Severity, Outcomes, and their Secular Changes in 33,870 Ischemic Stroke Patients with Atrial Fibrillation in a Hospital-Based Registry: Japan Stroke Data Bank.

AIM: Severity, functional outcomes, and their secular changes in acute atrial fibrillation (AF)-associated stroke patients were determined. METHODS: Acute ischemic stroke patients with AF in a hospital-based, multicenter, prospective registry from January-2000 through December-2020, were compared with those without AF. The co-primary outcomes were the initial severity assessed by the NIH Stroke Scale (NIHSS) score and favorable outcome assessed by the modified Rankin Scale scores 0-2 at hospital discharge. RESULTS: Of the 142,351 patients studied, 33,870 had AF. AF patients had higher NIHSS scores (median 9 vs. 3, adjusted coefficient 5.468, 95% CI 5.354-5.582) than non-AF patients. Favorable outcome was less common in AF patients than in non-AF patients in the unadjusted analysis (48.4% vs. 70.4%), but it was more common with adjustment for the NIHSS score and other factors (adjusted OR 1.110, 95% CI 1.061-1.161). In AF patients, the NIHSS score decreased throughout the 21-year period (adjusted coefficient -0.088, 95% CI -0.115 - -0.061 per year), and the reduction was steeper than in non-AF patients (P＜0.001). In AF patients, favorable outcome became more common over the period (adjusted OR 1.018, 95% CI 1.010-1.026), and the increase was steeper than in non-AF patients (P＜0.001); the increase was no longer significant after further adjustment by reperfusion therapy. CONCLUSIONS: Initial stroke severity became milder and functional outcomes improved in AF patients over the 21-year period. These secular changes were steeper than in non-AF patients, suggesting that AF-associated stroke seemed to reap more benefit of recent development of stroke care than stroke without AF.

A Novel Risk Score for Major Bleeding in Japanese Patients with Non-Valvular Atrial Fibrillation: The J-RISK AF Study.

AIM: Oral anticoagulants (OACs) reduce the risk of ischemic stroke but may increase the risk of major bleeding in patients with non-valvular atrial fibrillation (NVAF). Various risk scores, such as HAS-BLED, ATRIA, ORBIT, and DOAC, have been proposed to assess the risk of major bleeding in patients with NVAF receiving OACs. However, limited data are available regarding bleeding risk stratification in Japanese patients with NVAF. METHODS: Of the 16,098 NVAF patients from the J-RISK AF study, the combined data of the five major AF registries in Japan (J-RHYTHM Registry, Fushimi AF Registry, Shinken Database, Keio interhospital Cardiovascular Studies, and Hokuriku-Plus AF Registry), we analyzed 11,539 patients receiving OACs (median age, 71 years old; women, 29.6%; median CHA2DS2-VASc score, 3). RESULTS: During the 2-year follow-up period, major bleeding occurred in 274 patients (1.3% per patient-year). In a multivariate Cox proportional hazards analysis, an advanced age, hypertension (systolic blood pressure ≥ 150 mmHg), bleeding history, anemia, thrombocytopenia, and concomitant antiplatelet agents were significantly associated with a higher incidence of major bleeding. We developed a novel risk stratification system, HED-[EPA]2-B3 score, which had a better predictive performance for major bleeding (C-statistics 0.67, [95% confidence interval, 0.63-0.70]) than the HAS-BLED (0.64, [0.60-0.67], P for difference 0.02) and ATRIA (0.63, [0.60-0.66], P for difference ＜0.01) scores. Furthermore, it was non-significantly higher than the ORBIT (0.65, [0.62-0.68], P for difference 0.07) and DOAC (0.65, [0.62-0.68], P for difference 0.17) scores. CONCLUSION: Our novel risk stratification system, the HED-[EPA]2-B3 score, may be useful for identifying Japanese patients receiving OACs at a risk of major bleeding.

