Showing papers in "Diabetes in 1992"

Prospective Analysis of The Insulin-Resistance Syndrome (Syndrome X)

Abstract: Many studies have shown that hyperinsulinemia and/or insulin resistance are related to various metabolic and physiological disorders including hypertension, dyslipidemia, and non-insulin-dependent diabetes mellitus. This syndrome has been termed Syndrome X. An important limitation of previous studies has been that they all have been cross sectional, and thus the presence of insulin resistance could be a consequence of the underlying metabolic disorders rather than its cause. We examined the relationship of fasting insulin concentration (as an indicator of insulin resistance) to the incidence of multiple metabolic abnormalities in the 8-yr follow-up of the cohort enrolled in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease in Mexican Americans and non-Hispanic whites. In univariate analyses, fasting insulin was related to the incidence of the following conditions: hypertension, decreased high-density lipoprotein cholesterol concentration, increased triglyceride concentration, and non-insulin-dependent diabetes mellitus. Hyperinsulinemia was not related to increased low-density lipoprotein or total cholesterol concentration. In multivariate analyses, after adjustment for obesity and body fat distribution, fasting insulin continued to be significantly related to the incidence of decreased high-density lipoprotein cholesterol and increased triglyceride concentrations and to the incidence of non-insulin-dependent diabetes mellitus. Baseline insulin concentrations were higher in subjects who subsequently developed multiple metabolic disorders. These results were not attributable to differences in baseline obesity and were similar in Mexican Americans and non-Hispanic whites. These results support the existence of a metabolic syndrome and the relationship of that syndrome to multiple metabolic disorders by showing that elevations of insulin concentration precede the development of numerous metabolic disorders.

Spontaneous Long-Term Hyperglycemic Rat With Diabetic Complications: Otsuka Long-Evans Tokushima Fatty (OLETF) Strain

Abstract: A spontaneously diabetic rat with polyuria, polydipsia, and mild obesity was discovered in 1984 in an outbred colony of Long-Evans rats, which had been purchased from Charles River Canada (St. Constant, Quebec, Canada) in 1982. A strain of rats developed from this rat by selective breeding has since been maintained at the Tokushima Research Institute (Otsuka Pharmaceutical, Tokushima, Japan) and named OLETF. The characteristic features of OLETF rats are 1 ) late onset of hyperglycemia (after 18 wk of age); 2 ) a chronic course of disease; 3 ) mild obesity; 4 ) inheritance by males; 5 ) hyperplastic foci of pancreatic islets; and 6 ) renal complication (nodular lesions). Histologically, the changes of pancreatic islets can be classified into three stages: 7 ) an early stage (6–20 wk of age) of cellular infiltration and degeneration; 2 ) a hyperplastic stage (20–40 wk of age); and 3 ) a final stage (at >40 wk of age). These clinical and pathological features of disease in OLETF rats resemble those of human NIDDM.

Estimation of Insulin Secretion Rates from C-Peptide Levels: Comparison of Individual and Standard Kinetic Parameters for C-Peptide Clearance

Abstract: Insulin secretion rates can be accurately estimated from plasma C-peptide levels with a two-compartment model for C-peptide distribution and degradation. In previous studies, the kinetic parameters of C-peptide clearance were derived in each subject from the decay curve observed after bolus intravenous injection of biosynthetic human C-peptide. To determine whether standard parameters for C-peptide clearance could be defined and used to calculate insulin secretion without obtaining a decay curve in each subject, we analyzed 200 decay curves of biosynthetic human C-peptide obtained in normal, obese, and non-insulindependent diabetes mellitus subjects studied in ourlaboratory. This analysis showed that the volume of distribution and kinetic parameters of C-peptide distribution and metabolism vary by

Visceral Obesity in Men: Associations With Glucose Tolerance, Plasma Insulin, and Lipoprotein Levels

Abstract: The relations of regional adipose tissue (AT) distribution measured by computed tomography (CT) to plasma insulin-glucose homeostasis and lipoprotein-lipid levels were studied in 58 obese and 29 lean control men. In the group of obese men, the visceral AT area measured by CT was positively correlated with fasting plasma triglyceride and insulin levels and with glucose and insulin areas under the curves measured during a 75-g oral glucose tolerance test. Visceral AT area was also negatively associated with plasma high-density lipoprotein (HDL) and HDL2 cholesterol levels. The relative accumulation of abdominal fat, estimated by the ratio of abdominal to femoral AT areas obtained by CT, was also a significant correlate of indices of carbohydrate metabolism and was the best univariate correlate of plasma lipoprotein levels. No significant associations were observed between the visceral AT area, the ratio of abdominal to femoral AT areas, and indices of carbohydrate and lipoprotein metabolism in the group of lean men. On the other hand, the subcutaneous abdominal AT area was a significant correlate of the glucose area under the curve in both groups of men, but this association was not independent from the percentage of total body fat. No relationship was observed between the femoral AT area and indices of carbohydrate metabolism in either lean or obese groups. In obese men, however, the femoral AT area was negatively correlated with plasma triglyceride concentration and positively correlated with plasma HDL and HDL2 cholesterol levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoguanidine, a Novel Inhibitor of Nitric Oxide Formation, Prevents Diabetic Vascular Dysfunction

Abstract: Increased blood flow and vascular leakage of proteins preferentially affect tissues that are sites of diabetic complications in humans and animals. These vascular changes in diabetic rats are largely prevented by aminoguanidine. Glucose-induced vascular changes in nondiabetic rats are also prevented by aminoguanidine and by NG-monomethyl-L-arginine (NMMA), an established inhibitor of nitric oxide (NO.) formation from L-arginine. Aminoguanidine and NMMA are equipotent inhibitors of interleukin-1 beta-induced 1) nitrite formation (an oxidation product of NO.) and cGMP accumulation by the rat beta-cell insulinoma cell line RINm5F, and 2) inhibition of glucose-stimulated insulin secretion and formation of iron-nitrosyl complexes by islets of Langerhans. In contrast, NMMA is approximately 40 times more potent than aminoquanidine in elevating blood pressure in nondiabetic rats. These results demonstrate that aminoguanidine inhibits NO. production and suggest a role for NO. in the pathogenesis of diabetic vascular complications.

