Ethnic differences in serum adipokine and C-reactive protein levels: the multiethnic cohort.

BACKGROUND: Ethnic disparities in metabolic disease risk may be the result of differences in circulating adipokines and inflammatory markers related to ethnic variations in obesity and body fat distribution. SUBJECTS/METHODS: In a cross-sectional design, we compared serum levels of leptin, adiponectin, C-reactive protein (CRP), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in control subjects (321 men and 930 women) from two nested case-control studies conducted within the Multiethnic Cohort Study consisting of whites, Japanese Americans (JA), Latinos, African Americans (AA) and Native Hawaiians (NH). General linear models were applied to evaluate ethnic differences in log-transformed serum biomarker levels before and after adjusting for body mass index (BMI) at cohort entry. RESULTS: In comparison to whites, significant ethnic differences were observed for all biomarkers except TNF-α. JA men and women had significantly lower leptin and CRP levels than whites, and JA women also had lower adiponectin levels. Leptin was significantly higher in AA women (P < 0.01), adiponectin was significantly lower in AA men and women (P = 0.02 and P < 0.001), and CRP and IL-6 were significantly higher in AA men and women. Lower adiponectin (P < 0.0001) and CRP (P = 0.03) levels were the only biomarkers in NH women that differed from whites; no statistically significant differences were seen for NH men and for Latino men and women. When adjusted for BMI at cohort entry, the differences between the lowest and the highest values across ethnic groups decreased for all biomarkers except adiponectin in men indicating that ethnic differences were partially due to weight status. CONCLUSIONS: These findings demonstrate the ethnic variations in circulating adipokine and CRP levels before and after adjustment for BMI. Given the limitation of BMI as a general measure of obesity, further investigation with visceral and subcutaneous adiposity measures are warranted to elucidate ethnicity-related differences in adiposity in relation to disparities in obesity-related disease risk.

Dietary fat and prostate cancer: current status.

Efforts to elucidate the causes of prostate cancer have met with little success to date. All that is known with certainty is that the incidence increases exponentially with age, varies by geography and by race or ethnicity, and is higher among men whose father or brother had the disease. Because the incidence changes in migrants and their offspring, exogenous factors certainly contribute to the risk of prostate cancer. Early epidemiologic studies implicated dietary fat as a likely causal factor for this cancer. However, scientific support for such an association has diminished in recent years as more epidemiologic evidence has accrued. Accordingly, we reviewed the relevant English language literature on this topic, including epidemiologic and animal studies, as well as current concepts regarding the involvement of fat in carcinogenesis to re-examine the fat-prostate cancer hypothesis. We conclude that dietary fat may indeed be related to prostate cancer risk, although the specific fat components that are responsible are not yet clear. Given the diverse effects of fatty acids on cellular biology and chemistry, it seems likely that the relationship is complex, involving the interplay of fat with other dietary factors, such as antioxidant vitamins and minerals, or with genetic factors that influence susceptibility. Some suggestions for further research are offered.

Carotenoids up-regulate connexin43 gene expression independent of their provitamin A or antioxidant properties.

Epidemiological evidence and studies in whole animals and cell culture have indicated that carotenoids have cancer chemopreventive action. In mouse C3H10T1/2 cells, this activity is highly correlated with the ability of carotenoids to up-regulate gap junctional intercellular communication. Here, we report that in mouse cells, carotenoids increase the expression of connexin43, a gene that encodes a major gap junction protein. This effect appears unrelated to their provitamin A or antioxidant properties, since carotenoids with and without provitamin A activity increased levels of connexin43 mRNA and protein, whereas the antioxidants methyl-bixin and alpha-tocopherol were inactive. Moreover, the active carotenoid canthaxanthin did not induce the vitamin A-inducible gene retinoic acid receptor-beta. Connexin43 is the first carotenoid-inducible gene described in mammals. By indicating an additional pathway through which carotenoids function, these data provide a mechanistic basis for cancer chemoprevention by carotenoids and may lead to a re-evaluation of carotenoid physiology.

Lifestyle and nutritional correlates of cytochrome CYP1A2 activity: inverse associations with plasma lutein and alpha-tocopherol.

