Simulation of Hypothermic Perfusion of Rabbit Livers for Cryopreservation Applications

BACKGROUND

In cryopreservation of biological material, it is very important to precise control the perfusion of cryoprotectants (CPA) inside the sample. CPA concentration inside tissues and organs during the process was measured in a few studies. The simulation of the CPA perfusion inside the organ is still necessary to understand and optimize this complex process.

OBJECTIVE

This study simulates the diffusion of Me₂SO and PBS in a rabbit liver.

MATERIALS AND METHODS

The software COMSOL for computational fluid-dynamics has been used. A hypothermic perfusion is simulated where temperature and pressure at the entrance of the organ are constant.

RESULTS

The simulation shows that Me₂SO concentration increases within the porous medium until saturation. The variation of perfusion speed and pressure inside the organ is almost null with time.

CONCLUSION

Finite elements modelling shows that under hypothermic conditions it is possible a full and even loading of this organ with Me₂SO, keeping constant the perfusion parameters.

Preparation and Characterization of Antimicrobial Films Based on LDPE/Ag Nanoparticles with Potential Uses in Food and Health Industries

In this work, the antimicrobial effect of silver nanoparticles in polyethylene based nanocomposites has been investigated using a non-conventional processing method to produce homogeneous materials. High energy ball milling under cryogenic conditions was used to achieve a powder of well-blended low-density polyethylene and commercial silver nanoparticles. The final composites in the form of films were obtained by hot pressing. The effect of various silver nanoparticles content (0, 0.5, 1 and 2 wt %) on the properties of low-density polyethylene and the antimicrobial effectiveness of the composite against DH5α Escherichia coli were studied. The presence of silver nanoparticles did not seem to affect the surface energy and thermal properties of the materials. Apart from the inhibition of bacterial growth, slight changes in the aspect ratio of the bacteria with the content of particles were observed, suggesting a direct relationship between the presence of silver nanoparticles and the proliferation of DH5α E. coli (Escherichia coli) cells. Results indicate that these materials may be used to commercially produce antimicrobial polymers with potential applications in the food and health industries.

Changes in drug resistance patterns following the introduction of HIV type 1 non-B subtypes in Spain

Natural genetic variability at the pol gene may account for differences in drug susceptibility and selection of resistance patterns across HIV-1 clades. Spread of non-B subtypes along with changes in antiretroviral drug use may have modified drug resistance patterns in recent years. All HIV-1 clinical samples sent to a reference laboratory located in Madrid for drug resistance testing since January 2000 were analyzed. The pol gene was sequenced and HIV-1 subtypes were assigned using the Stanford algorithm and phylogenetic analyses for non-B subtypes. Drug resistance mutations were recorded using the IAS-USA mutation list (April 2008). A total of 3034 specimens from 730 antiretroviral-naive individuals (92 with non-B subtypes) and 1569 antiretroviral-experienced patients (97 with non-B subtypes) were examined. The prevalence of HIV-1 non-B subtypes in the study period increased from 4.4% (2000-2003) to 10.1% (2004-2007) (p < 0.01). The most predominant variants were CRF02_AG (41.8%) and G (17.5%). Thymidine analogue mutations (TAMs) were more prevalent in B than non-B subtypes, in both drug-naive (6.2% vs. 1%; p < 0.01) and treatment-experienced patients (49% vs. 30%, p < 0.01). K103N was most frequent in B than non-B subtypes (34% vs. 21%; p < 0.01); conversely, 106A/M was more prevalent in non-B than B clades (11% vs. 5%). Codon 179 mutations associated with etravirine resistance were more frequent in non-B than B subtypes. Finally, secondary protease resistance mutations were more common in non-B than B clades, with a potentially significant impact at least on tipranavir. The prevalence of HIV-1 non-B subtypes has increased since the year 2000 in a large drug resistance database in Spain, determining changes in drug resistance patterns that may influence the susceptibility to new antiretroviral drugs and have an impact on genotypic drug resistance interpretation algorithms.

