The “FIFTY SHADOWS” of the RALES Trial: Lessons about the Potential Risk of Dietary Potassium Supplementation in Patients with Chronic Kidney Disease

Hyperkalaemia (HK) is one of the most common electrolyte disorders and a frequent reason for nephrological consultations. High serum potassium (K⁺) levels are associated with elevated morbidity and mortality, mainly due to life-threatening arrhythmias. In the majority of cases, HK is associated with chronic kidney disease (CKD), or with the use of renin–angiotensin–aldosterone system inhibitors (RAASis) and/or mineral corticoid antagonists (MRAs). These drugs represent the mainstays of treatment in CKD, HF, diabetes, hypertension, and even glomerular diseases, in consideration of their beneficial effect on hard outcomes related to cardiovascular events and CKD progression. However, experiences in relation to the Randomised Aldactone Evaluation Study (RALES) cast a long shadow that extends to the present day, since the increased risk for HK remains a major concern. In this article, we summarise the physiology of K⁺ homeostasis, and we review the effects of dietary K⁺ on blood pressure and cardiovascular risk in the general population and in patients with early CKD, who are often not aware of this disease. We conclude with a note of caution regarding the recent publication of the SSaSS trial and the use of salt substitutes, particularly in patients with a limited capacity to increase K⁺ secretion in response to an exogenous load, particularly in the context of “occult” CKD, HF, and in patients taking RAASis and/or MRAs.

Occurrence of antibiotics and antibiotic-resistant bacteria (ARB) in the Nervión river

The main hydrometeorological, microbiological and physico-chemical characteristics of the Nervión river were monitored during a year, including 10 antibiotics and the presence of bacteria resistant to these antibiotics among faecal coliforms (FC) and total aerobic bacteria at 22 °C (TAB₂₂). The characteristics of the river water were variable without a clear seasonal component, strongly influenced by rainfall, with a good quality for drinking water production throughout the year according to the physico-chemical parameters. The antibiotic resistant bacteria isolated from the water of the Nervión river were especially resistant to β-lactams and macrolide antibiotics, highlighting the absence of resistance to derivatives of tetracyclines among strains of TAB₂₂. A third of the isolated strains were multi-resistant to antibiotics with a seasonal component in its presence, with multi-resistant FC more abundant during summer and multi-resistant TAB₂₂ more abundant during winter. The presence of antibiotics in the waters of the Nervión river was not very significant, with total absence of β-lactams, minocycline and ciprofloxacin. Erythromycin and clarithromycin can be considered ubiquitous with mean concentrations of 2.5 ± 2.3 ngL^-1 and 5.7 ± 4.6 ngL^-1 respectively, and the presence of sulfamethoxazole and trimethoprim was also noticeable with maximum concentrations of 78.3 ngL^-1 for sulfamethoxazole. Dilution due to the increase of rainfall was observed for several analysed antibiotics, but without significant seasonal differences.

Photo-bioconvection: towards light control of flows in active suspensions

The persistent motility of individual constituents in microbial suspensions represents a prime example of the so-called active matter systems. Cells consume energy, exert forces and move, overall releasing the constraints of equilibrium statistical mechanics of passive elements and allowing for complex spatio-temporal patterns to emerge. Moreover, when subject to physico-chemical stimuli their collective behaviour often drives large-scale instabilities of a hydrodynamic nature, with implications for biomixing in natural environments and incipient industrial applications. In turn, our ability to exert external control of these driving stimuli could be used to govern the emerging patterns. Light, being easily manipulable and, at the same time, an important stimulus for a wide variety of microorganisms, is particularly well suited to this end. In this paper, we will discuss the current state, developments and some of the emerging advances in the fundamentals and applications of light-induced bioconvection with a focus on recent experimental realizations and modelling efforts. This article is part of the theme issue 'Stokes at 200 (part 2)'.

