Biomedical subjects

D E Chapman

Publications and source records attributed to D E Chapman.

At least 19 recordsLinked to original sources

PubMed2001

Prevention of chemotherapy-induced alopecia in rats by CDK inhibitors.

Most traditional cytotoxic anticancer agents ablate the rapidly dividing epithelium of the hair follicle and induce alopecia (hair loss). Inhibition of cyclin-dependent kinase 2 (CDK2), a positive regulator of eukaryotic cell cycle progression, may represent a therapeutic strategy for prevention of chemotherapy-induced alopecia (CIA) by arresting the cell cycle and reducing the sensitivity of the epithelium to many cell cycle-active antitumor agents. Potent small-molecule inhibitors of CDK2 were developed using structure-based methods. Topical application of these compounds in a neonatal rat model of CIA reduced hair loss at the site of application in 33 to 50% of the animals. Thus, inhibition of CDK2 represents a potentially useful approach for the prevention of CIA in cancer patients.

Alopecia↗

PubMed2001

Long-term changes in basal ganglia function after a neurotoxic regimen of methamphetamine.

The abuse of psychostimulants, such as methamphetamine (METH), can cause long-lasting deficits in the dopamine (DA) innervation of the striatum. Although the consequences of large DA depletions on basal ganglia function have been well characterized, less is known about the alterations associated with smaller depletions, such as those produced by high doses of METH. The purpose of this study was to assess the long-term consequences of METH-induced DA depletion on basal ganglia function. Three weeks after rats were given multiple administrations of METH (5-10 mg/kg, four times at 2-h intervals), dose-related decreases in DA tissue content in striatum and tyrosine hydroxylase mRNA in the substantia nigra pars compacta were observed. In situ hybridization histochemistry revealed a selective decrease in preprotachykinin mRNA in striatum, predominantly at the highest dose of METH, and no change in striatal preprodynorphin, preproenkephalin, or neurotensin/neuromedin N mRNAs. Cytochrome oxidase activity was significantly elevated in the entopeduncular nucleus and substantia nigra pars reticulata of METH-treated rats, but not in the striatum, globus pallidus, or subthalamic nucleus, consistent with a selective decrease in striatonigral, but not striatopallidal, neuron function. Additionally, rats treated with a neurotoxic regimen of METH were impaired on a radial maze sequential learning task when tested 3 weeks following METH administration. These data indicate that exposure to a neurotoxic regimen of METH results in long-term changes in striatonigral, but not striatopallidal neuron function and, consequently, altered basal ganglia function.

Animals↗

PubMed1996

Catalysis of the dealkylation/debenzylation of phenoxazone ethers by hemoglobin in the absence of peroxides: implications for investigations of embryonic biotransformation.

Investigations of catalysis of the O-dealkylation and O-debenzylation of phenoxazone (resorufin) ethers in human and rodent embryonic tissue homogenates indicated that, with few exceptions, each conceptal tissue investigated contained enzymes capable of catalyzing each of the reactions under study. All observable reactions exhibited NADPH dependence and strong inhibition by carbon monoxide, ketoconazole, alternate electron acceptors, and by hypoxic incubation conditions; but, they were not strongly inhibited by several other classical cytochrome P450 (P450) inhibitors. Cyanide, azide, superoxide dismutase/catalase, and glutathione/glutathione peroxidase each also failed to inhibit the reactions significantly. Subcellular fractionation experiments revealed that cytosolic fractions contained a preponderance of the observable monooxygenase activities. Attempts to identify components responsible for the cytosolic catalytic activity indicated that cytosolic nitric oxide synthases did not contribute significantly. Column fractionation of the cytosol indicated that significant catalytic activity coeluted with fractions containing hemoglobin (Hgb), and experiments with purified Hgb as enzyme source showed that Hgb would catalyze all reactions under study at very slow rates in the absence of added reductases or peroxides. Additions of either reductases or peroxides, however, resulted in marked increases in rates of Hgb-catalyzed reactions. Further investigations strongly suggested that virtually all dealkylation or debenzylation of phenoxazone ethers catalyzed by embryonic cytosolic fractions could be accounted for by the presence of Hgb in those fractions. Conceptal microsomal fractions, however, exhibited definitive, P450-dependent monooxygenase activities attributable to specific individual, identifiable P450 isoforms.

