[The preparation of norA gene probe in Staphylococcus aureus]

OBJECTIVE

To prepare norA gene probe for studies on the mechanism of resistance to fluoroquinolones mediated by norA gene in S. aureus.

METHODS

The Dig-labeled norA gene probe was made by PCR.

RESULTS

This method is simple and feasible. We have got a lot of probes in a short time. The sensitivity of norA gene probe is high; the probe is secure, easy to use and can be stored for a long time.

CONCLUSION

The probe is applicable to further studies on the mechanism of resistance to fluoroquinolones mediated by norA in S. aureus.

Evasion of human innate and acquired immunity by a bacterial homolog of CD11b that inhibits opsonophagocytosis

Microbial pathogens must evade the human immune system to survive, disseminate and cause disease. By proteome analysis of the bacterium Group A Streptococcus (GAS), we identified a secreted protein with homology to the alpha-subunit of Mac-1, a leukocyte beta2 integrin required for innate immunity to invading microbes. The GAS Mac-1-like protein (Mac) was secreted by most pathogenic strains, produced in log-phase and controlled by the covR-covS two-component gene regulatory system, which also regulates transcription of other GAS virulence factors. Patients with GAS infection had titers of antibody specific to Mac that correlated with the course of disease, demonstrating that Mac was produced in vivo. Mac bound to CD16 (FcgammaRIIIB) on the surface of human polymorphonuclear leukocytes and inhibited opsonophagocytosis and production of reactive oxygen species, which resulted in significantly decreased pathogen killing. Thus, by mimicking a host-cell receptor required for an innate immune response, the GAS Mac protein inhibits professional phagocyte function by a novel strategy that enhances pathogen survival, establishment of infection and dissemination.

Uraemia suppresses central dopaminergic metabolism and impairs motor activity in rats

OBJECTIVE

Uraemia often provokes various neurological disorders, such as mental changes, malperception, confusion, seizures and coma. Since changes in neurotransmissions induce neurological symptoms, we investigated changes in the monoamine metabolism and motor activity in uraemic rats.

DESIGN

Prospective, randomised, controlled animal study.

SUBJECTS

Male Wistar rats.

INTERVENTIONS

Acute renal failure was induced by occlusion of bilateral renal arteries for 60 min, and the motor activity and brain monoamine turnover were examined 48 h later. The brain monoamine turnover was evaluated by the depletion of norepinephrine (NE) and dopamine (DA) induced by alpha-methyl-p-tyrosine (alpha-MT), or the accumulation of 5-hydroxyindoleacetic acid (5-HIAA) induced by probenecid.

MEASUREMENTS AND RESULTS

Marked damage in renal function was found in animals subjected to renal ischaemia 48 h after the operation. The motor activity of the uraemic rats was impaired. The turnover of DA in the striatum, mesencephalon and hypothalamus was decreased in these rats. The turnover of NE and 5-hydroxytryptamine (5-HT) was unchanged in all regions examined.

CONCLUSIONS

Suppression of the central DA turnover appears to be involved in the impairment of motor activity in uraemic rats.

Neuroprotective effect of low-dose lidocaine in a rat model of transient focal cerebral ischemia

BACKGROUND

A low concentration of lidocaine (10 microM) has been shown to reduce anoxic damage in vitro. The current study examined the effect of low-dose lidocaine on infarct size in rats when administered before transient focal cerebral isehemia.

METHODS

Male Wistar rats (weight, 280-340 g) were anesthetized with isoflurane, intubated, and mechanically ventilated. After surgical preparation, animals were assigned to lidocaine 2-day (n = 10), vehicle 2-day (n 12), lidocaine 7-day (n = 13), and vehicle 7-day (n = 14) groups. A 1.5-mg/kg bolus dose of ildocaine was injected intravenously 30 mm before isehemia in the lidocaine 2-day and 7-day groups. Thereafter, an infusion was initiated at a rate of 2 mg x kg(-1) x h(-1) until 60 min of reperfusion after isehemia. Rats were subjected to 90 min of focal cerebral isehemia using the intraluminal suture method. Infarct size was determined by image analysis of 2,3,5-triphenyltetrazolium chloride-stained sections at 48 h or hematoxylin and eosin-stained sections 7 days after reperfusion. Neurologic outcome and body weight loss were also evaluated.

