Autonomous electrochemical system for ammonia oxidation reaction measurements at the International Space Station

An autonomous electrochemical system prototype for ammonia oxidation reaction (AOR) measurements was efficiently done inside a 4'' x 4'' x 8'' 2U Nanoracks module at the International Space Station (ISS). This device, the Ammonia Electrooxidation Lab at the ISS (AELISS), included an autonomous electrochemical system that complied with NASA ISS nondisclosure agreements, power, safety, security, size constrain, and material compatibility established for space missions. The integrated autonomous electrochemical system was tested on-ground and deployed to the International Space Station as a "proof-of-concept" ammonia oxidation reaction testing space device. Here are discussed the results of cyclic voltammetry and chronoamperometry measurements done at the ISS with a commercially available channel flow-cell with eight screen-printed electrodes, including Ag quasi-reference (Ag QRE) and carbon counter electrodes. Pt nanocubes in Carbon Vulcan XC-72R were used as the catalyst for the AOR and 2 μL drop of Pt nanocubes/ Carbon Vulcan XC-72R, 20 wt%, ink was placed on the carbon working electrodes and allowed to dry in air. After the AELISS was prepared for launch to the ISS, a 4 days delayed (2 days in the space vehicle Antares and 2 days space transit to the ISS) cause a slight shift on the Ag QRE potential. Nevertheless, the AOR cyclic voltametric peak was observed in the ISS and showed ca. 70% current density decrease due to the buoyancy effect in agreement with previous microgravity experiments done at the zero-g aircraft.

Silver jubilee: 25 years of the first demonstration of the direct effect of phosphate on the parathyroid cell

Although phosphorus is an essential element for life, it is not found in nature in its native state but rather combined in the form of inorganic phosphates (PO₄^3-), with tightly regulated plasma levels that are associated with deleterious effects and mortality when these are out of bounds. The growing interest in the accumulation of PO₄^3- in human pathophysiology originated in its attributed role in the pathogenesis of secondary hyperparathyroidism (SHPT) in chronic kidney disease. In this article, we review the mechanisms by which this effect was justified and we commemorate the important contribution of a Spanish group led by Dr. M. Rodríguez, just 25 years ago, when they first demonstrated the direct effect of PO₄^3- on the regulation of the synthesis and secretion of parathyroid hormone by maintaining the structural integrity of the parathyroid glands in their original experimental model. In addition to demonstrating the importance of arachidonic acid (AA) and the phospholipase A2-AA pathway as a mediator of parathyroid gland response, these findings were predecessors of the recent description of the important role of PO₄^3- on the activity of the calcium sensor-receptor, and also fueled various lines of research on the importance of PO₄^3- overload not only for the pathophysiology of SHPT but also in its systemic pathogenic role.

In Situ X-ray Absorption Spectroscopy of PtNi-Nanowire/Vulcan XC-72R under Oxygen Reduction Reaction in Alkaline Media

Studying the oxygen reduction reaction (ORR) in the alkaline electrolyte has proven to promote better catalytic responses and accessibility to commercialization. Ni-nanowires (NWs) were synthesized via the solvothermal method and modified with Pt using the spontaneous galvanic displacement method to obtain PtNi-NWs. Carbon Vulcan XC-72R (V) was used as the catalyst support, and they were doped with NH₃ to obtain PtNi-NWs/V and PtNi-NWs/V-NH₃. Their electrocatalytic response for the ORR was tested and PtNi-NWs/V provided the highest specific activity with logarithmic values of 0.707 and 1.01 (mA/cm² _Pt) at 0.90 and 0.85 V versus reversible hydrogen electrode (RHE), respectively. PtNi-NWs showed the highest half-wave potential (E _1/2 = 0.89 V) at 1600 rpm and 12 μg_Pt/cm² in 0.1 M KOH at 25.00 ± 0.01 °C. Additionally, the catalysts followed a four-electron pathway according to the Koutecký-Levich analysis. Moreover, durability experiments demonstrated that the PtNi-NW/V performance loss was like that of commercial Pt/V along 10,000 cycles. Electrochemical ORR in situ X-ray absorption spectroscopy results showed that the Pt L₃ edge white line in the PtNi-NW catalysts changed while the electrochemical potential was lowered to negatives values, from 1.0 to 0.3 V versus RHE. The Pt/O region in the in situ Fourier transforms remained the same as the potentials were applied, suggesting an alloy formation between Pt and Ni, and Pt/Pt contracted in the presence of Ni. These results provide a better understanding of PtNi-NWs in alkaline electrolytes, suggesting that they are active catalysts for ORR and can be tuned for fuel cell studies.

