Biochemical and Structural Characterization of Selective Allosteric Inhibitors of the Plasmodium falciparum Drug Target, Prolyl-tRNA-synthetase

Plasmodium falciparum (Pf) prolyl-tRNA synthetase (ProRS) is one of the few chemical-genetically validated drug targets for malaria, yet highly selective inhibitors have not been described. In this paper, approximately 40,000 compounds were screened to identify compounds that selectively inhibit PfProRS enzyme activity versus Homo sapiens (Hs) ProRS. X-ray crystallography structures were solved for apo, as well as substrate- and inhibitor-bound forms of PfProRS. We identified two new inhibitors of PfProRS that bind outside the active site. These two allosteric inhibitors showed >100 times specificity for PfProRS compared to HsProRS, demonstrating this class of compounds could overcome the toxicity related to HsProRS inhibition by halofuginone and its analogues. Initial medicinal chemistry was performed on one of the two compounds, guided by the cocrystallography of the compound with PfProRS, and the results can instruct future medicinal chemistry work to optimize these promising new leads for drug development against malaria.

Increasing the structural coverage of tuberculosis drug targets

High-resolution three-dimensional structures of essential Mycobacterium tuberculosis (Mtb) proteins provide templates for TB drug design, but are available for only a small fraction of the Mtb proteome. Here we evaluate an intra-genus "homolog-rescue" strategy to increase the structural information available for TB drug discovery by using mycobacterial homologs with conserved active sites. Of 179 potential TB drug targets selected for x-ray structure determination, only 16 yielded a crystal structure. By adding 1675 homologs from nine other mycobacterial species to the pipeline, structures representing an additional 52 otherwise intractable targets were solved. To determine whether these homolog structures would be useful surrogates in TB drug design, we compared the active sites of 106 pairs of Mtb and non-TB mycobacterial (NTM) enzyme homologs with experimentally determined structures, using three metrics of active site similarity, including superposition of continuous pharmacophoric property distributions. Pair-wise structural comparisons revealed that 19/22 pairs with >55% overall sequence identity had active site Cα RMSD <1 Å, >85% side chain identity, and ≥80% PSAPF (similarity based on pharmacophoric properties) indicating highly conserved active site shape and chemistry. Applying these results to the 52 NTM structures described above, 41 shared >55% sequence identity with the Mtb target, thus increasing the effective structural coverage of the 179 Mtb targets over three-fold (from 9% to 32%). The utility of these structures in TB drug design can be tested by designing inhibitors using the homolog structure and assaying the cognate Mtb enzyme; a promising test case, Mtb cytidylate kinase, is described. The homolog-rescue strategy evaluated here for TB is also generalizable to drug targets for other diseases.

Selecting targets from eukaryotic parasites for structural genomics and drug discovery

The selection of targets is the first step for any structural genomics project. The application of structural genomics approaches to drug discovery also starts with the selection of targets. Here, three protocols are described that were developed to select targets from eukaryotic pathogens. These protocols could also be applied to other drug discovery projects.

A new drug for an old bug

There is an urgent need to develop new drugs for the treatment of tuberculosis, particularly against latent/persistent forms of the causative agent, Mycobacterium tuberculosis. In this issue of Chemistry & Biology, Krieger and colleagues use a structure-guided approach to develop novel inhibitors of malate synthase, a target in the glyoxylate shunt that is critical for pathogen survival in chronic infection.

Combining functional and structural genomics to sample the essential Burkholderia structome

Background

The genus Burkholderia includes pathogenic gram-negative bacteria that cause melioidosis, glanders, and pulmonary infections of patients with cancer and cystic fibrosis. Drug resistance has made development of new antimicrobials critical. Many approaches to discovering new antimicrobials, such as structure-based drug design and whole cell phenotypic screens followed by lead refinement, require high-resolution structures of proteins essential to the parasite.

