Importance of validation of immunoassays for intact proinsulin

The aim of this study was to compare results obtained from two commercially available immunoassay kits for intact proinsulin. Fasting and post-prandial samples were obtained from both healthy subjects and patients with type 2 diabetes mellitus and assays were carried out according to the manufacturers' instructions. Coefficient of variation of the duplicates in both assays was acceptable with the MLT Intact Proinsulin assay giving slightly better overall precision. Regression analysis indicated a good correlation between the assays (r=0.97), however, a procedure better designed to compare analytical methods demonstrated a considerable lack of agreement for some samples. Dilution of samples in the Dako assay greatly affected the results when compared to samples assayed undiluted, whereas in the MLT assay, dilution of samples produced the expected results. Repeat comparison, assaying samples neat in the MLT assay and diluted 1:5 in the Dako assay, resulted in a considerable improvement in the agreement between the Dako and MLT assays. This study underlines the importance of the use of validation procedures which demonstrate quantitative analytical recoveries from a variety of specimens over the working range of the assay method in question.

Pharmacokinetics of 125I-labeled insulin glargine (HOE 901) in healthy men: comparison with NPH insulin and the influence of different subcutaneous injection sites

OBJECTIVE

To determine the subcutaneous absorption rates and the appearance in plasma of 3 formulations of the long-acting human insulin analog insulin glargine (HOE 901) differing only in zinc content (15, 30, and 80 microg/ml).

RESEARCH DESIGN AND METHODS

We conducted 2 studies. Study 1 compared the subcutaneous abdominal injection of 0.15 U/kg of 125I-labeled insulin glargine[15], insulin glargine[80], NPH insulin, and placebo. In study 2, 0.2 U/kg of insulin glargine[30] was injected into the arm, leg, and abdominal regions. Both studies had a randomized crossover design; each enrolled 12 healthy men, aged 18-50 years.

RESULTS

In study 1, the time in hours for 25% of the administered radioactivity to disappear after bolus subcutaneous injection (T75%) for NPH insulin indicated a significantly faster absorption rate compared with the 2 insulin glargine formulations (3.2 vs. 8.8 and 11.0 h, respectively P < 0.0001). Mean residual radioactivity with NPH insulin was also significantly lower at 24 h (21.9 vs. 43.8 and 52.2%, P < 0.0001). The calculated plasma exogenous insulin concentrations after NPH insulin were substantially higher than those with insulin glargine, reaching a peak within the first 6 h after administration before declining. Insulin glargine, however, did not exhibit a distinct peak. Weighted average plasma glucose concentration between 0 and 6 h was significantly lower after NPH compared with insulin glargine (P < 0.001). In study 2, there were no significant differences in the absorption characteristics of insulin glargine between the 3 injection sites (T75% = 11.9, 15.3, and 13.2 h for arm, leg, and abdomen, respectively) or in residual radioactivity at 24 h.

CONCLUSIONS

Subcutaneous absorption of insulin glargine is delayed compared with NPH insulin. There is little or no difference in the absorption rate of insulin glargine between the main subcutaneous injection sites.

Increased prandial insulin secretion after administration of a single preprandial oral dose of repaglinide in patients with type 2 diabetes

OBJECTIVE

To examine the dose-related pharmacodynamics and pharmacokinetics of a single preprandial oral dose of repaglinide in patients with type 2 diabetes.

RESEARCH DESIGN AND METHODS

A total of 16 Caucasian men with type 2 diabetes participated in two placebo-controlled double-blind randomized cross-over studies. Patients were randomized to receive a single oral dose of repaglinide (0.5, 1.0, and 2.0 mg in study 1 and 4.0 mg in study 2) or placebo (both studies) administered 15 min before the first of two sequential identical standard meals (breakfast and lunch) that were 4 h apart. During each of the study days, which were 1 week apart, blood samples were taken at frequent intervals over a period of approximately 8 h for measurement of plasma glucose, insulin, C-peptide, and repaglinide concentrations.

RESULTS

During the first meal period (0-240 min), administration of repaglinide reduced significantly the area under the curve (AUC) for glucose concentration and significantly increased the AUC for insulin levels, C-peptide levels, and the insulin secretion rate. These results, compared with those of administering placebo, were dose dependent and log linear. The effect of repaglinide administration on insulin secretion was most pronounced in the early prandial period. Within 30 min, it caused a relative increase in insulin secretion of up to 150%. During the second meal period (240-480 min), there was no difference between repaglinide and placebo administration in the AUC for glucose concentration, C-peptide concentration, and the estimated insulin secretion rate.

CONCLUSIONS

A single dose of repaglinide (0.5-4.0 mg) before breakfast improves insulin secretion and reduces prandial hyperglycemia dose-dependently Administration of repaglinide had no effect on insulin secretion with the second meal, which was consumed 4 h after breakfast.

