The role of certain metabolic and morphofunctional changes in the development of non-alcoholic steatohepatitis (a clinical and experimental study)

The dissertation is devoted to the study of the role of certain metabolic and morphofunctional changes in the development of non-alcoholic steatohepatitis. The work is of a clinical and experimental character and combines the modeling of toxico-metabolic liver damage in laboratory animals with the examination of patients suffering from non-alcoholic fatty liver disease. The biochemical and histological manifestations of the pathological process are investigated, as well as the state of cellular respiration of hepatocytes, including cytochrome oxidase activity. The possibility of using statins for the correction of steatosis under experimental conditions is considered separately.

The practical significance of the work is connected with the substantiation of the expediency of performing a needle biopsy of the liver in patients with hepatomegaly with minimally expressed laboratory changes in order to clarify the activity and stage of fibrosis in non-alcoholic steatohepatitis, as well as with the characterization of the morphological picture of the disease in the latent and manifest variants of its clinical course.

In the clinical practice of the internist, liver pathology represented by chronic hepatitis is one of the most widespread groups of diseases. Among the adult population, chronic hepatitis occurs in more than 5% of cases, and in some regions of the world even more frequently (Angulo P., 2004; Карлейро де Мура М., 2005). The significance of these diseases is determined primarily by the fact that their development proceeds over a long period of time, while the development of hepatocellular insufficiency, as well as transformation into cirrhosis and primary carcinoma of the liver, constitute the most frequent cause of disability and mortality in these patients (Федоров И.Г. et al., 2004; Bacon B.R., 2005).

The main cause of the formation of chronic hepatitis is viral infection caused by such hepatotropic viruses as B, C, D, F, and G (Thomas H.C. et al., 1997; Cramp M.E. et al., 1999; Liu H. et al., 2002). In addition to this factor, chronic hepatitis may be caused by systematic alcohol intake, autoimmune causes, drug use, certain medications with hepatotoxic action, and other causes (Watson A.J.M., 1997; Буеверов А.О., Маевская М.В., 2003).

In recent years, there has been a surge of interest in the problem of liver damage in the cardiovascular metabolic syndrome. The clinical significance of the metabolic and hormonal disturbances united by this syndrome is determined by the fact that their combination sharply accelerates the development and progression of cardiovascular diseases, which occupy the first place among the causes of mortality in the population of industrially developed countries (Богомолов П.О., Павлова Т.В., 2003).

Within the framework of this syndrome, against the background of insulin resistance, abdominal-visceral obesity, dyslipidemia, arterial hypertension, and type 2 diabetes mellitus are considered, as well as early atherosclerosis, ischemic heart disease, and a number of other pathological conditions, including hepatic steatosis and non-alcoholic steatohepatitis (combined under the concept of non-alcoholic fatty liver disease) (Ивашкин В.Т., Шульпекова Ю.О., 2002; Буеверов А.О., Маевская М.В., 2004).

Non-alcoholic fatty liver disease covers a spectrum of liver lesions including fatty dystrophy, fatty dystrophy with inflammation and damage to hepatocytes (non-alcoholic (metabolic) steatohepatitis), and fibrosis (Angulo P., 2004; Богомолов П.О., Павлова Т.В., 2005).

In Europe and Japan, the prevalence of non-alcoholic fatty liver disease in the population reaches 10–40%, while in the United States it accounts for 69% of liver diseases, with non-alcoholic steatohepatitis being verified in almost 5% of cases (Diehl A.M., 2002; Clark J.M., 2003). However, the true prevalence of this disease is unknown.

Fatty dystrophy of the liver (fatty infiltration, hepatic steatosis, fatty liver) in the domestic literature has traditionally been regarded as a benign condition with a favorable prognosis; nevertheless, its transformation into liver cirrhosis occurs 2–3 times more often than in the general population (Day C.P. et al., 2003; Подымова С.Д., 2005). In addition, fatty dystrophy of the liver is associated with a high risk of developing primary carcinoma (Cannon C.P. et al., 2004).

This pathology substantially worsens the prognosis of the diseases associated with it, narrows the possibilities of pharmacotherapy, and creates a potential danger of the development of hepatic fibrosing and hepatic insufficiency in a proportion of patients (Оковитый С.В., 2005). At the same time, it is important to note that in the pathogenesis of liver damage in obesity, insulin resistance, dyslipidemia, and pathology of the cardiovascular system there are a large number of common links, among which the leading role belongs to the accumulation of lipids in hepatocytes and to the intensification of free-radical oxidation processes with the development of necrosis of hepatic cells (Cannon C.P. et al., 2004). This makes it possible, on the one hand, to recommend universal approaches to the therapy of steatoses and steatohepatitides (within the framework of pathogenetically oriented basic therapy) and, on the other hand, leaves the physician latitude in choosing pharmacotherapy and preventive measures for this pathology.

Aim of the study.

To investigate the features of certain metabolic and morphofunctional changes in toxico-metabolic liver damage in the experiment and in the clinic.

