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The Journal of Clinical Endocrinology & Metabolism Vol. 89, No. 2 979-985
Copyright © 2004 by The Endocrine Society

Enhanced Lipoprotein Lipase Secretion and Foam Cell Formation by Macrophages of Patients with Growth Hormone Deficiency: Possible Contribution to Increased Risk of Atherogenesis?

Omar Serri, Ling Li, Fritz Maingrette, Nicolas Jaffry and Geneviève Renier

Centre Hospitalier de l’Université de Montréal Research Centre, Notre-Dame Hospital, and Department of Nutrition, University of Montreal, Montreal, Canada H2L 4M1

Address all correspondence and requests for reprints to: Dr. Geneviève Renier, Centre Hospitalier de l’Université de Montréal Research Centre, Notre-Dame Hospital, 3rd floor, J. A. de Sève, Y-3622, 1560 Sherbrooke Street East, Montreal, Québec, Canada H2L 4M1. E-mail: genevieve.renier{at}umontreal.ca.


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Discussion
 References
 
GH deficiency is associated with increased prevalence of atherosclerosis, and recent data indicate a proatherogenic role for macrophage lipoprotein lipase (LPL) in the arterial wall. In this pilot study, we determined LPL expression and foam cell formation in monocyte-derived macrophages of 12 control subjects and nine patients with GH deficiency without GH replacement therapy. LPL mRNA levels, mass, and activity were increased in macrophages of patients with GH deficiency. In these subjects, macrophage LPL activity correlated with body mass index and fat mass. Incubation of patient macrophages with IGF-I for 24 h or differentiation of monocytes isolated from GH-deficient patients into macrophages in the presence of this growth factor decreased the amount of LPL mass. Compared with control cells, macrophages derived from GH-deficient patients took up and stored increased amounts of proatherogenic lipoproteins and were more easily converted to foam cells. In the supernatants of these cells, increased levels of free fatty acids and TNF{alpha} were also documented. These results demonstrate that macrophages of patients with GH deficiency secrete increased amounts of proatherogenic cytokines and are more susceptible to foam cell formation. These alterations may contribute to the increased cardiovascular risk in patients with GH deficiency.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Discussion
 References
 
DESPITE THE CONTROVERSY regarding the impact of GH deficiency on life span (1, 2), patients with hypopituitarism have increased prevalence of premature atherosclerosis (3, 4, 5) and enhanced cardiovascular morbidity and mortality (6, 7). It has been proposed that GH deficiency may contribute to increased cardiovascular disease in adult hypopituitarism. Indeed, GH-deficient patients have a higher incidence of cardiovascular risk factors including altered body composition with increased body fat and abnormal levels of serum lipids and lipoproteins (8, 9), both of which were improved by GH replacement therapy (9, 10, 11, 12). Furthermore, it has been shown that GH replacement therapy effectively reduces carotid artery intima-media thickness in these subjects (5, 13). Plausible mechanisms underlying the increased prevalence of atherosclerosis associated with GH deficiency include endothelial dysfunction (14, 15, 16, 17, 18), enhanced oxidative stress (19), and inflammation (20, 21, 22). It is now firmly established that atherosclerosis is an excessive chronic inflammatory response resulting from the intimal recruitment of immune cells in the arterial wall (23, 24, 25). Once in the intima, these cells are exposed to a milieu of modified lipoproteins, cytokines, chemoattractants, and growth factors, all of which can cause further activation and differentiation into tissue macrophages. Macrophages play a key role in atherogenesis, not only as scavenger cells, but also as immunocompetent cells that produce numerous growth factors and proinflammatory cytokines (25). Lipoprotein lipase (LPL) is a key enzyme in lipid metabolism that is secreted by macrophages in the atherosclerotic lesion (26, 27). In vitro, LPL mediates various atherogenic effects in the vessel wall. Indeed, LPL acts as an atherogenic ligand that associates with lipoproteins, thereby favoring their uptake by vascular cells (28, 29, 30) as well as their retention to the subendothelial matrix (31, 32). This enzyme also stimulates the production of the proinflammatory cytokine TNF{alpha} (33, 34), increases monocyte adhesion to endothelial cells (35, 36, 37), and enhances the proliferation of vascular smooth muscle cells (38). Furthermore, recent in vivo studies have confirmed the proatherogenic effects of macrophage LPL in the arterial wall (39, 40, 41, 42).

