| 1. |
- Asnake, Solomon, 1985-
(författare)
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Interaction of brominated flame retardants with the chicken and zebrafish androgen receptors
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The survival of organisms depends on their ability to use different signaling pathways to adapt to the environment. The endocrine system consists of glands that release hormones to the blood stream. Male reproductive functions are regulated by androgens through interactions with the androgen receptor (AR). AR has been characterized in chicken and zebrafish where they use testosterone and 11-ketotestosterone as their primary androgens, respectively. AR function has been disturbed by different endocrine disrupting compounds (EDCs) present in the environment causing detrimental effects on avian and fish species. Brominated flame retardants (BFRs) are a group of EDCs that are ubiquitous in the environment. Molecular modeling techniques using computer simulations such as docking and molecular dynamics are a useful tool in the identification of EDCs. The capacity to test thousands of compounds at once has helped in the early identification of EDCs that interact with AR. Two groups of BFRs, the 1,2-dibromo-4- cyclohexane diastereomers (TBECH) and the compounds synthesized from 2, 4, 6-tribromophenol, allyl 2,4,6-tribromophenyl ether (ATE), 2-bromoallyl 2,4,6- tribromophenyl ether (BATE) and 2,3-dibromopropyl 2,4,6-tribromophenyl ether (DPTE) interact and alter AR activity in human in vitro studies. As models for avian and fish species, chicken and zebrafish were used to test these BFRs. TBECH diastereomers were able to bind to the AR, estrogen receptors and thyroid receptors in the chicken and to the AR in zebrafish. ATE, BATE and DPTE were also able to interact with the chicken AR and zebrafish AR. Activation studies using cell lines showed that TBECH diastereomers acted as agonists to the cAR and zAR while ATE, BATE and DPTE acted as antagonists. The BFRs also altered multiple signaling pathways such as the apoptotic, antiapoptotic, immune, drug metabolizing and DNA methylation systems and in vivo studies resulted in physiological effects on zebrafish.
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| 2. |
- El Marghani, Ahmed
(författare)
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Regulatory aspects of innate immune responses
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Activation of innate immunity is regulated by a variety of signaling molecules within the immune cells. The present thesis was aimed to improve our understanding of innate signaling mechanism and their possible use as bio-indicators of exposure and disease. The first part of the thesis deals with the involvement of TOM1L1 (Target of Myb1 like 1) in innate immune signaling and regulation of inflammatory cytokines in immune cells (study I and II). The initial event of T-cells activation depend on the recruitment of Src family kinases Fyn and Lck, leading to interleukine-2 (IL-2) production in T cells. Understanding the regulatory aspects of IL-2 induction in T-cells is of importance as IL-2 is a key regulator for T-cell proliferation and survival. Interaction screening indicated the ability of TOM1L1 protein to interact with Fyn, and Lck, that is important for IL-2 production in Jurkat T-cells. TOM1L1 silencing decreased the levels of CD3/CD28 dependent induction of IL-2 in Jurkat T-cells, and LPS dependent induction of TNF-α in THP-1. Furthermore, overexpression of TOM1L1 in Jurkat T-cells causes an increase of STAT3 expression. This was accompanied by an increase in the levels of IL-1β dependent induction of IL-6 and TNF-α in THP-1 cells. These results indicate that TOM1L11 participate in regulation of innate immune response. The second part of the thesis deals with development of innate immune signaling responses used as a diagnosis tools for disease and exposure (study III and IV). Inflammatory diseases are associated with innate immune reactions. In response to inflammation, the immune cells release inflammatory cytokines such as IL-1-β, IL-2, IL-6, IL-10, TNF-α and CXCL8. These cytokines are regulated by stress related kinases include MAP kinase proteins such as ERK1-2, JNK, and MAPK p38, through activation of transcription factors AP-1, ATF-2, and NF-AT. In a clinical study, it was observed that activated MAPK p38 has a potential role in the regulation of IL-10 expression in intermittent claudication. However, expression of IL-10 and MAPK p38 was opposed in stable angina group. Therefore, targeting MAPK p38 in inflammatory disease such as cardiovascular diseases, diabetes, and rheumatoid arthritis might be useful in development of treatment strategies. Innate immune reactions can also be used to monitor stress related inflammatory responses following environmental exposure of immune cells. Inflammatory responses of exposure were studied by in vitro exposure to waters from sewage treatment works and recipient waters. The analysis shows that exposure to inland waters can result in activated immune responses and that these responses are both site dependent and vary over time.
