Biomedical subjects
Publications and source records attributed to S Hilton.
A-7-year-old boy was found to have histidinuria without histidinemia. Low concentrations of histidine in plasma were consistent with impaired intestinal and renal tubular absorption of histidine. The patient was developmentally delayed and had some minor anomalies. Only 4 other patients in 3 families have been reported. Each had abnormality of the central nervous system. All were male.
Aeromonas species secrete a glycerophospholipid-cholesterol acyltransferase (GCAT) which shares many properties with mammalian plasma lecithin-cholesterol acetyltransferase (LCAT). We have studied the stereochemical and positional specificity of GCAT against a variety of lipid substrates using NMR spectroscopy as well as other assay methods. The results show that both the primary and secondary acyl ester bonds of L-phosphatidylcholine can be hydrolyzed but only the sn-2 fatty acid can be transferred to cholesterol. The enzyme has an absolute requirement for the L configuration at the sn-2 position of phosphatidylcholine. The secondary ester bond of D-phosphatidylcholine cannot be hydrolyzed, and this lipid is not a substrate for acyl transfer. In contrast to the phospholipases, but similar to LCAT, the enzyme does not interact stereochemically with the phosphorus of phosphatidylcholine. In fact, the phosphorus is not required for enzyme activity, as GCAT will also hydrolyze monolayers of diglyceride, although at much lower rates.
Vibrio species release a lipase which shares many properties with mammalian lecithin-cholesterol acyltransferase. We have studied the action of the enzyme on phospholipid monolayers. At similar surface pressures, reaction velocities were higher with monolayers of dilauroylphosphatidylcholine than with the corresponding phosphatidylglycerol or phosphatidylethanolamine. The dependence of reaction velocity on molecular density was very similar for phosphatidylcholine and phosphatidylethanolamine monolayers. Lag times were shortest with phosphatidylglycerol at low molecular densities, but maximum velocity was reached at considerably lower densities than with the other two lipids. We have found [Hilton, S., McCubbin, N. D., Kay, C., & Buckley, J.T. (1990) Biochemistry 29, 9072-9078] that nicking of the enzyme with trypsin or other proteases results in an increase in its activity against lipids in membranes. Here we show that trypsin treatment results in a large change in the surface activity of the lipase, allowing it to penetrate monolayers at pressures higher than 40 mN.m-1.
Aeromonas hydrophila releases a protein which is a member of the lipase superfamily, similar in reaction mechanism to the important mammalian plasma enzyme lecithin-cholesterol acyltransferase. We have used chemical modification and site-directed mutagenesis of the protein to identify amino acids which may be involved in catalysis. The enzyme was unaffected by phenylmethylsulfonyl fluoride, but it was almost completely inhibited by another serine-reactive compound, diethyl p-nitrophenyl phosphate. A serine selectively modified by this reagent was identified by sequencing the amino-terminal region of the protein. It was located at position 16, in the short consensus sequence shared by the enzyme with other lipases. When this serine was changed to asparagine the product was an enzymatically inert protein which nevertheless retained the surface activity of the wild-type enzyme, suggesting its ability to bind to substrate was not changed. Diethylpyrocarbonate treatment drastically reduced the rate of acyl transfer by the native enzyme, but this did not appear to be due to modification of an essential histidine, since inhibition was not reversed by addition of hydroxylamine. We have shown that only two of the histidines in the enzyme can be involved in catalysis (Hilton, S., McCubbin, W. D., Kay, C.M., and Buckley, J. T. (1990) Biochemistry, 29, 9072-9078). Replacing both of these with asparagines had little or no effect on enzyme activity. These results indicate that, in apparent contrast to other lipases, histidine does not participate in the reaction catalyzed by the microbial enzyme. Since catalysis was not inhibited by sulfhydryl reagents, we conclude that a free cysteine is also not required for activity. This may distinguish the microbial enzyme from the mammalian acyltransferase.
