Inhibition of ornithine decarboxylase activity decreases polyamines and suppresses DNA synthesis in human colonic lamina propria lymphocytes

Re-print of "Intestinal luminal nitrogen metabolism: role of the gut microbiota and consequences for the host"

Alimentary and endogenous proteins are mixed in the small intestinal lumen with the microbiota. Although experimental evidences suggest that the intestinal microbiota is able to incorporate and degrade some of the available amino acids, it appears that the microbiota is also able to synthesize amino acids raising the view that amino acid exchange between the microbiota and host can proceed in both directions. Although the net result of such exchanges remains to be determined, it is likely that a significant part of the amino acids recovered from the alimentary proteins are used by the microbiota. In the large intestine, where the density of bacteria is much higher than in the small intestine and the transit time much longer, the residual undigested luminal proteins and peptides can be degraded in amino acids by the microbiota. These amino acids cannot be absorbed to a significant extent by the colonic epithelium, but are precursors for the synthesis of numerous metabolic end products in reactions made by the microbiota. Among these products, some like short-chain fatty acids and organic acids are energy substrates for the colonic mucosa and several peripheral tissues while others like sulfide and ammonia can affect the energy metabolism of colonic epithelial cells. More work is needed to clarify the overall effects of the intestinal microbiota on nitrogenous compound metabolism and consequences on gut and more generally host health.

Influence of breast milk polyamines on suckling rat immune system maturation

The aim of this study was to ascertain whether the supplementation of polyamines present in breast milk, i.e. spermine (SPM) and spermidine (SPD), influenced the post-natal maturation of the systemic and intestinal immune system in rats. From birth, pups daily received SPM or SPD. At 5, 11 and 18 days old, small intestine intraepithelial lymphocytes (IEL), lamina propria lymphocytes (LPL) and splenocytes were phenotypically characterized. SPM and, less evidently, SPD accelerated the maturation of CD8+ IEL, and enhanced the presence of intraepithelial NK cells and IEL related with specific immune responses on the proximal and distal small intestine, respectively. Polyamines increased the percentage of more mature CD4+ LPL and enhanced the early presence of splenic B cells and, later, that of NK cells. However, no effect on Ig-secretory function was detected. These results suggest that breast milk polyamines improve the maturation of the rat intestinal and systemic immune system.

Arginine and immunity: a unique perspective

Arginine functions in the body as a free amino acid, a component of most proteins, and the substrate for several non-protein, nitrogen-containing compounds, many of which function in immunity. Although arginine is synthesized in the body, it is not made in sufficient quantities to support growth or meet metabolic requirements during periods of stress. Based on the biochemical and physiological role of arginine in maintaining health and immunity, arginine is being added at pharmacologic concentrations to enteral formulas to boost immune function. Unfortunately, animal and human studies that investigate enteral arginine supplementation as the single variable do not show clear immunologic benefit. The inconsistent effects of arginine supplementation on immune function are due to numerous factors, such as the amount and timing of arginine supplementation, the animal species or strain of species, and the experimental model. Systematic study is required to determine whether a basal dietary intake of arginine is required to maintain immune function during health and how much arginine is required to meet metabolic requirements during periods of growth or stress.

Immunosuppressive effect of budesonide on human lamina propria lymphocytes

Budesonide, a beta-adreno-receptor agonist, is comparable to corticosteroid in the treatment of patients with inflammatory bowel disease with the advantage of minimal side effect. Although the immunomodulatory effects of budesonide on the circulatory and respiratory mucosal immune system have been reported, its effect on the human gut immune system has not been published. In this study, the effect of budesonide on the human gut immune system was compared to methyl-prednisolone. The cellular immune function was measured in-vitro by DNA synthesis, ornithine decarboxylase (ODC) activity and TNFalpha secretion. We found that both drugs have a comparable inhibitory effect on DNA synthesis, ODC activity and suppression of TNFalpha secretion. Exogenous addition of IL-2, did not restore the antiproliferative effect of both drugs. We conclude that budesonide has a comparative suppressive effect to methyl-prednisolone on the gut immune system which is not related to IL-2 secretion. The antiproliferative response may explain the therapeutic effect of budesonide on patients with inflammatory bowel disease.