Comparison of Prenatal Risk Calculation (PRC) with PIA Fetal Database software in first-trimester screening for fetal aneuploidy

OBJECTIVES

In February 2007 new software, Prenatal Risk Calculation (PRC), for calculating the risk of fetal aneuploidy was introduced in Germany. Our aim was to investigate its test performance and compare it with that of the PIA Fetal Database (PIA) software developed and used by The Fetal Medicine Foundation.

METHODS

Between 31 August 1999 and 30 June 2004 at the Women's Hospital of the Medical University of Hanover in Germany, 3120 singleton pregnancies underwent combined first-trimester screening at 11 + 0 to 13 + 6 weeks of gestation. Calculation of risk for fetal aneuploidy was computed prospectively using the PIA software. In a subsequent retrospective analysis, we recalculated risks for the 2653 of these datasets with known fetal outcome using the PRC software and compared the results.

RESULTS

Of the 2653 datasets analyzed, 17 were cases of aneuploidy. At a cut-off of 1 : 230, for the detection of fetal aneuploidy, the respective sensitivity, false-positive rate and positive predictive value were 70.6%, 4.1% and 9.9% for PRC and 76.5%, 2.9% and 14.6% for PIA. At a cut-off of 1 : 300, the equivalent values were 70.6%, 5.6% and 7.5% for PRC and 76.5%, 4.0% and 11.0% for PIA. The differences in test performance between the two types of software were highly significant (P < 0.0001).

DISCUSSION

The test performance of PRC was inferior to that of PIA, the sensitivity for detection of fetal aneuploidy being lower and the false-positive rate higher. Had PRC been employed prospectively in our study, 40% more women examined would have been offered unnecessarily an invasive procedure for fetal karyotyping.

Changing patterns in HIV reverse transcriptase resistance mutations after availability of tenofovir

Assessment of 1177 human immunodeficiency virus (HIV) resistance genotypes at an HIV/AIDS clinic showed a decrease in the incidence of the K65R mutation, from 15.2% of isolates during the period 2002-2004 to 2.7% of isolates during the period 2005-2006 (P < .001), despite elevated and stable rates of tenofovir use. A reduction in the rate of coadministration of didanosine (from 41.6% of patients in 2004 to 0.8% of patients in 2006; P < .001) largely explained this observation.

Prevalence of X4 tropic HIV-1 variants in patients with differences in disease stage and exposure to antiretroviral therapy

Viral tropism plays an important role in HIV pathogenesis. However, its correlation with the clinical outcome and following exposure to antiretroviral drugs are still unclear. HIV-1 co-receptor usage was examined in 206 infected individuals: 67 seroconverters, 52 chronically drug-naïve, and 87 antiretroviral-experienced patients. The V3 loop was sequenced from plasma HIV-RNA and co-receptor usage was inferred using a phenotype predictor software (http://genomiac2.ucsd.edu:8080/wetcat/v3.html), which classifies V3 sequences as R5 or X4. The overall prevalence of X4 viruses was 26.2%, with significant differences among groups: 13.4% in seroconverters, 25% in drug-naïve, and 36.8% in antiretroviral- experienced patients (P = 0.001). The presence of X4 variants in the latter group was associated with higher viral load (P = 0.002) but not with lower CD4 counts. There was no association between HIV tropism and gender, transmission route or age. Neither with the CCR5 Delta32 genotype. Moreover, no association was found between HIV-1 tropism and drug resistance mutations nor with failure to regimens based on either protease inhibitors or non-nucleoside reverse transcriptase inhibitors. Finally, no significant association was found between IL-7 plasma levels with HIV-1 tropism. In summary, X4 viruses are particularly frequent among antiretroviral-experienced patients with high viral loads, irrespective of the CD4 count. Thus, CCR5 antagonists should be used with special caution in this subset of patients.

Prevalence of darunavir resistance mutations in HIV-1-infected patients failing other protease inhibitors

BACKGROUND

To estimate to what extent darunavir might be effective in patients failing distinct protease inhibitors (PIs), the genotypic resistance scores recently reported for the drug were examined in a large clinical HIV-1 drug resistance database.

METHODS

All clinical specimens from HIV-infected patients failing PI-based regimens referred for drug resistance testing between 1999 and 2007 to a reference centre in Madrid were analysed. Darunavir-specific resistance mutations listed by the September 2006 IAS-USA panel update were considered.

