Ebikeme, Charles E.
Amino acid transporters & amino acid metabolism in Trypanosoma brucei brucei.
PhD thesis, University of Glasgow.
Full text available as:
The development of new drugs against Human African Trypanosomiasis is much needed due to toxicity, efficacy and availability problems with current drug treatments for this resurgent parasitic disease. Delivery of drugs into cells is an important determinant of therapeutic efficacy of drugs. An effective means of selective drug delivery is to use plasma membrane transport systems to mediate the entry of drugs into the cell.
Some amino acid transporters fulfil the criteria needed for successful exploitation of nutrient transport systems for drug delivery. The Trypanosoma brucei genomic database was screened to identify the full gene repertoire of amino acid transporters. From this, candidate genes were selected and functional genetic approaches were employed to characterise candidate amino acid transporter genes. Further characterisation of TbAATP1, a RNAi cell line shown to be a transporter of small neutral amino acids (serine, glycine, cysteine, asparagine and alanine), showed a role in threonine uptake.
Amino acid analogues were tested for trypanocidal activity. Of the 96 tested, two (Azaserine and Levodopa) were investigated in more detail, paying special attention to the nature of their trypanocidal action and possible route of entry through an amino acid transporter. Azaserine showed a trypanostatic action as well multiple routes of entry into the protozoan interior (as shown by inhibition of glutamine, phenylalanine and tyrosine uptake). The trypanocidal Levodopa showed entry through a tyrosine specific transporter. However, it is possible that Levodopa’s trypanocidal activity may not be as a result of the analogue itself, but secondary products of the analogue.
Amino acids are important for protozoa as energy sources as well as forming pools of soluble osmolites. Amino acid usage in trypanosomes was investigated. Upregulation of proline transport and catabolism in response to reduced glucose availability was exhibited by the genome strain of T. brucei. Moreover, this metabolic shift could be mimicked by addition of GlcNAc to the medium, which blocks the hexose transporter limiting glucose entry to the cell. Systems biology approaches were initiated to investigate the undergoing metabolic changes. More specifically, mass spectrometry methodologies were employed to investigate underlying metabolite changes in procyclic form trypanosomes grown in differing medium.
Actions (login required)