Ileal phosphorus digestibility of soybean meal for broiler chickens remains consistent across institutions in a collaborative study regardless of non-phytate phosphorus concentration in the pre-experimental starter diet.

The same experimental protocol was used in 4 institutions to evaluate the impact of non-phytate phosphorus (nPP) concentration in the starter diet on regression method-derived ileal P digestibility of soybean meal (SBM) during the subsequent grower phase. A total of 1,536 Ross 308 male broiler chickens on d 0 post hatching were allotted to 2 pre-experimental starter diets that contained 3.5 or 4.5 g nPP/kg (96 replicate cages per diet, 8 birds per cage) for 18 d. Subsequently, 576 birds from each starter diet were selected and allocated to 3 experimental semi-purified grower diets containing 400, 510, or 620 g SBM/kg (32 replicate cages per diet, 6 birds per cage) for 3 d until collection of ileal digesta. Statistical analysis was conducted as a randomized complete block design with the starter period as whole plot and the grower period as split-plot. The only significant 2-way interaction was between grower diet and experimental institution (P < 0.05) on BW gain and gain to feed ratio. The main effect of institution and grower diet impacted (P < 0.05) feed intake, the digestibility of DM, P, and calcium, and disappearance of inositol hexakisphosphate (InsP6) in the grower diets. Birds fed the 3.5 g nPP/kg starter diet had lower (P < 0.05) BW gain and feed intake during the grower period, but presented higher (P < 0.05) digestibility of P and disappearance of InsP6 compared with the birds that were fed the 4.5 g nPP/kg starter diet. Regression method-derived ileal P digestibility of SBM was determined to be 46 or 42% for the respective 3.5 or 4.5 g nPP/kg pre-experimental starter diet and was not affected by the nPP concentration or by the institution. In conclusion, the experimental protocol used in the current study resulted in similar estimates across multiple institutions and is thus endorsed for future application in studies that aim to expand the database of digestible P content in plant source feed ingredients.

Autofluorescence analysis of dermatitis and squamous cell carcinoma in paraffin wax-embedded skin samples.

BACKGROUND: Recent research has investigated the use of autofluorescence (AF) for distinguishing between normal and cancerous tissues according to different fluorescence characteristics. AIM: To analyze if AF can help differentiate cancerous lesions from other nonneoplastic lesions, such as dermatitis, in each layer of the skin ex vivo. METHODS: Paraffin wax-embedded tissue samples were obtained from patients who were histopathologically diagnosed with squamous cell carcinoma (SCC), psoriasis, chronic dermatitis (lichen simplex chronicus, prurigo nodularis) or acute dermatitis (atopic dermatitis). AF intensity was measured in four layers of the epidermis (corneal, granular, spinous and basal) and two layers of the dermis (papillary and reticular). RESULTS: AF was highest in all layers of psoriasis samples compared with all layers of all other groups. Higher AF values were seen in SCC compared with all skin layers of acute and chronic dermatitis; this finding was especially true in the corneal layer, papillary dermis and reticular dermis. CONCLUSIONS: This ex vivo AF study provides basic data for future in vivo studies of AF as a noninvasive diagnostic tool.

Coding for stable transmission of W-band radio-over-fiber system using direct-beating of two independent lasers.

We demonstrate experimentally Manchester (MC) coding based W-band (75 - 110 GHz) radio-over-fiber (ROF) system to reduce the low-frequency-components (LFCs) signal distortion generated by two independent low-cost lasers using spectral shaping. Hence, a low-cost and higher performance W-band ROF system is achieved. In this system, direct-beating of two independent low-cost CW lasers without frequency tracking circuit (FTC) is used to generate the millimeter-wave. Approaches, such as delayed self-heterodyne interferometer and heterodyne beating are performed to characterize the optical-beating-interference sub-terahertz signal (OBIS). Furthermore, W-band ROF systems using MC coding and NRZ-OOK are compared and discussed.

