Yonago Acta medica 2001;44:143–149

Plasma Leptin Level, the Adipocyte-Specific Product of the ObeseGene, Is Associated with Tumor Progression and Is a Marker of the
Nutritional Status of Patients with Gastric Cancer
Michio Maeta, Shinichi Oka*, Hiroaki Saito*, Masahide Ikeguchi*, Shunichi
Tsujitani* and Nobuaki Kaibara*
Department of Fundamental Nursing and *First Department of Surgery, Tottori University
Faculty of Medicine, Yonago 683-0826 Japan
Leptin, a product of the obese gene, is synthesized and released into the circulation in
response to increased energy storage in adipose tissue. Leptin plays an important rolein the regulation of body weight and energy balance. However, leptin levels in patientswith malignant tumor have not been fully examined. The purpose of the present study
is to clarify the clinical implications of leptin levels in the circulation in patients withgastric cancer. The subjects were 103 patients with gastric cancer at various stages.
Levels of leptin in the plasma were determined with a commercially available humanleptin-selective quantitative enzyme immunoassay kit. There were clear decreasing
trends in leptin levels along with tumor progression in both males and females, andstatistically significant differences were observed in males between stages II and IV,
and in females between stages I and IV. Plasma leptin levels of females were consistently
higher than those of males when we compared them with patients in the same stages.
Moreover, statistically significant decreases in leptin levels were observed postoperatively. However, there were no statistically significant relationships between leptin
levels and clinicopathological findings. There was a positive correlation between levelsof plasma leptin and values of the body mass index. These findings may indicate thatplasma leptin levels do not involve factors relevant to specific tumor growth but involvesome tumor-related nutritional status due to tumor progression. We conclude that
leptin levels are reflected during tumor-bearing status, and these are also useful markers
for both indicating tumor progression and discovering the nutritional status of patientswith gastric cancer.
Key words: gastric cancer; nutritional marker; plasma leptin level

Leptin, a product of the obese gene, is synthesized and released into the circulation in response to increased energy storage in adipose
tissue (Zhang et al., 1994; Campfield et al., 1995;
Halaas, et al., 1995; Pelleymounter et al., 1995).
Administration of recombinant leptin to obese
mice results in weight loss through both a reduction in food intake and an increase in energy
expenditure (Campfield et al., 1995; Halaas et al.,
1995; Pelleymounter et al., 1995). Therefore, it
has been suggested that leptin plays an impor-tant role in the regulation of body weight andenergy balance.
In humans, mutations of the leptin gene inadipose tissue (Montague et al., 1997; Strobel etal., 1998) and of the leptin receptor gene in the
hypothalamus (Tartaglia et al., 1995; Clement
et al., 1998) induce a decreased leptin level inthe circulation and result in morbid obesity.
Supplementation with recombinant humanleptin for such patients with leptin deficiency
leads to a sustained reduction in body weight asAbbreviations: BMI, body mass index; EIA, enzyme immunoassay

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M. Maeta et al.

a result of a loss of fat (Farooqi et al., 1999), as
is the case with obese mice. Leptin levels in thecirculation, in general, correlate positively withindexes of obesity (Maffei et al., 1995; Considine
et al., 1996; Havel et al., 1996; Giannini et al.,1999), such as body fat or the body mass index(BMI) (Kahn et al., 1997).
Although there is a gender difference in
leptin levels between males and females, females have higher plasma leptin concentrations
than males, which is attributable to the relatively greater body fat mass in females (Maffei etal., 1995; Havel et al., 1996; Giannini et al., 1999).
Whatever the initial concentration, weight loss
due to food restriction is associated with adecrease in plasma leptin in both obese andnormal weight humans (Maffei et al., 1995;
Rosenbaum et al., 1997). Therefore, leptin concentrations have been regarded as a simple
marker of the extent of obesity in humans.
However, the clinical implications of these
leptin levels in patients with malignant tumor
have not been clearly studied, excluding thoseof patients with leptin-producing pregnancyrelated gynecological placental tumor (nonadipose tissue production of leptin) (Masuzaki
et al., 1997).
Is malignancy-modified nutritional statusreflected in leptin levels or not? The purpose of
the present study is to examine plasma leptin
levels in relation to BMI values and to clarify
the clinical implications of leptin in patientswith gastric cancer.

