Metabolic aspects of the regulation of systemic pH

Static and Dynamic Biomaterial Engineering for Cell Modulation

In the biological microenvironment, cells are surrounded by an extracellular matrix (ECM), with which they dynamically interact during various biological processes. Specifically, the physical and chemical properties of the ECM work cooperatively to influence the behavior and fate of cells directly and indirectly, which invokes various physiological responses in the body. Hence, efficient strategies to modulate cellular responses for a specific purpose have become important for various scientific fields such as biology, pharmacy, and medicine. Among many approaches, the utilization of biomaterials has been studied the most because they can be meticulously engineered to mimic cellular modulatory behavior. For such careful engineering, studies on physical modulation (e.g., ECM topography, stiffness, and wettability) and chemical manipulation (e.g., composition and soluble and surface biosignals) have been actively conducted. At present, the scope of research is being shifted from static (considering only the initial environment and the effects of each element) to biomimetic dynamic (including the concepts of time and gradient) modulation in both physical and chemical manipulations. This review provides an overall perspective on how the static and dynamic biomaterials are actively engineered to modulate targeted cellular responses while highlighting the importance and advance from static modulation to biomimetic dynamic modulation for biomedical applications.

Initial Blood Ammonia Level Is a Useful Prognostication Tool in Out-of-Hospital Cardiac Arrest - Multicenter Prospective Study (SOS-KANTO 2012 Study)

BACKGROUND

Initial blood ammonia level is associated with neurologic outcomes in out-of-hospital cardiac arrest (OHCA). We tested the usefulness of blood ammonia for prediction of long-term neurological outcome of OHCA.Methods and Results:A total of 3,011 hospitalized adult OHCA patients were enrolled. Blood samples were obtained at the ED. Cut-offs (ammonia <100 μmol/L and lactate <12 mmol/L) were determined in a previous study. Neurological outcomes in survivors were assessed at 3 months. A logistic regression model with adjustment for within-hospital clustering and other risk factors was used to evaluate the association between biomarkers and outcomes. Of 3,011 patients, 380 (13.8%) had favorable neurological outcomes. Ammonia and lactate predicted neurological outcome with an AUC of 0.80 (95% CI: 0.76-0.84) and 0.77 (95% CI: 0.72-0.82), respectively. Adjusted OR for ammonia <100 μmol/L (4.55; 95% CI: 2.67-7.81) was higher than that for lactate <12 mmol/L (2.63; 95% CI: 1.61-4.28) and most other risk factors, such as cardiac etiology (3.47; 95% CI: 2.55-4.72), age<80 years (3.16; 95% CI: 2.17-4.61), bystander CPR (2.39; 95% CI: 1.70-3.38), and initial rhythm shockable (1.66; 95% CI: 1.16-2.37). The combination of ammonia and lactate had an increased predictive value (AUC, 0.86; 95% CI: 0.85-0.87) compared with that without biomarkers (AUC, 0.81; 95% CI: 0.80-0.82).

CONCLUSIONS

Initial blood ammonia level is as useful as other traditional prognostic indicators such as lactate. Measurement of both initial blood ammonia and lactate helped accurately predict neurological outcomes after OHCA.

