Association of myeloperoxidase levels with cardiometabolic factors and renal function in prepubertal children

Gender-related differences in cardiometabolic risk factors and oxidative stress among prepubertal children with obesity

OBJECTIVES

Gender-related differences in oxidative stress, nitric oxide bioavailability, and cardiometabolic risk factors were examined in a cross-sectional study involving 313 prepubertal children (8-9 years old) from the generation XXI birth-cohort.

METHODS

Anthropometric measurements, cardiometabolic variables, and redox markers were assessed, including plasma and urinary isoprostanes (P-Isop, U-Isop), plasma total antioxidant status (P-TAS), serum myeloperoxidase (MPO), plasma and urinary nitrates and nitrites (P-NOX, U-NOX), and urinary hydrogen peroxide (U-H2O2).

RESULTS

Girls showed higher levels of total/non-HDL cholesterol, triglycerides, and insulin resistance (HOMA-IR) compared to boys. Notably, U-H2O2 values were lower in girls. When stratifying by body mass index (BMI) and gender, both girls and boys exhibited higher MPO concentration and U-Isop values. Uric acid concentration was higher in overweight and obese girls than in normal weight girls, while no significant differences were observed among boys across BMI categories. Furthermore, U-NOX values differed only in boys, with higher levels observed in overweight and obese individuals compared to those with normal weight. Multivariate analysis, adjusted for age and BMI z-score, demonstrated inverse associations between U-H2O2 and pulse wave velocity values, as well as between U-NOX and total or non-HDL cholesterol, exclusively in boys. In girls, a positive association between U-Isop and HOMA-IR values was observed.

CONCLUSIONS

In conclusion, gender differentially impacts oxidative stress, nitric oxide bioavailability, and cardiometabolic risk factors in prepubertal children. Prepubertal girls appear more susceptible to oxidative stress-induced metabolic dysfunction, while in boys, elevated levels of redox and nitric oxide bioavailability markers seem to provide protection against arterial stiffness and lipid homeostasis.

Reactive oxygen species, toxicity, oxidative stress, and antioxidants: chronic diseases and aging

A physiological level of oxygen/nitrogen free radicals and non-radical reactive species (collectively known as ROS/RNS) is termed oxidative eustress or "good stress" and is characterized by low to mild levels of oxidants involved in the regulation of various biochemical transformations such as carboxylation, hydroxylation, peroxidation, or modulation of signal transduction pathways such as Nuclear factor-κB (NF-κB), Mitogen-activated protein kinase (MAPK) cascade, phosphoinositide-3-kinase, nuclear factor erythroid 2-related factor 2 (Nrf2) and other processes. Increased levels of ROS/RNS, generated from both endogenous (mitochondria, NADPH oxidases) and/or exogenous sources (radiation, certain drugs, foods, cigarette smoking, pollution) result in a harmful condition termed oxidative stress ("bad stress"). Although it is widely accepted, that many chronic diseases are multifactorial in origin, they share oxidative stress as a common denominator. Here we review the importance of oxidative stress and the mechanisms through which oxidative stress contributes to the pathological states of an organism. Attention is focused on the chemistry of ROS and RNS (e.g. superoxide radical, hydrogen peroxide, hydroxyl radicals, peroxyl radicals, nitric oxide, peroxynitrite), and their role in oxidative damage of DNA, proteins, and membrane lipids. Quantitative and qualitative assessment of oxidative stress biomarkers is also discussed. Oxidative stress contributes to the pathology of cancer, cardiovascular diseases, diabetes, neurological disorders (Alzheimer's and Parkinson's diseases, Down syndrome), psychiatric diseases (depression, schizophrenia, bipolar disorder), renal disease, lung disease (chronic pulmonary obstruction, lung cancer), and aging. The concerted action of antioxidants to ameliorate the harmful effect of oxidative stress is achieved by antioxidant enzymes (Superoxide dismutases-SODs, catalase, glutathione peroxidase-GPx), and small molecular weight antioxidants (vitamins C and E, flavonoids, carotenoids, melatonin, ergothioneine, and others). Perhaps one of the most effective low molecular weight antioxidants is vitamin E, the first line of defense against the peroxidation of lipids. A promising approach appears to be the use of certain antioxidants (e.g. flavonoids), showing weak prooxidant properties that may boost cellular antioxidant systems and thus act as preventive anticancer agents. Redox metal-based enzyme mimetic compounds as potential pharmaceutical interventions and sirtuins as promising therapeutic targets for age-related diseases and anti-aging strategies are discussed.