RESULTS

A total of 1021 genotypes from patients failing lopinavir (39.2%), nelfinavir (28.1%), saquinavir (14.5%), indinavir (13.7%), atazanavir (6.6%), fosamprenavir (5.3%) and tipranavir (1.1%) were identified. The prevalence of major darunavir resistance mutations was I50V 2.1%, I54M 1.3%, L76V 2.7% and I84V 14.5%. For minor darunavir resistance mutations, the rates were V11I 3.3%, V32I 3.9%, L33F 11%, I47V 2.1%, I54L 2.3%, G73S 12.8% and L89V 2.4%. Overall, 6.7% (n = 68) of the genotypes had three or more darunavir resistance mutations, which corresponded to a mean total number of PI resistance mutations of 12.3 +/- 1.9. In the multivariate analysis, prior fosamprenavir failure, prior saquinavir failure, the total number of PI resistance mutations and the number of prior PIs used were all independently associated with having more darunavir resistance mutations.

CONCLUSIONS

The prevalence of darunavir resistance mutations is low in patients failing other PI-based regimens, although prior failure to amprenavir and saquinavir might produce more cross-resistance to darunavir. Thus, darunavir may be a good option for patients who have failed other PI-based regimens.

Prevalence of the HIV-1 protease mutation I47A in clinical practice and association with lopinavir resistance

Mutation proI47A has recently been associated with lopinavir/ritonavir (LPV/r) resistance. Only four out of 1859 specimens (0.2%) sent for drug resistance testing (219 drug-naive and 1650 antiretroviral-experienced) showed I47A. All belonged to patients failing LPV/r. The prevalence among protease inhibitor-experienced patients was 0.6%. Phenotypic testing showed that proI47A caused high-level lopinavir resistance (> 100-fold) and cross-resistance to amprenavir, whereas it caused hypersusceptibility to saquinavir. ProI47A should thus be considered the primary lopinavir resistance mutation.

Plasma levels of atazanavir and the risk of hyperbilirubinemia are predicted by the 3435C-->T polymorphism at the multidrug resistance gene 1

The 3435C-->T polymorphism at the multidrug resistance gene 1 (MDR1) was examined in 74 patients with human immunodeficiency virus who initiated atazanavir therapy. The MDR1 genotype distribution at position 3435 was 28% CC, 45% CT, and 27% TT. Plasma levels of atazanavir were significantly higher in patients with genotype CC than in those with CT or TT, and bilirubin levels correlated with atazanavir concentrations.

Risk of selecting K65R in antiretroviral-naive HIV-infected individuals with chronic hepatitis B treated with adefovir

Seven antiretroviral-naive HIV-infected individuals with chronic hepatitis B treated with adefovir for longer than 6 months were assessed. Using bulk population sequencing and a sensitive limiting dilution analysis, the selection of K65R or other resistance mutations did not occur in HIV, suggesting that adefovir can be confidently used as hepatitis B virus (HBV) therapy in HIV/HBV-co-infected patients who do not require antiretroviral therapy.

Comparison of serological tests for the detection of ovine and caprine antibody to Brucella melitensis

The indirect enzyme-linked immunosorbent assay (IELISA), the competitive enzyme-linked immunosorbent assay (CELISA) and the fluorescence polarisation assay (FPA) were evaluated with sera from sheep experimentally infected with Brucella melitensis and negative Canadian sheep. The sensitivity and specificity of the assays were as follows: IELISA: 91.7% and 97.6%, CELISA: 75.0% and 99.8% and FPA: 91.7% and 89.5%. Sera from the same experimental population were divided according to serological reaction in the rose bengal agglutination test (RBT) and the complement fixation test (CFT). Reactivity relative to the RBT positive and CFT positive sera were as follows: IELISA: 99.7%, CELISA: 93.2% and FPA: 99.1%. Since sera from goats with proven B. melitensis infection were not available, 699 sera from goats judged positive in the buffered antigen plate agglutination test (BPAT) and CFT and 982 BPAT/CFT negative Canadian goats were used. The sensitivity and specificity of the assays relative to the BPAT and CFT positive sera were: IELISA: 99.4% and 98.0%, CELISA: 95.4% and 97.1% and FPA: 92.7% and 99.8%.

