the vlPAG at a dose of 100 pmol and into the RVM at doses of 40 and 100 pmol resulted in a significant increase in paw withdrawal threshold (PWT). Additionally, co-administration of D-Pro7-Ang-(1-7) at 50 pmol, an MrgD receptor antagonist, effectively blocked the analgesic effects of alamandine. Immunofluorescence analysis confirmed the presence of MrgD receptors in both the vlPAG and RVM regions. Importantly, an upregulation of MrgD receptor expression was observed following allodynia induction, suggesting a potential compensatory mechanism in response to pain. Our findings support the co-localization of MrgD receptors with NMDAR1 in vlPAG neurons, suggesting their ability to initiate analgesic pathways similar to those activated by NMDA receptors in the vlPAG. Furthermore, our results underscore a significant co-localization of MrgD receptors with the SERT in the RVM, underscoring their potential impact on serotonergic neurons involved in promoting analgesic effects.

Alamandine significantly reduces doxorubicin-induced cardiotoxicity in rats.

Doxorubicin (DOX) is an anthracycline antibiotic. Despite its unwanted side effects, it has been successfully used in tumor therapy. Given that oxidative stress and inflammatory factors are essential to cardiotoxicity caused by DOX, we assumed that alamandine, which enhances endogenous antioxidants and has anti-inflammatory effects, may prevent DOX-induced cardiotoxicity. Rats received DOX (3.75 mg/kg) i.p on days 14, 21, 28, and 35 (total cumulative dose = 15 mg/kg) and alamandine (50 µg/kg/day) via mini-osmotic pumps for 42 days. At the end of the 42-day period, we evaluated hemodynamic parameters, electrocardiogram, cardiac troponin I (cTnI), superoxidase dismutase (SOD), total antioxidant capacity (TAC), malondialdehyde (MDA), inflammatory cytokines (tumor necrosis factor-α (TNF-α), IL-1ß, NF-κB), apoptosis markers (caspase 3), and histopathology of haemotoxylin- and eosin-stained cardiac muscle fibers were evaluated. DOX significantly increased QT, corrected QT (QTc), and RR intervals. Alamandine co-therapy prevented ECG changes. Alamandine administration restored DOX-induced disruptions in the cardiac muscle architecture and vascular congestion. Alamandine co-therapy also alleviated other effects of DOX, including cardiac contractility, decreased systolic and diastolic blood pressure, and increased left ventricular end-diastolic pressure. Moreover, alamandine co-therapy substantially decreased the elevation of oxidative stress markers, inflammatory cytokines, and caspase 3 in DOX-treated rats. The results suggest that alamandine reduced DOX-induced cardiotoxicity via antioxidant, anti-inflammatory, and anti-apoptotic activities.

Effect of Prolonged Infusion of Alamandine on Cardiovascular Parameters and Cardiac ACE2 Expression in a Rat Model of Renovascular Hypertension.

Alamandine is a new member of the angiotensin family. Here, we studied the mRNA and protein expression of cardiac angiotensin-converting enzyme 2 (ACE2) in the chronic phase of a rat model of 2-kidney, 1-clip hypertension (2K1C), and the effects of 2-week alamandine infusion on blood pressure, cardiac indices, and ACE2 mRNA and protein expression in the hearts. The rats were subjected to to sham-operation or placement of plexiglass clips around the left renal artery. Alamandine, at a dose of 600 µg/kg/d, was administered for 2 weeks via an osmotic mini-pump. At 18 weeks, after induction of hypertension, blood pressure and cardiac indices of contractility were measured using a Powerlab Physiograph system. The ACE2 mRNA and protein levels were determined using real time-PCR and Western blotting, respectively. In the hypertensive rats, alamandine caused a significant decrease in systolic blood pressure (p < 0.001), diastolic blood pressure (p < 0.001), left ventricular end-diastolic pressure (p < 0.001) and, left ventricular systolic pressure (p < 0.001) and increase in the maximum rate of pressure change in the left ventricle (dP/dt(max)) (p < 0.05). Also, the ACE2 mRNA expression in the heart increased in the hypertensive rats compared to the normotensive rats (p < 0.05), and alamandine restored this to normal values, although these changes were only seen at the mRNA and not the protein level. Histological analysis of cardiac tissue confirmed that alamandine decreased cardiac fibrosis and hypertrophy in 2K1C hypertensive rats. Our results indicate that alamandine, which acts as a depressor arm of the renin-angiotensin system, could be developed for treating hypertension.