Catalytic oxidation of toluene in contaminant emission control systems using Mn-Ce/gamma-Al2O3.

Toluene, the alkyl benzene, is a common constituent of contaminant streams emitted by hydrocarbon fuel combustion systems. The oxidation of toluene to less toxic compounds can be enhanced through catalysis. The capacity of Mn-Ce/gamma-Al2O3 to catalyze toluene oxidation was investigated using a fixed bed flow reactor, operating within a temperature range of 160-400 degrees C. Mono-metallic catalysts were prepared with the manganese and cerium contents of 1-21 wt% on gamma-Al2O3, support and bi-metallic catalysts were prepared with cerium (0.5-21 wt%/) on 18.2 wt% manganese. The results indicate that the 18.2 wt% Mn-10.0 wt% Ce catalyst combination had the best catalytic efficiency for toluene oxidation. Increase in cerium loading reduces the surface area of catalytic materials measured by BET, but increases catalytic activity. Data obtained through TGA (Thermogravimetric analysis), XRD (X-ray diffraction) and toluene-TPR (Temperature Programmed Reduction) measurements show that the reduction of the catalysts in the process of toluene oxidation is directly proportional to observed weight loss under hydrogen flow. From these results, it is concluded that cerium improves the catalytic role of manganese in toluene oxidation. Oxygen mobility is also promoted in a redox mechanism in which MnO2 serves as the active sites. These results are useful in the development of toluene emission control systems for hydrocarbon fuel combustion systems.

p-Coumaric acid, a constituent of Sasa quelpaertensis Nakai, inhibits cellular melanogenesis stimulated by alpha-melanocyte stimulating hormone.

BACKGROUND: Recent study has demonstrated that Sasa quelpaertensis (Korean name, Jeju-Joritdae) extracts inhibit cellular melanogenesis implicating potential use in the control of skin pigmentation. OBJECTIVES: The purpose of the present study was to elucidate the active constituents of this plant inhibiting melanogenesis and the associated mechanism. METHODS: The effect of the plant-derived materials on melanin production and/or tyrosinase expression was examined in murine melanoma B16/F10 cells and neonatal human melanocytes. RESULTS: When tested in melanoma B16/F10 cells treated with the alpha-melanocyte stimulating hormone (alpha-MSH), the aqueous ethanol extract of S. quelpaertensis culm inhibited the cellular melanogenesis more effectively than its leaf extract. A major active compound was isolated from the culm extract by solvent fractionation and column chromatography, and identified to be p-coumaric acid by spectroscopic and chromatographic analyses. The compound (p-coumaric acid) inhibited alpha-MSH-stimulated cellular melanogenesis more effectively than arbutin or other structurally similar compounds including 3-(4-hydroxyphenyl) propionic acid, cinnamic acid and caffeic acid. It also attenuated alpha-MSH-dependent increase of tyrosinase protein. The antimelanogenic effect of p-coumaric acid was also verified in neonatal human melanocytes. CONCLUSIONS: The present study identified p-coumaric acid as a main constituent of S. quelpaertensis inhibiting cellular melanogenesis. Because of its structural similarity, p-coumaric acid may interfere with l-tyrosine action in the control of tyrosinase expression in response to alpha-MSH.

A buccal cell model comet assay: development and evaluation for human biomonitoring and nutritional studies.

The comet assay is a widely used biomonitoring tool for DNA damage. The most commonly used cells in human studies are lymphocytes. There is an urgent need to find an alternative target human cell that can be collected from normal subjects with minimal invasion. There are some reports of buccal cells, collected easily from the inside of the mouth, being used in studies of DNA damage and repair, and these were of interest. However, our preliminary studies following the published protocol showed that buccal cells sustained massive damage and disintegrated at the high pH [O. Ostling, K.J. Johanson. Microelectrophoretic study of radiation-induced DNA damages in individual mammalian cells. Biochem. Biophys. Res. Commun. 123 (1984) 291-298] used, but that at lower pH were extremely resistant to lysis, an essential step in the comet assay. Therefore, the aims of this study were to develop a protocol than enabled buccal cell lysis and DNA damage testing in the comet assay, and to use the model to evaluate the potential use of the buccal cell model in human biomonitoring and nutritional study. Specifically, we aimed to investigate intra- and inter-individual differences in buccal cell DNA damage (as strand breaks), the effect of in vitro exposure to both a standard oxidant challenge and antioxidant treatment, as well as in situ exposure to an antioxidant-rich beverage and supplementation-related effects using a carotenoid-rich food. Successful lysis was achieved using 0.25% trypsin for 30 min followed by proteinase K (1mg/ml) treatment for 60 min. When this procedure was performed on cells pre-embedded in agarose on a microscope slide, followed by electrophoresis (in 0.01 M NaOH, 1mM EDTA, pH 9.1, 18 min at 12 V), a satisfactory comet image was obtained, though inter-individual variation was quite wide. Pre-lysis exposure of cells to a standard oxidant challenge (induced by H2O2) increased DNA strand breaks in a dose related manner, and incubation of cells in Trolox (a water soluble Vitamin E analogue) conferred significant protection (P<0.05) against subsequent oxidant challenge. Exposure of buccal cell in situ (i.e. in the mouth) to antioxidant-rich green tea led to an acute decrease in basal DNA strand breaks. In a controlled human intervention trial, buccal cells from 14 subjects after 28 days' supplementation with a carotenoid-rich berry (Fructus barbarum L.) showed a small but statistically significant (P<0.05) decrease in DNA strand breaks. These data indicate that this buccal cell comet assay is a feasible and potentially useful alternative tool to the usual lymphocyte model in human biomonitoring and nutritional work.

