In vivo stimulation of insulin release by the monoethyl, monopropyl, monoisopropyl, monoallyl and diallyl esters of succinic acid

The methyl esters of succinic acid are potent insulin secretagogues, currently under investigation as possible tools in the treatment of non-insulin-dependent diabetes. The in vivo administration of these esters may result, however, in the undesirable generation of methanol. The present study reveals that other esters of succinic acid, such as the monoethyl, monopropyl, monoisopropyl, monoallyl and diallyl esters, stimulate insulin release when administered intravenously in a dose of 2 mumol/g body weight to anaesthetized fed rats. This indicates that several succinic acid esters, that are not susceptible to lead, through their intracellular hydrolysis, to the production of methanol remain efficient in vivo as insulin secretagogues.

D-glucose generation from [2-13C]pyruvate in rat hepatocytes: implications in terms of enzyme-to-enzyme channelling

In rat hepatocytes exposed to [2-13C]pyruvate, newly formed glucose was more efficiently labeled in the carbon C5 than C2, as well as in the carbon C6 than C1, suggesting enzyme-to-enzyme channeling of D-glyceraldehyde 3-phosphate between glyceraldehyde-3-phosphate dehydrogenase and phosphofructoaldolase. Likewise the C1/C2 and C6/C5 ratios for 13C abundance in newly formed glucose, which largely exceeded the C3/C2 ratio of lactate or alanine and could reflect reversibility in the fumarase reaction, were compatible with the enzyme-to-enzyme tunneling of symmetrical Krebs cycle intermediates in the sequence of reactions catalyzed by succinyl-CoA synthetase, succinate dehydrogenase, and fumarase. This study further indicates that the major fraction of pyruvate is metabolized via pyruvate carboxylase rather than pyruvate dehydrogenase.

Enzyme-to-enzyme channelling of Krebs cycle metabolic intermediates in Caco-2 cells exposed to [2-13c]propionate

The generation of 13C-labelled lactate by colon carcinoma cells of the Caco-2 line incubated for 120 min in the presence of [2-13C]propionate (10 mM) was assessed by 13C NMR. About 10% of the total amount of 13C-labelled lactate was recovered in the cell pellet and displayed a [2-13C]lactate/[3-13C]lactate isotopomer ratio of 1.18 +/- 0.01. An even higher isotopomer ratio of 1.53 +/- 0.14 was observed in the case of 13C-labelled lactate released by the cells into the incubation medium. These findings indicate that, in the Caco-2 cells, metabolic intermediates of the Krebs cycle undergo enzyme-to-enzyme channelling in the sequence of reactions catalysed by succinyl-CoA synthetase, succinate dehydrogenase and fumarase.

Enzyme-to-enzyme channelling of symmetric Krebs cycle intermediates in pancreatic islet cells

Tumoural islet cells of the RINm5F line were incubated for 120 min in the presence of [2-13C]propionate (10 mmol/l), and the 13C enrichment of lactate released in the incubation medium was monitored by 13C nuclear magnetic resonance. The C3/C2 ratio of resonance areas was much lower than that found with naturally 13C-enriched lactate. This reveals that symmetric Krebs cycle intermediates undergo oriented transfer in the sequence of reactions catalysed by succinate thiokinase, succinate dehydrogenate and fumarase in the mitochondria of islet cells.

Effects of succinic acid dimethyl ester infusion on metabolic, hormonal, and enzymatic variables in starved rats

BACKGROUND

Succinic acid dimethyl ester (SAD) is efficiently metabolized in several cell types as pancreatic islet cells, hepatocytes, and colonocytes. The purpose of this study was to assess the overall nutritional value of SAD in the whole organism.

METHODS

SAD was infused at a rate of 80 micromol/g body weight per day in rats starved for either 2 or 4 days. For comparison, similar experiments were conducted in starved rats receiving an equimolar infusion of D-glucose.

