Beta cell nuclear musculoaponeurotic fibrosarcoma oncogene family A (MafA) is deficient in type 2 diabetes

AIMS/HYPOTHESIS

The beta cell transcriptional factor musculoaponeurotic fibrosarcoma oncogene family A (MafA) regulates genes important for beta cell function. Loss of nuclear MafA has been implicated in beta cell dysfunction in animal models of type 2 diabetes. We sought to establish if nuclear MafA is less abundant in beta cell nuclei in humans with type 2 diabetes.

METHODS

Pancreas obtained at surgery from five non-diabetic individuals and six individuals with type 2 diabetes was immunostained for insulin, glucagon and MafA.

RESULTS

Beta cell nuclear MafA was markedly decreased in type 2 diabetes (1.6 ± 1.2% vs 46.3 ± 8.3%, p < 0.001).

CONCLUSIONS/INTERPRETATION

Beta cell nuclear MafA is markedly decreased in humans with type 2 diabetes, which may contribute to impaired beta cell dysfunction.

A low frequency of pancreatic islet insulin-expressing cells derived from cord blood stem cell allografts in humans

AIMS/HYPOTHESIS

We sought to establish if stem cells contained in cord blood cell allografts have the capacity to differentiate into insulin-expressing beta cells in humans.

METHODS

We studied pancreases obtained at autopsy from individuals (n = 11) who had prior opposite-sex cord blood transplants to reconstitute haematopoiesis. Pancreatic tissue sections were stained first by XY-fluorescence in situ hybridisation and then insulin immunohistochemistry. Pancreases obtained at autopsy from participants without cord blood cell infusions served as controls (n = 11).

RESULTS

In the men with prior transplant of female cord blood, there were 3.4 ± 0.3% XX-positive insulin-expressing islet cells compared with 0.32 ± 0.05% (p < 0.01) in male controls. In women with prior transplant of male cord blood cells we detected 1.03 ± 0.20% XY insulin-expressing islet cells compared with 0.03 ± 0.03 in female controls (p < 0. 001).

CONCLUSIONS/INTERPRETATION

Cord blood stem cells have the capacity to differentiate into insulin-expressing cells in non-diabetic humans. It remains to be established whether these cells have the properties of beta cells.

Adaptive changes in pancreatic beta cell fractional area and beta cell turnover in human pregnancy

AIMS/HYPOTHESIS

We sought to establish the extent and basis for adaptive changes in beta cell numbers in human pregnancy.

METHODS

Pancreas was obtained at autopsy from women who had died while pregnant (n = 18), post-partum (n = 6) or were not pregnant at or shortly before death (controls; n = 20). Pancreases were evaluated for fractional pancreatic beta cell area, islet size and islet fraction of beta cells, beta cell replication (Ki67) and apoptosis (TUNEL), and indirect markers of beta cell neogenesis (insulin-positive cells in ducts and scattered beta cells in pancreas).

RESULTS

The pancreatic fractional beta cell area was increased by approximately 1.4-fold in human pregnancy, with no change in mean beta cell size. In pregnancy there were more small islets rather than an increase in islet size or beta cells per islet. No increase in beta cell replication or change in beta cell apoptosis was detected, but duct cells positive for insulin and scattered beta cells were increased with pregnancy.

CONCLUSIONS/INTERPRETATION

The adaptive increase in beta cell numbers in human pregnancy is not as great as in most reports in rodents. This increase in humans is achieved by increased numbers of beta cells in apparently new small islets, rather than duplication of beta cells in existing islets, which is characteristic of pregnancy in rodents.

Relationship between fractional pancreatic beta cell area and fasting plasma glucose concentration in monkeys

AIMS/HYPOTHESIS

We sought to establish the relationship between fasting plasma glucose concentrations and pancreatic fractional beta cell area in adult cynomolgus monkeys (Macaca fascicularis).

METHODS

Fasting plasma glucose and pancreatic fractional beta cell area were measured in 18 control and 17 streptozotocin-treated adult primates (17.0 +/- 1.2 vs 15.4 +/- 1.2 years old).

RESULTS

Fasting plasma glucose was increased (12.0 +/- 2.0 vs 3.4 +/- 0.1 mmol/l, p < 0.01) and fractional beta cell area was decreased (0.62 +/- 0.13% vs 2.49 +/- 0.35%, p < 0.01) in streptozotocin-treated monkeys. The relationship between fasting plasma glucose and pancreatic fractional beta cell area was described by a wide range of beta cell areas in controls. In streptozotocin-treated monkeys there was an inflection of fasting blood glucose at approximately 50% of the mean beta cell area in controls with a steep increase in blood glucose for each further decrement in beta cell area.

CONCLUSIONS/INTERPRETATION

In adult non-human primates a decrement in fractional beta cell area of approximately 50% or more leads to loss of glycaemic control.

Pancreatic duct replication is increased with obesity and type 2 diabetes in humans

AIMS/HYPOTHESIS

In a high-fat-fed rat model of type 2 diabetes we noted increased exocrine duct replication. This is a predisposing factor for pancreatitis and pancreatic cancer, both of which are more common in type 2 diabetes. The aim of the study reported here was to establish if obesity and/or type 2 diabetes are associated with increased pancreatic ductal replication in humans.

METHODS

We obtained pancreas at autopsy from 45 humans, divided into four groups: lean (BMI <25 kg/m(2)); obese (BMI >27 kg/m(2)); non-diabetic; and with type 2 diabetes. Pancreases were evaluated after immunostaining for the duct cell marker cytokeratin and Ki67 for replication.

RESULTS

We show for the first time that both obesity and type 2 diabetes in humans are associated with increased pancreatic ductal replication. Specifically, we report that (1) replication of pancreatic duct cells is increased tenfold by obesity, and (2) lean subjects with type 2 diabetes demonstrate a fourfold increase in replication of pancreatic duct cells compared with their lean non-diabetic controls.

CONCLUSIONS/INTERPRETATION

Pancreatic duct cell replication is increased in humans in response to both obesity and type 2 diabetes, potentially providing a mechanism for the increased risk of pancreatitis and pancreatic cancer in those with obesity and/or type 2 diabetes.

Relationship between beta-cell mass and diabetes onset

Regulation of blood glucose concentrations requires an adequate number of beta-cells that respond appropriately to blood glucose levels. beta-Cell mass cannot yet be measured in humans in vivo, necessitating autopsy studies, although both pre- and postmorbid changes may confound this approach. Autopsy studies report deficits in beta-cell mass ranging from 0 to 65% in type 2 diabetes (T2DM), and approximately 70-100% in type 1 diabetes (T1DM), and, when evaluated, increased beta-cell apoptosis in both T1DM and T2DM. A deficit of beta-cell mass of approximately 50% in animal studies leads to impaired insulin secretion (when evaluated directly in the portal vein) and induction of insulin resistance. We postulate three phases for diabetes progression. Phase 1: selective beta-cell cytotoxicity (autoimmune in T1DM, unknown in T2DM) leading to impaired beta-cell function and gradual loss of beta-cell mass through apoptosis. Phase 2: decompensation of glucose control when the pattern of portal vein insulin secretion is sufficiently impaired to cause hepatic insulin resistance. Phase 3: adverse consequences of glucose toxicity accelerate beta-cell dysfunction and insulin resistance. The relative contribution of beta-cell loss versus beta-cell dysfunction to diabetes onset remains an area of controversy. However, because cytotoxicity sufficient to induce beta-cell apoptosis predictably disturbs beta-cell function, it is naive to attempt to distinguish the relative contributions of these linked processes to diabetes onset.

Pancreas volumes in humans from birth to age one hundred taking into account sex, obesity, and presence of type-2 diabetes

Our aims were (1) by computed tomography (CT) to establish a population database for pancreas volume (parenchyma and fat) from birth to age 100 years, (2) in adults, to establish the impact of gender, obesity, and the presence or absence of type-2 diabetes on pancreatic volume (parenchyma and fat), and (3) to confirm the latter histologically from pancreatic tissue obtained at autopsy with a particular emphasis on whether pancreatic fat is increased in type-2 diabetes. We measured pancreas volume in 135 children and 1,886 adults (1,721 nondiabetic and 165 with type-2 diabetes) with no history of pancreas disease who had undergone abdominal CT scan between 2003 and 2006. Pancreas volume was computed from the contour of the pancreas on each CT image. In addition to total pancreas volume, parenchymal volume, fat volume, and fat/parenchyma ratio (F/P ratio) were determined by CT density. We also quantified pancreatic fat in autopsy tissue of 47 adults (24 nondiabetic and 23 with type-2 diabetes). During childhood and adolescence, the volumes of total pancreas, pancreatic parenchyma, and fat increase linearly with age. From age 20–60 years, pancreas volume reaches a plateau (72.4 ± 25.8 cm³ total; 44.5 ± 16.5 cm³ parenchyma) and then declines thereafter. In adults, total (∼32%), parenchymal (∼13%), and fat (∼68%) volumes increase with obesity. Pancreatic fat content also increases with aging but is not further increased in type-2 diabetes. We provide lifelong population data for total pancreatic, parenchymal, and fat volumes in humans. Although pancreatic fat increases with aging and obesity, it is not increased in type-2 diabetes. Clin. Anat. 20:933–942, 2007. © 2007 Wiley-Liss, Inc.

