Interactions of calcium with serum albumin

Corrosion Behavior in Magnesium-Based Alloys for Biomedical Applications

Magnesium alloys exhibit superior biocompatibility and biodegradability, which makes them an excellent candidate for artificial implants. However, these materials also suffer from lower corrosion resistance, which limits their clinical applicability. The corrosion mechanism of Mg alloys is complicated since the spontaneous occurrence is determined by means of loss of aspects, e.g., the basic feature of materials and various corrosive environments. As such, this study provides a review of the general degradation/precipitation process multifactorial corrosion behavior and proposes a reasonable method for modeling and preventing corrosion in metals. In addition, the composition design, the structural treatment, and the surface processing technique are involved as potential methods to control the degradation rate and improve the biological properties of Mg alloys. This systematic representation of corrosive mechanisms and the comprehensive discussion of various technologies for applications could lead to improved designs for Mg-based biomedical devices in the future.

Exploiting Ultrashort α,β-Peptides in the Colloidal Stabilization of Gold Nanoparticles

Colloidal gold nanoparticles (GNPs) have found wide-ranging applications in nanomedicine due to their unique optical properties, ease of preparation, and functionalization. To avoid the formation of GNP aggregates in the physiological environment, molecules such as lipids, polysaccharides, or polymers are employed as GNP coatings. Here, we present the colloidal stabilization of GNPs using ultrashort α,β-peptides containing the repeating unit of a diaryl β^2,3-amino acid and characterized by an extended conformation. Differently functionalized GNPs have been characterized by ultraviolet, dynamic light scattering, and transmission electron microscopy analysis, allowing us to define the best candidate that inhibits the aggregation of GNPs not only in water but also in mouse serum. In particular, a short tripeptide was found to be able to stabilize GNPs in physiological media over 3 months. This new system has been further capped with albumin, obtaining a material with even more colloidal stability and ability to prevent the formation of a thick protein corona in physiological media.

A Nuisance-Free Inference Procedure Accounting for the Unknown Missingness with Application to Electronic Health Records

We study how to conduct statistical inference in a regression model where the outcome variable is prone to missing values and the missingness mechanism is unknown. The model we consider might be a traditional setting or a modern high-dimensional setting where the sparsity assumption is usually imposed and the regularization technique is popularly used. Motivated by the fact that the missingness mechanism, albeit usually treated as a nuisance, is difficult to specify correctly, we adopt the conditional likelihood approach so that the nuisance can be completely ignored throughout our procedure. We establish the asymptotic theory of the proposed estimator and develop an easy-to-implement algorithm via some data manipulation strategy. In particular, under the high-dimensional setting where regularization is needed, we propose a data perturbation method for the post-selection inference. The proposed methodology is especially appealing when the true missingness mechanism tends to be missing not at random, e.g., patient reported outcomes or real world data such as electronic health records. The performance of the proposed method is evaluated by comprehensive simulation experiments as well as a study of the albumin level in the MIMIC-III database.

Monodispersed calcium carbonate nanoparticles modulate local pH and inhibit tumor growth in vivo

The acidic extracellular environment of tumors potentiates their aggressiveness and metastasis, but few methods exist to selectively modulate the extracellular pH (pHe) environment of tumors. Transient flushing of biological systems with alkaline fluids or proton pump inhibitors is impractical and nonselective. Here we report a nanoparticles-based strategy to intentionally modulate the pHe in tumors. Biochemical simulations indicate that the dissolution of calcium carbonate nanoparticles (nano-CaCO3) in vivo increases pH asymptotically to 7.4. We developed two independent facile methods to synthesize monodisperse non-doped vaterite nano-CaCO3 with distinct size range between 20 and 300 nm. Using murine models of cancer, we demonstrate that the selective accumulation of nano-CaCO3 in tumors increases tumor pH over time. The associated induction of tumor growth stasis is putatively interpreted as a pHe increase. This study establishes an approach to prepare nano-CaCO3 over a wide particle size range, a formulation that stabilizes the nanomaterials in aqueous solutions, and a pH-sensitive nano-platform capable of modulating the acidic environment of cancer for potential therapeutic benefits.

