bluuebunny/crossref_metadata_2025 huggingface dataset:
Insulinlike Growth Factor Action and Production in Adipocytes and Endothelial Cells From Human Adipose Tissue
Authors: Kern Philip A , Svoboda Marjorie E , Eckel Robert H , Van Wyk Judson J
Published: September 2013

Primary cultures of microvascular endothelial cells and isolated adipocytes were prepared from human omental adipose tissue to study the potentially overlapping roles of insulin and insulinlike growth factors (IGFs) in human adipose tissue. To determine whether adipocytes contain type I IGF receptors, binding experiments were carried out with 125I-labeled IGF-I. At 16°C, saturation of specific binding to adipocytes was reached after 30 min and was 0.7% per 106 cells. At 37°C, chloroquine produced an increase in cell-associated 125I-IGF-I, suggesting that IGF-I is internalized and degraded in a manner analogous to insulin. In competition experiments, IGF-I competed for binding more effectively than rat IGF-II or insulin. The concentrations of IGF-I, rat IGF-II, and insulin necessary to displace 50% of 125I-IGF-I binding were 2.5,15, and 90 nM, respectively. In addition, a monoclonal antibody (α-IR3) that has been shown to block the type I IGF receptor was used in competition binding experiments. The antibody also inhibited binding of 125I-IGF-I to adipocytes. The biological effects of insulin and IGF-I were examined by studying adipocyte lipoprotein lipase (LPL). Insulin stimulated [14C]glucose incorporation into cellular lipid in a dose-dependent manner, with 50% effective concentration (EC50) of ∼.3 nM. However, an increase in LPL activity was observed only at a high insulin concentration, with an ECS0 of ∼30 nM. In contrast, IGF-I stimulated a progressive increase in LPL, with an EC50 of 3.2 nM. In addition, α-IR3 blocked the stimulatory effect of IGF-I on adipocyte LPL. To study the possible local production of IGFs in adipose tissue, adipose-derived human microvascular endothelial cells were cultured. The conditioned medium from these cells contained significant quantities of immunoreactive IGF. After passing the conditioned medium through a Deltapak C4100-Å column and eluting with an acetonitrile gradient, IGF was separated from binding protein, and most of the immunoreactive IGF in endothelial cell-conditioned medium consisted of IGF binding protein, with smaller contributions from IGF-II and IGF-I. Thus, in human adipose tissue, IGFs and IGF binding protein are produced by microvascular endothelial cells. In addition, type I IGF receptors are present on adipocytes, and LPL is stimulated through type I receptors.
Insulin-Sensitive and Insulin-Resistant Variants in NIDDM
Authors: Banerji Mary Ann , Lebovitz Harold E
Published: September 2013

To define the sequence of events that is involved in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM), we studied 16 NIDDM individuals (15 of 16 Black patients) with a mean age of 44 yr who had been near normoglycemic for 2–91 mo while off of antidiabetic medicine. With the euglycemic insulin clamp at 100 (μU/ml insulin, we defined two populations, one with normal peripheral insulin sensitivity (glucose disposal 7.51 ± 0.97 mg · kg−1 · min−1) and the other with insulin resistance (glucose disposal 3.35 ± 0.58 mg · kg−1 · min−1; P <.001). The populations did not differ in age, degree of obesity, fasting plasma glucose, glycosylated hemoglobin, clinical presentation, or clinical course. Basal plasma insulin levels were normal in the sensitive group and significantly elevated in the resistant group. Islet cell cytoplasmic antibodies were absent in all patients. Insulin action on the liver was normal in both groups. Basal hepatic glucose production measured with D-[3−3H]glucose was lower in the insulin-resistant group (1.53 ± 0.11 mg · kg−1 · min−1) than in the insulin-sensitive group (1.88 ± 0.06 mg · kg1 · min−1) or normal control subjects (1.93 ± 0.05 mg · kg−1 · min1). The decreased basal hepatic glucose production appeared to be secondary to the twofold higher fasting plasma insulin level seen in the insulin-resistant group. The insulin concentration necessary to suppress basal hepatic glucose production by 50% was 29.6 μU/ml in the insulin-sensitive group and 30.5 μU/ml in the insulin-resistant group. The absolute insulin-secretory responses to oral glucose and intravenous glucagon were significantly lower (50%) in the insulin-sensitive group than in the insulin-resistant group, whose absolute responses were similar to normal control subjects. Compared with individuals with impaired glucose tolerance, the insulin response to oral glucose in the insulin-resistant group was somewhat reduced. We hypothesize that NIDDM in this particular population consists of two subpopulations, one with primary insulin deficiency and normal insulin action and the other with primary peripheral insulin resistance and a mild impairment in glucose-mediated insulin secretion. In both, insulin action in the liver was initially normal.
MHC Molecules and β-Cell Destruction: Immune and Nonimmune Mechanisms
Authors: Harrison Leonard C , Campbell Iain L , Allison J , Miller J F A P
Published: September 2013

Hyperexpression of major histocompatibility complex (MHC) molecules by islet cells is a prominent, early feature of islet pathology in insulin-dependent diabetes mellitus and concomitant with β-cell failure after exposure of islets to specific cytokines or viruses. The transgenic expression of a class I MHC gene (H-2Kb) in the β-cells of either syngeneic or allogeneic mice leads to β-cell failure by a nonimmune mechanism. Several class II MHC transgenes, with one exception, have the same effect, but the expression of other transgenes that have products that are membrane proteins is not necessarily detrimental. Class I MHC molecules have been shown to interact directly with other membrane proteins. The inappropriate expression of MHC molecules could therefore interfere with key cellular functions. We postulate that the hyperexpression of MHC molecules in the β-cell, e.g., in response to viruses, is a primary, nonimmune mechanism of β-cell failure that precedes a secondary autoimmune response.
Membrane Lipid Alterations and Na+-Pumping Activity in Erythrocytes From IDDM and NIDDM Subjects
Authors: Baldini Patrizia , Incerpi Sandra , Lambert-Gardini Stefano , Spinedi Angelo , Luly Paolo
Published: September 2013

