Rudi Mueller

Neural Injury Biomarkers of Novel Shellfish Toxins, Spirolides: A Pilot Study Using Immunochemical and Transcriptional Analysis

In 1991, routine biotoxin monitoring of bivalve molluscs at aquaculture sites along the eastern shore of Nova Scotia, Canada revealed a group of novel seafood toxins called spirolides, whose origin was the dinoflagellate Alexandrium ostenfeldii. Result from this preliminary study in rodents demonstrates a highly toxic lethal response in rats and mice after intraperitoneal injections of lipophilic extracts. To elucidate the modes of action and toxicologic pathology, brain and internal organs were examined by histology and various biomarkers of neural injury were monitored by immunohistochemistry (IH) and/or transcriptional analysis. The histological and transcriptional data showed that the effects of spirolides are species dependent for mice and rats. Histopathology showed that in the mouse brain, the hippocampus and brain stem appeared to be the major target regions but no histological changes were observed in the rat. Transcriptional analysis in the mouse brain showed no alterations in the biomarkers whereas in the rat brain there were major changes in the markers of neuronal injury. These biomarkers included the early injury markers HSP-72, c-jun and c-fos which are essential for converting stimuli into intracellular changes within neurons. The potential effects of spirolides were also evaluated with respect to different subtypes of the acetylcholine receptors (AChRs) since earlier reports showed these as putative targets. Both the muscarinic and nicotinic AChRs were found to be upregulated. Hence, transcriptional and immunohistochemical analysis does provide insight to the molecular mechanisms of this novel group of shellfish toxins. No histological changes were observed in other tissues.

Influence of sources of dietary oils on the life span of stroke-prone spontaneously hypertensive rats

In recent studies, the life span of stroke-prone spontaneously hypertensive (SHRSP) rats was altered by a variety of dietary fats. It was relatively shorter in rats fed canola oil as the sole source of fat. The present study was performed to find out whether the fatty acid profile and the high content of sulfur compounds in canola oil could modulate the life span of SHRSP rats. SHRSP rats (47 d old, n=23/group) were matched by body weight and systolic blood pressure and fed semipurified diets containing 10% canola oil, high-palmitic canola oil, low-sulfur canola oil, soybean oil, high-oleic safflower oil, a fat blend that mimicked the fatty acid composition of canola oil, or a fat blend high in saturated fatty acids. A 1% sodium chloride solution was used as drinking water to induce hypertension. After consuming the diets for 37 d, five rats from each dietary group were killed for collection of blood and tissue samples for biochemical analysis. The 18 remaining animals from each group were used for determining their life span. The mean survival time of SHRSP rats fed canola oil (87.4±4.0 d) was not significantly different (P>0.05) from those fed low-sulfur canola oil (89.7±8.5 d), suggesting that content of sulfur in canola oil has no effect on the life span of SHRSP rats. The SHRSP rats fed the noncanola oil-based diets lived longer (mean survival time difference was 6–13 d, P<0.05) than those fed canola and low-sulfur canola oils. No marked differences in the survival times were observed among the noncanola oil-based groups. The fatty acid composition of the dietary oils and of red blood cells and liver of SHRSP rats killed after 37 d of treatment showed no relationship with the survival times. These results suggest that the fatty acid profile of vegetable oils plays no important role on the life span of SHRSP rat. However, phytosterols in the dietary oils and in liver and brain were inversely correlated with the mean survival times, indicating that the differential effects of vegetable oils might be ascribed, at least partly, to their different phytosterol contents.

Characterization of a Degenerative Cardiomyopathy Associated with Domoic Acid Toxicity in California Sea Lions (Zalophus californianus)

Domoic acid, produced by marine algae, can cause acute and chronic neurologic sequela in California sea lions (Zalophus californianus) from acute toxicity or sublethal exposure. Eight sea lions, representing acute and chronic cases, both sexes, and all age classes, were selected to demonstrate a concurrent degenerative cardiomyopathy. Critical aspects of characterizing the cardiomyopathy by lesion distribution and morphology were the development of a heart dissection and tissue-trimming protocol and the delineation of the cardiac conducting system by histomorphology and immunohistochemistry for neuron-specific protein gene product 9.5. Histopathologic features and progression of the cardiomyopathy are described, varying from acute to chronic active and mild to severe. The cardiomyopathy is distinguished from other heart lesions in pinnipeds. Based on histopathologic features, immunopositive staining for cleaved caspase-3, and comparison with known, similar-appearing cardiomyopathies, the proposed pathogenesis for the degenerative cardiomyopathy is the primary or at least initial direct interaction of domoic acid with receptors that are suspected to exist in the heart. L-Carnitine, measured in the heart and skeletal muscle, and troponin-I, measured in serum collected at the time of death from additional animals (n = 58), were not predictive of the domoic acid-associated cardiomyopathy. This degenerative cardiomyopathy in California sea lions represents another syndrome beyond central neurologic disease associated with exposure to domoic acid and may contribute to morbidity and mortality.

