Effects of Oral Sodium Bicarbonate Supplementation on Protein Metabolism and Inflammation in Iraqi Hemodialysis Patients: An Open-Label Randomized Controlled Trial

Background The effect of correcting metabolic acidosis on protein metabolism in hemodialysis patients is controversial. Objectives To study the effects of oral sodium bicarbonate on protein metabolism and markers of inflammation in acidotic hemodialysis patients. Patients and Methods. An open-label randomized controlled trial was conducted at a single center. Sixty-six clinically stable adult hemodialysis patients were recruited with an average predialysis serum bicarbonate level of <22 mmol/l and a dialysate bicarbonate concentration of 35 mmol/l. Forty-nine participants have completed the study. Oral sodium bicarbonate tablets of 500 mg were given daily in the intervention group (n = 25) for 12 weeks versus the standard of care in the control group (n = 24). Outcomes compared intervention versus nonintervention in both groups at equivalent time points (0 and 3 months). The clinical data, anthropometry, dialysis adequacy, albumin, normalized protein catabolism rate, blood gas analysis, and bicarbonate were recorded at 0 and 3 months. In addition, muscle mass and handgrip strength were measured. Finally, IL-6 as a marker of inflammation was measured at randomization and three months. Results Serum bicarbonate and pH increased significantly from 17.57 ± 3.34 mmol/L to 20.69 ± 2.54 mmol/L and from 7.26 ± 0.06 to 7.34 ± 0.04, respectively (p < 0.0001). Serum albumin was significantly higher in the intervention group at three months than in the control group, 4.11 ± 0.45 vs. 3.79 ± 0.47 (p value 0.011). Serum potassium significantly decreased in the intervention group at three months compared to the control group, 5.00 ± 0.43 mEq/l vs. 5.33 ± 0.63 mEq/l (p value 0.03). Muscle strength expressed as handgrip has improved significantly in the intervention group at three months compared to the control group, 45.01 ± 19.19 vs. 33.93 ± 15.06 (p value 0.03). The IL-6 values were less in the intervention group at 3 months with a p value of 0.01. The interdialytic weight of the intervention group at three months was 2.42 ± 0.64 compared to the 2.20 ± 1.14 control group, but this did not reach statistical significance (p value of 0.4). The composite of (albumin + nPCR) at three months was achieved in 59.18% of the intervention group compared to 14.28% with a p value of 0.01. Conclusions Correcting metabolic acidosis in hemodialysis patients improved serum albumin and nPCR without hypokalemia or significant interdialytic weight gain. This was particularly evident in patients with minimal inflammation with low IL-6 values.


