OBJECTIVE: During fasting, liver pivotally regulates blood glucose levels through glycogenolysis and gluconeogenesis. Kidney also produces glucose through gluconeogenesis. Gluconeogenic genes are transactivated by fasting, but their expression patterns are chronologically different between the two organs. We find that renal gluconeogenic gene expressions are positively correlated with the blood β-hydroxybutyrate concentration. Thus, we herein aim to investigate the regulatory mechanism and its physiological implications.
METHODS: Gluconeogenic gene expressions in liver and kidney were examined in hyperketogenic mice such as high-fat diet (HFD)-fed and ketogenic diet-fed mice, and in hypoketogenic PPARα knockout (PPARα-/-) mice. Renal gluconeogenesis was evaluated by rise in glycemia after glutamine loading in vivo. Functional roles of β-hydroxybutyrate in the regulation of renal gluconeogenesis were investigated by metabolome analysis and RNA-seq analysis of proximal tubule cells.
RESULTS: Renal gluconeogenic genes were transactivated concurrently with blood β-hydroxybutyrate uprise under ketogenic states, but the increase was blunted in hypoketogenic PPARα-/- mice. Administration of 1,3-butandiol, a ketone diester, transactivated renal gluconeogenic gene expression in fasted PPARα-/- mice. In addition, HFD-fed mice showed fasting hyperglycemia along with upregulated renal gluconeogenic gene expression, which was blunted in HFD-fed PPARα-/- mice. In vitro experiments and metabolome analysis in renal tubular cells showed that β-hydroxybutyrate directly promotes glucose and NH3 production through transactivating gluconeogenic genes. In addition, RNA-seq analysis revealed that β-hydroxybutyrate-induced transactivation of Pck1 was mediated by C/EBPβ.
CONCLUSIONS: Our findings demonstrate that β-hydroxybutyrate mediates hepato-renal interaction to maintain homeostatic regulation of blood glucose and systemic acid-base balance through renal gluconeogenesis regulation.

In a recent mechanistic study, octopamine was shown to promote proton transport over the branchial epithelium in green crabs, Carcinus maenas. Here, we follow up on this finding by investigating the involvement of octopamine in an environmental and physiological context that challenges acid-base homeostasis, the response to short-term high pCO2 exposure (400 Pa) in a brackish water environment. We show that hyperregulating green crabs experienced a respiratory acidosis as early as 6 h of exposure to hypercapnia, with a rise in hemolymph pCO2 accompanied by a simultaneous drop of hemolymph pH. The slightly delayed increase in hemolymph HCO3- observed after 24 h helped to restore hemolymph pH to initial values by 48 h. Circulating levels of the biogenic amine octopamine were significantly higher in short-term high pCO2 exposed crabs compared to control crabs after 48 h. Whole animal metabolic rates, intracellular levels of octopamine and cAMP, as well as branchial mitochondrial enzyme activities for complex I + III and citrate synthase were unchanged in posterior gill #7 after 48 h of hypercapnia. However, application of octopamine in gill respirometry experiments suppressed branchial metabolic rate in posterior gills of short-term high pCO2 exposed animals. Furthermore, branchial enzyme activity of cytochrome C oxidase decreased in high pCO2 exposed crabs after 48 h. Our results indicate that hyperregulating green crabs are capable of quickly counteracting a hypercapnia-induced respiratory acidosis. The role of octopamine in the acclimation of green crabs to short-term hypercapnia seems to entail the alteration of branchial metabolic pathways, possibly targeting mitochondrial cytochrome C in the gill. Our findings help advancing our current limited understanding of endocrine components in hypercapnia acclimation. SUMMARY STATEMENT: Acid-base compensation upon short-term high pCO2 exposure in hyperregulating green crabs started after 6 h and was accomplished by 48 h with the involvement of the biogenic amine octopamine, accumulation of hemolymph HCO3-, and regulation of mitochondrial complex IV (cytochrome C oxidase).

