Baicalein: an in vitro antigenotoxic compound from Scutellaria baicalensis

Acacia catechu (L.f.) Willd.: A Review on Bioactive Compounds and Their Health Promoting Functionalities

With the advent of pandemics and infectious diseases, numerous research activities on natural products have been carried out to combat them. Researchers are investigating natural products for the treatment and/or management of various infectious diseases and/or disorders. Acacia catechu (L.f.) Willd. belongs to the family Fabaceae (subfamily Mimosoideae) known as Khair or Cutch tree, possesses diverse pharmacological actions, and has been widely used in Asia and different parts of the world. The purpose of the present study is to highlight the phytochemical profile of different parts of A. catechu, the different biological activities of A. catechu extract, and the utilization of A. catechu as food and beverage. The present work constitutes a review of A. catechu; we performed searches (books, Google, Google Scholar, and Scopus publications) to compile the work/investigations made on A. catechu to the present. From our survey, it was concluded that the main phytochemicals compounds in A. catechu are protocatechuic acid, taxifolin, epicatechin, epigallocatechin, catechin, epicatechin gallate, procyanidin, phloroglucin, aldobiuronic acid, gallic acid, D-galactose, afzelchin gum, L-arabinose, D-rhamnose, and quercetin. The whole plant of A. catechu possesses a comprehensive variety of medicinal potentials such as antimicrobial, antidiarrheal, antinociceptive, antihyperlipidemic, antiulcer, antioxidant, antidiabetic, antiproliferative, haemolytic, and anti-inflammatory properties due to the presence of bioactive compounds like flavonoids, alkaloids, and tannins. However, even though the plant's metabolites were reported to have many different pharmacological uses, there is limited information about their toxicity or clinical trials. Further research on diverse metabolites of A. catechu should be carried out to ensure the safety or utilization of this plant in the pharma or food industries and in the development of potent plant-based drugs.

Baicalein Promotes Angiogenesis and Odontoblastic Differentiation via the BMP and Wnt Pathways in Human Dental Pulp Cells

Baicalein is an active flavonoid extracted from the root of Scutellaria baicalensis that has anticancer and anti-inflammatory properties; its effects on osteoblastic and angiogenic potential are controversial. The aim of this study was to investigate the effects of baicalein on odontoblastic differentiation and angiogenesis and the underlying mechanism in human dental pulp cells (HDPCs). Baicalein (1–10[Formula: see text][Formula: see text]M) had no cytotoxic effects and promoted alkaline phosphatase (ALP) activity, mineralization assayed by Alizarin Red-S staining, and the mRNA expression of marker genes, in a concentration-dependent manner. In addition, baicalein upregulated angiogenic factors and increased in vitro capillary-like tube formation. Moreover, baicalein upregulated bone morphogenetic protein (BMP)-2 mRNA and phosphorylation of Smad 1/5/8 and Wnt ligand mRNA, glycogen synthase kinase-3, and nuclear [Formula: see text]-catenin. The odontogenic and angiogenic effects of baicalein were abolished by the BMP antagonist noggin and the Wnt/[Formula: see text]-catenin receptor antagonist DKK-1. These results demonstrate that baicalein promoted odontoblastic differentiation and angiogenesis of HDPCs by activating the BMP and Wnt/[Formula: see text]-catenin signal pathways. Our findings suggest that baicalein may contribute to dental pulp repair and regenerative endodontics.

Regulation of bone formation by baicalein via the mTORC1 pathway

Osteoporosis is a systemic skeletal disease that is characterized by low bone density and microarchitectural deterioration of bone tissue. The increasing prevalence of osteoporosis has attracted much attention. In this study, MC3T3-E1 pre-osteoblasts were treated with the natural compound, baicalein (0.1 μmol/L, 1 μmol/L, 10 μmol/L), to stimulate differentiation over a 14-day period. In addition, a canonical ovariectomized (OVX) mouse model was used to investigate the effect of 3-month baicalein treatment (10 mg/kg per day) in preventing postmenopausal osteoporosis. In vitro, we found that baicalein induced activation of alkaline phosphatase, stimulated the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, and induced expression of osteoblast differentiation markers, ie, osteocalcin, osterix, collagen Iα1, and runt-related transcription factor 2 (RUNX2), in osteoblasts. In vivo, several bone parameters, including trabecular thickness, trabecular bone mineral density, and trabecular number, in the distal femoral metaphysis were significantly increased in OVX mice treated intragastrically with baicalein for 3 months compared with OVX mice that were not treated with baicalein. We also found that expression of osteocalcin and RUNX2 was decreased in primary ossified tissue from the OVX group, and baicalein increased the levels of osteocalcin and RUNX2 in OVX mice. These data suggest that baicalein can stimulate MC3T3-E1 cells to differentiate into osteoblasts via activation of the mTORC1 signaling pathway, which includes protein kinases and transcription factors such as P-4E/BP1 and P-S6K1.

