Effects of melamine on pregnant dams and embryo-fetal development in rats

Effects of melamine and cyanuric acid on placental and fetal development in rats

Melamine or cyanuric acid alone has low toxicity, but combined exposure to melamine and cyanuric acid was reported to cause unexpected toxicological effects. This study investigated the potential effects and toxic mechanism of combined exposure to melamine and cyanuric acid on placental and fetal development in rats. Exposure to melamine and cyanuric acid caused maternal toxicity manifested by increased abnormal symptoms and decreased body weight gain. Developmental toxic effects included a decrease in placental and fetal weights with increased fetal deaths and post-implantation loss. Melamine and cyanuric acid induced oxidative stress in the developing placenta and fetus. The placentas from rats treated with melamine and cyanuric acid showed shortening of the placental layers with histological changes, decreased cell proliferation, increased apoptotic changes, and decreased insulin-like growth factor (IGF)/IGF-binding proteins (IGFBPs) and placental lactogen (PL) expression levels. Fetuses from melamine- and cyanuric acid-treated dams showed increased apoptotic changes and suppressed cellular proliferation in their livers and vertebrae. Consequently, combined exposure to melamine and cyanuric acid resulted in high levels of oxidative stress and impaired placental development associated with impairment of the IGF/IGFBP and PL systems, resulting in increased apoptotic changes and reduced fetal cell proliferation.

Exposure to melamine and its derivatives and aromatic amines among pregnant women in the United States: The ECHO Program

BACKGROUND

Melamine, melamine derivatives, and aromatic amines are nitrogen-containing compounds with known toxicity and widespread commercial uses. Nevertheless, biomonitoring of these chemicals is lacking, particularly during pregnancy, a period of increased susceptibility to adverse health effects.

OBJECTIVES

We aimed to measure melamine, melamine derivatives, and aromatic amine exposure in pregnant women across the United States (U.S.) and evaluate associations with participant and urine sample collection characteristics.

METHODS

We measured 43 analytes, representing 45 chemicals (i.e., melamine, three melamine derivatives, and 41 aromatic amines), in urine from pregnant women in nine diverse ECHO cohorts during 2008-2020 (N = 171). To assess relations with participant and urine sample collection characteristics, we used generalized estimating equations to estimate prevalence ratios (PRs) for analytes dichotomized at the detection limit, % differences (%Δ) for continuous analytes, and 95% confidence intervals. Multivariable models included age, race/ethnicity, marital status, urinary cotinine, and year of sample collection.

RESULTS

Twelve chemicals were detected in >60% of samples, with near ubiquitous detection of cyanuric acid, melamine, aniline, 4,4'-methylenedianiline, and a composite of o-toluidine and m-toluidine (99-100%). In multivariable adjusted models, most chemicals were associated with higher exposures among Hispanic and non-Hispanic Black participants. For example, concentrations of 3,4-dichloroaniline were higher among Hispanic (%Δ: +149, 95% CI: +17, +431) and non-Hispanic Black (%Δ: +136, 95% CI: +35, +311) women compared with non-Hispanic White women. We observed similar results for ammelide, o-/m-toluidine, 4,4'-methylenedianiline, and 4-chloroaniline. Most chemicals were positively associated with urinary cotinine, with strongest associations observed for o-/m-toluidine (%Δ: +23; 95% CI: +16, +31) and 3,4-dichloroaniline (%Δ: +25; 95% CI: +17, +33). Some chemicals exhibited annual trends (e.g., %Δ in melamine per year: -11; 95% CI: -19, -1) or time of day, seasonal, and geographic variability.

DISCUSSION

Exposure to melamine, cyanuric acid, and some aromatic amines was ubiquitous in this first investigation of these analytes in pregnant women. Future research should expand biomonitoring, identify sources of exposure disparities by race/ethnicity, and evaluate potential adverse health effects.

