Pyridoindole stobadine is a potent scavenger of hydroxyl radicals

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.

Substituted pyridoindoles as biological antioxidants: drug design, chemical synthesis, and biological activity

Great effort has been devoted to design and synthesize biologically active and pharmacologically acceptable antioxidants. Although a number of efficient antioxidant compounds have been designed, synthesized, and tested in animals, none of them have demonstrated sufficient efficacy in human clinical trials without undesirable side effects. Thus new pharmacologically applicable antioxidants have been sought for. Substituted pyridoindoles represent a broad spectrum of pharmacologically active substances including highly effective scavengers of reactive oxygen species. The hexahydropyridoindole scaffold represents a valuable lead with a great deal of knowledge on molecular mechanisms of free radical scavenging, on bioavailability and toxicity. Its modification may yield congeners tailored according to specific requirements for antiradical efficacy, lipophilicity, and basicity, meeting the aim of providing a pharmacologically practicable antioxidant drug as exemplified by the novel derivative SMe1EC2.

Antioxidant action of the hexahydropyridoindole SMe1EC2 in the cellular system of isolated red blood cells in vitro

OBJECTIVES

The subject of this study was the hexahydropyridoindole compound SMe1EC2 with reported antioxidant and neuroprotective effects and low toxicity. In this study, the antioxidant action of SMe1EC2 was investigated in a greater detail in the system of isolated rat erythrocytes.

METHODS

First, the compound was subjected to the DPPH test. Second, the overall antioxidant action of the compound was studied in the cellular system of isolated rat erythrocytes oxidatively stressed by free radicals derived from either the hydrophilic azoinitiator AAPH or the lipophilic t-BuOOH, and compared with reference antioxidants.

RESULTS

The DPPH test revealed significant antiradical activity of SMe1EC2 comparable with that of the standard trolox. In the cellular system, SMe1EC2 protected red blood cells against free radical-initiated hemolysis. The overall antioxidant efficacy of SMe1EC2 relative to the reference antioxidant stobadine was strongly affected by the lipophilicity of the initiating free radical species.

CONCLUSIONS

The results proved high antiradical efficacy of SMe1EC2. In the system of t-BuOOH/isolated erythrocytes, a model cellular system of endogenously generated peroxyl radicals, SMe1EC2 significantly exceeded the parent stobadine in its antioxidant action. Considering the reported results of preclinical studies of SMe1EC2 showing its profound neuroprotective effects and low toxicity, the compound represents an example of a potential pharmacologically practicable antioxidant drug.

Ferritin oxidation and proteasomal degradation: Protection by antioxidants

The accumulation of oxidatively damaged proteins is a well-known hallmark of aging and several neurodegenerative diseases including Alzheimer's, Parkinson's and Huntigton's diseases. These highly oxidized protein aggregates are in general not degradable by the main intracellular proteolytic machinery, the proteasomal system. One possible strategy to reduce the accumulation of such oxidized protein aggregates is the prevention of the formation of oxidized protein derivatives or to reduce the protein oxidation to a degree that can be handled by the proteasome. To do so an antioxidative strategy might be successful. Therefore, we undertook the present study to test whether antioxidants are able to prevent the protein oxidation and to influence the proteasomal degradation of moderate oxidized proteins. As a model protein we choose ferritin. H2O2 induced a concentration dependent increase of protein oxidation accompanied by an increased proteolytic susceptibility. This increase of proteolytic susceptibility is limited to moderate hydrogen peroxide concentrations, whereas higher concentrations are accompanied by protein aggregate formation. Protective effects of the vitamin E derivative Trolox, the pyridoindole derivative Stobadine and of the standardized extracts of flavonoids from bark of Pinus Pinaster Pycnogenol and from leaves of Ginkgo biloba (EGb 761) were studied on moderate damaged ferritin.

