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Michael J Carvan

Publications and source records attributed to Michael J Carvan.

8 recordsLinked to original sources
PubMed2006

Fluorescence-based detection of thiols in vitro and in vivo using dithiol probes.

Thiols play a central role in maintaining biological homeostasis. Their levels can change dramatically in response to oxidative stress associated with toxic insults, bacterial infection, and disease. Therefore, a reagent that can monitor thiol levels both in vitro and in vivo would be useful for assays and as a biomarker. Such a reagent should (i) be selective for thiols, (ii) be able to penetrate cell walls, and (iii) have a low reduction potential so as not to create oxidative stress in a cell. We have developed such a fluorescent reagent (DSSA) based on a dithiol linker: (i) the use of a dithiol linker makes it selective for thiols; (ii) the use of fluorophores that populate neutral states at physiological pH improves cell wall penetration; and (iii) because of the reagent's low reduction potential (-0.60 V), it will not stress cells oxidatively. For example, 5 microM of reagent is responsive to changes in glutathione levels in the physiologically relevant range of 1 to 10mM, yet this would oxidize less than 1% of cellular glutathione. In Escherichia coli, decreased thiol levels were detected in cells deficient in glutathione synthesis. In zebrafish embryos, the DSSA reagent permitted detection of unusually high thiol levels in the zebrafish chorion.

Animals↗
PubMed2006

Gene expression changes related to endocrine function and decline in reproduction in fathead minnow (Pimephales promelas) after dietary methylmercury exposure.

BACKGROUND: Methylmercury (MeHg) is a known neurotoxic agent, but the mechanisms by which MeHg may act on reproductive pathways are relatively unknown. Several studies have indicated potential changes in hormone levels as well as declines in vertebrates with increasing dietary MeHg exposure. OBJECTIVES: The purpose of this study was to identify alterations in gene expression associated with MeHg exposure, specifically those associated with previously observed changes in reproduction and reproductive biomarkers. Fathead minnows, Pimephales promelas, were fed one of three diets that were similar to documented concentrations of MeHg in the diets of wild invertivorous and piscivorous fish. We used a commercial macroarray in conjunction with quantitative polymerase chain reaction to examine gene expression in fish in relation to exposure to these environmentally relevant doses of MeHg. RESULTS: Expression of genes commonly associated with endocrine disruption was altered with Hg exposure. Specifically, we observed a marked up-regulation in vitellogenin mRNA in individual Hg-exposed males and a significant decline in vitellogenin gene expression in female fish with increasing Hg concentrations. Other genes identified by the macroarray experiment included those associated with egg fertilization and development, sugar metabolism, apoptosis, and electron transport. We also observed differences in expression patterns between male and female fish not related to genes specifically associated with reproduction, indicating a potential physiological difference in the reaction of males and females to MeHg. CONCLUSION: Gene expression data may provide insight into the mechanisms by which MeHg affects reproduction in fish and indicate how MeHg differs in its effect from other heavy metals and endocrine-disrupting compounds.

Animal Feed↗
PubMed2005

Inhibition of follicular development, vitellogenesis, and serum 17beta-estradiol concentrations in zebrafish following chronic, sublethal dietary exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a potent endocrine disruptor with the ability to affect several biologic processes, including reproduction. In fish, sublethal exposure to TCDD is known to modulate overall reproductive capacity, but impacts on follicular development and vitellogenesis are unknown. Here we show that chronic, dietary exposure to 0.08, 0.32, or 0.80 ng TCDD female(-1) day(-1) decreased egg production by more than 50% and that spawning success was reduced by as much as 96%. Serum estradiol concentrations were decreased more than twofold, accounting, in part, for observed decreases in serum vitellogenin concentrations by as much as 29%. Our data suggest that decreased egg production is likely the result of TCDD-mediated inhibition of the transition from pre-vitellogenic stage follicles to vitellogenic stage follicles, as well as the induction of follicular atresia. The majority of reproductive toxicity of TCDD is likely due to direct impacts on the ovary, yet histopathologic observations suggest liver toxicity could also contribute to observed impacts on vitellogenesis. Importantly, even when overall egg production is not significantly affected, our data show that subtle physiologic changes induced by TCDD can lead to altered gonadogenesis. This suggests that long-term exposure to very low concentrations of TCDD could greatly affect fecundity and reproductive success in fishes.

Animals↗
PubMed2005

Accumulation, tissue distribution, and maternal transfer of dietary 2,3,7,8,-tetrachlorodibenzo-p-dioxin: impacts on reproductive success of zebrafish.

TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is a reproductive toxicant and endocrine disruptor in nearly all vertebrates; however, the mechanisms by which TCDD alters the reproductive system is not well understood. The zebrafish provides a powerful vertebrate model system to investigate molecular mechanisms by which TCDD affects the reproductive system, but little is known regarding reproductive toxic response of zebrafish following chronic, sublethal exposure to TCDD. Here we investigate the accumulation of TCDD in selected tissues of adult female zebrafish and maternal transfer to offspring following dietary exposure to TCDD (0.08-2.16 ng TCDD/fish/day). TCDD accumulated in tissues of zebrafish in a dose- and time-dependent manner, except for brain. Chronic dietary exposure resulting in the accumulation of 1.1-36 ng/g fish did not induce an overt toxic response or suppress spawning activity. The ovosomatic index was impacted with an accumulation of as little as 0.6 ng/g fish, and 10% of the females showed signs of ovarian necrosis following accumulation of approximately 3 ng/g TCDD. Offspring health was impacted with an accumulation of as little as 1.1 ng/g female; thus the lowest observed effect level (LOEL) for reproductive toxicity in female zebrafish is approximately 0.6-1.1 ng/g fish. Maternal transfer resulted in the accumulation of 0.094-1.2 ng/g, TCDD, which was sufficient to induce the typical endpoints of larval TCDD toxicity, commonly referred to as blue sac syndrome. This study provides the necessary framework to utilize the zebrafish model system for further investigations into the molecular mechanisms by which TCDD exerts its reproductive toxic responses.

Animals↗
PubMedDate not supplied

Ethanol effects on the developing zebrafish: neurobehavior and skeletal morphogenesis.

Exposure to ethanol during development can lead to a constellation of congenital anomalies, resulting in prenatal and postnatal failure to thrive, central nervous system (CNS) deficits, and a number of patterning defects that lead to defects in the cardiovascular system, facial structures, and limbs. The cellular, biochemical, and molecular mechanisms by which ethanol exerts its developmental toxicity and the genes that influence sensitivity to developmental ethanol exposure have yet to be discovered, despite being one of the more common nongenetic causes of birth defects. The zebrafish undergoes much the same patterning and morphogenesis as other vertebrate embryos do--including humans--that are distinct and cannot be studied in invertebrates. Developmental processes in zebrafish are affected by ethanol exposure in a dose-dependent manner, resulting in learning and memory deficits, cell death in the CNS, skeletal dysmorphogenesis, and alterations in startle reflex responses. Interestingly, significant ethanol effects on learning and behavioral endpoints occurred at concentrations well below those that induced cell death in the CNS. This work provides the foundation for identifying genes and pathways involved in developmental alcohol toxicity in vertebrates, leading to a more complete mechanistic understanding of fetal alcohol disorders in humans.

Alcohol-Induced Disorders, Nervous System↗
PubMedDate not supplied

Strain-dependent effects of developmental ethanol exposure in zebrafish.

Developmental ethanol exposure from maternal consumption of alcoholic beverages and many other consumer products has been linked to developmental abnormalities in humans and animal models. The sensitivity of an individual to ethanol-induced perturbation of developmental processes is strongly influenced by genetic factors. In this study, we show that there are strain- and dose-dependent differences in sensitivity to developmental ethanol exposure in zebrafish (Danio rerio), suggesting that genetic variation within regulatory factors, influencing critical developmental pathways, is responsible for these differences. Embryos/larvae from genetically distinct strains of zebrafish [Ekkwill (EK), AB, and Tuebingen (TU)] were treated with different concentrations of ethanol. Embryo/larval survival, neurocranial and craniofacial skeletal development, and CNS cell death were analyzed. EK was the most resistant strain to the embryolethal effects of ethanol exposure but had the greatest increase in ethanol-induced cell death. AB survival was affected moderately, as were the neurocranial and craniofacial skeletal structures and ethanol-induced cell death. TU had the lowest survival rate but was the most resistant to alterations in neurocranial and craniofacial skeletal elements. No single strain is the most sensitive or the most resistant to any of the phenotypes examined, suggesting that alcohol influences each of these pathways independently. Further analysis of the molecular and biochemical pathways underlying the strain-dependent differences reported herein could lead to a significant advancement in our mechanistic understanding of the teratogenic effects of ethanol in humans.

Alcohol-Induced Disorders, Nervous System↗