Metabolic acidosis up-regulates PTH/PTHrP receptors in UMR 106-01 osteoblast-like cells

The Effects of Acid on Calcium and Phosphate Metabolism

A variety of changes in mineral metabolism aiming to restore acid-base balance occur in acid loading and metabolic acidosis. Phosphate plays a key role in defense against metabolic acidosis, both as an intracellular and extracellular buffer, as well as in the renal excretion of excess acid in the form of urinary titratable acid. The skeleton acts as an extracellular buffer in states of metabolic acidosis, as the bone matrix demineralizes, leading to bone apatite dissolution and the release of phosphate, calcium, carbonate, and citrate into the circulation. The renal handling of calcium, phosphate and citrate is also affected, with resultant hypercalciuria, hyperphosphaturia and hypocitraturia.

Serum Bicarbonate Deficiency in Dogs with Acute and Chronic Kidney Disease

Serum bicarbonate deficiency is a disorder frequently found in human patients with acute (AKI) and chronic (CKD) kidney disease, due to abnormalities in kidney generation and reabsorption of bicarbonate. Although alkali supplementation is usually performed in both humans and veterinary CKD patients, data regarding the frequency of bicarbonate disorders in AKI and CKD dogs are scarce. The aim of the present study is to assess the frequency and the severity of bicarbonate deficiency of dogs affected by AKI, acute chronic kidney disease (ACKD), and CKD, and to investigate its possible association with the IRIS grade/stage as well as with disorders of calcium phosphate metabolism. A retrospective evaluation of the serum biochemical panels of all dogs with diagnoses of AKI, ACKD, and CKD referred to the nephrology and urology service of the Veterinary Teaching Hospital of the University of Pisa, between January 2014 and January 2022, was performed. Bicarbonate deficiency was defined as serum bicarbonate < 22 mmol/L and classified as moderate (between 18 and 22 mmol/L) or severe (<18 mmol/L). Serum bicarbonate deficiency was found in 397/521 dogs (76%), of which 142/397 (36%) showed moderate deficiency, and 255/397 (64%) severe deficiency. Dogs with AKI and ACKD showed a significantly higher frequency of bicarbonate deficiency (p = 0.004) and severe forms compared to CKD dogs (p = 0.02). In AKI and ACKD dogs, a negative linear correlation was found between serum bicarbonate and serum creatinine, urea, and phosphate. The frequency of bicarbonate deficiency was higher in the later stages of the disease in both AKI (p = 0.01), ACKD (p = 0.0003), and CKD dogs (p = 0.009). Dogs with serum CaxP ≥ 70 mg²/dL² showed a higher frequency of bicarbonate deficiency (p = 0.01) and showed severe forms (p = 0.01) compared to dogs with CaxP < 70 mg²/dL². Serum bicarbonate deficiency seems to be a very frequent disorder in both AKI, ACKD, and CKD dogs, with an increasing frequency and severity in more advanced stages of kidney disease. The higher frequency and severity of bicarbonate deficiency in AKI and ACKD may be caused by a more severe and sudden loss of kidney function, or extra-renal factors. Finally, the association between frequency and severity of bicarbonate deficiency and abnormal CaxP may suggest a potential connection between metabolic acidosis and bone mineral disorders.

Effects of diets differing in dietary cation-anion difference and calcium concentration on calcium homeostasis in neutered male sheep

Feeding low dietary cation-anion difference (DCAD) diets is one strategy to prevent milk fever in cows. The mechanism of action, as well as whether the calcium (Ca) supply of such diets combined with this feeding regimen should meet the requirements, is still unclear. Small ruminants are commonly used as models for cows. The goal of the present study was to demonstrate basic effects of DCAD against a background of different Ca supplies in a sheep model. Twenty-three castrated male East Friesian milk sheep, aged 11 to 12 mo, were randomly assigned to 4 different feeding groups. The ration of each group was either high (highDCAD) or low in DCAD (lowDCAD) combined with adequate (nCa) or restricted Ca supply (lowCa). At baseline, serum and urine were collected from all sheep and a peripheral quantitative computed tomography of the left metatarsus was performed. After a 14-d adaptation period to the different diets, the experiment started (d 0). Urine, feces, and serum were collected on d 0, 4, 7, 14, and 22, and peripheral quantitative computed tomography was performed on d 0 and 22. On d 22, the sheep were killed and sampled for functional studies. LowDCAD was significantly associated with lower urine pH, higher urinary Ca excretion, higher ionized Ca in blood, and higher serum Ca concentrations. Blood pH and bone parameters did not differ significantly between groups. It is unclear from which compartment the high amounts of Ca excreted with urine in the lowDCAD groups originated. Interestingly, lowDCAD resulted in higher renal mRNA abundance of parathyroid hormone receptor but unaffected mRNA abundance of Ca transporters. As neither renal abundance of these transporters nor Ca excretion were influenced by dietary Ca supply, our results support the hypothesis that increased urinary Ca observed with low DCAD diets represents a loss rather than an excretion of surplus Ca.