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| 3. |
- Erdtman, Edvin, 1981-
(författare)
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5-Aminolevulinic acid and derivatives thereof : properties, lipid permeability and enzymatic reactions
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 5-aminolevulinic acid (5-ALA) and derivatives thereof are widely usedprodrugs in treatment of pre-malignant skin diseases of the cancer treatmentmethod photodynamic therapy (PDT). The target molecule in 5-ALAPDTis protoporphyrin IX (PpIX), which is synthesized endogenously from5-ALA via the heme pathway in the cell. This thesis is focused on 5-ALA,which is studied in different perspectives and with a variety of computationalmethods. The structural and energetic properties of 5-ALA, itsmethyl-, ethyl- and hexyl esters, four different 5-ALA enols, and hydrated5-ALA have been investigated using Quantum Mechanical (QM) first principlesdensity functional theory (DFT) calculations. 5-ALA is found to bemore stable than its isomers and the hydrolysations of the esters are morespontaneous for longer 5-ALA ester chains than shorter. The keto-enoltautomerization mechanism of 5-ALA has been studied, and a self-catalysismechanism has been proposed to be the most probable. Molecular Dynamics(MD) simulations of a lipid bilayer have been performed to study themembrane permeability of 5-ALA and its esters. The methyl ester of 5-ALAwas found to have the highest permeability constant (PMe-5-ALA = 52.8 cm/s).The mechanism of the two heme pathway enzymes; Porphobilinogen synthase(PBGS) and Uroporphyrinogen III decarboxylase (UROD), have beenstudied by DFT calculations and QM/MM methodology. The rate-limitingstep is found to have a barrier of 19.4 kcal/mol for PBGS and 13.7kcal/mol for the first decarboxylation step in UROD. Generally, the resultsare in good agreement with experimental results available to date.
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| 4. |
- Kalbina, Irina, 1961-
(författare)
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The molecular mechanisms behind perception and signal transduction of UV-B irradiation in Arabidopsis thaliana
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Elevation of UV-B radiation (280-315 nm), occurring as a result of depletion of the stratospheric ozone, causes a number of physiological and biochemical changes in plants. Damage to the photosynthetic apparatus (including the bleaching of the pigments which trap the sun's energy), to the processes of cell division and growth regulation, and to the composition and replication of genetic material are just some of these changes. The consequences include reduction in growth yield, changes in levels and effects of plant hormones and secondary metabolites, and alteration of interactions between plants and other organisms.This thesis deals with several mechanistic questions related to regulation of responses during UV-B stress in plants. Our results show significant ecotype-specific variability in UV-B response in the model plant Arabidopsis thaliana. Differences at the molecular level (expression of PR-5 and steady-state concentration of H2O2) resulted in statistically significant differences in biomass, rosette size and leaf area. Therefore, it is of great importance to pay attention to the responses of the background ecotypes when for instance studying mechanisms of responses toward ultraviolet-B radiation in mutants.Using a DNA microarray approach, we found a number of novel genes to be differentially expressed under UV-B radiation. Two of the genes (PYROA and MEB5.2) were later used as molecular markers for monitoring of UV-B stress. Promoters of PYROA and MEB5.2 were compared with promoters of genes for the phenylpropanoid pathway. The comparisons indicated only few common elements with the UV-B-regulated promoters of CHS, PAL and CHI. In contrast, the genes identified as being UV-B regulated in this study (MEB5.2, PYROA and UBQ3), completely lacked elements required for the UV-B induction of CHS, indicating that these genes are regulated by different transcription factors. In addition, novel unidentified cis-elements are probably also present upstream of the transcription start.Reverse and forward genetics were used for searching novel genes responsive to UV-B and for examination of proposed candidates of the UV-B signal transduction chain. Screening of more than 2000 T-DNA mutants for differential response to UV-B resulted in the identification of a mutant displaying insensitivity to UV-B induced inhibition of hypocotyl growth. By using the corresponding knock-out mutants, the involvement of NADPH oxidase and MAPK phosphatase 1 in UV-B signalling was demonstrated.For the plant to be able to respond appropriately to UV-B irradiation, UV-B quanta have to be absorbed. There are indirect evidences for the existence of specific UV-B receptor(s), whereas the receptor itself still remains unknown. By the classical approach of action spectroscopy, we undertook an attempt to identify the absorption spectra of the chromophore(s) sensing UV-B radiation in plants. The investigated molecular markers revealed the presence of two potential chromophores absorbing in the UV-B region and peaking at 280-290 and 300 nm, respectively.
