| 265081. |
- Rudberg, P C, et al.
(författare)
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Leukotriene A(4) hydrolase - Identification of a common carboxylate recognition site for the epoxide hydrolase and aminopeptidase substrates
- 2004
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Ingår i: Journal of Biological Chemistry. - 1083-351X .- 0021-9258. ; 279:26, s. 27376-27382
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Tidskriftsartikel (refereegranskat)abstract
- Leukotriene ( LT) A(4) hydrolase is a bifunctional zinc metalloenzyme, which converts LTA(4) into the neutrophil chemoattractant LTB4 and also exhibits an anion-dependent aminopeptidase activity. In the x-ray crystal structure of LTA(4) hydrolase, Arg(563) and Lys(565) are found at the entrance of the active center. Here we report that replacement of Arg(563), but not Lys(565), leads to complete abrogation of the epoxide hydrolase activity. However, mutations of Arg(563) do not seem to affect substrate binding strength, because values of K-i for LTA(4) are almost identical for wild type and ( R563K) LTA(4) hydrolase. These results are supported by the 2.3-Angstrom crystal structure of (R563A) LTA(4) hydrolase, which does not reveal structural changes that can explain the complete loss of enzyme function. For the aminopeptidase reaction, mutations of Arg(563) reduce the catalytic activity (V-max = 0.3 - 20%), whereas mutations of Lys(565) have limited effect on catalysis (V-max = 58 - 108%). However, in (K565A)- and (K565M) LTA(4) hydrolase, i.e. mutants lacking a positive charge, values of the Michaelis constant for alanine-p-nitroanilide increase significantly (K-m = 480 - 640%). Together, our data indicate that Arg(563) plays an unexpected, critical role in the epoxide hydrolase reaction, presumably in the positioning of the carboxylate tail to ensure perfect substrate alignment along the catalytic elements of the active site. In the aminopeptidase reaction, Arg(563) and Lys(565) seem to cooperate to provide sufficient binding strength and productive alignment of the substrate. In conclusion, Arg(563) and Lys(565) possess distinct roles as carboxylate recognition sites for two chemically different substrates, each of which is turned over in separate enzymatic reactions catalyzed by LTA(4) hydrolase.
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| 265082. |
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| 265083. |
- Rudberg, Peter M., et al.
(författare)
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Beyond generic adaptive capacity : exploring the adaptation space of the water supply and wastewater sector of the Stockholm region, Sweden
- 2012
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Ingår i: Climatic Change. - : Springer Science and Business Media LLC. - 0165-0009 .- 1573-1480. ; 114:3/4, s. 707-721
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines the processes by which the generic adaptive capacity of a system is translated into adaptation to climate change, what form it takes, and what factors facilitate or restrain such processes. This is done by an in-depth analysis of climate change adaptation in the Water supply and Wastewater (WW) sector of the Stockholm region. Observed adaptations are categorized in terms of building adaptive capacity and implementing adaptive decisions, and these measures are analyzed using a model of the adaptation process based on organizational learning theories. In particular, the concept of an organization’s actual adaptation space is defined and used as a means to understand the adaptation options that different WW organizations can pursue, as well as why such options might be pursued. The paper finds that most adaptation measures in the WW sector of the Stockholm region are aimed at building the adaptive capacity of the sector. It also finds that the extent to which adaptation measures can be pursued by the WW organizations is determined principally by how able the organization is to justify the additional resources required for adaptation. The analysis shows that there are two main routes to address this: use of climate knowledge to argue that adaptation is needed, and reference to rules and regulations to show that it is required
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| 265084. |
- Rudberg, Tore, et al.