Melamine Disrupts Acetylcholine-Mediated Neural Information Flow in the Hippocampal CA3-CA1 Pathway

Considering the cognitive and synaptic deficits following intragastric administration of melamine, the aim of the current investigation was to test whether the hippocampal oscillations were affected. The local field potential (LFP) was recorded in the hippocampal CA3–CA1 pathway of Wistar rats during a spatial-dependent Y-maze task. The general partial directed coherence (gPDC) method was used to assess the directionality of neural information flow (NIF) between the CA3 and CA1 regions. The levels of acetylcholine (ACh) and its esterolytic protease, acetylcholinesterase (AChE), were detected in the hippocampus (HPC) following the behavioral test. The values of phase synchronization between the CA3 and CA1 regions in delta, low theta, and high theta oscillations were reduced significantly in the melamine-treated group. Moreover, the coupling directional index and the strength of CA3 driving CA1 were critically decreased in the above three frequency bands as well. Meanwhile, a reduction in ACh expression and an enhancement in AChE activity were found in the HPC of melamine-treated rats. Intrahippocampal infusion with ACh could mitigate the weakened neural coupling and directional NIF in parallel with spatial learning improvements. However, infusion of scopolamine, an acetylcholine receptor antagonist, could block the mitigative effects of ACh treatment in melamine rats. These findings provide first evidence that ACh-mediated neuronal coupling and NIF in the CA3–CA1 pathway are involved in spatial learning deficits induced by chronic melamine exposure.

Development of analytical method of melamine in placenta from pregnant women by isotope-dilution liquid chromatography/tandem mass spectrometry

RATIONALE

Melamine is ubiquitously present in our daily life. It has a known effect on the kidneys, but it may also adversely affect the reproduction system. We have developed an analytical method for measuring melamine levels in maternal placenta and correlated these levels with melamine concentrations in urine, a necessary step in finding out if melamine might cross the placenta and enter the circulation of the fetus.

METHODS

We used liquid-liquid extraction, clean up by solid-phase extraction (SPE), and isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) to measure melamine in placenta specimens. The results of this method were assessed for linearity, limits of quantitation (LOQs), and intra- and inter-assay precision as well as accuracy, matrix effect, and recovery rate.

RESULTS

Calibration curves indicated good linearity (r >0.995) over concentrations ranging from 5 to 500 ng/mL in placenta specimens, intra- and inter-assay precision from 0.89% to 27.07%, and accuracy from 92.4% to123.5%. Recovery ranged from 63.9 to 83.9%, and the LOQ was 5 ng/mL in placenta (0.2 g). Placental melamine levels ranged from 7.87 to19.64 ng/mL, all detectable (n = 8). Pregnant women with higher levels of urinary melamine had higher placenta melamine levels than those with non-detectable urinary melamine, though the results were not significantly different (p = 0.149, n = 4 in each group).

CONCLUSIONS

The results of this study suggest that pregnant women were exposed to low doses of melamine in their daily lives as measured in urine samples and placenta specimens. It is unclear whether placenta melamine concentrations can better represent long-term exposure than urine or whether melamine in the uterus can enter the fetus via this route.

Autophagy in Ovarian Follicular Development and Atresia

Autophagy is a mechanism that exists in all eukaryotes under a variety of physiological and pathological conditions. In the mammalian ovaries, less than 1% of follicles ovulate, whereas the remaining 99% undergo follicular atresia. Autophagy and apoptosis have been previously found to be involved in the regulation of both primordial follicular development as well as atresia. The relationship between autophagy, follicular development, and atresia have been summarized in this review with the aim to obtain a more comprehensive understanding of the role played by autophagy in follicular development and atresia.

An embryo-fetal development toxicity study with dimethylaminoethyl ginkgolide B in rats and rabbits

Ginkgo biloba (a herbal product) has long been used in traditional Chinese medicine to treat cerebrovascular and cardiovascular diseases. Ginkgolide B is one of the important pharmacologically active components of Ginkgo biloba. Dimethylaminoethyl ginkgolide B (a novel ginkgolide B derivative) has been developed to overcome the poor water-solubility of natural drugs and to achieve higher bioavailability. This study investigated the potential effects of dimethylaminoethyl ginkgolide B on pregnant dams and embryo-fetal development in Sprague-Dawley rats and New Zealand white rabbits following maternal exposure on gestational day (GD) 6-15 and GD 6-18, respectively. Dimethylaminoethyl ginkgolide B was administered by intravenous injection to pregnant rats (0, 10, 30 and 100 mg kg-1 d-1) and rabbits (0, 6, 18 and 60 mg kg-1 d-1). Maternal toxicity signs, such as lower maternal body weight gain and food consumption, were observed at 100 mg kg-1 d-1 in rats and 60 mg kg-1 d-1 in rabbits. The developmental toxic effects included a decrease in fetal and placental weights, increased incidences of skeletal variations and delay in fetal ossification. Fetal growth and development were affected by dimethylaminoethyl ginkgolide B in the high-dose group in rabbits. The no-observed-adverse-effect level of dimethylaminoethyl ginkgolide B is considered to be 30 mg kg-1 d-1 for rats and 18 mg kg-1 d-1 for rabbits.