Despite the abundance of information on the immune system in GH-deficient patients (43, 44, 45, 46, 47, 48, 49), the monocytic/macrophage function in these subjects has been poorly investigated. We have previously shown that GH-deficient patients present enhanced in vitro monocyte adhesion to the endothelium and increased monocyte TNF{alpha} and IL-6 secretion in comparison with healthy subjects (21). In the present study, we sought to investigate LPL expression in monocyte-derived macrophages of patients with adult-onset hypopituitarism and the direct in vitro effect of GH and IGF-I on this parameter. We also determined whether these cells are more susceptible to foam cell formation.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Discussion
 References
 
Patients

Nine patients, seven men, and two women, aged between 20 and 67 yr, with partial or total hypopituitarism were studied. Clinical and biochemical data are shown in Table 1Go. All patients had GH deficiency defined as maximum GH concentration less than 3 µg/liter on an insulin tolerance test (0.075–0.1 U/kg body weight iv of regular insulin). All patients but two had IGF-I lower than normal for age. One had isolated GH deficiency and eight had multiple hormone deficiencies and had hormone replacement therapies with T4, testosterone, or estrogen/progestin and hydrocortisone at standard doses but no GH replacement. The duration of GH deficiency in the study population varied from 2 to 38 yr. The causes of hypopituitarism were primary pituitary or hypothalamic pathologies, including one craniopharyngioma, one reticulosarcoma, and five pituitary adenomas. One patient had idiopathic GH deficiency and another had posttraumatic hypopituitarism. Six patients were previously treated by transphenoidal surgery, and one was treated by surgery followed by pituitary irradiation. Two patients did not receive any therapy. Twelve control subjects matched with patients for sex, age, and body mass index (BMI) were recruited from the hospital staff and relatives. Subjects with infectious or inflammatory conditions or treated by antiinflammatory or antioxidant drugs were excluded from the study. The protocol was approved by the Centre Hospitalier de l’Université de Montréal Research and ethics committee, and informed written consent was obtained from all subjects.


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  		TABLE 1. Clinical and metabolic characteristics of patients with hypopituitarism and control subjects

 
Body composition

Body composition (total fat and central fat) was determined in patients with GH deficiency by dual-energy x-ray absorptiometry, using Lunar DPX (Lunar Radiation Corp., Madison, WI) with an objective, highly reproducible measurement of central fat, using a computer-derived rectangle individually adjusted for each patient. The SD in similar patients approximates 5%.

Assays

Blood samples for lipid and lipoprotein analyses were drawn in the morning after an overnight fast before drug administration. Measurements of plasma lipids and lipoproteins were performed on a Beckman LX-20 multianalyzer (Beckman, CA). Lipoprotein fractions were determined on plasma samples obtained after a 14-h fasting period. Plasma total cholesterol concentrations were measured using a cholesterol esterase technique with dosage of the hydrolysis products (50). Levels of high-density lipoprotein cholesterol were determined by a timed end point with dextran-sulfate precipitation. Values of low-density lipoprotein (LDL) cholesterol were calculated using the Friedewald equation. Triglyceride levels were assayed using a lipase assay with determination of the hydrolysis products (51). Levels of free fatty acids were measured with a spectrophotometric assay kit (Wako Chemicals USA, Richmond, VA). The amount of LPL immunoreactive mass in the supernatant was measured by ELISA using the Markit-F-LPL kit (Dainippon Pharmaceutical, Osaka, Japan) (52). Extracellular LPL activity was determined in the supernatants using the Confluolip kit (Progen, Heidelberg, Germany) (53). Levels of LPL immunoreactive mass and activity were normalized to total cell protein levels.

Isolation of monocytes and culture of human monocyte-derived macrophages

Fresh heparinized blood (100 ml) was obtained from GH-deficient patients and healthy donors in the morning between 0800 and 0900 h. Peripheral blood mononuclear cells were isolated by density centrifugation using Ficoll (Life Technologies, Inc.-BRL, Grand Island, NY), allowed to aggregate in presence of fetal calf serum, and then further purified by rosetting technique (54, 55). After density centrifugation, recovery of highly purified monocytes (85–90%) as assessed by flow cytometry (FACScan, Becton Dickinson, Rutherford, NJ) was obtained. Differentiation of monocytes into monocyte-derived macrophages was obtained by culturing the cells in RPMI 1640 (Life Technologies, Inc.) supplemented with 20% autologous serum for 7 d. The culture medium was changed at d 4 and 7. Levels of LPL mRNA, mass, and activity were measured 24 h after the last medium change. The acute in vitro effect of GH and IGF-I on LPL secretion was assessed by incubating differentiated macrophages of controls and GH-deficient patients with GH or IGF-I for 24 h. To determine the chronic effect of these hormones on this parameter, freshly isolated monocytes of controls and GH-deficient patients were differentiated for 7 d into macrophages in 20% autologous serum supplemented with GH or IGF-I.

