Stem cell factor attenuates liver damage in a murine model of acetaminophen-induced hepatic injury

Pre-diagnostic plasma inflammatory proteins and risk of hepatocellular carcinoma in three population-based cohort studies from the United States and the United Kingdom

Previous studies suggest a role for inflammation in hepatocarcinogenesis. However, no study has comprehensively evaluated associations between circulating inflammatory proteins and risk of hepatocellular carcinoma (HCC) among the general population. We conducted a nested case-control study in the Nurses' Health Study (NHS) and the Health Professionals Follow-up Study (HPFS) with 56 pairs of incident HCC cases and controls. External validation was performed in the UK Biobank (34 HCC cases and 48,471 non-HCC controls). Inflammatory protein levels were measured in pre-diagnostic plasma using the Olink® Inflammation Panel. We used conditional logistic regression to calculate multivariable odds ratios (ORs) with 95% confidence intervals (CIs) for associations between a 1-standard deviation (SD) increase in biomarker levels and HCC risk, considering a statistically significant threshold of false discovery rate (FDR)-adjusted p < .05. In the NHS/HPFS, among 70 analyzed proteins with call rates >80%, 15 proteins had significant associations with HCC risk (pFDR < .05). Two proteins (stem cell factor, OR per SD = 0.31, 95% CI = 0.16-0.58; tumor necrosis factor superfamily member 12, OR per SD = 0.51, 95% CI = 0.31-0.85) were inversely associated whereas 13 proteins were positively associated with risk of HCC; positive ORs per SD ranged from 1.73 for interleukin (IL)-10 to 2.35 for C-C motif chemokine-19. A total of 11 proteins were further replicated in the UK Biobank. Seven of the eight selected positively associated proteins also showed positive associations with HCC risk by enzyme-linked immunosorbent assay, with ORs ranging from 1.56 for IL-10 to 2.72 for hepatocyte growth factor. More studies are warranted to further investigate the roles of these observed inflammatory proteins in HCC etiology, early detection, risk stratification, and disease treatment.

Unlocking the regenerative key: Targeting stem cell factors for bone renewal

Stem cell factors (SCFs) are pivotal factors existing in both soluble and membrane-bound forms, expressed by endothelial cells (ECs) and fibroblasts throughout the body. These factors enhance cell growth, viability, and migration in multipotent cell lineages. The preferential expression of SCF by arteriolar ECs indicates that arterioles create a unique microenvironment tailored to hematopoietic stem cells (HSCs). Insufficiency of SCF within bone marrow (BM)-derived adipose tissue results in decreased their overall cellularity, affecting HSCs and their immediate progenitors critical for generating diverse blood cells and maintaining the hematopoietic microenvironment. SCF deficiency disrupts BM function, impacting the production and differentiation of HSCs. Additionally, deleting SCF from adipocytes reduces lipogenesis, highlighting the crucial role of SCF/c-kit signaling in controlling lipid accumulation. This review elucidates the sources, roles, mechanisms, and molecular strategies of SCF in bone renewal, offering a comprehensive overview of recent advancements, challenges, and future directions for leveraging SCF as a key agent in regenerative medicine.

Association between Immunologic Markers and Cirrhosis in Individuals from a Prospective Chronic Hepatitis C Cohort

Background: Chronic hepatitis C virus (HCV) infection can affect immune response and inflammatory pathways, leading to severe liver diseases such as cirrhosis and hepatocellular carcinoma (HCC). Methods: In a prospective cohort of chronically HCV-infected individuals, we sampled 68 individuals who developed cirrhosis, 91 controls who did not develop cirrhosis, and 94 individuals who developed HCC. Unconditional odds ratios (ORs) from polytomous logistic regression models and canonical discriminant analyses (CDAs) were used to compare categorical (C) baseline plasma levels for 102 markers in individuals who developed cirrhosis vs. controls and those who developed HCC vs. cirrhosis. Leave-one-out cross validation was used to produce receiver operating characteristic curves to assess predictive ability of markers. Lastly, biological pathways were assessed in association with cirrhotic development compared to controls. Results: After multivariable adjustment, DEFA-1 (OR: C2v.C1 = 7.73; p < 0.0001), ITGAM (OR: C2v.C1 = 4.03; p = 0.0002), SCF (OR: C4v.C1 = 0.19; p-trend = 0.0001), and CCL11 (OR: C4v.C1 = 0.31; p-trend= 0.002) were all associated with development of cirrhosis compared to controls; these markers, together with clinical/demographics variables, improved prediction of cirrhosis from 55.7% (in clinical/demographic-only model) to 74.9% accuracy. A twelve-marker model based on CDA results further increased prediction of cirrhosis to 88.0%. While six biological pathways were found to be associated with cirrhosis, cell adhesion was the only pathway associated with cirrhosis after Bonferroni correction. In contrast to cirrhosis, DEFA-1 and ITGAM levels were inversely associated with HCC risk. Conclusions: Pending validation, these findings highlight the important role of immunological markers in predicting HCV-related cirrhosis even 11 years post-enrollment.

