Influence of renal function and diet on acid-base status in chronic kidney disease patients

Assessment of Dietary Acid Load in Children with Chronic Kidney Disease: An Observational Study

Introduction

Dietary acid load (DAL), which reflects the balance between acid- and alkaline-forming foods, is a modifiable risk factor for metabolic acidosis in CKD. Owing to the paucity of data in the Indian context, we undertook this cross-sectional study to estimate DAL and assess acid and alkaline food consumption in children with CKD2-5D (Chronic kidney disease stage 2 to 5 and 5D-those on hemodialysis).

Methods

Clinical profile, dietary assessment of energy, protein intake/deficits, and macronutrients were noted and computed using software created by the division of nutrition, St John's research institute based on Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines in clinically stable children with CKD2-5D. DAL was estimated using potential renal acid load (PRAL in mEq/day) = (0.49 × protein intake in g/day) + (0.037 × phosphorus-intake in mg/day) - (0.02 × potassium intake in mg/day) - (0.013 × calcium intake in mg/day) - (0.027 × magnesium intake in mg/day). A positive dietary PRAL (>0) favors acidic content and negative (<0) favors alkaline content. PRAL was stratified into quartiles for analysis. The association of various clinical and dietary parameters were analysed across these quartiles.

Results

Eighty-one children [of mean age 122 ± 47 months; 56 (69%) boys, 29 (36%) on dialysis, 62 (77%) non-vegetarians] were studied. Twenty-eight (34%) were on bicarbonate supplements. A positive PRAL (9.97 ± 7.7 mEq/day) was observed in 74/81 (91%) children with comparable proportions in those with CKD2-5 and 5D [47/52 (90%) vs. 27/29 (93%) respectively, P > 0.05]. Protein intake was significantly higher in the highest quartile compared to the lowest quartile of PRAL in CKD2-5 (55 ± 16 g/day vs. 40 ± 14 g/day, P < 0.001) and 5D groups (47 ± 15 g/day vs. 25 ± 11 g/day, P = 0.002). A majority of the participants 60/81 (74%) consumed highly acidic and minimal alkali foods.

Conclusion

In children with CKD2-5D, PRAL estimation revealed high DAL in the majority with a high consumption of acidic foods. These findings provide implications for appropriate dietary counseling in children with CKD.

Association of dietary acid load with serum bicarbonate in chronic kidney disease (CKD) patients

BACKGROUND/OBJECTIVES

Diet can affect the acid-base status depending on the balance between the intake of acid-inducing foods and base-inducing foods. The purpose of this study was to estimate the dietary acid load and evaluate its association with serum bicarbonate in patients with stages 3 and 4 chronic kidney disease.

SUBJECTS/METHODS

One hundred adults (aged ≥ 20 years) with chronic kidney disease (CKD) stages 3 and 4 were enrolled in a cross-sectional study. A food diary was used to estimate the animal and plant protein intakes, which were used in the potential renal acid load (PRAL) formula described by Remer and Manz. PRAL was divided into quartiles. Regression models unadjusted and adjusted for age, gender, body mass index, diabetes, systolic and diastolic blood pressure, creatinine clearance were performed using the stepwise regression method.

RESULTS

The median level (25th, 75th percentiles) of PRAL was 8.3 mEq/day (1.6, 15.6). The highest quartile of PRAL had a higher consumption of animal protein (77.8 ± 10.9%) and a reduced consumption of plant protein (22.2 ± 10.9%), compared to the lowest quartile (59.5 ± 18.6% animal protein, 40.5 ± 18.6% plant protein), p for trend <0.0001. In the adjusted analysis, a significant association was observed between the highest quartile of PRAL and serum bicarbonate in CKD patients compared to the lowest quartile (β: 2.07, 95% CI: 0.21-3.92). According to the multiple linear regression, for each increase of 1 unit of PRAL there was a reduction of 0.25 mmol/L in serum bicarbonate (HCO₃). Using the stepwise method, animal protein intake and PRAL were determinants of HCO₃ (r = 0.49).

CONCLUSIONS

In CKD patients of stages 3 and 4, the dietary acid load was associated with HCO₃. Limiting dietary acid load could be a complementary approach in the dietary treatment of CKD. In addition, studies are needed to analyze the effect of replacing animal protein with plant protein.