Dead-space-associated rebreathing of expired air and heat trapping with use of surgical masks and N95 respirators may underlie anecdotal reports of adverse symptoms associated with medical face barriers. Limited data exist directly comparing the physiological effects of masks and respirators at rest. We assessed the short-term physiological effects of both barrier types over 60 min at rest, including face microclimate temperature, end-tidal gases, and venous blood acid-base variables. We recruited 34 participants into two trials: surgical masks (n = 17) and N95 respirators (n = 17). In a seated position, participants underwent a 10-min baseline without a barrier and then wore a standardized surgical mask or dome-shaped N95 respirator for 60 min, followed by a 10-min washout. We instrumented healthy human participants with a peripheral pulse oximeter ([Formula: see text]) and a nasal cannula connected to a dual gas analyzer for measurement of the pressure of end-tidal [Formula: see text] and [Formula: see text], with an associated temperature probe for face microclimate temperature. Venous (v) blood samples were obtained at baseline and following 60-min mask/respirator wearing to assess [Formula: see text], [HCO3-]v and pHv. Compared with baseline during/following 60 min, temperature, [Formula: see text], [Formula: see text], and [HCO3-]v were mildly but significantly higher, and [Formula: see text] and [Formula: see text] were significantly lower, but [Formula: see text] was unaffected. The magnitude of effects was similar between barrier types. Temperature and [Formula: see text] returned to baseline levels within 1-2 min following removal of the barrier. These mild physiological effects may underlie reports of qualitative symptoms while wearing masks or respirators. However, the magnitudes were mild, not physiologically relevant and reversed immediately with the removal of the barrier.NEW & NOTEWORTHY Anecdotal reports suggest mild physiological effects of wearing surgical masks and/or N95 respirators, including heat trapping and rebreathing of expired air. There are limited data directly comparing the physiological effects of wearing medical barriers at rest. We found that the time course and magnitude of changes to face microclimate temperature, end-tidal gases, and venous blood gases and acid-base variables were mild in magnitude, not physiologically relevant, equivalent between barrier types, and immediately reversible on removal.

Kidney tubules play a pivotal role in the maintenance of body fluid homeostasis and pH regulation. Accordingly, kidney disorders are known to be strongly associated with hypertension and acid-base imbalance. In the kidney, the intercalated cells of the nephron are the main site of acid-base balance: type A are acid-secreting whereas type B are base-secreting. The chloride bicarbonate exchanger Pendrin is present in type B intercalated cells and participates actively in regulating blood pressure and NaCl balance. It is still not entirely deciphered how Pendrin activity is regulated; nevertheless, it was previously demonstrated that Pendrin is regulated by c-AMP/Protein Kinase A (PKA) signaling pathway. Consequently, in this study, our hypothesis is that the A-Kinase anchoring protein 2 (AKAP2), strongly expressed in the kidney, regulates in time and space the intracellular signal transduction. In order to investigate AKAP2 involvement in Pendrin regulation and trafficking to the apical plasma membrane, we generated an inducible and nephron-specific Akap2Pax8/LC1 mice knockout model. By confocal microscopy, fluorescent immunostaining on kidney tissue sections showed that AKAP2 is present in the tubules and most importantly colocalizes with Pendrin at the apical plasma membrane of the intercalated cells. To show that Pendrin and AKAP2 are interacting, we used the Proximity Ligation Assay (PLA) and, positively, we could reveal the association between the two proteins. The latter finding was also confirmed in vitro taking advantage of the Opossum Kidney Cell line (OKP) stably expressing Pendrin and co-transfected with AKAP2, we could co-immunoprecipitate Pendrin and AKAP2 after crosslinking on live cells. Fluorescent immunostaining in Akap2Pax8/LC1 show that Pendrin tends to be shifted from the apical membrane (seen in control mice) to intracellular compartments. In conclusion, our data suggest that AKAP2 and Pendrin are interacting, and AKAP2 may play a key role in Pendrin trafficking to the apical plasma membrane, hence in regulating its activity.

