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Title: Antioxidents or reduced oxygen tension as a defense system in T cells ex vivo and in vitro
Author: Marthandan, Shiva Shankar
ISNI:       0000 0004 2678 2899
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2009
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Age-related deterioration and dysregulation of T cell function, termed ‘immunosenescence’, may lead to increased mortality and morbidity in humans through greater susceptibility to infections and disease. Previous research from the group of Barnett, suggested that oxidative stress may play a role in the immunosenescence process, through resultant genomic instability, cell cycle delay and arrest. The aim of this research programme was to investigate the effect of the antioxidants, ebselen, NAcetyl L- Cysteine (NAC) or mitoQ or reduced oxygen (O2) tension on markers of T cell function and integrity using CD4+ T cell clones and ex vivo polyclonal human peripheral blood derived mononuclear cells or CD4+ T cells derived from healthy young and older aged donors. The results of this investigation revealed that 30μM ebselen or 7.5mM NAC supplementation significantly increased the lifespan and reduced levels of oxidative DNA damage in clones supplemented from a young in vitro age and in human peripheral blood mononuclear cells and CD4+ T cells ex vivo derived from either age group. The GSH:GSSG ratio was also significantly higher in supplemented clones and cells ex vivo. Ebselen or NAC were not able to bring about such biological effects in clones when supplemented from the midpoint of their in vitro lifespan. In this latter situation, age related changes in T cell physiology example: reduced DNA repair capacity, heat shock response and an accumulation of biomolecule damage may have contributed to these findings. Ebselen or NAC had similar antioxidant effects on polyclonal model system to those found for the in vitro clone model. MitoQ, a mitochondria targeted antioxidant, at 0.5μM or 1μM concentrations, protected T cell genomic DNA from endogenously produced and exogenously applied oxidative stress evident by significantly higher GSH:GSSG ratio and significantly decreased levels of oxidative DNA damage on supplementation. 0.1μM or 0.25μM mitoQ protected genomic DNA from oxidative stress applied exogenously. The antioxidant effect on genomic DNA may be due to saturating concentrations in the mitochondria and the presence of mitoQ in the cytosol. The inability of mitoQ at lower concentrations to protect DNA against endogenously produced ROS may indicate that these lower concentrations of mitoQ may be taken up by the mitochondria, but they were not able to reduce free radical release from the mitochondria explaining no significant differences in endogenous DNA damage levels and is reflected in the lack of changes to GSH:GSSG ratio. It may also be that mitochondrial ROS may not be the only source of oxidative genomic DNA damage. Low O2 culture conditions of 2% O2 for T cells did not reveal an antioxidant potential in T cells ex vivo in a separate study evident by higher levels of oxidative DNA damage and lower GSH:GSSG ratio compared to T cells maintained at 20% O2 culture conditions. The results of this PhD investigation suggest a potential in vivo antiimmunosenescent impact of these antioxidants at carefully selected concentrations.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available