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Biomedical subjects

S P Markey

Publications and source records attributed to S P Markey.

At least 19 recordsLinked to original sources
PubMed1992

Organic ion imaging using tandem mass spectrometry.

A triple-quadrupole mass spectrometer has been interfaced with a wide-angle secondary ion microprobe. The combination permits acquisition of data necessary to determine the distribution of targeted organic analytes even in the presence of overwhelming isobaric interference. Micrographs generated from secondary ion intensity alone are compared to those generated using secondary ionization with tandem mass spectrometry (MS/MS), both for image reference and to show the improvement in image quality that can be attained when MS/MS is employed. Inhomogeneous mixtures of glycerol, KCl, and asparagine on 1-cm-diameter aluminum targets were used to demonstrate the instrument's selectivity. Secondary ions generated from samples of this system include isobaric 133Cs+ implanted from the primary ion beam, the 41K(+)-glycerol adduct, and protonated asparagine.

Asparagine↗
PubMed1992

Human macrophages convert L-tryptophan into the neurotoxin quinolinic acid.

Substantial increases in the concentrations of the excitotoxin and N-methyl-D-aspartate-receptor agonist quinolinic acid (QUIN) occur in human patients and non-human primates with inflammatory diseases. Such increases were postulated to be secondary to induction of indoleamine 2,3-dioxygenase in inflammatory cells, particularly macrophages, by interferon-gamma. To test this hypothesis, human peripheral-blood macrophages were incubated with L-[13C6]tryptophan in the absence or presence of interferon-gamma. [13C6]QUIN was quantified by gas chromatography and electron-capture negative-chemical-ionization mass spectrometry. [13C6]QUIN was detected in the incubation medium of both unstimulated and stimulated cultures. Exposure to interferon-gamma substantially increased the accumulation of [13C6]QUIN in a dose- and time-dependent manner. The QUIN concentrations achieved exceeded those reported in both cerebrospinal fluid and blood of patients and of non-human primates with inflammatory diseases. Macrophages stimulated with interferon-gamma may be an important source of accelerated L-tryptophan conversion into QUIN in inflammatory diseases.

Carbon Isotopes↗
PubMed1992

Search for neurotoxins structurally related to 1-methyl-4-phenylpyridine (MPP+) in the pathogenesis of Parkinson's disease.

Immunoassays sensitive to a broad range of compounds structurally related to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP) and 1-methyl-4-phenylpyridine (MPP+) have been developed and used to test for the presence of possible chemically related neurotoxins in the brains of Parkinson's disease patients. The sensitivity and chemical reactivity of the polyclonal antibodies used in these assays have been characterized with a range of endogenous and chemically related materials. Two methods were developed and tested for extraction followed by chromatographic separation which would be applicable to stored or accumulated substances. The immunoassays were tested and applied to the assay of tissue extracts from MPTP or MPTP-analogue exposed animals, and indicated detectability of MPP(+)-immunoreactivity greater than 8 weeks after exposure to MPTP in monkey brain. No difference in immunoactivity was measured in extracts from human brains of Parkinson's disease patients or controls, and particularly low levels of immunoreactivity were found in the striatum relative to the levels measured in several cortical regions. From these studies, there is no evidence for the role of an environmental neurotoxin chemically related to MPTP in the pathogenesis of Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1992

Relationship of neurologic status in macaques infected with the simian immunodeficiency virus to cerebrospinal fluid quinolinic acid and kynurenic acid.

