Iron Metabolism in Obesity and Metabolic Syndrome

Obesity is an excessive adipose tissue accumulation that may have detrimental effects on health. Particularly, childhood obesity has become one of the main public health problems in the 21st century, since its prevalence has widely increased in recent years. Childhood obesity is intimately related to the development of several comorbidities such as nonalcoholic fatty liver disease, dyslipidemia, type 2 diabetes mellitus, non-congenital cardiovascular disease, chronic inflammation and anemia, among others. Within this tangled interplay between these comorbidities and associated pathological conditions, obesity has been closely linked to important perturbations in iron metabolism. Iron is the second most abundant metal on Earth, but its bioavailability is hampered by its ability to form highly insoluble oxides, with iron deficiency being the most common nutritional disorder. Although every living organism requires iron, it may also cause toxic oxygen damage by generating oxygen free radicals through the Fenton reaction. Thus, iron homeostasis and metabolism must be tightly regulated in humans at every level (i.e., absorption, storage, transport, recycling). Dysregulation of any step involved in iron metabolism may lead to iron deficiencies and, eventually, to the anemic state related to obesity. In this review article, we summarize the existent evidence on the role of the most recently described components of iron metabolism and their alterations in obesity

Placental Adaptive Changes to Protect Function and Decrease Oxidative Damage in Metabolically Healthy Maternal Obesity

Pregnancy-related disorders, including preeclampsia and gestational diabetes, are characterized by the presence of an adverse intrauterine milieu that may ultimately result in oxidative and nitrosative stress. This scenario may trigger uncontrolled production of reactive oxygen species (ROS) such as superoxide anion (OBLACK CIRCLE-) and reactive nitrogen species (RNS) such as nitric oxide (NO), along with an inactivation of antioxidant systems, which are associated with the occurrence of relevant changes in placental function through recognized redox post-translational modifications in key proteins. The general objective of this study was to assess the impact of a maternal obesogenic enviroment on the regulation of the placental nitroso-redox balance at the end of pregnancy. We measured oxidative damage markers-thiobarbituric acid-reacting substances (TBARS) and carbonyl groups (C=O) levels; nitrosative stress markers-inducible nitric oxide synthase, nitrosothiol groups, and nitrotyrosine residues levels; and the antioxidant biomarkers-catalase and superoxide dismutase (SOD) activity and expression, and total antioxidant capacity (TAC), in full-term placental villous from both pre-pregnancy normal weight and obese women, and with absence of metabolic complications throughout gestation. The results showed a decrease in C=O and TBARS levels in obese pregnancies. Although total SOD and catalase concentrations were shown to be increased, both activities were significantly downregulated in obese pregnancies, along with total antioxidant capacity. Inducible nitric oxide sintase levels were increased in the obese group compared to the lean group, accompanied by an increase in nitrotyrosine residues levels and lower levels of nitrosothiol groups in proteins such as ERK1/2. These findings reveal a reduction in oxidative damage, accompanied by a decline in antioxidant response, and an increase via NO-mediated nitrative stress in placental tissue from metabolically healthy pregnancies with obesity. All this plausibly points to a placental adaptation of the affected antioxidant response towards a NO-induced alternative pathway, through changes in the ROS/RNS balance, in order to reduce oxidative damage and preserve placental function in pregnancy

Plant catalases as NO and H2S targets

Catalase is a powerful antioxidant metalloenzyme located in peroxisomes which also plays a central role in signaling processes under physiological and adverse situations. Whereas animals contain a single catalase gene, in plants this enzyme is encoded by a multigene family providing multiple isoenzymes whose number varies depending on the species, and their expression is regulated according to their tissue/organ distribution and the environmental conditions. This enzyme can be modulated by reactive oxygen and nitrogen species (ROS/RNS) as well as by hydrogen sulfide (H2S). Catalase is the major protein undergoing Tyr-nitration [post-translational modification (PTM) promoted by RNS] during fruit ripening, but the enzyme from diverse sources is also susceptible to undergo other activity-modifying PTMs. Data on S-nitrosation and persulfidation of catalase from different plant origins are given and compared here with results from obese children where S-nitrosation of catalase occurs. The cysteine residues prone to be S-nitrosated in catalase from plants and from bovine liver have been identified. These evidences assign to peroxisomes a crucial statement in the signaling crossroads among relevant molecules (NO and H2S), since catalase is allocated in these organelles. This review depicts a scenario where the regulation of catalase through PTMs, especially S-nitrosation and persulfidation, is highlighted

Ghrelin's effects on proinflammatory cytokine mediated apoptosis and their impact on β-cell functionality

Ghrelin is a peptidic hormone, which stimulates cell proliferation and inhibits apoptosis in several tissues, including pancreas. In preclinical stage of type 1 diabetes, proinflammatory cytokines generate a destructive environment for β-cells known as insulitis, which results in loss of β-cell mass and impaired insulin secretion, leading to diabetes. Our aim was to demonstrate that ghrelin could preserve β-cell viability, turnover rate, and insulin secretion acting as a counter balance of cytokines. In the present work we reproduced proinflammatory milieu found in insulitis stage by treating murine cell line INS-1E and rat islets with a cytokine cocktail including IL-1β, IFNγ, and TNFα and/or ghrelin. Several proteins involved in survival pathways (ERK 1/2 and Akt/PKB) and apoptosis (caspases and Bcl-2 protein family and endoplasmic reticulum stress markers) as well as insulin secretion were analyzed. Our results show that ghrelin alone has no remarkable effects on β-cells in basal conditions, but interestingly it activates cell survival pathways, downregulates apoptotic mediators and endoplasmic reticulum stress, and restores insulin secretion in response to glucose when beta-cells are cytokine-exposed. These data suggest a potential role of ghrelin in preventing or slowing down the transition from a preclinical to clinically established diabetes by ameliorating the effects of insulitis on β-cells.This work was funded by a grant by the Andalusian Government (PI 0765-2011).Peer Reviewe

