Discovery of a novel glucose metabolism in cancer: The role of endoplasmic reticulum beyond glycolysis and pentose phosphate shunt

Cancer metabolism is characterized by an accelerated glycolytic rate facing reduced activity of oxidative phosphorylation. This “Warburg effect” represents a standard to diagnose and monitor tumor aggressiveness with ¹⁸F-fluorodeoxyglucose whose uptake is currently regarded as an accurate index of total glucose consumption. Studying cancer metabolic response to respiratory chain inhibition by metformin, we repeatedly observed a reduction of tracer uptake facing a marked increase in glucose consumption. This puzzling discordance brought us to discover that ¹⁸F-fluorodeoxyglucose preferentially accumulates within endoplasmic reticulum by exploiting the catalytic function of hexose-6-phosphate-dehydrogenase. Silencing enzyme expression and activity decreased both tracer uptake and glucose consumption, caused severe energy depletion and decreased NADPH content without altering mitochondrial function. These data document the existence of an unknown glucose metabolism triggered by hexose-6-phosphate-dehydrogenase within endoplasmic reticulum of cancer cells. Besides its basic relevance, this finding can improve clinical cancer diagnosis and might represent potential target for therapy.

Abstract 1182: Metformin affects breast cancer cell growth and disturbs an IGF1/insulin related gene network that correlates with breast cancer progression

Background

Obesity and the insulin resistance syndrome are risk factors for breast cancer and might also affect breast cancer progression. The anti-diabetic drug Metformin (METF) reduces the breast cancer risk in diabetic women. Insulin like growth factor 1 (IGF1) and insulin are involved in breast cancer tumorigenesis and progression.

We tested the effect of METF on the IGF1/insulin pathway and its involvement in breast cancer progression.

Methods

We developed a prognostic signature based on IGF1/insulin pathway genes using the Stockholm breast cancer microarray dataset of 149 cases for training and primary validation and the Uppsala dataset of 249 for external validation. The effect of METF on the prognostic gene set identified was tested in vitro on a panel of breast cancer cell lines. METF effects on proliferation and glucose metabolism were analyzed in vitro and in vivo. The insulin receptor substrate 2 (IRS2) was silenced by transfection with shRNA-lentiviral vectors. Xenograft growth, in the presence and absence of METF, was studied and 18FDG-uptake was measured in vitro and in vivo.

Results

A 15-gene signature (Insulin sensitivity score, ISS) was developed and predicted breast cancer metastasis with an accuracy similar to the Recurrence Score. ISS genes were expressed at variable levels in a breast cancer cell line panel and showed variable responsiveness to METF. The high expression correlation among the ISS genes observed in untreated breast cancer cell lines was lost upon treatment with METF. METF reduced breast cancer cell growth in vitro with IC50 values ranging from 1mM to 25mM. Growth of MDA-MB-231 cells and hyper-invasive subpopulations derived therefrom was reduced in vivo by oral administration of METF to xenografted nude mice. Response to METF in terms of IC50 values correlated with basal expression of the 15 ISS genes with the strongest inverse correlation observed for IRS2. Stable silencing of IRS2 reduced the MDA-231 cell responsiveness to METF in vitro.

Discussion

METF acts on the insulin/IGF1 axis by disturbing a network of breast cancer progression related genes and appears to depend in its action on the expression of IRS2 that inversely correlates with the sensitivity of cell lines to the drug. The disruption of the ISS gene network is expected to correlate with an effect on breast cancer growth and progression and in fact, mouse xenografts show reduced growth upon treatment with METF. IRS2 appears to be a major mediator of METF effects.

