|
|
||||||||
CLINICAL STUDY |
1 Division of Endocrinology and 2 Department of Medical and Surgical Sciences, School of Medicine, University of Padua, Via Ospedale 105, 35128 Padua, Italy and 3 Division of Endocrinology, Department of Internal Medicine, Università Politecnica delle Marche, Via Conca 1, 60020 Ancona, Italy
(Correspondence should be addressed to B Mariniello; Email: barbaramariniello{at}yahoo.it)
| Abstract |
|---|
|
|
|---|
Design and methods: We have performed a case-control study and studied omental adipose tissue from a total of 24 subjects (eight obese subjects, ten patients with Cushings syndrome due to adrenal adenoma, and six normal weight controls). Body mass index, blood pressure, plasma glucose, plasma insulin, plasma cortisol, urinary free cortisol and post dexamethasone plasma cortisol were measured with standard methods. 11ß-HSD1 mRNA and protein expression were evaluated in real-time PCR and western blot analysis respectively.
Results: 11ß-HSD1 mRNA was 13-fold higher in obese subjects compared with controls (P=0.001). No differences were found between Cushings patients and controls. Western blot analysis supported the mRNA expression results.
Conclusions: Our data show the involvement of 11ß-HSD1 enzyme invisceral obesity, which is more evident in severely obese patients than in Cushings syndrome patients. The lack of increase of 11ß-HSD1 expression in Cushings syndrome could suggest downregulation of the enzyme as a result of long-term overstimulation.
| Introduction |
|---|
|
|
|---|
However, studies on humans have mainly examined s.c. adipose tissue in vitro (1416) and in vivo (17) and an increased 11ß-HSD1 expression associated with indices of obesity and metabolic abnormalities has also been shown (18), although 11ß-HSD1 might be more important in omental fat. Many experiments have shown the involvement of peripheral fat in adipose endocrine function, but data supporting the hypothesis that 11ß-HSD1 is increased in omental adipose tissue in human obesity (19, 20) refer to a limited number of studies. To date, no studies have been performed in patients with Cushings syndrome.
In this work, 11ß-HSD1 gene expression has been evaluated in two different models of omental human adiposity: simple obesity and Cushings syndrome.
| Materials and methods |
|---|
|
|
|---|
All patients gave their written informed consent for the collection of adipose tissue and the study was approved by the local ethics committee. Omental tissue was obtained from 24 subjects and periadrenal tissue from three Cushings patients undergoing abdominal surgery.
For all the subjects, weight, height, body mass index (BMI), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were recorded. A BMI
25 kg/m2 was considered as an index of normality; a BMI>25 and < 30 kg/m2 was considered as an index of overweight and a BMI>30 kg/m2 was considered as an index of obesity. Control subjects had a gender-related body fat distribution. The following biochemical and hormonal parameters were also evaluated: fasting glucose and insulin, plasma F, urinary free F and plasma F after 1 mgovernight dexamethasone suppression test.
Adipose tissue samples were collected from ten patients with full-blown Cushings syndrome: two with pituitary adrenocorticotrophin (ACTH) secreting adenoma, not cured after pituitary surgery, and eight with hypercorti-solism ACTH-independent due to adrenal adenoma, who underwent surgery for bilateral and unilateral adrenal removal respectively. Only the two patients with pituitary ACTH-secreting adenoma were in treatment with ketoconazole (400 mg/day) before adrenal surgery.
Ten omental and three periadrenal adipose tissue samples were collected after adrenal surgery. Eight omental adipose tissue samples were obtained from obese patients undergoing surgery for gastric binding and the remaining omental samples were obtained from six control subjects during colecistectomy. All operations were for non-inflammatory and non-malignant conditions.
For RNA and protein isolation, about 2.0 g whole omental adipose tissue was immediately deep-frozen in liquid nitrogen and stored at 70 °C until extraction.
RNA extraction and reverese transcriptase (RT)
Total RNA extraction was performed with a trizol reaction kit (Invitrogen): 500 mg adipose tissue was homogenized with polytron in 1 ml trizol for each 50 mg tissue. Total RNA was separated from proteins and DNA by adding chloroform and centrifuging at 12 000 g, and then recovered from the aqueous phase by precipitation with isopropanol. The RNA concentration was measured by spectroscopy at OD260 after the treatment with RNase-Free DNase (Promega). RNA quality was confirmed by electrophoresis on 1% non-denaturing agarose gel.