SIRT5 regulation of ammonia-induced autophagy and mitophagy

In liver the mitochondrial sirtuin, SIRT5, controls ammonia detoxification by regulating CPS1, the first enzyme of the urea cycle. However, while SIRT5 is ubiquitously expressed, urea cycle and CPS1 are only present in the liver and, to a minor extent, in the kidney. To address the possibility that SIRT5 is involved in ammonia production also in nonliver cells, clones of human breast cancer cell lines MDA-MB-231 and mouse myoblast C2C12, overexpressing or silenced for SIRT5 were produced. Our results show that ammonia production increased in SIRT5-silenced and decreased in SIRT5-overexpressing cells. We also obtained the same ammonia increase when using a new specific inhibitor of SIRT5 called MC3482. SIRT5 regulates ammonia production by controlling glutamine metabolism. In fact, in the mitochondria, glutamine is transformed in glutamate by the enzyme glutaminase, a reaction producing ammonia. We found that SIRT5 and glutaminase coimmunoprecipitated and that SIRT5 inhibition resulted in an increased succinylation of glutaminase. We next determined that autophagy and mitophagy were increased by ammonia by measuring autophagic proteolysis of long-lived proteins, increase of autophagy markers MAP1LC3B, GABARAP, and GABARAPL2, mitophagy markers BNIP3 and the PINK1-PARK2 system as well as mitochondrial morphology and dynamics. We observed that autophagy and mitophagy increased in SIRT5-silenced cells and in WT cells treated with MC3482 and decreased in SIRT5-overexpressing cells. Moreover, glutaminase inhibition or glutamine withdrawal completely prevented autophagy. In conclusion we propose that the role of SIRT5 in nonliver cells is to regulate ammonia production and ammonia-induced autophagy by regulating glutamine metabolism.

Juvenile king scallop, Pecten maximus, is potentially tolerant to low levels of ocean acidification when food is unrestricted

The decline in ocean water pH and changes in carbonate saturation states through anthropogenically mediated increases in atmospheric CO₂ levels may pose a hazard to marine organisms. This may be particularly acute for those species reliant on calcareous structures like shells and exoskeletons. This is of particular concern in the case of valuable commercially exploited species such as the king scallop, Pecten maximus. In this study we investigated the effects on oxygen consumption, clearance rates and cellular turnover in juvenile P. maximus following 3 months laboratory exposure to four pCO₂ treatments (290, 380, 750 and 1140 µatm). None of the exposure levels were found to have significant effect on the clearance rates, respiration rates, condition index or cellular turnover (RNA: DNA) of individuals. While it is clear that some life stages of marine bivalves appear susceptible to future levels of ocean acidification, particularly under food limiting conditions, the results from this study suggest that where food is in abundance, bivalves like juvenile P. maximus may display a tolerance to limited changes in seawater chemistry.

The multi-systemic nature of diabetes mellitus: Genotype or phenotype?

BACKGROUND

This article discusses factors which materially influence the diagnosis, prevention and treatment of diabetes mellitus but which may be overlooked by the prevailing biomedical paradigm. That cognition can be mathematically linked to the function of the autonomic nervous system and physiological systems casts new light upon the mechanisms responsible for homeostasis and origins of disease. In particular, it highlights the limitations of the reductionist biomedical approach which considers mainly the biochemistry of single pathologies rather than considering the neural mechanisms which regulate the function of physiological systems, and inherent visceral organs; and which are subsequently manifest as biochemistries of varying degrees of complexity and severity. As a consequence, histopathological tests are fraught with inherent limitations and many categories of drugs are significantly ineffective.

AIMS

Such limitations may be explained if disease (in particular diabetes mellitus) has multiple origins, is multi-systemic in nature and, depending upon the characteristics of each pathology, is influenced by genotype and/or phenotype.

RESULTS

This article highlights the influence of factors which are not yet considered re. the aetiology of diabetes mellitus e.g. the influence of light and sensory input upon the stability of the autonomic nervous system; the influence of raised plasma viscosity upon rates of reaction; the influence of viruses and/or of modified live viruses given in vaccinations; systemic instability, in particular the adverse influence of drinks and lack of exercise upon the body's prevailing pH and its subsequent influence upon levels of magnesium and other essential trace elements.

CONCLUSIONS

This application of the top-down systems biology approach may provide a plausible and inclusive explanation for the nature and occurrence of diabetes mellitus.

Food mineral composition and acid-base balance in preterm infants

BACKGROUND

Due to a transient age-related low renal capacity for net acid excretion, preterm infants fed formula are at a considerable risk of spontaneously developing incipient late metabolic acidosis, clinically characterized by e.g., disturbed bone mineralization and impaired growth.