Antiretroviral recommendations may influence the rate of transmission of drug-resistant HIV type 1

BACKGROUND

Human immunodeficiency virus (HIV) treatment guidelines have evolved, shifting from more-aggressive to more-conservative approaches. The potential impact of these shifts on the transmission of drug-resistant virus is unknown.

METHODS

Drug-resistance genotypes were examined in all consecutive patients with recent HIV type 1 (HIV-1) seroconversion (hereafter, "HIV-1 seroconverters") seen at 10 Spanish hospitals since 1997. During the same period, the proportion of patients with chronic HIV-1 infection having undetectable viremia was examined, to estimate the extent and effectiveness of antiretroviral therapy.

RESULTS

A total of 141 recent HIV-1 seroconverters were identified, 67.4% of whom were men who have sex with men. The rate of primary drug-resistance mutations, by year of infection, was 33.3% for 1997, 29.4% for 1998, 20% for 1999, 14.3% for 2000, 3.4% for 2001, 15.4% for 2002, and 10.9% for 2003. On the other hand, the proportion of 8388 persons with chronic HIV-1 carriage who had an undetectable virus load was 33.4% for 1997, 34.6% for 1998, 39.7% for 1999, 47.5% for 2000, 52.9% for 2001, 39.7% for 2002, and 58.1% for 2003. A significant inverse correlation between transmission of drug-resistant HIV-1 and undetectable virus load was found (r=-0.955, by Spearman's test; P=.001). The lowest rate of transmission of drug-resistant HIV-1 was seen in 2001, when relatively "aggressive" treatment guidelines were used. Transmission of drug-resistant HIV-1 increased in 2002, in parallel with a reduction in the number of patients with chronic HIV-1 carriage and undetectable virus load, reflecting the popularity of drug holidays or treatment interruptions.

CONCLUSION

The rate of drug resistance in recent HIV-1 seroconverters inversely correlates with the proportion of chronically HIV-1-infected individuals who have undetectable virus loads in the same region, which indirectly reflects antiretroviral treatment rules at any given time.

Relationship between drug resistance mutations, plasma viremia, and CD4+T-cell counts in patients with chronic HIV infection

Transmission of drug-resistant viruses has been shown to be associated with lower virus replication capacity and higher CD4+ cell counts in recent human immunodeficiency virus (HIV) seroconvertors. The impact of drug resistance mutations on CD4 cell counts in chronically HIV-infected patients has not been examined. A total of 825 patients whose plasma specimens were submitted to a reference laboratory for genotypic testing from 1999 to 2002 were analyzed. There was no significant difference in the median CD4+ cell count when comparing 63 drug-naive and 762 treatment-experienced patients [399 (IQR, 141-525) vs. 319 (IQR, 174-521); P = 0.8]. In contrast, the median viral load was significantly higher in drug-naive than in pre-treated patients [4.6 (IQR, 4.1-5.25) vs. 4.1 (IQR, 3.4-4.7) logs; P < 0.0001]. Overall, drug resistance mutations appeared in 81% of patients, with a median number of 9 (IQR, 5-14). The rate of drug resistance genotypes was 9.5% for drug-naive patients and 86.7% for pre-treated individuals. In the univariate analysis, a lower viral load (P < 0.0001), the presence of drug-resistant viruses (P = 0.038), and specific mutations in the reverse transcriptase (RT) gene [presence of M184V (P = 0.016) or K70R (P < 0.0001), and lack of L74V (P < 0.003)] were all associated with higher CD4+ counts. However, in the multivariate analyses, only a lower viral load and the presence of K70R were significantly associated with higher CD4+ cell counts. In summary, drug-resistant viruses are associated with lower viral loads, but after adjusting for plasma viremia, subjects carrying drug-resistant viruses do not show significantly higher CD4 cell counts. Thus, keeping on treatment HIV-infected individuals failing virologically and harboring drug-resistant viruses may ameliorate their immunological deterioration until new drugs became available.

