Dietary lead: effects on hepatic fatty acid composition in chicks

Wax esters of uropygial gland secretion as biomarkers of endocrine disruption in birds exposed to treated sewage water

The chemical composition of the uropygial gland secretion of birds shows seasonal, sex and age-related variations following sex hormones fluctuations. We explore the use of the composition of the uropygial gland secretion as a non-invasive biomarker of endocrine disruption in 137 common moorhens (Gallinula chloropus) from Navaseca Pond, which receives the effluent of a wastewater treatment plant, and from the more pristine Tablas de Daimiel National Park in Spain. Wax ester and fatty acid compositions were measured by means gas chromatography - mass spectrometry (GC-MS) in the uropygial gland secretion of moorhens from both wetlands. Organochlorine compounds (p,p'-DDE and PCBs) were measured in blood and uropygial gland secretion of moorhens as indicators of anthropogenic pollutants, and this information was interpreted together with previous results of the accumulation of metals and metalloids in blood and feathers of these moorhens and a wide range of endocrine disrupting chemicals (EDCs) measured in water from both study sites. PCBs and p,p'-DDE were found in 32% of the blood and 51% of uropygial gland secretion samples, being at highest levels in Navaseca. Wax composition was dominated by monoesters of 35-38 carbons and displayed a clear seasonal variation, in which long-chain wax esters were more abundant in spring-summer than in autumn-winter. This seasonal change was less evident in birds from Navaseca, where the presence of shorter wax esters was associated with the higher concentration of PCBs in uropygial gland secretion. The observed effect may not be associated with this specific type of pollutants because moorhens in Navaseca are also exposed to a wide diversity endocrine disruptors as shown in a previous study. Uropygial gland secretion can be a useful non-invasive sample for integrating chemical monitoring of pollutants and their effects as endocrine disruptors in birds.

Fatty acid levels alterations in THP-1 macrophages cultured with lead (Pb)

OBJECTIVE

As cardiovascular events are one of the main causes of death in developed countries, each factor potentially increasing the risk of cardiovascular disease deserves special attention. One such factor is the potentially atherogenic effect of lead (Pb) on lipid metabolism, and is significant in view of the still considerable Pb environmental pollution and the non-degradability of Pb compounds.

METHODS

Analysis of saturated fatty acids (SFA) (caprylic acid (C8:0), decanoic acid (C10:0), lauric acid (C12:0), tridecanoic acid (C13:0), myristic acid (C14:0), pentadecanoic acid (C15:0), palmitic acid (C16:0), heptadecanoic acid (C17:0), stearic acid (C18:0), and behenic acid (C22:0)), monounsaturated fatty acid (MUFA) (palmitoleic acid (C16:1), oleic acid (18:1w9), trans-vaccenic acid (C18:1 trans11)), and polyunsaturated fatty acid (PUFA) (linoleic acid (C18:2n6), gamma-linolenic acid (C18:3n6), arachidonic acid (C20:4n6)), was conducted by gas chromatography. Analysis of stearoyl-CoA desaturase (SCD), fatty acid desaturase 1 (FADS1) and fatty acid desaturase 2 (FADS2) expression was performed using qRT-PCR. Oxidative stress intensity (malondialdehyde - MDA concentration) was measured using spectrophotometric method. Intracellular generation of reactive oxygen species (ROS) in macrophages was visualized by fluorescence microscopy and quantitatively measured by plate reader.

RESULTS

Pb caused quantitative alterations in FAs profile in macrophages; the effect was Pb-concentration dependent and selective (i.e. concerned only selected FAs). In general, the effect of Pb was biphasic, with Pb levels of 1.25 μg/dL and 2.5 μg/dL being stimulatory, and 10 μg/dL being inhibitory on concentrations of selected FAs. The most potent Pb concentration, resulting in increase in levels of 9 FAs, was 2.5 μg/dL, the Pb-level corresponding to the mean blood Pb concentrations of people living in urban areas not contaminated by Pb. Pb was found to exert similar, biphasic effect on the expression of FADS1. However, Pb decreased, in a concentration-dependent manner, the expression of SCD and FADS2. Pb significantly increased MDA and ROS concentration in macrophages.

CONCLUSION

Environmental Pb exposure might be a risk factor resulting in alterations in FAs levels, oxidative stress and increased MDA concentration in macrophages, which might lead to the formation of foam cells and to inflammatory reactions.

