Determination of l-asparagine in biological samples in the presence of l-asparaginase

The antileukaemic efficacy of l-asparaginase is related to the ability of the enzyme to induce the complete disappearance from plasma of l-asparagine, an amino acid essential to lymphoblastic leukaemia cells. It is not feasible to monitor l-asparagine plasma levels in patients under l-asparaginase treatment using the usual analytical procedures as the enzyme continues the hydrolysis of l-asparagine after blood samplaing and during plasma extraction. A method was therefore developed for the determination of l-asparagine in patients receiving l-asparaginase. Sulphosalicylic acid is added to blood samples to deproteinize and inactivate l-asparaginase rapidly. The samples are then analysed by HPLC using a Novapack C₁₈ column and fluorescence detection. With the same method l-asparagine is determined in blood cells and, by difference, plasma levels are calculated. This method is highly specific and sufficiently simple and sensitive for clinical use.