Author's response to reviews Title:Hyperphosphatemia as an Independent Risk Factor of Coronary Artery Calcification Progression in Peritoneal Dialysis Patients Authors: Da Shang (sdshangda@163.com) Qionghong Xie (qionghongxie@fudan.edu.cn) Xiaolin Ge (ge_xiaoling@hotmail.com) Huanqing Yan (flynowhere@126.com) Jing Tian (jingtianhuashan@163.com) Dingwei Kuang (dingweikuang@medmail.com.cn) Chuan-Ming Hao (chuanminghao@fudan.edu.cn) Tongying Zhu (zhuty25@medmail.com.cn) Version:3Date:18 March 2015 Author's response to reviews: see over
March 17, 2015 Dear Editor, Thank you for your reviewing of our manuscript entitled Hyperphosphatemia as an Independent Risk Factor of Coronary Artery Calcification Progression in Peritoneal Dialysis Patients (MS: 1924105222143414). We are very grateful to all of the reviewers for their careful reading and thoughtful comments. We have made modifications according to the comments in our revised manuscript. Below please find a point-by-point response addressing each of the reviewer s comments in detail. We hope the response has adequately addressed the main concerns of the reviewers and the revised manuscript is adequate for publication. Sincerely yours, ShangDa Division of Nephrology Huashan Hospital, Fudan University 12 Wulumuqi Road (middle), Shanghai 200040, China Tel: 86-21-52887798 Reviewer 1 1. Aim of the study was to identify modifiable risk factors for CAC progression in PD patients. High BMI was also found to be an independent risk factor for CAC progression, however this is not mentioned in the conclusion. Although the association between high BMI and CAC progression is not as strong as found for phosphorus, this point should be further stressed in the conclusion and the discussion section. If the primary endpoint was to investigate the association of phosphorus and the progression of CAC, then it wouldn t be necessary to mention the association with BMI particularly, but in this case the primary aim of the study should be adapted. Thanks for your constructive comments and suggestions. Our univariate analysis showed that high BMI was the independent risk factor for CAC progression, However, when we also added HDL into the multivariate analysis according to your suggestion, BMI lost the relevance (p=0.073). Although the effect of dyslipidemia on atherosclerosis is well
documented, its effect on media calcification is less well characterized in human, partially because that the technique to measure CAC can not differentiate atherosclerotic calcification and media calcification characteristic of ESRD patients. More studies are probably required to understand the association of metabolic disorder and vascular calcification in ESRD patients. 2. The authors concluded that serum phosphate is correlated with nutritional intake. Indeed the multivariate analysis revealed that higher transferrin, serum albumin and npcr, all markers for nutritional status, are independently associated with hyperphosphatemia. Although this indicate a higher daily phosphorus intake, in my opinion it doesn t allow the conclusion that serum phosphate is correlated with nutritional intake, because phosphorus intake was not documented in this study. Maybe the authors should change/weaken the conclusion (e.g. serum phosphorus was positively associated with nutritional markers, indicating a higher daily phosphorus intake ) Thanks for your suggestions. We have changed the serum phosphate was correlated with nutritional intake and PD adequacy to serum phosphate was positively associated with nutritional markers and PD adequacy, indicating a higher daily phosphate intake and PD inadequacy may accelerate the CAC progression in the revised manuscript. 3. I did not find any information about exclusion criteria, didn t they have any? This study did have exclusion criteria. We apologize for not described in the manuscript. We have added the exclusion criteria information in the text. The patients who received regular PD for more than 6 months and underwent CaCS measurements at least twice with an interval 6 months, were analyzed. The patients were excluded if they had acute infection, unstable cardiovascular disease or were clinically unstable with life expectancy shorter than 6 months. If the patient s active diseases were stable more than 2 months, the patients were eligible for this study. The study was approved by the ethics committee of Huashan Hospital at Fudan University. All of the patients were provided written informed consent. 4. I would also be interested in detailed information about dialysis regime (CAPD, CCPD, ) as well as about the primary cause of ESRD. We have added the dialysis regime and the cause of ESRD in the text and table 1. We thank the reviewer for the suggestion. More than 90% of patients in our study received continuous ambulatory peritoneal dialysis (CAPD), while others received daytime ambulatory peritoneal dialysis (DAPD). All of the peritoneal dialysate were Dianeal PD4 (calcium 1.25 mmol/l, 2 L) or/and Dianeal PD2 (calcium 1.75 mmol/l, 2 L) from Baxter Healthcare Corporation. About 93% of patients received 3 changes (62%) or 4 changes (31%) of the dialysate and the long dwelling time was 12 hours and short dwelling time was 4 to 6 hours. Icodextrin is not available in China, so no icodextrin was used in our center. There were no significant differences in the use of CAPD and Dianeal PD4/PD2 between the rapid and slow groups. There was no significant differences in the cause of ESRD (Table 1).