Heavy metal exposure in large game from a lead mining area: effects on oxidative stress and fatty acid composition in liver

The Pb mining area of the valley of Alcudia and the Sierra Madrona mountains (S. Spain) has been exploited intermittently for over 2100 years, since Roman occupation and up until the late 1900s. Red deer (n=168) and wild boar (n=58) liver and bone (metacarpus) were analyzed for Pb, Zn, Cu, Cd, As and Se. Lipid peroxidation, total and oxidized glutathione (GSH), superoxide dismutase (SOD), GSH peroxidase (GPX) and fatty acid composition were studied in liver of red deer. The concentrations of Pb in liver and bone of red deer and wild boar were higher in the mining area than in the control area, and higher in the wild boar than red deer, but well below the level associated with clinical signs of Pb poisoning. Liver levels of Cu, Cd and Se were also higher in red deer from the mining area. Red deer from the mining area had 39% less total GSH than in the control area. The percentage of docosahexaenoic acid in liver of red deer from the mining area was 16% lower than in the control area.

Phosphorus amendment reduces hepatic and renal oxidative stress in mallards ingesting lead-contaminated sediments

Lead poisoning of waterfowl has been reported for decades in the Coeur d'Alene River Basin (CDARB) in Idaho as a result of the ingestion of lead-contaminated sediments. This study was conducted to determine whether the addition of phosphoric acid to CDARB sediments would reduce the bioavailability and toxicity of lead to the liver and kidney of mallards (Anas platyrhynchos). Mallards received diets containing 12% clean sediment (controls) or 12% sediment from three different CDARB sites containing 4520, 5390, or 6990 microg/g lead (dry weight) with or without phosphoric acid amendment. Liver and kidney lead concentrations were significantly higher in all CDARB treatment groups and ranged from geometric mean values of 18.2 (liver) and 28.7 (kidney) for the first 2 sites to 22.5 (liver) and 45.6 (kidney) microg/g (wet weight) for the third site. With amendments all liver lead concentrations were reduced 36 to 55%, and all kidney lead concentrations were lowered 54 to 73%. Unamended CDARB sediment from the third site resulted in the following hepatic effects: over 1.6-fold elevation of liver glutathione (reduced form; GSH) concentration, higher GSH S-transferase and oxidized glutathione (GSSG) reductase activities, and lower protein-bound thiols (PBSH) concentration. Renal effects included higher kidney GSH concentrations for all CDARB sites, with over 2.1-fold higher for the third site. Resulting kidney GSSG to GSH ratios were lower at two sites. At the third site, gamma-glutamyl transferase (GGT) activity was elevated, and lipid peroxidation as thiobarbituric acid-reactive substances (TBARS) was 1.7-fold greater. Amendment restored all hepatic variables as well as the renal variables TBARS and GGT so they did not differ from controls. Although amendments of phosphorus substantially reduced the bioavailability of lead and some of the adverse effects, lead concentrations in the tissues of mallards fed the amended sediments were still above those considered to be harmful to waterfowl under the present conditions.

Lead exposure and (n-3) fatty acid deficiency during rat neonatal development alter liver, plasma, and brain polyunsaturated fatty acid composition

Lead (Pb) exposure has been reported to increase arachidonic (AA) and docosahexaenoic (DHA) acids. To determine whether Pb effects on fatty acid composition are influenced by dietary (n-3) fatty acid restriction, weanling female rats were fed either an (n-3)-adequate or -deficient diet to maturity and mated. At parturition, dams in each group were subdivided to receive either 0.2% Pb or Na-acetate in their drinking water during lactation only. Pups were analyzed for fatty acid content in liver, plasma, and brain at either 3 or 11 wk. The (n-3)-deficient diets markedly decreased total (n-3) fatty acids, and increased total (n-6) fatty acids including both AA and docosapentaenoic (n-6) in each compartment (P < 0.05). The main effects of Pb were in the livers of weanling rats where there was a 56% loss in total fatty acid concentration concurrent with increased relative percentages of AA and DHA. Thus, because there was a greater percentage of liver nonessential fatty acid lost relative to the essential fatty acids (EFA), there was no net change in AA concentration. There was a diet x Pb interaction for a decrease in liver DHA concentration evident only in the (n-3)-adequate group. There were also diet x Pb interactions in plasma at 11 wk and in brain at 3 wk. These data are consistent with the hypothesis of a Pb-induced increase in fatty acid catabolism, perhaps as a source of energy.