Methodology/Principal Findings

We experimentally identified 406 putative essential genes in B. thailandensis, a low-virulence species phylogenetically similar to B. pseudomallei, the causative agent of melioidosis, using saturation-level transposon mutagenesis and next-generation sequencing (Tn-seq). We selected 315 protein products of these genes based on structure-determination criteria, such as excluding very large and/or integral membrane proteins, and entered them into the Seattle Structural Genomics Center for Infection Disease (SSGCID) structure determination pipeline. To maximize structural coverage of these targets, we applied an “ortholog rescue” strategy for those producing insoluble or difficult to crystallize proteins, resulting in the addition of 387 orthologs (or paralogs) from seven other Burkholderia species into the SSGCID pipeline. This structural genomics approach yielded structures from 31 putative essential targets from B. thailandensis, and 25 orthologs from other Burkholderia species, yielding an overall structural coverage for 49 of the 406 essential gene families, with a total of 88 depositions into the Protein Data Bank. Of these, 25 proteins have properties of a potential antimicrobial drug target i.e., no close human homolog, part of an essential metabolic pathway, and a deep binding pocket. We describe the structures of several potential drug targets in detail.

Conclusions/Significance

This collection of structures, solubility and experimental essentiality data provides a resource for development of drugs against infections and diseases caused by Burkholderia. All expression clones and proteins created in this study are freely available by request.

Structure of nitrilotriacetate monooxygenase component B from Mycobacterium thermoresistibile

Mycobacterium tuberculosis belongs to a large family of soil bacteria which can degrade a remarkably broad range of organic compounds and utilize them as carbon, nitrogen and energy sources. It has been proposed that a variety of mycobacteria can subsist on alternative carbon sources during latency within an infected human host, with the help of enzymes such as nitrilotriacetate monooxygenase (NTA-Mo). NTA-Mo is a member of a class of enzymes which consist of two components: A and B. While component A has monooxygenase activity and is responsible for the oxidation of the substrate, component B consumes cofactor to generate reduced flavin mononucleotide, which is required for component A activity. NTA-MoB from M. thermoresistibile, a rare but infectious close relative of M. tuberculosis which can thrive at elevated temperatures, has been expressed, purified and crystallized. The 1.6 Å resolution crystal structure of component B of NTA-Mo presented here is one of the first crystal structures determined from the organism M. thermoresistibile. The NTA-MoB crystal structure reveals a homodimer with the characteristic split-barrel motif typical of flavin reductases. Surprisingly, NTA-MoB from M. thermoresistibile contains a C-terminal tail that is highly conserved among mycobacterial orthologs and resides in the active site of the other protomer. Based on the structure, the C-terminal tail may modulate NTA-MoB activity in mycobacteria by blocking the binding of flavins and NADH.

Structure of 3-ketoacyl-(acyl-carrier-protein) reductase from Rickettsia prowazekii at 2.25 Å resolution

Rickettsia prowazekii, a parasitic Gram-negative bacterium, is in the second-highest biodefense category of pathogens of the National Institute of Allergy and Infectious Diseases, but only a handful of structures have been deposited in the PDB for this bacterium; to date, all of these have been solved by the SSGCID. Owing to its small genome (about 800 protein-coding genes), it relies on the host for many basic biosynthetic processes, hindering the identification of potential antipathogenic drug targets. However, like many bacteria and plants, its metabolism does depend upon the type II fatty-acid synthesis (FAS) pathway for lipogenesis, whereas the predominant form of fatty-acid biosynthesis in humans is via the type I pathway. Here, the structure of the third enzyme in the FAS pathway, 3-ketoacyl-(acyl-carrier-protein) reductase, is reported at a resolution of 2.25 Å. Its fold is highly similar to those of the existing structures from some well characterized pathogens, such as Mycobacterium tuberculosis and Burkholderia pseudomallei, but differs significantly from the analogous mammalian structure. Hence, drugs known to target the enzymes of pathogenic bacteria may serve as potential leads against Rickettsia, which is responsible for spotted fever and typhus and is found throughout the world.

