Impact of a vancomycin loading dose on the achievement of target vancomycin exposure in the first 24 h and on the accompanying risk of nephrotoxicity in critically ill patients

Background

The advocated pharmacokinetic/pharmacodynamic (PK/PD) target for vancomycin, AUC/MIC ≥ 400 mg·h/L, may not be reached with a conventional fixed starting dose of 1000 mg in critically ill patients, but increasing the dose may cause nephrotoxicity.

Objectives

To evaluate the effect of a weight-based loading dose of 25 mg/kg vancomycin on PK/PD target attainment in the first 24 h (AUC_0–24) in critically ill patients and to evaluate whether this increases the risk of acute kidney injury (AKI).

Patients and methods

A prospective observational before/after study was performed in ICU patients, comparing the percentage of vancomycin courses with AUC_0–24 ≥ 400 mg·h/L and the incidence of AKI, defined as worsening of the risk, injury, failure, loss of kidney function and end-stage kidney disease (RIFLE) score. The conventional dose group received 1000 mg of vancomycin as initial dose; the loading dose group received a weight-based loading dose of 25 mg/kg. A population PK model developed using non-linear mixed-effects modelling was used to estimate AUC_0–24 in all patients.

Results

One hundred and four courses from 82 patients were included. With a loading dose, the percentage of courses achieving AUC_0–24 ≥ 400 mg·h/L increased significantly from 53.8% to 88.0% (P = 0.0006). The percentage of patients with new-onset AKI was not significantly higher when receiving a 25 mg/kg loading dose (28.6% versus 37.8%; P = 0.48). However, the risk of AKI was significantly higher in patients achieving AUC_0–24 > 400 mg·h/L compared with patients achieving AUC < 400 mg·h/L (39.0% versus 14.8%; P = 0.031).

Conclusions

A weight-based loading dose of 25 mg/kg vancomycin led to significantly more patients achieving AUC_0–24 ≥ 400 mg·h/L without increased risk of AKI. However, some harm cannot be ruled out since higher exposure was associated with increased risk of AKI.

Longitudinal sampling is required to maximize detection of intrahost A/H3N2 virus variants

Seasonal human influenza viruses continually change antigenically to escape from neutralizing antibodies. It remains unclear how genetic variation in the intrahost virus population and selection at the level of individual hosts translates to the fast-paced evolution observed at the global level because emerging intrahost antigenic variants are rarely detected. We tracked intrahost variants in the hemagglutinin and neuraminidase surface proteins using longitudinally collected samples from 52 patients infected by A/H3N2 influenza virus, mostly young children, who received oseltamivir treatment. We identified emerging putative antigenic variants and oseltamivir-resistant variants, most of which remained detectable in samples collected at subsequent days, and identified variants that emerged intrahost immediately prior to increases in global rates. In contrast to most putative antigenic variants, oseltamivir-resistant variants rapidly increased to high frequencies in the virus population. Importantly, the majority of putative antigenic variants and oseltamivir-resistant variants were first detectable four or more days after onset of symptoms or start of treatment, respectively. Our observations demonstrate that de novo variants emerge, and may be positively selected, during the course of infection. Additionally, based on the 4–7 days post-treatment delay in emergence of oseltamivir-resistant variants in six out of the eight individuals with such variants, we find that limiting sample collection for routine surveillance and diagnostic testing to early timepoints after onset of symptoms can potentially preclude detection of emerging, positively selected variants.

Sensitivity of C-reactive protein and procalcitonin measured by Point-of-Care tests to diagnose urinary tract infections in nursing home residents: a cross-sectional study

Background

Diagnosing urinary tract infections (UTIs) in nursing home residents is complex, as specific urinary symptoms are often absent and asymptomatic bacteriuria (ASB) is prevalent. The aim of this study was to assess the sensitivity of blood C-reactive protein (CRP) and procalcitonin (PCT), measured by point-of-care tests (PoCTs), to diagnose UTIs in this setting.

Methods

Elderly residents (≥65 years old) with a suspected UTI were recruited from psychogeriatric, somatic, or rehabilitation wards across 13 participating nursing homes. CRP and PCT were tested simultaneously in the same study participants. To assess the tests’ sensitivities, a stringent definition of “true” UTI was used that included the presence of symptoms, urinary leucocytes, a positive urine culture, and symptom resolution during antibiotic treatment covering isolated uropathogen(s). The original sample size was 440 suspected UTI episodes, in order to detect a clinically relevant sensitivity of at least 65% when calculated using the matched analysis approach to compare both PoCTs.

Results

After enrollment of 302 episodes (68.6% of the planned sample size), an unplanned and funder-mandated interim analysis was done, resulting in premature discontinuation of the study for futility. For 247 of 266 eligible episodes, all mandatory items required for the true UTI definition (92.9%) were available. In total, 49 episodes fulfilled our stringent UTI definition (19.8%). The sensitivities of CRP (cut-off, 6.5 mg/L) and PCT (cut-off, 0.025 ng/mL) were 52.3% (95% confidence interval [CI], 36.7–67.5%) and 37.0% (95% CI, 23.2–52.5%), respectively.

Conclusions

Our results indicate that CRP and PCT are not suitable tests for distinguishing UTI and ASB in nursing home residents.

Clinical Trials Registration

Netherlands Trial Registry NL6293.

"A false sense of confidence" The perceived role of inflammatory point-of-care testing in managing urinary tract infections in Dutch nursing homes: a qualitative study

BACKGROUND

Diagnosing urinary tract infections (UTI) in nursing home residents is complex, due to frequent non-specific symptomatology and asymptomatic bacteriuria. The objective of this study was to explore health care professionals' perceptions of the proposed use of inflammatory marker Point-Of-Care Testing (POCT) in this respect.

METHODS

We conducted a qualitative inquiry (2018-2019) alongside the multicenter PROGRESS study (NL6293), which assessed the sensitivity of C-reactive protein and procalcitonin POCT in UTI. We used semi-structured face-to-face interviews. The participants were physicians (n = 12) and nurses (n = 6) from 13 nursing homes in the Netherlands. Most respondents were not familiar with inflammatory marker POCT, while some used POCT for respiratory tract infections. Both the interview guide and the analysis of the interview transcripts were based on the Consolidated Framework for Implementation Research.

RESULTS

All respondents acknowledged that sufficiently sensitive POCT could decrease diagnostic uncertainty to some extent in residents presenting with non-specific symptoms. They primarily thought that negative test results would rule out UTI and justify withholding antibiotic treatment. Secondly, they described how positive test results could rule in UTI and justify antimicrobial treatment. However, most respondents also expected new diagnostic uncertainties to arise. Firstly, in case of negative test results, they were not sure how to deal with residents' persisting non-specific symptoms. Secondly, in case of positive test results, they feared overlooking infections other than UTI. These new uncertainties could lead to inappropriate antibiotics use. Therefore, POCT was thought to create a false sense of confidence.