Metabolic alkalosis is a widespread acid-base disturbance, especially in hospitalized patients. It is characterized by the primary elevation of serum bicarbonate and arterial pH, along with a compensatory increase in Pco2 consequent to adaptive hypoventilation. The pathogenesis of metabolic alkalosis involves either a loss of fixed acid or a net accumulation of bicarbonate within the extracellular fluid. The loss of acid may be via the gastrointestinal tract or the kidney, whereas the sources of excess alkali may be via oral or parenteral alkali intake. Severe metabolic alkalosis in critically ill patients-arterial blood pH of 7.55 or higher-is associated with significantly increased mortality rate. The kidney is equipped with sophisticated mechanisms to avert the generation or the persistence (maintenance) of metabolic alkalosis by enhancing bicarbonate excretion. These mechanisms include increased filtration as well as decreased absorption and enhanced secretion of bicarbonate by specialized transporters in specific nephron segments. Factors that interfere with these mechanisms will impair the ability of the kidney to eliminate excess bicarbonate, therefore promoting the generation or impairing the correction of metabolic alkalosis. These factors include volume contraction, low glomerular filtration rate, potassium deficiency, hypochloremia, aldosterone excess, and elevated arterial carbon dioxide. Major clinical states are associated with metabolic alkalosis, including vomiting, aldosterone or cortisol excess, licorice ingestion, chloruretic diuretics, excess calcium alkali ingestion, and genetic diseases such as Bartter syndrome, Gitelman syndrome, and cystic fibrosis. In this installment in the AJKD Core Curriculum in Nephrology, we will review the pathogenesis of metabolic alkalosis; appraise the precipitating events; and discuss clinical presentations, diagnoses, and treatments of metabolic alkalosis.

Cytoreg is an ionic therapeutic agent comprising a mixture of hydrochloric, sulfuric, phosphoric, hydrofluoric, oxalic, and citric acids. In diluted form, it has demonstrated efficacy against human cancers in vitro and in vivo. Although Cytoreg is well tolerated in mice, rats, rabbits, and dogs by oral and intravenous administration, its mechanism of action is not documented. The acidic nature of Cytoreg could potentially disrupt the pH and levels of ions and dissolved gases in the blood. Here, we report the effects of the intravenous administration of Cytoreg on the arterial pH, oxygen and carbon dioxide pressures, and bicarbonate, sodium, potassium, and chloride concentrations. Our results demonstrate that Cytoreg does not disturb the normal blood pH, ion levels, or carbon dioxide content, but increases oxygen levels in rats. These data are consistent with the excellent tolerability of intravenous Cytoreg observed in rabbits, and dogs. The study was approved by the Bioethics Committee of the University of the Andes, Venezuela (CEBIOULA) (approval No. 125) on November 3, 2019.

The objective of this study was to explore the effects of dietary acid load (DAL) and IGF1 and IL6 gene polymorphisms and their potential diet-gene interactions on metabolic traits. A total of 211 community-dwelling postmenopausal women were recruited. DAL was estimated using potential renal acid load (PRAL). Blood was drawn for biochemical parameters and DNA was extracted and Agena® MassARRAY was used for genotyping analysis to identify the signalling of IGF1 (rs35767 and rs7136446) and IL6 (rs1800796) polymorphisms. Interactions between diet and genetic polymorphisms were assessed using regression analysis. The result showed that DAL was positively associated with fasting blood glucose (FBG) (β = 0.147, p < 0.05) and there was significant interaction effect between DAL and IL6 with systolic blood pressure (SBP) (β = 0.19, p = 0.041). In conclusion, these findings did not support the interaction effects between DAL and IGF1 and IL6 single nucleotide polymorphisms (rs35767, rs7136446, and rs1800796) on metabolic traits, except for SBP. Besides, higher DAL was associated with higher FBG, allowing us to postulate that high DAL is a potential risk factor for diabetes.

The transepithelial transport of electrolytes, solutes, and water in the kidney is a well-orchestrated process involving numerous membrane transport systems. Basolateral potassium channels in tubular cells not only mediate potassium recycling for proper Na+,K+-ATPase function but are also involved in potassium and pH sensing. Genetic defects in KCNJ10 cause EAST/SeSAME syndrome, characterized by renal salt wasting with hypokalemic alkalosis associated with epilepsy, ataxia, and sensorineural deafness.
A candidate gene approach and whole-exome sequencing determined the underlying genetic defect in eight patients with a novel disease phenotype comprising a hypokalemic tubulopathy with renal salt wasting, disturbed acid-base homeostasis, and sensorineural deafness. Electrophysiologic studies and surface expression experiments investigated the functional consequences of newly identified gene variants.
We identified mutations in the KCNJ16 gene encoding KCNJ16, which along with KCNJ15 and KCNJ10, constitutes the major basolateral potassium channel of the proximal and distal tubules, respectively. Coexpression of mutant KCNJ16 together with KCNJ15 or KCNJ10 in Xenopus oocytes significantly reduced currents.
Biallelic variants in KCNJ16 were identified in patients with a novel disease phenotype comprising a variable proximal and distal tubulopathy associated with deafness. Variants affect the function of heteromeric potassium channels, disturbing proximal tubular bicarbonate handling as well as distal tubular salt reabsorption.

