The Therapeutic Effect of Catechin on Nephrolithiasis Induced by Co-Exposure to Melamine and Cyanuric Acid in Sprague-Dawley Rats

This study aimed to assess the therapeutic efficacy of catechin against experimentally induced kidney stones resulting from co-exposure to melamine (MEL) and cyanuric acid (CYA) in male Sprague-Dawley rats. To induce nephrolithiasis, a combination of MEL and CYA (1:1 ratio, each at a dose of 31.5 mg/kg bw/day) was administered to the rats for 28 consecutive days. After nephrolithiasis was successfully induced, the rats were randomly divided into two groups: a treatment group and a sham group. The treatment group was given a daily oral dose of 50 mg/kg of catechin for 28 days, while the sham group received no intervention. Urine and blood samples were collected throughout the treatment period, and kidney samples were taken on day 28. Our findings demonstrated that treatment with catechin significantly reduced crystal deposition and pathological damage in the rats from nephrolithiasis. Additionally, renal injury markers were significantly decreased in the treatment group compared to the sham group. These findings suggest that catechin has potential therapeutic benefits in treating nephrolithiasis induced by co-exposure to MEL and CYA.

Exosomes derived from calcium oxalate-treated macrophages promote apoptosis of HK-2 cells by promoting autophagy

Calcium oxalate (CaOx) crystals are the main component of kidney stones. Macrophages have the function of eliminating these crystals, and the underlying mechanism remains unclear. Here, we attempted to determine the role of macrophage-derived exosomes exposed to CaOx crystals in regulating apoptosis of human proximal tubular cells (HK-2). Exosomes (CaOx-Exo) were isolated from CaOx-treated macrophages and then incubated with HK-2 cells. CaOx-Exo treatment reduced cell viability and promoted apoptosis of HK-2 cells. The expression of Caspase-3 and Bax was increased, and Bcl-2 expression was decreased in HK-2 cells following CaOx-Exo treatment. Moreover, CaOx-Exo treatment caused an increase of LC3-II/LC3-I ratio and Beclin-1 expression and a downregulation of p62 in HK-2 cells. GFP-LC3 puncta were increased in HK-2 cells following CaOx-Exo treatment. Additionally, CaOx-Exo-treated HK-2 cells were treated with 3-methyladenine (3-MA) to inhibit autophagy activity. 3-MA treatment weakened the impact of CaOx-Exo on cell viability and apoptosis of HK-2 cells. 3-MA treatment also reduced the LC3-II/LC3-I ratio and Beclin-1 expression and enhanced p62 expression in CaOx-Exo-treated HK-2 cells. In conclusion, these data demonstrated that exosomes derived from CaOx-treated macrophages promote apoptosis of HK-2 cells by promoting autophagy. Thus, this work suggests that macrophage-derived exosomes may play a vital role in CaOx-induced human proximal tubular cell damage.

Effect of urinary pH upon the renal toxicity of melamine and cyanuric acid

In 2007, dietary exposure to "scrap melamine' resulted in the death of a large number of cats and dogs, which was attributed to the formation of melamine cyanurate crystals in their kidneys. In this study, we investigated if changes in urinary pH could diminish the renal toxicity associated with exposure to combinations of melamine and cyanuric acid. Female Sprague-Dawley rats were treated for three days with suspensions of melamine and cyanuric acid at doses that were expected to induce renal toxicity. Dosing was then discontinued and the rats were treated for seven days with drinking water solutions (i.e., ammonium chloride and sodium bicarbonate) that would alter urinary pH. The urinary pH of rats administered ammonium chloride drinking water decreased from pH 6.0-6.2 to pH 5.1-5.2. This was accompanied by a decrease in the incidence of melamine cyanurate crystals in the kidneys and a decrease in the incidence of renal lesions. These data suggest that acidification of urine may help overcome the renal toxicities associated with the formation of melamine cyanurate crystals in the kidney.

