Characteristics of Lactococcus petauri GB97 lysate isolated from porcine feces and its in vitro and in vivo effects on inflammation, intestinal barrier function, and gut microbiota composition in mice.

IMPORTANCE: Weaning is a crucial step in piglet management to improve pork production. During the weaning phase, disruption of epithelial barrier function and intestinal inflammation can lead to decreased absorption of nutrients and diarrhea. Therefore, maintaining a healthy intestine, epithelial barrier function, and gut microbiota composition in this crucial phase is strategic for optimal weaning in pigs. We isolated a lysate of Lactococcus petauri GB97 (LPL97) from healthy porcine feces and evaluated its anti-inflammatory activities, barrier integrity, and gut microbial changes in LPS-induced murine macrophages and DSS-induced colitis mice. We found that LPL97 regulated the immune response by downregulating the TLR4/NF-κB/MAPK signaling pathway both in vitro and in vivo. Furthermore, LPL97 alleviated the disruption of intestinal epithelial integrity and gut microbiota dysbiosis in colitis mice. This study indicates that LPL97 has the potential to be developed as an alternative feed additive to antibiotics for the swine industry.

Gamma irradiation delays tomato (Solanum lycopersicum) ripening by inducing transcriptional changes.

BACKGROUND: Tomato (Solanum lycopersicum) has a relatively short shelf life as a result of rapid ripening, limiting its transportability and marketability. Recently, gamma irradiation has emerged as a viable method for delaying tomato fruit ripening. Although few studies have shown that gamma irradiation delays the ripening of tomatoes, the underlying mechanism remains unknown. Therefore, the present study aimed to examine the effects of gamma irradiation on tomato fruit ripening and the underlying mechanisms using transcriptomics. RESULTS: Following gamma irradiation, the total microbial count, weight loss, and decay rate of tomatoes significantly reduced during storage. Furthermore, the redness (a*), color change (∆E), and lycopene content of gamma-irradiated tomatoes decreased in a dose-dependent manner during storage. Moreover, gamma irradiation significantly upregulated the expression levels of genes associated with DNA, chloroplast, and oxidative damage repairs, whereas those of ethylene and auxin signaling-, ripening-, and cell wall metabolism-related, as well as carotenoid genes, were downregulated. CONCLUSION: Gamma irradiation effectively delayed ripening by downregulating the expression of ripening-related genes and inhibiting microbial growth, which prevented decay and prolonged the shelf life of tomatoes. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Comparison of gamma irradiation and heating treatment on cytotoxicity, insulinotropic activity, and molecular structure change of mistletoe viscothionin.

Mistletoe offers health-promoting effects; however, it has toxicity, requiring careful application. Viscothionin is a polypeptide of mistletoe that while contributing to toxicity also demonstrates anti-cancer and anti-diabetic activities. The aim of this study was to evaluate whether gamma irradiation or heating treatment could selectively reduce viscothionin-mediated cytotoxicity. Gamma irradiation effectively inhibited viscothionin-induced cytotoxicity to RIN5mF cells, but heating treatment did not affect its cytotoxicity. Both heating and gamma irradiation further increased the insulinotropic activity of viscothionin, whereas the effect of gamma irradiation was dose-dependent and diminished above 20 kGy. Structural analysis showed that gamma irradiation significantly altered the ordered structure of viscothionin, unlike heating treatment, resulting in a change of its molecular properties, which could be linked to the observed changes in the cytotoxicity and insulinotropic activity of the polypeptide. These results suggest gamma irradiation as an alternative method for minimizing viscothionin toxicity without interfering with anti-diabetic effect.

Effects of X-ray irradiation on the postharvest quality characteristics of 'Maehyang' strawberry (Fragaria × ananassa).

