What Is a Meaningful Difference When Using Infarct Volume as the Primary Outcome?: Results From the HERMES Database.

BACKGROUND: Ischemic stroke lesion volume at follow-up is an important surrogate outcome for acute stroke trials. We aimed to assess which differences in 48-hour lesion volume translate into meaningful clinical differences. METHODS: We used pooled data from 7 trials investigating the efficacy of endovascular treatment for anterior circulation large vessel occlusion in acute ischemic stroke. We assessed 48-hour lesion volume follow-up computed tomography or magnetic resonance imaging. The primary outcome was a good functional outcome, defined as modified Rankin Scale (mRS) scores of 0 to 2. We performed multivariable logistic regression to predict the probability of achieving mRS scores of 0 to 2 and determined the differences in 48-hour lesion volume that correspond to a change of 1%, 5%, and 10% in the adjusted probability of achieving mRS scores of 0 to 2. RESULTS: In total, 1665/1766 (94.2%) patients (median age, 68 [interquartile range, 57-76] years, 781 [46.9%] female) had information on follow-up ischemic lesion volume. Computed tomography was used for follow-up imaging in 83% of patients. The median 48-hour lesion volume was 41 (interquartile range, 14-120) mL. We observed a linear relationship between 48-hour lesion volume and mRS scores of 0 to 2 for adjusted probabilities between 65% and 20%/volumes <80 mL, although the curve sloped off for lower mRS scores of 0-2 probabilities/higher volumes. The median differences in 48-hour lesion volume associated with a 1%, 5%, and 10% increase in the probability of mRS scores of 0 to 2 for volumes <80 mL were 2 (interquartile range, 2-3), 10 (9-11), and 20 (18-23) mL, respectively. We found comparable associations when assessing computed tomography and magnetic resonance imaging separately. CONCLUSIONS: A difference of 2, 10, and 20 mL in 48-hour lesion volume, respectively, is associated with a 1%, 5%, and 10% absolute increase in the probability of achieving good functional outcome. These results can inform the design of future stroke trials that use 48-hour lesion volume as the primary outcome.

Endovascular therapy in acute ischemic stroke with poor reperfusion is associated with worse outcomes compared with best medical management: a HERMES substudy.

BACKGROUND: Functional outcomes in patients with acute ischemic stroke (AIS) with large vessel occlusion (LVO) undergoing endovascular treatment (EVT) with poor reperfusion were compared with patients with AIS-LVO treated with best medical management only. METHODS: Data are from the HERMES collaboration, a patient-level meta-analysis of seven randomized EVT trials. Baseline characteristics and functional outcomes (modified Rankin Scale (mRS) score at 90 days) were compared between patients with poor reperfusion (defined as modified Thrombolysis in Cerebral Infarction Score 0-1 on the final intracranial angiography run as assessed by the central imaging core laboratory) and patients in the control arm with multivariable logistic ordinal logistic regression adjusted for pre-specified baseline variables. RESULTS: 972 of 1764 patients from the HERMES collaboration were included in the analysis: 893 in the control arm and 79 in the EVT arm with final mTICI 0-1. Patients with poor reperfusion who underwent EVT had higher baseline National Institutes of Health Stroke Scale than controls (median 19 (IQR 15.5-21) vs 17 (13-21), P=0.011). They also had worse mRS at 90 days compared with those in the control arm in adjusted analysis (median 4 (IQR 3-6) vs median 4 (IQR 2-5), adjusted common OR 0.59 (95% CI 0.38 to 0.91)). Symptomatic intracranial hemorrhage was not different between the two groups (3.9% vs 3.5%, P=0.75, adjusted OR 0.94 (95% CI 0.23 to 3.88)). CONCLUSION: Poor reperfusion after EVT was associated with worse outcomes than best medical management, although no difference in symptomatic intracranial hemorrhage was seen. These results emphasize the need for additional efforts to further improve technical EVT success rates.

Risk factors of unexplained early neurological deterioration after treatment for ischemic stroke due to large vessel occlusion: a post hoc analysis of the HERMES study.

