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Biomedical subjects

K Geisen

Publications and source records attributed to K Geisen.

At least 19 recordsLinked to original sources
PubMed2004

Analysis of the anorectic efficacy of HMR1426 in rodents and its effects on gastric emptying in rats.

OBJECTIVES: Pharmacodynamics of HMR1426 in rodents. SUBJECTS: Male and female rats and male mice. MEASUREMENTS: 24 h feed consumption was measured. From the time curves IC(50) values of HMR1426 were calculated. Microanalysis of feeding behavior was determined. Macronutrient preference was measured, by offering rats three different diets. Gastric emptying was measured after liquid gastric loads or solid meals. In rats with gastric cannulas, milk consumption was measured with closed or open cannulas. Diabetes-related parameters and thyroid hormones were measured. RESULTS: HMR1426 inhibited feed consumption dose-dependently in rodents. Microstructural analysis of feeding after HMR1426 differed from central acting anorectics. HMR1426 inhibited consumption of fat- and carbohydrate-enriched diets. Gastric emptying was dose- and time-dependently delayed. Gastric emptying correlated with the time course of the anorectic effect. In sham-fed rats, HMR1426 had no anorectic effect with open cannulas. Anorectic effect occurred with closed cannulas. We proved that HMR1426 is not a CCK(A) agonist. CONCLUSION: The correlation between anorectic properties of HMR1426 and gastric emptying suggests that gastric emptying may cause the anorectic properties of HMR1426. The differences in microstructural feeding behavior between HMR1426 and centrally active anorectics makes it unlikely that HMR1426 acts via the CNS. Evidence for a peripheral mode of action is derived from sham-fed rats with open gastric fistula. When the milk fed was drained, HMR1426 was ineffective. HMR1426 is not a CCK(A) agonist. The molecular action of HMR1426 causing gastric emptying and its anorectic properties are under investigation.

Animals↗
PubMed1996

Characterization of the molecular mode of action of the sulfonylurea, glimepiride, at beta-cells.

Glimepiride was compared with glibenclamide for its insulin secretion stimulating and beta-cell membrane depolarizing activity as well as for its binding kinetics to beta-cell membranes and for its beta-cell membrane binding proteins. Steady state, kinetic and competitive binding studies revealed a 3- to 4-fold lower binding affinity of glimepiride to isolated beta-cell membranes and intact beta-cells compared to glibenclamide. Direct photoaffinity labeling of beta-cell membrane proteins with the radiolabeled sulfonylureas identified a 65-kDa binding protein for glimepiride and a 140-kDa binding protein for glibenclamide which may be the basis for the different binding characteristics of the two sulfonylureas. The inhibition of binding and photoaffinity labeling of glimepiride and glibenclamide to the 65- and 140-kDa protein, respectively, by glibenclamide and glimepiride can be explained with allosteric interactions between two distinct sulfonylurea binding proteins, subunits of a KATP protein complex, each regulating the open/closed-state of a common separate pore-forming subunit by allosteric interactions. Whole-cell patch clamp experiments with RINm5F cells demonstrated a 3- to 4-fold lower depolarization activity of glimepiride compared to glibenclamide which correlates well with the lower binding affinity of glimepiride. The lower binding affinity and depolarization activity of glimepiride were not reflected in vitro in perifused islets and the isolated perfused pancreas of the rat. This discrepancy remains to be elucidated. The binding, depolarisation and insulin releasing characteristics of glimepiride and glibenclamide suggest that different sulfonylureas can interact with different components of KATP.

ATP-Binding Cassette Transporters↗
PubMed1996

Characterization of the molecular mode of action of the sulfonylurea, glimepiride, at adipocytes.

