β2-microglobulin amyloid deposition and the RAGE-related inflammation pathway in ligamentum flavum thickening among patients undergoing hemodialysis: a comparative cross-sectional study from Japan

Study Design: A comparative cross-sectional study using histological, biochemical, and molecular analyses of ligamentum flavum (LF). Purpose: To investigate whether LF hypertrophy in hemodialysis (HD) patients is associated with β2-microglobulin (B2M) amyloid and advanced glycation end-product (AGE) deposition, along with the receptor for AGE (RAGE)-related inflammatory activation. Overview of Literature: Lumbar spinal canal stenosis (LSCS) is common in HD patients. Although B2M amyloid is a hallmark of dialysisrelated amyloidosis, the role of the AGE-RAGE axis in LF pathology remains unclear. Methods: LF tissues from 33 patients with LSCS (HD, n=16; non-HD, n=17) were analyzed. Amyloid deposition was evaluated using direct fast scarlet (DFS) staining and B2M immunohistochemistry. Pentosidine and carboxymethyl-lysine (CML) levels were quantified by high-performance liquid chromatography in subsets (n=6 per group). Expression of RAGE-related inflammatory genes was measured using quantitative reverse transcription-polymerase chain reaction. Comparisons were made between the HD and non-HD groups, paired comparisons of DFS-stained areas on the dorsal and ventral sides of LF were performed within the HD group. Results: B2M amyloid deposition was observed exclusively in LF of HD group and predoninated dorsally (29.7%±8.6% vs. 11.9%±6.9%, p=0.001). Pentosidine levels were significantly higher in HD group than in non-HD group (28.5±10.6 μg/g vs. 16.1±4.2 μg/g, p=0.009), whereas CML levels didn't differ. On the dorsal side of LF, all examined RAGE-related inflammatory genes except toll-like receptor 4 was significantly upregulated in HD group; ventral expression showed no group differences. Immunohistochemical analysis demonstrated localized expression of RAGE, high-mobility group box 1, and nuclear factor-kappa B surrounding amyloid deposits. Conclusions: LF in HD patients exhibits B2M amyloid and AGE accumulation with upregulation of RAGE-related inflammatory genes and proteins, especially on the dorsal side. LF hypertrophy in dialysis-related LSCS appears to represent an inflammatory-amyloid phenotype, indicating the AGE-B2M-RAGE pathway as a potential therapeutic target.