BACKGROUND: Early neurological deterioration (END) after endovascular treatment (EVT) in patients with anterior circulation acute ischemic stroke (AIS) is associated with poor outcome. END may remain unexplained by parenchymal hemorrhage (UnEND). We aim to analyze the risk factors of UnEND in the medical management (MM) and EVT arms of the HERMES study. METHODS: We conducted a post-hoc analysis of anterior AIS patients who underwent EVT for proximal anterior occlusions. Risk factors of UnEND, defined as a worsening of ≥4 points between baseline National Institutes of Health Stroke Scale (NIHSS) and NIHSS at 24 hours without hemorrhage, were compared between both arms using mixed logistic regression models adjusted for baseline characteristics. An interaction analysis between the EVT and MM arms for risk factors of UnEND was conducted. RESULTS: Among 1723 patients assessable for UnEND, 160 patients experienced an UnEND (9.3%), including 9.1% (78/854) in the EVT arm and 9.4% (82/869) in the MM arm. There was no significant difference in the incidence of UnEND between the two study arms. In the EVT population, independent risk factors of UnEND were lower baseline NIHSS, higher baseline glucose, and lower collateral grade. In the MM population, the only independent predictor of UnEND was higher baseline glucose. However, we did not demonstrate an interaction between EVT and MM for baseline factors as risk factors of UnEND. UnEND was, similarly in both treatment groups, a significant predictor of unfavorable outcome in both the EVT (p<0.001) and MM (p<0.001) arms. CONCLUSIONS: UnEND is not an uncommon event, with a similar rate which ever treatment arm is considered. In the clinical scenario of AIS due to large vessel occlusion, no patient-related factor seems to increase the risk for UnEND when treated by EVT compared with MM.

Clinical outcome of patients with mild pre-stroke morbidity following endovascular treatment: a HERMES substudy.

BACKGROUND: Analyses of the effect of pre-stroke functional levels on the outcome of endovascular therapy (EVT) have focused on the course of patients with moderate to substantial pre-stroke disability. The effect of complete freedom from pre-existing disability (modified Rankin Scale (mRS) 0) versus predominantly mild pre-existing disability/symptoms (mRS 1-2) has not been well delineated. METHODS: The HERMES meta-analysis pooled data from seven randomized trials that tested the efficacy of EVT. We tested for a multiplicative interaction effect of pre-stroke mRS on the relationship between treatment and outcomes. Ordinal regression was used to assess the association between EVT and 90-day mRS (primary outcome) in the subgroup of patients with pre-stroke mRS 1-2. Multivariable regression modeling was then used to test the effect of mild pre-stroke disability/symptoms on the primary and secondary outcomes (delta-mRS, mRS 0-2/5-6) compared with patients with pre-stroke mRS 0. RESULTS: We included 1764 patients, of whom 199 (11.3%) had pre-stroke mRS 1-2. No interaction effect of pre-stroke mRS on the relationship between treatment and outcome was observed. Patients with pre-stroke mRS 1-2 had worse outcomes than those with pre-stroke mRS 0 (adjusted common OR (acOR) 0.53, 95% CI 0.40 to 0.70). Nonetheless, a significant benefit of EVT was observed within the mRS 1-2 subgroup (cOR 2.08, 95% CI 1.22 to 3.55). CONCLUSIONS: Patients asymptomatic/without disability prior to onset have better outcomes following EVT than patients with mild disability/symptoms. Patients with pre-stroke mRS 1-2, however, more often achieve good outcomes with EVT compared with conservative management. These findings indicate that mild pre-existing disability/symptoms influence patient prognosis after EVT but do not diminish the EVT treatment effect.

Functional Outcomes of Patients ≥85 Years With Acute Ischemic Stroke Following EVT: A HERMES Substudy.

BACKGROUND: Observational studies have shown endovascular treatment (EVT) for acute ischemic stroke to be effective in the elderly, despite resulting in poorer outcomes and higher rates of mortality compared with younger patients. Randomized data on the effect of advanced age on outcomes following EVT are, however, lacking. Our aim was to assess the EVT effect for ischemic stroke in patients aged ≥85 years and the influence of age on outcome in a large, randomized trial dataset. METHODS: Data were from the HERMES (Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke Trials) collaboration, a meta-analysis of 7 randomized trials published between January 1, 2010, and May 31, 2017, that tested the efficacy of EVT. A possible multiplicative interaction effect of age on the relationship between treatment and outcome was investigated. Ordinal logistic regression tested the association between EVT and 90-day functional outcome (modified Rankin Scale, primary outcome) in patients ≥85 years. Multivariable binary logistic regression was performed to compare primary and secondary outcomes (modified Rankin Scale score of 0-2/5-6) of patients ≥85 years versus those <85 years. RESULTS: We included 1764 patients in the analysis, of whom 77 (4.4%) were ≥85 years old. A significant interaction of age and treatment on poor outcome (modified Rankin Scale score of 5-6, P=0.020) and mortality (P=0.031) was observed, with older adults having worse functional outcomes at 90 days compared with younger patients (adjusted common odds ratio, 0.20 [95% CI, 0.13-0.33]). However, a benefit of EVT was observed in the ≥85-year-old patient subgroup (common odds ratio, 4.20 [95% CI, 1.56-11.32]). Age ≥85 years was not significantly associated with differing rates of symptomatic intracerebral hemorrhage or reperfusion (adjusted odds ratio, 1.92 [95% CI, 0.71-5.15] and adjusted odds ratio, 0.91 [95% CI, 0.40-2.06], respectively). CONCLUSIONS: Patients ≥85 years old with independent premorbid function more often achieve good functional outcomes and have lower rates of mortality when treated with EVT compared with conservative management, with an observed treatment effect modification of age on outcome. EVT should therefore not be withheld in this subgroup.

