Role of the Maillard reaction in aging of tissue proteins. Advanced glycation end product-dependent increase in imidazolium cross-links in human lens proteins

Dicarbonyl compounds such as glyoxal and methylglyoxal are reactive dicarbonyl intermediates in the nonenzymatic browning and cross-linking of proteins during the Maillard reaction. We describe here the quantification of glyoxal and methylglyoxal-derived imidazolium cross-links in tissue proteins. The imidazolium salt cross-links, glyoxal-lysine dimer (GOLD) and methylglyoxal-lysine dimer (MOLD), were measured by liquid chromatography/mass spectrometry and were present in lens protein at concentrations of 0. 02-0.2 and 0.1-0.8 mmol/mol of lysine, respectively. The lens concentrations of GOLD and MOLD correlated significantly with one another and also increased with lens age. GOLD and MOLD were present at significantly higher concentrations than the fluorescent cross-links pentosidine and dityrosine, identifying them as major Maillard reaction cross-links in lens proteins. Like the N-carboxy-alkyllysines Nepsilon-(carboxymethyl)lysine and Nepsilon-(carboxyethyl)lysine, these cross-links were also detected at lower concentrations in human skin collagen and increased with age in collagen. The presence of GOLD and MOLD in tissue proteins implicates methylglyoxal and glyoxal, either free or protein-bound, as important precursors of protein cross-links formed during Maillard reactions in vivo during aging and in disease.

Imidazolium crosslinks derived from reaction of lysine with glyoxal and methylglyoxal are increased in serum proteins of uremic patients: evidence for increased oxidative stress in uremia

Glyoxal (GO) and methylglyoxal (MGO) are reactive dicarbonyl compounds formed during autoxidation of both carbohydrates and lipids. They may react with lysine and arginine residues of proteins in Maillard or browning reactions, yielding advanced glycation or lipoxidation end products. Among these are the imidazolium crosslinks, N,N(-di(N(epsilon)-lysino))imidazolium (glyoxal-lysine dimer, GOLD) and N,N(-di(N(epsilon)-lysino))-4-methyl-imidazolium (methylglyoxal-lysine dimer, MOLD). We have detected and measured GOLD and MOLD in human serum by electrospray ionization/mass spectrometry/mass spectrometry (ESI/MS/MS), using 15N4-GOLD and 15N4-MOLD as internal standards. In this report we show that levels of GOLD and MOLD are significantly elevated (3-4-fold, P< 0.01) in sera of non-diabetic uremic patients, compared to age-matched controls, and represent a major class of non-enzymatic, Maillard reaction crosslinks in plasma proteins. These results provide strong evidence for increased non-enzymatic crosslinking of tissue proteins by GO and MGO in uremia, implicating oxidative stress and resultant advanced glycation and lipoxidation reactions in tissue damage in uremia.

N-epsilon-(carboxyethyl)lysine, a product of the chemical modification of proteins by methylglyoxal, increases with age in human lens proteins

Advanced glycation end-products and glycoxidation products, such as Nepsilon-(carboxymethyl)lysine (CML) and pentosidine, accumulate in long-lived tissue proteins with age and are implicated in the aging of tissue proteins and in the development of pathology in diabetes, atherosclerosis and other diseases. In this paper we describe a new advanced glycation end-product, Nepsilon-(carboxyethyl)lysine (CEL), which is formed during the reaction of methylglyoxal with lysine residues in model compounds and in the proteins RNase and collagen. CEL was also detected in human lens proteins at a concentration similar to that of CML, and increased with age in parallel with the concentration of CML. Although CEL was formed in highest yields during the reaction of methylglyoxal and triose phosphates with lysine and protein, it was also formed in reactions of pentoses, ascorbate and other sugars with lysine and RNase. We propose that levels of CML and CEL and their ratio to one another in tissue proteins and in urine will provide an index of glyoxal and methylglyoxal concentrations in tissues, alterations in glutathione homoeostasis and dicarbonyl metabolism in disease, and sources of advanced glycation end-products in tissue proteins in aging and disease.

Admission hyponatremia in the elderly: factors influencing prognosis

The authors studied the occurrence of admission hyponatremia and its association with selected patient and hospitalization characteristics and in-hospital mortality in a geriatric patient cohort (n = 4,123). Prevalence of admission hyponatremia was 3.5% and higher among women (4.6% vs 2.6%). In-hospital mortality was 16% for patients with admission hyponatremia versus 8.0% for patients without admission, hyponatremia. Adjusting for patient and hospitalization characteristics with a logistic regression analysis, admission hyponatremia was a significant independent predictor of mortality (RR = 1.95). Admission hyponatremia is associated with poor prognosis in the elderly hospitalized population.

