PubMed Health⌕ Search

Biomedical subjects

C Lam

Publications and source records attributed to C Lam.

At least 73 records · Page 4Linked to original sources
PubMed1991

SDZ MRL 953, a novel immunostimulatory monosaccharidic lipid A analog with an improved therapeutic window in experimental sepsis.

SDZ MRL 953, a new synthetic monosaccharidic lipid A, was investigated in vitro and in vivo for immunopharmacological activities. In experimental models of microbial infections, the compound was highly protective when it was administered prophylactically either once or three times to myelosuppressed or immunocompetent mice. The 50% effective doses of SDZ MRL 953 varied with the infectious agents and the route of its administration. In all cases, the 50% effective doses were about 10(3) times higher than those obtained with endotoxin from Salmonella abortus equi. SDZ MRL 953 was, however, less toxic than lipopolysaccharide by a factor of 10(4) to greater than 7 x 10(5) times in galactosamine-sensitized mice. The compound was also an effective inducer of tolerance to endotoxin. Hence, repeated dosing with the compound induced a transient resistance (greater than or equal to 1 week) to lethal challenges with endotoxin. In vitro, the compound was devoid of intrinsic antimicrobial activity, but it moderately induced the release of cytokines from monocytes and primed human neutrophils for the enhanced production of reactive oxygen metabolites in response to a soluble stimulus. The results presented here suggest that SDZ MRL 953 may be useful in a clinical setting for enhancing resistance to infections, particularly in patients undergoing myelosuppressive chemotherapy or irradiation, and for the prophylaxis of endotoxin shock.

Animals↗
PubMed1991

Effect of SDZ MRL 953 on the survival of mice with advanced sepsis that cannot be cured by antibiotics alone.

Stimulation of nonspecific immunity as an additional modality for therapy of sepsis that cannot be cured by antibiotics alone was investigated. SDZ MRL 953, a novel monosaccharidic lipid A analog as a prototype immunostimulant, and cefotaxime or gentamicin were administered to normal or myelosuppressed mice in a state of advanced sepsis caused by Escherichia coli or Staphylococcus aureus. In this novel model, antibiotic therapy was initiated when the infected mice appeared moribund. At this stage, neither pretreatment with the immunostimulant nor therapy with high doses of cefotaxime or gentamicin was effective in protecting the animals from fatal sepsis. However, pretreatment with a single dose of SDZ MRL 953 1 day prior to microbial inoculation dramatically improved the curative effects of the antibiotics. Hence, long-term survival was significantly enhanced with increasing doses of the immunostimulant in the combined therapy. Peritoneal macrophages from SDZ MRL 953-pretreated animals were primed for enhanced production of microbicidal reactive oxygen metabolites in vitro. In conclusion, the results of the present study indicate that SDZ MRL 953 is a potential candidate for use in a clinical setting as an adjunct to antimicrobial therapy for infections that cannot be treated successfully with appropriate antibiotics alone.

Animals↗
PubMed1991

Immunostimulatory, but not antiendotoxin, activity of lipid X is due to small amounts of contaminating N,O-acylated disaccharide-1-phosphate: in vitro and in vivo reevaluation of the biological activity of synthetic lipid X.

Lipid X, a precursor in the biosynthesis of lipid A, has been claimed to possess most of the immunostimulatory activity but none of the toxicity of endotoxin. However, recent work shows that synthetic lipid X can be contaminated with small amounts of N,O-acylated disaccharide-1-phosphate (H. Aschauer, A. Grob, J. Hildebrandt, E. Schuetze, and P. Steutz, J. Biol. Chem. 265:9159-9164, 1990). Because the impurities themselves exhibit immunostimulatory properties, it was necessary to establish whether chemically pure synthetic lipid X exhibits any of the endotoxinlike biological activities previously attributed to the native compound extracted from the Escherichia coli MN7 mutant. In the present study, two batches of synthetic lipid X were used: batch A contained the contaminating disaccharide, and batch B was pure lipid X. Batch A, previously believed to be pure on the basis of spectroscopic and microanalysis data, induced murine peritoneal macrophages to secrete tumor necrosis factor, interleukin-1, and prostaglandin E2 at a minimal dose of 10 micrograms/ml in vitro. Batch B, further purified by Sephadex LH 20 chromatography, was found virtually inactive in these in vitro assays. Furthermore, batch A was pyrogenic in rabbits at a dose of 0.05 mg/kg, whereas batch B was not pyrogenic at doses of up to greater than or equal to 2 mg/kg. However, both batches were equally tolerated by galactosamine-loaded mice at doses of up to 100 mg/kg. Surprisingly, while only batch A protected neutropenic mice against lethal infection with Pseudomonas aeruginosa (50% effective dose, 12.4 mg/kg), both batches were equally protective against infection with herpes simplex virus type 1 in mice and guinea pigs, even when lipid X was administered therapeutically. Interestingly, both batches of lipid X blocked endotoxin-induced expression of monocyte procoagulant activity and priming of human neutrophils for superoxide anion release. Similarly, both batches protected galactosamine-sensitized mice from otherwise lethal endotoxemia when administered prophylactically or simultaneously with the lipopolysaccharide challenge. Thus, our findings suggest that chemically pure lipid X (batch B) is devoid of the immunostimulatory properties of lipid A or endotoxin. Rather, it behaves as a competitive inhibitor of lipopolysaccharide. We conclude, therefore, that previous studies which attributed immunostimulatory activities to any batch of synthetic lipid X should be interpreted with caution.

