Inhibition of sarco-endoplasmic reticulum calcium ATPases (SERCA) by polycyclic aromatic hydrocarbons: lack of evidence for direct effects on cloned rat enzymes

Dual effect of polyaromatic hydrocarbons on sarco(endo)plasmic reticulum calcium ATPase (SERCA) activity of a teleost fish (Oncorhynchus mykiss)

Polycyclic aromatic hydrocarbons (PAHs) are embryo- and cardiotoxic to fish that might be associated with improper intracellular Ca2+ management. Since sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of intracellular Ca2+, the SERCA activity and the contractile properties of rainbow trout (Oncorhynchus mykiss) ventricle were measured in the presence of 3- and 4-cyclic PAHs. In unfractionated ventricular homogenates, acute exposure of SERCA to 0.1-1.0 μM phenanthrene (Phe), retene (Ret), fluoranthene (Flu), or pyrene (Pyr) resulted in concentration-dependent increase in SERCA activity, except for the Flu exposure, with maximal effects of 49.7-83 % at 1 μM. However, PAH mixture did not affect the contractile parameters of trout ventricular strips. Similarly, all PAHs, except Ret, increased the myotomal SERCA activity, but with lower effect (27.8-40.8 % at 1 μM). To investigate the putative chronic effects of PAHs on SERCA, the atp2a2a gene encoding trout cardiac SERCA was expressed in human embryonic kidney (HEK) cells. Culture of HEK cells in the presence of 0.3-1.0 μM Phe, Ret, Flu, and Pyr for 4 days suppressed SERCA expression in a concentration-dependent manner, with maximal inhibition of 49 %, 65 %, 39 % (P < 0.05), and 18 % (P > 0.05), respectively at 1 μM. Current findings indicate divergent effects of submicromolar PAH concentrations on SERCA: stimulation of SERCA activity in acute exposure and inhibition of SERCA expression in chronic exposure. The depressed expression of SERCA is likely to contribute to the embryo- and cardiotoxicity of PAHs by depressing muscle function and altering gene expression.

Organic chemicals from diesel exhaust particles affects intracellular calcium, inflammation and β-adrenoceptors in endothelial cells

Exposure to diesel exhaust particles (DEP) may contribute to endothelial dysfunction and cardiovascular disease. DEP, extractable organic material from DEP (DEP-EOM) and certain PAHs seem to trigger [Ca²⁺]_i increase as well as inflammation via GPCRs like βARs and PAR-2. In the present study we explored the involvement of βARs and PAR-2 in effects of DEP-EOM on [Ca²⁺]_i and expression of inflammation-associated genes in the endothelial cell-line HMEC-1. We exposed the human microvascular endothelial cell line HMEC-1 to DEP-EOM fractionated by sequential extraction with solvents of increasing polarity: n-hexane (n-Hex-EOM), dichloromethane (DCM-EOM), methanol (Methanol-EOM) and water (Water-EOM). While Methanol-EOM and Water-EOM had no marked effects, n-Hex-EOM and DCM-EOM enhanced [Ca²⁺]_i (2-3 times baseline) and expression of inflammation-associated genes (IL-1α, IL-1β, COX-2 and CXCL8; 2-15 times baseline) in HMEC-1. The expression of βARs (60-80% of baseline) and βAR-inhibitor carazolol suppressed the increase in [Ca²⁺]_i induced by both n-Hex- and DCM-EOM. Carazolol as well as the Ca²⁺-channel inhibitor SKF-96365 reduced the DCM-EOM-induced pro-inflammatory gene-expression. Overexpression of βARs increased DCM-EOM-induced [Ca²⁺]_i responses in HEK293 cells, while βAR-overexpression suppressed [Ca²⁺]_i responses from n-Hex-EOM. Furthermore, the PAR-2-inhibitor ENMD-1068 attenuated [Ca²⁺]_i responses to DCM-EOM, but not n-Hex-EOM in HMEC-1. The results suggest that βAR and PAR-2 are partially involved in effects of complex mixtures of chemicals extracted from DEP on calcium signalling and inflammation-associated genes in the HMEC-1 endothelial cell-line.

