Mechanisms of the effects of acidosis and hypokalemia on renal ammonia metabolism

Trimethoprim inhibits renal H+-K+-ATPase in states of K+ depletion

There is growing consensus that under physiological conditions, collecting duct H+ secretion is independent of epithelial Na+ channel (ENaC) activity. We have recently shown that the direct ENaC inhibitor benzamil acutely impairs H+ excretion by blocking renal H+-K+-ATPase. However, the question remains whether inhibition of ENaC per se causes alterations in renal H+ excretion. To revisit this question, we studied the effect of the antibiotic trimethoprim (TMP), which is well known to cause K+ retention by direct ENaC inhibition. The acute effect of TMP (5 µg/g body wt) was assessed in bladder-catheterized mice, allowing real-time measurement of urinary pH, electrolyte, and acid excretion. Dietary K+ depletion was used to increase renal H+-K+-ATPase activity. In addition, the effect of TMP was investigated in vitro using pig gastric H+-K+-ATPase-enriched membrane vesicles. TMP acutely increased natriuresis and decreased kaliuresis, confirming its ENaC-inhibiting property. Under control diet conditions, TMP had no effect on urinary pH or acid excretion. Interestingly, K+ depletion unmasked an acute urine alkalizing effect of TMP. This finding was corroborated by in vitro experiments showing that TMP inhibits H+-K+-ATPase activity, albeit at much higher concentrations than benzamil. In conclusion, under control diet conditions, TMP inhibited ENaC function without changing urinary H+ excretion. This finding further supports the hypothesis that the inhibition of ENaC per se does not impair H+ excretion in the collecting duct. Moreover, TMP-induced urinary alkalization in animals fed a low-K+ diet highlights the importance of renal H+-K+-ATPase-mediated H+ secretion in states of K+ depletion.NEW & NOTEWORTHY The antibiotic trimethoprim (TMP) often mediates K+ retention and metabolic acidosis. We suggest a revision of the underlying mechanism that causes metabolic acidosis. Our results indicate that TMP-induced metabolic acidosis is secondary to epithelial Na+ channel-dependent K+ retention. Under control dietary conditions, TMP does not per se inhibit collecting duct H+ secretion. These findings add further argument against a physiologically relevant voltage-dependent mechanism of collecting duct H+ excretion.

Nonhepatic hyperammonemic encephalopathy following bariatric surgery: A systematic review

BACKGROUND

Nonhepatic Hyperammonemic encephalopathy (NHAE) following Bariatric Surgery (BS), mainly Roux-en-Y Gastric Bypass (RYGB) and Biliopancreatic Diversion (BPD) is a potentially devastating condition if not diagnosed and managed promptly.

METHODS

A literature review was performed using PRISMA guidelines. Eighteen studies and 3 conference abstracts with a total of 33 patients were included in this review.

RESULTS

Majority (28 patients, 84.8 %) had RYGB. Seven patients (21.2 %) had associated metabolic disorders. 60 % of patients presented with neurological symptoms or signs such as confusion, cognitive and/or psychomotor changes, and decreased reflexes. Two patients presented with status epilepticus. In 30 of the 33 patients an elevated serum ammonia levels was reported (90.9 %). The overall mortality was 39.3 %.

CONCLUSION

NHAE is a rare condition following bariatric surgery (in particular bypass procedures), carrying a high mortality rate. The signs and symptoms are predominantly neurological and may be mistaken for Wernicke's encephalopathy or other more common neurological conditions. Serum ammonia levels should be checked in those who present with these symptoms and signs. Prompt treatment might be life saving in patients with NHAE.

The K-Cl cotransporter-3 in the mammalian kidney

PURPOSE OF REVIEW

We recently localized a new K-Cl cotransporters-3 (KCC3) transporter to the apical membrane of type-B intercalated cells. This gives us an opportunity to revisit the roles of the KCC3 in kidney and integrate the new findings to our current knowledge of the biology of the bicarbonate secreting cells.

RECENT FINDINGS

Here, we review the basic properties of the K-Cl cotransporter with a particular attention to the responsiveness of the transporter to cell swelling. We summarize what is already known about KCC3b and discuss new information gained from our localizing of KCC3a in type-B intercalated cells. We integrate the physiology of KCC3a with the main function of the type-B cell, that is, bicarbonate secretion through the well characterized apical Cl-/HCO3- exchanger and the basolateral Na-HCO3 cotransporter.

