# Do PPARγ Ligands Suppress the Growth of Cholangiocarcinoma or the Cholangiohepatitis  Induced by the Tumor?

Authors: Satoru Suzuki; Kiyoshi Hashizume
Journal: PPAR Research
 (2008)

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## Abstract

Cholangiocarcinoma is a predominantly fatal cancer, which can be difficult to treat. It has been reported that the administration of pioglitazone temporarily improved not only diabetic control, but also bile duct carcinoma-induced cholangiohepatitis. Pioglitazone is considered to have both direct and indirect mechanisms of action on the tumor-related hepatitis. Several molecules induced by thiazolidinedione, including Smad pathway-related molecules, adipokines, and other lipid metabolism-related proteins, may directly or indirectly suppress tumor development and/or tumor-induced cholangiohepatitis. Although the most frequent and critical side effect of thiazolidinedione is drug-induced hepatitis, it can probably be avoided by careful monitoring of serum hepatic enzyme levels. Thiazolidinedione should be considered for management of tumor-induced hepatitis in the presence of diabetes unless severe side effects occur.


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## Body

## 1. Introduction

The primary effects of thiazolidinedione, a peroxisome proliferator-activated
receptorγ (PPARγ) agonist, are the reduction of insulin resistance
and improvement of insulin sensitivity, resulting in reduction of fasting
plasma glucose, insulin, and free fatty acid levels [1].Cholangiocarcinoma
is a predominantly fatal cancer, which can be difficult to treat. We reported previously that administration of the thiazolidinedione, pioglitazone, in a 73-year-old male
patient who developed cholangiocarcinoma with cholangiohepatitis and diabetes
improved not only diabetic control, but also the tumor-induced
cholangiohepatitis, and improved the patient’s quality of life [2]. One and
half years after treatment, the patient again showed deterioration of
cholangiohepatitis and diabetic control. He finally died of obstructive jaundice.There are two possible mechanisms to
explain the initial improvement of hepatitis in our case: the PPARγ ligand may have directly suppressed the
abnormal cell growth, or the PPARγ ligand may have indirectly suppressed tumor growth after the ligand
improved hepatitis and/or diabetes.In this review, we discuss the mechanisms
of the temporary beneficial effects of the agent, especially the above two
possibilities, with regard to the literature concerning PPARγ and cholangiohepatitis. In addition, we
also discuss the positive choice of thiazolidinedione, despite elevated serum
concentrations of hepatic enzymes.


## 2. Direct Effects on the Development of Cholangiocarcinoma

These mechanisms
were supported by the results of basic experiments using various
cholangiocarcinoma cell lines [3–6]. PPARγ ligand mediates the inhibition of
cholangiocarcinoma cell growth through p53-dependent mechanisms [3]. The PPARγ ligand, 15-deoxy-delta 12,14-PGJ2,
induces apoptosis in cholangiocarcinoma cell lines although regulation of
apoptosis-related protein expression varies [4, 5], while artificial regulation
of PPARγ
expression in cholangiocarcinoma cell lines suggests that PPARγ may actually promote tumor cell growth viathe Smad pathway [6]. It has been reported that PPARγ ligands can suppress proliferation and
induce apoptosis although PPARγ itself may have divergent effects on cellular growth in
cholangiocarcinoma cell lines [7].


## 3. Indirect Effects on the Development of Cholangiocarcinoma

Thiazolidinedione seems not to improve
insulin sensitivity and glucose disposal by direct effects on either the liver
or muscle. PPARγ is
expressed preferentially in adipose tissue, and its levels of expression in the
liver and skeletal muscle are low [8]. Thus, it is more likely that the primary
effects of these drugs are on adipose tissue, followed by secondary benefits on
other target tissues of insulin [9]. In our case, there was no evidence that
pioglitazone directly reduced the tumor size. In contrast, cholangiohepatitis
was improved by administration of this agent. In addition, the progressive
cholangiohepatitis was probably related to the cholangiocarcinoma. In general,
cholangiocarcinoma development is based possibly upon the cytotoxicity of bile
constituents, that is, cytotoxic bile acids and lysolecithins. These humoral
factors may affect tumor progression. Thus, it was suggested that pioglitazone
indirectly improves cancer-mediated inflammation, such as cholangiohepatitis,
rather than directly suppressing tumor growth.As mentioned above, it is now generally
accepted that adipose cells send molecular signals, including cytokines, to
other tissues. Thus, it is possible that PPARγ activation controls one or more genes that regulate systemic tumor
promotion (see Figure 1). The interesting candidate genes in this regard are
TNF-α, adiponectin, and
leptin. Other lipid-related genes regulated by PPARγ ligands, such as lipoprotein lipase and
fatty acid binding protein, may also control tumor development [10].Figure 1
Inhibitory effects of PPARγ ligand on the
development of cholangiocarcinoma. PPARγ ligand directly suppresses tumor progression through
p53 and Smad pathways (red arrow) and also stimulates adipocyte and
hepatobiliary cells (gray arrow). Secretion of adipokines (TNF-α, adiponectin, and leptin) and production of
lipid-related proteins (FABP and LPL) are regulated by PPARγ ligand. Up- and downregulation of various gene signals
from adipocytes (yellow line) and hepatobiliary cells (broken line) promoted
suppression of tumor growth. As a result, PPARγ
indirectly suppressed tumor growth of cholangiocarcinoma through adipocytes and
hepatobiliary cells. Currently, evidence of suppressive signals from
hepatobiliary cells to cholangiocarcinoma is unavailable (broken line). FABP:
fatty acid binding protein, LPL: lipoprotein lipase, TNF-α: tumor necrosis factor-α.


