Copper: toxicological relevance and mechanisms.

Copper (Cu) is a vital mineral essential for many biological processes. The vast majority of all Cu in healthy humans is associated with enzyme prosthetic groups or bound to proteins. Cu homeostasis is tightly regulated through a complex system of Cu transporters and chaperone proteins. Excess or toxicity of Cu, which is associated with the pathogenesis of hepatic disorder, neurodegenerative changes and other disease conditions, can occur when Cu homeostasis is disrupted. The capacity to initiate oxidative damage is most commonly attributed to Cu-induced cellular toxicity. Recently, altered cellular events, including lipid metabolism, gene expression, alpha-synuclein aggregation, activation of acidic sphingomyelinase and release of ceramide, and temporal and spatial distribution of Cu in hepatocytes, as well as Cu-protein interaction in the nerve system, have been suggested to play a role in Cu toxicity. However, whether these changes are independent of, or secondary to, an altered cellular redox state of Cu remain to be elucidated.

Mitochondrial superoxide mediates labile iron level: evidence from Mn-SOD-transgenic mice and heterozygous knockout mice and isolated rat liver mitochondria.

Superoxide is the main reactive oxygen species (ROS) generated by aerobic cells primarily in mitochondria. It is also capable of producing other ROS and reactive nitrogen species (RNS). Moreover, superoxide has the potential to release iron from its protein complexes. Unbound or loosely bound cellular iron, known as labile iron, can catalyze the formation of the highly reactive hydroxyl radical. ROS/RNS can cause mitochondrial dysfunction and damage. Manganese superoxide dismutase (Mn-SOD) is the chief ROS-scavenging enzyme and thereby the primary antioxidant involved in protecting mitochondria from oxidative damage. To investigate whether mitochondrial superoxide mediates labile iron in vivo, the levels of labile iron were determined in the tissues of mice overexpressing Mn-SOD and heterozygous Mn-SOD-knockout mice. Furthermore, the effect of increased mitochondrial superoxide generation on labile iron levels was determined in isolated rat liver mitochondria exposed to various electron transport inhibitors. The results clearly showed that increased expression of Mn-SOD significantly lowered the levels of labile iron in heart, liver, kidney, and skeletal muscle, whereas decreased expression of Mn-SOD significantly increased the levels of labile iron in the same organs. In addition, the data showed that peroxidative damage to membrane lipids closely correlated with the levels of labile iron in various tissues and that altering the status of Mn-SOD did not alter the status of other antioxidant systems. Results also showed that increased ROS production in isolated liver mitochondria significantly increased the levels of mitochondrial labile iron. These findings constitute the first evidence suggesting that mitochondrial superoxide is capable of releasing iron from its protein complexes in vivo and that it could also release iron from protein complexes contained within the organelle.

Isoflavone-rich soy isolate reduces lipid peroxidation in mouse liver.

The purpose of this study was to determine if an isoflavone-rich soy isolate affords protection against peroxidative damage in vivo. Weanling C57BL6 male mice were fed a basal diet (AIN-93G) supplemented with either nothing or 1.08 gram isoflavone-rich soy isolate/kg diet for 60 days. The soy isolate contained 400 mg/g isoflavone aglycones (226 mg/g genistein and 174 mg/g daidzein). Immediately following sacrifice liver was processed for measuring the levels of lipid peroxidation products, malondialdehyde (MDA) and conjugated dienes, and the levels of alpha-tocopherol, glutathione (GSH), and ascorbic acid, as well as the activities of catalase, selenium-dependent glutathione peroxidase (Se-GPx), selenium-nondependent glutathione peroxidase (non-Se-GPx), and superoxide dismutase (SOD). Compared with the control group, mice fed the diet supplemented with soy isolate had significantly (p<0.05) lower hepatic levels of MDA and conjugated dienes. The activities of catalase and SOD were significantly increased (p<0.05) in the liver of soy isolate-supplemented mice. The levels of vitamin E, GSH, and ascorbic acid and the activities of Se-GPx and non-Se-GPx were not significantly altered by the soy isolate. The results obtained provide experimental evidence that isoflavone supplementation confers protection against peroxidative damage to membrane lipids in vivo, possibly through enhancing the activities of the antioxidant enzymes catalase and SOD.

Suppression of peroxisomal enzyme activities and cytochrome P450 4A isozyme expression by congeneric polybrominated and polychlorinated biphenyls.

The purpose of this study was to determine the effects of PCBs and PBBs on peroxisome proliferator-activated receptor-alpha-(PPARalpha-) associated enzyme activities or protein levels. Male Sprague-Dawley rats were administered a single IP injection (150 mu mol/kg) of either 3,3',4,4'-tetrabromobiphenyl, 3,3',4,4'-tetrachlorobiphenyl, 3,3',5,5'-tetrabromobiphenyl, 2',3,3',4,5-pentachlorobiphenyl, 3,3',4,4',5-pentachlorobiphenyl, 2,2',3,3',5,5'-hexachlorobiphenyl, or 3,3',4,4',5,5'-hexabromobiphenyl in corn oil (10 ml/kg). One week later, the activities of catalase, peroxisomal fatty acyl-CoA oxidase, and peroxisomal beta-oxidation as well as cytochrome P450 4A (CYP4A) protein content were determined in subcellular liver fractions. None of the peroxisomal enzyme activities were significantly increased by any of the halogenated biphenyl congeners tested. Except for minor (approx. 25%) increases in the total CYP4A content following treatment with 2,2',3,3',5,5'-hexachlorobiphenyl and 3,3',5,5'-tetrabromobiphenyl, CYP4A protein contents were not increased by any treatment. The two Ah receptor agonists, 3,3',4,4'-tetrabromobiphenyl and 3,3',4,4',5-pentachlorobiphenyl, significantly diminished the liver content of CYP4A proteins and activities of the peroxisomal enzymes studied. Since a range of congeners with different biologic and toxicologic activities were selected for this study, it may be concluded that the polyhalogenated biphenyls do not induce peroxisome proliferation in the male rat, but rather certain members of this class of compounds down regulate peroxisome-associated enzymes. Since PCBs and PBBs do not increase enzyme activities and expression of proteins associated with PPARalpha, these agents are therefore exerting their carcinogenic and promoting activities by some other mechanism.

Dietary vitamin E protects the fathead minnow, Pimephales promelas, against noise exposure.

The fathead minnow (Pimephales promelas) was employed to examine if dietary vitamin E supplementation could protect the inner ear from the deleterious effects of noise. Fish were fed one of the three experimental diets containing either: (1) low vitamin E content (14.5 mg/kg diet as alpha-tocopheryl acetate), (2) an adequate amount of vitamin E (50 mg/kg), or (3) high vitamin E content (450 mg/kg). After 4 weeks on the diet, fish were exposed to either 2 or 24 h of intense white noise (142 dB re: 1 microPa, bandwidth 0.3-4.0 kHz). Auditory thresholds were measured, using the auditory brainstem response (ABR) technique, within 0.5 days following noise exposure or within a recovery period of 1.5 days. Additionally, liver samples were analyzed for vitamin E content. Increased vitamin E supplementation was dose-dependently associated with a reduction in statistically significant threshold shifts after noise exposure and an enhancement of recovery (i.e., more complete recovery over a shorter period) for fish exposed to either 2 or 24 h of noise. The results obtained suggest that dietary vitamin E affords protection against noise exposure in a cyprinid fish.