SUMMARY

Both KCC3b and KCC3a seem to be needed for maintaining cell volume during enhanced inward cotransport of Na-glucose in proximal tubule and Na-HCO3 in intercalated cells. In addition, apical KCC3a might couple to pendrin function to recycle Cl-, particularly in conditions of low salt diet and therefore low Cl- delivery to the distal tubule. This function is critical in alkalemia, and KCC3a function in the pendrin-expressing cells may contribute to the K+ loss which is observed in alkalemia.

Association of serum bicarbonate with the development of kidney stones in patients with chronic kidney disease: a retrospective cohort study

BACKGROUND

Epidemiological studies demonstrate an association between kidney stones and risk of chronic kidney disease (CKD) and CKD progression. Metabolic acidosis, as a consequence of CKD, results in a reduced urine pH which promotes the formation of some types of kidney stones and inhibits the formation of others. While metabolic acidosis is a risk factor for CKD progression, the association of serum bicarbonate with risk of incident kidney stones is not well understood.

METHODS

We used an Integrated Claims-Clinical dataset of US patients to generate a cohort of patients with non-dialysis-dependent CKD with two serum bicarbonate values of 12 to <22 mmol/L (metabolic acidosis) or 22 to <30 mmol/L (normal serum bicarbonate). Primary exposure variables were baseline serum bicarbonate and change in serum bicarbonate over time. Cox proportional hazards models evaluated time to first occurrence of kidney stones during a median 3.2-year follow-up.

RESULTS

A total of 142 884 patients qualified for the study cohort. Patients with metabolic acidosis experienced post-index date kidney stones at greater frequency than patients with normal serum bicarbonate at the index date (12.0% vs 9.5%, P < .0001). Both lower baseline serum bicarbonate [hazard ratio (HR) 1.047; 95% confidence interval (CI) 1.036-1.057] and decreasing serum bicarbonate over time (HR 1.034; 95% CI 1.026-1.043) were associated with increased risk of kidney stone development.

CONCLUSIONS

Metabolic acidosis was associated with a higher incidence of kidney stones and shorter time to incident stone formation in patients with CKD. Future studies may investigate the role of correcting metabolic acidosis to prevent stone formation.

A review of basic to clinical studies of the association between hyperammonemia, methamphetamine

Methamphetamine (METH), an addictive psychostimulant drug, is the second most widely used type of drug all around the world. METH abusers are more likely to develop a psycho-neurological complication. Hyperammonemia (HAM) causes neuropsychiatric illnesses such as mental state changes and episodes of acute encephalopathy. Recently, there are some shreds of evidence about the relationship between METH complication and HAM. Both METH intoxication and HAM could induce psychosis, agitation, memory impairment, and psycho-neuronal disorders. They also have similar mechanisms of neuronal damages, such as excitotoxicity, oxidative stress, mitochondrial impairments, and inflammation responses, which can subsequently increase the glutamate level of the brain. Hence, the basic to clinical studies of the association between HAM and METH are reviewed by monitoring six case studies and a good body of animal studies literature. All instances of METH-associated HAM had changes in mental state and some level of confusion that were improved when the ammonia serum level returned to the normal level. Furthermore, most of them had typical vital signs. Several studies suggested some sources for METH-associated HAM, including METH-induced liver and renal damages, muscular hyperactivity, gut bacterial overgrowth, co-abuse of other substances, and using some forms of NH3 in METH cooking. In conclusion, it seems that mental status changes in METH abusers may be related to ammonia intoxication or HAM; therefore, it is important to assess the serum level of ammonia in METH intoxicated patients and resolve it.

A narrative review of nutritional abnormalities, complications, and optimization in the cirrhotic patient

OBJECTIVE

The purpose of this manuscript is to identify the pathophysiology of the metabolic abnormalities observed in cirrhosis and to uncover associations, if any, to its complications, such as sarcopenia and hepatic encephalopathy (HE).

BACKGROUND

Liver dysfunction in cirrhosis is known to be a precipitating factor in the disruption of many physiological pathways, specifically nutrient metabolism. As a result, affected patients are highly susceptible to derangements of processes affecting multiple classes of macro- and micronutrients, including proteins, carbohydrates, electrolytes, vitamins, and minerals. These disruptions are thought to be contributory to the pathogenesis of known complications of cirrhosis.

METHODS

Literature research of relevant topics was conducted for the above stated objective; sources were limited to articles from peer-reviewed journals published within the last 30 years.

