Levels of carbonyl groups in plasma proteins of type 2 diabetes mellitus subjects.

Carbonyl groups result from protein oxidation and their level in tissues and plasma is a relatively stable marker of oxidative damage. Carbonyl content of plasma proteins in 43 type 2 diabetic subjects, 30-87 years of age (25 males and 18 females) and in 20 age-matched healthy controls (31-89 years of age, 12 males and 8 females) was evaluated with 2,4-dinitro-phenyl-hydrazine method. In both groups, lipids, tocopherols (HPLC) and glycated hemoglobin (HPLC) were studied. Fasting blood glucose, glycated hemoglobin and lipids were significantly higher in the diabetic group; carbonyl content and alpha-tocopherol were slightly, but not significantly higher in the diabetic group (1.06 +/- 0.03 vs. 0.97 +/- 0.04 nmol/mg protein, 27. 07 +/- 2.82 vs. 31.55 +/- 2.11 micromol/l, respectively). Significant relationships between age and lipids, alpha-tocopherol and proteins were found in controls, but not in diabetics. Alpha-tocopherol correlated with lipids in both groups; glycated hemoglobin, a marker of glycemic control, was related to lipids, alpha-tocopherol and protein carbonyl groups in diabetics, while only the correlation with carbonyls was found in controls. These results suggest that impaired glycemic control is connected to protein oxidation. Glycation cascade also releases free radicals, becoming responsible for further oxidative attacks. In conclusion, increased oxidative stress, if any, in the diabetic group, is doubtlessly induced by hyperglycemia, and the tocopherols are not seriously affected by a worsening of the metabolic control.

Good glycaemic control reduces oxidation and glycation end-products in collagen of diabetic rats.

Blood glucose control plays a prominent role in the aetiology of diabetic complications. Recent data support the hypothesis that non-enzymatic pathways (glycation and oxidation) are involved in the pathogenesis of tissue damage in diabetes mellitus. In this study the level of pentosidine, a marker of glycation, and the intensity of collagen-linked fluorescence glycation (370/440 and 335/385 nm) and oxidation-related (356/460 and 390/460 nm), have been examined in spontaneously diabetic rats with good and poor glycaemic control. Pentosidine increased dramatically in rats with poor control, and slightly in those with good control. At the end of the study, after 6 months of diabetes, pentosidine levels were 13 +/- 5 and 2.1 +/- 0.5 pmol/mg collagen, respectively (control rats: 1.1 +/- 0.1 pmol/mg collagen). A similar pattern was observed for both glycation or oxidation-related fluorescence. The group of rats with poor control always showed elevated average values when compared to rats with good control, with a relative increase of over 200%. The results emphasize the role of good glycaemic control in preventing the growth of glycation or oxidation end-products in collagen. On comparison between the general mean level of all glycated haemoglobin and the mean pentosidine level of the three groups, a very good exponential correlation was found (r = 0.993, p < 0.001). The fluorescence values presented a less strong relationship, but a correlation with glycaemic control was still present. If the post-translational modifications of proteins play a leading role in the pathogenesis of complications it is possible to conclude that strict glycaemic control, obtained by accurate insulin therapy can prevent them by inhibiting the non-enzymatic modification of proteins and delaying their accumulation in collagen. The therapeutic implications are obvious.

Relationships between glycation and oxidation related fluorescences in rat collagen during aging. An in vivo and in vitro study.