Correlation Between Computed Tomography-Based Tissue Net Water Uptake and Volumetric Measures of Cerebral Edema After Reperfusion Therapy.

BACKGROUND: Cerebral edema after large hemispheric infarction is associated with poor functional outcome and mortality. Net water uptake (NWU) quantifies the degree of hypoattenuation on unenhanced-computed tomography (CT) and is increasingly used to measure cerebral edema in stroke research. Hemorrhagic transformation and parenchymal contrast staining after thrombectomy may confound NWU measurements. We investigated the correlation of NWU measured postthrombectomy with volumetric markers of cerebral edema and association with functional outcomes. METHODS: In a pooled individual patient level analysis of patients presenting with anterior circulation large hemispheric infarction (core 80-300 mL or Alberta Stroke Program Early CT Score ≤5) in the HERMES (Highly Effective Reperfusion Evaluated in Multiple Endovascular Stroke trials) data set, cerebral edema was defined as the volumetric expansion of the ischemic hemisphere expressed as a ratio to the contralateral hemisphere(rHV). NWU and midline-shift were compared with rHV as the reference standard on 24-hour follow-up CT, adjusted for hemorrhagic transformation and the use of thrombectomy. Association between edema markers and day 90 functional outcomes (modified Rankin Scale) was assessed using ordinal logistic regression. RESULTS: Overall (n=144), there was no correlation between NWU and rHV (rs=0.055, P=0.51). In sub-group analyses, a weak correlation between NWU with rHV was observed after excluding patients with any degree of hemorrhagic transformation (rs=0.211, P=0.015), which further improved after excluding thrombectomy patients (rs=0.453, P=0.001). Midline-shift correlated strongly with rHV in all sub-group analyses (rs>0.753, P=0.001). Functional outcome at 90 days was negatively associated with rHV (adjusted common odds ratio, 0.46 [95% CI, 0.32-0.65]; P<0.001) and midline-shift (adjusted common odds ratio, 0.85 [95% CI, 0.78-0.92]; P<0.001) but not NWU (adjusted common odds ratio, 1.00 [95% CI, 0.97-1.03]; P=0.84), adjusted for age, baseline National Institutes of Health Stroke Scale, and thrombectomy. Prognostic performance of NWU improved after excluding patients with hemorrhagic transformation and thrombectomy (adjusted odds ratio, 0.90 [95% CI, 0.80-1.02]; P=0.10). CONCLUSIONS: NWU correlated poorly with conventional markers of cerebral edema and was not associated with clinical outcome in the presence of hemorrhagic transformation and thrombectomy. Measuring NWU postthrombectomy requires validation before implementation into clinical research. At present, the use of NWU should be limited to baseline CT, or follow-up CT only in patients without hemorrhagic transformation or treatment with thrombectomy.

Cerebral Edema in Patients With Large Hemispheric Infarct Undergoing Reperfusion Treatment: A HERMES Meta-Analysis.

Background and Purpose: Whether reperfusion into infarcted tissue exacerbates cerebral edema has treatment implications in patients presenting with extensive irreversible injury. We investigated the effects of endovascular thrombectomy and reperfusion on cerebral edema in patients presenting with radiological evidence of large hemispheric infarction at baseline. Methods: In a systematic review and individual patient-level meta-analysis of 7 randomized controlled trials comparing thrombectomy versus medical therapy in anterior circulation ischemic stroke published between January 1, 2010, and May 31, 2017 (Highly Effective Reperfusion Using Multiple Endovascular Devices collaboration), we analyzed the association between thrombectomy and reperfusion with maximal midline shift (MLS) on follow-up imaging as a measure of the space-occupying effect of cerebral edema in patients with large hemispheric infarction on pretreatment imaging, defined as diffusion-magnetic resonance imaging or computed tomography (CT)-perfusion ischemic core 80 to 300 mL or noncontrast CT-Alberta Stroke Program Early CT Score ≤5. Risk of bias was assessed using the Cochrane tool. Results: Among 1764 patients, 177 presented with large hemispheric infarction. Thrombectomy and reperfusion were associated with functional improvement (thrombectomy common odds ratio =2.30 [95% CI, 1.32­4.00]; reperfusion common odds ratio =4.73 [95% CI, 1.66­13.52]) but not MLS (thrombectomy ß=−0.27 [95% CI, −1.52 to 0.98]; reperfusion ß=−0.78 [95% CI, −3.07 to 1.50]) when adjusting for age, National Institutes of Health Stroke Score, glucose, and time-to-follow-up imaging. In an exploratory analysis of patients presenting with core volume >130 mL or CT-Alberta Stroke Program Early CT Score ≤3 (n=76), thrombectomy was associated with greater MLS after adjusting for age and National Institutes of Health Stroke Score (ß=2.76 [95% CI, 0.33­5.20]) but not functional improvement (odds ratio, 1.71 [95% CI, 0.24­12.08]). Conclusions: In patients presenting with large hemispheric infarction, thrombectomy and reperfusion were not associated with MLS, except in the subgroup with very large core volume (>130 mL) in whom thrombectomy was associated with increased MLS due to space-occupying ischemic edema. Mitigating cerebral edema-mediated secondary injury in patients with very large infarcts may further improve outcomes after reperfusion therapies.

