Cholestasis

Cholestasis is a condition where the flow of bile from the liver to the duodenum is impaired. The two basic distinctions are: In many cases, patients may experience pain in the abdominal area. Localization of pain to the upper right quadrant can be indicative of cholecystitis or choledocholithiasis, which can progress to cholestasis. Pruritus or itching is often present in many patients with cholestasis. Patients may present with visible scratch marks as a result of scratching. Overnight, pruritus dramatically improves. This cycle can be attributed to an increase in the concentration of biliary elements during the day due to food consumption, and a decline at night. This is usually evident after physical examination as yellow pigment deposits on the skin, in the oral mucosa, or conjunctiva. Jaundice is an uncommon occurrence in intrahepatic (metabolic) cholestasis, but is common in obstructive cholestasis. The majority of patients with chronic cholestasis also experience fatigue. This is likely a result of defects in the corticotrophin hormone axis or other abnormalities with neurotransmission. These usually appear waxy and yellow, predominantly around the eyes and joints. This condition results from an accumulation of lipids within the blood. If gallstones prevent bile flowing from the pancreas to the small intestine, it can lead to gallstone pancreatitis. Physical symptoms include nausea, vomiting, and abdominal pain. Bile is required for the absorption of fat soluble vitamins. As such, patients with cholestasis may present with a deficiency in vitamins A, D, E, or K due to a decline in bile flow. Patients with cholestasis may also experience pale stool and dark urine.

Acute and chronic cholestasis can be caused by certain drugs or their metabolites. Drug induced cholestasis (DIC) falls under drug induced liver injury (DILI), specifically the cholestatic or mixed type. While some drugs (e. g., acetaminophen) are known to cause DILI in a predictable dose dependent manner (intrinsic DILI), most cases of DILI are idiosyncratic, i. e., affecting only a minority of individuals taking the medication. Seventy three percent of DIC cases can be attributed to a single prescription medication, commonly antibiotics & antifungals, anti diabetics, anti inflammatory, & cardiovascular drugs, psychotropic drugs. The exact pathomechanism may vary for different drugs and requires further elucidation. Clinically, DIC can manifest as acute bland (pure) cholestasis, acute cholestatic hepatitis, secondary sclerosing cholangitis (involving bile duct injury), or vanishing bile duct syndrome (loss of intrahepatic bile ducts). Bland cholestasis occurs when there is obstruction to bile flow in the absence of inflammation or biliary and hepatic injury, whereas these features are present in cholestatic hepatitis. while many drugs may cause cholestatic hepatitis, including penicillins, sulfonamides, rifampin, cephalosporins, fluoroquinolones, tetracyclines, and methimazole, among others. Prevalence of PBC ranges from 19 to 402 cases/million depending on geographic location, and median ages of diagnosis of 68.5 years for females and 54.5 years for males. At diagnosis, 50% of PBC patients are asymptomatic, indicative of an early stage of disease, while another 50% report fatigue and daytime sleepiness. Other symptoms include pruritus and skin lesions, and in prolonged cholestasis, malabsorption and steatorrhea leading to fat soluble vitamin deficiency. Disease progression is accompanied by intensifying portal hypertension and hepatosplenomegaly. Clinically, diagnosis generally requires a 1:40 or greater titer of anti mitochondrial antibody (AMA) against PDC E2 and elevated alkaline phosphatase persisting for 6+ months. Injury may induce cholangiocytes to undergo apoptosis, and during this process, the unique way in which cholangiocytes handle the degradation of PDC E2 (the E2 subunit of mitochondrial pyruvate dehydrogenase complex) may be a trigger for PSC. Specifically, PDC E2 in apoptotic cholangiocytes undergo a covalent modification that may render them recognizable to antibodies and thereby trigger a break in self tolerance. The pathogenesis of PSC remains unclear but probably involves a combination of environmental factors and genetic predisposition. PSC predominantly affects males (60 70%) of 30–40 years of age. The first theory involves immune mediated damage to bile ducts by T cells. In PSC, cholangiocytes and hepatocytes display aberrant expression of adhesion molecules, which facilitate homing of intestinal T cells to the liver.

Familial intrahepatic cholestasis (FIH) is a group of disorders that lead to intrahepatic cholestasis in children. Most often, FIH occurs during the first year of life, with an incidence rate of 1/50,000 to 1/100,000. There are three different versions of FIH, with each causing a different severity of jaundice. Typically, children exhibit recurrent jaundice episodes, which eventually become permanent. The ABCB11 gene encodes for the bile salt export pump (BSEP) protein, and the ABCB4 gene encodes for the multidrug resistance 3 (MDR3) protein. BSEP and MDR3 are respectively responsible for transporting bile salt and phospholipid, two major constituents of bile, across the apical membrane of hepatocytes.

