Using Computational Simulations to Model Deleterious Variation and Genetic Load in Natural Populations

AbstractDeleterious genetic variation is abundant in wild populations, and understanding the ecological and conservation implications of such variation is an area of active research. Genomic methods are increasingly used to quantify the impacts of deleterious variation in natural populations; however, these approaches remain limited by an inability to accurately predict the selective and dominance effects of mutations. Computational simulations of deleterious variation offer a complementary tool that can help overcome these limitations, although such approaches have yet to be widely employed. In this perspective article, we aim to encourage ecological and conservation genomics researchers to adopt greater use of computational simulations to aid in deepening our understanding of deleterious variation in natural populations. We first provide an overview of the components of a simulation of deleterious variation, describing the key parameters involved in such models. Next, we discuss several approaches for validating simulation models. Finally, we compare and validate several recently proposed deleterious mutation models, demonstrating that models based on estimates of selection parameters from experimental systems are biased toward highly deleterious mutations. We describe a new model that is supported by multiple orthogonal lines of evidence and provide example scripts for implementing this model (https://github.com/ckyriazis/simulations_review).

The genomic footprint of whaling and isolation in fin whale populations

Twentieth century industrial whaling pushed several species to the brink of extinction, with fin whales being the most impacted. However, a small, resident population in the Gulf of California was not targeted by whaling. Here, we analyzed 50 whole-genomes from the Eastern North Pacific (ENP) and Gulf of California (GOC) fin whale populations to investigate their demographic history and the genomic effects of natural and human-induced bottlenecks. We show that the two populations diverged ~16,000 years ago, after which the ENP population expanded and then suffered a 99% reduction in effective size during the whaling period. In contrast, the GOC population remained small and isolated, receiving less than one migrant per generation. However, this low level of migration has been crucial for maintaining its viability. Our study exposes the severity of whaling, emphasizes the importance of migration, and demonstrates the use of genome-based analyses and simulations to inform conservation strategies.

In Memoriam: Robert K. Wayne, a pioneer of evolutionary genomics for wildlife with an emphasis on endangered species

Robert (Bob) Keith Wayne lost his battle with cancer in his home on 26 December 2022 with his wife, Dr. Blaire Van Valkenburgh, by his side. This essay, written by his former graduate students, highlights the foundation that survives Bob and our vision of continuing his efforts in building a future for endangered species.

Selection against admixture and gene regulatory divergence in a long-term primate field study

Genetic admixture is central to primate evolution. We combined 50 years of field observations of immigration and group demography with genomic data from ~9 generations of hybrid baboons to investigate the consequences of admixture in the wild. Despite no obvious fitness costs to hybrids, we found signatures of selection against admixture similar to those described for archaic hominins. These patterns were concentrated near genes where ancestry is strongly associated with gene expression. Our analyses also show that introgression is partially predictable across the genome. This study demonstrates the value of integrating genomic and field data for revealing how "genomic signatures of selection" (e.g., reduced introgression in low-recombination regions) manifest in nature; moreover, it underscores the importance of other primates as living models for human evolution.

The critically endangered vaquita is not doomed to extinction by inbreeding depression

In cases of severe wildlife population decline, a key question is whether recovery efforts will be impeded by genetic factors, such as inbreeding depression. Decades of excess mortality from gillnet fishing have driven Mexico's vaquita porpoise (Phocoena sinus) to ~10 remaining individuals. We analyzed whole-genome sequences from 20 vaquitas and integrated genomic and demographic information into stochastic, individual-based simulations to quantify the species' recovery potential. Our analysis suggests that the vaquita's historical rarity has resulted in a low burden of segregating deleterious variation, reducing the risk of inbreeding depression. Similarly, genome-informed simulations suggest that the vaquita can recover if bycatch mortality is immediately halted. This study provides hope for vaquitas and other naturally rare endangered species and highlights the utility of genomics in predicting extinction risk.

Response to Bakker et al

Robinson and colleagues respond to the points raised about their paper by Bakker et al.

High-Resolution Estimates of Crossover and Noncrossover Recombination from a Captive Baboon Colony

Homologous recombination has been extensively studied in humans and a handful of model organisms. Much less is known about recombination in other species, including nonhuman primates. Here, we present a study of crossovers (COs) and noncrossover (NCO) recombination in olive baboons (Papio anubis) from two pedigrees containing a total of 20 paternal and 17 maternal meioses, and compare these results to linkage disequilibrium (LD) based recombination estimates from 36 unrelated olive baboons. We demonstrate how COs, combined with LD-based recombination estimates, can be used to identify genome assembly errors. We also quantify sex-specific differences in recombination rates, including elevated male CO and reduced female CO rates near telomeres. Finally, we add to the increasing body of evidence suggesting that while most NCO recombination tracts in mammals are short (e.g., <500 bp), there is a non-negligible fraction of longer (e.g., >1 kb) NCO tracts. For NCO tracts shorter than 10 kb, we fit a mixture of two (truncated) geometric distributions model to the NCO tract length distribution and estimate that >99% of all NCO tracts are very short (mean 24 bp), but the remaining tracts can be quite long (mean 4.3 kb). A single geometric distribution model for NCO tract lengths is incompatible with the data, suggesting that LD-based methods for estimating NCO recombination rates that make this assumption may need to be modified.

Genome-wide diversity in the California condor tracks its prehistoric abundance and decline

Due to their small population sizes, threatened and endangered species frequently suffer from a lack of genetic diversity, potentially leading to inbreeding depression and reduced adaptability.¹ During the latter half of the twentieth century, North America's largest soaring bird,² the California condor (Gymnogyps californianus; Critically Endangered³), briefly went extinct in the wild. Though condors once ranged throughout North America, by 1982 only 22 individuals remained. Following decades of captive breeding and release efforts, there are now >300 free-flying wild condors and ∼200 in captivity. The condor's recent near-extinction from lead poisoning, poaching, and loss of habitat is well documented,⁴ but much about its history remains obscure. To fill this gap and aid future management of the species, we produced a high-quality chromosome-length genome assembly for the California condor and analyzed its genome-wide diversity. For comparison, we also examined the genomes of two close relatives: the Andean condor (Vultur gryphus; Vulnerable³) and the turkey vulture (Cathartes aura; Least Concern³). The genomes of all three species show evidence of historic population declines. Interestingly, the California condor genome retains a high degree of variation, which our analyses reveal is a legacy of its historically high abundance. Correlations between genome-wide diversity and recombination rate further suggest a history of purifying selection against linked deleterious alleles, boding well for future restoration. We show how both long-term evolutionary forces and recent inbreeding have shaped the genome of the California condor, and provide crucial genomic resources to enable future research and conservation.

