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Bekhbat M, Chu K, Le NA, Woolwine BJ, Haroon E, Miller AH, Felger JC. Glucose and lipid-related biomarkers and the antidepressant response to infliximab in patients with treatment-resistant depression. Psychoneuroendocrinology 2018; 98:222-229. [PMID: 30249443 PMCID: PMC6214671 DOI: 10.1016/j.psyneuen.2018.09.004] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 07/29/2018] [Accepted: 09/05/2018] [Indexed: 01/04/2023]
Abstract
The tumor necrosis factor (TNF) antagonist infliximab was previously found to reduce depressive symptoms in patients with treatment-resistant major depression (TRD) who exhibited high baseline inflammation, as reflected by plasma C-reactive protein (CRP) >5 mg/L. Further predictors of antidepressant response to infliximab included differential expression of peripheral blood gene transcripts that were related not only to inflammation but also to glucose and lipid metabolism. To determine whether plasma biomarkers of glucose and lipid metabolism were similarly associated with antidepressant response to infliximab and with relevant gene transcripts, we measured concentrations of glucose, insulin, and protein hormones that regulate glucose homeostasis and metabolism (leptin, resistin, and adiponectin), as well as cholesterols, triglycerides, and non-esterified fatty acids (NEFA), in medically-stable TRD outpatients at baseline and 2 weeks after the first infusion of infliximab (n = 26) or placebo (n = 26). Treatment response was defined as 50% reduction in depressive symptoms at any point during the 12-week trial. We found that baseline cholesterol (total, low-density lipoprotein [LDL], and non-high-density lipoprotein [non-HDL]), triglycerides and NEFA were elevated in patients who exhibited an antidepressant response to infliximab (all p < 0.05) but not placebo (all p > 0.299). HDL and non-HDL cholesterol concentrations also correlated with two lipid-related gene transcripts that were predictive of antidepressant response (r = 0.33 to 0.39, p < 0.05). Although not associated with response to infliximab, resistin correlated with numerous glucose-related transcripts (r = -0.32 to 0.37, p < 0.05) and was higher at 2 weeks post-infusion in patients treated with infliximab compared to placebo (p = 0.028). Concentrations of cholesterol (total, LDL, HDL, non-HDL) were also lower at 2 weeks in patients treated with infliximab compared to placebo, but only in those patients with CRP >5 mg/L at baseline (all p < 0.05). These results are consistent with previous work showing that high inflammation in patients with depression is associated with metabolic alterations, which together predict response to both traditional and experimental antidepressant therapies. Additionally, our findings suggest a causal relationship between increased inflammation and high cholesterol in depression, as a single infusion of infliximab reduced cholesterol in TRD patients with high CRP compared to placebo.
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Affiliation(s)
- Mandakh Bekhbat
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States
| | - Karen Chu
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States
| | - Ngoc-Anh Le
- Biomarker Core Laboratory, Atlanta VAMC, Decatur, GA, 30033, United States
| | - Bobbi J Woolwine
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States
| | - Ebrahim Haroon
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States; The Winship Cancer Institute, Emory University, Atlanta, GA, 30322, United States
| | - Andrew H Miller
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States; The Winship Cancer Institute, Emory University, Atlanta, GA, 30322, United States
| | - Jennifer C Felger
- Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, 30322, United States; The Winship Cancer Institute, Emory University, Atlanta, GA, 30322, United States.
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Levenson AE, Haas ME, Miao J, Brown RJ, de Ferranti SD, Muniyappa R, Biddinger SB. Effect of Leptin Replacement on PCSK9 in ob/ob Mice and Female Lipodystrophic Patients. Endocrinology 2016; 157:1421-9. [PMID: 26824363 PMCID: PMC4816729 DOI: 10.1210/en.2015-1624] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Leptin treatment has beneficial effects on plasma lipids in patients with lipodystrophy, but the underlying mechanism is unknown. Proprotein convertase subtilisin/kexin type 9 (PCSK9) decreases low-density lipoprotein (LDL) clearance, promotes hypercholesterolemia, and has recently emerged as a novel therapeutic target. To determine the effect of leptin on PCSK9, we treated male and female ob/ob mice with leptin for 4 days via sc osmotic pumps (∼24 μg/d). Leptin reduced body weight and food intake in all mice, but the effects of leptin on plasma PCSK9 and lipids differed markedly between the sexes. In male mice, leptin suppressed PCSK9 but had no effect on plasma triglycerides or cholesterol. In female mice, leptin suppressed plasma triglycerides and cholesterol but had no effect on plasma PCSK9. In parallel, we treated female lipodystrophic patients (8 females, ages 5-23 y) with sc metreleptin injections (∼4.4 mg/d) for 4-6 months. In this case, leptin reduced plasma PCSK9 by 26% (298 ± 109 vs 221 ± 102 ng/mL; n = 8; P = .008), and the change in PCSK9 was correlated with a decrease in LDL cholesterol (r(2) = 0.564, P = .03). In summary, in leptin-deficient ob/ob mice, the effects of leptin on PCSK9 and plasma lipids appeared to be independent of one another and strongly modified by sex. On the other hand, in lipodystrophic females, leptin treatment reduced plasma PCSK9 in parallel with LDL cholesterol.
