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NON-THEMATIC REVIEW
Obesity and breast cancer: status of leptin and adiponectin
in pathological processes
Michael E. Grossmann &Amitabha Ray &
Katai J. Nkhata &Dmitry A. Malakhov &
Olga P. Rogozina &Soner Dogan &Margot P. Cleary
Published online: 7 September 2010
#Springer Science+Business Media, LLC 2010
Abstract It is well recognized that obesity increases the
risk of various cancers, including breast malignancies in
postmenopausal women. Furthermore, obesity may adversely
affect tumor progression, metastasis, and overall prognosis in
both pre- and postmenopausal women with breast cancer.
However, the precise mechanism(s) through which obesity
acts is/are still elusive and this relationship has been the
subject of much investigation and speculation. Recently,
adipose tissue and its associated cytokine-like proteins,
adipokines, particularly leptin and adiponectin, have been
investigated as mediators for the association of obesity with
breast cancer. Higher circulating levels of leptin found in
obese subjects could be a growth-enhancing factor as
supported by in vitro and preclinical studies, whereas low
adiponectin levels in obese women may be permissive for
leptin’s growth-promoting effects. These speculations are
supported by in vitro studies which indicate that leptin
promotes human breast cancer cell proliferation while
adiponectin exhibits anti-proliferative actions. Further, estro-
gen and its receptors have a definite impact on the response
of human breast cancer cell lines to leptin and adiponectin.
More in-depth studies are needed to provide additional and
precise links between the in vivo development of breast
cancer and the balance of adiponectin and leptin.
Keywords Breast tumorigenesis .Cancer progression .
Adiposity .Leptin .Adiponectin .Caloric restriction
1 Introduction
A number of studies indicate that obesity, as reflected by
increased body mass index (BMI), is associated with
increased risk of more aggressive breast cancer as well as
reduced survival [1–4]. Obesity plays a complex role in
breast cancer and is associated with increased inflamma-
tion, angiogenesis, and alterations in serum levels of
potential growth regulators such as adiponectin, leptin,
and estrogen [5,6]. In women diagnosed with breast
cancer, the balance of adiponectin and leptin may be a key
factor both in disease development and progression.
Reduced levels of serum adiponectin have been reported
in breast cancer patients compared to healthy controls,
particularly in postmenopausal women [7–9]. On the other
hand, the role of serum leptin levels in breast cancer
appears to be more complex. Some studies have shown that
serum leptin levels are increased in women with breast
cancer but others have found leptin to be decreased or
unchanged [10–14]. This may be due to confounding
factors such as menopausal status and disease stage. There
are several reports indicating that the presence of the leptin
receptor (Ob-R) in breast tumors and that high serum leptin
levels were associated with poor prognosis [15,16]possibly
in conjunction with hypoxia, and/or exposure to elevated
levels of insulin, insulin-like growth factor-I (IGF-I), and
estradiol. It may be that the levels of the receptors for
adiponectin and leptin as well as the balance of adiponectin
and leptin in the serum are critical factors in breast cancer
tumorigenesis.
Adiponectin and leptin are both secreted by adipose
tissue and appear to oppose each other’s actions. Adipo-
nectin, also known as adipocyte complement-related protein
of 30 kDa (Acrp30) [17], is measured in human serum in
the range of 2–20 μg/ml and is negatively correlated with
Michael E. Grossmann and Amitabha Ray contributed equally to this
review.
M. E. Grossmann :A. Ray :K. J. Nkhata :D. A. Malakhov :
O. P. Rogozina :S. Dogan :M. P. Cleary (*)
The Hormel Institute, University of Minnesota,
801-16th Avenue NE,
Austin, MN 55912, USA
e-mail: mpcleary@hi.umn.edu
Cancer Metastasis Rev (2010) 29:641–653
DOI 10.1007/s10555-010-9252-1
body weight, BMI, body fat, and serum leptin in women [18].
On the other hand, leptin is positively correlated with body
weight, BMI, and total body fat. Increased serum levels of
adiponectin are associated with a number of positive health
factors such as decreased levels of triglycerides, increased
insulin sensitivity, increased high-density lipoprotein choles-
terol levels, and general anti-inflammatory and anti-vascular
effects [19–21]. Conversely, increased serum leptin levels are
associated with negative health conditions such as type 2
diabetes, atherosclerosis, asthma, and other obesity-related
diseases [22]. Thus, adiponectin and leptin have global,
opposing effects on a number of different aspects of
pathophysiological conditions.