Adjuvants, Immunologic↗
PubMed1991

Design of a database with graphical analysis for X-ray quality assurance and dose information to assist in a programme for patient dose reduction.

A database system has been set up on an IBM PC to store X-ray quality assurance (QA) data and patient doses for all X-ray equipment operated by Grampian Health Board. Graphical analysis facilities have been developed to display data in a readily understandable form. Data on equipment specifications, QA test results, exposure factors for standard examinations, and thermoluminescent dosemeter (TLD) measurements of patient skin doses are stored in separate forms. X-ray machine outputs are fitted to a simple polynomial equation, and the data combined with information on exposure factors to calculate entrance doses for selected examinations. Data such as filtration and backscatter factors are derived from look-up tables for use in dose calculations. Histogram comparisons can be made between calculated doses, means of TLD measurements and National Radiological Protection Board reference levels to allow units giving high skin doses to be identified so that corrective actin can be taken.

Humans↗
PubMed1991

A comparative study of continuous- and pulsed-wave Doppler velocimetry in fetal and uteroplacental circulation.

Continuous-wave and pulsed-wave Doppler ultrasonography are the two common methods used to study the fetal and uteroplacental circulation. We used both methods in the same patient population in three different gestations and in various fetal and uteroplacental vessels to compare the results from both machines. Thirty-one normal patients were studied at 20, 28, and 36 weeks gestation. The results showed significant correlation with no statistically significant differences between the two types of machines for the peak systolic/end-diastolic ratios and resistance index for the umbilical artery and uterine arteries. Significant differences, however, were demonstrated when the arcuate artery was studied, or when the pulsatility index was used for comparison. We therefore conclude that when different machines are used for study, comparison of the results is only valid for selected vessels and indices. Results for arcuate arteries and pulsatility index should be compared with caution.

Blood Flow Velocity↗
PubMed1990

Simultaneous pulsed Doppler velocimetry of fetal aorta and inferior vena cava. Diagnosis of fetal congenital heart block; two case reports.

A simple technique for the diagnosis of fetal congenital heart block by simultaneous Doppler blood-flow velocimetry of the fetal abdominal aorta and inferior vena cava is described. Furthermore, a simple method of monitoring the fetal atrial reactivity during the antenatal period; and simultaneous recording of atrial and ventricular rates during labour are also described. These simple techniques can be applied for the diagnosis and monitoring of the fetus in other types of cardiac arrhythmias.

Adult↗
PubMed1990

In vitro and in vivo activity of human recombinant granulocyte-macrophage colony-stimulating factor in dogs.

Although it is well documented that human granulocyte-macrophage colony-stimulating factor (GM-CSF) controls the production and functional activity of human and nonhuman primate granulocytes and macrophages, relatively little is known about its effects on cells obtained from other species. The molecular cloning of the complementary DNA for human GM-CSF has made it possible to determine the cross-reactivity of the purified recombinant human material (rhGM-CSF) on cells of other species. The results presented herein show that specific receptors for human GM-CSF exist on dog bone marrow cells and mature circulating dog granulocytes. The number of the receptors and the apparent binding affinity of the rhGM-CSF to its receptors on granulocytes were similar to those observed either on human or monkey cells. In cultures of dog bone marrow cells, rhGM-CSF was capable of promoting colony formation in a dose-dependent manner. Human GM-CSF also primed dog granulocytes for increased production of reactive oxygen metabolites in response to either phorbolmyristic acetate-or zymosan-activated dog serum. In vivo, s.c. administration to healthy dogs of rhGM-CSF in daily doses of 15, 50, or 150 micrograms/kg body weight over a period of 7-20 days induced a dose-dependent rise of up to a maximum of a fourfold increase in peripheral WBC counts. The rise in WBC counts was mainly due to elevated neutrophil levels, but an increase in the numbers of monocytes and eosinophils was also observed. However, the rhGM-CSF-induced leukocytosis in dogs was not as dramatic as that observed in nonhuman primates. In all rhGM-CSF-treated dogs, circulating platelet counts dropped to nadir levels of about 20%-30% of normal numbers. Dogs that were treated with 150 micrograms/kg rhGM-CSF developed specific antibodies after about 10-12 days of treatment. These antibodies were able to neutralize the effect of rhGM-CSF in in vitro assays. In vivo WBC counts began to decline when specific antibodies developed, but they never dropped below normal levels. Taken together, the results suggest that human GM-CSF does not appear to exhibit absolute species specificity.

