Toxicity of melamine, an adulterant in fish feeds: experimental assessment of its effects on tilapia

Evaluation of sub-chronic toxicity of melamine via systematic or oral delivery in adult zebrafish based on behavioral endpoints

Melamine-tainted products have been found in the market and raised issues about food safety. Recent studies done in rodents and humans demonstrated the toxicities of melamine, especially in causing kidney damage and bladder stone formation. However, very few studies assessed its behavior toxicity in organisms, including fish. Therefore, in this study, the researchers aim to determine whether sub-chronic exposure to melamine via oral and systematic administration could induce behavioral abnormality in zebrafish. After 14 days of systematic exposure to melamine at doses of 0.1 and 10 ppm levels, zebrafish were subjected to multiple behavioral assays. Results from both exposure routes showed that melamine indeed slightly increased fish locomotion and altered their exploratory behaviors in the novel tank assay. Furthermore, tightened shoaling formation was also displayed by the treated fish in the waterborne exposure group. However, melamine exposure did not cause any obvious alterations in fish behaviors during other behavioral tests. In addition, in comparison with previously published data on the behavior toxicities of several solvents in zebrafish, our phenomic analysis suggests the relatively low behavior toxicities of melamine via either systematic exposure or oral administration to zebrafish compared to those solvents. Nevertheless, our data indicate that the potential neurotoxicity of chronic low-dose melamine should not be ignored.

Biomarkers of neurotoxicity, oxidative stress, hepatotoxicity and lipid peroxidation in Clarias gariepinus exposed to melamine and polyvinyl chloride

PURPOSE

Plastic particulates and chemicals are emerging environmental pollutants with significant impact on aquatic ecosystems. In this study, the effects of oral uptake of melamine, melamine formaldehyde, and polyvinyl chloride on serum biochemical profiles, antioxidant enzymes activities, lipid peroxidation levels and brain acetyl cholinesterase activities in Clarias gariepinus juveniles were investigated.

METHODS

Fish specimens were fed diets spiked with melamine, melamine formaldehyde and poly vinyl chloride at 0.3% (3.0 g Kg^-1) dietary inclusion for 45 days. Toxicity effect of these plastic chemicals was estimated by assaying relevant biomarkers.

RESULTS

After 45 days exposure, Serum glucose was significantly elevated, whereas plasma protein levels were substantially reduced in the exposed fish groups. Serum transaminases were significantly elevated in the exposed groups. Brain acetylcholinesterase and antioxidant enzyme activities declined significantly, while malondialdehyde levels were elevated in the exposed groups.

CONCLUSION

C. gariepinus is an important bioindicator to monitor the ecotoxicological impact of plastic chemicals such as melamine, and polyvinyl chloride.

Melamine and curcumin enriched diets modulate the haemato-immune response, growth performance, oxidative stress, disease resistance, and cytokine production in oreochromis niloticus

Currently, feed adulteration and contamination with melamine (MEL) are considered one of the serious issues in the aquatic industry. With the limited studies of MEL exposure alone in fish, its adverse impacts on fish cannot be evaluated well. Accordingly, this study aimed to investigate the effects of MEL containing diets on the immune response, disease resistance to Aeromonas hydrophila, growth performance, chemical composition, immune-related genes expression, and histopathology of both spleen and head kidneys. Also, the efficacy of curcumin (CUR) dietary supplementation to alleviate MEL negative impacts were evaluated. A total of 180 apparently healthy Oreochromis niloticus (O. niloticus) were divided into four groups with three replicates fed the basal diet only, basal diet fortified with 200 mg/kg CUR, basal diet containing 1 % MEL, or a basal diet containing CUR + MEL. The results displayed that MEL significantly reduced growth performance indices and body crude lipid contents. Anemic, leukopenic, lymphocytopenic, heterocytopenic, esonipenic, hypoproteinemic and hypoalbuminic conditions were apparent. Moreover, depleted immune and antioxidant indicators including lysozyme activity, nitric oxide, immunoglobulin M, complement 3, glutathione peroxidase, and superoxide dismutase enzyme activity were recorded. Also, MEL reduced the disease resistance of O. niloticus to bacterial infection. Furthermore, MEL induced downregulation of mRNA levels of interleukin 1β and tumor necrosis factor α in the spleen together with obvious pathological perturbations in both spleen and head kidneys. The CUR addition resulted in a significant enhancement in most indices. These results may conclude that MEL could alter both innate and adaptive immune responses via the negative transcriptional effect on immune-related genes together with the oxidative damage of the immune organs. Furthermore, CUR dietary supplements could be advantageous for mitigating MEL negative impacts, thus offering a favorable aquafeed additive for O. niloticus.

