Determination of urine melamine by validated isotopic ultra-performance liquid chromatography/tandem mass spectrometry

Assessment of chronic renal injury from melamine-associated pediatric urolithiasis: an eighteen-month prospective cohort study

BACKGROUND

The illegal use of melamine in powdered baby formula resulted in a widespread outbreak of melamine-associated pediatric urolithiasis and kidney damage in China in 2008. We conducted this study because more needs to be known about the long-term effects of melamine-associated urolithiasis and kidney damage.

OBJECTIVES

To determine the prognosis and long-term implications of chronic kidney damage in children with urolithiasis resulting from melamine consumption.

DESIGN

Prospective cohort study.

SETTING

Children's Hospital of Fudan University.

PATIENTS AND METHODS

Children six years of age or older with a history of having consumed melamine-contaminated milk powder were voluntarily screened. We measured urinary microprotein profiles [microalbumin (ALBU), immunoglobulin G (IgG), and n-acetyl-ß-d-glucosidase (NAG)] and creatinine (CR) results at 6 and 18 months in children with melamine-associated urolithiasis. This study was conducted from September 17 to October 15, 2008.

MAIN OUTCOME MEASURES

Changes in urinary microprotein profiles.

RESULTS

Of 8335 children screened, 102 children (1.22%) were diagnosed with melamine-associated urolithiasis. Follow-up rates at 6 and 18 months were 91.4% (96/105) and 89.2% (91/102), respectively. Eighteen months later, 90.3% patients had spontaneously passed a stone. The incidence rates of proteinuria and microscopic hematuria at 6 months were significantly higher than at 18 months (P=.029 and P=.017, respectively). The proportion of patients with abnormal ALBU/CR, IgG/CR and NAG/CR at 6 months (27.6%, 17.1% and 21.1%, respectively) was significantly higher than at 18 months (6.4%, 5.1% and 12.8%, respectively). The high concentration of melamine consumed was the primary factor correlated with the high microprotein levels. Approximately 90% melamine-associated urolithiasis cases can be resolved within 18 months by non-surgical therapy.

CONCLUSION

The long-term presence of stones associated with a previous exposure to melanine can cause chronic kidney glomerular and tubular injuries. Passing these stones as soon as possible can reduce kidney injury and accelerate recovery.

LIMITATIONS

We could not control for possible selection bias due to more visits to our hospital or visits to our hospital after diagnosis at other hospitals, which might have increased the rate of diagnosis.

Analysis of trace amounts of adulterants found in powders/supplements utilizing Raman spectroscopy coupled to direct analyte-probed nanoextraction-nanospray ionization-mass spectrometry

In the United States, all food products have to be regulated to inform the consumers of the ingredients contained within. Some ingredients are not included on the label and yet are still found in the products. Presented is a Raman imaging technique for rapid, nondestructive, and spatially relevant localization of adulterants in powders. Raman spectroscopy followed by direct analyte-probed nanoextraction coupled to nanospray ionization-mass spectrometry allows rapid determination of the presence of each adulterant, leading to positive identifications such as melamine. The location and identification of these trace particles can then be extracted using a nanomanipulator. The nanomanipulation technique uses a solvent filled capillary tip which can be positioned on the particle of interest. Direct mass spectrometric analysis via nanospray of the particulate of interest eliminates time consuming chromatographic techniques prior to mass spectrometry analysis. This coupled technique combines rapid Raman spectroscopy techniques with direct mass spectrometry to confirm the presence of an adulterant. This technique was applied to an FDA supplied test sample, in which sibutramine, phenolphthalein, and melamine were confirmed to be present.