Patients and Methods

Patients
The subjects were 103 patients with gastriccancer at various stages who had been treated in
the First Department of Surgery, Tottori University Hospital, between November 1995 andApril 1998. Among them, 97 patients (meanage, 63.3 ± 11.3 years; range, 33 to 85 years; 65
males, 32 females) underwent resection of a
primary gastric tumor, and the remaining 6
patients (mean age, 67.3 ± 8.3 years; range, 56
to 78 years; 1 male, 5 females) underwent

chemotherapy because of unresectable postoperative recurrent tumor from gastric cancer.
The clinicopathological findings were determined according to the rules of the Committee on the Japanese Classification of Gastric
Carcinoma (Japanese Research Society for
Gastric Cancer, 1993).
Fasting blood samples (early morning before breakfast) were obtained before surgery or
chemotherapy and stored at –80˚C prior to
analysis. Postoperative samples were obtained
3 weeks after surgery.

Methods
Levels of leptin in the plasma were determinedwith a commercially available human leptinselective quantitative enzyme immunoassay(EIA) kit (Immuno-Biological Laboratories
Co., Ltd., Fujioka, Japan) according to the
manufacturer’s instructions. In brief, a 100-µL
sample was added to each well of a microtiterplate, which had been precoated with rabbit
monoclonal antibody specific for human leptin,
and incubated at 37˚C for 1 h. After washing, a
100-µL solution of horseradish peroxidaseconjugated antibodies, raised in the rabbit
against human leptin, was added to each welland incubation was continued at 37˚C for 30
min. After further washing, color was developed by incubating each well with 100 µL of thechromogenic substrate solution. The colored
reaction product was quantified with a spectrometer at 450 nm. Quantification was achieved by the construction of a standard curve using
a known concentration of purified, recombinanthuman leptin. The limit of detection using thiskit was 0.78 ng/mL.
The BMI of each patient was calculated by
the following formula :[ BMI = body weight (kg)/height (m2) ].

Statistical analysis
Data were expressed as mean ± SD. The meanvalues were compared with Student’s t-test andtwo-way analysis of variance. P values of <0.05 were considered statistically significant.

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Leptin in gastric cancer patients

Table 1. Levels of preoperative plasma leptin and body mass index (BMI)
Stage
Stage I

Leptin (ng/mL)(mean ± SD)

BMI(mean ± SD)

4.3 ± 5.1

[60]

Stage II[10]

4.3 ± 4.9

Stage III[12]

3.8 ± 3.9

Stage IV[15]

1.3 ± 0.9

22.4 ± 2.5
P < 0.03
P < 0.03

23.7 ± 2.3
21.1 ± 2.7

P < 0.03

P < 0.02

21.2 ± 3.2

Recurrence [ 6]1.2 ± 0.7
[ ], number of patients.

19.5 ± 1.6

A Macintosh personal computer system and
StatView software (Abacus Concepts, Inc.,
Berkeley, CA) were used for all statisticalanalyses.

Results
Preoperative levels of plasma leptin and BMI inpatients with gastric cancer are shown in Table
1. Both the mean level of leptin and BMI, in
general, were associated with the tumor progression of the cancer and decreased along withstage progression. Statistically significant de-

P < 0.05
P < 0.008
P < 0.008

creases in leptin levels were found in patients instage IV, as compared to patients in stages I, II
and III, respectively. The differences of meanvalue among cancer stages were greater in leptin than in BMI, although values of SD werelower in BMI than those in leptin.
Since levels of plasma leptin have been reported to indicate gender and age differences(Maffei et al., 1995; Havel et al., 1996; Giannini
et al., 1999), these levels were analyzed interms of gender and age in each stage (Table 2).
There was no age difference in patients between
males and females in each stage. However, leptin
levels of females were consistently higher than

Table 2. Levels of preoperative plasma leptin and body mass index (BMI) analyzed in terms ofage and genderStage/genderStage I
Male
[38]
Female [22]Stage II
Male
[ 7]
Female [ 3]Stage IIIMale
[ 7]
Female [ 5]Stage IV
Male
[13]
Female [ 2]Recurrence
Male
[ 1]
Female [ 5][ ], number of patients.