A survey was made of the diabetic care given by general practitioners in six family practitioner committee areas. Replies were received from 388 practices, representing 1034 principals (effective response rate 69%), serving over two million patients. Fourteen per cent of practices offered mini-clinic facilities for their diabetic patients, although a much greater proportion professed to give either full or shared care to patients in ordinary surgery time. One quarter of practices kept a diabetes register, but fewer had a system of recall for patients to ensure anticipatory care. The barriers which general practitioners most often perceived in the provision of adequate care for diabetics were: lack of time, absence of a recall system and deficiency in their own clinical skills. Seventy seven of the doctors responding to the initial questionnaire participated in an audit of the level of supervision provided for 378 of their diabetic patients. Better levels of supervision of non-insulin dependent diabetics were shown in those practices where diabetes registers were kept, and where special arrangements were made for caring for diabetes. The levels of care provided by those doctors setting aside specific clinic times were not demonstrably superior to those who did not. The findings suggest that provision of support services, particularly expertise in dietetics, would help to increase general practitioners' confidence and enable more of them to improve their care of diabetic patients.
The study examined the relationship between type of non-psychotic diagnosis at time of hospitalization, pre-Navy non-psychotic condition, and paygrade for active duty, enlisted Navy personnel. The sample (N = 27,210) consisted of all hospitalized cases of active duty, enlisted Navy personnel from 1981 through 1984 with a nonpsychotic mental disorder as the primary diagnosis. Results indicated that personality disorders were more likely than other nonpsychotic diagnoses to be associated with a pre-Navy nonpsychotic condition and lower paygrades. More specifically, the strong relationship between a personality disorder diagnosis and a pre-Navy nonpsychotic condition was demonstrated only for paygrades E-1 through E-4.
A fatty acyltransferase with a reaction mechanism similar to that of mammalian lecithin: cholesterol acyltransferase has been purified from culture supernatants of a mutant Aeromonas salmonicida containing the cloned Aeromonas hydrophila structural gene. Typically, more than 35 mg of protein were isolated from 2 L of culture supernatant. The amino-terminal sequence, amino acid composition, and molecular weight of the purified protein corresponded to predictions based on the sequence of the gene, indicating that the signal sequence had been correctly removed during export but that no further processing had occurred. Analysis of the far-UV circular dichroic (CD) spectrum of the enzyme showed that it consists of 31% alpha-helix, 21% beta-sheet, and 16% beta-turn, with 12% of aperiodic form. Treatment of the purified protein with a variety of proteases resulted in nicking near the C-terminus. This led to an increase in enzyme activity against lipids in erythrocyte membranes and increased rate of hydrolysis of p-nitrophenyl butyrate. Activation was accompanied by a change in the CD spectrum and a change in its aggregation state. The trypsin cut site was located between the two cysteines in the enzyme. Evidence is presented that the cysteines are joined by a disulfide bond and therefore cannot participate in acyl transfer. This may distinguish the microbial enzyme from lecithin:cholesterol acyltransferase. This is the second extracellular A. hydrophila protein that we have shown can be activated by proteolysis after it is released.
Until recently, technological advances in general practice have generally been thought of as the applications of microcomputers in practice organization and record keeping. Advances in miniaturization and versatility of diagnostic technology will have a similarly large impact on the way general practitioners practice medicine in the next decade. This article reviews some of the newer tests that are already available to general practitioners, particularly in diagnostic biochemistry and microbiology. Preliminary evaluative work and research studies in general practice are also described.
This study examined the extent to which severity of mental health diagnosis and length of military service predict medical discharge disposition for Navy personnel (N = 1,450). Results corroborated the findings of a similar study related to back problems in which both severity and length of service were significant predictors. Examination of consistency of mental health diagnoses from time of hospitalization to last Physical Evaluation (PE) Board determination revealed that nonpsychotic primary diagnoses were likely to shift to psychotic diagnoses by the time of last PE Board determination. Last, the contribution of entitlement costs to the total costs of medical care are discussed.
