Assessment of in vivo glucose kinetics using stable isotope tracers to determine their alteration in humans during critical illness

An adapted isotope dilution 1H-13C heteronuclear single-quantum correlation (ID-HSQC) for rapid and accurate quantification of endogenous and exogenous plasma glucose

A wide variety of methods, such as enzymatic methods, LC-MS, and LC-MS/MS, are currently available for the concentration determination of plasma glucose in studies of diabetes, obesity, exercise, etc. However, these methods rarely discriminate endogenous and exogenous glucose in plasma. A novel NMR strategy for discriminative quantification of the endogenous and exogenous glucose in plasma has been developed using an adapted isotope dilution ¹H-¹³C heteronuclear single-quantum correlation (ID-HSQC) with uniformly ¹³C-labeled glucose as a tracer of exogenous glucose. This method takes advantage of the distinct ¹H-¹³C chemical shifts of the hemiacetal group of the α-D-glucopyranose and makes use of the ¹³C-¹³C one-bond J-coupling (¹J_CC) in uniformly ¹³C-labeled glucose to differentiate the ¹H-¹³C HSQC signal of labeled glucose from that of its natural counterpart when data are acquired in high-resolution mode. The molar ratio between the endogenous and exogenous plasma glucose can then be calculated from the peak intensities of the natural and labeled glucose. The accuracy and precision of the method were evaluated using a series of standard mixtures of natural and uniformly ¹³C-labeled glucose with varied but known concentrations. Application of this method is demonstrated for the quantification of endogenous and exogenous glucose in plasma derived from healthy and diabetic cynomolgus monkeys. The results nicely agree with our previous LC-MS/MS results. Considering the natural abundance of ¹³C isotope at the level of 1.1% in endogenous glucose, comparable peak intensities of quantitatively measurable signals derived from natural and labeled glucose imply that the ID-HSQC can tolerate a significantly high ratio of isotope dilution, with labeled/natural glucose at ~ 1%. We expect that the ID-HSQC method can serve as an alternative approach to the biomedical or clinical studies of glucose metabolism.

Response to nutritional support and therapeutic approaches of amino acid and protein metabolism in surgical patients

The response to critical illness involves alterations in all aspects of metabolic control, favoring catabolism of body protein. In particular, body protein loss occurring as a result of the alteration of protein metabolism has been reported to be inversely correlated with the survival of critically ill patients. Despite the availability of various therapeutic modalities aiming to prevent loss of the body protein pool, such as total parenteral nutrition, enteral nutrition designed to provide excessive calories as a form of energy substrate, and protein itself, the loss of body protein cannot be prevented by any of these. Loss of the boyd protein store occurs as a consequence of the alteration of the intermediate metabolism that works for the production of energy substrate. This alteration of substrate metabolism may be linked to the alteration of protein metabolism. However, no specific factors regulating amino acid and protein metabolism have been identified. Thus, further investigations evaluating amino acid and protein metabolism are required to obtain better understanding of metabolic regulation in the body, which may lead to the development of novel and more effective therapeutic modalities for nutrition in the future.