Ascorbate (vitamin C) is an essential micronutrient in primates, and exhibits multiple physiological functions. In addition to antioxidative action, ascorbate provides reducing power to α-ketoglutarate-dependent non-heme iron dioxygenases, such as prolyl hydroxylases. Demethylation of histones and DNA with the aid of ascorbate results in the reactivation of epigenetically silenced genes. Ascorbate and its oxidized form, dehydroascorbate, have attracted interest in terms of their roles in cancer therapy. The last step in the biosynthesis of ascorbate is catalyzed by l-gulono-γ-lactone oxidase whose gene Gulo is commonly mutated in all animals that do not synthesize ascorbate. One common explanation for this deficiency is based on the increased availability of ascorbate from foods. In fact, pathways for ascorbate synthesis and the detoxification of xenobiotics by glucuronate conjugation share the metabolic processes up to UDP-glucuronate, which prompts another hypothesis, namely, that ascorbate-incompetent animals might have developed stronger detoxification systems in return for their lack of ability to produce ascorbate, which would allow them to cope with their situation. Here, we overview recent advances in ascorbate research and propose that an enhanced glucuronate conjugation reaction may have applied positive selection pressure on ascorbate-incompetent animals, thus allowing them to dominate the animal kingdom.

Singlet oxygen prefers to react with an electron-rich double bonds. We observed that the oxidation rate for uric acid with singlet oxygen increased with increasing pH and the oxidation rate dramatically was elevated at around pH 5.4 and 9.8, which are the acidity constants of uric acid, pK_a1 and pK_a2, respectively. Furthermore, we observed that the absorbance near 200 nm and the molar extinction coefficient (ɛ) increased with increasing pH, similar to the change in oxidation rate. Computer calculations by Chong [Chong, J Theor Comput Sci 2013; 1(1)] revealed that uric acid elongates its C=N conjugated diene structure with increasing pH. This is correlated with an increase in the UV absorbance of C=C double bonds near 200 nm, and may indicate higher electron density in the double bonds. Therefore, we concluded that the increased oxidation rate is due to elongation of the C=N conjugated polyene system at higher pH. On the other hand, the major products were 4-hydroxyallantoin and parabanic acid (hydrolyzed to oxaluric acid at pH 10.7), suggesting that the reaction pathways were the same regardless of pH. Finally, possible reaction schemes are presented.

Increased 5-hydroxytryptamine may be associated with the development and progression of inflammatory bowel disease. In this study, we examined the suppressive effect of flavonoids on the increased intra- and extracellular 5-hydroxytryptamine levels in rat mast RBL-2H3 cells, known to produce 5-hydroxytryptamine by the phorbol 12-myristate 13-acetate stimulation. Among the flavonoids examined, luteolin and quercetin significantly reduced the cellular 5-hydroxytryptamine concentration. Gene and protein expression analyses revealed that luteolin significantly suppressed cellular tryptophan hydroxylase 1 expression induced by phorbol 12-myristate 13-acetate stimulation. Mitogen-activated protein kinase/extracellular signal-regulated kinase signaling was also suppressed by luteolin, suggesting that this pathway is one of targets of 5-hydroxytryptamine modulation by luteolin. An in vivo experimental colitis model was prepared by administering 2.5% dextran sodium sulfate in drinking water to C57BL/6 mice for seven days. The ingestion of 0.1% dietary luteolin suppressed the increasing 5-hydroxytryptamine in the colorectal mucosa. In conclusion, luteolin possesses a suppressive effect on extensive 5-hydroxytryptamine formation in both experimental RBL-2H3 cells and colitis models.

Caveolin-1 is a major protein of the caveolae structure in vascular endothelial cell membrane. Phosphorylation of caveolin-1 is one of the initial events leading to exacerbation of vascular permeability caused by oxidative stress. Although quercetin is known to be an anti-atherosclerosis factor that acts as a dietary antioxidant, little is known about its role in the regulation of caveolin-1 phosphorylation. In this study, we investigated the inhibitory effect of quercetin on hydrogen peroxide-induced caveolin-1 phosphorylation in human umbilical vein endothelial cells. Quercetin inhibited caveolin-1 phosphorylation in cells pretreated with quercetin for 24 h and then exposed to hydrogen peroxide. However, quercetin 3-O-β-glucuronide, a conjugated metabolite of quercetin, did not exert this inhibitory effect. Exposure to hydrogen peroxide increased vascular permeability and reduced mRNA expression of the intercellular adhesion protein, vascular endothelial cadherin (VE-cadherin). By contrast, pretreatment with quercetin suppressed the increase in vascular permeability and decreased VE-cadherin expression. These results indicate that deconjugated quercetin can play a role in the prevention of altered vascular permeability under oxidative stress by suppressing caveolin-1 phosphorylation. Thus, dietary quercetin may be beneficial for the maintenance of endothelial cell function.