Halogenated phenolic compounds in wild fish from Canadian Areas of Concern.

Concentrations of halogenated phenolic compounds were measured in the plasma of brown bullhead (Ameiurus nebulosus) from 4 Canadian Areas of Concern (AOCs), to assess exposure to suspected thyroid-disrupting chemicals. Hydroxylated polychlorinated biphenyls (OH-PCBs) were detected in every sample collected in 3 of the AOCs; the detection frequency was lower in samples from the Detroit River AOC. The OH-PCBs most frequently detected were pentachloro, hexachloro, and heptachloro congeners, which are structurally similar to thyroid hormones. Pentachlorophenol (PCP) was detected at highest concentrations (1.8 ng/g) in fish from Prince Edward Bay, the Bay of Quinte Lake reference site, and Hillman Marsh (the Wheatley Harbour reference site), suggesting local sources of contamination. Elevated PCP concentrations were also detected in the plasma of brown bullhead from exposed sites in the Toronto and Region AOC (0.4-0.6 ng/g). Triclosan was consistently detected in the Toronto and Region AOC (0.05-0.9 ng/g), consistent with wastewater emission. Greater concentrations were occasionally detected in the plasma of brown bullhead from the Bay of Quinte AOC. Concentrations of polybrominated diphenyl ethers were highest in the Toronto and Region AOC, and at 2 of the Bay of Quinte AOC exposed sites near Trenton and Belleville. Distribution patterns reflected the properties and usage of the compounds under investigation and the characteristics of each AOC. Environ Toxicol Chem 2017;36:2266-2273. © 2017 SETAC.

Assessment of the health status of wild fish from the Wheatley Harbour Area of Concern, Ontario, Canada.

The overall health and endocrine function of wild brown bullhead (Ameiurus nebulosus) and goldfish (Carassius auratus) from the Wheatley Harbour Area of Concern (Lake Erie, Ontario, Canada) was assessed using a suite of physiological and biochemical endpoints. Smaller gonads were detected in female brown bullhead and goldfish from Wheatley Harbour compared with Hillman Marsh (Ontario, Canada) reference fish. Female brown bullhead exhibited decreased in vitro synthesis of 17ß-estradiol. Female goldfish had decreased plasma vitellogenin concentrations. Plasma testosterone and 11-ketotestosterone were significantly depressed in males of both species. Perturbations in the thyroid status were detected, but varied between sexes and species. Observed differences included lower plasma concentrations of thyroid hormones and/or elevated liver deiodinase activity. Histological evaluation of the thyroid tissue indicated that in the case of female goldfish, those perturbations stimulated the thyroid (as indicated by increased thyroid epithelial cell height) and partially depleted the thyroxine reserves, as indicated by decreased colloid and elevated thyroid activation index. Increased mixed-function oxygenase activity in brown bullhead from Wheatley Harbour was consistent with exposure to planar aromatic contaminants. A principal component analysis of selected variables showed the separation of fish by collection site. The endpoints most strongly associated with the separation were generally those exhibiting significant differences between sites. The results of the present study indicate that the health of fish populations within Wheatley Harbour warrants continued attention.

Polychlorinated biphenyls and their hydroxylated metabolites in wild fish from Wheatley Harbour Area of Concern, Ontario, Canada.

