Presence of retinopathy and incident kidney and cardiovascular events in type 2 diabetes with normoalbuminuria - A post-hoc analysis of the PRIORITY randomized clinical trial

AIMS

Baseline diabetic retinopathy (DR) and risk of development of microalbuminuria, kidney function decline, and cardiovascular events (CVEs) in type 2 diabetes.

METHODS

Post-hoc analysis of the PRIORITY study including 1758 persons with type 2 diabetes and normoalbuminuria followed for a median of 2.5 (IQR: 2.0-3.0) years. DR diagnosis included non-proliferative and proliferative abnormalities, macular oedema, or prior laser treatment. Cox models were fitted to investigate baseline DR presence with development of persistent microalbuminuria (urinary albumin-creatinine ratio > 30 mg/g); chronic kidney disease (CKD) G3 (eGFR <60 ml/min/1.73m²); and CVE. Models were adjusted for relevant risk factors.

RESULTS

At baseline, 304 (17.3 %) had DR. Compared to persons without DR, they were older (mean ± SD: 62.7 ± 7.7 vs 61.4 ± 8.3 years, p = 0.019), had longer diabetes duration (17.9 ± 8.4 vs. 10.6 ± 7.0 years, p < 0.001), and higher HbA_1c (62 ± 13 vs. 56 ± 12 mmol/mol, p < 0.001). The adjusted hazard ratios of DR at baseline for development of microalbuminuria (n = 197), CKD (n = 166), and CVE (n = 64) were: 1.50 (95%CI: 1.07, 2.11), 0.87 (95%CI: 0.56, 1.34), and 2.61 (95%CI: 1.44, 4.72), compared to without DR.

CONCLUSIONS

Presence of DR in normoalbuminuric type 2 diabetes was associated with an increased risk of developing microalbuminuria and CVE, but not with kidney function decline.

Early detection of diabetic kidney disease by urinary proteomics and subsequent intervention with spironolactone to delay progression (PRIORITY): a prospective observational study and embedded randomised placebo-controlled trial

BACKGROUND

Microalbuminuria is an early sign of kidney disease in people with diabetes and indicates increased risk of cardiovascular disease. We tested whether a urinary proteomic risk classifier (CKD273) score was associated with development of microalbuminuria and whether progression to microalbuminuria could be prevented with the mineralocorticoid receptor antagonist spironolactone.

METHODS

In this multicentre, prospective, observational study with embedded randomised controlled trial (PRIORITY), we recruited people with type 2 diabetes, normal urinary albumin excretion, and preserved renal function from 15 specialist centres in ten European countries. All participants (observational cohort) were tested with the CKD273 classifier and classified as high risk (CKD273 classifier score >0·154) or low risk (≤0·154). Participants who were classified as high risk were entered into a randomised controlled trial and randomly assigned (1:1), by use of an interactive web-response system, to receive spironolactone 25 mg once daily or matched placebo (trial cohort). The primary endpoint was development of confirmed microalbuminuria in all individuals with available data (observational cohort). Secondary endpoints included reduction in incidence of microalbuminuria with spironolactone (trial cohort, intention-to-treat population) and association between CKD273 risk score and measures of impaired renal function based on estimated glomerular filtration rate (eGFR; observational cohort). Adverse events (particularly gynaecomastia and hyperkalaemia) and serious adverse events were recorded for the intention-to-treat population (trial cohort). This study is registered with the EU Clinical Trials Register (EudraCT 20120-004523-4) and ClinicalTrials.gov (NCT02040441) and is completed.

FINDINGS

Between March 25, 2014, and Sept 30, 2018, we enrolled and followed-up 1775 participants (observational cohort), 1559 (88%) of 1775 participants had a low-risk urinary proteomic pattern and 216 (12%) had a high-risk pattern, of whom 209 were included in the trial cohort and assigned to spironolactone (n=102) or placebo (n=107). The overall median follow-up time was 2·51 years (IQR 2·0-3·0). Progression to microalbuminuria was seen in 61 (28%) of 216 high-risk participants and 139 (9%) of 1559 low-risk participants (hazard ratio [HR] 2·48, 95% CI 1·80-3·42; p<0·0001, after adjustment for baseline variables of age, sex, HbA_1c, systolic blood pressure, retinopathy, urine albumin-to-creatinine ratio [UACR], and eGFR). Development of impaired renal function (eGFR <60 mL/min per 1·73 m²) was seen in 48 (26%) of 184 high-risk participants and 119 (8%) of 1423 low-risk participants (HR 3·50; 95% CI 2·50-4·90, after adjustment for baseline variables). A 30% decrease in eGFR from baseline (post-hoc endpoint) was seen in 42 (19%) of 216 high-risk participants and 62 (4%) of 1559 low-risk participants (HR 5·15, 95% CI 3·41-7·76; p<0·0001, after adjustment for basline eGFR and UACR). In the intention-to-treat trial cohort, development of microalbuminuria was seen in 35 (33%) of 107 in the placebo group and 26 (25%) of 102 in the spironolactone group (HR 0·81, 95% CI 0·49-1·34; p=0·41). In the safety analysis (intention-to-treat trial cohort), events of plasma potassium concentrations of more than 5·5 mmol/L were seen in 13 (13%) of 102 participants in the spironolactone group and four (4%) of 107 participants in the placebo group, and gynaecomastia was seen in three (3%) participants in the spironolactone group and none in the placebo group. One patient died in the placebo group due to a cardiac event (considered possibly related to study drug) and one patient died in the spironolactone group due to cancer, deemed unrelated to study drug.

INTERPRETATION

In people with type 2 diabetes and normoalbuminuria, a high-risk score from the urinary proteomic classifier CKD273 was associated with an increased risk of progression to microalbuminuria over a median of 2·5 years, independent of clinical characteristics. However, spironolactone did not prevent progression to microalbuminuria in high-risk patients.

FUNDING

European Union Seventh Framework Programme.

Characteristics of high- and low-risk individuals in the PRIORITY study: urinary proteomics and mineralocorticoid receptor antagonism for prevention of diabetic nephropathy in Type 2 diabetes

AIM

To compare clinical baseline data in individuals with Type 2 diabetes and normoalbuminuria, who are at high or low risk of diabetic kidney disease based on the urinary proteomics classifier CKD273.

METHODS

We conducted a prospective, randomized, double-blind, placebo-controlled international multicentre clinical trial and observational study in participants with Type 2 diabetes and normoalbuminuria, stratified into high- or low-risk groups based on CKD273 score. Clinical baseline data for the whole cohort and stratified by risk groups are reported. The associations between CKD273 and traditional risk factors for diabetic kidney disease were evaluated using univariate and logistic regression analysis.

RESULTS

A total of 1777 participants from 15 centres were included, with 12.3% of these having a high-risk proteomic pattern. Participants in the high-risk group (n=218), were more likely to be men, were older, had longer diabetes duration, a lower estimated GFR and a higher urinary albumin:creatinine ratio than those in the low-risk group (n=1559, P<0.02). Numerical differences were small and univariate regression analyses showed weak associations (R² < 0.04) of CKD273 with each baseline variable. In a logistic regression model including clinical variables known to be associated with diabetic kidney disease, estimated GFR, gender, log urinary albumin:creatinine ratio and use of renin-angiotensin system-blocking agents remained significant determinants of the CKD273 high-risk group: area under the curve 0.72 (95% CI 0.68-0.75; P<0.01).