The possibility of an insulin-independent blood glucose decreasing activity of sulfonylureas was re-evaluated. Single dose studies in dogs with different sulfonylureas revealed a ranking in the ratio of plasma insulin release/blood glucose decrease with glimepiride exhibiting the lowest and glibenclamide the highest ratio. This ranking suggests that sulfonylureas have extrapancreatic activity and that this is most pronounced for glimepiride. Further evidence for this was derived from single dose studies in rabbits, euglycemic hyperinsulinemic clamp studies in rats and subchronic studies in manifestly diabetic KK-AY mice. Extrapancreatic activity of sulfonylureas as deduced from the ranking in vivo between glimepiride and glibenclamide directly on peripheral tissues would imply a similar ranking between the two drugs in glucose utilizing processes in isolated muscle and fat cells. Indeed, glimepiride exhibits a higher potency compared to glibenclamide with respect to stimulation of glucose transport, glucose transporter isoform 4 (GLUT4) translocation and lipid and glycogen synthesis in normal and insulin-resistant adipocytes and in muscle cells, as well as of the potential underlying signalling processes examined at the molecular level. The molecular basis for the sulfonylurea-induced increase of glucose transport and non-oxidative glucose metabolism may rely on the dephosphorylation of key metabolic proteins/enzymes, like GLUT4 as demonstrated in isolated rat adipocytes. Activation of certain serine/threonine-specific protein phosphatases by insulin has been postulated to be mediated by the mitogen-activated protein kinase (MAPK) pathway and phosphatidylinositol (P1)-3'-kinase. However, there was no evidence that these pathways are involved in the regulation of protein phosphatase activity by sulfonylureas. Binding and photoaffinity studies showed that glimepiride associates in a time- and concentration dependent non-saturable manner with detergent-insoluble complexes of the plasma membrane which may correspond to caveolae. This association seems to be based on the interaction of glimepiride with glycosyl-phosphatidylinositol (GPI) lipids and membrane protein anchors. These were found to be enriched in detergent-insoluble complexes together with a GPI-specific phospholipase (PLC), the caveolae-specific coast protein, caveolin, and acylated tyrosine kinases of the src family. Sulfonylureas were found to stimulate the GPI-PLC and tyrosine phosphorylation of caveolin. This is presumably caused by direct interaction of the sulfonylurea into caveolar glycolipids and stimulation of a caveolar src tyrosine kinase, respectively. In accordance with the higher potency of glimepiride in vivo and in glucose transport/metabolism in vitro, the EC50 values for GPI-PLC activation and caveolin phosphorylation were lower for glimepiride than those for glibenclamide. The stimulation of protein tyrosine phosphorylation by sulfonylureas via this pathway not involving the insulin signaling cascade may be coupled to activation of specific protein phosphatases regulating glucose transport and metabolism. The concentrations required in vitro were higher than the reported therapeutic plasma concentrations. However, provided that the observed time-dependent accumulation of glimepiride in caveolae of peripheral cells were of functional relevance for stimulation of glucose transport/metabolism and would also occur in vivo, due to the longer exposure times even at lower drug concentrations the insulin-independent blood glucose decreasing activity of sulfonylureas might become effective in vivo.

Adipocytes↗
PubMed1996

Cardiovascular effects of conventional sulfonylureas and glimepiride.

Sulfonylureas have, in the past, been reported to have adverse cardiovascular effects. Glimepiride is a new sulfonylurea. In spite of stimulating less insulin secretion, it has, depending on the species, equal or higher blood glucose decreasing activity and according to preliminary studies less cardiovascular activity than glibenclamide. Further studies were performed to confirm the lower cardiovascular activity of glimepiride. The IC50 for inhibition of rilmakalim-activated KATP channel currents in isolated ventricular myocytes was 31.6 nM for glimepiride and 6.8 nM for glibenclamide. In endotoxin shock-rats at a dose of 1 x 2 mg/kg i.v., glibenclamide induced a significantly higher blood pressure increase than glimepiride. At two i.v. doses of 20 mg/kg 4 min apart, in normal rats, glibenclamide produced signs of ischemia in the ECG in nearly all animals, glimepiride almost none, in diabetic rats, glibenclamide produced in all animals a lethal cardiogenic shock preceeded by serious ECG changes, glimepiride only in one fifth of the animals. In open-chest dogs, on intracoronary infusion of equieffective blood glucose-lowering doses, glibenclamide, gliclazide and glimepiride all reduced coronary blood flow, increased coronary resistance, depressed the mechanical activity of the heart, enhanced myocardial O2-extraction, reduced the serum potassium level and induced a moderate endocardial ST-segment elevation, but glimepiride to a significantly less extent than glibenclamide and gliclazide. The presented data confirm that glimepiride at equivalent blood glucose decreasing doses has less cardiovascular activity than conventional sulfonylureas.