This study evaluated the effects of X-ray irradiation (0-1 kGy) on quality parameters of Korean strawberries during storage at 15 °C for 9 d. As compared to control, all irradiated samples exhibited dose-dependent decreases in microbial counts regardless of storage period. Irradiation significantly (p < 0.05) reduced weight loss and decay incidence of fruits during storage. Fruit firmness decreased immediately after irradiation, but no significant changes occurred after 3 d. Neither irradiation nor storage period significantly affected total soluble solids, pH, or titratable acidity. All treatments delayed color changes and pelargonidin accumulation during storage. The radical scavenging activities and total phenolic, ellagic acid, and catechin contents increased gradually during storage. Furthermore, irradiated fruits showed improved sensory characteristics throughout storage. Thus, X-ray irradiation (≤1 kGy) was confirmed as a effective phytosanitary treatment for strawberries to delay decay and negative physicochemical changes and extend shelf life with acceptable sensory attributes.

Rapid Identification Method for Gamma-Irradiated Soybeans Using Gas Chromatography-Mass Spectrometry Coupled with a Headspace Solid-Phase Microextraction Technique.

This study evaluated the applicability of a rapid analytical method using a headspace solid-phase microextraction gas chromatography/mass spectrometry (HS-SPME-GC/MS) technique to identify gamma-irradiated soybeans (0.1-5 kGy). From the partial least squares discriminant analysis used to discriminate between non-irradiated and irradiated soybean samples, 1,7-hexadecadiene was selected as the identifying marker. Response surface methodology experiments were used to determine the optimal HS-SPME extraction conditions including a carboxen/polydimethylsiloxane fiber with an extraction temperature of 98 °C and an extraction time of 55 min. 1,7-Hexdecadiene was detected in all samples irradiated at ≥ 0.1 kGy under the optimized HS-SPME-GC/MS conditions, and the unique presence of the marker in a gamma-irradiated sample was verified by comparing the results from heat, steam, microwave, sonication, and ultraviolet treatments. The comparisons of the identification properties for various conventional methods validated several advances in HS-SPME-GC/MS analysis in terms of rapid analysis, high sensitivity, and absence of solvent.

Gamma-Ray Irradiation Control of Whiteflies Bemisia tabaci (Hemiptera: Aleyrodidae) and Trialeurodes vaporariorum in the Exportation of Fresh Strawberries.

Whitefly pests, including the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood), are economically important in agriculture. With the annual growth of the domestic fresh fruit export market, various quarantine treatment methods are being used to export strawberries of better quality. The objective of the present study was to evaluate the effects of gamma rays on the development and reproductive sterility of B. tabaci and T. vaporariorum. In both species, the eggs were completely inhibited from hatching at 50 Gy, and the emergence of third-instar nymphs was completely suppressed at 150 Gy. Some adult B. tabaci and T. vaporariorum spawning occurred at 100 and 70 Gy, respectively; however, at these irradiation levels, F1 hatchability was completely inhibited. Dosimetry results showed that the penetrating power of gamma ray in the strawberry-filled box was the lowest at the mid-box position. Therefore, B. tabaci and T. vaporariorum were placed in the middle of the strawberry-filled box and irradiated. A gamma-ray irradiation of 100 Gy suppressed the development and reproduction of eggs and adults in both B. tabaci and T. vaporariorum. Our data suggest that at least 100 Gy should be used for the control of these two species of whitefly for strawberry export.

Viscothionin purified from mistletoe (Viscum album var. coloratum Ohwi) induces insulin secretion from pancreatic beta cells.

