Antimicrobial peptide killing of African trypanosomes

The diseases caused by trypanosomes are medically and economically devastating to the population of Sub-Saharan Africa. Parasites of the genus Trypanosoma infect both humans, causing African sleeping sickness, and livestock, causing Nagana. The development of effective treatment strategies has suffered from severe side effects of approved drugs, resistance and major difficulties in delivering drugs. Antimicrobial peptides (AMPs) are ubiquitous components of immune defence and are being rigorously pursued as novel sources of new therapeutics for a variety of pathogens. Here, we review the role of AMPs in the innate immune response of the tsetse fly to African trypanosomes, catalogue trypanocidal AMPs from diverse organisms and highlight the susceptibility of bloodstream form African trypanosomes to killing by unconventional toxic peptides.

Synthesis and iron sequestration equilibria of novel exocyclic 3-hydroxy-2-pyridinone donor group siderophore mimics

The synthesis of a novel class of exocyclic bis- and tris-3,2-hydroxypyridinone (HOPO) chelators built on N(2) and N(3) aza-macrocyclic scaffolds and the thermodynamic solution characterization of their complexes with Fe(III) are described. The chelators for this study were prepared by reaction of either piperazine or N,N',N''-1,4,7-triazacyclononane with a novel electrophilic HOPO iminium salt in good yields. Subsequent removal of the benzyl protecting groups using HBr/acetic acid gave bis-HOPO chelators N(2)(etLH)(2) and N(2)(prLH)(2), and tris-HOPO chelator N(3)(etLH)(3) in excellent yields. Solution thermodynamic characterization of their complexes with Fe(III) was accomplished using spectrophotometric, potentiometric, and electrospray ionization-mass spectrometry (ESI-MS) methods. The pK(a)'s of N(2)(etLH)(2), N(2)(prLH)(2), and N(3)(etLH)(3), were determined spectrophotometrically and potentiometrically. The Fe(III) complex stability constants for the tetradentate N(2)(etLH)(2) and N(2)(prLH)(2), and hexadentate N(3)(etLH)(3), were measured by spectrophotometric and potentiometric titration, and by competition with ethylenediaminetetraacetic acid (EDTA). N(3)(etLH)(3) forms a 1:1 complex with Fe(III) with log β(110) = 27.34 ± 0.04. N(2)(prLH)(2) forms a 3:2 L:Fe complex with Fe(III) where log β(230) = 60.46 ± 0.04 and log β(110) = 20.39 ± 0.02. While N(2)(etLH)(2) also forms a 3:2 L:Fe complex with Fe(III), solubility problems precluded determining log β(230); log β(110) was found to be 20.45 ± 0.04. The pFe values of 26.5 for N(3)(etLH)(3) and 24.78 for N(2)(prLH)(2) are comparable to other siderophore molecules used in the treatment of iron overload, suggesting that these hydroxypyridinone ligands may be useful in the development of new chelation therapy agents.

Iron Chelation Equilibria, Redox, and Siderophore Activity of a Saccharide Platform Ferrichrome Analogue

A complete characterization of the aqueous solution Fe(III) and Fe(II) coordination chemistry of a saccharide-based ferrichrome analogue, 1-O-methyl-2,3,6-tris-O-[4-(N-hydroxy-N-ethylcarbamoyl)-n-butyryl]-alpha-D-glucopyranoside (H3LN236), is reported including relevant thermodynamic parameters and growth promotion activity with respect to both Gram-negative and Gram-positive bacterial strains. The saccharide platform is an attractive backbone for the design and synthesis of ferrichrome analogues because of its improved water solubility and hydrogen-bonding capabilities, which can potentially provide favorable receptor recognition and biological activity. The ligand deprotonation constants (pKa values), iron complex (FeIII(LN236) and FeII(LN236)1-) protonation constants (KFeHxL-236-N), overall Fe(III) and Fe(II) chelation constants (beta110), and aqueous solution speciation were determined by spectrophotometric and potentiometric titrations, EDTA competition equilibria, and cyclic voltammetry. Log betaIII110 = 31.16 and pFe = 26.1 for FeIII(LN236) suggests a high affinity for Fe(III), which is comparable to or greater than ferrichrome and other ferrichrome analogues. The E1/2 for the FeIII(LN236)/FeII(LN236)1- couple was determined to be -454 mV (vs NHE) from quasi-reversible cyclic voltammograms at pH 9. Below pH 6.5, the E1/2 shifts to more positive values and the pH-dependent E1/2 profile was used to determine the FeII(LN236)1- protonation constants and overall stability constant log betaII110 = 11.1. A comparative analysis of similar data for an Fe(III) complex of a structural isomer of this exocyclic saccharide chelator (H3LR234), including strain energy calculations, allows us to analyze the relative effects of the pendant arm position and hydroxamate moiety orientation (normal vs retro) on overall complex stability. A correlation between siderophore activity and iron coordination chemistry of these saccharide-hydroxamate chelators is made.

