TLR4-dependant immune response, but not hepatitis B virus reactivation, is important in radiation-induced liver disease of liver cancer radiotherapy

Current Insights into Molecular Mechanisms and Potential Biomarkers for Treating Radiation-Induced Liver Damage

Highly conformal delivery of radiation therapy (RT) has revolutionized the treatment landscape for primary and metastatic liver cancers, yet concerns persist regarding radiation-induced liver disease (RILD). Despite advancements, RILD remains a major dose-limiting factor due to the potential damage to normal liver tissues by therapeutic radiation. The toxicity to normal liver tissues is associated with a multitude of physiological and pathological consequences. RILD unfolds as multifaceted processes, intricately linking various responses, such as DNA damage, oxidative stress, inflammation, cellular senescence, fibrosis, and immune reactions, through multiple signaling pathways. The DNA damage caused by ionizing radiation (IR) is a major contributor to the pathogenesis of RILD. Moreover, current treatment options for RILD are limited, with no established biomarker for early detection. RILD diagnosis often occurs at advanced stages, highlighting the critical need for early biomarkers to adjust treatment strategies and prevent liver failure. This review provides an outline of the diverse molecular and cellular mechanisms responsible for the development of RILD and points out all of the available biomarkers for early detection with the aim of helping clinicians decide on advance treatment strategies from a single literature recourse.

Hepatitis B Virus Envelope Antigen and Hepatitis B Virus Surface Antigen Both Contribute to the Innate Immune Response During Persistent Hepatitis B Virus Infection

This study aimed to investigate the changes of toll-like receptor 4 (TLR4), proinflammatory cytokine expression, hepatitis B virus surface antigen (HBsAg), and hepatitis B virus envelope antigen (HBeAg) expression as well as innate immune cell percentages in a mouse model of persistent hepatitis B virus (HBV) infection to better understand the innate immune response. Mouse models of persistent HBV infection, HBsAg expression, and HBeAg expression were developed using high-pressure tail-vein injection of recombinant adeno-associated viruses. Enzyme-linked immunosorbent assays (ELISAs) were used to determine the serum proinflammatory cytokine levels. Immunohistochemistry and western blot assays were used to detect TLR4 expression. Flow cytometric analysis was used to assess the percentage of innate immune cells in the whole blood. Persistent HBV infection, HBsAg expression, and HBeAg expression each significantly decreased the expression of TLR4. Persistent HBV infection significantly increased the percentages of T cells and monocytes, whereas it decreased the percentage of natural killer (NK) cells. Persistent HBeAg expression also decreased the percentage of NK cells, whereas persistent HBsAg expression increased the percentage of NK cells. Both persistent HBsAg and HBeAg expression increased the percentage of monocytes. However, both persistent HBsAg and HBeAg expression decreased the percentage of T cells. HBV as well as HBsAg and HBeAg showed similar effects on the expression of TLR4 and proinflammatory cytokines as well as the percentage of monocytes. Persistent HBV infection increased the percentage of T cells and decreased the percentage of NK cells, whereas only persistent HBeAg expression contributed to a decreased percentage of NK cells.

Radiation-induced liver injury and hepatocyte senescence

Radiation-induced liver injury (RILI) is a major complication of radiotherapy during treatment for liver cancer and other upper abdominal malignant tumors that has poor pharmacological therapeutic options. A series of pathological changes can be induced by radiation. However, the underlying mechanism of RILI remains unclear. Radiation can induce cell damage via direct energy deposition or reactive free radical generation. Cellular senescence can be observed due to the DNA damage response (DDR) caused by radiation. The senescence-associated secretory phenotype (SASP) secreted from senescent cells can cause chronic inflammation and aggravate liver dysfunction for a long time. Oxidative stress further activates the signaling pathway of the inflammatory response and affects cellular metabolism. miRNAs clearly have differential expression after radiation treatment and take part in RILI development. This review aims to systematically profile the overall mechanism of RILI and the effects of radiation on hepatocyte senescence, laying foundations for the development of new therapies.