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Affiliation(s)
- Amy E Levenson
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Mary E Haas
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Ji Miao
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Rebecca J Brown
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Sarah D de Ferranti
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Ranganath Muniyappa
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
| | - Sudha B Biddinger
- Division of Endocrinology (A.E.L., M.E.H., J.M., S.B.B.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Diabetes, Endocrinology, and Obesity Branch (R.J.B., R.M.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892; and Department of Cardiology (S.D.d.F.), Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115
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Arshadi S, Azarbayjani MA, Hajaghaalipor F, Yusof A, Peeri M, Bakhtiyari S, Stannard RS, Osman NAA, Dehghan F. Evaluation of Trigonella foenum-graecum extract in combination with swimming exercise compared to glibenclamide consumption on type 2 Diabetic rodents. Food Nutr Res 2015; 59:29717. [PMID: 26699937 PMCID: PMC4689800 DOI: 10.3402/fnr.v59.29717] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 11/30/2015] [Accepted: 12/01/2015] [Indexed: 12/31/2022] Open
Abstract
Background/objective The purpose of the present study was to evaluate the effect of fenugreek seed extract in combination with swimming exercise compared to glibenclamide consumption on type 2 diabetic rats. Design The acute toxicity test was carried out to choose the safe doses and identify the toxicity effects of the fenugreek seed extract. To investigate the hypoglycemic effect of the extract and its effect in combination with swimming training, 80 Wistar Kyoto male streptozotocin-induced diabetic rats were divided randomly into eight groups: diabetic control (C); fenugreek seed extract 0.8 g/kg (F1); fenugreek extract 1.6 g/kg (F2); swimming training (S); swimming training plus fenugreek extract 0.8 g/kg (SF1); swimming training plus fenugreek extract 1.6 g/kg (SF2); glibenclamide (G) and swimming training plus glibenclamide (SG). The rats were orally administrated with the treatments once a day with the respective treatment, and the training groups were subjected to swimming training every day for 60 min. Fasting blood samples were collected to measure fasting blood glucose, lipid profile, adiponectin, leptin, and insulin concentrations. Results The results obtained from acute toxicity study showed no toxicity effect of fenugreek seed extract on the tested dose. Biochemical analysis showed significant improvements in all of the groups compared to the control group (p<0.05). Plasma insulin concentration and insulin resistance (HOMA-IR) was significantly reduced in treated groups compared with the diabetic control group. Plasma leptin were significantly decreased in treated groups compared with the control group; while adiponectin had markedly increased (p<0.05). Conclusion The findings suggest that fenugreek seed consuming, alongside swimming exercise, has a strong therapeutic effect on the improvement of diabetic parameters.
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Affiliation(s)
- Sajad Arshadi
- Exercise Physiology Department, Faculty of Physical Education, Islamic Azad University South Tehran Branch, Tehran, Iran
| | | | - Fatemeh Hajaghaalipor
- Department of Molecular Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia
| | - Ashril Yusof
- Department of Exercise Science, Sports Centre, University of Malaya, Kuala Lumpur, Malaysia
| | - Maghsoud Peeri
- Exercise Physiology Department, Islamic Azad University Central Tehran Branch, Tehran, Iran
| | - Salar Bakhtiyari
- Department of Clinical Biochemistry, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran
| | - Robert S Stannard
- School of Sport and Exercise, Massey University, Palmerston North, New Zealand
| | - Noor Azuan Abu Osman
- Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia
| | - Firouzeh Dehghan
- Department of Exercise Science, Sports Centre, University of Malaya, Kuala Lumpur, Malaysia;
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Abstract
INTRODUCTION Leptin, a 16 kDa anti-obesity hormone, exhibits various physiological properties. Interestingly, skin wound healing was proven to delay in leptin-deficient ob/ob mice. However, little is known on the mechanisms of this phenomenon. In this study, we attempted to elucidate a role of leptin in wound healing of skin. METHODS Immunohistochemical analysis was performed to confirm the expression of the leptin receptor (Ob-R) in human and mouse skin. Leptin was topically administered to chemical wounds created in mouse back skin along with sustained-release absorbable hydrogel. The process of wound repair was histologically observed and the area of ulceration was measured over time. The effect of leptin on the proliferation, differentiation and migration of human epidermal keratinocytes was investigated. RESULTS Ob-R was expressed in epidermal cells of human and mouse skin. Topical administration of leptin significantly promoted wound healing. Histological analysis showed more blood vessels in the dermal connective tissues in the leptin-treated group. The proliferation, differentiation/function and migration of human epidermal keratinocytes were enhanced by exogenous leptin. CONCLUSION Topically administered leptin was proven to promote wound healing in the skin by accelerating proliferation, differentiation/function and migration of epidermal keratinocytes and enhancing angiogenesis around the wounded area. These results strongly suggest that topical administration of leptin may be useful as a treatment to promote wound healing in the skin.