The Na+-pumping activity of the erythrocyte plasma membrane in diabetic subjects was studied together with the lipid composition. Insulin-dependent diabetes mellitus (IDDM) patients (n = 25) were divided into young (28.1 ± 7.4 yr old, mean ± SD; n = 16) and old (71.7 ± 9.8 yr old; n = 10) subjects; the age of non-insulin-dependent (NIDDM) patients was 70.7 ± 11.5 yr (n = 10). The Na+-pumping activity, estimated from both Na+-K+-ATPase and ouabain binding, was significantly decreased in IDDM and NIDDM subjects, but its insulin sensitivity was retained only in young IDDM subjects. The total cholesterol and phospholipid content of the erythrocyte plasma membrane was lowered in IDDM subjects, and cholesterol-to-phospholipid molar ratio was significantly decreased. In NIDDM subjects the significant decrease of the two lipid components did not alter their ratio. The analysis of major phospholipid components of erythrocyte membranes revealed that only phosphatidylcholine is significantly increased in young diabetic subjects. The fatty acid composition of major phospholipid classes was significantly altered in all cases: the unsaturation index appeared to be increased in phosphatidylserine and sphingomyelin for both IDDM and NIDDM subjects and was also increased in phosphatidylcholine in the latter group.
Effects of Acute Metabolic Acidosis and Alkalosis on Leucine Metabolism in Conscious Dogs
Authors: Rodriguez Nancy R , Miles John M , Schwenk W Frederick , Haymond Morey W
Published: September 2013

To determine the effects of acute metabolic acidosis and alkalosis on leucine metabolism in vivo, mongrel dogs were infused with [1-14C] leucine for 8 h, along with NaCI, HCI, or NaHCO3 over the last 4 h. Arterial pH did not change from the basal value during NaCI infusion but decreased (P <.01) and increased (P <.01) during HCI and NaHCO3 infusions, respectively. Total leucine carbon entry did not change from the basal value during saline infusion but increased (P <.01) with acidosis and decreased (P <.05) with alkalosis. Compared with saline controls, acidosis increased (P <.01) leucine oxidation, whereas alkalosis decreased (P <.01) leucine oxidation. During acidosis, total plasma essential and nonessential amino acid concentrations increased (P <.05), whereas during alkalosis, total plasma essential and nonessential amino acid concentrations decreased (P <.05). These studies suggest that acute alterations in arterial pH may affect the regulation of protein metabolism in vivo and must be considered in the interpretation of results from experiments in which alterations of acid-base homeostasis may have occurred.
Differences in Humoral Insulin-Antibody Response Among Inbred Lou/M Rats and Epitope Presentation Differences in ELISA and Radioimmune Titration
Authors: Arquilla Edward R , Edwards Sandy , McDougall Brenda R , Mosqueda Lourdes , Stenger David P
Published: September 2013

Insulin antibodies were not detected in an insulin-capture enzyme-linked immunosorbent assay (ELISA), but they were easily detected in an insulin-copolymer-capture ELISA. Thus, there is a high degree of steric hindrance because of the proximity of the epitopes on the insulin monomer. This is circumvented by substituting an insulin copolymer for insulin in the capture ELISA. A regression analysis comparing the titers of 28 Lou/M rat insulin antiserums measured by liquid-phase radioimmune titration (RIT) with titers obtained in the direct insulin ELISA was not significant (P >.05). Thus, epitopes on insulin available and/or masked for antibody binding in the RIT differ from those available and/or masked in the direct insulin ELISA. As more of the epitopes become available when an insulin copolymer is substituted for monomeric insulin in the ELISAs, a significant positive correlation (P <.05) with the RIT was observed with these 28 insulin antiserums. Twenty-five percent (7 of 28) of these antiserums contained more antibodies that bound to epitopes available in the ELISAs that were masked in the RIT. Conversely, two antiserums contained more antibodies that bound to epitopes that were available in the RIT but were masked in the ELISAs. Thus, the amount of insulin antibodies measured in a given antiserum can vary substantially, depending on which epitopes are made available or are masked in the particular antibody-titration method used. These results demonstrate that the humoral immune response to insulin among inbred Lou/M rats can vary in insulin-antibody levels as well as the epitopes on insulin to which the antibodies bind.
Glucagonostatic and Insulinotropic Action of Glucagonlike Peptide I-(7–36)-Amide
Authors: Komatsu Ryoya , Matsuyama Tatsuo , Namba Mitsuyoshi , Watanabe Nobuaki , Itoh Hidehiko , Kono Norio , Tarui Seiichiro
Published: September 2013

We examined the effect of glucagonlike peptides (GLPs), which are cleaved from preproglucagon in the enteroglucagon cells, on rat endocrine pancreas with the isolated perfused system. GLP-I-(7–36)-amide, a truncated form of full-sequence GLP-I-(1–37), showed a potent inhibitory effect on glucagon secretion. This inhibitory effect of GLP-I-(7–36)-amide was demonstrated at concentrations of 0.25, 2.5, and 25 nM in 11.2 and 2.8 mM glucose. In contrast, insulin release was significantly stimulated by GLP-I-(7–36)-amide at its concentration from 0.025 to 25 nM in a high glucose concentration, whereas in a low glucose concentration, the stimulation was seen only at the highest concentration (25 nM). Neither GLP-I-(1–37) nor GLP-II showed any effect on glucagon and insulin release. Although several gastrointestinal hormones have been nominated as incretins, none of them may suppress the glucagon secretion. A truncated form of GLP-I, GLP-I-(7–36)-amide thus seems to be a unique incretin that exerts glucagonostatic action.
Decreased Insulin- and Glucagon-Pulse Amplitude Accompanying β-Cell Deficiency Induced by Streptozocin in Baboons
Authors: Goodner Charles J , Koerker Donna J , Weigle David S , McCulloch David K
Published: September 2013

