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

Early-life exposures and long-term health: adverse gestational environments and the programming of offspring renal and vascular disease

According to the Developmental Origins of Health and Disease hypothesis, exposure to certain environmental influences during early life may be a key determinant of fetal development and short- and long-term offspring health. Indeed, adverse conditions encountered during the fetal, perinatal, and early childhood stages can alter normal development and growth, as well as put the offspring at elevated risk of developing long-term health conditions in adulthood, including chronic kidney disease and cardiovascular diseases. Of relevance in understanding the mechanistic basis of these long-term health conditions are previous findings showing low glomerular number in human intrauterine growth restriction and low birth weight-indicators of a suboptimal intrauterine environment. In different animal models, the main suboptimal intrauterine conditions studied relate to maternal dietary manipulations, poor micronutrient intake, prenatal ethanol exposure, maternal diabetes, glucocorticoid and chemical exposure, hypoxia, and placental insufficiency. These studies have demonstrated changes in kidney structure, glomerular endowment, and expression of key genes and signaling pathways controlling endocrine, excretion, and filtration function of the offspring. This review aims to summarize those studies to uncover the effects and mechanisms by which adverse gestational environments impact offspring renal and vascular health in adulthood. This is important for identifying agents and interventions that can prevent and mitigate the long-term consequences of an adverse intrauterine environment on the subsequent generation.NEW & NOTEWORTHY Human data and experimental animal data show that suboptimal environments during fetal development increase the risk of renal and vascular diseases in adult-life. This is related to permanent changes in kidney structure, function, and expression of genes and signaling pathways controlling filtration, excretion, and endocrine function. Uncovering the mechanisms by which offspring renal development and function is impacted is important for identifying ways to mitigate the development of diseases that strain health care services worldwide.

Comparison of melamine exposure by feeding practices in babies aged 0-6 months

This study was conducted to estimate the daily dietary intakes of melamine for human milk-fed (HMF) babies and mixed-fed (MF) babies. It was carried out in 70 mother-baby pairs (40 babies in the HMF group and 30 babies in the MF group). Human milk, formula milk, and baby urine samples were collected to assess the dietary exposure of babies. Melamine concentrations were analyzed by using a competitive enzyme-linked immunosorbent assay. Melamine was determined in 82.5 % of the human milk samples in the HMF group (median: 0.75 µg/L) while it was present in 96.7 % of human milk samples (median: 1.25 µg/L) and 96.7 % in formula milk samples (median: 0.95 µg/kg) in the MF group. The mean urinary melamine concentration of HMF babies (1.20 ± 0.21 µg/L) was not significantly different than MF babies (1.35 ± 0.49 µg/L). Melamine exposure was calculated as 0.12 µg/kg bw/day and 0.24 µg/kg bw/day in HMF and MF babies, respectively. Melamine exposure in both groups was below the tolerable daily intake. There were no significant associations between melamine exposure and various features of babies and mothers. As a result, it can be suggested that Turkish babies (aged 0-6 months) are not at risk for high melamine exposure through the diet.

Leucine-rich repeat kinase 2 is protective during acute kidney injury through its activation of autophagy in podocytes

Leucine-rich repeat kinase 2 (LRRK2) is a known regulator of autophagy in a range of cell types. Here, we investigated the role of LRRK2-associated autophagy during acute kidney injury (AKI) and its underlying mechanism(s) of action. Male mice aged 8-weeks were treated with the LRRK2 inhibitor MLi-2 and exposed to lipopolysaccharide (LPS) through intraperitoneal injection or ischemia-reperfusion (IR) surgery. Mice were sacrificed 12 or 24 h post-LPS injection or IR operation and blood was collected for serum creatinine measurements. Kidney cortical tissues were collected for western blot analysis of podocyte-specific markers and autophagy-associated proteins. Renal histopathology was observed through hematoxylin-eosin staining. For cell-based assays, immortalized mouse podocytes were silenced for LRRK2 through siRNA transfection and exposed to LPS or cobalt chloride. Changes in cell viability were investigated using cell counting kit-8, flow cytometry and MTT assays. Expression of podocyte-specific markers and autophagy-associated proteins were analyzed by western blotting. We observed an increase in LRRK2 expression at 12 h post-LPS injection and IR surgery that was accompanied by enhanced autophagy. At 24 h post-treatment, both LRRK2 expression and autophagy declined. Kidney injury was most pronounced in mice treated with MLi-2. Podocytes silenced for LRRK2 showed a loss of cell viability, decreased levels of podocyte-specific protein expression and a suppression of autophagy. Together, these data reveal the protective effects of LRRK2 during AKI through enhanced podocyte autophagy and cell viability.

