Medical Physiology

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Browsing Medical Physiology by Subject "Adipose tissues"

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    Evaluation of mitochondrial and molecular derangements in cardiac adipose tissue during type 2 diabetes and relationship with cardiovascular risk
    (Stellenbosch : Stellenbosch University, 2023-06) Nyawo, Thembeka Amanda; Pheiffer, Carmen; Mazibuko-Mbeje, Sithandiwe; Phiwayinkosi, Dludla; Hanel, Sadie Van Gijsen; Hans, Strijdom; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Division of Medical Physiology.
    ENGLISH ABSTRACT: Cardiovascular disease (CVD) affects hundreds of millions of people globally, and 18.6 million deaths were attributed to CVD during 2019 alone. Type 2 diabetes (T2D) and obesity contribute significantly towards the increasing prevalence of CVD. Ageing and adipose tissue dysfunction are important mechanisms in the pathology of these metabolic diseases and their downstream cardiovascular complications. The roles of visceral (VAT) and subcutaneous (SAT) adipose depots in T2D and CVD development have been well documented; however, there is limited evidence on the pathological contribution of cardiac fat (CF) to CVD. The aim of this study was to elucidate the role of CF, in comparison to retroperitoneal (RF) and inguinal (IF) fat depots, representatives of VAT and SAT, respectively, in the development and progression of CVD in an experimental mouse model of obesity and diabetes. The study used male obese, diabetic db/db mice and their lean db/+ counterparts to explore morphological features of CF, gene expression signatures, mitochondrial bioenergetics, and associations with CVD risk factors. Briefly, mice were monitored for 8, 12 and 18 weeks, during which body weight and fasting blood glucose concentrations were measured weekly. Glucose tolerance was assessed using the oral glucose tolerance test one week prior to euthanasia. Blood and tissue samples of the heart, CF, RF, and IF were collected for assessment of biochemical markers, histological examination using Haematoxylin and Eosin staining, and gene expression analysis using quantitative real time PCR. In addition, CF, RF and IF were harvested for the assessment of mitochondrial function in adipose-derived stromal cells (ADSCs). Phenotypic and metabolic parameters deteriorated with disease and age, where db/db mice displayed conditions of hyperglycaemia, hyperinsulinaemia, hyperlipidaemia and glucose intolerance with ageing. In addition, an age-related increase in adiponectin serum levels were observed in db/+ mice, while in db/db mice, adiponectin levels decreased with age. Furthermore, histological analysis showed that adipocyte size in all depots increased over time in both the non-diabetic and diabetic state. Adipose depot-, disease- and age-related changes in gene expression signatures in CF, RF and IF were observed, with RF and IF in db/db mice exhibiting upregulation of genes involved in inflammation and oxidative stress, while CF appears to possess increased expression of genes representing thermogenic capacity. Disease- and age-related differential regulation of circulating CVD risk markers were observed. Dysregulation of markers such as metalloproteinase 9 (MMP9), intercellular adhesion molecule 1 (ICAM1), platelet endothelial cell adhesion molecule 1 (Pecam1) and Thrombomodulin (THBD) suggested vascular remodelling and dysfunction during CVD progression. Moreover, circulating levels of MMP9, ICAM and P-Selectin positively correlated with CF adipocyte size. In heart tissue, signs of histological myocardial changes with microarchitecture disruption and the presence of intramyocardial lipid droplets in db/db mice were observed in with ageing. Moreover, gene expression analysis in heart tissue revealed a disease- and age- related downregulation of brain natriuretic peptide (BNP) levels in db/db mice. Furthermore, ADSCs from CF had higher mitochondrial bioenergetics parameters compared to ADSCs from RF. This may be attributed to the higher uncoupling protein 1 (UCP1) expression in CF which reportedly decreases oxidative phosphorylation through thermogenesis. In conclusion, the positive correlation between CVD risk markers with CF adipocyte size in the diabetic state indicates a relationship with CF, supporting the notion that increased CF adiposity is associated with increased CVD risk. Importantly, CF, unlike RF and IF, displays beige-like adipocytes and thermogenic capacity, which may help mitigate the harmful effects of diabetes and its cardiovascular complications.
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    Physical exercise potentially targets epicardial adipose tissue to reduce cardiovascular disease risk in patients with metabolic diseases : oxidative stress and inflammation emerge as major therapeutic targets
    (MDPI, 2021-11-04) Nyawo, Thembeka A.; Pheiffer, Carmen; Mazibuko-Mbeje, Sithandiwe E; Mthembu, Sinenhlanhla X. H.; Nyambuya, Tawanda M.; Nkambule, Bongani B.; Sadie-Van Gijsen, Hanel; Strijdom, Hans; Tiano, Luca; Dludla, Phiwayinkosi V.