Day-to-day variability of fasting plasma glucose in newly diagnosed type 2 diabetic subjects

OBJECTIVE

To determine the day-to-day intraindividual variability of fasting plasma glucose (FPG) in newly diagnosed Caucasian type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

A total of 193 newly diagnosed, previously untreated, Caucasian type 2 diabetic subjects (135 men, 58 women) had FPG measured on two consecutive days (FPG1, FPG2). Ethical approval and subjects' full informed consent were obtained. Subjects fasted for 12 h before each study day and rested for at least 30 min before blood was taken. Plasma glucose was analyzed by a glucose oxidase method with intra- and interassay coefficients of variation (CVs) < 2%. Variability of FPG was assessed by comparison of percentage differences (PDs): PD = 100 (FPG2 - FPG1)/FPG1, with averaged FPG (FPGaver = [FPG1 + FPG2]/2). Biological and analytical variability were determined by use of SD2total = SD2biological + SD2analytical, where SD2analytical approximately equal to 2 x (CVglucose measurement)2. Given normally distributed data with zero mean, 95% of daily percentage differences will be expected to fall within a range of +/- 2 SDtotal.

RESULTS

Subjects were age 54 +/- 10 years (mean +/- SD) and had BMI of 29.3 +/- 5.3 kg/m2. FPG values for both days were 12.2 +/- 3.4 mmol/l (FPG1) and 12.1 +/- 3.3 mmol/l (FPG2), with a mean paired difference (95% CI) of 0.1 (0.0 to 0.3) mmol/l. The variance of these differences increased with increasing FPGaver. The PDs did not exhibit this effect and were normally distributed (mean -0.6% [-1.7 to 0.4]; SD 7.4% [6.8 to 8.3]), giving a 95% variability (2 SD) of 14.8%. Biological variability (2 SDbiological) was 13.7%. No significant difference in PD was found between men and women (mean difference 1.3% [-1.0 to 3.6]; SDmale 7.4%, SDfemale 7.3%; P = 0.62).

CONCLUSIONS

A total of 95% of the FPG values for this group of newly diagnosed type 2 diabetic subjects varied within approximately +/- 15% on a daily basis, with approximately 14% caused by biological variability. As these results are expressed in percentage terms, subjects in the group with higher FPG values are likely to experience larger changes in FPG values measured from day to day. This variability should be considered when using FPG for the diagnosis and/or monitoring of response to treatment in patients with type 2 diabetes.

Determining true glomerular filtration status in newly presenting type 2 diabetic subjects using age and sex adjustment

OBJECTIVE

To determine age- and sex-adjusted reference ranges (ASARRs) for glomerular filtration status using data from nondiabetic subjects and to apply these to newly presenting type 2 diabetic subjects.

RESEARCH DESIGN AND METHODS

Glomerular filtration rate corrected for body surface area (cGFR) was determined using a radionuclide (51Cr-EDTA) method in 75 non-diabetic subjects (37 men, 38 women) and 219 type 2 diabetic subjects (157 men, 62 women). The 95% constant reference ranges (CRRs) were calculated as mean nondiabetic cGFR+/-1.96 SD. The 95% ASARRs were calculated by Altman's method from the nondiabetic cGFR versus age regression residuals for both male and female subjects.

RESULTS

Using Altman's method, the intercepts, but not the gradients, of the cGFR versus age regressions were significantly different between male and female subjects (intercept difference [95% CI] 8.2 [1.3-15.1], gradient difference -0.4 [-1.1 to 0.3]). Fitting a common gradient, 95% ASARRs for normofiltration were found to be from 123.9 - (0.89 X age) to 181.7 - (0.89 x age) for male subjects, and from 116.0 - (0.89 X age) to 173.2 - (0.89 X age) for female subjects. The 95% CRR for normofiltration was 70.2-138.1 ml x min(-1) x (1.73 m)(-2). When applied to the diabetic cGFRs, the CRRs and ASARRs gave, respectively, 17% (37/219) versus 21% (46/219) hyperfiltrators and 83% (181/219) versus 79% (172/219) normofiltrators. Using the ASARRs, 14 normofiltrators (6 men, 8 women) were reclassified as hyperfiltrators (change [n/total n] [95% CI] 8% [14/181] [4-12]), and 5 hyperfiltrators (5 men, 0 women) were reclassified as normofiltrators (change 14% [5/37] [5-30]).

CONCLUSIONS

We conclude that age and sex adjustment are essential to assess glomerular filtration status.

