Correction: Oweira et al. Kynurenine Is the Main Metabolite of Tryptophan Degradation by Tryptophan 2,3-Dioxygenase in HepaRG Tumor Cells. J. Clin. Med. 2022, 11, 4794

There was an error in the original publication [...].

Kynurenine Is the Main Metabolite of Tryptophan Degradation by Tryptophan 2,3-Dioxygenase in HepG2 Tumor Cells

There are two main enzymes that convert tryptophan (Trp) to kynurenine (Kyn): tryptophan-2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO). Kyn accumulation can promote immunosuppression in certain cancers. In this study, we investigated Trp degradation to Kyn by IDO and TDO in primary human hepatocytes (PHH) and tumoral HepG2 cells. To quantify Trp-degradation and Kyn-accumulation, using reversed-phase high-pressure liquid chromatography, the levels of Trp and Kyn were determined in the culture media of PHH and HepG2 cells. The role of IDO in Trp metabolism was investigated by activating IDO with IFN-γ and inhibiting IDO with 1-methyl-tryptophan (1-DL-MT). The role of TDO was investigated using one of two TDO inhibitors: 680C91 or LM10. Real-time PCR was used to measure TDO and IDO expression. Trp was degraded in both PHH and HepG2 cells, but degradation was higher in PHH cells. However, Kyn accumulation was higher in the supernatants of HepG2 cells. Stimulating IDO with IFN-γ did not significantly affect Trp degradation and Kyn accumulation, even though it strongly upregulated IDO expression. Inhibiting IDO with 1-DL-MT also had no effect on Trp degradation. In contrast, inhibiting TDO with 680C91 or LM10 significantly reduced Trp degradation. The expression of TDO but not of IDO correlated positively with Kyn accumulation in the HepG2 cell culture media. Furthermore, TDO degraded L-Trp but not D-Trp in HepG2 cells. Kyn is the main metabolite of Trp degradation by TDO in HepG2 cells. The accumulation of Kyn in HepG2 cells could be a key mechanism for tumor immune resistance. Two TDO inhibitors, 680C91 and LM10, could be useful in immunotherapy for liver cancers.

Serum Caspase-Cleaved Cytokeratin (M30) Indicates Severity of Liver Dysfunction and Predicts Liver Outcome

BACKGROUND The Model for End-Stage Liver Disease (MELD) score is a well-established tool for assessing hepatic failure. The present retrospective study investigated whether serum keratin 18 (M65) and caspase-cleaved cytokeratin (M30) were associated with liver dysfunction and post-transplant graft failure. MATERIAL AND METHODS A total of 147 patients with liver cirrhosis were categorized into 2 groups according to their baseline MELD score (group I: MELD score <20, n=87, and group II: MELD score ≥20, n=60). Serum M65 and M30 levels were measured by ELISA. RESULTS Cirrhotic patients had significantly higher serum M65 and M30 levels than healthy controls (p<0.0001). Serum M65 was correlated with the MELD score and serum bilirubin (p≤0.007) and serum M30 was correlated with the MELD score, international normalized ratio, and serum bilirubin (p≤0.001). Group II had significantly higher serum M65 and M30 levels than group I (M65, p=0.025 and M30, p<0.001). Patients who lost the allograft during the first post-transplant year had significantly higher serum M30 levels than patients with a graft survival of >1 year (p=0.004). In the regression analysis, serum M30 was associated with the MELD score (odds ratio [OR]=2.545, p=0.005), serum bilirubin (OR=2.605, p=0.005) and 1-year graft loss (OR=3.61, p=0.006). CONCLUSIONS Our data indicate that serum M30 levels reflect the degree of liver dysfunction and can predict 1-year graft loss.

Association of Graft Effluent Parameters with Donor Body Mass Index, Graft Quality, and Post-Transplant Events

Background

We evaluated whether effluent parameters prior to reperfusion correlate with post-transplant outcomes in liver transplant recipients.

