Beneficial Effects of Dietary Fiber in Young Barley Leaf on Gut Microbiota and Immunity in Mice

The health benefits of young barley leaves, rich in dietary fiber, have been studied for several decades; however, their beneficial effects on the intestinal microenvironment remain to be elucidated. To investigate the effects of young barley leaf-derived dietary fiber (YB) on the gut microbiota and immunity, mice were fed an AIN-93G diet containing cellulose or YB and subjected to subsequent analysis. The population of MHC-II-positive conventional dendritic cells (cDCs) and CD86 expression in the cDCs of Peyer's patches were elevated in the YB-fed mice. MHC-II and CD86 expression was also elevated in the bone marrow-derived DCs treated with YB. 16S-based metagenomic analysis revealed that the gut microbiota composition was markedly altered by YB feeding. Among the gut microbiota, Lachnospiraceae, mainly comprising butyrate-producing NK4A136 spp., were overrepresented in the YB-fed mice. In fact, fecal butyrate concentration was also augmented in the YB-fed mice, which coincided with increased retinaldehyde dehydrogenase (RALDH) activity in the CD103+ cDCs of the mesenteric lymph nodes. Consistent with elevated RALDH activity, the population of colonic IgA+ plasma cells was higher in the YB-fed mice than in the parental control mice. In conclusion, YB has beneficial effects on the gut microbiota and intestinal immune system.

The binding selectivity of quercetin and its structure-related polyphenols to human serum albumin using a fluorescent dye cocktail for multiplex drug-site mapping

Human serum albumin (HSA) is a serum protein that carries flavonoids in blood circulation. In this report, the binding selectivity and strength of interactions to HSA-binding sites (sites I or II) by flavonoids were evaluated using competition experiments and the specific fluorescent dyes, dansylamide and BD140. Most tested flavonoids bound site I preferentially, with the binding strength dependent on the mother structure in the order flavonol > flavone > flavanone > flavan 3-ols. Glycosylation or glucuronidation reduced the binding of quercetin to site I of HSA, whereas sulfation increased binding. Quercetin 7-sulfate showed the strongest binding and molecular docking simulations supported this observation. Prenylation at any position or glucuronidation and sulfation at the C-4' or C-7 position of quercetin facilitated stronger binding to site II. The binding affinity of flavonoids toward site I correlated with the partition coefficient value (logP), whereas no corresponding correlation was observed for site II.

Enhancing effect of the coexisting alpha-tocopherol on quercetin absorption and metabolism

The aim of this study is to investigate the modulating effect of coexisting food components on the absorption and metabolism of quercetin and blood plasma antioxidant potentials. The combination of quercetin with α-tocopherol (αT), cellulose, or a commercially available vegetable beverage containing αT and dietary fiber was orally administered to mice. Compared to the single administration of quercetin aglycone, the coadministration of αT with quercetin significantly increased the plasma quercetin concentration at 0.5 h, whereas the combination of quercetin and cellulose decreased it. Interestingly, the administration of quercetin mixed with the vegetable beverage showed no significant change in the quercetin concentration in the mice plasma. The treatment of the cells with the blood plasma after the coadministration of αT with quercetin significantly upregulated the gene expression of the antioxidant enzyme (heme oxygenase-1), whereas the quercetin and cellulose combination did not. In the plasma of the quercetin-administered mice, eight types of quercetin metabolites were detected, and their quantities were affected by the combination with αT. The potentials of the heme oxygenase-1 gene expression by these metabolites were very limited, although several metabolites showed radical scavenging activities comparable to aglycone in the in vitro assays. These results suggested that the combination of αT potentiates the quercetin absorption and metabolism and thus the plasma antioxidant potentials, at least in part, by the quantitative changes in the quercetin metabolites.

Characterization of Rickets Type II Model Rats to Reveal Functions of Vitamin D and Vitamin D Receptor

Vitamin D has been known to exert a wide range of physiological effects, including calcemic, osteogenic, anticancer, and immune responses. We previously generated genetically modified (GM) rats and performed a comparative analysis of their physiological properties to elucidate the roles of vitamin D and vitamin D receptor (VDR). In this study, our primary goal was to investigate the manifestations of type II rickets in rats with the VDR(H301Q) mutation, analogous to the human VDR(H305Q). Additionally, we created a double-mutant rat with the VDR(R270L/H301Q) mutation, resulting in almost no affinity for 1,25-dihydroxy-vitamin D3 (1,25D3) or 25-hydroxy-vitamin D3 (25D3). Notably, the plasma calcium concentration in Vdr(R270L/H301Q) rats was significantly lower than in wild-type (WT) rats. Meanwhile, Vdr(H301Q) rats had calcium concentrations falling between those of Vdr(R270L/H301Q) and WT rats. GM rats exhibited markedly elevated plasma parathyroid hormone and 1,25D3 levels compared to those of WT rats. An analysis of bone mineral density in the cortical bone of the femur in both GM rats revealed significantly lower values than in WT rats. Conversely, the bone mineral density in the trabecular bone was notably higher, indicating abnormal bone formation. This abnormal bone formation was more pronounced in Vdr(R270L/H301Q) rats than in Vdr(H301Q) rats, highlighting the critical role of the VDR-dependent function of 1,25D3 in bone formation. In contrast, neither Vdr(H301Q) nor Vdr(R270L/H301Q) rats exhibited symptoms of alopecia or cyst formation in the skin, which were observed in the Vdr-KO rats. These findings strongly suggest that unliganded VDR is crucial for maintaining the hair cycle and normal skin. Our GM rats hold significant promise for comprehensive analyses of vitamin D and VDR functions in future research.

Gene therapy for alopecia in type II rickets model rats using vitamin D receptor-expressing adenovirus vector

Type II rickets is a hereditary disease caused by a mutation in the vitamin D receptor (VDR) gene. The main symptoms of this disease are bone dysplasia and alopecia. Bone dysplasia can be ameliorated by high calcium intake; however, there is no suitable treatment for alopecia. In this study, we verified whether gene therapy using an adenoviral vector (AdV) had a therapeutic effect on alopecia in Vdr-KO rats. The VDR-expressing AdV was injected into six 7-week-old female Vdr-KO rats (VDR-AdV rats). On the other hand, control-AdV was injected into 7-week-old female rats (control-AdV rats); non-infected Vdr-KO rats (control rats) were also examined. The hair on the backs of the rats was shaved with hair clippers, and VDR-AdV or control-AdV was intradermally injected. Part of the back skin was collected from each rat after AdV administration. Hair follicles were observed using hematoxylin and eosin staining, and VDR expression was examined using immunostaining and western blotting. VDR-AdV rats showed significant VDR expression in the skin, enhanced hair growth, and low cyst formation, whereas control-AdV and non-infected rats did not show any of these effects. The effect of VDR-AdV lasted for nearly 60 days. These results indicate that gene therapy using VDR-AdV may be useful to treat alopecia associated with type II rickets, if multiple injections are possible after a sufficient period of time.

Analysis of vitamin D metabolites in biological samples using a nanoluc-based vitamin D receptor ligand sensing system: NLucVDR

Many assays are currently being developed to measure the levels of vitamin D metabolites in various samples (such as blood, urine, and saliva). This study focused on the measurement of vitamin D metabolites in serum and urine using the NLucVDR assay system, which consists of a split-type nanoluciferase and ligand-binding domain (LBD) of the human vitamin D receptor. Blood and urine samples were collected from 23 participants to validate the NLucVDR assay. The 25(OH)D3 levels in the serum and urine determined by the NLucVDR assay showed good correlations with those determined by standard analytical methods (ECLIA for serum and LC-MS/MS for urine), with correlation coefficients of 0.923 and 0.844 for serum and urine samples, respectively. In the case of serum samples, 25(OH)D3 levels determined by the NLucVDR assay were in good agreement with those determined by ECLIA. Therefore, the NLucVDR assay is a useful tool for measuring serum 25(OH)D3 levels. The contribution of each vitamin D metabolite to the luminescence intensity obtained during the NLucVDR assay depends on its concentration and affinity for NLucVDR. Thus, the contribution of 25(OH)D3 in serum appears to be much higher than that of the other metabolites. In contrast, the 25(OH)D3 levels in the urine determined by the NLucVDR assay were more than 20-fold higher than those determined by a standard analytical method (LC-MS/MS), suggesting that some vitamin D metabolite(s) in the urine remarkably increased the luminescence intensity of the NLucVDR assay. Notably, the 25(OH)D3 concentration in the urine determined by the NLucVDR assay and the serum 25(OH)D3 concentration determined by standard analytical methods showed a significant positive correlation (r = 0.568). These results suggest that the analysis of a small amount of urine using the NLucVDR assay may be useful for predicting the serum 25(OH)D3 levels.