OFDM RF power-fading circumvention for long-reach WDM-PON.

We propose and demonstrate an orthogonal frequency division multiplexing (OFDM) radio-frequency (RF) power-fading circumvention scheme for long-reach wavelength-division-multiplexed passive-optical-network (LR-WDM-PON); hence the same capacity of 40 Gb/s can be provided to all the optical-networking-units (ONUs) in the LR-WDM-PON. Numerical analysis and proof-of-concept experiment are performed.

Surgical treatment of solid pseudopapillary neoplasms of the pancreas and risk factors for malignancy.

BACKGROUND: The aim of this study was to identify clinical predictors of malignancy and surgical strategies for pancreatic solid pseudopapillary neoplasm (SPN) by analysis of surgical outcomes at a single institution. METHODS: All patients who underwent surgery for SPN between 1995 and 2010 were identified. Histopathology slides of all patients were reviewed by a specialized pathologist and the neoplasms were classified according to the criteria of the World Health Organization 2010. RESULTS: Of the 106 patients identified, 85 (80·2 per cent) were female, and the median age was 36 (range 10-65) years. Median tumour size was 4·5 (range 1·0-15·0) cm. Some 17 patients (16·0 per cent) were classified as having a high-grade malignant SPN. Tumour size of at least 5 cm was associated with high-grade malignant potential (P = 0·022). Although lymph nodes were removed from 40 patients (37·7 per cent), there were no nodal metastases. A total of five patients underwent en bloc resection of adjacent structures, including two with portal vein involvement. After a median follow-up of 56·9 months, two patients with high-grade malignant SPN had evidence of tumour recurrence in the lymph nodes and liver. CONCLUSION: SPN with a diameter of 5 cm or more is associated with a high-grade malignant phenotype. Complete surgical removal is associated with low recurrence rates.

Ascites associated with uterine leiomyoma in a 22-year-old woman with systemic lupus erythematosus.

Ascites in systemic lupus erythematosus (SLE) patients has a variety of etiologies, which usually require different treatment options. Our case was a 22-year-old patient with an unusual combination of ascites, uterine leiomyoma and SLE. The patient presented with painless ascites of an inflammatory nature. However, the ascites was not related to peritonitis and SLE disease activity. The ascites disappeared following laparotomy and tumor resection without additional medication. Gynecologic benign tumors including uterine leiomyoma can be the cause of ascites in SLE patients. Clinicians should be aware of that possibility in case painless ascites occurs in females with SLE.

A scalable and continuous-upgradable optical wireless and wired convergent access network.

In this work, a scalable and continuous upgradable convergent optical access network is proposed. By using a multi-wavelength coherent comb source and a programmable waveshaper at the central office (CO), optical millimeter-wave (mm-wave) signals of different frequencies (from baseband to > 100 GHz) can be generated. Hence, it provides a scalable and continuous upgradable solution for end-user who needs 60 GHz wireless services now and > 100 GHz wireless services in the future. During the upgrade, user only needs to upgrade their optical networking unit (ONU). A programmable waveshaper is used to select the suitable optical tones with wavelength separation equals to the desired mm-wave frequency; while the CO remains intact. The centralized characteristics of the proposed system can easily add any new service and end-user. The centralized control of the wavelength makes the system more stable. Wired data rate of 17.45 Gb/s and w-band wireless data rate up to 3.36 Gb/s were demonstrated after transmission over 40 km of single-mode fiber (SMF).

Interferon consensus sequence-binding protein (ICSBP) promotes epithelial-to-mesenchymal transition (EMT)-like phenomena, cell-motility, and invasion via TGF-ß signaling in U2OS cells.