Biological evaluation and molecular docking of baicalin and scutellarin as Helicobacter pylori urease inhibitors

ETHNOPHARMACOLOGICAL RELEVANCE

Baicalin and scutellarin are the principal bioactive components of Scutellaria baicalensis Georgi which has extensively been incorporated into heat-clearing and detoxification formulas for the treatment of Helicobacter pylori-related gastrointestinal disorders in traditional Chinese medicine. However, the mechanism of action remained to be defined.

AIM OF THE STUDY

To explore the inhibitory effect, kinetics and mechanism of Helicobacter pylori urease (the vital pathogenetic factor for Helicobacter pylori infection) inhibition by baicalin and scutellarin, for their therapeutic potential.

MATERIALS AND METHODS

The ammonia formations, indicator of urease activity, were examined using modified spectrophotometric Berthelot (phenol-hypochlorite) method. The inhibitory effect of baicalin and scutellarin was characterized with IC50 values, compared to acetohydroxamic acid (AHA), a well known Helicobacter pylori urease inhibitor. Lineweaver-Burk and Dixon plots for the Helicobacter pylori urease inhibition of baicalin and scutellarin was constructed from the kinetic data. SH-blocking reagents and competitive active site Ni(2+) binding inhibitors were employed for mechanism study. Molecular docking technique was used to provide some information on binding conformations as well as confirm the inhibition mode. Moreover, cytotoxicity experiment using Gastric Epithelial Cells (GES-1) was evaluated.

RESULTS

Baicalin and scutellarin effectively suppressed Helicobacter pylori urease in dose-dependent and time-independent manner with IC50 of 0.82±0.07 mM and 0.47±0.04 mM, respectively, compared to AHA (IC50=0.14±0.05 mM). Structure-activity relationship disclosed 4'-hydroxyl gave flavones an advantage to binding with Helicobacter pylori urease. Kinetic analysis revealed that the types of inhibition were non-competitive and reversible with inhibition constant Ki of 0.14±0.01 mM and 0.18±0.02 mM for baicalin and scutellarin, respectively. The mechanism of urease inhibition was considered to be blockage of the SH groups of Helicobacter pylori urease, since thiol reagents (L,D-dithiothreitol, L-cysteine and glutathione) abolished the inhibitory action and competitive active site Ni(2+) binding inhibitors (boric acid and sodium fluoride) carried invalid effect. Molecular docking study further supported the structure-activity analysis and indicated that baicalin and scutellarin interacted with the key residues Cys321 located on the mobile flap through S-H·π interaction, but did not interact with active site Ni(2+). Moreover, Baicalin (at 0.59-1.05 mM concentrations) and scutellarin (at 0.23-0.71 mM concentrations) did not exhibit significant cytotoxicity to GES-1.

CONCLUSIONS

Baicalin and scutellarin were non-competitive inhibitors targeting sulfhydryl groups especially Cys321 around the active site of Helicobacter pylori urease, representing potential to be good candidate for future research as urease inhibitor for treatment of Helicobacter pylori infection. Furthermore, our work gave additional scientific support to the use of Scutellaria baicalensis in traditional Chinese medicine (TCM) to treat gastrointestinal disorders.