Liver Regeneration after Acetaminophen Hepatotoxicity: Mechanisms and Therapeutic Opportunities

Acetaminophen (N-acetyl-para-aminophenol; APAP) overdose is the most common cause of acute liver failure in the Western world, with limited treatment opportunities. For years, research on APAP overdose has been focused on investigating the mechanisms of hepatotoxicity, with limited success in advancing therapeutic strategies. Acute liver injury after any insult, including APAP overdose, is followed by compensatory liver regeneration, which promotes recovery and is a crucial determinant of the final outcome. Liver regeneration after APAP-induced liver injury is dose dependent and impaired after severe APAP overdose. Although robust regenerative response is associated with spontaneous recovery and survival, impaired regeneration results in faster progression of injury and death after APAP overdose. APAP hepatotoxicity-induced liver regeneration involves a complex time- and dose-dependent interplay of several signaling mediators, including growth factors, cytokines, angiogenic factors, and other mitogenic pathways. Compared with the liver injury, which is established before most patients seek medical attention and has proved difficult to manipulate, liver regeneration can be potentially modulated even in late-stage APAP-induced acute liver failure. Despite recent efforts to study the mechanisms of liver regeneration after APAP-induced liver injury, more comprehensive research in this area is required, especially regarding factors that contribute to impaired regenerative response, to develop novel regenerative therapies for APAP-induced acute liver failure.

Effects of Stem Cell Factor on Cell Homing During Functional Pulp Regeneration in Human Immature Teeth

Conventional root canal treatment in immature permanent teeth can lead to early tooth loss in children because root formation is discontinued. We investigated whether the stem cell factor (SCF) could facilitate cell homing in the pulpless immature root canal and promote regeneration of a functional pulp. In vitro, human mesenchymal stem cells (hMSCs) were exposed to SCF at various concentrations for assessing cell migration, proliferation, and differentiation toward odonto/osteoblasts by 3D-chemotaxis slides, WST-1 assay, and alkaline phosphatase activity, respectively. Fibrin gels were used to deliver 15 μg/mL SCF for in vivo experiments. The release kinetic of SCF was assessed in vitro. Two corresponding human immature premolars, with or without SCF, were placed at rat calvariae for 6 and 12 weeks. All tooth specimens were either analyzed histologically and the percentage of tissue ingrowth determined or the cells were extracted from the pulp space, and the mRNA level of DMP1, DSPP, Col1, NGF, and VEGF were assessed by quantitative polymerase chain reaction. In the presence of SCF, we saw an increase in hMSCs directional migration, proliferation, and odonto/osteogenic differentiation. SCF also increased the extent of tissue ingrowth at 6 weeks but not at 12 weeks. However, at this time point, the formed tissue appeared more mature in samples with SCF. In terms of gene transcription, DMP1, Col1, and VEGF were the significantly upregulated genes, while DSPP and NGF were not affected. Our results suggest that SCF can accelerate cell homing and the maturation of the pulp-dentin complex in human immature teeth.

Identification of Organ-Enriched Protein Biomarkers of Acute Liver Injury by Targeted Quantitative Proteomics of Blood in Acetaminophen- and Carbon-Tetrachloride-Treated Mouse Models and Acetaminophen Overdose Patients

Organ-enriched blood proteins, those produced primarily in one organ and secreted or exported to the blood, potentially afford a powerful and specific approach to assessing diseases in their cognate organs. We demonstrate that quantification of organ-enriched proteins in the blood offers a new strategy to find biomarkers for diagnosis and assessment of drug-induced liver injury (and presumably the assessment of other liver diseases). We used selected reaction monitoring (SRM) mass spectrometry to quantify 81 liver-enriched proteins plus three aminotransferases (ALT1, AST1, and AST2) in plasma of C57BL/6J and NOD/ShiLtJ mice exposed to acetaminophen or carbon tetrachloride. Plasma concentrations of 49 liver-enriched proteins were perturbed significantly in response to liver injury induced by one or both toxins. We validated four of these toxin-responsive proteins (ALDOB, ASS1, BHMT, and GLUD1) by Western blotting. By both assays, these four proteins constitute liver injury markers superior to currently employed markers such as ALT and AST. A similar approach was also successful in human serum where we had analyzed 66 liver-enriched proteins in acetaminophen overdose patients. Of these, 23 proteins were elevated in patients; 15 of 23 overlapped with the concentration-increased proteins in the mouse study. A combination of 5 human proteins, AGXT, ALDOB, CRP, FBP1, and MMP9, provides the best diagnostic performance to distinguish acetaminophen overdose patients from controls (sensitivity: 0.85, specificity: 0.84, accuracy: 85%). These five blood proteins are candidates for detecting acetaminophen-induced liver injury using next-generation diagnostic devices (e.g, microfluidic ELISA assays).

NADPH oxidase 4 regulates homocysteine metabolism and protects against acetaminophen-induced liver damage in mice

Glutathione is the major intracellular redox buffer in the liver and is critical for hepatic detoxification of xenobiotics and other environmental toxins. Hepatic glutathione is also a major systemic store for other organs and thus impacts on pathologies such as Alzheimer's disease, Sickle Cell Anaemia and chronic diseases associated with aging. Glutathione levels are determined in part by the availability of cysteine, generated from homocysteine through the transsulfuration pathway. The partitioning of homocysteine between remethylation and transsulfuration pathways is known to be subject to redox-dependent regulation, but the underlying mechanisms are not known. An association between plasma Hcy and a single nucleotide polymorphism within the NADPH oxidase 4 locus led us to investigate the involvement of this reactive oxygen species- generating enzyme in homocysteine metabolism. Here we demonstrate that NADPH oxidase 4 ablation in mice results in increased flux of homocysteine through the betaine-dependent remethylation pathway to methionine, catalysed by betaine-homocysteine-methyltransferase within the liver. As a consequence NADPH oxidase 4-null mice display significantly lowered plasma homocysteine and the flux of homocysteine through the transsulfuration pathway is reduced, resulting in lower hepatic cysteine and glutathione levels. Mice deficient in NADPH oxidase 4 had markedly increased susceptibility to acetaminophen-induced hepatic injury which could be corrected by administration of N-acetyl cysteine. We thus conclude that under physiological conditions, NADPH oxidase 4-derived reactive oxygen species is a regulator of the partitioning of the metabolic flux of homocysteine, which impacts upon hepatic cysteine and glutathione levels and thereby upon defence against environmental toxins.