The effect of β-cell deficiency on the spontaneous pulsatile secretory pattern of the islets of Langerhans was studied in the baboon. Measures of β-cell function were correlated with the secretory pattern before and at intervals after streptozocin administration. The degree of insulin deficiency was variable and ranged from mild to moderate. Highly regular pulses were less prevalent in baboons compared with rhesus monkeys and humans, but the mean frequency was similar and was not affected by treatment. The principal effect of β-cell destruction was to proportionately reduce the pulse amplitude of insulin (−39%, P < .003) without detectable change in pulse frequency, interhormonal phase relationship, or the regularity of pulses. Glucagon-pulse amplitude also fell (−19%, P < .09), but not significantly. However, glucagon-pulse amplitude was strongly correlated with insulin-pulse amplitude (r = −.59, P < .002), whereas mean fasting plasma concentrations of insulin and glucagon were not significantly changed after treatment. Because streptozocin affects only the β-cell, the data indicate a major influence of the insulin pulse on the α-cell secretory pulse. The data do not support the presence of a separate pacemaker for the α-cell but do not eliminate this possibility. The strong correlation of reduction in insulin-pulse amplitude with increasing fasting glucose and decreasing glucose disappearance lends support to growing evidence that the pattern of insulin secretion is an important determinant of normal glucose homeostasis.
Localization of βII Subspecies of Protein Kinase C in β-Cells
Authors: Ito Atsuko , Saito Naoaki , Taniguchi Hiroshi , Chiba Tsutomu , Kikkawa Ushio , Saitoh Yoichi , Tanaka Chikako
Published: September 2013

Protein kinase C (PKC) has been generally accepted to play a key role in stimulus-response coupling in various secretory cells, including pancreatic islets and pancreatic acini. The enzyme exists as a large family of multiple subspecies with highly related structures (α-, βI-, β:II-, γ-, δ-, ε-, and ζ-PKC). With an immunocytochemical procedure with subspecies-specific antibodies, βII-PKC-like immunoreactivity was identified to localize in the β-cells of the rat pancreatic islets. Neither βI- nor γ-PKC-like immunoreactivity was found in both islets and acini. Biochemical analysis confirmed that the rat whole pancreatic tissues contain a significant amount of α-PKC and a minute amount of βII-PKC but neither βI- nor γ-PKC. On the other hand, βII-PKC—like immunoreactivity was not detected in rat insulinoma cells, in which insulin secretion was induced in response to 12-O-tetradecanoylphorbol-13-acetate and carbachol but not in response to glucose. These findings suggest that βII-PKC is the major, if not the sole, subspecies of PKC in β-cells of rat pancreatic islets and a possible candidate for involvement in glucose-induced insulin secretion.
Increased Renal Aldose Reductase Activity, Immunoreactivity, and mRNA in Streptozocin-Induced Diabetic Rats
Authors: Ghahary Aziz , Luo Jiangming , Gong Yuewen , Chakrabarti Subrata , Simaand Anders A F , Murphy Liam J
Published: September 2013

Increased accumulation of renal sorbitol has been documented in the diabetic rat, and it has been suggested that this accumulation may be important in the pathogenesis of diabetic nephropathy. It is not clear whether sorbitol accumulation results from increases in substrate, activity of the aldose reductase (AR) protein molecule, or activity due to an increase in the amount of enzyme present. In this study, we have quantitated renal AR activity, immunoreactivity, and mRNA in rats 3 mo after induction of diabetes with streptozocin (STZ-D, 65 mg/kg body wt). Renal AR activity was significantly increased in diabetic rats compared with age-matched nondiabetic controls (0.95 ± 0.05 vs. 0.51 ± 0.03 U · mg−1 · h−1, respectively, P < .0005). Western blot analysis demonstrated that the antiserums recognized a single 40,000-Mr, protein species in renal homogenates from both diabetic and nondiabetic rats. When quantitated in an immunodot assay, AR immunoreactivity was significantly increased in diabetic rats compared with nondiabetic controls (0.57 ± 0.03 vs. 0.33 ± 0.02 U, respectively, P < .0005). Hybridization of Northern blots with a synthetic 36-nucleotide oligomer and an AR cDNA identified a 1.4-kilobase pair transcript; the abundance of the transcript was significantly increased in poly(A)+RNA from the kidneys of diabetic compared with nondiabetic rats (P < .005). This study demonstrates that renal AR activity is increased in the STZ-D rats and suggests that the increased AR activity can be in part explained by enhanced AR gene expression.
Disease Associations: Chance, Artifact, or Susceptibility Genes?
Authors: Cox Nancy J , Bell Graeme I
Published: September 2013

Numerous genes that might contribute to the development of diabetes mellitus and/or its complications have been isolated and characterized. One approach to determining whether these “candidate” genes influence susceptibility to diabetes is to compare the frequency of a DNA marker(s) (restriction-fragment–length polymorphism) for each gene in appropriately matched groups of patients and control subjects. The identification of a DNA-marker association would suggest that genetic variation at this gene may increase or reduce the risk of developing diabetes. However, the absence of an association does not necessarily imply that this gene does not contribute to the development of diabetes. We discuss the genetic rationale of disease association studies and the importance of sample size and disease-marker allele frequencies in these studies.
Mesangial Expansion as a Central Mechanism for Loss of Kidney Function in Diabetic Patients
Authors: Steffes Michael W , Østerby Ruth , Chavers Blanche , Mauer S Michael
Published: September 2013