Required competencies of occupational physicians: a Delphi survey of UK customers

BACKGROUND

Occupational physicians can contribute to good management in healthy enterprises. The requirement to take into account the needs of the customers when planning occupational health services is well established.

AIMS

To establish the priorities of UK employers, employees, and their representatives regarding the competencies they require from occupational physicians; to explore the reasons for variations of the priorities in different groups; and to make recommendations for occupational medicine training curricula in consideration of these findings.

METHODS

This study involved a Delphi survey of employers and employees from public and private organisations of varying business sizes, and health and safety specialists as well as trade union representatives throughout the UK. It was conducted in two rounds by a combination of computer assisted telephone interview (CATI) and postal survey techniques, using a questionnaire based on the list of competencies described by UK and European medical training bodies.

RESULTS

There was broad consensus about the required competencies of occupational physicians among the respondent subgroups. All the competencies in which occupational physicians are trained were considered important by the customers. In the order of decreasing importance, the competencies were: Law and Ethics, Occupational Hazards, Disability and Fitness for Work, Communication, Environmental Exposures, Research Methods, Health Promotion, and Management.

CONCLUSION

The priorities of customers differed from previously published occupational physicians' priorities. Existing training programmes for occupational physicians should be regularly reviewed and where necessary, modified to ensure that the emphasis of training meets customer requirements.

Possible Role of Relativistic Effects in the Plasticity of the Coordination Geometry of Cadmium(II). A Voltammetric Study of the Stability of the Complexes of Cadmium(II) with 12-Crown-4,15-Crown-5 and 18-Crown-6 in Aqueous Solution and the Structures of [Cd(benzo-18-crown-6)(NCS)2] and [K(18-crown-6)][Cd(SCN)3]

A differential pulse voltammetric study of complexes of Cd(II) and Pb(II) with crown ethers is reported. Measured log K(1) values for Cd(II) with 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane), and 12-crown-4 (1,4,7,10-tetraoxacyclododecane) are respectively 2.53 (+/-0.06), 1.97 (+/-0.07), and 1.72 (+/-0.08) and for Pb(II) with 18-crown-6 is 4.17 (+/-0.03), all at 25 degrees C in 0.1 M LiNO(3). Cd(II) is smaller than is usually associated with strong bonding with crown ethers. The high log K(1) values for Cd(2+) with crown ethers found here are discussed in terms of distortion of Cd(II) by relativistic effects. The resulting plasticity of the coordination geometry of the Cd(II) ion allows it to meet the metal ion size requirements of all the crown ethers, allowing high log K(1) values to occur. Crystal structures for [Cd(bz-18-crown-6)(SCN)(2)] (1) (bz-18-crown-6 = benzo-1,4,7,10,13,16-hexaoxacyclooctadecane) and [K(18-crown-6)][Cd(SCN)(3)] (2) are reported. 1 was triclinic, space group P1, a = 8.5413(2), b = 10.0389(2), and c = 13.4644(2) A, alpha = 94.424(1), beta = 102.286(1), and gamma = 93.236(1) degrees, Z = 2, and final R = 0.023. 2 was orthorhombic, space group Cmc2(1), a = 14.7309(3), b = 15.1647(3), and c = 10.6154(2) A, Z = 4, and final R = 0.020. In 1, the Cd occupies the cavity of the bz-18-crown-6 with long average Cd-O bond lengths of 2.65 A and is N-bonded to the thiocyanates with short average Cd-N bonds of 2.12 A. In [Cd(bz-18-crown-6)(SCN)(2)], the linear coordination involving the Cd and the two N-bonded thiocyanate groups in 1 is discussed in terms of the role of relativistic effects in the tendency to linear coordination geometry in group 12 metal ions. In 2 Cd forms a polymeric structure involving thiocyanate bridges between Cd atoms and K(+) occupies the cavity of the crown ether. 2 highlights the fact that cadmium is almost never S-bonded to thiocyanate except in bridging thiocyanates.