The RT protocol is as follows: 1 µg total RNA and 200 ng Random Examers (Applied Biosystems, Foster City, CA, USA) were initially denatured at 70 °C for 10 min. Ten units of multiscribe (RT) (Applied Biosys-tems), 2.5 mM magnesium chloride, 10 U RNase inhibitor and 0.25 mM each dNTP with 1x reaction buffer were added to the RNA and primers in 20 µl of final volume. The RT reaction was carried out at 42 °C for 50 min and the RT exonuclease activity was then heat-inactivated at 95 °C for 5 min.
Real-time PCR
Real-time PCR was used to make 11ß-HSD1 mRNA quantification. The reaction was carried out using an ABI9700 sequence detection system (Applied Bio-systems), which employs TaqMan chemistry for highly accurate quantitation of mRNA levels. Real-time PCR was performed in 25 µl volumes in a reaction buffer containing TaqMan Universal PCR Master Mix (Applied Biosystems), 3 mM Mn(Oac)2, 200 µM dNTPs, 1.25 U AmpliTaq Gold polymerase (Applied Biosystems), 1.25 U AmpErase UNG (Applied Biosystems), 200 nmol TaqMan probe, 900 nmol primers and 25 ng cDNA. All the reactions were performed for the 11ß-HSD1 gene (HSD11B1) and housekeeping gene (18S) at the same time. 18S preoptimized control probe (Applied Biosystems) was used. The data were obtained as Ct values according to the guidelines (the cycle number at which logarithmic PCR plots cross a calculated threshold line) and were used to determine
Ct values (
Ct=Ct of the target geneCt of the housekeeping gene). To calculate the fold changes in gene expression between two categories of patients (e.g. obese and non-obese), the following equation was used; 2
Ct. The measurements were carried out at least three times for each sample.
Primer sequences for HSD11B1 and 18S were obtained from Bujalska et al. (12).
Western blot analysis
Western blot analysis for 11ß-HSD1 enzyme was performed in adipose tissue. The samples (0.5 g each) were homogenized in 5 ml buffer containing 25 mM HEPES, 250 mM sucrose, 4 mM EDTA, 1 µM leupeptin, 1 µM aprotinine and 1 µM pepstatin, pH 7.4. Homogenates were centrifuged at 12 000 g for 10 min at 4 °C and the supernatant was collected, aliquoted and stored at 20 °C.
The proteins were measured by the Coomassie Protein Assay Reagent (Pierce) using BSA as a standard. Samples were incubated for 5 min at 95 °C and 20 µg protein was separated by SDS-PAGE on 10% running gel. The proteins were transferred overnight onto nitrocellulose filters in 20% methanol, 200 mM glycine, 25 mM Tris buffer, pH 8.3. Correct transfer on filters was confirmed by transfer of colour markers (Sigma). The filters were then blocked in 1x Tris-buffered saline (TBS) (TrisHCl and 3 M NaCl) and 5% BSA for 2 h at 42 °C, washed in 1x Tween 20 TBS (TTBS) and incubated in 1x TBS, 0.5% BSA and 11ß-HSD1 antibody for 2 h at room temperature. Excess antibody was removed by several washes in 1x TTBS. Polyclonal antibody against human 11ß-HSD1 raised in sheep (kindly provided by Prof Stewart PM and Bujalska IW) was used at 1:500 dilution. 11ß-HSD1 antibody was tested on human liver and kidney samples, used as control. The liver and kidney were obtained in the course of autopsy after a car accident. The detection of the immunocomplex was performed with 125I-labelled G-protein (Amersham) by incubation at room temperature for 45 min. The membranes were thoroughly washed and subjected to autoradiography for 72 h at 70 °C.
Biochemical assays
Insulin levels were determined using an immunoenzy-matic assay (AIA-PACK IRI, Eurogenetics Italy, Turin, Italy); the sensitivity of this method is 2.0 µU/l, intra-assay coefficient of variation (CV) is 4.6% and inter-assay CV is 4.5%.
