Butyric acid derivative induces allospecific T cell anergy and prevents graft-versus-host disease

The gut microbiota and graft-versus-host disease

Graft-versus-host disease (GvHD) is a common complication of hematopoietic cell transplantation that negatively impacts quality of life in recipients and can be fatal. Animal experiments and human studies provide compelling evidence that the gut microbiota is associated with risk of GvHD, but the nature of this relationship remains unclear. If the gut microbiota is a driver of GvHD pathogenesis, then manipulation of the gut microbiota offers one promising avenue for preventing or treating this common condition, and antibiotic stewardship efforts in transplantation may help preserve the indigenous microbiota and modulate immune responses to benefit the host.

Altered homeostatic regulation of innate and adaptive immunity in lower gastrointestinal tract GVHD pathogenesis

Lower gastrointestinal (GI) tract graft-versus-host disease (GVHD) is the predominant cause of morbidity and mortality from GVHD after allogeneic stem cell transplantation. Recent data indicate that lower GI tract GVHD is a complicated process mediated by donor/host antigenic disparities. This process is exacerbated by significant changes to the microbiome, and innate and adaptive immune responses that are critical to the induction of disease, persistence of inflammation, and a lack of response to therapy. Here, we discuss new insights into the biology of lower GI tract GVHD and focus on intrinsic pathways and regulatory mechanisms crucial to normal intestinal function. We then describe multiple instances in which these homeostatic mechanisms are altered by donor T cells or conditioning therapy, resulting in exacerbation of GVHD. We also discuss data suggesting that some of these mechanisms produce biomarkers that could be informative as to the severity of GVHD and its response to therapy. Finally, novel therapies that might restore homeostasis in the GI tract during GVHD are highlighted.

Relative abundance of short chain and polyunsaturated fatty acids in propionic acid-induced autistic features in rat pups as potential markers in autism

Background

Fatty acids are essential dietary nutrients, and one of their important roles is providing polyunsaturated fatty acids (PUFAs) for the growth and function of nervous tissue. Short chain fatty acids (SCFAs) are a group of compounds derived from the host microbiome that were recently linked to effects on the gut, the brain, and behavior. They are therefore linked to neurodevelopmental disorders such as autism. Reduced levels of PUFAs are associated with impairments in cognitive and behavioral performance, which are particularly important during brain development. Recent studies suggest that omega -3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are involved in neurogenesis, neurotransmission, and protection from oxidative stress. Omega-3 PUFAs mediate some of these effects by antagonizing Omega-6 PUFA (arachidonic acid, AA)-induced proinflammatory prostaglandin E₂; (PGE₂) formation.

Methods

In this work, the absolute and relative concentrations of propionic (PPA), butyric and acetic acids, as well as PUFAs and their precursors (α-Linolenic and linoleic), were measured in the brain tissue of PPA-neurointoxicated rat pups (receiving 250 mg PPA/Kg body weight for 3 consecutive days) as a rodent model with persistent autistic features compared with healthy controls.

Results

The data revealed remarkably lower levels of omega6/omega3, α-Linolenic/Linoleic, α-Linolenic/EPA, α-Linolenic/DHA, EPA/DHA, and AA/Linoleic acid ratios in PPA-intoxicated rats. The role of these impaired ratios is discussed in relation to the activity of desaturases and elongases, which are the two enzymatic groups involved in the synthesis of PUFAs from their precursors. The relationship between the abnormal relative concentrations of the studied fatty acids and oxidative stress, neurotransmission, and neuroinflammation is also discussed in detail.

Conclusions

This study demonstrates that fatty acid ratios are useful for understanding the mechanism of PPA neurotoxicity in a rodent model of autism. Therefore, it is possible to use these ratios for predictions in patients with this disorder.

