Determination of Biological and Molecular Attributes Related to Polystyrene Microplastic-Induced Reproductive Toxicity and Its Reversibility in Male Mice

Climate change, microplastics, and male infertility

PURPOSE OF REVIEW

Semen quality is on the decline. While the etiology is unknown, recent literature suggests there may be a relationship between climate change, environmental toxins and male fertility. This review relays new information regarding associations between our environment and male infertility.

RECENT FINDINGS

Several recent studies have documented a negative association between heat stress and spermatogenesis, which suggests that climate change may be a factor in declining in sperm counts. The influence of particle pollution on spermatogenesis has also been recently investigated, with studies demonstrating a negative association. Another possible factor are microplastics, which have been posited to reduce sperm production. Recent animal studies have shown that microplastic exposure alters both adult sperm production and prenatal male genital development. The relationship between endocrine disrupting chemicals and male fertility remains an area of active study, with recent animal and human studies suggesting an association between these chemicals and male fertility.

SUMMARY

The etiology of the decline in male fertility over the past decades is yet unknown. However, changes in our environment as seen with climate change and exposure to pollutants and endocrine disrupting chemicals are proposed mechanisms for this decline. Further studies are needed to investigate this association further.

Adverse effects and potential mechanisms of polystyrene microplastics (PS-MPs) on the blood-testis barrier

Microplastics (MPs) are defined as plastic particles or fragments with a diameter of less than 5 mm. These particles have been identified as causing male reproductive toxicity, although the precise mechanism behind this association is yet to be fully understood. Recent research has found that exposure to polystyrene microplastics (PS-MPs) can disrupt spermatogenesis by impacting the integrity of the blood-testis barrier (BTB), a formidable barrier within mammalian blood tissues. The BTB safeguards germ cells from harmful substances and infiltration by immune cells. However, the disruption of the BTB leads to the entry of environmental pollutants and immune cells into the seminiferous tubules, resulting in adverse reproductive effects. Additionally, PS-MPs induce reproductive damage by generating oxidative stress, inflammation, autophagy, and alterations in the composition of intestinal flora. Despite these findings, the precise mechanism by which PS-MPs disrupt the BTB remains inconclusive, necessitating further investigation into the underlying processes. This review aims to enhance our understanding of the pernicious effects of PS-MP exposure on the BTB and explore potential mechanisms to offer novel perspectives on BTB damage caused by PS-MPs.

Reactive Oxygen Species-Mediated Mitophagy and Cell Apoptosis are Involved in the Toxicity of Aluminum Chloride Exposure in GC-2spd

Aluminum chloride is an inorganic polymeric coagulant commonly found in daily life and various materials. Although male reproductive toxicity has been associated with AlCl3 exposure, the underlying mechanism remains unclear. This study aimed to examine the impact of AlCl3 exposure on mitophagy and mitochondrial apoptosis in testicular tissue and mouse spermatocytes. Reactive oxygen species (ROS) and ATP levels were measured in GC-2spd after AlCl3 exposure using a multifunctional enzyme labeler. The changes in mitochondrial membrane potential (MMP) and TUNEL were observed through confocal laser microscopy, and the expression of proteins associated with mitophagy and apoptosis was analyzed using Western blot. Our results demonstrated that AlCl3 exposure disrupted mitophagy and increased apoptosis-related protein expression in testicular tissues. In the in vitro experiments, AlCl3 exposure induced ROS production, suppressed cell viability and ATP production, and caused a decrease in MMP, leading to mitophagy and cell apoptosis in GC-2spd cells. Intervention with N-acetylcysteine (NAC) reduced ROS production and partially restored mitochondrial function, thereby reversing the resulting mitophagy and cell apoptosis. Our findings provide evidence that ROS-mediated mitophagy and cell apoptosis play a crucial role in the toxicity of AlCl3 exposure in GC-2spd. These results contribute to the understanding of male reproductive toxicity caused by AlCl3 exposure and offer a foundation for future research in this area.

Understanding the impact of nanoplastics on reproductive health: Exposure pathways, mechanisms, and implications

Microplastic pollution is a pressing global environmental concern with particular urgency surrounding the issue of nanoplastic particles. Plastic products exhibit a remarkable persistence in natural ecosystems, resisting easy degradation. Nanoplastics, characterized by their diminutive size, possess distinct properties when compared to their larger counterparts, which could potentially render them more ecologically detrimental. Microplastics themselves serve as carriers for toxic and hazardous substances, such as plastic additives, that enter and persist in the environmental cycle. Importantly, nanoplastics exhibit enhanced bioavailability upon entering the food chain. Notably, studies have demonstrated the adverse effects of nanoplastics on the reproductive function of aquatic organisms, and evidence of micro- and nanoplastics have emerged within human reproductive organs, including the placenta. However, a knowledge gap persists regarding the impacts of nanoplastics on the reproductive systems of mammals and, indeed, humans. This paper aims to elucidate the less frequently discussed sources and distribution of nanoplastics in the environment, along with the pathways of human exposure. We also emphasize the extent to which nanoplastics accumulate within the reproductive systems of organisms. Subsequently, we present an in-depth analysis of the effects of nanoplastics and their associated contaminants on mammalian and human reproductive health. The mechanisms through which nanoplastics contribute to reproductive disorders are comprehensively explored, highlighting their potential to disrupt endocrine levels in mammals and humans. Additionally, we scrutinize and discuss studies on biotoxicity of nanoplastics, offering insights into potential areas for future research.