ETHNOPHARMACOLOGICAL RELEVANCE: Mistletoe (Viscum album), an evergreen parasitic plant, has been widely used as an oriental phytomedicine to treat diabetes mellitus. However, it is unknown which mistletoe constituent exerts the beneficial effect against the disease. In this study, we examined the hypoglycemic activity of mistletoe and investigated whether the polypeptide viscothionin, purified from mistletoe, was responsible for the activity. MATERIALS AND METHODS: Mistletoe extracts were prepared by heating mistletoe powder made of leaves and twigs in water for 3, 6, 9, and 12 h. Rat insulinoma RINm5F cells were used to test the cytotoxicity of the extracts and their effects on the secretion of insulin and its precursor, C-peptide. The inhibitory effects of a mistletoe extract on glucose absorption were measured using an α-glucosidase inhibition assay. To determine the component of mistletoe responsible for the observed effects, the mistletoe extract was precipitated with ethanol or hydrolyzed with a protease for further testing. A potential active constituent of mistletoe was isolated by chromatography and molecular weight cut-off fractionation, and its ability to induce insulin secretion was investigated. RESULTS: A 12-h heat-treated mistletoe extract, showing no cytotoxicity, significantly increased the secretion of insulin and C-peptide by RINm5F cells and enhanced the expression of glucose transporter type 4 (GLUT-4), insulin receptor substrate 1 (IRS-1), and protein kinase B (also known as AKT) in differentiated C2C12 cells. The extract also inhibited α-glucosidase activity. After ethanol precipitation, the extract showed much stronger effects on insulin- and C-peptide-secreting activities of cells, whereas the enzyme-hydrolyzed extract was less effective than the original extract, suggesting that the effect was mediated by a proteinaceous constituent of mistletoe. Subsequent analysis showed that viscothionin, a heat-stable 6-kDa polypeptide isolated from mistletoe, increased the level of insulin secretion by more than 20-fold compared to that induced by the extract. CONCLUSIONS: Our study indicates that the hypoglycemic effect of mistletoe is mediated by its insulinotropic action and α-glucosidase inhibitory activity, and the effect is due to viscothionin, one of the major bioactive constituents of mistletoe.

Toxicological evaluation of 2-dodecylcyclobutanone, a unique radiolytic compound of palmitic acid.

This study was conducted to evaluate the toxic effects and potency of 2-dodecylcyclobutanone (2-dDCB), a unique compound derived from palmitic acid via irradiation. In a series of assays of bacterial reverse-mutation, in vitro chromosomal aberration, and in vivo micronucleus, negative responses were found by the treatment of 2-dDCB comparing vehicle control, dimethyl sulfoxide or corn oil. In the acute oral toxicity test, all of the mice administrated 2-dDCB survived, and there were no clinical and necropsy signs observed at any doses (0, 300, and 2000 mg/kg body weight) during the experimental period of 14 days. These results suggested that 2-dDCB is a relatively non-toxic substance with median lethality dose higher than 2000 mg/kg body weight. Moreover, there were no adverse effects noted in rats orally administrated 2-dDCB everyday via gavage for 28 days, even at the highest dose (2.0 mg/kg body weight/day) tested, which is 1000-times higher than the human daily intake of 2-dDCB estimated through an extreme exposure scenario. Overall, these results indicate that 2-dDCB is not likely to raise any human health concerns and irradiated foods containing palmitic acid can be recognized as safe for human consumption under the current international regulation systems for food irradiation.

Identification of red pepper powder irradiated with different types of radiation using luminescence methods: A comparative study.

The purpose of this study was to verify the reliability of photostimulated luminescence (PSL) and thermoluminescence (TL) methods for identifying irradiated foods, described in the European standards EN 13751:2002 and EN 1788:2001, respectively, which were established solely through interlaboratory studies on gamma-irradiated food. Red pepper powder samples irradiated with electron-beams (e-beams), gamma rays and high-energy X-rays were used as model foods. Samples irradiated with each radiation type at ⩾4 kGy could be correctly identified by the PSL method, whereas samples irradiated at ⩾0.5 kGy with each radiation type could be correctly recognized by the TL method when e-beams, gamma rays, or high-energy X-rays were used as normalization sources. However, different TL intensities were observed for minerals separated from red pepper powder for different irradiation sources, which was confirmed using pure quartz and K-feldspar minerals. Further interlaboratory studies are required to verify this phenomenon.