Butyrate in vitro immune-modulatory effects might be mediated through a proliferation-related induction of apoptosis

Survival and proliferation signals are two processes closely interrelated and finely controlled in most cell types, whose deregulation may lead to carcinogenesis. In the last decade, different studies have suggested that both cellular functions are also intimately associated with other cellular activities such as differentiation and cellular activation, especially in immune cells. The aim of this study was to evaluate the effects of the short-chain fatty acid (SCFA) butyrate on the proliferation and activation state of different cell types involved in inflammatory bowel disease. We focused on intestinal epithelial cells, macrophages and T-lymphocytes, using both primary non-transformed cultures and established cell lines. The results showed that low concentrations of butyrate inhibited the proliferation of all the immune cell types tested in this work, whereas it only induced apoptosis in activated T-lymphocytes, non-differentiated epithelial cells and macrophage cell lines, but not in differentiated epithelial cells or primary macrophages. Butyrate apoptosis induction was mediated by caspase-3/7 activation. This SCFA was only able to modify cell activation, measured as expression of inflammatory cytokines, in those cell types in which apoptosis was induced. In conclusion, our results suggest a cell type-specificity of the immune-modulatory effects of butyrate based on the proliferation/activation characteristic physiology of these processes in different cells types.

p21(Cip1) up-regulated during histone deacetylase inhibitor-induced CD4(+) T-cell anergy selectively associates with mitogen-activated protein kinases

Histone deacetylase inhibitor n-butyrate induced proliferative unresponsiveness in antigen-stimulated murine CD4(+) T cells. T cells anergized by n-butyrate demonstrated reduced interleukin-2 (IL-2) secretion and decreased activating protein 1 (AP-1) activity upon restimulation. Mechanistic studies determined that the cyclin-dependent kinase (cdk) inhibitor p21(Cip1) was up-regulated in the anergic CD4(+) T cells. p21(Cip1) is known to inhibit the cell cycle through its interaction with cdk, proliferating cell nuclear antigen (PCNA) or c-Jun N-terminal kinase (JNK). p21(Cip1) did not preferentially associate with PCNA or cdk in anergic T helper type 1 (Th1) cells. Instead, among the three interaction partners, p21(Cip1) was found to interact with phospho-JNK and phospho-c-jun selectively in the anergic CD4(+) T cells. The activity of c-jun and downstream transcription factor AP-1 were suppressed in the anergic Th1 cells. In contrast, p21(Cip1) and the two phospho-proteins were never detected concurrently in the control CD4(+) T cells. The n-butyrate-induced p21(Cip1)-mediated inhibition of JNK and c-jun represents a novel potential mechanism by which proliferative unresponsiveness was maintained in CD4(+) T cells.

Effect of a new immunosuppressant histon deacetylase (HDAC) inhibitor FR276457 in a rat cardiac transplant model

Histone deacetylase (HDAC) is a known modulator of gene transcription, and the immunosuppressive activity of HDAC inhibitors has been demonstrated in recent several reports. In this study, the HDAC inhibitor FR276457, a hydroxamic derivative, was found to have a similar inhibitory effect on all mammalian HDACs tested, but no isozyme selectivity. Both FR276457 and tacrolimus exerted an immunosuppressive effect on in vitro rat splenocyte proliferation stimulated with Concanavalin A. Next, the effect of FR276457 on allograft rejection when administered either as a monotherapy or in combination with tacrolimus was investigated in a rat heterotopic cardiac transplant model. Orally administered FR276457 prolonged the median survival times (MST) of the transplanted grafts in the vehicle group from 6 d to 17 or 21 d at doses of 20 or 40 mg/kg, respectively. Histopathological analysis showed the structures of the myocardium were not affected, but interstitial cellular infiltration could not be suppressed completely. Tacrolimus (0.032 mg/kg) prolonged allograft MST to 16 d. FR276457, when combined with tacrolimus, prevented allograft rejection at a dose lower than that of the monotherapy. The combination dose prolonged the MST in the groups treated with 10 and 20 mg/kg to >28 d, and cellular infiltration was suppressed completely. In conclusion, this study demonstrated that the oral administration of HDAC inhibitor FR276457 can prevent allograft rejection as a monotherapy, and has additive or synergistic effects when combined with tacrolimus.

