Oxidative Stress and Molecular Biomarkers of Male Infertility: From Redox Imbalance to Histological Injury

Abstract

Roughly one in six couples worldwide struggle with infertility, and a male factor is involved in about half of these cases. A growing body of work points to oxidative stress (OS) - an imbalance between reactive oxygen species (ROS) and the antioxidant systems meant to keep them in check - as one of the main biochemical threads connecting very different risk factors (infection, varicocele, obesity, smoking, environmental toxins) to a single downstream problem: damaged, poorly functioning sperm. This review brings together the histological and biochemical evidence on how oxidative stress injures the male reproductive tract, what molecular biomarkers are currently used to detect it, and how close (or far) this evidence is from being clinically useful. Low, tightly controlled levels of ROS are actually necessary for normal sperm capacitation, the acrosome reaction and fertilization; the problem starts once ROS output outpaces the antioxidant defenses of seminal plasma and sperm cells themselves. When that happens, membrane lipids peroxidize, sperm DNA fragments, and germ cells within the seminiferous epithelium begin to undergo apoptosis - changes that are visible histologically and measurable biochemically through markers such as malondialdehyde, 8-hydroxy-2'-deoxyguanosine, total antioxidant capacity, oxidation-reduction potential and pro-inflammatory cytokines. None of these markers work perfectly on its own, and none has an agreed clinical cut-off yet, which is exactly why they are usually discussed together rather than as a single diagnostic test. This review pulls that picture together and considers what would need to change for oxidative-stress testing to move from a research tool to routine practice