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Neutrophil to Lymphocyte Ratio Reflects the Proteolytic Activity of the Abdominal Aortic Aneurysm Wall

Background: This study aims to evaluate the local proteolytic activity from the level of Abdominal Aortic Aneurysm (AAA) wall and correlate the obtained values with the preoperative values of NLRs (Neutrophil-Lymphocyte Ratio), evaluating a possible association between the two variables and, implicitly, between the local proteolysis process and the systemic inflammatory response of those patients diagnosed with AAA. Methods: The current study is monocentric, observational, and prospective, taking place at the Department of Cardiovascular Surgery, Cluj-Napoca, Romania. Patients undergoing elective or emergency classical surgery for unruptured AAA or ruptured AAA were included in the study. During classical surgery, samples from the infrarenal aortic aneurysmal wall were collected in a standardized manner, from the central part of the anterior wall from uAAA and rAAA and were analyzed by gel zymography. Results: The concentration of MMP2 was similar in the ruptured/non-ruptured group, without any statistical significance. In the MMP-9 case, we obtained a mean of 821.35 U arb/µg at the level of unruptured aneurysmal wall and 1411.57 U arb/µg at the level of the ruptured aneurysmal wall. According to the ANOVA test, there is a significant difference between the two categories of aneurysms. The same correlation was observed regarding both the zymogen category, pro-MMP-2, as well as pro-MMP-9: they expressed significant higher quantities of inactive enzymes in rAAA. We splitted the study population into two categories: patients who presented preoperative NLR values < 5 and > 5. MMP-2 collagenase levels did not register statistical differences between the two groups, p = 0.3236. High levels of MMP-9 are positively associated with increased values of NLR, the NLR<5 group had an MMP-9 mean of 902.41(473.71) U arb/µg, statistically lower than the MMP-9 mean indicated in the NLR>5 group, 1474(521.21) U arb/µg. Similarly, MMP-2 and MMP-9 zymogens were found in statistically higher quantities (p < 0.05) in the NLR>5 group of patients. Conclusions: This is the first study that analyzes a possible correlation between the local proteolytic activity at the site of the dilated aneurysmal aortic wall and circulating levels of NLR. Following the results obtained, we conclude that the group of patients presenting with NLR>5 preoperatively, as in the rAAA group, significantly greater levels of MMP-9 and inactive proenzymes were identified. Local metalloproteinase MM9 activity is proportional to the systemic inflammatory activity. Concomitantly, we hypothesize that the increased sensitivity of NLR as a prognostic marker in AAA pathology, which is ensured and confirmed by its strong association with local proteolytic activity, directly implied in the evolution of the disease.