Mesenchymal stem cell-conditioned medium reduces liver injury and enhances regeneration in reduced-size rat liver transplantation

BACKGROUND

Mesenchymal stem cell (MSC) therapy can prevent parenchymal cell loss and promotes tissue repair through the action of trophic, secreted molecules. In this study, we investigated whether MSC-conditioned medium (MSC-CM) could protect hepatocytes and sinusoidal endothelial cells (SECs) and stimulate their regeneration in 50% reduced-size liver transplantation (RSLT).

MATERIALS AND METHODS

Rats were randomly divided into three groups: sham-operated group, MSC-CM group (rats with 50% RSLT receiving MSC-CM infusion), and medium group (rats with 50% RSLT receiving medium therapy). Graft function, proinflammatory cytokines, incidence of apoptosis, proliferation of hepatocytes and SECs, and the expression of vascular endothelial growth factor and matrix metallopeptidase 9 were assessed in this study.

RESULTS

Systemic infusion of MSC-CM prevented the release of liver injury biomarkers and provided a significant survival benefit. Furthermore, MSC-CM therapy resulted in reduction of apoptosis of hepatocytes and SECs. The number of proliferating hepatocytes and SECs increased 1.2- and 1.6-fold, respectively, accompanied by a decrease in the expression levels of several proinflammatory cytokines and a noticeable decrease in infiltration of neutrophils and activation of Kupffer cells. Also, increased expression of vascular endothelial growth factor and matrix metallopeptidase 9 in the grafts was observed after MSC-CM therapy.

CONCLUSIONS

These data suggest that MSC-CM therapy in RSLT provides trophic support to the injured liver by inhibiting SEC and hepatocellular death and stimulating their regeneration.

Liver sinusoidal endothelial dysfunction after LPS administration: a role for inducible-nitric oxide synthase

BACKGROUND & AIMS

Sepsis is associated with microvascular dysfunction, which contributes to organ failure. Intrahepatic endothelial dysfunction occurs after exposure to lipopolysaccharide (LPS). The upregulation of inducible nitric oxide synthase (iNOS) has been shown to contribute to systemic vascular dysfunction after LPS administration. However, little is known about the effects of iNOS induction on the liver microcirculation. This study aimed at exploring, in the isolated rat liver perfusion model, the role of iNOS induction in liver microvascular dysfunction associated with endotoxemia.

METHODS

All experiments were conducted in male Wistar rats, after 24 h of LPS (5 mg/kg i.p.) or saline administration in the presence or absence of the iNOS inhibitor 1400 W (3 mg/kg i.p.), administered 3 and 23 h after LPS/saline injection. Liver microvascular function was assessed by isolated liver perfusion, followed by molecular studies and liver function tests.

RESULTS

At 24 h, LPS induced liver endothelial dysfunction, as shown by a decreased vasodilatory response to acetylcholine and decreased eNOS phosphorylation at Ser(1176). This was associated with liver injury, assessed by an increase in liver transaminases and decreased indocyanin green clearance, and increased nitrooxidative stress. iNOS inhibition prevented liver endothelial dysfunction, blunted the development of liver injury and attenuated LPS-induced nitrooxidative stress.

CONCLUSIONS

iNOS upregulation contributes to liver microvascular dysfunction in endotoxemia. This suggests that this mechanism deserves further exploration in studies addressing liver protection in the context of severe acute bacterial infection.

Pathological process of liver sinusoidal endothelial cells in liver diseases

Cirrhosis develops from liver fibrosis and is the severe pathological stage of all chronic liver injury. Cirrhosis caused by hepatitis B virus and hepatitis C virus infection is especially common. Liver fibrosis and cirrhosis involve excess production of extracellular matrix, which is closely related to liver sinusoidal endothelial cells (LSECs). Damaged LSECs can synthesize transforming growth factor-beta and platelet-derived growth factor, which activate hepatic stellate cells and facilitate the synthesis of extracellular matrix. Herein, we highlight the angiogenic cytokines of LSECs related to liver fibrosis and cirrhosis at different stages and focus on the formation and development of liver fibrosis and cirrhosis. Inhibition of LSEC angiogenesis and antiangiogenic therapy are described in detail. Targeting LSECs has high therapeutic potential for liver diseases. Further understanding of the mechanism of action will provide stronger evidence for the development of anti-LSEC drugs and new directions for diagnosis and treatment of liver diseases.

