Sodium bicarbonate to improve physical function in patients over 60 years with advanced chronic kidney disease: the BiCARB RCT

BACKGROUND

Advanced chronic kidney disease is common in older people and is frequently accompanied by metabolic acidosis. Oral sodium bicarbonate is used to treat this acidosis, but evidence is lacking on whether or not this provides a net gain in health or quality of life for older people.

OBJECTIVES

The objectives were to determine whether or not oral bicarbonate therapy improves physical function, quality of life, markers of renal function, bone turnover and vascular health compared with placebo in older people with chronic kidney disease and mild acidosis; to assess the safety of oral bicarbonate; and to establish whether or not oral bicarbonate therapy is cost-effective in this setting.

DESIGN

A parallel-group, double-blind, placebo-controlled randomised trial.

SETTING

The setting was nephrology and geriatric medicine outpatient departments in 27 UK hospitals.

PARTICIPANTS

Participants were adults aged ≥ 60 years with advanced chronic kidney disease (glomerular filtration rate category 4 or 5, not on dialysis) with a serum bicarbonate concentration of < 22 mmol/l.

INTERVENTIONS

Eligible participants were randomised 1 : 1 to oral sodium bicarbonate or matching placebo. Dosing started at 500 mg three times daily, increasing to 1 g three times daily if the serum bicarbonate concentration was < 22 mmol/l at 3 months.

MAIN OUTCOME MEASURES

The primary outcome was the between-group difference in the Short Physical Performance Battery score at 12 months, adjusted for baseline. Other outcome measures included generic and disease-specific health-related quality of life, anthropometry, 6-minute walk speed, grip strength, renal function, markers of bone turnover, blood pressure and brain natriuretic peptide. All adverse events were recorded, including commencement of renal replacement therapy. For the health economic analysis, the incremental cost per quality-adjusted life-year was the main outcome.

RESULTS

In total, 300 participants were randomised, 152 to bicarbonate and 148 to placebo. The mean age of participants was 74 years and 86 (29%) were female. Adherence to study medication was 73% in both groups. A total of 220 (73%) participants were assessed at the 12-month visit. No significant treatment effect was evident for the primary outcome of the between-group difference in the Short Physical Performance Battery score at 12 months (-0.4 points, 95% confidence interval -0.9 to 0.1 points; p = 0.15). No significant treatment benefit was seen for any of the secondary outcomes. Adverse events were more frequent in the bicarbonate arm (457 vs. 400). Time to commencement of renal replacement therapy was similar in both groups (hazard ratio 1.22, 95% confidence interval 0.74 to 2.02; p = 0.43). Health economic analysis showed higher costs and lower quality of life in the bicarbonate arm at 1 year, with additional costs of £564 (95% confidence interval £88 to £1154) and a quality-adjusted life-year difference of -0.05 (95% confidence interval -0.08 to -0.01); placebo dominated bicarbonate under all sensitivity analyses for incremental cost-effectiveness.

LIMITATIONS

The trial population was predominantly white and male, limiting generalisability. The increment in serum bicarbonate concentrations achieved was small and a benefit from larger doses of bicarbonate cannot be excluded.

CONCLUSIONS

Oral sodium bicarbonate did not improve a range of health measures in people aged ≥ 60 years with chronic kidney disease category 4 or 5 and mild acidosis, and is unlikely to be cost-effective for use in the NHS in this patient group. Once other current trials of bicarbonate therapy in chronic kidney disease are complete, an individual participant meta-analysis would be helpful to determine which subgroups, if any, are more likely to benefit and which treatment regimens are more beneficial.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN09486651 and EudraCT 2011-005271-16. The systematic review is registered as PROSPERO CRD42018112908.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 24, No. 27. See the NIHR Journals Library website for further project information.

Perturbation of Akt Signaling, Mitochondrial Potential, and ADP/ATP Ratio in Acidosis-Challenged Rat Cortical Astrocytes

Cells switch to anaerobic glycolysis when there is a lack of oxygen during brain ischemia. Extracellular pH thus drops and such acidosis causes neuronal cell death. The fate of astrocytes, mechanical, and functional partners of neurons, in acidosis is less studied. In this report, we investigated the signaling in acidosis-challenged rat cortical astrocytes and whether these signals were related to mitochondrial dysfunction and cell death. Exposure to acidic pH (6.8, 6.0) caused Ca²⁺ release and influx, p38 MAPK activation, and Akt inhibition. Mitochondrial membrane potential was hyperpolarized after astrocytes were exposed to acidic pH as soon as 1 h and lasted for 24 h. Such mitochondrial hyperpolarization was prevented by SC79 (an Akt activator) but not by SB203580 (a p38 inhibitor) nor by cytosolic Ca²⁺ chelation by BAPTA, suggesting that only the perturbation in Akt signaling was causally related to mitochondrial hyperpolarization. SC79, SB203580, and BAPTA did not prevent acidic pH-induced cell death. Acidic pH suppressed ROS production, thus ruling out the role of ROS in cytotoxicity. Interestingly, pH 6.8 caused an increase in ADP/ATP ratio and apoptosis; pH 6.0 caused a further increase in ADP/ATP ratio and necrosis. Therefore, astrocyte cell death in acidosis did not result from mitochondrial potential collapse; in case of acidosis at pH 6.0, necrosis might partly result from mitochondrial hyperpolarization and subsequent suppressed ATP production. J. Cell. Biochem. 118: 1108-1117, 2017. © 2016 Wiley Periodicals, Inc.

