Comparison of influence of 2-oxoglutarate and glutamate on arginase activities in liver and kidney-cortex of rabbit, Oryctolagus cuniculus

Inhibition of Host Arginase Activity Against Staphylococcal Bloodstream Infection by Different Metabolites

Staphylococcus aureus is a notorious bacterial pathogen that often causes soft tissue and bloodstream infections and invariably garners resistance mechanisms against new antibiotics. Modulation of the host immune response by metabolites is a powerful tool against bacterial infections, but has not yet been used against S. aureus infections. In this study, we identified four metabolite biomarkers: L-proline, L-isoleucine, L-leucine, and L-valine (PILV), through a metabolomics study using animal models of S. aureus bloodstream infection. The exogenous administration of each metabolite or of PILV showed anti-infective effects, and a higher protection was achieved with PILV in comparison to individual metabolites. During the staphylococcal infection, the expression of most host arginase and nitric oxide synthase (NOS) isozymes was simultaneously induced in mouse liver, kidney, and blood samples. However, the induction of arginase isozymes was dramatically stronger than that of NOS isozymes. This elevated arginase activity was inhibited by the metabolite biomarkers thus killing S. aureus, and PILV exhibited the strongest inhibition of arginase activity and bacterial inhibition. The suppression of arginase activity also contributed to the metabolite-mediated phagocytic killing of S. aureus in mouse and human blood. Our findings demonstrate the metabolite-mediated arginase inhibition as a therapeutic intervention for S. aureus infection.

A metabolic exploration of the protective effect of Ligusticum wallichii on IL-1β-injured mouse chondrocytes

Background

Osteoarthritis (OA) is a metabolic disorder and able to be relieved by traditional Chinese medicines. However, the effect of Ligusticum wallichii on OA is unknown.

Methods

Cytokine IL-1β and L. wallichii extracts were used to stimulate the primary mouse chondrocytes. MTT assay was used to measure the cell viability. The mRNA and protein level of each gene were test by qRT-PCR and western blotting, respectively. The rate of apoptotic cell was measured by flow cytometry. GC/MS-based metabolomics was utilized to characterize the variation of metabolome.

Results

Here, we found that L. wallichii attenuated the IL-1β-induced apoptosis, inflammatory response, and extracellular matrix (ECM) degradation in mouse chondrocytes. Then we used GC/MS-based metabolomics to characterize the variation of metabolomes. The established metabolic profile of mouse chondrocytes showed that the abundance of most metabolites (n = 40) altered by IL-1β stimulation could be repressed by L. wallichii treatment. Multivariate data analysis identified that cholesterol, linoleic acid, hexadecandioic acid, proline, l-valine, l-leucine, pyruvate, palmitic acid, and proline are the most key biomarkers for understanding the metabolic role of L. wallichii in IL-1β-treated chondrocytes. Further pathway analysis using these metabolites enriched fourteen metabolic pathways, which were dramatically changed in IL-1β-treated chondrocytes and capable of being reprogrammed by L. wallichii incubation. These enriched pathways were involved in carbon metabolisms, fatty acid biosynthesis, and amino acid metabolisms.

Conclusions

These findings provide potential clues that metabolic strategies are linked to protective mechanisms of L. wallichii treatment in IL-1β-stimulated chondrocytes and emphasize the importance of metabolic strategies against inflammatory responses in OA development.

l-Proline protects mice challenged by Klebsiella pneumoniae bacteremia

OBJECTIVE

K. pneumoniae, a common pathogen that frequently causes bacteremia in clinic, is unresponsive to most of known antibiotics, thus cumulatively exacerbating empirical therapy failures. Effective strategies to control Klebsiella pneumoniae bacteremia are in high demand. One possibility is to mobilize host defense mechanisms against bacterial pathogens.

METHODS

We employed GC/MS-based metabolomics to identify the changes of metabolism in mice challenged by K. pneumoniae (ATCC 43816) bacteremia.