Increased concentrations of the excitotoxin quinolinic acid (QUIN) have been implicated in the neurologic deficits and brain atrophy that may accompany infection with the human immunodeficiency virus type-1. Key neuropathologic features of the AIDS encephalitis are replicated in some macaques following infection with the simian immunodeficiency virus (SIV). In the present studies, cerebrospinal fluid (CSF) QUIN concentrations increased within 2 weeks following infection of 11 rhesus macaques (Macaca mulatta) with a neurotropic sooty mangabey isolate of the simian immunodeficiency virus (SIVsm) and were sustained to greater than 2 standard deviations above uninfected control macaques. Highest CSF QUIN concentrations (up to 400-fold above pre-inoculation levels) were observed in 6 SIVsm-infected macaques with motor and behavioral abnormalities during life, brain atrophy on MRI scan and inflammatory lesions within the brain and meninges. Four of the 6 neurologic macaques deteriorated rapidly within 12 weeks after inoculation and had substantially larger increases in CSF QUIN levels than 2 other neurologic macaques and 5 macaques without neurologic signs which survived for longer than 37 weeks. Increases in serum QUIN and CSF kynurenic acid also occurred but generally to a lesser degree than the increases in CSF QUIN. In some animals, increases in serum L-kynurenine concentrations and reductions in CSF and serum L-tryptophan occurred and were consistent with activation of indoleamine-2, 3-dioxygenase, the first enzyme of the kynurenine pathway in extrahepatic tissues. CSF QUIN exceeded serum QUIN in 8.8% of samples from macaques with neurologic signs, supporting increased QUIN synthesis within the central nervous system. Production of [13C6]QUIN was demonstrated in one SIVsm-infected macaque and one uninfected control macaque following an intracisternal injection of [13C6]L-tryptophan and suggests that L-tryptophan is a substrate for QUIN synthesis within the nervous system or meninges, although the cellular localization of QUIN synthesis remain to be determined. We conclude that increases in kynurenine pathway metabolism occur in SIV-infected macaques and are most prominent in macaques with neurologic signs. Macaques infected with SIV offer a model to investigate the relationship between the metabolism of neuroactive kynurenines and neurologic disturbances associated with retroviral infection.

Animals↗
PubMed1992

Inter-relationships between quinolinic acid, neuroactive kynurenines, neopterin and beta 2-microglobulin in cerebrospinal fluid and serum of HIV-1-infected patients.

Quinolinic acid (QUIN) is an neurotoxic N-methyl-D-aspartate receptor agonist and an L-tryptophan metabolite of the kynurenine pathway. Increased concentrations of QUIN occur in both cerebrospinal fluid (CSF) and blood of patients infected with human immunodeficiency virus (HIV)-1, particularly those with neurologic disturbances. In the present study of HIV-1 infected patients in Walter Reed stages 4, 5 and 6, reductions in L-tryptophan accompanied proportional increases in L-kynurenine and QUIN in both serum and CSF. Further, close inter-correlations exist between QUIN kynurenic acid and L-kynurenine with both beta 2-microglobulin and neopterin in CSF and serum. These correlations support the hypotheses that the kynurenine pathway is activated in association with inflammation and induction of indoleamine-2,3-dioxygenase. There were no relationships between CSF QUIN, L-kynurenine or kynurenic acid with the ratio of serum:CSF albumin concentrations, which indicates that the increases in CSF QUIN, L-kynurenine or kynurenic acid were not dependent on a breakdown of the blood-brain barrier. Kynurenic acid is also a kynurenine pathway metabolite that can attenuate the excitotoxic effects of QUIN when present in higher molar concentrations. While CSF kynurenic acid levels were increased in HIV-1-infected patients, the magnitude of the increases were smaller than those of QUIN and the molar concentrations of kynurenic acid were consistently lower than QUIN by at least one order of magnitude. We conclude that immune activation increases the levels of neuroactive kynurenines within the central nervous system of HIV-1-infected patients secondary to activation of indoleamine-2,3-dioxygenase.

AIDS Dementia Complex↗
PubMed1992

Effects of immune activation on quinolinic acid and neuroactive kynurenines in the mouse.

