Monomethyl Succinate Research Articles

Exploring the phytochemical profile and therapeutic investigations on Moringa concanensis Nimmo pod husk extracts: An integrated in vitro and in silico approach

The present study aimed to determine the chemical profiling, antidiabetic, antioxidant, and antibacterial activity of Moringa concanensis pod husk (MCPH) by in vitro and in silico methods. Phytochemical analysis displayed significant ratios of secondary metabolites in all the extracts MPCH. Major compounds recorded during chemical profiling are 2,5-dimethylfuran-3,4(2H,5H)-dione (19.2%), oleic acid (13.4%) and campesterol (9%), pyranone (5.7%), monomethyl succinate (5.7%), and 1,2-cyclopentanedione (5.4%). In vitro pharmacological studies revealed that methanolic extract of MCPH had a significant effect on α-amylase (IC50 of 78.98 ± 0.58 μg/mL), α-glucosidase (IC50 of 40.80 ± 0.53 μg/mL) enzyme inhibition assays and antioxidant (IC50 of 54.60 ± 0.5 μg/mL for NO) activity. Antibacterial activity was evaluated against various bacterial strains and the ethyl acetate (MIC of 59.30 μg/mL), methanol (MIC of 14.84 μg/mL) and aqueous (MIC of 118.70 μg/mL) extracts of MCPH possessed potent inhibition effect against all the tested bacteria. Molecular docking investigation revealed that α-tocopherol acetate, palmitone, α-tocopherol, oleamide, β-sitosterol, and heptagonal had maximum binding affinity and docking score for all enzyme targets studied. Simulation studies indicate that α-tocopherol acetate could potentially be used as an activator to manage the enzymatic activity of α-amylase. The results showed that Moringa concanensis pod husk extracts are potential biological source of myriad phytoconstituents with pharmacological properties that can be further regulated for the discovery of novel drugs for the mankind.

Curtobacterium salicis sp. nov., isolated from willow tree stems in Washington state.

Curtobacterium sp. strain WW7 is a Gram-positive, non-motile, orange rod-shaped bacterium isolated from branches of wild willow (Salix sitchensis) trees. The WW7T strain has optimum growth in the temperature range between 25 and 30°C, a pH range of 6-7.7, and tolerates up to 5.5% (w/v) of NaCl. The genome sequencing of strain WW7T revealed a genome size of approximately 3.8 Mbp and a G + C content of 71.3mol%. The phylogenomic analyses support the WW7T affiliation to a novel Curtobacterium lineage, with Curtobacterium herbarum being the closest type-strain. Chemotaxonomic analysis indicates that the carbon sources assimilation profile of strain WW7T was similar to the type strains, i.e. Curtobacterium luteum, Curtobacterium albidum, and Curtobacterium flaccumfaciens, while no assimilation of the organic acids succinate, alpha-ketobutyrate, mono methyl-succinate, and lactate was observed. Finally, fatty acid methyl ester analysis identifies anteiso-C15:0 and anteiso-C17:0 as major cellular fatty acids which is a common feature for members of the Curtobacterium genus. Based on the results of phylogenomic and chemotaxonomic analyses, strain WW7T represents a novel Curtobacterium lineage, for which the name Curtobacterium salicis sp. nov. is proposed. The type strain is WW7T (DSM 34805T-NRRL B-68078T).

Synergistic chemoradiotherapy of cervical cancer cells using a pH- and radiation-sensitive doxorubicin-loaded β-cyclodextrin-based nanocomposite hydrogel containing MnO2 nanoparticles

It is an undoubted fact that remarkable clinical outcomes have demonstrated by synergistic chemoradiotherapy (CRT) approach, in comparison to solitary radiation therapy (RT) or chemotherapy (CT). Therefore, a novel pH- and radiation-sensitive nanocomposite hydrogel, β-cyclodextrin-graft-poly(succinic ethyl methacrylate)/MnO2 nanoparticles (β-CD-g-PSEMA/MnO2 NPs), was designed and developed through grafting 2-hydroxyethyl methacrylate (HEMA) onto functionalized β-CD through atom transfer radical polymerization (ATRP) followed by crosslinking β-CD-g-PHEMA-Br and bromine end-capped MnO2 NPs with Na2Se moiety to incorporate radiation-sensitive bonds into the hydrogel. The hydroxyl groups of PHEMA segments were converted to monomethyl succinate groups to induce pH sensitivity. Subsequently, the system was physically loaded with doxorubicin (Dox). In vitro drug release study revealed pH-dependent drug release behavior and the highest drug release value was obtained as 64.7% at pH 5. Oxygen generation from the developed drug delivery system (DDS) was confirmed, which the DDS could improve the efficiency of radiation therapy by oxygen generating in the cancer hypoxia environment. Intracellular uptake of the DDS was confirmed via FITC dye conjugation strategy. In contrast to free Dox, the developed DDS exhibited higher anticancer activity after 48 hours as validated by MTT and DAPI staining methods by synergistic CRT approach in moderate radiation dose.

