International Journal of Obesity (2000) 24, 340±344
ß 2000 Macmillan Publishers Ltd All rights reserved 0307±0565/00 $15.00
www.nature.com/ijo
In¯uence of heredity for obesity on adipocyte
lipolysis in lean and obese subjects
L HellstroÈm* and S Reynisdottir
Karolinska Institute, Department of Medicine at Danderyd Hospital, Danderyd, Sweden; and Karolinska Institute, Department of
Medicine and Clinical Research Center, at Huddinge University Hospital, Huddinge, Sweden
OBJECTIVE: To evaluate a possible in¯uence of a hereditary trait for obesity on the regulation of adipocyte
metabolism in vitro in subcutaneous fat cells in obese and non-obese subjects.
DESIGN: A biopsy from abdominal subcutaneous fat was obtained from consecutive subjects with or without a family
trait for obesity. A positive family history of obesity was considered present if one or more of the ®rst degree relatives
had a BMI of 27 kg=m2 or more.
SUBJECTS: 67 non-obese and 60 obese subjects, age 19 ± 60 y. A family trait for overweight was present in 42 of the
lean subjects and in 50 of the obese subjects.
MEASUREMENTS: Fat cells were isolated and incubated in vitro with isoprenaline (a non-selective beta-adrenoceptor
agonist), forskolin (activates the adenylyl cyclase) and dibutyryl cyclic AMP (stimulates the protein kinase hormonesensitive lipase complex). Glycerol release was measured and used as lipolytic index.
RESULTS: Maximal lipolytic response per g triglycerides was about 50% lower in obese subjects both with and
without a positive heredity and in non-obese subjects with a family trait for obesity as compared to non-obese
subjects without such trait (P ˆ 0.0001). Fat cell volume was twice as high in obese as compared to lean subjects.
Drug-induced maximal glycerol release per fat cell in the obese subjects, regardless of family history of obesity,
reached a similar level, but did not exceed that of the lean group without heredity.
CONCLUSIONS: Obesity is associated with catecholamine resistance with a relatively ineffective lipolysis in fat cells,
and presence of a family history of obesity was not associated with a further suppression of lipolysis. In the lean
subjects, heredity for obesity signi®cantly in¯uenced lipolysis to similar low levels as in the obese subjects.
International Journal of Obesity (2000) 24, 340±344
Keywords: fat cell; lipolysis; heredity; obesity
Introduction
Obesity has become a major health problem worldwide and the prevalence is steadily increasing.1,2 A
mixture of psychosocial and environmental factors are
responsible,3 but increasing evidence of in¯uence of
genetic factors has come forth through studies of
twins and families with obesity.4,5 Due to this complex aetiology of obesity in man, less is known about
the absolute genetic contribution. Since white fat mass
is a target organ in obesity, it is tempting to speculate
whether heredity one of the mechanisms responsible
for the regulation of storage and mobilization of body
fat mass could contribute to the overweight condition.
The speci®c mechanisms that control these reactions
in fat cell metabolism would therefore be of interest.
In man, lipids are mobilized from adipose tissue
through lipolysis, a hormonally strictly regulated
process where triglycerides are hydrolysed to the
end products, free fatty acids and glycerol. Catecholamines are the main lipolytic hormones in man and
*Correspondence: Lena HellstroÈm Department of Medicine,
Danderyd Hospital, S-182 88 Danderyd, Sweden.
E-mail: [email protected]
Received 14 April 1999; revised 12 July 1999; accepted
14 October 1999
stimulate lipolysis in adipocytes by binding to beta 1,
2 and 3-adrenoceptors,6,7 activating the lipolytic cascade, the last step being activation of the enzyme
hormone-sensitive lipase.8
There is evidence of several defects in lipolysis and
fat cell metabolism in obesity. This includes resistance to catecholamine action in particular in upperbody obese subjects, as demonstrated in vitro9 and
also in vivo.10 Less is known of whether these defects
are of pathophysiological importance for the development of obesity or if they are a consequence of the
overweight condition. Further, it is not known whether
defects in adipocyte metabolism could be part of a
genetic transmission that contributes to the aggregation of obesity seen in families.