C-Kit Promotes Growth and Migration of Human Cardiac Progenitor Cells via the PI3K-AKT and MEK-ERK Pathways

A recent phase I clinical trial (SCIPIO) has shown that autologous c-kit+ cardiac progenitor cells (CPCs) improve cardiac function and quality of life when transplanted into patients with ischemic heart disease. Although c-kit is widely used as a marker of resident CPCs, its role in the regulation of the cellular characteristics of CPCs remains unknown. We hypothesized that c-kit plays a role in the survival, growth, and migration of CPCs. To test this hypothesis, human CPCs were grown under stress conditions in the presence or absence of SCF, and the effects of SCF-mediated activation of c-kit on CPC survival/growth and migration were measured. SCF treatment led to a significant increase in cell survival and a reduction in cell death under serum depletion conditions. In addition, SCF significantly promoted CPC migration in vitro. Furthermore, the pro-survival and pro-migratory effects of SCF were augmented by c-kit overexpression and abrogated by c-kit inhibition with imatinib. Mechanistically, c-kit activation in CPCs led to activation of the PI3K and the MAPK pathways. With the use of specific inhibitors, we confirmed that the SCF/c-kit-dependent survival and chemotaxis of CPCs are dependent on both pathways. Taken together, our findings suggest that c-kit promotes the survival/growth and migration of human CPCs cultured ex vivo via the activation of PI3K and MAPK pathways. These results imply that the efficiency of CPC homing to the injury site as well as their survival after transplantation may be improved by modulating the activity of c-kit.

Stem cell factor improves lung recovery in rats following neonatal hyperoxia-induced lung injury

BACKGROUND

Stem cell factor (SCF) and its receptor, c-kit, are modulators of angiogenesis. Neonatal hyperoxia-induced lung injury (HILI) is characterized by disordered angiogenesis. The objective of this study was to determine whether exogenous SCF improves recovery from neonatal HILI by improving angiogenesis.

METHODS

Newborn rats assigned to normoxia (RA: 20.9% O2) or hyperoxia (90% O2) from postnatal day (P) 2 to 15, received daily injections of SCF 100 μg/kg or placebo (PL) from P15 to P21. Lung morphometry was performed at P28. Capillary tube formation in SCF-treated hyperoxia-exposed pulmonary microvascular endothelial cells (HPMECs) was determined by Matrigel assay.

RESULTS

As compared with RA, hyperoxic-PL pups had decrease in alveolarization and in lung vascular density, and this was associated with increased right ventricular systolic pressure (RVSP), right ventricular hypertrophy, and vascular remodeling. In contrast, SCF-treated hyperoxic pups had increased angiogenesis, improved alveolarization, and attenuation of pulmonary hypertension as evidenced by decreased RVSP, right ventricular hypertrophy, and vascular remodeling. Moreover, in an in vitro model, SCF increased capillary tube formation in hyperoxia-exposed HPMECs.

CONCLUSION

Exogenous SCF restores alveolar and vascular structure in neonatal rats with HILI by promoting neoangiogenesis. These findings suggest a new strategy to treat lung diseases characterized by dysangiogenesis.

Doxorubicin and 5-fluorouracil resistant hepatic cancer cells demonstrate stem-like properties

The efficacy of hepatocellular carcinoma (HCC) treatment is very low because of the high percentage of recurrence and resistance to anticancer agents. Hepatic cancer stem cells (HCSCs) are considered the origin of such recurrence and resistance. Our aim was to evaluate the stemness of doxorubicin and 5-fluorouracil resistant hepatic cancer cells and establish the new method to isolate the HCSCs from primary cultured HCC tumors. HCC biopsies were used to establish primary cultures. Then, primary cells were selected for HCSCs by culture in medium supplemented with doxorubicin (0, 0.1, 0.25, 0.5 or 1 μg/mL), 5-fluorouracil (0, 0.1, 0.25, 0.5 or 1 μg/mL) or their combination. Selection was confirmed by detection of HCSC markers such as CD133, CD13, CD90, and the side population was identified by rhodamine 123 efflux. The cell population with the strongest expression of these markers was used to evaluate the cell cycle, gene expression profile, tumor sphere formation, marker protein expression, and in vivo tumorigenesis. Selective culture of primary cells in medium supplemented with 0.5 μg/mL doxorubicin and 1 μg/mL 5-fluorouracil selected cancer cells with the highest stemness properties. Selected cells strongly expressed CD13, CD133, CD90, and CD326, efflux rhodamine 123 and formed tumor spheres in suspension. Moreover, selected cells were induced to differentiate into cells with high expression of CD19 and AFP (alpha-fetoprotein), and importantly, could form tumors in NOD/SCID mice upon injection of 1 × 10(5) cells/mouse. Selective culture with doxorubicin and 5-fluorouracil will enrich HCSCs, is an easy method to obtain HCSCs that can be used to develop better therapeutic strategies for patients with HCC, and particularly HCSC-targeting therapy.