CONCLUSIONS

Our study suggests that inflammatory marker POCT will only improve UTI management in nursing homes to some extent. To realize the expected added value, any implementation of POCT requires thorough guidance to ensure appropriate use. Developing UTI markers with high negative and positive predictive values may offer greater potential to improve UTI management in nursing homes.

Interleukin-10 and soluble tumor necrosis factor receptor II are potential biomarkers of Plasmodium falciparum infections in pregnant women: a case-control study from Nanoro, Burkina Faso

Background

Diagnosis of malaria in pregnancy is problematic due to the low sensitivity of conventional diagnostic tests (rapid diagnostic test and microscopy), which is exacerbated due to low peripheral parasite densities, and lack of clinical symptoms. In this study, six potential biomarkers to support malaria diagnosis in pregnancy were evaluated.

Methods

Blood samples were collected from pregnant women at antenatal clinic visits and at delivery. Microscopy and real-time PCR were performed for malaria diagnosis and biomarker analyses were performed by ELISA (interleukin 10, IL-10; tumor necrosis factor-α, TNF-α; soluble tumor necrosis factor receptor II, sTNF-RII; soluble fms-like tyrosine kinase 1, sFlt-1; leptin and apolipoprotein B, Apo-B). A placental biopsy was collected at delivery to determine placental malaria.

Results

IL-10 and sTNF-RII were significantly higher at all time-points in malaria-infected women (p < 0.001). Both markers were also positively associated with parasite density (p < 0.001 and p = 0.003 for IL-10 and sTNF-RII respectively). IL-10 levels at delivery, but not during pregnancy, were negatively associated with birth weight. A prediction model was created using IL-10 and sTNF-RII cut-off points. For primigravidae the model had a sensitivity of 88.9% (95%CI 45.7–98.7%) and specificity of 83.3% (95% CI 57.1–94.9%) for diagnosing malaria during pregnancy. For secundi- and multigravidae the sensitivity (81.8% and 56.5% respectively) was lower, while specificity (100.0% and 94.3% respectively) was relatively high. Sub-microscopic infections were detected in 2 out of 3 secundi- and 5 out of 12 multigravidae.

Conclusions

The combination of biomarkers IL-10 and sTNF-RII have the potential to support malaria diagnosis in pregnancy. Additional markers may be needed to increase sensitivity and specificity, this is of particular importance in populations with sub-microscopic infections or in whom other inflammatory diseases are prevalent.

Electronic supplementary material

The online version of this article (10.1186/s40364-017-0114-7) contains supplementary material, which is available to authorized users.

A molecular epidemiological perspective of rhinovirus types circulating in Amsterdam from 2007 to 2012

Rhinoviruses (RVs) are frequently detected respiratory viruses that cause mild common cold symptoms, but may also lead to more severe respiratory tract infections. The large number of RV types, classified into species A, B and C, hampers clear insights into the epidemiology and clinical significance of each RV type. The aim of this study was to map the circulation of RV types in the Amsterdam area. RV-positive nasopharyngeal and oropharyngeal samples, collected from 2007 to 2012 in the Academic Medical Centre (Amsterdam, the Netherlands), were typed based on the sequence of the region coding for capsid proteins VP4 and VP2. RV-A, RV-B and RV-C were found in proportions of of 52.4% (334/637), 11.3% (72/637), and 36.2% (231/637), respectively. We detected 129 of the 167 currently classified types. RVs circulated throughout the entire year with a peak in the autumn and a decline in the summer. Some RV types were observed throughout the entire sampling period and others had a more seasonal pattern. Nine RV-A and four RV-B novel provisionally assigned types were identified. This study provides an insight into the molecular epidemiology of RVs in the Amsterdam area. The RVs circulating are diverse and include several provisionally new types.

Companion Animals as a Source of Viruses for Human Beings and Food Production Animals

Companion animals comprise a wide variety of species, including dogs, cats, horses, ferrets, guinea pigs, reptiles, birds and ornamental fish, as well as food production animal species, such as domestic pigs, kept as companion animals. Despite their prominent place in human society, little is known about the role of companion animals as sources of viruses for people and food production animals. Therefore, we reviewed the literature for accounts of infections of companion animals by zoonotic viruses and viruses of food production animals, and prioritized these viruses in terms of human health and economic importance. In total, 138 virus species reportedly capable of infecting companion animals were of concern for human and food production animal health: 59 of these viruses were infectious for human beings, 135 were infectious for food production mammals and birds, and 22 were infectious for food production fishes. Viruses of highest concern for human health included hantaviruses, Tahyna virus, rabies virus, West Nile virus, tick-borne encephalitis virus, Crimean-Congo haemorrhagic fever virus, Aichi virus, European bat lyssavirus, hepatitis E virus, cowpox virus, G5 rotavirus, influenza A virus and lymphocytic choriomeningitis virus. Viruses of highest concern for food production mammals and birds included bluetongue virus, African swine fever virus, foot-and-mouth disease virus, lumpy skin disease virus, Rift Valley fever virus, porcine circovirus, classical swine fever virus, equine herpesvirus 9, peste des petits ruminants virus and equine infectious anaemia virus. Viruses of highest concern for food production fishes included cyprinid herpesvirus 3 (koi herpesvirus), viral haemorrhagic septicaemia virus and infectious pancreatic necrosis virus. Of particular concern as sources of zoonotic or food production animal viruses were domestic carnivores, rodents and food production animals kept as companion animals. The current list of viruses provides an objective basis for more in-depth analysis of the risk of companion animals as sources of viruses for human and food production animal health.

Changes in microbiota during experimental human Rhinovirus infection

Background

Human Rhinovirus (HRV) is responsible for the majority of common colds and is frequently accompanied by secondary bacterial infections through poorly understood mechanisms. We investigated the effects of experimental human HRV serotype 16 infection on the upper respiratory tract microbiota.

Methods

Six healthy volunteers were infected with HRV16. We performed 16S ribosomal RNA-targeted pyrosequencing on throat swabs taken prior, during and after infection. We compared overall community diversity, phylogenetic structure of the ecosystem and relative abundances of the different bacteria between time points.

Results

During acute infection strong trends towards increases in the relative abundances of Haemophilus parainfluenzae and Neisseria subflava were observed, as well as a weaker trend towards increases of Staphylococcus aureus. No major differences were observed between day-1 and day 60, whereas differences between subjects were very high.

Conclusions

HRV16 infection is associated with the increase of three genera known to be associated with secondary infections following HRV infections. The observed changes of upper respiratory tract microbiota could help explain why HRV infection predisposes to bacterial otitis media, sinusitis and pneumonia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1081-y) contains supplementary material, which is available to authorized users.