Modestly increased beta cell apoptosis but no increased beta cell replication in recent-onset type 1 diabetic patients who died of diabetic ketoacidosis

AIMS/HYPOTHESIS

Type 1 diabetes is characterised by a deficit in beta cell mass thought to be due to immune-mediated increased beta cell apoptosis. Beta cell turnover has not been examined in the context of new-onset type 1 diabetes with diabetic ketoacidosis.

METHODS

Samples of pancreas were obtained at autopsy from nine patients, aged 12 to 38 years (mean 24.3+/-3.4 years), who had had type 1 diabetes for less than 3 years before death due to diabetic ketoacidosis. Samples of pancreas obtained at autopsy from nine non-diabetic cases aged 11.5 to 38 years (mean 24.2+/-3.4 years) were used as control. Fractional beta cell area (insulin staining), beta cell replication (insulin and Ki67 staining) and beta cell apoptosis (insulin and TUNEL staining) were measured.

RESULTS

In pancreas obtained at autopsy from recent-onset type 1 diabetes patients who had died of diabetic ketoacidosis, the beta cell deficit varied from 70 to 99% (mean 90%). The pattern of beta cell loss was lobular, with almost all beta cells absent in most pancreatic lobules; islets in lobules not devoid of beta cells had reduced or a near-normal complement of beta cells. Beta cell apoptosis was increased in recent-onset type 1 diabetes, but to a surprisingly modest degree given the marked hyperglycaemia (30 mmol/l), acidosis and presumably high NEFA. Beta cell replication, scattered pancreatic beta cells and beta cells in exocrine ducts were not increased in recent-onset type 1 diabetes.

CONCLUSIONS/INTERPRETATION

These findings do not support the notion of active beta cell regeneration by replication in new-onset type 1 diabetes under conditions of diabetic ketoacidosis. The gluco-lipotoxicity reported in isolated human islets may be less evident in vivo.

Effects of the potential chemopreventive agent DMU-135 on adenoma development in the ApcMin+ mouse

DMU-135 (3,4-Methylenedioxy-3',4',5'-trimethoxy chalcone) is a novel anticancer prodrug designed to be activated into a potent tyrosine kinase inhibitor by the tumour selective enzyme activity of the cytochrome P450 enzyme CYP1B1. CYP1B1 is selectively expressed in a wide variety of tumours including colon. The hypothesis was tested that DMU-135 would inhibit Apc(Min/+) mouse gastrointestinal adenoma formation. From 4-18 weeks of age animals received DMU-135 (0.2% w:w) in AIN93G diet. DMU-135 was well tolerated, induced no systemic side-effects and reduced adenoma multiplicity by 46 +/- 18.3% compared to controls (p < 0.001). Further characterisation of this promising chemopreventive agent is required.

Increased islet beta cell replication adjacent to intrapancreatic gastrinomas in humans

AIMS/HYPOTHESIS

Type 1 and type 2 diabetes are characterised by a beta cell deficit. Islet hyperplasia has been described in patients with Zollinger-Ellison syndrome secondary to gastrin-producing tumours (gastrinomas), and gastrin therapy has increased beta cell mass in rodents and human islets in vitro. In the present studies we addressed the following questions: (1) In pancreas specimens from gastrinoma cases, is the fractional beta cell area increased? (2) If so, is this restricted to tumour-adjacent islets or also present in tumour-distant islets? (3) Is new beta cell formation (beta cell replication and islet neogenesis) increased and beta cell apoptosis decreased in pancreas specimens from gastrinoma cases?

METHODS

Pancreas was obtained at surgery from four patients with Zollinger-Ellison syndrome caused by pancreatic gastrinomas and 15 control subjects at autopsy.

RESULTS

Islet fractional beta cell area (p<0.001), islet size (p<0.001) and beta cell replication (Ki67 staining) (p<0.05) were increased in islets adjacent to the tumours, but not in tumour-distant pancreas, compared with control subjects. We did not observe any differences in beta cell apoptosis or in the number of insulin-positive cells in ducts either adjacent to or distant from the tumour.

CONCLUSIONS/INTERPRETATION

One or more factors released by human gastrinomas increase beta cell replication in islets immediately adjacent to the tumour, but not in tumour-distant islets. While these findings demonstrate that adult human beta cells can be driven into the cell cycle, they caution against the therapeutic usefulness of gastrin, since islets located >1 cm away from the gastrinomas did not exhibit changes in beta cell turnover, despite markedly elevated systemic gastrin levels sufficient to cause severe gastrointestinal symptoms.

Direct evidence of attempted beta cell regeneration in an 89-year-old patient with recent-onset type 1 diabetes

AIMS/HYPOTHESIS

We investigated whether there was evidence of attempted beta cell regeneration in the pancreas obtained from a patient with recent-onset type 1 diabetes, and if so by what mechanism this occurred.

SUBJECTS, MATERIALS AND METHODS

We examined pancreas tissue from a lean 89-year-old patient (BMI 18.0 kg/m(2)) with recent-onset type 1 diabetes who had had a distal pancreatectomy to remove a low-grade pancreatic intraepithelial neoplasia.

RESULTS

In the tumour-free tissue, the fractional beta cell area was 0.54+/-0.2% of pancreas area (about one-third of that in non-diabetic humans). CD3-positive T lymphocytes and macrophages had infiltrated the majority of the islets. Subclassification of the T cell population revealed a predominance of CD8-positive cells over CD4-positive cells. Beta cell apoptosis (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelling [TUNEL] staining) was greatly increased, consistent with ongoing immune-mediated beta cell destruction. There was also a marked increase (more than approximately 100-fold) in the frequency of beta cell replication (0.69+/-0.15% Ki67-positive beta cells) in all blocks examined.

CONCLUSIONS/INTERPRETATION

The present report provides direct evidence of attempted beta cell regeneration through the mechanism of beta cell replication in a case of newly diagnosed type 1 diabetes, and affirms that beta cell apoptosis is an important mechanism for beta cell loss in type 1 diabetes.

The mass, but not the frequency, of insulin secretory bursts in isolated human islets is entrained by oscillatory glucose exposure

Insulin is secreted in discrete insulin secretory bursts. Regulation of insulin release is accomplished almost exclusively by modulation of insulin pulse mass, whereas the insulin pulse interval remains stable at approximately 4 min. It has been reported that in vivo insulin pulses can be entrained to a pulse interval of approximately 10 min by infused glucose oscillations. If oscillations in glucose concentration play an important role in the regulation of pulsatile insulin secretion, abnormal or absent glucose oscillations, which have been described in type 2 diabetes, might contribute to the defective insulin secretion. Using perifused human islets exposed to oscillatory vs. constant glucose, we questioned 1) whether the interval of insulin pulses released by human islets is entrained to infused glucose oscillations and 2) whether the exposure of islets to oscillating vs. constant glucose confers an increased signal for insulin secretion. We report that oscillatory glucose exposure does not entrain insulin pulse frequency, but it amplifies the mass of insulin secretory bursts that coincide with glucose oscillations (P < 0.001). Dose-response analyses showed that the mode of glucose drive does not influence total insulin secretion (P = not significant). The apparent entrainment of pulsatile insulin to infused glucose oscillations in nondiabetic humans in vivo might reflect the amplification of underlying insulin secretory bursts that are detected as entrained pulses at the peripheral sampling site, but without changes in the underlying pacemaker activity.

Increased vulnerability of newly forming beta cells to cytokine-induced cell death

AIMS/HYPOTHESIS

Beta cell destruction in type 1 diabetes is apparently mediated by the release of cytokines. We questioned whether cytokine-induced apoptosis preferentially kills replicating beta cells.

MATERIALS AND METHODS

In the first experiment, rat insulinoma (RIN) cells were studied for 36 h by time-lapse video microscopy. Cells were exposed to three doses of a cytokine mixture (maximal concentration: IL-1beta 50 U/ml; TNF-alpha 1,000 U/ml; IFN-gamma 1,000 U/ml) or vehicle and analysed for the total cell number (2-h intervals) and timing of each cell death and division. In the second experiment, isolated human islets were incubated with the same cytokine mixture for 24 h and examined for replication and paired (postmitotic) apoptosis.

