bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the Receptor Binding Properties of Monoiodoinsulin Isomers and the Identification of Different Insulin Receptor Specificities in Hepatic and Extrahepatic Tissues
Authors: Podlecki D A , Frank B H , Kao M , Horikoshi H , Freidenberg G , Marshall S , Ciaraldi T , Olefsky J.M 
Published: September 2013

Insulin was iodinated with 125I using a modification of the lactoperoxidase method. This iodinated insulin mixture was then separated by HPLC, allowing studies to be performed on the pure monoiodoinsulin isomers labeled at the tyrosyl residuesat A14, B16, or B26.
Binding studies in adipocytes revealed the relative affinity for these isomers to be 1.00:0.99:1.30 (A14, B16, and B26, respectively). The increase in binding affinity was shown to be due to a slower dissociation rate rather than an accelerated association rate. Receptor mediated internalization of the different iodinated isomers was assessed and these results showed that the isomers were internalized and degraded in proportion to their relative binding affinities. The biologic activity of the B26 isomer to stimulate adipocyte glucose oxidation was measured and showed that the B26 isomer had 30% greater biologic potency compared with native insulin, consistent with its 30% increase in binding potency. Thus, the B26 monoiodoinsulin isomer behaves as a superagonist.
Binding studies using extrahepatic tissue (i.e., adipocytes, cultured human fibroblasts, IM-9 lymphocytes, and human placental membranes) consistently revealed that the relative binding affinity for the B26 isomer was always greater than the A14 isomer (1.29, 2.11,1.22, and 1.35, respectively) while the binding affinity of the B16 isomer was generally comparable to the A14 isomer. In hepatic tissue (whole cell, liver plasma membranes, and partially purified, solubilized liver receptors) binding studies illustrated that the B26 isomer consistently had a lower relative affinity when compared to the A14 isomer (0.75 : 0.69 : 0.77).
In conclusion, (1) the B26 monoiodoinsulin isomer exhibits higher binding affinity and greater biologic activity in adipocytes than native insulin, and (2) the B26 monoiodoinsulin isomer has a higher binding affinity in extrahepatic tissues but exhibits a lower binding affinity in hepatic tissues when compared with the A14 monoiodoinsulin isomer, indicating a striking difference in functional specificity between the hepatic and the extrahepatic insulin receptor.
Regulation of Triacylglycerol Lipolysis in the Perfused Hearts of Normal and Diabetic Rats
Authors: Murthy Veeraraghavan K , Bauman Mitchel D , Shipp Joseph C 
Published: September 2013

Effects of insulin, palmitate, and acetate on lipolysis of endogenous triacylglycerols were studied in the isolated perfused hearts of control and ketotic diabetic rats. In the absence of fatty acid, the rate and net amount of lipolysis were increased in diabetic hearts. After 120 min of perfusion, the residual triacylglycerol content was similar in both hearts, suggesting that the accumulation of triacylglycerols in the heart of ketotic diabetic rats was due to the expansion of the mobiliza-ble fraction. Insulin, in physiologic concentrations, inhibited triacylglycerol lipolysis in control hearts, provided glucose was present in the perfusate. In diabetic hearts perfused with glucose, insulin up to 500 μU/ml did not inhibit triacylglycerol lipolysis.
A physiologic concentration of palmitate (0.5 mM) completely inhibited triacylglycerol lipolysis in both control and diabetic hearts. Palmitate inhibition of lipolysis in both control and diabetic hearts could be observed in absence of perfusate glucose. Heart intra-cellular lipoprotein lipase activity was determined to check whether the inhibitory actions of insulin and palmitate could be explained by reduction in this lipase activity. Perfusion of control hearts with insulin and glucose had no effect on the lipase activity. Lipase activity of the control heart was unaffected and that of the diabetic heart was inhibited after perfusion with palmitate. The results of this study show (1) insulin in physiologic concentrations inhibits heart triacylglycerol lipolysis probably through increased glucose transport and glycolysis; (2) inclusion of palmitate in the perfusate results in inhibition of triacylglycerol lipolysis in both control and diabetic hearts and in the case of the diabetic heart, the palmitate effect is due to the inhibition of the intracellular lipoprotein lipase activity; and (3) an increased synthesis of triacylglycerol coupled with an inhibition of its lipolysis by free fatty acids and ketone bodies may explain the accumulation of triacylglycerols in the hearts of diabetic rats.
Normalization of Six Key Hepatic Enzymes After Fetal Pancreas Transplantation in Diabetic Rats
Authors: Makoff R K , Brown J , Mullen Y , Clark W R 
Published: September 2013