Predictors of selection of K65R: tenofovir use and lack of thymidine analogue mutations

Over the past 5 years, 1846 HIV-infected patients underwent drug resistance testing at our institution. None out of 216 drug-naive subjects showed K65R. However, it was recognized in 53 out of 1630 antiretroviral-experienced patients (3.3%), of whom 10 had never been exposed to tenofovir. The rate of K65R increased from 0.6% in 1999 to 11.5% in 2004. The recognition of K65R correlated negatively with the presence of thymidine analogue mutations but positively with Q151M.

Higher efavirenz concentrations determine the response to viruses carrying non-nucleoside reverse transcriptase resistance mutations

We examined the influence of both efavirenz plasma concentrations and non-nucleoside reverse transcriptase (NNRTI) resistance mutations on the antiviral activity of efavirenz in patients experiencing early virological failure under nevirapine-containing regimens. Up to 41% of patients reach less than 50 copies/ml at 48 weeks. No association was found between the presence of NNRTI resistance mutations and virological outcome. Nevertheless, patients responding virologically and carrying NNRTI-resistant viruses had higher efavirenz levels than those who did not respond.

Evidence for Differences in the Sexual Transmission Efficiency of HIV Strains with Distinct Drug Resistance Genotypes

BACKGROUND

The transmission of drug-resistant human immunodeficiency virus type 1 (HIV-1) is a matter of major concern, because it could compromise the response to antiretroviral therapy.

MATERIAL AND METHODS

From 1997 through 2003, genotypic drug resistance profiles in 89 patients with recent HIV-1 seroconversion were compared in a case-control study with HIV-1 genotypes obtained from 520 subjects identified at Hospital Carlos III in Madrid, Spain, as "potential transmitters" of drug-resistant virus. This group consisted of HIV-infected patients experiencing virologic failure of antiretroviral therapy.

RESULTS

Drug resistance mutations were recognized in 15 (16.8%) of 89 patients with recent HIV-1 seroconversion (the seroconverter group), providing resistance to nucleoside reverse-transcriptase inhibitors (NRTIs) in 14.6%, nonnucleoside reverse-transcriptase inhibitors (NNRTIs) in 3.4%, and protease inhibitors (PIs) in 3.4%. Among individuals who were potential transmitters of HIV-1 (the potential transmitter group), drug resistance mutations were found in 80%, providing resistance to NRTIs in 73.7%, NNRTIs in 36.4%, and PIs in 38.7%. The estimated ratio of individuals with recent HIV-1 seroconversion to potential transmitters for drug-resistance genotypes was 0.23 for resistance to NRTIs, 0.09 for resistance to NNRTIs, and 0.09 for resistance to PIs. For specific resistance mutations, the ratio of individuals with recent HIV-1 seroconversion to potential transmitters was 0.18 for 41L, 0.20 for 215Y/F (including revertants), 0.06 for 184V, 0.04 for 103N, and 0.14 for 181C when considering drug resistance mutations in the reverse transcriptase (RT) gene; the ratio was 0.12 for 46L, 0.06 for 82A/T/S, and 0.08 for 90L, when examining PI resistance mutations.

CONCLUSION

Strains of HIV with some drug resistance genotypes (41L, 215Y/F, and 181C in the RT gene and 46L in the protease gene) may be more efficiently transmitted than strains with other drug resistance mutations (184V and 103N in the RT gene and 82A/S/T and 90M in the protease gene).

Field uptake rates of hydrophobic organic contaminants by semipermeable membrane devices: environmental monitoring considerations

