Interaction between nitric oxide and subsets of human T lymphocytes with differences in glutathione metabolism

Mitochondrial-targeted curcumin inhibits T-cell activation via Nrf2 and inhibits graft-versus-host-disease in a mouse model

Anti-inflammatory and immune suppressive agents are required to moderate hyper-activation of lymphocytes under disease conditions or organ transplantation. However, selective disruption of mitochondrial redox has not been evaluated as a therapeutic strategy for suppression of T-cell-mediated pathologies. Using mitochondrial targeted curcumin (MitoC), we studied the effect of mitochondrial redox modulation on T-cell responses by flow cytometry, transmission electron microscopy, transcriptomics, and proteomics, and the role of Nrf2 was studied using Nrf2- /- mice. MitoC decreased mitochondrial TrxR activity, enhanced mitochondrial ROS (mROS) production, depleted mitochondrial glutathione, and suppressed activation-induced increase in mitochondrial biomass. This led to suppression of T-cell responses and metabolic reprogramming towards Treg differentiation. MitoC induced nuclear translocation and DNA binding of Nrf2, leading to upregulation of Nrf2-dependent genes and proteins. MitoC-mediated changes in mitochondrial redox and modulation of T-cell responses are abolished in Nrf2- /- mice. Restoration of mitochondrial thiols abrogated inhibition of T-cell responses. MitoC suppressed alloantigen-induced lymphoblast formation, inflammatory cytokines, morbidity, and mortality in acute graft-versus-host disease mice. Disruption of mitochondrial thiols but not mROS increase inculcates an Nrf2-dependent immune-suppressive disposition in T cells for the propitious treatment of graft-versus-host disease.

The role of declining adaptive homeostasis in ageing

Adaptive homeostasis is "the transient expansion or contraction of the homeostatic range for any given physiological parameter in response to exposure to sub-toxic, non-damaging, signalling molecules or events, or the removal or cessation of such molecules or events" (Davies, 2016). Adaptive homeostasis enables biological systems to make continuous short-term adjustments for optimal functioning despite ever-changing internal and external environments. Initiation of adaptation in response to an appropriate signal allows organisms to successfully cope with much greater, normally toxic, stresses. These short-term responses are initiated following effective signals, including hypoxia, cold shock, heat shock, oxidative stress, exercise-induced adaptation, caloric restriction, osmotic stress, mechanical stress, immune response, and even emotional stress. There is now substantial literature detailing a decline in adaptive homeostasis that, unfortunately, appears to manifest with ageing, especially in the last third of the lifespan. In this review, we present the hypothesis that one hallmark of the ageing process is a significant decline in adaptive homeostasis capacity. We discuss the mechanistic importance of diminished capacity for short-term (reversible) adaptive responses (both biochemical and signal transduction/gene expression-based) to changing internal and external conditions, for short-term survival and for lifespan and healthspan. Studies of cultured mammalian cells, worms, flies, rodents, simians, apes, and even humans, all indicate declining adaptive homeostasis as a potential contributor to age-dependent senescence, increased risk of disease, and even mortality. Emerging work points to Nrf2-Keap1 signal transduction pathway inhibitors, including Bach1 and c-Myc, both of whose tissue concentrations increase with age, as possible major causes for age-dependent loss of adaptive homeostasis.

Suppression of Human T Cell Proliferation Mediated by the Cathepsin B Inhibitor, z-FA-FMK Is Due to Oxidative Stress

The cathepsin B inhibitor, benzyloxycarbonyl-phenylalanine-alanine-fluoromethyl ketone (z-FA-FMK) readily inhibits anti-CD3-induced human T cell proliferation, whereas the analogue benzyloxycarbonyl-phenylalanine-alanine-diazomethyl ketone (z-FA-DMK) had no effect. In contrast, benzyloxycarbonyl-phenylalanine-alanine-chloromethyl ketone (z-FA-CMK) was toxic. The inhibition of T cell proliferation mediated by z-FA-FMK requires not only the FMK moiety, but also the benzyloxycarbonyl group at the N-terminal, suggesting some degree of specificity in z-FA-FMK-induced inhibition of primary T cell proliferation. We showed that z-FA-FMK treatment leads to a decrease in intracellular glutathione (GSH) with a concomitant increase in reactive oxygen species (ROS) levels in activated T cells. The inhibition of anti-CD3-induced T cell proliferation mediated by z-FA-FMK was abolished by the presence of low molecular weight thiols such as GSH, N-acetylcysteine (NAC) and L-cysteine, whereas D-cysteine which cannot be metabolised to GSH has no effect. The inhibition of anti-CD3-induced up-regulation of CD25 and CD69 expression mediated by z-FA-FMK was also attenuated in the presence of exogenous GSH. Similar to cell proliferation, GSH, NAC and L-cysteine but not D-cysteine, completely restored the processing of caspase-8 and caspase-3 to their respective subunits in z-FA-FMK-treated activated T cells. Our collective results demonstrated that the inhibition of T cell activation and proliferation mediated by z-FA-FMK is due to oxidative stress via the depletion of GSH.

