Biomedical subjects
Publications and source records attributed to A K Lee.
In this review, we focus on how biofilms comprising iron-respiring bacteria influence steel corrosion. Specifically, we discuss how biofilm growth can affect the chemistry of the environment around the steel at different stages of biofilm development, under static or dynamic fluid regimes. We suggest that a mechanistic understanding of the role of biofilm metabolic activity may facilitate corrosion control.
In the vast majority of brain areas, the firing rates of neurons, averaged over several hundred milliseconds to several seconds, can be strongly modulated by, and provide accurate information about, properties of their inputs. This is referred to as the rate code. However, the biophysical laws of synaptic plasticity require precise timing of spikes over short timescales (<10 ms). Hence it is critical to understand the physiological mechanisms that can generate precise spike timing in vivo, and the relationship between such a temporal code and a rate code. Here we propose a mechanism by which a temporal code can be generated through an interaction between an asymmetric rate code and oscillatory inhibition. Consistent with the predictions of our model, the rate and temporal codes of hippocampal pyramidal neurons are highly correlated. Furthermore, the temporal code becomes more robust with experience. The resulting spike timing satisfies the temporal order constraints of hebbian learning. Thus, oscillations and receptive field asymmetry may have a critical role in temporal sequence learning.
1. We used the patch-clamp technique, in conjunction with membrane capacitance measurement, fluorescence measurement of intracellular calcium concentration ([Ca(2+)](i)), and flash photolysis of caged Ca(2+) to study exo- and endocytosis in identified rat corticotrophs. 2. Exocytosis stimulated by depolarization pulses was typically followed by a 'slow' endocytosis that retrieved the membrane with a time constant of approximately 6 s. The efficiency (the endocytosis/exocytosis amplitude ratio) of 'slow' endocytosis was approximately 1.2 at [Ca(2+)](i) < 3 microM and increased to approximately 1.6 at [Ca(2+)](i) > 3 microM. 3. Whole-cell dialysis through a patch pipette did not affect the kinetics and the efficiency of 'slow' endocytosis, but the amplitude of exocytosis was reduced. 4. 'Slow' endocytosis did not require sustained [Ca(2+)](i) elevation and its kinetics was only weakly [Ca(2+)](i) dependent. Our results suggest that 'slow' endocytosis involves a Ca(2+) sensor with a high Ca(2+) affinity (approximately 500 nM). 5. At high [Ca(2+)](i) (> 10 microM), the 'slow' endocytosis was frequently preceded by a 'fast' endocytosis that comprised multiple steps of rapid decrease in membrane capacitance. 6. Neither calmodulin nor calcineurin appeared to be the Ca(2+) sensor for endocytosis because the two forms of endocytosis were not affected by the calmodulin inhibitor calmidazolium (500 microM) or the calcineurin inhibitors cyclosporin A (1 microM) and calcineurin autoinhibitory peptide (1 mg ml(-1)). Ba(2+), a poor activator of calmodulin, could support both forms of endocytosis but slowed the kinetics of 'slow' endocytosis approximately 2-fold. 7. Non-hydrolysable analogues of GTP (GDP-beta-S) and ATP (ATP-gamma-S) also failed to inhibit either form of endocytosis, indicating that neither GTP nor ATP was essential for endocytosis. 8. We suggest that the high Ca(2+) affinity of 'slow' endocytosis may be important for maintaining continuous cycles of exocytosis-endocytosis during sustained adrenocorticotropin secretion in corticotrophs.