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Umeki H, Tokuyama R, Ide S, Okubo M, Tadokoro S, Tezuka M, Tatehara S, Satomura K. Leptin promotes wound healing in the oral mucosa. PLoS One 2014; 9:e101984. [PMID: 25033454 PMCID: PMC4102470 DOI: 10.1371/journal.pone.0101984] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Accepted: 06/13/2014] [Indexed: 01/02/2023] Open
Abstract
INTRODUCTION Leptin, a 16 kDa circulating anti-obesity hormone, exhibits many physiological properties. Recently, leptin was isolated from saliva; however, its function in the oral cavity is still unclear. In this study, we investigated the physiological role of leptin in the oral cavity by focusing on its effect on wound healing in the oral mucosa. METHODS Immunohistochemical analysis was used to examine the expression of the leptin receptor (Ob-R) in human/rabbit oral mucosa. To investigate the effect of leptin on wound healing in the oral mucosa, chemical wounds were created in rabbit oral mucosa, and leptin was topically administered to the wound. The process of wound repair was histologically observed and quantitatively analyzed by measuring the area of ulceration and the duration required for complete healing. The effect of leptin on the proliferation, differentiation and migration of human oral mucosal epithelial cells (RT7 cells) was investigated using crystal violet staining, reverse transcription polymerase chain reaction (RT-PCR) and a wound healing assay, respectively. RESULTS Ob-R was expressed in spinous/granular cells in the epithelial tissue and vascular endothelial cells in the subepithelial connective tissue of the oral mucosa. Topical administration of leptin significantly promoted wound healing and shortened the duration required for complete healing. Histological analysis of gingival tissue beneath the ulceration showed a denser distribution of blood vessels in the leptin-treated group. Although the proliferation and differentiation of RT7 cells were not affected by leptin, the migration of these cells was accelerated in the presence of leptin. CONCLUSION Topically administered leptin was shown to promote wound healing in the oral mucosa by accelerating epithelial cell migration and enhancing angiogenesis around the wounded area. These results strongly suggest that topical administration of leptin may be useful as a treatment to promote wound healing in the oral mucosa.
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Affiliation(s)
- Hirochika Umeki
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Reiko Tokuyama
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Shinji Ide
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Mitsuru Okubo
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Susumu Tadokoro
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Mitsuki Tezuka
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Seiko Tatehara
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
| | - Kazuhito Satomura
- Department of Oral Medicine and Stomatology, Tsurumi University School of Dental Medicine, Yokohama, Kanagawa, Japan
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Dong H, Wang S, Jia Y, Ni Y, Zhang Y, Zhuang S, Shen X, Zhao R. Long-term effects of subacute ruminal acidosis (SARA) on milk quality and hepatic gene expression in lactating goats fed a high-concentrate diet. PLoS One 2013; 8:e82850. [PMID: 24376594 PMCID: PMC3871605 DOI: 10.1371/journal.pone.0082850] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 10/28/2013] [Indexed: 12/11/2022] Open
Abstract
PURPOSE The mechanism underlying the decline in milk quality during periods of feeding high-concentrate diets to dairy ruminants is not well documented. The aim of this study was to investigate the metabolic changes in the liver that contribute to the input of substrate precursors to the mammary gland after feeding a high-concentrate diet to lactating goats for a long period. EXPERIMENTAL DESIGN Eight mid-lactating goats with rumen cannulas were randomly assigned to two groups. For 9 weeks, the treatment group was fed a high-concentrate diet (60% concentrate of dry matter, HC) and the control group was fed a low-concentrate diet (40% concentrate of dry matter, LC). Ruminal fluid, plasma, and liver tissues were sampled, microarray techniques and real-time polymerase chain reaction were used to evaluate metabolic parameters and gene expression in liver. RESULTS Feeding a 60%-concentrate diet for 9 weeks resulted in a significant decrease in rumen pH. Changes in fat and protein content also occurred, which negatively affected milk quality. Plasma levels of leptin (p = 0.058), non-esterified fatty acid (p = 0.071), and glucose (p = 0.014) increased markedly in HC group. Plasma cortisol concentration was significantly elevated in the treatment group (p<0.05). Expression of the glucocorticoid receptor protein gene was significantly down-regulated (p<0.05) in the liver. The expression of genes for interleukin 1β, serum amyloid A, C-reactive protein, and haptoglobin mRNA was significantly increased (p<0.05) in the HC group. GeneRelNet analysis showed that gene expression involved in inflammatory responses and the metabolism of lipids, protein, and carbohydrate were significantly altered by feeding a high-concentrate diet for 9 weeks. CONCLUSIONS Activation of the acute phase response and the inflammatory response may contribute to nutrient partitioning and re-distribution of energy in the liver, and ultimately lead to a decline in milk quality.