Alagille syndrome is an autosomal dominant disorder that impacts five systems, including the liver, heart, skeleton, face, and eyes. Like FIH, the definitive treatment is a liver transplant. Almost all patients with Alagille syndrome have mutations of the genes involved in the Notch signaling pathway. Most have a mutation of the JAG1 gene, while a small minority have a mutation of the NOTCH2 gene.

A variety of factors associated with sepsis may cause cholestasis. Typically, patients have conjugated hyperbilirubinemia and alkaline phosphatase (ALP) elevation but not to extreme levels. Sepsis induced cholestasis may occur due to increased serum lipopolysaccharide levels. Lipopolysaccharides can inhibit and down regulate bile salt transporters in hepatocytes, thereby leading to cholestasis. Without appropriate intervention, symptoms can quickly exacerbate, leading to liver cirrhosis and failure. Intravenous glucose can also cause cholestasis as a result of increased fatty acid synthesis and decreased breakdown, which facilitates the accumulation of fats.

Intrahepatic cholestasis of pregnancy (ICP) is an acute cause of cholestasis that manifests most commonly in the third trimester of pregnancy. ICP is characterized by severe pruritus and elevated serum levels of bile acids as well as transaminases and alkaline phosphatase. These signs and symptoms resolve on their own shortly after delivery, though they may reappear in subsequent pregnancies for 45–70% of women. In the treatment of ICP, current evidence suggests ursodeoxycholic acid (UDCA), a minor secondary bile acid in humans, is the most effective drug for reducing pruritus and improving liver function. Although estrogen's exact pathomechanism in ICP remains unclear, several explanations have been offered. Estrogen may induce a decrease in the fluidity of the hepatic sinusoidal membrane, leading to a decrease in the activity of basolateral Na+/K+ ATPase. A weaker Na+ gradient results in diminished sodium dependent uptake of bile acids from venous blood into hepatocytes by the sodium/bile acid cotransporter. More recent evidence suggests that estrogen promotes cholestasis via its metabolite estradiol 17 β D glucuronide (E2). Genetic predisposition for ICP is suggested by familial and regional clustering of cases. More recently, studies have demonstrated involvement of BSEP mutations in at least 5% of cases.

Bile is secreted by the liver to aid in the digestion of fats. Bile formation begins in bile canaliculi that form between two adjacent surfaces of liver cells (hepatocytes) similar to the terminal branches of a tree. The canaliculi join each other to form larger and larger structures, sometimes referred to as the canals of Hering, which themselves join to form small bile ductules that have an epithelial surface. The ductules join to form bile ducts that eventually form either the right main hepatic duct that drains the right lobe of the liver, or the left main hepatic duct draining the left lobe of the liver. The two ducts join to form the common hepatic duct, which in turn joins the cystic duct from the gall bladder, to give the common bile duct. This duct then enters the duodenum at the ampulla of Vater. In cholestasis, bile accumulates in the hepatic parenchyma. One of the most common causes of extrahepatic, or obstructive cholestasis, is biliary obstruction. This is better known as choledocholithiasis where gallstones become stuck in the common bile duct.