Evidence for Distinctive and Intrinsic Defects in Insulin Action in Polycystic Ovary Syndrome

Abstract: Women with PCO have a unique but poorly characterized disorder of insulin action. Obese (n = 16) and nonobese (n = 14) PCO women and age- and weight-matched normal, nondiabetic ovulatory women (obese, n = 15; nonobese, n = 17) had insulin action determined in vivo with sequential multiple insulin dose euglycemic clamps and in isolated abdominal adipocytes to clarify the mechanisms of insulin resistance. PCO resulted in significant increases in the ED50 insulin for glucose utilization in vivo (P less than 0.001) and in adipocytes (P less than 0.01), without significant changes in adipocyte insulin-binding sites. PCO also resulted in significant decreases in maximal insulin-stimulated rates of glucose utilization in vivo (P less than 0.01) and in adipocytes (P less than 0.01). Obesity resulted in smaller decreases in insulin sensitivity than PCO (ED50 insulin, P less than 0.001 in vivo and P less than 0.05 in adipocytes), but greater decreases in insulin responsiveness (Vmax, P less than 0.001 in vivo and in adipocytes). The ED50 insulin for suppression of HGP was increased only in obese PCO women (P less than 0.001), and the interactions between PCO and obesity on this parameter were statistically significant. No significant correlations between androgen or estrogen levels and adipocyte insulin binding or action were found. Because insulin binding was not changed, we conclude that the major lesion causing insulin resistance in PCO is a striking decrease in insulin sensitivity secondary to a defect in the insulin receptor and/or postreceptor signal transduction. PCO also is associated with modest but significant decreases in glucose transport. These defects in insulin action appear to represent intrinsic abnormalities that are independent of obesity, metabolic derangements, body fat topography, and sex hormone levels. Conversely, changes in hepatic insulin sensitivity appear to be acquired with obesity.

Impaired Insulin-Mediated Skeletal Muscle Blood Flow in Patients With NIDDM

Abstract: Patients with non-insulin-dependent diabetes mellitus (NIDDM) exhibit decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Because IMGU is equal to the product of the arteriovenous glucose difference (AVG delta) across and blood flow (F) into muscle (IMGU = AVG delta x F), reduced tissue permeability (AVG delta) and/or glucose and insulin delivery (F) can potentially lead to decreased IMGU. The components of skeletal muscle IMGU were studied in six obese NIDDM subjects (103 +/- 9 kg) and compared with those previously determined in six lean (weight 68 +/- 3 kg), and six obese (94 +/- 3 kg) with normal glucose tolerance. The insulin dose-response curves for whole body and leg muscle IMGU were constructed using the combined euglycemic clamp and leg balance techniques during sequential insulin infusions (range of serum insulin 130-80,000 pmol/L). In lean, obese, and NIDDM subjects, whole body IMGU, femoral AVG delta, and leg IMGU increased in a dose-dependent fashion over the range of insulin with an ED50 of 400-500 pmol/L in lean, 1000-1200 pmol/L in obese, and 4000-7000 pmol/L in NIDDM subjects (P less than 0.01 lean vs. obese and NIDDM). In lean and obese subjects, maximally effective insulin concentrations increased leg blood flow approximately 2-fold from basal with an ED50 of 266 pmol/L and 957 pmol/L, respectively (P less than 0.01 lean vs. obese). In contrast, leg F did not increase from the basal value in NIDDM subjects (2.7 +/- 0.1 vs. 3.5 +/- 0.5 dl/min, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Prospective study of microalbuminuria as predictor of mortality in NIDDM.

Abstract: Retrospective studies of patients with non-insulin-dependent diabetes mellitus (NIDDM) have suggested that microalbuminuria predicts early all-cause (mainly cardiovascular) mortality independently of arterial blood pressure. These findings have not been confirmed in prospective studies, and it is not known whether the predictive power of microalbuminuria is independent of other major cardiovascular risk factors. During 1985-1987, we examined a representative group of 141 nonproteinuric patients with NIDDM for the prevalence of coronary heart disease and several of its established and putative risk factors, including raised urinary albumin excretion (UAE) rate. Thirty-six patients had microalbuminuria (UAE 20-200 micrograms/min), and 105 had normal UAE (less than 20 micrograms/min). At follow-up, an average of 3.4 yr later, 14 patients had died. There was a highly significant excess mortality (chiefly from cardiovascular disease) among those with microalbuminuria (28%) compared to those without microalbuminuria (4%, P less than 0.001). In univariate survival analysis, significant predictors of all-cause mortality included microalbuminuria (P less than 0.001), hypercholesterolemia (P less than 0.01), hypertriglyceridemia (P less than 0.05), and preexisting coronary heart disease (P less than 0.05). The predictive power of microalbuminuria persisted after adjustment for the effects of other major risk factors (P less than 0.05). We conclude that microalbuminuria is a significant risk marker for mortality in NIDDM, independent of the other risk factors examined. Its presence can be regarded as an index of increased cardiovascular vulnerability and a signal for vigorous efforts at correction of known risk factors.