Animals↗

PubMed1994

Induction in vitro and complete coding region sequence of cytochrome P4501A1 cDNA from cultured whole rat conceptuses during early organogenesis.

Exposures of cultured whole rat conceptuses during organogenesis to 3-methylcholanthrene (MC; 0.025-25 microM), 5,6-benzoflavone (BNF; 5-100 microM) or benz[a]anthracene (BA; 5-100 microM) were effected by placement of each of these "MC-type" inducing agents in the culture medium at the time of explantation on day 9.5 of gestation. Conceptuses were then cultured for 48 hr and evaluated on day 11.5 for increased expression of inducible conceptal cytochrome P450 (P450). The three agents each elicited concentration-dependent increases in 7,8-benzoflavone (ANF)-inhibitable ethoxyresorufin O-deethylase (EROD) activities and increased P4501A1 mRNA as detected by primer-specific reverse transcriptase-polymerase chain reaction (RT-PCR) in cell-free preparations of the treated, cultured conceptuses. At effective inducing concentrations, dysmorphogenic or other embryotoxic effects were not detectable. At 20 microM concentrations, the three agents exhibited roughly equal induction that was approximately equivalent in magnitude (6- to 13-fold) to that achieved previously with exposures to MC in utero. Additions to the culture medium of 2.5 to 10 microM concentrations of dexamethasone (DEX) did not alter significantly the magnitude of MC-elicited induction in vitro. Repeated full-length sequencing of an RT-PCR-amplified cDNA revealed a coding region sequence identical to that reported for the P4501A1 sequence from adult rat liver. The results provide a basis for investigations, in the absence of maternal influences, of the regulation of mammalian conceptal P4501A1 in intact tissues during organogenesis, a gestational period critical in terms of the dysmorphogenic and other embryotoxic effects of foreign organic chemicals. The results are also pertinent to studies of embryotoxicity, particularly to the transplacental carcinogenicity, mutagenicity and dysmorphogenicity of P4501A1 substrates.

Animals↗

PubMed1994

Benzene and benzene metabolites as embryotoxic agents: effects on cultured rat embryos.

Benzene and several of its metabolites were investigated for dysmorphogenic and embryotoxic effects after direct exposures of cultured whole rat conceptuses. Benzene produced no statistically significant effects at concentrations up to 1.6 mM. Inclusion with 1.6 mM benzene of an hepatic xenobiotic-biotransforming system (S9) resulted in only minor decreases in embryonic growth parameters and no detectable dysmorphogenesis. Phenol, a major benzene metabolite, also elicited only minimal embryotoxicity at 1.6 mM concentrations. However, inclusion of an S9 system with phenol resulted in significant dysmorphogenic and embryotoxic effects at concentrations as low as 0.01 mM. For phenol bioactivation, S9 from phenobarbital-induced rats was the most effective, with induction by pregnenolone-16 alpha-carbonitrile, isopropanol, Aroclor 1254, no inducer, and 3-methylcholanthrene following in order of effectiveness. Bioactivating activity resided solely in the microsomal fraction. Metabolites coeluting on HPLC with hydroquinone and catechol were the major metabolites generated from phenol by each S9 system, but no significant correlation between specific metabolite generation and embryotoxicity was apparent. Of the benzene metabolites studied, trans, trans-muconaldehyde exhibited the highest embryotoxic potency but was not detectably generated by any of the S9 systems. Hydroquinone, catechol, and benzoquinone were approximately equipotent, each producing 100% lethality at 0.1 mM. Combined additions to the culture medium of hydroquinone together with phenol resulted in greater than additive effects, indicating a possible synergistic interaction between these metabolites and suggesting that peroxidase activity may be important to the mechanism of phenol-elicited embryotoxicity.