Toll-like receptor 4 and its associated proteins as prognostic factors for HCC treated by post-radiotherapy surgery

Locally advanced hepatocellular carcinoma (HCC) treated by radiotherapy (RT) may be suited for further treatment with surgery. As a critical mediator of the post-RT immune response, Toll-like receptor 4 (TLR4) and its associated proteins may serve as prognostic factors for patients with HCC treated by post-RT surgery. In the present study, a total of 20 patients with HCC treated by post-RT surgery were enrolled. Resected tumor and peritumoral liver tissues were used to construct tissue microarrays that were assessed with immunohistochemical staining for the expression levels of TLR4, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and vascular endothelial growth factor receptor 2 (VEGFR2). The overall (OS) and disease-free (DFS) survival outcomes for each patient were assessed, and the severity of radiation-induced liver diseases (RILDs) was detected. The patients with low TLR4 or TRAIL expression exhibited significantly better OS times than those with high TLR4 (P=0.003) or TRAIL (P=0.007) expression, whereas the median DFS times for patients with low VEGFR2 or TRAIL were significantly longer than those with high VEGFR2 (P=0.003) or TRAIL (P=0.008) expression. No significant differences in OS or DFS times were identified according to the expression of TLR4, VEGFR2 or TRAIL in peritumoral liver tissue, although more severe RILDs were identified in patients with the high expression of these factors in the peritumoral liver tissue post-RT (P<0.05). Therefore, the expression levels of TLR4 and its associated proteins in HCC tumors may be suitable as prognostic factors for patients with HCC treated by post-RT surgery. The inhibition of TLR4, VEGFR2 and TRAIL expression in HCC and non-tumor liver tissue may lessen the severity of RILDs and improve survival outcomes in the future.

MicroRNA-146a-5p attenuates irradiation-induced and LPS-induced hepatic stellate cell activation and hepatocyte apoptosis through inhibition of TLR4 pathway

Elevated toll-like receptor 4 (TLR4) expression is associated with a high risk of radiation-induced liver disease (RILD). MicroRNA (miR)-146a-5p is a key regulator of lipopolysaccharide (LPS)/TLR4 signaling, but its role in modulation of RILD remains unclear. Here, we found that irradiation and LPS stimulation induced TLR4 and miR-146a-5p expression in the human hepatic stellate cell (HSC) line LX2. Ectopic expression of miR-146a-5p in LX2 inhibited irradiation-induced and LPS-induced pro-inflammatory cytokine secretion and cell proliferation, and promoted cell apoptosis by down-regulating the expression levels of TLR4, interleukin-1 receptor associated kinase 1 (IRAK1), tumor necrosis factor receptor associated factor 6 (TRAF6) and phosphorylation of nuclear factor-kappa B. In addition, the culture medium from the irradiated and LPS-stimulated HSCs transfected with miR-146a-5p significantly attenuated apoptosis in irradiated hepatocytes. Overexpression of miR-146a-5p reduced α-smooth muscle actin production in irradiated and LPS-stimulated LX2 cells, which was associated with inhibition of TRAF6-mediated JNK and Smad2 phosphorylation. Knockdown of TRAF6 or IRAK1 mimicked the effects of miR-146a-5p on HSC function. Furthermore, miR-146a-5p treatment alleviated irradiation-induced and endotoxin-induced hepatic inflammatory response and fibrogenesis in mice through inhibition of the TLR4 signaling pathway. Collectively, this study reveals the anti-pro-inflammatory and anti-fibrotic effects of miR-146a-5p on liver injury, and suggests a potential application of miR-146a-5p in the therapeutic prevention of RILD.

