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Biomedical subjects

J M Dickinson

Publications and source records attributed to J M Dickinson.

At least 19 recordsLinked to original sources
PubMed1997

A simplified squalene epoxidase assay based on an HPLC separation and time-dependent UV/visible determination of squalene.

A novel and highly simplified enzyme assay for squalene epoxidase (EC 1.14.99.7) has been developed. The assay relies on the UV/visible determination of squalene at 195 nm, as it elutes from an octadecylsilane HPLC column. An acetonitrile/water (95.5/0.5, v/v) mixture was found to provide an ideal mobile phase, into which aqueous enzyme reaction mixture aliquots could be injected. Squalene, the natural substrate for squalene epoxidase, may be quantitatively determined within the concentration range 0-30 microM, with a calibration curve exhibiting an r2 (where r2 is the square of the Pearson correlation coefficient r) of 0.995. The HPLC retention time for squalene was significantly longer (> 15 min) than that for any other component required to prepare an enzyme assay reaction mixture, so facilitating its identification and quantification. In this way HPLC was used to follow enzymic squalene consumption within aliquots taken over a 30-min period. Previously reported squalene epoxidase assays rely on the radiolabeling and subsequent monitoring of squalene as it is metabolized by the enzyme. A highly simplified enzyme assay for squalene epoxidase is therefore reported.

Chromatography, High Pressure Liquid↗
PubMed1997

Reduced transfer of male accessory gland proteins and monandry in female Aedes aegypti mosquitoes.

We examined whether female Aedes aegypti (L.) mosquitoes would remate after they first mated with a male that was reared on a suboptimal larval diet and that as a result, transferred reduced amounts of male accessory gland proteins. Accessory gland proteins from males labeled with 3H leucine were not detected in females allowed to male mate with the labeled males after they first mated with either low diet or high diet males. The amount of the male accessory gland protein transferred by smaller, low diet males was adequate to terminate female receptivity, even after one gonotrophic cycle, and females of this species appear to be monogamous.

Aedes↗
PubMed1997

Bioavailability of Chinese rifapentine during a clinical trial in Hong Kong.

SETTING: A clinical trial of rifapentine in Hong Kong. OBJECTIVE: Assessment of the bioavailability of the Chinese rifapentine used in the trial. DESIGN: The content of rifapentine in serum samples taken from 287 patients during the administration of four batches of the drug was measured by microbiological assay. RESULTS: An initial comparison of areas under curve obtained in a random allocation to 40 patients of rifapentine either of Western or Chinese origin indicated that the bioavailability of the Chinese drug was 74% of the Western drug. The bioavailability of the second batch was found to be about 66% of the Western drug. The dose of the last two batches of rifapentine was therefore increased from the planned 600 mg to 750 mg, or briefly to 900 mg; serum concentrations were then similar to those obtained with the Western drug. Bioavailability did not change during the use of each drug batch. CONCLUSION: A comparison of the results obtained in the trial with the initial two batches and the final batches will estimate the effects of rifapentine dose size on its efficacy and toxicity.

Adult↗
PubMed1996

Preventive chemotherapy of tuberculosis in Cornell model mice with combinations of rifampin, isoniazid, and pyrazinamide.

The efficacies of rifampin-containing preventive regimens were measured in Cornell model mice in which an initially severe infection with Mycobacterium tuberculosis H37Rv was first treated for 7 weeks with 25 mg of isoniazid and 1,000 mg of pyrazinamide per kg of body weight in the diet and then with one of four test regimens given by daily oral gavage for 6 weeks. These regimens were 15 mg of rifampin per kg alone (R), rifampin plus 25 mg of isoniazid per kg (RH), rifampin plus 150 mg of pyrazinamide per kg (RZ), or rifampin plus isoniazid and pyrazinamide (RHZ). The interval between the rifampin gavage and the gavage with the other drugs ranged from 10 to 45 min, so that interference with rifampin absorption did not occur. Mice were sacrificed at 11 and 20 weeks after the termination of chemotherapy, with each killing being preceded by 3 weeks of high-dose dihydrocortisone treatment. Entire spleens and lungs were cultured. The proportions of mice with positive spleens at either killing time were 74% of 43 mice treated with R, 63% of 41 mice treated with RH, 65% of 43 mice treated with RZ, and 53% of 45 mice treated with RHZ, a just significant (P = 0.04) trend for fewer positive spleens with increasing numbers of drugs in the regimen. However, no trend was found in the corresponding proportions of mice with positive spleens or lungs, which were 81, 63, 65, and 71% for mice treated with R, RH, RZ, and RHZ, respectively. Thus, in the Cornell model, R alone, RH, RZ, and RHZ all had similar efficacies.

