Cytotoxicity and apoptosis induction on RTG-2 cells of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209)

Recently, the environmental residues of polybrominated diphenyl ethers (PBDEs) have markedly increased. In particular, the levels of certain PBDE congeners in fish have raised concern regarding potential risks associated with dietary PBDEs exposures. However, little is known regarding PBDE-mediated cell injury in relevant in vitro fish cell models. In this study, the cytotoxic effects of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and decabrominated diphenyl ether (BDE-209) on RTG-2 cells were investigated. RTG-2 cells were incubated with different concentrations of BDE-47 and BDE-209 (1–100 μM) for 72 h, and a set of bioassays were conducted to measure: cell viability (evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and neutral red (NR) uptake), lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) formation and cell apoptosis. The results showed that BDE-47 and BDE-209 inhibited the cells viability, increased LDH leakage, and induced cell apoptosis in time and concentration-dependent manner. All significant effects were observed at concentrations of 12.5 μM and above for BDE-47 and 25 μM and above for BDE-209 (P < 0.05). At the concentration of 100 μM BDE-47 and BDE-209, the cell viability of the exposed cells dropped to about 40% and 50% of the control, and the apoptotic rates were 52.6% and 34.6%, respectively. After 12 h exposure, a concentration-dependent increases of BDE-47 and BDE-209 (12.5–100 μM) in ROS formation were observed. Collectively, the results of cell viability, LDH leakage, cell apoptosis and ROS formation demonstrated that the toxic mechanism of PBDEs on RTG-2 might be mediated by oxidative stress.     

Tissue disposition,excretion and metabolism of 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99) in the male Sprague-Dawley rat

1. A disposition, metabolism and excretion study of orally administered 2,2',4,4',5-pentabromodiphenyl ether (BDE-99) was conducted in the conventional and bile duct-cannulated male rat. 2. In the conventional rat, >50% of the radiolabelled dose was retained at 72 h, and lipophilic tissues were the preferred sites for disposition, i.e. adipose tissue, adrenals, gastrointestinal tract and skin. 3. Urinary excretion of BDE-99 was very low (<1% of dose), and glucuronidation of phenolic metabolites was suggested. 4. Biliary excretion of BDE-99 was slightly greater than observed in urine, i.e. 3.6% at 72h. 5. Over 43% of the dose in the conventional male rat and 86% in the bile duct-cannulated rat was excreted in the faeces, mainly as the unmetabolized parent compound. 6. Metabolites in bile and faeces were not conjugated. Mono- and di-hydroxylated pentabromodiphenyl ether metabolites were characterized by mass spectrometry. Two thiol metabolites were characterized in the bile. Oxidative debromination was also observed in the faecal metabolites. 7. Tissue BDE-99 was readily extractable, except for in the liver. The tissue ¹⁴C was not associated with lipids and was mainly the unmetabolized parent compound. 8. Total thyroxine (T4) plasma levels were elevated at 3 and 6 days, and returned to control levels by day 12.     

Tissue disposition,excretion and metabolism of 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100) in male Sprague–Dawley rats

The absorption, disposition, metabolism and excretion study of orally administered 2,2′,4,4′,6-pentabromodiphenyl ether (BDE-100) was studied in conventional and bile-duct cannulated male rats. In conventional rats, >70% of the radiolabelled oral dose was retained at 72?h, and lipophilic tissues were the preferred sites for disposition, i.e. adipose tissue, gastrointestinal tract, skin, liver and lungs. Urinary excretion of BDE-100 was very low (0.1% of the dose). Biliary excretion of BDE-100 was slightly greater than that observed in urine, i.e. 1.7% at 72?h, and glucuronidation of phenolic metabolites was suggested. Thiol metabolites were not observed in the bile as had been reported in other PBDE metabolism studies. Almost 20% of the dose in conventional male rats and over 26% in bile-duct cannulated rats was excreted in the faeces, mainly as the unmetabolized parent, although large amounts of non-extractable radiolabel were also observed. Extractable metabolites in faeces were characterized by mass spectrometry. Monohydroxylated pentabromodiphenyl ether metabolites were detected; mono- and di-hydroxylated metabolites with accompanying oxidative debromination were also observed as faecal metabolites. Tissue residues of [¹⁴C]BDE-100 in liver, gastrointestinal tract and adipose tissue contained only parent material. The majority of the 0–72-h biliary radioactivity was associated with an unidentified 79-kDa protein or to albumin.     