Vitamins C and E: acute interactive effects on biomarkers of antioxidant defence and oxidative stress.

Oxidative stress is implicated in the aetiology of many diseases; however, most supplementation trials with antioxidant micronutrients have not shown expected beneficial effects. This randomized, double-blinded, placebo-controlled study evaluated acute effects (at 90, 180min and 24h [fasting] post-ingestion) of single doses of Vitamins C (500mg) and E (400IU), alone and in combination, on biomarkers of plasma antioxidant status, lipid peroxidation and lymphocyte DNA damage in 12 healthy, consenting volunteers. Plasma ascorbic acid increased significantly (P < 0.01) within 2h of ingestion of Vitamin C, and alpha-tocopherol was significantly (P < 0.01) higher at 24h post-ingestion Vitamin E. The pattern of response was not significantly different whether Vitamin C (or Vitamin E) was taken alone or in combination, indicating no augmentation of response to one by co-ingestion of the other vitamin. No significant changes were seen in plasma FRAP in the group overall (although increases (P < 0.05) were seen at 90 and 180min post-ingestion in women after Vitamin C ingestion) or in MDA across treatments, and no evidence of increased DNA damage, or of DNA protection, was seen at any time point after Vitamin C and/or E ingestion. In conclusion, the data from this first controlled study of acute effects of single doses of Vitamin C and/or E show no evidence of either a protective or deleterious effect on DNA damage, resistance of DNA to oxidant challenge, or lipid peroxidation. No evidence of a synergistic or cooperative interaction between Vitamins C and E was seen, but further study is needed to determine possible interactive effects in a staggered supplementation cycle, and study of subjects under increased oxidative stress or with marginal antioxidant status would be useful. It would be of interest also to study the effects of these vitamins ingested with, or in, whole food, to determine if they are directly protective at doses above the minimum required to prevent deficiency, if combinations with other food components are needed for effective protection, or if Vitamins C and E are largely surrogate biomarkers of a 'healthy' diet, but are not the key protective agents.

Bone-protecting effect of safflower seeds in ovariectomized rats.

Safflower (Carthamus tinctorius L.) seeds have long been clinically used in Korea to promote bone formation and prevent osteoporosis. However, the beneficial effect has not been scientifically evaluated. Thus, in the present study we investigated whether phytoestrogen rich safflower seeds reduce bone loss in ovariectomized rats. Female Sprague-Dawley rats were subjected to bilateral ovariectomy or sham surgery. One week after the operation, ovariectomized rats were either fed a diet containing defatted safflower seeds or injected with 17b-estradiol (E2) for 4 weeks. As expected, ovariectomy resulted in a dramatic reduction in trabecular bone mass of the proximal tibia, increase in deposition of marrow fat, and in uterine atrophy. E2 treatment almost completely prevented bone loss as well as marrow adiposity, as examined by scanning electron microscopy and histomorphometry. Safflower seeds partially prevented ovariectomy-induced bone loss and slightly reduced marrow adiposity. Safflower seeds, in contrast to E2, exerted very weak uterotrophic action. In an attempt to elucidate the underlying mechanisms, effect of polyphenolic compounds extracted from safflower seeds on proliferation of osteoblast-like cells was also assessed in vitro. The mixed polyphenolic compounds stimulated growth of ROS 17/2.8 osteoblast-like cells in a dose-dependent manner (5-100 mg/ml), as potently as E2 and genistein. The present data provide the first direct in vivo evidence that safflower seeds have a protecting effect on bone loss caused by estrogen deficiency, without substantial effect on the uterus. The beneficial effect of safflower seeds may be mediated, at least in part, by the stimulating effect of polyphenolic compounds on proliferation of osteoblasts.

The wound-healing effect of a glycoprotein fraction isolated from aloe vera.