The Combined Antitumor Effects of 125I Radioactive Particle Implantation and Cytokine-Induced Killer Cell Therapy on Xenograft Hepatocellular Carcinoma in a Mouse Model

The combination of radiotherapy and immunotherapy has shown great promise in eradicating tumors. For example, ¹²⁵I radioactive particle implantation and cytokine-induced killer cell therapies have demonstrated efficacy in treating hepatocellular carcinoma. However, the mechanism of this combination therapy remains unknown. In this study, we utilized cytokine-induced killer cells obtained from human peripheral blood mononuclear cells along with ¹²⁵I radioactive particle implantation to treat subcutaneous hepatocellular carcinoma xenograft tumors in BALB/c nude mice. The effects of combination therapy on tumor growth, tumor cell apoptosis and proliferation, animal survival, and immune indexes were then assessed. The results indicated that ¹²⁵I radioactive particle implantation combined with cytokine-induced killer cells shows a much greater antitumor therapeutic effect than either of the therapies alone when compared to control treatments. Mice treated with a combination of radiotherapy and immunotherapy displayed significantly reduced tumor growth. ¹²⁵I radioactive particle implantation upregulated the expression of major histocompatibility complex (MHC) class I chain-related gene A in hepatocellular carcinoma cells and enhanced cytokine-induced killer cell–mediated apoptosis through activation of caspase-3. Furthermore, cytokine-induced killer cells supplied immune substrates to induce a strong immune response after ¹²⁵I radioactive particle implantation therapy. In conclusion, ¹²⁵I radioactive particle implantation combined with cytokine-induced killer cell therapy significantly inhibits the growth of human hepatocellular carcinoma cells in vivo and improves animal survival times through mutual promotion of antitumor immunity, presenting a promising therapy for hepatocellular carcinoma.

A mouse radiation-induced liver disease model for stereotactic body radiation therapy validated in patients with hepatocellular carcinoma

PURPOSE

Lower radiation tolerance of the whole liver hinders dose escalations of stereotactic body radiation therapy (SBRT) in hepatocellular carcinoma (HCC) treatment. This study was conducted to define the exact doses that result in radiation-induced liver disease (RILD) as well as to determine dose constraints for the critical organs at risk (OARs) in mice; these parameters are still undefined in HCC SBRT.

METHODS

This study consisted of two phases. In the primary phase, mice treated with helical tomotherapy-based SBRT were stratified according to escalating radiation doses to the livers. The pathological differences, signs [such as mouse performance status (MPS)], and serum aspartate aminotransferase (AST)/alanine aminotransferase (ALT)/albumin levels were observed. Radiation-induced disease severities of the OARs were scored using systematic evaluation standards. In the validation phase in humans, 13 patients with HCC who had undergone radiotherapy before hepatectomy were enrolled to validate RILD pathological changes in a mouse study.

RESULTS

The evaluation criteria of the mouse liver radiotherapy-related signs were as follows: MPS ≥ 2.0 ± 0.52, AST/ALT ≥ 589.2 ± 118.5/137.4 ± 15.3 U/L, serum albumin ≤ 16.8 ± 2.29 g/L. The preliminary dose constraints of the OARs were also obtained, such as those for the liver (average dose ≤ 26.36 ± 1.71 Gy) and gastrointestinal tract (maximum dose ≤ 22.63 Gy). Mouse RILD models were able to be developed when the livers were irradiated with average doses of ≥31.76 ± 1.94 Gy (single fraction). RILD pathological changes in mice have also been validated in HCC patients.

CONCLUSIONS

Mouse RILD models could be developed with SBRT based on the dose constraints for the OARs and evaluation criteria of mouse liver radiotherapy-related signs, and the authors' results favor the study of further approaches to treat HCC with SBRT.

Activation of the JNK-c-Jun pathway in response to irradiation facilitates Fas ligand secretion in hepatoma cells and increases hepatocyte injury

Background

It is well established that some irradiated liver non-parenchymal cells secrete pro-inflammatory cytokines to facilitate the development of radiation-induced liver disease. However, little is known on whether the irradiated hepatoma cells-mediated non-irradiated hepatocyte injury occurs in HCC patients. Here, we elucidated the roles of the irradiated hepatoma cells in driving non-irradiated hepatocyte injury and its underlying mechanism.

