Current Topics in Medicinal Chemistry - Volume 15, Issue 2, 2015

For more than half a century free radical-induced alterations at cellular and organ levels have been investigated as a probable underlying mechanism of a number of adverse health conditions. Consequently, significant research efforts have been spent for discovering more effective and potent antioxidants / free radical scavengers for treatment of these adverse conditions. Being by far the most used antioxidants among natural and synthetic compounds, mono- and polyphenols have been the focus of both experimental and computational research on mechanisms of free radical scavenging. Quantum chemical studies have provided a significant amount of data on mechanisms of reactions between phenolic compounds and free radicals outlining a number of properties with a key role for the radical scavenging activity and capacity of phenolics. The obtained quantum chemical parameters together with other molecular descriptors have been used in quantitative structure-activity relationship (QSAR) analyses for the design of new more effective phenolic antioxidants and for identification of the most useful natural antioxidant phenolics. This review aims at presenting the state of the art in quantum chemical and QSAR studies of phenolic antioxidants and at analysing the trends observed in the field in the last decade.

Flavonoids, a group of secondary metabolites widely distributed in the plant kingdom, have been acknowledged for their interesting medicinal properties. Among them, natural flavones, as well as some of their synthetic derivatives, have been shown to exhibit several biological activities, including antioxidant, anti-inflammatory, antitumor, anti-allergic, neuroprotective, cardioprotective and antimicrobial. The antioxidant properties of flavones allow them to demonstrate potential application as preventive and attenuating agents in oxidative stress, i.e., a biological condition that is closely associated to aging process and several diseases. Some flavones interfere in distinct oxidative-stress related events by directly reducing the levels of intracellular free radicals (hydroxyl, superoxide and nitric oxide) and/or of reactive species (e.g. hydrogen peroxide, peroxynitrite and hypochlorous acid) thus preventing their amplification and the consequent damage of other biomolecules such as lipids, proteins and DNA. Flavones can also hinder the activity of central free radical-producing enzymes, such as xanthine oxidase and nicotinamide adenine dinucleotide phosphate oxidase (NADPH-oxidase) or inducible nitric oxide synthase (iNOS) and can even modulate the intracellular levels of pro-oxidant and/or antioxidant enzymes. The evaluation of flavones antioxidant ability has been extensively determined in chemical or biological in vitro models, but in vivo therapy with individual flavones or with flavones-enriched extracts has also been reported. The present manuscript revises relevant studies focusing the preventive effects of flavones on stress-related diseases, namely the neurological and cardiovascular diseases, and diabetes and its associated complications.

Causative connections between infections and cancer are ascertained for several types of viruses, bacteria, and parasites. The mechanisms of cancer induction in chronically infected inflamed tissues strongly implicate oxygen- and nitrogen-centered reactive species, and an impairment of redox-sensitive molecular pathways involved in the tumorigenic transformation, tumor growth, altered immune defense, and in the mechanisms of tumor cell death and survival. Here, we briefly reviewed mechanistic data on carcinogenesis and tumor progression of three major infection-associated tumors, human papillomavirus-induced cervical cancer, hepatitis B virus-positive hepatocarcinoma, and Helicobacter pylori-positive gastric cancer. Notwithstanding the contradictory results of clinical studies on cancer chemoprevention with long-term, high dosage antioxidant vitamin/micronutrient supplementation, natural and synthetic agents with proven capacity to affect redox-dependent molecular pathways still hold the promise for preventing/delaying carcinogenesis initiation, as well as the overt malignancy evolution from dysplastic/ aplastic stages. Novel directions for a targeted antioxidant-based approach to the reduction of persistent infectiondriven cancer risk stems from the current knowledge of critical factors in the host-microbe interaction leading to oncogenesis. An emerging role of redox active substances in the chemotherapy of tumors relies on their stimulating effects towards TRAIL-related apoptosis and the induction of intracellular oxidative stress.

This review discusses the state of the art, challenges and perspectives in recent applications of electrochemistry in the life sciences. It deals mainly with the elucidation of molecular mechanisms of drug action, drug design and development, involving electron transfer, pharmaco-electrochemistry (the combination of electrochemical and pharmacological assays), and electrochemical studies of membrane models and drug delivery. It aims to shed light on the question: does electrochemistry really contribute to this area? It includes a general introduction for the use of electrochemistry in the life sciences, with a focus on how electrochemistry can uniquely provide both kinetic and thermodynamic information. A number of studies are reported in the literature and from the authors’ laboratories, including the investigation of biooxidative/bioreductive activation of pro-drugs, DNA alkylation, electrochemically- based release of reactive oxygen and nitrogen species, with a particular emphasis on quinones, ferrocifens and compounds with mixed-functionality. Within the context of drug delivery and bioavailability, the electrochemical investigation of supramolecular interactions of the chosen classes of compounds with cyclodextrins and lipid bilayers, in relation to their solubilization and vectorization was also carried out. The updated examples herein illustrate how relevant and challenging the integration of electrochemistry, supramolecular and materials chemistry, biochemistry and medical knowledge for the design and development of redox-selective molecular approaches is. Many questions related to these fields are still unclear and the search for selectivity toward redox therapeutic agents remains of expanding interest. This review hopes to stimulate researchers to become more involved in this fruitful interface between electrochemistry and the life sciences.