Material/Methods

Concentrations of high mobility group box 1 protein (HMGB1), uncleaved cytokeratin-18 (M65), caspase-cleaved cytokeratin 18 fragment (M30), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), and alkaline phosphatase (ALP) were measured in effluent samples from 53 adult liver recipients (42 survived for 1 year and 11 did not survive).

Results

Effluent concentrations of ALP (p=0.006), AST (p=0.050), and Ca⁺⁺ (p=0.003) were higher in patients with bacteriemia in the first post-transplant year and ALP (p=0.015) was higher in patients with early graft dysfunction (EAD). Multivariate analysis of effluent parameters showed that Ca⁺⁺ >0.30 mmol/l (p=0.012, odds ratio [OR]=7.12, confidence interval [CI]=1.56–32.58), and ALP ≥27 IU/l (p=0.033, OR=5.31, CI=1.14–27.74) were significantly associated with 1-year post-transplant bacteriemia, whereas ALP ≥27 IU/l (p=0.020, OR=5.56, CI=1.32–23.46) was significantly associated with EAD. HMGB1 >54 pg/ml (p=0.008, OR=6.05, CI=1.59–23.00) was significantly associated with the donor body mass index (p=0.008, OR=6.05, CI=1.59–23.00) and fatty liver (p=0.005, OR=11.68, CI=2.10–64.01).

Conclusions

Effluent parameters are indicators of liver quality and predict the outcome of liver transplantation. High effluent Ca⁺⁺ and ALP are risk factors of post-transplant bacteriemia. In addition, high ALP is a risk factor of EAD, and high HMGB1 is an indicator of liver quality.

Association of pre- and early post-transplant serum amino acids and metabolites of amino acids and liver transplant outcome

The aim of the present study was to investigate association of serum amino (AA) acids and metabolites of AAs with post-transplant outcome in liver transplant recipients. Eighty-nine patients with end-stage liver diseases and available pre- and early post-transplant serum were characterised as patients with (GI) and without one-year mortality (GII) and patients with and without early graft dysfunction (EAD). A panel of pre- and early post-transplant serum levels of AAs and early and metabolites of tryptophan were measured using tandem mass spectrometry. Patient groups had significantly higher pre-transplant serum levels of phenylalanine, tryptophan, and tryptophan metabolites than healthy controls (for all p<0.001). Pre-transplant serum levels of all these parameters were significantly higher in GI than in GII (for all p<0.001). GI had a higher MELD score and re-transplantation number than GII (p≤0.005 for both investigations). Serum bilirubin on day 5 and serum phenylalanine on day 10 post-transplant were associated parameters of mortality, whereas day 1post-transplant phenylalanine and kynurenine and female gender were associated parameters of EAD. Our results indicate that pre- and early post-transplant levels of phenylalanine, tryptophan and metabolites of tryptophan are increased in patients and are associated with EAD and one-year mortality in liver transplant recipients.

IL-23 plasma level is strongly associated with CMV status and reactivation of CMV in renal transplant recipients

Background

Cytomegalovirus seropositivity is an independent risk factor for atherosclerosis in patients with ESRD. Donor CMV seropositivity is associated with higher graft loss. Dendritic cells, macrophages and Th17 lymphocytes are defined as producers of IL-23. IL-23 is thought to be involved in the promotion of Th17 cell polarization. Latent CMV-induced Th17 might be involved in the pathogenesis of CMV infection in patients with ESRD. We aimed to evaluate associations of Th17-dependent cytokines with ESRD, CMV status and post-transplant outcome in kidney transplantation.

Results

IL-21 plasma levels were similar in patients and healthy controls (p = 0.47), whereas IL-9 (p = 0.02) and IL-23 (p < 0.0001) levels were significantly higher in ESRD patients. CMV-seronegative (p = 0.002) and –seropositive (p < 0.001) patients had significantly higher IL-23 plasma levels than controls. CMV-seropositive patients showed excessively higher IL-23 (p < 0.001) plasma levels than CMV-seronegative patients. Patients with post-transplant CMV reactivation had higher IL-23 plasma levels than patients without CMV reactivation (p = 0.025).