Interferon consensus sequence-binding protein (ICSBP) is a transcription factor induced by interferon gamma (IFN-γ) and a member of the interferon regulatory factor (IRF) family. ICSBP is predominantly expressed in hematopoietic cells and regulates the immune response and cell growth and differentiation. However, little is known about its function in non-hematopoietic cells. Here we show a novel function for ICSBP in epithelial-to-mesenchymal transition (EMT)-like phenomena (ELP), cell motility, and invasion in human osteosarcoma cell lines, including U2OS cells. IFN-γ treatment induced ICSBP expression and EMT-like morphological change in U2OS cells, which were suppressed by ICSBP knockdown. To further investigate the role of ICSBP in ELP, we established a stable U2OS cell line that overexpresses ICSBP. ICSBP expression caused U2OS cells to have a more elongated shape and an increased vimentin and fibronectin expression. ICSBP expression also promoted adhesiveness, motility, and invasiveness of U2OS cells. ICSBP upregulated transforming growth factor (TGF)-ß receptors and activated TGF-ß signaling cascades, which were responsible for ELP as well as increased cell motility and invasion. In addition, ICSBP-induced TGF-ß receptor activation resulted in the upregulation of Snail. Knockdown of Snail attenuated the ICSBP-induced augmentation of cell motility and invasion. Upregulation of Snail, ELP, and increased invasion by ICSBP expression were also observed in other osteosarcoma cell lines, such as Saos-2 and 143B. Furthermore, ICSBP and TGF-ß receptor I were expressed in 45/54 (84%) and 47/54 (87%) of human osteosarcoma tissues, respectively, and showed significant correlation (r=0.47, P=0.0007) with respect to their expression levels. Taken altogether, these data demonstrate a novel function for ICSBP in ELP, cell motility, and invasion through the TGF-ß and Snail signaling pathways.

Wired and wireless convergent extended-reach optical access network using direct-detection of all-optical OFDM super-channel signal.

We propose and demonstrate the feasibility of using all-optical orthogonal frequency division multiplexing (AO-OFDM) for the convergent optical wired and wireless access networks. AO-OFDM relies on all-optically generated orthogonal subcarriers; hence, high data rate (> 100 Gb/s) can be easily achieved without hitting the speed limit of electronic digital-to-analog and analog-to-digital converters (DAC/ADC). A proof-of-concept convergent access network using AO-OFDM super-channel (SC) is demonstrated supporting 40 - 100 Gb/s wired and gigabit/s 100 GHz millimeter-wave (MMW) ROF transmissions.

Surgical strategies for non-functioning pancreatic neuroendocrine tumours.

BACKGROUND: The purpose of this study was to identify management strategies for non-functioning pancreatic neuroendocrine tumours (NF-PNETs) by analysis of surgical outcomes at a single institution. METHODS: Archived records of patients with NF-PNETs who underwent surgery between 1994 and 2010 were reviewed. RESULTS: Among 125 patients, the median tumour size was 2·5 (range 0·15-20·5) cm. Of the 51 NF-PNETs with a diameter of no more than 2 cm, 12 (24 per cent) were diagnosed as carcinoma. Overall 20 patients (16·0 per cent) had metastases to the lymph nodes. The minimum size of the tumour with lymph node metastasis was 1·2 cm. Having a NF-PNET of 2 cm or larger significantly increased the probability of a poorly differentiated carcinoma (P = 0·006), and having a NF-PNET of at least 2·5 cm significantly increased the probability of lymph node metastasis (P = 0·048). The 5-year cumulative survival rate after curative resection was 89·7 per cent. During a median follow-up of 31·5 months, there were 27 recurrences (23·1 per cent) and 13 disease-specific deaths (11·1 per cent) among the 117 patients who had an R0 resection. All patients who underwent repeat operations were alive without additional recurrence after a mean(s.d.) follow-up of 27·1(18·0) months. CONCLUSION: Curative surgery should be performed for control of primary NF-PNETs. Lymph node dissection for NF-PNETs of 2·5 cm or larger and at least node sampling for tumours with a diameter of 1 cm or more are recommended. Debulking surgery should be considered for advanced tumours.