Cytochrome CYP1A2, a liver enzyme responsible for the metabolic activation of a number of putative human carcinogens, exhibits wide inter-individual differences in activity. In order to characterize sources of variability in CYP1A2 activity, we phenotyped (with the caffeine test) 90 subjects of various ethnic backgrounds in Hawaii. Forty-three subjects were patients with in-situ colorectal cancer treated by polypectomy and 47 were healthy population controls. Subjects were also administered a detailed lifestyle questionnaire, including a quantitative food frequency questionnaire, and were assessed for plasma levels of carotenoids, tocopherols, retinol, ascorbic acid, cholesterol and triglycerides. In a stepwise multiple regression, 27% of the overall variation in CYP1A2 activity was explained by seven variables. Plasma lutein explained the largest portion of the variance (7%) and was negatively associated with CYP1A2 activity (p < 0.01), as were use of menopausal replacement estrogens (p = 0.04), plasma alpha-tocopherol (p = 0.05) and alcohol consumption (p = < 0.01). Acetaminophen use (p = 0.05), coffee consumption (p = 0.05) and plasma lycopene (p = 0.06) were positively associated with CYP1A2 activity. After adjustment for these variables, no association was found between CYP1A2 activity and sex, race, age, education, smoking, physical activity, weight, vitamin E supplements, the other plasma micronutrients measured, and dietary intakes of red meat, processed meat and cruciferous vegetables. Results were similar for colorectal cancer cases and controls. Almost two-thirds (73%) of the variability in CYP1A2 activity remained unexplained. This study confirms an enhancing effect of acetaminophen and coffee on CYP1A2 activity and suggests and inhibitory effect of estrogens, alcohol and food sources of lutein and alpha-tocopherol on this enzyme.

Products of gamma-tocopherol reaction with NO2 and their formation in rat insulinoma (RINm5F) cells.

gamma-Tocopherol, commonly found in seed oils, is the major tocopherol in the U.S. diet, is superior to alpha-tocopherol in preventing neoplastic transformation, and demonstrates unique reactivity toward NO2. This article describes the products of reaction between gamma-tocopherol and low concentrations of gaseous nitrogen dioxide (NO2), as well as their endogenous formation in NO-producing RINm5F cells. gamma-Tocopherol in hexane reacts with NO2 to yield two products identified as 2,7,8-trimethyl-2(4,8,12-trimethyltridecyl)-5,6-chromaquinone++ +, "tocored," and 2,7,8 trimethyl-2(4,8,12-trimethyltridecyl) 5-nitro, 6-chromanol, "tocoyellow." Physical data for these two compounds and reaction characteristics are described. The formation of tocored is consistent with a proposed mechanism of gamma-tocopherol-mediated reduction of NO2 to NO involving initial reaction by NO2 at the C-5 position to form an intermediate nitrite ester tocopheryl radical, which then reacts internally to release NO and form 5,6 epoxy gamma-tocopherol. Tautomerization and further oxidation of the latter intermediate by NO2 yields tocored as the main product observed. The reaction of gamma-tocopherol with NO2 to form NO occurs independently of light, whereas alpha-tocopherol requires light to generate NO from NO2. gamma-Tocopherol and aminoguanidine, an NO synthase inhibitor, were superior to alpha-tocopherol in preventing RINm5F cell toxicity induced by Interleukin-1 beta (IL-1 beta). Both tocored and tocoyellow were observed to form in RINm5F cells loaded with gamma-tocopherol and producing NO constitutively, although a consistent increase in these products as a result of induced NO synthesis was not observed.

Association of tocopherols with circulating autoantibody levels against an oxidized DNA nucleoside in humans.

Autoantibodies against oxidized DNA bases are found in vivo and have been used as an indicator of oxidative damage, yet little is known concerning their individual variation and relation to serum micronutrients. Human plasma anti-5-hydroxymethyl-2'-deoxyuridine (HMdU) autoantibody (aAb) levels were repeatedly determined in 41 women and 11 men, and found to have small within-individual variation over time, but large between-individual differences. A positive association in both women (r = .5762, p = .0001) and men (r = .415, p = .2) between plasma total tocopherols and antibody levels was observed. Autoantibody levels were lower in postmenopausal women (8.37 +/- 1.61 vs. 17.18 +/- 2.85 in premenopausal women, p < .01), independently of plasma tocopherol. However, aAb titers in postmenopausal women were still significantly associated with plasma tocopherol levels and adjustment for menopausal status in women yielded a highly significant correlation between HMdU aAb levels and total tocopherol (r = .7342, p = .0001). Plasma malondialdehyde equivalents (MDA), a measure of lipid peroxidation, were also higher in individuals with either high plasma alpha-tocopherol or high beta+gamma-tocopherol levels. The positive association of tocopherols with markers of oxidative damage may reflect a response to the generation of endogenous oxidants associated with enhanced immune function. The decrease in aAb level in postmenopausal women may similarly reflect decreased immune function associated with decreased estrogen levels.

