A sensitive and reliable method for assaying true human insulin without interaction with human proinsulin-like molecules

The Relationship between Dietary, Serum and Hair Levels of Minerals (Fe, Zn, Cu) and Glucose Metabolism Indices in Obese Type 2 Diabetic Patients

The aim of this study was to assess the levels of Zn, Fe and Cu in the serum and hair, and dietary intake of type 2 diabetic patients and their association with glucose and lipid indices. The study was conducted on 62 people aged 40-78 years (31 diabetic patients and 31 healthy subjects, who were the control group). The content of trace elements in the hair and serum was analysed with the AAS method. The serum insulin, HbA1c, glucose, total cholesterol and triacylglycerol concentrations were measured by means of RIA, HPLC and colorimetric methods, respectively. The diabetic patients were found to have significantly higher dietary iron intake, higher hair Fe and lower serum Zn concentrations than the non-diabetic subjects, while the hair Zn and Cu contents were comparable in both groups. The serum Zn and Cu levels of the diabetic subjects were negatively correlated with the serum glucose, the serum Zn and Cu/Zn ratio was inversely correlated with the serum total cholesterol and the serum insulin level was positively associated with the hair Cu/Zn ratio. The results of this study indicate that the trace element status (Zn, Fe, Cu), as reflected in the blood serum and hair, may be disturbed due to metabolic derangement occurring in diabetes.

Effects of chromium brewer's yeast supplementation on body mass, blood carbohydrates, and lipids and minerals in type 2 diabetic patients

Chromium(III) is considered as an essential element for carbohydrate and lipid metabolism. The aim of this clinical study was to evaluate the efficacy of Cr brewer's yeast supplementation on body mass, carbohydrate, lipids and mineral indices in type 2 diabetic patients. Twenty adult type 2 diabetic subjects (11 males and 9 females aged 37-63) were supplemented with Cr brewer's yeast in dosages of 500 μg Cr/person/day or placebo for 8 weeks in a double-blind, placebo-controlled crossover design. It was found that supplemental Cr did not affect body mass, blood lipid profile, resistin levels, and the serum and hair Zn, Fe, and Cu levels, but increased serum Cr (by 116%) and hair Cr (by 20.6%) concentrations and improved some blood carbohydrate indices (significant increase in the β cell function index by 18.8%) in type 2 diabetic patients. In conclusion, Cr brewer's yeast has a weak hypoglycemic potential, but does not affect body mass, blood biochemical profile, and microelement levels in type 2 diabetic subjects.

Post-prandial responses to cereal products enriched with barley beta-glucan

BACKGROUND

High amounts of soluble beta-glucan in barley products may exert beneficial effects on glucose tolerance and blood lipids.

OBJECTIVE

To investigate the acute postprandial response on plasma glucose, insulin and lipids after consumption of two experimental products made from barley flour enriched with beta-glucan in comparison with similar products made from whole-wheat flour.

METHODS

A group of 10 healthy volunteers (5 males, age 25.4 +/- 0.5 y, BMI 22.6 +/- 0.7 Kg/m(2)) received at breakfast, in random order and in different days, portions (40g of available carbohydrate) of different cereal products or white bread consumed together with a load of 90000 UI retinol. Products were crackers and cookies made either from barley or whole-wheat flour in a 2 x 2 design, where the two factors were the cereal source of dietary fiber (DF), and the food processing. Barley products supplied 12 g DF, 50% soluble, with 3.5 g of beta-glucan per portion. Whole-wheat products supplied about 14 g of dietary fiber, mainly in the insoluble form, with negligible amount of beta-glucan. Fasting and post-prandial glucose and insulin were evaluated for 180 min after the meals; retinyl-palmitate (RP) and triacylglycerol (TAG) were evaluated hourly over 8 hours. Glycemic (GI) and Insulinemic (II) indexes of products were also assessed, using white bread as reference.