Whole-body polychlorinated biphenyls (ΣPCBs) and plasma hydroxylated PCBs (OH-PCBs) concentrations were determined in brown bullhead (Ameiurus nebulosus) from Wheatley Harbour, Ontario, Canada. Elevated ΣPCBs in Wheatley Harbour are suspected to have originated from industrial waste disposal and/or discharges from nearby fish processing through discarding of fish remains. Mean ΣPCB concentrations in brown bullhead from Wheatley Harbour were approximately 250 ng/g wet weight compared with approximately 40 ng/g wet weight for brown bullhead from the reference sites, Hillman Marsh and Turkey Creek (both in Ontario, Canada). A significant relationship was found between the concentrations of non-ortho and mono-ortho PCB concentrations (toxic equivalents) and liver mixed-function oxygenase in brown bullhead (r = 0.74, p < 0.001). Plasma OH-PCB concentrations were greater in Wheatley Harbour brown bullhead than in those from Hillman Marsh (3.6 vs 1.5 ng/g wet wt, p < 0.01), and were detected infrequently in those from Turkey Creek (0.1 ng/g wet wt, n = 2). The OH-PCB congeners most frequently detected were 4'-OH-CB172, 3'-OH-CB180, 4-OH-CB187, 4-OH-CB146, 3-OH-CB138, and 4-OH-CB130, which are structurally similar to the thyroid hormones. To test the hypothesis of fish waste as the cause of the observed PCB contamination of Wheatley Harbour brown bullhead, a principal component analysis (PCA) was used to compare the brown bullhead PCB congener data with equivalent data for Lake Erie walleye, Lake Erie sediment, and industrial Aroclor mixtures. The relative proportions of each Aroclor mixture were estimated using the conjugated gradient method. The high similarity between the congener signatures for Lake Erie walleye and Wheatley Harbour brown bullhead supports the hypothesis of contamination from the fish processing industry.

Variations of thiaminase I activity pH dependencies among typical Great Lakes forage fish and Paenibacillus thiaminolyticus.

The source of thiaminase in the Great Lakes food web remains unknown. Biochemical characterization of the thiaminase I activities observed in forage fish was undertaken to provide insights into potential thiaminase sources and to optimize catalytic assay conditions. We measured the thiaminase I activities of crude extracts from five forage fish species and one strain of Paenibacillus thiaminolyticus over a range of pH values. The clupeids, alewife Alosa pseudoharengus and gizzard shad Dorosoma cepedianum, had very similar thiaminase I pH dependencies, with optimal activity ranges (> or = 90% of maximum activity) between pH 4.6 and 5.5. Rainbow smelt Osmerus mordax and spottail shiner Notropis hudsonius had optimal activity ranges between pH 5.5-6.6. The thiaminase I activity pH dependence profile of P. thiaminolyticus had an optimal activity range between pH 5.4 and 6.3, which was similar to the optimal range for rainbow smelt and spottail shiners. Incubation of P. thiaminolyticus extracts with extracts from bloater Coregonus hoyi (normally, bloaters have little or no detectable thiaminase I activity) did not significantly alter the pH dependence profile of P. thiaminolyticus-derived thiaminase I, such that it continued to resemble that of the rainbow smelt and spottail shiner, with an apparent optimal activity range between pH 5.7 and 6.6. These data are consistent with the hypothesis of a bacterial source for thiaminase I in the nonclupeid species of forage fish; however, the data also suggest different sources of thiaminase I enzymes in the clupeid species.

Gizzard shad thiaminase activity and its effect on the thiamine status of captive American alligators Alligator mississippiensis.

Adult mortality and low egg hatch rate were observed among American alligators Alligator mississippiensis in Lake Griffin, Florida, between 1998 and 2003. Previous studies show that the alligator mortality is due to neurological impairment associated with thiamine (vitamin Bt) deficiency. This study determined the rate of thiaminase activity in gizzard shad Dorosoma cepedianum, a fish often eaten by alligators, and examined the thiamine status of captive adult alligators fed only gizzard shad. We found that the thiaminase activity of gizzard shad in Lake Griffin is 16,409 +/- 2,121 pmol/g/min (mean +/- 2SEs). This high rate of thiaminase activity was present in most months and across a wide range of shad sizes. Seven alligators were captured in the wild from Lake Griffin and Lake Woodruff, held in captivity, and fed gizzard shad. We monitored blood and muscle thiamine levels throughout the experiment and liver thiamine at the end. Over a period of 6-12 months, all of the alligators maintained weight but blood and muscle thiamine levels decreased to 25-50% of the original (healthy) values. Three animals with the greatest reduction in thiamine died, demonstrating mobility impairment and neural histopathology similar to those seen in wild alligators in Lake Griffin. Two alligators were fed shad for 10 months but then treated with thiamine. These animals showed a reduction in thiamine while eating shad, but treatment restored their thiamine levels to the initial values, which were comparable to those of normal wild Lake Griffin alligators. We demonstrated that thiamine deficiency can be induced by a diet of gizzard shad and cause neurological signs and death in alligators in captivity. We conclude that the thiaminase activity in gizzard shad is high enough to cause thiamine deficiency in wild alligators when shad are a major part of their diet.

