Nitrones as therapeutics in age-related diseases

Synthesis of Nitrones and Nitroalkanes via Chiral Cyclic Imines

A series of structurally chiral cyclic imines efficiently yields chiral nitrones and nitroalkanes. This is the first report of the synthesis of nitro groups by C═N bond cleavage of imines through a nitrone intermediate.

Development of Pharmacological Strategies with Therapeutic Potential in Ischemic Stroke

Acute ischemic stroke constitutes a health challenge with great social impact due to its high incidence, with the social dependency that it generates being an important source of inequality. The lack of treatments serving as effective neuroprotective therapies beyond thrombolysis and thrombectomy is presented as a need. With this goal in mind, our research group's collaborative studies into cerebral ischemia and subsequent reperfusion concluded that there is a need to develop compounds with antioxidant and radical scavenger features. In this review, we summarize the path taken toward the identification of lead compounds as potential candidates for the treatment of acute ischemic stroke. Evaluations of the antioxidant capacity, neuroprotection of primary neuronal cultures and in vivo experimental models of cerebral ischemia, including neurological deficit score assessments, are conducted to characterize the biological efficacy of the various neuroprotective compounds developed. Moreover, the initial results in preclinical development, including dose-response studies, the therapeutic window, the long-term neuroprotective effect and in vivo antioxidant evaluation, are reported. The results prompt these compounds for clinical trials and are encouraging regarding new drug developments aimed at a successful therapy for ischemic stroke.

NO news: S-(de)nitrosylation of cathepsins and their relationship with cancer

Tumor formation and progression have been much of a study over the last two centuries. Recent studies have seen different developments for the early diagnosis and treatment of the disease; some of which even promise survival of the patient. Cysteine proteases, mainly cathepsins have been unequivocally identified as putative worthy players of redox imbalance that contribute to the premonition and further progression of cancer by interfering in the normal extracellular and intracellular proteolysis and initiating a proteolytic cascade. The present review article focuses on the study of cancer so far, while establishing facts on how future studies focused on the cellular interrelation between nitric oxide (NO) and cancer, can direct their focus on cathepsins. For a tumor cell to thrive and synergize a cancerous environment, different mutations in the proteolytic and signaling pathways and the proto-oncogenes, oncogenes, and the tumor suppressor genes are made possible through cellular biochemistry and some cancer-stimulating environmental factors. The accumulated findings show that S-nitrosylation of cathepsins under the influence of NO-donors can prevent the invasion of cancer and cause cancer cell death by blocking the activity of cathepsins as well as the major denitrosylase systems using a multi-way approach. Faced with a conundrum of how to fill the gap between the dodging of established cancer hallmarks with cathepsin activity and gaining appropriate research/clinical accreditation using our hypothesis, the scope of this review also explores the interplay and crosstalk between S-nitrosylation and S-(de)nitrosylation of this protease and highlights the utility of charging thioredoxin (Trx) reductase inhibitors, low-molecular-weight dithiols, and Trx mimetics using efficient drug delivery system to prevent the denitrosylation or regaining of cathepsin activity in vivo. In foresight, this raises the prospect that drugs or novel compounds that target cathepsins taking all these factors into consideration could be deployed as alternative or even better treatments for cancer, though further research is needed to ascertain the safety, efficiency and effectiveness of this approach.

An Overview of Tetramethylpyrazine (Ligustrazine) and its Derivatives as Potent Anti-Alzheimer’s Disease Agents

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Tetramethylpyrazine (TMP), or ligustrazine, is an alkaloid isolated from the Chinese herb Ligusticum wallichii. It is known for its broad-spectrum medicinal properties against several diseases, and various studies have shown that it can modulate diverse biological targets and signaling pathways to produce neuroprotective effects, especially against Alzheimer’s disease (AD). This has attracted significant research attention evaluating TMP as a potent multitarget anti-AD agent. This review compiles the results of studies assessing the neuroprotective mechanisms exerted by TMP as well as its derivatives prepared using a multi-target-directed ligand strategy to explore its multitarget modulating properties. The present review also highlights the work done on the design, synthesis, structure-activity relationships, and mechanisms of some potent TMP derivatives that have shown promising anti-AD activities. These derivatives were designed, synthesized, and evaluated to develop anti-AD molecules with enhanced biological and pharmacokinetic activities compared to TMP. This review article paves the way for the exploration and development of TMP and TMP derivatives as an effective treatment for AD.

