Individual response of humans to ionising radiation: governing factors and importance for radiological protection.

Tissue reactions and stochastic effects after exposure to ionising radiation are variable between individuals but the factors and mechanisms governing individual responses are not well understood. Individual responses can be measured at different levels of biological organization and using different endpoints following varying doses of radiation, including: cancers, non-cancer diseases and mortality in the whole organism; normal tissue reactions after exposures; and, cellular endpoints such as chromosomal damage and molecular alterations. There is no doubt that many factors influence the responses of people to radiation to different degrees. In addition to the obvious general factors of radiation quality, dose, dose rate and the tissue (sub)volume irradiated, recognized and potential determining factors include age, sex, life style (e.g., smoking, diet, possibly body mass index), environmental factors, genetics and epigenetics, stochastic distribution of cellular events, and systemic comorbidities such as diabetes or viral infections. Genetic factors are commonly thought to be a substantial contributor to individual response to radiation. Apart from a small number of rare monogenic diseases such as ataxia telangiectasia, the inheritance of an abnormally responsive phenotype among a population of healthy individuals does not follow a classical Mendelian inheritance pattern. Rather it is considered to be a multi-factorial, complex trait.

Ikaros is a mutational target for lymphomagenesis in Mlh1-deficient mice.

Deficiencies in DNA mismatch repair (MMR) result in replication errors within key tumor suppressor genes or oncogenes, and cause hereditary nonpolyposis colorectal cancer (HNPCC). Hematological malignancy with microsatellite instability is also associated with defective MMR, but little is known about the target genes for MMR. Here we identified Ikaros, a master transcription factor of lymphoid lineage commitment and differentiation, as a mutational target in spontaneous and radiation-induced T-cell lymphomas in Mlh1-deficient mice. Three quarters of lymphomas lacked Ikaros protein expression, which resulted from a frameshift mutation that created a stop codon. Mononucleotide repeat sequences at 1029-1034(C)6 and 1567-1572(G)6 in Ikaros were mutational hot spots with a one-base deletion occurring with a frequency of 45 and 50%, respectively. Point mutations and splicing alterations were also observed. In total, 85% of the lymphomas showed aberrations in Ikaros. The characteristic of Mlh1-deficient lymphomas is harboring of multiple mutations simultaneously in the same tumor, displaying a combination of two frameshift mutations at different repeats, frameshift and point mutations, and/or deletion mutations. This is the first report of Ikaros mutations coupled with Mlh1 deficiency in lymphomagenesis.

Human cord blood cells transplanted into chronically damaged liver exhibit similar characteristics to functional hepatocytes.

Human umbilical cord blood (CB) cells have many advantages as a source for stem cell transplantation because of immaturity and availability. It has been reported that CB cells transplanted into an injured liver displayed hepatocyte-like phenotypes. However, there have been few studies to characterize CB-derived hepatocyte-like cells (HLCs). In this study, CB cells were transplanted into mice with 2 types of liver damage: transient and chronic damage. We analyzed the expression of hepatic differentiation markers in CB-derived HLCs. In the liver of NOD/SCID mice with transient damage, CB-derived HLCs were detected infrequently at 3 weeks after transplantation. In contrast, in the liver of SCID mice damaged chronically by a urokinase-type plasminogen activator transgene under the control of albumin promotor/enhancer (ALB-uPA/SCID mice), more human HLCs colonized the host liver compared with hosts with transiently damaged livers. The CB-derived HLCs in both the transiently and the chronically damaged liver expressed a few markers of human hepatocytes, whereas the transcripts related to mature hepatic functions, including cytochrome P450s, were detected only in the ALB-uPA/SCID mice. These data indicated that CB cells were able to display a similar phenotype to functional hepatocytes in the recipient liver with chronic damage. CB cells may represent a transplantable source for chronic decompensated liver disease.

Overexpression of mitochondrial manganese superoxide dismutase protects against radiation-induced cell death in the human hepatocellular carcinoma cell line HLE.