Isolation of Non-parenchymal Cells from the Mouse Liver

Hepatocytes comprise the majority of liver mass and cell number. However, in order to understand liver biology, the non-parenchymal cells (NPCs) must be considered. Herein, a relatively rapid and efficient method for isolating liver NPCs from a mouse is described. Using this method, liver sinusoidal endothelial cells, Kupffer cells, natural killer (NK) and NK-T cells, dendritic cells, CD4+ and CD8+ T cells, and quiescent hepatic stellate cells can be purified. This protocol permits the collection of peripheral blood, intact liver tissue, and hepatocytes, in addition to NPCs. In situ perfusion via the portal vein leads to efficient liver digestion. NPCs are enriched from the resulting single-cell suspension by differential and gradient centrifugation. The NPCs can by analyzed or sorted into highly enriched populations using flow cytometry. The isolated cells are suitable for flow cytometry, protein, and mRNA analyses as well as primary culture.

Modulation of liver oxidant-antioxidant system by ischemic preconditioning during ischemia/reperfusion injury in rats

AIM: To investigate effects of ischemic pre-conditioning on the liver endogenous oxidant-antioxidant system during ischemia/reperfusion injury.

METHODS: Twenty-four male Sprague-Dawley rats were randomly divided into sham-operated (Sham), ischemia/reperfusion (I/R), ischemic pre-conditioning plus ischemia/reperfusion (IPC) groups. Serum ALT, AST and hyaluronic acid levels were assayed and pathologic alterations observed. Liver malondialdehyde (MDA) contents, endogenous antioxidant enzymes, superoxidase dismutase (SOD), catalase (CAT), gultathionine peroxidase (GSH-Px) activities, neutrophils accumulation marker, myeloperoxidase (MPO) activities were measured respectively.

RESULTS: Compared with I/R group, sinusoidal endothelial cells as well as hepatocytes damages, as assessed biochemically and histochemically, were improved significantly in IPC group; neutrophils infiltration was also markedly reduced. In IPC group, liver peroxidation, as measured by MDA contents, was significantly decreased when compared with I/R group; endogenous antioxidant enzymes, SOD, CAT and GSH-Px activities were markedly higher than that in I/R group.

CONCLUSION: Ischemic pre-conditioning exerts protective effects on both hepatic sinusoidal endothelial cells and hepatocytes during liver I/R injury. Its mechanisms may involve dimunition of neutrophils infiltration and modulation of the imbalance of endogenous oxidant-antioxidant system in the organism.

Pericytes in the Liver

Liver pericytes, commonly named hepatic stellate cells (HSCs), reside in the space between liver sinusoidal endothelial cells (LSECs) and hepatocytes. They display important roles in health and disease. HSCs ensure the storage of the majority of vitamin A in a healthy body, and they represent the major source of fibrotic tissue in liver disease. Surrounding cells, such as LSECs, hepatocytes, and Kupffer cells, present a significant role in modulating HSC behavior. Therapeutic strategies against liver disease are being currently developed, where HSCs represent an ideal target. In this chapter, we will discuss HSC quiescence and activation in the context of healthy liver and diseases, such as fibrosis, steatohepatitis, and hepatocellular carcinoma.

Evaluation of IGL-1 preservation solution using an orthotopic liver transplantation model

AIM: To compare, in a pig liver transplantation model, the protective effect of UW with that of IGL-1, a high-sodium preservation solution containing polyethylene glycol (PEG) as an oncotic supply.

METHODS: All livers were harvested and grafted orthotopically according to standard techniques. The livers were washed out and preserved for 7 h in IGL-1 (n = 6) or in UW solution (n = 7) at 4°C. In a sham group (n = 4), the livers underwent a 60-min warm ischemia at 37°C. The hepatocellular injury was assessed in organ preservation solution washed out from the graft at the end of ischemic storage (before revascularization), and in serum 2 h after reperfusion and daily for up to 6 d.

RESULTS: Livers preserved in IGL-1 solution released markedly less AST than that preserved in the UW solution before and after revascularization (P < 0.05). Besides, the activity of creatine kinase-BB, a marker of sinusoidal lining cells injury, was higher in the UW group than in the IGL-1 group (P < 0.05). Histological results showed less necrotic regions in livers preserved in IGL-1 solution; however, no difference was observed for inflammation.

CONCLUSION: IGL-1 liquid effectively protects parenchymal and non-parenchymal cells against prese-rvation-reperfusion injuries.

