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Biomedical subjects

D Scicchitano

Publications and source records attributed to D Scicchitano.

10 recordsLinked to original sources
PubMed2000

[Inflammatory pseudotumor of the lung. Diagnostic-therapeutic effectiveness of its radical resection].

Clinical, therapeutical observations and experience in 3 cases of pulmonary inflammatory pseudotumors (PIP) are presented. A retrospective analysis is made of cases with pulmonary "mass" suspected as malignant tumor, resected in a general surgery department between 1988 and 1995, and finally diagnosed as inflammatory pseudotumor. Three of the 10 cases originally diagnosed as malignant lung tumor were inflammatory pseudotumor (30%). Pulmonary inflammatory pseudotumors, may be a pitfall diagnosing a lung mass and implicate legal problems. Surgical resection leads to the final diagnosis in doubtful cases. A wide resection has a diagnostic aim and may preserve healthy parenchyma. Clinicians, pathologists and surgeons should accurately inform patients with doubtful diagnosis of pulmonary malignancy. Any decision should be kept altogether either choosing the simple observation or the timely surgical diagnostic and therapeutical approach.

Diagnosis, Differential↗
PubMed1988

Use of oligodeoxynucleotides containing O6-alkylguanine for the assay of O6-alkylguanine-DNA-alkyltransferase activity.

A sensitive assay procedure was developed for the measurement of the activity of mammalian O6-alkylguanine-DNA-alkyltransferase. The procedure utilized oligodeoxynucleotides containing O6-methylguanine as substrates for the reaction. The oligodeoxynucleotides were end labeled with 32P by the reaction with polynucleotide kinase and [gamma-32P]ATP and allowed to react with organ or cell extracts containing the alkyltransferase. The unmethylated product which was formed was separated from the substrate by reverse-phase high-pressure liquid chromatography. Since the repair by the alkyltransferase is bimolecular, the second order rate constants for the reaction between the labeled oligomer and repair protein from several different sources were determined. The amount of alkyltransferase present was then calculated from the amount of product formed and the appropriate second order rate constant for the reaction. Excellent agreement was obtained between the alkyltransferase levels determined in this procedure and those measured by conventional assay procedures in a variety of cell lines having both high and low activity. The method also gave results in good agreement with other assay procedures for a number of rat tissues, although a few tissues gave anomalous results owing to a high level of nuclease activity which degraded the substrate. This method should prove useful for the measurement of alkyltransferase activity in samples in which the activity is very low or the amount of material available is limited.

DNA Repair↗
PubMed1987

Specificity of O6-alkylguanine-DNA alkyltransferase.

Extensive investigations of the specificity of O6-alkylguanine-DNA alkyltransferase (AAT) have been carried out. These studies have shown that: (i) the mammalian protein differs from that of Escherichia coli in lacking the ability to remove methyl groups from O4-methylthymine; (ii) the protein can remove longer alkyl groups from the O6 position but the rate of repair declines as the chain length increases; (iii) O6-methylguanine in RNA is much less active as a substrate for the protein than O6-methylguanine in double-stranded DNA; (iv) the free-base O6-alkylguanine is a very weak substrate for the protein so that reaction with it leads to the loss of alkyltransferase activity. (This property can be used to deplete AAT in cultured cells and in tissues and tumours after administration of O6-methylguanine); and (v) oligodeoxynucleotides containing O6-methylguanine are substrates for AAT. Such oligodeoxynucleotides can be labelled with 32P at very high specific activity and can be used in an ultrasensitive assay for AAT activity.

Alkylation↗
PubMed1986

Repair of oligodeoxynucleotides containing O6-methylguanine by O6-alkylguanine-DNA-alkyltransferase.