CONCLUSIONS

In this population of individuals with Type 2 diabetes and normoalbuminuria, traditional diabetic kidney disease risk factors differed slightly between participants at high risk and those at low risk of diabetic kidney disease, based on CKD273. These data suggest that CKD273 may provide additional prognostic information over and above the variables routinely available in the clinic. Testing the added value will be subject to our ongoing study. (European Union Clinical Trials Register: EudraCT 2012-000452-34 and Clinicaltrials.gov: NCT02040441).

Addition of once daily prandial lixisenatide to basal insulin therapy in patients with type-2 diabetes results in a reduction of HbA1c as an effect of postprandial glucose lowering

AIMS

Basal insulin has been shown to effectively reduce fasting blood glucose (FBG), but postprandial plasma glucose (PPG) excursions may remain higher than normal. Glucagon-like peptide (GLP)-1 receptor agonists such as the short-acting lixisenatide are able to control such excursions by slowing gastric emptying. However, data regarding its use in a real world clinical setting are scarce.

METHODS

24 week, prospective, multicentre, non-interventional study in 1437 patients with type-2 diabetes receiving 20μg lixisenatide once daily in combination with basal insulin. The per-protocol set (PPS) comprised 540 patients.

RESULTS

HbA_1c levels were found to decrease significantly over 24 weeks of treatment in the PPS (0.94±0.99% [7.9±8.5]; p≤0.001). An HbA_1c of <7% (53mmol/mol) was achieved in 26.9% of patients, with 9.8% reaching <6.5% (48mmol/mol) and 30.0% reaching their individual treatment goal. There was a slight decrease in FBG (2.84±30.4mg/dl; p≤0.001), and a significant reduction in PPG, with levels decreasing by between 35mg/dl (1.9mmol/l) and 38mg/dl (2.1mmol/l), respectively on average after all main meals in basal optimised patients (PPS; ≤140mg/dl). Body weight decreased from 101 to 98kg with a mean difference of 3.10±4.10kg (p≤0.001). There were few reports of hypoglycaemia and no reports of serious hypoglycaemia and need for external help. AEs were infrequent, and were in line with previous studies.

CONCLUSIONS

Lixisenatide in combination with basal insulin was shown to be an effective treatment strategy for patients with type 2 diabetes, controlling HbA_1c levels by reduction of PPG excursions during the whole day.

The FGFR Inhibitor NVP-BGJ398 Induces NSCLC Cell Death by Activating Caspase-dependent Pathways as well as Caspase-independent Apoptosis

BACKGROUND

Fibroblast growth factor receptors are expressed in diverse cell types. They play a critical role in tumor development. Their activation promotes cell-cycle progression, angiogenesis, and cell survival by induction/suppression of the expression of proteins involved.

MATERIALS AND METHODS

Non-small cell lung cancer (NSCLC) cells (line H1581) were treated with NVP-BGJ398 to evaluate effects on growth by western blot, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide assay and cell-cycle analysis.

RESULTS

NVP-BGJ398 induced cell death in H1581 cells by activating caspase-dependent mitochondrial and non-mitochondrial pathways. Caspase-independent apoptosis was also activated. Cells were found to be arrested in the G0/G1 phase. Furthermore, the expression of the tumor-suppressor gene programmed cell death 4 (PDCD4) was up-regulated with suppression of angiopoietin 2 (ANG2). This represents an additional mechanism by which NVP-BGJ389 inhibits tumor growth.

CONCLUSION

Various pathways induce apoptosis in NSCLC cells by employing NVP-BGJ398. These data reflect the potential of cancer treatment utilizing small FGFR inhibitors.

Efficacy of vildagliptin and sitagliptin in lowering fasting plasma glucose: Results of a randomized controlled trial

AIM

This study compared the efficacy of vildagliptin and sitagliptin in lowering fasting plasma glucose (FPG) as single-pill combinations (SPCs) with metformin.

METHODS

The randomized crossover, open-label, active-controlled study design assessed the FPG-lowering abilities of a vildagliptin/metformin (50/1000 mg twice daily) SPC compared with a sitagliptin/metformin (50/1000 mg twice daily) SPC after 2 weeks of treatment in 99 type 2 diabetes patients uncontrolled by stable metformin therapy (1000-2000 mg/day).

RESULTS

The change in FPG from baseline to day 14 was significantly greater (P < 0.02, Wilcoxon) with vildagliptin [-21.9 mg/dL (SD 27.0)] than with sitagliptin [-14.5 mg/dL (SD 23.0)]. After 14 days of treatment, the mean FPG was 137.8 mg/dL (SD 28.5) with vildagliptin and 140.1mg/dL (SD 26.5) with sitagliptin (P < 0.05, Wilcoxon).

CONCLUSION

Both of these DPP-4 inhibitors, given as SPCs twice daily with metformin, lowered FPG after 14 days of treatment. However, vildagliptin produced a significantly greater reduction in FPG vs baseline compared with sitagliptin, which may translate into clinical relevance.

Real-life effectiveness and tolerability of vildagliptin and other oral glucose-lowering therapies in patients with type 2 diabetes in Germany

INTRODUCTION

Metformin is an established first-line treatment for patients with type 2 diabetes mellitus (T2DM), but treatment intensification with other oral antidiabetes drugs (OADs) is usually required over time. Effectiveness of diabetes control with vildagliptin and vildagliptin/metformin was a 1-year, large observational study of 45,868 patients with T2DM across 27 countries which assessed effectiveness and safety of vildagliptin as add-on therapy to other OADs versus other comparator OAD combinations. Here, we present the data from Germany.

METHODS

Patients inadequately controlled with monotherapy were eligible only after the add-on treatment was finalized. Patients were assigned to either vildagliptin or comparator OADs [sulfonylureas, thiazolidinediones, glinides, α-glucosidase inhibitors or metformin, excluding dipeptidyl peptidase 4 (DPP-4) inhibitors or glucagon-like peptide-1 mimetic/analogues]. The primary efficacy endpoint was the proportion of patients achieving a glycosylated hemoglobin (HbA1c) reduction of >0.3% without peripheral edema, hypoglycemia, discontinuation due to a gastrointestinal event or weight gain ≥5%. One secondary efficacy endpoint was the proportion of patients achieving HbA1c <7% without hypoglycemia and weight gain. Change in HbA1c from baseline to study endpoint and safety were assessed.

RESULTS

Of 8,887 patients enrolled in Germany, 6,679 received vildagliptin and 1,695 received other OADs. The mean ± SD baseline age, HbA1c, and T2DM duration were 62.8 ± 11.0 years, 7.7 ± 1.2%, and 5.8 ± 4.9 years, respectively. The proportion of patients achieving the primary (34.5% vs. 30.5%, p < 0.01) and secondary (25.4% vs. 21.7%, p = 0.01) endpoints was higher with vildagliptin than comparator OADs. Vildagliptin showed a numerically greater reduction in HbA1c (0.7%) from baseline vs. comparator OADs (0.6%). The overall incidence of adverse events was similar.