Animals↗
PubMed1993

Turning intermittent regimens into daily regimens using blister-packs. An exploration in murine tuberculosis.

SETTING: Blisterpacks might be used to present low cost intermittent regimens while maintaining an easily remembered daily frequency of opening blisters, by alternating blisters containing 2 of the drugs of a 4-drug regimen with blisters containing the remaining 2 drugs. OBJECTIVE: The efficacy of the alternating regimens was examined in murine tuberculosis. DESIGN: 2 weeks after infection with Mycobacterium tuberculosis H37Rv, groups of mice were treated with rifampicin (R) 15 mg/kg, isoniazid (H) 25 mg/kg, pyrazinamide (Z) 300 mg/kg, ethambutol (E) 100 mg/kg three times weekly (RHZE3); RH/ZE, an alternating regimen of RH on days 1, 3 and 5 of the week and ZE on days 2, 4 and 6, RZ/HE or RE/HZ. RESULTS: Spleen and lung bacillary counts at 7 and 12 weeks indicated large differences in the efficacy of the regimens: RZ/HE > RE/HZ > RHZE3 > RH/ZE. Serum assays showed that Rifampicin (RMP) levels were much lower after HRZE and slightly lower after RZ, RE and RH than after R alone, whereas levels were similar when R was given before the remaining drugs; also, the absorption of Z was slightly increased by R. A second experiment used the same 4 regimens but gave R before other drugs. The organ colony forming units counts at 6 and 12 weeks were then similar. A third experiment examined continuation phase regimens of R3, R2, R2H2 and R2H6 given after daily RHZ treatment for 4 weeks. It found R2H2 only slightly superior to R2H6 and R3 much better than R2. CONCLUSION: 1. Alternating initial phase regimens were as effective as conventional intermittent regimens. 2. R3H6 might be an optimal continuation phase regimen for blisterpacks.

Animals↗
PubMed1992

Activity of two long-acting rifamycins, rifapentine and FCE 22807, in experimental murine tuberculosis.

The efficacy of the long-acting rifamycins, rifapentine (RPE) and FCE 22807 (FCE) in experimental murine tuberculosis was studied by counting viable bacilli in spleens. At 2 weeks after infection with Mycobacterium tuberculosis, strain H37Rv, treatment with isoniazid 25 mg/kg, rifampicin 10 mg/kg and pyrazinamide 150 mg/kg was given daily for 6 weeks. The mice were then divided into groups given RPE or FCE at intervals of 1, 2 or 3 weeks with spleen counts after 18 and 24 weeks of chemotherapy. The first experiment showed the great effect of the size of the dose of RPE, which, in once-weekly regimens, caused rapid sterilization at 16 mg/kg, less rapid sterilization at 10 mg/kg and incomplete activity at 6.25 mg/kg. Regimens of RPE given every 2 or 3 weeks were less effective, though 16 mg/kg fortnightly was as good as 6 mg/kg once-weekly. The second experiment compared RPE and FCE each given at 12 or 8 mg/kg. The results were similar though, at 8 mg/kg every 2 or 3 weeks, FCE was slightly more effective than RPE. Serum assays showed that the levels with 8 and 12 mg/kg FCE were lower than those produced even by 6.25 mg/kg RPE, suggesting that FCE would be a better drug than RPE if its bioavailability could be improved, and that the levels following 16 mg/kg RPE were similar to those found in man after 8 mg/kg RPE taken with a fat-rich meal, suggesting good prospects for effective once-fortnightly human treatment. The potential for long-acting rifamycins in the management of pulmonary tuberculosis is discussed.

Animals↗
PubMed1991

Efficacy of intermittent pyrazinamide in experimental murine tuberculosis.

CFLP mice were infected intravenously with Mycobacterium tuberculosis strain H37Rv and the progress of chemotherapy was followed by counts of viable bacilli in the lung and spleen. After spleen counts had reached log10 7.0, 12 experimental groups, each containing 10 mice, were treated for 8 weeks with pyrazinamide (PZA) given in mean daily dosages of 100, 200 or 400 mg/kg/day, with the interval between the doses within each dosage group being 1, 2, 4 or 8 days. All mice were also given 25 mg isoniazid/kg daily. An increase in the mean daily dosage from 100 mg PZA/kg to 400 mg PZA/kg resulted in a decrease of spleen viable counts at the end of treatment from log10 4.2 to log10 3.8. The organ counts, averaged over the full dosage range, were little altered by spacing out the interval between doses from 1-4 days, while increasing dose size proportionately: the counts with low mean dosages tended, however, to decrease (indicating improved efficacy) while those with high mean dosages increased (P less than 0.001). Counts increased when the interval was 8 days. Spacing out the doses while keeping the dose size constant resulted in progressive loss of efficacy. These findings suggest that, if PZA is given intermittently, the size of the dose should be increased, though not quite proportionately, to maintain full efficacy. Even with such an increase in dose, however, once weekly treatment would be less effective.