Genomic signatures of extensive inbreeding in Isle Royale wolves, a population on the threshold of extinction

The observation that small isolated populations often suffer reduced fitness from inbreeding depression has guided conservation theory and practice for decades. However, investigating the genome-wide dynamics associated with inbreeding depression in natural populations is only now feasible with relatively inexpensive sequencing technology and annotated reference genomes. To characterize the genome-wide effects of intense inbreeding and isolation, we performed whole-genome sequencing and morphological analysis of an iconic inbred population, the gray wolves (Canis lupus) of Isle Royale. Through population genetic simulations and comparison with wolf genomes from a variety of demographic histories, we find evidence that severe inbreeding depression in this population is due to increased homozygosity of strongly deleterious recessive mutations. Our results have particular relevance in light of the recent translocation of wolves from the mainland to Isle Royale, as well as broader implications for management of genetic variation in the fragmented landscape of the modern world.

Analysis of 100 high-coverage genomes from a pedigreed captive baboon colony

Baboons (genus Papio) are broadly studied in the wild and in captivity. They are widely used as a nonhuman primate model for biomedical studies, and the Southwest National Primate Research Center (SNPRC) at Texas Biomedical Research Institute has maintained a large captive baboon colony for more than 50 yr. Unlike other model organisms, however, the genomic resources for baboons are severely lacking. This has hindered the progress of studies using baboons as a model for basic biology or human disease. Here, we describe a data set of 100 high-coverage whole-genome sequences obtained from the mixed colony of olive (P. anubis) and yellow (P. cynocephalus) baboons housed at the SNPRC. These data provide a comprehensive catalog of common genetic variation in baboons, as well as a fine-scale genetic map. We show how the data can be used to learn about ancestry and admixture and to correct errors in the colony records. Finally, we investigated the consequences of inbreeding within the SNPRC colony and found clear evidence for increased rates of infant mortality and increased homozygosity of putatively deleterious alleles in inbred individuals.

Purging of Strongly Deleterious Mutations Explains Long-Term Persistence and Absence of Inbreeding Depression in Island Foxes

The recovery and persistence of rare and endangered species are often threatened by genetic factors, such as the accumulation of deleterious mutations, loss of adaptive potential, and inbreeding depression [1]. Island foxes (Urocyon littoralis), the dwarfed descendants of mainland gray foxes (Urocyon cinereoargenteus), have inhabited California's Channel Islands for >9,000 years [2-4]. Previous genomic analyses revealed that island foxes have exceptionally low levels of diversity and elevated levels of putatively deleterious variation [5]. Nonetheless, all six populations have persisted for thousands of generations, and several populations rebounded rapidly after recent severe bottlenecks [6, 7]. Here, we combine morphological and genomic data with population-genetic simulations to determine the mechanism underlying the enigmatic persistence of these foxes. First, through analysis of genomes from 1929 to 2009, we show that island foxes have remained at small population sizes with low diversity for many generations. Second, we present morphological data indicating an absence of inbreeding depression in island foxes, confirming that they are not afflicted with congenital defects common to other small and inbred populations. Lastly, our population-genetic simulations suggest that long-term small population size results in a reduced burden of strongly deleterious recessive alleles, providing a mechanism for the absence of inbreeding depression in island foxes. Importantly, the island fox illustrates a scenario in which genetic restoration through human-assisted gene flow could be a counterproductive or even harmful conservation strategy. Our study sheds light on the puzzle of island fox persistence, a unique success story that provides a model for the preservation of small populations.

Genomic Flatlining in the Endangered Island Fox

Genetic studies of rare and endangered species often focus on defining and preserving genetically distinct populations, especially those having unique adaptations [1, 2]. Much less attention is directed at understanding the landscape of deleterious variation, an insidious consequence of geographic isolation and the inefficiency of natural selection to eliminate harmful variants in small populations [3-5]. With population sizes of many vertebrates decreasing and isolation increasing through habitat fragmentation and loss, understanding the extent and nature of deleterious variation in small populations is essential for predicting and enhancing population persistence. The Channel Island fox (Urocyon littoralis) is a dwarfed species that inhabits six of California's Channel Islands and is derived from the mainland gray fox (U. cinereoargenteus). These isolated island populations have persisted for thousands of years at extremely small population sizes [6, 7] and, consequently, are a model for testing ideas about the accumulation of deleterious variation in small populations under natural conditions. Analysis of complete genome sequence data from island foxes shows a dramatic decrease in genome-wide variation and a sharp increase in the homozygosity of deleterious variants. The San Nicolas Island population has a near absence of variation, demonstrating a unique genetic flatlining that is punctuated by heterozygosity hotspots, enriched for olfactory receptor genes and other genes with high levels of ancestral variation. These findings question the generality of the small-population paradigm that maintains substantial genetic variation is necessary for short- and long-term persistence.

In situ degradation studies of two-dimensional WSe₂-graphene heterostructures

Heterostructures of two-dimensional materials can be vulnerable to thermal degradation due to structural and interfacial defects as well as thermal expansion mismatch, yet a systematic study does not exist in the literature. In this study, we investigate the degradation of freestanding WSe2-graphene heterostructures due to heat and charge flow by performing in situ experiments inside a transmission electron microscope. Experimental results show that purely thermal loading requires higher temperatures (>850 °C), about 150 °C higher than that under combined electrical and thermal loading. In both cases, selenium is the first element to decompose and migration of silicon atoms from the test structure to the freestanding specimen initiates rapid degradation through the formation of tungsten disilicide and silicon carbide. The role of the current flow is to enhance the migration of silicon from the sample holder and to knock-out the selenium atoms. The findings of this study provide fundamental insights into the degradation of WSe2-graphene heterostructures and inspire their application in electronics for use in harsh environments.

Demonstration of ignition radiation temperatures in indirect-drive inertial confinement fusion hohlraums

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

Isolation and Characterization of Neisseria meningitidis Groups A, C, X, and Y Polysaccharide Antigens

To prepare Neisseria meningitidis groups A, C, X, and Y polysaccharide antigens, culture supernatant fluids were subjected to serial processes of salt precipitation, alkaline hydrolysis, ethyl alcohol precipitation, and Sephadex G-200 chromatography. This method resulted in the isolation of large quantities of group antigens. All are acidic polysaccharides, the group C antigen being a polymer of n-acetyl neuraminic acid. Thiobarbituric acid assay failed to reveal sialic acids in the other group antigens. Protein was undetectable by absorption at 280 nm or by Folin analysis. These antigens are of similar molecular size, the majority of which are excluded by Sephadex G-200. They migrate in the upper one-third of sucrose density gradients and are retained by 5% acrylamide gel. All are highly group-specific and react only with homologous hyperimmune antisera in hemagglutination, complement fixation, and immunodiffusion systems. As little as 0.03 mumoles of n-acetyl neuraminic acid in group C antigen inhibits the hemagglutination of group C-sensitized red cells. All antigens are immunogenic in rabbits. These techniques afford a simplified method for the production of relatively large yields of highly specific group antigens which participate in multiple immunologic systems.