Citation Format: Alessia I. Esposito, Adriana Amaro, Giovanna Angelini, Laura Emionite, Alessandra Gennari, Stefano Indraccolo, Davide Maggi, Cecilia Marini, Barabara Salani, Gianmario Sambuceti, Maria Pia Sormani, Ulrich Pfeffer. Metformin affects breast cancer cell growth and disturbs an IGF1/insulin related gene network that correlates with breast cancer progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1182. doi:10.1158/1538-7445.AM2015-1182

Impaired increase of plasma abscisic Acid in response to oral glucose load in type 2 diabetes and in gestational diabetes

The plant hormone abscisic acid (ABA) is present and active in humans, regulating glucose homeostasis. In normal glucose tolerant (NGT) human subjects, plasma ABA (ABAp) increases 5-fold after an oral glucose load. The aim of this study was to assess the effect of an oral glucose load on ABAp in type 2 diabetes (T2D) subjects. We chose two sub-groups of patients who underwent an oral glucose load for diagnostic purposes: i) 9 treatment-naive T2D subjects, and ii) 9 pregnant women with gestational diabetes (GDM), who underwent the glucose load before and 8–12 weeks after childbirth. Each group was compared with matched NGT controls. The increase of ABAp in response to glucose was found to be abrogated in T2D patients compared to NGT controls. A similar result was observed in the women with GDM compared to pregnant NGT controls; 8–12 weeks after childbirth, however, fasting ABAp and ABAp response to glucose were restored to normal in the GDM subjects, along with glucose tolerance. We also retrospectively compared fasting ABAp before and after bilio-pancreatic diversion (BPD) in obese, but not diabetic subjects, and in obese T2D patients, in which BPD resulted in the resolution of diabetes. Compared to pre-BPD values, basal ABAp significantly increased 1 month after BPD in T2D as well as in NGT subjects, in parallel with a reduction of fasting plasma glucose. These results indicate an impaired hyperglycemia-induced ABAp increase in T2D and in GDM and suggest a beneficial effect of elevated ABAp on glycemic control.

IGF1 regulates PKM2 function through Akt phosphorylation

Pyruvate kinase M2 (PKM2) acts at the crossroad of growth and metabolism pathways in cells. PKM2 regulation by growth factors can redirect glycolytic intermediates into key biosynthetic pathway. Here we show that IGF1 can regulate glycolysis rate, stimulate PKM2 Ser/Thr phosphorylation and decrease cellular pyruvate kinase activity. Upon IGF1 treatment we found an increase of the dimeric form of PKM2 and the enrichment of PKM2 in the nucleus. This effect was associated to a reduction of pyruvate kinase enzymatic activity and was reversed using metformin, which decreases Akt phosphorylation. IGF1 induced an increased nuclear localization of PKM2 and STAT3, which correlated with an increased HIF1α, HK2, and GLUT1 expression and glucose entrapment. Metformin inhibited HK2, GLUT1, HIF-1α expression and glucose consumption. These findings suggest a role of IGFIR/Akt axis in regulating glycolysis by Ser/Thr PKM2 phosphorylation in cancer cells.

Direct inhibition of hexokinase activity by metformin at least partially impairs glucose metabolism and tumor growth in experimental breast cancer

Emerging evidence suggests that metformin, a widely used anti-diabetic drug, may be useful in the prevention and treatment of different cancers. In the present study, we demonstrate that metformin directly inhibits the enzymatic function of hexokinase (HK) I and II in a cell line of triple-negative breast cancer (MDA-MB-231). The inhibition is selective for these isoforms, as documented by experiments with purified HK I and II as well as with cell lysates. Measurements of ¹⁸F-fluoro-deoxyglycose uptake document that it is dose- and time-dependent and powerful enough to virtually abolish glucose consumption despite unchanged availability of membrane glucose transporters. The profound energetic imbalance activates phosphorylation and is subsequently followed by cell death. More importantly, the “in vivo” relevance of this effect is confirmed by studies of orthotopic xenografts of MDA-MB-231 cells in athymic (nu/nu) mice. Administration of high drug doses after tumor development caused an evident tumor necrosis in a time as short as 48 h. On the other hand, 1 mo metformin treatment markedly reduced cancer glucose consumption and growth. Taken together, our results strongly suggest that HK inhibition contributes to metformin therapeutic and preventive potential in breast cancer.