Uncorrected and Albumin-Corrected Calcium, Phosphorus, and Mortality in Patients Undergoing Maintenance Dialysis

Uncorrected serum calcium concentration is the first mineral metabolism metric planned for use as a quality measure in the United States ESRD population. Few studies in patients undergoing either peritoneal dialysis (PD) or hemodialysis (HD) have assessed the association of uncorrected serum calcium concentration with clinical outcomes. We obtained data from 129,076 patients on dialysis (PD, 10,066; HD, 119,010) treated in DaVita, Inc. facilities between July 1, 2001, and June 30, 2006. After adjustment for potential confounders, uncorrected serum calcium <8.5 and ≥10.2 mg/dl were associated with excess mortality in patients on PD or HD (comparison group uncorrected calcium 9.0 to <9.5 mg/dl). Additional adjustment for serum albumin concentration substantially attenuated the all-cause mortality hazard ratios (HRs) associated with uncorrected calcium <8.5 mg/dl (HR, 1.29; 95% confidence interval [95% CI], 1.16 to 1.44 for PD; HR, 1.17; 95% CI, 1.13 to 1.20 for HD) and amplified the HRs associated with calcium ≥10.2 mg/dl (HR, 1.65; 95% CI, 1.42 to 1.91 for PD; HR, 1.59; 95% CI, 1.53 to 1.65 for HD). Albumin-corrected calcium ≥10.2 mg/dl and serum phosphorus ≥6.4 mg/dl were also associated with increased risk for death, irrespective of dialysis modality. In summary, in a large nationally representative cohort of patients on dialysis, abnormalities in markers of mineral metabolism, particularly high concentrations of serum calcium and phosphorus, were associated with increased mortality risk. Additional studies are needed to investigate whether control of hypercalcemia and hyperphosphatemia in patients undergoing dialysis results in improved clinical outcomes.

554. Titration curves of whey constituents

Titration curves of calcium-containing and calcium-free solutions resembling milk serum indicated that precipitation of calcium from such solutions was greatly impeded by citrate. In the absence of citrate, precipitation of tricalcium phosphate was complete at pH 6·0, but, in solutions containing citrate, precipitation of tricalcium phosphate occurred gradually throughout the titration and was not complete at pH 10.

In some solutions precipitation of calcium phosphate ceased at about pH 9·7, even though the base added had been insufficient to neutralize tertiary hydrogen equivalent to the known calcium content. Precipitation of dicalcium phosphate must therefore have occurred.

The observed stability of calcium in these solutions was much greater than that predicted from the accepted solubility and dissociation constants. It is therefore concluded that detailed studies of these constants, and of the factors controlling precipitation of dior tricalcium phosphate, are needed.

Hypocalcemic tetany and metabolic alkalosis in a dialysis patient: an unusual event

The case is described of a 29-year-old man with renal failure and recurrent hyperparathyroidism who 3 weeks postparathyroidectomy developed hypocalcemic tetany because he was taking one-half the prescribed dose of calcitriol. He interpreted his symptoms as those of potassium intoxication and self-administered almost 1,500 mEq sodium bicarbonate. The increase in plasma sodium and osmolarity led to increased fluid intake, and at presentation he had an ionized calcium of 0.50 mmol/L, K 5.3 mmol/L, Na 148 mmol/L, total CO2 52.6 mmol/L, pO2 51.2 mm Hg, and pH of 7.61. He had gained 7 kg in weight. All abnormalities were corrected by dialysis, using initially a calcium-free dialyzate with extra calcium infused. The case illustrates the effect of alkalosis in reducing the amount of calcium that exists in ionized form, and it is suggested that complexing of calcium as calcium bicarbonate together with the pH change contributed to the decrease in ionized calcium. It is also an example of the hazards of treating patients who devise their own therapeutic regimens.

SOME CHARACTERISTICS OF PRIMARY HYPERPARATHYROIDISM IN VIETNAMESE IMMIGRANTS LIVING IN SOUTHERN CALIFORNIA

OBJECTIVE

To characterize primary hyperparathyroidism (PHP) in Vietnamese immigrants living in southern California and to summarize the results of treatment.

METHODS

We describe 11 patients (8 women and 3 men) with a mean age of 57.91 years who underwent follow-up from 1991 to 1995 after PHP was diagnosed. The patients had no specific complaints. Four patients had a history of kidney stones, and five had chronic hypertension. Only five patients had high levels of total serum calcium; the other six patients had normal or fluctuating levels of total serum calcium. All patients, however, had high levels of intact parathyroid hormone (PTH) and ionized calcium. Preoperatively, parathyroid imaging with technetium-99m sestamibi demonstrated persistently increased parathyroid gland uptake.