Plasma glucose was measured by photometric determination using the glucose deydrogenase method.
Plasma F (523 mg/dl, intra- and inter-assay CV values, 9 and 10.3% respectively) was measured by chemiluminescence (Immulite, Diagnostic Products Corporation, Los Angeles, CA, USA).
Urinary-free F was evaluated by RIA (Cortisol Bridge, Athens, Greece; range 7150 mcg/24 h, intra-assay CV 4.05%).
Statistical analysis
Statistical analysis was performed using the StatView v.4.1 software for Macintosh (Abacus Concepts Inc., Berkeley, CA, USA). Comparisons between groups were performed by ANOVA. Bonferronis correction was then applied to reduce the probability of differences arising by chance. The data are expressed as mean±S.D. Differences were considered statistically significant when P was less than 5%.
| Results |
|---|
|
|
|---|
|
No significant differences were found between Cushings and obese subjects in SBP, plasma glucose, insulin and plasma F levels (Table 1
).
According to ATP III criteria (21), 50% of both Cushings patients and obese subjects displayed the metabolic syndrome.
Adipose tissue expression of 11ß-HSD1
In omental adipose tissue, 11ß-HSD1 mRNA levels were significantly higher in obese subjects compared with both control subjects and Cushings patients (
Ct 13.62±0.15 vs 17.31±0.58 and 17.37±0.68 respectively; P=0.001). The mRNA expression was 13-fold higher in obese subjects compared with control subjects, whereas no differences were found between Cushings patients and controls in omental tissue (Table 2
and Fig. 1
). A slight increase was found in periadrenal adipose tissue of Cushings patients compared with controls (
Ct 15.03±0.98 vs 17.31± 0.58; Table 2
).
|
|
|
A significant positive correlation between 11ß-HSD1 mRNA expression and BMI was observed analyzing Cushings patients, obese and control subjects (r= 0.734; P<0.001).
No correlations between 11ß-HSD1 and F, age and gender were found.
| Discussion |
|---|
|
|
|---|
Bujalska et al. (10) demonstrated that the 11ß-HSD1 enzyme in omental adipose stromal cells generates active F from inactive E; F generated in this way may act in an autocrine manner on the stromal cells or in a paracrine manner on adjacent adipocytes to promote abdominal obesity. Glucocorticoid receptors found in adipocytes and stromal cells are responsible for adipocyte differentiation, maybe also through the activation of local reninangiotensin system. The authors suggest that central obesity may reflect Cushings disease of the omentum. Our data show a significantly higher 11ß-HSD1 mRNA expression in the omental adipose tissue of obese patients compared with control subjects, in accordance with Bujalska et al. (10). Our obese patients do not display increased plasma F and/or urinary-free F, supporting the hypothesis that local F produced by increased 11ß-HSD1 isoform in visceral adipose tissue is involved in adipocyte differentiation in an autocrine manner.
Moreover, although evaluated in a small series of samples, the increase of 11ß-HSD1 mRNA expression in the periadrenal adipose tissue of Cushings patients compared with omental mRNA levels in the same patients suggests a tissue-specific involvement of this enzyme in the adipose tissue of patients with Cushings syndrome.
Accordingly, with the hypothesis of 11ß-HSD1 tissue-specific involvement, our results are also supported by data from transgenic and knockout mice. Transgenic mice overexpressing HSD11B1 selectively in adipose tissue are obese, hypertensive, dyslipidaemic and insulin-resistant (7), while transgenic mice overexpressing HSD11B1 selectively in liver do not exhibit obesity, but display insulin resistance, fatty liver, dyslipidaemia and hypertension (24). Furthermore, HSD11B1 knockout mice are protected from these metabolic abnormalities (25).
