## 2 Materials and Methods
### Biochemical Analysis  
Serum lipid hydroperoxides (LOOHs) were measured using the ferrous oxidation of xylenol orange (FOX-1) assay. Serum samples were thawed and centrifuged at 3000 ref for 5 min at room temperature (Heraeus Labofuge 400R, Fisher Scientific, Loughborough, UK). Standards at concentrations ranging from 0 to 5 m were prepared using hydrogen peroxide (VWR, Leicestershire, UK) in distilled water (18.2 M\(\Omega\)). FOX-1 reagent was prepared in a total volume of 100 mL of 25 mM sulphuric acid (VWR, Leicestershire, UK), supplemented with 250 m ammonium iron (II) sulphate (VWR, Leicestershire, UK), 100 mM sorbitol (VWR, Leicestershire, UK), and 100 mM of xylenol orange (Sigma-Aldrich, Dorset, UK). Using a clear bottom 96-well plate format (Corning, Costar, Sigma-Aldrich, Dorset, UK), 180 mL of FOX-1 reagent was added to 20 mL of serum samples or standards. The reaction mix was incubated at room temperature in the dark for 30 min, and absorbance was measured at 560 nm using a plate reader (Tecan, Infinite M200 pro, software: Magellan). The LOOH concentration in each sample was determined using the generated hydrogen peroxide calibration curve.  
Superoxide dismutase (SOD) concentrations were determined using a commercially available kit (Cayman Chemicals, purchased from Cambridge Bioscience, Cambridge, UK), according to the manufacturer's guidelines. Briefly, standards were prepared as directed by the manufacturer, resulting in the generation of a calibration curve ranging from 0 to 0.050 U/mL SOD activity. Serum samples were thawed on ice and diluted in 1\(\times\) sample buffer at a ratio of 1:5, with 10 uL of each sample (in duplicate added to a well of a clear bottom 96-well plate). A radical detector was added in each well, and the reactions were initiated by adding 20 uL of diluted xanthine oxidase solution. After a 30 min incubation at room temperature, the absorbance of each well was measured at 450 nm using a plate reader (Tecan, Infinite M200 pro, software: Magellan). The SOD activity for each sample was calculated by comparison with the calibration curve and correction for the sample dilution.  
Total glutathione (GSH) was determined according to the manufacturer's guidelines, using a commercially available kit (Cayman Chemicals, Cambridge Bioscience Ltd., Cambridge, UK). Samples were deproteinated using metaphosphoric acid (100 g/L, 1:1 ratio acid to sample, incubated 5 min at room temperature) followed by centrifugation at 3000 rcf for 5 min at room temperature. The supernatant was collected and stored at -20 \({}^{\circ}\)C. Samples were then concentrated by lyophilisation (Edwards Modulo Freeze Dryer) for 24 h, and the residues were reconstituted using 1\(\times\) MES buffer to 1/3 of its original recovered volume from the deproteination step. Samples were adjusted to pH 7 by the addition of TEAM reagent (531 uL of triethanolamine (Sigma-Aldrich, T58300) and 469 uL of distilled water ((18.2 M\(\Omega\)), 50 uL per mL of the original recovered volume). Standards were also prepared using glutathione disulphide (GSSG) mixed with MES buffer at concentrations ranging from 0 to 8.0 uM. Samples or standards (50 uL) were added in duplicate to a clear bottom 96-well plate and assay cocktail (11.25 mL of 1\(\times\) MES buffer, 0.45 mL reconstituted cofactor mixture, 2.1 mL enzyme mixture, and 2.3 mL of 18.2 M\(\Omega\) water, 150 uL per well) was added. After a 25 min incubation at room temperature, absorbance was measured at 410 nm using a plate reader (Tecan, Infinite M200 pro, software, Magellan). Total GSSG was calculated for each sample by a comparison against the calibration curve.