Inhibition of alloxan-induced hyperglycaemia in mice by the pyridoindole stobadine

Development of Novel Indole-Based Bifunctional Aldose Reductase Inhibitors/Antioxidants as Promising Drugs for the Treatment of Diabetic Complications

Aldose reductase (AR, ALR2), the first enzyme of the polyol pathway, is implicated in the pathophysiology of diabetic complications. Aldose reductase inhibitors (ARIs) thus present a promising therapeutic approach to treat a wide array of diabetic complications. Moreover, a therapeutic potential of ARIs in the treatment of chronic inflammation-related pathologies and several genetic metabolic disorders has been recently indicated. Substituted indoles are an interesting group of compounds with a plethora of biological activities. This article reviews a series of indole-based bifunctional aldose reductase inhibitors/antioxidants (ARIs/AOs) developed during recent years. Experimental results obtained in in vitro, ex vivo, and in vivo models of diabetic complications are presented. Structure–activity relationships with respect to carboxymethyl pharmacophore regioisomerization and core scaffold modification are discussed along with the criteria of ‘drug-likeness”. Novel promising structures of putative multifunctional ARIs/AOs are designed.

Synthesis, structural characterization, antiradical and antidiabetic activities of copper(II) and zinc(II) Schiff base complexes derived from salicylaldehyde and beta-alanine

A series of copper(II) and zinc(II) complexes involving a tridentate O,N,O'-donor Schiff base derived from salicylaldehyde and beta-alanine {i.e. N-salicylidene-beta-alanine(2-), (L)}, having the composition [Cu(2)(L)(2)(H(2)O)].H(2)O (1), [Cu(L)(H(2)O)](n) (2), and [Zn(L)(H(2)O)](n) (3), have been prepared and characterized by elemental analyses, UV-visible (UV-VIS), FT-IR and ESI-MS spectra, and thermal analyses. Complexes 1 and 2 have been investigated by single crystal X-ray analysis and also by temperature dependent magnetic susceptibility measurements (294-80K). All prepared complexes have been evaluated by the antiperoxynitrite activity assay and alloxan-induced diabetes model. The significant antioxidant and antidiabetic activities have been found in the case of both copper(II) complexes 1 and 2. In spite of first two complexes, the zinc(II) complex 3, as well as the potassium salt of the ligand (KHL) showed only insignificant protective effect against the tyrosine nitration in vitro.

Antiradical activity of different copper(II) Schiff base complexes and their effect on alloxan-induced diabetes

Considering the important role of antioxidants in biological systems, the group of copper(II) complexes derived from salicylaldehyde and alpha- or beta-alanine and its thiourea derivative and copper(II) complexes derived from pyruvic acid and beta-alanine were studied. The antiradical activity of the tested compounds was studied by both in vitro and in vivo methods. The chemical methods based on inhibition of INT-formazane or 3-nitrotyrosine formation were used for the evaluation of SOD-mimic and antiperoxynitrite activity, respectively. In the case of in vivo activity evaluation, an alloxan-induced diabetes mellitus model in mice was used, the mechanism of action of alloxan being closely connected with the formation of free radicals selectively damaging the pancreatic beta-cells. Since all the substances studied showed different positive effects, it is obvious that they have not acted only as a source of copper(II) ions but their effect is related to their specific chelate structure. The obtained results are a contribution to the knowledge of copper(II) Schiff base complexes with ligands of aldimine or ketimine type and form the basis for further preclinical tests of these bioactive agents in biological models of oxidative stress.