Absorption,distribution, metabolism and excretion (ADME) study with 2,2′,4,4′,5,6′-hexabromodiphenyl ether (BDE-154) in male Sprague–Dawley rats

1. A metabolism study of orally administered 2,2′,4,4′,5,6′-hexabromodiphenyl ether (BDE-154; 11.3 μmoles kg^?1) was conducted in conventional and bile duct-cannulated male Sprague–Dawley rats.

2. In conventional rats, approximately 31% of the radiolabelled dose was retained at 72 h, and lipophilic tissues were the preferred sites for disposition.

3. Urinary excretion of BDE-154 was very low (1.0%), and parent compound was detected.

4. Cumulative biliary excretion was 1.3%, and glutathione conjugates were suggested.

5. Over 62% of the dose in conventional male rats was excreted in faeces, and was composed of parent compound (7.3%), free metabolites (13.1%), and covalently bound residues (41.4%). Faecal metabolites characterized by gas chromatography/mass spectrometry included multiple isomers of monohydroxylated hexa-/penta-/tetrabromodiphenyl ethers, and di-hydroxylated hexa/pentabromodiphenyl ethers.

6. The adipose tissue ¹⁴C was extractable BDE-154, but 40% of liver ¹⁴C was bound to macromolecules.

7. The study demonstrated the importance of performing individual polybrominated diphenyl ether (PBDE) metabolism studies to understand fully PBDE pharmacokinetics.

     

Roles of endoplasmic reticulum stress,apoptosis and autophagy in 2,2′,4,4′-tetrabromodiphenyl ether-induced rat ovarian injury

Endocrine disruptor 2,2′,4,4′-tetrabromodiphenylether (PBDE-47) can harm the female reproductive system. Recent studies showed that PBDE-47 neurotoxicity is associated with endoplasmic reticulum stress (ERS); however, the role of ERS in PBDE-47-induced ovarian injury is unclear. New-born female Sprague-Dawley rats were orally exposed to PBDE-47 (1, 5, or 10 mg/kg bw) on postnatal day 10. An additional 10 mg/kg bw PBDE-47 group was given the ERS inhibitor 4-PBA intraperitoneally for three weeks beginning on postnatal day 8. At 2 months of age, PBDE-47 exposure significantly reduced the ovarian coefficients, increased the expression of ERS and autophagy markers, including GRP78, IRE1, Caspase-12, Beclin1, LC3 and P62. In the 10 mg/kg bw PBDE-47 group, PARP and Caspase-3 were markedly activated, indicative of apoptosis. These were accompanied by histopathological damage. Intriguingly, 4-PBA attenuated all these effects. Thus, these results suggest that ERS plays a vital role in PBDE-47-induced ovarian injury by regulating autophagy and apoptosis.     

Disposition of 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE153) and its interaction with other polybrominated diphenyl ethers (PBDEs) in rodents

The disposition of the ¹⁴C-labelled polybrominated diphenyl ether (PBDE) 2,2′,4,4′,5,5′-hexaBDE (BDE153) was investigated in rodents following single and multiple doses and in a mixture with radiolabelled 2,2′,4,4′-tetraBDE (BDE47) and 2,2′,4,4′,5-pentaBDE (BDE99). In single exposure studies there was little or no effect of dose on BDE153 disposition in male rats in the range 1–100?µmol?kg^?1. No major sex or species differences in the in vivo fate of BDE153 were detected. BDE153 was absorbed in rats or mice following gavage by approximately 70%; retained in tissues; and poorly metabolized and slowly excreted. Mixture studies indicated that, relative to each other, more BDE47 was distributed to adipose tissue, more BDE153 accumulated in the liver, and BDE99 was metabolized to the greatest extent. BDE153 was probably retained in the liver due to minimal metabolism and elimination after ‘first-pass’ distribution to the tissue following gavage.     

Tissue distribution metabolism and excretion of 2,2′,4,4′, 5-pentachlorodiphenyl ether in the rat

The tissue distribution, metabolism and excretion of ¹⁴C-2,2,4,4,5-pentachlorodiphenyl ether (PCDE) were studied in the rat. Radioactivity was distributed in all tissues examined, with the highest concentrations being found in the fat followed by the skin, liver, kidney and muscle. Most of the radioactivity found in the tissues was due to unchanged PCDE. Decay of PCDE in the blood was fitted to a four-compartment pharmacokinetic model, and the last compartment had a half-life of 5.8 days. A total of 55% and 1.3% of an orally administered dose was excreted in feces and urine, respectively, in 7 days. More than 64% of the fecal radioactivity was due to unchanged PCDE, while hydroxylated PCDE accounted for 23%.     

