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Biomedical subjects

T Lee

Publications and source records attributed to T Lee.

At least 109 records · Page 6Linked to original sources
PubMed2000

Rac-related GTP-binding protein in elicitor-induced reactive oxygen generation by suspension-cultured soybean cells.

Plant cells produce reactive oxygen species (ROS) in response to many stimuli. However, the mechanism of ROS biosynthesis remains unclear. We have explored the hypothesis that the superoxide burst in plants mechanistically resembles the oxidative burst in neutrophils. First we have confirmed that ROS production, which occurs in suspension-cultured soybean (Glycine max) cells in response to hypo-osmotic shock, is inhibited by diphenylene iodonium, an inhibitor of the flavin-dependent oxidase of neutrophils. Because a Rac family G protein is an essential regulator of this NADPH oxidase, and because many plant homologs of Rac have been cloned, we next examined whether Rac-like proteins might be involved in the oxidative burst in the soybean cells. We identified a Rac-like 21-kD soybean protein that cross-reacts with antibodies to human Rac and garden pea Rop and also binds [gamma-(35)S] GTP, a diagnostic trait of small G proteins. This Rac-related protein translocated from the cytosol to microsomes during the oxidative burst. Moreover, soybean cells transiently transformed with either a dominant negative (RacN17) or a dominant positive (RacV12) form of Rac1 showed the anticipated altered responses to three different stimuli: hypo-osmotic shock, oligo-GalUA, and harpin. In response to these stimuli, cells transformed with RacN17 produced less ROS and cells transformed with RacV12 generated more ROS than control cells. These results strongly suggest that a Rac-related protein participates in the regulation of ROS production in soybean cells, possibly via activation of an enzyme complex similar to the NADPH oxidase of phagocytes in animal systems.

Animals↗
PubMed2000

Viscoelastic dissipation in compact bone: implications for stress-induced fluid flow in bone.

Viscoelastic properties of wet and dry human compact bone were studied in torsion and in bending for both the longitudinal and transverse directions at frequencies from 5 mHz to 5 kHz in bending to more than 50 kHz in torsion. Two series of tests were done for different longitudinal and transverse specimens from a human tibia. Wet bone exhibited a larger viscoelastic damping tan delta (phase between stress and strain sinusoids) than dry bone over a broad range of frequency. All the results had in common a relative minimum in tan delta over a frequency range, 1 to 100 Hz, which is predominantly contained in normal activities. This behavior is inconsistent with an optimal "design" for bone as a shock absorber. There was no definitive damping peak in the range of frequencies explored, which could be attributed to fluid flow in the porosity of bone.

Aged↗
PubMed2000

Alteration of substrate and inhibitor specificity of feline immunodeficiency virus protease.

Feline immunodeficiency virus (FIV) protease is structurally very similar to human immunodeficiency virus (HIV) protease but exhibits distinct substrate and inhibitor specificities. We performed mutagenesis of subsite residues of FIV protease in order to define interactions that dictate this specificity. The I37V, N55M, M56I, V59I, and Q99V mutants yielded full activity. The I37V, N55M, V59I, and Q99V mutants showed a significant increase in activity against the HIV-1 reverse transcriptase/integrase and P2/nucleocapsid junction peptides compared with wild-type (wt) FIV protease. The I37V, V59I, and Q99V mutants also showed an increase in activity against two rapidly cleaved peptides selected by cleavage of a phage display library with HIV-1 protease. Mutations at Q54K, I98P, and L101I dramatically reduced activity. Mutants containing a I35D or I57G substitution showed no activity against either FIV or HIV substrates. FIV proteases all failed to cut HIV-1 matrix/capsid, P1/P6, P6/protease, and protease/reverse transcriptase junctions, indicating that none of the substitutions were sufficient to change the specificity completely. The I37V, N55M, M56I, V59I, and Q99V mutants, compared with wt FIV protease, all showed inhibitor specificity more similar to that of HIV-1 protease. The data also suggest that FIV protease prefers a hydrophobic P2/P2' residue like Val over Asn or Glu, which are utilized by HIV-1 protease, and that S2/S2' might play a critical role in distinguishing FIV and HIV-1 protease by specificity. The findings extend our observations regarding the interactions involved in substrate binding and aid in the development of broad-based inhibitors.

