Primary biliary cholangitis: A historical perspective from xanthomatous lesions to modern molecular biology

Abstract

Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease characterized by damage and loss of the epithelial lining of small intrahepatic bile ducts, leading to ductopenia and cholestasis. In advanced stages, this process results in cirrhosis and liver failure. The disease belongs to cholangiopathies. The review addressed historical questions concerning: The history of the first mention of this disease; how its nomenclature was formed; when specific serological tests were discovered and their importance in the diagnosis of PBC; the history of ursodeoxycholic and other bile acids for the treatment of PBC; and the significance of modern data on impaired bicarbonate production by cholangiocytes in the pathogenesis of PBC.

Key Words: Nonobstructive biliary cirrhosis; Addison-Gull syndrome; La cirrhose hypertrophique avec ictère chronique; Hypertrophic cirrhosis Hanot; Xanthomatous biliary cirrhosis; Primary biliary cirrhosis; Primary biliary cholangitis

Core Tip: The present review was devoted to an examination of the historical aspects of primary biliary cholangitis. The initial references to the disease are examined, along with the evolution of its nomenclature. The importance of the development and the evolution of clinical, laboratory, and instrumental methods for the discovery and elucidation of the pathophysiological mechanisms of primary biliary cholangitis is shown.

INTRODUCTION

Primary biliary cholangitis (PBC) is a chronic cholestatic progressive liver disease characterized by the destruction, necrosis, and apoptosis of the biliary epithelium predominantly in the intralobular, interlobular, and septal bile ducts with the formation of antimitochondrial autoantibodies (an autoimmune component). In the terminal stage, liver cirrhosis develops.

The advent of new scientific methodologies has been instrumental in the identification of this disease, the initial characterization of its clinical, pathologo-anatomical, morphological, and laboratory manifestations, and the establishment of diagnostic techniques. From these positions we propose the consideration of the evolution of the historical view underlying the discovery, the description of the salient features of this disease, and the establishment of its diagnostic criteria.

EARLY DESCRIPTIONS OF BILIARY CIRRHOSIS

Significance of clinical and pathologo-anatomical methodologies in the identification of disease

An early description of one of the cutaneous signs of the disease now known as PBC dates back to the mid-nineteenth century. In 1851, an article “On a Certain Affectation of the Skin-Vitiligoidea-alpha plana, beta tuberosa” published by Thomas Addison and William Gull in the Guys Hospital Report was the first description of cutaneous clinical signs that the authors observed to be associated with liver pathology[1].

Thomas Addison (1793-1860) was an eminent English scientist, clinician, pathophysiologist, and anatomist. Thomas Addison, after graduating from the Faculty of Medicine at Edinburgh University in 1815, moved to London and took up residency at the Venereal Hospital. He subsequently continued his training at Guy’s Hospital, ultimately becoming a lecturer in practical medicine. Thomas Addison was considered an excellent diagnostician but was also a reserved person. He suffered from a depressive disorder and died by suicide on June 29, 1860[2,3].

Sir William Withey Gull, 1^st Baronet (1816-1890) was a physician of considerable erudition and is regarded as one of the foremost medical experts of the 19^th century. He was the personal physician to Queen Victoria. Sir William Gull was a highly regarded internist and a physician who devoted a great deal of time to his patients. In 1871, he successfully cured the Prince of Wales, who had fallen seriously ill with typhoid fever complicated by bronchitis, and was subsequently appointed as one of Queen Victoria's physicians. As well as Addison, he worked and lectured to medical students at Guy’s Hospital and later became the hospital’s manager. Gull’s scientific interests were in the study of skin diseases[3].

The authors drew attention to some unusual, rare skin lesions that differed from the then-known vitiligo and keloid. The authors introduced the term “Vitiligoidea” to describe them, presenting two forms of these changes: The former, designated “alpha plana”, manifested as flat plaque-like formations around the eyes (referred to as xanthelasmas in contemporary nomenclature); and the latter, termed “beta tuberosa”, presented as flat tuberous tubercles at sites of trauma and other regions of the body, including the ears, elbows, knees, and skin folds (now categorized as xanthomas)[3].

Xanthelasma has been previously documented. In 1826, Rayer published an atlas of skin diseases in which he first described xanthelasms around the eyes as yellow plaques the color of chamois leather, slightly raised, neither warm nor red, and sometimes disposed in a somewhat symmetrical manner[4]. However, until Addison and Gull no one had associated their occurrence with liver disease.

Addison and Gull described the morphology of xanthomas and xanthelasms and illustrated them with artistic reproductions. One such illustration is presented in the review of White and MacDonald[2], where the artist carefully painted flat formations rising above the skin (xanthelasms) on the upper and lower eyelids of a 43-year-old patient who "...during the last five years there has been a gradual change in the integument of the eyelids, giving her a strange expression..."[1,2].

A total of five observations were recorded and described; three of which bore a resemblance to the disease known today as PBC. The observed patients ranged in age from 24 to 43 years. Subsequent analysis of the descriptions of these observations showed that the skin changes detected in one female corresponded to tuberous sclerosis and in another to an eruptive xanthoma in diabetes mellitus[2]. In three females the presence of flat xanthomas and xanthelasmas on the skin was accompanied by prolonged jaundice, skin itching, and discomfort in the right subcostal area[2].

Despite the unavailability of lifetime histological examination to ascertain the involvement of the liver in the pathological process during that era, Addison and Gull rightly hypothesized the correlation between the appearance of “alpha plana” and “beta tuberosa” with liver damage in these patients[1,5]. Addison and Gull proposed the nomenclature “nonobstructive biliary cirrhosis” for the disorder of liver function manifested by skin changes in the form of “alpha plana” and “beta tuberosa”. In light of the seminal contributions made by Addison and Gull in establishing the correlation between cutaneous manifestations and hepatic impairment, the disease was delineated not solely as “nonobstructive biliary cirrhosis” but also as “Addison-Gull syndrome”[6].