Metformin, cancer and glucose metabolism

Metformin is the first-line treatment for type 2 diabetes. Results from several clinical studies have indicated that type 2 diabetic patients treated with metformin might have a lower cancer risk. One of the primary metabolic changes observed in malignant cell transformation is an increased catabolic glucose metabolism. In this context, once it has entered the cell through organic cation transporters, metformin decreases mitochondrial respiration chain activity and ATP production that, in turn, activates AMP-activated protein kinase, which regulates energy homeostasis. In addition, metformin reduces cellular energy availability and glucose entrapment by inhibiting hexokinase-II, which catalyses the glucose phosphorylation reaction. In this review, we discuss recent findings on molecular mechanisms that sustain the anticancer effect of metformin through regulation of glucose metabolism. In particular, we have focused on the emerging action of metformin on glycolysis in normal and cancer cells, with a drug discovery perspective.

Metformin impairs glucose consumption and survival in Calu-1 cells by direct inhibition of hexokinase-II

The anti-hyperglycaemic drug metformin has important anticancer properties as shown by the direct inhibition of cancer cells proliferation. Tumor cells avidly use glucose as a source for energy production and cell building blocks. Critical to this phenotype is the production of glucose-6-phosphate (G6P), catalysed by hexokinases (HK) I and II, whose role in glucose retention and metabolism is highly advantageous for cell survival and proliferation. Here we show that metformin impairs the enzymatic function of HKI and II in Calu-1 cells. This inhibition virtually abolishes cell glucose uptake and phosphorylation as documented by the reduced entrapment of ¹⁸F-fluorodeoxyglucose. In-silico models indicate that this action is due to metformin capability to mimic G6P features by steadily binding its pocket in HKII. The impairment of this energy source results in mitochondrial depolarization and subsequent cell death. These results could represent a starting point to open effective strategies in cancer prevention and treatment.

Caveolin-1 and polymerase I and transcript release factor: new players in insulin-like growth factor-I receptor signaling

Caveolae are plasma membrane regions enriched in Caveolin proteins which regulate vesicular transport, endocytosis, and cell signaling. IGF-I receptor (IGF-IR) localizes in caveolae and tyrosine phosphorylates Caveolin-1 (Cav-1), the most represented caveolar protein. Cav-1 participates to IGF-IR internalization and signaling directly interacting with IGF-IR and its substrates. Recently, polymerase I and transcript release factor (PTRF) or Cavin-1, has been identified in the caveolar backbone. PTRF does not play a Cav-1 ancillary role and emerging data support a direct role of PTRF in IGF-IR signaling. PTRF and Cav-1 can bind IGF-IR and regulate IGF-IR internalization and plasma membrane replacement, mechanisms frequently deregulated in cancer cells. Although the exact roles of Cav-1 and IGF-IR in human cancer continue to be a matter of some debate, there is a strong evidence for an association between Cav-1 and IGF-IR in cancer development. With the discovery of IGF-IR interaction with PTRF in caveolae, new insight emerged to understand the growing functions of these domains in IGF-I action.

Metformin temporal and localized effects on gut glucose metabolism assessed using 18F-FDG PET in mice

In the course of metformin treatment, staging abdominal cancer lesions with (18)F-FDG PET images is often hindered by the presence of a high bowel radioactivity. The present study aimed to verify the mechanism underlying this phenomenon.

METHODS

Fifty-three mice were submitted to dynamic acquisitions of (18)F-FDG kinetics under fasting conditions. Three small-animal PET scans were obtained over a 4-mo study period. The animals were subdivided into 4 groups according to the following metformin administration protocol: group 1, untreated mice (n = 15); group 2, mice exposed to metformin treatment (750 mg/kg/d) for the 48 h before each PET study (pulsed, n = 10); group 3, mice treated for the whole study period (prolonged, n = 10); and group 4, mice in which prolonged treatment was interrupted 48 h before PET (interrupted, n = 8). The rate constant of (18)F-FDG uptake was estimated by Patlak analysis. At the end of the study, the ileum and colon were harvested, washed, and counted ex vivo. Two further groups, of 5 animals each, were included to evaluate the effect of prolonged metformin treatment on phosphorylated adenosine monophosphate (AMP)-activated protein kinase (pAMPK) form and gene expression for thioredoxin-interacting protein (TXNIP).

RESULTS

Pulsed treatment did not modify gut tracer retention with respect to the untreated group. Conversely, prolonged treatment induced a progressive increase in (18)F-FDG uptake that selectively involved the colonic wall, without any significant contamination of bowel content. This effect persisted after a complete drug washout in the interrupted group. These responses were paralleled by increased pAMPK availability and by reduced expression of TXNIP messenger RNA in colonic enterocytes exposed to prolonged metformin treatment.