We investigated the potential role of mitochondrial manganese superoxide dismutase (Mn-SOD) in protective activity against irradiation by analyzing cell viability by a colony formation assay and by detecting apoptosis in stably human Mn-SOD gene-transfected HLE, a hepatocellular carcinoma cell line. We found that overexpression of Mn-SOD reduced the levels of reactive oxygen species in the mitochondria and intracellular phospholipid peroxidation product (4-hydroxy-2-nonenal) and prevented cell death. The production of intracellular nitric oxide after irradiation was not changed by Mn-SOD overexpression. The results suggested that Mn-SOD might play an important role in protecting cells against radiation-induced cell death by controlling the generation of mitochondrial reactive oxygen species and intracellular lipid peroxidation.

Increased serum vascular endothelial growth factor levels and intrathyroidal vascular area in patients with Graves' disease and Hashimoto's thyroiditis.

Vascular endothelial growth factor (VEGF) is one of the angiogenic factors. We examined both thyroid volume and intrathyroidal vascular area by color flow Doppler ultrasonography in patients with Graves' disease (GD), Hashimoto's thyroiditis (HT), and subacute thyroiditis. The serum concentrations of thyroid hormones, TSH, TSH receptor antibodies, and VEGF were also examined. There was a significant increase in serum VEGF levels in patients with untreated GD and goitrous HT compared with those in healthy subjects. The serum VEGF levels in untreated patients with subacute thyroiditis were significantly higher than those in patients with untreated GD or HT. There was a significant correlation between serum VEGF levels and the ratio of intrathyroidal vascular area and thyroid area in untreated patients with GD who had a goiter larger than or equal to 40 cm3. There was also a significant correlation between serum VEGF and TSH levels in patients with HT who were hypothyroid and had a goiter. Serum VEGF levels decreased significantly in these patients after treatment; this was accompanied by a significant decrease in intrathyroidal vascular area and thyroid volume. Our study demonstrates that VEGF appears to play an important role in intrathyroidal angiogenesis in patients with GD and goitrous HT.

Induction of apoptosis and necrosis by zinc in human thyroid cancer cell lines.

Zinc at concentrations of 150, microM or higher induced necrosis as well as apoptosis in thyroid cancer cell lines. Necrosis was induced by zinc in a dose-dependent manner, whereas apoptosis did not increase at higher concentrations of zinc. The expression of the antiapoptotic protein phosphorylated Bad was markedly increased, whereas the expression of the proapoptotic proteins Bax and Bad decreased following Zn(2+) exposure. Zn(2+) induced rapid degradation of IkappaB, and an increase in the binding of nuclear transcription factor-kappaB (NF-kappaB). These observations indicate that antiapoptotic pathways were activated in thyroid cancer cells following exposure to Zn(2+). This may be a self-defence mechanism against apoptosis and may underlie the general resistance of thyroid cancer cells to apoptotic stimuli. Zinc may be a potential cytotoxic agent for the treatment of thyroid cancer.

Molecular cloning and sequencing of cDNA encoding goat pre alpha-lactalbumin.

In poly(A)+RNA extracted from a lactating goat mammary gland, mRNA of about 750 nucleotides was shown to encode pre alpha-lactalbumin by using in vitro translation and immunoprecipitation. From the total poly(A)+RNA, the cDNA library was constructed using the Escherichia coli plasmid pUC18; it was screened with the oligodeoxyribonucleotide probe corresponding to the amino acid sequence of Trp60-Gln65 of goat alpha-lactalbumin. A plasmid containing almost full-length cDNA of goat pre alpha-lactalbumin, pGLA-1, was identified. The cDNA insert of pGLA-1 comprises 727 base pairs and contains the signal peptide and mature protein sequence.

Radiation-associated loss of heterozygosity at the Znfn1a1 (Ikaros) locus on chromosome 11 in murine thymic lymphomas.