RESULTS

The infarct size was significantly smaller in the lidocaine 2-day group (185.0+/-43.7 mm3) than in the vehicle 2-day group (261.3+/-45.8 mm3, P < 0.01). The reduction in the size of the infarct in the lidocaine 7-day group (130.4+/-62.9 mm3) was also significant compared with the vehicle 7-day group (216.6+/-73.6 mm3, P < 0.01). After 7 days of reperfusion, the rats in the lidocaine group demonstrated better neurologic outcomes and less weight loss.

CONCLUSIONS

The current study demonstrated that a clinical anriarrhythmic dose of lidocaine, when given before and during transient focal cerebral isehemia, significantly reduced infaret size, improved neurologic outcome, and inhibited postisehemic weight loss.

[Cytotoxic T lymphocyte activity induced by genetic immunization with NV-HC/NS]

OBJECTIVE

To investigate the immunoprophylactic and immunotherapeutic effects of DNA vaccine (NV-HC/NS(3)) after inoculation of mice by target tumor loading technique.

METHODS

Before or after inoculation with NV-HC/NS(3) intramuscularly, BALB/c mice in the experimental group were planted with target tumor cells (SP2/0-NS(3)), which were derived from BALB/c mice and stably transfected with the recombinant plasmid NV-HC/NS(3). Tumor growth and survival rate of the mice immunized with NV-HC/NS(3) were compared with those in the control group.

RESULTS

Tumor mass grew well in all mice in the control group in a few days, while no visible tumor mass growth in 40% mice immunized with NV-HC/NS(3) could be seen. The survival rate and life span of mice in the experimental group were significantly longer than those in the control group.

CONCLUSIONS

Specific immune activity could be induced by immunization with NV-HC/NS(3). Such effects are immunoprophylactic and immunotherapeutic.

Multilocus analysis of extracellular putative virulence proteins made by group A Streptococcus: population genetics, human serologic response, and gene transcription

Species of pathogenic microbes are composed of an array of evolutionarily distinct chromosomal genotypes characterized by diversity in gene content and sequence (allelic variation). The occurrence of substantial genetic diversity has hindered progress in developing a comprehensive understanding of the molecular basis of virulence and new therapeutics such as vaccines. To provide new information that bears on these issues, 11 genes encoding extracellular proteins in the human bacterial pathogen group A Streptococcus identified by analysis of four genomes were studied. Eight of the 11 genes encode proteins with a LPXTG(L) motif that covalently links Gram-positive virulence factors to the bacterial cell surface. Sequence analysis of the 11 genes in 37 geographically and phylogenetically diverse group A Streptococcus strains cultured from patients with different infection types found that recent horizontal gene transfer has contributed substantially to chromosomal diversity. Regions of the inferred proteins likely to interact with the host were identified by molecular population genetic analysis, and Western immunoblot analysis with sera from infected patients confirmed that they were antigenic. Real-time reverse transcriptase-PCR (TaqMan) assays found that transcription of six of the 11 genes was substantially up-regulated in the stationary phase. In addition, transcription of many genes was influenced by the covR and mga trans-acting gene regulatory loci. Multilocus investigation of putative virulence genes by the integrated approach described herein provides an important strategy to aid microbial pathogenesis research and rapidly identify new targets for therapeutics research.

Sustained norepinephrine stimulation induces different regulation of expression in three alpha1-adrenoceptor subtypes

The norepinephrine (NE)-induced regulation of alpha1-adrenoceptors (ARs) expression in human embryonic kidney (HEK) 293 cells stably expressing cloned alpha1-AR subtypes with similar receptor densities was investigated. In the presence of 10 microM propranolol, the treatment of cells with 10 microM NE for 4-72 h down-regulated alpha1A- and alpha1D-AR. but increased alpha1B-AR expression in a time-dependent manner. The down-regulation of alpha1A-AR reached maximum of 40.3 +/- 14.7 % at 48h. The down-regulation of alpha1D-AR reached maximum of 51.3 +/- 3.7% at 24h. With the stimulation of NE, alpha1B-AR density was increased maximally by 112.4 +/- 43.4% at 48h. The protein kinase C (PKC) inhibitor calphostin C or R0-31-8220 abolished the NE-induced down-regulation of alpha1A- and alpha1D-AR, but showed no effect on the up-regulation of alpha1B-AR. The PKC agonist PMA not only mimicked the NE-induced down-regulation of alpha1A- and alpha1D-AR, but also induced a down-regulation of alpha1B-AR. The endoplasmic reticulum Ca2+-ATPase inhibitor cyclopiazonic acid (CPA) or thapsigargin, or the calcium chelator BAPTA/AM did not affect the down-regulation of alpha1A-AR, but inhibited the up-regulation of alpha1B-AR induced by NE. Calmodulin antagonist W-7. tyrosine kinase inhibitor genistein or tyrphostin A25 had no effect on NE-induced up-regulation of alpha1B-AR. The results suggest that three alpha1-AR subtypes are differently regulated by sustained NE stimulation with different signal transduction pathways.