PURPOSE: Patients at low risk for prostate-specific antigen (PSA) failure following definitive local therapy are those with PSA of 10 or less, biopsy Gleason Score of 6 or less, and 1992 American Joint Committee on Cancer (AJCC) clinical Stage T1c or T2a. However, low-risk patients managed with radical prostatectomy and found to have prostatectomy Gleason score > or = 3+4 have a less favorable PSA outcome when compared to patients with prostatectomy Gleason score < or = 3+3. This study was performed to determine whether the percentage of positive prostate biopsy cores could predict upgrading from a biopsy Gleason score of 6 or less to a prostatectomy Gleason score > or = 3+4 in low-risk patients to optimize selection for prostate only radiation therapy. METHODS AND MATERIALS: Concordance testing of the biopsy Gleason score and the primary and secondary prostatectomy Gleason grades was performed in 427 prostate cancer patients treated with radical prostatectomy and at low risk for PSA failure. Logistic regression multivariable analysis was performed to test the ability of the established prognostic factors and the percentage of positive prostate biopsies (<34%, 34-50%, >50%) to predict for upgrading from biopsy Gleason score of 6 or less prostatectomy Gleason score > or = 3+4. PSA failure-free survival was reported using the actuarial method of Kaplan and Meier and comparisons were made using a log-rank test. RESULTS: Twenty-nine percent of the 427 study patients were upgraded from a biopsy Gleason score of 6 or less to a prostatectomy Gleason score > or = 3+4. The presence of greater than 50% positive biopsies was the only significant factor for predicting the upgrading from biopsy Gleason score of 6 or less to prostatectomy Gleason score > or = 3+4 on logistic regression multivariable analysis with the variables treated as continuous and categorical. Specifically, upgrading occurred in 26% vs. 59% of patients with 50% or less vs. greater than 50% positive biopsies, respectively. This translated into a 5-year PSA failure-free survival which was significantly higher (92% vs. 62%, p = 0.00001) for men with 50% or less vs. greater than 50% positive prostate biopsies, respectively. CONCLUSION: The presence of greater than 50% positive biopsies was associated with higher rates of pathologic upgrading which translated into lower 5-year PSA failure-free survival following radical prostatectomy (RP). Therefore, the percentage of positive biopsies may be useful in optimizing the selection of low-risk patients for prostate only radiation therapy such as external beam radiation or implant monotherapy.
True histiocytic lymphoma, as defined by strict criteria, is a very rare neoplasm. We describe three cases occurring as primary tumors in the central nervous system. The patients, two females and one male, ranged in age from 11 to 69 years. The tumors involved the brain in two cases and spinal cord in one, with a size ranging from 7 to 17 mm. Two patients died at 4 months and 8 months, respectively, and one was alive with disease at 5 months. Pathologically, the tumors comprised groups and sheets of noncohesive large cells with pleomorphic vesicular nuclei, distinct nucleoli, and abundant eosinophilic cytoplasm. A dense inflammatory infiltrate consisting of neutrophils, lymphocytes, plasma cells, and histiocytes was present, with multiple foci of necrosis and abscess formation. All three cases demonstrated an identical immunophenotype: positive for CD68 and lysozyme; focally positive for S-100 protein, CD45RB, and CD4; and negative for CD3, CD20, CD21/CD35, CD1a, CD30, ALK1, myeloperoxidase, glial fibrillary acidic protein, and cytokeratin. The proliferative index ranged from 20% to 35%. Ultrastructural examination further confirmed the histiocytic nature of the tumor cells, characterized by irregularly folded or multisegmented nuclei and abundant cytoplasm containing lysosomes; Birbeck granules, interdigitating cell processes, and cell junctions were not found. Although the presence of abundant inflammatory cells could obscure the neoplastic histiocytes, making the distinction from inflammatory conditions difficult, awareness of this unusual histologic feature and the invariable finding of pleomorphic cells in some areas of the lesion permit the correct diagnosis to be made.
Environmental iron concentrations coordinately regulate transcription of genes involved in iron acquisition and virulence via the ferric uptake regulation (fur) system. We identified and sequenced the fur gene and flanking regions of three Bartonella species. The most notable difference between Bartonella Fur and other Fur proteins was a substantially higher predicted isoelectric point. No promoter activity or Fur autoregulation was detected using a gfp reporter gene fused to the 204 nucleotides immediately upstream of the Bartonella fur gene. Bartonella henselae fur gene expression complemented a Vibrio cholerae fur mutant.
