Showing papers on "Proinsulin published in 1995"
TL;DR: The fat mutation represents the first demonstration of an obesity–diabetes syndrome elicited by a genetic defect in a prohormone processing pathway.
Abstract: Mice homozygous for the fat mutation develop obesity and hyperglycaemia that can be suppressed by treatment with exogenous insulin. The fat mutation maps to mouse chromosome 8, very close to the gene for carboxypeptidase E (Cpe), which encodes an enzyme (CPE) that processes prohormone intermediates such as proinsulin. We now demonstrate a defect in proinsulin processing associated with the virtual absence of CPE activity in extracts of fat/fat pancreatic islets and pituitaries. A single Ser202Pro mutation distinguishes the mutant Cpe allele, and abolishes enzymatic activity in vitro. Thus, the fat mutation represents the first demonstration of an obesity-diabetes syndrome elicited by a genetic defect in a prohormone processing pathway.
667 citations
TL;DR: It is concluded that fatty acids as well as ketone bodies diminish B-cell responsiveness to glucose in human islets by way of a glucose-fatty acid cycle.
Abstract: We previously demonstrated in the rat that long term exposure to fatty acids inhibits B-cell function in vivo and in vitro. To further assess the clinical significance of these findings, we tested in human islets the effects of fatty acids on glucose-induced insulin release and biosynthesis and on pyruvate dehydrogenase (PDH) activity. Human islets were obtained from the beta-Cell Transplant Unit (Brussels, Belgium). Exposure to 0.125 mmol/L palmitate or oleate for 48 h during tissue culture (RPMI-1640 and 5.5 mmol/L glucose) inhibited the postculture insulin response to 27 mmol/L glucose by 40% and 42% (P < 0.01 for difference). Inhibition was partly prevented by coculture with 1 mumol/L etomoxir, a carnitine-palmitoyl-transferase-I inhibitor (P < 0.05 for effect of etomoxir). Inhibitory effects on glucose-induced insulin secretion by previous palmitate were additive to the inhibitory effects exerted by previous high glucose (11 and 27 mmol/L). Palmitate-induced inhibition of insulin secretion was evident after exposure to 25 mumol/L added fatty acid. The insulin content of islets exposed to fatty acids was significantly reduced, and glucose-induced proinsulin biosynthesis was inhibited by 59% after palmitate addition and by 51% after oleate exposure (P < 0.01). These effects were partly prevented by etomoxir (P < 0.05). The activity of PDH in mitochondrial extracts of islets preexposed for 48 h to palmitate was decreased by 35% (P < 0.05) vs. that in control islets, whereas the activity of PDH kinase (which inactivates PDH) was significantly increased in the same preparations (P < 0.05). The effects of ketones were tested by 48-h exposure to beta-hydroxybutyrate (beta-D-OHB). Ten millimoles of D-beta-OHB per L inhibited the subsequently tested insulin response to 27 mmol/L glucose by 56% (P < 0.001). Half-maximal inhibitory effects of D-beta-OHB on insulin secretion and insulin content were seen at concentrations between 0.5-2.5 mmol/L. Inhibition by D-beta-OHB was partially reversed by etomoxir, whereas exposure to D-beta-OHB failed to affect PDH and PDH kinase activities. We conclude that fatty acids as well as ketone bodies diminish B-cell responsiveness to glucose in human islets by way of a glucose-fatty acid cycle. Increased plasma concentrations of fatty acids and ketones are likely to be important factors behind the negative influences on B-cell function exerted by a diabetic state in both type 1 and type 2 diabetes.
291 citations
TL;DR: Progression of neural development through the steps of cell proliferation, differentiation, maturation and survival is stimulated, at least in culture, by proinsulin and insulin and the IGFs, suggesting these factors might be important autocrine and paracrine signals during development of the CNS.
235 citations
TL;DR: Two specific syndromes have been defined: mutations in the insulin gene that lead to the production of biologically ineffective insulin have been described in several families and involved heterozygotes who produce normal insulin.
Abstract: Insulin, the central hormone controlling the utilization of fuel, is initially synthesized in pancreatic beta cells as its relatively inactive precursor, proinsulin. A series of enzymes that process prohormones act on proinsulin to produce mature insulin and C peptide. Abnormalities in the secretory products of beta cells are a rare but well-documented cause of impairment in glucose tolerance and hyperinsulinemia.1 Two specific syndromes have been defined. First, mutations in the insulin gene that lead to the production of biologically ineffective insulin have been described in several families.2–4 All cases described to date have involved heterozygotes who produce normal insulin . . .