Nrf2 expression and activity in human T lymphocytes: stimulation by T cell receptor activation and priming by inorganic arsenic and tert-butylhydroquinone

The transcription factor nuclear factor-erythroid 2-related-2 (Nrf2) controls cellular redox homeostasis and displays immunomodulatory properties. Nrf2 alters cytokine expression in murine T cells, but its effects in human T lymphocytes are unknown. This study investigated the expression and activity of Nrf2 in human activated CD4(+) T helper lymphocytes (Th cells) that mediate the adaptive immune response. Th cells were isolated from peripheral blood mononuclear cells and activated with antibodies against CD3 and CD28, mimicking physiologic Th cell stimulation by dendritic cells. Nrf2 is hardly detectable in unstimulated Th cells. Activation of Th cells rapidly and strongly increases the levels of Nrf2 protein by increasing NRF2 gene transcription. Th cell activation also enhances mRNA and protein levels of Nrf2 target genes encoding antioxidant enzymes. Blocking Nrf2 expression using chemical inhibitors or siRNAs prevents these gene inductions. Pretreatment with inorganic arsenic, a Nrf2 inducer that does not alter NRF2 gene expression, increases protein level and transcriptional activity of Nrf2 induced by Th cell stimulation. Inorganic arsenic enhances nuclear translocation of Nrf2, its interaction with the coactivator protein p300, and its DNA binding activity. Inhibition of Nrf2 expression abrogates the effects of inorganic arsenic on mRNA levels of antioxidant genes, but does not alter the expression of IL-2, TNF-α, interferon-γ, or IL-17 in Th cells activated in the absence or presence of the metalloid. In conclusion, this study demonstrates for the first time that stimulation of human Th cells increases transcription of the NRF2 gene and activity of the Nrf2 protein. However, modulation of Nrf2 levels does not modify the secretion of inflammatory cytokines from these T lymphocytes.

Aging-related differences in basal heat shock protein 70 levels in lymphocytes are linked to altered frequencies of lymphocyte subsets

Cell stress responses are ubiquitous in all organisms and are characterized by the induced synthesis of heat shock proteins (Hsp). Previous studies as well as recent reports by our group have consistently suggested that aging leads to an increase in the basal levels of Hsp70. Here we extend these studies by examining the differential Hsp70 response of peripheral blood lymphocyte (PBL) subsets. It is well established that with aging, one of the major changes in the T cell pool is an expansion of T cells with the memory phenotype as well as those deficient for the CD28 molecule. To determine if alterations in the frequency of T cell subsets might be responsible for the observations, we have carried out a more comprehensive flow cytometric analysis of the various phenotypes of PBL under unstimulated conditions. Cells were obtained from 10 young and 10 elderly normal subjects. The basal Hsp70 levels in the various PBL phenotypes were comparable between young and elderly subjects. However, different patterns of Hsp70 response were noticed among the PBL subtypes, which were similar in both young and elderly subjects. In particular, the memory cell phenotypes produced more Hsp70 than the naïve phenotypes. These results suggest that aging-related changes in basal Hsp70 levels in PBL are linked to the altered frequency of lymphocyte subsets and not to increases in aged lymphocytes per se. In addition, the increase in Hsp70 can be interpreted as the result of a tendency towards more pronounced cellular differentiation in aging.

