The role of carbonic anhydrases in renal physiology

Acetazolamide and human carbonic anhydrases: retrospect, review and discussion of an intimate relationship

Acetazolamide (AZM) is a strong pharmacological sulphonamide-type (R-SO2-NH2, pKa 7.2) inhibitor of the activity of several carbonic anhydrase (CA) isoforms, notably of renal CA II (Ki, 12 nM) and CA IV (Ki, 74 nM). AZM is clinically used for about eighty years in various diseases including epilepsy and glaucoma. Pharmacological AZM increases temporarily the urinary excretion of bicarbonate (HCO3-) and sodium ions (Na+) and sustainably the urinary pH. AZM is excreted almost unchanged over several hours at high rates in the urine. Closely parallel concentrations of circulating and excretory AZM are observed upon administration of therapeutical doses of AZM. In a proof-of-principle study, we investigated the effects of the ingestion of a 250-mg AZM-containing tablet by a healthy volunteer on the urinary excretion of organic and inorganic substances over 5 h (range, 0, 0.5, 1, 1.5, 2, 3, 4, 5 h). Measured analytes included: AZM, amino acids and their metabolites such as guanidinoacetate, i.e. the precursor of creatine, of asymmetrically (ADMA) and symmetrically (SDMA) dimethylated arginine, nitrite (O = N-O-, pKa 3.4) and nitrate (O2N-O-, pKa -1.37), the major metabolites of nitric oxide (NO), the C-H acidic malondialdehyde (MDA; (CHO)2CH2, pKa 4.5), and creatinine for correction of analytes excretion. All analytes were measured by validated isotopologues using gas chromatography-mass spectrometry (GC-MS) methods. AZM excretion in the urine reached its maximum value after 2 h and was fairly stable for the next 3 h. Time series analysis by the ARIMA method was performed. AZM ingestion increased temporarily the urinary excretion of the amino acids Leu + Ile, nitrite and nitrate, decreased temporarily the urinary excretion of other amino acids. AZM decreased sustainably the urinary excretion of MDA, a biomarker of oxidative stress (i.e. lipid peroxidation). Whether this decrease is due to inhibition of the excretion of MDA or attenuation of oxidative stress by AZM is unknown. The acute and chronic effects of AZM on the urinary excretion of electrolytes and physiological substances reported in the literature are discussed in depth in the light of its extraordinary pharmacokinetics and pharmacodynamics. Tolerance development/drug resistance to AZM in chronic use and potential mechanisms are also addressed.

Integrated approach of machine learning, Mendelian randomization and experimental validation for biomarker discovery in diabetic nephropathy

AIM

To identify potential biomarkers and explore the mechanisms underlying diabetic nephropathy (DN) by integrating machine learning, Mendelian randomization (MR) and experimental validation.

METHODS

Microarray and RNA-sequencing datasets (GSE47184, GSE96804, GSE104948, GSE104954, GSE142025 and GSE175759) were obtained from the Gene Expression Omnibus database. Differential expression analysis identified the differentially expressed genes (DEGs) between patients with DN and controls. Diverse machine learning algorithms, including least absolute shrinkage and selection operator, support vector machine-recursive feature elimination, and random forest, were used to enhance gene selection accuracy and predictive power. We integrated summary-level data from genome-wide association studies on DN with expression quantitative trait loci data to identify genes with potential causal relationships to DN. The predictive performance of the biomarker gene was validated using receiver operating characteristic (ROC) curves. Gene set enrichment and correlation analyses were conducted to investigate potential mechanisms. Finally, the biomarker gene was validated using quantitative real-time polymerase chain reaction in clinical samples from patients with DN and controls.

RESULTS

Based on identified 314 DEGs, seven characteristic genes with high predictive performance were identified using three integrated machine learning algorithms. MR analysis revealed 219 genes with significant causal effects on DN, ultimately identifying one co-expressed gene, carbonic anhydrase II (CA2), as a key biomarker for DN. The ROC curves demonstrated the excellent predictive performance of CA2, with area under the curve values consistently above 0.878 across all datasets. Additionally, our analysis indicated a significant association between CA2 and infiltrating immune cells in DN, providing potential mechanistic insights. This biomarker was validated using clinical samples, confirming the reliability of our findings in clinical practice.

CONCLUSION

By integrating machine learning, MR and experimental validation, we successfully identified and validated CA2 as a promising biomarker for DN with excellent predictive performance. The biomarker may play a role in the pathogenesis and progression of DN via immune-related pathways. These findings provide important insights into the molecular mechanisms underlying DN and may inform the development of personalized treatment strategies for this disease.

The relationship between anti-seizures medications and metabolic acidosis in craniotomy operations: is topiramate or zonisamide the cause of metabolic acidosis?

BACKGROUND/AIM

The most commonly prescribed anti-seizures medications (ASMs) for the treatment of epilepsy are currently topiramate, zonisamide, lacosamide, carbamazepine and levetiracetam. The objective of this study was to examine the correlation between preoperative, intraoperative, and postoperative metabolic acidosis and the use of ASMs prior to craniotomy operations.

MATERIALS AND METHODS

This retrospective cross-sectional study evaluated patients who underwent intracranial surgery with craniotomy under general anaesthesia between May 2020 and April 2023 and used ASMs. The patients were classified into four groups based on the pharmacological mechanisms of action of the ASMs administered before intracranial surgery (Group-I, zonisamide or topiramate; Group-II, lacosamide; Group-III, carbamazepine; Group-IV, levetiracetam). Metabolic acidosis severity was defined based on base excess (BE) levels: mild (-3 to -5), moderate (-5 to -10), and severe (below - 10). The study investigated the correlation between ASMs and the severity of metabolic acidosis in preoperative, intraoperative, and postoperative blood gas measurements.

RESULTS

Out of 35 patients, 24 patients underwent intracranial surgery and 11 patients underwent epilepsy surgery. There were statistically significant differences in the severity of metabolic acidosis between preoperative (p < 0.001), intraoperative (p < 0.001) and postoperative (p = 0.01) groups. The preoperative mean BE of group-I was - 4.7, which was statistically lower than that of group-III (p = 0.01) and group-IV (p < 0.001). Intraoperatively and postoperatively, group-I had a mean BE of -7.5 and - 3.2, respectively, which was statistically lower than that of groups II (p = 0.007; p = 0.04), III (p = 0.002; p = 0.03), and IV (p < 0.001; p = 0.009). There was no statistically significant difference in BE between groups II, III and IV at all three time points. Group I had the lowest BE at all three time points. Intraoperative bicarbonate was administered to all patients in group I, whereas no intraoperative bicarbonate was required in the other groups. In group I, 50% of patients required postoperative intensive care.

CONCLUSION

The use of ASMs in patients undergoing surgery is important in terms of mortality and morbidity. Topirimat and zonisamide are ASMs that can cause preoperative, intraoperative and postoperative metabolic acidosis. Patients receiving topirimat or zonisamide are particularly susceptible to metabolic acidosis. Special care should be taken in the management of anaesthesia in patients receiving these drugs, and monitoring of the perioperative metabolic status is essential.

A review of renal tubular acidosis

OBJECTIVE

To review the current scientific literature on renal tubular acidosis (RTA) in people and small animals, focusing on diseases in veterinary medicine that result in secondary RTA.

DATA SOURCES

Scientific reviews and original research publications on people and small animals focusing on RTA.

SUMMARY

RTA is characterized by defective renal acid-base regulation that results in normal anion gap hyperchloremic metabolic acidosis. Renal acid-base regulation includes the reabsorption and regeneration of bicarbonate in the renal proximal tubule and collecting ducts and the process of ammoniagenesis. RTA occurs as a primary genetic disorder or secondary to disease conditions. Based on pathophysiology, RTA is classified as distal or type 1 RTA, proximal or type 2 RTA, type 3 RTA or carbonic anhydrase II mutation, and type 4 or hyperkalemic RTA. Fanconi syndrome comprises proximal RTA with additional defects in proximal tubular function. Extensive research elucidating the genetic basis of RTA in people exists. RTA is a genetic disorder in the Basenji breed of dogs, where the mutation is known. Secondary RTA in human and veterinary medicine is the sequela of diseases that include immune-mediated, toxic, and infectious causes. Diagnosis and characterization of RTA include the measurement of urine pH and the evaluation of renal handling of substances that should affect acid or bicarbonate excretion.

CONCLUSIONS

Commonality exists between human and veterinary medicine among the types of RTA. Many genetic defects causing primary RTA are identified in people, but those in companion animals other than in the Basenji are unknown. Critically ill veterinary patients are often admitted to the ICU for diseases associated with secondary RTA, or they may develop RTA while hospitalized. Recognition and treatment of RTA may reverse tubular dysfunction and promote recovery by correcting metabolic acidosis.

Genomic and Phenotypic Adaptations of Rattus tanezumi to Cold Limit Its Further Northward Expansion and Range Overlap with R. norvegicus

Global climate change has led to shifts in the distribution ranges of many terrestrial species, promoting their migration from lower altitudes or latitudes to higher ones. Meanwhile, successful invaders have developed genetic adaptations enabling the colonization of new environments. Over the past 40 years, Rattus tanezumi (RT) has expanded into northern China (Northwest and North China) from its southern origins. We studied the cold adaptation of RT and its potential for northward expansion by comparing it with sympatric Rattus norvegicus (RN), which is well adapted to cold regions. Through population genomic analysis, we revealed that the invading RT rats have split into three distinct populations: the North, Northwest, and Tibetan populations. The first two populations exhibited high genetic diversity, while the latter population showed remarkably low genetic diversity. These rats have developed various genetic adaptations to cold, arid, hypoxic, and high-UV conditions. Cold acclimation tests revealed divergent thermoregulation between RT and RN. Specifically, RT exhibited higher brown adipose tissue activity and metabolic rates than did RN. Transcriptome analysis highlighted changes in genes regulating triglyceride catabolic processes in RT, including Apoa1 and Apoa4, which were upregulated, under selection and associated with local adaptation. In contrast, RN showed changes in carbohydrate metabolism genes. Despite the cold adaptation of RT, we observed genotypic and phenotypic constraints that may limit its ability to cope with severe low temperatures farther north. Consequently, it is less likely that RT rats will invade and overlap with RN rats in farther northern regions.

