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Biomedical subjects

W J Johnson

Publications and source records attributed to W J Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1987

Mechanisms and consequences of cellular cholesterol exchange and transfer.

It is apparent from consideration of the reactions involved in cellular cholesterol homeostasis that passive transfer of unesterified cholesterol molecules plays a role in cholesterol transport in vivo. Studies in model systems have established that free cholesterol molecules can transfer between membranes by diffusion through the intervening aqueous layer. Desorption of free cholesterol molecules from the donor lipid-water interface is rate-limiting for the overall transfer process and the rate of this step is influenced by interactions of free cholesterol molecules with neighboring phospholipid molecules. The influence of phospholipid unsaturation and sphingomyelin content on the rate of free cholesterol exchange are known in pure phospholipid bilayers and similar effects probably occur in cell membranes. The rate of free cholesterol clearance from cells is determined by the structure of the plasma membrane. It follows that the physical state of free cholesterol in the plasma membrane is important for the kinetics of cholesterol clearance and cell cholesterol homeostasis, as well as the structure of the plasma membrane. Bidirectional flux of free cholesterol between cells and lipoproteins occurs and rate constants characteristic of influx and efflux can be measured. The direction of any net transfer of free cholesterol is determined by the relative free cholesterol/phospholipid molar ratios of the donor and acceptor particles. Cholesterol diffuses down its gradient of chemical potential generally partitioning to the phospholipid-rich particle. Such a surface transfer process can lead to delivery of cholesterol to cells. This mechanism operates independently of any lipoprotein internalization by receptor-mediated endocytosis. The influence of enzymes such as lecithin-cholesterol acyltransferase and hepatic lipase on the direction of net transfer of free cholesterol between lipoproteins and cells can be understood in terms of their effects on the pool sizes and the rate constants for influx and efflux. Excess accumulation of free cholesterol in cells stimulates the rate of cholesteryl ester formation and induces deposition of cholesteryl ester inclusions in the cytoplasm similar to the situation in the 'foam' cells of atherosclerotic plaque. Clearance of cellular cholesteryl ester requires initial hydrolysis to free cholesterol followed by efflux of this free cholesterol. The rate of clearance of cholesteryl ester from cytoplasmic droplets is influenced by the physical state of the cholesteryl ester; liquid-crystalline cholesteryl ester is removed more slowly than cholesteryl ester in a liquid state.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Differential expression of murine macrophage-mediated tumor cytotoxicity induced by interferons.

The requirements for interferon (IFN)-induced priming of murine peritoneal macrophages for cytolysis of tumor cell lines of distinct histological origin were investigated. Lysis of B16 melanoma targets required exposure of elicited macrophages to recombinant murine gamma interferon plus lipopolysaccharide (LPS) together, while sequential treatment of macrophages with IFN-gamma then LPS resulted in lysis of P815 mastocytoma targets. The kinetics of macrophage activation by IFN-gamma and LPS for lysis of P815 and B16 melanoma targets varied considerably, 8 h being sufficient for P815 targets but 24 h being required for B16 targets. Pretreatment of the macrophages with the antibiotic polymyxin B was able to inhibit completely the induction of tumor lysis of B16 targets but not of P815 targets. In addition, IFN-alpha/beta was able to prime macrophages for lysis of P815 targets but not of B16. Finally, the kinetics of priming macrophages with IFN-gamma for lysis of B16 targets had a profound effect on the subsequent exposure time requirement for LPS. The results indicate that the induction of murine macrophage-mediated tumor cytotoxicity can vary considerably depending on the amount and type of interferon used, the presence of a second signal, and the type of tumor target used.

Animals↗
PubMed1987

Recombinant tumor necrosis factor and interleukin-1 both stimulate human synovial cell arachidonic acid release and phospholipid metabolism.

