Highlights of the 14th Japan Bioanalysis Forum Symposium.

The 14th Japan Bioanalysis Forum Symposium was held at Tower Hall Funabori, Japan from 1-3 March 2023. The conference theme, 'Bringing Together - the Expertise of Bioanalysis', aimed to enable people from various fields to gather, learn and collaborate together for the common goal of delivering medicines to patients faster. Approximately 360 participants from various fields, including pharmaceutical industries, contractors, academia and regulatory authorities, gathered at an in-person symposium which had an online participation option, for the first time in 4 years. The symposium offered a wide range of topics including ICH M10, new modalities, biomarkers, immunogenicity, electronization and patient-centric sampling. The latest research results were provided from domestic and overseas scientists. This report summarizes the major topics.

Nationwide Database Analysis of Risk Factors Associated with Decreased Activities of Daily Living in Patients with Alzheimer's Disease.

BACKGROUND: Preserving activities of daily living (ADL) is the key issue for Alzheimer's disease (AD) patients and their caregivers. OBJECTIVE: To clarify the ADL level of AD patients at diagnosis and the risk factors associated with decreased ADL during long-term care (≤3 years). METHODS: Medical records of AD patients in a Japanese health insurance claims database were analyzed retrospectively to determine ADL using the Barthel Index (BI) and identify the risk factors associated with decreased ADL. RESULTS: A total of 16,799 AD patients (mean age at diagnosis: 83.6 years, 61.5% female) were analyzed. Female patients were older (84.6 versus 81.9 years; p < 0.001) and had lower BI (46.8 versus 57.6; p < 0.001) and body mass index (BMI) (21.0 versus 21.7 kg/m2; p < 0.001) than male patients at diagnosis. Disability (BI≤60) increased at age≥80 years and was significantly higher in females. Complete disability was most frequent for bathing and grooming. Risk factors for decreased ADL were determined separately by sex through comparing the ADL-preserved and ADL-decreased groups using propensity score matching by age and BI and multivariable logistic regression analysis. In males, decreased ADL was significantly associated with BMI < 21.5 kg/m2, stroke, and hip fracture, and inversely associated with hyperlipidemia. In females, decreased ADL was significantly associated with BMI < 21.5 kg/m2 and vertebral and hip fractures, and inversely associated with lower back pain. CONCLUSION: AD patients with low BMI, stroke, and fractures had increased risks of decreased ADL; such patients should be identified early and managed appropriately, including rehabilitation to preserve ADL.

Pharmacological Profile of Difamilast, a Novel Selective Phosphodiesterase 4 Inhibitor, for Topical Treatment of Atopic Dermatitis.

PDE4 inhibitors are expected to be anti-inflammatory agents based on their mechanism of action, but the application of this drug class is limited by a narrow therapeutic window due to adverse effects associated with gastrointestinal function. Difamilast, a novel selective phosphodiesterase 4 (PDE4) inhibitor, demonstrated significant efficacy without adverse reactions such as nausea and diarrhea in patients with atopic dermatitis (AD) and was recently approved in Japan. In this study, we investigated the pharmacological and pharmacokinetic properties of difamilast to provide nonclinical data to help understand the clinical effects. Difamilast selectively inhibited recombinant human PDE4 activity in assays. The IC50 of difamilast against PDE4B, a PDE4 subtype that plays an important role in the inflammatory response, was 0.0112 µM, representing a 6.6-fold decrease compared with the IC50 against PDE4D (0.0738 µM), a subtype that can trigger emesis. Difamilast inhibited TNF-α production in human (IC50 = 0.0109 µM) and mouse (IC50 = 0.0035 µM) peripheral blood mononuclear cells and improved skin inflammation in a mouse model of chronic allergic contact dermatitis. These effects of difamilast on TNF-α production and dermatitis were superior to those of other topical PDE4 inhibitors: CP-80633, cipamfylline, and crisaborole. In pharmacokinetic studies using miniature pigs and rats, the concentrations of difamilast in the blood and brain after topical application were not sufficient to support pharmacological activity. This nonclinical study contributes to explain the efficacy and safety of difamilast with a sufficient therapeutic window in the clinical trials. SIGNIFICANCE STATEMENT: This is the first report on the nonclinical pharmacological profile of difamilast ointment, a novel topical PDE4 inhibitor that demonstrated utility in clinical trials in patients with atopic dermatitis. Difamilast, which has high PDE4 selectivity (especially for the PDE4B subtype), ameliorated chronic allergic contact dermatitis in mice after topical application, with a pharmacokinetic profile in animals that suggests few systemic side effects; thus, difamilast is a promising new therapeutic treatment for atopic dermatitis.