The Impact of Diabetes on the CNS

Abstract: The brain is not usually thought to be a target of chronic diabetes complications. Nonetheless, substantial evidence, summarized herein, suggests that diabetes causes brain damage. Clinical syndromes of diabetes-related brain abnormalities are discussed along with possible causes. Various physiological effects of diabetes are reviewed, and questions are raised about gaps in our knowledge. Appropriate directions for future research are suggested.

Role of cytokines in inducing hyperlipidemia.

Abstract: Plasma lipid levels are elevated in people with diabetes, and a direct relationship can be demonstrated between indices of diabetic control and plasma lipid levels. Many observations suggest that diabetes may be associated with enhanced cytokine production, raising the possibility that some of the metabolic abnormalities associated with diabetes may be due to or exacerbated by cytokine overproduction. Tumor necrosis factor induces a rapid increase in serum triglyceride levels caused by an increase in VLDL of normal composition. Although in vitro studies showed that TNF decreases adipose tissue lipoprotein lipase activity, recent studies with intact animals demonstrated that TNF increases serum triglyceride levels by stimulating hepatic lipid secretion, not by affecting clearance. The increase in hepatic VLDL triglyceride secretion induced by TNF is due to both the stimulation of hepatic de novo fatty acid synthesis and an increase in lipolysis. Other cytokines including IL-1, IL-6, and α-interferon increase hepatic de novo fatty acid synthesis. Similarly, cytokines such as IL-1 and α-, β-, and γ-interferon also increase lipolysis. Thus, a variety of cytokines acting at different receptors can affect multiple processes that can alter lipid metabolism and increase serum lipid levels. These cytokine-induced increases in serum lipoprotein levels may be a beneficial response for the host. Studies show that lipoproteins, including VLDL, bind endotoxin and can protect against the toxic effects of endotoxin. Moreover, lipoproteins bind a variety of viruses, reducing their infectivity. Lipoproteins also bind urate crystals, which reduces the inflammatory response induced by these crystals. Thus, it can be postulated that lipoproteins are part of a nonspecific immune response stimulated by cytokines, the hormones of the immune systems, that can decrease the toxicity of harmful biological and chemical agents. Although these changes may have benefit under some circumstances, the overproduction of cytokines in people with diabetes could lead to inappropriate metabolic effects, including hyperlipidemia, that in the long run could have adverse consequences, such as accelerated atherosclerosis.

Mechanistic studies of advanced glycosylation end product inhibition by aminoguanidine.

Abstract: Aminoguanidine-HCl inhibits the formation of advanced glycosylation end products (AGEs) in vitro and in vivo, but the mechanism by which this occurs has not been determined. Aminoguanidine inhibited glucose-derived AGE formation on RNase A by 67–85% at aminoguanidine-glucose molar ratios of 1:5 to 1:50 without affecting the concentration of Amadori products. Fast–atom-bombardment mass spectrometry of RNase peptides incubated with glucose alone or with glucose plus aminoguanidine showed that aminoguanidine inhibited the formation of AGEs without forming an adduct with glycosylated peptide. These data suggest that the primary mechanism of aminoguanidine action is reaction with Amadori-derived fragmentation products in solution. These findings are relevant to the potential clinical use of aminoguanidine in the prevention of diabetic complications.

Lilly Lecture: Molecular Mechanisms of Insulin Resistance: Lessons From Patients With Mutations in the Insulin-Receptor Gene

Abstract: Insulin resistance contributes to the pathogenesis of NIDDM. We have investigated the molecular mechanisms of insulin resistance in patients with genetic syndromes caused by mutations in the insulin-receptor gene. In general, patients with two mutant alleles of the insulin-receptor gene are more severely insulin-resistant than are patients who are heterozygous for a single mutant allele. These mutations can be put into five classes, depending upon the mechanisms by which they impair receptor function. Some mutations lead to a decrease in the number of insulin receptors on the cell surface. For example, some mutations decrease the level of insulin receptor mRNA or impair receptor biosynthesis by introducing a premature chain termination codon (class 1). Class 2 mutations impair the transport of receptors through the endoplasmic reticulum and Golgi apparatus to the plasma membrane. Mutations that accelerate the rate of receptor degradation (class 5) also decrease the number of receptors on the cell surface. Other mutations cause insulin resistance by impairing receptor function--either by decreasing the affinity to bind insulin (class 3) or by impairing receptor tyrosine kinase activity (class 4). The prevalence of mutations in the insulin receptor gene is not known. However, theoretical calculations suggest that approximately 0.1-1% of the general population are heterozygous for a mutation in the insulin-receptor gene; the prevalence is likely to be higher among people with NIDDM. Accordingly, it is likely that mutations in the insulin-receptor gene may be a contributory cause of insulin resistance in a subpopulation with NIDDM.

Maillard reaction-mediated molecular damage to extracellular matrix and other tissue proteins in diabetes, aging, and uremia.

Abstract: Recent progress in structure elucidation of products of the advanced Maillard reaction now allows probing specifically for the role of this reaction in the pathogenesis of age- and diabetes-related complications. Pyrraline is a glucose-derived advanced glycation end product against which polyclonal and monoclonal antibodies have been raised. Immunohistochemical localization studies revealed that pyrraline is found predominantly in the sclerosed extracellular matrix of glomerular and arteriolar renal tissues from both diabetic and aged nondiabetic individuals. Pentosidine and carboxymethyllysine are Maillard end products derived from both glucose and ascorbate. In addition, pentosidine can be formed from several other sugars under oxidative conditions, and in vitro studies suggest that a common intermediate involving a pentose is a necessary precursor molecule. The highest levels of these advanced Maillard products are generally found in the extracellular matrix, but these products are also present in lens proteins and in proteins with a fast turnover such as plasma proteins. Diabetes, and especially uremia, greatly catalyzes pentosidine formation. Both conditions are characterized by accelerated cataractogenesis, atherosclerosis, and neuropathy, suggesting that molecular damage by advanced Maillard reaction products may be a common mechanism in their development.

