Biomedical subjects
Publications and source records attributed to L H Breimer.
DNA repair limits the mutagenic, and thereby the carcinogenic, effect of DNA modifications. Free radicals, particularly reactive oxygen species, induce all forms of DNA damage, including base modifications, base free sites, strand breakage, and cross-links. These lesions are repaired by a variety of enzymes of partly overlapping substrate specificity, some of which may be induced.
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The calcitonin/CGRP multigene complex encodes a family of peptides: calcitonin, its C-terminal flanking peptide, katacalcin, and a third novel peptide, calcitonin gene-related peptide (CGRP). The 32-amino acid peptide calcitonin inhibits the osteoclast, thereby conserving skeletal mass during periods of potential calcium lack, such as pregnancy, growth, and lactation. This hormonal role is emphasized by observations that lower circulating calcitonin levels are associated with bone loss and that calcitonin replacement prevents further bone loss. Structurally, CGRP resembles calcitonin and has been implicated in neuromodulation and in the physiological regulation of blood flow. Here we review the molecular genetics, structure, and function of the calcitonin-gene peptides as analyzed in the laboratory and focus on more recent clinical studies relating to disorders and therapeutics.
The effects of epidural analgesia on plasma calcitonin gene-related peptide (CGRP) values during and after hysterectomy were investigated in 14 healthy patients. In seven patients who received general anaesthesia alone for pelvic surgery, there were no significant changes in plasma CGRP concentrations. In the remaining patients, who received extensive epidural blockade in addition to general anaesthesia, there were again no significant changes in plasma CGRP values. This was in spite of profound sympathetic blockade, as shown by marked hypotension and a significant decline in plasma catecholamines. The epidural group of patients showed the expected attenuation of the glucose, cortisol and growth hormone responses to surgery. The results show that circulating CGRP is unlikely to be involved in the modulation of peripheral vascular tone during pelvic surgery under either general or epidural anaesthesia.
Calcitonin (CT) is produced ectopically from a variety of non-thyroidal cancers. The CT genes also encode another peptide, calcitonin gene-related peptide (CGRP) which is a potent vasodilator. In the present study we have used immunochemical and chromatographic methods to demonstrate the presence and characterize the molecular forms of CGRP in cultured human cancer cells. Using two highly sensitive and specific radioimmunoassays, we have detected immunoreactive CGRP (i-CGRP) in cell extracts and cell-exposed media of cultured promyelocytic leukaemia (HL60) and bronchogenic carcinoma (BEN) cells. The mean i-CGRP content of the HL60 and BEN cell extracts was 2 and 45 pmol/g wet weight respectively. On gel filtration and high performance liquid chromatography, the immunoreactive material was found to be heterogeneous, though a major proportion co-eluted with synthetic human CGRP(1-37), suggesting structural identity with the intact CGRP molecule. Finally, we have discussed some interesting features of CT-gene peptide expression in tumour cells.
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Explore the source record for details and available documents.
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Despite being products from the same gene, there is clearly a marked divergence in the distribution and physiological role of calcitonin and CGRP. Whereas calcitonin is predominantly distributed in the thyroid, CGRP is abundant in the nervous system throughout the body. Though the peptides have only weak structural homologies, a generally similar conformation enables them to interact at each other's receptors. Hence the pharmacological effects of the peptides faintly resemble one another. Calcitonin receptors are mainly found on osteoclasts and at certain sites in the nervous system. CGRP binding sites are abundant in the cerebellum and blood vessels. Calcitonin is a circulating hormone controlling osteoclastic activity. CGRP acts as a neurotransmitter or neuromodulator centrally, and released from perivascular nerve terminals, it modulates arteriolar tone. Released from motoneurones, CGRP may also play a trophic role regulating the muscle acetylcholine receptor state. The next decade should establish the physiological role of CGRP and the regulation of the expression of the calcitonin/CGRP gene complex.
The spectrum of mutations induced by ionizing radiation at two non-essential genetic loci varies markedly. Those at the adenine phosphoribosyl transferase (aprt) locus predominantly have no detectable alterations of gene structure on Southern blots, while those at the hypoxanthine guanine phosphoribosyl transferase (hprt) locus are largely massive deletions eliminating all coding sequence. Insertion mutations were detected at both loci. To characterize the sequence alterations producing the minor changes at the aprt locus, two mutant genes were cloned from lambda genomic libraries and sequenced. One of these mutants proved to be a 20 base-pair deletion formed between two short (3 base-pair) direct repeat sequences, while the second was the result of a 58 base-pair insertion accompanied by a 13 base-pair deletion.
A DNA glycosylase activity which excises fragmented thymine residues has been identified in cell extracts from Drosophila melanogaster embryos. The enzyme has an apparent Mr = 40,000, acts preferentially on double-stranded polydeoxyribonucleotide substrate and requires no co-factors. The DNA glycosylase presumably acts in excision-repair of pyrimidines damaged by hydroxyl radicals and other oxidizing species. This is the first identification of a DNA glycosylase in Drosophila cells.
A DNA glycosylase which catalyzes the release of thymine residues damaged by ring saturation, fragmentation, or ring contraction from double-stranded DNA has been used to characterize such base derivatives in gamma-irradiated DNA. It is shown by chromatographic analysis that irradiation of DNA in neutral solution generates the ring-saturated forms cis-thymine glycol, trans-thymine glycol, and a monohydroxydihydrothymine, probably 6-hydroxy-5,6-dihydrothymine. The latter compound is only observed after irradiation under hypoxic conditions. The ring-contracted thymine derivative 5-hydroxy-5-methylhydantoin is also formed, and it is the major lesion after irradiation of DNA under O2. Ring-fragmented products such as methyltartronylurea were only generated in small quantities. Isolation and analysis of the DNA from gamma-irradiated human cells also revealed the formation of ring-saturated thymine derivatives, but 5-hydroxy-5-methylhydantoin was not found in this case.
The main forms of base damage in polydeoxyadenylic acid gamma-irradiated under hypoxic conditions are due to saturation and fragmentation of the adenine imidazole ring. An irradiated polymer was annealed with an equimolar amount of poly (dT) to generate a double-stranded polydeoxyribonucleotide containing scattered damaged base residues. On incubation of the latter with partially purified cell extracts of E.coli, imidazole ring-opened adenine, i.e. 4,6-diamino-5-formamidopyrimidine, was released in free form by a DNA glycosylase activity. The enzyme has been purified 4,500-fold, has Mr = 29,000, and appears to be identical with the previously described DNA repair enzyme formamidopyrimidine-DNA glycosylase.
A DNA glycosylase activity that excises oxidized, fragmented thymine residues from a polydeoxyribonucleotide has been purified 9,500-fold to apparent homogeneity from Escherichia coli. The purified enzyme also excises thymine glycol and cleaves DNA at apurinic sites, and appears to be identical with E. coli DNA endonuclease III. The enzyme catalyzes the release of several different forms of oxidized thymine, including urea, methyltartronylurea and 5-hydroxy-5-methylhydantoin. The molecular weight of the native protein is 25,000, and the same value is obtained for the denatured homogeneous protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
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