Glomerular hyperfiltration: part 2-clinical significance in children

Glomerular hyperfiltration (GHF) is a phenomenon that can occur in various clinical conditions affecting the kidneys such as sickle cell disease, diabetes mellitus, autosomal dominant polycystic kidney disease, and solitary functioning kidney. Yet, the pathophysiological mechanisms vary from one disease to another and are not well understood. More so, it has been demonstrated that GHF may occur at the single-nephron in some clinical conditions while in others at the whole-kidney level. In this review, we explore the pathophysiological mechanisms of GHF in relation to various clinical conditions in the pediatric population. In addition, we discuss the role and mechanism of action of important factors such as gender, low birth weight, and race in the pathogenesis of GHF. Finally, in this current review, we further highlight the consequences of GHF in the progression of kidney disease.

Proteinuria and nocturnal blood pressure dipping in hypertensive children and adolescents

BACKGROUND

The absence of nocturnal blood pressure dipping is associated with adverse cardiovascular outcomes in adults, and proteinuria is a risk factor for non-dipping in this population. Risk factors for non-dipping in children are largely unknown.

METHODS

We retrospectively identified patients aged 5-19 years who underwent 24-h ambulatory blood pressure monitoring (ABPM) from August 2018 to January 2019 and had a spot urine protein-to-creatinine ratio (PCR) within 1 year of their ABPM. Dipping was defined as ≥10% reduction in systolic and diastolic blood pressure from day to night. Multivariable logistic and linear regression models evaluated the association of proteinuria with non-dipping.

RESULTS

Among 77 children identified, 27 (35.1%) were non-dippers. Each two-fold higher urine PCR was associated with 38% higher odds of non-dipping, after adjusting for body mass index (BMI). Higher urine PCR was also associated with a lower diastolic dipping percentage by 1.33 (95% confidence interval 0.31-2.34), after adjusting for BMI, age, and estimated glomerular filtration rate.

CONCLUSIONS

Limitations of this study include its retrospective design and the time lapse between urine PCR and ABPM. Proteinuria appears to be associated with blood pressure non-dipping in children. This finding needs to be confirmed in prospective studies.

IMPACT

Our study demonstrates the association of proteinuria with non-dipping of blood pressure in children. This association has been explored in adults, but to our knowledge, this is the first time it is evaluated in children referred for evaluation of elevated blood pressure. Non-dipping is a modifiable risk factor for kidney function decline and cardiovascular disease in adulthood, and thus early identification in children is important. The association between proteinuria and non-dipping in children will allow us to more readily identify those at risk, with a future focus on interventions to modify blood pressure dipping patterns.

Impact of physical activity on redox status and nitric oxide bioavailability in nonoverweight and overweight/obese prepubertal children

Nutritional status might contribute to variations induced by physical activity (PA) in redox status biomarkers. We investigated the influence of PA on redox status and nitric oxide (NO) production/metabolism biomarkers in nonoverweight and overweight/obese prepubertal children. We performed a cross-sectional evaluation of 313 children aged 8-9 years (163 nonoverweight, 150 overweight/obese) followed since birth in a cohort study (Generation XXI, Porto, Portugal). Plasma total antioxidant status (P-TAS), plasma and urinary isoprostanes (P-Isop, U-Isop), urinary hydrogen peroxide (U-H₂O₂), myeloperoxidase (MPO) and plasma and urinary nitrates and nitrites (P-NOx, U-NOx) were assessed, as well as their association with variables of reported PA quantification (categories of PA frequency (>1x/week and ≤1x/week)and continuous PA index (obtained by the sum of points)) in a questionnaire with increasing ranks from sedentary to vigorous activity levels. U-NOx was significantly higher in children who presented higher PA index scores and higher PA frequency. Separately by BMI classes, U-NOx was significantly higher only in nonoverweight children who practiced PA more frequently (p = 0.037). In overweight/obese children, but not in nonoverweight, P-TAS was higher among children with higher PA frequency (p = 0.007). Homeostasis model assessment index (HOMA-IR) was significantly lower in more active overweight/obese children, but no differences were observed in nonoverweight children. In the fully adjusted multivariate linear regression models for P-TAS, in the overweight/obese group, children with higher PA frequency presented higher P-TAS. In the U-NOx models, U-NOx significantly increased with PA index, only in nonoverweight children. Our results provide additional evidence in support of a protective effect of physical activity, in nonoverweight by increasing NO bioavailability and in overweight/obese children by enhancing systemic antioxidant capacity and insulin sensitivity. These results highlight the importance of engaging in regular physical exercise, particularly among overweight/obese children, in which a positive association between oxidant status and cardiometabolic risk markers has been described.