Antiaging Therapies, Cognitive Impairment, and Dementia

Aging is a powerful risk factor for the development of many chronic diseases including dementia. Research based on disease models of dementia have yet to yield effective treatments, therefore it is opportune to consider whether the aging process itself might be a potential therapeutic target for the treatment and prevention of dementia. Numerous cellular and molecular pathways have been implicated in the aging process and compounds that target these processes are being developed to slow aging and delay the onset of age-associated conditions. A few particularly promising therapeutic agents have been shown to influence many of the main hallmarks of aging and increase life span in rodents. Here we discuss the evidence that some of these antiaging compounds may beneficially affect brain aging and thereby lower the risk for dementia.

Para-Substituted α-Phenyl-N-tert-butyl Nitrones: Spin-Trapping, Redox and Neuroprotective Properties

In this work, a series of para-substituted α-phenyl-N-tert-butyl nitrones (PBN) were studied. Their radical-trapping properties were evaluated by electron paramagnetic resonance, with 4-CF₃-PBN being the fastest derivative to trap the hydroxymethyl radical (^•CH₂OH). The redox properties of the nitrones were further investigated by cyclic voltammetry, and 4-CF₃-PBN was the easiest to reduce and the hardest to oxidize. This is due to the presence of the electron-withdrawing CF₃ group. Very good correlations between the Hammett constants (σ_p) of the substituents and both spin-trapping rates and redox potentials were observed. These correlations were further supported by computationally determined ionization potentials and atom charge densities. Finally, the neuroprotective effect of these derivatives was studied using two different in vitro models of cell death on primary cortical neurons injured by glutamate exposure or on glial cells exposed to ^t BuOOH. Trends between the protection afforded by the nitrones and their lipophilicity were observed. 4-CF₃-PBN was the most potent agent against ^t BuOOH-induced oxidative stress on glial cells, while 4-Me₂N-PBN showed potency in both models.

Nanocrystalline ZnO: A Competent and Reusable Catalyst for the Preparation of Pharmacology Relevant Heterocycles in the Aqueous Medium

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Nanoparticle catalyzed synthesis is a green and convenient method to achieve most of the chemical transformations in water or other green solvents. Nanoparticle ensures an easy isolation process of catalyst as well as products from the reaction mixture avoiding the hectic work up procedure. Zinc oxide is a biocompatible, environmentally benign and economically viable nanocatalyst with effectivity comparable to the other metal nanocatalyst employed in several reaction strategies. This review mainly focuses on the recent applications of zinc oxide in the synthesis of biologically important heterocyclic molecules under sustainable reaction conditions.

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Application of zinc oxide in organic synthesis: Considering the achievable advantages of this nanocatalyst, presently several research groups are paying attention in anchoring zincoxide or its modified structure in several types of organic conversions e.g. multicomponent reactions, ligand-free coupling reactions, cycloaddition reaction, etc. The advantages and limitations of this nanocatalyst are also demonstrated. The present study aims to highlight the recent multifaceted applications of ZnO towards the synthesis of diverse heterocyclic motifs. Being a promising biocompatible nanoparticle, this catalyst has an important contribution in the fields of synthetic chemistry and medicinal chemistry.

Facile one-pot synthesis of novel N-benzimidazolyl-α-arylnitrones catalyzed by salts of transition metals

A novel series of N-benzimidazol-2-yl-α-aryl nitrones 3a–j is synthesized via simple one-pot condensation/oxidation of 2-aminobenzimidazole, an aromatic aldehyde and m-chloro perbenzoic acid (m-CPBA) as an effective oxidant using Mn(NO₃)₂·6H₂O as an efficient catalyst at room temperature. All synthesized N-benzimidazolyl nitrones were identified using FTIR, NMR and mass spectroscopy. Also, stability energy theory calculations were performed and ¹H NMR computational spectra were generated for the isomeric structures of 3a; the results show that the stability order is oxaziridine (4) followed by the nitrones 3a_E and 3a_Z. Also, comparing the computational spectroscopy results with the experimental data shows great accordance with nitrone 3a_E. Among the remarkable points of this protocol, stable N-heterocyclic nitrones were prepared for the first time from raw materials under mild oxidative conditions. Therefore, they can easily be applied as high-potential intermediates for synthesizing valuable heterocycles in mild conditions. Due to benefits such as the use of inexpensive and available catalysts, short reaction times, high yields, facile workup to obtain pure product, and facile separation of the side product (m-chlorobenzoic acid), this simple protocol complies greatly with the principles of green chemistry.

A novel series of N-benzimidazol-2-yl-α-aryl nitrones 3a–j is synthesized via one-pot condensation/oxidation of 2-aminobenzimidazole, an aromatic aldehyde and m-CPBA as an effective oxidant using Mn(NO₃)₂·6H₂O as an efficient catalyst.

A Protocol To Transform Sulfones into Nitrones and Aldehydes

A simple method to transform sulfones into nitrones and therefore into the corresponding carbonyl derivatives has been developed. Some examples demonstrate that it is a new reliable and versatile reaction in the toolbox of sulfones that has great synthetic potential. NMR and computational studies were used to elucidate the mechanism.