Aloe-Emodin Derivative, an Anthraquinone Compound, Attenuates Pyroptosis by Targeting NLRP3 Inflammasome in Diabetic Cardiomyopathy.

Diabetic cardiomyopathy (DCM) is widely recognized as a major contributing factor to the development of heart failure in patients with diabetes. Previous studies have demonstrated the potential benefits of traditional herbal medicine for alleviating the symptoms of cardiomyopathy. We have chemically designed and synthesized a novel compound called aloe-emodin derivative (AED), which belongs to the aloe-emodin (AE) family of compounds. AED was formed by covalent binding of monomethyl succinate to the anthraquinone mother nucleus of AE using chemical synthesis techniques. The purpose of this study was to investigate the effects and mechanisms of AED in treating DCM. We induced type 2 diabetes in Sprague-Dawley (SD) rats by administering a high-fat diet and streptozotocin (STZ) injections. The rats were randomly divided into six groups: control, DCM, AED low concentration (50 mg/kg/day), AED high concentration (100 mg/kg/day), AE (100 mg/kg/day), and positive control (glyburide, 2 mg/kg/day) groups. There were eight rats in each group. The rats that attained fasting blood glucose of ˃16.7 mmol/L were considered successful models. We observed significant improvements in cardiac function in the DCM rats with both AED and AE following four weeks of intragastric treatment. However, AED had a more pronounced therapeutic effect on DCM compared to AE. AED exhibited an inhibitory effect on the inflammatory response in the hearts of DCM rats and high-glucose-treated H9C2 cells by suppressing the pyroptosis pathway mediated by the nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain 3 (NLRP3) inflammasome. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of differentially expressed genes showed a significant enrichment in the NOD-like receptor signaling pathway compared to the high-glucose group. Furthermore, overexpression of NLRP3 effectively reversed the anti-pyroptosis effects of AED in high-glucose-treated H9C2 cells. This study is the first to demonstrate that AED possesses the ability to inhibit myocardial pyroptosis in DCM. Targeting the pyroptosis pathway mediated by the NLRP3 inflammasome could provide a promising therapeutic strategy to enhance our understanding and treatment of DCM.

Insight into the green route to dimethyl succinate by direct esterification of bio-based disodium succinate using CO2 and CH3OH

The fermentation for succinic acid production outperforms other methods by low energy consumption and environmental benignity, with the resulting products mainly as disodium succinate (DSA). By directly esterifying DSA using CO2 and CH3OH, it is expected to avoid the use of inorganic acids. By high-resolution mass spectrometry analysis and theoretical calculation, this study establishes that the reaction consists of three steps, i.e., first forming 3-carboxypropanoate, then monomethyl succinate (MMS), and finally dimethyl succinate (DMS). A detailed kinetic analysis is further performed, the results demonstrate that the transformation of DSA to MMS is regarded to be a second-order reaction for reactant DSA, while the transformation of MMS to DMS is a first-order reaction for reactant MMS. The activation energy for the generation of MMS from DSA is 37.15 kJ·mol−1, and that for the generation of DMS from MMS is 85.80 kJ·mol−1, indicating the latter one is the rate-determining step.

Залежність адаптаційної здатності мітохондрій печінки від способу виділення клітин