222 citations
TL;DR: It is suggested that hyperinsulinemia attributable to augmented concentrations of proinsulin and insulin in plasma increase plasma PAI-1 activity and may contribute to acceleration of atherosclerosis and impairment of coronary thrombolysis in patients with NIDDM.
Abstract: Background Fasting hyperinsulinemia (reflected by elevations in immunoreactive “insulin”) is typical of patients with non–insulin-dependent diabetes mellitus (NIDDM) and is often associated with obesity and hypertension. The elevated concentrations detected are indicative not only of insulin but also of its immunologically cross-reactive precursors, including proinsulin. Fasting hyperinsulinemia appears to be associated with decreased fibrinolytic activity in blood, which results from increased activity of plasminogen activator inhibitor type-1 (PAI-1), a potential independent risk factor for coronary artery disease. Patients who were given proinsulin in a previous clinical study by others exhibited an increased incidence of cardiovascular events. Thus, a “proinsulin–PAI-1 axis” may predispose to coronary thrombosis. To define the possible presence of such an axis, this study was designed to determine whether insulin, its precursors, or both increase the concentrations of PAI-1 in rabbits in vivo. Methods...
190 citations
TL;DR: Application of this technique has demonstrated that abnormal β-cell function is present at a relatively early stage in the evolution of NIDDM, even before the onset of overt hyperglycemia, and is consistent with studies in the Zucker diabetic fatty rat.
Abstract: Pancreatic insulin secretion rates can be accurately derived by mathematical deconvolution of peripheral C-peptide concentrations either by using individual C-peptide kinetic parameters obtained by analysis of the decay curve of biosynthetic human C-peptide or by using published group parameters with appropriate adjustments for age and degree of obesity. Since the cross-reactivity of proinsulin and related peptides is low (< 10%) in many C-peptide assays, this experimental approach avoids the spurious increase in insulin immunoreactivity resulting from cross-reactivity with proinsulin and related peptides in the insulin assay. Application of this technique has demonstrated that the phenotypic expression of beta-cell dysfunction differs in subjects with different genetic mechanisms of non-insulin-dependent diabetes mellitus (NIDDM). Subjects who have maturity-onset diabetes of the young (MODY) due to mutations in the glucokinase gene demonstrate different patterns of altered insulin secretion when compared with subjects who have mutations in the MODY1 gene on chromosome 20. Glucokinase mutations affect the ability of the beta-cell to detect and respond to small increases in glucose above the basal level. However, compensatory mechanisms operative in vivo, which include a priming effect of glucose on insulin secretion, limit the severity of the observed insulin secretory defect, resulting in a generally mild clinical course in these subjects. In contrast, mutations in the MODY1 gene are associated with an inability to increase insulin secretion as the plasma glucose concentration increases above 7-8 mmol/l and the normal priming effect of glucose on insulin secretion is lost. These characteristics of the dose-response relationships between glucose and insulin secretion result in a more severe degree of hyperglycemia than observed in subjects with glucokinase mutations, and these subjects more frequently need insulin treatment. These alterations are evident in prediabetic subjects with normal glucose levels who carry the MODY1 mutation, suggesting that defective beta-cell function is the primary pathogenetic defect in the diabetic syndrome in these subjects. Studies performed in the classic form of NIDDM demonstrate that subjects with mild glucose intolerance and normal fasting glucose concentrations and glycosylated hemoglobin levels consistently demonstrate defective beta-cell function. These results are consistent with studies in the Zucker diabetic fatty rat, an animal model of NIDDM in which prediabetic animals demonstrate extensive alterations in expression of multiple genes involved in the regulation of insulin secretion. It thus appears that abnormal beta-cell function is present at a relatively early stage in the evolution of NIDDM, even before the onset of overt hyperglycemia.
157 citations
TL;DR: In pancreatic islets, formation of β-secretory granule cores involves early proinsulin homohexamerization and subsequent insulin condensation as mentioned in this paper, which occurs upon ER exit and arrival in immature secretory granules.
119 citations
TL;DR: Throughout life, IGFs are constitutvely expressed ubiquitous factors which help to maintain the survival of differentiated cells, Increased expression is found during growth and tissue repair, Six specific binding proteins, IGFBP 1‐6, allow additional tissue compartment specific control of IGF activity.
115 citations
TL;DR: Results demonstrate that by immunocytochemistry this anti-proinsulin MAb, although providing very specific results, reveals non-related molecules, due to the fact that these molecules exhibit similar short determinants.
