In vitro effects of dental monomer exposure - Dependence on the cell culture model.

Methacrylate monomers are major components of resin-based biomaterials. The polymerization of these materials is never complete, and methacrylates leaking from cured materials cause exposure of patients. Only some selected methacrylates have thoroughly been tested for possible interaction with living cells. In the current study, we compared the effects of 2-hydroxyethyl-methacrylate (HEMA; a carefully studied methacrylate) and hydroxypropyl-methacrylate (HPMA; a scarcely investigated methacrylate). Five cell lines differing in both source and cell type were used. The cells were exposed to methacrylates (1-8 mM). Cell viability, cell death, glutathione levels, reactive oxygen species (ROS), and cell growth pattern were measured. Both methacrylates reduced cell viability, and glutathione depletion was observed in all cell lines. The cell death pattern varied among the cell lines. The ROS levels and cell growth pattern also differed between the cell lines after exposure to methacrylate monomers. No difference between HEMA and HPMA exposures were observed in any of the cell lines. The variation between cell lines shows that the measured methacrylate toxicity depends heavily on the test system chosen. Further, the conformity between HEMA and HPMA effects suggests that the two methacrylates similarly affect living cells.

In-vitro cytocompatibility of dental resin monomers on osteoblast-like cells.

OBJECTIVES: Dental resin-based materials are widely used in modern dentistry. Especially, resin cements enjoy great popularity and are utilized in many applications. Nevertheless, monomers could be released from the resinous matrix, thus interact with surrounding tissues, cause adverse biological reactions and may lead in cases of implant retained restorations to peri-implant bone destruction. Hence, we performed an in-vitro study to determine cytotoxicity of resin monomers on osteoblast-like cells. METHODS: Three permanent osteoblast-like cell lines from tumor origin (MG-63 and Saos-2) as well as immortalized human fetal osteoblasts (hFOB 1.19) were used and treated with different concentrations of the main monomers: BisGMA, UDMA, TEGDMA and HEMA. The impact on cell viability was monitored using three different cytotoxicity tests: alamarBlue, XTT, and LDH assay. Mean±SEM were calculated and statistical analysis was performed with GraphPad Prism software. RESULTS: All monomers tested caused concentration dependent cytotoxic effects on the three investigated osteoblast-like cell lines. Although all three cell viability assays showed comparable results in cytotoxic ranking of the monomers (BisGMA > UDMA > TEGDMA > HEMA), higher differences in the absolute values were detected by the various test methods In addition, also a cell line dependent influence on cell viability could be identified with higher impact on the immortalized hFOB 1.19 cells compared to both osteosarcoma cell lines (MG-63, Saos-2). CONCLUSIONS: Monomer concentrations detected in elution studies caused toxic effects in osteoblast-like cells. Although the results from in-vitro studies cannot be directly transferred to a clinical situation our results indicate that released monomers from composite resin cements may cause adverse biological effects and thereby possibly lead to conditions favoring peri-implantitis and bone destruction. CLINICAL SIGNIFICANCE: The wide use of composite resin cements especially in implant-prosthetic treatments should be scrutinized to avoid possible clinical implications between eluted resin monomers and bone cells leading to conditions favoring peri-implantitis and bone destruction.

Interaction between LPS and a dental resin monomer on cell viability in mouse macrophages.