When conducting studies on isolated hepatocytes, it is important to obtain cells that retain the functional properties that are characteristic of the whole organ. Increased blood viscosity during liver perfusion, decreased perfusion pressure in blood vessels, and hence hypoxia, are among the factors that may affect the functional state of isolated hepatocytes. The functional state of cells can be estimated by the adaptive capacity of mitochondria, by inducing maximal respiration rate by uncoupling respiration and oxidative phosphorylation due to the addition of FCCP. The research aimed to investigate the adaptive capacity of mitochondria of isolated hepatocytes using in situ and in vitro liver perfusion. Hepatocytes were isolated by the two-staged Seglen method by in situ and in vitro liver perfusion. Isolated hepatocytes, after 15-minute incubation in the medium without addition or with respective oxidative substrate – glutamine, pyruvate, succinate, monomethyl succinate, α-ketoglutarate, dimethyl-α-ketoglutarate (at a concentration of 2 mM) or glucose (10 mM) – were added into the respiratory chamber and FCCP was added in increasing concentrations. It was established that at in situ liver perfusion maximal rate of uncoupled respiration and the optimal concentration of FCCP was higher than at in vitro liver perfusion. Addition of exogenous substrates to a medium increased the respiration rate of hepatocytes. Upon in situ liver perfusion maximal uncoupled respiration rate increased at all causes except glucose, and at in vitro liver perfusion – only when dimethyl-α-ketoglutarate, succinate and monomethyl succinate were used. The optimal concentration of FCCP at in vitro liver perfusion increased due to the addition of glutamine, pyruvate and monomethyl succinate to the medium, and at in situ liver perfusion – only upon glucose oxidation. In both perfusion methods, the highest maximal rate of uncoupled respiration is with the use of monomethyl succinate and the optimal FCCP concentration – upon pyruvate oxidation. Therefore, in situ liver perfusion is better method to obtain stable and metabolically active hepatocytes in support respiratory processes at a high level then in vitro perfusion.

Identification and characterization of Methyl succinate from Bacillus velezensis AR1

Identification of antifungal organic compound from B. velezensis AR1 culture supernatant was performed using high-performance liquid chromatography (HPLC) and subjected to proton (1H) and carbon (13C) nuclear magnetic resonance (NMR). From the analysis of the heteronuclear multiple bond correlation, the purified compound was identified as monomethyl succinate (MMSucc). The subsequent investigation of its antifungal activity demonstrated growth inhibition of 5.73 to 100%, 8.75 to 96.67%, and 7.17 to 71.3% on Rhizoctonia solani, Sclerotinia sclerotiorum and Botrytis cinerea at 25 and 550 µg mL− 1 MMSucc, respectively. The minimum inhibitory concentration was 550, 650 and 675 µg mL− 1 for R. solani, S. sclerotiorum and B. cinerea, respectively. Therefore, based on its broad antifungal activities, it is possible to suggest the compound as an alternative source of fungicide.

Asymmetric Primaquine and Halogenaniline Fumardiamides as Novel Biologically Active Michael Acceptors.

Novel primaquine (PQ) and halogenaniline asymmetric fumardiamides 4a–f, potential Michael acceptors, and their reduced analogues succindiamides 5a–f were prepared by simple three-step reactions: coupling reaction between PQ and mono-ethyl fumarate (1a) or mono-methyl succinate (1b), hydrolysis of PQ-dicarboxylic acid mono-ester conjugates 2a,b to corresponding acids 3a,b, and a coupling reaction with halogenanilines. 1-[bis(Dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate (HATU) was used as a coupling reagent along with Hünig′s base. Compounds 4 and 5 were evaluated against a panel of bacteria, several Mycobacterium strains, fungi, a set of viruses, and nine different human tumor cell lines. p-Chlorofumardiamide 4d showed significant activity against Staphylococcus aureus, Streptococcus pneumoniae and Acinetobacter baumannii, but also against Candida albicans (minimum inhibitory concentration (MIC) 6.1–12.5 µg/mL). Together with p-fluoro and p-CF3 fumardiamides 4b,f, compound 4d showed activity against Mycobacterium marinum and 4b,f against M. tuberculosis. In biofilm eradication assay, most of the bacteria, particularly S. aureus, showed susceptibility to fumardiamides. m-CF3 and m-chloroaniline fumardiamides 4e and 4c showed significant antiviral activity against reovirus-1, sindbis virus and Punta Toro virus (EC50 = 3.1–5.5 µM), while 4e was active against coxsackie virus B4 (EC50 = 3.1 µM). m-Fluoro derivative 4a exerted significant cytostatic activity (IC50 = 5.7–31.2 μM). Acute lymphoblastic leukemia cells were highly susceptible towards m-substituted derivatives 4a,c,e (IC50 = 6.7–8.9 μM). Biological evaluations revealed that fumardiamides 4 were more active than succindiamides 5 indicating importance of Michael conjugated system.

Glucose Acutely Reduces Cytosolic and Mitochondrial H2O2 in Rat Pancreatic Beta Cells.