Does nitric oxide mediate autoimmune destruction of beta-cells? Possible therapeutic interventions in IDDM.

Abstract: Cytokines have been implicated as immunological effector molecules that induce dysfunction and destruction of the pancreatic beta-cell. The mechanisms of cytokine action on the beta-cell are unknown; however, nitric oxide, resulting from cytokine-induced expression of nitric oxide synthase, has been implicated as the cellular effector molecule mediating beta-cell dysfunction. Nitric oxide is a free radical that targets intracellular iron-containing enzymes, which results in the loss of their function. The cytokine IL-1 beta induces the formation of nitric oxide in isolated rat islets and the insulinoma cell line, Rin-m5F. NMMA and NAME, both inhibitors of nitric oxide synthase, completely protect islets from the deleterious effects of IL-1 beta. These inhibitors are competitive in nature and inhibit both the cytokine-inducible and constitutive isoforms of nitric oxide synthase with nearly identical kinetics. This may preclude their use as therapeutic agents because of increases in blood pressure which result from the inhibition of constitutive nitric oxide synthase activity. Aminoguanidine, an inhibitor of nonenzymatic glycosylation of cellular and extracellular constituents associated with diabetic complications, recently has been reported to inhibit nitric oxide synthase. Aminoguanidine is approximately 40-fold more effective in inhibiting the inducible isoform of nitric oxide synthase, suggesting that aminoguanidine or analogues may serve as potential therapeutic agents to block diseases associated with nitric oxide production by the inducible isoform of nitric oxide synthase. In vivo administration of TNF IL-1 has been shown to induce anti-diabetogenic effects in the NOD mouse. This anti-diabetogenic effect of cytokines appears to conflict with evidence suggesting that cytokines mediate beta-cell dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet Abnormalities in Diabetes Mellitus

Abstract: Although platelets can contribute to atherosclerosis and its thromboembolic complications in the nondiabetic population, the role of platelets in enhanced vascular disease in the diabetic population remains unclear. Most studies indicate that platelet function in vitro is enhanced in platelets from people and animals with diabetes, and the mechanisms are being identified. There remains some controversy about whether platelet changes occur before, and therefore could contribute to, vascular complications or whether they are secondary to vascular disease. It is possible that only intervention trials to determine if inhibiting platelet function limits the progression of vascular disease in diabetic patients will definitively answer this question. The earlier premise that enhanced activity of the arachidonate pathway is responsible for the hypersensitivity of platelets from diabetic humans needs to be modified to recognize that additional mechanisms are involved in platelet activation and are modified in people with diabetes and also that altered activity of the arachidonate pathway may reflect changes in earlier pathways involved in platelet activation. Clearly, alterations in these nonarachidonate pathways need to be taken into account when considering the appropriate antiplatelet agents to use in intervention trials. Information about whether hypersensitivity of platelets from people with diabetes persists in vivo and, if so, how this influences platelet-vessel wall interactions and thrombotic tendencies needs to be pursued more intensely in suitable animal models so that the theories developed from studies in vitro can be tested in the more complex environment in vivo. These are important areas for research in the future.

Gene Expression of GLUT4 in Skeletal Muscle From Insulin-Resistant Patients With Obesity, IGT, GDM, and NIDDM

Abstract: In obesity, impaired glucose tolerance (IGT), non-insulin-dependent diabetes mellitus (NIDDM), and gestational diabetes mellitus (GDM), defects in glucose transport system activity, contribute to insulin resistance in target tissues. In adipocytes from obese and NIDDM patients, we found that pretranslational suppression of the insulin-responsive GLUT4 glucose transporter isoform is a major cause of cellular insulin resistance; however, whether this process is operative in skeletal muscle is not clear. To address this issue, we performed percutaneous biopsies of the vastus lateralis in lean and obese control subjects and in obese patients with IGT and NIDDM and open biopsies of the rectus abdominis at cesarian section in lean and obese gravidas and gravidas with GDM. GLUT4 was measured in total postnuclear membrane fractions from both muscles by immunoblot analyses. The maximally insulin-stimulated rate of in vivo glucose disposal, assessed with euglycemic glucose clamps, decreased 26% in obesity and 74% in NIDDM, reflecting diminished glucose uptake by muscle. However, in vastus lateralis, relative amounts of GLUT4 per milligram membrane protein were similar (NS) among lean (1.0 +/- 0.2) and obese (1.5 +/- 0.3) subjects and patients with IGT (1.4 +/- 0.2) and NIDDM (1.2 +/- 0.2). GLUT4 content was also unchanged when levels were normalized per wet weight, per total protein, and per DNA as an index of cell number. Levels of GLUT4 mRNA were similarly not affected by obesity, IGT, or NIDDM whether normalized per RNA or for the amount of an unrelated constitutive mRNA species. Because muscle fibers (types I and II) exhibit different capacities for insulin-mediated glucose uptake, we tested whether a change in fiber composition could cause insulin resistance without altering overall levels of GLUT4. However, we found that quantities of fiber-specific isoenzymes (phopholamban and types I and II Ca(2+)-ATPase) were similar in all subject groups. In rectus abdominis, GLUT4 content was similar in the lean, obese, and GDM gravidas whether normalized per milligram membrane protein (relative levels were 1.0 +/- 0.2, 1.3 +/- 0.1, and 1.0 +/- 0.2, respectively) or per wet weight, total protein, and DNA. We conclude that in human disease states characterized by insulin resistance, i.e., obesity, IGT, NIDDM, and GDM, GLUT4 gene expression is normal in vastus lateralis or rectus abdominis. To the extent that these muscles are representative of total muscle mass, insulin resistance in skeletal muscle may involve impaired GLUT4 function or translocation and not transporter depletion as observed in adipose tissue.