1. The patch clamp technique was used in conjunction with a fluorescent Ca2+ indicator (indo-1, or indo-1FF) to measure simultaneously cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis (changes in membrane capacitance) in single, identified rat corticotrophs. 2. Exocytosis could be stimulated by extracellular Ca2+ entry (via voltage-gated Ca2+ channels). A train of depolarizations could exhaust the pool of readily releasable granules and the pool replenished with a time constant of 42 s (at 22-25 C). 3. Recordings from cells with 0.5 mM intracellular cAMP showed that the amplitude of the depolarization-triggered exocytosis, the Ca2+ sensitivity of exocytosis, as well as the rate of replenishment of the readily releasable pool, were similar to the controls. 4. Exocytosis could also be stimulated by intracellular Ca2+ release from the inositol 1,4, 5-trisphosphate (IP3)-sensitive store (via flash photolysis of caged IP3). At comparable [Ca2+]i, extracellular Ca2+ entry and intracellular Ca2+ release had similar efficacy in triggering exocytosis. 5. The rate of exocytosis triggered via depolarization or intracellular Ca2+ release was much faster than that triggered via uniform elevation of [Ca2+]i (Ca2+ dialysis or flash photolysis of caged Ca2+). 6. The above findings suggest that both intracellular Ca2+ release and voltage-gated extracellular Ca2+ entry generate a spatial Ca2+ gradient, such that the local [Ca2+] near the exocytic sites was approximately 3-fold higher than the mean cytosolic [Ca2+]. However, neither cAMP nor the spatial Ca2+ gradient generated during depolarization could account for the high efficacy of corticotropin-releasing hormone (CRH) in stimulating adrenocorticotropic hormone (ACTH) secretion from corticotrophs.
We have characterized a host-induced virulence gene, mig-14, that is required for fatal infection in the mouse model of enteric fever. mig-14 is present in all Salmonella enterica subspecies I serovars and maps to a region of the chromosome that appears to have been acquired by horizontal transmission. A mig-14 mutant replicated in host tissues early after infection but was later cleared from the spleens and livers of infected animals. Bacterial clearance by the host occurred concomitantly with an increase in gamma interferon levels and recruitment of macrophages, but few neutrophils, to the infection foci. We hypothesize that the mig-14 gene product may repress immune system functions by interfering with normal cytokine expression in response to bacterial infections.
Salmonella pathogenicity island 2 (SPI-2) encodes a putative, two-component regulatory system, SsrA-SsrB, which regulates a type III secretion system needed for replication inside macrophages and systemic infection in mice. The sensor and regulator homologs, ssrAB (spiR), and genes within the secretion system, including the structural gene ssaH, are transcribed after Salmonella enters host cells. We have studied the transcriptional regulation of ssrAB and the secretion system by using gfp fusions to the ssrA and ssaH promoters. We found that early transcription of ssrA, after entry into macrophages, is most efficient in the presence of OmpR. An ompR mutant strain does not exhibit replication within cultured macrophages. Furthermore, footprint analysis shows that purified OmpR protein binds directly to the ssrA promoter region. We also show that minimal medium, pH 4.5, induces SPI-2 gene expression in wild-type but not ompR mutant strains. We conclude that the type III secretion system of SPI-2 is regulated by OmpR, which activates expression of ssrA soon after Salmonella enters the macrophage.
STUDY DESIGN: Prospective analysis of relationship between lifting capacity and multiple anthropometric variables. OBJECTIVES: To determine the relationship between lifting capacity and anthropometric variables and to model this relationship quantitatively. BACKGROUND: Low-back injuries commonly occur in individuals who perform lifting tasks. Objective data are needed to determine preinjury lifting capacity that, in turn, might be used to guide decisions during rehabilitation of these injuries. METHODS AND MEASURES: We recorded age and sex and measured the following variables for 35 men and 23 women between the ages of 22 and 40: height, weight, percentage of body fat, torso height, pelvic width, pelvic girth, arm length, thigh girth, and calf girth. Variables were selected for the study on the basis of theoretical modeling or previous research regarding the relationship between study variables and lifting capacity. Subjects also were tested to determine their maximum lifting capacity by using a lordotic lumbar spine lifting technique. RESULTS: Stepwise regression analysis indicated that the combination of sex, age, thigh girth, pelvic girth, and percentage body fat was significantly related to maximum lift capacity (multiple R2 = 0.76). The mean absolute difference (+/- SD) between lifted amount predicted by the regression model and the actual amount lifted was 118.6 +/- 86 N (26 +/- 19.3 lb), which corresponded to an average absolute error of 16% (SD = 14%) of the actual weight lifted. CONCLUSION: The results may be useful in estimating 1 aspect of preinjury lifting capacity. Similar studies are needed to model the requirements of frequency of lift, duration of lifting efforts, variety of hand-object coupling, and combined lifting and reaching.
