Reversible electrical breakdown of lipid bilayers: formation and evolution of pores.

The mechanism of reversible electric breakdown of lipid membranes is studied. The following stages of the process of pore development are substantiated. Hydrophobic pores are formed in the lipid bilayer by spontaneous fluctuations. If these water-filled defects extend to a radius of 0.3 to 0.5 nm, a hydrophilic pore is formed by reorientation of the lipid molecules. This process is favoured by a potential difference across the membrane. The conductivity of the pores depends on membrane voltage, and the type of this dependence changes with the radius of the pore. Hydrophilic pores of an effective radius of 0.6 up to more than 1 nm are formed, which account for the membrane conductivity increase observed. The characteristic times of changes in average radius and number of pores during the voltage pulse and after it are investigated.

Beyond proforma consent for childhood cancer research.

A critical negotiation is that of obtaining informed consent from those responsible for the child with cancer who is to be involved in clinical research. It requires that the researcher weigh the merits to society of the proposed research trial and the interests of the patient and family. The clinical setting in which agreement to participate is requested and the regulations of the DHHS for such investigations also place special demands on all of those involved. This article is an ethical and psychosocial analysis of informed consent. It is intended to provide pediatric physician-investigators with a better understanding of this complex process to improve their fiduciary relationship with decision makers.

Three versus five years of maintenance therapy are equivalent in childhood acute lymphoblastic leukemia: a report from the Childrens Cancer Study Group.

Childrens Cancer Study Group protocol 141 (CCG-141), a randomized trial, was designed in part to compare 3 v 5 years of maintenance therapy, to evaluate the role of late reinduction, and to identify factors that predict relapse after 3 years of continuous complete remission (CCR) in acute lymphoblastic leukemia (ALL). Of 880 patients entered on study, 827 (94%) achieved complete remission and 499 (56.7%) were in CCR after 3 years of maintenance therapy. Boys were required to have negative testicular biopsies before randomization. A total of 481 patients were eligible for the duration of therapy phase of the study. Of the 310 (64.4%) randomly assigned patients, 101 were entered on regimen A: discontinue therapy; 105 on regimen B: reinduction for 4 weeks, then discontinue therapy; and 104 on regimen C: continue maintenance therapy for 2 more years, then discontinue. After a median follow-up of over 72 months, no significant differences in disease-free survival (DFS) or survival were noted in the three regimens. At 6 years from randomization, 93.0%, 89.1%, and 89.1% of patients on regimens A, B, and C, respectively, remained in CCR. Isolated CNS or overt testicular relapses were not significantly different in any of the study regimens. Isolated testicular relapse after a negative biopsy occurred in only two of 137 randomized males (1.5%). DFS (P = .10) and survival (P = .83) were not significantly different for all boys and girls randomized to regimens A, B, or C. The relapse rate was higher in boys than in girls randomized to discontinue therapy (11% v 4%), but the difference was not statistically significant (P = .14). Except for the presence of occult testicular leukemia (TL) in males, no other factors were identified that predicted for adverse events after 3 years of CCR. We conclude that prolongation of maintenance therapy beyond 3 years does not improve survival or decrease the risk of relapse.

The prognostic value of testicular biopsy in childhood acute lymphoblastic leukemia: a report from the Childrens Cancer Study Group.

