ABSTRACT

Background and Aim: Amyloidosis is characterized by extracellular deposition of misfolded fibrillar proteins that can disrupt tissue architecture and function. Although amyloid deposition has been extensively investigated in several organs, testicular involvement remains poorly characterized. This study investigated whether sodium caseinate (CasNa) administration induces progressive amyloid deposition in the testes of adult male rats and characterized the associated histopathological, histochemical, and β-amyloid (Aβ) immunohistochemical changes.

Materials and Methods: Twenty healthy adult male Albino Wistar rats (Rattus norvegicus) were randomly allocated to control and treatment groups (n = 10/group). Controls received 3.0 mL/kg intraperitoneal distilled water, whereas treated rats received 3.0 mL/kg body weight of 8% (w/v) CasNa. Five rats from each group were euthanized on days 25 and 60. Testicular tissues were evaluated using hematoxylin and eosin staining, histomorphometric measurement of seminiferous tubule diameter, and Congo red staining for amyloid-associated deposits. Immunohistochemistry was performed to assess Aβ immunoreactivity.

Results: CasNa administration induced progressive testicular lesions. On day 25, treated rats showed seminiferous tubule alterations, vascular congestion and vasculitis, germinal epithelial detachment, impaired spermatogenesis, and proteinaceous deposition in the interstitium. By day 60, severe necrosis, loss of normal testicular architecture, and mononuclear inflammatory cell infiltration were evident. Seminiferous tubule diameter decreased significantly in treated rats, with a greater reduction on day 60 (241.4 ± 9.664) than on day 25 (301.7 ± 4.597) (p < 0.0001). Congo red staining demonstrated extracellular amyloid-associated deposits predominantly in the interstitial tissue and along seminiferous tubule basement membranes. Aβ immunoreactivity was absent in controls but was moderate on day 25 (30.42 ± 6.870) and intense on day 60 (61.34 ± 6.870) in treated rats. Immunoreactivity increased significantly in both treated groups compared with controls and was significantly greater on day 60 than on day 25 (p < 0.0001).

Conclusion: Chronic CasNa administration induces progressive testicular amyloid-associated deposition, substantial structural damage, and increasing Aβ immunoreactivity in adult male rats. These findings support this experimental model for investigating testicular amyloidosis; however, Congo red staining and Aβ immunoreactivity alone don’t conclusively establish the biochemical identity of the deposited protein. Therefore, complementary molecular and biochemical approaches are required to confirm the identity of the deposited amyloid protein and determine its effects on male reproductive function.

Keywords: amyloid deposition, β-amyloid, Congo red, histopathology, immunohistochemistry, sodium caseinate, testicular amyloidosis, Rattus norvegicus.