[The context of radiotherapy within a literature perspective]. / O contexto de um setor de radioterapia sob a perspectiva da literatura.

The present study is a review of the literature on radiotherapy and was undertaken in order to determine and analyse how the subject is approached by different investigators. The review covers textbooks that focus the evolution of physics on radiotherapy, and the issues of eight journals published over a ten-year period (1982-1992). Three of the journals are Brazilian, one is North American. Four of them are not specific for the area. Six CEPEN catalogues were also consulted. The analysis have shown gaps related to studies that approach the perspectives of patients, their families and the members of the health and nursing team on their daily experience of this treatment.

Efficacy of injectable anticholinergic drugs against soman-induced convulsive/subconvulsive activity.

Six FDA approved, injectable compounds [benztropine (BZT); biperiden (BIP); dicyclomine (DCL); l-hyoscyamine (HYO); orphenadrine (ORP); scopolamine (SCP)] were each compared to diazepam (DZ, the standard) in male guinea pigs against ongoing soman-induced convulsive or sub-CV (CV/sub-CV) activity. Three trained graders concurrently assigned CV/sub-CV scores to each animal based on signs of intoxication at various times post-soman. Animals received (im) pyridostigmine (26 micrograms/kg) 30 min before soman (56 micrograms/kg; 2 x LD50), atropine (2 mg/kg) admixed with 2-PAM (25 mg/kg) at one min after soman, and the candidate drug preparation at 5.67 min post soman, a time when CV activity was assured. BIP and SCP were effective over dosage ranges between 10 and 0.3, and 1.0 and 0.13 mg/kg, respectively, while the other preparations were less effective at their respective maximum dosages. At the most effective dosages of SCP (1.0 mg/kg) and BIP (10 mg/kg), the CV/sub-CV scores were significantly lower (p < 0.05) than those of DZ. Only 33% survival was observed at each of two doses of ORP and one dose of HYO; therefore, no further testing was done with these compounds. Using freshly prepared solutions, DCL (up to 40 mg/kg) and BZT (up to 96 mg/kg) were tested with mixed results; DCL lowered lethality while BZT increased lethality. CV/sub-CV scores for the most effective dose of DCL and BZT were, however, lower than those of DZ. SCP is an antimuscarinic drug devoid of antinicotinic activity, while BIP possesses antimuscarinic, antinicotinic, antispasmodic and anti-N-methyl-D-aspartate activity. Recent evidence suggests that, in late stages of intoxication by nerve agents, noncholinergic, excitatory amino acid receptors may become involved and necessitate the use of a multi-action drug like BIP. The findings herein suggest that SCP and BIP are superior to DZ, but further studies are needed to determine which drug or drug class should be pursued in more advanced testing.

Mutation in the Escherichia coli htpR locus results in stabilization of recombinant expression products that are susceptible to proteolytic degradation.

We compared the expression and degradation of three cloned malarial proteins in a pair of isogeneic strains of Escherichia coli that differed at the htpR locus. The htpR locus encodes an alternate sigma factor necessary for the transcription of heat shock promoters. Plasmodium sequences were cloned from polymerase chain reaction-amplified DNA initiated by oligonucleotide primers that were specific for the gene coding regions to be expressed. The amplified DNA was cloned and expressed in a vector that encodes a strong T7 promoter and translation--initiation signal. The total cell yield of two of the expressed proteins was found to be increased when synthesis occurred in a E. coli htpR mutant. Pulse--chase experiments showed that the increased protein yield correlated with a decrease in the degradation of the protein in the htpR strain. A two- to seven-fold increase in the half-life of the malaria proteins was observed in the E. coli htpR- background as compared to htpR+. We found no difference in survival of the E. coli K165 htpR mutant and isogeneic parent during thermal induction. Since the synthesis of the heat shock sigma factor did not significantly influence survival of E. coli and htpR expression results in increased degradation of foreign proteins, the E. coli htpR mutant was a valuable host strain for production of foreign proteins.

Bovine mitochondrial ribosomes possess a high affinity binding site for guanine nucleotides.