On the fate of sinking diatoms: the transport of active buoyancy-regulating cells in the ocean

Diatoms are one of the most abundant, diverse and ecologically relevant phytoplanktonic group, contributing enormously to global biogeochemical processes like the carbon and silica cycles. This large success has been partly attributed to the mechanical and optical properties of the silica shell (the frustule) that envelops their body. But since they lack motility it is difficult to conceive how they cope with the fast-fluctuating environment they live in and where distributions of resources are very heterogeneous and dynamical. This pinpoints an important but yet poorly understood feature of diatoms physiology: buoyancy regulation that helps them controlling their sinking speed and position in the water column. While buoyancy regulation by light and nutrients availability has been well studied, the effect of hydromechanical stress via fluid shear has been rather overlooked when considering diatoms dynamics. Here, we aim to start filling this gap by first presenting direct experimental evidences for buoyancy control in response to hydro-mechanical stress and then review recent theoretical models where simple couplings between local shear and buoyancy control always result in heterogeneous cell distributions, specific accumulation regions within complex flows and increased sedimentation times to the depths, features of direct ecological relevance. We conclude by suggesting future experiments aiming to unveil such coupling and therefore gain better understanding on the fate of these fascinating microorganisms in their natural habitat. This article is part of the theme issue 'Stokes at 200 (part 2)'.

Anaerobic submerged membrane bioreactor (AnSMBR) treating municipal wastewater at ambient temperature: Operation and potential use for agricultural irrigation

A 496 L pilot scale anaerobic submerged membrane bioreactor (AnSMBR) for the treatment of municipal wastewater was evaluated during a year of stable operation at ambient (28-10 °C) temperature, and inoculated with mesophilic inoculum. The temperature was the main parameter affecting the process performance. The chemical oxygen demand (COD) of the effluent was around 150 mg O₂/L in the summer period, operating with a volumetric loading rate (VLR) of 5 kg COD/m³ d and hydraulic retention time (HRT) of 8-10 h, with a specific methane production between 0.09 and 0.14 Nm³/kg COD_removed. However, during the winter season, an important increase of effluent COD was observed, and therefore the VLR was decreased to values around 1 kg COD/m³ d in order to recover the quality of the effluent. Biogas production was negligible in this period. The effluent complies with the parameters stipulated by Spanish law regarding the use of treated wastewater for agricultural irrigation.

Switch from epoetin to darbepoetin alfa in hemodialysis: dose equivalence and hemoglobin stability

Aim

The objective of the study reported here was to describe dose equivalence and hemoglobin (Hb) stability in a cohort of unselected hemodialysis patients who were switched simultaneously from epoetin alfa to darbepoetin alfa.

Methods

This was a multicenter, observational, retrospective study in patients aged ≥18 years who switched from intravenous (IV) epoetin alfa to IV darbepoetin alfa in October 2007 (Month 0) and continued on hemodialysis for at least 24 months. The dose was adjusted to maintain Hb within 1.0 g/dL of baseline.

Results

We included 125 patients (59.7% male, mean [standard deviation (SD)] age 70.4 [13.4] years). No significant changes were observed in Hb levels (mean [SD] 11.9 [1.3] g/dL, 12.0 [1.5], 12.0 [1.5], and 12.0 [1.7] at Months −12, 0, 12 and 24, respectively, P=0.409). After conversion, the erythropoiesis-stimulating agent (ESA) dose decreased significantly (P<0.0001), with an annual mean of 174.7 (88.7) international units (IU)/kg/week for epoetin versus 95.7 (43.4) (first year) and 91.4 (42.7) IU/kg/week (second year) for darbepoetin (65% and 64% reduction, respectively). The ESA resistance index decreased from 15.1 (8.5) IU/kg/week/g/dL with epoetin to 8.1 (3.9) (first year) and 7.9 (4.0) (second year) with darbepoetin (P<0.0001). The conversion rate was 354:1 in patients requiring high (>200 IU/kg/week) doses of epoetin and 291:1 in patients requiring low doses.

Conclusion

In patients on hemodialysis receiving ESAs, conversion from epoetin alfa to darbepoetin alfa was associated with an approximate and persistent reduction of 65% of the required dose. To maintain Hb stability, a conversion rate of 300:1 seems to be appropriate for most patients receiving low doses of epoetin alfa (≤200 IU/kg/week), while 350:1 would be better for patients receiving higher doses.

Cost-effectiveness analysis of the Spanish renal replacement therapy program

BACKGROUND

We undertook a cost-effectiveness analysis of the Spanish Renal Replacement Therapy (RRT) program for end-stage renal disease patients from a societal perspective. The current Spanish situation was compared with several hypothetical scenarios.

METHODS

A Markov chain model was used as a foundation for simulations of the Spanish RRT program in three temporal horizons (5, 10, and 15 years). The current situation (scenario 1) was compared with three different scenarios: increased proportion of overall scheduled (planned) incident patients (scenario 2); constant proportion of overall scheduled incident patients, but increased proportion of scheduled incident patients on peritoneal dialysis (PD), resulting in a lower proportion of scheduled incident patients on hemodialysis (HD) (scenario 3); and increased overall proportion of scheduled incident patients together with increased scheduled incidence of patients on PD (scenario 4).