In the ensuing years, a series of clinical and experimental papers have been published in the English, French, and German scientific literature, thereby confirming this relationship[4,7-9]. It is noteworthy that some of these works assume a primary role of xanthomatosis in the occurrence of biliary obstruction and the development of biliary cirrhosis[7,10,11]. Subsequent studies of autopsy material did not reveal xanthomatous changes in the epithelial lining of the bile ducts, which was written about by Maxon, Face, and Pure-Smith[7,10,11].

Victor Hanot and the emergence of the term hypertrophic cirrhosis with chronic jaundice (la cirrhose hypertrophique avec ictère chronique)

It is widely accepted that the initial description of the clinical manifestation of the disease that is now recognized as PBC was provided by Victor Charles Hanot, a French physician who was renowned for his contributions to the field of hepatology[4].

Victor Charles Hanot (1844-1896) was one of the most prominent French physicians of the 19^th century. Hanot made significant contributions to research in the field of hepatic cirrhosis and hemochromatosis. He was awarded his doctorate from the University of Paris in 1875, following the presentation of his thesis on the subject of “Hypertrophic cirrhosis with chronic jaundice” (“La cirrhose hypertrophique avec ictère chronique”)[4,12,13].

In his thesis, Hanot emphasized that the disease described by Addison and Gull was characterized by significant liver enlargement and prolonged jaundice. Hanot pointed out that in contrast to the primary liver enlargement observed in cases of portal cirrhosis the liver enlargement in the present context was not primary. However, it is permanent and persists throughout the course of the disease, without regression afterwards. The analysis of pathologo-anatomical data revealed that the liver enlargement and prolonged jaundice are accompanied by extensive fibrosis[9,12,13]. Subsequent analysis revealed fibrosis to be a hallmark of the disease[14].

Hanot noted that despite the absence of any visible gross obstruction of hepatic ducts, the main cause of the developing chronic process in the liver was the obstruction of bile outflow at the level of small intrahepatic bile ducts, which was confirmed by anatomical and morphological correspondence during autopsy of patients after death[4,12,13]. Hanot hypothesized that the obstruction of bile flow was most likely due to catarrhal inflammation of the smallest branches of the biliary system, resulting in intrahepatic rather than extrahepatic obstruction[4,12,13]. As demonstrated by the observations of Hanot and the works of other authors, it is evident that as the disease progresses, there is cellular infiltration and fibroblastic proliferation around the small bile ducts. Hanot’s merit lies in the fact that he clearly delineated the clinical picture of the disease, which is different from that of secondary biliary cirrhosis[13]. Concurrently, erroneous attributions were made concerning the potential role of syphilis in its etiology[12,13]. In addition to the term “hypertrophic cirrhosis with chronic jaundice”, the terms “hypertrophic cirrhosis Hanot” and “Hanot’s disease” were also utilized[5].

IMPORTANCE OF DEVELOPING CHEMICAL AND LABORATORY METHODS FOR STUDY OF THE DISEASE

Determination of the composition of xanthomas, xanthelasms, changes in blood lipid composition, and the emergence of the term “xanthomatous biliary cirrhosis”

The first report pertaining to the chemical composition of xanthomas and xanthelasms was made by Quinquaud in Paris in 1878 during a meeting of the clinical society[15]. As stated in Quinquaud’s published report, the occurrence of xanthomas and xanthelasms has been observed “...in cases of excess fat in the blood...”. According to the author’s data, the content of “fats” in the blood of such patients can exceed the physiological norm by six or more times[15]. On the basis of the data obtained, the author concluded that “...changes in blood composition play an important role in the development of this curious condition”.

In subsequent years, an escalating number of scientific studies described clinical observations of hepatic impairment accompanied by protracted jaundice and concomitant cutaneous manifestations in the form of xanthomas and xanthelasms[7,16-20]. By the end of the 19^th century, the characterization of the disease was based on clinical manifestations and the results of pathological autopsies of deceased patients[4]. In the first half of the 20^th century, new laboratory methods were developed and subsequently integrated into clinical practice, thus enabling the identification and recognition of laboratory signs of disease in patients diagnosed with Addison-Gull syndrome/Hanot’s disease. The assessment of lipid metabolism and determination of a lipid profile has enabled the development of a more comprehensive understanding of the mechanisms underpinning the formation of xanthomas and xanthelasma.

Thannhauser and his colleagues[20-23] in the late 1930s and early 1940s revealed a clear relationship between the appearance of xanthomas and xanthelasma with elevated levels of cholesterol and lecithin (four to eight times higher than normal) in the serum of these patients based on clinical signs and taking into account biochemical data. The authors suggested that the fundamental cause of the aforementioned condition is an imbalance in the processes of cholesterol formation and excretion[23]. Despite a substantial increase in cholesterol and lecithin levels in the blood serum, it remained clear and did not appear creamy[20,24]. Important laboratory signs of Addison-Gull Syndrome/Hanot’s Disease included: Elevated plasma cholesterol and lecithin levels in these patients.

In addition to describing new laboratory signs, the authors made significant additions to the known (presence of xanthomas and xanthelasma on the skin, enlargement of the liver and spleen, jaundice of multi-year duration) clinical signs[21-23]. Thannhauser and his colleagues[20] noted that: (1) “...all cases reported so far...” were represented by female patients between 30 and 50 years of age[25-30]; (2) Skin itching was one of the most important symptoms of the disease in these patients; and (3) despite Hanot’s suggestion of small bile duct inflammation, the patients did not have the fever and/or chills characteristic of inflammation.