Kinetics of hydrogen consumption by rumen fluid, anaerobic digestor sludge, and sediment

Michaelis-Menten kinetic parameters for H(2) consumption by three methanogenic habitats were determined from progress curve and initial velocity experiments. The influences of mass transfer resistance, endogenous H(2) production, and growth on apparent parameter estimates were also investigated. Kinetic parameters could not be determined for undiluted rumen fluid and some digestor sludge from gas-phase measurements of H(2), since mass transfer of H(2) across the gas-liquid interface was rate limiting. However, accurate values were obtained once the samples were diluted. H(2) consumption by digestor sludge with a long retention time and by hypereutrophic lake sediment was not phase transfer limited. The K(m) values for H(2) uptake by these habitats were similar, with means of 5.8, 6.0, and 7.1 muM for rumen fluid, digestor sludge, and sediment, respectively. V(max) estimates suggested a ratio of activity of approximately 100 (rumen fluid):10 (sludge):1 (sediment); their ranges were as follows: rumen fluid, 14 to 28 mM h; Holt sludge, 0.7 to 4.3 mM h; and Wintergreen sediment, 0.13 to 0.49 mM h. The principles of phase transfer limitation, studied here for H(2), are the same for all gaseous substrates and products. The limitations and errors associated with gas phase determination of kinetic parameters were evaluated with a mathematical model that combined mass transport and Michaelis-Menten kinetics. Three criteria are described which can be used to evaluate the possibility that a phase transfer limitation exists. If it does not exist, (i) substrate consumption curves are Michaelis-Menten and not first order, (ii) the K(m) is independent of initial substrate concentration, and (iii) the K(m) is independent of biomass (V(max)) and remains constant with dilution of sample. Errors in the Michaelis-Menten kinetic parameters are caused by endogenously produced H(2), but they were <15% for rumen fluid and 10% for lake sediment and digestor sludge. Increases in V(max) during the course of progress curve experiments were not great enough to produce systematic deviations from Michaelis-Menten kinetics.

Interspecies acetate transfer influences the extent of anaerobic benzoate degradation by syntrophic consortia

Benzoate degradation by an anaerobic, syntrophic bacterium, strain SB, in coculture with Desulfovibrio sp. strain G-11 reached a threshold value which depended on the amount of acetate added and ranged from about 2.5 to 29.9 (mu)M. Increasing acetate concentrations also uncompetitively inhibited benzoate degradation. The apparent V(infmax) and apparent K(infm) for benzoate degradation decreased with increasing acetate concentration, but the benzoate degradation capacities (V(infmax)/K(infm)) of cell suspensions remained comparable. The addition of an acetate-using bacterium to cocultures after the threshold was reached resulted in the degradation of benzoate to below the detection limit. Mathematical simulations showed that the benzoate threshold was not predicted by the inhibitory effect of acetate on benzoate degradation kinetics. With nitrate instead of sulfate as the terminal electron acceptor, no benzoate threshold was observed in the presence of 20 mM acetate even though the kinetics of benzoate degradation were slower with nitrate rather than sulfate as the electron acceptor. When strain SB was grown with Desulfovibrio sp. strain DG2 that had a fourfold-lower V(infmax) for hydrogen use than strain G-11, the V(infmax) for benzoate degradation was 37-fold lower than that of strain SB-G-11 cocultures. The Gibb's free energy for benzoate degradation was less negative in cell suspensions with a threshold than in suspensions without a threshold. These studies showed that the threshold was not a function of the inhibition of benzoate degradation by acetate or the toxicity of the undissociated form of acetate. Rather, a critical or minimal Gibb's free energy may exist where thermodynamic constraints preclude further benzoate degradation.

Kinetics of microbial dehalogenation of haloaromatic substrates in methanogenic environments

The kinetic parameters associated with the microbial dehalogenation of 3-chlorobenzoate, 3,5-dichlorobenzoate, and 4-amino-3,5-dichlorobenzoate were measured in anoxic sediment slurries and in an enriched methanogenic culture grown on 3-chlorobenzoate. The initial dehalogenation of the substrates exhibited Michaelis-Menten kinetics. The apparent K(m) values for the above substrates ranged from 30 to 67 muM. The pattern of degradation, however, was unusual. The enrichment culture accumulated partially dehalogenated intermediates to 72 and 98% of that possible when incubated with either 3,5-dichloro- or 4-amino-3,5-dichlorobenzoate, respectively, but did not accumulate significant amounts of benzoate when 3-chlorobenzoate was the sole carbon and energy source. The accumulated intermediates were rapidly metabolized only after the parent substrate concentrations were nearly depleted (<5 muM). A sequential Michaelis-Menten model was developed to account for the observed pattern of biodegradation. Using this model, we found that relative differences in the K(m) and V(max) parameters for substrate and intermediate dehalogenations alone were insufficient to explain the transitory accumulation of intermediates. However, by inserting a competitive inhibition term, with the primary substrate as the inhibitor, the observed pattern of degradation was simulated. Apparently, the dichlorinated substrates competitively inhibit the dehalogenation of the monochlorinated substrates. Similar kinetic patterns were noted for sediments, although the rates were slower than in the enrichment culture.

Recent progress in the discovery of macrocyclic compounds as potential anti-infective therapeutics

Novel therapeutic strategies are urgently needed for the treatment of serious diseases caused by viral, bacterial and parasitic infections, because currently used drugs are facing the problem of rapidly emerging resistance. There is also an urgent need for agents that act on novel pathogen-specific targets, in order to expand the repertoire of possible therapies. The high throughput screening of diverse small molecule compound libraries has provided only a limited number of new lead series, and the number of compounds acting on novel targets is even smaller. Natural product screening has traditionally been very successful in the anti-infective area. Several successful drugs on the market as well as other compounds in clinical development are derived from natural products. Amongst these, many are macrocyclic compounds in the 1-2 kDa size range. This review will describe recent advances and novel drug discovery approaches in the anti-infective area, focusing on synthetic and natural macrocyclic compounds for which in vivo proof of concept has been established. The review will also highlight the Protein Epitope Mimetics (PEM) technology as a novel tool in the drug discovery process. Here the structures of naturally occurring antimicrobial and antiviral peptides and proteins are used as starting points to generate novel macrocyclic mimetics, which can be produced and optimized efficiently by combinatorial synthetic methods. Several recent examples highlight the great potential of the PEM approach in the discovery of new anti-infective agents.