RESULTS

In the first experiment, after application of cytokines, apoptosis occurred most frequently immediately after the next or subsequent cell mitosis (p<0.05). In the second experiment, cytokines caused increased apoptosis in human islets, with an increase in the proportion of postmitotic apoptotic pairs (p<0.001).

CONCLUSIONS/INTERPRETATION

Cytokine-induced beta cell death preferentially affects newly forming beta cells, which implies that replicating beta cells might be more vulnerable to cytokine destruction. Efforts to expand beta cell mass in type 1 diabetes by fostering beta cell replication are likely to fail unless cytokine-induced apoptosis is concurrently suppressed.

Sustained beta cell apoptosis in patients with long-standing type 1 diabetes: indirect evidence for islet regeneration?

AIMS/HYPOTHESIS

Type 1 diabetes is widely held to result from an irreversible loss of insulin-secreting beta cells. However, insulin secretion is detectable in some people with long-standing type 1 diabetes, indicating either a small population of surviving beta cells or continued renewal of beta cells subject to ongoing autoimmune destruction. The aim of the present study was to evaluate these possibilities.

MATERIALS AND METHODS

Pancreatic sections from 42 individuals with type 1 diabetes and 14 non-diabetic individuals were evaluated for the presence of beta cells, beta cell apoptosis and replication, T lymphocytes and macrophages. The presence and extent of periductal fibrosis was also quantified.

RESULTS

Beta cells were identified in 88% of individuals with type 1 diabetes. The number of beta cells was unrelated to duration of disease (range 4-67 years) or age at death (range 14-77 years), but was higher (p<0.05) in individuals with lower mean blood glucose. Beta cell apoptosis was twice as frequent in type 1 diabetes as in control subjects (p<0.001), but beta cell replication was rare in both groups. The increased beta cell apoptosis in type 1 diabetes was accompanied by both increased macrophages and T lymphocytes and a marked increase in periductal fibrosis (p<0.001), implying chronic inflammation over many years, consistent with an ongoing supply of beta cells.

CONCLUSIONS/INTERPRETATION

Most people with long-standing type 1 diabetes have beta cells that continue to be destroyed. The mechanisms underlying increased beta cell death may involve both ongoing autoimmunity and glucose toxicity. The presence of beta cells despite ongoing apoptosis implies, by definition, that concomitant new beta cell formation must be occurring, even after long-standing type 1 diabetes. We conclude that type 1 diabetes may be reversed by targeted inhibition of beta cell destruction.

The cancer preventative agent resveratrol is converted to the anticancer agent piceatannol by the cytochrome P450 enzyme CYP1B1

Resveratrol is a cancer preventative agent that is found in red wine. Piceatannol is a closely related stilbene that has antileukaemic activity and is also a tyrosine kinase inhibitor. Piceatannol differs from resveratrol by having an additional aromatic hydroxy group. The enzyme CYP1B1 is overexpressed in a wide variety of human tumours and catalyses aromatic hydroxylation reactions. We report here that the cancer preventative agent resveratrol undergoes metabolism by the cytochrome P450 enzyme CYP1B1 to give a metabolite which has been identified as the known antileukaemic agent piceatannol. The metabolite was identified by high performance liquid chromatography analysis using fluorescence detection and the identity of the metabolite was further confirmed by derivatisation followed by gas chromatography-mass spectrometry studies using authentic piceatannol for comparison. This observation provides a novel explanation for the cancer preventative properties of resveratrol. It demonstrates that a natural dietary cancer preventative agent can be converted to a compound with known anticancer activity by an enzyme that is found in human tumours. Importantly this result gives insight into the functional role of CYP1B1 and provides evidence for the concept that CYP1B1 in tumours may be functioning as a growth suppressor enzyme.

Inhibition of lordosis behavior in male and female rats by androgens and progesterone

Several studies suggest that when manipulated experimentally in adulthood, the lordosis response to estrogen can be increased dramatically in male rats. Because adult-gonadectomized (Gx) animals were used in these studies, the lack of testicular hormones in adulthood may have been a factor. To examine this possibility, adult-Gx rats were implanted with blank (Bk)-, testosterone (T)-, 5alpha-dihydrotestosterone (DHT)-, or progesterone (P)-filled capsules, alone or in combination. We report a new finding, that a combined treatment of T plus P (T+P) at physiological doses for the male, but not T or P alone, reduced lordosis significantly in males, with and without estrogen priming. T+P did not inhibit lordosis in females, nor did this specific treatment affect open field, aggressive, and male copulatory behaviors. In confirming studies done with much higher doses, DHT reduced lordosis in both sexes. DHT and T+P also reduced lordosis in adrenalectomized/Gx males. Mechanisms responsible for the T+P inhibition of lordosis in males are not known, but they may include an upregulation of androgen receptors by P, and this possibility is discussed.

Decrease in beta-cell mass leads to impaired pulsatile insulin secretion, reduced postprandial hepatic insulin clearance, and relative hyperglucagonemia in the minipig

Most insulin is secreted in discrete pulses at an interval of approximately 6 min. Increased insulin secretion after meal ingestion is achieved through the mechanism of amplification of the burst mass. Conversely, in type 2 diabetes, insulin secretion is impaired as a consequence of decreased insulin pulse mass. beta-cell mass is reported to be deficient in type 2 diabetes. We tested the hypothesis that decreased beta-cell mass leads to decreased insulin pulse mass. Insulin secretion was examined before and after an approximately 60% decrease in beta-cell mass achieved by a single injection of alloxan in a porcine model. Alloxan injection resulted in stable diabetes (fasting plasma glucose 7.4 +/- 1.1 vs. 4.4 +/- 0.1 mmol/l; P < 0.01) with impaired insulin secretion in the fasting and fed states and during a hyperglycemic clamp (decreased by 54, 80, and 90%, respectively). Deconvolution analysis revealed a selective decrease in insulin pulse mass (by 54, 60, and 90%) with no change in pulse frequency. Rhythm analysis revealed no change in the periodicity of regular oscillations after alloxan administration in the fasting state but was unable to detect stable rhythms reliably after enteric or intravenous glucose stimulation. After alloxan administration, insulin secretion and insulin pulse mass (but not insulin pulse interval) decreased in relation to beta-cell mass. However, the decreased pulse mass (and pulse amplitude delivered to the liver) was associated with a decrease in hepatic insulin clearance, which partially offset the decreased insulin secretion. Despite hyperglycemia, postprandial glucagon concentrations were increased after alloxan administration (103.4 +/- 6.3 vs. 92.2 +/- 2.5 pg/ml; P < 0.01). We conclude that an alloxan-induced selective decrease in beta-cell mass leads to deficient insulin secretion by attenuating insulin pulse mass, and that the latter is associated with decreased hepatic insulin clearance and relative hyperglucagonemia, thereby emulating the pattern of islet dysfunction observed in type 2 diabetes.

Anesthesia rapidly suppresses insulin pulse mass but enhances the orderliness of insulin secretory process

Induction of anesthesia is accompanied by modest hyperglycemia and a decreased plasma insulin concentration. Most insulin is secreted in discrete pulses occurring at approximately 6- to 8-min intervals. We sought to test the hypothesis that anesthesia inhibits insulin release by disrupting pulsatile insulin secretion in a canine model by use of direct portal vein sampling. We report that induction of anesthesia causes an abrupt decrease in the insulin secretion rate (1.1 +/- 0.2 vs. 0.7 +/- 0.1 pmol. kg(-1). min(-1), P < 0.05) by suppressing insulin pulse mass (630 +/- 121 vs. 270 +/- 31 pmol, P < 0.01). Anesthesia also elicited an approximately 30% higher increase in insulin pulse frequency (P < 0.01) and more orderly insulin concentration profiles (P < 0.01). These effects were evoked by either sodium thiamylal or nitrous oxide and isoflurane. In conclusion, anesthesia represses insulin secretion through the mechanism of a twofold blunting of pulse mass despite an increase in orderly pulse frequency. These data thus unveil independent amplitude and frequency controls of beta-cells' secretory activity in vivo.

Non-haematological solid tumours as surrogate granulocytes: a possible mechanism for metastatic spread

The concept that non-haematological solid tumours utilize normal leukocyte mechanisms, specifically those of granulocytes, to facilitate metastatic spread is presented here. In this article we will address the question of whether the process of metastasis is a phenomenon unique to tumour cells that utilize unique processes that are only found in neoplastic cell populations, or whether neoplastic populations 'turn on' or co-opt latent leukocyte genes normally not expressed by the parental, normal tissue of origin. We suggest that ectopic expression of leukocyte genes in epithelial tumours may be the simplest method for solid tumours to acquire the mechanisms for neoplastic spread through metastasis and may also account for the observed lack of host immunosurveillance of such tumours.