Melamine induced changes in histopathology of the main organs and transcriptional levels of MAPK signaling genes in kidneys of female mice

Melamine is an important chemical raw material used in industries, which has potential health risks to animals and humans. Current research mainly focuses on the toxic effects of high-dose melamine ingestion. However, there are few reports on whether melamine at the current limited standard dose has adverse effects on various tissues and organs, and whether there are sensitive target genes for risk evaluation. For this, 24 female Kunming mice were fed 0, 1.8-, 3.6-, and 7.2- mg/kg/d melamine via drinking water for consecutive 28 days, respectively. The morphological changes of the ovarian, hepatic, and renal tissues were firstly observed. The results demonstrated that the histopathology of ovary, liver, and especially in kidney had been altered by melamine intake in female. And then, the transcriptional levels of MAPK signaling genes including p38, ERK1, ERK2, JNK1, and JNK2 in kidneys were investigated by real-time PCR. The data showed that ERK1 and p38 mRNAs expressions were up-regulated significantly by melamine, suggesting that ERK1 and p38 transcriptional levels in the kidney might to be considered as candidate targets for lower-dose melamine toxicity. This study not only provides potential targets for the diagnosis and prevention of melamine damage, but also helps to assess the health risks of the current minimum allowable levels of melamine in food and environment.

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.

Exposure to melamine and its derivatives in childcare facilities

Melamine (MEL) and its derivatives are widely used in many consumer products, including furniture, kitchenware, and plastics. However, very limited knowledge exists on human exposure to MEL and its derivatives, especially in the indoor environment. Here, we determined the occurrence and distribution of 11 MEL derivatives in childcare facilities and estimated children's exposure through dust ingestion and dermal absorption. We analyzed dust and samples of nap mats, a commonly used item in many childcares, from eight facilities located in the United States. Eight MEL-based compounds were detected in dust, and total MEL concentrations ranged from 429 to 117,000 ng/g. The most abundant compounds found in the dust samples were MEL, cyanuric acid (CYA), ammeline (AMN), and ammelide (AMD), with median concentrations of 1620, 585, 1060, and 299 ng/g, respectively. MEL, CYA, AMN and 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine (TBMMAT) were also detected in nap mats with median concentrations of 45.6, 19.8, 1510 and 2.5 ng/g, respectively. ΣMEL concentrations in mat covers (median 709 ng/g) were significantly higher than those in mat foam (median 15.1 ng/g). Estimated daily intakes (EDIs) of MEL and its derivatives via dust ingestion were two orders of magnitude higher than the EDIs through dermal absorption, but both were below the established tolerable daily intake levels. This is the first report on exposure to MEL and its derivatives in the childcare environment.

Melamine and cyanuric acid in foodstuffs from the United States and their implications for human exposure

We determined the concentrations of melamine, ammeline, ammelide, and cyanuric acid in meat, fish and seafood, cereal products, beverages, cooking oil, and vegetables (n = 121) collected from Albany, New York, United States. In addition, food packaging (n = 24) and animal feed (n = 12) were analyzed to determine the sources of melamine and its derivatives in foods. Among the six categories of foods analyzed, median concentrations of ∑melamine (sum of melamine and its three derivatives) in meat (23.6 ng/g fresh weight; fw) and cereal products (20.9 ng/g fw) were significantly (p < 0.05) higher than those in other food categories (<5.03 ng/g fw). Cyanuric acid and melamine were the major compounds, accounting for 51% and 26% of the total ∑melamine concentrations, respectively. ∑melamine was found ubiquitously in food packaging (median: 36.2 ng/g fw) and animal feed (56.5 ng/g fw), which are two important sources of melamine found in foodstuffs. The median estimated daily dietary intakes (including concentrations reported for dairy products in our previous study) of melamine and cyanuric acid were in the ranges of 13.4-72.7 and 75.4-347 ng/kg body weight/day, respectively, for various age groups. Dairy products, cereal products, and meat were major sources of dietary melamine (~76%) and cyanuric acid (~95%) exposure. The calculated hazard quotients for dietary exposure to melamine and cyanuric acid were well below 1.0, which suggested minimal risk from current exposures.