Taking into account the presence of xanthomas and xanthelasms in patients with cirrhosis associated with Addison-Gull Syndrome/Hanot’s Disease, MacMahon and Thannhauser[20] in 1949 proposed to the name “xanthomatous biliary cirrhosis” for this disease, distinguishing it as an independent pathology. In this study, the authors noted that “xanthomatous biliary cirrhosis” could not be classified in the “hypercholesterolemic familial xanthomatosis” group because “...no familial morbidity has been identified in the cases that have been previously described”[20].

The subject of generalized lipid accumulation and the development of xanthomatosis, first mentioned by Quinquaud[4,15], was developed further by Thannhauser and his colleagues[21-23]. These works attracted the attention of the renowned 20^th-century lipidologist Ahrens[31].

Ahrens and his proposed term “primary biliary cirrhosis”

The contributions of Ahrens[32] to the field of cholesterol metabolism have been significant, particularly in the area of understanding the impairment of lipid metabolism in liver disease, which is accompanied by xanthomatosis and hyperlipidemia.

Ahrens (1915-2000) was a famous lipidologist of the 20^th century. Ahrens received his Bachelor of Science (1937) and Doctor of Medicine (1941) degrees from Harvard University[33]. Throughout the course of his professional career, Ahrens was a known proponent of patient-centered research. He is best known for his book “The Crisis of Clinical Research” published in 1992. It examined the transition of medical science to laboratory research. In his work, he demonstrated the significance of comprehending the physicochemical characteristics of diverse classes of lipoproteins for various diseases. The clinical study that he conducted on the subject of lipid profiles in patients suffering from primary biliary cirrhosis is the most frequently cited by other researchers within the relevant field[24].

The findings of his research constituted the foundation for the advancement of diagnostic methodologies pertaining to “xanthomatous biliary cirrhosis”, which ensured his diagnosis at earlier stages.

Ahrens’ observations of 18 patients with “xanthomatous biliary cirrhosis” revealed that while there was an increase in serum lipids, this was not accompanied by the presence of xanthomas and xanthelasms. This finding suggested the existence of a pre-xanthomatous stage in these patients despite the development of cholestasis. The pre-xanthomatous stage, as defined by Ahrens, is characterized by a lesser degree of manifestation of biliary tract obstruction and a less pronounced increase in serum lipid levels[24]. Ahrens’ research demonstrated that the majority of patients are in the pre-xanthomatous stage and that the xanthomatous phase, as he defined it, signified only the most severe and dramatic terminal stage of the disease’s progression. According to Ahrens xanthomatosis in this disease was secondary, and the disease progresses through three stages: Pre-xanthomatous; xanthomatous; and terminal stages.

Ahrens also demonstrated the possibility of reverse development of xanthomas and xanthelasms. The progression to a marked xanthomatous stage and back depends on the degree of increase in serum cholesterol and lecithin levels. It has been shown that if serum lipids remain sufficiently elevated for a long period of time, the appearance of skin xanthomas can be predicted. If for any reason the obstruction is removed, serum lipids can be expected to fall to normal levels and the xanthomas and xanthelasms to dissipate[24].

At the same time, according to Ahrens, the changes in the lipid profile leading to skin xanthomatosis are strikingly different from those that define the presence of arterial atheromatosis. Therefore, no clinical, electrocardiographic, or radiographic signs of atherosclerosis or coronary artery disease were detected in these patients[24,34].

Ahrens[20,24] expressed concerns about the imprecision of the term “xanthomatous biliary cirrhosis” proposed by Thannhauser and colleagues due to the fact that xanthomas and xanthelasms occur in only 5%-10% of cases. A large proportion of early reports described patients with “xanthomatous biliary cirrhosis” at the terminal stage of disease. As a rule, the disease was diagnosed at late stages of pronounced cholestasis[31,33,35]. As a result, Ahrens et al[31], taking into account the morphological description of the final cirrhotic stage of the disease in 1950, justified and introduced the term “primary biliary cirrhosis” (PBC). Subsequent to that period, the terms “Addison-Gull syndrome” and “cirrhosis of Hanot” have become historical.

Ahrens emphasized the necessity of identifying specific criteria for the differential diagnosis of PBC (in which there is damage to small intralobular, interlobular, and intrahepatic bile ducts) and secondary biliary cirrhosis (initiated by obstructive lesions)[31]. The author drew attention to the paradox in blood lipid analysis in primary and secondary biliary cirrhosis, which he proposed to use for differential diagnosis of these conditions.

A comprehensive analysis of the literature data, encompassing long-term clinical and laboratory observations of patients diagnosed with PBC and “secondary biliary cirrhosis”, has shown: (1) In PBC the large bile ducts are always passable and bile can flow into the intestine through them, but extremely high values of total cholesterol (4-8 times higher than the reference value) as well as lecithin (4-10 times higher than the reference value) in serum are noted[20,24]. At the same time, neutral lipids are at low values; and (2) In “secondary biliary cirrhosis” associated with complete obstruction of large bile ducts and impaired bile outflow, there is no such significant increase in cholesterol and lecithin level [20,24].

According to Ahrens, serum lipid analysis, in addition to clinical findings, is the decisive factor for the diagnosis of “primary (xanthomatous) biliary cirrhosis”. The clinical and pathological features of PBC have been supplemented with laboratory tests. In the 1950s this approach promoted some successes in improving the diagnosis of this disease at earlier stages. The revealed disorders of lipid status in PBC were confirmed by the data on the study of bile and hepatobioptates of these patients using ³¹P-NMR spectroscopy[36]. By the close of the 1950s, the prerequisites for studies of the histopathological evolution of the disease had been established[3,37,38].