RESULTS

The incremental cost-effectiveness ratios (ICERs) of scenarios 2, 3, and 4, when compared with scenario 1, were estimated to be, respectively, -€83 150, -€354 977, and -€235 886 per incremental quality-adjusted life year (ΔQALY), evidencing both moderate cost savings and slight effectiveness gains. The net health benefits that would accrue to society were estimated to be, respectively, 0.0045, 0.0211, and 0.0219 ΔQALYs considering a willingness-to-pay threshold of €35 000/ΔQALY.

CONCLUSIONS

Scenario 1, the current Spanish situation, was dominated by all the proposed scenarios. Interestingly, scenarios 3 and 4 showed the best results in terms of cost-effectiveness. From a cost-effectiveness perspective, an increase in the overall scheduled incidence of RRT, and particularly that of PD, should be promoted.

Cost analysis of the Spanish renal replacement therapy programme

BACKGROUND

A cost analysis of the Spanish Renal Replacement Therapy (RRT) programme in the year 2010, for end-stage renal disease (ESRD) patients, was performed from the perspective of the Public Administration.

METHODS

The costs associated with each RRT modality [hemodialysis (HD), peritoneal dialysis (PD) and kidney transplantation (Tx)] were analysed. The Spanish ESRD incidence and prevalence figures in the year 2010 were forecasted in order to enable the calculation of an aggregate cost for each modality. Costs were mainly computed based on a review of the existing literature and of the Official Bulletins of the Spanish Autonomous Communities. Data from Oblikue Consulting eSalud health care costs database and from several Spanish public sources were also employed.

RESULTS

In the year 2010, the forecasted incidence figures for HD, PD and Tx were 5409, 822 and 2317 patients, respectively. The forecasted prevalence figures were 22,582, 2420 and 24,761 patients, respectively. The average annual per-patient costs (incidence and prevalence) were €2651 and €37,968 (HD), €1808 and €25,826 (PD) and €38,313 and €6283 (Tx). Indirect costs amounted to €8929 (HD), €7429 (PD) and €5483 (Tx). The economic impact of the Spanish RRT programme on the Public Administration budget was estimated at ~€1829 million (indirect costs included): €1327 (HD), €109 (PD) and €393 (Tx) million.

CONCLUSIONS

HD accounted for >70% of the aggregate costs of the Spanish RRT programme in 2010. From a costs minimization perspective, it would be preferable if the number of incident and prevalent patients in PD were increased.

[Intra-dialysis parenteral nutrition in chronic renal patients: consensus SEN-SENPE]

Given the high prevalence of the hyponutrition state among haemodialysis patients and knowing that this implies an increase in the rates of infection, hospitalisation and hospital stay, which translates into an increase in global morbid-mortality, the Spanish Society of Nephrology (SEN) and the Spanish Society of Parenteral and Enteral Nutrition (SENPE) have reached a consensus on the indications, contraindications, and limitations of Intra-Dialysis Parenteral Nutrition (IDPN.) This consensus considers IDPN as a valid alternative to other types of nutritional support when these show their lack of efficacy. The bases are set regarding the timing of nutritional intervention with IDPN, its ideal composition, the time of administration, its controls, follow-up schedules, and the time at which the nutritional support has to be discontinued.

[Dialysis and transplant. Spain in 2005]

In 2005, renal replace treatment (dialysis and transplant) was necessary for about 40,000 people, without being known the number accurate and either their basic characteristics, such as: time in treatment, modality or treatment changes. The presented data cover the 76% of the Spanish population and are the result of the cooperation among technicians of registries, nephrologists and transplant coordinations. 4,125 people started RRT in 2005, the total estimated acceptance rate for renal replacement therapy in adults in Spain was 126 pmp and regarding other European countries it locates us in an intermediate area. The incidence rate seems to keep stable in the last years although there were some differences among communities (from 104 pmp in Castile and Leon to 186 pmp in Canary Islands). Diabetes Mellitus is the most diagnosed cause of renal failure in 2005, more than 20% of patients, followed by vascular diseases. The estimated prevalence of renal replacement therapy in Spain at the end of 2005 was 903 pmp, with important variations among communities (from 806 pmp in Cantabria to 1056 pmp in Valencia Region). The 47% of prevalent RRT patients had a functioning transplant. Mortality on haemodialysis and peritoneal dialysis was 13.7% and 10.8% respectively. Mortality on transplant was 1.3%, one of the lowest values registered so far. Mortality on renal replacement therapy was around 5% among patients from 45 to 64 years, 11% between 65 and 74 years and 19% among the patients older than 75 years.