The supplementation of Korean mistletoe water extracts reduces hot flushes, dyslipidemia, hepatic steatosis, and muscle loss in ovariectomized rats.

Since Korean mistletoe (Viscum album) has been used for alleviating metabolic diseases, it may also prevent the impairment of energy, glucose, lipid, and bone metabolisms in an estrogen-deficient animal model. We determined that long-term consumption of Korean mistletoe water extract (KME) can alleviate menopausal symptoms such as hot flush, increased abdominal fat mass, dyslipidemia, hyperglycemia, and decreased bone mineral density in ovariectomized (OVX) rats fed a high-fat diet, and explored the mechanisms of the effects. OVX rats were divided into four groups and fed high-fat diets supplemented with either 0.6% dextrin (control), 0.2% lyophilized KME + 0.4% dextrin (KME-L), or 0.6% lyophilized KME (KME-H). Sham rats were fed with the high-fat diets with 0.6% dextrin as a normal-control without estrogen deficiency. After eight weeks, OVX rats exhibited impaired energy, glucose and lipid metabolism, and decreased uterine and bone masses. KME-L did not alleviate energy dysfunction. However, KME-H lowered serum levels of total-, LDL-cholesterol, and triglycerides and elevated serum HDL-cholesterol levels in OVX rats with dyslipidemia, to similar levels as normal-control rats. Furthermore, KME-H improved HOMA-IR, an indicator of insulin resistance, in OVX rats. Surprisingly, KME-H fed rats had greater lean mass in the abdomen and leg without differences in fat mass but neither dosage of KME altered bone mineral density in the lumbar spine and femur. The increased lean mass was related to greater phosphorylation of mTOR and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) in the quadriceps muscles. Hepatic triglyceride contents were lowered with KME-H in OVX rats by increasing carnitine palmitoyltransferase-1 (CPT-1) expression and decreasing fatty acid synthase (FAS) and sterol regulatory element-binding protein-1c (SREBP-1c) expression. In conclusion, KME may be useful for preventing some menopausal symptoms such as hot flushes, dyslipidemia, hepatic steatosis, and loss of muscle mass in post-menopausal women.

Viscothionin isolated from Korean mistletoe improves nonalcoholic fatty liver disease via the activation of adenosine monophosphate-activated protein kinase.

The present study investigated the effects of viscothionin, a compound isolated from Korean mistletoe (Viscum album coloratum), on nonalcoholic fatty liver disease (NAFLD) in both in vitro and in vivo models. A connection was discovered between viscothionin and the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, which is involved in lipid metabolism. Viscothionin was shown to significantly attenuate lipid accumulation in HepG2 cells treated with oleic acid, which induces lipid accumulation. Moreover, the phosphorylation of AMPK and acetyl-coenzyme A carboxylase in HepG2 cells was increased by viscothionin treatment. Viscothionin was orally administered to high fat diet-induced obese mice and subsequently histopathological analysis associated with AMPK signaling pathways was evaluated. A significant reduction in the extent of hepatic steatosis was revealed in viscothionin-treated obese mice. Thus, viscothionin mediates its beneficial effects on NAFLD via AMPK signaling pathways, suggesting that it may be a potential target for novel NAFLD treatments.

Rutin attenuates ethanol-induced neurotoxicity in hippocampal neuronal cells by increasing aldehyde dehydrogenase 2.

Rutin is derived from buckwheat, apples, and black tea. It has been shown to have beneficial anti-inflammatory and antioxidant effects. Ethanol is a central nervous system depressant and neurotoxin. Its metabolite, acetaldehyde, is critically toxic. Aldehyde dehydrogenase 2 (ALDH2) metabolizes acetaldehyde into nontoxic acetate. This study examined rutin's effects on ALDH2 activity in hippocampal neuronal cells (HT22 cells). Rutin's protective effects against acetaldehyde-based ethanol neurotoxicity were confirmed. Daidzin, an ALDH2 inhibitor, was used to clarify the mechanisms of rutin's protective effects. Cell viability was significantly increased after rutin treatment. Rutin significantly reversed ethanol-increased Bax, cytochrome c expression and caspase 3 activity, and decreased Bcl-2 and Bcl-xL protein expression in HT22 cells. Interestingly, rutin increased ALDH2 expression, while daidzin reversed this beneficial effect. Thus, this study demonstrates rutin protects HT22 cells against ethanol-induced neurotoxicity by increasing ALDH2 activity.

