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H P Ammon

Publications and source records attributed to H P Ammon.

At least 19 recordsLinked to original sources
PubMed2001

Methyl pyruvate initiates membrane depolarization and insulin release by metabolic factors other than ATP.

The role of mitochondria in stimulus-secretion coupling of pancreatic beta-cells was examined using methyl pyruvate (MP). MP stimulated insulin secretion in the absence of glucose, with maximal effect at 5 mM. K+ (30 mM) alone, or in combination with diazoxide (100 microM), failed to enhance MP-induced secretion. Diazoxide (100 microM) inhibited MP-induced insulin secretion. MP depolarized the beta-cell in a concentration-dependent manner (5-20 mM). The sustained depolarization induced by 20 mM MP was not influenced by 100 microM diazoxide, but the continuous spiking activity was suppressed by 500 microM diazoxide. Pyruvate failed to initiate insulin release (5-20 mM) or to depolarize the membrane potential. ATP production in isolated beta-cell mitochondria was detected as accumulation of ATP in the medium during incubation in the presence of malate or glutamate in combination with pyruvate or MP. There was no difference in ATP production induced by pyruvate/malate or MP/malate in isolated beta-cell mitochondria. ATP production by MP/glutamate was higher than that induced by pyruvate/glutamate, but it was much lower than that induced by alpha-ketoisocaproate/glutamate. Pyruvate (5 mM) or MP (5 mM) had no effect on the ATP/ADP ratio in whole islets, whereas glucose (20 mM) significantly increased the whole islet ATP/ADP ratio. It is concluded that MP-induced beta-cell membrane depolarization or insulin release does not relate directly to mitochondrial ATP production. Instead MP may exert a direct extramitochondrial effect, or it may stimulate beta-cell mitochondria to produce coupling factors different from ATP to initiate insulin release.

Adenosine Diphosphate↗
PubMed2001

Macroencapsulation of rat islets without alteration of insulin secretion kinetics.

Transplantation of encapsulated islets may restore endogenous insulin secretion in type 1 diabetics with no need of lifetime immunosuppression of the recipient. A biomaterial should be developed which combined immunoisolation with rapid and efficient diffusion of glucose and insulin. Rat islets were macroencapsulated in capillaries (molecular cut off 50 kD) of differently modified polysulphone. Macroencapsulated islets were perifused to study the kinetics of glucose induced insulin secretion into the perifusion medium. Blending polysulphone (PSU) with poly vinyl pyrrolidone or sodium dodecyl sulphate was not suited for islet macroencapsulation since glucose induced insulin release was absent after encapsulation. Hydroxy methylation (CH2OH) of PSU improved the secretory behaviour of macroencapsulated islets depending on the degree of substitution (DS). At 0.8 DS glucose induced insulin secretion was delayed and inefficient. At maximal degrees of PSU-substitution (1.8) the kinetics of insulin release and the efficiency of insulin release were very similar to that observed of free floating islets. In conclusion, highly substituted hydroxy methylated polysulphone allows a rapid and efficient insulin release after macroencapsulation and is suited for the further development of a bioartificial pancreas.

Animals↗
PubMed2001

Effects of gum resin of Boswellia serrata in patients with chronic colitis.

Patients studied here suffered from chronic colitis characterized by vague lower abdominal pain, bleeding per rectum with diarrhoea and palpable tender descending and sigmoid colon. The inflammatory process in colitis is associated with increased formation of leukotrienes causing chemotaxis, chemokinesis, synthesis of superoxide radicals and release of lysosomal enzymes by phagocytes. The key enzyme for leukotriene biosynthesis is 5-lipoxygenase. Boswellic acids were found to be non-redox, non-competitive specific inhibitors of the enzyme 5-lipoxygenase. We studied the gum resin of Boswellia serrata for the treatment of this disease. Thirty patients, 17 males and 13 females in the age range of 18 to 48 years with chronic colitis were included in this study. Twenty patients were given a preparation of the gum resin of Boswellia serrata (900 mg daily divided in three doses for 6 weeks) and ten patients were given sulfasalazine (3 gm daily divided in three doses for 6 weeks) and served as controls. Out of 20 patients treated with Boswellia gum resin 18 patients showed an improvement in one or more of the parameters: including stool properties, histopathology as well as scanning electron microscopy, besides haemoglobin, serum iron, calcium, phosphorus, proteins, total leukocytes and eosinophils. In the control group 6 out of 10 patients showed similar results with the same parameters. Out of 20 patients treated with Boswellia gum resin 14 went into remission while in case of sulfasalazine remission rate was 4 out of 10. In conclusion, this study shows that a gum resin preparation from Boswellia serrata could be effective in the treatment of chronic colitis with minimal side effects.