Effects of low-dose melamine exposure during pregnancy on maternal and fetal kidneys in rats

Despite the previous reports on melamine contamination in high concentrations some years ago, there were not many studies on low-level exposure in daily life, particularly in pregnancy. We investigated the effect of low-dose melamine on the kidneys of the pregnant rats and their developing embryos/fetuses during various gestational stages namely implantation, gastrulation, organogenesis, maturation and whole pregnancy. Our results showed that the repeated low level of melamine (12.5, 25, and 50 mg/kg bw/d) during pregnancy did not cause obstruction of renal tubules although more precipitating crystals were found in the early gestational periods. Simple hyperplasia in the maternal tubules and pelvic epithelium were more prominent after exposed to melamine during the whole gestational period. Neonatal kidneys significantly suffered more from congestion in glomeruli and interstitium, dilated tubules and interstitial edema after melamine administration to the mother in the late and the whole gestational periods. A trend of advance of glomerular development in fetuses was also observed. We conclude that in utero exposure of low-level melamine could post a risk on the kidneys of the pregnant mother as well as the developing fetuses, which may further increase the possibility of other health problems later in life.

Melamine, beyond the kidney: A ubiquitous endocrine disruptor and neurotoxicant?

Melamine is commonly used in a variety of consumer products such as furniture, dining ware, and food utensils. The chemical infamously gained worldwide attention by its illegal addition to a variety of foodstuffs in order to falsify protein content, which led to serious, sometimes fatal, health impacts in children and pets. This resulted in a large amount of published primary studies and reviews of the impacts of melamine exposure on kidney function. However, a growing body of literature suggests that melamine may have impacts beyond renal dysfunction. We conducted a scoping review of this literature which yielded more than 40 studies with human, animal, and in vitro findings. Neurological impacts, reproductive function, and anthropometric outcomes were identified as possible candidates for systematic review based on evidence stream and replication of endpoints. The results of this analysis provide a basis for prioritizing future research on health impacts associated with melamine exposure.

Adverse reproductive effects of maternal low-dose melamine exposure during pregnancy in rats

Melamine is a heterocyclic, aromatic amine and nitrogen-enriched environmental toxicant, found in not only adulterated foodstuffs but also industrial household tableware and paints. Previous studies demonstrated adverse effects of high-dose melamine on human infants and pregnant animals, but effects of low-dose melamine on pregnancy have not been reported. In this study, reproductive effects of low-dose melamine were investigated in pregnant rats. Melamine in the range of 12.5-50 mg/kg was administered to pregnant rats at different gestational stages. Maternal weight gain was not significantly affected, and other maternal morbidity was not observed. Low-dose melamine exposure during pregnancy increased fetal size but reduced somite number in gastrulation (GD8.5-GD10.5) and organogenesis (GD10.5-GD16.5) periods, and increased incidence of stillbirth in whole gestational period (GD0.5 to delivery). Embryotoxicity of melamine was further confirmed by whole embryo culture in vitro that melamine retarded embryonic growth, impaired development of brain and heart, and induced open neural tube and atrioventricular defects with increased apoptosis. In conclusion, adverse reproductive effects of low-dose melamine during pregnancy were identified in the developing rat embryos and the perinatal effects of melamine were gestational and developmental stage dependent. Detailed hazard and risk assessment of melamine in reproduction system are warrant. © 2015 Wiley Periodicals, Inc. Environ Toxicol 32: 131-138, 2017.