Mammalian mitochondrial ribosomes possess a binding site for guanine nucleotides. GTP binds in unit stoichiometry and with high affinity (Kd = 15.3 +/- 2.8 nM) to the small subunit of bovine mitochondrial ribosomes. This binding activity survives high salt washes, indicating that the nucleotide binds to an integral site within this subunit. GDP also binds to the small subunit with high affinity (Kd = 17 +/- 5.8 nm) and in unit stoichiometry. The GTP binding activity can be competed with GDP but not appreciably by other nucleotides, indicating that both GTP and GDP bind specifically and to the same site. The non-hydrolyzable analogs of GTP, guanylyl-5'-imidophosphate, and guanylyl-(beta,gamma-methylene)- diphosphonate also bind to the small subunit, but with reduced affinity. These results indicate that mammalian mitochondrial ribosomes, unlike other ribosomes, are able to interact directly with guanosine triphosphate, suggesting that the bound GTP may be involved in a novel regulatory mechanism in mitochondrial protein synthesis.

The translation system of mammalian mitochondria.

Oligoribonucleotides and mRNA were used to define properties of the bovine mitoribosomal mRNA binding site. The RNA binding domain on the 28 S subunit spans approx. 80 nucleotides of the template, based on ribosome protection experiments, but the major interaction with the ribosome occurs over a 30 nucleotide stretch. The binding site for E. coli IF3 is conserved in bovine mitoribosomes, but mitochondrial factors appear essential for proper interaction of mRNA with mitoribosomes. The small subunit of bovine mitoribosomes contains a high-affinity binding site for guanyl nucleotides, further indication of specialized mechanisms for initiation complex formation and function of mammalian mitochondrial ribosomes.

Methemoglobin formation resulting from administration of candidate 8-aminoquinoline antiparasitic drugs in the dog.

In vivo methemoglobin (MHb) formation caused by five 8-aminoquinoline compounds was tested in beagle dogs. Male beagle dogs were dosed orally once per day at 0.0116 mmol/kg for 4 consecutive days with primaquine (8-[4-amino-1-methylbutyl)amino]-6-methoxyquinoline, diphosphate), three candidate 8-aminoquinoline antimalarial drugs (WR 225,448 5-(3-trifluoromethyl)phenoxy-4-methyl primaquine, succinate); WR 238,605 2,6-dimethoxy-5-(3-trifluoromethyl)phenoxy-4-methyl primaquine, succinate; or WR 242,511 5-hexoxy-4-methyl primaquine, diphosphate dihydrate), or a candidate 8-aminoquinoline antileishmanial drug WR 6026 (8-[(6-diethylamino)amino]-6-methoxy-4-methyl quinoline, dihydrochloride). MHb and total hemoglobin levels were determined daily prior to dosing and for 29 days after drug administration. All compounds caused prolonged levels of MHb that peaked at Days 4 to 5 with disappearance half-lives of 5 to 9 days. Peak percentage MHb of primaquine, WR 6026, WR 238,605, WR 225,448, and WR 242,511 was 6.3, 20.7, 16.0, 25.3, and 48.1%, respectively. Total MHb as measured by area under the time-concentration curve was highest for WR 242,511, followed by WR 225,448, WR 238,605, WR 6026, and primaquine, respectively. The results of this study, in conjunction with other toxicity and efficacy studies, have been utilized to select one of these compounds for development as a replacement for the antimalarial drug primaquine, and also to characterize the MHb-forming properties of WR 6026.

Analysis of artesunic acid and dihydroqinghaosu in blood by high-performance liquid chromatography with reductive electrochemical detection.

A new high-performance liquid chromatography (HPLC) method using reductive electrochemical detection has been developed for the analysis of the antimalarial drugs artesunic acid (ARTS) and dihydroqinghaosu (DQHS) in blood. Presently, this method has been validated to 4 micrograms/ml for ARTS and 200 ng/ml for DQHS. Pharmacokinetic studies in the rabbit show that after intravenous administration (100 mg/kg) ARTS is metabolized rapidly to DQHS and has a t1/2 of 1.7 min in blood. DQHS data were fit to non-linear regression models consisting of the sum of two exponential terms. For phases 1 and 2, t1/2 values of 3.0 +/- 0.4 and 29 +/- 2 min were calculated, respectively. In vitro studies in which ARTS was incubated with blood from various species show that rabbit blood hydrolyzes ARTS at a much greater rate than rat or human blood. Incubation of ARTS with rabbit blood in the presence or absence of diisopropylfluorophosphate suggested that this hydrolysis reaction is catalyzed by plasma and red blood cell esterases. These results suggest that future pharmacokinetic studies in both animals and man should focus on the measurement of DQHS rather than ARTS.