RESULTS

In all nine patients who underwent surgical treatment, an adenoma was found in the parathyroid glands; two patients refused operative intervention. The mean serum phosphate was in the low-normal range and increased postoperatively (2.70 versus 3.52 mg/dL; P<0.001). The mean serum chloride level also decreased postoperatively (104.62 versus 100.78 mEq/L; P<0.001). The ratio of chloride/phosphate decreased significantly after adenoma removal (39.44 versus 29.21; P<0.001). Six patients received calcium gluconate either alone or in combination with vitamin D supplements for hypocalcemia postoperatively. The other three patients, however--who did not receive calcium supplements postoperatively--had persistently high levels of intact PTH but normal serum Ca++ levels and subsequently were treated effectively with calcium gluconate and vitamin D.

CONCLUSION

The presence of hypercalcemia, especially Ca++, and an increased level of intact PTH establishes the diagnosis of PHP. After parathyroidectomy, the persistence of high levels of intact PTH in association with normal serum Ca++ suggested the presence of secondary hyperparathyroidism, which was treated effectively with calcium gluconate and vitamin D. These patients had the same clinical picture as other ethnic groups with PHP, but they needed either calcium alone or calcium and vitamin D supplements after parathyroidectomy because of their bone loss from prolonged PHP.

Influence of ionic strength on the binding of sodium aurothiosulphate to human serum albumin

The effect of ionic strength on the binding of aurothiosulphate to human serum albumin has been studied at 37 degrees and neutral pH by equilibrium dialysis in unbuffered solutions. The effect of ionic strength is more pronounced on the lower association constants K2-K4 than on the high association constant K1. Furthermore a reduction in the number of lower affinity binding sites is observed at low ionic strength. The main ionic strength dependence on the association constants agrees with the Debye-Hückel theory. The extrapolated values of K1 and the sum of K2 to K4 at zero ionic strength are 7.6 X 10(5) M-1 and 1.1 X 10(5) M-1, respectively. It is shown that the observed changes in pH of the albumin solutions during dialysis contains valuable information of the aurothiosulphate-albumin interaction. A molecular binding mechanism is discussed.

The effects of N-B transition of human serum albumin on the specific drug-binding sites

In the pH range 6-9, human serum albumin undergoes a conformational change termed the neutral-base (N-B) transition. Recently, it has been shown that the N-B transition causes enhanced binding at the warfarin-binding site (site I). The present study used fluorescence and equilibrium dialysis to investigate the effects of the N-B transition, chloride, calcium and fatty acids on the specific binding sites I and II on human serum albumin. The effect of the N-B transition of human serum albumin provides a further distinction between site I and II binding characteristics. The N-B transition of albumin caused a change in conformation at site I which resulted in increased binding of drugs and fluorescent probes at this site, whereas there was no effect on acidic drug binding at site II. These effects on site I and II are qualitatively similar to those induced by fatty acids (increased drug binding at site I and no change at site II). However, the effects of increasing pH and fatty acids were additive, showing that they were caused by two different conformational changes. The effect of Cl- on site I binding was pH-dependent and was abolished by the presence of fatty acid. Ca2+ reduced the fluorescence of site I probes but had no effect on a site II fluorescent probe. Effects of pH were also investigated with drugs not binding to site I or II. Increasing pH caused a decrease in binding to indomethacin, increases in binding of L-tryptophan, tolmetin and quinidine and no change in the binding of salicylic acid, diflunisal and phenytoin.

A comparative study of some physico-chemical properties of human serum albumin samples from different sources--I. Some physico-chemical properties of isoionic human serum albumin solutions

Human serum albumin samples from different sources were investigated. The fatty acid content of the albumin before and after deionization on a mixed bed ion-exchange column varied from sample to sample. When an albumin sample from one source was deionized under standard conditions the amount of fatty acid bound by the albumin was reduced to a reproducible amount. In samples from different sources, however, the amount bound varied considerably. Also the isoionic pH of the albumin varied from sample to sample. This variation could be attributed to the difference in the fatty acid content and the different number of titratable histidines and acid amino-acid residues in the albumin from different sources. It can be concluded from the specific conductance of these isoionic solutions that ions other than H-, OH and protein are effectively removed by a mixed bed ion-exchange column. The specific conductance of the albumin samples is directly related to the isoionic pH. Therefore, the isoionic pH and the specific conductance of the albumins reflect the heterogeneity of the albumin samples with respect to their primary structure and fatty acid content.

