Investigation of the therapeutic effect of adrenomedullin on experimental autoimmune uveitis

Abstract

Purpose : Adrenomedullin (AM) is a peptide produced mainly by vascular endothelial cells and has various bioactivity, including anti-inflammatory, anti-apoptotic, and antioxidant stress effects. Experimental autoimmune uveitis (EAU) is a well-established model of human autoimmune uveitis. In this study, we investigated the therapeutic effect of AM-administration on EAU model in mice.

Methods : 10-week-old female C57BL/6J mice were used. To induce EAU, N-terminal peptide fragment of human interphotoreceptor retinoid-binding protein (hIRBP(1-20)) emulsified with complete Freund’s adjuvant containing Mycobacterium tuberculosis H37Ra was subcutaneously injected at the base of tails, followed by intraperitoneal injection of pertussis toxin. In the AM group, human recombinant AM was administered subcutaneously using an osmotic pump at an infusion rate of 29 μg/kg/day for 14 days. PBS was dosed to the vehicle group in the same manner, and those without EAU but given PBS were set as the control group. On day 14 after immunization, clinical and histological scores were evaluated. According to the severity of inflammatory findings, both scores were classified into 5 categories (0-4), respectively, as previously reported, with some modifications. We also counted the number of CD3-positive T cells. These scores and numbers were evaluated by two ophthalmologists in a blinded manner, and the average of both eyes was used as the result for each mouse. The expression of representative inflammatory genes in the retina was also evaluated by real-time PCR on day 7.

Results : Significant differences were found in the clinical score (p<0.05, n=5) and the number of T cells (p<0.0001, n=5) between AM-treated and vehicle-treated groups, but not in the histological score (p=0.3429, n=5). Furthermore, the retinas of AM-treated EAU mice showed significantly lower levels of TNF-α (p=0.001, n=4), IL-1β (p=0.0021, n=5) and IL-6 (p<0.0001, n=5) than those of the vehicle-treated EAU mice.

Conclusions : In the present study, AM treatment improved the clinical score, suppressed the number of T cells, and downregulated the expression of some inflammatory cytokine genes. Additional pathological and gene expression analysis would be necessary to elucidate the precise mechanism of AM's therapeutic effect on uveitis.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.