A Healthy and Ecologically Balanced Environment: An Argument for a Third Generation Right

Chymotrypsin-like serine proteases are found in high abundance in mast cell granules. By site-directed mutatgenesis, we have previously shown that basic amino acids in positions 143 and 192 (Arg and Lys respectively) of the human mast cell chymase are responsible for an acidic amino acid residue preference in the P2' position of substrates. In order to study the influence of these two residues in determining the specificity of chymase inhibitors, we have synthesized five different potent inhibitors of the human chymase. The inhibitory effects of these compounds were tested against the wild-type enzyme, against two single mutants Arg143Gln and Lys192Met and against a double mutant, Arg143Gln+Lys192Met. We observed a markedly reduced activity of all five inhibitors with the double mutant, indicating that these two basic residues are involved in conferring the specificity of these inhibitors. The single mutants showed an intermediate phenotype, with the strongest effect on the inhibitor by the mutation in Lys192. The Lys192 and the double mutations also affected the rate of cleavage of angiotensin I but did not seem to affect the specificity in the cleavage of the Tyr(4)-Ile(5) bond. A more detailed knowledge about which amino acids that confer the specificity of an enzyme can prove to be of major importance for development of highly specific inhibitors for the human chymase and other medically important enzymes

Glucose-induced cAMP elevation in β-cells involves amplification of constitutive and glucagon-activated GLP-1 receptor signalling

AIM: cAMP typically signals downstream of Gs -coupled receptors and regulates numerous cell functions. In β-cells, cAMP amplifies Ca2+ -triggered exocytosis of insulin granules. Glucose-induced insulin secretion is associated with Ca2+ - and metabolism-dependent increases of the sub-plasma-membrane cAMP concentration ([cAMP]pm ) in β-cells, but potential links to canonical receptor signalling are unclear. The aim of this study was to clarify the role of glucagon-like peptide-1 receptors (GLP1Rs) for glucose-induced cAMP signalling in β-cells. METHODS: Total internal reflection microscopy and fluorescent reporters were used to monitor changes in cAMP, Ca2+ and ATP concentrations as well as insulin secretion in MIN6 cells and mouse and human β-cells. Insulin release from mouse and human islets was also measured with ELISA. RESULTS: The GLP1R antagonist exendin-(9-39) (ex-9) prevented both GLP1- and glucagon-induced elevations of [cAMP]pm , consistent with GLP1Rs being involved in the action of glucagon. This conclusion was supported by lack of unspecific effects of the antagonist in a reporter cell-line. Ex-9 also suppressed IBMX- and glucose-induced [cAMP]pm elevations. Depolarization with K+ triggered Ca2+ -dependent [cAMP]pm elevation, an effect that was amplified by high glucose. Ex-9 inhibited both the Ca2+ and glucose-metabolism-dependent actions on [cAMP]pm . The drug remained effective after minimizing paracrine signalling by dispersing the islets and it reduced basal [cAMP]pm in a cell-line heterologously expressing GLP1Rs, indicating that there is constitutive GLP1R signalling. The ex-9-induced reduction of [cAMP]pm in glucose-stimulated β-cells was paralleled by suppression of insulin secretion. CONCLUSION: Agonist-independent and glucagon-stimulated GLP1R signalling in β-cells contributes to basal and glucose-induced cAMP production and insulin secretion

Glucose controls glucagon secretion by directly modulating cAMP in alpha cells

Aims/hypothesis Glucagon is critical for normal glucose homeostasis and aberrant secretion of the hormone aggravates dysregulated glucose control in diabetes. However, the mechanisms by which glucose controls glucagon secretion from pancreatic alpha cells remain elusive. The aim of this study was to investigate the role of the intracellular messenger cAMP in alpha-cell-intrinsic glucose regulation of glucagon release. Methods Subplasmalemmal cAMP and Ca2+ concentrations were recorded in isolated and islet-located alpha cells using fluorescent reporters and total internal reflection microscopy. Glucagon secretion from mouse islets was measured using ELISA. Results Glucose induced Ca2+-independent alterations of the subplasmalemmal cAMP concentration in alpha cells that correlated with changes in glucagon release. Glucose-lowering-induced stimulation of glucagon secretion thus corresponded to an elevation in cAMP that was independent of paracrine signalling from insulin or somatostatin. Imposed cAMP elevations stimulated glucagon secretion and abolished inhibition by glucose elevation, while protein kinase A inhibition mimicked glucose suppression of glucagon release. Conclusions/interpretation Glucose concentrations in the hypoglycaemic range control glucagon secretion by directly modulating the cAMP concentration in alpha cells independently of paracrine influences. These findings define a novel mechanism for glucose regulation of glucagon release that underlies recovery from hypoglycaemia and may be disturbed in diabetes

Mutations in Arg143 and Lys192 of the Human Mast Cell Chymase Markedly Affect the Activity of Five Potent Human Chymase Inhibitors

