In order to prevent cardiovascular diseases in the adult population, it is relevant to identify their biological predictors in childhood. Obesity is one of the risk factors for cardiometabolic disorders. This problem has received increasing attention due to the growth of overweight and obesity among the adult population in many countries including Russia, where the proportion of overweight people is more than 50% [1]. In the child population, the prevalence of obesity reaches 10% according to epidemiological studies [2][3].

Genetic predisposition to obesity and other negative factors (stress, overeating, low physical activity, etc.) [4] determine the progression of pathological processes in the body which can lead to cardiometabolic disorders already in childhood [5]. The prevalence of obesity and other manifestations of metabolic syndrome in children closely correlate with arterial hypertension [6–9], which is accompanied by an increase in left ventricular ejection fraction resulting in its remodeling [10]. Endothelial dysfunction, insulin resistance, dyslipidemia, obesity, and a number of other factors contribute to arterial hypertension [11–13]. These risk factors for hypertension are closely interrelated. In particular, an impaired blood lipid profile is a predictor of endothelial dysfunction (ED) as a result of the effect of low-density lipoprotein cholesterol on NO bioavailability and eNOS activity [14].

Despite the large number of scientific papers in this area of expertise, there have been no systematic studies of blood lipid profile features in obese children and adolescents depending on insulin resistance, ED, and minimal left ventricular diastolic dysfunction (mLVDD), which was the purpose of this research.

The research objective was to study the features of the lipid profile in obese children and adolescents depending on insulin resistance, ED, and mLVDD.

Characteristics of the examined children and adolescents

According to the Declaration of Helsinki of the World Medical Association "Ethical Principles for Medical Research Involving Human Subjects" (amended in 2000), as well as the "Rules of Clinical Practice in the Russian Federation" (approved by Order No. 266 of the Russian Ministry of Health of June 19, 2003), all research was conducted with the informed consent of the patients studied.

A one-time (cross-sectional) trial was conducted at the MBUZ (Municipal Budgetary Healthcare Institution) "Rostov-on-Don Children's City Polyclinic No. 4" for the period of 2018–2020. The survey involved a total of 370 obese children and adolescents aged 7 to 17 years (study group) with a body mass index (BMI) > 30 and 123 children of the same age without obesity (BMI ˂ 20), corresponding to >75 percentage percentile by sex and age (Table 1). Children and adolescents of the study group were divided into subgroups according to the insulin resistance criterion (based on HOMA IR Index calculation), as well as the presence of ED and/or mLVDD signs.

The body mass index was calculated by dividing the value of body weight (kg) by the square of height (m2). Body weight was measured using a medical scale, and height was measured using a stadiometer. To verify the body mass index, the researchers used percentile tables of the correlation between age-sex values and BMI.

Method of functional diagnosis of endothelial dysfunction

The endothelial mechanism of vascular tone regulation was performed by the brachial artery reactive hyperemia test (by D. Celermajer). Reactive hyperemia was modeled by cuff occlusion of the brachial artery for 3 minutes. Vasodilation was assessed with a 12 MHz ultrasound line transducer on a PhilipsAffinity 50 ultrasound scanner. The preserved endothelial vasomotor function was judged on the basis of 10% or more enlargement of the brachial artery (dPWV, %) in response to compression; an increase of less than 10% was indicative of ED. The results of the survey by this method are presented in Table 2.

Method of functional diagnosis of minimal left ventricle diastolic dysfunction

Minimal diastolic dysfunction was assessed by transthoracic Doppler echocardiography with Doppler B index (E-Ea) measurement. Trans-thoracic Doppler echocardiography with measurement of Doppler B (E-Ea) was performed using a Philips Affinity 50 ultrasound scanner with a cardiac transducer (frequency range of 2–4 MHz). The research team evaluated the ms-time interval between the onset of early diastolic left ventricular filling peak (LV) (E) and the peak of motion high amplitude echo signals corresponding to early LV diastolic filling (Ea) (Nelasov et al., 2012) (Table 3).

Biochemical methods

Biochemical parameters were determined in blood serum taken fasted in the morning, after 12–14 hours of fasting.

The blood serum lipid profile of the examined children and adolescents was studied, including determination of total cholesterol (Chol), triglycerides (TG), high-density lipoprotein cholesterol (HDL-Chol), low-density lipoproteins (LDL-Chol), very low-density lipoproteins (VLDL-Chol), and glucose levels using AO Vector Best (Russia) reagent kits. A Miura biochemical analyzer (Italy) was used to quantify the lipid profile and blood glucose level. Glucose in all subjects was within normal limits: children and adolescents with insulin resistance were on glucose control therapy.