O6-Alkylguanine-DNA-alkyltransferase is a DNA repair protein known to carry out the transfer of alkyl groups from the O6-position of guanine in alkylated DNA to a cysteine acceptor site contained within its own protein sequence. We have examined the ability of this protein isolated from either E. coli or mammalian cells to perform this repair reaction in short oligodeoxynucleotides. Dodecadeoxynucleotides of the sequence 5'-dCGNGAATTCm6GCG-3' where N is any one of the normal four bases were all repaired very rapidly by the protein with 50% repair in less than 15 s at 0 degree C. The hexadeoxynucleotide 5'-dCGCm6GCG-3' was repaired slightly more slowly with 50% removal taking 7 min at 0 degree C and 1.5 min at 37 degrees C. The tetradeoxynucleotide 5'-dTm6GCA-3' was also a substrate but was repaired much more slowly requiring 45 min for 50% repair at 37 degrees C. These results indicate that (a) the AGT has a strong but not absolute preference for double-stranded DNA substrates; (b) the repair of O6-methylguanine is independent of the base opposite the lesion; and (c) that oligodeoxynucleotides as short as tetramers are substrates for repair by this protein.

DNA Repair↗
PubMed1985

Repair of O6-propylguanine and O6-butylguanine in DNA by O6-alkylguanine-DNA alkyltransferases from rat liver and E. coli.

DNA substrates containing O6-n-butylguanine, O6-iso-butylguanine, O6-n-propylguanine and O6-iso-propylguanine were prepared by reaction of calf thymus DNA with the appropriate N-alkyl-N-nitrosourea. These substrates were used to test the ability of O6-alkylguanine-DNA alkyltransferases from Escherichia coli and rat liver to remove such alkyl groups from the O6-position of guanine. It was found that all of these adducts were removed by the alkyltransferases, but the branched alkyl chain iso-butyl- and iso-propyl adducts were removed very slowly. Also, when tested with a DNA substrate containing both O6-n-propylguanine and O6-iso-propylguanine, the alkyltransferases removed almost all of the n-propyl-adduct before the iso-propyl-adduct was attacked. Both alkyltransferases showed a decreasing rate of reaction as the size of the alkyl group increased, but there was a significant difference between the rat liver and E. coli alkyltransferase in the relative rates. The rat liver alkyltransferase repaired O6-methylguanine more slowly than the E. coli protein, but was considerably more rapid than the bacterial equivalent when acting on n-propyl- and n-butyl-adducts. The relative rates of repair were methyl much greater than ethyl greater than n-propyl greater than n-butyl greater than iso-propyl, iso-butyl for the E. coli alkyl-transferase and methyl greater than ethyl, n-propyl greater than n-butyl greater than iso-propyl, iso-butyl greater than 2-hydroxyethyl for the rat liver protein. These results indicate that differential rates of repair may contribute to the relative risks of carcinogenesis and mutagenesis by exposure to alkylating agents of different size and that rates of repair may be species specific and must be determined from specific measurements rather than extrapolated from data on other organisms.

Animals↗
PubMed1985

Studies of the repair of O6-alkylguanine and O4-alkylthymine in DNA by alkyltransferases from mammalian cells and bacteria.

O6-Methylguanine in DNA is repaired by the action of a protein termed O6-alkylguanine-DNA alkyltransferase (AT) which transfers the methyl group to a cysteine residue in its own sequence. Since the cysteine which is methylated is not regenerated rapidly, if at all, the capacity for repair of O6-methylguanine is limited by the number of molecules of the AT available within the cell. The level and inducibility of the AT differed greatly in different mammalian cell types and species with the highest levels in human tissues and in liver and the lowest levels in brain. Only a small induction occurred in rat liver in response to exposure to alkylating agents. In E. coli such exposure increased the activity more than 100-fold. The At was not specific for methyl groups but also removed ethyl, 2-hydroxyethyl, n-propyl, isopropyl and n-butyl groups from the O6-position in DNA. The protein isolated from E. coli removed methyl groups much more rapidly than the larger alkyl groups but the mammalian AT isolated from rat liver showed much less difference in rate with adducts of different size. Ethyl and n-propyl groups were removed by the rat liver AT only three to four times more slowly than methyl groups. Another important difference between the bacterial and mammalian ATs is that the bacterial protein was also able to remove methyl groups from the O4-position of thymine in methylated DNA or poly(dT) but the AT from rat liver or human fibroblasts did not repair O4-methylthymidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Comparison of repair of methylated pyrimidines in poly(dT) by extracts from rat liver and Escherichia coli.