Vitamin A and retinoic acids immunomodulation on human gut lymphocytes

Epidemiological studies have suggested an important immunomodulatory role for vitamin A and other related vitamin A compounds in adults and children. Although vitamin A is absorbed via the gastrointestinal tract, its affect on the gut mucosal immune cells has not been adequately investigated. We investigated the in-vitro effect of vitamin A (retinol) and its retinoid acid (RA) compounds (13-cis- and all trans-retinoic acids) on the human gut mucosal immune system as represented by colonic lamina propria lymphocyte (LPL) proliferation, and ornithine decarboxylase (ODC) activity. Results showed that retinol suppressed and trans-retinoic acid enhanced thymidine incorporation into LPL. 13-cis retinoic acid did not significantly affect LPL DNA synthesis. Similarly, retinol (0.025 microgram/ml and 10 micrograms/ml) and 13-cis retinoic acid (conc. 10 micrograms/m) suppressed, while all trans-retinoic acid (conc. 10 micrograms/ml) enhanced ODC activity in PHA-stimulated LPL. Interestingly, the effects of retinol and all trans-RA were abolished when LPL were previously depleted of macrophages. Addition of monocyte-associated lymphokines, IL-1 and IL-6, showed that IL-1 partially replaced the enhancing effect of all trans-RA previously observed on LPL thymidine incorporation. IL-6 did not affect LPL DNA synthesis irrespective of the vitamin A compound used. We conclude that retinol and retinoid acids (13-cis, all trans-) may alter the human colonic immune system possibly via IL-1 cytokine, but not via IL-6. The data suggest that vitamin A and its retinoid compounds may participate in the modulation of the gut immune system.

FK-506 and cyclosporine A (CsA) immunomodulation of the human gut mucosal immune system

FK-506 and cyclosporine A (CsA) are two immunosuppressive drugs used in the treatment of patients after liver and small intestine transplantation. A clinical advantage of FK-506 over CsA has been observed in these patients. Although the immunomodulation of both drugs has been well documented in the circulatory immune system, their effect on the mucosal immune system is not well established. In this study, the effect of FK-506 on the human gut mucosal immune system was compared to CsA. Proliferation of human colonic lamina propria lymphocytes (LPL) was measured by DNA synthesis and ornithine decarboxylase (ODC) activity. Results show that FK-506 and CsA suppress LPL DNA proliferation in a dose-dependent manner. FK-506 had a stronger antiproliferative effect compared to CsA. Moreover, the antiproliferative effect of both drugs was not dependent on monocytes or monocyte-associated factors (IL-1 beta, IL-6). In addition, exogenous addition of IL-2 did not restore the suppressive effect of either drug on LPL DNA synthesis. We conclude that: (1) both drugs have an antiproliferative effect on the human mucosal immune system; and (2) the stronger effect of FK-506 on human LPL compared to CsA may explain its superior clinical response observed in patients after liver/small intestine transplantation.

Profiling of basic amino acids and polyamines in microbial culture supernatants by electrospray mass spectrometry

As part of our efforts to investigate the biosynthesis of proferrioxamines in Erwinia amylovora, it was of interest to develop a methodology with which a large number of basic amino acids, di- and polyamines, and C- and N-hydroxy derivatives thereof could be monitored simultaneously. Towards this end, the on-line coupling of electrospray mass spectrometry with ion chromatography or reversed-phase chromatography was explored. Tandem mass spectrometry was found to be an excellent method for obtaining relevant structural information on underivatized polyamines and basic amino acid, including N-hydroxy derivatives. However, the coupling of ion chromatography with electrospray mass spectrometry for on-line extraction and separation of the underivatized compounds is hampered by compatibility problems. For most target compounds, on-line reversed-phase liquid chromatography/electrospray mass spectrometry was the method of choice but required derivatization and in this respect dansylation was preferred over benzoylation. Neither derivatization method is suitable for N-hydroxy compounds, which are base-sensitive.

Neuropeptide Y (NPY) enhances proliferation of human colonic lamina propria lymphocytes

Neuropeptide Y (NPY) is one member of a family of peptides with a wide range of physiological effects on the CNS, cardiovascular, and respiratory systems. NPY is widely distributed throughout the peripheral and central nervous systems. It has also been found within the colon, liver and gallbladder in close anatomic proximity to the mucosal immune system. In this study, we investigated the effect of NPY on human gut mucosal immune function. We examined colonic lamina propria lymphocyte (LPL) proliferation by measuring DNA synthesis, ornithine decarboxylase (ODC) activity, and polyamine biosynthesis. NPY enhanced ODC activity and polyamine biosynthesis in Con A-stimulated LPL, and enhanced thymidine incorporation into Con A-stimulated LPL but not into monocyte-depleted LPL. Moreover, exogenous IL1-beta partially restored NPY's stimulatory effect on monocyte-depleted LPL DNA synthesis. Our results demonstrate that NPY enhances human colonic LPL proliferation and that this effect is partially IL1-beta dependent. Our data also suggest that NPY's effect may be mediated via polyamine biosynthesis. We postulate that the NPY may have an important impact on human mucosal immune function.