Association of glomerular hyperfiltration with serum chemokine levels and metabolic features in prepubertal children with overweight/obesity

BACKGROUND AND AIMS

Glomerular hyperfiltration (GH) is proposed as one of the earliest events in obesity (OB)-associated renal disease. Children with GH and type-1 diabetes showed increased chemokine levels. Chemokine associations with glomerular filtration rate (GFR) and metabolic features in prepubertal children with overweight (OW)/OB are unknown.

METHODS AND RESULTS

Cross-sectional study. 75 prepubertal children (aged: 9.0 ± 1.7 years) with OW/OB were studied. Clinical and metabolic characteristics (including non-esterified fatty acids, NEFA) and GFR (combined Zappitelli equation) were assessed. GH was defined as GFR >135 ml/min.1.73 m². Serum levels of regulated on activation, normal T cell expressed and secreted (RANTES)/CCL5, interleukin-8 (IL-8)/CXCL8 and monokine-induced by interferon-γ (MIG)/CXCL9 were measured by ELISA. Age- and sex-adjusted correlations and differences were tested. 48% of the cohort was female and 13% were OW, 54% OB and 33% severe OB. Prepubertal children with GH showed lower z-BMI (-12%), NEFA (-26%) and uric acid (-22%) than those without GH (all p < 0.05). Similarly to high sensitivity C-reactive protein (hsCRP), there were no differences in serum chemokines between children with GH or not (all p > 0.05). Adjusted correlations were significant for RANTES and z-BMI (r = 0.26; p < 0.05) and for MIG with z-BMI (r = -0.26; p < 0.05) and with NEFA (r = 0.27; p < 0.05).

CONCLUSION

GH was not associated with higher chemokine levels in prepubertal children with OW/OB. Decreased rather than elevated GFR values were correlated with obesity and worse metabolic profiles. Chemokines levels in children with severe OB suggest a regulation of the immune response. Follow-up studies are needed to address the clinical implications of these findings.

Myeloperoxidase as cardiovascular risk marker in pre-pubertal preterm children?

BACKGROUND AND AIMS

To evaluate the biomarkers related to cardiovascular risk in pre-pubertal preterm children with a birth weight of less than 1,500 g and relate them to current nutritional status, insulin resistance, and inflammation.

METHODS & RESULTS

This is a cross-sectional, controlled study with pre-pubertal preterm children aged 5-9 years with a birth weight of less than 1500 g (Preterm group, n = 44) compared to full term children of adequate weight for gestational age (Control group, n = 30). Clinical evaluation: anthropometry and pubertal staging. Laboratory tests: total cholesterol and fractions, triglycerides, paraoxonase 1, apolipoproteins A-I and B, myeloperoxidase (MPO), high sensitivity C-reactive protein (hs-CRP), glycemia and insulin (to calculate HOMA-IR). In the preterm group, 19 (43.2%) were male, with mean birth weight and gestational age of 1157 ± 242 g and 30.0 ± 2.3 weeks, respectively. The preterm group showed lower concentrations of HDL-c (60.1 ± 10.1 vs. 69.0 ± 10.0 mg/dL; p < 0.001); higher concentrations of hs-CRP [0.55 mg/dL (0.30; 39.4) vs. 0.30 mg/dL (0.30; 10.80); p = 0.043], of MPO [21.1 ng/mL (5.7; 120.0) vs. 8.1 ng/mL (2.6; 29.6); p < 0.001] and of MPO/HDL-c ratio [0.39 (0.09; 2.07) ng/mg vs. 0.11 (0.05; 0.58)]. The MPO/HDL-c ratio was the variable that showed the best discriminatory power between the groups (AUC = 0.878; 95% CI; 0.795-0.961). MPO concentrations in the preterm group were correlated with those of hs-CRP (r = 0.390; p = 0.009), insulin (r = 0.448; p = 0.002) and HOMA-IR (r = 0.462; p = 0.002).

CONCLUSION

Prepubertal preterm children show high MPO concentrations and MPO/HDL-c ratio that are associated with inflammation and oxidative stress, which, in turn, may be associated with atherosclerosis.

