W. E. Donaldson

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.

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.

Changes in Organ Nonprotein Sulfhydryl and Glutathione Concentrations During Acute and Chronic Administration of Inorganic Lead to Chicks

The effects of dietary and injected lead (Pb) on organ nonprotein sulfhydryl (NPSH) and glutathione (GSH) concentrations in the chick were studied. Lead acetate·3H2O was administered either in the diet for 3 wk at 2000 ppm Pb or by intraperitoneal (ip) injection of 3-wkold chicks with 52 mg Pb/100 g body wt. In Exp. 1, NPSH concentrations in liver and kidney were increased by both dietary and injected Pb in comparison to chicks not receiving Pb. Thigh muscle NPSH was decreased by injected Pb, whereas dietary Pb had no effect. In Expt. 2, whole blood and plasma NPSH were measured at 0, 0.5, 1.0, 2.0, and 4.0 h following ip Pb injection. Both whole blood and plasma NPSH were increased by 30 min. Whole blood NPSH concentrations plateaued at 30 min, and plasma NPSH continued to rise for 2 h. In Expt. 3, injected Pb increased hepatic NPSH, but not GSH concentrations. The ratio of GSH/NPSH was therefore lowered. The incorporation of [1-14C]glycine into hepatic GSH was stimulated by injected Pb. Buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, reduced hepatic NPSH and [14C]glycine incorporation in Pb-treated chicks to below control (non-Pb injected) values. In Expt. 4, dietary Pb fed for 3 wk increased the hepatic concentrations of both NPSH and GSH such that the ratio of GSH/NPSH was unchanged in comparison to chicks not fed Pb. The data suggest that the initial response to acute Pb intoxication may involve a mobilization of nonprotein thiols via the interorgan translocation system for GSH. Such a response would help to maintain adequate levels of GSH in organs crucial to detoxification.

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.

Hexachlorobenzene-Induced Hyperparathyroidism and Osteosclerosis in Rats,

Hexachlorobenzene (HCB) exposure has been shown to alter the normal concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D3 in rats and to result in osteoporosis in humans. Experiments were undertaken to investigate the effects of HCB on the homeostatic mechanism of calcium metabolism and to determine its effect on bone in rats. Fischer 344 rats were dosed 5 days/week for 5, 10, or 15 weeks with 0, 0.1, 10.0, or 25.0 mg HCB/kg body wt. Body weight was not affected by any of the exposure conditions. Liver weight was significantly elevated above control values at the two higher dose levels at all three time periods. Kidney weight and kidney-to-body weight ratio were significantly elevated at the highest dose level after 10 weeks and at the two higher dose levels after 15 weeks of exposure. Serum alkaline phosphatase was significantly decreased at the two higher dose levels after both 10 and 15 weeks of exposure. 1,25-Dihydroxyvitamin D3 was measured in the 5-week exposure group only and was significantly elevated in the three higher dose levels. After 5 and 15 weeks of HCB exposure, parathyroid hormone concentration was significantly elevated at the two higher dose levels at both time periods. Wet femur density was significantly increased at the two higher dose levels of HCB after 10 weeks of exposure and the three higher dose levels after 15 weeks of exposure. Dry femur density was also increased in the cases where wet femur density was increased. However, femur weight was not affected at any dose level. The results from this study indicate that HCB induces hyperparathyroidism in rats, as demonstrated by increased serum parathyroid hormone levels and osteosclerosis of the femur.(ABSTRACT TRUNCATED AT 250 WORDS)

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 (MØ). 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 MØ acute inflammatory response. In the current study, we showed that the concentration of ArA in phospholipids of MØ elicited from turkey poults fed 100 ppm dietary Pb acetate was twice that of controls. In vitro production of eicosanoids by these MØ was substantially increased, and this effect was most pronounced following lipopolysaccharide stimulation: prostaglandin F2α was increased 11-fold, thromboxane B2 increased threefold, and prostaglandin E2 increased by 1.5 times. In vitro phagocytic potential of these MØ was suppressed, such that the percentage of MØ engulfing sheep red blood cell (RBC) targets was reduced to half that of control MØ. In vivo susceptibility of Pb-treated and control birds to Gram-negative bacteria challenge was also evaluated. The morbidity of chicks inoculated withSalmonella 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 MØ 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.

Morphometric analysis of osteosclerotic bone resulting from hexachlorobenzene exposure

Hexachlorobenzene (HCB) exposure has been shown to induce hyperparathyroidism and osteosclerosis in rats. Experiments were undertaken to investigate the effects of HCB-induced hyperparathyroidism and osteosclerosis on femur morphometry as well as femur breaking strength. Fischer 344 rats were dosed 5 d/wk for 15 wk with 0, 0.1, 1, 10, or 25 mg HCB/kg body weight. Hyperparathyroidism was produced in the two higher dose groups as reported previously (Andrews et al., 1989). Femur weight was significantly increased in the rats receiving 0.1, 1, and 25 mg HCB/kg body weight, whereas density was increased significantly at 1, 10, and 25 mg HCB/kg dose levels. Bone strength was also significantly increased at the three higher dose levels. Cross-sectional area of the midpoint of the femur was significantly increased at the 1 mg/kg HCB dose level. Cortical area and the proportion of the total area of the bone that the cortex occupied were significantly increased at the three higher dose levels. Medullary cavity area was significantly increased at the 0.1 mg/kg dose level but significantly decreased at the 2 higher dose levels of HCB. The right femur was significantly predominant to the left femur in weight, volume, and density through all dosing regimens. HCB exposure significantly altered bone morphometry and strength characteristics in the Fischer 344 rat.

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 × 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°C until it was placed in the feeders. Experiment 2 was a 2 × 2 × 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.

Impairment of calcium homeostasis by hexachlorobenzene (HCB) exposure in Fischer 344 rats.

Human exposure to hexachlorobenzene (HCB) has resulted in demineralization of bone and development of osteoporosis. Experiments were undertaken to investigate the effects of HCB on the homeostatic mechanism of calcium metabolism. Fischer 344 rats were dosed with 0, 0.1, 1.0, 10.0, or 25.0 mg HCB/kg body weight 5 d/wk for 5 wk while being fed normal rat diet or vitamin D3-deficient diet. Rats receiving the normal diet had a dose-related decrease in body weight gain and increased liver weight when compared to their controls. Serum cholesterol, alanine aminotransferase (ALT), 1, 25-dihydroxy-vitamin D3 [1,25-(OH)2D3], and parathyroid hormone (PTH) were significantly elevated when compared to control values. In the vitamin D3-deficient diet group, there was a dose related increase in liver weight, liver-to-body weight ratio and kidney-to-body weight ratio. Serum cholesterol and 1,25-(OH)2D3 were significantly elevated. Urinary calcium decreased significantly with increasing HCB dosage, indicating conservation of calcium. The data from this study indicate that HCB does affect calcium metabolism by altering the concentrations of two primary controlling factors in calcium homeostasis.

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.