A meta-analysis-based adverse outcome pathway for the male reproductive toxicity induced by microplastics and nanoplastics in mammals

The male reproductive toxicity of microplastics (MPs) and nanoplastics (NPs) has attracted great attention, but the latent mechanisms remain fragmented. This review performed the adverse outcome pathway (AOP) analysis and meta-analysis in 39 relevant studies, with the AOP analysis to reveal the cause-and-effect relationships of MPs/NPs-induced male reproductive toxicity and the meta-analysis to quantify the toxic effects. In the AOP framework, increased reactive oxygen species (ROS) is the molecular initiating event (MIE), which triggered several key events (KEs) at different levels. At the cellular level, the KEs included oxidative stress, mitochondrial dysfunction, sperm DNA damage, endoplasmic reticulum stress, apoptosis and autophagy of testicular cells, repressed expression of steroidogenic enzymes and steroidogenic acute regulatory protein, disrupted hypothalamic-pituitary-testicular (HPT) axis, and gut microbiota alteration. These KEs further induced the reduction of testosterone, impaired blood-testis barrier (BTB), testicular inflammation, and impaired spermatogenesis at tissue/organ levels. Ultimately, decreased sperm quality or quantity was noted and proved by meta-analysis, which demonstrated that MPs/NPs led to a decrease of 5.99 million/mL in sperm concentration, 14.62% in sperm motility, and 23.56% in sperm viability, while causing an increase of 10.65% in sperm abnormality rate. Overall, this is the first AOP for MPs/NPs-mediated male reproductive toxicity in mammals. The innovative integration of meta-analysis into the AOP analysis increases the rigorism of the results.

Microplastics exposure: implications for human fertility, pregnancy and child health

Plastics found in our everyday environment are becoming an increasing concern for individual and population-level health, and the extent of exposure and potential toxic effects of these contaminants on numerous human organ systems are becoming clear. Microplastics (MPs), tiny plastic particles, appear to have many of the same biological effects as their plastic precursors and have the compounded effect of potential accumulation in different organs. Recently, microplastic accumulation was observed in the human placenta, raising important questions related to the biological effects of these contaminants on the health of pregnancies and offspring. These concerns are particularly heightened considering the developmental origins of health and disease (DOHaD) framework, which postulates that in utero exposure can programme the lifelong health of the offspring. The current review examines the state of knowledge on this topic and highlights important avenues for future investigation.

PLASTAMINATION: Outcomes on the Central Nervous System and Reproduction

BACKGROUND

Environmental exposures to non-biodegradable and biodegradable plastics are unavoidable. Microplastics (MPs) and nanoplastics (NPs) from the manufacturing of plastics (primary sources) and the degradation of plastic waste (secondary sources) can enter the food chain directly or indirectly and, passing biological barriers, could target both the brain and the gonads. Hence, the worldwide diffusion of environmental plastic contamination (PLASTAMINATION) in daily life may represent a possible and potentially serious risk to human health.

OBJECTIVE

This review provides an overview of the effects of non-biodegradable and the more recently introduced biodegradable MPs and NPs on the brain and brain-dependent reproductive functions, summarizing the molecular mechanisms and outcomes on nervous and reproductive organs. Data from in vitro, ex vivo, non-mammalian and mammalian animal models and epidemiological studies have been reviewed and discussed.

RESULTS

MPs and NPs from non-biodegradable plastics affect organs, tissues and cells from sensitive systems such as the brain and reproductive organs. Both MPs and NPs induce oxidative stress, chronic inflammation, energy metabolism disorders, mitochondrial dysfunction and cytotoxicity, which in turn are responsible for neuroinflammation, dysregulation of synaptic functions, metabolic dysbiosis, poor gamete quality, and neuronal and reproductive toxicity. In spite of this mechanistic knowledge gained from studies of non-biodegradable plastics, relatively little is known about the adverse effects or molecular mechanisms of MPs and NPs from biodegradable plastics.

CONCLUSION

The neurological and reproductive health risks of MPs/NPs exposure warrant serious consideration, and further studies on biodegradable plastics are recommended.