Analysis of LPL mRNA expression

Expression of the LPL gene in human macrophages was performed by the PCR technique. Construction of a standard curve using known concentrations of the same fragment as template was used to demonstrate the linearity of the PCR assay (data not shown). Total RNA for use in the PCR was extracted from 2 x 106 human macrophages by an improvement of the acid-phenol technique of Chomczynski and Sacchi (56). Briefly, cells were lysed with TRIzol reagent and chloroform was added to the solution. After centrifugation, the RNA present in the aqueous phase was precipitated and resuspended in diethyl pyrocarbonate water. cDNA was synthesized from RNA by incubating total cellular RNA with 0.1 µg oligodT (Pharmacia, Piscataway, NJ) for 5 min at 98 C and then incubating the mixture with reverse transcription buffer for 60 min at 37 C. The cDNA obtained was amplified by using 0.8 µmol/liter of two synthetic primers specific for human LPL (5'-GAGATTTCTCTGTATGGCACC-3', 5'-CTGCAAATGAGACACTTTCTC-3') and human glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (5'-CCCTTCATTGACCTCAACTACATGG-3', 5'-AGTCTTCTGGGTGGCAGTGATGG-3'), used as internal standard in the PCR mixture. A 277-bp human LPL cDNA fragment and a 456-bp human GAPDH cDNA fragment were amplified enzymatically by 22 and 25 repeated cycles, respectively. An aliquot of each reaction mixture was then subjected to electrophoresis on 1% agarose gel containing ethidium bromide. The intensity of the bands was measured by an image analysis scanning system ({alpha} Imager 2000, Packard Instrument Co., Meriden, CT).

Uptake of oxidized LDL (oxLDL) by human macrophages

Native LDL was isolated from plasma obtained from healthy donors by sequential ultracentrifugation (57) and then extensively dialyzed at 4 C against 5 mmol/liter Tris/50 nmol/liter NaCl to remove EDTA. Minimally modified LDL (7.3 nmol malondialdehyde equivalent/mg protein) was obtained by storage of EDTA-free LDL at 4 C for 3 months. Labeling of oxLDL with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine (Dil) was performed as described previously (58, 59). To examine cell-associated oxLDL, human macrophages were seated in 8-well culture slides (FALCON) and incubated at 37 C for 3 h in medium containing 5% lipoprotein-deficient serum (Sigma, St. Louis, MO) with Dil-labeled oxLDL (80 µg/ml) in the presence or absence of a 50-fold excess of unlabeled LDL. At the end of the incubation period, cells were washed, mounted on coverslips, and examined by fluorescence microscopy. To measure amounts of Dil-oxLDL accumulated in the cells, Dil was extracted by isopropanol and the fluorescence was determined at 520/564 nm. Results were normalized to total cell protein concentrations.

Quantification of cellular lipid accumulation

Human monocytes were allowed to differentiate into macrophages for 7 d at 37 C. At the end of this incubation period, cells were treated or not with oxLDL (80 µg/ml) for 24 h, and cellular lipid accumulation was quantified as follows. Briefly, cells were washed with PBS and fixed with 10% formalin solution for 1 h at room temperature. The cells were then washed twice with PBS and stained with 0.5% Oil Red O (Sigma). Quantification of lipid accumulation was achieved by extracting Oil Red O from stained cells with isopropanol and measuring the OD of the extract at 510 nm.

Measurement of TNF{alpha} protein

Levels of TNF{alpha} protein in the culture medium were measured using a double-sandwich ELISA kit (R & D Systems, Minneapolis, MN). The minimum detectable concentration of TNF{alpha} with this assay is typically less than 4.4 pg/ml. The intra- and interassay coefficients of variation of this assay are less than 5.3 and 8.7%, respectively.

Determination of total cell protein concentrations

Total cell protein content was measured according to the Bradford method by using a colorimetric assay (Bio-Rad Laboratories, Mississauga, Ontario, Canada), and BSA as standard (60).

