colestasis en felinos

1. Metabolic Consequences of Cholestasis in Cats
ECVIM Congress 2015
Cynthia R.L. Webster
Tufts University, North Grafton, MA, USA
Cholestasis is derived from the Greek chole, bile, and stasis, standing still. Cholestasis occurs from
hepatobiliary dysfunction, intrahepatic or extrahepatic biliary obstruction and/or sepsis. It is a prominent
feature of the most common feline hepatobiliary disorders including acute and chronic cholangitis, hepatic
lipidosis and extrahepatic bile duct obstruction (EHBDO) due to cholangitis/pancreatitis or
biliary/pancreatic neoplasia. Icterus, a yellow discoloration of tissues due to deposition of bilirubin, is the
clinical manifestation of cholestasis. Biochemically, cholestasis is reflected in increased serum bilirubin and
bile acids.
Clinical manifestations of cholestasis include:
1. Fat malabsorption due to interruption of the enterohepatic circulation of bile acids
2. Hepatobiliary epithelial cell death due to retention of cytotoxic substances normally excreted in bile
3. Increased serum and tissue bile acids and bilirubin that are cytotoxic to non-hepatic cells
4. Changes in the composition of the gut intestinal biome
5. Altered intestinal permeability that promotes bacterial translocation and endotoxemia
Cholestasis disrupts the enterohepatic circulation of bile acids. Primary bile acids are synthesized in the
liver from cholesterol, conjugated to either glycine of taurine and then excreted by active transport into the
biliary canaliculus. The canaliculi drain into cholangioles which unite to form interlobular bile ducts.
Interlobular ducts anastomose into progressively larger intrahepatic ducts which finally enter into the main
hepatic ducts that unite to form the common bile duct. In the inter-digestive period, bile is diverted into the
gallbladder for storage and concentration. Following a meal, the gallbladder contracts and deposits bile into
the duodenum through the common bile duct. Bile serves as a way to excrete endogenous (e.g., bilirubin,
cholesterol, copper) and exogenous metabolites. In addition, bile acids within the duodenum are essential
for the absorption of fat. The majority of the primary conjugated bile acids are efficiently taken up by an ileal
conjugated bile acid transporter, then enter the portal circulation and are finally taken up a bile acid
transporter on the sinusoidal surface of the hepatocyte. This enterohepatic circulation of bile acids generates
the major driving force for bile formation. A small portion of bile acids in the intestinal lumen are converted
to secondary bile acids by the action of enteric bacteria. Both primary and secondary bile acids bind to
nuclear and cell surface receptors on intestinal epithelial and entero-endocrine cells to control the
postprandial response to a meal. Following a meal, the serum bile acid concentrations increase. This
postprandial increase in serum primary and secondary bile acids regulates whole body glucose and lipid
metabolism by activating nuclear and cell surface receptors.1
Disruption of the enterohepatic circulation during cholestasis modifies the intestinal microbiome. Luminal
bile acids normally keep bacterial populations in check, in part by direct bacteriostatic effects, but also
through bile acid-induced activation of the intestinal farnesoid X (FXR) bile acid receptor.2 Activation of FXR
upregulates gene products that promote intestinal defense mechanisms. In humans and rodent models, a
luminal deficiency of bile acids leads to small bowel bacterial overgrowth. It is unknown if the same
phenomena happen in cats, but if it does it might promote ascending pancreatic/biliary infection. We already
know that cats with chronic cholangitis have a triad of inflammatory disease involving the intestine and
pancreas3-5 that in part may be fueled by the cat's common channel for biliary and pancreatic secretion. We
believe that intestinal reflux into this common channel (i.e., union of the common bile duct and pancreatic
duct) predisposes cats to inflammation/infection in all three organs. The presence of small bowel bacterial