Pancreatic beta-cell responsiveness during meal tolerance test: model assessment in normal subjects and subjects with newly diagnosed noninsulin-dependent diabetes mellitus

A model-based method was developed to quantify pancreatic beta-cell responsiveness during a meal tolerance test (MTT). C peptide secretion was related in a linear fashion to glucose concentration, whereas the standard population model was used to derive transfer rate constants of the two compartmental model of C peptide kinetics. Two indexes of pancreatic beta-cell responsiveness were defined: 1) postprandial sensitivity M(I) (ability of postprandial glucose to stimulate beta-cell), and 2) basal sensitivity M0 (ability of fasting glucose to stimulate beta-cell). The method was evaluated using plasma glucose and C peptide measured over 180 min with a 10- to 30-min sampling interval during a MTT (75 g carbohydrates; 500 Cal) performed in 16 normal subjects (7 men and 9 women; age, 50 +/- 10 yr; body mass index, 29.2 +/- 3.6 kg/m2; fasting plasma glucose, 5.1 +/- 0.5 mmol/L; mean +/- SD) and 16 body mass index-matched subjects with newly diagnosed noninsulin-dependent diabetes mellitus (NIDDM; 15 men and 1 woman; age, 50 +/- 9 yr; body mass index, 29.3 +/- 3.7 kg/m2; fasting plasma glucose, 12.6 +/- 3.2 mmol/L). M(I) and M0 indexes were estimated with very good precision (coefficient of variation, < 15%). Subjects with NIDDM demonstrated lower postprandial sensitivity M(I) (17.7 +/- 11.4 vs. 90.0 +/- 43.3 x 10(-9)/min; NIDDM vs. normal, P < 0.001) and basal sensitivity M0 (5.4 +/- 2.2 vs. 10.3 +/- 4.9 x 10(-9)/min; P < 0.005). Deconvolution analysis documented that the relationship between C peptide secretion and glucose concentration is approximately linear during MTT in both normal subjects (plasma glucose range, 5-8 mmol/L) and subjects with NIDDM (12-17 mmol/L). We conclude that pancreatic responsiveness during glucose stimulation (M(I)) and under basal conditions (M0) can be obtained from this novel method during MTT in healthy and disease states.

Insulin secretion and sensitivity in newly diagnosed NIDDM Caucasians in the UK

Beta-cell secretion and insulin sensitivity was studied in healthy subjects and newly diagnosed Caucasian (Welsh) NIDDM patients. A standardized meal tolerance test (MTT) and frequent sampled intravenous glucose tolerance tests (FSIVGTT) were employed and the patients stratified according to fasting plasma glucose (FPG). A deficient early (first hour) post-prandial (MTT) insulin secretion was demonstrated in all NIDDM patients, deteriorating with increasing fasting hyperglycaemia. For the patient group fasting and post-prandial hyperproinsulinaemia was evident with diminishing post-prandial excursions as fasting hyperglycaemia increased. The early phase (0-10 min) insulin secretion to intravenous glucose (300 mg kg-1) was severely impaired in NIDDM patients. A shortlived paradoxical fall in plasma insulin concentrations was observed in those with FPG > 9 mmol l-1. Insulin sensitivity utilizing the insulin modified FSIVGTT demonstrated that all NIDDM patients had marked insulin insensitivity. Characteristic of the newly diagnosed previously untreated Caucasian NIDDM is a dysfunctional beta cell, resulting in a deficit in insulin secretion with relative hyperproinsulinaemia. The quantitative and qualitative secretory status of the beta cell decreases with increasing fasting hyperglycaemia. Insulin sensitivity is markedly reduced when FPG exceeds 7.0 mmol l-1 with little or no further discernible fall with deteriorating glycaemic control.

Dominant risk factors for retinopathy at clinical diagnosis in patients with type II diabetes mellitus

A study of 270 newly presenting, previously untreated, type II diabetic patents revealed that 38 patients (14%) had already developed diabetic retinopathy (DR). Among this group, 26 patients had lesions of background diabetic retinopathy and 12 patients already had maculopathy or preproliferative changes. The aim of this study was to determine the risk factors influencing susceptibility to retinopathy, and to provide an accurate predictive value for diabetic retinopathy from a detailed multiple regression analysis that involved 27 demographic variables and the metabolic and hormonal responses during a meal tolerance test (MTT) at presentation. Compared to the nonretinopaths, the retinopaths had higher fasting plasma glucose levels (FPG) (mean +/- SD) (13.9 +/- 3.1 versus 11.6 +/- 3.2 mmol/L, p < 0.001), lower body-mass index values (BMI) (26.1 +/- 3.8 versus 29.3 +/- 5.0 kg/m2, p < 0.001) and higher plasma urea concentrations (6.0 +/- 1.9 versus 5.3 +/- 1.2 mmol/L, p 0.05). In contrast, gender and levels of blood pressure and other lipid levels did not influence the prevalence of diabetic retinopathy. A multiple regression formula for the prediction of diabetic retinopathy was derived and then used to categorize patients into high-risk and low-risk groups. The retinopaths also had higher HbA1c (p < 0.001), higher plasma glucose are under curve (0-2 h, p < 0.001), lower plasma insulin area under curve (0-22 h, p < 0.001), lower C-peptide area under curve (0-2 h, p < 0.01). They were also leaner (p < 0.001) and older (p < 0.05). However, these variables did not feature significantly in the multiple regression formula. The retinopaths were found to have higher risk probability values (25.1 +/- 11.5 versus 13.1 +/- 10.4%, p < 0.001). In the high risk group, 81.6% of retinopaths were identified. In the low-risk group, 63.8% of nonretinopaths were found. The incidence of diabetic retinopathy in type II diabetic patients at clinical diagnosis was found to be highly related to the degree of hyperglycemia, body-mass index, and to a lesser extent, renal impairment.

