Ageing has been associated with increased oxidative stress(Reference Chung1) and elevated risk of developing CVD(Reference Fares2) and insulin resistance(Reference Fink3). Studies in middle-aged individuals suggest that elevated serum saturated fatty acids are indicative of greater CVD and type-2 diabetes risk(Reference Wang4). Furthermore, serum SFA levels increase with age, whereas levels of the cellular antioxidant glutathione decline(Reference Rebrin and Sohal5). Whether age-associated changes to SFA levels contribute to or arise from an ageing metabolic phenotype, altered redox state and/or vascular inflammation is unknown.
This work has determined the effect of the SFA, palmitate, on intracellular redox status and expression of the integrin CD11b in THP-1 monocytes, a cell surface marker that mediates monocyte interaction with the endothelium.
THP-1 cells were incubated with 50, 150 and 300 μm palmitate conjugated to albumin and albumin-vehicle control as previously described(Reference Gao, Griffiths and Bailey6). This was not associated with a significant loss of viability. The total intracellular level of glutathione (GSH+GSSG) was measured using a DTNB-dependent recycling assay and corrected for protein content determined by BCA assay(Reference Grant, Barber and Griffiths7). Monocyte CD11b expression was determined using flow cytometry(Reference Woollard, Phillips and Griffiths8).
Palmitate treatment (24 h) depleted total glutathione (GSH) levels in THP-1 monocytes: this was significant at 50 μm, but at higher concentrations of palmitate, the GSH levels were not significantly different to control values (Fig. 1). CD11b expression increased dose dependently with increasing palmitate concentration, confirming previous observations (Reference Gao, Griffiths and Bailey6).
Fig. 1. Monocyte incubation with palmitate for 24 h depletes cellular glutathione. *P<0.05 v. control.
The change to cellular glutathione levels indicates that the incubation of monocytes with 50 μm palmitate induces a redox shift after 24 h that is not evident at higher palmitate concentrations. However, the redox shift did not correlate with the enhanced CD11b expression observed with increasing palmitate concentrations.
Together, these data suggest that palmitate may mediate the increased CD11b expression leading to a pro-inflammatory monocyte phenotype typically seen in older adults and manifest as an increased binding of monocytes to endothelium. However, CD11b expression changes are not associated with a redox shift, suggesting that the two phenomena are unrelated.