Electrophoretic analysis of oxidatively modified eye lens proteins in vitro: implications for diabetic cataract

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of eye lens proteins showed that both progression of diabetic cataract in rats in vivo and precipitation of soluble eye lens proteins stressed by free radicals in vitro were accompanied by significant protein cross-linking. There was a noticeable contribution of disulfide bridges to protein cross-linking in diabetic eye lens in vivo. In contrast, under conditions in vitro, when eye lens proteins were exposed to hydroxyl or peroxyl radicals, we showed that the participation of reducible disulfide linkages in the formation of high molecular mass products was markedly lower. These in vivo--in vitro differences indicate that the generally accepted role of reactive oxygen species in diabetic cataractogenesis may be overestimated in connection with the processes of protein cross-linking.

Antioxidants prevented oxidative injury of SR induced by Fe2+/H2O2/ascorbate system but failed to prevent Ca2+-ATPase activity decrease

Dysfunction of sarcoplasmic reticulum (SR) Ca2+-ATPase induced by oxidative stress may be a contributing factor to the development of serious age related diseases. Incubation of sarcoplasmic reticulum (SR) vesicles of rabbit skeletal muscles with Fe2+/H2O2/ascorbate decreased the SH group content of SR approximately to 35% and Ca2+-ATPase activity to 50% of control not oxidized sample. Protein carbonyls increased twofold, lipid peroxidation was also significantly elevated. The antioxidant effects of trolox, the pyridoindole derivative stobadine and of the standardized extracts from bark of Pinus Pinaster PycnogenolR (Pyc) and from leaves of Ginkgo biloba (EGb 761) were studied on oxidatively injured SR. All antioxidants exerted preventive effects against the oxidized lipids and protein SH groups of SR vesicles. Trolox and stobadine did not influence protein carbonyl formation, while flavonoid extracts prevented carbonyl generation, probably by binding to protein. The preventive effects of the antioxidants studied on lipids and protein SH groups were however not associated with protection of Ca2+-ATPase activity. Stobadine and trolox exerted no effect on enzyme activity, Pyc and EGb 761 enhanced the inhibitory effect of Ca2+-ATPase activity in oxidatively injured SR. Concluding, under the conditions of oxidative stress induced by Fe2+/H2O2/ascorbate against SR of rabbit skeletal muscle, the agents studied demonstrated antioxidant effects yet failed to protect Ca2+-ATPase activity.

Pyridoindole antioxidant stobadine protected bovine serum albumin against the hydroxyl radical mediated cross-linking in vitro

On exposure to free radicals generated by the Fenton reaction system of Fe(2+)/EDTA/H(2)O(2)/ascorbate, bovine serum albumin (BSA), used as a model of water-soluble protein, was losing its water solubility depending on the concentration of the chelated iron. The precipitate was found irreversibly insoluble even in concentrated urea. In the soluble fraction, SDS-PAGE analysis proved the presence of dimers and trimers of BSA, accompanied by enhanced bityrosine fluorescence. The pyridoindole antioxidant stobadine inhibited the process of albumin insolubilization in a concentration-dependent manner, the protective effect being more efficient than that of 2-keto-4-methiolbutyric acid (KMBA). Stobadine was, however, less effective than trolox. The inhibitory effect of the antioxidants, expressed as IC(50), correlated well with the reciprocal values of corresponding second order rate constants for scavenging OHz.rad; radicals. The results indicated that the insolubilization of BSA induced by the Fenton system of Fe(2+)/EDTA/H(2)O(2)/ascorbate was caused by OHz.rad; radical mediated cross-linking of the albumin. The model system proved to be suitable for convenient testing of OHz.rad; radical scavenging ability of new antioxidants in a non-lipid environment.

Extraction and chromatographic separation methods in pharmacokinetic studies of Stobadine--an indole-related antioxidant and free-radical scavenger

This overview provides comprehensive information on the most relevant results of Stobadine preclinical disposition studies. In order to investigate pharmacokinetic processes of the drug in rats, dogs and in human volunteers, several bioanalytical assays based on radiometric, spectrofluorometric, as well as chromatographic determination methods were developed and implemented. In small laboratory animals, the drug absorption, distribution, metabolism and elimination were investigated by administering 3H-labeled Stobadine. Spectrofluorometry was used alternatively for the determination of cold/unlabeled Stobadine in extracts of biomaterials sampled from larger animal species. The chromatographic separation methods proved, however, to be the most advantageous for determining details of the drug disposition and fate in the body.