BACKGROUND: Aloe vera has been used as a family medicine for promoting wound healing, but it is not known which component of the plant is effective for this purpose. OBJECTIVES: To isolate and characterize the component effective in wound healing. METHODS: Chromatography, electrophoresis and spectroscopic methods were used. The cell-proliferation activity of each component isolated was measured by a [3H]thymidine uptake assay. The cell-proliferation activity of the effective component was tested on a three-dimensional raft culture (cell culture technique by which artificial epidermis is made from keratinocytes). The effect of the active component on cell migration and wound healing was observed on a monolayer of human keratinocytes and in hairless mice. RESULTS: A glycoprotein fraction was isolated and named G1G1M1DI2. It showed a single band on sodium dodecyl sulphate-polyacrylamide gel electrophoresis, with an apparent molecular weight of about 5.5 kDa. It exhibited significant [3H]thymidine uptake in squamous cell carcinoma cells. The effect of G1G1M1DI2 on cell migration was confirmed by accelerated wound healing on a monolayer of human keratinocytes. When this fraction was tested on a raft culture, it stimulated the formation of epidermal tissue. Furthermore, proliferation markers (epidermal growth factor receptor, fibronectin receptor, fibronectin, keratin 5/14 and keratin 1/10) were markedly expressed at the immunohistochemical level. The glycoprotein fraction enhanced wound healing in hairless mice by day 8 after injury, with significant cell proliferation. CONCLUSIONS: It is considered that this glycoprotein fraction is involved in the wound-healing effect of aloe vera via cell proliferation and migration.

Effects of dietary folate on DNA strand breaks within mutation-prone exons of the p53 gene in rat colon.

BACKGROUND & AIMS: Diminished folate status has been observed to increase colorectal cancer risk. Folate plays an important role in DNA synthesis and repair. This study investigated the effects of dietary folate on DNA strand breaks in the p53 and Apc genes, and how these changes are related to steady-state levels of the corresponding transcripts. METHODS: Three groups of rats were fed diets containing 0, 2 (basal requirement), or 8 mg folate/kg for 5 weeks. At each weekly time point, plasma and colonic mucosal folate concentrations were determined. Site-specific DNA strand breaks were assessed by semiquantitative PCR. Steady-state levels of messenger RNA were measured by semiquantitative RT-PCR. RESULTS: Dietary folate deficiency produced progressive DNA strand breaks within exons 5-8 of the p53 gene in rat colon (P<0.02). Accumulation of strand breaks was not observed in other exons of the p53 gene, in the Apc and beta-actin genes, or at the genomic level. Folate supplementation at 4 times the basal requirement significantly increased p53 integrity compared with the basal and deficient diets (P<0.05). p53 integrity in exons 5-8 was significantly correlated with folate status (P<0.03). Dietary folate deprivation progressively decreased, whereas supplementation increased, steady-state levels of p53 transcript over 5 weeks (P<0.05). No such changes were observed for the Apc gene. Steady-state levels of p53 transcript were significantly correlated with folate status and p53 integrity in exons 5-8 (P<0.002). CONCLUSIONS: These data provide a plausible mechanism by which folate deficiency promotes, and folate supplementation suppresses, colorectal carcinogenesis.

Effect of chronic alcohol consumption on total plasma homocysteine level in rats.

BACKGROUND: Chronic alcoholism in humans is associated with the development of hyperhomocysteinemia, the mechanism of which remains unclear. Among the causes of hyperhomocysteinemia is depletion of folate, vitamin B12, or vitamin B6. Population-based studies indicate that folate is the strongest vitamin determinant of hyperhomocysteinemia and, in most settings, folate supplementation effectively lowers elevated homocysteine levels. However, it is not clear whether folate deficiency is the cause of alcohol-related hyperhomocysteinemia. METHODS: In the present study, 10 male Sprague Dawley rats were fed ethanol-containing Lieber-DeCarli diets with 13 mg of folic acid per kilogram of diet. This represents a folate intake more than 20 times the basal requirement. Ethanol represented 36% of total energy, which yielded a concentration of 6.2% (vol/vol). The same number of rats were pair-fed with isocaloric control diets that contained an identical level of folate in which ethanol was entirely replaced by maltodextrin. RESULTS: At the end of 4 weeks, alcohol-fed rats did not show any significant reduction in plasma or hepatic folate concentrations, plasma pyridoxal-5'-phosphate concentration, or plasma vitamin B12 concentration. On the other hand, alcohol-fed rats were significantly hyperhomocysteinemic (17.24 +/- 4.63 micromol/liter,p < 0.01) compared to the nonalcohol group (10.73 +/- 2.76 micromol/liter). Alcohol-fed rats also had a significantly lower hepatic S-adenosylmethionine and higher hepatic S-adenosylhomocysteine levels. CONCLUSIONS: Chronic alcohol consumption produces hyperhomocysteinemia by a mechanism that is related to interference with one-carbon metabolism, and not through vitamin depletion.