Few studies in recent years have dealt with a
possible genetic effect on adipocyte lipolysis, but
there are some reports from family studies revealing
signi®cant heritability levels for adrenaline stimulated
lipolysis from abdominal adipocytes.11,12 In a recent
study13 we investigated possible hereditary or early
onset defects in the regulation of catecholamineinduced lipolysis in fat cells in normal weight subjects
with a family history of obesity. We found a resistance to catecholamine action in adipocytes with a
signi®cantly lower maximum induced lipolysis in
subjects that had obesity among their ®rst degree
relatives as compared to those that lacked a family
Lipolysis and heredity for obesity
L HellstroÈm and S Reynisdottir
history of overweight. It is not known how lipolysis is
regulated in obese subjects with or without a heredity
for obesity.
The aim of the present study was to further evaluate
the in¯uence of heredity for obesity on changes in
adipocyte metabolism and if this could be associated
with overweight. We investigated catecholamineinduced lipolysis in vitro in adipocytes obtained by
abdominal, subcutaneous fat biopsies from a large
number of obese and non-obese subjects that either
had a positive family history of obesity or lacked
obese members among their ®rst degree relatives.
Materials and methods
From an on-going prospective project characterizing
adipocyte metabolism by a subcutaneous fat biopsy in
lean and obese subjects, the possible family history of
obesity among the participants was investigated by
interviewing their ®rst-degree relatives about their
current height and weight. By the criteria to include
only subjects where complete data from nuclear
family members was obtained, 127 subjects aged
19 ± 60 y (41 men and 86 women) could be included
in this study. The body mass index (BMI) ranged from
17.8 to 60.2 kg=m2 and the waist-to-hip ratio ranged
from 0.716 to 1.085. Obesity was de®ned as a BMI of
27 kg=m2 or more, since epidemiological studies have
suggested that the mortality risk increases above this
cut-off point, as discussed previously14 By this de®nition, 67 subjects were classi®ed as being non-obese
(BMI range 17.8 ± 26.6 kg=m2) and the remaining 60
were obese (BMI range 27.2 ± 60.2 kg=m2), all otherwise healthy and drug-free.
Obesity occurred in the families of 50 of the 60
obese probands. In all except two of these families,
one or both parents, alternatively one parent and one
or several brothers and sisters, were obese and in 10
families all members were obese. In two families
obesity was found only in brothers and sisters.
Forty-two of the 67 lean subjects had at least one
obese member among ®rst degree relatives, but generally obesity was not as prevalent in the families of
these probands as compared with the corresponding
obese; in none of these families did obesity occur in
all members or in both parents. Twenty-®ve of the
lean subjects had only non-obese family members.
All subjects had given their informed consent prior
to entering the study. The study was approved by the
ethics committee of the Karolinska Institute.
Experimental protocol
The subjects were investigated in the morning after an
overnight fast. Height, body-weight and waist ± hip
ratio were measured. They then rested in the supine
position for 15 min, whereafter blood pressure was
recorded and venous blood samples were obtained for
the determination of glucose and lipids by the hospital's routine chemistry laboratory and of insulin by
our own laboratory (using a commercial radioimmunoassay kit from Pharmacia Upjohn; Uppsala,
Sweden). A subcutaneous fat biopsy (0.5 ± 2.5 g) was
obtained under local anaesthesia from the abdominal
region immediately to the right or the left of the
umbilicus. The local anaesthesia was given so that it
did not in¯uence the function of the removed adipose
tissue.15
341
Isolation of fat cells and lipolysis experiments
Isolated fat cells were prepared by incubation in
collagenase according to Rodbell.16 The cells were
then packed by centrifugation for 1 min at 600 rpm in
a Beckman centrifuge. Fat cell diameter was calculated from the cell diameter measurements of 100
cells in each individual. Total lipid content in the
incubate was measured by organic extraction. In this
way, the mean cell weight and volume and further the
number of fat cells in each incubate can be calculated
as described previously17
For performing the lipolysis assay, a diluted suspension of fat cells (about 5000 ± 10,000 cells=ml)
was incubated in duplicate samples with air as the gas
phase for 2 h at 37 C in Krebs ± Ringer phosphate
buffer (pH 7.4) supplemented with glucose (1 mg=ml),
ascorbic acid (0.1 mg=ml) and bovine serum albumin
(20 mg=ml) in the absence (basal) or presence of
different lipolytic agents. These were isoprenaline
(10ÿ9 ± 10ÿ5 mol=l), a non-selective beta-adrenoceptor
agonist, forskolin (10ÿ7 ± 10ÿ4 mol=l), stimulating
adenylyl cyclase and ®nally the phosphodiesteraseresistant cyclic AMP analogue dibutyryl cyclic AMP
(10ÿ5 ± 10ÿ3 mol=l), which stimulates the protein
kinase hormone-sensitive lipase complex. Increasing
concentrations of each drug were used in order to
identify the maximum effective concentration in adipocytes from each subject.