Chemical vapor detection using single-walled carbon nanotubes

Single-walled carbon nanotubes possess unique properties that make them a potentially ideal material for chemical sensing. However, their extremely small size also presents technical challenges for realizing a practical sensor technology. In this tutorial review we explore the transduction physics by which the presence of molecular adsorbates is converted into a measurable electronic signal, and we identify solutions to the problems such as nanotube device fabrication and large, low-frequency noise that have inhibited commercial sensor development. Finally, we examine strategies to provide the necessary chemical specificity to realize a nanotube-based detection system for trace-level chemical vapor detection.

Otago Diagnostic Laboratories' (ODL) Method for the detection of beta-lactamases in Enterobacteriaceae

AIM

The rapid evolvement of beta-lactamases in Enterobacteriaceae is an important concern and the clinical microbiology laboratory is required to detect them, where possible, using a rapid, reliable, simple and low cost methodology.

MATERIALS AND METHODS

A disc diffusion method using NCCLS breakpoints, Jarlier's principle and cefoxitin test for AmpC was carried out. It incorporated seven antimicrobial discs in one agar plate: cefotaxime, aztreonam, amoxicillin-clavulanate, ceftazidime, cefpodoxime, cefepime and cefoxitin. NCCLS disc confirmation test for extended-spectrum beta-lactamase (ESBL) was carried out simultaneously.

RESULTS

AmpC, ESBL, CTX-M, and K1 were detected using these tests. The prevalence of ESBL was <1% in the hospital.

CONCLUSION

The method is recommended for the phenotypic detection of beta-lactamases in Enterobacteriaceae or for confirmation after the results are obtained by conventional automated systems.

Structure-dependent nonenzymatic deamidation of glutaminyl and asparaginyl pentapeptides

Nonenzymatic deamidation rates for 52 glutaminyl and 52 asparaginyl pentapeptides in pH 7.4, 37.0 degrees C. 0.15 m Tris-HCl buffer have been determined by direct injection mass spectrometry. These and the previously reported 306 asparginyl rates have been combined in a self-consistent model for peptide deamidation. This model depends quantitatively upon peptide structure and involves succinimide, glutarimide and hydrolysis mechanisms. The experimental values and suitable interpolated values have been combined to provide deamidation rate values in pH 7.4, 37.0 degrees C. 0.15 m Tris-HCl buffer for the entire set of 648 single-amide permutations of ordinary amino acid residues in GlyXxxAsnYyyGly and GlyXxxGlnYyyGly. Thus, knowledge about sequence-dependent deamidation in peptides is extended to include very long deamidation half-times in the range of 2-50 years.

Five-year follow-up of hepatitis C-naïve heart transplant recipients who received hepatitis C-positive donor hearts

BACKGROUND

Due to the risk of transmission of hepatitis C virus, the use of hepatitis C seropositive donors in heart transplantation is controversial. The transmission rate of hepatitis C in this patient population is estimated to range from 67% to 80%. Long-term clinical outcomes of heart transplant recipients of hepatitis C-positive donor hearts are not well described. We report the 5-year long-term outcome of seven hepatitis C-naïve heart transplant recipients who received hepatitis C-positive donor hearts.

METHODS

Retrospective analysis of clinical course, liver biochemistry, serology, and hepatitis C virology data.

RESULTS

Seven hearts transplant recipients, six men and one woman were included in our study. After a mean follow-up of 63.3 +/- 20.4 months (range 28.2 to 85.9), four of seven (57.1%) patients are hepatitis C-negative, have normal liver function tests, and no clinical evidence of hepatitis. Three of seven (43%) have been diagnosed with hepatitis C by liver biopsy or the HCV-RNA reverse transcriptase polymerase chain reaction at a mean follow-up of 35.1 months (18.8 months posttransplantation). One had an accelerated course of hepatitis that was ultimately fatal, one was successfully treated with interferon, and the third died from other causes than liver injury. Overall, the 5-year survival was 71.4%.

CONCLUSIONS

The 5-year survival of hepatitis C-naïve recipients of hearts from hepatitis C-positive donors is similar to heart transplant recipients with hepatitis-negative donor hearts. Nevertheless, the transmission rate is high and hepatitis C infection in this population can lead to considerable morbidity and accelerated, fatal hepatitis.

Comparison of analytical methods for the evaluation of antibody responses against epitopes of polymorphic protein antigens

Surface exposed protein antigens of the malaria parasite Plasmodium falciparum frequently harbor multiple dimorphic amino acid positions. These are associated with parasite immune evasion and represent a major obstacle for subunit vaccine design. Here, we have analyzed the flexibility of the humoral immune response against a semiconserved sequence (YX(44)LFX(47)KEKMX(52)L) of the key malaria blood stage vaccine candidate merozoite surface protein-1 (MSP-1). Monoclonal antibodies (mAbs) raised against one of the six described natural sequence variants of MSP-1(43-53) were analyzed for cross-reactivity with the other allelic forms, which differ in one to three positions from the immunizing sequence. Enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) spectroscopy demonstrated marked differences in mAb binding avidity to the variant sequences and isothermal titration calorimetry (ITC) provided evidence for a very low affinity of some of the interactions. In immunofluorescence analysis (IFA) and Western blotting analysis, the mAbs nevertheless stained all analyzed parasite clones expressing MSP-1(43-53) variant sequences. When used for the evaluation of humoral immune responses in clinical malaria vaccine trials, these two commonly used methods may thus not be suitable to distinguish biologically functional high affinity antibody responses from irrelevant low-affinity cross-reactivities.

Ecstasy (MDMA): are the psychological problems associated with its use reversed by prolonged abstinence?

RATIONALE

Chronic, regular recreational use of ecstasy (MDMA) is associated with psychopathology, elevated behavioural impulsivity and persistent impairment of memory performance.

OBJECTIVE

The aim of the present study was to investigate which of these sequelae persist after at least 6 months of abstinence from ecstasy.

METHODS

Four groups of participants were compared: 18 current regular recreational ecstasy users, 15 ex-regular ecstasy users who had abstained from using the drug for an average of 2 years, 16 polydrug users who had never taken ecstasy and 15 drug-naive controls.

RESULTS

There were no significant group differences in age, education level, or pre-morbid intelligence and, generally, the use of illicit drugs other than ecstasy was not significantly different among the three drug-using groups. Both current and ex-ecstasy users exhibited elevated psychopathology and behavioural impulsivity compared with polydrug users and drug-naive controls, but current ecstasy users exhibited a broader range of psychopathology than ex-users. Both groups of ecstasy users also exhibited impaired working memory and verbal recall performance compared with drug-naive controls, but only ex-users exhibited impaired verbal recall relative to polydrug users. Regression analysis indicated that psychopathology was primarily predicted by the extent of previous consumption of cannabis rather than ecstasy, whereas the majority of the cognitive deficits were only predicted by the extent of previous ecstasy use.

