Overview: new perspectives on the stubborn challenge of preterm birth.
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Congresses as Topic↗
Biomedical subjects
R B Johnston
Publications and source records attributed to R B Johnston.
Clinical aspects of chronic granulomatous disease.
Data from a registry of 368 patients with chronic granulomatous disease (CGD) documenta shift in the most common infecting organisms away from staphylococci and enteric bacteria to Aspergillus species, although staphylococci remain a threat. A. nidulans appears to have a particular virulence in CGD. Burkholderia cepacia sepsis/pneumonia was the second most lethal infection in patients in the registry. Seventy-six percent of registry patients had the X-linked recessive (XLR) form of CGD. Chorioretinitis may be more common than previously appreciated, and boys with the XLR disease should probably have routine full eye exams. A new variant of CGD has been described that is caused by an inhibitory mutation in Rac2, which regulates activity of the neutrophil respiratory burst and actin assembly. Interferon-gamma, antibacterial prophylaxis, and, probably, antifungal prophylaxis with itraconazole reduce the rate of infection, and bone marrow transplantation can cure the disease if a histocompatible donor is available. Gene therapy can cure CGD in knockout mouse models. Having even a small percentage of phagocytes that are nicotinamide adenine dinucleotide phospate oxidase-positive can reduce the risk of serious infection, and procedures now under study appear close to achieving that goal, if not a cure.
Granulomatous Disease, Chronic↗
The phagocytosis-associated respiratory burst in human monocytes is associated with increased uptake of glutathione.
During the phagocytic respiratory burst, oxygen is converted to potent cytotoxic oxidants. Monocytes and macrophages are potentially long-lived, and we have hypothesized that protective mechanisms against oxidant stress are varied and fully expressed in these cells. We report here that the respiratory burst in monocytes is accompanied by an increase in the uptake of [35S]glutathione ([35S]GSH) after 20-30 min to levels up to 10-fold greater than those at baseline. By 30 min, 49% of the cell-associated radioactivity was in the cytosol, 41% was in membrane, and 10% was associated with the nuclear fraction. GSH uptake was inhibited by catalase, which removes hydrogen peroxide (H2O2), and micromolar H2O2 stimulated GSH uptake effectively in monocytes and also lymphocytes. Oxidation of GSH to glutathione disulfide with H2O2 and glutathione peroxidase prevented uptake. Acivicin, which inhibits GSH breakdown by gamma-glutamyl transpeptidase (GGT), had no effect on the enhanced uptake seen during the respiratory burst. Uptake of cysteine or cystine, possible products of GGT activity, stayed the same or decreased during the respiratory burst. These results suggest that a GGT-independent mechanism is responsible for the enhanced GSH uptake seen during the respiratory burst. We describe here a sodium-independent, methionine-inhibitable transport system with a Km (8.5 microM) for GSH approximating the plasma GSH concentration. These results suggest that monocytes have a specific GSH transporter that is triggered by the release of H2O2 during the respiratory burst and that induces the uptake of GSH into the cell. Such a mechanism has the potential to protect the phagocyte against oxidant damage.
Cysteine↗
Chronic granulomatous disease. Report on a national registry of 368 patients.
A registry of United States residents with chronic granulomatous disease (CGD) was established in 1993 in order to estimate the minimum incidence of this uncommon primary immunodeficiency disease and characterize its epidemiologic and clinical features. To date, 368 patients have been registered; 259 have the X-linked recessive form of CGD, 81 have 1 of the autosomal recessive forms, and in 28 the mode of inheritance is unknown. The minimum estimate of birth rate is between 1/200,000 and 1/250,000 live births for the period 1980-1989. Pneumonia was the most prevalent infection (79% of patients; Aspergillus most prevalent cause), followed by suppurative adenitis (53% of patients; Staphylococcus most prevalent cause), subcutaneous abscess (42% of patients; Staphylococcus most prevalent cause), liver abscess (27% of patients; Staphylococcus most prevalent cause), osteomyelitis (25% of patients; Serratia most prevalent cause), and sepsis (18% of patients; Salmonella most prevalent cause). Fifteen percent of patients had gastric outlet obstruction, 10% urinary tract obstruction, and 17% colitis/enteritis. Ten percent of X-linked recessive kindreds and 3% of autosomal recessive kindreds had family members with lupus. Eighteen percent of patients either were deceased when registered or died after being registered. The most common causes of death were pneumonia and/or sepsis due to Aspergillus (23 patients) or Burkholderia cepacia (12 patients). Patients with the X-linked recessive form of the disease appear to have a more serious clinical phenotype than patients with the autosomal recessive forms of the disease, based on the fact that they are diagnosed significantly earlier (mean, 3.01 years of age versus 7.81 years of age, respectively), have a significantly higher prevalence of perirectal abscess (17% versus 7%), suppurative adenitis (59% versus 32%), bacteremia/fungemia (21% versus 10%), gastric obstruction (19% versus 5%), and urinary tract obstruction (11% versus 3%), and a higher mortality (21.2% versus 8.6%).
