Lysosomes in the pathogenesis of liver injury in chronic copper poisoned sheep: an ultrastructural and morphometric study

A calix[2]triazole[2]arene-based fluorescent chemosensor for probing the copper trafficking pathway in Wilson's disease

We herein present a synthesis of a new fluorescent chemosensor for Cu²⁺and its application to Wilson's disease cell model to probe the copper trafficking pathway.

Saturable uptake of lipophilic amine drugs into isolated hepatocytes: mechanisms and consequences for quantitative clearance prediction

The hepatic uptake of quinine, fluvoxamine, and fluoxetine (0.1-10 microM) was investigated with freshly isolated rat hepatocytes. The cell-to-medium concentration ratios (K(p)) were concentration-dependent: the mean maximum K(p) values (at 0.1 microM) were 150 (quinine), 500 (fluvoxamine), and 2000 (fluoxetine). There was also a large capacity site that was not saturable over the concentration range used (possibly partition into the phospholipid component of membranes); representing this site, the mean minimum K(p) values (at 10 microM) were 30 (quinine), 200 (fluvoxamine), and 500 (fluoxetine). To eliminate concomitant metabolism, cells were pretreated with the irreversible P450 inhibitor, aminobenzotriazole. The saturable uptake was substantially eliminated after exposure to carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (ATP inhibitor). The difference between the maximum and minimum K(p) for these three amine drugs, as well as for dextromethorphan, propranolol, and imipramine, was within a limited range of 3-fold, indicating a common magnitude of saturable uptake. Basic, permeable drugs are expected to be sequestered into lysosomes, which actively maintain their low internal pH (approximately 5) using ATP, and this process is predictable from the combined effects of pH-driven ion accumulation and unsaturable binding representing partition into membranes. The resultant predicted maximum K(p) correlated strongly with the observed maximum K(p). Thus, at low substrate concentrations, the fraction of drug unbound in the hepatocyte incubation (critical for assessing drug clearance and drug-drug interaction potential) may be dependent upon saturable as well as unsaturable binding, and for lipophilic, basic drugs, this can be readily estimated assuming a common degree of uptake into lysosomes.

Early histological and functional effects of chronic copper exposure in rat liver

Cu is an essential trace element capable of producing toxic effects in animals and man when ingested acutely or chronically in excess. Although chronic Cu exposure is increasingly recognized as a public health issue, its early effects remain largely unknown. We approached the significance of a moderate chronic Cu load in young rats to correlate early hepatic histopathological changes with functional alterations of liver cells. For this purpose, supplementation with 1,200 ppm of Cu in rat food for 16 weeks was chosen. In these conditions, Cu load elicited a significant decrease in growth curves. There were mild light microscopy alterations in Cu-treated rats, although increasing intracellular Cu storage was correlated with longer Cu exposure both by histological and biochemical measurements. Ultrastructural alterations included lysosomal inclusions as well as mitochondrial and nuclear changes. Liver perfusion studies revealed higher rates of basal O(2) consumption and colloidal carbon-induced O(2) uptake in Cu-treated rats, with enhanced carbon-induced O(2)/carbon uptake ratios and NF-kappaB DNA binding activity. These changes were time-dependent and returned to control values after 12 or 16 weeks. It is concluded that subchronic Cu loading in young rats induces early hepatic morphological changes, with enhancement in Küpffer cell-dependent respiratory burst activity and NF-kappaB DNA binding, cellular responses that may prevent or alleviate the hepatotoxicity of the metal.

Intoxicação espontânea por Senecio brasiliensis (Asteraceae) em ovinos no Rio Grande do Sul