CONCLUSIONS

Selective impairments of neuropsychological performance associated with regular ecstasy use are not reversed by prolonged abstinence. This is consistent with evidence that ecstasy has potent and selective neurotoxic effects on brain serotonergic systems in humans.

High grazer toxicity of [D-Asp(3),(E)-Dhb(7)]microcystin-RR of Planktothrix rubescens as compared to different microcystins

Planktothrix rubescens, the dominant cyanobacterium in Lake Zürich, is generally considered to be toxic to zooplankton. The major toxin was determined by NMR spectroscopy and chemical analysis to be [D-Asp(3),(E)-Dhb(7)]microcystin-RR. The compound was isolated in high purity, and its 24-h acute grazer toxicity was compared with microcystin-LR, microcystin-RR, microcystin-YR, and nodularin using a Thamnocephalus platyurus bioassay. Based on LC(50) values [D-Asp(3),(E)-Dhb(7)]microcystin-RR was the most toxic microcystin tested. Nodularin was slightly more toxic under the conditions of the assay. The large number of individuals available for the grazer bioassay allowed the determination of dose-response curves of the different microcystins. These curves showed marked differences in their steepness. Microcystin-RR, which had nearly the same LC(50) as microcystin-LR and microcystin-YR, exhibited a very flat dose-response curve. This flat curve indicates that, for some individuals, lower concentrations of this microcystin are much more toxic than are the other two microcystins. Mortality of 100% requires much higher concentrations of microcystin-RR, indicating the resistance of some animals to the toxin. The purified [D-Asp(3),(E)-Dhb(7)]microcystin-RR exhibited a higher molar absorption coefficient determined by quantitative amino acid analysis than the coefficients generally used for other microcystins. This observation has consequences for the risk assessment for microcystins and makes a structural determination of microcystins an absolute requirement. The presence of the dehydrobutyrine residue may be the reason for the higher specific toxicity of [D-Asp(3),(E)-Dhb(7)]microcystin-RR when compared to the N-methyldehydroalanine-containing microcystins.

Exploiting conformationally constrained peptidomimetics and an efficient human-compatible delivery system in synthetic vaccine design

Peptide and protein mimetics are potentially of great value in synthetic vaccine design. The mimetics should function by stimulating the immune system to produce antibodies that recognize the intact parasite. Also the mimetics should be presented to the immune system in a way that leads to efficient antibody production. Here we investigate the application of cyclic peptidomimetics presented on immunopotentiating reconstituted influenza virosomes (IRIVs), a form of antigen delivery that is licensed already for human clinical use, in synthetic vaccine design. We focus on the central (NPNA)(n) repeat region of the circumsporozoite (CS) protein of the malaria parasite Plasmodium falciparum as a model system. Cyclic peptidomimetics of the NPNA repeats were incorporated into both an IRIV and (for comparison) a multiple-antigen peptide (MAP). Both IRIV and MAP delivery forms induced mimetic-specific humoral immune responses in mice, but only with the mimetic-IRIV preparations did a significant fraction of the elicited antibodies cross-react with sporozoites. The results demonstrate that IRIVs are a delivery system suitable for the efficient induction of antibody responses against conformational epitopes by use of cyclic template-bound peptidomimetics. Combined with combinatorial chemistry, this approach may have great potential for the rapid optimization of molecularly defined synthetic vaccine candidates against a wide variety of infectious agents.

Reproduction studies in the rat with shea oleine and hardened shea oleine

Shea oleine is an oil fraction derived from the nut of the tree Butyrospermum parkii, which grows in central and western Africa. There are several uses of shea oleine including its use as a frying oil and, after hardening, in margarine and toffee fat. This investigation was performed to examine the toxicity of 7 or 15% hardened shea oleine in comparison with 7 or 15% unhardened shea oleine and various commercially available materials, sheanut and palm oils, cocoa butter and toffee powder following dietary administration to rats during pre-mating, mating, pregnancy and offspring weaning in two separate investigations. Reproduction was assessed using number of litters and pups born plus survival and body weights at birth and at weaning on day 21. Skeletal evaluation using X-ray, clinical pathology and a macroscopic examination were also performed for F1 rats. Study measures for parent animals comprised evaluation of body weight, food consumption, clinical pathology, organ weights and macroscopic examination. Fatty acids and hydrocarbon levels were measured and an evaluation for lipogranulomata was made for various tissues. Results showed that shea oleine, whether unhardened or hardened, produced no evidence of reproduction toxicity and gave a similar profile to the other commercially available materials used in this study in the rat. Minor findings with shea oleine were not related to reproduction performance but comprised slightly reduced body weight gain and reduced cholesterol and raised alkaline phosphatase levels. None of the findings in this study were considered to be of toxicological significance. Thus, no evidence of reproduction toxicity was seen for both unhardened and hardened shea oleine in this investigation in the rat at levels equating to greater than 7.5 g/kg/day.

The health behavior selection process of young adolescents

The health behavior selection process of young adolescents was explored using the grounded theory research method. Data were generated from in-depth interviews, field notes from school settings, and memos. A conceptual model was generated identifying 4 major categories: assessing/valuing, confirming, choosing, and safeguarding. The processes identified in the model offer the potential of developing new strategies for school nurses to influence health behavior outcomes among young adolescents.

Extracorporeal photopheresis for the treatment of lung allograft rejection

OBJECTIVES

Acute and chronic rejection continue to limit the survival of lung transplant recipients. Extracorporeal photopheresis has evolved as a possible therapy for patients with acute nd chronic lung allograft rejection.

METHODS

We retrospectively reviewed 14 patients diagnosed with BOS who underwent therapy with extracorporeal photopheresis.

RESULTS

Three patients were classified as BOS 0'b', five as BOS 1, three as BOS 2, and, three as BOS 3 at the time of diagnosis. Of the patients with BOS 0'b' or BOS 1 seven remain alive and one died of lung cancer. Two have progressed to BOS 2. Of the patients with BOS 2 or 3, four have died of BOS, one died of lung cancer, and one was re-transplanted. In three patients with BOS and concurrent acute rejection, therapy with extracorporeal photopheresis led to the resolution of the acute rejection episode. Two of the 14 patients developed line related sepsis.

CONCLUSION

Extracorporeal photopheresis appears to be a promising therapy for patients with early BOS. It may also have a role in the treatment of acute lung allograft rejection.