Impact of end-stage renal disease care in planned dialysis start and type of renal replacement therapy—a Spanish multicentre experience

BACKGROUND

Timely referral, preparation and initiation of dialysis remain problematic issues. The purpose of this study is to analyse the effect of chronic renal disease care and education on the mode of dialysis start (planned vs non-planned) and on the modality of renal replacement therapy (RRT).

METHODS

A total of 1504 patients from 35 hospitals started RRT in 2003. Out-patient, scheduled initiation of dialysis with a permanent vascular or peritoneal access was considered planned.

RESULTS

About 46% of the patients started non-planned dialysis. Of all the patients, 75% had > or =3 months of nephrological follow-up, but nearly half were never educated on dialysis options. Haemodialysis (HD) occurred in 82% and peritoneal dialysis (PD) in 18%. Planned starts were associated (all P < 0.001) with many factors: younger age, longer renal and pre-dialysis follow-up, more education on RRT and general care, more medical visits, more PD (27 vs 8%), more follow-up by specific end-stage renal disease (ESRD) units, more permanent access and better biochemical status at the start of dialysis. Some global differences were found between patients: planned vs non-planned with > or =3 months of follow-up, vs non-planned <3 months follow-up or acute non-planned and <3 months of follow-up or acute patients. HD occurred in a similar rate (92%) in patients with non-planned start, no previous follow-up or who were never educated in dialysis modality options.

CONCLUSION

Although a high prevalence of nephrologic care and follow-up was provided among incident patients in dialysis, nearly half the patients did not have a planned dialysis start nor dialysis modality education. Planned start was associated with better analytical and multidisciplinary status. PD was more prevalent in planned starts and when education was given. Specific ESRD units were more likely to provide an optimal care.

[Guidelines of the Spanish Society of Nephrology. Clinical practice guidelines for peritoneal dialysis]

In Spain and in each of its autonomous communities, the dialysis treatment of chronic renal disease stage 5 is totally covered by public health. Peritoneal dialysis, in any of its modalities, is established as the preferred home dialysis technique and is chosen by high percentage of patients as their choice in dialysis treatment. The Spanish Society of Nephrology has promoted a project of creation of performance guides in the field of peritoneal dialysis, entrusting a work group composed of members of the Spanish Society of Nephrology a with the development of these guides. The information offered is based on levels of evidence, opinion and clinical experience of the most relevant publications of the topic. In these guides, after defining the concept of << peritoneal dialysis>>, the obligations and responsibilities of the sanitation team of the peritoneal dialysis unit are determined, and protocols and performance procedures that try to include all the aspects that concern the patient with chronic renal disease in substitute treatment with this technique are developed. They propose prescription objectives based on available clinical evidence and, lacking this, on the consensus of the experts' opinions. The final aim is to improve the care and quality of the of the patient in peritoneal dialysis, optimizing in this way the survival of the patient and of the technique. In Spain, as in other neighbouring countries, peritoneal dialysis has an incidence and prevalence that is much lower than that of hemodialysis, ranging in the last evaluation by the Spanish Society of Nephrology between 5 and 24% in the different autonomous communities. The great majority of peritoneal dialysis units form part of the public network of the Spanish state, with special representation as a Satellite Unit or Concerted Center related to the public hospital of reference, on which it must depend.

Prevalencia de la infección por el VIH en centros de diálisis en España y potenciales candidatos para trasplante renal: resultados de una encuesta española

INTRODUCTION

Patients with HIV infection and end-stage renal disease (ESRD) have improved their survival in the last few years. HIV infection is not considered a contradiction for renal transplantation, but little experience exists in renal transplantation in HIV infected individuals. There is no information about the prevalence of HIV infection in Spanish patients under renal replacement therapies (RRT).

METHODS

A survey was performed in Spanish dialysis units during 2004. The objective was to study the prevalence and characteristics of HIV infection in patients under RRT in Spain. We also aimed to know how many of them met the Spanish criteria to be included on the renal transplantation waiting list.

