Prediction of portal venous pressure in living donor liver transplantation: A retrospective study.

Liver transplantation is the definitive treatment for advanced liver cirrhosis with portal hypertension. In Japan, the scarcity of deceased donors leads to reliance on living donors, often resulting in smaller grafts. Managing portal venous pressure (PVP) is critical to prevent fatal posttransplant complications. This study explored the possibility of predicting intraoperative PVP. We analyzed 475 living donor liver transplant cases from 2006 to 2023, excluding those with acute liver failure or prior splenectomy or splenic artery embolization. Patients were divided into a training group (n = 425) and a test group (n = 50). We evaluated the correlation between preoperative factors and PVP at laparotomy to predict PVP at laparotomy and closure. The predictive model was validated with the test group data. PVP at laparotomy could be predicted using correlated preoperative factors: prothrombin time ( p < 0.001), predicted splenic volume ( p < 0.001), and presence of a portosystemic shunt ( p = 0.002), as follows: predicted PVP at laparotomy (mm Hg)=25.818 - 0.077 × (prothrombin time [%]) + 0.004 × (predicted splenic volume [mL]) - 2.067 × (1: with a portosystemic shunt) ( p < 0.001; R = 0.346). In addition, PVP at closure could be predicted using correlated operative factors, including measured PVP at laparotomy, as follows: predicted PVP at closure (mm Hg)=14.268 + 0.149 × (measured PVP at laparotomy [mm Hg]) - 0.040 × (GV/SLV [%]) - 0.862 × (1: splenectomy [if yes]) - 3.511 × (1: splenic artery ligation without splenectomy [if yes]) ( p < 0.001; R = 0.339). This study demonstrated the feasibility of predicting intraoperative PVP using preoperative factors in patients with decompensated cirrhosis undergoing liver transplant. This predictive approach could refine surgical planning, potentially improving patient outcomes.

Impact of ACSL4 on the prognosis of hepatocellular carcinoma: Association with cancer-associated fibroblasts and the tumour immune microenvironment.

BACKGROUND & AIMS: Recently, the association between hepatocellular carcinoma (HCC) and ferroptosis has been the focus of much attention. The expression of long chain fatty acyl-CoA ligase 4 (ACSL4), a marker of ferroptosis, in tumour tissue is related to better prognosis in various cancers. In HCC, ACSL4 expression indicates poor prognosis and is related to high malignancy. However, the mechanism remains to be fully understood. METHODS: We retrospectively enrolled 358 patients with HCC who had undergone hepatic resection. Immunohistochemistry (IHC) for ACSL4 was performed. Factors associated with ASCL4 expression were investigated by spatial transcriptome analysis, and the relationships were investigated by IHC. The association between ACSL4 and the tumour immune microenvironment was examined in a public dataset and investigated by IHC. RESULTS: Patients were divided into ACSL4-positive (n = 72, 20.1%) and ACSL4-negative (n = 286, 79.9%) groups. ACSL4 positivity was significantly correlated with higher α-fetoprotein (p = .0180) and more histological liver fibrosis (p = .0014). In multivariate analysis, ACSL4 positivity was an independent prognostic factor (p < .0001). Spatial transcriptome analysis showed a positive correlation between ACSL4 and cancer-associated fibroblasts; this relationship was confirmed by IHC. Evaluation of a public dataset showed the correlation between ACSL4 and exhausted tumour immune microenvironment; this relationship was also confirmed by IHC. CONCLUSION: ACSL4 is a prognostic factor in HCC patients and its expression was associated with cancer-associated fibroblasts and anti-tumour immunity.

Feasibility of venous cuff using an open round ligament or inferior mesenteric vein around the hepatic vein for a left lobe graft in living-donor liver transplantation.

Living-donor liver transplantation (LDLT) is an established treatment for patients with end-stage liver disease or acute liver failure, and outflow reconstruction is considered one of the most vital techniques in LDLT. To date, many strategies have been reported to prevent outflow obstruction, which can be refractory to liver dysfunction and can cause life-threatening graft loss or mortality. In addition, in this era of laparoscopic hepatectomy in donor surgery, especially LDLT using a left liver graft, it has been predicted that cutting the hepatic vein with automatic linear staplers will lead to more outflow-related problems than with conventional open hepatectomy because of the short neck of the anastomosis orifice. We herein review 10 cases of venoplasty performed with a novel venous cuff system using a donor's round ligament around the hepatic vein in LDLT with a left lobe graft, which makes anastomosis of the hepatic vein sterically easy for postoperative venous patency.