A new breakfast cereal containing guar gum reduces postprandial plasma glucose and insulin concentrations in normal-weight human subjects

A new guar-containing wheatflake product was developed to assess its effect on carbohydrate tolerance in normal-weight, healthy subjects. The extruded wheatflake breakfast cereals containing 0 (control) or approximately 90 g guar gum/kg DM were fed to ten fasting, normal-weight, healthy subjects using a repeated measures design. The meals were similar in energy (approximately 1.8 MJ), available carbohydrate (78 g), protein (15 g) and fat (5.4 g) content. The guar gum content of the test meals was 6.3 g. Venous blood samples were taken fasting and at 15, 30, 45, 60, 90, 120, 150 and 240 min after commencing each breakfast and analysed for plasma glucose, insulin and C-peptide. The guar wheatflake meal produced a significant main effect for glucose and insulin at 0-60 min and 0-240 min time intervals respectively, but not for the C-peptide levels compared with the control meal. Significant reductions in postprandial glucose and insulin responses were seen following the guar wheatflake meal compared with the control meal at 15 and 60 min (glucose) and 15, 60, 90 and 120 min (insulin). The 60 and 120 min areas under the curve for glucose and insulin were significantly reduced by the guar gum meal, as was the 240 min area under the curve for insulin. Thus, it can be concluded that the use of a severe method of heat extrusion to produce guar wheatflakes does not diminish the physiological activity of the guar gum.

Comparison of estimates of insulin sensitivity from minimal model analysis of the insulin-modified frequently sampled intravenous glucose tolerance test and the isoglycemic hyperinsulinemic clamp in subjects with NIDDM

Minimal model (MINMOD) analysis of the frequently sampled intravenous glucose tolerance test (FSIVGTT) is dependent on an adequate insulin response to the glucose load. As this is characteristically deficient in subjects with non-insulin-dependent diabetes mellitus (NIDDM), the technique has been modified by the use of an intravenous bolus of insulin. Previous validation of this modification in humans has relied on agreement between insulin sensitivity indexes (SI) estimated from tolbutamide- and insulin-modified tests and not on direct comparison with estimates derived from the isoglycemic glucose clamp. We have compared estimates of insulin sensitivity derived from minimal modeling of a 4-h insulin-modified FSIVGTT and the glucose clamp in subjects with NIDDM. Twelve subjects underwent an insulin-modified FSIVGTT and an isoglycemic hyperinsulinemic clamp in random order 2-4 weeks apart. Fasting plasma glucose (8.4 vs. 9.0 mmol/l) and immunoreactive insulin (IRI) concentrations (104.5 vs. 101.5 pmol/l) were not different between the 2 study days. SI(clamp) was derived from the steady-state glucose infusion rate during the 3rd h of the clamp, corrected for the ambient insulin and glucose concentrations. SI(ivgtt) was derived using MINMOD. SI(ivgtt) was 1.06 +/- 0.18 min-1.mU-1.ml x 10(4), and mean SI(clamp) was 4.97 +/- 0.69 l.min-1/pmol.l-1 x 10(4) (mean +/- SE). SI(ivgtt) was positively correlated with SI(clamp) (r = 0.73, P = 0.004) and negatively correlated with body mass index (r = -0.7, P = 0.005) and fasting IRI(ivgtt) (r = -0.64, P = 0.008). In summary, MINMOD analysis of the insulin-modified FSIVGTT provides a valid measure of insulin sensitivity in subjects with NIDDM.