The Role of Diet in Bone and Mineral Metabolism and Secondary Hyperparathyroidism

Bone disorders are a common complication of chronic kidney disease (CKD), obesity and gut malabsorption. Secondary hyperparathyroidism (SHPT) is defined as an appropriate increase in parathyroid hormone (PTH) secretion, driven by either reduced serum calcium or increased phosphate concentrations, due to an underlying condition. The available evidence on the effects of dietary advice on secondary hyperparathyroidism confirms the benefit of a diet characterized by decreased phosphate intake, avoiding low calcium and vitamin D consumption (recommended intakes 1000-1200 mg/day and 400-800 UI/day, respectively). In addition, low protein intake in CKD patients is associated with a better control of SHPT risk factors, although its strength in avoiding hyperphosphatemia and the resulting outcomes are debated, mostly for dialyzed patients. Ultimately, a consensus on the effect of dietary acid loads in the prevention of SHPT is still lacking. In conclusion, a reasonable approach for reducing the risk for secondary hyperparathyroidism is to individualize dietary manipulation based on existing risk factors and concomitant medical conditions. More studies are needed to evaluate long-term outcomes of a balanced diet on the management and prevention of secondary hyperparathyroidism in at-risk patients at.

Association of Pre-ESRD Serum Bicarbonate with Post-ESRD Mortality in Patients with Incident ESRD

BACKGROUND

Serum bicarbonate or total carbon dioxide (CO2) concentrations decline as chronic kidney disease (CKD) progresses and rise after dialysis initiation. While metabolic acidosis accelerates the progression of CKD and is associated with higher mortality among patients with end stage renal disease (ESRD), there are scarce data on the association of CO2 concentrations before ESRD transition with post-ESRD mortality.

METHODS

A historical cohort from the Transition of Care in CKD (TC-CKD) study includes 85,505 veterans who transitioned to ESRD from October 1, 2007, through March 31, 2014. After 1,958 patients without follow-up data, 3 patients with missing date of birth, and 50,889 patients without CO2 6 months prior to ESRD transition were excluded, the study population includes 32,655 patients. Associations between CO2 concentrations averaged over the last 6 months and its rate of decline during the 12 months prior to ESRD transition and post-ESRD all-cause, cardiovascular (CV), and non-CV mortality were examined by using hierarchical adjustment with Cox regression models.

RESULTS

The cohort was on average 68 ± 11 years old and included 29% Black veterans. Baseline concentrations of CO2 were 23 ± 4 mEq/L, and median (interquartile range) change in CO2 were -1.8 [-3.4, -0.2] mEq/L/year. High (≥28 mEq/L) and low (<18 mEq/L) CO2 concentrations showed higher adjusted mortality risk while there was no clear trend in the middle range. Consistent associations were observed irrespective of sodium bicarbonate use. There was also a U-shaped association between the change in CO2 and all-cause, CV, and non-CV mortality with the lowest risk approximately at -2.0 and 0.0 mEq/L/year among sodium bicarbonate nonusers and users, respectively, and the highest mortality was among patients with decline in CO2 >4 mEq/L/year.

CONCLUSION

Both high and low pre-ESRD CO2 levels (≥28 and <18 mEq/L) during 6 months prior to dialysis transition and rate of CO2 decline >4 mEq/L/year during 1 year before dialysis initiation were associated with greater post-ESRD all-cause, CV, and non-CV mortality. Further studies are needed to determine the optimal management of CO2 in patients with advanced CKD stages transitioning to ESRD.

Effect of duration of exposure to diets differing in dietary cation-anion difference on Ca metabolism after a parathyroid hormone challenge in dairy cows