Use of breath hydrogen and methane as markers of colonic fermentation in epidemiological studies: variability in excretion.

Breath hydrogen and methane are specific end products of colonic fermentation, a process which may play a protective role against colon cancer. To assess the possibility of using these markers in epidemiological studies, we characterized the intra- and intersubject variability of breath hydrogen and methane excretion over 15 consecutive days among 32 men and women of various ethnic backgrounds (16 Asians, 8 Caucasians, 8 Hawaiians). Participants were asked to collect four end-expiratory samples each day, which we had shown previously would optimally characterize daily hydrogen excretion. There was substantial within-subject variation in breath hydrogen over the study, although breath methane levels were more constant over time. We found that about 4 days of measurement of breath hydrogen and 1 day of measurement for breath methane are required to correctly characterize individuals according to their long-term excretion of these gases. This was true for Asians and non-Asians. Although breath methane appears to be more practical to measure, it is a less sensitive marker of colonic fermentation than breath hydrogen. Whereas all subjects excreted hydrogen, only 28% of the subjects excreted methane, and methane excretor status of a few participants varied during the study. Because the breath test is noninvasive and reliable, we tested the multiple day collection protocol among colon cancer patients and controls and found it to be well accepted. We conclude that it is practical to measure breath hydrogen and methane in large epidemiological studies conducted at the individual level. The potential use for these markers is discussed.

Exploring the feasibility and effects of a high-fruit and -vegetable diet in healthy women.

Based on reports that fruits and vegetables may protect against breast cancer, this randomized intervention study tested the feasibility of increasing fruit and vegetable intake among healthy women to 9 daily servings through individual dietary counseling and group activities. Adherence to the dietary recommendations was monitored by 24-h food recalls, log sheets, and plasma carotenoid assessments. To explore possible cancer protective mechanisms of fruits and vegetables, we investigated the treatment effect on plasma phenol levels and on thiobarbituric acid-reactive substances measured as malondialdehyde equivalents, a possible marker of oxidative damage. At baseline, women in the intervention (n = 13) and control (n = 16) group reported an average daily consumption of 3.3 and 3.2 fruit and vegetable servings, respectively. After 3 and 6 months of intervention, intake in the intervention group had increased to 8.3 and 7.4 servings, whereas the control group reported an average of 4.2 and 4.1 daily servings. An increase of plasma carotenoid levels from 1249 microg/liter at baseline to 1854 and 1827 microg/liter after 3 and 6 months confirmed compliance with the dietary recommendations in the intervention group. Plasma carotenoid levels among controls changed slightly from 1165 to 1231 and 1291 microg/liter Whereas total phenol levels did not respond according to our hypothesis, malondialdehyde levels decreased slightly in the intervention group. These results suggest that motivated women can substantially increase their fruit and vegetable intake, which leads to a notable increase in plasma carotenoid levels.

A pilot study on the use of plasma carotenoids and ascorbic acid as markers of compliance to a high fruit and vegetable dietary intervention.

The authors examined the feasibility of using plasma carotenoids and ascorbic acid as markers of compliance for dietary intervention trials aimed at increasing the quantity and variety of the fruit and vegetable intake of free-living individuals. Nineteen former cancer patients who had been successfully treated for a stage I or II squamous cell carcinoma of the mouth, pharynx, larynx, or lung were recruited. Subjects served as their own controls. However, in order to detect any seasonal trends, 4 individuals among the 19 were randomized to a nonintervention group. Subjects in the intervention group were counseled by dietitians with the goal of increasing their intake of fruits and vegetables to eight servings/day (1 serving each of dark green vegetables, yellow-orange vegetables, tomato products, and other vegetables; 3 servings of vitamin C-rich fruits; and 1 serving of other fruits). Subjects in the nonintervention group were advised to follow their usual diet. Three-day measured food records kept at base line and after 3 months of intervention, as well as unannounced 24-h dietary recalls, documented an increase in mean fruit and vegetable intake from 4.2 to 9.5 servings daily in the intervention group. A concomitant increase of 29% was observed in total plasma carotenoids (P = 0.02), with increases of 25% for plasma lycopene (P = 0.06), 31% for plasma lutein (P = 0.002), 39% for plasma beta-carotene (P = 0.01), and 57% for plasma alpha-carotene (P = 0.01). Mean plasma levels of ascorbic acid increased by 27% (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal variations in plasma micronutrients and antioxidants.

