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Biomedical subjects

H Weichert

Publications and source records attributed to H Weichert.

15 recordsLinked to original sources
PubMed2001

Enzymatic and non-enzymatic lipid peroxidation in leaf development.

Enzymatic and non-enzymatic lipid peroxidation has been implicated in programmed cell death, which is a major process of leaf senescence. To test this hypothesis we developed a high-performance liquid chromatography (HPLC) method for a simultaneous analysis of the major hydro(pero)xy polyenoic fatty acids. Quantities of lipid peroxidation products in leaves of different stages of development including natural senescence indicated a strong increase in the level of oxygenated polyenoic fatty acids (PUFAs) during the late stages of leaf senescence. Comprehensive structural elucidation of the oxygenation products by means of HPLC, gas chromatography/mass spectrometry and (1)H nuclear magnetic resonance suggested a non-enzymatic origin. However, in some cases a small share of specifically oxidized PUFAs was identified suggesting involvement of lipid peroxidizing enzymes. To inspect the possible role of enzymatic lipid peroxidation in leaf senescence, we analyzed the abundance of lipoxygenases (LOXs) in rosette leaves of Arabidopsis. LOXs and their product (9Z,11E,13S,15Z)-13-hydroperoxy-9,11,15-octadecatrienoic acid were exclusively detected in young green leaves. In contrast, in senescing leaves the specific LOX products were overlaid by large amounts of stereo-random lipid peroxidation products originating from non-enzymatic oxidation. These data indicate a limited contribution of LOXs to total lipid peroxidation, and a dominant role of non-enzymatic lipid peroxidation in late stages of leaf development.

Arabidopsis↗
PubMed2001

Activity of soybean lipoxygenase isoforms against esterified fatty acids indicates functional specificity.

In soybean (Glycine max L.) vegetative tissue at least five lipoxygenase isozymes are present. Four of these proteins have been localized to the paraveinal mesophyll, a layer of cells that is thought to function in assimilate partitioning. In order to determine the role of the lipoxygenase isozymes within the soybean plant, the leaf lipoxygenases were cloned into bacterial expression vectors and expressed in Escherichia coil. The recombinant lipoxygenases were then characterized as to substrate preference, pH profiles for the most common plant lipoxygenase substrates, linoleic acid, and alpha-linolenic acid, and the reaction products with the substrates linoleic acid, alpha-linolenic acid, arachidonic acid, gamma-linolenic acid, and the triacylglycerol trilinolein. All five enzymes were shown to be (13S)-lipoxygenases against linoleic acid. The results of these assays also indicate that two of these isozymes are highly active against esterified fatty acid groups, such as those found in triacylglycerols. Lipid analysis of leaves from plants subjected to sink limitation conditions indicates that the soybean leaf lipoxygenases are active in vivo against both free fatty acids and esterified lipids, and that the quantities of lipoxygenase products found in leaf tissue show a positive correlation with the level of lipoxygenase in the leaf. Implications for the putative role of these enzymes in the paraveinal mesophyll are discussed.

Arachidonic Acid↗
PubMed2001

Preferential induction of a 9-lipoxygenase by salt in salt-tolerant cells of Citrus sinensis L. Osbeck.

Recent findings in our laboratory suggested that in citrus cells the salt induction of phospholipid hydroperoxide glutathione peroxidase, an enzyme active in cellular antioxidant defense, is mediated by the accumulation of hydroperoxides. Production of hydroperoxides occurs as a result of non-enzymatic auto-oxidation or via the action of lipoxygenases (LOXs). In an attempt to resolve the role of LOX activity in the accumulation of peroxides we analyzed the expression of this protein under stress conditions and in cells of Citrus sinensis L. differing in sensitivity to salt. Lipoxygenase expression was induced very rapidly only in the salt-tolerant cells and in a transient manner. The induction was specific to salt stress and did not occur with other osmotic-stress-inducing agents, such as polyethylene glycol or mannitol, or under hot or cold conditions, or in the presence of abscisic acid. The induction was eliminated by the antioxidants dithiothreitol and kaempferol, thus once more establishing a correlation between salt and oxidative stresses. Analyses of both in vitro and in vivo products of LOX revealed a specific 9-LOX activity, and a very fast reduction of the hydroperoxides to the corresponding hydroxy derivatives. This suggests that one of the metabolites further downstream in the reductase pathway may play a key role in triggering defense responses against salt stress.