Amino Acid Sequence↗
PubMed2000

Regulation of Th2 cytokine gene transcription.

Because of the different functions of IL-4, IL-13 and IL-5, it would perhaps be surprising if common transcriptional mechanisms occur. However, because of the physical proximity of their genes within the human 5q locus, chromatin remodelling during T-cell differentiation may make transcription of all the genes permissible. If co-ordinate regulation were to take place, it might be argued that similar factors might be involved in expression of all of the cytokines. Emerging data on c-Maf and GATA3 regulation of IL-4 and IL-5 respectively argues that diverse proteins may be required for transcriptional activation. Alternatively, these factors may be responsible for regulating transcriptional competence, allowing fine control over generation of particular cytokines depending upon recognition of physiological cues. If competent for transcription, common factors, such as members of the NFAT and/or AP-1 families, may operate to regulate cytokine levels. To support this, we have recently identified a conserved palindrome located within the promoters of the different Th2-type cytokines, which acts as an enhancer of transcription. Central to the capacity to express Th2 cytokines is likely to be the ability to remodel chromatin at the locus. It remains to be determined whether a single factor, or combination of factors acts to regulate this event. It is also unclear what the boundaries of remodelling within the locus are, i.e. whether IL-4 and IL-13 may be within open chromatin and IL-5 in a closed environment, and whether there is a hierarchy which determines whether particular cytokines are preferentially expressed irrespective of competence.

Animals↗
PubMed2000

Attention to detail: injuries at altitude among U.S. Army Military static line parachutists.

Altitude injuries, defined as injuries sustained by military static line parachutists before ground impact, have not been reviewed for 50 years. There are indications that these injuries are increasing at Fort Bragg, North Carolina. Between May 1, 1994, and April 30, 1996, surveillance was conducted for parachute-related injuries and altitude injuries at Fort Bragg. The incidence of all jump-related injuries was 8.1/1,000 aircraft exits. Significant risk factors for injury included being 30 years of age or older (p < 0.001) and being female (p = 0.003). The overall incidence of altitude injuries was noted to be 0.46/1,000 aircraft exits. Risk factors for altitude injury included being 40 years of age or older (p = 0.005) and in the rank of E-1 to E-3 (p = 0.0001). Fifty-four percent of injuries occurred during exiting before complete parachute deployment, and 46% occurred during the opening shock of the parachute. Mechanisms of injury included static line entanglement (33%), riser/suspension-line entanglement (46%), aircraft strikes (21%), unsecured equipment strikes (1%), and opening shock deceleration (1%). The majority of severe altitude injuries are caused by riser/suspension-line entanglement (63%) and involve the knee joint (37%). Although the incidence of altitude injury is quite small, the potential risk for career-threatening and/or life-threatening injury is great. This risk can be reduced by appropriate training and attention to detail.

Adolescent↗
PubMed2000

The cost-effectiveness of varicella screening and vaccination in U.S. Army recruits.

Varicella outbreaks in the U.S. Army disrupt training, reduce readiness, and represent substantial costs. Vaccination of susceptible individuals may be cost-effective. We conducted a cost-effectiveness analysis comparing screening of all incoming recruits and vaccination of susceptible individuals at either initial entry training (IET) or medical entrance processing station (MEPS), universal vaccination at IET, and no intervention. Primary health outcomes included the number of varicella cases prevented during the 8-week initial training period. The varicella hospitalization rate was 21.6 per 10,000 per year. In 100,000 recruits, 36 cases of varicella are expected at a cost of $181,000 in the absence of an intervention. Screening at IET would prevent 4 cases but would cost an additional $3,255,000 more than no intervention. Screening at MEPS would prevent 3 cases and save $521,000 per case prevented during the IET but would cost $2,734,000 more than no intervention. Universal vaccination would prevent 2 cases but would cost $15,858,000 more than MEPS screening and $18,592,000 more than no intervention. These results are robust. Cost per case of varicella prevented ranged from $390,000 to $7.9 million. Scarce prevention resources could be more cost-effectively allocated to other prevention programs.