CONCLUSION

Metformin causes a selective increase in colonic (18)F-FDG uptake. This effect appears after a relatively long period of treatment and persists soon after drug washout. Accordingly, the increased bowel glucose metabolism reflects a biologic response to chronic metformin treatment characterized by increased levels of pAMPK and reduced levels of TXNIP.

The plant hormone abscisic acid increases in human plasma after hyperglycemia and stimulates glucose consumption by adipocytes and myoblasts

The plant hormone abscisic acid (ABA) is released from glucose-challenged human pancreatic β cells and stimulates insulin secretion. We investigated whether plasma ABA increased during oral and intravenous glucose tolerance tests (OGTTs and IVGTTs) in healthy human subjects. In all subjects undergoing OGTTs (n=8), plasma ABA increased over basal values (in a range from 2- to 9-fold). A positive correlation was found between the ABA area under the curve (AUC) and the glucose AUC. In 4 out of 6 IVGTTs, little or no increase of ABA levels was observed. In the remaining subjects, the ABA increase was similar to that recorded during OGTTs. GLP-1 stimulated ABA release from an insulinoma cell line and from human islets, by ∼10- and 2-fold in low and high glucose, respectively. Human adipose tissue also released ABA in response to high glucose. Nanomolar ABA stimulated glucose uptake, similarly to insulin, in rat L6 myoblasts and in murine 3T3-L1 cells differentiated to adipocytes, by increasing GLUT-4 translocation to the plasma membrane. Demonstration that a glucose load in humans is followed by a physiological rise of plasma ABA, which can enhance glucose uptake by adipose tissues and muscle cells, identifies ABA as a new mammalian hormone involved in glucose metabolism.

Circulating Reg1α proteins and autoantibodies to Reg1α proteins as biomarkers of β-cell regeneration and damage in type 1 diabetes

Type 1 diabetes is an autoimmune disease where β-cells are in a constant process of death and renewal. Reg genes play a role in β-cells regeneration. Reg proteins may be target of an autoimmune response in type 1 diabetes with consequent production of autoantibodies and failure of regeneration. The objective of this work was to characterize the role of Reg1α proteins and anti-Reg1α antibodies as biomarkers of β-cell regeneration and damage. Serum levels of Reg1α protein were investigated in 87 type 1 diabetic subjects (31 newly diagnosed and 56 long standing), 63 type 2 diabetic subjects, 39 subjects with systemic lupus erythematosus (SLE), a nonpancreatic autoimmune disorder, and 64 healthy subjects. The presence of anti-Reg1α antibodies and correlation with metabolic, immune, and genetic parameters were analyzed in diabetic subjects. Increased levels of Reg1α protein were observed in newly diagnosed (p=0.002), and long standing (p=0.001) type 1 diabetes patients and type 2 diabetic subjects (p<0.001). Anti-Reg1α antibodies were found in 47% of patients with type 1 diabetes. No correlation was found with metabolic, immune, and genetic parameters. Patients with SLE showed no increase in Reg1α protein. We report here for the first time raised serum Reg1α protein in type 1 and type 2 diabetes and anti-Reg1α antibodies in type 1 diabetes. Reg1α levels appear not to be influenced by genetic or metabolic control. These findings allow considering future studies on Reg1α protein and autoantibody as new tools in the evaluation and monitoring of β-cells regeneration and autoimmunity.

IGF-IR internalizes with Caveolin-1 and PTRF/Cavin in HaCat cells

BACKGROUND

Insulin-like growth factor-I receptor (IGF-IR) is a tyrosine kinase receptor (RTK) associated with caveolae, invaginations of the plasma membrane that regulate vesicular transport, endocytosis and intracellular signaling. IGF-IR internalization represents a key mechanism of down-modulation of receptors number on plasma membrane. IGF-IR interacts directly with Caveolin-1 (Cav-1), the most relevant protein of caveolae. Recently it has been demonstrated that the Polymerase I and Transcript Release Factor I (PTRF/Cavin) is required for caveolae biogenesis and function. The role of Cav-1 and PTRF/Cavin in IGF-IR internalization is still to be clarified.