OBJECTIVE: Lipopolysaccharide (LPS) from cariogenic microorganisms and resin monomers like HEMA (2-hydroxyethyl methacrylate) included in dentin adhesive are present in a clinical situation in deep dentinal cavity preparations. Here, cell survival, expression of proteins related to redox homeostasis, and viability of mouse macrophages exposed to LPS and HEMA were analyzed with respect to the influence of oxidative stress. METHODS: Cell survival of RAW264.7 mouse macrophages was determined using a crystal violet assay, protein expression was detected by Western blotting, and HEMA- or LPS-induced apoptosis (cell viability) was analyzed by flow cytometry. Cells were exposed to HEMA (0-8mM), LPS (0.1µg/ml) or combinations of both substances for 24h. The influence of mitogen-activated protein kinases (MAPK) was analyzed using the specific inhibitors PD98059 (ERK1/2), SB203580 (p38) or SP600125 (JNK), and oxidative stress was identified by the antioxidant N-acetylcysteine (NAC). RESULTS: Cell survival was reduced by HEMA. LPS, however, increased cell survival from 29% in cultures exposed to 8mM HEMA, to 46% in cultures co-exposed to 8mM HEMA/LPS. Notably, LPS-induced apoptosis was neutralized by 4-6mM HEMA but apoptosis caused by 8mM HEMA was counteracted by LPS. Expression of NOS (nitric oxide synthase), p47phox and p67phox subunits of NADPH oxidase, catalase or heme oxygenase (HO-1) was associated with HEMA- or LPS-induced apoptosis. While no influence of MAPK was detected, NAC inhibited cytotoxic effects of HEMA. SIGNIFICANCE: HEMA- and LPS-triggered pathways may induce apoptosis and interfere with physiological tissue responses as a result of the differential formation of oxidative stress.

BisGMA-induced cytotoxicity and genotoxicity in macrophages are attenuated by wogonin via reduction of intrinsic caspase pathway activation.

Bisphenol-A-glycidyldimethacrylate (BisGMA) is a frequently used monomer in dental restorative resins. However, BisGMA could leach from dental restorative resins after polymerization leading to inflammation in the peripheral environment. Wogonin, a natural flavone derivative, has several benefits, such as antioxidative, anti-inflammatory and neuroprotective properties. Pretreatment of macrophage RAW264.7 cells with wogonin inhibited cytotoxicity which is induced by BisGMA in a concentration-dependent manner. BisGMA induced apoptotic responses, such as redistribution of phosphatidylserine from the internal to the external membrane and DNA fragmentation, were decreased by wogonin in a concentration-dependent manner. In addition, BisGMA-induced genotoxicity, which detected by cytokinesis-blocked micronucleus and single-cell gel electrophoresis assays, were inhibited by wogonin in a concentration-dependent manner. Furthermore, wogonin suppressed BisGMA-induced activation of intrinsic caspase pathways, such as caspases-3 and -8. Parallel trends were observed in inhibition of caspase-3 and -8 activities, apoptosis, and genotoxicity. These results indicate wogonin suppressed the BisGMA-induced apoptosis and genotoxicity mainly via intrinsic caspase pathway in macrophages.

Epigallocatechin-3-Gallate Reduces Cytotoxic Effects Caused by Dental Monomers: A Hypothesis.

Resin monomers from dental composite materials leached due to incomplete polymerization or biodegradation may cause contact allergies and damage dental pulp. The cytotoxicity of dental resin monomers is due to a disturbance of intracellular redox equilibrium, characterized by an overproduction of reactive oxygen species (ROS) and depletion of reduced glutathione (GSH). Oxidative stress caused by dental resin monomers leads to the disturbance of vital cell functions and induction of cell apoptosis in affected cells. The nuclear factor-erythroid 2-related factor 2 (Nrf2) pathway plays a key role in the cellular defense system against oxidative and electrophilic stress. Epigallocatechin-3-gallate (EGCG) can activate the Nrf2 pathway and induce expression of a multitude of antioxidants and phase II enzymes that can restore redox homeostasis. Therefore, here, we tested the hypothesis that EGCG-mediated protection against resin monomer cytotoxicity is mediated by activation of the Nrf2 pathway. This study will help to elucidate the mechanism of resin monomer cytotoxicity and provide information that will be helpful in improving the biocompatibility of dental resin materials.

N-acetyl cysteine protects human oral keratinocytes from Bis-GMA-induced apoptosis and cell cycle arrest by inhibiting reactive oxygen species-mediated mitochondrial dysfunction and the PI3K/Akt pathway.