Absenteeism↗
PubMed2000

Elevation of vitreous leptin in diabetic retinopathy and retinal detachment.

PURPOSE: Leptin is a cytokine that regulates energy metabolism and is linked to diabetes mellitus through its metabolic actions. Leptin is angiogenic and promotes wound healing, and therefore this investigation was conducted to determine whether leptin is associated with neovascular and fibrotic complications of diabetes and other retinopathies. METHODS: Serum and vitreous samples were collected from patients classified by the presence and type of diabetic retinopathy or other ocular diseases. Leptin was measured in serum and vitreous by radioimmunoassay, and leptin and leptin receptor were localized in epiretinal membranes immunohistochemically. RESULTS: Leptin levels in serum and vitreous were higher in patients with diabetes than in those without, and vitreous leptin concentrations were especially elevated in patients with proliferative diabetic retinopathy or retinal detachment. Leptin and leptin receptor were detected in fibrovascular epiretinal membrane of patients with diabetes. CONCLUSIONS: Leptin in human vitreous is elevated in proliferative diabetic retinopathy, and retinal detachment and is present in fibrovascular epiretinal tissue. These data suggest an involvement of leptin in retinal disease.

Adolescent↗
PubMed2000

The epidemiology of varicella hospitalizations in the U.S. Army.

Varicella infections affect the U.S. Army, but the extent has not been quantified recently. We obtained 1990 to 1997 hospitalization data from the U.S. Army Medical Command and calculated rates using data from the Army Medical Surveillance Activity and the U.S. Army Training Command. There was a decline in the number and incidence of varicella hospitalizations for U.S. Army active duty soldiers from 1990 to 1997. Varicella incidence rates for active duty soldiers are significantly higher for females, blacks, those younger than 20 years, and those whose home of record were tropical island regions. Army initial entry training hospitalizations constitute 11.8% of active duty Army hospitalizations and have also declined. Varicella continues to affect the training and health of the U.S. Army; however, the impact has diminished over the years. A feasible approach to limit varicella in the U.S. Army is to target trainees for screening or vaccination. Refinement of this strategy should be determined from a follow-up cost-effectiveness analysis.

Adult↗
PubMed2000

A model for estimating mental health service needs in South Africa.

OBJECTIVE: To develop a model for estimating the services and human resources needed to care for people with severe psychiatric conditions in a hypothetical population of 100,000 people in South Africa. METHOD: Annual mental health service needs were estimated in terms of numbers of daily patient visits (DPV) in ambulatory care, the number of beds required, and staffing. Developed within a spreadsheet format, the model allows for the adjustment of key service variables according to estimated or existing service data. RESULTS: At 100% coverage, 87 DPV, 28 acute beds, and 10 medium-long stay beds are necessary for a population of 100,000 people. This would require 35.2 full-time equivalent mental health staff: 21.3 for inpatient care, 12.0 for ambulatory care, and 1.9 for management. CONCLUSION: Because the model can produce a range of service recommendations, the assumptions that inform it should be clearly stated and justified. This method makes the assumptions on which services are planned explicit and allows for a rational approach to decision making.

Adolescent↗
PubMed1999

A simple and sensitive antigen retrieval method for free-floating and slide-mounted tissue sections.