Calcimimetics in the chronic kidney disease-mineral and bone disorder

Mineral and bone disorders (MBD) are both an early and very common complication of chronic kidney disease (CKD). It is now accepted that they represent a significant risk factor, explaining the high cardiovascular morbidity and mortality in CKD patients. During the last decade, we have been witnessing many advances in the nomenclature, classification, pathophysiology, diagnosis, and treatment of CKD and some of its complications, such as CKD-MBD. The identification of the calcium-sensing receptor (CaSR) involvement in the pathogenesis of primary and secondary hyperparathyroidism (SHPT) and the availability of a new class of drugs called calcimimetics are two outstanding examples. Cinacalcet, the only available calcimimetic, has been shown to be a very effective therapeutic tool in CKD-MBD. Many clinical trials with cinacalcet in hemodialysis patients with SHPT have shown a reduction in parathyroid hormone, calcium (Ca), phosphate (P) and Ca x P product levels, allowing far greater success in reaching therapeutic goals as recommended by international guidelines. Additionally, some studies have shown that the use of cinacalcet may improve other aspects of CKD-MBD, reducing the risk of vascular calcification and parathyroidectomy, among others. Prospective studies on dialysis patients, with hard endpoint data, are currently underway. This review summarizes the most significant aspects of calcimimimetics based on both experimental and clinical results, underlining their possibilities not only for the treatment of isolated SHPT but also for other CKD-MBD related conditions.

The use of electrolyte redox potential to monitor the Ce(IV)/Ce(III) couple

Mathematical modelling of the oxidation reduction redox potential (ORP) of an electrolyte has been carried out for a batch system comprising an electrochemical reactor and an electrolyte circuit containing a redox couple. The ORP can be useful to monitor the environmental impact of chemical species in solution that represent a risk to the environment. Considerations of four fundamental equations, namely, the Nernst equation, a mass balance, Faraday's laws of electrolysis and a first order kinetic equation, leads to an expression for the electrolyte redox potential as a function of the batch time, the electrical charge and the redox concentration. Such an expression facilitates graphical plots which can be used to estimate kinetic parameters, current efficiency and the relative redox concentration. The Ce(IV)/Ce(III) system has been chosen as a model reaction for electrolyte redox potential measurement in a batch recycle system consisting of a pumped flow through a divided FM01-LC parallel-plate electrochemical reactor (64 cm(2) projected electrode area) and a well mixed tank (3,600 cm(3)). The differences between experimental and model predictions are discussed.

Dynamics of skeletal resistance to parathyroid hormone in the rat: effect of renal failure and dietary phosphorus

Secondary hyperparathyroidism develops in renal failure and is generally ascribed to factors directly affecting parathyroid hormone (PTH) production and/or secretion. These include hypocalcemia, phosphorus retention, and a calcitriol deficiency. However, not often emphasized is that skeletal resistance to PTH is an important factor. Our study evaluated: (1) the relative effects of uremia and dietary phosphorus on the skeletal resistance to PTH; and (2) how, during a PTH infusion, the dynamics of skeletal resistance to PTH were affected by renal failure. Renal failure was surgically induced and, based on serum creatinine, rats were divided into normal, moderate renal failure, and advanced renal failure. In each group, three diets with the same calcium (0.6%) but different phosphorus contents were used: high (1.2%, HPD); moderate (0.6%, MPD); and low (0.2%, LPD) phosphorus. The study diet was given for 14-16 days followed by a 48 h infusion of rat PTH(1-34) (0.11 microg/100 g per hour), a dose five times greater than the normal replacement dose. During the PTH infusion, rats received a calcium-free, low phosphorus (0.2%) diet. In both moderate and advanced renal failure, the PTH level was greatest in the HPD group (p < 0.05) and, despite normal serum calcium values, PTH was greater in the MPD than the LPD group (p < 0.05). Despite phosphorus restriction and normal serum calcium and calcitriol levels in the azotemic LPD groups, the PTH level was greater (p < 0.05) in the LPD group with advanced rather than moderate renal failure. During PTH infusion, the increase in serum calcium was progressively less (p < 0.05) in all groups as renal function declined. Furthermore, despite normal and similar serum phosphorus values at the end of PTH infusion, the serum calcium concentration was less (p < 0.05) in the HPD group than the other two groups and similar in the LPD and MPD groups.