Understanding of Structure and Thermodynamics of Melamine Association in Aqueous Solution from a Unified Theoretical and Experimental Approach

The aggregation propensity of melamine molecules in aqueous solutions in a range of melamine concentrations is investigated by means of a combination of theoretical and experimental approaches. It is observed that the hydrogen bonding interactions of sp³ nitrogen atoms of one melamine with sp² nitrogen atoms of another melamine play a major role in the melamine association. This finding is complemented by the observed favorable electrostatic energies between melamine molecules. The estimation of the orientational probability of melamine aromatic ring rules out any role of π-π interaction in melamine association. Further, the quantum chemical calculations suggest that a melamine molecule prefers to bind with another like molecule with a dihedral angle ranging from 36° to 46°. We have also determined the dimer existence autocorrelation functions to investigate the melamine-dimer stability with time in aqueous solution. Our results are well validated by the experimental findings (Chapman, R. P.; Averell, P. R.; Harris, R. R. Solubility of Melamine in Water. Ind. Eng. Chem. 1943, 35, 137-138. Ahromi, A. J.; Moosheimer, U. Oxygen Barrier Coatings Based on Supramolecular Assembly of Melamine. Macromolecules 2000, 33, 7582-7587. Yang, C.; Liu. Y. Studying on the Steady-State and Time-Resolved Fluorescence Characteristics of Melamine. Spectrochim. Acta A 2010, 75, 1329-1332. Mircescu, N. E.; Oltean, M.; Chis, V.; Leopold, N. FTIR, FT-Raman, SERS and DFT study on Melamine. Vib. Spectrosc. 2012, 62, 165-171. Makowski. S. J.; Lacher. M.; Schnick. W. Supramolecular Hydrogenbonded Structures between Melamine and N-Heterocycles. J. Mol. Struct. 2012, 1013, 19-25. Li, Z.; Chen, G.; Xu, Y.; Wang, X.; Wang, Z. Study of the Structural and Spectral Characteristics of C₃N₃(NH₂)₃(n = 1-4) Clusters. J. Phys. Chem. A 2013, 117, 12511-12518. Li, P.; Arman, D. H.; Wang, H.; Weng, L.; Alfooty, K.; Angawi, R. F.; Chen. B. Solvent Dependent Structures of Melamine: Porous or Non-porous. Cryst. Growth Des. 2015, 15, 1871-1875. Chen, J.; Lei, X.; Peng, B. Study on the Fluorescence Spectra of Melamine in Pure Milk. J. Opt. 2017, 46, 183-186.). Moreover, the thermodynamics of melamine association reveals that the association process is essentially driven by enthalpy, and this enthalpy-driven phenomenon is also confirmed by the experimental isothermal titration calorimetry measurements.

Combination exposure of melamine and cyanuric acid is associated with polyuria and activation of NLRP3 inflammasome in rats

The molecular mechanisms of melamine-induced renal toxicity have not been fully understood. The purpose of the study aimed to investigate whether melamine and cyanuric acid induced NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in the kidney, which may contribute to abnormal water and sodium handling in a rat model. Wistar rats received melamine (Mel; 200 mg·kg body wt−1·day−1), cyanuric acid (CA; 200 mg·kg body wt−1·day−1), or Mel plus CA (Mel + CA; 100 mg·kg body wt−1·day−1, each) for 2 wk. Mel + CA caused damaged tubular epithelial structure and organelles, dilated tubular lumen, and inflammatory responses. Crystals were observed in urine and serum specimen, also in the lumen of dilated distal renal tubules. The combined ingestion of Mel and CA in rats caused a markedly impaired urinary concentration, which was associated with reduced protein expression of aquaporin (AQP)1, 2, and 3 in inner medulla and α-Na-K-ATPase and Na-K-2Cl transporters in cortex and outer medulla. Mel + CA treatment was associated with increased protein expression of CD3 and mRNA levels of CD68 and F4/80 as well as phosphorylation of NF-κB in the kidney. Mel + CA treatment increased protein and mRNA expression of NLRP3 inflammasome components apoptosis-associated speck-like protein containing a caspase recruitment domain, caspase-1, and IL-1β in the inner medulla of rats. NF-κB inhibitor Bay 11-7082 reduced IL-1β expression induced by Mel + CA and prevented downregulation of AQP2 in inner medullary collecting duct cell suspensions. In conclusion, Mel + CA treatment caused urinary-concentrating defects and reduced expression of renal AQPs and key sodium transporters, which is likely due to the inflammatory responses and activation of NLRP3 inflammasome induced by crystals formed in the kidney.