Efficacy and safety of ethanol ablation for thyroglossal duct cysts.

BACKGROUND AND PURPOSE: TGDC is a common congenital neck lesion, which has been treated by surgery. Although surgery is curative, it has drawbacks such as scars and surgical morbidity. Therefore, we applied EA as an alternative treatment technique. The purpose of this study was the evaluation of the efficacy and safety of EA for TGDC. MATERIALS AND METHODS: Between May 2005 and July 2008, we performed EA in 11 patients with TGDC who refused surgery. All patients were confirmed as having benign lesions before treatment. US-guided aspiration of the cystic fluid was followed by injection of absolute ethanol (99%). The injected volume of ethanol was 50%-80% of the volume of fluid aspirated. We evaluated the therapeutic outcome, including volume reduction of the TGDC, improvement of cosmetic problems and symptoms, and complications. RESULTS: The initial volume of the cysts ranged from 0.67 to 29.39 mL (mean, 6.0 mL). The procedure was performed in 1-3 sessions (mean, 1.4 sessions). Follow-up US was performed in 10 patients from 3 to 29 months (mean, 13.6 months). The mean volume of the cyst was 6.0 ± 8.4 mL, and volume reduction was 43.9%-100% (mean, 81.3%, P = .005) at last follow-up. Therapeutic success (volume reduction of >50%) was observed in 8 patients (8/10, 80%). Significant improvement of symptom- (P = .005) and cosmetic-grading scores (P = .003) was observed at last follow-up. No significant complications were observed during the procedure or follow-up periods. CONCLUSIONS: EA seems to be an effective and safe treatment method for TGDC.

Induction of apoptosis by the ginsenoside Rh2 by internalization of lipid rafts and caveolae and inactivation of Akt.

BACKGROUND AND PURPOSE: Lipid rafts and caveolae are membrane microdomains with important roles in cell survival signalling involving the Akt pathway. Cholesterol is important for the structure and function of these microdomains. The ginsenoside Rh2 exhibits anti-tumour activity. Because Rh2 is structurally similar to cholesterol, we investigated the possibility that Rh2 exerted its anti-tumour effect by modulating rafts and caveolae. EXPERIMENTAL APPROACH: A431 cells (human epidermoid carcinoma cell line) were treated with Rh2 and the effects on cell apoptosis, raft localization and Akt activation measured. We also examined the effects of over-expression of Akt and active-Akt on Rh2-induced cell death. KEY RESULTS: Rh2 induced apoptosis concentration- and time-dependently. Rh2 reduced the levels of rafts and caveolae in the plasma membrane and increased their internalization. Furthermore, Akt activity was decreased and consequently, Akt-dependent phosphorylation of Bad, a pro-survival protein, was decreased whereas the pro-apoptotic proteins, Bim and Bax, were increased upon Rh2 treatment. Unlike microdomain internalization induce by cholesterol depletion, Rh2-mediated internalization of rafts and caveolae was not reversed by cholesterol addition. Also, cholesterol addition did not restore Akt activation or rescue cells from Rh2-induced cell death. Rh2-induced cell death was attenuated in MDA-MB-231 cells over-expressing either wild-type or dominant-active Akt. CONCLUSIONS AND IMPLICATIONS: Rh2 induced internalization of rafts and caveolae, leading to Akt inactivation, and ultimately apoptosis. Because elevated levels of membrane rafts and caveolae, and Akt activation have been correlated with cancer development, internalization of these microdomains by Rh2 could potentially be used as an anti-cancer therapy.

Profiling advanced disease in an Asian clinical human immunodeficiency virus cohort: comparison of two definitions for acquired immunodeficiency syndrome.