The insulin content was measured by enzyme immunoassay using an Infinite F50 semi-automatic analyzer (TecanAustriaGmbH, Austria) and by DRG reagent kits (Germany). The results of the insulin content study in the blood serum of the examined children and adolescents and the calculated HOMA IR are presented below (Table 4).

Statistics

Data statistics were carried out using the Statistica 10.10 software package. Calculated data with parametric distribution are presented as average and standard deviation (M±σ) and with nonparametric distribution are presented as the median and interquartile range (Me; 25–75%). Spearman's rank correlation coefficient was used to establish the relationship between insulin levels and lipid profiles. The significance level of p < 0.05 was used in the significance of differences.

Lipid profiles in the examined children and adolescents are presented in Tables 5–6.

The analysis revealed that in the blood of the examined obese patients without signs of ED and/or mLVDD and HOMA IR > 3.2, there was an increase in HDL and TG by 34% (p ˂0.001) and 30% (p ˂0.05), respectively, and a decrease in LDL by 33% (0.001) and CA by 32% (p˂0.001). Whereas, children and adolescents with a HOMA IR ˂ 3.2 with a similar history had an increase by 12% (p˂0.05) in HDL-Chol, a decrease by 12% (p˂0.05) in LDL, and a decrease by 20% (p˂0.05) in VLDL.

Children and adolescents with BMI > 30 with ED had a 27% (p ˂0.05) and 49% (p ˂0.0001) increase in VLDL and TG with HOMA IR > 3.2, and 17% (p ˂0.05) and 31% (p ˂0.001) with HOMA IR ˂ 3.2 relative to the control group, respectively. Also, children and adolescents with obesity, insulin resistance, and ED had a decrease by 39% in LDL (p ˂0.001) relative to control values.

With the lipid disorders in children and adolescents with minimal left ventricular dysfunction and HOMA IR > 3.2, there was an increase in VLDL by 66% (p ˂0.0001), TG by 75% (p ˂0.001) and CA by 30% (p ˂0.0001), and with a ˂ 3.2 value, an increase in HDL-Chol by 13% (p˂0.001) relative to the control group.

When the signs of ED and minimal diastolic dysfunction were combined in obese children and adolescents, the following was found. Those examined with HOMA IR > 3.2 had (p ˂0.0001) reduced HDL-Chol values by 15%, as well as an increase in LDL-Chol by 85% (p ˂0.0001) and in TG by 101% (p ˂0.0001), which was reflected in an increase in CA by 65% (p ˂0.0001) vs control values. In volunteers with HOMA IR 3.2, the level of LDL, VLDL, TG, and CA was higher by 19% (p 0.001), 49% (p 0.0001), 59% (p 0.0001), and 68% (p 0.0001), respectively, relative to the control values.

A correlation analysis aimed at identifying the relationship between the insulin level and lipid profile parameters revealed a high positive correlation between changes in insulin, total cholesterol, HDL cholesterol, and triglycerides in subjects with HOMA IR > 3.2 and signs of ED. In obese children and adolescents, HOMA IR ˂ 3.2, and signs of ED, there was a negative association between insulin and LDL levels, and a positive association between changes in insulin and triglyceride levels (Table 7).

Negative correlations were also established between changes in insulin levels and lipid profile parameters: total cholesterol and LDL in children and adolescents with HOMA IR ˂ 3.2 and minimal left ventricular dysfunction. When ED and minimal dysfunction were combined, the examined patients with HOMA IR ˂ 3.2 revealed negative associations of changes in insulin with the total cholesterol and low-density lipoproteins, as well as positive correlations between insulin and LDL and triglycerides.

The results obtained testify to the difference in mechanisms of blood lipid profile regulation in obese children and adolescents depending on the degree and nature of cardiometabolic disorders (insulin resistance, signs of ED and/or minimal diastolic dysfunction).

The lack of correlation between insulin levels and lipid profile parameters in the groups with obesity and HOMA IR > 3.2 (without signs of ED and minimal diastolic dysfunction, as well as with a combination of these two signs of cardiovascular disorders) may be the result of the small sample submitted for analysis. In this regard, it is relevant to continue studying this problem.