There are two different adiponectin receptors designated
as AdipoR1 and AdipoR2 [23]. Full-length adiponectin
binds with highest affinity to AdipoR2 [24] and cleaved
adiponectin, known as the globular form (gAcrp30) [25],
binds with highest affinity to AdipoR1 [23]. In vitro assays
have shown that a number of different breast cancer cell
lines express one or both of the adiponectin receptors and
undergo reduced growth and/or increased apoptosis in
response to the addition of adiponectin [26–29]. Adipo-
nectin signaling through its receptors can block phosphor-
ylation of Akt and reduce the expression of cyclin D1. It
was also found that adiponectin can interact with growth
factors such as platelet-derived growth factor (type BB),
basic fibroblast growth factor, and heparin-binding epider-
mal growth factor-like growth factor and that in vitro, the
normal response to growth factors of breast cancer cells
could be blocked by adiponectin [30]. Adiponectin
inhibited angiogenesis as assessed by in vitro and in vivo
assays of non-breast cancer cell lines [31] further illustrat-
ing the broad range of anti-tumor growth effects of
adiponectin. In these studies, endothelial cell proliferation
and migration assays were performed for the in vitro
assessment of adiponectin action. The in vivo studies
included measurement of avascular zone formation using
a chick chorioallantoic membrane assay, immunohisto-
chemical evaluation in a mouse corneal angiogenesis assay
and evaluation of tissue sections from xenograft T241
fibrosarcomas which were treated daily with intratumoral
injections of adiponectin (50 μg) for 2 weeks. Thus, the
effects of adiponectin are mediated by receptors found in a
number of cell types including breast cancer.
Leptin was originally identified in 1994 as the product of
the obese gene [32]. Leptin is generally present in human
serum in the range of 5–50 ng/ml [22]. However, in obese
individuals, levels in excess of 100 ng/ml are common [33–
35]. Leptin acts through receptors in the hypothalamus to
produce global effects on energy balance and body weight
[36]. In contrast to adiponectin, leptin has been implicated
as a growth-promoting factor for cancer including in vitro
proliferation of several human breast cancer cell lines [37–
40]. Preclinical studies also support a role for leptin in
mammary tumor development as evidenced by the fact that
mice deficient in leptin, Lep
ob
Lep
ob
[41], or with nonfunc-
tioning leptin receptors, Lepr
db
Lepr
db
[42], did not develop
transgene-induced mammary tumors. The ability of leptin
to enhance breast cancer development may be related to
several different facets of tumor growth. For example,
leptin can initiate signaling pathways that are activated
during stimulation of estrogen receptor-α(ERα)by
estradiol. Leptin can also induce aromatase activity in
MCF-7 breast cancer cells enhancing in situ estradiol
production and promoting estrogen-dependent breast cancer
proliferation [43]. Furthermore, leptin is able to interfere
with the anti-cancer effects of the anti-estrogen ICI 182,780
[43], all of which illustrates the potential leptin has to
enhance breast cancer growth.
Disease characteristics that are associated with obesity
and/or breast cancer are also associated with the adiponec-
tin to leptin ratio. For example, the adiponectin to leptin
ratio is higher in individuals with a normal BMI as
compared to overweight or obese individuals [18,44].
Studies also suggest that the adiponectin to leptin ratio is a
better indicator of insulin resistance than the levels of
adiponectin or leptin alone or the homeostasis model
assessment ratio estimated from fasting plasma glucose
and insulin levels [45]. Furthermore, the estimation of the
ratio between these two adipokines can be used as a
valuable index in the evaluation of other obesity-related
complications such as metabolic syndrome [46]and
endothelial dysfunction [47]. In a recent review article,
the adiponectin to leptin ratio has been discussed in detail
in relation to the pathogenesis of breast cancer [48].
Interestingly, a study found that the ratio of adiponectin to
leptin may indicate the presence of aggressive breast cancer
independent of BMI [49]. Thus, the balance of adiponectin
to leptin may be indicative of, or influence, a number of
different disease processes. Here, we present an overview
of pertinent studies related to both adipokines, leptin and
adiponectin, conducted in recent years, including our own,
that may help shed light on the important issues related to
the link between obesity and postmenopausal breast cancer.
2 Clinical studies on obesity and disease progression
A number of studies have revealed an influence of obesity on
the clinical stages and histopathological grades of breast
carcinoma. These two important classification systems are
closely associated with phenomena like metastasis of cancer
cells, survival, and overall prognosis. In a recent study, Stark
et al. observed that obesity at the time of diagnosis of breast
cancer was associated with an 80% increased risk of more
advanced stages (III/IV) and poorly differentiated grade
642 Cancer Metastasis Rev (2010) 29:641–653
compared with normal-weight women [50]. In a prospective
cohort study on invasive breast cancer consisting of 34%
obese patients, advanced grade and stage including lymph
node metastases were found more commonly among the
obese women [3]. Similarly, in a population-based follow-up
study on women younger than 45 years of age, the tumors of
the women in the highest quartile of BMI were more likely
to be high histologic grade, greater size and ER(−)[51].