Abstract: The immunocytochemical application of a monoclonal antibody (MAb) against the Arg-Arg region at the junction of the C-peptide and the insulin beta-chain of the human proinsulin molecule on rat pancreatic tissue resulted in positive immunogold labeling over the insulin- as well as the glucagon-secreting cells. In the insulin cells, the Golgi cisternae and the immature clathrin-coated granules were intensely labeled, and in the glucagon cells all the granules were labeled. Control experiments using the anti-proinsulin MAb adsorbed with proinsulin, insulin, and glucagon have confirmed the crossreactivity of this proinsulin antibody with glucagon. Furthermore, the anti-proinsulin MAb appears to crossreact not only with rat but also with human glucagon and with bovine and porcine insulin and glucagon. Examination of the amino acid sequences of proinsulin and proglucagon has shown that both molecules display this Arg-Arg dipeptide sequence, which could explain the labeling obtained on both cell types. In additi...
114 citations
TL;DR: Insulin-related growth factors, interestingly including proinsulin, are present in the developing chicken retina and appear to play an autocrine/paracrine stimulatory role in the progression of neurogenesis.
Abstract: Early neurogenesis progresses by an initial massive proliferation of neuroepithelial cells followed by a sequential differentiation of the various mature neural cell types. The regulation of these processes by growth factors is poorly understood. We intend to understand, in a well-defined biological system, the embryonic chicken retina, the role of the insulin-related growth factors in neurogenesis. We demonstrate the local presence of signaling elements together with a biological response to the factors. Neuroretina at days 6-8 of embryonic development (E6-E8) expressed proinsulin/insulin and insulin-like growth factor I (IGF-I) mRNAs as well as insulin receptor and IGF type I receptor mRNAs. In parallel with this in vivo gene expression, E5 cultured neuroretinas synthesized and released to the medium a metabolically radiolabeled immunoprecipitable insulin-related peptide. Furthermore, insulin-related immunoreactive material with a HPLC mobility close to that of proinsulin was found in the E6-E8 vitreous humor. Exogenous chicken IGF-I, human insulin, and human proinsulin added to E6 cultured neuroretinas showed relatively close potencies stimulating proliferation, as determined by [methyl-3H]thymidine incorporation, with a plateau reached at 10(-8) M. These factors also stimulated neuronal differentiation, indicated by the expression of the neuron-specific antigen G4. Thus, insulin-related growth factors, interestingly including proinsulin, are present in the developing chicken retina and appear to play an autocrine/paracrine stimulatory role in the progression of neurogenesis.
110 citations
TL;DR: This is the first demonstration of T cell reactivity to a proinsulin-specific peptide, and the first example of reactivities to a minimal peptide region shared between two human autoimmune disease-associated self antigens.
Abstract: Insulin (1) and glutamic acid decarboxylase (GAD) (2) are both autoantigens in insulin-dependent diabetes mellitus (IDDM), but no molecular mechanism has been proposed for their association. We have identified a 13 amino acid peptide of proinsulin (amino acids 24–36) that bears marked similarity to a peptide of GAD65 (amino acids 506–518) (G. Rudy, unpublished). In order to test the hypothesis that this region of similarity is implicated in the pathogenesis of IDDM, we assayed T cell reactivity to these two peptides in subjects at risk for IDDM. Subjects at risk for IDDM were islet cell antibody (ICA)-positive, first degree relatives of people with insulin-dependent diabetes. Peripheral blood mononuclear cells from 10 pairs of at-risk and HLA-DR matched control subjects were tested in an in vitro proliferation assay. Reactivity to both proinsulin and GAD peptides was significantly greater among at-risk subjects than controls (proinsulin; p < 0.008; GAD: p < 0.018). In contrast to reactivity to the GAD peptide, reactivity to the proinsulin peptide was almost entirely confined to the at-risk subjects. This is the first demonstration of T cell reactivity to a proinsulin-specific peptide. In addition, it is the first example of reactivity to a minimal peptide region shared between two human autoimmune disease-associated self antigens. Mimicry between these similar peptides may provide a molecular basis for the conjoint autoantigenicity of proinsulin and GAD in IDDM.
TL;DR: It is concluded that increased cardiovascular risk of the DD genotype is not mediated through insulin resistance or abnormalities in fibrinolysis, and an increased sensitivity in NIDDM subjects with the ACE DD genotypes is reported.