Animals↗
PubMed1990

Prenatal diagnosis of congenital fetal arrhythmias by simultaneous pulsed Doppler velocimetry of the fetal abdominal aorta and inferior vena cava.

Various methods have been used for the diagnosis of congenital fetal arrhythmias. Currently, M-mode echocardiography is the most widely used method. However, good tracings are often difficult to obtain because of unfavorable fetal positions, resulting in long durations of examination. In early gestation, the fetal heart is often too small for clear M-mode echocardiography. Doppler velocity waveforms of the fetal inferior vena cava represent the right atrial activity, whereas those of the aorta reflect ventricular contraction. Because of the proximity of the vessels, it is easy to obtain simultaneous recording in opposite channels of Doppler waveforms from both vessels. A visual relationship between the atrial and ventricular contractions may be clearly established and a diagnosis may be made. The findings of simultaneous pulsed Doppler velocimetry of the fetal aorta and inferior vena cava were assessed in different types of congenital fetal arrhythmia: congenital heart block, premature atrial ectopic contractions, premature ventricular ectopic contractions, and supraventricular tachycardia. The correct diagnosis was made as early as 13 weeks' gestation, showing the application of this method in early pregnancy.

Aorta, Abdominal↗
PubMed1988

Differing complement-mediated opsonic activity of rabbit interstitial fluids from autologous serum.

Lack of appropriate methods for withdrawing extravascular or interstitial fluid from an animal host has limited in vitro study on the role of complement in the local defence of the extravascular space. In the present study, we obtained fluids from membrane diffusion chambers (porosity 0.22 micron) implanted into the kidneys, peritoneal cavity and soft tissues in rabbits. The complement-mediated opsonic activity (CMOA) of these fluids for Staphylococcus aureus ATCC 502A and Escherichia coli 01 was then compared to that of autologous sera. Soft tissue and renal interstitial fluids were as opsonic for E. coli as autologous sera but were however, poor opsonins for S. aureus. The peritoneal fluid was marginally effective in opsonization of both bacterial strains. While chelation of the fluids with MgEGTA (to block the classical pathway) did not diminish CMOA for E. coli, it reduced the CMOA for S. aureus by half. Conversely, heat-inactivation of the fluids and serum eliminated the opsonic activity for E. coli but only decreased the opsonic activity for S. aureus by half. Following a 24 h in vivo growth of E. coli in the implanted chambers, the CMOA was drastically reduced. Concomitant to the reduction in functional complement in the fluids, E. coli recovered from the chambers were found coated, though not maximally, with C3b as evidenced by studies with fluorescent antibody. The differences in opsonic content of extravascular fluids observed here might explain why certain sites of the body may be more vulnerable to attack by some bacterial species which are not effectively opsonized and therefore phagocytized.

Animals↗
PubMed1988

Synthesis and expression in Escherichia coli of the gene encoding monocyte-derived neutrophil-activating factor: biological equivalence between natural and recombinant neutrophil-activating factor.

The neutrophil-activating factor (NAF) purified from the conditioned medium of lipopolysaccharide-stimulated human monocytes was sequenced and found to consist of 72 amino acids: SAKELRCQCIKTYSKPFHPKFIKELRVIESGPHCANTEIIVKLSDGRELCLDPKENWVQRVVEKFLKRA ENS. Purified preparations of natural NAF contained, in addition to this main form, minor amounts of three amino-terminal variants with 77 (+AVLPR), 70, and 69 residues. A gene coding for the 72-amino acid NAF was synthesized, cloned, and expressed in Escherichia coli. Western (immunologic) blot analysis of crude bacterial extracts, with an antiserum raised against natural NAF, revealed a single band that comigrated with natural NAF. Recombinant NAF purified to homogeneity had identical amino- and carboxyl-terminal sequences to the 72-amino acid natural NAF. Recombinant NAF was tested on human neutrophils and had the same activity and potency as natural NAF in inducing chemotaxis, rapidly increasing cytosolic free Ca2+, activating the respiratory burst, and releasing specific and azurophilic granular contents.

