Acute dyskinesias in monkeys elicited by halopemide, mezilamine and the "antidyskinetic" drugs, oxiperomide and tiapride

Phospholipase D: A new mediator during high phosphate-induced vascular calcification associated with chronic kidney disease

Vascular calcification (VC) is the pathological accumulation of calcium phosphate crystals in one of the layers of blood vessels, leading to loss of elasticity and causing severe calcification in vessels. Medial calcification is mostly seen in patients with chronic kidney disease (CKD) and diabetes. Identification of key enzymes and their actions during calcification will contribute to understand the onset of pathological calcification. Phospholipase D (PLD1, PLD2) is active at the earlier steps of mineralization in osteoblasts and chondrocytes. In this study, we aimed to determine their effects during high-phosphate treatment in mouse vascular smooth muscle cell line MOVAS, in the ex vivo model of the rat aorta, and in the in vivo model of adenine-induced CKD. We observed an early increase in PLD1 gene and protein expression along with the increase in the PLD activity in vascular muscle cell line, during calcification induced by ascorbic acid and β-glycerophosphate. Inhibition of PLD1 by the selective inhibitor VU0155069, or the pan-PLD inhibitor, halopemide, prevented calcification. The mechanism of PLD activation is likely to be protein kinase C (PKC)-independent since bisindolylmaleimide X hydrochloride, a pan-PKC inhibitor, did not affect the PLD activity. In agreement, we found an increase in Pld1 gene expression and PLD activity in aortic explant cultures treated with high phosphate, whereas PLD inhibition by halopemide decreased calcification. Finally, an increase in both Pld1 and Pld2 expression occurred simultaneously with the appearance of VC in a rat model of CKD. Thus, PLD, especially PLD1, promotes VC in the context of CKD and could be an important target for preventing onset or progression of VC.

The common marmoset (Callithrix jacchus) as a model for neuroleptic-induced acute dystonia

To examine whether acute dystonia is induced by neuroleptic treatment, common marmosets were treated with haloperidol orally twice a week over 25 weeks until dystonic behavior was elicited. Movement disorders such as acute dystonia were observed 6 weeks after the initial treatment, and had appeared in all treated animals by 25 weeks. Once these movement disorders were induced, they consistently reappeared after further treatment with haloperidol, and once haloperidol dosing was discontinued, the episodes vanished. Then, various neuroleptic drugs (bromperidol, chlorpromazine, risperidone thioridazine, sulpiride, tiapride, and clozapine) or a nonneuroleptic drug (diazepam) were administered orally instead of haloperidol in the above animals. All the neuroleptic drugs except for clozapine elicited similar abnormal behavior, while diazepam failed to induce any dystonia. An anticholinergic drug, trihexyphenidyl, which is known to reduce acute dystonia in patients, was also given orally to the above haloperidol-sensitized animals, followed by further treatment with haloperidol 30 min later. This clearly suppressed the induction of dystonia by haloperidol. The similarity between these findings for haloperidol-pretreated common marmosets and clinical findings suggests that the present model is useful for predicting the potential of antipsychotics to induce acute dystonia in humans.

SCH 23390 dissociated from conventional neuroleptics in apomorphine climbing and primate acute dyskinesia models

SCH 23390 induced only a negligible incidence of the acute dyskinetic syndrome, a predictor of neuroleptic-induced extrapyramidal liability, in squirrel monkeys. However, haloperidol-induced dyskinesias were potentiated by SCH 23390 and were blocked by the D-1 agonist, SKF 38393. When administered orally or intraperitoneally to mice, SCH 23390 showed a considerably wider dose separation than did conventional neuroleptics between antagonism of apomorphine climbing and antagonism of stereotyped sniffing. Clinically relevant distinctions may exist between D-1 and D-2 antagonists, with D-1 antagonists (exemplified by SCH 23390) showing lower, although possibly not negligible, potential to cause extrapyramidal side effects.

Halopemide, a new psychotropic agent. Cerebral distribution and receptor interactions

Halopemide is a new psychotropic agent, a structural analogue of the neuroleptics of the butyrophenone type but with different pharmacological and clinical properties. Preliminary clinical findings indicate that halopemide lacks the ability to induce parkinsonism and may be an effective drug in the treatment of psychosis characterized by autism, emotional withdrawal or apathy. Its pharmacological effects at a molecular level in comparison to structurally related neuroleptics and putative metabolites are reviewed.

