Biotech Values

[north40000]

Liraglutide V. Byetta...more horizons

Another post from the I-Village AMLN board by a Ph.D geneticist who is one of the sharpest researchers I have experienced on any message board:

http://www.investorvillage.com/smbd.asp?mb=2885&mn=31191&pt=msg&mid=2838330

>>The future of incretin mimetic therapy

Something that is easily forgotten in looking at liraglutide results is that AMLN’s future vis a vis incretin mimetics is not limited to Byetta and exenatide LAR. In a poster presentation at this year’s ADA meeting, AMLN showed results of a preclinical study of AC163794, a stable derivative of GIP, or glucose-dependent insulinotropic peptide (1). This derivative of GIP is resistant to degradation by DPP-IV and significantly increases insulin production in diabetic rats, while maintaining normal activity in non-diabetic rats (e.g., no risk of hypoglycemia is expected). AMLN also alluded to this peptide during the Research Breakfast last October. An exciting possibility would be to couple this GIP derivative with exenatide to target both the glp-1 and gip receptors. It is also of note that only AMLN presented data on a GIP derivative at the ADA meeting.



The importance of targeting gip goes beyond blood sugar control, and keeps in the tone of yesterday’s New York Times article. A review by Yip and Wolfe (2) indicates that the gip receptor is widely expressed throughout the body on such tissues as pancreas, gut, adipose tissue, heart and brain. It was known at that time that GIP given to test animals would increase expression of adiponectin, but it was unclear if this was a direct effect, or the result of some unknown pathway. The importance of adiponectin is now widely recognized as being a key adipocytokine that regulates weight control and has demonstrable cardiovascular protective effects. There are numerous reports that low levels of adiponectin correlates with high levels of proinflammatory cytokines, and vice versa. Low levels of adiponectin are also associated with obesity, and so adiponectin has been proposed as a central player in the connection between obesity, diabetes, insulin resistance, and cardiovascular disease.



The current view is that GIP has a direct effect on adipose tissue to increase adiponectin expression, and also to decrease expression of obesity and inflammation related adipocytokines. Among the studies that provide evidence is one by Hansotia et al. (3) of the Drucker lab. Using single incretin receptor knock-out mice and DIRKO (Double Incretin Receptor Knock Out) mice, they showed that not only does GIP have a direct effect on adiponectin, but also plasminogen activator inhibitor 1 and resistin. In addition, they tested exendin-4 and did not find a direct effect on the expression of adipocytokines.



However, there have been other reports that patients using Byetta have increased levels of adiponectin. Notably, AMLN presented evidence of this at the 2007 ADA meeting (4). This paper by Wintle et al. Showed that after two years of Byetta treatment, essentially all patients had significant decreases in HbA1c, most had lost weight, and even the weight neutral group had increased adiponectin levels. The data also show that the tertile that lost the most weight (an impressive average of 12 kg weight loss) also had the greatest reduction of HbA1c (1.6%, also impressive), and the greatest increase in adiponectin. The increase of 2.3 micrograms per mL of adiponectin for this subgroup puts them close to what some other reports in the literature cite as the range for non-obese, non-diabetic individuals. This is very exciting, but more follow-up study is needed to determine if these overall improvements result in decreased cardiovascular risk, as would be predicted by the current body of knowledge.



A curious thing is how Byetta might cause an increase in adiponectin although other studies did not find evidence of direct interaction with adipocytes. The possibility that the glp-1 receptor is expressed on those cells at low levels undetectable by current methods cannot be ruled out. In a study with L6 myotubes and 3T3 adipocytes, Idris et al. (5) found that exendin-4, but not glp-1, had an insulin-sensitizing effect through a PI3 kinase dependent pathway. Although later investigations showed that glp-1 also has PI3 kinase activity, albeit at a reduced level, the research raises the possibility that exendin-4 could have a direct effect on adipocyte gene expression.



However, another piece of evidence suggests an alternative explanation. Also presented at the 2007 ADA meeting was a report by Yukihiro et al. (6) showing that expression of GIP requires the transcription factors Pax6 and Pdx1. Stimulation of the glp-1 receptor by exendin-4 upregulates expression of Pdx1. It could be that exendin-4 exerts an indirect effect through this pathway. Such a prospect becomes more interesting when the fact that receptors for glp-1 and gip are co-expressed in many tissues.