Ambient Melamine Exposure and Urinary Biomarkers of Early Renal Injury

Information about environmental exposure to melamine and renal injury in adults is lacking. We investigated this relationship in 44 workers at two melamine tableware manufacturing factories in Taiwan (16 manufacturers, eight grinders, ten packers, and ten administrators) and 105 nonexposed workers (controls) at one shipbuilding company who were enrolled in August-December of 2012. For melamine workers, personal and area air samples were obtained at the worksite over 1 workweek (Monday-Friday). In the same week, pre- and post-shift one-spot urine samples were collected each workday and one first-spot urine sample was collected on each weekend morning and the following Monday morning. For each control, a one-spot urine sample was collected on Friday morning. A blood sample was also obtained from each participant at this time. Melamine levels were measured in air, urine, and serum, and early renal injury biomarkers were measured in urine. Urinary melamine concentrations in manufacturers increased sharply between pre- and post-shift measurements on Monday, remained significantly elevated throughout the workweek, and decreased over the weekend; changes in urinary melamine concentrations were substantially lower for other melamine workers. Manufacturers were exposed to the highest concentrations of ambient melamine and had significantly higher urinary and serum melamine concentrations than did the controls (P<0.001). Urinary melamine levels were positively associated with urinary N-acetyl β-d-glucosaminidase (NAG) levels but not microalbumin levels, and the detectable β2-microglobulin rate increased in the manufacturers group. In conclusion, ambient melamine exposure may increase the levels of urinary biomarkers of renal tubular injury in this occupational setting.

The true stone composition and abnormality of urinary metabolic lithogenic factors of rats fed diets containing melamine

To better understand the toxicity of melamine to humans, the stone composition and urinary metabolic lithogenic factors of rats fed diets containing melamine including the infant's melamine-induced stone composition were studied. Sixty 4-week-old male rats divided into three groups were, respectively, fed diets containing no melamine (control), 0.1% melamine, and 1% melamine for 4 weeks. At the end of experiment, the collected stones and 24-h urines from rats were, respectively, measured with compositions and metabolic lithogenic parameters. The stone from an infant who ingested melamine-adulterated formula was also included in compositional analysis. Across three groups, the stone was only detected in 1% melamine group, with composition of almost melamine different from the affected infant's stone composed of melamine and uric acid with a ratio of 1:2. Compared with control group, urine calcium and phosphate excretions were significantly increased in 1% melamine group. Urine uric acid excretion was significantly increased but citrate excretion was significantly decreased in 0.1% and 1% melamine groups. Urine oxalate excretion and pH were indicated without any significant difference. In addition based on urine physicochemical characters, melamine-uric acid stone seems difficult to be formed in the rats due to their characters of urine high-pH and low-uric acid. These results demonstrated that (1) the stone composition of rats fed melamine was not and could not be as that of infants fed melamine-adulterated formula, two species had a different mechanism of melamine-induced stone formation; (2) the exposure of melamine could result in abnormalities of urine metabolic lithogenic factors to rats, perhaps as well as human beings.

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.

Can melamine levels in 1-spot overnight urine specimens predict the total previous 24-hour melamine excretion level in school children?

BACKGROUND

We investigated whether melamine concentrations in 1-spot overnight urine sample can represent the previous 8- and 24-h total urinary melamine excretions in school children. The relationship between urinary melamine levels and several clinical biomarkers of early renal injury such as microalbumin and N-acetyl-beta-D-glucosaminidase (NAG) in urine was also examined.

METHODS

School children, aged 6-10 y, and their parents who were healthy and lived closely to Kaohsiung Medical University-affiliated hospitals were recruited. All study children had the first 1-spot overnight urine sample collected on the Sunday morning (the first day) immediately when they woke up, and then all the subsequent urine samples continued to be collected until the first 1-spot overnight urine sample on the morning of the next day (Monday, the second day). Two first 1-spot overnight urine samples from their parents on the same Sunday and Monday mornings were also collected. This protocol was completed in the July and August of 2011. All urine samples were measured for melamine, biomarkers of early renal injury, and creatinine.

RESULTS

There were 7 girls and 16 boys in this study. Except for one missing urine sample from 1-spot overnight urine sample on the morning of the second day, melamine levels in the rest of urine samples among the study children were all detectable. The median melamine levels of 1-spot overnight urine samples on the first and second day mornings were 0.93 and 1.73 μg/mmol of creatinine respectively. We found that melamine concentrations of 1-spot overnight urine samples on the second day morning were highly correlated with the previous 8- and 24-h total melamine excretions in urine (r=0.936, p<0.001, n=21 and r=0.616, p<0.001, n=21 respectively). Good correlation of 1-spot overnight urine sample on the first and second day mornings was also found (r=0.619, p=0.003, n=21). In contrast, there were no significant correlations of 24-h total urinary melamine and 24-h total urinary microalbumin and NAG excretions (r=-0.221, p=0.319, n=22 and r=0.084, p=0.710, n=22).