One of the objectives of Childrens Cancer Study Group (CCSG) study 141 (CCG-141) was to determine the frequency of occult testicular leukemia (TL) after 3 years of disease-free survival (DFS) and to retreat boys with occult TL to prolong their subsequent DFS. Of the 494 boys entered on study, 255 (51.6%) were in complete continuous remission (CCR) 3 years after entering remission and an additional eight were in CCR 3 years after localized extramedullary relapse and retreatment; 263 boys were eligible for testicular biopsy. Elective testicular biopsy was performed on 235 (89.4%) boys. Of the 204 (86.8%) boys with negative biopsies, 175 (85.8%) remained in CCR 10 to 12 years after diagnosis and 25 (12.3%) relapsed, 11 (44%) of whom died. Isolated overt TL occurred in four (2.0%) and all remained in CCR 22+ to 60+ months after re-treatment. Of the 26 boys with occult TL, 16 (62%) remained in CCR. Ten (38%) relapsed despite local testicular irradiation and systemic re-treatment; six of the 10 died. Of the 26 boys who did not undergo biopsy, 21 (80.8%) remained in CCR; two (7.7%) developed isolated overt TL. DFS after testicular biopsy was significantly better in boys without occult TL (P = .001). Occult TL after 3 years of CCR represents aggressive minimal-residual disease and carries a worse prognosis than absence of TL. Initial treatment should be directed at obviating occult and overt testicular relapse. Conventional therapy as used in this study was suboptimal in preventing subsequent bone marrow (BM) relapse and death. If occult TR is identified during or at the end of planned therapy, a higher salvage rate may require intensified alternate therapy. As such, testicular biopsies may be clinically useful. Further investigation is limited by the relative rarity of, and the lack of identifying features in boys with occult TL.

Reduction in central nervous system leukemia with a pharmacokinetically derived intrathecal methotrexate dosage regimen.

During the period 1976-1981, 3241 children were enrolled on three major studies of acute lymphoblastic leukemia by participating institutions of the Children's Cancer Study Group. Each study included a different method of central nervous system (CNS) prophylaxis: (1) standard therapy with cranial irradiation, 2400 rads, and intrathecal methotrexate at 12 mg/m2 six times during consolidation (CCG-141); (2) a modification of CCG-141 in which the intrathecal methotrexate was initiated during induction (CCG-141A); and (3) a reduced cranial irradiation dose of 1800 rads with intrathecal methotrexate given at the same frequency as a CCG-141A, with or without maintenance intrathecal methotrexate, but with a dosage regimen derived from CNS volume considerations rather than based on body surface area (CCG-160 series). Strategy 3, a change in the intrathecal methotrexate dosage, has resulted in the lowest incidence of CNS leukemia to date (p less than 0.007). The cumulative 3-yr CNS relapse rate has decreased from 8%-10% to 2%-5% in average-risk patients (p less than 0.02; life table estimate) and from 23%-27% to 6% in high-risk patients (p less than 0.0002; life table estimate), despite a reduction in the cranial irradiation dose from 2400 to 1800 rads. Maintenance intrathecal chemotherapy has had a marginal effect among patients randomized to receive this additional therapy (p = 0.06). The overall outcome has been an increase in the continuous complete remission rate (p = 0.04) but not in the estimated 3-yr continuous hematologic remission or survival rates.

Mortality in children and adolescents with sickle cell disease. Cooperative Study of Sickle Cell Disease.

A study of the natural history of sickle hemoglobinopathies was begun in March 1979. By August 1987, a total of 2824 patients less than 20 years of age were enrolled. There have been 14,670 person-years of follow-up. Seventy-three deaths have occurred. Most of the deaths were in patients with hemoglobin SS. The peak incidence of death was between 1 and 3 years of age, and the major cause in these young patients was infection. Cerebrovascular accidents and traumatic events exceeded infections as a cause of death in patients greater than 10 years of age. There was limited success in identifying risk factors for death. Comparison of this study's overall mortality of 2.6% (0.5 deaths per 100 person-years) with previous reports indicates improvement of survival in US patients less than 20 years of age with sickle hemoglobinopathies. This improvement is most likely due to parental education and counseling about the illness and the early institution of antibiotics in suspected infections.

The teaching of crisis counseling skills to pediatric residents: a one-year study.

Pediatric residents should learn to manage family crises such as informing parents that their child has a potentially life-threatening illness. Unfortunately, few training programs prepare residents to counsel parents of a child with cancer. An experiential parent crisis counseling program has been developed at the Children's Hospital National Medical Center in Washington, DC; this program has demonstrated that pediatric residents, with limited instruction, can be taught to give bad news to parents using effective information-giving and interpersonal skills.

