A molecular dynamics study of DMPC lipid bilayers interacting with dimethylsulfoxide-water mixtures.

The diffusion process of dimethylsulfoxide (DMSO) through zwitterionic dimyristoylphosphatidylcholine (DMPC) lipid bilayer was studied by means of molecular dynamics (MD) simulations. To account for the cryoprotectant concentration difference between the inside and the outside of the cell, dual DMPC lipid bilayers which separate two aqueous reservoirs with and without DMSO were modeled. The initial configuration of the simulation model had DMSO molecules present in one of the aqueous phases (outside the cell) at two different concentrations of ~3 and ~6 mol%. MD simulations were performed on the systems for 50 ns at 323 K and 1 bar. Although the simulation time considered in the study was insufficient for the DMSO molecules to reach the other aqueous phase and equilibrium, early stages of the diffusion process indicated that DMSO molecules had a tendency to diffuse towards the other aqueous phase. The effects of DMSO on bilayer structural characteristics during the diffusion process were investigated. Simulations were analyzed to correlate the following properties of lipid bilayers in the presence of two different aqueous phases: area per lipid, lipid thickness, mass density profiles, lipid tail order parameter and water dipole orientation. Area per lipid calculated for the leaflet facing the aqueous DMSO-water mixture did not show any significant difference compared to area per lipid for the DMSO-free pure DMPC bilayer. Mass density profiles revealed that DMSO molecules had a strong tendency to diffuse toward the aqueous phase with pure water. The lipid tail order parameter calculated for the sn-1 tail of the leaflet facing the aqueous DMSO-water mixture showed that the ordering of lipid tails decreased compared to the leaflet exposed to pure water. However, the ordering of lipid tails in a system where a single bilayer is hydrated by an aqueous DMSO-water mixture is far lower.

Comparison of the permeability properties and post-thaw motility of ejaculated and epididymal bovine spermatozoa.

There are very few experimental reports on the comparative water transport (membrane permeability) characteristics of ejaculated and epididymal mammalian spermatozoa during freezing. In the present study, we report the effects of cooling ejaculated and epididymal bovine sperm from the same males with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal bovine sperm suspensions were obtained at a cooling rate of 20 degrees C/min under two different conditions: (1) in the absence of any cryoprotective agents, CPAs and, (2) in the presence of 0.7 M glycerol. Using values published in the literature, we modeled the spermatozoa as a cylinder of length 39.8 microm and a radius of 0.4 microm with an osmotically inactive cell volume, V(b), of 0.61 V(o), where V(o) is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L(pg) and activation energy, E(Lp)). The predicted best-fit permeability parameters ranged from, L(pg)=0.021-0.038 microm/min-atm and E(Lp)=27.8-41.1 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal bovine spermatozoa under corresponding cooling conditions. If this observation is found to be more generally valid for other mammalian species as well, then in the future the sperm extracted from the testes of a postmortem male could be optimally cryopreserved using procedures similar to those derived for ejaculated sperm.

The Bouveret syndrome: an unusual cause of hematemesis.

Gallstones are usually silent. Less commonly, patients with cholelithiasis develop symptoms and/or complications; biliary fistula occurs in 3% to 5% of the cases. When a large stone is passed and occludes the duodenum, gastric outlet obstruction (the Bouveret syndrome) may result. In reported cases, the stones are usually larger than 2.5 cm. The usual presenting symptoms are those of bowel obstruction: abdominal pain, nausea, and vomiting. Less commonly, the patients experience melena and, rarely, hematemesis. We describe a patient who had the largest stone reported to cause hematemesis rather than bowel obstruction and to be diagnosed endoscopically. The 5 X 4 X 3 cm stone was extracted surgically. Endoscopic diagnosis and extraction of stones up to 3 cm in size has been reported, avoiding the need for surgery.

Cocaine-induced hepatonephrotoxicity: a case report.

Hepatotoxicity due to cocaine has been well described in animal models. There are few reports on cocaine-induced hepatic injury in humans; however, its link to rhabdomyolysis and renal failure is better known. We report a case of reversible acute hepatonephrotoxicity associated with recreational cocaine use. The proposed mechanisms responsible for its hepatic and renal toxicity are reviewed.

Papillary cystadenocarcinoma of the bile ducts resulting in hemobilia.

Cystadenocarcinoma is a rare tumor of the intrahepatic and a very rare tumor of the extrahepatic biliary system. In the reported cases, abdominal swelling is the most common presenting symptom, followed by right upper quadrant mass. Melena was the initial presenting symptom in the present case. Bleeding into the second part of the duodenum was observed only during the third diagnostic esophagogastroduodenoscopy. Hemobilia was suspected because of abnormal liver enzymes and a mass in the left lobe of the liver on computerized tomography. At laparotomy, we suspected that the mass was a hemangioma. Cystadenocarcinoma diagnosis was made only by histopathological examination.