Clinical impact of body mass index on outcomes of ischemic and hemorrhagic strokes.

BACKGROUND AND AIM: To investigate the prognostic implication of body mass index (BMI) on clinical outcomes after acute ischemic and hemorrhagic stroke. METHODS: The subjects of the study included adult patients with available baseline body weight and height data who had suffered an acute stroke and were registered in the Japan Stroke Data Bank-a hospital-based, multicenter stroke registration database-between January 2006 and December 2020. The outcome measures included unfavorable outcomes defined as a modified Rankin Scale (mRS) score of 5-6 and favorable outcomes (mRS 0-2) at discharge, and in-hospital mortality. Mixed effects logistic regression analysis was conducted to determine the relationship between BMI categories (underweight, normal weight, overweight, class I obesity, class II obesity; <18.5, 18.5-23.0, 23.0-25.0, 25-30, ⩾30 kg/m2) and the outcomes, after adjustment for covariates. RESULTS: A total of 56,230 patients were assigned to one of the following groups: ischemic stroke (IS, n = 43,668), intracerebral hemorrhage (ICH, n = 9741), and subarachnoid hemorrhage (SAH, n = 2821). In the IS group, being underweight was associated with an increased likelihood of unfavorable outcomes (odds ratio, 1.47 (95% confidence interval (CI):1.31-1.65)) and in-hospital mortality (1.55 (1.31-1.83)) compared to outcomes in those with normal weight. Being overweight was associated with an increased likelihood of favorable outcomes (1.09 (1.01-1.18)). Similar associations were observed between underweight and these outcomes in specific IS subtypes (cardioembolic stroke, large artery stroke, and small-vessel occlusion). Patients with a BMI ⩾30.0 kg/m2 was associated with an increased likelihood of unfavorable outcomes (1.44 (1.01-2.17)) and in-hospital mortality (2.42 (1.26-4.65)) in large artery stroke. In patients with ICH, but not those with SAH, being underweight was associated with an increased likelihood of unfavorable outcomes (1.41 (1.01-1.99)). CONCLUSIONS: BMI substantially impacts functional outcomes following IS and ICH. Lower BMI consistently affected post-stroke disability and mortality, while higher BMI values similarly affected these outcomes after large artery stroke.

Improvement of Functional Outcomes in Patients with Stroke who Received Alteplase for Over 15 Years: Japan Stroke Data Bank.

AIM: The nationwide verification of intravenous thrombolysis (IVT) was rarely performed after the extension of the therapeutic time window of alteplase or after the expansion of mechanical thrombectomy (MT). We aimed to examine the long-term change in accurate real-world outcomes of IVT in patients with acute ischemic stroke (AIS) using the Japan Stroke Databank, a representative Japan-wide stroke database. METHODS: We extracted all patients with AIS who received IVT with alteplase between October 11, 2005, the approval date for alteplase use for AIS in Japan, and December 31, 2020. Patients were categorized into three groups using two critical dates in Japan as cutoffs: the official extension date of the therapeutic time window for IVT to within 4.5 h of symptom onset and the publication date of the revised guideline, where the evidence level of MT was heightened. We assessed the yearly trend of IVT implementation rates and the secular changes and three-group changes in clinical outcomes at discharge. RESULTS: Of 124,382 patients with AIS, 9,569 (7.7%) received IVT (females, 41%; median age, 75 years). The IVT implementation rate has generally increased over time and plateaued in recent years. The proportion of favorable outcomes (modified Rankin Scale score of 0-2) increased yearly over 15 years. The results of the changes in the outcomes of the three groups were similar to those of the annual changes. CONCLUSIONS: We revealed that IVT implementation rates in patients with AIS increased, and the functional outcome in these patients improved over 15 years. Therefore, the Japanese IVT dissemination strategy is considered appropriate and effective.

Characteristics and outcomes of unknown onset stroke: The Japan Stroke Data Bank.