Objectives of the study.

1. To study, in an experimental model of steatohepatitis in animals, certain metabolic and structural features of the formation of the pathological process in the liver.

2. To determine the features of the course of the reparative process in the liver and the state of cellular respiration in animals with experimental steatohepatitis.

3. To study certain clinical and morphofunctional features in the liver in patients with non-alcoholic steatohepatitis.

4. To evaluate, in an experimental study, the possibility of using statins for the correction of steatosis in non-alcoholic steatohepatitis.

Scientific novelty.

A successful testing of an experimental model of steatohepatitis was carried out, the main morphofunctional features of which are the cytolytic syndrome, disturbance of pigment metabolism, development of signs of fatty dystrophy of hepatocytes, and slight inflammatory infiltration of the portal tracts and fibrosis of the organ.

It has been shown that in experimental steatohepatitis damage to the electron-transport chain of hepatocyte mitochondria occurs, primarily in the region of its NAD-dependent complex. One of the signs of its disturbance is the low activity of cytochrome oxidase.

It has been established that, regardless of the latent or manifest variant of the clinical course of hepatopathy, the examined patients reveal morphological signs of steatohepatitis in the form of inflammatory infiltration, sclerosis of the portal and periportal fields with extension of the inflammatory and fibrotic changes inside the lobule, as well as dystrophic changes in hepatocytes of varying degrees of severity.

For the first time, the influence of simvastatin on the morphofunctional state of the liver in experimental steatohepatitis has been studied. It has been proved that the action of the drug does not potentiate damage to the microsomal oxidation system in the liver and prevents damage to the NAD-dependent segment of the respiratory chain of hepatocyte mitochondria.

Practical significance.

The results of the conducted investigation indicate that in hepatomegaly, both in the latent and in the manifest variant of the course of non-alcoholic steatohepatitis, morphological signs of steatohepatitis are detected in the form of inflammatory infiltration of the portal tracts of varying degrees of severity.

The data obtained indicate the expediency of performing a needle biopsy of the liver in persons with hepatomegaly in non-alcoholic steatohepatitis in order to clarify the degree of fibrosis and the activity of the pathological process in the liver, even with a minimal degree of severity of laboratory signs of organ damage.

Principal statements submitted for defense.

1. The experimental model of steatohepatitis, even with minimal changes in laboratory markers of hepatocyte cytolysis, is characterized by the development of morphological signs of intralobular fatty dystrophy, slight inflammatory infiltration, and fibrosis of the portal tracts. One of the pathogenetic mechanisms of hepatocyte damage is the injury of the first complex of the NAD-dependent segment of the mitochondrial respiratory chain with disturbance of its functioning due to the low activity of cytochrome oxidase.

2. The formation of non-alcoholic steatohepatitis, regardless of the variant of the clinical course of the disease (manifest or latent), is characterized by inflammatory infiltration, sclerosis of the portal fields and periportal zone with extension of the inflammatory and fibrotic changes inside the lobule against the background of marked dystrophic changes in hepatocytes. A significant positive correlation has been established between the degree of hepatocyte dystrophy, their mitotic activity, and the severity of inflammatory infiltration of the portal tracts and the processes of fibrosing in the liver.

3. The use of simvastatin in experimental steatohepatitis is characterized by a reliable hypolipidemic and anticholestatic effect, with a substantial reduction in the severity of fatty dystrophy of the liver and no increase in the phenomena of fibrosis and inflammation. The drug does not potentiate damage to the microsomal oxidation system in the liver and prevents damage to the NAD-dependent segment of the respiratory chain of hepatocyte mitochondria.

Approbation and implementation of the work: On the topic of the dissertation, 7 scientific works have been published. The results of the work were reported at the Eighth World Congress on Cytology (Nice, France, 2004), the All-Russian Scientific Conference "Gastroenterology — Today" (Moscow, 2005), the All-Russian Scientific Conference "Gastro — 2005" (Saint Petersburg, 2005), and at the plenary session of the Saint Petersburg Society of Therapists named after S.P. Botkin (Saint Petersburg, 2005).

Implementation and introduction of the results of the investigation: The results of the investigations have been introduced into the Clinic of Propaedeutics of Internal Diseases of the Military Medical Academy and into the therapeutic departments of city hospitals No. 8 and No. 32. The materials of the investigation are used in the scientific and teaching work of the Department of Propaedeutics of Internal Diseases, in the lecture cycles for cadets and students of the faculties of physician training, and also in seminar classes for intern physicians and clinical residents.

Volume and structure of the dissertation: The dissertation is set out on 119 pages of typewritten text, and consists of an introduction, four chapters (a review of the literature, a description of the material and methods of the investigation, and two chapters of the results of the author's own investigations), a conclusion, conclusions, practical recommendations, and a bibliography comprising 167 sources, including 55 domestic and 112 foreign authors. The text contains 1 clinical example, is illustrated by 13 tables and 21 figures.