Abstract: Background The insertion/deletion (ID) polymorphism of the angiotensin-converting enzyme (ACE) gene has been associated with increased coronary heart disease (CHD), although the mechanism of this association is not apparent. We tested the hypothesis that the deletion allele of the ACE gene is associated with insulin resistance. Methods and Results We related ACE genotype to components of the insulin-resistance syndrome in 103 non–insulin-dependent diabetic (NIDDM) and 533 nondiabetic white subjects. NIDDM subjects with the DD genotype had significantly lower levels of specific insulin (DD 38.6, ID 57.1, and II 87.4 pmol · L−1 by ANOVA, P=.011). Non–insulin-treated subjects with the DD genotype had increased insulin sensitivity by HOMA % (DD 56.4%, II 29.4%, P=.027) and lower levels of des 31,32 proinsulin (DD 3.3, II 7.6 pmol · L−1, P=.012) compared with II subjects. There were no differences in prevalence of CHD or levels of blood pressure, serum lipids, or plasminogen activator inhibitor–1 (PAI-1) activ...
TL;DR: This study shows that young, nondiabetic, male survivors of myocardial infarction are truly hyperinsulinemic during an OGTT and suggests a close association between proinsulin and coronary atherosclerosis.
Abstract: Background Glucose intolerance and hyperinsulinemia are common disturbances in nondiabetic men with premature coronary artery disease (CAD). To investigate the relation between insulin-like molecules and severity of coronary atherosclerosis, 62 consecutive nondiabetic men presenting with a first myocardial infarction before the age of 45 were studied along with 41 healthy, age-matched, male, population-based control subjects. Methods and Results Specific two-site immunoradiometric assays were used to distinguish intact proinsulin, (des 31,32)proinsulin, and “true” insulin in fasting plasma and during an oral glucose tolerance test (OGTT). Global coronary atherosclerosis and number and severity of distinct stenoses were determined in the patients in 15 proximal coronary arterial segments by use of separate semiquantitative classification systems. The patients had a two- to threefold increase in insulin and insulin propeptide concentrations in the fasting state as well as during the OGTT. Severity of corona...
TL;DR: In islets from hyperglycemic rats an abnormal increased proportion of proinsulin was secreted, that was accompanied by an augmented release of PC2, PC3 and CP-H, which likely results from increased beta cell secretory demand, rather than a defect in theProinsulin processing enzymes per se.
Abstract: Hyperproinsulinemia in non-insulin-dependent diabetes mellitus (NIDDM) is due to an increased release of proinsulin from pancreatic beta cells. This could reside in increased secretory demand placed on the beta cell by hyperglycemia or in the proinsulin conversion mechanism. In this study, biosynthesis of the proinsulin conversion enzymes (PC2, PC3, and carboxypeptidase-H [CP-H]) and proinsulin, were examined in islets isolated from 48-h infused rats with 50% (wt/vol) glucose (hyperglycemic, hyperinsulinemic, and increased pancreatic proinsulin to insulin ratio), 20% (wt/vol) glucose (normoglycemic but hyperinsulinemic), and 0.45% (wt/vol) saline (controls). A decrease in the islet content of PC2, PC3, and CP-H from hyperglycemic rats was observed. This reduction did not correlate with any deficiency in mRNA levels or biosynthesis of PC2, PC3, CP-H, or proinsulin. Furthermore, proinsulin conversion rate was comparable in islets from hyperglycemic and control rats. However, in islets from hyperglycemic rats an abnormal increased proportion of proinsulin was secreted, that was accompanied by an augmented release of PC2, PC3 and CP-H. Stimulation of the beta cell's secretory pathway by hyperglycemia, resulted in proinsulin being prematurely secreted from islets before its conversion could be completed. Thus, hyperproinsulinemia induced by chronic hyperglycemia likely results from increased beta cell secretory demand, rather than a defect in the proinsulin processing enzymes per se.
TL;DR: In elderly prediabetic subjects disproportionately increased proinsulin concentration, an indicator of defective insulin secretion, is associated with conversion to diabetes over a short time period, independent of fasting glucose concentration at baseline.
