Irradiation induces a biphasic expression of pro-inflammatory cytokines in the lung

BACKGROUND AND PURPOSE

The precise pathophysiological mechanisms of radiation-induced lung injury are poorly understood, but have been shown to correlate with dysregulation of different cytokines. The purpose of this study was to evaluate the time course of the pro-inflammatory cytokines tumor necrosis factor-(TNF-)alpha, interleukin-(IL-)1alpha and IL-6 after whole-lung irradiation.

MATERIAL AND METHODS

The thoraces of C57BL/6J mice were irradiated with 12 Gy. Treated and control mice were sacrificed at 0.5, 1, 3, 6, 12, 24, 48, 72 h, 1, 2, 4, 8, 16, and 24 weeks post irradiation (p. i.). Real-time multiplex RT-PCR (reverse transcriptase polmyerase chain reaction) was established to evaluate the expression of TNF-alpha, IL-1alpha and IL-6 in the lung tissue of the mice. For histological analysis, lung tissue sections were stained by hematoxylin and eosin.

RESULTS

Multiplex RT-PCR analysis revealed a biphasic expression of these pro-inflammatory cytokines in the lung tissue after irradiation. After an initial increase at 1 h p. i. for TNF-alpha and at 6 h p. i. for IL-1alpha and IL-6, the mRNA expression of these pro-inflammatory cytokines returned to basal levels (48 h, 72 h, 1 week, 2 weeks p. i.). During the pneumonic phase, TNF-alpha, IL-1alpha and IL-6 were significantly elevated and revealed their maximum at 8 weeks p. i. Histopathologic evaluation of the lung sections obtained within 4 weeks p. i. revealed only minor lung damage in 5-30% of the lung tissue. By contrast, at 8, 16, and 24 weeks p. i., 70-90% of the lung tissue revealed histopathologically detectable organizing alveolitis.

CONCLUSION

Irradiation induces a biphasic expression of pro-inflammatory cytokines in the lung. The initial transitory cytokine response occurred within the first hours after lung irradiation with no detectable histopathologic alterations. The second, more persistent cytokine elevation coincided with the onset of histologically discernible organizing acute pneumonitis.

The bronchiolar epithelium as a prominent source of pro-inflammatory cytokines after lung irradiation

PURPOSE

To study in detail the temporal and spatial release of the pro-inflammatory cytokines tumor necrosis factor alpha, interleukin (IL)-1alpha, and IL-6 in the lung tissue of C57BL/6 mice after thoracic irradiation with 12 Gy.

METHODS AND MATERIALS

C57BL/6J mice were exposed to either sham irradiation or a single fraction of 12 Gy delivered to the thorax. Treated and sham-irradiated control mice were killed at 0.5 h, 1 h, 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, 1 week, 2 weeks, 4 weeks, 8 weeks, 16 weeks, and 24 weeks post-irradiation (p.i.). Real-time multiplex reverse transcriptase polymerase chain reaction was established to evaluate the relative messenger RNA (mRNA) expression of TNF-alpha, IL-1alpha, and IL-6 in the lung tissue of the mice (compared with nonirradiated lung tissue). Immunohistochemical detection methods (alkaline phosphatase anti-alkaline phosphatase, avidin-biotin-complex [ABC]) and automated image analysis were used to quantify the protein expression of TNF-alpha, IL-1alpha, and IL-6 in the lung tissue (percentage of the positively stained area).

RESULTS

Radiation-induced release of the pro-inflammatory cytokines TNF-alpha, IL-1alpha, and IL-6 in the lung tissue was detectable within the first hours after thoracic irradiation. We observed statistically significant up-regulations for TNF-alpha at 1 h p.i. on mRNA (4.99 +/- 1.60) and at 6 h p.i. on protein level (7.23% +/- 1.67%), for IL-1alpha at 6 h p.i. on mRNA (11.03 +/- 0.77) and at 12 h p.i. on protein level (27.58% +/- 11.06%), for IL-6 at 6 h p.i. on mRNA (6.0 +/- 3.76) and at 12 h p.i. on protein level (7.12% +/- 1.93%). With immunohistochemistry, we could clearly demonstrate that the bronchiolar epithelium is the most prominent source of these inflammatory cytokines in the first hours after lung irradiation. During the stage of acute pneumonitis, the bronchiolar epithelium, as well as inflammatory cells in the lung interstitium, produced high amounts of TNF-alpha (with the maximal value at 4 weeks p.i.: 9.47% +/- 1.78%), IL-1alpha (with the peak value at 8 weeks p.i.: 14.76% +/- 7.77%), and IL-6 (with the peak value at 8 weeks p.i.: 4.28% +/- 1.33%).