30-day oral toxicity study of domoic acid in Cynomolgus monkeys: Lack of overt toxicity at doses approaching the acute toxic dose

Domoic acid was orally administered to 3 cynomolgus monkeys at doses of 0.5 mg/kg for 15 days and then at 0.75 mg/kg for another 15 days. After the 30-day dosing period, the treated monkeys were killed. Parameters monitored as markers for toxicity included body weight, food and water consumption, clinical observations, hematology, serum chemistry, light microscopy of all major organs (including brain and retina), and glial fibrillary acid protein immunohistochemistry. Domoic acid in serum and 24-hour urine samples was measured at several time points. All parameters measured remained unremarkable. Domoic acid concentrations measured in the 24-hour urine samples indicated that gastrointestinal absorption in the monkey was approximately 4-7 percent of the administered dose, which is at least twice that previously reported for the rat.

Safety studies on an adenovirus recombinant vaccine for rabies (AdRG1.3-ONRAB®) in target and non-target species

A replication-competent human adenovirus vector in which the rabies virus glycoprotein gene was inserted (AdRG1.3-ONRAB) was given by direct instillation into the oral cavity to representatives of three wildlife vector species of concern in Ontario (red fox, raccoon and striped skunk) and to a variety of non-target wildlife species, domestic and laboratory species. Despite use of a relatively high dose of vaccine, no untoward clinical signs were observed. Subsequent to vaccine exposure, detection of vaccine virus in lung, spleen, intestine, liver, kidney and brain of each animal was attempted using an ONRAB-specific assay combining PCR with Southern blotting (PCR-SB). Of the 1280 tissue samples obtained from vaccinates or contact animals, 18 (1.4%) were found to be PCR-SB positive. Virus isolation attempts were performed utilizing cell culture for all PCR-SB positive tissues and a selection of PCR-SB negative tissues. Histological examination performed on all PCR-SB positive tissues failed to identify lesions attributed to the vaccine. A quantitative real-time PCR was used to determine the excretion of the vaccine in feces and in the oral cavity with 0.8% of oral swabs and 6.8% of fecal specimens found to be positive. The low rates of recovery of vaccine virus from tissues, feces and the oral cavity suggest that the likelihood of ONRAB causing a negative impact on wildlife species is unlikely.

Toxicological Effects of In Utero and Lactational Exposure of Rats to a Mixture of Environmental Contaminants Detected in Canadian Arctic Human Populations

As part of the program to investigate mixture effects of environmental pollutants, this study describes clinical, biochemical, and histopathological effects in rats perinatally exposed to a mixture of persistent organochlorine pollutants and methylmercury that simulates the blood contaminant profile of humans residing in the Canadian Arctic. Groups of pregnant rats were administered orally 0, 0.05, 0.5, or 5 mg/kg body weight (bw)/d of a reconstituted mixture of organochlorine pollutants (referred to as mixture hereafter) from gestational day (GD) 1 to postnatal day (PND) 23. Positive and vehicle controls were given Aroclor 1254 (Aroclor hereafter, 15 mg/kg bw) and corn oil (vehicle), respectively. After parturition, the pups were colled to 8 per litter on PND 4, and killed on PND 35, 77, or 350, when tissues were collected for analysis. Gestational and lactational exposure of rats to mixture up to 5 mg/kg bw produced adverse effects in the offspring, including growth suppression, decreased spleen and thymic weights, increased serum cholesterol and liver microsomal enzyme activities, lower liver retinoid levels, and histological changes in the liver, thyroid, and spleen. Histological changes in the liver consisted of hepatic inflammation, vacuolation, and hypertrophy, while alterations in the thyroid were characterized by hypertrophy and hyperplasia of follicles. The hepatic and thyroidal effects were mild even at the highest dose. The spleen showed a dose-dependent atrophy in the lymphoid nodules and periarteriolar lymphatic sheath regions. Aroclor produced effects similar to those seen in the highest mixture group. In summary, this study demonstrates that exposure to the reconstituted mixture at 5 mg/kg bw produced growth suppression, changes in organ weights, and biochemical and histopathological changes in liver, thyroid, and spleen. This study also demonstrated that the blood level in rats given the 5-mg/kg dose, where most of the effects were observed, is 100-fold higher than the blood level in the 0.05-mg/kg group, which is comparable to that found in humans living in the Canadian Arctic region.

