Gemma Macintosh

University of Adelaide, Tarndarnya, South Australia, Australia

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Publications (7)31.75 Total impact

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    ABSTRACT: Chronic saturated fatty acid (SFA) exposure causes β-cell apoptosis and thus contributes to Type 2 diabetes. Although endoplasmic reticulum (ER) stress and reduced ER-to-Golgi protein trafficking have been implicated, the exact mechanisms whereby SFA trigger β-cell death remain elusive. Using mass spectroscopic lipidomics and subcellular fractionation we now demonstrate that palmitate pre-treatment of MIN6 β-cells promoted ER remodelling of both phospholipids and sphingolipids, but only the latter was causally linked to lipotoxic ER stress. Thus overexpression of glucosylceramide synthase (GCS), previously shown to protect against defective protein trafficking and ER stress, partially reversed lipotoxic reductions in ER sphingomyelin (SM) content, and aggregation of ER lipid rafts as visualized using Erlin1-GFP. Using both lipidomics and a sterol response element reporter assay we confirmed that free cholesterol in the ER was also reciprocally modulated by chronic palmitate and GCS overexpression. This is consistent with the known co-regulation and association of SM and free cholesterol in lipid rafts. Inhibition of SM hydrolysis partially protected against ATF4/CHOP induction due to palmitate. Our results suggest that loss of SM in the ER is a key event for initiating β-cell lipotoxicity, which leads to disruption of ER lipid rafts, perturbation of protein trafficking, and initiation of ER stress.
    Journal of Biological Chemistry 07/2013; · 4.65 Impact Factor
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    ABSTRACT: The relationship between lipid metabolism with prediabetes (impaired fasting glucose and impaired glucose tolerance) and type 2 diabetes mellitus is poorly defined. We hypothesized that a lipidomic analysis of plasma lipids might improve the understanding of this relationship. We performed lipidomic analysis measuring 259 individual lipid species, including sphingolipids, phospholipids, glycerolipids and cholesterol esters, on fasting plasma from 117 type 2 diabetes, 64 prediabetes and 170 normal glucose tolerant participants in the Australian Diabetes, Obesity and Lifestyle Study (AusDiab) then validated our findings on 1076 individuals from the San Antonio Family Heart Study (SAFHS). Logistic regression analysis of identified associations with type 2 diabetes (135 lipids) and prediabetes (134 lipids), after adjusting for multiple covariates. In addition to the expected associations with diacylglycerol, triacylglycerol and cholesterol esters, type 2 diabetes and prediabetes were positively associated with ceramide, and its precursor dihydroceramide, along with phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol. Significant negative associations were observed with the ether-linked phospholipids alkylphosphatidylcholine and alkenylphosphatidylcholine. Most of the significant associations in the AusDiab cohort (90%) were subsequently validated in the SAFHS cohort. The aberration of the plasma lipidome associated with type 2 diabetes is clearly present in prediabetes, prior to the onset of type 2 diabetes. Lipid classes and species associated with type 2 diabetes provide support for a number of existing paradigms of dyslipidemia and suggest new avenues of investigation.
    PLoS ONE 01/2013; 8(9):e74341. · 3.73 Impact Factor
  • Biochemical Journal 11/2011; 439(3):517-8. · 4.65 Impact Factor
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    ABSTRACT: Traditional risk factors for coronary artery disease (CAD) fail to adequately distinguish patients who have atherosclerotic plaques susceptible to instability from those who have more benign forms. Using plasma lipid profiling, this study aimed to provide insight into disease pathogenesis and evaluate the potential of lipid profiles to assess risk of future plaque instability. Plasma lipid profiles containing 305 lipids were measured on 220 individuals (matched healthy controls, n=80; stable angina, n=60; unstable coronary syndrome, n=80) using electrospray-ionisation tandem mass spectrometry. ReliefF feature selection coupled with an L2-regularized logistic regression based classifier was used to create multivariate classification models which were verified via 3-fold cross-validation (1000 repeats). Models incorporating both lipids and traditional risk factors provided improved classification of unstable CAD from stable CAD (C-statistic=0.875, 95% CI 0.874-0.877) compared with models containing only traditional risk factors (C-statistic=0.796, 95% CI 0.795-0.798). Many of the lipids identified as discriminatory for unstable CAD displayed an association with disease acuity (severity), suggesting that they are antecedents to the onset of acute coronary syndrome. Plasma lipid profiling may contribute to a new approach to risk stratification for unstable CAD.
    Arteriosclerosis Thrombosis and Vascular Biology 09/2011; 31(11):2723-32. · 6.34 Impact Factor
