Potassium channel activators: pharmacological methods, models, and structure-activity relationships

Diazoxide in the treatment of schizophrenia: novel application of potassium channel openers in the treatment of schizophrenia

OBJECTIVE

Schizophrenia is a very common disorder, affecting 1% of the world population. People who develop schizophrenia experience severe suffering and approximately 10% commit suicide. The causes of schizophrenia are still largely unknown. The relative ineffectiveness of dopamine antagonists to treat some symptoms of schizophrenia has promoted many investigators to postulate the involvement of the neuronal system in the pathophysiology of this disease. It has been suggested that the dopamine-coupled adenosine triphosphate (ATP)-sensitive channels may function by hyperpolarizing cells during metabolic stress, a function that may be disrupted in people with schizophrenia. Therefore, application of potassium channel openers/activators may be beneficial in schizophrenia. Diazoxide is a benzothiadiazine derivative related to the thiazide diuretics and a potassium channel opener. The purpose of the present investigation was to assess the efficacy of diazoxide, as an adjuvant agent in the treatment of schizophrenia.

METHODS

Forty-two patients who met the DSM IV criteria for chronic schizophrenia completed the study. Patients were randomized to haloperidol 20 mg/day plus diazoxide 200 mg/day (21 subjects) or to haloperidol 20 mg/day plus placebo (21 subjects) in this 8-week double-blind study.

RESULTS

Although both protocols significantly decreased the score of the positive, negative and general psychopathological symptoms over the trial period, the combination of haloperidol and diazoxide showed a significant superiority over haloperidol alone in the treatment of positive and general psychopathology symptoms as well as positive and negative syndrome scale (PANSS) total scores. In addition, in the diazoxide group a rapid onset of action on the positive symptoms was observed in week 2, whereas in the placebo group there was no significant effect at week 2. No significant differences were observed between the two protocols on the negative scores.

CONCLUSION

The results of this study present a novel application for potassium channel openers/activators in the neuropsychiatric disorders and diazoxide may be an effective adjuvant agent in the management of schizophrenia.

Molecular modeling and QSAR studies on K(ATP) channel openers of the benzopyran type

The present paper describes our molecular modeling and quantitative structure-activity relationships (QSARs) studies on K(ATP) channel openers (KCOs) of the benzopyran type. In the first part we performed molecular modeling investigations with seven benzopyrans, varied at the C3- and C4-positions, in order to understand which molecular features at these positions are essentially effecting the biological activity. The impact of C6-substitution on biological activity was studied in the second part via HANSCH analysis. For this purpose physicochemical properties (charge distributions, lowest unoccupied molecular orbital (LUMO) energies, desolvation energies, volumes and dipole moments) were calculated for a set of 50 C6-varied benzopyrans. A QSAR equation was developed showing a relationship between the vasodilator activity and the direction of the dipole vector of the ligands. The conclusion can be drawn that a direct interaction between the C6-substituents and the receptor structure is not of primary importance. However, the substitutents influence the orientation of the whole ligand approaching the binding site. An unfavorably oriented ligand cannot bind to the binding site, thus exhibiting weak activity.

Nicorandil analogues containing NO-donor furoxans and related furazans

The synthesis and in vitro vasodilating properties of hybrid compounds in which furoxan (1,2,5-oxadiazole 2-oxide) moieties, endowed with different NO-donor properties, were substituted for the nitroxy function of Nicorandil are reported. The corresponding cyanoguanidine analogues are also considered. This approach has led to a series of vasorelaxing compounds devoid of affinity for K(ATP) channels, whose activity is prevalently due to their ability to activate sGC, at the concentrations of the experiments. Related furazan (1,2,5-oxadiazole) derivatives, unable to release nitric oxide were also prepared and studied for control. The amide analogues of Nicorandil display feeble vasorelaxing action not involving the activation of K+ channels, while in the guanidine analogues, this mechanism seems to underlie this action.

Novel potassium channel openers. Part 4: transformation of the 1,4-benzoxazine skeleton into 1,4-benzothiazine, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroquinoxaline, indoline, and 1,5-benzoxazepine

As part of a search for a new potassium channel opener, the 1,4-benzoxazine skeleton derived from the benzopyran skeleton of cromakalim, was transformed into other fused rings such as 1,4-benzothiazine, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroquinoxaline, indoline, and 1,5-benzoxazepine. The 1,4-benzothiazine derivative displayed approximately 20 times more potent vasorelaxant activity than cromakalim.

K+ channel openers and suppression of airway hyperreactivity

Openers of ATP-sensitive K+ channels (K(ATP) channels) can reduce obstruction to airflow by suppressing hyperreactivity of intact airways. This property can be observed in hyperreactive animals with doses that are insufficient to relax airway smooth muscle in situ in normal animals. Hence, the potency of openers of K(ATP) channels as inhibitors of bronchospasm is greater in hyperreactive than in normal animals. A closely analogous property has been described in clinical and laboratory studies of established anti-asthma drugs. Such findings raise the possibility that the therapeutic benefit of these drugs may depend upon an opening of K+ channels, either directly or indirectly. In this review, John Morley suggests that compounds that open K+ channels and impair expression of airway hyperreactivity in the absence of direct smooth muscle spasmolysis will provide a novel approach to symptomatic therapy in asthma.