Inflammatory and anti-inflammatory cytokines regulate the recovery from sublethal X irradiation in rat thymus

Early inflammatory changes in radiation-induced oral mucositis : Effect of pentoxifylline in a mouse model

Purpose

Early inflammation is a major factor of mucosal reactions to radiotherapy. Pentoxifylline administration resulted in a significant amelioration of radiation-induced oral mucositis in the mouse tongue model. The underlying mechanisms may be related to the immunomodulatory properties of the drug. The present study hence focuses on the manifestation of early inflammatory changes in mouse tongue during daily fractionated irradiation and their potential modulation by pentoxifylline.

Materials and methods

Daily fractionated irradiation with 5 fractions of 3 Gy/week (days 0–4, 7–11) was given to the snouts of mice. Groups of 3 animals per day were euthanized every second day between day 0 and 14. Pentoxifylline (15 mg/kg, s. c.) was administered daily from day 5 to the day before sacrifice. The expression of the inflammatory proteins TNFα, NF-κB, and IL-1β were analysed.

Results

Fractionated irradiation increased the expression of all inflammatory markers. Pentoxifylline significantly reduced the expression of TNFα and IL-1β, but not NF-κB.

Conclusion

Early inflammation, as indicated by the expression of the inflammatory markers TNFα, NF-κB, and IL-1β, is an essential component of early radiogenic oral mucositis. Pentoxifylline differentially modulated the expression of different inflammatory markers. The mucoprotective effect of pentoxifylline does not appear to be based on modulation of NF-κB-associated inflammation.

Quantifying initial cellular events of mouse radiation lymphomagenesis and its tumor prevention in vivo by positron emission tomography and magnetic resonance imaging

Radiation-induced thymic lymphoma (RITL) in mice is induced by fractionated whole-body X-irradiation (FX) and has served as a useful model for studying radiation carcinogenesis. In this model, the initial postirradiation cellular events in the thymus and bone marrow (BM) are critically important for tumorigenesis, and BM transplantation (BMT) prevents RITL. However, direct assessment of these events is so far restricted by the lack of noninvasive monitoring techniques. Here, we have developed positron emission tomography (PET) and magnetic resonance imaging (MRI) methods to quantify the events critical for RITL development and the effects of BMT in living animals. Apparent diffusion coefficients (ADCs) were calculated from diffusion-weighted MRI to evaluate the changes in the BM of mice receiving FX. ADC values dramatically changed in the irradiated BM, corresponding to pathological findings of the irradiated BM, returning to normal levels following BMT sooner than with spontaneous recovery. PET with 4'-[methyl-(11)C]thiothymidine, a novel tracer for cell proliferation, revealed that the irradiated thymus showed significantly higher tracer uptake than the unirradiated thymus 1 week after FX. Interestingly, its increased uptake was completely abolished by BMT, even with very few donor-derived cells in the thymus. Thereafter, the thymus receiving BMT had significantly increased tracer uptake. These findings suggest that BMT first suppresses FX-induced aberrant thymocyte proliferation and then accelerates thymic regeneration. This study demonstrates the feasibility of using PET and MRI for noninvasive monitoring of tumorigenic cellular processes in an animal model of radiation-induced cancer.

HIV-1 infection inhibits cytokine production in human thymic macrophages

OBJECTIVE

The thymus serves as a critical site of T-lymphocyte ontogeny and selection. Thymic infection by HIV-1 is known to disrupt thymocyte maturation by both direct and indirect means; however, the mechanism behind these effects remains poorly defined. Macrophages represent one of the most important peripheral targets of HIV-1 infection, are resident in the thymic stroma, and play a central role in thymocyte maturation.

MATERIALS AND METHODS

Studies presented here define three primary features and outcomes of thymic macrophages (TM) and HIV-1 infection: (1) The distinctive TM phenotype (surface markers and cytokine production measured by immunofluorescence, fluorescence-activated cell sorting, and reverse transcriptase polymerase chain reaction) relative to macrophages from other sources (blood [monocyte-derived macrophages] and bone marrow); (2) infection of TM by different HIV-1 subtypes (X4, R5, and X4/R5) measured by enzyme-linked immunosorbent assay and polymerase chain reaction; and (3) consequences of HIV-1 infection on cytokine production by TM measured by reverse transcriptase polymerase chain reaction.