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| 5. |
- Karlsson, Mattias, 1981-
(författare)
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Modulation of cellular innate immune responses by lactobacilli
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lactobacillus is a genus of lactic acid bacteria frequently used as healthpromoting probiotics. Using probiotics to treat or prevent infections is a novel experimental approach with vast impact on future therapy. Lactobacillus rhamnosus GR-1 is a probiotic investigated for its ability to reduce urogenital disease including urinary tract infections caused by pathogenic Escherichia coli. L. rhamnosus GR-1 has been shown to modulate immunity, thought to influence its probiotic effect. In this thesis, the aim was to study immunomodulation by L. rhamnosus GR-1 and other lactobacilli, with emphasis on elicited immune responses such as nuclear factor-kappaB (NF-κB) activation and cytokine release from human urothelial cells.Viable, heat-killed, and isolated released products from L. rhamnosus GR-1 augmented NF-κB activation in E. coli-challenged urothelial cells. Blocking of lipopolysaccharide binding to toll-like receptor 4 completely quelled this augmentation. Size-fractionation, urothelial cell challenge, and two-dimensional gel electrophoresis of L. rhamnosus GR-1 released products presented several candidate proteins with NF-κB modulatory actions including chaperonin GroEL, elongation factur Tu, and a protein from the NLP/P60 protein family. While tumor necrosis factor was correspondingly augmented by L. rhamnosus GR-1, the release of two other cytokines, interleukin (IL)-6 and CXCL8, was reduced. Similar effects were observed in macrophage-like cells stimulated with L. rhamnosus GR-1.Many immunomodulatory effects of lactobacilli are believed to be species and strain dependent. Therefore, twelve Lactobacillus strains were used to screen for their effects on CXCL8 release from urothelial cells. A majority of these strains were able to influence CXCL8 release from the cells. Phylogenetic analysis revealed close evolutionary linkage between lactobacilli with similar actions on CXCL8. Increased knowledge on probiotic bacterial products and the mechanism(s) of action could lead to improved future treatments for infections.
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| 6. |
- Khalaf, Hazem
(författare)
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Characterization and environmental influences on inflammatory and physiological responses
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pharmaceuticals are regularly released into the environment, in particular nonsteroidalanti-inflammatory drugs (NSAIDs) and antibiotics. The measuredconcentrations are relatively low and have therefore been considered to be harmless.However, several pharmaceuticals, including naproxen and atenolol, are stable for upto 1 year in the environment, which increases the risk for accumulation. Evaluation ofthe effects of pharmaceuticals on induced inflammatory responses is thereforenecessary for the assessment of potential risks. Since NF-κB and MAPK are the mainpathways known to be critical regulators of inflammatory responses, intracellularsignalling and effects on these systems were examined in vitro using human cell-lines.NSAIDs were shown to significantly reduce NF-κB activity at environmentallyrelevant concentrations. Suppression of immune responses may lead to progressiveinfections since inflammatory responses are controlled by a cooperative activity ofAP-1 and NF-κB. Alterations in the activity of transcription factors and proinflammatorycytokine and chemokine levels such as TNF, IL-6 and CXCL8 areassociated with several human diseases including cystic fibrosis and AIDS. PMAexposure resulted in a rapid NF-κB activation, while extended treatment suppressedNF-κB and activated AP-1. Suppression of NF-κB activity may be due to PKCdependentBcl10 degradation, which decreased in response to PMA and correlatedwith the NF-κB activity. Regulation of cytokine expression revealed that NF-κB wasessential for IL-6 but not CXCL8 expression following specific inhibition of NF-κB,without affecting AP-1 activity. Furthermore, several reports have indicated theimportance of a functional NF-κB complex in zebrafish embryogenesis, whereblockage of NF-κB activation resulted in a deformation of the tail. Our results indicatea suppression of apoptotic pathways following activation of inflammatory mediatorsin response to HK E. coli treatment. These signals acted to direct zebrafish sexdifferentiation towards feminization. NF-κB was shown to regulate zp2 geneexpression, an indicator of oocyte development. Zebrafish sex determination was alsoshown to start early, prior to 16 days post fertilization. The results support thetransition through a juvenile ovary stage and suggests that steriodogenesis is aconsequence of sex differentiation rather than a regulatory mechanism.Control of prescription, use and disposal of pharmaceuticals is therefore importantto preserve human health, biotic processes and to avoid developmental alterations inaquatic organisms. The complexity of regulatory systems involved in inflammationsuggest that there is a need to further evaluate the signalling pathways involved inorder to provide a better understanding of cellular responses to manmade substances,but also to offer an insight into possible development of alternative treatments forhuman diseases with elevated cytokine/chemokine levels.