Recent progress in the structural modification and pharmacological activities of ligustrazine derivatives

Ligustrazine is a main active fraction of the traditional medicine known as Ligusticum chuanxiong hort, which has been used as clinical medication for cerebral thrombosis, coronary heart disease and stenocardia recently. The rapid metabolism and short half-life of ligustrazine seriously limits its application in clinical practice. Therefore, derivatives of ligustrazine are designed and synthesized in our and other labs, including piperazine, cinnamic acid, styrene, acylguanidine, amides, curcumin and triterpenes derivatives of ligustrazine. Most of these compounds present better pharmacodynamics activities and more favorable pharmacokinetic properties compared to the parent compound. Besides, some new biological activities of these compounds are discovered. Hence, this review continues the previous review of our group as well as aims to highlight recent prominent advances in this field in the past ten years.

Alternative Route Toward Nitrones: Experimental and Theoretical Findings

Nitrones are important building blocks for natural and biologically active compounds, used as spin-trap reagents and therapeutic agents. All this makes nitrones intriguing and valuable compounds for fundamental studies and as useful chemicals in various synthetic strategies. Therefore, nitrones are still of great interest and in the limelight of researches. With our initial goal to solve synthetic problems toward 5-phenyl-2,2'-bipyridine (Phbpy), we found that this reaction can proceed through the formation of 6-phenyl-3-(pyridin-2-yl)-1,2,4-triazin-4(3H)-ol (4-OH), which rapidly isomerizes to a 3,4-dihydro-1,2,4-triazine-based nitrone, namely 6-phenyl-3-pyridin-2-yl-2,3-dihydro-1,2,4-triazin-4-oxide (4'), This encouraged us to study condensation of hydrazonophenylacetaldehyde oxime (2), obtained from 2-isonitrosoacetophenone (1), with other aldehydes. The reaction with both salicylaldehyde and p-tolualdehyde leads to the open-chain isomers, namely (2-hydroxybenzylidene)hydrazono-2-phenylacetaldehyde oxime (5) and (4-methylbenzylidene)hydrazono-2-phenylacetaldehyde oxime (6), respectively. The latter product exists in solution in equilibrium with its cyclic isomer 6-phenyl-3-(4-methylphenyl)-2,3-dihydro-1,2,4-triazin-4-oxide (6'), while the former one exists in solution exclusively in the open-chain form. It was also found that 2 reacts with acetone with the formation of 3,3-dimethyl-6-phenyl-2,3-dihydro-1,2,4-triazin-4-oxide (7'), which also exists in solution in equilibrium with its open-chain isomer 2-phenyl-2-(propan-2-ylidenehydrazono)acetaldehyde oxime (7). The static DFT as well as ab initio molecular dynamics simulations have corroborated the experimental findings.

Tetramethylpyrazine nitrone, a multifunctional neuroprotective agent for ischemic stroke therapy

TBN, a novel tetramethylpyrazine derivative armed with a powerful free radical-scavenging nitrone moiety, has been reported to reduce cerebral infarction in rats through multi-functional mechanisms of action. Here we study the therapeutic effects of TBN on non-human primate model of stroke. Thirty male Cynomolgus macaques were subjected to stroke with 4 hours ischemia and then reperfusion. TBN were injected intravenously at 3 or 6 hours after the onset of ischemia. Cerebral infarction was examined by magnetic resonance imaging at 1 and 4 weeks post ischemia. Neurological severity scores were evaluated during 4 weeks observation. At the end of experiment, protein markers associated with the stroke injury and TBN treatment were screened by quantitative proteomics. We found that TBN readily penetrated the blood brain barrier and reached effective therapeutic concentration after intravenous administration. It significantly reduced brain infarction and modestly preserved the neurological function of stroke-affected arm. TBN suppressed over-expression of neuroinflammatory marker vimentin and decreased the numbers of GFAP-positive cells, while reversed down-regulation of myelination-associated protein 2', 3'-cyclic-nucleotide 3'-phosphodiesterase and increased the numbers of NeuN-positive cells in the ipsilateral peri-infarct area. TBN may serve as a promising new clinical candidate for the treatment of ischemic stroke.

New developments of ketonitrones in organic synthesis

Various vinyl ketonitrones are prepared using new strategies and were applied to synthesize heterocycles in organic synthesis.

