Evidence that the multiflorine-derived substituted quinazolidine 55P0251 augments insulin secretion and lowers blood glucose via antagonism at α2 -adrenoceptors in mice

AIMS

To investigate the mechanism of action of 55P0251, a novel multiflorine-derived substituted quinazolidine that augments insulin release and lowers blood glucose in rodents, but does not act via mechanisms addressed by any antidiabetic agent in clinical use.

MATERIALS AND METHODS

Using male mice, we determined the effects of 55P0251 on glucose tolerance, insulin secretion from isolated islets and blood oxygen saturation, including head-to-head comparison of 55P0251 to its inverted enantiomer 55P0250, as well as to other anti-hyperglycaemic multiflorine derivatives discovered in our programme.

RESULTS

55P0251 was clearly superior to its inverted enantiomer in the glucose tolerance test (area under the curve: 11.3 mg/kg 55P0251, 1.19 ± 0.04 min*mol/L vs 55P0250, 1.80 ± 0.04 min*mol/L; P < .0001). For insulin release in vitro, this superiority became visible only under concomitant adrenergic background stimulation (glucose-stimulated insulin release, fmol*islet^-1 *30 min^-1 : without α₂ -adrenoceptor agonist: 500 μmol/L 55P0251, 390 ± 34, vs 55P0250, 459 ± 40, nonsignificant; with α₂ -adrenoceptor agonist: 250 μmol/L 55P0251, 138 ± 9, vs 55P0250, 21 ± 6; P < .0001). Since receptor binding assays suggested antagonism at α_2A -adrenoceptors as a potential mechanism of action, we measured oxygen saturation in capillary blood from the tail as a surrogate of vasoconstriction, which supported α₂ -antagonistic action in vivo (90 mg/kg 55P0251, 83 ± 3%, vs 55P0250, 57 ± 3%; P < .0001). Lack of association between glucose-lowering activities and α_2A -adrenoceptor binding affinity arising from comparison of multiflorine derivatives was attributed to differences in their pharmacokinetic properties.

CONCLUSIONS

Our findings suggest that 55P0251 and related multiflorine derivatives are to be categorized as α₂ -adrenoceptor antagonists with potential to lower blood glucose by blocking α_2A -adrenoceptors on pancreatic β cells.

Preclinical characterization of 55P0251, a novel compound that amplifies glucose-stimulated insulin secretion and counteracts hyperglycaemia in rodents

AIMS

55P0251 is a novel compound with blood glucose lowering activity in mice, which has been developed from a molecular backbone structure found in herbal remedies. We here report its basic pharmacological attributes and initial progress in unmasking the mode of action.

MATERIALS AND METHODS

Pharmacokinetic properties of 55P0251 were portrayed in several species. First efforts to elucidate the glucose lowering mechanism in rodents included numerous experimental protocols dealing with glucose tolerance, insulin secretion from isolated pancreatic islets and comparison to established drugs.

RESULTS

A single oral dose of 55P0251 improved glucose tolerance in mice with an ED₅₀ between 1.5 and 2 mg/kg (reductions in areas under the curve, 1 mg/kg, -18%; 5 mg/kg, -30%; 27 mg/kg, -47%). Pharmacokinetic studies revealed attractive attributes, including a plasma half-life of approximately 3 hours and a bioavailability of approximately 58% in rats. 55P0251 amplified glucose stimulated insulin release from isolated mouse islets and improved glucose tolerance via increased insulin secretion in rats (increase in area under the insulin curve, +184%). Unlike sulfonylureas and glinides, 55P0251 hardly stimulated insulin release under basal conditions and did not induce hypoglycaemia in vivo, but it amplified the secretory response to glucose and other insulinotropic stimuli (KCl, glucagon-like peptide-1). Comparison to established anti-diabetic agents and examination of interaction with molecular targets (K_ATP channel, dipeptidyl peptidase-4, glucagon-like peptide-1 receptor) excluded molecular mechanisms addressed by presently marketed drugs.

CONCLUSIONS

55P0251 is a novel compound that potently counteracts hyperglycaemia in rodents via amplification of glucose-stimulated insulin release.

