Functional characteristics of leukotriene C4- and D4-metabolizing enzymes (gamma-glutamyl transpeptidase, dipeptidase) within human plasma

gamma-Glutamyltransferase expression during all-trans retinoic acid-induced differentiation of hematopoietic cell lines

gamma-Glutamyltransferase activity, genes transcripts and differentiation by all-trans retinoic acid have been investigated in cultured HL-60, U937, and K562 cells. Acquisition of morphological and functional characteristics confirmed the terminal differentiation of HL-60 and U937 cells. All-trans retinoic acid increased gamma-glutamyltransferase activity in a cell type- and time dependent manner. Treatments with all-trans retinoic acid isomers and structurally analogs showed that only retinoids with carboxylic acid group were able to induce enzyme activity in terminal differentiated cells. Additionally, the analysis of gamma-glutamyltransferase genes transcription products demonstrated clearly that, both in untreated and in RA treated cells, only mRNA type I transcribed from the gene 6, was expressed.

The activity of gamma-glutamyl transpeptidase (gamma-GT) in populations of mononuclear cells from human peripheral blood

The activity of gamma-glutamyl transpeptidase (EC 2.3.2.2) was observed in populations of non-stimulated mononuclear cells of human peripheral blood selected with antibody-coated magnetic particles. The highest activities of gamma-GT were found in monocytes (7.3-20.0 pkat/10(6) cells). The examination of T lymphocytes revealed a significant difference between CD4-positive (4.1 pkat/10(6) cells) and CD8-positive cells (1.2 pkat/10(6) cells). B lymphocytes and NK cells showed the lowest activities of 0.3 and 1.3 pkat/10(6) cells, respectively. The obvious differences in gamma-GT activities demonstrated here may reflect different biochemical capacities of these cell types, related to their distinct functions in the immune system.

Heat shock induces alterations of the lipoxygenase pathway in human polymorphonuclear granulocytes

We have investigated the effect of the heat shock response on the leukotriene generation, chemotaxis, and generation of oxygen radicals of human polymorphonuclear granulocytes (PMNs) by preincubating the PMNs at 42 degrees C. Subsequently, the different test systems were performed at 37 degrees C. As we confirmed by the release of lactate dehydrogenase and beta-glucuronidase the elevated temperatures did not result in cytotoxic or degranulating processes. After heat shock treatment the generation of leukotrienes induced by the Ca(++)-ionophore A23187, fMLP or opsonized zymosan was inhibited in a time and temperature dependent manner (preincubation phase) as was measured by HPLC-analysis. In contrast, the conversion of 14C-arachidonic acid revealed the generation of LTB4, 5-HPETE and 5-HETE solely as a result of the preincubation at 42 degrees C without any further stimulation. In addition, the chemiluminescence response induced by opsonized zymosan and the chemotaxis against C5a and LTB4 was clearly inhibited after heat shock treatment. With regard to enzyme activities of the heat treated PMNs the protein kinase C activities were enhanced whereas the LTD4-dipeptidase and the LTB4-omega-hydroxylase were not affected.

Leukotriene C4 in children with atopic asthma. I. Plasma levels in acute asthma

The leukotrienes C4, D4 and E4 are potent biologic mediators, and are thought to play an important role in obstructive airways disease such as asthma. In this study, plasma immunoreactive LTC4 (iLTC4) levels in asthmatic children were measured using radioimmunoassay after Sep-pak extraction in order to determine whether LTC4 is released in vivo during an asthmatic attack. In 10 non-atopic children, the mean +/- SEM of plasma iLTC4 level was 0.031 +/- 0.013 pmol/ml. Significantly higher plasma iLTC4 levels were recognized at all stages in asthmatic children, both in remission (p less than 0.01) and during an attack (p less than 0.01). PaO2 levels during an attack were significantly lower in the high iLTC4 group. In 15 asthmatic children, the plasma iLTC4 levels during an attack (0.134 +/- 0.017 pmol/ml) significantly decreased during recovery (0.078 +/- 0.012 pmol/ml) (p less than 0.05). Plasma iLTC4 levels correlated closely with lung function (p less than 0.01). The high iLTC4 levels in plasma in asthmatic children suggest a role for LTC4 in the pathophysiology of asthma.

Leukotriene C4 in children with atopic asthma. II. Plasma levels in bronchial challenge with specific allergen

Peptide leukotrienes C4, D4 and E4 are considered to be major mediators of hypersensitivity reactions. In this study, immunoreactive leukotriene C4 (iLTC4) in plasma, taken from asthmatic children who had undergone bronchial challenge with a specific allergen, was measured using radioimmunoassay in order to determine whether LTC4 is released in vivo during human allergic reactions. With regard to the bronchial challenge of 10 asthmatic children, plasma iLTC4 levels at the post-challenge stage (0.131 +/- 0.037 pmol/ml) were significantly elevated compared to the pre-challenge stage (0.065 +/- 0.016 pmol/ml) (p less than 0.01). The bronchial response was not directly related to the increased plasma iLTC4 levels, but the strength of the bronchial response did relate to the plasma iLTC4 levels at the pre-challenge (p less than 0.05) and post-challenge (p less than 0.01) states. The pre-challenge levels are relevant to bronchial reactivity, and the post-challenge levels are relevant to bronchoconstriction caused by exposure to allergens. The in vivo release of LTC4 following exposure to a specific allergen suggests that leukotrienes are important in the pathogenesis of asthma.