Transcriptome and proteome profiling reveal complementary scavenger and immune features of rat liver sinusoidal endothelial cells and liver macrophages

BACKGROUND

Liver sinusoidal endothelial cells (LSECs) and Kupffer cells (KCs; liver resident macrophages) form the body's most effective scavenger cell system for the removal of harmful blood-borne substances, ranging from modified self-proteins to pathogens and xenobiotics. Controversies in the literature regarding the LSEC phenotype pose a challenge when determining distinct functionalities of KCs and LSECs. This may be due to overlapping functions of the two cells, insufficient purification and/or identification of the cells, rapid dedifferentiation of LSECs in vitro, or species differences. We therefore characterized and quantitatively compared expressed gene products of freshly isolated, highly pure LSECs (fenestrated SE-1/FcγRIIb2⁺) and KCs (CD11b/c⁺) from Sprague Dawley, Crl:CD (SD), male rats using high throughput mRNA-sequencing and label-free proteomics.

RESULTS

We observed a robust correlation between the proteomes and transcriptomes of the two cell types. Integrative analysis of the global molecular profile demonstrated the immunological aspects of LSECs. The constitutive expression of several immune genes and corresponding proteins of LSECs bore some resemblance with the expression in macrophages. LSECs and KCs both expressed high levels of scavenger receptors (SR) and C-type lectins. Equivalent expression of SR-A1 (Msr1), mannose receptor (Mrc1), SR-B1 (Scarb1), and SR-B3 (Scarb2) suggested functional similarity between the two cell types, while functional distinction between the cells was evidenced by LSEC-specific expression of the SRs stabilin-1 (Stab1) and stabilin-2 (Stab2), and the C-type lectins LSECtin (Clec4g) and DC-SIGNR (Clec4m). Many immune regulatory factors were differentially expressed in LSECs and KCs, with one cell predominantly expressing a specific cytokine/chemokine and the other cell the cognate receptor, illustrating the complex cytokine milieu of the sinusoids. Both cells expressed genes and proteins involved in antigen processing and presentation, and lymphocyte co-stimulation.

CONCLUSIONS

Our findings support complementary and partly overlapping scavenging and immune functions of LSECs and KCs. This highlights the importance of including LSECs in studies of liver immunity, and liver clearance and toxicity of large molecule drugs and nano-formulations.

Liver endothelial cells in NAFLD and transition to NASH and HCC

Non-alcoholic fatty liver disease (NAFLD) is considered as the hepatic manifestation of metabolic syndrome, which is characterised by obesity, insulin resistance, hypercholesterolemia and hypertension. NAFLD is the most frequent liver disease worldwide and more than 10% of NAFLD patients progress to the inflammatory and fibrotic stage of non-alcoholic steatohepatitis (NASH), which can lead to end-stage liver disease including hepatocellular carcinoma (HCC), the most frequent primary malignant liver tumor. Liver sinusoidal endothelial cells (LSEC) are strategically positioned at the interface between blood and hepatic parenchyma. LSECs are highly specialized cells, characterised by the presence of transcellular pores, called fenestrae, and exhibit anti-inflammatory and anti-fibrotic characteristics under physiological conditions. However, during NAFLD development they undergo capillarisation and acquire a phenotype similar to vascular endothelial cells, actively promoting all pathophysiological aspects of NAFLD, including steatosis, inflammation, and fibrosis. LSEC dysfunction is critical for the progression to NASH and HCC while restoring LSEC homeostasis appears to be a promising approach to prevent NAFLD progression and its complications and even reverse tissue damage. In this review we present current information on the role of LSEC throughout the progressive phases of NAFLD, summarising in vitro and in vivo experimental evidence and data from human studies.

Transplantation of Thy1+ Cells Accelerates Liver Regeneration by Enhancing the Growth of Small Hepatocyte-Like Progenitor Cells via IL17RB Signaling