RESULTS

The ester failed to prevent the starvation-induced fall in body weight, paraovarian fat mass, and liver or muscle protein content. The infusion of SAD minimized, however, the decrease in plasma glucose and insulin concentrations, liver glycogen content, hepatic glucokinase activity, and islet secretory responsiveness to glucose, otherwise caused by starvation. Likewise, the infusion of SAD delayed the rise in free fatty acid and beta-hydroxybutyrate plasma concentration occurring during starvation. Nevertheless, SAD was less efficient than glucose, infused in an equimolar amount, in preventing the starvation-induced fall in liver glycogen content, decrease in the pancreatic B-cell secretory responsiveness to glucose, and stimulation of lipolysis and ketogenesis.

CONCLUSIONS

SAD displays a significant nutritional value when infused in starved rats. It could thus be used as a tool to prevent the imbalance between ATP generation and use in selected metabolic situations.

Nutritional efficiency of succinic acid and glutamic acid dimethyl esters in colon carcinoma cells

The dimethyl esters of succinic acid (SAD) and glutamic acid (GME) were found to be efficiently metabolized in colon carcinoma cells of the Caco-2 line. The rate of [1,4-14C]SAD and [2,3-14C]SAD conversion to radioactive acidic metabolites, CO2, amino acids, pyruvic acid, and lactic acid suggested that the catabolism of the ester-derived succinic acid occurred mainly through the sequence of reactions catalyzed by succinate dehydrogenase, fumarase, and the malic enzyme. This coincided with a marked sparing action of SAD on the utilization of D-[2-(3)H]glucose and D-[5-(3)H]glucose and generation of 14C-labeled acid metabolites, CO2, and lactic acid from D-[U-14C]glucose by the enterocytes. Likewise, the conversion of [U-14C]GME to 14C-labeled amino acids, its oxidation compared with that of [1-(14)C]GME, and the production of NH4+ in the absence or presence of GME indicated efficient catabolism of the latter ester. Like SAD, GME decreased the utilization of D-[5-(3)H]glucose and generation of 14C-labeled acidic metabolites, pyruvate, and CO2 from D-[6-(14)C]glucose, while increasing the generation of 14C-labeled amino acids from the labeled hexose. The oxidation of D-[6-(14)C]glucose was even more severely inhibited by GME. In normal rat intestinal cells, SAM, SAD, and GME also exerted a marked sparing action on D-[U-14C]glucose oxidation. The present findings suggest, therefore, that these esters could possibly be used to sustain ATP generation in intestinal cells.

Effects of the methyl esters of pyruvate, succinate and glutamate on the secretory response to meglitinide analogues in rat pancreatic islets

The insulinotropic action of the meglitinide analogues KAD-1229, A-4166 and repaglinide was examined in rat pancreatic islets deprived of exogenous nutrient or incubated in the presence of nutrient secretagogues such as D-glucose and the methyl esters of pyruvic acid, succinic acid and glutamic acid. The meglitinide analogues exerted little effect on insulin release in the absence of exogenous nutrient or in the presence of methyl pyruvate. They caused obvious stimulation of insulin output in the presence of D-glucose, dimethyl succinate or dimethyl glutamate. It is proposed, therefore, that suitable esters of dicarboxylic nutrients could be used to potentiate the secretory response to meglitinide analogues in non-insulin-dependent diabetes mellitus.

Restricted effect of formycin A and non-glucidic nutrients upon insulin release in islets from rats with hereditary or acquired non-insulin-dependent diabetes

Pancreatic islets isolated from control rats, Goto-Kakizaki rats and adult rats that were injected with streptozotocin during the neonatal period were incubated for two successive period of 90 min each in the presence of D-glucose (11.1 mM) with or without formycin A (1.0 mM), and in the presence of the dimethyl ester of succinic acid (SAD, 10.0 mM) with or without palmitate (1.0 mM). Although formycin A augmented glucose-stimulated insulin release in both control and diabetic rats, it failed to compensate for the impaired secretory response to D-glucose in the latter animals. Likewise, non-glucidic nutrients such as SAD and/or palmitate failed to display a more efficient insulinotropic action, relative to basal insulin output, in diabetic than control rats. These results indicate that both formycin A and non-glucidic nutrients are unable, through their immediate insulinotropic action, to restore a normal output of insulin in islets of animals with inherited or acquired non-insulin-dependent diabetes.