Bio-inspired ultrasensitive colorimetric detection of methyl isothiocyanate on nylon-6 nanofibrous membrane: A comparison of biological thiol reactivities

Living organisms, including human beings, rapidly show skin color changes after chemical poisonings, a result of toxicological or detoxification reactions caused by biological thiol compounds. On the other side, quick and portable detection of highly-volatile toxicants is an urgent need for improving human safety and personal protection, especially real-time monitoring of fumigants at low level for protection of farm workers and residents from overexposure of fumigants, vaporous pesticides. Here, we designed a rapid and portable detection method for methyl isothiocyanate (MITC) vapor by mimicking detoxification reactions of biological thiols in human bodies with MITC. The detection reaction was implemented on a nylon-6 nanofibrous membrane with ultrahigh surface areas to show color signals with the addition of Ellman's reagent. The reactivities of glutathione, N-acetyl-L-cysteine, L-homocysteine, cysteamine, and thioglycolic acid toward MITC were experimentally explored and theoretically discussed. The detection sensitivity is tunable in different biological thiol systems, which broadens the sensor applications in detection of trace amount of MITC in ambient environment and improves the protection of human safety. The new sensor system reduced the sensor operation time to 15 min and achieved the detection limit of 99 ppb, much lower than its permissible exposure limit (220 ppb).

The behavior of melamine in biological wastewater treatment system

Melamine (MA) is a significant raw material for industry and home furnishing, and an intermediate for pharmacy. However it is also a hazardous material when being added to food as a protein substitute due to the high nitrogen content. In this study, the behavior of MA in activated sludge was investigated. Experiments showed that MA was removed during biological wastewater treatment process, and the removal was mainly achieved by activated sludge adsorption instead of biodegradation. Low levels of MA (0.001-0.10mg/L) in wastewater had negligible influence on the performance of activated sludge, but high levels of MA deteriorated biological nitrogen and phosphorus removal. The presence of MA (1.00 and 5.00mg/L) decreased total nitrogen removal efficiency from 94.15% to 79.47% and 68.04%, respectively. The corresponding concentration of effluent phosphorus increased from 0.11 to 1.45 and 2.06mg/L, respectively. It was also observed that MA inhibited the enzyme activities of nitrite oxidoreductase, nitrate reductase, nitrite reductase and exopolyphosphatase, which were closely relevant to nitrogen and phosphorus removal. Further investigation showed that the presence of high MA concentrations promoted the consumption and synthesis of glycogen, thereby providing the advantage for the growth of glycogen accumulating organisms.

Pathophysiological changes associated with dietary melamine and cyanuric acid toxicity in red tilapia

This study examined the adverse effects of feed-delivered melamine (MEL) and cyanuric acid (CYA) in red tilapia. Diet 1 (without MEL and CYA), diets 2-4 (with MEL and CYA at 2.5, 5 and 7.5 g kg(-1) diet, respectively) and diets 5 and 6 (with either MEL or CYA at 10 g kg(-1) diet) were examined. MEL alone lowered both growth and FCR (P < 0.05), and CYA alone reduced the FCR of tilapia. Protein efficiency ratio and apparent net utilization of fish on diets 2-6 were poor (P < 0.05). The renal tubules of fish ingested MEL-CYA combination had melamine-cyanurate crystals. On the other hand, diets with only one chemical did not induce such crystals. MEL and CYA in whole body, fillet or viscera reflected their dietary inclusion levels. The levels of Hsp70 were increased in the liver of fish that ingested MEL and CYA, in combination or singly (P < 0.05). However, in the kidney, such an increase was visible only in the fish that received diet 4 (P < 0.05). Combination of MEL and CYA at inclusion levels > 5 g kg(-1) diet induced the activity of catalase in liver and the activity of glutathione peroxidase in liver and kidneys. Therefore, these adulterants should not be included in fish feeds.

Melamine-cyanurate complexes and oxidative stress markers in trout kidney following melamine and cyanuric acid long-term co-exposure and withdrawal

In 2007, renal failure and death in pets were linked to pet food containing both melamine (MEL) and cyanuric acid (CYA). In mammals and fish, the co-administration of MEL and CYA causes renal crystal formation. Moreover, little is known about the process of crystal removal in fish. The aim of this study was to evaluate the formation of MEL-cyanurate crystals in kidney of rainbow trout (Oncorhynchus mykiss) fed combined MEL and CYA diets for 10 weeks at 250, 500 and 1,000 mg/kg in feed (equivalent to 2.5, 5, 10 mg/kg body weight of trout fed 1 % body weight per day). During the exposure trial and throughout a withdrawal period, prooxidant effects of MEL and CYA were evaluated on oxidative stress markers such as catalase, glutathione S-transferase and malondialdehyde. Crystal formation was dose and time dependent, and after six withdrawal weeks, crystals persisted in kidney of trout treated the highest triazine dose. Catalase and glutathione S-transferase activity in kidney of trout exposed to both triazines for 10 weeks indicated that MEL (with or without CYA) can exert a higher prooxidant effect than CYA dispensed singly. Although the enzymes activity increase appears to be reverted after two MEL withdrawal weeks, persistence of crystals may lead to severe damage in renal cells of fish.

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.

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.