Micro- and macrovesicular steatotic liver model for transplantation induced by ethanol and protein-deficient diet

Effect of Melatonin as an Antioxidant Drug to Reverse Hepatic Steatosis: Experimental Model

Introduction

The hepatic steatosis of the nonalcoholic origin or NAFLD is increasing at present, particularly in Western countries, parallel to the increase in obesity, constituting one of the most prevalent hepatic processes in the Western society. Melatonin has been successfully tested in experimental models in mice as a drug capable of reversing steatosis. The effect of melatonin on fat metabolism can be summarized as a decrease in lipid peroxidation and a decrease in oxidative stress, biochemical phenomena intimately related to fat deposition in the hepatocyte. There are hardly any studies in large animals.

Objective

In this study, we investigate the effects of melatonin administered orally at a dose of 10 mg/kg/day to reverse established hepatic steatosis induced by a special diet in a porcine animal model.

Materials and Methods

We analyze the parameters of oxidative stress: malondialdehyde (MDA), 4-hydroxyalkenals (4-HDA), and carbonyls, degree of fat infiltration (analyzed by direct vision by a pathologist and by means of a computer program of image treatment), and serological parameters of lipid metabolism and hepatic damage. These parameters were analyzed in animals to which hepatic steatosis was induced by means of dietary modifications.

Results

We have not been able to demonstrate globally a beneficial effect of melatonin in the improvement or reversal of liver steatosis once established, induced by diet in a porcine animal model. However, we have found several signs of improvement at the histological level, at the level of lipid metabolism, and at the level of oxidative stress parameters. We have verified in our study that, in the histological analysis of the liver sample by means of the program image treatment (free of subjectivity) of the animals that continue with the diet, those that consume melatonin do not increase steatosis as much as those that do not consume it significantly (p=0.002). Regarding the parameters of oxidative stress, MDA modifies in a significant manner within the group of animals that continue with the diet and take melatonin (p=0.004). As for lipid metabolism, animals that maintain the steatotic diet and take melatonin lower total and LDL cholesterol levels and increase HDL levels, although these results do not acquire statistical significance.

Conclusions

In this study, it has not been possible to demonstrate a beneficial effect of melatonin in the improvement or reversal of liver steatosis once established and induced by diet in the porcine model. It is true that signs of improvement have been found at the histological level, at the level of lipid metabolism, and at the level of oxidative stress phenomena, when comparing animals with established steatosis that are treated with melatonin with those who do not take it. This work is the first study conducted in a large animal model in which the effect of melatonin is studied as a treatment in the reversal of established hepatic steatosis.

Ex situ machine perfusion as a tool to recondition steatotic donor livers: Troublesome features of fatty livers and the role of defatting therapies. A systematic review

Long-standing research has shown that increased lipid content in donor livers is associated with inferior graft outcomes posttransplant. The global epidemic that is obesity has increased the prevalence of steatosis in organ donors, to the extent that it has become one of the main reasons for declining livers for transplantation. Consequently, it is one of the major culprits behind the discrepancy between the number of donor livers offered for transplantation and those that go on to be transplanted. Steatotic livers are characterized by poor microcirculation, depleted energy stores because of an impaired capacity for mitochondrial recovery, and a propensity for an exaggerated inflammatory response following reperfusion injury culminating in poorer graft function postoperatively. Ex situ machine perfusion, currently a novel method in graft preservation, is showing great promise in providing a tool for the recovery and reconditioning of marginal livers. Hence, reconditioning these steatotic livers using machine perfusion has the potential to increase the number of liver transplants performed. In this review, we consider the problematic issues associated with fatty livers in the realm of transplantation and discuss pharmacological and nonpharmacological options that are being developed to enhance recovery of these organs using machine perfusion and defatting strategies.

Ethanol and fatty acids impair lipid homeostasis in an in vitro model of hepatic steatosis

Excess ethanol consumption and fatty acid intake lead to a cumulative effect on liver steatosis through still unclear mechanisms. This study aimed to characterize the lipid homoeostasis alterations under the exposure of hepatocytes to ethanol alone or combined with fatty acids. FaO hepatoma cells were incubated in the absence (C) or in the presence of 100 mM ethanol (EtOH) or 0.35 mM oleate/palmitate (FFA) alone or in the combination (FFA/EtOH). Content of intra- and extra-cellular triglycerides (TAGs) and of lipid droplets (LDs), expression of lipogenic and lipolytic genes, and oxidative stress-related parameters were evaluated. Exposure to either FFAs or EtOH given separately led to steatosis which was augmented when they were combined. Our results show that FFA/EtOH: (i) increased the LD number, but reduced their size compared to separate treatments; (ii) up-regulated PPARγ and SREBP-1c and down-regulated sirtuin-1 (SIRT1); (iii) impaired FFA oxidation; (iv) did not change lipid secretion and oxidative stress. Our findings indicate that one of the major mechanisms of the metabolic interference between ethanol and fat excess is the impairment of FFA oxidation, in addition to lipogenic pathway stimulation. Interestingly, ethanol combined with FFAs led to a shift from macrovesicular to microvesicular steatosis that represents a more dangerous condition.