RESULTS

HIV prevalence was 1.15% (95%CI 0.85-1.45) of 4,962 patients who were under RRT, mostly under hemodialysis and, less commonly, peritoneal dialysis. The most frequent risk factor for HIV infection was parenteral drug use (58%). The most common causes of ESRD were glomerulonephritis (44%). The median time under RRT was 46 months. Coinfections with hepatitis C (60%) and B (7%) were found. Thirty-four percent of patients had a history of aids-defining events. Eighty-six percent were under HAART. The median CD4 cell count was 333 cells/.l and the viral load was undetectable in 68%. Of 40 patients with a completed clinical questionnaire, 9 (22.5%) met the Spanish criteria for renal transplantation.

CONCLUSION

HIV prevalence in patients under RRT in Spain is 1.15% (0.85%-1.45%) and 22.5% percent of these patients met the Spanish criteria to be included on a renal transplantation waiting list.

[Vascular access guidelines for hemodialysis]

Quality of vascular access (VA) has a remarkable influence in hemodialysis patients outcomes. Dysfunction of VA represents a capital cause of morbi-mortality of these patients as well an increase in economical. Spanish Society of Neprhology, aware of the problem, has decided to carry out a revision of the issue with the aim of providing help in comprehensión and treatment related with VA problems, and achieving an homogenization of practices in three mayor aspects: to increase arteriovenous fistula utilization as first vascular access, to increment vascular access monitoring practice and rationalise central catheters use. We present a consensus document elaborated by a multidisciplinar group composed by nephrologists, vascular surgeons, interventional radiologysts, infectious diseases specialists and nephrological nurses. Along six chapters that cover patient education, creation of VA, care, monitoring, complications and central catheters, we present the state of the art and propose guidelines for the best practice, according different evidence based degrees, with the intention to provide help at the professionals in order to make aproppiate decissions. Several quality standars are also included.

Renal cell carcinoma co-existent with other renal disease: clinico-pathological features in pre-dialysis patients and those receiving dialysis or renal transplantation

BACKGROUND

Patients on chronic dialysis are prone to developing acquired cystic kidney disease (ACKD), which may lead to the development of renal cell carcinoma (RCC). The risk factors for the development of RCC so far have not been determined in pre-dialysis patients with co-existent renal disease. The aim of this study was to evaluate the clinico-pathological features of RCC in pre-dialysis patients with associated renal diseases or in those undergoing chronic dialysis and renal transplantation.

METHODS

We studied 32 kidneys from 31 patients with RCC and associated renal diseases. Of those, 18 kidneys were from 17 patients not on renal replacement therapy (RRT) when diagnosed with RCC; 14 patients received dialysis or dialysis followed by renal transplantation. Several clinico-pathological features were analysed and compared between the two groups.

RESULTS

Overall, there was a preponderance of males (75%); nephrosclerosis was the predominant co-existent disease (31%). The median intervals from renal disease to RCC in the dialysis and transplanted groups were significantly longer than in the pre-dialysis group (15.8+/-1.1 vs 2.4+/-0.7 years, P<0.0001). In contrast to pre-dialysis RCC, the dialysis and transplant RCC groups had greater frequency of ACKD (100 vs 28%, P<0.0001), papillary type RCC (43 vs 11%, P<0.05) and multifocal tumours (43 vs 5%, P<0.05). At the end of the study, 71% of dialysis and transplanted patients and 72% of pre-dialysis patients were alive.

CONCLUSIONS

ACKD develops in dialysis patients, as it does in those with renal disease prior to RRT. The duration of renal disease, rather than the dialysis procedure itself, appears to be the main determinant of ACKD and RCC. The RCC occurring in patients with ACKD and prolonged RRT is more frequently of the papillary type and multifocal than the RCC occurring in patients with no or few acquired cysts and a short history of renal disease. Long-term outcomes did not differ between the two groups.

[Intracellular pH changes induced by sclerosing agents in peritoneal fibroblasts]

Sclerosing encapsulating peritonitis secondary to peritoneal dialysis has been associated to acetate-containing dialysis fluids, hypertonic glucose and disinfectants. Physiopathologic mechanisms of fibrotic proliferation that implicate those agents are not totally explained. With an experimental approach using cultured peritoneal fibroblasts, we have studied intracellular pH changes and Na+/H+ antiporter activity under cells perfusion with peritoneal dialysis liquids containing acetate, lactate, hypertonic glucose and interleukin-1. All experiments were performed at extracellular pH 7.4 and physiologic HCO3/CO2 concentration.