Carmichael et al. noted that breast cancer in obese women
was associated with worse Nottingham prognostic index
(i.e., tumor grade, size, angiogenesis, and positive lymph
nodes) [52]. However, they did not observe any statistically
significant differences in overall and disease-free survival
between obese and non-obese group.
Several investigators documented a positive association
between obesity and advanced stage of breast cancer at
diagnosis [53–57]. On the contrary, Chagpar et al. reported
that increased BMI did not lead to a worse stage at
presentation [58]. In an earlier study, Abe et al. found a
relatively advanced clinical stage, positive lymph node,
high vascular involvement, and low 5-year survival rate
among obese patients with primary breast cancer in
comparison with non-obese patients [59]. Similarly, a
recent report revealed higher prevalence of aggressive/
advanced stage malignancies in overweight/obese breast
cancer patients [60]. Interestingly, Healy et al. reported that
newly diagnosed postmenopausal breast cancer patients
with pathological stage (II–IV) were significantly more
likely to be obese, hyperglycemic, and hyperinsulinemic
with the majority exhibiting metabolic syndrome compared
with those with early stage of the disease [61]. Furthermore,
among obese patients, Litton et al. detected a significantly
higher number of hormone-negative cancers, stage III
tumors, and worse overall survival at a median follow-up
time of 4.1 years [62]. An analysis of nearly 2,000 women
diagnosed with invasive breast cancer indicated that
overweight women had significantly larger tumor size
compared with normal-weight patients [63]. Tumor size is
another important component to assess cancer stage and
Maehle et al. demonstrated a significant association
between body weight and tumor diameter in older patients
(more than 50 years of age) with hormone receptor-negative
breast cancer [64]. Several studies have also found a
positive relationship between body weight and lymph node
metastasis [2,3,65–70]. Recent reports on the association
of obesity with cancer cell metastases, disease recurrence,
and patients’survival have been summarized in Table 1[2,
71–89]. Although the influence of obesity on estrogen
availability and hormonal effects on breast cancer prognosis
have been considered to be an important component of the
interrelationship of obesity and breast cancer [90], adipo-
kines also appear to play a significant role in the
progression of malignancies (Fig. 1)[16,91–94].
3 Studies on breast cancer which considered both leptin
and adiponectin
A number of epidemiological studies have been carried out to
investigate the roles of adiponectin and leptin in breast cancer.
In an earlier study, Mantzoros et al. [8] found a significant
inverse association between serum adiponectin levels and
breast cancer risk among postmenopausal women, but there
appeared to be no association for leptin. A total of 174
women with newly diagnosed histologically confirmed
breast cancer and 167 women in the control group were
included; 125 cases and 123 controls belonged to the
postmenopausal group, and the remaining (i.e., 49 cases
and 44 controls) were premenopausal women. Another study
conducted in Taiwan reported decreased serum adiponectin
and increased leptin levels in breast cancer patients [49]. The
study analyzed various clinicopathological parameters along
with serum adiponectin and leptin concentrations in 100
breast cancer patients and 100 women in the control group.
The investigators did not find any significant differences
between the levels of leptin or adiponectin in patients within
the younger age group in comparison to older patients. In
addition, neither premenopausal nor postmenopausal patients
had any significant differences in leptin or adiponectin
levels. However, an interesting finding was that the serum
leptin to adiponectin ratio increased significantly in breast
cancer patients as compared with controls; and this ratio had
a positive and significant correlation with tumor size. In
another study, Hou et al. [95] analyzed blood samples of 80
breast cancer patients (43 premenopausal and 37 postmen-
opausal) and 50 healthy women (26 premenopausal and 24
postmenopausal). They found that serum adiponectin levels
were significantly lower whereas serum levels of leptin were
significantly higher in postmenopausal breast cancer patients
compared to controls. Furthermore, they observed that the
reduced levels of adiponectin and elevated leptin were
associated with lymph node metastasis. Interestingly, patients
with high histological grade tumors had lower serum
adiponectin in comparison to patients with low grade tumors
andleptinlevelspositivelycorrelatedwithtumorsize.Ina
recent study that included 561 breast cancer cases and an
equal number of matched controls from the participants of
The Northern Sweden Health and Disease Cohort, it was
reported that plasma adiponectin levels were negatively
correlated with leptin, and there was a trend of increased
risk for stage II–IV tumors with higher levels of leptin [96].
Surprisingly, leptin levels were inversely associated with
stage I breast cancer in this study. It is possible that the
associations of both leptin and adiponectin with breast cancer
differ depending on the pathological process or disease
course.
Analysis of human breast tumor tissues has also
suggested roles for leptin and adiponectin in breast cancer
Cancer Metastasis Rev (2010) 29:641–653 643
development and progression. In a recent study, Jarde et al.
