Plasma amino-acids in human cancer: the individual role of tumour, malnutrition and glucose tolerance

Abstract Fasting plasma amino-acid levels were measured in 24 controls and in 42 untreated cancer patients. Patients were subdivided into different groups according to the degree of tumour spread, glucose tolerance and malnutrition. The aromatic amino-acids, tyrosine, phenylalanine and free tryptophan, as well as methionine, proline, glutamic acid and ornithine were significantly higher in cancer patients than in controls. Malnutrition clearly decreased the levels of the gluconeogenic amino-acids, alanine, glycine and threonine. Free tryptophan levels were found to directly correlate with the severity of malnutrition. Branched-chain amino-acid levels were not affected by the nutritional status. Neither the degree of the tumour spread nor glucose tolerance affected the amino-acid profile. The alterations of those amino-acids which were independent of the degree of tumour spread, glucose intolerance and malnutrition, may result from an increased muscle protein turnover induced by the presence of malignancy.