PubMed Health⌕ Search

Biomedical subjects

R C Knight

Publications and source records attributed to R C Knight.

At least 19 recordsLinked to original sources
PubMed1989

The Rh-negative donor.

By typing fully for Rh, donor samples found to be D-negative but C-positive and/or E-positive on the Kontron Groupamatic G2000, the incidence of Ccddee (r'r) was found to be 0.44%, ccddEe (r"r) 0.50% and Du 0.30%. A total of 15,000 samples typed on the Groupamatic as D-, C- and E-negative were tested by an antiglobulin technique for Du, but none was found to be positive. A new strategy was therefore adopted for routine Rh typing of donations that includes typing first-time donors on the Groupamatic for C, D and E antigens; those that type as D-negative, C-positive and/or E-positive are further tested but no routine Du testing of D-, C- and E-negative donations is performed. Donations are labelled according to their D type, and the once used terminology 'Rh-positive donor, Rh-negative recipient' is no longer used except for those rare Rh D-positive donors belonging to the D category VI of Tippett & Sanger (1962).

Blood Banks↗
PubMed1989

Electrochemical characteristics of nitro-heterocyclic compounds of biological interest. II. Nitrosochloramphenicol.

The electrochemical characteristics of nitrosochloramphenicol have been studied in aqueous buffer systems (pH 7.1) using direct current (d.c.) and differential pulse polarography, cyclic voltammetry and coulometric techniques. Up to 4 charge-transfer steps can be identified. The first reduction step is reversible both chemically and electrochemically, the charge-transfer product showing no tendency to undergo further reaction on the electrochemical time-scale. In contrast, the second reduction step is irreversible, with the product undergoing a fast following reaction to yield a redox-active species which was detected by cyclic voltammetry. From the data and by comparison with related systems, two reduction mechanisms are possible and are discussed.

Chloramphenicol↗
PubMed1988

Anagrelide: a new drug for treating thrombocytosis.

Anagrelide is a member of the imidazo (2,1-b) quinazolin-2-one series of compounds, with a powerful antiaggregating effect on platelets. During studies in humans, anagrelide in small doses has produced thrombocytopenia. We therefore evaluated it in the treatment of thrombocytosis, and to date, platelet levels in 15 of 17 patients with primary thrombocythemia, 2 patients with polycythemia vera and thrombocytosis, and 1 patient with chronic granulocytic leukemia and thrombocytosis have been well controlled with the use of this agent. Induction doses of 1.0 to 1.5 mg given orally every six hours have produced a decrease in the platelet count, starting on day 5 and reaching a normal level by day 12. Side effects of anagrelide have been minimal. Maintenance therapy with 1.5 to 4.0 mg a day has continued to control the platelet count in patients for up to 28 months. This new agent appears promising in the treatment of thrombocytosis in patients with chronic myeloproliferative disease.

Adult↗
PubMed1987

DNA damage induced by reduced nitroimidazole drugs.

Five nitroimidazole drugs were reduced electrolytically and by gamma-radiolysis at fast (300 mumoles or 100% per hr) and slow (3-9 mumoles or 1-3% per hr) reduction rates in the presence of Escherichia coli DNA and single stranded or double stranded DNA from the bacteriophage phi X174. The degree of DNA damage depends upon the rate of drug reduction, where slow reduction produces more damage than fast reduction. The efficiency of damage produced is in the order metronidazole greater than ornidazole greater than azomycin greater than misonidazole greater than benznidazole which reveals a linear correlation between the one-electron reduction potential (E17) and the negative logarithm of the concentration of reduced drug at which 37% of the original DNA activity remains. Damage is not influenced by the presence of O2 at least between about 1-100 ppm. We suggest the protonated one-electron nitro radical anion as a possible candidate for the active damaging species and explain the basis of the relative cytotoxicity of these drugs under conditions of hypoxia.

DNA↗
PubMed1986

DNA damage induced by reductively activated nitroimidazoles--pH effects.

The effect of pH on E. coli DNA damage measured viscometrically and induced by electrolytically reduced metronidazole and misonidazole has been studied, together with the effect on the statistical average number of electrons required for reduction, measured by high-resolution coulometry, and nitrite production measured colorimetrically. In general, nitroimidazole-induced DNA damage is greatest at acid pH and decreased at alkaline pH, but whereas metronidazole exhibits a linear relationship between DNA damage and increased pH, misonidazole shows a plateau between pH 6 and 8. The electron requirements for complete reduction (n) vary with pH. For misonidazole n increases with an increase in pH both in the absence and presence of DNA with a shallow plateau between pH 6 and 8. In contrast, for metronidazole, n decreases with increased pH and exhibits breakpoints between pH 6 and 8. Nitrite (NO2-) production is linear with increased pH for misonidazole but for metronidazole (NO2-) production shows a sudden increase at 7.5 yielding ca. 35% on a molar basis. The results may reflect differences in the relative stability and reactivity of the nitro radical anion.