Part of table 1 Total (n = 207) Slow Group (n = 137) Rapid Group (n = 70) P-value Cause of ESRD 0.311 Glomerulonephritis 124 (59.9%) 84 (61.3%) 40 (57.1%) Diabetes mellitus 61 (29.5%) 34 (24.8%) 27 (38.6%) Polycystic kidney 5 (2.4%) 4 (2.9%) 1 (1.4%) Hypertension 5 (2.4%) 5 (3.6%) 0 (0%) Others 12 (5.8%) 10 (7.3%) 2 (2.9%) 5. No information is given about the occurrence of deaths and cardiovascular events during follow-up. During the follow-up period, 57 patients died and 54 patients experienced CVEs. Among the patients who died, 25 patients died of CVEs and 14 patients died of infections. 25 patients died in the rapid group (70 patients), while 32 patients died in the slow group (137 patients). We have added this information into the revised manuscript. 6. The authors mentioned in the methods section that CVD was also recorded at the baseline, but they didn t report on this. I didn t find any information about the proportion of CVD in the results/ tables. Detailed information, especially on previous ischemic heart disease would be interesting with regard to the progression of CaCS. 8 patients had history of the CVEs at the baseline, and there was no significant differences between the groups (1/70 vs 7/137, p=0.195). We have added this information into the revised manuscript. Thank you for your suggestion. 7. The use of calcium carbonate was documented. Did the authors also analyze the relationship between medication and CAC progression? If not, this would be of interest. According to phosphorus levels, also the association between treatment with phosphate binders/ calcitriol would be interesting. Our univariate analysis shows that calcium carbonate use was associated with CAC progression (78/137 vs 55/70; p=0.002). Because in our cohort, only those patients with hyperphosphatemia were prescribed calcium carbonate, we considered they are two dependent variables. Therefore we did not put calcium carbonate into multivariate analysis. However, we analyzed the correlation of the serum phosphate and CaCS progression with partial correlation analysis, adjusting calcium carbonate, age, BMI, sex, renal residual Ccr and basic CaCS. It showed that serum phosphate was associated with the CaCS progression. 8. In the discussion the authors wrote that approximately two-thirds of the patients were recruited at the beginning of PD treatment. However, no detailed information is given about the PD therapy duration at baseline. This would be of interest, because some studies have shown an association between PD duration and progression of CAC. If available, PD duration should also be tested as a risk factor for progression of CAC.
We thank the reviewer for the suggestion. 70 patients started PD before this study (from 0.5 9 years). The average duration of PD therapy for all the patients at baseline was 1.08 (-0.26-7.10) months and there were no significant differences between the groups. We have added the PD duration at baseline in the text. 9. The authors mentioned in the results that patients with rapid progression had a lower HDL however this variable was not included the multivariate analysis. Why? Thanks for your suggestions. We analyzed the HDL in the multivariate analysis, and found that age (p=0.023) and serum phosphate (p=0.031) were associated with the CaCS progression, while the BMI (p=0.073) and HDL(p=0.569) were not. Therefore, we revised the multivariate analysis result ( Table 2). 10. In the discussion section the authors wrote: In addition, the restriction of phosphorus intake and increase of PD adequacy were useful for slowing the progression of vascular calcification. This sentence confuses me a little bit- did the authors mean that restriction of phosphorus intake and increase of PD adequacy may be useful for slowing the progression of vascular calcification? Thanks for your suggestions. We changed In addition, the restriction of phosphorus intake and increase of PD adequacy were useful for slowing the progression of vascular calcification to Therefore, the restriction of phosphorus intake and increase of PD adequacy may be useful for slowing the progression of vascular calcification. Minor Essential Revisions 1. I am missing figure/table titles and the figures and tables should be numbered. Also I would suggest removing most of the abbreviations in the table legend, referring reader to text. Thanks for your suggestion. We have numbered the figures/tables and removing most of the abbreviations in the table legend. 2. In table 1 the authors termed the two groups group 0 and group 1, but either in the text nor in the figure legend the slow group is defined as 0 and the rapid group as 1. Thanks for your suggestion. We have changed group 0 to slow group and group 1 to rapid group in the table 1. 3. Just minor changes for table 1: Follow time -> Follow-up time Some of the variables are uncapitalised (age, smoking) Lipid-lowering drud use -> Lipid-lowering drug use
Thanks for your suggestion. We have changed Follow time to Follow-up time ; age to Age ; smoking to Smoking and Lipid-lowering drud use to Lipid-lowering drug use in table 1. Reviewer 2 MAJOR COMPULSORY REVISIONS 1. My main concern is the heterogeneity of the slow progression group due to the inclusion in this category of both the subjects without coronary calcification and those with lower progression parameters. Because the severity of baseline calcification seems directly correlated with the probability and degree of coronary calcification progression over time (as shown by Chertow GM et al. for the Treat To Goal working group, Kidney Int. 2002), it is conceivable that different risk factors contribute to the initiation and progression of vascular calcification. Therefore, I suggest to form three groups of subjects: non-progressors, slow progressors and rapid