CONCLUSION

In real life, treatment with vildagliptin is associated with a higher proportion of patients reaching target HbA1c without hypoglycemia and weight gain compared with other OADs in Germany.

Real-life efficacy and safety of vildagliptin compared with sulfonylureas as add-on to metformin in patients with type 2 diabetes mellitus in Germany

OBJECTIVE

Metformin is an established first-line treatment for type 2 diabetes mellitus (T2DM) patients, but intensification of oral anti-diabetes therapy is usually required over time. A large observational study of 45,868 T2DM patients in 27 countries (EDGE) was conducted to compare the effectiveness and safety of vildagliptin as add-on therapy to another oral anti-diabetes drug (OAD) vs other dual OAD combinations. This report presents results from a post-hoc analysis of patients in Germany who received vildagliptin or a sulfonylurea (SU) in combination with metformin.

RESEARCH DESIGN AND METHODS

Patients inadequately controlled with monotherapy became eligible only after the add-on treatment was finalized. Patients included were assigned to receive either vildagliptin or another OAD (SUs, thiazolidinediones, glinides, α-glucosidase inhibitors, or metformin; DPP-4 inhibitors or glucagon-like peptide-1 [GLP-1] mimetics/analogs were excluded). The primary end-point was the proportion of patients achieving a reduction in HbA1c >0.3% without peripheral edema, hypoglycemia, discontinuation due to gastrointestinal event, or weight gain ≥5%.

RESULTS

Of 8887 patients enrolled in Germany, 6439 received vildagliptin and 971 received SUs as add-on to metformin. The primary end-point was reached in 34.9% and 29.6% of patients in the vildagliptin and SU groups, respectively, with an unadjusted odds ratio of 1.27 (95% CI = 1.09, 1.47; p = 0.001). HbA1c decreased in both cohorts from baseline (-0.7% with vildagliptin vs -0.5% with SUs), with a mean between-group difference of -0.2% (95% CI = -0.22, -0.09). The number of hypoglycemic events was 4-fold higher in the SU group than in the vildagliptin group (vildagliptin = 0.11%; SU = 0.41%).

CONCLUSIONS

In a real-life setting, vildagliptin was associated with a numerically greater reduction in HbA1c, less hypoglycemia, and more patients reaching target HbA1c without hypoglycemia or weight gain compared with SUs. Open-label design and under reporting of adverse events are limitations of this post hoc analysis.

Effectiveness and tolerability of second-line therapy with vildagliptin vs. other oral agents in type 2 diabetes: a real-life worldwide observational study (EDGE)

AIM

Real-life studies are needed to confirm the clinical relevance of findings from randomised controlled trials (RCTs). This study aimed to assess the effectiveness and tolerability of vildagliptin add-on vs. other oral antihyperglycaemic drugs (OADs) added to OAD monotherapy in a real-life setting, and to explore the advantages and limitations of large-scale 'pragmatic' trials.

METHODS

EDGE was a prospective, 1-year, worldwide, real-life observational study in which 2957 physicians reported on the effects of second-line OADs in 45,868 patients with T2DM not reaching glycaemic targets with monotherapy. Physicians could add any OAD, and patients entered either vildagliptin or (pooled) comparator cohort. The primary effectiveness and tolerability end-point (PEP) evaluated proportions of patients decreasing HbA(1c) > 0.3%, without hypoglycaemia, weight gain, peripheral oedema or gastrointestinal side effects. The most clinically relevant secondary end-point (SEP 3) was attainment of end-point HbA(1c) < 7% without hypoglycaemia or ≥ 3% increase in body weight.

RESULTS

In this large group of T2DM patients, a second OAD was added at mean HbA(1c) of 8.2 ± 1.3%, with no baseline HbA(1c) difference between cohorts. Second-line OAD therapy attained the PEP in the majority of patients, with higher attainment in those prescribed a vildagliptin-based regimen. The adjusted odds ratio was 1.49 (95% CI: 1.42, 1.55; p < 0.001). In patients with baseline HbA(1c) ≥ 7%, SEP 3 was achieved by 35% of patients on a vildagliptin-based combination and by 23% of those receiving comparator combinations. The adjusted odds ratio was 1.96 (95% CI: 1.85, 2.07; p < 0.001). Safety events were reported infrequently and safety profiles of vildagliptin and other OADs were consistent with previous data.

CONCLUSION

EDGE demonstrates that in a 'real-life' setting, vildagliptin as second OAD can lower HbA(1c) to target without well-recognised OAD side effects, more frequently than comparator OADs. In addition, EDGE illustrates that conducting large-scale, prospective, real-life studies poses challenges but yields valuable clinical information complementary to RCTs.

Molecular cloning of a cDNA encoding for the GLP-1 receptor expressed in rat lung

Recent data revealed the existence, localization and possible function of specific receptors for glucagon-like peptide 1 (7-36) amide (GLP-1) in rat lung. This receptor has different biochemical features than the GLP-1 receptor in endocrine pancreas. Therefore, we aimed to clone the lung receptor cDNA in order to analyze whether biochemical and functional diversity of the GLP-1 receptors in lung and pancreas is based upon genetic differences. A cDNA library from rat lung in a lambda gt11 vector was screened with a cDNA probe coding for the rat pancreas GLP-1 receptor. Thereby, we found a lung GLP-1 receptor cDNA which shows nearly complete homology to the pancreatic beta-cell receptor cDNA. Only one base exchange occurred at base 1 of a codon at position 977 resulting in a change of valine residue for isoleucine at position 323 of the amino acid sequence within the fifth transmembrane region. Northern blot hybridization identified transcripts at 2.7, 3.4, and 3.6 Kb. Expression of the recombinant lung GLP-1 receptor cDNA in CHO cells displayed a pharmacological profile similar to that seen with cells expressing the beta-cell derived cDNA. Therefore, we conclude that tissue-specificity for GLP-1 receptors is based upon posttranslational modifications of the receptor protein (for example glycosilation) or alternative splicing of primary transcripts and not on variations within the coding sequence of the receptor gene.

The bisphosphonate zoledronic acid inhibits the growth of HCT-116 colon carcinoma cells and induces tumor cell apoptosis

Besides its preventive action on bone resorption the third generation bisphosphonate zoledronic acid (ZOL) has been shown to display potent inhibitory action on the formation of bone metastases of various human cancers. Recent research also indicates an antitumoral effect on primary tumors and visceral metastases. Here we investigate for the first time the effect of ZOL on the human colon carcinoma cell line HCT-116. ZOL strongly inhibited the proliferation and soft agar colony formation of HCT-116 cells and caused a G1 cell cycle arrest in a population of ZOL treated cells. This cell cycle arrest was accompanied by an induction of apoptosis via a caspase dependent mechanism. Activation of Caspases 3, 7, 8 and 9, cleavage of PARP as well as the release of cytochrome C into the cytosol were detected in HCT-116 cells treated with low micromolar concentrations of ZOL. The induction of the mitochondrial pathway of apoptosis was accompanied by a translocation of Bax into the mitochondria, Bid activation and a decrease of overall Bcl-2 expression. We also detected a cytosolic increase of apoptosis inducing factor (AIF), a trigger of caspase-independent apoptosis. Taken together, our data indicate a potent antitumoral and apoptosis inducing effect of ZOL on HCT-116 colon carcinoma cells.

