Lactate dehydrogenase as a biomarker of hemolysis-associated nitric oxide resistance, priapism, leg ulceration, pulmonary hypertension, and death in patients with sickle cell disease

Abstract

Pulmonary hypertension is prevalent in adult patients with sickle cell disease and is strongly associated with early mortality and markers of hemolysis, in particular, serum lactate dehydrogenase (LDH). Intravascular hemolysis leads to impaired bioavailability of nitric oxide (NO), mediated by NO scavenging by plasma oxyhemoglobin and by arginine degradation by plasma arginase. We hypothesized that serum LDH may represent a convenient biomarker of intravascular hemolysis and NO bioavailability, characterizing a clinical subphenotype of hemolysis-associated vasculopathy. In a cohort of 213 patients with sickle cell disease, we found statistically significant associations of steady-state LDH with low levels of hemoglobin and haptoglobin and high levels of reticulocytes, bilirubin, plasma hemoglobin, aspartate aminotransferase, arginase, and soluble adhesion molecules. LDH isoenzyme fractionation confirmed predominance of LD1 and LD2, the principal isoforms within erythrocytes. In a subgroup, LDH levels closely correlated with plasma cell-free hemoglobin, accelerated NO consumption by plasma, and impaired vasodilatory responses to an NO donor. Remarkably, this simple biomarker was associated with a clinical subphenotype of pulmonary hypertension, leg ulceration, priapism, and risk of death in patients with sickle cell disease. We propose that LDH elevation identifies patients with a syndrome of hemolysis-associated NO resistance, endothelial dysfunction, and end-organ vasculopathy.

Figure 1.

Serum LDH levels and isoenzyme distribution in patients with sickle cell disease. (A) Distribution of LDH levels on 50 occasions in 33 patients with sickle cell disease. Nearly all results are above the normal range (113-226 IU/L). (B) LDH isoenzyme fractionation of each sample suggests a tendency for the patient values to fall above the normal range (vertical bars to the right of each distribution) for LD1 and LD2 and below the normal range for LD3, LD4, and LD5 isoenzymes.

Figure 2.

Serum LDH as a marker of intravascular hemolysis and NO resistance in 26 patients with sickle cell disease. Serum LDH levels correlate with plasma heme levels (A) and the amount of plasma NO consumption (B) as measured by an in vitro assay (Spearman correlation). (C) Patients with higher LDH levels (340-589 IU/L, n = 13) have NO resistance compared to patients with lower LDH levels (190-337 IU/L, n = 13) as indicated by the blunted degree of increased forearm blood flow induced by brachial artery infusion of the NO donor sodium nitroprusside at 0.8, 1.6, and 3.2 μg/min, measured by venous occlusion plethysmography (P = .016, ANOVA with repeated measures). Results are depicted as mean ± SEM.

Figure 3.

Relationship of serum LDH levels and history of vasculopathic complications. (A) The frequency distribution of 213 patients with sickle cell disease by LDH level in hundreds is indicated by the vertical bars. For comparison of the prevalence of selected sickle cell complications, data from 213 patients are divided into 3 groups according to serum LDH levels. The low LDH is defined by LDH levels lower than 1 SD below the overall mean (range, 121-189 IU/L), medium LDH by overall mean LDH level plus or minus 1 SD (range, 190-511 IU/L), and high LDH higher than 1 SD above the overall mean (range, 512-1171 IU/L). The prevalences of pulmonary hypertension (B), leg ulcers (C), and in men, priapism (D) are also related to LDH group. All statistics are significant by χ² test for trend. The number of patients in each group (n) is indicated above each bar.

Figure 4.

Serum LDH levels are associated with pulmonary hypertension and early mortality. (A) Compared to patients without pulmonary hypertension (TRV < 2.5 m/s, n = 138), higher mean LDH values are seen with mild pulmonary hypertension (TRV 2.5-2.9 m/s, n = 51) and moderate-severe pulmonary hypertension (TRV > 2.9 m/s, n = 21; P < .001, Kruskal-Wallis test). (B) Kaplan-Meier plot of survival of patients with lower or higher than median steady-state LDH levels (defined as < 315 IU/L or ≥ 315, respectively; P = .02, log-rank test).