Abstract: Insulin resistance and impaired insulin secretion are thought to be the primary defects in the pathogenesis of non-insulin-dependent diabetes mellitus (NIDDM). Disproportionately increased proinsulin relative to insulin levels are suggested to be an early indicator of a failing pancreas. We examined the relationship of fasting specific insulin, proinsulin, and 32, 33 split proinsulin concentrations, and the proinsulin: insulin ratio to the risk of developing NIDDM 3.5 years later in 65–74-year-old non-diabetic Finnish subjects participating in a populationbased study (n=892) on diabetes and heart disease. Altogether 69 subjects developed NIDDM over a 3.5-year follow-up (cases). The cases were compared to randomly-selected gender-matched control subjects (n=69) and control subjects matched for gender, glucose tolerance status (normal or impaired), and body mass index (n=69). There were no differences in insulin concentrations between cases and random or matched control subjects [median and interquartile range; 123 (77–154), 108 (74–143), 118 (83–145) pmol/l, p=0.271]. Random control subjects had lower proinsulin and 32,33 split proinsulin concentrations and split proinsulin: insulin ratios compared to cases [5.7 (3.8–9.0) vs 7.3 (4.8–10.0) pmol/l, p=0.005; 7.3 (4.5–13.0) vs 10.4 (7.1–18.0) pmol/l, p=0.002; 0.073 (0.057–0.110) vs 0.097 (0.060–0.135), p=0.003]. Matched control subjects had lower proinsulin concentrations and proinsulin: insulin ratios compared to cases [5.9 (4.0–7.7) vs 7.3 (4.8–10.0) pmol/l, p=0.019; 0.048 (0.035–0.071) vs 0.064 (0.045–0.100), p=0.008]. When cases were compared to matched control subjects a 1 SD increase in baseline proinsulin: insulin ratio was associated with a 1.37-fold risk (p=0.020) of developing diabetes. Moreover, this association was independent of fasting glucose concentration at baseline. Thus, in elderly prediabetic subjects disproportionately increased proinsulin concentration, an indicator of defective insulin secretion, is associated with conversion to diabetes over a short time period.
TL;DR: It is concluded that small dense LDL may form part of the insulin resistance syndrome in non-diabetic subjects and is significantly associated with high triglyceride level, decreased HDL cholesterol, hypertension and impaired glucose tolerance.
Abstract: Recently, the presence of small dense low density lipoprotein (LDL) has been postulated to be a stronger risk factor for coronary heart disease than large LDL. While small dense LDL has been associated with individual components of the insulin resistance syndrome such as hypertension, high triglyceride level, low high density (HDL) cholesterol, and diabetess mellitus, there has been little work exploring whether LDL size is decreased in subjects with multiple metabolic disorders. We examined the association of LDL size and pattern to specific insulin (which does not cross-react with proinsulin), proinsulin, increased triglyceride, decreased HDL, hypertension and impaired glucose tolerance in 488 non-diabetic subjects from the San Antonio Heart Study. LDL size was significantly related to specific insulin, proinsulin and the fasting proinsulin/insulin ratio. Small dense LDL was significantly associated with high triglyceride level, decreased HDL cholesterol, hypertension and impaired glucose tolerance. LDL size (a) decreased in a stepwise fashion with increasing number of the metabolic disorders described above (zero 262.6±9.4; one 257.0±9.3; two 256.4±9.4; three 249.0±9.1; and four 244.9±9.0). These results were similar in men and women and in non-Hispanic whites and Mexican Americans. The association between LDL size and the number of metabolic disorders remained statistically significant even after adjustment for obesity, body fat distribution, gender, ethnicity, proinsulin and insulin concentrations. Furthermore, decreases in LDL size are also significantly associated with both a selective beta-cell defect (as estimated by the fasting proinsulin/insulin ratio) and insulin resistance (as estimated by the fasting insulin concentrations) although the association was some-what stronger for the latter. We conclude that small dense LDL may form part of the insulin resistance syndrome in non-diabetic subjects.
TL;DR: Co-expression of PC1 and PC2 with proinsulin in islet beta-cells indicates that these proteases are actively involved, probably in a sequential manner, in the conversion ofproinsulin into insulin.
Abstract: Endoproteolytic cleavage of pairs of basic amino acids is the key mechanism in the specific processing of precursor hormone molecules. Two endoproteases, PC1 (or PC3) and PC2, have recently been implicated in the conversion of proinsulin. Using antibodies against these proteases and proinsulin, followed by protein A-gold complex, we performed an immunocytochemical study for precise identification of the subcellular compartments involved in the processing of insulin. Both PC1 and PC2 immunoreactivities followed a pattern of gradually increasing density along the secretory pathway, being higher in the immature granules. Proinsulin labeling was detected in the Golgi apparatus and in the coated immature secretory granules located mainly in the Golgi area. Using double labeling, we demonstrated the presence of PC1 and/or PC2 in the majority of proinsulin-rich granules. In addition, we provided evidence that PC1 and PC2 are co-localized within the same granules. Co-expression of PC1 and PC2 with proinsulin in islet beta-cells indicates that these proteases are actively involved, probably in a sequential manner, in the conversion of proinsulin into insulin.
TL;DR: In IN-rats, islet B cell mass reduction is distinguished by non-immune-mediated programmed cell death, while GLU-rats exhibit A cell mass Reduction by cytoplasmic retraction and selective exocrine apoptosis.