OBJECTIVE: To compare advanced human immunodeficiency virus disease defined immunologically and clinically by evaluating the characteristics of human immunodeficiency virus patients in Hong Kong. DESIGN: Retrospective observational study. SETTING: A human immunodeficiency virus cohort database established at a university and the major human immunodeficiency virus specialist services in Hong Kong. PATIENTS: Patients diagnosed with acquired immunodeficiency syndrome at the study centres between 1985 and 2006 were included. MAIN OUTCOME MEASURES: Comparison of advanced human immunodeficiency virus disease defined (a) clinically as World Health Organization stage IV, and (b) immunologically as a CD4 count lower than 350/microL. RESULTS: Between 1985 and 2006, a total of 1317 patients, a majority of whom Chinese, were evaluated. Of these, 914 (69%) and 335 (25%) fulfilled the criteria for immunologically and clinically defined advanced disease, respectively. The mean age of the study population was 38 years and male-to-female ratio 4:1. There were two peaks in the frequency distribution of CD4 counts, one at a low count of less than 100/microL and the other between 200 and 400/microL. All except four with clinically defined advanced disease had CD4 counts lower than 350/microL on presentation. Of those with immunologically defined advanced disease, men having sex with men accounted for a lower proportion in the clinically advanced category, and Pneumocystis pneumonia was the commonest advanced disease at presentation. CONCLUSIONS: Both clinical and immunological definitions provide a consistent means for assessing advanced disease, the implications of which are different. Such profiling has been made possible through the operation of a standardised cohort database, which is useful in (1) enhancing human immunodeficiency virus epidemiology studies, and (2) evaluating the performance of public health services.

Validity of interferon-γ-release assays for the diagnosis of latent tuberculosis in haemodialysis patients.

Haemodialysis patients are at higher risk of developing active tuberculosis (TB) infection. However, tuberculin skin tests (TST) have limitations and the diagnostic usefulness of interferon-γ-release assays (IGRAs) remains unclear in immunocompromised hosts including haemodialysis patients. Haemodialysis patients were enrolled from a dialysis centre in Korea, an intermediate TB-burden country with a high bacille Calmette-Guérin (BCG) vaccination rate. The QuantiFERON-Gold TB In tube test (QFT) and the T-SPOT TB test (TSPOT) were performed, along with the TST. We stratified patients to low- and high-risk groups, according to the risk factors for latent TB. Association between each of the three diagnostic tests and the risk of latent TB was analysed. One hundred and sixty-seven patients were enrolled. The positive rates for the TST, the QFT and TSPOT were 23.5, 45.9 and 60.4%, respectively. Previous BCG vaccination increased the TST-positive rate in the low-risk group (OR 4.438), whereas it affected neither QFT nor TSPOT. The positive QFT rates were 41.2 and 62.5% in the low- and high-risk groups, respectively. The QFT was associated with the high-risk group (OR 2.578), whereas the TST was not. The positive TSPOT rates were 58.9 and 65.7% in the low- and high-risk groups, respectively. The frequency of indeterminate results was higher for the QFT (12.6%) compared with the TSPOT (4.8%). In conclusion, the IGRAs can be useful for the diagnosis of latent TB infection in haemodialysis patients.

Comparison of breath-hold 2D phase-contrast with non breath-hold cine phase-contrast MRA in the assessment of azygos venous blood flow in portal hypertension.