Translational regulation of autoimmune inflammation and lymphoma genesis by programmed cell death 4

Both inflammatory diseases and cancer are associated with heightened protein translation. However, the mechanisms of translational regulation and the roles of translation factors in these diseases are not clear. Programmed cell death 4 (PDCD4) is a newly described inhibitor of protein translation. To determine the roles of PDCD4 in vivo, we generated PDCD4-deficient mice by gene targeting. We report here that mice deficient in PDCD4 develop spontaneous lymphomas and have a significantly reduced life span. Most tumors are of the B lymphoid origin with frequent metastasis to liver and kidney. However, PDCD4-deficient mice are resistant to inflammatory diseases such as autoimmune encephalomyelitis and diabetes. Mechanistic studies reveal that upon activation, PDCD4-deficient lymphocytes preferentially produce cytokines that promote oncogenesis but inhibit inflammation. These results establish that PDCD4 controls lymphoma genesis and autoimmune inflammation by selectively inhibiting protein translation in the immune system.

Effects of the tyrosine kinase inhibitor imatinib on neuroendocrine tumor cell growth

AIM

We investigated the effects of the tyrosine kinase inhibitor imatinib (Gleevec) on neuroendocrine tumor cells.

METHODS

Neuroendocrine tumor cells were incubated without and with imatinib. The effects on growth were examined by methylthiazoletetrazolium (MTT) assay. The c-Kit expression in human endocrine tumor tissue and cell lines was determined by immunohistochemistry and Western blot analysis, respectively. Cytotoxicity assay was performed by fluorescence-activated cell sorting. The telomerase activity was determined using the telomeric repeat amplification protocol.

RESULTS

28% of the insulinomas, 100% of the gastrinomas, and 38% of the carcinoids expressed c-Kit. Imatinib at concentrations >5 microM inhibited cell proliferation and induced apoptosis in both c-Kit-positive and c-Kit-negative cell lines. The PI-3K inhibitor wortmannin did not enhance the effects of imatinib. Imatinib did not sensitize endocrine tumor cells to doxorubicin and 5-fluorouracil. Imatinib inhibited the telomerase activity.

CONCLUSION

Imatinib inhibits neuroendocrine tumor cell growth independently of c-Kit by inhibition of other tyrosine kinases or through tyrosine kinase independent pathways.

The Rap-B-Raf signalling pathway is activated by glucose and glucagon-like peptide-1 in human islet cells

AIMS/HYPOTHESIS

Glucose and glucagon-like peptide-1 have been shown to activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase in beta cells. We examined the contributions of the small GTPases Rap and Ras and the serine-threonine kinases B-Raf and Raf-1 to the activation of these kinases in human islet cells.

METHODS

The expression of Rap, Ras, B-Raf and Raf-1 in human islets was examined by immunohistochemistry and immunoblotting. Human islets were incubated in glucose at concentrations of 2.5 and 15 mmol/l and were stimulated with 10 nmol/l glucagon-like peptide-1. The activation of ERK and Raf kinases was examined by phosphorylation-specific antibodies and immuno-complexed kinase assays. The activation of Rap and Ras was determined by pull-down assays. Stimulation of phosphoinositide 3-kinase was detected by immuno-complexed lipid kinase assays.

RESULTS

Extracellular-regulated kinase and protein kinase B (a downstream target of phosphoinositide 3-kinase) were activated in islets stimulated with glucose and glucagon-like peptide-1. In these islets, the Rap-B-Raf signalling pathway was activated preferentially compared with Ras and Raf-1, and activated Rap and B-Raf mediated ERK stimulation in kinase assays in vitro. In addition, Rap rather than Ras mediated activation of phosphoinositide 3-kinase in islets stimulated with glucose and glucagon-like peptide-1.

CONCLUSIONS/INTERPRETATION

In human islet cells, glucose and glucagon-like peptide-1 activate the Rap and B-Raf signalling module, which mediates ERK activation in assays in vitro. Rap also activates phosphoinositide 3-kinase, delineating central roles for Rap and B-Raf as therapeutic targets for beta cell growth in diabetes mellitus.

Flavone initiates a hierarchical activation of the caspase-cascade in colon cancer cells

There is emerging evidence that dietary factors can prevent cancer by affecting the process of carcinogenesis. Flavonoids present in vegetarian food possess antioxidant activities, have scavenging effects on activated carcinogens and mutagens, affect cell cycle progression and alter gene and protein expression. We report here that flavone, the core structure of the flavone subgroup, potently inhibits proliferation and induces apoptosis in HCT-116 colon cancer cells. Flavone induces the activation of caspases 2, 3, 8, 9 and 10 and a decrease of mitochondrial anti-apoptotic Bcl(2) protein expression. Further analysis revealed that caspase 10 activation is mediated via caspase 1. Additionally, treatment with flavone results in release of the mitochondrial apoptosis-inducing factor (AIF), the key trigger of caspase-independent apoptosis, into the cytosol. In summary, our data show that flavone induces apoptosis in a caspase-dependent and -independent manner.

Nuclear survivin is a powerful novel prognostic marker in gastroenteropancreatic neuroendocrine tumor disease

Gastroenteropancreatic neuroendocrine tumors represent a heterogeneous tumor entity. The growth pattern ranges from very slowly to fast growing, aggressive types of tumors. Survivin, a member of the family of apoptosis inhibitors, is a bifunctional protein that suppresses apoptosis and regulates cell division. In this study we determined the prognostic value of survivin in this tumor entity. Tumor specimens from 104 patients (38 foregut, 53 midgut, 13 hindgut) were studied immunohistochemically for cytoplasmic and nuclear survivin expression as well as for ki-67 antigen expression. 5-year-follow-up was complete in 89 patients. 29 patients with localized, well-differentiated gastroenteropancreatic neuroendocrine tumors (WDET, WHO class 1) had been curatively treated by surgical or endoscopic tumor resection. 50 patients suffered from well-differentiated endocrine carcinomas (WDEC, WHO class 2), 10 patients were diagnosed with poorly differentiated neuroendocrine carcinomas (PDEC, WHO class 3). Survivin expression was correlated with survival for the 50 patients with metastatic WDEC disease. All 29 WDETs were negative for nuclear survivin, whereas all 10 PDECs stained positive for nuclear survivin. In the 50 patients with metastatic WDECs, 5/50 (10%) tumors were nuclear survivin positive. Those 5 patients had a statistically significant worse prognosis (survival of 41 vs. 103 months, p=0.01). ki-67 was not a prognostic factor in this subgroup of patients. Nuclear survivin expression thus appears to be upregulated during progression of gastroenteropancreatic neuroendocrine tumors. The analysis of nuclear survivin expression identifies subgroups in metastatic disease (WHO class 2) with good (survivin-) or with less favorable prognosis (survivin+). We propose that the determination of nuclear survivin expression could be used to individualize therapeutic strategies in this tumor entity in the future.