Along with the emergence of new laboratory methods of investigation, morphological methods were being developed and improved. The incorporation of percutaneous puncture liver biopsy into clinical practice has engendered the capacity to undertake lifetime histochemical and morphological studies of liver biopsy specimens. This, in turn, has facilitated the enhancement of diagnostic capabilities, enabling the identification of disease at its earliest stages.

MORPHOLOGICAL AND ELECTRON MICROSCOPIC METHODS IN THE STUDY OF PBC

Morphological classifications of PBC

In the 1960s Rubin et al[39] first described the spectrum of histological changes of the liver detected in “primary (xanthomatous) biliary cirrhosis” in liver biopsy specimens. The authors noted that the primary damage occurs in the smallest bile ducts, which is accompanied by a cellular, granulomatous reaction in the portal tract and in the connective tissue where there are lymphatic vessels[39-42]. Bile thrombi are detected in intralobular bile ducts, i.e. in cholangioles and canaliculi. The surfaces of hepatocytes in close proximity to damaged canaliculi undergo degenerative and even necrotic changes[39,41]. For the majority of the duration of the disease, the patient appears to be in good health[4]. This is due to the fact that the liver cells are only slightly damaged, and the effects of portal hypertension and hepatic failure are only evident in the later stages of the disease. It is only at this point, after many years, that the disease ultimately results in death.

The advent of lifetime morphological and histochemical studies of liver biopsy specimens has led to the establishment of morphological classifications that delineate the developmental stages of PBC. In 1967 Scheuer[37] presented a detailed description of the four histological stages of this disease (Table 1)[38]. A little later Popper and Schaffner[43] and Schaffner and Bacchin[44] presented a comprehensive analysis of the morphological changes that occur at various stages of the disease, with particular emphasis on their correlation with the clinical manifestations of cholestasis. The authors underscored the significance of these morphological changes in relation to the disturbances in bile acid metabolism[44]. In 1978 Ludwig et al[38] having analyzed 219 individual biopsy specimens from 101 patients with the established morphological diagnosis of “chronic non-purulent destructive cholangitis” (the syndrome of PBC) proposed their classification of the stages of the disease (Table 1).

Table 1 The morphological classification of stages of primary biliary cholangitis, adapted from Ludwig et al[38].

Ref.	Morphologic findings on biopsy
	Stage I	Stage II	Stage III	Stage IV
Scheuer[37]	Portal Portal hepatitis	Periportal Periportal hepatitis	Septal Bridging necrosis (passive septa) or septal fibrosis (active septa), or both	Cirrhosis
Popper and Schaffner[43]	Cholangitis Portal hepatitis with duct lesions	Ductular proliferation Same as stage II of Scheuer	Precirrhosis Same as stage III of Scheuer	Cirrhosis
Ludwig et al[38]	Florid duct lesion Portal hepatitis with duct lesions, or periportal hepatitis with duct lesions but without ductular proliferation	Ductular proliferation Periportal hepatitis (and bridging necrosis?), with ductular proliferation but without fibrosis	Scarring Septal fibrosis but absence of true regenerative nodules	Cirrhosis

The use of different terminology in the nomenclature of the individual morphological stages of PBC serves to emphasize, reflect, and clarify the essence of the ongoing pathological processes without contradicting each other. The classification system has been in continuous use for many decades; this is partly due to the fact that the descriptions of the stages in these classifications are based on uniform histological criteria that apply to all specimens and are easily reproducible. All classifications concur that in the early stages the principal changes occur in the small bile ducts. It is only as cholestasis progresses that hepatocyte damage occurs and fibrosis develops (stage three).

The famous pathomorphologist Professor Aruin has noted that the morphological changes in liver biopsy specimens are characterized by a peculiar ‘mosaic’ of damage[45]. Signs of at least two different stages can always be seen in histological preparations. This phenomenon can be attributed to the fact that the sequential progression from one stage to another may be subject to differential expression in different areas of the liver[45,46].

Electron microscopic changes in PBC

Electron microscopic and electron histochemical studies of liver biopsy material from patients diagnosed with PBC revealed stereotypical changes in ultrastructure that are characteristic of the unfolded cholestasis stage: Local divergence of hepatocytes with an increase in intercellular spaces; partial hypertrophy and vacuolization of smooth and rough endoplasmic reticulum of hepatocytes; accumulation of lipid droplets in liver cells and formation of myelin-like structures; and changes in the shape and structure of mitochondria, characterized by a decrease in the number of inner membrane cristae[46]. The osmiophilic, myelin-like, and cholesterol-digitonin structures are likely to represent intracellular complexes of cholesterol, phospholipids, and bile acids formed in response to cholestasis[46]. It can be hypothesized that osmiophilic, myelin-like, and cholesterol-digitonin structures represent micellar-lamellar complexes of bile acids with cholesterol and phospholipids. Indirectly, the presence of these structures indicates that the damage of hepatocytes in chronic cholestasis is caused by the accumulation of bile acids in them.

The data from electron microscopic studies demonstrating the disturbance of intercellular contacts in cholestasis syndrome are in agreement with the results of cell adhesion assessment. A quantitative adhesiometric method was developed for the study of hepatobioptates in patients with various chronic liver diseases[47]. The application of this method has revealed that in PBC there is a weakening of interhepatocyte interactions (contacts) due to increased pressure in bile capillaries resulting from intrahepatic cholestasis in small bile ducts[47].

As illustrated in Table 1, the allocation of four stages of the disease is accepted by all morphologists, but only the fourth stage of the disease is universally presented by all as cirrhosis and corresponds to the generally accepted criteria of this disease[45].