IN CONCLUSION

(1) uremia and phosphorus each had separate and major effects on skeletal resistance to PTH; (2) skeletal resistance to PTH was an important cause of secondary hyperparathyroidism, even in moderate renal failure; (3) during PTH infusion, the dynamics of skeletal resistance to PTH changed because all groups received a low phosphorus diet, and the adaptation to a new steady state was delayed by the degree of renal failure and the previous dietary phosphorus burden; and (4) normal serum phosphorus may not be indicative of body phosphorus stores during states of disequilibrium.

The calcemic response to PTH in the rat: effect of elevated PTH levels and uremia

Secondary hyperparathyroidism (2 degrees HPT) is a consistent finding in renal failure. A decreased calcemic response (CR) to parathyroid hormone (PTH) contributes to the development of 2 degrees HPT. Since parathyroidectomy (PTX) corrects the decreased CR to PTH in azotemic animals, down-regulation of PTH receptors induced by an elevation of PTH has been advanced as an important factor in the development of 2 degrees HPT. The goal of the study was to determine in azotemic rats whether a progressive reduction of PTH improves the CR to PTH and whether the maintenance of normal PTH levels corrects the CR to PTH. Seven groups of pair-fed rats were studied. Three groups of rats had normal renal function (NRF groups) and received either a high phosphorus (HPD-NRF), a moderate phosphorus (MPD-NRF), or a low phosphorus (LPD-NRF) diet. Three azotemic (NX) groups received similar diets (HPD-NX, MPD-NX and LPD-NX groups) in order to vary the magnitude of 2 degrees HPT. A PTX was performed in a fourth azotemic group (PTX-NX) to induce the complete absence of PTH. After 14 to 16 days on the maintenance diets, the CR to PTH was determined with a 48 hour infusion of 1-34 rat PTH.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors in the development of secondary hyperparathyroidism during graded renal failure in the rat

Secondary hyperparathyroidism (2 degree HPT) develops as a result of renal failure. Hypocalcemia, phosphorus retention, calcitriol deficiency and skeletal resistance to the calcemic action of parathyroid hormone (PTH) are closely interrelated pathogenic factors important for the development of 2 degrees HPT in renal failure. Since previous studies have mainly focused on advanced renal failure, only limited data are available in early renal failure. The goal of the present study was to evaluate how alterations in the dietary calcium and phosphorus composition affect the factors known to contribute to the genesis of 2 degrees HPT in early and more advanced renal failure. To achieve this goal, graded differences in renal function were surgically induced in 453 rats while the dietary content of calcium and phosphorus was varied. Three different diets were used: (1) a high phosphorus diet (HPD), to induce phosphorus retention and stimulate 2 degrees HPT; (2) a high calcium diet (HCaD), to inhibit calcitriol synthesis; and (3) a moderate calcium-moderate phosphorus diet (MCaPD), to separate the effects of high dietary phosphorus and calcium. Based on the serum creatinine (SCr) concentration rats were assigned to one of four different groups: (1) normal renal function (SCr < or = 0.3 mg/dl); (2) mild renal failure (SCr 0.4 to 0.6 mg/dl); (3) moderate renal failure (SCr 0.7 to 0.8 mg/dl); or (4) advanced renal failure (SCr > or = 0.9 mg/dl). As the severity of renal failure increased, progressive 2 degrees HPT developed in each of the dietary groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of intramammary treatment in unbred and primigravid dairy heifers

A total of 73 breeding-age and primigravid Jersey heifers in 4 herds was randomly allotted to treatment and control groups according to expected calving date. Thirty-five heifers were injected intramammarily with a nonlactating cow product containing penicillin/streptomycin. Thirty-eight heifers served as untreated controls. Of the 35 treated heifers, 34 (97.1%) were infected at time of treatment. In the untreated control group, all 38 heifers (100%) were infected at treatment time. At parturition, prevalence of intramammary infection in treated heifers decreased to 40%, whereas in the control group, prevalence remained about the same (97.4% of heifers). Prevalence of Staphylococcus aureus mastitis in treated heifers was reduced from 17.1% to 2.9% after treatment. In the control group, prevalence of S aureus mastitis decreased from 26.3% to 15.8%. Heifers treated during the second trimester of pregnancy had the greatest reduction in prevalence of mastitis and in somatic cell count at parturition, compared with controls. Findings indicated that intramammary treatment during pregnancy in primigravid heifers was effective in reducing prevalence of mastitis and somatic cell counts at parturition.