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| 7. |
- Khan, Faisal Ahmad, 1986-
(författare)
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Carbapenemase-Producing Enterobacteriaceae in Wastewater-Associated Aquatic Environments
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The emergence of carbapenem resistance due to the carbapenem-hydrolyzing enzymes (carbapenemases) in Enterobacteriaceae has led to limited therapeutic options. The increased resistance to these “last-resort” antibiotics is fueled by overuse and misuse of antibiotics in human medicine and agriculture. According to the One-Health concept, the microbiomes of humans, animals and natural environments are interconnected reservoirs of antibiotic resistance genes (ARGs) and changes in one compartment will affect the other compartments. Thus, the environmental waters exposed to the pathogens, ARGs and other contaminants of human origin can play a significant role in the spread of resistance. The study aimed to characterize carbapenemase-producing Enterobacteriaceae (CPE) and ARGs in wastewaters and associated river and lake waters in Örebro, Sweden. The study also analyzed de novo development of resistance in Klebsiella oxytoca during long-term growth in river water and the effect of temperature on the emergence of resistance. OXA-48-producing Escherichia coli (ST131) and VIM-1-producing K.oxytoca (ST172) were repeatedly detected in the wastewaters and associated river, suggesting that these isolates were persistently present in these environments. Furthermore, K. oxytoca ST172 isolated from the river was genetically similar to two isolates previously recovered from patients in a local hospital, which shows the possibility of transmission of CPE from hospital to aquatic environments. A high diversity of ARGs was detected in these environments especially in hospital wastewater where ten different carbapenemase genes were detected. These results emphasized that the effective treatment of wastewaters must be ensured to reduce or eliminate the spread of antibiotic resistance. Increased resistance to meropenem (up to 8-fold) and ceftazidime (>10-fold) was observed in K. oxytoca after exposure to both river and tap water after 600 generations and resistance emerged earlier when the bacteria was grown at the higher temperature. The exposure to contaminants and increased environmental temperature may induce similar changes in the environmental microbiome, generating novel resistant variants at accelerated rates that may pose a significant threat to human health.
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| 8. |
- Larsson, Anders, 1977-
(författare)
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Androgen receptors and endocrine disrupting substances
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Throughout the animal kingdom, organisms are dependent on substances such as steroid hormones to help them maintain internal balances. Examples of important tasks that are under regulation of steroid hormones are somatic and gonadal development, sexual performance and behavior (both social and sexual) as well as sex differentiation. Balance in the biology of reproduction is important for all organisms, and is sensitive to alterations and disturbances. If the environment is altered in a manner that lead to higher estrogenic or androgenic levels, the sex ratio of organisms that do not rely on genetic differences in the sex differentiation, will be biased towards more females or males in the population. It has been known for some time that there are pollutants in the environment that affect steroid pathways, such as the estrogenic and thyroid systems, but not much has been known about the androgenic systems. Examples of populations being masculinized have been recorded, and estrogenic compounds have been known to act as antiandrogens, but not until recently the first androgen agonist was identified. We used a combination of in vitro and computational modeling to identify the brominated flame retardant, 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane, as a potent androgen agonist to the human androgen receptor.In addition to this we cloned and characterized the androgen receptor from, a frequently used model organism, zebrafish (Danio rerio) as a receptor primarily activated by 11-ketotestosterone. This is a feature the zebrafish share with several other teleost fishes, such as the three-spined stickleback. Thus fish androgen receptors differ from most mammalian androgen receptors, where dihydrotestosterone is the most potent activator.
