Tryptophan metabolites kynurenine and serotonin regulate fibroblast activation and fibrosis

Fibrosis is a pathological form of aberrant tissue repair, the complications of which account for nearly half of all deaths in the industrialized world. All tissues are susceptible to fibrosis under particular pathological sets of conditions. Though each type of fibrosis has characteristics and hallmarks specific to that particular condition, there appear to be common factors underlying fibrotic diseases. One of these ubiquitous factors is the paradigm of the activated myofibroblast in the promotion of fibrotic phenotypes. Recent research has implicated metabolic byproducts of the amino acid tryptophan, namely serotonin and kynurenines, in the pathology or potential pharmacologic therapy of fibrosis, in part through their effects on development of myofibroblast phenotypes. Here, we review literature underlying what is known mechanistically about the effects of these compounds and their respective pathways on fibrosis. Pharmacologic administration of kynurenine improves scarring outcomes in vivo likely not only through its well-characterized immunosuppressive properties but also via its demonstrated antagonism of fibroblast activation and of collagen deposition. In contrast, serotonin directly promotes activation of fibroblasts via activation of canonical TGF-β signaling, and overstimulation with serotonin leads to fibrotic outcomes in vivo. Recently discovered feedback inhibition between serotonin and kynurenine pathways also reveals more information about the cellular physiology of tryptophan metabolism and may also underlie possible paradigms for anti-fibrotic therapy. Together, understanding of the effects of tryptophan metabolism on modulation of fibrosis may lead to the development of new therapeutic avenues for treatment through exploitation of these effects.     

Structure, expression, and function of kynurenine aminotransferases in human and rodent brains

Kynurenine aminotransferases (KATs) catalyze the synthesis of kynurenic acid (KYNA), an endogenous antagonist of N-methyl-d-aspartate and alpha 7-nicotinic acetylcholine receptors. Abnormal KYNA levels in human brains are implicated in the pathophysiology of schizophrenia, Alzheimer’s disease, and other neurological disorders. Four KATs have been reported in mammalian brains, KAT I/glutamine transaminase K/cysteine conjugate beta-lyase 1, KAT II/aminoadipate aminotransferase, KAT III/cysteine conjugate beta-lyase 2, and KAT IV/glutamic-oxaloacetic transaminase 2/mitochondrial aspartate aminotransferase. KAT II has a striking tertiary structure in N-terminal part and forms a new subgroup in fold type I aminotransferases, which has been classified as subgroup Iε. Knowledge regarding KATs is vast and complex; therefore, this review is focused on recent important progress of their gene characterization, physiological and biochemical function, and structural properties. The biochemical differences of four KATs, specific enzyme activity assays, and the structural insights into the mechanism of catalysis and inhibition of these enzymes are discussed.     

Temporal storage of kynurenine and 3-OH-kynurenine in the fat body of metamorphosingEphestia kühniella

Summary During the pharate pupal stage a massive accumulation of kynurenine and 3-OH-kynurenine is observed in the fat body ofEphestia kühniella. By injection it can be demonstrated that this organ is capable of sequestering at least 3-OH-kynurenine, the dominating tryptophan metabolite inEphestia. It is suggested that the fat body reduces a possibly harmfull excess of tryptophan metabolites at the beginning of metamorphosis. These sequestered metabolites provide a precursor depot for ommochrome synthesis in later development.     

Disease resistance in farm animals

Genetic variations in disease resistance of farm animals can be observed at all levels of defence against infectious agents. In most cases susceptibility to infections has polygenic origins. In domestic animals only a few instances of a single genetic locus responsible for disease resistance are known. A well-examined example is the Mx1 gene product of certain mice strains conferring selective resistance to influenza virus infections. Attempts to improve disease resistance by gene transfer of different gene constructs into farm animals include the use of monoclonal antibody gene constructs, transgenes consisting of antisense RNA genes directed against viruses and Mx1 cDNA containing transgenes.     

Radiation carcinogenesis in experimental animals

Exposure of man to relatively high doses of ionizing radiation is generally restricted to accidental situations, with very limited knowledge about the actual doses received. Animal experiments can be performed under standardized and controlled conditions and can provide information on the dose-response relationships for radiation carcinogenesis. The risk of inducing neoplastic late effects after total-body irradiation with relatively high doses has been demonstrated for larger animals, such as monkeys and dogs. The bone marrow, the mammary glands and the lungs are among the tissues with the highest susceptibility for radiation carcinogenesis. Experimental results on tumour induction in rodents are summarized with emphasis on the effectiveness in dependence on radiation quality and fractionation or dose rate.     

