Renal handling of NH3/NH4+: recent concepts

To be appropriately excreted in urine, NH4+, the major component of urinary acid excretion, must be synthesized by proximal tubular cells, secreted into the proximal tubular fluid, reabsorbed by the medullary thick ascending limb (MTAL) to be accumulated in the medullary interstitium, and finally secreted in medullary collecting ducts. Several targets have been identified to account at the gene expression level for the adaptation of renal NH4+ synthesis and transport in response to a chronic acid load. These targets are the key enzymes of ammoniagenesis (mitochondrial glutaminase and glutamate dehydrogenase) and gluconeogenesis (phosphoenolpyruvate carboxykinase) and the Na+/H+(NH4+) exchanger NHE3 in the proximal tubule, the apical Na+-K+(NH4+)-2Cl- cotransporter of the MTAL, the basolateral Na+-K+(NH4+)-2Cl- cotransporter, and likely the epithelial Rh B and C glycoproteins in the collecting ducts. An acid pH per se appears to be a major factor in the control of the expression of these genes during metabolic acidosis probably through activation of pH sensors. Glucocorticoids may also act in concert with an acid pH to coordinate the adaptation of various tubular cell types. The present review focuses on some new aspects of NH3/ NH4+ transport and of regulations of gene expression that have recently emerged.     

Knowledge and attitudes of health care professionals with respect to AIDS and the risk of occupational transmission of HIV in 2 Moroccan hospitals

We carried out a survey of 266 health care workers at two hospitals, in Rabat and Casablanca, to evaluate the level of knowledge, attitudes and behavior of these individuals with respect to AIDS. We also analyzed working conditions presenting a risk of occupational transmission of HIV, with the aim of developing appropriate preventive measures. We carried out a cross-sectional study, using a standardized questionnaire. The study population consisted of 91 doctors (34.2%), 106 nurses (39.8%), 12 laboratory technicians (8. 8%) and 47 support staff (17.6%) working in various departments. The mean age was 32.7 years. This study population was young, with 83% less than 40 years old and more than half having worked in the hospital for less than ten years. We found that the personnel knew a great deal about the usual means of transmission of HIV, but much less about possible occupational contamination. One person in two was unaware of the ways in which HIV in the hospital environment can be inactivated (bleach - 70% alcohol) and only 18.4% knew that HIV is sensitive to heat. Half the study population thought that the systematic exclusion of patients with HIV was essential and two thirds suggested that every patient admitted to the hospital should undergo systematic HIV testing. Anxiety when caring for seropositive patients was expressed by 56% of doctors and 62% of paramedical workers and 85% thought that health workers were at high risk of contamination during their work. The frequency of occupational injuries was found to be high and such accidents were rarely declared (declaration rate 7%). Protection measures were not in place in more than 50% of cases and too little information and resources were available to increase the awareness of the health care workers. These data show that greater efforts should be made to educate and inform health workers by means of the occupational medicine units recently set up for the benefit of the staff.     

Chronic neutral phosphate supplementation induces sustained, renal metabolic alkalosis.

The aim of the present study was to test whether intravenous neutral phosphate supplementation, recently shown in our laboratory to acutely stimulate proton secretion in the distal nephron, was able to induce a sustained metabolic alkalosis. Neutral Na and K phosphate supplementation for seven days, with equivalent reduction in chloride supply and unchanged intake of sodium and potassium, in ADX rats receiving fixed physiological doses of aldosterone and dexamethasone (group 1, N = 7), was responsible for a severe metabolic alkalosis (MA; delta [HCO3] 11 +/- 1.3 mM, and delta pH 0.11 +/- 0.06 unit). Metabolic alkalosis was at least in part of renal origin, since net acid excretion (NAE) transiently increased, principally due to an increment in titratable acid excretion rate. Balances were equilibrated for sodium and negative for chloride and potassium, which may have contributed to the severity of the MA. Chronic i.v. neutral Na phosphate, without change in potassium and chloride supply, in ADX rats receiving the same doses of steroids (group 2, N = 5), was responsible for a less severe MA (delta [HCO3] 7.5 +/- 0.9 mM, and delta pH 0.07 +/- 0.01 unit), also of renal origin. In this group, balances were positive for chloride and sodium and equilibrated for potassium. Finally, neutral Na and K phosphate supplementation with reduction in chloride supply in intact rats (group 3, N = 4) was also able to induce a MA (delta [HCO3] 5.5 +/- 1.8 mM, and delta pH 0.06 +/- 0.01 unit) of renal origin, with balances negative for chloride and equilibrated for potassium and sodium. In all groups, the generation and maintenance of MA probably resulted from stimulated proton secretion in the distal nephron, as suggested by the observed increase of PCO2 over HCO3 concentration ratio in the urine and a fall in urine pH despite augmented urinary buffer content throughout the phosphate infusion period. Glomerular filtration rate did not significantly vary in any group. In conclusion, chronic supplementation of neutral phosphate appears to stimulate per se proton secretion in the distal nephron, independently of sodium, chloride, and potassium balances, and adrenal steroid secretion. Thus neutral phosphate supplementation should be added to the previously known factors able to induce MA.     