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| 9. |
- Mangu, Jagadish, 1986-
(författare)
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Influence of gut microbiota on xenobiotic toxicity in a Caenorhabditis elegans model with a focus on arsenic and PFAS
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Exposure to environmental toxins presents a hazard to humans. Inorganic metalloid- arsenic (As), organic chemicals- per and poly-fluoroalkyl substances (PFAS) are frequently detected in the environment. Exposure to As and PFAS is associated with multiple adverse effects in humans and animals. However, little attention has been given to the interaction between host microbiota and pollutants. Gut microbiota interactions with the host and xenobiotics, is hy-pothesized to decrease xenobiotic toxicity. However, the role of microbiota on host responses during these exposure scenarios is poorly understood. Therefore, the aim was to study the influence of gut microbes on Caenorhabditis elegans responses using As and PFAS as environmental toxins. Specific objectives were to study the role of single microbes, and simple three microbe combinations with tractable diversity in nematode responses to As and PFAS. The study examined C. elegans physiological responses to As in the presence of single As resistant microbe Lysinibacillus sphaericus (Paper I) and simple 3-bacteria combinations (Paper IV). These studies showed that gut microbes decrease As toxicity and increase nematode survival through mediating host stress responses and fat metabolism. Combinations of microbes with toxins in microbiota also affect lifespan (Paper III). Furthermore, effects of PFAS mixtures were also analyzed on C. elegans and pathogen Staphylococcus aureus (Paper II); and role of gut microbe combinations during exposures to PFOS (Paper V). Exposure to PFAS/ PFOS increased virulence of pathogens and decreased host immunity, stress response and survival with opportunists; with non-pathogens C. elegans showed increased stress response and lived longer. These results emphasized that gut microbes contribute to alter xenobiotic toxicity in the host. Finally, this thesis presents novel insights into the role of gut microbes in modulating host physiological responses during As and PFAS exposures.
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| 10. |
- Musa, Klefah Abrahem Klefah
(författare)
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Computational studies of photodynamic drugs, phototoxic reactions and drug design
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The most important criterion when designing new drugs or improving old ones in order to prevent side effects or at least diminish them is drug safety. Treatment of all diseases generally needs use of either topical application or systemic medications (transported in the blood) during a certain period of time. These treatments are associated with a number of adverse effects. Photosensitivity is one of those side effects, with phototoxicity as one of the photosensitivity disorders. This adverse side effect arises because of a reaction between UV or visible-light and the drug molecule, its active form or photoproduct(s). Due to phototoxic side effect, unexpected symptoms varying from just a simple rash to severe cutaneous affectations can appear. Furthermore, biomolecular damage occurs once the drug-light interaction takes place persistently and ends with cell death.Several drug families, such as over-the-counter drugs in the non-steroidal anti-inflammatory drug family of 2-arylpropionic acid derivatives, or prescription required fluoroquinolone drugs, have the capability to absorb mainly UV light radiation which in turn causes different phototoxic reactions by forming radical derivatives, reactive oxygen species or both. These may effect DNA, protein and lipid cell components leading to photogenotoxicity, photoallergy and lipid peroxidation, respectively. The photodegradation mechanisms of drugs belonging to the above mentioned families including ketoprofen, ibuprofen, flurbiprofen, naproxen, the active form of nabumetone, diclofenac and its main photoproduct, suprofen, tiaprofenic acid, naphazoline, norfloxacin and lomefloxacin are investigated in more detail in this thesis.The results obtained by computational density functional theory (DFT) and time-dependent-DFT (TD-DFT) are in line with experimental data available to date. The studies provide detailed insight into the molecular basis and understanding of the full photodegradation mechanisms of drugs mentioned above. This also plays an important role in preventing or at least reducing the phototoxic adverse effects by enabling the development of safe drugs in this area. Hence, new modified non-steroid anti-inflammatory molecules were designed by computational techniques. Obtained results suggest possibility of their future usage as pharmaceuticals with reduced photodegradation and cyclooxygenase 1 induced adverse side effects compared to the parent compounds.
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| 11. |
- Paylar, Berkay, 1990-
(författare)
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New Approaches for Daphnia magna Toxicity Assessment
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Risk assessment plays a crucial role in evaluating and managing the potential hazards and health effects associated with exposure to substances. In recent decades, the field of risk assessment has undergone significant expansion, embracing innovative approaches and methodologies. Despite these advancements, it's noteworthy that the standards governing experimental setups have remained largely unchanged. This thesis focuses on enhancing environmental risk assessment methodologies, particularly in the context of exposure protocols, by incorporating toxicogenomics and machine learning approaches as well as suggestions for improved toxicity testing setup. The main objectives of the Paper I was to assess the sensitivity differences and shared responses of different animal models to exposure settings. Seven different organisms were tested with varying metal concentrations. Paper II investigated the effects of altering exposure media parameters, particularly water hardness. Paper III utilized computational advancements in toxicogenomics for gene ranking and exposure prediction. Paper IV investigated a larger number of genes by utilizing transcriptomics to discover novel biomarkers and molecular functions affected by metal exposures at the boundaries of Zn and Cu homeostasis. The research findings revealed that traditional toxicity assessment setups may not fully provide a base to capture the complexity of occurring toxicity. Therefore, the study proposes deviations from standard test protocols and emphasizes the need for holistic models that consider multiple factors to accurately assess toxicity risks in aquatic environments.