2. overgrowth might increase the likelihood of infection and fits with the observation that cats with biliary
disease have a high incidence of positive bile cultures.6 Treatment of bile duct-obstructed rodents with FXR
agonists restores normal bacterial flora. Currently a FXR agonist, obeticholic acid, is undergoing phase III
clinical trials in humans with cholestatic disease.7
Another consequence of disruption of the enterohepatic circulation is fat malabsorption. This can lead to
steatorrhea and fat-soluble vitamin deficiencies. In human patients with cholestatic disease, deficiencies in
vitamin K, E, and D occur, particularly in paediatric patients with chronic cholestasis.8,9 Although overt
clinical signs of vitamin E, D and A deficiency have not been reported in cholestatic cats, it is possible that
reduced levels may be present. Studies looking at vitamin E and D levels in cats with cholestatic liver disease
are needed. Due to the critical role of vitamin K (VK) in coagulation and the need for invasive procedures
(liver biopsy, E tube placement, biliary surgery) in cats with cholestatic disease, VK status in cats with
cholestatic disease has been investigated. VK status has been evaluated indirectly by looking at factor VII, PT,
aPTT and proteins inactivated by VK and by evaluating response to parenteral VK therapy.10-12 The results
suggest that VK deficiency is common (45% to 73%) in cats with cholestasis. VK deficiency is likely due to a
combination of factors including fat malabsorption, decreased intake and selective depopulation of VK
generating bacteria by antibiotic use.
Many cats with cholestatic liver disease are anemic or develop a progressive anemia while hospitalized.
This anemia is a negative prognostic indicator in hepatic lipidosis and despite correction of vitamin K-
dependent coagulopathy necessitates perioperative blood product support in up to 50% of cats with
EHBDO.12-14 The basis for this anemia has not been fully determined, but we hypothesized that it might be
associated with occult coagulopathy. Conventional serum-based coagulation testing has failed to identify
hypo-coagulable states beyond VK deficiency. We therefore did a pilot study evaluating
thromboelastography (TEG). TEG permits evaluation of clot formation as well as clot strength and stability
and can define both hypo- and hypercoagulable states. We compared TEG values in 17 cats with cholestatic
disease to normal values derived from 30 clinically normal cats.15 TEG was performed post VK therapy and
identified only 3 cats as hypo-coagulable, 2 of which also had non-VK responsive increases in PT. The other
cat who had normal PT, aPTT and platelet count would have been labeled normo-coagulable with
conventional testing. One cat had a profoundly hyper-fibrinolytic tracing. Many cats, however, were
hypercoagulable including 5/7 cats with concurrent pancreatitis and 3/3 cats with EHBDO. This observation
fits with our previous report of portal vein thrombosis in cats with hepatic disease.16 These preliminary
studies suggest the true coagulation state of cats with cholestatic disease may require more than standard
serum-based assays.
Refractory hypotension is a common perioperative complication in cats with obstructive cholestasis.
Approximately 70% of cats have episodes of intraoperative hypotension (systolic < 80 mm Hg), many of
whom are refractory to vasopressors.13,14,17 The pathophysiology of this refractory hypotension is
incompletely understood, but data in animal models suggest that decreased vascular responsiveness to
vasopressors plays a role. Poor vascular responsiveness is due to systemic endotoxemia, increased
production of the vasodilatory compound nitric oxide, and from vagal effects related to manipulation of the
biliary tract. Endotoxemia is linked to bacterial translocation from the gut secondary to the absence of
intraluminal bile acids and decreased gut barrier function.17,18 In addition, bile acids promote vasodilation
by binding to cell surface receptor on endothelial cells.19 Although therapeutic interventions in humans to
decrease endotoxemia such as oral bile acids, lactulose or parenteral nutrition have had limited success in
improving surgical outcome in patients with biliary obstruction, these strategies have not been tested in cats
with cholestasis.
Another potential cause for refractory hypotension in cholestatic cats could be the presence of adrenal
insufficiency. Activation of the hypothalamic-pituitary-adrenal axis and increased release of cortisol are
necessary to maintain normal vascular responsiveness during times of stress. In obstructive jaundice, this