Programmed cell death protein 4 suppresses CDK1/cdc2 via induction of p21(Waf1/Cip1)

We show that the recently discovered tumor suppressor pdcd4 represses the transcription of the mitosis-promoting factor cyclin-dependent kinase (CDK)1/cdc2 via upregulation of p21(Waf1/Cip1). p21(Waf1/Cip1) inhibits CDK4/6 and CDK2. Decrease of CDK4/6 and CDK2 enhances the binding of pRb to E2F/DP, which in turn together bind to and repress the cdc2 promoter. Upregulation of CDK1/cdc2 accompanied by a malignant change was previously reported in colon cancer. We show that expression of pdcd4 as an indirect suppressor of CDK1/cdc2 is lost in progressed carcinomas of lung, breast, colon, and prostate. Furthermore, it seems that localization and expression of pdcd4 directly correlate with tumor progression. Finally, the CDK1/cdc2 inhibitor roscovitine reduces the proliferation of several tumor cell lines, suggesting that inhibition of CDK1/cdc2 may be a useful strategy against malignant transformation. Therefore, pdcd4 might serve as a novel target for antineoplastic therapies.

Programmed cell death protein 4 (pdcd4): a novel target for antineoplastic therapy?

Pdcd4 is a novel gene first identified as a differentially expressed protein during apoptosis. In the meantime not only the impact of Pdcd4 in programmed cell death but also an implication in transformation suppression by inhibition of protein translation is discussed. These features implicate a potential value of Pdcd4 as a molecular target in cancer therapy. This review summarizes the current knowledge about expression, structure and function of Pdcd4.

Programmed Cell Death Protein 4 (PDCD4) Acts As a Tumor Suppressor in Neuroendocrine Tumor Cells

PDCD4 is a new tumor suppressor gene. In the current study, we show that overexpression of PDCD4 in carcinoid cells results in inhibition of cell proliferation. This is most likely caused by a PDCD4-induced downregulation of carbonic anhydrase type II which catalyzes the production of bicarbonate, a fundamental substrate for many cellular pathways.

Pdcd4 inhibits growth of tumor cells by suppression of carbonic anhydrase type II

To identify new genes that are upregulated during apoptosis we previously cloned rat pdcd4. While the role of pdcd4 is still unclear it seems to possess a tumor suppressor activity. Pdcd4 directly interacts with the RNA helicase eIF4A and inhibits protein synthesis by interfering with the assembly of the cap-dependent translation initiation complex. In the present study, we show that pdcd4 suppresses carbonic anhydrase type II protein expression in HEK293 and Bon-1 carcinoid cells. Since tumor cells require a high bicarbonate flux for their growth, carbonic anhydrase suppression results in growth inhibition. Similar to pdcd4, carbonic anhydrase inhibitor ethoxyzolamide reduces growth of several endocrine tumor cell lines. Thus, the translation inhibitor pdcd4 represses endocrine tumor cell growth by suppression of carbonic anhydase II. Furthermore, carbonic anhydrase inhibitors might represent promising tools for anti-endocrine tumor treatment.

Bisphenol A diglycidyl ether-induced apoptosis involves Bax/Bid-dependent mitochondrial release of apoptosis-inducing factor (AIF), cytochrome c and Smac/DIABLO

(1) Bisphenol A diglycidyl ether (BADGE) is a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) antagonist, which is able to induce apoptosis in tumor cells independently of PPAR-gamma in caspase-dependent and -independent manners. Additionally, BADGE promotes TRAIL-induced apoptosis. (2) We report that BADGE activates via Bax and caspases-2 and -8 both the intrinsic and extrinsic apoptotic pathways using Bid as a shunt. (3) BADGE stimulates the mitochondrial release of apoptosis-inducing factor (AIF), cytochrome c and second mitochondria-derived activator of caspase/direct IAP-binding protein with low pl (Smac/DIABLO). The release of cytochrome c could not be blocked by inhibitors of caspases-3, -8 and -9 indicating that BADGE acts upstream of caspases-3 and -9 and does not involve caspase-8 to release cytochrome c. (4) While the caspase-independent apoptotic effect might be mediated by AIF, the sensitizing effect of BADGE against other apoptotic substances is most likely mediated by the X-linked inhibitor of apoptosis inhibitor Smac/DIABLO. (5) Our data suggest that BADGE or BADGE derivatives could represent promising substances for the treatment of neoplasms improving the antitumoral activity of TRAIL.

Radioiodide treatment after sodium iodide symporter gene transfer is a highly effective therapy in neuroendocrine tumor cells

This study evaluates the possibility of treating Bon1 and QGP pancreatic neuroendocrine tumor cells with radioactive iodide ((131)I) after stable transfection with the thyroid sodium iodide symporter (NIS). NIS expression was driven either by the strong viral cytomegalovirus promoter or by the tissue-specific chromogranin A promoter. Using either approach, NIS expression was confirmed by reverse transcription-PCR and Western blotting. Uptake of radioactive iodide was increased approximately 20-fold by chromogranin A promoter-driven NIS expression and approximately 50-fold by cytomegalovirus promoter-driven NIS expression. Maximal uptake was reached within 15 min in QGP cells and 30 min in Bon1 cells. Effective half-life was 5 min in QGP and 30 min in Bon1 cells. No evidence of organification was detected by high-performance liquid chromatography and gel filtration chromatography. (131)I was a highly effective treatment in NIS-expressing QGP and Bon1 cells, reducing clone formation by 99.83 and 98.75%, respectively, in the in vitro clonogenic assay. In contrast, clone formation was not reduced in QGP and Bon1 cells without NIS expression after incubation with the same activity concentration of (131)I as compared with mock treated cells. Absorbed doses to QGP and Bon1 cells are up to 150 and 30 Gy, respectively. In addition, a direct cytotoxic effect of radioiodide was demonstrated in NIS-expressing Bon1 cells after (131)I incubation. In conclusion, radioiodide treatment after NIS gene transfer appears to be a promising novel approach in the therapy of neuroendocrine tumors if its highly encouraging in vitro effectiveness can be transferred to the in vivo situation.

DUG is a novel homologue of translation initiation factor 4G that binds eIF4A

To elucidate the molecular mechanisms of cell death, we have cloned a new gene, designated death-upregulated gene (DUG), from rat insulinoma cells. DUG is constitutively expressed at very low levels in normal cells but is dramatically upregulated in apoptotic cells following serum/glucose starvation or death receptor ligation by Fas ligand. The DUG mRNA is present in two splicing forms: a long form that encodes a protein of 469 amino acids and a short form that gives rise to a polypeptide of 432 amino acids. The predicted DUG protein sequence contains two putative nuclear localization signals and multiple phosphorylation sites for protein kinases and two conserved MA3 domains. Importantly, DUG is homologous to eukaryotic translation initiation factor (eIF) 4G and binds to eIF4A presumably through MA3 domains. Upon transfection, DUG inhibits both intrinsic and extrinsic pathways of apoptosis. Thus, DUG is a novel homologue of eIF4G that regulates apoptosis.