In diabetic rats transplanted with fetal pancreata we measured the activities of six important enzymes to assess the return of liver metabolism to normal. Comparison was made among the responses of transplanted rats with and without renal-portal vein shunts and of those not transplanted and injected with insulin in varying doses. Insulin supply was not limited since three or four fetal pancreata were first grown in normal rats before transfer into the diabetic animals.
Transplantation normalized blood and urine glucose and the rate of disappearance of intravenous glucose. Glucokinase and pyruvate kinase activities in liver rose toward normal at 7 days after transplantation and reached normal levels at 30 and 90 days. The response of the other four enzymes, glucose-6-phosphate dehy-drogenase, citric lyase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase, was more rapidly restored to normal at 7 days and remained normal at 30 and 90 days. No difference was observed in the enzyme activities of transplanted-shunted rats to nonshunted animals.
Glucokinase activity was restored to normal after 1 wk of daily injections of 1 U of PZI; pyruvate kinase restoration required 3 U/day. Glucose-6-phosphate dehydrogenase and citric lyase required 2 U/day to be restored to normal; 3 U daily resulted in temporary supernormal activities. The gluconeogenic enzymes, fructose-1,6-bisphosphatase and glucose-6-phospha-tase, were only partially suppressed toward normal by insulin even with 3 U daily for 3 wk.
These findings indicate that pancreas transplantation is a more effective regulator of liver metabolism in diabetes than insulin injections.
Degradation of Insulin by Isolated Mouse Pancreatic Acini: Evidence for Cell Surface Protease Activity
Authors: Goldfine Ira D , Williams John A , Bailey Anne C , Wong K Y , Iwamoto Yasuhiko , Yokono Koichi , Baba Shigeaki , Roth Richard A 
Published: September 2013

In the present study, we have used isolated mouse pancreatic acini to investigate the relationship between 125I-insulin binding and its degradation in order to probe the nature and cellular localization of the degradative process. In these cells, the proteolysis of 125I-insulin was dependent on time and cell concentration, and was saturated by unlabeled insulin with a Km of 290 nM. Since this value was much higher than the Kd for insulin binding to its receptor (1.1 nM), the data indicated that 125I-insulin degradation by acini occurred primarily via nonreceptor mechanisms.
Several lines of evidence suggested that insulin was being degraded by the neutral thiol protease, insulin degrading enzyme (IDE). First, insulin degradation was inhibited by thiolreacting agents such as N-ethylmaleimide and p-chloromercuribenzoate. Second, the Km for degradation in acini was similar to the reported Km for IDE in other tissues. Third, the enzyme activity had a relative mol wt of approximately 130,000 by gel filtration, a value similar to that reported for purified IDE. Fourth, the degrading activity was removed with a specific antibody to IDE.
Other lines of evidence suggested that enzymes located on the cell surface played a role in insulin degradation by acini. First, the nonpenetrating sulfhydryl reacting agent 5,5′dithiobis-2-nitrobenzoic acid blocked 125I-insulin degradation. Second, a specific antibody to IDE identified the presence of the enzyme on the cell surface. Third, chloroquine, leupeptin and antipain, agents that inhibit lysosomal function, did not influence 125I-insulin degradation. Fourth, highly purified pancreatic plasma membranes degraded 125I-insulin.
Possible Role of Endogenous Arachidonic Acid Metabolites in Stimulated Release of Insulin and Glucagon from the Isolated, Perfused Rat Pancreas
Authors: Walsh Mary F , Pek Sumer Belbez 
Published: September 2013

