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P Gorden

Publications and source records attributed to P Gorden.

At least 19 recordsLinked to original sources
PubMed2001

Repaglinide-induced factitious hypoglycemia.

We report the first case of repaglinide-induced factitious hypoglycemia in a young male. This case posed a challenging diagnostic dilemma because commercial assays for repaglinide are not available. Furthermore, the patient had a series of positive diagnostic tests such as high proinsulin and localizing intra-arterial calcium stimulation suggestive of insulinoma. This case, again, demonstrates the importance of pure clinical judgment in the face of often-conflicting laboratory data in making a correct diagnosis and the requirement of definitive data for an appropriate therapeutic resolution.

Adolescent↗
PubMed2000

Forty-eight-hour fast: the diagnostic test for insulinoma.

Insulinoma causes fasting hypoglycemia due to inappropriate insulin secretion. Its diagnosis is based on demonstrating Whipple's triad during a supervised 72-h fast. For 75 yr, the 72-h fast has been the cornerstone for the diagnosis; however, it has never been critically assessed using newer assays for insulin, C peptide, and proinsulin. Thus, the aim of the current study is to assess the need for a full 72-h fast for the diagnosis of insulinoma. Patients with suspected hypoglycemia with documented glucose concentrations below 45 mg/dL were admitted to the NIH. Data obtained during the supervised fast of patients with pathologically proven insulinoma over a 30-yr period (1970-2000) were reviewed. We identified 127 patients with insulinoma. The average age of patients was 42.7 +/- 15.9 yr, with a predominance of females (62%). 107 patients had a benign tumor, 20 had malignant insulinoma, and 15 patients had multiple endocrine neoplasia type 1. The fast was terminated due to hypoglycemia in 44 patients (42.5%) by 12 h, 85 patients (66.9%) by 24 h, and 120 (94.5%) by 48 h. Seven patients fasted beyond 48 h despite subtle neuroglycopenic symptoms and glucose and insulin concentrations diagnostic of insulinoma. Immunoreactive proinsulin was elevated at the beginning of the fast in 90% of 42 patients. Proinsulin in noninsulinoma, in contrast to insulinoma, patients is usually suppressible; therefore, samples taken in the suppressed state have the greatest diagnostic value. We conclude that with the current available insulin and proinsulin assays, the diagnosis of insulinoma can be made within 48 h. Thus, the 48-h fast should replace the 72-h fast in textbooks and hospital protocols as the new diagnostic standard.

Adolescent↗
PubMed1998

Effects of proteasomal inhibitors on the maturation of the insulin proreceptor: an anatomical paradox.

Inhibitors of proteasomal functions Carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG132) and Carbobenzoxy-L-isoleucyl-gamma-t-butyl-L-alanyl-L-leucinal (PSI) were found to inhibit the conversion of the Insulin proreceptor to its mature alpha and beta subunits. By contrast no effect of these inhibitors was found on 125-I insulin binding, internalization and degradation. Since the insulin proreceptor is an integral membrane protein that is compartmentally separated from the cytoplasmic 26S proteasome, the inhibition of the normal biosynthetic processing of the insulin proreceptor presents an anatomical paradox.

3T3 Cells↗
PubMed1998

Operative management of islet-cell tumors arising in the head of the pancreas.

BACKGROUND: Pancreatic islet cell tumors (ICTs) can be treated by enucleation or pancreatic resection. We reviewed our experience with ICTs in the head of the pancreas to define indications for enucleation versus pancreaticoduodenectomy. METHODS: Between January 1982 and December 1997, 48 patients underwent surgical resection for presumed ICTs of the pancreatic head. Of these, 18 were found on pathologic examination to be disease in a lymph node. Thirty patients had 32 true pancreatic head ICTs. We reviewed the operative results and postoperative courses in these patients. RESULTS: Mean diameter of the ICTs was 15 mm. Twenty-seven patients (90%) underwent successful enucleations. Three patients failed enucleation and underwent pancreaticoduodenectomy. There was no operative mortality. The median time to regular diet was 7 days. The median time to removal of all drains was 22 days. The most common complication was pancreatic fistula (15%). No patient required reoperation for treatment of a fistula. CONCLUSION: Most ICTs of the pancreatic head can be removed with enucleation, preserving pancreatic tissue and avoiding the morbidity of pancreaticoduodenectomy. The primary indication for pancreaticoduodenectomy is not the size of the lesion but its proximity to the pancreatic duct.