Routine admission laboratory testing for general medical patients

We evaluated the usefulness of commonly ordered routine admission laboratory tests in 301 patients admitted consecutively to the internal medicine wards of a university teaching hospital. Using a consensus analysis approach, three Department of Medicine faculty members reviewed the charts of admitted patients to determine the impact of the test results on patient care. The evaluated tests were the urinalysis, hematocrit, white blood cell count, platelet count, six-factor automated multiple analysis (serum sodium, potassium, chloride, bicarbonate, glucose, and blood urea nitrogen), prothrombin time, partial thromboplastin time, chest x-ray, and electrocardiogram. Forty-five percent of the 3,684 tests were ordered for patients without recognizable medical indications. Twelve percent of these routine tests were abnormal, 5% led to additional laboratory testing, but only 0.5% led to change in the treatment of patients. We conclude that the impact of routine admission laboratory testing on patient care is very small and that there is little justification for ordering tests solely because of hospital admission.

Usefulness of routine admission complete blood cell counts on a general medical service

The usefulness of three components of the routine admission complete blood cell count (leukocyte count, hematocrit, and platelet count) was evaluated in 301 patients consecutively admitted to the internal medicine wards of a university teaching hospital. Using a consensus analysis approach, three faculty members reviewed the patients' charts to determine which tests were performed routinely, which tests were abnormal, and which routine tests led to diagnostic or therapeutic changes. Overall, 55.3% of the tests were considered routine admission tests. Abnormalities were detected in 13.6% of the routine leukocyte counts, in 8.2% of the routine hematocrit levels, and in 12.4% of the routine platelet counts. However, treatment was changed for only three patients, all of whom had low hematocrits; this amounted to 0.6% of all tests. Furthermore, only one of the three patients received appropriate treatment that might have been withheld if a routine hematocrit determination had not been ordered. The authors conclude that the impact of routine admission complete blood cell counts on patient management is small and that the practice of ordering this test for all hospitalized patients could be eliminated with little adverse effect on patient care.

Efficacy of the routine admission urinalysis

The clinical efficacy of routine admission urinalyses was evaluated in 301 patients admitted to the internal medicine wards of a university teaching hospital. Using a consensus analysis approach, three Department of Medicine faculty members reviewed the patients' charts to determine which tests were performed routinely and which test results led to diagnostic or therapeutic management changes. Of the 243 urinalyses performed, 123 (51 percent) were ordered routinely for patients without recognizable medical indications. Results of the routine urinalyses were abnormal in 42 (34 percent) of the patients and led to additional laboratory testing in 20 (16 percent) of the cases. However, the test results led to therapeutic changes in only three (2.4 percent) of the patients, and in two of these patients, the treatment instituted probably was unnecessary. It is concluded that the impact of routine admission urinalysis on patient care is very small and that there is little justification for ordering this test for all patients admitted to the hospital.

Cardiovascular pathology in renal transplant recipients

Various cardiovascular complications are among the major causes of mortality in renal transplant recipients. The authors examined the cardiovascular findings from necropsy of 18 renal transplant patients. All but three of the patients showed one or more pathological abnormalities. Five patients exhibited severe coronary arteriosclerosis with acute myocardial infarction with a history of myocardial infarction noted in four patients. In addition, one patient showed moderate and two showed mild coronary arteriosclerosis. Also prevalent were left ventricular (LV) hypertrophy (10/18), right ventricular (RV) hypertrophy (7/18), LV dilatation (4/18), RV dilatation (8/18), left atrial dilatation (3/18), and right atrial dilatation (6/18). Valvular abnormalities consisted of dilatations of mitral ring (1/18), pulmonic valve (2/18), and tricuspid valve (3/18). Pericarditis was found in two patients and aortic atherosclerosis in ten patients. Findings on routine chest roentgenograms and electrocardiograms did not always correspond with the anatomical findings noted on necropsy examination. The results demonstrate a marked increase in the incidence of various cardiac abnormalities in renal transplant recipients.

Feasibility and usefulness of depression screening in medical outpatients

Depression is common in medical outpatients, but the diagnosis is frequently missed. We introduced the Beck Depression Index into our clinic as a screening tool to determine the feasibility of depression screening, the prevalence of depression in our patients, and the clinical usefulness of the depression index. The questionnaire was easily implemented and well accepted by the 375 patients screened. Moderate or severe depression was identified in 32% of our patients. By several measures, the Beck Depression Index proved to be a highly useful clinical tool. It provided information significant enough to change the plan in 20% of the entire population of patients screened. The severity or presence of depression would probably have been missed without the screening. Depression screening should be considered in all primary care settings.

Usefulness of screening chest roentgenograms in preoperative patients

We proposed that clinical criteria could define a group of patients very unlikely to have abnormal preoperative chest roentgenograms. Nine hundred five surgical admissions were screened for the presence of clinical factors we thought would make those patients more likely to have abnormal preoperative chest roentgenograms. Of these, 368 had no risk factors. One patient (0.3%) of the 368 had an abnormal x-ray film, which did not affect the surgery. No material abnormalities were found in the remainder of the group without risk factors. Five hundred four patients had identifiable risk factors. Of these, 114 (22%) were found to have serious abnormalities on preoperative chest roentgenogram.