Characterization of the rod photoresponse isolated from the dark-adapted primate ERG

The a-wave of the human dark-adapted ERG is thought to derive from activity of rod photoreceptors. However, other sources within the retina could potentially perturb this simple equation. We investigated the extent to which the short-latency dark-adapted rod a-wave of the primate ERG is dominated by the rod photoresponse and the applicability of the phototransduction model to fit the rod a-wave. Dark-adapted Ganzfeld ERGs were elicited over a 5-log-unit intensity range using short bright xenon flashes, and the light-adapted cone responses were subtracted to isolate the rod ERG a-wave. Intravitreal 4-phosphono-butyric acid (APB) and cis-2,3-piperidine-dicarboxylic acid (PDA) were applied to isolate the photoreceptor response. The Hood and Birch version of the phototransduction model, Rmax[1 - e(-I x S x (t-t(eff)))2], was fitted to the a-wave data while allowing Rmax and S to vary. Three principle observations were made: (1) At flash intensities > or =0.77 log sc-td-s the leading edge of the normalized rod ERG a-wave tracks the isolated photoreceptor response across the first 20 ms or up to the point of b-wave intrusion. The rod ERG a-wave was essentially identical to the isolated receptor response for all intensities that produce peak responses within 14 ms after the flash. (2) The best fit of sensitivity (S) was not affected by APB and/or PDA, suggesting that the inner retina contributes very little to the dark-adapted a-wave. (3) APB always reduced the maximum dark-adapted a-wave amplitude (by 15-30%), and PDA always increased it (by 7-15%). Using the phototransduction model, both events can be interpreted as a scaling of the photoreceptor dark current. This suggests that activity of postreceptor cells somehow influences the rod dark current, possibly by feedback through horizontal cells (although currently not demonstrated for the rod system), or by altering the ionic concentrations near the photoreceptors, or by neuromodulator effects mediated by dopamine or melatonin.

[Influence of moderate hypothermia on the contents of 6-KETO-PGF1 alpha and TXB2 in brain tissues after cardiac arrest and resuscitation in dogs]

To investigate the effect of moderate hypothermia of whole brain (30 degrees C to 32 degrees C) on the levels of prostacyclin and thromboxane A2 in brain tissues after cardiac arrest and resuscitation. Twenty-one dogs were divided into four groups: Group A, nonischemic controls (n = 4); Group B, 15 minute cardiac arrest without reperfusion (n = 4); Group C, 15 minute cardiac arrest and standard resuscitation (n = 6); Group D, 15 minute cardiac arrest and moderate hypothermia (30 degrees C-32 degrees C). The results showed that as compared with those in Group A, the 6-Keto-PGF1 alpha levels remained substantially unchanged in Group C and D (P > 0.05), and the levels of TXB2 and TXB2/6-Keto-PGF1 alpha ratio increased significantly in Group C (P < 0.01), but both maintained basically stable in Group D (P > 0.05). In comparison with those in Group C, the levels of TXB2 and TXB2/6-Keto-PGF1 alpha ratio decreased dramatically (P < 0.01). It is concluded that the moderate hypothermia can depress the arachidonic acid metabolism and keep a certain balance between the activities of TXA2 and PGI2 during cerebral resuscitation.

[Characterization of cefoperazone resistance gene on plasmid pFC in E. coli HX88108]

OBJECTIVE

To investigate the characterization of cefoperazone resistance gene (CPZr) on plasmid pFC in E. coli HX88108 and inquire into the mechanism of resistance to CPZ at the molecular level.

METHODS

E. coli HX88108 strain which demonstrated high-level resistance to cefoperazone (MIC, > 512 micrograms/ml) was isolated from a severely infected patient in 1988. Five plasmids coexisting in the strain were designated pFC, pFT1; pFT2, pFT3 and pFX, respectively. Four plasmids except pFX conferred CPZ resistance. Cefoperazone resistance gene (CPZr) has been cloned from plasmid pFC. beta-lactamase assays with Nitrocefin were performed.

