Effects of tris(hydroxymethyl)aminomethane on biosynthesis and release of insulin in the pancreatic Langerhans islets

Tris(hydroxymethyl)aminomethane (Tris) has been shown to inhibit selectively the Golgi apparatus and Golgi-endoplasmic reticulum-lysosomal system (GERL system) of several kinds of cells including pancreatic B cells. This study was designed to assess the effect of Tris on insulin, glucagon and somatostatin release and insulin synthesis in pancreatic B cells by using isolated rat pancreatic islets. Tris suppressed glucose-induced insulin release, whereas it did not affect the glucagon and somatostatin release. Furthermore, the incorporation of [3H]leucine into the insulin fraction was suppressed by 10 mM Tris, but the sum of the radioactivity of both proinsulin and insulin fraction were not influenced. The present study suggests that the Golgi apparatus and GERL system may play a role in insulin secretion and biosynthesis in pancreatic B cells.     

Contact allergy to 2-hydroxy-5-tert-butyl benzylalcohol and 2,6-bis(hydroxymethyl)-4-tert-butylphenol, components of a phenolic resin used in marking pens

2-hydroxy-5-tert-butyl benzylalcohol and 2,6-bis(hydroxymethyl)-4-tert-butylphenol were identified as contact allergens in a phenolic resin used as a tackifier in the ink of a marking pen, which, after being used directly on the skin, caused an acute contact dermatitis on the hand of a 13-year-old boy. The patient also reacted to 4-tert-butylphenol-formaldehyde resin (BPF resin) 1% pet, included in the European standard series.     

Rapid and efficient synthesis of stable isotope labeled [13C4, D4]‐5‐(hydroxymethyl)thiazole: versatile building block for biologically interesting compounds

5‐(Hydroxymethyl)thiazole is a versatile building block for many biologically active compounds. A rapid and efficient four‐step synthesis of its stable isotope labeled counterpart with four ¹³C and four deuterium atoms in 32% total yield is reported. Condensation of [¹³C₂]‐chloro acetic acid with [¹³C]‐thiourea gave [¹³C₃]‐2,4‐thiazolidinedione. Reaction of [¹³C₃]‐2,4‐thiazolidinedione with phosphorus oxybromide and [¹³C, D]‐DMF (Me₂N¹³CDO) produced [¹³C₄, D]‐2,4‐dibromo‐thiazole‐5‐carboxaldehyde. The resultant aldehyde was then reduced by sodium borodeuteride to [¹³C₄, D₂]‐(2,4‐dibromo‐thiazol‐5‐yl)‐methanol. Catalytic deuteration of [¹³C₄, D₂]‐(2,4‐dibromo‐thiazol‐5‐yl)‐methanol by palladium black with deuterium gas at 1 atm pressure and room temperature produced completely de‐brominated [¹³C₄, D₄]‐5‐(hydroxymethyl)thiazole. De‐bromination of the 2,4‐dibromothiazole by the catalysis of palladium black provides a simple and convenient synthetic method for the stable isotope labeled and potentially radioactive isotope labeled thiazole compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Antisecretory actions of Baccharis trimera (Less.) DC aqueous extract and isolated compounds: analysis of underlying mechanisms

Ethnopharmacological relevance

Baccharis trimera (Less.) DC. (Asteraceae) is a species native to South America used in Brazilian folk medicine to treat gastrointestinal and liver diseases, kidney disorders and diabetes. Previous studies from this laboratory confirmed the antacid and antiulcer activities of the plant aqueous extract (AE) in rat and mouse models.

Aim of the study

To investigate the mechanisms involved in the antacid action of AE and isolated compounds from Baccharis trimera.

Materials and methods

AE was assayed in vivo in cold-restraint stress gastric ulcers and in pylorus-ligated mice. Nine fractions (F2-F10) previously isolated from AE were assayed in vitro on acid secretion measured as [¹⁴C]-aminopyrine ([¹⁴C]-AP) accumulation in rabbit gastric glands, and on gastric microsomal H⁺, K⁺-ATPase preparations. Chlorogenic acids (F2, F3, F6, F7), flavonoids (F9), an ent-clerodane diterpene (F8) and a dilactonic neo-clerodane diterpene (F10) have been identified in these fractions.