(författare)
-
Robust Detection of Nuclear Quadrupole Resonance Signals in a Non-shielded Environment
- 2011
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Ingår i: European Signal Processing Conference. - 2219-5491. ; 2011, s. 2079-2083
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedNuclear quadrupole resonance (NQR) is a non-invasiveradio-frequency technique allowing for a practically unique%ngerprint for molecules containing quadrupolar nuclei,making the technique very promising for detection purposes.If properly excited, these nuclei will emit electromagnetic radiation,the frequency of which is governed mainly by wherein the molecule the nuclei are positioned. However, the resultingNQR signals are inherently weak and are prone tostrong interference signals from the measurement environment,making detection challenging. In this paper, we developa robust and reliable detection algorithm that generalizeearlier techniques and incorporates both ef%cient interferencecancellation and the ability to handle multiple polymorphsin the sought substance. The usefulness of the algorithmis motivated by comparisons using realistic simulations.
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| 265085. |
- Rudbäck, Johanna, 1984, et al.
(författare)
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A sensitive method for determination of allergenic fragrance terpene hydroperoxides using liquid chromatography coupled with tandem mass spectrometry
- 2013
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Ingår i: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 36:8, s. 1370-1378
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Tidskriftsartikel (refereegranskat)abstract
- Different compositions of monoterpenes are utilized for their pleasant scent in cosmetics and perfumes. However, the most commonly used fragrance terpenes easily oxidize upon contact with air, forming strongly skin-sensitizing hydroperoxides. Due to their thermolability and low UV absorbance, detection methods for hydroperoxides are scarce. For the first time, a simple and sensitive method using LC/ESI-MS/MS was developed to quantitatively determine hydroperoxides from the common fragrance compounds linalool, linalyl acetate, and limonene. The method was applied to autoxidized petitgrain oil and sweet orange oil. A separation was accomplished using a C3 column. The method LOD for the investigated hydroperoxides in the essential oils was below 0.3 μg/mL, corresponding to 0.3 ppm. For prevention purposes and according to EU regulations, concentrations in cosmetics exceeding 100 ppm in “rinse-off” and 10 ppm in “stay-on” products of linalool and limonene must be labeled. However, the products may still contain allergens, such as hydroperoxides, formed by oxidative degradation of their parent terpenes. The sensitivity and selectivity of the presented LC/MS/MS method enables detection of hydroperoxides from the fragrance terpenes linalool, linalyl acetate, and limonene. However, for routine measurements, the method requires further validation.
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| 265086. |
- Rudbäck, Johanna, 1984
(författare)
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Allergenic Oxidation Products from Fragrance Terpenes. Chemical Analysis and Determination of Sensitizing Potency
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ubiquitous presence of fragrance compounds in consumer products has resulted in a high frequency of contact allergy to fragrances in the population. For prevention purposes and according to EU regulations, cosmetics must be labeled when containing the most prominent fragrance allergens in concentrations exceeding 0.001% in “stay-on” products and 0.01% in “rinse-off” products. Previous studies have shown that the most common fragrance terpenes oxidize upon contact with air, forming hydroperoxides which are strong skin sensitizers. Thus, cosmetics may contain allergens in form of oxidation products formed by air exposure of the fragrance terpenes. In this thesis allergenic oxidation products from fragrance terpenes have been investigated. The studies have included development of analytical methods and chemical analyses for detection of hydroperoxides in complex mixtures. Furthermore, structure-activity relationships (SARs) were investigated based on studies of oxidation products and sensitizing potencies from autoxidation of the monoterpenes a-terpinene and citronellol. Monoterpene hydroperoxides are generally difficult to determine as they have weak chromophores, exhibit low thermostability, and fragment in a similar way as parent compounds and other oxidation products in mass spectrometry. For the first time, analytical methods for detection of the highly sensitizing hydroperoxides in complex mixtures are now available utilizing mass spectrometry in combination with either liquid chromatography or gas chromatography. Low detection limits were achieved using liquid chromatography/mass spectrometry, while a high peak capacity useful for separation of hydroperoxide isomers was obtained with gas chromatography/mass spectrometry. The methods presented are sensitive