After incubation an aliquot of the medium was
removed and glycerol, which was used as a measurement of the lipolysis rate, was analysed using a
bioluminescence method.18 Since fat cell size differed
between the studied groups, the results were expressed
using both triglyceride weight (g) and number of cells
in the incubation medium as denominators.
Drugs and chemicals
Bovine scrum albumin (fraction V, lot 63F-0748),
clostridium histolyticum collagenase type I, forskolin
and dibutyryl cAMP were obtained from Sigma (St
Louis, MO, USA). Isoprenaline came from HaÈssle
(MoÈlndal, Sweden). ATP monitoring reagent containing ®re¯y luciferase was from LKB Wallac (Turku,
Finland). All other chemicals were of the highest
grade of purity commercially available. Collagenase
and other ingredients in the incubation buffers were
from the same batches throughout the study.
International Journal of Obesity
Lipolysis and heredity for obesity
L HellstroÈm and S Reynisdottir
342
signi®cant difference in basal lipolysis between the
two groups of lean subjects. As seen in Table 1, fat
cell weight was almost twice as high in obese as in
lean subjects and expressed per cell, basal lipolysis
was about 50% higher in the obese subjects. A family
history of obesity did not in¯uence fat cell weight in
the obese or lean group respectively.
Maximum stimulated lipolysis data expressed as
glycerol release=g triglycerides are shown in Figure
1. Regarding the lean subjects, the catecholamineinduced rate of lipolysis was about 40% higher in
those without heredity for obesity than in those with a
positive family history and this was also true when
lipolysis was stimulated with isoprenaline or at postreceptor levels with forskolin and dibutyryl cyclic
AMP (P ˆ 0.006 or less). Since the fat cell weight
did not differ between these subgroups of lean subjects, the difference in lipolysis rate was of the same
magnitude when data were expressed per cell (Figure
2). These ®ndings in non-obese subjects are in accordance with our earlier study.13 There was no difference in lipolysis rate among obese subjects with or
without heredity for obesity regardless of whether the
values were expressed per g triglycerides or per cell
(Figures 1 and 2).
When maximum lipolysis rate was compared in
lean and obese subjects, glycerol levels were about
50% lower in obese individuals as compared to those
in lean subjects without heredity when expressed per g
triglycerides (Figure 1). This was true for lipolysis
stimulated both at the receptor and at the postreceptor
level. On the other hand, lipolysis rate did not differ
between the obese group and those lean subjects that
had a family history of obesity, with a minor exception in isoprenaline-induced lipolysis where obese
subjects with heredity had a slightly but signi®cantly
lower lipolysis as compared to lean subjects with
heredity.
If, instead, glycerol release was expressed per cell
(Figure 2) and compared in lean and obese subjects,
the latter group had signi®cantly higher maximum
induced lipolysis by about 40% as compared to lean
Statistical analysis
Data are presented as means standard error of the
mean (s.e.). Data were compared using analysis of
variance (ANOVA).