Objectives of the experiment were to determine the length of exposure to an acidogenic diet that would elicit changes in acid-base balance, mineral digestion, and response to parathyroid hormone (PTH)-induced changes in blood Ca and vitamin D₃ in prepartum dairy cows. Nonlactating parous Holstein cows (n = 20) at 242 d of gestation were blocked by lactation (1 or >1) and pretreatment dry matter (DM) intake and, within block, they were randomly assigned to a diet with a dietary cation-anion difference (DCAD) of +200 mEq/kg of DM (DCAD +200) or an acidogenic diet with -150 mEq/kg of DM (DCAD -150). Water and DM intake were measured and blood was sampled daily. Urine was sampled every 3 h for 36 h, and then daily. During PTH challenges on d 3, 8, and 13, cows received i.v. PTH 1-34 fragment at 0.05 µg/kg of body weight every 20 min for 9 h to mimic the pulsatile release of endogenous PTH. Blood was sampled at 0 h, and hourly thereafter until 10 h, and at 12, 18, 24, 36, and 48 h relative to each challenge. Acid-base measures and concentrations of ionized Ca (iCa) in whole blood, and total Ca, Mg, P, and vitamin D metabolites in plasma were evaluated. On d 2 and 7, Ca, Mg, and P balances were evaluated. Cows fed DCAD -150 had smaller blood pH (7.431 vs. 7.389) and HCO₃^- (27.4 vs. 22.8 mM) compared with DCAD +200, and metabolic acidosis in DCAD -150 was observed 24 h after dietary treatments started. Concentrations of iCa begin to increase 24 h after feeding the acidogenic diet, and it was greater in DCAD -150 compared with DCAD +200 by 3 d in the experiment (1.23 vs. 1.26 mM). During the PTH challenges, cows fed DCAD -150 had greater concentration of iCa and area under the curve for iCa than those fed DCAD +200 (48.2 vs. 50.7 mmol/L × hour), and there was no interaction between treatment and challenge day. Concentration of 1,25-dihydroxyvitamin D₃ in plasma did not differ during the PTH challenge, but change in 1,25-dihydroxyvitamin D₃ relative to h 0 of the challenge was smaller in cows fed DCAD -150 than cows fed DCAD +200 (44.1 vs. 32.9 pg/mL). Urinary loss of Ca was greater in cows fed DCAD -150 compared with DCAD +200 (1.8 vs. 10.8 g/d); however, because digestibility of Ca increased in cows fed DCAD -150 (19.7 vs. 36.6%), the amount of Ca retained did not differ between treatments. Diet-induced metabolic acidosis was observed by 24 h after dietary treatment started, resulting in increases in concentration of iCa in blood observed between 1 and 3 d. Collectively, present results indicate that tissue responsiveness to PTH and changes in blood concentrations of iCa and digestibility of Ca are elicited within 3 d of exposure to an acidogenic diet. The increased apparent digestibility of Ca compensated for the increased urinary loss of Ca resulting in similar Ca retention.

Cause and effect of microenvironmental acidosis on bone metastases

Skeletal involvement is a frequent and troublesome complication in advanced cancers. In the process of tumor cells homing to the skeleton to form bone metastases (BM), different mechanisms allow tumor cells to interact with cells of the bone microenvironment and seed in the bone tissue. Among these, tumor acidosis has been directly associated with tumor invasion and aggressiveness in several types of cancer although it has been less explored in the context of BM. In bone, the association of local acidosis and cancer invasiveness is even more important for tumor expansion since the extracellular matrix is formed by both organic and hard inorganic matrices and bone cells are used to sense protons and adapt or react to a low pH to maintain tissue homeostasis. In the BM microenvironment, increased concentration of protons may derive not only from glycolytic tumor cells but also from tumor-induced osteoclasts, the bone-resorbing cells, and may influence the progression or symptoms of BM in many different ways, by directly enhancing cancer cell motility and aggressiveness, or by modulating the functions of bone cells versus a pro-tumorigenic phenotype, or by inducing bone pain. In this review, we will describe and discuss the cause of acidosis in BM, its role in BM microenvironment, and which are the final effectors that may be targeted to treat metastatic patients.

Biased signaling of the proton-sensing receptor OGR1 by benzodiazepines

GPCRs have diverse signaling capabilities, based on their ability to assume various conformations. Moreover, it is now appreciated that certain ligands can promote distinct receptor conformations and thereby bias signaling toward a specific pathway to differentially affect cell function. The recently deorphanized G protein-coupled receptor OGR1 [ovarian cancer G protein-coupled receptor 1 ( GPR68)] exhibits diverse signaling events when stimulated by reductions in extracellular pH. We recently demonstrated airway smooth muscle cells transduce multiple signaling events, reflecting a diverse capacity to couple to multiple G proteins. Moreover, we recently discovered that the benzodiazepine lorazepam, more commonly recognized as an agonist of the γ-aminobutyric acid A (GABAA) receptor, can function as an allosteric modulator of OGR1 and, similarly, can promote multiple signaling events. In this study, we demonstrated that different benzodiazepines exhibit a range of biases for OGR1, with sulazepam selectively activating the canonical Gs of the G protein signaling pathway, in heterologous expression systems, as well as in several primary cell types. These findings highlight the potential power of biased ligand pharmacology for manipulating receptor signaling qualitatively, to preferentially activate pathways that are therapeutically beneficial.-Pera, T., Deshpande, D. A., Ippolito, M., Wang, B., Gavrila, A., Michael, J. V., Nayak, A. P., Tompkins, E., Farrell, E., Kroeze, W. K., Roth, B. L., Panettieri, R. A. Jr Benovic, J. L., An, S. S., Dulin, N. O., Penn, R. B. Biased signaling of the proton-sensing receptor OGR1 by benzodiazepines.

Children and adolescents with cystic fibrosis display moderate bone microarchitecture abnormalities: data from high-resolution peripheral quantitative computed tomography

We investigated whether bone microstructure assessed by high-resolution peripheral quantitative tomography (HR-pQCT) could be altered in children and teenagers with cystic fibrosis (CF). In comparison to their healthy counterparts, bone microstructure was mildly affected at the tibial level only.

INTRODUCTION

Cystic fibrosis-related bone disease (CFBD) may alter bone health, ultimately predisposing patients to bone fractures. Our aim was to assess bone microstructure using high-resolution peripheral quantitative tomography (HR-pQCT) in a cohort of children and teenagers with CF in comparison to age-, puberty-, and gender-matched healthy volunteers (HVs).

METHODS

In this single-center, prospective, cross-sectional study, we evaluated the HR-pQCT bone parameters of CF patients and compared them to those of the healthy volunteers.

RESULTS

At a median age of 15.4 [range, 10.5-17.9] years, 37 CF patients (21 boys) with 91% [range, 46-138%] median forced expiratory volume in 1 s were included. At the ultradistal tibia, CF patients had a smaller bone cross-sectional area (579 [range, 399-1087] mm²) than HVs (655 [range, 445-981] mm²) (p = 0.027), related to a decreased trabecular area, without any significant differences for height. No other differences were found (trabecular number, separation, thickness, or distribution) at the radial or tibial levels. Bone structure was different in patients receiving ursodeoxycholic acid and those bearing two F508del mutations.

CONCLUSION

In our cohort of children and teenagers with good nutritional and lung function status, bone microstructure evaluated with HR-pQCT was not severely affected. Minimal microstructure abnormalities observed at the tibial level may be related to the cystic fibrosis transmembrane conductance regulator defect alone; the long-term consequences of such impairment will require further evaluation.

Acid Load and Phosphorus Homeostasis in CKD

BACKGROUND

The kidneys maintain acid-base homeostasis through excretion of acid as either ammonium or as titratable acids that primarily use phosphate as a buffer. In chronic kidney disease (CKD), ammoniagenesis is impaired, promoting metabolic acidosis. Metabolic acidosis stimulates phosphaturic hormones, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF-23) in vitro, possibly to increase urine titratable acid buffers, but this has not been confirmed in humans. We hypothesized that higher acid load and acidosis would associate with altered phosphorus homeostasis, including higher urinary phosphorus excretion and serum PTH and FGF-23.

STUDY DESIGN

Cross-sectional.

SETTING & PARTICIPANTS

980 participants with CKD enrolled in the Chronic Renal Insufficiency Cohort (CRIC) Study.

PREDICTORS

Net acid excretion as measured in 24-hour urine, potential renal acid load (PRAL) estimated from food frequency questionnaire responses, and serum bicarbonate concentration < 22 mEq/L.

OUTCOME & MEASUREMENTS

24-hour urine phosphorus and calcium excretion and serum phosphorus, FGF-23, and PTH concentrations.

RESULTS

Using linear and log-linear regression adjusted for demographics, kidney function, comorbid conditions, body mass index, diuretic use, and 24-hour urine creatinine excretion, we found that 24-hour urine phosphorus excretion was higher at higher net acid excretion, higher PRAL, and lower serum bicarbonate concentration (each P<0.05). Serum phosphorus concentration was also higher with higher net acid excretion and lower serum bicarbonate concentration (each P=0.001). Only higher net acid excretion associated with higher 24-hour urine calcium excretion (P<0.001). Neither net acid excretion nor PRAL was associated with FGF-23 or PTH concentrations. PTH, but not FGF-23, concentration (P=0.2) was 26% (95% CI, 13%-40%) higher in participants with a serum bicarbonate concentration <22 versus ≥22 mEq/L (P<0.001). Primary results were similar if stratified by estimated glomerular filtration rate categories or adjusted for iothalamate glomerular filtration rate (n=359), total energy intake, dietary phosphorus, or urine urea nitrogen excretion, when available.

LIMITATIONS

Possible residual confounding by kidney function or nutrition; urine phosphorus excretion was included in calculation of the titratable acid component of net acid excretion.

CONCLUSIONS

In CKD, higher acid load and acidosis associate independently with increased circulating phosphorus concentration and augmented phosphaturia, but not consistently with FGF-23 or PTH concentrations. This may be an adaptation that increases titratable acid excretion and thus helps maintain acid-base homeostasis in CKD. Understanding whether administration of base can lower phosphorus concentrations requires testing in interventional trials.