METHODOLOGY/PRINCIPAL FINDINGS

We have investigated the interaction of IGF-IR with Cav-1 and PTRF/Cavin in the presence of IGF1in human Hacat cells. We show that IGF-IR internalization triggers Cav-1 and PTRF/Cavin translocation from plasma membrane to cytosol and increases IGF-IR interaction with these proteins. In fact, Cav-1 and PTRF/Cavin co-immunoprecipitate with IGF-IR during receptor internalization. We found a different time course of co-immunoprecipitation between IGF-IR and Cav-1 compared to IGF-IR and PTRF/Cavin. Cav-1 and PTRF/Cavin silencing by siRNA differently affect surface IGF-IR levels following IGF1 treatment: Cav-1 and PTRF/Cavin silencing significantly affect IGF-IR rate of internalization, while PTRF/Cavin silencing also decreases IGF-IR plasma membrane recovery. Since Cav-1 phosphorylation could have a role in IGF-IR internalization, the mutant Cav-1Y14F lacking Tyr14 was transfected. Cav-1Y14F transfected cells showed a reduced internalization of IGF-IR compared with cells expressing wild type Cav-1. Receptor internalization was not impaired by Clathrin silencing. These findings support a critical role of caveolae in IGF-IR intracellular traveling.

CONCLUSIONS/SIGNIFICANCE

These data indicate that Caveolae play a role in IGF-IR internalization. Based on these findings, Cav-1 and PTRF/Cavin could represent two relevant and distinct targets to modulate IGF-IR function.

Beta-cell function improvement after biliopancreatic diversion in subjects with type 2 diabetes and morbid obesity

In subjects with obesity and type 2 diabetes mellitus (T2DM), biliopancreatic diversion (BPD) improves glucose stimulated insulin secretion, whereas the effects on other secretion mechanisms are still unknown. Our objective was to evaluate the early effects of BPD on nonglucose-stimulated insulin secretion. In 16 morbid obese subjects (9 with T2DM and 7 with normal fasting glucose (NFG)), we measured insulin secretion after glucose-dependent arginine stimulation test and after intravenous glucose tolerance test (IVGTT) before and 1 month after BPD. After surgery the mean weight lost was 13% in both groups. The acute insulin response during IVGTT was improved in T2DM after BDP (from 55 +/- 10 to 277 +/- 91 pmol/l, P = 0.03). A reduction of insulin response to arginine was observed in NFG, whereas opposite was found in T2DM. In particular, acute insulin response to arginine at basal glucose concentrations (AIR(basal)) was reduced but insulin response at 14 mmol/l of plasma glucose (AIR(14)) was increased. Therefore, after BPD any statistical difference in AIR(14) between NFG and T2DM disappeared (1,032 +/- 123 for NFG and 665 +/- 236 pmol/l for T2DM, P = ns). The same was observed for Slope(AIR), a measure of glucose potentiation, reduced in T2DM before BPD but increased after surgery, when no statistically significant difference resulted compared with NFG (Slope(AIR) after BPD: 78 +/- 11 in NFG and 56 +/- 18 pmol/l in T2DM, P = ns). In conclusion, in obese T2DM subjects 1 month after BPD we observed a great improvement of both glucose- and nonglucose-stimulated insulin secretions. The mechanisms by which BDP improve insulin secretion are still unknown.

Optimization of flow reserve measurement using SPECT technology to evaluate the determinants of coronary microvascular dysfunction in diabetes

PURPOSE

The aim of this study was to validate a new method to measure regional myocardial perfusion reserve (MPR) with technetium-labelled tracers in patients with type 2 diabetes mellitus (DM2).

METHODS

A total of 40 consecutive DM2 patients without history of coronary artery disease (CAD) and 7 control subjects were recruited. Dipyridamole myocardial blood flow index (MBF) was assessed by measuring first transit counts in the pulmonary artery and myocardial count rate from gated SPECT images using (99m)Tc-labelled tracers. The corresponding MBF index was estimated 2 h later according to the same procedure. Regional myocardial perfusion reserve (MPR) was defined as the ratio between dipyridamole and baseline MBF using a 17-segment left ventricular (LV) model. Coronary flow reserve (CFR) was estimated by transthoracic contrast echo Doppler monitoring of flow velocity in the left anterior descending coronary artery (LAD) during the same session.