Introduction
End-stage kidney disease (ESKD) is a worldwide health problem with 11-13% global prevalence, causing a signifcant health care and economic burden. Renal transplantation is the best form of renal replacement therapy as it provides a survival beneft over remaining on dialysis [1].
Historically, the uremic milieu was always regarded as a state of acidosis, and it is currently termed the metabolic acidosis (MA) of chronic kidney disease (CKD). MA is usually evident but unaccompanied by signs or symptoms of uremia. Regardless of the term, it is defned as persistently low bicarbonate levels of less than 22 mEq/L [2]. It is usually evident when the glomerular fltration rate (GFR) is lower than 30 mL/min/1.73 m 2 . Below this level of fltration, the body may tolerate acute acidemia but cannot completely correct the base defcit on chronic bases [3].
Te prevalence of MA is approximately 15-19% in CKD stage 3-5 patients, which tends to increase with the progressive loss of GFR. Furthermore, studies reveal the importance of MA in the etiopathogenesis of CKD patients' increased morbidity and mortality [4,5].
Metabolic acidosis of CKD/ESKD leads has a detrimental efect on multiple metabolic pathways. Tese include increased parathyroid hormone synthesis, bone resorption, altered glucose metabolism, and increased protein catabolism. Te latter leads to MIA (malnutrition-infammationatherosclerosis) syndrome and sarcopenia [6,7].
Acid directly stimulates hepatic glutamine production and accelerates muscle protein degradation, releasing amino acids to synthesize glutamine in the liver. Moreover, acidemia increases the oxidation of branched-chain amino acids (valine, leucine, and isoleucine) in muscle to provide much of the nitrogen used in the hepatic synthesis of glutamine. It activates the rate-limiting enzyme for the irreversible decarboxylation of BCAA and branched-chain ketoacid dehydrogenase (BCKAD) in muscle, and this response accounts for BCAA degradation and decreased albumin synthesis [7].
Animal studies proved the proteolytic efect of MA [8]. It is both catabolic and antianabolic, and it acts synergistically with other catabolic factors, such as infammatory cytokines and insulin resistance, inducing protein catabolism and increasing the risk of malnutrition [9].
Metabolic acidosis also contributes to the infammatory milieu of uremia with upregulation of infammatory cytokines like IL-6 and consequent proteolysis and loss of muscle mass [10]. Tus, correction of MA may, at least, partially alleviate the deleterious efect of infammation on muscle protein synthesis.
In CKD patients, bicarbonate supplementation slows the progression of kidney disease to ESKD. It improves nutritional status [11]. Correction of MA in HD patients efectively improves nutritional status. Tis can be achieved by higher dialysate bicarbonate or an oral bicarbonate supplement [12]. In chronic ambulatory peritoneal dialysis (CAPD) patients, correction of acidosis decreased the whole body degradation [13]. Tus, bicarbonate supplements can be given to maintain serum bicarbonate of 24_26 mEq/L (KDOQI Clinical Practice Guideline FOR Nutrition in CKD 2020 update) throughout the interdialytic interval to compact the harmful efect of uncorrected acidosis [14].
In Iraq, there are about 7000 prevalent HD patients. In a recent multicenter study, 49.8% of Iraqi adult HD patients were malnourished [15].
Tis study investigates the efects of supplementing oral sodium bicarbonate in acidotic hemodialysis patients on protein metabolism and markers of infammation.

Patients and Methods
An open-label randomized controlled trial was conducted in a single governmental hemodialysis unit from August 1, 2021, to December 31, 2021.
Patients: adult ESRD patients on regular HD for >3 months. Eligibility criteria include three times hemodialysis a week, documented serum bicarbonate level of <22 mmol/l, with a dialysate bicarbonate concentration of 35 mmol/l, no residual renal function (24 hours urine output <200 ml), arteriovenous fstulae as dialysis access and the patients should be in a steady clinical state and willing to provide written informed consent.
Te exclusion criteria were as follow: (1) Acute illness or infection in the last three months, including coronavirus (COVID-19) (2) Patients with an anticipated life expectancy of 6 months (e.g., due to metastatic malignancy or terminal disease) (3) Advanced senility and impaired cognition (4) Clinically evident cachexia and sarcopenia (5) Ongoing enteral or parenteral nutrition (6) Patients with uncontrolled blood pressure (>160/90) (7) Patients who primarily have predialysis potassium levels of less than 4 mmols/L (8) Use of steroids or immunosuppressive agents (9) If the patient is already using oral sodium bicarbonate therapy.
Sixty-six patients fulflled the eligibility criteria. Seven patients were transferred to other satellite dialysis units that could not be followed, whereas the other nine refused to consent.

Hemodialysis Protocol.
Patients receive three weekly dialysis sessions, 4 hours each, using a Baxter Polyfux 21 L (Low fux) dialyzed. Te dialysis blood fow (Qb) ranges between 230 and 300 ml/min, while the dialysate fow (Qd) ranges between 550 and 750 ml/min. Still, HDF is not widely applicable in Iraqi dialysis practice.

Randomization.
Te study participants were randomly allocated in 1 : 1 ratio to intervention (N � 25) and control (N � 25) groups by a nonresearch team health personnel sealed envelopes. Enrolled patients were stratifed by nPCR.

Intervention.
Patients in the intervention group were assigned to receive oral sodium bicarbonate tablets 500 mg fxed dose daily. Te unit-specialized pharmacist assessed adherence to the prescribed dose of sodium bicarbonate and reported the medication records, the home use of the oral capsules, and drug-related side efects.

Data collection.
Te medical history and sociodemographic characteristics were recorded by direct interviewing the study participants. Te dialysis and laboratory data were collected from the patient's charts and records. Blood pressure values were taken as the mean of predialysis measurements of the last three dialysis sessions. In addition, anthropometric measurements were recorded.

