Melamine poisoning became widely known in China recently after babies and children were exposed to melamine-tainted milk. Kidney damage is caused by kidney stones formed by melamine, uric acid and cyanuric acid. Urine metabolomics was performed to assess the overall biochemical changes induced by melamine intake and ARI in rats. The results showed that melamine caused serious nephrotoxicity by disrupting amino acid metabolism including tryptophan, polyamine and tyrosine metabolism, altering the tricarboxylic acid cycle and intestinal microflora structure. Microbiological transformation of melamine in the intestinal tract produces cyanuric acid, which is an indispensable calculus component responsible for melamine-induced renal toxicity in rats. It should be noted that when antibiotics inhibit intestinal microbial activity, melamine toxicity decreases and excretion increases. Urine amino acid analysis showed that hydroxyproline increased in a manner consistent with chemical and histopathological findings. In addition, the highest urinary hydroxyproline concentrations were found in rats with renal fibrosis. Men were slightly more affected than women, a finding supported by the excretion of hydroxyproline. Therefore, hydroxyproline may be a non-invasive urine biomarker for the detection of ARI associated with renal fibrosis. Another 1N NMR metabolomics study showed increased levels of asparagine, choline, creatinine, cysteine, ethanolamine, glucose, isoleucine, glutamine, and inositol in medullary tissue, but decreased levels of glucol, phenylalanine, tyrosine, and Sn-glycero-3. Ethanolamine, hypoxanthine, isoleucine, and o-phosphoethanolamine increased in the renal cortex, while formate, glucose, glutathione, threonine, and inositol decreased. Histological analysis showed epithelial degeneration and necrotic cell death in proximal and distal tubules.
MUF and MF resins are more resistant to moisture than UF resins. But melamine is much more expensive than urea. MF and MUF resins are used for plywood splicing and end joints of structural timbers for protected external exposure. In addition, these resins are used to bond low – and high-pressure laminates and coatings. In many ways, the formation chemistry of melamine-based resins is very similar to that of UF resins. However, adding formaldehyde to the amino group of melamine is faster and more complete than adding formaldehyde to urea. As a result, complete hydroxymethylation of melamine occurs (Pizzi, 1983), as noted above, but not urea. Another important difference is that the condensation of hydroxymethylated melamine occurs not only under acidic conditions, but also under neutral and slightly alkaline conditions (Pizzi, 1994; Pizzi and Mittal, 1994). In addition, products bonded with MF resin appear to be less prone to formaldehyde release than UF resin bonded products.
