RESUMEN
The anti-plasmodium activity of angiotensin II and its analogs have been described in different plasmodium species. Here we synthesized angiotensin II Ala-scan analogs to verify peptide-parasite invasion preservation with residue replacements. The analogs were synthesized by 9-fluorenylmethoxycarbonyl (Fmoc) and tert-butyloxycarbonyl (t-Boc) solid phase methods, purified by liquid chromatography and characterized by mass spectrometry. The results obtained in Plasmodium falciparum assays indicated that all analogs presented some influence in parasite invasion, except [Ala(4)]-Ang II (18% of anti-plasmodium activity) that was not statistically different from control. Although [Ala(8)]-Ang II presented a lower biological activity (20%), it was statistically different from control. The most relevant finding was that [Ala(5)]-Ang II preserved activity (45%) relative to Ang II (47%). In the results of Plasmodium gallinaceum assays all analogs were not statistically different from control, except [Ala(6)]-Ang II, which was able to reduce the parasitemia about 49%. This approach provides insight for understanding the importance of each amino acid on the native Ang II sequence and provides a new direction for the design of potential chemotherapeutic agents without pressor activity.
Asunto(s)
Angiotensina II/farmacología , Antimaláricos/farmacología , Eritrocitos/parasitología , Malaria/parasitología , Plasmodium falciparum/efectos de los fármacos , Plasmodium gallinaceum/efectos de los fármacos , Angiotensina II/análogos & derivados , Angiotensina II/síntesis química , Antimaláricos/síntesis química , Antimaláricos/química , Humanos , Malaria/tratamiento farmacológico , Péptidos/síntesis química , Péptidos/química , Péptidos/farmacología , Plasmodium falciparum/fisiología , Plasmodium gallinaceum/fisiologíaRESUMEN
The anti-plasmodial activity of conformationally restricted analogs of angiotensin II against Plasmodium gallinaceum has been described. To observe activity against another Plasmodium species, invasion of red blood cells by Plasmodium falciparum was analyzed. Analogs restricted with lactam or disulfide bridges were synthesized to determine their effects and constraints in the peptide-parasite interaction. The analogs were synthesized using tert-butoxycarbonyl and fluoromethoxycarbonyl solid phase methods, purified by liquid chromatography, and characterized by mass spectrometry. Results indicated that the lactam bridge restricted analogs 1 (Glu-Asp-Arg-Orn-Val-Tyr-Ile-His-Pro-Phe) and 3 (Asp-Glu-Arg-Val-Orn-Tyr-Ile-His-Pro-Phe) showed activity toward inhibition of ring formation stage of P. falciparum erythrocytic cycle, preventing invasion in about 40% of the erythrocytes. The disulfide-bridged analog 10 (Cys-Asp-Arg-Cys-Val-Tyr-Ile-His-Pro-Phe) was less effective yet significant, showing a 25% decrease in infection of new erythrocytes. In all cases, the peptides presented no pressor activity, and hydrophobic interactions between the aromatic and alkyl amino acid side chains were preserved, a factor proven important in efficacy against P. gallinaceum. In contrast, hydrophilic interactions between the Asp(1) carboxyl and Arg(2) guanidyl groups proved not to be as important as they were in the case of P. gallinaceum, while interactions between the Arg(2) guanidyl and Tyr(4) hydroxyl groups were not important in either case. The ß-turn conformation was predominant in all of the active peptides, proving importance in anti-plasmodial activity. This approach provides insight for understanding the importance of each amino acid residue on the native angiotensin II structure and a new direction for the design of potential chemotherapeutic agents.
Asunto(s)
Angiotensina II/análogos & derivados , Angiotensina II/farmacología , Antimaláricos/farmacología , Plasmodium falciparum/efectos de los fármacos , Células Cultivadas , Eritrocitos/parasitología , Humanos , Fragmentos de PéptidosRESUMEN
Plasmodium falciparum causes the most serious complications of malaria and is a public health problem worldwide with over 2 million deaths each year. The erythrocyte invasion mechanisms by Plasmodium sp. have been well described, however the physiological aspects involving host components in this process are still poorly understood. Here, we provide evidence for the role of renin-angiotensin system (RAS) components in reducing erythrocyte invasion by P. falciparum. Angiotensin II (Ang II) reduced erythrocyte invasion in an enriched schizont culture of P. falciparum in a dose-dependent manner. Using mass spectroscopy, we showed that Ang II was metabolized by erythrocytes to Ang IV and Ang-(1-7). Parasite infection decreased Ang-(1-7) and completely abolished Ang IV formation. Similar to Ang II, Ang-(1-7) decreased the level of infection in an A779 (specific antagonist of Ang-(1-7) receptor, MAS)-sensitive manner. 10(-7) M PD123319, an AT(2) receptor antagonist, partially reversed the effects of Ang-(1-7) and Ang II. However, 10(-6) M losartan, an antagonist of the AT(1) receptor, had no effect. Gs protein is a crucial player in the Plasmodium falciparum blood cycle and angiotensin peptides can modulate protein kinase A (PKA) activity; 10(-8) M Ang II or 10(-8) M Ang-(1-7) inhibited this activity in erythrocytes by 60% and this effect was reversed by 10(-7) M A779. 10(-6) M dibutyryl-cAMP increased the level of infection and 10(-7) M PKA inhibitor decreased the level of infection by 30%. These results indicate that the effect of Ang-(1-7) on P. falciparum blood stage involves a MAS-mediated PKA inhibition. Our results indicate a crucial role for Ang II conversion into Ang-(1-7) in controlling the erythrocytic cycle of the malaria parasite, adding new functions to peptides initially described to be involved in the regulation of vascular tonus.