The natural polyamines and the immune system

Virulence attributes of successful methicillin-resistant Staphylococcus aureus lineages

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of severe and often fatal infections. MRSA epidemics have occurred in waves, whereby a previously successful lineage has been replaced by a more fit and better adapted lineage. Selection pressures in both hospital and community settings are not uniform across the globe, which has resulted in geographically distinct epidemiology. This review focuses on the mechanisms that trigger the establishment and maintenance of current, dominant MRSA lineages across the globe. While the important role of antibiotic resistance will be mentioned throughout, factors which influence the capacity of S. aureus to colonize and cause disease within a host will be the primary focus of this review. We show that while MRSA possesses a diverse arsenal of toxins including alpha-toxin, the success of a lineage involves more than just producing toxins that damage the host. Success is often attributed to the acquisition or loss of genetic elements involved in colonization and niche adaptation such as the arginine catabolic mobile element, as well as the activity of regulatory systems, and shift metabolism accordingly (e.g., the accessory genome regulator, agr). Understanding exactly how specific MRSA clones cause prolonged epidemics may reveal targets for therapies, whereby both core (e.g., the alpha toxin) and acquired virulence factors (e.g., the Panton-Valentine leukocidin) may be nullified using anti-virulence strategies.

Contribution of Arginine Catabolic Mobile Element and Copper and Mercury Resistance Element in Methicillin-Resistant Staphylococcus aureus: A Vantage Point

Different clones of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are dominating geographically. One of the significant, hypervirulent, CA-MRSA and a significant health concern clones is USA3000, found worldwide regionally with varying frequencies. The clone harbors several mobile genetic elements (MGEs) including, arginine catabolic mobile element (ACME) and copper and mercury resistance genes (COMER), accomplished by horizontal gene transfer from S. epidermidis. Evidence suggests that ACME and COMER have a more prominent role in enhancing biofilm capacity and ultimately persistent infections. This review highlights the comprehensive view on ACME and COMER structure, their distribution, and the mechanism of action along with pathogenetic features of USA3000 encompassing their role in biofilm formation, adhesion, quorum sensing, resistance to antibiotics, chemotaxis, and nutrient uptake. We also provided an insight into the role of ACME and COMER genes in the survival of bacterium. Our results shed light on the emergence of two independent clones possessing ACME (North American) and COMER (South American) elements which later disseminated to other regions. ACME and COMER both are adjacent to staphylococcal cassette chromosome mec type IV (SCCmec IV). The acquisition of mecA, followed by COMER or ACME has been shown as a significant factor in the rise and fall of MRSA strains and their complex ability to adapt to hostile environments. The presence of ACME increases fitness, thereby allowing bacteria to colonize the skin and mucous membrane while COMER contributes to genetic stability by knocking over the copper-mediated killing in macrophages. Evidence suggests that ACME and COMER have a more prominent role in enhancing biofilm capacity and ultimately persistent infections. Interestingly, ACME strains have been shown to possess the ability to counteract skin acidity, thereby allowing increased skin colonization. A profound understanding of MGEs in S. aureus plays an important role in the prevention of epidemic clones.

Association of the characteristics of the blood metabolome and gut microbiome with the outcome of methotrexate therapy in psoriasis

Metabolic status and gut microecology are implicated in psoriasis. Methotrexate (MTX) is usually the first-line treatment for this disease. However, the relationship between MTX and host metabolic status and the gut microbiota is unclear. This study aimed to characterize the features of blood metabolome and gut microbiome in patients with psoriasis after treatment with MTX. Serum and stool samples were collected from 15 patients with psoriasis. Untargeted liquid chromatography–mass spectrometry and metagenomics sequencing were applied to profile the blood metabolome and gut microbiome, respectively. We found that the response to MTX varied according to metabolomic and metagenomic features at baseline; for example, patients who had high levels of serum nutrient molecular and more enriched gut microbiota had a poor response. After 16 weeks of MTX, we observed a reduction in microbial activity pathways, and patients with a good response showed more microbial activity and less biosynthesis of serum fatty acid. We also found an association between the serum metabolome and the gut microbiome before intervention with MTX. Carbohydrate metabolism, transporter systems, and protein synthesis within microbes were associated with host metabolic clusters of lipids, benzenoids, and organic acids. These findings suggest that the metabolic status of the blood and the gut microbiome is involved in the effectiveness of MTX in psoriasis, and that inhibition of symbiotic intestinal microbiota may be one of the mechanisms of action of MTX. Prospective studies in larger sample sizes are needed to confirm these findings.