Enhancement of arachidonic acid metabolism results in increased insulin secretion. To determine which pathways of arachidonic acid metabolism were involved in this stimulation, we studied the effects of various inhibitors of arachidonate metabolism on arginine-induced insulin and glucagon secretion in the isolated, perfused rat pancreas. The release of PGE2 from the pancreas was monitored to document the efficacy of the inhibitory drugs.
p-Bromophenacyl bromide, a phospholipase A2 inhibitor, diminished PGE2 release and significantly inhibited both the early and late phases of insulin and glucagon release in response to arginine. Flurbiprofen, a specific cyclooxygenase inhibitor, decreased the early phase of insulin release and inhibited both phases of arginine-stimulated glucagon secretion; these decreases were concurrent with a large inhibition of PGE2 release. Nordihydroguaiaretic acid, a li-poxygenase inhibitor, at a dose of 10-5 M did not affect PGE2 release, inhibited the early phase of insulin release, and did not modify glucagon secretion. The combination of flurbiprofen and nordihydroguaiaretic acid, although the most potent in inhibiting PGE2, lowered only the early phase of insulin and had no effect on glucagon secretion.
We conclude that: (1) endogenous cyclooxygenase-derived metabolites of arachidonic acid promote insulin and glucagon release, (2) endogenous lipoxygenase products preferentially stimulate insulin release, and (3) phospholipase A2 activity has an intrinsic modulatory effect on insulin and glucagon secretion.
Nicotinamide Does Not Protect Islet B-Cell Metabolism Against Alloxan Toxicity
Authors: Sandler S , Welsh M , Andersson A 
Published: September 2013

Nicotinamide, a poly(ADP-ribose)synthetase inhibitor, protected NMRI mice against alloxan-induced hyperglycemie when given 10 min before, but not 10 min after, the injection of the drug. Pretreatment in vivo with nicotinamide induced hyperglycemia at the time of alloxan injection, and this could account for the protective action of nicotinamide against alloxan diabetes. Exposure of islets to alloxan (2 mM) in vitro caused a marked inhibition of both glucose-stimulated proinsulin biosynthesis and insulin release, and this was not affected by the action of nicotinamide. Alloxan-impaired islet glucose oxidation was partly restored by nicotinamide. The decreased islet content of NADH plus NAD, which was observed after alloxan treatment, could be prevented by nicotinamide. Glucose-stimulated islet oxygen uptake was abolished after treatment with alloxan, and nicotinamide had no protective effect in this process. Leucine (10 mM) plus glutamine (10 mM), however, were still able to evoke an islet respiratory response after alloxan exposure. Alloxan caused an immediate increase in the islet efflux of radiolabeled nucleotides, which was followed after about 5 min by a further increase. This latter increase of the radio efflux was inhibited by the addition of nicotinamide.
The inability of nicotinamide to prevent the alloxan-induced impairment of proinsulin biosynthesis, insulin release, and oxygen uptake, together with the failure of nicotinamide to prevent the development of diabetes when given after alloxan, does not support a current hypothesis that the major cytotoxic effect of alloxan is primarily due to DNA damage. The present data suggest that organelles other than the nuclei, e.g., the mitochondria or the plasma membrane, are the primary sites of B-cell injury by alloxan. It is also concluded that the B-cell-toxic action of alloxan is different from that Of StreptOZOCin.
The Onset of Liver Glycogen Synthesis in Fasted-Refed Rats: Effects of Streptozocin Diabetes and of Peripheral Insulin Replacement
Authors: Werve G Van De , Sestoft L , Folke M , Kristensen L Ø 
Published: September 2013