Cancer-associated fibroblasts promote tumor cell growth via miR-493-5p in intrahepatic cholangiocarcinoma.

The association between tumor microenvironment (TME) and cancer-associated fibroblasts (CAFs) in intrahepatic cholangiocarcinoma (ICC) progression is poorly understood. This study aimed to reveal whether specific microRNAs (miRNAs) in extracellular vesicles (EVs) derived from CAFs were involved in ICC progression. Conditioned medium (CM) and EVs in the CM of CAFs and normal fibroblasts (NFs) derived from ICC specimens were used to investigate the effects on tumor cell lines. miRNA microarray assay was used to examine the miRNAs of EVs derived from CAFs and NFs in ICC, and the effects of miR-493-5p on tumor cell lines were examined. Additionally, databases were used to identify miR-493-5p targets, and the relationship between prognosis of ICC patients and cocaine- and amphetamine-regulated transcript propeptide (CARTPT), one of the targets of miR-493-5p, expression in ICC tissues was retrospectively analyzed. Compared with NF-derived CM and EVs, CAF-derived CM and EVs promoted cell lines in proliferation, scratch, migration, and invasion assays. miRNA microarray analysis revealed that miR-493-5p was significantly increased in CAF-derived EVs compared to NF-derived EVs. Tumor cell lines transfected with miR-493-5p were promoted in proliferation and scratch assays. Immunohistochemical staining was performed on 76 ICC specimens; both overall and recurrence-free survival rates were significantly worse in the CARTPT-negative group. Univariate and multivariate analyses showed that low CARTPT expression was an independent poor prognostic factor for overall and recurrence-free survival. Overall, our data suggest that CAFs in the ICC TME suppress CARTPT in tumor cells and promote tumor cells via miR-493-5p in EVs.

Clinical Significance of Signal Regulatory Protein Alpha (SIRPα) Expression in Hepatocellular Carcinoma.

BACKGROUND: Signal regulatory protein alpha (SIRPα), expressed in the macrophage membrane, inhibits phagocytosis of tumor cells via CD47/SIRPα interaction, which acts as an immune checkpoint factor in cancers. This study aimed to clarify the clinical significance of SIRPα expression in hepatocellular carcinoma (HCC). METHODS: This study analyzed SIRPα expression using RNA sequencing data of 372 HCC tissues from The Cancer Genome Atlas (TCGA) and immunohistochemical staining of our 189 HCC patient cohort. The correlation between SIRPα expression and clinicopathologic factors, patient survival, and intratumor infiltration of immune cells was investigated. RESULTS: Overall survival (OS) was significantly poorer with high SIRPα expression than with low expression in both TCGA and our cohort. High SIRPα expression correlated with lower recurrence-free survival (RFS) in our cohort. High SIRPα expression was associated with higher rates of microvascular invasion and lower serum albumin levels and correlated with greater intratumor infiltration of CD68-positive macrophages and myeloid-derived suppressor cells (MDSCs). Multivariate analysis showed that SIRPα expression and high infiltration of CD8-positive T cells and MDSCs were predictive factors for both RFS and OS. Patients with high SIRPα expression and infiltration of CD8-positive T cells and MDSCs had significantly lower RFS and OS rates. In spatial transcriptomics sequencing, SIRPα expression was significantly correlated with CD163 expression. CONCLUSIONS: High SIRPα expression in HCC indicates poor prognosis, possibly by inhibiting macrophage phagocytosis of tumor cells, promoting MDSC infiltration and inducing antitumor immunity. Treatment alternatives using SIRPα blockage should be considered in HCC as inhibiting macrophage antitumor immunity and MDSCs.

Preoperative serum brain-derived neurotrophic factor as a predictive biomarker for sepsis after living-donor liver transplantation.

AIM: Although the survival rate after living-donor liver transplantation (LDLT) is improving, sepsis still limits the prognosis. Immune dysfunction and sarcopenia are often observed in LDLT patients, and increase susceptibility to infection. Brain-derived neurotrophic factor (BDNF) is a myokine produced by immune cells and skeletal muscle. We aimed to determine whether serum BDNF could be a feasible biomarker for sepsis of LDLT patients. METHODS: We measured serum samples from 124 patients who underwent LDLT and 9 healthy volunteers for BDNF. We examined its correlation with incidence rate of sepsis. To clarify the source of BDNF, we examined its expression in lymphocytes, skeletal muscle cells, and hepatocytes. RESULTS: Patients who experienced sepsis showed worse short-term survival. Preoperative serum BDNF was lower in LDLT patients compared with healthy volunteers, and was also lower in Child-Pugh C compared with Child-Pugh A or B. Serum BDNF was inversely correlated with Model for End-Stage Liver Disease and controlling nutritional status (CONUT) scores, but had a weak positive correlation with skeletal muscle mass index (SMI). Multivariate analysis revealed that serum BDNF was independently associated with sepsis. Preoperative serum BDNF was a better predictor of sepsis in LDLT patients than CONUT score or SMI. Serum BDNF was positively correlated with lymphocyte counts, especially T cells. In vitro, T cells and skeletal muscle cells produced BDNF. CONCLUSIONS: Preoperative serum BDNF could be a predictive biomarker for sepsis after LDLT, by reflecting the systemic condition including hepatic function, nutritional status, and immune status.

Clinical association between intraoperative indocyanine green fluorescence imaging pattern, preoperative Gd-EOB-DTPA-enhanced magnetic resonance imaging findings, and histological differentiation in hepatocellular carcinoma.

AIM: We aimed to evaluate the association between the intraoperative indocyanine green (ICG) fluorescence imaging (FI) pattern, preoperative magnetic resonance imaging (MRI) findings using gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA), preoperative diffusion-weighted imaging (DWI) of MRI, and histological differentiation of hepatocellular carcinoma (HCC). METHODS: We retrospectively reviewed the data for 80 tumors of 64 patients. Intraoperative ICG FI patterns were classified into cancerous or rim-positive type. We evaluated the signal intensity ratio of the tumor and the surrounding liver tissue in the portal phase (SIRPP) and intensity in the hepatobiliary phase (HBP) of Gd-EOB-DTPA-enhanced MRI, the apparent diffusion coefficient (ADC) in the DWI of MRI, and clinicopathologic factors. RESULTS: In the rim-positive group, the rate of poorly differentiated HCC and hypointensity type in HBP were significantly higher, and SIRPP and ADC were significantly lower than the rim-negative group. In the cancerous group, the rate of well or moderately differentiated HCC and hyperintensity type in HBP, SIRPP, and ADC were significantly higher than the noncancerous group. Multivariate analysis identified low SIRPP, low ADC, and hypointensity type in HBP as the significant predictive factors for rim-positive HCC and high SIRPP, high ADC, and hyperintensity type in HBP as the significant predictive factors for cancerous HCC. The positive rate of programmed cell death 1-ligand 1 and vessels that encapsulate tumor clusters status of the rim-positive HCC and HCC with low SIRPP were significantly higher than the control group. CONCLUSIONS: The intraoperative ICG FI pattern of HCC closely correlated with histological differentiation, preoperative SIRPP and intensity type in the Gd-EOB-DTPA MRI, and preoperative ADC in the DWI of MRI.

Prediction Model with HLA-A*33:03 Reveals Number of Days to Develop Liver Cancer from Blood Test.

The development of liver cancer in patients with hepatitis B is a major problem, and several models have been reported to predict the development of liver cancer. However, no predictive model involving human genetic factors has been reported to date. For the items incorporated in the prediction model reported so far, we selected items that were significant in predicting liver carcinogenesis in Japanese patients with hepatitis B and constructed a prediction model of liver carcinogenesis by the Cox proportional hazard model with the addition of Human Leukocyte Antigen (HLA) genotypes. The model, which included four items-sex, age at the time of examination, alpha-fetoprotein level (log10AFP) and presence or absence of HLA-A*33:03-revealed an area under the receiver operating characteristic curve (AUROC) of 0.862 for HCC prediction within 1 year and an AUROC of 0.863 within 3 years. A 1000 repeated validation test resulted in a C-index of 0.75 or higher, or sensitivity of 0.70 or higher, indicating that this predictive model can distinguish those at high risk of developing liver cancer within a few years with high accuracy. The prediction model constructed in this study, which can distinguish between chronic hepatitis B patients who develop hepatocellular carcinoma (HCC) early and those who develop HCC late or not, is clinically meaningful.