Direct measurement of pulsatile insulin secretion from the portal vein in human subjects

Insulin is secreted in a high frequency pulsatile manner. These pulses are delivered directly into the portal vein and then undergo extraction and dilution before delivery into the systemic circulation. The reported frequency of these insulin pulses estimated in peripheral blood varies from an interpulse interval of 4-20 min. We postulated that this discrepancy is due to the attenuation of the pulse signal in the systemic circulation vs. the portal circulation. In the present study we measured pulsatile insulin release directly in the portal circulation of human subjects who had indwelling transjugular intrahepatic portasystemic stent shunts (TIPSS) to decompress portal hypertension. We quantitated pulsatile insulin secretion in both the overnight fasted state (fasting) and during a hyperglycemic clamp (8 mmol/L). Direct portal vein sampling established that pulsatile insulin secretion in humans has an interval (periodicity) of approximately 5 min. The amplitude (and mass) of the insulin concentration oscillations observed in the portal vein was approximately 5-fold greater than that observed in the arterialized vein and was similar to that observed in the dog. Increased insulin release during hyperglycemia was achieved through amplification of the insulin pulse mass. In conclusion, direct portal vein sampling in humans revealed that the interpulse interval of insulin pulses in humans is about 5 min, and this frequency is also observed when sampling from the systemic circulation using a highly specific insulin assay and 1-min sampling, but is about 4-fold greater than the frequency observed at this site using single site RIAs. We confirm that enhanced insulin release in response to hyperglycemia is achieved by amplification of these high frequency pulses.

Overnight inhibition of insulin secretion restores pulsatility and proinsulin/insulin ratio in type 2 diabetes

Impaired insulin secretion in type 2 diabetes is characterized by decreased first-phase insulin secretion, an increased proinsulin-to-insulin molar ratio in plasma, abnormal pulsatile insulin release, and heightened disorderliness of insulin concentration profiles. In the present study, we tested the hypothesis that these abnormalities are at least partly reversed by a period of overnight suspension of beta-cell secretory activity achieved by somatostatin infusion. Eleven patients with type 2 diabetes were studied twice after a randomly ordered overnight infusion of either somatostatin or saline with the plasma glucose concentration clamped at approximately 8 mmol/l. Controls were studied twice after overnight saline infusions and then at a plasma glucose concentration of either 4 or 8 mmol/l. We report that in patients with type 2 diabetes, 1) as in nondiabetic humans, insulin is secreted in discrete insulin secretory bursts; 2) the frequency of pulsatile insulin secretion is normal; 3) the insulin pulse mass is diminished, leading to decreased insulin secretion, but this defect can be overcome acutely by beta-cell rest with somatostatin; 4) the reported loss of orderliness of insulin secretion, attenuated first-phase insulin secretion, and elevated proinsulin-to-insulin molar ratio also respond favorably to overnight inhibition by somatostatin. The results of these clinical experiments suggest the conclusion that multiple parameters of abnormal insulin secretion in patients with type 2 diabetes mechanistically reflect cellular depletion of immediately secretable insulin that can be overcome by beta-cell rest.

Assessment of insulin secretion in relatives of patients with type 2 (non-insulin-dependent) diabetes mellitus: evidence of early beta-cell dysfunction

To examine beta-cell function in glucose-tolerant offspring of type 2 diabetic families, 41 insulin-resistant (hyperinsulinemic-euglycemic clamp, P < .001) first-degree relatives and 32 controls underwent oral (OGTT) and intravenous (IVGTT) glucose tolerance tests and a constant intravenous glucose infusion (4.0 or 4.5 mg/kg/min) with blood sampling every minute for insulin determinations. Insulin concentration time-series were analyzed with complementary mathematical models (deconvolution and autocorrelation analysis, approximate entropy [ApEn], and coefficient of variation [CV] for a 6-point moving average, together with a combined index for regularity and stationarity [RaS] based on the last 2 measures). During the OGTT, the area under the curve (AUC) for plasma glucose was moderately (11%) but significantly (P < .01) elevated in the relatives despite a trend for increased serum insulin (AUC, P = .14). The acute-phase serum insulin response (IVGTT) did not differ between groups (2,055 +/- 330 v 1,766 +/- 229 pmol/L x 10 min, P = .84) but was inappropriately low (individually, P < .05 v control group) for the degree of insulin resistance in 16 relatives. Deconvolution analysis of the insulin time-series did not uncover differences in either the intersecretory pulse interval (5.8 +/- 0.2 v5.7 +/- 0.2 min/pulse) or the fractional secretory burst amplitude (133% +/- 10% v 116% +/- 7% over basal) between the 2 groups. Similarly, significant autocorrelation coefficients were observed in a comparable number of relatives and control subjects (P = .74). In contrast, the RaS index was significantly higher (ie, insulin time-series was more irregular and nonstationary) in the relatives (0.221 +/- 0.194) than in the controls (-0.318 +/- 0.176, P < .05), primarily attributed to the pattern of insulin secretion in relatives with a strong genetic burden. In conclusion, nonstationary and disorderly insulin secretion patterns during glucose stimulation and a low acute-phase serum insulin response associated with significant insulin resistance suggest early beta-cell regulatory dysfunction in individuals genetically predisposed to type 2 diabetes mellitus prior to any evident alterations in insulin secretory burst frequency or mass.

The mechanism of islet amyloid polypeptide toxicity is membrane disruption by intermediate-sized toxic amyloid particles

NIDDM is characterized by islet amyloid deposits and decreased beta-cell mass. Islet amyloid is derived from the locally expressed protein islet amyloid polypeptide (IAPP). While it is now widely accepted that abnormal aggregation of IAPP has a role in beta-cell death in NIDDM, the mechanism remains unknown. We hypothesized that small IAPP aggregates, rather than mature large amyloid deposits, are cytotoxic. Consistent with this hypothesis, freshly dissolved human (h)-IAPP was cytotoxic when added to dispersed mouse and human islet cells, provoking the formation of abnormal vesicle-like membrane structures in association with vacuolization and cell death. Human islet cell death occurred by both apoptosis and necrosis, predominantly between 24 and 48 h after exposure to h-IAPP. In contrast, the addition to dispersed islet cells of matured h-IAPP containing large amyloid deposits of organized fibrils was seldom associated with vesicle-like structures or features of cell death, even though the cells were often encased in the larger amyloid deposits. Based on these observations, we hypothesized that h-IAPP cytotoxicity is mediated by membrane damage induced by early h-IAPP aggregates. Consistent with this hypothesis, application of freshly dissolved h-IAPP to voltage-clamped planar bilayer membranes (a cell-free in vitro system) also caused membrane instability manifested as a marked increase in conductance, increased membrane electrical noise, and accelerated membrane breakage, effects that were absent using matured h-IAPP or rat IAPP solutions. Light-scattering techniques showed that membrane toxicity corresponded to h-IAPP aggregates containing approximately 25-6,000 IAPP molecules, an intermediate-sized amyloid particle that we term intermediate-sized toxic amyloid particles (ISTAPs). We conclude that freshly dissolved h-IAPP is cytotoxic and that this cytotoxicity is mediated through an interaction of ISTAPs with cellular membranes. Once ISTAPs mature into amyloid deposits comprising >10(6) molecules, the capacity of h-IAPP to cause membrane instability and islet cell death is significantly reduced or abolished. These data may have implications for the mechanism of cell death in other diseases characterized by local amyloid formation (such as Alzheimer's disease).

Gonadal steroid-dependent GAL-IR cells within the medial preoptic nucleus (MPN) and the stimulatory effects of GAL within the MPN on sexual behaviors

More GAL-I cells exist within sexually dimorphic cell groups of the medial preoptic nucleus (MPN) in male rate than females, a large percentage of estrogen-concentrating cells within MPN cell groups are also GAL-immunoreactive (GAL-IR), and significantly more GAL-IR cells are visible with estrogen or its precursor, testosterone. Gonadal steroids also increase the size (diameter) of MPN GAL-IR cells and the number of GAL-IR cell processes within a portion of the MPN called the "GAL-IR MPOA plexus," which exists in males only. GAL microinjected into the MPN stimulated male-typical sexual behaviors, with more testosterone required in females than males. Immunoneutralization with anti-GAL serum inhibited male-typical sexual behavior, indicating a role for endogenous GAL within the MPN. Microinjection of GAL into the MPN also stimulated female-typical sexual behaviors in estrogen-treated females and males, and GAL within the MPN dramatically overrode an inhibition of lordosis by dihydrotestosterone in rats of both sexes.