RESULTS

35 mM acetate produced a huge intracellular acidosis (ipH = 6.80 +/- 0.08). Lactate effect was less important (6.95 +/- 0.07), with a slow ipH recovery in about 30 min in both cases. IL-1, 10(-6) M also reduced ipH to 7.10 +/- 0.03. Acidosis was linked to Ca2+ outflow via Ca/H exchange and was blocked with Cd 20 nM. Extracellular Na = 0 and amiloride totally inhibited ipH recovery after acetate, lactate, or interleukin-induced acidosis. Hypertonic glucose perfusion increased ipH (7.31 +/- 0.06) for 5-7 min. This increase was also inhibited by amiloride or extracellular Na absence. Na+/H+ exchanger activity increased to 58%, and kept activated after ipH recovery. In conclusion, acetate, hypertonic glucose and IL-1 showed the common effect of stimulating the sodium-proton exchanger by different mechanisms, giving a possibility of potentiation. Activated Na+/H+ exchanger may act as a signal-transduction increasing fibroblast proliferation and explaining the cellular mechanism of sclerosing peritonitis.

Amoebicidal and giardicidal compounds from the leaves of Zanthoxylum liebmannianun

The crude ethanol extract from the leaves of Zanthoxylum liebmannianum exhibited inhibitory effect on the reproduction of trophozoites of Entamoeba histolytica (IC(50)=3.48 microg/ml) and Giardia lamblia (IC(50)=58.00 microg/ml). From this extract, asarinin, hyperin, beta-sitosterol, and beta-sitosterol glucoside were isolated. Among them, asarinin was the most active with IC(50) values of 19.86 microg/ml for E. histolytica and 35.45 microg/ml for G. lamblia. The remaining compounds showed moderate activity against both parasites.

Structural levansucrase gene (lsdA) constitutes a functional locus conserved in the species Gluconacetobacter diazotrophicus

Levansucrase (EC 2.4.1.10) was identified as a constitutive exoenzyme in 14 Gluconacetobacter diazotrophicus strains recovered from different host plants in diverse geographical regions. The enzyme, consisting of a single 60-kDa polypeptide, hydrolysed sucrose to synthesise oligofructans and levan. Sugar-cane-associated strains of the most abundant genotype (electrophoretic type 1) showed maximal values of levansucrase production. These values were three-fold higher than those of the isolates recovered from coffee plants. Restriction fragment length polymorphism analysis revealed a high degree of conservation of the levansucrase locus (IsdA) among the 14 strains under study, which represented 11 different G. diazotrophicus genotypes. Targeted disruption of the lsdA gene in four representative strains abolished their ability to grow on sucrose, indicating that the endophytic species G. diazotrophicus utilises plant sucrose via levansucrase.

Levansucrase from Acetobacter diazotrophicus SRT4 is secreted via periplasm by a signal-peptide-dependent pathway

Acetobacter diazotrophicus SRT4 secretes a constitutive levansucrase (LsdA) (EC 2.4.1.10) that is responsible for sucrose utilization. Immunogold electron microscopical studies revealed that LsdA accumulates in the periplasm before secretion. The periplasmic and extracellular forms of the enzyme were purified to homogeneity. Both proteins exhibited similar physical and biochemical characteristics indicating that LsdA adopts its final conformation in the periplasm. The N-terminal sequence of mature LsdA was pGlu-Gly-Asn-Phe-Ser-Arg as determined by PSD-MALDI-TOFMS (post-source decay-matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry). Comparison of this sequence with the predicted precursor protein revealed the cleavage of a 30-residue typical signal peptide followed by the formation of the pyroglutamic acid (pGlu) residue. Thus, in contrast with other Gram-negative bacteria, A. diazotrophicus secretes levansucrase by a signal-peptide-dependent mechanism.

Substitution of Asp-309 by Asn in the Arg-Asp-Pro (RDP) motif of Acetobacter diazotrophicus levansucrase affects sucrose hydrolysis, but not enzyme specificity

beta-Fructofuranosidases share a conserved aspartic acid-containing motif (Arg-Asp-Pro; RDP) which is absent from alpha-glucopyranosidases. The role of Asp-309 located in the RDP motif of levansucrase (EC 2.4.1.10) from Acetobacter diazotrophicus SRT4 was studied by site-directed mutagenesis. Substitution of Asp-309 by Asn did not affect enzyme secretion. The kcat of the mutant levansucrase was reduced 75-fold, but its Km was similar to that of the wild-type enzyme, indicating that Asp-309 plays a major role in catalysis. The two levansucrases showed optimal activity at pH 5.0 and yielded similar product profiles. Thus the mutation D309N affected the efficiency of sucrose hydrolysis, but not the enzyme specificity. Since the RDP motif is present in a conserved position in fructosyltransferases, invertases, levanases, inulinases and sucrose-6-phosphate hydrolases, it is likely to have a common functional role in beta-fructofuranosidases.

