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Biomedical subjects

L L Wong

Publications and source records attributed to L L Wong.

At least 19 recordsLinked to original sources
PubMed2004

Oriented immobilization of Pseudomonas putida putidaredoxin at a gold (111)-buffer interface: a real time scanning tunnelling microscopy study.

A scanning tunnelling microscopy study of adsorption of wild-type Pseudomonas putida putidaredoxin at a gold (111)-buffer interface has been made in real time. Reversible adsorption has been observed reflecting weak interaction of the wild-type protein with a gold (111) electrode. A genetically engineered mutant, C73S-D58C, which contains a surface thiol, has been used for 'immobilization' and 'orientated adsorption' on the gold surface. The implication of such orientated immobilization in development of a bio-electrode surface has been predicted.

Adsorption↗
PubMed2001

Direct electrochemistry of pentachlorophenol hydroxylase.

The direct electrochemistry of the flavin-containing monooxygenase, pentachlorophenol hydroxylase (PCPH), at an edge plane graphite electrode was observed and a catalytic response, linear with concentration, was found with the substrate pentachlorophenol (PCP).

Bioreactors↗
PubMed2001

Screening for auditory neuropathy in a school for hearing impaired children.

OBJECTIVE: Hearing loss in children may be due to a wide variety of pathologies. Recently, use of otoacoustic emission technology has led to identification of auditory neuropathy as a distinct hearing disorder. Children with auditory neuropathy require audiological and educational management that may differ from that required by other hearing impaired students. For this reason, screening for auditory neuropathy may be appropriate for children attending schools for the hearing impaired. The study investigated the utility of using otoacoustic emission measures for school screening of hearing impaired children. METHODS: In this study, 81 children aged 6-12 years who attended one school for the deaf were screened for indications of auditory neuropathy. Children found to have consistent otoacoustic emissions were given a full diagnostic audiological test battery. RESULTS: Two children had transient otoacoustic emission results indicating normal outer hair cell function in one or both ears. A follow-up diagnostic assessment for the two positive cases was strongly suggestive of auditory neuropathy. CONCLUSIONS: There is a need for routine auditory neuropathy screening at schools for hearing impaired children.

Auditory Perceptual Disorders↗
PubMed2001

Vasopressin V2 receptor antagonists.

Hyponatremia due to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) and disorders of water retention such as congestive heart failure and cirrhosis is a common problem encountered in the care of the medical patient. Thus far, available treatment modalities for disorders of excess arginine vasopressin (AVP) secretion or action have been suboptimal. The development of nonpeptide AVP V2 receptor antagonists represents a promising treatment option to directly antagonize the effects of elevated plasma AVP concentrations by increasing the water permeability of renal collecting tubules, thereby promoting excretion of retained water and normalizing hypoosmolar hyponatremia. In this review, SIADH and other water retaining disorders are briefly discussed, after which the published preclinical and clinical studies in the development of several nonpeptide AVP V2 receptor antagonists are summarized. The likely therapeutic indications and potential complications of these compounds, as well as their vascular effects, are also described.

Animals↗
PubMed2001

Safety and efficacy of radiofrequency thermal ablation in advanced liver tumors.

HYPOTHESIS: Radiofrequency thermal ablation (RFA) can be performed safely and effectively to control local disease in patients with advanced, unresectable liver tumors. DESIGN, SETTING, AND PATIENTS: Prospective study of 76 patients with unresectable liver tumors who underwent RFA at a private tertiary referral hospital. INTERVENTIONS: Ninety-nine RFA operations were performed to ablate 328 tumors. MAIN OUTCOME MEASURES: Complications and local recurrence. RESULTS: There was 1 death (1%), major complications occurred in 7 operations (7%), and minor complications occurred in 10 operations (10%). Local recurrence was identified in 30 tumors (9%) at a mean follow-up of 15 months. Size (P<.001), vascular invasion (P<.001), and total volume ablated (P<.001) were associated with recurrence but the number of tumors was not (P =.39). CONCLUSION: Radiofrequency thermal ablation provides local control of advanced liver tumors with low recurrence and acceptable morbidity.

Adult↗
PubMed2001

Oxidation of polychlorinated benzenes by genetically engineered CYP101 (cytochrome P450(cam)).