enough for detection of hydroperoxides at concentrations that people may come in contact with. Thus, the analytical methods open up the possibility of investigating the clinical relevance of products in the patients’ environment through chemical analysis. Fragrance compounds in essential oils are often stated to be protected from autoxidation due to the presence of natural antioxidants. This study showed that hydroperoxides were present in the investigated essential oils already upon arrival from the supplier and that the hydroperoxide concentrations steadily increased with time and air exposure. The hydroperoxides were formed to the same extent in the essential oils compared to what is seen at air exposure of the corresponding fragrance terpenes. Thus, no significant protection against autoxidation by antioxidant activity could be observed. Neither was the rate of autoxidation substantially affected by the experimental conditions; stirring and intensity of daylight did not have any considerable effects. Autoxidation studies of -terpinene and citronellol were performed to gain knowledge regarding oxidation products and sensitizing potencies, and the results were compared to previously studied fragrance terpenes. It was shown that minor structural differences have a major impact on the dominant oxidation pathway and the stability of the oxidation products. For both compounds the sensitizing potency (as examined by the murine local lymph node assay) after air exposure was largely enhanced, around ten-fold. This shows the importance of testing with oxidized material in clinical studies and not only with the pure terpenes. In the risk assessment of fragrance chemicals, the possibility of autoxidation should be considered. To summarize, the studies in this thesis have contributed to a method toolbox of complementary analytical methods with focus on mass spectrometry for detection and quantification of fragrance hydroperoxides. In addition, fragrance terpenes as constituents of essential oils form hydroperoxides, showing that the essential oils are not natural protectors for the formation of oxidation products but rather stabilize the hydroperoxides formed. Furthermore, this thesis shows that minor structural differences between fragrance terpenes can have a major impact on the dominant autoxidation pathway and oxidation products formed. Increased understanding of how fragrance terpenes can be activated to skin sensitizers by autoxidation is necessary to obtain valid SARs for this type of compounds. In the risk assessment, their susceptibility to autoxidation as well as the sensitizing potency of formed oxidation products should be considered.
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| 265087. |
- Rudbäck, Johanna, 1984, et al.
(författare)
-
alpha-Terpinene, an Antioxidant in Tea Tree Oil, Autoxidizes Rapidly to Skin Allergens on Air Exposure
- 2012
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Ingår i: Chemical Research in Toxicology. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 25:3, s. 713-721
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Tidskriftsartikel (refereegranskat)abstract
- The monoterpene alpha-terpinene is used as a fragrance compound and is present in different essential oils. It is one of the components responsible for the antioxidant activity of tea tree oil. alpha-Terpinene is structurally similar to other monoterpenes, e.g., limonene, known to autoxidize on air exposure and form allergenic compounds. The aim of the present study was to investigate the possible autoxidation of alpha-terpinene at room temperature. To investigate the sensitization potency of air-exposed alpha-terpinene and the oxidation products formed, the murine local lymph node assay was used. Chemical analysis showed that alpha-terpinene degrades rapidly, forming allylic epoxides and p-cymene as the major oxidation products and also hydrogen peroxide. Thus, the oxidation pathway differs compared to that of, e.g., limonene, which forms highly allergenic hydroperoxides as the primary oxidation products on autoxidation. The sensitization potency of alpha-terpinene was increased after air-exposure. The allylic epoxides and a fraction, in which only an alpha,beta-unsaturated aldehyde could be identified, were shown to be strong sensitizers in the local lymph node assay. Thus, we consider them to be the major contributors to the increased sensitization potency of the autoxidized mixture. We also investigated the presence of alpha-terpinene and its oxidation products in four different tea tree oil samples of various ages. alpha-Terpinene and its oxidation products were identified in all of the tea tree oil samples. Thus, from a technical perspective, alpha-terpinene is a true antioxidant since it autoxidizes rapidly compared with many other compounds, preventing these from degradation. However, as it easily autoxidizes to form allergens, its suitability can be questioned when used in products for topical applications, e.g., in tea tree oil but also in cosmetics and skin care products.
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| 265088. |
- Rudbäck, Johanna, 1984, et al.
