Protection and Recycling of α-Tocopherol in Human Erythrocytes by Intracellular Ascorbic Acid (2023)

The imbalance between pro-oxidants and antioxidants in favour of high levels of pro-oxidants may result in several chronic diseases, including CVD and complications associated with its risk factors such as metabolic syndrome and diabetes mellitus. Increased production of reactive oxygen species (ROS) implicated in the pathogenesis of CVD, and it is probably mediated in part by the oxidative modification of lipoproteins like LDL and HDL. Oxidation of LDL results in endothelial dysfunction and plays a vital role in the atherogenic process and vascular diseases. Moreover, ROS play a critical role in endothelial dysfunction, vascular smooth muscle cell remodelling, and monocyte migration, initiation of inflammation, and development of metabolic disorders. The pro-oxidant-antioxidant balance (PAB) assay is a relatively simple, rapid, and cheap technique that attempts to assess pro and antioxidant activities in a single assay. Since it strives to provide an integrated value for the concentration of pro-oxidants and antioxidants, the PAB assay is calibrated based on different proportions of hydrogen peroxide and uric acid. It serves as an appropriate standard for detecting the capacity of the pro-and antioxidant present in biological fluids. A high serum PAB may be expected to be associated with an increased ROS production that would cause the oxidation of bio-molecules and cellular injury. Serum PAB as a prognostic index in assessing the risk of atherosclerosis and inflammation process was known. This review summarized the association of serum PAB with CVD and its traditional risk factors.

Erythrocytes (RBCs) have been widely investigated as a promising carrier system for the efficient delivery of active molecules. Resealed RBCs possess some outstanding features, for instance, excellent biocompatibility, as well as biodegradability, extended half-life in the bloodstream, as well as the good entrapping ability for a wide range of drugs, which make RBCs superior over other carriers. Resealed RBCs can be obtained by collecting them through blood samples from the source of interest (e.g., human, rats, rabbits, pig, etc.) following the separation of RBCs. Afterward, several techniques such as hypotonic dialysis, hypotonic dilution, hypotonic preswelling, endocytosis, lipid-fusion, electric cell-fusion, and chemical perturbation are employed for efficient loading of drugs. Moreover, resealed RBCs have shown great aptitude as a drug carrier with an exceptional capacity to improve the therapeutic index. Besides, RBCs have been reported for the incredible potential to attain site-specific delivery along with the extended-release of active molecules. Eventually, this chapter provides deep insight into various drug-loading techniques, characterization, as well as applications of RBCs in biomedical applications.

Four tocopherols are available in nature and are absorbed with the diet, but only one RRR-α-tocopherol satisfies the criteria of being a vitamin. The biological activity of the different tocopherols studied in the rat by the resorption-gestation test has been inconsistently extrapolated to human beings where the tocopherols have no influence on a successful pregnancy. Diminution of RRR-α-tocopherol intake results in diseases characterized by ataxia, whose pathogenetic mechanism, despite vigorous claims, has not been clarified. The calculation of the Daily Reference Intake (DRI), necessary to prevent disease, is based on an obsolete test, the peroxide-induced erythrocyte hemolysis, called the gold standard, but of highly questioned validity. If many epidemiological studies have given positive results, showing prevention by high vitamin E containing diets of cardiovascular events, neurodegenerative disease, macular degeneration and cancer, the clinical confirmatory intervention studies were mostly negative. On the positive side, besides preventing vitamin E deficiency diseases, vitamin E has shown efficacy as anti-inflammatory and immune boosting compound. It has also shown some efficacy in protecting against nonalcoholic hepato-steatosis. At a molecular level, vitamin E and some of its metabolites have shown capacity of regulating cell signaling and modulating gene transcription.

Free Radical Biology and Medicine, Volume 74, 2014, pp. 35-49

Hydrogen peroxide (H₂O₂) metabolism in human erythrocytes has been thoroughly investigated, but unclear points persist. By integrating the available data into a mathematical model that accurately represents the current understanding and comparing computational predictions to observations we sought to (a) identify inconsistencies in present knowledge, (b) propose resolutions, and (c) examine their functional implications. The systematic confrontation of computational predictions with experimental observations of the responses of intact erythrocytes highlighted the following important discrepancy. The high rate constant (10⁷–10⁸M⁻¹s⁻¹) for H₂O₂ reduction determined for purified peroxiredoxin II (Prx2) and the high abundance of this protein indicate that under physiological conditions it consumes practically all the H₂O₂. However, this is inconsistent with extensive evidence that Prx2’s contribution to H₂O₂ elimination is comparable to that of catalase. Models modified such that Prx2’s effective peroxidase activity is just 10⁵M⁻¹s⁻¹ agree near quantitatively with extensive experimental observations. This low effective activity is probably due to a strong but readily reversible inhibition of Prx2’s peroxidatic activity in intact cells, implying that the main role of Prx2 in human erythrocytes is not to eliminate peroxide substrates. Simulations of the responses to physiological H₂O₂ stimuli highlight that a design combining abundant Prx2 with a low effective peroxidase activity spares NADPH while improving potential signaling properties of the Prx2/thioredoxin/thioredoxin reductase system.