Structure-activity relationships of putative primaquine metabolites causing methemoglobin formation in canine hemolysates.

A rapid and reproducible in vitro test system was developed to measure the methemoglobin (MHb)-forming properties of various 8-aminoquinoline derivatives. Initial rates and extents of reaction were measured spectrophotometrically with either canine hemolysates from which ferrihemoglobin reductase was removed, or with purified human oxyhemoglobin (Hb). The results demonstrate that primaquine derivatives that can be oxidized to quinones or iminoquinones (5-hydroxy,6-desmethyl primaquine; 5-hydroxyprimaquine; 5,6-dihydroxy-8-aminoquinoline; and 5-hydroxy, 6-methoxy-8-aminoquinoline) are potent MHb-forming compounds. Studies on the extent of reaction in hemolysates and purified oxyhemoglobin suggest that the extent of MHb formation may be limited by the rate at which the corresponding iminoquinones or quinones arylate nucleophiles. The effects of glutathione, mannitol, ascorbate, and superoxide dismutase on the rate and extent of hemoglobin oxidation by 5,6-dihydroxy-8-aminoquinoline suggest that these compounds oxidize Hb similar to the mechanism known for dimethylaminophenol (DMAP), in which Hb oxidizes the quinoline to semiquinone radical and quinone species which are the oxidizing and arylating agents.

High-performance liquid chromatographic method for the analysis of a candidate 8-aminoquinoline antileishmanial drug using oxidative electrochemical detection.

An analytical method was developed for the quantitation of a candidate antileishmanial drug, 6-methoxy-8-(6-diethylaminohexylamino)-4-methylquinoline, dihydrochloride, in canine plasma. The assay utilized internal standard technique with a structural similar 8-aminoquinoline, 6-methoxy-8-(7-diethylaminoheptylamino)-4-methylquinoline, dihydrochloride, as the internal standard. The method employs a liquid-solid extraction procedure with prepackaged silica gel columns upon which the drug and internal standard are adsorbed, then selectively washed and eluted. Reversed-phase chromatography was then employed to analyze the extracted sample by means of oxidative electrochemical detection at +0.75 V. Good accuracy and precision were obtained over the range of concentration tested (10-1500 ng/ml plasma). Analyses of plasma samples from human volunteers given the drug demonstrate the method is also suitable for analysis of human plasma samples. The entire procedure is relatively simple and requires only 1 ml of plasma.

Deficiencies and improvement of methemoglobin assay.

A day-to-day variability in results was encountered when using the Dubowski method for the routine clinical determination of methemoglobin in blood. Therefore, studies were performed to determine the source(s) of variability in the method as described by Dubowski. It was determined that complete lysing of red blood cells is dependent upon both temperature of the buffer and the amount of lysing agent. Low buffer temperatures (less than 14 degrees C) produced highly variable results. This variability can be reduced by increasing the level of lysing agent to 40 mg per 20 mL of diluted blood. It was found that by using 37 degrees C buffer solution temperature and 40 mg Triton X-100 as lysing agent per 20 mL of diluted blood (1:20 with 0.25M sodium phosphate buffer, pH 7.4), the precision (percent coefficient of variation = 2%) and the accuracy (percent coefficient variation = 5.5%) were excellent.

Alteration of digoxin toxicity by 6-hydroxydopamine and soironolactone.

The possibility that the Na+-K+ ATPase of cardiac adrenergic neurons is the toxic receptor site of cardiac glycosides was investigated by performing a chemical sympathectomy in dogs using 6-hydroxydopamine to destroy the adrenergic neurons. No alteration was seen in the therapeutic, toxic, or lethal dose of digoxin after the administration of 6-hydroxydopamine, indicating that the toxic receptor of digoxin is not located on the adrenergic nerve endings. Pretreatment of control dogs with spironolactone increased the toxic and lethal dose of digoxin without changing the therapeutic dose of digoxin. However, spironolactone pretreatment of chemically sympathectomized dogs produced an increase pretreatment of chemically sympathectomized dogs produced an increase in the therapeutic, toxic, and lethal doses of digoxin. Therefore, the destruction of this neuronal tissue decreases the therapeutic effectiveness of digoxin in the presence of spironolactone, and abolishes the ability of spironolactone to alter the therapeutic ratio of digoxin.