Determination of cell viability

Cell viability following treatment of monocyte-derived macrophages with GH or IGF-I was assessed by trypan blue exclusion. Cell viability was consistently found to be higher than 85%.

Statistical analysis

Data are expressed as the mean ± SEM. Statistical differences between the variables were determined using Student’s t test for paired data and nonparametric test (Wilcoxon and rank sum tests) for unpaired data. For multiple comparisons, data were analyzed by one-way ANOVA followed by the Tukey test or the Dunn test. Linear regression analysis was used to determine whether correlation existed between variables. P < 0.05 was considered statistically significant.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Discussion
 References
 
Mean values for age, body weight, BMI, total fat mass, trunk fat mass, and fat-free mass in patients with GH deficiency and control subjects are shown in Table 1Go. Serum levels of total cholesterol, cholesterol/high-density lipoprotein, triglycerides, and free fatty acids were significantly greater (P < 0.05, P < 0.001, P < 0.01, P < 0.05, respectively) in GH-deficient patients than in healthy subjects. Mean fasting serum glucose level was similar in both groups (Table 1Go).

Macrophage LPL mRNA levels in patients with GH deficiency

LPL mRNA levels in monocyte-derived macrophages of patients with GH deficiency cultured in their own sera were significantly greater than those in control subjects (Fig. 1AGo). Under these experimental conditions, no modulation of the mRNA expression of GAPDH was observed (Fig. 1BGo). LPL mRNA levels normalized to the levels of GAPDH mRNA are presented in Fig. 1CGo (LPL mRNA levels (percent over control values): controls: 100 ± 44; GH-deficient patients: 509 ± 83, P = 0.008).



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  		FIG. 1. LPL mRNA levels in monocyte-derived macrophages of control subjects and patients with GH deficiency. Monocytes isolated from control subjects or patients with GH deficiency were cultured for 7 d in RPMI 1640 medium containing 20% of their own sera. Twenty-four hours after the last medium change, cells were lysed and LPL (A) and GAPDH (B) mRNA expression was analyzed by RT-PCR. The graph bar (C) represents LPL mRNA levels normalized to the levels of GAPDH. Results represent the mean ± SEM of data obtained from 12 control subjects and nine patients with GH deficiency. ***, P < 0.005 vs. controls.

 
Macrophage LPL secretion in patients with GH deficiency

Macrophages of patients with GH deficiency secreted significantly higher LPL mass (Fig. 2AGo) than macrophages isolated from control subjects [LPL mass (nanogram per milligram cell protein per milliliter): controls: 42 ± 7; GH-deficient patients: 84 ± 8, P = 0.006]. Levels of LPL activity were also higher in the supernatants of macrophages of patients with GH deficiency, compared with those measured in the supernatants of control cells (LPL activity (picomoles per milligram cell protein per milliliter): controls: 126 ± 4; GH-deficient patients: 142 ± 4, P = 0.047) (Fig. 2BGo). In patients with GH deficiency, a positive correlation was established between macrophage LPL activity and BMI (r2 = 0.67; P = 0.024) as well as between this parameter and fat mass (r2 = 0.78; P = 0.0084). In contrast, no correlation was found between macrophage LPL mRNA levels or mass and parameters of body composition or lipid profile.



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  		FIG. 2. Levels of LPL mass and activity in supernatants of monocyte-derived macrophages of control subjects and patients with GH deficiency. Monocytes isolated from control subjects or patients with GH deficiency were cultured for 7 d in RPMI 1640 medium containing 20% of their own sera. Twenty-four hours after the last medium change, LPL mass (A) and activity (B) were determined in the cell supernatants. Data represent the mean ± SEM. *, P < 0.05; **, P < 0.01 vs. controls.

 
In vitro effect of GH and IGF-I on macrophage extracellular LPL mass and activity

Treatment of control monocyte-derived macrophages for 24 h or 7 d with IGF-I or GH had no effect on extracellular LPL mass and activity. In contrast, short- (24 h) and long-term (7 d) incubation of monocyte-derived macrophages of GH-deficient patients with IGF-I significantly decreased the levels of LPL mass secreted by these cells (Fig. 3Go, A and B). Such inhibitory effect was not observed when monocyte-derived macrophages of GH-deficient patients were treated with GH (Fig. 3Go, A and B). Neither IGF-I nor GH affected the levels of macrophage LPL activity secreted by macrophages of GH-deficient patients (data not shown).