Azygos venous blood flow as an index of blood flow through the gastroesophageal collaterals and varices is of value in the prediction of gastrointestinal bleeding. Measurement of azygos venous blood flow has been achieved by non breath-hold (NBH) cine phase-contrast magnetic resonance imaging. The objective of this study was to compare the faster breath-hold (BH) phase-contrast technique with the standard (NBH) cine phase-contrast technique in the measurement of azygos blood flow. Thirty-two cirrhotic patients with esophageal varices were examined by magnetic resonance imaging using a BH technique and a NBH cine phase-contrast technique to measure the flow velocity, flow volume and calibre of the azygos vein at the mid-right atrial level. The flow values were obtained on the velocity image of the phase-contrast study. Values obtained from the two methods were evaluated statistically for the strength and significance of correlation by the Pearson test. Measurement by the BH method performed at full-inspiration as well as end-expiration was also obtained in 15 healthy volunteers. The breath-hold phase-contrast method has significant but weak correlation with non BH cine phase-contrast method in the measurement of azygos venous blood flow volume (r = 0.55, p < 0.01) and flow velocity (r = 0.43, p = 0.01). However, the calibre of the azygos vein gave a strong correlation in these two methods (0.82). In the subgroup of patients whose azygos blood flow velocity was greater than 7.4 cm/s, the correlation of azygos blood flow volume is strong (r = 0.80, p < 0.01). The azygos vein calibre remains highly correlated between the BH and NBH method, in both high flow velocity (r = 0.73) and low flow velocity (r = 0.83) groups. Breath-hold sequence leads to higher values for flow velocity and flow volume in the cirrhotic patients and also the control group. In patients with portal hypertension, BH 2D phase-contrast (PC) magnetic resonance angiography (MRA) could give a comparable estimation of the calibre of the azygos vein as the NBH 2D cine PC MRA but not for azygos flow volume. In patients with high azygos flow velocity, the strong correlation in flow volume between the BH and NBH method suggests that the BH method may be a time-saving alternative to the NBH method.

Economic analysis of celecoxib versus diclofenac plus omeprazole for the treatment of arthritis in patients at risk of ulcer disease.

AIM: To evaluate the economic impact of celecoxib therapy vs. diclofenac plus omeprazole therapy for the treatment of arthritis in Chinese patients with a high risk of bleeding, from the perspective of a public health organization in Hong Kong. METHODS: The medical records of 287 Chinese arthritic patients with a history of bleeding ulcers who had previously participated in a randomised study of celecoxib 200 mg twice daily and extended-release diclofenac 75 mg twice daily plus 20 mg of omeprazole daily for 6 months were reviewed. RESULTS: Compared to the diclofenac plus omeprazole group, the average total direct cost per patient in the celecoxib group showed a significant reduction of 11%, from HK 10,915 (range HK dollars 10,915-57,899) to HK dollars 9714 (range HK dollars 9714-89,770) (P<0.0001) (1 US dollars=7.8 HK dollars). The median direct medical cost for routine management in the celecoxib group was significantly lower (11%) than that for the diclofenac plus omeprazole group [HK dollars 10,915 (range 10,915-28,048) vs. HK dollars 9714 (range HK dollars 6946-26,179) (P<0.0001)]. In patients who experienced recurrent bleeding, the celecoxib group showed a significantly higher median cost of management of recurrent bleeding than the diclofenac plus omeprazole group [HK dollars 8466 (range 572-29,851) vs. HK dollars 23,210 (range HK dollars 12,318-65,823)] (P=0.036). CONCLUSIONS: Celecoxib therapy appears to cost less compared with diclofenac plus omeprazole for treatment of arthritis in Chinese patients with a high risk of bleeding.

Differential activation of phospholipases by mitogenic EGF and neurogenic PDGF in immortalized hippocampal stem cell lines.

In several neuronal systems, nerve growth factor (NGF) and platelet-derived growth factor (PDGF) act as neurogenic agents, whereas epidermal growth factor (EGF) acts as a mitogenic agent. Hippocampal stem cell lines (HiB5) immortalized by the expression of a temperature-sensitive SV40 large T antigen also respond differentially to EGF and PDGF. While EGF treatment at the permissive temperature induces proliferation, the addition of PDGF induces differentiation at the non-permissive temperature. However, the mechanism responsible for these different cellular fates has not been clearly elucidated. In order to clarify possible critical signaling events leading to these distinct cellular outcomes, we examined whether either EGF or PDGF differentially induces the activation of phospholipases, such as phospholipase A(2) (PLA(2)), C (PLC), or D (PLD). Although EGF stimulation did not induce phospholipases, PDGF caused a rapid and transient activation of PLC and PLD, but not PLA(2). When the activation of PLC or PLD was blocked, the neurite outgrowth induced by PDGF was significantly inhibited. Although the activation of PLD occurred faster than PLC, blocking of PLD activity by transient expression of lipase-inactive mutants did not inhibit the induction of PLC activity by PDGF. These results suggest that the differential activation of phospholipases may play an important role in signal transduction by mitogenic EGF and neurotrophic PDGF in HiB5 neuronal hippocampal stem cells. In particular, the activation of phospholipase C and D may contribute to neuronal differentiation by neurogenic PDGF in the HiB5 cells.

