L-色氨酸增强氯苯氨丁酸的镇痛作用

小鼠在ip氯苯氨丁酸(baclofen)6.4mg/kg出现镇痛效应时,脑内5-HT及5-HIAA均无明显增多。L-TP负荷明显增强ip氯苯氨丁酸镇痛强度及时程,与同时增多脑内5-HT及5-HIAA相关,亦增强脑室注射氯苯氨丁酸的镇痛作用。ip PCPA 3d后5-HIAA降至39％,而镇痛作用仍存在。虽然氯苯氨丁酸由激活GABA受体而镇痛,脑内5-HT系统功能的增强可协同镇痛作用。     

A new structural class of proteasome inhibitors identified by microbial screening using yeast-based assay

A yeast-based growth interference assay was developed utilizing a yeast strain in which expression of Xenopus cyclin A1 was induced to elevate cell division cycle 28 (Cdc28) kinase activity. Since the hyperactivation of Cdc28 kinase in yeast results in a growth-arrest phenotype, compounds which could rescue the cyclin A1-induced growth arrest might be potential new, antitumor drug candidates acting on the cyclin-dependent, kinase-mediated, cell cycle regulation pathway. In the course of our microbial screening program, the new Streptomyces metabolites, belactosins, were identified. As reported previously, belactosin A induced cell cycle arrest at G2/M phase in human cancer cells. However, the molecular mechanism of action was unknown. We herein demonstrate the proteasome inhibition by belactosin A. Belactosin A did not inhibit yeast Cdc28 kinase and human cyclin-dependent kinase in vitro. On the other hand, it inhibited the chymotrypsin-like activity of the rabbit 20S proteasome. From the initial SAR studies, we identified a hydrophobic belactosin A derivative, KF33955, which exhibited a 100-fold greater growth-inhibitory activity against HeLa S3 cells than belactosin A, presumably due to its higher cell permeability. The biochemical analysis using KF33955 suggested that the proteasome inhibitory activity of KF33955 were irreversible and required the beta-lactone moiety to inhibit the proteasome. KF33955 increased the intracellular levels of protein ubiquitination in NIH3T3 cells. In addition, KF33955 treatment resulted in the accumulation of known proteasome substrates in HeLa S3 cells. These results identify belactosin A as a useful lead compound to target proteasome for the treatment of disease whose etiology is dependent on the unregulated ubiquitin-proteasome pathway.     

Synthesis and biological activities of some cholecystokinin analogues substituted in position 29 by a β-alanine

Syntheses of analogues of the C-terminal heptapeptide of cholecystokinin are described. These analogues were obtained by replacing glycine 29 by a β-alanine. The C-terminal phenylalanine amide was in some cases substituted by 2-phenylethyl alcohol and/or residues of the C-terminal tetrapeptide by their d -enantiomers. These compounds were tested for their action on stimulation of amylase release from rat pancreatic acini and for their ability to inhibit binding of labeled CCK to rat pancreatic acini and guinea pig brain membranes. Some of these derivatives behaved as CCK receptor antagonists.     

Factors affecting β-ODAP content in Lathyrus sativus and their possible physiological mechanisms

A neuroexcitatory non-protein amino acid, β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP), present in the seeds of the hardy legume crop grass pea (Lathyrus sativus L.), was considered responsible for human lathyrism. The levels of β-ODAP were reported to vary in different tissues during plant development, and to be affected by a wide range of environmental stresses. In this paper, dynamic changes in β-ODAP level at specific stages of plant development as well as the influences of various environmental factors, including nutrient deficiency, drought, salinity, toxic heavy metals, and Rhizobium symbiosis on β-ODAP levels were analyzed, highlighting the relationship between changes in β-ODAP concentrations and Rhizobium growth. Possible mechanisms underlying β-ODAP accumulation are proposed and future research is suggested.     

Genetic improvement of grass pea for low neurotoxin (β-ODAP) content

Grass pea is a promising crop for adaptation under climate change because of its tolerance to drought, water-logging and salinity, and being almost free from insect-pests and diseases. In spite of such virtues, global area under its cultivation has decreased because of ban on its cultivation in many countries. The ban is imposed due to its association with neurolathyrism, a non-reversible neurological disorder in humans and animals due to presence of neurotoxin, β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP) in its seedlings and seeds. The traditional varieties of grass pea contain 0.5-2.5% β-ODAP. Exploitable genetic variability for β-ODAP has been observed for development of low ODAP varieties, which along with improved agronomic and detoxification practices can help reduce the risk of lathyrism. Collaborative efforts between ICARDA and NARS have resulted in development of improved varieties such as Wasie in Ethiopia, Ratan, Prateek and Mahateora in India, and BARI Khesari-1 and BARI Khesari-2 in Bangladesh with <0.10% β-ODAP. Soil application of 15-20 kg ha⁻¹ zinc sulphate, early planting, and soaking seeds in water have shown significant effects on β-ODAP. Because of the often cross-pollination nature, the current breeding procedures being followed in grass pea requires paradigm shift in its approach for a possible genetic breakthrough.     

