Bile acid malabsorption (BAM), known also as bile acid diarrhea, is a cause of several gut-related problems, the main one being chronic

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

. It has also been called bile acid-induced diarrhea, cholerheic or choleretic enteropathy, bile salt diarrhea or bile salt malabsorption. It can result from

malabsorption Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract. Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and a variety ...

secondary to

gastrointestinal disease Gastrointestinal diseases (abbrev. GI diseases or GI illnesses) refer to diseases involving the gastrointestinal tract, namely the oesophagus, stomach, small intestine, large intestine and rectum, and the accessory organs of digestion, the liv ...

, or be a primary disorder, associated with excessive

bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Prima ...

production. Treatment with bile acid sequestrants is often effective.

Signs and symptoms

A persistent (chronic) history of

, with watery or mushy, unformed stools, (types 6 and 7 on the

Bristol stool scale The Bristol stool scale is a diagnostic medical tool designed to classify the form of human faeces into seven categories. It is used in both clinical and experimental fields. It was developed at the Bristol Royal Infirmary as a clinical asse ...

), sometimes with

steatorrhea Steatorrhea (or steatorrhoea) is the presence of excess fat in feces. Stools may be bulky and difficult to flush, have a pale and oily appearance, and can be especially foul-smelling. An oily anal leakage or some level of fecal incontinence may oc ...

, increased frequency and urgency of

defecation Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging ...

are common manifestations, often with

fecal incontinence Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is refer ...

and other gastrointestinal symptoms such as abdominal swelling,

bloating Abdominal bloating (or simply bloating) is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, pressu ...

and

abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Common causes of pain in the abdomen include gastroenteritis and irritable bowel syndrome. About 15% of people have a ...

. People with this disorder often report impairments of

mental health Mental health encompasses emotional, psychological, and social well-being, influencing cognition, perception, and behavior. It likewise determines how an individual handles stress, interpersonal relationships, and decision-making. Mental healt ...

and

well-being Well-being, or wellbeing, also known as wellness, prudential value or quality of life, refers to what is intrinsically valuable relative ''to'' someone. So the well-being of a person is what is ultimately good ''for'' this person, what is in t ...

, including

fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

dizziness Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a common medical ...

anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat w ...

about leaving home (primarily due to fear of

), depression, one survey reports. It contributes in delays in diagnosis.

Pathogenesis

Enterohepatic circulation of bile salts

Bile acids Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts. Primary b ...

(also called bile salts) are produced in the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

, secreted into the biliary system, stored in the

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, alth ...

and are released after meals stimulated by

cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac ( gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat a ...

. They are important for the

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intes ...

and

absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion ** Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials * Absorption (skin), a route by which ...

of fats (lipids) in the

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through ...

. Usually over 95% of the bile acids are absorbed in the terminal

ileum The ileum () is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine ...

and are taken up by the liver and resecreted. This enterohepatic circulation of bile acids takes place 4-6 times in 24 hours and usually less than 0.5 g of bile acids enter the

large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before being ...

per 24 h. When larger amounts of bile acids enter the

, they stimulate water secretion and intestinal motility in the colon, which causes symptoms of chronic

Intestinal absorption of bile acids

The

is very efficient at absorbing the glyco- and

taurine Taurine (), or 2-aminoethanesulfonic acid, is an organic compound that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine, and accounts for up to 0.1% of total human body weight. I ...

-conjugated forms of the bile salts. The apical sodium-dependent bile salt transporter (ASBT, IBAT, gene symbol ''SLC10A2'') is the first step in absorption at the brush-border membrane. The cytoplasmic ileal bile acid binding protein (IBABP, ILBP, gene symbol ''FABP6'') and the basolateral heterodimer of OSTα and OSTβ transfer bile acids through and out of the cell where they eventually enter the

portal vein The portal vein or hepatic portal vein (HPV) is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to the liver. This blood contains nutrients and toxins extracted from digested contents. Approxi ...

. These bile acid transporters are all highly expressed in the ileum but not in the liver, jejunum or colon. When expression of these specialized transporters is reduced, the intestine is less efficient at bile acid reabsorption (Type 1 bile acid malabsorption). If intestinal motility is affected by gastro-intestinal surgery, or bile acids are deconjugated by

small intestinal bacterial overgrowth Small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive bacterial growth in the small intestine. Unlike the colon (or large bowel), which is r ...

, absorption is less efficient (Type 3 bile acid malabsorption). A very small proportion of the patients with no obvious disease (Type 2 bile acid malabsorption) may have mutations in ASBT, but this mutation is not more common in most patients and does not affect function.

Overproduction of bile acids

Primary bile acid diarrhea (Type 2 bile acid "malabsorption") may be caused by an overproduction of bile acids. Several groups of workers have failed to show any defect in ileal bile acid absorption in these patients, and they have an enlarged bile acid pool, rather than the reduced pool expected with malabsorption. The synthesis of bile acids in the liver is negatively regulated by the ileal hormone fibroblast growth factor 19 ( FGF19), and lower levels of this hormone result in overproduction of bile acids, which are more than the ileum can absorb.