Animals↗

PubMed1993

Spontaneous apoptosis in NS-1 myeloma cultures: effects of cell density, conditioned medium and acid pH.

Apoptosis is a form of cell death which plays an important role in many biological processes including the regulation of B and T lymphocyte functions. We report here the spontaneous development of extensive apoptosis in cultures of the NS-1 mouse myeloma cell line following overgrowth. The apoptosis was identified by both its ultrastructural features and its DNA fragmentation pattern. High cell density and conditioned medium, but not acid pH, were found to be major inducers of apoptosis in this experimental system.

Animals↗

PubMed1992

Inhibition of growth factor binding, Ca2+ signaling and cell growth by polysulfonated azo dyes related to the antitumor agent suramin.

The ability of the polysulfonated antitumor drug suramin and six related polysulfonated azo dyes to inhibit the cell growth, platelet-derived growth factor (PDGF)-receptor binding, and intracellular Ca2+ signaling of Swiss 3T3 fibroblasts was studied. Some of the azo dyes were more potent inhibitors of PDGF binding than was suramin. The concentration giving 50% inhibition (IC50) of PDGF binding was 0.5 microM for the most potent azo dye as compared with 10 microM for suramin. The azo dyes were generally more potent inhibitors of nonmitochondrial Ca2+ uptake and of inositol(1,4,5)trisphosphate-mediated Ca2+ release in permeabilized Swiss 3T3 cells than was suramin, and they were more potent inhibitors of PDGF-induced Ca2+ signaling in intact Swiss 3T3 cells. The azo dyes were only as effective as or less effective than suramin in inhibiting the growth of Swiss 3T3 cells, with IC50 values of between 74 and 361 microM being noted for the dyes as compared with 70 microM for suramin. The difference between the growth-inhibitory activity of the azo dyes and that of suramin could not be explained by metabolism of the compounds, which was not detectable in either Swiss 3T3 cells or human liver slice preparations. The results suggest that suramin and some of the azo dyes have actions on cell growth in addition to inhibition of growth factor binding and of Ca2+ signaling.

3T3 Cells↗

PubMed1992

Metabolism of 2,6-dinitro[3-3H]toluene by human and rat liver microsomal and cytosolic fractions.

1. 2,6-Dinitrotoluene (2,6-DNT) metabolism by human liver and male Fischer F344 rat liver subcellular fractions under aerobic (100% oxygen) and anaerobic (100% nitrogen) incubation conditions was examined. Under aerobic conditions the major 2,6-DNT metabolite formed by hepatic microsomes was 2,6-dinitrobenzyl alcohol (2,6-DNBalc); under anaerobic conditions 2-amino-6-nitrotoluene (2Am6NT) was the major metabolite. 2. Rates of 2,6-DNBalc formation by human and rat liver microsomes under aerobic conditions were 247 and 132 pmol/min per mg protein, respectively. Rates of 2Am6NT formation by human and rat liver microsomes under anaerobic conditions were 292 and 285 pmol/min per mg protein, respectively. Anaerobic reduction of 2,6-DNT to 2Am6NT by rat and human liver microsomes was inhibited by carbon monoxide and metyrapone, which indicates that microsomal metabolism of 2,6-DNT to 2Am6NT is mediated by cytochrome P-450. 3. Liver cytosolic fractions also metabolized 2,6-DNT to 2Am6NT under anaerobic conditions. Formation of 2Am6NT by human and rat liver cytosols was supported by hypoxanthine, NADPH and NADH. Allopurinol inhibited the hypoxanthine-supported anaerobic metabolism of 2,6-DNT by rat, but not human, liver cytosol. Dicumarol inhibited the NADPH-supported anaerobic metabolism of 2,6-DNT by human, but not rat, liver cytosol. These results indicate that xanthine oxidase contributes to the hypoxanthine-supported anaerobic metabolism of 2,6-DNT by human liver cytosol.

Animals↗

PubMed1991

In vivo and in vitro effects of helenalin on mouse hepatic microsomal cytochrome P450.