[97] analyzed the immunohistochemical expression of
adiponectin and leptin in 45 primary breast ductal cancers,
14 ductal carcinomas in situ, and 40 normal breast tissues
located adjacent to breast cancer. They found adiponectin
and leptin immunoreactivity in 75% and 80% of normal
breast tissue samples, respectively. Furthermore, leptin was
expressed in a similar manner in invasive ductal carcinoma
and in situ lesions; 80% of cases were positive in both
groups. In contrast, no tissue from in situ ductal carcinoma
exhibited adiponectin expression. However, 15% of cases
involving invasive cancer revealed immunoreactivity of
adiponectin. It was an interesting observation that these two
adipokines were inversely expressed in breast tissue. For
Table 1 Summary of studies that found a positive association of obesity with prognostic parameters such as distant metastasis, recurrence, and
survival in women with breast carcinoma
Investigators Study details Salient findings
Gillespie et al.
(2010) [71]
1,312 patients with stage I–III primary breast cancer/Michigan Obesity was associated with higher rates of tumor
neovascularization.
de Azambuja et
al. (2010) [72]
2,887 node-positive breast cancer patients/Belgium Obesity remained an independent prognostic factor for
shorter overall survival and disease-free survival.
Chen et al.
(2010) [73]
5,042 breast cancer patients with median follow-up of
46 months/Shanghai, China
Women with obesity at diagnosis and post-diagnostic
weight gain had higher mortality.
Majed et al.
(2009) [74]
Observational cohort of patients followed since a first
unilateral breast cancer without distant dissemination/France
Obese patients presented significantly higher risks of death
and metastasis recurrences.
Vona-Davis et
al. (2008) [75]
Retrospective study on 620 White patients/West Virginia Obesity was present in 50% cases with triple negative
tumors (ER−,PR−, HER2−)
Caan et al.
(2008) [76]
Prospective cohort study of 1,692 breast cancer survivors,
7 years of follow-up/Northern California
Obesity before breast cancer diagnosis was associated with
increased risk of recurrence and poorer survival.
Dal Maso et al.
(2008) [77]
1,453 women with incidence of breast cancer/Italy Increased risk of death for breast cancer among obese
patients.
Kerlikowske et
al. (2008) [78]
287,115 postmenopausal women not using hormone therapy/
California
Higher rates of advanced disease, including large invasive
tumors, advanced-stage, and high nuclear grade
malignancies among overweight and obese subjects.
Dawood et al.
(2008) [79]
602 patients with locally advanced breast cancer/Texas Obese or overweight patients had a significantly worse
overall survival and recurrence-free survival and a higher
incidence of recurrence.
Majed et al.
(2008) [80]
Cohort of 14,709 patients/Paris, France Obesity appeared as a negative prognosis factor for several
events such as metastatic recurrence, shorter disease-free
interval and overall survival, and second primary cancer.
Demirkan et al.
(2007) [81]
266 patients/Turkey Postmenopausal obese patients had worse disease-free
survival and distant disease-free survival.
Abrahamson et
al. (2006) [82]
1,254 women diagnosed with invasive breast cancer/
metropolitan Atlanta and New Jersey
Increased mortality in women who were obese.
Dignam et al.
(2006) [83]
4,077 women with node-negative, ER(−) breast cancer/North
America
Obesity was associated with greater risk for second
cancers, contralateral breast cancer, and mortality.
Loi et al.
(2005) [2]
Population-based study of 1,360 women with breast cancer
before the age of 60 years/Australia
Obesity was associated with larger tumors, more involved
axillary nodes, increased breast cancer recurrence, and
death.
Whiteman et al.
(2005) [84]
3,924 women with incidence of breast cancer/U.S. Obese women were significantly more likely to die of
breast cancer than lean women.
Kroenke et al.
(2005) [85]
5,204 participants under Nurses’Health Study diagnosed with
breast cancer/US
Pre-diagnosis obesity and weight gain were related to
higher rates of breast cancer recurrence and mortality.
Tillman et al.
(2005) [86]
139 Native American women with breast cancer/Phoenix,
Arizona
Obesity significantly correlated with larger tumor size and
more advanced stage.
Enger et al.
(2004) [87]
Retrospective cohort study of 1,376 patients followed up for a
median of 6.8 years/California
Women with higher body weight with early stage ER(−)
tumors had a nearly fivefold increased risk of dying
compared to lower weight and ER(+) tumors.
Dignam et al.
(2003) [88]
3,385 patients enrolled in National Surgical Adjuvant Breast
and Bowel Project (NSABP)/US
Obesity was associated with increased risk of contralateral
breast cancer.
Borugian et al.
