Renal tubular acidosis and osteopetrosis with carbonic anhydrase II deficiency: pathogenesis of impaired acidification

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

Carbonic anhydrase II deficiency syndrome with amelogenesis imperfecta linked to a homozygous CA2 deletion

We performed a study to present a phenotypic and genotypic characterization of a patient clinically diagnosed with carbonic anhydrase II (CAII) deficiency syndrome. Medical records were reviewed, and oral examination was performed. Sanger sequencing was undertaken for molecular diagnosis. The patient presented with osteopetrosis, renal tubular acidosis, cerebral calcification, blindness, deafness, and development delay. The oral manifestations included anterior open bite, posterior crossbite, tooth eruption impairment, and hypoplastic amelogenesis imperfecta (AI). Molecular analysis revealed a CA2 homozygous deletion (c.753delG, p.Asn252Thrfs*14) and confirmed the clinical diagnosis. This study suggests that AI can be another feature of CAII deficiency syndrome. For the first time, a CA2 disease-causing variant is reported to be associated with syndromic AI.

Hereditary Metabolic Bone Diseases: A Review of Pathogenesis, Diagnosis and Management

Hereditary metabolic bone diseases are characterized by genetic abnormalities in skeletal homeostasis and encompass one of the most diverse groups among rare diseases. In this review, we examine 25 selected hereditary metabolic bone diseases and recognized genetic variations of 78 genes that represent each of the three groups, including sclerosing bone disorders, disorders of defective bone mineralization and disorder of bone matrix and cartilage formation. We also review pathophysiology, manifestation and treatment for each disease. Advances in molecular genetics and basic sciences has led to accurate genetic diagnosis and novel effective therapeutic strategies for some diseases. For other diseases, the genetic basis and pathophysiology remain unclear. Further researches are therefore crucial to innovate ways to overcome diagnostic challenges and develop effective treatment options for these orphan diseases.

Acute kidney injury manifesting as renal tubular acidosis with proximal and distal renal tubular dysfunction in a dog with acute pancreatitis

Objective

To describe the clinical presentation and management of a critically ill dog with profound renal tubular acidosis (RTA) with proximal and distal renal tubular dysfunction.

Case Summary

A 3‐year‐old neutered female Border Terrier was presented with frequent regurgitation resulting from acute pancreatitis with severe ileus. Venous acid–base analysis and complete urinalysis confirmed the presence of normal anion gap metabolic acidosis with inappropriately alkaline urine (pH 8), consistent with distal RTA. Urinalysis, urine amino acids, and urinary fractional excretion of electrolytes revealed glycosuria (with normoglycemia), aminoaciduria, and increased fractional excretion of sodium, calcium, and phosphate consistent with generalized proximal renal tubulopathy or Fanconi syndrome. The dog responded well to supportive care and alkaline therapy and made a complete recovery.

New or Unique Information Provided

To the authors’ knowledge, this is the first description of RTA with proximal and distal renal tubular dysfunction in the veterinary literature. Furthermore, the authors hypothesize that the transient RTA was a manifestation of acute kidney injury secondary to acute pancreatitis, the first report of this in the literature.

Use of Urine Electrolytes and Urine Osmolality in the Clinical Diagnosis of Fluid, Electrolytes, and Acid-Base Disorders

We discuss the use of urine electrolytes and urine osmolality in the clinical diagnosis of patients with fluid, electrolytes, and acid-base disorders, emphasizing their physiological basis, their utility, and the caveats and limitations in their use. While our focus is on information obtained from measurements in the urine, clinical diagnosis in these patients must integrate information obtained from the history, the physical examination, and other laboratory data.

Proteomic Profiling of the First Human Dental Pulp Mesenchymal Stem/Stromal Cells from Carbonic Anhydrase II Deficiency Osteopetrosis Patients