Evaluation of a small organ procurement organization in the Basque country, Spain

A limited supply of organs is the main obstacle for organ transplantation. The shortage reflects not only a shortage of donors but also a failure to make use of existing donors. The Basque Country Transplant Coordination Team is an organ procurement organization that operates in the Basque country, an area of 7260 km2 with 2.1 million inhabitants. From January 1, 1990, to December 31, 1995, the number of potential cadaveric organ donors found by the team increased, to 70 donors per million inhabitants in 1995. Since 1993, the organization has had more than 30 donors per million persons and has procured more than 90 cadaveric organs, including more than 60 cadaveric kidneys, per million persons. Because of these rates, the team coordinated 61.7 cadaveric kidney transplants per million persons during 1995. This paper describes some characteristics of the Basque organ procurement organization that might explain these results.

Ambulatory vs. In-Patient Stapedectomy: A Randomized Twenty-Patient Pilot Study

A prospective study was undertaken to determine whether stapedectomy can safely be performed in an outpatient setting. Twenty patients with otosclerosis amenable to surgical treatment were divided into two groups; those in the hospitalized group were admitted the day before surgery and discharged 24 hours after the procedure. The patients in the ambulatory group were admitted on the day surgery was scheduled and released 1 or 2 hours after the procedure. We analyzed the intensity and duration of postoperative vertigo, and the hearing gain obtained, studying the speech frequencies (500 to 2000 Hz) separately from the high frequencies (4000 to 8000 Hz). No significant difference was found at 4, 3, and 6 months of follow-up in any of the parameters studied, concluding that small-fenestra stapedectomy can safely be performed as an outpatient procedure.

Ambulatory vs. in-patient stapedectomy: a randomized twenty-patient pilot study

A prospective study was undertaken to determine whether stapedectomy can safely be performed in an outpatient setting. Twenty patients with otosclerosis amenable to surgical treatment were divided into two groups; those in the hospitalized group were admitted the day before surgery and discharged 24 hours after the procedure. The patients in the ambulatory group were admitted on the day surgery was scheduled and released 1 or 2 hours after the procedure. We analyzed the intensity and duration of postoperative vertigo, and the hearing gain obtained, studying the speech frequencies(500 to 2000 Hz) separately from the high frequencies (4000 to 8000 Hz). No significant difference was found at 1, 3, and 6 months of follow-up in any of the parameters studied, concluding that small-fenestra stapedectomy can safely be performed as an outpatient procedure.

Isolation and enzymic properties of levansucrase secreted by Acetobacter diazotrophicus SRT4, a bacterium associated with sugar cane

Acetobacter diazotrophicus, a nitrogen-fixing bacterium associated with sugar cane, secretes a levansucrase (sucrose-2,6-beta-D-fructan 6-beta-D-fructosyltransferase; EC 2.4.1.10). This enzyme is constitutively expressed and represents more than 70% of the total proteins secreted by strain SRT4. The purified protein consists of a single 58 kDa polypeptide with an isoelectric point of 5.5. Its activity is optimal at pH 5.0. It catalyses transfructosylation from sucrose to a variety of acceptors including water (sucrose hydrolysis), glucose (exchange reaction), fructan (polymerase reaction) and sucrose (oligofructoside synthesis). In vivo the polymerase activity leads to synthesis of a high-molecular-mass fructan of the levan type. A. diazotrophicus levansucrase catalyses transfructosylation via a Ping Pong mechanism involving the formation of a transient fructosyl-enzyme intermediate. The catalytic mechanism is very similar to that of Bacillus subtilis levansucrase. The kinetic parameters of the two enzymes are of the same order of magnitude. The main difference between the two enzyme specificities is the high yield of oligofructoside, particularly 1-kestotriose and kestotetraose, accumulated by A. diazotrophicus levansucrase during sucrose transformation. We discuss the hypothesis that these catalytic features may serve the different biological functions of each enzyme.