Animals↗
PubMed1995

Aminoguanidine does not inhibit the initial phase of experimental diabetic retinopathy in rats.

We have previously shown that long-term administration of aminoguanidine, an inhibitor of advanced glycosylation product formation, reduces the extent of experimental diabetic retinopathy in the rat by 85%. In order to determine whether the residual retinopathy that developed despite aminoguanidine was attributable to advanced glycation endproduct formation, a time-course study was performed in three different groups of male Wistar rats: non-diabetic controls (NC), streptozotocin-diabetic controls (DC) and streptozotocin-diabetic rats treated with aminoguanidine HCL, 50 mg/100 ml drinking water (D-AG). Eyes were obtained at 24, 32, 44 and 56 weeks of diabetes/treatment duration and morphologic evaluation was done on retinal digest preparations. At 56 weeks, retinal basement membrane thickness was additionally measured. After 24 weeks of diabetes, the number of acellular capillaries was significantly elevated in DC (44.6 +/- 5.7/mm2 of retinal area, NC 19.6 +/- 4.9; p < 0.001) and increased continuously over time (DC 56 weeks 87.4 +/- 15.1; p < 0.001 vs DC24 weeks). In contrast, acellular capillaries in D-AG increased over the first 24 weeks and then remained constant for the rest of the study (D-AG 24 weeks 35.7 +/- 5.18; p < 0.01 vs NC 24 weeks and NS vs DC 24 weeks; D-AG 56 weeks 42.0 +/- 6.20; p NS vs D-AG 24 weeks).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Extrapancreatic effects of sulfonylureas--a comparison between glimepiride and conventional sulfonylureas.

The contribution of extrapancreatic effects of sulfonylureas to the blood glucose-decreasing activity was reevaluated in vivo and in vitro with several conventional sulfonylureas and with the new one glimepiride. In vivo, in dogs, after single approximately equipotent blood glucose-decreasing doses, the sulfonylureas were tested for a ranking in the ratios of mean plasma insulin-increasing and blood glucose-decreasing activity. Studies were also performed in hyperglycemic hyperinsulinemic KK-Ay mice under once daily treatment for 8 weeks. In vitro, glimepiride and glibenclamide were tested for the ranking of their extrapancreatic activity with respect to the stimulation of glucose transport and glucose metabolizing processes in normal and insulin-resistant fat cells as well as in the isolated diaphragm. Furthermore, in vitro studies were performed, especially with glimepiride, in order to characterize the molecular mechanism for the extrapancreatic activity. The dog studies revealed a marked ranking in the ratios of plasma insulin-increasing and blood glucose-decreasing activity between the different sulfonylureas (glimepiride < glipizide < gliclazide < glibenclamide). In the hyperglycemic hyperinsulinemic KK-Ay mice, glimepiride reduced blood glucose by 40%, plasma insulin by 50% and HBA1c by 33%, whereas glibenclamide and gliclazide had no effect on these parameters. In vitro, glimepiride and glibenclamide had extrapancreatic effects within the lower microM range, with glimepiride exhibiting 2-3-fold lower ED50 values than glibenclamide. In the absence of insulin, both stimulated glucose transport--up to 60% of the maximum insulin response in the rat diaphragm and up to 35% in 3T3 adipocytes. Glycogenesis was stimulated in the rat diaphragm--up to 55% of the maximum insulin effect; lipogenesis in 3T3 adipocytes--up to 40%. The studies on the molecular mechanism of extrapancreatic activity with rat adipocytes and diaphragm suggest that these direct insulin-mimetic effects rely on the induction of GLUT4 translocation from internal stores to the plasma membrane and on the activation of the key metabolic enzymes, glycogen synthase and glycerol-3-phosphate acyltransferase. These processes occur within the same drug concentration range and with the same ranking between glimepiride and glibenclamide as observed for glucose utilization and transport. The direct effects of sulfonylureas may ultimately be regulated by a glycosyl-phosphatidylinositol-specific phospholipase C, shown to be activated by glimepiride in rat adipocytes. Lipolytic cleavage products thereby generated from glycolipidic structures may in turn stimulate specific protein phosphatases which activate key regulatory proteins/enzymes of glucose and lipid metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipocytes↗
PubMed1994

Sorbitol-accumulating pyrimidine derivatives.

