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Biomedical subjects

C F Arlett

Publications and source records attributed to C F Arlett.

At least 19 recordsLinked to original sources
PubMed1992

Growth retardation and immunodeficiency in a patient with mutations in the DNA ligase I gene.

DNA ligases are required for the replication, repair, and recombination of DNA. A cell line derived from a young woman with growth retardation, sun sensitivity, and immunodeficiencies, who died aged 19 with lymphoma, showed two different miscoding mutations at the DNA ligase I locus on chromosome 19, one in each allele. One of the mutations was inherited from the mother and has also been detected in two healthy brothers. The patient had features similar to those of Bloom's syndrome (BS), but cell lines from BS patients do not have mutations in the DNA ligase I gene. This patient seems to represent a distinct genetic entity.

Cell Line↗
PubMed1992

A comparison of the response of unstimulated and stimulated T-lymphocytes and fibroblasts from normal, xeroderma pigmentosum and trichothiodystrophy donors to the lethal action of UV-C.

Unstimulated T-lymphocytes from normal donors are significantly more sensitive to the lethal effects of UV-C than either stimulated T-lymphocytes or fibroblasts as judged by colony-forming ability. Data from other studies suggest that excision repair is more effective in stimulated than unstimulated T-lymphocytes leading to the prediction that these differences in survival should be minimal in cells established from excision defective donors. The prediction was met with XP6BR, a donor of unknown complementation group. For 3 XP's from complementation group D, however, enhanced survival in stimulated T-cells was observed. With cells from an excision-defective TTD who was included in complementation group D of XP both fibroblasts and unstimulated T-lymphocytes were hypersensitive. For a second excision defective TTD patient who was excluded from complementation group D, the unstimulated T-lymphocytes were more resistant than those of normal donors although the fibroblasts were hypersensitive. These results suggest that the in vitro response of stimulated T-lymphocytes or fibroblasts may not reflect the in vivo response of cells, as measured by the response of unstimulated T-lymphocytes.

Adult↗
PubMed1992

UV-C sensitivity of unstimulated and stimulated human lymphocytes from normal and xeroderma pigmentosum donors in the comet assay: a potential diagnostic technique.

We have studied incision-break formation in unstimulated and stimulated populations of human T-lymphocytes using the comet (single-cell microgel electrophoresis) assay. The frequency of strand breaks 1 h after UV-irradiation appears to be far greater in unstimulated than in stimulated lymphocytes from normal donors and the excess of strand breaks was observed for a far longer time after irradiation. This result corroborates the greater sensitivity of UV-C irradiation observed in a colony-forming assay but suggests that the defect may relate to a defect in strand rejoining rather than a defect in incision. Few strand breaks were seen in either unstimulated or stimulated lymphocytes of four xeroderma pigmentosum donors, suggesting that the method may offer a rapid diagnostic assay for XP.

Cells, Cultured↗
PubMed1992

Elevated hprt mutant frequency in circulating T-lymphocytes of xeroderma pigmentosum patients.

The mutant frequency to 6-thioguanine resistance in circulating T-lymphocytes from 10 xeroderma pigmentosum patients (including complementation groups D and G and XP variants) has been determined. A highly significantly elevated frequency was observed, compared to age-matched, non-smoking control donors (x 2.1-fold higher than the mutant frequency in normal control donors, adjusted for age and cloning efficiency, p less than 0.001). The mutant frequency of 5 XP heterozygotes was in the normal range, when age, smoking habit and log cloning efficiency were taken into account. A number of possible factors which may account for the elevated mutant frequency seen in the XP donors (including an elevated spontaneous mutation rate, UV mutagenesis of the T-cells as they pass through the skin, an effect of environmental mutagens such as tobacco smoke, or as a consequence of immune deficiency) are discussed.

Adult↗
PubMed1991

Possible association between mutant frequency in peripheral lymphocytes and domestic radon concentrations.