Regardless of what the actual mechanism turns out to be, that exendin-4 has positive effects on blood glucose, weight, and cytokines that are important for cardiovascular health is very exciting. As the conventional wisdom of treating diabetes expands to include more than just blood sugar, this should give diabetics increased hope of avoiding complications, especially cardiovascular disease. Even more exciting is the preclinical work AMLN has shown in developing a gip derivative to treat diabetes. Just as Symlin’s future lies beyond diabetes in treating obesity along with other anorexic peptides, the future of Byetta seems to be more than exenatide LAR. A combination of glp-1 and gip receptor agonists might turn out to be a dynamic duo that is very hard to beat.



Best regards,



Marty





1. Insulinotropic Actions of a Long Acting GIP Analog AC163794 In Vivo

Year: 2007

Abstract Number: 1485-P



Authors:



BRONISLAVA GEDULIN, DIANE HARGROVE, PAMELA SMITH, VED SRIVASTAVA, SOUMITRA GHOSH, ANDREW YOUNG, ALAIN BARON, DAVID PARKES, San Diego, CA



Results:



Glucose-dependent insulinotropic peptide (GIP) is an incretin hormone released from intestinal K cells in response to nutrient ingestion. AC163794 is a novel peptidic GIP analog that has similar binding potency as native GIP at the GIP receptor and is resistant to DPPIV cleavage. This study compares in vivo insulinotropic actions of GIP and AC163794 during an intravenous glucose tolerance test (IVGTT) in normal rats (Harlan Sprague-Dawley, HSD) and in rat models of diabetes. Fed HSD rats were anesthetized and continuously infused (IV, from t=-30 through t=90 min) with vehicle (saline), GIP or AC163794 (100 pmol/kg/min). At t=0 min, glucose was administered (5.7 mmol/kg, IV bolus). Mean baseline insulin concentration at t=-30 min was 1.0 ng/mL. Prior to the glucose challenge (t=-30 to t = 0 min) plasma insulin significantly increased 3.2- to 3.8-fold in rats infused with GIP or AC163794 (P<0.05) and did not change in saline infused rats. After glucose administration, insulin peaked at 5 min to a maximum of 2.9 (+/-0.3) ng/ml in saline infused rats and 12.4 (+/-1.8) and 11.4 (+/-0.8) ng/ml in rats infused with GIP or AC163794 respectively (P<0.001 for both groups vs saline controls). In separate studies, the duration of insulinotropic action was tested by administering the peptides as a single subcutaneous (SC) injection (3 microg per rat) at time points up to 4 hours before IV glucose. GIP administered by SC injection at t=-30 min produced no significant change in glucose-stimulated insulin compared to the saline group (peak insulin, saline: 2.8 and GIP: 3.3 ng/mL), while AC163794 injected SC at -30, -60 or -120 min before IV glucose exhibited a significant insulinotropic effect with maximal insulin levels of 10.8, 9.5 and 11.2 ng/mL (P<0.001 for all groups vs control). In summary, the GIP analog AC163794, under the infusion conditions in this study, demonstrated insulinotropic activity similar to GIP in normal rats and when acutely delivered exhibited a significantly prolonged duration of action.





2. Life Sci. 2000;66(2):91-103. GIP biology and fat metabolism.Yip RG, Wolfe MM.

Department of Medicine, Boston University School of Medicine, Boston Medical Center, MA 02118, USA.



The gastrointestinal hormone, gastric inhibitory polypeptide (GIP), is synthesized and released from the duodenum and proximal jejunum postprandially. Its release depends upon several factors including meal content and pre-existing health status (ie. obesity, diabetes, age, etc.). It was initially discovered and named for its gastric acid inhibitory properties. However, its more physiologically relevant role appears to be as an insulinotropic agent with a stimulatory effect on insulin release and synthesis. Accordingly, it was later renamed glucose-dependent insulinotropic polypeptide because its action on insulin release depends upon an increase in circulating levels of glucose. GIP is considered to be one of the principle incretin factors of the enteroinsular axis. The GIP receptor is a G-protein-coupled receptor belonging to the family of secretin/VIP receptors. GIP receptor mRNA is widely distributed in peripheral organs, including the pancreas, gut, adipose tissue, heart, adrenal cortex, and brain, suggesting it may have other functions in addition to the ones mentioned above. An overactive enteroinsular axis has been suggested to play a role in the pathogenesis of diabetes and obesity. In addition to stimulating insulin release, GIP has been shown to amplify the effect of insulin on target tissues. In adipose tissue, GIP has been reported to (1) stimulate fatty acid synthesis, (2) enhance insulin-stimulated incorporation of fatty acids into triglycerides, (3) increase insulin receptor affinity, and (4) increase sensitivity of insulin-stimulated glucose transport. In addition, although controversial, lipolytic properties of GIP have been proposed. The mechanism of action of GIP-induced effects on adipocytes is unknown, and it is unclear whether these effects of GIP on adipocytes are direct or indirect. However, there is now evidence that GIP receptors are expressed on adipocytes and that these receptors respond to GIP stimulation. Given the location of its release and the timing of its release, GIP is an ideal anabolic agent and expanding our understanding of its physiology will be needed to determine its exact role in the etiology of diabetes mellitus and obesity.





