The Investigation of the Calcium Metabolism Changes in Rheumatic Mitral Valve Patients

Aziz İnan Çelik1, Reşit Coşkun2, Muhammet Buğra Karaaslan3, Tahir Bezgin1, Süleyman Karakoyun4, Metin Çağdaş1

1Clinic of Cardiology, Heart Center, Gebze Fatih State Hospital, Kocaeli, Turkey
2Department of Cardiology, Erzincan Binali Yıldırım University Faculty of Medicine, Erzincan, Turkey
3Clinic of Cardiology, Osmancık State Hospital, Çorum, Turkey
4 Clinic of Cardiology, Akademi Hospital, Kocaeli, Turkey

Keywords: Mitral valve; parathyroid hormone; vitamin D; inflammation

Abstract

Introduction: Rheumatic mitral valve disease (RMVD) is associated with autoimmune heart valve injury. Parathyroid hormone (PTH) and vitamin D are two essential molecules that have effects on the immune system. In this study, we aimed to evaluate the relationship between PTH and vitamin D in patients with RMVD.

Patients and Methods: We investigated 81 patients with RMVD and 75 healthy subjects. According to Wilkins score, baseline clinical, laboratory, and echocardiographic parameters were recorded, and all RMVD patients were analyzed. Multivariate logistic regression analysis was performed between the groups.

Results: Vitamin D levels were significantly low in the RMVD group. Patients were stratified according to Wilkins score [Wilkins score <7 (n= 50) vs. Wilkins score ≥7 (n= 31)]. Age, BMI, and PTH were significantly higher, and mitral valve area was significantly lower in Wilkins score ≥7 patients. In multivariate analysis, age (OR= 1.052; 95% CI 1.005-1.100, p= 0.028) and PTH (OR= 1.017; 95% CI 1.000-1.033, p= 0.047) were found to be independent predictors of high Wilkins score.

Conclusion: This study showed that vitamin D levels were low in patients with RMVD. According to the Wilkins score, PTH levels were significantly high in patients with a high Wilkins score. Changes in PTH and vitamin D levels may trigger inflammation and be responsible for valve damage.

Introduction

Rheumatic mitral valve disease (RMVD) is the most common cause of mitral valve stenosis worldwide, is more common in developing countries, and progresses faster. It is an immune response that occurs with cross-reactivity between streptococcal antigen and valve tissue(1). Patients who have recurrent acute rheumatic fever carditis are more likely to develop RMVD. Mitral valve can be affected in 50% of patients and results in mitral stenosis, mitral insufficiency, or both(2,3). Inflammation, fibrosis, and calcification are the essential factors in the progression of mitral stenosis due to autoimmune heart valve damage after streptococcal infection. Wilkins calcification scoring is a widely used scoring system to determine the disease’s severity in rheumatic mitral stenosis(4).

Parathyroid hormone (PTH) and vitamin D are the primary regulators of calcium balance and bone mineral turnover. Increased PTH (primary or secondary) levels bear a high risk of cardiovascular mortality and cause cardiovascular diseases such as coronary microvascular dysfunction, valvular calcification, increased vascular stiffness, endothelial dysfunction, and hypertension(5,6). On the other hand, vitamin D, another vital hormone of calcium metabolism, is involved in suppressing the inflammatory process(7). Studies conducted in previous years have shown that low levels of vitamin D are associated with RMVD(8). On the other hand, high levels of vitamin D have been shown to play a role in tissue calcification(9-11). Therefore, abnormally high or abnormally low vitamin D can cause heart valve diseases with different mechanisms.

This study aimed to examine the relationship between PTH, vitamin D, serum calcium, and serum phosphate levels in patients with RMVD.

Materials and Methods

Eighty-one patients with RMVD and 75 healthy age and gender-matched control subjects were enrolled after the exclusion criteria. Exclusion criteria were defined as follows; age <18, pregnancy, alcohol consumption, chronic renal failure (Cockcroft-Gault GFR< 60 mL/min/1.73 m2 ) (n= 5), chronic hepatic failure (ALT and AST levels higher than 3-folds of normal levels), pancreatitis, celiac disease, malignancy (n= 1), tumor lysis syndrome, primary hypoparathyroidism, and hyperparathyroidism, hypothyroidism (n= 7), hyperthyroidism (n= 3), acute or chronic inflammatory, and autoimmune diseases, metabolic bone diseases, heart valve surgery history, bariatric surgery history, medication use that may affect PTH levels (n= 9). The study protocol was reviewed and approved by the Local Ethics Committee and the study was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all participants. The patients’ age, gender, smoking status, body mass index (BMI), systolic blood pressure, heart rate, laboratory and echocardiographic parameters were recorded in detail.