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Affiliation(s)
- Haibo Dong
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Shaoqing Wang
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Yuanyuan Jia
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Yingdong Ni
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
- * E-mail:
| | - Yuanshu Zhang
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Su Zhuang
- College of Animal Sciences and Technology, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Xiangzhen Shen
- Institute of Small Animal Disease, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, Jiangsu, China
| | - Ruqian Zhao
- Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, Jiangsu, China
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Habitante CA, Oyama LM, Bueno AA, Ribeiro EB, Estadella D, Dâmaso AR, Nascimento CMOD. Exercise training in rats impairs the replenishment of white adipose tissue after partial lipectomy. Eur J Appl Physiol 2010; 109:371-7. [PMID: 20112028 DOI: 10.1007/s00421-010-1358-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/08/2010] [Indexed: 11/29/2022]
Abstract
The aim of this study was to evaluate the effect of exercise training on the metabolism of rats following the partial removal of fat pads. Three-month-old male Wistar rats were subjected to the partial removal (L) of retroperitoneal white adipose tissue (RET) and epididymal white adipose tissue (EPI), or a sham operation (Sh). Seven days after surgery, both sets of rats were subdivided into exercised (LE or ShE) (swimming 90 min/day, 5 days/week, 6 weeks) and sedentary (LS or ShS) groups. Partial removal of the fat pads increased the lipogenesis rates in both the RET and EPI and decreased the weight and lypolysis rate of the EPI, while the RET weight was not significantly affected by lipectomy. In both lipectomized and sham-operated groups, exercise training caused a reduction in carcass lipid content, food intake, RET and EPI weights, and RET lipogenesis rate. On the other hand, the exercise training increased the percentage of diet-derived lipid accumulation in both tissues, either in sham and lipectomized rats. These results confirmed that regrowth is not uniform and depends on the particular fat pad that is excised. They also demonstrated that exercise training following the partial removal of fat pads modified adipose tissue metabolism, impaired the replenishment of adipose tissue, and decrease body adiposity.
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Affiliation(s)
- Carlos A Habitante
- Institute of Biological and Health Science, Universidade Federal do Mato Grosso, Mato Grosso, MT, Brazil
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Penn DM, Jordan LC, Kelso EW, Davenport JE, Harris RBS. Effects of central or peripheral leptin administration on norepinephrine turnover in defined fat depots. Am J Physiol Regul Integr Comp Physiol 2006; 291:R1613-21. [PMID: 16840651 DOI: 10.1152/ajpregu.00368.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Leptin preserves lean tissue but decreases adipose tissue by increasing lipolysis and/or inhibiting lipogenesis. The sympathetic nervous system (SNS) is a primary regulator of lipolysis, but it is not known if leptin increases norepinephrine turnover (NETO) in white adipose tissue. In this study, we examined the effect of leptin administered either as a chronic physiological dose (40 microg/day for 4 days from ip miniosmotic pumps) or as an acute injection in the third ventricle (1.5 microg injected two times daily for 2 days) on NETO and the size of brown and white fat depots in male Sprague Dawley rats. NETO was determined from the decline in tissue norepinephrine (NE) during 4 h following administration of the NE synthesis inhibitor alpha-methyl-para-tryrosine. The centrally injected leptin-treated animals demonstrated more dramatic reductions in food intake, body weight, and fat pad size and an increase in NETO compared with the peripherally infused animals. Neither route of leptin administration caused a uniform increase in NETO across all fat pads tested, and in both treatment conditions leptin decreased the size of certain fat pads independent of an increase in NETO. Similar discrepancies in white fat NETO were found for rats pair fed to leptin-treated animals. These results demonstrate that leptin acting either centrally or peripherally selectively increases sympathetic outflow to white fat depots and that a leptin-induced change in fat pad weight does not require an increase in NETO.
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Affiliation(s)
- Dawn M Penn
- Department of Foods and Nutrition, University of Georgia, Dawson Hall, Athens, GA 30602, USA.