Endoproteolysis by isolated membrane peptidases reveal metabolic stability of glucagon-like peptide-1 analogs, exendins-3 and -4

These in vitro studies aimed to characterize the pattern and the kinetics of endoproteolysis of the insulinotropic hormone glucagon-like peptide-1 (GLP-1) and related peptides by native ectopeptidases. Peptides were incubated with isolated rat or pig kidney brush-border microvilli membranes, which are a rich source of the ectopeptidases that are responsible for the post-secretory metabolism of peptide hormones. The proteolytic products were separated by reversed-phase HPLC column chromatography and characterised by molecular mass and primary structure. The relative importance of specific peptidases was established by measuring the effects of specific peptidase inhibitors on the kinetics of proteolysis. Dipeptidyl-peptidase-IV was found to be rate-limiting in the endoproteolysis of GLP-1. GLP-1 homologs, exendins-3 and -4, exhibited exceptional stability in the presence of isolated kidney microvilli membranes. Our finding that exendin-4 is several orders of magnitude more stable than GLP-1 and Ser-8-GLP-1 is especially noteworthy given this peptide's widely reported insulinotropic potency.

Bisphenol A diglycidyl ether induces apoptosis in tumour cells independently of peroxisome proliferator-activated receptor-gamma, in caspase-dependent and -independent manners

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors which are involved in many biological processes, such as regulation of cell differentiation, lipid metabolism, inflammation and cell death. PPARs consist of three families, PPAR-alpha, PPAR-delta and PPAR-gamma. Bisphenol A diglycidyl ether (BADGE) has been described as a pure antagonist of PPAR-gamma. However, recent data also revealed PPAR-gamma-agonistic activities of BADGE. Here we show that BADGE kills transformed cells by apoptosis and promotes the cytotoxic effects of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and indomethacin. The cytotoxic effect of BADGE does not require PPAR-gamma expression and is mediated in caspase-dependent and caspase-independent manners.

Pioglitazone inhibits growth of carcinoid cells and promotes TRAIL-induced apoptosis by induction of p21waf1/cip1

BACKGROUND/AIMS

We investigated the effect of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist pioglitazone on growth and TRAIL-induced apoptosis in carcinoid cells.

METHODS

Carcinoid cells were incubated without and with pioglitazone. Effects on growth were examined by cell count and cell cycle analysis. p21waf1/cip1 expression was determined by Western blotting. Cytotoxicity assay was performed by FACS analysis.

RESULTS

Pioglitazone suppressed the growth and induced apoptosis of carcinoid cells. Additionally, pioglitazone significantly enhanced carcinoid cell death induced by tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL). The enhancement of TRAIL-induced apoptosis was associated with an upregulation of cyclin-dependent kinase inhibitor p21waf1/cip1 in pioglitazone-treated carcinoid cells. Importantly, overexpression of p21waf1/cip1 in carcinoid cells by adenoviral gene transfer of p21 sensitized them to TRAIL-induced apoptosis.

CONCLUSIONS

These results suggest that pioglitazone inhibits cell growth and sensitizes cells to TRAIL-induced apoptosis by induction of p21waf1/cip1. Therefore, pioglitazone can be an effective therapeutic adjuvant for the treatment of carcinoid tumors.

In vitro evaluation of an enhanced human serum amyloid A (SAA2) promoter-regulated soluble TNF receptor fusion protein for anti-inflammatory gene therapy

Tumour necrosis factor (TNF)-alpha contributes to the pathogenesis of many inflammatory diseases. Recombinant soluble TNF receptor fusion proteins (sTNFR:Ig) are potent TNF antagonists, both in vitro and in vivo. The concentration of serum amyloid A (SAA) increases by up to 1000-fold during inflammation, largely owing to cytokine-driven transcriptional upregulation. A reporter plasmid, comprising the proximal 0.7 kb of the human SAA2 promoter fused to a luciferase gene, was used in transient transfection experiments in human HepG2 hepatoma cells to assess the quantitative and qualitative TNF antagonist properties of a construct in which sTNFR:Ig synthesis is under the control of a chimera of the SAA2 promoter and a tat/HIV element. The SAA2-tat/HIV-sTNFR:Ig construct retained the fine-tuned cytokine responsiveness of the SAA2 promoter, while exhibiting the quantitatively enhanced level of protein expression conferred by the tat/HIV element. It produced a biologically significant TNF inhibition that was at least as strong as that achieved using a CMV promoter-driven sTNFR:Ig construct. There was a dose- and time-dependent relationship between the pro-inflammatory cytokine used, and the generation of TNF antagonist activity by SAA2-tat/HIV-sTNFR:Ig. Although sTNFR:Ig protein can be induced by either TNF-alpha or interleukin (IL)-1beta, its antagonist activity is limited to the former cytokine. The SAA2-tat/HIV-sTNFR:Ig construct, and derivatives thereof, may therefore be ideally suited to gene therapy applications that require the local production of potent and specific immune modifiers only when there is active pathology. It may consequently be of particular use in the future treatment of diseases such as rheumatoid arthritis.

Roles of TNF-related apoptosis-inducing ligand in experimental autoimmune encephalomyelitis

TRAIL, the TNF-related apoptosis-inducing ligand, induces apoptosis of tumor cells, but not normal cells; the roles of TRAIL in nontransformed tissues are unknown. Using a soluble TRAIL receptor, we examined the consequences of TRAIL blockade in an animal model of multiple sclerosis. We found that chronic TRAIL blockade in mice exacerbated experimental autoimmune encephalomyelitis induced by myelin oligodendrocyte glycoprotein. The exacerbation was evidenced primarily by increases in disease score and degree of inflammation in the CNS. Interestingly, the degree of apoptosis of inflammatory cells in the CNS was not affected by TRAIL blockade, suggesting that TRAIL may not regulate apoptosis of inflammatory cells in experimental autoimmune encephalomyelitis. By contrast, myelin oligodendrocyte glycoprotein-specific Th1 and Th2 cell responses were significantly enhanced in animals treated with the soluble TRAIL receptor. Based on these observations, we conclude that unlike TNF, which promotes autoimmune inflammation, TRAIL inhibits autoimmune encephalomyelitis and prevents activation of autoreactive T cells.

