Evelyne Tarnus

The antioxidant properties of serum albumin

Free radicals are a normal component of cellular oxygen metabolism in mammals. However, free radical‐associated damage is an important factor in many pathological processes. Glycation and oxidative damage cause protein modifications, frequently observed in numerous diseases. Albumin represents a very abundant and important circulating antioxidant. This review brings together recent insights on albumin antioxidant properties. First, it focuses on the different activities of albumin concerning protein antioxidation. In particular, we describe the role of albumin in ligand binding and free radical‐trapping activities. In addition, physiological and pathological situations that modify the antioxidant properties of albumin are reported.

Bioactive phenolics and antioxidant propensity of flavedo extracts of Mauritian citrus fruits: Potential prophylactic ingredients for functional foods application

The flavedo extracts of twenty-one varieties of citrus fruits (oranges, satsumah, clementine, mandarins, tangor, bergamot, lemon, tangelos, kumquat, calamondin and pamplemousses) grown in Mauritius were examined for their total phenolic, flavonoid and vitamin C contents and antioxidant activities. Total phenolics correlated strongly with the trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant capacity (FRAP) and hypochlorous acid (HOCl) scavenging activity assays (r > 0.85). Based on their antioxidant activities in these three assays nine citrus fruits namely, one orange, clementine, tangor and pamplemousse variety, two tangelo varieties and three mandarin varieties, were further characterized for their flavanone, flavonol and flavone levels by HPLC and their antioxidant activities were assessed by the copper-phenanthroline and iron chelation assays. The flavanone, hesperidin, was present at the highest concentrations in all flavedo extracts except for pamplemousses where it was not detected. Contents in hesperidin ranged from 83 ± 0.06 to 234 ± 1.73 mg/g FW. Poncirin, didymin, diosmin, isorhoifolin and narirutin were also present in all extracts whereas naringin was present only in one mandarin variety. The nine flavedo extracts exhibited good DNA protecting ability in the cuphen assay with IC₅₀ values ranging from 6.3 ± 0.46 to 23.0 ± 0.48 mg FW/mL. Essentially the flavedos were able to chelate metal ions however, tangor was most effective with an IC₅₀ value of 9.1 ± 0.08 mg FW/mL. The flavedo extracts of citrus fruits represent a significant source of phenolic antioxidants with potential prophylactic properties for the development of functional foods.

Citrus Fruit Extracts Reduce Advanced Glycation End Products (AGEs)- and H2O2-Induced Oxidative Stress in Human Adipocytes

Diabetes is a reactive oxygen species (ROS)-mediated pathology, with a worldwide prevalence estimated to double by 2030. A major effort has been launched to find therapeutic means to improve health conditions of diabetic patients. Recent data show that supplemental natural antioxidants represent a potential strategy as adjunct therapy. Despite the major role of adipocytes in the etiology of diabetes, little is known about the effect of natural antioxidants on adipocyte response to oxidative stress. Using a diabetes-like oxidative stress model, the potential protective effect of antioxidative flavedo, albedo, and pulp extracts of (1) tangor Elendale (Citrus reticulata × Citrus sinensis) and (2) tangelo Minneola (C. reticulata × Citrus paradisis) was investigated on human adipocytes. Besides the retardation of free-radical-induced hemolysis of human erythrocytes, non-cytotoxic concentrations of tangelo and tangor flavedo extracts significantly reduced the levels of protein carbonyls in response to advanced glycation end products (AGEs) generated by albumin glycation in SW872 cells. Flavedo extracts lowered carbonyl accumulation in H2O2-treated adipocytes, while tangelo and tangor flavedo, albedo, and pulp extracts suppressed ROS production in SW872 cells with or without the addition of H2O2. Our results clearly show that Mauritian Citrus fruit extracts represent an important source of antioxidants, with a novel antioxidative role at the adipose tissue level.

Apolipoprotein E limits oxidative stress-induced cell dysfunctions in human adipocytes

Oxidative stress in adipose tissue constitutes a pathological process involved in obesity‐linked metabolic disorders. Apolipoprotein E (apoE), which exhibits antioxidant properties in plasma and brain, is highly produced by adipose tissue and adipocytes. In this study, we investigated the role of apoE in the human adipocyte response to oxidative stress. We first demonstrated that apoE secretion by adipocytes was stimulated by oxidative stress. We also observed that apoE overexpression protected adipocytes from hydrogen peroxide‐induced damages, by mitigating intracellular oxidation and exerting extracellular antioxidant properties. Our findings clearly show a novel antioxidant role for apoE in adipose tissue.

Effects of nutritional antioxidants on AAPH- or AGEs-induced oxidative stress in human SW872 liposarcoma cells.