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Nasri H, Shirani S, Baradaran A. Lipids in Association with Leptin in Maintenance Hemodialysis Patients. JOURNAL OF MEDICAL SCIENCES 2006. [DOI: 10.3923/jms.2006.173.179] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Dridi S, Ververken C, Hillgartner FB, Arckens L, Lutgarde A, Van der Gucht E, Cnops L, Decuypere E, Buyse J. FAS inhibitor cerulenin reduces food intake and melanocortin receptor gene expression without modulating the other (an)orexigenic neuropeptides in chickens. Am J Physiol Regul Integr Comp Physiol 2006; 291:R138-47. [PMID: 16455759 DOI: 10.1152/ajpregu.00899.2005] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Cerulenin, a natural fatty acid synthase (FAS) inhibitor, and its synthetic analog C75 are hypothesized to alter the metabolism of neurons in the hypothalamus that regulate ingestive behavior to cause a profound decrease of food intake and an increase in metabolic rate, leading to body weight loss. The bulk of data exclusively originates from mammals (rodents); however, such effects are currently lacking in nonmammalian species. We have, therefore, addressed this issue in broiler chickens because this species is selected for high growth rate and high food intake and is prone to obesity. First, we demonstrate that FAS messenger and protein are expressed in the hypothalamus of chickens. FAS immunoreactivity was detected in a number of brain regions, including the nucleus paraventricularis magnocellularis and the nucleus infundibuli hypothalami, the avian equivalent of the mammalian arcuate nucleus, suggesting that FAS may be involved in the regulation of food intake. Second, we show that hypothalamic FAS gene expression was significantly (P < 0.05) decreased by overnight fasting similar to that in liver, indicating that hypothalamic FAS gene is regulated by energy status in chickens. Finally, to investigate the physiological consequences of in vivo inhibition of fatty acid synthesis on food intake, we administered cerulenin by intravenous injections (15 mg/kg) to 2-wk-old broiler chickens. Cerulenin administration significantly reduced food intake by 23 to 34% (P < 0.05 to P < 0.0001) and downregulated FAS and melanocortin receptors 1, 4, and 5 gene expression (P < 0.05). However, the known orexigenic (neuropeptide Y, agouti gene-related peptide, orexin, and orexin receptor) and anorexigenic (pro-opiomelanocortin and corticotropin-releasing hormone) neuropeptide mRNA levels remained unchanged after cerulenin treatment. These results suggest that the catabolic effect of cerulenin in chickens may be mediated through the melanocortin system rather than the other neuropeptides known to be involved in food intake regulation.
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Affiliation(s)
- Sami Dridi
- Laboratory of Physiology and Immunology of Domestic Animals, Catholic University of Leuven, Heverlee, Belgium.
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Lulu Strat A, Kokta TA, Dodson MV, Gertler A, Wu Z, Hill RA. Early signaling interactions between the insulin and leptin pathways in bovine myogenic cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1744:164-75. [PMID: 15950750 DOI: 10.1016/j.bbamcr.2005.03.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2005] [Revised: 02/18/2005] [Accepted: 03/16/2005] [Indexed: 11/25/2022]
Abstract
Cross-talk between hormone signaling pathways provides mechanisms to facilitate flexibility in the cellular response to extracellular conditions. One function of insulin is to signal high extracellular glucose, while leptin may signal the abundance of extracellular lipid, both energy sources being readily utilized by muscle. The present study reports early signaling events in the insulin and leptin cascades in primary bovine myogenic cells (BMC). BMC were treated with insulin, or leptin for 1, 10, 30 and 120 min, or pretreated with leptin for 10 min followed by insulin for 1, 10, 30 and 120 min. BMC were insulin resistant, showing a significant inhibition of IRS-1 association with the insulin receptor (IR) following insulin stimulation, a corresponding increase in PI 3-kinase association with the IR, and a slow and modest increase in GLUT4 recruitment to the plasma membrane. Pretreatment of BMC for 10 min leptin, followed by insulin time-course, caused IRS-1 recruitment to be unresponsive, but evoked a rapid, phasic response of PI 3-kinase recruitment to the IR and abrogated the response of GLUT4 translocation to the plasma membrane evoked by insulin alone. The lack of insulin response was independent of IR abundance or affinity. JAK-2 association with the ObR and JAK-2 tyrosine phosphorylation were responsive to all three treatments. Insulin alone down-regulated the leptin signaling pathway, JAK-2 association with ObR decreased at all time-points, and JAK-2 phosphorylation decreased similarly. Leptin alone also appeared to down-regulate JAK-2 association with the ObR, but stimulated the down-regulated pathway to signal, JAK-2 tyrosine phosphorylation being increased at later time-points. Pretreatment with leptin followed by insulin time-course showed marked up-regulation of the early leptin signaling pathway, JAK-2 association with the ObR being increased by insulin while JAK-2 tyrosine phosphorylation was also increased. The contrasting responses of BMC to insulin alone, leptin alone and the sequential leptin-insulin treatment may point to the ability of these cells to respond to energy substrate availability, as bovine muscle has evolved to utilize lipids and fatty acids in response to a metabolism which provides only limited glucose. This cross-talk between insulin and leptin signaling pathways points to a better understanding of the mechanisms driving energy substrate utilization in ruminant muscle and may provide a useful model for greater understanding of the molecular mechanisms underlying the development of insulin resistance and Type 2 diabetes in man.