Helenalin, a natural plant product with significant antitumor activities, decreased male BDF1 mouse hepatic microsomal cytochrome P450 contents in vivo and in vitro. A single i.p. dose of 25 mg helenalin/kg body weight significantly (P less than 0.05) decreased microsomal cytochrome P450 contents and inhibited cytochrome P450-dependent mixed-function oxidase activities within 1-2 hr post-exposure. Helenalin (1.0 mM) decreased microsomal cytochrome P450 contents in vitro by 11% in the absence of NADPH and by 32% in the presence of NADPH. These in vitro and in vivo decreases in cytochrome P450 were accompanied by comparable decreases in total microsomal heme contents. Helenalin (1.0 mM) increased mouse hepatic microsomal oxygen consumption and NADPH utilization by 3.2 and 5.4 nmol/min/mg protein respectively. Helenalin (1.0 mM) significantly (P less than 0.05) increased microsomal lipid peroxidation in vitro, and this helenalin-induced increase in lipid peroxidation was inhibited completely by the addition of 0.05 mM EDTA. However, microsomal cytochrome P450 contents were equally affected by helenalin in the presence or absence of EDTA, suggesting that lipid peroxidation did not contribute to the helenalin-induced decrease in cytochrome P450. The addition of 0.05 mM hemin to microsomes treated in vitro with 1.0 mM helenalin resulted in a 58% recovery of cytochrome P450 contents. This ability of hemin to reconstitute cytochrome P450 in helenalin-treated microsomes suggests that helenalin produced a selective loss of heme from the cytochrome P450 holoprotein, and that the resulting cytochrome P450 apoprotein remained intact after helenalin treatment. The increased loss of microsomal cytochrome P450 produced by helenalin in the presence of NADPH suggests that a helenalin metabolite may be responsible for heme loss and the in vitro destruction of cytochrome P450.

Animals↗

PubMed1991

Disposition and metabolism in mice of the potential antitumor and anti-human immunodeficiency virus-1 agent, 2-chloro-2',3'-dideoxyadenosine.

A high-performance liquid chromatographic (HPLC) procedure was developed to examine the preclinical pharmacology and pharmacokinetics of 2-chloro-2',3'-dideoxyadenosine (ClddAd). The HPLC assay for ClddAd in human plasma was linear from 0.25 to 500 micrograms ClddAd/ml. Coefficients of variation for the measurement of ClddAd in human plasma were 9.7%, 4.1%, and 2.7% at 2.5, 25, and 250 micrograms/ml, respectively. Binding of ClddAd to human and mouse plasma proteins was determined by filtration to be 26.9% and 34.4%, respectively. ClddAd concentrations decreased by less than 5% when ClddAd was stored for 126 h at 37 degrees C in 0.9% NaCl or 0.1 M NaH2PO4 (pH 7.4) or when ClddAd was stored for 24 h at 37 degrees C in citrate-buffered human blood or plasma. Estimates of the lethal dose for 50% (LD50) and 10% (LD10) of male CD2F1 mice that received a single i.v. dose of ClddAd were 27 and 24 mg/kg, respectively. Elimination of a 24-mg/kg i.v. bolus dose of ClddAd from mouse plasma was biphasic, with half-lives of 0.73 and 14.7 min. The apparent volume of distribution of ClddAd was 215 ml/kg and the total body clearance was 20 ml min-1 kg-1. No ClddAd metabolites were detected in mouse plasma after in vivo exposure or in human whole blood or plasma after in vitro incubation. ClddAd was detected in the urine of mice within 2 min after exposure, and the total urinary excretion of unchanged ClddAd for 24 h after exposure to 24 mg/kg was 3.4% of the delivered dose. At least two possible ClddAd metabolites were detected in mouse urine; they did not co-elute with 2-chloro-2',3'-dideoxyinosine,2-chloradenine, or 2-chlorohypoxanthine.

Animals↗

PubMed1991

Metabolism of the flame retardant plasticizer tris(2-chloroethyl)phosphate by human and rat liver preparations.