Results

Intraduodenal injection of AE (1.0 and 2.0 g/kg) in 4 h pylorus-ligated mice decreased the volume (20 and 50%) and total acidity (34 and 50%) of acid secretion compared to control values. Administered orally at the same doses AE protected against gastric mucosal lesions induced in mice by restraint at 4 °C. Exposure of isolated rabbit gastric glands to fractions F8 (10-100 μM) and F9 (10-300 μg/ml) decreased the basal [¹⁴C]-AP uptake by 50 and 60% of control (Ratio = 6.2 ± 1.1), whereas the remaining fractions were inactive. In the presence of the secretagogues F2 and F4 (30-300 μg/ml) decreased the [¹⁴C]-AP uptake induced by histamine (His) with a 100-fold lower potency than that of ranitidine. F5 and F6 reduced the [¹⁴C]-AP uptake stimulated by carbachol (CCh), but they were 10 to 20-fold less potent than atropine. F8 (diterpene 2) and F9 (flavonoids) decreased both the His- and CCh-induced [¹⁴C]-AP uptake, whereas F10 (diterpene 1) was inactive against the [¹⁴C]-AP uptake stimulated by secretagogues. Diterpene 2 was the most active of all tested compounds being 7-fold less potent than ranitidine and equipotent to atropine in reducing acid secretion in vitro. This compound also reduced the gastric H⁺, K⁺-ATPase activity by 20% of control, while the remaining fractions were inactive on the proton pump in vitro.

Conclusions

The results indicate that Baccharis trimera presents constituents that inhibit gastric acid secretion by acting mainly on the cholinergic regulatory pathway. The plant extract also contains compounds that exert moderate inhibition of the histaminergic regulatory pathway of acid secretion and the gastric proton pump. Altogether these active constituents appear to provide effective inhibition of acid secretion in vivo, which may explain the reputed antiulcer activity of the plant extract.     

Activation of distinct P2Y receptor subtypes stimulates insulin secretion in MIN6 mouse pancreatic β cells

Extracellular nucleotides and their receptor antagonists have therapeutic potential in disorders such as inflammation, brain disorders, and cardiovascular diseases. Pancreatic β cells express several purinergic receptors, and reported nucleotide effects on insulin secretion are contradictory. We studied the effect of P2Y receptors on insulin secretion and cell death in MIN6, mouse pancreatic β cells. Expression of P2Y₁ and P2Y₆ receptors was revealed by total mRNA analysis using RT-PCR. MIN6 cells were stimulated in the presence of 16.7 mM glucose with or without P2Y₁ and P2Y₆ agonists, 2-MeSADP and Up₃U, respectively. Both the agonists increased insulin secretion with EC₅₀ values of 44.6 ± 7.0 nM and 30.7 ± 12.7 nM respectively. The insulin secretion by P2Y₁ and P2Y₆ agonists was blocked by their selective antagonists MRS2179 and MRS2578, respectively. Binding of the selective P2Y₁ receptor antagonist radioligand [¹²⁵I]MRS2500 in MIN6 cell membranes was saturable (K_D 4.74 ± 0.47 nM), and known P2Y₁ ligands competed with high affinities. Inflammation and glucose toxicity lead to pancreatic β cell death in diabetes. Flow cytometric analysis revealed that Up₃U but not 2-MeSADP protected MIN6 cells against TNF-α induced apoptosis. Overall, the results demonstrate that selective stimulation of P2Y₁ and P2Y₆ receptors increases insulin secretion that accompanies intracellular calcium release, suggesting potential application of P2Y receptor ligands in the treatment of diabetes.     