Stobadine: bellwether of a broader view of drug actions

Stobadine was recognized early in its development as having antioxidant properties. A number of laboratories found associations between the antioxidant properties of stobadine and its potential beneficial effects. We found that stobadine acted as an antioxidant in a modification of an oxygen radical absorbance capacity (ORAC) assay. Similar results were observed with other drugs, including tirilazad and pramipexole. We suggest that stobadine and certain other drugs exhibit antioxidant properties in both hydrophilic and hydrophobic environments. Other drugs have been developed for their antioxidant properties and some currently marketed drugs have antioxidant properties. Although they may not have been explicitly sought during development, at least some of the beneficial effects may be related to antioxidant properties and/or scavenging of free radicals. Because stobadine was one of the first drugs for which useful properties were associated with its antioxidant actions, stobadine may be seen as a bellwether of a broader view of pharmacological actions--a view that encompasses antioxidant properties as a useful basis of therapeutic effects.

Stobadine protects against ischemia-reperfusion induced morphological alterations of cerebral microcirculation in dogs

Vascular diseases of the CNS are a major medical, social and economic problem. From the number of causes leading to nervous malfunction and damage, ischemia is most prominent. Thus, neuronal protection from ischemic damage may provide significant preventive and treatment potential. This study was designed to test possible protective effects of stobadine in a canine model of global cerebral ischemia. Seven minute ischemia was induced by four vessel ligation and maintained using a controlled systemic hypotension. Stobadine pretreated animals were infused with 2 mg/kg stobadine 30 minutes prior to ischemia, while control animals received vehicle. After a 24 hour reperfusion phase, animals were perfusion-fixed and evaluated using electron microscopy. Stobadine pretreated dogs showed much less damage to both endothelial lining and pericapillary structures of the blood-brain barrier. This included preservation of cellular shape of the endothelium, patency of microvessels, lack of intraluminal blebs material, near normal cytoplasmic osmiophilia, decreased thickness of endothelial basement membrane, significantly less edema of astrocyte end-feet, and preservation of fine mitochondrial structure compared to the control group. Ischemic neuronal changes were observed less frequently in the stobadine pretreated group. In summary, we conclude that stobadine protects both cerebral microcirculation and neurons from injury induced by global cerebral ischemia and reperfusion.

Antimutagenic effects of stobadine: review of results

The paper summarizes the results of our previously published studies testifying the hypothesis of the antimutagenic effect of stobadine (STB) in vivo and in vitro. The micronucleus test was used in in vivo experiments with ICR mice. Oral pretreatment with STB significantly decreased the mutagenic effect of cyclophosphamide (CP) in a concentration-dependent way. The protective effect of STB was confirmed in fetuses of CP-treated mice. STB pretreatment exerted also a radioprotective effect in Co60-irradiated mice. The ineffectiveness of STB posttreatment is indicative of its effect operative in the initiation of mutagenesis and of its radical-scavenging mechanism. The ability of STB to reduce N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)induced gene mutations and MNNG-induced calcinosis/Raynaud's phenomenon/esophageal dysmotility/sclerodactyly/telangiectasia variant of scleroderma (CREST)-positive and CREST-negative micronuclei in V79 cells was tested in in vitro experiments. We found that this drug reduced the level of both gene mutations and CREST-negative micronuclei mainly if given as pretreatment before exposure of cells to MNNG. We conclude that STB may have inhibited mutagenesis not only by scavenging reactive oxygen species, but also as a result of induction of metabolic enzymes, which reduced the level of DNA lesions.