Concerns have recently grown about the health effects of secondhand smoke exposure and heated tobacco products. The analysis of tobacco smoke biomarkers is critical to assess the health effects of tobacco smoke exposure. For this purpose, the simultaneous determinations of exposure markers and health effect markers would provide a better evaluation of smoke exposure. In this study, nicotine metabolites (nicotine, cotinine, trans-3'-hydroxycotinine) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in urine were analyzed as exposure markers. The DNA damage markers, 7-methylguanine and 8-hydroxy-2'-deoxyguanosine, were simultaneously measured as health effect markers. The results revealed significant levels of urinary nicotine metabolites and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in the subjects exposed to secondhand smoke and heated tobacco products. In addition, the urinary levels of 7-methylguanine and 8-hydroxy-2'-deoxyguanosine tended to be high for secondhand smoke and heated tobacco products exposures, as compared to those of non-smokers. These biomarkers will be useful for evaluating tobacco smoke exposure.

Leukocyte activation and the resulting oxidative stress induced by bioincompatible materials during hemodialysis impact the prognosis of patients. Despite multiple advances in hemodialysis dialyzers, the prognosis of hemodialysis patients with complications deeply related to oxidative stress, such as diabetes mellitus, remains poor. Thus, we re-evaluated the effects of hemodialysis on multiple reactive oxygen species using electron spin resonance-based methods for further improvement of biocompatibility in hemodialysis. We enrolled 31 patients in a stable condition undergoing hemodialysis using high-flux polysulfone dialyzers. The effects of hemodialysis on reactive oxygen species were evaluated by two methods: MULTIS, which evaluates serum scavenging activities against multiple hydrophilic reactive oxygen species, and i-STrap, which detects lipophilic carbon-center radicals. Similar to previous studies, we found that serum hydroxyl radical scavenging activity significantly improved after hemodialysis. Unlike previous studies, we discovered that scavenging activity against alkoxyl radical was significantly reduced after hemodialysis. Moreover, patients with diabetes mellitus showed a decrease in serum scavenging activity against alkyl peroxyl radicals and an increase in lipophilic carbon-center radicals after hemodialysis. These results suggest that despite extensive improvements in dialyzer membranes, the forms of reactive oxygen species that can be eliminated during dialysis are limited, and multiple reactive oxygen species still remain at increased levels during hemodialysis.

Metastasis, which accounts for the majority of all cancer-related deaths, occurs through several steps, namely, local invasion, intravasation, transport, extravasation, and colonization. Glycyrrhizin has been reported to inhibit pulmonary metastasis in mice inoculated with B16 melanoma. This study aimed to identify the mechanism through which glycyrrhizin ameliorates the extravasation of melanoma cells into mouse lungs. Following B16 melanoma cell injection, mice were orally administered glycyrrhizin once every two days over 2 weeks; lung samples were then obtained and analyzed. Blood samples were collected on the final day, and cytokine plasma levels were determined. We found that glycyrrhizin ameliorated the extravasation of melanoma cells into the lungs and suppressed the plasma levels of interleukin-6, tumor necrosis factor-α, and transforming growth factor-β. Furthermore, glycyrrhizin ameliorated the lung tissue expression of high mobility group box-1 protein (HMGB1), receptor for advanced glycation end products (RAGE), Toll-like receptor (TLR)-4, RAS, extracellular signal-related kinase, NF-κB, myeloid differentiation primary response 88, IκB kinase complex, epithelial-mesenchymal transition markers, and vascular endothelial growth factor-A. Our study demonstrates that glycyrrhizin ameliorates melanoma metastasis by regulating the HMGB1/RAGE and HMGB1/TLR-4 signal transduction pathways.

Inflammatory bowel diseases, including Crohn’s disease and ulcerative colitis, are chronic inflammatory disorders associated with oxidative stress. The intestines produce 5-hydroxytryptamine that may negatively affect disease state under inflammatory conditions when overproduced. 5-Hydroxytryptamine is a sub­strate for myeloperoxidase and is converted into reactive tryptamine-4,5-dione. Here, an experimental colitis model was established through oral administration of 5% dextran sulfate sodium to ICR mice for 7 days. Furthermore, the formation of tryptamine-4,5-dione in the colorectal mucosa/submucosa and colorectal tissue was analyzed by chemical and immunochemical methodologies. First, free tryptamine-4,5-dione in the homogenate was chemically trapped by o-phenylenediamine and analyzed as the stable phenazine derivative. Tryptamine-4,5-dione locali­zation as adducted proteins in the colorectal tissue was immunohistochemically confirmed, and as demonstrated by both methods, this resulted in the significant increase of tryptamine-4,5-dione in dextran sulfate sodium-challenged mice compared with control mice. Immunohistochemical staining confirmed tryptamine-4,5-dione-positive staining at the myeloperoxidase accumulation site in dextran sulfate sodium-challenged mice colorectal tissue. The tryptamine-4,5-dione locus in the mice was partly matched with that of a specific marker for myeloperoxidase, halogenated tyrosine. Overall, the results possibly indicate that tryptamine-4,5-dione is generated by neutrophil myeloperoxidase in inflammatory tissue and may contribute to the development of inflammatory bowel disease.