Previous studies indicate that tris(2-chloroethyl)phosphate (TCP) preferentially produces hippocampal brain lesions in female versus male rats, and the expression of these lesions is inversely related to the in vivo rate of TCP metabolism. In the present studies, TCP (0.17 mM in all incubations) was metabolized in vitro by liver slices and microsomes from human and Fischer 344N rat liver to bis(2-chloroethyl) hydrogen phosphate (BCP), 2-chloroethanol (CE), and three unidentified metabolites. The rate of TCP metabolism by male rat liver microsomes and liver slices was 0.049 nmol/min/mg protein and 2.53 nmol/min/g liver, respectively. TCP metabolism by male rat liver microsomes was inhibited by 10 microM diisopropyl fluorophosphate, 10 microM paraoxon and carbon monoxide. TCP did not appear to be metabolized by female rat liver microsomes, but female rat liver slices metabolized TCP at a rate of 1.51 nmol/min/g liver. TCP was metabolized by male and female rat plasma at a rate of 0.156 and 0.169 nmol/ml plasma, respectively. TCP was metabolized by male and female human liver microsomes at a rate of 0.027 and 0.031 nmol/min/mg protein, respectively. TCP was metabolized by male and female human liver slices at a rate of 1.37 and 1.82 nmol/min/g liver, respectively. BCP and CE were the major metabolites formed in all studies, except for liver slices and microsomes from two human male subjects in which an unidentified metabolite constituted 29 to 38% of the total TCP metabolism. TCP was not metabolized by plasma or whole blood from male or female human subjects. These results support the previously reported sex-specific difference in TCP metabolism by male and female Fischer 344N rats. However, no sex-specific difference in rates of TCP metabolism by male and female human liver microsomes or slices was observed.

Adult↗

PubMed1991

Enhanced mobilization of intracellular Ca2+ induced by halothane in hepatocytes isolated from swine susceptible to malignant hyperthermia.

Halothane, in a dose-dependent manner, induced the release of intracellular Ca2+ in hepatocytes prepared from swine. The magnitude of the release induced by halothane was greater for hepatocytes prepared from animals susceptible to malignant hyperthermia (MH) than for those from normal swine. Two different methods were used to ascertain the release of Ca2+ induced by halothane: 1) the release of 45Ca2+ from nonmitochondrial stores of saponin-permeabilized hepatocytes was measured; and 2) changes in luminescence from intact hepatocytes loaded with the Ca2(+)-sensitive photoprotein aequorin were recorded. It was also observed that, although 1,4,5-inositol trisphosphate (IP3), guanosine-5-triphosphate, and arachidonic acid all induced a significant release of 45Ca2+ from permeabilized swine hepatocytes, only the quantities of 45Ca2+ released by IP3 were significantly greater for the hepatocytes prepared from the animals susceptible to MH. These data indicate an abnormal Ca2+ homeostasis in hepatocytes isolated from swine susceptible to MH, which supports the hypothesis that membrane systems from multiple organs may be affected in this genetic disorder.

Animals↗

PubMed1990

Clonal analysis of the effect of iron on human cytotoxic and proliferating T lymphocytes.

The immunoregulatory effect of non-transferrin-bound iron (Fe3+) on the proliferative and cytotoxic responses of normal human T lymphocytes was studied using a sensitive limit-dilution technique capable of detecting the responses of individual lymphocytes. Iron, present in the form of ferric citrate at concentrations from 0.03 to 1.0 mmol/L, significantly reduced the cloning frequency of peripheral blood T lymphocytes. The effect of iron appeared, however, to be targeted to individual clones in that some clones that did grow in the presence of iron achieved a normal rate of proliferation. Thus, iron was not non-specifically toxic. At these same concentrations ferric citrate also produced significant reductions in the cloning frequency of CD4+ CD8-precursor T lymphocytes. Reductions in the response of T lymphocyte precursors capable of cytotoxic activity occurred in the presence of ferric citrate from 0.1 to 1.0 mmol/L. These data support the hypothesis that non-transferrin-bound iron has an immunoregulatory role in cell-mediated immunity.