Use of urinary renal biomarkers to evaluate the nephrotoxic effects of melamine or cyanuric acid in non-pregnant and pregnant rats

Although traditional assessments of renal damage detect loss of kidney function, urinary renal biomarkers are proposed to indicate early changes in renal integrity. The recent adulteration of infant formula and other milk-based foods with melamine revealed a link between melamine ingestion and nephropathy. Thus, the effects of melamine and related analogs (e.g., cyanuric acid) should be assessed in other potentially sensitive groups. We evaluated whether urinary Kim-1, clusterin, and osteopontin could detect the effects of high doses of melamine or cyanuric acid in pregnant and non-pregnant female rats gavaged with 1000 mg/kg bw/day for 10 days. We demonstrate that these biomarkers can differentiate the severity of effects induced by melamine or cyanuric acid. All melamine-treated animals experienced adverse effects; however, pregnant rats were most sensitive as indicated by increased SCr, BUN, and kidney weights, decreased body weight, and presence of renal crystals. These effects coincided with elevated urinary biomarker levels as early as day 2 of exposure. One cyanuric acid-treated rat displayed effects similar to melamine, including increased urinary biomarker levels. This work illustrates that these biomarkers can detect early effects of melamine or cyanuric acid crystal-induced nephropathy and further supports the use of urinary protein immunoassays as a powerful, non-invasive method to assess nephrotoxicity.

Krüppel-like factor 5 associates with melamine-cyanurate crystal-induced nephritis in rats

BACKGROUND

Melamine and cyanuric acid (M/CA), when orally administered together to rats, can induce crystal formation within renal tubules and cause acute kidney injury.

METHODS

To investigate the pathomechanism of crystal-induced nephritis, melamine and/or cyanuric acid were administered to 3-week-old (young) and 8-week-old (adult) rats, respectively.

RESULTS

Crystal formation, blood urea nitrogen elevation, tubular cell injury and macrophage infiltration were noted in rats fed with M/CA, but not in rats fed with vehicle, melamine or CA alone. These parameters were significantly higher in young rats than those in adult rats fed with M/CA 200 mg/kg body weight (BW) for 3 days. Krüppel-like factor 5 (KLF5) was expressed on distal tubule cells, especially when crystals deposited within the lumens. Both mRNA and protein levels were higher in young rats than those in adult rats fed with M/CA (200 mg/kg BW). KLF5 expression has been shown to modulate renal tissue cytokine production, and we found that proinflammatory cytokines like monocyte chemoattractant protein-1 and interlukin-6 were increased in kidney tissues of young rats fed with M/CA for 3 days. In contrast, interlukin-10, an anti-inflammatory cytokine, was upregulated in kidneys of adult rats fed with M/CA for 3 days.

CONCLUSIONS

Crystals are prone to deposition in distal tubules of young rats fed with M/CA. M/CA Crystal-related nephritis might be induced by the KLF5 expression, which modulated macrophage recruitment and proinflammatory cytokine production, subsequently leading to renal tubular injury and interstitial inflammation.

Long-term follow-up of nephrotoxicity in rats administered both melamine and cyanuric acid

Background

Melamine was recently identified as a risk factor for renal calculi following the milk powder contamination in China. However, the long-term natural history of melamine exposure and its renal effects remain unknown. We evaluated renal function and other adverse health effects using a rat model administered melamine and cyanuric aid, considering age and sex.

Methods

Twelve male F334/N rats each of ages 6, 10, and 26 weeks (N = 36) were equally assigned to Group M + C or controls. Group M + C rats were administered 12 mg · kg^-1 · day^-1 of melamine and cyanuric acid for 28 days. Serum and urine samples and kidney sections were evaluated on day 28. Six-week-old male and female F344/N rats were administered 12 mg of melamine and cyanuric acid for 28 days. Body weights were measured weekly; on days 0, 28, 90, and 180 after the 28-day period of melamine and cyanuric acid administration, serum samples and kidney sections were obtained.

Results

Although the control group had no crystals, 6-week-old Group M + C rats had more crystals compared to the 10- and 26-week old Group M + C rats. Male rats also had significantly more crystals than females of the same age. Male rats were affected to a greater extent than females.

Conclusion

Younger rats experienced more severe renal failure and greater renal crystal deposition following melamine and cyanuric acid administration. However, after melamine and cyanuric acid administration cessation, crystal deposition and renal failure improved and did not cause growth arrest. Therefore, early diagnosis of melamine-associated calculi is critical.

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.