Archives of Biochemistry and Biophysics, Volume 662, 2019, pp. 111-120

Toxicity mediated by free heme has emerged as an important element of end organ injuries and adverse outcomes in critically ill disease states. Free heme is thought to be derived from oxidative denaturation of free hemoglobin, secondary to red cell hemolysis. In this study, we evaluated the ability of oxidants (H₂O₂, nitrite, peroxynitrite and hypochlorous acid) formed during inflammation to cause heme release from purified hemoglobin and hemolysates, at pH 7.4 and 6.8. Supraphysiological concentrations of nitrite, peroxynitrite or hypochlorous acid were required to cause appreciable heme release from either free hemoglobin or hemolysates. However, H₂O₂ administered as a bolus or generated in situ, was more potent at promoting free heme release with free hemoglobin. With hemolysates, only in situ H₂O₂ formation resulted in significant free heme release. In all cases, free heme release was higher at lower pH and required oxidation of ferrous heme, but was not dependent on ferrylHb formation. Moreover, ligating ferric heme with cyanide or blocking the β93Cys did not prevent, but in fact increased free heme release. The salient observations from this study are that free heme release is likely mediated by continuous generation of H₂O₂ versus other heme oxidants, and facilitated at low pH.

Clinica Chimica Acta, Volume 457, 2016, pp. 125-129

Bioorganic & Medicinal Chemistry Letters, Volume 24, Issue 21, 2014, pp. 5107-5110

Efficient methods for the preparation of 5′-substituted 5′-amino-5′-deoxy-N⁶-ureidoadenosine derivatives are described. Compounds were screened for antiproliferative activity against a panel of murine and human cell lines (L1210, CEM, and HeLa) and/or against the NCI-60. The most potent derivative inhibited the lung adenocarcinoma cell line NCI-H522 at low nanomolar concentrations (GI₅₀=9.7nM).

Environmental Toxicology and Pharmacology, Volume 37, Issue 3, 2014, pp. 897-906

Around the world scientists try to design successful cures against still incurable diseases, especially cancers. New targets for prevention and new agents for therapy need to be identified. We synthesized novel metal complexes [Au(L1)(L2)Pt]Cl2 and [Ru(L1)2(L2)Pt]Cl2 for determining their cytotoxic and apoptotic effects. The complexes are synthesized by using 1,8-diaminonaphthalene (L1), and bis-1,4-di[([1,10]phenanthroline-5-il)aminomethyl]cyclohexane (L2) as ligands. This is the first study to examine these metals and these molecules in cancer treatment. We elucidated the effects of test compounds with embryonic rat fibroblast-like cells (F2408) and H-ras oncogene activated embryonic rat fibroblast-like cancer cells (5RP7). Results showed that our complexes are more effective than cisplatin to kill ras-transformed cells. Although the [Au(L1)(L2)Pt]Cl2 compound showed a cytotoxic potency higher than [Ru(L1)2(L2)Pt]Cl2 against cancer cells, it proved to be almost five times less effective in decreasing cell viability over healthy cells. Au(III) compound selectively targets the cancer cells but not the healthy cells.

DNA Repair, Volume 21, 2014, pp. 165-170

The ability of the radiomimetic anti-tumor enediyne C-1027 to induce DNA inter-strand crosslinks (ICLs), in addition to the expected DNA strand breaks, is unique among traditional DNA targeted cancer therapies. Importantly, radiation therapy and most radiomimetic drugs have diminished effect in hypoxic environments due to decreased induction of DNA strand breaks, which is an oxygen requiring process. However, C-1027's induction of ICLs is enhanced under hypoxia and it is actually more potent against hypoxic cells, overcoming this common tumor resistance mechanism. In this study, an analog of C-1027, 20′-deschloro-C-1027 was examined for its ability to induce DNA ICLs under hypoxic conditions. Deschloro-induced ICLs were detected under hypoxic cell-free conditions, with a concomitant reduction in the induction of DNA strand breaks. In cells deschloro behaved similarly, inducing cellular ICLs under hypoxic conditions with a reduction in DNA breaks. The cytotoxicity of deschloro treatment was similar in normoxic and hypoxic cells, suggesting that the ICL induction allows deschloro to retain its cytotoxic activity under hypoxia. It appears that rational engineering of the C-1027 family of radiomimetics holds promise toward overcoming the radioresistance associated with the hypoxic environment associated with solid tumors.