Age (year)(mean ± SD)

Leptin (ng/mL)(mean ± SD)

BMI(mean ± SD)

62.0 ± 10.0
67.9 ± 12.9

2.6 ± 2.2
7.2 ± 7.1

58.9 ± 10.3
69.0 ± 6.9

3.8 ± 4.5
5.8 ± 6.4

63.9 ± 10.0
59.0 ± 18.5

2.4 ± 2.2
5.7 ± 5.5

62.4 ± 9.8
57.5 ± 16.2

1.2 ± 0.8
1.5 ± 0.7

20.9 ± 3.4
21.5 ± 1.6 P < 0.03
P < 0.03
21.5 ± 3.1
19.3 ± 3.6

63.0
68.2 ± 9.0

0.78
1.3 ± 0.7

19.5
19.5 ± 1.8

145

P < 0.001

22.4 ± 2.5
22.4 ± 2.6
23.8 ± 2.6
23.5 ± 1.8

P < 0.02
P < 0.05

M. Maeta et al.
Table 3. Relationship between preoperative plasma leptin levels and clinicopathologicalfindings
Variable
Male[65]

Leptin (ng/mL)
P-value
Female(vertical)†[32]

P-value(vertical)†P-value(horizontal)‡

Gross finding
Early cancer
2.6 ± 2.3 [33]NS
7.6 ± 7.1 [17]NS
< 0.001
Invasive cancer
Localized
2.2 ± 2.2 [10]7.8 ± 7.9 [ 5]NSInfiltrative
1.7 ± 2.0 [22]4.0 ± 3.9 [10]< 0.04
Histology
Intestinal type2.7 ± 2.8 [33]NS
6.9 ± 7.6 [14]NS
< 0.02
Diffuse type2.0 ± 1.9 [32]6.2 ± 5.7 [18]
< 0.001
Depth of cancer invasion
T1
2.6 ± 2.3 [34]NS
7.4 ± 7.1 [18]NS
< 0.001
T2
2.7 ± 3.3 [ 9]5.7 ± 7.4 [ 5]NST3,4
1.9 ± 2.2 [22]5.3 ± 5.3 [ 9]< 0.02
Nodal involvement
Negative
2.6 ± 2.4 [41]NS
7.3 ± 7.0 [24]NS
< 0.001
Positive
2.1 ± 2.4 [24]4.3 ± 4.6 [ 8]NS
Lymphatic vessel invasion
Negative
2.7 ± 2.7 [42]NS
7.5 ± 7.1 [18]NS
< 0.001
Positive
1.8 ± 1.7 [23]5.2 ± 5.7 [14]< 0.02
Blood vessel invasion
Negative
2.5 ± 2.5 [45]NS
7.2 ± 6.8 [26]NS
< 0.001
Positive
2.2 ± 2.3 [20]3.5 ± 4.7 [ 6]NSPeritoneal metastasis
Negative
2.5 ± 2.5 [61]NS
6.7 ± 6.6 [31]NS
< 0.001
Positive
2.2 ± 2.3 [ 4]3.5 ± 4.7 [ 1]NS
Liver metastasis
Negative
2.5 ± 2.5 [61]NS
6.5 ± 6.6 [32]NS
< 0.001
Positive
1.6 ± 1.5 [ 4]—[ ], number of patients.
NS, not significant.
† Vertical analysis: statistical difference between specific variables in the same gender.
‡ Horizontal analysis: statistical difference in each specific variable between males and females.

those of males when we compared them in thesame stage, and there was a statistically significant difference in patients in stage I. There
were still clear decreasing trends in leptin levels
along with stage progression in both males andfemales, and statistically significant differenceswere observed in males between stages II andIV, and in females between stages I and IV. With
respect to BMI values, there were no genderdifferences in each stage. The decreasing trend
in the value of BMI along with stage progression was observed in both males and females;
however, it was not so consistent comparedwith that in cases of leptin. In females, there

were statistically significant differences in BMI
between recurrent cases and stage I or II, respectively.
Relationships between the preoperative
levels of plasma leptin and clinicopathologicalfindings of gastric cancer are shown in Table 3.
In both males and females, although the samegender showed no statistically significant differences between variables (vertical analysis),plasma leptin had a decreased trend accompanied with tumor progression in each variable.
However, gender differences in levels of leptin
were obvious in each variable (horizontal analysis), as shown in Table 3.