Structural genomics of infectious disease drug targets: the SSGCID

The Seattle Structural Genomics Center for Infectious Disease (SSGCID) is a consortium of researchers at Seattle BioMed, Emerald BioStructures, the University of Washington and Pacific Northwest National Laboratory that was established to apply structural genomics approaches to drug targets from infectious disease organisms. The SSGCID is currently funded over a five-year period by the National Institute of Allergy and Infectious Diseases (NIAID) to determine the three-dimensional structures of 400 proteins from a variety of Category A, B and C pathogens. Target selection engages the infectious disease research and drug-therapy communities to identify drug targets, essential enzymes, virulence factors and vaccine candidates of biomedical relevance to combat infectious diseases. The protein-expression systems, purified proteins, ligand screens and three-dimensional structures produced by SSGCID constitute a valuable resource for drug-discovery research, all of which is made freely available to the greater scientific community. This issue of Acta Crystallographica Section F, entirely devoted to the work of the SSGCID, covers the details of the high-throughput pipeline and presents a series of structures from a broad array of pathogenic organisms. Here, a background is provided on the structural genomics of infectious disease, the essential components of the SSGCID pipeline are discussed and a survey of progress to date is presented.

Wheat germ cell-free expression system as a pathway to improve protein yield and solubility for the SSGCID pipeline

Recombinant expression of proteins of interest in Escherichia coli is an important tool in the determination of protein structure. However, lack of expression and insolubility remain significant challenges to the expression and crystallization of these proteins. The SSGCID program uses a wheat germ cell-free expression system as a rescue pathway for proteins that are either not expressed or insoluble when produced in E. coli. Testing indicates that the system is a valuable tool for these protein targets. Further increases in solubility were obtained by the addition of the NVoy polymer reagent to the reaction mixture. These data indicate that this eukaryotic cell-free expression system has a high success rate and that the addition of specific reagents can increase the yield of soluble protein.

Design and initial characterization of the SC-200 proteomics standard mixture

High-throughput (HTP) proteomics studies generate large amounts of data. Interpretation of these data requires effective approaches to distinguish noise from biological signal, particularly as instrument and computational capacity increase and studies become more complex. Resolving this issue requires validated and reproducible methods and models, which in turn requires complex experimental and computational standards. The absence of appropriate standards and data sets for validating experimental and computational workflows hinders the development of HTP proteomics methods. Most protein standards are simple mixtures of proteins or peptides, or undercharacterized reference standards in which the identity and concentration of the constituent proteins is unknown. The Seattle Children's 200 (SC-200) proposed proteomics standard mixture is the next step toward developing realistic, fully characterized HTP proteomics standards. The SC-200 exhibits a unique modular design to extend its functionality, and consists of 200 proteins of known identities and molar concentrations from 6 microbial genomes, distributed into 10 molar concentration tiers spanning a 1,000-fold range. We describe the SC-200's design, potential uses, and initial characterization. We identified 84% of SC-200 proteins with an LTQ-Orbitrap and 65% with an LTQ-Velos (false discovery rate = 1% for both). There were obvious trends in success rate, sequence coverage, and spectral counts with protein concentration; however, protein identification, sequence coverage, and spectral counts vary greatly within concentration levels.

Biological and structural characterization of a host-adapting amino acid in influenza virus

Two amino acids (lysine at position 627 or asparagine at position 701) in the polymerase subunit PB2 protein are considered critical for the adaptation of avian influenza A viruses to mammals. However, the recently emerged pandemic H1N1 viruses lack these amino acids. Here, we report that a basic amino acid at position 591 of PB2 can compensate for the lack of lysine at position 627 and confers efficient viral replication to pandemic H1N1 viruses in mammals. Moreover, a basic amino acid at position 591 of PB2 substantially increased the lethality of an avian H5N1 virus in mice. We also present the X-ray crystallographic structure of the C-terminus of a pandemic H1N1 virus PB2 protein. Arginine at position 591 fills the cleft found in H5N1 PB2 proteins in this area, resulting in differences in surface shape and charge for H1N1 PB2 proteins. These differences may affect the protein's interaction with viral and/or cellular factors, and hence its ability to support virus replication in mammals.