Effect of albumin conformation on binding of phenylbutazone and oxyphenbutazone to human serum albumin

The binding of phenylbutazone (I) and oxyphenbutazone (II) to human serum albumin over pH 6.9-9.3 was studied by difference spectrophotometry and equilibrium dialysis. At each pH tested, there was higher binding affinity of I to human serum albumin than II. Equilibrium dialysis showed that over the pH 7-8.2 range both agents had a single high-affinity site and several sites of lower affinity, with the highest binding constant and number of binding sites at pH 7.4 for both I and II. Both techniques showed that the affinity of both drugs to albumin was higher for the neutral form than for the basic form and this transition occurred in both cases around the neutral region (7-7.4). Both the ionized and unionized forms of I and II participated in the binding. In the neutral region, magnesium ion increased the affinity of both drugs to albumin while chloride ion decreased it slightly.

The role of albumin conformation in the binding of diazepam to human serum albumin

The effect of hydrogen, chloride and calcium ions on the binding of diazepam to human serum albumin has been studied by circular dichroism and equilibrium dialysis. In all cases the molar ellipticity of the diazepam-albumin complex increases with pH over the pH range 5 to 9. Under these conditions the free concentration of diazepam at a constant low drug to protein ratio decreases with pH. This free concentration is higher in the presence of chloride and calcium ions. With a two state conformational model for albumin it was shown, that the pH dependences of molar ellipticity of the diazepam-albumin complex and of the free concentration of diazepam are linked. It was demonstrated that the N-B transition of albumin is involved in the pH dependent binding of diazepam. The consequences of these findings for equilibrium dialysis procedures in determining free plasma levels of diazepam are discussed.

Structure-volume relationships: singular volume effects produced by cupric ion-globular protein interaction

The nature of the volume isotherms produced by the coordination of Cu(II) with ovalbumin and bovine serum albumin differs substantially from the adsorption isotherms produced by these systems. Whereas there was increased binding of Cu(II) associated with a pH increase from pH 5.3 to pH 7.4, the volume isotherms for these systems did not exhibit this type of pH dependence. The volume changes were determined at 30.0 +/- 0.001 degrees C with microdilatometers which could be read to 0.01 muL. The binding isotherms for ovalbumin at pH 5.3 and 7.4 and for bovine serum albumin at pH 5.3 was resolved by a Scatchard plot to yield the appropriate thermodynamic parameters. An algorithm was derived to calculate the distribution of the individual PMi complexes, i.e., PMi-1 + M in equilibrium (Ki) PMi where i equals 1, 2, 3, ..., n moles of cation, M, bound per mole of protein, P, for the above systems. The volume isotherms were then resolved in terms of the constituent delta Vi terms, i.e., the volume change produced by the formation of the individual PMi complexes. These values were verified by an independent graphical differentiation procedure. The coordination of Cu(II) to BSA at pH 7.4 produced a cooperative adsorption isotherm which was not amenable to a Scatchard analysis. The resultant anomalous volume isotherm was resolved into a component related to Cu(II)-site interaction and a negative volume effect attributable to a conformational change induced by complex formation. This structural transition which occurs at physiological pH may constitute a control mechanism for regulating the serum level of Cu(II) and possibly other divalent ions.

Conformational changes in human serum albumin around the neutral pH from circular dichroic measurements

The molar ellipticity of the warfarin-albumin complex at 310 nm increases with pH from 6 to 9. This pH dependence runs parallel with that of the molar ellipticity of the albumin alone at 292 nm. The change in molar ellipicity with pH occurs in a smaller pH interval after addition of the physiological concentration of calcium ions. These findings give support to the assumption that the binding site for warfarin on the albumin molecule is affected by the neutral-to-base transition in the protein.

An interfering factor in the automated analysis of calcium

The widespread use of stainless steel for sample probes, connectors, and sample stream splitters in autoanalyser systems can lead to significant differences in the amount of calcium available for analysis. At alkaline pH calcium can be adsorbed onto the metallic components of the sampling system, and under more acidic conditions calcium can be released. Thus an alkaline sample will have an apparently reduced calcium content, while a more acidic sample may have an apparently increased concentration of calcium. By using non-metallic components in the sampling system this source of error an be eliminated.

A constant-volume ultrafiltration technique for the calculation of equilbrium binding data

A constant-volume ultrafiltration technique is described, and details of its assessment presented. The retention characteristics of two membranes were evaluated using molecules of known molecular weight. The technique is rapid, precise, economical of material and yields equilibrium data. In these respects, it compares favourably with conventional techniques such as equilibrium dialysis.