Ferroptosis is induced by lenvatinib through fibroblast growth factor receptor-4 inhibition in hepatocellular carcinoma.

The tyrosine kinase inhibitor lenvatinib is used to treat advanced hepatocellular carcinoma (HCC). Ferroptosis is a type of cell death characterized by the iron-dependent accumulation of lethal lipid reactive oxygen species (ROS). Nuclear factor erythroid-derived 2-like 2 (Nrf2) protects HCC cells against ferroptosis. However, the mechanism of lenvatinib-induced cytotoxicity and the relationships between lenvatinib resistance and Nrf2 are unclear. Thus, we investigated the relationship between lenvatinib and ferroptosis and clarified the involvement of Nrf2 in lenvatinib-induced cytotoxicity. Cell viability, lipid ROS levels, and protein expression were measured using Hep3B and HuH7 cells treated with lenvatinib or erastin. We examined these variables after silencing fibroblast growth factor receptor-4 (FGFR4) or Nrf2 and overexpressing-Nrf2. We immunohistochemically evaluated FGFR4 expression in recurrent lesions after resection and clarified the relationship between FGFR4 expression and lenvatinib efficacy. Lenvatinib suppressed system Xc - (xCT) and glutathione peroxidase 4 (GPX4) expression. Inhibition of the cystine import activity of xCT and GPX4 resulted in the accumulation of lipid ROS. Silencing-FGFR4 suppressed xCT and GPX4 expression and increased lipid ROS levels. Nrf2-silenced HCC cells displayed sensitivity to lenvatinib and high lipid ROS levels. In contrast, Nrf2-overexpressing HCC cells displayed resistance to lenvatinib and low lipid ROS levels. The efficacy of lenvatinib was significantly lower in recurrent HCC lesions with low-FGFR4 expression than in those with high-FGFR4 expression. Patients with FGFR4-positive HCC displayed significantly longer progression-free survival than those with FGFR4-negative HCC. Lenvatinib induced ferroptosis by inhibiting FGFR4. Nrf2 is involved in the sensitivity of HCC to lenvatinib.

Outcomes of living-donor liver transplantation for acute-on-chronic liver failure based on newly proposed criteria in Japan.

AIM: Recently, new diagnostic criteria for acute-on-chronic liver failure (ACLF) were established in Japan. However, there is little evidence regarding the feasibility of classifying patients undergoing living-donor liver transplantation (LDLT). The aim was to re-evaluate the impact of these new diagnostic criteria on ACLF and the severity classification of patients undergoing LDLT. METHODS: We collected data of 82 recipients who underwent LDLT for liver failure between 1997 and 2020 and reviewed it retrospectively. RESULTS: Of the 82 patients with liver failure, 31 (37.8%) were diagnosed with ACLF; Grade 0 (n = 6), Grade 1 (n = 7), Grade 2 (n = 9), and Grade 3 (n = 9). There was no substantial difference in overall survival (OS) and the occurrence of postoperative complications between liver failure patients with and without ACLF. The OS after LDLT was significantly different among the four groups of ACLF patients (P = .036). Interestingly, ACLF Grade 3 patients had substantially lower OS compared to other ACLF groups even after LDLT (P = .006; 5-year OS rates, 33.3% vs. 85.9%). CONCLUSION: Proper use of the new diagnostic criteria for ACLF in Japan demonstrated that the presence and severity of ACLF, especially the presence of multiple organ failures, leads to morbidity and mortality even in an LDLT setting. Considering that the patients with ACLF Grade 3 do not have the favorable outcomes of LDLT, deceased-donor liver transplantation usage, or LDLT before reaching the severity of Grade 3 may be suitable for further research.

Donor Skeletal Muscle Quality Affects Graft Mortality After Living Donor Liver Transplantation- A Single Center, Retrospective Study.