Abstract: Effects of transplantable rat insulinomas (IN) and glucagonomas (GLU) on the endogenous pancreas were analyzed using morphometry, immunocytochemistry, in situ hybridization, and staining for apoptotic cells. Hyperinsulinemia (IN-rats) and hyper-GLP-1/glucagonemia (GLU-rats) were both associated with marked islet atrophy (67 and 76% of control average planimetrical islet area, respectively). Selective islet B cell inhibition of proinsulin (I and II) genes as well as of expression of the insulin gene transcription factor, IPF1/STF1, was found in IN-rats. Moreover, these islets were characterized by significant B cells apoptosis in the absence of infiltrating lymphocytes. In GLU-rats selective islet A cell inhibition was observed at the level of glucagon mRNA. These islets contained small, highly condensed but clearly active B cells with prominent IPF1/STF1-positive nuclei, surrounded by densely packed glucagon-negative cells with reduced cytoplasm. Furthermore, an active apoptotic process was found exclusively in the exocrine pancreas of GLU-rats. Thus, in IN-rats, islet B cell mass reduction is distinguished by non-immune-mediated programmed cell death, while GLU-rats exhibit A cell mass reduction by cytoplasmic retraction and selective exocrine apoptosis.
TL;DR: In Japanese-American men, elevated PI and PI/IRI ratio are markers of B-cell dysfunction, and these are not the result of obesity, and central adiposity confers an additional risk for CHD independent of insulin.
Abstract: Obesity is associated with noninsulin-dependent diabetes mellitus (NIDDM) and coronary heart disease (CHD), and these interactions have usually been related to changes in immunoreactive insulin (IRI) levels. A role of proinsulin (PI) in this association has been suggested. We, therefore, examined IRI, PI, and true insulin levels and the PI/IRI ratio by glucose tolerance or CHD status in a cross-sectional study of 170 Japanese-American men (45-74 yr old) in whom 2 measures of adiposity (body mass index and intraabdominal fat) were made to assess potential associations in this population with a high prevalence of both NIDDM and CHD. Subjects were classified as having normal glucose tolerance (n = 58), impaired glucose tolerance (IGT; n = 55), or NIDDM (n = 57) or were classified by CHD status (without CHD, n = 127; with CHD, n = 43). A positive linear relationship existed between obesity, determined either as the body mass index or intraabdominal fat, and IRI, PI, and true insulin, but not the PI/IRI ratio....
TL;DR: To investigate the effect of an omega‐3 fatty acid concentrate K85 on serum lipids, lipoproteins, insulin metabolism and blood pressure in subjects with combined hyperlipidaemia.
Abstract: . Objectives. To investigate the effect of an omega-3 fatty acid concentrate K85 on serum lipids, lipoproteins, insulin metabolism and blood pressure in subjects with combined hyperlipidaemia.
Design. After a run-in dietary period of 10 weeks, subjects were randomly allocated to receive either encapsulated K85 (n = 28) or corn oil (n = 29). The intervention was double-blind.
Setting. An outpatient centre in Stavanger, Norway.
Subjects. Fifty-seven of 141 individuals, who, after the run-in period continued to meet the inclusion criteria: serum triglycerides of ≥ 2.0 mmol L−1 and total serum cholesterol of ≥ 6.0 mmol L−1.
Intervention. Encapsulated K85, containing 85% eicosapentaenoic acid (EPA)/docosahexaenoic acid (DHA), or corn oil, both administered in a daily dose of 4 g for 12 weeks.
Main outcome measures. Change in metabolic and haemodynamic parameters related to intervention. Results. Serum EPA and DHA increased significantly in the K85 group during the treatment period. The body-mass index remained unchanged. A 28% reduction in serum triglycerides was noted in the K85 group from the first 4 weeks. Total serum cholesterol was significantly reduced with both regimens. Serum high-density lipoprotein cholesterol increased significantly during the first 8 weeks in the K85 group. Significant reductions in systolic and diastolic blood pressures were noted in subjects on K85. The treatment did not affect serum glucose, plasma insulin and proinsulin levels. Insulin: glucose and proinsulin: glucose ratios remained unchanged.
Conclusions. The atherogenic risk profile was improved with K85 in subjects with combined hyperlipidaemia, but n-3 fatty acids supplementation did not affect glucose/insulin homeostasis.
Patent•
14 Nov 1995TL;DR: In this article, a one-step process for selectively acylating the free eamino group of insulin, insulin analog, or proinsulin in the presence of a free α-amino groups was described.
Abstract: The present invention relates to the acylation of proteins. More particularly, the invention relates to a one-step process for selectively acylating the free e-amino group of insulin, insulin analog, or proinsulin in the presence of a free α-amino group.