Doctors from 34 practices participated in an audit study which examined inhaler technique in up to 20 of their patients. A new scoring system, applicable to all forms of device, was used. Although the majority of the 422 patients (63%) was using metered dose inhalers, a broad range of other devices was included; most frequently Rotahalers (15%) and spacer devices (9%). For analysis, technique scores were rated as 'good' (score 4 out of 4), 'adequate' (score 3 or 4) and 'inadequate' (score 2 or less). Overall, 25% of patients had inadequate technique. Of all devices, the Turbohaler had the highest proportion of patients with good technique (78%), and metered dose inhalers the lowest (45%). This audit confirms that technique is unsatisfactory for a significant proportion of patients, regardless of the device used. A simple scoring system promotes consistent testing of technique within a practice.
Two different patient education programmes for asthma in general practice were evaluated in a controlled trial. Knowledge, self management, and morbidity due to asthma were assessed in 339 patients by means of a questionnaire. One group then received a maximum education programme, a second group received a limited education programme, and a third acted as a control group. 274 patients were reassessed after one 1 year. In both the intervention groups, understanding of asthma was greater after the trial. Only in the maximum intervention group was a significant improvement in knowledge of asthma shown. Neither group showed any change in self-management ability or asthma morbidity that differed significantly from changes in the control group. These simple informational education programmes were ineffective when applied to a general practice population. Further studies of factors affecting attitudes, beliefs, and actions are needed to improve the advice and support given to asthma patients.
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An open cross-over trial comparing astemizole with intra-nasal aqueous beclomethasone dipropionate was carried out in forty-five perennial rhinitis patients attending a S.W. London general practice. Each drug was given for 12 weeks, separated by 4-8 weeks without medication. The principal outcome measure was a 7-day symptom diary completed by patients during weeks 4, 8 and 12. Patients were skin tested to seven common inhalant allergens. Half the patients beginning either regime failed to respond adequately within 2 weeks. Doubling the dose in these patients achieved satisfactory symptom control in an additional 67% on beclomethasone dipropionate and 45% on astemizole. Symptom diary scores showed beclomethasone dipropionate to be significantly more effective than astemizole in the treatment of skin test negative patients; but the two drugs were of equal benefit in the treatment of skin test positive patients. Sneezing and rhinorrhoea were the same on both drugs, but nasal blockage tended to be less severe on beclomethasone dipropionate. There was no significant difference between drugs in the frequency or duration of side effects. Beclomethasone dipropionate and astemizole are equally effective in the symptomatic treatment of atopic perennial rhinitis, but beclomethasone dipropionate may offer superior symptom relief in non-atopic perennial rhinitis.
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The sonographic detection of echogenic, soft-tissue mass within the veins of the lower extremities assures the diagnosis of deep venous thrombosis (DVT). However, the sonographic diagnosis remains inconclusive when fresh thrombus and/or artifacts are present within the lumen of the vein. The present study attempts to augment the clinical utility of real-time sonography in the detection of DVT, based on the premise that total obliteration of the vein lumen by probe compression should not be possible in the presence of venous thrombi. Sonography and contrast venography of the lower extremity were performed in 20 patients with clinical suspicion of DVT. The presence of thrombi was confirmed in 14 patients. Probe compression failed to obliterate the lumen of the veins containing thrombi. The authors conclude that the technique of probe compression is useful for rapid and noninvasive detection of venous thrombi.
One-hundred and eight women participated in a study which screened for depressive symptoms in the antenatal period. Of these women, 92 completed at least two further screenings during the postnatal year. The screening tool was the Hamilton Depression Rating Scale, adapted for self-rating, and administered by a microcomputer. It was found that mean scores and the prevalence of depressive symptoms rose throughout pregnancy, with a sharp peak in the third trimester. Following delivery there was an abrupt fall in the prevalence of depressive symptoms, followed by another rise, with a postnatal peak at six months.There were significant associations, at all levels of severity, between raised scores antenatally, and those developing postnatally in women completing the study. These were more marked in multiparae than primiparae. There was also a significant association between a past history of treated depression and the development of raised postnatal scores for depression.The routine use of a microcomputer to administer questionnaires to patients has proved feasible within general practice.