Conclusions

Our results indicate that latent CMV induces IL-23. IL-23 might be an inflammatory mediator of latent CMV infection in patients with ESRD and predisposes patients for post-transplant CMV reactivation.

Early post-operative acute phase response in patients with early graft dysfunction is predictive of 6-month and 12-month mortality in liver transplant recipients

Early allograft dysfunction (EAD) after liver transplantation is mostly a reversible event caused by factors related to ischemia/reperfusion (I/R) injury. EAD represents a hepatic injury associated with pre- and early post-transplant inflammatory cytokine responses. Aim of the present study was to evaluate the prognostic and diagnostic value of CRP in liver transplant recipients with EAD.

MATERIALS AND METHODS

Forty-seven patients with EAD were compared with 115 non-EAD patients. Pre- and post-transplant parameters were analyzed. EAD was defined based on postoperative liver function tests such as INR, bilirubin and liver enzymes. Statistical analysis was performed using SPSS version 18.0.

RESULTS

Pre-transplant liver enzyme were not significantly different in the two groups. At day 3, 5 and 10 post-transplant CRP was significantly higher in patients with EAD than in non-EAD patients (p⩽0.001 for all investigations) and remained consistently high in patients with EAD and low in non-EAD patients. EAD patients with high CRP at post-transplant days 3 and 5 showed lower survival at 6-month and 12-month post-transplant than patients with low CRP.

CONCLUSION

Our results indicate a prognostic and diagnostic value of CRP in patients with early graft dysfunction and predict 6-month and 12-month mortality in liver transplant recipients.

Early pregnancy serum neopterin concentrations predict spontaneous preterm birth in asymptomatic pregnant women

OBJECTIVE

To investigate if early pregnancy serum neopterin concentrations (EPSN) could predict spontaneous preterm birth (SPB).

METHODS

EPSN was measured in 92 sera collected from 46 pregnant women with birth at term and 40 sera from 20 pregnant women with preterm birth. Two sera were collected for each case: in the first and early second trimester.

RESULTS

EPSN concentrations correlate with gestational age (ρ=0.275, P=0.001), a correlation which was present in both groups: term and preterm birth. EPSN were higher in pregnancies with SPB compared with normal pregnancies (6.27±1.03 vs. 6.04±0.15, P=0.039). Patients with SPB showed a considerable increase of EPSN in the second trimester compared with patients with birth at term (7.30±1.53 vs. 6.16±0.23, P=0.043). A sharper increase was found in the group with SPB before 32 weeks of pregnancy (wp) (9.83±4.36 vs. 6.16±0.23, P=0.016). Pregnant women with an early second trimester serum neopterin value of above 8 nmol/L are associated with a risk of SPB before 32 wp (odds ratio=14.4, P=0.01) and of SPB before 34 wp (odds ratio=3.6, P=0.05), respectively.

CONCLUSIONS

EPSN increases with the gestational age and predicts SPB in asymptomatic pregnant women.

Association of low serum TGF-β level in hantavirus infected patients with severe disease

Background

Hantaviruses are emerging zoonotic pathogens which cause hemorrhagic fever with renal syndrome, an immune-mediated pathogenesis is discussed. The aim of the present study was to investigate the role of TGF-β expression in acute hantavirus infection.

Results

We retrospectively studied 77 patients hospitalised with acute Puumala infection during a hantavirus epidemic in Germany in 2012. Hantavirus infection was confirmed by positive anti-Puumala hantavirus IgG and IgM. Plasma levels of transforming growth factor (TGF)-β1 and TGF-β2 were analysed. Based on glomerular filtration rate on admission, patients were divided in mild and severe course of disease. Puumala virus RNA was detected by PCR amplification of the viral L segment gene. Out of 77 Puumala virus infected patients, 52 (68%) were male. A seasonal distribution was detected in our cohort with a peak in summer 2012, the highest incidence was observed in the age group of 30–39 years. Puumala virus RNA was detectable in 4/77 cases. Patients with severe disease had a significant longer hospital stay than patients with mild disease (6.2 vs 3.6 days). Thrombocyte count (186 vs 225 per nl), serum TGF-β1 (74 vs 118 ng/l) and TGF-β2 (479 vs 586 pg/l) were significantly lower in severe compared to mild disease. However, C-reactive protein (CRP) was significantly higher in patients with severe disease (62 vs 40 mg/l). TGF-β1/Cr was the most sensitive and specific marker associated with renal dysfunction.