Preparedness for admission of patients with suspected Ebola virus disease in European hospitals: a survey, August-September 2014

In response to the Ebola virus disease (EVD) outbreak in West Africa, the World Health Organization has advised all nations to prepare for the detection, investigation and management of confirmed and suspected EVD cases in order to prevent further spread through international travel. To gain insights into the state of preparedness of European hospitals, an electronic survey was circulated in August–September 2014 to 984 medical professionals representing 736 hospitals in 40 countries. The survey addressed the willingness and capacity to admit patients with suspected EVD as well as specific preparedness activities in response to the current Ebola crisis. Evaluable responses were received from representatives of 254 (32%) hospitals in 38 countries, mostly tertiary care centres, of which 46% indicated that they would admit patients with suspected EVD. Patient transfer agreements were in place for the majority of hospitals that would not admit patients. Compared with non-admitting hospitals, admitting hospitals were more frequently engaged in various preparedness activities and more often contained basic infrastructural characteristics such as admission rooms and laboratories considered important for infection control, but some gaps and concerns were also identified. The results of this survey help to provide direction towards further preparedness activities and prioritisation thereof.

Profiling of humoral immune responses to influenza viruses by using protein microarray

The emergence of pandemic A(H1N1) 2009 influenza showed the importance of rapid assessment of the degree of immunity in the population, the rate of asymptomatic infection, the spread of infection in households, effects of control measures, and ability of candidate vaccines to produce a response in different age groups. A limitation lies in the available assay repertoire: reference standard methods for measuring antibodies to influenza virus are haemagglutination inhibition (HI) assays and virus neutralization tests. Both assays are difficult to standardize and may be too specific to assess possible partial humoral immunity from previous exposures. Here, we describe the use of antigen-microarrays to measure antibodies to HA1 antigens from seven recent and historical seasonal H1, H2 and H3 influenza viruses, the A(H1N1) 2009 pandemic influenza virus, and three avian influenza viruses. We assessed antibody profiles in 18 adult patients infected with A(H1N1) 2009 influenza virus during the recent pandemic, and 21 children sampled before and after the pandemic, against background reactivity observed in 122 persons sampled in 2008, a season dominated by seasonal A(H1N1) influenza virus. We show that subtype-specific and variant-specific antibody responses can be measured, confirming serological responses measured by HI. Comparison of profiles from persons with similar HI response showed that the magnitude and broadness of response to individual influenza subtype antigens differs greatly between individuals. Clinical and vaccination studies, but also exposure studies, should take these findings into consideration, as they may indicate some level of humoral immunity not measured by HI assays.

Evaluation of the antiviral response to zanamivir administered intravenously for treatment of critically ill patients with pandemic influenza A (H1N1) infection

A retrospective nationwide study on the use of intravenous (IV) zanamivir in patients receiving intensive care who were pretreated with oseltamivir in the Netherlands was performed. In 6 of 13 patients with a sustained reduction of the viral load, the median time to start IV zanamivir was 9 days (range, 4-11 days) compared with 14 days (range, 6-21 days) in 7 patients without viral load reduction (P = .052). Viral load response did not influence mortality. We conclude that IV zanamivir as late add-on therapy has limited effectiveness. The effect of an immediate start with IV zanamivir monotherapy or in combination with other drugs need to be evaluated.

High incidence of peripheral blood plasmacytosis in patients with dengue virus infection

Little is known about polyclonal peripheral blood plasmacytosis in dengue virus (DENV)-infected patients. We initiated this prospective observational study to quantify and describe the kinetics and phenotype of peripheral blood plasma cells (PCs) in these patients. Morphological examination and flow cytometric (FC) analysis for the characterization and immunophenotyping of lymphocyte subsets and PCs were performed in 35 and 31 patients suspected of DENV infection, respectively. Our results show that blood plasmacytosis is a very common haematological finding. Depending on the days of illness at presentation, blood plasmacytosis was observed in 64% to 73% of patients. Blood plasmacytosis was most pronounced before 7 days of illness and declined rapidly thereafter, to completely disappear after 14 days of illness. Blood plasmacytosis was higher in secondary DENV infection. The majority of CD138(+) PCs (89%) had a shared immunophenotype (CD45(+)/CD19(-)/CD56(-)) and in all cases the PCs were polyclonal. Blood plasmacytosis, characterized by a transient presence of polyclonal PCs in the circulation, is a common event in DENV infection.

Fluoroquinolone resistance detection in Mycobacterium tuberculosis with locked nucleic acid probe real-time PCR

SETTING

Pham Ngoc Thach Hospital for Tuberculosis and Lung Diseases, Ho Chi Minh City, Vietnam.

OBJECTIVE

Fluoroquinolones (FQs) are increasingly used in the treatment of tuberculosis (TB) and are the second-line drugs of choice for treatment of multidrug-resistant TB. We aimed to set up a polymerase chain reaction (PCR) based assay to detect the most common FQ-resistance-associated mutations in gyrase A (gyrA) of Mycobacterium tuberculosis.

DESIGN

A total of 42 FQ-resistant and 40 FQ-susceptible isolates were collected in 2005-2006 and sequenced in gyrA. Using sequencing results as gold standard, a real-time PCR using three locked nucleic acid probes (LNA-PCR) was designed to detect mutations at positions 90, 91 and 94 (97% of gyrA FQ-resistance-associated mutations) and evaluated.

RESULTS

Sequencing of 42 FQ-resistant isolates revealed no gyrA mutations in 10 isolates, 20 isolates had a single mutation and 12 isolates showed double peaks at resistance-associated alleles, suggesting a heterogeneous population. With LNA-PCR, all wild-type and 19/20 mutant isolates were correctly identified. Eleven of 12 heterogeneous isolates were correctly identified as resistant mutants. Overall, 71% ([19 + 11]/42) of phenotypically FQ-resistant isolates were detected. Specificity was 100% on 40 FQ-susceptible isolates.

CONCLUSION

This assay provides a simple and rapid means to reliably detect FQ-resistance-associated gyrA mutations in M. tuberculosis.

Widely distributed and predominant CTX-M extended-spectrum beta-lactamases in Amsterdam, The Netherlands

Three hundred sixty Enterobacteriaceae and nonfermenting gram-negative bacilli, isolated during one week in May 2004 at five hospitals in Amsterdam, The Netherlands, were evaluated for the presence of extended-spectrum beta-lactamases (ESBLs). A prevalence of 7.8% was found, in contrast to the 1% observed in 1997. CTX-M ESBLs dominated, and four types were identified in 18 isolates.