Effects of known and potential antioxidants on animal models of pathological processes (diabetes, gastric lesions, allergic bronchospasm)

Highly reactive oxygen-free radicals are implicated in the pathogenic process of various diseases. Using an animal model of diabetes (alloxan-induced hyperglycaemia in mice), a model of gastric ulcer (indomethacin-induced gastric lesion in rats), and a model of bronchial asthma (ovalbumin-induced allergic bronchospasm in guinea pigs), a potential therapeutic effect was tested in known antioxidant drugs (alpha-tocopherol, ubiquinone), the thio-compound mesna, and drugs with a possible antioxidant effect (substances derived from the ergoline structure: 6-hydroxynicotinic acid and 4-hydroxypyridine). The pre-treatment with ubiquinone and 6-hydroxynicotinic acid almost completely prevented alloxan-induced hyperglycaemia (94 and 93% inhibition of hyperglycaemia, respectively). A weaker effect was shown by alpha-tocopherol and 4-hydroxypyridine (31 and 27% inhibition of hyperglycaemia, respectively). Mesna negligibly increased hyperglycaemia. 32% and 21% inhibitions of the number of gastric lesions were shown after administration of 6-hydroxynicotinic acid and alpha-tocopherol, respectively. Other drugs, most markedly mesna, aggravated gastric lesions. The most marked protective effect on ovalbumin-induced bronchospasm was exerted by 6-hydroxynicotinic acid (the pulmonary ventilation was increased by 84% in comparison with control group), while mesna and (alpha-tocopherol had a weaker effect (amelioration by 50 and 51 %, respectively). Ubiquinone and 4-hydroxypyridine aggravated pulmonary ventilation. The most marked protective effect in the animal models used was shown by 6-hydroxynicotinic acid.

Oxidative modification of serum albumin in an experimental glycation model of diabetes mellitus in vitro: effect of the pyridoindole antioxidant stobadine

Under conditions of an experimental in vitro glycation model, the pyridoindole antioxidant stobadine significantly inhibited glycation-related fluorescence changes of bovine serum albumin as well as the yield of 2,4-dinitrophenylhydrazine-reactive carbonyls with an efficacy comparable to that of the reference antioxidants Trolox C and 2-keto-4-methiolbutyric acid, and more efficiently than did aminoguanidine. Since stobadine did not affect the covalent binding of glucose, the protective effect may be explained by the ability of the drug to eliminate free radical intermediates of glyco-oxidation reactions, operative after the preceding glycation steps.

Evaluation of long-term administration of the antioxidant stobadine on exploratory behaviour in rats of both genders

Stobadine (STO) is a prospective neuro- and cardioprotective drug with high antioxidative properties. The aim of this study was to ascertain the effect of long-term administration of STO on exploratory behaviour and habituation processes in adult virgin female and male rats. Stobadine was administered by oral gavage in a single dose of 50 mg kg(-1) day(-1) for a total of 56 days. The animals were tested for exploratory behaviour-intensity of motor and vertical activity in an open field test in three blocks of measurements (initial screening; after 56 days of STO administration; and 28 days after the last treatment). The rate of decline of motor activity was evaluated during four consecutive days of testing (interrupted habituation). Administration of STO resulted in transient inhibition of exploratory behaviour in female rats without overtly detectable toxicity. Exploratory behaviour of males was not affected by STO treatment.