The masking of antigens by aldehyde-containing fixatives or by paraffin embedding procedures is a problem for immunohistochemical studies. Enzymatic digestion, formic acid treatment, microwave heating and autoclave heating have been used to deal with this problem, with microwave heating-based antigen retrieval having become widely used as the method of choice. Microwave heating, however, has the shortcoming that it is difficult to precisely control the heating temperature and it is difficult to apply this method of heating to free-floating sections without damaging the sections. We describe here a simple, reliable and sensitive antigen retrieval method that uses water-bath heating. By this method, the temperature can be precisely controlled to yield effective antigen retrieval with minimal tissue damage in free-floating or paraffin-embedded slide-mounted sections. We found that the best results were obtained with a 30 min incubation in a 10-50 mM sodium citrate solution (pH 8.5-9.0) preheated to and maintained at 80 degrees C in a water-bath, followed by 30 min incubation in 0.3-3% nonfat dry milk to reduce nonspecfic staining. This method is highly effective for both 40 microm free floating sections, slide-mounted cryostat sections and paraffin-embedded slide-mounted sections, and it works well for tissue from diverse species (human, rat, mouse, pigeon, and zebra finch) and for diverse antigens (e.g. enkephalin, substance P, huntingtin, GluR1, GFAP, and ubiquitin). This method was also found to enhance immunolabeling in glutaraldehyde-fixed tissue that had been prepared for ultrastructural examination, without having a deleterious effect on the ultrastructure.

Animals↗
PubMed1999

Rapid induction of behavioral and neurochemical tolerance to cocaethylene, a model compound for agonist therapy of cocaine dependence.

RATIONALE: Tolerance to abused drugs may impact on patterns of abuse, and in the case of agonist therapies, may be beneficial in that it reduces the reward value of a given dose of abused drug. Cocaethylene, a psychoactive metabolite resulting from concurrent alcohol and cocaine consumption, was examined because of its use in human research studies of drug reward mechanisms, and its potential as a model compound for an agonist based therapy for cocaine dependence. OBJECTIVE: Comparisons were made between cocaine and cocaethylene in the acute development of tolerance to the neurochemical and behavioral effects of cocaine. With chronic exposure, tolerance to the behavioral effects of cocaine was examined. METHODS: In awake rats with a microdialysis probe in the nucleus accumbens and a jugular catheter, an IV bolus/3-h infusion of cocaine or cocaethylene and a subsequent cocaine challenge was administered while extracellular dopamine and locomotion were monitored. Chronic IV treatment with cocaine, cocaethylene, and a water control was accomplished for 7 days using osmotic minipumps attached to jugular catheters. Animals were then challenged with an IV bolus of cocaine. RESULTS: With acute treatment, the IV bolus of cocaethylene at the beginning of the infusion period resulted in an initial behavioral activation equivalent to that caused by cocaine, after which there was a striking difference in that the cocaethylene group displayed a return to predrug levels of activity, while the cocaine group showed high levels of activity throughout the 3-h period. Both cocaethylene and cocaine resulted in an initial increase in the extracellular concentration of dopamine. However, after that initial increase, levels of dopamine dropped in the cocaethylene group while the cocaine group levels remained elevated. A 1-week infusion of cocaine or cocaethylene resulted in tolerance to the behavioral activating effects of a subsequent cocaine challenge. CONCLUSIONS: These results demonstrate a rapid induction of tolerance to the behavioral and neurochemical properties of cocaethylene, resulting in a diminished behavioral response to a cocaine challenge both acutely, and after 7 days. The relevance of these data for the use of cocaethylene as a model compound for an agonist approach to therapy for cocaine dependence is discussed.

Animals↗
PubMed1999

The delivery of BCNU to brain tumors.

This paper reports the development of three-dimensional simulations to study the effect of various factors on the delivery of 1-3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to brain tumors. The study yields information on the efficacy of various delivery methods, and the optimal location of polymer implantation. Two types of drug deliveries, namely, systemic administration and controlled release from polymers, were simulated using fluid dynamics analysis package (FIDAP) to predict the temporal and spatial variation of drug distribution. Polymer-based delivery provides higher mean concentration, longer BCNU exposure time and reduced systemic toxicity than bolus injection. Polymer implanted in the core gives higher concentration of drug in both the core and viable zone than the polymer in the viable zone case. The penetration depth of BCNU is very short. This is because BCNU can get drained out of the system before diffusing to any appreciable distance. Since transvascular permeation is the dominant means of BCNU delivery, the interstitial convection has minor effect because of the extremely small transvascular Peclet number. The reaction of BCNU with brain tissues reduces the drug concentration in all regions and its effect increases with rate constant. The implantation of BCNU/ethylene-vinyl acetate copolymer (EVAc) matrix at the lumen of the viable zone immediately following the surgical removal of 80% of the tumor may be an effective treatment for the chemotherapy of brain tumors. The present study provides a quantitative examination on the working principle of Gliadel wafer for the treatment of brain tumors.