Covalent adduction of serotonin-derived quinones to the SARS-CoV-2 main protease expressed in a cultured cell

The SARS-CoV-2 main protease is an essential molecule for viral replication and is often targeted by medications to treat the infection. In this study, we investigated the possible inhibitory action of endogenous quinones on the enzyme. Recombinant SARS-CoV-2 main protease was exposed to tryptamine-4,5-dione (TD) or quinone from 5-hydroxyindoleacetic acid (Q5HIAA). As a result, the protease activity was considerably decreased in a dose-dependent manner. The IC50 values of the quinones toward the enzyme were approximately 0.28 μM (TD) and 0.49 μM (Q5HIAA). Blot analyses using specific antibodies to quinone-modified proteins revealed that quinones were adducted to the enzyme at concentrations as low as 0.12 μM. Intact mass analyses showed that one or two quinone molecules were covalently adducted onto the main protease. Chymotrypsin-digested main protease analyses revealed that the quinones bind to thiol residues at the enzyme's active site. When TD or Q5HIAA were exposed to cultured cells expressing the viral enzyme, quinone-modified enzyme was identified in the cell lysate, suggesting that even extracellularly generated quinones could react with the viral enzyme expressed in an infected cell. Thus, these endogenous quinones could act as inhibitors of the viral enzyme.

Effect of Oral Administration of Polyethylene Glycol 400 on Gut Microbiota Composition and Diet-Induced Obesity in Mice

Polyethylene glycol (PEG) is a commonly used dispersant for oral administration of hydrophobic agents. PEG is partly absorbed in the small intestine, and the unabsorbed fraction reaches the large intestine; thus, oral administration of PEG may impact the gut microbial community. However, to the best of our knowledge, no study evaluated the effects of PEG on gut commensal bacteria. Herein, we aimed to determine whether oral administration of PEG modifies the gut microbiota. Administration of PEG400 and PEG4000 altered gut microbial diversity in a concentration-dependent manner. Taxonomic analysis revealed that Akkermansia muciniphila and particularly Parabacteroides goldsteinii were overrepresented in mice administered with 40% PEG. PEG400 administration ameliorated the high-fat diet (HFD)-induced obesity and adipose tissue inflammation. Fecal microbiome transplantation from PEG400-administered donors counteracted the HFD-induced body and epididymal adipose tissue weight gain, indicating that PEG400-associated bacteria are responsible for the anti-obesity effect. Conversely, carboxymethyl cellulose, also used as a dispersant, did not affect the abundance of these two bacterial species or HFD-induced obesity. In conclusion, we demonstrated that oral administration of a high concentration of PEG400 (40%) alters the gut microbiota composition and ameliorates HFD-induced obesity.

Effect of Wheat-Derived Arabinoxylan on the Gut Microbiota Composition and Colonic Regulatory T Cells

The health benefits of wheat-derived arabinoxylan, a commonly consumed dietary fiber, have been studied for decades. However, its effect on the gut microenvironment and inflammatory bowel disease remains unclear. The objective of this study was to understand the effect of wheat-derived arabinoxylan on gut microbiota, colonic regulatory T cells (Tregs), and experimental colitis. In this study, healthy and chronic colitis model mice were fed chow containing cellulose or wheat-derived arabinoxylan for 2-6 weeks and subjected to subsequent analysis. A 16S-based metagenomic analysis of the fecal DNA revealed that Lachnospiraceae, comprising butyrate-producing and Treg-inducing bacteria, were overrepresented in arabinoxylan-fed mice. In line with the changes in the gut microbiota, both the fecal butyrate concentration and the colonic Treg population were elevated in the arabinoxylan-fed mice. In a T cell transfer model of chronic colitis, wheat-derived arabinoxylan ameliorated body weight loss and colonic tissue inflammation, which may, in part, be mediated by Treg induction. Moreover, wheat-derived arabinoxylan suppressed TNFα production from type 1 helper T cells in this colitis model. In conclusion, wheat-derived arabinoxylans, by altering the gut microenvironment, may be a promising prebiotic for the prevention of colitis.

Transfer of quercetin ingested by maternal mice to neonatal mice via breast milk

This is the first study that quantified quercetin (QUE) and its 16 metabolites in the breast milk of QUE-fed maternal mice, the plasma and urine of that, and neonatal mice. Interestingly, the QUE aglycone concentration in the milk was much higher than in the plasma of maternal mice, suggesting that QUE may exert biological activity in neonates.

Effects of common genetic variants of human uridine diphosphate glucuronosyltransferase subfamilies on irinotecan glucuronidation

The adverse effects (diarrhea and neutropenia) of irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin) are associated with genetic variants of uridine diphosphate glucuronosyltransferase 1A subfamilies (UGT1As). UGT1As are enzymes that metabolize the active form of irinotecan, 7-ethyl-10 hydroxycamptothecin (SN-38), by glucuronidation in the liver. They are widely known as predictive factors of severe adverse effects, such as neutropenia and diarrhea. Some studies have suggested that variants of UGT1As affect SN-38 glucuronidation activities, thus exerting severe adverse effects. We aimed to identify UGT1A isoforms that show SN-38 glucuronidation activity and determine the relationship between UGT1A variants and SN-38 glucuronidation in vitro. We found that UGT1A1 and UGT1A6-UGT1A10 displayed SN-38 glucuronidation activity. Among these, UGT1A1 was the most active. Furthermore, the variants of these isoforms showed decreased SN-38 glucuronidation activity. In our study, we compared the different variants of UGT1As, such as UGT1A1.6, UGT1A1.7, UGT1A1.27, UGT1A1.35, UGT1A7.3, UGT1A8.4, UGT1A10M59I, and UGT1A10T202I, to determine the differences in the reduction of glucuronidation. Our study elucidates the relationship between UGT1A variants and the level of glucuronidation associated with each variant. Therefore, testing can be done before the initiation of irinotecan treatment to predict potential toxicities and adverse effects.

Development of nanoluciferase-based sensing system that can specifically detect 1α,25-dihydroxyvitamin D in living cells

Previously, we reported a FLucN-LXXLL+LBD-FLucC system that detects VDR ligands using split firefly luciferase techniques, ligand binding domain (LBD) of VDR, and LXXLL sequences that interact with LBD after VDR ligand binding. In vivo, 25-hydroxyvitamin D₃ (25(OH)D₃) and 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃) act as VDR ligands that bind to VDR, and regulate bone-related gene expression. Therefore, the amount of 25(OH)D₃ and 1α,25(OH)₂D₃ are indicators of bone-related diseases such as rickets and osteoporosis. In this study, we have developed a novel LgBiT-LXXLL+LBD-SmBiT system using NanoLuc Binary Technology (NanoBiT), which has an emission intensity several times higher than that of the split-type firefly luciferase. Furthermore, by using genetic engineering techniques, we attempted to construct a novel system that can specifically detect 1α,25(OH)₂D₃. Because histidine residues at positions 305 and 397 play important roles in forming a hydrogen bond with a hydroxyl group at position C25 of 25(OH)D₃ and 1α,25(OH)₂D₃, His305 and His397 were each substituted by other amino acids. Consequently, the three mutant VDRs, H305D, H397N, and H397E were equally useful to detect 1α,25(OH)₂D₃ specifically. In addition, among the 58 variants of the LXXLL sequences, LPYEGSLLLKLLRAPVEE showed the greatest increase in luminescence upon the addition of 25(OH)D₃ or 1α,25(OH)₂D₃. Thus, our novel system using NanoBiT appear to be useful for detecting native vitamin D or its derivatives.

