Natural flouride levels in water sources in the English-speaking Caribbean: initial results from 11 countries [abstract]

Initial results from 11 of the 18 countries involved in an ongoing regional study are presented. The levels of flouride in various water sources in the Caribbean were hitherto unknown. This study provides the first comprehensive documentation of the regional distribution of natural flouride levels in water by spatial location, source and approximate population coverage. The aim is to discuss the public health implications as well as the significance in caries-prevention. A total of 594 water samples were collected from 9 different sources in 11 countries during the dry and wet seasons using a standard protocol. Flouride levels were determined using the ion-selective electrode. Duplicate analysis was conducted on 25 percent randomly selected samples in each batch. Detectable levels were classified in mg/ based on a five-point ordinal scale as flouride-free (< 0.1); low (>0.1-0.3); sub-optimal (0.3-0.6); optimal (> 0.6-0.7); and high (> 0.7), respectively. Flouride levels ranged from 0.01 to 2.9 mg/l. Most samples (61.3 percent) were flouride-free while 16.2 percent and 9.64 percent contained optimal and high levels, respectively. Areas with levels above 0.7 mg/l were recorded in 7 countries while trace amounts of flouride were recorded for all samples obtained from Cayman Islands, Monsterrat and St. Vincent. The significant variations in flouride levels recorded in samples obtained from the same location underscore the need for routine flouride analysis, especially in areas with high levels. Natural flouride levels in regional water sources are generally below the optimal required for maximum caries reduction with minimal prevalence of enamel flourosis in tropical environments. Localized deflouridation of water supplies should be considered in areas with flouride levels in excess of 2 mg/l if a high prevalence of moderate and severe enamel flourosis is detected among residents. Given the current water sources, supply and distribution systems and respective populations served, the findings of this study indicate that water flouridation is not a feasible or cost-effective option for caries prevention in the region. Further research on the availability of non-dairy flouride sources is required. (AU)

Investigating the enzyme-substrate interactions of cytochrome c oxidase: a computer-assisted approach [abstract]

Although the enzyme cytochrome c oxidase (COX) is critical to respiration and has been studied extensively, the interactions between this enzyme and its substrate cytochrome c are still not very well understood. We employed a computer assisted approach to study these interactions. We used the Swiss-pdb v 2.5 computer programme, which measures the percentage accessibility of residues and the online server ANOLEA, which calculates the non-local energy of residues in a polypeptide chain, to analyze the respective molecular structures of cytochrome c and COX. The accessibility studies showed that, compared to the oxidized, the reduced form of cytochrome c normally had the greater proportion of more highly accessible residues: for reduced cytochrome c, 7 of the 8 residues exhibiting 55 percent accessibility were lysines. Interestingly enough, lysine 13, shown by other studies to be important for substrate binding, was not significantly accessible. For COX, neither asparate 158 nor glutamate 198 residues, reported to be important for substrate binding and catalysis, were significantly accessible either. The energy studies showed that whereas oxidized cytochrome c was a stable structure of low energy, approximatley 81 percent of the protein was reduced. For COX, a few small regions, including 4 residues in the vicinity of CuA, which functions as the enzyme's electron entry port, were of high energy. Since lysine 13, aspartate 158 and glutamate 198 are known to play important roles in enzyme-substrate interactions, it must be that these residues become more accessible when the two proteins interact. The results of the accessibility studies therefore appear to suggest that COX employs a mix of induced-fit and strain mechanisms when it binds substrate. On the basis of the energy studies, we conclude that the structure of reduced cytochrome c (the substrate) resembles a high energy transition-state intermediate and that when this protein binds and reduces oxidized COX, the structures of both proteins are stabilized. (AU)

Cytochrome c oxidase: structural evidence for conformational switching between two substrate binding sites [abstract]

Cytochrome c oxidase, the final member of the electron transport chain is critical to aerobic respiration and the absence, deficiency or malnutrition of this enzyme causes a number of myopathies and other diseases, some of which are fatal. In spite of its importance, the enzyme is still not well understood and whether one or two binding sites for its substrate cytochrome c remains unresolved. In an attempt to answer this question, we prepared 1:1 covalent enzyme-substrate complexes under conditions of low ionic strength. In addition to the `traditional' complex formed between oxidized cytochrome c and the oxidized enzyme, we prepared a new complex under `steady-state' reducing conditions. For both complexes, we investigated the ability of the covalently bound enzyme to catalyze the oxidation of unbound (exogenous) ferrocytochrome c. Whereas for the `traditional' oxidized complex, cytochrome c became bound exclusively to subunit II of the enzyme, for the `steady-state'complex, cytochrome c became bound to subunits II, VIa and VIb. Steady-state spectral analysis (400-630nm), combined with Stopped-Flow studies, confirmed that the bound cytochrome c mediated the efficient transfer of electrons from the reducing agent ascorbate to the enzyme. Additionally, pre-steady state analysis at 550nm showed haem a within both covalent complexes catalyzed the oxidation of exogenous ferrocytochroms c. The second order rate constant for these reactions was approximately 25-50 percent of those observed for controls. Our results suggests (i) that electrons are able to enter cytochrome c oxidase via two independent pathways and (ii) that during enzyme turnover the enzyme cycles between two conformers, one of with a substrate binding site at subunit II and the other wth a site at subunits VIa and VIb. Structural analysis suggests that Glu 43, Asp 64 and Glu 83 of subunit VIa and Asp 73, Asp 74 and Glu 78 of subunit VIb are residues that might possibly be involved at the latter site. (AU)