Drugs may induce cholestasis by interfering with 1) hepatic transporters, 2) bile canaliculi dynamics, and/or 3) cell structure and protein localization. Hepatic transporters are essential for maintaining enterohepatic bile flow and bile acid homeostasis. Therefore, their direct inhibition by certain drugs may lead to cholestasis. Relevant transporters implicated include BSEP, MDR3, MRP2 4, and NTCP. Antifungal azoles such itraconazole have been shown to inhibit both MDR3 and BSEP,  thus giving them higher cholestatic potential. With a few exceptions, the optimal test for cholestasis would be elevations of serum bile acid levels. However, this is not normally available in most clinical settings necessitating the use of other biomarkers. If 5' nucleosidase and ALP enzymes are elevated, imaging studies such as computed tomography (CT) scan, ultrasound, and magnetic resonance imaging (MRI) are used to differentiate intrahepatic cholestasis from extrahepatic cholestasis. However, an elevation that exceeds 10 times the upper baseline limit is strongly indicative of either intrahepatic or extrahepatic cholestasis and requires further investigation. However, measurement of serum aminotransferase levels alone is not a good marker to determine cholestasis. In up to a third of patients, ALP levels may be elevated without the presence of cholestasis. Many labs cannot measure 5' nucleosidase and ALP levels so, GGT may be measured in some cases. As such, GGT elevations lack the necessary specificity to be a useful confirmatory test for cholestasis. but, is often insufficient in determining the level of biliary obstruction or its cause because it can pick up bowel gas that may interfere with readings. CT scans are not impacted by bowel gas and may also be more suitable for overweight patients. MRI scans provide similar information to CT scans but are more prone to interference from breathing or other bodily functions. Although CT, ultrasound, and MRI may help differentiate intrahepatic and extrahepatic cholestasis, the cause and extent of obstruction is best determined by cholangiography. In case of anatomical anomalies, or if endoscopic retrograde cholangiography is unsuccessful, percutaneous transhepatic cholangiography may be used. In both non obstructive and obstructive cholestasis, there is an accumulation of substances that are typically secreted in the bile, as well as degeneration of hepatocytes. The most significant feature from a histopathological perspective includes pigmentation resulting from the retention of bilirubin. Under a microscope, the individual hepatocytes will have a brownish green stippled appearance within the cytoplasm, representing bile that cannot get out of the cell. Pigmentation can involve regurgitation of bile into the sinusoidal spaces caused by phagocytosis from Kupffer cells, an accumulation of bilirubin within hepatocytes, and inspissated bile in the canaliculi. Under the microscope, hepatocytes in the perivenular zone appear enlarged and flocculent. Cholestasis is often marked by cholate stasis, which are a set of changes that occur in the periportal hepatocytes. Cholate stasis is more common in obstructive cholestasis compared to non obstructive cholestasis. During the cholate stasis process, hepatocytes first undergo swelling and then degeneration. Under the microscope, this is evident as a lucent cell periphery and enlarged cytoplasm around the nucleus. Due to the retention of bile, which contains copper, stains made for staining copper associated protein can be used to visualize bile accumulation in the hepatocytes. Cholestatic liver cell rosettes may occur in children with chronic cholestasis. Histologically, this is evident as two or more hepatocytes in a pseudotubular fashion that encircle a segment of enlarged bile canaliculi. Giant cell formation is likely caused by the detergent properties of bile salts causing a loss of the lateral membrane and joining of hepatocytes. In the case of Alagille syndrome, hepatocyte degeneration is uncommon. Cholangitis lenta can also cause changes to the portal tracts. This occurs during chronic cases of sepsis and results in dilation of the bile ductules. Portal tract edema may also occur as a result of bile retention, as well as periductular infiltration of neutrophils. Infection is mostly caused by coliforms and enterococci and is evident from a large migration of neutrophils to the duct lumina. If bile stones are present in the common bile duct, an endoscopic sphincterotomy can be conducted either with or without placing a stent. Later, the endoscopist can place a stent in the common bile duct to soften any remaining stones and allow for bile drainage. If needed, a balloon catheter is available to remove any leftover stones. If these stones are too large with these methods, surgical removal may be needed. Patients can also request an elective cholecystectomy to prevent future cases of choledocholithiasis. In case of narrowing of the common bile duct, a stent can be placed after dilating the constriction to resolve the obstruction. The treatment approach for patients with obstructive cholestasis resulting from cancer varies based on whether they are a suitable candidate for surgery. In most cases, surgical intervention is the best option. This can reestablish bile flow into the small intestine, thereby bypassing the blockage. In cases where a patient is not a suitable candidate for surgery, an endoscopic stent can be placed. If this is not possible or successful, a percutaneous transhepatic cholangiogram and percutaneous biliary drainage can be used to visualize the blockage and re establish bile flow.

A significant portion of patients with cholestasis (80%) will experience pruritus at some point during their disease. This is a condition that can severely decrease a patient's quality of life as it can impact sleep, concentration, work ability, and mood. Many treatments exist, but how effective each option is depends on the patient and their condition. Assessment using a scale, such as a visual analogue scale or a 5 D itch scale will be useful to identify an appropriate treatment. Possible treatment options include antihistamines, ursodeoxycholic acid, and phenobarbital. Nalfurafine hydrochloride can also be used to treat pruritus caused by chronic liver disease and was recently approved in Japan for this purpose. Bile acid binding resins like cholestyramine are the most common treatment. Side effects of this treatment are limited and include constipation and bloating. Other commonly used treatments include rifampin, naloxone, and sertraline. In cholestatic liver disease, when bilirubin concentration starts to build up, a deficiency of fat soluble vitamins may also occur. To manage this, doses of vitamin A, D, E, and K are recommended to retain appropriate vitamin levels. Cholestatic liver disease can impact lipids, and possibly lead to dyslipidemia, which may present a risk for coronary artery disease. Statins and fibrates are generally used as lipid lowering therapy to treat patients with cholestatic liver disease. For intrahepatic cholestasis in pregnant women, S adenosylmethionine has proven to be an effective treatment. Dexamethasone is a viable treatment in regards to the symptom of intensive itching.