Hydrolysis of succinic acid dimethyl ester in rat pancreatic islets

The hydrolysis of the dimethyl ester of [1,4-14C]succinic acid and/or [2,3-14C]succinic acid was measured in homogenates of rat pancreatic islets, liver, jejunum, brain, BC3H1 mouse myocytes, NG108-19 mouse neuroblastoma x rat glioma hybrid cells, and Caco-2 human colon adenocarcinoma cells. The specific activity of the enzyme was much higher in liver, jejunum, and Caco-2 cells than in the other cell types. The affinity of the enzyme for succinic acid dimethyl ester (SAD) was also much higher in liver than in islet homogenates. In the latter case, both particulate and cytosolic activity were observed upon subcellular fractionation. The activity found in islet homogenates was commensurate with the rate of SAD hydrolysis in intact cells. While the intracellular pool of acidic metabolites generated from SAD remained fairly stable over a 15- to 120-min incubation and was mainly located in the cytosolic compartment, the amount of acidic metabolites released in the extracellular milieu progressively increased with the length of incubation. Such metabolites included both monocarboxylic and dicarboxylic acids, the latter consisting mainly of succinic acid and, to a much lesser extent, of fumaric acid and malic acid. However, at variance with SAD, succinic acid failed to be taken up by intact islets. There was no close parallelism between the specific activity of the SAD esterase and the extent of SAD utilization in distinct cell types.

Metabolism of succinic acid methyl esters in myocytes

The metabolism of the dimethyl ester of succinic acid (SAD) was examined in myocytes. When expressed in terms of CO(2) output, the oxidation of SAD (10 mM) only represented 30-40% of that of an equimolar concentration of D-glucose. Except for a modest decrease in D-[5-(3)H]glucose utilization, SAD failed to affect the catabolism of exogenous D-glucose. SAD also failed, like D-glucose, to augment O(2) consumption by the myocytes. These findings indicate that SAD is less efficiently metabolized in myocytes than in hepatocytes or pancreatic islets. It is nevertheless argued that the methyl esters of succinic acid could be efficiently used as nutrients by myocytes in situations of ATP depletion.

Morphologic and morphometric evaluation of the effect of ICRF-187 on bleomycin-induced pulmonary toxicity

Morphologic and morphometric studies were made of the protective effects of ICRF-187 against the pulmonary damage induced by bleomycin in male and female C57/BL6 mice. Sixty minutes prior to the subcutaneous administration of 15 mg/kg of bleomycin, animals received either saline or ICRF-187 (300 or 150 mg/kg) intraperitoneally, twice a week for 4 weeks. The lungs of animals treated with bleomycin alone showed inflammation, hyperplasia of type II epithelial cells, squamous cell metaplasia and fibrosis. The extent of fibrosis was quantified by means of a color videometric system and histologic sections of lung stained according to a modified Masson trichrome method. The severity of these alterations, particularly of fibrosis, was reduced in all groups of animals pretreated with ICRF-187. The fibrosis was reduced to a similar extent in female mice treated with the 300 mg/kg and the 150 mg/kg doses of ICRF-187, from 39.3% to 17.6% and 13.3%, respectively. ICRF-187 induced significantly different degrees of reduction in fibrosis in the 2 groups of male mice treated with the 150 mg/kg and the 300 mg/kg doses, from 30% to 19.7% and 12.2%, respectively. In vitro studies indicated that both ICRF-187 and its open-ring hydrolysis product (ADR-925) remove iron slowly from the bleomycin-iron complex. This observation provides a basis for the concept that ICRF-187 protects by chelating iron involved in the formation of the bleomycin-Fe3+ complex that generates reactive oxygen radicals capable of causing pulmonary damage.

Metabolism of succinic acid methyl esters in neural cells

The metabolism and metabolic effects of succinic acid methyl esters were examined in both NG108-15 mouse neuroblastoma x rat glioma hybrid cells and normal rat brain cells. The conversion of the dimethyl ester of 14C-labeled succinic acid (10 mM) to 14CO2 only represented 5% or less of that found at an equimolar concentration of D-[U- 14C]glucose. Neither the monomethyl nor the dimethyl ester of succinic acid exerted any significant effect upon the metabolism of D-glucose. Likewise, D-glucose (10 mM) failed to significantly affect the oxidation of the dimethyl ester of either [1,4- 14C]succinic acid or [2,3- 14C]succinic acid. It is concluded that, at variance with the situation recently documented in rat pancreatic islets and hepatocytes, the methyl esters of succinic acid are poorly metabolized in neural cells.

