Lillian E. Dyck

Olanzapine and quetiapine protect PC12 cells from β-amyloid peptide25–35-induced oxidative stress and the ensuing apoptosis

We previously found that the atypical antipsychotic drugs (APDs) clozapine, olanzapine, quetiapine, and risperidone reduce PC12 cell death induced by hydrogen peroxide, N‐methyl‐4‐phenylpyridinium ion, or β‐amyloid peptide (Aβ25–35). Such neurotoxic substances have in common the capability of causing oxidative stress. Atypical APDs have been used in treating schizophrenia and in treating psychotic symptoms of patients with Alzheimers disease (AD), in which Aβ is involved by causing oxidative stress. Therefore, we hypothesized that atypical APDs might alleviate oxidative stress in PC12 cells, thus protecting them from apoptosis. PC12 cells were seeded in plates or chambers for 24 hr and cultured for another 24 hr with olanzapine or quetiapine in the medium, and then the cells were cultured in the new medium containing Aβ25–35 and/or olanzapine, quetiapine, but not serum, for various periods. It was shown that cultures treated with olanzapine + Aβ25–35, or quetiapine + Aβ25–35, had significantly higher cell viabilities and lower rates of apoptosis compared with the cultures exposed only to Aβ25–35. In addition, the drugs blocked the activation of caspase‐3 caused by Aβ25–35. Furthermore, olanzapine and quetiapine prevented Aβ25–35‐induced overproduction of intracellular reactive oxygen species, Aβ25–35‐induced decrease in mitochondrial membrane potential, and Aβ25–35‐induced changes in activities of the key antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase. In consideration of the wealth of evidence linking oxidative stress to the pathophysiology of schizophrenia and AD, these findings give us a new insight into the therapeutic actions of atypical antipsychotics in patients with the disorders.

Effects of deuterium substitution on the catabolism of β-phenylethylamine: an in vivo study

Abstract: β‐Phenylethylamine (PE) hydrochloride injected intraperitoneally into rats was distributed evenly throughout the various regions of rat brain. Similarly, when a mixture of PE and α, α, β, β‐deuterated PE ([2H4]PE) was injected, no regional differences were observed in the ratios of the amounts of [2H4]PE and PE present; however, significantly more [2H4]PE than PE was present, although a 1:1 mixture had been administered. Further experiments in which the amounts of [2H4]PE and PE in whole rat brain, liver, and plasma were quantified confirmed this finding. The maximum [2H4]PE‐to‐PE ratios observed were 67 in whole brain 1 h after injection and 8 in liver and in plasma 45 min after injection. The whole brain [2H4]PE‐to‐PE ratios were decreased by pargyline pretreatment. Subsequent experiments showed that more α, α‐[2H4]PE than PE was present in whole brain, liver, and plasma of rats injected with an equimolar mixture of α, α‐[2H4]PE and PE. In contrast, β, β‐[2H4]PE was not enriched in comparison to PE under the same experimental conditions. We concluded that the basis for the enrichment of [2H4]PE and α, α‐[2H4]PE compared to PE was due to protection of the deuterated analogs from the actions of monoamine oxidase and perhaps aldehyde dehydrogenase; this protection led to pronounced deuterium substitution effects in vivo especially in the brain.

Aliphatic propargylamines: New antiapoptotic drugs

Two series of drugs, the aliphatic‐N‐methyl propargylamines and the aliphatic propargylamines, have been synthesised and shown to be specific, irreversible, and potent monoamine oxidase B inhibitors and neural rescue agents. In the latter case, an absolute stereochemical requirement for the R isomer exists. Both series of compounds have been shown, in numerous in vitro and in vivo experimental paradigms, to be effective neuronal rescue agents. Candidates from both series exhibit excellent bioavailability and pharmacokinetics and offer opportunities for treating neurodegenerative disorders and stroke and cognitive decline in companion animals. Drug Dev. Res. 42:150–156, 1997.

Atypical antipsychotics attenuate neurotoxicity of β-amyloid(25–35) by modulating Bax and Bcl-Xl/s expression and localization

We have demonstrated recently that atypical antipsychotics possess neuroprotective actions in H2O2‐mediated and serum‐withdrawal models of cell death. In the present study, we compared the ability of atypical and typical antipsychotics to protect against an insult mediated by Aβ(25–35), an apoptogenic fragment of the Alzheimers disease‐related β‐amyloid (Aβ) peptide. Treatment of PC12 cell cultures with Aβ(25–35) did not significantly alter total cellular expression levels of Bax, a proapoptotic Bcl‐2 family member, or levels of Bcl‐XL, an antiapoptotic analogue. Treatment with Aβ(25–35), however, did result in mitochondrial translocation of Bax, which effectively increased the mitochondrial ratio of Bax to Bcl‐XL. This relative increase in proapoptotic molecules was reduced by pretreatment with atypical (quetiapine and olanzapine) and typical (haloperidol) antipsychotics. We also observed a selective increase in proapoptotic Bcl‐XS immunodetection in haloperidol‐treated cells, which was evident particularly in the mitochondrial compartment. This increase in proapoptotic molecules may account for the lower neuroprotective potential of haloperidol, as determined by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium (MTT) reduction assay. The disparate neuroprotective effects of atypical and typical antipsychotics/neuroleptics may be due to their respective abilities to regulate pro‐ and anti‐apoptotic protein translocation and expression.