Sheila Sherlock, analysis and critique of the term PBC

Given that cirrhosis in these patients develops only in the late stages of the disease, the world-renowned scientist, hepatologist Sheila Sherlock, already in 1959 began to oppose the term “primary biliary cirrhosis” proposed by Ahrens.

Sherlock[35] (1918-2001) was a world-renowned physician, scientist, gastroenterologist, and a leading hepatologist. In 1945, Sherlock[35] was awarded the Edinburgh MD degree (and gold medal) for her thesis on “The Liver in Disease: With special reference to aspiration biopsy of the liver”. At the age of 30, she established the world’s first liver disease unit. In 1950, she cofounded the American Association for the Study of the Liver with Hans Popper, and in 1958, she became the first president of the International Association for the Study of the Liver. Sherlock[35] published an outstanding monograph in 1955, entitled “Diseases of the Liver and Biliary System”. This monograph has been reprinted many times (eight editions during her lifetime). It has also been translated into at least six languages, demonstrating its international appeal and importance[48,49].

In the course of long-term observation of patients diagnosed with PBC, Sherlock[35] showed that in most cases the disease proceeds without the presence of cirrhosis, thus allowing her to distinguish the pre-cirrhotic stage of the disease[50]. She described 42 clinical observations of patients diagnosed with PBC who she supervised for 15 years[35]. In describing the clinical features, Sherlock carefully described the timing of appearance of skin itching, jaundice, the sites of xanthomas and xanthelasma depending on the level of plasma cholesterol elevation, as well as laboratory abnormalities of alkaline phosphatase, gamma glutamyl transpeptidase (GGT) activity, and histological changes ascertained from examination of liver biopsy and/or autopsy material.

According to her descriptions, in a significant portion of patients (20 patients, 48%) skin itching appeared long before the appearance of jaundice (from several months to 11 years), but in 14 patients (33%) itching appeared against the background of pronounced jaundice. Xanthomas on the extensor surfaces of elbows, wrists, buttocks, knees, and ankles were observed in 20 patients (48%), all with high serum cholesterol. Six cases of patients had flat xanthelasma on the eyelids. In several cases hepatomegaly was diagnosed in the absence of any specific complaints (this may have been the first description of an asymptomatic course of the disease). In no case was fever or abdominal pain syndrome observed. The diagnosis was usually verified after surgical intervention (37 patients, 88%!!!) or by liver biopsy. The latter was performed in few patients, as it was still a very rare procedure in the early 1950s, but one that Sherlock successfully mastered.

An examination of biopsy and autopsy material revealed that the majority of patients did not exhibit the conventional pattern of cirrhosis and disruption of the liver lobule architecture[35]. It was emphasized that in the early stages of PBC, nodular regeneration is inconspicuous. Fibrosis development is only noted in the later stages, at which point it becomes evident that the zonal architecture is distorted, creating a “…mixed picture of portal and biliary cirrhosis”. The absence for many years of clinical and morphological signs of cirrhosis led Sherlock to propose the term “chronic intrahepatic obstructive jaundice” for this disease[35]. However, the term proposed by Sherlock[35] was not widely supported and accepted. Meanwhile, Ahrens’ term, PBC, continued to be used until 2015.

During the mid-1960s, clinical immunology and immunological techniques underwent rapid development, which proved to be a significant moment for the diagnosis of the earliest and most asymptomatic stages of the disease.

IMMUNOLOGICAL METHODS IN THE STUDY OF PBC

Development of immunology and its significance in the study and diagnosis of PBC

By the mid-1960s, most of the clinical, biochemical, and histopathological features of PBC had been established. Concurrently, the field of immunology was undergoing rapid development with the discovery of immunoglobulin classes and subtypes and the introduction of new immunological methods. During the same time, the hypothesis that PBC may have an immunological basis was put forward[3].

Using immunological methods Paronetto et al[51] found and described antibodies directed against protein components of the bile ducts. These antibodies were found in cases of viral hepatitis (67%), secondary biliary cirrhosis (43%), extrahepatic biliary obstruction (32%), and alcoholic cirrhosis (22%)[52].

Concurrently, Deborah Doniach, a prominent immunologist in Britain, approached the equally distinguished Sherlock with a proposal to conduct immunological testing on patients diagnosed with PBC.

Deborah Doniach (1912-2004) was a world-renowned scientist, a British clinical immunologist, and a pioneer in the field of autoimmune diseases. She finished the Royal Free Medical School and started working in an organized department of immunology. Doniach was a pioneer in the establishment of new paradigms in immunology. She had extremely fruitful collaborations with many talented scientists and clinicians, including Sherlock and Geoffrey Walker. This collaboration has been extremely fruitful and has identified the presence of antimitochondrial antibodies (AMA) in patients with PBC as one of the pathognomonic features. Doniach soon became an Honorary Consultant Immunopathologist and Professor of Clinical Immunology.

Doniach’s proposal was motivated by the observation that some patients with this disease manifest Hashimoto’s thyroiditis, characterized by the presence of circulating anti-thyroglobulin antibodies[3]. In experimental models of thyroiditis, rabbits have been observed to exhibit lymphocytic infiltration, which is analogous to that observed in liver biopsy specimens from patients with PBC[53]. Sherlock agreed and delegated the execution of immunological studies in PBC to Geoffrey Walker, a trainee under her supervision who demonstrated a keen interest in the emerging field of immunology[3].

The study used an immunofluorescence test with sera from 32 patients with PBC and showed non-specific cytoplasmic fluorescence in unfixed sections of thyroid, stomach, kidney, and peripheral blood lymphocytes[52]. Concurrently, the sera of 33 patients in the control group who had biliary obstruction or suffered from other types of cholestasis exhibited negative results in the immunofluorescence test[52]. The study revealed that the antibodies detected in the serum of patients with PBC exhibited neither species nor organ specificity.

