PnPP-19 Peptide Restores Erectile Function in Hypertensive and Diabetic Animals Through Intravenous and Topical Administration

Abstract

Introduction: With the aim of overcoming the high toxicity of PnTx2-6 (or δ-CNTX-Pn2a), a toxin from the venom of the armed spider (Phoneutria nigriventer), the 19-aminoacid peptide, PnPP-19 (P nigriventer potentiator peptide), was synthesized based on molecular modeling studies of PnTx2-6. PnPP-19 improved the erectile function of normotensive rats and mice, without eliciting side effects, and no signs of toxicity were observed. In addition, PnPP-19 was able to potentiate the effect of sildenafil.

Aim: To evaluate the efficacy of PnPP-19 in hypertensive and diabetic mouse/rat models in restoring erectile function, after topical administration; verify the biodistribution of PnPP-19 administration (topical and intravenous), permeation, and cyclic guanosine monophosphate (cGMP)/nitric oxide via implication.

Methods: Corpus cavernosum relaxation was evaluated using cavernous strips from male spontaneous hypertensive rats (SHR) and from streptozotocin (STZ)-diabetic mice contracted with phenylephrine and submitted to electrical field stimulation before and after incubation with PnPP-19 (10^-8 mol/L, 10 minutes) or vehicle. This procedure was also used to determine cGMP/nitric oxide levels, at 8 Hz and to check the effect of PnPP-19 with sildenafil citrate. Biodistribution assays were performed using iodine 123-radiolabeled PnPP-19. In vivo erectile function was evaluated using intracavernosal pressure/main arterial pressure ratio in STZ-diabetic rats after PnPP-19 topical administration.

Main outcome measures: PnPP-19 may become a new drug able to fill the gap in the pharmacologic treatment of erectile dysfunction, especially for hypertensive and diabetic individuals RESULTS: PnPP-19 potentiated corpus cavernosum relaxation, in both control and SHR rats. SHR-cavernosal tissue treated with PnPP-19 (1-32 Hz) reached the same relaxation levels as control Wistar rats (16 and 32 Hz). PnPP-19 treatment improved cavernosal tissue relaxation in STZ-diabetic mice and rats. PnPP-19 enhanced cGMP levels in STZ-diabetic mice corpus cavernosum strips. After topical or intravenous administration in rats, ¹²³I-PnPP-19 was mainly recruited to the penis. When topically administered (400 μg/rat), PnPP-19 restores erectile function in STZ-diabetic rats, also improving it in healthy rats by increasing the intracavernosal pressure/main arterial pressure ratio. PnPP-19 exhibited an additive effect when co-administered with sildenafil, showing a novel mode of action regardless of phosphodiesterase type 5 inhibition.

Clinical implications: PnPP-19 seems to be an indicated drug to be tested to treat ED in diabetic and hypertensive patients.

Strength & limitations: PnPP-19, although active by topical application and showing safety to human beings (not shown), has low permeability, about 10% of the applied dose.

Conclusion: Our results showed that PnPP-19 may emerge as a potent new drug that can be topically administered, becoming a promising alternative for erectile dysfunction treatment. Nunes da Silva C, Pedrosa Nunes K, De Marco Almeida F, et al. PnPP-19 Peptide Restores Erectile Function In Hypertensive And Diabetic Animals Through Intravenous And Topical Administration. J Sex Med 2019;16:365-374.

Keywords: Diabetes; Erectile Function/Dysfunction; Hypertension; Intravenous Administration; PnPP-19; Topical Administration.