Adult↗
PubMed2001

In vitro test of new biomaterials for the development of a bioartificial pancreas.

The implantation of macroencapsulated islets has the potential to restore endogenous insulin secretion in type 1 diabetics, with no need for lifetime immunosuppression. To match the physiological fluctuations of blood glucose concentrations with appropriate insulin release, the macroencapsulation material must combine immunoprotection with optimal diffusion properties for glucose and insulin. The impact of chemical modifications of polysulphone (PSU) capillary polymers with a cutoff of 50 kD on glucose-induced insulin secretion of macroencapsulated rat islets was studied in perifusion experiments. The insulin release of free-floating islets showed the typical rapid response to glucose stimulation. Total insulin release (AUC between minute 30 and 120 of perifusion) reached 117+/-22 ng/ml. Blending PSU with polyvinylpyrrolidone or sodium-dodecyl-sulfate was not suitable for islet macroencapsulation, since glucose-induced insulin release was absent or disturbed. Hydroxy-methylation (CH2OH) of PSU improved the secretory behavior of macroencapsulated islets depending on the degree of PSU substitution (DS 0.8, AUC 62+/-15 ng/ml; DS 1.8, 111+/-24 ng/ml). In highly substituted PSU-capillaries the kinetics of glucose-induced insulin release was very similar to that observed in free-floating islets. Two consecutive glucose stimulations potentiated insulin release of free-floating islets during the second period of stimulation. Furthermore, freshly isolated macroencapsulated islets responded with more efficient insulin secretion after the initial priming. In conclusion, in vitro membrane screening identified highly substituted hydroxy-methylated PSU as the material of choice for islet encapsulation in a bioartificial pancreas.

Animals↗
PubMed2001

Distribution and stimulation by gastrin-releasing peptide of protein kinase C subfamilies in insulin-secreting cells.

The role of the different isoforms of protein kinase C (PKC) in modulating insulin secretion is still widely unknown. The aim of our studies was to investigate which isoforms are influenced by gastrin-releasing peptide (GRP), a neuropeptide which has been shown to modulate insulin secretion by activating PKC. Presence of PKC isoforms alpha, beta, gamma, delta, epsilon and zeta was tested by immunoblot analysis in whole pancreatic islets of mouse and rat and in the insulinoma cell line RINm5F. Effects of GRP, the truncated peptide GRP1-16 and KCl were also measured on translocation of PKC isoforms. In pancreatic islets of mouse and rat, the PKC isoforms alpha, beta, gamma, delta, epsilon and zeta could be detected. No PKCgamma activity was present in the pancreatic tumor cell line RINm5F. Incubation of mouse or rat islets or of RINm5F cells with GRP induced translocation of the PKC isoforms alpha, beta and zeta. The N-terminal portion of the peptide GRP1-16 induced partial translocation only of the PKC isoforms alpha, beta and zeta in mouse and rat islets in 4 out of 10 cases, but failed to show any effect on PKC isoforms in RINm5F cells. Depolarization of the islets by KCl did not translocate any tested PKC isoform. However, incubation with GRP followed by depolarization with KCl led to translocation of the PKC isoforms alpha, beta and zeta. It is suggested that PKC alpha, beta and/or zeta may play a role in the modulation of insulin secretion by GRP.

Animals↗
PubMed2000

MEK-1/2 inhibition prevents 5-lipoxygenase translocation in N-formylpeptide-challenged human neutrophils.

In order to elucidate the role of mitogen-activated protein kinase kinase (MEK-1/2) in 5-lipoxygenase (5-LO) activation we studied the N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced 5-LO translocation in human blood neutrophils (PMNs). In non-primed, Ca(2+)-repleted PMNs, fMLP consistently stimulated MEK-1/2 phosphorylation, but induced 5-LO translocation and product formation (430+/-128 pmol; SEM, n=13) only in 13 of 18 PMN preparations from different healthy donors. In fMLP-responsive cells, the MEK-1/2 inhibitor PD098059 (50 microM) attenuated MEK phosphorylation and abolished 5-LO activation at the translocation step. The fMLP-mediated 5-LO product formation was also sensitive to MEK inhibition by U0126 and to p38 inhibition by SB203580. But in contrast to PD098059, U0126 at 10 microM and SB203580 at 20-50 microM impaired 5-LO activity in the cell-free assay setting, suggesting direct actions of higher concentrations of U0126 and SB203580 on 5-LO apart from MEK and p38 inhibition, respectively. These data show that fMLP initiates 5-LO product formation in non-primed, Ca(2+)-repleted human blood PMNs from healthy donors, and that MEK signaling is pivotal, but not sufficient for 5-LO activation in response to the receptor agonist fMLP.

