Panos N. Kourounakis

Effect of hydroxyethyl rutosides and related compounds on lipid peroxidation and free radical scavenging activity. Some structural aspects.

Abstract— Four hydroxyethyl rutosides, 7,3′,4′‐trihydroxyethyl quercetin, quercetin and a commercial standardized mixture of hydroxyethyl rutosides were investigated on non‐enzymatic lipid peroxidation, for hydroxyl radical scavenging activity and interaction with 1,1‐diphenyl‐2‐picrylhydrazyl stable free radical (DPPH). It was found that the tested compounds exhibited a considerable inhibition of microsomal lipid peroxidation. They were less active than the reference compound quercetin, and this was attributed to their structural characteristics. They were also found to be potent hydroxyl radical scavengers and to interact with DPPH. As hydroxyl radical scavengers, they were more potent than the known hydroxyl radical scavengers mannitol and dimethyl sulphoxide. These properties could be considered as a useful and exploitable combination.

Synthesis and pharmacological evaluation of novel derivatives of anti-inflammatory drugs with increased antioxidant and anti-inflammatory activities

The role of reactive oxygen species in inflammatory processes has been well documented, while several antioxidant compounds have been shown to exhibit anti‐inflammatory activity. We designed novel compounds as potential agents that combine enhanced antioxidant and anti‐inflammatory activities. Derivatives of indomethacin, diclofenac, tolfenamic acid, and ibuprofen, four widely used nonsteroidal anti‐inflammatory drugs, with cysteamine, a polar antioxidant molecule, were synthesized. The compounds were evaluated for their effect on free radical processes (protection against rat hepatic microsomal lipid‐peroxidation and interaction with the stable free radical 1,1‐diphenyl‐2‐picrylhydrazyl), as well as on carrageenan‐induced inflammation (mouse paw edema inhibition). Furthermore, ulcerogenicity tests in rats were performed in order to evaluate the gastrointestinal irritation of the novel indomentacin derivative. It was found that all compounds were very potent antioxidants in vitro; they could inhibit lipid peroxidation very significantly, having IC50 values ranging from 55 to 510 μM, while they could also interact ∼90% with DPPH at equimolar concentrations. We attribute these activities to their sulfhydryl group, as well as to their increased lipophilicity compared to cysteamine. Furthermore, the derivatives demonstrated significant anti‐inflammatory activity, comparable to that of the parent molecules, while they showed significantly reduced ulcerogenic potency. Our results indicate that the combined pharmacological properties of these new derivatives may prove useful for the design and development of novel cytoprotective/anti‐inflammatory molecules with potentially important therapeutic applications. Drug Dev. Res. 47:9–16, 1999.

Alkannin and shikonin: effect on free radical processes and on inflammation - a preliminary pharmacochemical investigation.

Alkannin and shikonin, two natural products from Alkanna tinctoria and Lithospermum erhythrorhizon (Boraginaceae), are used in folk medicine where they are claimed to possess, among other properties, wound healing and anti‐inflammatory activity. We investigated, together with the structurally related naphthazarin, their in vitro antioxidant and hydroxyl radical scavenging activity as well as their in vivo antiinflammatory activity. I was found that all examined compounds significantly inhibited in vitro lipid peroxidation of ra hepatic microsomal membranes, competed with DMSO for free hydroxyl radicals, and reduced inflammation (mouse paw edema induced by FCA) very efficiently.The examined compounds proved equal or superior to the common reference compounds for each of these properties. I is concluded that the claimed and/or proven actions of alkannin and shikonin are attributable at least partly to their intervention in free radical processes.

Antioxidant activity of guaiazulene and protection against paracetamol hepatotoxicity in rats

The effect of guaiazulene, a lipophilic azulene derivative widely found in nature, on radical‐mediated processes is examined. The ability of guaiazulene to inhibit rat hepatic microsomal membrane lipid peroxidation and to scavenge hydroxyl radicals, as well as to interact with 1,1‐diphenyl‐2‐picrylhydrazyl radical (DPPH), was estimated.

Reduction of gastrointestinal toxicity of NSAIDs via molecular modifications leading to antioxidant anti-inflammatory drugs

Reactive oxygen species and free radical reactions are related to several pathologic conditions including inflammation and gastric ulceration. The latter is the major undesired side-effect of almost all NSAIDs. Since this effect of NSAIDs is greatly influenced not only by the type of cyclooxygenase which is inhibited but also by the acidic nature of the molecule, we considered it interesting to modify their structure in such a way that it would lead to an antioxidant, neutral molecule or a molecule with greatly reduced acidic character. Thus, we synthesized amide derivatives of four well-known NSAIDs, i.e. diclofenac acid, tolfenamic acid, ibuprofen and indomethacin, with cysteamine, a well-known antioxidant. The synthesized derivatives, with demonstrated good anti-inflammatory and antioxidant activities, showed very significant reduction of ulcerogenicity in the investigation of gastrointestinal (GI) toxicity. As indices of ulcerogenic toxicity in rats, we used the mortality (%), the incidence of GI ulcers (%), body weight reduction (g/100 g BW) and the incidence of melena. All amide derivatives of the NSAIDs with cysteamine were almost non-toxic in the GI tract, under our experimental conditions, in contrast to their parent NSAIDs. These results are attributed to the acquired antioxidant activity as well as to the reduction of acidic character compared with the parent compounds. Therefore, it can be concluded that the combination of these two properties, anti-inflammatory and antioxidant activity, with a simultaneous drastic reduction of acidic character, may lead to the development of novel, useful anti-inflammatory and cytoprotective pharmacomolecules, with potentially important therapeutic applications.