Nationwide database analysis of insomnia, depression, and sleeping pill prescriptions in hepatocellular carcinoma patients.

OBJECTIVE: To clarify the status of insomnia and depression and the prescription of sleeping pills in hepatocellular carcinoma (HCC) patients before and after HCC diagnosis and treatment. METHODS: Patients' data from a Japanese health insurance claims database were analyzed retrospectively to determine the incidence of insomnia and depression and their association with sleeping pill prescriptions during the 6 months before and after HCC diagnosis and treatment. RESULTS: A total of 9,109 HCC patients (median age at diagnosis = 71.5 years, 68.1% male) were analyzed. The incidences of insomnia and depression increased significantly after HCC diagnosis. Insomnia was reported in 15.0% of patients before diagnosis, and it increased to 27.6% after diagnosis. Similarly, depression was reported in 6.3% and 11.3% before and after diagnosis, respectively. The incidences of insomnia and depression before diagnosis were higher in patients with concomitant liver diseases including hepatitis, cirrhosis, and hepatic encephalopathy. However, the rate of sleeping pill prescription was significantly lower in patients with concomitant liver diseases after diagnosis. The incidence of fracture was higher in insomnia or depression patients than others and in patients treated with sleeping pills than without before and after diagnosis. CONCLUSIONS: HCC patients had increased risks of insomnia and depression after diagnosis. The high risk of fracture in HCC patients with insomnia and depression and treated with sleeping pills suggests that it is difficult to optimize the management of HCC patients, especially those with concomitant liver diseases.

A deep learning algorithm for sleep stage scoring in mice based on a multimodal network with fine-tuning technique.

Sleep stage scoring is important to determine sleep structure in preclinical and clinical research. The aim of this study was to develop an automatic sleep stage classification system for mice with a new deep neural network algorithm. For the purpose of base feature extraction, wake-sleep and rapid eye movement (REM) and non- rapid eye movement (NREM) models were developed by extracting defining features from mouse-derived electromyogram (EMG) and electroencephalogram (EEG) signals, respectively. The wake-sleep model and REM-NREM sleep model were integrated into three different algorithms including a rule-based integration approach, an ensemble stacking approach, and a multimodal with fine-tuning approach. The deep learning algorithm assessing sleep stages in animal experiments by the multimodal with fine-tuning approach showed high potential for increasing accuracy in sleep stage scoring in mice and promoting sleep research.

Real-world database analysis of the characteristics and treatment patterns of patients with endometrial cancer in Japan.

OBJECTIVE: The aim was to identify the characteristics and treatment patterns of early and advanced stage endometrial cancer patients using real-world data. METHODS: Patients' data extracted from a Japanese health insurance claims database were analyzed. RESULTS: Of the 12,449 endometrial cancer patients, 74.4% were in stage I, 5.1% in stage II, 12.0% in stage III, and 8.4% in stage IV. Their median age was 60.5 years, higher in advanced stages (III/IV) than in early stages (I/II). Overall, 11,055 patients (88.8%) underwent surgery, and 4977 patients (40.0%) received post-surgery treatment, including chemotherapy (4441: 35.7%), chemoradiation therapy (379: 3.0%), and radiation therapy (157 patients: 1.3%); 1394 patients (11.2%) were not treated by surgery, and 742 patients (6.0%) received other treatment, with chemotherapy (548: 4.4%), radiation therapy (105: 0.8%), and chemoradiation therapy (89: 0.7%). The rate of patients undergoing surgery decreased, and that receiving chemotherapy increased significantly as cancer stage progressed. Paclitaxel/carboplatin was the most frequent first-line regimen (85.4% of patients), whereas various combination and monotherapy regimens were used as second- and third-line regimens. The most frequent second-line monotherapy was paclitaxel. The rate of monotherapy increased as the treatment line progressed (first-line 3.5%, second-line 22.0%, and third-line 36.4%). CONCLUSIONS: The characteristics and treatment patterns of endometrial cancer patients differed between early and advanced stages, as did the chemotherapy regimens among first-, second-, and third-lines. Since various regimens were used for second- and third-line chemotherapies, development of appropriate second- and third-line chemotherapy regimens is warranted. A real-world analysis of cancer patients using a nationwide claims database may be a valuable approach to identifying unmet medical needs.

