Maternal lead exposure during lactation persistently impairs testicular development and steroidogenesis in male offspring

Effect of Psidium guajava Juice on The Seminiferous Tubules Diameter and Epithelium Thickness in Rattus norvegicus Exposed by Lead Acetate

Lead is one of humans and animals' most common and hazardous heavy metals. This study aimed to investigate the effect of white guava (Psidium guajava) fruit juice on the seminiferous tubule diameter and epithelium thickness in rats (Rattus norvegicus) exposed to lead acetate. The research design was a completely randomized design (CRD). A total of 25 male rats with an average weight of 200 grams were used for the study, divided into 5 treatment groups, each consisting of 5 rats. The treatments were as follows: the control group (C) was given distilled water orally; the T0 group was induced with lead acetate (50 mg/Kg BW) orally; the T1, T2, T3 groups were induced with lead acetate (50 mg/Kg BW) and then given 25%, 50%, and 100% concentration of white guava fruit juice, respectively. All the treatments were conducted for 14 days. The histopathology slides of the testis were made with HE staining, and the seminiferous tubule diameter and epithelium thickness were measured. The data were analyzed using One Way ANOVA and Duncan test (p<0.05). The results showed that the control group (C) which was given distilled water only had a seminiferous tubule diameter and epithelium thickness of 336.24±23.32 µm and 66.46±4.39 µm, respectively. The T0 group which was induced with lead acetate only showed a reduction in the diameter and epithelium thickness of seminiferous tubules (243.38±49.35 µm and 44.08±14.45 µm). The members of the T1, T2 and T3 groups showed positive effects on the diameter (323.49±22.82 µm; 314.41±13.04 µm; 325.04±16.88 µm, respectively) and epithelium thickness (56.36±3.36 µm; 60.50±3.81 µm; 66.744±9.50 µm, respectively). There was no significant difference reported between each group. The administration of guava juice to rats induced with lead acetate can positively affect the diameter and epithelium thickness of seminiferous tubules.

High-fat diet in mice led to increased severity of spermatogenesis impairment by lead exposure: perspective from gut microbiota and the efficacy of probiotics

BACKGROUND

The mechanism of multifactorial spermatogenesis impairment is unclear. This study aimed to investigate the reproductive toxicity of lead (Pb) in mice fed a high-fat diet (HFD) and to delineate the important role of gut microbiota.

RESULTS

Results showed that, compared with mice fed a normal diet (ND), Pb exposure caused more severe spermatogenesis impairment in HFD-fed mice, including decreased sperm count and motility, seminiferous tubule injury, serum and intratesticular testosterone decline, and downregulated expression level of spermatogenesis-related genes. Besides, 16S sequencing indicated that HFD-fed mice had increased severity of gut microbiota dysbiosis by Pb exposure compared to ND-fed mice. With fecal microbiota transplantation, the same trend of spermatogenesis impairment occurred in recipient mice, which confirmed the important role of gut microbiota. Moreover, probiotics supplementation restored the gut microbial ecosystem, and thus improved spermatogenic function.

CONCLUSION

Our work suggested that a population with HFD might face more reproductive health risks upon Pb exposure, and revealed an intimate linkage between microbiota dysbiosis and spermatogenesis impairment, accompanied by the potential usefulness of probiotics as prophylactic and therapeutic. © 2022 Society of Chemical Industry.

Glycine protects the male reproductive system against lead toxicity via alleviating oxidative stress, preventing sperm mitochondrial impairment, improving kinematics of sperm, and blunting the downregulation of enzymes involved in the steroidogenesis

Lead (Pb) is a highly toxic heavy metal widely dispersed in the environment because of human industrial activities. Many studies revealed that Pb could adversely affect several organs, including the male reproductive system. Pb-induced reproductive toxicity could lead to infertility. Thus, finding safe and clinically applicable protective agents against this complication is important. It has been found that oxidative stress plays a fundamental role in the pathogenesis of Pb-induced reprotoxicity. Glycine is the simplest amino acid with a wide range of pharmacological activities. It has been found that glycine could attenuate oxidative stress and mitochondrial impairment in various experimental models. The current study was designed to evaluate the role of glycine in Pb-induced reproductive toxicity in male mice. Male BALB/c mice received Pb (20 mg/kg/day; gavage; 35 consecutive days) and treated with glycine (250 and 500 mg/kg/day; gavage; 35 consecutive days). Then, reproductive system weight indices, biomarkers of oxidative stress in the testis and isolated sperm, sperm kinetic, sperm mitochondrial indices, and testis histopathological alterations were monitored. A significant change in testis, epididymis, and Vas deferens weight was evident in Pb-treated animals. Markers of oxidative stress were also significantly increased in the testis and isolated sperm of the Pb-treated group. A significant disruption in sperm kinetic was also evident when mice received Pb. Moreover, Pb exposure caused significant deterioration in sperm mitochondrial indices. Tubular injury, tubular desquamation, and decreased spermatogenic index were histopathological alterations detected in Pb-treated mice. It was found that glycine significantly blunted oxidative stress markers in testis and sperm, improved sperm mitochondrial parameters, causing considerable higher velocity-related indices (VSL, VCL, and VAP) and percentages of progressively motile sperm, and decreased testis histopathological changes in Pb-exposed animals. These data suggest glycine as a potential protective agent against Pb-induced reproductive toxicity. The effects of glycine on oxidative stress markers and mitochondrial function play a key role in its protective mechanism.

