Effect of ammonium chloride and dietary phosphorus in the azotaemic rat. Part II--Kidney hypertrophy and calcium deposition

Risk factors and implications associated with ultrasound-diagnosed nephrocalcinosis in cats with chronic kidney disease

BACKGROUND

Microscopic nephrocalcinosis is a common pathological feature of chronic kidney disease (CKD) in cats. Detection of macroscopic nephrocalcinosis using ultrasonography and its implications remain unexplored.

OBJECTIVES

Identify risk factors associated with ultrasound-diagnosed nephrocalcinosis and evaluate the influence of nephrocalcinosis on CKD progression.

ANIMALS

Thirty-six euthyroid client-owned cats with CKD.

METHODS

Prospective cohort study. Cats with CKD with and without ionized hypercalcemia were enrolled for renal ultrasonography. Cats were categorized according to the presence or absence of ultrasound-diagnosed nephrocalcinosis. Binary logistic regression was performed to identify nephrocalcinosis risk factors. The influence of nephrocalcinosis on CKD progression was assessed using linear mixed models.

RESULTS

Ultrasound-diagnosed nephrocalcinosis was evident in 61% of CKD cats overall, with increased prevalence (81%) in those with hypercalcemia. At enrollment, higher blood ionized calcium concentration (odds ratio [OR], 1.27 per 0.1 mg/dL; P = .01), plasma phosphate concentration (OR, 1.16 per 0.1 mg/dL; P = .05), plasma creatinine concentration (OR, 1.29 per 0.1 mg/dL; P = .02) and alanine aminotransferase activity (OR, 2.08 per 10 U/L; P = .04) were independent nephrocalcinosis risk factors. The rate of change in log-transformed fibroblast growth factor-23 differed significantly between groups (P = .04). Cats with CKD and nephrocalcinosis had increasing plasma creatinine concentrations (.03 ± .01 mg/dL/month; P = .04) and phosphate concentrations (.06 ± .02 mg/dL/month; P < .001) and decreasing body weight (.02 ± .01 kg/month; P < .001) over time.

CONCLUSIONS AND CLINICAL IMPORTANCE

Nephrocalcinosis is prevalent in cats with CKD, especially in those with hypercalcemia. This pathological feature appears to be associated with CKD progression in cats.

Detection of nephrocalcinosis using ultrasonography, micro-computed tomography, and histopathology in cats

BACKGROUND

Identification of nephrocalcinosis in cats with chronic kidney disease (CKD) is of clinical interest but the ability of ultrasonography to detect nephrocalcinosis is uncertain.

OBJECTIVES

To compare ultrasonography, micro-computed tomography (μCT) and histopathology for identification of nephrocalcinosis.

ANIMALS

Twelve kidneys from 7 euthyroid client-owned cats with CKD.

METHODS

Descriptive study. Renal ultrasonography was performed ante-mortem for nephrocalcinosis detection. Kidneys were grouped based on nephrocalcinosis: present, suspected, or absent. When cats died, necropsy was performed. Renal tissue was evaluated using μCT for macroscopic nephrocalcinosis, and nephrocalcinosis volume-to-kidney tissue ratio (macro-VN:KT) and sagittal nephrocalcinosis area-to-kidney tissue ratio (macro-AN:KT) were calculated. Each kidney subsequently was bisected longitudinally, formalin-fixed, and paraffin-embedded for microscopic nephrocalcinosis assessment using von Kossa and Alizarin red staining with AN:KT (VK-micro-AN:KT and AR-micro-AN:KT) quantified using ImageJ. Data are presented as median (range). Relationships between macroscopic and microscopic AN:KT were assessed using Spearman's correlation.