Broncho-oesophageal fistula associated with tuberculosis is rarely reported in the literature and has not been reported in Hong Kong. We describe a 30-year-old Chinese human immunodeficiency virus (HIV)-negative man with double tuberculous broncho-oesophageal fistulas proven by histology. Constitutional symptoms of active tuberculosis were absent and chest radiograph did not show an obvious lung lesion. Our case shows that broncho-oesophageal fistula can be the sole manifestation of active tuberculosis and that the diagnosis should be suspected in patients who are seen with chronic respiratory symptoms in areas where the prevalence of tuberculosis is high.
Previous studies have shown that induction of microsomal epoxide hydrolase (mEH) and glutathione S-transferase (GST) by oltipraz correlated with the radioprotective effect. The present study was designed to investigate the expression of the antioxidant enzymes and the radioprotective effect by imidazole (IM). Northern blot analysis revealed that IM increased the mEH and GST mRNA levels in the rat liver in a dose-dependent manner. Rats irradiated with 3 Gy of gamma-rays in combination with IM showed enhanced increases in mEH and rGSTA2 mRNAs, as compared to either IM or irradiation alone. IM prevented elevations in the hepatic GSH content by gamma-irradiation. In contrast to IM, cysteine blocked radiation-inducible increases in the mRNAs with no suppression of the GSH content. The radioprotective effect by IM was greater than that by cysteine, as assessed by the 30-day survival rate of mice (i.e. 80% and 69%, respectively, vs. 48% in control). These results demonstrated that IM enhanced radiation-inducible mEH and GST expression with prevention of the increase in GSH content, which correlated with the radioprotective effect, and that the mechanistic basis of radioprotection by IM differed from that by cysteine.
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Haemophilus influenzae (Hi) causes many clinical illnesses such as meningitis, bacteremia, epiglottitis, pneumonia, otitis media, sinusitis and tracheobronchitis. Before the introduction of the Haemophilus influenzae type b (Hib) conjugate vaccine in 1988, Hib caused more than 95 percent of invasive Hi disease in developed countries. Conjugate vaccines were licensed for use in children > or = 15 months of age in 1989 and for use in children > or = 2 months of age in 1990. During 1987-1995, the incidence of invasive Hi disease among children < 5 years of age decreased 96 percent in the United States. This report summarizes the trend in invasive disease caused by Hi among Oklahoma children < 5 years of age. The data represents cases reported to the OSDH as part of the infectious disease surveillance system. Invasive Hi disease has been reportable by law in Oklahoma since 1983.
BACKGROUND: This is the first ophthalmic report--to our knowledge--of an anterior uveitis secondary to sarcoidosis in a patient infected with human immunodeficiency virus (HIV). Other reported causes of uveitis in HIV-infected patients have included HIV, herpes zoster, tuberculosis, syphilis, toxoplasmosis, cryptococcus, rifabutin prophylaxis for mycobacterium, and protease inhibitors such as ritonavir and indinavir. Uveitis secondary to sarcoidosis in the non-HIV population is classically seen in young, female, African-American patients. There are rare reports, found exclusively in the pulmonary literature, of sarcoidosis in HIV-infected patients. CASE REPORT: A 38-year-old African-American male infected with HIV was treated for chronic recurrent anterior uveitis secondary to sarcoidosis. His sarcoidosis was diagnosed 1 month earlier, along with the onset of his uveitis. During the previous 6 years he has been treated with anti-HIV antivirals as well as prophylaxis for opportunistic infections. To date, his infectious disease specialist continues to treat his HIV and systemic sarcoidosis. CONCLUSION: Patients with HIV infection in whom sarcoidosis with secondary uveitis develops are very rare. Management of these patients requires careful use of topical and oral steroidal anti-inflammatories to control ocular and systemic sequelae of sarcoidosis. This case initiates some interesting questions about the immunology of sarcoidosis and its presence in immunocompromised patients. Use of steroids in an immunocompromised patient is clinically complex. Further clinical study is needed to elicit the full clinical significance of sarcoidosis and HIV infection.