Effects of furosemide, acetazolamide and amiloride on renal cortical and medullary tissue oxygenation in non-anaesthetised healthy sheep

It has been proposed that diuretics can improve renal tissue oxygenation through inhibition of tubular sodium reabsorption and reduced metabolic demand. However, the impact of clinically used diuretic drugs on the renal cortical and medullary microcirculation is unclear. Therefore, we examined the effects of three commonly used diuretics, at clinically relevant doses, on renal cortical and medullary perfusion and oxygenation in non-anaesthetised healthy sheep. Merino ewes received acetazolamide (250 mg; n = 9), furosemide (20 mg; n = 10) or amiloride (10 mg; n = 7) intravenously. Systemic and renal haemodynamics, renal cortical and medullary tissue perfusion andP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ , and renal function were then monitored for up to 8 h post-treatment. The peak diuretic response occurred 2 h (99.4 ± 14.8 mL/h) after acetazolamide, at which stage cortical and medullary tissue perfusion andP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ were not significantly different from their baseline levels. The peak diuretic response to furosemide occurred at 1 h (196.5 ± 12.3 mL/h) post-treatment but there were no significant changes in cortical and medullary tissue oxygenation during this period. However, cortical tissueP O 2 ${P_{{{\mathrm{O}}_{\mathrm{2}}}}}$ fell from 40.1 ± 3.8 mmHg at baseline to 17.2 ± 4.4 mmHg at 3 h and to 20.5 ± 5.3 mmHg at 6 h after furosemide administration. Amiloride did not produce a diuretic response and was not associated with significant changes in cortical or medullary tissue oxygenation. In conclusion, clinically relevant doses of diuretic agents did not improve regional renal tissue oxygenation in healthy animals during the 8 h experimentation period. On the contrary, rebound renal cortical hypoxia may develop after dissipation of furosemide-induced diuresis.

An investigation of gill and blood carbonic anhydrase characteristics in three basal actinopterygian species: alligator gar (Atractosteus spatula), white sturgeon (Acipenser transmontanus) and Senegal bichir (Polypterus senegalus)

Many teleosts possess a unique set of respiratory characteristics allowing enhanced oxygen unloading to the tissues during stress. This system comprises three major components: highly pH sensitive haemoglobins (large Bohr and Root effects), rapid red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of membrane-bound plasma-accessible carbonic anhydrase (paCA; absence in the gills). The first two components have received considerable research effort; however, the evolutionary loss of branchial paCA has received little attention. In the current study, we investigated the availability of branchial membrane-bound CA, along with several other CA-related characteristics in species belonging to three basal actinopterygian groups: the Lepisosteiformes, Acipenseriformes and Polypteriformes to assess the earlier hypothesis that Root effect haemoglobins constrain branchial paCA availability. We present the first evidence suggesting branchial membrane-bound CA presence in a basal actinopterygian species: the Senegal bichir (Polypterus senegalus) and show that like the teleosts, white sturgeon (Acipenser transmontanus) and alligator gar (Atractosteus spatula) do not possess branchial membrane-bound CA. We discuss the varying respiratory strategies for these species and propose that branchial paCA may have been lost much earlier than previously thought, likely in relation to the changes in haemoglobin buffer capacity associated with the increasing magnitude of the Bohr effect. The findings described here represent an important advancement in our understanding of the evolution of the unique system of enhanced oxygen unloading thought to be present in most teleosts, a group that encompasses half of all vertebrates.

Empagliflozin in Heart Failure: Regional Nephron Sodium Handling Effects

SIGNIFICANCE STATEMENT

The effect of sodium-glucose cotransporter-2 inhibitors (SGLT2i) on regional tubular sodium handling is poorly understood in humans. In this study, empagliflozin substantially decreased lithium reabsorption in the proximal tubule (PT) (a marker of proximal tubular sodium reabsorption), a magnitude out of proportion to that expected with only inhibition of sodium-glucose cotransporter-2. This finding was not driven by an "osmotic diuretic" effect; however, several parameters changed in a manner consistent with inhibition of the sodium-hydrogen exchanger 3. The large changes in proximal tubular handling were acutely buffered by increased reabsorption in both the loop of Henle and the distal nephron, resulting in the observed modest acute natriuresis with these agents. After 14 days of empagliflozin, natriuresis waned due to increased reabsorption in the PT and/or loop of Henle. These findings confirm in humans that SGLT2i have complex and important effects on renal tubular solute handling.

BACKGROUND

The effect of SGLT2i on regional tubular sodium handling is poorly understood in humans but may be important for the cardiorenal benefits.

METHODS

This study used a previously reported randomized, placebo-controlled crossover study of empagliflozin 10 mg daily in patients with diabetes and heart failure. Sodium handling in the PT, loop of Henle (loop), and distal nephron was assessed at baseline and day 14 using fractional excretion of lithium (FELi), capturing PT/loop sodium reabsorption. Assessments were made with and without antagonism of sodium reabsorption through the loop using bumetanide.

RESULTS

Empagliflozin resulted in a large decrease in sodium reabsorption in the PT (increase in FELi=7.5%±10.6%, P = 0.001), with several observations suggesting inhibition of PT sodium hydrogen exchanger 3. In the absence of renal compensation, this would be expected to result in approximately 40 g of sodium excretion/24 hours with normal kidney function. However, rapid tubular compensation occurred with increased sodium reabsorption both in the loop ( P < 0.001) and distal nephron ( P < 0.001). Inhibition of sodium-glucose cotransporter-2 did not attenuate over 14 days of empagliflozin ( P = 0.14). However, there were significant reductions in FELi ( P = 0.009), fractional excretion of sodium ( P = 0.004), and absolute fractional distal sodium reabsorption ( P = 0.036), indicating that chronic adaptation to SGLT2i results primarily from increased reabsorption in the loop and/or PT.

CONCLUSIONS

Empagliflozin caused substantial redistribution of intrarenal sodium delivery and reabsorption, providing mechanistic substrate to explain some of the benefits of this class. Importantly, the large increase in sodium exit from the PT was balanced by distal compensation, consistent with SGLT2i excellent safety profile.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

ClinicalTrials.gov ( NCT03027960 ).

Regionalization of cell types in silk glands of Larinioides sclopetarius suggest that spider silk fibers are complex layered structures

In order to produce artificial silk fibers with properties that match the native spider silk we likely need to closely mimic the spinning process as well as fiber architecture and composition. To increase our understanding of the structure and function of the different silk glands of the orb weaver Larinioides sclopetarius, we used resin sections for detailed morphology, paraffin embedded sections for a variety of different histological stainings, and a histochemical method for localization of carbonic anhydrase activity. Our results show that all silk glands, except the tubuliform glands, are composed of two or more columnar epithelial cell types, some of which have not been described previously. We observed distinct regionalization of the cell types indicating sequential addition of secretory products during silk formation. This means that the major ampullate, minor ampullate, aciniform type II, and piriform silk fibers most likely are layered and that each layer has a specific composition. Furthermore, a substance that stains positive for polysaccharides may be added to the silk in all glands except in the type I aciniform glands. Active carbonic anhydrase was found in all silk glands and/or ducts except in the type I aciniform and tubuliform glands, with the strongest staining in aggregate glands and their ductal nodules. Carbonic anhydrase plays an important role in the generation of a pH gradient in the major ampullate glands, and our results suggest that some other glands may also harbor pH gradients.

4-(3-Phenyl-4-(3,4,5-trimethoxybenzoyl)-1H-pyrrol-1-yl)benzenesulfonamide, a Novel Carbonic Anhydrase and Wnt/β-Catenin Signaling Pathway Dual-Targeting Inhibitor with Potent Activity against Multidrug Resistant Cancer Cells

We synthesized new pyrrole and indole derivatives as human carbonic anhydrase (hCA) inhibitors with the potential to inhibit the Wnt/β-catenin signaling pathway. The presence of both N1-(4-sulfonamidophenyl) and 3-(3,4,5-trimethoxyphenyl) substituents was essential for strong hCA inhibitors. The most potent hCA XII inhibitor 15 (Ki = 6.8 nM) suppressed the Wnt/β-catenin signaling pathway and its target genes MYC, Fgf20, and Sall4 and exhibited the typical markers of apoptosis, cleaved poly(ADP-ribose)polymerase, and cleaved caspase-3. Compound 15 showed strong inhibition of viability in a panel of cancer cells, including colorectal cancer and triple-negative breast cancer cells, was effective against the NCI/ADR-RES DOX-resistant cell line, and restored the sensitivity to doxorubicin (DOX) in HT29/DX and MDCK/P-gp cells. Compound 15 is a novel dual-targeting compound with activity against hCA and Wnt/β-catenin. It thus has a broad targeting spectrum and is an anticancer agent with specific potential in P-glycoprotein overexpressing cell lines.