Augmentation of Pectoral Fin Teratogenicity by Thalidomide in Human Cytochrome P450 3A-Expressing Zebrafish

The pharmacological and toxicological effects of active metabolites of enzymes including cytochrome P450 (CYP) are important. While it has been believed for a long time that thalidomide causes characteristic limb malformation only in rabbits and primates including humans, the involvement of their CYP3A subtypes (CYP3As) has been suggested. Recently, however, it was reported that zebrafish were sensitive to thalidomide, showing defects of pectoral fins, homologous organs of forelimbs in mammals, as well as other deformities. In this study, we prepared human CYP3A7 (hCYP3A7)-expressing zebrafish (F0) using a transposon system. Thalidomide caused pectoral fin defects and other malformations including pericardial edema in hCYP3A7-expressing embryos/larvae but not in wild-type and hCYP1A1-expressing embryos/larvae. Thalidomide also reduced the expression of fibroblast growth factor 8 in pectoral fin buds in only hCYP3A7-expressing embryos/larvae. The results suggest the involvement of human-type CYP3A in thalidomide teratogenicity.

Functional analysis of vitamin D receptor (VDR) using adenovirus vector

Recently, we generated type II rickets model rats, including Vdr(R270L), Vdr(H301Q), Vdr(R270L/H301Q), and Vdr-knockout (KO), by genome editing. All generated animals showed symptoms of rickets, including growth retardation and abnormal bone formation. Among these, only Vdr-KO rats exhibited abnormal skin formation and alopecia. To elucidate the relationship between VDR function and rickets symptoms, each VDR was expressed in human HaCaT-VDR-KO cells using an adenovirus vector. We also constructed an adenovirus vector expressing VDR(V342M) corresponding to human VDR(V346M) which causes alopecia. We compared the nuclear translocation of VDRs after adding 1α,25-dihydroxyvitamin D3 (1,25D3) or 25-hydroxyvitamin D3 (25D3) at final concentrations of 10 and 100 nM, respectively. Both 25D3 and 1,25D3 induced the nuclear translocation of wild type VDR and VDR(V342M). Conversely, VDR(R270L) translocation was observed in the presence of 100 nM 25D3, with almost no translocation following treatment with 10 nM 1,25D3. VDR(R270L/H301Q) failed to undergo nuclear translocation. These results were consistent with their affinity for each ligand. Notably, VDR(R270L/H301Q) may exist in an unliganded form under physiological conditions, and factors interacting with VDR(R270L/H301Q) may be involved in the hair growth cycle. Thus, this novel system using an adenovirus vector could be valuable in elucidating vitamin D receptor functions.

Effect of soluble oat fiber on intestinal microenvironment and TNBS-induced colitis

Soluble oat fibers, including β-glucan, have been shown to alter the gut microbiome composition and ameliorate DSS-induced colitis; however, the beneficial effect of soluble oat fiber on colonic inflammation is not yet fully understood. In this study, we demonstrated that soluble oat fibers ameliorate T cell-dependent colitis through the induction of peripherally induced regulatory T cells (pTregs). Soluble oat fibers elevated colonic butyrate production dose-dependently, which coincided with the overrepresentation of Faecalibaculum rodentium (an analog of butyrate-producing Holdemanella biformis) in the gut microbiome. Soluble oat fibers promoted the growth of F. rodentium and H. biformis even in vitro, and increased the concentration of butyrate in the culture supernatant. These results indicate that soluble oat fibers are an energy source for butyrate-producing bacteria and are a fermentation substrate. Soluble oat fibers increased the percentage of colonic pTregs and ameliorated the weight loss and inflammation in acute 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis; this may in part be mediated by the increase in IL-10-producing T cells. In conclusion, our results suggest that the administration of soluble oat fibers is a promising prebiotic treatment for the prevention of colitis mediated via altered gut microbiota composition and elevated butyrate production.

Transgenic Zebrafish Expressing Rat Cytochrome P450 2E1 (CYP2E1): Augmentation of Acetaminophen-Induced Toxicity in the Liver and Retina

Metabolic activation is the primary cause of chemical toxicity including hepatotoxicity. Cytochrome P450 2E (CYP2E) is involved in this process for many hepatotoxicants, including acetaminophen (APAP), one of the most common analgesics and antipyretics. Although the zebrafish is now used as a model for toxicology and toxicity tests, the CYP2E homologue in zebrafish has not been identified yet. In this study, we prepared transgenic zebrafish embryos/larvae expressing rat CYP2E1 and enhanced green fluorescent protein (EGFP) using a β-actin promoter. Rat CYP2E1 activity was confirmed by the fluorescence of 7-hydroxycoumarin (7-HC), a metabolite of 7-methoxycoumarin that was specific for CYP2 in transgenic larvae with EGFP fluorescence (EGFP [+]) but not in transgenic larvae without EGFP fluorescence (EGFP [-]). APAP (2.5 mM) caused reduction in the size of the retina in EGFP [+] larvae but not in EGFP [-] larvae, while APAP similarly reduced pigmentation in both larvae. APAP at even 1 mM reduced the liver size in EGFP [+] larvae but not in EGFP [-] larvae. APAP-induced reduction of liver size was inhibited by N-acetylcysteine. These results suggest that rat CYP2E1 is involved in some APAP-induced toxicological endpoints in the retina and liver but not in melanogenesis of the developing zebrafish.

Robust osteogenic efficacy of 2α-heteroarylalkyl vitamin D analogue AH-1 in VDR (R270L) hereditary vitamin D-dependent rickets model rats

Active vitamin D form 1α,25-dihydroxtvitamin D₃ (1,25(OH)₂D₃) plays pivotal roles in calcium homeostasis and osteogenesis via its transcription regulation effect via binding to vitamin D receptor (VDR). Mutated VDR often causes hereditary vitamin D-dependent rickets (VDDR) type II, and patients with VDDR-II are hardly responsive to physiological doses of 1,25(OH)D₃. Current therapeutic approaches, including high doses of oral calcium and supraphysiologic doses of 1,25(OH)₂D_3, have limited success and fail to improve the quality of life of affected patients. Thus, various vitamin D analogues have been developed as therapeutic options. In our previous study, we generated genetically modified rats with mutated Vdr(R270L), an ortholog of human VDR(R274L) isolated from the patients with VDDR-II. The significant reduced affinity toward 1,25(OH)₂D₃ of rat Vdr(R270L) enabled us to evaluate biological activities of exogenous VDR ligand without 1α-hydroxy group such as 25(OH)D₃. In this study, 2α-[2-(tetrazol-2-yl)ethyl]-1α,25(OH)₂D₃ (AH-1) exerted much higher affinity for Vdr(R270L) in in vitro ligand binding assay than both 25(OH)D₃ and 1,25(OH)₂D₃. A robust osteogenic activity of AH-1 was observed in Vdr(R270L) rats. Only a 40-fold lower dose of AH-1 than that of 25(OH)D₃ was effective in ameliorating rickets symptoms in Vdr(R270L) rats. Therefore, AH-1 may be promising for the therapy of VDDR-II with VDR(R274L).

The Impact of Low-Viscosity Soluble Dietary Fibers on Intestinal Microenvironment and Experimental Colitis: A Possible Preventive Application of Alpha-Cyclodextrin in Intestinal Inflammation

SCOPE

The purpose of this study is to compare the impact of four low-viscosity soluble dietary fibers (DFs) on the intestinal microenvironment, in terms of microbiota composition, short-chain fatty acid (SCFA) production, proportion of colonic peripherally induced regulatory T cells (pTregs), and experimental colitis in mice.