RESULTS

Glucose curves were significantly different between types of food processing (p < 0.01) but not between cereal sources of DF (p = 0.07). On the contrary, the effect of fiber but not of processing was evident when glucose response was expressed as Glycemic Index (effect of DF p < 0.01, effect of processing p = 0.69). Individual GI values were 78, 81, 49 and 34 for whole-wheat crackers (WWCr), whole-wheat cookies (WWc), barley crackers (BCr) and barley cookies (Bc) respectively. Insulin curves were significantly different both between type of processing and fiber source (p < 0.001 for both effects). Again, insulin indices were different between fiber but not between processing (p < 0.5 and p = 0.174 respectively). RP and TAG daily profiles were not significantly different between the factors studied.

CONCLUSIONS

Products prepared from barley flour enriched with beta-glucan exhibit favourable responses on glucose metabolism, and particularly on insulinemic responses. In general, cookies responded better to the addition of barley fiber than crackers. Our results highlight the complexity of the effect that barley fiber may exert when added to different food products in reducing postprandial metabolic responses.

Postabsorptive and insulin-stimulated energy and protein metabolism in patients with myotonic dystrophy type 1

BACKGROUND

Exaggerated insulin resistance was described as the major metabolic abnormality in myotonic dystrophy type 1 (DM1). We reported recently that the severity of the impairment in insulin-stimulated glucose metabolism in these patients was overestimated.

OBJECTIVE

The aim was to dissect out insulin action with respect to whole-body energy homeostasis and glucose, protein, and lipid metabolism in patients with DM1 to assess the relevance of insulin resistance to the heterogeneous clinical manifestations of this syndrome.

DESIGN

Ten nondiabetic patients with DM1 and 10 matched healthy control subjects were studied by means of 1) dual-energy X-ray absorptiometry; 2) a euglycemic-hyperinsulinemic clamp (40 mU. m(-2). min(-1)) combined with a primed, continuous infusion of [6,6-d(2)]glucose and [1-(13)C]leucine; 3) indirect calorimetry; and 4) localized (1)H magnetic resonance spectroscopy of the calf muscles.

RESULTS

Patients with DM1 had less lean body mass, greater fat mass, and greater intramyocellular lipid contents than did healthy control subjects. Energy expenditure and glucose and lipid metabolism did not differ significantly between the groups. In contrast, markers of proteolysis were higher in DM1 patients in the postabsorptive and insulin-stimulated conditions and were associated with lower plasma concentrations of insulin-like growth factor 1 (P < 0.03) and higher plasma concentrations of tumor necrosis factor alpha receptor 2 (P = 0.04).

CONCLUSIONS

Despite greater body fat and intramyocellular lipid contents in patients with DM1, insulin sensitivity was not significantly different between patients and control subjects. In contrast, the loss of lean body mass in patients with DM1 was associated with abnormal postabsorptive and insulin-stimulated regulation of protein breakdown. Lower plasma insulin-like growth factor 1 concentrations and higher tumor necrosis factor system activity might be involved in the muscle wasting of DM1.

Contribution of abnormal insulin secretion and insulin resistance to the pathogenesis of type 2 diabetes in myotonic dystrophy

OBJECTIVE

Myotonic dystrophy (MyD), the most common adult form of muscular dystrophy, is often complicated by diabetes. MyD is dominantly inherited and is due to heterozygosity for a trinucleotide repeat expansion mutation in a protein kinase gene able to induce derangement of RNA metabolism responsible of an aberrant insulin receptor expression.

RESEARCH DESIGN AND METHODS

To assess insulin sensitivity and secretion before the onset of diabetes, we studied 10 MyD patients, 10 offspring of type 2 diabetes (OFF), and 10 healthy subjects with no family history of diabetes (control subjects) with dual X-ray energy absorption, euglycemic-hyperinsulinemic clamp (40 mU/[m(2). min]) combined with infusion of [6,6-D(2)]-glucose and oral glucose tolerance test (OGTT).