The novel compounds SDI 157 (2-methyl-4(4-N,N-dimethylaminosulfonyl-1-piperazino)pyrimid ine, CAS 131816-54-1) and SDI 158 (2-hydroxymethyl-4-(4-N,N-dimethylaminosulfonyl-1- piperazino) pyrimidine, CAS 140687-51-0) have been found to be inhibitors of sorbitol dehydrogenase. In normal and diabetic animals both compounds induced a dose-dependent increase of tissue sorbitol, especially in the peripheral nerve, without alteration of the blood glucose. In contrast to SDI 158, SDI 157 does not act in vitro. However, in the isolated perfused rat liver SDI 157 induced a high sorbitol release and plasma samples of animals treated with SDI 157 induced a sorbitol accumulation in vitro in erythrocytes like SDI 158. SDI 157 seems to be a prodrug. In accordance with the polyol theory, the chronic administration of SDI 157 to diabetic rats accelerated the cataract development and depleted the lens of total and oxidized glutathione. Surprisingly, however, it accelerated the motor nerve conduction velocity in normal and diabetic rats, normalized the glomerular filtration rate in diabetic rats and did not induce retinal capillary lesions in normal rats or aggravate those in diabetic rats. At single oral doses up to 100 mg/kg, SDI 157, was well tolerated by diabetic and normal rats. Except for a reduction of drinking water consumption, the chronic administration of SDI 157 in drinking water at doses up to 100 mg/kg per day had no side effects in normal, diabetic and galactoselfructose-rich diet rats.

Animals↗
PubMed1991

Aminoguanidine treatment inhibits the development of experimental diabetic retinopathy.

Retinal capillary closure induced by hyperglycemia is the principal pathophysiologic abnormality underlying diabetic retinopathy, but the mechanisms by which this induction occurs are not clear. Treatment of diabetic rats for 26 weeks with aminoguanidine, an inhibitor of advanced glycosylation product formation, prevented a 2.6-fold accumulation of these products at branching sites of precapillary arterioles where abnormal periodic acid/Schiff reagent-positive deposits also occurred. Aminoguanidine treatment completely prevented abnormal endothelial cell proliferation and significantly diminished pericyte dropout. After 75 weeks, untreated diabetic animals developed an 18.6-fold increase in the number of acellular capillaries and formed capillary microaneurysms, characteristic pathologic features of background diabetic retinopathy. In contrast, aminoguanidine-treated diabetic animals had only a 3.6-fold increase in acellular capillaries and no microaneurysms. These findings indicate that advanced glycosylation product accumulation contributes to the development of diabetic retinopathy and suggest that aminoguanidine may have future therapeutic use in this disorder.

Animals↗
PubMed1988

Special pharmacology of the new sulfonylurea glimepiride.

Glimepiride (Hoe 490) is a new sulfonylurea. After oral administration of Hoe 490 to rabbits, blood glucose was lowered 3.5 times more than after glibenclamide (HB 419) and after intravenous administration, 2.5 times more. This superiority in efficacy was demonstrated by onset, maximum and duration of action. In rats, intravenous and oral Hoe 490 has a much shorter effect on blood glucose than HB 419, but the initial effect of Hoe 490 orally was up to 6 times and i.v. up to 2 times stronger than that of HB 419. In dogs, oral and intravenous Hoe 490 had a considerably longer blood glucose-lowering effect than HB 419. However, the effect of intravenous Hoe 490 was only half as intense as that of HB 419 in the first hours after treatment and the effect of oral Hoe 490 was initially stronger and thereafter temporarily distinctly weaker than that of HB 419. The more rapid decrease in blood glucose in the dog after oral administration of Hoe 490 was accompanied by a correspondingly earlier and higher plasma insulin increase. In accordance with the less intense initial blood glucose decrease in the dog after intravenous Hoe 490 there was a weaker and slower rise and faster drop of plasma insulin. The long action of oral and intravenous Hoe 490 in the dog can, however, not be sufficiently explained by the plasma insulin values. In the isolated rat pancreas perfused with glucose-free medium, HB 419 released glucagon beside insulin and somatostatin. The threshold concentration for the glucagon secretion was lower as those for the insulin and somatostatin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1986

Biological activity in vivo of insulin analogues modified in the N-terminal region of the B-chain.