METHODS AND RESULTS

Mice are administered 5% w/v low-viscosity soluble DFs in drinking water for 2 weeks. The gut microbiota composition is determined using 16S rRNA sequencing. Luminal SCFAs are quantified by gas chromatography, and colonic pTregs are analyzed using flow cytometry. All low-viscosity soluble DFs promote the growth of beneficial bacteria such as Akkermansia muciniphila and Bacteroides acidifaciens, while eliminating pathogenic bacteria such as Clostridium perfringens. Moreover, two low-viscosity soluble DFs significantly increase the abundance of commensal bacteria and promote the accumulation of propionate and butyrate, leading to marked induction of colonic pTregs. Consistently, these two fibers, in particular α-cyclodextrin, show remarkable anti-inflammatory properties in a colitis mouse model.

CONCLUSION

Mice administered any low-viscosity soluble DF show comparable gut microbiota compositions, but differ in terms of bacterial abundance, SCFA concentration, pTreg population, and colitis development. This exploratory study suggests that administration of α-cyclodextrin may be a possible strategy for the prevention of colitis.

Comparison of metabolism and biological properties among positional isomers of quercetin glucuronide in LPS- and RANKL-challenged RAW264.7 cells

The major quercetin metabolite, quercetin-3-glucuronide, exerts various biological activities, including anti-inflammatory effects. This study aimed to evaluate the metabolic profiles and biological properties of the positional isomers of quercetin monoglucuronides (Q3G, Q7G, Q3'G, and Q4'G) in activated macrophages. In addition to quercetin aglycone, Q7G was more cytotoxic than the other quercetin monoglucuronides (QGs), which corresponded to its lower stability under neutral pH conditions. Q3G was most effective in inhibiting both LPS-dependent induction of IL-6 and RANKL-dependent activation of tartrate-resistant acid phosphatase; however, Q3'G and Q4'G may also help exert biological activities without potential cytotoxicity. The deconjugation efficacy to generate quercetin aglycone differed among QGs, with the highest efficacy in Q3G. These results suggest that the chemical or biological properties and metabolic profiles may depend on the stability of QGs to generate quercetin aglycone using β-glucuronidase.

Isoliquiritigenin Attenuates Adipose Tissue Inflammation and Metabolic Syndrome by Modifying Gut Bacteria Composition in Mice

SCOPE

Isoliquiritigenin (ILG) has been reported to attenuate adipose tissue inflammation and metabolic disorder; however, the underlying mechanisms remain to be elucidated. The aim of this study is to elucidate whether ILG shows the anti-inflammatory and antimetabolic syndrome effects through gut microbiota modification.

METHODS AND RESULTS

Mice are fed a high-fat diet (HFD) with or without ILG for up to 12 weeks. The effect of ILG on body weight, blood glucose level, adipose tissue inflammation, gut barrier function, and gut microbiota composition are investigated. ILG supplementation alleviates HFD-induced obesity, glucose tolerance, and insulin resistance and suppresses inflammatory gene expression in epididymal white adipose tissue (eWAT). Moreover, ILG supplementation modifies gut bacterial composition by increasing the abundance of antimetabolic disease-associated species (e.g., Parabacteroides goldsteinii and Akkemansia muciniphila) and up-regulated genes associated with gut barrier function. Fecal microbiome transplantation (FMT) from ILG-fed donors counteract HFD-induced body and eWAT weight changes, inflammation-related gene expression, glucose tolerance, and insulin resistance, thereby suggesting that ILG-responsive gut bacteria exerts anti-inflammatory and antimetabolic syndrome effects.

CONCLUSION

Alterations in gut bacteria underly the beneficial effects of ILG against adipose tissue inflammation and metabolic disorders. ILG may be a promising prebiotic for the prevention and treatment of metabolic syndrome.

Comparison of the stability of CYP105A1 and its variants engineered for production of active forms of vitamin D

CYP105A1 from Streptomyces griseolus converts vitamin D3 to its biologically active form, 1α,25-dihydroxy vitamin D3. R73A/R84A mutation enhanced the 1α- and 25-hydroxylation activity for vitamin D3, while M239A mutation generated the 1α-hydroxylation activity for vitamin D2. In this study, the stability of six CYP105A1 enzymes, including 5 variants (R73A/R84A, M239A, R73A/R84A/M239A (=TriA), TriA/E90A, and TriA/E90D), was examined. Circular dichroism analysis revealed that M239A markedly reduces the enzyme stability. Protein fluorescence analysis disclosed that these mutations, especially M239A, induce large changes in the local conformation around Trp residues. Strong stabilizing effect of glycerol was observed. Nondenaturing PAGE analysis showed that CYP105A1 enzymes are prone to self-association. Fluorescence analysis using a hydrophobic probe 8-anilino-1-naphthalenesulfonic acid suggested that M239A mutation enhances self-association and that E90A and E90D mutations, in cooperation with M239A, accelerate self-association with little effect on the stability.

Heteroconjugates of quercetin with 4'-O-sulfate selectively accumulate in rat plasma due to limited urinary excretion

Quercetin and methylquercetin are present in a variety of sulfate and glucuronide conjugates in the plasma of quercetin-fed rats and humans. Quercetin conjugates exhibit various physiological activities, depending on the type and position of conjugation. However, little is known regarding the type and position of isomers of quercetin conjugates in the plasma, their accumulation in the liver and kidneys, and their excretion via urine. Using authentic standards of quercetin conjugates and liquid chromatography-tandem mass spectrometry (LC/MS/MS) analysis, we identified and quantified various quercetin conjugates in blood plasma, urine, liver, and kidney tissues 1, 4, and 10 h after orally administering 33.1 μmol kg^-1 quercetin glucosides to rats. The profiles of quercetin conjugates were largely different among plasma, urine, liver, and kidneys. Very limited heteroconjugates (7-O-glucuronide-4'-O-sulfate) of quercetin and methylquercetin dominated in the plasma, but these heteroconjugates were much less excreted via urine and did not largely accumulate in the liver and kidneys. Heteroconjugates constituting sulfates other than 4' position sulfate, 7-O-glucuronide-3'-O-sulfate, 4'-O-glucuronide-7-O-sulfate, and 3'-O-glucuronide-7-O-sulfate were major metabolites in urine, but were minimally detected in the plasma. We also found that mono-sulfate conjugates were abundant in the liver and renal tissues. These results suggest that excretion of quercetin conjugates, especially heteroconjugates, into urine is highly selective. The heteroconjugates with 4'-O-sulfate may be scarcely excreted via urine, and thus accumulate in the blood plasma. Further research is necessary to evaluate the physiological effects of heteroconjugates accumulated in the plasma.

Food phytochemicals, epigallocatechin gallate and myricetin, covalently bind to the active site of the coronavirus main protease in vitro

SARS-CoV-2 main protease is a possible target for protection against viral infection. This study examined the inhibitory effect of food phytochemicals on the main protease of SARS-CoV-2 by determining a cleaved product after chromatographic separation. First, 37 phytochemicals, including glycosides and metabolites, were screened at 20 µM; epigallocatechin gallate, myricetin, theaflavin, herbacetin, piceatannol, myricitrin, and isothiocyanates inhibited the enzyme in varying degrees. The IC₅₀ values were estimated from 0.4 to 33.3 µM against the 0.5-µM enzyme. The dose-dependent adduction of epigallocatechin gallate and myricetin was confirmed by quinone staining of protein blotted onto a membrane. The enzyme activity was decreased by increasing the concentration of the two phytochemicals, accompanied by increasing the respective adducted molecule estimated by intact mass spectrometry. Reduced glutathione canceled the formation of conjugate and the inhibitory effect of epigallocatechin gallate or myricetin on the enzyme, suggesting that the formation of the quinone moiety in the phytochemicals is critical for the inhibition. The covalent binding of epigallocatechin gallate or myricetin to the cysteine residue at the active site was confirmed by analyzing peptides from the chymotrypsin-digested main protease.

