Huda, Shahzya Shahnaz
Metabolic pathways in normal and pre-eclamptic
MD thesis, University of Glasgow.
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Maternal metabolism undergoes dramatic changes in pregnancy in order to sustain and nourish the developing fetus. During healthy pregnancy the mother goes from an anabolic state in early pregnancy to a state of catabolism in late pregnancy with increased lipolysis together with a significant reduction in insulin sensitivity. Pre-eclampsia (PE) characterised by hypertension and proteinuria is a major cause of maternal and perinatal morbidity. There is acute ‘atherosis’ in PE placenta, and lipid accumulation within glomerular cells and liver. PE women have an early, excessive triglyceride and free fatty acid (FFA) rise and greater cardiovascular disease (CVD) risk in later life. The cause of these lipid abnormalities in PE is unknown but disordered adipocyte function including exaggerated lipolysis and aberrant release of adipokines (such as IL-6 and TNF alpha) is a major candidate pathway. Elevations in FFAs, and pro-inflammatory adipokines could underpin the oxidative stress, endothelial dysfunction, inflammation, and insulin resistance - characteristic features of PE.
The aims of this thesis were to acquire a better understanding of lipid metabolism and function in normal pregnancy, to determine if adipocyte function was altered in PE and, if so, to establish mechanisms. In addition I planned to corroborate epidemiological evidence of increased future CVD risk and to establish which risk factors accounted for this increased risk.
I collected subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) biopsies in non-labouring pregnant healthy (n=31) and PE (n=14) women who underwent caesarean section. Maternal blood was collected prior to delivery and phenotyping of the mother was performed including plasma assay for cholesterol, triglyceride, HDL-cholesterol, IL-6, TNF-α, leptin, adiponectin, high sensitivity CRP, glucose and insulin concentrations. Maternal BMI at booking, standardised blood pressure measurements and birth weight centile were also recorded. I determined ex vivo lipolytic activity (basal, isoprotenerol stimulated and insulin suppression of lipolysis) and adipokine production in response to lipopolysaccharide (LPS) stimulation from these biopsies. The gene expression of relevant target genes and macrophage densities in each adipose depot by immunocytochemistry (ICC) was also performed. In addition I performed carotid ultrasound assessment of women with a previous history of PE (n=31) and matched controls (n=29). Ethical approval was obtained from Glasgow Royal Infirmary LREC and all patients gave their informed consent.
I found that in normal pregnancy, adipocyte lipolytic function is independent of maternal BMI. Adipocyte lipolytic function of SAT and VAT are also independent of each other. Adipose tissue is very metabolically flexible and the rate of whole body lipolysis is still insulin sensitive in late gestation. VAT is more closely related to markers of maternal insulin resistance (IR) and is more sensitive to catecholamine stimulation and less sensitive to insulin suppression of lipolysis than SAT, the basis of the “portal paradigm”. Increasing BMI is associated with an increase in VAT cell size, with increased lipolysis and an increase in pro-inflammatory adipokines, a potential mechanism through which increasing obesity could predispose to metabolic complications of pregnancy. In contrast SAT cell size is not closely related to BMI and this may reflect the adaptation of this depot to increasing fat mass through both hypertrophy and hyperplasia, a metabolically advantageous response. TNF alpha is an important correlate of basal lipolysis in SAT.
In PE there is decreased insulin sensitivity of both SAT and VAT compared to controls as calculated by the fat cell insulin sensitivity index (or responsiveness to insulin once the tissue is stimulated by isoproterenol). This would potentially make a significant impact on total circulating FFA as almost 60% of circulating FFA are from these adipose depots. The rise in FFA in PE occurs early in pregnancy and contributes significantly to IR. Therefore the IR of adipose tissue could lead to a vicious cycle of increased lipolysis, increased FFA and further exacerbation of IR. In contrast to controls, SAT cell size is intimately related to BMI suggesting that adaptation to increasing fat mass is mainly through adipocyte hypertrophy which could lead to increased endoplasmic reticulum stress, increased IR and increased release of inflammatory adipokines. I have shown that SAT cell size does relate to adipokine release in PE, with increased release of leptin, CRP and PAI-1 and paradoxical increase in the anti-inflammatory IL-10. I had hypothesised that in addition to an inherent defect in adipocyte function there was an additional factor present in maternal serum of women with PE released from the placenta which excessively stimulated lipolysis. I failed to demonstrate any effect of maternal serum on adipocyte lipolysis in either controls or PE.
I also found that after stimulation with LPS, there was increased release of TNF alpha and IL-6 in VAT in PE but not in controls, with higher gene expression of these adipokines. TNF alpha release also correlated negatively with the fat cell insulin sensitivity index (FCISI) of VAT implicating a paracrine effect in this tissue. I also demonstrated an increase in gene expression of cfms (activated macrophages) relative to control gene, and increased density of cfms+ macrophages/adipocytes in the VAT of PE women implicating activated adipose tissue macrophages as a potential source of the increased release of inflammatory adipokines.
Lastly I attempted to corroborate epidemiological evidence for the increase future risk of CVD women with a history of PE by assessing two surrogate markers for atherosclerosis - carotid IMT and carotid plaque scores. Both were found to be increased, with plaque scores significantly so. Classic risk factors such as age, lipids, BP and smoking did not attenuate this effect and BMI only marginally attenuated it, therefore only partially explaining this increased risk.
In summary the data presented in this thesis provides further evidence that PE is a “metabolic syndrome of pregnancy” with disordered adipocyte function and metabolism, with an increased future risk of CVD in later life. Further studies on adipose accumulation, function and composition in normal and complicated human pregnancy are warranted.
||Pregnancy, pre-eclampsia, adipose tissue, subcutaneous fat, visceral fat, lipoysis, adipokines, carotid ultrasound, cardiovascular disease
||R Medicine > RG Gynecology and obstetrics
||College of Medical Veterinary and Life Sciences
||Sattar, Prof. Naveed and Freeman, Dr. Dilys J.
|Date of Award:
Dr Shahzya S Huda
||Copyright of this thesis is held by the author.
||09 May 2011
||10 Dec 2012 13:56
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