Acupuncture can improve absorption of baicalin from extracts of Scutellaria baicalensis Georgi in rats

The aim of this research was to explore whether acupuncture could improve the absorption of baicalin from extracts of Scutellaria baicalensis Georgi in normal rats. Twenty male Sprague-Dawley (SD) rats were divided randomly into two groups. Group A was treated with a combination of oral administration of Scutellaria baicalensis Georgi extracts and acupuncture. Group B was treated only with oral administration of Scutellaria baicalensis Georgi extracts, in the same dosage as Group A. After treatment, the plasma concentration of baicalin was detected and pharmacokinetic analysis was conducted using high performance liquid chromatography (HPLC). The results showed that the plasma concentration of baicalin in Group A was significantly higher than in Group B, and that acupuncture at the acupoints Jizhong (Du6), Dazhui (Du14) and Zhongwan (Ren12) made the plasma concentration-time course of baicalin produce a bimodal phenomenon, increased the area under the curve (AUC) and slowed the elimination of baicalin, thus significantly improving the absorption of baicalin from extracts of Scutellaria baicalensis Georgi in rats.

Inhibitory effects of Baicalin on ultraviolet B-induced photo-damage in keratinocyte cell line

Baicalin, one kind of Chinese herbal medicine with anti-inflammatory and anti-oxidant property, has been commonly used as a clinical medicine. However, little has been known about the effects of Baicalin on ultraviolet (UV) induced photo-aging and photo-carcinogenesis. The photoproduct is critical to the initial event of UV-induced photo-carcinogenesis. The purpose of the present study was to investigate whether Baicalin, in immortalized human keratinocyte HaCaT cells, could inhibit ultraviolet-B (UVB) induced skin damage and its possible underlying mechanisms, such as inhibiting UVB-induced cytotoxicity and apoptosis, cyclobutane pyrimidine dimers (CPDs), down-regulating the expression of regulatory proteins which are related to cell apoptosis and DNA damage/repair. Our study revealed that Baicalin treatment could inhibit the UVB-induced cytotoxicity, apoptosis and CPD level. It also decreased the mRNA expression of apoptosis-regulatory genes (p53-p21 and c-fos), the protein levels of p53, proliferating cell nuclear antigen (PCNA) and repair protein A (RPA), and the secretion of cytokines [interleukin(IL)-6 and tumor necrosis factor (TNF-alpha)]. These results suggested that Baicalin may have an inhibitory effect on the UVB-induced photo-damage by blocking the relevant cytokine secretion and expression of p53-p21, c-fos, PCNA and RPA genes.

Baicalein stimulates osteoblast differentiation via coordinating activation of MAP kinases and transcription factors

The identification of anabolic agents that directly stimulate bone formation has recently attracted greater interest. Here, baicalein was identified as a natural compound that stimulates the differentiation of mouse osteoblastic MC3T3-E1 subclone 4 cells. Baicalein induced the activation of NF-kappaB in the initiation stage of osteoblast differentiation, and it activated the MAP kinase/NF-kappaB signaling pathway and induced the expression of osteoblast differentiation markers in the early stage. In the late stage, baicalein stimulated the calcium deposition with the activation of MAP kinases and AP-1 family members such as Fra-1 and Fra-2. Another transcription factor, NFATc1, was slightly induced by baicalein in the late stage. Thus, baicalein could stimulate the osteoblast differentiation via the activation of complexly coordinated signaling pathways that include MAP kinases and transcription factors such as NF-kappaB, AP-1, and NFATc1.

Baicalein inhibits osteoclast differentiation and induces mature osteoclast apoptosis

In bone remodeling, an imbalance caused by increased bone resorption over bone formation leads to adult skeletal diseases such as osteoporosis. Therefore, the development of anti-resorptive agents has still gained more interest. In this study, using cell-based assay systems in RAW264.7 murine macrophage cells, we found that baicalein significantly inhibited the receptor activator of NF-kappaB ligand (RANKL)-induced tartrate-resistance acid phosphatase (TRAP) activity and the formation of multinucleated osteoclasts in a dose-dependent manner. Interestingly, baicalein inhibited RANKL-induced activation of signaling molecules (Akt, ERK/MAP kinase and NF-kappaB) and mRNA expression of osteoclast-associated genes (TRAP, matrix metalloproteinase 9 and c-Src) and another transcription factors (c-Fos, Fra-2 and NFATc1). In addition, baicalein inhibited the bone resorptive activity of mature osteoclasts by inducing apoptosis. The inhibitory effects of baicalein on the formation of mouse bone marrow macrophage-derived osteoclasts and their bone resorptive activity were also observed. In conclusion, although further studies are needed to determine its biological efficacy and precise mechanism in bone, the present results demonstrated that baicalein has a potential to inhibit osteoclast differentiation and induce mature osteoclast apoptosis.