Ameliorative Effects of Antioxidants on the Hippocampal Accumulation of Pathologic Tau in a Rat Model of Blast-Induced Traumatic Brain Injury

Traumatic brain injury (TBI) can lead to early onset dementia and other related neurodegenerative diseases. We previously demonstrated that damage to the central auditory pathway resulting from blast-induced TBI (bTBI) could be significantly attenuated by a combinatorial antioxidant treatment regimen. In the current study, we examined the localization patterns of normal Tau and the potential blast-induced accumulation of neurotoxic variants of this microtubule-associated protein that are believed to potentiate the neurodegenerative effects associated with synaptic dysfunction in the hippocampus following three successive blast overpressure exposures in nontransgenic rats. We observed a marked increase in the number of both hyperphosphorylated and oligomeric Tau-positive hilar mossy cells and somatic accumulation of endogenous Tau in oligodendrocytes in the hippocampus. Remarkably, a combinatorial regimen of 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) resulted in striking reductions in the numbers of both mossy cells and oligodendrocytes positively labeled for these pathological Tau immunoreactivity patterns in response to bTBI. This treatment strategy represents a promising therapeutic approach for simultaneously reducing or eliminating both primary auditory injury and nonauditory changes associated with bTBI-induced hippocampal neurodegeneration.

Oxidation of N,N-Disubstituted Hydroxylamines to Nitrones with Hypervalent Iodine Reagents

Hypervalent iodine compounds are viable reagents for the oxidation of N,N-disubstituted hydroxylamines to the corresponding nitrones, with IBX performing best. The procedure is very simple and user-friendly and affords the target compounds with high efficiency and regioselectivity, highlighting IBX as the reagent of choice for preparation of aldonitrones from nonsymmetric hydroxylamines. Evidence for a mechanism involving nitrogen to iodine coordination has been collected.

Nitrone-based therapeutics for neurodegenerative diseases: their use alone or in combination with lanthionines

The possibility of free radical reactions occurring in biological processes led to the development and employment of novel methods and techniques focused on determining their existence and importance in normal and pathological conditions. For this reason the use of nitrones for spin trapping free radicals became widespread in the 1970s and 1980s, when surprisingly the first evidence of their potent biological properties was noted. Since then widespread exploration and demonstration of the potent biological properties of phenyl-tert-butylnitrone (PBN) and its derivatives took place in preclinical models of septic shock and then in experimental stroke. The most extensive commercial effort made to capitalize on the potent properties of the PBN-nitrones was for acute ischemic stroke. This occurred during 1993-2006, when the 2,4-disulfonylphenyl PBN derivative, called NXY-059 in the stroke studies, was shown to be safe in humans and was taken all the way through clinical phase 3 trials and then was deemed to be ineffective. As summarized in this review, because of its excellent human safety profile, 2,4-disulfonylphenyl PBN, now called OKN-007 in the cancer studies, was tested as an anti-cancer agent in several preclinical glioma models and shown to be very effective. Based on these studies this compound is now scheduled to enter into early clinical trials for astrocytoma/glioblastoma multiforme this year. The potential use of OKN-007 in combination with neurotropic compounds such as the lanthionine ketamine esters is discussed for glioblastoma multiforme as well as for various other indications leading to dementia, such as aging, septic shock, and malaria infections. There is much more research and development activity ongoing for various indications with the nitrones, alone or in combination with other active compounds, as briefly noted in this review.

Potential implication of the chemical properties and bioactivity of nitrone spin traps for therapeutics

Nitrone therapeutics has been employed in the treatment of oxidative stress-related diseases such as neurodegeneration, cardiovascular disease and cancer. The nitrone-based compound NXY-059, which is the first drug to reach clinical trials for the treatment of acute ischemic stroke, has provided promise for the development of more robust pharmacological agents. However, the specific mechanism of nitrone bioactivity remains unclear. In this review, we present a variety of nitrone chemistry and biological activity that could be implicated for the nitrone's pharmacological activity. The chemistries of spin trapping and spin adduct reveal insights on the possible roles of nitrones for altering cellular redox status through radical scavenging or nitric oxide donation, and their biological effects are presented. An interdisciplinary approach towards the development of novel synthetic antioxidants with improved pharmacological properties encompassing theoretical, synthetic, biochemical and in vitro/in vivo studies is covered.

Novel multi-functional nitrones for treatment of ischemic stroke

Ischemic stroke resulting from obstruction of blood vessels is an enormous public health problem with urgent need for effective therapy. The co-administration of thrombolytic/antiplatelet agent and neuroprotective agent improves therapeutic efficacy and agent possessing both thrombolytic/antiplatelet and antiradical activities provides a promising strategy for the treatment of ischemic stroke. We have previously reported a novel compound, namely TBN, possessing both antiplatelet and antiradical activities, showed significant neuroprotective effect in a rat stroke model. We herein report synthesis of a series of new pyrazine derivatives, and evaluation of their biological activities. Their mechanisms of action were also investigated. Among these new derivatives, compound 21, armed with two nitrone moieties, showed the greatest neuroprotective effects in vitro and in vivo. Compound 21 significantly inhibited ADP-induced platelet aggregation. In a cell free antiradical assay, compound 21 was the most effective agent in scavenging the three most damaging radicals, namely (·)OH, O(2)(·-) and ONOO(-).