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International Journal of Nephrology Te baseline biochemistry data included serum bicarbonate, arterial pH, renal function, serum sodium, and serum potassium. Serum albumin was measured by the green bromocresol method. Blood samples were taken after the longest interdialytic interval for pre-and postdialysis urea, and the Kt/V and normalized protein catabolic rate (nPCR) were calculated. In addition, IL-6 levels were measured at baseline and three months using a Roche Cobas e411 (Roche Diagnostics GmbH, Mannheim, Germany, 2020).
Values of acid-base parameters were derived from the blood gas analysis performed as a specifc study procedure using IRMA (Blood Analysis System/2018/Germany). Samples of 2 mL were collected in heparinized syringes before a midweek dialysis session. Samples were collected from the indwelling needle puncturing the arteriovenous fstula's arterial limb. After collection, the syringe was immediately transported to the laboratory.

Anthropometric Data
(i) Height measurement, based on recently documented measures from the patient's record (ii) Weight measurement, based on the documented last postdialysis weight measurements (iii) Body mass index (BMI) was calculated by dividing the dry weight over the squared height in meters (iv) Interdialytic weight gain was calculated as the patient's weight at the beginning of each HD session (predialysis weight) minus the weight after (postdialysis weight) the previous HD session. [16]. Dialysis adequacy was estimated by calculating midweek, single pool Kt/V according to

Dialysis Adequacy
where R: predialysis urea/postdialysis urea, t: dialysis time in hours, −ln: negative natural logarithm, UF: ultrafltration volume, W: the body weight after the HD session, and a Kt/V of 1.2 was considered the minimum clinically acceptable value in our dialysis unit.

Te Normalized Protein Catabolic Rate (nPCR).
Te protein catabolic rate (PCR) refects the amount of protein catabolized more than the amount synthesized daily, determined in stable chronic hemodialysis patients to evaluate dietary protein intake [17]. nPCR was calculated using two equations, and the average was taken in our study [18].
Daily protein intake of 1.1-1.2 g/kg/day was recommended in HD patients in our study, so less than 1 g/kg/day was regarded as poor nutritional status.

Muscle Function and Strength. Hand Dynamometer
Grip Strength Measurement (CAMRY DIGITAL HAND DYNAMOMETER, EH101, USA): measured before dialysis; by squeezing the hand dynamometer with maximum efort for at least 5 seconds and repeated three times by a nonfstulous arm. After testing, the maximum grip value is considered, and a grip value status bar shows the status of "weak," "normal," or "strong" according to age and gender preset for each test.

Skinfold Tickness.
Triceps skinfold (TSF) thickness (XTDGN Skinfold Body Fat Caliper, China): the halfway distance between the acromion and the olecranon (posterior surface) was marked. After holding a fold of skin, the TSF measurement was taken using a Lange skinfold caliper, with the caliper's jaws at the level of the marked skin.
Te handgrip strength and triceps skinfold thickness were measured by an independent examiner expert in using these tools blinded to treatment status.

Outcome
Te primary endpoint is to assess the efcacy of sodium bicarbonate therapy in improving nutritional parameters {nPCR with a target of 1.2 (g/kg per day) and serum albumin with a target of 4 (gm/dl)} and to ameliorate infammation by reducing IL-6. Te secondary endpoint is to assess intervention safety regarding volume retention and hypokalemia.

Administrative and Ethical Approval
Te ethical and scientifc committee of the Arab Board for Health Specialties-Clinical Nutrition fellowship program and the Ministry of Health Ethics Committee approved the study protocol in July 2021 (Number: 2021032/Baghdad). Te study's objectives and the confdentiality of the data were explained to the participants. According to the National Research Ethics Code, all participants provided written informed consent.

Statistical Analysis
Data were entered and analyzed using IBM SPSS Statistics for Windows (version 24.0, IBM Corp., Armonk, NY). Descriptive statistics are presented as percentages, frequencies, means, and standard deviations according to the variable type. Te diferences between and within groups were compared using the t-test and chi-square International Journal of Nephrology tests. For variables with skewed values, a Mann-Whitney test was used. Because of the small sample size and the possible imbalances between some outcomes, we used repeated measure ANOVA to account for diferences in the baseline characteristics. A bivariate Pearson correlation was used to assess the correlation between two numerical variables. Statistical signifcance was set at p < 0.05.

