Biomedical subjects
D Heaton
Publications and source records attributed to D Heaton.
Mutational analysis of the mitochondrial copper metallochaperone Cox17.
The copper metallochaperone Cox17 is proposed to shuttle Cu(I) ions to the mitochondrion for the assembly of cytochrome c oxidase. The Cu(I) ions are liganded by cysteinyl thiolates. Mutational analysis on the yeast Cox17 reveals three of the seven cysteinyl residues to be critical for Cox17 function, and these three residues are present in a Cys-Cys-Xaa-Cys sequence motif. Single substitution of any of these three cysteines with serines results in a nonfunctional cytochrome oxidase complex. Cells harboring such a mutation fail to grow on nonfermentable carbon sources and have no cytochrome c oxidase activity in isolated mitochondria. Wild-type Cox17 purified as untagged protein binds three Cu(I) ions/molecule. Mutant proteins lacking only one of these critical Cys residues retain the ability to bind three Cu(I) ions and are imported within the mitochondria. In contrast, Cox17 molecules with a double Cys --> Ser mutation exhibit no Cu(I) binding but are still localized to the mitochondria. Thus, mitochondrial uptake of Cox17 is not restricted to the Cu(I) conformer of Cox17. COX17 was originally cloned by virtue of complementation of a mutant containing a nonfunctional Cys --> Tyr substitution at codon 57. The mutant C57Y Cox17 fails to accumulate within the mitochondria but retains the ability to bind three Cu(I) ions. A C57S Cox17 variant is functional, and a quadruple Cox17 mutant with C16S/C36S/C47S/C57S substitutions binds three Cu(I) ions. Thus, only three cysteinyl residues are important for the ligation of three Cu(I) ions. A novel mode of Cu(I) binding is predicted.
Cellulitis of the breast as a complication of breast-conserving surgery and irradiation.
Breast-conserving therapy (BCT) has become a standard treatment option for patients with early-stage breast cancer. We have observed cellulitis of the treated breast as a complication occurring before, during, and after breast irradiation. The cases of five women (median follow-up, 28 months; range, 24-65 months) who developed cellulitis before (n = 1), during (n = 2), or after (n = 2) breast irradiation were reviewed. A consecutive series of BCT patients at Emory University was reviewed to determine the incidence of this complication. Four of five women had an axillary dissection, yielding a median of 14 negative lymph nodes (range, 6-22 nodes). Two of four patients developed axillary seromas requiring aspiration. In these four patients, only the breast was irradiated. A fifth patient had no axillary dissection and had breast and supraclavicular/axillary irradiation. The median whole breast dose was 50 Gy (range, 46-50.4 Gy). The clinical features of cellulitis included erythema, edema, tenderness, and warmth in all patients. Cellulitis was a relapsing problem for four of the five patients. The incidence of this complication in our series of BCT patients was approximately 1%. Cellulitis in the ipsilateral breast can be a relapsing complication of BCT and can be seen before, during, or after breast irradiation. Axillary seromas and aspiration seem to indicate a subset of patients at risk of early cellulitis. Late cellulitis may be caused by a variety of factors related to modifications of vascular and skin integrity by surgery and radiotherapy. Prompt diagnosis and appropriate antibiotic therapy is recommended. This problem need not interrupt a course of breast irradiation, and does not necessarily lead to a poor cosmetic result.
Metal ion binding to apo, holo, and reconstituted horse spleen ferritin.
The binding of Cd2+, Zn2+, Cu2+, Ni2+, Co2+, Mn2+, and Mg2+ to apo, holo, reconstituted horse spleen ferritin (HoSF), and native holo HoSF with phosphate removed was measured by gel-exclusion chromatography. Three classes of strong binding interactions (Kd < 10(-7) M) with apo HoSF at pH 7.5 were found for the various M2+ studied: high stoichiometric binding (30-54 M2+/HoSF) for Cd2+, Zn2+, Cu2+, with two protons released per metal bound; intermediate binding (16 M2+/HoSF) for Ni2+ and Co2+, with one proton released per metal bound; and low levels of binding (2-12 M2+/HoSF) for Mn2+, Mg2+, and Fe2+, with < 0.5 protons released per metal bound. M2+ binding to apo HoSF was nearly abolished at pH 5.5, except for Fe2+ and Cu2+, which remained unaffected by pH alteration. Holo HoSF bound much higher levels of M2+, a result directly attributable to the presence of phosphate binding sites. This conclusion was confirmed by decreased binding of M2+ to HoSF reconstituted in the absence of phosphate and by native holo HoSF with phosphate chemically removed. The binding of Cd2+ to apo HoSF was 54 per HoSF, but in the presence of developing core, the amount bound decreased to about 30 Cd2+/HoSF. This result indicated that Cd2+ and developing core were competing for the same sites on the HoSF interior, suggesting that 24 of the Cd2+ were bound to the inside surface. No other M2+ studied bound to the interior of HoSF by this criterion. Several of the M2+ appeared to bind strongly to the phosphate-free mineral core surface in reconstituted HoSF.