Breast meat quality of broiler chickens can be affected by managing the level of nitric oxide

The objective of this study was to investigate the effects of nitric oxide (NO) on the quality of broiler chicken meat during postmortem storage. Eighteen broiler chickens were slaughtered and breast meat was randomly assigned to 1 of 3 treatments including the control group, nitric oxide synthase (NOS) inhibitor group, and NO enhancer group. The breast samples were incubated with water, NO enhancer, and NO inhibitor for 1 d and then stored at 4°C under atmospheric conditions for 4 and 7 d. Left side of breast meat was used to determine protein oxidation, lipid oxidation, water-holding capacity, and pH, whereas the right side was used for the measurement of color and drip loss. Breast meat from NO enhancer group showed the lowest water-holding capacity during refrigerated storage, whereas drip losses were not significantly (P > 0.05) different among 3 treatments. Lipid oxidation showed a significant difference (P < 0.05) only at 7 d in which NOS inhibitor group showed the highest, whereas the NO enhancer group showed the lowest levels of lipid oxidation. Carbonyl content in NO enhancer group was significantly higher than the control and NOS inhibitor treatment at 1 and 4 d of refrigerated storage. Lightness of breast meat in the NOS inhibitor group was greater, whereas redness was lower than the control and NO enhancer group at 4 and 7 d of refrigerated storage. The ultimate pH of 3 treatments was not significantly (P > 0.05) different from one another. These data indicate that NO could play a significant role in modulating the quality of fresh broiler breast meat during refrigerated storage.

Induction of intracellular calcium concentration by environmental benzo(a)pyrene involves a β2-adrenergic receptor/adenylyl cyclase/Epac-1/inositol 1,4,5-trisphosphate pathway in endothelial cells

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (B(a)P) are widely distributed environmental contaminants, known as potent ligands of the aryl hydrocarbon receptor (AhR). These chemicals trigger an early and transient increase of intracellular calcium concentration ([Ca(2+)](i)), required for AhR-related effects of PAHs. The mechanisms involved in this calcium mobilization were investigated in the present study. We demonstrated that B(a)P-mediated [Ca(2+)](i) induction was prevented in endothelial HMEC-1 cells by counteracting β2-adrenoreceptor (β2ADR) activity using pharmacological antagonists, anti-β2ADR antibodies, or siRNA-mediated knockdown of β2ADR expression; by contrast, it was strongly potentiated by β2ADR overexpression in human kidney HEK293 cells. B(a)P was shown, moreover, to directly bind to β2ADR, as assessed by in vitro binding assays and molecular modeling. Pharmacological inhibition and/or siRNA-mediated silencing of various signaling actors acting downstream of β2ADR in a sequential manner, such as G protein, adenylyl cyclase, Epac-1 protein, and inositol 1,4,5-trisphosphate (IP(3))/IP(3) receptor, were next demonstrated to prevent B(a)P-induced calcium signal. Inhibition or knockdown of these signaling elements, as well as the use of chemical β-blockers, were finally shown to counteract B(a)P-mediated induction of cytochrome P-450 1B1, a prototypical AhR target gene. Taken together, our results show that B(a)P binds directly to β2ADR and consequently utilizes β2ADR machinery to mobilize [Ca(2+)](i), through activation of a G protein/adenylyl cyclase/cAMP/Epac-1/IP(3) pathway. This β2ADR-dependent signaling pathway activated by PAHs may likely be crucial for PAH-mediated up-regulation of AhR target genes, thus suggesting a contribution of β2ADR to the health-threatening effects of these environmental pollutants.

Consumption of oxidized oil increases oxidative stress in broilers and affects the quality of breast meat

A total of 120 4-week-old broiler chickens were allotted to 12 pens and fed one of three diets including control, oxidized diet (5% oxidized oil), or antioxidant-added diet (500 IU vitamin E) for 2 weeks. Blood samples were collected at the end of feeding trial, and breast muscles were sampled immediately after slaughter. Breast meats were also collected 24 h after slaughter and used for meat quality measurements. Oxidative stress in blood, lipid and protein oxidation, and sarcoplasmic reticulum Ca²(+)-ATPase (SERCA) activity of breast muscle were determined. The oxidized diet increased oxidative stress in blood and increased carbonyl content in breast meat compared with the other two dietary treatments (P < 0.05). Lipid oxidation of breast muscles with the antioxidant-supplemented diet was lower than that with the oxidized and control diet groups (P < 0.05). Meat from birds fed the oxidized diet showed higher drip loss after 1 and 3 days of storage and greater 0-1 h post-mortem pH decline (P < 0.05). Significant differences in specific SERCA activity in breast muscles from birds fed control and oxidized diets (P < 0.05) were detected. This suggested that dietary oxidized oil induced oxidative stress in live birds and increased lipid and protein oxidation in breast muscle. Decrease in SERCA activity in breast muscles due to oxidative stress in live animals accelerated post-mortem glycolysis, which sped the pH drop after slaughter and increased drip loss, indicating that oxidation of diet can cause PSE-like (pale, soft, and exudative) conditions in broiler breast muscles.