Diabetic nephropathy leading to kidney failure is a major complication of both type I (insulin-dependent) and type II (non-insulin-dependent) diabetes mellitus, and glomerular structural lesions (especially expansion of the mesangium) may constitute the principal cause of decline in kidney function experienced by a significant fraction of diabetic patients. Although the biochemical bases of these mesangial abnormalities remain unknown, an understanding of the natural history of diabetic nephropathy from a combined structural and functional approach can lead to greater pathophysiological insight. Work in animals has supported the concept that the metabolic disturbances of diabetes mellitus cause diabetic nephropathy, with structural and functional lesions prevented or reversed with improved or normalized glycemie control. Additional research must address this fundamental issue in humans, especially the response of advancing mesangial lesions to improved glycemie control. Factors not directly related to the metabolic perturbations of diabetes may serve to accelerate or diminish the pathophysiological processes of diabetic nephropathy. The elucidation and management of these factors, when coupled with improved glycemie control, may moderate the development or progression of diabetic kidney lesions in humans.
Skeletal Muscle Proteolysis in Rats With Acute Streptozocin-Induced Diabetes
Authors: Smith Ora L K , Wong Clara Y , Gelfand Robert A
Published: September 2013

Skeletal muscle proteolysis was studied in rats 1 day after induction of diabetes with 65 mg/kg streptozocin. An evisceration procedure, including functional hepatectomy-nephrectomy, was performed, and the rate of proteolysis in the remaining tissues, primarily skeletal muscles, was evaluated over 2 h. With cycloheximide to block protein synthesis, total protein breakdown was measured from the rate of rise in plasma tyrosine concentration. The rate of degradation of contractile (myofibrillar) protein was estimated from the rate of rise in plasma concentration of 3-methylhistidine released from the breakdown of actomyosin. Compared with nondiabetic control preparations, the total protein degradation rate was increased 30% by diabetes (P < .001), and myofibrillar catabolism was accelerated by 60% (P < .005). In diabetes, the increase in proteolysis was accompanied by reductions in circulating insulin to 25–50% of normal level, whereas food intake did not differ from control. Treatment of diabetic rats with exogenous insulin, including acute infusions postoperatively, completely reversed the proteolytic effects of diabetes. The findings demonstrate that the hypoinsulinemia of acute diabetes increases the catabolism of skeletal muscle protein and that the inhibitory effect of normal levels of insulin includes a specific action to restrain myofibrillar proteolysis.
Effects of Phosphatidic Acid on Islet Cell Phosphoinositide Hydrolysis, Ca2+, and Adenylate Cyclase
Authors: Dunlop Marjorie E , Larkins Richard G
Published: September 2013

Phosphatidic acid may be raised in glucose-stimulated islet cells through hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) and de novo synthesis with glucose-derived trioses. The mechanism by which exogenous phosphatidic acid from egg yolk lecithin may augment insulin secretion was investigated in neonatal β-cells. In whole cells labeled with [2,8-3H]-adenine, a dose-dependent increase in phosphatidic acid-stimulated adenylate cyclase activity was seen, and a small intracellular transient free-Ca2+ rise was seen in Fura 2AM-loaded cells. In [γ-32P]ATP-labeled membranes from those β-cells, phosphatidic acid effected PIP2 hydrolysis. These phosphatidic acid-stimulated effects were not sensitive to preincubation with Bordetella pertussis exotoxin. The findings are consistent with a stimulatory effect of exogenous phosphatidic acid on insulin release and indicate an effect at the plasma membrane. It is possible that newly synthesized phosphatidic acid may function similarly to amplify intracellular events in glucose-stimulated islet cells through both local Ca2+ concentration and cyclic AMP-sensitive mechanisms. The participation of newly synthesized phosphatidic acid derived from glucose could provide a link between the metabolism of glucose and insulin release.
Differences in Lipoprotein Subfraction Composition and Distribution Between Type I Diabetic Men and Control Subjects
Authors: James Richard W , Pometta Daniel
Published: September 2013

Subfractions of very-low-density and low-density lipoproteins were examined in 10 male normolipidemic type I (insulin-dependent) diabetic patients before and after improvement of metabolic control and were compared with subfractions from male control subjects matched to the diabetic patients at entry for age, body mass index, plasma cholesterol, and plasma triglycerides. Two consistent differences in subfraction composition were noted between the diabetic patients at entry and the control subjects. First, subfractions from diabetic patients tended to be cholesterol-ester poor and triglyceride rich; this was particularly marked for the low-density lipoprotein subfractions. Second, the subfractions from pretreatment diabetic patients contained higher proportions of non-apolipoprotein B apolipoproteins. This compositional anomaly, but not the lipid modifications, responded to but was not completely normalized by improved glycemic control, which was also accompanied by reductions in the plasma concentrations of all subfractions. Treatment modified subfraction distribution so that the lipoprotein profile of posttreatment diabetic patients more closely resembled the profile observed in the control subjects. These changes were achieved without significant modification of daily insulin dose. In the context of blood lipid risk factors, the results argue for the need to maintain optimal insulinization even in apparently normolipidemic diabetic patients to avoid modifications of the lipoprotein pattern toward a potentially more atherogenic profile.
Participation of Glucokinase Inactivation in Inhibition of Glucose-Induced Insulin Secretion by 2-Cyclohexen-1-One
Authors: Miwa Ichitomo , Murata Tomiyasu , Mitsuyama Sachie , Okuda Jun
Published: September 2013

