Angiogenic, apoptotic and autophagic profiling of chronic myeloid leukaemia patients’ platelets ex vivo before and after treatment with Imatinib

Abstract

Chronic myeloid leukaemia (CML) is a malignancy of the hematopoietic stem cells. The primary line of treatment for CML, especially in developing countries, remains the administration of Imatinib, a first generation tyrosine kinase inhibitor (TKI). Patients with CML are frequently diagnosed with platelet abnormalities. However, the specific mechanism of platelet abnormalities in CML remains unclear and is poorly understood.

The aim of this study was to determine the angiogenic, apoptotic, and autophagic profiles of chronic myeloid leukaemia patients ex vivo on platelets before and after treatment with Imatinib. Platelet morphology, counts, viability and activation were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and human cluster of differentiation (CD) 41 and -62 markers. The possible occurrence of apoptosis and autophagy was measured by means of flow cytometry and western blot analysis via Annexin V-fluorescein isothiocyanate (FITC), caspase 3, autophagy related gene 5 (Atg5) and light chain I and II (LC3) markers. Angiogenesis expression was determined through vascular endothelial growth factor (VEGF) and transforming growth factor β (TGFβ) markers.

Qualitative data of SEM and TEM revealed that CML patient’s platelets were prone to aggregation and coagulation at time of diagnosis; the samples that were not aggregated at time of diagnosis showed typical discoid shaped platelets without evidence of activation which was comparable to control participants’ platelets. TEM results of CML patients’ platelets at diagnosis showed that internal granular constituents including dense bodies were decreased in comparison to control participants. In all CML patients, platelets appeared activated after 6 months of treatment with Imatinib with membrane structure abnormalities and constituent variations including formation of giant granules, large numbers of lysosomes and increased content of channels of the dense tubular system.

Data revealed that CML patients’ platelet counts were elevated upon diagnosis and levels were statistically significantly decreased after 6 months of treatment with Imatinib (P-value of <0.05). Platelet activation was statistically significantly increased after 6 months of treatment with Imatinib compared to levels at diagnosis (P-value <0.05) which was corroborated by SEM and TEM morphology findings. Similarly, platelet apoptosis was also increased after 6 months of treatment with Imatinib in CML patients.

In addition, a statistically significant increase in autophagy in CML patient’s platelets after 6 months of treatment with Imatinib was observed compared to autophagy levels at time of diagnosis as measured with the Atg5 marker via flow cytometry and LC3-I and LC3-II expression and ratios as measured via western blot analysis (P-value <0.05) also contributing to the decrease in platelet counts found. An increase in the expression of both VEGF and TGFβ in CML patient’s platelets at time of diagnosis was determined compared to VEGF and TGFβ levels after 6 months of treatment with Imatinib.

The results of the current study implicate the impact of CML pathogenesis on platelets, seemingly as a result of alterations in typical haematopoiesis which impact the typical differentiation of megakaryocyte precursors and subsequent differentiation of atypical platelets. Abnormalities in platelet functioning observed in this study may partly be due to clonal proliferation of haematopoietic cells mentioned in CML patients, specifically of megakaryocyte precursors, as well as the inhibition of platelet tyrosine kinases and the inhibition of platelet-derived growth factor due to Imatinib treatment that disrupts typical homeostasis of platelets. Recognising and understanding the impact of CML disease progression on platelets is of importance to aid improved patient treatment. Platelets’ role has over the years transformed as knowledge regarding platelets has expanded to include inflammation, cancer progression, and metastasis. Platelet functions are interrelated; activation of the inflammatory function results in thrombosis and, moreover, in various disease conditions, can result in worsened or chronic pathogenesis, including CML. The role and contribution of platelets in a multitude of pathophysiological events during hemostasis, thrombosis, inflammation, cancer progression, and metastasis is an important focus for ongoing research.