CLINICAL PHARMACOLOGY
Mechanism Of Action
Cholic acid is a primary bile acid synthesized from
cholesterol in the liver. In bile acid synthesis disorders due to SEDs in the
biosynthetic pathway, and in PDs including Zellweger spectrum disorders,
deficiency of primary bile acids leads to unregulated accumulation of
intermediate bile acids and cholestasis. Bile acids facilitate fat digestion
and absorption by forming mixed micelles, and facilitate absorption of
fat-soluble vitamins in the intestine.
Endogenous bile acids including cholic acid enhance bile
flow and provide the physiologic feedback inhibition of bile acid synthesis.
The mechanism of action of cholic acid has not been fully established; however,
it is known that cholic acid and its conjugates are endogenous ligands of the
nuclear receptor, farnesoid X receptor (FXR). FXR regulates enzymes and
transporters that are involved in bile acid synthesis and in the enterohepatic
circulation to maintain bile acid homeostasis under normal physiologic
conditions.
Pharmacokinetics
Orally administered cholic acid is subject to the same
metabolic pathway as endogenous cholic acid.
Cholic acid is absorbed by passive diffusion along the
length of the gastrointestinal tract. Once absorbed, cholic acid enters into
the body's bile acid pool and undergoes enterohepatic circulation mainly in
conjugated forms.
In the liver, cholic acid is conjugated with glycine or
taurine by bile acid-CoA synthetase and bile acid-CoA: amino acid
Nacetyltransferase. Conjugated cholic acid is actively secreted into bile
mainly by the Bile Salt Efflux Pump (BSEP), and then released into the small
intestine, along with other components of bile.
Conjugated cholic acid is mostly re-absorbed in the ileum
mainly by the apical-sodium-dependent-bile acid transporter, passed back to the
liver by transporters including sodium-taurocholate cotransporting polypeptide
and organic anion transport protein and enters another cycle of enterohepatic
circulation. Any conjugated cholic acid not absorbed in the ileum passes into
the colon where deconjugation and 7-dehydroxylation are mediated by bacteria to
form cholic acid and deoxycholic acid which may be re-absorbed in the colon or
excreted in the feces. The loss of cholic acid is compensated by de-novo
synthesis of cholic acids from cholesterol to maintain the bile acid pool in
healthy subjects.
Animal Toxicology And/Or Pharmacology
In the PEX2-/-mouse model of peroxisomal
disorders, feeding with a combination of cholic acid and ursodeoxycholic acid
normalized C24 bile acid concentrations in bile to that of untreated control
animals. Although growth was only mildly improved, there was near complete
normalization of stool fat content, resolution of steatorrhea, and improved
survival. Bile acid feeding reduced the number of cholestatic deposits in bile
ducts and alleviated cholangitis, but exacerbated the degree of hepatic
steatosis and mitochondrial and cellular damage in the peroxisome-deficient
livers of these animals.
Clinical Studies
Bile Acid Synthesis Disorders Due To Single Enzyme
Defects
The effectiveness of CHOLBAM at dosages of 10 to 15 mg/kg
per day in patients with SEDs was assessed in:
- Trial 1: a non-randomized, open-label, uncontrolled,
trial in 50 patients over an 18 year period.
- Trial 2: an extension trial of 12 new patients along with
21 patients who rolled-over from Trial 1 (n=33 total). Efficacy data are
available for 21 months of treatment.
- A published case series of 15 patients.
Enrollment criteria in Trials 1 and 2 were based on
abnormal urinary bile acid by Fast Atom Bombardment ionization -Mass
Spectrometry (FAB-MS) analysis.
Pre-and post-treatment liver biopsies were performed in a
limited number of patients. Documentation of adherence to treatment,
concomitant medications and response to treatment were incomplete during Trial
1. Additional interventions in some patients included supplementation with
fat-soluble vitamins, as dictated by the patient's clinical signs and symptoms.
Trials 1 and 2
On average, patients were 4 years of age at the start of
cholic acid treatment (range three weeks to 36 years). The majority of patients
were treated for an average of 310 weeks (6 years). Patient ages at the end of
treatment ranged from 19 to 36 years.