Influenza viruses that originate from avian species likely have to acquire adapting amino acid changes to replicate efficiently in mammals. Two amino acid changes in the polymerase PB2 protein—a glutamic acid to lysine change at position 627 or an aspartic acid to asparagine change at position 701—are known to allow influenza viruses of avian origin to replicate efficiently in mammals. Interestingly, the pandemic H1N1 viruses (which possess an avian-like PB2 gene) do not encode the ‘human-type’ amino acids PB2-627K and PB2-701N. Here, we report that a basic amino acid at position 591 of PB2 can compensate for the lack of PB2-627K and allows efficient replication of highly pathogenic H5N1 and pandemic H1N1 viruses in mammalian species. We also present the X-ray crystal structure of the C-terminal portion of a pandemic H1N1 PB2 protein. The basic amino acid at position 591 fills a distinctive cleft found in the PB2 proteins of H5N1 viruses. We also speculate on the biological significance of the altered surface of the H1N1 PB2 protein.

The Seattle Structural Genomics Center for Infectious Disease (SSGCID)

The NIAID-funded Seattle Structural Genomics Center for Infectious Disease (SSGCID) is a consortium established to apply structural genomics approaches to potential drug targets from NIAID priority organisms for biodefense and emerging and re-emerging diseases. The mission of the SSGCID is to determine approximately 400 protein structures over the next five years. In order to maximize biomedical impact, ligand-based drug-lead discovery campaigns will be pursued for a small number of high-impact targets. Here we review the center's target selection processes, which include pro-active engagement of the infectious disease research and drug therapy communities to identify drug targets, essential enzymes, virulence factors and vaccine candidates of biomedical relevance to combat infectious diseases. This is followed by a brief overview of the SSGCID structure determination pipeline and ligand screening methodology. Finally, specifics of our resources available to the scientific community are presented. Physical materials and data produced by SSGCID will be made available to the scientific community, with the aim that they will provide essential groundwork benefiting future research and drug discovery.

Targeted, haplotype-resolved resequencing of long segments of the human genome

Currently, challenges exist to acquire long-range (hundreds of kilobase pairs) phase-discriminated sequence across substantial numbers of individuals. We have developed a straightforward method for isolating and characterizing specific genomic regions in a haplospecific manner. Real-time PCR is carried out to STS content map and genotype pools of fosmid clones arrayed in 384-well microtiter plates. Single-nucleotide polymorphisms, microsatellite markers, and insertion-deletion polymorphisms are used to differentiate the target region into haplotype-specific tiling paths. DNA of clones from these tiling paths is retrieved from the library and either sequenced by standard shotgun methods or amplified in vitro and sequenced by a primer-based, directed method. This approach provides convenient access to complete, haplotype-resolved resequencing data from multiple individuals across tens to hundreds of thousands of basepairs. We illustrate its implementation with a detailed example of more than 400 kbp from the human CFTR region, across 15 individuals, and summarize our experience applying it to many other human loci.

Implementation and evaluation of local-level priority setting for stroke

We aimed to develop and evaluate a prioritisation process to combine the evidence base with stakeholder involvement within a stroke programme for a Health Improvement Programme (HImP). Implementation involved: formation of a district stroke group (DSG); review of the evidence; survey of DSG members; survey of other key professionals; consensus within the DSG; consultation with local users of the service. Evaluation was through semi-structured interviews and documentary analysis. The process was accepted as appropriate and valuable by the majority of participants, and a district HImP implementation group allocated pound sterling 100 000 for stroke development as a result of this process. However, some felt that stroke itself had been an imposed, rather than an agreed, local priority. The priority setting process was not clear to all participants and change of personnel, particularly in the NHS trusts, led to some perceived lack of ownership. Professionals from secondary care participated, but later criticised the process when they felt that the priorities in the HImP could limit their ability to access money for other service developments. The user consultation days occurred too late to influence the 1999/2002 HImP. We have shown that it is possible to develop an approach that is broadly accepted by stakeholders and balance the evidence base with local ownership. The participation of stakeholders, clarity of procedures, local ownership and awareness of local politics are important in effective priority setting. The model developed will be of value in other settings.