Although information on the molecular pathways in radiation carcinogenesis is accumulating, the data are still relatively scanty. To find the tumor suppressor locus associated with radiation carcinogenesis, we determined the frequency and distribution of loss of heterozygosity (LOH) of X-ray-induced thymic lymphomas of B6C3F(1) mice using 58 microsatellite markers and compared the results with those for spontaneous lymphomas and N-ethylnitrosourea (ENU)-induced lymphomas. Based on the results, we describe a unique locus with frequent LOH in the centromeric region of chromosome 11 of X-ray-induced lymphomas. This locus has never been observed to be altered similarly in either ENU-induced or spontaneous lymphomas, suggesting radiation-specific molecular alteration. The LOH patterns of individual thymic lymphomas indicated that the common region of LOH was located within 1.6 cM between D11Mit62 and D11Mit204, a region syntenic to human chromosome 7p13. Linkage analysis revealed that the markers of the common LOH region were genetically linked to Ikaros (now known as Znfn1a1), a master gene of lymphopoiesis. Although the presence of radiation-associated LOH in other loci cannot be ruled out, these results suggest a novel molecular pathway in induction of thymic lymphomas by ionizing radiation.

Low frequency of Ras gene mutation in spontaneous and gamma-ray-induced thymic lymphomas of scid mice.

Scid mice, which have a defect in the capacity to repair DNA double-strand breaks, were highly prone to the induction of thymic lymphomas after exposure to ionizing radiation; approximately 70% of mice developed lymphomas within 1 year after exposure to 1-3 Gy, whereas approximately 20% of unirradiated control mice developed lymphomas. To gain information on the possible role of Ras activation in development of thymic lymphomas in scid mice, we have examined both the frequency and the spectrum of Kras and Nras mutations in spontaneous and radiation-induced lymphomas. Neither activated Kras nor Nras genes were detected in spontaneous lymphomas, while Kras mutations increased in a dose-dependent manner in radiation-induced lymphomas. However, Kras mutations were infrequent (6% in lymphomas in mice exposed to 1 Gy, 12.5% in those exposed to 2 Gy, 16.7% in those exposed to 3 Gy), and no mutations were detected in Nras genes, suggesting that Ras mutation was not significantly involved in the development of thymic lymphomas in scid mice. Analysis of the spectrum of Kras mutations demonstrated unique mutations in both codons 13 (GGC to GAC) and 61 (CAA to CTA) in addition to the commonly identified substitution of GAT for GGT in codon 12 of Kras.

Gastric mucosal blood flow and gastric secretion following intravenous administration of 5-fluorouracil in anesthetized rats.

Acute gastric mucosal lesions are often observed after the intravenous administration of high doses of anticancer drugs. To investigate the acute toxic effects of such anticancer therapy on the gastric mucosa, 5-fluorouracil (5-FU) was administered intravenously to anesthetized rats. Gastric mucosal blood flow (GMBF) was measured continuously using laser Doppler velocimetry. Acid secretion was measured using a perfusion method for 1 h after the administration of 5-FU. No significant change was observed with a low dose of 5-FU (50 mg/kg), but a high doses of 5-FU (100 or 200 mg/kg) caused a significant decrease in GMBF in a dose-dependent manner. The selective antagonist of the muscarinic acetylcholine receptor, pirenzepine, prevented the decrease in GMBF with high doses of 5-FU. Acid secretion decreased after the administration of 5-FU, but not significantly. This study indicates that a decrease in GMBF may be an important factor in gastric mucosal injury induced by chemotherapy. Pirenzepine may prevent the gastric mucosal lesions which are induced by the administration of 5-FU.

Genetic susceptibility to thymic lymphomas and K-ras gene mutation in mice after exposure to X-rays and N-ethyl-N-nitrosourea.