Evolution and adaptation of H5N1 influenza virus in avian and human hosts in Indonesia and Vietnam

Highly pathogenic avian influenza virus H5N1 is endemic in poultry in East and Southeast Asia with disease outbreaks recently spreading to parts of central Asia, Europe and Africa. Continued interspecies transmission to humans has been reported in Vietnam, Thailand, Cambodia, Indonesia and China, causing pandemic concern. Here, we genetically characterize 82 H5N1 viruses isolated from poultry throughout Indonesia and Vietnam and 11 human isolates from southern Vietnam together with sequence data available in public databases to address questions relevant to virus introduction, endemicity and evolution. Phylogenetic analysis shows that all viruses from Indonesia form a distinct sublineage of H5N1 genotype Z viruses suggesting this outbreak likely originated from a single introduction that spread throughout the country during the past two years. Continued virus activities in Indonesia were attributed to transmission via poultry movement within the country rather than through repeated introductions by bird migration. Within Indonesia and Vietnam, H5N1 viruses have evolved over time into geographically distinct groups within each country. Molecular analysis of the H5N1 genotype Z genome shows that only the M2 and PB1-F2 genes were under positive selection, suggesting that these genes might be involved in adaptation of this virus to new hosts following interspecies transmission. At the amino acid level 12 residues were under positive selection in those genotype Z viruses, in the HA and PB1-F2 proteins. Some of these residues were more frequently observed in human isolates than in avian isolates and are related to viral antigenicity and receptor binding. Our study provides insight into the ongoing evolution of H5N1 influenza viruses that are transmitting in diverse avian species and at the interface between avian and human hosts.

[Severe diarrhea and eosinophilic colitis attributed to pinworms (Enterobius vermicularis)]

In a 32-year-old woman suffering from severe diarrhoea, eosinophilic infiltration of colonic mucosa and a peripheral eosinophilia, microbiological investigations only revealed large numbers of Enterobius vermicularis (pinworm) in the faeces. Treatment with mebendazole resulted in a rapid resolution of symptoms and disappearance of the eosinophilia, which strongly suggested a causative role of this pinworm in the clinical syndrome of the patient. E. vermicularis is generally regarded as an innocent nematode, which at most causes perianal pruritus due to migration of worms from the colon and expulsion of eggs onto the perianal skin. Although the pinworm maturates and lives in the gut, gastrointestinal symptoms have seldom been reported. E. vermicularis infection should be considered in patients with unexplained eosinophilic enteritis.

Usefulness of Gram stain for diagnosis of lower respiratory tract infection or urinary tract infection and as an aid in guiding treatment

During a prospective study of 8 months duration conducted in the Department of Internal Medicine and the Department of Pulmonary Diseases of the Academic Medical Centre, Amsterdam, Gram stainings of sputa and urine were performed for all patients whose clinical symptoms indicated an acute urinary tract infection or pulmonary infection. On the test request, the physician reported which antibiotic treatment he would prescribe if a microscopic examination was not available. The results of the Gram stain were discussed by the microbiologist with the physician, and the antibiotic therapy recommended by the microbiologist was recorded. This recommendation was compared with the antibiotic prescription noted in the patient record 1 day later. Two days after the results of final cultures and susceptibility tests became available, the patient record was again investigated for changes in the antibiotic regimen. Of 57 urine samples and 103 sputa, 27 and 85, respectively, were derived from patients with an infection of the urinary tract or respiratory tract. The results of the Gram stain confirmed the physician's suspicion 91% of the time for urinary tract infections and 81% of the time for pulmonary infections. In 67% of the patients with suspected lower respiratory tract infections and in 58% of patients with suspected urinary tract infections, the antibiotic treatment recommended on the basis of the results of the Gram stain differed significantly from the antibiotic treatment that the physician would have prescribed had a microscopic examination not been performed. The microbiologist's advice on antibiotic treatment was followed in 79% of the cases of respiratory tract infection and in 65% of the cases of urinary tract infection. The antibiotic treatment was adjusted to the final results of culture and antimicrobial susceptibility testing in 54% of the urinary tract infections and in 31% of the respiratory tract infections. The results indicate that the examination of sputa and urine in patients suspected to have an infection of the respiratory tract or urinary tract influences the antibiotic choice considerably.

Molecular diagnosis of visceral herpes zoster

Patients with disseminated herpes zoster may present with severe abdominal pain that results from visceral involvement of varicella-zoster-virus infection. In the absence of cutaneous eruptions of herpes zoster, visceral herpes zoster is extremely difficult to diagnose. This diagnostic difficulty has the potential to cause devastating delays in treatment. We report a case series of four patients with visceral herpes zoster in whom large concentrations of DNA from varicella zoster virus were detectable in blood by PCR before signs of infection appeared on the skin, thus enabling early diagnosis and treatment.

Introduction of an N-glycosylation site increases secretion of heterologous proteins in yeasts

Saccharomyces cerevisiae is often used to produce heterologous proteins that are preferentially secreted to increase economic feasibility. We used N-glycosylation as a tool to enhance protein secretion. Secretion of cutinase, a lipase, and llama V(HH) antibody fragments by S. cerevisiae or Pichia pastoris improved following the introduction of an N-glycosylation site. When we introduced an N-glycosylation consensus sequence in the N-terminal region of a hydrophobic cutinase, secretion increased fivefold. If an N-glycosylation site was introduced in the C-terminal region, however, secretion increased only 1.8-fold. These results indicate that the use of N glycosylation can significantly enhance heterologous protein secretion.

Quantitation of varicella-zoster virus DNA in whole blood, plasma, and serum by PCR and electrochemiluminescence

We describe a highly sensitive assay for quantitation of varicella-zoster virus (VZV) DNA in blood, involving PCR amplification, solution hybridization with Tris-(2, 2'-bipyridine)-ruthenium(II) chelate-labeled probes, and measurement by electrochemiluminescence (ECL). Extraction and amplification efficiencies were monitored by the inclusion of internal control (IC) DNA, mimicking the VZV target, in the DNA extraction. Viral DNA load was calculated from the ratio of VZV and IC ECL signals. The lower limit of sensitivity was 20 VZV DNA copies/ml of plasma or serum and 80 copies/ml of whole blood. In reconstruction experiments, expected and calculated VZV DNA loads were in excellent accordance. Blood specimens from 42 VZV-infected patients were tested for the presence of VZV DNA and showed detection rates of 86% in patients with varicella and 81% in patients with herpes zoster. In specimens obtained during the first week after onset of the rash, detection rates were 100 and 89%, respectively. Viral DNA was detected in all immunocompromised patients with herpes zoster, emphasizing the risk of disseminated disease in this patient group. VZV DNA load was similar in patients with varicella and multidermatomal herpes zoster and lower in patients with unidermatomal zoster. Despite the cell-associated nature of the virus, VZV DNA was detected in serum and plasma at high copy numbers, and at similar frequencies compared to whole-blood specimens. Quantitation of VZV DNA in blood is of potential importance for diagnosis and clinical management of VZV-infected patients. Plasma and serum provide convenient matrices for this purpose.