SAM prevents impairment of glucose-stimulated insulin secretion caused by hexose deprivation or starvation

Succinic acid monomethyl ester (SAM) was recently proposed as an insulinotropic tool in non-insulin-dependent diabetes mellitus. Three models were now used to investigate whether SAM protects the B-cell against the impairment of glucose-stimulated insulin release caused by either glucose deprivation or starvation. In the first model, preincubation of the islets for 180 min at low glucose concentration in the presence of SAM prevented the decrease in the secretory response to D-glucose otherwise observed during a subsequent incubation. In the second model, an impaired secretory response to D-glucose was observed after 3-day culture at low (2.8 or 5.6 mM) as distinct from high (11.1 mM) hexose concentration and the presence of SAM in the culture medium again protected against this anomaly. In the third model, the infusion of SAM for 3 days to starved rats restored the secretory potential of isolated islets to a level comparable to that otherwise found in fed rats. Thus, during glucose deprivation or starvation, SAM is indeed able to maintain B-cell responsiveness to D-glucose.

Metabolic effects and fate of succinic acid methyl esters in rat hepatocytes

The metabolic fate and metabolic effects of succinic acid methyl esters were examined in rat isolated hepatocytes. Both the monomethyl ester (SAM) and dimethyl ester (SAD) of succinic acid inhibited D-glucose metabolism. Such an inhibition affected, in order of increasing severity, the direct incorporation of D-glucose into glycogen and futile cycling between the hexose and its 6-phosphate ester, the phosphorylation of D-glucose, the generation of triose phosphates from the hexose, and the production of 14C-labeled lactate, pyruvate, and amino acids from D-[U-14C]glucose and its oxidation. The dimethyl ester of [1,4-14C]succinic acid ([1,4-14C]SAD) or [2,3-14C]-succinic acid ([2,3-14C]SAD) was efficiently converted to acidic metabolites. The oxidation of [1,4-14C]SAD largely exceeded that of [2,3-14C]SAD. Inversely the generation of newly formed radioactive D-glucose and glycogen appeared higher in cells exposed to [2,3-14C]SAD, rather than [1,4-14C]SAD. It is proposed that SAM and SAD are suitable nutrients both to cover the energy need of hepatocytes and to act as gluconeogenic precursors.

Glycogen synthase, glycogen phosphorylase and alpha-amylase activity in homogenates of islets of GK rats: comparison with hepatic and pancreatic extracts

Glycogen accumulation in pancreatic islet cells in situations of sustained hyperglycaemia may participate in the phenomenon of so-called B-cell glucotoxicity. Unexpectedly, however, previously little if any glycogen was found in islet cells of non-insulin-dependent diabetic Goto-Kakizaki rats (GK rats). Therefore, the activities of glycogen synthase, glycogen phosphorylase and alpha-amylase were measured in islets of control and GK rats. No significant difference in enzymatic activity was observed between the control and diabetic animals. In the liver, the activity of glycogen synthase appeared even somewhat higher in GK rats than in control animals. It is concluded that the diabetic syndrome in the GK rats does not involve any major anomaly of glycogen synthase and glycogen phosphorylase activity in the liver of these animals, as well as alpha-amylase, in pancreatic islets.

Hexose metabolism in pancreatic islets UDP-glucose pyrophosphorylase activity

UDP-glucose pyrophosphorylase was measured in rat pancreatic islets, the generation of D-glucose 1-phosphate from UDP-glucose and PPI being eventually coupled to the generation of L-[U-14C]glutamate from 14C-labelled alpha-ketoglutarate. The activity of the enzyme was about one order of magnitude lower in islet than liver homogenates. The affinity of the enzyme for either UDP-glucose or PPi was comparable, however, in liver and islets. The activity of UDP-glucose pyrophosphorylase was somewhat lower in islets from animals with inherited or acquired diabetes mellitus than in those from control rats. These findings are considered in connection with the accumulation of glycogen in islets of hyperglycemic animals.