Effect of stobadine on oxygen free radical generation in stimulated human polymorphonuclear leukocytes

The generation both superoxide and a mixture of reactive oxygen species was recorded in a suspension of human polymorphonuclear leukocytes stimulated with phorbol myristate acetate. While stobadine dose-dependently decreased chemiluminescence, only its highest concentration used reduced significantly superoxide generation. The results suggest that stobadine is a more effective scavenger of free radicals rather than a quencher of superoxide anion.

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.

Iron-induced inhibition of Na+, K(+)-ATPase and Na+/Ca2+ exchanger in synaptosomes: protection by the pyridoindole stobadine

The effect of oxidative stress, induced by Fe(2+)-EDTA system, on Na+,K(+)-ATPase, Na+/CA2+ exchanger and membrane fluidity of synaptosomes was investigated. Synaptosomes isolated from gerbil whole forebrain were incubated in the presence of 200 microM FeSO4-EDTA per mg of protein at 37 degrees C for 30 min. The oxidative insult reduced Na+,K(+)-ATPase activity by 50.7 +/- 5.0% and Na+/Ca2+ exchanger activity measured in potassium and choline media by 47.1 +/- 7.2% and 46.7 +/- 8.6%, respectively. Membrane fluidity was also significantly reduced as observed with the 1,6-diphenyl-1,3,5-hexatriene probe. Stobadine, a pyridoindole derivative, prevented the decrease in membrane fluidity and in Na+/Ca2+ exchanger activity. The Na+,K(+)-ATPase activity was only partially protected by this lipid antioxidant, indicating a more complex mechanism of inhibition of this protein. The results of the present study suggest that the Na+/Ca2+ exchanger and the Na+,K(+)-ATPase are involved in oxidation stress-mediated disturbances of intracellular ion homeostasis and may contribute to cell injury.

Effect of stobadine on Cu(++)-mediated oxidation of low-density lipoprotein

The pyridoindole derivative stobadine [(-)-cis-2,8-dimethyl-2,3,4,4a,5,9b-hexahydro-1H-pyrido(4,3b) indole] has been described as a drug with antihypoxic and antiarrhythmic cardioprotective properties. The antioxidative properties of this compound were studied during Cu(++)-mediated low-density lipoprotein (LDL) oxidation. Stobadine (concentration 0-5 microM) prolonged the lag phase (in min produced by one molecule antioxidant per LDL particle) as measured by diene formation more effectively than did ascorbate, trolox, or alpha-tocopherol. It also has the ability to decrease the rate of diene formation during the propagation phase very efficiently. Diene formation, Trp destruction, and alpha-tocopherol consumption were measured in the presence and absence of stobadine. Stobadine (10 microM) did not influence tocopherol consumption during oxidation and the Trp fluorescence quenching of Cu++ was not influenced by this compound. From these results, as well as polarographic measurements, we conclude that the antioxidative effect of stobadine is not simply a result of Cu(++)-ion complexation. In contrast to ascorbate, this compound is stable in the presence of Cu++. Stobadine inhibits the oxidation of LDL-Trp residues very efficiently via its radical scavenging properties, and may even have the ability to reduce Trp radicals to tryptophan. The concentration of stobadine used for LDL oxidation was in the range found in plasma (stobadine given p.o. in human and rats results in plasma concentrations between 0.2-3.9 microM.

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.

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

Alloxan-induced hyperglycaemia was used as a model of free radical pathology to test the antioxidant activity of the pyridoindole drug, stobadine, in the intact mouse. Stobadine was injected intraperitoneally in a dose range 7.5-60 mg/kg prior to intravenous injection of alloxan (50 mg/kg), and blood glucose concentration 72 hr after alloxan administration was used as an index of alloxan toxicity. Stobadine efficiently suppressed the alloxan-induced hyperglycaemia in a dose-dependent manner. This protection against the diabetogenic effect of alloxan is consistent with the high efficacy of stobadine to scavenge hydroxyl radicals.