Osteopetrosis is a hereditary disorder characterized by sclerotic, thick, weak, and brittle bone. The biological behavior of mesenchymal cells obtained from osteopetrosis patients has not been well-studied. Isolated mesenchymal stem/stromal cells from dental pulp (DP-MSSCs) of recently extracted deciduous teeth from osteopetrosis (OP) patients and healthy controls (HCs) were compared. We evaluated whether the dental pulp of OP patients has a population of MSSCs with similar multilineage differentiation capability to DP-MSSCs of healthy subjects. Stem/progenitor cells were characterized using immunohistochemistry, flow cytometry, and proteomics. Our DP-MSSCs were strongly positive for CD44, CD73, CD105, and CD90. DP-MSSCs obtained from HC subjects and OP patients showed similar patterns of proliferation and differentiation as well as gene expression. Proteomic analysis identified 1499 unique proteins with 94.3% similarity in global protein fingerprints of HCs and OP patients. Interestingly, we observed subtle differences in expressed proteins of osteopetrosis disease-related in pathways, including MAPK, ERK 1/2, PI3K, and integrin, rather than in the stem cell signaling network. Our findings of similar protein expression signatures in DP-MSSCs of HC and OP patients are of paramount interest, and further in vivo validation study is needed. There is the possibility that OP patients could have their exfoliating deciduous teeth banked for future use in regenerative dentistry.

Molecular modelling and dynamics of CA2 missense mutations causative to carbonic anhydrase 2 deficiency syndrome

Carbonic anhydrase 2 (CA2) enzyme deficiency caused by CA2 gene mutations is an inherited disorder characterized by symptoms like osteopetrosis, renal tubular acidosis, and cerebral calcification. This study has collected the CA2 deficiency causal missense mutations and assessed their pathogenicity using diverse computational programs. The 3D protein models for all missense mutations were built, and analyzed for structural divergence, protein stability, and molecular dynamics properties. We found M-CAP as the most sensitive prediction method to measure the deleterious potential of CA2 missense mutations. Free energy dynamics of tertiary structure models of CA2 mutants with DUET, mCSM, and SDM based consensus methods predicted only 50% of the variants as destabilizing. Superimposition of native and mutant CA2 models revealed the minor structural fluctuations at the amino acid residue level but not at the whole protein structure level. Near native molecular dynamic simulation analysis indicated that CA2 causative missense variants result in residue level fluctuation pattern in the protein structure. This study expands the understanding of genotype-protein phenotype correlations underlying CA2 variant pathogenicity and presents a potential avenue for modifying the CA2 deficiency by targeting biophysical structural features of CA2 protein. Communicated by Ramaswamy H. Sarma.

DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE

Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.

Clinical and laboratory approaches in the diagnosis of renal tubular acidosis

In the absence of a gastrointestinal origin, a maintained hyperchloremic metabolic acidosis must raise the diagnostic suspicion of renal tubular acidosis (RTA). Unlike adults, in whom RTA is usually secondary to acquired causes, children most often have primary forms of RTA resulting from an inherited genetic defect in the tubular proteins involved in the renal regulation of acid-base homeostasis. According to their pathophysiological basis, four types of RTA are distinguished. Distal type 1 RTA, proximal type 2 RTA, mixed-type 3 RTA, and type 4 RTA can be differentiated based on the family history, the presenting manifestations, the biochemical profile, and the radiological findings. Functional tests to explore the proximal wasting of bicarbonate and the urinary acidification capacity are also useful diagnostic tools. Although currently the molecular basis of the disease can frequently be discovered by gene analysis, patients with RTA must undergo a detailed clinical study and laboratory work-up in order to understand the pathophysiology of the disease and to warrant a correct and accurate diagnosis.

Efficacy and Safety of Topiramate for Essential Tremor: A Meta-Analysis of Randomized Controlled Trials

Essential tremor (ET) is the most common movement disorder that is frequently treated by propranolol or primidone. However, 30% of patients with ET do not respond to either propranolol or primidone. The objective of this study was to assess the efficacy and safety of topiramate for ET.We searched the MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials for relevant randomized controlled trials on the effects of topiramate for ET. A meta-analysis technique was applied to estimate the efficacy and safety of topiramate. The primary outcome was the change in the Fahn-Tolosa-Marin tremor rating scale (TRS). The secondary outcomes included the respective change in the location, motor tasks/function and function disability scores, and adverse events.We included 3 randomized controlled trials with a total of 294 participants. Topiramate was significantly better than placebo in reducing TRS of patients with ET (mean difference [MD] -8.58, 95% confidence interval [CI] -15.46 to -1.70). Changes from the scales of upper limb tremor severity (MD -5.12, 95% CI -7.79 to -2.45), motor tasks/function (MD -5.07, 95% CI -7.12 to -3.03), and functional disability (MD -4.72, 95% CI -6.77 to -2.67) were significantly greater with topiramate than with placebo. More participants taking topiramate experienced adverse events leading to withdrawal than those taking placebo (risk difference 19%, 95% CI 11%-27%).There is consistent evidence supporting the efficacy of topiramate in treating ET; however, a significant proportion of participants withdrew due to its adverse effects.