CONCLUSIONS

In the present study we have clearly demonstrated the immediate expression of the pro-inflammatory cytokines TNF-alpha, IL-1alpha, and IL-6 in the bronchiolar epithelium in the first hours after lung irradiation. A second, long-lasting release of these cytokines by the bronchiolar and alveolar epithelium, as well as by inflammatory cells, was observed at the onset of acute pneumonitis. Therefore, we postulate that lung irradiation causes immediate epithelial reaction, with the bronchiolar epithelium becoming a significant source of pro-inflammatory cytokines capable of promoting inflammation through recruitment and activation of inflammatory cells.

Increased expression of pro-inflammatory cytokines as a cause of lung toxicity after combined treatment with gemcitabine and thoracic irradiation

BACKGROUND AND PURPOSE

Preclinical evidence suggesting gemcitabine potentiates the anti-tumor effects of irradiation has resulted in clinical trials to evaluate the treatment efficacy of gemcitabine and concurrent thoracic irradiation in non-small-cell lung cancer (NSCLC). Although these studies demonstrated favorable tumor response, this combined treatment modality was accompanied by severe treatment-related toxicities predominantly of the lung. In an attempt to elucidate the determinants of lung toxicity for gemcitabine, we analyzed the expression of the pro-inflammatory cytokines TNF-alpha, IL-1alpha and IL-6 in the lung tissue of mice treated with gemcitabine and concurrent thoracic irradiation.

MATERIALS AND METHODS

Four study groups were defined: C57BL/6J mice that received neither irradiation nor gemcitabine (NT-group), those that received gemcitabine (120 mg/kg intraperitoneal, i.p.) but no irradiation (GEM-group), those that underwent thoracic irradiation (12 Gy) without gemcitabine (XRT-group), and those that received both gemcitabine (120 mg/kg i.p., 2 h before irradiation) and thoracic irradiation (GEM/XRT-group). The mice were sacrificed at 1 h, 1 and 3 days, 1, 2 and 4 weeks post-treatment (p.t.). The mRNA expression of TNF-alpha, IL-1alpha and IL-6 in the lung tissue was quantified by competitive RT-PCR. The cellular origin of the cytokine expression was identified by immunohistochemistry. The cytokine expression was correlated with histopathological alterations.

RESULTS

The TNF-alpha, IL-1alpha and IL-6 expression in the lung tissue of the GEM/XRT mice was clearly higher at all assessment time points compared to the NT mice (statistically significant at 1 h, 1 and 3 days, 1, 2 and 4 weeks p.t.), XRT mice (statistically significant at 1 week p.t.) or GEM mice (statistically significant at 1 h, 1 and 2 weeks p.t.). Maximal treatment-induced cytokine expression in the lung tissue of the GEM/XRT mice occurred already at 1 week p.t. (TNF-alpha: 30.9 +/- 5.3/IL-1alpha: 28.3 +/- 5.0/IL-6: 4.9 +/- 0.1 times basal level), and coincides with pathohistologically discernable interstitial pneumonitis. The elevated levels of TNF-alpha and IL-1alpha have been found to correlate with immunohistochemical staining of the bronchiolar epithelium and predominantly of inflammatory cells.

CONCLUSIONS

Our data provide evidence that the increased expression of pro-inflammatory cytokines and the induction of a cytokine-triggered inflammatory response may be a determinant of the observed elevated lung toxicity after concurrent treatment with gemcitabine and thoracic irradiation.

Inhibition of induced chemoresistance by cotreatment with (E)-5-(2-bromovinyl)-2'-deoxyuridine (RP101)

Induced chemoresistance leads to the reduction of apoptotic responses. Although several drugs are in development that circumvent or decrease existing chemoresistance, none has the potential to prevent or reduce its induction. Here, we present data from a drug that could perhaps fill this gap. Cotreatment of chemotherapy with (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU, RP101) prevented the decrease of apoptotic effects during the course of chemotherapy and reduced nonspecific toxicity. Amplification of chemoresistance genes (Mdr1 and Dhfr) and overexpression of gene products involved in proliferation (DDX1) or DNA repair (UBE2N and APEX) were inhibited, whereas activity of NAD(P)H: quinone oxidoreductase 1 (NQO1) was enhanced. During recovery, when treatment was with BVDU only, microfilamental proteins were up-regulated, and proteins involved in ATP generation or cell survival (STAT3 and JUN-D) were down-regulated. That way, in three different rat tumor models, the antitumor efficiency of chemotherapy was optimized, and toxic side effects were reduced. Because of these beneficial properties of BVDU, a clinical pilot Phase I/II study with five human tumor entities has been started at the University of Dresden (Dresden, Germany). So far, no unwanted side effects have been observed.

Ewing's sarcoma and peripheral primitive neuroectodermal tumor cells produce large quantities of bioactive tumor necrosis factor-alpha (TNF-alpha) after radiation exposure

PURPOSE

In the present study, we examined human Ewing's sarcoma (ES) and peripheral primitive neuroectodermal tumor (pPNET) cell lines that are able to produce TNF-alpha as part of the response to irradiation. Radiation-induced tumor cell production of TNF-alpha may enhance irradiation efficacy and improve the effect of local tumor irradiation. On the other hand, radiation-induced tumor cell production of TNF-alpha may adversely affect the normal tissue.