Chiral Gd-DOTA as a Versatile Platform for Hepatobiliary and Tumor Targeting MRI Contrast Agents

The leakage of gadolinium ions (Gd3+) from commercial Gd3+-based contrast agents (GBCAs) in patients is currently the major safety concern in clinical magnetic resonance imaging (MRI) scans, and the lack of task-specific GBCAs limits its usage in the early detection of disease and imaging of specific biological regions. Herein, ultrastable GBCAs were constructed via decorating chiral Gd-DOTA with a phenylic analogue to one of the pendent arms, and the stability constant was determined as high as 27.08, accompanied by negligible decomplexation in 1 M of HCl over 2 years. A hepatic-specific chiral Gd-DOTA was screened out as a potential alternative to commercial Gd-EOB-DTPA, while combination with functional molecules favored chiral Gd-DOTA as tumor targeting probes. Therefore, the novel chiral Gd-DOTA is believed to be an ideal platform for designing the next generation of GBCAs for various clinical purposes due to its outstanding inert nature.

Ibuprofen-Induced Renal Tubular Acidosis: Case Report on a Not-So-Basic Clinical Conundrum

Rationale

Renal tubular acidosis (RTA) is a cause of non-anion gap metabolic acidosis (NAGMA) that is infrequently diagnosed and is due to various underlying etiologies that impair the kidney's ability to retain bicarbonate or excrete acid. Ibuprofen is an over-the-counter non-steroidal anti-inflammatory medication that is used by patients widely for a variety of reasons. Although it is well known that ibuprofen and other non-steroidal anti-inflammatory drugs may have nephrotoxic effects, the role of ibuprofen as a cause of RTA and hypokalemia is not well recognized.

Presenting Concerns

A 66-year-old man with chemotherapy-treated lymphoma in remission and ongoing heavy ibuprofen use for chronic pain presented to hospital with a 1-week history of increasing lethargy and otherwise unremarkable review of systems. Investigations showed acute kidney injury, hypokalemia, hyperchloremia, and NAGMA with elevated urinary pH and positive urine anion gap.

Diagnoses

The final diagnosis of distal RTA secondary to ibuprofen was made after ruling out gastrointestinal bicarbonate loss and additional secondary causes of RTA, including other medications, autoimmune conditions, and obstructive uropathy.

Interventions

The patient was admitted and treated with intravenous sodium bicarbonate for 24 hours with correction of hypokalemia via oral supplementation. His ibuprofen-containing medication was discontinued.

Outcomes

His acute kidney injury and electrolyte abnormalities resolved within 48 hours of initiating treatment with concurrent resolution of his lethargy. He was discharged home and advised to stop taking ibuprofen.

Lessons Learned

We report a case of patient with hypokalemia and NAGMA secondary to ibuprofen and highlight the importance of monitoring for this side effect in patients taking ibuprofen.

Screening of Antiglaucoma, Antidiabetic, Anti-Alzheimer, and Antioxidant Activities of Astragalus alopecurus Pall-Analysis of Phenolics Profiles by LC-MS/MS

Astragalus species are traditionally used for diabetes, ulcers, leukemia, wounds, stomachaches, sore throats, abdominal pain, and toothaches. Although the preventive effects of Astragalus species against diseases are known, there is no record of the therapeutic effects of Astragalus alopecurus. In this study, we aimed to evaluate the in vitro antiglaucoma, antidiabetic, anti-Alzheimer's disease, and antioxidant activities of the methanolic (MEAA) and water (WEAA) extracts of the aerial part of A. alopecurus. Additionally, its phenolic compound profiles were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). MEAA and WEAA were evaluated for their inhibition ability on α-glycosidase, α-amylase, acetylcholinesterase (AChE), and human carbonic anhydrase II (hCA II) enzymes. The phenolic compounds of MEAA were analyzed by LC-MS/MS. Furthermore, total phenolic and flavonoid contents were determined. In this context, the antioxidant activity was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), N,N-dimethyl-p-phenylene diamine (DMPD), ferric reducing antioxidant power (FRAP), cupric ions (Cu²⁺) reducing antioxidant capacity (CUPRAC), ferric ions (Fe³⁺) reducing, and ferrous ions (Fe²⁺) chelating methods. MEAA and WEAA had IC₅₀ values of 9.07 and 2.24 μg/mL for α-glycosidase, 693.15 and 346.58 μg/mL for α-amylase, 1.99 and 2.45 μg/mL for AChE, and 147.7 and 171.7 μg/mL for hCA II. While the total phenolic amounts in MEAA and WEAA were 16.00 and 18.50 μg gallic acid equivalent (GAE)/mg extract, the total flavonoid contents in both extracts were calculated as 66.23 and 33.115 μg quercetin equivalent (QE)/mg, respectively. MEAA and WEAA showed, respectively, variable activities on DPPH radical scavenging (IC₅₀: 99.02 and 115.53 μg/mL), ABTS radical scavenging (IC₅₀: 32.21 and 30.22 µg/mL), DMPD radical scavenging (IC₅₀: 231.05 and 65.22 μg/mL), and Fe²⁺ chelating (IC₅₀: 46.21 and 33.01 μg/mL). MEAA and WEAA reducing abilities were, respectively, Fe³⁺ reducing (λ₇₀₀: 0.308 and 0.284), FRAP (λ₅₉₃: 0.284 and 0.284), and CUPRAC (λ₄₅₀: 0.163 and 0.137). A total of 35 phenolics were scanned, and 10 phenolic compounds were determined by LC-MS/MS analysis. LC-MS/MS revealed that MEAA mainly contained isorhamnetin, fumaric acid, and rosmarinic acid derivatives. This is the first report indicating that MEAA and WEAA have α-glycosidase, α-amylase, AChE, hCA II inhibition abilities, and antioxidant activities. These results demonstrate the potential of Astragalus species through antioxidant properties and enzyme inhibitor ability traditionally used in medicine. This work provides the foundation for further research into the establishment of novel therapeutics for diabetes, glaucoma, and Alzheimer's disease.

Effect of isorhamnetin on carbonic anhydrase IX expression and tumorigenesis of bladder cancer by activating PPARγ/PTEN/AKT pathway

BACKGROUND

To clarify the research prospect and mechanism analysis of isorhamnetin as a therapeutic drug for bladder cancer.

METHODS

Firstly, the effects of different concentrations of isorhamnetin on the expression of PPARγ/PTEN/Akt pathway protein, CA9, PPARγ, PTEN and AKT protein were discussed by western blot. The effects of isorhamnetin on the growth of bladder cells were also analyzed. Secondly, we verified whether the effect of isorhamnetin on CA9 was related to PPARγ/PTEN/Akt pathway by western blot, and the mechanism of isorhamnetin on the growth of bladder cells is related to this pathway by CCK8, cell cycle and ball formation experiment. Further, nude mouse model of subcutaneous tumor transplantation was constructed to analyze the effects of isorhamnetin, PPAR and PTEN on 5637 cell tumorigenesis and the effects of isorhamnetin on tumorigenesis and CA9 expression through PPARγ/PTEN/Akt pathway.

RESULTS

Isorhamnetin inhibited the development of bladder cancer, and regulated the expression of PPAR, PTEN, AKT, CA9. Isorhamnetin inhibits cell proliferation and the transition of cells from G0/G1 phase to S phase, and tumor sphere formation. Carbonic anhydrase IX is a potential downstream molecule of PPARγ/PTEN/AKT pathway. Overexpression of PPARγ and PTEN inhibited expression of CA9 in bladder cancer cells and tumor tissues. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

CONCLUSION

Isorhamnetin has the potential to become a therapeutic drug for bladder cancer, whose antitumor mechanism is related to PPARγ/PTEN/AKT pathway. Isorhamnetin reduced CA9 expression in bladder cancer via PPARγ/PTEN/AKT pathway, thereby inhibiting bladder cancer tumorigenicity.

Potential Novel Role of Membrane-Associated Carbonic Anhydrases in the Kidney

Carbonic anhydrases (CAs), because they catalyze the interconversion of carbon dioxide (CO₂) and water into bicarbonate (HCO₃^-) and protons (H⁺), thereby influencing pH, are near the core of virtually all physiological processes in the body. In the kidneys, soluble and membrane-associated CAs and their synergy with acid-base transporters play important roles in urinary acid secretion, the largest component of which is the reabsorption of HCO₃^- in specific nephron segments. Among these transporters are the Na⁺-coupled HCO₃^- transporters (NCBTs) and the Cl^--HCO₃^- exchangers (AEs)-members of the "solute-linked carrier" 4 (SLC4) family. All of these transporters have traditionally been regarded as "HCO₃^-" transporters. However, recently our group has demonstrated that two of the NCBTs carry CO₃^2- rather than HCO₃^- and has hypothesized that all NCBTs follow suit. In this review, we examine current knowledge on the role of CAs and "HCO₃^-" transporters of the SLC4 family in renal acid-base physiology and discuss how our recent findings impact renal acid secretion, including HCO₃^- reabsorption. Traditionally, investigators have associated CAs with producing or consuming solutes (CO₂, HCO₃^-, and H⁺) and thus ensuring their efficient transport across cell membranes. In the case of CO₃^2- transport by NCBTs, however, we hypothesize that the role of membrane-associated CAs is not the appreciable production or consumption of substrates but the minimization of pH changes in nanodomains near the membrane.

Arterial bicarbonate is associated with hypoxic burden and uncontrolled hypertension in obstructive sleep apnea - The ESADA cohort

OBJECTIVE

Blood bicarbonate concentration plays an important role for obstructive sleep apnea (OSA) patients to maintain acid-base balance. We investigated the association between arterial standard bicarbonate ([HCO3^-]) and nocturnal hypoxia as well as comorbid hypertension in OSA.

