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Several studies in the last decade have highlighted the importance of the hexose sugars and especially glucose, as being responsible for alterations to living protein and other molecules. The phenomenon of nonenzymatic glycation--by which the carbonyl group of glucose can directly condense with a free amino group--may be relevant for the process of aging and for the pathogenesis of late diabetic complications. Thus life-long exposure to normoglycemia in non diabetic subjects or a shorter exposure but continued association with a hyperglycemic milieu, as in diabetes mellitus, have both been shown to lead to the formation and accumulation of irreversible and highly reactive advanced glycation endproducts (AGE) over long-lived, fundamental molecules such as the constituents of arterial wall collagen, basement membranes, nerve myelin, DNA and others. For example, the introduction of foreign AGE groups into proteins might alter their tertiary structure and therefore modify their function or activity. By increasing protein-to-protein cross-links AGE could reduce protein turnover, with consequential increases in levels of modified and thus less reactive molecules. Moreover, AGE could initiate an immune response with the production of specific antibodies. Reducing the extent of nonenzymatic glycation could effectively reduce the accumulation of AGE. Many authors are experimenting with methods to achieve this aim. Amongst the products tested are aspirin and aminoguanidine which compete with glucose for the same protein amino group. D-lysine is also being investigated on the principle that by reacting with glucose in circulation, it could effectively prevent it from reaching the amino group on the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The non enzymatic glycation of circulating and structural proteins is the main biochemical consequence of the chronic hyperglycaemia of diabetes mellitus. Retinol binding protein (RPB) is a 21K plasma globulin with an half life of 12 hr; its non enzymatic glycation may reflect the variation of short term metabolic control (1-4 days). In this study two blood samples were withdrawn at four days interval from 24 non insulin dependent diabetic patients. Glycated RBP was measured by a two-site immunoradiometric assay and its variations correlated with the correspondent changes in the blood glucose level. A significant correlation (r = 0.471; p less than 0.02) was found between the time 4/time 0 ratios of glycated RBP and the time 4/time 0 ratios of blood glucose. These data suggest that measurement of non-enzymatically glycated RBP may be a useful tool to evaluate the short term state of non enzymatic glycation in diabetes.

Islet cell antibodies (ICA) are present in the sera of most patients with Type 1 diabetes at diagnosis and in some of their genetically susceptible, but otherwise normal, first degree relatives. In this study we have investigated basal and stimulated insulin release by mouse islets following preincubation with human sera (with or without the addition of guinea pig complement) belonging to: 15 normal first degree relatives of diabetic probands; 7 patients with Type 1 diabetes; 7 control subjects with no history of diabetes. All sera had been previously screened for conventional (IgG), complement fixing (CF) and surface (S) ICA. Basal insulin release was not altered by any of the sera. The response to stimulus after incubation with ICA negative and IgG-ICA positive (but CF-ICA negative) sera was similar whether complement was present or not. Stimulated insulin release was significantly inhibited by complement and sera from 2 relatives and 3 diabetic patients. These sera were CF-ICA positive, the sera of the 2 relatives being also ICSA positive. One relative developed Type 1 diabetes 14 months later. This study demonstrates for the first time that sera containing CF-ICA and belonging to individuals susceptible to Type 1 diabetes, can impair insulin release in vitro. It is therefore likely that antibody-dependent, complement-mediated mechanisms are involved in the pathogenesis of Type 1 diabetes.

Enhanced non-enzymic glycation of proteins has been suggested to play a role in the pathogenesis of diabetic microangiopathy. Thus pharmacological inhibition of this reaction could be envisaged to delay the development of late diabetic complications. In the present study we have investigated the effect of a new compound, 1-Benzylindazole-3-oxyacetic acid, Bendazac (BDZ) on the in vitro glycation of soluble proteins (albumin and fibrinogen) and isolated glomerular basement membrane (GBM). The data obtained indicate that BDZ is capable of reducing significantly the glycation of albumin and fibrinogen (p less than 0.001). When present in concentrations usually found in patients undergoing therapy (40-80 micrograms/ml), an inhibitory effect on soluble proteins was also observed. Inhibition of glycation of GBM was found only in the presence of the active metabolite (5 hydroxy BDZ) and at high glucose concentrations. These results suggest that BDZ could interfere with protein non-enzymic glycation and its use in patients with diabetes may be then taken into consideration to evaluate the effect on late diabetic complications.

In search of a marker for monitoring the progression of diabetic nephropathy from the stage of charge- to that of size-selectivity loss, attention has been focused on the evaluation of immunoglobulin G (IgG) subclasses in the urine. We have developed a new sensitive enzyme immunoassay for the quantitation of urinary IgG1 and IgG4. Mouse monoclonal antibodies specific for each subclass were bound to microtitre wells precoated with rabbit anti-mouse immunoglobulin antibody. IgG1 and IgG4 of standard preparations (or of samples to be tested) were revealed using peroxidase-conjugated rabbit anti-human IgG. The procedure was carried out at 4 degrees C. This method can detect about 2 ng/ml of IgG4 and 20 ng/ml of IgG1. The monoclonal antibodies used were shown to be highly subclass-specific. IgG1 and IgG4 have a similar molecular weight but a different pH (about 9 and 4.6 respectively); a change in their ratio in the urine of diabetic patients may indicate a progressive deterioration of kidney function at the stage of incipient diabetic nephropathy.