Obesity in childhood and adolescence is a modern public health problem because it increases the risk of cardiovascular disease and reduced life expectancy [15][16]. Although severe cardiovascular disease in children is rare, early signs are described in obese and overweight children [17]. When considering this issue, the literature focuses on remodeling (longitudinal and circumferential deformation) and left ventricular dysfunction [18][19], as well as ED in children with overweight and obesity [20]. There is evidence of contractile cardiac malfunction preceding the clinical manifestations of left ventricular dysfunction in obese children [19][21][22].

The mechanisms underlying cardiometabolic abnormalities in obese children and adolescents are not sufficiently investigated. The main risk factor for cardiovascular disease at this age is hypertension [23–26] provoking left ventricular diastolic dysfunction. In addition, obesity is directly related to the activation of the sympathetic and renin-angiotensin-aldosterone system, synthesis of biologically active substances that promote myocardial growth, and metabolic disorders that accompany obesity, which, in turn, provide conditions for increased cardiac workload by increasing vascular sclerosis [27].

This paper analyzed the lipid profile in obese children and adolescents but with different insulin resistance indices (HOMA IR) and signs of ED and/or mLVDD. Of the 129 obese children and adolescents with insulin resistance examined at the pediatric outpatient clinic during 2018–2020, 15 (12%) had signs of ED, 35 (27%) showed signs of mLVDD, 67 (52%) had signs of ED and mLVDD, and 12 (9%) examined had no such signs. That is, most obese children and adolescents with insulin resistance had signs of ED or a combination of ED and mLVDD.

The distribution of obese patients and insulin resistance index below 3.2 was similar: 35% of children and adolescents had signs of ED and 27% with a combination of signs of ED and mLVDD. The rest had signs of either ED (18%) or the absence of both cardiovascular disorder signs (18%). It can be assumed that obesity in childhood and adolescence increases, first of all, the risk of mLVDD or the combination of this pathology with ED. Moreover, with the insulin resistance progression, the risk of concomitant pathology increases. In this regard, it is important to identify predictors of cardiovascular disorders in childhood and adolescence obesity.

In a lipid profile study, increased triglycerides were found in all obese children and adolescents with an insulin resistance index ˂ 3.2 regardless of the presence of signs of ED and/or mLVDD, and in the group with obesity and an insulin resistance index ˂ 3.2, only those with signs of ED, including those combined with mLVDD. At the same time, increased LDL, which are currently associated with a high risk of cardiovascular disease [28][29], are found only in obese patients with an insulin resistance index ˂ 3.2 and a combination of ED and mLVDD. However, there have been reports that increased LDL may not be associated with this risk, but rather the increased blood triglyceride levels determine it [30–32]. Hypertriglyceridemia is often accompanied by further lipid disorders including increased very low density lipoproteins, as well as a decrease in HDL-Chol [33]. Indeed, most subgroups of obese subjects had increased VLDL with the exception of those without signs of ED and/or mLVDD, and the mLVDD group with an insulin resistance index of ˂ 3.2.

Based on this study, one can assume that cardiometabolic disorders in obesity in childhood and adolescence are accompanied, first of all, by hypertriglyceridemia, which entails further the lipid disorders. There was also a positive correlation between changes in insulin and triglyceride levels in obese children and adolescents with ED, as well as in patients with HOMA IR ˂ 3.2 and combined ED and minimal dysfunction. Although the relationship between these pathogenetic factors has long been recognized [34][35], the question of which of these factors is a trigger in the progression of cardiometabolic disorders or their influence is bidirectional has not yet been fully investigated [36][37]. Only one study has shown that elevated triglyceride and HDL-Chol contribute to increasing insulin suggesting a potential role of these lipid metabolism parameters in the insulin resistance progression [38].

However, further research on this issue is needed to clarify the mechanisms underlying different dyslipidemias in ED and minimal left ventricular dysfunction in obese children and adolescents.

Thus, based on the study of lipid disorders in obese children and adolescents with signs of ED and/or minimal left ventricular dysfunction, it can be concluded that obesity at this age is more often accompanied by mLVDD or a combination of ED and left ventricular dysfunction. The insulin resistance progression leads to an increase in co-morbidities (ED and mLVDD). Hypertriglyceridemia has an important role in the progression of cardiometabolic disorders in childhood and adolescence obesity which is associated with high insulin and presumably determines the development of insulin resistance.