Animals↗
PubMed1990

In vitro activities against mycobacteria of two long-acting rifamycins, FCE22807 and CGP40/469A (SPA-S-565).

The in vitro activities of two new long-acting rifamycins, FCE22807 a derivative of FCE22250, and CGP40/469A (SPA-S-565) were studied. When compared with rifampicin, the minimal inhibitory concentrations (MIC) against Mycobacterium tuberculosis of both were 4 times lower but neither was particularly active against rifampicin-resistant strains of M. tuberculosis nor against M. avium-intracellulare-scrofulaceum complex strains. A drug is likely to be particularly effective in widely spaced intermittent dosage if it has a long half-life and high bactericidal activity. When tested against M. tuberculosis in the logarithmic and in the stationary phase of growth, FCE22807 was amongst the most bactericidal of the rifamycins while CGP40/469A had little bactericidal activity.

Anti-Bacterial Agents↗
PubMed1989

Slide culture sensitivity tests.

A new method for slide culture sensitivity tests of Mycobacterium tuberculosis is described in which smear-positive sputum spread on slides is incubated without prior decontamination in a selective lysed human blood medium. Results are available 7 days after setting up the tests and are particularly useful for guiding the treatment of smear-positive patients with a long history of unsuccessful chemotherapy. Drug concentrations and definitions of resistance are suggested for tests against isoniazid, streptomycin, PAS, rifampicin ethambutol and ethionamide. A good correlation was seen between the results of these tests and those of standard indirect sensitivity tests.

Antitubercular Agents↗
PubMed1988

In vitro metabolism of formononetin and biochanin A in bovine rumen fluid.

The phyto-estrogens formononetin (7-hydroxy-4'methoxyisoflavone) and biochanin A (5-7-dihydroxy-4'-methoxyisoflavone) were independently incubated in vitro at 39 degrees C in bovine rumen fluid from a fistulated steer receiving an alfalfa hay diet. Formononetin was incubated in studies 1 and 2, whereas biochanin A was incubated in study 3. The isoflavones were separated and quantified by high performance liquid chromatography. In study 1, formononetin concentration, 14.80 micrograms/ml at time 0, declined to 1.16 micrograms/ml by 12 h and to .76 micrograms/ml by 24 h. Daidzein (7,4-dihydroxyisoflavone), .18 micrograms/ml at time 0, peaked at 12.92 micrograms/ml at 6 h and decreased to 1.30 micrograms/ml by 24 h. Equol (7,4'-dihydroxyisoflavan), detected at 6 h, peaked at 16.94 micrograms/ml at 18 h and dropped to 12.64 micrograms/ml at 24 h. In incubation study 2, formononetin declined from 17.57 micrograms/ml at time 0 to 7.08 micrograms/ml by 6 h. Daidzein concentration was 1.75 micrograms/ml at time 0 and increased to 12.03 micrograms/ml by 6 h. Equol was detected at 3 h and increased to 2.32 micrograms/ml at 6 h. The half-lives were 4.3 for formononetin and 9.8 h for daidzein in this in vitro system. In study 3, biochanin A, 8.54 micrograms/ml at time 0, decreased to 0 micrograms/ml by 12 h in incubation 3, whereas genistein (5,7,4'-trihydroxyisoflavone), 3.17 micrograms/ml at 1 h, peaked at 7.35 micrograms/ml at 4 h and decreased to .32 micrograms/ml at 24 h. Equol was not detected in incubation study 3. The half-lives of biochanin A and genistein were 3.9 and 5.5 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

In vitro properties of rifapentine (MDL473) relevant to its use in intermittent chemotherapy of tuberculosis.

In a comparison of in vitro properties of rifapentine (RIF) and rifampicin (RMP), the minimal inhibitory concentration of RIF against Mycobacterium tuberculosis in Tween-albumin liquid medium was usually 0.02 micrograms/ml, 2-3 times lower than for RMP; the bactericidal activity against a log phase culture was slightly less than that of RMP and the recovery after pulsed exposures to 1 microgram/ml of RIF or RMP lasting 6, 24 and 96 h was identical for the two rifamycins. These findings are used to interpret published data from the chronic experimental murine tuberculosis model and support the view that in the mouse, the efficacy of RIF in widely spaced intermittent chemotherapy is the result of its long half-life.