RESULTS

The results demonstrate that TM display a distinctive phenotype of HIV-1 receptors (CD4(lo), CXCR4(lo), CCR5(med), CCR3(hi)), chemokine production (macrophage inflammatory protein-1α(+); regulated on activation, normal T expressed and secreted(+); macrophage inflammatory protein-1b(-); stromal cell-derived factor -1(-)); and cytokine production (tumor necrosis factor-α(+), interleukin-8(+), macrophage colony-stimulating factor(+), interleukin-6(-)) relative to either monocyte-derived macrophages or bone marrow. TM were infected in vitro with R5 and X4/R5-tropic HIV-1 subtypes, and developed syncytia formation during long-term X4/R5 culture. In contrast, TM supported only transient replication of X4-tropic HIV-1. Lastly, infection of TM with HIV-1 abolished the production of all cytokines tested in long-term in vitro cultures.

CONCLUSIONS

Taken together, these results indicate that TM are a potential direct target of in situ HIV-1 infection, and that this infection may result in the disruption of macrophage functions that govern normal thymocyte maturation.

Vascular homeostasis regulators, Edn1 and Agpt2, are upregulated as a protective effect of heat-treated zinc yeast in irradiated murine bone marrow

PURPOSE

To elucidate the mechanism underlying the in vivo radioprotection activity by Zn-containing, heat-treated Saccharomyces cerevisiae yeast (Zn-yeast).

MATERIALS AND METHODS

Zn-yeast suspension was administered into C3H/He mice immediately after whole body irradiation (WBI) at 7.5 Gy. Bone marrow was extracted from the mice 6 hours after irradiation and analyzed on a microarray. Expression changes in the candidate responsive genes differentially expressed in treated mice were re-examined by qRT-PCR. The bone marrow was also examined pathologically at 6 h, 3, 7, and 14 days postirradiation.

RESULTS

Thirty-six genes, including Edn1 and Agpt2, were identified as candidate responsive genes in irradiated mouse bone marrow treated with Zn-yeast by showing a greater than three-fold change compared with control (no irradiation and no Zn-yeast) mice. The expressions of Cdkn1a, Bax, and Ccng, which are well known as radioresponsive genes, were upregulated in WBI mice and Zn-yeast treated WBI mice. Pathological examination showed the newly formed microvessels lined with endothelial cells, and small round hematopoietic cells around vessels in bone marrow matrix of mice administered with Zn-yeast after WBI, while whole-body irradiated mice developed fatty bone marrow within 2 weeks after irradiation.

CONCLUSION

This study identified a possible mechanism for the postirradiation protection conferred by Zn-yeast. The protective effect of Zn-yeast against WBI is related to maintaining the bone marrow microenvironment, including targeting endothelial cells and cytokine release.

Strategies for reconstituting and boosting T cell-based immunity following haematopoietic stem cell transplantation: pre-clinical and clinical approaches

Poor immune recovery is characteristic of bone marrow transplantation and leads to high levels of morbidity and mortality. The primary underlying cause is a compromised thymic function, resulting from age-induced atrophy and further compounded by the damaging effects of cytoablative conditioning regimes on thymic epithelial cells (TEC). Several strategies have been proposed to enhance T cell reconstitution. Some, such as the use of single biological agents, are currently being tested in clinical trials. However, a more rational approach to immune restoration will be to leverage the evolving repertoire of new technologies. Specifically, the combined targeting of TEC, thymocytes and peripheral T cells, together with the bone marrow niches, promises a more strategic clinical therapeutic platform.

Ultrastructural alterations of the cortical epithelial cells of the irradiated and recovering rat thymus

To understand the roles of cortical thymic epithelial cells (CTECs) in T-lymphocyte development, we analyzed rat thymi recovering from irradiation (6Gy), at the ultrastructural level. The morphological alterations in the CTECs were most prominent during the third to fifth day of recovery, when proliferating thymocytes were observed in the vicinity of the CTECs. The most striking finding among the alterations in the CTECs after irradiation was a cytoplasmic vacuolization with an increased amount of granular and membranous content. The granular content was observed as loosely aggregated structures or finely dispersed granules and dense bodies. The membranous content appeared in various forms including vesicular, tubular, and irregular membranous structures and myelin figures. The above features are characteristic of the hyperfunctional state of CTECs with increased secretion activities, which suggests their important roles in the repopulation and maturation of the cortical thymocytes during recovery after irradiation.