METHODS AND MATERIALS

Twelve different ES/pPNET cell lines were investigated in vitro and (after establishment as tumor xenografts in athymic nude mice) in vivo for their TNF-alpha mRNA expression (real-time quantitative reverse transcriptase polymerase chain reaction) and TNF-alpha protein production (in vitro: enhanced amplified sensitivity immunoassay; in vivo: immunohistochemistry) after exposure to different irradiation doses (2, 5, 10, 20, 30, or 40 Gy) and after different time intervals (1, 3, 6, 12, 24, 48, or 72 h after irradiation). The bioactivity of the TNF-alpha protein was evaluated in chromogenic cytotoxicity and neutralization assays.

RESULTS

Nine out of 12 ES/pPNET cell lines express constitutively significant quantities of bioactive TNF-alpha in vitro. ES/pPNET cells originating from primary tumors secreted higher TNF-alpha levels than cells derived from metastatic lesions. In 5 of the 9 TNF-alpha-producing cell lines, TNF-alpha mRNA and protein levels were upregulated after irradiation exposure in a time- and dose-dependent manner. After establishment of the ES/pPNET cell lines in athymic nude mice, the radiation-induced TNF-alpha release could be demonstrated also in the xenograft tumors in vivo (analogous to the in vitro experiments). Using the same methods for quantitative analysis, it was determined that the TNF-alpha expression of the radiation-responsive tumor cells was up to 2000-fold higher compared to the maximal radiation-induced TNF-alpha release in normal lung tissue measured during the pneumonic phase.

CONCLUSION

Certain ES/pPNET cell lines produce extremely large quantities of bioactive TNF-alpha after radiation exposure in a time- and dose-dependent manner. Radiation-induced TNF-alpha production of tumor cells may be of paramount importance in respect to not only tumor behavior, but also to potential damage to normal tissue and the clinical status of the host.

Modulation of radiation-induced tumour necrosis factor α (TNF-α) expression in the lung tissue by pentoxifylline

PURPOSE

The lung is the major dose-limiting organ for radiotherapy of cancer in the thoracic region. Immediate cellular damage after irradiation is supposed to result in cytokine-mediated multicellular interactions with induction and progression of inflammatory and fibrotic tissue reactions. Pentoxifylline (PTX) down-regulates the production of proinflammatory cytokines, particularly TNF-alpha, in response to noxious stimuli and may therefore provide protection against radiation-induced, cytokine-mediated cellular damage. The purpose of this study was to investigate the temporal and spatial release of TNF-alpha in the lung tissue after thoracic irradiation with 12Gy. In addition, we evaluated the ability of PTX to reduce the radiation-induced TNF-alpha release in this animal model of thoracic irradiation.

MATERIALS AND METHODS

C57BL/6J mice were exposed to either sham irradiation or single fraction of 12Gy delivered to the thorax. Four study groups were defined: those that received neither irradiation nor PTX (NT group), those that received PTX but no irradiation (PTX group), those that underwent irradiation without PTX (XRT group) and those that received both PTX and irradiation (PTX/XRT group). Treated and sham-irradiated mice were sacrificed corresponding to the latent period and the pneumonic phase. The TNF-alpha mRNA expression in the lung tissue was quantified by 'real-time' quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Immunohistochemical detection methods (alkaline phosphatase anti-alkaline phosphatase (APAAP)) and automated image analysis were used for objective quantification of TNF-alpha protein expression.

RESULTS

Following thoracic irradiation with a single dose of 12Gy (XRT group), radiation-induced TNF-alpha mRNA release in the lung tissue was significantly increased during the acute phase of pneumonitis (P<0.05). The elevated levels of TNF-alpha mRNA during the pneumonic phase correlate with a significant increase of positive inflammatory cells, predominantly macrophages, in the lung parenchyma (P<0.05). In contrast to the radiation-only group (XRT-group), the lung tissue of the PTX-treated mice (PTX/XRT group) revealed only a minor radiation-mediated TNF-alpha response on mRNA and protein level.

CONCLUSIONS

This study demonstrates a significant radiation-induced increase of TNF-alpha (on mRNA and protein level) in the lung tissue during the pneumonic phase. The predominant localisation of TNF-alpha in areas of inflammatory cell infiltrates suggests involvement of this cytokine in the pathogenesis of radiation-induced lung injury. In addition, we observed a pronounced reduction of the TNF-alpha mRNA and protein production in the study group that received both PTX and radiation (PTX/XRT group) as compared to the radiation-only group (XRT group). Therefore our results indicate that PTX down-regulates the TNF-alpha mRNA and protein production in the lung tissue in response to radiation.