Adolescent↗
PubMed1998

Long-term medical treatment of ectopic ACTH syndrome.

BACKGROUND: The morbidity of hypercortisolemia due to ectopic production of ACTH by various tumors may be greater than the morbidity of the tumor itself. METHODS: We report three cases of long-term treatment of ectopic ACTH syndrome due to metastatic bronchial carcinoid, islet cell carcinoma, and malignant thymoma tumors. Clinical and biochemical eucortisolemia was achieved in each case and was sustained from 24 to 55 months. We review the therapeutic options and their reported efficacy. RESULTS: Cessation of therapy resulted in recurrence of hypercortisolemia in each case, showing the effectiveness of therapy. CONCLUSION: Long-term treatment of ectopic ACTH-induced hypercortisolemia by blocking adrenal steroidogenesis is clinically effective and well tolerated.

ACTH Syndrome, Ectopic↗
PubMed1997

Intraarterial calcium stimulation and intraoperative ultrasonography in the localization and resection of insulinomas.

BACKGROUND: Standard imaging studies (computed tomography, magnetic resonance imaging, somatostatin receptor scintigraphy, ultrasonography, and angiography) correctly localize insulinomas in less than 50% of patients and provide no information about the feasibility of enucleation based on proximity of tumor to pancreatic duct. We reviewed our experience with intraarterial calcium stimulation (Ca-Stim) and intraoperative ultrasonography (IOUS) to localize and guide management of insulinomas. METHODS: Thirty-six patients (14 men, 22 women, median age 44 years) with insulinomas were treated between August 1989 and June 1996. Preoperative imaging studies were obtained. Patients underwent abdominal exploration with IOUS. Fourteen were evaluated by a surgeon blinded to preoperative imaging results. RESULTS: Tumors (4 to 50 mm) were resected by enucleation (67%) or partial pancreatectomy (33%); all were cured. Sensitivities of computed tomography, magnetic resonance imaging, somatostatin receptor scintigraphy, ultrasonography, angiography, and Ca-Stim in localizing insulinomas were 24%, 45%, 17%, 13%, 43%, and 94%, respectively. Tumors were identified by blinded surgical exploration with IOUS in 12 of 14 patients (86%). CONCLUSIONS: All insulinomas were identified before operation; however sensitivity of individual noninvasive tests was low (less than 50%). In contrast, Ca-Stim was correct in 94% of cases, thus allowing a focused pancreatic exploration and obviating use of blind distal pancreatectomy. IOUS can then be used to guide safe enucleation.

Adolescent↗
PubMed1997

Non-insulin dependent diabetes--the past, present and future.

Diabetes, known since antiquity, has been defined by glycosuria. In 1886, when Minkowski demonstrated that pancreatectomized dogs developed diabetes, the islets of Langerhans became a focus of the search for an active principle culminating in the discovery and the isolation of insulin in 1921 by Banting, Best and Collip. In 1959, the radioimmunoassay of Yalow and Berson solidified the concept of insulin resistance in non-insulin dependent diabetes (NIDDM). In 1971, the insulin receptor was defined as a cell surface protein that initiated the insulin signal transduction cascade. Today, we know that NIDDM accounts for at least 90% of all diabetes worldwide and involves approximately 100 million people. The microvascular complications of NIDDM are the same as for insulin dependent diabetes (IDDM) and are related to the intensity and duration of hyperglycaemia. Further, it is clear from the Diabetes Control and Complications Trial (DCCT) that all microvascular complications can be reduced with intensive control of the blood glucose. Macrovascular disease is also accelerated in NIDDM, including both hypertension and dyslipidemia. The major risk factor for NIDDM are age, obesity, physical inactivity, and genetic background. The earliest features seen in individuals destined to develop NIDDM is insulin resistance, but for hyperglycaemia to ensure there must be a defect in insulin secretion. Thus, insulin resistance defines the prehyperglycaemic phase of NIDDM, but varying degrees of insulin secretory deficiency define the hyperglycaemic phase. Macrovascular risk occurs throughout the lifetime of the individual, whereas microvascular risk ensues with the inception of hyperglycaemia. Tomorrow, we will understand more clearly whether lifestyle changes, such as diet and exercise, or new classes of drugs, can delay or prevent NIDDM. Clinical trials are now beginning to test whether impaired glucose tolerance (IGT) can be delayed or prevented from moving to overt NIDDM. The genetics of NIDDM are under intense study. Mutations in the insulin receptor lead to NIDDM in a small number of patients, and mutations in the glucokinase gene lead to maturity onset diabetes of the young (MODY). Work is now underway to study other candidate genes as well as work on positional cloning techniques to identify diabetes genetic loci. The hormone Leptin has just been discovered and is a major regulator of body weight. In summary, the most important new emphasis on the treatment of NIDDM is the recognition of the importance of hyperglycaemia and our ability to both treat and possibly prevent this metabolic perturbation. This joins the longer-term emphasis on cardiovascular risk reduction from both treatment and prevention of hypertension and dyslipidemia.