Development of In Vitro and In Vivo Evaluation Systems for Vitamin D Derivatives and Their Application to Drug Discovery

We have developed an in vitro system to easily examine the affinity for vitamin D receptor (VDR) and CYP24A1-mediated metabolism as two methods of assessing vitamin D derivatives. Vitamin D derivatives with high VDR affinity and resistance to CYP24A1-mediated metabolism could be good therapeutic agents. This system can effectively select vitamin D derivatives with these useful properties. We have also developed an in vivo system including a Cyp27b1-gene-deficient rat (a type I rickets model), a Vdr-gene-deficient rat (a type II rickets model), and a rat with a mutant Vdr (R270L) (another type II rickets model) using a genome editing method. For Cyp27b1-gene-deficient and Vdr mutant (R270L) rats, amelioration of rickets symptoms can be used as an index of the efficacy of vitamin D derivatives. Vdr-gene-deficient rats can be used to assess the activities of vitamin D derivatives specialized for actions not mediated by VDR. One of our original vitamin D derivatives, which displays high affinity VDR binding and resistance to CYP24A1-dependent metabolism, has shown good therapeutic effects in Vdr (R270L) rats, although further analysis is needed.

Elucidation of metabolic pathways of 25-hydroxyvitamin D3 mediated by CYP24A1 and CYP3A using Cyp24a1 knockout rats generated by CRISPR/Cas9 system

CYP24A1-deficient (Cyp24a1 KO) rats were generated using the CRISPER/Cas9 system to investigate CYP24A1-dependent or -independent metabolism of 25(OH)D3, the prohormone of calcitriol. Plasma 25(OH)D3 concentrations in Cyp24a1 KO rats were approximately twofold higher than in wild-type rats. Wild-type rats showed five metabolites of 25(OH)D3 in plasma following oral administration of 25(OH)D3, and these metabolites were not detected in Cyp24a1 KO rats. Among these metabolites, 25(OH)D3-26,23-lactone was identified as the second major metabolite with a significantly higher T_max value than others. When 23S,25(OH)₂D3 was administered to Cyp24a1 KO rats, neither 23,25,26(OH)₃D3 nor 25(OH)D3-26,23-lactone was observed. However, when 23S,25R,26(OH)₃D3 was administered to Cyp24a1 KO rats, plasma 25(OH)D3-26,23-lactone was detected. These results suggested that CYP24A1 is responsible for the conversion of 25(OH)D3 to 23,25,26(OH)₃D3 via 23,25(OH)₂D3, but enzyme(s) other than CYP24A1 may be involved in the conversion of 23,25,26(OH)₃D3 to 25(OH)D3-26,23-lactone. Enzymatic studies using recombinant human CYP species and the inhibitory effects of ketoconazole suggested that CYP3A plays an essential role in the conversion of 23,25,26(OH)₃D3 into 25(OH)D3-26,23-lactone in both rats and humans. Taken together, our data indicate that Cyp24a1 KO rats are valuable for metabolic studies of vitamin D and its analogs. In addition, long-term administration of 25(OH)D3 to Cyp24a1 KO rats at 110 μg/kg body weight/day resulted in significant weight loss and ectopic calcification. Thus, Cyp24a1 KO rats could represent an important model for studying renal diseases originating from CYP24A1 dysfunction.

Genetic variants of UDP-glucuronosyltransferases 1A1, 1A6, and 1A9 in cynomolgus and rhesus macaques

1. In the cynomolgus macaque, UDP-glucuronosyltransferases (UGTs) 1As have similar molecular and enzymatic characteristics to those of their human orthologs. However, genetic polymorphisms in major cynomolgus UGT1A1/6/9 have not been investigated. 2. We re-sequenced UGT1A1, UGT1A6, and UGT1A9 in 186 cynomolgus macaques (bred in Cambodia, China, or Indonesia) and 54 rhesus macaques and found 15, 13, and 26 non-synonymous variants, respectively. 3. Of these UGT1A1, UGT1A6, and UGT1A9 variants, respectively, 10, 9, and 12 were unique to cynomolgus macaques; 4, 1, and 2 were unique to rhesus macaques; and 1, 2, and 5 were found in both cynomolgus and rhesus macaques. The frequency of the UGT1A1 mutation G69R was 23%, 28%, and 63% in cynomolgus macaques bred in Cambodia, China, and Indonesia, respectively, and 97% in rhesus macaques. 4. The O-glucuronidation activities of liver microsomes from cynomolgus and rhesus macaques with respect to estradiol, serotonin, and propofol were measured. Among these activities, liver microsomes from cynomolgus macaques heterozygous for UGT1A1 G69R (n = 11) showed significantly reduced estradiol 3-O-glucuronidation activities compared with those from wild-type animals (n = 38). 5. These results suggest genetic variants such as UGT1A1 G69R could influence the UGT1A1-mediated glucuronidation of drugs in cynomolgus and rhesus macaques.

Identification and in silico prediction of metabolites of tebufenozide derivatives by major human cytochrome P450 isoforms

Cytochrome P450 (CYP) enzymes constitute a superfamily of heme-containing monooxygenases. CYPs are involved in the metabolism of many chemicals such as drugs and agrochemicals. Therefore, examining the metabolic reactions by each CYP isoform is important to elucidate their substrate recognition mechanisms. The clarification of these mechanisms may be useful not only for the development of new drugs and agrochemicals, but also for risk assessment of chemicals. In our previous study, we identified the metabolites of tebufenozide, an insect growth regulator, formed by two human CYP isoforms: CYP3A4 and CYP2C19. The accessibility of each site of tebufenozide to the reaction center of CYP enzymes and the susceptibility of each hydrogen atom for metabolism by CYP enzymes were evaluated by a docking simulation and hydrogen atom abstraction energy estimation at the density functional theory level, respectively. In this study, the same in silico prediction method was applied to the metabolites of tebufenozide derivatives by major human CYPs (CYP1A2, 2C9, 2C19, 2D6, and 3A4). In addition, the production rate of the metabolites by CYP3A4 was quantitively analyzed by frequency based on docking simulation and hydrogen atom abstraction energy using the classical QSAR approach. Then, the obtained QSAR model was applied to predict the sites of metabolism and the metabolite production order by each CYP isoform.

Whole-cell dependent biosynthesis of N- and S-oxides using human flavin containing monooxygenases expressing budding yeast

Flavin containing monooxygenases (FMOs) represent one of the predominant types of phase I drug metabolizing enzymes (DMEs), and thus play an important role in the metabolism of xeno- and endobiotics for the generation of their corresponding oxides. These oxides often display biological activities, however they are difficult to study since their chemical or biological synthesis is generally challenging even though only small amounts are required to evaluate their efficacy and safety. Previously, we constructed a DME expression system for cytochrome P450, UDP-glucuronosyltransferase (UGT), and sulfotransferase (SULT) using yeast cells, and successfully produced xenobiotic metabolites in a whole-cell dependent manner. In this study, we developed a heterologous expression system for human FMOs, including FMO1-FMO5, in Saccharomyces cerevisiae and examined its N- and S-oxide productivity. The recombinant yeast cells expressed each of the FMO successfully, and the FMO4 transformant produced N- and S-oxide metabolites at several milligrams per liter within 24 h. This whole-cell dependent biosynthesis enabled the production of N- and S-oxides without the use of the expensive cofactor NADPH. Such novel yeast expression system could be a powerful tool for the production of oxide metabolites.