Regulation of TRAIL-induced apoptosis by transcription factors

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a newly identified member of the TNF family. Unlike many other members of the TNF family, TRAIL selectively induces apoptosis of tumor cells, but not normal cells. The mechanisms whereby TRAIL-induced apoptosis is regulated in various cell types are not clear. We report here that the peroxisome proliferator-activated receptor (PPAR)-gamma and nuclear factor (NF)-kappaB play distinct roles in regulating TRAIL-induced apoptosis. Activation of PPAR-gamma by its agonist pioglitazone significantly enhanced TRAIL-induced apoptosis. This was associated with inhibition of proliferation and cell cycle progression. On the other hand, inhibition of NF-kappaB by sulfasalazine also significantly enhanced TRAIL-induced apoptosis. These results strongly suggest that while transcription factor PPAR-gamma promotes TRAIL-induced apoptosis, NF-kappaB inhibits it. Thus, PPAR-gamma agonists and NF-kappaB inhibitors are potent enhancers of TRAIL-induced apoptosis.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an inhibitor of autoimmune inflammation and cell cycle progression

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of tumor cells but not normal cells; its role in normal nontransformed tissues is unknown. We report here that chronic blockade of TRAIL in mice exacerbated autoimmune arthritis, and that intraarticular TRAIL gene transfer ameliorated the disease. In vivo, TRAIL blockade led to profound hyperproliferation of synovial cells and arthritogenic lymphocytes and heightened the production of cytokines and autoantibodies. In vitro, TRAIL inhibited DNA synthesis and prevented cell cycle progression of lymphocytes. Interestingly, TRAIL had no effect on apoptosis of inflammatory cells either in vivo or in vitro. Thus, unlike other members of the tumor necrosis factor superfamily, TRAIL is a prototype inhibitor protein that inhibits autoimmune inflammation by blocking cell cycle progression.

Specific calcitonin gene-related peptide binding sites present throughout rat intestine

Calcitonin gene-related peptide is found extensively in the innervation of the intestine and has potent pharmacological effects on secretion, blood flow, and motility. Although essential for assessing the physiological significance of CGRP, detailed information concerning the distribution of its receptor(s) within the intestine is lacking. By using autoradiographic methods, we identified specific binding sites for 125I-tyr0-CGRP-alpha in all regions of the rat small and large intestine. Particularly dense saturatable binding is observed within the lamina propria. There is moderate saturatible binding in the myenteric plexuses. These findings clearly support the notion that CGRP has a neuroeffector role in intestinal functions.

The genomic organization of the human GLP-1 receptor gene

The genomic organization of the human gene encoding the receptor for glucagon-like peptide-1 (GLP-1 (7-37)/(7-36) amide) was analyzed to reveal the relationship to other G-protein-coupled receptors. The coding sequence of the GLP-1 receptor is interrupted by 12 introns. These introns are uniformly distributed within the open reading frame. The length of the introns varies between 6.6 kb and 100 bp, in contrast to the relative constant length of 100 bp of the exons. All of the exon/intron splice junctions characterized followed the consensus GT-AG rule. A comparison of the genomic structure with other related receptor genes indicates that the exon/intron organization is well-conserved among the VIP/ glucagon/secretin receptor family.

Biological actions of glucagon-like peptide(GLP)-2 revealed--how pluripotential is the glucagon gene?

Recently published data from the group of Drucker indicate that glucagon-like peptide (GLP)-2 induces intestinal epithelial proliferation. This is the first biological effect assigned to this proglucagon-derived peptide (PGDP) and represents, perhaps, the most convincing evidence, so far, to support the existing hypothesis that PGDPs can act to promote intestinal epithelial growth and adaptation. Also, these findings prompt certain clinical considerations. Here, we summarise the reported effects of GLP-2 and highlight the important questions which need to be addressed with special reference to the clinical implications.

Neuropeptide Y2 receptors on nerve endings from the rat neurohypophysis regulate vasopressin and oxytocin release

Neuropeptide Y and peptide YY are important central and peripheral modulators of cardiovascular and neuroendocrine functions, that act through multiple receptor subtypes, Y1 through Y5. A neuropeptide Y-binding site of the Y2 type was characterized by ligand-binding studies in isolated nerve terminals from the rat neurohypophysis. Functionally, neuropeptide Y and peptide YY dose-dependently triggered arginine 8-vasopressin and oxytocin release from perfused isolated terminals, and potentiated the arginine-8-vasopressin release induced by depolarization. Osmotic stimulation by salt loading of rats for two and seven days caused a more than three-fold increase in the neuropeptide Y content of the nerve endings. However, the Y2 receptor expression and arginine-8-vasopressin content declined, showing that the neuropeptide Y system is dynamic and suggesting that it plays a physiological role in salt and water homeostasis. Two sets of observations suggest the arginine-8-vasopressin release by neuropeptide Y may not be explained by neuropeptide Y effects on intracellular Ca2+. First, absence of Ca2+ from the perfusion medium did not affect the arginine-8-vasopressin release, and secondly neuropeptide Y did not change intraterminal Ca2+ concentrations. Pretreatment with pertussis toxin blocked arginine-8-vasopressin secretion by neuropeptide Y, suggesting activation of Gi or Go heterotrimeric G-proteins are required for secretion. It is concluded, that the nerve endings of the neurohypophysis contain a complete neuropeptide Y system with ligand and receptors. Neuropeptide Y may act in an autocrine fashion via activation of Y2 neuropeptide Y receptors to stimulate the release of vasopressin and oxytocin via a Gi/Go dependent secretory mechanism.

The positive charge of the imidazole side chain of histidine7 is crucial for GLP-1 action

Glucagon-like peptide-1(7-36)amide/(7-37) (GLP-1) is an incretin hormone which plays an important role in postprandial glucose homeostasis. Since GLP-1 potentiates glucose-induced insulin secretion, stimulates insulin biosynthesis and inhibits glucagon release, it is a potential tool for the treatment of diabetes mellitus. For this, an exact understanding of the structural/functional moieties of the peptide is mandatory. The present study investigates the importance of structural features of histidine7 at the N-terminus for GLP-1 action. Based upon binding and activity data obtained from ten different GLP-1 analogues we show that not the positive charge of the free alpha-amino group but the positive charge of the imidazole side chain of histidine is crucial for GLP-1 action. The presence of a ring structure and a basic function as well as the correct positioning of both seems to be decisive.

Reciprocal cellular distribution of glucagon-like peptide-1 (GLP-1) immunoreactivity and GLP-1 receptor mRNA in pancreatic islets of rat

The respective cellular distribution of glucagon-like peptide-1 (GLP-1) immunoreactivity and mRNA expression of the GLP-1 receptor was compared in rat pancreas by means of immunohistochemistry and in situ hybridization. GLP-1 immunoreactivity was present in the marginal zone of rat pancreatic islets. In contrast, GLP-1 receptor mRNA signals were confined to the central part of pancreatic islets. Neither GLP-1 immunoreactivity nor GLP-1 receptor mRNA signals were detected in the exocrine pancreatic acinar cells or duct cells. The differential distribution of GLP-1 immunoreactivity and GLP-1 receptor mRNA signals indicates that the GLP-1 amino acid sequence is present in the alpha-cell zone of pancreatic islets, whereas the GLP-1 receptor is expressed mainly by beta cells. Thus, our data by in situ hybridization demonstrates the significant expression of GLP-1 receptors on beta cells but makes a significant expression on alpha cells rather unlikely.