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  		FIG. 3. In vitro effect of GH and IGF-I on the levels of LPL mass secreted by monocyte-derived macrophages of GH-deficient patients. A, Totally differentiated macrophages of GH-deficient patients were incubated for 24 h with GH (20 ng/ml) or IGF-I (250 ng/ml). At the end of this incubation period, LPL mass was determined in the cell supernatants. B, Freshly isolated monocytes of GH-deficient patients were differentiated for 7 d into macrophages in 20% autologous serum supplemented with GH (10 ng/ml) or IGF-I (150 ng/ml). Twenty-four hours after the last medium change, LPL mass was determined in the cell supernatants. Data represent the mean ± SEM *, P < 0.05; **, P < 0.01 vs. untreated patient macrophages.

 
Free fatty acid levels in the supernatants of control and patient macrophages

The amounts of free fatty acids in the culture supernatants of macrophages were significantly higher (P < 0.05) in the patient group (0.50 ± 0.07 mEq/liter) than in the control one (0.21 ± 0.03 mEq/liter).

Foam cell formation and uptake of oxLDL by macrophages of patients with GH deficiency

When compared with control cells, macrophages of patients with GH deficiency were more susceptible to foam cell formation, as assessed by Oil red O staining (Fig. 4Go, A–D) and showed increased lipid accumulation as determined by Oil red O extraction (absorbance per milligram protein: controls: 0.06 ± 0.02; patients: 0.15 ± 0.02, P < 0.05). Uptake of oxLDL, as measured by fluorescence microscopy (data not shown) and extraction of Dil (Fig. 4EGo) was also enhanced in these cells.



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  		FIG. 4. Foam cell formation and oxLDL uptake in macrophages of control subjects (n = 5) and patients with GH deficiency (n = 6). A–D, Totally differentiated macrophages of control subjects (A, C) and GH-deficient patients (B, D) were untreated (A, B) or treated for 24 h with 80 µg/ml oxLDL (C,D) and then stained with Oil red O. E, Differentiated macrophages of control subjects and patients with GH deficiency were treated for 3 h with 80 µg/ml Dil oxLDL. Fluorescence of Dil was measured at 520/564 nm. *, P < 0.05 vs. controls.

 
TNF{alpha} production by macrophages of patients with GH deficiency

Basal macrophage TNF{alpha} production was significantly higher (P < 0.005) in the GH deficiency group than in the control group (controls: 9.1 ± 2.9 pg/ml; GH-deficient patients: 36.9 ± 7.1 pg/ml).


   Discussion
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
References
 
Tissue-specific regulation of LPL expression plays a pivotal role in lipid and energy metabolism. Imbalances in the partitioning of fatty acids among peripheral tissues resulting from dysregulation of tissue-specific LPL expression have major metabolic consequences including dyslipidemia, obesity, and atherosclerosis. GH-deficient patients have abnormal levels of serum lipids and lipoproteins and increased body fat. In these subjects, administration of GH is associated with inhibition of adipose tissue LPL activity, with no apparent effect on muscle LPL activity (61, 62). This effect may be involved in the reduction in adipose tissue mass commonly seen after GH treatment in GH-deficient patients.

Macrophage-secreted LPL plays a prominent role in atherogenesis and is up-regulated in several diseases associated with increased risk for atherosclerosis (63, 64). Thus, enhanced macrophage LPL may contribute to the high prevalence of atherosclerosis in GH-deficient patients. The present study demonstrates for the first time that monocyte-derived macrophages of adults with GH deficiency express greater levels of LPL mRNA and secrete larger amounts of LPL mass and activity than macrophages isolated from healthy subjects. The parallel increase of LPL mRNA levels and secretion in GH-deficient patients suggests that induction of macrophage LPL in these subjects may involve transcriptional events. Our results showing that macrophage LPL activity increased modestly, compared with mass, further suggest a posttranslational regulation of this enzyme in these patients. Positive regulators of macrophage LPL gene expression include glucose, fatty acids, leptin, homocysteine, and oxidative stress (65, 66, 67, 68, 69). Because serum leptin (70) and blood lipid-derived free radicals (71) are increased in patients with GH deficiency and that homocysteine levels are, in these subjects, in a range associated with high cardiovascular risk (72), these factors may theoretically contribute to the induction of macrophage LPL mRNA levels in adult GH deficiency. Alternatively, up-regulation of macrophage LPL gene expression in GH-deficient patients may occur as a result of increased cholesterol levels. This possibility is supported by the findings that cholesterol-enriched lipoproteins stimulate macrophage LPL secretion (73) and that LPL expression is subject to regulation by cellular sterol levels through interaction of sterol regulatory element binding proteins, with a sterol regulatory element spanning from -90 to -81 in the LPL promoter (74, 75).