Preferential effect of lead exposure during lactation on non-essential fatty acids in maternal organs

This study determined the effects of lead exposure during the lactational period on maternal organ FA compositions in rat dams that were fed either an n-3 adequate (n-3 Adq) or deficient (n-3 Def) diet prior to conception. On giving birth, dams were subdivided into four groups in a 2 x 2 design with n-3 FA supply and Pb exposure as the dependent variables. Pb acetate (0.2 wt%) was administered in the drinking water from the time they gave birth to weaning 3 wk later. Following weaning, the dams were decapitated, and the liver, plasma, kidney, brain, and retina analyzed for FA composition. The n-3 deficient diets markedly decreased the percentages of total n-3 FA, including docosahexaenoic acid (DHA), and increased total n-6 FA including both arachidonic (AA) and n-6 docosapentaenoic acids in all tissues (P < 0.05). The principal effects of Pb occurred in the liver and plasma, where 20-32% losses in total FA concentration concurrent with increased relative percentages of AA (P < 0.05) were observed. In kidney, the percentages of AA and DHA also increased after Pb exposure (P < 0.05) with lesser effects in the nervous system. There was a diet x Pb interaction for liver, plasma, and retinal 20-C n-6 PUFA (P < 0.05). Generally, shorter-chain saturated and monounsaturated FA concentrations were decreased after Pb exposure. An analysis of the changes in the tissue concentrations induced by Pb indicated that the increases in the percentages of PUFA likely reflected a preferential loss of non-EFA. The mechanisms by which Pb affects saturated and monounsaturated FA concentration are unknown.

Relation of fatty acid composition in lead-exposed mallards to fat mobilization, lipid peroxidation and alkaline phosphatase activity

The increase of n-6 polyunsaturated fatty acids (PUFA) in animal tissues has been proposed as a mechanism of lead (Pb) poisoning through lipid peroxidation or altered eicosanoids metabolism. We have studied fatty acid (FA) composition in liver and brain of mallards (Anas platyrhynchos) feeding for 3 weeks on diets containing combinations of low or high levels of vitamin E (20 or 200 UI/kg) and Pb (0 or 2 g/kg). Saturated FA, n-6 PUFA and total concentrations of FA were higher in livers of Pb-exposed mallards, but not in their brains. The percentage of n-6 PUFA in liver and brain was slightly higher in Pb-exposed mallards. The increase of n-6 PUFA in liver was associated with decreased triglycerides and increased cholesterol in plasma, thus could be in part attributed to feed refusal and fat mobilization. The hepatic ratios between adrenic acid (22:4 n-6) and arachidonic acid (20:4 n-6) or between adrenic acid and linoleic acid (18:2 n-6) were higher in Pb exposed birds, supporting the existing hypothesis of increased fatty acid elongation by Pb. Among the possible consequences of increased n-6 PUFA concentration in tissues, we found increased lipid peroxidation in liver without important histopathological changes, and decreased plasma alkaline phosphatase activity that may reflect altered bone metabolism in birds.

Effects of vitamin E and/or C on reactive oxygen species-related lead toxicity in the rat sperm

This study was undertaken to investigate whether treatment with vitamin E (VE) and/or vitamin C (VC) protects rat sperm by inhibiting reactive oxygen species generation induced by lead (Pb) exposure. Male Sprague-Dawley rats were assigned to the following five groups: vitamin-unsupplemented; 150 mg VE/kg chow supplemented; 300 mg VE/kg chow supplemented; 500 mg VC/l drinking water supplemented and 150 mg VE/kg chow + 500 mg VC/l drinking water supplemented group. Rats in each group were divided into Pb-unexposed and Pb-exposed subgroups, received weekly intraperitoneal injection of 10 mg sodium acetate or 10 mg Pb acetate/kg for 6 weeks, respectively. The blood and sperm Pb levels were analyzed by graphite furnace atomic absorption spectrophotometer. Chemiluminescence was measured to evaluate the generation of sperm reactive oxygen species (ROS). Motility and sperm-oocyte penetration rate (SOPR) were measured. In Pb-unexposed rats, epididymal sperm counts, motility, ROS, and SOPR were not different in the five supplemented groups. Lead exposure might decrease the defense capacity of sperm to the oxidative stress and therefore elevate the ROS generation, reduce sperm motility, and reduce SOPR. Supplementation with VE and/or VC reduced ROS generation, prevented loss of motility and capacity of oocyte penetration in Pb-exposed rats. This study suggests that supplementation with VE and/or VC inhibits Pb-related ROS generation, protects spermatozoa from loss of motility and oocyte penetration capability.