A thermosensitive chitosan-based hydrogel for the local delivery of paclitaxel.

A novel injectable thermosensitive in situ gelling hydrogel has been developed. The system, which falls under the BST-Gel platform technology developed at Biosyntech Inc. (Laval, QC, Canada), consists of a chitosan solution (C) neutralized with beta-glycerophosphate (GP) that is liquid at room temperature but gels when heated to body temperature. We propose to use this thermosensitive hydrogel for the sustained release of paclitaxel at tumor resection sites in order to prevent local tumor recurrence. The in vitro release profiles demonstrated controlled delivery over 1 month. The initial drug loading substantially affected the release. Local delivery of paclitaxel from the formulation injected intratumorally was investigated using EMT-6 tumors implanted subcutaneously on Balb/c mice. These experiments showed that one intratumoral injection of the thermosensitive hydrogel containing paclitaxel was as efficacious as four intravenous injections of Taxol in inhibiting the growth of EMT-6 cancer cells in mice, but in a less toxic manner. Further histological analysis revealed that while the proportion of necrotic areas was similar for the C/GP/paclitaxel and the Taxol-treated tumors, a disparity between tumor-associated inflammatory cell populations may suggest differing anti-tumor mechanisms.     

Perhexiline maleate-induced cirrhosis.

The authors report the cases of 2 patients who died from cirrhosis after receiving perhexiline maleate, a drug widely used in Europe for the treatment of angina pectoris. Perhexiline maleate had been ingested for 24 and 28 mo, respectively. Manifestations of cirrhosis included jaundice, hepatic encephalopathy, ascites, and portal hypertension. Associated manifestations of intolerance to perhexiline maleate included peripheral neuropathy in 1 patient and marked weight loss in both. Histologic lesions resembled those observed in patients with alcoholic liver disease. Ultrastructural lesions included numerous enlarged lysosomes containing myeloid figures. Histochemical stains demonstrated increased phospholipid content of the hepatocytes. These findings are consistent with the view that prolonged administration of perhexiline maleate may induce both histologic lesions resembling those of alcoholic liver disease and ultrastructural and histochemical lesions resembling those of phospholipidosis.     

Biological reaction to polyethylene particles in a murine calvarial model is highly influenced by age

Particle‐induced osteolysis is driven by multiple factors including bone metabolism, inflammation, and age. The objective of this study was to determine the influence of age on polyethylene (PE) particle‐induced osteolysis in a murine calvarial model comparing 2‐month‐old (young) versus 24‐month‐old (old) mice. After PE particle implantation, calvaria were assessed at days (D) 3, D7, D14, and D21 via chemoluminescent imaging for inflammation (L‐012 probe). In addition micro‐computed tomography (micro‐CT) and histomorphometry end points addressed the bone reaction. Inflammation peaked at D7 in young mice and D14 in old mice. Using micro‐CT, a nadir of mature bone was recorded at D7 for young mice, versus D21 for old mice. Besides, regenerating bone peaked at distinct timepoints: D7 for young mice versus D21 for old mice. In the young mice group, the histomorphometric findings correlated with micro‐CT regenerating bone findings at D7, associated with ample osteoïd deposition. No osteoïd could be histologically quantified in the old mice group at D7. This study demonstrated that the biological reaction to polyethylene particles is highly influenced by age. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:574–580, 2016.     