The full-length dengue virus NS3 protein has been successfully expressed as a 94-kDa GST fusion protein in Escherichia coli. Treatment of the purified fusion protein with thrombin released a 68-kDa protein which is the expected molecular mass for the DEN1 NS3 protein. The identity of this protein was confirmed by Western blotting using dengue virus antisera. Two related activities of the recombinant NS3 protein were characterized, which were the binding of the protein to the 3'-noncoding region of the dengue virus RNA genome and NTPase activity. We demonstrated using a band shift assay that the DEN1 NS3 protein could form a complex with the stem-loop structure in the 3'-noncoding region (3'-NCR), although sites outside the stem-loop may also participate in binding. Using various unlabeled homopolymeric and heteropolymeric RNAs as competitors for binding, it was further shown that the DEN1 NS3 protein exhibits preferential binding to a 94-nt RNA transcript from the 3'-NCR of the dengue virus. The NTPase activity of the recombinant DEN1 NS3 protein was characterized using a thin-layer chromatography assay. We found that the DEN1 NS3 protein possesses some aspects of NTPase activity, which are distinct from those found in other flaviviruses. Although the NS3 protein was able to utilize all four ribonucleoside triphosphates as its substrates, the NS3 protein showed a distinct preference for purine triphosphates (i.e., ATP and GTP). The addition of poly(U) did not stimulate NTPase activity in DEN1 NS3 protein, which contrasts with the reports for other flaviviral NS3 proteins. However, NTPase activity was specifically stimulated by the viral NS5 protein, which was manifested by a more than twofold increase in the rate of ATP hydrolysis and a 25% increase in the yield of ADP at the end of a 120-min reaction. These data suggest that the NTPase activity of the NS3 protein may be regulated by the viral NS5 protein during virus replication.
1. 2-(Allylthio)pyrazine protects the liver against acetaminophen- and carbon tetrachloride-induced injury through inhibition of cytochrome P4502E1 and induction of glutathione S-transferases (GSTs). By comparison, the effects of allylthiobenzimidazole (ATB) on the levels of several hepatic cytochrome P450, microsomal epoxide hydrolase (mEH) and GST expression have been studied in the rat herein. 2. Western immunoblotting analyses revealed that ATB treatment (50 mg/kg/day for 5 days) failed to alter cytochrome P4501A2, P4502B1/2 and P4502E1 levels in the liver, whereas the expression of P4502C11 was reduced approximately 50% by ATB. 3. Treatment of rat with a single dose of ATB resulted in 2-21-fold increases in mEH mRNA levels at 24 h with an ED50 = 60 mg/kg. mEH mRNA level was elevated 9- and 21-fold at 12 and 24 h after treatment at 200 mg/kg respectively as compared with control. Western blot analysis revealed that ATB induced mEH protein levels by 2-fold relative to control. 4. ATB induced the major GST mRNA levels as a function of dose, resulting in rGSTA2, rGSTA3/5 and rGSTM1 mRNA levels elevated by 20-, 6- and 8-fold at 24 h respectively. The relative rGSTM2 mRNA level was minimally affected. Time-course studies showed that mEH, rGSTA2 and rGSTM1 mRNA levels were significantly increased at 12 and 24 h after ATB treatment, returning to control levels by 48 h. Treatment of rat with ATB (20-50 mg/kg/day for 5 days) resulted in 2-3-fold increases in mEH, rGSTA1/2, rGSTA3/5 and rGSTM1 mRNA levels with the induction of GST subunits. 5. ATB failed to block carbon tetrachloride-induced liver toxicity in rat and mouse. ATB treatment (50 mg/kg day for 3 days) prior to a lethal dose of acetaminophen significantly reduced acetaminophen-induced liver toxicity in mouse, as assessed by both plasma alanine aminotransferase activity and histopathological examination. The 30-day survival rate of mouse gamma-irradiated at 8 Gy failed to be improved by ATB pretreatment (100 mg/kg/day for 2 days). 6. These results provided evidence that ATB stimulated mEH and GST gene expression at early times and reduced the P4502C11 level in the absence of P4502E1 suppression. ATB was only partially effective in protecting the liver against toxicant-induced injury despite the presence of allylthio moiety in its chemical structure.
The green fluorescent protein (GFP) gene was expressed on a plasmid in B. henselae, and GFP-expressing bacteria were visualized by fluorescence microscopy. HEp-2 cells infected with GFP-expressing bacteria were separated from uninfected cells with a fluorescence activated cell sorter. Promoter fusions of B. henselae chromosomal DNA to gfp were examined by flow cytometry, and a B. henselae groEL promoter fusion which induced expression at 37 degreesC was isolated.