Animals↗
PubMed1995

Receptor-mediated internalization of insulin. Potential role of pp120/HA4, a substrate of the insulin receptor kinase.

pp120/HA4 is a hepatocyte membrane glycoprotein phosphorylated by the insulin receptor tyrosine kinase. In this study, we have investigated the role of pp120/HA4 in insulin action. Transfection of antisense pp120/HA4 cDNA in H35 hepatoma cells resulted in inhibition of pp120/HA4 expression and was associated with a 2-3-fold decrease in the rate of insulin internalization. Furthermore, insulin internalization in NIH 3T3 fibroblasts co-transfected with insulin receptors and pp120/HA4 was increased 2-fold compared with cells expressing insulin receptors alone. In contrast, no effect on internalization was observed in cells overexpressing a naturally occurring splice variant of pp120/HA4 that lacks the phosphorylation sites in the intracellular domain. Insulin internalization was also unaffected in cells expressing three site-directed mutants of pp120/HA4 in which the sites of phosphorylation by the insulin receptor kinase had been removed (Y488F, Y488F/Y513F, and S503A). Our data suggest that pp120/HA4 is part of a complex of proteins required for receptor-mediated internalization of insulin. It is possible that this function is regulated by insulin-induced phosphorylation of the intracellular domain of pp120/HA4.

3T3 Cells↗
PubMed1995

Localization of insulinomas to regions of the pancreas by intra-arterial stimulation with calcium.

OBJECTIVE: To determine the sensitivity of calcium injected into pancreatic arteries in localizing insulin-secreting tumors to regions of the pancreas. DESIGN AND PATIENTS: To stimulate the release of insulin, 25 patients with surgically proven insulinomas (average diameter, 15 mm) had calcium gluconate (0.025 mEq Ca++/kg body weight) injected before surgery into the arteries supplying the pancreatic head (gastroduodenal and superior mesenteric arteries) and the body and tail (splenic artery) of the pancreas. SETTING: Tertiary referral hospital. MEASUREMENTS: Insulin levels were measured in samples taken from the right and left hepatic veins before and 30, 60, and 120 seconds after calcium injection. A twofold increase in insulin level in the sample taken from the right hepatic vein 30 or 60 seconds after injection localized the insulinoma to the segment of the pancreas supplied by the selectively injected artery. Localization done using calcium stimulation was compared with localization done using transcutaneous ultrasonography (n = 22), computed tomography (n = 23), magnetic resonance imaging (n = 21), arteriography (n = 25), and portal venous sampling (n = 9). RESULTS: Calcium stimulation localized 22 of 25 insulinomas (sensitivity, 88% [95% CI, 68% to 97%]) to the correct region of the pancreas. The sensitivities of the other imaging methods were 9% for ultrasonography (CI, 1% to 23%), 17% for computed tomography (CI, 5% to 39%), 43% for magnetic resonance imaging (CI, 22% to 66%), 36% for arteriography (CI, 18% to 57%), and 67% for portal venous sampling (CI, 30% to 93%). Calcium stimulation added only a few minutes to the time needed for pancreatic arteriography and caused no morbid conditions. CONCLUSION: Intra-arterial calcium stimulation with right hepatic vein sampling for insulin gradients is the most sensitive preoperative test for localizing insulinomas.

Adult↗
PubMed1994

Insulin-induced activation of phosphatidyl inositol 3-kinase. Demonstration that the p85 subunit binds directly to the COOH terminus of the insulin receptor in intact cells.

