Imbalance in Arachidonic Acid to Docosahexaenoic Acid Ratios in the Sickle Red Cell Is Associated with Inflammation.

The polyunsaturated fatty acids (PUFAs): arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are structural and functional components of normal cell membranes. These fatty acids are precursors of several bioactive lipid mediators including eicosanoids, resolvins and protectins that regulate many cellular functions including inflammation (Annu Rev Pathol Mech Dis 3:279; 2008). We investigated whether the red cell membrane PUFA composition was abnormal in children with homozygous HbSS disease (HbSS) in an attempt to identify whether any of the pathobiologic processes such as inflammation and/or hemolysis noted in HbSS are related to PUFA deficiency. The study population included 18 children with HbSS (ages 2 to 16 years) and 10 age- and race- matched controls. Fatty acid content of membrane phospholipids (PLPs) was measured by capillary gas chromatography following isolation of total red cell lipids and transmethylation of resolved PLPs. PLPs analyzed included phosphatidylcholine or PC (an outer leaflet membrane PLP), phosphatidylserine or PS and phosphatidylethanolamine or PE (two inner leaflet membrane PLPs). Since the n-6 PUFA, AA, is a precursor of pro-inflammatory eicosanoids, and since the n-3 PUFA, DHA, contributes to the generation of anti-inflammatory resolvins and protectins, we also determined AA/DHA ratios to assess for imbalances in AA to DHA in each of these PLP fractions.

As shown in the Table, the AA/DHA ratios were increased in all three PLP fractions. In the PC and PS fractions, this change in ratio was due to significant decreases in membrane DHA. In the PE fraction the abnormal AA/DHA ratio was due to an elevation in AA content. We next assessed whether DHA deficiency in children with HbSS disease was associated with abnormal inflammatory and/or hemolytic biomarkers. Hemolytic markers evaluated were plasma LDH, hemoglobin, hematocrit, and reticulocyte count. Inflammatory markers assessed included WBC count, absolute polys, and plasma levels of high sensitivity C-reactive protein or hs-CRP (Nat Clin Pract Cardiovasc Med 2:29; 2005). Correlations with these biomarkers were tested for both membrane DHA content and the AA/DHA ratio. Hs-CRP was the only biomarker that demonstrated significant correlations. Hs-CRP correlated positively with AA/DHA ratios from all three PLP fractions (r=0.51 to 0.58, P=0.01 to 0.03) and negatively with DHA content (r=−0.43 to −0.52, P=0.03 to 0.05). Recent evidence suggest that inflammation plays a role in sickle cell disease (SCD) pathophysiology including microvessel occlusion. A previous pilot study in adult patients with SCD has also demonstrated that oral EPA and DHA supplementation (as in fish oil) decreased the number of vaso-occlusive or painful episodes (Thromb Haemost 85:966; 2001). Such previous reports together with our current data which demonstrate an imbalance in membrane AA and DHA (the precursors of potent pro- and anti-inflammatory mediators) suggest that the n-3 and n-6 PUFAs may play a role in SCD microvessel pathophysiology.

No relevant conflicts of interest to declare.