We aimed to determine the impact of high-fructose intake during pregnancy on the fetal-placental unit in rats, which may be the initial mechanism of the programming effect of fructose. Pregnant Sprague–Dawley rats were randomly assigned to three groups and respectively provided tap water (n = 10), 10% (w/v) fructose solution (n = 10), and 10% (w/v) glucose solution (n = 10) from embryonic day 0 to 20. Compared with the control and glucose groups, significantly lower fetal length, fetal weight, placental weight, and fetus/placenta ratio were found in the fructose group on embryonic day 20 (all p<0.05). In parallel with markedly increased uric acid concentrations in the dams, significantly decreased antioxidant enzymes activities and mRNA expression levels were observed in placentas in the fructose group (all p<0.05). In the fructose group, placental mRNA and protein expression of nuclear factor erythroid 2-related factor 2 was markedly downregulated and kelch-like ECH-associated protein 1 was significantly upregulated (all p<0.05). In conclusion, high-fructose consumption during pregnancy drives augmented oxidative stress in rats. Placental insufficiency under oxidative stress contributes to asymmetrical fetal growth restriction.

We examined the effects of a test food containing anthocyanin, astaxanthin, and lutein on the eye function in healthy Japanese adults with eye fatigue after operating visual display terminals. Forty-four subjects were randomly but equally assigned to the active or placebo group. Two active or placebo capsules were taken once daily for 6 weeks. Accommodative function, tear film break-up time, visual acuity, the value of Schirmer’s test, macular pigment optical density level, muscle hardness, and a questionnaire were evaluated before and after a 6-week intervention. Each group included 20 subjects in the efficacy analysis. The active group showed a significant improvement in the percentage of pupillary response of an average of both eyes and dominant eye pre- and post-visual display terminal operation at 6 weeks compared with the placebo group. Moreover, the active group showed a significant improvement in the scores of “A sensation of trouble in focusing the eyes” and “Difficulty in seeing objects in one’s hand and nearby, or fine print” compared with the placebo group between before and after ingestion. Therefore, 6-weeks consumption of the test food inhibited a decrease in the accommodative function caused by visual display terminal operation (UMIN000036989).

Reflux esophagitis is known to be more prevalent in males, and previous studies have suggested sex differences in its risk factors. However, little is known about sex differences in the time-course of risk factors before reflux esophagitis onset. Thus, we conducted a retrospective longitudinal study using health checkup records. From the records of 230,056 individuals obtained from nine institutes in Japan, we selected 1,558 male reflux esophagitis cases, 3,116 male controls, 508 female reflux esophagitis cases, and 1,016 female controls were selected. We compared time-courses of risk factors between the case and control groups and identified abdominal circumference (AC), diastolic blood pressure, alanine transaminase (ALT), and current smoking in males and body mass index (BMI) in females as sex-specific risk factors. We also found that AC and ALT in males and BMI in females were significantly different between the reflux esophagitis case and control groups during the five years before reflux esophagitis onset. Our results suggest that visceral fat-type obesity and fatty liver in males and higher BMI in females are more frequently observed in reflux esophagitis cases several years before reflux esophagitis onset, and that proactive intervention to lifestyle can help prevent reflux esophagitis in both males and females.

Korean fermented kimchi is probiotic food preventing Helicobacter pylori (H. pylori)-associated atrophic gastritis in both animal and human trial. In order to reveal the effect of fermented kimchi against H. pylori infection, we performed clinical trial to docu­ment the changes of fecal microbiota in 32 volunteers (H. pylori (−) chronic superficial gastritis (CSG), H. pylori (+) CSG, and H. pylori (+) chronic atrophic gastritis (CAG) with 10 weeks kimchi. Each amplicon is sequenced on MiSeq of Illumina and the sequence reads were clustered into operational taxonomic units using VSEARCH and the Chao, Simpson, and Shannon Indices. Though significant difference in α- or β-diversity was not seen in three groups, kimchi intake led to significant diversity of fecal microbiome. As results, Klebsiella, Enterococcus, Ruminococcaceae, Streptococcus, Roseburia, and Clostirdiumsensu were significantly increased in H. pylori (+) CAG, while Akkermansia, Citrobacter, and Lactobacillus were significantly decreased in H. pylori (+) CAG. With 10 weeks of kimchi administration, Bifidobacterium, Lactobacillus, and Ruminococcus were significantly increased in H. pylori (+) CAG, whereas Bacteroides, Subdoligranulum, and Eubacterium coprostanolines were significantly decreased in H. pylori (−) CAG. 10 weeks of kimchi intake significantly improved pepsinogen I/II ratio (p<0.01) with significant decreases in interleukin-1β. Conclusively, fermented kimchi significantly changed fecal microbiota to mitigate H. pylori-associated atrophic gastritis.