Arachidonate 5-Lipoxygenase↗
PubMed2000

Workup-dependent formation of 5-lipoxygenase inhibitory boswellic acid analogues.

Pentacyclic triterpenes from the 11-keto-boswellic acid series were identified as the active principal ingredients of Boswellia resin, inhibiting the key enzyme of leukotriene biosynthesis, 5-lipoxygenase (5-LO). Of the genuine boswellic acids hitherto characterized, 3-O-acetyl-11-keto-beta-boswellic acid, AKBA (1), proved to be the most potent inhibitor of 5-LO. In the course of purification of further boswellic acid derivatives from Boswellia resin, we observed the degradation of the natural compound 3-O-acetyl-11-hydroxy-beta-boswellic acid (2) to the thermodynamically more stable product 3-O-acetyl-9, 11-dehydro-beta-boswellic acid (4). The metastable intermediate of this conversion, under moderate conditions of workup in methanolic solutions, was identified as 3-O-acetyl-11-methoxy-beta-boswellic acid (3). The novel artifactual boswellic acid derivatives inhibited 5-LO product formation in intact cells with different characteristics: 4 almost totally abolished 5-LO activity, with an IC(50) of 0.75 microM, whereas 3 and 9,11-dehydro-beta-boswellic acid (5), the deacetylated analogue of 4, were incomplete inhibitors. The data suggest that the conditions chosen for the workup of Boswellia extracts could significantly influence the potency of their biological actions and their potential therapeutic effectiveness.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

[Ca(2+)](i)- and insulin-stimulating effect of the non-membranepermeable phosphatase-inhibitor microcystin-LR in intact insulin-secreting cells (RINm5F).

1. Microcystin-LR, a specific and effective inhibitor of serine/threonine phosphatases type 1/2A which does not permeate cells, was used to distinguish intracellular and extracellular effects of phosphatase inhibitors on insulin secretion by RINm5F cells. 2. Incubation of intact RINm5F cells with microcystin-LR (0.1 - 2 microM) almost doubled basal insulin release at 3 mM glucose but left maximal insulin release induced by KCl (30 mM) unaffected. 3. In parallel, there was an increase in cytosolic Ca(2+) by up to half maximum, which could be suppressed by the Ca(2+)-channel blocker D600. 4. In contrast, microcystin-LR incubation of intact cells did not affect phosphatase activity but significantly reduced phosphatase activity when used in cellular fractions. 5. From these data we conclude that microcystin-LR could affect Ca(2+)-channels and insulin release by inhibiting an extracellular phosphatase-like activity.

Animals↗
PubMed2000

Concentration-dependent potentiating and inhibitory effects of Boswellia extracts on 5-lipoxygenase product formation in stimulated PMNL.

Preparations from the gum of Boswellia spec. have been used in the traditional medicine for the treatment of inflammatory diseases. Extracts from B. serrata gum were shown to inhibit leukotriene biosynthesis by impairing the 5-lipoxygenase (5-LO) activity. In order to identify the minimal effective concentrations of extracts in vitro we studied the effects of ethanolic extracts from commercially available resins from two regions (B. serrata gum from India and Olibanum in granis from Arabia) on the 5-LO product formation from endogenous substrate in calcium and ionophore stimulated neutrophils in a defined concentration range. Both extracts inhibited 5-LO product formation in vitro in concentrations greater than 10 to 15 micrograms/ml as reported previously for an ethanolic B. serrata extract. In contrast, lower concentrations of extracts (1 to 10 micrograms/ml) even potentiated 5-LO product formation, especially the biosynthesis of 5(S)-HETE. The in vitro data underline the major importance of drug standardization when Boswellia resin containing preparations are used for the treatment of diseases.

Arachidonate 5-Lipoxygenase↗
PubMed2000

3-Acetoxy group of genuine AKBA (acetyl-11-keto-beta-boswellic acid) is alpha-configurated.