T cell tolerance induced by histone deacetylase inhibitor is mediated by P21cip1

MEB [n-butyrate 2-(4-morpholinyl) ethyl butyrate hydrochloride], a histone deacetylase inhibitor and G1 blocker, has been shown to induce unresponsiveness in antigen-activated Th1 cells. MEB was tested for here for its ability to inactivate naive alloantigen-specific T cells from DBA/2 and C57BL/10 mice. Since T cells from these two strains of mice have been shown to differ in their cell cycle regulation, it we hoped that this comparison would provide information concerning the role of cycle regulatory proteins in mediating MEB-induced T cell unresponsiveness. MEB inhibited proliferation in a one-way mixed lymphocyte reaction (MLR) in which spleen cells from DBA/2 mice (H-2d) or C57BL/10 mice (H-2b) were stimulated with spleen cells from C57BL/10 or DBA/2 mice, respectively. C57BL/10 responder T cells isolated from the MEB-treated primary MLR remained unresponsive to alloantigen following restimulation in a secondary MLR that did not contain MEB. T cells from DBA/2 mice were less sensitive to MEB-induced unresponsiveness and required a longer exposure or pretreatment with IL-2 to become tolerant. In all cases responsiveness to MEB-induced tolerance in the alloantigen-stimulated T cells corresponded with the levels of the cyclin-dependent kinase inhibitor p21cip1. Additional experiments showed that T cells from p21cip1-deficient mice, unlike T cells from p21cip1 wild-type littermates, were resistant to MEB-induced tolerance. These results underscore the role of p21cip1 in mediating T cell tolerance induced by the histone deacetylase inhibitor MEB.

Histone deacetylase inhibitors induce antigen specific anergy in lymphocytes: a comparative study

Induction of immune tolerance to transplanted tissue continues to be a challenge for organ transplantation. In the present study, six widely used histone deacetylase inhibitors (HDAI), sodium butyrate (n-butyrate), Trichostatin A, Oxamflatin, Scriptaid, HDAC I and HDAC III, were examined for ability to induce antigen-specific immune anergy in cloned and naïve murine CD4(+) T cells. When first compared for their ability to inhibit histone deacetylation Trichostatin A was found to be 10 times more potent than HDAC III, Oxamflatin and Scriptaid and 10(4) times more potent than n-butyrate. When we compared ability to inhibit CD4(+) T cell proliferation in response to IL-2 stimulation, Trichostatin A was the most potent with 100% inhibition using 100 nM Trichostatin A, while 1 muM of HDAC III, Oxamflatin and Scriptaid and 1 mM of n-butyrate were required for this effect. When the tolerogenic activity of Trichostatin A, Scriptaid and n-butyrate were compared using cloned Th1 cells specific for keyhole limpet hemocyanin (KLH), all three HDAI were effective, but Trichostatin A was again the most potent. Finally, Trichostatin A (0.05 mM) was shown to induce anergy in OT-II ovalbumin-specific naïve CD4(+) T-cells. We concluded that Trichostatin A was the most potent HDAI with regard to inhibition of histone deacetylation and the ability to induce antigen-specific anergy in both cloned and naïve CD4(+) T cells. These results will guide future studies examining HDAIs for ability to induce clinical tolerance in organ transplantation.

Macrophage production of inflammatory mediators is potently inhibited by a butyric acid derivative demonstrated to inactivate antigen-stimulated T cells

The butyric acid derivative, 2-(4-morpholynl) ethyl butyrate hydrochloride (MEB), has been reported to induce antigen-specific T cell unresponsiveness and to block T cell-mediated graft-versus-host disease. As a potential therapeutic agent, it was important to determine the effects of MEB on other cells that contribute to immunopathology. Accordingly, we tested the effects of MEB on macrophage functions. MEB did not affect macrophage viability, phagocytic activity, or the activation-induced up-regulation of molecules associated with antigen presentation: MHC-II, CD86, CD40, or ICAM-1. However, MEB potently inhibited activation-induced production of inflammatory mediators, including tumor necrosis factor-alpha (TNF-alpha), IL-6, chemokine CCL2 and nitric oxide (NO). MEB inhibited the induction of NO synthase (NOS2), which is necessary for inducible NO, and inhibited nuclear translocation of NFkappaB, suggesting that MEB interferes with the signaling pathway involved in NOS2 induction. Thus, while inducing specific T cell unresponsiveness, MEB also exerts anti-inflammatory activity by acting on macrophages to suppress production of cytokines and NO.