TL;DR: A system based on the peroxidase‐catalyzed iodination of tyrosine residues which continuously monitors the exposure of internal domains of proinsulin proposes that internal domains contain co‐localized signals for Bip binding and for degradation.
Abstract: The signal for degradation of proteins in the endoplasmic reticulum (ER) is thought to be the exposure of internal domains which are buried when the protein has adopted its correct conformation and which are also exposed in assembly intermediates. This raises the question of why the intermediates are not degraded. We developed a system based on the peroxidase-catalyzed iodination of tyrosine residues which continuously monitors the exposure of internal domains of proinsulin. In CHO cells this system discriminated between assembly intermediates of wild type (wt) proinsulin and misfolded proinsulin, as shown by the exclusive iodination of a misfolded mutant which was finally degraded in the ER. Iodination in vitro showed that the assembly intermediates of wt proinsulin also exposed internal domains. This iodination was inhibited by the addition of the molecular chaperone Bip which was co-immunoprecipitated with proinsulin in CHO cells. The results obtained with the mutant proinsulin support the assumption that exposed internal domains represent the signal for degradation in the ER. Observations of wt proinsulin show that Bip masks internal domains of normal assembly intermediates during the entire assembly process, thereby suppressing their degradation. We propose that internal domains contain co-localized signals for Bip binding and for degradation.
TL;DR: GIP not only enhances insulin secretion but also insulin gene expression and, therefore, it is a true insulinotropic hormone.
TL;DR: In this paper, the relationship of levels of insulin, intact proinsulin and des-31,32 pro-insulin to blood pressure, lipids, fibrinogen, factor VII and albumin excretion rate in 270 europids with normal glucose tolerance was examined.
Abstract: Elevated concentrations of proinsulin-like molecules, other than insulin, may be associated with abnormalities of cardiovascular risk factors, promoting atherogenesis and thrombosis Using specific assays we examined the relationship of levels of insulin, intact proinsulin and des-31,32 proinsulin to blood pressure, lipids, fibrinogen, factor VII and albumin excretion rate in 270 europids with normal glucose tolerance After correcting for age and body mass index, fasting and 2-h insulin concentrations were significantly associated with those of total and LDL-cholesterol (r=018–022), HDL-cholesterol (both r=−020) and triglycerides (r=021 and 018), but not with blood pressure Concentrations of intact and des-31,32 proinsulin showed significant associations with those of total and LDL-cholesterol (r=020–023), HDL-cholesterol (r=−031 and −032) and triglycerides (r=022 and 026) Fasting insulin and intact proinsulin concentrations were significantly associated with fibrinogen (r=015 and 018) Concentrations of proinsulin-like molecules comprised less than 10% of all insulin-like molecules, and so were calculated not to influence previously described relationships between insulin concentrations and cardiovascular risk factors measured using non-specific assays In multiple regression analyses des-31,32 proinsulin concentration was more strongly associated with those of HDL-cholesterol (negatively), LDL-cholesterol and triglycerides than fasting insulin concentrations, while intact proinsulin replaced insulin concentrations in their relationships with fibrinogen Our results show correlations between dyslipidaemia and proinsulin-like molecules at concentrations at which biological, insulin-like, activity appears unlikely We also show relationships between LDL-cholesterol and fibrinogen and the proinsulin-like molecules These results suggest that a causal relationship mediated by hyperinsulinaemia and insulin resistance is unlikely
TL;DR: The data suggest that both increased insulin resistance and abnormal processing of proinsulin are present in offspring of parents with diabetes, and these differences remained statistically significant after adjustment for obesity, body fat distribution, and glucose tolerance.
Abstract: Both insulin resistance and decreased insulin secretion have been hypothesized to be precursors of non-insulin-dependent diabetes. An elevated proinsulin concentration reflects abnormal proinsulin processing and could indicate abnormal insulin secretion. We examined fasting insulin (measured by a radioimmunoassay that does not cross-react with proinsulin), as a marker of insulin resistance, and proinsulin and the fasting proinsulin-to-insulin ratio, as markers of impaired proinsulin processing, in 597 nondiabetic Mexican-Americans from the San Antonio Heart Study. Fasting insulin, proinsulin, and the fasting proinsulin-to-insulin ratio were higher in subjects with a parental history of diabetes than in subjects without such a history. These differences remained statistically significant after adjustment for obesity, body fat distribution, and glucose tolerance. A parental history of diabetes in nondiabetic Mexican-Americans is associated with an increase in fasting specific insulin and a disproportionate increase in proinsulin relative to insulin. These data suggest that both increased insulin resistance and abnormal processing of proinsulin are present in offspring of parents with diabetes.