To investigate whether previously found geographical correlations between leukaemia incidence and exposure to radon are reflected in a detectable mutagenic effect on individuals, the frequency of mutations in the hypoxanthine guanine phosphoribosyl transferase gene (hprt) in peripheral blood T lymphocytes was measured in subjects with known domestic radon concentrations. These concentrations were measured in December, 1989, in houses in Street, Somerset, UK, by passive alpha-track radon detectors. 20 non-smoking subjects aged 36-55 years were selected from the patient list at the local health centre on the basis of the radon concentrations in their homes--the range selected varied by a factor of ten. Blood samples for preparation of T lymphocytes were taken in July, 1990. There was a significant association between the log mutant frequency and radon concentration (t = 3.47, p less than 0.01). A second analysis of a further set of radon measurements (October, 1990, to January, 1991), in both living rooms and bedrooms, and repeated mutant frequency determinations also showed a significant relation, which remained significant even after exclusion of the highest frequency and adjustment for subject's age and cloning efficiency. These data must be regarded as preliminary and further more extensive studies should be done to determine whether the observed association is causal.

Acute Disease↗
PubMed1991

Molecular analysis of ultraviolet-induced mutations in a xeroderma pigmentosum cell line.

We have isolated and characterized 47 ultraviolet light-induced hprt mutants from a simian virus 40-transformed excision-repair-deficient xeroderma pigmentosum cell line (complementation group A). Twenty-one independent mutations were found, of which the majority were point mutations. Eleven of these were identified as base changes, nine of which could be attributed to ultraviolet damage on the transcribed DNA strand. Both transitions and transversions were found among the single base changes. A large proportion of the mutations (13/21) resulted in aberrant splicing of the hprt gene, suggesting that the target size for mutations resulting in aberrant splicing must be quite large. A small number of spontaneous mutations were identified, most of which were large deletions. Our data provide a spectrum for the intrinsic mutations resulting from ultraviolet damage in human cells in the absence of repair.

Base Sequence↗
PubMed1991

Comparative human cellular radiosensitivity: III. Gamma-radiation survival of cultured skin fibroblasts and resting T-lymphocytes from the peripheral blood of the same individual.

Skin and blood samples were obtained from 34 donors, for whom there was no indication of abnormal radiosensitivity. From these, in 33 cases both fibroblast and T-lymphocyte cultures were obtained and in 26 cases at least three fibroblast and at least two G0 (resting) T-lymphocyte survival assays were possible. Within this set of results, differences in radiosensitivity between donors were significant for fibroblasts but not T-lymphocytes, although the range of radiosensitivity was similar for the two cell types (D 0.90-1.68 Gy for fibroblasts; 1.26-2.15 Gy for T-lymphocytes). Furthermore, there was little evidence for a correlation in radiosensitivity between the two cell types. These results suggest limitations in the predictive value of conventional measurement of cell survival.

Cell Survival↗
PubMed1991

Comparative human cellular radiosensitivity: IV. The increased sensitivity of human neonatal cord blood lymphocytes to gamma-irradiation compared with lymphocytes from children and adults.

We have compared the gamma-irradiation survival of G0 peripheral blood lymphocytes from 18 neonatal cord blood samples in a cloning assay with results from 21 controls (age range 1-65 years and consisting of 20 adults and one child). Using mean inactivation dose as the discriminating parameter, the cord blood cells showed a significantly greater radiosensitivity (mean inactivation dose for pooled data = 1.54 Gy) than the normal controls (mean inactivation dose for pooled data = 1.90 Gy, p less than 0.001). These results confirm and extend earlier work suggesting that T-lymphocytes in newborn children are more radiosensitive than normal controls, and this may have implications for the radiation protection of the unborn child.

Adult↗
PubMed1991

Abnormal erythemal response and elevated T lymphocyte HRPT mutant frequency in Cockayne's syndrome.