Tissue-protective cytokines: structure and evolution

Cytokines are important mediators of host defense and immunity, and were first identified for their role in immunity to infections. It was then found that some of them are pathogenic mediators in inflammatory diseases and much of the emphasis is now on pro-inflammatory cytokines, also in consideration of the fact that TNF inhibitors became effective drugs in chronic inflammatory diseases. The recent studies on the tissue-protective activities of erythropoietin (EPO) led to the term "tissue-protective cytokine." We discuss here how tissue-protective actions might be common to other cytokines, particularly those of the 4-alpha helical structural superfamily.

Comparison of in vitro hepatogenic differentiation potential between various placenta-derived stem cells and other adult stem cells as an alternative source of functional hepatocytes

Mesenchymal stem cells (MSCs) are powerful sources for cell therapy in regenerative medicine. The capability to obtain effective stem cell-derived hepatocytes would improve cell therapy for liver diseases. Recently, various placenta-derived stem cells (PDSCs) depending on the localization of placenta have been suggested as alternative sources of stem cells are similar to bone marrow-derived MSC (BM-MSCs) and adipose-derived MSC (AD-MSCs). However, comparative studies for the potentials of the hepatogenic differentiation among various MSCs largely lacking. Therefore, we investigated to compare the potentials for hepatogenic differentiation of PDSCs with BM-MSCs, AD-MSCs, and UCB-MSCs. Several MSCs were isolated from human term placenta, adipose tissue, and umbilical cord blood and characterized isolated MSCs and BM-MSCs was performed by quantitative reverse transcription-PCR (RT-PCR) and special stains after mesodermal differentiation. The hepatogenic potential of PDSCs was compared with AD-MSCs, UCB-MSCs, and BM-MSCs using RT-PCR, PAS stain, ICG up-take assays, albumin expression, urea production, and cytokine assays. MSCs isolated from different tissues all presented similar characteristics of MSCs. However, the proliferative potential of PDSCs and the expression of hepatogenic markers in differentiated PDSCs were higher than other MSCs. Interestingly, the expression of hepatocyte growth factor (HGF) increased in PDSCs after hepatogenic differentiation. Interestingly, stem cell factor (SCF) expression in chorionic plate-derived MSCs, one of the PDSCs, was significantly higher than in the other PDSCs. Taken together, the results of the present study suggest that MSCs isolated from various adult tissues can be induced to undergo hepatogenic differentiation in vitro, and that PDSCs may have the greatest potential for hepatogenic differentiation and proliferation. Therefore, PDSCs could be used as a stem cell source for cell therapy in liver diseases.

Transplantation of bone marrow cells decreases tumor necrosis factor-α production and blood-brain barrier permeability and improves survival in a mouse model of acetaminophen-induced acute liver disease

BACKGROUND AIMS

Acute liver failure (ALF), although rare, remains a rapidly progressive and frequently fatal condition. Acetaminophen (APAP) poisoning induces a massive hepatic necrosis and often leads to death as a result of cerebral edema. Cell-based therapies are currently being investigated for liver injuries. We evaluated the therapeutic potential of transplantation of bone marrow mononuclear cells (BMC) in a mouse model of acute liver injury.

METHODS

ALF was induced in C57Bl/6 mice submitted to an alcoholic diet followed by fasting and injection of APAP. Mice were transplanted with 10(7) BMC obtained from enhanced green fluorescent protein (GFP) transgenic mice.

RESULTS

BMC transplantation caused a significant reduction in APAP-induced mortality. However, no significant differences in serum aminotransferase concentrations, extension of liver necrosis, number of inflammatory cells and levels of cytokines in the liver were found when BMC- and saline-injected groups were compared. Moreover, recruitment of transplanted cells to the liver was very low and no donor-derived hepatocytes were observed. Mice submitted to BMC therapy had some protection against disruption of the blood-brain barrier, despite their hyperammonemia, and serum metalloproteinase (MMP)-9 activity similar to the saline-injected group. Tumor necrosis factor (TNF)-α concentrations were decreased in the serum of BMC-treated mice. This reduction was associated with an early increase in interleukin (IL)-10 mRNA expression in the spleen and bone marrow after BMC treatment.

CONCLUSIONS

BMC transplantation protects mice submitted to high doses of APAP and is a potential candidate for ALF treatment, probably via an immunomodulatory effect on TNF-α production.

Phyllanthus urinaria extract attenuates acetaminophen induced hepatotoxicity: involvement of cytochrome P450 CYP2E1

Acetaminophen is a commonly used drug for the treatment of patients with common cold and influenza. However, an overdose of acetaminophen may be fatal. In this study we investigated whether mice, administered intraperitoneally with a lethal dose of acetaminophen, when followed by oral administration of Phyllanthus urinaria extract, may be prevented from death. Histopathological analysis of mouse liver sections showed that Phyllanthus urinaria extract may protect the hepatocytes from acetaminophen-induced necrosis. Therapeutic dose of Phyllanthus urinaria extract did not show any toxicological phenomenon on mice. Immunohistochemical staining with the cytochrome P450 CYP2E1 antibody revealed that Phyllanthus urinaria extract reduced the cytochrome P450 CYP2E1 protein level in mice pre-treated with a lethal dose of acetaminophen. Phyllanthus urinaria extract also inhibited the cytochrome P450 CYP2E1 enzymatic activity in vitro. Heavy metals, including arsenic, cadmium, mercury and lead, as well as herbicide residues were not found above their detection limits. High performance liquid chromatography identified corilagin and gallic acid as the major components of the Phyllanthus urinaria extract. We conclude that Phyllanthus urinaria extract is effective in attenuating the acetaminophen induced hepatotoxicity, and inhibition of cytochrome P450 CYP2E1 enzyme may be an important factor for its therapeutic mechanism.