Immunobiology of histiocytosis-X.

Recent laboratory investigations of patients with histiocytosis-X and their pathologic tissues demonstrate the close immunologic relationship between the Langerhans-like cells of these patients and normal epidermal Langerhans cells of the mononuclear phagocytic system. A deficiency of a peripheral blood lymphocyte subpopulation is seen in histiocytosis-X patients. Its relevance to the pathogenesis of the disease is yet to be determined. The granuloma of histiocytosis-X contains large numbers of cells similar to epidermal Langerhans cells, components of the mononuclear phagocytic system. The Langerhans cells of histiocytosis-X can now be characterized by a number of immunologic and immunohistochemical techniques. Similarities and differences between them and other components of the mononuclear phagocytic system have been recognized, supporting the concept of the duality of the system's proliferative disorders. There is a deficiency of suppressor T lymphocytes in patients with active histiocytosis-X and a rise in the number of suppressor cells after in vitro incubation with thymic hormones. Increases in the peripheral blood suppressor cell number occur spontaneously or inconsistently after parenteral administration of thymic hormone. It is not known at present what the relationship is between the decrease in suppressor lymphocytes and the reports of thymic abnormalities in these patients. More investigations are needed in patients with active and inactive disease: measuring serum thymic factors, performing clinical trials with thymic products, determining monocyte or macrophage function, and evaluating other possible dysfunctions of suppressor T lymphocytes.

The treatment of medulloblastoma. Results of a prospective randomized trial of radiation therapy with and without CCNU, vincristine, and prednisone.

In a prospective randomized trial designed to study the effectiveness of adjuvant chemotherapy following standard surgical treatment and radiation therapy, 233 eligible patients with medulloblastoma were treated by members of the Children's Cancer Study Group and the Radiation Therapy Oncology Group. Eligible patients were randomly assigned to receive radiation therapy with or without adjuvant chemotherapy consisting of 1-(2-chloroethyl)-3-cyclohexyl-nitrosourea (CCNU), vincristine, and prednisone. The estimated 5-year event-free survival probability was 59% for patients treated with radiation therapy and chemotherapy and 50% for patients treated with radiation therapy alone, a difference which is not statistically significant. The 5-year survival probability was 65% for both groups. Although the treatment difference was not statistically significant when all patients were combined, in the small number of patients with more extensive tumors, event-free survival was better in the group receiving chemotherapy (48% vs. 0%, p = 0.006). In these latter patients the survival time is also significantly prolonged. Extent of disease (as measured by the M staging criteria described by Chang) and age at diagnosis were significantly associated with outcome; advanced disease and young age had a worse prognosis. The extent of tumor resection was not an independent prognostic factor. It is concluded that chemotherapy does not benefit patients with low-stage medulloblastoma, but may benefit those with more advanced stages of disease.

Surface membrane determinants on childhood acute lymphocytic leukemia cells: immunoglobulin, Fc and C3 receptors.

Most reports have now described two populations of childhood ALL patients: those with thymic (T) cell receptors and those lacking receptors on their neoplastic cells. Assays for the surface receptors of the T and thymic-independent (B) system were used to study forty-seven patients with ALL whose bone marrow contained a mean of 85% leukaemic cells. Two patients had T-cell disease and thirty-six were non-T and non-B. nine patients were identified whose leukaemic cells had membrane properties associated with the B-cell system: surface immunoglobulin, Fc receptors and/or complement receptors. Combined T and B receptors were found in one case. The same surface characteristics were found on leukaemic cells from these patients' bone marrow, blood, pleural and cerebrospinal fluid. Studies showed that the leukaemic cells were not of monocytic or granulocytic origin. Although a remission was obtained in each patient, the relapse rate of the B-cell group was worse than a similarly treated group of thirty-six non-T, non-B ALL patients (P less than 0.001). Initial total leucocyte counts of the B-cell group were greater than the non-T, non-B group (P 0.05), but when the patients in both groups with total leucocyte counts greater than 25,000/mm3 were compared, the relapse rate of the B-cell patients was significantly worse (P less than 0.025). The results show that patients with leukaemic cells possessing B-cell properties comprise a significant proportion of ALL cases, and their presence on leukaemic cells has an ominous significance.