Stimulation of [3H]-arachidonic acid labeled human synovial cells with 3.0 X 10(-10)M recombinant interleukin-1 or tumor necrosis factor resulted in the release of incorporated radiolabel (41.1% and 27.7% respectively). Analysis of [3H]-arachidonic acid labeled phospholipids showed that interleukin-1 and tumor necrosis factor diminished [3H]-arachidonic acid in phosphatidyl-choline phosphatidylserine and phosphatidylinositol. Treatment of [3H]-arachidonic acid labeled cells with 10(-3)M dibutyryl cyclic AMP or 10(-6)M PGE2 did not affect spontaneous or stimulated [3H] arachidonic acid release significantly. These data show that recombinant interleukin-1 and tumor necrosis factor stimulate human synovial cell phospholipase activity in a similar manner and that this activity is not affected significantly by agents that elevate cyclic AMP.

Arachidonic Acid↗
PubMed1987

Effect of antiarthritic drugs on the enhanced interleukin-1 (IL-1) production by macrophages from adjuvant-induced arthritic (AA) rats.

The effect of antiarthritic drugs on hindpaw edema and enhanced IL-1 production by macrophages from adjuvant arthritic (AA) rats was determined. Hindpaw edema was inhibited by indomethacin (INDO), methotrexate (MTX) or prednisolone (PRED) but not by D-penicillamine (D-PEN) or chloroquine (CQ). IL-1 production by splenic adherent cells was decreased by MTX and PRED; whereas, IL-1 production by peritoneal exudate cells was decreased by PRED, INDO and D-PEN. This normalization in IL-1 production is not caused by a direct inhibition of IL-1 production by the drugs but most likely reflects clinical improvement in the disease. Whether reduction in IL-1 levels provides a more meaningful parameter than paw edema for assessing clinical efficacy of disease-modifying drugs remains to be determined.

Animals↗
PubMed1987

Rat macrophage treatment with lipopolysaccharide leads to a reduction in respiratory burst product secretion and a decrease in NADPH oxidase affinity.

The effect of LPS on the respiratory burst in resident rat peritoneal macrophages has been examined. Rat macrophages secreted high levels of both O2- and H2O2 in response to triggering with phorbol esters, opsonized zymosan, and immune complexes. After culture in vitro with LPS these macrophages exhibited a marked diminution in their capacity to secrete high levels of respiratory burst products. The LPS-mediated loss of secretory activity was apparent after 2 hr of exposure to LPS and was inhibitable by polymyxin B in a dose-dependent fashion. The effect was not selective for any triggering agent type as inhibition of secretory activity occurred after triggering with PMA, zymosan and immune complexes. PGE2 added at levels secreted by the macrophages in response to LPS also inhibited respiratory burst product secretion. In addition, indomethacin prevented the LPS-mediated inhibition of secretion. Because the inhibition of secretion was common to all triggering agents tested, this suggested that the basis for the impaired secretion was at a level other than the receptor for the triggering agent. Both LPS and PGE2 treatment of the macrophages increased the Km of the oxidase for NADPH (1.7- to 2.3-fold) without affecting significantly the Vmax of the enzyme. These data suggest that stimulation of rat peritoneal macrophages by LPS results in an impaired ability to secrete respiratory burst products as a result of a PGE2-mediated decrease in NADPH oxidase affinity and that this alteration is independent of alterations in tumoricidal activity.

Animals↗
PubMed1987

Functional status of patients with end-stage renal disease.

A longitudinal study of 979 patients with end-stage renal disease from 27 dialysis centers in the Upper Midwest was conducted to measure the patients' functional status with use of the Karnofsky Activity Scale. At the initiation of dialysis, 50% of all patients were rehabilitated or caring for themselves, and the three variables that most influenced the initial rehabilitation score were age, diabetic status, and sex. Initial functional status was also analyzed for three cohorts of dialysis patients, grouped according to outcome (renal transplantation, continued dialysis, and death). Patients who received a renal transplant had initial rehabilitation scores that were higher than those who underwent dialysis for 2 years or those who died. In the group of patients who underwent dialysis for 2 years, a statistically significant improvement in rehabilitation scores was noted at 2 years in comparison with the scores obtained at the initiation of dialysis. Initial rehabilitation scores were good predictors of the 2-year scores. Of the patients in the 2-year dialysis cohort, 78% maintained or had improvement in their functional status.