RESULTS

The expression product of CPZr was beta-lactamase. The high level beta-lactamase enzymatic activities against cephaloridine of CPZr transformants which were detected spectrophotometrically at 260 nm wave length demonstrated high level similarities to that of pFC. MICs of 18 antibiotics were determined according to a guideline of NCCLS by broth dilution method. CPZr transformants showed moderate level resistance to ampicillin, cefazolin, cefazolin, cefamandole and CPZ (MIC, 64 micrograms/ml). Meanwhile, susceptibility testing results demonstrated that the level of resistance to CPZ of pFC transformant in this study (MIC, 64 micrograms/ml) was much lower than that in 1988 (MIC, > 512 micrograms/ml) and resistance to nofloxacin and aminoglycosides was not observed. Induction experiment and temperature-sensitive mutation of CPZ resistance were performed. CPZr colonal strains revealed the higher-level of resistance to CPZ (MIC, 512 micrograms/ml) due to antibiotic CPZ induction rather than temperature sensitive mutation.

CONCLUSION

This observation suggests that resistance to antibiotics encoded by plasmid might have been lower or lost under no antibiotic stress in a certain period, but higher under heavy stress.

NADPH diaphorase activity in the rabbit retina is modulated by glutamatergic pathways

NADPH diaphorase activity in the rabbit retina is modulated by the state of visual adaptation. In this study, we tested possible glutamatergic control of this phenomenon. Rabbits were injected intravitreally with agonists and antagonists of glutamate. After adaptation (3 hours) to either room light or darkness, the rabbits were killed and the retinae were prepared for NADPH diaphorase histochemistry. Kainic acid significantly reduced the number of NADPH diaphorase amacrine cells but augmented NADPH diaphorase activity in horizontal cells in both light- and dark-adapted animals. 6,7-Dinitroquinoxaline-2,3(1H,4H)-dione exerted no effect on amacrine cells but eliminated NADPH diaphorase activity in horizontal cells. 2-Amino-4-phosphono butyric acid did not affect NADPH diaphorase activity in horizontal cells but reduced the degree of staining in the neuronal processes of amacrine cells. MK-801 and N-methyl-D-aspartic acid (NMDA) had no effect on NADPH diaphorase activity in horizontal cells. However, MK-801 reduced staining in the neuronal processes of amacrine cells but not in their cell bodies. NMDA effects were expressed in a significant reduction in the number and size of amacrine cells that were NADPH diaphorase positive. These results indicate that activation of NADPH diaphorase in horizontal cells by darkness is mediated by the activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid (KA)-type glutamate receptors. The ON pathway in the retina is probably involved in modulation of NADPH diaphorase in the neuronal processes of amacrine cells. Amacrine cells that are NADPH diaphorase positive contain NMDA-type and AMPA/KA-type receptors and are highly susceptible to NMDA and kainic acid toxicity.

Toward a genome-scale understanding of group A Streptococcus pathogenesis

Recent significant contributions have been made to the understanding of Group A Streptococcus (GAS) pathogenesis. New regulatory pathways have been discovered, insight into the molecular basis of epidemics of serotype M1 disease has been obtained, the crystal structures of four toxins have been reported and a genome sequence of one GAS strain has been determined. Genome-scale approaches to the study of GAS pathogenesis are now rapidly emerging and will advance our fundamental understanding of the molecular basis of host-pathogen interactions.

Visual evoked cortical potential can be used to differentiate between uncorrected refractive error and macular disorders

The visual evoked cortical potential (VECP) is widely used to verify complaints of reduced visual performance and to identify the site of the disorder. In this study, we investigated the correlation between reduced visual acuity and VECP in volunteers with normal corrected visual acuity and in patients suffering from inherited macular degeneration or from age related macular degeneration (ARMD). Flash evoked VECP was not affected by the visual acuity in the cases of refractive error and in ARMD patients but was reduced in amplitude and delayed in implicit time in the patients suffering from inherited macular degeneration. The VECP elicited by pattern reversal checkerboard (PVECP) was not affected by the quality of the visual image in volunteers with uncorrected refractive error when checks of 60' or larger were used but were considerably reduced in size and prolonged in implicit time for checks smaller than 15'. In both groups of patients suffering from macular dysfunction, pattern reversal VECP was very subnormal and was characterized by prolonged implicit time compared to values expected from their visual acuity. These findings indicate that the PVECP does not directly correlate with visual acuity but rather with foveal function. Therefore, we suggest that recordings of PVECP can be used to differentiate between refractive error and macular disorders as causing reduction in visual acuity when other clinical signs are missing or not available.