Study on the interaction mechanism between DNA and the main active components in Scutellaria baicalensis Georgi

Binding of baicalein, wogonin and baicalin to fish sperm DNA was studied by using ethidium bromide dye as a fluorescence probe. To study the binding mechanism, the absorption, fluorescence, melting temperature and viscosity measurement were carried out. The experimental results indicated that the planar of flavonoids intercalated to the DNA helix. When bound to DNA, flavonoids showed hyperchromic and blue shift in the absorption spectra and fluorescence quenching (>50%) in the fluorescence spectra. Furthermore, the intercalative binding was consistent with the red shift in the position of λ _max in the fluorescence spectra. It was also found that ionic strength had little or no effect on the binding of flavonoids and DNA. Stern-Volmer plots at 25 and 37 °C showed that the quenching of fluorescence by flavonoids was a combined quenching process. The binding site number n, apparent binding constant K _A at 25 and 37 °C, and the corresponding thermodynamic parameters ΔG, ΔH, ΔS at 25 °C were obtained. The interaction of flavonoid-metal complexes with DNA was also studied by spectral methods, and the results suggested that the complexes intercalated into DNA.

A medicinal extract of Scutellaria baicalensis and Acacia catechu acts as a dual inhibitor of cyclooxygenase and 5-lipoxygenase to reduce inflammation

A mixed extract containing two naturally occurring flavonoids, baicalin from Scutellaria baicalensis and catechin from Acacia catechu, was tested for cyclooxygenase (COX) and 5-lipoxygenase (5-LOX) inhibition via enzyme, cellular, and in vivo models. The 50% inhibitory concentration for inhibition of both ovine COX-1 and COX-2 peroxidase enzyme activities was 15 microg/mL, while the mixed extract showed a value for potato 5-LOX enzyme activity of 25 microg/mL. Prostaglandin E2 generation was inhibited by the mixed extract in human osteosarcoma cells expressing COX-2, while leukotriene production was inhibited in both human cell lines, immortalized THP-1 monocyte and HT-29 colorectal adenocarcinoma. In an arachidonic acid-induced mouse ear swelling model, the extract decreased edema in a dose-dependent manner. When arachidonic acid was injected directly into the intra-articular space of mouse ankle joints, the mixed extract abated the swelling and restored function in a rotary drum walking model. These results suggest that this natural, flavonoid mixture acts via "dual inhibition" of COX and LOX enzymes to reduce production of pro-inflammatory eicosanoids and attenuate edema in an in vivo model of inflammation.

Pharmacokinetics of baicalein, baicalin and wogonin after oral administration of a standardized extract ofScutellaria baicalensis, PF-2405 in rats

The pharmacokinetics of active components such as baicalein, wogonin and oroxylin A were evaluated after oral administration of a purified extract of Scutellaria baicalensis GEORGI (PF-2405) containing the high contents of baicalein, wogonin and oroxylin A to rats. Following oral administration of PF-2405 at 10, 20 and 40 mg/kg dose (equivalent to 4.5, 9.0 and 18 mg/kg baicalein), a major constituent baicalein and its active metabolite baicalin showed dose-linear pharmacokinetics as evidenced by unaltered dose-normalized AUC, dose-normalized Cmax, Ae(0-30h) and GI(30h) values. Following oral administration of PF-2405 at three doses (equivalent to 0.4, 0.8 and 1.6 mg/kg wogonin), dose-normalized Cmax and dose-normalized AUC were comparable between the 20 and 40 mg/kg PF2405 doses, but plasma concentrations of wogonin at 10 mg/kg of PF-2405 were not measurable as they were below limit of quantitation (LOQ; 18 pmol/mL). Following oral administration of PF-2405 at the three doses (equivalent to 1.5, 3.0 and 6.0 mg/kg oroxylin A), the concentrations of oroxylin A in plasma, urine and gastrointestine samples were below the assay LOQ (18 pmol/mL). Significant differences in AUCs, Ae(0-30h) and GI(30h) values for baicalein and baicalin were observed after oral administration of pure baicalein (18 mg/kg) and PF-2405 (40 mg/kg). The increases in AUCs of baicalein and baicalin after oral administration of PF-2405 may have been due to the significant decrease in GO(30h) values for baicalein.

