Correlation between Leptin with Diastolic Function in Young Adult Obesity

Background: Obesity is one of the global health problems with increasing prevalence, and the complication is related to the alteration of the left ventricle. An obese person without symptoms has impaired diastolic function compares to a normal population, but the mechanism is still unclear. One of the evolving theories is caused by chronic inflammation, characterized by the increase of proinflammatory adipocytokines in an obese person. Leptin is a chronic inflammatory marker which is synthesized by all adipose tissues and has a positive correlation with the body mass index. Leptin level are influenced by age except young adult group. The aim of this study is to investigate the correlation between leptin level and diastolic function of the left ventricle in young adult obese. Method: This study was conducted in a single centre with cross-sectional design. The subject of this study consists of all young adult obese, worked in Dr. Hasan Sadikin General Hospital, between June-August 2018. The diastolic function of the left ventricle was measured by examining the ventricle relaxation (E/mean e’) by tissue doppler imaging method. The examination of leptin level was done by sandwich-ELISA test method. Pearson correlation test was done to assess the correlation between those two. Result: This study consisted of 38 patients with the mean of age 30.75±7.25 years old, 68% were males. The mean score of E/mean e’ was 6.49±3.02 ng/mL and the median of leptin was 13.95 (9.1–25.4) mg/L. After data log transformation of leptin was done, there was a significant positive correlation (r= 0.5892, p<0.001) between leptin level and E/mean e’. Conclusion: There was a significant correlation between the level of leptin and diastolic function of the left ventricle in young adult obese.


INTRODUCTION
Obesity is still global health problem and incidence continuous to increase. The prevalence continues to increase in last two decades, with a total population of obesity in 2016 is 650 million, which is around 13% of the entire adult population in the world. 1,2 One of obesity complication is related to the alteration of the left ventricle. 3 Obesity causes dysfunction of adipose tissue and change in regulation to synthesize and secretion of adipocytokines, increased synthesis and secretion of proinflammation adipocytokines, this condition cause the activation of inflammatory signaling pathway in the systemic circulation. Systemic effects that happen is a chronic systemic inflammatory condition that can be found in obesity. Adipocytokine which has an important role in the mechanism of systemic inflammatory on obesity among others are tumor necrosis factor-alpha (TNFα), interleukin-6 (IL-6), C-reactive protein (CRP), and leptin. Hyperleptinemia is one of the conditions that occurred in obesity and leptin is the most correlated inflammatory marker with BMI compared to other inflammatory markers. [4][5][6][7][8][9][10][11][12] In addition to adipose tissue, leptin and its receptor isoforms are expressed in various other tissues. These include cardiovascular tissues, such as endothelial cells, 13 smooth muscle cells, 14 and cardiomyocytes. 15 These findings suggest that leptin has specific effect on myocardium. 16 Leptin level are influenced by age except young adult group. Considering cardiac structure and function, leptin levels have been suggested to be associated with left ventricular hypertrophy, 17 increased myocardial wall thickness, 18 and impaired cardiac contractile function. 19 Indeed, elevated leptin levels have been associated with heart failure in patients with both reduced and preserved ejection fraction. [20][21][22] Recent study showed that high leptin levels are independently associated with diastolic dysfunction in the general population, especially in women. 23 Thus, leptin exhibits a wide range of cardiovascular effects and is associated with cardiovascular outcome. The association between leptin and cardiovascular diseases could emerge from direct cellular effects in both cardiac and vascular tissues. To our knowledge the association between leptin levels and cardiac structure and function has not been studied in young adult obese population. Therefore, we tested the hypothesis that leptin levels are associated with cardiac function in patients with obese in young adult group.

Study population
A total of 67 consecutive obese person works in Dr. Hasan Sadikin General Hospital, Bandung between June-August 2018 were included in this cross-sectional study. Obese person aged between 20-39 years old were included in the study, whereas obese with diabetes mellitus, hypertension, hypertensive heart disease, arrhythmia, coronary artery disease, congenital heart disease, valvular heart disease, all type of cardiomyopathy, pericardial disease, myocarditis, heart failure, infection, malignancy and poor echocardiography window during examination were excluded.
Written informed consent was obtained from each subject following a detailed explanation of the objective and protocol of the study which was conducted in accordance with the ethical principles stated in the "Declaration of Helsinki", this study was approved by the institutional ethic committee.