Accumulation of quinolinic acid and neuroactive kynurenines derived from tryptophan are of potential significance in human neuropathologic diseases because of their neurotoxic and convulsant properties. Clinical studies have established that sustained elevations of quinolinic acid, L-kynurenine and kynurenic acid within the cerebrospinal fluid occur in patients with a broad spectrum of inflammatory diseases and correlate with markers of immune activation and interferon-gamma activity. The present study describes an animal model that replicates these clinical observations and investigates the role of interferon-gamma as a mediator between immune activation and increased kynurenine pathway metabolism. Marked elevations in quinolinic acid, L-kynurenine and 3-hydroxykynurenine as well as an increased ratio of quinolinic acid: kynurenic acid in brain occurred 24 h after systemic pokeweed mitogen administration to C57BL6 mice. In plasma, L-tryptophan and kynurenic acid levels were reduced by pokeweed mitogen, while the concentrations of L-kynurenine, 3-hydroxykynurenine and quinolinic acid were increased. Interferon-gamma, pokeweed mitogen and lipopolysaccharide induced indoleamine-2,3-dioxygenase, the first enzyme of the kynurenine pathway, and increased both L-kynurenine and quinolinic acid concentrations of brain and systemic tissues, particularly in the lung, gastrointestinal tract and spleen. In contrast, hepatic tryptophan-2,3-dioxygenase activity was either reduced or unaffected. Increases in kynurenine pathway metabolism were sustained in mice given daily injections of interferon-gamma for seven days and subsequent responses to interferon-gamma were further enhanced. In contrast, daily administration of lipopolysaccharide was associated with subsequent attenuated responsiveness (tolerance) to lipopolysaccharide, pokeweed mitogen and interferon-gamma. Systemic administration of a monoclonal antibody to mouse interferon-gamma either attenuated or abolished the responses of kynurenine pathway metabolism to pokeweed mitogen and interferon-gamma. We conclude that acute and chronic increases in quinolinic acid and neuroactive kynurenines follow immune stimulation in mice, and result from indoleamine-2,3-dioxygenase induction. The results demonstrate that interferon-gamma is an important mediator between immune stimulation and indoleamine-2,3-dioxygenase induction. These increases in kynurenine pathway metabolism closely parallel the responses documented in patients with a broad spectrum of inflammatory diseases. Mice treated with immune stimuli are a useful model to investigate the relationships between immune activation and kynurenine pathway metabolism.

Animals↗
PubMed1992

Poliovirus induces indoleamine-2,3-dioxygenase and quinolinic acid synthesis in macaque brain.

Accumulation of the neurotoxin quinolinic acid within the brain occurs in a broad spectrum of patients with inflammatory neurologic disease and may be of neuropathologic significance. The production of quinolinic acid was postulated to reflect local induction of indoleamine 2,3-dioxygenase by cytokines in reactive cells and inflammatory cell infiltrates within the central nervous system. To test this hypothesis, macaques received an intraspinal injection of poliovirus as a model of localized inflammatory neurologic disease. Seventeen days later, spinal cord indoleamine 2,3-dioxygenase activity and quinolinic acid concentrations in spinal cord and cerebrospinal fluid were both increased in proportion to the degree of inflammatory responses and neurologic damage in the spinal cord, as well as the severity of motor paralysis. The absolute concentrations of quinolinic acid achieved in spinal cord and cerebrospinal fluid exceeded levels reported to kill spinal cord neurons in vitro. Smaller increases in indoleamine 2,3-dioxygenase activity and quinolinic acid concentrations also occurred in parietal cortex, a poliovirus target area. In frontal cortex, which is not a target for poliovirus, indoleamine 2,3-dioxygenase was not affected. A monoclonal antibody to human indoleamine 2,3-dioxygenase was used to visualize indoleamine 2,3-dioxygenase predominantly in grey matter of poliovirus-infected spinal cord, in conjunction with local inflammatory lesions. Macrophage/monocytes in vitro synthesized [13C6]quinolinic acid from [13C6]L-tryptophan, particularly when stimulated by interferon-gamma. Spinal cord slices from poliovirus-inoculated macaques in vitro also converted [13C6]L-tryptophan to [13C6]quinolinic acid. We conclude that local synthesis of quinolinic acid from L-tryptophan within the central nervous system follows the induction of indoleamine-2,3-dioxygenase, particularly within macrophage/microglia. In view of this link between immune stimulation and the synthesis of neurotoxic amounts of quinolinic acid, we propose that attenuation of local inflammation, strategies to reduce the synthesis of neuroactive kynurenine pathway metabolites, or drugs that interfere with the neurotoxicity of quinolinic acid offer new approaches to therapy in inflammatory neurologic disease.

Animals↗
PubMed1992

Progressive slowing of reaction time and increasing cerebrospinal fluid concentrations of quinolinic acid in HIV-infected individuals.