Perfusion Characteristics of the Human Hepatic Microcirculation Based on Three-Dimensional Reconstructions and Computational Fluid Dynamic Analysis

The perfusion of the liver microcirculation is often analyzed in terms of idealized functional units (hexagonal liver lobules) based on a porous medium approach. More elaborate research is essential to assess the validity of this approach and to provide a more adequate and quantitative characterization of the liver microcirculation. To this end, we modeled the perfusion of the liver microcirculation using an image-based three-dimensional (3D) reconstruction of human liver sinusoids and computational fluid dynamics techniques. After vascular corrosion casting, a microvascular sample (±0.134 mm3) representing three liver lobules, was dissected from a human liver vascular replica and scanned using a high resolution (2.6 μm) micro-CT scanner. Following image processing, a cube (0.15 × 0.15 × 0.15 mm3) representing a sample of intertwined and interconnected sinusoids, was isolated from the 3D reconstructed dataset to define the fluid domain. Three models were studied to simulate flow along three orthogonal directions (i.e., parallel to the central vein and in the radial and circumferential directions of the lobule). Inflow and outflow guidances were added to facilitate solution convergence, and good quality volume meshes were obtained using approximately 9 × 106 tetrahedral cells. Subsequently, three computational fluid dynamics models were generated and solved assuming Newtonian liquid properties (viscosity 3.5 mPa s). Post-processing allowed to visualize and quantify the microvascular flow characteristics, to calculate the permeability tensor and corresponding principal permeability axes, as well as the 3D porosity. The computational fluid dynamics simulations provided data on pressure differences, preferential flow pathways and wall shear stresses. Notably, the pressure difference resulting from the flow simulation parallel to the central vein (0–100 Pa) was clearly smaller than the difference from the radial (0–170 Pa) and circumferential (0–180 Pa) flow directions. This resulted in a higher permeability along the central vein direction (kd,33 = 3.64 × 10−14 m2) in comparison with the radial (kd,11 = 1.56 × 10−14 m2) and circumferential (kd,22 = 1.75 × 10−14 m2) permeabilities which were approximately equal. The mean 3D porosity was 14.3. Our data indicate that the human hepatic microcirculation is characterized by a higher permeability along the central vein direction, and an about two times lower permeability along the radial and circumferential directions of a lobule. Since the permeability coefficients depend on the flow direction, (porous medium) liver microcirculation models should take into account sinusoidal anisotropy.

Gene expression in livers of BALB/C and C57BL/6J mice fed a high-fat diet

We previously demonstrated that high-fat diet (HFD)-induced hepatic lipid accumulation is more severe in BALB/c mice than in C57BL/6J (B6) mice. To understand the changes in liver metabolism, we studied blood chemistry, gene expression, and histopathological changes of the liver in nine-week HFD-fed BALB/c and B6 mice and one- or four-week HFD-fed BALB/c mice. Serum total cholesterol and triglyceride levels were significantly increased in all HFD-fed groups, and one- and four-week HFD-fed BALB/c groups, respectively. Histopathology revealed that vacuolation of hepatocytes was severe in nine-week HFD-fed BALB/c mice, although it was less severe in the other groups. Microarray analysis of mRNA expression of nine-week HFD-fed BALB/c mice showed up-regulation of genes involved in fatty acid uptake and biosynthesis, such as Cd36, Acaca, Acly, and Fasn. Some changes were observed in the one- and four-week HFD-fed BALB/c groups and the nine-week HFD-fed B6 group, however these changes in mRNA expression were not so marked. In conclusion, the fatty accumulation observed in BALB/c mice may be caused, at least in part, by up-regulation of fatty acid uptake and biosynthesis. Cd36, Acaca, Acly and Fasn may be involved in these metabolic processes.