(2003) [89]
603 patients with incident breast cancer/Vancouver,
British Columbia, Canada
Waist-to-hip ratio was directly related to breast cancer
mortality in postmenopausal women.
644 Cancer Metastasis Rev (2010) 29:641–653
instance, myoepithelial cells of normal tissue adjacent to
breast cancer exhibited 65% positivity for adiponectin
while no cells in this group were positive for leptin
expression. In contrast, in ductal carcinoma in situ, high
levels of leptin expression and no adiponectin expression
were observed. This study has highlighted a fascinating role
of myoepithelial cells in the leptin–adiponectin interaction;
the normal myoepithelial cells, which strongly expressed
adiponectin, might protect normal breast epithelial cells by
secreting adiponectin locally (in a paracrine manner).
Overall, the study has provided some evidence of antago-
nistic effects between leptin and adiponectin in breast
cancer development.
4In vitro studies focusing on both leptin
and adiponectin
In order to understand the relationship of adiponectin and
leptin in breast cancer development, our laboratory has
examined in vitro effects of both of these adipokines on
breast cancer cells. In our first study, a low physiological
level of adiponectin (1 μg/ml) and a high physiological level
of leptin (50 ng/ml) were used to reflect serum levels of
obese women. We examined how this adipokine combina-
tion affected cell signaling, apoptosis, and proliferation in
breast cancer cell lines with respect to two significant
characteristics, i.e., presence or absence of the estrogen
receptor (ER) and overexpression of HER2/neu. These two
biomarkers in breast tumor pathology are extremely impor-
tant factors in clinical outcome. Five breast cancer cell lines
[MCF-7 (ER+, HER2−), T47-D (ER+, HER2−), MDA-MB-
231 (ER−,HER2−), MDA-MB-361 (ER+, HER2+), and
SK-BR-3 (ER−, HER2+)] were used; and results were
influenced by cell line [98]. Highlights of the findings
include that the adiponectin treatment increased the expres-
sion of both short and long isoforms of leptin receptors
(Ob-R and Ob-Rb) in T47-D cells; whereas in MDA-MB-
231 cells, protein expression of these receptors was reduced
by the addition of adiponectin. In general, adiponectin
decreased AdipoR1 expression in MCF-7, T47-D, MDA-
MB-231, and SK-BR-3 cells. In MCF-7 cells, adiponectin
stimulated leptin levels, although it suppressed adiponectin
expression. On the other hand, addition of leptin elevated
both leptin and adiponectin expression levels in MCF-7 cells.
Interestingly, simultaneous exposure to both leptin and
adiponectin caused overexpression of the progesterone
receptor-α(PRα) in MCF-7 cells, while adiponectin
inhibited PRα, but raised PRβexpression in T47-D cells.
Androgen receptor levels were increased by leptin in MCF-7
cells, and by adiponectin in T47-D cells. Two important
hormone-binding proteins, i.e., sex hormone-binding globu-
lin and insulin-like growth factor binding protein-3, were
increased in MCF-7 cells by adiponectin. It is worth
mentioning that both leptin and adiponectin may participate
in the maintenance of energy homoeostasis, which is
disturbed in obesity. These results were perhaps the
consequences of differential effects of these adipokines on
human breast cancer cell lines with diverse hormonal
sensitivities.
It has been reported that the ER-negative breast cancer
cell line, MDA-MB-231, is responsive to adiponectin as
Fig. 1 Possible role of
adipose tissue in breast
cancer progression. ER estrogen
receptor, PR progesterone
receptor, EGFR epidermal
growth factor receptor, SHBG
sex hormone-binding globulin,
IGF-I insulin-like growth
factor-I, upwards arrow
increase, downwards
arrow decrease
Cancer Metastasis Rev (2010) 29:641–653 645
reflected by decreased proliferation [26]. To further
investigate the effects of adiponectin in relationship to the
presence or absence of estrogen receptor status, the ERα
gene was introduced into MDA-MB-231 cells by liposome-
mediated transfection. Several ER+ stably transfected
MDA-MB-231 cell lines exhibited higher levels of prolif-
eration compared to the original MDA-MB-231 cells
following addition of either estradiol or leptin. One of the
transfected cell lines designated as MDA-MB-231 ERα7
(MDA-ERα7) was selected for further study. This cell line
and the parental wild type MDA-MB-231 cells (MDA-wt)
expressed both adiponectin and leptin receptors. These two
cell lines were used to investigate the effects of full-length
adiponectin and globular adiponectin in the presence or
absence of leptin. The addition of 50 ng/ml of leptin
resulted in increased proliferation of both MDA-wt and
MDA-ERα7 cells, whereas a reduction in proliferation was
evident after addition of adiponectin and globular adipo-
nectin. Furthermore, cell proliferation assays were per-
formed using different ratios of adiponectin to leptin to
represent women with different body weight status, i.e.,
high adiponectin and low leptin levels for lean persons and
the reverse situation for the obese condition. Interestingly,
we found that an increasing adiponectin to leptin ratio
reduced cell proliferation, while a decreasing ratio failed to
influence the proliferation of both MDA-wt and MDA-
ERα7 cells [99].