Pentosidine Formation in Skin Correlates With Severity of Complications in Individuals With Long-Standing IDDM

Abstract: Pentosidine is an advanced glycosylation end product and protein cross-link that results from the reaction of pentoses with proteins. Recent data indicate that long-term glycation of proteins with glucose also leads to pentosidine formation through sugar fragmentation. In this study, the relationship between the severity of diabetic complications and pentosidine formation was investigated in collagen from skin-punch biopsies from 25 nondiabetic control subjects and 41 IDDM patients with diabetes duration >17 yr. Pentosidine was significantly elevated in all IDDM patients versus control subjects ( P P P P P P P P > 0.05). A high correlation between pentosidine levels and long-wave collagen-linked fluorescence also was observed, suggesting that pentosidine is a generalized marker of accelerated tissue modification by the advanced glycosylation/Maillard reaction, which is enhanced in IDDM patients with severe complications.

Association of HbA1c with prevalent cardiovascular disease in the original cohort of the Framingham heart study

Abstract: We studied the cross-sectional relationship between HbA1c and cardiovascular disease (CVD) in the survivors of the original cohort of the Framingham Heart Study (n = 1045). HbA1c was significantly related to prevalent CVD among women but not men. HbA1c was also related to hypertension and to the ratio of total to high-density lipoprotein cholesterol levels. In regression analyses that controlled for these and other potential risk factors, HbA1c remained significantly related to CVD among women. The relative odds of CVD increased 1.39-fold (95% confidence interval 1.06-1.83) for increases in HbA1c of 1% (e.g., for HbA1c from 5 to 6%). The relationship was not weakened when known diabetic subjects or subjects taking beta-blocker or thiazide medications were excluded from analysis. In contrast, there was no significant relationship between "casual" blood glucose and prevalent CVD. Our results reveal a strong, significant, independent association between hyperglycemia, measured by HbA1c, and CVD among older women.

The Metabolic Profile of NIDDM Is Fully Established in Glucose-Tolerant Offspring of Two Mexican-American NIDDM Parents

Abstract: NIDDM patients with overt fasting hyperglycemia are characterized by multiple defects involving both insulin secretion and insulin action. At this point of the natural history of NIDDM, however, it is difficult to establish which defects are primary and which are acquired secondary to insulinopenia and chronic hyperglycemia. To address this question, we have studied the glucose-tolerant offspring (probands) of two Mexican-American NIDDM parents. Such individuals are at high risk for developing NIDDM later in life. The probands are characterized by hyperinsulinemia in the fasting state and in response to both oral and intravenous glucose. Insulin-mediated glucose disposal (insulin clamp technique), measured at two physiological levels of hyperinsulinemia (approximately 240 and 450 pM [approximately 40 and 75 microU/ml]), was reduced by 43 and 33%, respectively. During both the low- and high-dose insulin clamp steps, impaired nonoxidative glucose disposal, which primarily represents glycogen synthesis, was the major defect responsible for the insulin resistance. During the lower dose insulin clamp step only, a small decrease in glucose oxidation was observed. No defect in suppression of HGP by insulin was demonstrable. The ability of insulin to inhibit lipid oxidation (measured by indirect calorimetry) and plasma FFA concentration was impaired at both levels of hyperinsulinemia. These results indicate that the glucose-tolerant offspring of two NIDDM parents are characterized by hyperinsulinemia and manifest all of the metabolic abnormalities that characterize the fully established diabetic state, including insulin resistance, a major impairment in nonoxidative glucose disposal, a quantitatively less important defect in glucose oxidation, and a diminished insulin-mediated suppression of lipid oxidation and plasma FFA concentration.

Chromatographic quantitation of plasma and erythrocyte pentosidine in diabetic and uremic subjects.

Abstract: Pentosidine is a fluorescent advanced Maillard/glycosylation product and protein cross-link present in elevated amounts in skin from diabetic and uremic subjects. A high-performance liquid chromatographic (HPLC) assay was developed to quantitate pentosidine in plasma and erythrocytes and other tissue proteins with low levels of pentosidine. High protein content and presence of basic amino acids and O2 during acid hydrolysis led to the formation of fluorescent artifacts that could be separated from true pentosidine through combined reverse-phase ion-exchange HPLC. No true pentosidine was formed during acid hydrolysis of ribated protein, suggesting that Amadori products do not generate artifactual pentosidine during hydrolysis. With the combined reverse-phase ion-exchange chromatographic assay, we found a 2.5-fold (P less than 0.001) and a 23-fold (P less than 0.001) elevation of mean +/- SD plasma protein pentosidine in diabetic (2.4 +/- 1.2 pmol/mg) and uremic (21.5 +/- 10.8 pmol/mg) subjects compared with healthy (0.95 +/- 0.33 pmol/mg) subjects. Pentosidine in hemolysate was normal in diabetes but dramatically elevated in uremia (0.6 +/- 0.4 pmol/mg hemoglobin, P less than 0.001). Although the precise nature of the pentosidine precursor sugar is unknown, plasma pentosidine may be a useful marker for monitoring the biochemical efficacy of trials with aminoguanidine or other treatment modalities. Furthermore, pentosidine in plasma proteins may act as a signal for advanced glycosylation end product-mediated receptor uptake by macrophages and other cells and contribute to accelerated atherosclerosis in diabetes and uremia.