The recipient muscle status is closely associated with postoperative poor survival in recipients of living donor liver transplantation (LDLT). However, it is uncertain whether LDLT donor muscle quality and quantity affect graft quality. Hence, we analyzed the correlation between donor muscle status and graft function. We measured the skeletal muscle mass index (SMI) and intramuscular adipose tissue content (IMAC) of 380 LDLT donors. We examined the correlation between donor SMI or IMAC and graft mortality, the occurrence rates of small-for-size graft (SFSG) syndrome, and 6-month graft survival rates. The donor SMI had no effect on the occurrence of SFSG syndrome and graft survival, while a high IMAC in both male and female donors was significantly correlated with the rate of SFSG syndrome [high vs low: (male donors) 15.8% vs. 2.5%, p = 0.0003; (female donors) 12.8% vs. 3.1%, p = 0.0234] and 6-month graft survival rates [(male donors) 87.7% vs 95.9%, p = 0.02; (female donors) 83.0% vs. 99.0%, p < 0.0001]. Multivariate analysis revealed that a high donor IMAC (HR; 5.42, CI; 2.13-13.8, p = 0.0004) was an independent risk factor for 6-month graft survival, and the donor IMAC is useful for donor selection for high-risk recipients.

The ratio of serum des-gamma-carboxy prothrombin to tumor volume as a new biomarker for early recurrence of resected hepatocellular carcinoma.

BACKGROUND: Early recurrence (ER) of hepatocellular carcinoma (HCC) (within 1 year after resection) is known to be a poor prognostic factor. The aim was to identify the risk factors associated with ER after HCC resection. METHODS: Data were analyzed retrospectively from patients who underwent primary resection for HCC from two hospitals. For cross-validation, HCC resection cases were divided into the training and testing cohort. The clinicopathological factors between the ER and non-ER groups and factors for predicting ER and prognosis after HCC resection were compared. RESULTS: Out of 173 patients in the training dataset, 33 patients had ER and the ER group showed larger tumor size, more intrahepatic metastasis (IM), and a higher ratio of serum des-gamma-carboxy prothrombin (DCP) to tumor volume (TV) (DCP/TV) than the non-ER group. Out of 203 patients in the testing dataset, 30 patients had ER and the ER group demonstrated larger tumor size, more IM, and higher serum alpha-fetoprotein, AFP/TV, DCP/TV, AFP/tumor maximum diameter (TMD), and DCP/TMD than the non-ER group. The patients were divided into high and low DCP/TV groups and high serum DCP/TV was associated with unfavorable overall survival in the training and testing dataset. Multivariate analysis confirmed that high serum DCP/TV and IM were independently associated with ER. CONCLUSION: Preoperative high serum DCP/TV may be useful for stratifying patients at risk of early HCC recurrence after curative resection.

Low syntaxin 17 expression in donor liver is associated with poor graft prognosis in recipients of living donor liver transplantation.

AIM: Liver transplantation (LT) is the only curative therapy for decompensated liver cirrhosis. For recipients of living donor LT (LDLT), restoration of liver function after transplantation is highly dependent on liver regenerative capacity, which requires large amounts of intracellular energy. Mitochondrial metabolism provides a stable supply of adenosine 5'-triphosphate (ATP) for liver regeneration. Mitophagy is a selective process in which damaged, non-functional mitochondria are degraded and replaced with new functional mitochondria. We investigated the relationship between expression of Syntaxin17 (STX17), a key protein in mitophagy regulation, in donor livers and graft survival. METHODS: We examined STX17 expression in grafts from 143 LDLT donors who underwent right lobe resection and investigated the relationship between STX17 expression and graft function. We investigated the correlations among STX17 expression, mitochondrial membrane potential and cell proliferation, using a STX17-knockdown hepatocyte cell line. RESULTS: Recipients transplanted with low STX17-expression grafts had significantly lower graft survival rates than recipients transplanted with high STX17-expression grafts (88.9% vs. 100%, p < 0.01). Multivariate analysis showed that low STX17 expression (HR: 10.7, CI: 1.29-88.0, p < 0.05) and the absence of splenectomy (HR: 6.27, CI: 1.59-24.8, p < 0.01) were independent predictive factors for small-for-size graft syndrome, which is the severe complication in LDLT. In the vitro experiments, the percentage of depolarized damaged mitochondria was increased in the STX17-knockdown hepatocyte cell line, suggesting decreased mitophagy and ATP synthesis. Cell proliferation was significantly decreased in the STX17-knockdown hepatocyte cell line. CONCLUSION: STX17 contributes to mitophagy and maintenance of mitochondrial function in hepatocytes and may be a predictor of graft dysfunction in LDLT patients.