Two novel CAII mutations causing carbonic anhydrase II deficiency syndrome in two unrelated Chinese families

The carbonic anhydrase II (CAII) deficiency syndrome is a rare autosomal recessive osteopetrosis with renal tubular acidosis (RTA) and cerebral calcifications (MIM259730). CAII deficiency syndrome is caused by mutations in the gene CAII, which encodes the enzyme carbonic anhydrase II. CAII mutations are rarely reported in the Asian population. Here, we described two unrelated CAII deficiency families of Chinese Han origin with clinical and genetic analysis. Altogether, 106 subjects, including 2 probands, 4 unaffected family members from two non-consanguineous Chinese families, and 100 healthy controls were recruited. All seven exons and the exon-intron boundaries of the CAII gene were amplified and directly sequenced. Reverse transcription PCR (RT-PCR) was used to study the effect of splice site mutation. All clinical and biochemical parameters of the probands were collected. Two novel mutations of CAII gene were identified by mutational analysis: A nonsense mutation in exon 4 (c.T381C p.Y127X) in both families; a splice mutation at the splice donor site of intron 3 (c.350+2T>C, IVS3+2T>C) in one family. The splice-site mutation causes exon 3 skipping in patient's mRNA resulting in an in-frame deletion and a novel premature stop codon. These mutations were predicted to result in a loss of function of CAII. This is the first report of CAII deficiency syndrome in Chinese population. Our findings extent the spectrum of CAII mutations observed in patients with CAII deficiency syndrome.

Decreased Renal Expression of H(+)-ATPase and Pendrin in a Patient with Distal Renal Tubular Acidosis Associated with Sjögren's Syndrome

A 31-year-old woman with no significant past medical or family history was admitted with complaints of general weakness. Laboratory tests revealed: serum potassium 3.0 mEq/L, arterial blood pH 7.28, serum bicarbonate 17.8 mEq/L and urinary pH 7.0. Double-labeling confocal fluorescence microscopy using H(+)-ATPase and pendrin antibodies demonstrated a decreased expression of these proteins in the patient's renal collecting duct compared to normal controls. Anti-Sjögren's-syndrome-related antigen A (Anti-Ro/SS-A) and anti-Sjögren's syndrome type B (anti-La/SS-B) antibodies were strongly positive with very high titers, consistent with Sjögren's syndrome. We present a case of distal renal tubular acidosis-associated Sjögren's syndrome with a defect in H(+)-ATPase and pendrin in the renal collecting duct.

High-throughput capillary electrophoresis-mass spectrometry: from analysis of amino acids to analysis of protein complexes

Recent advances in capillary electrophoresis-mass spectrometry (CE-MS) interfacing using porous tip is leading to commercialization of CE-MS with a sheathless interface for the first time. The new sheathless interface in conjunction with CE capillary coatings using self-coating background electrolytes (BGE) has significantly simplified CE-MS analysis of complex mixtures. CE-MS, with its high separation efficiency, compound identification capability, and ability to rapidly separate compounds with a wide range of mass and charge while consuming only nanoliters of samples, has become a valuable analytical technique for the analysis of complex biological mixtures. These advances have allowed a single capillary to analyze a range of compounds including amino acids, their D/L enantiomers, protein digests, intact proteins, and protein complexes. With these capabilities, CE-MS is poised to become the multipurpose tool of separation scientists. More recently, an eight-capillary CE in conjunction with an 8-inlet mass spectrometry has allowed 8 CE-MS analyses to be performed concurrently, significantly increasing throughput.

