Mass spectrometry of advanced glycation end products

Thirty years of fruitful collaborations between a physician and mass spectrometrists in diabetes field

The nonenzymatic protein glycation and the subsequent formation of advanced glycation end products is a process involved in the long-term complications of diabetes. In this context the collaboration, in the last 30 years, between my research group, operating in the DPT of Medicine of Padua University, and the mass spectrometric group, operating in CNR of Padua, are described and discussed. The development of new mass spectrometric techniques has allowed investigation more indepth, starting from the applications on small molecules responsible for the browning observed in the interactions between sugars and proteins, and growing up to intact proteins as albumin, immunoglobulin, hemoglobin, and so forth, with the determination of their glycation levels as well as their glycation sites. This study has helped to clarify the role of advanced glycation end products in the pathogenesis of the chronic complications of diabetes. In particular the results obtained in diabetic nephropathy, diabetic cardiovascular disease and in placenta samples of patients affected by gestational diabetes are described in this review.

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

A decade of HPLC-MS/MS in the routine clinical laboratory--goals for further developments

During the past decade, tandem mass spectrometry hyphenated to liquid chromatography separation systems (HPLC-MS/MS) has developed to an important technology in clinical chemistry - not only for research purposes but also for routine use. At present, most important application fields are target analyses in therapeutic drug monitoring (TDM) and metabolic disorders diagnosis. The essential strengths of HPLC-MS/MS include potentially high analytical specificity, wide range of applicability to small and large molecules, capability of multi- and mega-parametric tests, and the opportunity to develop powerful assays with a high degree of flexibility within a short time frame. The technique has overcome important limitations of GC-MS and is characterized by short analytical runtimes, applicability to thermo labile, polar and large molecules, and straightforward sample preparation. However, implementation of HPLC-MS/MS assays still requires substantial expertise and know-how. At the present, its application is limited to a rather small number of clinical routine laboratories. Nonetheless, HPLC-MS/MS has the potential to be further developed to a commonly applied high-throughput technique in clinical chemistry, complementary to present standard techniques as photometry and ligand binding methods. This review intends to characterize working characteristics of present day HPLC-MS/MS instrumentations used in clinical routine laboratories. Limitations of currently available systems and applications will be critically discussed. Required instrument improvements supporting the successful spreading of HPLC-MS/MS in laboratory medicine within the next decade will be outlined.

Nuclear ADP-ribosylation reactions in mammalian cells: where are we today and where are we going?

Since poly-ADP ribose was discovered over 40 years ago, there has been significant progress in research into the biology of mono- and poly-ADP-ribosylation reactions. During the last decade, it became clear that ADP-ribosylation reactions play important roles in a wide range of physiological and pathophysiological processes, including inter- and intracellular signaling, transcriptional regulation, DNA repair pathways and maintenance of genomic stability, telomere dynamics, cell differentiation and proliferation, and necrosis and apoptosis. ADP-ribosylation reactions are phylogenetically ancient and can be classified into four major groups: mono-ADP-ribosylation, poly-ADP-ribosylation, ADP-ribose cyclization, and formation of O-acetyl-ADP-ribose. In the human genome, more than 30 different genes coding for enzymes associated with distinct ADP-ribosylation activities have been identified. This review highlights the recent advances in the rapidly growing field of nuclear mono-ADP-ribosylation and poly-ADP-ribosylation reactions and the distinct ADP-ribosylating enzyme families involved in these processes, including the proposed family of novel poly-ADP-ribose polymerase-like mono-ADP-ribose transferases and the potential mono-ADP-ribosylation activities of the sirtuin family of NAD(+)-dependent histone deacetylases. A special focus is placed on the known roles of distinct mono- and poly-ADP-ribosylation reactions in physiological processes, such as mitosis, cellular differentiation and proliferation, telomere dynamics, and aging, as well as "programmed necrosis" (i.e., high-mobility-group protein B1 release) and apoptosis (i.e., apoptosis-inducing factor shuttling). The proposed molecular mechanisms involved in these processes, such as signaling, chromatin modification (i.e., "histone code"), and remodeling of chromatin structure (i.e., DNA damage response, transcriptional regulation, and insulator function), are described. A potential cross talk between nuclear ADP-ribosylation processes and other NAD(+)-dependent pathways is discussed.