The uptake rates of selected hydrophobic organic contaminants (HOCs) by semipermeable membrane devices (SPMDs)--a polyethylene layflat containing the lipid triolein--were investigated under natural conditions. SPMDs were exposed in three sampling sites (industrial, urban, and agricultural areas) in the Tajo River (Toledo, Spain) for 5, 11 and 20 d. The organochlorine compounds 4,4'-DDT, 4,4'-DDE, alpha-HCH, gamma-HCH, pentachlorobenzene, hexachlorobenzene, and polychlorinated biphenyls (PCBs), and the 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) were detected in the SPMDs deployed in the three sampling sites. A linear uptake rate was found for DDTs and for 4-Cl- and 5-Cl-substituted PCB congeners in all sampling sites. Concentrations of HCHs (80.3 ng g(-1) SPMD for alpha-HCH and 109 ng g(-1) SPMD for gamma-HCH after 20 d of exposure) increased according to a linear uptake rate in the SPMDs deployed in the sampling site located in the agricultural area. Likewise, a marked increase of total PAH concentration (up to 300 ng g(-1) SPMD after 20 d of exposure) was solely found in the sampling site situated near a thermoelectric power station. Examination of individual PAHs revealed that PAHs with log K(OW) between 4.2 and 5.7 displayed a linear uptake rate over the 20 d of exposure. Water concentrations (ng L(-1)) of HCB (0.80-2.48), lindane (1.30-11.5), 4,4'-DDT (0.61-2.02), 4,4'-DDE (6.89-11.6) and total PAHs (12.0-26.7) estimated by a linear uptake kinetic model were found to be high in comparison with other polluted aquatic systems, and similar to concentrations in other Spanish rivers. Our results suggest that SPMD kinetic uptake studies in the natural environment are recommended for identifying point-pollution sources, and that shorter times of SPMD exposure (approximately 1 week) are desirable to minimize one of the main problems of field SPMD deployment, i.e., the biofouling, which negatively affects the estimation of the dissolved HOC concentrations.

Field trial of the brucellosis fluorescence polarization assay

Fluorescence polarization assay (FPA) is a homogeneous technique which was applied to the serological diagnosis of bovine brucellosis. Because of its simplicity and because it may be performed very rapidly, it was an ideal test to adapt to field use. The FPA was used to test cattle on six dairy farms in Baja California, Mexico. Anticoagulated blood, serum, and milk were collected from each animal. The anticoagulated blood was tested immediately on the farm while serum and milk were tested subsequently in the laboratory. Cattle on one farm (n = 140) were thought not to be infected with Brucella abortus and the other farms were thought to have high prevalence of the infection. The whole blood FPA (FPA(bld)) did not detect antibody in any of the cattle on the first premise. This finding was confirmed using a number of other serological tests, including the buffered antigen plate agglutination test, the complement fixation test, the indirect and competitive enzyme immunoassays, and the FPA using serum and milk. Cattle on the other premises (n = 1122) were tested in a similar fashion. The sensitivity of the FPA(bld), relative to the serum FPA (considered the definitive test), was 99.1% and the relative specificity of the FPA(bld) was 99.6%. These results compared favourably with those obtained using the other serological tests.

Indinavir plasma concentrations and resistance mutations in patients experiencing early virological failure

Virological failure under protease inhibitor (PI)-based antiretroviral regimens is often not explained by the selection of resistance mutations. The role of low indinavir (IDV) plasma levels in treatment failure was assessed in 46 subjects experiencing early virological failure to a first-line IDV-containing triple combination. Overall, 69% of patients showed subtherapeutic IDV plasma levels (it was not detected at all in 75% of them). Subjects with detectable but suboptimal IDV levels developed more IDV resistance mutations. Thus, drug monitoring may be useful to assess treatment adherence and risk of drug resistance in early virological failures. This information may be crucial for choosing the most appropriate rescue intervention.

Changes in the human immunodeficiency virus p7-p1-p6 gag gene in drug-naive and pretreated patients

Resistance to antiretroviral agents often results from mutations within the human immunodeficiency virus (HIV) pol gene. Moreover, insertions within the p6 gag-pol region have recently been found to be involved with resistance to nucleoside analogs. Overall, we found that 21% of 156 specimens collected from HIV-infected individuals (17.6% from 74 drug-naive patients and 24.4% from 82 pretreated patients) harbored these insertions. Insertions around the KQE (Lys-Gln-Glu) motif were found in 12.2% of the pretreated patients but in none of the drug-naive subjects (P = 0.002). In contrast, insertions around the PTAP (Prol-Thre-Ala-Prol) motif were seen at similar rates ( approximately 15%) among drug-naive and pretreated patients, which supports the idea that they may be natural polymorphisms.

Decline in the rate of genotypic resistance to antiretroviral drugs in recent HIV seroconverters in Madrid

Genotypic resistance to antiretroviral drugs was analysed in plasma from 57 acute or recent HIV seroconverters in Madrid. The overall prevalence of drug-associated primary resistance mutations was 25.8% in 1997-1999, but declined to 3.8% in 2000-2001. The lower rate in recent years suggested that most new HIV infections derive from viraemic individuals unaware of their HIV- positive status, rather than from those failing antiretroviral treatment. Drug-resistance testing is thus not required before beginning antiretroviral therapy.