### 3.1. TNF-α

Thiazolidinedione reduces TNF-α expression in human and rodent adipocytes
[11]. A series of studies using cholangiocarcinoma cell lines demonstrated that
TNF-α itself attenuates
the growth of cholangiocarcinoma cells and induces apoptosis [11–13]. However,
several recent studies have demonstrated that TNF-α promotes invasiveness and accelerates
migration of cholangiocarcinoma cells [14–16]. These
observations imply that the suppression of TNF-α production may attenuate the progressive invasion of tumor cells into
healthy hepatobiliary cells.


### 3.2. Adiponectin and Leptin

PPARγ agonists have been reported to increase the expression and circulating
levels of adiponectin, an adipocyte-derived protein with insulin-sensitizing
activity [17], in diabetic rodents and in patients with type 2 diabetes [18].
There have been many reports, especially in breast cancer, that adiponectin
plays roles in the inhibition of tumor cell growth [19]. The expression of
leptin, a suppressor of feeding behavior, is negatively regulated by
thiazolidinediones [20]. Leptin has been reported to induce tumor development
in breast cancer [21], suggesting that suppression of leptin secretion may
reduce tumor progression.


### 3.3. Other Lipid-Related Proteins

Other lipid-related proteins, such as lipoprotein lipase
(LPL) and fatty acid binding proteins (FABPs), are positively regulated by the
PPARγ
ligand GW1929 [22]. Although there have been no studies related to cholangiocarcinoma
and these lipid-associated proteins, there is a great deal of evidence that the
proteins promote reduction of tumor growth. Intestinal polyp formation was
suppressed by increasing LPL activity [23]. As FABPs play roles not only as
lipid chaperones but also as free radical scavengers, the molecules may affect
tumor progression through the oxidative stress pathways. The protein expression
of liver FABP was reduced in neoplastic lesions of CuZn superoxide
dismutase-deficient mice [24]. It has been reported that FABP reduces cellular
damage from hypoxia/reoxygeneration [25]. These lipid-related proteins may also
play roles in the reduction of tumor growth and/or suppression of
tumor-mediated liver damage.


## 3.1. TNF-α

Thiazolidinedione reduces TNF-α expression in human and rodent adipocytes
[11]. A series of studies using cholangiocarcinoma cell lines demonstrated that
TNF-α itself attenuates
the growth of cholangiocarcinoma cells and induces apoptosis [11–13]. However,
several recent studies have demonstrated that TNF-α promotes invasiveness and accelerates
migration of cholangiocarcinoma cells [14–16]. These
observations imply that the suppression of TNF-α production may attenuate the progressive invasion of tumor cells into
healthy hepatobiliary cells.


## 3.2. Adiponectin and Leptin

PPARγ agonists have been reported to increase the expression and circulating
levels of adiponectin, an adipocyte-derived protein with insulin-sensitizing
activity [17], in diabetic rodents and in patients with type 2 diabetes [18].
There have been many reports, especially in breast cancer, that adiponectin
plays roles in the inhibition of tumor cell growth [19]. The expression of
leptin, a suppressor of feeding behavior, is negatively regulated by
thiazolidinediones [20]. Leptin has been reported to induce tumor development
in breast cancer [21], suggesting that suppression of leptin secretion may
reduce tumor progression.


## 3.3. Other Lipid-Related Proteins

Other lipid-related proteins, such as lipoprotein lipase
(LPL) and fatty acid binding proteins (FABPs), are positively regulated by the
PPARγ
ligand GW1929 [22]. Although there have been no studies related to cholangiocarcinoma
and these lipid-associated proteins, there is a great deal of evidence that the
proteins promote reduction of tumor growth. Intestinal polyp formation was
suppressed by increasing LPL activity [23]. As FABPs play roles not only as
lipid chaperones but also as free radical scavengers, the molecules may affect
tumor progression through the oxidative stress pathways. The protein expression
of liver FABP was reduced in neoplastic lesions of CuZn superoxide
dismutase-deficient mice [24]. It has been reported that FABP reduces cellular
damage from hypoxia/reoxygeneration [25]. These lipid-related proteins may also
play roles in the reduction of tumor growth and/or suppression of
tumor-mediated liver damage.


## 4. Hepatic Side Effects

The most frequent and
critical side effect of thiazolidinedione that must be taken
into consideration before starting thiazolidinedione administration in cases of
cholangiocarcinoma is drug-induced hepatitis. Although some data are available from animal studies suggesting that
hepatic toxicity may be a characteristic of the thiazolidinedione class [26],
current clinical evidence indicates that pioglitazone treatment does not result
in liver toxicity [27]. However, this agent causes mild transient increases in
serum ALT levels. The FDA recommends monitoring ALT levels and not using these
drugs in patients with liver disease [28]. Moreover, it was reported that
patients receiving pioglitazone may develop serious liver injury and should be
monitored for evidence of hepatitis [29].Unlike other
existing antidiabetic medications that show a very rapid onset of activity,
pioglitazone and rosiglitazone exhibit a characteristic delay of 4–12 weeks in the
onset of their therapeutic effects. It has been suggested that thiazolidinedione
should be continued for at least one month to obtain results. In our case,
initial improvement of the elevated hepatic enzymes was observed two weeks
after starting administration of this agent. These data indicate that the
effectiveness in cases of tumor-related hepatitis could be assessed within two
weeks rather than 4–12 weeks when
diabetic control is obtained.


## 5. Perspectives

Taken together with
these considerations, as PPARγ ligands are probably effective in the suppression
of tumor development, especially on the reduction of tumor invasiveness through
molecular signals from adipocytes, thiazolidinedione should be chosen not only for diabetic control, but
also as an attenuator of tumor progression in patients with diabetes.
Drug-induced hepatitis can be avoided by meticulous monitoring of serum hepatic
enzyme levels.



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