Do inflammatory cytokines and oxidative stress impair Leydig cell steroidogenesis and sperm quality?

Evidence regarding the impact of systemic inflammation and oxidative stress on male reproductive health indicates a well-characterized pathway of Leydig cell dysfunction, particularly relevant in the context of age-related "inflammaging."

Mechanistic impairment of steroidogenesis

The primary disruption occurs within the Leydig cell mitochondria, the site of the rate-limiting step in testosterone synthesis.

• StAR Protein Suppression: Pro-inflammatory cytokines, specifically TNF-α and IL-1β, significantly downregulate the expression of the Steroidogenic Acute Regulatory (StAR) protein. StAR is essential for transporting cholesterol into the mitochondria; its inhibition creates a biosynthetic bottleneck.
• Mitochondrial Integrity: Oxidative stress (ROS) induces mitochondrial membrane depolarization and lipid peroxidation. This damages the mitochondrial ultrastructure and inhibits cytochrome P450 side-chain cleavage (P450scc), the enzyme responsible for converting cholesterol to pregnenolone.
• Cellular Senescence: Chronic inflammatory signaling can lead to Leydig cell senescence and interstitial fibrosis, further reducing the population of functional steroidogenic cells.

Clinical impact on testosterone and sperm quality

The transition from molecular impairment to clinical outcomes is supported by robust observational and mechanistic data.

• Testosterone Deficiency: In middle-aged men, elevated high-sensitivity C-reactive protein (hs-CRP) is associated with an 80% increased risk of biochemical hypogonadism. Studies show that IL-2 infusions can acutely lower testosterone levels without altering LH, confirming a direct inhibitory effect on Leydig cells.
• Sperm Degradation: While intratesticular testosterone is critical for Sertoli cell function and the blood-testis barrier, oxidative stress independently damages sperm. High seminal levels of IL-6 and ROS are strongly correlated with increased sperm DNA fragmentation (DFI) and lipid peroxidation of the sperm plasma membrane, which directly impairs motility and morphological integrity.

Bottom line

Inflammatory cytokines and oxidative stress impair the StAR-mediated transport of cholesterol into Leydig cell mitochondria, directly reducing testosterone production and compromising sperm DNA integrity and motility. This pathway represents a primary mechanism for declining reproductive function in aging males.