RESULTS

Estimated MPR was higher in control subjects than in patients (3.36 +/- 0.66 vs 1.91 +/- 0.61, respectively, p < 0.01). In patients, LAD CFR and LAD MPR were 2.01 +/- 0.78 vs 1.93 +/- 0.63, respectively (p = ns). The agreement between the two techniques was documented by their close correlation (r = 0.92, p < 0.001) and confirmed by the Bland-Altman analysis. Reversible perfusion defects occurred in 13 patients (32%) who showed similar MPR values as the remaining 27 (2.10 +/- 0.71 vs 1.83 +/- 0.71, respectively, p = ns). Finally, MPR was closely correlated with age (r = -0.50, p < 0.01) and time elapsed from the diagnosis of DM2 (r = -0.51, p < 0.01).

CONCLUSION

LV regional MPR can be accurately estimated with the broadly available single photon technology. Application of this method to DM2 patients documents the presence of a microvascular dysfunction homogeneously distributed throughout the LV walls and most frequently not associated with reversible perfusion defects.

Hypoadiponectinemia in lipodystrophic HIV individuals: a metabolic marker of subclinical cardiac damage

BACKGROUND AND AIM

To evaluate cardiovascular abnormalities in highly active antiretroviral therapy (HAART) treated HIV patients with no signs or symptoms of cardiovascular impairment, and to assess the relative role of multiple concomitant risk factors.

METHODS AND RESULTS

Forty-four consecutive HIV subjects (mean age 41+/-6 yrs) were enrolled. Inclusion criteria were HIV infection, CD4+cell count>150/ml, HAART treatment for at least 4 years. Metabolic serum levels, morphological and functional echocardiographic parameters were assessed in all subjects. Sixteen healthy age and sex matched subjects with no cardiovascular risk factors were recruited as controls. HIV patients showed increased left ventricular mass index with reduced mid-wall fractional shortening (mFS) when compared to controls (50.2+/-10.5 vs. 38.6+/-14.4, p=0.05 and 18.3+/-0.6 vs. 21.9+/-0.7, p<0.05, respectively). Twenty-nine patients were lipodystrophic (LD) and showed a longer HAART period (p=0.0004) and greater use of protease inhibitors (PI) (p=0.001). Coronary flow reserve (CFR) was significantly reduced in HIV patients as compared to controls (p<0.0001), as it was in LD subjects when compared to non-lipodystrophic ones (NLD) (p<0.001). Adiponectin concentrations were found to be significantly lower in LD subjects than in NLD ones (7.8+/-0.8 vs. 13.8+/-1.2 microg/ml, p=0.01), and showed a direct correlation with CFR. In multiple regression analysis, insulin, HDL and adiponectin accounted for 63% of CFR variations.

CONCLUSIONS

Left ventricular hypertrophy, depressed mFS and reduced CFR represent the main signs of subclinical cardiac damage in HIV subjects treated with HAART. Hypoadiponectinemia in these subjects seems to be a metabolic risk factor of cardiovascular impairment.

Caveolin-1 down-regulation inhibits insulin-like growth factor-I receptor signal transduction in H9C2 rat cardiomyoblasts

Caveolin (Cav)-1, the major caveolar protein, directly interacts with IGF-I receptor (IGF-IR) and its intracellular substrates. To determine the role of Cav-1 in IGF-IR signaling, we transfected H9C2 cells with small interfering RNA specific for Cav-1-siRNA. The selective down-regulation of Cav-1 (90%) was associated with a smaller reduction of Cav-2, whereas Cav-3 expression was unaffected. A significant reduction of IGF-IR tyrosine phosphorylation in Cav-1-siRNA H9C2 cells was found compared with H9C2 control cells (Ctr-siRNA). The reduced IGF-IR autophosphorylation resulted in a decrease of insulin receptor substrate-1, Shc, and Akt activation. In addition, in Cav-1-siRNA H9C2 cells, IGF-I did not prevent apoptosis, suggesting that Cav-1 is required to mediate the antiapoptotic effect of IGF-I in cardiomyoblasts. The down-regulation of Cav-1 decreased IGF-IR activation and affected the ability of IGF-I to prevent apoptosis after serum withdrawal also in human umbilical vein endothelial cells. These results demonstrate that: 1) Cav-1 down-regulation negatively affects IGF-IR tyrosine phosphorylation; 2) this effect causes a reduced activation of insulin receptor substrate-1, Shc, and Akt; and 3) Cav-1 is involved in IGF-IR antiapoptotic signaling after serum deprivation.