Development of a method for the determination of polyamines including N-acetylated forms in human saliva via benzoylation and gas chromatography-mass spectrometry

A simple method for the determination of polyamines and their N-acetylated forms was developed using benzoyl chloride as derivatization reagent, and 1,6-diaminohexane as internal standard, followed by liquid-liquid extraction with ethyl acetate. The organic extract was injected in a gas chromatograph using a programmed temperature vaporizer and the determination and quantification was performed with a quadrupole mass spectrometer. There was no matrix effect with the proposed method, so internal calibration was used to quantify the corresponding derivatives. Good linear responses were obtained in the range from the limits of detection to 500 µg L^-1 (50 µg L^-1 for spermidine), with correlation coefficients varying from 0.9591 to 0.9968. The limits of quantification (S/N = 10) ranged 1.0 - 8.3 µg L^-1. Recoveries were found between 82 - 117%, showing the good accuracy of the proposed method. Intra- and inter-day precision assays, expressed as relative standard deviation (RSD) were evaluated at two different concentration levels (low and high), showing values in the range of 2.4 - 6.1% and 5.2 - 9.0% for repeatability and reproducibility, respectively (6.9 - 9.7% and 14.1 - 14.6% for spermidine). Successful determination of the studied polyamines and their N-acetylated forms was performed on the saliva of 17 volunteers.

Genome Sequence of a Highly Virulent pvl-positive Vancomycin intermediate- resistant Staphylococcus aureus Sequence Type 30

Background:

Staphylococcus aureus isolates expressing the Panton-Valentine Leukocidin (PVL) have been related to a wide range of diseases. Recently, pvl-positive community-associated methicillin-resistant S. aureus belonging to USA1100 (ST30/CC30/SCCmec IV) lineage has emerged in Brazilian hospitals.

Objective:

The aim of this work was to sequence the genome of a pvl-positive USA1100 Vancomycin- Intermediate-Resistant S. aureus (VISA) isolate from Rio de Janeiro, Brazil.

Methods:

The 13420 genome was sequenced using the HiSeq 2500 platform. The draft genome, plasmids annotation, and genome analysis were performed using RAST. Comparison of the relative pvl gene expression of six S. aureus isolates was performed by qRT-PCR.

Results:

The isolate presented the ϕPVL phage codifying for the H2b PVL protein isoform, and another prophage carrying a PVL variant named lukF and lukS-PV.2. The 13420 genome presented a high number of virulence determinants, such as genes codifying for serine-protease proteins, enterotoxins (egc), the immune evasion cluster (IEC), adhesion proteins, spermine/spermidine acetyltransferase gene (blt), superantigen-like proteins, as well as the ica operon. Point mutations at vraS, tcaA, and tcaB genes were detected. Moreover, the PVL mRNA relative expression of the 13420 isolate was five times higher than mRNA PVL levels of the USA300/ST8 reference strain.

Conclusion:

We described for the first time the genome sequence of a VISA isolate harboring two pvl-associated genes and other virulence factors that may improve the USA1100/ST30 lineage fitness and impact its pathogenicity and spreading at Brazilian hospitals.

Polyamines, folic acid supplementation and cancerogenesis

Clinical practice and experimental studies have shown the necessity of sufficient quantities of folic acid intake for normal embryogenesis and fetal development in the prevention of neural tube defects (NTDs) and neurological malformations. So, women of childbearing age must be sure to have an adequate folate intake periconceptionally, prior to and during pregnancy. Folic acid fortification of all enriched cereal grain product flour has been implemented in many countries. Thus, hundreds of thousands of people have been exposed to an increased intake of folic acid. Folate plays an essential role in the biosynthesis of methionine. Methionine is the principal aminopropyl donor required for polyamine biosynthesis, which is up-regulated in actively growing cells, including cancer cells. Folates are important in RNA and DNA synthesis, DNA stability and integrity. Clinical and epidemiological evidence links folate deficiency to DNA damage and cancer. On the other hand, long-term folate oversupplementation leads to adverse toxic effects, resulting in the appearance of malignancy. Considering the relationship of polyamines and rapidly proliferating tissues (especially cancers), there is a need for better investigation of the relationship between the ingestion of high amounts of folic acid in food supplementation and polyamine metabolism, related to malignant processes in the human body.