Results
Based on the BMI, the participants were classi®ed as
being lean or obese and each of these groups in turn
was subdivided according to whether obesity occurred
in the family or not. The data on BMI of ®rst degree
relatives were for practical reasons obtained from
interviews. We have earlier demonstrated that this is
a method with satisfactory accuracy.13
Clinical data are presented in Table 1. A majority,
or 50 of the 60 obese subjects, had a positive family
history of obesity while only 10 of the obese subjects
had only normal weight ®rst degree relatives. Using
analysis of variance (ANOVA), there was no difference between the two groups of lean subjects with or
without heredity for obesity as regards all parameters
listed in Table 1. With some reservation for the small
number of obese subjects without heredity there were
likewise no differences in this respect between the two
groups of obese subjects. All groups were comparable
as regards age. The obese subjects generally had
signi®cantly higher levels of plasma insulin and
blood glucose and lower HDL-cholesterol as well as
higher blood pressure as compared to the lean subjects, and they further had almost twice as large fat
cells (P < 0.005 or less by ANOVA).
As regards lipolysis data, basal lipolysis rate (ie
without lipolytic agents present in the incubation
medium) was signi®cantly higher in obese as compared to lean subjects. The values, presented as mmol
glycerol=g triglycerides were in lean subjects 0.81
(with heredity), 1.1 (without heredity) and 1.3 for
obese subjects with as well as without heredity for
obesity (P < 0.005 using ANOVA). There was no
Table 1
Clinical characteristics
Non-obese
Age(y)
BMI
Waist/hip ratio
SBP (mmHg)
DBP (mmHg)
Glucose (mmol/l)
Insulin (mU/l)
Fat cell volume (pl)
Fat cell weight (ng)
Cholesterol (mmol/l)
HDL cholesterol (mmol/l)
Triglycerides (mmol/l)
Obese
pos her
(n ˆ 42)
neg her
(n ˆ 25)
pos her
(n ˆ 50)
neg her
(n ˆ10)
P-value
38.7 1.1
23.7 0.3
0.885 0.01
122 2
74 1
5.0 0.1
7.9 0.7
426 23
389 21
5.2 0.2
1.3 0.06
1.3 0.1
34.2 2.2
22.4 0.5
0.874 0.01
118 4
73 2
4.8 0.06
6.1 0.6
411 35
376 32
4.9 0.2
1.5 0.09
1.3 0.2
38.5 1.3
41.4 1.1
0.965 0.01
135 2.8
83 2
6.2 0.3
19.2 1.5
814 28
745 26
5.5 0.2
1.2 0.05
2.4 0.4
36.3 3.5
39.6 1.9
0.931 0.02
139 5
84 3
5.3 0.1
15.0 3.5
778 72
712 66
5.4 0.4
1.3 0.11
1.8 0.2
0.27
0.0001
0.0001
0.0001
0.0001
0.0003
0.0001
0.0001
0.0001
0.26
0.015
0.07
Values are mean s.e. Data was compared using analysis of variance (ANOVA). Pos her ˆ positive
heredity for obesity, neg her ˆ negative heredity for obesity, SBP ˆ systolic blood pressure,
DBP ˆ diastolic blood pressure.
International Journal of Obesity
Lipolysis and heredity for obesity
L HellstroÈm and S Reynisdottir
343
Figure 1 Maximum induced lipolysis in abdominal, subcutaneous fat cells in non-obese and obese subjects with and without
a family history of obesity. Adipocytes were incubated with
increasing concentrations of isoprenaline (10ÿ9 ± 10ÿ5 mol=l), forskolin (10ÿ7 ± 10ÿ4 mol=l), and dibutyryl cyclic AMP (10ÿ5 ±
10ÿ3 mol=l). Mean values of glycerol release at the maximum
effective concentration of each agent are shown. The data are
expressed per g of triglycerides, compared using analysis of
variance and are expressed as mean s.e.
subjects with heredity. However, lipolysis in the obese
group reached an equal level to, but did not exceed,
that of the lean group without heredity.