Transthoracic echocardiographic examinations were performed using Philips Epiq 7G Ultrasound System (Philips, The Netherlands) (S8-3, 3-8 MHz probes). Left ventricular ejection fraction (EF), systolic pulmonary arterial pressure (sPAP), planimetric mitral valve area, mitral valve gradients, mitral valve pressure half-time, mitral insufficiency (MR), and aortic insufficiency (AR) were measured with 2D-transthoracic echocardiography. Wilkins scores (leaflet mobility, valvular calcification, valvular thickening, and subvalvular thickening) were calculated in RMVD. All valvular measurements were performed and classified according to the 2020 AHA/ACC Guideline for the Management of Patients with Valvular Heart Disease(12).

Venous blood samples were obtained to dry tubes from all patients on admission. Fasting blood glucose, creatinine, sodium, potassium, albumin, calcium, corrected calcium [measured total Ca (mg/dL) + 0.8 (4.0 - serum albumin) (g/dL)] and phosphorus were measured using a Roche Cobas C501 autoanalyzer system (Roche Diagnostics, Indianapolis, IN, USA). A standard enzymatic method with an AU6B0 autoanalyzer (Beckman Coulter, Brea, CA) was used for the measurement of total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride levels. A standard nephelometry method was used to measure C-reactive protein levels (CRP) (Cobas c311; Roche Diagnostics, Mannheim, Germany) with a sensitivity of 0.1 mg/L. Vitamin D concentration was measured with automatic direct electrochemiluminescence immunoassay (Elecsys; Roche Diagnostics), and the electrochemiluminescence microparticle immunoassay was used to measure PTH levels with a Cobase 601 kit (Roche Diagnostics).

Data were analyzed using SPSS 22.0 version (SPSS Inc, Chicago, Illinois). The continuous variables with a normal distribution of mean ± SD and t-test are used in group comparison. In contrast, those without a normal distribution are presented as median (interquartile range). Categorical variables are shown as numbers and percent (%). Categorical data were compared using the Chi-square or Fisher’s exact test. Group comparison was performed with the Mann-Whitney U test. Correlations between variables were assessed by the Pearson correlation test for continuous variables and the Spearman test for non-continuous variables. Statistical significance was defined as a p-value <0.05. Multivariate logistic regression analysis was used to determine the independent predictors of the high Wilkins score.

Results

A total of 156 patients (81 RMVD group and 75 control group) were enrolled. Fifty-five patients (67.9%) in the RMVD group and 45 patients (60%) in the control group were female. Baseline characteristics and laboratory parameters of the study population are demonstrated in Table 1. All baseline characteristics and laboratory parameters were similar between the two groups except albumin, vitamin D, and HDL-C. albumin, vitamin D and HDL-C levels were significantly low in RMVD group [4.3 ± 0.3 vs. 4.5 ± 0.4, p= 0.003; 11.3 (8.7-16.3) vs. 17.7 (11.8-21), p< 0.001; 40 (37-43) vs. 44 (39-51), p< 0.001, respectively]. However, there were no differences in PTH, calcium, corrected calcium, and phosphorus levels.

Table 1. The baseline clinical and laboratory characteristics of the RMVD patients and control group

Patients were stratified according to Wilkins score [Wilkins score <7 (n= 50) vs. Wilkins score ≥7 (n= 31)]. Age, BMI, PTH, mean pressure gradient, pressure half-time of the mitral valve, and sPAP were significantly higher, and mitral valve area was significantly lower in Wilkins score ≥7 patients [40.5 (30-47) vs. 48 (40-56), p= 0.015; 25.2 ± 3.7 vs. 27.2 ± 4.2, p= 0.026; 56.1 (39.5-78.6) vs. 79 (57-91), p= 0.008; 2.5 (1.8-3.5) vs. 5.7 (3-7.2), p<0.001; 88.6 ± 13.3 vs. 136.9 ± 43.7, p< 0.001; 18.5 ± 2.8 vs. 28.8 ± 12.1, p< 0.001; 4 (3-4.5) vs. 2.1 (1.4-2.9), p< 0.001, respectively] (Table 2). There was no symptomatic severe MR and AR (stage D) in either group. Progressive MR (stage B) and asymptomatic severe MR (stage C) were significantly higher in patients with a Wilkins score of ≥7 for MR (p= 0.029). Similarly, stage A and stage B AR were significantly higher in patients with a Wilkins score of ≥7 (p= 0.002).