METHODS

A cross-sectional analysis of 3329 patients in the European Sleep Apnea Database (ESADA) was performed. Arterial blood gas analysis and lung function test were performed in conjunction with polysomnographic sleep studies. The 4% oxygen desaturation index (ODI), mean and minimum oxygen saturation (SpO₂), and percentage of time with SpO₂ below 90% (T90%) were used to reflect nocturnal hypoxic burden. Arterial hypertension was defined as a physician diagnosis of hypertension with ongoing antihypertensive medication. Hypertensive patients with SBP/DBP below or above 140/90 mmHg were classified as controlled-, uncontrolled hypertension, respectively.

RESULTS

The [HCO3^-] level was normal in most patients (average 24.0 ± 2.5 mmol/L). ODI, T90% increased whereas mean and minimum SpO₂ decreased across [HCO3^-] tertiles (ANOVA, p = 0.030, <0.001, <0.001, and <0.001, respectively). [HCO3^-] was independently associated with ODI, mean SpO₂, minimum SpO₂, and T90% after adjusting for confounders (β value [95%CI]: 1.21 [0.88-1.54], -0.16 [-0.20 to -0.11], -0.51 [-0.64 to -0.37], 1.76 [1.48-2.04], respectively, all p < 0.001). 1 mmol/L elevation of [HCO3^-] was associated with a 4% increased odds of uncontrolled hypertension (OR: 1.04 [1.01-1.08], p = 0.013).

CONCLUSION

We first demonstrated an independent association between [HCO3^-] and nocturnal hypoxic burden as well as uncontrolled hypertension in OSA patients. Bicarbonate levels as an adjunctive measure provide insight into the pathophysiology of hypertension in OSA.

Functional complexity in the chorioallantoic membrane of an oviparous snake: Specializations for calcium uptake from the eggshell

The chorioallantoic membrane of oviparous reptiles forms a vascular interface with the eggshell. The eggshell contains calcium, primarily as calcium carbonate. Extraction and mobilization of this calcium by the chorioallantoic membrane contributes importantly to embryonic nutrition. Development of the chorioallantoic membrane is primarily known from studies of squamates and birds. Although there are pronounced differences in eggshell structure, squamate and bird embryos each mobilize calcium from eggshells. Specialized cells in the chicken chorionic epithelium transport calcium from the eggshell aided by a second population of cells that secrete protons generated by the enzyme carbonic anhydrase. Calcium transporting cells also are present in the chorioallantoic membrane of corn snakes, although these cells function differently than those of chickens. We used histology and immunohistology to characterize the morphology and functional attributes of the chorioallantoic membrane of corn snakes. We identified two populations of cells in the outer layer of the chorionic epithelium. Calbindin-D_28K , a cellular marker for calcium transport expressed in squamate chorioallantoic membranes, is localized in large, flattened cells that predominate in the chorionic epithelium. Smaller cells, interspersed among the large cells, express carbonic anhydrase 2, an enzyme not previously localized in the chorionic epithelium of an oviparous squamate. These findings indicate that differentiation of chorionic epithelial cells contributes to extraction and transport of calcium from the eggshell. The presence of specializations of chorioallantoic membranes for calcium uptake from eggshells in chickens and corn snakes suggests that eggshell calcium was a source of embryonic nutrition early in the evolution of Sauropsida.

Response of Oreochromis niloticus (Teleostei: Cichlidae) exposed to a guanitoxin-producing cyanobacterial strain using multiple biomarkers

Changes in environmental conditions in aquatic ecosystems caused by anthropic actions can modify the composition of primary producers, promoting the excessive proliferation of cyanobacteria. These organisms can form cyanobacterial blooms, which directly affect aquatic life. The present study investigated the mutagenicity of the cyanobacterium Sphaerospermopsis torques-reginae (strain ITEP-024), guanitoxin-producing (natural organophosphate), and sublethal effects on fish in relevant environment concentrations. For this, the Ames test (Salmonella/microsome) was performed as a mutagenic assay for extracts of the ITEP-024 strain. Specimens of Oreochromis niloticus (Teleostei: Cichlidae) were subjected to acute 96 h exposure to different concentrations of aqueous extract of the strain: C = control group; T1 = 31.25 mg/L; T2 = 62.5 mg/L; T3 = 125 mg/L; and T4 = 250 mg/L. Genotoxic, biochemical, osmoregulatory, and physiologic biomarkers were analyzed. Our results showed that the cyanobacterium had a weak mutagenic response for the TA102 strain of Salmonella with and without metabolic activation by S9. Strains TA98 and TA100 were not affected. Fish from treatments T3 and T4 showed changes in oxidative stress (CAT, SOD, and GST enzymes), inhibition of the enzyme acetylcholinesterase activity, micronucleus formation, and osmoregulatory disorders. No guanitoxin accumulation was detected in the different tissues of O. niloticus by LC-MS/MS. Our results showed unprecedented mutagenicity data of the guanitoxin-producing cyanobacteria by the Ames test and biochemical, osmoregulatory, and genotoxic disorders in fish, providing efficient aquatic contamination biomarkers. Despite the great concern related to the presence of guanitoxin in blooms in freshwater ecosystems, its concentration is not yet regulated, and thus there is no monitoring agenda in current legislation.

Expression Regulation of Water Reabsorption Genes and Transcription Factors in the Kidneys of Lepus yarkandensis

Lepus yarkandensis is a desert-dwelling animal that has various adaptations to cope with drought. The kidney maintains water and acid-base balance mainly through the vasopressin-regulated water reabsorption pathway and proximal tubular bicarbonate reabsorption pathway. In this study, we compared the differentially expressed genes (DEGs) and transcription factors in the kidneys of L. yarkandensis and Oryctolagus cuniculus to explore the relationship between the DEGs in kidneys and the animals’ adaptations. Transcriptome sequencing data were used to predict the differentially-expressed water reabsorption genes and their transcription factors. Quantitative real-time PCR, immunohistochemistry, and western blotting were used to detect and verify the expression of DEGs in the kidney at mRNA and protein levels. Transcriptome analysis of the kidney of L. yarkandensis and O. cuniculus showed that 6,610 genes were up-regulated and 5,727 genes down-regulated in data shared by both species. According to the data, 232 transcription factors and their corresponding target genes were predicted, from which genes and transcription factors related to renal water reabsorption were screened. Quantitative RT-PCR results showed AQP1, AQP2, ADCY3, HIF1A, CREB3, and NFATc1 had higher expression in the L. yarkandensis kidney; in comparison, FXYD2 mRNA expression levels were lower. In western blotting, transcription factors HIF1A, NFATc1, NF-κB1, and critical genes ADCY3, ATPA1, and SLC4A4, were highly expressed in the kidneys of L. yarkandensis. Immunohistochemical results showed that the ADCY3 protein was in the basolateral membrane of the collecting duct, the ATP1A1 protein was in the basolateral membrane and medulla of proximal tubules, and the SLC4A4 protein was in the basolateral membrane of proximal tubules. According to these results can be inferred that HIF1A, NFATc1, and NF-κB1 play a certain role in regulating the expression of genes related to water reabsorption in the kidney of L. yarkandensis, thus improving the water reclamation efficiency of L. yarkandensis, so as to adapt to the arid desert environment.

Snapshots of nascent RNA reveal cell- and stimulus-specific responses to acute kidney injury

The current strategy to detect acute injury of kidney tubular cells relies on changes in serum levels of creatinine. Yet serum creatinine (sCr) is a marker of both functional and pathological processes and does not adequately assay tubular injury. In addition, sCr may require days to reach diagnostic thresholds, yet tubular cells respond with programs of damage and repair within minutes or hours. To detect acute responses to clinically relevant stimuli, we created mice expressing Rosa26-floxed-stop uracil phosphoribosyltransferase (Uprt) and inoculated 4-thiouracil (4-TU) to tag nascent RNA at selected time points. Cre-driven 4-TU-tagged RNA was isolated from intact kidneys and demonstrated that volume depletion and ischemia induced different genetic programs in collecting ducts and intercalated cells. Even lineage-related cell types expressed different genes in response to the 2 stressors. TU tagging also demonstrated the transient nature of the responses. Because we placed Uprt in the ubiquitously active Rosa26 locus, nascent RNAs from many cell types can be tagged in vivo and their roles interrogated under various conditions. In short, 4-TU labeling identifies stimulus-specific, cell-specific, and time-dependent acute responses that are otherwise difficult to detect with other technologies and are entirely obscured when sCr is the sole metric of kidney damage.

Blessing in disguise: when head trauma solves the riddle of carbonic anhydrase II deficiency

Carbonic anhydrase II deficiency is a rare autosomal recessive disorder with a classical triad of renal tubular acidosis, intracerebral calcifications and osteopetrosis. We present a case of a 6-year and 4-months old male patient presented to our pediatric gastroenterology outpatients' clinic with parental concern of poor growth. The patient is a known case of unexplained global developmental delay, recurrent fractures and constipation since birth. As a result of the patient's hyperactivity, he hit his head with the clinic's door resulting in a cut wound. Brain computed tomography scan showed abnormal symmetrical calcifications seen in both basal ganglia, thalami and subcortical white matter associated with increased bone density of the skull and upper cervical spine reassembling osteopetrosis. The suspicion of carbonic anhydrase II deficiency was confirmed by arterial blood gases revealing a marked metabolic acidosis fulfilling the diagnostic triad. The patient was discharged on sodium bicarbonate therapy, lactulose and vitamin D3 supplements and has been followed up regularly.

Presumptive renal tubular acidosis secondary to topiramate administration in a cat

OBJECTIVE

To describe renal tubular acidosis (RTA) and secondary acquired hyperaldosteronism in a cat as an adverse effect of topiramate therapy.