Oxidative stress in chronic kidney disease

Oxidative stress (OS), defined as disturbances in the pro-/antioxidant balance, is harmful to cells due to the excessive generation of highly reactive oxygen (ROS) and nitrogen (RNS) species. When the balance is not disturbed, OS has a role in physiological adaptations and signal transduction. However, an excessive amount of ROS and RNS results in the oxidation of biological molecules such as lipids, proteins, and DNA. Oxidative stress has been reported in kidney disease, due to both antioxidant depletions as well as increased ROS production. The kidney is a highly metabolic organ, rich in oxidation reactions in mitochondria, which makes it vulnerable to damage caused by OS, and several studies have shown that OS can accelerate kidney disease progression. Also, in patients at advanced stages of chronic kidney disease (CKD), increased OS is associated with complications such as hypertension, atherosclerosis, inflammation, and anemia. In this review, we aim to describe OS and its influence on CKD progression and its complications. We also discuss the potential role of various antioxidants and pharmacological agents, which may represent potential therapeutic targets to reduce OS in both pediatric and adult CKD patients.

Altered gene expression in antipsychotic-induced weight gain

Antipsychotic drugs are one of the largest types of prescribed drugs. However, antipsychotic-induced weight gain (AIWG) is a major problem for the patients. AIWG increases cardiovascular and cerebrovascular morbidity and mortality, and reduces quality of life and drug compliance. To characterize changes in gene expression related to AIWG, we sequenced total messenger RNA from the blood samples of two groups of schizophrenia patients before and after 3 months of treatment with antipsychotics. The "weight gain" group was defined by an increase of body mass index (BMI) >1.5 points (18 patients; median BMI increase = 2.69) and the "no weight gain" group was defined by a change of BMI between <1.0 and >-1.0 points (18 patients; median BMI increase = 0.26). We found 115 genes with significant differential expression in the weight gain group before and after medication and 156 in the no weight gain group before and after medication. The weight gain group was significantly enriched with genes related to "obesity" and "BMI" (Fisher; p = 0.0002 and 0.01, respectively) according to the Gene Reference into Function (GeneRIF) database. In the no weight gain group, the enrichment was much smaller (Fisher; p = 0.02 and 0.79). This study is a first step toward detecting genetic factors that cause AIWG and to generating prediction tests in future studies with larger data sets.

Mechanistic Role of the Calcium-Dependent Protease Calpain in the Endothelial Dysfunction Induced by MPO (Myeloperoxidase)

MPO (myeloperoxidase) is a peroxidase enzyme secreted by activated leukocytes that plays a pathogenic role in cardiovascular disease, mainly by initiating endothelial dysfunction. The molecular mechanisms of the endothelial damaging action of MPO remain though largely elusive. Calpain is a calcium-dependent protease expressed in the vascular wall. Activation of calpains has been implicated in inflammatory disorders of the vasculature. Using endothelial cells and genetically modified mice, this study identifies the µ-calpain isoform as novel downstream signaling target of MPO in endothelial dysfunction. Mouse lung microvascular endothelial cells were stimulated with 10 nmol/L MPO for 180 minutes. MPO denitrosylated µ-calpain C-terminus domain, and time dependently activated µ-calpain, but not the m-calpain isoform. MPO also reduced Thr¹⁷² AMPK (AMP-activated protein kinase) and Ser¹¹⁷⁷ eNOS (endothelial nitric oxide synthase) phosphorylation via upregulation of PP2A (protein phosphatase 2) expression. At the functional level, MPO increased endothelial VCAM-1 (vascular cell adhesion molecule 1) abundance and the adhesion of leukocytes to the mouse aorta. In MPO-treated endothelial cells, pharmacological inhibition of calpain activity attenuated expression of VCAM-1 and PP2A, and restored Thr¹⁷² AMPK and Ser¹¹⁷⁷ eNOS phosphorylation. Compared with wild-type mice, µ-calpain deficient mice experienced reduced leukocyte adhesion to the aortic endothelium in response to MPO. Our data first establish a role for calpain in the endothelial dysfunction and vascular inflammation of MPO. The MPO/calpain/PP2A signaling pathway may provide novel pharmacological targets for the treatment of inflammatory vascular disorders.

Serum cardiovascular risk biomarkers in pre-pubertal obese children

BACKGROUND

Childhood obesity is associated with premature cardiovascular complications. However, little is known about the effect of a family-based behavioural intervention on the relationship between arterial function, blood pressure and biomarkers in pre-pubertal children with obesity.