Adolescent↗
Preclinical evaluation of a rheolytic catheter for percutaneous coronary artery/saphenous vein graft thrombectomy.
The presence of thrombus increases the rate of acute complications and restenosis in percutaneous revascularization of native coronary arteries and saphenous vein grafts. Rheolytic thrombectomy uses high velocity saline jets to create a Bernoulli effect for thrombus entrainment, dissociation, and evacuation of debris, providing a novel approach to the treatment of thrombotic lesions. The study objective was to determine the preclinical safety and effectiveness of a 5 French rheolytic thrombectomy catheter designed for use in coronary arteries and saphenous vein grafts. In vitro testing was performed to evaluate catheter effectiveness (clot removal rate) and safety (particle generation and hemolysis). This was followed by acute (n = 6) and chronic (n = 6) canine studies to determine hemodynamic, angiographic, and histopathologic effects of the catheter. The results showed effective clot removal with minimal embolization: 99.4% of the total clot volume was removed with only 0.1% proximal embolization and 0.5% distal embolization. 98.4% of the embolic particles were less than 10 microm. Canine studies revealed no significant angiographic, hemodynamic, histopathologic, or electrocardiographic abnormalities with the exception of transient heart block in one animal. There was transient hemolysis which normalized within 24 hours with no adverse effects. These results demonstrate the effectiveness and safety of coronary rheolytic thrombectomy and provided the basis for clinical trials to further evaluate this promising new approach for coronary thrombectomy.
Animals↗
Effect of lower extremity muscular fatigue on motor control performance.
PURPOSE: The purpose of this study was to determine whether lower extremity fatigue affects the ability of an individual to balance on an unstable platform. METHODS: Twenty healthy subjects (average age, 29 yr, range, 20 to 39 yr) were tested on an instrumented balance assessment system. Static tests were done on the limbs unilaterally and then bilaterally, and finally a dynamic test was performed in which the subject moved the platform in a circular manner to chase a moving object on a computer screen. After testing, subjects were fatigued using an isokinetic dynamometer, which imposes closed kinetic chain antagonistic exercise on the ankle, knee, and hip, similar to a stair stepper. No rest was allowed, and subjects were fatigued to less than 50% of their initial tested force. Subjects were then immediately retested on the unstable platform using the same testing protocol. All subjects completed the testing. RESULTS: Analysis of pre- and post-fatigue balance results demonstrated significant decreases in motor control performance on the three static tests following exercise to fatigue in all subjects (P < 0.001). CONCLUSIONS: Our findings support anecdotal evidence that fatigued individuals are at increased risk of injury because of loss of balance. Avoidance of fatigue and preconditioning may prevent injury.
Accidental Falls↗
Augmentation of human macrophage candidacidal capacity by recombinant human myeloperoxidase and granulocyte-macrophage colony-stimulating factor.