Bisphenol-A-glycidyl methacrylate (Bis-GMA) released from dental resin materials causes various toxic effects on gingival epithelium. Thus the underlying mechanisms of its cytotoxicity should be elucidated for safety use. One potential cause of cell damage is the generation of reactive oxygen species (ROS) beyond the capacity of a balanced redox regulation. In this study, we found that exposure of human oral keratinocytes (HOKs) to Bis-GMA caused apoptosis and G1/S cell cycle arrest in parallel with an increased ROS level. Moreover, Bis-GMA induced a depletion of mitochondrial membrane potential, an increase in the Bax/Bcl-2 ratio, an activation of caspase-3 and altered expressions of cell cycle-related proteins (p21, PCNA, cyclinD1). Furthermore, the co-treatment of the ROS scavenger N-acetyl cysteine (NAC) obviously attenuated Bis-GMA-induced toxicity. Here we also evaluated the effects of Bis-GMA on the ROS-related PI3k/Akt pathway. We found that Bis-GMA inhibited the phosphorylation of Akt, whereas the amount of phosphorylated Akt was reverted to the control level in the presence of NAC. Our findings suggested that the toxic effects of Bis-GMA were related to ROS production and the antioxidant NAC effectively reduced Bis-GMA-mediated cytotoxicity.

Clinical-epidemiological features of contact dermatitis in rural and urban communities in northern Ethiopia: correlation with environmental or occupational exposure.

BACKGROUND: The widespread diffusion of low-quality products as well as the local cultural habits could be a relevant cause of allergic diseases in developing countries. In the present observational study, we explored the prevalence of allergic contact dermatitis in both rural and urban settings in northern Ethiopia, where skin diseases represent a frequent cause of morbidity. Clinical features and specific reactivities in association with environmental or occupational exposure were investigated. PATIENTS AND METHODS: We patch tested 480 consecutive patients, visited at the Mekele IDC, exhibiting symptoms of contact dermatitis. A detailed medical history of each patient was collected. RESULTS: A positive patch-test response was observed in 50% of subjects; nickel was the most frequent sensitizer (26.2%), followed by p-tert-butylphenol formaldehyde resin (10%), fragrance mix (7.1%), potassium dichromate (5.4%), cobalt chloride (4.6%), disperse blue (2.3%), and p-phenylenediamine (1.7%). Gender-related differences were analyzed for single allergen. Eczema represented the most common manifestation, affecting the head and neck as primary skin areas. While reactivity to nickel interested almost all the occupational categories, sensitization to other allergens could be ascribed to working habits or environmental exposure. CONCLUSIONS: The results gathered from this study, the first one conducted within the Tigray region in Ethiopia, confirm the need to take appropriate measures to limit the nickel rate in metal objects and may be useful to design allergenic series suitable for patch testing in those geographical settings.

Antioxidant responses and renal crystal formation in rainbow trout treated with melamine administered individually or in combination with cyanuric acid.

In 2007 and 2008, renal stone formation and kidney damage in human infants were linked to consumption of melamine (MEL)-contaminated infant formula, as well as renal failure and death in pets due to pet food containing both MEL and cyanuric acid (CYA). The aim of this study was to examine the effects of MEL and CYA administered individually or in combination on concentrations of certain metabolites and enzyme activities that serve as markers for oxidative stress in kidney and liver of rainbow trout. In addition, the levels of muscle MEL and renal crystal formation were determined. Trout were fed MEL and/or CYA for 8 wk at 250, 500, or 1000 mg of each compound/kg in feed. Fish muscle residues of MEL exhibited a dose-response relationship. Coexposure of trout to MEL and CYA at the highest dose led to lower MEL residue concentrations in muscle compared to exposure to MEL alone. Renal MEL-CYA complexes were found in kidneys of fish treated with combined MEL and CYA. A dose response was evident with respect to both (1) number of trout displaying renal crystals and (2) number of crystals per fish. Changes in concentration of antioxidant parameters, such as glutathione, superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase, were recorded in both tissues of MEL- and CYA-dosed trout. Lipid peroxidation was more pronounced in kidney than liver. Therefore, feed contaminated with both MEL and CYA could be problematic for fish, as MEL administered to trout, individually or in combination with CYA, may facilitate the onset of oxidative damage in trout.