Aims: Whether H2O2 contributes to the glucose-dependent stimulation of insulin secretion (GSIS) by pancreatic β cells is highly controversial. We used two H2O2-sensitive probes, roGFP2-Orp1 (reduction/oxidation-sensitive enhanced green fluorescent protein fused to oxidant receptor peroxidase 1) and HyPer (hydrogen peroxide sensor) with its pH-control SypHer, to test the acute effects of glucose, monomethyl succinate, leucine with glutamine, and α-ketoisocaproate on β cell cytosolic and mitochondrial H2O2 concentrations. We then tested the effects of low H2O2 and menadione concentrations on insulin secretion. Results: RoGFP2-Orp1 was more sensitive than HyPer to H2O2 (response at 2-5 vs. 10 μM) and less pH-sensitive. Under control conditions, stimulation with glucose reduced mitochondrial roGFP2-Orp1 oxidation without affecting cytosolic roGFP2-Orp1 and HyPer fluorescence ratios, except for the pH-dependent effects on HyPer. However, stimulation with glucose decreased the oxidation of both cytosolic probes by 15 μM exogenous H2O2. The glucose effects were not affected by overexpression of catalase, mitochondrial catalase, or superoxide dismutase 1 and 2. They followed the increase in NAD(P)H autofluorescence, were maximal at 5 mM glucose in the cytosol and 10 mM glucose in the mitochondria, and were partly mimicked by the other nutrients. Exogenous H2O2 (1-15 μM) did not affect insulin secretion. By contrast, menadione (1-5 μM) did not increase basal insulin secretion but reduced the stimulation of insulin secretion by 20 mM glucose. Innovation: Subcellular changes in β cell H2O2 levels are better monitored with roGFP2-Orp1 than HyPer/SypHer. Nutrients acutely lower mitochondrial H2O2 levels in β cells and promote degradation of exogenously supplied H2O2 in both cytosolic and mitochondrial compartments. Conclusion: The GSIS occurs independently of a detectable increase in β cell cytosolic or mitochondrial H2O2 levels.

The effect of gamma radiation on some succinic acid derivatives in the solid state

2,2-dimethyl succinic acid, 2,3-dimethyl succinic acid and monomethyl succinate were exposed to gamma radiation in the form of powder. EPR measurements were carried out to investigate the free radicals produced in all of them, following irradiation. Three of the radical species formed after irradiation were identified and spectroscopic parameters were discussed thereafter. The radical species were attributed to the ĊHCH2, HOOCCH(CH3)2ĊCOOH and H3COOCCH2ĊHCOOH radicals, respectively. The hyperfine splitting constants for all radicals were confirmed by the simulation of the experimental spectra. The radiation sensitivity of the samples was mainly attributed to the EPR line properties of stable radicals.

Synthesis, characterization antibacterial and antifungal activity of some transition metal complexes

Some new transition metal complexes with monomethyl succinate are reported. Several physical techniques, such as elemental analysis and melting point, and in addition various spectroscopic techniques including 1H-, 13C-NMR and UV/visible and infrared spectroscopy were used to study the chemical structure of the prepared complexes. The octahedral geometry is proposed on the basis of these spectral techniques. The synthesized complexes were also exposed to various bacteria and fungi to establish their bioactivities.

Diorganotin complexes of carboxylates: synthesis and characterization

Diorganotin complexes of monoisopropyl and monomethyl nadiate, succinate, and phthalate were synthesized and characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, and 119Sn NMR spectroscopic techniques. The spectroscopic investigation demonstrated that carboxylate is bidentate in the diorganotin complexes. On the basis of 1 J(119Sn–13C) and 2 J(119Sn–1H) values, C–Sn–C bond angles were also calculated. The newly synthesized complexes were also screened for their antibacterial activities against Gram-positive and Gram-negative pathogenic strains of bacteria.