Low molecular weight versus unfractionated heparin. A clinical and economic appraisal.
Unfractionated heparin (UFH) has been in clinical use for over 50 years and extensive clinical trials have demonstrated its effectiveness in the prevention and treatment of thrombotic disease. In the last 2 decades, low molecular weight heparins (LMWHs) have been developed and subjected to extensive laboratory and clinical studies. In clinical comparison with UFH in the treatment of venous thromboembolism, LMWHs appear to offer a superior benefit-risk profile. In addition, the ease of drug administration and lack of drug monitoring associated with LMWHs are attractive clinical features. We calculated the overall costs of UFH and LMWH therapy using recently published clinical data and local cost information. Although the acquisition costs of LMWHs are higher than for UFH, LMWHs are more cost effective in surgical prophylaxis of deep venous thrombosis (DVT) if the costs of failed prophylaxis are considered. The costs of using subcutaneous (SC) LMWH as therapy for established DVT are lower than those of UFH administered by intravenous infusion. The financial benefit of using LMWH treatment becomes more pronounced when the rates of antithrombotic failure and bleeding complications are incorporated. If UFH is given by SC injection, however, the cost differential favouring LMWH for the treatment of DVT is not so great. If current trials demonstrate that LMWH treatment can be given on an ambulatory outpatient basis, the economic advantages of LMWH will be considerable. However, the extent of this will vary from place to place depending on local funding arrangements.
Enhancement of X-ray toxicity in squamous cell carcinoma cell lines by DNA polymerase inhibitors.
The effect of the DNA polymerase inhibitors adenine 9-beta-arabinofuranoside (ara-A), cytosine 1-beta-arabinofuranoside (ara-C), and aphidicolin on X-radiation sensitivity was studied in a group of exponentially growing squamous cell carcinoma cell lines. The tumour cell lines varied in radiation sensitivity, with D0 (radiation sensitivity) values ranging from 1.0 to 3.9 Gy. The addition of non-toxic concentrations of ara-A 30 min before irradiation and removal 30 min after irradiation potentiated cell killing in five of eight cell lines. Four of these five responsive cell lines were relatively radioresistant lines, having D0 > 2.0 Gy. One of the cell lines was more radiosensitive (D0 = 1.4 Gy). Ara-A was also effective in potentiating killing in the radioresistant cell lines even when added 60 min after irradiation. Pre- or post-treatment with ara-A had no effect on X-ray sensitivity of the other three relatively sensitive cell lines (D0 ranging from 1.0 to 1.3 Gy). Both ara-C and aphidicolin were effective in potentiating X-ray sensitivity in JSQ-3, a relatively resistant cell line that was sensitized by ara-A treatment, but they had no effect on the X-ray sensitivity of SCC-61, a relatively radiosensitive cell line that was insensitive to ara-A effects on X-ray response. At the concentrations used, the polymerase inhibitors were equally effective in inhibiting DNA synthesis.
Secondary acute myeloid leukemia in children previously treated with alkylating agents, intercalating topoisomerase II inhibitors, and irradiation.
PURPOSE: Patient records were reviewed to identify cases of secondary acute myeloid leukemia (AML) with clinical and cytogenetic features characteristic of classic epipodophyllotoxin-related AML in patients whose prior treatment for cancer did not include these agents. PATIENTS AND METHODS: Four cases of secondary AML with chromosomal abnormalities involving bands 11q23 and 21q22, in the absence of prior treatment with etoposide or teniposide, were identified among patients treated at St Jude Children's Research Hospital between January 1980 and April 1992. RESULTS: The four identified patients were initially treated for rhabdomyosarcoma, non-Hodgkin's lymphoma (n = 2), and Hodgkins' disease. Prior chemotherapy included relatively low cumulative doses of doxorubicin (median, 150 mg/m2; range, 120 to 375 mg/m2) and cyclophosphamide (median, 3,100 mg/m2; range, 2,250 to 11,400 mg/m2). All four patients had received radiation therapy: 59.4 Gy to the right middle ear for rhabdomyosarcoma; 15 Gy and 12 Gy to the abdomen and right lower quadrant, respectively, for non-Hodgkin's lymphoma; 27 Gy to the right orbit for non-Hodgkin's lymphoma; and 36.6 Gy to the mantle-paraaortic-spleen regions plus 20.4 Gy inverted-Y radiation at relapse for Hodgkin's disease. Secondary AML was diagnosed a median of 38 months after initial diagnosis (range, 14 to 55). Leukemic cell translocations involved band 11q23 in two cases and band 21q22 in two. Although all patients obtained a complete remission (CR), only one remains disease-free (at 34 months), following an allogeneic bone marrow transplant. CONCLUSION: Intercalating topoisomerase II inhibitors (doxorubicin, dactinomycin), when combined with alkylating agents and irradiation, may cause secondary AML.