Comparative genome-scale modelling of Staphylococcus aureus strains identifies strain-specific metabolic capabilities linked to pathogenicity

Staphylococcus aureus is a preeminent bacterial pathogen capable of colonizing diverse ecological niches within its human host. We describe here the pangenome of S. aureus based on analysis of genome sequences from 64 strains of S. aureus spanning a range of ecological niches, host types, and antibiotic resistance profiles. Based on this set, S. aureus is expected to have an open pangenome composed of 7,411 genes and a core genome composed of 1,441 genes. Metabolism was highly conserved in this core genome; however, differences were identified in amino acid and nucleotide biosynthesis pathways between the strains. Genome-scale models (GEMs) of metabolism were constructed for the 64 strains of S. aureus These GEMs enabled a systems approach to characterizing the core metabolic and panmetabolic capabilities of the S. aureus species. All models were predicted to be auxotrophic for the vitamins niacin (vitamin B3) and thiamin (vitamin B1), whereas strain-specific auxotrophies were predicted for riboflavin (vitamin B2), guanosine, leucine, methionine, and cysteine, among others. GEMs were used to systematically analyze growth capabilities in more than 300 different growth-supporting environments. The results identified metabolic capabilities linked to pathogenic traits and virulence acquisitions. Such traits can be used to differentiate strains responsible for mild vs. severe infections and preference for hosts (e.g., animals vs. humans). Genome-scale analysis of multiple strains of a species can thus be used to identify metabolic determinants of virulence and increase our understanding of why certain strains of this deadly pathogen have spread rapidly throughout the world.

Changes in the proteomic profile during the differential polarization status of the human monocyte-derived macrophage THP-1 cell line

Macrophages are heterogeneous and plastic populations that are an essential component of inflammation and host defense. To understand how macrophages respond to cytokine signals, we used 2DE to identify protein profiles in macrophages stimulated with interleukin 4 (M2) and those stimulated with lipopolysaccharide and interferon γ (M1). In total, 32 differentially expressed proteins in THP-1 cells were identified by MALDI-TOF MS/MS analysis. The different proteins were mainly involved in cellular structure, protein metabolism, stress response, oxidative response, and nitric oxide production during macrophage polarization. In particular, proteins playing important roles in production of nitric oxide (NO) were downregulated in M2 macrophages. Many antioxidant and heat shock proteins, which are related to oxidative response, were upregulated in M2 macrophages. More importantly, a remarkable decrease in intracellular ROS and NO production were detected in M2 macrophages. Our results provide a proteomic profile of differentially polarized macrophages and validate the function of the identified proteins, which may indicate possible mechanism of macrophage polarization process.

Emergence of the epidemic methicillin-resistant Staphylococcus aureus strain USA300 coincides with horizontal transfer of the arginine catabolic mobile element and speG-mediated adaptations for survival on skin

The arginine catabolic mobile element (ACME) is the largest genomic region distinguishing epidemic USA300 strains of methicillin-resistant Staphylococcus aureus (MRSA) from other S. aureus strains. However, the functional relevance of ACME to infection and disease has remained unclear. Using phylogenetic analysis, we have shown that the modular segments of ACME were assembled into a single genetic locus in Staphylococcus epidermidis and then horizontally transferred to the common ancestor of USA300 strains in an extremely recent event. Acquisition of one ACME gene, speG, allowed USA300 strains to withstand levels of polyamines (e.g., spermidine) produced in skin that are toxic to other closely related S. aureus strains. speG-mediated polyamine tolerance also enhanced biofilm formation, adherence to fibrinogen/fibronectin, and resistance to antibiotic and keratinocyte-mediated killing. We suggest that these properties gave USA300 a major selective advantage during skin infection and colonization, contributing to the extraordinary evolutionary success of this clone.