막걸리로부터 항산화 화합물의 단리.정제 및 동정

The present study was carried out to isolate and identify of antioxidants from makgeolli. Makgeolli (3 L) was filtered and the residue was extracted by MeOH. The combined filtrates and MeOH extracts were successively solvent- fractionated by n-hexane, EtOAc, and BuOH. In the antioxidative activity against DPPH and ABTS + radicals of each fraction obtained after solvent-fractionation, EtOAc and BuOH layers showed higher activities than other fractions. Therefore, the two layers were respectively purified by column chromatography and HPLC. The isolated compounds were subjected to NMR and MS analyses and identified as 4-hydroxybenzaldehyde (1, 2.0 mg), 2-(4-hydroxyphenyl)ethanol (2, tyrosol, 15.3 mg), trans- and cis-ferulic acids (3 and 4, 1.2 mg), 1H-indole-3-ethanol (5, tryptophol, 3.4 mg), dimethyl succinate (6, 14.9 mg), succinic acid (7, 7.4 mg), and mono-methyl succinate (8, 7.8 mg). The presence of 1-5 in makgeolli have never before been reported.

Acetoacetate and β-hydroxybutyrate in combination with other metabolites release insulin from INS-1 cells and provide clues about pathways in insulin secretion

Mitochondrial anaplerosis is important for insulin secretion, but only some of the products of anaplerosis are known. We discovered novel effects of mitochondrial metabolites on insulin release in INS-1 832/13 cells that suggested pathways to some of these products. Acetoacetate, beta-hydroxybutyrate, alpha-ketoisocaproate (KIC), and monomethyl succinate (MMS) alone did not stimulate insulin release. Lactate released very little insulin. When acetoacetate, beta-hydroxybutyrate, or KIC were combined with MMS, or either ketone body was combined with lactate, insulin release was stimulated 10-fold to 20-fold the controls (almost as much as with glucose). Pyruvate was a potent stimulus of insulin release. In rat pancreatic islets, beta-hydroxybutyrate potentiated MMS- and glucose-induced insulin release. The pathways of their metabolism suggest that, in addition to producing ATP, the ketone bodies and KIC supply the acetate component and MMS supplies the oxaloacetate component of citrate. In line with this, citrate was increased by beta-hydroxybutyrate plus MMS in INS-1 cells and by beta-hydroxybutyrate plus succinate in mitochondria. The two ketone bodies and KIC can also be metabolized to acetoacetyl-CoA and acetyl-CoA, which are precursors of other short-chain acyl-CoAs (SC-CoAs). Measurements of SC-CoAs by LC-MS/MS in INS-1 cells confirmed that KIC, beta-hydroxybutyrate, glucose, and pyruvate increased the levels of acetyl-CoA, acetoacetyl-CoA, succinyl-CoA, hydroxymethylglutaryl-CoA, and malonyl-CoA. MMS increased incorporation of (14)C from beta-hydroxybutyrate into citrate, acid-precipitable material, and lipids, suggesting that the two molecules complement one another to increase anaplerosis. The results suggest that, besides citrate, some of the products of anaplerosis are SC-CoAs, which may be precursors of molecules involved in insulin secretion.

Synergistic Potent Insulin Release by Combinations of Weak Secretagogues in Pancreatic Islets and INS-1 Cells

Insulin secretion by the beta cell depends on anaplerosis in which insulin secretagogues are metabolized by mitochondria into molecules that are most likely exported to the extramitochondrial space where they have signaling roles. However, very little is known about the products of anaplerosis. We discovered an experimental paradigm that has begun to provide new information about these products. When various intracellular metabolites were applied in combination to overnight-cultured rat or human pancreatic islets or to INS-1 832/13 cells, they interacted synergistically to strongly stimulate insulin release. When these same metabolites were applied individually to these cells, insulin stimulation was poor. Discerning the contributions of the individual compounds to metabolism has begun to allow us to dissect some of the pathways involved in insulin secretion, which was not possible from studying individual secretagogues. Monomethyl succinate (MMS) combined with a barely stimulatory concentration of alpha-ketoisocaproate (KIC) (2 mm) stimulated insulin release in cultured rat islets 18-fold (versus 21-fold for 16.7 mm glucose). MMS plus low glucose (2 mm) or pyruvate (5 mm) gave 11- and 9-fold stimulations. These agents also potentiated MMS-induced insulin release in fresh islets, and KIC plus MMS gave synergistic insulin release in cultured human islets. In INS-1 cells, neither MMS nor KIC (10 mm) was an insulin secretagogue, but when added together KIC (2 mm) and MMS stimulated insulin release 7-fold (versus 12-fold for glucose). In islets and INS-1 cells, conditions that stimulated insulin release caused large relative increases in acetoacetate, which is a precursor of pathways to short chain acyl-CoAs. Liquid chromatography-tandem mass spectrometry measurements of acetyl-CoA, acetoacetyl-CoA, succinyl-CoA, hydroxymethylglutaryl-CoA, and malonyl-CoA confirmed that they were increased by insulin secretagogues. The results suggest a new mechanism of insulin secretion in which anaplerosis increases short chain acyl-CoAs that have roles in insulin exocytosis.