Hexose metabolism in pancreatic islets: glycogen synthase and glycogen phosphorylase activities

The activity of glycogen synthase and glycogen phosphorylase was measured in rat pancreatic islet homogenates. For this purpose, the sensitivity of current radioisotopic procedures for the assay of these enzymes in liver extracts was increased by about two orders of magnitude. Even so, the measurement of glycogen synthase and phosphorylase in islet homogenates was hampered by a potent amylase-like activity, resulting in the hydrolysis of preformed or newly formed 14C-labeled glycogen. Acarbose suppressed the latter phenomenon which was found attributable to both minute contamination of isolated islets by acinar cells and genuine alpha-amylase activity in purified islet beta-cells. As measured by the more sensitive method in the presence of acarbose, the a/(a+b) ratio for glycogen synthase activity in islet homogenates was increased in islets preincubated in the presence as distinct from absence of D-glucose and decreased after preincubation with forskolin. These changes represented a mirror image of those evoked by D-glucose and forskolin in the a/(a+b) ratio for glycogen phosphorylase activity. It is concluded that glycogen synthesis and breakdown are regulated in the endocrine pancreas in a manner qualitatively comparable to that prevailing in hepatocytes, the possible participation of an amylase-like activity to glycogen metabolism in intact islet beta-cells requiring further investigation.

Synergistic effect of probimane on anticancer cytotoxicity of doxorubicin in vitro

Using 3-(4,5-dimethythiazole)-2,5-diphenyltetrazolium bromide (MTT) method, the effect of probimane (Pro) on doxorubicin (Dox) cytotoxicity was studied. Pro 0.313, 0.625, and 1.25 micrograms.ml-1 potentiated cytotoxicity of Dox in Ehrlich ascites carcinoma (EAC) cells. Incubation of EAC cells with Dox 10 micrograms.ml-1 and Pro 116.5, 233, and 466 micrograms.ml-1 resulted in an increase in intracellular drug accumulation from 0.69 +/- 0.06 to 1.08 +/- 0.10 micrograms/10(7) cells. In S37-bearing mice, Pro 23.3, 46.6, and 116.5 micrograms.ml-1 enhanced the malondialdehyde (MDA) formation in tumor and liver mitochondria and decreased MDA formation in liver mitochondria. These results suggested that the increases of Dox accumulation and MDA formation in tumor cells by Pro might be the reasons for synergistic effect of Pro on Dox cytotoxicity.

Synergistic effect of oridonin and cisplatin on cytotoxicity and DNA cross-link against mouse sarcoma S180 cells in culture

Oridonin (Ori) is an active principle isolated from Rabdosia rubescens. The cytotoxic effect of the combination of Ori and cisplatin was tested by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] colorimetric assay. IC50 of cisplatin to cultured S180 cells in 24 h was 9.38 micrograms.ml-1. When the cells were treated with cisplatin plus Ori 0.5 and 1 microgram.ml-1, the IC50 were 1/3.4 and 1/6.7, respectively, of that with cisplatin alone. Modified alkaline elution was used to detect the DNA interstrand cross-link and DNA-protein cross-link in S180 cells induced by the 2 drugs. A greater amount of DNA cross-link was detected when the cells were treated with cisplatin plus Ori than with cisplatin alone (P < 0.05). After lysis by proteinase K, a reduction in DNA cross-link was seen, which suggested that the drugs could produce both kinds of DNA cross-link.

[Studies on the chemical components of essential oil from the aerial parts of Ligusticum chuanxiong Hort]

Qualitative and quantitative analyses of the essential oil steamdistilled from the aerial parts of Ligusticum chuanxiong were made by means of GC-MS and GC. Forty-six components which make up 85.82% of the total oil were identified.

