Effect of acute acid loading on acid-base and calcium metabolism

Dietary protein and bone health: towards a synthesised view

The present paper reviews published literature on the relationship between dietary protein and bone health. It will include arguments both for and against the anabolic and catabolic effects of dietary protein on bone health. Adequate protein intake provides the amino acids used in building and maintaining bone tissue, as well as stimulating the action of insulin-like growth factor 1, which in turn promotes bone growth and increases calcium absorption. However, the metabolism of dietary sulphur amino acids, mainly from animal protein, can lead to increased physiological acidity, which may be detrimental for bone health in the long term. Similarly, cereal foods contain dietary phytate, which in turn contains phosphate. It is known that phosphate consumption can also lead to increased physiological acidity. Therefore, cereal products may produce as much acid as do animal proteins that contain sulphur amino acids. The overall effect of dietary protein on physiological acidity, and its consequent impact on bone health, is extremely complex and somewhat controversial. The consensus is now moving towards a synthesised approach. Particularly, how anabolic and catabolic mechanisms interact; as well as how the context of the whole diet and the type of protein consumed is important.

Incomplete distal renal tubular acidosis from a heterozygous mutation of the V-ATPase B1 subunit

Congenital distal renal tubular acidosis (RTA) from mutations of the B1 subunit of V-ATPase is considered an autosomal recessive disease. We analyzed a distal RTA kindred with a truncation mutation of B1 (p.Phe468fsX487) previously shown to have failure of assembly into the V1 domain of V-ATPase. All heterozygous carriers in this kindred have normal plasma HCO3- concentrations and thus evaded the diagnosis of RTA. However, inappropriately high urine pH, hypocitraturia, and hypercalciuria were present either individually or in combination in the heterozygotes at baseline. Two of the heterozygotes studied also had inappropriate urinary acidification with acute ammonium chloride loading and an impaired urine-blood Pco2 gradient during bicarbonaturia, indicating the presence of a H+ gradient and flux defects. In normal human renal papillae, wild-type B1 is located primarily on the plasma membrane, but papilla from one of the heterozygote who had kidney stones but not nephrocalcinosis showed B1 in both the plasma membrane as well as diffuse intracellular staining. Titration of increasing amounts of the mutant B1 subunit did not exhibit negative dominance over the expression, cellular distribution, or H+ pump activity of wild-type B1 in mammalian human embryonic kidney-293 cells and in V-ATPase-deficient Saccharomyces cerevisiae. This is the first demonstration of renal acidification defects and nephrolithiasis in heterozygous carriers of a mutant B1 subunit that cannot be attributable to negative dominance. We propose that heterozygosity may lead to mild real acidification defects due to haploinsufficiency. B1 heterozygosity should be considered in patients with calcium nephrolithiasis and urinary abnormalities such as alkalinuria or hypocitraturia.

High-protein diets and renal health

High-protein diets (i.e., protein content of more than 25% of energy or more than 2 g/kg body weight per day) based on meat and dairy products are repeatedly promoted for weight reduction and better health, but the evidence supporting these notions is quite dubious. As described in the present review, there is a reason to be concerned about adverse effects of such diets, including glomerular hyperfiltration, hypertensive effects of a concomitant increase in dietary sodium, and an increased risk of nephrolithiasis. These diet-induced physiological consequences might lead to an increase in the prevalence of chronic kidney disease in the general population without preexisting kidney disease. Accordingly, we find medical reasons to refrain from promoting high-protein diets, in particular those based on meat and dairy products, until clear-cut evidence for the safety and for the superiority of such diets on human health has been provided.

Fluids and diuretics for acute ureteric colic

BACKGROUND

Acute ureteric colic is commonly associated with severe and debilitating pain. Theoretically, increasing fluid flow through the affected kidney might expedite stone passage, thereby improving symptoms more quickly. The efficacy and safety of interventions such as high volume intravenous (IV) or oral fluids and diuretics aimed at expediting ureteric stone passage is, however, uncertain.