Subsequent studies demonstrated that the autoantibodies detected were directed against subcellular organelles or soluble cellular proteins, which were present not only in the liver but also in numerous other organs[54]. Later immunological studies demonstrated that the antigen that reacted with sera from patients diagnosed with PBC was predominantly located within the mitochondrial fraction of tissue homogenates obtained by differential centrifugation[55]. Furthermore, the research conducted by Berg et al[55] demonstrated that the antigen was situated on the inner membrane of mitochondria. The findings obtained by Walker, Doniach, and Sherlock constituted a seminal discovery[52,55,56]. This study identified the presence of AMAs in patients with PBC as one of the pathognomonic features.

The subsequent 25 years of research concentrated on the identification of the antigen to which mitochondrial antibodies are formed. It had been hypothesized that the antigen was associated with mitochondrial ATPase[57]. However, subsequent research revealed that pure ATPase fractions prepared by alternative methods exhibited no reactivity with the sera of patients diagnosed with PBC[58,59]. The employment of immunological methodologies has enabled the identification of nine distinct types of antibodies, each directed towards varying antigenic structures of mitochondria (M1-M9)[60]. It has been identified that M2 antigenic components are specific for the sera of patients with PBC[61]. In addition to M2, other mitochondrial antigens and antibodies to them have been shown to have diagnostic and prognostic significance for PBC[62]. Detection of anti-M9 is associated with the early stages of the disease[63]. Mitochondrial anti-M4 and anti-M8 are detected exclusively in M2 positive patients[62]. Their appearance in the serum of patients with PBC is associated with a marked progression of the disease[64].

The development and application of molecular genetic techniques has allowed the identification of M2 antigen as the E2 subunit of the pyruvate dehydrogenase (PDH) complex[63]. The antigen that reacts with the serum of patients with PBC has been characterized as a lipoprotein localized on the inner mitochondrial membrane[65]. This was later confirmed by electron microscopic studies by Bianchi et al[66]. The specificity of antibodies to this antigen for the diagnosis of PBC was striking[58].

The significance of the discovery of AMAs for the diagnosis of PBC

Walker et al[52] demonstrated that the diagnostic value of other tests in differentiating between PBC and biliary obstruction was extremely limited[56]. The presence of AMA was detectable by indirect immunofluorescence and has been observed in most of the patients diagnosed with PBC[67]. It was therefore recommended that mitochondrial antibody tests be used as an alternative to surgery for the purpose of confirming a diagnosis of PBC[50,68].

In addition to AMA antinuclear antibodies were detected in a proportion of patients with PBC[69]. The presence of AMA and antinuclear antibodies was the reason to consider PBC as a prototype of autoimmune disease and to describe it as a paradigmatic model of autoimmune disease[70] that some authors are currently questioning.

The presence of a significant AMA titer (> 1:40) has been demonstrated to provide strong evidence for the diagnosis of PBC, even in the absence of symptoms and with normal serum alkaline phosphatase levels[71]. Typical, early histological signs of PBC can be detected by examining liver biopsy specimens from individuals whose sole manifestation of the disease is a positive serum AMA test[71]. The true prevalence of asymptomatic and subclinical cases of the disease became evident following the determination of AMAs and the wider availability of routine screening of liver biochemical tests[72].

The identification of features pertaining to the manifestation of initial signs and the progression of the disease formed the foundation for the establishment of clinical classifications of stages and variants in the course of PBC.

Classification of clinical stages and variants in the course of PBC

In 1984, Proka, a graduate student of academician Loginov, distinguished the following variants of the initial manifestations of PBC in his PhD thesis, based on the initial manifestations of the disease[73]: (1) The disease commences with symptoms of cholestasis but without jaundice (the most prevalent form of the onset of PBC); (2) The onset of the disease was characterized by nonspecific symptoms and manifestations (cholecystic and dyspeptic, hematological, articular-muscular, and other manifestations); and (3) The disease begins with a combination of skin itching and jaundice (the picture of advanced cholestasis).

The classification proposed by Sasaki et al[74] in 1985 most completely, concisely, and accurately reflected the stages of the clinical course of the disease in the majority of patients suffering from PBC: (1) Asymptomatic stage; (2) Pruritus stage; (3) Jaundice stage; and (4) Terminal stage.

A more detailed description of the stages of the course of PBC was presented in the classification of Poupon[75], published in 1991: (1) Preclinical, asymptomatic stage (characterized by the appearance of AMA in the blood, moderate increases in GGT, alkaline phosphatase, and 5’-nucleotidase activity); (2) Clinical stage of the disease (usually lasting from 5 to 19 years and characterized by the manifestation of all clinical signs of PBC); and (3) Terminal stage of the disease with the development of fibrosis, cirrhosis, and their complications (portal hypertension, ascites, esophageal-gastric bleeding).

Treatment

The enhanced diagnostic capacity for PBC, coupled with the presumed autoimmune nature of the condition, has given rise to the use of corticosteroids[76] and immunosuppressants[77-79]. According to a number of authors, the use of corticosteroids was led to a decrease in weakness, intensity of skin itching, a slight decrease of plasma alkaline phosphatase activity[76,80], and even accompanied by some positive alteration in the histological picture of the liver[77]. However, as experience with corticosteroids in treating patients with PBC was accumulated, it became apparent that there was no unequivocal positive therapeutic effect as seen in other autoimmune diseases. According to Mann[4] since he first initiated the use of corticosteroids to treat patients with PBC in 1960, he has had the impression that their use may have a favorable effect on the course of the disease. However, he still tends to consider that corticosteroids are of limited or negligible therapeutic effect.