Generation of novel genetically modified rats to reveal the molecular mechanisms of vitamin D actions

Recent studies have suggested that vitamin D activities involve vitamin D receptor (VDR)-dependent and VDR-independent effects of 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) and 25-hydroxyvitamin D₃ (25(OH)D₃) and ligand-independent effects of the VDR. Here, we describe a novel in vivo system using genetically modified rats deficient in the Cyp27b1 or Vdr genes. Type II rickets model rats with a mutant Vdr (R270L), which recognizes 1,25(OH)₂D₃ with an affinity equivalent to that for 25(OH)D₃, were also generated. Although Cyp27b1-knockout (KO), Vdr-KO, and Vdr (R270L) rats each showed rickets symptoms, including abnormal bone formation, they were significantly different from each other. Administration of 25(OH)D₃ reversed rickets symptoms in Cyp27b1-KO and Vdr (R270L) rats. Interestingly, 1,25(OH)₂D₃ was synthesized in Cyp27b1-KO rats, probably by Cyp27a1. In contrast, the effects of 25(OH)D₃ on Vdr (R270L) rats strongly suggested a direct action of 25(OH)D₃ via VDR-genomic pathways. These results convincingly suggest the usefulness of our in vivo system.

Molecular characterization of functional UDP-glucuronosyltransferases 1A and 2B in common marmosets

UDP-glucuronosyltransferases (UGTs) are essential drug-conjugation enzymes that metabolize a variety of endobiotic and xenobiotic substrates. The molecular characteristics of UGTs have been extensively investigated in humans, but remain to be investigated in common marmosets, a nonhuman primate species widely used in drug metabolism studies. In this study, 11 UGT cDNAs (UGT1A1, 1A3, 1A4, 1A6, 1A7, and 1A9; and UGT2B49, 2B50, 2B51, 2B52, and 2B53) were isolated and characterized in marmosets. Marmoset UGT1As had high sequence identities (89-93%) with human UGT1As, but the sequence identities of marmoset UGT2Bs were lower (82-86%). Marmoset UGTs were found to be phylogenetically close to human UGTs. Just as human UGT1As do, marmoset UGT1A genes shared exons 2-5 and contained a variable exon 1 unique to each gene; in contrast, marmoset UGT2B genes contained six unique exons. Moreover, marmoset and human UGT1A and UGT2B gene clusters were located in corresponding regions in their respective genomes. Among the five tissue types tested, marmoset UGT mRNAs were most abundantly expressed in liver, jejunum, and/or kidney, i.e., in tissues important for drug metabolism, just as human UGTs are. Among the 11 marmoset UGT mRNAs investigated, marmoset UGT1A9, 1A4, and 1A6 mRNAs were the most abundantly expressed in liver, small intestine, and kidney, respectively. Marmoset liver microsomes and recombinant UGT1A proteins catalyzed the glucuronidation of the same substrates that human UGT1As catalyze, including estradiol, trifluoperazine, 4-methylumbelliferone, serotonin, 4-nitrophenol, and propofol. Trifluoperazine was glucuronidated by marmoset liver microsomes, but not by any of the UGT1A isoforms examined under the present conditions. These results collectively suggest that functional marmoset UGTs have generally similar molecular characteristics to human UGTs.

Dynamics of the Cellular Metabolism of Leptosperin Found in Manuka Honey

Leptosperin (methyl syringate β-d-gentiobioside) is abundantly found in manuka honey, which is widely used because of its antibacterial and possible anti-inflammatory activities. The aim of this study was to examine the molecular mechanism underlying the metabolism of leptosperin. Five phytochemicals (leptosperin, methyl syringate (MSYR), glucuronate conjugate of MSYR (MSYR-GA), sulfonate conjugate of MSYR (MSYR-S), and syringic acid (SYR)) were separately incubated with HepG2 and Caco-2 cells. After incubation, we found that the concentration of MSYR decreased, whereas the concentrations of SYR, MSYR-GA, and MSYR-S increased. By profiling with inhibitors and carboxylesterases (CES1, 2), we found that the conversion from MSYR to SYR was mediated by CES1. Lipopolysaccharide-stimulated RAW264.7 cells restored MSYR-GA to MSYR possibly by the secreted β-glucuronidase. All of the mice administered with leptosperin, MSYR, or manuka honey showed higher MSYR (13.84 ± 11.51, 14.29 ± 9.19, or 6.66 ± 2.30 nM) and SYR (1.85 ± 0.66, 6.01 ± 1.20, or 8.16 ± 3.10 nM) levels in the plasma compared with that of the vehicle controls (3.33 ± 1.45 (MSYR) and 1.85 ± 0.66 (SYR) nM). The findings of our study indicate that the unique metabolic pathways of these compounds may account for possible functionalities of manuka honey.

Comprehensive Analyses of Quercetin Conjugates by LC/MS/MS Revealed That Isorhamnetin-7- O-glucuronide-4'- O-sulfate Is a Major Metabolite in Plasma of Rats Fed with Quercetin Glucosides

Quercetin glycosides in the diet are absorbed and converted to glucuronides, sulfates, or mixed conjugates of glucuronide and sulfate in plasma. Physiological effects of quercetin conjugates (Q-conjugates) differ depending on the type and position of conjugation. We developed a comprehensive analysis of Q-conjugates, including mixed conjugates, by LC/MS/MS. The whole species of Q-conjugates in tail blood plasma was measured on days 1, 3, and 12 in rats fed a 0.24% quercetin glucoside-containing diet. Twenty-three Q-conjugate molecules were detected, and 16 Q-conjugates among these were quantified using standard compounds. The most abundant metabolite in the plasma was mixed conjugates, comprising isorhamnetin-7- O-glucuronide-4'- O-sulfate, followed by quercetin-7- O-glucuronide-4'- O-sulfate; together, they accounted for 86% of total Q-conjugates on day 12. The profile of quercetin conjugate species did not significantly change during 12 days. The total Q-conjugate molecules quantified by our method was comparable with the total Q-conjugates quantified using an enzymatic deconjugation method.

Functional and molecular characterization of UDP-glucuronosyltransferase 2 family in cynomolgus macaques

UDP-glucuronosyltransferases (UGTs) are essential enzymes metabolizing endogenous and exogenous chemicals. However, characteristics of UGTs have not been fully investigated in molecular levels of cynomolgus macaques, one of non-human primates widely used in preclinical drug metabolism studies. In this study, three UGT2A cDNAs (UGT2A1, 2A2, and 2A3) were isolated and characterized along with seven UGT2Bs previously identified in cynomolgus macaques. Several transcript variants were found in cynomolgus UGT2A1 and UGT2A2, like human orthologs. Cynomolgus UGT2A and UGT2B amino acid sequences were highly identical (87-96%) to their human counterparts. By phylogenetic analysis, all these cynomolgus UGT2s were more closely clustered with their human homologs than with dog, rat, or mouse UGT2s. Especially, UGT2As showed orthologous relationships between humans and cynomolgus macaques. All the cynomolgus UGT2 mRNAs were expressed in livers, jejunum, and/or kidneys abundantly, except that UGT2A1 and UGT2A2 mRNAs were predominantly expressed in nasal mucosa, like human UGT2s. UGT2A and UGT2B genes together form a gene cluster in the cynomolgus and human genome. Among the seven cynomolgus UGT2Bs heterologously expressed in yeast, UGT2B9 and UGT2B30 showed activities in estradiol 17-O-glucuronidation and morphine 3-O-glucuronidation but did not show activities in estradiol 3-O-glucuronidation, similar to human UGT2Bs. In liver microsomes, cynomolgus macaques showed higher estradiol 17-O-glucuronidase and morphine 3-O-glucuronidase activities than humans, suggesting functional activities of the responsible UGT2B enzymes in cynomolgus macaques. Therefore, cynomolgus UGT2s had overall molecular similarities to human UGT2s, but also showed some differences in UGT2B enzyme properties.

