The stimulation of arachidonic acid metabolism by organic lead and tin compounds in human HL-60 leukemia cells

Toxicity, migration and transformation characteristics of lead in soil-plant system: Effect of lead species

Lead (Pb) is a typical hazardous element of high concern in species characteristics involving toxicity, migration and transformation. A greenhouse experiment was conducted using Solanum nigrum L. grown in soils treated by divalent (Pb²⁺), tetravalent (Pb⁴⁺), trimethyl (TML) and triethyl (TEL) lead for 60 days. Results of physio-biochemical parameters indicated Pb toxicity was ranked as TEL > TML > Pb²⁺ > Pb⁴⁺ in a dose-dependent manner, and the correlation levels of organic species were higher than inorganic species. S. nigrum L. adopted phytostabilization strategy through fixing Pb in roots and restricting its transfer to shoots. More phytotoxic Pb was absorbed from soils treated by Pb²⁺ than Pb⁴⁺ as well as TEL than TML. In soils, inorganic Pb species were mainly present in residues while organic Pb species in Fe/Mn oxide and exchangeable fractions. Although most of Pb species in plant existed in the low-bioavailable extractions of 1 M NaCl and 2% HAC, the water-soluble Pb extracted by d-H₂O and 80 % ethanol were increased to a large extent under high-level exposure. The occurrence of reduction and (de)alkylation were considered as the major pathways in the biotransformation of Pb species. This study will conduce to the ecological risk management for Pb-contaminated soils.

Changes in fatty acid composition of lipids from birds, rodents, and preschool children exposed to lead

Chronic treatment with inorganic lead (Pb) has been shown to increase the proportion of arachidonic acid (ArA), as well as the arachidonate/linoleate (ArA/LA) ratio, in the fatty acids of lipids from a variety of avian tissues. Changes in two fatty acid-mediated phenomena, peroxidation of membrane lipids and synthesis of eicosanoid cytokines, are associated with this enhanced ArA content. The authors are not aware of any reports in the literature in which these effects of Pb have been described for any animals other than birds. In the current study, the authors investigated the effect of Pb on lipid metabolism in three species: avian, rodent, and human. The group of children identified as suffering environmental Pb exposure were from a Pb-surveillance program and had blood Pb concentrations (PbB) averaging 23 microg/dL. Turkey poults fed 100 ppm dietary Pb as Pb acetate-trihydrate for 19 d had a PbB of 46 microg/dL. Gastric intubation of rats with 80 mg Pb/kg/d for 10 d resulted in a PbB of 74 microg/dL. We analyzed fatty acid composition of whole blood from children, poults, and virgin rats. Low-dose (nongrowth inhibitory) Pb exposure resulted in significantly increased ArA concentration and ArA/LA ratio in blood from all species. Also analyzed were plasma and liver of poults, virgin rats, and pregnant rats and their fetuses. In plasma and liver from Pb-treated poults and virgin rats, ArA and the ArA/LA ratio were again enhanced. Pb intoxication also affected omega3 composition, increasing the concentrations of all long-chain omega3 fatty acids of fetuses from Pb-treated pregnant dams. The authors propose that altered fatty acid metabolism may be responsible for some indications of Pb poisoning. Possible consequences mediated through lipid peroxidation and production of ArA-derivative eicosanoids are considered.

Lead disrupts eicosanoid metabolism, macrophage function, and disease resistance in birds

Lead (Pb) affects elements of humoral and cell-mediated immunity, and diminishes host resistance to infectious disease. Evidence is presented supporting a hypothesis of Pb-induced immunosuppression stemming from altered fatty acid metabolism, and mediated by eicosanoids and macrophages (MO). Chronic Pb exposure increases the proportion of arachidonate (ArA) among fatty acids in lipid from avian tissues, and this change provides precursors for eicosanoids, the oxygenated derivatives of ArA that mediate MO acute inflammatory response. In the current study, we showed that the concentration of ArA in phospholipids of MO elicited from turkey poults fed 100 ppm dietary Pb acetate was twice that of controls. In vitro production of eicosanoids by these MO was substantially increased, and this effect was most pronounced following lipopolysaccharide stimulation: prostaglandin F2 alpha was increased 11-fold, thromboxane B2 increased threefold, and prostaglandin E2 increased by 1.5 times. In vitro phagocytic potential of these MO was suppressed, such that the percentage of MO engulfing sheep red blood cell (RBC) targets was reduced to half that of control MO. In vivo susceptibility of Pb-treated and control birds to Gram-negative bacteria challenge was also evaluated. The morbidity of chicks inoculated with Salmonella gallinarum and fed either control or 200 ppm Pb acetate-supplemented diets was similar, except early in the course of the disease when mortality among Pb-treated birds was marginally greater. In these studies, effects of Pb that could influence immunological homeostasis were demonstrated for MO metabolism of ArA, for production of eicosanoids, and for phagocytosis. There was also the suggestion that these in vitro indices of immune function are related to in vivo disease resistance.