Insulin activates the insulin receptor tyrosine kinase to phosphorylate signaling molecules such as insulin receptor substrate-1 (IRS-1). Phosphorylated IRS-1 binds to SH2 domains in the p85 regulatory subunit of phosphatidyl inositol (PI) 3-kinase, thereby stimulating the catalytic activity of PI 3-kinase. For most growth factor receptor tyrosine kinases (including receptors for epidermal growth factor and platelet-derived growth factor), the p85 regulatory subunit of PI 3-kinase binds directly to phosphorylated YXXM motifs contained in the cytoplasmic domain of the receptor itself. Previous studies in cell-free systems have shown that the phosphorylated YHTM sequence (amino acid residues 1322-1325) in the COOH terminus of the insulin receptor has the ability to bind to the p85 subunit of PI 3-kinase, thereby activating the enzyme. In this investigation, we demonstrate the occurrence of the same direct binding interaction in intact cells. Subsequent to insulin-stimulated phosphorylation of the insulin receptor, a complex is formed that contains the insulin receptor and PI 3-kinase. This complex can be immunoprecipitated by antibodies directed against either the insulin receptor or the p85 subunit of PI 3-kinase. The delta 43 mutant insulin receptor that lacks 43 amino acids at the COOH terminus does not bind p85. In addition, the delta 43 truncation impairs the ability of the receptor to mediate the activation of PI 3-kinase. Thus, by binding directly to p85, the phosphorylated YHTM motif in the COOH terminus of the insulin receptor contributes partially to mediating the effect of insulin to activate PI 3-kinase.

3T3 Cells↗
PubMed1994

Rescue and activation of a binding-deficient insulin receptor. Evidence for intermolecular transphosphorylation.

Binding of insulin to the alpha subunit of the insulin receptor (IR) leads to autophosphorylation of the beta subunit. The reaction proceeds as intramolecular transphosphorylation between alpha beta half-receptors of the heterotetrameric receptor dimer (alpha 2 beta 2). Since IRs are mobile in the plane of the plasma membrane, it is also possible that transphosphorylation may occur between adjacent holoreceptors (alpha 2 beta 2) by an intermolecular reaction. To address this question, we cotransfected NIH-3T3 cells with two IR cDNA constructs: a truncated but functionally normal IR lacking the C-terminal 43 amino acids (delta 43) and a full-length Leu323 mutant receptor that is expressed on the cell surface but that does not bind insulin. A clonal cell line was selected from cells cotransfected with a 1/5 ratio of delta 43 cDNA/Leu323 cDNA. The two homodimers (Leu323 and delta 43) were expressed without detectable formation of hybrid receptors. By using specific antibodies, we demonstrate that in cells coexpressing both homodimers, the Leu323 mutant receptor was phosphorylated in vivo by the delta 43 IR in an insulin-dependent manner. However, when the Leu323 mutant receptor was expressed alone, no phosphorylation was detected. In addition, we demonstrate the association of the phosphorylated Leu323 mutant receptor with insulin receptor substrate-1 and with phosphatidylinositol 3-kinase. These findings indicate that insulin binding is not required for phosphorylation of the Leu323 mutant receptor, that the phosphorylation of the Leu323 mutant receptor occurs by an intermolecular transphosphorylation mechanism, and, finally, that the Leu323 mutant receptor, once phosphorylated, can associate with insulin receptor substrate-1 and phosphatidylinositol 3-kinase.

3T3 Cells↗
PubMed1994

Structural basis by which a recessive mutation in the alpha-subunit of the insulin receptor affects insulin binding.

Recently, a mutation substituting Leu for Ser323 in the alpha-subunit of the human insulin receptor has been identified in an insulin-resistant patient. The Leu323 mutation leads to a severe impairment in insulin binding without significantly altering the processing or cell surface expression of the receptor. In order to study how alpha beta half-receptors interact to form the insulin-binding site, we cotransfected NIH-3T3 cells with two insulin receptor cDNA constructs: a truncated insulin receptor lacking the C-terminal 43 amino acids (delta 43) and the full-length Leu323 mutant receptor. A clonal cell line from cotransfected cells expresses a hybrid receptor consisting of a Leu323 half-receptor and a delta 43 half-receptor. We demonstrate that the Leu323-delta 43 hybrid receptor binds insulin with high affinity. Furthermore, by cross-linking 125I-insulin to immobilized hybrid receptors, we show that only the alpha beta delta half of the hybrid receptor binds insulin. Since the isolated half-insulin receptor has low affinity for insulin, this suggests that the addition of even a non-binding alpha-subunit can result in high affinity binding to the holoreceptor (alpha alpha mut beta delta beta). Both beta and beta delta-subunits of the Leu323-delta 43 hybrid receptor are phosphorylated in vivo and in vitro in an insulin-dependent manner, suggesting an intramolecular transphosphorylation mechanism and that the presence of the Leu323 mutant receptor that lacks an intrinsic high affinity binding site does not prevent the associated beta-subunit from functioning either as a tyrosine kinase or as a phosphate acceptor in the hybrid insulin receptor molecule (alpha alpha mut beta delta beta). Furthermore, we show that the hybrid receptor can phosphorylate insulin receptor substrate-1 (IRS-1) in response to insulin and can be coimmunoprecipitated together with IRS-1 by anti-IRS-1 antibody.