RESULTS

Nephrocalcinosis by ultrasonography was considered to be absent in 3, suspected in 3, and present in 5 kidneys; 1 kidney had nephrolithiasis with nephrocalcinosis. The macro-VN:KT was 0.001%, 0.001%, and 0.019%, and the macro-AN:KT was 0.08%, 0.30%, and 1.47%, respectively. Histologically, VK-micro-AN:KT was 0.21%, 2.85%, and 4.56%, and AR-micro-AN:KT was 1.73%, 5.82%, and 8.90% for kidneys where ultrasonographic macro-nephrocalcinosis was absent, suspected, or present, respectively. A strong correlation was identified between macroscopic (macro-AN:KT) and microscopic (VK-micro-AN:KT) nephrocalcinosis (rs = 0.76; P = .01).

CONCLUSIONS AND CLINICAL IMPORTANCE

Ultrasonographically diagnosed nephrocalcinosis correlates well with macroscopic and microscopic nephrocalcinosis at necropsy despite their separation in time.

Hidden Acid Retention with Normal Serum Bicarbonate Level in Chronic Kidney Disease

Management of metabolic acidosis is crucial for preserving bone, muscle, and renal health, as evidenced by the results of several interventional studies conducted on patients with chronic kidney disease (CKD). Considering the continuity of CKD progression over time, it is reasonable to deduce that a subclinical form of metabolic acidosis may exist prior to the manifestation of overt metabolic acidosis. Covert H⁺ retention with normal serum bicarbonate level in patients with CKD may result in maladaptive responses that contribute to kidney function deterioration, even in the early stages of the disease. The loss of adaptive compensatory mechanisms of urinary acid excretion may be a key factor in this process. Early modulation of these responses could be an important therapeutic strategy in preventing CKD progression. However, to date, the optimal approach for alkali therapy in subclinical metabolic acidosis in CKD remains uncertain. There is a lack of established guidelines on when to initiate alkali therapy, potential side effects of alkali agents, and the optimal blood bicarbonate levels based on evidence-based practices. Therefore, further research is necessary to address these concerns and establish more robust guidelines for the use of alkali therapy in patients with CKD. Herein, we provide an overview of recent developments on this subject and examine the potential therapeutic approaches that interventional treatments may present for patients with hidden H⁺ retention, exhibiting normal serum bicarbonate levels - commonly described as subclinical or eubicarbonatemic metabolic acidosis in patients with CKD.

Risk factors and implications associated with renal mineralization in chronic kidney disease in cats

Background

Nephrocalcinosis is a pathological feature of chronic kidney disease (CKD). Its pathophysiological implications for cats with CKD are unexplored.

Objectives

Identify nephrocalcinosis risk factors and evaluate its influence on CKD progression and all‐cause mortality.

Animals

Fifty‐one euthyroid client‐owned cats with International Renal Interest Society (IRIS) stages 2‐3 azotemic CKD.

Methods

Retrospective cohort study. Histopathological kidney sections were assessed for nephrocalcinosis (von Kossa stain). Nephrocalcinosis severity was determined by image analysis (ImageJ). Ordinal logistic regressions were performed to identify nephrocalcinosis risk factors. The influence of nephrocalcinosis on CKD progression and mortality risk were assessed using linear mixed model and Cox regression, respectively. Cats were categorized by their owner‐reported time‐averaged phosphate‐restricted diet (PRD) intake, where PRD comprised ≥50%, 10‐50%, or none of food intake.

Results

Nephrocalcinosis was rated as mild‐to‐severe in 78.4% and absent‐to‐minimal in 21.6% of cases. Higher baseline plasma total calcium concentration (tCa; odds ratio [OR] = 3.07 per 1 mg/dL; P = .02) and eating a PRD (10%‐50%: OR = 8.35; P = .01; ≥50%: OR = 5.47; P = .01) were independent nephrocalcinosis risk factors. Cats with absent‐to‐minimal nephrocalcinosis had increasing plasma creatinine (0.250 ± 0.074 mg/dL/month; P = .002), urea (5.06 ± 1.82 mg/dL/month; P = .01), and phosphate (0.233 ± 0.115 mg/dL/month; P = .05) concentrations over a 1‐year period, and had shorter median survival times than cats with mild‐to‐severe nephrocalcinosis.