In three children with Cockayne's syndrome (CS), skin exposed to ultraviolet radiation responded transiently either with erythematous papules or an exaggerated sunburn-like response, without chronic actinic damage. Irradiation monochromator tests demonstrated an abnormal delay or reduction in the threshold to ultraviolet (UVB) irradiation-induced erythema similar to that of xeroderma pigmentosum (XP). As with XP there was an elevated frequency of mutants resistant to 6-thioguanine in circulating T lymphocytes. The mutant frequency in a single obligate heterozygote was normal. In contrast to XP, in the two CS individuals studied, adaptive cell-mediated immunity and natural killer cell function were normal. Because the risk of skin cancer is very high in XP but not in CS, the normal immune function in CS provides evidence that immune surveillance may be important in UV tumorigenesis.

Child, Preschool↗
PubMed1991

Long-term survival and preservation of natural killer cell activity in a xeroderma pigmentosum patient with spontaneous regression and multiple deposits of malignant melanoma.

A 67-year-old man with xeroderma pigmentosum (XP) originally presented with malignant melanoma at the age of 28 years. This recurred 22 years later and subsequently numerous primary and secondary melanomas developed on the skin, several of which underwent spontaneous regression. Despite a marked lymphopenia, the proportion of natural killer cells was elevated and it is proposed that this led to the regression of the melanomas. Skin-derived fibroblasts from the patient were more sensitive to UVC (D10 approximately 3 J/m-2) than those from normal individuals (D10 approximately 15 J/m-2). The fibroblast culture was shown to be defective in excision repair with less than 10% of residual activity compared with controls. No assignment to a complementation group has yet been made. There was an elevated frequency of mutants resistant to 6-thioguanine in the circulating T lymphocytes.

Adult↗
PubMed1990

Inherent sensitivity and induced resistance to chemotherapeutic drugs and irradiation in human cancer cell lines: relationship to mutation frequencies.

Metastatic nonseminomatous testicular germ cell tumors are curable using combination chemotherapy in approximately 80% of patients. In contrast, most other patients with other types of cancer either present with or acquire drug-resistant disease following chemotherapy. Cell lines derived from testis tumors retain hypersensitivity to both drugs and radiation in vitro, thus providing a model system with which to investigate the genetic basis of hypersensitivity to these agents. This study compared the spontaneous and both ethyl methanesulfonate- and cisplatin-induced frequencies of mutation of 6-thioguanine resistance in 3 human bladder and 3 testis tumor cell lines and a bladder and a testis cell line with cisplatin resistance induced in vitro. The two tumor types showed similar frequencies of both spontaneous and induced mutation frequencies at this locus. Therefore, we failed to provide evidence for the hypothesis that the curability of testis tumors is associated with a low frequency of mutation to drug resistance.

Antineoplastic Agents↗
PubMed1990

Relationship between pyrimidine dimers, 6-4 photoproducts, repair synthesis and cell survival: studies using cells from patients with trichothiodystrophy.

Trichothiodystrophy is a genetic disease which in the majority of cases studied is associated with a deficiency in the ability to repair UV damage in cellular DNA. Three categories of UV response have been identified. In type 1 the response is completely normal, whereas type 2 cells are deficient in excision-repair, with properties indistinguishable from those of XP complementation group D. Type 3 cells have normal survival following UV-irradiation and normal rates of removal of cyclobutane pyrimidine dimer sites. Nevertheless repair synthesis is reduced by 50% in these cell strains and this is associated with a marked reduction in the repair of 6-4 photoproducts from cellular DNA. The present results show that 50% or more of repair synthesis at early times after irradiation of normal primary human fibroblasts is attributable to repair of 6-4 products. They also suggest that repair of cyclobutane dimers is crucial for cell survival.

Cell Survival↗
PubMed1990

Variation in the loss of O6-methylguanine-DNA methyltransferase during immortalization of human fibroblasts.