Identification and immunogenicity of group A Streptococcus culture supernatant proteins

Extracellular proteins made by group A Streptococcus (GAS) play critical roles in the pathogenesis of human infections caused by this bacterium. Although many extracellular GAS proteins have been identified and characterized, there has been no systematic analysis of culture supernatant proteins. Proteins present in the culture supernatant of strains of serotype M1 (MGAS 5005) and M3 (MGAS 315) mutants lacking production of the major extracellular cysteine protease were separated by two-dimensional gel electrophoresis and identified by amino-terminal amino acid sequencing and interrogation of available databases, including a serotype M1 genome sequence. In the aggregate, amino-terminal amino acid sequence data for 66 protein spots were generated, 53 unique sequences were obtained, and 44 distinct proteins were identified. Sixteen of the 44 proteins had apparent secretion signal sequences and 27 proteins did not. Eight of the 16 proteins with apparent secretion signal sequences have not been previously described for GAS. Antibodies against most of the apparently secreted proteins were present in sera from mice infected subcutaneously with MGAS 5005 or MGAS 315. Humans with documented GAS infections (pharyngitis, acute rheumatic fever, and severe invasive disease) also had serum antibodies reacting with many of the apparently secreted proteins, indicating that they were synthesized in the course of GAS-human interaction. The genes encoding four of the eight previously undescribed and apparently secreted culture supernatant proteins were cloned, and the proteins were overexpressed in Escherichia coli. Western blot analysis with these recombinant proteins and sera from GAS-infected mice and humans confirmed the immunogenicity of these proteins. Taken together, the data provide new information about the molecular aspects of GAS-host interactions.

Stability and peptide binding specificity of Btk SH2 domain: molecular basis for X-linked agammaglobulinemia

X-linked agammaglobulinemia (XLA) is caused by mutations in the Bruton's tyrosine kinase (Btk). The absence of functional Btk leads to failure of B-cell development that incapacitates antibody production in XLA patients leading to recurrent bacterial infections. Btk SH2 domain is essential for phospholipase C-gamma phosphorylation, and mutations in this domain were shown to cause XLA. Recently, the B-cell linker protein (BLNK) was found to interact with the SH2 domain of Btk, and this association is required for the activation of phospholipase C-gamma. However, the molecular basis for the interaction between the Btk SH2 domain and BLNK and the cause of XLA remain unclear. To understand the role of Btk in B-cell development, we have determined the stability and peptide binding affinity of the Btk SH2 domain. Our results indicate that both the structure and stability of Btk SH2 domain closely resemble with other SH2 domains, and it binds with phosphopeptides in the order pYEEI > pYDEP > pYMEM > pYLDL > pYIIP. We expressed the R288Q, R288W, L295P, R307G, R307T, Y334S, Y361C, L369F, and 1370M mutants of the Btk SH2 domain identified from XLA patients and measured their binding affinity with the phosphopeptides. Our studies revealed that mutation of R288 and R307 located in the phosphotyrosine binding site resulted in a more than 200-fold decrease in the peptide binding compared to L295, Y334, Y361, L369, and 1370 mutations in the pY + 3 hydrophobic binding pocket (approximately 3- to 17-folds). Furthermore, mutation of the Tyr residue at the betaD5 position reverses the binding order of Btk SH2 domain to pYIIP > pYLDL > pYDEP > pYMEM > pYEEI. This altered binding behavior of mutant Btk SH2 domain likely leads to XLA.

[Effect of long-term no-tillage and application of organic manure on some properties of soil fertility in rice/wheat rotation]

A field experiment from June 1983 to October 1997 was conducted to study the effect of long-term no-tillage and application of manure on soil fertility properties. The results showed that the contents of soil organic C, total N and available N in the treatment of fourteen consecutive year no-tillage were all significantly higher in 0-5 cm soil layer, while, lower in 5-10 and 10-20 cm layers than in conventional tillage. The content of water stable aggregate in 0-20 cm layer was increased in no-tillage in that the soil structure was less destroyed. Based on various soil fertility properties, the contribution order of different fertilization treatments to soil fertility was as follows: pig manure > straw > green manure > chemical fertilizer > no fertilizer.

