胶束液相色谱法测定动物肌肉中三聚氰胺残留量

目的 建立胶束HPLC测定动物肌肉中三聚氰胺残留量的分析方法。方法 样品在酸性条件下，用乙 腈-磷酸盐缓冲液提取。以胶束溶液作为流动相，用HPLC测定，外标法定量。结果 线性范围为（0.1～10.0）mg/L，相关系数为0.9996。动物肌肉在（0.5～5.0）mg/kg添加水平范围内，回收 率在80%～110%。相对标准偏差〈10%。方法的最低检出限0.5mg/kg。结论该法实用、准确，为动物肌肉中 三聚氰胺残留量检测提供了可行的方法。     

Effect of melamine on [Ca2+]i and viability in PC3 human prostate cancer cells

Melamine is thought to be an endocrine disrupter that affects physiology in cells. This study examined the effect of melamine on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) and viability in PC3 human prostate cancer cells. Melamine evoked [Ca²⁺]_i rises concentration-dependently. Melamine-evoked Ca²⁺ entry was inhibited by nifedipine, econazole, SKF96365, GF109203X and phorbol 12-myristate 13 acetate. In Ca²⁺-free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin inhibited melamine-evoked [Ca²⁺]_i rise. Conversely, treatment with melamine abolished thapsigargin-evoked [Ca²⁺]_i rise. Inhibition of phospholipase C with U73122 did not alter melamine-evoked [Ca²⁺]_i rise. Melamine at 500–800 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Collectively, our data suggest that in PC3 cells, melamine induced [Ca²⁺]_i rises by evoking phospholipase C-independent Ca²⁺ release from the endoplasmic reticulum, and Ca²⁺ entry via protein kinase C-regulated store-operated Ca²⁺ entry. Melamine also caused Ca²⁺-independent cell death.     

Detection of melamine based on the suppressed anodic response of uric acid by a Au–Ag nanoparticles modified glassy carbon electrode

We demonstrated a sensitive electrochemical method for the determination of nonelectroactive melamine (Mel) using a modified glassy carbon electrode (GCE), with uric acid (UA) as the signal reporter. To increase the anodic response of UA, GCE was coated with Au–Ag nanoparticles and a Nafion thin film (Au–Ag/Nafion/GCE). The sensing mechanism was based on the competitive adsorption behavior of Mel on the Au–Ag/Nafion/GCE, which reduces the electroactive surface area of nanoparticles and thus hinders anodic response of UA. Under optimal conditions and the use of an analytical method of differential pulse voltammetry, this modified electrode detected Mel concentrations ranging from 2.5 to 70 nM, with a detection limit of 1.8 nM. The Au–Ag/Nafion/GCE demonstrated satisfactory reproducibility and stability, with relative standard deviations (RSDs) of 9.3% and 7.1%, respectively. The proposed electrochemical method was then successfully used to determine the Mel content in spiked milk powder and cat food samples, with RSDs of 1.7%–9.3% and recoveries of 92.4%–103.7%.     

The recovery of bladder epithelial hyperplasia caused by a melamine diet-induced bladder calculus in mice

Applying a model of bladder epithelial hyperplasia (BEH) caused by melamine-induced bladder calculus (BC), the recovery of BEH after melamine withdrawal was investigated. One experiment, comprising untreated, melamine and recovery groups, was conducted in Balb/c mice. Each group included 4 subgroups. Mice were fed normal-diet in untreated or a melamine-diet in other groups. The melamine-diet was then substituted with normal-diet in recovery group. Both of BC and BEH were observed after 14 and 56 days of melamine-diet. The BC is relatively uniform at the same melamine-diet durations. The BEH was diffuse with many mitotic figures, 4–7 rows of nuclei, and well-defined umbrella/intermediate cells. No marked differences in BEH degree were observed in the two different melamine-diet durations. On 4–42 days after melamine withdrawal, BC was not found, as the progressive regression with complete regression of BEH was observed, along with well-defined ageing/apoptotic cells in the superficial regions of BEH regression tissue. Conclusion, the melamine-induced BEH is relatively uniform, may be self-limiting in rows of nuclei, and can return to normal. Melamine withdrawal duration is critical for the BEH regression. Tissue of the BEH and its regression is ideal for exploring the renewal as well as growth biology of mammalian urothelium.     

Urinary melamine: Proposed parameter of melamine adulteration of food

Melamine is widely being reported as a food adulterant. Although its toxicity is currently recognized, melamine adulterations of food items are ongoing for falsely inflating the protein content of the food. Melamine alone or in combination with cyanuric acid or uric acid causes nephrotoxicity, and melamine-induced nephrotoxicity is now a global concern. It has been proven that when consumed, melamine is metabolized at a slower rate and excreted unchanged in urine. There is every possibility that when individuals consume melamine-adulterated food items, the melamine may be excreted unchanged in the urine. Therefore, melamine estimation in urine may be a yardstick to check for melamine adulteration of food items. In the present review, recent literature on this subject is analyzed justifying.     