Increased BAEP latency and reduced brain cytochrome c oxidase activity observed in the Suzuki model of Alzheimer's disease [abstract]

Cytochrome c oxidase (COX), the terminal respiratory enzyme, is reported to be deficient and to exhibit reduced activity in a number of neurodegenerative disorders. The Alzheimer's rabbit model is based on the intracerebral injection of Holt's adjuvant, an aluminum salt solution. This model was used to compare the brain activity and the activity of brain COX in treated and controlled rabbits. Of a total of 26 New Zealand white rabbits, thirteen were injected intracerebrally with Holt's adjuvant solution, five with physiologically saline solution and the remainder were kept as controls. The auditory responses (BAEP) of the rabbits were monitored for 14 days before injections and 14 days thereafter. The animals were then sacrificed and brain mitochondrial extracts were used for SDS-PAGE analysis, difference spectra spectrophotometry and polarographic assays. The results of SDS-PAGE showed that there were no differences in the protein composition of the brain mitochondria of the three groups. Similarly, difference spectra (reduced minus oxidized, 400-630 nm) from both treated groups were identical to that of the control with characteristic maxima centered around 434, 550 and 604 nm. Polarographic assays, however, showed that while the enzyme from both treated groups displayed the characteristic biphasic kinetics, there was reduced activity in the enzymes from the brain of rabbits receiving the adjuvant but not the saline solution. This result is significant in light of the fact that several researchers have reported reduced activity of COX from Alzheimer's disease (AD) patients. Of particular significance, BAEP results reveal an increase in the interpeak latency between peaks III and V of the Holt's injected but not the saline injected or control rabbits. This latter result suggests that monitoring the BAEP might provide a simple non-invasive method for confirming AD. (AU)

Understanding the mechanism of action of Cytochrome c Oxidase in normal and disease states: shark heart enzyme, a potential model

Cytochrome c oxidase, the final member of the electron transport chain, is crucial to respiration and also contributes to the synthesis of cellular ATP. The total absence of this enzyme is incompatible with life and its deficiency or malfunction leads to a number of serious disease states. Understanding the mechanism of action of this enzyme, which is an important prerequisite to unravelling its role in the pathogenesis of disease states, is hampered by the lack of suitable enzyme models. The bovine enzyme, which are structually simple, appear to follow a different mechanism of action. The hammer head shark is a seasonal resident of the warm waters of the Caribbean Sea. The work presented here indicates that, like the bovine enzyme, the enzyme of the heart of this shark (i) possesses thirteen subunits and two substrate binding sites and (ii) exhibits biphasic kinetics. The work also confirms that, unlike the bovine enzyme which is dimeric, the shark enzyme functions as a monomer. Given this latter simplifying feature, in conjunction with its kinetic and structural similarities to the more complex mammalian varieties, we propose that shark heart cytochrome c oxidase replace the bovine and bacterial forms as the enzyme of choice for model studies.(Au)

Entrance qualifications and student performance in a hybrid problem bases and traditional medical programme

A hybrid problem based learning (PBL) and traditional programme was started at the Trinidad campus of the University of the West Indies in 1989. Analyses were carried out to determine the extent to which the entrance qualifications of the students were related to their performances at the examinations in the Phase I (preclinical and paraclinical) and Phase II (clinical) programmes. Students who were admitted on the basis of their results in the secondary school General Certificate of Examination (GCE), "A" level scored higher at the Phase I, but not at the Phase II, level than those who already had university education. Among the "A" level students, there was positive correlation between the total "A" level scores and the examination marks in the medical programme, particularly at the Phase I level. Futhermore, multiple regression analyses indicated that the grades in "A" level chemistry and, to a lesser extent in biology, had the most influence on performance at the Phase I examinations, with much less influence on performances at the Phase II examinations. These results suggest that good grades at "A" level examination are significant factors, but not the only important ones, that favour high achievement in the initial stages of this type of PBL/traditional medical programme.(AU)

