Analysis of the relationship between central adiposity and biomechanical, histological, and immunohistochemical properties of the anterior wall of abdominal aortic aneurysms

Abstract

Objective

Adipose tissue plays a role in atherogenesis and degeneration of the vascular wall. However, the relationship between aortic abdominal aneurysm (AAA) and adipose tissue is controversial. This study aimed to correlate the biomechanical properties (elasticity and resistance), histology and immunohistochemistry findings of aortic tissue fragments from abdominal aortic aneurysms (AAAs) with the abdominal fat distribution determined by computed tomography scans.

Methods

This retrospective study analyzed data from biomechanical tests performed on fragments of the anterior wall of AAA obtained during open surgical repair. A uniaxial test was used to determine the tissue's failure tensile strength, tension, stress, and elasticity (strain). Preoperative computed tomography scans were used to quantify abdominal circumference at the L3-L4 and umbilical levels. Visceral and subcutaneous fat areas were quantified at these levels using tissue radiodensity. Univariate analysis and multiple regression models were used to correlate adiposity measures with biomechanical variables, considering factors such as hypertension, diabetes, and smoking status. Histological analysis (hematoxylin and eosin staining) was performed on twenty-five specimens, and immunohistochemical analysis (CD20, CD68, CD45, peroxisome proliferator activated receptor-γ [PPAR-γ], KLF5, and tumor necrosis factor-α) was performed on 13 specimens.

Results

The most common risk factors were hypertension (82%) and smoking (85%). Diabetes mellitus was present in 21.8%. No correlation was found between visceral fat area and biomechanical parameters or maximum AAA diameter. Predominance of visceral adipose tissue at L3-L4 and the umbilical level was associated with lower fibrosis in all layers of the abdominal wall (subcutaneous, 61% vs visceral, 41%), higher PPAR-γ expression in the tunica media (subcutaneous, 170.5-199.0 positive cells/mm² vs visceral, 957.88-1038.50 positive cells/mm²; P = .033), and lower elastic fiber concentration in the tunica media. (subcutaneous, 40.5% vs visceral, 31.5%).

Conclusions

No relationship was found between the biomechanical parameters of the AAA wall and visceral or subcutaneous fat areas. The predominance of visceral fat was associated with increased adipocyte cellularity and decreased elastic fiber concentration in the tunica media of the anterior AAA wall.