Zinc-Doped Carbon Dots Shield Sperm Cells From Microplastic Damage

Microplastics have become one of the most pervasive environmental contaminants of the modern era, and mounting evidence suggests they may be quietly undermining male fertility. Polystyrene microplastics, in particular, are small enough to infiltrate food, water, and ultimately human tissues, including the testes. Now, a research team writing in Materials Today Bio has reported a striking new therapeutic concept: ultrasmall carbon nanodots, doped with zinc and derived from a natural plant flavonoid, that can protect sperm-producing cells from microplastic damage by simultaneously restoring antioxidant defenses and suppressing a recently discovered form of cell death called cuproptosis. The findings, demonstrated in both cultured cells and a mouse model, point toward a new generation of bioinspired nanomedicines designed for the complex, multi-pathway injuries inflicted by environmental pollutants.

The scale of the problem is considerable. Chronic exposure to polystyrene microplastics has been linked to testicular histopathological damage, reduced sperm count and motility, elevated rates of sperm abnormality, and disrupted testosterone synthesis. At the molecular level, oxidative stress has emerged as a central driver of this injury: microplastic exposure triggers excessive production of reactive oxygen species, depletes key antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase, elevates lipid peroxidation markers like malondialdehyde, and activates stress-responsive signaling cascades including p38 MAPK and NF-κB. The end result is apoptotic death of spermatogenic cells and breakdown of the blood-testis barrier, the tightly regulated structure that shields developing germ cells from harmful circulating substances.

In their new study, the researchers established a mouse model in which animals received polystyrene microplastics through drinking water at doses of 0.1, 1, and 10 milligrams per kilogram per day for eight consecutive weeks, designed to mimic chronic human exposure scenarios. Histopathological examination revealed progressively worsening damage with increasing dose: the seminiferous epithelium became loosened and disorganized, germ cells exfoliated, vacuoles appeared, and both seminiferous and interstitial spaces enlarged. Quantitative morphometry confirmed dose-dependent declines in the tubule-to-epithelium ratio and Johnson’s spermatogenic function score, alongside significant increases in interstitial area. Sperm quality deteriorated in parallel, with declining counts and rising abnormality rates, consistent with human population studies reporting that microplastics detected in semen correlate negatively with sperm concentration and motility.

Perhaps the most provocative discovery came from probing deeper molecular mechanisms. The team found that microplastic exposure disrupted testicular copper homeostasis in a distinctive pattern: the copper influx transporter SLC31A1 was upregulated while the efflux chaperone ATP7B was downregulated, driving intracellular copper overload. Concurrently, LIAS and FDX1, established executors of cuproptosis, were elevated. Cuproptosis is a form of regulated cell death mechanistically distinct from apoptosis, ferroptosis, and necroptosis. It depends on mitochondrial respiration and is triggered when copper directly binds lipoylated proteins of the tricarboxylic acid cycle, causing protein aggregation, loss of iron-sulfur cluster proteins, proteotoxic stress, and eventual cell death. The researchers also observed dose-dependent suppression of Nrf2 and its downstream antioxidant effector HO-1, the master endogenous defense pathway against oxidative damage. Notably, even at the environmentally relevant low dose of 0.1 milligrams per kilogram per day, comparable to estimated human dietary intake, molecular perturbations were detectable without overt histological damage, indicating subclinical reproductive injury from chronic low-level exposure.

Confronted with this dual threat of oxidative damage and copper-mediated cell death, conventional antioxidant supplementation appeared inadequate, since it typically addresses only one arm of the pathology. The team instead turned to rational nanomaterial design. They selected trifolirhizin, a naturally occurring flavonoid glycoside with documented antioxidant and anti-inflammatory properties, and co-processed it with zinc nitrate via a one-pot hydrothermal reaction, incorporating citric acid and ethylenediamine as additional precursors. Zinc was a deliberate choice: it is an essential trace element for male reproductive health with established roles in testicular development, spermatogenesis, sperm membrane stabilization, and hormone regulation. Critically, zinc is redox-inert, meaning it does not directly generate oxidative stress unlike redox-active metals such as iron and copper. Furthermore, given the competitive antagonism between zinc and copper in intestinal absorption and metal transporter binding, zinc might plausibly modulate cuproptosis through copper homeostasis, a hypothesis the study set out to test directly.

The resulting zinc-doped trifolirhizin-derived carbon dots, termed ZnTFZCDs, were thoroughly characterized. Transmission electron microscopy revealed well-dispersed ultrasmall spheres roughly four to six nanometers in hydrodynamic diameter, with lattice fringes indicating locally ordered carbon domains formed during carbonization. X-ray diffraction showed a broad peak characteristic of amorphous, turbostratic carbon. Spectroscopic analyses confirmed abundant oxygen- and nitrogen-containing functional groups on the dot surfaces, alongside characteristic Zn-O signals and Zn 2p peaks at 1021.62 and 1044.60 electron volts, providing solid evidence of successful zinc incorporation. This structural profile, the authors argue, creates an ideal platform combining the bioactivity of the precursor molecule with the enhanced stability, cellular uptake, and multi-functionality of carbon-based nanomaterials.