The mechanism of liver glycogen synthesis after refeeding has been investigated in diabetic rats, diabetic insulin-treated rats, and in control rats fasted for 48 h. The accumulation of liver glycogen was the same in diabetic rats and in control rats after 2 h of feeding, but did not proceed any further in the diabetic group during the next 2 h. Insulin-treated diabetic rats synthesized five times more hepatic glycogen than the control rats after 1 h of refeeding, but the amount accumulated at the end of the refeeding period was the same. Feeding resulted in a transient activation of glycogen synthase in untreated as well as in treated diabetic rats. In control rats, however, glycogen synthase was already partially in the active form before access to food, and the onset of glycogen synthesis occurred without further activation of the enzyme. A transient inactivation of phosphorylase was observed in all groups during the meal, but was very slight in the untreated diabetic rats in which phosphorylase a values were already reduced before the access to food.
Peripheral glycemia was markedly increased upon refeeding in treated and untreated diabetic rats, but remained normal in control rats. Peripheral insulinemia was increased by feeding in the control rats and remained low in the diabetic rats and high in the insulin-treated diabetic rats.
The results indicate that, in normal controls in contrast to diabetic rats, synthase activation is not a prerequisite for the initiation of glycogen synthesis after a meal; phosphorylase inactivation may be of major importance in normal controls, but also appears to play a role in the diabetic animals. The changes are triggered by glucose as well as insulin.
Impaired Auditory Brainstem-evoked Responses in Insulin-dependent Diabetic Subjects
Authors: Fedele Domenico , Martini Alessandro , Cardone Claudio , Comacchio Francesco , Bellavere Federico , Molinari Giorgio , Negrin Paolo , Crepaldi Gaetano 
Published: September 2013

Auditory brainstem-evoked responses (ABR) were recorded from the scalp of 30 normoacoustic insulin-dependent diabetic subjects, aged between 15 and 41 yr (29 ± 7 yr). Three different stimulus repetition rates (11, 37, and 87 cps) were used. The results were compared with those obtained from 20 age- and sex-matched, normoacoustic control subjects. In diabetic patients, metabolic control (mean daily plasma glucose, glycosylated hemoglobin) and the presence of retinopathy, nephropathy, and somatic neuropathy were also investigated. The latencies (ms) of ABR waves were significantly impaired in diabetic subjects as compared with normals. Peripheral transmission time (wave I) and central transmission time (waves I–V) were also significantly delayed in diabetic subjects. Moreover, by increasing stimulus repetition rates, a significant increase in waves I–V shift was observed in diabetic patients. ABR impairment was not related to glucose balance, to the duration of diabetes, or to the presence of the diabetic retinopathy, nephropathy, and somatic neuropathy.
In conclusion, diabetic neuropathy is characterized not only by somatic and autonomie nerve dysfunctions, but also by the early involvement of the central nervous system (CNS). ABR recording can represent a useful, noninvasive, simple procedure to detect both acoustic nerve and CNS damage.
Terbium, a Fluorescent Probe for Insulin Receptor Binding: Evidence for a Conformational Change in the Receptor Protein Due to Insulin Binding
Authors: Williams Paul F , Turtle John R 
Published: September 2013

Terbium (Tb3+), an ion of the lanthanide series that has been used as a fluorescent probe for calcium (Ca2+) binding sites in proteins, binds to the proteins in both solubilized and purified human placental insulin receptor preparations. Tb3+ fluorescence was determined directly and the effect of insulin binding on Tb3+-enhanced fluorescence was studied without the need to separate bound and free ligands. Tb3+ behaved similarly to, but was more potent (50-fold) than, Ca2+ in increasing the insulin bound to its receptor.
When insulin bound to its receptor, the Tb3+ fluorescence of the receptor preparation decreased. When various insulin analogues were tested, the decrease in Tb3+ fluorescence was proportional to the biologic activity of the insulin analogues. In addition, Tb3+ could be displaced from insulin-sensitive sites by Ca2+, indicating that there were Ca2+ (and Tb3+) binding sites on or near the insulin receptor. These sites, when filled, were responsible for the increased insulin receptor affinity. The decrease in Tb3+ fluorescence after insulin binding may be indicative of a conformational change in the insulin receptor precipitated by the binding of insulin. This conformational change may be related to the release of Ca2+ by insulin binding, is associated with a decrease in insulin receptor affinity, and suggests that an allosteric mechanism involving both Ca2+ and insulin binding sites may be responsible for the observed changes in insulin receptor affinity.
Diabetes Induction by Subdiabetogenic Doses of Streptozotocin in BALB/cBOM Mice: Noninvolvement of Host B-Lymphocyte Functions
Authors: Blue Marie-Luise , Shin Seung-Il 
Published: September 2013