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.

Lead exposure causes generation of reactive oxygen species and functional impairment in rat sperm

The relationships between blood lead, sperm lead, sperm reactive oxygen species (ROS) level, and sperm fertile capability were investigated to understand the effects of lead exposure on sperm function and the mechanism of these effects. Male Sprague-Dawley rats, 7 weeks old, were randomly divided into control group and lead-treated group. The controls and lead-treated animals received intraperitoneal injection of 10 mg sodium acetate and 10 mg lead acetate/kg body weight, respectively, weekly for 6 or 9 weeks. The blood lead and epididymal sperm lead were analyzed by graphite furnace atomic absorption spectrophotometer. Chemiluminescence was measured to evaluate the generation of sperm ROS. Sperm-oocyte penetration rate (SOPR) was measured to evaluate sperm function. After 6 weeks of lead exposure, the rats had average blood lead levels of 32 microg/dl, sperm lead levels of 0.67 +/- 0.11 microg/10(9) sperm, unchanged epididymal sperm counts, percent of motile sperms, and motile epididymal sperm counts compared with control animals. However, after 9 weeks of lead exposure, the rats had average blood lead levels of 48.0 +/- 4.3 microg/dl, sperm lead levels of 0.88 +/- 0.16 microg/10(9) sperm, statistically lower epididymal sperm counts, and lower motile epididymal sperm counts. There was a good correlation between the blood lead and sperm lead(r2 = 0.946, P < 0.001). The sperms of lead-exposed rats produced significantly higher counts ofchemiluminescence than did those from the control rats (P < 0.001). The chemiluminescence counts were positively associated with sperm lead level (r2 = 0.613, P < 0.001). Epididymal sperm counts, motility and motile epididymal sperm counts were negatively associated with sperm chemiluminescence (r2 = 0.255, 0.152, and 0.299; P < 0.01, 0.05, and 0.01, respectively). The SOPR were positively associated with epididymal sperm counts, motility and motile epididymal sperm counts (r2 = 0.136, 0.285, and 0.264; P < 0.05, 0.01, and 0.001, respectively). The sperm chemiluminescence was negatively associated with SOPR (r2 = 0.519, P < 0.001). It is concluded that lead exposure probably affected the sperm function by activating one of the pathways of ROS generation.

Lead-induced abnormalities in blood-brain barrier permeability in experimental chronic toxicity

The aim of this paper was to determine whether prolonged drinking of lead acetate-containing water by adult rats, which imitates environmental exposure to lead (Pb), affects some morphological and biochemical properties of rat brain microvessels. We noted a significant increase of lead level in capillaries and synaptosomes obtained from brains of rats under chronic toxicity conditions. Intravenously injected horseradish peroxidase (HRP) was used to evaluate the functional state of the blood-brain barrier (BBB). The results indicate that, systematically administered at low doses, lead induces BBB dysfunction. The changes, revealed in light microscopy and confirmed by electron microscopic studies, are typical for "leaky" microvessels, reported for variety of neuropathological conditions associated with BBB damage. Enhanced pinocytotic activity of the endothelial cells and the opening of interendothelial tight junctions, together with enormous phagocytizing action of the pericytes, are the most characteristic ultrastructural features noted. The presence of specific type of perivascular cells containing droplets of lipids in the cytoplasm, together with changes in phospholipid profile in brain capillaries, suggest that altered lipid composition of membranes may, at least in part, be responsible for changes in observed membrane permeability.

Dietary lead alters fatty acid composition and membrane peroxidation in chick liver microsomes

Inorganic Pb acetate is a pro-oxidant, and peroxidation damage to cellular membrane lipids, leading to membrane fragility and permeability, is a likely consequence of Pb poisoning. In addition to the systemic peroxidation that occurs in vivo, Pb-contaminated feedstuffs can contribute preformed peroxides. Treatments with dietary Pb that have been shown to increase tissue peroxide levels in animals may be related to the consumption of preformed peroxides from the diet. In the current study, we evaluated the possible separate effects of feed and systemic peroxides by administering equivalent doses of Pb acetatetrihydrate to chicks via either 1,500 ppm Pb in the diet or via gastric intubation. Peroxidation of lipids in hepatic microsomal membranes (assessed as malonyldialdehyde production) from birds intoxicated with Pb by either route of administration was more than double that of untreated controls. Also, both routes of Pb exposure doubled the concentration of hepatic microsomal arachidonic acid, a peroxidizable polyunsaturated fatty acid. In the data reported here, we show that tissue peroxide levels are unaffected by the method of oral Pb administration and thus, by inference, independent of peroxide content of the feed.