BACKGROUND: Clinical outcomes of unknown onset stroke (UOS) are influenced by the enlargement of the therapeutic time window for reperfusion therapy. This study aimed to investigate and describe the characteristics and clinical outcomes of patients with UOS. METHODS: Patients with acute ischemic stroke (AIS) who were admitted within 24 h of their last known well time, from January 2017 to December 2020, were included. Data were obtained from a long-lasting nationwide hospital-based multicenter prospective registry: the Japan Stroke Data Bank. The co-primary outcomes were the National Institutes of Stroke Scale (NIHSS) scores on admission and unfavorable outcomes at discharge, corresponding to modified Rankin Scale (mRS) scores of 3-6. RESULTS: Overall, 26,976 patients with AIS were investigated. Patients with UOS (N = 5783, 78 ± 12 years of age) were older than patients with known onset stroke (KOS) (N = 21,193, 75 ± 13 years of age). Age, female sex, higher premorbid mRS scores, atrial fibrillation, and congestive heart failure were associated with UOS in multivariate analysis. UOS was associated with higher NIHSS scores (median = 8 [interquartile range [IQR]: 3-19] vs. 4 [1-10], adjusted incidence rate ratio = 1.37 [95% CI: 1.35-1.38]) and unfavorable outcomes (52.1 vs. 33.6%, adjusted odds ratio = 1.27 [1.14-1.40]). Intergroup differences in unfavorable outcomes were attenuated among females (1.12 [0.95-1.32] vs. males 1.38 [1.21-1.56], P = 0.040) and in the subgroup that received reperfusion therapy (1.10 [0.92-1.33] vs. those who did not receive therapy 1.23 [1.08-1.39], P = 0.012). CONCLUSIONS: UOS was associated with unfavorable outcomes but to a lesser degree among females and patients receiving reperfusion therapy.

Satisfaction Survey for Regional Clinical Pathway for Stroke Patients in Acute and Rehabilitation Hospitals in Japan.

Objectives: We collected opinions about the use of a stroke-specific regional clinical pathway for facilitating collaboration between acute and rehabilitation hospitals in Japan. Methods: The study surveys were administered in acute hospitals designated as primary stroke centers and certified by the Japan Stroke Association (n=961) and in rehabilitation hospitals affiliated with the Kaifukuki Rehabilitation Ward Association (n=1237). The survey collected information on interfacility collaboration when caring for patients admitted during the acute phase following non-traumatic stroke from April 2020 to March 2021. We examined the pathway's usefulness and challenges relative to facility type using the χ2 test. Results: Of 422 acute hospitals and 223 rehabilitation hospitals that responded to our survey, 259 (62.1%) acute hospitals and 164 (85.4%) rehabilitation hospitals used the pathway. Fewer rehabilitation hospitals than acute hospitals considered that the pathway was useful (52.0% vs. 63.8%, P=0.02). Fewer rehabilitation hospitals did not experience pathway-related problems when compared with acute hospitals (38.0% vs. 55.8%, P<0.01). Conclusions: Personnel at rehabilitation hospitals were less satisfied with the regional clinical care pathway than those in acute hospitals. These results suggest that the current stroke-specific regional clinical pathway could be improved.

Impact of baseline blood pressure on adverse outcomes in Japanese patients with non-valvular atrial fibrillation: the J-RISK AF.