Results
Of the sixty-six eligible patients, ffty were recruited (age range 20-80 years, 55.1% female). However, after randomization, one participant from the control group withdrew according to his will (Figure 1). Table 1 represents the baseline characteristics of the study groups at time 0.
Te participants were in good nutritional status with normal BMI and serum albumin. Te mean nPCR for both groups was 0.98 + 0.24 g/kg/day, below the recommended target by most guidelines. Twenty-nine participants (29/49, 59.18%) were with values <1 g/kg/day ( Figure 2).
Te arterial pH signifcantly increased at three months in the intervention group compared to the control group (p value 0.001). Tis also applies to serum bicarbonate at three months compared to baseline and the control group (p value <0.001 and 0.05, respectively). Table 2 represents the intervention and control groups' clinical, laboratory, and nutritional data at three months of oral sodium bicarbonate therapy. Considering any imbalances between the groups in some of the outcomes, repeated measures ANOVA was used, and the results are represented in Table 3.

Primary Outcome
Tere was a statistically signifcant diference in the nPCR in the intervention group at three months (p value 0.03) and, in comparison, to the control group at three months (p value 0.033). In addition, the serum albumin was signifcantly higher at three months in the intervention group than in the control group (p value 0.011).
Supplementing acidotic hemodialysis patients with oral sodium bicarbonate improved protein metabolism by increasing serum albumin and nPCR. Serum albumin increased in the intervention group with a relative risk of 3.75, p value of 0.006; the nPCR increased in the intervention group with a relative risk of 4.48, p value of 0.008 (Table 4).
Te IL-6 values were highly skewed; thus, a Mann-Whitney test was used to assess the diference between time 0 and 3 months. Te exact 2-sided value was 0.009, and the p value was 0.01 ( Figure 3).
Bivariate Pearson's correlation analysis revealed no correlation between serum albumin and IL-6 with blood PH and bicarbonate in the intervention group at three months.
Muscle strength expressed as handgrip has improved signifcantly in the intervention group at three months (p value 0.001) compared to the control group (p value 0.03).

Secondary and Other Outcomes
At three months, the intervention group showed a small but signifcant increment in serum sodium from time 0 (p value 0.034). Still, there was no statistically signifcant diference from the control group at three months (p value 0.28).
Te intervention group showed a small increment in body weight at three months (p value 0.03). Still, it was not statistically signifcant compared to the control group at three months (p value 0.29). Furthermore, it was not refected in a substantial Interdialytic weight gain (p value 0.405). In addition, both study groups had no statistically signifcant diferences in systolic and diastolic blood pressure at three months.
Serum potassium signifcantly decreased in the intervention group at three months (p value <0.001) compared to the control group (p value 0.03).