[Preclinical and clinical efficacy of orexin receptor antagonist Lemborexant (Dayvigo®) on insomnia patients].

Orexin receptor antagonists have been approved for insomnia, and the insomnia pharmacotherapy is being greatly progressed. Orexin is a neuropeptide produced in the lateral hypothalamic area, and its physiological role has been suggested to be a key mediator controlling the sleep-wake state. Orexin receptor antagonists are thought to induce physiological sleep by acting specifically on the sleep-wake cycle. Lemborexant is a dual antagonist acting on both two orexin receptors, the orexin 1 (OX1R) and 2 receptor (OX2R), with stronger inhibitory effects on OX2R. Since it binds to and dissociates from orexin receptors rapidly, the pharmacokinetics of its blood concentration may have an impact on its pharmacological action. In rats, lemborexant exhibited a sleep-inducing effect without altering sleep architecture. In the phase III studies in patients with insomnia, lemborexant significantly improved difficulties in falling asleep and maintaining sleep. While somnolence occurred as treatment-related adverse events in a dose-dependent manner, lemborexant was generally well-tolerated. Also, the effects on body sway and driving skills 8-9 hours after administration did not differ from those in the placebo group, suggesting little next morning residual effects. Subgroup analysis has shown that efficacy and safety of lemborexant were similar in patients with insomnia with comorbidities, suggesting lemborexant may also be useful for those patients. Based on the above results and others, lemborexant has been approved for the indication of insomnia in January 2020 in Japan. Lemborexant will give a new treatment option for patients with insomnia.

Pharmacokinetics and metabolism of brexpiprazole, a novel serotonin-dopamine activity modulator and its main metabolite in rat, monkey and human.

The pharmacokinetics of brexpiprazole were investigated in the in vitro and in vivo.The total body clearance of brexpiprazole in rat and monkey was 2.32 and 0.326 L/h/kg, respectively, after intravenous administration, and oral availability was 13.6% and 31.0%, respectively. Dose-dependent exposures were observed at dose ranges between 1-30 mg/kg in the rat and 0.1-3 mg/kg in the monkey.Brexpiprazole distributed widely to body tissues, and Vd,z were 2.81 and 1.82 L/kg in rat and monkey, respectively. The serum protein binding of brexpiprazole was 99% or more in animals and human. Uniform distribution character among the species was suggested by a traditional animal scale-up method.A common main metabolite, DM-3411 was found in animals and humans in the metabolic reactions with the liver S9 fraction. CYP3A4 and CYP2D6 were predominantly involved in the metabolism.The affinity of DM-3411 for D2 receptors was lower than that of brexpiprazole, and neither DM-3411 nor any metabolites with affinity other than M3 were detected in the brain, demonstrating that brexpiprazole is only involved in the pharmacological effects.Overall, brexpiprazole has a simple pharmacokinetic profile with good metabolic stability, linear kinetics, and no remarkable species differences with regard to metabolism and tissue distribution.

Clinical relevance of increased serum preneoplastic antigen in hepatitis C-related hepatocellular carcinoma.

BACKGROUND: The prognosis of hepatocellular carcinoma (HCC) patients remains poor despite advances in treatment modalities and diagnosis. It is important to identify useful markers for the early detection of HCC in patients. Preneoplastic antigen (PNA), originally reported in a rat carcinogenesis model, is increased in the tissues and serum of HCC patients. AIM: To determine the diagnostic value of PNA for discriminating HCC and to characterize PNA-positive HCC. METHODS: Patients with hepatitis C virus (HCV)-related hepatic disorders were prospectively enrolled in this study, which included patients with hepatitis, with cirrhosis, and with HCC. A novel enzyme-linked immunosorbent assay was developed to measure serum PNA concentrations in patients. RESULTS: Serum PNA concentrations were measured in 89 controls and 141 patients with HCV infections (50 hepatitis, 44 cirrhosis, and 47 HCC). Compared with control and non-HCC patients, PNA was increased in HCC. On receiver operating characteristic curve analysis, the sensitivity of PNA was similar to the HCC markers des-γ-carboxy-prothrombin (DCP) and α-fetoprotein (AFP), but the specificity of PNA was lower. There was no correlation between PNA and AFP and a significant but weak correlation between PNA and DCP in HCC patients. Importantly, the correlations with biochemical markers were completely different for PNA, AFP, and DCP; glutamyl transpeptidase was highly correlated with PNA, but not with AFP or DCP, and was significantly higher in PNA-high patients than in PNA-low patients with HCV-related HCC. CONCLUSION: PNA may have the potential to diagnose a novel type of HCC in which glutamyl transpeptidase is positively expressed but AFP or DCP is weakly or negatively expressed.