Expression of stem cell factor and its receptor c-Kit during the development of intrahepatic cholangiocarcinoma

Stem cell factor (SCF) and its receptor, c-Kit, constitute an important signal transduction system with proliferative and anti-apoptotic functions. Besides regulating hemopoietic stem cell proliferation and liver regeneration, it has been implicated in the regulation of human malignancies. However, the cellular expression of the SCF-c-Kit gene system in the liver during cholangiocarcinogenesis has not been studied to date. The protein- and mRNA-expression levels of SCF and c-Kit genes were examined in normal rat liver, in isolated normal rat liver cells and in a thioacetamide-induced rat model of intrahepatic cholangiocarcinoma (CC). Immunohistochemical analysis of the normal liver showed that SCF is expressed in the wall of the hepatic artery and in some cells, which were located along the sinusoids, although it was absent from hepatocytes and biliary epithelial cells. The mRNA analysis of isolated normal liver cell populations revealed a co-expression of SCF- and c-Kit-mRNA in sinusoidal endothelial cells and in Kupffer cells, whereas passaged and cultured liver myofibroblasts (MFs) expressed only SCF. Low levels of the SCF- and c-Kit-mRNA expression could be detected in isolated hepatocytes of the normal liver. Immunohistochemical analysis of the CC tissue showed SCF positivity in proliferating biliary cells (CK-19(+)), in macrophages (ED-1(+)) and in MFs (alpha-smooth-muscle-actin, alpha-SMA(+)) of the tumoral microenvironment. c-Kit-positivity could be detected on hepatocytes of the regenerating nodules and on the proliferating bile ducts of CC. Compared with the normal liver tissue, SCF-mRNA from the CC tissue was upregulated up to 20-fold, whereas c-Kit-mRNA was upregulated up to fivefold. These data indicate that several cell populations may become able to express SCF and/or c-Kit during cholangiocarcinogenesis. Therefore, the SCF-c-Kit system may contribute to tumor development, for instance, by inducing proliferation of hepatocytes and of biliary cells and by acting as a surviving factor for CC cells.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor and its receptor, c-kit, are important for hepatocyte proliferation in wild-type and tumor necrosis factor receptor-1 knockout mice after 70% hepatectomy

BACKGROUND

Stem cell factor (SCF) has well-known proliferative effects on hematopoietic cells. SCF also has effects on differentiation and proliferation in other cell types. Interleukin-6 (IL-6) and tumor necrosis factor (TNF)-alpha have proliferative effects in the liver. Recent studies in our laboratory have linked SCF's hepatoproliferative actions to those of IL-6, demonstrating that IL-6-induced hepatocyte proliferation depends, at least in part, on SCF. We now hypothesize that TNF-alpha's hepatoproliferative effects are also dependent on SCF.

METHODS AND RESULTS

In vitro studies using primary mouse hepatocytes show that SCF is induced by TNF-alpha; anti-SCF antibody treatment in this system inhibits TNF-alpha-induced hepatocyte proliferation, suggesting that TNF-alpha-induced hepatocyte proliferation is also SCF dependent. Additional in vivo experiments were performed in which wild type and/or TNF-alpha receptor-1 knockout mice (TNFR1(-/-)) were subjected to 70% hepatectomy or sham laparotomy. TNFR1(-/-) mice are known to have delayed hepatic regeneration after partial hepatectomy. Initial experiments demonstrated that the SCF receptor, c-kit, is upregulated after partial hepatectomy in wild-type mice, further emphasizing the importance of this system in the restoration of hepatic mass. SCF administration to TNFR1(-/-) mice in the context of partial hepatectomy restores hepatocyte proliferation to normal. Further, SCF administration to TNFR1(-/-) mice before hepatectomy increases phosphotyrosine signal transducer and activator (p-stat-3) levels, suggesting that SCF-induced increases in hepatocyte proliferation may also be stat-3 mediated.

CONCLUSIONS

These data suggest that TNF-alpha-induced hepatocyte proliferation depends, at least in part, on SCF and that SCF and its receptor, c-kit, are important for the liver's regenerative processes.

Physiological variations of stem cell factor and stromal-derived factor-1 in murine models of liver injury and regeneration

BACKGROUND/AIMS

Stem cell factor (SCF) and stromal-derived factor-1 (SDF-1) regulate the regenerative response to liver injury, possibly through activation of liver progenitor 'oval' cells and recruitment of circulating, marrow-derived progenitors.

METHODS

We performed a detailed analysis of SCF, SDF-1 and oval cell proliferation induced by tyrosinaemia, 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or liver irradiation in mice by ELISA and immunofluorescence.