Antioxidant and pharmacodynamic effects of pyridoindole stobadine

1. The review summarizes the most important data known so far on chemistry, pharmacodynamics, toxicology and clinics of the investigational agent, pyridoindole stobadine. 2. Stobadine was shown to be able to scavenge hydroxyl, peroxyl and alkoxyl radicals, to quench singlet oxygen, to repair oxidized amino acids and to preserve oxidation of SH groups by one-electron donation. These effects originated from its ability to form a stable nitrogen-centered radical on indole nitrogen. Consequently, it was able to diminish lipid peroxidation and protein impairment under oxidative stress. 3. In various in vitro and in vivo animal models, stobadine was shown to diminish the impairment of the myocardium induced by mechanisms involving reactive oxygen species (e.g., myocardial infarction, hypoxia/ reoxygenation, catecholamine overexposure). 4. The neuroprotective effect of stobadine was demonstrated in a series of in vivo and in vitro models (brain in situ, brain slices, spinal cord, autonomic ganglia, etc.) during ischemia/reperfusion and hypoxia/ reoxygenation or in the presence of chemical systems generating free oxygen radicals, and so forth. Stobadine improved animal survival rate and synaptic transmission recovery, maintained SH tissue level and diminished lipid peroxidation as well as impairment of Ca-sequestering intracellular systems. 5. Oxidation of low-density lipoproteins (LDLs), which plays a major role in the development of atherosclerosis, was decreased by stobadine in vitro. Both lipid and protein (apo B) components of LDL were protected against Cu(2+)-induced oxidation by this agent. 6. Stobadine proved to be an effective protectant in models of free radical pathology in vivo, such as cyclophosphamide-, MNNG- or 60Co-induced mutagenesis and alloxan-induced hyperglycemia. 7. Besides other remarkable pharmacodynamic effects, stobadine exerts antidysrhythmic, local anesthetic, alpha-adrenolytic, antihistaminic, myorelaxant and antiulcerogenic actions. 8. Pharmacokinetic analyses demonstrated that stobadine was readily absorbed from the gastrointestinal tract. Thanks to its balanced lipo-hydrophilic properties, it was distributed over both water and lipid phases in biological tissues. It was shown to easily penetrate the blood-brain barrier. 9. Acute, subchronic and chronic toxicity studies in several animal species, as well as numerous analyses of embryotoxicity, teratogenicity, mutagenicity and genotoxicity, revealed only a negligible toxic potential of this agent. 10. Phase-one clinical study demonstrated safety of the compound. Only slight side effects--namely, a slight hypotension and a slight sedative effect--were observed subsequent to the highest dose used. In phase-two clinical study, the patients with angina pectoris treated for 4 weeks with stobadine showed a significant decrease in the frequency of anginal attacks, in the number of self-administrations of sublingual nitroglycerine and in plasma lipoprotein, cholesterol and triglyceride levels. A slight decrease in systolic and diastolic blood pressure also was observed. 11. It is suggested that stobadine may be considered a contribution to the search for new effective cardio- and neuroprotectants based on antioxidant or free radical scavenging mechanisms of action.

The pyridoindole antioxidant stobadine inhibited glycation-induced absorbance and fluorescence changes in albumin

We studied the effect of the pyridoindole antioxidant stobadine on glycation-induced absorbance and fluorescence changes in bovine serum albumin (BSA), used as a model protein. Incubation of BSA (4 mg/ml) with glucose (100-400 mM) in 0.12 M phosphate buffer, pH 7.4, in the presence of 100 microM Cu2+ at 37 degrees C resulted in a time-dependent increase of absorbance (320 nm) and fluorescence (excitation 350 nm, emission 415 nm). The process was found to be dependent on the presence of oxygen and transition metal ions, but equimolar iron could not fully substitute for the activity of copper. The glucose-induced chromo- and fluorophore formation was reduced significantly by stobadine. For 200 mM glucose, in 7- and 14-day incubations, 51%-60% inhibition was obtained at a stobadine concentration of 0.1 mM, and the effect leveled off at higher concentrations of the drug. No inhibition was observed with N-acetyl stobadine, a derivative with restricted antioxidant activity. Since stobadine did not affect the Amadori product formation determined by the thiobarbituric acid (TBA) method as 5-hydroxymethyl furfural (5-HMF) released in boiling oxalic acid, the inhibitory action of stobadine may be explained by its interference with metal-catalyzed oxidation reactions following after the glycation step. The results obtained suggest that antioxidant therapy could be used to limit the damage from adverse glycation-induced processes in diabetes mellitus.

The pyridoindole antioxidant stobadine prevents alloxan-induced lipid peroxidation by inhibiting its propagation

Under in vitro conditions, the pyridoindole stobadine inhibited alloxan-induced lipid peroxidation in a model biological membrane with the efficacy comparable with that of the standard Trolox. Intermediary alloxan radicals and hydroxyl radicals were not directly involved in the process of lipid peroxidation, however, the presence of iron chelate was a necessary prerequisite. Since stobadine did not affect the kinetics of alloxan redox-cycling in the presence of GSH, we suggest that the protective action of stobadine against the alloxan-induced lipid peroxidation was mediated predominantly by its ability to quench peroxyl radicals, inhibiting thus the propagation stage of the oxidative damage. The results also indicate that toxic effects of alloxan may well be mediated by mechanism(s) not involving hydroxyl radicals.