Change in fluidity of brain endoplasmic reticulum membranes by oxygen free radicals: a protective effect of stobadine, alpha-tocopherol acetate, and butylated hydroxytoluene

Effect of various oxygen free radical generating systems and an oxidant H2O2 on brain endoplasmic reticulum (ER) membrane fluidity was examined using fluorescent membrane probe 1,6-diphenyl-1,3,5-hexatriene, DPH. The relative potency of free radical generating systems to decrease membrane fluidity increased in this order: FeCl3-EDTA, FeSO4-EDTA, FeSO4-EDTA/hydrogen peroxide. Potency to decrease membrane fluidity correlated well with these systems' potencies to induce lipid peroxidation, as detected by conjugated diene formation. Treatment of ER membranes with H2O2 had no effect on fluidity or conjugated diene formation. Using the two most potent free radical generating systems, FeSO4-EDTA and FeSO4-EDTA/hydrogen peroxide, a protective effect of the novel antihypoxic and antiarrhytmic drug stobadine was tested. Stobadine and two well-known antioxidants, alpha-tocopherol acetate and butylated hydroxytoluene, demonstrated the ability to prevent free radical induced alterations in ER membrane fluidity. These results provide new evidence of stobadine's protective effect on membranes attacked by oxygen free radicals.

Protective effect of stobadine, a pyridoindole antioxidant, in hypoxia-reoxygenation injury of ganglionic and hippocampal neurotransmission

Hypoxia (HYP) followed by reoxygenation (REOX) occurs frequently in the pathophysiology of the CNS. Free oxygen radicals (FOR) may participate in cerebral injury under such circumstances. Pharmacological control of the generation and/or subsequent effects of FOR by new effective compounds might contribute to the treatment of disorders such as stroke and cerebral trauma. Effects of stobadine, a pyridoindole antioxidant that is able to interact with some FOR, were analyzed on synaptic transmission in rat superior cervical ganglia and hippocampal slices during HYP-REOX procedure in vitro. The amplitude of compound action potential in the ganglion evoked by supramaximal electrical stimulation of preganglionic nerve was reduced to approximately 20% of the control value during HYP (90 min). The action potential did not recover during REOX (60 min). Stobadine (10 mM) applied before, during, and after HYP, did not change the HYP-induced inhibition; however, a significant recovery of transmission (to 78.5% +/- 8.3) occurred during REOX. A similar effect was observed in the presence of the antioxidant Trolox (0.2 mM), a derivative of alpha-tocopherol. Stobadine, in concentrations of > 30 microM inhibited ganglionic transmission in a concentration-dependent manner. HYP lasting more than 2-3 min fully depressed field action potentials evoked in hippocampal CA1 region neurons by supramaximal electrical stimulation of Schäffer collaterals. If HYP exceeded 8 min, transmission did not recover during REOX. Stobadine (10 microM) applied during HYP significantly enhanced the probability of transmission recovery in the REOX period. Some preparations recovered following HYP lasting as long as 13-15 min. On applying the compound before, during, and after HYP that lasted for 8 min, the transmission recovery was 72.6% +/- 21.8 of the control value, compared to only 16.1% +/- 12.7 in the untreated preparations. In concentrations ranging from 0.3-1.73 mM, stobadine inhibited hippocampal transmission. Stobadine proved to be an effective agent in the protection of synaptic transmission against HYP-REOX-induced injury in both neuronal preparations studied in vitro. This effect might be linked to the antioxidant and free radical scavenging effects of stobadine.

Radioprotective effect of stobadine in the mouse micronucleus test

Induction of micronuclei was studied 40 h post irradiation in peripheral blood reticulocytes of male mice treated or not with stobadine dipalmitate (70.07 mg/kg body weight) at two time intervals (2 h or 1 h) prior to and immediately after 6.5 Gy 60Co exposure. A significant decrease of micronucleated reticulocytes was observed in the group of mice pretreated 2 h (P < 0.05) or 1 h (P < 0.01) before irradiation. 60Co irradiation followed by treatment with stobadine did not lead to the same protective effect in the micronucleus assay. It is therefore assumed that a radical-scavenging mechanism must be involved in radioprotection by stobadine.