Multiple subdiabetogenic doses of streptozotocin induce an insulin-dependent progressive hyperglycemia in genetically susceptible strains of mice. We have shown previously that T-cell-dependent autoimmune mechanisms play an obligatory role in this model of diabetogenesis by demonstrating that athymic nude mice and lethally irradiated euthymic mice are selectively resistant to diabetes induction and that the susceptibility can be reconstituted by grafting thymus in nude mice or by giving B-cell-depleted splenic lymphocytes to the irradiated mice.
In this report we investigate more directly the possible role of host B-cell functions in the induction of hyperglycemia. Mice were rendered selectively deficient in functional B lymphocytes by repeated injections of a polyclonal antiserum against mouse IgM, starting immediately after birth. These B-cell-suppressed mice had no detectable ability to produce antibodies against a test antigen but appeared to have normal levels of T cells. When treated with multiple low doses of streptozotocin, they developed progressive hyperglycemia in a manner indistinguishable from control mice with normal B-cell functions. These results suggest that host B cells, in contrast to host T cells, are not etiologically involved in the development of diabetes induced by multiple subdiabetogenic doses of streptozotocin.
Anti-Beta-Cell Immunity in Insulinopenic Diabetic Dogs
Authors: Sai Pierre , Debray-Sachs Monique , Jondet Andreé , Gepts Willy , Assan Roger 
Published: September 2013

Anti-islet immunity was studied in six spontaneously insulin-dependent diabetic (IDD) dogs, using mouse islets of Langerhans cells as targets, in vitro. Insulinopenia was demonstrated in all dogs by an i.v. glucose tolerance test. A significant lymphocytopenia was detected in the peripheral blood of this diabetic group. Pancreatic tissue from one of these animals was obtained shortly after death and the islets displayed a marked loss in beta cells without significant changes in the other types of islet cells. No insulitis was observed.
Circulating mononuclear cells from the diabetic dogs induced an increased basal insulin (IRI) release from islet cells and a suppressed stimulated IRI release. Damage to or depth of beta cells may account for these findings.
The stimulated IRI release was also suppressed when islets were incubated with the diabetic sera + complement, while the D-cell response to arginine was not altered, and the A-cell response was reduced but not abolished. A lysis of islet cells in the presence of IDD sera + complement was demonstrated by an increased release of 51Cr from labeled cells. These anomalies were observed neither when complement was heat-inactivated nor in the presence of control sera + complement.
Canine IDD may be a new animal model for the study of anti-islet cellular and humoral immunities.
Effect of EDTA on Insulin Binding and Insulin Action in Isolated Cardiocytes from Adult Rat: Evidence for a Functional Role of Low-Affinity Insulin Receptors
Authors: Eckel Jürgen , Reinauer Hans 
Published: September 2013

Calcium-tolerant myocytes from the adult rat heart were used to study the effects of EDTA on insulin binding and insulin action. Treatment of cardiocytes with EDTA resulted in a 60% inhibition of insulin binding. This effect was partially reversible by subsequent addition of calcium or magnesium. Scatchard analysis of equilibrium binding data in the presence of calcium and magnesium showed a curvilinear plot with a high-affinity segment having a Kd of 5.7 × 10−10 mol/L. In the presence of EDTA a linear Scatchard plot was observed with a Kd of 5.6 × 10 −9 mol/L. The total number of insulin receptors remained unaltered under these conditions. In contrast to insulin binding, insulin internalizaron was not affected by EDTA treatment.
Insulin action was studied by measuring the effect of the hormone on the transport of 3-O-methylglucose. Half-maximal action occurred at an insulin concentration of 3 × 10−10 mol/L and 10−8 mol/L in control and EDTA-treated cells, respectively. Maximal transport stimulation, however, was not significantly different in both groups (130% and 106%, respectively).
In conclusion, low-affinity insulin receptors in cardiac myocytes mediate a biologic response comparable to that of high-affinity sites; moreover, they may be involved in the process of internalization in this tissue. The data suggest a functional role of low-affinity insulin receptors in cardiac muscle.