Restoration of acute insulin response in T2DM subjects 1 month after biliopancreatic diversion

OBJECTIVE

Biliopancreatic diversion (BPD) restores normal glucose tolerance in a few weeks in morbid obese subjects with type 2 diabetes, improving insulin sensitivity. However, there is less known about the effects of BPD on insulin secretion. We tested the early effects of BPD on insulin secretion in obese subjects with and without type 2 diabetes.

METHODS AND PROCEDURES

Twenty-one consecutive morbid obese subjects, 9 with type 2 diabetes (T2DM) and 12 with normal fasting glucose (NFG) were evaluated, just before and 1 month after BPD, by measuring body weight (BW), glucose, adipocitokines, homeostasis model assessment of insulin resistance (HOMA-IR), acute insulin response (AIR) to e.v. glucose and the insulinogenic index adjusted for insulin resistance ([DeltaI5/DeltaG5]/HOMA-IR).

RESULTS

Preoperatively, those with T2DM differed from those with NFG in showing higher levels of fasting glucose, reduced AIR (57.9 +/- 29.5 vs. 644.9 +/- 143.1 pmol/l, P < 0.01) and reduced adjusted insulinogenic index (1.0 +/- 0.5 vs. 17.6 +/- 3.9 1/mmol(2), P < 0.001). One month following BPD, in both groups BW was reduced (by approximately 11%), but all subjects were still severely obese; HOMA-IR and leptin decreased significanlty, while high-molecular weight (HMW) adiponectin and adjusted insulinogenic index increased. In the T2DM group, fasting glucose returned to non-diabetic values. AIR did not change in the NFG group, while in the T2DM group it showed a significant increase (from 58.0 +/- 29.5 to 273.8 +/- 47.2 pmol/l, P < 0.01). In the T2DM group, the AIR percentage variation from baseline was significantly related to changes in fasting glucose (r = 0.70, P = 0.02), suggesting an important relationship exists between impaired AIR and hyperglycaemia.

DISCUSSION

BPD is able to restore AIR in T2DM even just 1 month after surgery. AIR restoration is associated with normalization of fasting glucose concentrations.

High-molecular weight adiponectin isoforms increase after biliopancreatic diversion in obese subjects

OBJECTIVE

Our objective was to test the effect of biliopancreatic diversion (BDP) in adiponectin multimerization. Adiponectin, the major protein secreted by adipose tissue, circulates in plasma in different isoforms. The most clinically relevant oligomers are high-molecular weight (HMW) multimers and low-molecular weight (LMW) trimers. Contrasting data on the effect of weight loss on adiponectin isoforms have been reported.

RESEARCH METHODS AND PROCEDURES

We measured total plasma adiponectin and HMW and LMW adiponectin oligomers (by Western blot analysis) before and 1 month after BPD, in 18 severely obese subjects.

RESULTS

One month after BPD, body weight decreased approximately 11%. Total adiponectin showed significant increase after BPD. In addition, we found a significant increase in HMW (percentage) adiponectin oligomers. We found a significant inverse correlation between HMW (percentage) and BMI before and after BPD. Homeostasis model of assessment-insulin resistance decreased significantly after the BPD, without any significant correlation with total serum adiponectin and adiponectin oligomers.

DISCUSSION

A moderate weight loss after BPD increases total and HMW adiponectin oligomers. The significant correlation between BMI and HMW (percentage) adiponectin oligomers but not between BMI and total adiponectin might indicate a role of body fat mass in regulation of adiponectin multimerization. These data suggest that HMW oligomers represent a very sensitive parameter to short-term BMI changes after BPD.