We assessed our speculation that 2-cyclohexen-1-one (CHX) impairs glucose-induced insulin secretion through inactivation of glucokinase. Treatment of pancreatic islets with CHX at concentrations (0–5 mM) that caused a dose-dependent inactivation of glucokinase activity similarly inhibited glucoseinduced insulin secretion. Another glucosephosphorylating enzyme (hexokinase) in pancreatic islets was little affected by CHX. CHX-induced inactivation of glucokinase was blocked by the presence of its substrates (glucose and mannose) and an inhibitor (N-acetylglucosamine), all of which also protected against the inhibitory effect of the drug on glucose-induced insulin secretion. CHX also impaired insulin secretion induced by D-glyceraldehyde and dimethyl succinate, which are believed to stimulate the release of the hormone by being directly oxidized by glyceraldehyde-3-phosphate dehydrogenase, by entering the midstream of the glycolytic pathway as glyceraldehyde 3-phosphate, or by entering the tricarboxylic acid cycle in mitochondria after intracellular hydrolysis. The inhibitory effect of CHX on glucose-induced insulin secretion, however, was far more marked than that on insulin secretion evoked by D-glyceraldehyde and dimethyl succinate at any CHX concentrations used. Our study revealed that the inhibitory action of CHX on glucose-induced insulin secretion is exerted mainly, but not solely, through inactivation of glucokinase. This conclusion supports the view that glucokinase is a key enzyme in the recognition of glucose as an insulin secretagogue in pancreatic islets.
Increased Transcapillary Escape Rate of Albumin in Nondiabetic Men in Response to Hyperinsulinemia
Authors: Nestler John E , Barlascini Cornelius O , Tetrault Gregory A , Fratkin Melvin J , Clore John N , Blackard William G
Published: September 2013

Diabetic patients manifest increased vascular permeability. To determine whether insulin per se might increase vascular permeability, five nondiabetic men were studied by the hyperinsulinemic-euglycemic clamp technique. Each subject received a 0.72-nmol/kg body wt i.v. insulin bolus, followed by a 72-pmol · kg−1 ·min−1 insulin infusion for 4 h. Euglycemia was maintained by the Biostator glucose controller. At 7 h of study, 10 μCi i.v. 125I-labeled albumin was injected as bolus dose. Frequent blood samples were drawn during the next 70 min for determination of the transcapillary escape rate (TER) of albumin. Subjects returned 1–2 wk later for a control study, during which 0.45% saline was infused at a rate identical to the dextrose and insulin infusion rates during the hyperinsulinemic clamp. The mean ± SE serum insulin levels during the hyperinsulinemic clamp and saline infusion were 9786 ± 126 and 46 ± 4 pM, respectively, whereas serum glucose during the two sessions was similar (5.0 ± 0.2 vs. 4.8 ± 0.1 mM, NS). Identical fluid volumes were infused during the two sessions (1767 ± 197 ml/7 h), and urine outputs did not differ significantly (1615 ± 309 vs. 1035 ± 248 ml/7 h). The TER of albumin was greater in all five men after hyperinsulinemia than after saline infusion (18.3 ± 2.7 vs. –2.8 ± 2.3%/h, P = 0.01). The serum albumin level at the end of the hyperinsulinemic-euglycemic clamp study was 14% lower than the value at the start of the study (37 ± 1 vs. 42 ± 1 g/L, P < 0.05), whereas no significant change in serum albumin levels occurred during the saline infusion. These observations suggest that acute hyperinsulinemia can increase the TER of radiolabeled albumin, probably by increasing vascular permeability.
Actions of Novel Antidiabetic Agent Englitazone in Hyperglycemic Hyperinsulinemic ob/ob Mice
Authors: Stevenson Ralph W , Hutson Nancy J , Krupp Michael N , Volkmann Robert A , Holland Gerald F , Eggler James F , Clark David A , McPherson R Kirk , Hall Karla L , Danbury Bernice H , Gibbs E Michael , Kreutter David K
Published: September 2013

The effects of CP 68722 (racemic englitazone) were examined in ob/ob mice, in adipocytes and soleus muscles from ob/ob mice, and in 3T3-L1 adipocytes. Administration of englitazone at 5–50 mg · kg−1 · day−1 lowered plasma glucose and insulin dose dependently without producing frank hypoglycemia in either the diabetic or nondiabetic lean animals. The glucoselowering effect in ob/ob mice preceded the reduction in hyperinsulinemia. On cessation of drug, plasma insulin returned to untreated levels within 48 h, whereas plasma glucose rose slowly over 5 days. Englitazone (50 mg/kg) for 11 days lowered plasma glucose (22.2 ± 1.4 to 14.0 ± 1.9 mM), insulin (7.57 ± 0.67 to 1.64 ± 0.60 nM), nonesterified fatty acids (1813 ± 86 to 914 ± 88 μM), glycerol (9.20 ± 0.98 to 4.94 ± 0.03 mM), triglycerides (1.99 ± 0.25 to 1.03 ± 0.11 g/L), and cholesterol (6.27 ± 0.96 to 3.87 ± 0.57 mM), but no effects were observed 3 h after a single dose. Basal and insulin-stimulated lipogenesis were enhanced in adipocytes from ob/ob mice treated with 50 mg/kg englitazone for 11 days compared with lipogenesis in cells from vehicle-treated controls. Treatment of ob/ob mice with 50 mg/kg englitazone reversed the defects in insulin-stimulated glycolysis (from [3-3H]glucose) and glycogenesis and basal glucose oxidation (from [1-14C]glucose) in isolated soleus muscles. Englitazone (30 μM) stimulated 2- deoxy-D-glucose transport in 3T3-L1 adipocytes from 0.37 ± 0.03 to 0.65 ± 0.06 and 1.53 nmol · min−1 · mg−1 protein at 24 and 48 h, respectively. Thus, englitazone has 1) insulinomimetic and insulin-enhancing actions in vitro and 2) glucose-, insulin-, triglyceride-, and cholesterol-lowering properties in an animal model of non-insulin-dependent diabetes mellitus (NIDDM) in which sulfonylureas have little or no effect. Thus, this new agent may have beneficial effects including a reduced risk of hypoglycemia in patients with NIDDM.
Studies on Autoimmunity for Initiation of β-Cell Destruction: VI. Macrophages Essential for Development of β-Cell–Specific Cytotoxic Effectors and Insulitis in NOD Mice
Authors: Ihm Sung-Hee , Yoon Ji-Won
Published: September 2013