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Leptin in gastric cancer patients

Males

Females(ng/mL)
30

10

25

8

20

Leptin

Leptin(ng/mL)
12

6

15

4

10

2

5

0

0
16

18

20

22

24

26

28

16

30

18

20

22

24

26

BMI

BMI

y = 0.385 x - 6.103, r = 0.435, P = 0.0002

y = 1.719 x - 31.615, r = 0.6, P = 0.0002

28

Fig. 1. Correlations between preoperative levels of plasma leptin and body mass index (BMI).

There was a positive correlation in bothmales and females between preoperative levelsof plasma leptin and the BMI, as shown in
Fig. 1.
Table 4 compares plasma leptin levels before and after surgery. Statistically significant
decreases were observed postoperatively.

Discussion
Circulating leptin, which is a product of theobese gene, provides feedback information on
the size of fat stores to central obese receptors
that control food intake and body weight homeostasis. Recent studies of plasma leptin
levels in patients with obesity or metabolic disorder have given us a wealth of novel informa-tion; however, little knowledge was given aboutplasma leptin levels of patients with malignant
tumors. Masuzaki et al. (1997) reported thatplasma leptin levels were markedly elevated inpatients with hydatidiform mole or choriocarcinoma and were reduced after surgical treatment
or chemotherapy, suggesting nonadipose tissue
production of leptin; namely, placental trophoblasts and amnion cells from the uteri of pregnant women. Since breast cancer has been associated with obesity and reproductive hormones, leptin levels of patients with carcinoma
in situ of the breast were examined and analyzed for putative involvement of leptin in the
etiology of breast cancer (Mantzoros et al.,1999). A possible association has been reviewed between the cancer-associated anorexiacachexia syndrome and leptin (Inui, 1999).

Table 4. Comparisons of pre- and postoperative plasma leptin levels
Stage
I and II
Male
[45]
Female[25]
III and IV
Male
[20]
Female[ 7][ ], number of patients.

Leptin (ng/mL)
Preoperative
Postoperative

P-value

2.8 ± 2.7
7.0 ± 6.9

1.3 ± 1.0
3.9 ± 3.90.00100.03871.7 ± 1.7
4.6 ± 5.0

0.9 ± 0.5
1.8 ± 1.3

0.02250.1059147

M. Maeta et al.

However, systematic analyses of leptin levels inpatients with malignant tumors and its clinicalimplications have not yet been studied.
In this series, plasma leptin levels, as awhole, including both males and females, decreased along with stage progression in gastriccancer patients (Table 1). As reported previously, there is a gender difference in leptin
levels (Maffei et al., 1995; Havel et al., 1996;
Giannini et al., 1999), and therefore, these levels
were analyzed separately for males and females. Leptin levels were consistently higher infemales than males when we compared them inthe same stage. There was a clear reduction in
leptin with stage progression in both males andfemales, as shown in Table 2.
Patients with recurrent tumors from gastriccancer have a serious nutritional disorder due togastrointestinal passage failure of oral foodintake. In this study, patients with recurrent
cancer showed the lowest leptin levels amonggroups of patients including those who underwent gastrectomy of the primary tumor. Moreover, significant postoperative decreases in leptin levels were observed. However, there wereno statistically significant relationships between leptin levels and specific clinicopathological findings. These findings may indicatethat plasma leptin levels do not involve factors
relevant to specific tumor progression but
involve tumor-related nutritional status due totumor progression and/or due to limitation oforal food intake during a relatively short period
after gastrectomy. Thus, leptin is not only asimple marker of obesity in humans but also amarker of tumor progression and/or nutritional
status in patients with malignant tumor.
BMI is an index of obesity and there is no
gender difference in BMI, as shown in Table 2.
Leptin levels correlated positively with BMI
when data were analyzed separately between
males and females (Fig. 1).
We conclude that leptin concentrations in
the circulation have been indicated as a simple
marker of the obesity; however, the role of leptin is exerted in not only metabolic disorders but
also in tumor-bearing status, and it is also a useful nutritional marker for patients with malignancy. We notice that we have little adequate

markers for evaluating postoperative nutritional
status and/or quality of life when surgeons
analyze the superiority of operative proceduresfrom various reconstruction methods of thealimentary tract for patients with gastric cancer.
Postoperative long-term follow-up of the plasma leptin level as a marker may be useful forthese analyses.

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149

Received July 6, 2001; accepted July 29, 2001
Corresponding author: Prof. Michio Maeta