Amino Acid Sequence↗
PubMed1988

Inositol regulates phosphatidylglycerolphosphate synthase expression in Saccharomyces cerevisiae.

The enzyme phosphatidylglycerolphosphate synthase (PGPS; CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase; EC 2.7.8.5) catalyzes the committed step in the synthesis of cardiolipin, a phospholipid found predominantly in the mitochondrial inner membrane. To determine whether PGPS is regulated by cross-pathway control, we analyzed PGPS expression under conditions in which the regulation of general phospholipid synthesis could be examined. The addition of inositol resulted in a three- to fivefold reduction in PGPS expression in wild-type cells in the presence or absence of exogenous choline. The reduction in enzyme activity in response to inositol was seen in minutes, suggesting that inactivation or degradation of the enzyme plays an important role in inositol-mediated repression of PGPS. In cho2 and opi3 mutants, which are blocked in phosphatidylcholine synthesis, inositol-mediated repression of PGPS did not occur unless choline was added to the media. Three previously identified genes that regulate general phospholipid synthesis, INO2, INO4, and OP11, did not affect PGPS expression. Thus, ino2 and ino4 mutants, which are unable to derepress biosynthetic enzymes involved in general phospholipid synthesis, expressed wild-type levels of PGPS activity under derepressing conditions. PGPS expression in the opi1 mutant, which exhibits constitutive synthesis of general phospholipid biosynthetic enzymes, was fully repressed in the presence of inositol and partially repressed even in the absence of inositol. These results demonstrate for the first time that an enzymatic step in cardiolipin synthesis is coordinately controlled with general phospholipid synthesis but that this control is not mediated by the same genetic regulatory circuit.

Gene Expression Regulation↗
PubMed1987

Effect of a diazaborine derivative (Sa 84.474) on the virulence of Escherichia coli.

The scope of selective inhibition of lipopolysaccharide (LPS) biosynthesis in virulent organisms with a diazaborine derivative (Sa 84.474) as a means to render them avirulent was explored. A serum resistant Escherichia coli 0111:B4 became serum sensitive following its cultivation in vitro in media containing 1.5 mg/l of Sa 84.474, a concentration shown previously to inhibit over 95% of normal LPS biosynthesis in its mutant J5 strain. An encapsulated E. coli 01:K1 was also converted to serum sensitivity. In addition, Sa 84.474-pretreatment increased the efficiency with which the previously resistant organisms were opsonized in normal human serum and subsequently phagocytosed by granulocytes. In vivo, intravenously inoculated, Sa 84.474-pretreated bacteria were rapidly removed from the blood circulation and were significantly (P less than 0.05) less virulent in inducing lethal peritoneal infections in mice (LD50 4.9 +/- 1 X 10(6) cfu) when compared to untreated control bacteria (LD50 2.2 +/- 0.97 X 10(6) cfu). The results suggest that the LPS plays an important role in the virulence of the two bacterial strains and imply that agents acting in a similar manner but with acceptable selective toxicity might be novel drugs for therapy of Gram-negative bacterial infections.

Animals↗
PubMed1987

Efficacy of recombinant human granulocyte-macrophage colony-stimulating factor in rhesus monkeys.

The glycosylated and the non-glycosylated recombinant human granulocyte-macrophage colony-stimulating factor (rh GM-CSF) expressed in Chinese hamster ovary cells and E. coli, respectively, were administered in rhesus monkeys either by the subcutaneous (three times daily) or intravenous route (6-hr infusions) for seven consecutive days. Within 24 hr peripheral white blood cells (WBC) increased 2-3 fold over normal values. Thereafter, the WBC increased steadily in a dose-dependent manner to reach maximum levels on the last day of or one day after the treatment period. The differential counts showed that neutrophils contributed to 50-80%, eosinophils to 10-20%, monocytes to 2-7%, and lymphocytes to 15-30% of the WBC rise. No effect was found on platelets and erythrocytes. After termination of treatment, WBC counts returned to normal levels within one week. Subcutaneously administered CSF was more effective in inducing leukocytosis than that injected intravenously In addition to the rise in WBC, the administered rh GM-CSF also enhanced the oxidative metabolism and bactericidal activity of the circulating mature granulocytes isolated from the blood of monkeys treated with rh GM-CSF. These results show that glycosylated or non-glycosylated rh GM-CSF is both an effective stimulator of leukocytosis and a potent activator of the functional activity of mature granulocytes in vivo.

