An Exploratory Retrospective Evaluation of Ropinirole-Associated Psychotic Symptoms in an Outpatient Population Treated for Restless Legs Syndrome or Parkinson's Disease

Parkinson's disease and schizophrenia interactomes contain temporally distinct gene clusters underlying comorbid mechanisms and unique disease processes

Genome-wide association studies suggest significant overlaps in Parkinson's disease (PD) and schizophrenia (SZ) risks, but the underlying mechanisms remain elusive. The protein-protein interaction network ('interactome') plays a crucial role in PD and SZ and can incorporate their spatiotemporal specificities. Therefore, to study the linked biology of PD and SZ, we compiled PD- and SZ-associated genes from the DisGeNET database, and constructed their interactomes using BioGRID and HPRD. We examined the interactomes using clustering and enrichment analyses, in conjunction with the transcriptomic data of 26 brain regions spanning foetal stages to adulthood available in the BrainSpan Atlas. PD and SZ interactomes formed four gene clusters with distinct temporal identities (Disease Gene Networks or 'DGNs'1-4). DGN1 had unique SZ interactome genes highly expressed across developmental stages, corresponding to a neurodevelopmental SZ subtype. DGN2, containing unique SZ interactome genes expressed from early infancy to adulthood, correlated with an inflammation-driven SZ subtype and adult SZ risk. DGN3 contained unique PD interactome genes expressed in late infancy, early and late childhood, and adulthood, and involved in mitochondrial pathways. DGN4, containing prenatally-expressed genes common to both the interactomes, involved in stem cell pluripotency and overlapping with the interactome of 22q11 deletion syndrome (comorbid psychosis and Parkinsonism), potentially regulates neurodevelopmental mechanisms in PD-SZ comorbidity. Our findings suggest that disrupted neurodevelopment (regulated by DGN4) could expose risk windows in PD and SZ, later elevating disease risk through inflammation (DGN2). Alternatively, variant clustering in DGNs may produce disease subtypes, e.g., PD-SZ comorbidity with DGN4, and early/late-onset SZ with DGN1/DGN2.

Relative prevalence of 10 types of pharmacodynamic interactions in psychiatric treatment

OBJECTIVE

To assess the relative prevalence and factors affecting the prescription of medication combinations with a theoretical efficacy limiting pharmacodynamic interaction, defined as two medications with opposing indications and side effects or antagonistic action at the primary receptor of mechanism of action.

METHOD

One hundred sixteen combinations were identified for 10 types of pharmacodynamic interactions. PubMed was searched for each combination to assess the quality of evidence either supporting clinical use or verifying reduced efficacy. Micromedex was searched to determine the presence of warnings to prescribers of reduced efficacy. The prevalence in clinical practice was determined by computer review of the Genoa Healthcare database for all prescribers at 10 participating community mental health centers. The expected prevalence was calculated as the product of the probability of each medication prescribed alone and was compared with the actual prevalence of the combination using the test of proportions.

RESULTS

The frequency of prescription of eight combinations met the Bonferroni corrected level of significance of p < 0.001. Four were combinations of amphetamine and D2 antagonists and each were prescribed less often than chance, p = 0.0001 consistent with epidemiological studies and multiple animal studies verifying an efficacy limiting interaction. Despite epidemiological studies indicating increased risk of accidents, alprazolam and amphetamine were prescribed more often than chance, p = 0.0001. Micromedex generated warnings for efficacy limiting interactions for five other combinations, but with no subsequent change in prescription frequency.

CONCLUSIONS

Neither presence of medical evidence nor warnings from Micromedex consistently affect the prescription of combinations with pharmacodynamic efficacy limiting interactions.

Gabapentin treatment in clozapine-induced restless legs syndrome: two cases and a review of the literature

Restless legs syndrome (RLS) is a neuro-sensorimotor disorder affecting 2-4% of adults. It is characterized by intense urges to move the legs, associated with unpleasant sensory disturbances in the legs occurring at rest and manifests mostly in the evening and night, relieved by movement. Diagnosis is primarily based on clinical presentation and the consensus criteria for the diagnosis have been established. Antipsychotics, the dopamine antagonists, have been reported to induce RLS. Dopamine agonists, the effective first-line treatment of RLS, carry the risk of inducing or worsening psychosis. Many nondopaminergic agents including antiepileptic medications have also been used in the treatment of primary RLS. In this report we describe clozapine-induced RLS in two patients with schizophrenia and its successful treatment with gabapentin, a nondopaminergic agent. In addition, we have reviewed the available literature on clozapine-induced RLS and its management.

The effect of dopamine agonists on adaptive and aberrant salience in Parkinson's disease

Clinical evidence suggests that after initiation of dopaminergic medications some patients with Parkinson's disease (PD) develop psychotic symptoms, such as hallucinations and delusions. Here, we tested the hypothesis that the neurocognitive basis of this phenomenon can be defined as the formation of arbitrary and illusory associations between conditioned stimuli and reward signals, called aberrant salience. Young, never-medicated PD patients and matched controls were assessed on a speeded reaction time task in which the probe stimulus was preceded by conditioned stimuli that could signal monetary reward by color or shape. The patients and controls were re-evaluated after 12 weeks during which the patients received a dopamine agonist (pramipexole or ropinirole). Results indicated that dopamine agonists increased both adaptive and aberrant salience in PD patients, that is, formation of real and illusory associations between conditioned stimuli and reward, respectively. This effect was present when associations were assessed by means of faster responding after conditioned stimuli signaling reward (implicit salience) and overt rating of stimulus-reward links (explicit salience). However, unusual feelings and experiences, which are subclinical manifestations of psychotic-like symptoms, were specifically related to irrelevant and illusory stimulus-reward associations (aberrant salience) in PD patients receiving dopamine agonists. The learning of relevant and real stimulus-reward associations (adaptive salience) was not related to unusual experiences. These results suggest that dopamine agonists may increase psychotic-like experiences in young patients with PD, possibly by facilitating dopaminergic transmission in the ventral striatum, which results in aberrant associations between conditioned stimuli and reward.

Adenosine A(2A) Receptor Antagonists Do Not Disrupt Rodent Prepulse Inhibition: An Improved Side Effect Profile in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra. Current treatments for PD focus on dopaminergic therapies, including L-dopa and dopamine receptor agonists. However, these treatments induce neuropsychiatric side effects. Psychosis, characterized by delusions and hallucinations, is one of the most serious such side effects. Adenosine A_2A receptor antagonism is a nondopaminergic treatment for PD with clinical and preclinical efficacy. The present studies assessed A_2A antagonists SCH 412348 and istradefylline in rodent prepulse inhibition (PPI), a model of psychosis. Dopamine receptor agonists pramipexole (0.3–3 mg/kg), pergolide (0.3–3 mg/kg), and apomorphine (0.3–3 mg/kg) significantly disrupted PPI; ropinirole (1–30 mg/kg) had no effect; L-dopa (100–300 mg/kg) disrupted rat but not mouse PPI. SCH 412348 (0.3–3 mg/kg) did not disrupt rodent PPI; istradefylline (0.1–1 mg/kg) marginally disrupted mouse but not rat PPI. These results suggest that A_2A antagonists, unlike dopamine agonists, have an improved neuropsychiatric side effect profile.