[Testicular injection of lipopolysaccharide: An effective method for establishing the mouse model of orchitis]

To search for a method of establishing a reliable mouse model of orchitis and investigate the association of orchitis with the activation of the inflammasome.

We equally randomized 40 adult male KM mice into groups A (sham operation), B (intraperitoneal injection of lipopolysaccharide ［LPS］), C (unilateral testicular injection of glacial acetic acid ［GAA］), and D (unilateral testicular injection of LPS). At 3 weeks after modeling, we measured the sperm concentration and percentage of progressively motile sperm (PMS) in the epididymis by computer-assisted semen analysis, observed the pathological changes in the testis tissue by HE staining, and determined the expressions of the Caspase-1 and interleukin (IL)-1β proteins by Western blot.

The sperm concentration in the epididymis was significantly decreased in groups B (［25.74 ± 3.19］ ×10⁶/ml), C (［17.16 ± 4.41］ ×10⁶/ml) and D (［16.92 ± 7.13］ ×10⁶/ml) as compared with that in group A (［28.20 ± 1.63］ ×10⁶/ml) (all P < 0.05), even more significantly in B than in C and D (P < 0.01), and so was PMS in groups B (［29.57 ± 2.16］%), C (［18.10 ± 2.38］%) and D (［7.34 ± 1.63］%) in comparison with group A (［59.34 ± 1.10］%) (P < 0.01), even more significantly in B and C than in D (P < 0.01). Light microscopy revealed different degrees of pathological changes in the testis tissue, most significant in group D, followed by C and B. Both the expressions of Caspase-1 and IL-1β were remarkably up-regulated in groups B, C and D compared with those in group A (P < 0.01), even more markedly in D than in B and C (P < 0.05).

Unilateral testicular injection of LPS is a more efficient method than either unilateral testicular injection of GAA or intraperitoneal injection of LPS for establishing the mouse model of orchitis. Orchitis may be pathologically associated with the activation of the NLRP3 inflammasome.