The antioxidant capacity of erythrocyte concentrates is increased during the first week of storage and correlated with the uric acid level

Background and Objectives: Red blood cells (RBCs) suffer from lesions during cold storage, depending in part on their ability to counterbalance oxidative stress by activating their antioxidant defence. The aim of this study was to monitor the antioxidant power (AOP) in erythrocyte concentrates (ECs) during cold storage. Materials and Methods: Six ECs were prepared in saline-adenine-glucose-mannitol (SAGM) additive solution and followed during 43 days. The AOP was quantified electrochemically using disposable electrode strips and compared with results obtained from a colorimetric assay. Haematological data, data on haemolysis and the extracellular concentration of uric acid were also recorded. Additionally, a kinetic model was developed to extract quantitative kinetic data on the AOP behaviour. Results: The AOP of total ECs and their extracellular samples attained a maximum after 1 week of storage prior to decaying and reaching a plateau, as shown by the electrochemical measurements. The observed trend was confirmed with a colorimetric assay. Uric acid had a major contribution to the extracellular AOP. Interestingly, the AOP and uric acid levels were linked to the sex of the donors. Conclusion: The marked increase in AOP during the first week of storage suggests that RBCs are impacted early by the modification of their environment. The AOP behaviour reflects the changes in metabolism activity following the adjustment of the extracellular uric acid level. Knowing the origin, interdonor variability and the effects of the AOP on the RBCs could be beneficial for the storage quality, which will have to be further studied

MODELING HEME MONOOXYGENASES WITH CATIONIC METALLOPORPHYRINS IN NON-AQUEOUS MEDIA

As models for cytochrome P450, cationic manganese porphyrin complexes were used to study oxygen atom transfer reactions in non-aqueous solvents. Typically water-soluble, cationic metalloporphyrins when converted to a hexafluorophosphate (PF6) salt are soluble in organic solvents affording catalysts for epoxidation and hydroxylation of olefins and hydrocarbons. Of the catalysts tested, MnTM-4-PyP[PF6]4, manganese(III) [(5,10,15,20-tetrakis(N-methylpyridinium-4-yl) porphyrin)] yielded the highest conversion of cyclooctene to cyclooctene epoxide in dry acetonitrile with iodosylbenzene. The effect of electron withdrawing groups on the porphyrin macrocycle was investigated by chlorination of the TM-4-PyP ligand. MnOCTM-4-PyP[PF6]4, manganese(III) β-octa-chlorinated tetrakis(N-methylpyridinium-4-yl)porphyrin was synthesized with sulfuryl chloride via a nickel porphyrin intermediate for the complete β-chlorination of the porphyrin macrocycle. β-chlorination led to destabilization of the porphyrin macrocycle and subsequent bleaching of the ligand, resulting in lower turnover for epoxidation compared to un-chlorinated MnTM-4-PyP[PF6]4. The reactivity of oxo-manganese porphyrins toward C-H abstraction and oxygen atom transfer has been studied using three radical clocks substrates. Products from the manganese porphyrin oxidation of bicyclohexane, norcarane and bicyclopentane, substrates with krearr ranging from 2 x 107 s-1 to 2 x 109 s-1, demonstrated a hydrogen abstraction and radical rebound mechanism for hydroxylation. From the observed ratio of unrearranged to rearranged products from the manganese porphyrin oxidation of bicyclohexane, norcarane and bicyclopentane, the rebound rate (kreb) was determined for hydroxylation by MnTM-4-PyP ranging from 109 to 1011 s-1. In addition to hydroxylated products, bicyclohexane and norcarane yielded products by desaturation. Desaturation arises from the regioselective oxidation at an alternative C-H bond, generating a carbon-centered radical beta to a cyclopropyl followed by a second hydrogen abstraction from a hydroxo-manganese(IV) intermediate generating an olefin. For the oxidation of more structurally complex substrates, manganese, iron and ruthenium porphyrin catalysts were successful in preparing metabolites of the anti-malarial drug artemisinin. The hydroxylation of artemisinin demonstrates the utility of a metalloporphyrin screen for late-stage C-H activation of drug molecules affording substrate diversification. In summary, metalloporphyrin model systems have been shown to be efficient catalysts for modeling a variety of reactions undertaken by cytochrome P450 including hydroxylation, epoxidation and desaturation