Cytochrome c oxidase: a new conformational model

Cytochrome c oxidase and zinc cytochrome c were cross-linked to form a 1:1 enzyme-substrate convalent complex. The reaction was catalyzed by 1-ethyl-3-[3-(dimethylamino) propyl] carbodiimide (EDC) and cytochrome c, the substrate, became attached to the binding site located at submit II of the enzyme. This covalent complex could still be reduced by unbound ferrocytochrome c, suggesting the existence of more than one substrate binding site [1]. Previously [2] we reported that the reduction of heme a triggered a major conformational change within cytochrome c oxidase. Here we propose a model which incorporates these two findings with other established features of cytochrome c oxidase. The most prominent features of this model are (i) Electrons may enter the enzyme via both heme and CUa. Thus cytochrome oxidas may be regarded as having two substrate binding sites, one near heme a and the other near CUa. (ii) At any instant however, only one site is normally available for the binding of substrate. (iii) Subsequent to binding, a substrate molecule transfers an electron to the redox center at the site; reduction of the redox centre triggers a conformational transition which abolishes that binding site and simultaneously leads to the formation of an adjacent substrate binding site near the other redox centre. (iv) The two sites possess approximately equivalent affinity for substrate(AU)

Cardiovascular abnormalities in the acquired immune deficiency syndrome - abstract

Serious organ system failure has been documented in the pulmonary, gastrointestinal, renal and central nervous systems in patients with cquired immune deficiency syndrome (AIDS). Clinical cardiac involvement has received little attention world-wide until the last few years, and in particular there has been no documentation or assessment of the cardiac involvement in patients with AIDS either in Barbados or the Caribbean. This study aims to assess the clinical cardiovascular findings in AIDS patients. A retrospective review and analysis of the case notes of AIDS patients who had died at the Queen Elizabeth Hospital, Barbados, in 1990 was undertaken. Prospective clinical assessment, including electrocardiography and echocardiography, was performed on a further set of patients admitted to hospital with HIV-related illness. The case notes of 31 (91 per cent) of the 34 patients with AIDS who died durng 1990 were reviewed. These patients were admitted to hospital on 77 occasions for AIDS-related illness. All patients were stage 3 or 4 according to the revised CDC/WHO classification. A clinical suspicion of cardiac involvement was entertained in 7 patients, 4 of whom were subsequently diagnosed as having a pericardial effusion - 2 of which were determined to be related to the presence of severe renal failure. Electrocardiography was performed on 7 patients; S-T segment elevation was noted in 2 of these patients. T-wave inversion in 1 patient and the effects of hyperkalaemia in 1 patient. Cardiac manifestations demonstrated in the AIDS patients studied prospectively will be presented. Cardiac involvement among AIDS patients admitted to hospital in Barbados is not clinically overt. A truer and higher incidence of cardiac manifestations in these patients will become evident by more detailed and systematic assessment (AU)

Gender-related renal damage in severe essential hypertension in black patients - abstract

Malignant nephrosclerosis occurs twice as often in black Barbadian males as in their female counterparts. We therefore examined the possibility that renal impairment might occur more commonly in black males than in black females with severe hypertension. Between January 1982 and May 1987, 106 patients (67 females and 39 males) were referred to the Renal/Hypertension Clinic of the Queen Elizabeth Hospital for management of "intractable" hypertension. Patients whose diastolic blood pressures fell below 90 mm Hg on two-drug therapy were dropped from the study as were patients with secondary hypertension. Of the 46 patients requiring 3 drugs for blood pressure control, 28 were female and 18 were male. Assessment of renal function was made in these patients, using the formula of Cockcroft and Gault for estimation of creatinine clearance. Renal impairment was diagnosed when estimated creatinine clearance was more than 20 percent below the mean value given by Kampmann et al for adults at different ages. Left ventricular mass index was determined by echocardiography in 27 females and all males, and left ventricular hypertrophy was diagnosed when LVMI was greater than 132 g/m2 in males and greater than 109 g/m2 in females. Echocardiographic diagnosis of left ventricular hypertrophy was made in 22 females (85 percent) and in 13 males (73 percent); there was no difference with respect to the prevalence of left ventricular hypertrophy (chi-square test). In contrast, when age, gender, weight and body surface area were allowed for in the estimation of creatinine clearance, there was a gender-related difference in the prevalence of renal insufficiency. Seventeen females and all 18 males had renal insufficiency (p<0.002; Fisher's exact probability test). In this series of patients with severe essential hypertension, males appear more susceptible than females to the development of renal impairment (AU)

