The use of cryosurgery in the treatment of uterine fibroids is emerging as a possible treatment modality. The two known mechanisms of direct cell injury during the tissue freezing process are linked to intracellular ice formation and cellular dehydration. These processes have not been quantified within uterine fibroid tumor tissue. This study reports the use of a combination of freeze-substitution microscopy and differential scanning calorimetry (DSC) to quantify freeze-induced dehydration within uterine fibroid tumor tissue. Stereological analysis of histological tumor sections was used to obtain the initial cellular volume (Vo) or the Krogh model dimensions (ΔX, the distance between the microvascular channels = 15.5/μm, rvo, the initial radius of the extracellular space = 4.8 μm, and L, the axial length of the Krogh cylinder = 19.1 μm), the interstitial volume (∼23%), and the vascular volume (∼7%) of the fibroid tumor tissue. A Boyle-van't Hoff plot was then constructed by examining freeze-substituted micrographs of "equilibrium"-cooled tissue slices to obtain the osmotically inactive cell volume, Vb = 0.47Vo. The high interstitial volume precludes the use of freeze-substitution microscopy data to quantify freeze-induced dehydration. Therefore, a DSC technique, which does not suffer from this artifact, was used to obtain the water transport data. A model of water transport was fit to the calorimetric data at 5 and 20°C/min to obtain the "combined best fit" membrane permeability parameters of the embedded fibroid tumor cells, assuming either a Krogh cylinder geometry, Lpg = 0.92 × 10 -13 m3/Ns (0.55 μm/min atm) and ELp = 129.3 kJ/mol (30.9 kcal/mol), or a spherical cell geometry (cell diameter = 18.3 μm), Lpg = 0.45 × 10-13 m3/Ns (0.27 μm/min atm) and ELp = 110.5 kJ/mol (26.4 kcal/mol). In addition, numerical simulations were performed to generate conservative estimates, in the absence of ice nucleation between -5 and -30°C, of intracellular ice volume in the tumor tissue at various cooling rates typical of those experienced during cryosurgery (≤100°C/min). With this assumption, the Krogh model simulations showed that the fibroid tumor tissue cells cooled at rates ≤50°C/min are essentially dehydrated; however, at rates >50°C/min the amount of water trapped within the tissue cells increases rapidly with increasing cooling rate, suggesting the formation of intracellular ice.
Bibliographical noteFunding Information:
Received January 18, 2001; accepted July 12, 2001. This work was funded by NSF-BES 9703326 and a grant from Materials Research Science and Engineering Center (MRSEC) at the University of Minnesota. 1 To whom correspondence should be addressed.
- Differential scanning calorimetry
- ELT-3 leiomyomas
- Krogh model
- Low temperature microscopy
- Membrane permeability