The reproductive and transgenerational toxicity of microplastics and nanoplastics: A threat to mammalian fertility in both sexes

Microplastics (MPs) and nanoplastics (NPs) are extensively distributed in the environment. However, a comprehensive review and in-depth discussion on the effects of MPs and NPs to reproductive capacity and transgenerational toxicity on mammals, especially on humans, is lacked. It is suggested that microplastics and nanoplastics could accumulate in mammalian reproductive organs and exert toxic effects on the reproductive system for both sexes. For males, the damage of microplastics consists of abnormal testicular and sperm structure, decreased sperm vitality, and endocrine disruption, which were caused by oxidative stress, inflammation, apoptosis of testicular cells, autophagy, abnormal cytoskeleton, and abnormal hypothalamic-pituitary-testicular axis. For females, the damage of microplastics includes abnormal ovary and uterus structure and endocrine disruption, which were caused by oxidative stress, inflammation, granulosa cell apoptosis, hypothalamic-pituitary-ovary axis abnormalities, and tissue fibrosis. For transgenerational toxicity, premature mortality existed in the rodent offspring after maternal exposure to microplastics. Among the surviving offspring, metabolic disorders, reproductive dysfunction, immune, neurodevelopmental, and cognitive disorders were detected, and these events directly correlated with transgenerational translocation of MPs and NPs. Studies on human-derived cells or organoids demonstrated that transgenerational toxicity studies for both sexes are yet in the phase of exploring suitable experimental models, and more detailed research on the threat of MPs and NPs to human fertility is still urgently needed. Further studies will help assess the MPs and NPs threat to public fertility and reproductive health risks.

A short-term high-fat diet alters rat testicular activity and blood-testis barrier integrity through the SIRT1/NRF2/MAPKs signaling pathways

Background

Overweight/obesity are metabolic disorder resulting from behavioral, environmental, and heritable causes. WHO estimates that 50% of adults and 30% of children and adolescents are overweight or obese, and, in parallel, an ongoing decline in sperm quality and male fertility has been described. Numerous studies demonstrated the intimate association between overweight/obesity and reproductive dysfunction due to a highly intricate network of causes not yet completely understood. This study expands the knowledge on the impact of a short-term high-fat diet (st-HFD) on rat testicular activity, specifically on steroidogenesis and spermatogenesis, focusing on the involved molecular mechanisms related to mitochondrial dynamics, blood-testis barrier (BTB) integrity, and SIRT1/NRF2/MAPKs pathways.

Methods

Ten adult Male Wistar rats were divided into two groups of five and treated with a standard diet or an HFD for five weeks. At the end of the treatment, rats were anesthetized and sacrificed by decapitation. Blood was collected for serum sex hormone assay; one testis was stored at -80ÅãC for western blot analysis, and the other, was fixed for histological and immunofluorescence analysis.

Results

Five weeks of HFD results in reduced steroidogenesis, increased apoptosis of spermatogenic cells, and altered spermatogenesis, as highlighted by reduced protein levels ofmeiotic and post-meiotic markers. Further, we evidenced the compromission of the BTB integrity, as revealed by the downregulation of structural proteins (N-Cadherin, ZO-1, occludin, connexin 43, and VANGL2) other than the phosphorylation of regulative kinases (Src and FAK). At the molecular level, the impairment of mitochondrial dynamics (fission, fusion, andbiogenesis), and the dysregulation of the SIRT1/NRF2/MAPKs signaling pathways, were evidenced. Interestingly, no change was observed in the levels of pro-inflammatory markers (TNFα, NF-kB, and IL-6).

Conclusions

The combined data led us to confirm that overweight is a less severe state than obesity. Furthermore, understanding the molecular mechanisms behind the association between metabolic disorders and male fertility could improve the possibility of identifying novel targets to prevent and treat fertility disorders related to overweight/obesity.

Mitophagy contributes to zinc-induced ferroptosis in porcine testis cells

Zinc (Zn) is a critical microelement for physiological process, but excess exposure can cause testicular dysfunction. However, the underlying mechanism of Zn-induced ferroptosis via regulating mitophagy is unknown. In this study, a total of 60 male weaned pigs were randomly divided into three groups and the content of Zn were 75 mg/kg (control), 750 mg/kg (Zn-I), 1500 mg/kg (Zn-II). Meanwhile, testicular cells were treated with ZnSO4 (0, 50 and 100 μM), and in combination of ZnSO4 (100 μM) and ferrostation-1, ML-210, or 3-methyladenine for 24 h. Our results verified that Zn could cause ferroptosis and lipid peroxidation, which were characterized by down-regulating level of SLC7A11, GPX4, and ferritin, and up-regulating levels of MDA, CD71, TF, and HMGB1 by Western blot, immunohistochemistry, immunofluorescence, peroxidase assay, et.ac. The opposite effect was shown after treatment with ferrostation-1 or ML-210. Meanwhile, the mitophagy-related proteins (PINK, Parkin, ATG5, LC3-II/LC3-I) were significantly upregulated in vivo and in vitro. Most importantly, 3-methyladenine observably relieved ferroptosis under Zn treatment through inhibiting mitophagy. Collectively, we demonstrated that mitophagy contributes to Zn-induced ferroptosis in porcine testis cells, providing a new insight into Zn toxicology.