Fate of ethanol topically applied to skin

Ethanol is a major component of many aerosol sprays and consumer products that are designed to contact the skin. It is theoretically possible that small amounts of ethanol from alcohol-based sprays can be absorbed across the skin or inhaled during spraying. In order to assess the potential systemic dose, three parameters were measured: the evaporation of [14C]ethanol from the skin surface, the in vitro penetration of [14C]ethanol through excised pig skin and the ethanol concentration in the blood of human volunteers following simulated use of an alcohol based deodorant spray. The rate of evaporation from Benchkote and whole pig skin was similar (t(1/2)=13.6 sec and 11.7 sec, respectively) while that from glass was longer (t(1/2)=24.8 sec). Ethanol penetration through pig skin in vitro was greater in occluded cells than in non-occluded cells (2.19 mg/cm(2) and 0.10 mg/cm(2) in 24 hours, respectively). At the maximum flux seen in this experiment under occlusion, the amount of ethanol penetrating from a 1 m(2) area of skin would give a blood alcohol level of about 4 mg% in a 70-kg man. In the human use study, none of the blood samples taken from 16 human volunteers exhibited a detectable level of alcohol. These studies provide evidence that a systemic dose of ethanol is likely to be very low after the use of formulations delivering ethanol to the skin.

Becaplermin and necrobiosis lipoidicum diabeticorum: results of a case control pilot study

Necrobiosis lipoidica diabeticorum (NLD) is a rare skin condition associated with diabetes, which characteristically occurs in the pretibial region of the lower limbs (Boulton et al., 1988). The lesions generally appear as well-circumscribed reddish plaques, which are most often asymptomatic, resulting primarily in cosmetic disability. Currently, there is no reliable form of treatment for NLD, although many regimens have been tried (Shall et al., 1990)

Analysis of antibody A6 binding to the extracellular interferon gamma receptor alpha-chain by alanine-scanning mutagenesis and random mutagenesis with phage display

The monoclonal antibody A6 binds a conformational epitope comprising mainly the CC' surface loop on the N-terminal fibronectin type-III domain of the extracellular interferon gamma receptor (IFNgammaR). The crystal structure of an A6 Fab-IFNgammaR complex revealed an interface rich in the aromatic side chains of Trp, Tyr, and His residues. These aromatic side chains appear to interact with both polar and hydrophobic groups at the interface, a property which, in general, may be advantageous for ligand binding. To analyze these interactions in more detail, the affinities of 19 A6 alanine-scanning mutants for the IFNgammaR have been measured, using engineered A6 single chain variable region fragments, and a surface plasmon resonance biosensor. Energetically important side chains (DeltaG(mutant) - DeltaG(wt) > 2.4 kcal/mol), that form distinct hot spots in the binding interface, have been identified on both proteins. These include V(L)W92 in A6, whose benzenoid ring appears well situated for a pi-cation (or pi-amine) interaction with the side chain of receptor residue K47 and simultaneously for T-stacking onto the indole ring of W82 in the receptor. At another site, energetically important residues V(H)W52 and V(H)W53, as well as V(H)D54 and V(H)D56, surround the aliphatic side chain of the hot receptor residue K52. Taken together, the results show that side chains distributed across the interface, including many aromatic ones, make key energetic contributions to binding. In addition, the receptor CC' loop has been subjected to random mutagenesis, and receptor mutants with high affinity for A6 have been selected by phage display. Residues previously identified as important for receptor binding to A6 were conserved in the clones isolated. Some mutants, however, showed a much improved affinity for A6, due to changes at Glu55, a residue that appeared to be energetically unimportant for binding the antibody by alanine-scanning mutagenesis. An E55P receptor mutant bound A6 with a 600-fold increase in affinity (K(D) approximately 20 pM), which is one of the largest improvements in affinity from a single point mutation reported so far at any protein-protein interface.

Traumatic hyphema: a comprehensive review of the past half century yields 8076 cases for which specific medical treatment reduces rebleeding 62%, from 13% to 5% (P<.0001)

PURPOSE

To eliminate the continuing so-called "controversy" regarding, and opposition to, the specific medical management of traumatic hyphema (TH) with systemic antifibrinolytic agents including aminocaproic acid (ACA) and tranexamic acid (TXA) and steroids (prednisone); to illuminate the role of topical steroids.

METHOD

Review of all (English language) studies since 1950 of these medical treatments of TH, and contemporary no specific medical treatment controls.

RESULTS

The difference between the average rebleeding rate in the specifically medically treated group, 4.89%, and that rate in the untreated group, 13.02%, was statistically a true difference due not to chance but to the difference in therapy with a probability of <0.0001 by Chi Square Test, Yates Corrected Chi Square Test and Fisher's Exact Test. This was also true individually respectively and with identical probabilities of p=<0.0001 for systemic steroids, topical steroids, ACA and TXA. Combined topical steroids and systemic ACA or TXA did not further improve results.

CONCLUSION

Preventing rebleeding episodes remains a major treatment objective in the clinical management of TH. This is best accomplished by the Yasuna systemic steroid No Touch or No Touch PLUS treatment protocol, the only treatment protocols consistently yielding zero rebleed rates in non-Scandinavian populations.

Direct action of naturally occurring estrogen metabolites on human osteoblastic cells

This article describes experiments that were performed to examine the direct action of estrogen metabolites on cultured human osteoblast cells. The human fetal osteoblastic cell line, hFOB/ER9, which expresses high levels of the estrogen receptor (ER) alpha, was used to examine the direct effects of 16alpha-hydroxyestrone (16alpha-OHE1) and 2-hydroxyestrone (2-OHE1) on osteoblast differentiation. The 16alpha-OHE1 caused a decrease in osteocalcin (OC) secretion to a maximum of 40% of control values (vehicle-treated cells) at 10(-7) M. Alkaline phosphatase (AP) activity was significantly induced at 10(-7) M 16alpha-OHE1 with greater than 500% of control at 10(-6) M 16alpha-OHE1. Finally, AP steady-state messenger RNA (mRNA) levels were increased within 24 h of 16alpha-OHE1 treatment. In contrast to 16alpha-OHE1, 2-OHE1 had no effects on the secretion of OC, AP activity, or AP gene expression. The 2-OHE1 also did not display any antiestrogen activity because treatment in combination with 17beta-estradiol (E2) and 16alpha-OHE1 had no significant effect on the reduction in OC secretion or induction of AP activity. Similar to E2, 16alpha-OHE1 stimulated the expression of an early response gene, a TGF-beta inducible early gene, designated TIEG, as early as 60 minutes after treatment, whereas treatment with 2-OHE1 displayed no effect. Support that the 16alpha-OHE1 regulation of these osteoblasts (OB) markers was mediated through the ER is shown by the fact that the estrogen antagonist ICI 182,780 abrogated these effects. These data suggest that is a potent estrogen agonist on human osteoblastic hOB/ER9 cells. In contrast, 2-OHE1 displayed no estrogenic or antiestrogenic activity in this human osteoblast cell model.