Abscisic Acid↗
PubMed2000

Expression of cucumber lipid-body lipoxygenase in transgenic tobacco: lipid-body lipoxygenase is correctly targeted to seed lipid bodies.

A particular isoform of lipoxygenase (LOX, EC 1.13.11.12) localized on lipid bodies has been shown by earlier investigations to play a role during seed germination in initiating the mobilization of triacylglycerols. On lipid bodies of germinating cucumber (Cucumis sativus L.) seedlings, the modification of linoleoyl moieties by this LOX precedes the hydrolysis of the ester bonds. We analyzed the expression and intracellular location of this particular LOX form in leaves and seeds of tobacco (Nicotiana tabacum L.) transformed with one construct coding for cucumber lipid-body LOX and one construct coding for cucumber LOX fused with a hemagglutinin epitope. In both tissues, the amount of lipid-body LOX was clearly detectable. Biochemical analysis revealed that in mature seeds the foreign LOX was targeted to lipid bodies, and the preferred location of the LOX on lipid bodies was verified by immunofluorescence microscopy. Cells of the endosperm and of the embryo exhibited fluorescence based on the immunodecoration of LOX protein whereas very weak fluorescent label was visible in seeds of untransformed control plants. Further cytochemical analysis of transformed plants showed that the LOX protein accumulated in the cytoplasm when green leaves lacking lipid bodies were analyzed. Increased LOX activity was shown in young leaves of transformed plants by an increase in the amounts of endogenous (2E)-hexenal and jasmonic acid.

Aldehydes↗
PubMed2000

Formation of 4-hydroxy-2-alkenals in barley leaves.

In barley leaves 13-lipoxygenases are induced by jasmonates. This leads to induction of lipid peroxidation. Here we show by in vitro studies that these processes may further lead to autoxidative formation of (2E)-4-hydroxy-2-hexenal from (3Z)-hexenal.

Aldehydes↗
PubMed2000

Metabolic profiling of oxylipins upon sorbitol treatment in barley leaves.

In barley leaves 13-lipoxygenases (LOXs) are induced by salicylate and jasmonate. Here, we analyse by metabolic profiling the accumulation of oxylipins upon sorbitol treatment. Although 13-LOX-derived products are formed and specifically directed into the reductase branch of the LOX pathway, accumulation is much later than in the cases of salicylate and jasmonate treatment. In addition, under these conditions only the accumulation of jasmonates as additional products of the LOX pathway has been found.

Aldehydes↗
PubMed1999

Metabolic profiling of oxylipins upon salicylate treatment in barley leaves--preferential induction of the reductase pathway by salicylate(1).

In barley leaves, 13-lipoxygenases (13-LOXs) are induced by salicylate (SA) and jasmonate. Here, we show by metabolic profiling that upon SA treatment, free linolenic acid and linoleic acid accumulate in a 10:1 ratio reflecting their relative occurrence in leaf tissues. Furthermore, 13-LOX-derived products are formed and specifically directed into the reductase branch of the LOX pathway leading mainly to the accumulation of (13S,9Z,11E,15Z)-13-hydroxy-9, 11,15-octadecatrienoic acid (13-HOT). Under these conditions, no accumulation of other products of the LOX pathway has been found. Moreover, exogenously applied 13-HOT led to PR1b expression suggesting for the time a role of hydroxy polyenoic fatty acid derivatives in plant defense reactions.

Enzyme Induction↗
PubMed1999

Formation of lipoxygenase-pathway-derived aldehydes in barley leaves upon methyl jasmonate treatment.