Direct detection of ototoxicant-induced reactive oxygen species generation in cochlear explants

The proposal that free-radical generation contributes to the ototoxicities of several chemical agents was studied utilizing electron paramagnetic resonance (EPR) spectrometry to detect directly ototoxicant-induced reactive oxygen species formation in cochlear tissue. Guinea pig cochlear explants in chelexed artificial perilymph (AP: 200 microliters) were exposed to an ototoxicant or AP for 10 min. Ototoxic agents included gentamicin sulfate (4.0 mM), kanamycin monosulfate (4.0 mM), ethacrynic acid (0.5 mM), furosemide (0.3 mM), cisplatin (0.1 mM), trimethyltin chloride (0.1 mM), and quinine HCl (3.0 mM). Following incubation, 20 microliters of AP/ototoxicant mixture was replaced by the filtered spin trap, 5,5-dimethylpyrroline-N-oxide (DMPO). After 10 min, the EPR spectrum of the mixture was obtained. Four line EPR spectra of relative intensities 1:2:2:1, associated with hydroxyl radical (OH)/DMPO adduct formation, were evidenced by reaction mixtures containing cochlear explants exposed to each ototoxicant. Cisplatin, quinine and the loop diuretics produced weak OH-associated EPR signals in the absence of a cochlear explant, which were amplified in its presence. Deferoxamine quenched all OH spectral peaks. Peroxide levels, assayed in parallel experiments, were diminished by each ototoxicant relative to those seen following AP exposure, suggesting possible H2O2 conversion to OH. These data support the proposal that various ototoxic agents are capable of reactive oxygen species generation or promotion in cochlear tissues.

Effects of hexadecylphosphocholine on fatty acid metabolism: relation to cytotoxicity

The cytotoxicity of the antineoplastic drug hexadecylphosphocholine (HePC) was determined in a human monocytic tumor cell line, THP1, and in primary cultures of rat mesangial cells. Both cell types were susceptible to HePC toxicity, the concentrations producing 50% inhibition of cell viability (LD50 values) being 7 micrograms/ml for THP1 cells and 19 micrograms/ml for mesangial cells. The degree of toxicity was dependent on the culture conditions. In the absence of serum, HePC was highly toxic independent of cell proliferation. As a potential molecular mechanism, the effect of HePC on long-chain fatty acyl metabolism was investigated. HePC had no effect on fatty acid incorporation into cellular lipids or on release of fatty acids from lipid stores. The distribution of labeled fatty acids, however, was shifted from the phospholipid fraction to the triacylglycerol fraction. This effect was in accordance with an inhibition of the activity of the reacylating enzyme lysophosphatide acyltransferase. There was, however, no correlation between the interference with fatty acid distribution and HePC cytotoxicity in vitro. The data argue against interference with membrane fatty acid metabolism as a necessary prerequisite of HePC toxicity, the mechanism of which remains to be elucidated.

Drug metabolism and signal transduction: possible role of Ah receptor and arachidonic acid cascade in protection from ethanol toxicity

It has become increasingly clear that the so-called 'drug-metabolizing enzymes,' and the receptors controlling them, play a key role in regulating the steady-state levels of ligands important in the transcription of genes involved in cell division, differentiation, apoptosis, homeostasis, and neuroendocrine functions. In this Chapter is presented an example of the possible role of the high-affinity Ah receptor in protection against ethanol-induced inflammation by way of the arachidonic acid cascade. Ethanol consumption is associated with cancer, inflammation, birth defects, and other toxic effects. Ethanol-induced toxicity appears to be mediated by many of the same oxidative stress signal transduction pathways used by other tumor promoters, teratogens, mitogens and comitogens.