Aims: This study aimed to investigate the impact of baseline blood pressure (BP) on adverse outcomes in patients with atrial fibrillation (AF), using a pooled analysis performed on data from J-RISK AF, a large-scale cohort of Japanese patients with AF. Methods and results: Of the 16 918 patients from five major AF registries including the J-RHYTHM Registry, Fushimi AF Registry, Shinken Database, Keio interhospital Cardiovascular Studies, and Hokuriku-Plus AF Registry, 15 019 non-valvular AF (NVAF) patients with baseline BP values (age, 70.0 ± 11.0 years; men, 69.1%) were analysed. Incidence rates of adverse events were evaluated between patients divided into baseline systolic BP quartiles or at 150 mmHg. During the follow-up period of 730 days, ischaemic stroke, major bleeding, all-cause death, and cardiovascular death occurred in 277, 319, 718, and 275 patients, respectively. Hazard ratios (HRs) for ischaemic stroke and major bleeding were comparable among the quartiles, whereas HRs for all-cause and cardiovascular deaths in the lowest quartile with systolic BP <114 mmHg were significantly higher [HR 1.43, 95% confidence interval (CI) 1.13-1.81; and HR 1.47, 95% CI 1.01-2.12, respectively] than in the third quartile, even after adjusting for known confounding factors. In patients with a systolic BP of ≥150 mmHg, adjusted HR for major bleeding was significantly higher than that of <150 mmHg (HR 1.64, 95% CI 1.12-2.40). Conclusion: In Japanese patients with NVAF, a baseline systolic BP <114 mmHg was significantly associated with higher all-cause and cardiovascular mortality. In contrast, a systolic BP ≥150 mmHg was an independent risk factor for major bleeding.

Etiology and Outcome of Ischemic Stroke in Patients With Renal Impairment Including Chronic Kidney Disease: Japan Stroke Data Bank.

BACKGROUND AND OBJECTIVES: Chronic kidney disease is a worldwide public health problem that is recognized as an established risk factor for stroke. It remains unclear whether its distribution and clinical impact are consistent across ischemic stroke subtypes in patients with renal impairment. We examined whether renal impairment was associated with the proportion of each stroke subtype vs ischemic stroke overall and with functional outcomes after each stroke subtype. METHODS: Study participants were 10,392 adult patients with an acute stroke from the register of the Japan Stroke Data Bank, a hospital-based multicenter stroke registration database, between October 2016 and December 2019, whose baseline serum creatinine levels or a dipstick proteinuria result were available. All ischemic strokes were classified according to the Trial of Org 10172 in Acute Stroke Treatment criteria. Unfavorable functional outcome was defined as modified Rankin Scale (mRS) score 3-6 at discharge. Mixed effect logistic regression was used to determine the relationship between the outcomes and the estimated glomerular filtration rate (eGFR), eGFR strata (<45, 45-59, ≥60 mL/min/1.73 m2), or dipstick proteinuria ≥1 adjusted for covariates. RESULTS: Overall, 2,419 (23%) patients had eGFR 45-59 mL/min/1.73 m2 and 1,976 (19%) had eGFR <45 mL/min/1.73 m2, including 185 patients (1.8%) receiving hemodialysis. Both eGFR 45-59 and eGFR <45 mL/min/1.73 m2 were associated with a higher proportion of cardioembolic stroke (odds ratio [OR], 1.21 [95% CI, 1.05-1.39] and 1.55 [1.34-1.79], respectively) and a lower proportion of small vessel occlusion (0.79 [0.69-0.90] and 0.68 [0.59-0.79], respectively). A similar association with the proportion of these 2 subtypes was proven in the analyses using decreased eGFR as continuous values. Both eGFR <45 mL/min/1.73 m2 and proteinuria were associated with unfavorable functional outcomes in patients with cardioembolic stroke (OR, 1.30 [95% CI, 1.01-1.69] and 3.18 [2.03-4.98], respectively) and small vessel occlusion (OR, 1.44 [1.01-2.07] and 2.08 [1.08-3.98], respectively). DISCUSSION: Renal impairment contributes to the different distributions and clinical effects across specific stroke subtypes, particularly evident in cardioembolic stroke and small vessel occlusion. This possibly indicates shared mechanisms of susceptibility and potentially enhancing pathways.

Twenty-Year Change in Severity and Outcome of Ischemic and Hemorrhagic Strokes.