Adult↗
PubMed1987

Tetranitromethane modification of human high density lipoprotein (HDL3): inactivation of high density lipoprotein binding is not related to cross-linking of phospholipids to apoproteins.

Treatment of human high density lipoprotein (HDL) with tetranitromethane (TNM) inhibits its binding to HDL-specific binding sites of cells and isolated membranes. The mechanism of this inhibition, however, is not known; during treatment of HDL with TNM, in addition to the expected nitration of tyrosine residues, cross-linking of lipids to apoproteins and of apoproteins to one another occurs. In order to determine whether the cross-linking of lipids to apoproteins occurs through the carbon-carbon double bonds in the acyl chains, and to determine whether the cross-linking of phospholipids to apoproteins is a possible mechanism of inhibition of binding, we have prepared a reconstituted HDL3 in which the native phospholipids were replaced with dimyristoyl phosphatidylcholine (DMPC). As a control, a reconstituted HDL3 (C-r-HDL3) was also prepared using the total apoproteins and the total lipid constituents of native HDL3. The reconstituted DMPC-containing HDL3 (DMPC-r-HDL3) was similar to native HDL3 and to C-r-HDL3 in its agarose gel electrophoretic mobility, in its chemical composition, and in its binding to rat liver plasma membranes. When treated with TNM, DMPC-r-HDL3, like the native HDL3 and C-r-HDL3, lost its ability to bind to the HDL binding sites of rat liver plasma membranes, as determined by competitive binding assays with 125I-labeled human HDL3 as the tracer. Nitrated DMPC-r-HDL3 contained only traces of phospholipids covalently linked to apoproteins, whereas 21-26% of the total phospholipids were cross-linked to apoproteins of nitrated C-r-HDL3 and nitrated native HDL3.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Cytolytic interactions between murine macrophages, tumor cells, and monoclonal antibodies: characterization of lytic conditions and requirements for effector activation.

Because of recent successes in inducing the effective rejection of neoplasms in vivo by administration of monoclonal antibodies (MAb), we analyzed lytic interactions in vitro that occur between macrophages and several combinations of tumor targets and MAb that can lead to such successful immunotherapy. Murine macrophages, interacting with MAb of the IgG1, IgG2a, IgG2b, and IgG3 isotypes directed against SW-1116 carcinoma cells, destroyed the tumor targets efficiently over 24 to 48 hr in vitro. Lysis was dependent on both concentration of the MAb and density of the macrophages. Binding and lysis of the targets in the presence of MAb of the IgG2a isotype was dependent on intact Fc gamma 2aR on the macrophages; target binding was necessary but not sufficient for subsequent lysis. The lytic step appeared to have an oxidative basis, at least in part, as shown by inhibition of lysis with a nonspecific scavenger of H2O2 or under either anaerobic or glucose-deprived conditions. TG-elicited or pyran-elicited macrophages, which are incompletely activated for antibody independent kill of tumor cells, were effective in mediating ADCC. By contrast, macrophages fully activated for direct cytolysis by administration of BCG or Propionibacterium acnes in vivo or by MAF and LPS in vitro, had diminished capacity for ADCC. A spectrum of five other tumor cells and antibodies, four of which are also involved in successful models of immunotherapy in vivo, were also killed over 48 hr more effectively by thioglycolate-elicited than by BCG-activated macrophages. Taken together, the data indicate that macrophages can lyse tumor cells in an ADCC reaction that has application to some models of the destruction of tumors in vivo, but that the lysis is slow and requires the macrophages to be activated in a specific way(s).

Animals↗
PubMed1986

The bidirectional flux of cholesterol between cells and lipoproteins. Effects of phospholipid depletion of high density lipoprotein.