RESULTS

Compared with the mice that compromised from K. pneumoniae bacteremia, mice that survived from infection displayed the varied metabolomic profile. The differential analysis of metabolome showed that Ethanedioic acid, d-Glucose, l-Glutamine, Myo-inositol, and l-Proline were more likely associated with the host surviving a K. pneumoniae bacteremia. Further pathway enrichment analysis proposed that arginine and proline metabolism involved in outcome of K. pneumoniae bacteremia. The follow-up data showed that exogenous l-Proline but not d-Proline could decline the loads of Klebsiella pneumonia in infected blood and tissues (lung, liver and spleen) and increase the mouse survival.

CONCLUSION

Our study provides an exercisable strategy of identifying metabolic biomarkers from surviving host and highlights the possibility of utilizing the metabolic biomarker as a therapy for K. pneumoniae bacteremia.

Exogenous l-Valine Promotes Phagocytosis to Kill Multidrug-Resistant Bacterial Pathogens

The emergence of multidrug-resistant bacteria presents a severe threat to public health and causes extensive losses in livestock husbandry and aquaculture. Effective strategies to control such infections are in high demand. Enhancing host immunity is an ideal strategy with fewer side effects than antibiotics. To explore metabolite candidates, we applied a metabolomics approach to investigate the metabolic profiles of mice after Klebsiella pneumoniae infection. Compared with the mice that died from K. pneumoniae infection, mice that survived the infection displayed elevated levels of l-valine. Our analysis showed that l-valine increased macrophage phagocytosis, thereby reducing the load of pathogens; this effect was not only limited to K. pneumoniae but also included Escherichia coli clinical isolates in infected tissues. Two mechanisms are involved in this process: l-valine activating the PI3K/Akt1 pathway and promoting NO production through the inhibition of arginase activity. The NO precursor l-arginine is necessary for l-valine-stimulated macrophage phagocytosis. The valine-arginine combination therapy effectively killed K. pneumoniae and exerted similar effects in other Gram-negative (E. coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. Our study extends the role of metabolism in innate immunity and develops the possibility of employing the metabolic modulator-mediated innate immunity as a therapy for bacterial infections.

L-arginine metabolism in dog kidney and isolated nephron segments

The renal basic amino acid metabolism often differs in rodents, strict carnivores, and omnivore species. Given the pivotal role of L-arginine and L-ornithine in several metabolic pathways and the fact that the dog is closely related to humans, being also an omnivore, we tested whether L-arginine metabolism and L-ornithine catabolism take place in the dog kidney. We examined the metabolism of L-arginine in dog cortical tubules to integrate local L-arginine metabolism into a general physiological and metabolic framework. To achieve these goals, we first ascertained the protein expression of relevant enzymes by Western blot. L-Arginine catabolism was studied in suspensions of canine cortical proximal tubules, medullary thick ascending limbs, and papillary collecting ducts either incubated without exogenous L-arginine being added (small endogenous quantities) or incubated with L-arginine being added in supraphysiological amounts (2 mmol/L with or without the presence of alternative metabolic substrates, 2 mmol/L L-glutamine, or lactate). The results revealed that dog kidneys consumed L-citrulline and released L-arginine and L-ornithine. Argininosuccinate synthetase and lyase, arginase II, and ornithine aminotransferase were detected in the renal cortex. Arginase II activity was found in a suspension of proximal tubules by measuring the amounts of urea and L-ornithine produced. A fraction of this L-ornithine was further partially metabolized through the intramitochondrial ornithine aminotransferase pathway, leading to changes in L-glutamate, glucose, L-alanine, and ammonia metabolism without L-proline accumulation. Medullary thick ascending limbs expressed a very low arginase activity, whereas papillary collecting ducts did not. In conclusion, the dog kidney produces L-arginine. Part of this L-arginine is further catabolized by arginase II, suggesting that its physiological role was to produce L-ornithine for the body.