NOD mice were treated with silica (which is selectively toxic to macrophages) from 4 or 20.5 wk of age. Syngeneic neonatal pancreases were transplanted into the renal subcapsular space of the NOD mice at 21 wk of age. Silica treatment was continued until 24 wk of age, and then the mice were killed for examination of islet morphology. Neither the islets in transplanted pancreases nor the host pancreatic islets from the early long-term silica-treated animals revealed 1insulitis. In contrast, most of the islets in transplanted pancreases from the late short-term silica-treated animals showed severe insulitis and β-cell necrosis, as did the host islets. A further experiment was performed to compare the effect of late short-term silica treatment with that of anti-L3T4-antibody treatment of the same time and duration. In contrast to the late short-term silica-treated animals, the transplanted pancreases in the anti-L3T4-antibodytreated animals revealed intact islets, although most of the host islets showed insulitis. The control group, which received no treatment but did receive neonatal pancreases, revealed severe insulitis and β-cell necrosis of both transplanted and host islets. These results suggest that early macrophage depletion can abolish the development of β-cell-specific immunologic effectors but that late macrophage depletion, after the development of insulitis, does not affect the destruction of β-cells by preexisting effectors other than macrophages. We conclude that macrophages are essential for the development of β-cell-specific cytotoxic effectors in the initial phase of insulitis in NOD mice.
Mapping Genes in Diabetes: Genetic Epidemiological Perspective
Authors: Rich Stephen S
Published: September 2013

Research on mapping diabetes-susceptibility genes is dependent on several factors, including the existence of a single major gene for susceptibility, genetic homogeneity, and the existence of appropriate clinical material. The power to detect susceptibility genes is dependent on the risks in relatives and the distance of genetic markers from the susceptibility genes. For insulin-dependent diabetes mellitus (IDDM), the bestfitting risk models are those with a single major locus with residual polygenic factors. The major locus effect is likely represented by genes in the HLA complex, because specific genotypes have been found to affect IDDM risk significantly. Thus, mapping the remaining polygenic IDDM susceptibility factors—each of small effect—is a difficult and long task. For non-insulindependent diabetes mellitus (NIDDM), the likely risk models result in few genes with moderate effect. Models of NIDDM have significant residual polygenic variation remaining, reflecting the importance of multiple loci with small effect, environmental effects, or genetic heterogeneity; however, the prospects for mapping genes that provide at least moderate susceptibility for NIDDM now appear promising.
Long-Term Culture of Neonatal Rat Pancreatic Endocrine Cells as Model for Insulin-Secretion and Ion-Channel Studies
Authors: Schwartz Jean-Louis , Mealing Geoffrey A R , Whitfield James F , Braaten Jan T
Published: September 2013

So far, only freshly isolated cells or short-term cultures have been used to study ion-channel activity in pancreatic nontumor β-cells. We report a procedure for the long-term cultivation of pancreatic endocrine cells to study the relationship between ion channels and insulin secretion. Using thimerosal to suppress fibroblastoid cell proliferation and a preliminary 2-day cell exposure to alternating normal (5.6 mM) and high (16.7 mM) glucose levels, we observed a significant secretory responsiveness of the cells to a glucose challenge for at least 4 wk in culture. Cells also responded to glucose or other secretagogues, such as quinine and the sulfonylurea glyburide, with membrane voltage oscillations. In the cell-attached configuration of the patch-clamp technique, a 65-pS-conductance K+ channel was observed, which was inhibited by glucose, quinine, and glyburide. In the inside-out configuration, the activity of this channel was suppressed by ATP applied to the cytoplasmic side of the membrane. A K+ channel with a conductance of 200 pS was also observed, which was activated by intracellular Ca2+. A 13-pS-conductance glucoseinsensitive K+ channel was present in both cellattached and inside-out patch recordings. Even after 3 wk, the characteristics of these currents and channels were comparable to those reported by other investigators with freshly dissociated or short-termcultured β-cells from neonatal and adult rats and adult mice. Therefore, the neonatal rat endocrine cell culture characterized herein provides an improved model for long-term investigations combining secretion and electrophysiological studies.
Insulin and Hypertension: Relationship to Obesity and Glucose Intolerance in Pima Indians
Authors: Saad Mohammed F , Knowler William C , Pettitt David J , Nelson Robert G , Mott David M , Bennett Peter H
Published: September 2013