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    ABSTRACT: Inflammation characterizes obesity and is nutritionally modifiable. The hypothesis of this study is that full-fat dairy foods influence circulating inflammatory and atherogenic biomarkers according to fermentation status. Thirteen overweight subjects participated in five test meals. Single breakfasts containing control low-fat milk or 45 g fat from butter, cream, yoghurt or cheese were tested over 3 weeks. Plasmas obtained 3 and 6 h were later analyzed for inflammatory markers interleukin (IL)-6, IL-1β, tumor necrosis factor-α and high-sensitive C-reactive protein, and atherogenesis-related markers monocyte chemoattractant protein-1, macrophage inflammatory protein-1α, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. A 4-week study in 12 subjects compared the effects on these biomarkers of diets containing ≈50 g dairy fat daily as either butter, cream and ice cream (non-fermented) or cheese plus yoghurt (fermented) dairy foods. In single-meal study, one outlier subject showed marked increments in biomarkers, hence the following results apply to 12. Within group analysis includes significant falls at 3 h in four inflammatory markers after cream, butter and low fat, and three atherogenesis-related biomarkers after cream. Changes were few after cheese and yoghurt. By 6 h, most values returned to baseline. However, between group analysis showed no differences between the five meals. The 4-week study showed no significant differences in fasting biomarker concentrations between non-fermented and fermented dairy diets. Single high-fat meals containing sequentially four different full-fat dairy foods did not increase eight circulating biomarkers related to inflammation or atherogenesis. Among subjects, significant falls occurred at 3 h in inflammatory biomarkers after cream and butter but were not specific for full-fat dairy foods. We could not confirm the reported increments in inflammation after fat meals.
    European journal of clinical nutrition 08/2011; 66(1):25-31. · 3.07 Impact Factor
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    ABSTRACT: Saturated fatty acids promote lipotoxic ER (endoplasmic reticulum) stress in pancreatic β-cells in association with Type 2 diabetes. To address the underlying mechanisms we employed MS in a comprehensive lipidomic screen of MIN6 β-cells treated for 48 h with palmitate. Both the overall mass and the degree of saturation of major neutral lipids and phospholipids were only modestly increased by palmitate. The mass of GlcCer (glucosylceramide) was augmented by 70% under these conditions, without any significant alteration in the amounts of either ceramide or sphingomyelin. However, flux into ceramide (measured by [3H]serine incorporation) was augmented by chronic palmitate, and inhibition of ceramide synthesis decreased both ER stress and apoptosis. ER-to-Golgi protein trafficking was also reduced by palmitate pre-treatment, but was overcome by overexpression of GlcCer synthase. This was accompanied by increased conversion of ceramide into GlcCer, and reduced ER stress and apoptosis, but no change in phospholipid desaturation. Sphingolipid alterations due to palmitate were not secondary to ER stress since they were neither reproduced by pharmacological ER stressors nor overcome using the chemical chaperone phenylbutyric acid. In conclusion, alterations in sphingolipid, rather than phospholipid, metabolism are more likely to be implicated in the defective protein trafficking and enhanced ER stress and apoptosis of lipotoxic β-cells.
    Biochemical Journal 01/2011; 435(1):267-76. · 4.65 Impact Factor
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    ABSTRACT: BMP [bis(monoacylglycero)phosphate] is an acidic phospholipid and a structural isomer of PG (phosphatidylglycerol), consisting of lysophosphatidylglycerol with an additional fatty acid esterified to the glycerol head group. It is thought to be synthesized from PG in the endosomal/lysosomal compartment and is found primarily in multivesicular bodies within the same compartment. In the present study, we investigated the effect of lysosomal storage on BMP in cultured fibroblasts from patients with eight different LSDs (lysosomal storage disorders) and plasma samples from patients with one of 20 LSDs. Using ESI-MS/MS (electrospray ionization tandem MS), we were able to demonstrate either elevations or alterations in the individual species of BMP, but not of PG, in cultured fibroblasts. All affected cell lines, with the exception of Fabry disease, showed a loss of polyunsaturated BMP species relative to mono-unsaturated species, and this correlated with the literature reports of lysosomal dysfunction leading to elevations of glycosphingolipids and cholesterol in affected cells, processes thought to be critical to the pathogenesis of LSDs. Plasma samples from patients with LSDs involving storage in macrophages and/or with hepatomegaly showed an elevation in the plasma concentration of the C(18:1)/C(18:1) species of BMP when compared with control plasmas, whereas disorders involving primarily the central nervous system pathology did not. These results suggest that the release of BMP is cell/tissue-specific and that it may be useful as a biomarker for a subset of LSDs.
    Biochemical Journal 05/2008; 411(1):71-8. · 4.65 Impact Factor