CASE SUMMARY

An 8-year-old neutered female cat on chronic oral topiramate therapy at a recommended dose (11.9 mg/kg q 8 h) for seizure control was presented with severe metabolic acidosis and hypokalemia. Plasma electrolyte and acid-base analysis identified a severe metabolic acidosis (pH 7.153, reference interval: 7.31-7.46), hypokalemia (2.08 mmol/L [2.08 mEq/L], reference interval: 3.5-4.8 mmol/L [3.5-4.8 mEq/L]), and ionized hypercalcemia (1.85 mmol/L [1.85 mEq/L], reference range: 1.1-1.4 mmol/L [1.1-1.4 mEq/L]). Urinalysis revealed a urine specific gravity of 1.021 and a pH of 7.0. Diagnostic workup suggested distal RTA as a cause of the cat's acid-base and electrolyte disturbances. Aldosterone concentration was moderately increased, suggestive of secondary hyperaldosteronism. The metabolic abnormalities resolved with supportive care and discontinuation of topiramate.

NEW OR UNIQUE INFORMATION PROVIDED

Topiramate is suggested to have led to the development severe RTA in a cat.

Carbonic anhydrase and soluble adenylate cyclase regulation of cystic fibrosis cellular phenotypes

Several aspects of the cell biology of cystic fibrosis (CF) epithelial cells are altered including impaired lipid regulation, disrupted intracellular transport, and impaired microtubule regulation. It is unclear how the loss of cystic fibrosis transmembrane conductance regulator (CFTR) function leads to these differences. It is hypothesized that the loss of CFTR function leads to altered regulation of carbonic anhydrase (CA) activity resulting in cellular phenotypic changes. In this study, it is demonstrated that CA2 protein expression is reduced in CF model cells, primary mouse nasal epithelial (MNE) cells, excised MNE tissue, and primary human nasal epithelial cells (P < 0.05). This corresponds to a decrease in CA2 RNA expression measured by qPCR as well as an overall reduction in CA activity in primary CF MNEs. The addition of CFTR-inhibitor-172 to WT MNE cells for ≥24 h mimics the significantly lower protein expression of CA2 in CF cells. Treatment of CF cells with l-phenylalanine (L-Phe), an activator of CA activity, restores endosomal transport through an effect on microtubule regulation in a manner dependent on soluble adenylate cyclase (sAC). This effect can be blocked with the CA2-selective inhibitor dorzolamide. These data suggest that the loss of CFTR function leads to the decreased expression of CA2 resulting in the downstream cell signaling alterations observed in CF.

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.

Carbonic Anhydrases as Potential Targets Against Neurovascular Unit Dysfunction in Alzheimer’s Disease and Stroke

The Neurovascular Unit (NVU) is an important multicellular structure of the central nervous system (CNS), which participates in the regulation of cerebral blood flow (CBF), delivery of oxygen and nutrients, immunological surveillance, clearance, barrier functions, and CNS homeostasis. Stroke and Alzheimer Disease (AD) are two pathologies with extensive NVU dysfunction. The cell types of the NVU change in both structure and function following an ischemic insult and during the development of AD pathology. Stroke and AD share common risk factors such as cardiovascular disease, and also share similarities at a molecular level. In both diseases, disruption of metabolic support, mitochondrial dysfunction, increase in oxidative stress, release of inflammatory signaling molecules, and blood brain barrier disruption result in NVU dysfunction, leading to cell death and neurodegeneration. Improved therapeutic strategies for both AD and stroke are needed. Carbonic anhydrases (CAs) are well-known targets for other diseases and are being recently investigated for their function in the development of cerebrovascular pathology. CAs catalyze the hydration of CO₂ to produce bicarbonate and a proton. This reaction is important for pH homeostasis, overturn of cerebrospinal fluid, regulation of CBF, and other physiological functions. Humans express 15 CA isoforms with different distribution patterns. Recent studies provide evidence that CA inhibition is protective to NVU cells in vitro and in vivo, in models of stroke and AD pathology. CA inhibitors are FDA-approved for treatment of glaucoma, high-altitude sickness, and other indications. Most FDA-approved CA inhibitors are pan-CA inhibitors; however, specific CA isoforms are likely to modulate the NVU function. This review will summarize the literature regarding the use of pan-CA and specific CA inhibitors along with genetic manipulation of specific CA isoforms in stroke and AD models, to bring light into the functions of CAs in the NVU. Although pan-CA inhibitors are protective and safe, we hypothesize that targeting specific CA isoforms will increase the efficacy of CA inhibition and reduce side effects. More studies to further determine specific CA isoforms functions and changes in disease states are essential to the development of novel therapies for cerebrovascular pathology, occurring in both stroke and AD.

Carbonic Anhydrase IV Selective Inhibitors Counteract the Development of Colitis-Associated Visceral Pain in Rats

Persistent pain affecting patients with inflammatory bowel diseases (IBDs) is still very difficult to treat. Carbonic anhydrase (CA) represents an intriguing pharmacological target considering the anti-hyperalgesic efficacy displayed by CA inhibitors in both inflammatory and neuropathic pain models. The aim of this work was to evaluate the effect of inhibiting CA IV, particularly when expressed in the gut, on visceral pain associated with colitis induced by 2,4-di-nitrobenzene sulfonic acid (DNBS) in rats. Visceral sensitivity was assessed by measuring animals' abdominal responses to colorectal distension. Repeated treatment with the selective CA IV inhibitors AB-118 and NIK-67 effectively counteracted the development of visceral pain induced by DNBS. In addition to pain relief, AB-118 showed a protective effect against colon damage. By contrast, the anti-hyperalgesic activity of NIK-67 was independent of colon healing, suggesting a direct protective effect of NIK-67 on visceral sensitivity. The enzymatic activity and the expression of CA IV resulted significantly increased after DNBS injection. NIK-67 normalised CA IV activity in DNBS animals, while AB-118 was partially effective. None of these compounds influenced CA IV expression through the colon. Although further investigations are needed to study the underlying mechanisms, CA IV inhibitors are promising candidates in the search for therapies to relieve visceral pain in IBDs.

Comprehensive Analysis of the Systemic Transcriptomic Alternations and Inflammatory Response during the Occurrence and Progress of COVID-19

The pandemic of the coronavirus disease 2019 (COVID-19) has posed huge threats to healthcare systems and the global economy. However, the host response towards COVID-19 on the molecular and cellular levels still lacks full understanding and effective therapies are in urgent need. Here, we integrate three datasets, GSE152641, GSE161777, and GSE157103. Compared to healthy people, 314 differentially expressed genes were identified, which were mostly involved in neutrophil degranulation and cell division. The protein-protein network was established and two significant subsets were filtered by MCODE: ssGSEA and CIBERSORT, which comprehensively revealed the alternation of immune cell abundance. Weighted gene coexpression network analysis (WGCNA) as well as GO and KEGG analyses unveiled the role of neutrophils and T cells during the progress of the disease. Based on the hospital-free days after 45 days of follow-up and statistical methods such as nonnegative matrix factorization (NMF), submap, and linear correlation analysis, 31 genes were regarded as the signature of the peripheral blood of COVID-19. Various immune cells were identified to be related to the prognosis of the patients. Drugs were predicted for the genes in the signature by DGIdb. Overall, our study comprehensively revealed the relationship between the inflammatory response and the disease course, which provided strategies for the treatment of COVID-19.

A novel 111indium-labeled dual carbonic anhydrase 9-targeted probe as a potential SPECT imaging radiotracer for detection of hypoxic colorectal cancer cells

Tumor hypoxia is a common feature in colorectal cancer (CRC), and is associated with resistance to radiotherapy and chemotherapy. Thus, a specifically targeted probe for the detection of hypoxic CRC cells is urgently needed. Carbonic anhydrase 9 (CA9) is considered to be a specific marker for hypoxic CRC diagnosis. Here, a nuclear imaging Indium-111 (¹¹¹In)-labeled dual CA9-targeted probe was synthesized and evaluated for CA9 detection in in vitro, in vivo, and in human samples. The CA9-targeted peptide (CA9tp) and CA9 inhibitor acetazolamide (AAZ) were combined to form a dual CA9-targeted probe (AAZ-CA9tp) using an automatic microwave peptide synthesizer, which then was conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for radioisotope (¹¹¹In) labeling (¹¹¹In-DOTA-AAZ-CA9tp). The assays for cell binding, stability, and toxicity were conducted in hypoxic CRC HCT15 cells. The analyses for imaging and biodistribution were performed in an HCT15 xenograft mouse model. The binding and distribution of ¹¹¹In-DOTA-AAZ-CA9tp were detected in human CRC samples using microautoradiography. AAZ-CA9tp possessed good CA9-targeting ability in hypoxic HCT15 cells. The dual CA9-targeted radiotracer showed high serum stability, high surface binding, and high affinity in vitro. After exposure of ¹¹¹In-DOTA-AAZ-CA9tp to the HCT15-bearing xenograft mice, the levels of ¹¹¹In-DOTA-AAZ-CA9tp were markedly and specifically increased in the hypoxic tumor tissues compared to control mice. ¹¹¹In-DOTA-AAZ-CA9tp also targeted the areas of CA9 overexpression in human colorectal tumor tissue sections. The results of this study suggest that the novel ¹¹¹In-DOTA-AAZ-CA9tp nuclear imaging agent may be a useful tool for the detection of hypoxic CRC cells in clinical practice.