Radiostrontium distribution measured in vitro between bound and free forms in the soft tissues of rat

The distribution of 89Sr (carrier-free) in the bound (non-diffusible) and free (diffusible) forms was studied in vitro in the soft tissues of the albino rat by the ultrafiltration method. The influence of factors such as time and temperature of incubation with 89Sr, concentration and medium of the homogenate, pH and age of the animal on the binding of 89Sr was investigated. The binding increased with rise in pH, being maximum in the pH range 7.0--9.0. The distribution pattern varied with the tissues, the bound form (at pH 7.4) being as high as 84 per cent in the small intestine and as low as 20 per cent in the skin, whereas it was about 40--45 per cent in kidney, liver, lung, skeletal muscle and blood serum. The bound form in most of the tissues of the weanling rats was in general lower than that in 6-month or 1-year-old rats. In the serum, 89Sr was mostly bound to globulins. The bound form of 89Sr was also determined by the method of equilibrium dialysis for comparison.

Protein-metal ion interaction: volume effects produced by the interaction of proteins with metal ions

The interaction of metal cations with single chain globular proteins produces volume increases, the magnitude of which is determined primarily by the ion and to a lesser extent by the protein. The cations are listed in ascending order of volume change: K(I) less than Mg(II) less than Sr(II) less than Ca(II) less than Co(II) less than Ni(II) less than Cd(II) less than Zn(II) less than Cu(II) less than Pb(II). This sequence held for all cation-protein systems investigated except for Cd(II) which produced a slightly larger volume effect than Zn(II) with lysozyme. The volume changes attributed to protein-cation interaction are positive and range from 8 ml/10(5) g of protein for the reaction on 0.05 M KNO3 with bovine plasma albumin to 2320 ml/10(5) g of protein produced by the 0.20 M Pb(NO3)2-myoglobin system. A similar classification scheme was not possible for the proteins. For example, volume increases of 45, 50, 80 and 95 ml/10(5) g of protein were produced when 0.05 M Mg(II) reacted with bovine serum albumin, ovalbumin, sperm whale myoglobin and lysozyme, respectively. However, when 0.2 M Pb(II) was the reactant the values were 1930, 846, 2320, and 1120 ml/10(5) g of protein. Volume effects produced by Cr(III), Al(III) and Fe(III) were determined, but the calculated results are considered dubious because the volume changes are a complicated function of protein-cation and protein-proton interaction.

Murexide for determination of free and protein-bound calcium in model systems

The determination with murexide of free and protein-bound calcium in model systems of known composition, ionic strength, and pH was investigated. The spectra of calcium murexide in the presence of varying amounts of calcium ions indicated that the absorption maximum fo calcium murexide complex occurs at 480 nm while that of murexide ion is at 520 nm. The absorbance at 509 nm is independent of calcium ion concentration and, therefore, could be used to measure the total dye. The spectra are pH dependent but constant in the range 6.5 to 7.0. The apparent dissociation constant of calcium murexide is dependent upon ionic environment, ionic strength, and free calcium ion concentration. The relationship between the apparent dissociation constant and free calcium concentration was established. Whole casein had no effect on the absorption spectra of calcium murexide and no affinity for calcium murexide complex or murexide ion. Beta-casein, at the concentrations employed, did not influence the dissociation fo calcium murexide. At pH 7.0, ionic strength .1, and 2 C, Beta-casein bound calcium as if there were 8.65 binding sites per molecule, each of pK 2.23, corresponding to an intrinsic association constant of 168.9 liters per mole.

Adsorption of serum calcium by plastic sample cups

Sera left overnight in plastic AutoAnalyzer sample cups may give low calcium values; the effect is attributed to adsorption of calcium onto the walls of the vessel. The adsorption is brought about by a rise in the pH of the sera, and factors which promote the rise in pH increase the adsorption. This phenomenon is of practical importance because as much as 10% of the calcium in the serum may be adsorbed. Adsorption occurs particularly onto the walls of polystyrene cups, and when polypropylene cups were used the adsorption was reduced. The phenomenon cannot be evaluated or controlled by the use of control sera. In order to avoid the sampling error, serum for calcium analysis should be used fresh or stored at 4 degrees C under conditions such that any change in pH is minimal. Sera should not be left to stand in AutoAnalyzer cups at room temperature for longer than three hours before analysis.