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In conjunction with biopsy and Doppler studies, we analysed by high resolution proton NMR spectroscopy the blood plasma of 22 heart transplant recipients. There was a significant variation in the glycosylated residues of proteins with the development of acute cardiac rejection. A more extensive study is underway to assess the sensitivity and specificity of this approach for the early diagnosis of acute cardiac rejection.

Proton NMR spectroscopy allows the detection in plasma of resonances arising from N-acetyl-glucosamine (NAG) and N-acetyl-neuraminic acid (NANA) which have been shown to be borne by acute phase glycoproteins. These resonances can be identified using 2 different protocols of spectrum acquisition detecting different physical states in the global pool of glycoproteins, ie mobile and less mobile moieties of glycosylated chains. In this study we demonstrate that NMR spectroscopy allows a precise monitoring of the variations of glycosylated residues in cancers, inflammatory processes and bone marrow transplantation. The most important findings are that: i), the distribution of glycosylated residues varies with the origin of the cancerous tissue; ii), the level of these residues is a function of tumor development; iii), the concentrations in NAG and NANA are well correlated with the standard biological parameters of acute phase and leucocyte activation. Proton NMR spectroscopy of glycosylated residues in plasma may offer a new means of monitoring sialic acid in cancer and other pathological conditions.

The total sialic acid content of blood platelets from rats raised for 8 weeks or 12 months on a diet containing 1% linoleic acid (1LA) was significantly lower (by over 30%) than that from those raised on an isocalorific diet containing 6% linoleic acid (6LA). The transfer of sialic acid to endogenous glycoprotein acceptor was also significantly lower (up to almost 4-fold) in 1LA platelet and megakaryocyte-rich preparations but the transfer to exogenous glycoprotein acceptor was similar in both 1LA and 6LA platelets. The megakaryocyte-rich fraction of 1LA animals showed a reduced phosphodolichol-sensitive N-acetylglucosaminyl (but not mannosyl) transfer to endogenous glycoprotein compared with 6LA animals. No significant difference was found between the megakaryocytes of 1LA and 6LA animals in the incorporation of radioactive mannose and glucosamine into the glycoprotein of the whole cells. It was concluded that the decreased transfer of sialic acid to glycoproteins of platelets and megakaryocyte of animals on the 1LA diet was due to the decreased availability of sialyl acceptor. The formation of N-linked oligosaccharide was the same in both 1LA and 6LA megakaryocytes, and thus any differences in phosphodolichol-mediated N-glycosylation did not account for this decreased availability of sialyl acceptor.