55P0110, a Novel Synthetic Compound Developed from a Plant Derived Backbone Structure, Shows Promising Anti-Hyperglycaemic Activity in Mice

Starting off with a structure derived from the natural compound multiflorine, a derivatisation program aimed at the discovery and initial characterisation of novel compounds with antidiabetic potential. Design and discovery of the structures was guided by oral bioactivities obtained in oral glucose tolerance tests in mice. 55P0110, one among several new compounds with distinct anti-hyperglycaemic activity, was further examined to characterise its pharmacology and mode of action. Whereas a single oral dose of 55P0110 did not affect basal glycaemia, it markedly improved the glucose tolerance of healthy and diabetic mice (peak blood glucose in glucose tolerance test, mmol/l: healthy mice with 90 mg/kg 55P0110, 17.0 ± 1.2 vs. 10.1 ± 1.1; diabetic mice with 180 mg/kg 55P0110, 23.1 ± 0.9 vs. 11.1 ± 1.4; p<0.001 each). Closer examination argued against retarded glucose resorption from the gut, increased glucose excretion in urine, acute insulin-like or insulin sensitising properties, and direct inhibition of dipeptidyl peptidase-4 as the cause of glucose lowering. Hence, 55P0110 seems to act via a target not exploited by any drug presently approved for the treatment of diabetes mellitus. Whereas the insulinotropic sulfonylurea gliclazide (16 mg/kg) distinctly increased the circulating insulin-per-glucose ratio under basal conditions, 55P0110 (90 mg/kg) lacked such an effect (30 min. after dosing, nmol/mol: vehicle, 2.49 ± 0.27; 55P0110, 2.99 ± 0.35; gliclazide, 8.97 ± 0.49; p<0.001 each vs. gliclazide). Under an exogenous glucose challenge, however, 55P0110 increased this ratio to the same extent as gliclazide (20 min. after glucose feeding: vehicle, 2.53 ± 0.41; 55P0110, 3.80 ± 0.46; gliclazide, 3.99 ± 0.26; p<0.05 each vs. vehicle). By augmenting the glucose stimulated increase in plasma insulin, 55P0110 thus shows distinct anti-hyperglycaemic action in combination with low risk for fasting hypoglycaemia in mice. In summary, we have discovered a novel class of fully synthetic substituted quinazolidines with an attractive pharmacological profile that recommends the structures for further evaluation as candidates for the treatment of diabetes mellitus.

Mechanisms of antihyperglycaemic action of efaroxan in mice: time for reappraisal of α2A-adrenergic antagonism in the treatment of type 2 diabetes?

AIMS/HYPOTHESIS

Inspired by recent speculation about the potential utility of α(2A)-antagonism in the treatment of type 2 diabetes, the study examined the contribution of α(2)-antagonism vs other mechanisms to the antihyperglycaemic activity of the imidazoline (±)-efaroxan.

METHODS

Effects of the racemate and its pure enantiomers on isolated pancreatic islets and beta cells in vitro, as well as on hyperglycaemia in vivo, were investigated in a comparative manner in mice.

RESULTS

In isolated perifused islets, the two enantiomers of efaroxan were equally potent in counteracting inhibition of insulin release by the ATP-dependent K(+) (K(ATP)) channel-opener diazoxide but (+)-efaroxan, the presumptive carrier of α(2)-antagonistic activity, was by far superior in counteracting inhibition of insulin release by the α(2)-agonist UK14,304. In vivo, (+)-efaroxan improved oral glucose tolerance at 100-fold lower doses than (-)-efaroxan and, in parallel with observations made in vitro, was more effective in counteracting UK14,304-induced than diazoxide-induced hyperglycaemia. The antihyperglycaemic activity of much higher doses of (-)-efaroxan was associated with an opposing pattern (i.e. with stronger counteraction of diazoxide-induced than UK14,304-induced hyperglycaemia), which implicates a different mechanism of action.

CONCLUSIONS/INTERPRETATION

The antihyperglycaemic potency of (±)-efaroxan in mice is almost entirely due to α(2)-antagonism, but high doses can also lower blood glucose via another mechanism. Our findings call for reappraisal of the possible clinical utility of α(2A)-antagonistic compounds in recently identified subpopulations of patients in which a congenitally higher level of α(2A)-adrenergic activation contributes to the development and pathophysiology of type 2 diabetes.