AIM OF THE STUDY

From acid-base data in blood and urine under different diets of modified human milk or preterm formulas is attempted to explore the impact of food mineral (and protein) composition on renal regulation and systemic acid-base balance in preterm infants.

PATIENTS AND METHODS

Data were collected from 48 infants fed their own mother's milk (28 native human milk, 20 enriched with fortifier) and 34 patients on formula (23 on a standard batch, 11 on a modified batch with reduced acid load). Intake of food was measured and acid-base data were determined in blood and timed-urine (8-12 h) samples.

RESULTS

Differences in mineral composition of the diets led to considerable differences of daily "alkali-intake", without significant effects on non-respiratory (base excess, BE) and respiratory (PCO(2)) acid-base data in the blood. In contrast, a highly significant proportionality between individual dietary alkali intake and daily renal base (Na(+) + K(+)-Cl(-)) excretion was observed (y = 0.32x-0.70, n = 80, r = 0.77, P < 0.0001), irrespective of the type of the diet.

CONCLUSION

Renal base saving mechanisms are normally effective in preterm infants to compensate for differences in dietary acid-base load. Generally, nutritional acid-base challenges can be judged much earlier and more safely by urinary than by blood acid-base analysis. Taking into account the age specific low capacity for renal NAE, the relatively high nutritional acid load of preterm standard formula should be reduced.

Clinical review: Renal tubular acidosis--a physicochemical approach

The Canadian physiologist PA Stewart advanced the theory that the proton concentration, and hence pH, in any compartment is dependent on the charges of fully ionized and partly ionized species, and on the prevailing CO₂ tension, all of which he dubbed independent variables. Because the kidneys regulate the concentrations of the most important fully ionized species ([K⁺], [Na⁺], and [Cl^-]) but neither CO₂ nor weak acids, the implication is that it should be possible to ascertain the renal contribution to acid–base homeostasis based on the excretion of these ions. One further corollary of Stewart's theory is that, because pH is solely dependent on the named independent variables, transport of protons to and from a compartment by itself will not influence pH. This is apparently in great contrast to models of proton pumps and bicarbonate transporters currently being examined in great molecular detail. Failure of these pumps and cotransporters is at the root of disorders called renal tubular acidoses. The unquestionable relation between malfunction of proton transporters and renal tubular acidosis represents a problem for Stewart theory. This review shows that the dilemma for Stewart theory is only apparent because transport of acid–base equivalents is accompanied by electrolytes. We suggest that Stewart theory may lead to new questions that must be investigated experimentally. Also, recent evidence from physiology that pH may not regulate acid–base transport is in accordance with the concepts presented by Stewart.

Food mineral composition and acid-base balance in rabbits

BACKGROUND

Alkali-rich diets are often recommended in human medicine to prevent the pathological consequences of nutritional acid load in conditions of impaired renal function.

AIM OF THE STUDY

This study was undertaken in rabbits as common laboratory animals for basic medical research to explore the impact of high versus low dietary alkali intake on systemic acid-base balance and renal control in a typical herbivore.

METHODS

Male rabbits (2.3-4.8 kg) were kept in a metabolism cage. The 24h urine and arterial blood samples were analysed for acid-base data. The metabolic CO2 production was measured to calculate alveolar ventilation. Three randomized groups of animals were fed ad libitum with rabbit chow providing sufficient energy but variable alkali load, assessed by the ashes' cation-anion difference.