3. J Clin Invest. 2007 Jan;117(1):143-52. Extrapancreatic incretin receptors modulate glucose homeostasis, body weight, and energy expenditure.Hansotia T, Maida A, Flock G, Yamada Y, Tsukiyama K, Seino Y, Drucker DJ.



Banting and Best Diabetes Centre, Department of Medicine, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada.



The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) control glucose homeostasis through well-defined actions on the islet beta cell via stimulation of insulin secretion and preservation and expansion of beta cell mass. We examined the importance of endogenous incretin receptors for control of glucose homeostasis through analysis of Glp1r(-/-), Gipr(-/-), and double incretin receptor knockout (DIRKO) mice fed a high-fat (HF) diet. DIRKO mice failed to upregulate levels of plasma insulin, pancreatic insulin mRNA transcripts, and insulin content following several months of HF feeding. Both single incretin receptor knockout and DIRKO mice exhibited resistance to diet-induced obesity, preservation of insulin sensitivity, and increased energy expenditure associated with increased locomotor activity. Moreover, plasma levels of plasminogen activator inhibitor-1 and resistin failed to increase significantly in DIRKO mice after HF feeding, and the GIP receptor agonist [D-Ala(2)]GIP, but not the GLP-1 receptor agonist exendin-4, increased the levels of plasma resistin in studies of both acute and chronic administration. These findings extend our understanding of how endogenous incretin circuits regulate glucose homeostasis independent of the beta cell via control of adipokine secretion and energy expenditure.



Free full text at:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=17187081



4. Increased Adiponectin Improved Glycemic Control and Reduced Body Weight With Long-Term Exenatide Treatment in Patients With T2D

Year: 2007

Abstract Number: 2208-PO



Authors:



MATTHEW WINTLE, DEEPAK BHOLE, XUESONG GUAN, CATHERINE SCHNABEL, JARET MALLOY, ROBERT BRODOWS, DENNIS KIM, San Diego, CA, Indianapolis, IN



Results:



Decreased circulating concentrations of the adipose tissue-derived, insulin-sensitizing hormone adiponectin (ADPN) are associated with increased risk of cardiovascular disease (CVD), the leading cause of mortality and morbidity in patients with type 2 diabetes (T2D). The incretin mimetic exenatide improved glycemic control, reduced body weight, and was associated with an improved CV risk profile in patients with T2D treated with metformin and/or sulfonylureas. This post-hoc analysis examined changes in ADPN in patients with evaluable plasma samples completing 2 to 2.5 y of exenatide treatment in open-label extension studies. In this cohort (N=93, 65% M, 99 (+/-20) kg, BMI 33 (+/-6) kg/m2, FPG 163 (+/-44) mg/dL, A1C 8.3 (+/-1.1) %, ADPN 5.2 (+/-3.0) microg/mL [mean+/-SD]), exenatide treatment for at least 2 y resulted in mean reductions from baseline of -1.0 (+/-0.14) % in A1C (mean+/-SE), -16.8 (+/-5.2) mg/dL in fasting plasma glucose, and -5.8 (+/-0.6) kg in body weight with 81% of the cohort experiencing weight reduction. Mean serum ADPN concentrations increased significantly from baseline by +1.5 (+/-0.26) microg/mL (28% increase; p<0.0001) with a median of +1.0 microg/mL. Multiple regression analysis showed significant associations between endpoint ADPN levels and changes in BMI and A1C (p=0.0001, <0.05, respectively). Tertile analysis by weight change showed the tertile with the greatest weight reduction had the most pronounced improvements in A1C and ADPN.



[Delta] from baseline (mean+/-SE)
Tertile 1 (N=31)
Tertile 2 (N=31)
Tertile 3 (N=31)

Body weight (kg)
-12.0+/-0.6
-5.7+/-0.2
+0.2+/-0.5

A1C (%)
-1.6+/-0.3
-0.7+/-0.2
-0.7+/-0.3

Adiponectin (microg/mL)
+2.3+/-0.4
+1.6+/-0.5
+0.6+/-0.4




In addition to its known improvements in glycemic control and weight reduction, exenatide treatment for at least 2 y resulted in a significant increase in ADPN. Further studies are warranted to establish the clinical relevance of this finding.