2,2′,4,4′-四溴联苯醚(BDE-47)诱导孕烷X受体(PXR)活化能力的探讨

目的探讨2,2′,4,4′-四溴联苯醚(BDE-47)是否为孕烷X受体(pregnane X receptor,PXR)的诱导剂及其诱导PXR受体下游基因细胞色素P4503A4(CYP3A4)的转录表达能力。方法采用CCK-8法测定分析BDE-47对人肝肿瘤细胞株HepG2的细胞毒性作用,并以BDE-47分别处理双萤光素酶hPXR报告基因系统和稳定高表达hPXR的HepG2细胞株,观察其对CYP3A4的诱导作用和对其mRNA及蛋白表达的诱导作用。结果BDE-47对HepG2细胞有明显的细胞毒性作用,且在6～48h呈明显剂量-时间-效应关系(P0.01)。48h为毒作用兴奋点,其半数抑制浓度(IC50)为110μmol/L。BDE-47能诱导CYP3A4表达量的增高,呈明显剂量-时间-效应关系(P0.01)。Q-PCR和Western Blot分析发现,其对CYP3A4的mRNA转录和蛋白表达有显著诱导作用,并呈剂量-效应关系(P0.01),对PXR受体诱导能力明显高于已知的阳性诱导物利福平。结论在本试验条件下,BDE-47是PXR受体的强力诱导剂,可能通过激活PXR受体而发挥其一系列毒性作用。     

2,2′,4,4′-Tetrabromodiphenyl ether disrupts spermatogenesis,impairs mitochondrial function and induces apoptosis of early leptotene spermatocytes in rats

Our objective was to explore molecular markers and mechanism of BDE47 on spermatogenesis in mammals. Adult male SD rats were gavaged daily with corn oil containing 0, 0.001, 0.03, 1 or 20 mg BDE47/kg bw for eight weeks. Testes morphology was analyzed using electron microscopy, TUNEL, immunohistochemistry and morphometry. Differential proteome profile and western blotting were applied to determine molecular markers and protein expression. GC1-spg cells (mouse spermatogonial cells) were used to verify mechanism of BDE47. Data showed BDE47 reduced tubular epithelial thickness, impaired mitochondrial function and induced apoptosis in early leptotene spermatocytes. Proteomic study identified 70 differential spots corresponding to 64 proteins. 20 proteins related to apoptosis, 15 located in mitochondria. Exposure of GC1-spg cells showed BDE47 induced apoptosis, impaired mitochondria and decreased Bcl-2 in cells. Data indicate that BDE47 disrupts spermatogenesis, impairs mitochondrial function and induces apoptosis of early leptotene spermatocytes in rats probably via mitochondrial pathway.     

2,2′,3′,4,4′,5,5′-Heptachlorobiphenyl (PCB 180) — on its toxicokinetics,biotransformation and porphyrinogenic action in female rats

The toxicokinetics and biotransformation of 2,2,3,4,4,5,5-heptachlorobiphenyl, as well as its influence on the activity of microsomal and cytosolic enzymes and on the porphyrin pathway in the liver were studied in female rats following oral treatment with 7 mg/kg every other day for 3 months. One day after cessation of treatment the concentration of the compound in liver, spleen, CNS and blood was 100–500 times and in the trachea it was only 5 times less than in the adipose tissue. The daily excretion with the feces and urine amounted to 35 and 1.5 g, respectively. In both excreta, heptachlorobiphenylol was identified as a metabolite. The biotransformation rate was estimated to be about 5%. Investigations of the liver revealed increases in the relative liver weight, total cytochrome P-450 content, O-deethylation of 7-ethoxycoumarin and in the activity of glutathione S-transferases. Disturbances of the hepatic porphyrin pathway were not detected. Only at the end of a post-dosing period of 12 months did the hepatic uroporphyrinogen decarboxylase show diminished activity. Only one of these animals with diminished enzyme activity showed drastically elevated porphyrins. In these animals, the fecal and urinary porphyrins did not differ from controls. At no time did heptachlorobiphenyl influence the urinary excretion of delta-aminolevulinic acid and porphobilinogen. The results indicate 1) that this congener shows expected toxicokinetics with the exception of being accumulated in the trachea and 2) that this congener induces disturbances of the hepatic porphyrin pathway several months after cessation of treatment.     

