Heme Concentration As a Biomarker of Sickle Cell Disease Severity: Its Role in Steady-State and in Crisis Patients

Abstract

Background: Sickle cell disease (SCD) is a heredity group of anemia characterized by hemolysis, chronic inflammation, and vaso-occlusive/painful crisis. The heme is a product of erythrocytes' lyses and is increased in hemolytic diseases. Objectives: To investigate associations between hematological/biochemistry biomarkers and total plasma heme levels between SCD patients groups (in crisis and in steady-state) and healthy controls. To identify molecules related to hemolysis, inflammation, hepatic dysfunction, renal and lipid metabolism. Methods: We evaluated a total of 125 SCD steady-state patients, 22 SCD in crisis patients, and 32 healthy individuals age- and sex-matched with patients groups. Hematological analyses were performed by automatic cell counter, and hemoglobin profile by HPLC. Biochemistry analyses of inflammatory and infection markers, as well as lipid, hepatic, and kidney metabolism markers were investigated by immunochemistry assays. Plasma concentration of total free heme was measured by QuantiChrom Heme Assay Kit. Results: SCD patients groups (steady state and crisis) had higher heme concentration when compared to healthy individuals (p < 0.0001). However, significant difference of heme level was not finding in the comparison between SCD in steady state and SCD crisis patients groups. Biomarkers analyses of steady-state SCD patients showed negative correlation between heme levels and: red blood cell (r = -0.36, p<0.0001); hematocrit (r = -0.38, p <0.0001); hemoglobin (r = -0.34, p <0.0001); and HDL-C (r = -0.42, p <0.0001). Heme level showed positive correlation with: platelets (r = 0.35, p <0.0001); lactic dehidrogenase (r = 0.40, p <0.0001); reticulocytes count (r = 0.19, p =0.04); monocytes count (r = 0.36, p <0.0001); HbS concentration (r = 0.54, p <0.0001); total proteins (r = 0.22, p =0.01); AST (r = 0.41, p <0.0001); ALT (r = 0.18, p= 0.04); serum iron (r =0.21, p =0.03); total cholesterol (r = 0.23, p =0.01); LDL-C (r = 0.22, p= 0.02); VLDL-C (r = 0.65, p <0.0001); and triglycerides (r = 0.63, p <0.0001). In steady state SCD patients there was no difference of clinical manifestations history and heme levels. Conclusions: The finding of similar heme concentration between steady state and crisis SCD patients may be explained by the hyperhemolysis phenomenon, showing that even in steady-state, these patients continue to have hemolysis and generate heme and reactive oxygen species. It was also shown that high concentration of free heme increases hemolytic and inflammatory biomarkers, such as LDH, bilirubin's, reticulocytes count, and lipids, contributing to a severe clinical modulation of SCD. Disclosures No relevant conflicts of interest to declare.

Prospective Biomarkers from Plasma Metabolomics of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Implicate Redox Imbalance in Disease Symptomatology

“…Heme consists of an iron ion centered in a large organic ring and is mainly found in hemoglobin, but also in a few other important hemoproteins, with varying functions all related to redox chemistry. Free heme is highly cytotoxic and deleterious to tissues via its pro-oxidative and pro-inflammatory properties, as it is capable of catalyzing free radical formation [33,34,35].…”

“…Because we used plasma, which is a cell-free matrix, it is anticipated that there is a greater contribution from “free heme” to the measurement of heme abundance unless substantial hemolysis occurred. High concentration of free heme in plasma is a biomarker for sickle cell disease severity, in which increased levels of inflammatory biomarkers such as lactate dehydrogenase, bilirubin, high reticulocytes count, and lipids are detected [35]. Three forms of bilirubin as well as biliverdin were assessed in our samples and were also present in higher abundance in patients vs. controls, demonstrating a general disturbance in the heme degradation pathway, with the last step occurring in the liver.…”

Altered HDL particle in sickle cell disease: decreased cholesterol content is associated with hemolysis, whereas decreased Apolipoprotein A1 is linked to inflammation

“…Plasma hemin levels were increased in SCD patients compared to the almost-undetectable levels in controls. Hemin is produced by the oxidation of heme [26], a molecule which was suggested to be a biomarker of disease severity in SCD [27]. It has also been shown that hemin causes oxidative damage to plasma lipoproteins, such as LDL and HDL [28].…”

Vaso-occlusive crisis in sickle cell disease: a vicious cycle of secondary events

“…As a result, free heme accumulates in the system [ 35 ]. Elevated levels of free heme are associated with increased incidence of VOC [ 36 ]. Free heme stimulates the migration of leukocytes to the endothelial wall where they bind to P- and E-selectins and promote the production of reactive oxygen species (ROS) [ 37 ].…”