CONCLUSION

Melamine levels in 1-spot overnight urine sample can predict the previous 8- and 24-h total melamine excretions in urine. Since melamine exposure levels in these school children were relatively low, its association with clinical biomarkers of early renal injury was not found. A future study is necessary to increase the sample size and to find the more sensitive preclinical biomarkers of renal injury to link with low melamine exposure in children in the community.

Characterization of melamine-associated urinary stones in children with consumption of melamine-contaminated infant formula

BACKGROUND

Crystalline morphology and compositions of melamine-associated urinary stones caused by consumption of melamine-contaminated infant formula are reported.

METHODS

Twelve melamine-associated urinary stone samples were obtained from 12 children aged from 3 to 36 months who were treated in Lanzhou University Second Hospital. The crystalline morphology and compositions of these stone samples were analyzed using a combination of infrared spectrum, SEM and XRD. The presence of melamine in 12 stones was determined by HPLC.

RESULTS

Diversity of crystalline morphology in 10 stone samples was revealed by SEM observation. Infrared spectral data revealed that 8 of the 10 stone samples predominantly consisted of the crystal forms of urate: 1 of sodium urate monohydrate, 2 of uricite and 5 of uric acid dihydrate and ammonium urate. However, ammonium magnesium phosphate hexahydrate, ammonium urate and carbonate apatite were also identified in 1 stone sample. The content of melamine in all of the 12 stone samples was determined by HPLC and found to range from 200 to 339,000 μg/g. XRD analysis in 6 stone samples showed that amorphous mineral phase was involved in the calculogenesis.

CONCLUSIONS

Melamine and uric acid are the main possible etiologic factors closely related to melamine-associated urinary stone formation in humans.

Enzyme-Linked Immunosorbent Assay Detection of Melamine in Infant Formula and Wheat Food Products

The adulteration of food products with melamine to inflate the nitrogen content necessitates the establishment of analytical methods that can distinguish between proteinaceous ingredients and such adulterants. The specificity and ability to detect melamine by two commercial enzyme-linked immunosorbent assay (ELISA) kits were evaluated along with three protocols for sample preparation. Both ELISAs displayed cross-reactivity with ammeline, but neither was able to detect ammelide or cyanuric acid, indicating either a requirement for the 4,6-diamino-1,3,5-triazine structure or inability to bind 1,3,5-triazine-4,6-diones. The limits of detection for melamine in powder infant formula ranged from 0.2 to 3 μg/g depending on the ELISA kit and the method used to prepare the sample. The limits of detection for melamine in liquid infant formula and wheat products were &lt;1 μg/ml and &lt;2.5 μg/g, respectively. The ELISA kits provide an effective alternative for the analysis of samples suspected of containing melamine without relying on extensive sample preparation or expensive instrumentation.

Determination of melamine and cyanuric acid in human urine by a liquid chromatography tandem mass spectrometry

Melamine was found to be the etiological factor for the urinary stones epidemic in infants and young children in China in 2008. Urine level of melamine and its analog cyanuric acid may be useful markers for the evaluation of toxic effects. Liquid chromatography tandem mass spectrometry methods for the individual determination of melamine and cyanuric acid in human urine are described. Using isotope labeled internal standards during liquid-liquid extraction, the method was fully validated by verifying specificity, linearity, LLOQ, intra- and inter-assay precision and accuracy, matrix effect, recovery and stability. Calibration curves with good linearity (r=0.9999) over the concentration range from 10 to 5000 ng/ml, intra-assay precision <10% and inter-assay precision <15%, accuracy between 93.0 and 111.6% were obtained with multiple reaction monitoring mode for melamine and cyanuric acid in human urine. The methods were successfully applied to the analysis of urine samples collected from 86 infants and 110 adults.