Quantitation of varicella-zoster virus DNA in whole blood, plasma, and serum by PCR and electrochemiluminescence

We describe a highly sensitive assay for quantitation of varicella-zoster virus (VZV) DNA in blood, involving PCR amplification, solution hybridization with Tris-(2, 2'-bipyridine)-ruthenium(II) chelate-labeled probes, and measurement by electrochemiluminescence (ECL). Extraction and amplification efficiencies were monitored by the inclusion of internal control (IC) DNA, mimicking the VZV target, in the DNA extraction. Viral DNA load was calculated from the ratio of VZV and IC ECL signals. The lower limit of sensitivity was 20 VZV DNA copies/ml of plasma or serum and 80 copies/ml of whole blood. In reconstruction experiments, expected and calculated VZV DNA loads were in excellent accordance. Blood specimens from 42 VZV-infected patients were tested for the presence of VZV DNA and showed detection rates of 86% in patients with varicella and 81% in patients with herpes zoster. In specimens obtained during the first week after onset of the rash, detection rates were 100 and 89%, respectively. Viral DNA was detected in all immunocompromised patients with herpes zoster, emphasizing the risk of disseminated disease in this patient group. VZV DNA load was similar in patients with varicella and multidermatomal herpes zoster and lower in patients with unidermatomal zoster. Despite the cell-associated nature of the virus, VZV DNA was detected in serum and plasma at high copy numbers, and at similar frequencies compared to whole-blood specimens. Quantitation of VZV DNA in blood is of potential importance for diagnosis and clinical management of VZV-infected patients. Plasma and serum provide convenient matrices for this purpose.

Summary of the II International Symposium on Cytomegalovirus

Human cytomegalovirus (HCMV) is a highly species-specific DNA virus belonging to the Betaherpesvirinae subfamily of the herpesviridae family. Like other herpesviruses, primary infection with HCMV is followed by persistence of the virus in a latent form. The sites of latency are still largely undefined, but they probably include bone marrow progenitor cells and peripheral blood monocytes. From these sites, the virus can reactivate, resulting in renewed shedding of the virus, or, in immunocompromized persons, development of disease. Humans are the only reservoir of HCMV and transmission occurs by person-to-person contact. Infection with HCMV is common. In most developed countries, HCMV seroprevalence steadily increases after infancy and 10-20% of children are infected before puberty. In adults, the prevalence of antibodies ranges from 40 to 100%. Although HCMV has a world-wide distribution, infection with HCMV is more common in the developing countries and in areas of low socioeconomic conditions, which is predominantly related to the closeness of contacts within these populations. Except for a mononucleosis-like illness in some persons, infection with HCMV rarely causes disease in immunocompetent individuals. However, HCMV can cause severe morbidity and mortality in congenitally infected newborns and immunocompromized patients, most notably transplant-recipients and HIV-infected persons. This article provides a review of the information presented at the Second International Symposium on Cytomegalovirus organized and convened by The Macrae Group (New York City, NY) in Acapulco, Mexico on 24-28 April 1998. During this symposium, the state-of-the-art knowledge on diagnosis, treatment and prophylaxis of HCMV infections were discussed, and, based on this information, attempts to highlight the future directions in basic and clinical research areas that need to be stimulated to facilitate advancement in prevention and treatment of CMV disease.

Effects of renal cytoprotective agents on erythrocyte membrane stability

To elucidate potential mechanisms of ischemic renal injury, investigators often use drugs that interfere with specific pathological pathways and study their protective efficacy in in vitro models of ischemia, such as isolated renal proximal tubules subjected to hypoxia. However, the protective effects of certain drugs may depend on non-specific membrane-stabilizing properties. We have studied the effects of several drugs on membrane integrity using osmotic lysis of erythrocytes as a model system. Freshly isolated rabbit erythrocytes were subjected to a hypotonic shock, and the protective effects of various calcium channel blockers, phospholipase inhibitors, free fatty acids, the NO-synthase inhibitor L-NAME, the amino acid glycine and its receptor-analogue strychnine, and two chloride channel blockers were examined. Most agents protected erythrocytes against hypotonic hemolysis when added to the medium in the same concentration range as used in suspensions of hypoxic proximal tubules. Only the protective agents that proposedly act via a blockade of chloride influx (glycine, strychnine and the chloride channel blockers), did not attenuate hypotonic hemolysis. The erythrocyte hemolysis assay may provide an easy and rapid method to screen for non-specific membrane-stabilizing effects of potentially cytoprotective agents.

Pre-embedding immunolabeling for electron microscopy: an evaluation of permeabilization methods and markers

For scarce antigens or antigens which are embedded in a dense macromolecular structure, on-section labeling, the first method of choice, is not always successful. Often, the antigen can be localized by immunofluorescence microscopy, usually by a pre-embedding labeling method. Most of these methods lead to loss of ultrastructural details and, hence, labeling at electron microscope resolution does not add essential information. The scope of this paper is to compare five permeabilization methods for pre-embedding labelling for electron microscopy. We aim for a method that is easy to use and suitable for routine investigations. For our ongoing work, special attention is given to labeling of the cell nucleus. Accessibility of cytoplasmic and nuclear antigens is monitored with a set of different marker antibodies. From this investigation, we suggest that prefixation with formaldehyde/glutaraldehyde is necessary to stabilize the ultrastructure before using a detergent (Triton X-100 or Brij 58) to permeabilize or remove the membranes. The experimental conditions for labeling should be checked first with fluorescence or fluorescence-gold markers by fluorescence microscopy. Then either ultrasmall gold particles (with or without fluorochrome) with silver enhancement or, if the ultrasmall gold particles are obstructed, peroxidase markers are advised. The most promising technique to localize scarce antigens with good contrast is the combination of a pre-embedding peroxidase/tyramide-FITC or -biotin labeling followed by an on-section colloidal gold detection.

Patterns of T-cell repopulation, virus load reduction, and restoration of T-cell function in HIV-infected persons during therapy with different antiretroviral agents

The effect of antiretroviral therapy on both T-cell numbers and T-cell function in peripheral blood was studied. CD4+ and CD8+ T-cell numbers, T-cell reactivity to CD3 monoclonal antibodies (mAb), and viral RNA load date were obtained from patients treated for at least 28 weeks with either the HIV-1 protease inhibitor ritonavir, the nonnucleoside HIV-1 reverse transcriptase (RT) inhibitor nevirapine, or the nucleoside-analogue RT inhibitor zidovudine. Compared with both RT inhibitors, treatment with the protease inhibitor ritonavir resulted in the most significant and persistent elevation of CD4+ and CD8+ T-cell counts. However, in vitro T-cell functional improvement was of limited duration in the ritonavir-treated group and was inversely correlated with viral RNA load changes during the entire follow-up period. Thus, despite what can be assumed of responses during RT inhibitor therapy, quantitative responses on therapy did not necessarily correlate with qualitative immunologic responses, as can be seen during treatment with ritonavir. For optimal immune reconstitution, both numeric and functional immunologic improvements are essential. During antiretroviral therapy, measurement of in vitro improvement in immune function will be useful as a correlate for transient drug-induced alteration of immunodeficiency.