Polychlorinated benzenes are recalcitrant environmental pollutants primarily because they are resistant to attack by dioxygenases commonly used by micro-organisms for the biodegradation of aromatic compounds. We have investigated the oxidation of polychlorinated benzenes by mutants of the haem mono-oxygenase CYP101 (cytochrome P450(cam)) from Pseudomonas putida with the aim of generating novel systems for their biodegradation. Wild-type CYP101 had low activity for the oxidation of dichlorobenzenes and trichlorobenzenes to the chlorophenols, but no products were detected for the heavily chlorinated benzenes. Increasing the active-site hydrophobicity with the Y96F mutation increased the activity up to 100-fold, and both pentachlorobenzene and hexachlorobenzene were oxidized slowly to pentachlorophenol. Decreasing the space available at the top of the active site with the F87W mutation to force the substrate to be bound closer to the haem resulted in a further 10-fold increase in activity with most substrates. Introducing the F98W mutation, also at the top of the active site, decreased the NADH-turnover rates but increased the coupling efficiencies, and > 90% coupling was observed for 1,3-dichlorobenzene and 1,3,5-trichlorobenzene with the F87W--Y96F--F98W mutant. The V247L mutation generally increased the NADH-turnover rates, and the F87W--Y96F--V247L mutant showed reasonably fast NADH turnover (229 min(-1)) with the highly insoluble pentachlorobenzene without the need for surfactants or organic cosolvents. As all chlorophenols are degraded by micro-organisms, novel biodegradation systems could be constructed in which CYP101 mutants convert the inert polychlorinated benzenes to the phenols, which are then readily degraded by natural pathways.

Benzene Derivatives↗
PubMed2001

Protein engineering of Bacillus megaterium CYP102. The oxidation of polycyclic aromatic hydrocarbons.

Cytochrome P450 (CYP) enzymes are involved in activating the carcinogenicity of polycyclic aromatic hydrocarbons (PAHs) in mammals, but they are also utilized by microorganisms for the degradation of these hazardous environmental contaminants. Wild-type CYP102 (P450(BM-3)) from Bacillus megaterium has low activity for the oxidation of the PAHs phenanthrene, fluoranthene and pyrene. The double hydrophobic substitution R47L/Y51F at the entrance of the substrate access channel increased the PAH oxidation activity by up to 40-fold. Combining these mutations with the active site mutations F87A and A264G lead to order of magnitude increases in activity. Both these mutations increased the NADPH turnover rate, but the A264G mutation increased the coupling efficiency while the F87A mutation had dominant effects in product selectivity. Fast NADPH oxidation rates were observed (2250 min-1 for the R47L/Y51F/F87A mutant with phenanthrene) but the coupling efficiencies were relatively low (< 13%), resulting in a highest substrate oxidation rate of 110 min-1 for fluoranthene oxidation by the R47L/Y51F/A264G mutant. Mutation of M354 and L437 inside the substrate access channel reduced PAH oxidation activity. The PAHs were oxidized to a mixture of phenols and quinones. Notably mutants containing the A264G mutation showed some similarity to mammalian CYP enzymes in that some 9,10-phenanthrenequinone, the K-region oxidation product from phenanthrene, was formed. The results suggest that CYP102 mutants could be useful models for PAH oxidation by mammalian CYP enzymes, and also potentially for the preparation of novel PAH bioremediation systems.

Animals↗
PubMed2001

Engineering the CYP101 system for in vivo oxidation of unnatural substrates.

The protein engineering of CYP enzymes for structure-activity studies and the oxidation of unnatural substrates for biotechnological applications will be greatly facilitated by the availability of functional, whole-cell systems for substrate oxidation. We report the construction of a tricistronic plasmid that expresses the CYP101 monooxygenase from Pseudomonas putida, and its physiological electron transfer co-factor proteins putidaredoxin reductase and putidaredoxin in Escherichia coli, giving a functional in vivo catalytic system. Wild-type CYP101 expressed in this system efficiently transforms camphor to 5-exo-hydroxycamphor without further oxidation to 5-oxo-camphor until >95% of camphor has been consumed. CYP101 mutants with increased activity for the oxidation of diphenylmethane (the Y96F-I395G mutant), styrene and ethylbenzene (the Y96F-V247L mutant) have been engineered. In particular, the Y96F-V247L mutant shows coupling efficiency of approximately 60% for styrene and ethylbenzene oxidation, with substrate oxidation rates of approximately 100/min. Escherichia coli cells transformed with tricistronic plasmids expressing these mutants readily gave 100-mg quantities of 4-hydroxydiphenylmethane and 1-phenylethanol in 24-72 h. This new in vivo system can be used for preparative scale reactions for product characterization, and will greatly facilitate directed evolution of the CYP101 enzyme for enhanced activity and selectivity of substrate oxidation.