The Chromosome-Level Genome of Triplophysa dalaica (Cypriniformes: Cobitidae) Provides Insights into Its Survival in Extremely Alkaline Environment

Lake Dali Nur, located in Inner Mongolia, North China, is alkaline, with Triplophysa dalaica one of the three fish species that not only survive, but thrive, in the lake. To investigate the presence of molecular mutations potentially responsible for this adaptation, the whole-genome sequence of the species was sequenced. A total of 126.5 and 106 Gb data, covering nearly 200× of the estimated genome, were generated using long-read sequencing and Hi-C technology, respectively. De novo assembly generated a genome totalled 607.91 Mb, with a contig N50 of 9.27 Mb. Nearly all whole-genome sequences were anchored and oriented onto 25 chromosomes, with telomeres for most chromosomes also being recovered. Repeats comprised approximately 35.01% of the whole genome. A total of 23,925 protein-coding genes were predicted, within which, 98.62% could be functionally annotated. Through comparisons of T. dalaica, T. tibetana, and T. siluroides gene models, a total of 898 genes were identified as likely being subjected to positive selection, with several of them potentially associated with alkaline adaptation, such as sodium bicarbonate cotransporter, SLC4A4. Demographic analyses suggested that the Dali population might have diverged from endemic freshwater Hai River populations, approximately 1 Ma. The high-quality T. dalaica genome, created in this study, not only aids in the analyses of alkaline adaptation, but may also assist in revealing the mysteries of the highly divergent genus Triplophysa in the future.

Overlapping Immunohistochemical Features of Adenocarcinoma of the Nonpigmented Ciliary Body Epithelium and Renal Cell Carcinoma

PURPOSE

To find immunohistochemical markers that distinguish adenocarcinoma of the nonpigmented ciliary epithelium (NPCE) from metastatic carcinoma, especially metastatic renal cell carcinoma.

DESIGN

Retrospective case series.

METHODS

Three cases of adenocarcinoma of the NPCE were examined histologically with hematoxylin-eosin stain and immunohistochemical stains including vimentin, AE1/AE3, Cam 5.2, CK7, PAX2, PAX8, AMACR, and CAIX. We also reviewed previously reported cases of this tumor.

RESULTS

We found that the immunohistochemical profile of adenocarcinoma of the NPCE can overlap with renal cell carcinoma. Both tumors can express vimentin, cytokeratin AE1/AE3, Cam 5.2, PAX2, PAX8, and AMACR. One of the adenocarcinomas of the NPCE in our series also expressed CD10 and the renal cell carcinoma marker (RCC Ma). Carbonic anhydrase IX (CAIX) was not detected in any of the 3 tumors.

CONCLUSIONS

Adenocarcinomas arising in phthisic eyes can be diagnostically challenging. We have found it particularly difficult to distinguish adenocarcinoma of the NPCE from metastatic carcinoma, especially metastatic clear cell renal cell carcinoma and papillary renal cell carcinoma. Because of the immunophenotypic overlap, most patients will require systemic workup including imaging of the kidneys to be certain of the diagnosis.

Carbonic Anhydrase in Pacific Abalone Haliotis discus hannai: Characterization, Expression, and Role in Biomineralization

Carbonic anhydrases (CAs) are universal zinc ion containing metalloenzymes that play a pivotal role in various physiological processes. In this study, a CA I (designated as Hdh CA I) was isolated and characterized from the mantle tissue of Pacific abalone, Haliotis discus hannai. The full-length cDNA sequence of Hdh CA I was 1,417-bp in length, encoding a protein of 337 amino acids with molecular weight of 37.58 kDa. Hdh CA I sequence possessed a putative signal peptide of 22 amino acids and a CA catalytic function domain. The predicted protein shared 94 and 78% sequence identities with Haliotis gigantea and Haliotis tuberculata CA I, respectively. Results of phylogenetic analysis indicated that Hdh CA I was evolutionarily close to CA I of H. gigantea and H. tuberculata with high bootstrap values. Significantly higher levels of Hdh CA I mRNA transcript were found in mantle than other examined tissues. In situ hybridization results showed strong hybridization signals in epithelial cells of the dorsal mantle pallial, an area known to synthesize and secrete proteins responsible for the nacreous layer formation of shell. This is the first study on Hdh CA I in H. discus hannai and the results may contribute to further study its physiological functions in shell biomineralization of abalone.

Large pH oscillations promote host defense against human airways infection

The airway mucosal microenvironment is crucial for host defense against inhaled pathogens but remains poorly understood. We report here that the airway surface normally undergoes surprisingly large excursions in pH during breathing that can reach pH 9.0 during inhalation, making it the most alkaline fluid in the body. Transient alkalinization requires luminal bicarbonate and membrane-bound carbonic anhydrase 12 (CA12) and is antimicrobial. Luminal bicarbonate concentration and CA12 expression are both reduced in cystic fibrosis (CF), and mucus accumulation both buffers the pH and obstructs airflow, further suppressing the oscillations and bacterial-killing efficacy. Defective pH oscillations may compromise airway host defense in other respiratory diseases and explain CF-like airway infections in people with CA12 mutations.

Hepatobiliary acid-base homeostasis: Insights from analogous secretory epithelia

Many epithelia secrete bicarbonate-rich fluid to generate flow, alter viscosity, control pH and potentially protect luminal and intracellular structures from chemical stress. Bicarbonate is a key component of human bile and impaired biliary bicarbonate secretion is associated with liver damage. Major efforts have been undertaken to gain insight into acid-base homeostasis in cholangiocytes and more can be learned from analogous secretory epithelia. Extrahepatic examples include salivary and pancreatic duct cells, duodenocytes, airway and renal epithelial cells. The cellular machinery involved in acid-base homeostasis includes carbonic anhydrase enzymes, transporters of the solute carrier family, and intra- and extracellular pH sensors. This pH-regulatory system is orchestrated by protein-protein interactions, the establishment of an electrochemical gradient across the plasma membrane and bicarbonate sensing of the intra- and extracellular compartment. In this review, we discuss conserved principles identified in analogous secretory epithelia in the light of current knowledge on cholangiocyte physiology. We present a framework for cholangiocellular acid-base homeostasis supported by expression analysis of publicly available single-cell RNA sequencing datasets from human cholangiocytes, which provide insights into the molecular basis of pH homeostasis and dysregulation in the biliary system.

Characterization of CD147, CA9, and CD70 as Tumor-Specific Markers on Extracellular Vesicles in Clear Cell Renal Cell Carcinoma

Extracellular vesicles (EVs) are secreted by healthy and tumor cells and are involved in cell–cell communication. Tumor-released EVs could represent a new class of biomarkers from liquid biopsies. The aim of this study was to identify tumor-specific EV markers in clear cell renal carcinoma (ccRCC) using cell lines and patient-derived tissue samples. EVs from ccRCC cell lines (786-O, RCC53, Caki1, and Caki2) and patient tissues were isolated via ultracentrifugation. EVs were characterized using transmission electron microscopy, nanoparticle tracking analysis, and Western blotting using exosome and putative tumor markers (epithelial cell adhesion molecule (EpCAM), carbonic anhydrase 9 (CA9), CD70, CD147). The tumor markers were verified using immunohistochemistry. CA9 was expressed in Caki2 cells and EVs, and CD147 was found in the cells and EVs of all tested ccRCC cell lines. In tumor tissues, we found an increased expression of CA9, CD70, and CD147 were increased in cell lysates and EV fractions compared to normal tissues. In contrast, EpCAM was heterogeneously expressed in tumor samples and positive in normal tissue. To conclude, we developed an effective technique to isolate EVs directly from human tissue samples with high purity and high concentration. In contrast to EpCAM, CA9, CD70, and CD147 could represent promising markers to identify tumor-specific EVs in ccRCC.

Carbonic anhydrases enhance activity of endogenous Na-H exchangers and not the electrogenic Na/HCO3 cotransporter NBCe1-A, expressed in Xenopus oocytes

KEY POINTS

According to the HCO 3 - metabolon hypothesis, direct association of cytosolic carbonic anhydrases (CAs) with the electrogenic Na/HCO3 cotransporter NBCe1-A speeds transport by regenerating/consuming HCO 3 - . The present work addresses published discrepancies as to whether cytosolic CAs stimulate NBCe1-A, heterologously expressed in Xenopus oocytes. We confirm the essential elements of the previous experimental observations, taken as support for the HCO 3 - metabolon hypothesis. However, using our own experimental protocols or those of others, we find that NBCe1-A function is unaffected by cytosolic CAs. Previous conclusions that cytosolic CAs do stimulate NBCe1-A can be explained by an unanticipated stimulatory effect of the CAs on an endogenous Na-H exchanger. Theoretical analyses show that, although CAs could stimulate non- HCO 3 - transporters (e.g. Na-H exchangers) by accelerating CO2 / HCO 3 - -mediated buffering of acid-base equivalents, they could not appreciably affect transport rates of NBCe1 or other transporters carrying HCO 3 - , CO 3 = , or NaCO 3 - ion pairs.