The bidirectional surface transfer of free cholesterol (FC) between Fu5AH rat hepatoma cells and human high density lipoprotein (HDL) was studied. Cells and HDL were prelabeled with [4-14C]FC and [7-3H]FC, respectively. Influx and efflux of FC were measured simultaneously from the appearance of 3H counts in cells and 14C counts in medium. Results were analyzed by a computerized procedure which fitted sets of kinetic data to a model assuming that cell and HDL FC populations each formed a single homogeneous pool and that together the pools formed a closed system. This analysis yielded values for the first-order rate constants of FC influx and efflux (ki and ke), from which influx and efflux of FC mass (Fi and Fe) could be calculated. With normal HDL, the uptake and release of FC tracers conformed well to the above-described model; Fi and Fe were approximately equal, suggesting an exchange of FC between cells and HDL. HDL was depleted of phospholipid (PL) by treatment with either phospholipase A2 or heparin-releasable rat hepatic lipase, followed by incubation with bovine serum albumin. PL depletion of HDL had little or no effect on ki, but reduced ke, indicating that PL-deficient HDL is a relatively poor acceptor of cell cholesterol. The reduction in ke resulted in initial Fi greater than Fe and, thus, in net uptake of FC by the cells. This result explained previous results demonstrating net uptake of FC from PL-depleted HDL. In the presence of an inhibitor of acyl coenzyme A:cholesterol acyltransferase, the steady state distribution of FC mass between cells and HDL was accurately predicted by the ratio of rate constants for FC flux. This result provided additional validation for describing FC flux in terms of first-order rate constants and homogeneous cell and HDL FC pools.

Animals↗
PubMed1986

Macrophage activation in rat models of inflammation and arthritis. Systemic activation precedes arthritis induction and progression.

The association between the induction and progression of adjuvant-induced arthritis (AA) and the development of synovial and systemic macrophage activation was assessed by studying the temporal development of these parameters in a rat model. Rats with AA developed significant edema of the uninjected hind leg beginning 10 days post-adjuvant injection, with progressive increases in edema continuing through day 17. Several parameters of macrophage activation, including the enhanced ability to secrete interleukin-1 and prostaglandin E2, kill tumor cells, accumulate fluorescent cyanine dyes, emigrate into the peritoneal cavity and synovium, and express Ia antigen, as well as the decreased ability to secrete superoxide anion, were associated temporally with the development of the arthritic lesion. In addition to the temporal association between macrophage activation and development of arthritis, a positive correlation between macrophage activation and arthritis induction was seen with the use of synthetic adjuvants at arthritogenic and nonarthritogenic doses. These data taken together suggest that induction and progression of AA in rats is associated with both systemic (blood, spleen, and peritoneal cavity) and local (synovium) macrophage activation.

Animals↗
PubMed1986

Macrophage activation in rat models of inflammation and arthritis: determination of markers of stages of activation.

Disease-associated alterations in macrophage functions were assessed by investigating the stages of activation of peritoneal macrophages obtained from adjuvant-induced arthritic rats. The stages of activation were established by defining several functional parameters in macrophages obtained from normal, sterile-irritant injected and Propionibacterium acnes injected animals. Peritoneal macrophages taken from arthritic rats 17 days post adjuvant injection displayed parameters characteristic of activated, but not elicited or resident macrophages. Specifically, an increased number of macrophages was recovered from arthritic rats which spread readily in culture, exhibited enhanced Fc receptor-mediated phagocytosis, increased leucine aminopeptidase ectoenzyme activity, enhanced secretion of prostaglandin E2 and interleukin 1, and ability to lyse tumor cells spontaneously. In addition, these macrophages were impaired in their ability to secrete superoxide anion. These data demonstrate distinct differences in parameters of peritoneal macrophage activation in rats compared to mice and that macrophage activation is associated with disease progression in adjuvant-induced arthritic rats.

Animals↗
PubMed1986

Interpretation of serum aluminum values in dialysis patients.