Trypanosoma brucei brucei: A systematic screening for alternatives to the salicylhydroxamic acid-glycerol combination

Salicylhydroxamic acid (SHAM) and glycerol, when administered together, cause destruction of bloodstream forms of Trypanosoma brucei brucei, both in vitro and in vivo, but the dose required is exceedingly high. In an attempt to improve the efficacy of this drug combination, we examined the ability of various polyols and hydroxamic acids to substitute for glycerol and SHAM, respectively. No satisfactory substitute for glycerol was found. The inhibition of the trypanosomal α-glycerophosphate oxidase system (GPO) by SHAM (K_i 21 μM) was uncompetitive. Only primary and secondary aromatic hydroxamates were inhibitory. Among a series of 19 benzhydroxamates, no correlation existed between their acidity or their affinity for iron and their inhibition of the GPO in a cell free preparation. The K_i's of most of the primary hydroxamates ranged from 10 to 24 μM, with the more lipophilic derivatives being slightly more active. The K_i's of secondary hydroxamates were more variable, the best having K_i's of about 10 μM. Several other classes of iron chelators were also evaluated. Tropolones were active with 3-bromo-4,5-benzotropolone being as active as SHAM. 3,4-Dihydroxybenzaldehyde (K_i 15 μM) also inhibited the GPO. On the other hand, diphenylamine and 8-hydroxyquinoline, known inhibitors of the GPO, were 30 to 50 times less active. The results suggest that a lipophilic aromatic iron-chelating agent may be useful as a substitute for SHAM in combination therapy.     

Paramagnetic species in the plasma of dogs with lymphoma prior to and after treatment with doxorubicin. An ESR study

Doxorubicin is a potent cytostatic drug which is applied for the treatment of various kinds of malignant diseases. In spite of the routine use of this drug its major adverse effect, the dose-dependent cardiotoxicity, cannot be prevented yet. However, several clinical trials indicated that iron chelators are able to moderate the noxious effect more efficiently than radical scavenging antioxidants. This in turn supports the idea that doxorubicin-iron complexes are involved in triggering the cardiotoxicity of this drug by catalyzing the formation of oxygen radicals. However, both the mode of generation of doxorubicin-iron complexes and the consequences in vivo are not understood so far. In order to figure out whether or not doxorubicin can utilize iron from the transport protein transferrin for complex formation and prooxidative activities we studied the redox state of iron and its regulatory control by ceruloplasmin and ascorbate in the plasma of dogs suffering from malignant lymphoma by electron spin resonance spectroscopy. The respective electron spin resonance intensities prior to and after treatment with doxorubicin were compared with those from healthy controls. Our results revealed that dogs with lymphoma exhibit lower levels of paramagnetic copper in ceruloplasmin (-22%) and iron in transferrin (-33%) than healthy animals. Likewise the concentration of ascorbate radicals was lower in patients with lymphoma than in healthy subjects. The decreased cupric state of ceruloplasmin is equivalent to a diminished ferroxidase activity in plasma and therefore indicates indirectly an impaired antioxidant activity in these patients. Administration of doxorubicin in vivo further reduced the concentration of paramagnetic copper (-18%) and iron (-13%) while the concentration of ascorbate radicals remained unchanged. This decrease was also seen during the in vitro incubation of plasma with doxorubicin suggesting a direct interaction of the drug with the paramagnetic metal species. Model experiments revealed that the effect is based on a doxorubicin-induced release of iron from transferrin which is enhanced by ascorbate and the subsequent formation of doxorubicin-iron complexes. This mechanism was shown to trigger the formation of hydroxyl radicals from H(2)O(2) and to cause an oxidation of the antioxidant ceruloplasmin. Our data demonstrate that cardiotoxic doxorubicin-iron complexes are not only formed in cardiomyocytes itself as generally assumed, but are also present in the circulation. Therefore, these findings provide an additional rationale for potential benefit of iron chelators during doxorubicin chemotherapy.     

beta-Endorphin in neuroblastoma x glioma hybrid cells

Acid extracts from mouse Neuroblastoma x rat Glioma hybrid cells have been purified by means of Sep-Pak C-18 and fractionated by high performance liquid chromatography. Each fraction has been submitted to a sensitive beta-endorphin radioimmunoassay and an immunoreactivity peak at camel beta-endorphin retention time was found.     