[The intestinal hormone glucagon-like peptide 1 (GLP-1): from experiment to the clinic]

A functional connection between the small intestine and endocrine pancreas was proved in the sixties, after it became possible to determine the exact amount of insulin in plasma. The insulin response after oral doses of glucose is substantially stronger than after intravenous doses of sugar, even when identical glucose plasma levels are attained. This incretin effect is explained by the connection of the entero-insular axis. The intestinal hormones, that are released by the small intestine after meals, circulate measurably in plasma, and strengthen the glucose-induced insulin secretion, are responsible for this effect. In addition to the classical incretin hormone "Gastric inhibitory polypeptide-1" (GIP), "Glucagon-like peptide-1" (GLP-1) is very interesting to investigators today. In a relatively short amount of time, GLP-1 has matured from a physiologically interesting incretin hormone candidate to a potentially therapeutical alternative for the treatment of diabetes mellitus. GLP-1 stimulates glucose-dependent insulin secretion, decreases plasma glucagon levels, delays gastric emptying, and putatively exerts an additional effect on peripheral glucose utilization. On top of that, GLP-1 has effects on the central nervous system thereby impacting on feeding behavior.

Five out of six tryptophan residues in the N-terminal extracellular domain of the rat GLP-1 receptor are essential for its ability to bind GLP-1

Oligonucleotide-directed mutagenesis was utilized to investigate the requirement of tryptophan residues located in the N-terminal domain of the glucagon-like peptide-1 (GLP-1) receptor for the ability to bind its ligand and to induce cAMP generation. W39, W72, W87, W91, W110, and W120 were mutated into alanine. Two of the six tryptophan residues, W72 and W110, are highly conserved within the receptor subfamily. After transfection of mutated cDNAs in COS-7 or CHL cells, it appeared that mutant W87 A bound [125I] GLP-1 with the same affinity as wild-type receptor and induced signal transduction to a comparable extent. In contrast, mutant receptors W39A, W72A, W91A, W110A, and W120A lost the ability to bind [125I] GLP-1. Because all mutated receptor cDNAs were transcribed on RNA level (Northern blot) and the receptor proteins were expressed at the plasma membrane level (Western blot), it is concluded that with the exception of W87 all trytophan residues are essential for receptor ligand interaction. This indicates the significance of hydrophobic interactions within the N-terminal domain of the GLP-1 receptor.

Endoproteolysis of glucagon-like peptide (GLP)-1 (7-36) amide by ectopeptidases in RINm5F cells

This study concerns whether the pancreatic beta cell expresses cell-surface ectopeptidases that are capable of proteolysis of peptide hormones and neuropeptides that modify glucose-dependent insulin release. These biochemical investigations of the RINm5F cell line found that these cells express ectopeptidases. We have characterized the limited endoproteolysis of GLP-1 (7-36) amide that occurs in the presence of RINm5F plasma membranes. The products and the sensitivity to specific peptidase inhibitors of the proteolysis is characteristic of neutral endopeptidase (NEP) 24.11. Vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), amylin, glucagon, glucose-dependent insulinotropic polypeptide (GIP), and exendin-4 also undergo proteolysis in the presence of RIN cell membranes. NEP 24.11-activity in RIN cell membranes was confirmed using a specific fluorogenic assay, by histochemistry, and by comparison with the recombinant enzyme with respect to the kinetics of proteolysis of GLP-1 (7-36) amide and of a fluorogenic substrate. Specific fluorogenic assays revealed the presence of aminopeptidase N and the absence of aminopeptidase A and of dipeptidylpeptidase IV.

The isolated N-terminal extracellular domain of the glucagon-like peptide-1 (GLP)-1 receptor has intrinsic binding activity

The glucagon-like peptide 1 (7-37)/(7-36) amide (GLP-1) receptor belongs to a new subclass of seven transmembrane domain, G-protein coupled receptors comprising several receptors for peptide hormones. The receptors of this family share many common motifs including a relatively large N-terminal extracellular domain. The GLP-1 receptor is presently attracting much attention, since it is the target protein of the antidiabetic gut hormone GLP-1. To establish the functional significance of the N-terminal part of the GLP-1 receptor for ligand binding, the extracellular domain was isolated and purified. Utilizing CHL cells expressing the cloned GLP-1 receptor, we demonstrate that the isolated, solubilized N-terminal part of the receptor protein competes for GLP-1 binding with the intact wild-type receptor. Moreover, in cross-linking experiments radiolabeled GLP-1 was covalently attached to the isolated N-terminus, thereby demonstrating direct physical interaction of both components. By Western blot analysis two specific bands were detectable, representing the N-terminal receptor protein in the presence or absence of bound ligand. These data underline the significance of the N-terminal domain of the GLP-1 receptor for ligand binding.

Central administration of GLP-1-(7-36) amide inhibits food and water intake in rats

Glucagon-like peptide (GLP)-1-(7-36) amide and its pancreatic receptors are important for control of blood glucose levels. However, rat GLP-1 receptors are also localized in the brain, in hypothalamus, and in areas without a blood-brain barrier. When rats were kept on a food restriction schedule, intracerebroventricular injection of GLP-1 just before food was offered inhibited food intake. However, peripheral GLP-1 administration by intraperitoneal injection had little effect. GLP-1 effects on water intake and output were also investigated. Intracerebroventricular GLP-1 profoundly inhibited angiotensin II-induced drinking behavior in rats, and water intake was suppressed by exogenous GLP-1 in rats habituated to a water restriction schedule. These effects were reproduced by intraperitoneal administration of GLP-1. Furthermore, intracerebroventricular GLP-1 stimulated urinary excretion of water and sodium. The centrally elicited effects were blocked by the GLP-1 antagonist exendin-(9-39) amide, whereas the N-terminally extended and inactive GLP-1-(1-36) amide had no effect on feeding and drinking. GLP-1 had no effect in behavioral assays measuring exploratory locomotor activity and conditioned taste aversion. In conclusion, GLP-1 may play a physiological role in regulation of both ingestion and the water and salt homeostasis.

Exchange of W39 by A within the N-terminal extracellular domain of the GLP-1 receptor results in a loss of receptor function

The proglucagon-derived glucagon-like peptide-1 (GLP-1) secreted by the L-cells exerts an insulinotropic effect at pancreatic beta-cells. The GLP-1 receptor belongs to a new subfamily of the superfamily of seven transmembrane, G-protein-coupled receptors (7 TM receptors). We show that a single point mutation within a nonconserved motif of the N-terminal, extracellular domain of the GLP-1 receptor results in a dramatic impairment of receptor function. Thus, substitution of W39 by A or F is followed by a loss of GLP-1 binding. Exchange of K38 with A (mutant K) slightly decreased GLP-1 binding affinity. Replacement of the negatively charged Q37 by K and K38 by A, which is identical with a shift of the positively charged K one position upstream, resulted in a receptor mutant able to bind GLP-1 with higher affinity as the wild-type receptor and mutant K. Therefore, the presence of an imidazol ring structure in the investigated receptor region is necessary for an intact receptor function Furthermore, a positive charge at this location is important for the receptor-ligand interaction.