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| 12. |
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| 13. |
- Rahman, Aminur, 1984-
(författare)
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Bioremediation of Toxic Metals for Protecting Human Health and the Ecosystem
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heavy metal pollutants, discharged into the ecosystem as waste by anthropogenic activities, contaminate drinking water for millions of people and animals in many regions of the world. Long term exposure to these metals, leads to several lethal diseases like cancer, keratosis, gangrene, diabetes, cardio- vascular disorders, etc. Therefore, removal of these pollutants from soil, water and environment is of great importance for human welfare. One of the possible eco-friendly solutions to this problem is the use of microorganisms that can accumulate the heavy metals from the contaminated sources, hence reducing the pollutant contents to a safe level.In this thesis an arsenic resistant bacterium Lysinibacillus sphaericus B1-CDA, a chromium resistant bacterium Enterobacter cloacae B2-DHA and a nickel resistant bacterium Lysinibacillus sp. BA2 were isolated and studied. The minimum inhibitory concentration values of these isolates are 500 mM sodium arsenate, 5.5 mM potassium chromate and 9 mM nickel chloride, respectively. The time of flight-secondary ion mass spectrometry and inductively coupled plasma-mass spectroscopy analyses revealed that after 120 h of exposure, the intracellular accumulation of arsenic in B1-CDA and chromium in B2-DHA were 5.0 mg/g dwt and 320 μg/g dwt of cell biomass, respectively. However, the arsenic and chromium contents in the liquid medium were reduced to 50% and 81%, respectively. The adsorption values of BA2 when exposed to nickel for 6 h were 238.04 mg of Ni(II) per gram of dead biomass indicating BA2 can reduce nickel content in the solution to 53.89%. Scanning electron micrograph depicted the effect of these metals on cellular morphology of the isolates. The genetic composition of B1-CDA and B2-DHA were studied in detail by sequencing of whole genomes. All genes of B1-CDA and B2-DHA predicted to be associated with resistance to heavy metals were annotated.The findings in this study accentuate the significance of these bacteria in removing toxic metals from the contaminated sources. The genetic mechanisms of these isolates in absorbing and thus removing toxic metals could be used as vehicles to cope with metal toxicity of the contaminated effluents discharged to the nature by industries and other human activities.
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| 14. |
- Ristilä, Mikael
(författare)
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Vitamin B6 as a potential antioxidant : a study emanating from UV-B-stressed plants
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased influx of solar UV-B radiation (280-320 nm), due to a decreasing stratospheric ozone layer, impacts severely on plants. Some of the UV-B effects on plants are related to stress induced by produced reactive oxygen species (ROS). Pyridoxine (vitamin B6) has been reported to be a potential quencher of ROS.Previous studies have shown that the PDX1.3 gene (encoding a key enzyme in vitamin B6 biosynthesis) is up-regulated by UV-B. We showed that this up-regulation also occurs at the protein level in UV-B exposed Col-0 wild-type plants. Studies performed using pdx1 knock-out mutants of Arabidopsis thaliana showed elevated transcripts levels for LHCB1*3 and PR-5 compared with the Col-0 wild-type. The pdx1 knock-out mutants showed an increased sensitivity towards H2O2-stress, but no increased sensitivity towards low dose UV-B-stress.To study the postulated role of pyridoxine as quencher of ROS in more detail, both theoretical and experimental studies were performed. Theoretical and experimental UV absorption spectra obtained at different protonation/deprotonation states of pyridoxine showed a very close resemblance at low and high pH. However, for the computational studies at physiological pH addition of counterions were required to accurately describe the experimental spectra.When theoretically studying the reactivity of pyridoxine towards three different ROS, .OH, .OOH and .O2-, the hydroxyl radical (.OH) was shown to be the most reactive species, while the superoxide radical (.O2-) showed no reactivity towards pyridoxine.In order to study the role of G-proteins in UV-B signal transduction pathways, UV-B irradiated G-protein mutants of Arabidopsis thaliana were studied. The regulation of the PDX1.3 gene was not affected in the G-protein mutants, regardless of the developmental stage of the plant. However, the expression of CHS was affected in the Ga subunit mutants.