Selective inhibition of syncytium-inducing and nonsyncytium-inducing HIV-1 variants in individuals receiving didanosine or zidovudine, respectively

By studying changes in the clonal composition of HIV-1 populations during the first weeks of zidovudine (ZDV) treatment before the development of ZDV resistance-conferring mutations, we demonstrated previously a selective inhibition of nonsyncytium-inducing (NSI) HIV-1, even when present as coexisting population in individuals also harboring syncytium-inducing (SI) HIV-1. In this study, we observed the opposite in individuals receiving didanosine (ddI) treatment. In these individuals (n = 7) a median -0.98 log change (range -1.55-0.08) in infectious cellular SI load was observed, whereas the coexisting NSI load was only minimally affected (median -0.15 log, range -1.27-0.50; P = 0.03). The virus phenotype-dependent treatment responses were independent of the clonal composition of HIV-1 populations at baseline. Individuals treated with a combination of ZDV and ddI revealed an equal decline of both NSI and SI infectious cellular load (n = 4; NSI: median -1.55 log, range -2.19 to -1.45; SI: median -1.47 log, range -1.81 to -0.86; P = 0.56). To test the hypothesis that the previously reported optimal activation of ZDV and ddI in activated and resting T cells, respectively, in combination with the differential T cell tropism of NSI and SI HIV-1 is the basis for the observed virus phenotype specific efficacy of nucleoside analogs, we studied the effect of treatment with a protease inhibitor that does not require intracellular activation. Individuals receiving ritonavir (n = 4) indeed showed equal declines in NSI and SI infectious cellular load (NSI: median -2.37 log, range -2.59 to -2.16; SI: median -2.82 log, range -3.14 to -2.50; P = 0.25). Our data suggest HIV-1 phenotype as an additional parameter in the design of optimal treatment regimens.

Overshoot of HIV-1 viraemia after early discontinuation of antiretroviral treatment

OBJECTIVE

To determine whether, as predicted by predator-prey dynamics, early withdrawal of antiretroviral therapy, i.e. when the number of CD4+ lymphocytes is still elevated, results in an overshoot of HIV-1 viraemia due to infection of increased numbers of available target cells at that time.

DESIGN AND METHODS

Five HIV-1-infected individuals were identified who discontinued antiretroviral therapy for various reasons after 8-19 days, and from whom stored serum samples obtained before, during, and shortly after treatment were available for measurement of HIV-1 RNA load. A mathematical model was designed to assess whether increased target cell availability could quantitatively explain the clinical observations.

RESULTS

After therapy withdrawal, increases in the HIV-1 RNA load to levels exceeding pretreatment values by log10 0.6-1.5 copies/ml were observed after 2-17 days in all four of the individuals who had treatment-induced increases in CD4+ cell counts at the time of therapy withdrawal. Increases in viraemia were maximal within a few days, and subsequently seemed to wane until the pretreatment equilibrium between virus and its target cells was attained. Mathematical modelling confirms that these transient increases in viraemia can be explained by increased availability of target cells at the time of therapy withdrawal.

CONCLUSIONS

Transient rises in HIV-1 viraemia do occur following early therapy withdrawal. These rises especially warrant consideration in short-term antiretroviral regimens for prevention of mother-to-child transmission, as are being studied in developing countries, since they could result in an increased transmission risk during the post-partum period through breast-feeding. This possibility needs to be investigated urgently.

High-dose nevirapine in previously untreated human immunodeficiency virus type 1-infected persons does not result in sustained suppression of viral replication

High-dose nevirapine treatment has been reported to confer sustained antiretroviral effects, despite a rapid development of resistance. The use of this strategy was evaluated in 20 previously untreated human immunodeficiency virus type 1 (HIV-1) p24 antigenemic persons with CD4 cell counts between 100 and 500/mm3. Treatment consisted of 400 mg of nevirapine, after a 2-week lead-in dose of 200 mg. Rash was the most frequently reported adverse event, occurring in 25%. While sustained declines in p24 antigen levels were observed in the majority, serum HIV-1 RNA load and CD4 cell counts returned to baseline values within 12 weeks in virtually all subjects. The resistance-conferring tyrosine-to-cysteine substitution at reverse transcriptase position 181 was detected after 4 weeks in most subjects. These observations suggest that plasma drug levels attained with high-dose nevirapine were not sufficient to inhibit nevirapine-resistant virus, although they were approximately 2-fold higher than reported IC50 values of resistant virus.

A comparison of serum HIV-1 RNA levels as measured by two quantitative assays in zidovudine-treated, asymptomatic, HIV-infected individuals

HIV-1 RNA levels as measured by two commercially available quantitative assays were compared before and during zidovudine treatment. HIV-1 RNA levels were measured in stored serum samples from 24 Dutch zidovudine-treated participants of a zidovudine efficacy study (European-Australian Collaborative Group Study 017) at weeks -3, 0, 4 and 8, using quantitative nucleic acid sequence-based amplification (NASBA; Organon Technika) and quantitative reverse transcriptase-polymerase chain reaction (Amplicor; Roche Molecular Systems). HIV-1 RNA copy numbers and changes from baseline as measured by each assay were compared. Individual responses to treatment were compared using definitions based on the within-subject variation of each assay. Before treatment, HIV-1 RNA levels as measured by NASBA were 0.49 logs higher than the levels measured by the Amplicor assay (95% confidence interval (CI) 0.32-0.66). During treatment, this difference decreased significantly to 0.27 logs (95% CI 0.01-0.53; difference 0.22 logs; 95% CI 0.05-0.37). The smaller difference between the results of the two assays during treatment was a consequence of a larger decline in RNA level as measured by NASBA compared with that measured by the Amplicor assay (mean change after 4 weeks 0.77 and 0.49 logs, respectively). At week 8, the mean HIV-1 RNA level was still significantly below baseline values as measured by NASBA, but not when measured by the Amplicor assay. Discrepancies in individual responses as measured by the two assays were also observed. In conclusion, marked differences exist between the NASBA and Amplicor quantitative assays, in both HIV-1 RNA copy numbers without treatment and changes in RNA level during treatment. These differences should be considered in interpreting analyses of clinical trials and relationships between HIV-1 RNA level and clinical outcome, as well as in the use of RNA level in the management of HIV-infected patients.