Developmental exposure to methylmercury and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB153) affects cerebral dopamine D1-like and D2-like receptors of weanling and pubertal rats

MeHg (0.5 mg/kg/day) and/or PCB153 (5 mg/kg/day) effects, administered orally to rat dams (GD7-PND21), were explored in PND21 and PND36 offspring brain in terms of density (Bmax) and affinity (Kd) of dopamine D1-like (D1-Rs) and D2-like receptors (D2-Rs), by saturation binding studies. D1-Rs decreased density in both cortex and striatum (15–30%) by MeHg and PCB153, either alone or combined, without additivity in PND21 males. Changes disappeared by PND36. In females, only MeHg caused a 15% Bmax decrease in striatum. D2-Rs enhanced density (23–50%) and reduced affinity in cortex to a similar extent by all treatments in both weanling and pubertal males. Affinity was also decreased in females by all types of exposure at both ages, while density was enhanced by PCB153 only in a delayed manner (PND36). No changes were detected in striatum. In MeHg and MeHg + PCB153 pup cortex, Hg concentrations ranged, on PND21, between 0.25 and 0.89 and 0.94–1.40 μg/g tissue, respectively, and were 5- to sixfold lower 2 weeks later. PCB153 levels, in PCB153 ± MeHg treated rats, were about 15 μg/g tissue (PND21) and 4–8 μg/g tissue (PND36). In striatum, the Hg and PCB153 concentrations were similar to those in cortex. Brain kinetics trend also applied to blood PCB153 or Hg levels. Perinatal exposure to MeHg and/or PCB153 affects D1- and D2-Rs in a gender-, time-, and brain area-dependent manner. Combined treatment does not exacerbate the neurochemical effects of the individual compounds.     

Inhibitory effects of 4,4′-diisothiocyano stilbene-2,2′-disulfonic acid (DIDS) in the response of isolated hepatocytes to phalloidin

Summary The influence of pretreatment with monooxygenase inducers on total irreversible binding of metabolically activated [³H]-benzo(a)pyrene to cellular DNA and the formation of benzo(a)pyrene metabolite-deoxyribonucleoside adducts after cytochrome P-448 induction was studied in perfused rat lungs. Pretreatment with the cytochrome P-448 inducer -naphthoflavone increasing binding by a factor of 23. In lungs of induced animals, 0.45 pmoles of benzo(a)pyrene equivalents were bound per mg DNA. Binding to RNA and to protein was also considerably induced by -naphthoflavone. Phenobarbital treatment did not significantly increase binding to cellular macromolecules of rat lung. Analysis of hydrolyzed DNA of lungs from -naphthoflavone-treated rats by Sephadex LH 20 chromatography revealed the formation of at least two nucleoside adducts with metabolically activated benzo(a)pyrene one of which is probably due to modification of the DNA with a benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide and the other to modification of DNA with secondary metabolites of benzo(a)pyrene phenols.This study was supported by the Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg.In part subject of the doctoral thesis of Erik Klaus, Fachbereich Biologie, University of Mainz.     

Determination of sulfamonomethoxine in tilapia (Oreochromis niloticus × Oreochromis mossambicus) by liquid chromatography-tandem mass spectrometry and its application pharmacokinetics study

A precise and reliable analytical method to measure trace levels of sulfamonomethoxine (SMM) and N⁴-acetyl metabolite in tilapia samples using liquid chromatography-tandem mass spectrometry was developed. Optimized chromatographic separation was performed on C18 reversed-phase columns using gradient elution with methanol and 5 mmol/L of an ammonium acetate aqueous solution (adjusted to pH 3.5 using formic acid). This study investigated the pharmacokinetic properties and tissue distribution of SMM and its major metabolite N⁴-acetyl sulfamonomethoxine (AC-SMM) in tilapia after a single dose of 100 mg kg^?1 body weight of orally administered SMM. Blood and tissues were collected between 0.5 and 192 h with 14 total sampling time points. SMM was rapidly absorbed, and extensively distributed in the bile and liver through systemic circulation. Enterohepatic circulation of SMM was observed in the tilapia body. Acetylation percentages were 45% (blood), 90% (liver), 62% (kidney), 98% (bile), and 52% (muscle). High concentrations of AC-SMM accumulated in the tilapia bile. At 192 h, AC-SMM concentration in the bile remained at 4710 μg kg^?1. The k_e value of AC-SMM (0.015 h^?1) in the blood was lower than that of SMM (0.032 h^?1). This study demonstrated effective residue monitoring and determined the pharmacokinetic properties of SMM and AC-SMM in tilapia.     