Semiquantitative Detection of Cytokine Messages in X-Irradiated and Regenerating Rat Thymus

We investigated the expression of cytokine mRNA derived from thymocytes or thymic epithelial cells in X-irradiated (8 Gy) and recovering rat thymuses, according to our previous observation (Mizutani et al., Radiat. Res. 157, 281-289, 2002). The changes in mRNA expression level of interleukin 2 (Il2), Il4, tumor necrosis factor alpha (Tnf), interferon gamma (Ifng), and transforming growth factor beta (Tgfb) were examined. The mRNA expression of Il2 and Il4 decreased from day 5 to day 14 after irradiation. Thereafter, the expression level of Il2 mRNA recovered to normal control levels; however, the expression of Il4 mRNA tended toward significantly low levels. Tnf mRNA expression decreased on day 5 after irradiation and then showed a gradual increase back to normal control levels. Tgfb mRNA expression did not change significantly. Ifng mRNA expression was transiently enhanced from day 11 to day 14. The mRNA expression levels of Il10 increased significantly from day 3 to day 7 after irradiation. In addition, the mRNA expression of thymic epithelial cell-derived Il7 showed a transient decrease on day 3; however, then it showed a continuous increase from day 5 to day 21, finally reaching twice the normal control levels after X irradiation. These observations suggest that the expression of cytokine messages in the irradiated thymus changed significantly and did not return to normal for a long time after 8 Gy irradiation.

Morphological and immunohistochemical changes to thymic epithelial cells in the irradiated and recovering rat thymus

The present study analyzed morphological and immunohistochemical changes of thymic epithelial cells in the irradiated and recovering rat thymus. Observations showed the number of thymocytes was initially severely reduced after irradiation but abruptly increased on days 3 to 5 after 6 Gy and on days 7 to 11 after 8 Gy irradiation. To analyse the mechanisms for this abrupt recovery of the thymocytes after irradiation, the expression of p63 in the normal and irradiated thymus was immunohistochemically studied as the expression of this antigen may be related to the proliferation of epithelial cells. In the fetal thymus tissue, thymic epithelial cells were the principal cell type that stained strongly positive for p63. The sporadic expression of p63 was also observed in the normal adult thymus tissue, especially in the subcapsular region. An increased number of p63- positive cells in the thymus after irradiation indicates that repair or renewal of the thymic epithelial cells may be taking place because p63 is more specific to transient amplifying thymic epithelial cells. A RT-PCR analysis of p63 expression in irradiated and regenerating thymus tissue also showed an increased expression of p63 after irradiation compared with that of the normal thymus. These results suggest that changes in the thymic microenvironment-especially in relation to the repair and renewal of thymic epithelial cells- may have an important influence on thymocyte proliferation in the normal thymus as well as in the irradiated and recovering thymus.

Expression of PAC1 receptor in rat thymus after irradiation

In the present work, PAC1-R (G-protein-coupled receptor specific for PACAP) was detected on cells in the normal thymus. Immunohistochemically PAC1-R was expressed strongly in stromal cells of the thymic medulla. Positive cells were also observed in the thymus of fetal and old adult rats. After 8 Gy irradiation to 9-week-old rats, PAC1-R expressions in the thymus decreased and almost recovered by day 21. The expression of PAC1-R mRNA was weak in the thymus and decreased further after irradiation. The expression almost recovered by day 28. Hip and hip/hop variants, which were not expressed in the normal thymus, were expressed in the thymus on days 3, 5 and 21 after irradiation. The expressions of IL-6 and IL-10 tended to increase initially after irradiation then decreased. Histologically, the thymic structures were destroyed on day 3 after irradiation and the thymus almost recovered by day 21. Thus PACAP is thought to be one of the important factors for cross-talk between cells involved in thymic regeneration.

