Correlation of Polymorphisms of Lipoprotein Lipase (LpL) and Apolipoprotein E (Apo E) With Lipid Profile of Children With Acute Lymphoblastic Leukaemia During Therapy With L - Asparaginase

Haematological malignancies constitute the most common neoplastic disease in child population, with acute leukemia occupying the number one spot with a percentage of 32.8%. In children, leukaemia is primarily encountered in its acute form (97%) and in the majority of the cases it is presented as Acute Lymphoblastic Leukaemia - ALL (80%). Acute Non-Lymphoblastic Leukemia - ANLL is encountered less frequently (17%) and it includes Acute Myelogenous Leukaemia - AML (15%) and some other rare forms (2%), while the remainder 3% corresponds to chronic leukaemia.

L-Asparaginase (L-ASP) is a fundamental component during the loading phase with regards to achieving remission of the disease and, likewise, during the maintenance phase with the intention of establishing that remission in both children and adults suffering from ALL. The cytotoxic effect of the exogenous administration of Asparaginase is caused by the depletion of the reserve of asparagine in the blood. Asparaginase (ASP) acts as a catalyst for the hydrolysis of asparagine to aspartic acid and ammonia. Asparagine is vital for protein and cell synthesis and, therefore, for their survival. The normal cells of the human body have the ability to produce asparagine from aspartic acid, with the assistance of the enzyme asparagine synthetase. However, the neoplastic cells either lack the enzyme completely or contain minute amounts of it resulting in their inability to synthesize asparagine de novo. The survival of these cells and their ability to synthesize proteins depends entirely on receiving asparagine from the blood. Thus, the administration of ASP leads to the inhibition of DNA, RNA and protein synthesis which, in turn, results in the apoptosis of these cells.

Despite L-ASP's paramount importance in the chemotherapy treatment of leukaemia, it is responsible for a plethora of toxic adverse effects that sometimes even require the termination of its administration. A critical adverse event of ASP is a disorder in the metabolism of lipids. Specifically, it appears that the activation of the endogenous pathway that produces triglycerides through hepatic synthesis leads to hypertriglyceridaemia. The liver is capable of synthesizing VLDL (Very Low Density Lipoproteins) that are rich in triglycerides. Utilising the effect of the enzyme Lipoprotein Lipase (LpL), located on the vascular endothelium, the triglycerides detach from the VLDL causing the latter to transform into IDL (Intermediate Density Lipoproteins) and afterwards into LDL (Low Density Lipoproteins). The triglycerides are later extracted from the blood circulatory system and stored in the adipose tissue, while the LDL particles connect with tissue receptors or macrophage receptors. The final products of the breakdown (coming from the peripheral hydrolysis of triglycerides with the help of LpL) of chylomicrons, VLDL, the remnants of lipoproteins, will eventually be removed by hepatic receptors. Apolipoprotein E (Apo-E) plays an important role in this procedure, it binds these remnants in the presence of LpL and hepatic lipase. Along the duration of the treatment with ASP, reduced LpL functionality is recorded, resulting in impaired plasma clearance of triglycerides and an increase in their levels, while L-ASP appears to cause disorders in other lipid factors, such as cholesterol, HDL and apolipoprotein A. Disorders of lipid metabolism have been found to be associated with polymorphisms of the LpL and Apo-E genes, sometimes with positive and sometimes with negative effects on the lipid profile and more likely participation in cardiovascular complications. The current study will evaluate, the lipid profile of children with ALL, the effect of L-ASP on the lipid profile of the aforementioned patients, as well as the correlation between the polymorphisms of Lipoprotein Lipase (LpL) and Apolipoprotein E (ApoE) with the values of the lipids during chemotherapy. Both the universal and national bibliography that pertain to the effect of ASP on the potency of LpL and App E and to the values of the lipids in children that suffer from ALL during chemotherapy with L-ASP is limited, while there exists no bibliographic reference correlating the genetic background to LpL and Apo E and the relation of the lipid profile. The current study will examine for the first time gene polymorphisms of LpL and Apo E in children with ALL during treatment with ASP.