Practical low-cost visual communication using binary images for deaf sign language

Deaf sign language transmitted by video requires a temporal resolution of 8 to 10 frames/s for effective communication. Conventional videoconferencing applications, when operated over low bandwidth telephone lines, provide very low temporal resolution of pictures, of the order of less than a frame per second, resulting in jerky movement of objects. This paper presents a practical solution for sign language communication, offering adequate temporal resolution of images using moving binary sketches or cartoons, implemented on standard personal computer hardware with low-cost cameras and communicating over telephone lines. To extract cartoon points an efficient feature extraction algorithm adaptive to the global statistics of the image is proposed. To improve the subjective quality of the binary images, irreversible preprocessing techniques, such as isolated point removal and predictive filtering, are used. A simple, efficient and fast recursive temporal prefiltering scheme, using histograms of successive frames, reduces the additive and multiplicative noise from low-cost cameras. An efficient three-dimensional (3-D) compression scheme codes the binary sketches. Subjective tests performed on the system confirm that it can be used for sign language communication over telephone lines.

Non-extraction treatment of a thirteen-year-old boy with a Class III skeletal discrepancy and severe crowding in both the upper and lower dentitions

A thirteen-year-old boy presented with a Class III skeletal tendency in association with severe crowding in both the upper and lower arches. Whilst there was not a frank posterior crossbite, it was felt that the upper arch was narrow and that the lower arch was similarly constricted. Taking this into account along with the fact that his upper lip was flat and the nasolabial angle obtuse, it was decided to pursue a non-extraction treatment, with the aim of providing by expansion an extra 16 mm of space in the upper arch and 8 mm in the lower arch to accommodate the full dentition, and with a view to extracting third molar teeth later. This proved to be successful, albeit over an extended period of time, with active treatment taking nearly three and a half years. A realistic alternative would have been to remove four bicuspid teeth and pursue an orthodontic/surgical approach to treatment. In retrospect, and with the benefit of reviewing his records without surgical intervention, the treatment plan decided upon has been well justified.

Video compression with binary tree recursive motion estimation and binary tree residue coding

Binary tree predictive coding (BTPC) is an efficient general-purpose still-image compression scheme, competitive with JPEG for natural image coding and with GIF for graphics. We report the extension of BTPC to video compression using motion estimation and compensation techniques which are simple, efficient, nonlinear and predictive. The new methods, binary tree recursive motion estimation coding (BTRMEC), and binary tree residue coding (BTRC) exploit the hierarchical structure of BTPC, in the first case giving progressively refined motion estimates for increasing numbers of pels and in the second case providing efficient residue coding. Compression results for BTRMEC and BTBC are compared against conventional block-based motion compensated coding as provided by MPEG. They show that both BTRMEC and BTRC are efficient methods to code video sequences.

A(3) adenosine receptor activation attenuates neutrophil function and neutrophil-mediated reperfusion injury

This study tested the hypothesis that A(3) adenosine receptors inhibit neutrophil (PMN) function and PMN-mediated reperfusion injury. 2-Chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide (Cl-IB-MECA), an A(3) agonist, did not attenuate superoxide production or myeloperoxidase release from stimulated PMNs. However, Cl-IB-MECA reduced platelet-activating factor-stimulated PMN adherence to coronary endothelium at low concentrations: 52 +/- 27, 45 +/- 10, and 87 +/- 23 PMNs/mm(2) at 0.1, 1.0, and 10 nM vs. 422 +/- 64 PMNs/mm(2) with platelet-activating factor alone. This inhibition was not blocked by A(1) (5 microM KW-3902) or A(2a) (5 microM KF-21326) antagonists: 44 +/- 3 and 43 +/- 2 PMNs/mm(2), respectively. Endothelial pretreatment with 1 nM Cl-IB-MECA reduced PMN adherence, which was reversed by the A(3) antagonist MRS-1220 (100 nM). PMN-mediated reperfusion injury was initiated in isolated rabbit hearts by infusion of 28 x 10(6) PMNs/min for 10 min early in reperfusion. PMNs caused a significant decrease in recovery of left ventricular developed pressure and positive and negative time derivatives of pressure (23 +/- 3, 25 +/- 3, and 23 +/- 3% of baseline, respectively) vs. buffer-perfused hearts (43 +/- 7, 44 +/- 7, and 45 +/- 6%, respectively). Cl-IB-MECA (10 nM) given at reperfusion attenuated the PMN-mediated loss of contractile recovery (40 +/- 3, 46 +/- 5, and 42 +/- 4% of baseline). Cl-IB-MECA reduced myeloperoxidase release activity (5.3 +/- 0.6 absorbance units/min) and CD18-positive cells (54 +/- 9 cells/slide) compared with the untreated PMN group (17.9 +/- 1.7 absorbance units/min and 183 +/- 68 cells/slide). We conclude that Cl-IB-MECA attenuates reperfusion injury by decreasing PMN-endothelial cell interactions. These results suggest that the A(3) adenosine receptor may be a novel therapeutic target for treatment of myocardial ischemia and reperfusion.

Cloning and sequencing of the coenzyme B(12)-binding domain of isobutyryl-CoA mutase from Streptomyces cinnamonensis, reconstitution of mutase activity, and characterization of the recombinant enzyme produced in Escherichia coli

Isobutyryl-CoA mutase (ICM) catalyzes the reversible, coenzyme B(12)-dependent rearrangement of isobutyryl-CoA to n-butyryl-CoA, which is similar to, but distinct from, that catalyzed by methylmalonyl-CoA mutase. ICM has been detected so far in a variety of aerobic and anaerobic bacteria, where it appears to play a key role in valine and fatty acid catabolism. ICM from Streptomyces cinnamonensis is composed of a large subunit (IcmA) of 62.5 kDa and a small subunit (IcmB) of 14.3 kDa. icmB encodes a protein of 136 residues with high sequence similarity to the cobalamin-binding domains of methylmalonyl-CoA mutase, glutamate mutase, methyleneglutarate mutase, and cobalamin-dependent methionine synthase, including a conserved DXHXXG cobalamin-binding motif. Using IcmA and IcmB produced separately in Escherichia coli, we show that IcmB is necessary and sufficient with IcmA and coenzyme B(12) to afford the active ICM holoenzyme. The large subunit (IcmA) forms a tightly associated homodimer, whereas IcmB alone exists as a monomer. In the absence of coenzyme B(12), the association between IcmA and IcmB is weak. The ICM holoenzyme appears to comprise an alpha(2)beta(2)-heterotetramer with up to two molecules of bound coenzyme B(12). The equilibrium constant for the ICM reaction at 30 degrees C is 1.7 in favor of isobutyryl-CoA, and the pH optimum is near 7.4. The K(m) values for isobutyryl-CoA, n-butyryl-CoA, and coenzyme B(12) determined with an equimolar ratio of IcmA and IcmB are 57 +/- 13, 54 +/- 12, and 12 +/- 2 microM, respectively. A V(max) of 38 +/- 3 units/mg IcmA and a k(cat) of 39 +/- 3 s(-1) were determined under saturating molar ratios of IcmB to IcmA.