Occurrence of Melamine and Its Derivatives in Breast Milk from the United States and Its Implications for Exposure in Infants

Melamine received public and regulatory attention in 2008 following a scandal that involved the adulteration of milk and infant formula in China that affected tens of thousands of infants. Little is known about human exposure and the food chain transfer of melamine and its derivatives. In this study, melamine, cyanuric acid, ammeline, and ammelide were analyzed in 100 human milk samples collected from the United States during the period of 2009-2012. ∑Melamine (sum of melamine and its three derivatives) was found in breast milk at concentrations that ranged from 0.176 to 10.0 ng/mL (median: 1.40 ng/mL). Cyanuric acid was the major derivative, accounting for 73% of the total concentrations, followed by melamine (21%). No remarkable associations were noted between melamine and cyanuric acid concentrations and maternal/infant characteristics. The cumulative daily intakes of melamine (16.9-30.6 ng/kg bw/day) and cyanuric acid (88.8-161 ng/kg bw/day) were calculated for breast-fed infants and were found to be 1-2 orders of magnitude below the current tolerable daily intake. This is the first study to report the distribution of melamine and its derivatives in breast milk from the United States.

Occurrence and Profiles of Melamine and Cyanuric Acid in Bovine Feed and Urine from China, India, and the United States

Melamine and cyanuric acid have been reported to occur in animal products. Nevertheless, information that pertains to the occurrence of melamine and cyanuric acid in cattle feed and urine is lacking. In this study, the occurrence of melamine and its three derivatives (i.e., cyanuric acid, ammeline, and ammelide) was determined in 183 bovine urine and 29 matched feed samples collected from China, India, and the United States. ∑Melamine (sum of four target compounds) was found in all urine samples at concentrations that ranged from 4.2 to 5280 ng/mL (median: 370 ng/mL); cyanuric acid was the major derivative, accounting for 97% of the total concentrations, followed by melamine (2.2%). The ubiquitous occurrence of ∑Melamine in feed (21-6230 ng/g) suggests that it is the major source of melamine and its derivatives in bovines. Urinary concentrations of melamine and cyanuric acid varied significantly among the three countries, with samples from China as having the highest concentrations, followed by the United States and India. The calculated cumulative daily intakes of melamine and cyanuric acid were at least 10-fold below the current tolerable daily intake recommended for humans. Our study provides evidence-based data on exposure patterns and sources of melamine and cyanuric acid in cattle.

Inter-day and inter-individual variability in urinary concentrations of melamine and cyanuric acid

Melamine is used extensively in household products, such as furniture, dinnerware, and food utensils. Several studies have shown that melamine adversely affects kidney function. Nevertheless, little is known about urinary melamine concentrations, and its temporal variability. In this study, 213 first-morning-void urine samples were collected from 19 volunteers for over a month to assess longitudinal variability in concentrations of melamine and its three structural analogues, i.e., cyanuric acid, ammeline, and ammelide. Target analytes were found in all urine samples at mean concentrations of 3.3, 16, 0.99, and 0.62 ng/mL, for melamine, cyanuric acid, ammelide, and ammeline, respectively. Cyanuric acid was the major compound found in all urine samples, accounting for 74-80% of the total concentrations, followed by melamine (12-20%), ammelide (4-6%), and ammeline (2-4%). Gender- and age-related differences in melamine concentrations were observed, although no such pattern was found for cyanuric acid. After adjusting for creatinine, melamine and cyanuric acid concentrations were moderately predictable with inter-day intraclass correlation coefficients (ICCs) in the range of 0.541-0.763. Nevertheless, substantial inter-individual variation in melamine levels existed even after creatinine adjustment, as evidenced by low ICCs (0.008-0.108). Cumulative daily intake of melamine and cyanuric acid was calculated on the basis of urinary concentrations and the mean values were found to be at least 10-fold below the current tolerable daily intake.