Contribution of the β-ureidopropionase (UPB1) gene alterations to the development of fluoropyrimidine-related toxicity

BackgroundAn impairment of the 5-fluorouracil (5-FU) catabolic pathway, represented by alterations in the dihydropyrimidine dehydrogenase (DPYD) gene, is considered a crucial factor contributing to the development of 5-FU-related toxicity. The β-ureidopropionase (BUP1) enzyme catalyzes the final step in the 5-FU catabolic pathway; however, alterations in the UPB1 gene coding for the BUP1 enzyme have not yet been analyzed in fluoropyrimidine (FP)-treated patients suffering from 5-FU-related toxicity.MethodsWe have performed a mutation analysis of the entire coding sequence of UPB1 based on denaturing high-performance liquid chromatography in 113 cancer patients treated by FP-containing regimes. These patients included 67 individuals suffering from severe 5-FU-related toxicity and 46 individuals with excellent tolerance of chemotherapy.ResultsNine UPB1 variants were detected in the subpopulation of patients with severe toxicity, including a novel mutation affecting the coding sequence (c.872_873 + 11del13). An analysis of UPB1 variants on 5-FU-related toxicity in the population of all analyzed patients revealed an association between the c.-80C > G (rs2070474) variant and gastrointestinal toxicity. A strong positive correlation was found between the carriers of the c.-80 GG genotype and the development of severe (grade 3–4) mucositis (OR = 7.5; 95% CI = 2.60 – 21.60; p = 0.0002).ConclusionOur results suggest that UPB1 variants may contribute to the development of 5-FU-related toxicity in some FP-treated patients; however, the role of UPB1 alterations is probably less significant than that of DPYD alterations.     

New Hurghamids from a Red Sea Sponge of the Genus Hippospongia

Abstract

Three new N-acyl-2-methylene-β-alanine methyl esters, Hurghamides E-G (5–7), were isolated from a Red Sea sponge Hippospongia sp. Their structures were elucidated by extensive spectroscopic studies.     

Taurine conjugate of ursodeoxycholate plays a major role in the hepatoprotective effect against cholestasis induced by taurocheno-deoxycholate in rats

ABSTRACT— Rats which were taurine-deprived through ß-alanine administration and untreated rats were used to elucidate the mechanism of hepatoprotective effects of ursodeoxycholate (UDC). Animals were infused with taurochenodeoxycholate (TCDC, 0.4 μmol · min^-1 · 100 g^-1) alone or in combination with tauroursodeoxycholate (TUDC), or with UDC (both 0.6 μmol · min-1 · 100 g^-1) for 2 h. Ursodeoxycholate as well as TUDC prevented severe cholestasis and liver damage induced by TCDC infusion in both untreated and taurine-deprived rat groups. In untreated rats, however, UDC was less effective in hepatoprotection than TUDC as indicated by sequential changes in biliary LDH output during the period of 30 to 120 min (P<0.05). In rats receiving UDC and TCDC, total biliary output of LDH for 2 h was significantly higher in taurine-deprived rats than that in the control (73.40±10.10 vs 41.14±12.56: P < 0.05), suggesting that the difference became greater upon taurine deprivation. In contrast, in rats receiving TUDC and TCDC, the protective effect was comparable for the taurine-deprived and untreated rats. When the animals were infused with UDC and TCDC, taurine-deprived rats exhibited a biliary excretion rate for TUDC half that of control rats (P<0.05). Furthermore, a highly significant correlation was observed between the biliary excretion rate of TUDC and biliary output of LDH (r = –0.886, P<0.0001). These results suggest that UDC conjugates, especially TUDC, and not UDC may play a major role in the prevention of cholestasis and liver cell damage caused by TCDC infusion.     

Binding of [H]glycine, [H]β-alanine and [H]strychnine in cultured rat spinal cord and brain stem

Cultures of rat brain stem and spinal cord were used to visualize binding sites for [³H]glycine, [³H]β-alanine and their antagonist [³H]strychnine by light microscopic autoradiography. In spinal cord cultures, all radio-ligands were bound mainly to large neurones, probably motoneurones whereas in brain stem cultures, both medium-sized and large neurones were labelled. In contrast, glial cells did not show binding sites for any of the compounds studied, suggesting that glial elements may not possess receptors for glycine and β-alanine.     

Metabolites of 5-fluorouracil, ·-fluoro-‚-alanine and fluoroacetic acid,directly injure myelinated fibers in tissue culture

The neurotoxicity of two 5-fluorouracil (5-FU) derivatives, tegafur (FT) and carmofur (HCFU), which selectively induce leukoencephalopathy involving the cerebral white matter in humans and vacuolation of myelinated fibers in dogs and cats, was examined in vitro. The common metabolites of these drugs, α-fluoro-β-alanine (FBAL) and fluoroacetic acid (FA), were added to the medium of cultured murine cerebellar myelinated fibers. On day 1 of exposure to 7 μM FBAL and FA, which corresponds to their blood concentrations 2 h after oral administration of 10 mg · kg^–1 HCFU to dogs that induced central nervous system vacuolation after 30 days, partial splits of the myelinic intraperiod line were observed by electron microscopy. On days 4–7, phase contrast microscopy revealed spindle-shaped swelling and granulation of myelin and electron microscopy demonstrated prominent dissociation of the myelinic intraperiod line with monolocular and multilocular vacuolation. More severe changes, such as myelin loss, were found in cultures exposed to a higher concentration (70 μM) of FBAL and FA, but no remarkable neuronal, astrocytic or oligodendrocytic changes occurred. Quantitative evaluation of myelin injury by electron microscopy revealed significant toxicity of FBAL and FA, at concentrations of 7 and 70 μM, on day 4. However, groups treated with 0.7 μM FBAL and FA, 5-FU (7 μM) and controls exposed to β-alanine and acetic acid concentrations of 0.7, 7 and 70 μM showed no marked injury. We concluded that these anticancer drug metabolites injure myelin fibers directly, resulting in vacuolation due to myelin splitting and destruction. Received: 6 September 1995 / Revised, accepted: 11 January 1996