[AlaB5]Insulin as well as a hybrid analogue of insulin and "insulin-like growth factor" (IGF-I), in which the N-terminal amino-acid sequence H-Phe-Val-Asn-Gln- of the B-chain has been replaced by the tripeptide H-Gly-Pro-Glu-of IGF-I, have been prepared by the partial-synthetic route. Their biological activity in vivo has been compared with that of other analogues in rabbits, mice and rats as far as data are available. These rodents respond differently, rats being less sensitive to modifications than rabbits and mice. The results explain unexpected discrepancies discussed in previous papers.

Amino Acid Sequence↗
PubMed1985

Inhibition of 3H-glibenclamide binding to sulfonylurea receptors by oral antidiabetics.

Specific binding of 3H-glibenclamide (HB 419) is observed with membranes from rat cerebral cortex and rat beta-cell tumor. 3H-Glibenclamide binding is of high affinity, reversible, saturable, and can be displaced by oral antidiabetics of different structural types. Half maximal inhibition of binding correlates with the hypoglycemic action of the compounds.

Animals↗
PubMed1984

Stabilisation of dissolved proteins against denaturation at hydrophobic interfaces.

Studies with insulin delivery devices have shown that denaturation of dissolved proteins at hydrophobic interfaces is a basic obstacle to long-term insulin stability in pumps. This study shows that polypropylene glycol/polyethylene glycol block polymers prevent both the adsorption of dissolved proteins to hydrophobic interfaces and the resultant aggregation. At a concentration of 0.001% (w/v), the block polymer Genapol PF-10 stabilises insulin solutions over a wide range of concentrations. Insulin solutions thus stabilised are at present being clinically tested. The effectiveness of molecular variants of Genapol PF-10 to stabilise other proteins (human gamma-globulin, myoglobin and serum albumin) is presented also.

Adsorption↗
PubMed1982

[Exchange of A1-glycine in bovine insulin with L- and D-tryptophan].

Substitution of A1-glycine of insulin by L-amino acids yields in analogues with low biological activity. With D-amino acids in A1 biological activity is essentially retained. Synthesis of [A1-L-tryptophan]- and [A1-D-tryptophan]-insulin should provide information about the position of the side chains of L- and D-amino acids relative to A19-tyrosine, e.g. by evaluation of intramolecular resonance energy transfer between the fluorescent side chains. [A1-D-Tryptophan]-insulin exhibits full biological activity.

Adipose Tissue↗
PubMed1981

[Continuous blood glucose monitoring and infusion in freely mobile dogs (author's transl)].

With the system recently developed, continuous glucose determinations and programmed infusions are also possible in the freely mobile dog. The animal is kept in a dog box and wears a dog jacket to which a plastic plate is fitted. A bite- and twist-proof flexible hollow pipeline is connected rigidly to this plate. The pipeline goes through a hole in the centre of the roof of the dog box to a newly developed rotary adaptor system for three catheters. The rotary adaptor is fitted to a vertical sliding bar system with counter movement. The three catheters run along the inside of the hollow pipeline down to the animal's back where two of them connect to a double-lumen catheter (DLC) inserted in the jugular vein. Through one tube, heparin solution is transported to the tip of the DLC. There it is sucked back together with blood through the second tube and transported to the glucose analyser. Through the third catheter, insulin or glucose is infused into the other jugular vein. The flow of the extracorporeally heparinized blood is regular. Occlusion of the DLC does not occur. During a 24-h study period, 70 ml of blood are taken from the animal. The DLC is simple to manufacture and, if suitably developed, might also be used in humans instead of the usual rigid double-lumen plastic cannular system.

Animals↗
PubMed1981

Long-term continuous intraperitoneal insulin infusion with an implanted remote-controlled insulin infusion device.

This is a report of the implantation and first 100-day operation using a remote-controlled programmable insulin infusion device in an insulin-dependent diabetic. To prevent insulin aggregation, a special surface-active polymer developed by Hoechst AG, Frankfurt, was used as an additive. Implantation was completed on April 8, 1981, and good metabolic control was reached immediately and has continued to date (July 1981), with this unit providing the only source of insulin. There have been no hypoglycemic attacks. Patient acceptance is very good. The Siemens unit, PFA 01 (external) and DFA 01 (implanted) has proved reliable and precise.

Blood Glucose↗