Generation of 1,25-dihydroxyvitamin D3 in Cyp27b1 knockout mice by treatment with 25-hydroxyvitamin D3 rescued their rachitic phenotypes

We have reported that 25-hydroxyvitamin D₃ [25(OH)D₃] binds to vitamin D receptor and exhibits several biological functions directly in vitro. To evaluate the direct effect of 25(OH)D₃ in vivo, we used Cyp27b1 knockout (KO) mice, which had no detectable plasma 1α,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] when fed a diet containing normal Ca and vitamin D. Daily treatment with 25(OH)D₃ at 250 μg kg^-1 day^-1 rescued rachitic phenotypes in the Cyp27b1 KO mice. Bone mineral density, female sexual cycles, and plasma levels of Ca, P, and PTH were all normalized following 25(OH)D₃ administration. An elevated Cyp24a1 mRNA expression was observed in the kidneys, and plasma concentrations of Cyp24a1-dependent metabolites of 25(OH)D₃ were increased. To our surprise, 1,25(OH)₂D₃ was detected at a normal level in the plasma of Cyp27b1 KO mice. The F1 to F4 generations of Cyp27b1 KO mice fed 25(OH)D₃ showed normal growth, normal plasma levels of Ca, P, and parathyroid hormone, and normal bone mineral density. The curative effect of 25(OH)D₃ was considered to depend on the de novo synthesis of 1,25(OH)₂D₃ in the Cyp27b1 KO mice. This suggests that another enzyme than Cyp27b1 is present for the 1,25(OH)₂D₃ synthesis. Interestingly, the liver mitochondrial fraction prepared from Cyp27b1 KO mice converted 25(OH)D₃ to 1,25(OH)₂D₃. The most probable candidate is Cyp27a1. Our findings suggest that 25(OH)D₃ may be useful for the treatment and prevention of osteoporosis for patients with chronic kidney disease.

Novel biosensor using split-luciferase for detecting vitamin D receptor ligands based on the interaction between vitamin D receptor and coactivator

Vitamin D receptor (VDR) ligands, such as 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃] and its analogs, have been investigated for their potential clinical use in the treatment of various diseases such as type I rickets, osteoporosis, psoriasis, leukemia, and cancer. Previously, we reported a split-luciferase-based biosensor that can detect VDR ligands and assess their affinity for the ligand binding domain (LBD) of the VDR in a short time. However, a further increase in its sensitivity was required to detect plasma levels of 1α,25(OH)₂D₃ and its analogs. In this study, a novel type of biosensor called LXXLL + LBD was successfully developed. Here, the split luciferase forms a functional complex based on the intermolecular interaction between the LXXLL motif and the ligand-bound form of the LBD. This biosensor has an approximately 10-fold increase in the light intensity compared to the previous versions. Additionally, the binding affinity of the vitamin D analogs for the wild-type and the rickets-associated mutant R274L of VDR was evaluated.

Novel split luciferase-based biosensors for evaluation of vitamin D receptor ligands and their application to estimate CYP27B1 activity in living cells

Recently, we successfully generated a novel detection system for vitamin D receptor (VDR) ligands in vivo and in vitro, using a split-luciferase technique called the LucN-LBD-LucC biosensor that is a chimeric fusion protein of firefly luciferase with the ligand binding domain (LBD) of VDR. In this system, the luciferase light intensity of the LucN-LBD-LucC biosensor was decreased by binding of VDR ligands. Although this system is quite useful for evaluation of VDR ligands in a short time, the sensitivity of the LucN-LBD-LucC biosensor is not high enough. In this study, LXXLL motif peptides involved in the interaction between LBD and coactivators, such as the steroid receptor coactivator-1 (SRC-1), transcriptional intermediary factor 2 (TIF2), and the vitamin D receptor interacting protein 205 (DRIP205) were each inserted between LucN and LBD of the LucN-LBD-LucC biosensor. Surprisingly, the resulting LucN-LXXLL-LBD-LucC biosensor increased the light intensity in response to natural VDR ligands. This high-sensitivity biosensor system may be a powerful tool for discovery of high-affinity ligands for the mutant VDR. In addition, we have successfully estimated the activity of the wild-type and mutant CYP27B1 using the LucN-LXXLL-LBD-LucC biosensor in living cells within 90 min.

Simultaneous collection of the portal and superior vena cava blood in conscious rats defined that intestinal epithelium is the major site of glucuronidation, but not sulfation and methylation, of quercetin

Quercetin is a flavonoid with many physiological effects. Absorbed quercetin is rapidly conjugated in the intestinal epithelium and liver. Different positional isomers of quercetin conjugates have different physiological properties. However, the mechanisms of quercetin conjugation in the intestine are not fully clarified. We examined the regioselective quercetin conjugate formation in the intestine after oral administration of quercetin glycosides, by simultaneous sampling of blood from the portal vein and superior vena cava, and quantifying various positional isomers of quercetin glucuronides and sulfates in conscious rats. Concentrations of quercetin glucuronides were higher in blood from the portal vein than the superior vena cava, showing that glucuronidation mainly occurred in the intestine. Such differences were not observed for quercetin sulfates. Regioselectivity of the intestinal glucuronidation in quercetin hydroxyl groups were 7- >3'- >3- >4'-OH. Quercetin was mainly sulfated on 3'-OH at 30 min, but on 4'-OH at 240 min.

Limited expression of functional cytochrome p450 2c subtypes in the liver and small intestine of domestic cats

1. Compared to information for herbivores and omnivores, knowledge on xenobiotic metabolism in carnivores is limited. The cytochrome P450 2C (CYP2C) subfamily is recognized as one of the most important CYP groups in human and dog. We identified and characterized CYP2C isoforms and variants in cat, which is an obligate carnivore. 2. Quantitative RT-PCR and immunoblot analyses were carried out to evaluate the expression of CYP2C in the liver and small intestine. A functional CYP2C isoform was heterologously expressed in yeast microsomes to determine the enzymatic activity. 3. Cat had two CYP2C genes, 21 and 41, in the genome; however, CYP2C21P was a pseudogene that had many stop codons. Three splicing variants of CYP2C41 were identified (v1-v3), but only one of them (v1) showed a complete deduced amino acid sequence as CYP2C protein. Transcripts of feline CYP2C41v1 were detected but the amounts were negligible or very small in the liver and small intestine. Immunoreactivity to an antihuman CYP2C antibody was confirmed in the recombinant feline CYP2C41v1 but not in the feline liver. 4. Recombinant feline CYP2C41v1 metabolized several substrates, including dibenzylfluorescein that is specific to human CYP2C. 5. The results suggest a limited role of functional CYP2C isoforms in xenobiotic metabolism in cat.

Metabolism of 2α-[2-(tetrazol-2-yl)ethyl]-1α,25-dihydroxyvitamin D3 by CYP24A1 and biological activity of its 24R-hydroxylated metabolite

Our previous study revealed that the 2α-substituted vitamin D analog 2α-[2-(tetrazol-2-yl)ethyl]-1α,25(OH)₂D₃ (AH-1) exhibited a higher osteocalcin promoter transactivation activity in human osteosarcoma cells and a greater effect on bone mineral density in a rat model of osteoporosis than 1α,25(OH)₂D₃　without increasing blood calcium concentration. Thus, we hypothesized that AH-1 could be a promising therapeutic agent for osteoporosis without any serious side effects. In this study, we compared the CYP24A1-dependent metabolism of AH-1 with that of 1α,25(OH)₂D₃. The resistance to CYP24A1-dependent metabolism could be an important property of vitamin D analogs in prolonging their biological effects. A kinetic analysis was performed using a membrane fraction prepared from recombinant E. coli expressing human CYP24A1. The k_cat/K_m (μM^-1 min^-1) value for AH-1 was 31% of that for 1α,25(OH)₂D₃, suggesting that AH-1 is not as resistant to CYP24A1-dependent metabolism as the other C2-substituted vitamin D analogs such as eldecalcitol [2β-hydroxypropoxy-1α,25(OH)₂D₃]. The major metabolite of AH-1 was the 24R-hydroxylated metabolite, which had high vitamin D receptor (VDR) binding affinity and high HL-60 cell differentiation activity similar to AH-1 itself. In contrast, 1α,25(OH)₂D₃ was metabolized by multistep monooxygenation reactions, which led to the loss of affinity for VDR. Thus, the greater therapeutic effects of AH-1 than those of 1α,25(OH)₂D₃ in in vivo studies using osteoporosis rat models may be due to 24R-hydroxy-AH-1 whose VDR affinity was 91% of that of AH-1.