Liquid chromatography with tandem mass spectrometry for the simultaneous determination of baicalein, baicalin, oroxylin A and wogonin in rat plasma

A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for the determination of baicalein, baicalin, oroxylin A and wogonin, Scutellaria baicalensis active components in rat plasma was developed. After liquid-liquid extraction with 2-(3,4-dimethoxy-phenyl)-5,7-dihydroxy-chromen-4-one as internal standard, baicalein, baicalin, oroxylin A and wogonin were eluted from an Atlantis C(18) column within 7 min with isocratic mobile phase consisting of methanol and 0.1% formic acid (60:40, v/v). The analytes were detected using an electrospray ionization tandem mass spectrometry in the multiple reaction monitoring (MRM) mode. The standard curves were linear (r=1.000) over the concentration ranges of 5-500 ng/ml for baicalein, wogonin and oroxylin A and 5-5000 ng/ml for baicalin. The coefficients of variation and relative errors of baicalein, wogonin, oroxylin A and baicalin for intra- and inter-assay at three or four quality control (QC) levels were 0.8-6.1% and -4.0 to 5.8%, respectively. The lower limits of quantification for baicalein, wogonin, oroxylin A and baicalin were 5ng/ml using 50 microl of plasma sample. This method was successfully applied to the pharmacokinetic study of baicalein, baicalin, wogonin and oroxylin A after an intravenous administration of Scutellariae radix extract to male Sprague-Dawley rats.

Role of Intestinal First-Pass Metabolism of Baicalein in its Absorption Process

PURPOSE

The aim of the present study was to investigate the role of intestinal first-pass metabolism of baicalein (B) in its absorption process.

METHODS

The intestinal absorption of B was characterized using Caco-2 cell monolayer model and rat in situ single-pass intestinal perfusion model. In addition, preliminary metabolic kinetics of B was evaluated in both rat and human intestinal S9 fractions.

RESULTS

B was well absorbed and extensively metabolized to baicalin (BG), baicalein-7-O-beta-glucuronide, in rat intestinal perfusion model, whereas less extent of metabolism was observed in the Caco-2 cell monolayer model. Moreover, BG generated in the intestinal epithelium during the absorption of B also rapidly transported to both the apical side (the apical chamber of Caco-2 model and the perfusate of the intestinal perfusion model) as well as the basolateral side of the small intestine (the basal chamber of Caco-2 model and the mesenteric vein of the intestinal perfusion model). From the preliminary metabolic studies, it was found that a higher loading dose of B resulted in a less extent of metabolism in intestine. In addition, the extent of metabolism of B was similar in jejunum and ileum when 50 microM of B was perfused through different sections of rat small intestine.

CONCLUSION

The first-pass metabolism of B in small intestine may play an important role in its low oral bioavailability.

Aqueous extract of herba Scutellaria barbatae, a chinese herb used for ovarian cancer, induces apoptosis of ovarian cancer cell lines

OBJECTIVES

Given the increasingly common use of complementary medicine in cancer patients, we tested the in vitro cytotoxicity of aqueous extracts of 15 traditional Chinese herbs with purported anticancer properties on ovarian and breast cancer cell lines.

METHODS

Cell viability after treatment with herbal extract was measured by metabolism of a tetrazolium substrate. Apoptosis was measured by nuclear and DNA fragmentation and Annexin V binding.

RESULTS

One herb, Herba Scutellaria barbatae, was cytotoxic to 100% (11 of 11) of actively proliferating ovarian lines tested and 50% (2 of 4) of actively proliferating breast cell lines tested. Confluent cultures were resistant to killing by herb, whereas subconfluent cultures were sensitive. Resistant proliferating cell lines expressed higher levels of bcl2. Transfection of the most sensitive ovarian cancer cell line (A2780) with bcl2 resulted in a noticeable protection against apoptosis, but there was no protection in other transfected lines.

CONCLUSIONS

These results will be useful in guiding future studies of herbal aqueous extracts, as well as providing information for clinicians when patients are concurrently using these herbs along with conventional cancer therapies.