Growth and development in sickle cell anemia. Preliminary report.

Historically, adults with sickle cell anemia were described as being short, thin, and eunuchoid in appearance with a particular body habitus. More current investigations in children have suggested decreased height, weight, and hypogonadism although Jamaican studies suggest supranormal heights in adolescence. All studies to date have evaluated children at one point in time. We evaluated children with sickle cell anemia longitudinally at six monthly intervals over 3 years to assess somatic growth and the development of sexual maturation. Our data support reduced height and weight as compared to National Health Statistic norms, with normal skin fold thickness. Bone ages were significantly retarded. When a patient's chronological age was replaced by his bone age and tanner staging was done, sexual development was appropriate for bone age, suggesting delayed sexual maturation. In addition, menarche was significantly delayed. Pituitary gonadotropins showed an appropriate increase with puberty. Gonadal end organ hormones supported normal responsiveness, although an occasional patient showed depressed levels. Longitudinal data is necessary to assess children with suspected delay in somatic and sexual development. Hormonal replacement does not seem warranted in the majority of patients.

Insulin binding of acute lymphocytic leukemia cells.

Because of differences in insulin binding of cultured lymphoic cell lines, T- and B-cell surface receptor and 125I-insulin binding studies were performed on the bone marrow and peripheral blood leukocytes of 13 children with active acute lymphocytec leukemia. Based on surface receptors, nine patients had null-cell disease and four had T-cell disease. The mean per cent insulin binding of the bone marrow cells from the null-cell patients was 10.0% +/- 8.1 and from the T-cell patients was 0.18% +/- 0.13. The mean insulin binding of the cell suspensions of the peripheral blood from the null-cell patients was 7.3% +/- 7.5 and 0.07% +/- 0.06 from the T-cell patients. Displacement studies with nonradioactive insulin indicated that null leukemic cells bore specific binding sites. These results indicated that there may be metabolic as well as surface membrane heterogeneity among the acute lymphocytic leukemias of childhood.

Membrane fusion: overcoming of the hydration barrier and local restructuring.

The early stages of membrane fusion have been investigated theoretically. It has been shown that the hydration repulsion, operating between apposed membranes, is overcome locally under the action of out-of-plane thermal fluctuations of the bilayers. The fluctuations lead to the formation of close (less than 0.5 nm) contact between the membranes within a small area (approximately 10 nm2). Increasing hydration repulsion between apposed polar heads of lipid molecules in this area causes the rupture of interacting monolayers. The rupture results in monolayer fusion of the membranes, i.e. in the formation of a bridge connecting the monolayers, which is usually named the monolayer stalk. The influence of degree of hydration of the monolayers and their spontaneous curvature on conditions of monolayer fusion have been analysed. The proposed mechanism of early stages of fusion process can proceed without preliminary formation of tight dehydrated contact between the membranes and even without any dehydration.

Liver resection in children with hepatic neoplasms.

In the past ten years, 28 patients with primary tumors of the liver have been treated. There were 11 benign tumors, including four hamartomas, three patients with focal nodular hyperplasia, and two each with congenital cysts and hemangioma. Hamartomas and masses of focal nodular hyperplasia should be excised when possible, but both are benign lesions; therefore life threatening excisions at the porta hepatis should be avoided. Cysts are often resectable, but when occupying all lobes of the liver, they can be successfully managed by marsupialization into the free peritoneal cavity. If resectable, hemangiomas should be removed; when occupying most of the liver as they often do, patients may be subject to platelet trapping or to cardiac failure. In some instances these lesions have been controlled by steroids, radiation therapy or hepatic artery ligation. Of 17 malignant tumors seen, 12 proved to be hepatoblastomas. Nine of the 12 patients underwent liver resection, of whom four are cured, (33%). There were three children with hepatocellular carcinomas and two with embryonal rhabdomyosarcoma. One child from each of these groups is cured by surgical excision. At present the only known cures in children with primary malignant liver neoplasms have been achieved by operative removal.