Another study examined the effects of adiponectin to
leptin ratios on proliferation of human breast cancer cell
lines, MCF-7, T47-D, MDA-MB-231, MDA-MB-361, and
SK-BR-3 cells [100]. The cells were treated for 48 h with
10, 25, and 50 ng/ml of leptin and 100, 200, 500, 1,000,
and 5,000 ng/ml of adiponectin, respectively. Increasing the
adiponectin to leptin ratio resulted in reduced proliferation
of MCF-7 and T47-D cells. On the contrary, MDA-MB-
231, MDA-MB-361, and SK-BR-3 cells had an increase in
cell proliferation at lower adiponectin to leptin ratios. In
MCF-7 cells, adiponectin and leptin co-treatment enhanced
apoptosis; however, there were no significant differences in
cell cycle distribution between leptin-treated, adiponectin
and leptin co-treated and untreated cells. Overall, different
cell lines exhibited varied responses to different adiponectin
to leptin ratios. These studies indicate the complex
interaction of the characteristics of the breast cancer cell
line with respect to response to both leptin and adiponectin
as well as to the ratio of these two adipokines.
5 Preclinical studies of both leptin and adiponectin
in relation to mammary tumorigenesis
To evaluate the role of obesity and adipokine levels in the
development of breast cancer, several xenograft studies
were conducted using human breast cancer cells which had
been found to be responsive in vitro to leptin and/or
adiponectin. In one set of studies, CD-1 mice were made
obese by injecting them with goldthioglucose [101]. Serum
leptin levels were significantly higher in the obese mice
compared to lean ones while adiponectin levels were not
affected. The adiponectin to leptin ratio was significantly
reduced in the obese mice although it was not related to the
presence or absence of tumors formed following inocula-
tion of T47-D human breast cancer cells. This may be
partially attributable to the relatively low number of mice
with tumors. In an additional study, dietary-induced obesity
was used in conjunction with tumor formation from ER+
MCF-7 human breast cancer cells [102]. CD-1 ovariecto-
mized nude mice were fed a purified high-fat diet from
15 weeks of age (high-fat group, n= 46) while the control
mice, (low-fat group, n=7) were maintained on a purified
low-fat diet (AIN-93M) throughout the study. At 22–
23 weeks of age, all mice were inoculated with MCF-7
cells, implanted with estradiol pellets, and followed for
tumor development. The study was terminated when the
mice reached 42 weeks of age. In contrast to other strains of
mice, high-fat CD-1 mice did not exhibit any significant
differences in body weight, fat pad weight, or serum
adiponectin levels compared to low-fat mice (Table 2).
Serum leptin and IGF-I levels were 65% and 72% higher in
the high-fat mice compared to low-fat mice, respectively.
Interestingly, western blot analysis of mammary fat pads
from low-fat mice exhibited significantly higher levels of
AdipoR2 compared to those from high-fat mice (Fig. 2).
Immunohistochemical staining of tumor tissue detected
expression of Ob-R in 21% of high-fat mice (Fig. 3and
Table 3). For the low-fat group, Ob-R expression was
detected in 75% of the tumors; additionally, expression of
leptin was detected in all tumors in this group. On the other
hand, both adiponectin receptors (AdipoR1 and AdipoR2)
were almost equally expressed in tumors from high-fat mice
(43% vs. 46%, respectively). For the low-fat mice,
AdipoR2 was expressed in all tumors, whereas 75% of
the tumors were positive for AdipoR1 expression. These
findings suggest that a high-fat diet can influence both
mammary tissue and tumor adipokine-related factors
independent of effects on body weight.
Another interesting aspect of this study was that of all the
MCF-7 tumors analyzed, only one of 32 had ERαidentifiable
by immunohistochemistry (Table 3). Thus, the originally
ER+ MCF-7 cells formed tumors which no longer appeared
to be estrogen-responsive. Recent studies have shown an
influence of estrogenic environment on the functions of both
leptin and adiponectin [101,103]. Therefore, in the above-
mentioned study, this phenomenon probably played a role on
the expression of leptin, Ob-R, and adiponectin receptors in
the developing mammary tumors.