Disease resistance in farm animals

Genetic variations in disease resistance of farm animals can be observed at all levels of defence against infectious agents. In most cases susceptibility to infections has polygenic origins. In domestic animals only a few instances of a single genetic locus responsible for disease resistance are known. A well-examined example is the Mx1 gene product of certain mice strains conferring selective resistance to influenza virus infections. Attempts to improve disease resistance by gene transfer of different gene constructs into farm animals include the use of monoclonal antibody gene constructs, transgenes consisting of antisense RNA genes directed against viruses and Mx1 cDNA containing transgenes.     

Radiation carcinogenesis in experimental animals

Summary Exposure of man to relatively high doses of ionizing radiation is generally restricted to accidental situations, with very limited knowledge about the actual doses received. Animal experiments can be performed under standardized and controlled conditions and can provide information on the dose-response relationships for radiation carcinogenesis.The risk of inducing neoplastic late effects after total-body irradiation with relatively high doses has been demonstrated for larger animals, such as monkeys and dogs. The bone marrow, the mammary glands and the lungs are among the tissues with the highest susceptibility for radiation carcinogenesis. Experimental results on tumour induction in rodents are summarized with emphasis on the effectiveness in dependence on radiation quality and fractionation or dose rate.     

Heat-labile natural anti-digestive antibodies in animals

Résumé Les rats et les lapins normaux possèdent dans leur serum des anticorps thermolabiles qui réagissent en immunofluorescence avec des antigènes glandulaires de la muqueuse digestive autologue, isologue, et hétérologue. Ces anticorps disparaissent après chauffage à 56 °C pendant 30 min. Ces anticorps sont absents chez l'homme et le Chien.     

Peritoneal dialysis in small laboratory animals

Summary Healthy rats and guinea-pigs were treated with a simple method of continuous peritoneal dialysis for 12, 24 and 48 h. Increasing with time, both animal species developed severe hypoproteinemia and hemoconcentration due to protein loss into the dialyzate fluid. These changes were associated with a high mortality rate, when Sterofundin^® was used for dialysis. Therefore, protein loss should be substituted and the type of dialyzate must be considered in experimental long-term dialysis using these small laboratory animals.Supported by Deutsche Forschungsgemeinschaft, Bonn-Bad Godesberg, La 369/1.Acknowledgment. Our thanks are due to Jutta Otto and Ulrich Oberdieck for expert technical assistance.     

Biochemical ecology of deep-sea animals

Deep-sea ecosystems contain unique endemic species whose distributions show strong vertical patterning in the case of pelagic animals and sharp horizontal patterning in the case of benthic animals living in or near the deep-sea hydothermal vents. This review discusses the biochemical adaptations that enable deep-sea animals to exploit diverse deep-sea habitats and that help establish biogeographic patterning in the deep-sea. The abilities of deep-sea animals to tolerate the pressure and temperature conditions of deep-sea habitats are due to pervasive adaptations at the biochemical level: enzymes exhibit reduced perturbation of function by pressure, membranes have fluidities adapted to deep-sea pressures and temperatures, and proteins show enhanced structural stability relative to homologous proteins from cold-adapted shallow-living species. Animals from the warmest habitable regions of hydrothermal vent ecosystems have enzymes and mitochondria adapted to high pressure and relatively high temperatures. The low metabolic rates of bathypelagic fishes correlate with greatly reduced capacities for ATP turnover in locomotory muscle. Reduced light and food availability in bathypelagic regions select for low rates of energy expenditure in locomotory activity. Deep-sea animals thus reflect the importance of biochemical adaptations in establishing species distribution patterns and appropriate rates of metabolic turnover in different ecosystems.     

Suppression of tryptophan pyrrolase induction in porphyric animals

Zusammenfassung Nachweis, dass Phenylhydrazin die von Tryptophan, nicht aber von Kortison hervorgerufene Induktion der Tryptophanpyrrolase in der Rattenleber hemmt. Die Hemmung der Enzyminduktion durch Phenylhydrazin dürfte auf Anomalien des Porphyrin-stoffwechsees beruhen.     

Impaired metabolism of arachidonate in selenium deficient animals

Cellular and Molecular Life Sciences - Arachidonate-induced respiratory distress in mice was aggravated in a selenium deficient group as compared with a selenium supplemented one. The aggravation...