Dietary acid load, kidney function and risk of chronic kidney disease: A systematic review and meta-analysis of observational studies

Aim: Study findings examining the association between dietary acid load (DAL), kidney function and risk of chronic kidney disease (CKD) are inconsistent and there has been no meta-analysis on the relationship between DAL, kidney function and risk of CKD, hence we investigated this association in this paper. Methods: PubMed, ISI web of science and Scopus were searched up to January 2018 to identify all relevant articles. Effect sizes of eligible studies were pooled in random- effect model using the Der Simonian-Laird method. The I² index was used to assess the amount of heterogeneity. Result: Twenty three studies with 200092 subjects were included. Meta-analysis of 9 observational studies showed that DAL had a positive significant association with risk of CKD (1.31; 95% CI: 1.06, 1.62; P = 0.011). Furthermore, increased DAL can decrease urine pH (-0.47; 95% CI: -0.85, -0.08; P = 0.017) significantly. Subgroup analysis could not identify the sources of heterogeneity about the association of DAL and risk of CKD. However, it showed the method of measurement was the source of heterogeneity about the association of DAL and urine pH (24 h urine pH: -0.62; 95% CI: -0.70, -0.54; P < 0.0001; Fasting urine pH: -0.08; 95% CI: -0.18, 0.02; P = 0.111). Conclusion: Our study showed that DAL can increase the risk of CKD and have an inverse association with urine pH.

One-Year Conservative Care Using Sodium Bicarbonate Supplementation Is Associated with a Decrease in Electronegative LDL in Chronic Kidney Disease Patients: A Pilot Study

Background

Chronic kidney disease (CKD) patients develop metabolic acidosis when approaching stages 3 and 4, a period in which accelerated atherogenesis may ensue. Studies in vitro show that low pH may increase low-density lipoprotein (LDL) oxidation, suggesting a role for chronic metabolic acidosis in atherosclerosis. The present study attempted to evaluate the effects of conservative care using oral sodium bicarbonate (NaHCO₃) supplementation on the electronegative LDL [LDL(-)], a minimally oxidized LDL, plasma levels in CKD patients.

Methods

Thirty-one CKD patients were followed by a multidisciplinary team during 15 months of care in which 1.0 mmol/kg/day oral NaHCO₃ supplementation was first given in the third month. Blood samples were collected 3 months before the initiation of oral NaHCO₃ supplementation (T1), at the time of the beginning of supplementation (T2), and thereafter, each 4 months (T3, T4 and T5) until month 15 of care. Blood parameters and LDL(-) were measured from these collections.

Results

After 12 months of conservative care, creatinine clearance (MDRD) was kept stable, and serum bicarbonate (HCO₃^-) increased from 20.5 ± 2.9 to 22.6 ± 1.1 mM (p < 0.003). LDL(-) plasma levels declined from 4.5 ± 3.3 to 2.1 ± 0.9 U/L (p < 0.007) after reaching mean serum HCO₃^- levels of 22.6 ± 1.1 mM.

Conclusions

Conservative care using oral NaHCO₃ supplementation was able to stabilize renal function and decrease serum levels of LDL(-), a modified proatherogenic lipoprotein, only when mean serum HCO₃^- levels approached 22 mM. This study constitutes evidence that alkali therapy, in addition to its beneficial effect on renal disease progression, might serve as a preventive strategy to attenuate atherogenesis in CKD patients.

Molecular mechanisms of insulin resistance in chronic kidney disease

Insulin resistance refers to reduced sensitivity of organs to insulin-initiated biologic processes that result in metabolic defects. Insulin resistance is common in patients with end-stage renal disease but also occurs in patients with chronic kidney disease (CKD), even when the serum creatinine is minimally increased. Following insulin binding to its receptor, auto-phosphorylation of the insulin receptor is followed by kinase reactions that phosphorylate insulin receptor substrate-1 (IRS-1), phosphatidylinositol 3-kinase (PI3K) and Akt. In fact, low levels of Akt phosphorylation (p-Akt) identifies the presence of the insulin resistance that leads to metabolic defects in insulin-initiated metabolism of glucose, lipids and muscle proteins. Besides CKD, other complex conditions (e.g., inflammation, oxidative stress, metabolic acidosis, aging and excess angiotensin II) reduce p-Akt resulting in insulin resistance. Insulin resistance in each of these conditions is due to activation of different, E3 ubiquitin ligases which specifically conjugate ubiquitin to IRS-1 marking it for degradation in the ubiquitin-proteasome system (UPS). Consequently, IRS-1 degradation suppresses insulin-induced intracellular signaling, causing insulin resistance. Understanding mechanisms of insulin resistance could lead to therapeutic strategies that improve the metabolism of patients with CKD.