Conclusion and Clinical Importance

Higher plasma tCa at CKD diagnosis and PRD intake are independently associated with nephrocalcinosis. However, nephrocalcinosis is not associated with rapid CKD progression in cats.

Protein quality and safety evaluation of sarcoplasmic protein derived from silver carp (Hypophthalmichthys molitrix) using a rat model

Consisting of 25 to 30% of protein in carp, water-soluble sarcoplasmic proteins lost in wash water, have been recovered and freeze-dried into a protein-rich powder. Study objectives were to evaluate protein quality and safety of a silver carp sarcoplasm derived protein powder (CSP) compared to commercial protein supplements, casein, and whey. In vivo protein quality assessment of CSP showed a lower (P < 0.05) protein digestibility corrected amino acid score compared to the commercial protein sources. Despite greater (P < 0.05) fecal amino acid excretion in casein-fed rats, there were no significant differences in liver and muscle amino acid profiles. All low (10% kcal) protein diets supported growth with the normal range. However, whey protein supplementation resulted in greater (P < 0.05) adiposity. CSP, casein, or whey-fed rats showed no differences in major organ weights, renal damage biomarkers, or bone indices. Collectively, results indicated CSP was safe with protein quality comparable to casein. PRACTICAL APPLICATION: As much as 40 percent of protein in fish can be lost due to sarcoplasmic protein solubilization in processing wash water. Silver carp sarcoplasm protein powder may have similar commercial potential as a sustainable and nutritious alternative to whey and casein proteins. This project aimed to verify the protein quality and safety of this economical protein source.

Approach to the Treatment of Chronic Metabolic Acidosis in CKD

Chronic metabolic acidosis is not uncommon in patients with chronic kidney disease (CKD). Clinical practice guidelines suggest that clinicians administer alkali to maintain serum bicarbonate level at a minimum of 22 mEq/L to prevent the effects of acidosis on bone demineralization and protein catabolism. Small interventional studies support the notion that correcting acidosis slows CKD progression as well. Furthermore, alkaline therapy in persons with CKD and normal bicarbonate levels may also preserve kidney function. Observational studies suggest that targeting a serum bicarbonate level near 28 mEq/L may improve clinical outcomes above and beyond targeting a value ≥ 22 mEq/L, yet values > 26 mEq/L have been reported to be associated with incident heart failure and mortality in the CRIC (Chronic Renal Insufficiency Cohort) Study. Furthermore, correcting acidosis may provoke vascular calcification. This teaching case discusses several uncertainties regarding the management of acidosis in CKD, such as when to initiate alkali treatment, potential side effects of alkali, and the optimum serum bicarbonate level based on current evidence in CKD. Suggestions regarding the maximum sodium bicarbonate dose to administer to patients with CKD to achieve the target serum bicarbonate concentration are offered.

Acidosis: progression of chronic kidney disease and quality of life

Metabolic acidosis (MA) is relatively common in patients with chronic kidney disease (CKD) particularly in stages 4 and 5. It is assumed to play a contributory role in the development of several complications including bone disease, skeletal muscle wasting, altered protein synthesis, and degradation. Recent evidence also suggests that even mild acidosis might play a role in progressive glomerular filtration rate loss. Experimental and clinical studies suggest that correction of acidosis by alkali therapy attenuates these complications and improves quality of life. Despite several recent small and single-center studies supporting this notion, more robust evidence is required with regard to the long-term benefits of alkali therapy, type of alkali supplements, and the optimal level of serum bicarbonate.