Alkanes↗
PubMed2001

Organ procurement 1999-2000: how is Hawaii doing?

With the advent of The Final Rule, the state of Hawaii should have potential organ donor identification and referral rates of 100%. However, a retrospective chart review of 4,697 deaths in 1999 and 4,730 deaths in 2000, revealed identification rates of 80% and 84%, and referral rates of 53% and 71%, respectively. Proper recognition and referral of all potential donors is essential to bridging the enormous gap between the supply of organs and its demand.

Hawaii↗
PubMed2000

Needle-tract implantation from hepatocellular cancer: is needle biopsy of the liver always necessary?

Percutaneous needle biopsies are frequently used to evaluate focal lesions of the liver. Needle-tract implantation of hepatocellular cancer has been described in case reports, but the true risk for this problem has not been clearly defined. We retrospectively reviewed 91 cases of hepatocellular cancer during a 4-year period from 1994 to 1997. Data on diagnostic studies, therapy, and outcome were noted. Of 91 patients with hepatocellular cancer, 59 patients underwent percutaneous needle biopsy as part of their diagnostic workup for a liver mass. Three patients (5.1%) were identified with needle-tract implantation of tumor. Two patients required en bloc chest wall resections for implantation of hepatocellular cancer in the soft tissues and rib area. The third patient, who also received percutaneous ethanol injection of his tumor, required a thoracotomy and lung resection for implanted hepatocellular cancer. Percutaneous needle biopsy of suspicious hepatic lesions should not be performed indiscriminately because there is a significant risk for needle-tract implantation. These biopsies should be reserved for those lesions in which no definitive surgical intervention is planned and pathological confirmation is necessary for a nonsurgical therapy.

Adult↗
PubMed2000

Comparison of supraspinatus tendon and glenohumeral joint axes in MR imaging of the shoulder.

OBJECTIVE: In magnetic resonance (MR) imaging of the shoulder, oblique coronal images are used for evaluating the supraspinatus tendon (SST) of patients with suspected rotator cuff tear or impingement. This study aimed to compare orientation of the SST long axis with planes perpendicular to the glenohumeral joint (GHJ). DESIGN AND PATIENTS: The axial scans of 100 consecutive patients referred for MR imaging or MR arthrography of the shoulder were reviewed. Using the electronic cursors of a computer workstation, the angle of the SST long axis was measured and compared with the angle obtained through the GHJ utilizing three different landmarks: perpendicular to the joint (GHJ-90), joint-humeral head center axis (GHJ-H) and joint-scapular body axis (GHJ-S). RESULTS: Differences in angulation between axes of the SST and the three GHJ axes averaged only about 5 degree [range of means 4.5-5.3 degrees, range of standard deviation (SD) 3.8-4.6 degrees]. In the majority of shoulders, angular differences measured 4 or less for all SST/GHJ comparisons. Similarly, small angular differences in the three GHJ axes were found: 4.5 degrees (SD 3.3 degrees) for GHJ-90/GHJ-S, 5.0 degree (SD 4.0 degrees) for GHJ-S/GHJ-H and 2.9 degrees (SD 3.0 degrees) for GHJ-90/GHJ-H. Correlation between the GHJ-90 and GHJ-H axes was particularly good, with differences of 4 degree or less in 84% of shoulders. The orientations of the GHJ axes and that of the SST long axis are comparable. CONCLUSION: The GHJ may potentially be used as a landmark for obtaining oblique coronal images of the SST.

Adolescent↗
PubMed2000

A scanning tunnelling study of immobilised cytochrome P450cam.

A site-specifically engineered surface cysteine residue, located in a region where the haem moiety is closest to the surface, is used to anchor cytochrome P450cam enzyme molecules covalently to a gold electrode. More reproducibly ordered adsorption, at high coverage, occurs with this K344C mutant than with the wild-type enzyme. The subsequently formed close-packed monolayer arrays have been probed by scanning tunnelling microscopy under ambient conditions and under aqueous (buffered) solution at high resolution. Initial indications suggest that the immobilised enzyme is both electrochemically addressable and catalytically active.

Camphor 5-Monooxygenase↗
PubMed2000

Catalytic reductive dehalogenation of hexachloroethane by molecular variants of cytochrome P450cam (CYP101).