FT‐IR kinetic and product study of the OH radical and Cl‐atom–initiated oxidation of dibasic esters

AbstractUsing a relative kinetic technique, rate coefficients have been measured, at 296 ± 2 K and 740 Torr total pressure of synthetic air, for the gas‐phase reaction of OH radicals with the dibasic esters dimethyl succinate [CH3OC(O)CH2CH2C(O)OCH3], dimethyl glutarate [CH3OC(O)CH2CH2CH2C(O)OCH3], and dimethyl adipate [CH3OC(O)CH2CH2CH2CH2C(O)OCH3]. The rate coefficients obtained were (in units of cm3 molecule−1 s−1): dimethyl succinate (1.89 ± 0.26) × 10−12; dimethyl glutarate (2.13 ± 0.28) × 10−12; and dimethyl adipate (3.64 ± 0.66) × 10−12. Rate coefficients have been also measured for the reaction of chlorine atoms with the three dibasic esters; the rate coefficients obtained were (in units of cm3 molecule−1 s−1): dimethyl succinate (6.79 ± 0.93) × 10−12; dimethyl glutarate (1.90 ± 0.33) × 10−11; and dimethyl adipate (6.08 ± 0.86) × 10−11. Dibasic esters are industrial solvents, and their increased use will lead to their possible release into the atmosphere, where they may contribute to the formation of photochemical air pollution in urban and regional areas. Consequently, the products formed from the oxidation of dimethyl succinate have been investigated in a 405‐L Pyrex glass reactor using Cl‐atom–initiated oxidation as a surrogate for the OH radical. The products observed using in situ Fourier transform infrared (FT‐IR) absorption spectroscopy and their fractional molar yields were: succinic formic anhydride (0.341 ± 0.068), monomethyl succinate (0.447 ± 0.111), carbon monoxide (0.307 ± 0.061), dimethyl oxaloacetate (0.176 ± 0.044), and methoxy formylperoxynitrate (0.032–0.084). These products account for 82.4 ± 16.4% C of the total reaction products. Although there are large uncertainties in the quantification of monomethyl succinate and dimethyl oxaloacetate, the product study allows the elucidation of an oxidation mechanism for dimethyl succinate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 431–439, 2001

Defective stimulus-secretion coupling in islets of Psammomys obesus, an animal model for type 2 diabetes.

Psammomys obesus is a model of type 2 diabetes that displays resistance to insulin and deranged beta-cell response to glucose. We examined the major signaling pathways for insulin release in P. obesus islets. Islets from hyperglycemic animals utilized twice as much glucose as islets from normoglycemic diabetes-prone or diabetes-resistant controls but exhibited similar rates of glucose oxidation. Fractional oxidation of glucose was constant in control islets over a range of concentrations, whereas islets from hyperglycemic P. obesus showed a decline at high glucose. The mitochondrial substrates alpha-ketoisocaproate and monomethyl succinate had no effect on insulin secretion in P. obesus islets. Basal insulin release in islets from diabetes-resistant P. obesus was unaffected by glucagon-like peptide 1 (GLP-1) or forskolin, whereas that of islets of the diabetic line was augmented by the drugs. GLP-1 and forskolin potentiated the insulin response to maximal (11.1 mmol/l) glucose in islets from all groups. The phorbol ester phorbol myristic acid (PMA) potentiated basal insulin release in islets from prediabetic animals, but not those from hyperglycemic or diabetes-resistant P. obesus. At the maximal stimulatory glucose concentration, PMA potentiated insulin response in islets from normoglycemic prediabetic and diabetes-resistant P. obesus but had no effect on islets from hyperglycemic P. obesus. Maintenance of islets from hyperglycemic P. obesus for 18 h in low (3.3 mmol/l) glucose in the presence of diazoxide (375 pmol/l) dramatically improved the insulin response to glucose and restored the responsiveness to PMA. Immunohistochemical analysis indicated that hyperglycemia was associated with reduced expression of alpha-protein kinase C (PKC) and diminished translocation of lambda-PKC. In summary, we found that 1) P. obesus islets have low oxidative capacity, probably resulting in limited ability to generate ATP to initiate and drive the insulin secretion; 2) insulin response potentiated by cyclic AMP-dependent protein kinase is intact in P. obesus islets, and increased sensitivity to GLP-1 or forskolin in the diabetic line may be secondary to increased sensitivity to glucose; and 3) islets of hyperglycemic P. obesus display reduced expression of alpha-PKC and diminished translocation of lambda-PKC associated with impaired response to PMA. We conclude that low beta-cell oxidative capacity coupled with impaired PKC-dependent signaling may contribute to the animals' poor adaptation to a high-energy diet.

