Analysis of the structural and mechanistic factors in antioxidants that preserve mitochondrial function and confer cytoprotection

Multifunctional radical quenchers as potential therapeutic agents for the treatment of mitochondrial dysfunction

Mitochondrial dysfunction is associated with a wide range of human diseases, including neurodegenerative diseases, and is believed to cause or contribute to the etiology of these diseases. These disorders are frequently associated with increased levels of reactive oxygen species. One of the design strategies for therapeutic intervention involves the development of novel small molecules containing redox cores, which can scavenge reactive oxygen radicals and selectively block oxidative damage to the mitochondria. Presently, we describe recent research dealing with multifunctional radical quenchers as antioxidants able to scavenge reactive oxygen radicals. The review encompasses ubiquinone and tocopherol analogs, as well as novel pyri(mi)dinol derivatives, and their ability to function as protective agents in cellular models of mitochondrial diseases.

Idebenone: Novel Strategies to Improve Its Systemic and Local Efficacy

The key role of antioxidants in treating and preventing many systemic and topical diseases is well recognized. One of the most potent antioxidants available for pharmaceutical and cosmetic use is Idebenone (IDE), a synthetic analogue of Coenzyme Q10. Unfortunately, IDE's unfavorable physicochemical properties such as poor water solubility and high lipophilicity impair its bioavailability after oral and topical administration and prevent its parenteral use. In recent decades, many strategies have been proposed to improve IDE effectiveness in the treatment of neurodegenerative diseases and skin disorders. After a brief description of IDE potential therapeutic applications and its pharmacokinetic and pharmacodynamic profile, this review will focus on the different approaches investigated to overcome IDE drawbacks, such as IDE incorporation into different types of delivery systems (liposomes, cyclodextrins, microemulsions, self-micro-emulsifying drug delivery systems, lipid-based nanoparticles, polymeric nanoparticles) and IDE chemical modification. The results of these studies will be illustrated with emphasis on the most innovative strategies and their future perspectives.

Oligomeric amyloid β preferentially targets neuronal and not glial mitochondrial-encoded mRNAs

INTRODUCTION

Our laboratories have demonstrated that accumulation of oligomeric amyloid β (OAβ) in neurons is an essential step leading to OAβ-mediated mitochondrial dysfunction.

METHODS

Alzheimer's disease (AD) and matching control hippocampal neurons, astrocytes, and microglia were isolated by laser-captured microdissection from the same subjects, followed by whole-transcriptome sequencing. Complementary in vitro work was performed in OAβ-treated differentiated SH-SY5Y, followed by the use of a novel CoQ₁₀ analogue for protection. This compound is believed to be effective both in suppressing reactive oxygen species and also functioning in mitochondrial electron transport.

RESULTS

We report decreases in the same mitochondrial-encoded mRNAs in Alzheimer's disease laser-captured CA1 neurons and in OAβ-treated SH-SY5Y cells, but not in laser-captured microglia and astrocytes. Pretreatment with a novel CoQ₁₀ analogue, protects neuronal mitochondria from OAβ-induced mitochondrial changes.

DISCUSSION

Similarity of expression changes in neurons from Alzheimer's disease brain and neuronal cells treated with OAβ, and the effect of a CoQ₁₀ analogue on the latter, suggests a pretreatment option to prevent OAβ toxicity, long before the damage is apparent.

Lipophilic methylene violet analogues as modulators of mitochondrial function and dysfunction

In an effort to identify methylene blue analogues having improved antioxidant activity, a series of new methylene violet analogues have been designed and synthesized. The analogues were prepared following a synthetic route that is more efficient than the previously reported methods, both in terms of yield and purity of the final products. The route involves the Smiles rearrangement as one of the crucial steps. Smiles rearrangement of suitably substituted diphenyl sulfide intermediates afforded the corresponding phenothiazine analogues in high yields, which were subsequently converted to the final products. The methylene violet analogues were evaluated for their ability to preserve mitochondrial function in Friedreich's ataxia (FRDA) lymphocytes. The analogues were shown to be efficient ROS scavengers, and able to protect cultured FRDA lymphocytes from oxidative stress resulting from inhibition of complex I. The analogues also preserved mitochondrial membrane potential and augmented ATP production. The analogues were found to be better antioxidants than the parent compounds methylene blue and methylene violet.

Influence of substituent heteroatoms on the cytoprotective properties of pyrimidinol antioxidants

Recently, we described the optimization of novel pyrimidinol-based antioxidants as potential therapeutic molecules for targeting mitochondrial diseases. That study focused on improving the potency and metabolic stability of pyrimidinol antioxidants. This led us to consider the possibility of altering the positions of the exocyclic alkoxy and alkylamino substituents on the pyrimidinol scaffold. Twelve new analogues were prepared and their biological activities were investigated. The metabolic stability of the prepared regioisomers was also assessed in vitro using bovine liver microsomes. Unexpectedly, the 2-alkoxy-4-alkylamino substituted pyrimidinol antioxidants were found to have properties in protecting mitochondrial function superior to the isomeric 4-alkoxy-2-alkylamino substituted pyrimidinols evaluated in all earlier studies. This observation suggests a possible mode of action involving the intermediacy of an ortho-iminoquinone, a species not previously associated with mitochondrial respiratory chain function.