Effect on morphology, oxidative stress and energy metabolism enzymes in the testes of mice after a 13-week oral administration of melamine and cyanuric acid combination.

Cases of pet poisoning and infant renal calculus have attracted much attention to the toxicity of melamine and its derivatives, such as cyanuric acid. Although individually melamine and cyanuric acid have low toxicity, their simultaneous presence can cause severe damage. Little is known about their adverse effects on the reproductive system. In this study, mice were orally administrated 1, 5 or 25 mg/kg/d of both melamine and cyanuric acid for 13 weeks. Lethargy, rough hair, and reduction of food and water intake and of body and testis weight were found after exposure to the combination, and pathological changes were found in the morphology of the testes, such as disruption of the seminiferous tubule structure, decrease of the spermatogenic cell series and coagulation necrosis. Total antioxidant capacity and superoxide dismutase activities and glutathione concentration was lower and malondialdehyde concentration was higher than in control mice. The activities of malate dehydrogenase, lactate dehydrogenase and Na(+)/K(+)-ATPase were also lower in combination treated mice than in control mice. These results indicate that the combined exposure to both melamine and cyanuric acid damaged testes in mice by either a direct or indirect effect, which may be related to renal failure and secondary anorexia. Oxidative stress and lower energy production levels both contributed to the testicular damage.

Cytotoxicity and alkaline phosphatase activity evaluation of endosequence root repair material.

INTRODUCTION: The purpose of this in vitro study was to evaluate the cytotoxicity and alkaline phosphatase (ALP) activity of a new bioceramic root repair material, EndoSequence Root Repair Material (ESRRM; Brasseler USA, Savannah, GA), and to compare these characteristics with those of ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK) and Geristore (GR; Den-Mat LLC, Santa Maria, CA). METHODS: Human Saos-2 osteoblast-like cells were exposed to 1-, 3-, and 7-day elutes of the materials (100% and 50% strength) for 24 hours after which the bioactivity and ALP activity of the cells were evaluated using a methylthiazol sulfophenyl (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay and para-Nitrophenylphosphate colorimetric assay, respectively. In the positive control group, Triton X-100 (Boehringer Mannheim Corp, Indianapolis, IN) was used to lyse the cells, representing 100% cytotoxicity, and in the negative control group cells received fresh culture medium only. Data were statistically analyzed using the unpaired t test and 1-way analysis of variance. RESULTS: The results revealed that the bioactivity of the cells as well as ALP activity were significantly decreased after exposure to ESRRM elutes in almost all time periods, both in 100% and 50% concentrations, with the exception of ALP activity of day 1 elutes of ESRRM at 50% concentration. MTA did not change the bioactivity or ALP activity of the cells. GR elutes of 100% concentration reduced the bioactivity on days 1 and 3, whereas GR elutes of 50% concentration affected the cells only on day 1. None of the GR elutes had any effect on ALP activity of the cells. CONCLUSIONS: It was concluded that ESRRM elutes of all time periods in general reduced the bioactivity and ALP activity of osteoblast-like cells. GR reduced bioactivity only, whereas MTA had no effect on the cells.

Proteome of melamine urinary bladder stones and implication for stone formation.