Melamine Impairs Renal and Vascular Function in Rats

Melamine incident, linked to nephrotoxicity and kidney stone in infants previously exposed to melamine-contaminated milk products, was unprecedentedly grave in China in 2008 as little was known about the mechanistic process leading to renal dysfunction in affected children. This study investigates whether neonatal ingestion of melamine leads to renal and vascular dysfunction in adulthood; and whether ingestion of melamine in pregnant rats leads to renal dysfunction in their offspring. A combination of approaches employed includes functional studies in rat renal arteries, renal blood flow measurement by functional magnetic resonance imaging, assay for pro-inflammatory and fibrotic biomarkers, immunohistochemistry, and detection of plasma and renal melamine. We provide mechanistic evidence showing for the first time that melamine reduces renal blood flow and impairs renal and vascular function associated with overexpression of inflammatory markers, transforming growth factor-β1, bone morphogenic protein 4 and cyclooxygenase-2 in kidney and renal vasculature. Melamine also induces renal inflammation and fibrosis. More importantly, melamine causes nephropathies in offsprings from pregnant rat exposed to melamine during pregnancy, as well as in neonatal rat exposed to melamine afterbirth, thus supporting the clinical observations of kidney stone and acute renal failure in infants consuming melamine-contaminated milk products.

Ovarian Toxicity in Female Rats after Oral Administration of Melamine or Melamine and Cyanuric Acid

Although the toxicity of melamine to the kidneys and testes is well known, few studies have investigated the effects of melamine on female reproductive organs. Therefore, this study explores the effects of oral administration melamine or melamine and cyanuric acid for 28 days on the ovaries of female rats. Rats that were exposed to the mixture exhibited reduced ovarian and uterine weights, a shorter estrous cycle, and reduced serum estrogen and progesterone levels compared to rats that were exposed to melamine and control rats. Furthermore, morphological analysis revealed pathological changes in the ovaries of rats exposed to melamine or the mixture, such as more atretic follicles and necrosis of oocytes and granulosa cells. TUNEL staining revealed that the exposed groups had a higher proportion of TUNEL-positive granulosa cells than the control group, and the mRNA expressions of SOD1, GPX1, GPX2, P450scc, 17β-HSD I, and 17β-HSD II were reduced in the exposure groups compared with the control group. These results indicated that exposure to melamine alone or to the melamine-cyanuric acid mixture could damage the ovaries in rats.

Use of urinary renal biomarkers to evaluate the nephrotoxic effects of melamine or cyanuric acid in non-pregnant and pregnant rats

Although traditional assessments of renal damage detect loss of kidney function, urinary renal biomarkers are proposed to indicate early changes in renal integrity. The recent adulteration of infant formula and other milk-based foods with melamine revealed a link between melamine ingestion and nephropathy. Thus, the effects of melamine and related analogs (e.g., cyanuric acid) should be assessed in other potentially sensitive groups. We evaluated whether urinary Kim-1, clusterin, and osteopontin could detect the effects of high doses of melamine or cyanuric acid in pregnant and non-pregnant female rats gavaged with 1000 mg/kg bw/day for 10 days. We demonstrate that these biomarkers can differentiate the severity of effects induced by melamine or cyanuric acid. All melamine-treated animals experienced adverse effects; however, pregnant rats were most sensitive as indicated by increased SCr, BUN, and kidney weights, decreased body weight, and presence of renal crystals. These effects coincided with elevated urinary biomarker levels as early as day 2 of exposure. One cyanuric acid-treated rat displayed effects similar to melamine, including increased urinary biomarker levels. This work illustrates that these biomarkers can detect early effects of melamine or cyanuric acid crystal-induced nephropathy and further supports the use of urinary protein immunoassays as a powerful, non-invasive method to assess nephrotoxicity.

Melamine negatively affects oocyte architecture, oocyte development and fertility in mice

STUDY QUESTION

Does melamine have a toxic effect on oocyte development and fertility in vivo?

SUMMARY ANSWER

Melamine had toxic effects on oocyte quality and fertility due to its effects on the oocyte cytoskeleton, apoptosis and autophagy induction, and epigenetic modifications in an in vivo mouse model.

WHAT IS KNOWN ALREADY

Melamine is a chemical compound that is widely used during the manufacture of amino resins and plastics. In 2008, melamine was reported to adulterate milk and infant formulas in China, which sparked food safety concerns worldwide. Ingesting melamine may result in reproductive damage, and bladder or kidney stones, which can lead to bladder cancer.