Animals↗
PubMed1987

Protection of mice against lethal endotoxemia by lipid X is mediated through inhibition of neutrophil function.

The effects of lipid X and 3-aza-lipid X on in vitro neutrophil function were related to their ability to inhibit the toxicity of endotoxin in galactosamine-sensitized mice. In vitro, lipid X and 3-aza-lipid X (100 ng/ml) blocked completely endotoxin (100 ng/ml)-enhanced neutrophil aggregation, superoxide anion generation, and release of beta-glucuronidase in response to a chemotactic tripeptide, f-met-leu-phe (10(-7) M). In vivo, lipid X at 250 micrograms/mouse (but not 3-aza-lipid X at a similar dose) protected groups of 10 mice from an otherwise lethal dose of endotoxin in galactosamine-sensitized mice when it was administered IV 4 hr or 2 hr before endotoxin challenge. The minimum effective dose of lipid X that could protect 50% of the challenged mice was calculated to be 715 micrograms/kg. However, lipid X failed to suppress neutrophil infiltration into the lungs. The ability of lipid X to inhibit endotoxin-induced neutrophil responses and to protect against lethal endotoxemia may be due to induction of early phase tolerance to endotoxin by the compound.

Animals↗
PubMed1987

Recombinant human GM-CSF induces leukocytosis and activates peripheral blood polymorphonuclear neutrophils in nonhuman primates.

The in vivo efficacy of glycosylated and nonglycosylated recombinant human granulocyte macrophage colony-stimulating factor (rh GM-CSF) expressed in Chinese hamster ovary cells and Escherichia coli respectively was studied in rhesus monkeys following a daily subcutaneous (SC; three times) or intravenous (IV; over six hours) dose for seven consecutive days. The monkeys responded to the rh GM-CSF with a prompt (within 24 hours) rise in circulating white blood cells (WBCs). Thereafter the total cell counts increased steadily in a dose-dependent manner with repeated dosing to numbers six times over the pretreatment levels. Overall, granulocyte counts increased fivefold, lymphocytes twofold to fourfold, and monocytes threefold to fourfold. Platelets and erythrocytes were unaffected. Within 1 week after the end of treatment the leukocytosis had disappeared. Of the two routes of treatment, SC (three times daily)-administered rh GM-CSF was more effective than the same dose given by a six-hour IV infusion. In addition to inducing leukocytosis, parenterally administered rh GM-CSF primed mature circulating granulocytes for enhanced oxidative metabolism and killing of an E coli strain. These results show that exogenously administered glycosylated or nonglycosylated rh GM-CSF is both an effective stimulator of leukocytosis and a potent activator of the phagocytic function of mature granulocytes in monkeys.

Animals↗
PubMed1986

Isolation and characterization of highly serum-dependent cells released early from collagenase digested calvaria.

A subclass of highly serum-dependent bone cells has been identified among the cells released early from calvaria following digestion in collagenase. Partial purification for these cells has been carried out based on the observation that they require serum for attachment to polystyrene culture flasks. This subclass of bone cells differs from adherent cells and late released osteoblasts, in that they express almost no cAMP response to PTH, require high levels of serum (10%) for initial growth and proliferation, and do not increase DNA synthesis in response to PTH. In common with adherent cells and late released osteoblasts, their proliferation is decreased by 1,25(OH)2D3 at doses above 0.2 ng/ml and they respond to PGE2 with increased DNA synthesis. These similarities suggest an ontogenic relationship with osteoblasts. Based on their differences, however, provisional identification of these cells as relatively undifferentiated mesenchymal cells is suggested.

Animals↗
PubMed1986

Membrane-disorganizing property of polymyxin B nonapeptide.

The possibility of improving the antibacterial activities of drugs normally excluded by Gram-negative bacteria with polymyxin B nonapeptide (PMBN) has been explored. In vitro, PMBN rendered clindamycin, erythromycin, novobiocin, rifampicin and vancomycin very active against a number of Gram-negative enteric bacteria. The drug also sensitized the previously resistant bacterial strains to human, mouse or guinea pig serum. However, parenterally administered PMBN failed to influence bacterial growth in chambers implanted into mice and guinea pigs. It was also ineffective in experimental septicaemia at a dose of up to 200 mg/kg or when combined with antibiotics with which it interacted synergistically in vitro.

Animals↗