Mortality of United Kingdom oil refinery and petroleum distribution workers, 1951-1998

The mortality experienced by cohorts of 28 630 oil refinery workers and 16 480 petroleum distribution workers has been investigated. Study subjects were all those male employees first employed in the period 1946-1974 at one of eight UK oil refineries or at one of 476 UK petroleum distribution centres; all subjects had a minimum of 12 months employment with some employment after 1 January 1951. The observed numbers of cause-specific deaths were compared with expectations based on national mortality rates. The resultant standardized mortality ratios (SMRs) were significantly below 100 for all causes, in both oil refinery workers (observed, 9341; expected, 10 649.7; SMR = 88) and petroleum distribution workers (observed, 6083; expected, 6460.3; SMR = 94). Significantly elevated SMRs were shown in oil refinery workers for cancer of the gall bladder (observed, 24; expected, 14.0; SMR = 172), cancer of the pleura (observed, 38; expected, 15.0; SMR = 254) and melanoma (observed, 36; expected, 22.2; SMR = 162). Significantly elevated SMRs were not found in petroleum distribution workers for any site of cancer. SMRs for selected causes of death were calculated by period from commencing employment, by year of hire and by job type. The only findings that suggested the presence of an occupational cancer hazard were an excess of mesothelioma in oil refinery workers and an excess of leukaemia in petroleum distribution workers, both excesses occurring in long-term follow-up for workers first employed >30 years ago.

Guidance on standards of health for clinical health care workers

Judgements about the health of clinical health care workers in relation to fitness to practice are made by a variety of doctors. These guidelines have been written to assist with such judgements and to facilitate equitable decision making in matters of employment.

Occupational exposure to magnetic fields relative to mortality from brain tumours: updated and revised findings from a study of United Kingdom electricity generation and transmission workers, 1973-97

OBJECTIVE

To investigate whether risk of brain tumour is related to occupational exposure to magnetic fields.

METHODS

The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All workers were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972).

RESULTS

Based on serial mortalities for England and Wales, deaths from brain cancer were close to expectation (observed 158, expected 146.4). No significant positive trends were shown for risks of brain tumours either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years.

CONCLUSIONS

There are no discernible excess risks of brain tumours as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.

Leukaemia mortality in relation to magnetic field exposure: findings from a study of United Kingdom electricity generation and transmission workers, 1973-97

OBJECTIVE

To investigate whether risks of leukaemia are related to occupational exposure to magnetic fields.

METHODS

The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All employees were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations were performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972).

RESULTS

Based on serial mortalities for England and Wales, the standardised mortality ratio of 84 for all leukaemias (observed 111, expected 132.3) was similar to that of 83 for all causes (observed 14 845, expected 17 918). No significant positive trends were found for the risks of various types of leukaemia (chronic lymphatic leukaemia, acute myeloid leukaemia, chronic myeloid leukaemia, all leukaemia) either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years.

CONCLUSIONS

There are no discernible excess risks of leukaemia as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.

A cohort mortality study of U.K. carbon black workers, 1951-1996

BACKGROUND

Carbon black, a powdered form of elemental carbon is used in the manufacture of rubber products, paints, plastics, and inks. In 1974, the Health and Safety Executive initiated a cohort mortality study on possible carcinogenic effects on carbon black workers.

METHODS

The mortality of a cohort of 1,147 male manual workers from five U.K. factories manufacturing carbon black was investigated for the period 1951-1996. All subjects were employed in the carbon black industry for 12 months or more, and all were first employed before 1975. Limited work histories were used to calculate estimates of individual cumulative exposure to carbon black, using a job-exposure matrix derived by the study team.