The pentacyclic triterpenoid 3-acetyl-11-keto-beta-boswellic acid (AKBA) from the resin of Boswellia spec. is a potent inhibitor of 5-lipoxygenase (5-LO). We noticed discrepancies in the nomenclature and stereochemistry of the 3-acetoxy group of boswellic acids. Isolation of AKBA under mild conditions and the data from the first X-ray crystallography study evidence the 3 alpha-orientation of AKBA's acetoxy function.

Crystallography, X-Ray↗
PubMed2000

Oxidative stress increases potassium efflux from pancreatic islets by depletion of intracellular calcium stores.

Oxidative stress to B-cells is thought to be of relevance in declining B-cell function and in the process of B-cell destruction. In other tissues including heart, brain and liver, oxidative stress has been shown to elevate the intracellular free calcium concentration and to provoke potassium efflux. We studied the effect of oxidative stress on Ca2+ and K+ (Rb+) outflow from pancreatic islets using the thiol oxidants DIP and BuOOH. Both compounds reversibly increased 86Rb+ efflux in the presence of 3 and 16.7 mmol/l glucose. Stimulation of 86Rb+ efflux was also evident in the absence of calcium. DIP evoked release of 45Ca2+ from the pancreatic islets both in the presence or absence of extracellular calcium. Employing inhibitors of the calcium-activated potassium channel (KCa) and the high conductance K+-channel (BKCa), the effect of DIP on 86Rb+ efflux was slightly diminished. Tolbutamide had no effect on 86Rb+ efflux in the presence of DIP. On the other hand thapsigargin, a blocker of the Ca+-ATPase of the endoplasmic reticulum, completely suppressed the DIP-mediated 86Rb+ outflow. The data suggest that thiol oxidant-induced potassium efflux from pancreatic islets is mainly mediated through liberation of intracellular calcium and subsequent stimulation of calcium-activated potassium efflux.

Adenosine Diphosphate↗
PubMed1999

Interference of H2O2 with stimulus-secretion coupling in mouse pancreatic beta-cells.

1. We have reported previously that in mouse pancreatic beta-cells H2O2 hyperpolarizes the membrane and increases the ATP-sensitive K+ current recorded in the perforated patch configuration of the patch-clamp technique. The present study was undertaken to elucidate the underlying mechanisms. 2. The intracellular ATP concentration measured by chemoluminescence was reduced by H2O2. The ADP concentration increased in parallel during the first 10 min, resulting in a pronounced decrease in the ATP/ADP ratio. 3. Consistent with these results, glucose-stimulated insulin secretion from isolated islets was inhibited by H2O2. 4. Membrane hyperpolarization measured with intracellular microelectrodes in intact islets and inhibition of insulin secretion were counteracted by tolbutamide, indicating that the channels are still responsive to inhibitors and that the ATP concentration is not too low to trigger exocytosis. However, the sensitivity of the beta-cells to tolbutamide was reduced after treatment with H2O2. 5. H2O2 increased the intracellular Ca2+ activity ([Ca2+]i) in a biphasic manner. A first transient rise in [Ca2+]i due to mobilization of Ca2+ from intracellular stores was followed by a sustained increase, which was at least partly dependent on Ca2+ influx. The first phase seems to reflect Ca2+ mobilization from mitochondria. 6. Our results demonstrate that H2O2 interferes with glucose metabolism, which influences the membrane potential and ATP-sensitive K+ current via the intracellular concentration of ATP. These events finally lead to an inhibition of insulin secretion despite an increase in [Ca2+]i.

Adenosine Triphosphate↗
PubMed1999

Boswellic acids and malignant glioma: induction of apoptosis but no modulation of drug sensitivity.

Steroids are essential for the control of oedema in human malignant glioma patients but may interfere with the efficacy of chemotherapy. Boswellic acids are phytotherapeutic anti-inflammatory agents that may be alternative drugs to corticosteroids in the treatment of cerebral oedema. Here, we report that boswellic acids are cytotoxic to malignant glioma cells at low micromolar concentrations. In-situ DNA end labelling and electron microscopy reveal that boswellic acids induce apoptosis. Boswellic acid-induced apoptosis requires protein, but not RNA synthesis, and is neither associated with free radical formation nor blocked by free radical scavengers. The levels of BAX and BCL-2 proteins remain unaltered during boswellic acid-induced apoptosis. p21 expression is induced by boswellic acids via a p53-independent pathway. Ectopic expression of wild-type p53 also induces p21, and facilitates boswellic acid-induced apoptosis. However, targeted disruption of the p21 genes in colon carcinoma cells enhances rather than decreases boswellic acid toxicity. Ectopic expression of neither BCL-2 nor the caspase inhibitor, CRM-A, is protective. In contrast to steroids, subtoxic concentrations of boswellic acids do not interfere with cancer drug toxicity of glioma cells in acute cytotoxicity or clonogenic cell death assays. Also, in contrast to steroids, boswellic acids synergize with the cytotoxic cytokine, CD95 ligand, in inducing glioma cell apoptosis. This effect is probably mediated by inhibition of RNA synthesis and is not associated with changes of CD95 expression at the cell surface. Further studies in laboratory animals and in human patients are required to determine whether boswellic acids may be a useful adjunct to the medical management of human malignant glioma.

