Quantitative Analysis and Toxicological Mechanisms of Various Male Infertility Inducers: A Network Meta-Analysis and Pharmacological Approach

Network meta-analysis of 201 rodent studies ranks microplastics alongside chemotherapy drugs for reproductive toxicity, with sperm counts dropping to ~19 million/mL

Journal: Reproductive Toxicology | Published: 2025-12-05 | Type: Systematic Review, Network Meta-Analysis | PMID: 41354316 Authors: Arif et al., Chongqing Medical University (China); with co-authors from Temple University and University of Malaya Funding/COI: Funding not listed. Authors declare no competing financial interests.

Summary

This network meta-analysis pooled 201 rodent studies (3,412 animals) to rank nine male infertility inducers by severity of reproductive damage. Microplastics, cyclophosphamide, and streptozotocin produced the worst outcomes across sperm count, motility, and testosterone. Oxidative stress — specifically via NFE2L2, SOD1, and HMOX1 — emerged as the mechanistic through-line shared by all nine inducers.

Claims

• Microplastics reduced mean sperm count to 18.97 ± 11.1 × 10⁶/mL and motility to 31.32 ± 10.2% — the worst count among the nine inducers tested
• Cyclophosphamide: sperm count 30.08 ± 19.1 × 10⁶/mL, motility 31.73 ± 6.1%
• Streptozotocin (diabetic model): sperm count 38.13 ± 8.2 × 10⁶/mL, motility 30.74 ± 4.1%
• Across all inducers: sperm count fell 1.46-fold, motility 1.21-fold, testosterone 1.16-fold
• Bisphenol-A, lead acetate, valproic acid, tripterygium glycosides, high-fat diet, and heat stress rounded out the nine agents
• Network pharmacology analysis flagged NFE2L2, SOD1, and HMOX1 as shared oxidative stress targets
• Trend analysis (2009–2024) shows rising research volume on microplastics, high-fat diet, and lead acetate

Study Quality

This is a network meta-analysis — methodologically the right tool for comparing multiple exposures without head-to-head trials. The inclusion of 201 studies and 3,412 animals gives it reasonable statistical weight for a rodent dataset. The authors appropriately used NMA to generate indirect comparisons across inducers that were never tested side-by-side, and the network pharmacology layer adds mechanistic context that pure NMAs typically lack.

The translational framing, however, outpaces the evidence. Every single study in this meta-analysis is a rodent model. The authors claim "clinical relevance" and call their findings applicable to "risk assessment and mitigation strategies" for humans — that's a large inferential leap. Rodent infertility models use doses that often don't reflect real-world human exposure levels. The paper does not appear to systematically address dose comparability across studies, which is a significant gap when ranking inducers by severity.

Red Flags

• Entirely animal data — 201 studies, 3,412 rodents, zero humans. All clinical extrapolation is speculative.
• Dose equivalence unaddressed — comparing microplastic exposure in a gavage study to cyclophosphamide chemotherapy without dose normalization makes the severity ranking potentially meaningless for human risk assessment
• Funding not listed — unusual for a multi-institution study; raises questions about undisclosed support
• "First integrated analysis" claim — common in abstracts, rarely true; not independently verified here
• STZ as a comparator — streptozotocin induces diabetes in rodents; its sperm toxicity may be partly secondary to metabolic disease, not direct reproductive toxicity, which complicates the ranking
• High heterogeneity is expected in this kind of cross-inducer NMA but is not prominently discussed in the abstract

Strengths

• Large dataset (201 studies) with a structured, reproducible NMA framework
• Nine mechanistically diverse inducers compared in a single analysis — genuinely useful for understanding relative effect sizes in animal models
• Network pharmacology integration identifies shared molecular targets, giving the findings some mechanistic coherence
• Trend analysis across 15 years contextualizes which exposures are getting research attention and why
• No declared conflicts of interest

Verdict

This paper is worth reading as a synthesis of the animal literature on reproductive toxicants — it's the most comprehensive rodent-model comparison to date and the microplastics finding will get traction. But treat the "clinical relevance" framing with skepticism. Ranking chemotherapy alongside dietary plastic particles in rodents, then implying this informs human risk assessment, requires dose-normalized human data that doesn't exist here. The mechanistic oxidative stress story is plausible and consistent with prior literature; the leap to therapeutic targets is premature. Solid rodent-model meta-analysis, oversold conclusion section.