Identification of novel candidate genes involved in mineralization of dental enamel by genome-wide transcript profiling

The gene repertoire regulating vertebrate biomineralization is poorly understood. Dental enamel, the most highly mineralized tissue in mammals, differs from other calcifying systems in that the formative cells (ameloblasts) lack remodeling activity and largely degrade and resorb the initial extracellular matrix. Enamel mineralization requires that ameloblasts undergo a profound functional switch from matrix-secreting to maturational (calcium transport, protein resorption) roles as mineralization progresses. During the maturation stage, extracellular pH decreases markedly, placing high demands on ameloblasts to regulate acidic environments present around the growing hydroxyapatite crystals. To identify the genetic events driving enamel mineralization, we conducted genome-wide transcript profiling of the developing enamel organ from rat incisors and highlight over 300 genes differentially expressed during maturation. Using multiple bioinformatics analyses, we identified groups of maturation-associated genes whose functions are linked to key mineralization processes including pH regulation, calcium handling, and matrix turnover. Subsequent qPCR and Western blot analyses revealed that a number of solute carrier (SLC) gene family members were up-regulated during maturation, including the novel protein Slc24a4 involved in calcium handling as well as other proteins of similar function (Stim1). By providing the first global overview of the cellular machinery required for enamel maturation, this study provide a strong foundation for improving basic understanding of biomineralization and its practical applications in healthcare.

Requirements for ion and solute transport, and pH regulation during enamel maturation

Transcellular bicarbonate transport is suspected to be an important pathway used by ameloblasts to regulate extracellular pH and support crystal growth during enamel maturation. Proteins that play a role in amelogenesis include members of the ABC transporters (SLC gene family and CFTR). A number of carbonic anhydrases (CAs) have also been identified. The defined functions of these genes are likely interlinked during enamel mineralization. The purpose of this study is to quantify relative mRNA levels of individual SLC, Cftr, and CAs in enamel cells obtained from secretory and maturation stages on rat incisors. We also present novel data on the enamel phenotypes for two animal models, a mutant porcine (CFTR-ΔF508) and the NBCe1-null mouse. Our data show that two SLCs (AE2 and NBCe1), Cftr, and Car2, Car3, Car6, and Car12 are all significantly up-regulated at the onset of the maturation stage of amelogenesis when compared to the secretory stage. The remaining SLCs and CA gene transcripts showed negligible expression or no significant change in expression from secretory to maturation stages. The enamel of CFTR-ΔF508 adult pigs was hypomineralized and showed abnormal crystal growth. NBCe1-null mice enamel was structurally defective and had a marked decrease in mineral content relative to wild-type. These data demonstrate the importance of many non-matrix proteins to amelogenesis and that the expression levels of multiple genes regulating extracellular pH are modulated during enamel maturation in response to an increased need for pH buffering during hydroxyapatite crystal growth.

The neurology of carbonic anhydrase type II deficiency syndrome

Carbonic anhydrase type II deficiency syndrome is an uncommon autosomal recessive disease with cardinal features including osteopetrosis, renal tubular acidosis and brain calcifications. We describe the neurological, neuro-ophthalmological and neuroradiological features of 23 individuals (10 males, 13 females; ages at final examination 2-29 years) from 10 unrelated consanguineous families with carbonic anhydrase type II deficiency syndrome due to homozygous intron 2 splice site mutation (the 'Arabic mutation'). All patients had osteopetrosis, renal tubular acidosis, developmental delay, short stature and craniofacial disproportion with large cranial vault and broad forehead. Mental retardation was present in approximately two-thirds and varied from mild to severe. General neurological examinations were unremarkable except for one patient with brisk deep tendon reflexes and two with severe mental retardation and spastic quadriparesis. Globes and retinae were normal, but optic nerve involvement was present in 23/46 eyes and was variable in severity, random in occurrence and statistically correlated with degree of optic canal narrowing. Ocular motility was full except for partial ductional limitations in two individuals. Saccadic abnormalities were present in two, while half of these patients had sensory or accommodative strabismus, and seven had congenital nystagmus. These abnormalities were most commonly associated with afferent disturbances, but a minor brainstem component to this disorder remains possible. All internal auditory canals were normal in size, and no patient had clinically significant hearing loss. Neuroimaging was performed in 18 patients and repeated over as long as 10 years. Brain calcification was generally progressive and followed a distinct distribution, involving predominantly basal ganglia and thalami and grey-white matter junction in frontal regions more than posterior regions. At least one child had no brain calcification at age 9 years, indicating that brain calcification may not always be present in carbonic anhydrase type II deficiency syndrome during childhood. Variability of brain calcification, cognitive disturbance and optic nerve involvement may imply additional genetic or epigenetic influences affecting the course of the disease. However, the overall phenotype of the disorder in this group of patients was somewhat less severe than reported previously, raising the possibility that early treatment of systemic acidosis with bicarbonate may be crucial in the outcome of this uncommon autosomal recessive problem.