Plasma samples were collected at monthly intervals for a period of 1 year from a group of healthy nonsmoking men and women (n = 21) living in Honolulu, HI. Analysis of plasma cholesterol and triglyceride levels showed marked seasonal variations, with higher mean levels in winter months and lower values in the summer. Cholesterol and triglycerides were highly and inversely correlated with plasma levels of the provitamin A carotenoids. Mean beta- and alpha-carotene levels were highest in late summer and fall. Plasma retinol levels were significantly lower in the summer and higher in the winter. Variations (either between individuals or seasonally) in plasma retinol were unrelated to plasma provitamin A carotenoid levels. Plasma levels of alpha-tocopherol, gamma-tocopherol, beta-cryptoxanthin, and lutein were also higher in the winter and lower in the summer. Significant seasonal correlations, both positive and negative, with environmental variables, such as temperature, solar UV radiation, and rainfall, are noted for many of these plasma micronutrients. The number of samples required to accurately characterize long-term plasma levels for an individual generally ranged from 1 to 4. However, plasma retinol levels exhibited the highest ratio of intra- to interindividual variability, suggesting the need for multiple sampling (> 8 samples) for this micronutrient. Some of this variability for retinol was associated with seasonal changes. Assessment by a diet history of food and supplement intake of micronutrients and phytochemicals for 1 year showed good agreement with 1-year mean plasma levels for most carotenoids, vitamin C, and alpha-tocopherol. Retinol, gamma-tocopherol, cholesterol, and triglyceride levels in plasma were unrelated to estimates of dietary intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlations between mutagen sensitivity and plasma nutrient levels of healthy individuals.

Increased mutagen sensitivity and decreased intake of antioxidant-rich fruits and vegetables have been associated with an increased risk of upper aerodigestive tract cancers. The objective of this study was to investigate the intraindividual variation in mutagen sensitivity and its possible correlation with plasma nutrient levels in a group of 25 healthy individuals in Hawaii. Mutagen sensitivity, as assessed by bleomycin-induced chromosomal breaks in cultured peripheral blood lymphocytes and plasma nutrient levels were measured monthly for 11 months. The monthly numbers of chromosomal breaks/cell ranged from 0.04 to 0.80 and showed considerable intraindividual variation. Based on individual means, significant inverse correlations were found between mutagen sensitivity scores and the plasma levels of alpha-carotene (r = -0.64), total carotenoids (r = -0.41), and ascorbic acid (r = -0.40). There were also significant inverse associations between monthly mean plasma levels of alpha-carotene (r = -0.58), beta-carotene (r = -0.76) and total carotenoids (r = -0.72) and monthly mean chromosomal breaks. In contrast, there was a significant positive correlation between monthly mean plasma triglyceride level (r = 0.60) and monthly mean mutagen sensitivity. These results suggest that mutagen sensitivity as assessed by the bleomycin assay may be influenced by plasma levels of certain nutrients and could potentially be modified by dietary interventions or micronutrient supplementation.

Predictors of N-acetyltransferase activity: should caffeine phenotyping and NAT2 genotyping be used interchangeably in epidemiological studies?

To determine whether NAT2 genotyping could be used interchangeably with caffeine phenotyping in assessing N-acetyltransferase activity in epidemiological studies, sources of interindividual variability in N-acetyltransferase activity were assessed among 90 subjects of various ethnic backgrounds in Hawaii. Forty-three subjects were patients with in situ colorectal cancer treated by polypectomy, and 47 were healthy population controls. Subjects were administered a lifestyle questionnaire and were evaluated for N-acetyltransferase activity by caffeine phenotyping. NAT2 genotype was also assessed by PCR amplification of peripheral leukocyte DNA for the M1, M2, and M3 variant alleles. Fifty-four % of the overall variation in acetylation activity was explained by the three genotype categories (homozygous variant, heterozygous, and homozygous wild-type). This proportion was reduced to 42% when genotype was modeled using only two categories ("slow" being homozygous variant; "rapid" being all others). Use of gout medications (probenecid or allopurinol), consumption of heavily browned fish, and P450IA2 activity (also measured by caffeine phenotyping), together explained another 11% of the variance. No association was found between acetylation activity and sex; race; age; education; smoking; physical activity; weight; consumption of coffee, alcohol, red meat, processed meat, and cruciferous vegetables; or use of menopausal estrogens, after taking genotype into account. Results were similar for colorectal cancer patients and controls. Considerable variation in acetylation activity was observed within the homozygous wild-type group. This study suggests that the use of genotyping, instead of phenotyping, to assess the association of acetylation with cancer risk is unlikely to introduce major misclassification or bias, especially when the three genotype categories are modeled and the sample size is large. However, when the rapid acetylation phenotype is the at-risk group (e.g., when studying colon career), phenotyping appears judicious given the variability in acetylation activity within this group.

