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Biomedical subjects

M Brownlee

Publications and source records attributed to M Brownlee.

118 records · Page 7Linked to original sources
PubMed1980

Measurement of glycosylated amino acids and peptides from urine of diabetic patients using affinity chromatography.

An affinity chromatography system has been developed that retains glycosylated amino acids and peptides. Using this system, synthetic 14C-glycosylated lysine (reduced with NaB3H4) was completely separated from a mixture of reduced 14C-glycosylated lysine and unmodified 3H-lysine. Amino acid analysis of the retained peak from hydrolyzed human diabetic hemoglobin previously reduced with NaB3H4 revealed an equimolar mixture of glycosylated valine and glycosylated lysine, in agreement with previously published data obtained using other methodologies. These data demonstrate that in alkaline solution, the NaB3H4-reducible breakdown products of nonenzymatically glycosylated proteins are adsorbed to m-aminophenyl boronic acid immobilized on Bio-Gel P-6, while nonglycosylated amino acids are not. This affinity chromatography system should facilitate the rapid evaluation of nonenzymatic glycosylation in a large number of diabetic tissues. Levels of retained compounds in urine from diabetic and normal patients were determined by measuring ninhydrin-positive material. Amino acid analysis of NaB3H4-reduced hydrolysates of these peaks showed that glycosylated lysine was the major borohydride-reducible adduct present (67%--86%). Linear regression analysis showed that the quantity of excreted compounds in normals correlated with body weight (r = 0.63). The mean level (mumol leucine-equivalent/24 h/kg body weight) in diabetics was over 1.5 times that found in urine from normal subjects (P < 0.005).

Carbon Radioisotopes↗
PubMed1979

A glucose-controlled insulin-delivery system: semisynthetic insulin bound to lectin.

A stable, biologically active glycosylated insulin derivative that is complementary to the major combining site of concanavalin A has been synthesized. Hormone release is proportional to the quantity of glucose present. Glucose regulation of exogenous insulin delivery could have important applications in the therapy of diabetes mellitus.

Blood Glucose↗
PubMed1979

Insulin treatment of diabetes.

Normal blood glucose levels can be achieved and maintained in many, possibly most, diabetics who need insulin by basing dosage on currently available clinical-laboratory ahd home-monitoring techniques, thereby postponing or minimizing complications.

Diabetes Mellitus↗
PubMed1979

Glomerular basement membrane metabolism in the diabetic rat. In vivo studies.

The effect of diabetes on the metabolism of the renal glomerular basement membrane has been studied in the rat with the aid of injected tracer doses of tritiated proline. At various times after administration of the labeled amino acid, the specific radioactivities of the proline and hydroxyproline of the basement membranes from alloxan diabetic rats were determined and compared with those of age-matched normal rats. In both normal and diabetic animals the incorporation of radioactivity into the basement membrane was slow and, after a maximum was reached, an extended period of almost constant specific activity of proline and hydroxyproline was observed. The diabetic basement membrane, however, differed from the normal by attaining specific activities of the amino acids which were about twice as high as normal (P less than 0.001 at 42 h after injection of radioisotope). Although the proline concentration of serum and renal cortical fluid was the same in normal and diabetic rats, there were substantial differences in the specific activity of this precursor amino acid in these pools that had to be taken into account to compare the two types of animals. The results of the present study are consistent with an accelerated rate of glomerular basement membrane polypeptide synthesis and proline hydroxylation in diabetes.

Animals↗
PubMed1976

alpha1-Macroglobulin and reduced basement-membrane degradation in diabetes.

Thickening of the capillary basement membrane is the fundamental morphological alteration of diabetic microangiopathy. Leucocyte neutral proteases can degrade basement membrane in vivo. The activity of a purified neutral protease from granulocytes is inhibited by alpha2-macroglobulin. It is suggested that the reported increase in the concentration of alpha 2-macroglobulin in the blood of diabetic patients inhibits the activity of leucocyte neutral proteases which normally degrade basement membrane. The resultant decreased rate of breakdown would contribute to the increase in basement-membrane material seen in diabetes.

Basement Membrane↗
PubMedDate not supplied

Role of advanced glycosylation products in complications of diabetes.

Glucose and other reducing sugars can react with proteins and nucleic acids, without the aid of enzymes, to form stable covalent adduct. These reactions, although studied by food chemists, have recently been found to occur in vivo. This has led to studies on the accumulation of these advanced glycosylation end products (AGE) and the role it plays in the aging of long-lived proteins and nucleic acids. In contrast to the Amadori product, which is in equilibrium with glucose, AGE is irreversibly attached to the proteins. The AGE moieties are brown, fluorescent chromophores that can cross-link proteins. We have identified and characterized two specific AGE glucose-derived cross-links in proteins 2-furoyl-4(5)-(2-furanyl)-1H-imidazole (FFI) and 1-alkyl-2-formyl-3,4-diglycosylpyrrole (AFGP). By use of a radioimmunoassay for FFI identification, it has been possible to demonstrate the presence of FFI in situ in proteins that had been exposed to glucose in vitro and in vivo. Recently, we found that reducing sugars react with amino groups on DNA nucleotides in a manner analogous to the nonenzymatic glycosylation of amino groups on proteins. The AGE-DNA formed in this manner has spectral and fluorescent properties similar to those of AGE-proteins. We have observed that formation of AGE on DNA decreases the ability of the single-stranded virus f1 to transfect Escherichia coli. When the plasmid pBR322 containing ampicillin- and tetracycline-resistant genes is incubated with reducing sugars, specific mutations are observed. These mutations have been found to be caused by insertions and deletions of the DNA. Further studies are needed for measuring the amounts of AGE-DNA and proteins linked to DNA by AGE. Potential mechanisms for repair of AGE-DNA also needs to be explored further.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