Zn2+-induced ERK activation mediated by reactive oxygen species causes cell death in differentiated PC12 cells.

Recent studies have provided evidence that Zn2+ plays a crucial role in ischemia- and seizure-induced neuronal death. However, the intracellular signaling pathways involved in Zn2+-induced cell death are largely unknown. In the present study, we investigated the roles of mitogen-activated protein kinases (MAPKs), such as c-Jun N-terminal kinase (JNK), p38 MAPK and extracellular signal-regulated kinase (ERK), and of reactive oxygen species (ROS) in Zn2+-induced cell death using differentiated PC12 cells. Intracellular accumulation of Zn2+ induced by the combined application of pyrithione (5 microM), a Zn2+ ionophore, and Zn2+ (10 microM) caused cell death and activated JNK and ERK, but not p38 MAPK. Preventing JNK activation by the expression of dominant negative SEK1 (SEKAL) did not attenuate Zn2+-induced cell death, whereas the inhibition of ERK with PD98059 and the expression of dominant negative Ras mutant (RasN17) significantly prevented cell death. Inhibition of protein kinase C (PKC) and phosphatidylinositol-3 kinase had little effect on Zn2+-induced ERK activation. Intracellular Zn2+ accumulation resulted in the generation of ROS, and antioxidants prevented both the ERK activation and the cell death induced by Zn2+. Therefore, we conclude that although Zn2+ activates JNK and ERK, only ERK contributes to Zn2+-induced cell death, and that ERK activation is mediated by ROS via the Ras/Raf/MEK/ERK signaling pathway.

Multiple ligand interaction of alpha-synuclein produced various forms of protein aggregates in the presence of Abeta25-35, copper, and eosin.

Various protein aggregates of alpha-synuclein developed by way of the common protein self-oligomerization in the presence of Abeta25-35, copper, and eosin were examined. All the aggregates exhibited congo red birefringence although the actual amounts of the aggregates were varied as determined by thioflavin T binding fluorescence. When their morphologies were analyzed in relation to in vitro cytotoxicity, the smallest granular aggregates obtained with copper exhibited the highest cytotoxicity, while the fibrous structures by eosin did not affect the cell.

Supramolecular assembly and acid resistance of Helicobacter pylori urease.

Helicobacter pylori, an etiologic agent in a variety of gastroduodenal diseases, produces a large amount of urease, which is believed to neutralize gastric acid by producing ammonia for the survival of the bacteria. Up to 30% of the enzyme associates with the surface of intact cells upon lysis of neighboring bacteria. The role of the enzyme at the extracellular location has been a subject of controversy because the purified enzyme is irreversibly inactivated below pH 5. We have determined the crystal structure of H. pylori urease, which has a 1.1 MDa spherical assembly of 12 catalytic units with an outer diameter of approximately 160 A. Under physiologically relevant conditions, the activity of the enzyme remains unaffected down to pH 3. Activity assays under different conditions indicated that the cluster of the 12 active sites on the supramolecular assembly may be critical for the survival of the enzyme at low pH. The structure provides a novel example of a molecular assembly adapted for acid resistance that, together with the low Km value of the enzyme, is likely to enable the organism to inhabit the hostile niche.