To determine the significance of serum aluminum levels in dialysis patients, the authors retrospectively analyzed a series of patients on maintenance hemodialysis (HD) and continuous ambulatory peritoneal dialysis (CAPD). All patients had always been treated with a dialysate containing negligible amounts of aluminum. The serum aluminum levels of hemodialysis and CAPD patients were not significantly different, not related to age or sex, and not affected by the presence of diabetes or vitamin D intake. The most important determinant of serum aluminum level in the hemodialysis patients was the current dose of aluminum-containing phosphate-binding medication. This relationship was most striking in the compliant patients. In hemodialysis patients, after an increase during the first one to two years, the aluminum levels plateaued. Aluminum levels remained stable more than five years in CAPD patients. Red blood cell mean corpuscular volume was negatively correlated with serum aluminum level. In 28 dialysis patients who had bone biopsy, aluminum levels were positively correlated to histochemical aluminum staining and bone aluminum content. A level greater than 100 ng/mL was a reliable indicator of aluminum-associated osteomalacia, although a lower level did not exclude the presence of low turnover bone disease or mixed uremic osteodystrophy--two disorders possibly related to aluminum. In the presence of a high serum aluminum, elevated levels of immunoreactive parathyroid hormone (iPTH) were useful in detecting the presence of hyperparathyroidism; low levels of iPTH did not allow the authors to distinguish between other subtypes of uremic osteodystrophy.

Aluminum↗
PubMed1985

Biosynthesis of polyisoprenoid lipids in the rat tapeworm Hymenolepis diminuta.

The possible occurrence of isoprenoid lipids in the tapeworm, Hymenolepis diminuta, was investigated by analytic and biosynthetic methods. Two-dimensional thin layer chromatography (TLC) resolved the worm's non-saponifiable lipids into cholesterol, farnesol, and several unknown compounds, two of which migrated with dolichol standards on TLC and reacted with phthalic anhydride, a probe for alcohols; the major compound also exhibited a mass spectrum very similar to that of a dolichol standard. A third unknown compound separable by TLC, apparently a quinone, was intrinsically red, was decolorized by treatment with sodium dithionite and migrated on TLC in a more polar position than either ubiquinone-50 or vitamin K1. All three compounds, as well as farnesol, were labelled when worms were incubated with [14C]-mevalonolactone, suggesting that they are endogenous isoprenoids.

Animals↗
PubMed1984

Antibody-dependent cytolysis (ADCC) of tumor cells by activated murine macrophages is a two-step process: quantification of target binding and subsequent target lysis.

To analyze the antibody-dependent cell-mediated cytotoxicity (ADCC) reaction between tumor cells and activated murine macrophages in detail, it must be first determined if physical binding occurred between the two cell types. Over 15-20 min in vitro, antibody-coated HSB neoplastic targets became so firmly attached to the activated macrophages that they resisted removal with 4 vigorous washes. When a quantitative assay of binding was employed, attachment of tumor cells to activated macrophages was found to depend on the concentration of antibody and on the density of the macrophages. These two variables also determined the subsequent extent of cytolysis. Binding of antibody-coated targets by macrophages elicited with thioglycollate broth or activated by bacillus Calmette-Guerin (BCG) was comparable. Lysis by the activated macrophages, however, was far greater. Binding occurred at 4, 22, or 37 degrees C, while the subsequent lytic reaction occurred only at 37 degrees C. Thioglycollate broth effectively inhibited lysis but had no effect on binding. A porous filter placed between activated macrophages and targets resulted in abrogation of binding and lysis, even when antibody-coated targets were placed beneath the filters. When labeled, uncoated targets were added to cultures of macrophages in the presence of unlabeled antibody-coated targets, no lysis of the bystander (i.e., uncoated) targets was seen. The data suggest that ADCC is a multistep reaction, that vigorous physical binding of antibody-coated targets by activated macrophages is an initial and necessary step in ADCC, that such binding is not sufficient for ADCC, that such binding controls the selectivity of lysis in ADCC, and that the second step in ADCC results in target lysis.

Animals↗