Combined Effects of Micro- and Nanoplastics at the Predicted Environmental Concentration on Functional State of Intestinal Barrier in Caenorhabditis elegans

The possible toxicity caused by nanoplastics or microplastics on organisms has been extensively studied. However, the unavoidably combined effects of nanoplastics and microplastics on organisms, particularly intestinal toxicity, are rarely clear. Here, we employed Caenorhabditis elegans to investigate the combined effects of PS-50 (50 nm nanopolystyrene) and PS-500 (500 nm micropolystyrene) at environmentally relevant concentrations on the functional state of the intestinal barrier. Environmentally, after long-term treatment (4.5 days), coexposure to PS-50 (10 and 15 μg/L) and PS-500 (1 μg/L) resulted in more severe formation of toxicity in decreasing locomotion behavior, in inhibiting brood size, in inducing intestinal ROS production, and in inducting intestinal autofluorescence production, compared with single-exposure to PS-50 (10 and 15 μg/L) or PS-500 (1 μg/L). Additionally, coexposure to PS-50 (15 μg/L) and PS-500 (1 μg/L) remarkably caused an enhancement in intestinal permeability, but no detectable abnormality of intestinal morphology was observed in wild-type nematodes. Lastly, the downregulation of acs-22 or erm-1 expression and the upregulation expressions of genes required for controlling oxidative stress (sod-2, sod-3, isp-1, clk-1, gas-1, and ctl-3) served as a molecular basis to strongly explain the formation of intestinal toxicity caused by coexposure to PS-50 (15 μg/L) and PS-500 (1 μg/L). Our results suggested that combined exposure to microplastics and nanoplastics at the predicted environmental concentration causes intestinal toxicity by affecting the functional state of the intestinal barrier in organisms.

Effects of Micro(nano)plastics on the reproductive system: A review

Microplastics (100nm-5 mm) and nanoplastics (1-100 nm) are collectively referred to as micro(nano)plastics (MNPs), which are refractory to degradation, easy to migration, small in size, strong in adsorption, and can widely present in human living environment. A number of studies have confirmed that MNPs can be exposed to the human body through a variety of routes, and can penetrate various barriers to enter the reproductive system, suggesting that MNPs may pose potential harm to human reproductive health. Current studies most were limited to phenotypic studies and their subjects were basically lower marine organisms and mammals. Therefore, in order to provide theoretical base for further exploring the effects of MNPs on the human reproductive system, this paper searched the relevant literature at home and abroad, mainly analyzed rodent experiments, and concluded that the main exposure routes of MNPs are dietary intake, air inhalation, skin contact and medical plastics. After entering the reproductive system, MNPs produce reproductive toxicity mainly through oxidative stress, inflammation, metabolic disorders, cytotoxicity and other mechanisms. More work is required to comprehensively identify the exposure routes, improve the detection methods to evaluate the effective exposure and deeply study the specific mechanisms of toxic effects, withing the aim of conducting relevant studies at the population level in the next step.

Polystyrene nanoplastics inhibit StAR expression by activating HIF-1α via ERK1/2 MAPK and AKT pathways in TM3 Leydig cells and testicular tissues of mice

Microplastics (MPs) and nanoplastics (NPs) are widely found in water, food and air, and have been found in human blood, lung and feces. Several studies in vivo have shown that MPs and NPs decrease testosterone level. However, the molecular mechanism of MPs and NPs leading to testosterone reduction remains unclear. In the present study, mice were treated with 50 μg/kg·day polystyrene (PS)-NPs by tail vein injection once daily for two consecutive days, the mRNA and protein levels of steroidogenic acute regulatory protein (StAR) decreased significantly in testis. TM3 Leydig cells were treated with non-toxic doses of PS-NPs, hypoxia-inducible factor-1α (HIF-1α) mRNA translation was induced by PS-NPs through mTOR/4E-BP1 pathway, which was activated by the ERK1/2 MAPK and AKT pathways. Simultaneously, increased HIF-1α protein inhibited StAR transcription. Additionally, reactive oxygen species production induced by PS-NPs played a central role in the activation of ERK1/2 MAPK/mTOR and AKT/mTOR signaling pathways. These results suggest that PS-NPs down-regulate StAR expression by increasing HIF-1α, which is induced by activation of mTOR/4E-BP1 through the ERK1/2 MAPK and AKT signaling pathways. Our findings provide new insight into the potential molecular mechanism by which PS-NPs impair testosterone synthesis and male reproductive function.