RESULTS

Liver injury in the tyrosinaemia mouse is characterized by a dramatic decline in plasma SCF and absence of oval cell proliferation. In contrast, DDC induces bile duct (BD) and oval cell proliferation, and a modest decline in plasma SCF. Focal liver irradiation increases plasma SCF, but not oval cell density. In normal mouse liver, SCF is localized primarily to Kupffer cells, cholangiocytes and arterial smooth muscle, with little or no expression in hepatocytes. However, SCF appears in hepatocyte nuclei after injury, where its function is unknown. In all three models, SDF-1 is expressed exclusively in BD epithelium, indicating that tissue SDF-1 levels are proportional to the total mass of oval cells and cholangiocytes. However, increased plasma levels of SDF-1 in fumaryl acetoacetate hydroxylase-null mice were not accompanied by oval cell proliferation.

CONCLUSION

Changes in SCF and SDF-1 varied with the nature of liver injury and were not directly related to oval cell proliferation.

Elevation of serum stem-cell factor in postoperative biliary atresia

BACKGROUND

Biliary atresia (BA) is one of the most common causes of neonatal cholestasis. Stem-cell factor (SCF) has been implicated in the development of fibrosis in various diseases. The objective of the present study was to examine the significant role of SCF in BA.

METHODS

Fifty-seven pediatric patients with BA after Kasai operation and 30 healthy children were recruited. The mean ages of BA patients and controls were 6.1 +/- 0.6 years and 6.1 +/- 0.7 years, respectively. The patients were categorized into two groups according to their serum levels of total bilirubin (TBil < 2 mg/dL, no jaundice vs TBil > or = 2 mg/dL, persistent jaundice) and alanine aminotransferase (ALT < 100 vs ALT > or = 100 U/L). The serum SCF levels were determined on commercially available enzyme-linked immunosorbent assay.

RESULTS

The mean serum SCF level of the BA children was higher than that of normal controls (748.3 +/- 17.9 pg/mL vs 582.2 +/- 17.3 pg/mL; P < 0.001). Subsequent analysis demonstrated that the BA patients with serum ALT > or = 100 U/L had significantly greater levels of serum SCF compared to those with serum ALT < 100 U/L (796.5 +/- 22.6 pg/mL vs 694.7 +/- 25.0 pg/mL, respectively; P = 0.002). In addition, serum SCF levels were significantly elevated in the patients with portal hypertension (PH) compared with those without PH (810.0 +/- 18.8 pg/mL vs 634.1 +/- 20.1 pg/mL, P < 0.001).

CONCLUSION

The current study showed that BA patients had higher serum SCF levels compared with controls. The significant elevation in SCF levels is associated with the presence of PH and the degree of hepatic injury. These findings suggest that SCF may play a part in the pathogenesis of hepatic fibrosis in BA patients after Kasai procedure.

Serum levels of stem cell factor and thrombopoietin are markedly decreased in fulminant hepatic failure patients with a poor prognosis

BACKGROUND AND AIM

Hematopoietic growth factors including stem cell factor (SCF), thrombopoietin (TPO) and granulocyte colony stimulating factor (G-CSF) have a potential role in inducing bone marrow hematopoietic stem cells to move into the circulation, and the association of these factors with liver regeneration has received a lot of attention recently. The aim of this study was to determine the serum levels of such factors in patients with acute liver injury.

METHODS

The subjects were 25 patients with acute hepatitis (AH) who had a favorable prognosis and 26 patients with fulminant hepatitis (FH), of whom 11 were alive and 15 had died. Sixty-six healthy subjects matched for age and sex served as controls. Serum samples were collected before treatment, and the levels of SCF, TPO and G-CSF were measured using enzyme-linked immunosorbant assays.

RESULTS

The levels of SCF and TPO were significantly lower in FH patients than in AH patients and the controls, and were also significantly lower in the FH patients who died, compared to the surviving patients. The G-CSF levels did not differ among them.

CONCLUSIONS

These results suggest that low serum levels of SCF and TPO may be linked to poor prognosis in patients with severe liver injury.

Role of innate immunity in acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) hepatotoxicity is currently the single most important cause of acute liver failure in the US, and is associated with a significant number of deaths. The toxic response to APAP is triggered by a highly reactive metabolite N-acetyl-p-benzoquinone-imine. Following the hepatocellular initiation events, such as glutathione depletion and covalent binding, intracellular stress simultaneously activates signal transduction and transcription factor pathways that are protective or toxic (directly or through sensitisation). Subsequently, pro- and anti-inflammatory cascades of the innate immune system are simultaneously activated, the balance of which plays a major role in determining the progression and severity of APAP-induced hepatotoxicity. The threshold and susceptibility to APAP hepatotoxicity is determined by the interplay of injury promoting and inhibiting events downstream of the initial production of toxic metabolite. The environmental and genetic control of these intracellular and intercellular responses to toxic metabolites may be of critical importance in determining susceptibility to APAP hepatotoxicity and presumably idiosyncratic drug hepatotoxicity.

Implication of stem cell factor in human liver regeneration after transplantation and resection

The stem cell factor (SCF), besides regulating hemopoietic stem cells homing and proliferation, has proliferative effects on hepatocytes and may be involved in liver regeneration. We investigate if liver transplantation (LT) and hepatic resection (HR) modify the concentration of soluble SCF (s-SCF) in peripheral blood of 15 LT and 7 HR. s-SCF was measured by ELISA as ng/ml. s-SCF basal levels were higher in LT that in HR (818 +/- 349 vs. 479 +/- 79, p = 0.005). A significant increase of s-SCF, peaking at postoperative day +3, was seen after LT (from 818 +/- 349 to 1212 +/- 461, p = 0.01) and HR (from 479 +/- 79 to 698 +/- 122, p = 0.004). s-SCF peak levels were higher after LT than HR (p = 0.0008). At day +7 s-SCF concentration returned to baseline values. LT have a higher basal s-SCF level than HR. These data show for the first time that liver injury affects s-SCF level and suggest that SCF may be involved also in clinical liver regeneration.