Hypertrophic cardiomyopathy experience in Barbados - abstract

Hypertrophic cardiomyopathy is defined as ventricular hypertrophy without identifiable cause, and althought it usually involves only the ventricular septum, it may involve the left and right ventricular free walls as well. A retrospective study was made of patients with this diagnosis seen in a cardiolgy practice and at the QEH during the period February, 1982 to November, 1985. Echocardiography (M-Mode and Real Time) was used to make the diagnosis in all patients, using standard echcardiographic guidelines. Eithteen patients, 15 men and 3 women ranging in age from 31 to 73 years, were diagnosed as having hypertrophic cardiomyopathy. Exertional dyspnoea, palpitations and chest pain or tightness were the main presenting symptoms. Most patients had mid-systolic murmurs in the aortic areas and at the apex. ECGs were abnormal in 12 patients, with LVH and ST, T-wave changes being the most common abnormalities found. M-Mode echocardiography revealed asymmetric septal hypertrophy (ASH) in 14 patients and systolic anterior motion (SAM) of the mitral valve in 13. At real time echocardiography, ASH was seen in all patients, with involvement of the entire septum in 12 and with hypertrophy involving the sub-aortic area in 3, and the mid-septal area in 3. Eleven patients required treatment with drugs, 9 with áblockers, and 2 with calcium antagonist drugs, mainly with good results. Hypertrophic cardiomyopathy, although uncommon, does occur in Barbados, and often presents with symptoms similar to ischaemic heart disease and congestive cardiac failure, and with murmurs that are often mistaken for mitral incompetence or aortic stenosis. The diagnosis is readily made by echocardiography. áblockers and calcium antagonist drugs are the treatment of choice, rather than digitalis, diuretics, and vasodilators which often make the symptoms worse (AU)

A review of the initial two years of a cardio-diagnostic programme in a small island community - abstract

In January 1982, regular right and left cardiac catheterizations and angiography, and detailed examination of cardiac structures in dynamic motion by Real Time (2-D) echocardiography were started at the QEH. During the past 2 years, 64 patients - 45 from Barbados, 7 from St. Lucia, 4 each from Dominica and Trinidad, 3 from Grenada and 1 from Antigua (age 3 weeks to 64 years) underwent cardiac catheterization and angiography with no mortality and minimal morbidity. All of the patients had Real-Time Echocardiography prior to catheterization, and the correct (catheterization) diagnosis was made in all but 5 cases. Thirty-one patients have undergone cardiac surgery - 17 at North Shore University Hospital in New York by special arrangement whereby there was no cost or nominal cost to the patient: 3 at the hospital of their choice in North America; 5 at UHWI in Jamaica, and 6 at the QEH. Eight of the 17 patients going to North Shore have been recatheterized, and our echo and catheterization diagnoses remained unchanged. The other 9 patients underwent surgery without recatheterization, and our echo and catheterization data were confirmed at surgery. There have been 2 operative deaths and 2 late deaths. All of the other post surgical patients are significantly improved and most are living normal or near normal lives. This Report shares the initial 2 years' experience of a Cardio-Diagnostic programme at the QEH, and the subsequent surgical results. Real-time (2-D) echocardiography in our hands has been accurate (92 percent of the time); cardiac catheterization has been safe; and the surgical results are satisfying (AU)

A review of the first two years of the clinical application of echocardiography at the Queen Elizabeth Hospital, Barbados - abstract

Echocardiography was first used extensively as a non-invasive cardio-diagnostic procedure in the late 1960's and early 1970's. Since that time, it has become invaluable as a reliable, reproducible and easily performed investigation which encompasses a wide range of clinical applications. The procedure has been in use in the English-speaking Caribbean countries for a period of only 3 -4 years, and in Barbados for the past 2 years. The reports of all echocardiograms performed over the 2-year period were reviewed and recorded together with other relevant data. A total of 710 echocardiograms were performed. The age range of patients studied was < 1 year (31 patients) to > 74 years (19 patients), with 30 percent of echocardiograms being performed on patients <14 years of age and 14 percent on patients >54 years. Of the 710 echocardiograms, 473 were carried out on outpatients, and 223 on inpatients; 14 were unrecorded. The listed indications for requesting an echocardiogram were suspected or process: congenital heart disease, 246; acquired valvular heart disease, 185; coronary artery disease, 42; mitral valve prolapse, 117; pericardial effusion, 53; suspected cardiac pathology, 85; postoperative assessment, 39; pre-cardioversion, 7; and routine requirement in minoxidil study, 43. On several occasioins more than one indication was listed as the reason for requesting the study. A detailed analysis was undertaken of the echocardiograms of patients in the previously mentioned diagnostic categories together with patients who subsequently underwent cardia catheterisation. The financial cost of the servicing and repair of the echocardiographic nachine used together with cost of re-usables over the 2 years was BD$20,714.00. The results of this study indicate that echocardiography, though relatively costly, has become a very useful, widely applied and highly recognised non-invasive cardio-diagnostic procedure in Barbados (AU)