CYP101 (cytochrome P450cam) catalyses the oxidation of camphor but has also been shown to catalyse the reductive dehalogenation of hexachloroethane and pentachloroethane. This reaction has potential applications in the biodegradation of these environmental contaminants. The hexachloroethane dehalogenation activity of CYP101 has been investigated by mutagenesis. The effects of active-site polarity and volume were probed by combinations of active-site mutations. Increasing the active-site hydrophobicity by the Y96A and Y96F mutations strengthened hexachloroethane binding but decreased the rate of reaction. Increasing the polarity with the F87Y mutation drastically weakened hexachloroethane binding but did not affect the rate of reaction. The Y96H mutation had little effect at pH 7.4, but weakened hexachloroethane binding while increasing the rate of dehalogenation by up to 40% at pH 6.5, suggesting that the imidazole side-chain was partially protonated at pH 6.5 but not at pH 7.4. Substitutions by bulkier side-chains at F87, T101 and V247 weakened hexachloroethane binding but increased the dehalogenation rate. The effect of the individual mutations was additive in multiple mutants, and the most active mutant for hexachloroethane reductive dehalogenation at pH 7.4 was F87W-V247L (80 min-1 or 2.5 x the activity of the wild-type). The results suggested that the CYP101 active site shows good match with hexachloroethane, the Y96 side-chain plays an important role in both hexachloroethane binding and dehalogenation, and hexachloroethane binding and dehalogenation places conflicting demands on active-site polarity and compromises were necessary to achieve reasonable values for both.

Binding Sites↗
PubMed2000

Improved survival with screening for hepatocellular carcinoma.

Hepatocellular cancer (HCC) is a frequent cause of cancer death worldwide. Although successful screening programs exist in Asian countries, the role for screening in the United States is not clear. The purpose of this study is to determine if screening has an effect on survival in a predominantly Asian population in Hawaii. We retrospectively reviewed cases of HCC from 1993 to 1998 for demographic data, risk factors, symptoms, stage, treatment, and survival. Patients were divided into 3 groups according to presentation: symptomatic (S), asymptomatic (A), and asymptomatic but screened for disease (A/Sc). Kaplan-Meier analysis was performed on overall survival by group. Ninety-one patients were referred for HCC. There were 56 patients in group S, 19 patients in group A, and 16 patients in group A/Sc. Patients in group A/Sc survived significantly longer than those in group S (P =.009), with the former group having a median survival of 1,399 versus 234 days for group S. Median survival for group A was 545 days and did not differ significantly from the other groups. Patients who are asymptomatic and screened for HCC have an increased survival compared with those patients who present with symptoms. This may justify the use of a formal screening program for HCC in Hawaii, but we would need to investigate this prospectively.

Adult↗
PubMed2000

Protein engineering of cytochrome p450(cam) (CYP101) for the oxidation of polycyclic aromatic hydrocarbons.

Mutations of the active site residues F87 and Y96 greatly enhanced the activity of cytochrome P450(cam) (CYP101) from Pseudomonas putida for the oxidation of the polycyclic aromatic hydrocarbons phenanthrene, fluoranthene, pyrene and benzo[a]pyrene. Wild-type P450(cam) had low (<0.01 min(-1)) activity with these substrates. Phenanthrene was oxidized to 1-, 2-, 3- and 4-phenanthrol, while fluoranthene gave mainly 3-fluoranthol. Pyrene was oxidized to 1-pyrenol and then to 1,6- and 1,8-pyrenequinone, with small amounts of 2-pyrenol also formed with the Y96A mutant. Benzo[a]pyrene gave 3-hydroxybenzo[a]pyrene as the major product. The NADH oxidation rate of the mutants with phenanthrene was as high as 374 min(-1), which was 31% of the camphor oxidation rate by wild-type P450(cam), and with fluoranthene the fastest rate was 144 min(-1). The oxidation of phenanthrene and fluoranthene were highly uncoupled, with highest couplings of 1.3 and 3.1%, respectively. The highest coupling efficiency for pyrene oxidation was a reasonable 23%, but the NADH turnover rate was slow. The product distributions varied significantly between mutants, suggesting that substrate binding orientations can be manipulated by protein engineering, and that genetic variants of P450(cam) may be useful for studying the oxidation of polycyclic aromatic hydrocarbons by P450 enzymes.

Amino Acid Substitution↗
PubMed2000

Attitudes on organ donation among Hawaii physicians.

A survey of physicians attending the recent Hawaii Medical Association meeting was conducted in order to assess physician attitudes on organ donation. Physicians were asked 6 questions and demographics were collected. Results indicate that Hawaii physicians generally support organ donation and are aware of some of the current federal legislation regarding donation.

Attitude of Health Personnel↗