Peter Eickelmann

Empagliflozin, a novel selective sodium glucose cotransporter‐2 (SGLT‐2) inhibitor: characterisation and comparison with other SGLT‐2 inhibitors

Aims: Empagliflozin is a selective sodium glucose cotransporter‐2 (SGLT‐2) inhibitor in clinical development for the treatment of type 2 diabetes mellitus. This study assessed pharmacological properties of empagliflozin in vitro and pharmacokinetic properties in vivo and compared its potency and selectivity with other SGLT‐2 inhibitors.

Long-term treatment with empagliflozin, a novel, potent and selective SGLT-2 inhibitor, improves glycaemic control and features of metabolic syndrome in diabetic rats.

Empagliflozin is a potent, selective sodium glucose co‐transporter‐2 inhibitor that is in development for the treatment of type 2 diabetes. This series of studies was conducted to assess the in vivo pharmacological effects of single or multiple doses of empagliflozin in Zucker diabetic fatty rats. Single doses of empagliflozin resulted in dose‐dependent increases in urinary glucose excretion and reductions in blood glucose levels. After multiple doses (5 weeks), fasting blood glucose levels were reduced by 26 and 39% with 1 and 3 mg/kg empagliflozin, respectively, relative to vehicle. After 5 weeks, HbA1c levels were reduced (from a baseline of 7.9%) by 0.3 and 1.1% with 1 and 3 mg/kg empagliflozin, respectively, versus an increase of 1.1% with vehicle. Hyperinsulinaemic–euglycaemic clamp indicated improved insulin sensitivity with empagliflozin after multiple doses versus vehicle. These findings support the development of empagliflozin for the treatment of type 2 diabetes.

Functional characterisation of human SGLT-5 as a novel kidney-specific sodium-dependent sugar transporter

Sodium glucose cotransporters (SGLT) actively catalyse carbohydrate transport across cellular membranes. Six of the 12 known SGLT family members have the capacity to bind and/or transport monosaccharides (SGLT‐1 to 6); of these, all but SGLT‐5 have been characterised. Here we demonstrate that human SGLT‐5 is exclusively expressed in the kidney. Four splice variants were detected and the most abundant SGLT‐5‐mRNA was functionally characterised. SGLT‐5 mediates sodium‐dependent [14C]‐α‐methyl‐d‐glucose (AMG) transport that can be inhibited by mannose, fructose, glucose, and galactose. Uptake studies using demonstrated high capacity transport for mannose and fructose and, to a lesser extent, glucose, AMG, and galactose. SGLT‐5 mediated mannose, fructose and AMG transport was weakly (μM potency) inhibited by SGLT‐2 inhibitors. In summary, we have characterised SGLT‐5 as a kidney mannose transporter. Further studies are warranted to explore the physiological role of SGLT‐5.

CDK5 Regulatory Subunit-associated Protein 1-Like 1 (CDKAL1) Is a Tail-anchored Protein in the Endoplasmic Reticulum (ER) of Insulinoma Cells

Background: Cdkal1 is a type 2 diabetes (T2D) susceptibility gene responsible for tRNALys modification. Results: CDKAL1 is a tail-anchored protein inserted in the ER via the TRC40/Get3 pathway. Its down-regulation affects the expression of some insulin granule proteins and the ER stress marker CHOP10. Conclusion: CDKAL1 participates in translation of insulin granule proteins and ER stress. Significance: Characterizing CDKAL1 contributes to T2D research. Genome-wide association studies have led to the identification of numerous susceptibility genes for type 2 diabetes. Among them is Cdkal1, which is associated with reduced β-cell function and insulin release. Recently, CDKAL1 has been shown to be a methylthiotransferase that modifies tRNALys to enhance translational fidelity of transcripts, including the one encoding proinsulin. Here, we report that out of several CDKAL1 isoforms deposited in public databases, only isoform 1, which migrates as a 61-kDa protein by SDS-PAGE, is expressed in human islets and pancreatic insulinoma INS-1 and MIN6 cells. We show that CDKAL1 is a novel member of the tail-anchored protein family and exploits the TCR40/Get3-assisted pathway for insertion of its C-terminal transmembrane domain into the endoplasmic reticulum. Using endo-β-N-acetylglucosaminidase H and peptide:N-glycosidase F sensitivity assays on CDKAL1 constructs carrying an N-glycosylation site within the luminal domain, we further established that CDKAL1 is an endoplasmic reticulum-resident protein. Moreover, we observed that silencing CDKAL1 in INS-1 cells reduces the expression of secretory granule proteins prochromogranin A and proICA512/ICA512-TMF, in addition to proinsulin and insulin. This correlated with reduced glucose-stimulated insulin secretion. Taken together, our findings provide new insight into the role of CDKAL1 in insulin-producing cells and help to understand its involvement in the pathogenesis of diabetes.

Inhibition of SH2‐domain containing inositol phosphatase 2 (SHIP2) in insulin producing INS1E cells improves insulin signal transduction and induces proliferation

Inhibition of the lipid phosphatase SH2‐domain containing inositol phosphatase 2 (SHIP2) in L6‐C10 muscle cells, in 3T3‐L1 adipocytes and in the liver of db/db mice has been shown to ameliorate insulin signal transduction and established SHIP2 as a negative regulator of insulin action. Here we show that SHIP2 inhibition in INS1E insulinoma cells increased Akt, glycogen synthase kinase 3 and extracellular signal‐regulated kinases 1 and 2 phosphorylation. SHIP2 inhibition did not prevent palmitate‐induced apoptosis, but increased cell proliferation. Our data raise the interesting possibility that SHIP2 inhibition exerts proliferative effects in β‐cells and further support the attractiveness of a specific inhibition of SHIP2 for the treatment of type 2 diabetes.

Pharmacological inhibition of Eph receptors enhances glucose-stimulated insulin secretion from mouse and human pancreatic islets

Aims/hypothesisType 2 diabetes is characterised by impaired glucose-stimulated insulin secretion (GSIS) from pancreatic islets. Since erythropoietin-producing hepatoma (Eph)–ephrin bidirectional signalling fine-tunes GSIS from pancreatic beta cells, we investigated Eph receptor tyrosine kinases (RTK) as potential drug targets for selectively increasing GSIS.MethodsInsulin secretion assays were carried out using mouse and human pancreatic islets as well as mouse insulinoma (MIN6) cells in the presence or absence of two Eph RTK inhibitors. Furthermore, the most potent inhibitor was injected into mice to evaluate its effects on glucose tolerance and plasma insulin levels.ResultsWe showed that the Eph RTK inhibitors selectively increased GSIS from MIN6 cells as well as mouse and human islets. Our results also showed that the insulin secretory effects of these compounds required Eph–ephrin signalling. Finally, pharmacological inhibition of Eph receptor signalling improved glucose tolerance in mice.Conclusions/interpretationWe showed for the first time that Eph RTKs represent targets for small molecules to selectively increase GSIS and improve glucose tolerance.