Abstract
BackgroundAccumulating evidence suggests that the brain's nitric oxide (NO) signalling system may be involved in the pathophysiology of schizophrenia and could thus constitute a novel treatment target. The study was designed to investigate the benefit of L-lysine, an amino acid that interferes with NO production, as an add-on treatment for schizophrenia.MethodsL-lysine, 6 g/day, was administered to 10 patients with schizophrenia as an adjunctive to their conventional antipsychotic medication. The study was designed as a single-blinded, cross-over study where patients were randomly assigned to initial treatment with either L-lysine or placebo and screened at baseline, after four weeks when treatment was crossed over, and after eight weeks.ResultsL-lysine treatment caused a significant increase in blood concentration of L-lysine and was well tolerated. A significant decrease in positive symptom severity, measured by the Positive And Negative Syndrome Scale (PANSS), was detected. A certain decrease in score was also observed during placebo treatment and the effects on PANSS could not unequivocally be assigned to the L-lysine treatment. Furthermore, performance on the Wisconsin Card Sorting Test was significantly improved compared to baseline, an effect probably biased by training. Subjective reports from three of the patients indicated decreased symptom severity and enhanced cognitive functioning.ConclusionsFour-week L-lysine treatment of 6 g/day caused a significant increase in blood concentration of L-lysine that was well tolerated. Patients showed a significant decrease in positive symptoms as assessed by PANSS in addition to self-reported symptom improvement by three patients. The NO-signalling pathway is an interesting, potentially new treatment target for schizophrenia; however, the effects of L-lysine need further evaluation to decide the amino acid's potentially beneficial effects on symptom severity in schizophrenia.Trial registrationNCT00996242
Highlights
Accumulating evidence suggests that the brain’s nitric oxide (NO) signalling system may be involved in the pathophysiology of schizophrenia and could constitute a novel treatment target
Two patients showed no change in L-lysine concentration and were treated as non-responders and included in an “Intention to Treat” group (n = 10), which was analyzed in parallel with the responders (n = 8) in the statistical analysis
Positive symptom scores were significantly improved during treatment Symptom severity as measured by the positive symptoms sub-scale of Positive And Negative Syndrome Scale (PANSS) showed a significant decrease (F(2,14) = 13.11, P < 0.001)
Summary
Accumulating evidence suggests that the brain’s nitric oxide (NO) signalling system may be involved in the pathophysiology of schizophrenia and could constitute a novel treatment target. Negative symptoms and the cognitive deficits are to a large extent resistant to antipsychotic treatment [1,2]. The inducible NO synthase inhibitor, minocycline, was recently suggested to have beneficial effects as an add-on treatment in patients with schizophrenia [7,8]. Accumulating evidence indicates that alterations in NO function may be involved in the pathophysiology of schizophrenia and these original findings motivate further investigations of the potential utility of NO modulation as a novel pharmacological treatment rationale for schizophrenia (for review, see [9])
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