In the field of infectious diseases the multifaceted amino acid arginine has reached special attention as substrate for the host´s production of the antimicrobial agent nitric oxide (NO). A variety of infectious organisms interfere with this part of the host immune response by reducing the availability of arginine. This prompted us to further investigate additional roles of arginine during pathogen infections. As a model we used the intestinal parasite Giardia intestinalis that actively consumes arginine as main energy source and secretes an arginine-consuming enzyme, arginine deiminase (ADI). Reduced intestinal epithelial cell (IEC) proliferation is a common theme during bacterial and viral intestinal infections, but it has never been connected to arginine-consumption. Our specific question was thereby, whether the arginine-consumption by Giardia leads to reduced IEC proliferation, in addition to NO reduction. In vitro cultivation of human IEC lines in arginine-free or arginine/citrulline-complemented medium, as well as in interaction with different G. intestinalis isolates, were used to study effects on host cell replication by MTT assay. IEC proliferation was further analyzed by DNA content analysis, polyamine measurements and expressional analysis of cell cycle regulatory genes. IEC proliferation was reduced upon arginine-withdrawal and also in an arginine-dependent manner upon interaction with G. intestinalis or addition of Giardia ADI. We show that arginine-withdrawal by intestinal pathogens leads to a halt in the cell cycle in IECs through reduced polyamine levels and upregulated cell cycle inhibitory genes. This is of importance with regards to intestinal tissue homeostasis that is affected through reduced cell proliferation. Thus, the slower epithelial cell turnover helps the pathogen to maintain a more stable niche for colonization. This study also shows why supplementation therapy of diarrhea patients with arginine/citrulline is helpful and that citrulline especially should gain further attention in future treatment strategies.
Stocking programs using hatchery-reared salmon are often implemented for augmenting natural populations. However, survival of these fish is often low compared with wild conspecifics, possibly because of genetic, physiological, and behavioural deficiencies. Here, we compared presmolt Atlantic salmon (Salmo salar) from three different environmental treatments (barren environment, plastic tube enrichment, and plastic shredding enrichment) with regard to plasma cortisol levels, shelter-seeking behaviour, and fin deterioration. Basal plasma cortisol levels were higher in barren-reared fish, indicating higher stress levels, while no differences were found in acute cortisol response after a 30 min confinement test. Shelter-seeking was higher in salmon reared in enriched tanks when tested alone, but not when tested in small groups. Barren-reared fish had higher levels of fin deterioration over winter, potentially owing to higher aggression levels. These results suggest that enrichment can reduce the impact of stressors experienced in the hatchery and thus increase fish welfare. Tank enrichment may also be used to produce salmon better adapted for the more complex environment encountered after release.
Cells depend on polyamines for growth and their depletion represents a strategy for the treatment of cancer. Polyamines assemble de novo through a pathway sensitive to the inhibitor, ␣-difluoromethylornithine (DFMO). However, the presence of cellsurface heparan sulfate proteoglycans may provide a salvage pathway for uptake of circulating polyamines, thereby sparing cells from the cytostatic effect of DFMO. Here we show that genetic or pharmacologic manipulation of proteoglycan synthesis in the presence of DFMO inhibits cell proliferation in vitro and in vivo. In cell culture, mutant cells lacking heparan sulfate were more sensitive to the growth inhibitory effects of DFMO than wild-type cells or mutant cells transfected with the cDNA for the missing biosynthetic enzyme. Moreover, extracellular polyamines did not restore growth of mutant cells, but completely reversed the inhibitory effect of DFMO in wild-type cells. In a mouse model of experimental metastasis, DFMO provided in the water supply also dramatically diminished seeding and growth of tumor foci in the lungs by heparan sulfate-deficient mutant cells compared with the controls. Wild-type cells also formed tumors less efficiently in mice fed both DFMO and a xylose-based inhibitor of heparan sulfate proteoglycan assembly. The effect seemed to be specific for heparan sulfate, because a different xyloside known to affect only chondroitin sulfate did not inhibit tumor growth. Hence, combined inhibition of heparan sulfate assembly and polyamine synthesis may represent an additional strategy for cancer therapy.metastasis ͉ proteoglycans ͉ spermine ͉ chemotherapy ͉ xylosides
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