Risk factors associated with secondary hyperparathyroidism in patients with chronic kidney disease

Secondary hyperparathyroidism (SHPT) is common in patients with chronic kidney disease (CKD), and its development and progression are affected by various factors. The aim of the present study was to identify the risk factors for SHPT in patients with CKD. A retrospective study was performed in 498 patients (305 males and 193 females) with CKD, observed in the The First Hospital of Jilin University between January 2008 and December 2012. The demographic, clinical and laboratory data were collected. Patients were divided into the SHPT group (n=424) with elevated serum parathyroid hormone (PTH) expression levels and the control group (n=74) with normal serum PTH expression levels. Univariate and multivariate regression analyses were employed to explore the risk factors for SHPT. Serum PTH expression levels in women with CKD were significantly higher than in men (P=0.047). Serum PTH expression levels were positively correlated with the expression levels of serum creatinine (P<0.01), phosphorus (P<0.01), C-reactive protein (P<0.05), triglyceride (P<0.05), cholesterol (P<0.05) and low-density lipoprotein cholesterol (P<0.05), but were negatively correlated with the expression levels of hemoglobin (P<0.05), calcium (P<0.01) and CO₂ combining power (P<0.01) in patients with CKD. Multivariate analysis showed that the serum expression levels of creatinine [µmol/l; odds radio (OR), 1.003; 95% confidence interval (CI), 1.002-1.004; P=0.001] and phosphorus (mmol/l; OR, 2.19; 95% CI, 1.254-3.826; P=0.006) in patients with CKD significantly influenced serum PTH expression levels. The SHPT risk factors include female gender, low calcium, high phosphorus, acidosis, anemia, hypertension, hyperlipidemia and micro-inflammation, with blood phosphorus and creatinine being independent risk factors.

Current status of bicarbonate in CKD

Metabolic acidosis was one of the earliest complications to be recognized and explained pathologically in patients with CKD. Despite the accumulated evidence of deleterious effects of acidosis, treatment of acidosis has been tested very little, especially with respect to standard clinical outcomes. On the basis of fundamental research and small alkali supplementation trials, correcting metabolic acidosis has a strikingly broad array of potential benefits. This review summarizes the published evidence on the association between serum bicarbonate and clinical outcomes. We discuss the role of alkali supplementation in CKD as it relates to retarding kidney disease progression, improving metabolic and musculoskeletal complications.

Causal assessment of dietary acid load and bone disease: a systematic review & meta-analysis applying Hill's epidemiologic criteria for causality

Background

Modern diets have been suggested to increase systemic acid load and net acid excretion. In response, alkaline diets and products are marketed to avoid or counteract this acid, help the body regulate its pH to prevent and cure disease. The objective of this systematic review was to evaluate causal relationships between dietary acid load and osteoporosis using Hill's criteria.

Methods

Systematic review and meta-analysis. We systematically searched published literature for randomized intervention trials, prospective cohort studies, and meta-analyses of the acid-ash or acid-base diet hypothesis with bone-related outcomes, in which the diet acid load was altered, or an alkaline diet or alkaline salts were provided, to healthy human adults. Cellular mechanism studies were also systematically examined.

Results

Fifty-five of 238 studies met the inclusion criteria: 22 randomized interventions, 2 meta-analyses, and 11 prospective observational studies of bone health outcomes including: urine calcium excretion, calcium balance or retention, changes of bone mineral density, or fractures, among healthy adults in which acid and/or alkaline intakes were manipulated or observed through foods or supplements; and 19 in vitro cell studies which examined the hypothesized mechanism. Urine calcium excretion rates were consistent with osteoporosis development; however calcium balance studies did not demonstrate loss of whole body calcium with higher net acid excretion. Several weaknesses regarding the acid-ash hypothesis were uncovered: No intervention studies provided direct evidence of osteoporosis progression (fragility fractures, or bone strength as measured using biopsy). The supporting prospective cohort studies were not controlled regarding important osteoporosis risk factors including: weight loss during follow-up, family history of osteoporosis, baseline bone mineral density, and estrogen status. No study revealed a biologic mechanism functioning at physiological pH. Finally, randomized studies did not provide evidence for an adverse role of phosphate, milk, and grain foods in osteoporosis.

Conclusions

A causal association between dietary acid load and osteoporotic bone disease is not supported by evidence and there is no evidence that an alkaline diet is protective of bone health.