Descreve-se a ocorrência de um surto de intoxicação espontânea por Senecio brasiliensis em ovinos em um estabelecimento do município de Mata, Estado do Rio Grande do Sul, em meados de janeiro de 1997. De um total de 94 ovinos, 51 (54,25%) animais adoeceram e 50 (53,2%) morreram. Esse rebanho permaneceu durante aproximadamente 7 meses (de junho de 1996 a janeiro de 1997) em piquetes de pastagem nativa onde havia grande quantidade de S. brasiliensis. O quadro clínico manifestado pelos animais afetados consistia em fotossensibilização, emagrecimento progressivo, apatia, fraqueza, perturbações neurológicas como depressão, andar a esmo e desequilibrado, icterícia e hemoglobinúria. Houve melhora das lesões de pele naqueles ovinos que desenvolveram fotossensibilização hepatógena depois que foram retirados do sol. As principais lesões macroscópicas observadas em 9 dos 10 ovinos necropsiados incluíam fígado diminuído de tamanho, firme, difusamente marrom amarelado ou esverdeado, com quantidades variáveis de nódulos de 1-3 mm de diâmetro, bem circunscritos, salientes na cápsula, amarelados, distribuídos aleatoriamente por todo o parênquima. A vesícula biliar estava repleta e preenchida por bile verde escura e espessa. Havia também derrames cavitários (hidropericárdio e ascite). Crise hemolítica aguda fatal associada à intoxicação crônica hepatógena por cobre foi observada em cinco ovinos. Além das lesões hepáticas macroscópicas já mencionadas, foi observada icterícia generalizada da carcaça, rins tumefeitos, friáveis, difusamente escurecidos ou com fino pontilhado enegrecido; a urina era marrom escura (hemoglobinúria). As principais lesões microscópicas foram observadas no fígado e consistiam em hepatomegalocitose, proliferação de ductos biliares (hiperplasia ductal) e fibrose periportal moderada acompanhada de infiltrado inflamatório mononuclear. Macrófagos carregados de pigmento acastanhado formavam aglomerados nas tríades portais ou estavam dispersos entre os hepatócitos remanescentes. O material armazenado no citoplasma desses macrófagos correspondia a ceróide e cobre, positivo nas técnicas de PAS e rodanina, respectivamente. Nos rins de cinco animais, havia nefrose hemoglobinúrica caracterizada por degeneração e necrose do epitélio tubular, presença de hemoglobina e hemossiderina no citoplasma das células epiteliais dos túbulos contorcidos e cilindros de hemoglobina na luz tubular. Evidência morfológica de encefalopatia hepática incluía degeneração esponjosa (status spongiosus) da substância branca do encéfalo. Achados ultra-estruturais no fígado incluíam graus variáveis de degeneração hepatocelular caracterizada pelo acúmulo de numerosas gotas lipídicas no citoplasma das células hepáticas e presença de lisossomos carregados de material eletrodenso que, na maioria dos casos, correspondia à lipofuscina-ceróide. Adicionalmente, havia discreta dilatação do retículo endoplasmático rugoso e moderada hiperplasia do retículo endoplasmático liso em algumas regiões do citoplasma dos hepatócitos. No epitélio dos túbulos contorcidos proximais do rim foi observado edema intracelular e diversas alterações mitocondriais de caráter degenerativo que incluíam tumefação, desorganização e ruptura das cristas, matriz finamente granular, acúmulo de gotículas de gordura e ruptura das membranas em alguns casos. Lisossomos contendo material fortemente eletrodenso foram observados em muitas células tubulares renais. O exame laboratorial de fragmentos de fígado e rim dos ovinos afetados revelou níveis elevados de cobre que variaram respectivamente de 369 ppm a 1248 ppm e 152 ppm a 687 ppm com base na matéria seca. O diagnóstico de intoxicação por Senecio brasiliensis baseou-se em dados epidemiológicos, clínicos, de necropsia, histopatológicos e laboratoriais.

Sensitivity and specificity of serum copper determination for detection of copper deficiency in feeder calves

OBJECTIVE

To determine the relationship between serum and liver copper concentrations and evaluate serum copper determination for diagnosis of copper deficiency in juvenile beef calves.

DESIGN

Cross-sectional study.

ANIMALS

105 juvenile beef calves.

PROCEDURE

Copper concentrations were measured in paired liver and serum samples from 6- to 9-month-old beef calves. Regression models that predicted liver copper concentration as a function of serum copper concentration were developed. Sensitivity and specificity of serum copper concentration for detection of low liver copper concentration were determined, using a range of serum copper concentrations as test endpoints. Positive and negative predictive values were calculated.

RESULTS

The association between serum and liver copper concentrations was significant; however, regression models accounted for only a small portion of the variation in liver copper concentrations. For a serum copper concentration endpoint of 0.45 microg/g, sensitivity and specificity for detection of low liver copper concentration were 0.53 and 0.89, respectively. Positive and negative predictive values of serum copper concentration for detection of low liver copper concentration ranged from 0.37 to 0.85 and 0.63 to 0.94, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Regression models are inappropriate for predicting copper status as a function of serum copper concentration. Serum copper concentration is fairly specific for detection of low liver copper concentration but only marginally sensitive when serum copper concentration of 0.45 microg/g is used as a test endpoint. The value of serum copper concentration as a diagnostic indicator depends on prevalence of copper deficiency.