Histopathology of staphylococcal mastitis in unbred dairy heifers

Histologic observations of mammary tissue samples from unbred heifers revealed that secretory parenchyma from uninfected quarters was undeveloped, exhibiting small alveoli with a limited luminal area and a large interalveolar stromal area. Tissues from quarters infected with Staphylococcus aureus were less developed, exhibiting less alveolar epithelial and luminal areas and more interalveolar stroma compared with tissues from uninfected quarters. Such quarters also demonstrated minimal secretory activity. Macroscopic and microscopic abscesses were observed in one quarter with S. aureus intramammary infection. Staphylococcus aureus-infected quarters showed greater leukocyte infiltration into mammary parenchymal components and cistern lining compared with uninfected quarters. Quarters infected with non-aureus staphylococci also exhibited greater leukocyte infiltration and greater percentages of interalveolar stroma compared with uninfected controls. Results demonstrated that presence of infection increased leukocytosis into the mammary gland and reduced secretory activity in heifers, suggesting a deleterious effect on future milk production.

Antimicrobial susceptibilities of staphylococcal species isolated from mammary glands of unbred and primigravid dairy heifers

Staphylococcal isolates from teat canal keratin and mammary secretion samples of unbred and primigravid Jersey heifers were tested in vitro for susceptibility to 12 antimicrobial agents. More than 92% of the 311 isolates were susceptible to all antimicrobial agents tested. Staphylococci other than Staphylococcus aureus demonstrated an overall susceptibility of 98.3% to all antibiotics, and Staphylococcus aureus demonstrated a 97% susceptibility. Across all staphylococcal species, susceptibility of isolates from secretion samples was 98.1%, and susceptibility of isolates from teat canal keratin samples was 93.1%. Differences in susceptibilities were observed among herds.

Prevalence of intramammary infection and teat canal colonization in unbred and primigravid dairy heifers

Teat canal keratin (n = 461) and mammary gland secretions (n = 370) were collected from 31 unbred and 85 primigravid Jersey heifers from one research and three commercial dairy herds. Of 97 heifers from which secretion samples were obtained, 96.9% had intramammary infections and 29% showed clinical symptoms. Seventy-five percent of quarters were infected. Staphylococcus aureus were isolated from 36 (37.1%) heifers and 55 (14.9%) quarters. One hundred and eight (93.1%) heifers and 326 (70.7%) quarters had teat canals colonized with mastitis pathogens. Staphylococcus aureus were isolated from teat canal keratin samples from 36 (31%) heifers and 57 (12.3%) quarters. The three most common species isolated from secretion and teat canal keratin samples were Staphylococcus chromogenes, Staphylococcus hyicus, and S. aureus. Secretions from infected (n = 240) and uninfected (n = 85) quarters had SCC of 13.6 X 10(6)/ml and 5.7 X 10(6)/ml. Macrophages were the most numerous cell type in secretions of infected and uninfected quarters. Quarters with teat canal colonization, but with no intramammary infections, exhibited higher SCC in secretion (9.3 X 10(6)/ml) than quarters without both teat canal colonizations and intramammary infections (4.9 X 10(6)/ml). Data indicated that intramammary infections and teat canal colonizations were more prevalent and SCC higher than previously realized in dairy heifers.

Local immunostimulation of the bovine mammary gland with interleukin-2

One day after drying off, miniosmotic pumps releasing interleukin-2 were implanted into teat cisterns of six Jersey cows. Each cow had two quarters with (sensitized) and without (unsensitized) chronic Staphylococcus aureus infection. At 1 and 3 wk after implantation, three cows were sacrificed and mammary tissues processed to examine the cytological response to interleukin-2. Concentrations of lymphoid cells were determined in tissues lining teat and gland cistern linings, and plasma cells were characterized by Ig class. For total lymphoid cell and IgG1 and IgG2 plasma cell concentrations, sensitized placebo quarters and unsensitized interleukin-2 quarters were similar, indicating interleukin-2 stimulated a cellular immune response equal to that of quarters infected with S. aureus. Greatest response was observed in sensitized interleukin-2 quarters, suggesting that the cytokine was more effective in quarters with prior exposure to S. aureus antigens. Greater numbers of lymphocytes and macrophages were found in secretions of interleukin-2 quarters than in secretion of control quarters. Local interleukin-2 immunostimulation may supplement immunization procedures and enhance protection against natural S. aureus challenge.