Surfactant sealing of membranes permeabilized by ionizing radiation.

Acute tissue injury and subsequent inflammation, including tissue edema and erythema, can be caused by sufficiently high levels of exposure to gamma radiation. The mechanism of this tissue injury is related to the generation of reactive oxygen intermediates (ROI) which chemically alter biological molecules and cell physiology. Cell membrane lipids are vulnerable to ROI-mediated lipid peroxidation that then leads to many of the acute tissue effects. We hypothesize that increased cell membrane permeability leading to osmotic swelling and vascular transudation is one of these effects. Thus we used adult postmitotic rhabdomyocytes in culture and microscopic fluorescence techniques to quantify radiation-induced changes in cell membrane permeability. Based on time-resolved dye flux measurements, a characteristic lag time of 34 +/- 3 min was determined between exposure to 160 Gy of gamma radiation and the decrease in membrane permeability. Administration of 0.1 mM nonionic surfactant Poloxamer 188 added to the cell medium after irradiation completely inhibited the dye loss over the time course of 2 h. Thus a reproducible model was developed for studying the mechanism of acute radiation injury and the efficacy of membrane-sealing agents. As only supportive measures now exist for treating the acute, nonlethal injuries from high-dose radiation exposure, agents that can restore cell membrane function after radiation damage may offer an important tool for therapy.

Kinetics of sealing for transient electropores in isolated mammalian skeletal muscle cells.

Permeabilization of the plasma membrane by electrical forces (electroporation) can be either transient or stable. Although the exact molecular mechanics have not yet been described, electroporation is believed to initiate primarily in the lipid bilayer. To better understand the kinetics of membrane permeabilization, we sought to determine the time constants for spontaneous transient pore sealing. By using isolated rat flexor digitorum brevis skeletal muscle cells and a two-compartment diffusion model, we found that pore sealing times (tau p) after transient electroporation were approximately 9 min. tau p was not significantly dependent on the imposed transmembrane potential. We also determined the transmembrane potential (delta Vm) thresholds necessary for transient and stable electroporation in the skeletal muscle cells. delta VmS ranging between 340 mV and 480 mV caused a transient influx of magnesium, indicating the existence of spontaneously sealing pores. An imposed delta Vm of 540 mV or greater led to complete equilibration of the intracellular and extracellular magnesium concentrations. This finding suggests that stable pores are created by the larger imposed transmembrane potentials. These results may be useful for understanding nerve and skeletal muscle injury after an electrical shock and for developing optimal strategies for accomplishing transient electroporation, particularly for gene transfection and cell transformation.

Significance of pretreatment hemoglobin level in patients with T1 glottic cancer.

Recent reports have suggested that pretreatment hemoglobin level (Hgb) is significantly associated with local control (LC) and overall survival (OS) in patients with T1 and T2 squamous cell carcinoma of the glottic larynx. To further evaluate the association of pretreatment Hgb level and other factors with outcome, we performed a retrospective review limited to patients with T1 squamous cell carcinoma of the glottic larynx treated with external beam radiation therapy. One-hundred thirty-nine patients with T1 squamous cell carcinoma of the glottic larynx were analyzed. Median follow-up was 5 years (range 2-22). Median pretreatment Hgb was 14.4 gm/dl (range 8.2-17.2). The following parameters were analyzed for their impact on LC, OS, and disease specific survival (DSS): age; gender; pretreatment Hgb; tumor grade; anterior commissure involvement; field size; total dose; dose per fraction; and overall treatment time. Five-year actuarial LC was 84%. Pretreatment Hgb was not a significant predictor for LC when assessed as a continuous variable (P = 0.38), nor as a dichotomous variable with a cutoff at 13 gm/dl. Local control was 82% for patients with Hgb >13 vs. 92% for Hgb < or = 13 (P= 0.13). No other factor was significant for LC. Five-year actuarial OS was 74%. Univariate analysis revealed that, pretreatment Hgb, total dose, and patient age were significant factors for OS. Overall survival was 78% for patients with pretreatment Hgb > 13 gm/dl vs. 68% for patients with Hgb < or = 13 gm/dl (P = 0.004). Overall survival was 77% for patients treated with > 66 Gy vs. 67% for those treated with < or =66 Gy (P = 0.0013), and 80% for patients < or =61 years as opposed to 69% for patients older than 61 years (P = 0.017). Multivariate analysis revealed that only age (P = 0.014) and Hgb concentration (P = 0.001) retained significance. Five-year actuarial DSS was 92%. Pretreatment Hgb was not a prognostic factor for DSS, nor were any other analyzed factors. Pretreatment Hgb is not a significant prognostic factor for LC in patients with T1 squamous cell carcinoma of the glottic larynx, but it does predict for a poorer OS without affecting DSS. This suggests that patients with lower pretreatment Hgb may have confounding medical problems that detract from their overall survival.