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Affiliation(s)
- A Lulu Strat
- Department of Animal and Veterinary Science, University of Idaho, Moscow, 8344, USA
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12
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Abstract
Obesity, a state of apparent "leptin resistance" is well known to be associated with insulin resistance. In diet-induced obesity (DIO), hepatic insulin signaling is impaired but the link between leptin and insulin signaling pathways is only incompletely defined. The aim of the present study was to evaluate the effects of DIO on leptin and insulin cross-signaling in the liver. Leptin receptor expression was measured by in situ hybridization with pan-leptin receptor probes and by immunoblotting. Furthermore, intracellular signaling was investigated in vivo under basal conditions and at 45 and 360 min after stimulation with a bolus of human recombinant leptin (hrec-leptin; 1 mg/kg body wt) or saline. At baseline, all forms of the leptin receptor were markedly to completely down-regulated in DIO rats. Hrec-leptin bolus injection stimulated leptin-dependent signaling with a fivefold increase in JAK-2pY in lean but not in DIO rats. Basal IRpY, IRS-1pY, IRS-1p85, IRS-2pY, IRSp85, and PKBpT308 levels were reduced (P<0.01) in DIO rats as compared with lean controls. Basal GSK-3beta serine phosphorylation (S9) was higher (P<0.01) in lean animals along with lower basal PEPCK activity compared with DIO rats consistent with the insulin and leptin resistance of the latter. Only in lean animals phosphorylation of PKB (T308) and GSK-3beta (S9) was acutely stimulated by leptin at 45 min followed by inhibition at 6 h after application. AMPKalpha protein levels as well as basal and leptin-stimulated total and alpha-specific AMPK activity were comparable in both groups. These data show that in a model of dietary-induced obesity 1) leptin receptors and subsequent signaling events are down-regulated, 2) basal insulin signaling is impaired, and 3) the cross-talk between leptin and insulin signaling is differentially regulated by the nutritional status, which is sensed by AMPK in rat liver. Thus, the liver seems to play a major role in the modulation of the leptin signal and insulin resistance in obesity.
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Affiliation(s)
- Georg Brabant
- Department of Gastroenterology, Hepatology and Endocrinology, Hannover Medical School, Hannover, Germany.
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13
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Rooks CR, Penn DM, Kelso E, Bowers RR, Bartness TJ, Harris RBS. Sympathetic denervation does not prevent a reduction in fat pad size of rats or mice treated with peripherally administered leptin. Am J Physiol Regul Integr Comp Physiol 2005; 289:R92-102. [PMID: 15731403 DOI: 10.1152/ajpregu.00858.2004] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Leptin increases sympathetic nervous system (SNS) activity in brown adipose tissue and renal nerves. Experiments described here tested whether SNS innervation is required for peripheral, physiological concentrations of leptin to reduce body fat. In experiment 1, one epididymal (EPI) fat pad was sympathectomized by local injection of 6-hydroxydopamine (6OHDA) in C57BL/6 mice that were then infused for 13 days with PBS or 10 microg leptin/day from an intraperitoneal miniosmotic pump. Surprisingly, EPI denervation increased total body fat of PBS-infused mice but leptin decreased the size of both injected and noninjected EPI pads in 6OHDA mice. Experiment 2 was identical except for the use of male Sprague-Dawley rats that were infused with 50 microg leptin/day. Leptin had little effect on EPI weight or norepinephrine (NE) content, but denervation of one EPI pad decreased the effect of leptin on intact EPI, inguinal and retroperitoneal (RP) fat and increased the size of the mesenteric fat pad. Experiment 3 included groups in which either one EPI or one RP pad was denervated. RP denervation reduced RP NE content but did not prevent a leptin-induced reduction in fat pad mass. Therefore, the SNS is not required for low doses of leptin to reduce body fat. EPI denervation significantly increased adipocyte number in contralateral EPI and RP fat pads and this was prevented by leptin. These changes in intact pads of rats with one denervated fat pad imply communication between fat depots and suggest that both leptin and the SNS regulate the size of individual depots.
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Affiliation(s)
- Cherie R Rooks
- Department of Foods and Nutrition, Dawson Hall, University of Georgia, Athens, GA 30602, USA
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14
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Abstract
Muscle contains the largest reservoir of glycogen (Glyc), a depot that is closely regulated and with influence on insulin sensitivity. The current study examines muscle Glyc in type 2 diabetes mellitus (T2DM) and obesity and with respect to muscle fiber type, intramyocellular lipid content (IMCL), and mitochondrial function (oxidative enzyme activity; OX-Enz). There is increasing interest in the relation of IMCL and mitochondrial dysfunction with insulin resistance (IR), yet the association with muscle Glyc has not been examined with regard to these parameters. Using a quantitative histological approach specific to muscle fiber types, we assessed muscle Glyc, IMCL, and OX-Enz in vastus lateralis obtained by percutaneous biopsy in lean nondiabetic (L; n = 16), obese nondiabetic (Ob; n = 15), and T2DM volunteers (n = 14). Insulin sensitivity was estimated using homeostasis model assessment (HOMA)-IR. Muscle Glyc was reduced in T2DM, a deficit evident for type IIa fibers, yet minor in types I and IIb fibers. Low Glyc in T2DM correlated with fasting hyperglycemia. Also, in T2DM and Ob, there was significantly higher IMCL and lower OX-Enz in all fiber types. The IMCL-to-OX-Enz ratio, especially for type I fibers, correlated strongly with IR. Similarly, a Glyc-to-OX-Enz ratio correlated with IR, particularly for type IIb fibers. This ratio tended to be higher in Ob and T2DM. In summary, there is decreased muscle Glyc in T2DM yet a disproportional Glyc-to-OX-Enz relationship that is related to IR, although not as robustly as the IMCL-to-OX-Enz ratio.