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| 15. |
- Scherbak, Nikolai, 1967-
(författare)
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Characterization of stress-inducible short-chain dehydrogenases/reductases (SDR) in plants : study of a novel small protein family from Pisum sativum (pea)
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In pea (Pisum sativum), the short-chain alcohol dehydrogenase-like protein (SAD) gene family consists of at least three members (SAD-A, -B, and -C). The SAD genes are transiently expressed in plants after short exposures to ultraviolet-B radiation, which in turn leads to formation of SAD protein in leaf and stem tissue upon prolonged irradiation. SAD gene expression is also seen as a result of wounding stress.The recombinant SAD-C protein (which was the most highly over-expressed isoform in Escherichia coli of the isoforms) was shown to be a tetramer that probably consists of a dimer of dimers and which possesses quinone-reducing capability. The enzyme shows approximately the same NADH- and NADPH-dependent activity with 2,5- and 2,6-dimethylbenzoquinone and menadione as substrates.Western blotting and immunohistochemistry (IHC) shows that the SAD protein is present to a smaller or larger extent in all the different pea tissues examined. Environmental stress such as UV-B radiation clearly increases the content of SAD in leaf and stem tissue but not in roots. This indicates that increased expression of the SAD genes, as a result of UV-B exposure, is limited to the exposed tissue. This is substantiated by the heterologous GUS expression from the pea SAD-C promoter in Arabidopsis during wounding. Only the wound site and the vicinal tissue show transcription from this promoter. In non-stressed tissue (as well as in UV-B-stressed leaves and stem), SAD predominantly occurred in epidermal or sub-epidermal cells as judged by IHC. The protoderm of the pea seed cotyledonary axis contains the most heavily stained cells. This indicates a possible role for the SAD protein in development as well as in protection against environmental stress. Also, discrete staining was obtained in particular cell types of the ovary.To be able to understand the biochemical and physiological role of the SAD enzyme, an in silico modeling study of the SAD protein structure was performed. The simulations of our SAD protein, as well as of related proteins with known crystal structure (3alfa,20beta-hydroxysteroid dehydrogenase and secoisolariciresinol dehydrogenase), allowed us to obtain an energy-minimized structure for the monomeric SAD as well as important data on the cofactor interaction in the active site.Crystallization of recombinant SAD-C has been performed. The needle-like crystals, which diffract to 3.5Å, contain probably eight monomers in the asymmetric unit, presumably containing a pair of tetramers.SAD enhances the reduction rates of quinones with NADH. However, NADH can also accomplish reduction of certain quinones non-enzymatically. Both theoretical calculations and experimental techniques were used to elucidate the structural and electronic pre-requisites for this non-enzymatic quinone reduction.
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| 16. |
- Seyoum, Asmerom, 1977-
(författare)
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Toxicogenomic responses in Daphnia magna
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Detection of various organic contaminants in the aquatic environment at low concentrations, has raised concerns for animal and human health. Structural similarities of these compounds to estrogens and ecdysones suggests that organic pollutants may interfere with hormonal system of aquatic organisms. Techniques of traditional toxicity tests that are based on observable physiological defects may fail to identify sub-lethal / subobservable effects. Under these techniques the mode of action of pollutants cannot be investigated. Thus, there is a need for more sensitive techniques that are capable to evaluate effects at molecular level and provide an early warning to environmental pollution. Toxicogenomic is proposed to be a useful tool to meet this goal. However, there is a limited data that compare toxicogenomic and traditional toxicity test approaches. The aim of this thesis is to evaluate the utility of qRT-PCR based toxicogenomic analysis in risk assessment. To achieve this goal, we first analyzed toxicogenomic and physiological responses of Daphnia manga exposed to three class of widely detected organic pollutant sphthalates, perfluorinated alkylated substances and brominated flame retardant in Paper I-III. Investigated endpoints included effects on hatching, acute toxicity, survival, developmental abnormalities, reproduction success, swimming and feeding behavior, fat metabolism, and life span. Result of these studies demonstrated a high degree of correlation between transcriptional data and the traditional physiological data. Besides, toxicogenomic approach was able to identify effects of sublethal concentrations. Thus, in Paper IV we analyzed environmental sample from Akaki river in Ethiopia using transcriptional approach and showed toxicogenomic tools utility in environmental risk assessment. Overall, the finding of these studies showed that the use of toxicogenomic can improve traditional physiological based toxicity assay to determine environmental risk assessment. Furthermore, toxicogenomic analysis can be performed with relatively short time and limited volume of samples.