Longitudinal study of plasma lipoproteins and hormones during pregnancy in normal and diabetic women.

Abstract: Plasma lipoproteins were studied longitudinally at the 1st, 2nd, and 3rd trimester of gestation and at postpartum and postlactation in 12 age-matched PGDM women, 9 GDM women, and 12 healthy control subjects. FPG and HbA 1c were higher in every case in PGDM women than in control subjects, whereas in GDM patients, glucose was augmented only after parturition. FFA and β-hydroxybutyrate levels were higher in both PGDM and GDM patients than in control subjects during gestation but not after parturition. Total TGs and VLDL, LDL, and HDL TGs increased with gestational time in the three groups and declined at postpartum, and although total cholesterol and VLDL, LDL, and HDL cholesterol followed a similar trend, their rise was less pronounced, and the decline after parturition was slower than that of the TGs in the three groups, with no difference among them. The VLDL TG/cholesterol ratio declined in the three groups at the 3rd gestational trimester, whereas in both LDL and HDL, the TG/cholesterol ratio, but not the cholesterol/phospholipid ratio, increased during gestation in the three groups, indicating a specific enrichment of TGs in these particles. The increase in apoA-I and apoB with gestation was parallel to the respective changes in HDL and LDL cholesterol and, again, no difference was observed between the three groups. Plasma levels of β-estradiol, progesterone, and prolactin increased sharply with gestation and declined at postpartum in the three groups, but absolute values of β-estradiol and prolactin, at the three trimesters of gestation, were lower in PGDM patients, but progesterone levels were lower than controls in GDM women only at the 3rd trimester. The logarithm for each of these hormones correlated linearly with VLDL, LDL, and HDL TGs, and the highest correlation coefficient value corresponded to the regression between β-estradiol and HDL TGs. Because estrogens are known to increase VLDL production, decrease hepatic lipase activity, and increase HDL TG levels, we propose that the decreased estradiol levels in our diabetic patients impede an exaggerated rise of circulating lipoproteins above the normal range. We also propose that the development or lack of development of a dyslipidemic condition in diabetic pregnancy depends on the balance between the metabolic control and the level of sex hormones.

1,25-Dihydroxyvitamin D3 prevents insulitis in NOD mice.

Abstract: The active form of vitamin D, 1,25(OH)2D3, can prevent various forms of experimentally induced autoimmune disorders. The aim of this study was to confirm these findings in NOD mice that spontaneously develop an autoimmune type of diabetes mellitus. Therefore, the effect of a long-term 1,25(OH)2D3 treatment on the incidence of insulitis, the histological lesion preceding diabetes, was studied. Forty-three NOD mice were treated with 1,25(OH)2D3 (5 micrograms/kg) i.p. every other day from age 21 days on, when no insulitis was present yet. At day 100, 16 control mice receiving the treatment vehicle (arachis oil) had an incidence of insulitis of 75%, whereas only 41% of the 1,25(OH)2D3-treated animals developed insulitis (P < 0.025). Calcemia, determined 24 h after the last 1,25(OH)2D3 injection was 2.5 +/- 0.1 mM, which was higher than in control animals (2.3 +/- 0.1 mM), but was well tolerated. Cellular immunity, as assessed with the mixed lymphocyte reaction performed at day 100, was not impaired significantly. This study demonstrates that long-term treatment with high doses of 1,25(OH)2D3 is able to decrease the incidence of insulitis in spontaneous autoimmune diabetes without major side effects.

Iatrogenic hypoglycemia as a cause of hypoglycemia-associated autonomic failure in IDDM. A vicious cycle.

Abstract: Three hypoglycemia-associated clinical syndromes in people with insulin-dependent diabetes mellitus (IDDM)--defective glucose counterregulation, hypoglycemia unawareness, and elevated glycemic thresholds for symptoms and activation of counterregulatory systems during effective intensive therapy--have much in common. They segregate together, are associated with increased frequency of severe iatrogenic hypoglycemia, and share several pathophysiological features, including reduced autonomic nervous system responses to a given degree of hypoglycemia. In the setting of reduced glucagon responses, the reduced adrenomedullary epinephrine responses play a key role in the pathogenesis of iatrogenic hypoglycemia in affected patients. Thus, these syndromes are examples of hypoglycemia-associated autonomic failure in IDDM, a disorder distinct from classical diabetic autonomic neuropathy. The pathogenesis of hypoglycemia-associated autonomic failure is not known, need not be the same in all three syndromes, and could be multifactorial even in a given syndrome. The recent finding that short-term antecedent hypoglycemia results in reduced symptomatic and autonomic (including adrenomedullary) responses to subsequent hypoglycemia in nondiabetic humans leads logically to the following hypothesis concerning one potential pathogenetic mechanism: recent antecedent iatrogenic hypoglycemia is a major cause of hypoglycemia-associated autonomic failure in IDDM, and hypoglycemia-associated autonomic failure, by reducing both symptoms of and defenses against developing hypoglycemia, results in recurrent severe hypoglycemia, thus creating a vicious cycle. If this hypothesis is confirmed, it will suggest strategies to reduce the frequency of iatrogenic hypoglycemia in people with IDDM.