The relationship between exercise work intervals and duration of exercise on lower extremity training induced by electrical stimulation in humans with spinal cord injuries

A group of 90 male paraplegics were studied to determine the optimal training protocol for isokinetic exercise induced by functional electrical stimulation of the quadriceps muscles. The parameters that were varied were the number of training sessions a week, the length of the training sessions each day, and the work-rest intervals in each training session. Training for 3 days a week for 30 min a day with 6 s of exercise and 6 s of rest proved the optimal protocol. Training for 5 days or for 1 day a week was not as effective in training strength or endurance. A combination of 50% work and 50% rest produced a much greater gain in strength and endurance than work:rest ratios of 66%:33% or 25%:75%. When training was conducted for 5 min, 15 min or 30 min each day, the greatest increase was found when the muscles were exercised for 30 min each day. While more variables need to be examined, this study has provided some initial guidelines for isokinetic training of humans using electrical stimulation.

Patients as teachers: a qualitative study of patients' views on their role in a community-based undergraduate project

OBJECTIVES

Patients have been used in clinical medical education for many years with, traditionally, a relatively passive role. Following the General Medical Council recommendations for curricular change and the development of more community-based teaching, 'ordinary patients' in the community are increasingly being partnered with undergraduate students for particular projects. Very little research has been undertaken on patients' perceptions of this role.

DESIGN

Semi-structured interviews were carried out with 20 people to explore the views of patients taking part in a community-based undergraduate medical student project (the 'patient study') at Newcastle Medical School about their role as teachers of medical students, what they felt they had gained from participating, any problems or concerns and suggestions for change or improvement.

SETTING

Newcastle Medical School, UK.

SUBJECTS

Second-year medical students.

RESULTS

Two major themes emerged. First, patients saw themselves in active roles as teachers: as experts in their medical condition; as exemplars of their condition; and as facilitators of the development of students' professional skills and attitudes. Secondly, patients felt they had benefited from participation, through talking about their problems; learning more about themselves; the satisfaction of helping; and from receiving gifts. In addition, a number of other issues were identified including interpersonal dynamics, gender and ethnic differences, inadequate briefing of participants and whether such community-based patient involvement might, in some situations, be felt to be exploitative.

CONCLUSIONS

The study has shown that patients see themselves clearly as having specific contributions to make to medical students' education and training. This has implications for the further development of community-based teaching.

Nurses in academic departments of general practice and primary care

In 1997, the authors conducted a survey of registered nurses working in the academic departments of general practice and primary care in UK and Irish medical schools. The survey aimed to determine the number, demographic and professional profile of nurses employed in these academic departments, including their employment status and their views on their clinical work and professional development. The majority of nurses were professionally experienced, had higher degrees, worked in a research capacity, and were likely to have short-term contracts. Contrary to professional perceptions, the majority of nurses stated that clinical work is important to their current job and expressed a need for research support and recognition of their autonomy as healthcare professionals.

Evaluation of death registers in general practice

BACKGROUND

General practitioners (GPs) do not routinely receive information about the deaths of those patients whose death certificates they have not completed. We developed and evaluated a system for producing death registers for GPs.

AIM

To evaluate GPs' and practice managers' views on, and uses of, the death register.

METHOD

General practitioners in Newcastle (n = 161) and Sunderland Family Health Service Authority (n = 144) areas were sent a questionnaire on their sources and use of information about patients' deaths. Death registers were sent to Newcastle practices; Sunderland practices were the control group. A follow-up questionnaire was sent to Newcastle (n = 173) and Sunderland (n = 140) GPs after two years. Newcastle practice managers (n = 45) were interviewed after their practice had received death registers for one year.

RESULTS

Ninety-two per cent of Newcastle responders had seen the death register. Seventy-three per cent saw it regularly. Of those who saw it, 92% found it useful for communication within the primary health care team, bereavement follow-up, and administration and medical audit. One fifth of GPs named the death register as their first source of information about their patients' deaths. Newcastle GPs reported greater levels of change in use of patient death information than the control group. Practice managers circulated, used, and recorded information from the death register.