Vanin-1-/- mice exhibit a glutathione-mediated tissue resistance to oxidative stress

Vanin-1 is an epithelial ectoenzyme with pantetheinase activity and generating the amino-thiol cysteamine through the metabolism of pantothenic acid (vitamin B(5)). Here we show that Vanin-1(-/-) mice, which lack cysteamine in tissues, exhibit resistance to oxidative injury induced by whole-body gamma-irradiation or paraquat. This protection is correlated with reduced apoptosis and inflammation and is reversed by treating mutant animals with cystamine. The better tolerance of the Vanin-1(-/-) mice is associated with an enhanced gamma-glutamylcysteine synthetase activity in liver, probably due to the absence of cysteamine and leading to elevated stores of glutathione (GSH), the most potent cellular antioxidant. Consequently, Vanin-1(-/-) mice maintain a more reducing environment in tissue after exposure to irradiation. In normal mice, we found a stress-induced biphasic expression of Vanin-1 regulated via antioxidant response elements in its promoter region. This process should finely tune the redox environment and thus change an early inflammatory process into a late tissue repair process. We propose Vanin-1 as a key molecule to regulate the GSH-dependent response to oxidative injury in tissue at the epithelial level. Therefore, Vanin/pantetheinase inhibitors could be useful for treatment of damage due to irradiation and pro-oxidant inducers.

Use of Reference Gene Expression in Rat Distal Colon after Radiation Exposure: A Caveat

Research on the effects of ionizing radiation exposure includes transcriptome studies using real-time reverse transcription polymerase chain reaction (RT-PCR). These studies require the use of a reference gene that normalizes for cDNA quantity and corrects for transcription between different samples. In this study, several criteria are reviewed that allow the choice of a reference gene. With the example of five genes selected from the widely used standard housekeeping genes, Gapd (glyceraldehyde-3-phosphate dehydrogenase), Hprt (hypoxanthine-guanine phosphoribosyl transferase), cyclophilin A, AcRP0 (acidic ribosomal protein P0) and 18S, we show that the use of a reference gene without a preliminary study is hazardous. We have shown in rat colon after a hemi-body irradiation that expression of a gene of interest, the serotonin receptor type 1F (5-HT(1F)), was either increased or unchanged, with the result depending on the reference gene used. This work has led us to propose the use of two reference genes, a ribosomal gene, 18S, and another gene with a level of expression closer to that of the gene of interest. The methodology reported here may be applied to other studies of gene expression levels to evaluate the effects of experimental treatment on the expression of potential reference genes.

Elevated interleukin-9 receptor expression and response to interleukins-9 and -7 in thymocytes during radiation-induced T-cell lymphomagenesis in B6C3F1 mice

Dysregulation of cytokine receptor expression and responsiveness to cytokines is hypothesized to play an important role in the development and expansion of preneoplastic cells or progression of neoplastic cells during the early and late stages of leukemogenesis. To determine the crucial changes in initiated cells that confer significant growth during the early stage of radiation-induced lymphomagenesis, we examined both the expression of receptors for thymus-derived cytokines and thymocyte response to cytokines before the onset of T cell lymphomas in B6C3F1 mice after split-dose irradiation. After irradiation, thymic T cell subsets underwent delayed regeneration consisting of two phases as determined by receptor expression. The first phase occurred within 1 week post-irradiation and was accompanied by transient expansion of T cell subsets strongly expressing receptor genes for IL-1, IL-2, IL-6, IL-7, IL-15, and TNF alpha. The second phase occurred 12 weeks after irradiation and was characterized by increased expression of IL-9R alpha. Thymocytes from non-irradiated control mice were unresponsive to IL-9. However, IL-9 acted synergistically with IL-7 and PHA to stimulate the proliferation of irradiated cells during the second post-irradiation phase. Moreover, these cells showed hyper-responsiveness to IL-7 or PHA alone compared to age-matched non-irradiated control thymocytes. These results suggest that the unusual expression of IL-9 receptors and/or increased responsiveness of thymocytes to cytokines are key processes in the development of radiation-induced T cell lymphomas.