CONCLUSION

This research established that there is positive correlation between nutrient derangements and the increased risk of complications of cirrhosis, which themselves carry significant morbidity and mortality risk. It also established that some nutrient and electrolyte abnormalities are independent indicators of prognosis and adverse outcomes, such as mortality. This also highlights the importance of comprehension of anomalous metabolism and its complications as it necessitates serious consideration in clinical care. In addition to medical management, cirrhotic patients also require ancillary assessment, such as comprehensive nutritional evaluation, to identify and treat reversible nutritional derangements. This consideration provides the best opportunity to achieve maximal health outcomes in the cirrhotic patient population.

Anatomophysiology of the Henle's Loop: Emphasis on the Thick Ascending Limb

The loop of Henle plays a variety of important physiological roles through the concerted actions of ion transport systems in both its apical and basolateral membranes. It is involved most notably in extracellular fluid volume and blood pressure regulation as well as Ca²⁺ , Mg²⁺ , and acid-base homeostasis because of its ability to reclaim a large fraction of the ultrafiltered solute load. This nephron segment is also involved in urinary concentration by energizing several of the steps that are required to generate a gradient of increasing osmolality from cortex to medulla. Another important role of the loop of Henle is to sustain a process known as tubuloglomerular feedback through the presence of specialized renal tubular cells that lie next to the juxtaglomerular arterioles. This article aims at describing these physiological roles and at discussing a number of the molecular mechanisms involved. It will also report on novel findings and uncertainties regarding the realization of certain processes and on the pathophysiological consequences of perturbed salt handling by the thick ascending limb of the loop of Henle. Since its discovery 150 years ago, the loop of Henle has remained in the spotlight and is now generating further interest because of its role in the renal-sparing effect of SGLT2 inhibitors. © 2022 American Physiological Society. Compr Physiol 12:1-21, 2022.

Hyperammonemia in azotemic cats

OBJECTIVES

Hyperammonemia occurs in cats with hepatobiliary and nutritional (cobalamin and arginine deficiency) disorders, and has also been documented in four cats with renal azotemia. We hypothesized that in cats with renal azotemia, fasting hyperammonemia would correlate with indices of worsening kidney function, and would be independent of cobalamin, potassium, systemic inflammation or urinary tract infection (UTI) with urease-producing bacteria.

METHODS

A fasted blood sample was prospectively collected for ammonia and cobalamin analysis from 18 client-owned cats with renal azotemia (creatinine [Cr] ⩾1.6 mg/dl, urine specific gravity <1.030 or documentation of historical chronic kidney disease [CKD]). Correlations between blood ammonia and selected biochemical parameters were analyzed using Pearson's correlation coefficient.

RESULTS

Seven castrated males and 11 spayed females with a median age of 12 years (range 4-19 years) were enrolled. Ten of 18 (56%) cats presented for acute kidney injury (AKI) or acute on chronic kidney disease (AoCKD), and 8/18 (44%) presented for progressive CKD. The median Cr was 5.9 mg/dl (range 1.9-24.7 mg/dl). Hyperammonemia was documented in 4/18 (22%) cats, with a median of 95 µmol/dl (range 85-98 µmol/dl), and all four of these cats were classified as AKI/AoCKD. Blood ammonia concentrations had a significant moderate positive correlation between blood urea nitrogen (BUN) (r = 0.645, P = 0.003), Cr (r = 0.578, P = 0.012) and serum phosphorus (r = 0.714, P = 0.0009) but not with cobalamin, potassium or white blood cell count. No cats had UTIs with urease-producing bacteria.

CONCLUSIONS AND RELEVANCE

A correlation exists between blood ammonia and BUN, Cr and phosphorus in cats with renal azotemia. Future studies are warranted in a larger population of cats to determine the true prevalence, etiology and potential therapeutic effect of medical management of hyperammonemia on long-term prognosis in cats with kidney disease.

Pathophysiology of Hepatic Encephalopathy

Hepatic encephalopathy (HE) is one of the major clinical decompensations of cirrhosis, with a high impact on health care resource utilization and cost. For an effective and comprehensive management of HE, the clinicians need to understand the pathophysiologic mechanisms of HE. This review describes the multiorgan processes involved in HE and how several HE precipitants and treatment strategies act on ammonia production, excretion, and neurotoxicity, including the impact of diabetes and use of cannabinoids. The authors also discuss the current and future role of gut microbiome, systemic/central inflammation, and various neurotransmitters for the pathogenesis and treatment of HE.

Approximation of bicarbonate concentration using serum total carbon dioxide concentration in patients with non-dialysis chronic kidney disease

Background

We investigated the relationship between serum total carbon dioxide (CO₂) and bicarbonate ion (HCO₃⁻) concentrations in pre-dialysis chronic kidney disease (CKD) patients and devised a formula for predicting low bicarbonate (HCO₃⁻< 24 mmol/L) and high bicarbonate (HCO₃⁻ ≥ 24 mmol/L) using clinical parameters.