PURPOSE: Ras activation is one of the major mechanisms for the development of murine thymic lymphomas by radiation and chemical carcinogens. To gain insight into the relationship between genetic susceptibility and ras gene mutation, the frequency and spectrum of ras gene mutation was examined in thymic lymphomas from susceptible and resistant mice. MATERIALS AND METHODS: K- and N-ras mutations in thymic lymphomas that arose in X-ray-irradiated and N-ethyl-N-nitrosourea (ENU)-treated mice of susceptible C57BL/6, rather resistant C3H and their hybrid B6C3F1 were analysed by polymerase chain reaction-single-strand conformation polymorphism and subsequent DNA sequencing. RESULTS: C57BL/6 exhibited a higher incidence of thymic lymphomas after exposure to X-rays and ENU than C3H, with B6C3F1 being intermediate. K-ras gene mutations occurred frequently in the pathogenesis of ENU-induced thymic lymphomas in susceptible C57BL/6 as opposed to resistant C3H. The ras mutations were more frequent in ENU-induced thymic lymphomas than X-ray-induced thymic lymphomas, and with the latter, there was no clear evidence for strain differences, suggesting that the genetic susceptibility to X-rays was independent of ras activation. The mutations of K-ras in thymic lymphomas from C57BL/6 were predominantly GGT to GAT in codon 12, whereas this mutation type was never found in those from C3H. No strain difference was observed in the nucleotide sequence or expression levels of O(6)-alkylguanine alkyltransferase, indicating that this enzyme did not account for the genetic susceptibility to ras activation. CONCLUSIONS: The results indicate that there is a clear strain and carcinogen dependency of K-ras mutation and that the frequency of ras mutation might determine the genetic susceptibility to ENU-induced lymphomagenesis, whereas pathways independent of ras activation might determine the susceptibility to X-ray-induced lymphomagenesis.

Characteristic association between K-ras gene mutation with loss of heterozygosity in X-ray-induced thymic lymphomas of the B6C3F1 mouse.

PURPOSE: To elucidate the characteristics of radiation carcinogenesis, the spectra of K- and N-ras oncogene mutations, loss of heterozygosity (LOH) and their association in X-ray-induced thymic lymphomas (TL) were determined by comparing with those of N-ethyl-N-nitrosourea (ENU)-induced and spontaneously occurring TL. MATERIALS AND METHODS: TL that arose in untreated, X-ray-irradiated and ENU-treated B6C3F1 mice were examined both for K- and N-ras mutations by PCR-SSCP and DNA sequencing and for LOH by PCR with polymorphic microsatellite markers. RESULTS: (1) ras gene mutations were found in a proportion of TL from X-ray-exposed (approximately 20%) and ENU-treated (30-40%) mice while no ras gene mutations were found in spontaneous TL. N-ras mutations were rare. (2) The spectrum of ras gene mutations was diverse and seemed to differ little between X-ray-induced and ENU-induced TL, even though there was a higher frequency of ras mutations in ENU-induced TL that clustered to K-ras codon 12. (3) The X-ray-induced TL showing K-ras mutation were associated with LOH on chromosome 6, while those showing no K-ras mutation were associated with high frequency of LOH on chromosomes 4, 11 and 12. CONCLUSION: These results demonstrate that, in the B6C3F1 mouse TL, X-ray-induced lymphomagenesis showed both the co-expression, yet low occurrence of allelic imbalance on chromosome 6 and K-ras mutation, and exclusive expression of frequent allelic imbalance on chromosomes 4, 11 and 12 and K-ras mutation.

Muscle weakness in Parkinson's disease: a follow-up study.

We compared isokinetic muscle strength between initial and subsequent measurements in 10 patients who could repeat the same testing later among 23 previously described patients with Parkinson's disease. Patients were divided into two groups according to changes in clinical condition between the times of the first and the subsequent measurements. For patients who had improved, both extension and flexion on the more affected side showed significantly greater torque at 15 rpm in the later than the earlier measurement. For patients who had worsened, both extension and flexion on the more affected side showed significantly less torque at 5 and 15 rpm in the later than the earlier measurement. Although isokinetic muscle strength is likely to depend on movement velocity in the early stages of Parkinson's disease, it may be influenced by bradykinesia, as the disease progresses. Speed-force correlation seen in these patients may give clues to the understanding of the pathophysiology of bradykinesia.