A novel assay in vitro of human islet amyloid polypeptide amyloidogenesis and effects of insulin secretory vesicle peptides on amyloid formation

Human islet amyloid polypeptide (IAPP) is a 37-residue peptide that is co-secreted with insulin by the beta-cell and might be involved in the pathogenesis of non-insulin-dependent diabetes mellitus. We developed an improved assay in vitro based on the fluorescence of bound thioflavin T to study factors affecting amyloidogenesis. Monomeric IAPP formed amyloid fibrils, as detected by increased fluorescence and by electron microscopy. Fluorimetric analysis revealed that the initial rate of amyloid formation was: (1) proportional to the peptide monomer concentration, (2) maximal at pH 9.5, (3) maximal at 200 mMKCl, and (4) proportional to temperature from 4 to 37 degreesC. We found that 5-fold and 10-fold molar excesses of proinsulin inhibited fibril formation by 39% and 59% respectively. Insulin was somewhat more potent with 5-fold and 10-fold molar excesses inhibiting fibril formation by 69% and 73% respectively, whereas C-peptide had no effect at these concentrations. Thus at physiological ratios of IAPP to insulin, insulin and proinsulin, but not C-peptide, can retard amyloidogenesis. Because insulin resistance or hyperglycaemia increase the IAPP-to-insulin ratio, increased intracellular IAPP compared with insulin expression in genetically predisposed individuals might contribute to intracellular amyloid formation, beta-cell death and the genesis of non-insulin-dependent diabetes mellitus.

Further evidence for a possible role of conformation in the immunogenicity and antigenicity of the oxidative DNA lesion, 8-oxo-2'deoxyguanosine

Damage to DNA by reactive oxygen species is acknowledged to be an important factor in a number of pathological conditions, including ageing and carcinogenesis. As a consequence, the development of methods for the sensitive detection and quantitation of oxidative DNA lesions has been of paramount importance. The oxidatively modified base product which has achieved most attention is 8-oxodeoxyguanosine (8-oxodG) and is a recognised marker of oxidative DNA damage. Although both polyclonal and monoclonal antibodies have previously been raised to 8-oxodG these have, for the most part failed to recognise this lesion within the DNA polymer. We have, through dilution cloning, produced a monoclonal antibody which appears to preferentially recognise 8-oxodG over deoxyguanosine (dG) in single-stranded oxidatively modified DNA. Such discrimination was not apparent when the DNA was double-stranded. Previous work has shown that 8-oxodG favours the syn glycosidic conformation due to steric repulsion, whereas dG assumes the anti. We present initial data that appear to support the postulate that it is these differences in conformation, in addition to structural recognition of the lesion itself, which are responsible for the discrimination, by our antibody of 8-oxodG over dG in single-stranded DNA.

Islet amyloid-associated diabetes in obese A(vy)/a mice expressing human islet amyloid polypeptide

We have previously shown that hemizygous transgenic mice expressing human islet amyloid polypeptide (hIAPP) in pancreatic beta-cells have no diabetic phenotype, whereas in the homozygous state, they developed severe, early-onset hyperglycemia associated with impaired insulin secretion and beta-cell death. We investigated the possibility that when the hemizygous mice are crossed onto an obese, insulin-resistant strain such as agouti viable yellow (A(vy)/a), they would exhibit a phenotype more akin to human type 2 diabetes. The hIAPP-expressing A(vy) males (TG-Y) displayed fasting hyperglycemia at 90 days of age and by 1 year progressed to severe hyperglycemia relative to their nontransgenic counterparts. Plasma insulin concentrations and pancreatic insulin content dropped 10- to 20-fold, suggesting severe impairment of beta-cell function. Histopathological findings revealed beta-cell degeneration and loss consistent with the drop in the plasma insulin concentration. In addition, large deposits of IAPP amyloid were present in TG-Y islets. We conclude that in transgenic mice expressing hIAPP, insulin resistance can induce overt, slow-onset diabetes associated with islet amyloid and decreased beta-cell mass.

Effects of testosterone and progesterone on brain 5alpha-reductase and aromatase in Long-Evans males and comparison of aromatase in Long-Evans vs. Sprague-Dawley rats

We investigated medial basal hypothalamic-preoptic area (MBH-POA) 5alpha-reductase and aromatase enzyme activities in gonadally intact and castrated adult Long-Evans (L-E) male rats treated with testosterone (T), progesterone (P), and a combination of T+P. MBH-POA 5alpha-reductase and aromatase activities did not differ significantly among the groups. The lack of a difference in MBH-POA aromatase between control and castrated L-E animals was unexpected. In two further experiments, MBH-POA aromatase was examined in intact and castrated L-E and Sprague-Dawley (S-D) rats, using direct and indirect assays. The activity in castrated S-D (but again, not in L-E) rats significantly decreased compared to control values. These data suggest that the absence of gonads does not decrease MBH-POA aromatase in adult L-E rats.

Glucagon-like peptide 1 increases mass but not frequency or orderliness of pulsatile insulin secretion

Glucagon-like peptide 1 (GLP-1) is a peptide hormone that is released from the gut after luminal stimulation. The hormone is a potent insulin secretagogue and is a potential novel pharmaceutical adjuvant in the treatment of NIDDM. Insulin is secreted as a series of punctuated secretory bursts superimposed on a basal insulin release. Recently, the contribution of these secretory bursts to overall insulin secretion has been evaluated, and studies using catheterization across the pancreas in a canine model and studies using deconvolution in humans have revealed that the majority of insulin is released during these secretory bursts. Moreover, the main regulation of insulin secretion is through perturbation of mass and frequency of these secretory bursts. The mode of delivery of insulin into the circulation seems important for insulin action, and it is therefore important to know the impact of a potential therapeutic insulin secretagogue on the mode of insulin secretion. To assess the effects of GLP-1 on the mass, frequency, amplitude, and overall contribution of pulsatile insulin secretion, we used a recently validated deconvolution model to examine these variables before and during infusion of GLP-1 in eight healthy men (age 28 +/- 2 years; BMI 24 +/- 2 kg/m2). At a constant glucose infusion (2.5 mg x kg-1 x min-1), near-steady state was reached at 75 min, and sampling was performed every minute at t = 75-115 and 145-185 min. At t = 115 min, an infusion of saline or GLP-1 (50 pmol x kg-1 x min-1) was given. The regularity of insulin secretion was measured by approximate entropy, a recently developed mathematical statistic, applied herein to assess the regularity in a hormone concentration time series. After GLP-1 infusion, there was an abrupt increase in the peripheral concentrations of serum C-peptide (696 +/- 65 vs. 1,538 +/- 165 pmol/l) and insulin (49 +/- 8 vs. 138 +/- 21 pmol/l) concentrations. This increase was mainly due to an increase in the pulsatile component of insulin secretion that was achieved by a fourfold increase in secretory burst mass (28.2 +/- 4.4 vs. 100.1 +/- 15.8 pmol x l-1 x pulse-1; P < 0.001), and amplitude (12.7 +/- 2.2 vs. 4.3 +/- 7.7 pmol x l-1 x min-1; P < 0.002), whereas the secretory burst frequency was not affected by GLP-1 (11.5 +/- 0.7 vs. 12.6 +/- 0.6 pulses/h; P = 0.4). As a consequence, the detected contribution of pulsatile to overall insulin secretion was increased from 56 +/- 4 to 77 +/- 4% (P < 0.005). The orderliness of the insulin release process was not deteriorated by short-term GLP-1 infusion as assessed by approximate entropy (1.19 +/- 0.04 vs. 1.18 +/- 0.04; P = 0.7).

In humans at least 75% of insulin secretion arises from punctuated insulin secretory bursts

Detection of insulin secretory bursts in peripheral blood is hampered by hepatic insulin extraction, dilution in the systemic insulin pool, and time-delayed damping of secretory burst amplitude. Previous studies in dogs in vivo and other experiments in vitro have shown that approximately 70% of all insulin is released within distinct insulin secretory bursts. To establish a method for detection and quantification of pulsatile insulin release in humans on the basis of peripheral insulin concentration measurements, we used a high-sensitivity, -specificity, and -precision insulin enzyme-linked immunosorbent assay (ELISA) and optimized an established deconvolution methodology to quantify the frequency, mass, and amplitude of insulin secretory bursts as well as to estimate the relative contribution of pulsatile insulin release to overall insulin secretion. By use of minutely sampled serum insulin concentrations measured by a highly sensitive insulin ELISA and insulin kinetics of 2.8 min (first half-life), 5.0 min (second half-life), and a fractional slow component of 0.28, the deconvolved insulin secretion rates in 20 healthy subjects during glucose infusion (4.5 mg.kg-1.min-1) could be resolved into a series (4.7 +/- 0.1 min/pulse) of approximately symmetric insulin secretory bursts with a mean mass of 87 +/- 12 pmol.l-1 pulse-1 and a mean amplitude (maximal release rate) of 35 +/- 4.7 pmol.l-1.min-1. The relative contribution of pulsatile to overall insulin secretion was 75 +/- 1.6% (range 59-85%). We conclude that in vivo insulin secretion in humans during nominal glucose stimulation consists of a series of punctuated insulin secretory bursts accounting for > or = 75% of total insulin secretion.