Effects of PBN and OKN007 in rodent glioma models assessed by 1H MR spectroscopy

Gliomas, the most common primary brain tumors in adults, have a poor outcome. PBN (α-phenyl-tert-butylnitrone) and OKN007 (2,4-disulfophenyl-PBN) are nitrones that have demonstrated beneficial effects in many aging diseases. In this study, we evaluated the anti-tumor effects of PBN and OKN007 in several rodent glioma models (C6, RG2, and GL261) by assessing metabolite alterations with magnetic resonance spectroscopy (MRS). PBN or OKN007 was administered in drinking water before or after tumor formation. MR imaging and single-voxel point-resolved spectroscopy were done to assess tumor morphology and metabolites, after therapy. Major metabolite ratios (choline, N-acetylaspartate, and lipid (methylene or methyl), all compared to creatine), as well as quantification of individual metabolite concentrations, were assessed. Nitrones induced tumor metabolism changes that resulted in restoring major metabolite ratios close to their normal levels, in the glioma regression phase. Nitrone treatment decreased the lipid (methylene)-to-creatine ratio, as well as the estimated concentration of lipid (methylene) significantly. Alterations in lipids can be a useful marker for the evaluation of the efficacy associated with treatment and were found in this study to be related to the reduction of necrosis, but not apoptosis. OKN007 was more effective than PBN when administered after tumor formation in the C6 glioma model. In conclusion, (1)H MRS and conventional MRI are useful methods to assess and follow the response of varied glioma models to anti-tumor treatments.

Synthesis and biological evaluations of novel apocynin analogues

We have designed and synthesized a series of novel apocynin analogues, and evaluated their biological activity. Compound 10, an apocynin dimer analogue, compound 12, the lipoic acid (LA) and apocynin conjugate, were the most potent in protecting cells from lipopolysaccharide (LPS)-induced cytotoxicity, had significant activity scavenging ROS induced by LPS, and greatly decreased LPS-induced P67(phox) protein expression. SAR analysis suggests that modification of apocynin can increase its activity. Our results demonstrate that arming apocynin with a powerful antioxidant such as lipoic acid is a valid strategy to design new apocynin analogues with enhanced biological activity.

Fast reactivity of a cyclic nitrone-calix[4]pyrrole conjugate with superoxide radical anion: theoretical and experimental studies

Nitrone spin traps have been employed as probes for the identification of transient radical species in chemical and biological systems using electron paramagnetic resonance (EPR) spectroscopy and have exhibited pharmacological activity against oxidative-stress-mediated diseases. Since superoxide radical anion (O2(•-)) is a major precursor to most reactive oxygen species and calix[4]pyrroles have been shown to exhibit high affinity to anions, a cyclic nitrone conjugate of calix[4]pyrrole (CalixMPO) was designed, synthesized, and characterized. Computational studies at the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level suggest a pendant-type linkage between the calix[4]pyrrole and the nitrone to be the most efficient design for spin trapping of O2(•-), giving exoergic reaction enthalpies (ΔH(298K,aq)) and free energies (ΔG(298K,aq)) of -16.9 and -2.1 kcal/mol, respectively. (1)H NMR study revealed solvent-dependent conformational changes in CalixMPO leading to changes in the electronic properties of the nitronyl group upon H-bonding with the pyrrole groups as also confirmed by calculations. CalixMPO spin trapping of O2(•-) exhibited robust EPR spectra. Kinetic analysis of O2(•-) adduct formation and decay in polar aprotic solvents using UV-vis stopped-flow and EPR methods gave a larger trapping rate constant for CalixMPO and a longer half-life for its O2(•-) adduct compared to the commonly used nitrones. The unusually high reactivity of CalixMPO with O2(•-) was rationalized to be due to the synergy between the α-effect and electrostatic effect by the calix[4]pyrrole moiety on O2(•-) and the nitrone, respectively. This work demonstrates for the first time the application of an anion receptor for the detection of one of the most important radical intermediates in biological and chemical systems (i.e., O2(•-)).

