Specialized Pro-Resolving Mediator (SPM) Profile in Blood from Children with Sickle Cell Disease (SCD): Comparison with Age-, and Race- Matched Controls

Introduction: Specialized Pro-resolving Mediators (SPMs) are lipid mediators, biosynthesized from the n-3 polyunsaturated fatty acids (PUFAs) docosahexaenoic acid (DHA), docosapentaenoic acid (DPA) and eicosapentaenoic acid (EPA); and the n-6 PUFA arachidonic acid (AA). SPMs are grouped into four families of lipid mediators including resolvins, protectins, maresins and lipoxins; and these mediators play a role in the resolution of inflammation. Inflammation plays a crucial role in the pathogenesis of clinical complications in sickle cell disease (SCD). In addition, multiple studies in SCD have documented decreased levels of anti-inflammatory fatty acids DHA and EPA in blood cells and plasma. We assessed whether the decreased DHA and EPA content play a role in modulation of peripheral blood SPM levels in SCD.

Methods: Using targeted liquid chromatography (LC)-tandem mass spectrometry (MS/MS), we investigated plasma SPM profile in children with SCD in steady state (n=45, subjects with confirmed SCD genotypes SS and Sβ⁰ thalassemia, ages 2-20 years), and compared to that from an age- and race-matched control group (n=24). Analysis also included the SPM pathway markers, prostaglandins, thromboxane and leukotriene and their metabolites. (n-3) PUFA content in total blood cells was measured in both groups using capillary gas chromatography.

Results: Consistent with the published results, a significant decrease in (n-3) PUFA content (measured as percent of total fatty acids) was noted in children with SCD (2.14% ± 0.47% in SCD vs 2.39% ± 0.45% in control, mean ± SD, P=0.04). In plasma from both SCD and controls, we identified and quantitated 6 SPMs which included DHA-derived resolvin (Rv) D1, RvD3 and 17R-RvD3; EPA-derived RvE2; and DPA(n-3)-derived RvD5(n-3) and protectin D (PD)-1 (n-3). Median RvD1 level (pg/ml) in SCD plasma was significantly elevated (65 in SCD vs 36 in controls, P=0.002). Levels of other SPMs were not significantly different between the two groups. Multiple SPM pathway markers including mono-hydroxy-PUFAs (EPA-derived 5-HEPE, 12-HEPE, 15-HEPE and 18-HEPE; DHA-derived 4-HDHA, 7-HDHA and 14-HDHA; and AA-derived 5-HETE, 12-HETE and 15-HETE) were present in both control and SCD plasma. Levels (median, pg/ml) of 5-lipoxygenase-derived EPA-metabolite 5-HEPE (212 vs 122, P=0.027) and DHA-derived metabolite 7-HDHA (62 vs 39, P=0.036), and 12-lipoxygenase-derived AA-metabolite 12-HETE (16783 vs 11796, P=0.025) were increased significantly in SCD compared to those from the controls. 15-Lipoxygenase derived pathway markers (15-HEPE and 15-HETE) were not different between the two groups. The cyclo-oxygenase-derived eicosanoids identified and quantitated in both groups included PGE2, PGD2 and TxB2 with a significant increase observed in TxB2 level in SCD plasma (1213 vs 970 pg/ml, P=0.038). Leukotriene (LT) B4 (an AA-derived pro-inflammatory mediator) and lipoxins (AA-derived SPMs), and their metabolites 20-OH-LTB4 and 20-COOH-LTB4 were absent in plasma from both SCD and control.

Conclusions: Our results taken together demonstrate that the decreased bioavailability of (n-3) PUFA in children with SCD does not appear to limit SPM production in steady state as documented with normal/increased plasma levels of SPMs and their pathway markers. Whether the SPM profile in circulation is different in SCD pathologies associated with inflammation including vaso-occlusive pain crisis and acute chest syndrome, compared to steady state disease, require further investigation.

No relevant conflicts of interest to declare.