Small heat shock proteins inhibit in vitro A beta(1-42) amyloidogenesis

We demonstrate that small heat shock proteins (sHsp) inhibit in vitro amyloid formation by the Alzheimer's A beta(1-42) polypeptide as detected by a thioflavine T fluorescence assay and electron microscopy. Human sHsp27 (0.50-3.0 microM) inhibited amyloid formation from 20 microM A beta(1-42) by 23-75%, in 24 h. In contrast, treatment of pre-formed amyloid with 0.5-3.0 microM sHsp27 only reduced the fluorescence signal by 6-36%. The data suggest that ordered fibril formation may represent a form of off-pathway aggregation that can be prevented by chaperone action. The data raise the possibility that age-related changes in chaperone function could contribute toward the pathogenesis of Alzheimer's and other amyloid-associated diseases.

IGF-I inhibits burst mass of pulsatile insulin secretion at supraphysiological and low IGF-I infusion rates

Insulin-like growth factor I (IGF-I) shares structural and functional features with insulin, affects carbohydrate metabolism, and inhibits insulin secretion. Insulin secretion is pulsatile, and it is regulated by changing frequency and/or mass of secretory bursts. To examine the mechanism of IGF-I's inhibition of insulin secretion, eight healthy volunteers were studied three times. During glucose infusion (2.5 mg x kg(-1) x min(-1)) blood was sampled minutely at time 75-200 min for triplicate insulin concentration measurements by enzyme-linked immunosorbent assay (ELISA; coefficient of variation 2.1%). Time 125 min infusion of saline, low-dose IGF-I (0.025 microg x kg(-1) x min(-1)) or high-dose IGF-I (0.15 microg x kg(-1) x min(-1)) was commenced and continued until 200 min. Data were compared before (75-125 min) vs. during infusion (150-200 min). Insulin concentration time series were deconvolved, using validated pulse-detection criteria, to assess insulin secretory burst mass and frequency. During saline infusion no time effect occurred. After IGF-I infusion, serum C-peptide decreased (582 +/- 85 vs. 481 +/- 82 pM, low-dose IGF-I, P < 0.05; 539 +/- 84 vs. 427 +/- 69 pM, high-dose IGF-I, P < 0.01). Total insulin secretion rates decreased by 17 and 21%, respectively, via specific inhibition of the insulin secretory burst mass (31 +/- 8 vs. 20 +/- 4 pmol/ml, low-dose IGF-I, P = 0.06; 22 +/- 4 vs. 17 +/- 3 pmol/ml, high-dose IGF-I, P < 0.05), whereas the frequency was not affected (10.5 +/- 1.3 vs. 10.7 +/- 1.3 pulses/h, low-dose IGF-I, P = 0.85; 8.7 +/- 1.0 vs. 11.1 +/- 1.2 min/pulse, high-dose IGF-I, P = 0.15). We conclude that IGF-I inhibits pulsatile insulin secretion by specific inhibition of mass but not frequency of secretory bursts.

Disorderly and nonstationary insulin secretion in relatives of patients with NIDDM

To further explore the role of the beta-cell as a pathogenic factor behind non-insulin-dependent diabetes mellitus (NIDDM), insulin secretion at modest hyperglycemia was examined in 15 healthy first-degree relatives of NIDDM patients and 13 anthropometrically and age-matched controls. The oral glucose tolerance test was normal in all, but the relatives had impaired insulin-stimulated glucose uptake (P < 0.05). During a constant intravenous glucose infusion we performed a time-series analysis of serum insulin in samples obtained at 1-min intervals for 75 min (60-135 min). The recently introduced scale- and model-independent statistic approximate entropy (ApEn) and the coefficient of variation for a 6- (9 and 15) point moving average (MA) were applied to test regularity and stationarity, respectively, of insulin secretion. Both ApEn and 6-point MA were able to significantly discern the insulin time series of the two groups (P < 0.05), demonstrating a higher degree of irregularity and nonstationarity among the offspring. Moreover, when the two complementary sets of statistics were combined into a single "index of nonpulsatility," an even more notable distinction was available (P < 0.01). No relationship was found between altered insulin secretion and insulin resistance. In conclusion, this experimental and statistical model demonstrates that the stimulated insulin secretion of glucose-tolerant relatives of NIDDM patients is characterized by disorderliness. Whether the model can predict the risk for developing a clinically important beta-cell dysfunction remains to be clarified.

Mechanisms of sulfonylurea's stimulation of insulin secretion in vivo: selective amplification of insulin secretory burst mass

Although sulfonylureas enhance insulin secretion, it is unknown whether these hypoglycemic chemicals stimulate insulin secretion through the augmentation of the pulsatile or basal modes of insulin release. Enhanced pulsatile insulin could occur in turn through amplification of the burst mass or an increase in burst frequency. To address the mechanism of sulfonylurea action, we employed a recently validated canine model with a portal vein sampling catheter and flow probe to measure pulsatile insulin secretion in vivo directly in response to tolbutamide infusion or ingestion. After a 16-h fast, seven dogs were studied in the postabsorptive basal state and during a tolbutamide (0.2 mg/min) infusion when their plasma glucose concentrations were clamped at euglycemia. Insulin concentrations in the carotid artery (basal vs. tolbutamide, 85 +/- 12 vs. 325 +/- 66 pmol/l; P < 0.01) and portal vein (basal vs. tolbutamide, 345 +/- 55 vs. 1,288 +/- 230 pmol/l; P < 0.01) increased during tolbutamide infusion, but the portal vein plasma flow did not change. Increased plasma insulin concentrations were achieved by a fourfold increase in the total insulin secretion rate (2.3 +/- 0.2 to 9.4 +/- 1.9 pmol x kg(-1) x min(-1); basal vs. tolbutamide, P < 0.01). The augmented total insulin secretion was achieved mechanistically via a marked and selective increase in the insulin secretory burst mass (basal vs. tolbutamide, 266 +/- 64 vs. 817 +/- 144 pmol/pulse; P < 0.01), with no change in portal-vein insulin pulse frequency (basal vs. tolbutamide, 10.1 +/- 0.6 vs. 11.1 +/- 0.8 pulses/h; P = 0.3). Oral (250 mg) tolbutamide also magnified the endogenous insulin secretion rate by the preferential amplification of the secretory pulse mass (basal vs. tolbutamide, 167 +/- 37 vs. 362 +/- 50 pmol/pulse; P < 0.01). Neither the infusion nor the ingestion of tolbutamide changed the calculated clearance rates of endogenously secreted insulin. We conclude that sulfonylurea (tolbutamide) induced insulin secretion in vivo is achieved by the highly selective amplification of insulin secretory burst mass with no change in basal insulin release or the frequency of the beta-cell-network pacemaker.

Effects of glucose ingestion versus infusion on pulsatile insulin secretion. The incretin effect is achieved by amplification of insulin secretory burst mass

In the present studies, we used a recently validated canine model to determine 1) if glucose ingestion stimulates insulin secretion by amplifying the pulsatile component of insulin release, and if so, 2) whether this effect is achieved preferentially through burst mass or frequency modulation, and 3) if the mechanism of incretin effect of insulin secretion is mediated via the pulsatile mode of secretion. We report that 30 g of glucose ingestion stimulates an approximately 550% increase in the overall rate of insulin secretion (1.8 +/- 0.2 to 11.6 +/- 1.5 pmol.kg-1.min-1), which is achieved via an approximately 400% increase in the mass of insulin secreted per burst (202 +/- 38 to 1,003 +/- 147 pmol/pulse, P < 0.001) and a approximately 40% increase in burst frequency (8.7 +/- 0.5 to 12.3 +/- 0.6 pulse/h, P < 0.001). Of the insulin secreted after glucose ingestion, 68% (+/-4) was released in discrete secretory bursts. Further analyses showed that the incretin effect of ingested (GPO) versus infused glucose (GIV) is achieved through regulation of pulsatile insulin secretion. Glucose ingestion led to an approximately 70% greater rate of insulin secretion than intravenous glucose delivery (10.0 +/- 1.6 vs. 5.9 +/- 0.9 pmol.kg-1.min-1, P < 0.005, GPO vs. GIV). This incretin effect was achieved by the specific mechanism of an approximately 70% greater pulse mass (930 +/- 196 vs. 558 +/- 97 pmol/pulse, P < 0.02, GPO vs. GIV) but with a comparable pulse frequency (13.1 +/- 0.9 vs. 12.0 +/- 0.5 pulses/h, P = 0.14, n = 9 dogs, GPO vs. GIV). We conclude that in vivo glucose regulates overall insulin secretion almost exclusively by amplification of the pulsatile mode of insulin secretion, and that the incretin effect is achieved by preferential enhancement of insulin secretory burst mass.