Antineoplastic Agents, Alkylating↗
PubMed1999

Variation of clinical target volume definition in three-dimensional conformal radiation therapy for prostate cancer.

PURPOSE: Currently, three-dimensional conformal radiation therapy (3D-CRT) planning relies on the interpretation of computed tomography (CT) axial images for defining the clinical target volume (CTV). This study investigates the variation among multiple observers to define the CTV used in 3D-CRT for prostate cancer. METHODS AND MATERIALS: Seven observers independently delineated the CTVs (prostate +/- seminal vesicles [SV]) from the CT simulation data of 10 prostate cancer patients undergoing 3D-CRT. Six patients underwent CT simulation without the use of contrast material and serve as a control group. The other 4 had urethral and bladder opacification with contrast medium. To determine interobserver variation, we evaluated the derived volume, the maximum dimensions, and the isocenter for each examination of CTV. We assessed the reliability in the CTVs among the observers by correlating the variation for each class of measurements. This was estimated by intraclass correlation coefficient (ICC), with 1.00 defining absolute correlation. RESULTS: For the prostate volumes, the ICC was 0.80 (95% confidence interval [CI]: 0.56-0.96). This changed to 0.92 (95% CI: 0.75-0.99) with the use of contrast material. Similarly, the maximal prostatic dimensions were reliable and improved. There was poor agreement in defining the SV. For this structure, the ICC never exceeded 0.28. The reliability of the isocenter was excellent, with the ICC exceeding 0.83 and 0.90 for the prostate +/- SV, respectively. CONCLUSIONS: In 3D-CRT for prostate cancer, there was excellent agreement among multiple observers to define the prostate target volume but poor agreement to define the SV. The use of urethral and bladder contrast improved the reliability of localizing the prostate. For all CTVs, the isocenter was very reliable and should be used to compare the variation in 3D dosimetry among multiple observers.

Humans↗
PubMed1999

Failure of measles virus to activate nuclear factor-kappa B in neuronal cells: implications on the immune response to viral infections in the central nervous system.

Neurons are postmitotic cells that foster virus persistence. These cells lack the HLA class I molecules required for clearance of infected cells. Previously, we showed that HLA class I is induced by measles virus (MV) on glial cells, which is primarily mediated by IFN-beta. In contrast, MV was unable to induce HLA class I or IFN-beta in neuronal cells. This failure was associated with lack of NF-kappa B binding to the positive regulatory domain II element of the IFN-beta promoter, which is essential for virus-induced IFN-beta gene activity. In this study, we demonstrate that the failure to activate NF-kappa B in neuronal cells is due to the inability of MV to induce phosphorylation and degradation of I kappa B, the inhibitor of NF-kappa B. In contrast, TNF-alpha induced degradation of I kappa B alpha in the neuronal cells, suggesting that failure to induce I kappa B alpha degradation is likely due to a defect in virus-mediated signaling rather than to a defect involving neuronal I kappa B alpha. Like MV, mumps virus and dsRNA failed to induce I kappa B alpha degradation in the neuronal cells, suggesting that this defect may be specific to viruses. Autophosphorylation of the dsRNA-dependent protein kinase, a kinase possibly involved in virus-mediated I kappa B alpha phosphorylation, was intact in both cell types. The failure of virus to induce I kappa B alpha phosphorylation and consequently to activate NF-kappa B in neuronal cells could explain the repression of IFN-beta and class I gene expression in virus-infected cells. These findings provide a potential mechanism for the ability of virus to persist in neurons and to escape immune surveillance.

DNA-Binding Proteins↗