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

The synthesis, structure, theoretical and experimental in vitro antioxidant properties using the DPPH, ORAC, and benzoic acid, as well as preliminary in vitro pharmacological activities of (Z)-α-aryl and heteroaryl N-alkyl-nitrones 6-15, 18, 19, 21, and 23, is reported. In the in vitro antioxidant activity, for the DPPH radical test, only nitrones bearing free phenol groups gave the best RSA (%) values, nitrones 13 and 14 showing the highest values in this assay. In the ORAC analysis, the most potent radical scavenger was nitrone indole 21, followed by the N-benzyl benzene-type nitrones 10 and 15. Interestingly enough, the archetypal nitrone 7 (PBN) gave a low RSA value (1.4%) in the DPPH test, or was inactive in the ORAC assay. Concerning the ability to scavenge the hydroxyl radical, all the nitrones studied proved active in this experiment, showing high values in the 94-97% range, the most potent being nitrone 14. The theoretical calculations for the prediction of the antioxidant power, and the potential of ionization confirm that nitrones 9 and 10 are among the best compounds in electron transfer processes, a result that is also in good agreement with the experimental values in the DPPH assay. The calculated energy values for the reaction of ROS (hydroxyl, peroxyl) with the nitrones predict that the most favourable adduct-spin will take place between nitrones 9, 10, and 21, a fact that would be in agreement with their experimentally observed scavenger ability. The in vitro pharmacological analysis showed that the neuroprotective profile of the target molecules was in general low, with values ranging from 0% to 18.7%, in human neuroblastoma cells stressed with a mixture of rotenone/oligomycin-A, being nitrones 18, and 6-8 the most potent, as they show values in the range 24-18.4%.

Superoxide dismutase mimics: chemistry, pharmacology, and therapeutic potential

Oxidative stress has become widely viewed as an underlying condition in a number of diseases, such as ischemia-reperfusion disorders, central nervous system disorders, cardiovascular conditions, cancer, and diabetes. Thus, natural and synthetic antioxidants have been actively sought. Superoxide dismutase is a first line of defense against oxidative stress under physiological and pathological conditions. Therefore, the development of therapeutics aimed at mimicking superoxide dismutase was a natural maneuver. Metalloporphyrins, as well as Mn cyclic polyamines, Mn salen derivatives and nitroxides were all originally developed as SOD mimics. The same thermodynamic and electrostatic properties that make them potent SOD mimics may allow them to reduce other reactive species such as peroxynitrite, peroxynitrite-derived CO(3)(*-), peroxyl radical, and less efficiently H(2)O(2). By doing so SOD mimics can decrease both primary and secondary oxidative events, the latter arising from the inhibition of cellular transcriptional activity. To better judge the therapeutic potential and the advantage of one over the other type of compound, comparative studies of different classes of drugs in the same cellular and/or animal models are needed. We here provide a comprehensive overview of the chemical properties and some in vivo effects observed with various classes of compounds with a special emphasis on porphyrin-based compounds.

Anti-cancer activity of nitrones in the Apc(Min/+) model of colorectal cancer

Abstract The nitrones of alpha-phenyl-tert-butyl nitrone (PBN) and 4-hydroxyl-PBN (4-OH-PBN) that have anti-cancer activity in models of liver cancer and glioblastomas were tested in the ApcMin/+ mouse model. Mice were administered PBN and 4-OH-PBN in drinking water and intestinal tumour size and number assessed after 3-4 months. Throughout the experiment, contrast-enhanced magnetic resonance imaging (MRI) was used to monitor colon tumours. MRI data showed a time-dependent significant increase in total colonic signal intensity in sham-treated mice, but a significant decrease for PBN-treated mice and slight decrease for 4-OHPBN treated mice, probably due to the limited water solubility of 4-OH-PBN. Final pathological and percentage survival data agreed with the MRI data. PBN had little effect on oxaliplatin-mediated killing of HCT116 colon cancer cells and caused only a slight decrease in the amount of active fraction caspase 3 in oxaliplatin-treated cells. PBN has significant anti-cancer activity in this model of intestinal neoplasia.

Lipophilic beta-cyclodextrin cyclic-nitrone conjugate: synthesis and spin trapping studies

Nitrone spin traps are commonly employed as probes for the identification of transient radicals in chemical and biological systems using electron paramagnetic resonance (EPR) spectroscopy. Nitrones have also found applications as therapeutic agent in the treatment of radical-mediated diseases. Therefore, a spin trap that incorporates high reactivity to superoxide radical anion (O2(*-)), more persistent superoxide adduct, enhanced bioavailability, and selective targeting in one molecular design is desirable. In this work, the synthesis of a nitrone spin trap, 4, that is tethered via amide bonds to a beta-cyclodextrin (beta-CD) and a dodecyl chain was achieved with the expectation that the beta-cyclodextrin would lead to increased reactivity to O2(*-) and persistent O2(*-) adduct while the lipophilic chain would impart membrane targeting property. The two constitutional racemic isomers, 4a and 4b, were separated using preparative HPLC, and structural analysis and self-aggregation properties were carried out using NMR, induced circular dichroism, dynamic light scattering, transmission electron microscopy, and computational approach. EPR spin trapping of O2(*-) by 4a and 4b was only successful in DMSO and not in an aqueous system, due most likely to the amphiphilic character of 4 that can favor conformations (or aggregation) hindering radical addition to nitrone. Kinetics of formation and decay of the 4a-O2H adduct in polar aprotic solvents show faster reactivity to O2(*-) and more persistent O2(*-) adduct compared to nitrones not conjugated to beta-CD. Computational analysis of 4a and 4b as well as 4a-OOH and 4b-OOH adducts were carried out, and results show that isomerism, both constitutional and stereochemical, affects the orientations of aminoxyl-NO and/or hydroperoxyl groups relative to the beta-CD annulus for optimal H-bond interaction and stability.