Our data are discordant with those reported by Tomlinson and colleagues (19), who showed the lack of increased 11ß-HSD1 expression in human obesity. However, it is important to underline that these obese patients had BMI much lower than the BMI of our patients (33 vs 44 kg/m2). To this regard, we believe that the different degree of obesity observed between the two groups is determinant for 11ß-HSD1 expression in adipose tissue. The positive correlation of 11ß-HSD1 expression with BMI found in the present study seems to suggest that a marked increase of 11ß-HSD1 is evident only when there is severe obesity and is in accordance with metabolic variables reflecting insulin sensitivity, as shown by Lindsay et al. (26). As for patients with Cushings syndrome, their BMI is similar to that of the obese patients studied by Tomlinson (19), but again, the data are not comparable because Cushings syndrome is characterized by hypercortisolism, which is absent in obese subjects, and abdominal adiposity, which is reversible when F levels fall within the normal range, after pharmacological or surgical treatment.
Interestingly, we have found a different expression of 11ß-HSD1 between obese and Cushings patients. Cushings patients have a lower 11ß-HSD1 expression in omental tissue compared with obese subjects and their 11ß-HSD1 expression is not different from normal weight controls. The large difference in BMI between obese subjects and Cushings patients could be one explanation for the different 11ß-HSD1 expression. Cushings patients develop abdominal obesity, but generally do not display severe obesity as observed in our obese subjects.
Literature data show that F enhances 11ß-HSD1 expression in omental adipose tissue (10, 18), so that in the presence of hypercortisolism, i.e. in Cushings syndrome, it is licit to expect an increased expression of this enzyme in such tissue. However, this hypothesis is not confirmed by our results.
The finding of 11ß-HSD1 levels in Cushings patients that are comparable to those observed in normal weight controls, allow us to reckon that F excess in such patients is not able to induce the expected enzyme upregulation. The lack of increase of 11ß-HSD1 expression in Cushings syndrome in response to high plasma F levels could suggest a downregulation of the enzyme as a result of long-term overstimulation.
As a possible explanation, we could hypothesize that there is a local defensive mechanism of the adipose tissue in Cushings patients that prevents 11ß-HSD1 expression, which, in turn, would be responsible for a further F increase.
It would be interesting to evaluate the adipose tissue composition of obese subjects and Cushings patients also in order to see if a different percentage of preadipocytes and mature adipocytes, as well as adipocyte cell size, could alter the response to F.
Several factors, including some proinflammatory cytokines (27), could regulate and increase 11ß-HSD1 expression in visceral adipose tissue, so that the F produced might be an important autocrine regulator of fat mass in obese subjects despite normal circulating F levels.
Our expression data are supported by western blot analyses also that showed higher 11ß-HSD1 protein expression in obese subjects. We have found two bands of 34- and 68-kDa in liver; our study therefore confirms not only the dimeric nature of 11ß-HSD1 in liver demonstrated by Maser et al. (28), but also highlights the presence of an additional 50-kDa band strongly expressed in omental adipose tissue, consistent with the data reported by Kannisto et al. (29). The 50-kDa 11ß-HSD1 protein has not been previously reported in other tissues and neither the nature nor the function of this 11ß-HSD1 subtype is known.
We also observed a significant positive correlation between BMI and 11ß-HSD1 expression analyzing Cushings patients, obese and control subjects to support a tight correlation between obesity and 11ß-HSD1, in agreement with the previous data on s.c. adipose tissue (1416). To this regard, the difference in 11ß-HSD1 expression found between obese subjects and all other subjects could be related to the different degree of obesity, which is much more marked in the first group.
The lack of correlation between circulating F levels and 11ß-HSD1 expression in both obese subjects and Cushings patients, demonstrates that this enzyme is not directly regulated by plasma F concentrations.
In conclusion, the increased expression of 11ß-HSD1 enzyme in omental adipose tissue seems to support its involvement in severe obesity. The higher 11ß-HSD1 expression in obese subjects, compared with control subjects, could sustain that central obesity increases active F from E. The lack of increase of 11ß-HSD1 expression in Cushings syndrome, in response to high plasma F levels, could suggest a downregulation of the enzyme as a result of long-term over stimulation.
| Acknowledgements |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
A. Balachandran, H. Guan, M. Sellan, S. van Uum, and K. Yang Insulin and Dexamethasone Dynamically Regulate Adipocyte 11{beta}-Hydroxysteroid Dehydrogenase Type 1 Endocrinology, August 1, 2008; 149(8): 4069 - 4079. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |