U-373 MG glioblastoma and IMR-32 neuroblastoma cell lines express the dopamine and vesicular monoamine transporters

Homogentisate 1,2 dioxygenase is expressed in brain: implications in alkaptonuria

Alkaptonuria is an ultra-rare autosomal recessive disease developed from the lack of homogentisate 1,2-dioxygenase (HGD) activity, causing an accumulation in connective tissues of homogentisic acid (HGA) and its oxidized derivatives in polymerized form. The deposition of ochronotic pigment has been so far attributed to homogentisic acid produced by the liver, circulating in the blood, and accumulating locally. In the present paper, we report the expression of HGD in the brain. Mouse and human brain tissues were positively tested for HGD gene expression by western blotting. Furthermore, HGD expression was confirmed in human neuronal cells that also revealed the presence of six HGD molecular species. Moreover, once cultured in HGA excess, human neuronal cells produced ochronotic pigment and amyloid. Our findings indicate that alkaptonuric brain cells produce the ochronotic pigment in loco and this may contribute to induction of neurological complications.

Antipsychotic drugs influence transport of the β-adrenergic antagonist [3H]-dihydroalprenolol into neuronal and blood cells

The amine hypothesis suggests that the cause of schizophrenic or depressive psychosis is dysfunction of noradrenergic or serotonergic neurotransmission. We investigated pharmacological properties of [3H]-dihydroalprenolol (DHA) transport into C6, IMR32, native lymphocytes, B-lymphoblastoids and MOLT-3 cells. DHA transport was inhibited by a heterogeneous group of structurally related compounds exhibiting an amine group and various aromatic ring structures. It was verified on cells of neuronal/glial and blood cell origin but in detail on B-lymphoblastoids. The latter once showed strongest inhibition of DHA transport using tricyclic antidepressants (amitriptyline: IC50 = 2.86 microM, imipramine: IC50 = 3.33 microM) and haloperidol (IC50 = 3.98 microM) as a neuroleptic. Antipsychotics like clozapine (IC50 = 11 microM), olanzapine (IC50 = 15 microM), spiperone (IC50 = 66 microM) and EMD 49980 (ICso >> 100 microM) were less effective. In contrast to cells of blood origin, a stimulation of DHA transport by antipsychotics was not detectable using neuronal cells. As antipsychotics showed a distinct inhibition and, concerning cells of blood origin, a stimulation of transport after pre-incubation, further investigations seem to be of interest in respect to its involvement in the cellular uptake of drugs and therefore its impact on the quality of therapy of psychiatric patients.

Identification of tissue-restricted transcripts in human islets

The purpose of our study was to identify transcripts specific for tissue-restricted, membrane-associated proteins in human islets that, in turn, might serve as markers of healthy or diseased islet cell masses. Using oligonucleotide chips, we obtained gene expression profiles of human islets for comparison with the profiles of exocrine pancreas, liver, and kidney tissue. As periislet presence of type 1 interferon is associated with the development of type 1 diabetes, the expression profile of human islets treated ex vivo with interferon-alpha2beta (IFNalpha2beta) was also determined. A set of genes encoding transmembrane- or membrane-associated proteins with novel islet-restricted expression was resolved by determining the intersection of the islet set with the complement of datasets obtained from other tissues. Under the influence of IFNalpha2beta, the expression levels of transcripts for several of the identified gene products were up- or down-regulated. One of the islet-restricted gene products identified in this study, vesicular monoamine transporter type 2, was shown to bind [3H]dihydrotetrabenazine, a ligand with derivatives suitable for positron emission tomography imaging. We report here the first comparison of gene expression profiles of human islets with other tissues and the identification of a target molecule with possible use in determining islet cell masses.

Effect of 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) on human serotonergic cells

The tryptamine-derived dopaminergic neurotoxin 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline ('TaClo'), which was found to occur in humans after intake of the hypnotic chloral hydrate, was also shown to strongly disturb serotonergic cells. Incubation experiments using the human serotonergic cell line JAR clearly revealed TaClo to significantly reduce serotonin (5-HT) uptake (IC(50) = 59 microM) and to induce a distinct loss of cellular viability at increasing TaClo concentrations. In contrast to well-known serotonergic neurotoxins such as amphetamines, however, TaClo toxicity is not mediated by the 5-HT transporter (5-HTT). In the presence of the specific 5-HTT inhibitor imipramine, the uptake of TaClo into JAR cells was not reduced, hinting at an exclusively passive penetration of this highly lipophilic beta-carboline through cell membranes. Similar toxic effects towards JAR cells were also observed for the 5-HT-related TaClo analog 6-hydroxy-1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline ('6-OH-TaClo') (IC50 = 26 gM). The dopamine-derived alkaloid-type heterocycle 6,7-dihydroxy-1-trichloromethyl-1,2,3,4-tetrahydroisoquinoline ('DaClo'), by contrast, was found to be less toxic, showing only a weak inhibitory activity (IC50 = 260 microM) on 5-HT uptake. The pronounced toxicitiy of TaClo and 6-OH-TaClo against serotonergic cells became also evident from morphological findings: Dose-dependently, the survival of JAR cells was significantly impaired, while human dopaminergic IMR-32 cells were only moderately affected at similar toxin concentrations.

Dopamine neurotoxicity in cortical neurons

Dopamine (DA), at concentrations greater than 100 microM, has previously been demonstrated to be toxic to mesencephalic, striatal and dorsal root ganglion cell cultures. Pharmacological experiments suggest that DA also may play a role in the cortical neurotoxicity caused by systemic administration of N-methyl-D-aspartate receptor antagonists such as phencyclidine and MK-801. In this study, the potential toxicity of DA in primary cortical cell cultures was determined in vitro. Using calcein and ethidium homodimer fluorescence as a marker for live and dead cells, respectively, we observed that a 24 h treatment with 10-100 microM DA produced a concentration-dependent increase in the number of ethidium homodimer-labelled cells. The cell death induced by 10 microM DA was dramatically reduced by co-administration of either superoxide dismutase and catalase or deferoxamine mesylate, an iron chelator. To verify this observation, the effects of 10 microM DA on the release of cytoplasmic lactate dehydrogenase (LDH) was measured. DA increased LDH release in a manner that was inhibited by both superoxide dismutase/catalase and deferoxamine. Nomifensine potentiated the effect of DA on LDH release, suggesting a protective role for DA uptake in this system. On the other hand, neither D1 nor D2 antagonists were able to prevent DA-induced LDH release. These data suggest that relatively low concentrations of DA can be injurious to cortical neurons through a mechanism that likely involves DA autooxidation and the formation of reactive oxygen species such as superoxide anion and hydroxyl radical. This mechanism may be important in the toxic effects of psychomotor stimulants such as amphetamine. However, the failure of DA receptor antagonists to affect DA-induced injury argues that the effect of DA on cortical neurons in culture does not model the toxic effect of phencyclidine and MK-801 observed in vivo.