These trials were carried out over many years and data
are not available on all patients. Thirty-nine patients in Trial 1 and 5 new
patients in Trial 2 received at least one dose of CHOLBAM and had sufficient
data available to assess baseline liver function and effects of CHOLBAM
treatment. A responder analysis was performed to determine the response to
treatment with CHOLBAM.
Response to CHOLBAM treatment was assessed by the
following laboratory criteria:
- ALT or AST values reduced to less than 50 U/L, or
baseline levels reduced by 80%;
- total bilirubin values reduced to less than or equal to 1
mg/dL; and
- no evidence of cholestasis on liver biopsy;
and the following clinical criteria:
- body weight increased by 10% or stable at greater than
the 50th percentile; and
- survival for greater than 3 years on treatment or alive
at the end of Trial 2
CHOLBAM responders were defined as patients who either:
- met at least two laboratory criteria and were alive at
the last follow-up; or
- met at least one laboratory criterion, had increased body
weight and were alive at the last follow-up.
Overall, 28 of 44 patients (64%) were responders. The
breakdown by defect type is as follows:
Table 4: Response to CHOLBAM Treatment by Type of
Single Enzyme Defect
Single Enzyme Defect |
Responders/Number Treated (%) |
3β-HSD |
22/37 (59%) |
AKR1D1 |
3/4 (75%) |
CTX |
2/2 (100%) |
AMACR |
1/1 (100%) |
CYP7A1 |
N/A* |
Smith-Lemli-Opitz |
N/A* |
*N/A indicates no evaluable patients in the defect subgroup
represented. |
Among SED responsive patients,
45% of the responders met the two clinical criteria plus 1 to 3 laboratory
criteria and 55% met the weight criteria.
Only six patients had pre-and
post-treatment liver biopsies in Trial 1. Where biopsies were available,
pre-treatment biopsies showed varying degrees of inflammation, bridging
fibrosis, and giant cell formation. Post-treatment biopsies generally showed reduced
or absent inflammation and reduced or absent giant cell formation. Fibrosis
remained but did not progress.
It is difficult to evaluate
long term survival in patients with SEDs since there is little natural history
survival data for comparison. Overall, 41 of 62, or 67%, of patients with SEDs
survived greater than 3 years from trial entry. Thirteen of these 41 patients,
or 32%, were “long-term” survivors (range of 10 to 24 years on treatment).
Four patients in Trial 1
underwent liver transplant, including two patients diagnosed with AKR1D1
deficiency, one with 3β-HSD deficiency, and one with CYP7A1 deficiency and
two patients in Trial 2, both with AKR1D1.
CHOLBAM had no effect on
extrahepatic manifestations of SEDs such as neurologic symptoms.
Case Series
A published report of a case
series described 15 patients with SEDs; thirteen were diagnosed with
3β-HSD deficiency and two with AKR1D1 deficiency by mass spectrometry and
gene sequencing. All patients were treated with cholic acid with a median
duration of treatment of 12.4 years (range 5.6 to 15 years). Therapy started at
a median age of 3.9 years (range 0.3 to 13.1 years). The mean dose at the start
of cholic acid treatment was 13 mg/kg and the mean dose at last follow up was 6
mg/kg. Eight patients were initially treated with oral ursodeoxycholic acid
prior to receiving a diagnosis of bile acid synthesis defect, after which they
were switched to cholic acid. Initial signs and symptoms included jaundice,
hepatosplenomegaly, steatorrhea, or symptoms related to deficiency of a fat
soluble vitamin (K, D or E).
Of the 8 patients who received
ursodeoxycholic acid initially, the six with 3β-HSD deficiency
demonstrated mild clinical improvement. Following treatment with cholic acid, all
patients experienced resolution of their pre-existing jaundice and steatorrhea,
and all but one experienced resolution of hepatosplenomegaly. Weight and height
improved and sexual maturation progressed normally in all patients. Liver
biopsies were performed in 14 patients after at least 5 years of cholic acid
treatment and all showed resolution of cholestasis. In one patient with
3β-HSD deficiency, biliary bile acid analysis while on cholic acid therapy
showed enrichment of the bile with cholic acid.