A survey of carbonic anhydrase mRNA expression in enamel cells

Enamel formation requires rigid control of pH homeostasis during all stages of development to prevent disruptions to crystal growth. The acceleration of the generation of bicarbonate by carbonic anhydrases (CA) has been suggested as one of the pathways used by ameloblasts cells to regulate extracellular pH yet only two isozymes (CA II and CA VI) have been reported to date during enamel formation. The mammalian CA family contains 16 different isoforms of which 13 are enzymatically active. We have conducted a systematic screening by RT-PCR on the expression of all known CA isoforms in mouse enamel organ epithelium (EOE) cells dissected from new born, in secretory ameloblasts derived from 7-day-old animals, and in the LS8 ameloblast cell line. Results show that all CA isoforms are expressed by EOE/ameloblast cells in vivo. The most highly expressed are the catalytic isozymes CA II, VI, IX, and XIII, and the acatalytic CA XI isoform. Only minor differences were found in CA expression levels between 1-day EOE cells and 7-day-old secretory-stage ameloblasts, whereas LS8 cells expressed fewer CA isoforms than both of these. The broad expression of CAs by ameloblasts reported here contributes to our understanding of pH homeostasis during enamel development and demonstrates its complexity. Our results also highlight the critical role that regulation of pH plays during the development of enamel.

Effect of topiramate on acid-base balance: extent, mechanism and effects

Topiramate is licensed for the treatment of epilepsy and for migraine prophylaxis, but is also used off-licence for a wide range of indications. With the increasing use of topiramate, reports have emerged that topiramate can cause metabolic acidosis in some patients. It does this by impairing both the normal reabsorption of filtered HCO(3)(-) by the proximal renal tubule and the excretion of H(+) by the distal renal tubule. This combination of defects is termed mixed renal tubular acidosis (RTA). The mechanism involves the inhibition of the enzyme carbonic anhydrase, which is consistent with the fact that genetic deficiency of carbonic anhydrase is associated with mixed RTA. Topiramate-induced RTA can make patients acutely ill, and chronically, can lead to nephrolithiasis, osteoporosis and, in children, growth retardation. There is no proven method for predicting or preventing the effect of topiramate on acid-base balance, but patients with a history of renal calculi or known RTA should not receive topiramate. The utility of regular monitoring of HCO(3)(-) levels has not been proven and is not routine practice currently. For patients with persistent RTA, topiramate should usually be discontinued as alternative agents are available.

Increased propensity for calcium phosphate kidney stones with topiramate use

Topiramate (TPM) is a neuromodulatory agent that was initially approved as an antiepileptic drug and is increasingly used in the treatment of a number of neurological and metabolic disorders. Among its various pharmacological actions, TPM has been shown to inhibit the activity of specific carbonic anhydrase enzymes in the kidney. This action is associated with the development of metabolic acidosis, hypocitraturia, hypercalciuria and elevated urine pH, leading to an increased risk of kidney stone disease. Despite the cautionary note in the package insert of TPM, the extent of these complications has not been fully explored. Few prescribing physicians are aware of these complications, underscoring the need for improved surveillance. Because the drug is among the most frequently prescribed agents in the US, more controlled studies are required to determine the prevalence of kidney stone disease among TPM users, and the optimal approach to prevent and treat nephrolithiasis in these individuals.