Folate and carcinogenesis: an integrated scheme.

Collectively, the evidence from epidemiologic, animal and human studies strongly suggests that folate status modulates the risk of developing cancers in selected tissues, the most notable of which is the colorectum. Folate depletion appears to enhance carcinogenesis whereas folate supplementation above what is presently considered to be the basal requirement appears to convey a protective effect. The means by which this modulation of cancer risk is mediated is not known with certainty, but there are several plausible mechanisms which have been described. Folate plays a major role in the formation of S-adenosylmethionine, the universal methyl donor, as well as in the formation of purine and thymidine synthesis for DNA and RNA. Therefore, most mechanistic studies performed to date have focused on alterations in DNA methylation, disruption of DNA integrity and disruption of DNA repair, all of which have been observed with folate depletion. These aberrations in DNA are believed to enhance carcinogenesis by altering the expression of critical tumor suppressor genes and proto-oncogenes. Recently, the role of a common polymorphism of the methylenetetrahydrofolate reductase gene has been highlighted as well. This review presents those mechanisms which are the most likely candidates to explain folate's effects and it proposes an integrated scheme to explain how these mechanisms might interact.

The effect of dietary folate on Apc and p53 mutations in the dimethylhydrazine rat model of colorectal cancer.

Dietary inadequacy of folate enhances and folate supplementation suppresses colorectal carcinogenesis in the dimethylhydrazine rat model. Folate is an essential factor for DNA methylation and the de novo biosynthesis of nucleotides, aberrations of which play important roles in mutagenesis. This study investigated whether the mutational hot spots of the Apc and p53 genes for human colorectal cancer are mutated in dimethylhydrazine-induced colorectal neoplasms and whether dietary folate can modulate mutations in these regions. Rats were fed diets containing 0, 2 (basal requirement), 8 or 40 mg folate/kg diet. Five weeks after diet initiation, dimethylhydrazine was injected weekly for 15 weeks. Mutations were determined by direct sequencing in 11 low and seven high grade dysplasias and 13 invasive adenocarcinomas. A total of six Apc mutations were found in four dysplastic and carcinomatous lesions: two in two low grade dysplasias, two in one high grade dysplasia and two in one adenocarcinoma. All mutations were single base substitutions, four of which were A:T-->G:C transitions. Five of the six mutations were located upstream from the region corresponding to the human APC mutation cluster region. Dietary folate had no effect on the frequency and type of Apc mutations. No mutations were detected in exons 5-9 of the p53 gene in neoplastic lesions. These data suggest that in the dimethylhydrazine rat model of colorectal cancer, the Apc gene is mutated in early stages, albeit to a lesser degree than observed in human colorectal cancer, whereas the mutational hot spot of the p53 gene for human colorectal cancer is not commonly mutated. Although the low frequency of Apc mutations and the small number of neoplasms studied in this study might have precluded our ability to observe modulatory effects of folate, dietary folate appears to have no significant effect on Apc and p53 mutations.

Dietary folate protects against the development of macroscopic colonic neoplasia in a dose responsive manner in rats.

BACKGROUND AND AIMS: Diminished folate status is associated with enhanced colorectal carcinogenesis. This study investigated the potential chemopreventive role of dietary folate in the dimethylhydrazine colorectal cancer model. SUBJECTS AND METHODS: Sprague-Dawley rats were fed diets containing either 0, 2 (daily dietary requirement), 8 or 40 mg folate/kg diet for 20 weeks. After five weeks of diet, rats were injected with dimethyl-hydrazine (44 mg/kg) weekly for 15 weeks. Fifteen weeks after the first injection of dimethylhydrazine, all rats were killed. Folate status was determined, and the entire colorectum from each rat was analysed for macroscopic and microscopic neoplasms. RESULTS: Plasma and colonic folate concentrations correlated directly with dietary folate levels (p < 0.005). The incidence of microscopic neoplasms was similar among the four groups. However, the incidence and the average number of macroscopic tumours per rat decreased progressively with increasing dietary folate levels up to 8 mg/kg diet (p < 0.05). In the strongly procarcinogenic milieu used in this study, folate supplementation at 20 times the basal requirement was associated with rates of macroscopic tumour development that were intermediate, and not statistically distinct, from rates observed at either 0 or 8 mg/kg diet. CONCLUSIONS: These data indicate that in this rat model, (a) increasing dietary folate up to four times the basal requirement leads to a progressive reduction in the evolution of macroscopic neoplasms from microscopic foci; and (b) folate supplementation beyond four times the requirement does not convey further benefit.