Discussion
In this study, a fxed oral dose of sodium bicarbonate, 500 mg/day, has signifcantly corrected acidosis and improved nPCR with a possible reduction of an infammatory marker.
Moderate to severe MA in HD patients exert a detrimental efect on serum albumin concentration, partially independent of protein intake as evaluated by nPCR, taking into consideration other nutritional parameters of concomitant infammatory status as reported by Movilli et al. [21]. Correction of acidosis is one of the primary purposes of renal replacement treatment. However, interventional studies of correcting MA in HD patients generated conficting results regarding the ability to improve serum albumin concentration, protein degradation, or nutritional status [11,22].
Te mean nPCR for the study groups was 0.98 + 0.24 g/ kg/day, and it may refect better dialysis management than previous Iraqi data with nPCR of 0.87 ± 0.24 g/kg/day [23]. Still, the nPCR of Iraqi maintenance HD patients is below the recommended targets and could refect signifcant protein restriction in Iraqi HD practice. A previous report by William et al. demonstrated that in CKD/ESKD patients, the metabolic adaptation to low-protein diets is impaired. Such patients should not be prescribed a restricted protein diet without correcting acidosis. If a low-protein diet is prescribed in these circumstances, it will likely be less efcient in achieving its primary objectives. It could also simultaneously expose the patient to the risk of the accelerated loss of lean body mass [24,25].
At a steady state, nPCR is assumed to be approximately equal to dietary protein intake. It is used as an objective tool to quantify protein intake and patients' compliance with the dietary prescription in HD patients. It may provide an index of protein catabolism. It does not diferentiate between proteins derived from dietary sources or the catabolism of endogenous proteins. In the current study, correction of acidosis has increased nPCR in concordance with Bastani et al. [26,27]. 4 International Journal of Nephrology Te low serum albumin concentration in HD patients is an early and sensitive marker of protein malnutrition and mortality. It is also a negative acute-phase reactant that decreases in response to infammation [28,29]. Te correction of MA in the intervention group was associated with a signifcant increase in serum albumin concentration. It is either due to acidosis correction or decreased infammation, as indicated by lower IL-6 in this group. Brady et al.
concluded that correcting acidosis does not afect serum albumin levels. Tese fndings suggest that the correction of MA in patients with only minimal or absent chronic infammation may positively afect serum albumin concentrations. In contrast, in those with more pronounced chronic infammation, this condition's inhibitory efect on albumin synthesis prevents serum albumin concentrations from increasing, as Movilli et al. [22,30]. Tere was no linear  International Journal of Nephrology correlation between serum albumin and bicarbonate or IL-6. Larger cohorts and longer follow up should provide better data. Although the enrolled patients were virtually free of clinically evident acute infection, IL-6 concentrations were widely distributed. An acidic milieu appears to stimulate the production of proinfammatory cytokines and chemokines, providing additional mechanisms leading to more kidney injury, muscle destruction, and wasting. It may be essential to clarify the mechanism behind this. As a measure of infammation, IL-6 was lower in the intervention group than in the control group after three months; this may be the efect of the correction of acidosis [19]. In this study, highly sensitive CRP values were unavailable for all patients, so we did not include hs-CRP in the analysis.
In the intervention group, predialysis blood pressure and interdialytic weight gain did not show any signifcance in the observed changes, refecting no volume retention, despite a minimal increase in plasma sodium level at two periods of the study groups. It was consistent with Movilli et al.'s result that correction of MA by oral bicarbonate supplementation in the range of 1 to 4 g/day does not lead to greater IWG and fuid overload [31]. In this study, a single fxed dose of 500 mg/day was used, and such a low dose may explain the minimum volume retention and blood pressure.      International Journal of Nephrology An interesting fnding was the reduction in serum potassium in the intervention group compared with the control group, and this was concordant with reports by Melamed and Raphael [20,32].
Treating acidosis might improve muscle strength and function by reducing muscle breakdown. It improves lower extremity muscle mass and strength and positively afects the physical function and exercise capacity of ESKD/HD. Muscle strength was measured by a Handgrip dynamometer, which increased signifcantly in the intervention group compared with the control [33]. Furthermore, correction of acidosis did not improve TSF thickness at three months compared to the control [34].
In this study, more frequent arterial blood gas analyses would add a better assessment of the acid-base status of the study groups but laboratory logistics limited this. Accordingly, it has limited dose titration, and only a fxed-dose protocol is used. Te dialysis blood fow rates were remarkably low, likely explaining the magnitude of predialysis acidemia, which is a limiting factor that could refect the local practice of dialysis delivery. In addition, the dietary behavior and protein intake may vary during the 3-month study period, which is another limiting factor. Furthermore, the study design was limited by being not blinded and with no placebo control. Extensive and long-term studies should be conducted to assess the efect of correction of acidosis on other electrolytes and micronutrients, including vitamins and minerals and assess nutritional status and quality of life in CKD/ESKD patients.
In conclusion, even a small dose of oral sodium bicarbonate supplementation improved protein metabolism with no signifcant interdialytic weight gain nor clinically signifcant hypokalemia. Furthermore, correcting metabolic acidosis increases serum albumin in HD patients with minimal infammation.

Data Availability
All data will be available on e-mail request, as we should have institutional approval frst.

Conflicts of Interest
Te authors declare that there are no conficts of interest.  International Journal of Nephrology 7