BACKGROUND: Glycation and oxidation are spontaneous chemical modifications of body proteins. Usually these reactions have been studied separately by assessing their fluorescent final products. Glycation of protein and its related fluorescence increases during aging, whereas the level of the fluorescence related to protein adducts from lipoperoxidation side products is unknown. Moreover, no data on the fluorescence, at different wavelengths, connected to the two reactions in the same sample are available. Nevertheless recent in vitro studies support the possibility of an interaction between the two spontaneous reactions. EXPERIMENTAL DESIGN: In this study, we evaluated the modification of proteins due to glycation and to lipoperoxidation side products, by measuring their specific fluorescence levels in the collagen of 65 healthy Wistar rats during the aging process. The relationships among the fluorescence at different wavelengths were also reported. The fluorescence pattern of insoluble collagen was characterized by a tridimensional study after the incubation of insoluble collagen with probable precursors of protein glycation (ribose) and oxidation (malondialdehyde and hydroxynonenal); the maximum peaks of fluorescence were recognized and compared. RESULTS: An increase of all fluorescence intensities was observed in rat collagen during aging: the glycation-related ones (y370/440 = 28.3 e0.08x, r = 0.808, p < 0.01; y335/385 = 66.7 e0.06x, r = 0.798, p < 0.01) and the hydroxynonenal adduct-related (y356/460 = 44.3 e0.06x, r = 0.810, p < 0.01) were exponential, whereas that derived from MDA-adduct was almost linear (y390/460 = 17.7 + 4.1x, r = 0.661, p < 0.01). A different accumulation rate might explain this result. Significant correlation coefficients were found within the age-adjusted fluorescence intensities of both reactions, suggesting a close relationship between glycation and oxidation, besides a mutual influence due to the broad spectrum area. The in vitro study confirmed a good specificity of collagen fluorescence after incubation with a reducing sugar (ribose 0.5 M for 6 hours) for protein glycation, and after incubation with malondialdehyde (0.1 mM for 3 hours) for lipoperoxidation adducts; surprisingly enough hydroxynonenal (0.5 mM for 3 hours) significantly increased the fluorescence related to pentosidine-like products (335 nm excitation/385 nm emission) suggesting that this compound might be the precursor of products with a fluorescence similar to pentosidine or of pentosidine itself. CONCLUSIONS: The in vivo results of this study confirm that nonenzymatic reactions, glycation and oxidation, significantly modify collagen fluorescence during aging and can play a role in tissue damage related to age. The close relationships among fluorescences may be due to a reciprocal interconnection rather than to a parallel increase of both reactions during aging; this hypothesis is supported by the in vitro findings of this study.

Malondialdehyde (MDA) level in diabetic subjects. Relationship with blood glucose and glycosylated hemoglobin.

The relationships between plasma malondialdehyde (MDA) and metabolic parameters in type I and II diabetic subjects have been studied at different levels of glycemic control. In 67 diabetics (20 type I, 47 type II, aged 53 +/- 1.2) and 40 healthy subjects (aged 47 +/- 1.75), triglycerides (TG), total cholesterol (CT) and C-HDL, fasting blood glucose (FBG), glycosylated hemoglobin (GHb) and MDA were measured. Diabetic population as a whole showed higher MDA plasma levels compared to controls, together with higher FBG, TG, GHb. MDA showed a significant correlation with both FBG and GHb, but was not correlated to plasma lipids. The patients with a poor metabolic control showed the highest plasma MDA concentrations, significantly different from the group with a better control: GHb less than 10% = MDA 2.77 +/- 0.28 nmol/ml - GHb greater than 10% = MDA 4.22 +/- 0.39 nmol/ml (z = 2.10, a less than 0.02); FBG less than 150 mg/dl = MDA 2.74 +/- 0.32 nmol/ml - FBG greater than 150 mg/dl = MDA 4.15 +/- 0.37 nmol/ml (z = 2.22, a less than 0.02). Glycemic equilibrium seemed to influence plasma MDA, increasing free radical production. This phenomenon probably occurred either because of enhanced glycosylation and platelet aggregation, or impairment of cellular antioxidant protective systems. The increased free radical production may play a role in the pathogenesis of metabolic vasculopathy.

[Insulin secretion and hepatic extraction in juvenile non-insulin-dependent diabetes]. / Secrezione insulinica ed estrazione epatica nel diabete non insulino dipendente giovanile.

Beta-cell secretion is still a point of controversy. As the liver is the major site of insulin metabolism, evaluation of hepatic insulin extraction is crucial for correct measurement of beta-cell secretion. Methods for calculating the secretion and hepatic extraction of insulin indirectly from peripheral C-peptide concentration have been proposed by some investigators. To characterize the low insulin response of a group of young non-insulin-dependent diabetics we evaluated secretion and hepatic insulin extraction during an oral glucose tolerance test by peripheral IRCP determination and IRCP/IRI molar ratio. Our data show that in this population of young non-insulin-dependent diabetics, the low peripheral insulin response to an oral glucose challenge is a possible consequence of diminished beta-cell secretion, as hepatic insulin extraction is at near normal value.

[Therapy of trophic ulcers in diabetes mellitus]. / Terapia delle ulcere trofiche in corso di diabete mellito.

Trophic lesions of the lower limbs are very frequent in diabetic patients, especially after long periods of poor glycemic control. These lesions are caused by some diabetic sequelae, namely neuropathy and angiopathy. The human and social cost of trophic lesions is very high; for this reason education of diabetics who are likely to develop such lesions is extremely important. When trophic lesions have developed, conservative management is based on local and general therapy. Amputation is taken into account only when conservative management has failed.