Reduced sensitivity to and ras mutation spectrum of N-ethyl-N-nitrosourea-induced thymic lymphomas in adult C.B-17 scid mice.

Scid mice are defective in the ability to repair DNA double strand breaks and, as a consequence, their cells are radiosensitive. Further, they have been shown to be prone to develop thymic lymphomas (TLs) after small doses of ionizing radiation. Little is known, however, on the role of scid mutation in chemical carcinogenesis. To determine if scid mutation increased predisposition to chemical carcinogenesis, we examined both the susceptibility of scid mice to N-ethyl-N-nitrosourea (ENU)-induced lymphomagenesis and the involvement of ras gene activation. Adult female mice at 8 weeks of age were given ENU in their drinking water at 400 ppm for 2-10 weeks. Contrary to expectations, we observed a two to three-fold reduction in TL development in the scid mice. The highest incidence was achieved by ENU treatment for 8 weeks for scid and wild-type C.B-17 mice, of 42 and 85%, respectively (P<0.05). We investigated whether this was attributable to the usage of the ras mutation pathway. There was, however, no significant difference in the frequency and spectrum of K-ras mutation between the scid and wild-type C.B-17 mice. Most of the K-ras mutations were either GGT to GAT transition in codon 12 (11/23: 48%) or CAA to CCA transversion in codon 61 (8/23: 35%) that was independent of scid background. The incidence of N-ras mutation was very low. These results indicate that scid mice are less susceptible to ENU-induced lymphomagenesis and ras gene mutation frequently occurs in both scid and wild-type C.B-17 mice.

Biosynthesis of kalafungin in Streptomyces tanashiensis.

The mutants of Streptomyces tanashiensis strain Kala, which were specifically blocked in the synthesis of the benzoisochromanequinone antibiotic kalafungin, were isolated and classified into seven phenotypic classes on the basis of the antibiotic activity and cosynthetic properties. The polarity of cosynthetic reactions and the production of kalafungin by a converter strain showed that the seven mutant classes could be arranged in the most probable linear sequence of biosynthetic blocks. Since kalafungin, which closely resembles the undimerized form of actinorhodin, was accumulated in one of the biosynthetically blocked mutants of the actinorhodin-producing Streptomyces coelicolor A3(2), the cosynthesis between kalafungin-nonproducing mutants of S. tanashiensis and actinorhodin-nonproducing mutants of S. coelicolor was performed. The results of these experiments showed that the early steps in kalafungin biosynthesis in S. tanashiensis and actinorhodin biosynthesis in S. coelicolor were similar, but the entire biosynthetic pathway of kalafungin in these two streptomycetes was not identical.

Cloning of large DNA fragments, which hybridize with actinorhodin biosynthesis genes, from kalafungin and nanaomycin A methyl ester producers and identification of genes for kalafungin biosynthesis of the kalafungin producer.

Large actI, III-homologous DNA fragments were isolated from genomic libraries of the strains that produce the benzoisochromanequinone antibiotics kalafungin and nanaomycin A methyl ester, Streptomyces tanashiensis strain Kala and Streptomyces sp. OM-173, respectively. These libraries were prepared in Escherichia coli JM108 by using a novel Streptomyces-E. coli bifunctional cosmid, pKU205, and screened with polyketide synthase genes (actI and III) for actinorhodin biosynthesis from Streptomyces coelicolor A3(2) as probes. The cloned DNA fragments (28 and 42 kb) were analyzed by hybridization with DNA containing actinorhodin biosynthetic genes (actI, II, III, IV, VA, VB, VI and VII). Both fragments hybridized with the actI, III, VA and VI regions, but not with the actII, IV, VB and VII regions. The cloned fragment of S. tanashiensis DNA was analyzed by complementation tests with kalafungin-nonproducing mutants. Seven genes (kalI approximately VII), which correspond to seven steps in kalafungin biosynthesis, were found to be located on a 14 kb continuous DNA fragment. Five of the genes were located on the regions homologous to the genes for actinorhodin biosynthesis, but the other two genes were not. Although kalafungin is an intermediate or shunt product in actinorhodin biosynthesis in S. coelicolor A3(2), the genes for kalafungin biosynthesis in S. tanashiensis are not identical with those in S. coelicolor A3(2).