The first encouraging results of immunosuppressants[77] such as azathioprine[81], cyclosporine[82], and other drugs including colchicine[83,84], methotrexate[85,86], and chlorambucil[87] were not confirmed in randomized controlled trials. The lack of a therapeutic effect and the emergence of serious side effects have led to the abandonment of further use of these medications for the treatment of PBC.

Copper metabolism disorder and associated cutaneous hyperpigmentation in PBC[88,89] prompted the use of D-penicillamine in these patients[90]. However, the use of D-penicillamine in randomized controlled trials has not confirmed positive results with its use[90]. This is due to the fact that copper in PBC accumulates in the organs and tissues of the body in a non-toxic, ceruloplasmin-bound form, and the use of the drug is associated with a number of adverse side effects[89,90].

Cutaneous pruritus is one of the early clinical signs of PBC that requires treatment but is often difficult to manage. The use of opioid receptor antagonists (e.g., naloxone, naltrexone, etc.)[91], ion-exchange resins (e.g., cholestyramine, cholestipol, etc.), phenobarbital, and rifampicin[92,93] helps to reduce the intensity of skin itching observed in this disease. Rifampicin has been recommended as an alternative second-line drug for the treatment of cutaneous pruritus associated with chronic cholestasis. But given its hepatotoxicity, it should not be used long-term and in patients with stages 3 and 4 PBC. The data available in the literature on the use of these drugs suggest that they are all useful for short-term relief of pruritus, although the mechanism of this effect remains unknown[93]. Recently, it has been thought that endogenous opioids may modulate signaling pathways involved in hepatic pruritus; however, they are unlikely to be major pruritogenic factors in liver disease[94].

Ursodeoxycholic acid as a first-line drug in the treatment of PBC

In 1987 the German hepatologists Leuschner and Kurtz[95] reported a positive effect of ursodeoxycholic acid (UDCA) in patients with PBC. The drug has been studied in many randomized, placebo-controlled trials in patients with stages I-IV of PBC, with both positive and equivocal results[96-101]. Clinical studies have shown that oral administration of UDCA at a dose of 13-15 mg/kg/day is well tolerated by patients and has a positive therapeutic effect in cholestatic liver diseases[102]. Scientific publications have noted that UDCA improves biochemical markers of cholestasis (alkaline phosphatase, GGT) in most patients, slows disease progression, delays liver transplantation and death in most patients, and improves survival rates[103,104].

Subsequent studies have demonstrated a direct correlation between the efficacy of UDCA use and the stage of the disease, with the therapeutic response being more pronounced in cases where treatment is initiated at an earlier stage (stage I-II). The administration of UDCA in PBC has been shown to slow down the progression of histological manifestations and prolong patient survival without the necessity for liver transplantation. Consequently, this medication is currently recommended as a first-line therapeutic option for all patients with PBC[102,105,106]. The precise mechanism through which UDCA renders a positive effect remains to be fully elucidated. Nevertheless, it is evident that this effect is dependent on its physicochemical properties, in addition to its metabolic processes and enterohepatic circulation[107,108].

For 35 years UDCA has been a unique agent of choice for the treatment of patients with PBC. In recent years, there has been an expansion in the list of hydrophilic bile acids that are used to treat cholestatic liver disease, including PBC. In addition to UDCA, the potential use of obeticholic acid, tauroursodeoxycholic acid, and norursodeoxycholic acid as pharmaceutical agents has also been considered[107,108].

Advancements in the domain of liver transplantation techniques have been instrumental in extending the lifespan of patients afflicted with terminal PBC[109,110]. Despite the emergence of drug therapy, liver transplantation continues to be a prominent treatment option for patients with advanced disease. Liver transplantation has been demonstrated to be a highly efficacious therapeutic modality for individuals afflicted with end-stage PBC[109,110].

NOMENCLATURE CHANGE FROM CIRRHOSIS TO CHOLANGITIS

The presence of asymptomatic preclinical stage, in conjunction with the protracted absence of any physical indications of the disease, served to substantiate the inaccuracy and ineligibility of the nomenclature PBC, a conclusion that had previously been emphasized by Sherlock[35,111]. Therefore, the 2^nd monothematic conference of the European Association for the Study of the Liver dedicated to PBC was held on May 23-24, 2014 in Milan, Italy. At the conference, it was proposed to change the nomenclature from “primary biliary cirrhosis” to “primary biliary cholangitis”. Two important arguments were put forward in favor of this proposal.

The term “primary biliary cholangitis” is more accurate in reflecting the processes occurring during the development of the disease, which includes damage to biliary epithelial cells of small intrahepatic bile ducts, with the subsequent development of ductulopenia, intrahepatic cholestasis and slowly progressive fibrosis. The disease is characterized by elevated alkaline phosphatase activity, the presence of AMAs, and the manifestation of a specific histological picture in a liver biopsy. In the asymptomatic and clinical stages, according to morphological and clinical criteria, patients do not have signs of cirrhosis. The development of cirrhosis is considered to be a late terminal stage of the disease, and therefore the term primary biliary cholangitis is more correct.

The term PBC is also more acceptable to patients. The word “cirrhosis” is perceived by the majority of patients as a fatal, terminal illness with death sentence. From a psychological standpoint, the diagnosis of primary biliary cirrhosis instills a sense of dread in patients, as it is often perceived to portend a poor prognosis, which can exacerbate its course and the weighting of the condition, particularly in its early stages. At present, the course of the disease usually has a slowly progressive course, accompanied by a gradual deterioration in patient quality of life. At the same time, treatment requires lifelong medication. However, with scientific progress in recognizing new mechanisms of the disease and the efforts of scientists to develop new drugs, there is hope that patients can live with the disease rather than die from it.