Pregnenolone-16alpha-carbonitrile inhibits rodent liver fibrogenesis via PXR (pregnane X receptor)-dependent and PXR-independent mechanisms

The effect of liver growth stimulation [using the rodent PXR (pregnane X receptor) activator PCN (pregnenolone-16alpha-carbonitrile)] in rats chronically treated with carbon tetrachloride to cause repeated hepatocyte necrosis and liver fibrogenesis was examined. PCN did not inhibit the hepatotoxicity of carbon tetrachloride. However, transdifferentiation of hepatic stellate cells and the extent of fibrosis caused by carbon tetrachloride treatment was significantly inhibited by PCN in vivo. In vitro, PCN directly inhibited hepatic stellate cell transdifferentiation to a profibrogenic phenotype, although the cells did not express the PXR (in contrast with hepatocytes), suggesting that PCN acts independently of the PXR. Mice with a functionally disrupted PXR gene (PXR-/-) did not respond to the antifibrogenic effects of PCN, in contrast with wild-type (PXR+/+) mice, demonstrating an antifibrogenic role for the PXR in vivo. However, PCN inhibited the transdifferentiation of PXR-/--derived mouse hepatic stellate cells in vitro, confirming that there is also a PXR-independent antifibrogenic effect of PCN through a direct interaction with hepatic stellate cells. These data suggest that the PXR is antifibrogenic in rodents in vivo and that a PXR-independent target for PXR activators exists in hepatic stellate cells that also functions to inhibit fibrosis.

Improvement of mortality rate and decrease in histologic hepatic injury after human cord blood stem cell infusion in a murine model of hepatotoxicity

BACKGROUND AND AIMS

Because of their plasticity potential local and systemic application of cord blood stem cells may represent excellent candidates for cell-based therapeutic strategies in toxic liver injuries. It is already known that intraperitoneal administration of hematopoietic stem cells provides rapid liver homing in animal models of hepatic injury. We sought to assess the efficacy of a hematopoietic stem cell infusion to decrease the histologic damage and the mortality rate of animals previously damaged by allyl alcohol.

MATERIAL AND METHODS

NOD/SCID mice were divided into two groups. (1) animals treated by intraperitoneal administration of allyl alcohol and (2) animals treated with allyl alcohol and 24 hours later with an intraperitoneal infusion of human cord blood cells. Flow cytometry, histology, immunohistochemistry, and RT-PCR were performed to monitor human cell engraftment by evidences of human hepatic markers.

RESULTS

Human stem cells were able to transdifferentiate into hepatocytes, improve liver regeneration after damage, and reduce the mortality rate even when requiring qualitative and quantitative differences in the transdifferentiation processes. The mortality rate decreased from 70% to 20%, with a significant improvement in the histologic findings.

CONCLUSION

We demonstrated that the infusion of hematopoietic stem cells into the liver in the early stage of damage might initiate endogenous hepatic tissue regeneration that oppose the injury inflicted by toxicants.

[Which stem cells for adult liver?]

While hepatocytes can be considered conceptually as unipotent stem cells, the presence of true stem or progenitor cells within adult livers has been largely debated. It is now accepted that the atypical ductular reaction observed in livers with sub-massive hepatitis represents the proliferation of hepatic progenitor cells similar to rat oval cells and able to differentiate towards the biliary and the hepatocytic lineage through intermediate progeny. In the normal liver, the identification of progenitor cells with a panel of markers including c-kit, CD34, Ov6, CK7, CK19, chromogranine A, CD56 remains difficult because these cells are very few and most of the markers are not specific. These progenitor cells could be located either within the canals of Hering or in periductular situation or both. Mechanisms leading to the activation and the proliferation of hepatic progenitor cells are still largely unknown: they involve growth factors as the stem cell factor, ligand of c-kit, cytokines, chemokines as SDF1 a and vagal or sympathetic innervatioñ. Other potential stem cells for liver could be hematopoietic stem cells from bone marrow. First publications have showed that hematopoietic stem cells were able to differentiate into hepatocytes and cholangiocytes and to yield high level engraftment of injured livers. However it appears now that this phenomenon is minimal or even absent in physiological and usual pathological conditions. It does occur in extreme experimental conditions either by true transdifferentiation or cell fusion. The shared property of stem cells and tumor cells to proliferate endlessly, rises the question of the potential role of progenitor cells in liver carcinogenesis. In a number of animal models of hepatocarcinogenesis, tumors originate from oval cells. The identification of progenitor cells close to murine oval cells in the human liver raises the hypothesis of a potential role of these cells in the development of human liver tumors. Liver progenitor cells have been identified morphologically and phenotypically in dysplastic foci of cirrhotic livers and hepatocellular adenomas. More generally speaking, typical hepatocellular carcinomas and cholangiocarcinomas are at the two ends of a spectrum which includes transitional-type tumors intermediate between hepatocellular carcinoma and cholangiocarcinoma and combined hepato-cellular cholangiocarcinoma; these intermediate and combined types can be more easily explained as deriving from progenitor cells. Despite the difficulties, the doubts and the potential dangers, new experimental modalities to obtain efficient repopulation of the liver from bone marrow stem cells are currently under study: exogenous administration of cytokines and chemokines involved in cell homing and differentiation or development of selective pressure strategies. Other cell types as intra-hepatic progenitor cells, bone marrow multipotent adult progenitor cells (MAPCs) or fetal hepatocytes could be alternative sources for liver cell therapy. Thus, progressing knowledge about stem cells in adult liver would allow to better understand mechanisms of hepatic homeostasia and regeneration and would open the way to cell-based therapy for liver diseases.