(författare)
-
Characterization of skin sensitizers from autoxidized citronellol - impact of the terpene structure on the autoxidation process
- 2014
-
Ingår i: Contact Dermatitis. - : Wiley. - 0105-1873 .- 1600-0536. ; 70:6, s. 329-339
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Tidskriftsartikel (refereegranskat)abstract
- Background. Citronellol is a frequently used fragrance compound in consumer products. It is present in fragrance mix II, which is used for screening of contact allergy to fragrances. Because of its chemical structure, citronellol could be susceptible to autoxidation. Objectives. To compare the behaviour of citronellol with that of the structurally similar compounds linalool and geraniol, in terms of ability to autoxidize, the products formed, and the sensitization potencies of these. Methods. Citronellol was exposed to air, and autoxidation was followed by gas chromatography-mass spectrometry (GC-MS) analysis after derivatization of thermolabile compounds. The sensitizing potencies of the oxidation mixture and its major oxidation compounds were examined with the local lymph node assay. Results. The concentration of citronellol decreased while the sensitization potency increased in air-exposed samples over time, with hydroperoxides being identified as the major oxidation products and main skin sensitizers. Conclusions. The present study shows the impact of the absence of the 2,3-double bond in the citronellol structure on the oxidation pathways for formation of oxidation products. The study also shows the usefulness of our new GC-MS method for quantification of the citronellol oxidation products, especially the hydroperoxides. The investigated citronellol hydroperoxides could be important allergens, owing to the high concentrations detected and frequent exposure to citronellol in the population.
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| 265089. |
- Rudbäck, Johanna, 1984, et al.
(författare)
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Determination of allergenic hydroperoxides in essential oils using gas chromatography with electron ionization mass spectrometry
- 2014
-
Ingår i: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 37:8, s. 982-989
-
Tidskriftsartikel (refereegranskat)abstract
- Fragrance monoterpenes are widely used commercially due to their pleasant scent. In previous studies, we have shown that air-exposed monoterpenes form hydroperoxides that are strong skin sensitizers. Methods for detection and quantification of the hydroperoxides in essential oils and scented products are thus desirable. Due to thermolability and low UV absorbance, this is a complicated task. We have recently developed a sensitive LC-ESI-MS method, but with limited structural information and separation efficiency for positional isomers and stereoisomers. In the present study, we investigated derivatization with a trimethyl silyl reagent and subsequent GC with electron ionization MS for the determination of monoterpene hydroperoxides. All investigated monoterpene hydroperoxides could be chromatographed as thermostable trimethyl silyl derivatives and yielded the fragment m/z 89 ([OSi(CH3)(3)](+)) at a higher extent compared to corresponding alcohols. Limonene-2-hydroperoxide and four other hydroperoxide isomers of limonene were separated and detected in sweet orange oil autoxidized for two months. The concentration of limonene-2-hydroperoxide isomers was found to be 19 g/mg in total. Also isomers of linalyl acetate hydroperoxide and linalool hydroperoxide were detected in autoxidized petitgrain oil (two months). The presented GC-MS method showed concentrations in the same order as previous LC-MS/MS analysis of the same type of oils.
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| 265090. |
- Rudbäck, Johanna, 1984, et al.
(författare)
-
Essential oils can contain allergenic hydroperoxides at eliciting levels, regardless of handling and storage.
- 2015
-
Ingår i: Contact dermatitis. - : Wiley. - 1600-0536 .- 0105-1873. ; 73:4, s. 253-4
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Tidskriftsartikel (refereegranskat)abstract
- Essential oils in perfumed products are important skin sensitizers (1). Upon air exposure, lavender oil, with the major components linalool and linalyl acetate, has been shown to produce strongly allergenic hydroper- oxides (2). Furthermore, linalool of natural origin was found to contain a higher concentration of hydroperox- ides than synthesized linalool (3). We have previously studied autoxidation of sweet orange oil (main compound R -limonene)andpetitgrainoil(majorcompoundslinaloo and linalyl acetate) with liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) (4). The investigation was performed at room temperature, under a daylight lamp (12hrs a day), and the oils were stirred 1hr four times a day, according to previous experience (5, 6). In the present study, the importance of handling con- ditions for hydroperoxide formation was investigated. The hydroperoxide concentrations of R -limonene, linalool and linalyl acetate were analysed over time.
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