Treatment of 29 patients with bulky squamous cell carcinoma of the cervix with simultaneous cisplatin, 5-fluorouracil, and split-course hyperfractionated radiation therapy.
Attempting to improve local disease control in bulky (greater than 8 cm) primary or recurrent pelvic tumors, 29 patients with squamous cell carcinoma of the cervix (stage II, 4; III, 10; IV, 6; recurrent, 9) were treated with concomitant chemotherapy and split-course hyperfractionated radiation therapy between April 1983 and August 1988. Cisplatin (CDDP) and 5-fluorouracil (5-FU) have been shown to be radiation enhancers; furthermore, CDDP, radiation therapy, and continuous-infusion 5-FU have elicited high local response rates in head and neck squamous cell carcinoma. A pilot study of cyclical week on/week off CDDP, continuous-infusion 5-FU, and hyperfractionated radiation therapy was developed. Radiation was administered at 116 cGy twice daily, Days 1-5, every other week for a median dose of 4600 cGy to a pelvic field, with paraaortic extension if indicated. Concomitant chemotherapy included CDDP 60 mg/m2 IV Day 1 and 5-FU 600 mg/m2 IV continuous infusion for 96 hr following CDDP infusion. Patients received a median of four cycles of combined treatment, and intracavitary or interstitial brachytherapy followed in 21 patients. Local pelvic response was achieved in 29 of 29 (100%): complete response (CR) in 19 of 29 (66%), partial response (PR) in 10 of 29 (34%). Among CR patients 10 of 19 (53%) were without evidence of disease at a mean follow-up of 29 (range 12-76) months. Five-year actuarial disease-free survival among complete responders was 65%. Of the 10 CR patients 2 failed in the pelvis, for a local control rate of 17/19 (89%). Chemotherapy-related and acute radiation morbidity was minimal but 2 patients required surgical correction of radiation injury. Aggressive combination of split-course hyperfractionated radiation therapy with radiation enhancers resulted in promising local control of bulky pelvic tumor, with an acceptable complication rate, in this otherwise very poor prognostic group of patients.
Immune changes associated with insulin dependent diabetes may remit without causing the disease: a study in identical twins.
Activation of T lymphocytes and islet cell antibodies were studied in two groups of insulin dependent diabetics and their non-diabetic identical cotwins. Group 1 comprised 12 "short term" twin pairs (diabetic twin diagnosed less than five years previously) in whom only a third of the cotwins were likely to develop diabetes; 10 of the 12 non-diabetic cotwins showed increased values of activated T lymphocytes, islet cell antibodies, or both. Group 2 comprised 10 "long term" twin pairs (diabetic twin diagnosed more than 11 years previously) in whom none of the non-diabetic cotwins was likely to develop diabetes; these pairs were selected because all the non-diabetic cotwins had shown islet cell antibodies at some time in the past, but only two still did so (one with an increased value of activated T cells). There was relative glucose intolerance in the cotwins of the short term group but not in those of the long term group. Non-diabetic cotwins of diabetics may show the immune changes associated with insulin dependent diabetes and relative glucose intolerance, but these changes may remit without leading to diabetes.
Transabdominal chorionic villus sampling.
Transabdominal chorionic villus sampling, carried out with a fine-bore needle and cannula under ultrasound guidance, was as successful as transcervical aspiration but avoided the risks of bacterial contamination associated with the latter technique. The transabdominal procedure can be carried out under local anaesthesia, and multiple samples can be obtained, if necessary, through a single cannula.
Prenatal diagnosis of argininosuccinicaciduria by analysis of cultured chorionic villi.
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Another case of megaloblastic anemia of infancy due to maternal pernicious anemia.
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Diagnosis, four hours after chorion biopsy, of female fetus in pregnancy at risk of Duchenne muscular dystrophy.
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