Small hepatocyte-like progenitor cells (SHPCs) transiently form clusters in rat livers treated with retrorsine (Ret)/70% partial hepatectomy (PH). When Thy1+ cells isolated from d-galactosamine-treated rat livers were transplanted into the livers of Ret/PH-treated rats, the mass of the recipient liver transiently increased during the first 30 days after transplantation, suggesting that liver regeneration was enhanced. Here we addressed how Thy1+ cell transplantation stimulates liver regeneration. We found that the number and size of SHPC clusters increased in the liver at 14 days after transplantation. GeneChip analysis revealed that interleukin 17 receptor b (IL17rb) expression significantly increased in SHPCs from livers transplanted with Thy1+ cells. We subsequently searched for ligand-expressing cells and found that sinusoidal endothelial cells (SECs) and Kupffer cells expressed Il17b and Il25, respectively. Moreover, extracellular vesicles (EVs) separated from the conditioned medium of Thy1+ cell culture induced IL17b and IL25 expression in SECs and Kupffer cells, respectively. Furthermore, EVs enhanced IL17rb expression in small hepatocytes (SHs), which are hepatocytic progenitor cells; in culture, IL17B stimulated the growth of SHs. These results suggest that Thy1-EVs coordinate IL17RB signaling to enhance liver regeneration by targeting SECs, Kupffer cells, and SHPCs. Indeed, the administration of Thy1-EVs increased the number and size of SHPC clusters in Ret/PH-treated rat livers. Sixty days post-transplantation, most expanded SHPCs entered cellular senescence, and the enlarged liver returned to its normal size. In conclusion, Thy1+ cell transplantation enhanced liver regeneration by promoting the proliferation of intrinsic hepatic progenitor cells via IL17RB signaling. Stem Cells 2017;35:920-931.

Liver Tumor Microenvironment

The tumor microenvironment (TME) has recently been recognized as an important part of tumor development and growth. TME is a dynamic system orchestrated by immune, cancer and inflammatory cells, as well as the stromal tissue and surrounding extracellular matrix. While TME of primary hepatic tumors is usually characterized by a strong inflammatory background, the TME of liver metastases typically consists of otherwise healthy liver tissue. Chronic inflammation and hypoxia are key to the development and progression of primary liver cancer. The injury caused by chronic inflammation creates a condition of immune evasion that initiates a cascade of events that eventually leads to liver carcinogenesis.With liver metastases, primary tumors "prime" the target organs via secreting factors that induce expansion of myeloid cell populations and create a solid ground for successful cancer settlement. Once in the liver, metastatic cells begin a neovascularization process that is driven mainly by VEGF and FGF. Due to high mortality rates associated with liver cancer, as well as the limited effective treatment options for advanced disease, new therapies are urgently needed. Targeting a single molecule in a number of interactions between the tumor and the TME is highly unlikely to reduce tumor growth. Future trials should focus on combination therapies (i.e. targeted therapies combined with immunotherapy) to treat liver malignancies efficiently.

Noninvasive imaging diagnosis of sinusoidal obstruction syndrome: a pictorial review

Sinusoidal obstruction syndrome (SOS) is a rare liver disorder due to hepatic vascular injury. Its rapid and accurate diagnosis is crucial for patient survival. SOS is often established clinically, based on Baltimore, modified Seattle, or European Society for Blood and Marrow Transplantation (EBMT) criteria. Unfortunately, such criteria are not highly specificity and fail to provide a timely, reliable differential diagnosis. The use of noninvasive imaging techniques, such as ultrasound (US), computed tomography (CT), magnetic resonance imaging (MRI), and fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), has recently grown in this setting, some key imaging features offering diagnostic improvement. This review provides a synopsis of current noninvasive imaging techniques used for this purpose, summarizing accurate and reliable diagnostic features of SOS.

Localization of ATP-sensitive K+ channel subunits in rat liver

BACKGROUND

ATP-sensitive K⁺ (K_ATP) channels were originally found in cardiac myocytes by Noma in 1983. K_ATP channels were formed by potassium ion-passing pore-forming subunits (Kir6.1, Kir6.2) and regulatory subunits SUR1, SU2A and SUR2B. A number of cells and tissues have been revealed to contain these channels including hepatocytes, but detailed localization of these subunits in different types of liver cells was still uncertain.

AIM

To investigate the expression of K_ATP channel subunits in rat liver and their localization in different cells of the liver.

METHODS

Rabbit anti-rat SUR1 peptide antibody was raised and purified by antigen immunoaffinity column chromatography. Four of Sprague-Dawley rats were used for liver protein extraction for immunoblot analysis, seven of them were used for immunohistochemistry both for the ABC method and immunofluorescence staining. Four of Wistar rats were used for the isolation of hepatic stellate cells (HSCs) and Kupffer cells for both primary culture and immunocytochemistry.