Discussion
In this study, we have investigated the possible
in¯uence of a family history of obesity on fat cell
metabolism in obese and non-obese subjects with or
without heredity for obesity. The data suggest that the
lipolytic action of drugs acting on the beta-adrenoceptor, as well as on the post-receptor level, is
Figure 2 Maximum induced lipolysis expressed as glycerol
release per number of fat cells. Values were compared using
analysis of variance and expressed as mean s.e. See legend to
Figure 1 for further details.
impaired and relatively inef®cient both in lean subjects with obese ®rst degree relatives and in obese
subjects regardless of whether a family history of
obesity was present or not, and more ef®cient in
lean subjects that lacked heredity for obesity.
The results in lean subjects demonstrated an
approximately 50% higher drug-induced maximum
glycerol release in non-obese individuals without a
family trait for obesity as compared to those with
obesity among ®rst degree relatives. Thus, we have so
far con®rmed the results of our previous study in this
new and larger cohort.13 We here found no differences
in plasma insulin, blood lipids or other clinical parameters between the two non-obese subgroups.
Obesity was generally associated with a suppressed
lipolysis as compared to lean subjects when glycerol
release was expressed per g of triglycerides. Of note
International Journal of Obesity
Lipolysis and heredity for obesity
L HellstroÈm and S Reynisdottir
344
was the fact that when data were expressed per fat cell
we found that despite twice as large fat cells, obese
subjects achieved only 40% higher maximum glycerol
values than did non-obese subjects with a family trait
for obesity and the level did not exceed that of the
lean subjects that lacked a heredity for obesity. This
indicates a less ef®cient lipolytic activity per fat cell
in obese subjects.
When lipolysis data were compared between the
groups of obese subjects with or without heredity for
obesity, the statistical calculations showed no differences in maximum induced glycerol release, neither
when lipolysis was stimulated at the overall beta-adrenoceptor level with isoprenaline, of at post-receptor
levels with forskolin or dibutyryl cyclic AMP. A majority of the obese participants in the study had obese ®rst
degree relatives. Thus, only 10 of the 60 obese participants recruited lacked a family history of obesity completely. This ®nding was not surprising since it is well
known that obese parents are more likely to have obese
children than are lean parents.19,20 This fact, however,
contributes to dif®culties in studying this speci®c group
of obese subjects with only non-obese family members.
Since this latter group was small, data must be interpreted with care, especially as regards conclusions about
the possible in¯uence of heredity for obesity on lipolysis
in the obese group and since besides a possible genetic
in¯uence a large number of factors can have an effect on
lipolysis in man.
Lipolysis data taken together indicate that a defect
in lipolysis in non-obese subjects with a family history
of obesity and in obese subjects resides in the lipolytic
chain near the level of the hormone-sensitive lipase. A
decreased activity of this enzyme was earlier demonstrated in another smaller cohort of lean subjects with
a positive heredity for obesity.13 Unfortunately, not
enough fat tissue could be obtained from a suf®cient
number of subjects to allow a further analysis of the
mechanism involved in this lipolytic defect, including
measurement of the hormone-sensitive lipase.
A cautious speculation when looking upon the data
altogether would be that a hereditary trait for obesity
contributes to suppression of lipolysis in fat cells in
lean subjects, while when a subject already has
become obese the presence of a genetic predisposition
for obesity plays a minor role for lipolysis. In this
latter situation, other factors might be of greater
importance, such as higher plasma insulin concentrations, which can lower lipolysis in human fat cells by
downregulation of beta-adrenoceptors.21
In summary, this study has provided evidence for a
lipolysis defect in obese subjects with a relatively
inef®cient glycerol release per fat cell regardless of
whether a family history of obesity was present or not.
In lean subjects, heredity for obesity signi®cantly
reduced lipolysis to similar low levels as in the obese
subjects. What impact these defects in lipolysis regulation might have for the development of obesity and what
importance the genetic contribution may have can only
be answered by long-term prospective studies.
International Journal of Obesity
Acknowledgements
The study was supported by grants from Knut and
Alice Wallenberg Foundation, The Swedish Medical
Society, The Swedish Foundation for Strategic
Research and the Karolinska Institute, Sweden.
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