2,2′,4,4′-Tetrabromodiphenyl ether injures cell viability and mitochondrial function of mouse spermatocytes by decreasing mitochondrial proteins Atp5b and Uqcrc1

Our object was to explore direct effects and mechanism of BDE47 on GC2 (immortalized mouse spermatocyte). GC2 were exposed to DMSO, 0.1, 1, 10, 100 μM BDE47 for 48 h. Cell viability was detected by trypan-blue exclusion; ultrastructure by electron-microscopy; cell cycle, mitochondrial membrane motential (MMP), reactive oxygen species (ROS) by flow-cytometry; ATP production by luminometer; Atp5b, Uqcrc1, Bcl-2 level by WB. To explore whether the decreased mitochondrial proteins play an important role in apoptosis, MMP and apoptosis were detected after Atp5b or Uqcrc1 knockdown in GC2.Results showed BDE47 reduced cell viability, caused condensation of nuclear and vacuolated mitochondria, decreased MMP and ATP, induced ROS, cell cycle arrest at S and G2/M phase, reduced Atp5b, Uqcrc1, Bcl-2 in GC2. Knockdown of Atp5b or Uqcrc1 decreased MMP, induced apoptosis in GC2. Results suggested that BDE47 reduced cell viability, injured mitochondria in spermatocytes probably by decreasing mitochondrial protein Atp5b and Uqcrc1.     

A neurotoxicity screening battery for use in safety evaluation: Effects of acrylamide and 3′,3′-iminodipropionitrile

The effects of two known neurotoxicants, acrylamide (ACR) and 3′,3′-iminodipropionitrile (IDPN), were assessed using a functional observational battery (FOB), a measurement of motor activity (MA), and neuropathology (NP) in the context of a safety evaluation study. One hundred Sprague-Dawley rats (10/sex/group) were tested initially and then doses with vehicle, ACR (10 or 30 mg/kg/day), or IDPN (50 or 125 mg/kg/day) by oral gavage 7 days/week for 5 weeks (except where otherwise indicated). Neurobehavioral assessments were conducted prior to initiating treatment at 1, 6, and 24 hr after the first dose, and weekly thereafter. Body weight and food consumption were determined weekly, and animals were observed twice daily for signs of toxicity. Blood samples were obtained at termination for routine clinical pathology studies. At termination three animals/sex/group were perfused in situ for neuropathology evaluations and the remaining animals were necropsied for standard histological evaluations. Prominent neurological signs were observed in high-dose animals after 2 weeks, and significant mortality occurred in high-dose ACR animals during Week 3. A 7- or 10-day recovery period was initiated after 20 or 22 daily doses for high-dose IDPN and ACR animals, respectively. ACR and IDPN affected body weight, body-weight gain, food consumption, general activity (horizontal and vertical), urination, muscle tone (grip strength), motor reflexes, gait, and posture. Significant sex effects were seen in animals exposed to IDPN, with males being more severely affected. Microscopic examination of nervous system tissue and selected organs revealed minimal to moderately severe axonal swelling characterized by the presence of enlarged balloon-like axons in the brainstem and the cervical and lumbar cord of IDPN-treated animals. This change was most prominent in males and most severe in the lumbar spinal cord. An increased incidence of chronic progressive nephropathy was also noted in IDPN-treated rats. ACR-treated animals exhibited minimal to moderate degeneration in the cervical and lumbar spinal cord, the gasserian and dorsal root ganglia, and the tibial, sciatic, and sural nerves which were characterized by changes in axonal diameter, increased argyrophilia of axons, and disruption, fragmentation, and distortion of axons and the myelin sheath. Granulomatous inflammation in the lungs of high-dose ACR animals resulted from inhalation of feed, most probably due to partial paralysis or incoordination during feeding.     

Metabolism of 2,2′,3,3′,6,6′-hexachlorobiphenyl (PCB 136) atropisomers in tissue slices from phenobarbital or dexamethasone-induced rats is sex-dependent

Abstract

1. Chiral polychlorinated biphenyls (PCBs) such as PCB 136 enantioselectively sensitize the ryanodine receptor (RyR). In light of recent evidence that PCBs cause developmental neurotoxicity via RyR-dependent mechanisms, this suggests that enantioselective PCB metabolism may influence the developmental neurotoxicity of chiral PCBs. However, enantioselective disposition of PCBs has not been fully characterized.