Vascular damage correlates between heparin-induced thrombocytopenia and the antiphospholipid syndrome

Antibody-mediated disorders of heparin-induced thrombocytopenia and antiphospholipid antibody syndrome have remarkably similar clinical presentations, both of which can progressively result in severe vascular and thrombotic disorders. We hypothesized that the mechanism of platelet activation as occurs in heparin-induced thrombocytopenia may also occur in antiphospholipid antibody syndrome particularly at the vascular wall, that endothelial injury may be similar in heparin-induced thrombocytopenia and antiphospholipid antibody syndrome, and that these alterations may be caused by related antibodies. Antibody titers and vascular endothelial damage in patients with heparin-induced thrombocytopenia and antiphospholipid antibody syndrome were studied in plasma samples collected from normals (n = 17), heparin-induced thrombocytopenia patients (n = 15), antiphospholipid antibody syndrome patients (n = 30), and patients clinically diagnosed with antiphospholipid antibody syndrome and heparin-induced thrombocytopenia (n = 8). Diagnosis of heparin-induced thrombocytopenia was confirmed by 14C-serotonin release assay or positive antiheparin-platelet factor 4 antibody titer, and antiphospholipid antibody syndrome was confirmed by positive anti-beta 2-glycoprotein (GP) 1/cardiolipin (IgG or IgM) antibody titer. The antiheparin-platelet factor 4 antibody was not detected in any patient with antiphospholipid antibody syndrome. Patients with heparin-induced thrombocytopenia did not have elevated IgG anti-beta 2-GP1 titers, but three (20%) patients had low-positive IgM anti-beta 2-GP1 titers. The endothelial damage markers of soluble thrombomodulin, soluble P-selectin (p < 0.05 vs. normal), plasminogen activator inhibitor-1 and tissue factor were elevated in heparin-induced thrombocytopenia and antiphospholipid antibody syndrome patients. The soluble E-selectin was elevated only in the patients with both heparin-induced thrombocytopenia and antiphospholipid antibody syndrome (p < 0.05 vs. normal). Levels of soluble L-selectin and von Willebrand factor were not different from normals. The pathogenesis of heparin-induced thrombocytopenia and antiphospholipid antibody syndrome appears to be due to two distinct antibodies but associated with similar damage to the vascular endothelium in both diseases.

Insertional inactivation of methylmalonyl coenzyme A (CoA) mutase and isobutyryl-CoA mutase genes in Streptomyces cinnamonensis: influence on polyketide antibiotic biosynthesis

The coenzyme B(12)-dependent isobutyryl coenzyme A (CoA) mutase (ICM) and methylmalonyl-CoA mutase (MCM) catalyze the isomerization of n-butyryl-CoA to isobutyryl-CoA and of methylmalonyl-CoA to succinyl-CoA, respectively. The influence that both mutases have on the conversion of n- and isobutyryl-CoA to methylmalonyl-CoA and the use of the latter in polyketide biosynthesis have been investigated with the polyether antibiotic (monensin) producer Streptomyces cinnamonensis. Mutants prepared by inserting a hygromycin resistance gene (hygB) into either icmA or mutB, encoding the large subunits of ICM and MCM, respectively, have been characterized. The icmA::hygB mutant was unable to grow on valine or isobutyrate as the sole carbon source but grew normally on butyrate, indicating a key role for ICM in valine and isobutyrate metabolism in minimal medium. The mutB::hygB mutant was unable to grow on propionate and grew only weakly on butyrate and isobutyrate as sole carbon sources. (13)C-labeling experiments show that in both mutants butyrate and acetoacetate may be incorporated into the propionate units in monensin A without cleavage to acetate units. Hence, n-butyryl-CoA may be converted into methylmalonyl-CoA through a carbon skeleton rearrangement for which neither ICM nor MCM alone is essential.

Plasmapheresis with intravenous immunoglobulin G is effective in patients with elevated panel reactive antibody prior to cardiac transplantation

BACKGROUND

Patients with a PRA >10% are considered to be at greater risk for the development of not only acute cellular and humoral rejection but also increased mortality when compared to nonsensitized patients following transplantation. All patients with a PRA >10% at our institution are treated with plasmapheresis and intravenous immunoglobulin G immediately prior to cardiac transplantation.

METHODS

Sixteen (Group 1) of 118 patients awaiting cardiac transplantation were found to be sensitized. These patients underwent plasmapheresis followed by 20 gm of intravenous immunoglobulin G (IVIG) immediately prior to cardiac transplantation. Group 1 was compared to the remaining 102 patients with a PRA <10% (Group 2).

RESULTS

Despite more patients in Group 1 having a positive crossmatch, pulmonary hypertension, and requiring mechanical circulatory support, there was no statistically significant difference in length of stay or mortality at a mean follow-up of 21.6+/-15.0 months. There was no difference in the occurrence of mild, moderate or severe cellular rejection or humoral rejection in these sensitized patients when compared to Group 2.

CONCLUSIONS

Pretransplant plasmapheresis followed by intravenous immunoglobulin G may be an effective therapy that obviates the need for a prospective crossmatch and allows sensitized patients to undergo cardiac transplantation. There is no increase in the post transplant length of stay, occurrence of rejection or short term mortality. Long term follow up is necessary to evaluate whether there is a difference in the development of late rejection, transplant vasculopathy and survival.

Apheresis in thoracic organ transplantation

The beneficial addition of cyclosporine and tacrolimus to the immunosuppressive armamentarium have unfortunately only partially solved the problems of acute and chronic rejection in thoracic organ transplantation. Apheresis techniques offer creative avenues for modifications of allograft rejection. Plasmapheresis can be used for mechanical reduction of alloantibody burdens in highly sensitized patients and permit transplantation in an otherwise almost hopeless situation and can also be used on a short-term basis for the treatment of acute humoral rejection. Extracorporeal photochemotherapy holds promise as a possibly synergistic adjunct to conventional therapy and may even reduce the severity of graft vasculopathy. The increasing availability of highly specific column immunoadsorption techniques may further increase the applicability of apheresis in transplantation.