IMPORTANCE

Over the past 15 years, methicillin-resistant Staphylococcus aureus (MRSA) has become a major public health problem. It is likely that adaptations in specific MRSA lineages (e.g., USA300) drove the spread of MRSA across the United States and allowed it to replace other, less-virulent S. aureus strains. We suggest that one major factor in the evolutionary success of MRSA may have been the acquisition of a gene (speG) that allows S. aureus to evade the toxicity of polyamines (e.g., spermidine and spermine) that are produced in human skin. Polyamine tolerance likely gave MRSA multiple fitness advantages, including the formation of more-robust biofilms, increased adherence to host tissues, and resistance to antibiotics and killing by human skin cells.

The neurobiology of suicide - A Review of post-mortem studies

The neurobiology of suicidal behaviour, which constitutes one of the most serious problems both in psychiatry and general medical practice, still remains to a large degree unclear. As a result, scientists constantly look for new opportunities of explaining the causes underlying suicidality. In order to elucidate the biological changes occurring in the brains of the suicide victims, studies based on post-mortem brain tissue samples are increasingly being used. These studies employ different research methods to provide an insight into abnormalities in brain functioning on various levels, including gene and protein expression, neuroplasticity and neurotransmission, as well as many other areas. The aim of this paper to summarize the available data on the post-mortem studies, to provide an overview of main research directions and the most up-to-date findings, and to indicate the possibilities of further research in this field.

Natural polyamine inhibits mouse skin inflammation and macrophage activation

OBJECTIVE

Natural polyamines are some of the most abundant polycationic molecules in eukaryotic cells, regulating gene expression. Polyamines have been reported to possess anti-inflammatory activities in many model inflammation systems. However, there is no report on their role in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced dermal edema.

METHODS

Mouse ear edema was induced by TPA. Edema biopsies were investigated using H&E staining. Levels of nitric oxide (NO) were determined using the Griess reaction. Tumor necrosis factor α (TNFα) and interleukin (IL)-1β levels in cell supernatants were measured by TNFα and IL-1β ELISA kits.

RESULTS

Spermidine and spermine caused significant decreases in ear thickness, water content, and neutrophil infiltrations in comparison with negative control (p < 0.05). External polyamines reduced the levels of inflammatory mediators such as NO, TNFα, and IL-1β in lipopolysaccharide (LPS)-stimulated RAW264.7 murine macrophages. Spermine had a higher inhibitory effect on the production of cytokines such as IL-1β and TNFα in LPS-stimulated murine macrophages compared to other polyamines.

CONCLUSION

Our findings clearly demonstrated that polyamines are involved in the anti-inflammatory effect by reducing dermal edema thickness and other inflammatory mediators like NO and cytokines in a dose-dependent manner.

Arginine catabolic mobile element encoded speG abrogates the unique hypersensitivity of Staphylococcus aureus to exogenous polyamines

Polyamines, including spermine (Spm) and spermidine (Spd), are aliphatic cations that are reportedly synthesized by all living organisms. They exert pleiotropic effects on cells and are required for efficient nucleic acid and protein synthesis. Here, we report that the human pathogen Staphylococcus aureus lacks identifiable polyamine biosynthetic genes, and consequently produces no Spm/Spd or their precursor compounds putrescine and agmatine. Moreover, while supplementing defined medium with polyamines generally enhances bacterial growth, Spm and Spd exert bactericidal effects on S. aureus at physiological concentrations. Small colony variants specifically lacking menaquinone biosynthesis arose after prolonged Spm exposure and exhibited reduced polyamine sensitivity. However, other respiratory-defective mutants were no less susceptible to Spm implying menaquinone itself rather than general respiration is required for full Spm toxicity. Polyamine hypersensitivity distinguishes S. aureus from other bacteria and is exhibited by all tested strains save those belonging to the USA-300 group of community-associated methicillin-resistant S. aureus (CA-MRSA). We identified one gene within the USA-300-specific arginine catabolic mobile element (ACME) encoding a Spm/Spd N-acetyltransferase that is necessary and sufficient for polyamine resistance. S. aureus encounters significant polyamine levels during infection; however, the acquisition of ACME encoded speG allows USA-300 clones to circumvent polyamine hypersensitivity, a peculiar trait of S. aureus.