Animals↗
PubMed1999

Acetyl-11-keto-beta-boswellic acid induces apoptosis in HL-60 and CCRF-CEM cells and inhibits topoisomerase I.

Antiproliferative action of different pentacyclic triterpenes has repeatedly been reported, and some lipoxygenase inhibitors have been shown to induce cell death in various cell systems. Acetyl-11-keto-beta-boswellic acid (AKBA) is a pentacyclic triterpene that inhibits 5-lipoxygenase in a selective, enzymedirected, nonredox, and noncompetitive manner. To investigate a possible effect of AKBA on leukemic cell growth, proliferation of HL-60 and CCRF-CEM cells was assayed in the presence of AKBA and a structural analog without effect on 5-lipoxygenase, amyrin. Cell counts and [3H]thymidine incorporation were significantly reduced in a dose-dependent manner in the presence of AKBA (IC50 = 30 microM) but not amyrin. An additive effect of AKBA with the crosslinking of the CD95 receptor was also observed. Flow cytometric analysis of propidium iodide-stained cells indicated that the cells underwent apoptosis. This was confirmed by flow cytometric detection of sub-G1 peaks in AKBA-treated cells and by DNA laddering. However, because HL-60 and CCRF-CEM do not express 5-lipoxygenase mRNA constitutively, a mechanism distinct from inhibition of 5-lipoxygenase must account for the effect of AKBA. In a DNA relaxation assay with phiX174RF DNA, AKBA inhibited topoisomerase I from calf thymus at concentrations of >/=10 microM. A semiquantitative cDNA polymerase chain reaction approach was used to estimate the relative level of expression of topoisomerases in both cell lines. The data suggest that induction of apoptosis in HL-60 and CCRF-CEM by AKBA may be due to inhibition of topoisomerase I in these cells.

Animals↗
PubMed1998

Effects of Boswellia serrata gum resin in patients with bronchial asthma: results of a double-blind, placebo-controlled, 6-week clinical study.

The gum resin of Boswellia serrata, known in Indian Ayurvedic system of medicine as Salai guggal, contains boswellic acids, which have been shown to inhibit leukotriene biosynthesis. In a double-blind, placebo-controlled study forty patients, 23 males and 17 females in the age range of 18 - 75 years having mean duration of illness, bronchial asthma, of 9.58 +/- 6.07 years were treated with a preparation of gum resin of 300 mg thrice daily for a period of 6 weeks. 70% of patients showed improvement of disease as evident by disappearance of physical symptoms and signs such as dyspnoea, rhonchi, number of attacks, increase in FEV subset1, FVC and PEFR as well as decrease in eosinophilic count and ESR. In the control group of 40 patients 16 males and 24 females in the age range of 14-58 years with mean of 32.95 +/- 12.68 were treated with lactose 300 mg thrice daily for 6 weeks. Only 27% of patients in the control group showed improvement. The data show a definite role of gum resin of Boswellia serrata in the treatment of bronchial asthma.

Adolescent↗
PubMed1998

Distribution of protein phosphatases type 1 and 2A in RINm5F cells.

In the insulin producing cell line RINm5F distribution of serine/threonine specific protein phosphatases type 1 (PP1) and 2A (PP2A) was studied. Using different agents which inhibit or stimulate PP1 and PP2A we found that in membrane and nuclear fractions phosphatase activity was inhibited by okadaic acid (OA), protamine, heparin, and inhibitor-2 in a concentration-dependent manner. C2-ceramide had no effect. In the cytosolic fraction the inhibitory effect of okadaic acid was tenfold higher. Protamine stimulated phosphatase activity at low concentrations and became inhibitory at higher concentrations. Inhibitor-2 and heparin caused a decrease in phosphatase activity whereas C2-ceramide led to a slight activation. The data suggest that in membrane and nuclear fractions of RINmSF cells predominantly PP1 is present, whereas in the cytosol PP1 as well as PP2A can be detected.

Animals↗