Melamine can cause urinary stones related to nephropathy of the kidney and hyperplasia or carcinoma of the bladder, but the mechanism of stone formation is not well understood. In this study, male rats were administered melamine for thirteen weeks to establish melamine bladder stone models and the stones were analysed by Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) and western blot, respectively, for the composition and proteome, and to explore the implication of proteins for stone formation. The results showed bladder stones were composed of predominant melamine and a few amount of proteins. The proteins had a wide range of molecular weights and 1051 proteins were identified. Gene Ontology (GO) classification of the identified proteins showed most proteins were from injured cells, involved in various metabolic processes and had binding functions. Of the identified proteins, there were a few inflammatory proteins and urinary proteins. Physicochemical characteristics of the identified proteins showed that 67.1% proteins' isoelectric points (pI) value was below 7.0, 91.1% proteins' grand average of hydropathicity (GRAVY) scores were below 0 and nearly half of the proteins were stable. Our data indicated proteins might play an important role in melamine bladder stone formation.

Effects of water uptake on melamine renal stone formation in mice.

BACKGROUND: Melamine-tainted food can induce kidney stones both in humans and animals and in domestic animals, severe cases caused acute kidney failure and death. Although increasing water intake can ameliorate kidney stone formation, its effect on melamine (Mel)-induced kidney stones has not been studied. METHODS: We have analysed the effect of restricted ingestion of drinking water on melamine stone formation in mice. They were given melamine and cyanuric acid orally and received drinking water either freely or for a restricted time. Kidney stone formation and renal function were monitored. RESULTS: Mice receiving drinking water for a restricted 10-h period initially lost body weight, which returned to normal within 2 days. No other abnormalities were observed. Ingestion of melamine alone failed to induce kidney stones even under conditions of restricted drinking water. In mice treated with melamine together with cyanuric acid for 3 days, no renal stones were formed when the supply of drinking was normal. However, when drinking water was limited, stone formation was observed and accompanied by high levels of serum urea and creatinine. An increase in urine haemoglobin and glucose levels was also found. The administration resulted in up-regulated tissue osteopontin, kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin messenger RNA expression and macrophage infiltration. CONCLUSIONS: Our results indicate the importance of water intake in the formation of melamine-induced renal stone formation in the mouse and provide new information on the mechanisms of melamine stone formation.

Transplacental transfer of melamine.

OBJECTIVE: To characterize transplacental transfer of melamine and related mechanisms as well as toxicity using human placental perfusion and cultured cells. METHODS: Transfer and toxicity were analyzed in 4-h perfusions with 10 µM or 1 mM melamine, or 10 µM melamine with 10 nM cyanuric acid (CYA). Efflux transporters were studied in accumulation assay and toxicity in BeWo cells by MTT assay. RESULTS: Of added melamine 34-45% was transferred to fetal circulation and CYA made no difference. Histology, hCG production, and PLAP activity indicated functionality of placental tissue with no grave toxicity. Highest concentration of melamine used (2 mM) with CYA and long treatment time decreased viability of BeWo cells. Inhibitors of ABCB1, ABCG2, ABCC2 did not affect the accumulation of melamine in cells. CONCLUSION: Melamine goes through human term placenta with no contribution of efflux transporters. Toxicity of melamine is low in placental tissue and BeWo cells.

In-vitro study of cellular viability and nitric oxide production by J774 macrophages stimulated by interferon gamma with ceramic, polycarbonate, and polyoxymethylene brackets.

INTRODUCTION: Ceramic brackets are chemically inert in the oral cavity, whereas polycarbonate and polyoxymethylene brackets can degrade and release bisphenol-A and formaldehyde, respectively. More reliable tests are needed to assess the potential toxicity of these materials. In addition to traditional cytotoxicity tests, the study of nitric oxide (NO) cellular production stimulated by a specific material has been shown to be a reliable tool for evaluating cytotoxic potential. The purpose of this study was to assess, with esthetic brackets, cellular viability by 3,(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide assay (Sigma, St. Louis, Mo) in the macrophage cell line J774 stimulated with interferon gamma. Interferon gamma is a key cytokine in the activation of macrophages, plays an important role in immunologic processes, and also quantifies NO production by these macrophages. METHODS: Well plates were seeded with 2 x 104 J774 cells per well, in a volume of 100 microL, resuspended in Roswell Park Memorial Institute Supplemented Medium 1640. The macrophage cell line J774 was stimulated with interferon gamma. Ceramic, polycarbonate, and polyoxymethylene brackets were added and kept in the culture for 24, 48, or 72 hours in 5% carbon dioxide at 37 degrees C; the control samples did not include brackets. At the end of each incubation period, the supernatant was collected for posterior NO quantification, and the cells were evaluated for cytotoxicity. RESULTS: Cellular viability in all groups was higher at 72 hours than at 24 hours. The final means in the bracket groups did not show significant differences compared with the control group. NO production was significantly greater in all groups at the final time than at the initial time. However, the brackets with the interferon gamma stimulation did not result in greater NO production than did the cells in the control group.