Evidence of altered polyamine concentrations in cerebral cortex of suicide completers

Recent studies have implicated alterations in the expression of polyamine-related genes in the brains of suicide completers including widespread downregulation of spermidine/spermine N1-acetyltransferase, the key enzyme in polyamine catabolism, suggesting compensatory mechanisms attempting to increase brain levels of polyamines. Given the complexity of the polyamine system, quantification of the levels of the polyamines is an essential step in understanding the downstream effects of dysregulated gene expression. We developed a method using high-resolution capillary gas chromatography (GC) in combination with mass spectrometry (MS) for quantitation of polyamines from post-mortem brain tissue, which allowed us to accurately measure spermidine and putrescine concentrations in post-mortem brain tissues. Using this method, we analyzed putrescine and spermidine levels in a total of 126 samples from Brodmann areas 4, 8/9, and 11, from 42 subjects, comprising 16 suicide completers with major depression, 13 non-depressed suicide completers, and 13 control subjects. Both putrescine and spermidine levels fell within the expected nanomolar ranges and were significantly elevated in the brain of suicide completers with a history of major depression as compared with controls. These results were not accounted by possible confounders. This is the first GC-MS study to analyze the expression of putrescine and spermidine from post-mortem brain tissue and confirms the hypothesis raised by previous studies indicating alterations in putrescine and spermidine levels in suicide/major depression.

activated polyamine catabolism in acute pancreatitis: alpha-methylated polyamine analogues prevent trypsinogen activation and pancreatitis-associated mortality

Polyamines are essential for normal cellular growth and function. Activation of polyamine catabolism in transgenic rats overexpressing spermidine/spermine N(1)-acetyltransferase, the key enzyme in polyamine catabolism, results in severe acute pancreatitis. Here, we investigated the role of polyamine catabolism in pancreatitis and studied the effect of polyamine analogues on the outcome of the disease. Polyamine depletion was associated with arginine- and cerulein-induced pancreatitis as well as with human acute necrotizing and chronic secondary pancreatitis. Substitution of depleted polyamine pools with methylspermidine partially prevented arginine-induced necrotizing pancreatitis whereas cerulein-induced edematous pancreatitis remained unaffected. Transgenic rats receiving methylated polyamine analogues after the induction of pancreatitis showed less pancreatic damage than the untreated rats. Most importantly, polyamine analogues dramatically rescued the animals from pancreatitis-associated mortality. Induction of spermidine/spermine N(1)-acetyltransferase in acinar cells isolated from transgenic rats resulted in increased trypsinogen activation. Pretreatment of acini with bismethylspermine prevented trypsinogen activation, indicating that premature proteolytic activation is one of the effects triggered by polyamine depletion. Our data suggest that activation of polyamine catabolism is a general pathway in the pathogenesis of acute pancreatitis and that experimental disease can be ameliorated with stable polyamine analogues.

Dendritic cells are defective in breast cancer patients: a potential role for polyamine in this immunodeficiency

Introduction

Dendritic cells (DCs) are antigen-presenting cells that are currently employed in cancer clinical trials. However, it is not clear whether their ability to induce tumour-specific immune responses when they are isolated from cancer patients is reduced relative to their ability in vivo. We determined the phenotype and functional activity of DCs from cancer patients and investigated the effect of putrescine, a polyamine molecule that is released in large amounts by cancer cells and has been implicated in metastatic invasion, on DCs.

Methods

The IL-4/GM-CSF (granulocyte–macrophage colony-stimulating factor) procedure for culturing blood monocyte-derived DCs was applied to cells from healthy donors and patients (17 with breast, 7 with colorectal and 10 with renal cell carcinoma). The same peroxide-treated tumour cells (M74 cell line) were used for DC pulsing. We investigated the effects of stimulation of autologous lymphocytes by DCs pulsed with treated tumour cells (DC-Tu), and cytolytic activity of T cells was determined in the same target cells.

