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A total of 55 metabolites were significantly different between samples from patients with SCD at baseline and healthy control samples.
The research indicated that the distinctions were determined by metabolites produced by red blood cell (RBC)-related pathways, such as the glycolytic and purinergic signaling pathway that mediate hypoxic metabolic programming, carnitine derivatives involved in turnover and repair of the RBC membrane, and polyamines that may stabilize the RBC membrane.
The investigator team from Utrecht University reported that after 8 weeks, treatment with mitapivat showed changes in an acyl carnitine and purine nucleotide compared to baseline.
“We conclude that the distinct metabolic profile from healthy controls is a promising starting point to further unravel the underlying pathophysiology of SCD and to characterize the endogenous and exogenous effects of pyruvate kinase activators and other novel therapies,” wrote presenting author Myrthe J. van Dijk, Central Diagnostic Laboratory, Research, University Medical Center Utrecht.
One of the most common inherited RBC disorders, the disease is characterized by polymerization of sickle hemoglobin (HbS) upon deoxygenation resulting in chronic life-threatening complications. The pathophysiology of the disease is multifactorial and highly complex.
Novel anti-sickling agents under development for SCD include oral, small molecule pyruvate kinase activators such as mitapivat. The agent could reduce HbS polymerization by decreasing the level of the glycolytic intermediate metabolite 2,3-diphosphoglycerate (2,3-DPG) and subsequently increasing the oxygen affinity of hemoglobin and the level of adenosine triphosphate (ATP) to increase cellular energy.
As an exploratory outcome, investigators examined changes in untargeted metabolomics on dried blood spots of patients with SCD treated with mitapivat in the 8-week Dose Finding Period of the open-label, phase 2 ESTIMATE study.
Investigators performed untargeted metabolomics by direct-infusion high-resolution mass spectrometry on dried blood spots of patients 16 years or older with SCD (HbSS, HBS/β0 or HbS/β+-thalassemia). It was collected at baseline and at completion of the 8-week Dose Finding Period.
Within this period, individuals received initial dosing of 20 mg mitapivat twice daily with a maximum of two sequential dose escalations to 50 mg and 100 mg twice daily every two weeks depending on the observed safety. Dried blood spot samples were collected from healthy adults and used to calculate Z-scores.
Moreover, distinct metabolic profiles between baseline samples of patients with SCD and healthy controls were identified by multivariate principal component analysis and partial least square discriminant analysis. Independent two-sample t-tests with equal group variance were also used.
False Discovery Rate (FDR) adjusted p-values corrected for multiple testing. The distinctive increased or decreased metabolites were analyzed at treatment week 8 and compared to baseline in the cohort of patients with SCD.
Overall, a total of 1907 unique metabolite features were identified in DBS of 9 patients with SCD (HbSS, n = 7; HbS/β0, n = 1; HbS/β+-thalassemia, n = 1). The 9 patients with SCD (median age, 22 years; 6 female [67%]), were compared to 29 healthy controls (mean age, 38 years; 21 female [72%]). A single HbSS patient and one healthy control were then determined as outliers and excluded from the final analysis.
The findings indicate a total of 55 metabolites were significantly different between patient samples at baseline and healthy control samples. A heat map showed the top 35, including acyl carnitines, derivatives of polyamines, purines and pyrimidines, and decreased carbohydrates and benzenoids.
Patient samples indicated 8 of 55 distinct metabolite features between patients with SCD and healthy controls were significantly increased after 8 weeks of treatment with mitapivat when compared to the patient's baseline sample (unadjusted p-value <.05).
Meanwhile, a significant increase was observed in 2 of 1907 unique metabolite features after 8 weeks of treatment with mitapivat compared to baseline. This included butenylcarnitine, an acyl carinitine and inosinic acid, or inosine-5-monophosphate, which is a purine nucleotide (FDR-adjusted p-value, <.05).
The poster, “9 Untargeted Metabolomics on Dried Blood Spots of Patients with Sickle Cell Disease Treated with the Pyruvate Kinase Activator Mitapivat,” was presented at ASH 2022.