Angiotensin‑(1‑7) prevents lipopolysaccharide‑induced hepatocellular inflammatory response by inhibiting the p38MAPK/AP‑1 signaling pathway

125I-Angiotensin 1-7 binds to a different site than angiotensin 1-7 in tissue membrane preparations

PURPOSE

To study the receptor for Angiotensin (Ang) 1-7 using a radioligand (¹²⁵I-Ang 1-7)-binding assay. For more than a decade, Mas has been viewed as the receptor for Ang 1-7; however, Ang 1-7 binding has not been pharmacologically characterized in tissue membrane preparations.

METHODS

Radioligand-binding assays were carried out using tissue membrane preparations using radioiodinated Angiotensin 1-7 (¹²⁵I-Ang 1-7) to characterize its binding site. Non-radioactive ¹²⁷I-Ang 1-7 was used to test if the addition of an iodine to the tyrosine⁴ moiety of Ang 1-7 changes the ability of Ang 1-7 to competitively inhibit ¹²⁵I-Ang 1-7 binding.

RESULTS

¹²⁵I-Ang 1-7 binds saturably, with moderately high affinity (10-20 nM) to a binding site in rat liver membranes that is displaceable by ¹²⁷I-Ang 1-7 at nanomolar concentrations (IC₅₀ = 62 nM) while Ang 1-7 displaces at micromolar concentrations (IC₅₀ = 80 µM) at ~22 °C. This binding was also displaceable by inhibitors of metalloproteases at room temperature. This suggests that ¹²⁵I-Ang 1-7 binds to MMPs and/or ADAMs as well as other liver membrane elements at ~ 22 °C. However, when ¹²⁵I-Ang 1-7-binding assays were run at 0-4 °C, the same MMP inhibitors did not effectively compete for ¹²⁵I-Ang 1-7.

CONCLUSIONS

The addition of an iodine molecule to the tyrosine in position 4 of Ang 1-7 drastically changes the binding characteristics of this peptide making it unsuitable for characterization of Ang 1-7 receptors.

Angiotensin-(1-7) treatment blocks lipopolysaccharide-induced organ damage, platelet dysfunction, and IL-6 and nitric oxide production in rats

Sepsis can lead to shock, multiple organ failure, and even death. Platelets play an active role in the pathogenesis of sepsis-induced multiple organ failure. Angiotensin (Ang)-(1–7), a biologically active peptide, counteracts various effects of Ang II and attenuates inflammatory responses, reactive oxygen species production, and apoptosis. We evaluated the effects of Ang-(1–7) on organ injury and platelet dysfunction in rats with endotoxaemia. We treated male Wistar rats with saline or lipopolysaccharide (LPS, 10 mg, intravenously) then Ang-(1–7) (1 mg/kg, intravenous infusion for 3 h beginning 30 min after LPS administration). We analysed several haemodynamic, biochemical, and inflammatory parameters, as well as platelet counts and aggregation. Ang-(1–7) improved hypotension and organ dysfunction, and attenuated plasma interleukin-6, chemokines and nitric oxide production in rats after LPS administration. The LPS-induced reduction in platelet aggregation, but not the decreased platelet count, was restored after Ang-(1–7) treatment. The protein expression of iNOS and IκB, but not phosphorylated ERK1/2 and p38, was diminished in Ang-(1–7)-treated LPS rats. The histological changes in liver and lung were significantly attenuated in Ang-(1–7)-treated LPS rats. Our results suggest that Ang-(1–7) ameliorates endotoxaemic-induced organ injury and platelet dysfunction, likely through the inhibition of the inflammatory response and nitric oxide production.