OBJECTIVES

To look at the benefits and harms of diuretics and high volume (above maintenance) IV or oral fluid therapy for treating adult patients presenting with uncomplicated acute ureteric colic.

SEARCH METHODS

We searched the Cochrane Renal Group's specialised register (3 January 2012). Previously we searched the Cochrane Central Register of Controlled Trials (CENTRAL The Cochrane Library), MEDLINE (from 1966), EMBASE (from 1980) and handsearched reference lists of nephrology and urology textbooks, review articles, relevant studies, and abstracts from nephrology scientific meetings.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTs (including the first period of randomised cross-over studies) looking at diuretics or high volume IV or oral fluids for treating uncomplicated acute ureteric colic in adult patients presenting to the emergency department for the first time during that episode were included.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study quality and extracted data. Statistical analyses were performed using the random-effects model for multiple studies of the same outcomes, otherwise the fixed-effect model was used. Results were expressed as risk ratios (RR) for dichotomous outcomes or as mean differences (MD) for continuous data with 95% confidence intervals (CI).

MAIN RESULTS

Two studies (enrolling 118 participants) examined the association between intense hydration and ureteric colic outcomes. There was no significant difference in pain at six hours (1 study, 60 participants: RR 1.06, 95% CI 0.71 to 1.57), surgical stone removal (1 study, 60 participants: RR 1.20, 95% CI 0.41 to 3.51) or manipulation by cystoscopy (1 study, 60 participants: RR 0.67, 95% CI 0.21 to 2.13) when no fluids over six hours was compared to three litres IV fluids administered over a six hour period. There was no difference in stone clearance (1 study 43 participants: RR 1.38, 95% CI 0.50 to 3.84), hourly pain score or patients' narcotic requirements (P > 0.05 for all comparisons) when forced IV hydration of two litres over four hours was compared with minimal IV hydration at 20 mL/hour.One study did not provide any details which would have allowed us to assess any of the risk of bias items (selection, detection, performance, attrition or reporting bias). The second study did not report the method of randomisation or allocation (selection bias - unclear), they reported that the patients were blinded to therapy (low risk of bias), analgesics were administered according to predetermined pain score criteria (low risk), and assessment of stone passage was unlikely to have been biased by knowledge of group assignment (low risk). However the second study also reported a high percentage of participants excluded post randomisation (26%; high risk of bias). We were unable to assess or ascertain any of the other risk of bias items.

AUTHORS' CONCLUSIONS

We found no reliable evidence in the literature to support the use of diuretics and high volume fluid therapy for people with acute ureteric colic. However, given the potential positive therapeutic impact of fluids and diuretics to facilitate stone passage, the capacity of these interventions warrants further investigation to determine safety and efficacy profiles.

History, epidemiology and regional diversities of urolithiasis

Archeological findings give profound evidence that humans have suffered from kidney and bladder stones for centuries. Bladder stones were more prevalent during older ages, but kidney stones became more prevalent during the past 100 years, at least in the more developed countries. Also, treatment options and conservative measures, as well as 'surgical' interventions have also been known for a long time. Our current preventive measures are definitively comparable to those of our predecessors. Stone removal, first lithotomy for bladder stones, followed by transurethral methods, was definitively painful and had severe side effects. Then, as now, the incidence of urolithiasis in a given population was dependent on the geographic area, racial distribution, socio-economic status and dietary habits. Changes in the latter factors during the past decades have affected the incidence and also the site and chemical composition of calculi, with calcium oxalate stones being now the most prevalent. Major differences in frequency of other constituents, particularly uric acid and struvite, reflect eating habits and infection risk factors specific to certain populations. Extensive epidemiological observations have emphasized the importance of nutritional factors in the pathogenesis of urolithiasis, and specific dietary advice is, nowadays, often the most appropriate for prevention and treatment of urolithiasis.

Diet-induced acidosis: is it real and clinically relevant?