AMPK pathway is implicated in low level lead-induced pubertal testicular damage via disordered glycolysis

Lead (Pb) is a common environmental pollutant. It has been demonstrated that long-term exposure to Pb at environmental levels may cause severe and irreversible damage to the male reproductive system. Of note, the impairments may originate from environmental Pb exposure at puberty. However, the underlying mechanisms remain unclear. In this study, we administrated male ICR mice with 200 mg/L Pb through the drinking water for 30-, 60-, 90-day from postnatal day 28. RNA sequencing was performed in the control group and the 90-day Pb exposure group. It was found that Pb exposure induced testicular damage, increased oxidative stress levels and poor sperm quality. Bioinformatic analysis displayed 199 genes up-regulated (such as GLUT1 and MCT4 genes) and 156 genes down-regulated (such as GLUT3, PFK1, LDH, CD147 and AMPK genes) in the Pb exposure group compared to the control group. Gene ontology (GO) terms enrichment analysis showed differentially expressed genes (DEGs) are involved in the protein catabolic, cellular catabolic and triglyceride catabolic processes. KEGG pathways enrichment analysis indicated glycerolipid metabolism and AMPK signaling were significantly enriched. Furthermore, experimental verification showed that Pb exposure induces energy dysmetabolism and decreases glycolysis products in mice testicular tissue. The AMPK signaling pathway was found to be deactivated after Pb exposure. The GLUT1, GLUT3, PFK1 and LDH proteins, which play a critical role in the cell glycolysis process, also were decreased. Besides, the expression of CD147 was decreased and the location of CD147 was altered upon Pb exposure. Together, these findings indicated the implication of the AMPK signaling pathway in Pb exposure induced pubertal testicular damage and poor sperm quality by inhibiting cell glycolysis and disordering lactate transportation in testicular cells.

Improvement roles of zinc supplementation in low dose lead induced testicular damage and glycolytic inhibition in mice

Lead (Pb) is a toxic metal that affects the male reproductive system. This study aimed to investigate the effects of zinc (Zn) intake between recommended dietary allowances (RDAs) and tolerable upper intake levels (ULs) in preventing male testis damage induced by low-dose Pb. Forty-five mice were randomly divided into control, Pb, and Pb + Zn groups. They were given distilled water ad libitum with 0, 200 mg/L Pb²⁺, or 15 mg/L Zn²⁺ mixed with 200 mg/L Pb²⁺ for 90 consecutive days. The Zn levels in the blood and testis of the Pb group were significantly lower than those of the control group. The Pb levels in the blood and testis of the Pb + Zn group were significantly lower than those of the Pb group. Additionally, a significant decrease in sperm density and viability, with a significant increase in sperm abnormality rate and DNA fragmentation index, was observed in the Pb group. Zn supplementation significantly improved the above sperm parameters. Moreover, Zn supplementation decreased low-dose Pb-induced lipid peroxidation and increased glutathione, total superoxide dismutase (SOD), and copper/Zn-SOD levels. Furthermore, Zn treatment improved glycolysis products and lactate transporters in Pb-treated mouse testes. Our findings suggest that Zn intake between RDAs and UL can act as a therapeutic agent in protecting against the reproductive impairments associated with Pb exposure.