Inhibition by polycyclic aromatic hydrocarbons of ATPase activities in Sebastiscus marmoratus larvae: relationship with the development of early life stages

Sebastiscus marmoratus larvae were exposed to waterborne polycyclic aromatic hydrocarbons (PAHs) containing 3-5 rings, benzo[a]pyrene (BaP), pyrene (Py) or phenanthrene (Phe), respectively at 0.01, 0.1 and 1 μg L⁻¹. Cumulative mortality, frequency of dorsal curvature and rate of pericardial and yolk sac edema in larvae treated for 8 days were significantly increased in a dose-dependent manner. All three PAHs resulted in reduction of the lower jaw, and the extent of reduction increased with increasing concentrations of the PAHs. Na+/K+-ATPase and Ca²+-ATPase activity in larvae exposed to the three PAHs were all significantly inhibited in a dose-dependent manner. Analysis using the Pearson correlation coefficient indicated a significant correlation between the rate of the dorsal curvature and edema and the inhibition of Na+/K+-ATPase and Ca²+-ATPase activity, suggesting that the developmental defects caused by PAHs were related to their inhibition of Na+/K+-ATPase and Ca²+-ATPase activity.

Inhibition of free DNA degradation by the deformation of DNA exposed to trace polycyclic aromatic hydrocarbon contaminants

A rapid inhibitory effect of polycyclic aromatic hydrocarbons (PAHs) on DNA degradation was examined by conventional spectral analysis and microtitration. The purpose was to determine whether PAHs inhibited free DNA degradation by the enzyme DNase I. The results showed that model PAHs phenanthrene and pyrene combined with free DNA to decelerate DNA degradation by DNase I. Phenanthrene-induced inhibition was stronger than that of pyrene. Trace level of PAHs did not induce DNase I deactivation. The DNase I enzyme exhibited only slight shifts in IR absorption bands related to amide II and III upon PAH exposure, and no change was observed with other bands. The decelerating degradation of DNA is attributed to the changes in structure, backbone composition, and guanine constituents of DNA induced by PAHs inserted into double strands, and to the imidazole-like derivates from the combination of imidazole rings with pyrene.

Ryanodine Receptor-Mediated Rapid Increase in Intracellular Calcium Induced by 7,8-Benzo(a)Pyrene Quinone in Human and Murine Leukocytes

Benzo(a)pyrene (BaP) is an environmentally prevalent polycyclic aromatic hydrocarbon (PAH) known to produce immunotoxicity in murine and human lymphocytes. Previous studies by our lab have shown that certain BaP metabolites increase intracellular Ca(2+) in human and murine lymphocytes. The mechanism by which these BaP metabolites increase Ca(2+) may involve src kinase activation and mitochondrial oxidative stress. We have implicated a new pathway of Ca(2+) elevation in lymphocytes produced by a novel BaP metabolite, BaP-7,8-dione (7,8-BPQ). This ortho quinone is produced from BaP-7,8-dihydrodiol by aldoketoreductase 1C1 (AKR1C) isoforms in human cells. We have previously shown that 7,8-BPQ increases Ca(2+) levels in an in vitro rabbit skeletal muscle sarcoplasmic reticulum (SR) vesicle model via interaction with ryanodine receptors (RyR). In the present study, we found that 7,8-BPQ produced a RyR-dependent rapid increase in intracellular Ca(2+) in the Daudi human B cell line. However, other BP-diones including 1,6-, 3,6-, and 6,12-BPQs failed to produce a rapid increase in Ca(2+). Instead they produced a late increase in intracellular Ca(2+), presumably via a redox-cycling-dependent loss of Ca(2+) buffering capacity by mitochondria. Functional RyR were detected in Daudi using a (3)H-ryanodine binding assay. The studies were extended to normal human peripheral blood and murine spleen cells, where it was found that 7,8-BPQ rapidly elevated intracellular Ca(2+) in B cells and T cells in both species. The Ca(2+)-elevating effect of 7,8-BPQ was prevented by pretreatment with a high concentration of ryanodine (500 muM). Collectively, these results demonstrate a novel mechanism of Ca(2+) elevation by an environmentally relevant metabolite of BaP in murine and human lymphocytes.