Residual oil fly ash worsens pulmonary hyperreactivity in chronic allergic mice

BALB/c mice received saline (SAL groups) or ovalbumin (OVA groups) intraperitoneally (days 1, 3, 5, 7, 9, 11 and 13). After 27 days, a burst of intratracheal OVA or SAL (days 40, 43 and 46) was performed. Animals were then divided into four groups (N=8, each) and intranasally instilled with saline (SAL-SAL and OVA-SAL) or residual oil fly ash (SAL-ROFA and OVA-ROFA). 24h later, total, initial and difference resistances (Rtot, Rinit, Rdiff) and static elastance (Est) were measured. Lung responsiveness to methacholine was assessed as slope and sensitivity of Est, Rtot, Rinit, and Rdiff. Lung morphometry (collapsed and normal areas and bronchoconstriction index) and cellularity (polymorphonuclear, mononuclear and mast cells) were determined. OVA or ROFA similarly impaired lung mechanics and increased the amount of polymorphonuclear cells and collapsed areas. OVA-ROFA showed even higher hyperresponsiveness, bronchoconstriction and mast cell infiltration. Thus, we concluded that ROFA exposure may add an extra burden to hyperresponsive lungs.     

Paracoccidioidomycosis: chronic adult unifocal form

Paracoccidioidomycosis is a highly prevalent systemic mycosis in Brazil. The primary cutaneous form is rare and occurs in the absence of pulmonary involvement. Lesions located in the distal regions of the lower limbs are not uncommon and particularly in the feet may go unnoticed or even be confused with infectious or neoplastic lesions of different etiologies. We report a case of paracoccidioidomycosis affecting the left great toe of a man, leading to complete destruction of the nail plate. Treatment was done with the sulfamethoxazole plus trimethoprim with excellent results.     

Pseudohypoaldosteronism type II: proximal renal tubular acidosis and dDAVP-sensitive renal hyperkalemia

The mechanisms of metabolic acidosis and hyperkalemia were investigated in a patient with chronic mineralocorticoid-resistant renal hyperkalemia (5.3-6.9 mmol/l), metabolic acidosis (arterial blood pH 7.27, total CO2 17 mmol/l), arterial hypertension, undetectable plasma renin activity (less than 0.10 ng/ml/h), high plasma aldosterone level (32-100 ng/dl), and normal glomerular filtration rate (131 ml/min/1.73 m2). During the hyperkalemic period, urine was highly acidic (pH 4.6-5.0), urinary NH4 excretion (10-13 microEq/min) and urinary net acid excretion (19-24 microEq/min) were not supernormal as expected from a chronic acid load. During NaHCO3 infusion, the maximal tubular HCO3 reabsorption was markedly diminished (19.8 mmol/l glomerular filtrate), and the fractional excretion of HCO3 (FE HCO3) when plasma HCO3 was normalized was 20%. Urine minus blood PCO2 increased normally during NaHCO3 infusion (31 mm Hg), and the urinary pH remained maximally low (less than 5.3) when the buffer urinary excretion sharply increased after NH4Cl load. When serum K was returned toward normal limits, metabolic acidosis disappeared, urinary NH4 excretion rose normally after short NH4Cl loading while the urinary pH remained maximally low (4.9-5.2), the maximal tubular HCO3 reabsorption returned to normal values (24.8 mmol/l glomerular filtrate), and FE HCO3 at normal plasma HCO3 was 1%. Nasal insufflation of 1-desamino-8-D-Arginine Vasopressin (dDAVP) resulted in an acute normalization of the renal handling of K and in an increase in net urinary acid excretion. We conclude that: the effect of dDAVP on renal handling of K may be explained by the reversal of the distal chloride shunt and/or an increase in luminal membrane conductance to K; the distal acidification seems to be normal which in the event of distal chloride shunt impairing distal hydrogen secretion might be explained by the presence of systemic acidosis which is a potent stimulus of hydrogen secretion, and metabolic acidosis in the steady state was accounted for by the diminution of bicarbonate reabsorption and ammonia production in the proximal tubule secondary to chronic hyperkalemia.