Diagnosis

Several methods have been developed to identify the disorder but there are difficulties with all of them. Diagnosis of bile acid malabsorption is easily and reliably made by the SeHCAT test. This

nuclear medicine Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...

test involves two scans a week apart and so measures multiple cycles of bile acid excretion and reabsorption. There is limited radiation exposure (0.3 mSv). Retention of SeHCAT at 7 days is normally above 15%; values less than 15%, 10% and 5% predict respectively mild, moderate and severe abnormal retention and an increasing likelihood of response to bile acid sequestrants. This test is not licensed in the USA, and is underutilized even where it is available. Older methods such as the ¹⁴C-glycocholic breath test are no longer in routine clinical use. Measurement of 7α-Hydroxy-4-cholesten-3-one, (C4), a bile acid precursor, in serum, shows the increased bile acid synthesis found in bile acid malabsorption. This test is an alternative diagnostic means when available. Fasting blood FGF19 values may have value in the recognition of the disease and prediction of response. The various biomarkers give similar diagnostic yields of around 25% in patients with functional bowel disorders with diarrhea. In countries such as the USA, where SeHCAT is not available, fecal bile acids and C4 are available to make the diagnosis.

Classification

Bile acid malabsorption was first recognized in patients with ileal disease. When other causes were recognized, and an idiopathic, primary form described, a classification into three types was proposed: * Type 1: Bile acid malabsorption, secondary to ileal resection, or ileal inflammation (e.g. in

Crohn's disease Crohn's disease is a type of inflammatory bowel disease (IBD) that may affect any segment of the gastrointestinal tract. Symptoms often include abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever, abdominal distension, ...

) * Type 2: Idiopathic bile acid malabsorption, Primary bile acid diarrhea * Type 3: Secondary to various gastrointestinal diseases including

cholecystectomy Cholecystectomy is the surgical removal of the gallbladder. Cholecystectomy is a common treatment of symptomatic gallstones and other gallbladder conditions. In 2011, cholecystectomy was the eighth most common operating room procedure performed ...

vagotomy A vagotomy is a surgical procedure that involves removing part of the vagus nerve. Types A plain vagotomy eliminates the parasympathetic supply from the stomach to the left side of the transverse colon. Other techniques focus on branches leadi ...

, radiation enteropathy,

celiac disease Coeliac disease (British English) or celiac disease (American English) is a long-term autoimmune disorder, primarily affecting the small intestine, where individuals develop intolerance to gluten, present in foods such as wheat, rye and barle ...

chronic pancreatitis Chronic pancreatitis is a long-standing inflammation of the pancreas that alters the organ's normal structure and functions. It can present as episodes of acute inflammation in a previously injured pancreas, or as chronic damage with persistent pa ...

, etc.

Treatment

Bile acid sequestrants are the main agents used to treat bile acid malabsorption.

Cholestyramine Colestyramine ( INN) or cholestyramine ( USAN) (trade names Questran, Questran Light, Cholybar, Olestyr) is a bile acid sequestrant, which binds bile in the gastrointestinal tract to prevent its reabsorption. It is a strong ion exchange resin, w ...

and colestipol, both in powder form, have been used for many years. Unfortunately, many patients find them difficult to tolerate; although the diarrhea may improve, other symptoms such as abdominal pain and bloating may worsen.

Colesevelam Colesevelam is a bile acid sequestrant administered orally. It was developed by GelTex Pharmaceuticals and later acquired by Genzyme. It is marketed in the U.S. by Daiichi Sankyo under the brand name Welchol and elsewhere by Genzyme as Cholestag ...

is a tablet and some patients tolerate this more easily. A proof of concept study of the

farnesoid X receptor The bile acid receptor (BAR), also known as farnesoid X receptor (FXR) or NR1H4 (nuclear receptor subfamily 1, group H, member 4), is a nuclear receptor that is encoded by the ''NR1H4'' gene in humans. Function FXR is expressed at high levels ...

agonist

obeticholic acid Obeticholic acid (OCA), sold under the brand name Ocaliva, is a semi-synthetic bile acid analogue which has the chemical structure 6α-ethyl-chenodeoxycholic acid. It is used as a medication used to treat primary biliary cholangitis. Intercep ...

has shown clinical and biochemical benefit. As of March 15, 2016, Novartis Pharmaceuticals is conducting a phase II clinical study involving a farnesoid X receptor agonist named LJN452.

Epidemiology

Bile acid malabsorption is common in

but not always recognized. Most people with previous ileal resection and chronic diarrhea will have abnormal SeHCAT tests and can benefit from bile acid sequestrants. People with primary bile acid diarrhea are frequently misdiagnosed as having

irritable bowel syndrome Irritable bowel syndrome (IBS) is a "disorder of gut-brain interaction" characterized by a group of symptoms that commonly include abdominal pain and or abdominal bloating and changes in the consistency of bowel movements. These symptoms may ...

. When SeHCAT testing is performed, the diagnosis of primary bile acid diarrhea is commonly made. In a review of 18 studies of the use of SeHCAT testing in diarrhea-predominant

patients, 32% of 1223 people had a SeHCAT 7-day retention of less than 10%, and 80% of these reported a response to cholestyramine, a

bile acid sequestrant The bile acid sequestrants are a group of resins used to bind certain components of bile in the gastrointestinal tract. They disrupt the enterohepatic circulation of bile acids by combining with bile constituents and preventing their reabsorption f ...

. Estimates of the population prevalence suggest that 1% of the adult population could have primary bile acid diarrhea (Type 2 bile acid malabsorption).

References

External links

{{DEFAULTSORT:Bile Acid Malabsorption Diseases of intestines * Gastrointestinal tract disorders