3T3 Cells↗
PubMed1994

Mutational analysis of the NH2-terminal glycosylation sites of the insulin receptor alpha-subunit.

The insulin receptor is synthesized as a single chain of 190 kiloDaltons, which is processed to disulfide-linked mature alpha- and beta- subunits, containing N- and O-linked oligosaccharides and fatty acids. Previously (Collier E, Carpentier J-L, Beitz L, Caro LHP, Taylor SI, Gorden P: Biochemistry 32:7818-23, 1993), site directed mutagenesis of the asparagine in the first four sites of N-linked glycosylation to glutamine resulted in a receptor that was retained in the endoplasmic reticulum and not processed past the proreceptor form. In this study, mutation of these sites individually and in various combinations is studied. Mutation in the first or second glycosylation site does not significantly impair processing of the receptor; the receptor is found on the cell surface and binds insulin normally. If both the first and second sites are mutated, a significant reduction occurs in the amount of receptor found on the cell surface and in insulin binding. There is some processing of the receptor in cells expressing this mutant compared with the four-part mutant. If only the third and fourth sites are mutated, processing is impaired less than in the mutant with the first and second sites mutated. However, the amount of receptor found on the cell surface is less than in the mutant of only the first or only the second site. In all of these glycosylation mutants, the amount of receptor on the cell surface correlates with the level of 125I-labeled insulin binding on the cell surface.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1994

A novel human insulin receptor gene mutation uniquely inhibits insulin binding without impairing posttranslational processing.

The precise nature of the insulin-binding site of the insulin receptor (IR) has not been determined, although the importance of several regions of the alpha-subunit in insulin binding has been demonstrated. A naturally occurring mutation in a patient with severe insulin resistance that changes the Ser323 codon in the alpha-subunit of the IR to a leucine codon is associated with markedly impaired insulin binding to cells from the patient and to transfected cells expressing the mutant receptor. However, unlike other IR alpha-subunit mutations associated with decreased insulin binding, this mutation does not lead to a defect in posttranslational processing or cell-surface expression of IRs. Thus, the defect in insulin binding associated with the Leu323 mutant IR is a direct result of an alteration in the insulin-binding site. No natural IR mutation described thus far is associated with both decreased insulin binding and normal cell-surface expression of the mutant receptor. This study demonstrates the critical role that Ser323 of the IR alpha-subunit plays in insulin binding, either by forming part of the binding site or by stabilizing its conformation.

3T3 Cells↗
PubMed1993

Specific glycosylation site mutations of the insulin receptor alpha subunit impair intracellular transport.

The insulin receptor is a transmembrane protein found on multiple cell types. This receptor is synthesized as a 190-kDa proreceptor which is cleaved to produce mature alpha and beta subunits. The proreceptor contains 18 potential sites for N-linked glycosylation: 14 on the alpha subunit and 4 on the beta subunit. The codons for asparagine in the first four sites at the amino terminus of the alpha subunit were mutated to code for glutamine. This mutant receptor cDNA was stably transfected into NIH 3T3 cells. The insulin receptor produced in these cells remained in the proreceptor form; no mature alpha and beta subunits were produced. The proreceptor was slightly smaller on SDS-PAGE gels than the wild-type proreceptor and contained four less oligosaccharide chains by tryptic peptide mapping. The carbohydrate chains on the mutant proreceptor remained endoglycosidase H sensitive. However, in the presence of brefeldin A, these oligosaccharide chains could be processed to endoglycosidase H resistant chains. By immunofluorescence, the mutant proreceptor was shown to be localized to the endoplasmic reticulum. No insulin receptors could be found on the cell-surface either with cell surface labeling with biotin or with 125I-insulin binding. Thus, glycosylation of the first four N-linked glycosylation sites of the insulin receptor is necessary for the proper processing and intracellular transport of the receptor. This is in contrast to glycosylation at the four sites on the beta subunit which appear not to be important for processing but necessary for signal transduction. Therefore, N-linked glycosylation of the insulin receptor at specific sites has multiple distinctive roles.

3T3 Cells↗