CONCLUSION

Death registers are valued and have demonstrable benefits with regard to administration, bereavement care, and medical audit.

The vexed question of authorship: views of researchers in a British medical faculty

OBJECTIVE

To assess knowledge, views, and behaviour of researchers on criteria for authorship and causes and control of gift authorship.

DESIGN

Interview survey of stratified sample of researchers.

SETTING

University medical faculty.

SUBJECTS

66 staff (94% response rate) comprising several levels of university academic and research appointments.

MAIN OUTCOME MEASURES

Awareness and use of criteria for authorship, views on which contributions to research merit authorship, perceptions about gift authorship and strategies for reducing it, and experiences of authorship problems.

RESULTS

50 (76%) respondents supported criteria for authorship, but few knew about or used available criteria. Of the five people who could specify all three criteria of the International Committee of Medical Journal Editors, only one knew that all criteria had to be met. Forty one respondents (62%) disagreed with this stipulation. A range of practical and academic contributions were seen as sufficient for authorship. Gift authorship was perceived as common, promoted by pressure to publish, to motivate research teams, and to maintain working relationships. A signed statement justifying authorship and a published statement of the contribution of each author were perceived as practical ways of tackling gift authorship. Most researchers had experienced problems with authorship, most commonly the perception that authorship had been deserved but not awarded (49%).

CONCLUSION

There seems to be a gap between editors' criteria for authorship and researchers' practice. Lack of awareness of criteria is only a partial explanation. Researchers give more weight than editors to practical research contributions. Future criteria should be agreed by researchers and not be imposed by editors.

Use facilitated case discussions for significant event auditing

An important type of review undertaken routinely in health care teams is analysis of individual cases. This informal process can be turned into a structured and effective form of audit by using an adaptation of the "critical incident" technique in facilitated case discussions. Participants are asked to recall personal situations that they feel represent either effective or ineffective practice. From such review of individual cases arise general standards to improve the quality of care. On the basis of a study of audit of deaths in general practice, we describe how to implement such a system, including forming and maintaining the discussion group, methodology, and guidelines for facilitators. Problems that may arise during the case discussions are outlined and their management discussed, including problems within the team and with the process of the discussions.

Palliative care in the community: setting practice guidelines for primary care teams

BACKGROUND

Previous studies have demonstrated deficiencies in palliative care in the community. One method of translating the results of research into clinical practice, in order to produce more effective health care, is the development of clinical guidelines. Setting standards for such care has been performed by care teams in both hospital and hospice settings but not in primary care.

AIM

This study set out to develop guidelines for primary care teams to follow in the provision of palliative care in the community using facilitated case discussions with the members of such teams, as a form of internal audit.

METHOD

Five practices were randomly chosen from the family health services authority medical list. Meetings between the facilitators and primary care teams were held over a period of one year. The teams were asked to describe good aspects of care, areas of concern and suggestions to improve these, in recent cases of patient deaths.

RESULTS

In total 56 cases were discussed. All practices felt that cohesive teamwork, coordinated management, early involvement of nursing staff and the identification of a key worker were essential for good terminal care. Concerns arose in clinical and administrative areas but the majority were linked to poor communication, either between patient and professionals within the primary care team or between primary and secondary care. All the positive aspects of care, concerns and suggestions were collated by the facilitators into guidelines for teams to refer to from the initial diagnosis of a terminal illness through to the patient's death and care of the relatives afterwards.

CONCLUSION

Developing multidisciplinary as opposed to medical guidelines for palliative care allows primary health care teams to create standards that are acceptable to them and stimulates individuals within the teams to accept responsibility for initiating the change necessary for more effective care. The process of facilitating teams to discuss their work allows for recognition and respect of individuals' roles and more importantly provides shared ownership, an important contributory factor in the implementation of guidelines.

Information about patients' deaths: general practitioners' current practice and views on receiving a death register

BACKGROUND

Although general practitioners are involved in the care of most dying patients, they do not routinely receive information about their deceased patients for whom they did not complete the death certificate, and often they rely upon informal communication channels.

