Nucleoside 5'-phosphorothioate derivatives as oxidative stress protectants in PC12 cells

DNA Backbone Sulfur-Modification Expands Microbial Growth Range under Multiple Stresses by its anti-oxidation function

DNA phosphorothioate (PT) modification is a sulfur modification on the backbone of DNA introduced by the proteins DndA-E. It has been detected within many bacteria isolates and metagenomic datasets, including human pathogens, and is considered to be widely distributed in nature. However, little is known about the physiological function of this modification, and thus its evolutionary significance and application potential remains largely a mystery. In this study, we focused on the advantages of DNA PT modification to bacterial cells coping with environmental stresses. We show that the mesophile Escherichia coli and the extremophile Shewanella piezotolerans both expanded their growth ranges following exposure to extreme temperature, salinity, pH, pressure, UV, X-ray and heavy metals as a result of DNA phophorothioation. The phophorothioated DNA reacted to both H₂O₂ and hydroxyl radicals in vivo, and protected genomic DNA as well as sensitive enzymes from intracellular oxidative damage. We further demonstrate that this process has evolved separate from its associated role in DNA restriction and modification. These findings provide a physiological role for a covalent modification widespread in nature and suggest possible applications in biotechnology and biomedicine.

Nucleoside-2′,3′/3′,5′-bis(thio)phosphate antioxidants are also capable of disassembly of amyloid beta42-Zn(ii)/Cu(ii) aggregates via Zn(ii)/Cu(ii)-chelation

Nucleoside-2′,3′/3′,5′-bis(thio)phosphate antioxidants were identified as efficient agents of disassembly of Aβ₄₂-Zn(ii)/Cu(ii) aggregates by M(ii)-chelation, thus making promising scaffolds for new Alzheimer's disease therapeutics.

Identification of Highly Promising Antioxidants/Neuroprotectants Based on Nucleoside 5'-Phosphorothioate Scaffold. Synthesis, Activity, and Mechanisms of Action

With a view to identify novel and biocompatible neuroprotectants, we designed nucleoside 5'-thiophosphate analogues, 6-11. We identified 2-SMe-ADP(α-S), 7A, as a most promising neuroprotectant. 7A reduced ROS production in PC12 cells under oxidizing conditions, IC50 of 0.08 vs 21 μM for ADP. Furthermore, 7A rescued primary neurons subjected to oxidation, EC50 of 0.04 vs 19 μM for ADP. 7A is a most potent P2Y1-R agonist, EC50 of 0.0026 μM. Activity of 7A in cells involved P2Y1/12-R as indicated by blocking P2Y12-R or P2Y1-R. Compound 7A inhibited Fenton reaction better than EDTA, IC50 of 37 vs 54 μM, due to radical scavenging, IC50 of 12.5 vs 30 μM for ADP, and Fe(II)-chelation, IC50 of 80 vs >200 μM for ADP (ferrozine assay). In addition, 7A was stable in human blood serum, t1/2 of 15 vs 1.5 h for ADP, and resisted hydrolysis by NPP1/3, 2-fold vs ADP. Hence, we propose 7A as a highly promising neuroprotectant.

A review on the chemical synthesis of pyrophosphate bonds in bioactive nucleoside diphosphate analogs

Currently, there is an ongoing interest in the synthesis of nucleoside diphosphate analogs as important regulators in catabolism/anabolism, and their potential applications as mechanistic probes and chemical tools for bioassays. However, the pyrophosphate bond formation step remains as the bottleneck. In this Digest, the chemical synthesis of the pyrophosphate bonds of representative bioactive nucleoside diphosphate analogs, i.e. phosphorus-modified analogs, nucleoside cyclic diphosphates, and nucleoside diphosphate conjugates, will be described.

ATP-γ-S-(α,β-CH2) protects against oxidative stress and amyloid beta toxicity in neuronal culture

Amyloid beta (Aβ) oligomers and oxidative stress, typical of Alzheimer's disease, are highly neurotoxic. Previously we identified ATP-γ-S as a most promising antioxidant and neuroprotectant. To further improve both potency and metabolic stability of ATP-γ-S, we designed a related analogue, ATP-γ-S-(α,β-CH2). We found that ATP-γ-S-(α,β-CH2) effectively inhibited ROS formation in PC12 cells subjected to Fe(II)-oxidation, slightly better than ATP-γ-S (IC50 0.18 and 0.20 μM, respectively). Moreover, ATP-γ-S-(α,β-CH2) rescued primary neurons from Aβ42 toxicity, 4-fold more potently than ATP-γ-S, (IC50 0.2 and 0.8 μM, respectively). In addition, the metabolic stability of ATP-γ-S-(α,β-CH2) in PC12 cells during 4 h of incubation, was up to 20% greater than that of ATP-γ-S and ATP. Previously, we found that ATP-γ-S-(α,β-CH2) resisted hydrolysis by ecto-nucleotidases such as, NPPs and TNAP, and was found to be ∼7-fold more potent agonist than ATP at P2Y11 receptor. Therefore, we propose ATP-γ-S-(α,β-CH2) as a promising agent for rescue of neurons from insults typical of Alzheimer's disease.