Early analysis of viremia and clinical tests in patients with epidemic hemorrhagic fever

We analysed the early viremia and clinical tests in 82 patients with epidemic hemorrhagic fever (EHF). The results showed that the changes in viremia and clinical tests are related to the severity of the disease and prognosis. Higher concentrations of the virus in infected patients might cause a more unfavourable prognosis and more abnormalities in clinical tests. CK-MB, SGOT, SGPT, serum creatinine and urea nitrogen contents increased markedly, while serum total protein, albumin and calcium contents decreased markedly, indicating that the heart, liver and kidney in EHF patients were severely damaged. Markedly increased WBC and monocytes showed that the patients were seriously infected. Platelet count, antithrombin-III and plasminogen decreased markedly, demonstrating that there were marked changes in the coagulation-anticoagulation and fibrinolytic system of the EHF patients. Changes in RBC, Hb and HCT contents indicated that the blood in the EHF patients had a higher concentration. This study gives further evidence that EHFV plays an important role in the pathogenesis of EHF.

Long-term survival of autologous adrenal medulla grafts in the great omentum of the rat

The omentum, a rich source for trophic and angiogenic factors, was explored as a potential intermediate transplant site to facilitate long-term survival of chromaffin tissue. Autologous rat adrenal medullas were grafted into omental pockets. All grafts became densely vascularized. The grafted chromaffin tissue exhibited strong immunoreactivities for tyrosine hydroxylase, synaptophysin and chromogranin A throughout the observation period of 16 weeks. The expression of these markers implies that grafted chromaffin cells retained the key enzyme for catecholamine biosynthesis and the organelles required for catecholamine secretion. Moreover, intermediate transplant of chromaffin tissue to the omentum could provide a favourable conditioning microenvironment thus augmenting the potential for survival of functional chromaffin tissue.

Inhibitory effect of dioxopiperazine compounds on malondialdehyde formation induced by doxorubicin in rat liver mitochondria in vitro

The isolated rat liver mitochondria were used in vitro to study the effect of doxorubicin on lipid peroxidation. We found that NADH-dependent mitochondrial peroxidation, measured by thiobarbituric acid (TBA) method, was stimulated to fourfold by doxorubicin (50 mumol.L-1). The addition of Fe3+ produced a significant increase of malondialdehyde (MDA) formation induced by doxorubicin. Doxorubicin enhanced the peroxidation of lipids in liver mitochondria through enzymatic mechanism especially in the presence of Fe3+. Probimane, bimolane, dexrazoxane (dioxopiperazine compounds), and edetic acid (EDTA) inhibited the formation of MDA in doxorubicin or doxorubicin+FeCl3 systems in a concentration-dependent manner. The inhibitory rates of MDA formation by probimane at the concentrations of 0.01, 0.05, 0.1, and 0.25 mmol.L-1 were 27.80%, 25.19%, 47.80%, and 59.77% respectively; bimolane were 21.04%, 25.55%, 24.83%, and 54.13%; dexrazoxane were 11.29%, 20.68%, 34.94%, and 58.65%; EDTA were 57.52%, 55.67%, 61.62%, and 63.16% in Dox and FeCl3 system. The inhibitory rates of MDA formation by probimane at concentration 0.01, 0.05, 0.1, and 0.25 mmol.L-1 were 19.27, 39.02, 59.60, and 58.63% respectively; bimolane were 6.10, 17.19, 41.58, and 53.22%; dexrazoxane were 27.24, 33.26, 58.21, and 59.11%; EDTA were 63.76, 67.43, 61.68, and 63.27% respectively in Dox system. These results suggested that protection against cardiotoxicity of doxorubicin afforded by probimane, bimolane, and dexrazoxane may be related to their ability to combine with the complex iron so that the iron was no longer able to take part in free radical reactions.

Effect of schisandrin B on lipoperoxidative damage to plasma membrane of rat liver in vitro

The effect of schisandrin B (Sin B) on oxygen free radicals--induced lipoperoxidative damage to plasma membrane of rat hepatocytes was investigated. When the plasma membrane of rat hepatocytes was incubated with iron/cysteine or Vit C/NADPH, the production of malondialdehyde (MDA) and consumption of NADPH increased, while the membrane fluidity reduced. Addition of Sin B (3-25 micrograms.ml-1) to the incubation mixture inhibited all these alterations of the plasma membrane induced by iron/cysteine and Vit C/NADPH. The results indicated that Sin B could maintain membrane stability of rat hepatocytes under oxidative stress.