Methods for determining the efficacy of radical-trapping antioxidants

Hydrocarbon autoxidation is the free radical chain reaction primarily responsible for the oxidative degradation of organic materials, including those that make up cells, tissues, and organs. The identification of compounds that slow this process (antioxidants) and the quantitation of their efficacies have long been goals of academic and industrial researchers. Antioxidants are generally divided into two types: preventive and radical-trapping (also commonly referred to as chain-breaking). Preventive antioxidants slow the rate of initiation of autoxidation, whereas radical-trapping antioxidants slow the rate of propagation by reacting with chain-propagating peroxyl radicals. The purpose of this review is to provide a comprehensive overview of different approaches to measure the kinetics of the reactions of radical-trapping antioxidants with peroxyl radicals, and their use to study the inhibition of hydrocarbon (lipid) autoxidation in homogeneous solution, as well as biphasic media (lipid bilayers) and cell culture. Direct and indirect approaches are presented and advantages and disadvantages of each are discussed in order to facilitate method selection for investigators seeking to address particular questions in this immensely popular field.

Synthesis and antiangiogenic activity of 6-amido-2,4,5-trimethylpyridin-3-ols

We recently reported that 6-aminoalkyl-2,4,5-trimethylpyridin-3-ols, novel series of 6-aminopyridin-3-ol-based antioxidants, have high antiangiogenic activities. In pursuit of wider variety in the analogues, we here report the synthesis and antiangiogenic activities of 6-amidoalkyl-2,4,5-trimethylpyridin-3-ols, which would not be considered excellent antioxidants because of the poorer electron-donating effect of the C(6)-amido group than the corresponding C(6)-amino group. The selected 6-amido compounds showed up to several fold-higher antiangiogenic activities and up to an order of magnitude better antitumor activities in the chick embryo chorioallantoic membrane (CAM) assay than SU4312, a positive control. We also found that paracetamol, as a direct phenolic analogue of our simplest 6-amidopyridin-3-ol, showed a moderate level of antiangiogenic activity. We propose this study will offer a basis for a scaffold of novel angiogenesis inhibitors that can perturb angiogenesis-related pathologies.

6-Amino-2,4,5-trimethylpyridin-3-ols: a new general synthetic route and antiangiogenic activity

A new synthetic strategy for preparation of a wide range of 6-amino-2,4,5-trimethylpyridin-3-ols from pyridoxine·HCl via a six-step sequence has been developed. This approach features an introduction of various amino groups to C(6)-position of 3-benzyloxy-6-bromo-2,4,5-trimethylpyridine (13), a key intermediate, by a Buchwald-Hartwig amination reaction using palladium(0) transition metal, which certainly renders an expanded scope of amino substituents. Some analogs prepared using the methods described here showed high level of antiangiogenic and antitumor activities in chick chorioallantoic membrane (CAM) assay, demonstrating the potential of these new aminopyridinols as antiangiogenic agents.

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

The incorporation of nitrogen atoms into the aromatic ring of phenolic compounds has enabled the development of some of the most potent radical-trapping antioxidants ever reported. These compounds, 3-pyridinols and 5-pyrimidinols, have stronger O-H bonds than equivalently substituted phenols, but possess similar reactivities toward autoxidation chain-carrying peroxyl radicals. These attributes suggest that 3-pyridinols and 5-pyrimidinols will be particularly effectiveco-antioxidants when used in combination with more common, but less reactive, phenolic antioxidants such as 2,6-di-tert-butyl-4-methylphenol (BHT), which we demonstrate herein. The antioxidants function in a synergistic manner to inhibit autoxidation; taking advantage of the higher reactivity of the 3-pyridinols/5-pyrimidinols to trap peroxyl radicals and using the less reactive phenols to regenerate them from their corresponding aryloxyl radicals. The present investigations were carried out in chlorobenzene and acetonitrile in order to provide some insight into the medium dependence of the synergism and the results, considered with some from our earlier work, prompt a revision of the H-bonding basicity value of acetonitrile to β2 (H) of 0.39. Overall, the thermodynamic and kinetic data presented here enable the design of co-antioxidant systems comprising lower loadings of the more expensive 3-pyridinol/5-pyrimidinol antioxidants and higher loadings of the less expensive phenolic antioxidants, but which are equally efficacious as the 3-pyridinol/5-pyrimidinol antioxidants alone at higher loadings.

Experimental and computational study on molecular structure and vibrational analysis of 4,5-Bis(hydroxymethyl)-2-methylpyridin-3-ol by normal coordinate treatment

The experimental and theoretical vibrational spectra of 4,5-Bis(hydroxymethyl)-2-methylpyridin-3-ol were investigated. The experimental FT-IR (450-4000cm(-1)) and FT-Raman spectra (100-3600cm(-1)) of the molecule in the solid phase were recorded. Theoretical vibrational frequencies and geometric parameters (bond lengths and bond angles) were calculated using ab initio Hartree Fock (HF) and density functional B3LYP method with 6-31G(d), 6-311++G(d,p) basis sets by Gaussian program, for the first time. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The formation of the hydrogen bond was investigated using NBO calculations. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule.

An optimized pyrimidinol multifunctional radical quencher

A series of aza analogues (4-9) of the experimental neuroprotective drug idebenone (1) have been prepared and evaluated for their ability to attenuate oxidative stress induced by glutathione depletion and to compensate for the decrease in oxidative phosphorylation efficiency in cultured Friedreich's ataxia (FRDA) fibroblasts and lymphocytes and also coenzyme Q10-deficient lymphocytes. Modification of the redox core of the previously reported 3 improved its antioxidant and cytoprotective properties. Compounds 4-9, having the same redox core, exhibited a range of antioxidant activities, reflecting side chain differences. Compounds having side chains extending 14-16 atoms from the pyrimidinol ring (6, 7, and 9) were potent antioxidants. They were superior to idebenone and more active than 3, 4, 5, and 8. Optimized analogue 7 and its acetate (7a) are of interest in defining potential therapeutic agents capable of blocking oxidative stress, maintaining mitochondrial membrane integrity, and augmenting ATP levels. Compounds with such properties may find utility in treating mitochondrial and neurodegenerative diseases such as FRDA and Alzheimer's disease.