A simplified method to quantify dysregulated tyrosine transport in schizophrenia.
BACKGROUND
Schizophrenia is associated with altered tyrosine transport across plasma membranes. This is typically demonstrated by measuring the uptake of radiolabeled tyrosine in cultured human fibroblasts. Our primary goal was to determine whether tyrosine uptake could be characterized using unlabeled tyrosine. A secondary goal was to assess the effect of antipsychotic drugs added during the incubation.


METHODS
Epithelium-derived fibroblast cultures were generated from patients with schizophrenia (n=6) and age-matched controls (n=6). Cells between cycles 8-12 were exposed to an amino acid free medium for 60min and then for 1min to media containing tyrosine (0.008-1.0mM). Amino acid levels were measured and Michaelis-Menten parameters determined. Uptake of tyrosine (0.5mM) was also measured in control cells after antipsychotic drugs were introduced during the depletion or uptake phases.


RESULTS
Tyrosine uptake was sodium-independent. The maximal transport velocity (Vmax) was significantly lower in patients with schizophrenia than in controls (p<0.01). The transporter affinity (Km) did not differ between the groups. Tyrosine uptake was differentially affected (p<0.001) by inclusion of 10(-4)M haloperidol, chlorpromazine or clozapine during different periods of incubation.


CONCLUSIONS
Dysregulated tyrosine kinetics in schizophrenia can be readily studied without the use of radiolabeled tracers. The data also indicate that tyrosine uptake may be subject to complex pharmacological effects.
Psychiatry Service, Louis Stokes Cleveland DVAMC, Cleveland, OH 44106, United States. Electronic address: rodolfo.bongiovanni@yahoo.com.
Rodolfo
R
Bongiovanni
Sherry
S
Leonard
George E
GE
Jaskiw
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000596:Amino Acids / Q000378:metabolism; D000704:Analysis of Variance; D014150:Antipsychotic Agents / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002855:Chromatography, Thin Layer; D005260:Female; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D012559:Schizophrenia / Q000473:pathology*; D014443:Tyrosine / Q000378:metabolism*
D000596:Amino Acids; D014150:Antipsychotic Agents; D014443:Tyrosine
Chlorpromazine; Clozapine; Fibroblast; Haloperidol; Schizophrenia; Tyrosine