Genetic toxicity of a standardized mixture of citrus polymethoxylated flavones

Flavonoids are a ubiquitous family of phytochemicals that display a variety of biological effects, both beneficial and adverse depending on the individual compound. Certain flavonoids are genotoxic while others inhibit the genotoxicity of other mutagens. In the present studies, the mutagenicity of a mixture of polymethoxylated flavones (PMFs) purified from citrus peel oil was evaluated. The mixture consisted of nobiletin (32.5%), 3,3',4',5,6,7,8-heptamethoxyflavone (25.0%), tangeretin (14.0%), trimethylscutellarein (9.1%), sinensetin (3.9%), 5-demethyl-nobiletin (2.8%), hexa-O-methylquercetagetin (3.3%), 5-demethyl-tetramethylscutellarein (0.7%), 5-hydroxy-3,3',4',6,7,8-hexamethoxyflavone (0.7%), and a small quantity of unidentified flavonoid compounds (3.9%). In vitro addition of the PMF mixture over a concentration range that spanned four log doses (0.0005-5.0 mg/plate) did not reveal any evidence of mutagenicity in five bacterial tester strains (Salmonella typhimurium TA98, TA100, TA102, TA1535 and TA1537) either in the absence or presence of S9 activation. The PMF mixture exhibited a statistically significant increase in mutagenicity of L5178Y tk(+/-) mouse lymphoma cells at 0.05 (38.5 x 10(-6); P<0.05) and 0.1 mg/ml (61 x 10(-6); P<0.01) compared with vehicle-treated controls (mutation frequency=19.7 x 10(-6)). However, these responses were within historical values observed in negative control cultures and extremely small compared to the positive control (EMS 0.5 microl/ml; 1685.3 x 10(-6)). Furthermore, in the presence of S9 there was no indication of genetic toxicity in L5178Y tk(+/-) cells. These results demonstrate that the PMF mixture is not genotoxic in in vitro assay systems.

Protective effects of baicalein and wogonin against benzo[a]pyrene- and aflatoxin B(1)-induced genotoxicities

To evaluate the protective effects of baicalein and wogonin against benzo[a]pyrene- and aflatoxin (AF) B(1)-induced toxicities, the effects of these flavonoids on the genotoxicities and oxidation of benzo[a]pyrene and AFB(1) were studied in C57BL/6J mice. Baicalein and wogonin reduced benzo[a]pyrene and AFB(1) genotoxicities as monitored by the umuC gene expression response in Salmonella typhimurium TA1535/pSK1002. Baicalein added in vitro decreased liver microsomal benzo[a]pyrene hydroxylation (AHH) activity with an ic(50) of 33.9 +/- 1.4 microM at 100 microM benzo[a]pyrene. Baicalein also inhibited AFQ(1) and AFB(1)-epoxide formation from AFB(1) (50 microM) oxidation (AFO) with ic(50) values of 22.8 +/- 1.4 and 5.3 +/- 0.8 microM, respectively. However, the in vitro inhibitory effects of wogonin on AHH and AFO activities in liver microsomes were less than those of baicalein as inhibition by 500 microM wogonin was only about 51-65%. Treatment of mice with liquid diets containing 5 mM baicalein and wogonin resulted in 22 and 49% decreases in hepatic AHH activities, respectively. Baicalein treatment resulted in 39 and 32% decreases in AFQ(1) and AFB(1)-epoxide formation from liver microsomal AFO, respectively. Wogonin treatment resulted in 39 and 47% decreases in AFQ(1) and AFB(1)-epoxide formation, respectively. A 1-week pretreatment with wogonin significantly decreased hepatic DNA adduct formation in mice treated with 200 mg/kg of benzo[a]pyrene via gastrogavage. These in vitro and in vivo effects suggested that baicalein and wogonin might have beneficial effects against benzo[a]pyrene- and AFB(1)-induced hepatic toxicities and that wogonin had a stronger protective effect in vivo.

Antimutagenic activity against trp-P-1 of the edible Thai plant, Oroxylum indicum vent

A methanolic extract of Oroxylum indicum strongly inhibited the mutagenicity of Trp-P-1 in an Ames test. The major antimutagenic constituent was identified as baicalein with an IC50 value of 2.78+/-0.15 microM. The potent antimutagenicity of the extract was correlated with the high content (3.95+/-0.43%, dry weight) of baicalein. Baicalein acted as a desmutagen since it inhibited the N-hydroxylation of Trp-P-2.