We have examined O6-methylguanine-DNA methyltransferase (MT) activity in four human fibroblast cell lines during immortalization. Transfection of primary fibroblasts with the plasmid pSV3gpt or pSV3neo, which encode the SV40 large T antigen, confers a transformed phenotype but not immediate immortality. After a period of growth (pre-crisis) the cells enter a quiescent phase (crisis) from which an immortal clone of cells eventually grows out. From measurements of MT activity in extracts of cells taken at different defined stages of the immortalization process, we conclude that the establishment of a Mex- (MT-deficient) cell population is not specifically associated with cellular transformation or with any particular stage of immortalization. It appears that in different cell populations the change from Mex+ to Mex- may occur at different times during the immortalization process and that the change may be very abrupt.

Antigens, Polyomavirus Transforming↗
PubMed1990

Immune function, mutant frequency, and cancer risk in the DNA repair defective genodermatoses xeroderma pigmentosum, Cockayne's syndrome, and trichothiodystrophy.

There is evidence for defective DNA repair in xeroderma pigmentosum, Cockayne's syndrome, and trichothiodystrophy, but for increased cancer risk only in xeroderma pigmentosum. Natural and adaptive immune surveillance and mutant frequency to 6-thioguanine resistance in circulating T-lymphocytes were studied in five patients with xeroderma pigmentosum, two with Cockayne's syndrome, and one with trichothiodystrophy. Forty-eight-hour cutaneous hypersensitivity responses to recall antigens excluded anergy and circulating CD3+, CD4+, CD8+, and CD16+ cell numbers were within normal limits in all patients tested, as were proliferative lymphocyte responses to PHA, except in the trichothiodystrophy patient. Proliferative responses to recall antigens (PPD, SKSD, and Candida) showed that all patients responded to one or more antigens. Direct natural killer cytotoxicity measured against the human erythromyeloid leukaemia cell line K562 using a 4-h 51Cr release assay was significantly reduced in xeroderma pigmentosum (specific cytotoxicity less than mean +/- SD greater than 17.4 +/- 9.4 per cent, with effector:target cell ratio of 50:1) compared to normal controls (45.8 +/- 17.8), but normal in Cockayne's syndrome and trichothiodystrophy. Generation of lymphokine activated killer cell activity was normal in the two xeroderma pigmentosum lines tested. The mutant frequency in the xeroderma pigmentosum donors was significantly increased (p less than 0.01) and was elevated in the two Cockayne's syndrome donors, taking age into account. No mutants were observed from the single trichothiodystrophy donor. These findings suggest that reduced natural killer cell activity may contribute to the greatly increased susceptibility to skin cancer in xeroderma pigmentosum.

Antigens, CD↗
PubMed1990

Radiobiological studies in the naevoid basal cell carcinoma syndrome.

The naevoid basal cell carcinoma syndrome is described in a 43-year-old male. The response of dividing fibroblasts from this patient to the lethal effects of ionizing radiation was indistinguishable from that of a normal control: mean inactivation dose (D) = 1.74 Gy and 1.68 Gy, respectively. However, these cells were defective in the repair of potentially lethal damage (D = 2.36 Gy and 3.26 Gy, respectively). The response to radiation of Go T lymphocytes derived from the patient was similar to that of the control. The frequency of mutant circulating T lymphocytes resistant to 6-thioguanine was 17 x 10(-6) which was elevated when compared with age-matched controls. These results suggest an abnormality in the response of the fibroblasts to ionizing radiation damage.

Adult↗
PubMed1990

An instance of clinical radiation morbidity and cellular radiosensitivity, not associated with ataxia-telangiectasia.

A 14-year-old boy received standard induction chemotherapy for acute lymphoblastic leukaemia followed by standard dose cranial radiation prophylaxis (18 Gy). Severe chemosensitivity and acute radiation reactions occurred and he died at 8 months from late radiation damage. In vitro radiobiological studies of the boy's fibroblasts in culture demonstrated an enhanced radiosensitivity indistinguishable from ataxia-telangiectasia (A-T) cells. However, unlike A-T cells, DNA synthesis following irradiation was inhibited in a normal manner. This patient represents yet another example of extreme radiosensitivity, and the possibility of clinical prediction in the future is discussed.

Adolescent↗