Arginine metabolism is markedly impaired in polymicrobial infected mice

ciency state, there is an ongoing controversial debate about arginine supplementation in the treatment of patients with sepsis. Little is known, however, about the diff erent cata bolic and anabolic downstream and upstream products or byproducts in arginine metabolism in the course of sepsis. Using a clinical chemistry and mass spectrometric approach we analyzed metabolites related to arginine metabolism from plasma samples of polymicrobial infected mice at 6 hours and 24 hours post sepsis induction in comparison with healthy animals. Following ethical approval by the responsible animal welfare committee (Th ueringer Landesamt fuer Lebensmittelsicher heit und Verbraucherschutz; TVA 02-10/10), animals (male C57BL/6N mice) were randomized into three groups: healthy controls without any intervention, mice 6 hours post sepsis induction, and mice 24 hours post sepsis induction. Peritonitis in mice was induced as described in more detail for a rat model [1] by injection of stool suspension into the right lower quadrant of the abdomen with a 21-gauge cannula. Blood samples were drawn using direct needle puncture of the right ventricle. EDTA-anticoagulated blood was immediately centri fuged, and plasma was collected and snap-frozen in liquid nitrogen and stored at –80°C until use. Mass spectrometric analysis was performed using the API4000TM LC/MS/MS system (AB SCIEX, Foster City, CA, USA) equipped with an electrospray ionization source. All animals received a standard pellet rodent diet (ssniff , Soest, Germany) and water ad libitum. Th e pellets contain 33% proteins, 58% carbohydrates and 9% fats. In our translational approach we did not focus on an additional nutritional support. To avoid the infl uence of sepsis-induced anorexia, however, we limited the observational period to 24 hours. Our data clearly show that the arginine plasma concentration is substantially decreased in sepsis, which is not caused by lower availability of amino acids glutamine or citrulline (Table 1). Th e data support the concept that the arginine catabolic pathway outweighs the anabolic pathway, producing for example proline. Increased arginase activity synthesizes ornithine and urea, the latter signifi cantly enhanced in the late phase during sepsis. Th e increased urea plasma concentration might refl ect not only enhanced arginase activity but also a developing state of acute renal injury. Furthermore, ornithine might be catalyzed rapidly by ornithine de carboxy lase to synthesize putrescine, which is the com mitted reaction in the synthesis of polyamines. Further explanation for the observed decrease in concentration of ornithine, however, cannot be given from our present data and remains unclear. Interestingly, whilst the putrescine plasma concentration was signifi cantly increased, the concentration of spermidine decreased after 24 hours. Th e increasing putrescine pool might indicate a restricted activity of spermidine synthase resulting in an insuffi cient converted concentration of spermidine. Th is fi nding might be interest ing because polyamines exert pleiotropic biological activities, including modulation of cell signaling, cell growth as well as cell apoptosis [2]. Furthermore, it is important to note that administration of polyamines can function as either protective or harmful in lethal experimental sepsis [3]. Proline plays various roles in cell metabolism and physiology; for example, in cell growth, wound healing, scavenging oxidants as well as in polyamine and protein syntheses [4]. In our model, the plasma concentration of proline was signifi cantly decreased during sepsis compared with healthy controls. One could speculate that, beside the reduced arginine availability, increasing hydroxy lation of proline to hydroxyproline – an essential step to provide collagen for tissue repair, remodeling or wound healing – contributes to the substantially reduced proline plasma concentration during sepsis even in the early phase of the disease [5]. Consequently, targeting arginine defi ci ency might be essential in patients with sepsis. Owing to the complexity of arginine metabolism © 2010 BioMed Central Ltd Arginine metabolism is markedly impaired in polymicrobial infected mice