Antibodies, Monoclonal↗

PubMed1989

In vitro inhibition of mouse hepatic mixed-function oxidase enzymes by helenalin and alantolactone.

The sesquiterpene lactones (STL) helenalin and alantolactone were effective in vitro inhibitors of the mouse hepatic microsomal mixed-function oxidase (MFO) enzymes, aminopyrine demethylase (APD), aniline hydroxylase (ANH) and 7-ethoxyresorufin deethylase (ERD). Helenalin and alantolactone concentrations of 0.5 mM produced a 50-60% inhibition of APD and ERD, and a 20-30% inhibition of ANH. An increase in substrate (aminopyrine) concentration from 0.5 to 25 mM decreased STL inhibition of APD by 12-32%. APD was also inhibited at low aminopyrine concentrations (0.5 mM) by the helenalin derivative 2,3,11,13-tetrahydrohelenalin (tetrahydrohelenalin). The STL produced type I binding spectra with oxidized microsomes; Ks values for helenalin and alantolactone were 161 and 9 microM respectively. These results suggest that STL inhibition of the MFO system results, in part, from STL binding to the substrate-binding site of cytochrome P-450. It has been reported that the irreversible alkylation of protein cysteinyl residues is responsible for STL inhibition of several different enzymes, and second-order rate constants for the reaction of helenalin and alantolactone with glutathione were 25.1 and 1.80 mM-1.hr-1 respectively. Tetrahydrohelenalin did not react with glutathione. However, the subsequent addition of 3.0 mM thiols, i.e. L-cysteine, N-acetylcysteine or glutathione, to STL-treated (0.5 mM) microsomes reversed helenalin and alantolactone inhibition of APD and ERD by 50-80%. The ability of thiols to reverse STL inhibition of APD was decreased 20-43% by the coincubation of STL and microsomes with an NADPH-generating system. In addition, established effects of sulfhydryl-reactive compounds on the MFO system, i.e. inhibition of NADPH-cytochrome c reductase and conversion of cytochrome P-450 to cytochrome P-420, were not observed after addition of helenalin (1.0 mM) or alantolactone (0.5 mM) to mouse hepatic microsomes. These results suggest that STL inhibition of MFO enzymes may not be dependent upon the reactivity of the STL towards sulfhydryl groups. Instead, we suggest that STL binding to the substrate-binding site of cytochrome P-450 and subsequent metabolism of the STL may contribute to inhibition of the MFO system.

Aminopyrine N-Demethylase↗

PubMed1989

Isolation, identification and biological activity of a phyllanthoside metabolite produced in vitro by mouse plasma.

The antitumor agent phyllanthoside is rapidly metabolized in vitro by mouse plasma. This metabolite has now been isolated from mouse plasma and its structural properties and cytotoxicity characterized. The isolated metabolite was estimated to be greater than 98% pure by HPLC analysis. Mass spectral analysis (fast atom bombardment and tandem mass spectrometry) indicated that the metabolite was the aglycone of phyllanthoside that resulted from the cleavage of the ester bond linking the aglycone and the disaccharide moieties of phyllanthoside. This identification was based on identical collision-induced dissociation spectra of both phyllanthoside and the metabolite. The aglycone was not formed by mouse plasma that had been boiled, filtered to remove proteins, or treated with 1.0 mM diisopropyl fluorophosphate. These results suggest that aglycone formation occurs as a result of plasma esterase activity. Michaelis-Menten constants, Vmax and Km, for conversion of phyllanthoside to the aglycone at 22 degrees C were estimated to be 1.1 mmol/ml plasma/min and 2.0 mM, respectively. Concentrations of phyllanthoside and metabolite required to inhibit cell-colony formation by human A204 rhabdomyosarcoma in vitro were 0.47 nM and 24 microM, respectively. The toxicity of phyllanthoside, and perhaps its efficacy as an antitumor agent in mice, may depend on its rate of conversion to the aglycone.