STUDY DESIGN, SIZE, DURATION

Mice were randomly assigned to three groups and fed a diet that included melamine (0, 10 and 50 mg/kg/day) for 8 weeks. The in vivo effect of melamine on female reproduction was examined.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We used immunofluorescent staining, western blotting and qRT-PCR to examine the effect of melamine on oocyte quality.

MAIN RESULTS AND THE ROLE OF CHANCE

Our results showed the following effects of this melamine-containing diet. (i) Ovary weights were reduced in melamine fed mice. Oocyte developmental competence was also reduced, as shown by reduced polar body extrusion rates. (ii) Melamine feeding resulted in abnormal oocyte cytoskeletons, as shown by increased rates of aberrant spindles and reduced actin microfilament expression. (iii) Melamine exposed oocytes had higher rates of abnormal mitochondrial distributions and early stage apoptosis/autophagy, which were shown by increased microtubule-associated protein 1 light chain 3 (LC3) protein expression level and caspase 9, autophagy-related protein 14 (atg14), and lc3 mRNA levels. (iv) Fluorescence intensity analysis showed that DNA methylation levels were reduced in the oocytes of melamine fed mice. Histone methylation levels were also altered, as Di-methyl-Histone H3 (Lys4) (H3K4me2) level was increased and Tri-methyl-Histone H3 (Lys9) (H3K9me3), Di-methyl-Histone H3 (Lys9) (H3K9me2), and Tri-methyl-Histone H3 (Lys27) (H3K27me3) levels were reduced in oocytes from melamine fed mice. (v) The litter sizes of melamine fed mice were significantly reduced when compared with those of controls.

LIMITATIONS, REASONS FOR CAUTION

Although we examined the possible effects of melamine on oocyte quality and fertility, we did not determine the effect of melamine on offspring development.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that melamine plays a major role in oocyte quality and fertility. This information could contribute to a better understanding of melamine toxicity in female reproduction.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by the National Basic Research Program of China (2014CB138503) and the Natural Science Foundation of Jiangsu Province (BK20140030). The authors have no conflict of interest to disclose.

Spectroscopic analyses and studies on respective interaction of cyanuric acid and uric acid with bovine serum albumin and melamine

In this work, the fluorescence quenching was used to study the interaction of cyanuric acid (CYA) and uric acid (UA) with bovine serum albumin (BSA) at two different temperatures (283 K and 310 K). The bimolecular quenching constant (Kq), apparent quenching constant (Ksv), effective binding constant (KA) and corresponding dissociation constant (KD), binding site number (n) and binding distance (r) were calculated by adopting Stern-Volmer, Lineweaver-Burk, Double logarithm and overlap integral equations. The results show that CYA and UA are both able to obviously bind to BSA, but the binding strength order is BSA+CYA<BSA+UA. And then, the interactions of CYA and UA with melamine (MEL) under the same conditions were also studied by using similar methods. The results indicates that both CYA and UA can bind together closely with melamine (MEL). It is wished that these research results would facilitate the understanding the formation of kidney stones and gout in the body after ingesting excess MEL.

Toxicity of melamine: the public health concern

Melamine contamination in food has resulted in sickness and deaths of human infants, pets, and farm animals in the past decade. The majority of the victims suffered from acute kidney injury, nephrolithiasis, and urolithiasis. Since then, animal studies have revealed the possible target organs of the melamine toxicity and the extent of the adverse effects of the contaminant. State-of-the-art analytical methods have been developed to achieve the "zero tolerance" aim for such economically motivated adulteration. These studies provide in-depth understanding of the melamine toxicity and promising analytical methods, which can help us safeguard our dairy food source.

Melamine in prenatal and postnatal organs in rats

Melamine can be transferred to fetus in utero through placenta and to infant ex utero by breast feeding. In this study, we characterized the pharmacokinetics of melamine in prenatal and postnatal organs in rats. Single bolus of melamine was administered to pregnant rats at different gestational stages and to infants at different postnatal stages. Distribution of melamine in maternal serum was about 30% higher in late pregnancy than that in early pregnancy; and it was 2 folds higher in postnatal serum in early infants in young adulthood. Distribution of melamine in all postnatal organs was higher than that in prenatal organs. Postnatal kidneys in early infants had the highest maximum concentration and the lowest clearance of melamine than the other postnatal organs. It may relate to the high vulnerability to the toxicity of melamine in this population.