Methods

In total, 305 samples of venous blood collected from 207 pre-dialysis patients assessed by CKD stage (G1 + G2, 46; G3, 50; G4, 51; G5, 60) were investigated. The relationship between serum total CO₂ and HCO₃⁻ concentrations was analyzed using Pearson’s correlation coefficient. An approximation formula was developed using clinical parameters correlated independently with HCO₃⁻ concentration. Diagnostic accuracy of serum total CO₂ and the approximation formula was evaluated by receiver operating characteristic curve analysis and a 2 × 2 table.

Results

Serum total CO₂ correlated strongly with HCO₃⁻ concentration (r = 0.91; P < 0.001). The following approximation formula was obtained by a multiple linear regression analysis: HCO₃⁻ (mmol/L) = total CO₂ − 0.5 × albumin − 0.1 × chloride − 0.01 × (estimated glomerular filtration rate + blood glucose) + 15. The areas under the curves of serum total CO₂ and the approximation formula for detection of low bicarbonate and high bicarbonate were 0.981, 0.996, 0.993, and 1.000, respectively. This formula had superior diagnostic accuracy compared with that of serum total CO₂ (86.6% vs. 81.3%).

Conclusion

Serum total CO₂ correlated strongly with HCO₃⁻ concentration in pre-dialysis CKD patients. An approximation formula including serum total CO₂ showed superior diagnostic accuracy for low and high bicarbonate compared with serum total CO₂.

Serum Electrolyte Levels and Outcomes in Patients Hospitalized with Hepatic Encephalopathy

INTRODUCTION AND AIMS

Serum electrolyte derangements are common in patients with decompensated cirrhosis hospitalized for hepatic encephalopathy. There are limited data describing the association between electrolyte levels and outcomes in hepatic encephalopathy. We assessed the association between initial serum electrolyte values and outcomes in patients with hepatic encephalopathy.

MATERIAL AND METHODS

A total of 385 consecutive patients hospitalized with encephalopathy were included in the study. Baseline electrolyte levels (sodium, potassium, chloride, bicarbonate, calcium and phosphorus) were measured at the time of admission and assessed for association with outcomes, which included survival, admission to the intensive care unit, requirement for mechanical ventilation, and length of hospital stay. P-values ≤ 0.0083 were considered significant after adjustment for multiple testing.

RESULTS

In unadjusted analysis, significant associations were identified regarding both bicarbonate and phosphorus (admission to intensive care unit), and calcium (mechanical ventilation); however these findings weakened and no longer approached statistical significance when adjusting for confounding variables. No other significant associations between serum electrolyte measurements and outcomes were observed.

CONCLUSIONS

Our findings suggest that in patients hospitalized with encephalopathy, serum electrolyte measurements are not strong predictors of patient outcome.

Postoperative Compensatory Ammonium Excretion Subsequent to Systemic Acidosis in Cardiac Patients

Background

Postoperative acid-base imbalances, usually acidosis, frequently occur after cardiac surgery. In most cases, the human body, not suffering from any severe preexisting illnesses regarding lung, liver, and kidney, is capable of transient compensation and final correction. The aim of this study was to correlate the appearance of postoperatively occurring acidosis with renal ammonium excretion.

Materials and Methods

Between 07/2014 and 10/2014, a total of 25 consecutive patients scheduled for elective isolated coronary artery bypass grafting with cardiopulmonary bypass were enrolled in this prospective observational study. During the operative procedure and the first two postoperative days, blood gas analyses were carried out and urine samples collected. Urine samples were analyzed for the absolute amount of ammonium.

Results

Of all patients, thirteen patients developed acidosis as an initial disturbance in the postoperative period: five of respiratory and eight of metabolic origin. Four patients with respiratory acidosis but none of those with metabolic acidosis subsequently developed a base excess > +2 mEq/L.

Conclusion

Ammonium excretion correlated with the increase in base excess. The acidosis origin seems to have a large influence on renal compensation in terms of ammonium excretion and the possibility of an overcorrection.