Consequences and therapy of the metabolic acidosis of chronic kidney disease

Metabolic acidosis is common in patients with chronic kidney disease (CKD), particularly once the glomerular filtration rate (GFR) falls below 25 ml/min/1.73 m(2). It is usually mild to moderate in magnitude with the serum bicarbonate concentration ([HCO(3)(-)]) ranging from 12 to 23 mEq/l. Even so, it can have substantial adverse effects, including development or exacerbation of bone disease, growth retardation in children, increased muscle degradation with muscle wasting, reduced albumin synthesis with a predisposition to hypoalbuminemia, resistance to the effects of insulin with impaired glucose tolerance, acceleration of the progression of CKD, stimulation of inflammation, and augmentation of β(2)-microglobulin production. Also, its presence is associated with increased mortality. The administration of base to patients prior to or after initiation of dialysis leads to improvement in many of these adverse effects. The present recommendation by the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF KDOQI) is to raise serum [HCO(3)(-)] to ≥ 22 mEq/l, whereas Caring for Australians with Renal Impairment (CARI) recommends raising serum [HCO(3)(-)] to >22 mEq/l. Base administration can potentially contribute to volume overload and exacerbation of hypertension as well as to metastatic calcium precipitation in tissues. However, sodium retention is less when given as sodium bicarbonate and sodium chloride intake is concomitantly restricted. Results from various studies suggest that enhanced metastatic calcification is unlikely with the pH values achieved during conservative base administration, but the clinician should be careful not to raise serum [HCO(3)(-)] to values outside the normal range.

Acidosis and progression of chronic kidney disease

PURPOSE OF REVIEW

Chronic kidney disease progressively impairs the ability of kidneys to excrete hydrogen ions owing to the reduced capacity of the kidney to synthesize ammonia resulting in metabolic acidosis. There is good experimental evidence that metabolic acidosis contributes to protein energy wasting disorder and progression of chronic kidney disease (CKD). However, there was a lack of robust clinical evidence to support these experimental observations.

RECENT FINDINGS

Three recent publications have confirmed the experimental evidence and the only randomized controlled study of its kind has suggested that the correction of acidosis by sodium bicarbonate in patients with advanced CKD is associated with attenuation of the rate of decline of renal function, reduction in the incidence of end stage renal disease and improvement of nutritional parameters.

SUMMARY

In light of these recent studies, it appears that this cheap and simple strategy, which is in line with current renal recommendations, has the potential of translating into significant economic, quality of life and clinical outcome benefits in an expanding pool of patients with CKD.

Consumption of krill protein concentrate prevents early renal injury and nephrocalcinosis in female Sprague-Dawley rats

Female Sprague-Dawley rats provide an animal model for studying the role of nutrition in renal health due to their sensitivity to diet-induced alterations in kidney function. Nephrocalcinosis, a common renal abnormality found in rats, has been implicated in subsequent renal failure. Simple dietary manipulations, such as changing the source of dietary protein, may influence nephrocalcinosis. This study evaluates the consumption of krill protein concentrate (KPC), a novel and high-quality protein, on renal and bone health. Young female Sprague-Dawley rats (n = 10/group) were individually housed in metabolic cages and fed ad libitum diets consisting of 10% crude protein supplied as KPC or casein for 4 weeks. Diets were isocaloric, isonitrogenous, and matched for calcium (Ca) and phosphorus (P). Urinary n-acetyl glucosaminidase (NAG) was measured and kidney histology performed to assess kidney damage. Biomarkers of kidney function were determined by calorimetric assays. Ca and P balance and bone concentrations were measured using inductively coupled plasma mass spectrometry. Femoral strength was determined by three-point bend testing. Rats fed KPC had lower (P = 0.005) urinary NAG levels and minimal microtubular Ca deposition compared to rats fed casein. There was a tendency (P < 0.06) for higher glomerular filtration rates and lower proteinuria, and higher (P = 0.03) urinary output in rats fed KPC compared to casein. There were no differences in Ca and P balance or bone measurements of total bone mineral content, Ca, P or strength between rats fed KPC and casein. Based on the study results, KPC prevented early renal injury leading to nephrocalcinosis and potential bone loss.