Effect of age and sex on liver damage due to excess dietary copper in Fischer 344 rats

OBJECTIVE

The aim of this study was to investigate the morphologic and biochemical effects of excess dietary copper in young and adult rats of different sex.

METHODS

Adult Fischer 344 male and female rats were given a diet containing 1500 ppm copper for 18 weeks. Young male and female rats were fed a similar copper-loaded diet from birth until 16 weeks of age. Age- and sex-matched control rats were fed a normal rodent diet (<10 ppm copper). Serum liver enzyme activity was determined in all rats. Livers were sampled for histology, histochemistry (rhodanine), immunohistochemical detection of metallothionein and copper analysis by atomic absorption spectrophotometry. Hepatic metallothionein and zinc concentrations were measured in adult rats.

RESULTS

Excess dietary copper caused substantial liver injury, as evidenced by morphologic changes and increased activity of serum ALT, GGT, and SDH. All copper-loaded rats had significantly (p< 0.05) increased hepatic copper concentrations compared to controls. However, young copper-loaded rats accumulated more hepatic copper, had more severe liver changes, and had higher serum liver enzyme activities than adult rats. Histologic changes in copper-loaded rats consisted of multifocal hepatitis and widespread single-cell necrosis. Cytoplasmic copper was detected histochemically in centroacinar zone 1 (portal) and mid-zone in copper-loaded rats. Immunoreactivity for metallothionein was prominent in necrotic hepatocytes and within inflammatory foci in copper-loaded rats. However, differences in hepatic metallothionein concentrations were not detected between adult copper-loaded and control rats.

CONCLUSIONS

Young Fischer 344 rats are more susceptible than adults to copper-induced liver injury.

Regulation of mitochondrial cytochrome b mRNA by copper in cultured human hepatoma cells and rat liver

Copper overload and deficiency are known to cause morphological and functional mitochondrial abnormalities. The reverse transcriptase-polymerase chain reaction (RT-PCR)-based method of differential display of mRNA was used to identify genes with altered expression in cultured human hepatoma cells (Hep G2) exposed to increasing concentrations of copper (0-100 microM, 24 h). Copper regulation of a cloned PCR product, identified as the gene for the mitochondrially encoded cytochrome b, was confirmed by Northern analysis and in situ hybridization. Copper toxicity increased cytochrome b mRNA abundance up to 3.6-fold, and copper chelation reduced it by 50%. Hepatic cytochrome b mRNA was also increased in rats fed a high-copper diet. Thapsigargin treatment resulted in a significant increase in cytochrome b mRNA, suggesting that an increase in intracellular calcium may be involved in the mechanism of copper action. Furthermore, although cyclohexamide (CHX) alone did not increase cytochrome b mRNA, the addition of CHX and copper resulted in a sixfold increase. These data suggest a role for cytochrome b in the response to increases or decreases in hepatic copper.

Association of copper to metallothionein in hepatic lysosomes of Long-Evans cinnamon (LEC) rats during the development of hepatitis [se e comments]

BACKGROUND

The Long-Evans cinnamon (LEC) rat has a mutation homologous to the human Wilson's disease gene, leading to copper-induced hepatotoxicity. The mechanism of how excess copper damages the liver or what chemical form of copper is toxic is still unclear.

RESULTS

In liver cytosol, copper levels were highest just before the onset of hepatitis and declined thereafter. In cytosol, total copper was bound to metallothionein (MT). Considerable amounts of both copper and iron accumulated in lysosomes with increasing age and development of liver damage. Lysosomal levels of presumably reactive non-MT-bound copper were increased. In severely affected livers, large amounts of copper were associated with insoluble material of high density which, upon ultrastructural information, was found to be derived from the lysosomes of Kupffer cells. This copper-rich material is considered to consist of polymeric degradation products of copper-MT.

CONCLUSION

We suggest that chronic copper toxicity in LEC rats involves the uptake of copper-loaded MT into lysosomes, where it is incompletely degraded and polymerizes to an insoluble material containing reactive copper. This copper, together with iron, initiates lysosomal lipid peroxidation, leading to hepatocyte necrosis. Subsequent to phagocytosis by Kupffer cells, the reactive copper may amplify liver damage either directly or through stimulation of these cells.