Dose- and time-dependent oval cell reaction in acetaminophen-induced murine liver injury

We examined the response of murine oval cells, that is, the putative liver progenitor cells, to acetaminophen. Female C57BL/6J mice were injected intraperitoneally with varying doses of N-acetyl-paraaminophen (APAP) (250, 500, 750, and 1,000 mg/kg of weight) and sacrificed at 3, 6, 9, 24, and 48 hours. In preliminary studies, we showed that anticytokeratin antibodies detected A6-positive cells with a sensitivity and specificity of greater than 99%. The oval cell reaction was quantified, on immunostaining for biliary-type cytokeratins, as both number and density of oval cells per portal tract, analyzed by size of portal tract. Acetaminophen injury was followed by periportal oval cell accumulation displaying a moderate degree of morphological homogeneity. Oval cell response was biphasic, not temporally correlating with the single wave of injury seen histologically. Increases in oval cells were largely confined to the smallest portal tracts, in keeping with their primary derivation from the canals of Hering, and increased in a dose-dependent fashion. The timing of the two peaks of the oval cell reaction also changed with increasing dose, the first becoming earlier and the second later. In conclusion, our studies indicate a marked oval cell activation during the height of hepatic injury. Oval cells appear to be resistant to acetaminophen injury. The close fidelity of mechanism and histology of acetaminophen injury between mouse and human livers makes it a useful model for investigating liver regeneration and the participation of stem/progenitor cells in that process.

A human umbilical cord stem cell rescue therapy in a murine model of toxic liver injury

BACKGROUND

Several studies have demonstrated that bone marrow contains a subpopulation of stem cells capable of participating in the hepatic regenerative process, even if some reports indicate quite a low level of liver repopulation by human stem cells in the normal and transiently injured liver.

AIMS

In order to overcome the low engraftment levels seen in previous models, we tried the direct intraperitoneal administration of human cord blood stem cells, using a model of hepatic damage induced by allyl alcohol in NOD/SCID mice.

METHODS

We designed a protocol based on stem cell infusion following liver damage in the absence of irradiation. Flow cytometry, histology, immunohistochemistry and RT-PCR for human hepatic markers were performed to monitor human cell engraftment.

RESULTS

Human stem cells were able to transdifferentiate into hepatocytes, to improve liver regeneration after damage and to reduce the mortality rate both in both protocols, even if with qualitative and quantitative differences in the transdifferentiation process.

CONCLUSIONS

We demonstrated for the first time that the intraperitoneal administration of stem cells can guarantee a rapid liver engraftment. Moreover, the new protocol based on stem cell infusion following liver damage in the absence of irradiation may represent a step forward for the clinical application of stem cell transplantation.

Neuronally expressed stem cell factor induces neural stem cell migration to areas of brain injury

Neural stem/progenitor cell (NSPC) migration toward sites of damaged central nervous system (CNS) tissue may represent an adaptive response for the purpose of limiting and/or repairing damage. Little is known of the mechanisms responsible for this migratory response. We constructed a cDNA library of injured mouse forebrain using subtractive suppression hybridization (SSH) to identify genes that were selectively upregulated in the injured hemisphere. We demonstrate that stem cell factor (SCF) mRNA and protein are highly induced in neurons within the zone of injured brain. Additionally, the SCF receptor c-kit is expressed on NSPCs in vitro and in vivo. Finally, we demonstrate that recombinant SCF induces potent NSPC migration in vitro and in vivo through the activation of c-kit on NSPCs. These data suggest that the SCF/c-kit pathway is involved in the migration of NSPCs to sites of brain injury and that SCF may prove useful for inducing progenitor cell recruitment to specific areas of the CNS for cell-based therapeutic strategies.

Drug-induced liver disease in 2003

Drug-induced liver disease remains an important topic of concern for all prescribers as well as drug manufacturers. The withdrawal of troglitazone (Rezulin) and bromfenac (Duract) a few years ago remains fresh in the minds of regulatory authorities as well as clinicians and researchers who are focusing renewed attention on ways to better understand mechanisms of injury to predict and avert serious drug-induced liver disease in the future from drugs under development as well as existing agents known to cause liver injury. As in past years, this review describes new and first-time reports of various aspects of drug-induced liver disease for several classes of compounds, including herbal products (such as kava kava), reviews the risk factors seen with antiretroviral and antituberculosis agents among others. It provides a sampling of experimental hepatoprotection studies that may hold the key to treatment and prevention of drug-induced liver disease in the future and discusses the ongoing approaches to be taken to restrict the availability of acetaminophen that have proved successful in reducing the number of overdoses, deaths, and liver transplantations from this drug in the United Kingdom. Given the fact that acetaminophen is the single most important cause of acute liver failure here and abroad, such efforts to limit its use seem appropriate for other nations as well.