A class of imidazolium salts is anti-oxidative and anti-fibrotic in hepatic stellate cells

A class of imidazolium salts (IMSs) is routinely used in organic synthetic chemistry as precursors to generate N-heterocyclic carbenes (NHCs) with catalytic activity. However, their biological properties are largely unknown. The current study investigates the biological activity of a typical NHC precursor DBZIM and its trimer TDBZIM in hepatic stellate cells (HSCs), which is an in vitro model for studying liver fibrosis. The results show that HSCs treated with IMSs have an enhanced GSH/GSSG ratio and a reduced level of reactive oxygen species (ROS), which may consequently contribute to the attenuation in gene expression of fibrogenic molecules such as smooth muscle actin-alpha (SMAA), transforming growth factor-beta 1 (TGF-beta1), procollagen alphaI(I) and fibronectin. Further, the in vivo experiments demonstrate that DBZIM is an anti-fibrotic agent in a mouse model of liver fibrosis. These findings suggest that the versatile IMSs could be a potential source for developing novel therapeutics to treat liver fibrosis and other fibrogenic disorders caused by oxidative stress and TGF-beta1 mal-signalling.

Synthesis of N-arylpyridinium salts bearing a nitrone spin trap as potential mitochondria-targeted antioxidants

The generation of excess reactive oxygen species (ROS) in mitochondria is responsible for much of the oxidative stress associated with ageing (aging), and mitochondrial dysfunction is part of the pathology of neurodegeneration and type 2 diabetes. Lipophilic pyridinium ions are known to accumulate in mitochondria and this paper describes a general route for the preparation of nitrone-containing N-arylpyridinium salts having a range of lipophilicities, as potential therapeutic antioxidants. The compatibility of nitrones with the Zincke reaction is the key to their synthesis. Their trapping of carbon-centred radicals and the EPR spectra of the resulting nitroxides are reported.

Reactivity of superoxide radical anion and hydroperoxyl radical with alpha-phenyl-N-tert-butylnitrone (PBN) derivatives

Nitrones have exhibited pharmacological activity against radical-mediated pathophysiological conditions and as analytical reagents for the identification of transient radical species by electron paramagnetic resonance (EPR) spectroscopy. In this work, competitive spin trapping, stopped-flow kinetics, and density functional theory (DFT) were employed to assess and predict the reactivity of O(2)(*-) and HO(2)(*) with various para-substituted alpha-phenyl-N-tert-butylnitrone (PBN) spin traps. Rate constants of O(2)(*-) trapping by nitrones were determined using competitive UV-vis stopped-flow method with phenol red (PR) as probe, while HO(2)(*) trapping rate constants were calculated using competition kinetics with 5,5-dimethylpyrroline N-oxide (DMPO) by employing EPR spectroscopy. The effects of the para substitution on the charge density of the nitronyl-carbon and on the free energies of nitrone reactivity with O(2)(*-) and HO(2)(*) were computationally rationalized at the PCM/B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level of theory. Theoretical and experimental data show that the rate of O(2)(*-) addition to PBN derivatives is not affected by the polar effect of the substituents. However, the reactivity of HO(2)(*) follows the Hammett equation and is increased as the substituent becomes more electron withdrawing. This supports the conclusion that the nature of HO(2)(*) addition to PBN derivatives is electrophilic, while the addition of O(2)(*-) to PBN-type compounds is only weakly electrophilic.