Primary sclerosing cholangitis (PSC) is one of the most common cholestatic liver diseases, yet treatment options remain limited. Treatment for primary biliary cholangitis (PBC) is often done with ursodeoxycholic acid (UDCA) and with no other suitable alternative, it poses a problem for those that are not responsive to (UDCA). However, with advancing technology in the molecular biochemistry field and higher understanding of bile acid regulation, novel pharmacological treatments have been considered. For patients with primary biliary cholangitis, current guidelines recommend about 13–15 mg/kg of ursodeoxycholic acid as a first line treatment. This drug stimulates biliary bicarbonate secretion, improves survival without having to resort to a liver transplantation, and is very well tolerated— making it an ideal treatment. However, around 40% of patients with primary biliary cholangitis are not responsive to UDCA. Obeticholic acid has been approved by the US Food and Drug Administration for PBC in 2016 after experiments found beneficial improvements for the liver in half of patients with inadequate response to UDCA. Primary sclerosing cholangitis is a challenging liver disease as treatment options are limited. There is still uncertainty about the efficacy of ursodeoxycholic acid for PSC and researchers offer conflicting recommendations. One study found UDCA had improved biochemical functions but did lower the rate for death or transplant free survival.

An important regulator in bile acid homeostasis is the alpha and delta isoforms of the peroxisome proliferator activated receptor (PPARα, PPARδ). The function of PPARα is that it promotes bile acid excretion and lowers inflammation by acting on nuclear transcription factors. A well known agonist are fibrates and in the clinical trials, there was a significant biochemical response in most patients. A combination therapy with bezafibrate showed remarkable biochemical improvement, with 67% of patients normalizing their alkaline phosphatase levels. Another study of 48 patients with PBC found a combination of bezafibrate and UDCA showed a decrease of alkaline phosphatase in all patients. Further, the study found those treated had a marked relief in pruritus. However, fibrates are associated with a number of adverse effects including arthritis, leg edema, polydipsia, and myalgias.

A new novel treatment option is the farnesoid X receptor is responsible for regulating bile acid homeostasis. An agonist of this nuclear hormone receptor is seen as a possible treatment as it can downregulate bile acid synthesis and reabsorption. Further the farnesoid X receptor is partly responsible for lipid and glucose homeostasis, as well as pathogen recognition. An agonist for the farnesoid X receptor can therefore lead to an anti cholestatic environment to minimize the effect of toxic bile acids on the liver. In fact, in February 2018, the FDA gave a black box warning for OCA. A recent study did find that if the drug is given with UDCA, the incidence for cirrhosis and liver transplants decreases. Another target that is being looked into is the all trans retinoic acid (ATRA), an activator for the retinoid X receptor. In vitro and animal studies found ATRA had lowered the amount of bile acid and decreased hepatic inflammation.

A recent scientific breakthrough for cholestasis that has allowed us to evaluate a new treatment option is that a hydrophilic environment and bicarbonate production protects hepatocytes from bile acid. Mouse models have found promising results with norUDCA with the drug showing antiproliferative and anti inflammatory properties. A recent clinical trial found norUDCA had significant dose dependent reductions for ALP levels. This makes norUDCA a viable possibility to look into as it clearly plays a significant role in the treatment of cholestasis.

In PBC, the liver is filled with T cells and B cells that contribute to a worsening condition. Therefore, some treatments are looking into targeting the antigens of these immune cells. The monoclonal antibody rituximab targets the CD20 antigen on the B cells, and is already used in a wide array of other rheumatologic diseases. In an open label study, six patients that were unresponsive to UDCA had improvement in ALP levels after rituximab infusions. However, the efficacy of rituximab is still uncertain, and awaits further studies and trials. PBC can also lead to higher levels of interleukin 12 and interleukin 23. This was what motivated researches to look at the viability of ustekinumab, a monoclonal antibody targeted against interleukin 12 and 23. An experiment found though it did not significantly improve serum ALP levels. The researchers were further even criticized for placing patients at risk by allowing them to move to advanced disease stages where immunomodulatory therapies may not even be an option.

In several chronic liver diseases, the gut microbiome, which regulates both the innate and adaptive immune systems, is implicated. This can result in abnormal immunological development and an accumulation of primary bile acids. Using this information a bile acid–intestinal microbiota–cholestasis triangle is thought to be involved in the pathogenesis of PBC and PSC. After all, bile acids do modulate the gut microbiota; a disturbance here can result in development and progression of cholestasis. This information has prompted researchers into manipulating the microbiota via antibiotics and probiotics for new treatment options. Some antibiotics examined for PSC include vancomycin, which has extensively studied and reviewed. The usage of the drug is found along with a significant decrease in ALP levels, although the long term clinical benefit is unknown. As biochemistry technology becomes more advanced, promising targets have appeared, prompting numerous studies and trials to evaluate the feasibility. Fibrates, FXR agonists, and norUDCA are all innovative therapies for cholestasis.