Importance: Whether recent changes in demographic characteristics and therapeutic technologies have altered stroke outcomes remains unknown. Objective: To determine secular changes in initial neurological severity and short-term functional outcomes of patients with acute stroke by sex using a large population. Design, Setting, and Participants: This nationwide, hospital-based, multicenter, prospective registry cohort study used the Japan Stroke Data Bank and included patients who developed acute stroke from January 2000 through December 2019. Patients with stroke, including ischemic and hemorrhagic strokes, who registered within 7 days after symptom onset were studied. Modified Rankin Scale scores were assessed at hospital discharge for all patients. Exposure: Time. Main Outcomes and Measures: Initial severity was assessed by the National Institutes of Health Stroke Scale for ischemic stroke and intracerebral hemorrhage and by the World Federation of Neurological Surgeons grading for subarachnoid hemorrhage. Outcomes were judged as favorable if the modified Rankin Scale score was 0 to 2 and unfavorable if 5 to 6. Results: Of 183 080 patients, 135 266 (53 800 women [39.8%]; median [IQR] age, 74 [66-82] years) developed ischemic stroke, 36 014 (15 365 women [42.7%]; median [IQR] age, 70 [59-79] years) developed intracerebral hemorrhage, and 11 800 (7924 women [67.2%]; median [IQR] age, 64 [53-75] years) developed subarachnoid hemorrhage. In all 3 stroke types, median ages at onset increased, and the National Institutes of Health Stroke Scale and World Federation of Neurological Surgeons scores decreased throughout the 20-year period on multivariable analysis. In ischemic stroke, the proportion of favorable outcomes showed an increase over time after age adjustment (odds ratio [OR], 1.020; 95% CI, 1.015-1.024 for women vs OR, 1.015; 95% CI, 1.011-1.018 for men) but then stagnated, or even decreased in men, on multivariate adjustment including reperfusion therapy (OR, 0.997; 95% CI, 0.991-1.003 for women vs OR, 0.990; 95% CI, 0.985-0.994 for men). Unfavorable outcomes and in-hospital deaths decreased in both sexes. In intracerebral hemorrhage, favorable outcomes decreased in both sexes, and unfavorable outcomes and deaths decreased only in women. In subarachnoid hemorrhage, the proportion of favorable outcomes was unchanged, and that of unfavorable outcomes and deaths decreased in both sexes. Conclusions and Relevance: In this study, functional outcomes improved in patients with ischemic stroke during the past 20 years in both sexes presumably partly owing to the development of acute reperfusion therapy. The outcomes of patients with hemorrhagic stroke did not clearly improve in the same period.

A Novel Risk Stratification System for Ischemic Stroke in Japanese Patients With Non-Valvular Atrial Fibrillation.

BACKGROUND: Recently, identification of independent risk factors for ischemic stroke in Japanese non-valvular atrial fibrillation (NVAF) patients was made by analyzing the 5 major Japanese registries: J-RHYTHM Registry, Fushimi AF Registry, Shinken Database, Keio interhospital Cardiovascular Studies, and the Hokuriku-Plus AF Registry.Methods and Results:The predictive value of the risk scheme in Japanese NVAF patients was assessed. Of 16,918 patients, 12,289 NVAF patients were analyzed (mean follow up, 649±181 days). Hazard ratios (HRs) of each significant, independent risk factor were determined by using adjusted Cox-hazard proportional analysis. Scoring system for ischemic stroke was created by transforming HR logarithmically and was estimated by c-statistic. During the 21,820 person-years follow up, 241 ischemic stroke events occurred. Significant risk factors were: being elderly (aged 75-84 years [E], HR=1.74), extreme elderly (≥85 years [EE], HR=2.41), having hypertension (H, HR=1.60), previous stroke (S, HR=2.75), type of AF (persistent/permanent) (T, HR=1.59), and low body mass index <18.5 kg/m2(L, HR=1.55) after adjusting for oral anticoagulant treatment. The score was assigned as follows: 1 point to H, E, L, and T, and 2 points to EE and S (HELT-E2S2score). The C-statistic, using this score, was 0.681 (95% confidence interval [CI]=0.647-0.714), which was significantly higher than those using CHADS2(0.647; 95% CI=0.614-0.681, P=0.027 for comparison) and CHA2DS2-VASc scores (0.641; 95% CI=0.608-0.673, P=0.008). CONCLUSIONS: The HELT-E2S2score may be useful for identifying Japanese NVAF patients at risk of ischemic stroke.