ABSTRACT

The HCO 3 - metabolon hypothesis predicts that cytosolic carbonic anhydrase (CA) binds to NBCe1-A, promotes HCO 3 - replenishment/consumption, and enhances transport. Using a short step-duration current-voltage (I-V) protocol with Xenopus oocytes expressing eGFP-tagged NBCe1-A, our group reported that neither injecting human CA II (hCA II) nor fusing hCA II to the NBCe1-A carboxy terminus affects background-subtracted NBCe1 slope conductance (GNBC ), which is a direct measure of NBCe1-A activity. Others - using bovine CA (bCA), untagged NBCe1-A, and protocols keeping holding potential (Vh ) far from NBCe1-A's reversal potential (Erev ) for prolonged periods - found that bCA increases total membrane current (ΔIm ), which apparently supports the metabolon hypothesis. We systematically investigated differences in the two protocols. In oocytes expressing untagged NBCe1-A, injected with bCA and clamped to -40 mV, CO2 / HCO 3 - exposures markedly decrease Erev , producing large transient outward currents persisting for >10 min and rapid increases in [Na+ ]i . Although the CA inhibitor ethoxzolamide (EZA) reduces both ΔIm and d[Na+ ]i /dt, it does not reduce GNBC . In oocytes not expressing NBCe1-A, CO2 / HCO 3 - triggers rapid increases in [Na+ ]i that both hCA II and bCA enhance in concentration-dependent manners. These d[Na+ ]i /dt increases are inhibited by EZA and blocked by EIPA, a Na-H exchanger (NHE) inhibitor. In oocytes expressing untagged NBCe1-A and injected with bCA, EIPA abolishes the EZA-dependent decreases in ΔIm and d[Na+ ]i /dt. Thus, CAs/EZA produce their ΔIm and d[Na+ ]i /dt effects not through NBCe1-A, but endogenous NHEs. Theoretical considerations argue against a CA stimulation of HCO 3 - transport, supporting the conclusion that an NBCe1-A- HCO 3 - metabolon does not exist in oocytes.

The Anticancer Activity for the Bumetanide-Based Analogs via Targeting the Tumor-Associated Membrane-Bound Human Carbonic Anhydrase-IX Enzyme

The membrane-bound human carbonic anhydrase (hCA) IX is widely recognized as a marker of tumor hypoxia and a prognostic factor within several human cancers. Being undetected in most normal tissues, hCA-IX implies the pharmacotherapeutic advent of reduced off-target adverse effects. We assessed the potential anticancer activity of bumetanide-based analogues to inhibit the hCA-IX enzymatic activity and cell proliferation of two solid cancer cell lines, namely kidney carcinoma (A-498) and bladder squamous cell carcinoma (SCaBER). Bumetanide analogues efficiently inhibit the target hCA-IX in low nanomolar activity (IC₅₀ = 4.4–23.7 nM) and have an excellent selectivity profile (SI = 14.5–804) relative to the ubiquitous hCA-II isoform. Additionally, molecular docking studies provided insights into the compounds’ structure–activity relationship and preferential binding of small-sized as well as selective bulky ligands towards the hCA-IX pocket. In particular, 2,4-dihydro-1,2,4-triazole-3-thione derivative 9c displayed pronounced hCA-IX inhibitory activity and impressive antiproliferative activity on oncogenic A-498 kidney carcinoma cells and is being considered as a promising anticancer candidate. Future studies will aim to optimize this compound to fine-tune its anticancer activity as well as explore its potential through in-vivo preclinical studies.

Acetazolamide causes renal [Formula: see text] wasting but inhibits ammoniagenesis and prevents the correction of metabolic acidosis by the kidney

Carbonic anhydrase (CAII) binds to the electrogenic basolateral Na+-[Formula: see text] cotransporter (NBCe1) and facilitates [Formula: see text] reabsorption across the proximal tubule. However, whether the inhibition of CAII with acetazolamide (ACTZ) alters NBCe1 activity and interferes with the ammoniagenesis pathway remains elusive. To address this issue, we compared the renal adaptation of rats treated with ACTZ to NH4Cl loading for up to 2 wk. The results indicated that ACTZ-treated rats exhibited a sustained metabolic acidosis for up to 2 wk, whereas in NH4Cl-loaded rats, metabolic acidosis was corrected within 2 wk of treatment. [Formula: see text] excretion increased by 10-fold in NH4Cl-loaded rats but only slightly (1.7-fold) in ACTZ-treated rats during the first week despite a similar degree of acidosis. Immunoblot experiments showed that the protein abundance of glutaminase (4-fold), glutamate dehydrogenase (6-fold), and SN1 (8-fold) increased significantly in NH4Cl-loaded rats but remained unchanged in ACTZ-treated rats. Na+/H+ exchanger 3 and NBCe1 proteins were upregulated in response to NH4Cl loading but not ACTZ treatment and were rather sharply downregulated after 2 wk of ACTZ treatment. ACTZ causes renal [Formula: see text] wasting and induces metabolic acidosis but inhibits the upregulation of glutamine transporter and ammoniagenic enzymes and thus suppresses ammonia synthesis and secretion in the proximal tubule, which prevented the correction of acidosis. This effect is likely mediated through the inhibition of the CA-NBCe1 metabolon complex, which results in cell alkalinization. During chronic ACTZ treatment, the downregulation of both NBCe1 and Na+/H+ exchanger 3, along with the inhibition of ammoniagenesis and [Formula: see text] generation, contributes to the maintenance of metabolic acidosis.

Carbonic Anhydrase 4 serves as a Clinicopathological Biomarker for Outcomes and Immune Infiltration in Renal Cell Carcinoma, Lower Grade Glioma, Lung Adenocarcinoma and Uveal Melanoma

Background: Carbonic anhydrase 4 (CA4) maintains homeostasis of carbon dioxide and bicarbonate. It is suggested to be a potential prognostic biomarker, while the correlations between CA4 and different cancers are indistinct. Methods: Differential mRNA expression of CA4 among different cancers and corresponding normal tissues was compared based on datasets on the Cancer Genome Atlas (TCGA) platforms. Then, survival analysis was performed using Tumor-immune system interactionsplatform and TCGA cohort on the basis of distinct comparison expression of CA4 in five kinds of tumors. In addition, molecular penal analysis and functional annotations of CA4-related genes was elaborated. The correlation between CA4 mRNA expression and tumor immune microenvironment were analyzed in detail. Results: Compared with adjacent normal tissues, CA4 mRNA expressions were found significantly lower in various tumors. Moreover, decreased expression of CA4 was significantly related to worse overall survival (OS) and progression-free survival (PFS) in kidney renal clear cell carcinoma (KIRC), brain lower grade glioma (LGG), lung adenocarcinoma (LUAD) and uveal melanoma (UVM), and worse OS of prostate adenocarcinoma (PRAD) (p<0.05). Cox regression analyses indicated that CA4 was a significant prognostic biomarker in KIRC, LGG, LUAD and UVM. Moreover, CA4 showed markedly relationship with tumor immune environment and diverse immune infiltration signatures in KIRC, LGG, LUAD and UVM. Conclusions: Our study revealed that CA4 was a potential biomarker for aggressive progression and poor prognosis in KIRC, LGG, LUAD, PRAD and UVM, correlated with immune infiltration in various tumor environments. These results suggested that CA4 possibly served as a promising prognostic and immune infiltration biomarker in many cancers.

Progress in the development of human carbonic anhydrase inhibitors and their pharmacological applications: Where are we today?

Carbonic anhydrases (CAs, EC 4.2.1.1) are widely distributed metalloenzymes in both prokaryotes and eukaryotes. They efficiently catalyze the reversible hydration of carbon dioxide to bicarbonate and H⁺  ions and play a crucial role in regulating many physiological processes. CAs are well-studied drug target for various disorders such as glaucoma, epilepsy, sleep apnea, and high altitude sickness. In the past decades, a large category of diverse families of CA inhibitors (CAIs) have been developed and many of them showed effective inhibition toward specific isoforms, and effectiveness in pathological conditions in preclinical and clinical settings. The discovery of isoform-selective CAIs in the last decade led to diminished side effects associated with off-target isoforms inhibition. The many new classes of such compounds will be discussed in the review, together with strategies for their development. Pharmacological advances of the newly emerged CAIs in diseases not usually associated with CA inhibition (neuropathic pain, arthritis, cerebral ischemia, and cancer) will also be discussed.

Transcriptomic and Ultrastructural Signatures of K+-Induced Aggregation in Phytophthora parasitica Zoospores

Most pathogenic oomycetes of the genus Phytophthora spread in water films as flagellated zoospores. Zoospores perceive and produce signals attracting other zoospores, resulting in autoaggregation in vitro or biofilm formation on plant surface. The mechanisms underlying intercellular communication and consequent attraction, adhesion and aggregation are largely unknown. In Phytophthora parasitica, the perception of a K⁺ gradient induces coordinated motion and aggregation. To define cellular and molecular events associated with oomycete aggregation, we combined transcriptomic and ultrastructural analyses. Results indicate involvement of electroception in K⁺ sensing. They establish that the transcriptome repertoire required for swimming and aggregation is already fully functional at zoospore release. At the time points analyzed, aggregates are mainly constituted of zoospores. They produce vesicular and fibrillary material discharged at cell-to-cell contacts. Consistently, the signature of transcriptome dynamics during transition to aggregates is an upregulation of genes potentially related to vesicular trafficking. Moreover, transcriptomic and functional analyses show a strong enhancement of carbonic anhydrase activity, indicating that pH homeostasis may contribute to aggregation by acting on both zoospore movement and adhesion. This study poses the molecular and cellular bases of aggregative behavior within oomycetes and expands the current knowledge of ion perception-mediated dissemination of propagules in the rhizosphere.

Developmental loss, but not pharmacological suppression, of renal carbonic anhydrase 2 results in pyelonephritis susceptibility

Carbonic anhydrase II knockout (Car2^-/-) mice have depleted numbers of renal intercalated cells, which are increasingly recognized to be innate immune effectors. We compared pyelonephritis susceptibility following reciprocal renal transplantations between Car2^-/- and wild-type mice. We examined the effect of pharmacological CA suppression using acetazolamide in an experimental murine model of urinary tract infection. Car2^-/- versus wild-type mice were compared for differences in renal innate immunity. In our transplant scheme, mice lacking CA-II in the kidney had increased pyelonephritis risk. Mice treated with acetazolamide had lower kidney bacterial burdens at 6 h postinfection, which appeared to be due to tubular flow from diuresis because comparable results were obtained when furosemide was substituted for acetazolamide. Isolated Car2^-/- kidney cells enriched for intercalated cells demonstrated altered intercalated cell innate immune gene expression, notably increased calgizzarin and insulin receptor expression. Intercalated cell number and function along with renal tubular flow are determinants of pyelonephritis risk.