Neurodegeneration is the hallmark of many chronic progressive neurogical disorders characterized by specific clinical, morphological and biochemical features. Central nervous system is very sensitive to oxidative stress, which is considered as a key factor of neurodegenerative disorders. Therefore, many therapeutical strategies are focused on molecules with redox activity to re-establish the equilibrium between pro and antioxidants. Due to the fact that melatonin readily crosses the blood- brain-barrier, concomitant with its safety profile at the highest dosages makes this dietary supplement very useful in possible clinical application in neurodegeneration. Melatonin is currently marketed in several countries as a dietary supplement with no prescription. Clinical trials have shown different effectiveness of melatonin supplementation in several disorders, including neurodegenerative disorders. Melatonin has unique biochemical properties such as scavenging of hydroxyl, carbonate, alkoxyl, peroxyl and aryl cation radicals and stimulation of activities main antioxidative enzymes (glutathione peroxidase, superoxide dismutase etc.). Moreover, it can suppress nitric oxide synthase. The present paper highlighted the potential clinical role of melatonin in main neurodegenerative diseases including Alzheimer disease, Parkinson disease, amylotrophic lateral sclerosis and multiple sclerosis. Moreover, in this review the main molecular aspects of melatonin in brain cell protection and survival mechanisms were discussed. Therefore, melatonin is regarded as a potential therapeutical agent in clinical application in neurodegenerative disorders, but this findings needs to be confirmed by the larger, more well-designed clinical trials.

Radiation and some chemotherapeutic agents used in conventional cancer treatment generate reactive oxygen species (ROS), and a high ROS level diminishes cellular antioxidant capacity and leads to apoptosis and cancer cell death. Antioxidant supplements are consumed widely by cancer patients in order to prevent toxic side effects of cancer treatment to normal tissues and organs. However, the effects of antioxidant supplementation in cancer therapy were largely disappointing. There is still no consensus on the efficacy and safety of dietary antioxidant supplementation during conventional cancer therapy. In some studies, antioxidant supplements did not reduce the risk for cancer or prevent tumour growth; at the contrary, these interventions resulted in some cases to be harmful to the patients. Therefore, a guidance on antioxidant supplementation based on large clinical trials is urgently needed in order to obtain the best possible care and to avoid risky treatments for cancer patients.

The potential role of polyphenolic acetate (PA) in causing diverse biological and pharmacological actions has been well studied in our laboratory. Our investigations, for the first time, established the role of calreticulin transacetylase (CRTAase) in catalyzing the acetylation of nitric oxide synthase (NOS) by Pas leading to robust activation of NOS. 7, 8- Diacetoxy-4-methylcoumarin (DAMC) and other acetoxycoumarins augmented the expression of thioredoxin (TRX) and vascular endothelial growth factor (VEGF) in human peripheral blood mononuclear cells (PBMCs). These findings substantiated our earlier observations that DAMC was a superb inducer of angiogenesis. The enhanced expression of thioredoxin reductase (TRXR) and diminished expression of thioredoxin interacting protein (TRXIP) leading to increased expression and activity of TRX in PBMCs due to the action of DAMC was revealed by real time RT-PCR analysis. The possible activation of TRX due to acetylation was confirmed by the fact that TRX activity of PBMCs was enhanced by variousacetoxycoumarins in tune with their affinities to CRTAase as substrates. DAMC caused enhanced production of NO by way of acetylation of NOS as mentioned above and thereby acted as an inducer of VEGF. Real time RT-PCR and VEGF ELISA results also revealed the overexpression of TRX. DAMC and other PAs were found to reduce the oxidative stress in cells as proved by significant reduction of intracellular ROS levels. Thus, the crucial role of TRX in DAMCinduced angiogenesis with the involvement of VEGF was established.

A proper balance between oxidants and antioxidants is necessary in maintaining health and longevity. Alterations in this balance may result in oxidative stress causing functional disorders and diseases. Oxidative stress is considered to play a vital role in the pathogenesis of diabetes and its complications. Flavanones and flavanones-rich botanical extracts have been a subject of great interest for scientific research. Citrus flavanones like naringin and hesperidin exert a variety of biological activities such as anti-oxidant, anti-inflammatory, antihyperglycemic, anti-apoptotic etc. Naringin and hesperidin along with their respective aglycones, naringenin and hesperetin have been shown to attenuate diabetes and its related complications. This review discusses the role of flavanones as a possible emerging treatment for diabetes and its complications along with the possible mechanistic explanations.