Phagocyte myeloperoxidase (MPO) is believed to be particularly important in defense against candida infection. We reported earlier that monocytes, rich in MPO, killed Candida albicans at a significantly higher rate and extent than did monocyte-derived macrophages, known to lack MPO, and that C. albicans is less resistant to MPO-dependent oxidants than less pathogenic Candida species. We hypothesized, therefore, that the capacity of macrophages to kill C. albicans might be improved in the presence of MPO. In this study, we evaluated the ability of recombinant human MPO (rhMPO) to augment the killing of C. albicans by resident macrophages and macrophages activated by recombinant human granulocyte-macrophage colony-stimulating factor. Addition of rhMPO (concentration range, 0.8 to 6.4 U/ml) to suspensions of resident and activated macrophages and opsonized C. albicans resulted in concentration-dependent and significant increases in candida killing. This enhancement was particularly pronounced with activated macrophages, whether C. albicans was opsonized or unopsonized and ingested through the macrophage mannose receptor. rhMPO did not affect the killing of C. albicans by monocytes, nor did it affect phagocytosis of opsonized or unopsonized C. albicans. These results indicate that exogenous rhMPO can augment the candidacidal capacity of both resident and activated macrophages, with a more profound effect on activated cells. We suggest that rhMPO may be effective in the treatment of invasive candidiasis.
Candida albicans↗
Characterization of multiple cysteine and cystine transporters in rat alveolar type II cells.
Cysteine availability is rate limiting for the synthesis of glutathione, an important antioxidant in the lung. We used rat alveolar epithelial type II cells to study the mechanism of cysteine and cystine uptake. Consistent with carrier-mediated transport, each uptake process was saturable with Michaelis-Menten kinetics and was inhibited at 4 degrees C and by micromolar levels of amino acids or analogs known to be substrates for a specific transporter. A unique system XAG was found that transports cysteine and cystine (as well as glutamate and aspartate, the only substrates previously described for system XAG). We also identified a second Na(+)-dependent cysteine transporter system, system ASC, and two Na(+)-independent transporter systems, system xc for cystine and system L for cysteine. In the presence of glutathione at levels measured in rat plasma and alveolar lining fluid, cystine was reduced to cysteine and was transported on systems ASC and XAG, doubling the transport rate. Cysteinylglycine, released from glutathione at the cell surface by gamma-glutamyl transpeptidase, also stimulated uptake after reduction of cystine. These findings suggest that, under physiological conditions, cysteine and cystine transport is influenced by the extracellular redox state.
Amino Acids↗
American Pediatric Society Presidential Address 1997: the ever-whirling wheel of change.
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History of Medicine↗
Fortifying food with folic acid.
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Adolescent↗
Folic acid: new dimensions of an old friendship.
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Adolescent↗
Protein S-thiolation and dethiolation during the respiratory burst in human monocytes. A reversible post-translational modification with potential for buffering the effects of oxidant stress.
Stimulation of the respiratory burst in mouse macrophages or human neutrophils results in the formation of disulfide bonds between low m.w. thiols and sulfhydryl groups on specific cytosolic proteins (S-thiolation). S-thiolation is reversible in certain chemical systems. The aim of the present study was to analyze the dynamic nature of this process in human monocytes under physiologic conditions. We report here that the extent of S-thiolation and the rate of respiratory burst stimulated by opsonized zymosan or phorbol diester increased for 10 to 20 min and then declined (dethiolation) in close association. Individual proteins underwent S-thiolation and dethiolation at different rates. H2O--appeared particularly effective in mediating S-thiolation, based on inhibition of S-thiolation by added catalase and accentuation by azide, which inhibits cellular catalase. S-thiolation did not occur in stimulated monocytes from patients with chronic granulomatous disease. The addition of H2O2 to monocytes or lymphocytes induced rapid S-thiolation (1 to 3 min); a subsequent dethiolation returned most of the proteins to baseline by 15 to 30 min. At 0 degrees C and after addition of 1,3-bis-(2-chloroethyl)-1-nitrosourea, there was effective S-thiolation on exposure to H2O2, but dethiolation was inhibited, suggesting a possible role for glutathione (GSH)/thioredoxin reductase systems in this process. GSH was determined to be the most abundant low m.w. thiol bound to S-thiolated proteins, but gamma-glutamylcysteine and cysteine were also bound. The time of maximal reduction in cytosolic GSH during the respiratory burst (10 min) coincided with the time at which protein-bound GSH was highest. S-thiolation-dethiolation represents a reversible post-translational modification that could protect cellular proteins from irreversible oxidative damage.
Blood Proteins↗
Diamide primes neutrophils for enhanced release of superoxide anion: relationship to S-thiolation of cellular proteins.