Is lead toxicosis a reflection of altered fatty acid composition of membranes?

1. The premise of this review is that many of the biological effects of Pb are reflection of tissue peroxidation. 2. Enhanced tissue levels of arachidonic acid in Pb toxicosis appear to be involved in the peroxidative changes. 3. The altered arachidonate metabolism may be related to changes in membrane structure and function. 4. The induction of enhanced glutathione levels in animal tissues by Pb may afford protection from peroxidative damage.

Interactions of dietary lead with fish oil and antioxidant in chicks

Two experiments were conducted with day-old broiler chicks reared to 18 or 19 d of age. The objectives were: (1) to examine the effects of the antioxidant ethoxyquin (EQ) on peroxidation in feeds containing fish oil (FO) or lead (Pb), and (2) to determine whether systemic effects of Pb, which are attributed to tissue peroxidation, can be reversed by dietary EQ. Experiment 1 was a 2 x 2 factorial arrangement with the factors being 4% dietary cottonseed oil (CSO) vs FO and dietary Pb as lead acetate trihydrate (0 vs 1000 ppm). Feed was mixed 1 d prior to initiation of the experiment and stored at 4 degrees C until it was placed in the feeders. Experiment 2 was a 2 x 2 x 2 factorial arrangement with the factors being 3.5% dietary oil (CSO vs FO), dietary Pb (0 vs 1000 ppm), and EQ (0 vs 75 ppm). Feed was mixed 1 d prior to initiation of the experiment and held at room temperature thereafter. Growth depression by FO and Pb was less pronounced in Experiment 1 than in Experiment 2. In Experiment 2, FO and Pb increased the concentration of feed peroxide, and the increases were prevented by EQ. The growth depression by FO was completely reversed by EQ. EQ reversal of Pb-induced growth depression, although substantial, was not complete. The FO diet without Pb had a peroxide content (12.4 meq/kg feed) similar to the CSO + Pb diet (12.3 meq/kg feed); however, growth was not similar (407 vs 213 g body weight at 19 d, respectively). The results suggest that the toxic effects of Pb are mediated by peroxidative alterations both in the feed and in tissues. The ability of EQ to reverse significantly Pb effects on growth suggests a systemic action of this antioxidant.

Lead-induced tissue fatty acid alterations and lipid peroxidation

Previous work showed that dietary lead (Pb) increases the relative concentration of arachidonic acid (20:4) as a percentage of total fatty acids, and decreases the relative proportion of linoleic acid (18:2) to arachidonic acid (18:2/20:4) in chick liver, serum, and erythrocyte membranes. The present investigation was undertaken to examine the time-course and magnitude of the fatty acid alterations with increasing dietary Pb levels. We also examined the effects of Pb on the fatty acid composition and lipid peroxide content of hepatic subcellular organelles. In Exp. 1, chicks were fed diets containing 0, 62.5, 125, 250, 500, or 1000 ppm added Pb (as Pb acetate trihydrate) from 1 to 21 d of age. After 21 d, no growth effects were observed; however, Pb lowered the 18:2/20:4 ratio and increased 20:4 concentration in total liver and serum lipids, and in total hepatic phospholipids in a dose-dependent manner. Hepatic mitochondrial membrane fatty acids were not altered, nor was there any increase in hepatic lipid peroxidation. In Exp.2, chicks were fed diets containing 0, 500, 1000, or 2000 ppm added Pb from 1 to 21 or 22 d of age. Pb depressed growth in a dose-dependent manner. In addition, Pb lowered the 18:2/20:4 ratio and increased 20:4 concentration in total liver lipids and in hepatic mitochondrial and microsomal membranes in a dose-dependent manner. Total hepatic lipid peroxidation was increased over control values by 1000 ppm Pb, and hepatic microsomal lipid peroxidation was increased by dietary Pb levels of 1000 and 2000 ppm. In Exp. 3, body weight, hepatic microsomal lipid peroxidation, and fatty acid composition were determined in 4-, 9-, 14-, 18-, and 23-d-old chicks fed 0 or 1500 ppm added Pb. Body weights of Pb-treated chicks were significantly lower than those of control chicks by day 18. Microsomal 20:4 concentration and peroxidation increased, and the 18:2/20:4 ratio decreased with age in both groups, but the changes were of greater magnitude in the Pb-treated chicks. The results suggest that some of the manifestations of Pb toxicity may be a reflection of increased concentration of 20:4 in specific membranes. Further, since the Pb-induced alterations in fatty acid composition were noted in the absence of any growth depression, we propose that fatty acid composition is more sensitive than growth rate to the presence of lead in the diet.