Bicarbonate supplementation slows progression of CKD and improves nutritional status

Bicarbonate supplementation preserves renal function in experimental chronic kidney disease (CKD), but whether the same benefit occurs in humans is unknown. Here, we randomly assigned 134 adult patients with CKD (creatinine clearance [CrCl] 15 to 30 ml/min per 1.73 m(2)) and serum bicarbonate 16 to 20 mmol/L to either supplementation with oral sodium bicarbonate or standard care for 2 yr. The primary end points were rate of CrCl decline, the proportion of patients with rapid decline of CrCl (>3 ml/min per 1.73 m(2)/yr), and ESRD (CrCl <10 ml/min). Secondary end points were dietary protein intake, normalized protein nitrogen appearance, serum albumin, and mid-arm muscle circumference. Compared with the control group, decline in CrCl was slower with bicarbonate supplementation (5.93 versus 1.88 ml/min 1.73 m(2); P < 0.0001). Patients supplemented with bicarbonate were significantly less likely to experience rapid progression (9 versus 45%; relative risk 0.15; 95% confidence interval 0.06 to 0.40; P < 0.0001). Similarly, fewer patients supplemented with bicarbonate developed ESRD (6.5 versus 33%; relative risk 0.13; 95% confidence interval 0.04 to 0.40; P < 0.001). Nutritional parameters improved significantly with bicarbonate supplementation, which was well tolerated. This study demonstrates that bicarbonate supplementation slows the rate of progression of renal failure to ESRD and improves nutritional status among patients with CKD.

Metabolic acidosis inhibits soft tissue calcification in uremic rats

Metabolic acidosis is common in patients with chronic kidney disease, which is known to affect bone metabolism. We examined the effect of metabolic acidosis on the development of vascular and other soft-tissue calcifications in uremic rats treated with calcitriol. Extraskeletal calcification was measured in vivo, in control rats and rats with a remnant kidney model of uremia with or without ammonium chloride-induced acidosis. Soft-tissue calcification was assessed histologically, by measurement of the expression of the sodium-dependent phosphate cotransporter Pit-1 and by quantification of tissue calcium and phosphorus. Calcitriol administration to uremic rats resulted in significant deposition of material positive for von Kossa stain in the aorta, stomach, and kidney, elevated aortic calcium and phosphorus, increased aortic Pit-1 expression, and high mortality. Calcitriol-treated uremic rats with acidosis did not develop aortic or soft-tissue calcification, did not increase aortic Pit-1 expression, and had significantly lower mortality. Additionally, an acidotic environment prevented calcification of vascular smooth muscle cells in vitro. Our study shows that metabolic acidosis inhibits extraskeletal calcification.

Metabolic Acidosis of CKD: Diagnosis, Clinical Characteristics, and Treatment

Metabolic acidosis is noted in the majority of patients with chronic kidney disease (CKD) when glomerular filtration rate (GFR) decreases to less than 20% to 25% of normal, although as many as 20% of individuals can have acid-base parameters close to or within the normal range. Acidosis generally is mild to moderate in degree, with plasma bicarbonate concentrations ranging from 12 to 22 mEq/L (mmol/L), and it is rare to see values less than 12 mEq/L (mmol/L) in the absence of an increased acid load. Degree of acidosis approximately correlates with severity of renal failure and usually is more severe at a lower GFR. The metabolic acidosis can be of the high-anion-gap variety, although anion gap can be normal or only moderately increased even with stage 4 to 5 CKD. Several adverse consequences have been associated with metabolic acidosis, including muscle wasting, bone disease, impaired growth, abnormalities in growth hormone and thyroid hormone secretion, impaired insulin sensitivity, progression of renal failure, and exacerbation of beta 2 -microglobulin accumulation. Administration of base aimed at normalization of plasma bicarbonate concentration might be associated with certain complications, such as volume overload, exacerbation of hypertension, and facilitation of vascular calcifications. Whether normalization of plasma bicarbonate concentrations in all patients is desirable therefore requires additional study. In the present review, we describe clinical and laboratory characteristics of metabolic acidosis, discuss potential adverse effects, and address benefits and complications of therapy.