Stimulation of the respiratory burst in phagocytes induces the formation of mixed disulfides between sulfhydryl groups of proteins and low-molecular-weight thiols. We hypothesized that this process (S-thiolation) might be involved in turning off the respiratory burst. However, induction of S-thiolation by pretreatment of neutrophils with diamide, a direct thiol oxidizing agent, actually primed the cells for a two- to fivefold increase in total release and fourfold increase in rate of release of 02- on stimulation by f-Met-Leu-Phe. Generation of intracellular oxidants (hydroethidine fluorescence) was increased ninefold. Priming and S-thiolation were apparent at 1 min of incubation and peaked at 5-10 min. Diamide pretreatment also reduced the lag time between addition of phorbol diester and release of 02- by a mean of 23 s (41%). Dithioerythritol, a sulfhydryl-reducing agent, abolished both the S-thiolation and priming mediated by diamide. H202 also induced priming and S-thiolation; and these were eliminated by dithioerythritol. In contrast to the effect of endotoxin, diamide priming did not affect Ca2+ homeostasis of the neutrophils. Diamide did not significantly alter NADPH oxidase activity in a cell-free system. These findings suggest that sulfhydryl groups on one or more proteins play an important role in modulating the respiratory burst.
Blood Proteins↗
Folic acid supplementation--when and how.
The periconceptional intake of 400 micrograms of folic acid can prevent 50-70% of neural tube defects. It is difficult to achieve this intake with diet alone, even with the recently approved levels for grain-food fortification. Therefore, a daily multivitamin with folic acid is recommended for all women of childbearing potential. Obstetrician-gynecologists should exercise every opportunity to educate their patients to this end. Although raised as a concern, the potential of masking the megaloblastic anemia of pernicious anemia is unlikely with these levels of supplementation, and considering the rarity of the disease in women of reproductive age.
Female↗
Bone-patellar tendon-bone grafts for anterior cruciate ligament reconstruction: the effects of graft pretensioning.
Viscoelastic creep is a well-known phenomenon associated with collagenous soft tissues under sustained tensile load. Despite our understanding of this phenomenon and the potential for "loosening" of the graft over time, pretensioning of bone-patellar tendon-bon (B-PT-B) grafts for reconstruction of the anterior cruciate ligament (ACL) to eliminate this elastic deformation is not commonly practiced. This investigation quantified viscoelastic creep in B-PT-B grafts using both an in vivo and an in vitro model. In vivo, 10-mm B-PT-B grafts were procured and prepared in a standard manner for arthroscopically assisted ACL reconstruction. A total of 153 grafts were evaluated. During preparation, each graft was tensioned using a commercially available graft preparation board (Smith & Nephew DonJoy). An initial tensile load of 2.25 N (0.5 lb) was applied to the graft and a measurement was taken between bone-tendon junctions at either end. A sustained load of 89 N (20 lb) was then applied for a minimum of 4 minutes and the measurement repeated. In the in vitro model, grafts were harvested in a standard manner, then placed in a servohydraulic for tensile loading. A differential variable reluctance transducer was implanted in each graft to quantify net displacement during 15 minutes of sustained tensile loading at 89 N (20 lb). A total of 13 specimens were evaluated. In the in vivo model, mean pretension bone-tendon junction length was 43.6 mm (range, 29 to 64 mm; SD, +/- 6.7). Mean post-tension bone-tendon length was 49.6 mm (range, 33 to 71 mm; SD, +/- 7.1), representing a mean increase in length of 6.0 mm (range, 2 to 12; SD, +/- 2.1) or 14.0% (range, 3.8 to 28.6; SD, +/- 5.2). In the in vitro model, the mean pretension tendon length was 42.81 m (range, 35.20 to 51.48; SD, 4.54). The mean post-tension length was 47.11 mm (range, 38.05 to 56.23; SD, +/- 5.04) representing a mean increase of 4.30 mm or 10.12%. These data would seem to support the hypothesis that without pretensioning, significant postimplantation graft creep will occur.
Adolescent↗
Hyperoxia enhances expression of gamma-glutamyl transpeptidase and increases protein S-glutathiolation in rat lung.