Methods

SMMC7721 cells were cultured and divided into irradiated (4-Gy X-ray, R) and non-irradiated (NR) groups. At 24th hour after irradiation, conditioned medium (CM) from these cultures was mixed with normal culture medium in specific proportions, and termed as 7721-R-CM and 7721-NR-CM. Following incubation with these CM compound, the biological characteristics of L02 cells related to liver cell injury including viability, apoptosis and liver dysfunction indices were comparatively analyzed. Simultaneously, the levels of proliferation- and apoptosis-related cytokines in irradiated and non-irradiated SMMC7721 cells were also measured. FasL as a cytokine with significantly differential expression, was selected to clarify its effects on L02 apoptosis. Subsequently, FasL expression following irradiation was examined in SMMC7721 and other HCC cells with varying malignant potentials, as well as in HCC tissues, the related mechanism of higher expression of FasL in irradiated HCC cells was further investigated.

Results

Apoptosis and liver dysfunction indices were all significantly enhanced in L02 cells treated with 7721-R-CM, whereas viability was suppressed, compared to those with 7721-NR-CM stimulation. FasL was identified as a leading differential cytokine in the irradiated SMMC7721 cells. Higher proportion of apoptosis was also found in L02 cells following FasL incubation. A recombinant Fas-Fc protein, which blocks Fas-FasL interaction, ameliorated 7721-R-CM-induced apoptosis in L02 cells. FasL was highly expressed in a dose-dependent manner, and peaked at the 24th hour post-irradiation in different HCC cells and their culture supernatant. Meanwhile, phosphorylation levels of JNK, ERK, Akt, and p38 were all upregulated significantly in irradiated HCC cells. But, only JNK inhibition was validated to block radiation-induced FasL expression in HCC cells. c-Jun, the target transcription factor of JNK, was also activated.

Conclusion

In HCC cells, the JNK-c-Jun pathway plays an important role in mediating irradiation- induced FasL expression, which may be critical in determining non-irradiated hepatocyte injury.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0394-z) contains supplementary material, which is available to authorized users.

TLR4-dependent immune response promotes radiation-induced liver disease by changing the liver tissue interstitial microenvironment during liver cancer radiotherapy

Liver tissue interstitial fluid (TIF) a special microenvironment around liver cells, which may play a vital role in cell communication during liver injury. Moreover, toll-like receptor 4 (TLR4) is an important trigger of the immune response that may also play a role in liver injuries, including radiation-induced liver disease (RILD). Therefore, the purpose of this study was to identify the roles of the TLR4-dependent immune response and TIFs in RILD after radiation therapy (RT) for liver cancer. This study consisted of two phases, and in the primary phase, the livers of TLR4 mutant (TLR4(-)) and normal (TLR4(+)) mice were irradiated with 30 Gy. TIF was then obtained from mouse livers and assessed by cytokine array analysis 20 days after irradiation, and cytokines in the TIFs, TLR4 and RILD were analyzed. In the second or validation phase, hepatocytes were isolated from TLR4(+) or TLR4(-) mice irradiated with 8 Gy and were co-cultured with TIFs from mouse livers, apoptosis of the hepatocytes was then measured using flow cytometry. We found that severe RILD was accompanied by higher expression of granulocyte macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and vascular endothelial growth factor receptor 2(VEGFR-2) in liver TIFs, from in TLR4(+) mice compared with TLR4(-) mice (P < 0.05). In both TLR4(+) and TLR4(-) hepatocytes, apoptosis after irradiaton was increased significantly after co-culture in TIFs from TLR4(+) mice that had their livers irradiated, compared with TIFs from TLR4(-) mice that had their livers irradiated or TIFs from unirradiated mice (P < 0.05). In summary, these findings indicate that the TLR4-dependent immune response may promote RILD by enhancing the expression of GM-CSF, VEGFR-2 and TRAIL in liver TIFs.