AIM

This study set out to assess how general practitioners obtained, recorded and used information about deceased patients and to determine their views on receiving a death register.

METHOD

A questionnaire was sent to all 305 general practitioners in the Newcastle upon Tyne and Sunderland Family Health Services Authority areas.

RESULTS

A total of 225 questionnaires were returned (response rate 74%). General practitioners usually first learnt about their patients' deaths from hospital discharge summaries (54%) and patients' relatives (46%) and less commonly from newspaper obituary columns (20%) and hospital telephone calls (9%). Two thirds of respondents recorded information about decreased patients, mainly listing personal details and the immediate cause of death. One third or fewer of those recording information listed contributory causes. The information was used mainly for following up bereaved relatives and notifying hospitals and other agencies.

CONCLUSION

Current informal systems for handling information about patients' deaths are inadequate. General practitioners need and would welcome prompt, accurate and comprehensive information about all their deceased patients.

The effect of training on endurance and the cardiovascular responses of individuals with paraplegia during dynamic exercise induced by functional electrical stimulation

Endurance for dynamic exercise, cardiac output, blood pressure, heart rate, ventilation, and oxygen consumption was measured in eight individuals with paraplegia at the end of 4-min bouts of exercise on a friction braked cycle ergometer. Movement of the subjects' legs was induced by electrically stimulating the quadriceps, gluteus maximus and hamstring muscles with a computer-controlled biphasic square--wave current at a frequency of 30 Hz. The friction braked cycle ergometer was pedalled at work rates which varied between 0 and 40 W. Measurements were repeated after 3 and 6 months to assess the affect of training. After 3 months of training it was found that endurance increased from 8 min at a work rate of 0 W to 30 min at a work rate of 40 W. Compared to the cardiovascular responses in non-paralyzed subjects, computerized cycle ergometry was found to be associated with higher relative stresses for a given level of absolute work. Mean blood pressure, for example, increased by over 30% during maximal work in individuals with paralysis compared to the typical response obtained for able-bodied subjects. Analysis of the data showed that instead of the 20-30% metabolic efficiency commonly reported for cycle ergometry, the calculated metabolic efficiency during computer-controlled cycle ergometry was only 3.6%.

Effects of submicronic sulfuric acid aerosol on human pulmonary function

The effects of a 4-hr exposure in an environmental chamber to an average 108 micrograms/m3 sulfuric acid (H2SO4 (MMAD, 0.5 micrograms)] on pulmonary function were examined in healthy young men. Subjects were randomly assigned to either experimental (N = 18) or control (N = 17) groups. All subjects were exposed to clean air on the first day. On the second day, experimental subjects were exposed to H2SO4 while control subjects were re-exposed to air. Subjects exercised for 15 min at 1.5 and 3.5 hr of exposure at an intensity equivalent to 75% of predicted maximal heart rate. Ventilation was monitored during the initial 14 min of each exposure. Pulmonary function was assessed prior to, and 2 hr and 4 hr of each exposure. Exposure to H2SO4 had no significant effect on minute ventilation, respiratory frequency, or tidal volume, nor did it affect pulmonary function as assessed by measures of airway resistance, specific airway conductance, forced vital capacity (FVC), forced expiratory flow in 1 sec (FEV 1.0), FEV 1.0/FVC, mean expiratory flow rate between 25% and 75% FVC, and expiratory flow rate at 50% and 25% FVC. It was concluded that no changes in pulmonary function resulted from exposure to H2SO4 under the above conditions.

Core cooling after hypoxia and ischaemia

Two patients sustained severe circulatory inadequacy before and during thoracotomy for coronary surgery. Both patients were promptly cote cooled to between 20 degrees and 25 degrees C. After coronary surgery, each patient was rewarmed and the operation was terminated uneventfully in each case, No important cerebral deficit was apparent despite periods of circulatory insufficiency and arrest which were well beyond the usually accepted limits. It is suggested that prompt core cooling may exert a protective effect in this context.