Different roles of neuronal and endothelial nitric oxide synthases on ischemic nitric oxide production in gerbil striatum

The production of nitric oxide (NO) in gerbil striatum during ischemia and reperfusion was monitored by measuring total NO metabolites in dialysates, and the effects of 7-nitroindazole (7-NI), a selective inhibitor of neuronal NO synthase, and N(G)-nitro-L-arginine methyl ester (L-NAME), a non-selective inhibitor of NO synthase, were examined. The effects of these agents on ischemic neuronal damage were histologically evaluated 7 days after transient ischemia for 5 or 10 min. 7-NI and L-NAME decreased the NO production to similar extents in non-ischemic gerbils. 7-NI inhibited the increased NO production after 5 min of ischemia, and partly attenuated the increase in NO production after 10 min of ischemia, but had no effect on the increase after 15 min of ischemia. L-NAME completely abolished the increased NO production after different durations of ischemia. The extent of ischemic neuronal damage by 5-min ischemia was aggravated by either 7-NI or L-NAME, while damage by 10-min ischemia was marked in all groups. These results indicate that neuronal and endothelial NO synthases make different contributions to the post-ischemic NO production and the histological outcomes in gerbil striatum.

Vibrio harveyi NADPH-FMN oxidoreductase arg203 as a critical residue for NADPH recognition and binding

Luminous bacteria contain three types of NAD(P)H-FMN oxidoreductases (flavin reductases) with different pyridine nucleotide specificities. Among them, the NADPH-specific flavin reductase from Vibrio harveyi exhibits a uniquely high preference for NADPH. In comparing the substrate specificity, crystal structure, and primary sequence of this flavin reductase with other structurally related proteins, we hypothesize that the conserved Arg203 residue of this reductase is critical to the specific recognition of NADPH. The mutation of this residue to an alanine resulted in only small changes in the binding and reduction potential of the FMN cofactor, the K(m) for the FMN substrate, and the k(cat). In contrast, the K(m) for NADPH was increased 36-fold by such a mutation. The characteristic perturbation of the FMN cofactor absorption spectrum upon NADP(+) binding by the wild-type reductase was abolished by the same mutation. While the k(cat)/K(m,NADPH) was reduced from 1990 x 10(5) to 46 x 10(5) M(-1) min(-1) by the mutation, the mutated variant showed a k(cat)/K(m,NADH) of 4 x 10(5) M(-1) min(-1), closely resembling that of the wild-type reductase. The deuterium isotope effects (D)V and (D)(V/K) for (4R)-[4-(2)H]-NADPH were 1.7 and 1.4, respectively, for the wild-type reductase but were increased to 3.8 and 4.0, respectively, for the mutated variant. Such a finding indicates that the rates of NADPH and NADP(+) dissociation in relation to the isotope-sensitive redox steps were both increased as a result of the mutation. These results all provide support to the critical role of the Arg203 in the specific recognition and binding of NADPH.

Retinal toxicity of commercial intravitreal tissue plasminogen activator solution in cat eyes

BACKGROUND

We previously reported retinal toxic reactions in rabbit eyes receiving intravitreal injections of commercial tissue plasminogen activator (tPA) in concentrations greater than or equal to 50 microg/0.1 mL, and recent clinical experience suggests that intravitreal tPA solution may produce toxic effects in human eyes. We therefore investigated the dose-dependent retinal toxicity of intravitreal commercial recombinant tPA solution in cat eyes, which have a vascularized inner retina and vitreous volume similar to that of human eyes.

METHODS

Commercial tPA in L-arginine solution was injected into the mid vitreous cavity of normal cat eyes in doses of 25, 50, 75, and 100 microg/0.1 mL and 200 microg/0.2 mL. Control (fellow) eyes received an equal volume of sterile saline solution. After injection, eyes were evaluated by ophthalmoscopy and electroretinography for 14 days and then enucleated for histopathological evaluation.

RESULTS

Fundus pigmentary alterations were observed in eyes receiving doses greater than or equal to 50 microg/0.1 mL. Changes were centered in the area around the injection site, and the area's size increased in proportion to the dosage. Mean electroretinography B-wave amplitude measured at 14 days was significantly reduced in eyes receiving greater than or equal to 50 microg of tPA in a dose-dependent fashion. Light microscopy of the involved areas showed loss of photoreceptor elements with necrosis and proliferation of the retinal pigment epithelium.