progressors, and to redone the statistical analysis accordingly. We thank the reviewer for the very constructive suggestion. According the reviewer s suggestion, we analyzed the subjects without coronary calcification throughout the study, those with slow progression of coronary calcification and those with rapid progression as defined. In univariate analysis, serum phosphate levels in rapid progressors (5.0 ± 0.88 mg/dl) were significantly higher than slow progressors (4.37 ± 0.86 mg/dl) (p < 0.001) and consistent with our previous result. However the serum phosphate levels in those with no coronary calcification throughout study (4.84 ± 1.06 mg/dl) was no different compared with rapid progressors (p=0.36) and significantly higher than slow progressors. In multivariate analysis, serum phosphate was the independent risk factor of CAC progression after adjusting the age, gender, basic CaCS, total Ccr, hemoglobin, BMI (p=0.048). This result may suggest that the serum phosphate was not the risk factor contributes to the initiation of vascular calcification (non-progressors vs rapid progressors; p=0.36), but it was the independent risk factor in multivariate analysis after adjusting the age, gender, basic CaCS, total Ccr, hemoglobin, BMI (slow progressors vs rapid progressors; p = 0.048). MINOR ESSENTIAL REVISIONS 1. I suggest to add the absolute change in calcification score (at the end of observation period versus baseline) as a study parameter. Thanks for your suggestion. We added the absolute change in calcification score as a study parameter in Table 1. In univariate analysis, the patients with rapid progression had higher absolute change in calcification score at the end of observation period (absolute CAC) versus baseline compared with the slow group 2. Detailed comments on the significantly higher percentage of calcium carbonate users in the rapid progression group should be added in the Results and Discussion sections.
Thanks for your suggestion. In the results section, we added that among these patients, 133 (64.3%) received calcium carbonate (78/137 vs 55/70; p=0.002). and 143 (69.1%) patients received calcitriol for treatment. In the discussion section, we added that Our univariate analysis showed that calcium carbonate use was associated with CAC progression in (78/137 vs 55/70; p=0.002). Because in our cohort, only those patients with hyperphosphatemia were prescribed calcium carbonate, we considered they are two dependent variables. Therefore we did not put calcium carbonate into multivariate analysis. However, we analyzed the correlation of the serum phosphate and CaCS progression with partial correlation analysis, adjusting calcium carbonate, age, BMI, sex, renal residual Ccr and basic CaCS. It showed that serum phosphate was associated with the CaCS progression. Therefore, our study suggested the serum phosphate was the independent risk factor of CaCS progression, but our study does not exclude the possible association between calcium carbonate and CaCS. 3. The fact that diabetes mellitus had a trend to be more prevalent (0.053) in the rapid progression group warrants some remarks. Thanks for your suggestion. We added Our study found that diabetes mellitus had a trend to be more prevalent (p=0.053) in the rapid progression group in univariate analysis. This may be associated with the stimulation of glycoxidation and hypoxia under hyperglycaemia to the artery. Further studies are required to identify the metabolic factors that are related to diabetes that contribute to aortic calcification diabetic PD patients. in discussion section. 4. Comments on the possible relation with renal residual function would be interesting, especially since recently serum phosphate was correlated with renal residual function and it was suggested that this could contribute to the lesser extent of cardiac valve calcifications in PD versus HD patients (Rroji M et al., Int Urol Nephrol 2014:175-182) Thanks for your suggestion. We added Rroji M s study shows that the residual renal function in PD patients contributes significantly to the maintenance of phosphate balance and may explain the lower prevalence of valve calcification in PD patients compared with HD patients. Renal residual function not only provides small solute clearance but also plays an important role in maintaining fluid balance, phosphate control, and the removal of middle molecule uremic toxins. In our study, dialysis adequacy were associated with CAC progression in univariate analysis, underlining the importance of RRF in control of the vascular calcification. in discussion section. 5. The reference for the statement In addition, the restriction of phosphorus intake and increase of PD adequacy were useful for slowing the progression of vascular calcification (page 10, first paragraph) should be inserted (if this is not cited from
previously published literature and is the authors own statement, it should be clearly presented as hypothesis because no therapeutic intervention was investigated in the current study, so it can not be sustained by the results). Thanks for your suggestion. We have changed the In addition, the restriction of phosphorus intake and increase of PD adequacy were useful for slowing the progression of vascular calcification to Therefore, the restriction of phosphorus intake and increase of PD adequacy may be useful for slowing the progression of vascular calcification. DISCRETIONARY REVISIONS 1. It is better to use the same term all through the manuscript for serum phosphate (because hyperphosphatemia rather refers to serum phosphate, as most phosphorus in the body is bound in organic phosphate compounds, this term is preferable to serum phosphorus ). Thanks for your suggestion. We have changed the phosphorus to phosphate all through the manuscript.