[3H]dopamine uptake by platelet storage granules in schizophrenia

Actualities in immunological markers and electrochemical sensors for determination of dopamine and its metabolites in psychotic disorders (Review)

Psychotic disorders represent a serious health concern. At this moment, anamnestic data, international criteria for diagnosis/classification from the Diagnostic and Statistical Manual of Mental Disorders-5 and the International Classification of Diseases-10 and diagnostic scales are used to establish a diagnosis. The most commonly used biomarkers in psychotic illnesses are those regarding the neuroimmune system, metabolic abnormalities, neurotrophins and neurotransmitter systems and proteomics. A current issue faced by clinicians is the lack of biomarkers to help develop a more accurate diagnosis, with the possibility of initiating the most effective treatment. The detection of biological markers for psychosis has the potential to contribute to improvements in its diagnosis, prognosis and treatment effectiveness. The mixture of multiple biomarkers may improve the ability to differentiate and classify these patients. In this sense, the aim of this study was to analyze the literature concerning the potential biomarkers that could be used in medical practice and to review the newest developments in electrochemical sensors used for dopamine detection, one of the most important exploited biomarkers.

Alterations of the dopamine transporter in resting lymphocytes of patients with different psychotic disorders

The aim of our study was to investigate and compare the dopamine (DA) transporter (DAT) in resting lymphocytes of 20 psychotic patients and 20 healthy control subjects, by means of both the binding parameters (Bmax and Kd) of 3H-WIN 35,428, and the reuptake parameters (Vmax and Km) of 3H-DA. The results showed that both the Bmax of 3H-WIN 35,428 binding and the Vmax of 3H-DA reuptake of the patients were significantly lower than those of healthy subjects, while the Kd or Km did not show any change. These findings, while indicating a reduced density of the lymphocyte DAT proteins, provide further support of the role of DA in psychoses and suggest that DA alterations may not be limited to brain structures.

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.

Presence and characterization of the dopamine transporter in human resting lymphocytes

The paucity of information on the presence of the dopamine transporter (DAT) in blood cells, prompted us to explore it in human resting lymphocytes by means of the binding of 3H-WIN 35,428, a compound which is currently considered the most selective ligand for labelling this protein, and by means of the specific reuptake of 3H-dopamine (3H-DA). Lymphocytes were obtained by 15 healthy subjects. The results showed the presence of a specific and saturable binding of 3H-WIN 35,428, which labelled one site only. A specific 3H-DA reuptake was also measured. The pharmacological characterization of both binding and reuptake was overlapping. These findings would indicate that human resting lymphocytes carry the DAT, whose functions in periphery are still unknown.

Binding of 3H-WIN-35,428 and 125I-RTI-121 to Human Platelet Membranes

The dopamine transporter (DAT) is a protein regulating dopamine concentration in the synaptic cleft through the re-uptake mechanism. The DAT is the main target of psychostimulants and seems to play a pivotal role in neuronal degeneration and different neuropsychiatric disorders involving the dopamine system. Exhaustive research, however, regarding the presence of this protein in human platelets is still inconclusive, although it is thought that it might provide a peripheral tool to serve as a mean of exploring the same structure present in the brain. Therefore, we assessed some binding assays in platelets derived from healthy human subjects by means of 3H-WIN 35,428, a compound which is considered a selective ligand for the labelling of this protein, and by means of 125I-RTI-121, another compound with high specificity for DAT. The results showed that the binding of 3H-WIN-35,428 was too low to enable the detection of any structure; the binding of 125I-RTI-121, on the other hand, revealed the presence of two binding sites with pharmacological profiles similar to that of the serotonin transporter (SERT). In conclusions, therefore, platelets would not seem to be a useful model for exploring the DAT, given the prevalence therein of the SERT and the difficulty of labelling the DAT with the currently available ligands.

Dopamine uptake by platelet storage granules in first-degree relatives of Tourette's syndrome patients

BACKGROUND

Considering that platelets have been established to be good peripheral markers for the study of catecholaminergic neurons, we have applied an assay to measure the uptake of (3H)-dopamine (DA) into platelet storage granules (PSG). Recently, we reported that Tourette's syndrome (TS) patients (pts) show decreased DA uptake into PSG.

METHODS

In the present study, 28 first-degree relatives (3 with chronic motor tics, 3 with transient tics, 6 with obsessive-compulsive behavior, and 16 without symptomatology) belonging to the families of 13 patients, and 14 unrelated healthy controls were studied.

RESULTS

Double reciprocal plots were constructed for each subject, and the apparent maximum velocity (Vmax) and Michaelis constant (K(m)) were determined by linear regression analysis (Lineaweaver-Burke plots). The uptake of DA (0.5-5 mumol/L) (mean +/- SEM) by PSG from relatives with symptomatology was similar to the TS patients (symptomatic relatives Vmax 181 +/- 22.2 fmol/mg protein, K(m) (mumol/L) 6.42 +/- 0.29; TS pts Vmax 108 +/- 6.9, K(m) 7.79 +/- 0.64). Relatives without symptomatology on the contrary showed DA affinity characteristics similar to the controls (t test, paired t test, multivariate analysis of variance, and log transformation).

CONCLUSIONS

The data presented suggest that TS is hereditary, but they do not distinguish between an autosomal dominant inheritance and a mixed or polygenic model.

Decreased dopamine uptake into platelet storage granules in Gilles de la Tourette disease

The movement disorder of Gilles de la Tourette (GdlT) disease may reflect hyperactivity of the basal ganglionic dopamine system. Since platelets have been suggested as peripheral models for the study of catecholamine neurons, we developed a method to measure the uptake of [3H]-DA into platelet storage granules (PSG). In the present report, PSG were incubated with [3H] DA, and Vmax and Km values were calculated by linear regression analysis (Lineweaver Burke plot). The uptake of DA (0.5-5 microM) by PSG from 18 GdlT patients was significantly lower (p < .0001) compared to 15 controls (Vmax mean +/- SD, 107.5 +/- 42.5 and 265.3 +/- 66.5 fmole/mg protein resp.). The decrease of DA uptake in GdlT may reflect compensatory presynaptic changes that reduce DA activity.

[3H] dopamine uptake by platelet storage granules in Parkinson's disease

[3H] Dopamine (DA) uptake by platelet storage granules was determined in 10 never-treated patients with Parkinson's disease (PD) (in 6 of them, also after 6 months of levodopa treatment), in 18 long-term levodopa-treated patients and in 15 age-matched normal controls. Maximum velocity (Vmax) of DA uptake was significantly lower in the group of never-treated PD subjects compared to healthy controls (P < 0.001) and also lower compared to the PD long-term treated patients (P < 0.025). The Vmax of PD never-treated changed after submitting the patients to 6 months treatment (P < 0.025) and became similar to the Vmax in the treated group. The apparent Michaelis constant (Km) of DA uptake in PD never-treated was also significantly different from controls (P < 0.005) and also different (but not significantly) from PD "long-term" treated patients. Decreased DA uptake by platelet storage granules in PD may reflect a generalized defect of dopaminergic cells with an impairment in the vesicularization of DA which may contribute to the symptomatology of this motor disease.