Metabolic acidosis lowers circulating adiponectin through inhibition of adiponectin gene transcription

BACKGROUND

Metabolic acidosis (MA) adversely affects protein and lipid metabolism as well as endocrine function. Adipose tissue communicates with the rest of the body through synthesis and release adipokines, such as leptin, adiponectin and TNF-alpha. Adiponectin enhances insulin sensitivity and possesses anti-atherogenic and anti-inflammatory properties. Circulating adiponectin correlates inversely with cardiovascular events. It is possible that MA negatively regulates adiponectin contributing to poor patient outcome. The present study investigates the effect of MA on adiponectin in vivo and in vitro.

METHODS

Twenty healthy female volunteers underwent a 7-day course of oral ammonium chloride (NH4Cl)-induced acidosis. Serum adiponectin was determined before and after NH4Cl ingestion. Adipocytes were differentiated from their precursors, human mesenchymal stem cells (hMSCs), in culture. Concentrated HCl was added to the media to lower pH. Adiponectin mRNA and protein were determined at 48 and 96 h by real-time RT-PCR and ELISA, respectively.

RESULTS

After a 7-day course of NH4Cl, serum bicarbonate decreased significantly associated with the increase in urine ammonium and titratable acid. Adiponectin decreased significantly from 10,623 to 9723 pg/mL (P<0.005). MA suppressed adiponectin mRNA in hMSC-derived adipocytes at 48 and 96 h (P<0.01). The amount of adiponectin released into the culture media declined corresponding to the mRNA levels (P<0.001). MA did not affect adipocyte triglyceride or protein content.

CONCLUSIONS

MA lowered circulating adiponectin through inhibition of adiponectin gene transcription in adipocytes.

Early acceleration phase and late stationary phase of remodeling imbalance in long bones of male rats exposed to long-standing acidemia: a 10-month longitudinal study using bone histomorphometry

Chronic metabolic acidosis (CMA) is known to have a detrimental effect on bone metabolism as a result of accelerated bone resorption and impaired bone formation. Typically, a number of compensatory adaptations must have occurred which may help palliate negative calcium balance and acidemia, e.g., increased intestinal calcium and phosphorus absorption. The final outcome with respect to bone remodeling after exposure to CMA for several months was, therefore, elusive. Herein, we investigated bone changes in male rats fed 1.5% NH(4)Cl in drinking water for up to 10 months to induce CMA with plasma pH of 7.2-7.3. Significant decreases in bone mineral density and content were detected by dual-energy X-ray absorptiometry after 6 months of CMA, whereas histomorphometric analysis revealed a significant decrease in bone volume already at week 2 after CMA induction. Exposure to CMA longer than 2 weeks also decreased trabecular number, trabecular thickness, osteoblast surface, mineral apposition rate, and bone formation rate, while increasing trabecular separation, osteoclast surface, and eroded surface. Bone resorption was rapid during weeks 2-16 (acceleration phase) and thereafter persisted at a slower rate (stationary phase) until week 40. Furthermore, CMA markedly reduced the total calcium content in bone and enhanced urinary calcium excretion as measured by atomic absorption spectrophotometry. It could be concluded that, after exposure to a long-standing acidemia, the enhanced bone resorption and suppressed bone formation led to osteopenia throughout the 10-month period, with accelerated bone loss seen only during the first 6 months. Thereafter, the compensatory adaptations appeared to help stabilize bone mass at a subnormal level.

miR-8 microRNAs regulate the response to osmotic stress in zebrafish embryos

MicroRNAs (miRNAs) are highly conserved small RNAs that act as translational regulators of gene expression, exerting their influence by selectively targeting mRNAs bearing complementary sequence elements. These RNAs function in diverse aspects of animal development and physiology. Because of an ability to act as rapid responders at the level of translation, miRNAs may also influence stress response. In this study, we show that the miR-8 family of miRNAs regulates osmoregulation in zebrafish embryos. Ionocytes, which are a specialized cell type scattered throughout the epidermis, are responsible for pH and ion homeostasis during early development before gill formation. The highly conserved miR-8 family is expressed in ionocytes and enables precise control of ion transport by modulating the expression of Nherf1, which is a regulator of apical trafficking of transmembrane ion transporters. Ultimately, disruption of miR-8 family member function leads to an inability to respond to osmotic stress and blocks the ability to properly traffic and/or cluster transmembrane glycoproteins at the apical surface of ionocytes.

Formulations for intermittent release of parathyroid hormone (1-34) and local enhancement of osteoblast activities

The objective of these studies was to develop simple, implantable devices that intermittently release PTH(1-34) and thus could be used for locally stimulating bone formation. The formulations were based on the association polymer system of cellulose acetate phthalate and Pluronic F-127. Release profiles for intermittent devices showed five discrete peaks, whereas sustained devices exhibited zero-order kinetics. Osteoblastic activity was greater for cells intermittently treated with PTH(1-34) compared to sustained exposure. These controlled release devices delivering PTH(1-34) in an intermittent manner may be useful for affecting osteoblast activities in a localized area.