Islet amyloid and islet amyloid polypeptide in cynomolgus macaques (Macaca fascicularis): an animal model of human non-insulin-dependent diabetes mellitus

To further characterize spontaneous diabetes mellitus in cynomolgus macaques (Macaca fascicularis) as a model for human non-insulin-dependent diabetes mellitus (NIDDM), we evaluated the morphologic characteristics of the endocrine pancreas of 4 diabetic and 12 age-matched nondiabetic cynomolgus macaques. In addition, the cDNA-predicted amino acid sequence for islet amyloid polypeptide (IAPP) of this species was determined. Islet amyloid deposits exhibiting typical congophilia and green birefringence were found in 4/4 diabetic animals and in 8/12 nondiabetics. Islet amyloid deposits were significantly more extensive in the diabetic macaques (P = 0.001), in which they occupied a mean of 60% of the islet area. In contrast, in the nondiabetic group the maximum islet area occupied by amyloid was 24% (group mean = 6.8%), with four animals having no detectable islet amyloid. Amyloid deposits consistently showed immunoreactivity for IAPP but not for insulin. Comparisons between group means for diabetic versus nondiabetic macaques showed significantly greater islet area (P = 0.01, 85,390 versus 36,540 microns 2) and significantly greater islet area fraction (P = 0.02, 0.065 versus 0.032) for the diabetic group. The cDNA-predicted amino acid sequence for cynomolgus IAPP was identical to that previously reported for pig-tail macaques (M. nemestrina) and had 92%, 86%, and 84% amino acid sequence identity with human, domestic cat, and murine IAPPs, respectively. These findings support the use of cynomolgus macaques as an animal model of human NIDDM.

Treatment with growth hormone and dexamethasone in mice transgenic for human islet amyloid polypeptide causes islet amyloidosis and beta-cell dysfunction

Islet amyloid derived from islet amyloid polypeptide (IAPP) is a well-recognized feature of type II diabetes. However, the mechanism of islet amyloidogenesis is unknown. In vitro studies suggest that amino acid residues 20-29 in human, but not mouse, IAPP confer amyloidogenicity consistent with the absence of spontaneous islet amyloidosis in mice. Several clinical and in vitro studies suggest that increased synthetic rates of IAPP predispose to IAPP-amyloidosis. In the present study, we sought to test the hypothesis that pharmacological induction of insulin resistance in a mouse transgenic (TG) for human IAPP would induce islet amyloid and beta-cell dysfunction. TG and non-transgenic (N-TG) control mice were treated with both rat growth hormone (12 micrograms/day) and dexamethasone (0.24 mg/day) (dex/GH) or received no treatment for 4 weeks, after which animals were killed to examine islet morphology. Treatment with dex/GH caused hyperglycemia (7.3 +/- 0.4 vs. 5.2 +/- 0.1 mmol/l, TG vs. N-TG, P < 0.001) associated with a decreased plasma insulin concentration (595 +/- 51 vs. 996 +/- 100 pmol/l, TG vs. N-TG, P < 0.05) in TG versus control mice. Islet amyloid was induced in treated TG mice but not in control mice. Islet amyloid was identified in both intra- and extracellular deposits, the former being associated with evidence of beta-cell degeneration. We conclude that dex/GH treatment in mice TG for human IAPP induces IAPP-derived islet amyloid, hyperglycemia, and islet dysfunction. The present model recapitulates the islet morphology and phenotype of type II diabetes.

Spontaneous diabetes mellitus in transgenic mice expressing human islet amyloid polypeptide

The islet in non-insulin-dependent diabetes mellitus (NIDDM) is characterized by loss of beta cells and large local deposits of amyloid derived from the 37-amino acid protein, islet amyloid polypeptide (IAPP). We have hypothesized that IAPP amyloid forms intracellularly causing beta-cell destruction under conditions of high rates of expression. To test this we developed a homozygous transgenic mouse model with high rates of expression of human IAPP. Male transgenic mice spontaneously developed diabetes mellitus by 8 weeks of age, which was associated with selective beta-cell death and impaired insulin secretion. Small intra- and extracellular amorphous IAPP aggregates were present in islets of transgenic mice during the development of diabetes mellitus. However, IAPP derived amyloid deposits were found in only a minority of islets at approximately 20 weeks of age, notably after development of diabetes mellitus in male transgenic mice. Approximately 20% of female transgenic mice spontaneously developed diabetes mellitus at 30+ weeks of age, when beta-cell degeneration and both amorphous and amyloid deposits of IAPP were present. We conclude that overexpression of human IAPP causes beta-cell death, impaired insulin secretion, and diabetes mellitus. Large deposits of IAPP derived amyloid do not appear to be important in this cytotoxicity, but early, small amorphous intra- and extracellular aggregates of human IAPP were consistently present at the time of beta-cell death and therefore may be the most cytotoxic form of IAPP.

Effects of somatostatin on pulsatile insulin secretion: elective inhibition of insulin burst mass

Although it is well known that somatostatin inhibits net insulin secretion, it is unknown whether this is achieved by regulation of the basal or pulsatile components of insulin secretion and, if the latter, whether this is through modulation of pulse mass or frequency. We addressed these questions with a canine model. Portal vein blood was sampled at 1-min intervals in five dogs for 60 min before (basal) and 90 min after ingestion of 30 g glucose on two different occasions, during a saline (SAL) or a somatostatin (SMS, 175 ng/min) infusion. Plasma glucose concentrations were similar during SAL and SMS. SMS had no effect on pulse frequency before (8.4 +/- 0.7 vs. 9.2 +/- 1.0 pulses/h, SMS vs. SAL, P = 0.54) or after glucose (13.3 +/- 1.1 vs. 11.6 +/- 0.9 pulses/h, SMS vs. SAL, P = 0.22). In contrast, SMS decreased insulin pulse mass in the postabsorptive (84 +/- 28 vs. 214 +/- 73 pmol/pulse, SMS vs. SAL, P < 0.05) and fed states (676 +/- 143 vs. 913 +/- 183 pmol/pulse, SMS vs. SAL, P < 0.05). In the postabsorptive state, SMS decreased insulin clearance by approximately 50% (0.32 +/- 0.04 vs. 0.60 +/- 0.09 l/min, P < 0.05), but after glucose ingestion, insulin clearance was comparable during SMS or SAL (0.72 +/- 0.04 vs. 0.80 +/- 0.08 l/min, P = 0.4). SMS appeared to alter insulin clearance through modulation of insulin pulse amplitude, because in the postabsorptive state clearance was closely correlated to the pulse amplitude (r = + 0.87, P < 0.0001). In conclusion, somatostatin regulates the rate of insulin secretion by selective inhibition of pulsatile insulin secretion. Regulation of secretory burst mass (and amplitude) may secondarily influence transhepatic and thus total body clearance of endogenously secreted insulin and thereby serve as a novel mechanism to dictate the systemic insulin concentration.

Galanin microinjected into the medial preoptic nucleus facilitates female- and male-typical sexual behaviors in the female rat

Galanin (GAL) microinjected within the sexually dimorphic medial preoptic nucleus (MPN) facilitates male-typical sexual behaviors in the male rat, a response that requires the presence of testosterone. As in the male, GAL-immunoreactive cells located within the MPN of the female also concentrate gonadal steroids and become less immunoreactive after gonadectomy. Thus, to investigate sexual behaviors in the female and to determine whether effects are comparable to those obtained in the male, GAL was microinjected unilaterally within the MPN of female rats. We report that GAL stimulated female-typical lordosis behavior after estrogen priming, and that the effect was not due to general arousal as measured by nonspecific locomotor activities. In a separate experiment, GAL microinjected within the MPN dose-responsively increased mount frequencies and decreased mount latencies in testosterone-primed females. A higher dose of testosterone was required in females for this stimulation of male-typical sexual behavior than required in a previous experiment in males.

Comparison of the ability of bread versus bread plus meat to treat and prevent subsequent hypoglycemia in patients with insulin-dependent diabetes mellitus

We sought to determine whether treatment of hypoglycemia with a snack containing both protein and carbohydrate results in more prolonged protection against subsequent hypoglycemia than ingestion of carbohydrate alone. We studied six insulin-dependent diabetic subjects on two occasions. On both occasions subjects received a variable overnight insulin infusion to achieve euglycemia followed by a constant insulin infusion (approximately 0.5 mU x kg(-1) x min(-1)) designed to produce hypoglycemia. When glucose reached 50 mg/dL, subjects were fed a snack consisting of either bread (approximately 85 kcal) or bread plus meat (approximately 205 kcal). Both contained 15 g of carbohydrate. The insulin infusion was continued for the next 3 h or until glucose again fell to 50 mg/dL. Although bread plus meat resulted in a more marked rise (P < 0.05) in glucagon than did bread alone, neither the post treatment peak glucose concentration (73 +/- 4 vs. 70 +/- 6 mg/dL) nor the subsequent rate of fall of glucose (0.42 +/- 0.10 us. -0.35 +/- 0.07 mg/dL/min) differed. The present study shows that the rate of redevelopment of hypoglycemia does not differ after eating bread or bread plus meat. Therefore treatment of hypoglycemia with a protein-enriched snack merely adds calories rather prolonged protection against subsequent hypoglycemia.