Combined radiation and chemotherapy in posttransplant lymphoproliferative disorder.

The optimal treatment for posttransplant lymphoproliferative disorder which has progressed despite a reduction in immunosuppression has not been defined. We report on two patients with stage I posttransplant lymphoproliferative disorder who developed progressive disease despite a reduction in the level of immunosuppression. Both patients were treated with combined short course CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy followed by involved-field radiation therapy. In both patients, a rapid response was obtained followed by complete remission. Combined modality therapy can be utilized successfully in progressive limited stage posttransplant lymphoproliferative disorder.

Transient and stable ionic permeabilization of isolated skeletal muscle cells after electrical shock.

Electroporation of skeletal muscle cell membranes has been postulated to cause myonecrosis in victims of major electrical trauma. To evaluate this concept we carried out a series of experiments to measure the transmembrane potential (delta Vm) threshold for skeletal muscle membrane electroporation using isolated mammalian skeletal muscle cells and compared this threshold with the expected range of delta Vm in victims of electrical trauma. Alterations in membrane Mg2+ or Ca2+ permeability in response to applied extracellular field pulses were quantified by measuring the kinetics of influx before and after field exposure. To avoid heating effects, 4-msec duration field pulses were used. The resting intracellular [Mg2+] was 0.86 +/- 0.01 mmol/l, and [Ca2+] was 0.1 +/- 0.01 microns. The delta Vm threshold for transient or stable electropore formation was determined by performing experiments over a wide range of applied fields. A delta Vm of 340 mV produced no significant change in intracellular [Mg2+]. Delta Vms ranging between 340 to 480 mV caused only a transient influx of Mg2+, indicating that spontaneous sealing of the membrane electropores occurred. A delta Vm of greater than 540 mV caused stable electropore formation. In addition, the efficacy of two surface active polymers as membrane sealing agents was tested. Either 1 mmol/L Poloxamer-188 (8.1 kDa) or 1 mmol/L neutral dextran (10.1 kDa) prevented Mg2+ influx after delta Vms greater than 540 mV (p < 0.001, n = 7). These results suggest that the fields produced in victims of electric shock are sufficient to damage cell membranes by a nonthermal mechanism and that nonionic surfactants may rapidly seal electropores.

A review of the biophysical basis for the clinical application of electric fields in soft-tissue repair.

Interest in the role of electrical interactions as epigenetic regulators of wound healing had its beginnings nearly 40 years ago. Because the mechanisms of action are not understood (which obviates rational therapy), the empiric application of fields to wounds has produced mixed results. However, taken collectively, clinical trials have demonstrated some beneficial effects. Tests on soft tissues of animals have shown that electric stimulation can influence the rate of wound healing and scar strength. Natural epithelial-derived sodium currents have been discovered in the wounds of invertebrates and mammals. It is theorized that these currents may be a normal controlling factor in wound healing. Therefore, perturbation of these signals is important to understand. The purpose of this review is to put into proper perspective the biophysical, physiological, and clinical data pertaining to use of electricity to control wound healing, with the goal of minimizing much of the prevailing confusion.