Abstract P147: Production of Anti-inflammatory Peptide N-Acetyl-Seryl-Aspartyl-Lysyl-Proline (Ac-SDKP) in Kidney

Abstract

Ac-SDKP is a natural peptide with anti-fibrotic and anti-inflammatory properties in vascular, myocardial and kidney tissues. It is released from thymosin B4 (TB4) by two step enzymatic reactions by meprin and the prolyl oligopeptidase enzymes (POP) and degraded by angiotensin converting enzyme (ACE). Treatment with ACE inhibitors (ACEi) increases Ac-SDKP plasma concentration. Kidney has been proposed as clearance organ for Ac-SDKP. Thus after Ac-SDKP filtration, 90% is degraded and only 10% is excreting in the urine. However, in rodents the decrease of glomerular filtration rate did not affect the amount of Ac-SDKP in urine and prevention of Ac-SDKP filtration at the glomerular level by using neutralizing antibodies also did no change the urinary Ac-SDKP content; This suggest that mechanisms other than only filtration can be present. We hypothesized that Ac-SDKP is produced in the kidney. We evaluated the presence of TB4 and POP mRNA by analyzing the trascriptome in each segment of the nephron using the public access NHI database ESBL. We confirmed kidney expression of POP enzyme by immunohistochemistry (IHC). Finally the stop flow pressure technique was used to evaluate the Ac-SDKP formation in different segments of the nephron, in normal condition, under POP inhibition (POPi) and ACEi. All experiments were performed in Sprague-Dawley rats.TB4 mRNA was present in all the nephron segments, mainly in the distal parts (1941±949.8 RPKM) in comparison with proximal tubule (101.4±73.7 RPKM) (p<0.05). POP enzyme mRNA was present in proximal tubule, loop of Henle (inner medulla) and distal nephron (distal, connecting and collecting tubules). POP enzyme expression by IHC was observed in the distal convoluted tubule in cortex and mainly in the medullary region. The Stop flow technique showed the high Ac-SDKP/Inulin ratio in the distal nephron: 10.5±0.8 vs. 4.2±0.1 in the proximal segments (p<0.01). POPi infusion into the kidney decreased Ac-SDKP/Inulin in comparison to the vehicle group in distal (10.5±0.8 vs 5.6±0.8, p<0.01) and proximal nephron segments (4.22±0.1 vs. 2.1±0.2, p<0.01). ACEi increased the Ac-SDKP content in all nephron segments, mainly in the distal part. We conclude that Ac-SDKP is synthetized in kidney, predominantly in the distal nephron.