Procyanidin C1 causes vasorelaxation through activation of the endothelial NO/cGMP pathway in thoracic aortic rings.

The aim of this study was to clarify the efficacy of procyanidin C1 (Pro C1) for modulating vascular tone. Pro C1 induced a potent vasorelaxant effect on phenylephrine-constricted endothelium-intact thoracic aortic rings, but had no effect on denuded thoracic aortic rings. Moreover, Pro C1 caused a significant increase in nitric oxide (NO) production in endothelial cells. Pro C1-induced vasorelaxation and Pro C1-induced NO production were significantly decreased in the presence of a nonspecific potassium channel blocker (tetraethylammonium chloride [TEA]), an endothelial NO synthase inhibitor (N(G)-monomethyl-L-arginine [L-NMMA]), and a store-operated calcium entry inhibitor (2-aminoethyl diphenylborinate [2-APB]). Pro C1-induced vasorelaxation was also completely abolished by an inhibitor of soluble guanyl cyclase, which suggests that the Pro C1 effects observed involved cyclic guanosine monophosphate (cGMP) production. Interestingly, Pro C1 significantly enhanced basal cGMP levels. Taken together, these results indicate that Pro C1-induced vasorelaxation is associated with the activation of the calcium-dependent NO/cGMP pathway, involving potassium channel activation. Thus, Pro C1 may represent a novel and potentially therapeutically relevant compound for the treatment of cardiovascular diseases.

Procyanidin dimer B2-mediated IRAK-M induction negatively regulates TLR4 signaling in macrophages.

Polyphenolic compounds have been found to possess a wide range of physiological activities that may contribute to their beneficial effects against inflammation-related diseases; however, the molecular mechanisms underlying this anti-inflammatory activity are not completely characterized, and many features remain to be elucidated. In this study, we investigated the molecular basis for the down-regulation of toll-like receptor 4 (TLR4) signal transduction by procyanidin dimer B2 (Pro B2) in macrophages. Pro B2 markedly elevated the expression of the interleukin (IL)-1 receptor-associated kinase (IRAK)-M protein, a negative regulator of TLR signaling. Lipopolysaccharide (LPS)-induced expression of cell surface molecules (CD80, CD86, and MHC class I/II) and production of pro-inflammatory cytokines (tumor necrosis factor-α, IL-1ß, IL-6, and IL-12p70) were inhibited by Pro B2, and this action was prevented by IRAK-M silencing. In addition, Pro B2-treated macrophages inhibited LPS-induced activation of mitogen-activated protein kinases such as extracellular signal-regulated kinase 1/2, p38, and c-Jun N-terminal kinase and the translocation of nuclear factor κB and p65 through IRAK-M. We also found that Pro B2-treated macrophages inactivated naïve T cells by inhibiting LPS-induced interferon-γ and IL-2 secretion through IRAK-M. These novel findings provide new insights into the understanding of negative regulatory mechanisms of the TLR4 signaling pathway and the immune-pharmacological role of Pro B2 in the immune response against the development and progression of many chronic diseases.

Effect of gamma irradiation on mistletoe (Viscum album) lectin-mediated toxicity and immunomodulatory activity.