Along with the observation that macrophages of GH-deficient patients express higher LPL mRNA levels, we found that these cells secreted significantly higher amounts of active LPL. Such increase in macrophage LPL secretion may be due to GH deficiency itself or other changes associated with hypopituitarism. In support for a hormonal regulation of macrophage LPL secretion, we found that short- (24 h) and long-term (7 d) in vitro treatment of macrophages of GH-deficient patients with IGF-I reduces LPL mass by 30%. Whether this partial inhibitory in vitro effect of IGF-I on LPL secretion could be related to the presence of some IGF-I inhibitors or alternatively to the absence of some permissive factors in the sera of patients remains to be determined. Because such effect was not observed after exposure of these cells to GH, these results suggest that induction of macrophage LPL secretion in adult GH deficiency could, at least partly, be IGF-I related. Besides IGF-I, other mechanisms may be involved in the up-regulation of macrophage LPL in patients with GH deficiency. Indeed, the incubation of macrophages of GH-deficient patients with IGF-I did not normalize macrophage LPL induction, decreasing this parameter by only 30%.

Interestingly, the inhibitory effect of IGF-I on LPL secretion was restricted to macrophages of GH-deficient patients, not being observed in control macrophages. This may be explained by differences of macrophage sensitivity to IGF-I in controls and GH-deficient patients. Indeed, it is well demonstrated that decreased levels of circulating IGF-I that occur in GH deficiency cause a dramatic enhancement in the levels of IGF-I receptor mRNA and binding to mononuclear cells (76). Whereas effective in reducing LPL mass, IGF-I treatment of patient macrophages had no effect on LPL enzymatic activity, probably because of the minor increase of LPL activity in macrophages of GH-deficient patients. Alternatively, one may postulate that macrophage LPL activity is not an IGF-I-regulated process. This possibility is supported by the observations of Behr and Kraemer et al. (77), who reported that in vitro treatment of macrophages with IGF-I does not affect the levels of extracellular LPL activity. Intriguingly, we found that levels of macrophage LPL activity were closely related to BMI and most particularly to fat mass in GH-deficient patients. Although the meaning of this observation remains uncertain, one may speculate that proinflammatory adipokines secreted by the adipose tissue may regulate macrophage LPL. In support for this possibility, it has been shown that secretion of macrophage LPL is increased as part of the response to inflammation (78) and that leptin enhances macrophage LPL secretion (68). Further studies aimed at examining macrophage LPL expression in human obesity are needed to explore the impact of inflammation associated with obesity on macrophage LPL regulation.

Although the precise contribution of LPL to atherogenesis in GH deficiency remains speculative, our data showing that macrophages of GH-deficient patients produce higher amounts of TNF{alpha} and are more easily converted to foam cells identify macrophages as potential key targets for therapeutic intervention aimed at preventing atherosclerosis associated with GH deficiency. Because LPL promotes foam cell formation (79) and because the up-regulation of this enzyme in macrophages of GH-deficient patients appears to be associated with enhanced hydrolysis of lipoproteins, increased LPL expression might promote foam cell formation in these subjects.

In conclusion, this study demonstrates that monocyte-derived macrophages of patients with GH deficiency overproduce proatherogenic cytokines and exhibit increased susceptibility to foam cell formation. Whether GH substitutive therapy in these patients corrects LPL overproduction will be further assessed in our population study. Reduction of macrophage LPL secretion may reflect one of the mechanisms by which GH replacement therapy could modulate the atherosclerotic process with beneficial effects.


   Acknowledgments
 
The authors thank their research nurse, Mrs. Chantal Riel, for her precious collaboration.


   Footnotes
 
This work was supported in part by Eli Lilly.

Abbreviations: BMI, Body mass index; Dil, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LDL, low-density lipoprotein; LPL, lipoprotein lipase; oxLDL, oxidized LDL.

Received May 23, 2003.

Accepted October 31, 2003.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Discussion
 References
 

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