Visbal-Onufrak, Michelle A.

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    Protein denaturation during magnetic fluid hyperthermia at a constant thermal dose
    (2012) Visbal-Onufrak, Michelle A.; Juan-García, Eduardo J.; College of Engineering; Rinaldi-Ramos, Carlos; Toledo-Quiñones, Manuel; Department of Electrical and Computer Engineering; Calderón, Andrés
    Although the exact pathways leading to cell killing during hyperthermia are still not fully understood, it appears that protein denaturation is crucial in such process. To determine if the manner in which the magnetic field is applied has an effect on the amount of protein denaturation induced, three different magnetic field profiles were applied during Magnetic Fluid Hyperthermia (MFH) with equivalent thermal dose or Cumulative Equivalent Minutes under a reference temperature of 43oC (CEM43oC). Conformational changes induced by thermal denaturation of Bovine serum albumin (BSA) protein were monitored by changes in fluorescence of 8-anilinonaphthalene-1-sulfonic acid (1,8-ANS) bound to the protein's hydrophobic sites. Iron oxide nanoparticles coated with covalently attached carboxymethyl-dextran (IO-covCMDx) were added to samples at a concentration of 0.6 mg IO core/ml. MFH under the different conditions and hot water hyperthermia (HWH) were applied to ANS-BSA samples until an equivalent thermal dose of 60 CEM43oC was achieved. For MFH, average induction heater power values of 44% (average magnetic field intensity of H = 40.5 kA/m) for TSP = 43oC and 55% (average magnetic field intensity of H = 45.7 kA/m) for TSP = 45oC were used, with the following schedules: constant power, and three different square waveforms with high power level working cycles of A - 67%, B - 33%, and C - 50%. ANS-BSA exposed to MFH at 43oC exhibited greater denaturation than standard HWH treatment under equal temperature set points and CEM43oC of 60 minutes. Moreover, for a temperature set point of 45oC and equal CEM43oC, fluorescence recovery of ANS-BSA observed between MFH and HWH showed similar behavior to the temperature set point of 43oC. Between the different MFH conditions applied, results showed statistically similar denaturation was achieved using constant power versus Condition A, whereas Condition B achieved greater denaturation than the previous two conditions. For Condition C, denaturation achieved was similar to that under Condition A, for both temperature set points. Importantly, the results demonstrate that under same conditions of CEM43°C MFH results in greater irreversible protein denaturation, compared to HWH. Furthermore, the results demonstrate that even under conditions of equal average power and equal medium temperature, alternating magnetic field working cycles with higher power application result in greater irreversible protein denaturation contrary to expectations based on continuum heat transfer arguments. However as the heat dissipation rate for IO-covCMDx does not increase linearly with magnetic field intensity, the average SAR values applied for higher power values were not equivalent during all conditions even though average power was used.