Alternating release of different bioactive molecules from a complexation polymer system

Regeneration of bone is driven by the action of numerous biomolecules. However, most osteobiologic devices mainly depend on delivery of a single molecule. The present studies were directed at investigating a polymeric system that enables localized, alternating delivery of two or more biomolecules. The osteotropic biomolecules studied were simvastatin hydroxyacid (Sim) and parathyroid hormone (1-34) (PTH(1-34)), and the antimicrobial peptide cecropin B (CB) was also incorporated. Loaded microspheres were made using the complexation polymer system of cellulose acetate phthalate and Pluronic F-127 (blend ratio, 7:3). By alternating layers of the different types of microspheres, 10-layer devices were made to release CB and Sim, CB and PTH, or Sim and PTH. In vitro experiments showed five discrete peaks for each molecule over a release period of approximately two weeks. MC3T3-E1 osteoblastic cells alternately exposed to the osteotropic biomolecules showed enhanced proliferation and early osteoblastic activity. Alternating delivery of 10nm Sim and either 500pg/ml or 5ng/ml PTH showed additive effects compared to the CB/Sim or CB/PTH devices. These implantable formulations may be useful for alternating delivery of different biomolecules to stimulate concurrent biological effects in focal tissue regeneration applications.

Chronic metabolic acidosis alters osteoblast differentiation from human mesenchymal stem cells

Bone histology of distal renal tubular acidosis patients showed decreased bone formation with impaired bone matrix mineralization that is not entirely explained by an alteration in the mineral balance. Data from in vitro studies suggests a direct inhibitory effect of metabolic acidosis on osteoblast function. We investigated the effects of chronic metabolic acidosis on osteoblast differentiation from mesenchymal stem cells (MSCs). Human MSCs were allowed to differentiate into osteoblasts in culture. Concentrated hydrochloric acid was added to the medium to lower the bicarbonate concentration and pH. The expression of various osteoblastic genes and proteins and bone matrix mineralization were examined. Chronic metabolic acidosis enhanced the messenger RNA (mRNA) and protein expression of early osteoblast transcription factor, runx-2, whereas inhibiting osterix and having no effect on ATF-4. The expression of type I collagen, the most abundant bone matrix protein, was increased following the same pattern of runx-2. Likewise, metabolic acidosis slightly enhanced the expression of mature osteoblastic gene, osteocalcin. Study on mineralization revealed suppressed alkaline phosphatase mRNA and enzyme activity. Despite the augmented collagen deposit in acidic culture, bone matrix mineralization was impaired. In conclusion, chronic metabolic acidosis alters osteoblast differentiation from MSCs through its diverse effect on osteoblastic genes and proteins resulting in an impairment of bone formation.

Overcoming physiologic barriers to cancer treatment by molecularly targeting the tumor microenvironment

It is widely recognized that the vasculature of the tumor is inadequate to meet the demands of the growing mass. The malformed vasculature is at least in part responsible for regions of the tumor that are hypoxic, acidotic, and exposed to increased interstitial fluid pressure. These unique aspects of the tumor microenvironment have been shown to act as barriers to conventional chemotherapy or radiation-based therapies. It now seems that while the vasculature initiates these tumor-specific conditions, the cells within the tumor respond to these stresses and add to the unique solid tumor physiology. Gene expression changes have been reported in the tumor for vascular endothelial growth factor, carbonic anhydrase IX, and pyruvate dehydrogenase kinase 1. The activity of these gene products then influences the tumor physiology through alterations in vascular permeability and interstitial fluid pressure, extracellular acidosis, and mitochondrial oxygen consumption and hypoxia, respectively. Novel molecular strategies designed to interfere with the activities of these gene products are being devised as ways to overcome the physiologic barriers in the tumor to standard anticancer therapies.

Increased osteoblastic activity and expression of receptor activator of NF-kappaB ligand in nonuremic nephrotic syndrome

