Interplay Between Sperm Function and Seminal Plasma Biochemical Profile in a Group of Normozoospermic Subjects

Seminal plasma regulates sperm function; oxidative stress (OS) and inflammation can impair semen biochemical homeostasis. This study investigated seminal biochemical/enzymatic compounds and Trolox Equivalent Antioxidant Capacity (TEAC) in seminal plasma and spermatozoa from normozoospermic men (>5th percentile) assessing their relationship with sperm quality. The strongest significant (p < 0.001 ***) negative correlations (r) were found for normal sperm morphology and albumin (ALB, r = −0.515 ***), cholesterol (CHO, r = −0.386 ***), lactate dehydrogenase (LDH, r = −0.514 ***), sperm TEAC (r = −0.438 ***) and homocysteine (Hcy; r = −0.381 ***); sperm progressive motility with ALB (r = −0.495 ***), CHO (r = −0.349 ***), LDH (r = −0.355 ***) and sperm TEAC (r = −0.295 ***); sperm vitality with creatine kinase (CK, r = −0.486 ***) and LDH (r = −0.380 ***). Total prostate-specific antigen (TPSA) was positively correlated with sperm quality. After stratification, subjects with low-normal sperm parameters showed significantly higher levels of ALB, CHO, CK, LDH, interleukin 6 (IL-6), Hcy and sperm TEAC vs. high-normal parameter subjects. ALB, Hcy and LDH were increased in individuals with progressive motility, normal morphology and vitality < 25th percentile indicating their involvement in OS, inflammation and accessory gland activity. These findings suggest that World Health Organization lower reference limits are not a strict cutoff between normal and abnormal semen quality but rather define a baseline of biochemical efficiency and sperm function, highlighting the synergy between spermatozoa and seminal plasma.