Quantitative estimation of the degree of hepatic macrovesicular steatosis in a disease-free population: a single-center experience in mainland China

The aim of this study was to derive a simple equation to enable the extent of hepatic macrovesicular steatosis (HMS) to be predicted quantitatively from data obtained noninvasively and hence avoid unnecessary liver biopsies. One hundred sixty-seven potential living liver donors and 45 subjects suspected of having nonalcoholic fatty liver disease (NAFLD) underwent percutaneous liver biopsy to evaluate HMS quantitatively. Their hepatic unenhanced computed tomography (CT) attenuation, body mass index (BMI), and indices of serum lipids were reviewed. Logistic regression analysis was undertaken to screen for independent predictors of HMS. Linear regression analysis was then used to plot the relationship between the severity of histologically confirmed HMS and identified independent predictors of HMS. For potential donors with HMS of severity > or = 5% by histological assessment, the following equation was derived: HMS = 47.7 + 1.48BMI - 1.14CT (R2 = 0.74)The calculated HMS for potential donors with histologically confirmed HMS of severity < 5% seemed to be unreliable (R(2) = = 0.230, P < 0.3). In addition, in subjects suspected of having NAFLD, there was a close agreement between values for histologically confirmed HMS and calculated values for HMS derived from the equation (intraclass correlation coefficient = 0.88). Hepatic CT imaging in conjunction with other noninvasive clinical data may enable the extent of HMS to be accurately predicted with the equation derived from potential donors with appreciable degrees of histologically confirmed HMS.

Effect of graft steatosis on liver function and organ survival after liver transplantation

BACKGROUND

It was the aim to determine the effect of graft steatosis on intraoperative organ blood flow, postoperative liver function, and organ survival.

METHODS

A total of 225 consecutive liver transplants were reviewed. Liver blood flow, hepatic function (AST, ALT, prothrombin time), and organ survival were determined. Donor liver grafts were categorized into 2 subgroups: mild (<30%) (n = 175) and moderate to severe (>/=30%) (n = 50) macrovesicular steatosis.

RESULTS

Moderate to severe steatosis was associated with significantly increased AST and ALT levels and significantly diminished prothrombin time on the first and second postoperative day. By day 7 differences in liver function were no longer evident. Organ blood flow was not affected by steatosis. After adjustment for potential confounders, organ survival did not depend on the degree of donor steatosis (5-year-survival rates: 68% and 58% with steatosis <30%, or >/= 30%, respectively) (hazard ratio .754, confidence interval .458-1.242, P = .268).

CONCLUSION

Steatotic livers can be transplanted safely with good results for long-term organ survival if other contraindications are absent.

Regenerative capacity differs between micro- and macrovesicular hepatic steatosis

INTRODUCTION

Independent of etiology, the hepatic microvesicular steatosis has a worse prognosis compared with macrovesicular steatosis. Proliferation compensates for apoptosis and reflects regenerative mechanisms following liver injury. It is unknown whether these two types of fatty liver have differences in regenerative capacity and apoptosis, which could have an impact on their prognosis.

METHODS

Two groups of pigs were studied for 72 days under a protein-deficient diet. One group received only protein-deficient diet (n=6), the other was treated in addition to the diet with 6g ethanol/kg/day by means of a percutaneous intragastric catheter (n=6). The rate of proliferating and apoptotic hepatocytes was determined, respectively, by proliferation cell nuclear antigen (PCNA) and ISEL/TUNEL staining for apoptosis in liver biopsies with similar steatosis grade in pigs with micro- or macrovesicular fatty liver.

RESULTS

The ethanol-treated group developed microvesicular steatosis, the other group developed macrovesicular steatosis. Proliferation index was significantly increased in macrovesicular in comparison with microvesicular steatosis (p<0.05). Apoptosis rate was similar in both groups.

CONCLUSIONS

Regeneration, but not apoptosis rate differs between micro- and macrovesicular steatosis. The reduced regenerative capacity in microvesicular steatosis may contribute to the worse prognosis of this subtype of fatty liver disease.

Steatosis as a risk factor in liver surgery

OBJECTIVE

To review present knowledge of the influence of hepatic steatosis in liver surgery as derived from experimental and clinical studies.

SUMMARY BACKGROUND DATA

Hepatic steatosis is the most common chronic liver disease in the Western world, and it is associated with obesity, diabetes, and metabolic syndrome. Fatty accumulation affects hepatocyte homeostasis and potentially impairs recovery of steatotic livers after resection. This is reflected clinically in increased mortality and morbidity after liver resection in patients with any grade of steatosis. Because of the epidemic increase of obesity, hepatic steatosis will play an even more significant role in liver surgery.

METHODS

A literature review was performed using MEDLINE and key words related to experimental and clinical studies concerning steatosis.

RESULTS

Experimental studies show the increased vulnerability of steatotic livers to various insults, attributed to underlying metabolic and pathologic derangements induced by fatty accumulation. In clinical studies, the severity of steatosis has an important impact on patient outcome and mortality. Even the mildest form of steatosis increases the risk of postoperative complications.

CONCLUSIONS

Hepatic steatosis is a major factor determining patient outcome after surgery. Further research is needed to clarify the clinical relevance of all forms and severity grades of steatosis for patient outcome. Standardized grading and diagnostic methods need to be used in future clinical trials to be able to compare outcomes of different studies.