RESULTS

The average daily nutritional alkali load (+/- SEM) was 67.1 +/- 2.2 mEq x kg(-1) (N = 58) in the group on high, 45.4 +/- 2.5 mEq x kg(-1) (N = 31) in the group on normal and 1.7 +/- 0.5 mEq x kg(-1) (N = 11) in the group on low alkali food. Respective mean arterial base excess values (BE) were 1.4 +/- 0.3 mM, 0.3 +/- 0.4 mM and 0.0 +/- 0.3 mM, being significantly higher on high alkali food (P < 0.05) than in the other groups. Arterial PCO2, alveolar ventilation and metabolic CO2 production were not significantly different between groups. On normal and high-alkali chow, an alkaline urine (pH(u) > 8.0) with 18-20 mmol x kg(-1) bicarbonate/carbonate was excreted daily, typically containing an insoluble precipitate of 35-60% carbonate. On low-alkali diet, the mean pH(u) decreased to 6.26 +/- 0.14, due to a strong reduction of daily excreted soluble bicarbonate and precipitated carbonate to 1.2 +/- 0.6 and 0.7 +/- 0.2 mmol x kg(-1), respectively. Thereby, nearly complete fractional base reabsorption of 97.8 +/- 0.7 % was reached.

CONCLUSION

Herbivore nutritional alkali-load elicited large rates of renal base excretion including precipitates, to which the urinary tract of the rabbits appeared to be adapted. Dietary base variations were more accurately reflected in the urine than by the blood acid-base status. A strongly base-deficient diet exerted maximum impact on renal base saving mechanisms, implying a critical precondition for growing susceptibility to metabolic acidosis also in the rabbit.

Ureagenesis: evidence for a lack of hepatic regulation of acid-base equilibrium in humans

Ureagenesis in the liver consumes up to 1,000 mmol of HCO3-/day in humans as a result of 2NH4+ + 2HCO3- --> urea + CO2 + 3H2O. Whether the liver contributes to the regulation of acid-base equilibrium by controlling the rate of ureagenesis and, therefore, HCO3- consumption in response to changes in plasma acidity has not been adequately evaluated in humans. Rates of ureagenesis were measured in eight healthy volunteers during control, chronic metabolic acidosis (induced by oral administration of CaCl2 3.2 mmol.kg body wt-1.day-1 for 11 days), and recovery as well as during bicarbonate infusion (200 mmol over 240 min; acute metabolic alkalosis). Rates of ureagenesis were correlated negatively with plasma HCO3- concentration both during adaption to metabolic acidosis and during the chronic, steady-state phase. Thus ureagenesis, an acidifying process, increased rather than decreased in metabolic acidosis. During bicarbonate infusion, rates of ureagenesis decreased significantly. Thus ureagenesis did not appear to be involved in the regulated elimination of excess HCO3-. The finding of a negative correlation between ureagenesis and plasma HCO3- concentration over a wide range of HCO3- concentrations, altered both chronically and acutely, suggests that the ureagenic process per se is maladaptive for acid-base regulation and that ureagenesis has no discernible homeostatic effect on acid-base equilibrium.

NH4+ metabolism and the intracellular pH in isolated perfused rat liver

The effects of NH4+ on the intracellular pH (pHi) and on the ATP content in isolated perfused rat liver were studied by 31P n.m.r. spectroscopy. In the initial phase of perfusion an average pHi of 7.29 +/- 0.04 was estimated. The presence of low (0.5 mmol/l) and high (10 mmol/l) doses of NH4Cl induced significant intracellular acidification by -0.06 +/- 0.03 and -0.11 +/- 0.03 pH unit respectively. This effect was in contrast with the transient intracellular alkalinization observed in preliminary studies on isolated hepatocytes, which was caused by a passive entry of NH3 by non-ionic diffusion and subsequent conversion into NH4+. During application of 0.5 mmol/l NH4Cl the liver released 0.54 +/- 0.06 mumol of urea/min per g into the perfusate. When the intracellular availability of HCO3- was decreased by acetazolamide (0.5 mmol/l) or by removal of HCO3- from the perfusion medium, the decrease in pHi by NH4Cl application was significantly lower than under control conditions. Furthermore, synthesis of urea was significantly inhibited by the decrease in intracellular HCO3-. Under these conditions, 10 mmol/l NH4Cl caused the transient alkalinization that was expected because of the passive uptake of uncharged NH3. Therefore, it is concluded that the intracellular acidification induced by NH4Cl is caused by the continuous utilization of intracellular HCO3- via the synthesis of urea. This metabolic effect on pHi dominates the effects of passive NH3 entry. The rate of urea formation depends on continuous efflux of H+, which is strictly limiting the degree of intracellular acidification within a small range. If the extrusion of H+ by the Na+/H+ exchanger was inhibited by amiloride (0.5 mmol/l) during the NH4Cl application, the decrease in pHi was amplified and the formation of urea was significantly inhibited. The application of NH4Cl at 0.5 or 10 mmol/l decreased the ATP content by 11% or 22% respectively.