In vitro experiments using GC-2 spermatocytes and RAW264.7 macrophages demonstrated the superiority of the doped formulation. While free trifolirhizin offered only marginal protection and undoped carbon dots moderate rescue, ZnTFZCDs produced the most pronounced restoration of cell viability under microplastic challenge, with maximal efficacy at 100 micrograms per milliliter. The nanoparticles most effectively scavenged reactive oxygen species, rescued depleted antioxidant enzyme activities, and reduced malondialdehyde accumulation. At the mitochondrial level, microplastic exposure caused severe depolarization of mitochondrial membrane potential, visualized by a shift in JC-1 fluorescence from red aggregates to green monomers. ZnTFZCDs produced the strongest recovery of membrane potential and significantly reduced lipid peroxidation, restoring the reduced-to-oxidized BODIPY-C11 fluorescence ratio and upregulating GPX4, the principal enzyme that detoxifies phospholipid hydroperoxides within cellular membranes. This multi-layered protection effectively breaks the vicious cycle linking mitochondrial dysfunction, ROS overproduction, and membrane lipid damage.

Pharmacological inhibitor experiments added a crucial layer of mechanistic clarity. When GC-2 cells were treated with inhibitors targeting cuproptosis, ferroptosis, autophagy, and NLRP3-pyroptosis respectively, the copper chelator TTM exerted the strongest protective effect, the ferroptosis inhibitor Ferrostatin-1 provided only partial rescue, and the autophagy and pyroptosis inhibitors failed to restore viability. This indicated that cuproptosis is the predominant mediator of microplastic-induced germ cell injury. Accordingly, ZnTFZCDs were shown to rebalance copper trafficking by rescuing ATP7B expression, suppressing abnormal SLC31A1 overexpression, and normalizing elevated LIAS and FDX1 levels, thereby correcting the copper-mediated metabolic perturbation that primes lipoylated protein aggregation and proteotoxic stress. The treatment also restored expression of CYP11A1, SOX9, STRA8, and GPX4, proteins governing steroidogenesis, Sertoli cell support, meiotic initiation, and antioxidant defense, effectively reactivating the full spermatogenic molecular program.

The in vivo results were equally compelling. In mice co-administered ZnTFZCDs alongside microplastic exposure, the nanoparticles preserved ordered seminiferous tubular architecture, mitigated germ cell shedding, elevated sperm counts, decreased abnormal sperm ratios, and improved Johnson scores compared with free trifolirhizin or undoped carbon dots. Western blot analysis of testicular tissues confirmed that the doped dots maintained spermatogenesis-related proteins, reversed copper transporter dysregulation, suppressed cuproptosis executors, and reactivated the Nrf2/HO-1 antioxidant axis. Just as importantly, comprehensive biosafety testing revealed no cytotoxicity up to 200 micrograms per milliliter, negligible hemolysis, stable liver and kidney function markers over fourteen days of administration, and no histopathological abnormalities in heart, liver, spleen, lung, or kidney, all critical prerequisites for a therapeutic intended for repeated administration in reproductive contexts.

The study’s authors emphasize that ZnTFZCDs should be understood not merely as antioxidants but as multifunctional regulators establishing a complete axis from upstream stress alleviation to downstream functional recovery. By integrating natural-product bioactivity, functional metal doping, and carbon dot nanoengineering, the platform illustrates how programmable multi-target interventions may outperform single-pathway strategies against complex environmental exposures. The team cautions that future work must evaluate long-term biodistribution, metabolic fate, and efficacy in more clinically relevant models, including chronic low-dose regimes and potentially non-human primates. Nevertheless, as microplastic contamination continues to accumulate globally and human exposure becomes unavoidable, this bioinspired nanotherapeutic approach offers a genuinely new paradigm: rather than merely mopping up free radicals, it addresses the intertwined redox, mitochondrial, and copper-homeostatic disruptions that together drive environmentally induced male reproductive decline.

Subject of Research: Bioinspired zinc-doped carbon dots as a nanotherapeutic strategy against polystyrene microplastic-induced male reproductive toxicity through Nrf2 activation and cuproptosis suppression

Article Title: Bioinspired zinc-doped carbon dots protect against polystyrene microplastic-induced spermatogenic dysfunction through Nrf2 activation and cuproptosis suppression

Article References: Li, T., Li, K., Yang, S., Pan, H., Cai, Z., Hua, X., Liao, G., Luo, B., & Zhang, J. (2026). Bioinspired zinc-doped carbon dots protect against polystyrene microplastic-induced spermatogenic dysfunction through Nrf2 activation and cuproptosis suppression. Materials Today Bio, 41, Article 103675. https://doi.org/10.1016/j.mtbio.2026.103675

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103675

Keywords: microplastics, polystyrene, carbon dots, male fertility, cuproptosis, Nrf2, oxidative stress, zinc, spermatogenesis, nanomedicine, testicular injury, GPX4