Induction of tardive dyskinesia in Cebus apella and Macaca speciosa monkeys: a review

Two different studies were performed in subhuman primates in an attempt to induce symptoms of tardive dyskinesia. The first study lasted for over 5 years. This involved elderly Macaca speciosa. The animals were given first 25 mg of fluphenazine decanoate and later the enanthate IM (3.2 mg/kg) every 2 weeks and on 5 days a week, haloperidol, first IM and later PO. Haloperidol was given first in doses of 1.0 mg/kg and ultimately after years of therapy, in doses of 6.4 mg/kg per day. Those animals who survived gained weight to over 10 kg. After neuroleptic withdrawal, tardive dyskinesia became evident in 1 month. The symptoms of tardive dyskinesia following cessation of medication lasted a maximum of 1 year. This animal model produced very impressive symptoms in one of the three animals treated who survived. This is not a very practical animal model from the aspects of economics (costly), time (5 years), and animal availability (rare and endangered species). However, the symptoms of tardive dyskinesia are very striking and identical with human tardive dyskinesia in a susceptible animal. A more practical experimental animal model involved Cebus apella. Depot fluphenazine (0.1 to 3.2 mg/kg) was given continuously every 2 weeks for 1 year. In this species the symptoms of tardive dyskinesia became progressively prolonged and intense with each course of fluphenazine therapy and withdrawal, suggesting that reversible tardive dyskinesia may turn into irreversible tardive dyskinesia. With each succeeding course of fluphenazine therapy (1 month) and withdrawal (1-3 months), the animals appeared to be sensitized to both the acute extrapyramidal and the tardive dyskinesia symptoms. These animals were also given various experimental drug treatments including biperiden lactate, benztropine mesylate, and d-amphetamine after they developed signs of tardive dyskinesia.

Progressive changes in the acute dyskinetic syndrome as a function of repeated elicitation in squirrel monkeys

Various neuroleptic-induced motor disorders that appear in primates previously treated with neuroleptics are collectively designated the acute dyskinetic syndrome. The relative incidence of these motor disorders was examined as the syndrome was repeatedly elicited by haloperidol and other dopamine antagonists in individual monkeys. After several weekly or biweekly treatments with haloperidol (1.25 mg/kg orally), catalepsy began to appear, which was then accompanied by athetoid movements (writhing and limb extensions) as intermittent neuroleptic treatment continued. Other dyskinetic movements ('duck walk', oral dyskinesias, pushing of the head into a cage corner, and perseverative circling) that were suggestive of hyperkinesia subsequently began to be elicited by haloperidol and other neuroleptics after additional treatments with these drugs had intervened. As intermittent treatments continued, tolerance to the athetoid movements gradually developed and, eventually, only circling and pushing could be consistently elicited by haloperidol. In monkeys that had reached this phase, the athetoid movements were not again induced by higher doses of haloperidol (up to 5 mg/kg), chlorpromazine (3 mg/kg), or metoclopramide (3 mg/kg). In these tolerant monkeys, haloperidol impaired Sidman avoidance performance less and benztropine more than in drug-naive monkeys. Neither pharmacokinetic changes nor behavioral tolerance could readily account for these results. It is hypothesized that they reflect progressive functional alterations in dopaminergic or cholinergic neurotransmission.

Differential reversal of various dopamine antagonists by anticholinergics in Sidman avoidance: possible relationship to adrenergic blockade

Various dopamine receptor antagonists have divergent clinical and neurochemical properties. The relative ability of anticholinergics (benztropine and scopolamine) to reverse these drugs was assessed in squirrel monkeys and rats performing a Sidman avoidance task. In monkeys, benztropine markedly attenuated the effects of oxiperomide, metoclopramide, halopemide, tiapride and mezilamine as well as haloperidol. Chlorpromazine and fluphenazine were antagonized to a moderate extent; thioridazine and perlapine were not antagonized; and clozapine was actually potentiated by benztropine. In the rat, benztropine antagonized haloperidol strongly but reversed fluphenazine, thioridazine or clozapine only weakly or not at all. The overall effects of scopolamine in both species were similar to those of benztropine. The dopamine receptor antagonists that were most completely reversed by benztropine were found to inhibit 3H-spiroperidol more strongly than 3H-WB-4101 binding in calf caudate, while the reverse was true for drugs that were antagonized only moderately or not at all by benztropine. These results support a previous suggestion that anticholinergic reversal is less marked against dopamine antagonists with alpha-adrenergic blocking properties. Benztropine reversal of experimental dopamine receptor antagonists in the squirrel monkey Sidman avoidance test may contribute to their preclinical characterization.