Comparative health effects of margarines fortified with plant sterols and stanols on a rat model for hemorrhagic stroke

There is increased acceptance of fortifying habitual foods with plant sterols and their saturated derivatives, stanols, at levels that are considered safe. These sterols and stanols are recognized as potentially effective dietary components for lowering plasma total and LDL cholesterol. Our previous studies have shown that daily consumption of plant sterols promotes strokes and shortens the life span of stroke-prone spontaneously hypertensive (SHRSP) rats. These studies question the safety of plant sterol additives. The present study was performed to determine whether a large intake of plant stanols would cause nutritional effects similar to those seen with plant sterols in SHRSP rats. Young SHRSP rats (aged 26–29 d) were fed semipurified diets containing commercial margarines fortified with either plant stanols (1.1 g/100 g diet) or plant sterols (1.4 g/100 g diet). A reference group of SHRSP rats was fed a soybean oil diet (0.02 g plant sterols/100 g diet and no plant stanols). Compared to soybean oil, both plant stanol and plant sterol margarines significantly (P<0.05) reduced the life span of SHRSP rats. At the initial stages of feeding, there was no difference in the survival rates between the two margarine groups, but after approximately 50 d of feeding, the plant stanol group had a slightly, but significantly (P<0.05), lower survival rate. Blood and tissue (plasma, red blood cells, liver, and kidney) concentrations of plant sterols in the plant sterol margarine group were three to four times higher than the corresponding tissue concentrations of plant stanols in the plant stanol group. The deformability of red blood cells and the platelet count of SHRSP rats fed, the plant sterol margarine were significantly (P<0.05) lower than those of the plant stanol margarine and soybean oil groups at the end of the study. These parameters did not differ between the soybean oil and plant stanol margarine groups. These results suggest that, at the levels tested in the present study, plant stanols provoke hemorrhagic stroke in SHRSP rats to a slightly greater extent than plant sterols. The results also suggest that the mechanism by which plant stanols shorten the life span of SHRSP rat might differ from that of plant sterols.

Effects of Environmentally Relevant Mixtures of Persistent Organic Pollutants on the Developmental Neurobiology in Rats

We report the developmental neuropathology for rat pups at postnatal day (PND) 37 and PND 77 and the molecular biomarkers for PND 35, 75, and 350 after perinatal exposure to a reconstituted mixture of persistent organochlorine pollutants (POPs) based on the blood profiles of people living in the Great Lake Basin. The developmental neuropathology included routine histopathology evaluation, quantification of cell proliferation and death in the subventricular zone, linear morphometric measurements, and transcriptional analysis. No histopathological, structural, or stereological changes were observed in animals treated with the POPs or Aroclor 1254, on PND 37 or PND 77. While no transcriptional changes were found in Arcolor-treated animals, significant transcriptional changes were observed on PND 350 in female offspring perinatally exposed to 0.13 mg/kg of the POP mixture. Markers of the cholinergic system including acetylcholinesterase and the muscarinic receptors (subtypes M1–M5) were downregulated 2- to 6-fold. In addition, structural genes including neurofilaments (NFLs) and microtubule-associated protein (MAP-2) were downregulated at least 2-fold or greater. Our results support that in utero and lactational exposure to the chemical mixture of POPs lead to developmental changes in adult rat brains.

Cloning and characterization of glutamate receptors in Californian sea lions (Zalophus californianus).

Domoic acid produced by marine algae has been shown to cause acute and chronic neurologic sequelae in Californian sea lions following acute or low-dose exposure. Histological findings in affected animals included a degenerative cardiomyopathy that was hypothesized to be caused by over-excitation of the glutamate receptors (GluRs) speculated to be present in the sea lion heart. Thus tissues from five sea lions without lesions associated with domoic acid toxicity and one animal with domoic acid-induced chronic neurologic sequelae and degenerative cardiomyopathy were examined for the presence of GluRs. Immunohistochemistry localized mGluR 2/3, mGluR 5, GluR 2/3 and NMDAR 1 in structures of the conducting system and blood vessels. NMDAR 1 and GluR 2/3 were the most widespread as immunoreactivity was observed within sea lion conducting system structures. PCR analysis, cloning and subsequent sequencing of the seal lion GluRs showed only 80% homology to those from rats, but more than 95% homologous to those from dogs. The cellular distribution and expression of subtypes of GluRs in the sea lion hearts suggests that exposure to domoic acid may induce cardiac damage and functional disturbances.