Pathological metabolic conditions such as ischemia induce the rupture of the mitochondrial envelope and the release of pro-apoptotic proteins, leading to cell death. At the onset of this process, the inner mitochondrial membrane becomes depolarized and permeable to osmolytes, proposedly due to the opening of a non-selective protein channel of unknown molecular identity. A recent study purports that this channel, referred to as Mitochondrial Permeability Transition Pore (MPTP), is formed within the c-subunit ring of the ATP synthase, upon its dissociation from the catalytic domain of the enzyme. Here, we examine this claim for two c-rings of different lumen width, through calculations of their ion conductance and selectivity based on all-atom molecular dynamics simulations. We also quantify the likelihood that the lumen of these c-rings is in a hydrated, potentially conducting state rather than empty or blocked by lipid molecules. These calculations demonstrate that the structure and biophysical properties of a correctly assembled c-ring are inconsistent with those attributed to the MPTP.DOI: http://dx.doi.org/10.7554/eLife.23781.001

While surgery is at the foundation of cancer treatment, its access is limited in low-income countries. Here, we describe development of a low-cost alternative therapy based on intratumoral ethanol injection suitable for resource-limited settings. Although ethanol-based tumor ablation is successful in treating hepatocellular carcinomas, the necessity for multiple treatments, injection of large fluid volumes, and decreased efficacy in treatment of non-capsulated tumors limit its applicability. To address these limitations, we investigated an enhanced ethanol ablation strategy to retain ethanol within the tumor through the addition of ethyl cellulose. This increases the viscosity of injected ethanol and forms an ethanol-based gel-phase upon exposure to the aqueous tumor environment. This technique was first optimized to maximize distribution volume, using tissue-simulating phantoms. Then, chemically-induced epithelial tumors in the hamster cheek pouch were treated. As controls, pure ethanol injections of either four times or one-fourth the tumor volume induced complete regression of 33% and 0% of tumors, respectively. In contrast, ethyl cellulose-ethanol injections of one-fourth the tumor volume induced complete regression in 100% of tumors. These results contribute to proof-of-concept for enhanced ethanol ablation as a novel and effective alternative to surgery for tumor treatment, with relevance to resource-limited settings.

Ethanol ablation, the injection of ethanol to induce necrosis, was originally used to treat hepatocellular carcinoma, with survival rates comparable to surgery. However, efficacy is limited due to leakage into surrounding tissue. To reduce leakage, we previously reported incorporating ethyl cellulose (EC) with ethanol as this mixture forms a gel when injected into tissue. To further develop EC-ethanol injection as an ablative therapy, the present study evaluates the extent to which salient injection parameters govern the injected fluid distribution. Methods: Utilizing ex vivo swine liver, injection parameters (infusion rate, EC%, infusion volume) were examined with fluorescein added to each solution. After injection, tissue samples were frozen, sectioned, and imaged. Results: While leakage was higher for ethanol and 3%EC-ethanol at a rate of 10 mL/hr compared to 1 mL/hr, leakage remained low for 6%EC-ethanol regardless of infusion rate. The impact of infusion volume and pressure were also investigated first in tissue-mimicking surrogates and then in tissue. Results indicated that there is a critical infusion pressure beyond which crack formation occurs leading to fluid leakage. At a rate of 10 mL/hr, a volume of 50 µL remained below the critical pressure. Conclusions: Although increasing the infusion rate increases stress on the tissue and the risk of crack formation, injections of 6%EC-ethanol were localized regardless of infusion rate. To further limit leakage, multiple low-volume infusions may be employed. Significance: These results, and the experimental framework developed to obtain them, can inform optimizing EC-ethanol to treat a range of medical conditions.

Ethanol provides a rapid, low-cost ablative solution for liver tumors with a small technological footprint but suffers from uncontrolled diffusion in target tissue, limiting treatment precision and accuracy. Incorporating the gel-forming polymer ethyl cellulose to ethanol localizes the distribution. The purpose of this study was to establish a non-invasive methodology based on CT imaging to quantitatively determine the relationship between the delivery parameters of the EC-ethanol formulation, its distribution, and the corresponding necrotic volume. The relationship of radiodensity to ethanol concentration was characterized with water–ethanol surrogates. Ex vivo EC-ethanol ablations were performed to optimize the formulation (n = 6). In vivo ablations were performed to compare the optimal EC-ethanol formulation to pure ethanol (n = 6). Ablations were monitored with CT and ethanol distribution volume was quantified. Livers were removed, sectioned and stained with NADH-diaphorase to determine the ablative extent, and a detailed time-course histological study was performed to assess the wound healing process. CT imaging of ethanol–water surrogates demonstrated the ethanol concentration-radiodensity relationship is approximately linear. A concentration of 12% EC in ethanol created the largest distribution volume, more than eight-fold that of pure ethanol, ex vivo. In vivo, 12% EC-ethanol was superior to pure ethanol, yielding a distribution volume three-fold greater and an ablation zone six-fold greater than pure ethanol. Finally, a time course histological evaluation of the liver post-ablation with 12% EC-ethanol and pure ethanol revealed that while both induce coagulative necrosis and similar tissue responses at 1–4 weeks post-ablation, 12% EC-ethanol yielded a larger ablation zone. The current study demonstrates the suitability of CT imaging to determine distribution volume and concentration of ethanol in tissue. The distribution volume of EC-ethanol is nearly equivalent to the resultant necrotic volume and increases distribution and necrosis compared to pure ethanol.