This study evaluated the effect of gamma irradiation on the reduction of the toxicity of mistletoe lectin using both in vitro and in vivo models. To extract the lectin from mistletoe, an (NH4)2SO4 precipitation method was employed and the precipitant purified using a Sepharose 4B column to obtain the pure lectin fraction. Purified lectin was then gamma-irradiated at doses of 0, 5, 10, 15, and 20 kGy, or heated at 100 °C for 30 min. Toxic effects of non-irradiated, irradiated, and heat-treated lectins were tested using hemagglutination assays, cytotoxicity assays, hepatotoxicity, and a mouse survival test and immunological response was tested using cytokine production activity. Hemagglutination of lectin was remarkably decreased (P < 0.05) by irradiation at doses exceeding 10 kGy and with heat treatment. However, lectin irradiated with 5 kGy maintained its hemagglutination activity. The cytotoxicity of lectin was decreased by irradiation at doses over 5 kGy and with heat treatment. In experiments using mouse model, glutamate oxaloacetate transaminase (GOT) and glutamic pyruvic transaminase (GPT) levels were decreased in the group treated with the 5 kGy irradiated and heat-treated lectins as compared to the intact lectin, and it was also shown that 5 kGy irradiated and heat-treated lectins did not cause damage in liver tissue or mortality. In the result of immunological response, tumor necrosis factor (TNF-α) and interleukin (IL-6) levels were significantly (P < 0.05) increased in the 5 kGy gamma-irradiated lectin treated group. These results indicate that 5 kGy irradiated lectin still maintained the immunological response with reduction of toxicity. Therefore, gamma-irradiation may be an effective method for reducing the toxicity of lectin maintaining the immune response.

The procyanidin trimer C1 induces macrophage activation via NF-κB and MAPK pathways, leading to Th1 polarization in murine splenocytes.

Numerous studies have shown various relationships between foods with a high nutritional value and a robust immune response, particularly studies that have focused on host protection and cytokine networks. This study aimed to clarify the role played by the procyanidin trimer C1 in innate and adaptive immunity. Procyanidin C1 did not exert cytotoxicity at concentrations ranging from 7.8 to 62.5 µg/ml in macrophage cells; therefore, concentration of 62.5 µg/ml was used as the maximum dose of procyanidin C1 throughout subsequent experiments. Procyanidin C1 enhanced inducible nitric oxide synthase-mediated nitric oxide production in a concentration-dependent manner. In addition, procyanidin C1 functionally induced macrophage activation by augmenting the expression of cell surface molecules (CD80, CD86, and MHC II) and proinflammatory cytokine production (tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, and IL-6) via activation of mitogen-activated protein kinase (MAPK), e.g., p38, ERK, and JNK and nuclear factor (NF)-κB signaling pathways. Interestingly, procyanidin C1 effectively polarized T helper type 1 (Th1) by secreting Th1-mediated cytokines (interferon-γ, IL-12p70, and IL-2) and inducing splenocyte proliferation, indicating that procyanidin C1 contributes to Th1 polarization of the immune response. Accordingly, these findings confirms that the procyanidin C1 induces macrophage activation via NF-κB and MAPK pathways, leading to Th1 polarization in murine splenocytes, which suggests that procyanidin C1 regulates innate and adaptive immunity by macrophage activation and Th1 polarization.

The procyanidin trimer C1 inhibits LPS-induced MAPK and NF-κB signaling through TLR4 in macrophages.

Natural products and dietary components rich in polyphenols have been shown to reduce inflammation; however, the molecular mechanisms underlying this anti-inflammatory activity are not completely characterized, and many features remain to be elucidated. This research was carried out to clarify the potential role of procyanidin trimer C1 in the anti-inflammatory effect of polyphenols. Procyanidin C1 inhibited inducible nitric oxide synthase-mediated nitric oxide production and the release of pro-inflammatory cytokines (interleukin-6 and tumor necrosis factor-α) in lipopolysaccharide (LPS)-induced macrophages. Treatment with procyanidin C1 resulted in a significant decrease in prostaglandin E2 and cyclooxygenase-2 levels, as well as the expression of cell surface molecules (CD80, CD86, and MHC class II), which was induced by LPS. Furthermore, our data demonstrated that the anti-inflammatory effect of procyanidin C1 occurs through inhibition of mitogen-activated protein kinase (p38 and c-Jun N-terminal kinase) and nuclear factor-κB signaling pathways. These 2 factors play a major role in controlling inflammation, through toll-like receptor 4, suggesting that procyanidin C1 plays a potent role in promoting anti-inflammatory activity in macrophages. These results represent a novel and effective therapeutic intervention for the treatment of inflammatory disease.