Intranasal insulin: the effects of three dose regimens on postprandial glycaemic profiles in type II diabetic subjects

In both fasting normal and diabetic subjects, nasally administered insulin achieves significant falls in plasma glucose concentrations. Repeated administration before and during a meal has been necessary to lower postprandial glycaemic excursion in subjects with NIDDM. We have studied the use of Novolin Nasal which employs a non-irritant, lecithin-based enhancer as a vehicle for human insulin, on postprandial glucose profiles in NIDDM subjects to determine efficacy, optimal dose frequency, and tolerability. Seventeen NIDDM subjects (15 men, 2 women) participated in a randomized, partially blinded, placebo-controlled, crossover trial of three active treatment regimens (nasal insulin, 120 U at 0 min, 60 U at 0 and +20 min or 120 U at +20 min) in relation to a standardized mixed meal given at 0 min. All active treatments significantly reduced postprandial glucose concentrations compared to placebo. Intranasal insulin given at 0 min at a dose of 60 U or 120 U resulted in a 50% reduction in postprandial incremental glucose compared to placebo over the first 2 h, whereas treatment with 60 U both at 0 and 20 min lead to a 70% reduction over the 240 min postprandial period. Post-prandial intravenous insulin was the least effective. There were no episodes of symptomatic hypoglycaemia. Local tolerability was excellent with only four reports of transient nasal irritation out of a total of 68 doses. The delivery device was accurate with intra-device CV of delivered dose of 4.8%.(ABSTRACT TRUNCATED AT 250 WORDS)

A glimpse of the 'natural history' of established type 2 (non-insulin dependent) diabetes mellitus from the spectrum of metabolic and hormonal responses to a mixed meal at the time of diagnosis

The reported glucose and immunoreactive insulin (IRI) responses to oral and intravenous glucose in subjects with Type 2 diabetes have not always been consistent. This may have resulted from variations in the method of glucose administration, the ethnic backgrounds of subjects, the diagnostic criteria applied, the duration of the disease or IRI assay methods. The use of a mixed meal rather than glucose has been shown to provide a more physiological stimulus to the pancreatic beta-cell due to both glucose and non-glucose secretagogues. We have analysed the metabolic and hormonal responses of 188 newly diagnosed Caucasian subjects with Type 2 diabetes and 38 non-diabetic subjects to a 500 kcal mixed meal. The diabetic subjects were stratified according to fasting plasma glucose (FPG) (< 9, 9-12, 12-15 and > or = 15 mmol/l) and body mass index (BMI) (< 26.5, 26.5-30 and > or = 30 kg/m2). Increasing FPG was associated with higher peak glucose concentrations and increasing failure to achieve basal glucose levels by 4 h. Median fasting IRI concentrations were similar to those of normal subjects, but all diabetic subjects had reduced early-phase insulin secretion. Diabetic subjects with FPG < 9 mmol/l showed augmented IRI area under the curve (AUC) at 2 and 4 h, whereas those with FPG > 9 mmol/l had progressive falls in IRI AUC to below that of the normal subjects (P < 0.0001 for the trend). Peak IRI concentrations declined progressively with increasing FPG. Despite equivalent glucose exposure simple trends of increasing AUC, IRI with increasing BMI were statistically significant (P < 0.001, P < 0.02, P < 0.001 and P < 0.01, respectively for each FPG group). Both fasting and AUC non-esterified fatty acid concentrations increased significantly with FPG regardless of BMI (P < 0.001 for the trends). These results using a more physiological mixed meal challenge in a large number of recently diagnosed Type 2 diabetic subjects demonstrate a marked and increasing loss of beta-cell secretory function with increasing fasting hyperglycaemia aggravated by insulin resistance with increasing obesity.

Reduced sampling protocols in estimation of insulin sensitivity and glucose effectiveness using the minimal model in NIDDM

Recent work in healthy subjects, the aged, and subjects with gestational diabetes or drug-induced insulin resistance using minimal model analysis of the tolbutamide-modified frequently sampled intravenous glucose tolerance test suggested that a reduced sampling regimen of 12 time points produced unbiased and generally acceptable estimates of insulin sensitivity (SI) and glucose effectiveness (SG) compared with a full sampling schedule of 30 time points. We have used data from 26 insulin-modified frequently sampled intravenous glucose tolerance tests in 21 subjects with NIDDM to derive and compare estimates of SI and SG from the full sampling schedule (SI(30), SG(30)) with those estimated from the suggested 12 time points (SI(12), SG(12)) and those estimated with the addition of a 25-min time point (SI(13), SG(13)). Percentage relative errors were calculated relative to the corresponding 30 time-point values. A statistically significant bias of 15% (97% confidence interval from 7.4 to 25.6%, interquartile range 25%) was introduced by the estimation of SI(12) but not SI(13) (1%, 97% confidence interval from -9.4 to 9.3%, interquartile range 21%). Results for SG(12) (-12%, 97% confidence interval from -46.7 to 1.2%, interquartile range 49%) and SG(13) (-5%, 97% confidence interval from -27.8 to 6.8%, interquartile range 37%) were statistically equivocal. The precision of estimation of SI(12), SG(12), and SG(13) measured by the interquartile range of the percentage relative errors was poor. The precision of determination measured by the median minimal model coefficient of variation was 18, 29, and 27% for SI(30), SI(12), and SI(13) and 9, 11, and 11% for SG(30), SG(12), and SG(13), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The pharmacokinetics of five pre-mixed combinations of 'short-' and 'intermediate-acting' (NPH) insulins in healthy subjects following subcutaneous administration