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Affiliation(s)
- Jing He
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
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15
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Maloney CA, Gosby AK, Phuyal JL, Denyer GS, Bryson JM, Caterson ID. Site-specific changes in the expression of fat-partitioning genes in weanling rats exposed to a low-protein diet in utero. OBESITY RESEARCH 2003; 11:461-8. [PMID: 12634446 DOI: 10.1038/oby.2003.63] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVE Intrauterine growth restriction is associated with increased prevalence of the metabolic syndrome in adult life, including increased adiposity. The aim of this study was to investigate if maternal protein energy malnutrition is associated with changes in expression of genes involved in fat partitioning in weanling rats. RESEARCH METHODS AND PROCEDURES Time-mated mothers were placed on one of two isocaloric diets, low protein [(LP), 8% protein] or control (20% protein). All mothers remained on the diet throughout pregnancy and lactation. A third group received control for 2 weeks and was switched to LP for the last week of pregnancy and lactation [late low protein (LLP) group]. Offspring were analyzed at weaning for serum glucose, nonesterified fatty acids, triglyceride, and insulin. Expression of the genes acetyl-coenzyme A carboxylase, fatty acid synthase, and carnitine palmitoyl transferase 1 were measured in liver, quadriceps muscle, and subcutaneous white adipose tissue using semiquantitative reverse transcription-polymerase chain reaction. RESULTS LLP and LP offspring were shorter, weighed less, had reduced serum insulin and nonesterified fatty acids, and had increased serum glucose, serum triglycerides, and hepatic triglycerides. Hepatic gene expression of acetyl-coenzyme A carboxylase and fatty acid synthase was increased 2-fold in LLP and LP offspring (p < 0.001). These changes were not seen in muscle or subcutaneous white adipose tissue. CPT-1 gene expression was unaltered in all tissues examined. DISCUSSION Maternal protein energy malnutrition programs gene expression of lipogenic enzymes in the liver of weanling offspring in a manner favoring fat synthesis that may predispose these offspring to fat accumulation and insulin resistance later in life.
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Affiliation(s)
- Chris A Maloney
- Human Nutrition Unit, School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales, Australia.
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16
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Margetic S, Gazzola C, Pegg GG, Hill RA. Leptin: a review of its peripheral actions and interactions. Int J Obes (Lond) 2002; 26:1407-33. [PMID: 12439643 DOI: 10.1038/sj.ijo.0802142] [Citation(s) in RCA: 619] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2001] [Revised: 04/02/2002] [Accepted: 05/27/2002] [Indexed: 12/11/2022]
Abstract
Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain.
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Affiliation(s)
- S Margetic
- Central Queensland University, School of Chemical and Biomedical Sciences, Queensland, Australia
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17
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Wu DM, Shen MH, Chu NF. Relationship between plasma leptin levels and lipid profiles among school children in Taiwan--the Taipei Children Heart Study. Eur J Epidemiol 2002; 17:911-6. [PMID: 12188009 DOI: 10.1023/a:1016280427032] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Leptin, an adipose tissue-derived of gene product, is important in energy metabolism. However, the role of leptin in the metabolism of lipids is still not clear in humans. The purpose of this study was to evaluate the association of plasma leptin concentrations and lipid profiles among school children in Taiwan. After multistage sampling of 85 junior high schools in Taipei, we randomly selected 1264 children (617 boys and 647 girls) aged 12-16 years for this study. We measured the anthropometric variables, lifestyle factors and biochemical parameters among these children. Anthropometric measurements included body height (BH) and weight (BW) and we calculated body mass index (BMI) as the ratio of the BW to the square of the BH, expressed in kg/m2. Plasma leptin levels were measured by radioimmunoassay. We also measured lipid profiles including serum total cholesterol (CHOL), triglyceride (TG), high density lipoprotein-cholesterol (HDL-C), apolipoprotein-A1 (Apo-A1), apolipoprotein-B (Apo-B), and lipoprotein(a) (Lp(a)) levels, and calculated low density lipoprotein-cholesterol (LDL-C) levels and CHOL to HDL-C ratio (TCHR). Girls had higher leptin, CHOL, TG, HDL-C, (LDL-C), Apo-A1, Apo-B, and Lp(a) levels and lower BMI than boys did. Plasma leptin concentrations were significantly positively correlated with TG, LDL-C, and Apo-B, but negatively with HDL-C and Apo-A1 in both the genders. Children with higher plasma leptin levels (>75th percentiles) have significantly higher TG, HDL-C, LDL-C, TCHR, and Apo-B than those with relatively lower leptin levels. In multivariate regression analyses, the association between plasma leptin level and lipid profiles (such as CHOL, TG, and Apo-B) were still significant (p < 0.05) even after adjusting for BMI among boys. However, this association became attenuated and insignificant among girls. Finally, in the model that included the standard covariates, plasma leptin was the most predictive of CHOL, TG and Apo-B levels among those school children in Taiwan. Our results suggest that plasma leptin and BMI were independently associated with the lipids and lipoprotein profiles among Taiwanese Children. In both genders, children in the top 25% of the leptin distribution have more adverse lipid and lipoprotein profiles.