Results

Certain differences were observed between donors and breast cancer patients. The yield of DCs was dramatically weaker, and expression of MHC class II was lower and the percentage of HLA-DR^-Lin^- cells higher in patients. Whatever combination of maturating agents was used, expression of markers of mature DCs was significantly lower in patients. Also, DCs from patients exhibited reduced ability to stimulate cytotoxic T lymphocytes. After DC-Tu stimulation, specific cytolytic activity was enhanced by up to 40% when DCs were from donors but only up to 10% when they were from patients. IFN-γ production was repeatedly found to be enhanced in donors but not in patients. By adding putrescine to DCs from donors, it was possible to enhance the HLA-DR^-Lin^- cell percentage and to reduce the final cytolytic activity of lymphocytes after DC-Tu stimulation, mimicking defective DC function. These putrescine-induced deficiencies were reversed by treating DCs with all-trans retinoic acid.

Conclusion

These data are consistent with blockade of antigen-presenting cells at an early stage of differentiation in patients with breast cancer. Putrescine released in the microenvironmement of DCs could be involved in this blockade. Use of all-trans retinoic acid treatment to reverse this blockade and favour ex vivo expansion of antigen-specific T lymphocytes is of real interest.

Altered maturation of peripheral blood dendritic cells in patients with breast cancer

Tumours have at least two mechanisms that can alter dendritic cell (DC) maturation and function. The first affects the ability of haematopoietic progenitors to differentiate into functional DCs; the second affects their differentiation from CD14+ monocytes, promoting an early but dysfunctional maturation. The aim of this study was to evaluate the in vivo relevance of these pathways in breast cancer patients. For this purpose, 53 patients with invasive breast cancer were compared to 68 healthy controls. To avoid isolation or culture procedures for enrichment of DCs, analyses were directly performed by flow cytometry on whole-blood samples. The expression of surface antigens and intracellular accumulation of regulatory cytokines upon LPS stimulation were evaluated. The number of DCs, and in particular of the myeloid subpopulation, was markedly reduced in cancer patients (P<0.001). Patient DCs were characterized by a more mature phenotype compared with controls (P=0.016), and had impaired production of IL-12 (P<0.001). These alterations were reverted by surgical resection of the tumour. To investigate the possible role of some tumour-related immunoactive soluble factors, we measured the plasmatic levels of vascular endothelial growth factor, IL-10 and spermine. A significant inverse correlation between spermine concentration and the percentage of DCs expressing IL-12 was found. Evidence was also obtained that in vitro exposure of monocyte-derived DCs to spermine promoted their activation and maturation, and impaired their function. Taken together, our results suggest that both the above-described mechanisms could concomitantly act in breast cancer to affect DC differentiation, and that spermine could be a mediator of dysfunctional maturation of DCs.

Induction of hypersensitive cell death by hydrogen peroxide produced through polyamine degradation in tobacco plants

Screening immediate-early responding genes during the hypersensitive response (HR) against tobacco mosaic virus infection in tobacco (Nicotiana tabacum) plants, we identified a gene encoding ornithine decarboxylase. Subsequent analyses showed that other genes involved in polyamine biosynthesis were also up-regulated, resulting in the accumulation of polyamines in apoplasts of tobacco mosaic virus-infected leaves. Inhibitors of polyamine biosynthesis, alpha-difluoromethyl-ornithine, however, suppressed accumulation of polyamines, and the rate of HR was reduced. In contrast, polyamine infiltration into a healthy leaf induced the generation of hydrogen peroxide and simultaneously caused HR-like cell death. Polyamine oxidase activity in the apoplast increased up to 3-fold that of the basal level during the HR, and its suppression with a specific inhibitor, guazatine, resulted in reduced HR. Because it is established that hydrogen peroxide is one of the degradation products of polyamines, these results indicate that one of the biochemical events in the HR is production of polyamines, whose degradation induces hydrogen peroxide, eventually resulting in hypersensitive cell death.

Arginase I expression and activity in human mononuclear cells after injury

OBJECTIVE

To determine the effect of trauma on arginase, an arginine-metabolizing enzyme, in cells of the immune system in humans.

SUMMARY BACKGROUND DATA

Arginase, classically considered an enzyme exclusive to the liver, is now known to exist in cells of the immune system. Arginase expression is induced in these cells by cytokines interleukin (IL) 4, IL-10, and transforming growth factor beta, corresponding to a T-helper 2 cytokine profile. In contrast, nitric oxide synthase expression is induced by IL-1, tumor necrosis factor, and gamma interferon, a T-helper 1 cytokine profile. Trauma is associated with a decrease in the production of nitric oxide metabolites and a state of immunosuppression characterized by an increase in the production of IL-4, IL-10, and transforming growth factor beta. This study tests the hypothesis that trauma increases arginase activity and expression in cells of the immune system.