By participating in glutathione (GSH) synthesis, gamma-glutamyl transpeptidase (GGT) influences the GSH redox cycle, which is a major contributor in protecting against reactive oxygen metabolites. This study determined the effect of prolonged exposure of neonatal rats to > 98% oxygen on expression of GGT and on GSH metabolism. Lungs of neonatal rats chronically exposed to hyperoxia had increased expression of GGT mRNA, resulting in significantly higher GGT protein levels and enzyme activity than in lungs of animals raised in room air. Hyperoxia also upregulated glucose-6-phosphate dehydrogenase, but Na-K-ATPase activity was not changed. GGT mRNA, protein level, and enzyme activity returned to control levels after recovery in room air for 3 days. Levels of GSH, glutathione disulfide, and protein-bound GSH (S-glutathiolated protein) rose with hyperoxia and fell during recovery. S-glutathiolation is likely a mechanism for protection and a regulatory modification of protein sulfhydryl groups. Hyperoxia-induced upregulation of GGT and the concomitant increase in protein S-glutathiolation appear to be additional components fundamental in protecting the lung against oxidative injury.
Animals↗
Evidence for participation of vicinal dithiols in the activation sequence of the respiratory burst of human neutrophils.
Phenylarsine oxide (PAO) specifically forms a stable ring complex with vicinal dithiols that can be reversed with 2,3-dimercaptopropanol (DMP). Pretreatment of human neutrophils with micromolar concentrations of PAO inhibited release of superoxide anion (O2-) stimulated by N-formyl-methionyl-leucyl-phenylalanine (FMLP) or phorbol 12-myristate 13-acetate (PMA); the inhibition was reversed with DMP, but not with 2-mercaptoethanol. PAO did not affect O2- release in previously stimulated cells. PAO did not affect the FMLP-induced Ca2+ response, suggesting that PAO affects a postreceptor event that does not modulate the Ca2+ transient. Treatment of isolated membrane or cytosolic fractions with PAO did not change the rates of arachidonate-stimulated O2- production in a cell-free system. Pretreatment of unstimulated neutrophils with PAO inactivated cytosolic protein kinase C (PKC); the inactivation was reversed with DMP. However, PAO did not affect PMA-induced translocation of beta-PKC protein or reduce the PKC activity translocated to the membrane. PAO had no effect on tyrosine kinase activity but inactivated phosphotyrosine phosphatase; stimulus-induced tyrosine phosphorylation of several proteins was markedly enhanced. These results suggest that vicinal dithiols play an essential role in activation of the respiratory burst oxidase. Possible sites for the activity of these essential vicinal dithiols include PKC and the regulatory balance of tyrosine phosphatase activity and tyrosine phosphorylation.
Arachidonic Acid↗
Reversal of flecainide-induced ventricular arrhythmia by hypertonic sodium bicarbonate in dogs.
Flecainide occasionally produces incessant ventricular tachycardia that is difficult to treat. Reports of uncontrolled clinical studies have suggested a therapeutic role for hypertonic sodium bicarbonate (NaHCO3). To test this observation, spontaneous and pacing-induced arrhythmia canine models were designed. In the spontaneous model, flecainide was infused at 0.5 mg/kg/min until ventricular tachycardia occurred spontaneously. In the pacing-induced model, flecainide was infused at 1.0 mg/kg/min load (0.5 mg/kg/min maintenance) stepwise until the QRS was widened 50%, 75%, and 100%, with programmed ventricular stimulation at each step until ventricular arrhythmia was induced. Dogs who developed spontaneous arrhythmia were treated blindly with three doses of either NaHCO3 (3 mEq/kg/dose, with 1 minute between doses) or normal saline. Dogs who were induced in the second model were treated with the same three doses, 10 minutes apart, with programmed stimulation between each dose. Before unblinding in both protocols, dogs were classified as "responders" or "nonresponders" to therapy. In the spontaneous model, of 14 dogs with spontaneous ventricular tachycardia, all 7 dogs treated with NaHCO3 showed response, compared with only 1 of 7 dogs treated with saline (P < .01). Ventricular QRS complexes/min were reduced by NaHCO3 in that protocol. In the induced arrhythmia protocol, of 14 dogs with inducible arrhythmia, 6 of 7 responded to NaHCO3, and 1 of 7 responded to placebo (P < .05). In both protocols, arterial pH and the serum sodium concentration were increased by NaHCO3 but not by normal saline control treatment. QRS interval duration was shortened by NaHCO3 therapy.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