Animals↗
PubMed1987

In vitro activity of new rifamycins against rifampicin-resistant M. tuberculosis and MAIS-complex mycobacteria.

Comparisons were made of the in vitro activity of rifampicin, and the rifamycin derivatives, rifapentine, rifabutin, CGP 29861, CGP 7040 and CGP 27557, against rifampicin-sensitive and rifampicin-resistant strains of Mycobacterium tuberculosis and against the Mycobacterium avium/intracellulare/scrofulaceum (MAIS) complex. The new rifamycins had MICs four to eight times lower than those of rifampicin against sensitive M. tuberculosis strains. Of the 35 rifampicin-resistant strains of M. tuberculosis, 31% were sensitive to rifabutin but only 3-11% to the other rifamycins. The proportions of the MAIS strains found to be sensitive were 35% for rifampicin, 50-60% for CGP 27557, rifapentine and rifabutin and 85-92% for CGP 29861 and CGP 7040.

Antitubercular Agents↗
PubMed1987

In vitro observations on the suitability of new rifamycins for the intermittent chemotherapy of tuberculosis.

The bactericidal activity of six new rifamycin derivatives--rifabutin (RBU), FCE 22250 (F22), rifapentine (RPE), CGP 29861 (C29), CGP 7040 (C70) and CGP 27557 (C27) and rifampicin (RMP)--have been measured against log phase and, as a better test of sterilising activity, against stationary phase cultures of Mycobacterium tuberculosis, H37Rv. The order of activity of 1.0 and 0.2 mg/l rifamycin against log phase cultures was RMP greater than RPE & C27 greater than RBU & C29 greater than C70. The order of activity of 1.0 and 0.4 mg/l, adjusted for stability of the rifamycin, against stationary phase cultures was F22 & RMP greater than RBU greater than RPE greater than C27 & C29 greater than C70. Viable counts were done during and after pulsed exposures of 6, 24 or 96 h to C29 and RMP. The curves were similar though C29 was less bactericidal and the lag period before recovery was 1-2 days longer. F22, having high bactericidal activity against stationary organisms and a long half-life, was considered likely to be the most effective sterilising drug.

Antitubercular Agents↗
PubMed1985

Activity of the combination of fludalanine and cycloserine against mycobacteria in vitro.

The initial steps in the incorporation of alanine into the bacterial cell wall include the conversion of natural to D-alanine by a racemase followed by the coupling of 2 D-alanine molecules by a synthetase to yield a dipeptide. A combination of fludalanine (3-fluoro-2-deutero-D-alanine), an analogue of D-alanine that irreversibly inactivates the racemase, and cycloserine, which inhibits the synthetase, has been found to be more active against a wide range of non-mycobacterial organisms than either fludalanine or cycloserine alone. When tested against 16 strains of slowly growing mycobacteria including M. tuberculosis, the combination was no more active than cycloserine alone. However the cycloserine minimal inhibitory concentration (MIC) of the combination against the rapidly growing species M. phlei and M. fortuitum was much lower than the MIC of cycloserine alone, particularly with low ratios of fludalanine to cycloserine, and was within the range attainable by therapeutic cycloserine plasma concentrations in man, suggesting its possible use in the treatment of disease due to M. fortuitum.

Alanine↗
PubMed1981

Experimental models to explain the high sterilizing activity of rifampin in the chemotherapy of tuberculosis.

Model systems were set up in vitro to explore the reasons why rifampin is a better sterilizing drug than isoniazid in short-course chemotherapy of tuberculosis. When the growth rate of Mycobacterium tuberculosis strain H37Rv was reduced uniformly by lowering the incubation temperature or the pH of the culture medium, the bactericidal activity of rifampin and isoniazid decreased to a similar extent. However, when a culture was maintained at 8 degrees C and incubated for daily periods of 1 or 6 h at 37 degrees C, rifampin killed more rapidly than isoniazid. Maintenance of control cultures without antimicrobials at 8 degrees C with or without periods at 37 degrees C, had little or no effect on their viability, ability to commence logarithmic growth at 37 degrees C, or to incorporate [14C]uridine. Old cultures left undisturbed or to which small additions of fresh culture medium were regularly added were killed more rapidly by rifampin than by isoniazid. These experiments supported the view that the special part of the bacterial population that is killed more rapidly by rifampin than by isoniazid during short-course chemotherapy consists of bacilli dormant much of the time but occasionally metabolising for short periods.

Culture Media↗