Database analysis of patients with hepatocellular carcinoma and treatment flow in early and advanced stages.

Despite recent developments in treatment modalities and diagnosis, the prognosis of advanced hepatocellular carcinoma (HCC) remains unsatisfactory. To gain insight into treatment decisions for HCC patients, their characteristics and treatment flow in the early and advanced stages were examined. HCC patients' characteristics and treatment flow were retrospectively analyzed using the Japanese medical claims database. The 8999 patients' mean age at HCC diagnosis was 71.1 years, with no difference between early (Stage I/II) and advanced (Stage III/IV) stages. The mean observation period was 26.2 months, shorter in advanced than in early stages. HCV hepatitis was reported in 52.0% of HCC patients, with concomitant hypertension in 53.4%, type 2 diabetes in 45.8%, cirrhosis in 39.3%, and hyperlipidemia in 15.5%. The rates of HCV hepatitis, hypertension, and hyperlipidemia decreased with stage progression. Analysis of treatment flow showed that, at all disease stages, transcatheter arterial chemoembolization (TACE) was the most common first to fourth-line treatment. Epirubicin was the most frequently (44.1%) used chemotherapeutic agent for first-line TACE, followed by miriplatin (23.6%) and cisplatin (12.3%). With stage progression, cisplatin use increased. Sorafenib was used concomitantly for first-line TACE in 3.2% of patients, and its use increased significantly in advanced stages. Clear differences in baseline characteristics and treatment flow between early and advanced stages were identified. Continuous analysis of the database with longer follow-up may provide useful information about treatment selection and prediction of outcome such as survival.

[Preclinical study for antitumor mechanism of lenvatinib and clinical studies for hepatocellular carcinoma].

Lenvatinib is an oral multikinase inhibitor that targets VEGF receptors 1-3, FGF receptors 1-4, PDGF receptor α, RET, and KIT. The preclinical studies of lenvatinib for hepatocellular carcinoma (HCC) suggest that lenvatinib exerts the potent antitumor effect on the basis of the inhibitory actions on VEGF and FGF-induced tumor angiogenesis and on FGF-induced tumor cell growth. Phase I and II trials were conducted in Japan and Korea evaluating the maximal tolerated dose, efficacy, and safety of lenvatinib for HCC patients and have produced promising results. Considering the relationship between body weight, AUC and dose in HCC patients, the recommended starting dose was determined to be 8 mg/day for patients weighing lower than 60 kg and 12 mg/day for patients of 60 kg and higher. A phase III REFLECT study have demonstrated that the non-inferiority of lenvatinib to sorafenib in overall survival was confirmed and that lenvatinib was significantly superior to sorafenib in the analysis of progression-free survival and response rate. Based on these results, lenvatinib has been approved for the treatment of patients with unresectable HCC in Japan, US, EU and others this year. Clinical studies of lenvatinib combination therapy with transarterial chemoembolization (TACE) and with immune checkpoint inhibitors are currently on-going. Because of the potent antitumor effect, lenvatinib may change treatment strategy for HCC patients in the future.

Activation of apoptosis inhibitor of macrophage is a sensitive diagnostic marker for NASH-associated hepatocellular carcinoma.

BACKGROUND: A diagnostic marker is needed enabling early and specific diagnosis of hepatocellular carcinoma (HCC) associated with non-alcoholic steatohepatitis (NASH). Our recent findings have indicated that circulating apoptosis inhibitor of macrophage (AIM), which usually associates with IgM pentamer in the blood, is activated by its dissociation from IgM. We investigated the serum levels of IgM-free AIM for AIM activation and its possible relationship with development of HCC in NASH. METHODS: Serum levels of IgM-associated and IgM-free AIM were evaluated in patients with non-alcoholic fatty liver, NASH, and NASH-HCC using enzyme-linked immunosorbent assays and immunoblots. Liver biopsy specimens were graded and staged using Brunt's classification. RESULTS: Forty-two patients with fatty liver, 141 with NASH, and 26 with NASH-HCC were evaluated. Patients with stage 4 or grade 3 NASH (with or without HCC) exhibited significantly higher levels of both IgM-free and total AIM than those with fatty liver, whereas the ratio of IgM-free-to-total AIM was equivalent in these groups. Among patients with the same fibrosis stage of NASH, those with HCC had significantly higher IgM-free but not total AIM levels, resulting in a proportional increase in the IgM-free/total AIM ratio. Analysis of the areas under the receiver operating characteristic curves indicated the high sensitivity of the IgM-free AIM for NASH-HCC. CONCLUSIONS: Our observations suggest the activation of AIM in blood in the presence of NASH-HCC, with a significant increase in IgM-free AIM levels. IgM-free AIM serum levels appear to be a sensitive diagnostic marker for NASH-HCC.