Blunted Reducing Power Generation in Erythrocytes Contributes to Oxidative Stress in Prepubertal Obese Children with Insulin Resistance

Childhood obesity, and specifically its metabolic complications, are related to deficient antioxidant capacity and oxidative stress. Erythrocytes are constantly exposed to multiple sources of oxidative stress; hence, they are equipped with powerful antioxidant mechanisms requiring permanent reducing power generation and turnover. Glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH) are two key enzymes on the pentose phosphate pathway. Both enzymes supply reducing power by generating NADPH, which is essential for maintaining the redox balance within the cell and the activity of other antioxidant enzymes. We hypothesized that obese children with insulin resistance would exhibit blunted G6PDH and 6PGDH activities, contributing to their erythrocytes' redox status imbalances. We studied 15 control and 24 obese prepubertal children, 12 of whom were insulin-resistant according to an oral glucose tolerance test (OGTT). We analyzed erythroid malondialdehyde (MDA) and carbonyl group levels as oxidative stress markers. NADP+/NADPH and GSH/GSSG were measured to determine redox status, and NADPH production by both G6PDH and 6PGDH was assayed spectrophotometrically to characterize pentose phosphate pathway activity. Finally, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR) activities were also assessed. As expected, MDA and carbonyl groups levels were higher at baseline and along the OGTT in insulin-resistant children. Both redox indicators showed an imbalance in favor of the oxidized forms along the OGTT in the insulin-resistant obese group. Additionally, the NADPH synthesis, as well as GR activity, were decreased. H2O2 removing enzyme activities were depleted at baseline in both obese groups, although after sugar intake only metabolically healthy obese participants were able to maintain their catalase activity. No change was detected in SOD activity between groups. Our results show that obese children with insulin resistance present higher levels of oxidative damage, blunted capacity to generate reducing power, and hampered function of key NADPH-dependent antioxidant enzymes.This research was funded by Spanish Government through the Carlos III Health Institute (Sanitary Research Fund (FIS)), code PI18/01316. A.G.-D. is supported by an intramural grant from the Biomedical Research and Innovation Institute of Cadiz (INiBICA), code LII19/16IN-CO24

Structural and functional analysis of APOA5 mutations identified in patients with severe hypertriglyceridemia

During the diagnosis of three unrelated patients with severe hypertriglyceridemia, three APOA5 mutations [p.(Ser232_Leu235)del, p.Leu253Pro, and p.Asp332ValfsX4] were found without evidence of concomitant LPL, APOC2, or GPIHBP1 mutations. The molecular mechanisms by which APOA5 mutations result in severe hypertriglyceridemia remain poorly understood, and the functional impairment/s induced by these specific mutations was not obvious. Therefore, we performed a thorough structural and functional analysis that included follow-up of patients and their closest relatives, measurement of apoA-V serum concentrations, and sequencing of the APOA5 gene in 200 nonhyperlipidemic controls. Further, we cloned, overexpressed, and purified both wild-type and mutant apoA-V variants and characterized their capacity to activate LPL. The interactions of recombinant wild-type and mutated apoA-V variants with liposomes of different composition, heparin, LRP1, sortilin, and SorLA/LR11 were also analyzed. Finally, to explore the possible structural consequences of these mutations, we developed a three-dimensional model of full-length, lipid-free human apoA-V. A complex, wide array of impairments was found in each of the three mutants, suggesting that the specific residues affected are critical structural determinants for apoA-V function in lipoprotein metabolism and, therefore, that these APOA5 mutations are a direct cause of hypertriglyceridemia.</p

Excess hydrocortisone hampers placental nutrient uptake disrupting cellular metabolism

Low birth weight increases neonatal morbidity and mortality, and surviving infants have increased risk of metabolic and cardiovascular disturbances later in life, as well as other neurological, psychiatric, and immune complications. A gestational excess of glucocorticoids (GCs) is a well-known cause for fetal growth retardation, but the biological basis for this association remains elusive. Placental growth is closely related to fetal growth. The placenta is the main regulator of nutrient transport to the fetus, resulting from the difference between placental nutrient uptake and the placenta’s own metabolism. The aim of this study was to analyze how excess hydrocortisone affects placental glucose and lipid metabolism. Human placenta explants from term physiological pregnancies were cultured for 18 hours under different hydrocortisone concentrations (2.75, 5.5, and 55mM; 1, 2, and 20mg/ml). Placental glucose and lipid uptake and the metabolic partitioning of fatty acids were quantified by isotopic techniques, and expression of specific glucose transporterGLUT1was quantified bywestern blot.Cell viabilitywas assessed byMTT, immunohistochemistry and caspase activity. We found that excess hydrocortisone impairs glucose uptake and lipoprotein lipase (LPL) activity, coincident with a GC-dose dependent inhibition of fatty acid oxidation and esterification. None of the experimental conditions showed an increased cell death. In conclusion, our results show that GC overexposure exerts a dysfunctional effect on lipid transport and metabolism and glucose uptake in human placental explants. These findings could well be directly related to a reduced placental growth and possibly to a reduced supply of nutrients to the fetus and the consequent fetal growth retardation and metabolic programming