Amine nitrosation by sodium nitroprusside.

Nitrosamine formation from the reaction of nitroprusside with morpholine was found to be a light-dependent reaction. Maximum nitrosation occurred when the reactants were exposed to UV light (lambda = 275-300 nm). However, considerable nitrosation also occurred with light in the visible spectrum up to 500 nm. No significant nitrosamine formation was observed when the reactants were kept in the dark. Data concerning the effects of other physical and chemical factors such as pH, temperature and reactant concentration on the reaction between morpholine and sodium nitroprusside are also presented.

N-nitrosation and N-nitration of morpholine by nitrogen dioxide: inhibition by ascorbate, glutathione and alpha-tocopherol.

Ascorbate anion and glutathione were found to inhibit the aqueous reaction between nitrogen dioxide (NO2) and morpholine (MOR) and thereby prevented the formation of N-nitrosomorpholine (NMOR) and N-nitromorpholine (NTMOR) at both pH 7.4 and 12.5. These antioxidants are approximately 3 orders of magnitude more reactive towards NO2 than is MOR and may play an important role in the prevention of carcinogen formation in the lung due to inhaled NO2. Ammonium sulfamate was ineffective at preventing nitrosation or nitration by NO2 at either pH 7.4 or 12.5.

Effects of tamoxifen on nitric oxide synthesis and neoplastic transformation in C3H 10T1/2 fibroblasts.

Tamoxifen (TAM) is used in the prevention and treatment of breast cancer, however, its mechanisms of therapeutic action as well as its pathologic effects are not fully understood. We report that TAM (10(-7)-10(-5) M) inhibits 3-methylcholanthrene-induced transformation of C3H 10T1/2 murine fibroblasts in a dose-responsive manner. Over this concentration range, TAM (>10(-6) M) potentiates inducible nitric oxide synthase (iNOS) activity in 10T1/2 cells. This increase in NO synthase activity was mediated through an increase in iNOS protein for cells stimulated with interferon-gamma (IFN-gamma) and bacterial lipopolysaccharide (LPS). Significant increases in NO formation were observed when TAM (10(-5)) was added prior to or simultaneously with IFN-gamma/LPS treatment, whereas the addition of TAM 48 h after IFN-gamma/LPS treatment had no effect on NO synthesis. The morphologic changes seen with cells treated with TAM are similar to those observed in cells treated with TGF-beta1. TGF-beta1 inhibited NO production at high doses and slightly enhanced NO formation at low doses in IFN-gamma/LPS-stimulated cells. The transformation inhibitory effects of TAM did not appear to be related to the effects on cellular proliferation of neoplastic cells as TAM did not inhibit the growth of neoplastic cells into foci in the presence of normal confluent C3H 10T1/2 fibroblasts.

Enhancement of methylcholanthrene-induced neoplastic transformation in murine C3H 10T1/2 fibroblasts by antisense phosphorothioate oligodeoxynucleotide sequences.

Antisense phosphorothioate oligodeoxynucleotides (ODNs) are increasingly used to target specific proteins for inhibition. Previous reports of antisense inhibition of the inducible nitric oxide synthase (iNOS) gene suggested its utility in defining the role of nitric oxide (NO) in carcinogenesis, as NO is mutagenic and chemical inhibitors of iNOS block neoplastic transformation in C3H 10T1/2 fibroblasts. Treatment with ODNs (0.025-25 microM) directed against 15mer sequences in the iNOS coding region decreased NO production consistent with a reduction of iNOS protein and iNOS mRNA, however, control ODNs (2.5 microM) also showed considerable nonspecific inhibition of NO synthesis. Treatment with both iNOS antisense and missense ODNs during the promotional phase of the C3H10T1/2 transformation assay significantly increased the number of neoplastic foci in 3-methylcholanthrene (MCA) treated cells which corresponded with the ability of the ODN to inhibit NO production. Enhanced neoplastic transformation and non-specific inhibition of NO synthesis resulting from exposure to antisense ODNs suggest limitations to their long-term use in humans at higher doses.