In-vitro study of the cellular viability and nitric oxide production by J774 macrophages with ceramic, polycarbonate, and polyoxymethylene brackets.

INTRODUCTION: Studies show that ceramic brackets are chemically inert in the oral cavity, whereas polycarbonate and polyoxymethylene brackets can degrade, releasing bisphenol-A and formaldehyde, respectively. In addition to the traditional cytotoxicity tests, the study of nitric oxide cellular production stimulated by a specific material has been shown to be a reliable tool for evaluating its cytotoxic potential. METHODS: We aimed to assess cellular viability by MTT (Sigma, St. Louis, Mo): 3,(4,5-dimethylthiazol-2-yl)-2,5diphenyl tetrazolium bromide assay in a murine macrophage cell line J774 with esthetic brackets and quantify nitric oxide production by these macrophages. Cell cultures were evaluated at 3 times: 24, 48, and 72 hours. RESULTS: Cellular viability in all groups was higher at 72 hours compared with 24 hours. This increase was significant in the control and ceramic brackets groups. Final means in the bracket groups showed no significant differences compared with the control group. Nitric oxide production was significantly greater in all groups at final time. There was no significant difference between the final means of the bracket groups and the control group, although polyoxymethylene brackets showed significantly greater means at 24 and 48 hours. CONCLUSIONS: Final means in the bracket groups showed no significant differences compared with the control group.

Cytotoxicity evaluation of two root canal sealers and a commercial calcium hydroxide paste on THP1 cell line by Trypan Blue assay.

OBJECTIVE: The aim of this investigation was to evaluate the cytotoxicity of two brands of root canal sealers, epoxy-resin based and zinc oxide-eugenol based, and one commercial calcium hydroxide paste on a monocyte cell line THP-1. MATERIAL AND METHODS: Undiluted (crude extract) and diluted extracts to 10%, 1%, 0.1%, 0.01%, 0.001% and 0.0001% of the sealers were tested for cytotoxicity to THP-1 cells using the trypan blue assay. Extracts were obtained according to ISO standard. Data were analyzed statistically by the Kruskal-Wallis and Mann-Whitney tests at 5% significance level. RESULTS: Crude extract of AH Plus and Fill Canal killed approximately 90% of THP-1 cells versus 36% of THP-1 cells killed by L&C crude extract (p<0.05). Ten-fold dilutions of L&C, Fill Canal and AH Plus killed 24, 35 and 61% of THP-1 cells (p<0.05), respectively. Dilutions lesser than 1% caused minimal cell death as compared to the control groups (p>0.05), except for L&C 1% extract. CONCLUSIONS: The results revealed that the L&C paste crude extract was less cytotoxic to THP-1 cells than AH Plus or Fill Canal crude extracts.