Patients with CKD are at elevated risk of metabolic acidosis due to impaired net acid excretion (NAE). Identifying early markers of acidosis may guide prevention in chronic kidney disease (CKD). This study compared NAE in participants with and without CKD, as well as the NAE, blood pressure (BP), and metabolomic response to bicarbonate supplementation.
Randomized order, cross-over study with controlled feeding.
Participants consisted of 8 patients with CKD (estimated glomerular filtration rate 30-59mL/min/1.73m2 or 60-70mL/min/1.73m2 with albuminuria) and 6 patients without CKD. All participants had baseline serum bicarbonate concentrations between 20 and 28 mEq/L; they did not have diabetes mellitus and did not use alkali supplements at baseline.
Participants were fed a fixed-acid-load diet with bicarbonate supplementation (7 days) and with sodium chloride control (7 days) in a randomized order, cross-over fashion.
Urine NAE, 24-hour ambulatory BP, and 24-hour urine and plasma metabolomic profiles were measured after each period.
During the control period, mean NAE was 28.3±10.2 mEq/d overall without differences across groups (P=0.5). Urine pH, ammonium, and citrate were significantly lower in CKD than in non-CKD (P<0.05 for each). Bicarbonate supplementation reduced NAE and urine ammonium in the CKD group, increased urine pH in both groups (but more in patients with CKD than in those without), and increased; urine citrate in the CKD group (P< 0.2 for interaction for each). Metabolomic analysis revealed several urine organic anions were increased with bicarbonate in CKD, including 3-indoleacetate, citrate/isocitrate, and glutarate. BP was not significantly changed.
Small sample size and short feeding duration.
Compared to patients without CKD, those with CKD had lower acid excretion in the form of ammonium but also lower base excretion such as citrate and other organic anions, a potential compensation to preserve acid-base homeostasis. In CKD, acid excretion decreased further, but base excretion (eg, citrate) increased in response to alkali. Urine citrate should be evaluated as an early and responsive marker of impaired acid-base homeostasis.
National Institute of Diabetes and Digestive and Kidney Diseases and the Duke O\'Brien Center for Kidney Research.
Registered at ClinicalTrials.gov with study number NCT02427594.

The objective of this study was to evaluate the productive performance and quality of eggs and bones of Japanese quails that received different dietary electrolyte balance (EB) and were submitted to thermoneutrality or heat stress conditions. Eight hundred Japanese quails of 21 days of age were selected and distributed randomly in two bioclimatic chambers: thermoneutral chamber (23 °C ± 2 °C) and heat-stress chamber (33 °C ± 2 °C). The treatments were in a 2 × 5 factorial arrangement, with two temperatures and five EB levels (165, 215, 265, 315, 365 mEq/kg) with four replicates of 20 birds each. The productive performance and egg quality (in 3 cycles of 21 days) were measured. At 105 days old, the bone quality was evaluated. Data were analyzed by Minitab, and the means were compared by Tukey\'s test and regression test for levels (P < 0.05). Quails submitted to thermoneutrality showed better performance and egg and bone quality. The highest production rate was the EB level of 265 mEq/kg. Low values of EB (165 and 215 mEq/kg) and high values (365) impaired egg quality, and the ideal was 315 mEq/kg. Lower levels of balance provided poor bone density. In conclusion, the results of this study indicated that heat stress impairs the production and quality of quail eggs and bones. Furthermore, by using intermediate EB levels (265 and 315) mEq/kg, it is possible to improve egg production and egg quality, and using high levels increases bone mineral density.