Separation of Acidic and Basic Proteins by Nanoparticle-Filled Capillary Electrophoresis

We present the first example of the analysis of acidic and basic proteins by nanoparticle-filled capillary electrophoresis. Compared to the didodecyldimethylammonium bromide (DDAB)-coated capillary, the DDAB-capped gold nanoparticles (AuNPs) as pseudostationary phase were found to form more stable coating on the capillary wall, thus leading to greater separation efficiency and high reproducibility. In addition to their advantages for protein separation, DDAB-capped AuNPs can generate high reversed electroosmotic flow, which is 75% greater than DDAB at pH 3.5. To allow strong interactions with proteins, the AuNPs were modified with poly(ethylene oxide) via noncovalent bonding to form gold nanoparticles/polymer composites (AuNPPs). Using a capillary dynamically coated with DDAB-capped AuNPs and filled with AuNPPs under acidic conditions (10 mM phosphate, pH 3.5), we have demonstrated the separation of acidic and basic proteins with peak efficiencies ranging from 71 000 to 1 007 000 plates/m and relative standard deviations of migration time less than 0.6%. Additionally, the proposed method has been applied to the analyses of biological samples, including saliva, red blood cells, and plasma. With simplicity, high resolving power, and high reproducibility, the proposed method has shown great potential for proteomics applications and clinical diagnosis.

Biochemical and Stone-Risk Profiles With Topiramate Treatment

BACKGROUND

Topiramate is a novel neuromodulatory agent commonly prescribed for the treatment of seizure disorders and for migraine headache prophylaxis. Calcium phosphate kidney stones have been observed with topiramate treatment, but a comprehensive elucidation of stone-risk profile was not reported previously. This study explores the relationship between topiramate treatment and propensity for kidney stone formation.

METHODS

Thirty-two topiramate-treated subjects and 50 healthy volunteers participated in a cross-sectional study in which serum chemistry test and 24-hour urine collection results were evaluated for stone risk. Furthermore, a short-term longitudinal study was conducted in 7 patients to assess stone risk before and 3 months after topiramate treatment.

RESULTS

Serum bicarbonate levels were lower with topiramate treatment. Urinary pH, urinary bicarbonate excretion, and fractional excretion of bicarbonate increased, whereas urinary citrate excretion was significantly lower (737 +/- 329 versus 278 +/- 226 mg/d; P < 0.001). Net acid excretion did not change. The relative saturation ratio for brushite increased with topiramate treatment (3.14 +/- 1.69 versus 1.27 +/- 1.26; P < 0.001) because of urinary alkalinization and decreased urinary citrate levels. Urinary saturation of undissociated uric acid decreased (41 +/- 52 versus 76 +/- 60 mg/d; P < 0.001).

CONCLUSION

Treatment with topiramate causes systemic metabolic acidosis, markedly lower urinary citrate excretion, and increased urinary pH. These changes increase the propensity to form calcium phosphate stones.

Clinical and molecular findings in a family with the carbonic anhydrase II deficiency syndrome

Carbonic anhydrase II (CA2) deficiency syndrome is an autosomal recessive disorder leading to osteopetrosis, renal tubular acidosis, and cerebral calcifications. Affected members of an Arab family with the CA2 deficiency syndrome carried the "Egyptian mutation" in CA2, i.e., c.191 del A, H64fsX90. One affected member, homozygote for the mutation, developed primary pulmonary hypertension. Primary pulmonary hypertension was never described before in patients with this unique syndrome. The likelihood of both occurring randomly in a single individual is very low. We therefore speculate that there might be a possibility of an etiologic link between these entities.

On-Line Concentration of Microheterogeneous Proteins by Capillary Electrophoresis Using SDS and PEO as Additives

In this paper, we describe a method for analyzing large-volume protein samples using capillary electrophoresis in conjunction with laser-induced fluorescence detection (CE-LIF). To improve the stacking and separation efficiencies of proteins, we added either 0.01% sodium dodecyl sulfate (SDS) or 0.01% poly(ethylene oxide) (PEO) to the Tris-borate solutions (pH 10.0) used to prepare the protein samples. After injection of the large-volume samples (ca. 1.0 microL, 0.1 microM), the proteins migrate against the electroosmotic flow (EOF) and enter the PEO zone; this process causes them to slow and stack at the boundary between the PEO and sample zones. As a result, the limits of detection (LODs) at a signal-to-noise (S/N) of 3 for most proteins are sub-nM to several nM. For instance, the LOD (S/N = 3) for alpha-lactalbumin is 0.48 nM, which is an 84-fold sensitivity enhancement over the traditional method. By applying a short plug of 0.2% SDS prior to sample injection, a greater number of peaks, representing the microheterogeneity of the proteins, were resolved and the stacking efficiency of the proteins increased slightly. This method allowed us to detect 12 peaks when injecting a large volume of sample containing six model proteins (0.1 microM). We also analyzed the microheterogeneities of the proteins by using CE with UV-Vis absorption detection when injecting a large volume of sample containing six model proteins (1.0 microM) in the presence of a 1.0% SDS plug. The practical method is validated by the detection of human serum albumin in a urine sample, obtained from a healthy female, without sample pretreatment; its concentration was 0.18 microM. We further demonstrate the capability of this method to detect low amounts of proteins through the detection of 45 nM hemoglobin after injecting ca. 1.0 microL of ultradilute lysed red blood cells. The experimental results indicate that our proposed method has great potential for use in diagnosis and proteomics applications.