Chymotrypsin-like serine proteases are found in high abundance in mast cell granules. By site-directed mutatgenesis, we have previously shown that basic amino acids in positions 143 and 192 (Arg and Lys respectively) of the human mast cell chymase are responsible for an acidic amino acid residue preference in the P2' position of substrates. In order to study the influence of these two residues in determining the specificity of chymase inhibitors, we have synthesized five different potent inhibitors of the human chymase. The inhibitory effects of these compounds were tested against the wild-type enzyme, against two single mutants Arg143Gln and Lys192Met and against a double mutant, Arg143Gln+Lys192Met. We observed a markedly reduced activity of all five inhibitors with the double mutant, indicating that these two basic residues are involved in conferring the specificity of these inhibitors. The single mutants showed an intermediate phenotype, with the strongest effect on the inhibitor by the mutation in Lys192. The Lys192 and the double mutations also affected the rate of cleavage of angiotensin I but did not seem to affect the specificity in the cleavage of the Tyr(4)-Ile(5) bond. A more detailed knowledge about which amino acids that confer the specificity of an enzyme can prove to be of major importance for development of highly specific inhibitors for the human chymase and other medically important enzymes

γ-Hydroxybutyrate does not mediate glucose inhibition of glucagon secretion

Hypersecretion of glucagon from pancreatic α-cells strongly contributes to diabetic hyperglycemia. Moreover, failure of α-cells to increase glucagon secretion in response to falling blood glucose concentrations compromises the defense against hypoglycemia, a common complication in diabetes therapy. However, the mechanisms underlying glucose regulation of glucagon secretion are poorly understood and likely involve both α-cell-intrinsic and intraislet paracrine signaling. Among paracrine factors, glucose-stimulated release of the GABA metabolite γ-hydroxybutyric acid (GHB) from pancreatic β-cells might mediate glucose suppression of glucagon release via GHB receptors on α-cells. However, the direct effects of GHB on α-cell signaling and glucagon release have not been investigated. Here, we found that GHB (4-10 μm) lacked effects on the cytoplasmic concentrations of the secretion-regulating messengers Ca and cAMP in mouse α-cells. Glucagon secretion from perifused mouse islets was also unaffected by GHB at both 1 and 7 mm glucose. The GHB receptor agonist 3-chloropropanoic acid and the antagonist NCS-382 had no effects on glucagon secretion and did not affect stimulation of secretion induced by a drop in glucose from 7 to 1 mm Inhibition of endogenous GHB formation with the GABA transaminase inhibitor vigabatrin also failed to influence glucagon secretion at 1 mm glucose and did not prevent the suppressive effect of 7 mm glucose. In human islets, GHB tended to stimulate glucagon secretion at 1 mm glucose, an effect mimicked by 3-chloropropanoic acid. We conclude that GHB does not mediate the inhibitory effect of glucose on glucagon secretion

Identification of potent biodegradable adjuvants that efficiently break self-tolerance--a key issue in the development of therapeutic vaccines

Monoclonal antibodies are used successfully in the treatment of many human disorders. However, these antibodies are expensive and have in many countries put a major strain on the health care economy. Therapeutic vaccines, directed against the same target molecules, may offer a solution to this problem. Vaccines usually involve lower amount of recombinant protein, approximately 10,000-20,000 times less, which is significantly more cost effective. Attempts to develop such therapeutic vaccines have also been made. However, their efficacy has been limited by the lack of potent immunostimulatory compounds, adjuvants, for human use. To address this problem we have conducted a broad screening for adjuvants that can enhance the efficacy of therapeutic vaccines, whilst at the same time being non-toxic and biodegradable. We have now identified adjuvants that show these desired characteristics. A combination of Montanide ISA720 and phosphorothioate stabilized CpG stimulatory DNA, induced similar or even higher anti-self-antibody titers compared to Freund's adjuvant, currently the most potent, but also toxic, adjuvant available. This finding removes one of the major limiting factors in the field and facilitates the development of a broad range of novel therapeutic vaccines

Structures of the five different chymase inhibitors used in this study.

<p>Five different patented inhibitors of the HC originating from 5 different companies were synthesized. The inhibitors were subsequently used to determine the dependence of the basic amino acids Arg143 and Lys192 for the specificity in the interaction between the enzyme and the inhibitor. Compound A (TY51184) originates from Tao Eiyo (patent no WO 2002 022595), compound B from Teijin (patent no WO 2007 068621), compound C from Johnson & Johnson (patent no WO 2005 073214), compound D from Roche (patent no WO 2000 003997) and compound E from Boehringer Ingelheim (patent no WO 2009 023655).</p

The effect of mutations in Arg143 and Lys192 mutants on the processing of Ang I.

<p>The Arg143 and Lys192 variants ability to process Ang I was analysed by cleaving 10 µg of Ang I in a 20 µl reaction volume. Ang I (Asp₁-Arg₂-Val₃-Tyr₄-Ile₅-His₆-Pro₇-Phe₈-His₉-Leu₁₀, MW∼1297) is converted to Ang II (MW∼1046) by cleavage after the Phe₈ bond. As reference samples we also used the wt enzyme and the double mutant (Arg143+Lys192). Approximately the same amount of protease, as determined by cleavage of the chromogenic substrate LLVY-pNA, was used in each reaction (Right panel). Two µl samples were removed at different time points and analysed by mass spectrometry. The obtained results were compared in order to estimate the generated products aswell as a semi-quantitative measurement of the cleavage rate and its dependence on residues Arg143 and Lys192 and the double mutant. These experiments were independently performed three times with similar results.</p

Visualization of the different positions of Lys40, Arg143 and Lys192 found in X-ray structures.

<p>The flexibility of the basic residues can be explained by crystal packing and the differences between the inhibitors used. X-rays structures included have the following PDB codes: 2HVX, 3S0N, 1T31, 3N7O.</p