Association between serum cystatin C and early impairment of cardiac function and structure in type 2 diabetes patients with normal renal function

Abstract Background Type 2 diabetes mellitus (T2DM) patients may have cardiac remodeling and dysfunction from the early stage of disease. This study aimed to determine the association between cystatin C (CysC) and early cardiac functional or structural impairment in T2DM patients without renal dysfunction. Methods A total of 1135 T2DM patients without renal dysfunction and known heart diseases were included in our study. Cardiac function and structure were evaluated by echocardiography. Patients were diagnosed as left ventricular hypertrophy (LVH), impaired left ventricular (LV) diastolic function, and categorized into four different LV geometry patterns including normal, concentric remodeling, concentric hypertrophy, and eccentric hypertrophy. Results In multivariate linear regression analyses, CysC was positively associated with interventricular septum, LV mass index, left atrial volume index, E/e' ratio, and negatively associated with Tissue Doppler e', E/A ratio (p < .05). As a continuous variable, increasing CysC levels were associated with prevalence of LVH (OR: 1.47, 95% confidence interval [CI]: 1.22–1.77), impaired LV diastolic function (OR: 1.58, 95% CI: 1.33–1.87), concentric hypertrophy (OR: 1.54, 95% CI: 1.23–1.93) and eccentric hypertrophy (OR: 1.34, 95% CI: 1.00–1.80) according to multivariate logistic regression analyses. While as a categorical variable, the highest CysC quartile (CysC > 1.04 mg/L) was associated with LVH (OR: 2.95, 95% CI: 1.74–5.00), impaired LV diastolic function (OR: 4.09, 95% CI: 2.54–6.60), and concentric hypertrophy (OR: 3.26, 95% CI: 2.05–5.18). Conclusions CysC was significantly associated with early LV remodeling and cardiac functional impairment in T2DM patients with normal renal function. It could be a reliable and convenient biomarker detecting early impairment of cardiac function and structure in T2DM patients.

patients are likely to have cardiac remodeling and dysfunction regardless of CAD, especially in the early stage of disease. 2 Therefore, early detection and intervention of cardiac functional and structural impairment are essential for T2DM patients, otherwise, it will develop into symptomatic heart failure. Furthermore, previous studies demonstrated the differences in biomarker profiles in patients with and without T2DM, indicating the clinical importance to explore the novel biomarkers for early detection of cardiac remodeling and dysfunction in T2DM patients. 3,4 Cystatin C (CysC), a potent cysteine protease inhibitor that plays pleiotropic roles in human vascular pathophysiology, 5 is generated by nucleated cells and removed from the bloodstream by the glomeruli.
It has been considered to be a reliable biomarker of renal function 6 and not influenced by age, gender, or muscle mass. 7,8 Previous studies have suggested that CysC is preferable than creatinine (Cr) for detecting early decrease in renal function, especially for diabetes patients. 9 Although CysC has already been shown to be a risk factor of CVD morbidity and mortality regardless of patients with nephropathy or not, [10][11][12] the exact mechanisms remained controversial. In addition, it has been reported that CysC was independently associated with microvascular complications such as diabetic retinopathy and DN in T2DM patients. 13,14 Diabetes promotes cardiac remodeling partially by cardiac muscle-specific microvascular complication, thereby aggravating impairment of cardiac function and structure. 15 These effects occur independent of other structure heart diseases such as CAD and hypertensive heart disease. 2 Therefore, we hypothesized that CysC is associated with early impairment of cardiac structure and function in T2DM patients. We performed a cross-sectional study in T2DM patients without overt heart failure and known structural heart diseases to test this hypothesis. To avoid the influence of renal dysfunction, we also excluded the patients with abnormal renal function which was assessed by Cr and Cr-based estimated glomerular filtration rate (eGFR).

| Study population and data collection
This cross-sectional observational study consecutively enrolled type 2 diabetic patients who admitted in the Third Affiliated Hospital of Sun Yat-sen University for glycemic control and finished echocardiography examination from April 2019 to May 2020. T2DM was diagnosed according to the 1999 criteria of the World Health Organization (WHO). 16 Patients were excluded in cases of the following conditions: (1) eGFR <60 ml/min per 1.73 m 2 which was defined as renal dysfunction 17 ; (2) overt heart failure with a New York Heart Association (NYHA) functional classification of III of IV; (3) left ventricular ejection fraction (LVEF) less than 50%; (4) known organic heart diseases including coronary heart disease, valvular heart disease, primary cardiomyopathy, alcoholic cardiomyopathy or congenital heart disease; (5) chronic atrial fibrillation; (6) insufficient clinical data which was essential for our study. Ethical approval was obtained from the Third Affiliated Hospital of Sun Yat-sen University Network Ethics Committee. Informed consent was obtained from all participants.

| Data collection and laboratory measurements
Demographic and clinical data, including gender, age, height, weight, systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), lifestyles (smoking status and alcohol consumption), comorbidity, duration of diabetes and medications in the past 2 weeks were obtained for all patients by a well-trained researcher. Blood pressure and HR were measured in the right upper arm using oscillometric methods after 10 min of rest. Body mass index (BMI) was calculated as body weight divided by the square of height. Hypertension was diagnosed as SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg or current use of antihypertensive medication. 18 Blood and urine samples were levels were evaluated by high-pressure liquid chromatography (Bio-Rad, D-10 analyzer). The concentration of serum CysC was measured by particle-enhanced turbidimetric immunoassay (HITACHI, 7600-020 autonomic analyzer).

| Echocardiography examination
Transthoracic echocardiography (IE33 echocardiography system) was performed on all participants according to the recommendations of the American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACI) 19  (2) septal e' < 7 cm/s; (3) TR velocity > 2.8 m/s; (4) LAVi > 34 ml/m 2 .  After exclusion of individuals with known heart diseases, impaired renal function, or missing CysC data, a total of 1135 patients (644 men and 491 women, mean age 58.97 ± 7.25 years) were eligible for analysis (Supporting Information: Figure 1). Clinical characteristics of the subjects are presented in Table 1. Patients with higher serum CysC levels were older, more hypertensive, longer diabetes duration, lower hemoglobin, higher UA, and lower FBG. Of the renal function indices, CysC levels were significantly correlated to Cr, eGFR, and BUN. As for the medications, proportion of ACEI/ARB, CCB, β blocker, and diuretic intakes varied among groups while there were no significant differences of other drugs. However, there were no significant differences of lipid profiles, HbA1c, proportion of smoker, and drinker among groups.

| Association between serum CysC levels and cardiac structural and functional parameters
The echocardiographic parameters reflecting cardiac structure and function were compared among the four CysC quartiles first (Figure 1, association between serum CysC levels and cardiac structural or functional abnormalities. [30][31][32] However, these studies did not exclude subjects with chronic kidney diseases. Recently, CysC was considered to be a more reliable biomarker of renal function rather than Cr especially in some particular situations. 6

| CONCLUSION
In summary, our study demonstrated that elevated serum CysC was significantly associated with early LV remodeling and cardiac functional impairment in T2DM patients with normal renal function, mostly reflecting in LVH, impaired LV diastolic function, and LV concentric hypertrophy. These associations indicated that CysC could be a reliable and convenient biomarker detecting early impairment of cardiac function and structure in T2DM patients. Xiaomin Ye collected the data needed for our study. Yifen Lin and Xiangbin Zhong were responsible for the modification of manuscript.