RESULTS

MyD had reduced lean body mass, but peripheral insulin sensitivity was not different to that of control subjects in contrast to OFF, which showed insulin resistance. Insulin secretion, obtained by deconvolution of OGTT data, was also shown to be comparable with that of OFF and control subjects (index of beta-cell function = Phi; P = 0.91) even if increased parameters of insulin secretion were found during the first 30 min (Phi(30); P = 0.05) of the oral glucose challenge. Fasting plasma proinsulin concentrations (P = 0.01) and the ratio to insulin (P = 0.01) were increased in MyD patients. The proinsulin levels also failed to be suppressed during the clamp and showed exaggerated response after the OGTT. Increased proinsulin levels were shown to be peculiar of MyD patients when compared with OFF.

CONCLUSIONS

In nondiabetic, young MyD patients, insulin sensitivity was preserved, and an increased early secretory response to oral glucose was detected. Abnormal plasma proinsulin levels in the fasting state, during the clamp, and during the OGTT were shown to be secretory dysfunctions peculiar of MyD patients and may be more important than insulin resistance in determining the high risk to develop diabetes in these patients.

Normal insulin sensitivity and IMCL content in overweight humans are associated with higher fasting lipid oxidation

Intramyocellular lipid (IMCL) storage is considered a local marker of whole body insulin resistance; because increments of body weight are supposed to impair insulin sensitivity, this study was designed to assess IMCL content, lipid oxidation, and insulin action in individuals with a moderate increment of body fat mass and no family history of diabetes. We studied 14 young, nonobese women with body fat <30% (n = 7) or >30% (n = 7) and 14 young, nonobese men with body fat <25% (n = 7) or >25% (n = 7) by means of the euglycemic-insulin clamp to assess whole body glucose metabolism, with indirect calorimetry to assess lipid oxidation, by localized (1)H NMR spectroscopy of the calf muscles to assess IMCL content, and with dual-energy X-ray absorptiometry to assess body composition. Subjects with higher body fat had normal insulin-stimulated glucose disposal (P = 0.80), IMCL content in both soleus (P = 0.22) and tibialis anterior (P = 0.75) muscles, and plasma free fatty acid levels (P = 0.075) compared with leaner subjects in association with increased lipid oxidation (P < 0.05), resting energy expenditure (P = 0.046), resting oxygen consumption (P = 0.049), and plasma leptin levels (P < 0.01) in the postabsorptive condition. In conclusion, in overweight subjects, preservation of insulin sensitivity was combined with increased lipid oxidation and maintenance of normal IMCL content, suggesting that abnormalities of these factors may mutually determine the development of insulin resistance associated with weight gain.

Incorporation of the fasting plasma FFA concentration into QUICKI improves its association with insulin sensitivity in nonobese individuals

Insulin resistance plays a major role in the pathophysiology of diabetes and is associated with obesity and cardiovascular disease. Excellent methods exist for the assessment of insulin sensitivity in the laboratory setting, such as the glucose clamp. However, these methods are not suitable for large population studies, and, thus, surrogate estimates of insulin sensitivity based on measurements in a single blood sample have been developed. Recently an index based on the logarithm and the reciprocal of the insulin-glucose product (QUICKI) has been proposed. QUICKI correlated with insulin sensitivity across the entire spectrum of glucose tolerance, but its performance was less satisfactory in normal subjects. Aim of this study was to ascertain whether the inclusion of fasting plasma free fatty acids concentration into QUICKI improves its association with insulin sensitivity in nonobese subjects. To test this hypothesis, we performed a euglycemic hyperinsulinemic clamp [40 mU/(m(2).min)] in 57 young, healthy, nonobese individuals with (n = 17) or without (n = 40) first-degree relatives affected by type 2 diabetes (the former group being an in vivo model of mild insulin resistance). We then compared the clamp-based index of insulin sensitivity with both QUICKI and a revised QUICKI, the latter index including the contribution of fasting free fatty acid concentration as well. The revised QUICKI considerably improved the relationship with the clamp-based index of insulin sensitivity (r = 0.51, P < 0.0001) with respect to QUICKI (r = 0.27, P < 0.05). In addition, the revised QUICKI revealed a reduction of insulin sensitivity in the offspring of type 2 diabetes (10%; P < 0.006) that QUICKI was unable to detect (3%; P = 0.28). In conclusion, this study suggests that the incorporation of fasting free fatty acid level into QUICKI is useful to improve its correlation with the clamp-based index of insulin sensitivity and its discriminatory power in case of mild insulin resistance. Further investigation is needed to ascertain its applicability to patients with obesity and type 2 diabetes.