The concept of diet-induced ‘acidosis’ as a cause of disease has been a subject of interest for more than a century. The present article reviews the history of our evolving understanding of physiological pH, the physiological support for the concept of ‘acidosis’, the causes of acidosis, how it is recognised, its short-term effects as well as the long-term clinical relevance of preventative measures, and the research support for normalisation of pH. Further, we suggest differentiation of the terms ‘acidosis’ and ‘acidaemia’ as a way to resolve the conflation of these topics which has led to confusion and controversy. The available research makes a compelling case that diet-induced acidosis, not diet-induced acidaemia, is a real phenomenon, and has a significant, clinical, long-term pathophysiological effect that should be recognised and potentially counterbalanced by dietary means.

Acid-base status affects renal magnesium losses in healthy, elderly persons

Magnesium and calcium deficiency in humans is related to a number of pathological phenomena such as arrhythmia, osteoporosis, migraine, and fatal myocardial infarction. Clinically established metabolic acidosis induces renal losses of calcium. In normal subjects, even moderate increases in net endogenous acid production (NEAP) impair renal calcium reabsorption but no information is available whether this also influences renal magnesium handling. The aim of the study was to examine the relation between NEAP and renal magnesium excretion in healthy, free-living, elderly subjects. The subjects (age 64 +/- 4.7 y, n = 85) were randomly selected from the population register in Gothenburg (Sweden). Magnesium, calcium, and potassium were measured in 24-h urine samples and NEAP was quantified as renal net acid excretion (NAE). NAE was positively correlated with excretions of magnesium (R(2) = 0.27, P < 0.0001) and calcium (R(2) = 0.30, P < 0.0001) but not potassium. When 24-h urinary magnesium excretion was adjusted for 24-h urinary potassium excretion, a biomarker for dietary potassium intake, the association between magnesium excretion and NAE remained significant (R(2) = 0.21, P < 0.0001). The significant association between potassium-adjusted magnesiuria and NAE suggests that the acid-base status affects renal magnesium losses, irrespectively of magnesium intake. Magnesium deficiency could thus, apart from an insufficient intake, partly be caused by the acid load in the body.

Fluids and diuretics for acute ureteric colic

BACKGROUND

Acute ureteric colic is a common cause of severe and debilitating pain. Theoretically, increasing fluid flow through the affected kidney might expedite stone passage, thereby improving symptoms more quickly. Unfortunately, for interventions such as high volume intravenous or oral fluids and diuretics that are aimed at doing this, the efficacy and safety is uncertain.

OBJECTIVES

To look at the benefits and harms of diuretics and high volume (above maintenance) intravenous or oral fluid therapy for treating adult patients presenting with uncomplicated acute ureteric colic.

SEARCH STRATEGY

We searched the Cochrane Renal Group's specialised register (July 2004), the Cochrane Central Register of Controlled Trials (CENTRAL - The Cochrane Library, issue 3, 2004), MEDLINE (1966 - July 2004), EMBASE (1980 - July 2004) and handsearched reference lists of nephrology and urology textbooks, review articles, relevant trials, and abstracts from nephrology scientific meetings. We sent letters seeking information about unpublished or incomplete trials to investigators known to be involved in previous trials.

SELECTION CRITERIA

All randomised controlled trials (RCTs) and quasi-RCTS (including the first period of randomised cross-over studies) looking at diuretics or high volume intravenous or oral fluids for treating uncomplicated acute ureteric colic in adult patients presenting to the emergency department for the first time during that episode were to be included.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes or weight mean difference (WMD) for continuous data with 95% confidence intervals (CI).

MAIN RESULTS

One trial (60 participants) was identified. This study compared no fluids for six hours versus three litres of IV fluids received over a six hour period. There was no significant difference in pain at six hours (RR 1.06, 95% CI 0.71 to 1.57), surgical stone removal (RR 1.20, 95% CI 0.41 to 3.51) or manipulation by cystoscopy (RR 0.67, 95% CI 0.21 to 2.13).

AUTHORS' CONCLUSIONS

Unfortunately, we could find no credible evidence in the literature regarding either of these two treatment modalities. Given their potential positive impact, the role of diuretics and high volume fluid therapy in acute ureteric colic should be examined to determine their safety and efficacy in facilitating stone passage.