Egg fatty acid composition from lake trout fed two Lake Michigan prey fish species.

We previously demonstrated that there were significant differences in the egg thiamine content in lake trout Salvelinus namaycush fed two Lake Michigan prey fish (alewife Alosa pseudoharengus and bloater Coregonus hoyi). Lake trout fed alewives produced eggs low in thiamine, but it was unknown whether the consumption of alewives affected other nutritionally important components. In this study we investigated the fatty acid composition of lake trout eggs when females were fed diets that resulted in different egg thiamine concentrations. For 2 years, adult lake trout were fed diets consisting of four combinations of captured alewives and bloaters (100% alewives; 65% alewives, 35% bloaters; 35% alewives, 65% bloaters; and 100% bloaters). The alewife fatty acid profile had higher concentrations of arachidonic acid and total omega-6 fatty acids than the bloater profile. The concentrations of four fatty acids (cis-13, 16-docosadienoic, eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids) were higher in bloaters than in alewives. Although six fatty acid components were higher in lake trout eggs in 2001 than in 2000 and eight fatty acids were lower, diet had no effect on any fatty acid concentration measured in lake trout eggs in this study. Based on these results, it appears that egg fatty acid concentrations differ between years but that the egg fatty acid profile does not reflect the alewife-bloater mix in the diet of adults. The essential fatty acid content of lake trout eggs from females fed alewives and bloaters appears to be physiologically regulated and adequate to meet the requirements of developing embryos.

Influence of thiamine deficiency on lake trout larval growth, foraging, and predator avoidance.

Diet-related thiamine deficiency increases the acute mortality, known as early mortality syndrome, of salmonines from some of the Great Lakes. The consequences of thiamine deficiency as measured at the egg stage for other important early life stage processes like growth, foraging efficiency, and predator avoidance that may also result in mortality, are unknown. Accordingly, we investigated the impacts of low thiamine on the specific growth rate (SGR) of first-feeding fry, the ability of first-feeding fry to capture Daphnia, fry emergence in the presence of a potential predator (round goby Apollina [formerly Neogobius] melanostomus), and predation by slimy sculpin Cottus cognatus. We used a combination of thiamine-deficient and thiamine-replete wild stocks of lake trout Salvelinus namaycush for this purpose. From these investigations we developed predictive relationships. Specific growth rate was related to egg thiamine concentration. From the exponential relationship, it was predicted that the threshold egg thiamine concentrations associated with 20% and 50% reductions in SGR are 8.1 and 5.1 nmol/g, respectively. The foraging rate on Daphnia was also related to egg thiamine concentration by an exponential relationship. It was predicted that the threshold concentrations associated with 20% and 50% reductions in this rate are 6.9 and 2.9 nmol/g, respectively. The presence of a round goby significantly reduced emergence success, but the level of goby predation was unrelated to egg thiamine concentration. Sculpin predation was related, although weakly, to the initial egg thiamine concentration. This research found that thiamine deficiency affected growth, foraging, and predator avoidance in lake trout fry. Growth effects resulting from thiamine deficiency may represent the most sensitive means of monitoring the impact of the secondary consequences of thiamine deficiency. Mortality associated with the combined effects of reduced growth and foraging has the potential to seriously impair lake trout recruitment.

Thiamine deficiency effects on the vision and foraging ability of lake trout fry.

The exact causes of the historical recruitment failures of Great Lakes lake trout Salvelinus namaycush are unknown. Thiamine deficiency has been associated with neurological abnormalities in lake trout that lead to early mortality syndrome (EMS) in salmonine swim-up fry, and EMS-related mortality at the swim-up stage is a factor that contributes to the reproductive failure of lake trout populations in the Great Lakes. The potential for adverse effects of thiamine deficiency beyond the swim-up stage is unknown. We investigated the effects of low egg thiamine on behavioral functions in young, post-swim-up lake trout fry. The behavioral endpoints included visual acuity and prey capture rates in the same groups of lake trout fry from each family. Low-thiamine eggs were produced by feeding lake trout broodstock diets entailing thiaminase activity. The thiamine content of the spawned eggs ranged from 0.3 to 26.1 nmol/g. Both visual acuity and prey capture rates were affected by the thiamine content of the eggs. The visual acuity of lake trout was severely affected by low egg thiamine, mainly at thiamine concentrations below the threshold of 0.8 nmol/g but also at higher concentrations in field-collected eggs. Feeding was also reduced with low egg thiamine content. The reduction of prey capture rates was dramatic below 0.8 nmol/g and less dramatic, but still significant, in a portion of the families with egg thiamine concentrations of less than 5.0 nmol/g from both laboratory and field samples. Approximately one-third of the latter families had reduced feeding rates. Deficits in visual acuity may be part of the mechanism leading to decreased feeding rates in these fry. The effects of low egg thiamine on both of the behavioral endpoints studied increase the risk of low recruitment rates in Great Lakes lake trout populations.