    ENGLISH ABSTRACT: Excess epicardial adiposity, within a state of obesity and metabolic syndrome, is emerging as an important risk factor for the development of cardiovascular diseases (CVDs). Accordingly, increased epicardial fat thickness (EFT) implicates the exacerbation of pathological mechanisms involving oxidative stress and inflammation within the heart, which may accelerate the development of CVDs. This explains increased interest in targeting EFT reduction to attenuate the detrimental effects of oxidative stress and inflammation within the setting of metabolic syndrome. Here, we critically discuss clinical and preclinical evidence on the impact of physical exercise on EFT in correlation with reduced CVD risk within a setting of metabolic disease. This review also brings a unique perspective on the implications of oxidative stress and inflammation as major pathological consequences that link increased EFT to accelerated CVD risk in conditions of metabolic disease.
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    The therapeutic efficacy of ascorbic acid 2 phosphate, n-acetylcysteine and metformin against diabetes mellitus associated cellular senescence.
    (Stellenbosch : Stellenbosch University, 2023-03) Govender, Saiuree; Van de Vyver, Mari; Johnson, Rabia; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences. Division of Medical Physiology.
    ENGLISH ABSTRACT: Background: The incidence of diabetes mellitus (DM) is widespread. In DM, the systemic pathological microenvironment consists of elevated glucose levels (hyperglycaemia), advanced glycation end products (AGEs), chronic inflammation and oxidative stress. The combined effect of these factors inflicts DNA damage and induce premature cellular senescence. An accumulation of senescent cells within adipose tissue (amongst other) contribute to tissue dysfunction, disease progression and the development of comorbidities. The secretome of premature senescent cells namely, the senescence associated secretory phenotype (SASP) amplifies inflammation and oxidative stress through its paracrine action. There is thus a need for adjuvant treatments aimed at preventing disease progression by either preventing the onset of premature senescence or by restoring the function of senescent cells in DM. The purpose of this study was to develop a physiologically relevant in vitro model of premature cellular senescence associated with DM and investigate the therapeutic efficacy of different preventative and/or restorative therapies. Methods: In this research study, all experiments were conducted using a primary human adipose tissue derived stromal cell line (ADSCs). Serial passaging of ADSCs was performed to determine the point of onset for replicative senescence to rule it out as confounder. All subsequent experiments were conducted at low passages in healthy ADSCs. Cellular growth, morphology viability (crystal violet staining), and senescence (β-galactosidase (SA-β-gal) staining) were assessed in ADSCs following exposure to different concentrations of glucose (low 5mM; high 25mM), AGE-BSA (25, 50,100, 200, 400 µg/mL) and TNF-α (0.001, 0.005, 0.01, 0.02 µg/mL) in isolation or in combination for a period of 3 days. The optimal culture conditions using a combination of these factors were determined by quantifying the ratio of senescent to non-senescent cells. The SA-β-gal staining was corroborated by assessing the SASPs (IFNγ, TNF-α, IL1β, IL6, IL8, IL10) using a multiplex bead array cytokine assay to analyse the conditioned media derived from ADSCs. These results were further corroborated using quantitative polymerase chain reaction (qPCR) to assess the mRNA expression of p53, p16INK4A, p21cip1, TNF-α, IL6, PTX3, IL10, Arg1, NOS2, PPARγ, UCP3. The therapeutic effectiveness of N-acetylcysteine (NAC), Ascorbic acid 2 phosphate (AAP), and Metformin was evaluated using 3 different intervention strategies: a) pre-treatment prior to induction of senescence (preventative); b) combined intervention whilst inducing senescence; c) treatment following induction of senescence (restorative). A dose response experiment was performed to determine the highest non-toxic concentration of NAC (3.75mM) and AAP (0.6mM), whereas the human equivalent dose was used for Metformin (50 µg/mL). Results: Under high glucose (25mM) conditions, the exposure of ADSCs to a combination of AGE-BSA (400ug/mL) and TNF-α (0.02ug/mL) in culture for a period of 3 days, induced a 3- fold increase in the ratio of senescent to non-senescent cells. This observation was accompanied by a significant increase in the expression of SASP factors on both protein (IFNγ, TNF-α, IL1β, IL6, IL10) and mRNA level (TNF-α, IL6). Therapeutic intervention consisting of either pretreatment or restorative treatment with NAC, AAP or Metformin effectively reduced the ratio of senescent to non-senescent cells (SA-β-gal staining) compared to the induced premature senescent ADSCs without intervention. Conclusion: This study developed an in vitro model to induce premature cellular senescence by mimicking the DM microenvironment in culture. It was furthermore demonstrated that therapeutic intervention using either antioxidants such as NAC and AAP or the anti-diabetic drug, Metformin can potentially delay the onset of premature senescence and/or restore the function of senescent cells.