RESULTS

Based on serial rates for the general population of England and Wales, significantly elevated mortality was observed in the main study cohort for all causes (Obs 372, Exp 328.7, SMR 113, P < 0.05) and for lung cancer (Obs 61, Exp 35.3, SMR 173, P < 0.001). There were highly elevated lung cancer SMRs at two of the factories, and unexceptional SMRs at the remaining three factories. There was no indication of lung cancer SMRs increasing with period from first employment. Poisson regression analyses failed to find significant trends of lung cancer risks increasing either with cumulative exposure to carbon black (4 levels) or with duration of employment at the participating factories (4 levels).

CONCLUSIONS

Confident interpretation of the elevated SMRs found for lung cancer in two of the factory subcohorts is not possible but the study has been unable to link cumulative exposure to carbon black with elevated risks of lung cancer.

Lung cancer in Yorkshire chrome platers, 1972-97

OBJECTIVES

To investigate mortality from lung cancer in chrome platers, a group exposed to chromic acid.

METHODS

The mortality of a cohort of 1087 chrome platers (920 men, 167 women) from 54 plants situated in the West Riding of Yorkshire, United Kingdom, was investigated for the period 1972-97. All subjects were employed as chrome platers for >/=3 months and all were alive on 31 May 1972. Mortality data were also available for a cohort of 1163 comparison workers with no known occupational exposure to chrome compounds (989 men, 174 women). Information on duration of chrome work and smoking habits collected for a cross sectional survey carried out in 1969-72 were available for 916 (84.3%) of the chrome platers; smoking habits were available for 1004 (86.3%) comparison workers. Two analytical approaches were used, indirect standardisation and Poisson regression.

RESULTS

Based on serial mortality rates for the general population of England and Wales, significantly increased mortality from lung cancer was observed (obs) in male chrome platers (obs 60, expected (exp) 32.5, standardised mortality ratio (SMR) 185, p<0. 001) but not in male comparison workers (obs 47, exp 36.9, SMR 127). Positive trends were not shown for duration of employment exposed to chrome, although data on working after 1972 were not available.

CONCLUSIONS

Confident interpretation is not possible but occupational exposures to hexavalent chromium may well have been involved in the increased mortality from lung cancer found in this cohort of chrome platers.

Assessment of the sensitivity of the relation between current exposure to carbon black and lung function parameters when using different grouping schemes

BACKGROUND

Equations using variance components in exposure data to predict attenuation and standard error of exposure--response slopes have been published recently. However, to date, no comparisons have been made between results of applying these equations to a real data set with the exposure-response relations estimated directly.

METHODS

Data on lung function parameters and personal inhalable and respirable dust exposure levels from the European carbon black respiratory health study were used. The predicted attenuation and standard error of the relation between current inhalable and respirable dust levels and lung function parameters (FVC and FEV(1)) were calculated for various exposure grouping schemes. These results were compared with the observed exposure-response relations. Workers were grouped by Job Category, the combination of factory and Job Category and five a posteriori created Exposure Groups. In addition, the individual approach was also used, as exposure data were available for each worker.

RESULTS

The rank orders of the coefficients from the regression analyses using the different grouping schemes were similar to those predicted by the equations, although the differences were larger than predicted. When using inhalable dust exposure, the predicted standard errors of the exposure-response slopes were slightly lower than those estimated directly; for respirable dust the predicted standard errors were about a factor two to three smaller than those from the regression analyses. When considering FVC, the predicted exposure-response relations were all statistically significant, whilst the observed relation was only significant when using the five a posteriori Exposure Groups. When reviewing the relations between dust exposure and level of FEV(1), all relations were statistically significant, with the exception of the (observed) relation between respirable dust and FEV(1), when the individual approach was used.

CONCLUSIONS

Using different grouping schemes for estimating exposure can have large effects on the slope and standard error of the exposure-response relation. It is, therefore, important that the effect of the different grouping schemes on the level and precision of the exposure-response slope be estimated. Despite violation of most of the assumptions when applying the equations to predict attenuation and the standard error of the exposure-response slope, the similarities in predicted and observed exposure-response relations and standard errors are indicative of the robustness of these equations. Therefore, the equations appear to be a useful tool in establishing the most efficient way of utilizing exposure measurements.