Acute copper intoxication after a Cu-Ca EDTA injection in rats

It has been claimed that Cu-Ca EDTA releases the Cu slowly into the blood when injected as a therapeutic agent for Cu deficiency, but when overdosing occurs, animals may die in a few hours after the injection, suggesting that Cu release is faster than expected. A total of 30 rats were divided into six equal groups and injected with Cu-Ca EDTA at 4, 6, 13, 33 or 64 mg/kg body weight, the sixth group acted as control. All rats were sacrificed 24 h later, with the exception of rats from groups 33 and 64 that died 7 and 2 h postinjection respectively. The rate of Cu transference to the liver increased linearly with the dose, from (X +/- S.E.) 14.88 +/- 3.14 in group 4, to 134.47 +/- 21.86 microg/h in group 64. Injected animals developed liver and kidney degeneration, hemorrhage and necrosis, which increased in severity with the Cu dose. Liver Cu accumulation was highest for group 13 (866.8 +/- 84.23 ppm DM), while in group 64 reached only 167.0 +/- 14.99 ppm. It is concluded that during acute Cu poisoning, the rate of transfer is responsible for the liver and kidney damage, rather than the total amount of transferred Cu to those organs, as it is the case in chronic Cu poisoning. The high rate of Cu transfer possibly surpasses the intrinsic mechanisms of Cu deposition and free Cu is left into the cell with the development of necrosis.

A review of drug-induced lysosomal disorders of the liver in man and laboratory animals

Lysosomotropic agents are selectively taken up into lysosomes following their administration to man and animals [de Duve et al. (1974) Biochem. Pharmacol. 23:2494-2531] The effects of lysosomotropic drugs studied in vivo and in vitro can be used as models of lysosomal storage diseases. These agents include many drugs still used in clinical medicine: aminoglycosides used in antibiotics [Tulkens (1988)]; phenothiazine derivatives; such antiparasitic drugs as chloroquine and suramin; antiinflammatory drugs like gold sodium thiomalate; and cardiotonic drugs like sulmazol [Schneider (1992) Arch. Toxicol. 66:23-33]. Side-effects to these drugs can be caused by their lysosomotropic properties. In addition to drugs, other compounds to which man and animals are exposed (e.g., metals, cytostatics, vitamins, hormones) are also lysosomotropic. Liver cells, especially Kuppfer cells, are known to accumulate lysosomotropic agents. Here we review studies which evaluate lysosomal changes in the liver following administration of lysosomotropic agents to experimental animals, and relate them to toxic side-effects or pharmacological action, as was suggested by de Duve et al. (1974). Common features of lysosomal changes include, the overload of liver lysosomes by non-digestible material; increased size and number of liver lysosomes; inhibition of several lysosomal enzymes; secondary increase in the activity of some lysosomal enzymes; increased autophagy, and fusion disturbances. There was no significant change in endocytosis, except for an increase in the Triton WR 1339 model.

Glucose-6-phosphate dehydrogenase activity in erythrocytes from chronically copper-poisoned sheep

The present study was undertaken to investigate the capacity to generate reducing equivalents in erythrocytes from experimentally copper-poisoned sheep. Ten ewes were dosed orally with CuSO4 to induce the Cu toxicity. Copper dosing was stopped at the first day of hemolysis. The activity of glucose-6-phosphate dehydrogenase (G6PD) in the erythrocytes, the levels of reduced glutathione (GSH) and glucose (in serum and erythrocytes) was examined at frequent intervals. The copper-poisoned sheep had reduced levels (25-35% less) of glucose in serum and erythrocytes than controls. The activity of G6PD in erythrocytes from sheep was 50-60% of typical levels found in human erythrocytes. Immediately before the hemolytic period, the copper-poisoned sheep showed decreased activity of G6PD, declining to 65% of the initial activity. In addition, we found decreased blood levels of reduced GSH in copper-poisoned sheep. There appears to be a relationship between decreased capacity to generate reducing equivalents and the overload of copper in sheep erythrocytes.

The pathology and trace element status of the toxic milk mutant mouse

The toxic milk (tx) mouse is a mutant in which copper metabolism is abnormal. Homozygous tx adults do not show overt signs of disease, but litters born to such parents are deficient in copper and die at about 2 weeks of age unless copper is provided. The results reported here clearly indicate that adults accumulate copper in the liver, kidney, spleen, brain, muscle, serum and red blood cells. The concentration of zinc is also elevated in liver, brain and muscle. In adult animals there is damage to hepatocytes with marked changes to the nuclei. Haemolysis occurs with subsequent deposition of haemosiderin in the kidney. This mutant provides a useful model for studies of the pathogenesis and treatment of copper toxicity in animals and man.