TL;DR: The 12 exons of the PC2 gene of 60 NIDDM subjects were screened for mutations that might explain the observed association using the technique of single-strand conformational polymorphism analysis, and a single variant was noted in exon 1.
Abstract: Proinsulin is converted to insulin by the concerted action of two sequence-specific subtilisin-like proteases termed prohormone convertase 2 (PC2) and prohormone convertase 3. PC2 is a type II proinsulin-processing enzyme, and it cleaves the proinsulin molecule on the COOH-terminal side of dibasic peptide, Lys64-Arg65, which joins the C-peptide and the A-chain domains. We have previously cloned and characterized the exon-intron organization of the human PC2 gene (gene symbol PCSK2), localized this gene to human chromosome 20 band p11.2 by fluorescence in situ hybridization, and identified a simple tandem-repeat DNA polymorphism (STRP) in intron 2 of the form (CA)n, suitable for genetic studies. Since non-insulin-dependent diabetes mellitus (NIDDM) is associated with increased secretion of proinsulin and proinsulin-like molecules, we conducted a case-control study to determine whether a genetic variation in PCSK2 might contribute to the development of NIDDM. The study population consisted of 152 Japanese NIDDM subjects and 102 normal healthy nondiabetic control subjects matched for age and body mass index. The subjects were genotyped at the STRP in intron 2, and the results indicated a significant difference (P = 0.004) in the overall allele frequency distribution between the two groups. The A1 allele was found more frequently in NIDDM than in nondiabetic subjects (11 vs. 4%, P = 0.0068). The NIDDM patients were divided into two subgroups according to the presence or absence of the A1 allele.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: The data suggest that the marked insulin depletion observed in diabetic islets is probably due to a hyperglycemia-driven increase in secretory demand that is not met by the enhanced biosynthetic capacity of these islets, which leads to relative enrichment of the depleted diabetic islet with immature secretory granules of a higher proinsulin content.
Abstract: We have recently shown that the diabetic syndrome in Psammomys obesus is characterized by severe depletion of islet immunoreactive insulin (IRI) stores together with a marked increase in the islet proinsulin to insulin ratio. In the present in vitro studies, we show marked enhancement of proinsulin biosynthesis in islets from diabetic P. obesus (approximately 8-fold compared to nondiabetic islets). Proinsulin to insulin conversion and insulin degradation do not differ significantly between diabetic and nondiabetic islets. The rate of IRI secretion at a stimulatory concentration of glucose (16.7 mM) is comparable in diabetic and nondiabetic animals, but at a nonstimulatory glucose concentration (0 mM), islets obtained from diabetic animals show significant IRI release. beta-Cells from diabetic P. obesus also exhibited increased secretion of newly synthesized proinsulin and conversion intermediates under stimulatory conditions. Moreover, a novel secretory compartment, highly enriched in newly synthesized C ...
Journal Article•
TL;DR: The results show that the introduction of insulin cDNA into a human hepatoma cell line results in synthesis, storage and acute regulated insulin release and lend credence to the possibility of engineering a liver cell to secrete insulin acutely in response to physiological stimuli.
Abstract: To develop a model somatic gene therapy system for diabetes, a human hepatoma cell line (HEP G2) was transfected with a mammalian expression vector carrying the full-length human insulin cDNA. More proinsulin than insulin was released daily by the stably transformed cell line (HEP G2ins). However, on acute stimulation with 5mM 8-Br-cAMP and 10mM theophylline the HEP G2ins cells released predominantly insulin into the medium. The cells did not secrete insulin in response to glucose. Examination of acid-ethanol extracts confirmed insulin was preferentially being stored. Immunohistochemical analysis of the cells also showed (pro)insulin was being stored. Electron microscopy revealed large membrane-bound vacuoles, containing electron-dense material, which were not seen in control cells. Glucokinase activity and albumin secretion of the transfectants were unaltered from the controls. Five-minute pulse-chase labelling of the HEP G2ins cells with 3H-leucine confirmed insulin synthesis in the presence of 20mM glucose and 5mM 8-Br-cAMP. A dose-response curve for insulin synthesis was also generated to increasing concentrations of glucose with a half Vmax of 4.9mM. Our results show that the introduction of insulin cDNA into a human hepatoma cell line results in synthesis, storage and acute regulated insulin release and lend credence to the possibility of engineering a liver cell to secrete insulin acutely in response to physiological stimuli.
TL;DR: The results are consistent with the view that G. australis and holarctic lampreys arose from a common stock but have been separated for a considerable period and Geotria pancreas is unable to synthesize a SPC2-type prohormone convertase.