In barley leaves, the application of jasmonates leads to dramatic alterations of gene expression. Among the up-regulated gene products lipoxygenases occur abundantly. Here, at least four of them were identified as 13-lipoxygenases exhibiting acidic pH optima between pH 5.0 and 6.5. (13S,9Z,11E,15Z)-13-hydroxy-9,11,15-octadecatrienoic acid was found to be the main endogenous lipoxygenase-derived polyenoic fatty acid derivative indicating 13-lipoxygenase activity in vivo. Moreover, upon methyl jasmonate treatment > 78% of the fatty acid hydroperoxides are metabolized by hydroperoxide lyase activity resulting in the endogenous occurrence of volatile aldehydes. (2E)-4-Hydroxy-2-hexenal, hexanal and (3Z)- plus (2E)-hexenal were identified as 2,4-dinitro-phenylhydrazones using HPLC and identification was confirmed by GC/MS analysis. This is the first proof that (2E)-4-hydroxy-2-hexenal is formed in plants under physiological conditions. Quantification of (2E)-4-hydroxy-2-hexenal, hexanal and hexenals upon methyl jasmonate treatment of barley leaf segments revealed that hexenals were the major aldehydes peaking at 24 h after methyl jasmonate treatment. Their endogenous content increased from 1.6 nmol.g-1 fresh weight to 45 nmol.g-1 fresh weight in methyl-jasmonate-treated leaf segments, whereas (2E)-4-hydroxy-2-hexenal, peaking at 48 h of methyl jasmonate treatment increased from 9 to 15 nmol.g-1 fresh weight. Similar to the hexenals, hexanal reached its maximal amount 24 h after methyl jasmonate treatment, but increased from 0.6 to 3.0 nmol.g-1 fresh weight. In addition to the classical leaf aldehydes, (2E)-4-hydroxy-2-hexenal was detected, thereby raising the question of whether it functions in the degradation of chloroplast membrane constituents, which takes place after methyl jasmonate treatment.

Acetates↗
PubMed1997

The glutathione level of retinal Müller glial cells is dependent on the high-affinity sodium-dependent uptake of glutamate.

The dependence of intracellular glutathione, an important radical scavenger, on the extracellular glutamate and cystine concentration and the velocity of the high affinity sodium/glutamate transporter was studied in freshly-isolated Müller glial cells of the guinea-pig, kept in vitro for up to 11 h. To this end the relative Müller cell glutathione levels were measured using the fluorescent dye monochlorobimane, using different concentrations of glutamate and cystine in Ringer solution. In some experiments L-buthionine-[S,R]-sulfoximine, a blocker of glutathione synthesis, or L-trans-pyrrolidine-2,4-dicarboxylic acid and L-alpha-aminoadipic acid, inhibitors of glutamate uptake, were added. The Müller cells maintained about 80% of the normal glutathione level when maintained in Ringer solution containing 100 microM glutamate for 11 h. When under these conditions 100 microM cystine was added, the glutathione level increased to values, which were even higher than those at the beginning of the incubation period. Addition of cystine without glutamate caused a run down of the glutathione level to about 45% of the normal level, which is comparable to the run down in pure Ringer solution. Likewise, application of L-buthionine-[S,R]-sulfoximine (5 mM) lead to a strong run down of the glutathione level even in glutamate/cystine (100 microM)-containing solution. A similar suppressing effect was observed using L-trans-pyrrolidine-2,4-dicarboxylic acid and L-alpha-aminoadipic acid in the presence of 100 microM cystine and glutamate. We conclude that the intracellular glutamate concentration of the Müller cells is determined by the extracellular glutamate concentration and the velocity of the sodium/glutamate uptake. Consequently, cystine uptake into Müller cells, which is performed by the cystine/glutamate antiporter, is fueled by the sodium/glutamate transporter with intracellular glutamate. Both glutamate and cystine are also substrates for glutathione synthesis. The glutathione level is logically limited by the capacity of the sodium/glutamate transporter to provide glutamate intracellularly for, first, cystine uptake and, second, direct insertion into glutathione. Accordingly, the glutathione level is reduced when the sodium/glutamate transporter is blocked. Thus, a diminution of the glutathione level should be taken into consideration when the effects of sodium/glutamate uptake failure and reduced intracellular glutamate concentrations are discussed.