Measurement of insulin pulsatility by sampling directly from the portal vein: a surgical model for placement of long-term prehepatic vascular sampling catheters

A practical and repeatable method for measurement of pulsatile insulin release in the dog was developed by direct, chronic cannulation of the portal vein cephalad to the pancrease and the entry point of the cranial pancreaticoduodenal vein, with subsequent exteriorization of the sampling catheter. Mixed breed male dogs of various body weights and ages underwent midline laparotomy for exposure of the portal vein system. After exposure the portal vein was dissected free and cannulated through a purse-string suture placed just caudad (approximately 1 cm) to the entry point of the cranial pancreaticoduodenal vein with a cuffed, medical grade, silastic catheter. The catheter was advanced cranial to a point just distal to the level of the liver and secured in place via the purse-string suture and a single stay suture. The catheter was then passed through the dorsolateral abdominal wall and routed subcutaneously to a point between the shoulder blades. After catheter plug attachment the catheter was tested for patency, flushed, heparin locked, then was secured to the subcutaneous tissue between the scapulas. The dorsal skin wound and abdominal incision were closed in a routine manner, and the dogs recovered from anesthesia. Catheter patency and function in all dogs were maintained for periods up to 4 weeks. No postoperative complications such as catheter tract infections occurred, maintenance was minimal, and all dogs were afforded complete freedom of movement and activity throughout the study, with no requirement for cumbersome jackets or wraps.

Diabetes mellitus in cystic fibrosis is characterized by islet amyloidosis

A high proportion of patients with cystic fibrosis (CF) develop diabetes mellitus. In common with type II diabetes mellitus, diabetes mellitus in CF is characterized by a progressive decline in beta-cell function and an approximately 50% decline in beta-cell mass. It is not known whether islet amyloidosis (characteristic of type II diabetes mellitus) is present in diabetes mellitus complicating CF. To address this, pancreatic samples were obtained at autopsy from 9 control cases (without CF) and 41 cases of CF that were, in turn, subdivided into 13 nondiabetic, 12 borderline diabetic, and 16 diabetic cases based on clinical criteria. Islet amyloid was detected by light microscopy in 69% cases of CF with diabetes mellitus, 17% of cases with borderline diabetes mellitus, and none of the nondiabetic cases. Islet amyloid was not present in any of the control cases. Islet amyloidosis derived from islet amyloid polypeptide is a characteristic feature of diabetes mellitus in CF as well as type II diabetes mellitus.

Impact of sampling technique on appraisal of pulsatile insulin secretion by deconvolution and cluster analysis

Little is known about the optimal experimental conditions for assessing pulsatile insulin secretion in vivo. To address this, we employed a recently validated canine model (n = 12) to determine the consequences of 1) sampling from the systemic circulation (SC) vs. the portal vein (PV), 2) sampling intensity and duration, and 3) deconvolution vs. cluster analysis on assessing pulsatile insulin secretion. PV vs. SC sampling resulted in a approximately 40% higher pulse frequency by deconvolution (9.0 +/- 0.5 vs. 6.6 +/- 0.9 pulses/h, P < 0.02) and cluster analysis (7.5 +/- 0.3 vs. 5.6 +/- 0.6 pulses/h, P < 0.01) due to a higher signal-to-noise ratio (19 +/- 4.8 PV vs. 12 +/- 1.8 SC). PV sampling also disclosed a higher calculated contribution of the pulsatile vs. nonpulsatile mode of delivery to total insulin secretion (57 +/- 4 vs. 28 +/- 5%, P < 0.001). Analysis of the relevance of sampling intensity revealed that 1-min data yielded a markedly higher estimate of pulse frequency with PV sampling than 2-min data (9.0 +/- 0.5 vs. 5.4 +/- 0.5, P < 0.02, deconvolution; 7.5 +/- 0.3 vs. 4.3 +/- 0.6 pulses/h, P < 0.001, cluster). Optimal sampling duration was shown to be 40 min or more. We conclude that the resolving power of the analytical tool, the anatomic site of blood withdrawal, the frequency of blood sampling, and the duration of the total observation interval all significantly influence estimated insulin secretory pulse frequency and the fraction of insulin secreted in pulses. With the assumption that PV 1-min insulin data constitute the "gold standard," our in vivo inferences of 7.5-9.0 insulin pulses/h closely recapitulate in vitro islet secretory activity.

Human islet amyloid polypeptide expression in COS-1 cells. A model of intracellular amyloidogenesis

Non-insulin-dependent diabetes mellitus is characterized by concurrent loss of beta-cells and deposition of islet amyloid derived from islet amyloid polypeptide (IAPP). We have previously demonstrated that IAPP-derived amyloid forms intracellularly in humans with chronic excess insulin expression (eg, insulinoma and insulin receptor antibody-induced insulin resistance). To determine whether overexpression of IAPP results in intracellular amyloid in mammalian cells, we transfected COS cells with vectors expressing amyloidogenic human IAPP or non-amyloidogenic rat IAPP. Transfected COS-1 cells secreted comparable amounts of human IAPP and rat IAPP (2.1 to 2.8 nmol/L/48 hours). After 96 hours, 90% of cells expressing human IAPP contained amyloid fibrils and were degenerating or dead, whereas cells transfected with rat IAPP lacked amyloid and were viable. Thus, overexpression of human IAPP can result in intracellular amyloid formation that is associated with cell death, suggesting that intracellular amyloid may play a role in beta-cell loss in non-insulin-dependent diabetes mellitus.

Islet amyloid polypeptide in pancreatic tissue of children with persistent hyperinsulinemic hypoglycemia caused by primary islet hyperplasia and nesidioblastosis

Islet amyloid is a recognized characteristic finding in insulinoma and secondary islet hyperplasia resulting from severe insulin resistance. Little information is available about the presence of islet amyloid in primary islet hyperplasia (nesidioblastosis) of childhood. Here we report that islet amyloid was not present in 12 children with primary islet hyperplasia associated with hyperinsulinemic hypoglycemia.

Islet amyloidosis in a patient with chronic massive insulin resistance due to antiinsulin receptor antibodies

We report islet hyperplasia, nesidioblastosis, and abundant islet amyloidosis (derived from islet amyloid polypeptide) in a case of severe insulin resistance due to a circulating antiinsulin receptor antibody. Massive chronic beta-cell stimulation (as well as noninsulin-dependent diabetes mellitus and insulinoma) appears to be associated with islet amyloid.

Augmented effect of short-term pulsatile versus continuous insulin delivery on lipid metabolism but similar effect on whole-body glucose metabolism in obese subjects

The present study was designed to examine the effect of pulsatile versus continuous insulin delivery on glucose and lipid metabolism in insulin-resistant subjects. Six obese women (body mass index, 40.0 +/- 2.8 kg/m2) underwent a euglycemic glucose clamp (plasma glucose, 90 mg/dL) twice. In random order, insulin was infused intravenously for 375 minutes either at a constant rate (0.4 mU/kg/min) or in a pulsatile manner (2.4 mU/kg/min for 2 minutes followed by an off interval of 10 minutes). Endogenous insulin release was suppressed by infusion of somatostatin (250 micrograms/h). Mean circulating insulin concentrations were similar during the two protocols (pulsatile v continuous infusion, 60 +/- 10 v 56 +/- 9 mU/L), but pulsatile infusion was accompanied by oscillations with an amplitude of 120 mU/L. After 6 hours of pulsatile versus continuous insulin, isotopically determined total glucose disposal (3-3H-glucose) and hepatic glucose production (HGP) were comparable (pulsatile v continuous, 2.80 +/- 0.56 v 2.82 +/- 0.51 and 0.37 +/- 0.14 v 0.32 +/- 0.17 mg/kg/min). However, the rate of glucose oxidation (indirect calorimetry) was augmented (P < .05), whereas lipid oxidation tended to be diminished (.10 > P > .05) following pulsatile infusion. In addition, blood glycerol was more suppressed with pulsatile (31 +/- 9 nmol/L) than with continuous infusion (36 +/- 10 nmol/L, P < .05), whereas blood lactate, alanine, and 3-hydroxybutyrate were similar in the two infusion protocols.(ABSTRACT TRUNCATED AT 250 WORDS)