The role of low molecular weight thiols in T lymphocyte proliferation and IL-2 secretion

Glutathione (GSH) is an abundant intracellular tripeptide that has been implicated as an important regulator of T cell proliferation. The effect of pharmacological regulators of GSH and other thiols on murine T cell signaling, proliferation, and intracellular thiol levels was examined. l-Buthionine-S,R-sulfoximine (BSO), an inhibitor of GSH synthesis, markedly reduced GSH levels and blocked T cell proliferation without significant effect on cell viability. N-acetylcysteine markedly enhanced T cell proliferation without affecting GSH levels. Cotreatment of T cells with N-acetylcysteine and BSO failed to restore GSH levels, but completely restored the proliferative response. Both 2-ME and l-cysteine also reversed the BSO inhibition of T cell proliferation. Intracellular l-cysteine levels were reduced with BSO treatment and restored with cotreatment with NAC or l-cysteine. However, 2-ME completely reversed the BSO inhibition of proliferation without increasing intracellular cysteine levels. Therefore, neither GSH nor cysteine is singularly critical in limiting T cell proliferation. Reducing equivalents from free thiols were required because oxidation of the thiol moiety completely abolished the effect. Furthermore, BSO did not change the expression of surface activation markers, but effectively blocked IL-2 and IL-6 secretion. Importantly, exogenous IL-2 completely overcame BSO-induced block of T cell proliferation. These results demonstrate that T cell proliferation is regulated by thiol-sensitive pathway involving IL-2.

Vitamin C supplementation influences the antioxidant response and nitric oxide handling of erythrocytes and lymphocytes to diving apnea

OBJECTIVE

We have investigated the influence of vitamin C diet supplementation on the antioxidant response and nitrite levels in lymphocytes and erythrocytes during diving apnea.

SUBJECTS

Seven male professional apnea divers participated in a double blind crossover study. Divers were randomly assigned to either vitamin C supplemented or placebo groups. The subjects did not take any other supplements than the ones provided for this study.

INTERVENTION

One group was supplemented with vitamin C capsules (1 g per day) for 7 days while the other group took a placebo composed of lactose. The usual dietary habits of participants were assessed using a self-reported 7-days 24-h recall before the day of the study. Blood samples were taken under basal conditions, immediately after diving apnea for 4 h and after 1 h of recovery.

RESULTS

Catalase activity increased in erythrocytes (23%) and superoxide dismutase increased in lymphocytes (35%) during the recovery only in the placebo group. Lymphocyte ascorbate levels increased in the supplemented group after diving (85%) and maintained high at recovery. Plasma nitrite levels increased about twofold in both groups during the recovery. Erythrocyte nitrite levels increased after diving (50%) and about twofold during the recovery in the supplemented group. Nitrite levels and iNOS levels in lymphocytes were higher in the placebo group than in the supplemented during the recovery. Erythrocyte carbonyl derivates were unchanged in all situations.

CONCLUSIONS

Vitamin C supplementation influenced the antioxidant response and NO handling in erythrocytes and lymphocytes to the oxidative stress induced by hypoxia-reoxygenation.

Different sensitivity of lamina propria T-cell subsets to nitric oxide-induced apoptosis explains immunomodulatory activity of a nitric oxide-releasing derivative of mesalamine in rodent colitis

BACKGROUND & AIMS

Uncontrolled T-cell activation plays a critical role in the pathogenesis of inflammatory bowel diseases. Therefore, pharmacological strategies directed toward restoring the normal responsiveness of the immune system could be effective in the treatment of these pathologic conditions. The addition of a nitric oxide-releasing moiety to conventional drugs, such as aspirin and other anti-inflammatory analgesic drugs, results in new chemical entities with potent immunomodulatory activities. The aim of this study was to investigate the immunomodulatory activity of a nitric oxide-releasing derivative of mesalamine (NCX-456), as compared with standard mesalamine, in 2,4,6-trinitrobenzene sulfonic acid-induced colitis in mice.

METHODS

Cells and tissues from mice with 2,4,6-trinitrobenzene sulfonic acid-induced colitis and from interleukin 10-deficient mice with spontaneous chronic colitis receiving treatment with several doses of NCX-456 or mesalamine were analyzed for morphology, cytokine production, and apoptosis.

RESULTS

NCX-456, but not mesalamine, administration resulted in a marked reduction in clinical, histological, and immunologic signs of colitis in both models. NCX-456 inhibited the release of T-helper type 1-derived cytokines and increased the release of the regulatory T cell-derived cytokines interleukin 10 and transforming growth factor beta. In vitro analyses showed that NCX-456 inhibited proliferation and caused selective apoptosis of the subset of activated lamina propria T-helper type 1 cells, whereas it was ineffective for regulatory T-cell function and survival.

CONCLUSIONS

Collectively, these data show that NCX-456 inhibits lamina propria T-helper type 1 function and stimulates the activity of interleukin 10- and transforming growth factor beta-secreting cells, thus restoring mucosal immune homeostasis and suppressing intestinal inflammation.