2-Methoxy-3,8,9-trihydroxy coumestan: a new synthetic inhibitor of Na+,K+-ATPase with an original mechanism of action

The aim of the present work was to analyse the interaction between Na⁺,K⁺-ATPase and one of our recent synthesized coumestans, namely the original molecule 2-methoxy-3,8,9-trihydroxy coumestan (PCALC36). Rat brain (mainly α2 and α3 Na⁺,K⁺-ATPase isoforms) and kidney (α1 isoform) fractions enriched with Na⁺,K⁺-ATPase were utilized to compare the inhibition promoted by PCALC36 with that of classical inhibitors like ouabain and vanadate. Analysis of inhibition curves revealed that unlike ouabain, which was about a thousand times more potent to inhibit brain isoforms than kidney isoform, PCALC36 had a similar affinity for brain ( μM) and kidney ( μM) isoforms. The inhibitory effect of PCALC36 was not antagonized by 1-10 mM K⁺, as observed with ouabain. Whereas vanadate was more potent in ionic conditions promoting the E2 conformation of the enzyme, the inhibitory effect of PCALC36 was equal in ionic conditions favouring either the E1 or E2 conformations. Equilibrium binding assays with []ouabain revealed that the addition of 2-10 μM PCALC36 did not change the K_d of ouabain but decreased its maximal binding (B_max) in a concentration-dependent manner (from 76.6 to 44.0 pmol/mg protein). This inhibitory effect of PCALC36 was not reverted after an extensive washing procedure indicating that it forms a very stable complex with Na⁺,K⁺-ATPase. We conclude that PCALC36, a new molecule with a non-steroidal skeleton, inhibits the Na⁺,K⁺-ATPase by a mechanism of action different from the cardiac glycosides and could thus serve as a structural paradigm to develop new inotropic drugs.     

Inflammation and inducible nitric oxide synthase have no effect on monoamine oxidase activity in glioma cells

Heightened monoamine oxidase (MAO) and inducible nitric oxide synthase (iNOS) activity can contribute to oxidative stress, the formation of active neurotoxins, and associated neurodegenerative diseases of the brain. Although these enzymes co-exist within astrocytes, there has been little research examining the correlation between the two during inflammation. In this study, C6 glioma cells were stimulated with lipopolysaccharide (LPS):Escherichia coli 0111:B4 (6 micro g/mL):rat interferon-gamma (IFN-gamma) (100U/mL). In LPS/IFN-gamma-treated cells, the MAO substrates dopamine (DA) and tyramine caused a concentration-dependent attenuation of NO(2)(-) and NO(3)(-). In contrast, treatment with an MAO-A inhibitor (clorgyline) or an MAO-B inhibitor ((-)-deprenyl) did not reverse these effects. MAO activity was inhibited effectively by clorgyline and deprenyl; however, neither MAO inhibitor had an effect on NO(2)(-) in stimulated cells. Inversely, increasing concentrations of LPS/IFN-gamma resulted in heightened iNOS protein expression and NO(2)(-); however, these events did not correlate with any distinctive change in MAO enzyme activity. Moreover, a selective iNOS inhibitor, N(6)-(1-iminoethyl)-L-lysine, in LPS/IFN-gamma-stimulated cells caused a concentration-dependent attenuation of NO(2)(-) with no effects on MAO activity or iNOS protein expression. The attenuating effects of DA on iNOS were blocked completely by ICI 118-551 [(+/-)-1-[2,3-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride], indicating a role for the beta(2)-adrenergic receptor. In conclusion, these data indicate that activity or expression of iNOS does not influence MAO activity in activated rat glioma cells. Moreover, DA exerts an inhibitory effect on glial iNOS through a receptor-mediated cascade.