Replacement of mouse embryonic fibroblasts with bone marrow stromal cells for use in establishing and maintaining embryonic stem cells in mice.

We have investigated the use of BMSC (bone marrow stromal cell) as a feeder cell for improving culture efficiency of ESC (embryonic stem cell). B6CBAF1 blastocysts or ESC stored after their establishment were seeded on to a feeder layer of either SCA-1+/CD45-/CD11b- BMSC or MEF (mouse embryonic fibroblast). Feeder cell activity in promoting ESC establishment from the blastocysts and in supporting ESC maintenance did not differ significantly between BMSC and MEF feeders. However, the highest efficiency of colony formation after culturing of inner cell mass cells of blastocysts was observed with the BMSC line that secreted the largest amount of LIF (leukaemia inhibitory factor). Exogenous LIF was essential for the ESC establishment on BMSC feeder, but not for ESC maintenance. Neither change in stem cell-specific gene expression nor increase in stem cell aneuploidy was detected after the use of BMSC feeder. We conclude that BMSC can be utilized as the feeder of ESC, which improves culture efficiency.

Specificity of human aldo-keto reductases, NAD(P)H:quinone oxidoreductase, and carbonyl reductases to redox-cycle polycyclic aromatic hydrocarbon diones and 4-hydroxyequilenin-o-quinone.

Polycyclic aromatic hydrocarbons (PAHs) are suspect human lung carcinogens and can be metabolically activated to remote quinones, for example, benzo[a]pyrene-1,6-dione (B[a]P-1,6-dione) and B[a]P-3,6-dione by the action of either P450 monooxygenase or peroxidases, and to non-K region o-quinones, for example B[a]P-7,8-dione, by the action of aldo keto reductases (AKRs). B[a]P-7,8-dione also structurally resembles 4-hydroxyequilenin o-quinone. These three classes of quinones can redox cycle, generate reactive oxygen species (ROS), and produce the mutagenic lesion 8-oxo-dGuo and may contribute to PAH- and estrogen-induced carcinogenesis. We compared the ability of a complete panel of human recombinant AKRs to catalyze the reduction of PAH o-quinones in the phenanthrene, chrysene, pyrene, and anthracene series. The specific activities for NADPH-dependent quinone reduction were often 100-1000 times greater than the ability of the same AKR isoform to oxidize the cognate PAH-trans-dihydrodiol. However, the AKR with the highest quinone reductase activity for a particular PAH o-quinone was not always identical to the AKR isoform with the highest dihydrodiol dehydrogenase activity for the respective PAH-trans-dihydrodiol. Discrete AKRs also catalyzed the reduction of B[a]P-1,6-dione, B[a]P-3,6-dione, and 4-hydroxyequilenin o-quinone. Concurrent measurements of oxygen consumption, superoxide anion, and hydrogen peroxide formation established that ROS were produced as a result of the redox cycling. When compared with human recombinant NAD(P)H:quinone oxidoreductase (NQO1) and carbonyl reductases (CBR1 and CBR3), NQO1 was a superior catalyst of these reactions followed by AKRs and last CBR1 and CBR3. In A549 cells, two-electron reduction of PAH o-quinones causes intracellular ROS formation. ROS formation was unaffected by the addition of dicumarol, suggesting that NQO1 is not responsible for the two-electron reduction observed and does not offer protection against ROS formation from PAH o-quinones.