Dietary modification of lead toxicity: effects on fatty acid and eicosanoid metabolism in chicks

1. The influence of nutrition and chronic lead (Pb) administration on the level of eicosanoids and their precursors was evaluated in serum and liver from chicks fed defined diets. 2. Dietary Pb consistently increased arachidonic acid, the arachidonate/linoleate ratio, and hepatic non-protein sulfhydryl concentration. 3. Hepatic microsomal fatty acid elongation activity was decreased by Pb. 4. Cottonseed oil, calcium and methionine interacted with Pb, affecting liver and serum fatty acid profiles. 5. Tissue levels of leukotriene C4 rose significantly with Pb or correlated with Pb-compromised body weight in only one experiment. Serum prostaglandins E2 and F2 alpha were unchanged by treatments. 6. The results suggest that an increase in precursors is not consistently reflected by tissue levels of eicosanoids.

Lead toxicity in chickens. Interaction with toxic dietary levels of selenium

Two experiments were conducted in which varying levels of lead (up to 2000 ppm as lead acetate trihydrate) and selenium (up to 40 ppm as Na2SeO3) were fed, either alone or in combination, to chicks from day-old through 18 or 20 d. Lead additions depressed growth in a dose-dependent manner without affecting mortality. Selenium addition at 20 ppm was severely growth inhibitory, but mortality was not affected. The growth inhibition of 20 ppm Se was partially alleviated by feeding it in combination with 2000 ppm Pb; however, mortality was increased significantly by the combination. In contrast 40 ppm Se resulted in almost complete cessation of growth and 85% mortality, whereas the combination with 2000 ppm Pb partially overcame the growth inhibition and eliminated the excess mortality. When Pb or Se were fed alone, hepatic levels of the fed element were elevated. There were further significant elevations of hepatic levels of both elements when fed in combination at identical dietary concentrations as the single element additions. The results suggest that Pb and Se are antagonistic. The nature of the interaction of these elements is such that although 2000 ppm Pb partially overcomes the growth inhibition by 20 or 40 pm Se, the reverse (relief of Pb inhibition by Se) is not observed.

Effects of dietary lead, cadmium, mercury, and selenium on fatty acid composition of blood serum and erythrocyte membranes from chicks

A series of experiments was conducted to study the effects of dietary and injected lead (as Pb acetate-3H2O) and of dietary Cd, Hg, and Se on fatty acid composition of serum lipids of chicks as measured by gas-liquid chromatography. The effect of dietary Pb on fatty acid composition of erythrocyte membranes was measured also. Dietary Pb (1000 ppm) increased the serum concentration of arachidonic acid (20:4, first no. = no. of carbon atoms:second no. = no. of double bonds) and decreased the concentration of linoleic acid (18:2) and the ratio 18:2/20:4. Intraperitoneal injection of Pb (52 mg/100 g body weight) did not alter serum fatty acid composition by 4 h post-injection. The separate effects of 2000 ppm Pb, 60 ppm Cd, 500 ppm Hg, and 10 ppm Se added to the diet on serum fatty acids were measured in a single experiment. In comparison to controls, Pb and Cd lowered serum concentration of 18:2. Only Pb raised serum 20:4. Pb lowered the ratio 18:2/20:4, whereas Cd and Hg raised the ratio and Se was without effect. Dietary Pb (2000 ppm) raised the concentration of 20:4 and lowered the ratio 18:2/20:4 in erythrocyte membranes. The different effects of injected and dietary Pb on the serum 18:2/20:4 ratio suggest that Pb alters 20:4 synthesis from 18:2 rather than mobilization of 20:4 from tissues. The Pb-induced increase of lipid peroxida-tion in erythrocytes observed by other workers may be a reflection of increased 20:4 level in erythrocyte membranes.