Cell-mediated immunity to respiratory syncytial virus induced by inactivated vaccine or by infection.

Transformation and increased mitotic activity in donor lymphocytes exposed to specific antigens is considered by many to be a manifestation of cell-mediated immunity. In attempts to understand the apparent "sensitization" of individuals to respiratory syncytial virus (RSV) as a result of receiving inactivated RSV vaccine, in vitro lymphocyte transformation studies were carried out on infants who had received inactivated RSV vaccine and on infants who had received a similarly prepared inactivated African green monkey kidney (AGMK) cell-grown parainfluenza type 1 virus vaccine or a trivalent parainfluenza vaccine prepared in hen's eggs. Each group included some infants who had, and others who had not, undergone natural RSV infection under our observation before the lymphocyte studies. Lymphocytes were studied from 21 infants and young children who had received the inactivated RSV vaccine, 14 who had received a similarly prepared inactivated parainfluenza 1 vaccine, and 5 who received a trivalent parainfluenza vaccine. Twelve of the RSV vaccinees and 14 of the parainfluenza vaccinees had been naturally infected with RSV as indicated by virus recovery and/or antibody rise between the time of vaccination and the lymphocyte studies. In comparing the arithmetic mean for RSV-specific transformation and mitotic activity there was a significant difference between RSV vaccinees and parainfluenza vaccinees whether one compared those who had undergone natural RSV infection or those who had not undergone natural infection. The difference between RSV vaccinees who had not undergone natural RSV infection and RSV-infected parainfluenza vaccinees also was significant. There was a greater level of transformation and mitotic activity in those who had experienced natural infection than those who had not among both RSV vaccinees and parainfluenza vaccinees, but these differences were not significant statistically.

Stalk mechanism of vesicle fusion. Intermixing of aqueous contents.

A mechanism for rupture of a separating bilayer, resulting from vesicle monolayer fusion is investigated theoretically. The stalk mechanism of monolayer fusion, assuming the formation and expansion of a stalk between two interacting membranes is considered. The stalk evolution leads to formation of a separating bilayer and mechanical tension appearance in the system. This tension results in rupture of the separating bilayer and hydrophilic pore formation. Competition between the mechanical tension and hydrophilic pore energy defines the criteria of contacting bilayer rupture. The tension increases with an increase of the absolute value of the negative spontaneous curvature of the outer membrane monolayer, Kos. The pore edge energy decreases with an increase of the positive spontaneous curvature of the inner membrane monolayer, Kis. The relations of spontaneous curvatures of outer and inner monolayers, leading to separating bilayer rupture, is calculated. It is demonstrated that his process is possible, provided spontaneous curvatures of membrane monolayers have opposite signs: Kos less than O, Kis greater than O. Experimental data concerning the fusion process are analysed.

Giving information for a life-threatening diagnosis. Parents' and oncologists' perceptions.

We surveyed pediatric oncologists throughout the United States and families of children with acute lymphocytic leukemia diagnosed between 1977 and 1980 at Children's Hospital National Medical Center, Washington, DC, to determine what information is perceived by both parents and physicians as essential to convey during the initial presentation of a life-threatening diagnosis. Both groups considered the following topics critical for discussion at the initial conference: diagnosis and prognosis of disease, explanation of disease process, additional tests needed to confirm and/or supplement the diagnosis, immediate therapeutic plan, and the physician's availability. Additionally, both parents and physicians, with minor variations, agreed about the order in which information about the disease should be conveyed. Although acute lymphocytic leukemia was used as a model, this study suggests guidelines that could be utilized to train residents and guide physicians in crisis-counseling techniques in the presentation to parents of a diagnosis of life-threatening illness in their child.