Mechanisms stimulating muscle wasting in chronic kidney disease: the roles of the ubiquitin-proteasome system and myostatin

Catabolic conditions including chronic kidney disease (CKD), cancer, and diabetes cause muscle atrophy. The loss of muscle mass worsens the burden of disease because it is associated with increased morbidity and mortality. To avoid these problems or to develop treatment strategies, the mechanisms leading to muscle wasting must be identified. Specific mechanisms uncovered in CKD generally occur in other catabolic conditions. These include stimulation of protein degradation in muscle arising from activation of caspase-3 and the ubiquitin-proteasome system (UPS). These proteases act in a coordinated fashion with caspase-3 initially cleaving the complex structure of proteins in muscle, yielding fragments that are substrates that are degraded by the UPS. Fortunately, the UPS exhibits remarkable specificity for proteins to be degraded because it is the major intracellular proteolytic system. Without a high level of specificity cellular functions would be disrupted. The specificity is accomplished by complex reactions that depend on recognition of a protein substrate by specific E3 ubiquitin ligases. In muscle, the specific ligases are Atrogin-1 and MuRF-1, and their expression has characteristics of a biomarker of accelerated muscle proteolysis. Specific complications of CKD (metabolic acidosis, insulin resistance, inflammation, and angiotensin II) activate caspase-3 and the UPS through mechanisms that include glucocorticoids and impaired insulin or IGF-1 signaling. Mediators activate myostatin, which functions as a negative growth factor in muscle. In models of cancer or CKD, strategies that block myostatin prevent muscle wasting, suggesting that therapies that block myostatin could prevent muscle wasting in catabolic conditions.

Systemic acid load from the diet affects maximal-exercise RER

A maximal-exercise RER (RER(max) ≥ 1.10 is commonly used as a criterion to determine whether a "true" maximal oxygen uptake (V˙O(2max)) has been attained during maximal-effort exercise testing. Because RER(max) is heavily influenced by CO2 production from acid buffering during maximal exercise, we postulated that dietary acid load, which affects acid-base regulation, might contribute to variability in RER(max).

PURPOSE

The study's purpose was to determine whether a habitual dietary intake that promotes systemic alkalinity results in higher RER(max) during V˙O(2max) testing.

METHODS

Sedentary men and women (47-63 yr, n = 57) with no evidence of cardiovascular disease underwent maximal graded treadmill exercise tests. V˙O(2max) and RER(max) were measured with indirect calorimetry. Habitual diet was assessed for its long-term effect on systemic acid-base status by performing nutrient analysis of food diaries and using this information to calculate the potential renal acid load (PRAL). Participants were grouped into tertiles on the basis of PRAL.

RESULTS

The lowest PRAL tertile (alkaline PRAL) had higher RERmax values (1.21 ± 0.01, P ≤ 0.05) than the middle PRAL tertile (1.17 ± 0.01) and highest PRAL tertile (1.15 ± 0.01). There were no significant differences (all P ≥ 0.30) among PRAL tertiles for RER at submaximal exercise intensities of 70%, 80%, or 90% V˙O2max. After controlling for age, sex, V˙O(2max), and HRmax, regression analysis demonstrated that 19% of the variability in RER(max) was attributed to PRAL (r = -0.43, P = 0.001). Unexpectedly, HRmax was lower (P ≤ 0.05) in the low PRAL tertile (164 ± 3 beats·min⁻¹) versus the highest PRAL tertile (173 ± 3 beats·min⁻¹).

CONCLUSIONS

These results suggest that individuals on a diet that promotes systemic alkalinity may more easily achieve the RER(max) criterion of ≥ 1.10, which might lead to false-positive conclusions about achieving maximal effort and V˙O(2max) during graded exercise testing.

Simiao pill ameliorates urate underexcretion and renal dysfunction in hyperuricemic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Simiao pill is one of the most frequently prescription in traditional Chinese medicine to treat gout and hyperuricemia.

AIM OF THE STUDY

We investigated the effects of Simiao pill on urate excretion and renal function and examined whether renal organic ion transporters are involved in potassium oxonate-induced hyperuricemic mice.

MATERIALS AND METHODS

Water extract of Simiao pill at 507, 1014 and 2028mg/kg was orally administered to hyperuricemic and normal mice for 7 days, and allopurinol (5mg/kg) was given as a positive control. Serum and urine levels of uric acid and creatinine, and fractional excretion of uric acid (FEUA) were measured in hyperuricemic and normal mice treated with Simiao pill and allopurinol. Simultaneously, the mRNA and protein levels of mouse urate transporter 1 (mURAT1), glucose transporter 9 (mGLUT9) and organic anion transporter 1 (mOAT1) and organic cation/carnitine transporters (mOCT1, mOCT2, mOCTN1 and mOCTN2) in the kidney were analyzed by semi-quantitative RT-PCR and Western blotting methods, respectively.

RESULTS

Simiao pill significantly reduced serum uric acid levels and increased FEUA dose-dependently in hyperuricemic mice. And it effectively reversed oxonate-induced alterations in renal mURAT1, mGLUT9 and mOAT1 mRNA and protein levels, resulting in the enhancement of renal urate excretion in mice. Moreover, Simiao pill decreased serum creatinine levels, as well as increased renal mOCT1, mOCT2, mOCTN1 and mOCTN2 mRNA and protein levels, leading to improve renal dysfunction in this model.

CONCLUSION

These findings suggest that Simiao pill processes uricosuric and nephroprotective actions by regulating renal organic ion transporters in hyperuricemic animals.