Angeliki P. Kourounakis

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.

ANTI-INFLAMMATORY PROPERTIES OF DICLOFENAC TRANSITION METALLOELEMENT COMPLEXES

As part of our research into understanding drug-metalloelement interactions, we have prepared complexes of Cu(II), Co(II), Ni(II), Mn(II), Fe(II), Fe(III), and Pd(II) with Diclofenac, in order to investigate their anti-inflammatory activity. Their inhibitory effects on rat or mouse paw edema induced by Carrageenan, Con-A, Nystatin, and Bakers yeast were compared with those of Diclofenac. Furthermore, the action of Diclofenacs metalloelement complexes on phagocytosis of yeast by rat peritoneal cells, as well as the capacity of some of the metalloelement complexes to inhibit lipid peroxidation of liver microsomal membranes was also investigated. These complexes exhibited a strong inhibitory effect on Carrageenan-, ConA-, and Nystatin-induced edemas (35-80% inhibition) comparable to the inhibition caused by Diclofenac (61-76% inhibition). Furthermore, complexes with Co(II), Ni(II), Pd(II), and Mn(II) were found to have an anti-inflammatory profile (35-50% inhibition) superior to diclofenac (17% inhibition) when inhibiting inflammations due to Bakers yeast, the mechanism of which involves mainly the activation of lipoxygenase and/or complement system. Complexes of Ni(II) and Pd(II), which showed significant inhibition of induced-edemas in rats, were also tested in mice at lower and higher doses and showed a significant dose-dependent inhibition of edemas in mice. Some of these complexes also interfere with in vitro phagocytosis. The most active anti-inflammatory complexes Co(II), Pd(II), and Ni(II), also offered significant protection against lipid peroxidation in vitro, acting as antioxidant compounds, properties that are not demonstrated by Diclofenac. Finally, it is noted that almost all metalloelement complexes of Diclofenac showed high anti-inflammatory activity at molecular concentrations much lower than that of Diclofenac. From the present study it is suggested that the anti-inflammatory activity of Diclofenac is enhanced by the formation of coordination complexes with transition metalloelements.

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.

Novel benzoxazine and benzothiazine derivatives as multifunctional antihyperlipidemic agents.

Atherosclerosis is a multifactorial disease with several mechanisms participating in its manifestation. To address this disorder, we applied a strategy involving the design of a single chemical compound able to simultaneously modulate more than one target. We hereby present the development of novel benzoxazine and benzothiazine derivatives that significantly inhibit in vitro microsomal lipid peroxidation and LDL oxidation as well as squalene synthase activity (IC(50) of 5-16 μM). Further, these compounds show antidyslipidemic and antioxidant properties in vivo, decreasing total cholesterol, LDL, triglyceride, and MDA levels of hyperlipidemic rats by 26-74%. Finally, by determination of their in vivo concentration (up to 24 h) in target tissues (blood/liver), it is shown that compounds reach their targets in the low micromolar range. The new compounds seem to be interesting multifunctional molecules for the development of a new pharmacophore for disease-modifying agents useful in the treatment of atherosclerosis.

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.

Squalene Synthase Inhibitors: An Update on the Search for New Antihyperlipidemic and Antiatherosclerotic Agents

Atherosclerosis and related heart disease is strongly associated with elevated blood levels of total (and LDL) cholesterol. Due to the widespread incidence as well as severity of this pathological condition, major efforts have been made for the discovery and development of hypocholesteroleamic agents. In the past few decades, HMG-CoA reductase inhibitors (statins) are being extensively used as lipid lowering drugs. These agents act predominantly by inhibiting the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) that is the rate limiting step of cholesterol biosynthesis. Both the success as well as drawbacks of HMGRIs, have led to the investigation and design of inhibitors of other (downstream) enzymes involved in the multistep cholesterol biosynthetic pathway. One such class of agents consists of the squalene sythase inhibitors which act at the first and solely committed step towards the biosynthesis of the cholesterol nucleus. This target is considered not to interfere with the biosynthesis of other biologically important molecules and thus a better side-effect profile is expected for these inhibitors. Several classes of squalene synthase inhibitors (SQSIs), such as substrate or transition-state analogues, zaragozic acids or 2,8- dioxabicyclo[3.2.1]octane derivatives, dicarboxylic acid and quinuclidine derivatives, 4,1-benzoxazepine as well as substituted morpholine derivatives, have been studied as potent inhibitors of squalene synthase. So far only one benzoxazepine derivative (TAK-475) has been evaluated in advanced clinical trials. In this article we review the up to date research and literature on the therapeutic potential of this relatively new class of compounds, the drug discovery efforts towards the development of active squalene synthase inhibitors, their activity profile and effectiveness, as well as their structure-activity relationships.

Design of more potent squalene synthase inhibitors with multiple activities

With the increasing realization that modulating a multiplicity of targets can be an asset in the treatment of multifactorial disorders, we hereby report the synthesis and evaluation of the first compounds in which antioxidant, anti-inflammatory as well as squalene synthase (SQS) inhibitory activities are combined by design, in a series of simple molecules, extending their potential range of activities against the multifactorial disease of atherosclerosis. The activity of the initially synthesized antihyperlipidemic morpholine derivatives (1-6), in which we combined several pharmacophore moieties, was evaluated in vitro (antioxidant, inhibition of SQS and lipoxygenase) and in vivo (anti-dyslipidemic and anti-inflammatory effect). We further compared the in vitro SQS inhibitory action of these derivatives with theoretically derived molecular interactions by performing an in silico docking study using the X-ray crystal structure of human SQS. Based on low energy preferred binding modes, we designed potentially more potent SQS ligands. We proceeded with synthesizing and evaluating these new structures (7-12) in vitro and in vivo, to show that the new derivatives were significantly more active than formerly developed congeners, both as SQS inhibitors (20-70-fold increase in activity) and antioxidants (4-30-fold increase in activity). A significant correlation between experimental activity [Log(1/IC(50))] and the corresponding binding free energy (ΔG(b)) of the docked compounds was shown. These results, taken together, show a promising alternative and novel approach for the design and development of multifunctional antiatherosclerosis agents.