The pharmacokinetics of five pre-mixed insulin preparations in the ratio of soluble to NPH insulin of 10:90, 20:80, 30:70, 40:60 and 50:50, were examined in a two part study in fasting healthy subjects. Each received by bolus subcutaneous injection into the anterior abdominal wall, on separate occasions one to two weeks apart, 20U of each of three pre-mixed insulin preparations in random order. In Part 1, nine subjects received Penmix 10:90, Penmix 20:80 and Penmix 30:70 and were observed over a period of 24 hours. In Part 2, eight subjects received Penmix 30:70, Penmix 40:60 and Penmix 50:50 and were observed over an 8 hr post-injection period. Three subjects were common to both parts of the study. Plasma glucose, C-peptide and insulin levels were measured frequently throughout both study periods. Increasing soluble insulin content in the pre-mixtures was reflected in increasing peak plasma insulin concentrations and a greater hypoglycaemic response. There were highly significant differences between the five premixtures and preparations in the 0-4 and 0-8 hours area under the curve (AUC) values for plasma glucose, C-peptide and immunoreactive insulin concentration (p < 0.01). Whereas a gradual difference between the premixtures was seen no two adjacent ones were significantly different, however an overall highly significant difference between the five preparations tested was observed.

Intravenous insulin simulates early insulin peak and reduces post-prandial hyperglycaemia/hyperinsulinaemia in type 2 (non-insulin-dependent) diabetes mellitus

In NIDDM patients the deficient initial rise in insulin is a consistent finding. This early phase of insulin secretion influences the degree of hyperglycaemia following a meal. In this study insulin was infused intravenously into newly diagnosed NIDDM patients in an attempt to mimic the non-diabetic insulin response to a mixed meal and to determine the effect of early insulin availability on post-prandial glucose, C-peptide and insulin concentrations in NIDDM patients. The study involved standardized meal tolerance tests (MTT) with and without insulin on 2 separate days, 1 week apart. Insulin was given by intravenous infusion (2.5 U Actrapid over 30 min) immediately following the start of a 500 kcal MTT. The subjects were divided into non-obese and obese sub-groups with 8 subjects in each group (BMI 24.0 vs 32.0 kg/m2, HbA1, 12.7 vs 9.8%, age 44.4 vs 43.0 yrs, respectively). Following intravenous insulin in non-obese diabetics a peak plasma insulin concentration of 0.393 pmol/ml was observed at 15 min compared to 0.148 pmol/ml at 90 min without exogenous insulin. The post-prandial glucose excursion between 60 and 120 min was significantly lowered with insulin (p less than 0.01). Similarly in the obese patients a higher and earlier insulin peak was achieved with intravenous insulin, with a lower level during the second half of the 4 h post-prandial period, the difference reaching significance at 150 min (p less than 0.05). No differences were observed in the C-peptide concentrations between the 2 study days.(ABSTRACT TRUNCATED AT 250 WORDS)

Allelic variants at insulin-receptor and insulin gene loci and susceptibility to NIDDM in Welsh population

A cohort of 132 well-documented White Welsh non-insulin-dependent diabetic (NIDDM) subjects were genotyped for 5 restriction-fragment-length polymorphisms (RFLPs) at the insulin-receptor gene (IRG) locus and a polymorphic locus 5' to the insulin gene. There was no significant difference in RFLP frequencies between the NIDDM subjects and a group of 87 matched White control subjects. Paired haplotype analysis of the IRG RFLPs suggested a difference between NIDDM and control groups for the endonuclease combinations Bgl II-Rsa I and Bgl II-Xba I. Analysis of implied haplotypes defined by the endonucleases Bgl II, Rsa I, and Xba I revealed one haplotype to be more prevalent in the NIDDM group; whereas, another haplotype was associated with the control group (P less than 0.02). Subset analysis within the NIDDM cohort compared the metabolic response of NIDDM subjects with the differing IRG haplotypes to a standard meal tolerance test. Both groups showed equivalent basal and postprandial glucose excursions, but one group revealed a significantly exaggerated plasma insulin response compared with the other (P less than 0.05). This may reflect the influence of genetic variation at the IRG locus on insulin sensitivity in patients with NIDDM.