Development of a highly sensitive in vitro system to detect and discriminate between vitamin D receptor agonists and antagonists based on split-luciferase technique

Split-luciferase techniques are widely used to detect protein-protein interaction and bioactive small molecules including some hormones and vitamins. Previously, we successfully expressed chimeric proteins of luciferase and the ligand binding domain (LBD) of the vitamin D receptor (VDR), LucC-LBD-LucN in COS-7 cells. The LucC-LBD-LucN biosensor was named split-luciferase vitamin D biosensor (SLDB). This biosensor can detect and discriminate between VDR agonists and antagonists in mammalian cells. In this study, we established an in vitro screening system for VDR ligands using the SLDB proteins expressed in Escherichia coli (E. coli) cells. Our in vitro screening system using cell lysate of recombinant E. coli cells could be completed within 30min, and its activity was unchanged after 10 freeze-thaw cycles. This highly sensitive and convenient system would be quite useful to screen VDR ligands with therapeutic potential for various bone-related diseases, age-related cognitive disorders, cancer, and immune disorders. In addition, our system might be applicable to diagnostic measurement of serum concentrations of 25-hydroxyvitamin D₃ and 1α,25-dihydroxyvitamin D₃.

[Metabolism of Sesamin and Drug-Sesamin Interaction]

　Sesamin, derived from sesame seeds, is known to have various biological effects. Since some of these effects appear to be derived from its metabolites, the elucidation of sesamin metabolism is essential to understanding the molecular mechanism of its effects. In addition, it is important to clarify drug-sesamin interactions in order to address safety concerns, as some food factors are known to affect drug metabolism. Our previous studies revealed that sesamin was sequentially metabolized by cytochrome P450 (CYP) and UDP-glucuronosyltransferase or sulfotransferase. Whereas sesamin metabolism is mainly mediated by CYP2C9 in human liver, sesamin causes a mechanism-based inhibition (MBI) of CYP2C9. However, we found that the metabolite-intermediate complex between CYP2C9 and sesamin was unstable, and the effects of sesamin appeared to be minimal. To confirm this assumption, in vivo studies using rats were conducted. After the administration of sesamin to rats for 3 d, diclofenac (an NSAID) was administered to measure the time course of plasma concentration of diclofenac. No significant differences were observed in the diclofenac C_max, T_max, and AUC_{0-24 h} between the group that was administered sesamin and the group that was not. Based on these results, it could be concluded that no significant interaction occurs in people who take sesamin supplements at a standard dose.

Whole-cell-dependent biosynthesis of sulfo-conjugate using human sulfotransferase expressing budding yeast

Cytosolic sulfotransferases (SULTs), one of the predominant phase II drug metabolizing enzymes (DME), play important roles in metabolism of xeno- and endobiotics to generate their sulfo-conjugates. These sulfo-conjugates often have biological activities but are difficult to study, because even though only small amounts are required to evaluate their efficacy and safety, chemical or biological synthesis of sulfo-conjugatesis is often challenging. Previously, we constructed a DME expression system for cytochrome P450 and UGT, using yeast cells, and successfully produced xenobiotic metabolites in a whole-cell-dependent manner. In this study, we developed a yeast expression system for human SULTs, including SULT1A1, 1A3, 1B1, 1C4, 1E1, and 2A1, in Saccharomyces cerevisiae and examined its sulfo-conjugate productivity. The recombinant yeast cells expressing each of the SULTs successfully produced several hundred milligram per liter of xeno- or endobioticsulfo-conjugates within 6 h. This whole-cell-dependent biosynthesis enabled us to produce sulfo-conjugates without the use of 3'-phosphoadenosine-5'-phosphosulfate, an expensive cofactor. Additionally, the production of regiospecific sulfo-conjugates of several polyphenols was possible with this method, making this novel yeast expression system a powerful tool for uncovering the metabolic pathways and biological actions of sulfo-conjugates.

S-Equol Activates cAMP Signaling at the Plasma Membrane of INS-1 Pancreatic β-Cells and Protects against Streptozotocin-Induced Hyperglycemia by Increasing β-Cell Function in Male Mice

Background:S-equol, which is enantioselectively produced from daidzein by gut microbiota, has been suggested as a chemopreventive agent against type 2 diabetes mellitus (T2DM), but the underlying mechanisms remain unclear.Objective: We investigated the effects of S-equol on pancreatic β-cell function.Methods: β-Cell growth and insulin secretion were evaluated with male Institute of Cancer Research mice and isolated pancreatic islets from the mice, respectively. The mechanisms by which S-equol stimulated β-cell response were examined in INS-1 β-cells. The effect of S-equol treatment on β-cell function was assessed in low-dose streptozotocin-treated mice. S-equol was used at 10 μmol/L for in vitro and ex vivo studies and was administered by oral gavage (20 mg/kg, 2 times/d throughout the experimental period) for in vivo studies.Results:S-equol administration for 7 d increased Ki67-positive β-cells by 27% (P < 0.01) in mice. S-equol enantioselectively enhanced glucose-stimulated insulin secretion in mouse pancreatic islets by 41% (P < 0.001). In INS-1 cells, S-equol exerted stronger effects than daidzein on cell growth, insulin secretion, and cAMP-response element (CRE)-mediated transcription. These S-equol effects were diminished by inhibiting protein kinase A. The effective concentration of S-equol for stimulating cAMP production at the plasma membrane was lower than that for phosphodiesterase inhibition. S-equol-stimulated CRE activation was negatively controlled by the knockdown of G-protein α subunit group S (stimulatory) and positively controlled by that of G-protein-coupled receptor kinase-3 and -6. Compared with vehicle-treated controls, S-equol gavage treatment resulted in an increase in β-cell mass of 104% (P < 0.05), a trend toward high plasma insulin concentrations (by 118%; P = 0.06), and resistance to hyperglycemia after streptozotocin treatment (78% of AUC after glucose challenge; P < 0.01). S-equol administration significantly increased the number of Ki67-positive proliferating β-cells by 62% (P < 0.01) and decreased that of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive apoptotic β-cells by 75% (P < 0.05).Conclusions: Our results show that S-equol boosts β-cell function and prevents hypoglycemia in mice, suggesting its potential for T2DM prevention.

Protein engineering of CYP105s for their industrial uses

Cytochrome P450 enzymes belonging to the CYP105 family are predominantly found in bacteria belonging to the phylum Actinobacteria and the order Actinomycetales. In this review, we focused on the protein engineering of P450s belonging to the CYP105 family for industrial use. Two Arg substitutions to Ala of CYP105A1 enhanced its vitamin D₃ 25- and 1α-hydroxylation activities by 400 and 100-fold, respectively. The coupling efficiency between product formation and NADPH oxidation was largely improved by the R84A mutation. The quintuple mutant Q87W/T115A/H132L/R194W/G294D of CYP105AB3 showed a 20-fold higher activity than the wild-type enzyme. Amino acids at positions 87 and 191 were located at the substrate entrance channel, and that at position 294 was located close to the heme group. Semi-rational engineering of CYP105A3 selected the best performing mutant, T85F/T119S/V194N/N363Y, for producing pravastatin. The T119S and N363Y mutations synergistically had remarkable effects on the interaction between CYP105A3 and putidaredoxin. Although wild-type CYP105AS1 hydroxylated compactin to 6-epi-pravastatin, the quintuple mutant I95T/Q127R/A180V/L236I/A265N converted almost all compactin to pravastatin. Five amino acid substitutions by two rounds of mutagenesis almost completely changed the stereo-selectivity of CYP105AS1. These results strongly suggest that the protein engineering of CYP105 enzymes greatly increase their industrial utility. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.