Comparison of Effects of High and Low Carbohydrate Diets on Plasma Lipoproteins and Insulin Sensitivity in Patients With Mild NIDDM

Abstract: Previous studies indicate that diets rich in digestible carbohydrates improve glucose tolerance in nondiabetic individuals, but may worsen glycemic control in NIDDM patients with moderately severe hyperglycemia. The effects of such high-carbohydrate diets on glucose metabolism in patients with mild NIDDM have not been studied adequately. This study compares responses to an isocaloric high-carbohydrate diet (60% of total energy from carbohydrates) and a low-carbohydrate diet (35% of total energy from carbohydrates) in 8 men with mild NIDDM. Both diets were low in saturated fatty acids, whereas the low-carbohydrate diet was rich in monounsaturated fatty acids. The two diets were matched for dietary fiber content (25 g/day). All patients were randomly assigned to receive first one and then the other diet, each for a period of 21 days, in a metabolic ward. Compared with the low-carbohydrate diet, the high-carbohydrate diet caused a 27.5% increase in plasma triglycerides and a similar increase in VLDL-cholesterol levels; it also reduced levels of HDL cholesterol by 11%. Plasma glucose and insulin responses to identical standard breakfast meals were studied on days 4 and 21 of each period, and these did not differ significantly between the two diets. At the end of each period, a euglycemic hyperinsulinemic glucose clamp study with simultaneous infusion of [3- 3 H]glucose revealed no significant changes in hepatic insulin sensitivity; and peripheral insulin-mediated glucose disposal remained unchanged (14.7 ± 1.4 vs. 16.5 ± 2.3 μM · kg −1 · min −1 on the high-carbohydrate and low-carbohydrate diets, respectively). We conclude that in patients with mild NIDDM, high-carbohydrate diets do not improve glycemic control nor insulin sensitivity, and they raise plasma triglyceride and VLDL-cholesterol concentrations and reduce HDL-cholesterol levels, which may not be desirable.

Cell and Matrix Components of the Glomerular Mesangium in Type I Diabetes

Abstract: In a cross-sectional study, glomerular basement membrane (GBM) width, the volume fractions of the mesangium (VvMes), its cell (VvCell) and matrix (VvMatx) components, and surface density of the peripheral capillary surface (SvPGBM) were measured in renal biopsies from 187 nondiabetic living related and cadaveric donors of kidneys for transplantation and from 150 patients with insulin-dependent (type I) diabetes mellitus of 1–41 yr duration. In the diabetic patients, the matrix was the major factor in the expansion of the mesangium. However, both VvCell (0.11 ± 0.04) and VvMatx (0.20 ± 10) in diabetic patients exceeded the same measurements in nondiabetic subjects (0.07 ± 0.02 for each component) ( P < 0.001 in each case). Linear regression analysis demonstrated significant correlations ( P < 0.001 for all) between GBM width, VvMes, VvCell, VvMatx, or SvPGBM and either urinary albumin excretion and creatinine clearance, with the higher correlation coefficients in all cases with albuminuria. Of the structural parameters, VvMatx correlated best with either functional measure by stepwise regression, with GBM as an added factor only with albuminuria. Therefore, although models of diabetic glomerulopathy must consider enlargement of both mesangial cells and matrix, the predominant factor in the progression of structural and functional renal disease is mesangial matrix expansion.

Effect of vitamin C on glycosylation of proteins.

Abstract: Twelve nondiabetic subjects consumed 1 g/day vitamin C for 3 mo. A fasting blood sample was taken at the start of the study and at the end of each month for the measurement of plasma and intraerythrocyte glucose, vitamin C, glycosylated hemoglobin (affinity chromatography and electrophoresis), and glycosylated albumin (affinity chromatography). Although there were no significant changes in fasting glycemia, glycosylated hemoglobin (affinity chromatography) decreased 18%, from 6.18 +/- 0.48% (mean +/- SD) at the start to 5.05 +/- 0.50% (P less than 0.0001) after 3 mo, whereas, HbA1 measured by electrophoresis increased 16%, from 6.17 +/- 0.61 to 7.16 +/- 0.59% (P less than 0.0001) in this period. Glycosylated albumin decreased 33%, from 1.56 +/- 0.24 to 1.04 +/- 1.01% (P less than 0.0001) after 3 mo. This discrepancy between glycosylated hemoglobin measured by electrophoresis and affinity chromatography was due to methodological differences between the two techniques, with affinity chromatography measuring "true" glycosylated hemoglobin. The greater decrease found with glycosylated albumin was probably due to the different distribution of vitamin C between plasma and within the erythrocyte, levels after 1 mo of supplementation being 109 +/- 19 and 59 +/- 9 microM, respectively (P less than 0.001). This indicates that administration of oral vitamin C may inhibit the glycosylation of proteins in vivo by a competitive mechanism.

Power Spectral Analysis of Heart-Rate Variations Improves Assessment of Diabetic Cardiac Autonomic Neuropathy

Abstract: Power spectral analysis (PSA) of heart-rate variations has recently proved a useful tool in evaluating cardiovascular autonomic activity. It offers the possibility of examining both the functioning of parasympathetic and sympathetic pathways through breakdown into two frequency bands, and of their effects on heart-rate cyclic variability. We applied an autoregressive model for PSA to study overall autonomic tone in 20 male age-matched control subjects and 53 insulin-dependent (type I) diabetic subjects, subdivided into three groups of 20, 15, and 18, each group presenting different degrees of autonomic involvement. We found that 1 ) power spectrum density (PSD) values at high-frequency bands (parasympathetic dependent) were similar in diabetic subjects without cardiac autonomic neuropathy (CAN) and in control subjects, but differed significantly from diabetic subjects with mild CAN and severe CAN, both standing and lying; 2 ) PSD values at low frequency (mainly sympathetic dependent) were similar, or slightly different, in diabetic subjects without CAN and in control subjects, but differed significantly from diabetic subjects with mild and severe CAN, both standing and lying; 3 ) as an expression of parasympathetic versus sympathetic coherence, correlations, both standing and lying, existed between PSD values at low- and high-frequency bands in control and diabetic subjects without CAN, but not in diabetic subjects with CAN; and 4 ) different degrees of correlation characterized the PSD values of high and low frequencies versus traditional cardiovascular test values in the diabetic subjects. The best correlation was between PSD low-frequency values and the lying-to-standing maneuver. frequency values and the lying-to-standing maneuver. These data indicate that PSA 1 ) can discriminate between differing degrees of parasympathetic involvement, 2 ) can discriminate between different degrees of sympathetic involvement, and 3 ) offers a picture of overall autonomic activity that can be explored only partially by traditional cardiovascular autonomic tests and 4 ) can reveal parasympathetic versus sympathetic dyssynergia. These data suggest that cardiovascular autonomic tests may reflect different aspects of autonomic pathways. Hence, PSA appears to be a powerful tool in the determination of autonomic tone in diabetic CAN.