646 Cancer Metastasis Rev (2010) 29:641–653
In general, it is thought that postmenopausal obesity favors
the development of hormone-dependent breast cancer [104,
105]. On the other hand, obesity does not seem to be a risk
factor for the development of ER-negative breast cancer. In
support of this idea, a study using mice that overexpress
HER2/neu (MMTV-neu) showed no differences in tumor
incidence between low-fat and high-fat diet groups [106]. In
a recent study also using MMTV-neu mice [107], it was
reported that the time of onset of the first tumor and tumor
growth rates were not altered between high- and low-fat diet
groups, although the mice on a high-fat diet had an earlier
onset of second tumors along with a greater incidence of
multiple tumors. It is worth noting that dietary fat reduction
has been reported to improve the relapse-free survival in
women with hormone receptor-negative disease [108]. This
receptor-negative situation may be comparable with the
MCF-7 tumors in CD-1 mice [102] where the majority of
the tumors that arose had lost expression of ER. It may be
that MCF-7 breast cancer cells which express adiponectin,
leptin, and their associated receptors can provide a model for
the ER-negative breast cancer proliferative responses to
varying fat intake and adiposity.
It is speculated that besides estrogenic influences, adipo-
kines can stimulate breast cancer growth and metastasis in a
number of different ways [109]. Recent reports using an
adiponectin null mouse model of mammary cancer (MMTV-
PyV-mT/APN knockout mice) that resembles HER2/neu-
amplified human breast cancer indicated reduced vasculari-
zation resulting in nutrient deprivation of the tumors and
associated cell death; however, at the later stage, more
aggressive tumor behaviors were found in these mice [110,
111]. In contrast, an anti-angiogenic role of adiponectin in
cancer has been documented [31,112]. Accumulating
evidence also indicates a role for both adiponectin and leptin
with inflammation and oxidative stress [113–117] which are
pathological processes associated with carcinogenesis [118].
In fact, pro-inflammatory pathways may play a pivotal role
in tumor development even in the absence of obesity. This is
supported by the fact that fatless A-Zip/F1 mice exhibit
accelerated skin papilloma formation [119]. Despite the lack
of fat tissue, A-Zip/F1 mice have close similarities with the
obese condition as they are hyperlipidemic and diabetic with
high blood levels of insulin, IGF-I, as well as pro-
inflammatory cytokines such as interleukin-6, IL-4, and
monocyte chemotactic protein-1. In addition, they have
elevated levels of vascular endothelial growth factor and
increased activity of several kinases including phosphatidy-
linositol 3-kinase, extracellular signal-regulated kinase, and
protein tyrosine kinase ErbB2 [119,120]. Many of these
proteins are linked with the signaling pathways of leptin.
Lack of adipose tissue associated with negligible adipokines
like an extremely low level of adiponectin may lead to
increased susceptibility to tumor growth in A-Zip/F1 mice
[121]. Remarkably, low levels of adiponectin most probably
are pathognomonic of obesity-related diseases. Therefore,
both obesity and the above-mentioned lipodystrophic condi-
tion generate a state of chronic inflammation, which is
perhaps coupled with oxidative stress. In a recent report on
breast cancer patients, leptin has been shown to be positively
correlated with oxidative stress parameters [122]. A study
from our laboratory on MCF-7 breast cancer cells docu-
mented a stimulating effect of leptin on the expression of
CYP1B1 [40], which is a phase I enzyme associated with
oxidativedamage[123] and metabolic activation of procar-
cinogens [124]. Unlike lipodystrophic conditions, obesity is
a common health problem connected with a derangement of
adipokines, particularly leptin and adiponectin, which possi-
bly creates an imbalanced state between various oxidants and
the body’s detoxifying system with one consequence being
the development of malignancies.
