Secretory Phospholipase A2(sPLA2) in Patients with Sickle Cell Disease (SCD) Hospitalized for Vaso-Occlusive Pain Episodes (VOE)

Introduction: Acute chest syndrome (ACS) is a leading cause of morbidity and mortality in patients with SCD. Severe ACS often develops during the course of an acute VOE with symptoms ranging from fever and chest pain (CP) to respiratory distress. SPLA₂ is a potent inflammatory mediator that is elevated in multiple human chronic diseases such as rheumatoid arthritis, viral and bacterial infections, and septic shock among others. Previous studies in SCD have reported elevated levels of sPLA₂ in patients presenting with ACS and suggest a role for sPLA₂ in predicting development of ACS. Understanding the role of sPLA₂ in the pathogenesis of ACS could provide insights into the inflammatory mechanisms underlying this complication and offer potential therapeutic targets for improving patient outcomes in SCD.

Objective: To assess sPLA₂ levels and ACS in patients with SCD hospitalized for VOE receiving intravenous (IV) arginine therapy vs placebo.

Methods: Secondary analysis of samples collected from a pK/PD and phase II randomized placebo-controlled trial of IV arginine in patients 3-21 years with SCD-VOE. Plasma sPLA₂ levels at emergency department (ED) presentation and hospital discharge (DC) were analyzed via ELISA. Plasma levels ≥ 20 ng/mL are considered elevated based on non-SCD studies with a higher cutoff ≥48 ng/mL previously established for SCD. Vital signs, clinical labs, and plasma amino acids were analyzed.

Results: 105 patients (mean 12.7±3.7 years, 48% male, 67% HbSS and 70% on Hydroxyurea) were included. Mean plasma sPLA₂ at ED presentation was (41.4±38.2 ng/mL), with elevated sPLA₂ levels ≥20 ng/mL found in 64% of patients, and levels ≥48 ng/mL found in 33% (n=35) of patients. There were no significant differences in patient demographics based on sPLA₂ ≥ vs < 48 ng/mL. In this cohort, 11 subjects (10.5%) were diagnosed with ACS and 46 (44%) had CP during admission. SPLA₂ levels trended higher in patients with ACS vs No ACS at ED presentation (61.3±35.0 vs 40.0±38.0 ng/mL, p=0.08) and became significantly different on Day 2 of hospital stay (88.1±47.7 vs 53.4±47.0 ng/mL, p=0.02) remaining significantly elevated at DC (70.6±42.3 vs 41.4±34.7, p=0.01). Mean sPLA2 levels in patients with and without CP-No ACS were similar, however sPLA2 levels trended higher in patients with ACS vs CP-No ACS (61.3±35.0 vs 37.3±37.4, p=0.06). Plasma sPLA₂ levels ≥20 ng/mL were observed in 82% of subjects with ACS and 60% of those with CP, nearly identical to patients without ACS. Using the SCD-specific cutoff of 48 ng/mL, sPLA₂ elevation was predominantly seen in patients with ACS vs no ACS (64% vs 30%, p=0.02). Plasma sPLA₂ levels remained elevated ≥48 ng/mL in 35% of subjects at DC. A SCD cutoff of sPLA₂ ≥48 ng/mL in this cohort yielded a sensitivity=64%, specificity=70%, NPV=94% and PPV=20% in predicting ACS. Patients with fever at presentation had significantly higher mean sPLA₂ vs no fever (70.0±40.6, n=14 vs 37.8±36.1 ng/mL, n=91, p=0.003). Plasma sPLA₂ levels positively correlated with respiratory rate (r=0.32, p=0.0009), pulse (r=0.28, p=0.004), temperature (r= 0.32, p=0.0009), blood neutrophil count (r=0.43, p<0.0001), absolute neutrophil count (r=0.22, p=0.03), and aspartate amino transferase (r=0.24, p=0.02) in the ED, negatively correlating with lymphocyte count (r= -0.37, p=0.0001). An inverse correlation was identified between baseline sPLA₂ and plasma arginine (r= -0.24, p= 0.02) and citrulline levels (r= -0.33, p= 0.0005). Notably, the larger the increase in plasma arginine concentration, the greater the decrease in sPLA₂ from baseline to DC (r= -0.25, p= 0.04). Of patients with elevated sPLA₂ ≥48 ng/mL, plasma levels decreased significantly by DC only in patients who received IV arginine vs placebo (-27.8±38.1 ng/mL, p=0.002, n=23 vs -15.0±41.2 ng/mL, p=0.23, n=12) respectively.

Conclusion: Elevated sPLA₂ levels are prevalent in patients with SCD-VOE, with the most pronounced increase occurring in ACS, consistent with prior studies. Given the high NPV, low sPLA₂ levels may be most helpful in ruling out ACS. Lower arginine levels were associated with higher sPLA₂, while arginine therapy was associated with a greater decrease in sPLA₂ levels at DC vs placebo. This suggests a potential role for arginine in modulating inflammation in patients with SCD-VOE not previously reported. Further research is warranted to explore the mechanistic links between sPLA₂, ACS and arginine in SCD.