Antioxidant potential of natural and synthesised polyprenylated hydroquinones.

The metabolites 2-octaprenyl-1,4-hydroquinone (1) and 2-(24-hydroxy)-octaprenyl-1,4-hydroquinone (2), isolated from the sponge Ircinia spinosula, along with a series of synthetic derivatives, were evaluated for their antioxidant capacity, in order to establish a potential relationship between structural characteristics and antioxidant activity. The antioxidant potential of both natural and synthesised compounds was evaluated in vitro by their ability: (1) to interact with the stable free 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and (2) to inhibit the peroxidation, induced by the Fe(++)/ascorbate system, of heat inactivated hepatic microsomal membrane lipids. Metabolite 1 presented a strong interaction with DPPH and had a moderate effect on lipid peroxidation, while metabolite 2 interacted extensively with DPPH and exhibited a significant effect against lipid peroxidation. All derivatives retaining the free 1,4-hydroquinone system maintained fully or partly the free radical scavenging capacity.

Protective effect of a novel antioxidant non-steroidal anti-inflammatory agent (compound IA) on intestinal viability after acute mesenteric ischemia and reperfusion

Reactive oxygen species play an important role in the basic pathophysiology of ischemia-reperfusion injury. We investigated whether the administration of a novel non-steroidal anti-inflammatory compound with antioxidant properties, the compound [5-(2-amino-ethylamino)-1-phenyl-2-pentanone] (compound IA), has a beneficial effect on the repair process of the intestinal mucosa after transient mesenteric ischemia in a randomized blind trial. Six groups of rats were subjected to a model of 60 min of intestinal ischemia that was produced by occluding the superior mesenteric artery. At the end of ischemia, compound IA was administered intravenously and the clamp was removed allowing reperfusion. At 60 min after reperfusion, animals were sacrificed and a 10 cm section of terminal ileum was resected. The outcome was evaluated by histopathologic assessment, measurement of polymorphonuclear leukocytes and the extent of lipid peroxidation measuring the small intestine tissue malondialdehyde. After 1 h of reperfusion, the mucosal damage was less in IA-treated rats compared with the control group. Moreover, the number of polymorphonuclear leukocytes in intestinal mucosa was significantly lower in IA group. Compound IA resulted in a statistically significant reduction of the concentration of small intestine tissue malondialdehyde, compared to those of controls. Administration of compound IA decreased the mucosal damage in rats that were subjected to 60 min of ischemia followed by 60 min of reperfusion. The mechanism of compound IA action is considered to be mediated via its potent antioxidant, free radical scavenging activities and inhibition of polymorphonuclear leukocytes infiltration.

Medicinal Chemistry: Synthesis and Pharmacochemical Investigation of Some Novel 1, 2, 4‐4H‐triazoles with Potential Antiviral Activity

We report the synthesis of some mercaptotriazole derivatives in an effort to discover underlying structural requirements for antiviral activity. A preliminary antiviral study was performed and the contribution of the compounds to free radical processes was investigated. Because lipophilicity influences both biological activity and antioxidant potential we calculated lipophilicity and attempted to correlate this with antioxidant activity.

Lipid-Lowering (Hetero)Aromatic Tetrahydro-1,4-Oxazine Derivatives with Antioxidant and Squalene Synthase Inhibitory Activity

A number of newly synthesized 2-[4-(hetero)aromatic]phenyl-2-hydroxy-tetrahydro-1,4-oxazine derivatives were found to inhibit lipid peroxidation (IC50 of the most potent was 20 microM) as well as rat squalene synthase (IC50 for most between 1-10 microM). Antidyslipidemic action was demonstrated in vivo: the most active compound decreased triglycerides, total cholesterol, and LDL-cholesterol of hyperlipidemic rats by 64, 67, and 82%, respectively, at 56 micromol/kg (ip). Most of the novel compounds are more active than the structurally related and reference biphenyl-morpholine, pointing to useful structural approaches for the design of antiatherosclerotic agents.

Novel piperidine derivatives: inhibitory properties towards cytochrome P450 isoforms, and cytoprotective and cytotoxic characteristics

The ability of a series of eight piperidine derivatives, substituted at positions 1, 3 and 4, to inhibit P450-dependent metabolism of specific substrates, is reported. Five different P450 isoforms (1A1, 1A2, 2B1, 2E1 and 3A1) in differentially induced rat liver microsomes were used for this purpose. From the results it is concluded that compound 2 was the most potent and moreover, highly selective inhibitor for P4502B1 with an IC(50) of 2.5 μM. Compound 3 appeared to have high selectivity for P4501A1 but not for P4501A2 (IC(50)s 80 and > 1000 μM, respectively). P4502B1 was found to be the most susceptible P450 isoform for inhibition by compounds 2, 3 and 6, while P4502E1 was largely insensitive to the inhibitory properties of all piperidine derivatives. A preliminary SAR study for the cytotoxicity, cytoprotective and P450 inhibitory properties of the piperidine derivatives, was also attempted. Using freshly isolated rat hepatocytes, the toxicity of the compounds was estimated and expressed as lactate dehydrogenase (LDH) leakage, lipid peroxidation (LPO) levels and GSH depletion. Considering the P450 inhibition and cytotoxicity results, compounds 2 and 3 were tested for possible protective activity against paracetamol-induced cytotoxicities. It was found that compound 2 protects completely against LDH leakage and LPO caused by paracetamol in rat hepatocytes isolated from β-naphthoflavone (β-NF) pretreated rats. It is concluded that the piperidine structures studied proved to be potentially valuable lead compounds for the design of potent and selective P450 inhibitors and for non-toxic cytoprotective agents as well.