Topiramate-valproate-induced hyperammonemic encephalopathy syndrome: case report

A 15-year-old boy with inverted duplication of chromosome 15 was admitted for acute onset of irritability, increasing sleepiness, and worsening of seizures. He had been on valproate and other anti-convulsants. However, he was found to have hyperammonemia within 2 weeks after the addition of low-dose topiramate to valproate. He recovered within 7 days after discontinuation of valproate. Topiramate was tailed off. The reintroduction of valproate monotherapy caused hyperammonemia again without clinical features of encephalopathy. He also developed anticonvulsant hypersensitivity syndrome following the use of phenytoin. We propose the term topiramate-valproate-induced hyperammonemic encephalopathy syndrome to include the following features: excessive sleepiness or somnolence, aggravation of seizures, hyperammonemia, and absence of triphasic waves on electroencephalography in any individual on simultaneous topiramate-valproate therapy. The ammonia level ranged from 1.5 to 2 times normal. The serum valproate level might be within the therapeutic range. The possible mechanism is topiramate-induced aggravation of all the known complications of valproate monotherapy. This condition is reversible with cessation of either valproate or topiramate.

Molecular mechanisms of electrogenic sodium bicarbonate cotransport: structural and equilibrium thermodynamic considerations

The electrogenic Na(+)-HCO(3)(-) cotransporters play an essential role in regulating intracellular pH and extracellular acid-base homeostasis. Of the known members of the bicarbonate transporter superfamily (BTS), NBC1 and NBC4 proteins have been shown to be electrogenic. The electrogenic nature of these transporters results from the unequal coupling of anionic and cationic fluxes during each transport cycle. This unique property distinguishes NBC1 and NBC4 proteins from other sodium bicarbonate cotransporters and members of the bicarbonate transporter superfamily that are known to be electroneutral. Structure-function studies have played an essential role in revealing the basis for the modulation of the coupling ratio of NBC1 proteins. In addition, the recent transmembrane topographic analysis of pNBC1 has shed light on the potential structural determinants that are responsible for ion permeation through the cotransporter. The experimentally difficult problem of determining the nature of anionic species being transported by these proteins (HCO(3)(-) versus CO(3)(2-)) is analyzed using a theoretical equilibrium thermodynamics approach. Finally, our current understanding of the molecular mechanisms responsible for the regulation of ion coupling and flux through electrogenic sodium bicarbonate cotransporters is reviewed in detail.

Structural determinants and significance of regulation of electrogenic Na(+)-HCO(3)(-) cotransporter stoichiometry

Na(+)-HCO(3)(-) cotransporters play an important role in intracellular pH regulation and transepithelial HCO(3)(-) transport in various tissues. Of the characterized members of the HCO(3)(-) transporter superfamily, NBC1 and NBC4 proteins are known to be electrogenic. An important functional property of electrogenic Na(+)-HCO(3)(-) cotransporters is their HCO(3)(-):Na(+) coupling ratio, which sets the transporter reversal potential and determines the direction of Na(+)-HCO(3)(-) flux. Recent studies have shown that the HCO(3)(-):Na(+) transport stoichiometry of NBC1 proteins is either 2:1 or 3:1 depending on the cell type in which the transporters are expressed, indicating that the HCO(3)(-):Na(+) coupling ratio can be regulated. Mutational analysis has been very helpful in revealing the molecular mechanisms and signaling pathways that modulate the coupling ratio. These studies have demonstrated that PKA-dependent phosphorylation of the COOH terminus of NBC1 proteins alters the transport stoichiometry. This cAMP-dependent signaling pathway provides HCO(3)(-) -transporting epithelia with an efficient mechanism for modulating the direction of Na(+)-HCO(3)(-) flux through the cotransporter.