[Role of environmental factors in the development of insulin-dependent diabetes mellitus (IDDM) in Venezuelan children]

In view of the controversy surrounding the role of environmental factors, such as the presence of bovine albumin in milk, or viral infections, in the etiology of IDDM, a study was undertaken to determine the relationship between these events and the subsequent risk of developing IDDM. On 40 venezuelan diabetic children (< 18 y) and forty, age, sex and race-matched controls were studied at the same time. Parents of children completed a questionnaire on the infant's feeding habits, its environment and family history. The X2 method and the Fischer's exact test were used to analyze the results. We found that 20% of the controls, and 10% of IDDM (NS), were never breast-fed. In 95% of controls vs 65% of IDDM (p < 0.001), cow's milk was given exclusively from birth, or combined with breast-feeding, 65% of IDDM and 60% of controls (NS) were breast-fed (alone or combined with milk substitutes) for more than three months. These results do not support the hypothesis that early exposure to breast milk substitutes increases the risk of IDDM in venezuelan children. The study revealed, however, that a family history of diabetes mellitus was present in 55% of IDDM vs 30% of controls (p < 0.05) and mumps infection before the onset of diabetes was recorded in 42.5% of IDDM in comparison with 12.5% of controls (p = 0.005). Other viral infections (rubella, chicken pox) had no statistical significance. The latter results suggest an association between a family history of diabetes mellitus and viral infections with the development of IDDM among this group of children.

Intracellular acidification associated with changes in free cytosolic calcium. Evidence for Ca2+/H+ exchange via a plasma membrane Ca(2+)-ATPase in vascular smooth muscle cells

The purpose of this study was to define the mechanism whereby agonists that increase free cytosolic calcium (Cai2+) affect intracellular pH (pHi) in smooth muscle. Rat aortic vascular smooth muscle cells grown on coverslips were loaded with BCECF/AM or fura-2/AM for continuous monitoring of pHi or Cai2+, respectively, in a HCO3-/CO2- containing medium. Recovery from rapid increases in Cai2+ produced by 1 microM angiotensin (Ang) II (delta Cai2+ -229 +/- 43 nM) or 1 microM ionomycin (delta Cai2+ -148 +/- 19 nM) was accompanied by a fall in pHi (delta pHi, -0.064 +/- 0.0085 P < 0.01, and -0.05 +/- 0.012 pH units, P < 0.01, respectively). Neither the fall in pHi nor the rise in Cai2+ elicited by Ang II was prevented by pretreatment with agents which block the action of this agonist on pHi via the stimulation of the Cl/HCo3 exchangers (DIDS, 50 microM) or the Na+/H+ antiporter (EIPA, 50 microM). In the presence of DIDS and EIPA, Ang II produced a fall in pHi (delta pHi, -0.050 +/- 0.014, P < 0.01) and a rise in Cai2+ (delta Ca2+ 252 +/- 157 nM, P < 0.01). That the change in pHi was secondary to changes in Cai2+ was inferred from the finding that, when the rise in Cai2+ elicited by Ang II was prevented by preincubation with a Ca2+ buffer, BAPTA (60 microM), the fall in pHi was abolished as well (delta pHi, 0.0014 +/- 0.0046). The pHi fall produced by Ang II and ionomycin was prevented by cadmium at a very low concentration (20 nM) which is known to inhibit plasma membrane Ca(2+)-ATPase activity (delta pHi -0.002 +/- 0.0006 and -0.0016 pH units, respectively). Cadmium also blunted Cai2+ recovery after Ang II and ionomycin. These findings suggest that the fall in pHi produced by these agents is due to H+ entry coupled to Ca2+ extrusion via the plasma membrane Ca(2+)-ATPase. Our results indicate that agonists that increase Cai2+ cause intracellular acidification as a result of Ca2+/H+ exchange across the plasma membrane. This process appears to be mediated by a plasma membrane Ca(2+)-ATPase which, in the process of extruding Ca2+ from the cell, brings in [H+] and thus acidifies the cell.

En bloc kidney and bladder transplantation from an anencephalic donor into an adult recipient

The visceral block, composed of both kidneys and their vascular pedicles, inferior vena cava, ureters and bladder, was removed from a 3-day-old male anencephalic donor and transplanted into a 32-year-old adult in chronic renal failure. The urinary tract was reconstructed by vesicovesicostomy for technical ease, and prevention of reflux and ureteral stenosis. Maximum urine output was 150 ml. per day and the kidney grafts were lost owing to rejection 5 months after transplantation.