Evaluating the effect of stressors on thiaminase activity in alewife.

No consistent explanation has been found for the variability in the thiaminase activity of alewives Alosa pseudoharengus despite the role of alewife thiaminase in large-scale salmonine mortality in the Laurentian Great Lakes. We conducted experiments to evaluate the effect of two stressors, reduced salt content in the water and food limitation, on alewife thiaminase activity. Alewives were subjected to treatments in replicated tanks in which conductivity was lowered (< 100 microS/cm) for 8 d and feeding was limited for 39 d. Circulating white blood cells, plasma cortisol, plasma glucose, and whole-body thiaminase were measured in individual alewives to assess their response to these experimental treatments. Alewives from the controls had significantly larger numbers of circulating white blood cells than those in the salt-reduced and food-limited treatments (24,000 and 19,000 cells/microL and 11,000 and 9,000 cells/microL for alewives from the two control and salt-reduced treatment tanks, respectively, and 34,000 and 30,000 cells/microL and 21,000 and 16,000 cells/microL for alewives from the two control and food-limited treatment tanks). No significant differences in alewife thiaminase activity were found between treatment fish and their controls. The mean thiaminase activity in the alewives studied increased from 6,900 to 16,000 pmol x g(-1) x min(-1) from the time of their collection in Cayuga Lake to the start of laboratory experiments 1.5-2.5 years later; the latter value was more than twice that of previously reported levels of thiaminase activity from alewives collected in the wild. These data suggest that the variability in alewife thiaminase is not related to stress from salt reduction or food limitation, but laboratory holding conditions significantly increased thiaminase through a mechanism not evaluated by our experimental treatments.

PCBs can diminish the influence of temperature on thyroid indices in rainbow trout (Oncorhynchus mykiss).

The influence of PCBs on the thyroid status of rainbow trout was assessed at various temperatures to identify if PCB mixtures, as well OH-PCBs produced via biotransformation of parent PCBs, can illicit thyroid effects in fish. Juvenile rainbow trout (Oncorhynchus mykiss) held at 8, 12 or 16 degrees C were exposed to dietary concentrations of an environmentally relevant mixture of PCBs for 30 days followed by a depuration phase. Two additional treatments at 12 degrees C included higher concentrations of PCBs (congeners 77, 126 and 169) known to induce CYP1A in fish (referred to as CYP1A treatment) and PCBs (congeners 87, 99, 101, 153, 180, 183 and 194) known to induce CYP2B in mammals (referred to as CYP2 treatment), to assess the influence of more biologically relevant PCB congeners on thyroid indices in fish. Growth rate and liver somatic index varied with water temperature (p<0.05) but did not differ between PCB exposed and control fish (p>0.05) and mortality was low in all treatments. Changes in some measures of thyroid status were apparent in PCB-exposed fish held in the 12 and 16 degrees C treatments while other measures showed no change in any treatment. The natural inverse relationship between thyroid epithelial cell height (TECH) and temperature, was diminished after 30 days of exposure to PCBs as the epithelial cell height in PCB-exposed fish was significantly augmented in the 12 and 16 degrees C treatments compared to controls at these temperatures (p<0.05). However, after 20 days of depuration, TECH values in the PCB exposed fish returned to control values. The natural linear gradient between T(4) outer-ring deiodinase activity (ORD) and temperature was also diminished after 30 days of exposure to PCBs. PCB-exposed fish from the 16 degrees C treatment had significantly lower deiodinase activities (p<0.05) compared to controls at this temperature, but deiodinase activities returned to normal by day 20 of depuration. No differences were observed in T(3) inner-ring deiodinase (IRD) activities and plasma concentrations of T(3) and T(4) in any of the treatments (p>0.05). EROD activity in fish from the CYP1A and CYP2 treatments were elevated compared to control and high dose PCB-exposed treatments (p<0.05), but the inclusion of CYP inducing congeners did not appear to influence any index of thyroid status. Results of this study suggest that exposure of rainbow trout to high concentrations of PCBs and/or OH-PCBs may alter some indices of thyroid status when water temperatures are high, but these changes are within the compensatory scope of the thyroid system based on no change in circulating hormone concentrations, growth rates or mortality.

Role of temperature and enzyme induction in the biotransformation of polychlorinated biphenyls and bioformation of hydroxylated polychlorinated biphenyls by rainbow trout (Oncorhynchus mykiss).