Prevalence of G333D/E in naive and pretreated HIV-infected patients

A substitution at codon 333 (G -->D/E) within the reverse transcriptase (RT) gene causes resistance to both zidovudine (AZT) and lamivudine (3TC) in a background of mutations associated with loss of sensitivity to both drugs. In the absence of G333D/E, M184V restores the sensitivity to AZT in viruses harboring AZT-resistant genotypes. In this study, we examined the prevalence of the G333D/E mutation in plasma samples from 401 HIV-infected individuals from a routine clinical practice. Genotypic results could be obtained in 277 (81%) specimens belonging to pretreated subjects and in all 65 samples from treatment-naive individuals. The overall prevalence of the G333D/E mutation was 13.2%, without significant differences when comparing naive (10.8%) and treatment-experienced patients (13.7%). The codon 333 mutation was associated with AZT/3TC-resistant genotypes in 76.3% of pretreated individuals but in none of the treatment-naive individuals. In conclusion, the G333D/E mutation must be considered a natural polymorphism, which appears in 11% of treatment-naive HIV-infected individuals. In AZT-experienced patients, it might be advisable to exclude its presence before adding 3TC in combination in the hope of obtaining a restoration of AZT sensitivity if M184V develops.

Enhanced neurofibrillary degeneration in transgenic mice expressing mutant tau and APP

JNPL3 transgenic mice expressing a mutant tau protein, which develop neurofibrillary tangles and progressive motor disturbance, were crossed with Tg2576 transgenic mice expressing mutant beta-amyloid precursor protein (APP), thus modulating the APP-Abeta (beta-amyloid peptide) environment. The resulting double mutant (tau/APP) progeny and the Tg2576 parental strain developed Abeta deposits at the same age; however, relative to JNPL3 mice, the double mutants exhibited neurofibrillary tangle pathology that was substantially enhanced in the limbic system and olfactory cortex. These results indicate that either APP or Abeta influences the formation of neurofibrillary tangles. The interaction between Abeta and tau pathologies in these mice supports the hypothesis that a similar interaction occurs in Alzheimer's disease.

Neurofibrillary tangles, amyotrophy and progressive motor disturbance in mice expressing mutant (P301L) tau protein

Neurofibrillary tangles (NFT) composed of the microtubule-associated protein tau are prominent in Alzheimer disease (AD), Pick disease, progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). Mutations in the gene (Mtapt) encoding tau protein cause frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), thereby proving that tau dysfunction can directly result in neurodegeneration. Expression of human tau containing the most common FTDP-17 mutation (P301L) results in motor and behavioural deficits in transgenic mice, with age- and gene-dose-dependent development of NFT. This phenotype occurred as early as 6.5 months in hemizygous and 4.5 months in homozygous animals. NFT and Pick-body-like neuronal lesions occurred in the amygdala, septal nuclei, pre-optic nuclei, hypothalamus, midbrain, pons, medulla, deep cerebellar nuclei and spinal cord, with tau-immunoreactive pre-tangles in the cortex, hippocampus and basal ganglia. Areas with the most NFT had reactive gliosis. Spinal cord had axonal spheroids, anterior horn cell loss and axonal degeneration in anterior spinal roots. We also saw peripheral neuropathy and skeletal muscle with neurogenic atrophy. Brain and spinal cord contained insoluble tau that co-migrated with insoluble tau from AD and FTDP-17 brains. The phenotype of mice expressing P301L mutant tau mimics features of human tauopathies and provides a model for investigating the pathogenesis of diseases with NFT.

Self-organized networks of competing boolean agents

A model of Boolean agents competing in a market is presented where each agent bases his action on information obtained from a small group of other agents. The agents play a competitive game that rewards those in the minority. After a long time interval, the poorest player's strategy is changed randomly, and the process is repeated. Eventually the network evolves to a stationary but intermittent state where random mutation of the worst strategy can change the behavior of the entire network, often causing a switch in the dynamics between attractors of vastly different lengths.