Synthesis and characterization of the hexenuronic acid model methyl 4-deoxy-β-l-threo-hex-4-enopyranosiduronic acid

A facile synthetic scheme for the preparation of methyl 4-deoxy-beta-L-threo-hex-4-enopyranosiduronic acid utilizing the commercially available methyl alpha-D-galactopyranoside as starting material has been developed. The synthesis sequence comprises six high yielding reaction steps: TEMPO oxidation, acetylation, methanolysis of the lactone, acetylation, beta-elimination, and final removal of the protecting groups. Only one column chromatographic purification is needed throughout the whole sequence. The overall yield is 60%. The final product has been characterized by NMR, Raman, UVRR, FTIR, and HRMS.

An optimized CZE method for analysis of mono- and oligomeric aldose mixtures

An optimized capillary electrophoresis (CZE) method to analyze complex mixtures of aldoses was developed. The approach allows simultaneous quantitative analysis of all four isomeric aldopentoses, eight aldohexoses, as well as xylo- and cellooligosaccharides up to the tetraoses. UV tagging with 4-aminobenzoic acid ethyl ester (ABEE) in combination with reductive amination was used as pre-column derivatization. With optimum baseline separation and short run times, the method is very robust, and especially suited to follow reaction and isomerization kinetics of monosaccharides.

Kinetic and chemical studies on the isomerization of monosaccharides in N-methylmorpholine-N-oxide (NMMO) under Lyocell conditions

The Lyocell process is a modern and environmentally fully compatible industrial fiber-making technology. Cellulosic pulp is dissolved without chemical derivatization in a melt of N-methylmorpholine-N-oxide monohydrate (NMMO). In the present work, the reactions of monosaccharides under Lyocell conditions were investigated in detail, using capillary zone electrophoresis as the analytical technique to clarify the composition of reaction mixtures and to follow the kinetics. Under Lyocell conditions, xylose and glucose undergo two competitive reactions: rapid conversion to nonreducing products, and complete isomerization involving the whole carbohydrate backbone, via ketose intermediates. Sugar acids are present in minor amounts only, as demonstrated by employing isotopically labeled material for NMR techniques.

Crystal and molecular structure of methyl 4-O-methyl-β-d-ribo-hex-3-ulopyranoside

Methyl 4-O-methyl-beta-D-ribo-hex-3-ulopyranoside (2), a model compound for partially oxidized anhydroglucose units in cellulose, was crystallized from CHCl(3)/n-hexane by vapor diffusion to give colorless plates. Crystal structure determination revealed the monoclinic space group P2(1) with Z = 2C(8)H(14)O(6) and unit cell parameters of a = 8.404(2), b = 4.5716(10), c = 13.916(3)A, and beta = 107.467(4) degrees. The structure was solved by direct methods and refined to R = 0.0476 for 1655 reflections and 135 parameters. The hexulopyranoside occurs in a distorted chair conformation. Both hydroxyls are involved in hydrogen bonding and form zigzag bond chains along the b-axis. One of the two hydrogen bonds is bifurcated. The solid-state (13)C NMR spectrum of exhibits eight carbon resonances, with well-separated signals for the two methoxyls (1-OMe: 55.72 ppm, 4-OMe: 61.25 ppm) and a keto resonance with relatively large downfield shift (206.90 ppm). Differences in the C-4 and the methoxyls' chemical shifts in the solid and liquid states were found.

Synthesis of oxidized methyl 4-O-methyl-beta-D-glucopyranoside and methyl beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside derivatives as substrates for fluorescence labeling reactions

The synthetic cellulose model compounds methyl 4-O-methyl-beta-D-glucopyranoside and methyl 4-O-methyl-beta-D-glucopyranosyl-(1-->4)-beta-D-glucopyranoside and related 6-O-protected intermediates were oxidized in good to fair yields using Swern-conditions or bromine/bis(tributyltin) oxide, respectively, to afford compounds containing 6-aldehyde, 3-keto, and 2,3-diketo groups. Cellobiose and oxidized monosaccharides were then labeled with the carbonyl-selective fluorescence marker 9-(7-amino-1,4,7-trioxaheptyl)-9H-carbazolecarboxamide (CCOA). The labeled derivatives serve as model compounds for the determination of minute amounts of carbonyl groups in cellulosic polysaccharides.