Vitamin D3 protects against lead-induced testicular toxicity by modulating Nrf2 and NF-κB genes expression in rat

Lead (Pb) is an environmental toxin that has the ability to alter biological processes by inducing oxidative stress (OS) and inflammation. Nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-κB) are two transcriptional factors that participate in the regulation of cellular responses against OS and inflammation. This study was conducted to evaluate the effects of vitamin D3 (VD) on the prevention of testicular damages of Pb and its association with Nrf2 and NF-κB gene expression levels and their downstream molecules. Forty male Wistar rats were divided into four groups and treatments were performed as following for four weeks: control group received no treatment, VD group were injected intramuscularly with 1000 IU of VD/Kg every other day, Pb group received 1000 mg of Pb/L of drinking water, and Pb + VD group were exposed to Pb and VD simultaneously. The results demonstrated significant decrease in the levels of tissue antioxidants, and increase in inflammatory cytokines in the Pb-intoxicated group, with increased Nrf2 and NF-κB mRNA levels. A remarkable reduction in sperm criteria and a significant disruption in serum hormones were also observed. Anyhow, VD supplementation during exposure to Pb showed a significant protective effect against all pathophysiologic alterations caused by Pb. Furthermore, VD affected the expression of Nrf2 and NF-κB and mitigated the harsh effects of Pb. In conclusion, our findings indicate that VD attenuated the toxic impacts of Pb on testis through modulation of Nrf2 and NF-κB gene expression levels which further regulated the OS and inflammatory responses.

Effects of heavy metals on reproduction owing to infertility

The reproductive performance of most of the species is adversely affected by hazardous heavy metals like lead, cadmium, mercury, arsenic, zinc, and copper. Heavy metals are liberated in the environment by natural sources like rock weathering, volcanic eruption, and other human activities like industrial discharge, mineral mining, automobile exhaust, and so forth. Heavy metals alter several reproductive functions in both males and females like a decrease in sperm count, motility, viability, spermatogenesis, hormonal imbalance, follicular atresia, and delay in oocyte maturation, and so forth, and thus, forms an important aspect of reproductive toxicology. The present review compiles toxicity aspects of various heavy metals and their efficacy and mechanism of action in mammals.

Maternal cadmium exposure during late pregnancy causes fetal growth restriction via inhibiting placental progesterone synthesis

Cadmium (Cd) is a major environmental pollutant. Maternal Cd exposure throughout pregnancy caused fetal growth restriction (FGR). However, the pivotal time window of Cd-evoked FGR and its mechanism are unknown. Here, we will establish a murine model to explore the effects of maternal Cd exposure at different stages of gestation on fetal growth and placental progesterone biosynthesis. Pregnant mice were randomly divided into four groups. For Cd groups, mice were given with CdCl₂ (150 mg/L) through drinking water at early (GD0-GD6), middle (GD7-GD12) and late (GD13-GD17) gestation, respectively. The controls received reverses osmosis (RO) water. Results showed that maternal cadmium exposure only in late gestation lowered fetal weight and length. Correspondingly, placental Cd level in late gestational Cd exposure is the highest among three different gestational stages. Although gestational Cd exposure had few adverse effects in the weight and diameter of mouse placenta, placental vascular development, as determined by H&E staining and cluster of differentiation-34 (CD-34) immunostaining, was impaired in mice exposed to Cd during late pregnancy. Additionally, late gestational exposure to cadmium markedly reduced progesterone level in maternal serum and placenta. In line, the expression of key progesterone synthetases, including steroidogenic acute regulatory protein (StAR) and 3β-hydroxyl steroid dehydrogenase (3β-HSD), was obviously downregulated in placenta from mice was exposed Cd during late pregnancy. These data suggest that maternal Cd exposure during late pregnancy, but not early and middle pregnancy, induces fetal growth restriction partially via inhibiting placental progesterone synthesis.

Low concentrations of lead decrease the sperm fertilization ability by altering the acrosome reaction in mice

Lead (Pb) exposure at high concentrations is associated with poor sperm quality, acrosome alterations, and low fertilization rate. Sperm capacitation and the acrosome reaction (AR) are required for successful fertilization. Actin polymerization is crucial for correct capacitation, and small GTPases, such as RhoA, Rac1, and Cdc42, are involved. This study aimed to evaluate the effects of Pb on sperm fertilization ability, capacitation, AR, and the mechanisms involved in mice exposed to low Pb concentrations. CD1 mice were exposed to 0.01% Pb²⁺ for 45 days through their drinking water and their spermatozoa were collected from the cauda epididymis-vas deferens to evaluate the following: AR (oAR: initial, sAR: spontaneous, and iAR: induced) using the PNA-FITC assay, sperm capacitation (P-Tyr levels), actin polymerization (phalloidin-TRITC), MDA production (stress oxidative marker), the RhoA, Rac1, and Cdc42 protein levels, and the in vitro fertilization (IVF). After the treatment, the blood Pb (PbB) concentration was 9.4 ± 1.6 μg/dL. Abnormal sperm morphology and the oAR increased (8 and 19%, respectively), whereas the iAR decreased (15%) after a calcium ionophore challenge, and the actin polymerization decreased in the sperm heads (59%) and tails (42%). Rac1 was the only Rho protein to significantly decrease (33%). Spermatozoa from the Pb-treated mice showed a significant reduction in the fertilization rate (19%). Our data suggest that Pb exposure at environmental concentrations (PbB < 10 μg/dL) decreases the acrosome function and affects the sperm fertilization ability; this is probably a consequence of the low Rac1 levels, which did not allow adequate actin polymerization to occur.