5. Biochem Pharmacol. 2002 Mar 1;63(5):993-6. Exendin-4 increases insulin sensitivity via a PI-3-kinase-dependent mechanism: contrasting effects of GLP-1. Idris I, Patiag D, Gray S, Donnelly R.

Division of Vascular Medicine, School of Medical and Surgical Sciences, University of Nottingham, Derbyshire Royal Infirmary, DE1 2QY, Derby, UK.



The insulinotropic agent, exendin-4, is a long-acting analogue of glucagon-like peptide-1 (GLP-1) which improves glucose tolerance in humans and animals with diabetes, but the underlying mechanisms and the effects of exendin-4 on peripheral (muscle/fat) insulin action are unclear. Previous in vivo and clinical studies have been difficult to interpret because of complex, simultaneous changes in insulin and glucagon levels and possible effects on hepatic metabolism. Thus, the comparative effects of exendin-4 and GLP-1 on insulin-stimulated 2-[3H]deoxyglucose (2-DOG) uptake were measured in fully differentiated L6 myotubes and 3T3-adipocytes, including co-incubation with inhibitors of the PI-3-kinase (wortmannin) and mitogen-activated protein (MAP) kinase (PD098059) pathways. In L6 myotubes, there was a concentration-dependent and PI-3-kinase-dependent increase in insulin-stimulated 2-DOG uptake with exendin-4 and GLP-1, e.g. for exendin-4 the C(I-200) value (concentration of insulin required to increase 2-DOG uptake 2-fold) decreased from 1.3 +/- 1.4 x 10(-7)M (insulin alone, n=16) to 5.9 +/- 1.3 x 10(-8)M (insulin+exendin-4 0.1nM, n=18, P<0.03). A similar insulin-sensitizing effect was observed with exendin-4 in 3T3-adipocytes, but GLP-1 had no effect on adipocyte insulin sensitivity. In conclusion, this is the first direct evidence showing that exendin-4 increases insulin-stimulated glucose uptake in muscle and fat derived cells via a pathway that involves PI-3-kinase activation. Furthermore, the contrasting responses of exendin and GLP-1 in 3T3-adipocytes suggest that the peripheral insulin-sensitizing effect of exendin-4 (in contrast to the insulinotropic effect) does not involve the GLP-1 receptor pathway.





6. Combined Expression of Pax6 and Pdx1 are Required for GIP Production

Year: 2007

Abstract Number: 1451-P



Authors:



YUKIHIRO FUJITA, JEANNIE W. CHUI, DAVID S. KING, TIANJIAO ZHANG, SCOTT POWNALL, ANTHONY T. CHEUNG, TIMOTHY J. KIEFFER, Vancouver, BC, Canada



Results:



Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are released during meals from endocrine cells located in the gut mucosa and stimulate insulin secretion from pancreatic beta-cells in a glucose-dependent manner. There appears to be a different gradient in the expression of GIP and GLP-1 along the length of the gut, with the concentration of GIP producing cells (K-cells) greatest in the upper gut and GLP-1 producing cells (L-cells) highest in the lower gut. We sought to determine the transcription factors that specify the expression pattern of GIP along the gut. We examined the co-localization of specific transcription factors with GIP and GLP-1 in human and rodent gut sections by immmunohistochemistry. K-cells were always positive for expression of Pax6 and Pdx1. In proximal duodenum, most of the epithelial cells expressed Pdx1, but GIP expression was limited to those cells that co-expressed Pax6. In the ileum, GLP-1 was co-localized with Pax6, but not Pdx1 in L-cells. Interestingly, approximately one third of GLP-1 positive cells also expressed GIP. Those K/L-cells were also positive for both Pax6 and Pdx1 indicating Pdx1 does not hamper proglucagon expression. Notably, Pax6 and Pdx1 also co-localized with GIP in rare cells of the mouse retina. To determine if Pax6 and Pdx1 activate GIP expression, we transfected a human GIP promoter/reporter construct into undifferentiated gut cells (IEC-6) with Pax6 or Pdx1. Pax6 and Pdx1 enhanced GIP promoter activity by 6- and 4-fold, respectively. Moreover, the exogenous promoter activity in GIP-expressing enteroendocrine cells (STC-1) was significantly attenuated by addition of a dominant-negative mutant of Pax6. In the same cells, sequential deletion and site-directed mutational analysis of the GIP promoter demonstrated that the sequence between -184bp and -145bp is critical for GIP expression. Binding of Pax6 and Pdx1 to this proximal region of the GIP promoter was inferred from EMSA studies. We conclude that combined expression of Pax6 and Pdx1 are likely necessary for GIP production.<<