A supplementary infusion of glucose-dependent insulinotropic polypeptide (GIP) with a meal does not significantly improve the beta cell response or glucose tolerance in type 2 diabetes mellitus

Newly diagnosed, previously untreated patients with type 2 diabetes mellitus (n = 6) were studied on two separate days after overnight fasts. On each day they were given a 500-kcal mixed meal plus an infusion of either porcine glucose-dependent insulinotropic polypeptide (GIP) (0.75 pmol/kg/min) or control solution (CS) from 0 to 30 min in random order. Frequent measurements of plasma glucose, C-peptide, insulin and GIP concentrations were made. Fasting GIP levels were similar on both days. During the meal plus GIP infusion plasma GIP levels increased from a basal value of 7.6 +/- 1.5 pmol/1 to a peak of 88.6 +/- 5.4 pmol/1 at 30 min. Following the meal infusion of CS GIP increased from a fasting level of 10.3 +/- 1.2 pmol/1 to a significantly lower peak of 58.0 +/- 8.3 pmol/1 at 60 min. During the meal plus GIP infusion GIP levels were higher at 10-45 min and at 90 min (P less than 0.05-0.001). Fasting and postprandial glucose, C-peptide and insulin levels were, however, similar on both study day. A supplementary infusion of porcine GIP with a mixed meal did not significantly alter the beta cell response or glucose tolerance in this group of patients with type 2 diabetes mellitus.

Sensitive and specific two-site immunoradiometric assays for human insulin, proinsulin, 65-66 split and 32-33 split proinsulins

Monoclonal antibody-based two-site immunoradiometric assays are described for human insulin, proinsulin, 65-66 split and 32-33 split proinsulin. The detection limits of the assays lie in the range 0.8-2.5 pM. The assays for 65-66 and 32-33 split proinsulins do not distinguish between these substances and their respective C-terminal di-desamino derivatives. The assay of 65-66 split proinsulin does not cross-react with insulin, proinsulin or 32-33 split proinsulin. This material was undetectable (less than 1.0 pM) in plasma taken after an overnight fast in eight normal male subjects and the maximum individual concentration reached in plasma taken during an oral glucose tolerance test of these subjects was 3.8 pM. The proinsulin assay cross-reacted 66% with 65-66 split proinsulin but not with insulin or 32-33 split proinsulin. The 32-33 split proinsulin assay cross-reacted 84 and 60% with proinsulin and 65-66 split proinsulin respectively. The insulin assay cross-reacted 5.3, 62 and 5.0% with intact proinsulin, 65-66 split proinsulin and 32-33 split proinsulin respectively. The very low concentration of 65-66 split proinsulin meant that this derivative did not interfere significantly with the specificity of the assays of proinsulin and insulin. The concentration of 32-33 split proinsulin could be calculated by subtracting the cross-reactivity of the measured proinsulin. The mean concentrations of insulin, proinsulin and 32-33 split proinsulin in eight young male subjects in the fasting state were (pM +/- S.E.M.) 20 +/- 0.3, 2.3 +/- 0.3 and 2.1 +/- 0.7 and at the maximum reached during an oral glucose tolerance test, 150 +/- 26, 9.9 +/- 1.4 and 19.7 +/- 6.0 respectively.

Insulin deficiency in non-insulin-dependent diabetes

A highly specific two-site immunoradiometric assay for insulin was used to measure the plasma insulin response to 75 g glucose administered orally to 49 patients with non-insulin-dependent diabetes (NIDDM). The plasma insulin concentration 30 min after glucose ingestion was lower in the diabetic patients than in matched controls for both non-obese (11-83 pmol/l vs 136-297 pmol/l, p less than 0.01) and obese subjects (23-119 pmol/l vs 137-378 pmol/l, p less than 0.01). By means of another two-site immunoradiometric assay, the basal intact proinsulin level was found to be higher in the NIDDM patients than in the controls for both non-obese (7.1 [SEM 1.2] pmol/l vs 2.4 [0.4] pmol/l, p less than 0.01) and obese subjects (14.4 [2.2] pmol/l vs 5.9 [1.9] pmol/l, p less than 0.01). The basal level of 32-33 split proinsulin was also raised in NIDDM. Previous failure to show clear separation between normal and NIDDM insulin responses was probably due to the high concentrations of proinsulin-like molecules in the plasma of NIDDM patients. These substances cross-react as insulin in most, if not all, insulin radioimmunoassays but have very little biological insulin-like activity. It is therefore now possible and necessary to designate most NIDDM patients as insulin deficient.