Ameliorative effects of Spirulina maxima and Allium sativum on lead acetate-induced testicular injury in male albino rats with respect to caspase-3 gene expression

The present study was conducted to evaluate the ameliorative effects of Allium sativum (garlic) as well as Spirulina maxima on lead acetate toxicity in rat testes. Forty adult, male, albino rats were divided into four groups (10 rats/each): group I served as the control; group II contained rats that received lead acetate (100 mg/kg); group III contained rats that received both lead acetate (100 mg/kg) and garlic (600 mg/kg); and group IV contained rats that received both lead acetate (100 mg/kg) and spirulina (500 mg/kg). All treatments were performed daily for one month. Serum testosterone levels, oxidative stress parameters, expression of the caspase-3 gene and histological, histo-morphometric and ultrastructure alterations in the testes were investigated. The results revealed that the Pb-treated group exhibited a significant increase in MDA concentration concomitantly with a decrease in serum testosterone levels, antioxidative marker levels and caspase-3 gene expression. Several histological and histo-morphometric alterations were observed in this group. Co-administration with spirulina or garlic caused a significant increase in testosterone levels, testicular SOD and CAT activities, and caspase-3 gene expression and a decrease in MDA levels, with improvement in histological and histo-morphometric alterations. These results suggested that spirulina was more effective at providing protection against Pb-induced reproductive damage in rats than garlic, indicating the beneficial role of spirulina in improvement of spermatogenesis and steroidogenesis after lead exposure.

Maternal lipopolysaccharide exposure results in glucose metabolism disorders and sex hormone imbalance in male offspring

An adverse intrauterine environment may be an important factor contributing to the development of type 2 diabetes in later life. The present study investigated the longitudinal effects of maternal lipopolysaccharide (LPS) exposure during the third trimester on glucose metabolism and sex hormone balance in the offspring. Pregnant mice were intraperitoneally injected with LPS (50 μg/kg) daily from gestational day (GD) 15 to GD17. Glucose tolerance test (GTT) and insulin tolerance test (ITT) were assessed at postnatal day (PND) 60 and PND120. Sex hormones, their receptors, and metabolic enzymes (aromatase) were measured in male offspring at different phases of development (PND14: juvenile; PND35: adolescence; PND60: adulthood; and PND120: middle age). LPS-exposed male offspring exhibited glucose intolerance and insulin resistance by GTT and ITT at middle age, accompanied by an increase in fasting blood glucose and reductions in serum insulin levels and hepatic phosphorylated (p) -AKT/AKT ratio. However, glucose intolerance and insulin resistance were not observed in LPS-exposed female offspring. Maternal LPS exposure upregulated hepatic aromatase proteins and mRNA levels in male offspring at all time points. At adolescence, the testosterone/estradiol ratio (T/E2) was markedly reduced in LPS-exposed male offspring. Moreover, maternal LPS exposure significantly increased hepatic estrogen receptor (ER) α expressions and decreased hepatic androgen receptor (AR) expressions in male offspring. At adulthood, maternal LPS exposure increased serum estradiol levels, decreased serum testosterone levels and elevated hepatic ERβ expressions in male offspring. In conclusion, maternal LPS exposure upregulated aromatase expressions, followed by a reduction in the T/E2 ratio and an alteration in sex hormone receptor activity, which might be involved in the development of glucose metabolism disorders in middle-aged male offspring. This study provides a novel clue and direction to clarify the pathogenesis of maternal infection-related diabetes in male offspring.