Classification of patients with non-alcoholic fatty liver disease using rapid immunoassay of serum type IV collagen compared with liver histology and other fibrosis markers.

AIM: Non-alcoholic fatty liver disease (NAFLD) can progress to non-alcoholic fatty liver (NAFL) or non-alcoholic steatohepatitis (NASH). We investigated the association among serum type IV collagen level, liver histology, and other fibrosis markers in NAFLD progression. METHODS: We evaluated 184 patients diagnosed with NAFLD following biopsy, including 89 males and 95 females with an average age of 52.6 and 62.6 years, respectively. Non-alcoholic fatty liver disease was classified as NAFL or NASH using Matteoni's classification, and the grade and stage of NASH were assessed using Brunt's classification. Serum type IV collagen was measured by a rapid and sensitive latex particle-enhanced turbidimetric immunoassay. RESULTS: Forty-two patients with NAFL and 142 patients with NASH were included in this study. Compared with patients with NAFL, patients with NASH showed more significant liver function disorder and increased expression of fibrosis markers including type IV collagen, collagen 7S, Mac2-binding protein (M2BP), and hyaluronic acid (HA). Expression of type IV collagen and collagen 7S, but not M2BP and HA, was more significantly elevated in patients with stage 1 NASH than in patients with NAFL, indicating that type IV collagen and collagen 7S may be better discriminators of NASH and NAFL than M2BP and HA at an early stage of fibrosis. When patients were stratified by NAFLD activity score, type IV collagen and collagen 7S were significantly elevated as NAFLD activity score progressed, whereas M2BP and HA expression were not significantly elevated. CONCLUSION: Type IV collagen may be a useful measure of NASH severity as latex particle-enhanced turbidimetric immunoassay-based rapid type IV collagen assay can be carried out routinely.

Leucine-rich Alpha-2 Glycoprotein is a Serum Biomarker of Mucosal Healing in Ulcerative Colitis.

BACKGROUND AND AIMS: Although several noninvasive and easily accessible biomarkers for inflammatory bowel disease [IBD] are available, their sensitivity and specificity are not adequate to be used as single markers and do not overrule the need for endoscopic evaluation. We previously reported that serum leucine-rich alpha-2 glycoprotein [LRG] was a novel biomarker for rheumatoid arthritis and IBD. We herein investigated whether LRG could indicate endoscopic activity in patients with ulcerative colitis [UC]. METHODS: Serum LRG concentrations were determined by enzyme-linked immunosorbent assay [ELISA] in consecutive 129 patients with UC in two tertiary care hospitals, and associations of LRG with clinical and endoscopic activities were evaluated. Clinical activity index [CAI] < 6 was defined as clinical remission, and mucosal healing [MH] and complete mucosal healing were defined as Matts' endoscopic grades of 1 or 2 and grade of 1, respectively. RESULTS: Serum LRG levels were significantly increased and correlated with clinical and endoscopic activities in patients with UC. LRG levels were associated with both clinical and endoscopic activities even in patients with normal serum C-reactive protein [CRP] levels. Furthermore, LRG levels were significantly lower in patients with complete MH and deep remission. Serial measurements of LRG levels in a subset of patients demonstrated that LRG was significantly elevated during the endoscopically active stage compared with that during the MH stage. CONCLUSIONS: Serum LRG is a novel biomarker for detecting MH during disease course in patients with UC and a surrogate marker of endoscopic inflammation in patients with normal CRP levels.

Pharmacokinetics and Metabolism of Delamanid, a Novel Anti-Tuberculosis Drug, in Animals and Humans: Importance of Albumin Metabolism In Vivo.