Endogenously produced prostanoids stimulate calcium reabsorption in the rabbit cortical collecting system

1. The influence of endogenously produced prostanoids on active transepithelial Ca2+ transport and cAMP formation was investigated in immunodissected rabbit kidney connecting and cortical collecting tubule cells grown to confluency on permeable supports. 2. The cyclo-oxygenase inhibitor indomethacin dose-dependently (IC50 = 18 nM) reduced the net apical-to-basolateral Ca2+ transport by 57%. Inhibition was reversed in medium obtained from monolayers incubated in the absence of indomethacin. 3. HPLC analysis following incubation with 14C-labelled arachidonic acid revealed the presence of a wide variety of radiolabelled prostanoids in both the apical and basolateral media. These findings are compatible with the endogenous production and subsequent release of stimulatory prostanoids. 4. The inhibitory action of indomethacin was reversed by the addition of the prostanoids PGE1, PGE2 and PGA2, but not PGD2, PGF2 alpha, the stable PGI2 analogue cicaprost or the thromboxane A2 mimetic U-46619. PGE2 stimulated transepithelial Ca2+ transport dose dependently (EC50 = 3 nM), irrespective of the compartment of which it was added. The stimulatory effect of PGE2 was paralleled by increased cAMP formation, suggesting the apical and basolateral presence of stimulatory prostanoid receptors EP2 and/or EP4. 5. Sulprostone, an analogue selective for EP1 and EP3 receptors, inhibited transepithelial Ca2+ transport in indomethacin-treated monolayers only when applied basolaterally, suggesting the exclusive presence of inhibitory EP receptors on the basolateral membrane. 6. The percentage by which parathyroid hormone and arginine vasopressin increased both transepithelial Ca2+ transport and cAMP formation was dramatically increased in indomethacin-inhibited cells as compared with control cells, demonstrating that indomethacin unmasks the actions of these hormones to their full extent.

Human immunodeficiency virus type 1 drug susceptibility determination by using recombinant viruses generated from patient sera tested in a cell-killing assay

A simple approach for the determination of drug susceptibilities by using human immunodeficiency virus type 1 (HIV-1) RNA from the sera of patients is described. HIV-1 RNA was extracted from patient sera, and the 5' part of the reverse transcriptase (RT) gene was transcribed into DNA and amplified in a nested PCR. The amplified fragment covers the 3' part of the protease gene and amino acids 1 to 304 of the RT gene. This fragment can be introduced through homologous recombination, as described previously, into a novel HIV-1 reference strain (pHXB2 delta 2-261RT) from which amino acids 2 to 261 of RT have been deleted. The resulting recombinant virus expresses all properties of the HXB2 reference strain except for those encoded by the introduced part of the patient RT gene. Recombinant viruses were subsequently tested for drug susceptibility in a microtiter format killing assay [3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay] as well as in the standard HeLa CD4+ plaque reduction assay. Similar susceptibility profiles were obtained by each assay with recombinant viruses derived from patients receiving alternating nevirapine and zidovudine treatment or lamivudine-zidovudine combination therapy. In conclusion, this approach enables high-through-put determination of the drug susceptibilities of serum RNA-derived RT genes, independent of the patient's viral background, and generates the possibility of relating changes in susceptibility to changes in viral genotypes.

Changes in cellular virus load and zidovudine resistance of syncytium-inducing and non-syncytium-inducing human immunodeficiency virus populations under zidovudine pressure: a clonal analysis

Zidovudine treatment preferentially benefits persons with only non-syncytium-inducing (NSI) human immunodeficiency virus type 1 (HIV-1) variants. To understand this differential efficacy, changes in cellular virus load, clonal composition of HIV-1 populations, and development of resistance-conferring reverse transcriptase mutations were studied in 17 persons initiating zidovudine therapy. Zidovudine treatment resulted in larger and more sustained decreases in cellular virus load in persons with NSI variants only compared with persons also carrying syncytium-inducing (SI) variants. Although the former group had a delayed emergence of resistance mutations, differences in initial responses between the 2 groups were independent of the emergence of resistance mutations. Changes in virus load in subjects also carrying SI variants were due mainly to loss of coexisting NSI virus. Resistance mutations emerged at similar rates in both coexisting variants. Data suggest that mechanisms other than drug resistance are necessary to completely explain the phenotype-dependent benefit of zidovudine.

A controlled trial of nevirapine plus zidovudine versus zidovudine alone in p24 antigenaemic HIV-infected patients. The Dutch-Italian-Australian Nevirapine Study Group

OBJECTIVES

Nevirapine is a non-nucleoside reverse transcriptase inhibitor of HIV-1 which exhibits synergy in vitro with zidovudine (ZDV) and also is active against ZDV-resistant HIV. We evaluated the activity and safety of nevirapine in combination with ZDV in patients receiving long-term ZDV therapy.

METHODS

We conducted a randomized, open-label, controlled 28-week study of nevirapine (200 mg daily for 2 weeks followed by 200 mg twice daily for 26 weeks) and continued ZDV (500-600 mg daily) versus continued ZDV alone in 49 HIV-1 p24 antigenaemic patients with CD4+ lymphocyte counts < 500 x 10(6)/l and who had been treated with ZDV for at least 6 months.

RESULTS

Addition of nevirapine to ZDV resulted in a significant and rapid reduction in circulating RNA load (mean, 0.65), a mean CD4+ lymphocyte rise of 34 x 10(6)/l, a reduction in serum beta 2-microglobulin and a median fall in immune complex dissociated p24 antigen levels of 69%. These changes remained statistically significant for 4, 4, 12 and at least 28 weeks, respectively. The principal adverse event due to nevirapine was a hypersensitivity reaction comprising rash with or without fever and mucositis in eight (32%) patients, which was dose-limiting in seven patients.

CONCLUSION

Nevirapine exhibits significant although transient anti-HIV activity in ZDV-pretreated patients but its use is frequently associated with a hypersensitivity reaction.

Host-parasite dynamics and outgrowth of virus containing a single K70R amino acid change in reverse transcriptase are responsible for the loss of human immunodeficiency virus type 1 RNA load suppression by zidovudine

The association between human immunodeficiency virus type I (HIV-1) RNA load changes and the emergence of resistant virus variants was investigated in 24 HIV-1-infected asymptomatic persons during 2 years of treatment with zidovudine by sequentially measuring serum HIV-1 RNA load and the relative amounts of HIV-1 RNA containing mutations at reverse transcriptase (RT) codons 70 (K-->R), 41 (M-->L), and 215 (T-->Y/F). A mean maximum decline in RNA load occurred during the first month, followed by a resurgence between 1 and 3 months, which appeared independent of drug-resistance. Mathematical modeling suggests that this resurgence is caused by host-parasite dynamics, and thus reflects infection of the transiently increased numbers of CD4+ lymphocytes. Between 3 and 6 months of treatment, the RNA load returned to baseline values, which was associated with the emergence of virus containing a single lysine to arginine amino acid change at RT codon 70, only conferring an 8-fold reduction in susceptibility. Despite the relative loss of RNA load suppression, selection toward mutations at RT codons 215 and 41 continued. Identical patterns were observed in the mathematical model. While host-parasite dynamics and outgrowth of low-level resistant virus thus appear responsible for the loss of HIV-1 RNA load suppression, zidovudine continues to select for alternative mutations, conferring increasing levels of resistance.