Neuropsychological functioning and cerebrospinal fluid concentrations of an endogenous neurotoxin, quinolinic acid (QUIN) were evaluated in 52 HIV-positive individuals (71% without constitutional symptoms) and 33 HIV-seronegative controls (including 15 psychiatric patients with adjustment disorders). Although the HIV-positive subjects did not differ from controls on standard neuropsychological tests, simple and choice reactions times (RT) were slow at initial evaluation (P less than 0.01) and became progressively slower at 6-month re-evaluation (P less than 0.05). Cerebrospinal fluid (CSF) QUIN was elevated at initial evaluation and increased during the 6-month interval (P less than 0.05). Moreover, during this 6-month interval, progressive slowing of RT was highly correlated with increasing levels of CSF QUIN (r = 0.85, df = 15, P less than 0.0001) but not with changes in mood, constitutional symptoms, or CD4 cell count. These findings suggest that RT may provide a sensitive behavioral measure of relatively early central nervous system involvement in HIV-infected individuals and that QUIN may play an important role in the pathogenesis of HIV-related neurological dysfunction.

AIDS Dementia Complex↗
PubMed1992

Zinc, a neurotoxin to cultured neurons, contaminates cycad flour prepared by traditional guamanian methods.

We have used cultured ventral mesencephalic and cerebellar granule cells to test the toxicity of extracts of cycad seeds (genus Cycas) and cycad-derived flours traditionally prepared in Guam. There was no significant difference in the toxicity of extracts prepared from the female gametophyte tissue of C. circinalis, C. revoluta, and C. media, common wheat flour, and 13 of 17 cycad flour samples. However, extracts prepared from 4 of 17 Guamanian flour samples exhibited marked dose-dependent neurotoxicity to mesencephalic and granule cell cultures. There was no correlation between toxicity and 2-amino-3-(methylamino)-propanoic acid (BMAA) content, and the concentration of BMAA in the medium arising from these extracts was far below that required to be neurotoxic. Toxicity of extracts was not blocked by the NMDA receptor antagonist MK-801 or the non-NMDA receptor antagonist 6-cyano-7-dinitroquinoxaline-2,3-dione, indicating that toxicity was not mediated by excitatory amino acid receptors. Analysis of the four toxic processed flour samples indicated high zinc content. Zinc produced a concentration-dependent neurotoxic response in mesencephalic and granule cell cultures that paralleled the calculated concentrations of zinc in the cultures derived from the four toxic flour samples. When sliced C. circinalis gametophyte tissue was "processed" in our laboratory by soaking in a galvanized container, there was a time-dependent increase in zinc content.

Animals↗
PubMed1991

The role of lactic acid in autocrine B-cell growth stimulation.

Growth and survival of Epstein-Barr virus (EBV)-immortalized B lymphocytes cultured at low cell densities require autocrine soluble factors. In this study, we have purified a low molecular weight autocrine soluble factor that promotes growth of EBV-immortalized B cells in serum-free conditions and identified it as lactic acid (LA). Synthetic LA stimulated growth in EBV-immortalized B cells at 1-10 mM, a concentration of LA measured in the culture supernatant of EBV-immortalized cell lines. LA alone was found to account for greater than 70% of the autocrine growth factor activity in serum-free supernatants of EBV-immortalized B cells. Aminooxyacetate, a glutamate-oxaloacetate transaminase inhibitor, specifically inhibited B-cell growth induced by LA, suggesting that this process requires mitochondrial-cytosol transfers. Thus, LA is an autocrine stimulatory molecule that in serum-free conditions is essential for the continuous proliferation of EBV-immortalized B cells. This represents an unexpected function for LA.

Animals↗
PubMed1991

2-amino-3-(methylamino)-propanoic acid (BMAA) pharmacokinetics and blood-brain barrier permeability in the rat.