Risk Factors Associated With Ischemic Stroke in Japanese Patients With Nonvalvular Atrial Fibrillation.

Importance: Despite the development of risk stratification schemes that have been widely used to determine the risk for thromboembolism in patients with nonvalvular atrial fibrillation (NVAF), risk stratification schemes in Asian patients with NVAF remain undetermined. Objective: To determine risk factors for ischemic stroke in Japanese patients with NVAF. Design, Setting, and Participants: This cohort study analyzed individual patient data from 5 AF registries in Japan: J-RHYTHM (Japanese Rhythm Management Trial for Atrial Fibrillation) Registry, Fushimi AF Registry, Shinken Database, Keio Interhospital Cardiovascular Studies (Keio Study), and Hokuriku-Plus AF Registry. Patients with atrial fibrillation were registered from 158 institutions in the J-RHYTHM Registry, 80 in the Fushimi AF Registry, a single hospital in Shinken Database, 11 in the Keio Study, and 19 in the Hokuriku-Plus AF Registry. Patients with valvular AF or lacking data were excluded. Data were collected and integrated in March 2016, and those from the Keio Study were updated in April 2018. Data were analyzed from April 2018 to February 2020. Main Outcomes and Measures: Significant risk factors for ischemic stroke were determined by adjusted Cox proportional hazards analysis. Results: In total, 12 289 patients with NVAF (3758 [31%] female; mean [SD] age 70.2 [11] years) were analyzed with a mean (SD) follow-up period of 649 (181) days (1.8 [0.5] years). During 21 820 person-years of follow-up, 241 cases of ischemic stroke were reported. Risk factors associated with ischemic stroke after adjustment for oral anticoagulant use at enrollment were age (75-84 years: hazard ratio [HR], 1.74; 95% CI, 1.32-2.30; P < .001; and ≥85 years: HR, 2.41; 1.63-3.56; P < .001), hypertension (HR, 1.60; 95% CI, 1.15-2.23; P = .006), previous stroke (HR, 2.75; 95% CI, 2.09-3.62; P < .001), persistent or permanent AF (HR, 1.59; 95% CI, 1.21-2.10; P = .001), and body mass index less than 18.5 (HR, 1.55; 95% CI, 1.05-2.29; P = .03). Neither diabetes nor heart failure were identified as risk factors for ischemic stroke. Conclusions and Relevance: Previous stroke, advanced age, hypertension, persistent or permanent AF, and low body mass index were independent risk factors associated with ischemic stroke in Japanese patients with NVAF.

Transcriptional Analysis of Hair Follicle-Derived Keratinocytes from Donors with Atopic Dermatitis Reveals Enhanced Induction of IL32 Gene by IFN-γ.

We cultured human hair follicle-derived keratinocytes (FDKs) from plucked hairs. To gain insight into gene expression signatures that can distinguish atopic dermatitis from non-atopic controls without skin biopsies, we undertook a comparative study of gene expression in FDKs from adult donors with atopic dermatitis and non-atopic donors. FDK primary cultures (atopic dermatitis, n = 11; non-atopic controls, n = 7) before and after interferon gamma (IFN-γ) treatment were used for microarray analysis and quantitative RT-PCR. Comparison of FDKs from atopic and non-atopic donors indicated that the former showed activated pathways with innate immunity and decreased pathways of cell growth, as indicated by increased NLRP2 expression and decreased DKK1 expression, respectively. Treatment with IFN-γ induced the enhanced expression of IL32, IL1B, IL8, and CXCL1 in the cells from atopic donors compared to that in cells from non-atopic donors at 24 h after treatment. IL1B expression in FDKs after IFN-γ treatment correlated with IL32 expression. We hypothesized that overexpression of IL32 in hair follicle keratinocytes of patients with atopic dermatitis would lead to the excessive production of pro-IL1ß and that the activation of IL1ß from pro-IL1ß by inflammasome complex, in which NLRP2 protein might be involved, would be augmented. This is the first report to show enhanced induction of cytokine/chemokine genes by IFN-γ in atopic dermatitis using cultured FDKs.

