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

Álvaro González-Domínguez,Beatriz Ruiz-Mateos,Rosa María Mateos,Jesus Domínguez-Riscart,Ana Saez-Benito,Alfonso M Lechuga-Sancho,Francisco Visiedo

doi:10.3390/antiox10020244

Abstract

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.

Highlights

Worldwide, more than 300 million children and teenagers between the ages of 5 and 19 years and 41 million children under the age of 5 were overweight or obese in 2016 according to the WHO’s reports [1,2]
Our data suggest that the availability of NADPH in compromised situations of metabolic stress, induced by glucose intake, plays a pivotal role in the antioxidant response of erythrocytes
We have found a relation between erythrocytes’ altered reducing power supplies and the oxidative stress-mediated pathophysiology of insulin resistance in prepubertal obese children

Summary

Introduction

More than 300 million children and teenagers between the ages of 5 and 19 years and 41 million children under the age of 5 were overweight or obese in 2016 according to the WHO’s reports [1,2]. Obesity is defined as excessive adiposity caused by energetic imbalance. Oxidative stress plays a physiological role by inducing adaptive responses (phenomenon known as oxidative eustress), but it may lead to damage (oxidative distress) [5]. Cell tolerance to oxidative stress is primarily enhanced through induction of antioxidant enzymes which may be compromised as the disease evolves, switching from a eustress to a distress situation [7]. Oxidative stress plays a pivotal role in the development of a wide variety of diseases, such as diabetes, certain types of cancers, as well as neurodegenerative and cardiovascular diseases [8,9,10,11,12]

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