Delamanid, a new anti-tuberculosis drug, is metabolized to M1, a unique metabolite formed by cleavage of the 6-nitro-2,3-dihydroimidazo[2,1-b] oxazole moiety, in plasma albumin in vitro. The metabolic activities in dogs and humans are higher than those in rodents. In this study, we characterized the pharmacokinetics and metabolism of delamanid in animals and humans. Eight metabolites (M1-M8) produced by cleavage of the imidazooxazole moiety of delamanid were identified in the plasma after repeated oral administration by liquid chromatography-mass spectrometry analysis. Delamanid was initially catalyzed to M1 and subsequently metabolized by three separate pathways, which suggested that M1 is a crucial starting point. The major pathway in humans was hydroxylation of the oxazole moiety of M1 to form M2 and then successive oxidation to the ketone form (M3) mainly by CYP3A4. M1 had the highest exposure among the eight metabolites after repeated oral dosing in humans, which indicated that M1 was the major metabolite. The overall metabolism of delamanid was qualitatively similar across nonclinical species and humans but was quantitatively different among the species. After repeated administration, the metabolites had much higher concentrations in dogs and humans than in rodents. The in vitro metabolic activity of albumin on delamanid probably caused the species differences observed. We determined that albumin metabolism is a key component of the pharmacokinetics and metabolism of delamanid. Nonhepatic formation of M1 and multiple separate pathways for metabolism of M1 suggest that clinically significant drug-drug interactions with delamanid and M1 are limited.

Metabolic Mechanism of Delamanid, a New Anti-Tuberculosis Drug, in Human Plasma.

The metabolism of delamanid (OPC-67683, Deltyba), a novel treatment of multidrug-resistant tuberculosis, was investigated in vitro using plasma and purified protein preparations from humans and animals. Delamanid was rapidly degraded by incubation in the plasma of all species tested at 37°C, with half-life values (hours) of 0.64 (human), 0.84 (dog), 0.87 (rabbit), 1.90 (mouse), and 3.54 (rat). A major metabolite, (R)-2-amino-4,5-dihydrooxazole derivative (M1), was formed in the plasma by cleavage of the 6-nitro-2,3-dihydroimidazo(2,1-b)oxazole moiety of delamanid. The rate of M1 formation increased with temperature (0-37°C) and pH (6.0-8.0). Delamanid was not converted to M1 in plasma filtrate, with a molecular mass cutoff of 30 kDa, suggesting that bioconversion is mediated by plasma proteins of higher molecular weight. When delamanid was incubated in plasma protein fractions separated by gel filtration chromatography, M1 was observed in the fraction consisting of albumin, γ-globulin, and α1-acid glycoprotein. In pure preparations of these proteins, only human serum albumin (HSA) metabolized delamanid to M1. The formation of M1 followed Michaelis-Menten kinetics in both human plasma and the HSA solution, with similar Km values: 67.8 µM in plasma and 51.5 µM in HSA. The maximum velocity and intrinsic clearance values for M1 were also comparable in plasma and HSA. These results strongly suggest that albumin is predominantly responsible for metabolizing delamanid to M1. We propose that delamanid degradation by albumin begins with a nucleophilic attack of amino acid residues on the electron-poor carbon at the 5 position of nitro-dihydro-imidazooxazole, followed by cleavage of the imidazooxazole moiety to form M1.

Comprehensive kinetic analysis and influence of reaction components for chlorzoxazone 6-hydroxylation in human liver microsomes with CYP antibodies.

1. Chlorzoxazone (CLZ) is currently being used as a marker substrate in vitro/vivo studies to quantify cytochrome P450 2E1 (CYP2E1) activity in humans. Although in CLZ 6-hydroxylation several CYPs are responsible, previous studies have presented the monophasicity of the reaction in human liver microsomes (HLMs). Furthermore, the Km values of CYP2E1 for the 6-hydroxylation in HLMs were reported to be lower than those of its recombinant enzymes. 2. This study aimed to provide the comprehensive Km values for the CLZ 6-hydroxylation in HLMs using CYP antibodies. The Eadie-Hofstee plots revealed a biphasic profile and indicate that the reaction was mainly mediated by CYP1A2 as well as CYP2E1. The formation of 6-hydroxychlorzoxazone was more specific for CYP2E1 activity at higher substrate concentration in HLMs. 3. Moreover, KOH as a vehicle for substrate or sucrose included in HLMs preparation had some effect on the activity of CLZ 6-hydroxylase. These constituents seemed to be casually related to the apparent monophasic kinetics and variability in Km values for the CLZ 6-hydroxylation in HLMs. 4. The Km of CYP1A2 and CYP2E1 in HLMs was 3.8 µmol/L and 410 µmol/L, respectively, and the value of CYP2E1 was close to that of recombinant CYP2E1.