Histidine and other amino acids in blood and urine after administration of Bretschneider solution (HTK) for cardioplegic arrest in patients: effects on N-metabolism

Bretschneider (histidine-tryptophan-ketoglutarate, HTK) solution employed for induction of cardioplegic arrest possesses a high histidine concentration (198 mM). Due to the large volume administered, massive amounts of histidine are incorporated. The aim of the study was to evaluate alterations in amino acid and nitrogen metabolism originating from histidine degradation. Between 07/2014 and 10/2014, a total of 29 consecutive patients scheduled for elective isolated coronary artery bypass grafting with cardiopulmonary bypass (CPB) were enrolled in this prospective observational study. The patients received 1.6 L cardioplegic Bretschneider solution on average. Blood gas and urine samples obtained were analyzed for amino acid as well as urea and ammonium concentrations. After CPB initiation, plasma histidine concentration greatly increased to 21,000 µM to reach 8000 µM at the end. Within the operative period, plasma concentrations of aspartate, glutamate, asparagine, alanine, and glutamine increased variable in magnitude. During the same time, urinary analysis revealed histidine excretion of 19,500 µmol in total and marked elevations in glutamate and glutamine excretion. The absolute amounts of urea and ammonium excreted additionally were 3 mmol and 8 mmol, respectively. Already during CPB, distinct amounts of the histidine administered are metabolized, mainly to other amino acids, but only small amounts to urea and ammonia. Thus, the impact of the histidine incorporated on acid–base status in the intraoperative phase is minor. On the other hand, intraoperative provision of several amino acids arising from histidine metabolism might mitigate postaggression syndrome.

Refining the ammonia hypothesis: a physiology-driven approach to the treatment of hepatic encephalopathy

Hepatic encephalopathy (HE) is one of the most important complications of cirrhosis and portal hypertension. Although the etiology is incompletely understood, it has been linked to ammonia directly and indirectly. Our goal is to review for the clinician the mechanisms behind hyperammonemia and the pathogenesis of HE to explain the rationale for its therapy. We reviewed articles collected through a search of MEDLINE/PubMed, Cochrane Database of Systematic Reviews, and Google Scholar between October 1, 1948, and December 8, 2014, and by a manual search of citations within retrieved articles. Search terms included hepatic encephalopathy, ammonia hypothesis, brain and ammonia, liver failure and ammonia, acute-on-chronic liver failure and ammonia, cirrhosis and ammonia, portosytemic shunt, ammonia and lactulose, rifaximin, zinc, and nutrition. Ammonia homeostatsis is a multiorgan process involving the liver, brain, kidneys, and muscle as well as the gastrointestinal tract. Indeed, hyperammonemia may be the first clue to poor functional reserves, malnutrition, and impending multiorgan dysfunction. Furthermore, the neuropathology of ammonia is critically linked to states of systemic inflammation and endotoxemia. Given the complex interplay among ammonia, inflammation, and other factors, ammonia levels have questionable utility in the staging of HE. The use of nonabsorbable disaccharides, antibiotics, and probiotics reduces gut ammoniagenesis and, in the case of antibiotics and probiotics, systemic inflammation. Nutritional support preserves urea cycle function and prevents wasting of skeletal muscle, a significant site of ammonia metabolism. Correction of hypokalemia, hypovolemia, and acidosis further assists in the reduction of ammonia production in the kidney. Finally, early and aggressive treatment of infection, avoidance of sedatives, and modification of portosystemic shunts are also helpful in reducing the neurocognitive effects of hyperammonemia. Refining the ammonia hypothesis to account for these other factors instructs a solid foundation for the effective treatment and prevention of hepatic encephalopathy.

Acute liver failure in dogs and cats

OBJECTIVE

To define acute liver failure (ALF), review the human and veterinary literature, and discuss the etiologies and current concepts in diagnostic and treatment options for ALF in veterinary and human medicine.

ETIOLOGY

In veterinary medicine ALF is most commonly caused by hepatotoxin exposure, infectious agents, inflammatory diseases, trauma, and hypoxic injury.

DIAGNOSIS

A patient may be deemed to be in ALF when there is a progression of acute liver injury with no known previous hepatic disease, the development of hepatic encephalopathy of any grade that occurs within 8 weeks after the onset of hyperbilirubinemia (defined as plasma bilirubin >50 μM/L [>2.9 mg/dL]), and the presence of a coagulopathy. Diagnostic testing to more specifically characterize liver dysfunction or pathology is usually required.

THERAPY

Supportive care to aid the failing liver and compensate for the lost functions of the liver remains the cornerstone of care of patients with ALF. Advanced therapeutic options such as extracorporeal liver assist devices and transplantation are currently available in human medicine.

PROGNOSIS

The prognosis for ALF depends upon the etiology, the degree of liver damage, and the response to therapy. In veterinary medicine, the prognosis is generally poor.