Replication of a pre-existing resistant HIV-1 subpopulation in vivo after introduction of a strong selective drug pressure

Recent reports indicate a high rate of viral replication during all phases of HIV-1 infection. This rapid turnover presents a continuous drive towards mutations in the HIV-1 genome, which may include those conferring drug resistance. Although the natural occurrence of drug-resistant variants has been reported, the implication on viral kinetics of the subsequent introduction of a selective pressure, in the form of antiviral treatment, remains to be elucidated. We analysed proviral DNA from nine previously untreated participants in a nevirapine study for the presence of the nevirapine resistance-conferring tyrosine to cysteine substitution at codon 181 of HIV-1 reverse transcriptase. In one individual, a minor proviral subpopulation containing this mutation was detected. A rapid selective outgrowth of this minor drug-resistant subpopulation during subsequent treatment with nevirapine was evidenced by a nearly complete replacement of the wild-type HIV-1 RNA population by 181-cysteine variant virus in serum within 1 week, and a reversal of the proportions of tyrosine- and cysteine-encoding proviruses within 2 weeks of treatment, which contrasted with other subjects tested. The rapid emergence of a drug-resistant virus variant clearly resulted in a lack of replication inhibition by nevirapine: whereas other patients demonstrated a median 1.2 log10 decrease in serum HIV-1 RNA load during the first week of treatment, an increase of 0.6 log10 was observed in this patient. The extensive repercussions for subsequent treatment of even a minor subpopulation of naturally occurring drug-resistant variants observed in this study must be considered in future therapeutic strategies.

Alternating nevirapine and zidovudine treatment of human immunodeficiency virus type 1-infected persons does not prolong nevirapine activity

The potential use of an alternating treatment strategy with nevirapine and zidovudine in prolonging the antiretroviral effects of nevirapine was evaluated. Ten human immunodeficiency virus type 1 (HIV-1)-infected p24 antigen-positive persons who had not received prior antiretroviral therapy were treated for 9-13 weeks with an alternating regimen of 1 week of nevirapine (200 mg/day) and 3 weeks of zidovudine (600 mg/day). Serum p24 antigen levels declined during the first week of nevirapine treatment (median, 59%); however, subsequent courses of nevirapine were characterized by rising p24 antigen levels, while antigen levels remained stable or declined during zidovudine treatment. Serum beta 2-microglobulin levels and CD4+ cell counts exhibited similar responses. HIV-1 isolates obtained from 2 patients revealed 40- and 1000-fold reductions in nevirapine sensitivity after 8 weeks. These findings demonstrate that alternating treatment with zidovudine and nevirapine does not prolong the effectiveness of nevirapine and does not prevent the development of nevirapine resistance.

Clinical, virological and immunological features of primary HIV-1 infection

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Glucose transporters do not serve as water channels in renal and intestinal epithelia

Glucose carriers have been shown to serve as water channels in macrophages and in oocytes injected with messenger ribonucleic acid (mRNA) encoding the glucose carrier protein (Fischbarg et al. The contribution, therefore, of glucose carriers to osmotic water permeability (Pf) in renal and intestinal epithelial cells was investigated. Pf of brush border membrane vesicles (BBMVs) and of basolateral membrane vesicles (BLMVs) was studied using stopped-flow spectrophotometry. Osmotic shrinkage of renal vesicles exhibited fast and slow components at 4 degrees C and 37 degrees C. The fast component could be inhibited by HgCl2 or dimethylsulphoxide (DMSO) at these temperatures, whereas the slow component was inhibited only at 4 degrees C. Osmotic shrinkage of intestinal BBMVs and BLMVs was homogeneous at 4 degrees C and 37 degrees C and was slightly inhibitable by HgCl2 or DMSO at 4 degrees C but not 37 degrees C. In both tissues, vesicle uptake of glucose was sensitive to HgCl2, but not to DMSO. Phlorizin and phloretin inhibited D-glucose uptake in BBMVs and BLMVs respectively, but had no significant effect on Pf. In membrane vesicles of kidney origin, Pf was tenfold higher than in membranes from intestine. This difference was not reflected by the phlorizin- and phloretin-sensitive D-glucose uptakes. Our study concludes that glucose transporters do not serve as water channels in kidney or intestine. Although membrane proteins contribute slightly to Pf at 4 degrees C, this contribution is insignificant at 37 degrees C. A membrane protein serving specifically as a water channel could only be demonstrated in renal cortical membranes.

Functional unit of 30 kDa for proximal tubule water channels as revealed by radiation inactivation

The high water permeability of kidney proximal tubules is of paramount importance for isotonic reabsorption of 70% of the glomerular filtrate, and water channels have been postulated to account for the high water permeability. Target analysis following radiation inactivation was used to probe the molecular size of the water channel. Samples of brush border membranes from rat renal cortex were subjected to 3-MeV electron pulses from the Van de Graaff accelerator at a temperature of -130 degrees C. The inactivation of the renal brush border enzymes, alkaline phosphatase, and maltase was used for internal standardization of accumulated dose measurements in target analysis of the water channel. Osmotic water permeability was measured by following the change in scattered light intensity upon rapid mixing of vesicles with a hypertonic solution using stopped-flow spectrophotometry. The vesicle shrinkage response was biphasic and the rate of the fast phase decreased dose dependently by irradiation corresponding to a target size of 30 +/- 3.5 kDa. The total change in scattered light intensity was unaltered, indicating that irradiation did not destroy the lipid barrier. Our results provide strong support for the hypothesis that the high osmotic water permeability of renal proximal tubules results from a water channel-specific protein with a functional unit of 30 kDa.

[Pneumocystis carinii infection during prophylaxis with nebulized pentamidine in a patient with AIDS]

Since the introduction of aerosolised pentamidine for prophylaxis against Pneumocystis carinii pneumonia (PCP) in HIV-seropositive persons and patients with AIDS, an increasing number of cases of atypical manifestations of infection with Pneumocystis carinii have been reported in the United States, viz. upper lobe pneumonia, extrapulmonary Pneumocystis carinii infection and spontaneous pneumothorax. An association between these atypical manifestations of Pneumocystis carinii infection and the use of aerosolised pentamidine seems likely. This report is the first description in the Netherlands of an atypical Pneumocystis carinii infection in an AIDS patient while using aerosolised pentamidine for prophylaxis against PCP. Since aerosolised pentamidine for prophylaxis against PCP is increasingly being used in the Netherlands, a rise in incidence of atypical manifestations of Pneumocystis carinii infection can be expected.