In vitro studies on the interaction of the pyridoindole antioxidant stobadine with rat liver microsomal P450

1. Stobadine, a pyridoindole antioxidant agent, elicited medium affinity, low capacity interaction with type I binding sites of the hepatic microsomal cytochromes P450 derived from control and acetone-pretreated rats. Reverse type I interaction of low affinity and low capacity was observed in microsomes from phenobarbital-treated rats. 2. Stobadine led to an increase of H2O2 production when added to liver microsomes derived from differently pretreated rats in an NADPH-dependent process with concomitantly increased oxygen consumption. 3. Stobadine, at concentrations stimulating H2O2 formation, was found to prevent NADPH-induced microsomal lipid peroxidation, assessed as thiobarbituric acid-reactive product accumulation. 4. Only a weak inhibitory effect of stobadine on either NADPH- or cumene hydroperoxide-dependent aminopyrine N-demethylation and aniline hydroxylation was observed in microsomes from control and phenobarbital-pretreated rats. An approximately 10 times higher inhibitory potency towards aminopyrine N-demethylase activity was observed in acetone-pretreated rats. 5. In spite of the direct interaction of stobadine with microsomal P450, the compound only marginally affected aminopyrine and aniline metabolism both by monooxygenase and peroxidase modes of action of the P450 enzyme system. The potent antioxidant activity of stobadine was not diminished by the ability of the drug to stimulate the oxidase function of P450.

Interaction of the pyridoindole stobadine with peroxyl, superoxide and chromanoxyl radicals

The pyridoindole derivative stobadine [(-)-cis-2,8-dimethyl-2,3,4,4a,5,9b-hexahydro-1H-pyrido(4,3b)indole] has been described as a drug with antihypoxic and antiarrhythmic cardioprotective properties. Here its reactivity with peroxyl radicals in liposomes using a lipid-soluble azo-initiator of peroxyl radicals, 2,2'-azo-bis(2,4-dimethyl-valeronitrile) (AMVN), was examined. Stobadine exerted scavenging as evidenced by the inhibition of: (i) cis-parinaric acid fluorescence decay (half-maximal effect at 20 microM), or (ii) luminol-sensitized chemiluminescence (half-maximal effect at 33 microM). In rat liver microsomes, stobadine was equally efficient in inhibiting lipid peroxidation induced by lipid-soluble (AMVN) or water-soluble 2,2'-azo-bis(2-aminopropane)-HCl (AAPH), azo-initiators of peroxyl radicals with half-maximal effect at 17 microM. Stobadine partitions in a two-phase system (octanol-water) with the coefficient log P = 0.57 +/- 0.03, explaining its ability to quench peroxyl radicals in both lipid and aqueous phases. Stobadine is not an efficient scavenger of superoxide radicals. The second order rate constant for the reaction of stobadine with superoxide was estimated to be 7.5 x 10(2) M-1 sec-1 as measured by superoxide-induced lucigenin-amplified chemiluminescence. ESR measurements showed that stobadine in liposomes does not reduce the chromanoxyl radical of a vitamin E homologue with a 6-carbon side-chain, 2,5,7,8-tetramethyl-2-(4'-methylpentyl)chroman-6-ol(chromanol++ +-alpha-C6), in agreement with pulse-radiolysis results obtained using Trolox in homogeneous solution (Steenken et al., Chem Res Toxicol 5: 355-360, 1992). Stobadine increased the magnitude of the chromanoxyl and ascorbyl radical ESR signal generated by lipoxygenase+arachidonate. This was interpreted to be due to the interaction of stobadinyl radicals with the chromanol ring and ascorbate, respectively. It is suggested that high reactivity of stobadine radicals requires the presence of reducing antioxidants (vitamin E, vitamin C) to exhibit its antioxidant effects in physiological systems.