METHODS

Seventeen severely traumatized patients were prospectively followed up in the intensive care unit for 7 days. Twenty volunteers served as controls. Peripheral mononuclear cells were isolated and assayed for arginase activity and expression, and plasma was collected for evaluation of levels of arginine, citrulline, ornithine, nitrogen oxides, and IL-10.

RESULTS

Markedly increased mononuclear cell arginase activity was observed early after trauma and persisted throughout the intensive care unit stay. Increased arginase activity corresponded with increased arginase I expression. Increased arginase activity coincided with decreased plasma arginine concentration. Plasma arginine and citrulline levels were decreased throughout the study period. Ornithine levels decreased early after injury but recovered by postinjury day 3. Increased arginase activity correlated with the severity of trauma, early alterations in lactate level, and increased levels of circulating IL-10. Increased arginase activity was associated with an increase in length of stay. Plasma nitric oxide metabolites were decreased during this same period.

CONCLUSIONS

Markedly altered arginase expression and activity in cells of the human immune system after trauma have not been reported previously. Increased mononuclear cell arginase may partially explain the benefit of arginine supplementation for trauma patients. Arginase, rather than nitric oxide synthase, appears to be the dominant route for arginine metabolism in immune cells after trauma.

Attenuation of isoproterenol-mediated myocardial injury in rat by an inhibitor of polyamine synthesis

OBJECTIVE

Ornithine decarboxylase (ODC) is an initial rate-limiting enzyme in the synthesis of polyamines (putrescine, spermidine, and spermine) that play a role in cell growth and differentiation. Recent studies have shown that spermidine and spermine cause injury to a variety of cells including myocytes in vitro. In this investigation, we used alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ODC activity and polyamine synthesis to test the hypothesis that polyamines contribute to myocardial injury in rat.

METHODS

Male Sprague Dawley rats were treated with (i) saline (0.2 ml/day, s.c.), (ii) isoproterenol (ISO) (5 mg/kg/day for 8 days, s.c.) to produce necrotizing myocardial injury, or with (iii) DFMO + ISO. DFMO was started 2 days before the initiation of ISO and both ISO and DFMO were continued until the end of the experimental period. Myocardial injury was assessed by determining the increased release of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) into the plasma, and by morphometric analysis of the lesion area in heart sections stained with Gomori trichrome.

RESULTS

ISO induced the release of CPK and LDH by 6 hr and 24 hr, respectively, and produced subendocardial necrosis, which was both acute and resolving following 8 days of ISO. DFMO treatment inhibited ISO-induced increases in (i) ODC activity and putrescine and spermidine levels in heart, (ii) CPK and LDH activity in plasma, and (iii) the area of subendocardial lesions.

CONCLUSIONS

These observations suggest that polyamines are one of the intracellular factors that contribute to ISO-mediated cardiac injury in the rat.

Modulation of the induction of ornithine decarboxylase by some opioid receptor agonists in immune cells and cardiomyocytes

The ability of natural and synthetic opioids to modulate the induction of ornithine decarboxylase (ODC) was investigated in immune cells and cardiomyocytes in culture. In particular, Leu-enkephalin, which shows preference for delta-receptors, enhanced ODC activity in both thymocytes and cardiomyocytes, whereas the effect of U-50488H, a synthetic kappa-selective agonist, was cell-specific. In thymocytes, U-50488H markedly inhibited the induction of the enzyme elicited by the mitogen concanavalin A (Con A) or by a combined treatment with PMA and A23187, and also reduced basal ODC activity. However the drug did not affect ODC induced by other stimuli. The inhibition of the induction of ODC activity was accompanied by a reduction of ODC mRNA level and an acceleration of ODC turnover. The action of U-50488H in thymocytes does not appear to be mediated by kappa or other classical opioid receptors lacking both stereospecificity and antagonist sensitivity, but may involve a pertussis toxin-sensitive G protein. Splenocytes also showed the ODC inhibiting effect of U-50488H, although they were less sensitive compared to thymocytes. In contrast, U-50488H enhanced ODC activity in cardiomyocytes and this effect was blocked by a specific kappa-antagonist. In conclusion, these results indicate that some opioid agonists can modulate ODC expression in non neural cells. In particular, kappa-opioid receptors may be involved in the U-50488H action in cardiomyocytes, and a distinct site, linked to inhibition of cell proliferation, may operate in immune cells.