Leptin measurement and echocardiography
After fulfilling the inclusion and exclusion criteria, subject underwent several data collection such as patient demographics (age, gender) anthropometrics (height, weight, body mass index (BMI), upper arm circumference). BMI was calculated as weight (kg) divided by height squared (m 2 ).
Venous blood samples were drawn into EDTA tubes after a 12-h overnight fast using standardized methods. Plasma leptin levels were determined by a commercial enzymelinked immunosorbent assay kit (BioVendor; Cat No: RD 191001100, USA).
Two-dimensional, M-mode, and Doppler echocardiography were performed according to the American Society of Echocardiography (ASE) guidelines by one cardiologist utilising a Philips Affiniti 50 ultrasound machine. The echocardiographic parameters chosen for further study were left ventricular mass index (LVMI), left ventricular ejection fraction (EF), left atrium diameter (LAD), left atrium volume index (LAVI) measured by dividing LA volume by both body surface area (BSA). Tissue Dopplerderived peak early diastolic septal mitral annular velocity (e'), ratio of peak early diastolic mitral velocity to tissue Doppler-derived peak early diastolic mitral annular velocity (E/e').

Statistical analysis
The statistical analysis was performed using computer software (SPSS version 21.0, SPSS Inc. Chicago, IL, USA). For numerical data, the data distribution tested using the Shapiro-Wilk method. Data that was normally distributed in the univariate analysis were expressed in mean and standard deviation, while data with abnormal sample distribution are expressed in median with range. Bivariate analysis was carried out after the univariate analysis to see the relationship between two variables. If the variables showed normal data distribution, then bivariate analysis was done using Pearson correlation and if it was not normal Spearman rank was used. The p value was less than 0.05 that considered statistically significant.

DISCUSSION
In the present study we have shown a clear association between leptin levels and left ventricular diastolic filling in young adult obese population. High fasting plasma leptin levels were associated with one of markers of impaired diastolic function. To our knowledge, the association between high leptin levels and impaired diastolic function has not been previously reported in young adult obese population.
We found a correlation between leptin and diastolic function with exclusion of confounding factors such as hypertension, diabetes mellitus, coronary artery disease and age limitation. These result support previous studies about correlation between leptin and diastolic function such as Puurunen et al. 24 , Kamimura et al. 25 , and Fontes-Carvalho et al. 23 .
Puurunen et al. conducted a study in Finland, the study using coronary artery disease (CAD) population and was divided in 4 quartiles based on the leptin. 24 Based on this study elevated plasma leptin levels are associated with impaired left ventricular diastolic function in patients with CAD independently of obesity and other confounding variables. Leptin may be one of the mechanistic links explaining the development of congestive heart failure in obese subjects. 24 The results in this research show that there is a negative correlation between leptin levels with left ventricular diastolic function using E/mean e' ratio parameter (r=-0.589, p<0.001), so it can be concluded that the higher levels of leptin will cause the higher the parameter of E/mean e' ratio. E/mean e' ratio, namely whether leptin's role is as a cause or as a marker. Previous theories stated that the role of leptin as a cause of decreased diastolic left ventricular function were: (1) leptin has the effect of profibrotic against the heart that can increase the levels of collagen in the extracellular matrix in muscle cells of the heart and the advent of changes in the heart muscle cell biology, 24 (2) leptin can cause interference to systems renin-angiotensin-aldosterone, renin-angiotensin in disorderaldosterone can increase collagen in extracellular matrix of the cardiac muscle cells effect on increasing the rigidity myocyte. 26 Correlation of leptin level and left ventricular diastolic function is supported by the research of the large cohort studies conducted by Fontes-Carvalho et al. 23 asserting that leptin as a cause of decreased in left ventricular diastolic function based on the results of studies which found that higher leptin level associated with decreased in diastolic function measured by echocardiography using Tissue doppler imaging (TDI) in follow up for 5 years. The association was independent of age, gender, ethnicity, systolic blood pressure, heart rate, smoking status, and BMI.  The theory of leptin as a cause of decreased diastolic left ventricular function is also supported by experimental studies conducted by Abe et al. 27 doing the study that states that exposure to leptin against the heart muscle cells cause changes the structure of the heart muscle cells than mice without leptin exposure groups. The research was also supported by Madani et al. 28 who conducted research on experimental mice with leptin exposure in the heart muscle cells causes changes in the structure of the heart muscle cells than mice without the exposure groups leptin.
There are several limitations in this study. Analysis of influence of gender between leptin and diastolic function cannot be measured due to unbalance participant in both groups. Due to the design of this study, further analysis through a prospective cohort study and length of obese is needed to explain whether a high leptin is the cause of the decrease diastolic function.

CONCLUSION
There was a significant correlation between leptin level and diastolic function in young adult obesity. The higher leptin level, the lower diastolic function.