CONCLUSION

Intravitreal injection of commercial tPA solution results in dose-dependent retinal toxicity in cat eyes.

CLINICAL RELEVANCE

Because cat eyes are similar to human eyes regarding retinal vascularity and vitreous volume, intravitreal injections of commercial tPA (with L-arginine vehicle) in concentrations greater than 25 microg/0.1 mL are potentially unsafe in human eyes.

[Study on uptake of fluoroquinolones by Staphylococcus aureus]

This study aimed to investigate the mechanism of Staphylococcus aureus' resistance to fluoroquinolones. The uptake of lomefloxacin, ofloxacin by Staphylococcus aureus and the effect of CCCP on the uptake were studied by the fluorescence method. The uptake of lomefloxacin, ofloxacin by sensitive organisms is higher than that by resistant organisms; CCCP had different influences on different organisms, but no significant difference between the effects of CCCP on sensitive strains and on resistant strains was noted. The uptake of lomefloxacin, ofloxacin by SA2-16 was much lower than that by SA2-16's parent, and after the addition of CCCP, the uptake of both quinolones by SA2-16 increased rapidly, but the concentration did not reach its parent's concentration in stable condition. These results indicate that the decreasing of the uptake of fluoroquinolones is one of the mechanisms responsible for Staphylococcus aureus to resistance fluoroquinolones, and as a mechanism of resistance to drugs, it plays different roles in different strains.

Probing the mechanisms of the biological intermolecular transfer of reduced flavin

NAD(P)H-flavin oxidoreductases [flavin reductases (FR)] are a class of enzymes capable of producing reduced flavin for bacterial bioluminescence and other biological processes. Bacterial luciferase utilizes oxygen, reduced FMN (FMNH2) and a long-chain aliphatic aldehyde as substrates for light emission. The Vibrio harveyi luciferase and FRP (for which we have cloned the gene and determined the crystal structure) is a model for the elucidation of the reduced flavin transfer mechanism using both a flavin reductase single-enzyme assay monitoring the NADPH oxidation and a flavin reductase-luciferase coupled assay measuring bioluminescence intensity or quantum output. The FRP exhibits a ping-pong kinetic pattern in the single-enzyme assay but changes to a sequential pattern in the coupled assay. Furthermore, FMN at >2x10(-6) mol/L reduced both the light intensity and quantum yield of the coupled reaction by noncompetitively inhibiting NADPH and competitively inhibiting luciferase. These results support a scheme in which the luciferase forms specific complex(es) with FRP. Indeed, such complexes were shown by fluorescence anisotropy to exist between luciferase and monomeric FRP either in the holo- or apoenzyme form. Furthermore, the reduced flavin cofactor of FRP is transferred directly to luciferase for bioluminescence, whereas the reduced flavin product of FRP is inefficient in supporting the luminescence reaction. The mechanism of reduced flavin transfer is apparently flavin and flavin reductase specific.

Action mechanism of antitubercular isoniazid. Activation by Mycobacterium tuberculosis KatG, isolation, and characterization of inha inhibitor

Activation of the antitubercular isoniazid (INH) by the Mycobacterium tuberculosis KatG produces an inhibitor for enoyl reductase (InhA). The mechanism for INH activation remains poorly understood, and the inhibitor has never been isolated. We have purified the InhA-inhibitor complex generated in the M. tuberculosis KatG-catalyzed INH activation. The complex exhibited a 278-nm absorption peak and a shoulder around 326 nm with a characteristic A(326)/A(278) ratio of 0.16. The complex was devoid of enoyl reductase activity. The inhibitor noncovalently binds to InhA with a K(d) < 0.4 nM and can be dissociated from denatured InhA for chromatographic isolation. The free inhibitor showed absorption peaks at 326 (epsilon(326) 6900 M(-1) cm(-1)) and 260 nm (epsilon(260) 27,000 M(-1) cm(-1)). The inactive complex can be reconstituted from InhA and the isolated inhibitor. The InhA inhibitor from the KatG-catalyzed INH activation was identical to that from a slow, KatG-independent, Mn(2+)-mediated reaction based on high pressure liquid chromatography analysis and absorption and mass spectral characteristics. By monitoring the formation of the InhA-inhibitor complex, we have found that manganese is not essential to the INH activation by M. tuberculosis KatG. Furthermore, the formation of the InhA inhibitor in the KatG reaction was independent of InhA.