Generation and metabolism of leukotrienes and release of histamine from human dispersed tonsillar cells

We studied the generation and metabolism of leukotrienes (LT) and the release of histamine by human tonsillar cell suspensions. Human tonsils were dissected and mechanically dispersed. This procedure yielded a single cell suspension with 1.6 +/- 0.5 X 10(8) cells/g tissue consisting of 97.3 +/- 0.4% lymphocytes, 1.4 +/- 0.3% granulocytes, 1.3 +/- 0.3% macrophages/monocytes, and 0.03 +/- 0.02% mast cells/basophils. The cells were stimulated either with Ca-ionophore A 23187, melittin, or anti-human IgE. Determination of the 5-lipoxygenase products LTB4 and LTC4 was performed with specific radioimmunoassays (RIA), and histamine release was measured by the fluorophotometric technique. A time- and dose-dependent release of the mediators was monitored. LTB4 exceeded the amount of LTC4 in the supernatants. The concentration of leukotrienes ranged between 0.8 and 5.4 ng LTB4/1 X 10(8) cells or 0.5 and 1.5 ng LTC4/1 X 10(8) cells, depending on the stimulus. Histamine release after stimulation ranged between 25 and 35% of the total histamine content, whereas buffer controls amounted to 17%. The incubation of the cells (1 X 10(8) with exogenously added LTB4 resulted in the formation of omega-oxidated products (20-OH and 20-COOH-LTB4) and a novel unpolar metabolite, as identified by thin layer chromatography. This metabolite was not immunoreactive in the LTB4-RIA used. LTC4 and LTD4 were converted into LTE4 when added either to sonicated cells or to the cell-free supernatants of prestimulated tonsillar cells, indicating the release of gamma-glutamyltranspeptidase and dipeptidase, respectively. Our data clearly demonstrate the generation and metabolism of the 5-lipoxygenase products LTB4 and LTC4 as well as the release of histamine from human dispersed tonsillar cells, suggesting that they have a modulatory function with respect to the inflammatory potential at local sites.

Immunological aspects of tonsils and of tonsillitis

The human tonsils are responsible for the final antigen-induced differentiation of B-cells to plasma cells. Their main function could be the expansion of memory IgA-B-cells, allowing J-chain expression and final differentiation under secondary signals. IgA/J+-cells have been shown to migrate into mucosal membranes, allowing a protection against microorganisms. Recurrent tonsillitis obviously interferes with this complex immunological network, possibly resulting in a reduced mucosal protection by IgA. Furthermore, bacterial antigens can initiate the liberation of biochemical inflammatory mediators. Among these, arachidonic acid products can play a key role. They can induce epithelial damage and decreased ciliary function. Furthermore, they influence tonsillar immunological reactions.

Metabolism of leukotriene B4 by polymorphonuclear granulocytes of severely burned patients

Leukotriene B4 release from polymorphonuclear granulocytes of severely burned patients was reduced as compared to healthy donor cells. This decrease is due to an enhanced conversion of LTB4 into the 20-hydroxy- and 20-carboxy-metabolites and further to a decreased LTB4-synthesis. In addition, studies on the exogenous LTB4-conversion revealed an unidentified compound which was derived from LTB4. Our data suggest a modulation of the enzymatic activities involved in omega-oxidation of LTB4 (isoenzymes of cytochrome P-450).

Release and functional characterization of the leukotriene D4-metabolizing enzyme (dipeptidase) from human polymorphonuclear leucocytes

Polymorphonuclear leucocytes released LTD4-dipeptidase activity in a time-, calcium-, and cell number-dependent fashion. The LTD4-dipeptidase released from polymorphonuclear leucocytes (PMN) by incubation with calcium (0.91 mM) was detectable up to a cell concentration of 1 X 10(6)/ml and increased with higher concentrations. Maximal LTD4-dipeptidase activity within the extracellular environment was detected after 15 min of incubation (2 X 10(7)/ml) in the presence of 2-4.5 mM calcium or after 30 min, when stimulation was carried out with 0.91 mM calcium. The activity of the released LTD4-dipeptidase was modulated by various metal ions and other compounds. The addition of Mn2+, Co2+, and Zn2+ (final concentration 1 mM) enhanced the LTD4-dipeptidase activity, while Cu2+ led to a complete inhibition. In the absence of exogenous calcium EDTA inhibited LTD4-dipeptidase. Calcium up to a concentration of 5 and 10 mM decreased the dipeptidase activity. The LTD4-dipeptidase is not affected by bestatin, leupeptin, or N-ethyl-maleinimide (NEM). The Km of LTD4-dipeptidase for LTD4 was 0.95 +/- 0.2 microM and Vmax was 737.5 +/- 112.5 pmol/min X mg protein (n = 3 +/- SEM). The highest LTD4-dipeptidase activity was obtained at physiological pH values. LTD4-dipeptidase activity can also be released from other cell types, but the enzyme activity from human PMN exceeded that of other cells (e.g. human lymphocytes/monocytes and basophils (LMB) and human lung cell suspension).

Studies on the degradation of imipenem within serum and a renal kidney fraction

The degradation of imipenem in vitro was analyzed using reversed-phase HPLC. The incubation of imipenem with a microsomal kidney fraction revealed the generation of two metabolites (UV-maxima at 275 or 308 nm, respectively). The metabolism of imipenem by the renal enzyme was completely inhibited by cilastatin (2 micrograms/ml). The lowest detectable inhibitory concentration of cilastatin was at 6.5 X 10(-10) M. The recovery of imipenem from serum was 52.6% after incubation for 2 h at 37 degrees C. The stability of the antibiotic within serum was improved by 13.9% in the presence of EDTA (10 mM) indicating a possible involvement of serum dipeptidases in the systemic breakdown of the imipenem molecule.