The relationships among blood pressure, obesity, glucose tolerance, and serum insulin concentration were studied in 2873 Pima Indians aged 18–92 yr (mean 37 yr). Age- and sex-adjusted to the Pima population, the prevalence of hypertension (systolic blood pressure ≥160 mmHg, diastolic blood pressure ≥95 mmHg, or receiving drug treatment) was 7.1% for subjects with normal glucose tolerance compared with 13.0% for subjects with impaired glucose tolerance (IGT) and 19.8% for those with non-insulin-dependent diabetes mellitus (NIDDM) (P < 0.001). The prevalence ratio of hypertension was 1.8 (95% confidence interval [Cl] 1.2–2.5) for IGT and 2.6 (95% Cl 2.0–3.2) for NIDDM compared with normal glucose tolerance, controlled for age, sex, and body mass index (BMI). In logistic regression analysis, hypertension was positively related to age, male sex, BMI, glucose tolerance, and fasting but not 2-h postload serum insulin concentration. Among subjects not taking antihypertensive drugs, however, neither fasting nor 2-h postload serum insulin was significantly related to hypertension. Furthermore, in 2033 subjects receiving neither antihypertensive nor antidiabetic drugs, blood pressure was not significantly correlated to fasting insulin concentration, and 2-h postload serum insulin was negatively correlated with diastolic blood pressure. In conclusion, insulin is not significantly related to blood pressure in Pima Indians not receiving antihypertensive drugs. Higher insulin concentrations in drug-treated hypertensive patients might result from the treatment rather than contribute to the pathogenesis of hypertension. Thus, these data do not support a major role for insulin in determining the occurrence of hypertension or regulation of blood pressure in Pima Indians.
Glucose-Induced Electrical Activity in β-Cells: Feedback Control of ATP-Sensitive K+ Channels by Ca2+
Authors: Henquin Jean-Claude
Published: September 2013

Glucose regulates Ca2+ influx in β-cells by controlling a rhythmic electrical activity (slow waves with spikes). However, the glucose-sensitive feedback system that triggers repolarization at the end of the slow waves, and thus stops Ca2+ influx, is unknown. Raising extracellular Ca2+ to 10 mM shortened slow waves in mouse β-cells perifused with medium containing 15 mM glucose and restored slow waves when persistent depolarization and continuous spike activity were induced by 30 mM glucose. The effects of high Ca2+ were reversed or prevented by tolbutamide, whereas 1 mM tetraethylammonium only increased spike amplitude. This suggests that a feedback action of Ca2+ on ATP-sensitive K+ channels rather than on voltage- and Ca2+-activated K+ channels may be involved in slow wave generation. Metabolic modulation of this feedback could be central in the regulation of electrical activity and, hence, insulin release.
Influence of Obesity, Impaired Glucose Tolerance, and NIDDM on LDL Structure and Composition: Possible Link Between Hyperinsulinemia and Atherosclerosis
Authors: Barakat Hisham A , Carpenter John W , McLendon Virginia D , Khazanie Prabhaker , Leggett Nancy , Heath Judith , Marks Richard
Published: September 2013

The possible causes of the enhanced risk for coronary heart disease (CHD) were examined in morbidly obese women with normoglycemia, impaired glucose tolerance (IGT), and non-insulin-dependent diabetes mellitus (NIDDM) before and after gastric bypass surgery. Compared with age-matched lean women, plasma lipid and apolipoprotein concentrations of the obese women before surgery favored atherogenesis. The risk for CHD may further be exacerbated in the IGT and NIDDM groups by the prevalence of smaller and denser low-density-lipoprotein (LDL) particles. LDL size correlated negatively with plasma insulin levels independent of triglyceride levels, age, or body mass index (BMI). After surgery, BMI, plasma insulin, and triglyceride levels decreased, but LDL size increased, and LDL density decreased. Neither cholesterol nor LDL cholesterol levels were affected after surgery, but high-density-lipoprotein cholesterol was increased in all patients after surgery. Although the mechanisms underlying the changes in the properties of LDL could not be determined from this study, these changes appear to be of benefit in reducing CHD risk in these patients.
Inducement by Fat Feeding of Basal Hyperglycemia in Rats With Abnormal β-Cell Function: Model for Study of Etiology and Pathogenesis of NIDDM
Authors: Pascoe Wendy S , Storlien Leonard H
Published: September 2013

Non-insulin-dependent diabetes mellitus (NIDDM) is a heterogenous disorder characterized by defects in insulin action and secretion. This study was aimed at developing a rat model in which these pathogenic factors might be studied. Male Wistar rats were injected at 2 days of age with 45 or 30 mg/kg streptozocin (STZ) or vehicle (control). Fasting plasma glucose and insulin levels were not significantly different between the two groups between 5 and 8 wk of age. At 8 wk, half of each group was randomly assigned to isocaloric diets high in either fat (59% of calories) or starch (70% of calories). After 1 wk on the diets, 45-mg/kg-STZ-administered fat-fed animals displayed significant fasting hyperglycemia (8.6 ± 0.2 mM; P < 0.01), which was exacerbated by the stress of anesthesia and/or cannulation, whereas no changes were observed in any of the other groups before (STZ starch fed, 6.7 ± 0.1 mM; control fat fed, 6.8 ± 0.1 mM; control starch fed; 6.4 ± 0.1 mM) or after anesthesia and/or cannulation. In the 30-mg/kg-STZ animals, fat feeding did not significantly elevate plasma glucose concentration, but a significant hyperglycemic response was seen with anesthesia and/or cannulation. In all STZ groups, substantial impairment of glucose-induced insulin secretion was observed, particularly early-phase insulin secretion. Further studies indicated that STZ animals on a diet conferring normal insulin sensitivity (starch) maintained basal normoglycemia and mildly impaired (i.v.) glucose tolerance despite this gross insulin secretory defect. However, addition of dietary fatinduced insulin resistance resulted in basal hyperglycemia and marked deterioration of glucose tolerance. These results highlight the interaction between diet, insulin secretion and action, and the autonomic nervous system in the development of hyperglycemia.
Metabolic Effects of 1200-kcal Diet in Obese Pregnant Women With Gestational Diabetes
Authors: Magee Michael S , Knopp Robert H , Benedetti Thomas J
Published: September 2013