Ultrasensitive determination of melamine in milk products and biological fluids by luminol-hydrogen peroxide chemiluminescence

An ultrasensitive chemiluminescence (CL) method for determination of melamine at picogram level was reported in a flow system. It was found that melamine can accelerate the electrons transferring rate of excited 3-aminophthalate with notable enhanced CL intensity of luminol-hydrogen peroxide reaction. The increased CL intensity was proportional to the concentration of melamine in the range from 2.5 to 250 pg mL⁻¹ (R² = 0.9953), with a detection limit of 0.9 pg mL⁻¹ (3σ) and the relative standard deviations lower than 5.0%. The proposed method was successfully applied to determine the melamine in liquid milk, yogurt, human urine and serum samples with the recovery of 98–105%, 93–105%, 98–105%, 97–109%, respectively.     

Estimating meat withdrawal times in pigs exposed to melamine contaminated feed using a physiologically based pharmacokinetic model

Recently melamine was found to have contaminated the feed of multiple food production species leading to concern over the ability to establish an appropriate withdrawal interval and protect the safety of the food supply. To establish an appropriate withdrawal interval, a physiologically based pharmacokinetic (PBPK) model for melamine was developed for rats and extrapolated to pigs. The rat model underpredicted plasma concentrations, but better predicted tissue residues. Correlation values for plasma, kidney, and liver were 0.59, 0.76, and 0.73, respectively. The pig model underpredicted early plasma time points but had greater accuracy at later time points which is relevant to withdrawal times. Correlation (R²) between predicted and observed plasma values was 0.89 with a negative intercept of −0.76. The pig model estimated a withdrawal interval (based on kidney tissue residues) of 19.2 and 20.9 h for single oral exposures of 3.0 and 5.12 mg/kg of melamine, respectively. Chronic oral dosing (3.0 and 5.12 mg/kg twice daily for 7 days) yielded withdrawal intervals of 20 and 21.3 h, respectively. PBPK models, such as this one, provide evidence of the usefulness in species extrapolation over a range of dosing scenarios and can be used to protect the food supply after accidental exposure in the face of little in the target species.     

A Survey on Occurrence of Melamine and Its Analogues in Tainted Infant Formula in China

Objective To investigate the occurrence and concentrations of melamine and its analogues in tainted infant formula and to identify the etiologic factors for the urinary stones epidemic in infants and young children in China in 2008. Methods Sanlu infant formula samples were collected from families of the affected children in Gansu province, and markets in Gansu and Hebei provinces and Beijing city. Melamine and its analogues, including cyanuric acid, ammeline, and ammelide were measured by gas chromatography/tandem mass spectrometry. Results High prevalence and concentrations of melamine were found in Sanlu infant formula samples, with low concentrations of cyanuric acid, ammeline and ammelide. Melamine were detected in 87 out of 111 Sanlu infant formula samples with a range of 118 to 4 700 mg/kg, Conclusion The results provide strong evidence for melamine as the etiological factor for the urinary stones epidemic in infants and young children in China in 2008.     

The melamine excretion effect of the electrolyzed reduced water in melamine-fed mice

Our hypothesis is that the intake of functional water, electrolyzed reduced water (ERW) can excrete melamine in body was evoked by melamine-tainted feed (MTF). To address this issue, we investigated the effect of ERW in MTF-mice model by way of body weight gain, incidence of urinary crystals and bladder stone, biochemical and haematological examination, histopathologic finding of kidney and urinary bladder, and the evaluation of bladder stone.We found that the rate of body weight gain was significantly more increased in MTF + ERW group than MTF + PW group. Accordingly, the number of immunocytes such as leukocyte, neutrophil and monocyte as well as the mean weight of spleen was significantly increased in MTF + ERW group. The incidence of urinary crystals was significantly higher in MTF + ERW group, whereas the incidence of urinary bladder stones was lower in MTF + ERW group (52.4%) than in MTF + PW group (38.1%). Also, urinary crystals were more precipitated in MTF + ERW group than MTF + PW group, and urinary bladder stone consists of 100% melamine. Collectively, our data clearly show that ERW intake is helpful to excrete of melamine in MTF mice model and this is the first report on the melamine excretion and clinically implying the safer fluid remedy for melamine-intoxicated hosts.     

Cognitive deficits induced by melamine in rats

Many studies reported that infants and animals were affected by food containing melamine, and the renal pathology was the main manifestation in intoxicated case. Our previous studies showed that melamine could impair hippocampal function and inhibited differentiated PC12 cell proliferation in vitro. The present study aimed to examine the effect on hippocampus and the possible mechanism induced by melamine in vivo. To address the hypothesis that melamine would impair the hippocampal function in vivo and then induce cognitive deficits, male Wistar rats were used to establish an animal model and melamine administered at a dose of 300 mg kg/day for 4 weeks. Morris water maze (MWM) test was employed to evaluate the learning and memory. The long term potentiation (LTP) from Schaffer collaterals to CA1 region in the hippocampus was recorded. The result of MWM test showed that there were significant deficits of learning and memory induced by melamine. LTP test presented that field excitatory postsynaptic potentials (fEPSPs) slopes were significantly lower in melamine group compared to that in control group. In conclusion, melamine had a toxic influence on hippocampus, which induced the learning and memory deficits. It suggested that the potential mechanism was associated with impairments of synaptic plasticity.