Production of the new antibiotic tetrahydrokalafungin by transformants of the kalafungin producer Streptomyces tanashiensis.

The new antibiotic tetrahydrokalafungin was produced by the transformants of kalafungin producing S. tanashiensis and kalafungin-nonproducing mutants carrying the recombinant plasmid pKU523. This plasmid consists of pKU501 (J. Antibiotics 44: 995 approximately 1005, 1991) which contains the gene cluster for kalafungin biosynthesis, and additional 5 kb stability region of SCP2*.

Pradimicins T1 and T2, new antifungal antibiotics produced by an actinomycete. II. Structures and biosynthesis.

Pradimicins T1 and T2 are new members of the pradimicin family of antibiotics produced by an actinomycete strain AA3798. Pradimicins T1 and T2 are dihydrobenzo[a]naphthacenequinones substituted with 3 and 2 sugar moieties, respectively. The salient feature in their structures is an L-xylose attached to the phenolic hydroxyl group at C-11. Bioconversion experiments using a blocked mutant B-54 of strain AA3798 not only explored a plausible biosynthetic pathway of pradimicins T1 and T2, but also provided evidence of 5S,6S configuration.

Biosynthesis of the pradimicin family of antibiotics. I. Generation and selection of pradimicin-nonproducing mutants.

Germinated spores of Actinomadura verrucosospora subsp. neohibisca E-40, a high pradimicins producer, were mutagenized by N-methyl-N'-nitro-N-nitrosoguanidine and/or UV treatment. Thirty-seven mutants which did not produce pradimicin were selected to test for cosynthesis ability, and classified into nine classes. On the basis of their cosynthesis ability and bioconversion results, we concluded that strain JN-213 (class III) was a true converter and that strains JN-219 (class IV), JN-47 (class V) and JNU-46 (class VI) were secretors accumulating biosynthetic intermediates of pradimicin, and that strains JN-59 (class VII), JN-58 (class VIII) and JN-207 (class IX) were producers of shunt metabolites of pradimicin biosynthesis. TLC and HPLC analyses of the fermentation broths of individual strains showed that 8 new compounds were produced along with pradinone I, pradimicinone I, 11-O-demethylpradimicinone II and 7-O-methylpradimicinone II.

Biosynthesis of the pradimicin family of antibiotics. III. Biosynthetic pathway of both pradimicins and benanomicins.

The biosynthetic pathway of the pradimicin-benanomicin family of antibiotics was investigated by using sinefungin and blocked mutants derived from Actinomadura verrucosospora subsp. neohibisca E-40 (a high pradimicin producer) or Actinomadura sp. AB1236 (a benanomicin producer). Addition of sinefungin to strain E-40, pradimicin A aglycone-producing mutant or strain AB1236 inhibited the formation of 11-O-demethyl-7-methoxypradinone II (11dM-7M-PN II), resulting in the accumulation of 11-O-demethylpradimicinone II and pradimicinone II. By feeding pradimicin A aglycone and its analogs to mutants blocked early in pradimicin or benanomicin biosynthesis, the following results were obtained: 11-O-demethylpradinone II, 11dM-7M-PN II 11-O-demethylpradinone I, 11-O-demethylpradimicinone I and pradimicinone I were converted to pradimicin A or benanomicin A; the remaining 6 aglycone analogs were not incorporated into the antibiotics. Pradimicin B, dexylosylpradimicin C and dexylosylbenanomicin A were converted to pradimicin A, pradimicin C and benanomicin A, respectively. A biosynthetic pathway for the antibiotics is proposed.