Effect of neonatal hypothyroidism on prepubertal mouse testis in relation to thyroid hormone receptor alpha 1 (THRα1)

Thyroid hormones (THs) are important for growth and development of many tissues, and altered thyroid status affects various organs and systems. Testis also is considered as a thyroid hormone responsive organ. Though THs play an important role in regulation of testicular steroidogenesis and spermatogenesis, the exact mechanism of this regulation remains poorly understood. The present study, therefore, is designed to examine the effect of neonatal hypothyroidism on prepubertal Parkes (P) strain mice testis in relation to thyroid hormone receptor alpha 1 (THRα1). Hypothyroidism was induced by administration of 6-propyl-2-thiouracil (PTU) in mother's drinking water from birth to day 28; on postnatal day (PND) 21 only pups, and on PND 28, both pups and lactating dams were euthanized. Serum T₃ and T₄ were markedly reduced in pups at PND 28 and in lactating mothers, while serum and intra-testicular testosterone levels were considerably decreased in pups of both age groups. Further, serum and intra-testicular levels of estrogen were significantly increased in hypothyroid mice at PND 28 with concomitant increase in CYP19 expression. Histologically, marked changes were noticed in testes of PTU-treated mice; immunohistochemical and western blot analyses of testes in treated mice also revealed marked decrease in the expression of THRα1 at both age groups. Semiquantitative RT-PCR and western blot analyses also showed reductions in both testicular mRNA and protein levels of SF-1, StAR, CYP11A1 and 3β-HSD in these mice. In conclusion, our results suggest that neonatal hypothyroidism alters localization and expression of THRα1 and impairs testicular steroidogenesis by down-regulating the expression SF-1, thereby affecting spermatogenesis in prepubertal mice.

Effect of polybrominated diphenyl ether (BDE-209) on testicular steroidogenesis and spermatogenesis through altered thyroid status in adult mice

Polybrominated diphenyl ethers (PBDEs), a class of brominated flame retardants (BFRs), have been widely used in many products to minimize the risk of fire, mainly by mixing in polymer products. BDE-209, a congener of PBDEs having structural similarity with thyroid hormones, acts as an endocrine disruptor by interfering with thyroid homeostasis. However, little is known about the effect of BDE-209 exposure on testicular steroidogenesis and spermatogenesis. This study was therefore conducted in adult mice to examine the effect of BDE-209 on testicular steroidogenesis and spermatogenesis in relation to thyroid status, and to explore possible mechanism(s) of its action. Adult Parkes strain male mice were orally gavaged with 750 and 950mg/kg BW of BDE-209 in corn oil for 35days. Significant reductions were noted in the levels of serum total T_3, T₄ and testosterone in mice treated with 950mg/kg BW of BDE-209 compared to controls; histologically, testes showed nonuniform degenerative changes in the seminiferous tubules as both affected and normal tubules were observed in the same section; further, number and viability of spermatozoa were also adversely affected in cauda epididymidis of these mice. Semiquantitative RT-PCR and western blot analyses also showed significant reductions in both testicular mRNA and protein levels of steroidogenic factor 1 (SF-1), steroidogenic acute regulatory (StAR) protein, cytochrome P450scc (CYP11A1), 3β-hydroxysteroid dehydrogenase (3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD) in 950mg dose treated-mice compared to controls. Immunohistochemical and immunoblot analyses further revealed a marked decrease in proliferating cell nuclear antigen (PCNA) positive cells in testes of 950mg dose of BDE-209-treated mice. However, 750mg dose of BDE-209 had no effect on the above parameters. In conclusion, our results suggest that exposure of BDE-209 to adult mice causes reduction in serum levels of thyroid hormones and altered thyroid status may partly result into impairment of testicular steroidogenesis because of down-regulated expression of SF-1, thereby causing suppression of spermatogenesis.

Targeting testis-specific proteins to inhibit spermatogenesis: lesson from endocrine disrupting chemicals

INTRODUCTION

Exposure to endocrine disrupting chemicals (EDCs) has recently been linked to declining fertility in men in both developed and developing countries. Since many EDCs possess intrinsic estrogenic or androgenic activities, thus, the gonad is one of the major targets of EDCs.

AREAS COVERED

For the past 2 decades, studies found in the literature regarding the disruptive effects of these EDCs on reproductive function in human males and also rodents were mostly focused on oxidative stress-induced germ cell apoptosis, disruption of steroidogenesis, abnormal sperm production and disruption of spermatogenesis in particular cell adhesion function and the blood-testis-barrier (BTB) function. Herein, we highlight recent findings in the field illustrating testis-specific proteins are also targets of EDCs.

EXPERT OPINION

This information should be helpful in developing better therapeutic approach to manage ECD-induced reproductive toxicity. This information is also helpful to identify potential targets for male contraceptive development.