Patients with nephrotic syndrome (NS), even with normal GFR, often display altered mineral homeostasis and abnormal bone histology. However, the latter, mostly osteomalacia and increased bone resorption, cannot be readily explained by the prevalent concentrations of parathyroid hormone and vitamin D metabolites. The transmembrane receptor activator of NF-kappaB ligand (RANKL) of osteoblasts is essential for osteoclast formation and differentiation. Osteoblasts activity and the expression of RANKL were tested in cultures of normal human osteoblasts with sera obtained from patients with NS and normal GFR (129 +/- 26 ml/min per 1.73 m2) during relapse and remission of their NS. Osteoblasts that were cultured in vitro with sera during relapse displayed elevated concentrations of alkaline phosphatase (AP) and increased expression of RANKL. By contrast, during remission, AP concentrations were significantly lower (P < 0.05) and RANKL expression notably attenuated or absent. AP correlated with the proteinuria (r = 0.5, P < 0.05) and was not significantly affected by the therapeutic administration of corticosteroids. Whereas parathyroid hormone levels were normal (35 +/- 21 pg/ml), the serum markers of bone formation (osteocalcin and bone-specific alkaline phosphatase) were lower during relapse compared with remission. Thus, sera from patients with NS and normal GFR stimulate the activity of osteoblasts and upregulate their expression of RANKL. These alterations, more prominent during clinically active NS, are transient and reversible upon remission. These disturbances of bone biology may play an important pathogenic role in the abnormal bone histology observed in patients with NS even before a decline in GFR occurs.

Metabolic acidosis in maintenance dialysis patients: clinical considerations

Metabolic acidosis in maintenance dialysis patients: Clinical considerations. Metabolic acidosis is a common consequence of advanced chronic renal failure (CRF) and maintenance dialysis (MD) therapies are not infrequently unable to completely correct the base deficit. In MD patients, severe metabolic acidosis is associated with an increased relative risk for death. The chronic metabolic acidosis of the severity commonly encountered in patients with advanced CRF has two well-recognized major systemic consequences. First, metabolic acidosis induces net negative nitrogen and total body protein balance, which improves upon bicarbonate supplementation. The data suggest that metabolic acidosis is both catabolic and antianabolic. Emerging data also indicate that metabolic acidosis may be one of the triggers for chronic inflammation, which may in turn promote protein catabolism among MD patients. In contrast to these findings, metabolic acidosis may be associated with a decrease in hyperleptinemia associated with CRF. Several studies have shown that correction of metabolic acidosis among MD patients is associated with modest improvements in the nutritional status. Second, metabolic acidosis has several effects on bone, causing physicochemical dissolution of bone and cell-mediated bone resorption (inhibition of osteoblast and stimulation of osteoclast function). Metabolic acidosis is probably also associated with worsening of secondary hyperparathyroidism. Data on the effect of correction of metabolic acidosis on renal osteodystrophy, however, are limited. Preliminary evidence suggest that metabolic acidosis may play a role in beta2-microglobulin accumulation, as well as the hypertriglyceridemia seen in renal failure. Given the body of evidence pointing to the several systemic consequences of metabolic acidosis, a more aggressive approach to the correction of metabolic acidosis is proposed.

Role of acidosis-induced increases in calcium on PTH secretion in acute metabolic and respiratory acidosis in the dog

Recently, we showed that both acute metabolic acidosis and respiratory acidosis stimulate parathyroid hormone (PTH) secretion in the dog. To evaluate the specific effect of acidosis, ionized calcium (iCa) was clamped at a normal value. Because iCa values normally increase during acute acidosis, we now have studied the PTH response to acute metabolic and respiratory acidosis in dogs in which the iCa concentration was allowed to increase (nonclamped) compared with dogs with a normal iCa concentration (clamped). Five groups of dogs were studied: control, metabolic (clamped and nonclamped), and respiratory (clamped and nonclamped) acidosis. Metabolic (HCl infusion) and respiratory (hypoventilation) acidosis was progressively induced during 60 min. In the two clamped groups, iCa was maintained at a normal value with an EDTA infusion. Both metabolic and respiratory acidosis increased (P < 0.05) iCa values in nonclamped groups. In metabolic acidosis, the increase in iCa was progressive and greater (P < 0.05) than in respiratory acidosis, in which iCa increased by 0.04 mM and then remained constant despite further pH reductions. The increase in PTH values was greater (P < 0.05) in clamped than in nonclamped groups (metabolic and respiratory acidosis). In the nonclamped metabolic acidosis group, PTH values first increased and then decreased from peak values when iCa increased by > 0.1 mM. In the nonclamped respiratory acidosis group, PTH values exceeded (P < 0.05) baseline values only after iCa values stopped increasing at a pH of 7.30. For the same increase in iCa in the nonclamped groups, PTH values increased more in metabolic acidosis. In conclusion, 1) both metabolic acidosis and respiratory acidosis stimulate PTH secretion; 2) the physiological increase in the iCa concentration during the induction of metabolic and respiratory acidosis reduces the magnitude of the PTH increase; 3) in metabolic acidosis, the increase in the iCa concentration can be of sufficient magnitude to reverse the increase in PTH values; and 4) for the same degree of acidosis-induced hypercalcemia, the increase in PTH values is greater in metabolic than in respiratory acidosis.