Following a period of deliberation, the conference participants indicated their support for the proposal of the Board of the European Association for the Study of the Liver to effect a change in the nomenclature from primary biliary cirrhosis to primary biliary cholangitis. The decision under discussion was supported and endorsed by a number of professional associations and organizations during the period 2014-2015. These included the American Association for the Study of Liver Disease, the American Gastroenterological Association, the United European Gastroenterology Governing Board and the Asian Pacific Association for the Study of the Liver. The decision of all public organizations was submitted to the World Health Organization, which also expressed support for the decision to change the nomenclature of primary biliary cirrhosis to primary biliary cholangitis without changing the abbreviation of the disease. The World Health Organization further recommended adjustments to the relevant code of the International Classification of Diseases 10^th (K.74.3) and 11^th (DB37.2) revisions. Since 2015 the disease has been recognized by the global medical community as primary biliary cholangitis.

ADVENT OF NOVEL DATA AND THE EVOLUTION OF CONTEMPORARY REPRESENTATIONS PERTAINING TO PBC

Despite the fact that the etiology of PBC has not yet been identified, a significant volume of scientific data has been accumulated to date, allowing the formation of hypotheses regarding the mechanisms that trigger the processes of damage to small biliary epithelial cells (cholangiocytes), the formation of AMA, and the development of the first clinical signs of the disease.

Because PBC affects predominantly females, a genetic study has been conducted that is dedicated to the contribution of the X chromosome to the genetics of PBC. In 2021 the first report on this topic was published[112]. A number of genes have been identified that the authors express as possibly contributing, each with modest effects, to the development of this disease[112].

Data obtained using molecular genetic techniques have demonstrated that X-linked epigenetic alterations are induced in females with PBC for unknown reasons, leading to increased expression of microRNA 506 in cholangiocytes[113]. The latter regulates the functioning of transmembrane proteins responsible for the flow of bicarbonate from the cholangiocyte into the lumen of the bile duct. The suppression of the expression of type 3 receptor to inositol triphosphate and chlorine/bicarbonate anion exchanger 2 (AE2) was observed in liver biopsy specimens and blood mononuclear cells of patients with PBC. The resulting suppression of type 3 receptor to inositol triphosphate and AE2 activity leads to insufficient bicarbonate entry into the bile duct lumen[113-115]. An insufficient supply of bicarbonate into bile ducts in PBC results in a shift of the pH of intraductal (hepatic) bile to the slightly acidic region and an increase of pH inside cholangiocytes to the slightly alkaline region.

The discovery and analysis of these data allowed the development of the concept of the pathogenesis of damage to small biliary epithelial cells, with subsequent development of the initial clinical and laboratory signs of PBC[89,116,117]. The presented concept was a pioneering advancement in the field, as it facilitated the understanding of the underlying mechanisms that underpin the emergence of the initial indications of PBC in the asymptomatic stage of the disease. In addition, it allows a response to the following research questions: (1) Why are only cholangiocytes that line small and medium-sized bile ducts susceptible to damage in PBC?[115,118-120]; (2) How does the E2 antigen of the PDH complex, located on the inner mitochondrial membrane, undergo immunomodification and become accessible to immune cells, thus facilitating the subsequent antibody formation?[117]; (3) Why are antibodies selective formed only to the E2 subunit, while the E1 and E3 subunits of PDH immunotolerance is remain?[117]; and (4) What is the mechanism of AMA formation?[117].

This concept provides a clear indication that not AMA but the accumulation of bile acids within small cholangiocytes in the PBC is the primary damaging factor. Accumulation of bile acids in small biliary epithelial cells and their incomplete apoptosis redirected to necrosis can lead to damage of membrane structures and their death, with subsequent development of ductulopenia and cholestasis[116,121]. As cholestasis intensifies, hepatocytes are involved in the pathological process, which is accompanied by the gradual development of fibrosis and cirrhosis.

The treatment of PBC remains challenging as the cause of this chronic, slowly progressive cholestatic liver disease has not been identified. The advent of novel scientific data has the potential to inform future new drug development, with the objective of local suppression of microRNA 506 activity or activation of the AE2 anion exchanger in cholangiocytes. This is likely to be one of the new therapeutic trends in the treatment of PBC in addition to or to replace the existing bile acid drugs.

CONCLUSION

PBC is a chronic cholestatic liver disease belonging to cholangiopathies. Almost 175 years ago, the initial descriptions of the individual signs of the disease were made using solely clinical methods, such as interviews and examinations, and the results of pathological anatomical autopsies (Figure 1).

Figure 1 The significance of methods in the discovery and study of primary biliary cholangitis.

The advent of novel scientific research methods has facilitated a more profound comprehension of the progression of the disease and the subsequent body changes, thereby paving the way for the potential enhancement of diagnostic methods. The historical stages of disclosure and description of various signs, mechanisms of their development, outlined in this review, demonstrate the importance and contribution of laboratory (chemical, biochemical, morphological, immunological, molecular-genetic, and others) and instrumental (percutaneous puncture liver biopsy) methods in the study of PBC. The advent of immunology and the development of immunological research methodologies have had a significant impact on the diagnosis of this disease. The identification of antimitochondrial autoantibodies, in conjunction with elevated activity of alkaline phosphatase and GGT, facilitates the diagnosis of PBC in the asymptomatic stage of the disease.

In spite of the fact that the etiology of this disease is not known, disclosure of pathogenetic mechanisms involved in PBC progression promoted development of modern ways of treatment of this disease, including use of bile acid preparations (UDCA, tauroursodeoxycholic acid, obeticholic acid, norusodeoxycholic acid). In the near future, research efforts directed towards elucidating the etiology and pathogenesis of the disease are expected to result in the development of novel pharmacotherapeutic agents capable of halting its progression and preventing its occurrence.