Genetic and environmental determinants of type II diabetes in Mexico City and San Antonio.

Abstract: To study genetic and environmental determinants of non-insulin-dependent (type II) diabetes, we compared a random sample of 35- to 64-yr-old Mexican-American men and women living in several low-income barrio neighborhoods of San Antonio to similarly aged Mexicans living in a low-income colonia of Mexico City (Colonia Liberales). A total of 1138 Mexican Americans, representing 64.3% of the original sample, and 646 Mexicans, representing 69.2% of the original sample, participated in the survey. Diabetes was diagnosed using World Health Organization criteria. Genetic susceptibility to type II diabetes was inferred from the percentage of Native American genetic admixture as estimated from skin reflectance measurements. The prevalence of diabetes was 36% higher among San Antonio Mexican Americans than among Mexicans in Mexico City; this difference was highly statistically significant (age- and sex-adjusted prevalence ratio 1.36, P = 0.006). This excess was observed despite the fact that genetic susceptibility, as inferred from the admixture estimates, was similar in the two cities. On the other hand, Mexicans were somewhat leaner as measured by body mass index and skin folds. Mexican women consumed fewer total calories than Mexican-American women, but there was no difference in the caloric intake of men. Mexico City residents ate less fat (18–19% of total calories vs. 31–32% in San Antonio, P < 0.001), more carbohydrate (64–65 vs. 49%, P < 0.001), and performed more physical activity than San Antonio Mexican Americans. Mexicans appeared to consume more refined sugar than Mexican Americans. Mexicans had lower total cholesterol but higher triglyceride and fasting insulin concentrations than Mexican Americans (all P < 0.002). The latter two observations are compatible with the hypothesis that the high-carbohydrate diet in Mexico City stimulated carbohydrate-induced hypertriglyceridemia, which was not offset by the greater degree of physical activity and leanness of Mexicans compared with Mexican Americans. The results of this study suggest that environmental factors can override genetic susceptibility in the expression of the type II diabetes trait.

Dual functional role of membrane depolarization/Ca2+ influx in rat pancreatic B-cell.

Abstract: Transient exposure of rat pancreatic B-cell to 50 mM K+ ([K+50]) makes exocytosis unresponsive to further depolarization, i.e., stimulation with 100 mM K+ or 1 uM glyburide, which closes the ATP-sensitive K+ (K+ATP) channel, simultaneously with [K+50] does not produce any greater insulin secretion compared with [K+50] alone. In sharp contrast, 16.7 mM glucose ([G16.7]) applied simultaneously with [K+50] elicits an insulin response markedly greater than that produced by [K+50] alone, which is not attenuated by 100 uM diazoxide, an inhibitor of K+ATP channel closure. [G16.7]-induced insulin secretion at the basal K+ concn of 4.7 mM was greatly (93%) suppressed by 100 uM diazoxide. Insulin secretion induced by [K+50] plus [G16.7] ([K+50 + G16.7]) was markedly suppressed (70%) by 1 uM nifedipine, a Ca(2+)-channel blocker and was completely abolished by 2 mM 2-cyclohexen-1-one, which reportedly decreases reduced glutathione level and blocks glucokinase. This finding indicates that insulin release induced by [K+50 + G16.7] is not due to leakage produced by toxic stimuli but to activation of exocytosis. When graded concentrations (25 and 50 mM) of K+ were applied simultaneously with [G16.7] in the presence of 100 uM diazoxide, insulin response was clearly dependent on K+ concentration, indicating that the physiological range of membrane depolarization also activates the glucose-responsive effector. Membrane depolarization/Ca2+ influx directly stimulates hormone exocytosis on one hand and activates the K+ATP channel-independent glucose-responsive effector or effectors on the other in the B-cell. The nature of the glucose-responsive effector or effectors remains to be established.

Electrophysiology of stimulus-secretion coupling in human β-cells

Abstract: Herein, we review the applicability to human β-cells of an electrophysiologically based hypothesis of the coupling of glucose metabolism to insulin secretion. According to this hypothesis, glucose metabolism leads to the generation of intracellular intermediates (including ATP), which leads to closure of ATP-sensitive K+ channels. Channel closure results in membrane depolarization, the onset of electrical activity, and voltage-dependent Ca2+ entry. The resultant rise in cytosolic Ca2+ leads to Ca2+-dependent exocytosis of insulin granules. We found that most of the published experimental evidence for human β-cells supports this hypothesis. In addition, we present three other emerging lines of evidence in support of this hypothesis for human islet β-cells: 1 ) the effects of pH1-altering maneuvers on insulin secretion and electrical activity; 2 ) preliminary identification of LVA and HVA single Ca2+ channel currents; and 3 ) validation of the feasibility of C m measurements to track insulin granule exocytosis. On the basis of this last new line of evidence, we suggest that combinations of C m measurements and electrical activity/membrane current measurements may help define the roles of diverse electrical activity patterns, displayed by human β-cells, in stimulus-induced insulin secretion.