Localization of the mutation responsible for osteopetrosis in the op rat to a 1.5-cM genetic interval on rat chromosome 10: identification of positional candidate genes by radiation hybrid mapping

Osteopetrosis is caused by a heterogenous group of bone diseases that result in an increase in skeletal mass because of inadequate osteoclastic bone resorption. In the op osteopetrotic rat, the disease has been linked to a single genetic locus located at the proximal end of rat chromosome 10. In this study, we identified a 1.5-cM genetic interval that contains the mutation. We then generated an improved radiation hybrid (RH) map of this region to identify potential functional and positional candidates for the op gene. Using the rat genome radiation hybrid panel, we mapped 57 markers including 24 genes (14 that have not yet been mapped in the rat) and 10 expressed sequence tag markers. Included in the mapped genes are several candidate genes that might significantly influence the biochemical pathways involved in osteopetrosis. These include genes involved in osteoclast differentiation, apoptosis, and the functional capabilities of mature osteoclasts to resorb bone. Further analysis of the genes and expressed transcripts mapped to this region may yield important insights into the multifactorial control of osteoclast function and the mechanisms of failed bone homeostasis in diseases such as osteopetrosis, osteoporosis, and rheumatoid arthritis in which failed bone homeostasis is an instigating or exacerbating circumstance of the disease process.

Analysis of carbonic anhydrase in human red Blood cells using capillary electrophoresis/ electrospray ionization-mass spectrometry

Capillary electrophoresis/electrospray ionization-mass spectrometry (CE/ESI-MS) was applied to the analysis of human red blood cells (RBCs) using the split-flow technique for interfacing CE to MS. By using a long (approximately125-cm) and narrow (approximately 15-microm-i.d.) capillary, the four major proteins of the RBC, which are hemoglobin (Hb, alpha- and beta-chains, 900 amol/chain), carbonic anhydrase I (CAI, approximately 7 amol/cell), and carbonic anhydrase II (CAII, approximately 0.8 amol/cell), were separated from each other and detected at low-attomole levels in one run and minimal sample preparation. Under these conditions, the detection limits for CAI and CAII in lysed RBCs were approximately 20 and approximately 44 amol, respectively. The approximately 20-amol detection limit of CAI was confirmed by the CE/ESI-MS analysis of three intact RBCs that had been drawn into the capillary under a microscope. A shorter capillary (approximately 55 cm long) provided faster analysis time but did not separate CAII from the beta-chain of hemoglobin, causing the CAII signal to be masked by the background chemical noise generated by the approximately 1,000 x molar excess of the beta-chain. Under this condition, the CAII detection limit increased to approximately 500 amol. From three methods of sample introduction (injection of lysed blood, injection of intact cells under microscope, and injection of intact cells suspended in saline solution), injection of lysed blood provided the optimum sensitivity. It was found that a background electrolyte (BGE) containing 0.1% acetic acid in water worked best for the analysis of intact cells, while a BGE containing 0.1% acetic acid in water + acetonitrile (50/50 by volume) worked best for the analysis of lysed blood.

Differential regulation of the carbonic anhydrase II gene expression by hormonal nuclear receptors in monocytic cells: identification of the retinoic acid response element

The Carbonic Anhydrase II (CAII) gene that encodes an enzyme involved in proton production is expressed in several cell types including monocyte/macrophage-derived osteoclasts. We have analyzed the regulation of the chicken CAII promoter/reporter construct by nuclear hormone receptors of the VDR subfamily in HD11 avian macrophages. The CAII expression is stimulated by 1, 25-dihydroxyvitamin D(3) but not by 9-cis retinoic acid and repressed by VDR overexpression due to RXR squelching. It is also stimulated by all-trans retinoic acid only when RARalpha is overexpressed, and is dependent on a RARE located in the distal part of the promoter and bound by RARalpha homodimer. Finally, in macrophages, unlike in erythrocytes, the CAII promoter is unresponsive to thyroid hormone. Our results demonstrate the first retinoic acid response element in the CAII promoter and show that according to cell type, different nuclear receptors of the VDR subfamily can regulate the CAII gene.