Partially purified preparations of O6-alkylguanine-DNA alkyltransferase from rat liver and E. coli were tested for their ability to repair O4-methylthymine in a methylated poly(dT) X poly(dA) substrate. The bacterial preparation readily carried out this reaction, but no loss of O4-methylthymine was obtained with the rat liver protein. These results indicate a significant difference in specificity between the mammalian and bacterial proteins which could have important consequences for carcinogenesis and mutagenesis by alkylating agents in mammalian cells.

Animals↗
PubMed1984

Comparison of the rates of repair of O6-alkylguanines in DNA by rat liver and bacterial O6-alkylguanine-DNA alkyltransferase.

The rates of loss of O6-methylguanine and O6-ethylguanine from rat liver DNA were determined over a time period of 15 min to 4 hr after various doses (5 micrograms/kg to 2 mg/kg) of dimethylnitrosamine and diethylnitrosamine which produced total amounts of these adducts in the range of 300 to 16,000 molecules/cell. This amount is considerably less than the content of O6-alkylguanine-DNA alkyltransferase protein (approximately 60,000 molecules/hepatocyte), and during the time period studied, the adducts were found to be lost with pseudo-first order kinetics. The half-life for O6-methylguanine was 47 min. O6-Ethylguanine was removed 3.6 times more slowly with a half-life of 172 min. The ability of partially purified rat liver O6-alkylguanine-DNA alkyltransferase to remove O6-methylguanine and O6-ethylguanine from [3H]alkyl-labeled DNA substrates in vitro was measured, and it was found that O6-methylguanine was removed 3.4 times more rapidly than was O6-ethylguanine. These results are consistent with the hypothesis that most, if not all, of the repair of these adducts which occurs within the first 4 hr after treatment is due to the alkyltransferase protein. Diethylnitrosamine, which is slightly more potent as a carcinogen to rat liver, produced a total amount of O6-ethylguanine of 3.7 mumol/mol guanine/mg compared to O6-methylguanine (28 mumol/mol guanine/mg) given by dimethylnitrosamine. The slower rate of loss of the ethyl adduct is not sufficient to account for this difference, and the results, therefore, support the concept that other DNA adducts (possibly O-alkylpyrimidines) contribute to the initiation of tumors by diethylnitrosamine. Preliminary evidence that the rat liver alkyltransferase can also remove hydroxyethyl groups from DNA at a rate slower than removal of ethyl groups was also obtained. Bacterial O6-alkylguanine-DNA alkyltransferase was shown to remove methyl, ethyl, and hydroxyethyl groups from the O6 position of guanine in DNA using fluorescence detection to quantitate these adducts. The bacterial protein removed methyl groups very rapidly but was much slower than the rat liver protein on the larger adducts. These results suggest that the relative rates of repair of different alkyl groups may be species specific and must be determined experimentally in the cell of interest before conclusions concerning biological effects can be drawn.

Alkylation↗
PubMedDate not supplied

[Reconversion after Hartmann's procedure. Our experience].

An increasing number of intestinal reconversion after Hartmann have been performed in recent years, especially due to improved surgical techniques and progressively lengthened lifespan. The authors report 33 cases of intestinal recanalization of 100 interventions according to Hartmann from 1984 to 1996 (21 not neoplastic pathologies, 12 neoplasias). The variables considered included: patient age, type of disease requiring intervention according to Hartmann, oncologic characteristic of patients with neoplasia, interval between the two interventions, preoperative examinations performed, morbidity and mortality after reconversion. Furthermore, the fundamental indications for reconversion are described, in particular in patients with neoplasias (CEA, transanal echo, total body Ct, anal manometry). The low frequency of preoperative complications, zero mortality, satisfactory long-term follow-up (only one patient with neoplastic relapse) indicate that colon-rectal reconversion can also be performed in the elderly and patients with neoplasias with favorable prognosis.

Aged↗