DNA, Bacterial↗
PubMed1986

Satranidazole: mechanism of action on DNA and structure-activity correlations.

Satranidazole (CG-10213-Go), a novel nitroimidazole possessing a C-N linkage at C2 of the imidazole ring has been examined, during reduction, for its ability to damage DNA. Physical damage to DNA was measured by viscometry, thermal denaturation and renaturation, and hydroxyapatite chromatography. Biologically relevant DNA damage was measured by a bacteriophage transfection assay. The drug produces extensive DNA damage characterized by helix destabilization and strand breakage. Its comparison with other 2- and 5-nitroimidazoles indicate it may be more active towards anaerobes than many 5-nitroimidazoles because its relatively high redox potential may make it more resistant to inactivation by oxygen.

Chromatography↗
PubMed1985

Electrolytic reduction of nitroheterocyclic drugs leads to biologically important damage in DNA.

The effect of electrolytic reduction of nitroimidazole drugs on biologically active DNA was studied. The results show that reduction of the drugs in the presence of DNA affects inactivation for both double-stranded (RF) and single-stranded phi X174 DNA. However, stable reduction products did not make a significant contribution to the lethal damage in DNA. This suggests that probably a short-lived intermediate of reduction of nitro-compounds is responsible for damage to DNA.

Bacteriophage phi X 174↗
PubMed1984

The mechanism of nitroimidazole damage to DNA: coulometric evidence.

A high resolution coulometric technique has been developed to measure the electron requirement for reduction of 12 nitroimidazoles, both in the presence and absence of DNA. The cytotoxic species is shown to be a light sensitive intermediate of drug reduction and a common mechanism of cytotoxicity proposed which involves electron transfer from DNA to the one-electron radical anion (R-NO2-).

DNA, Bacterial↗
PubMed1984

Photosensitive interaction of RSU 1069 with DNA.

RSU 1069 is a 2-nitroimidazole radiosensitizer with an aziridine-containing side chain. In light (360 nm) the absorbance maximum of the nitro group at 325 nm disappears, which is accompanied by expulsion of the nitro group as the nitrite ion. We suggest an intramolecular cyclization of the aziridine side chain and the C2 of the imidazole ring as a possible explanation. This photosensitive effect was used to determine separately the damage to DNA induced by the reduced nitro group and the alkylating property of the aziridine. The aziridine-induced DNA damage is maximized in the dark when the nitro group is either absent (electrolytically reduced prior to the addition of DNA) or non functional (unreduced). In the light, damage is reduced. Typical DNA damage includes helix disruption leading to single strand breaks and the release of thymidine. Alkaline filter elution studies show evidence only for strand breakage and none for cross-linking indicating the drug is capable of mono-functional alkylation only.

Aziridines↗
PubMed1983

Studies on the action of nitroimidazole drugs. The products of nitroimidazole reduction.

The electron requirements for the electrolytic reduction of misonidazole, metronidazole and 4(5)-nitroimidazole have been measured using high-resolution coulometry. Eleven of the labelled final reduction products of metronidazole (a 5-nitroimidazole) have been separated by high-performance liquid chromatography and identified. These appear to be formed without the prior generation of a stable intermediate. In contrast, the reduction products of misonidazole (a 2-nitroimidazole) show little similarity to those of metronidazole but are likely to be formed via the four-electron hydroxylamine derivative. None of the final reduction products show toxicity towards Clostridium bifermentans or Escherichia coli suggesting that the short-lived cytotoxic agent of nitroimidazoles is a reduction product formed by the addition of not more than three electrons.

Chemical Phenomena↗
PubMed1983

Molecular basis of chloramphenicol and thiamphenicol toxicity to DNA in vitro.

The action of thiamphenicol and reduced chloramphenicol on DNA has been investigated in vitro. Reduced chloramphenicol causes DNA damage which is dependent upon reduction of the nitro group and which is characterized by helix destabilization and strand breakage. Although the reduction process requires six electrons indicating formation of the amine in 100% yield the toxic agent is most probably a short-lived reduction intermediate. We propose the one-electron nitro radical anion rather than the nitroso derivative as the toxic agent responsible for DNA damage related to aplastic anaemia. In contrast, thiamphenicol produces no such effects on DNA.

Chloramphenicol↗
PubMed1981

Interaction of nitroimidazole drugs with DNA in vitro: structure-activity relationships.

An electrolytic reduction system has been developed to model the cytotoxic action of a range of nitroimidazole drugs against DNA hypoxic cells or anaerobic microorganisms. THe degree of damage induced by these drugs (measured as the release of [14C]-dT from DNA) and their relative rates of reduction have been correlated with their redox potentials. The results show that the correlation of drug-induced damage and electron affinity is related to the amount of drug reduced, and supports the hypothesis that at the molecular level the cytotoxic mechanism of reduced nitroimidazoles is identical in hypoxic mammalian cells, bacteria and protozoa.

Cell Survival↗