Copper and zinc toxicity in two rat hepatoma cell lines varying in differentiation

1. The differentiation status of cells is considered to represent an important factor in determining the effects of toxic components. 2. Two rat hepatoma cell lines, MH1C1 and HTC, were used to study differences in the sensitivity to two toxic metals: copper and zinc. 3. The differentiation of the cell lines was characterized using light microscopy, growth pattern, gamma glutamyltransferase (GGT) activity and albumin production as parameters. 4. The MH1C1 cell line was described to be more differentiated. 5. Albumin production in the MH1C1 cells was significantly higher than in the HTC cells whereas the GGT activity was only slightly different. 6. Toxicity of Cu and Zn was compared. Zn appeared to be more toxic to the cells than Cu, when leakage of lactate dehydrogenase and potassium were measured, whereas both metals were equally toxic when expressed as DNA remaining after 24 hr. 7. The MH1C1 cell line appeared to be more sensitive to Cu and Zn than the HTC. 8. The two metals appeared to have different targets in the cell; Cu may affect the nucleus and Zn the cell membrane.

Drug-induced lysosomal disorders in laboratory animals: new substances acting on lysosomes

Several substances with lysosomotropic activity were investigated in toxicological studies. AR-L 115 BS (sulmazol, a cardiotonic agent) was tested on beagle dogs; HX-CH 44 BS (a beta-blocker) and SX-AB 1316 SE (an antithrombotic agent) were tested on rats, and AF-CX 1325 XX (an antiepileptic agent) was tested on both rats and beagle dogs. All organ systems were examined morphologically by light and/or electron microscopy. When an increase in the number of lysosomes occurred this was confirmed by the pigment scheme according to Krutsay (1971) as well as by the detection of acid phosphatase and compared with earlier histochemical results. At higher dosages, all substances caused very marked proliferation of lysosomes in the liver and/or kidneys. HX-CH 44 BS also caused such proliferation in striated muscles and in the lungs. A brown discolouration of the kidneys was found with sulmazol and AF-CX 1325 XX. This finding corresponded to the microscopically detectable occurrence of numerous lipofuscin granules. The reticulum cells in the lymph nodes of dogs were also affected by AF-CX 1325 XX. It is concluded that the proliferation of lysosomes in various organs after administration of the above-mentioned substances is due to an excess of substance. The increased substance in the body is then stored in the lysosomes. With HX-CH 44 BS, lysosomal autodigestion of mitochondria in the skeletal musculature and in the alveolar macrophages of the lungs was found. The selective lysosomal incorporation of mitochondria has not been described up to now and in our opinion, this constitutes a special feature. The results otherwise largely correspond to those already described in the literature. Systemic phospholipidosis such as occurs with some other substances was not detectable. The incorporation of the substance causes several types of lysosomal inclusion. Uptake of the substance in lysosomes either leads to overt autodigestion of organelles such as mitochondria (HX-CH 44 BS) or peroxisomes or to residual lysosomes of dense structure which histochemically resemble lipofuscin. SX-AB 1316 SE serves as an example of a substance which is stored directly by lysosomes in crystalline form. Above all, in the liver the substance is taken up not only by the sinusoidal stellate cells but also by hepatocytes.

Experimental copper and heliotrope intoxication in sheep: morphological changes

Young Merino wethers were used to determine the effects of copper and heliotrope, fed together or separately, on the development of toxicity and the concentration of trace elements in the liver and kidney. In one experiment copper and heliotrope were given concurrently, in a second experiment heliotrope was fed for 12 weeks and copper administration commenced 8 weeks later. The 10 sheep fed heliotrope alone did not show signs of clinical illness but one died and was found to have severe liver damage. Eleven sheep were given copper alone and three developed the clinical signs and lesions of haemolysis. Fourteen sheep were given copper and heliotrope and 13 became ill. Of these, three developed haemolysis, eight became jaundiced and two became weak without developing jaundice. The concentrations of copper in the livers of control and heliotrope-treated sheep, were comparable. In the animals given copper alone, the concentration of copper in the liver was twice as high as that in controls and in those given heliotrope and copper, it was three times as high as in the liver of control sheep. Feeding heliotrope alone induced the histological changes of pyrrolizidine alkaloid toxicity in the liver, but this was not associated with an excessive accumulation of copper or the development of clinical illness. However, it did predispose the animals to the effects of a second toxin since giving heliotrope and copper concurrently, or giving copper subsequent to feeding heliotrope, markedly enhanced the toxicity of the two substances and caused an excessive accumulation of copper in the liver.