3. homeostatic mechanism may be disrupted.20,21 In humans, a condition known as the hepato-adrenal
syndrome develops in which there is inadequate cortisol reserve for the severity of illness. This syndrome is
associated with greater short-term mortality, a higher incidence of circulatory and renal complications and
an increased susceptibility to sepsis.21 In times of severe stress, patients with this syndrome become
seriously ill with what has been called critical illness-related corticosteroid insufficiency (CIRCI).22The
hallmark of CIRCI is the presence of hemodynamic instability. In order to examine if a similar hepatoadrenal
syndrome occurs in cats with cholestasis, we did a pilot study evaluating the results of ACTH stimulation in
20 cats with cholestasis. Delta cortisol, the difference between the pre- and post-ACTH values, was used as
an indication of adrenal reserve. The results show that cholestatic cats had high basal and ACTH stimulated
cortisol values and that a > 2-fold increase in basal cortisol values as well as a delta cortisol less than 110
nMol/L (4.00 µg/dL) were both associated with increased short-term mortality. Three cats with refractory
hypotension had a lower mean delta cortisol than cats with normal blood pressure, but this was not
significant (p = 0.18). These preliminary studies suggest that there may be a population of cats with
cholestatic disease that have inadequate adrenal reserve and further evaluation of adrenal function in these
cats is necessary. This is particularly important in lieu of the fact that administration of supplemental
corticosteroids could benefit these cats. In a study in dogs undergoing surgery for congenital portosystemic
shunts, 6/16 had suboptimal delta cortisol after ACTH stimulation, and 2 of these dogs both with refractory
hypoglycemia and prolonged anesthetic recovery times responded to corticosteroid therapy.23
Cholestasis leads to the retention of potentially hepatotoxic substances (bile acids, copper, bilirubin) in
serum and tissues. For the last several years, my lab has studied the biological basis for bile acid-induced
hepatocyte injury. Our studies have shown that bile acids induce hepatocyte apoptosis through an
endoplasmic reticulum stress-mediated pathway controlled by sequential activation of a kinase cascade
involving phosphoinositide-3 kinase gamma and c-Jun N-terminal kinase. In addition, hepatic bile acids also
stimulate a pro-inflammatory response in the liver. Collectively these bile acid mediated events lead to
mitochondrial injury and cell death.
Copper balance in the body is maintained by the liver. During cholestasis, biliary copper excretion is
reduced and can lead to accumulation of potentially toxic levels of this pro-oxidant in hepatocytes. Two
recent studies examined hepatic copper levels in cats with cholestatic disorders.24,25 In one looking at semi-
quantitative staining of hepatic biopsies with rubeanic acid, 12/104 cases had positive copper staining.23 Six
of these cats had chronic cholestatic disorders. None of the cats with lipidosis were positive. In another
report, quantitative copper analysis in 37 cats with cholangitis showed a median hepatic copper of 238 ppm
(63–1004 ppm, reference range < 180 ppm) with 8/17 cats having values > 700 ppm. With EHBDO median
hepatic copper was 320 ppm (40–1110 ppm) with only one cat having values > 700 ppm and 5/14 having
normal values. Only 1/8 cats with lipidosis had increased copper. Cats with chronic cholestatic disorders
(cholangitis and EBHDO) appear to be more likely to accumulate copper than cats with acute disorders
(lipidosis). Currently it is unknown whether mechanisms to reduce hepatic copper (diet, zinc, penicillamine)
would be beneficial in cats with this secondary copper accumulation.
Mild increases in bilirubin have cytoprotective antioxidant properties while higher concentrations are
cytotoxic.27,28 Kernicterus is the name given to neuronal toxicity due to high levels of unconjugated bilirubin.
In this condition, which has been reported in the dog and a kitten, bilirubin damages neuronal and astrocyte
mitochondria, endoplasmic reticulum and plasma membranes.29-31 A so-called cholaemic nephropathy
occurs in people and animal models of obstructive jaundice in which renal tubular injury occurs, leading to
expression of pro-inflammatory and pro-fibrotic cytokines ultimately resulting in tubulo-interstitial kidney
fibrosis.32 Histological evaluation of the brain and kidneys in cats with cholestasis has not been done.

4. Bile acids can be cytotoxic to pancreatic acinar cells, cardiac myocytes and gastric and intestinal epithelial
cells. One could speculate that these toxic effects have a role in several complications seen in feline
cholestasis, such as:
1. Development of concurrent pancreatitis
2. Gastrointestinal ulceration
3. Increases in intestinal permeability that allows absorption of noxious bacterial products such as
endotoxin
4. The refractory hypotension/relative adrenal insufficiency (?) that occurs particularly perioperatively
in cats with obstructive jaundice
Since bile acids represent a family of molecules that differ in their cytotoxic potential, displacing the "bad"
bile acid with cytoprotective bile acid such as ursodeoxycholate might be a beneficial therapeutic approach.
In addition, antioxidant therapy with N-acetylcysteine or s-adenosylmethionine to raise glutathione levels
or with vitamin E to decrease lipid peroxidation are likely to have beneficial effects in cholestatic disorders
in cats.33

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