Calorie restriction is widely used as a primary therapy for obese pregnant women with gestational diabetes. To better understand the metabolic consequences of marked calorie restriction, we performed a randomized prospective trial under metabolic ward conditions. Obese gestationally diabetic women were randomized to control (n = 5) and calorie-restricted (n = 7) groups. All patients consumed an ∼2400-kcal/day diet during the 1st wk of the study, and at the end of the 1st wk, metabolic features of the two groups were statistically indistinguishable. During the 2nd wk, the control group continued to consume ∼2400 kcal/day, whereas the calorie-restricted group consumed -1200 kcal/day. Twenty-four-hour mean glucose levels remained unchanged in the control group (6.7 ± 0.8 mM wk 1 vs. 6.8 ± 0.8 mM wk 2), although they dropped dramatically in the calorie-restricted group (6.7 ± 1.0 mM wk 1 vs. 5.4 ± 0.5 mM wk 2, P < 0.01). Fasting plasma insulin also declined in the calorierestricted group (265 ± 165 pM wk 1 vs. 145 ± 130 pM wk 2), resulting in a significant change between groups (P < 0.02). Surprisingly, fasting plasma glucose and glucose tolerance measured by the 3-h oral glucose tolerance test did not change within or between groups. Fasting levels of β-hydroxybutyrate rose in the calorie-restricted group (290 ± 240 μM wk 1 vs. 780 ± 30 μM wk 2) but not in the control group (P < 0.01). Finally, urine ketones increased significantly (P < 0.02) in the calorie-restricted group, whereas they remained absent in the control group. We conclude that diets in the range of ∼1200 kcal/day improve glycemic status in obese pregnant women with gestational diabetes but cause significant increases in ketonemia and ketonuria. Because the impact of maternal ketonemia and ketonuria on fetal well-being remains controversial, these changes are of concern. This level of calorie restriction appears unwise for general clinical usage. Further studies are needed to characterize the metabolic consequences of 1600- to 1800-kcal/day diets that have recently been reported to improve glycemic status without causing ketonuria or profound ketonemia.
Reduced Membrane Fluidity in Platelets From Diabetic Patients
Authors: Winocour Peter D , Bryszewska Maria , Watala Cezary , Rand Margaret L , Epand Richard M , Kinlough-Rathbone Raelene L , Packham Marian A , Mustard J Fraser
Published: September 2013

Platelets from diabetic patients are hypersensitive to agonists in vitro. Membrane fluidity modulates cell function, and reduced membrane fluidity in cholesterol-enriched platelets is associated with platelet hypersensitivity to agonists, including thrombin. Decreased membrane fluidity of these platelets is attributed to an increased cholesterolphospholipid molar ratio in platelet membranes. We examined the response of platelets from diabetic subjects to thrombin, platelet membrane fluidity, and platelet cholesterol-phospholipid molar ratio. Twelve poorly controlled diabetic subjects were compared with 12 age- and sex-matched control subjects. In response to a low concentration of thrombin, mean values for release of [14C]serotonin from washed prelabeled platelets were not significantly different between diabetic and control subjects, but in 8 of 12 diabetic subjects, the release response was greater than in their paired control subjects. Mean steady-state fluorescence polarization values in 1,6-diphenyl-1,3,5- hexatriene-labeled platelets prepared from diabetic subjects were significantly greater than in control subjects; this indicates a decreased membrane fluidity in platelets from diabetic subjects. Total or very-low-density (VLDL), low-density (LDL), or highdensity (HDL2, HDL3) lipoprotein cholesterol concentrations in plasma were not significantly different between groups; however, the ratio of VLDL + LDL to HDL2 + HDL3 was significantly greater in diabetic than in control subjects. There was no difference in the total platelet cholesterol-phospholipid molar ratio between groups. Thus, reduced membrane fluidity of platelets from diabetic patients could account for their increased sensitivity to agonists; reduced membrane fluidity does not appear to result from a change in the plasma or platelet cholesterol content but is associated with an increase in the ratio of plasma VLDL + LDL to HDL2 + HDL3.
Pilot Study on ω-3 Fatty Acids in Type I Diabetes Mellitus
Authors: Landgraf-Leurs Martina M C , Drummer Christian , Fröschl Henriette , Steinhuber Robert , Schacky Clemens Von , Landgraf Rüdiger
Published: September 2013

Patients with diabetes mellitus are prone to develop vascular complications. Because ω-3 polyunsaturated fatty acid (ω-3FA) intake has a potential protective effect on cardiovascular disease, we studied the influence of ω-3FA supplementation (5.4 g eicosapentaenoic acid and 2.3 g docosahexaenoic acid daily) for 4 wk in 13 well-controlled type I (insulin-dependent) diabetic subjects on a vascular risk profile. Each subject served as his/her own control in a pre- and post-ω-3FA-intake phase. In plasma and platelets, phospholipids eicosapentaenoic acid and docosahexaenoic acid increased at the expense of arachidonic acid and linoleic acid. There was no significant change in blood pressure and glycosylated proteins. Only small changes were noted in blood glucose levels and insulin dose. Side effects were not noted. Triglycerides decreased significantly in the first 14 days, and total cholesterol increased slightly, probably because of an elevation of high-density lipoprotein cholesterol, although low-density lipoprotein cholesterol remained unchanged. Platelet aggregation induced by low doses of AOP and collagen, which was higher in diabetic than nondiabetic subjects, decreased during ω-3FA intake to levels of healthy control subjects. Thromboxane production after ADP- and collagen-induced platelet aggregation decreased significantly. Thromboxane liberation during clotting of whole blood and urinary excretion of thromboxane were markedly lowered during ω-3FA supplementation. The results show that even short-term intake of ω-3FAs leads tobeneficial changes of vascular risk factors without significant changes in glucose homeostasis.