Animals↗

PubMed1988

Acute toxicity of helenalin in BDF1 mice.

The acute toxicity of helenalin, a sesquiterpene lactone isolated from Helenium microcephalum, was examined in male BDF1 mice. The 14-day LD50 for a single ip dose of helenalin in male mice was 43 mg/kg. A single ip injection of 25 mg helenalin/kg increased serum alanine aminotransferase (ALT), lactate dehydrogenase (LDH), urea nitrogen (BUN), and sorbitol dehydrogenase within 6 hr of treatment. Multiple helenalin exposures, ip injection of 25 mg helenalin/kg for 3 days, increased differential polymorphonuclear leukocyte counts and decreased lymphocyte counts. Serum ALT, BUN, and cholesterol levels were also increased by multiple helenalin exposures at 25 mg helenalin/kg/day. Helenalin significantly reduced liver, thymus, and spleen relative weights and histologic evaluation revealed substantial effects of multiple helenalin exposures on lymphocytes of the thymus, spleen, and mesenteric lymph nodes. No helenalin-induced histologic changes were observed in the liver or kidney. Multiple helenalin exposures (25 mg/kg/day) significantly inhibited hepatic microsomal enzyme activities (aminopyrine demethylase and aniline hydroxylase) and decreased microsomal cytochromes P-450 and b5 contents. Three concurrent days of diethyl maleate (DEM) pretreatment (3.7 mmol DEM/kg, 0.5 hr before helenalin treatment) significantly increased the toxicity of helenalin exposure. The present studies indicate that the hepatic microsomal drug metabolizing system and lymphoid organs are particularly vulnerable to the effects of helenalin. In addition, helenalin toxicity is increased by DEM pretreatments which have been shown to decrease glutathione concentrations.

Animals↗

PubMed1987

The effect of experimental iron-overload on splenic T cell function: analysis using cloning techniques.

The effect of iron-overload on cell-mediated immunity was examined in C57 mice. Two methods of iron-loading were used: (i) dietary carbonyl iron which produced iron-loading primarily of parenchymal cells or (ii) intraperitoneal administration of iron-dextran which produced iron-loading predominantly of Kupffer cells. Both methods of iron-loading resulted in a diminished capacity of spleen cells to generate an allo-specific cytotoxic response in the absence of exogenous interleukin 2 (IL-2). Exogenous IL-2, however, restored the ability of spleen cells from iron-loaded mice to generate allo-specific cytotoxicity in bulk culture. Clonal assays for the precursor cells of cytotoxic T lymphocytes (CTL-P), performed in the presence of added IL-2, demonstrated that iron-loaded mice contained normal numbers of CTL-P. However, cultures of spleen cells from carbonyl iron-loaded mice generated less IL-2 following Concanavalin A stimulation, apparently as a result of a reduction in the number of IL-2-secreting cells amongst the spleen cell population. This work presents further evidence that iron-overload is associated with defective immunoregulatory control.

Animals↗

PubMed1986

The effect of iron (Fe3+) on the cloning efficiency of human memory T4+ lymphocytes.

The effect of iron (Fe3+) and normal human liver ferritin on the proliferative response of normal human lymphocytes to tetanus toxoid was examined. This proliferative response involved memory T4+ lymphocytes as shown by a selective depletion study. Limit dilution analysis revealed that iron, present as ferric citrate, affected the initiation of clone development, and that concentrations of ferric citrate from 30 microM to 1 nM were able to reduce significantly the cloning efficiency of precursor T cells (up to 90% reduction). The reduced cloning frequency was not due to immunological suppression. Clone size was also reduced when iron was present during culture. In contrast, the presence of normal human liver ferritin during culture (concentration range: 300 micrograms/1-10,000 micrograms/1) had no effect on lymphocyte proliferation. The data indicate that low molecular weight iron (as ferric citrate) in concentrations similar to those which have been reported in the serum of patients with iron overload diseases, can interfere with antigen-specific lymphocyte responses and this may have implications for the development of infections and neoplasia in diseases of iron-overload.

Antigens, Surface↗