2-Amino-3-(methylamino)-propanoic acid (BMAA) is a neurotoxic, excitatory amino acid which has been linked through cycad use and consumption with the onset of a variant of amyotrophic lateral sclerosis occurring with high incidence in the western Pacific region. We have studied BMAA pharmacokinetics, oral bioavailability and blood-brain barrier permeability in the rat in an attempt to better define the possible role for BMAA in this disease. To evaluate its kinetics and uptake, BMAA (25-400 mg/kg) was administered to rats, either acutely or chronically, and then plasma and brain concentrations were determined at various times thereafter by combined gas chromatography mass spectrometry. After single dose i.v. injection, BMAA was cleared from plasma in a rapid distribution phase (Vd approximately 16 liters/kg) followed by a slower elimination phase (t1/2 approximately 1 day). Brain uptake was limited by a low blood-brain barrier permeability-surface area product of 2 to 5 x 10(-5) ml/sed/g. Brain BMAA levels peaked within 8 hr after injection, and then declined with a t1/2 similar to that of plasma. After two weeks of continuous infusion (100 mg/kg/day), steady-state brain concentrations equalled 10 to 30 micrograms/g, and only moderately exceeded those in plasma. The results suggest that BMAA may reach potentially toxic levels in brain (i.e., greater than 250 microM) after large doses (greater than 100 mg/kg). However, such doses are orders of magnitude greater than those available from dietary or medicinal use of cycads.

Administration, Oral↗
PubMed1991

Chronic effects of gamma-interferon on quinolinic acid and indoleamine-2,3-dioxygenase in brain of C57BL6 mice.

Chronic infections are associated with increased concentrations of the neuroactive kynurenine pathway metabolite, quinolinic acid (QUIN), in blood and cerebrospinal fluid. In the present study, repeated injections of gamma-interferon (5000 IU, every 3 days for 39 days) to C57BL6 mice were associated with persistent activation of indoleamine-2,3-dioxygenase (IDO), the first enzyme of the kynurenine pathway, in lung and brain, sustained increases in brain QUIN concentration and increases in plasma L-kynurenine and QUIN levels. Mice chronically treated with gamma-interferon offer an animal model to investigate the effects of sustained immune stimulation on kynurenine pathway metabolism.

Animals↗
PubMed1991

Cerebral cortex and lung indoleamine-2,3-dioxygenase activity is increased in type-D retrovirus infected macaques.

Increased concentrations of the neuroactive kynurenine pathway metabolites, quinolinic acid (QUIN) and kynurenic acid (KYNA), occur in the CSF of humans infected with the human immunodeficiency virus and macaques infected with retroviruses, including the D/1/California serotype. In the present study, increased activity of indoleamine-2,3-dioxygenase (IDO), the first enzyme of the kynurenine pathway, occurred in cerebral cortex and lung of macaques with clinical SAIDS. Such increases provide a mechanism to accelerate the formation of kynurenine pathway metabolites in both systemic tissues and the central nervous system.

Animals↗
PubMed1991

Regional brain and cerebrospinal fluid quinolinic acid concentrations in Huntington's disease.

Many of the characteristics neuroanatomical and neurochemical features of Huntington's disease (HD) are produced in experimental animals by an intrastriatal injection of the endogenous N-methyl-D-aspartate receptor agonist quinolinic acid (QUIN). Conceivably, a chronic over-production of QUIN in brain could be involved in the pathogenesis of HD. To investigate this hypothesis, concentrations of QUIN were measured both in cerebrospinal fluid (CSF) and postmortem tissue from patients with HD and neurologically normal age-matched controls. CSF QUIN concentrations were slightly lower in patients with HD, however the changes were not significant. Mean concentrations of QUIN tended to be lower in HD putamen, dentate nucleus and several cortical regions, although significant reductions were found only in Brodmann areas 17, 20 and 28. The mechanisms responsible for these small reductions in brain QUIN concentrations remain to be determined. These results do not support the hypothesis that a chronic increase of QUIN production is responsible for neurodengeneration in HD.

Adult↗
PubMed1991

Stable isotope-labeled tryptophan as a precursor for studying the disposition of quinolinic acid in rabbits.

The utility of stable isotope-labeled tryptophan as a precursor for studying the disposition of quinolinic acid was investigated. TRP-D5 at doses of 50, 25 or 10 mg/kg was administered to rabbits. Blood and CSF samples were taken for up to 6 hours. There was no loss of deuterium from the tryptophan and the specifically tri-deuterated quinolinic acid measured in plasma and CSF. CSF levels of QUIN-D3 remained elevated 6 hours following TRP-D5 administration. Further studies of the CNS disposition of quinolinic acid and other metabolites of the kynurenine pathway employing stable isotope-labeled tryptophan as precursor at appropriate doses and with extended sampling are in progress.

Animals↗