Table 2. Clinical, laboratory and echocardiographic parameters according to Wilkins score

The correlation between age, vitamin D, PTH levels and mitral valve area, mean pressure gradient of the mitral valve, and Wilkins score was investigated. There was a negative correlation between advanced age and mitral valve area; a positive correlation between mean pressure gradient and Wilkins score found (-0.269, p= 0.015; 0.235, p= 0.035; 0.291, p= 0.008). There is a significant correlation between vitamin D and the mitral valve area (0.223, p= 0.045). A negative correlation between PTH and mitral valve area, a positive correlation between mean pressure gradient and Wilkins score were found (-0.403, p< 0.001; 0.291, p= 0.008; 0.327, p= 0.003) (Table 3) (Figure 1-2).

Table 3. Correlation between age, vitamin D and PTH with high Wilkins score

Figure 1. Negative correlation between PTH and mitral valve area. PTH: Parathyroid hormone.

Figure 2. Positive correlation between PTH and Wilkins score. PTH: Parathyroid hormone.

Multivariate logistic regression analysis was performed using parameters (age, BMI, and PTH) that differed between the groups to determine the independent predictors of the high Wilkins score. In multivariate analysis, age (OR= 1.052; 95% CI 1.005-1.100, p= 0.028) and PTH (OR= 1.017; 95% CI 1.000- 1.033, p= 0.047) were found to be independent predictors of high Wilkins score.

Discussion

To the best of our knowledge, this is the first study to assess the serum vitamin D and PTH in RMVD. We aimed to evaluate the changes in calcium metabolism at the beginning of the disease. The present study found that vitamin D levels were significantly lower in RMVD than in control subjects. However, there was no significant difference in PTH between the two groups. When patients were grouped according to Wilkins score, the opposite results were obtained. PTH was significantly higher in the high Wilkins score group (Wilkins score≥ 7). Yet, this difference was not significant for vitamin D. When the literature was reviewed, very few studies examined calcium metabolism changes in patients with RMVD. In addition, chronic inflammation, recurrent carditis attacks, low socioeconomic status, and increased PTH levels were associated with a high Wilkins score.

Molecular similarities between streptococcal antigens such as M protein and cardiac tissue proteins activate the CD4 + T cells and cause valve damage(13). RMVD is an autoimmune valvular disorder that causes progressive and devastating consequences. Disequilibrium between pro- and anti-inflammatory cells induces the target organ damage in all autoimmune diseases(14). These CD4 + T cells transform into Th1 helper cells, causing tissue damage by secreting cytokines such as tumor necrosis factor-alpha (TNF-a), interferon, interleukin (IL)-17, IL-22. TNF has also been shown to increase calcification by promoting differentiation of valve interstitial cells to osteoblasts(15-18).

Vitamin D has several effects on T cells that can modulate the immune response(19). This effect occurs through vitamin D receptors (VDR), identified on CD4 + T cells(20). VDRs are in the nuclear steroid/thyroid hormone receptor family and are located in the bone marrow and thymus(21). Besides CD4 + T cells, VDRs have also been identified in mononuclear cells, dendritic cells, and activated B lymphocytes. Vitamin D inhibits the proliferation of effector CD4 + T cells while contributing to the development of anti-inflammatory T cells(22, 23). Vitamin D also inhibits the production of inflammatory cytokines such as TNF-a produced by Th1 helper T cells, ¡ interferon, and IL17 produced by Th17 helper T cells(24,25). Th1 functions are inhibited by IL-4 and IL-10, which were produced by another T cell, Th2. Overberg et al. have shown that vitamin D increases IL-4 levels in in-vivo conditions(26).