Peroxisomal Disorders Including
Zellweger Spectrum Disorders
The effectiveness of CHOLBAM at
a dosage of 10 to 15 mg/kg per day in patients with PDs including Zellweger
spectrum disorders was assessed in patients in the same trials described in
section 14.1.
- Trial 1 treated 29 patients with PDs over an 18 year
period.
- Trial 2 treated 2 new patients along with 10 patients who
rolled-over from Trial 1 (n=12 total). Efficacy data are available from Trial 2
for 21 months of treatment.
- Additional efficacy data were obtained from published
case reports of 3 patients.
Enrollment criteria in Trials 1
and 2 were based on abnormal urinary bile acids analysis by Fast Atom
Bombardment ionization -Mass Spectrometry (FAB-MS) and a neurologic exam. Most
patients received concomitant DHA (docosahexaenoic acid) and Vitamins A, D, E
and K. Documentation of adherence to treatment, concomitant medications and
response to treatment were incomplete during Trial 1.
Trials 1 and 2
The majority of patients (80%,
25/31) were less than 2 years of age at the start of CHOLBAM treatment (range 3
weeks to 10 years). The majority of patients were treated for an average of 254
weeks (4.8 years).
Sufficient data were available
to assess baseline liver function and effects of CHOLBAM treatment in 23
patients in Trial 1 and in one new patient in Trial 2. A responder analysis was
performed in the patients who had received at least one dose of CHOLBAM and had
sufficient data available to assess baseline liver impairment.
Response to CHOLBAM treatment
was assessed by the following laboratory criteria:
- ALT or AST values reduced to less than 50 U/L, or
baseline levels reduced by 80%;
- total bilirubin values reduced to less than or equal to 1
mg/dL; and
- no evidence of cholestasis on liver biopsy;
and the following clinical criteria:
- body weight increased by 10% or stable at greater than
the 50th percentile; and
- survival for greater than 3 years on treatment or alive
at the end of Trial 2
CHOLBAM responders were defined as patients who either:
- met at least two laboratory criteria and were alive at
the last follow-up; or
- met at least one laboratory criterion, had increased body
weight and were alive at the last follow-up.
Overall, 11 of 24 patients
(46%) were responders. The breakdown by disorder is as follows:
Table 5: Response to CHOLBAM
Treatment by Type of Peroxisomal Disorders including Zellweger Spectrum
Disorders
Peroxisomal Disorder |
Responders/Number Treated (%) |
Neonatal Adrenoleukodystropyhy |
3/6 (50%) |
Generalized Peroxisomal Disorder |
1/1 (100%) |
Refsum Disease |
3/4 (75%) |
Zellweger Syndrome |
3/8 (38%) |
Peroxisomal Disorder, Type Unknown |
1/5 (20%) |
Among responsive patients with
PDs, 38% of the responders met the two clinical criteria plus 1 to 3 laboratory
criteria and 63% met the weight criteria. There were no PD patients that
underwent liver transplant.
No evidence of improvement in
survival over that seen in historical controls could be demonstrated from the
data presented. Overall, 13 of 31, or 42%, of patients survived greater than 3
years from the time of trial entry. Eight of these 13 patients, or 62% were
“longterm” survivors (range of 10 to 17 years on treatment).
Nine patients had both pre-and
post-treatment liver biopsies. One patient showed improvement in histology,
while the majority of patients remained unchanged. Two patients demonstrated
worsening histology, which was consistent with a worsening of other liver
laboratory parameters (bilirubin, serum transaminase values).
CHOLBAM had no effect on
extrahepatic manifestations of PDs including Zellweger spectrum disorders, such
as neurologic symptoms.
One patient, who did not have
cholestasis on pre-treatment liver biopsy, developed cholestasis on treatment
with CHOLBAM and subsequently died.
Case Reports
In case reports from the
literature, a 6 month old patient with Zellweger syndrome treated with a
combination of cholic and chenodeoxycholic acids experienced normalization of
serum transaminases and bilirubin, improvement in liver histology, reduced
serum and urinary atypical bile acid intermediates, and improvement in
steatorrhea and growth. Two patients with Zellweger syndrome treated with oral
bile acids showed decreased serum transaminases.