Relationship between dietary, serum, and tissue levels of carotenoids.

A study was undertaken to assess the utility of the buccal scrape technique for measuring tissue levels of carotenoids in short-term intervention trials and epidemiologic studies. In 14 healthy volunteers a good correlation was found between serum beta-carotene levels and recent dietary intake of beta-carotene as estimated from measured food records. Supplementation with 30 mg/day of beta-carotene for 1 week resulted in a sixfold increase in average serum levels, while serum lycopene concentrations remained constant. Presupplementation levels of beta-carotene and lycopene in the buccal mucosa cells were not correlated with dietary intakes or with serum levels. After supplementation, levels of both carotenoids were found to increase in buccal cells, however, most of this increase was found to be an artifact due to repeated sampling. After correcting for this artifact, beta-carotene was found to increase less than twofold in tissue after supplementation.

Effects of micronutrients and antioxidants on lipid peroxidation in human plasma and in cell culture.

Plasma levels of triglycerides, retinol, cholesterol, lipid-phase antioxidants (alpha-, gamma-tocopherols, beta-carotene, alpha-carotene, lycopene, beta-cryptoxanthin and lutein/zeaxanthin), and thiobarbituric acid-reactive substances (TBA-RS), as an indicator of lipid peroxidation, were repeatedly determined in nine individuals over a 3-month period. Levels of TBA-RS were positively correlated with plasma triglycerides and gamma-tocopherol, and negatively correlated with plasma carotenoids. These results were consistent with in vitro cell culture studies which showed increased TBA-RS for cells supplemented with linolenic acid and decreased levels when treated with beta-carotene. We conclude that TBA-RS measurements in plasma accurately reflect the level of peroxidizable substrate as modified by the presence of a variety of dietary antioxidants, particularly carotenoids. Although the inter- and intra-individual variabilities for TBA-RS are comparable with the micronutrients and antioxidants measured in this study, high interassay variability and the strong association with the more commonly measured plasma triglycerides suggest the TBA-RS assay to be of limited use in epidemiologic studies. However, this assay does appear to be useful in cell culture studies where experimental conditions can be better controlled. Low ratios of inter- to intra-individual variability in some of the plasma micronutrient and lipid-phase antioxidants measured suggest that multiple samples may be required to characterize individuals in studies evaluating the relation between these plasma constituents and disease incidence.

Use of breath hydrogen and methane as markers of colonic fermentation in epidemiologic studies: circadian patterns of excretion.

Fermentation in the large bowel has been postulated to play a protective role against colon cancer. Hydrogen and methane are end products of this fermentation process and are absorbed into the bloodstream and excreted via expired air in the breath. Breath levels of hydrogen and, to a lesser extent, methane correlate strongly with colonic fermentation and may serve as useful biomarkers for this process. In a preliminary study to assess the usefulness of these two markers in epidemiologic studies, we followed the hourly excretion of the two gases in expired alveolar air for 48 hr in 20 healthy subjects, using a Quintron gas chromatograph equipped with a solid-state detector specific for reducing gases. All subjects excreted hydrogen, but 71% did not excrete methane. Possible atmospheric contamination of the samples was corrected for on the basis of breath carbon dioxide levels. A clear circadian pattern of excretion was observed for breath hydrogen, with a decrease during the early morning followed by a progressive increase during the rest of the day. Methane excretion was constant throughout the day. This study shows that four samples collected at convenient times (0600, 1300, 1800, and 2200 hr) are optimal to characterize individuals by their breath excretions of hydrogen and methane during a 24-hr period.

Light-mediated conversion of nitrogen dioxide to nitric oxide by carotenoids.

Plants are more susceptible to the toxic effects of nitrogen dioxide when exposure takes place in the dark. Beta-carotene and other common carotenoids react with nitrogen dioxide in the dark to yield intermediate nitrosating agents consistent with the formation of nitrate esters. Simultaneous exposure of carotenoids to NO2 and light significantly reduced formation of nitrosating intermediates and resulted in the release of nitric oxide (NO) into the gas phase. Light-mediated reduction of NO2 to NO by carotenoids may be an important mechanism for preventing damage in plants exposed to NO2. The formation of nitrosating agents from the reaction of carotenoids with NO2 suggests that their ability to prevent nirosative damage associated with NO2 exposure in both plants and animals may be limited in the absence of light.