Prognostic impact of tumor microvessels in intrahepatic cholangiocarcinoma: association with tumor-infiltrating lymphocytes.

Tumor microvessel density (MVD) is a prognostic factor for patients with intrahepatic cholangiocarcinoma (ICC). Tumor-infiltrating lymphocytes (TILs) are also key components of the tumor microenvironment that play important roles in ICC progression. This study aimed to clarify the relationships between the MVD and immune status and prognosis in patients with ICC. Immunohistochemical staining for cluster of differentiation 34 (CD34), cluster of differentiation 8 (CD8), forkhead box protein P3 (Foxp3), and programmed death-ligand 1 (PD-L1) was performed. The relationships between the MVD and clinicopathological characteristics and outcomes were analyzed. Additionally, the correlations between the MVD, CD8+ and Foxp3+ TIL counts, and PD-L1 expression were evaluated. One hundred ICC patients were classified into high (n = 50) and low (n = 50) MVD groups. The serum platelet and carbohydrate antigen 19-9 levels were higher in the low MVD group than in the high MVD group (P = 0.017 and P = 0.008, respectively). The low MVD group showed a significantly larger tumor size (P = 0.016), more frequent microvascular invasion (P = 0.001), and a higher rate of intrahepatic (P = 0.023) and lymph node (P < 0.001) metastasis than the high MVD group. Moreover, the MVD showed a high positive correlation with CD8+ TILs (r = 0.754, P < 0.001) and a negative correlation with Foxp3+ TILs (r = -0.302, P = 0.003). In contrast, no significant correlation was observed between the MVD and PD-L1 expression in cancer cells (P = 0.817). Patients with low MVDs had a significantly worse prognosis than those with high MVDs. Furthermore, multivariable analyses revealed that a low MVD influenced recurrence-free survival. A decreased intratumoral MVD might predict ICC patient outcomes. Tumor microvessels might be associated with ICC progression, possibly by altering TIL recruitment.

Lymphocyte-to-C-reactive protein ratio as a prognostic factor for hepatocellular carcinoma.

BACKGROUND: Systemic inflammation has been correlated with worse survival for some cancers. We evaluated prognostic values of various inflammatory factor combinations in patients who underwent resections for hepatocellular carcinoma (HCC). METHODS: We retrospectively analysed 306 consecutive patients with HCC who underwent curative liver resections. After assessing eight combinations of inflammatory markers for predictive value for recurrence, we focused on lymphocyte-to-C-reactive protein ratio (LCR) to elucidate its associations with recurrence-free survival (RFS) and overall survival (OS) in univariate and multivariate analyses (Cox proportional hazards model). We also used immunohistochemical CD34 and CD8 staining to investigate the mechanism of LCR elevation. RESULTS: LCR showed the highest association with RFS in HCC patients among the compared indices. High preoperative LCR correlated with a high serum albumin concentration, small tumour size, early Barcelona Clinic Liver Cancer stage and low rates of microscopic vascular invasion and microscopic intrahepatic metastasis. Higher preoperative LCR was an independent predictor of longer RFS and OS in this cohort. High LCR patients had fewer vessels encapsulating tumour clusters, and higher intratumoural CD8+ T-cell counts than low LCR patients. CONCLUSIONS: Preoperative LCR is a novel and convenient prognostic marker for patients with HCC, and is associated with the tumour microenvironment immune status.

[Immune Response on Outcomes in Hepatocellular Carcinoma].

Recently, immune checkpoint inhibitors(ICI)has been developed considerably. ICI has already been approved for malignant melanoma, lung cancer and renal cancer. We expected ICI to be taken for many cancers in the future. Therefore, the development of biomarker for them are needed. The recent large phase Ⅲ study IMbrave 150 evaluated atezolizumab plus bevacizumab vs sorafenib as the first treatment for patients with unresectable hepatocellular carcinoma(HCC). IMbrave 150 demonstrated statistically significant and clinically meaningful improvements in both OS and RFS for atezolizumab plus bevacizumab compared with sorafenib in HCC patients. A paradigm shift in the treatment of unresectable HCC is about to occur. In this article, we discussed the significance and biomarkers of tumor immunity in HCC microenvironment.