Spermine inhibits proinflammatory cytokine synthesis in human mononuclear cells: a counterregulatory mechanism that restrains the immune response

The local production of proinflammatory cytokines mediates the host response to inflammation, infection, and injury, whereas an overexpression of these mediators can injure or kill the host. Recently, we identified a class of multivalent guanylhydrazone compounds that are effective inhibitors of proinflammatory cytokine synthesis in monocytes/macrophages. The structure of one such cationic molecule suggested a molecular mimicry with spermine, a ubiquitous endogenous biogenic amine that increases significantly at sites of inflammation and infection. Here, we addressed the hypothesis that spermine might counterregulate the innate immune response by downregulating the synthesis of potentially injurious cytokines. When spermine was added to cultures of human peripheral blood mononuclear cells stimulated with lipopolysaccharide (LPS), it effectively inhibited the synthesis of the proinflammatory cytokines tumor necrosis factor (TNF), interleukin-1 (IL-1), IL-6, MIP-1alpha, and MIP-1beta. The inhibition of cytokine synthesis was specific and reversible, with significant inhibition of TNF synthesis occurring even when spermine was added after LPS. The mechanism of spermine-mediated cytokine suppression was posttranscriptional and independent of polyamine oxidase activity. Local administration of spermine in vivo protected mice against the development of acute footpad inflammation induced by carrageenan. These results identify a distinct molecular counterregulatory role for spermine in downregulating the monocyte proinflammatory cytokine response.

Polyamine deprivation prevents the development of tumour-induced immune suppression

Mice grafted with the 3LL (Lewis lung) carcinoma exhibit immune suppression: spleen cells showed decreased spontaneous interleukin 2 (IL-2) production and T-CD4+ and T-CD8+ lymphocyte populations; in addition the polyamine content in the spleen was increased. By treating the mice with a polyamine-deficient diet containing neomycin, metronidazole and inhibitors of ornithine decarboxylase and polyamine oxydase, tumour growth was reduced and the immune abnormalities were reversed. The spleen cells overproduced IL-2 by reducing exogenous sources of polyamines, but total blockade of all major polyamine sources was necessary to obtain an optimal effect both on IL-2 production and on spleen polyamine content. Irrespective of whether polyamine deprivation was started at an early or at an advanced stage of tumour growth, T-lymphocyte populations were restored to normal values, demonstrating that polyamine deprivation not only prevents tumour-induced immune suppression, but reverses established immunological disorders. In contrast to what was observed regarding IL-2 production by spleen cells and natural killer (NK) cell activity, the polyamine oxidase (PAO) inhibitor did not enhance the number of T lymphocytes. These findings are consistent with a direct effect of the polyamines on immune effector cell metabolism. They suggest an important role of the gastrointestinal polyamines and of PAO activity in the regulation of IL-2 production.

Stimulation in vitro of vitamin B12-dependent methionine synthase by polyamines

Vitamin B12-dependent methionine synthase is an important enzyme for sulphur amino acid, folate polyamine metabolism, S-adenosylmethionine metabolism and also in the methylation pathway of DNA, RNA, proteins and lipids. Consequently, studies aiming at exploring the control and regulation of methionine synthase are of particular interest. Here we report the modulation of enzyme activity in vitro by polyamines. Although putrescine, cadaverine, spermine and spermidine all stimulated enzyme activity, the last two were the most potent, causing increases in enzyme activity up to 400%. The EC50 for spermine was determined as 8 microM and for spermidine 40 microM. The physiological concentration for spermine has been reported to be 15-19 microM. Spermine was found to increase both the Km and the V(max) with respect to methyltetrahydrofolate for the enzyme. These data support the hypothesis that spermine and spermidine are feedback regulators of methionine synthase both in vivo and in vitro and are consistent with the polyamines' regulating cell signalling pathways.