2. The effect of sex and cytochrome P450 (P450) enzyme induction on the enantioselective metabolism of PCB 136 was studied using liver tissue slices prepared from naïve control (CTL), phenobarbital (PB; CYP2B inducer) or dexamethasone (DEX; CYP3A inducer) pretreated adult Sprague-Dawley rats. PCB 136 metabolism was also examined in hippocampal slices derived from untreated rat pups.

3. In liver tissue slices, hydroxylated PCB (OH-PCB) profiles depended on sex and inducer pretreatment, and OH-PCB levels followed the rank orders male?>?female and PB?>?DEX?>?CTL. In contrast, the enantiomeric enrichment of PCB 136 and its metabolites was independent of sex and inducer pretreatment. Only small amounts of PCB 136 partitioned into hippocampal tissue slices and no OH-PCB metabolites were detected.

4. Our results suggest that enantioselective metabolism, sex and induction status of P450 enzymes in the liver may modulate the neurotoxic outcomes of developmental exposure to chiral PCBs.     

Quantification of haemoglobin binding of 4,4′-methylenebis(2-chloroaniline)(MOCA) in rats

4,4-Methylenebis(2-chloroaniline) (MOCA) is used as a curing agent in the production of polyurethane. MOCA is carcinogenic in experimental animals. Haemoglobin adducts have been proposed as dosimeters of aromatic amines for biological monitoring. A quantitative method to determine the adduct has now been worked out in female Wistar rats dosed per os with 3.82, 14.2 and 16.2 mol/kg¹⁴C-ring labeled MOCA or 0.25 and 0.50 mmol/kg unlabeled MOCA. MOCA bound in decreasing amounts to DNA, RNA and proteins of the lung, liver and kidney. Fractions of 0.19% and 0.026% of the dose were bound to the blood proteins haemoglobin and albumin, respectively. MOCA released by hydrolysis from haemoglobin was determined by HPLC with electrochemical detection or by GC-MS. Albumin did not form any hydrolysable adducts with MOCA.     

Effects on Development,Growth Responses and Thyroid-Hormone Systems in Eyed-Eggs and Yolk-Sac Larvae of Atlantic Salmon (Salmo salar) Continuously Exposed to 3,3′,4,4′-Tetrachlorobiphenyl (PCB-77)

Thyroid hormones (triiodothyronine, T3; and thyroxine, T4) play significant roles in development, metamorphosis, metabolism, homeostasis, cellular proliferation, and differentiation, for which the effects are mediated through thyroid hormone receptors (TRα and TRβ). Similarly, the insulin-like growth factor (IGF) is involved in growth and development through regulation of somatic growth. This study was designed to examine the effects of the dioxin-like 3,3’,4,4’-tetrachlorobiphenyl (PCB-77) on responses related to growth and thyroid hormone system in eyed eggs and yolk-sac larvae of Atlantic salmon. Salmon eggs were continuously exposed to two waterborne concentrations of PCB-77 (1 or 10 ng/L) over a period of 50 d covering hatching and through yolk-sac absorption stages. Sampling was performed regularly throughout the exposure period and at different time intervals. Gene expression patterns were performed on whole-body homogenate at age 500, 548, 632, 674, and 716 dd (dd: day degrees) using quantitative polymerase chain reaction (PCR). Total T3 (TT3) and total T4 (TT4) were measured using radioimmunoassay (RIA). Data showed that 10 ng PCB-77 increased dioiodinase 2 (Dio2) at 500 dd and both PCB-77 concentrations decreased dio2 expression at 548 dd. PCB-77 elevated cellular TT3 at 500 dd and was lowered at 548 dd only at 10 ng. Otherwise, time-related reduction was not affected by PCB-77 exposure as observed for the rest of the exposure period. For TT4, 1 ng PCB-77 produced a rise at 500 dd, and an apparent concentration decrease at 548 dd, before a total inhibition at 632 dd. The IGF-1 and IGF-1R were variably affected by PCB-77. For IGF-2, PCB-77 produced a concentration-dependent increase at 548 dd, and thereafter an elevation (1 ng) and fall (10 ng) at 632 dd. TRβ mRNA demonstrated PCB-77 related increases during the exposure period, and this effect returned to control levels at 716 dd. For TRα, a rise was noted only after exposure to 10 ng PCB-77 at 500 dd. Overall, the present study demonstrates some possible growth and developmental consequences following exposure to PCB-77 during early life stages of Atlantic salmon.