High levels of oxidative stress were reported in obesity-linked type 2 diabetes and were associated with elevated formation of advanced glycation end products (AGEs). Many studies have focused on the effect of antioxidants on vascular and circulating cells such as macrophages. However, despite the major role of adipocytes in the etiology of diabetes, little is known about the effect of natural antioxidants on adipocyte response to oxidative stress. The present study reports the differential protective effects of plant nutrients toward adipose cells subjected to oxidative stress. Caffeic acid, quercetin, l-ascorbic acid, and α-tocopherol were tested on SW872 liposarcoma cells subjected to a free radical generator or to AGEs. Proliferation, viability, free radical formation, and superoxide dismutase expression were assessed in treated cells. Caffeic acid and quercetin appeared as the most potent antioxidant nutrients. Our findings clearly show a novel antioxidant role for caffeic acid and quercetin at the adipose tissue level. These new data confirm the beneficial role of phytotherapy as an interesting alternative mean for the development of novel therapeutical and nutritional strategy to prevent metabolic disorders inherent to obesity-linked diabetes.

High expression of apolipoprotein E impairs lipid storage and promotes cell proliferation in human adipocytes.

Apolipoprotein E (apoE), a key regulator of lipid metabolism, is highly produced by adipose tissue and adipocytes. However, there is little information about its role on adipocyte functions. Because apoE‐deficiency in adipocytes was shown to impair adipocyte differentiation, we investigated the consequences of apoE high expression on differentiation and proliferation of a human adipocytic cell line (SW872). SW872 cells were transfected with human apoE to induce a fivefold increase in apoE production and secretion. Adipocyte differentiation and proliferation were assayed by measuring lipid content, adipogenic gene expression, cell number, cell resistance to serum deprivation, and cell division kinetics. Cultured apoE‐transfected cells accumulated less triglycerides and less cholesterol than control cells. This decrease in lipid accumulation was associated with a strong downregulation of peroxisome proliferator‐activated receptors γ1 and γ2 and stearoyl‐CoA desaturase 1. The decrease in lipid accumulation was not dependent on the presence of lipids, lipoproteins, or PPAR‐γ agonists in the culture medium, nor was it observed with exogenously added apoE. Moreover, we observed that apoE‐transfected cells were more resistant to death induced by serum deprivation, and that these cells underwent more cell divisions than control cells. These results bring new evidence of apoE‐involvement in metabolic disorders at the adipocyte level. J. Cell. Biochem. 106: 608–617, 2009.

Effect of apoA-I on cholesterol release and apoE secretion in human mature adipocytes

BackgroundThe risk of cardiovascular disease is inversely correlated to level of plasma HDL-c. Moreover, reverse cholesterol transport (RCT) from peripheral tissues to the liver is the most widely accepted mechanism linked to the anti-atherosclerotic activity of HDL. The apolipoprotein A-I (apoA-I) and the ABC transporters play a key role in this process.Adipose tissue constitutes the bodys largest pool of free cholesterol. The adipose cell could therefore be regarded as a key factor in cholesterol homeostasis. The present study investigates the capacity of primary cultures of mature human adipocytes to release cholesterol and explores the relationships between apoA-I, ABCA1, and apoE as well as the signaling pathways that could be potentially involved.ResultsWe demonstrate that apoA-I induces a strong increase in cholesterol release and apoE secretion from adipocytes, whereas it has no transcriptional effect on ABCA1 or apoE genes. Furthermore, brefeldin A (BFA), an intracellular trafficking inhibitor, reduces basal cholesterol and apoE secretion, but does not modify induction by apoA-I. The use of statins also demonstrates that apoA-I stimulated cholesterol release is independent of HMG-CoA reductase activation.ConclusionOur work highlights the fact that adipose tissue, and particularly adipocytes, may largely contribute to RCT via a mechanism specifically regulated within these cells. This further supports the argument that adipose tissue must be regarded as a major factor in the development of cardiovascular diseases, in particular atherosclerosis.

Opinion: What is the scale on my histological drawings? A blood tip at la Reunion Island University

Several of our laboratories in Animal Physiology consist of having undergraduate students observe and draw histological preparations. Students are asked to view the slide, observe and locate the features that they will draw. Representations of the tissue in the physiology lessons and in the pre-laboratory settings help students identify structures. On their answer sheet, students should include above the drawing, a title and magnification under which they observed the slide. Actually students specify only the microscope magnification without taking into account the magnification factor of their drawing. In other words, we noticed that students drawing from identical slides wrote the same magnification (for example X100) despite very different drawings in size by students. In our laboratories in Physiology when students have to perform histological drawings, they are taught the importance of including a scale and a “blood tip” to do so is provided.