Effects of cryopreservation on in vitro and in vivo long-term function of human islets

BACKGROUND

The possibility of performing transplantation several days after explant seems to be a peculiarity of islet grafts, and the opportunity to cryopreserve human islets may permit an indefinite period for modulating the recipient immune system. The aim of the present study was the evaluation of in vitro and in vivo functional properties of cryopreserved human islets.

METHODS

We used six consecutive human islet preparations not suitable for an immediate transplantation in diabetic patients because the limited islet mass separated. The in vitro function of cryo and fresh islets was studied by determination of insulin and glucagon secretion in response to such classical stimuli as glucose (16.7 mM), glucose (16.7 mM) + 3-isobutyl-1-methylxanthine (0.1 mM), arginine (10 mM), and tolbutamide (100 microM). In vivo islet function was assessed through intravenous glucose tolerance tests performed at 15, 30, 60, and 90 days after transplantation of 1000 hand-picked fresh or cryopreserved islets in nude mice.

RESULTS

Basal secretion of true insulin was significantly higher in cryopreserved islets than in fresh ones. The response of cryopreserved islets to arginine and glucose + isobutyl-1-methylxanthine seemed partially impaired. Proinsulin-like molecule secretion seemed higher in cryopreserved than in fresh islets in response to all secretagogues used, and the difference was statistically significant for arginine. The capacity of human cryopreserved islets to maintain a correct metabolic control in diabetic nude mice was progressively lost in 3 months.

CONCLUSIONS

These findings showed that cryopreservation affects the function of isolated human islets, maintaining in vivo function for a limited period of time.

Highly specific radioimmunoassay for human insulin based on immune exclusion of all insulin precursors

We describe a rapid and simple insulin RIA in which proinsulin and conversion intermediates do not interfere. Three monoclonal antibodies (S1, S2, and S53) were selected for their specificity (directed, respectively, against the B10 region, the junction between A chain and C-peptide, and the junction between B chain and C-peptide), their affinity constant (∼1010 L/mol), and their interactive properties in mixture. S2 and S53 were able to bind simultaneously to the same proinsulin molecule, whereas neither could bind simultaneously with S1. Preincubation of serum samples with an excess of S2 resulted in capture of proinsulin and conversion intermediates modified at the junction between B chain and C-peptide into immune complexes that no longer reacted with S1. Similarly, preincubation with S53 prevented proinsulin and conversion intermediates modified at the junction between A chain and C-peptide from reacting with S1. Preincubation with an excess of both S2 and S53 left insulin as the sole reactant with S1. Thus, separation of insulin precursors from insulin by mutually exclusive antibodies is feasible, and on the basis of this new principle, a highly specific RIA for insulin was designed. The detection limit was 11 pmol/L, and the inter- and intraassay coefficients of variation were 11% and 5%, respectively. The potential of the assay for use in clinical studies was verified by application to serum samples from control subjects and patients with diabetes or insulinoma.

Anti-insulin antibodies in insulin immunometric assays: a still possible pitfall

Insulin was assayed directly using radioimmunoassay and immunometric assay in 31 sera containing anti-insulin antibodies. Anti-insulin antibodies were determined by radio-binding-assay. Insulin measurements were compared with those of free (unbound to antibodies, polyethylene glycol precipitated) insulin measurements. Compared with free insulin concentrations, radioimmunoassay and immunometric assay yielded falsely increased insulin results. The degree of overestimation by radioimmunoassay and by immunometric assay correlated with the anti-insulin antibody value. Anti-insulin antibodies still remain a possible pitfall in the insulin-specific immunometric assays which are now being widely used.