2-Aminoadipic Acid↗
PubMed1997

[Surgical therapy of diffuse peritonitis--staged lavage].

Better understanding of pathophysiology and improved techniques of intensive medical care resulted in new concepts of aggressive treatment for diffuse peritonitis. All consider the importance of surgical removal of the infectious focus but also the necessity of further treatment following first surgical intervention in cases of severe peritonitis. No randomised clinical study yet exists. Indication and application of selected therapeutic technique result from clinical criteria and experience. Presently used concepts are described and evaluated from a clinical viewpoint.

Adult↗
PubMed1995

In vitro production of monoclonal antibodies in high concentration in a new and easy to handle modular minifermenter.

This paper describes a new and easy to handle reusable minifermenter for high-density culture of hybridoma and other cells. The culture apparatus is composed of two modules: a 40 ml disposable cell culture and antibody production chamber (the 'production module') and a 550 ml medium reservoir (the 'supply module'). The two modules are separated from each other by a dialysis membrane allowing passage of low molecular mass nutrients and metabolites. The monoclonal antibodies are produced and enriched in the production module. The outer part of this module is made from a thin gas-permeable silicone rubber membrane allowing exchange of gases (oxygen and carbon dioxide). To start the culture, the cells are injected into the production module through ports in the silicone rubber which are equipped with Luer Lock connectors. Samples can be removed in the same way. For culturing, the minifermenter is rolled on a roller apparatus in a carbon dioxide-supplied incubator. Depending on the individual properties of the hybridoma cells cultured, cell densities of more than 10 x 10(6) (in some cases up to 35 x 10(6)) cells per ml and monoclonal antibody concentrations of several mg per ml can be obtained in the new minifermenter. On average, 61 mg (range: 9-159 mg) could be produced within 1-4 weeks. In terms of their properties the monoclonal antibodies produced in the new modular minifermenter were indistinguishable from antibodies prepared from ascitic fluid or from the supernatant of conventional stationary culture. The culture method is a useful alternative to the in vivo production method in mice. In addition, it represents a completely new, inexpensive and easy to handle general solution to the problem of culturing cells in high density and obtaining cellular products in high concentrations.

Antibodies, Monoclonal↗
PubMed1991

The MTT-assay as a rapid test for cell proliferation and cell killing: application to human peripheral blood lymphocytes (PBL).

The possibility to use the colorimetric MTT assay for measuring proliferation and cell death of human peripheral blood lymphocytes (PBL) was studied. In a range from 100,000-800,000 cells/well a linear correlation between the optical signal (OD signal at 570 nm) and the cell number was found. It is necessary to incubate the cells with the MTT at least 2 hours. After stimulation by different PHA concentrations a very good correlation between [3H] thymidine incorporation and MTT assay was found. A comparison of daunomycin cytotoxicity, measurement by trypan blue exclusion and MTT assay, gave also a good correlation between both methods. It can be pronounced that the MTT assay is a suitable method to measure cell proliferation and cell death of human PBL. The assay is easy to handle, a large number of probes can be assayed in a relatively short time and no radioactivity is necessary. For the measurement of the colored product a common ELISA reader can be used.

Cell Death↗
PubMed1990

Culture and stimulation of human T- and B-lymphocytes.

The cultivation and stimulation of human peripheral blood cells by different mitogens were studied using a serum-free culture technique. It shows the possibility to culture human PBL in a commercially available serum-free medium over a period of at least 7 days. In a serum-free medium with high protein content the viability of the cells was higher than in one with low protein content or in a serum containing medium. It is possible to stimulate human T cells by phytohaemagglutinin in a serum-free medium. After measurement of [3H]thymidine incorporation, a significant difference between control and test cultures was found. There is also a difference between serum-free medium with high and low protein content. Human peripheral B lymphocytes stimulated by pokeweed mitogen did not show any measurable IgG-secretion if they were cultured in serum-free medium.

B-Lymphocytes↗