3-methylcholanthrene inhibits lymphocyte proliferation and increases intracellular calcium levels in common carp (Cyprinus carpio L)

Polycyclic aromatic hydrocarbons (PAHs) are an important class of environmental pollutants that are known to be carcinogenic and immunotoxic. Many authors have focused on macrophage activities in fish exposed to PAHs. However, fewer studies have reported decrease in specific immunity in such fish. We investigated the intracellular mechanisms by which the 3-methylcholanthrene (3-MC) decreased lymphocyte proliferation in carp. T- and B-lymphocyte proliferation induced by Concanavalin A (Con A) and lipopolysaccharide (LPS) were inhibited by 3-MC (0.5-50 microM). 3-MC also produced a rapid and a sustained increase in intracellular calcium concentration ([Ca(2+)](i)) (2 h minimum). However, the cytochrome p450 1A and Ah receptor inhibitor, alpha-naphtoflavone (a-NF), also inhibited lymphocyte proliferation and did not reverse the effects of 3-MC. Moreover, since a-NF and 3-MC increased [Ca(2+)](i) and inhibited lymphocyte proliferation it was possible that calcium release played a role in 3-MC-inhibited lymphocyte proliferation. The rise in [Ca(2+)](i) induced by 3-MC was potentiated by the inhibitor of the endoplasmic reticulum calcium ATPases, thapsigargin. Treating cells with 3-MC decreased calcium mobilization caused by thapsigargin. These results suggest that 3-MC acts on the endoplasmic reticulum, perhaps directly on calcium ATPases, to increase intracellular calcium levels in carp leucocytes.

3-Methylcholanthrene increases phorbol 12-myristate 13-acetate-induced respiratory burst activity and intracellular calcium levels in common carp (Cyprinus carpio L) macrophages

Phagocytic cells play a key role in the fish immune system. They secrete reactive oxygen species (ROS) involved in their bactericidal activity. These cells are highly sensitive to pollution by polycyclic aromatic hydrocarbons and other organic pollutants. We have investigated the intracellular mechanisms by which 3-methylcholanthrene (3-MC) increased bactericidal activity of carp phagocytes. Macrophages isolated from head kidney (pronephros) and incubated 1 h with 3-MC enhanced their production of ROS when they were stimulated 1.25 h with phorbol 12-myristate 13-acetate (PMA), a direct activator of protein kinase C (PKC). 3-MC also produced a rapid and a sustained increase in [Ca(2+)](i) (2 h minimum). However, the cytochrome P450 1A and Ah receptor inhibitor, alpha-naphtoflavone (alpha-NF), inhibited the potentiation of PMA-induced ROS production, suggesting 3-MC metabolic activation. Moreover, alpha-NF increased [Ca(2+)](i) without macrophage ROS production, suggesting that some mechanism other than calcium release is playing a role in the stimulation of the macrophages by 3-MC. The rise in [Ca(2+)](i) induced by 3-MC was potentiated by the inhibitor of the endoplasmic reticulum calcium ATPases, thapsigargin. And treating the cells with 3-MC decreased the calcium mobilization caused by thapsigargin. These results suggest that 3-MC acts on the endoplasmic reticulum, perhaps directly on calcium ATPases, to increase intracellular calcium levels in carp phagocytes.

Depletion of glutathione by benzo(a)pyrene metabolites, ionomycin, thapsigargin, and phorbol myristate in human peripheral blood mononuclear cells

Previous studies in this laboratory have shown that polycyclic aromatic hydrocarbons (PAHs) alter Ca2+ homeostasis and inhibit activation of both B and T lymphocytes obtained from rodents and humans. In the present studies, we demonstrate that alpha-naphthoflavone (ANF), an inhibitor of cytochrome P4501A activity, reduced the Ca2+ elevation produced by BaP in human peripheral blood mononuclear cell (HPBMC) lymphocytes. These results suggested that BaP metabolites may play a role in intracellular Ca2+ homeostasis in human lymphocytes. Reactive oxidative intermediates of BaP produced in HPMBC are known to be highly carcinogenic and have also been shown to be immunosuppressive. We examined the effects of benzo(a)pyrene (BaP), 7,12-dimethylbenz(a)anthracene (DMBA), benzo(e)pyrene (BeP), and anthracene, as well as certain BaP metabolites, on the levels of intracellular Ca2+ and glutathione in HPBMC. While BaP, DMBA, BeP, and anthracene did not cause a statistically significant decrease in GSH in HPBMC at concentrations of 1 or 10 microM following a 6-, 48-, or 72-hr exposure, reactive BaP metabolites including 4,5-epoxide BaP and 7,8-diol-9,10-epoxide BaP consistently produced a 20-30% depletion of glutathione in HPBMC following a 6-hr treatment period. These BaP metabolites also elevated intracellular Ca2+ in HPBMC during a 6-hr incubation. Results of these experiments suggest that metabolism of BaP to certain epoxide metabolites may be responsible for sulfhydryl damage leading to transient GSH depletion and Ca2+ elevation. These results are consistent with the hypothesis that sulfhydryl damage by certain PAH metabolites may lead to altered Ca2+ homeostasis, leading to inhibition of cell activation and proliferation in HPBMC.