Nitrones as therapeutics

Nitrones have the general chemical formula X-CH=NO-Y. They were first used to trap free radicals in chemical systems and then subsequently in biochemical systems. More recently several nitrones, including alpha-phenyl-tert-butylnitrone (PBN), have been shown to have potent biological activity in many experimental animal models. Many diseases of aging, including stroke, cancer development, Parkinson disease, and Alzheimer disease, are known to have enhanced levels of free radicals and oxidative stress. Some derivatives of PBN are significantly more potent than PBN and have undergone extensive commercial development for stroke. Recent research has shown that PBN-related nitrones also have anti-cancer activity in several experimental cancer models and have potential as therapeutics in some cancers. Also, in recent observations nitrones have been shown to act synergistically in combination with antioxidants in the prevention of acute acoustic-noise-induced hearing loss. The mechanistic basis of the potent biological activity of PBN-related nitrones is not known. Even though PBN-related nitrones do decrease oxidative stress and oxidative damage, their potent biological anti-inflammatory activity and their ability to alter cellular signaling processes cannot readily be explained by conventional notions of free radical trapping biochemistry. This review is focused on our studies and others in which the use of selected nitrones as novel therapeutics has been evaluated in experimental models in the context of free radical biochemical and cellular processes considered important in pathologic conditions and age-related diseases.

Clair DK, Batinić-Haberle I. Pharmacokinetics of the potent redox-modulating manganese porphyrin, MnTE-2-PyP(5+), in plasma and major organs of B6C3F1 mice

Mn(III) tetrakis(N-ethylpyridinium-2-yl)porphyrin, MnTE-2-PyP(5+), a potent catalytic superoxide and peroxynitrite scavenger, has been beneficial in several oxidative stress-related diseases thus far examined. Pharmacokinetic studies are essential for the better assessment of the therapeutic potential of MnTE-2-PyP(5+) and similar compounds, as well as for the modulation of their bioavailability and toxicity. Despite high hydrophilicity, this drug entered mitochondria after a single 10 mg/kg intraperitoneal injection at levels high enough (5.1 muM; 2.95 ng/mg protein) to protect against superoxide/peroxynitrite damage. Utilizing the same analytical approach, which involves the reduction of MnTE-2-PyP(5+) followed by the exchange of Mn(2+) with Zn(2+) and HPLC/fluorescence detection of ZnTE-2-PyP(4+), we measured levels of MnTE-2-PyP(5+) in mouse plasma, liver, kidney, lung, heart, spleen, and brain over a period of 7 days after a single intraperitoneal injection of 10 mg/kg. Two B6C3F1 female mice per time point were used. The pharmacokinetic profile in plasma and organs was complex; thus a noncompartmental approach was utilized to calculate the area under the curve, c(max), t(max), and drug elimination half-time (t(1/2)). In terms of levels of MnTE-2-PyP(5+) found, the organs can be classified into three distinct groups: (1) high levels (kidney, liver, and spleen), (2) moderate levels (lung and heart), and (3) low levels (brain). The maximal levels in plasma, kidney, spleen, lung, and heart are reached within 45 min, whereas in the case of liver a prolonged absorption phase was observed, with the maximal concentration reached at 8 h. Moreover, accumulation of the drug in brain continued beyond the time of the experiment (7 days) and is likely to be driven by the presence of negatively charged phospholipids. For tissues other than brain, a slow elimination phase (single exponential decay, t(1/2)=60 to 135 h) was observed. The calculated pharmacokinetic parameters will be used to design optimal dosing regimens in future preclinical studies utilizing this and similar compounds.

Puzzles, promises and a cure for ageing

Recent discoveries in the science of ageing indicate that lifespan in model organisms such as yeast, nematodes, flies and mice is plastic and can be manipulated by genetic, nutritional or pharmacological intervention. A better understanding of the targets of such interventions, as well as the proximate causes of ageing-related degeneration and disease, is essential before we can evaluate if abrogation of human senescence is a realistic prospect.

Compounds that confer thermal stress resistance and extended lifespan

The observation that long-lived and relatively healthy animals can be obtained by simple genetic manipulation prompts the search for chemical compounds that have similar effects. Since aging is the most important risk factor for many socially and economically important diseases, the discovery of a wide range of chemical modulators of aging in model organisms could prompt new strategies for attacking age-related disease such as diabetes, cancer and neurodegenerative disorders [Collins, J.J., Evason, K., Kornfeld, K., 2006. Pharmacology of delayed aging and extended lifespan of Caenorhabditis elegans. Exp. Gerontol.; Floyd, R.A., 2006. Nitrones as therapeutics in age-related diseases. Aging Cell 5, 51-57; Gill, M.S., 2006. Endocrine targets for pharmacological intervention in aging in Caenorhabditis elegans. Aging Cell 5, 23-30; Hefti, F.F., Bales, R., 2006. Regulatory issues in aging pharmacology. Aging Cell 5, 3-8]. Resistance to multiple types of stress is a common trait in long-lived genetic variants of a number of species; therefore, we have tested compounds that act as stress response mimetics. We have focused on compounds with antioxidant properties and identified those that confer thermal stress resistance in the nematode Caenorhabditis elegans. Some of these compounds (lipoic acid, propyl gallate, trolox and taxifolin) also extend the normal lifespan of this simple invertebrate, consistent with the general model that enhanced stress resistance slows aging.