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| 17. |
- Sid Ahmed, Mazen, 1970-
(författare)
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Molecular Epidemiology and Mechanisms of Antibiotic Resistance in Clinical Isolates of Pseudomonas aeruginosa from Qatar
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inappropriate and excessive use of antibiotics promotes antimicrobial resistance (AMR), particularly in Gram-negative bacteria (GNB). There is a noticeable increase in nosocomial infections caused by multidrug-resistant (MDR) Pseudomonas aeruginosa, which is associated with significant morbidity, mortality, and an increase in cost management. Although this is a global problem, there is a lack of sufficient data on regional differences that can contribute towards effective AMR management. This thesis presents a study of MDR-P. aeruginosa at five different hospitals in Qatar conducted prospectively between October 2014 - September 2017. The aim was to study the epidemiology, microbiological and clinical characteristics of MDR-P. aeruginosa infections as well as investigate the activity of new antibiotic combinations against these bacteria. The prevalence of MDR-P. aeruginosa isolates in the first year was 8.1% (205/2533), isolated from different clinical specimens, but the majority were from respiratory infections (44.9%, n=92). Most cases were exposed to antibiotics during the 90 days prior to isolation (85.4%, n=177), and the resistance to cefepime, ciprofloxacin, piperacillin/tazobactam, meropenem was >90%. To compare pre- and post-Antimicrobial Stewardship Program, there was a significant reduction in antibiotic consumption by 30.4% of total inpatient antibiotic prescriptions (p=0.008) and the prevalence of MDR-P. aeruginosa significantly declined from 9% to 5.4% (p=0.019). The in vitro investigation of ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T) against MDR-P. aeruginosa isolates, showed promising results with susceptibility of 68.8% (n=141/205) and 62.9% (n=129/205), respectively, which was higher than other antipseudomonal agents except colistin. Seventy-five isolates that were sequenced belonged to 29 different sequence types, with ST235 being predominant at 21.3% (16/75). Among the 42 isolates that were resistant to CZA and/or C/T, the most prevalent genes were blaOXA-488 and blaVEB-9 detected in 45.2% (19/42) of isolates. Spearman’s analysis showed that resistance to CZA and C/T were positively correlated with the presence of blaOXA-10, blaPDC-2a, blaVIM-2, and blaVEB-9 , respectively. The study highlights potential key mechanisms that could explain the resistance of MDR-P. aeruginosa to the new antibiotic combinations.
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- Stighäll, Kristoffer, 1971-
(författare)
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Habitat composition and restocking for conservation of the white-backed woodpecker in Sweden
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden, intense human land use, especially forestry, has led to profound changes in the landscape over time, especially within the forest ecosystems. A consequence of this is that several specialist species have become endangered. One group of specialists is the woodpeckers. The middle spotted woodpecker became extinct in Sweden in 1982 and the white-backed woodpecker is today Sweden’s most critically endangered forest-living bird. The white-backed woodpecker is dependent on old deciduous forests, rich in dead wood. The woodpecker is areademanding and hence one of the best indicators or umbrella species for biodiversity in this region. A long-term goal within the conservation of the species is to be able to make more accurate predictions of what is needed in the species habitat to establish a viable population, both in terms of composition of landscape and breeding territories. In addition to earlier studies better tools are needed for measuring the distribution of suitable and potential habitats and finding faster ways of creating optimal habitats. In an attempt to secure the future existence of the white-backed woodpecker in Sweden, restocking of birds are carried out. This presupposes availability of suitable habitats as well as strong enough landscape. Due to intense forestry the presumption for the species is, as stated above, alarming. Comparing the different populations around the Baltic Sea and Norway, great differences but also similarities can be seen, in landscape as well as in territory composition. It seems that fragmentation of foraging patches as well as amount of dead deciduous wood within the breeding territory is critical matters. Grey alder stands in Sweden should have high priority in conservation of habitat for the species.
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