Proteomic analysis of rat kidney under maleic acid treatment by SWATH-MS technology

RATIONALE

Maleic acid is an industrial-grade chemical that is often used in adhesives, stabilizers, and preservatives. It is unknown whether long-term consumption of maleic acid modified starch is harmful to humans. However, many studies have indicated that maleic acid causes renal tubular damage in animal models, even as the associated pathways remain unclear. Sequential window acquisition of all theoretical fragment ion spectra (SWATH) is the most innovative of the label-free quantitative technologies which have better quantification performance. Therefore, SWATH technology was used to investigate the effect of maleic acid on the rat kidney proteome in this study.

METHODS

Sprague-Dawley(SD) rats were treated with 0 mg/kg (control), 6 mg/kg (low-dose), 10 mg/kg (medium-dose), and 60 mg/kg (high-dose) of maleic acid. After kidney protein extraction, 28% SDS-PAGE was used, followed by in-gel digestion and desalting. Next, the samples were analyzed with ultra-performance liquid chromatography (UPLC) coupled with quadrupole time-of-flight mass spectrometry (Q-TOF MS), and data-dependent acquisition (DDA) and SWATH technology were also used. The gene ontology and pathway analysis were accomplished. Ultimately, these protein biomarkers were validated by using scheduled high-resolution multiple reaction monitoring (sMRM^HR ).

RESULTS

Comparisons of the control group with the other three groups revealed that 95, 130, and 103 proteins were expressed at significantly different levels in the control group and in the low-dose, medium-dose, and high-dose groups, respectively. According to the gene ontology analysis, the major processes that these proteins were involved in were metabolic processes, biological regulation, cellular processes, and responses to stimuli; the major functions that these proteins were involved in were binding, hydrolase activity, catalytic activity, and oxidoreductase activity; and the major cellular components hat they were involved in were the cytoplasm, extracellular region, membrane, and mitochondria. According to the KEGG pathway analysis, these proteins were involved in 35 pathways, five of which, the carbohydrate metabolism, folate biosynthesis, renal tubular resorption, amino acid metabolism, and Ras signaling pathways, are discussed in this study. Ultimately, 19 proteins involved in 12 important pathways were validated by sMRM^HR .

CONCLUSIONS

It was demonstrated that maleic acid caused insufficient energy production, which might lead to a decrease in the activity of the sodium-potassium ATP pump and hydrogen ion ATP pump, which could in turn have caused renal tubular resorption and hydrogen ion regulation to be blocked, thus leading to the accumulation of hydrogen ions in the renal tubules, which would then result in renal tubular acidification followed finally by Fanconi syndrome.

Chemical compounds, antioxidant activity, and in vitro and in silico litholytic effects of Zizyphus lotus extracts

Background The aim of this study was to evaluate the antioxidant activity and to determine the chemical compounds of organic extracts of fruits and leaves of Zizyphus lotus. The litholytic effect was determined on the basis of the in vitro effect of the aqueous extracts on the formation of crystals of stones. Finally, chemical compounds were investigated to identify their target using an in silico approach. Methods The antioxidant activity was determined with the diphenylpicrylhydrazyl radical trapping method. An aliquot of 2 mL of urine and 100 μL of an infusion of fruit and leaf aqueous extract of Z. lotus at different concentrations were used. The induction of calcium oxalate (CaOx) crystals was done by the addition of oxalic acid at 0.1 mol/L. The effect of aqueous extracts was compared with two inhibitors (citrate and magnesium) used as references. In silico modelization was carried out using SwissTargetPrediction. Results The antioxidant activity test showed that the methanol extract was active with an IC50 of 5 mg/mL. The aqueous extracts of fruits and leaves inhibit the formation of crystals of CaOx. Then, the composition of the methanol extracts of the leaves and fruits in high-performance liquid chromatography showed majority compounds such as quercetin-3-galactoside and hyperin. In silico assays showed that the identified molecules exert their effect by targeting enzymes responsible for calcium regulation, urate regulation, and maintenance of acid-base balance, and that had anti-inflammatory properties. Conclusions The present study showed that Z. lotus may be considered as a functional or nutraceutical food. However, further studies should be carried out in order to extract and purify these compounds to test their effect on urinary lithiasis.

Nanoscale Analysis of Randall's Plaques by Electron Energy Loss Spectromicroscopy: Insight in Early Biomineral Formation in Human Kidney

Idiopathic kidney stones originate mainly from calcium phosphate deposits at the tip of renal papillae, known as Randall's plaques (RPs), also detected in most human kidneys without stones. However, little is known about the mechanisms involved in RP formation. The localization and characterization of such nanosized objects in the kidney remain a real challenge, making their study arduous. This study provides a nanoscale analysis of the chemical composition and morphology of incipient RPs, characterizing in particular the interface between the mineral and the surrounding organic compounds. Relying on data gathered from a calculi collection, the morphology and chemical composition of incipient calcifications in renal tissue were determined using spatially resolved electron energy-loss spectroscopy. We detected microcalcifications and individual nanocalcifications found at some distance from the larger ones. Strikingly, concerning the smaller ones, we show that two types of nanocalcifications coexist: calcified organic vesicles and nanometric mineral granules mainly composed of calcium phosphate with carbonate in their core. Interestingly, some of these nanocalcifications present similarities with those reported in physiological bone or pathological cardiovascular biominerals, suggesting possible common formation mechanisms. However, the high diversity of these nanocalcifications suggests that several mechanisms may be involved (nucleation on a carbonate core or on organic compounds). In addition, incipient RPs also appear to present specific features at larger scales, revealing secondary calcified structures embedded in a fibrillar organic material. Our study proves that analogies exist between physiological and pathological biominerals and provides information to understand the physicochemical processes involved in pathological calcification formation.

pH-controlled histone acetylation amplifies melanocyte differentiation downstream of MITF

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. This involves the rapid and selective induction of melanocyte maturation genes, while concomitantly the expression of other effector genes is maintained. In this study, using cell-based and zebrafish model systems, we report on a pH-mediated feed-forward mechanism of epigenetic regulation that enables selective amplification of the melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of the enzyme carbonic anhydrase 14 (CA14). Nuclear localization of CA14 leads to an increase of the intracellular pH, resulting in the activation of the histone acetyl transferase p300/CBP. In turn, enhanced H3K27 histone acetylation at selected differentiation genes facilitates their amplified expression via MITF. CRISPR-mediated targeted missense mutation of CA14 in zebrafish results in the formation of immature acidic melanocytes with decreased pigmentation, establishing a central role for this mechanism during melanocyte differentiation in vivo. Thus, we describe an epigenetic control system via pH modulation that reinforces cell fate determination by altering chromatin dynamics.

Metalation and Maturation of Zinc Ectoenzymes: A Perspective

Numerous zinc ectoenzymes are folded and activated in the compartments of the early secretory pathway, such as the ER and the Golgi apparatus, before reaching their final destination. During this process, zinc must be incorporated into the active site; therefore, metalation of the nascent protein is indispensable for the expression of the active enzyme. However, to date, the molecular mechanism underlying this process has been poorly investigated. This is in sharp contrast to the physiological and pathophysiological roles of zinc ectoenzymes, which have been extensively investigated over the past decades. This manuscript concisely outlines the present understanding of zinc ectoenzyme activation through metalation by zinc and compares this with copper ectoenzyme activation, in which elaborate copper metalation mechanisms are known. Moreover, based on the comparison, several hypotheses are discussed. Approximately 80 years have passed since the first zinc enzyme was identified; therefore, it is necessary to improve our understanding of zinc ectoenzymes from a biochemical perspective, which will further our understanding of their biological roles.

Mitochondrial dysfunction, AMPK activation and peroxisomal metabolism: A coherent scenario for non-canonical 3-methylglutaconic acidurias

The occurrence of 3-methylglutaconic aciduria (3-MGA) is a well understood phenomenon in leucine oxidation and ketogenesis disorders (primary 3-MGAs). In contrast, its genesis in non-canonical (secondary) 3-MGAs, a growing-up group of disorders encompassing more than a dozen of inherited metabolic diseases, is a mystery still remaining unresolved for three decades. To puzzle out this anthologic problem of metabolism, three clues were considered: (i) the variety of disorders suggests a common cellular target at the cross-road of metabolic and signaling pathways, (ii) the response to leucine loading test only discriminative for primary but not secondary 3-MGAs suggests these latter are disorders of extramitochondrial HMG-CoA metabolism as also attested by their failure to increase 3-hydroxyisovalerate, a mitochondrial metabolite accumulating only in primary 3-MGAs, (iii) the peroxisome is an extramitochondrial site possessing its own pool and displaying metabolism of HMG-CoA, suggesting its possible involvement in producing extramitochondrial 3-methylglutaconate (3-MG). Following these clues provides a unifying common basis to non-canonical 3-MGAs: constitutive mitochondrial dysfunction induces AMPK activation which, by inhibiting early steps in cholesterol and fatty acid syntheses, pipelines cytoplasmic acetyl-CoA to peroxisomes where a rise in HMG-CoA followed by local dehydration and hydrolysis may lead to 3-MGA yield. Additional contributors are considered, notably for 3-MGAs associated with hyperammonemia, and to a lesser extent in CLPB deficiency. Metabolic and signaling itineraries followed by the proposed scenario are essentially sketched, being provided with compelling evidence from the literature coming in their support.