Substrate and pH effects on glutamine synthesis in rat liver. Consequences for acid-base regulation

Switching in acidosis of hepatic nitrogen disposal from urea synthesis to NH4+ and net glutamine production was demonstrated in the isolated perfused livers of starved male Wistar rats. Lactate was preferred to glucose as the substrate for the carbon skeleton of glutamine synthesized over the pH range 6.9-7.5. This is necessary if the switch away from a proton-producing process (ureagenesis) in acidosis is to constitute an acid-base regulating system intrinsic to the liver. Glutamine balance shifted with pH from marked net uptake to small net output under acidotic conditions (pH 7.5-6.9), an effect due solely to a decrease in glutamine uptake. NH4+ uptake by the liver had a linear relationship with pH, being markedly decreased in acidosis because glutamine synthesis was insufficient to compensate for the decreased incorporation into urea. Animals rendered chronically acidotic showed a lower central venous plasma urea concentration and a raised NH4+ concentration, but their livers synthesized no more glutamine when perfused at an acidotic pH than did normal livers. We conclude that perivenous hepatocytes may not be efficient scavengers of NH4+ ions, which must be partly disposed of elsewhere by non-proton-generating pathways if inhibition of ureagenesis is to represent a hepatic acid-base regulating system.

Bicarbonate-dependent and -independent intracellular pH regulatory mechanisms in rat hepatocytes. Evidence for Na+-HCO3- cotransport

Using the pH-sensitive dye 2,7-bis(carboxyethyl)-5(6)-carboxy-fluorescein and a continuously perfused subconfluent hepatocyte monolayer cell culture system, we studied rat hepatocyte intracellular pH (pHi) regulation in the presence (+HCO3-) and absence (-HCO3-) of bicarbonate. Baseline pHi was higher (7.28 +/- 09) in +HCO3- than in -HCO3- (7.16 +/- 0.14). Blocking Na+/H+ exchange with amiloride had no effect on pHi in +HCO3- but caused reversible 0.1-0.2-U acidification in -HCO3- or in +HCO3- after preincubation in the anion transport inhibitor 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). Acute Na+ replacement in +HCO3- alos caused acidification which was amiloride independent but DIDS inhibitible. The recovery of pHi from an intracellular acid load (maximum H+ efflux rate) was 50% higher in +HCO3- than in -HCO3-. Amiloride inhibited H+ effluxmax by 75% in -HCO3- but by only 27% in +HCO3-. The amiloride-independent pHi recovery in +HCO3- was inhibited 50-63% by DIDS and 79% by Na+ replacement but was unaffected by depletion of intracellular Cl-, suggesting that Cl-/HCO3- exchange is not involved. Depolarization of hepatocytes (raising external K+ from 5 to 25 mM) caused reversible 0.05-0.1-U alkalinization, which, however, was neither Na+ nor HCO3- dependent, nor DIDS inhibitible, findings consistent with electroneutral HCO3- transport. We conclude that Na+-HCO3- cotransport, in addition to Na+/H+ exchange, is an important regulator of pHi in rat hepatocytes.