Obesity is associated with increased post-prandial GIP levels which are not reduced by dietary restriction and weight loss

Obesity is characterised by fasting and post-prandial hyperinsulinaemia. One factor which may contribute to this is overactivity of the enteroinsular axis. Glucose tolerance, beta-cell response and GIP profiles were therefore compared during oral glucose (OGTT), mixed meal (MTT) and intravenous glucose tolerance tests (IVGTT) in both lean (IBW less than 120%) and obese (IBW greater than 120%) healthy subjects. The tests were repeated in the obese group after a period of dietary restriction and weight loss. Fasting GIP concentrations were similar, but postprandial levels were significantly greater in the obese subjects during both the OGTT and MTT. Glucose profiles were similar but associated with basal and stimulated hyperinsulinaemia in the obese subjects indicating insulin resistance. GIP levels did not change during the IVGTT and were similar in the two groups throughout the test. Following diet and weight-reduction there was a significant decrease in both fasting and post-prandial insulin levels in the obese subjects but there were no significant changes in glucose or GIP concentrations. In conclusion the endogenously stimulated plasma GIP response is exaggerated in obese healthy subjects but this increased response is not decreased by short term diet and weight loss. The increased GIP concentrations may contribute the observed hyperinsulinaemia in obesity, but its contribution is likely to be small in view of the decrease in insulin concentrations following diet and weight-loss which was independent of any change in GIP.

The effects of glucose-dependent insulinotropic polypeptide infused at physiological concentrations in normal subjects and type 2 (non-insulin-dependent) diabetic patients on glucose tolerance and B-cell secretion

The effects of porcine glucose-dependent insulinotropic polypeptide given by continuous intravenous infusion in normal subjects (n = 6) and Type 2 (non-insulin-dependent) diabetic patients (n = 6) have been investigated. The subjects were studied on 2 separate days after overnight fasts. On each day 25 g of glucose was infused from 0-30 min plus an infusion of either porcine glucose-dependent insulinotropic polypeptide (0.75 pmol . kg-1 . min-1) or control solution. During the glucose-dependent insulinotropic polypeptide infusion plasma glucose values were reduced in normal subjects from 30-60 min (p less than 0.01) and in Type 2 diabetic patients at 45 and 60 min (p less than 0.05). In the normal subjects insulin concentrations were greater from 10-35 min (p less than 0.01) following glucose-dependent insulinotropic polypeptide infusion and peak values were increased by 123%. In the Type 2 diabetic patients following glucose-dependent insulinotropic polypeptide infusion insulin levels were increased from 4-40 min (p less than 0.01) but peak values were only increased by 27%. In the normal subjects C-peptide values were greater from 25-45 min (p less than 0.01) following glucose-dependent insulinotropic polypeptide infusion and peak C-peptide levels were increased by 82%. In the Type 2 diabetic patients following the glucose-dependent insulinotropic polypeptide infusion C-peptide levels were increased from 6-55 min (p less than 0.01) and peak values were increased by 20%. Plasma glucose-dependent insulinotropic polypeptide levels were within the physiological post prandial range during the glucose-dependent insulinotropic polypeptide infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Dawn phenomenon: its frequency in non-insulin-dependent diabetic patients on conventional therapy

The frequency of the dawn phenomenon has been studied in non-insulin-dependent diabetic (NIDDM) patients while they continued with their conventional therapy. Plasma glucose (PG) and immunoreactive insulin (IRI) were estimated hourly from 0300 to 0900 h in 19 NIDDM patients; 9 patients were treated by diet alone (group 1), and 10 patients were treated by diet and oral hypoglycemic agents (group 2). The dawn rise of plasma glucose was demonstrated in 17 (89.5%) of the 19 patients with mean +/- SE plasma glucose at 0300 h of 7.0 +/- 0.5 mM and at 0800 h of 8.4 +/- 0.6 (P less than .01). IRI in all patients rose from 14.7 +/- 1.3 microU/ml at 0500 h to 18.1 +/- 1.8 microU/ml at 0700 h (P less than .05). The changes in IRI levels at any time from 0300 to 0800 h in groups 1 and 2 when considered separately were insignificant. Thus, the dawn phenomenon occurs commonly in NIDDM patients taking their conventional therapy.

A comparison of the uptake of human and porcine insulins given intraperitoneally to patients with diabetes mellitus on continuous ambulatory peritoneal dialysis

Intraperitoneal absorption of human insulin (crb) and porcine insulin was examined in 9 diabetic patients with renal failure, and on Continuous Ambulatory Peritoneal Dialysis (CAPD). Serial blood sampling was performed to determine the characteristics of insulin absorption and glycaemic control. Four patients received successive equal doses of human and porcine insulins, 2 received different doses and 3 received human insulin only. Glycaemic control was similar after both insulins. Mean insulin levels were consistently higher after human insulin with significant differences at 90, 300 and 360 min. It is concluded that, if required, patients may be transferred from i.p. purified porcine to i.p. human insulin without a change in insulin dose.