Upregulation of genes orchestrating keratinocyte differentiation, including the novel marker gene ID2, by contact sensitizers in human bulge-derived keratinocytes.

In the epidermis, keratinocytes are involved in physical and first-line immune protection of the host. In this study, we analyzed the molecular responses to certain contact sensitizers (2,4-dinitrochlorobenzene and NiSO(4)) and irritants (sodium dodecyl sulfate and benzalkonium chloride) in cultured human keratinocytes from the bulge region of a plucked hair follicle (bulge-derived keratinocytes [BDKs]) and compared these molecular responses to those with the human monocytic leukemia cell line, THP-1. The BDKs, individually established without invasive biopsies, showed high reactivity to these stimulants. As a primary response to the contact sensitizers, the NRF2-mediated signaling pathway was upregulated in BDKs and THP-1. The expression of IL1B and IL8 genes was not induced by the irritants but by the sensitizers in THP-1. However, the expression of the IL1B and IL8 genes was induced at higher levels by the irritants in BDKs than by the sensitizers. Many genes orchestrating keratinocyte differentiation, including ID2, were significantly upregulated in response to the sensitizers in BDKs but not those in THP-1. The use of the ID2 gene to discriminate between sensitizers and irritants might be effective as a novel marker for application during in vitro sensitization with BDKs.

Human keratinocytes derived from the bulge region of hair follicles are refractory to differentiation.

Human keratinocyte strains derived from the bulge region of plucked human follicles were successfully established from all 43 donors (age 24-76) regardless of the age and gender. The total cell number, number of population doublings and population doubling time were similar among the strains. These bulge-derived keratinocytes, BDKs, expressed keratin family genes specific to basal cell layers of the epidermis. They also expressed CD34, one of the bulge stem cell marker genes. The growth behavior and positivity of CD34 indicate that BDKs contain stem cells. BDKs were cultured until confluency or treated with CaCl2 to induce differentiation. Morphology and expression of keratin family genes in BDKs before and after differentiation induction with CaCl2 were similar to those of epidermal keratinocytes obtained from skin biopsies (NHEKs). However, expression levels of keratin-10, a prickle cell layer marker, in CaCl2-treated BDKs were lower than those in CaCl2-treated NHEKs. Higher expression of integrin-alpha6, a basal cell layer marker, was also noted in BDKs than in NHEKs after differentiation induction. Expression of stem cell marker genes other than CD34, including CD200, Sox2 and NANOG, was about the same at confluency in both cells, but significantly higher in BDKs than NHEKs after differentiation. These results indicate that BDKs were more refractory to differentiation than NHEKs. We then examined Wnt signaling inhibitor genes, DKK-3 and WIF-1 that function as tumor suppressors. DKK-3 expression decreased in both BDKs and NHEKs after CaCl2-induced differentiation. Expression of WIF-1 decreased 50% in BDKs one day after CaCl2 treatment and remained low, but was induced 1.7 times in NHEKs one day after CaCl2 treatment and further induced thereafter (>2.5 times), suggesting that WIF-1 may be involved in maintaining the differentiation-refractory status of BDKs. Since cancer stem cells in the skin have been reported to be similar to bulge-derived stem cells, our BDK strains may be of use in studying characteristics of cancer stem cells of the epidermis.