Conclusion

High serum CRP and low serum TGF-β in the early phase of hantavirus infection is associated with a severe course of disease. Our results support the hypothesis of an immune-mediated pathogenesis in hantavirus infection.

Strong association of phenylalanine and tryptophan metabolites with activated cytomegalovirus infection in kidney transplant recipients

Infection-induced inflammation triggers catabolism of proteins and amino acids. Phenylalanine and tryptophan are 2 amino acids related to infections that regulate immune responses. Polyomavirus BK (BKV) and cytomegalovirus (CMV) are important pathogens after kidney transplantation. We investigated the clinical relevance of phenylalanine, tryptophan, and tryptophan metabolites (kynurenine and quinolinic acid) plasma levels in kidney transplant recipients with active CMV (BKV(-)CMV(+), n = 12) or BK virus infection (BKV(+)CMV(-), n = 37). Recipients without active viral infections (CMV(-)BKV(-), n = 28) and CMV(-)BKV(-) healthy individuals (HCs, n = 50) served as controls. In contrast to BKV infection, activated CMV infection is tightly linked to increased phenylalanine and tryptophan metabolite plasma levels (p ≤ 0.002). The association of phenylalanine (cutoff 50 μmol/L) with CMV infection demonstrates high sensitivity (100%) and specificity (94%). By contrast, kynurenine (p = 0.029) and quinolinic acid (p = 0.003) values reflect the severity of CMV infection. In this early proof-of-concept trial, evidence indicates that activated CMV infection is strongly associated with increased phenylalanine as well as kynurenine and quinolinic acid plasma levels. Moreover, tryptophan metabolite levels correlate with disease severity. Measurement of these amino acids is an inexpensive and fast method expected to complete conventional diagnostic assays.

Function of the tryptophan metabolite, L-kynurenine, in human corneal endothelial cells

PURPOSE

Penetrating keratoplasty has been the mainstay for the treatment of blindness and is the most common form of tissue transplantation worldwide. Due to significant rates of rejection, treatment of immunological transplant reactions is of wide interest. Recently in a mouse model, the overexpression of indoeleamine 2,3 dioxigenase (IDO) was led to an extension in corneal allograft survival. L-kynurenine is a tryptophan metabolite, which may render activated T-cells apoptotic and therefore might modulate an allogenous transplant reaction. The function of L-kynurenine in the human cornea remains unclear. We analyzed the expression levels of IDO in human corneal endothelial cells (HCECs) and downstream tryptophan/kynurenine mechanisms in cell culture.

METHODS

An immunological activation profile was determined in proliferation assays of monocytes from healthy donors. Reversed-phase high pressure liquid chromatography (HPLC), western blot, real time polymerase chain reaction (PCR), and microarray analyses were used. The expression of IDO and immunological infiltration of rejected human corneal allografts (n=12) were analyzed by immunohistochemistry.

RESULTS

We found IDO and an associated tryptophan/kynurenine transporter protein exchange mechanism upregulated by inflammatory cytokines in HCECs. The inhibition of T-cell proliferation might depend on rapid delivery of the tryptophan metabolite, L-kynurenine, to the local corneal environment. Microarray analysis gives evidence that the large amino acid transporter 1 (LAT1) transporter protein is responsible for this mechanism.

CONCLUSIONS

Our data support that adequate levels of functional L-kynurenine might contribute to the maintenance of a relative immune privilege in the ocular anterior chamber, thereby contributing to the preservation of corneal allogeneic cells.