Nucleoside 5'-phosphorothioate derivatives are highly effective neuroprotectants

The brain is especially sensitive to oxidative stress due to its high rate of oxidative metabolism, relatively low levels of antioxidant enzymes, and high concentrations of Fe/Cu ions. During the neurodegeneration process, the aggregation of proteins Aβ, accompanies oxidative stress. We explored the potential of thiophosphate derivatives to rescue neurons from oxidative stress and Aβ toxicity. We evaluated the neuroprotective effect of ATP-γ-S, ADP-β-S, and GDP-β-S on primary cortical neuronal cells exposed to several insults, including treatment with FeSO4, co-application of H2O2 and FeSO4, and addition of Aβ42. Upon treatment with FeSO4, phosphorothioate analogues exhibited up to 3000-fold better neuroprotectant activity than the corresponding parent nucleotides. Likewise, phosphorothioate analogues proved to be up to 30-fold better neuroprotectants than the corresponding parent nucleotides upon treatment with both H2O2 and FeSO4. When we exposed primary neuron and astrocyte cultures to 50 μM Aβ42-induced cell death, we found that ATP-γ-S significantly improved cell morphology and maintained culture viability with an IC50 value of 0.8 μM. Finally, we evaluated the viability of neuroblastoma cells under hypoxic conditions in the presence of ATP-γ-S and found that the latter was involved in the regulation of HIF-1a and stabilized mRNA levels of vascular endothelial growth factor (VEGF) and glucose transporter 1 (GLUT-1), which promote cell survival and proliferation. Based on its high potency as a neuroprotectant, we propose ATP-γ-S as a highly promising, biocompatible, and water-soluble drug candidate for the treatment of neurodegenerative disorders.

Nucleoside-2',3'/3',5'-bis(thio)phosphate analogues are promising antioxidants acting mainly via Cu+/Fe2+ ion chelation

We synthesized a series of adenine/guanine 2',3'- or 3',5'-bisphosphate and -bisphosphorothioate analogues, 1-6, as potential Cu(+)/Fe(2+) chelators, with a view to apply them as biocompatible and water-soluble antioxidants. We found that electron paramagnetic resonance (EPR)-monitored inhibition of OH radicals production from H2O2, in an Fe(2+)-H2O2 system, by bisphosphate derivatives 1, 3, and 5 (IC50 = 36, 24, and 40 μM, respectively), was more effective than it was by ethylenediaminetetraacetic acid (EDTA), by a factor of 1.5, 2, and 1.4, respectively. Moreover, 2'-deoxyadenosine-3',5'-bisphosphate, 1, was 1.8- and 4.7-times more potent than adenosine 5'-monophosphate (AMP) and adenosine 5'-diphosphate (ADP), respectively. The bisphosphorothioate derivatives 2, 4, and 6 (IC50 = 92, 50, and 80 μM, respectively), exhibited a dual antioxidant activity, acting as both metal-ion chelators and radical scavengers [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assay data indicates IC50 = 50, 70, and 108 μM vs 27 μM for Trolox]. Only 2'-deoxyadenosine-3',5'-bisphosphorothioate, 2, exhibited good inhibition of Cu(+)-induced H2O2 decomposition (IC50 = 78 vs 224 μM for EDTA). Nucleoside-bisphosphorothioate analogues (2, 4, and 6) were weaker inhibitors than the corresponding bisphosphate analogues (1, 3, and 5), due to intramolecular oxidation under Fenton reaction conditions. (1)H- and (31)P NMR monitored Cu(+) titration of 2, showed that Cu(+) was coordinated by both 3',5'-bisphosphorothioate groups, as well as N7-nitrogen atom, while adenosine-2',3'-bisphosphorothioate, 6, coordinated Cu(+) only by 2',3'-bisphosphorothioate groups. In conclusion, an additional terminal phosphate group on AMP/guanosine 5'-monophosphate (GMP) resulted in Fe(2+)-selective chelators highly potent as Fenton reaction inhibitors.