RESULTS

Immunoblot analysis showed that the five kinds of K_ATP channel subunits, i.e. Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B, were detected in liver. Immunohistochemical staining showed that Kir6.1 and Kir6.2 were weakly to moderately expressed in parenchymal cells and sinusoidal lining cells, while SUR1, SUR2A, and SUR2B were mainly localized to sinusoidal lining cells, such as HSCs, Kupffer cells, and sinusoidal endothelial cells. Immunoreactivity for SUR2A and SUR2B was expressed in the hepatocyte membrane. Double immunofluorescence staining further showed that the pore-forming subunits Kir6.1 and/or Kir6.2 colocalized with GFAP in rat liver sections and primary cultured HSCs. These K_ATP channel subunits also colocalized with CD68 in liver sections and primary cultured Kupffer cells. The SUR subunits colocalized with GFAP in liver sections and colocalized with CD68 both in liver sections and primary cultured Kupffer cells. In addition, five K_ATP channel subunits colocalized with SE-1 in sinusoidal endothelial cells.

CONCLUSION

Observations from the present study indicated that K_ATP channel subunits expressed in rat liver and the diversity of K_ATP channel subunit composition might form different types of K_ATP channels. This is applicable to hepatocytes, HSCs, various types of Kupffer cells and sinusoidal endothelial cells.

Ultrastructural changes in porcine liver sinusoidal endothelial cells of machine perfused liver donated after cardiac death

BACKGROUND

The machine perfusion (MP) preservation including hypothermic MP (HMP) and midthermic MP (MMP) has been considered as a promising strategy to preserve the functions of liver donated after cardiac death. The importance of understanding liver sinusoidal endothelial cells (LSEC) damage in regulating liver injury during MP has been emphasized. However, the ultrastructural changes in the LSEC and sinusoids around them after MP are unclear.

AIM

To investigate the ultrastructural changes in the LSEC and sinusoids around them after MP.

METHODS

Porcine liver grafts undergo a warm ischemia time of 60 minutes perfused for 4 h with modified University of Wisconsin gluconate solution. Group A grafts were preserved with HMP at 8 °C constantly for 4 h. Group B grafts were preserved with a rewarming solution at 22 °C by MMP for 4 h. Then the ultrastructural changes in the LSEC and sinusoids in Group A and B were comparatively analyzed by using osmium-maceration scanning electron microscopy with complementary transmission electron microscopy methods.

RESULTS

An analysis of the LSEC after warm ischemia revealed that mitochondria with condensed-shaped cristae, abnormal vesicles, reduction of ribosomes and the endoplasmic reticulum (ER) surround the mitochondria appeared. The MP subsequent after warm ischemia alleviate the abnormal vesicles and reduction of ribosomes in LSEC, which indicated the reduction of the ER damage. However, MMP could restore the tubular mitochondrial cristae, while after HMP the condensed and narrow mitochondrial cristae remained. In addition, the volume of the sinusoidal space in the liver grafts after MMP were restored, which indicated a lower risk of pressure injury than HMP.

CONCLUSION

MMP alleviates the ER damage of LSEC by warm ischemia, additionally restore the metabolism of LSEC via the normalization of mitochondria and prevent the share stress damage of liver grafts.

Significance of combined detection of HIF-1α, TXB2, 6-keto-PGF1α and HA in the diagnosis of hepatic microcirculatory disturbance in patients with chronic hepatitis B

AIM: To evaluate the significance of combined detection of HIF-1α, TXB2, 6-keto-PGF1α and HA in the diagnosis of hepatic microcirculatory disturbance in patients with chronic hepatitis B (CHB).

METHODS: In total, 275 patients with CHB and 15 normal volunteer were included. The ultrastructure of the liver was observed by transmission electron microscopy (TEM). HIF-1α expression in liver biopsies was detected by immunohistochemistry. Plasma levels of TXB2 and 6-keto-PGF1α were determined by chemiluminescence, and serum HA levels was measured by RIA.

RESULTS: As the pathological changes of the liver were aggravated, erythrocyte aggregation, stenosis and blockage of sinus hepaticas, collagen fiber deposition, and basal membrane formation became worsened, the strength and range of expression of HIF-1α was enhanced, the levels of serum HA and plasma TXB2 were raised gradually, and plasma levels of 6-keto-PGF1α slightly declined.

CONCLUSION: Combined detection of HIF-1α, TXB2, 6-keto-PGF1α and HA can help accurately diagnose hepatic microcirculatory disturbance in patients with CHB.