Hydroxylated PCBs (OH-PCBs) are metabolites of polychlorinated biphenyls (PCBs) that have recently been found in the plasma of Great Lakes fish. Studies have shown that the ability of laboratory-held rainbow trout (Oncorhynchus mykiss) to bioform OH-PCBs from dietary mixtures of PCB congeners is complex and may be attributed to factors such as temperature and/or enzyme induction. Past studies have also suggested that CYP1A- and 2B-like enzymes are the likely mechanism for forming OH-PCBs, but this has not been directly studied in a controlled setting. To address these issues, we exposed rainbow trout (-80 g) to dietary concentrations of a mixture of three Aroclors (1248, 1254, and 1260), at three water temperatures (8, 12, and 16 oC), as well as additional PCBs known to induce CYP1A- and CYP2B-like isoforms in mammals. PCB half-lives in trout were inversely related to water temperature, but biotransformation of PCBs was positively related to water temperature. Thirty-one OH-PCBs were observed in trout plasma after 30 days of dietary exposure to the Aroclor mixtures, although approximately 40% of the sigmaOH-PCBs concentrations were OH-PCB for which no standards were available. Concentration of OH-PCBs in the trout plasma increased with increasing temperature and with the addition of CYP2B-like inducing congeners but not with the addition of CYP1A-inducing congeners to food. The results of this study provide the first in vivo evidence that rainbow trout are responsive to CYP2B-like induction by PCBs and that this enzyme system can influence PCB concentrations and OH-PCB formation in fish.

Biotransformation of polychlorinated biphenyls (PCBs) and bioformation of hydroxylated PCBs in fish.

Hydroxylated PCBs (OH-PCBs) are a class of organic contaminants that have been found recently in the plasma of Great Lakes fish, the source of which is either bioformation from PCBs or accumulation from the environment. To address the potential for fish to biotransform PCBs and bioform OH-PCBs juvenile rainbow trout (Oncorhynchus mykiss; approximately 80 g) were exposed to dietary concentrations of an environmentally relevant mixture of PCBs. Eight OH-PCBs were found in the plasma of rainbow trout after 30 days of exposure to the PCBs, the relative pattern of which was similar to those observed in wild lake trout (Salvelinus namaycush) from Lake Ontario. Hydroxylated-PCBs were not found (detection limit 0.02 pg/g) in the food or control (not PCB-exposed) fish. A curvilinear logt(1/2)-logK(ow) relationship for recalcitrant PCBs was found, similar to previously reported relationships, although t(1/2) values were longer and shorter than studies using smaller fish or cooler temperatures, respectively. A number of PCB congeners fell below the logt(1/2)-logK(ow) relationship providing the first estimates of non-chiral PCB biotransformation rates in fish. Enantioselective degradation of the chiral congeners PCBs 91 and 136, also indicated biotransformation. Biotransformation of PCBs was structure-dependent with greater biotransformation of PCBs with vicinal hydrogen atoms in the meta/para positions, suggesting CYP 2B-like biotransformation. Other chiral congeners with a meta/para substitution pattern showed no enantioselective degradation but were biotransformed based on the logt(1/2)-logK(ow) relationship. The results of this study demonstrate that laboratory held rainbow trout can biotransform a number of PCB congeners and that bioformation is likely an important source of OH-PCBs in wild salmonids of the Great Lakes.

Effects of maternally transferred organochlorine contaminants on early life survival in a freshwater fish.

Laboratory research has shown that female fish can pass toxic organochlorines (OCs) from their bodies to their eggs, killing their offspring if sufficient quantities are transferred. We conducted a controlled incubation study using gametes from a wild, OC-contaminated walleye (Sander vitreus) population (Bay of Quinte, Lake Ontario, Canada) in order to assess among-female variation in offspring early life survival in relation to ova concentrations of planar OCs (polychlorinated dibenzo-p-dioxins and furans and planar polychlorinated biphenyls) and a suite of other maternal and ova characteristics. Equal volumes of ova from each female were fertilized, pooled, and incubated together as an experimental cohort. Relative survival of each female's offspring was estimated as the proportion of surviving larvae (at approximately 5 d posthatch) that she contributed to the cohort as determined by microsatellite DNA parentage assignment. Total planar OC concentration (expressed as toxic equivalency of 2,3,7,8-tetrachlorodibenzo-p-dioxin) of ova was positively related to maternal age and size and to ova lipid content. However, early life survival did not decline with increasing ova planar OC concentrations. Similarly, we observed no significant relationships between early life survival and ova thiamine content, ova fatty acid composition, or maternal age or size. Early life survival was more strongly correlated with date of spawn collection, thyroid hormone status of the ova, and ovum size. Maternally transferred planar OCs do not appear to negatively influence female reproductive success in this walleye population.