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Affiliation(s)
- D M Wu
- Department of Public Health, Tri-Service General Hospital, National Defense Medical Center, Taipei, Taiwan, ROC
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18
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Diraison F, Dusserre E, Vidal H, Sothier M, Beylot M. Increased hepatic lipogenesis but decreased expression of lipogenic gene in adipose tissue in human obesity. Am J Physiol Endocrinol Metab 2002; 282:E46-51. [PMID: 11739082 DOI: 10.1152/ajpendo.2002.282.1.e46] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine whether increased lipogenesis contributes to human obesity, we measured (postabsorptive state), in lean and obese subjects, lipid synthesis (deuterated water method) and the mRNA concentration (RT-competitive PCR) in subcutaneous adipose tissue of fatty acid synthase (FAS) and sterol regulatory element-binding protein (SREBP)-1c. Before energy restriction, obese subjects had an increased contribution of hepatic lipogenesis to the circulating triglyceride pool (14.5 +/- 1.3 vs. 7.5 +/- 1.9%, P < 0.01) without enhancement of cholesterol synthesis. This increased hepatic lipogenesis represented an excess of 2-5 g/day of triglycerides, which would represent 0.7-1.8 kg on a yearly basis. The lipogenic capacity of adipose tissue appeared, on the contrary, decreased with lower FAS mRNA levels (P < 0.01) and a trend for decreased SREBP-1c mRNA (P = 0.06). Energy restriction in obese patients decreased plasma insulin (P < 0.05) and leptin (P < 0.05) and normalized hepatic lipogenesis. FAS mRNA levels were unchanged, whereas SREBP-1c increased. In conclusion, subjects with established obesity have an increased hepatic lipogenesis that could contribute to their excessive fat mass but no evidence for an increased lipogenic capacity of adipose tissue.
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Affiliation(s)
- Frédérique Diraison
- Institut National de la Santé et de la Recherche Médicale Unité 499, Faculté RTH Laennec, 69008 Lyon, France
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Steinberg GR, Dyck DJ. Development of leptin resistance in rat soleus muscle in response to high-fat diets. Am J Physiol Endocrinol Metab 2000; 279:E1374-82. [PMID: 11093926 DOI: 10.1152/ajpendo.2000.279.6.e1374] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Direct evidence for leptin resistance in peripheral tissues such as skeletal muscle does not exist. Therefore, we investigated the effects of different high-fat diets on lipid metabolism in isolated rat soleus muscle and specifically explored whether leptin's stimulatory effects on muscle lipid metabolism would be reduced after exposure to high-fat diets. Control (Cont, 12% kcal fat) and high-fat [60% kcal safflower oil (n-6) (HF-Saff); 48% kcal safflower oil plus 12% fish oil (n-3)] diets were fed to rats for 4 wk. After the dietary treatments, muscle lipid turnover and oxidation in the presence and absence of leptin was measured using pulse-chase procedures in incubated resting soleus muscle. In the absence of leptin, phospholipid, diacylglycerol, and triacylglycerol (TG) turnover were unaffected by the high-fat diets, but exogenous palmitate oxidation was significantly increased in the HF-Saff group. In Cont rats, leptin increased exogenous palmitate oxidation (21.4 +/- 5.7 vs. 11.9 +/- 1.61 nmol/g, P = 0.019) and TG breakdown (39.8 +/- 5.6 vs. 27.0 +/- 5.2 nmol/g, P = 0.043) and decreased TG esterification (132.5 +/- 14.6 vs. 177.7 +/- 29.6 nmol/g, P = 0.043). However, in both high-fat groups, the stimulatory effect of leptin on muscle lipid oxidation and hydrolysis was eliminated. Partial substitution of fish oil resulted only in the restoration of leptin's inhibition of TG esterification. Thus we hypothesize that, during the development of obesity, skeletal muscle becomes resistant to the effects of leptin, resulting in the accumulation of intramuscular TG. This may be an important initiating step in the development of insulin resistance common in obesity.
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Affiliation(s)
- G R Steinberg
- Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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