Table 2 Final body weights, mammary and visceral fat weights, serum adiponectin and leptin with their ratios, and IGF-I for CD-1 nude mice
inoculated with MCF-7 cells
Final body
wt. (g)
MFP
wt. (g)
Visceral fat
wt. (g)
Serum Acrp30
(μg/mL)
Serum leptin
(ng/mL)
Acrp30:leptin
ratio
Serum IGF-I
(ng/mL)
High-fat diet group (n=46) 31.58± 0.82 0.71 ± 0.08 1.24 ± 0.18 9.03± 0.46 8.63 ± 1.44 2.71± 0.55 446.9± 28.5a
Control, low-fat diet (n=7) 32.24 ±0.47 0.80±0.18 1.01 ± 0.27 8.70 ±1.24 5.22± 1.76 3.32 ±0.90 259±75.4b
ttest P=0.7432 P= 0.6719 P= 0.6229 P= 0.7974 P= 0.3626 P= 0.6678 P=0.0209
Values represent mean ± standard error of the mean. Values with lowercase letters indicate a significant difference after student’sttest
MFP mammary fat pad, Acrp30 adiponectin, IGF-I insulin-like growth factor-I
0.00
0.25
0.50
0.75
b
a
AdipoR2:beta actin rati o
(densit ometry units)
*
Fig. 2 Relative expression levels of AdipoR2 in mammary fat pads
between controls and animals on a high-fat diet by western blot
analyses. acontrols (low-fat diet group) and bhigh-fat diet group
student’sttest, *p<0.0001
Cancer Metastasis Rev (2010) 29:641–653 647
6 Prevention of breast cancer through dietary alteration
of the leptin–adiponectin ratio
If leptin and adiponectin play roles in breast cancer
development, being able to alter their circulating levels
may be an approach towards prevention. Interestingly,
several studies reported that leptin and/or adiponectin levels
can be modulated by dietary factors resulting in an
alteration in the adiponectin to leptin ratio. For instance, it
has been observed that bitter melon (Momordica charantia)
ameliorated fructose diet-induced hyperleptinemia and
reversed hypoadiponectinemia [125]. Similarly, dietary
conjugated linoleic acid supplementation has been shown
to reduce the levels of leptin and increase the mRNA
expression of adiponectin in the adipose tissue of obese rats
[126]. In general, leptin concentrations decreased and
adiponectin increased after weight loss [127]. In a study
conducted by Fenton et al. [128], calorie-restricted mice
displayed increased serum levels of adiponectin. In con-
trast, diet-induced obese (high calorie diet, fed ad libitum)
mice exhibited increased leptin levels [128]. In this
connection, our laboratory has been studying the impact
Fig. 3 Immunohistochemical expression of different parameters related to leptin and adiponectin in tumor tissues developed from MCF-7 cells in
CD-1 mice. aImmunohistochemically negative control. bExpression of leptin, cOb-R, dAdipoR1, eAdipoR2, and fERαexpression
Table 3 Overexpression of leptin and adiponectin receptors in tumors developed from MCF-7 human breast cancer cells in CD-1 mice
Groups Mice with tumor Tested Ob-R Leptin AdipoR1 AdipoR2 ERα
Controls, low-fat diet (n=7) 4 (tumor incidence= 57%) 4 3/4 (75.0%) 4/4 (100%) 3/4 (75.0%) 4/4 (100%) 0/4 (0%)
High-fat diet (n=46) 28 (tumor incidence= 61%) 28 6/28 (21.4%) 0/28 (0%) 12/28 (42.9%) 13/28 (46.4%) 1/28 (3.6%)
No tumor tissue showed overexpression of estrogen receptor β, sex hormone-binding globulin (SHBG), epidermal growth factor receptor
(EGFR), and p53
648 Cancer Metastasis Rev (2010) 29:641–653
of caloric restriction in mammary tumorigenesis, particu-
larly the protective role of intermittent caloric restriction
[129–132]. In a recently completed study, we found that
intermittent caloric-restricted mice had higher serum adi-
ponectin and lower serum leptin levels after 64 weeks of
caloric restriction. Moreover, the adiponectin to leptin ratio
was significantly higher in intermittent caloric-restricted
groups compared to the ad libitum-fed mice [133]. Howell
et al. [134] analyzed the influence of intermittent caloric
restriction versus chronic calorie restriction on biomarkers
of breast cancer risk and revealed that both approaches are
effective in improving various parameters including reduc-
tion of serum leptin levels. A recent study of obese women
who consumed a low-calorie diet showed an increase of
adiponectin concentrations and a decrease in the levels of
leptin [135]. Thus, preclinical as well as clinical studies
suggest that there are multiple mechanisms available to
influence the ratio of leptin to adiponectin.
7 Concluding remarks
It is clear that nutrition and overnutrition can have a profound
effect on breast cancer inhibition and growth [136]. A
comprehensive report by the World Cancer Research Fund/
American Institute for Cancer Research found that body
fatness, abdominal fatness, and adult weight gain all
represented a probable or convincing increased risk of
postmenopausal breast cancer [137]. Epidemiological studies
have found that the leptin to adiponectin ratio is influenced by
changes in body fatness. Increasing evidence suggests that it
is the ratio of adiponectin to leptin that is the key determinant
of the effects of these adipokines on breast cancer tumorigen-
esis. There appear to be multiple mechanisms of action
including direct cell proliferation, regulation of growth factors,
influences on angiogenesis, and alterations in oxidative stress,
and inflammation. Fortunately, there are also multiple
potential interventions including calorie restriction and alter-
ation of specific dietary factors. Continued investigations will
help clarify the role of body weight status and adipokines in
the development and/or prevention of breast cancer.
Acknowledgements We are thankful to Dr. Joseph P. Grande of the
Mayo Foundation, Rochester, Minnesota, for his pathological diagnosis
of the tumors. We also thank The Breast Cancer Research Foundation,
NCI grant CA101858 and the Hormel Foundation for the support.
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