Cytotoxicity evaluation of two root canal sealers and a commercial calcium hydroxide paste on THP1 cell line by Trypan Blue assay

OBJECTIVE: The aim of this investigation was to evaluate the cytotoxicity of two brands of root canal sealers, epoxy-resin based and zinc oxide-eugenol based, and one commercial calcium hydroxide paste on a monocyte cell line THP-1. MATERIAL AND METHODS: Undiluted (crude extract) and diluted extracts to 10 percent, 1 percent, 0.1 percent, 0.01 percent, 0.001 percent and 0.0001 percent of the sealers were tested for cytotoxicity to THP-1 cells using the trypan blue assay. Extracts were obtained according to ISO standard. Data were analyzed statistically by the Kruskal-Wallis and Mann-Whitney tests at 5 percent significance level. RESULTS: Crude extract of AH Plus and Fill Canal killed approximately 90 percent of THP-1 cells versus 36 percent of THP-1 cells killed by L&C crude extract (p<0.05). Ten-fold dilutions of L&C, Fill Canal and AH Plus killed 24, 35 and 61 percent of THP-1 cells (p<0.05), respectively. Dilutions lesser than 1 percent caused minimal cell death as compared to the control groups (p>0.05), except for L&C 1 percent extract. CONCLUSIONS: The results revealed that the L&C paste crude extract was less cytotoxic to THP-1 cells than AH Plus or Fill Canal crude extracts.

Re-evaluation of kidney histopathology from 13-week toxicity and two-year carcinogenicity studies of melamine in the F344 rat: morphologic evidence of retrograde nephropathy.

The histopathologic changes induced in F344 rat kidney by oral administration of melamine for 13-week and 2-year periods in studies conducted by the National Toxicology Program, NIH,(25) from 1976 to 1983 have been re-evaluated and described in detail. A constellation of tubule changes extending from papilla to cortex consistently included tubule dilatation and tubule basophilia as salient features at the subchronic time point. By 2 years, these lesions had usually resolved into fibrotic scars, in which tubule loss and collagen deposition were prominent, running from superficial cortex into the medulla. These fibrotic lesions required discrimination from chronic scars resulting from infarcts and foci of chronic progressive nephropathy (CPN). A case is presented here for interpreting the constellation of histologic changes induced in rats by melamine as representing an ascending form of nephropathy. The term retrograde nephropathy is considered to be the appropriate nomenclature for both the acute and chronic lesions. The cause for the reflux, emanating from the lower urinary tract, appeared not to be infection as an inflammatory response was not prominent. It can be speculated that melamine precipitation in the lower urinary tract created pressure effects through transient obstruction leading to the renal changes. These changes were different from those involved in a major US outbreak of renal disease and death in cats and dogs associated with triazine-contaminated pet food, in which crystalluria from insoluble melamine/cyanuric acid complexes occurred in the kidney. However, the rat findings may be relevant to melamine-associated kidney disease recently reported in infants in China.

N-Acetyl cysteine restores viability and function of rat odontoblast-like cells impaired by polymethylmethacrylate dental resin extract.

There is concern that dental-resin materials directly loaded on a prepared tooth adversely affect dental pulp tissue by releasing the resin chemicals through dentinal tubes. This study determined whether self-curing polymethyl methacrylate (PMMA)-based dental resin extract adversely affected the viability and function of odontoblast-like cells and whether the cytotoxicity of this resin, if any, could be eliminated by N-acetyl cysteine, an antioxidant amino acid derivative. Odontoblast-like cells isolated from rat maxillary incisor dental pulp tissue were exposed to a PMMA resin extract with or without N-acetyl cysteine for 1 h and then cultured in osteoblastic media. The percentage of viable cells 24 h after seeding was 20% in cells exposed to the resin extract without N-acetyl cysteine, whereas 45% of cells were viable after exposure to the N-acetyl cysteine-supplemented extract. The cells that had been exposed to the extract showed a strong tendency for apoptosis associated with the increased reactive oxygen species production and decreased intracellular glutathione level, which was improved by the addition of N-acetyl cysteine. N-Acetyl cysteine supplementation almost completely restored the significantly reduced alkaline phosphatase activity and matrix mineralization by the resin extract. These results conclusively demonstrated that exposure of odontoblast-like cells to the resin extract impaired the cell viability and function and, more intriguingly, N-acetyl cysteine supplementation to the extract significantly prevented these toxic effects.