Glucose-induced insulin secretion from islets of fasted rats: modulation by alternate fuel and neurohumoral agonists.

Islets from fed and 24-h-fasted rats were studied immediately after collagenase isolation. (1) After a 24-h fast, the insulin secretory responses to 8 mM glucose measured during perifusion were reduced by more than 90% from islets of fasted donors. (2) Increasing glucose to 11 or 27.5 mM resulted in enhanced insulin secretion from islets of fasted animals. (3) Fasting did not reduce islet insulin content. (4) Responses to 8 or 27.5 mM glucose were not affected if fatty acid-free albumin was used during the perifusion. (5) Inclusion of alpha-ketoisocaproate (5 mM), monomethyl succinate (10 mM) or carbachol (10 microM) significantly amplified insulin release from fasted islets in the simultaneous presence of 8 mM glucose. (6) Phospholipase C activation by glucose, carbachol or their combination was not adversely affected by fasting. (7) The response to the protein kinase C activator, phorbol 12-myristate 13-acetate (500 nM), was reduced by about 60% after fasting. (8) Extending the fast to 48 h resulted in a severe decline in response to 11 mM glucose; however, the further addition of 10 microM carbachol still enhanced release from these islets. The results confirm that caloric restriction impairs islet sensitivity to glucose stimulation and that protein kinase C may be involved in the reduction of glucose-induced insulin release from these islets. The activation of phospholipase C by cholinergic stimulation may contribute to the maintenance of insulin secretion from calorically restricted animals. These results also demonstrate that free fatty acids are not essential for glucose to evoke secretion from isolated islets of fasted donors.

Functional group interactions in the fragmentation of protonated and methylated succinic acid derivatives

The methane chemical ionization (CI) mass spectra of succinic acid monoamide and monomethyl succinate have been determined. In addition, the unimolecular metastable ion fragmentation reactions and low-energy collision-induced dissociation reactions of the MH + and M.CH 3 + ions of these compounds have been determined. In the CH 4 CI mass spectra extensive fragmentation of the MH + ions is observed, indicative of functional group interactions. An important fragmentation reaction for the protonated monoamide involves formation of NH 4 + and it is suggested that this occurs through the intermediacy of a protonated succinic anhydride/ammonia ion-neutral complex. The [MH–H 2O] + and [MH–CH 3OH] + fragment ions formed in the CH 4 CI of monomethyl succinate give collision-induced dissociation (CID) spectra which are in agreement with the spectra obtained for methylated and protonated succinic anhydride, respectively; these results strongly support the suggestions that the formation of stable cationated cyclic anhydride structures are one of the factors which result in extensive fragmentation of protonated and cationated dicarboxylic acid derivatives. The M.CH 3 + adduct of succinic acid monoamide gives a CID spectrum which is distinctly different from that obtained for the protonated monomethyl ester of succinic acid monoamide. This result indicates that little addition of CH 3 + to the free COOH group of the monoamide occurs. The CID spectrum of the M.CH 3 + adduct of monomethyl succinate also shows substantial differences from the CID mass spectrum of protonated dimethyl succinate.

Distillation with Chemical Reaction and Apparatus Selection

Abstract Reactive distillation was studied practically and theoretically for the esterification of succinic anhydride with methanol to produce in a first step monomethyl succinate and in a second one dimethyl succinate and water. It was shown that simulations using the ASPEN PLUS rigorous distillation model RADFRAC corresponds with experimental data quite well. With this fundament further calculations were performed simulating several kinds of reactive and distillation equipment. On basis of this, an apparatus selection is made related on energy consumption and relative conversion. Key parameters, as reaction velocity for the reaction term and the relative volatility (α from 1.2 to 14), affect markedly the selection of the apparatus of choice. The reaction column is the apparatus of choice for fast reactions and high volatilities considering the energy input. For low relative volatilities the choice is between the reaction column or the reactor with evaporation, depending on whether operating costs or inv...