DESIGN

This was a single centre randomized controlled trial (RCT) including 74 children randomized to a 6-month behavioural intervention to treat obesity. In 48 children (13 controls and 35 interventions), we assessed: serum level of cytokine (CCL2), adiponectin, and neutrophil product (MMP-8), as well as carotid intima-media thickness, flow-mediated dilation (FMD), nitroglycerin-mediated dilation; arterial stiffness (incremental elastic modulus, Einc), pulse wave velocity (PWV), resting and 24-hour blood pressure (BP).

RESULTS

At baseline, resting systolic BP was positively associated with MMP-8 levels which was significantly higher in children with hypertension (P = 0.033). Biochemical markers were not related to endothelial function at baseline, but they globally increased after 6 months in the intervention group. The significant increase of CCL2 levels in the intervention group was associated with a decrease in diastolic BP. Furthermore, adiponectin change was positively related to a change in FMD and negatively to change in Einc and PWV.

CONCLUSIONS

The usefulness of serum biomarkers for the detection of cardiovascular diseases is not well established in children. In our population, MMP-8 concentration was higher in hypertensive children. Furthermore, behavioural interventions resulted in a paradoxical increase in some biomarkers in children, with potentially beneficial effects detected with CCL2 changes. Caution should be taken when using nonspecific serum biomarkers for the clinical monitoring of children with obesity.

Neutrophil elastase and myeloperoxidase mRNA expression in overweight and obese subjects

Neutrophil elastase and myeloperoxidase enzymes have been implicated in high-fat diet-induced obesity, insulin resistance (IR) and atherosclerosis in animal models. The aim of the present study was to explore neutrophil elastase and myeloperoxidase mRNA expressions in the peripheral blood leukocytes (PBL) in overweight and obese subjects, and to correlate those mRNA expressions with BMI, IR and cardiovascular biomarkers. In this cross-sectional study, 74 apparently healthy subjects including 22 lean, 27 overweight and 25 obese subjects were recruited. Cardiovascular and metabolic biomarkers were evaluated from fasting blood samples. The mRNA levels of neutrophil elastase and myeloperoxidase genes in the PBL were quantified by real-time PCR. Compared to lean group, the overweight and obese groups showed significant upregulation of both neutrophil elastase (p < 0.001) and myeloperoxidase (p < 0.03) mRNA expressions in the PBL. But no difference was found between overweight and obese groups. The neutrophil elastase and myeloperoxidase mRNA levels showed significant positive correlation with BMI, serum triglyceride, atherogenic index of plasma and 10-year risk of developing cardiovascular disease. But no correlation was found with glucose, insulin or IR. It was concluded that the neutrophil elastase and myeloperoxidase genes are up-regulated in both overweight and obese subjects and are associated with BMI and markers of cardiovascular disease.

Cardiovascular risk biomarkers and metabolically unhealthy status in prepubertal children: Comparison of definitions

BACKGROUND AND AIMS

The early onset of cardio-metabolic abnormalities, known as metabolically unhealthy (MU) status, is highly associated with obesity and cardiovascular disease (CVD), as well as with increased morbidity and mortality later in life. Given the lack of a consensus MU classification for prepubertal children, we aimed to compare available MU definitions in terms of their association with CVD risk biomarkers.

METHODS AND RESULTS

A total of 930 prepubertal children (622 with overweight/obesity, 462 males) aged 5-10.9 years were recruited, anthropometric measures were taken and biomarkers were analyzed. Children were classified using eight MU definitions based on different cut-offs for blood pressure, triacylglycerides, high-density lipoprotein cholesterol, glucose and homeostasis model assessment for insulin resistance (HOMA-IR). MU prevalence in children with overweight/obesity ranged between 30% and 60% across definitions. Plasma concentrations of resistin, leptin, myeloperoxidase (MPO) and total plasminogen activator inhibitor 1 (tPAI-1) were higher, and those of adiponectin were lower, in MU compared to MH children with overweight/obesity. Linear regression analyses confirmed the contribution of MPO and tPAI-1 concentrations to MU status, with most significant results derived from definitions that use age and sex-specific criteria and that account for HOMA-IR.

CONCLUSION

Plasma concentrations of MPO and tPAI-1 are increased in prepubertal MU children irrespective of having normal-weight or overweight/obesity. Inclusion of age and sex-specific cut-offs for cardio-metabolic components as well as insulin resistance criteria increases the quality of MU definitions as seen by their stronger association with CVD biomarkers concentrations.