On the other hand, vitamin D inhibits B lymphocyte proliferation, conversion to plasma cells, and antibody secretion. In vitamin D deficiency, this inflammatory balance is disrupted in favor of proinflammation and contributes to valve damage in RMVD. Clinical studies support this molecular mechanism. In the study conducted by Yusuf et al., vitamin D levels were significantly lower in patients with damaged and severe calcified RMVD than in patients with less damaged and non-calcified RMVD(27). In the same study, vitamin D levels correlated with the Wilkins score and Wilkins calcification score. In another study conducted by Yavuz et al., the control and patient groups with RMVD were compared. Patients with RMVD had a significantly lower vitamin D level than the control group and correlated with Wilkins score(8). As in the literature, in our study, the vitamin D levels of patients with RMVD were lower than in the control group. There is also a significant correlation between vitamin D and the mitral valve area. According to Wilkins score, vitamin D level was lower in patients with high Wilkins scores, but this finding was not statistically significant.

Parathyroid hormone (PTH) is the primary regulator of calcium balance in physiological and pathological conditions and plays an essential role in bone hemostasis. PTH may play a role beyond the one in mineral and bone metabolism in the pathophysiology of vascular and cardiovascular diseases. Clinically, patients with primary hyperparathyroidism have a higher risk of cardiovascular mortality and have a broad spectrum of cardiovascular diseases such as coronary microvascular dysfunction, subclinical aortic valve calcification, increased aortic stiffness, endothelial dysfunction, and hypertension(28). Besides, secondary hyperparathyroidism, a significant complication in patients with chronic kidney disease, causes abnormal bone disorders, non-skeletal calcification such as vascular and valvular calcification, and increased cardiovascular mortality. Many studies have shown that high serum PTH levels have a proinflammatory effect. In a study by Cheng et al., a relation was found between high PTH levels and various inflammatory markers (C-reactive protein, the modified Glasgow Prognostic Score, red cell distribution width, and the platelet-to-lymphocyte ratio)(29).

There is a strong relationship between vitamin D and PTH. A decrease in vitamin D levels leads to a reduction in calcium absorption from the intestine, and the organism responds by increasing the secretion of PTH. As a result, there is an inverse correlation between PTH and vitamin D. In a study by Linhartova et al., high PTH and low vitamin D levels are associated with calcific aortic stenosis in coronary artery patients(10). In another study, Eren et al. compared 56 chronic heart valve patients (AR and MR) with the control group. Compared to the control group, vitamin D levels are significantly low, and PTH is higher in patients with heart valve disease(30). Yusuf et al. demonstrated the relationship between the severity of the disease and the PTH level in patients with RMVD(27). In our study, RMVD had higher PTH levels than the control group; however, there were no significant differences between the two groups. According to the Wilkins score, PTH was significantly higher in patients with a high Wilkins score. Apart from the Wilkins score, there is a positive correlation between PTH and the mitral valve area and a negative correlation between PTH and the mean pressure gradient.

The present study has several limitations. First, the number of patients was relatively low. Second, this study involves only non-stenotic rheumatic mitral valves. However, stenotic rheumatic mitral valves may affect calcium metabolism more significantly. Third, this study did not contain the follow-up data of the patients. Finally, it has a cross-sectional design.

Conclusion

In conclusion, in this study, we investigated the inflammatory response caused by the change in PTH and vitamin D levels and the resulting contribution to rheumatic change in the mitral valve. Vitamin D level was lower in patients with RMVD compared to the control group. According to the Wilkins score, the PTH level was significantly higher in patients with a high score. Future studies with larger populations are warranted to clearly identify the relationship between RMVD and vitamin D and PTH.

Ethics Committee Approval

The study was approved by the Health Sciences University Kocaeli Derince Training and Research Hospital Clinical Research Ethics Committee (Date: 25.02.2021, Decision No: 2020/135).

Peer Review

Externally peer-reviewed.

Author Contributions

Concept/Design - AİÇ; Analysis/Interpretation - SK; Data Collection - AİÇ; Writing - TB; Critical Revision - MÇ; Final Approval - RC; Statistical Analysis - MÇ; Overall Responsibility - RC.

Conflict of Interest

The authors declared that there was no conflict of interest during the preparation and publication of this article.

Financial Disclosure

The authors declared that this study has received no financial support.

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Figure and Tables

Figure 1. Negative correlation between PTH and mitral valve area. PTH: Parathyroid hormone.
Figure 2. Positive correlation between PTH and Wilkins score. PTH: Parathyroid hormone.
Table 1. The baseline clinical and laboratory characteristics of the RMVD patients and control group
Table 2. Clinical, laboratory and echocardiographic parameters according to Wilkins score
Table 3. Correlation between age, vitamin D and PTH with high Wilkins score