Ammonium chloride acidosis; a report of six cases

The administration of 6 to 8 Gm. of enteric coated ammonium chloride daily for 7 to 45 days to 6 patients resulted in severe, and in 2 instances nearly fatal, acidosis. Five of the 6 patients had congestive heart failure and one, subacute glomerulonephritis; each of the 5 patients with congestive failure had organic renal disease. The clinical manifestations, differentiation from the low salt syrndrome and the therapy are discussed.

Varying role of extracellular electrolytes in metabolic acidosis and alkalosis

The responses of plasma and extracellular space to different types of acids and alkalis were studied in nephrectomized cats. Compensation for mineral acids can largely be accounted for by changes which are detectable in extracellular constituents. These changes are movement of Na+ and K+ into the extracellular space (ECS) and loss of HCO3– from the ECS. Organic acids which penetrate cells rapidly and may be expected to cause an intracellular and extracellular acidosis, produce negligible changes in extracellular content of Na and K. Alkalosis produced by NaOH or NaHCO3 was compensated for mainly by extracellular gain of bicarbonate and loss of Na. The response to NH4OH was unusual in that this alkaline solution caused an acidosis with movement of K into the ECS. The site of compensation for the various acids and alkalis was indicated by a comparison of the volume of agent infused with the change in volume of the ECS. The distribution of Na in these animals was not related as much to the concentration of Na in the ECS as it was to the pH produced by the solution infused. The response of the living organism to different types of acids and alkalis is variable and seems mainly related to the distribution of the material in the body.

Severe acidosis and hyperpotassemia treated with sodium bicarbonate infusion

Four uremic patients with severe acidosis, hyperpotassemia, and electrocardiographic signs of toxicity were treated with intravenous sodium bicarbonate. Serial determinations showed a fall in plasma potassium, a rise in blood pH, and regression of the electrocardiogram toward normal. The mechanisms responsible for these changes are discussed.

RELATIONSHIP OF PNH3 OF TUBULAR CELLS TO RENAL PRODUCTION OF AMMONIA

Renal excretion of ammonia, addition of ammonia to renal venous blood, and total renal production of ammonia were measured in acidotic dogs before and during the intravenous infusion of ammonium chloride at rates of 0.5 and 1.0 mmole/min. Infusion of ammonium chloride increased urinary excretion of ammonia, reversed the direction of diffusion of ammonia between tubular cells and blood, i.e., induced the extraction of ammonia from blood, and reduced cellular production of ammonia. Production of ammonia was an inverse function of pNH3 of tubular cells. The infusion of ammonium lactate-N15 into one renal artery increased total ammonia excretion but decreased production of ammonia-N14 from normal blood-borne precursors. The intravenous infusion of ammonium chloride reduced extraction of glutamine from renal blood, yet increased the concentration of free glutamine in renal cortical cells. Our data suggest that an increase in pNH3 of tubular cells results in competitive inhibition of the glutaminase-1 reaction. We further suggest that the pNH3 of tubular cells is one factor governing renal production of ammonia; i e., the higher the cellular pNH3, the lower is the renal production of ammonia.

RENAL AMMONIA RELEASE DURING AMMONIUM CHLORIDE ACIDOSIS

The effect of prolonged oral ammonium chloride administration on the simultaneous release of ammonia into urine and renal venous blood was examined in the dog. Quantitatively, chronic ammonium chloride acidosis was accompanied by an almost identical average elevation of both urine ammonia excretion and renal venous ammonia release. Although not definitive, the results are entirely consistent with the prevailing concept that ammonia enters urine and renal venous blood via a pH-dependent process of non-ionic diffusion.

ACETOACETATE TURNOVER AND OXIDATION RATES IN OVINE PREGNANCY KETOSIS

Labeled acetoacetic acid (AcAc) was administered as a tracer dose and as a continuous infusion to 24 twin-pregnant ewes with varying degrees of spontaneous or fasting hypoglycemic ketosis. The mean AcAc turnover rate of five normal twin-pregnant sheep (plasma AcAc < 1 mg/100 ml) was only 0.04 g/hr kg3/4 or 1.0 g/sheep hr. During ketosis the turnover rate of AcAc was directly proportional to the plasma AcAc concentration until a maximal concentration of about 10 mg/100 ml was attained (total ketone bodies, expressed as acetone, would be about 20 mg/100 ml). At higher plasma concentrations, the AcAc turnover rates remained constant at nearly 0.4 g/hr kg3/4 (9 g/sheep hr). About one-half of this AcAc was oxidized to CO2 regardless of the actual amount utilized. The mean percentage of the total exhaled CO2 derived from AcAc metabolism increased from 2% in normal ewes to a maximum of about 20% during pregnancy ketosis. Comparisons of these data to values obtained in previous experiments on artificially ketotic nonpregnant sheep indicate that an overproduction of ketone bodies, rather than an underutilization, is the major cause of ruminant ketosis.