Distribution of serotonin, 5-hydroxyindolacetic acid and homovanillic acid in biological fluids of psycotic patients treated with clozapine

Introduction: The dopaminergic and serotoninergic systems are known to be related to several mental illnesses such as schizophrenia, depression and affective disorders. A change in levels of neurotransmitters including dopamine and serotonin (and/or their metabolites) may lead to pathological processes with specific clinical manifestations. The introduction of atypical antipsychotics acting on multiple neurotransmitters has improved therapeutic results. In particular, clozapine, the parent drug of the atypical antipsychotics, is more effective for reducing symptoms of schizophrenia than the older typical antipsychotics because of its profile of binding to serotonergic as well as dopamine receptors. Methods: A high-performance liquid chromatographic method was developed for the simultaneous determination of serotonin, 5-hydroxyindolacetic and homovanillic acids in dried blood spots and in platelet poor and rich plasma samples. Analyses were carried out on a C18 reversed-phase column using a mobile phase composed of methanol and aqueous citrate buffer. Coulometric detection was used, operating at +0.400 V. For the clean-up of the biological samples a novel solid-phase extraction procedure, based on mixed-mode reversed-phase – strong anion exchange cartridges, was implemented. Results: The analytical method was linear over the on-column concentration range of 0.1–22.5 ng mL ⁻¹ for serotonin and 5-hydroxyindolacetic acid and of 0.25–22.5 ng mL ⁻¹ for homovanillic acid. Extraction yields of the analytes from all these matrices were satisfactory, being always higher than 89.0%. Results were satisfactory in terms of sensitivity, precision, selectivity and accuracy. Discussion: The analytical method was successfully applied to the analysis of serotonin, 5-hydroxyindolacetic and homovanillic acids in human platelet poor and rich plasma samples and in dried blood spots from volunteers and some psychotic patients treated with clozapine. Assays are currently in progress to apply this method to biological fluids from numerous psychiatric patients for studies regarding neuroendocrine responses.