Release of some endogenous trace amines from rat striatal slices in the presence and absence of a monoamine oxidase inhibitor

The basal and 50 mM K+-stimulated release of m-tyramine (mTA), p-tyramine (pTA), tryptamine (TR) and phenylethylamine (PE) from striatal slices obtained from rats pretreated with a monoamine oxidase inhibitor (MAOI) was investigated. A K+-stimulated release of mTA and pTA was observed, but K+ did not stimulate either TR or PE release. The latter two amines, therefore, are unlikely to be conventional neurotransmitters in the rat striatum. The release of endogenous striatal pTA from control rats was also investigated. Veratridine stimulated endogenous pTA release, but 50 mM K+ did not. It is possible, therefore, that endogenous pTA can be released in a transmitter-like fashion.

Hydroxylation of β-phenylethylamine in the rat

Abstract ortho , meta and para Tyramine, as their dansyl derivatives, have been identified and quantitated by mass spectrometry in rat urine. After intraperitoneal injection of phenylethylamine labelled either with deuterium or tritium in the presence of pargyline, the amount of urinary tyramines excreted was 0.8% ( para , 0.74%; meta , 0.12%; ortho , 0.008%) of the injected dose. The advantages of involving stable isotopes and mass spectrometry in metabolic studies of pharmacologically active compounds is discussed.

Biosynthesis and excretion of meta and para tyramine in the rat

Abstract Meta and para tyramine, after conversion to their bis dansyl derivatives, have been identified and quantitated by mass spectrometry in rat urine. The daily para to meta excretion ratio of 1.69 ± 0.10 is quite constant which suggests an endogenous origin for these amines. Following intraperitoneal injection of [ 14 C] labelled dopa and dopamine more meta than para tyramine is excreted; after i.p. injection of para tyrosine only small amounts of para tyramine could be identified. This implies that some para tyramine is synthesised by a route other than dehydroxylation or decarboxylation.

Demonstration of an anti-oxidative stress mechanism of quetiapine: implications for the treatment of Alzheimer's disease.

We have shown that quetiapine, a new antipsychotic drug, protects cultured cells against oxidative stress‐related cytotoxicities induced by amyloid β (Aβ)25‐35, and that quetiapine prevents memory impairment and decreases Aβ plaques in the brains of amyloid precursor protein (APP)/presenilin‐1 (PS‐1) double‐mutant mice. The aim of this study was to understand why quetiapine has these protective effects. Because the cytotoxicity of both Aβ(25‐35) and Aβ(1‐40) requires fibril formation, our first experiments determined the effect of quetiapine on Aβ(25‐35) aggregation. Quetiapine inhibited Aβ(25‐35) aggregation in cell‐free aqueous solutions and blocked the fibrillar aggregation of Aβ(25‐35), as observed under an electron microscope. We then investigated why quetiapine inhibits Aβ(25‐35) aggregation. During the aggregation of Aβ(25‐35), a hydroxyl radical (OH•) was released, which in turn amplified Aβ(25‐35) aggregation. Quetiapine blocked OH•‐induced Aβ(25‐35) aggregation and scavenged the OH• produced in the Fenton system and in the Aβ(25‐35) solution, as analyzed using electron paramagnetic resonance spectroscopy. Furthermore, new compounds formed by quetiapine and OH• were observed in MS analysis. Finally, we applied Aβ(25‐35) to PC12 cells to observe the effect of quetiapine on living cells. Aβ(25‐35) increased levels of intracellular reactive oxygen species and calcium in PC12 cells and caused cell death, but these toxic effects were prevented by quetiapine. These results demonstrate an anti‐oxidative stress mechanism of quetiapine, which contributes to its protective effects observed in our previous studies and explains the effectiveness of this drug for Alzheimer’s disease patients with psychiatric and behavioral complications.

Potentiation of the behavioural effects of the antidepressant phenelzine by deuterium substitution

Phenelzine in the rat induced biphasic behavioural stimulation, which was profoundly potentiated by deuterium substitution. Doses of 12.5 or 25.0 mg/kg phenelzine had little or no effect on spontaneous activity, whereas the same doses of deuterated phenelzine produced hyperactivity, wetdog shakes, forepaw padding, splayed hind limbs, backward walking, sniffing and stereotyped grooming 2–12 h after injection. Similarly, the behavioural response induced by 50.0 mg/kg phenelzine was strongly potentiated by deuterium substitution. It appears likely that the increased behavioural response induced by deuterated phenelzine may be due to its greater potency as a monoamine oxidase inhibitor compared to undeuterated phenelzine. Since phenelzine is an antidepressant that is particularly efficacious in the treatment of severe anxiety, a deuterated analogue of the drug seems likely to be clinically useful.

Formation of β-phenylethylamine from the antidepressant, β-phenylethylhydrazine

Abstract To determine whether the monoamine oxidase inhibitor phenelzine was metabolized in vivo to produce β-phenylethylamine (PE) and p-hydroxy-β-phenylethylamine [p-tyramine (pTA)], a deuterated analogue, α,α,,β,β-2H-phenelzine (d4-phenelzine) was synthesized and injected i.p. into rats. In the first experiment, rat striata from d4-phenelzine-treated rats were analyzed for the presence of d4-PE and d4-pTA at a time at which phenelzine was known to cause particularly large increases in striatal pTA. While d4-PE was found to be present in these rat striata at a concentration equivalent to the endogenous PE, no d4-pTA was present. The amounts of d4-PE produced at various times after the i.p. injection of 50 mg/kg d4-phenelzine were measured; at 1 hr post-injection, 371 ± 60, 1295 ± 682 and 1242 ± 394 ng/g (mean ± S.E.M.) d4-PE were present in whole brain, liver and kidney. Rat urine collected for a 24-hr period after this treatment contained (mean ± S.E.M.) 88.5 ± 14.0 μg d4-PE. These results clearly indicate that the antidepressant phenelzine was metabolized in vivo to produce the trace amine PE.