Human melanoma-associated retinopathy (MAR) antibodies alter the retinal ON-response of the monkey ERG in vivo

PURPOSE

Melanoma-associated retinopathy (MAR) is a paraneoplastic condition that causes visual symptoms of night-blindness and photopsias. The electroretinogram (ERG) of MAR patients is characteristically abnormal in a way that implicates retinal depolarizing bipolar cell (DBC) dysfunction. Whether an injection of IgG from MAR patients into the vitreous of monkeys would alter the ERG acutely as a demonstration of a functional basis for patients' visual symptoms was explored.

METHODS

MAR IgG was isolated from three visually symptomatic melanoma patients. Control IgG was from melanoma patients with no vision problems. The ERG was monitored after intravitreal injections into monkey eyes. One eye was injected with 2-amino-4-phosphonobutyric acid (APB), which is known to block DBC ON-pathway responses. Retinal immunocytochemistry was performed using fluorescein isothiocyanate-labeled goat anti-human IgG.

RESULTS

Within 1 to 3 hours after MAR IgG injection, the ERG photopic b-wave was diminished, with far less effect on the a- and d-waves. These changes are characteristic of DBC dysfunction and were similar to the effects of APB. The scotopic ERG b-wave, which reflects activity of rod-driven DBCs, showed a loss of amplitude and threshold sensitivity after MAR IgG. Retinal immunocytochemistry with anti-IgG antibody showed IgG penetration throughout the retinal layers, but staining was not specific for a single type of retinal neuron.

CONCLUSIONS

Intravitreal injection of human MAR IgG altered the monkey ERG acutely in ways that implicate functional disruption of retinal DBC signaling. These results support the hypothesis that MAR IgG circulating antibodies are responsible for the reported visual symptoms. Bipolar cells in the ON-pathway appear to be affected more than OFF-pathway bipolar cells of the cone pathway in this acute preparation.

[Evaluation of effectiveness of hepatitis B plasma derived vaccine and a survey of hepatitis C virus infection in preschool children in Chengdu, Sichuan]

This study was undertaken to evaluate the effectiveness of hepatitis B plasma-derived vaccine and investigate the character of hepatitis C virus infection in preschool children. The anti-HBs, HBsAg and anti-HCV of 985 plasma samples were examined by ELISA. The results showed that the positive rate of HBsAg in the children (aged < 7 yr) in the communities was 0.89% and the effectiveness of the vaccine was 91.38%. The positive rate of anti-HBs decreased with the increase in age; the positive rate of HBsAg did not increase with age. The positive rate of HBsAg was as high as 4.69% in the children from hospitals, so supervision and enhanced vaccination should be administered properly in this group. The positiverate of anti-HCV was 1.18% in the communities, but 3.17% in hospitals. It is worthy to investigate how children get infected with HCV.

Measurement of total nitric oxide metabolite (NO(x)(-)) levels in vivo

The measurement of the total level of nitric oxide (NO) metabolite (NO(x)(-)) by microdialysis has recently been used to assess the production of NO in the in vivo brain [D. Luo, S. Knezevich, S.R. Vincent, N-Methyl-D-aspartate-induced nitric oxide release: an in vivo microdialysis study, Neuroscience, 57 (1993), 897-900; K. Ohta, N. Arai, M. Shibata, J. Hamada, S. Komatsumoto, K. Shimazu, Y. Fukuuchi, A novel in vivo system for consecutive measurement of brain nitric oxide production combined with the microdialysis technique, Neurosci. Lett., 176 (1994), 165-168; K. Shintani, S. Kanba, T. Nakai, K. Sato, G. Yagi, R. Kato, M. Arai, Measurement by in vivo microdialysis of nitric oxide release in the rat cerebellum, J. Psychiatr. Neurosci., 3 (1994), 217-221; H. Togashi, K. Mori, K. Ueno, M. Matsumoto, N. Suda, H. Saito, M. Yoshika, Consecutive evaluation of nitric oxide production after transient cerebral ischemia in the rat hippocampus using in vivo brain microdialysis, Neurosci. Lett., 240 (1998), 53-57]. Although several methods are available for detecting NO(x)(-) levels in dialysates, these methods are either not sensitive enough or require expensive experimental equipment. The method described herein provides a convenient and sensitive procedure for determining NO(x)(-) levels in dialysates. This method is useful for the in vivo study of NO production from various brain regions in various pathological conditions, and can be applied to other tissues.