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Biomedical subjects

B Rubinsky

Publications and source records attributed to B Rubinsky.

At least 55 records · Page 3Linked to original sources
PubMed1992

Inhibition of Ca2+ and K+ currents by "antifreeze" proteins.

For the last two decades, the research on fish "antifreeze" proteins has focused exclusively on their ability to depress noncolligatively blood plasma freezing points, presumably by binding to ice crystals. We report evidence that antifreeze polypeptides from the winter flounder (Pseudopleuronectes americanus) have another special property, the ability to block ion channels. In experiments with porcine granulosa cells we show, using the patch-clamp technique in the whole cell configuration, that these proteins suppress effectively calcium and potassium currents. The results of dose-response studies indicate a protein-protein interaction mechanism.

Animals↗
PubMed1992

Cryomicroscopic analysis of freezing in liver of the freeze-tolerant wood frog.

The technique of directional solidification coupled with low-temperature scanning electron microscopy was applied to analyze the freezing of liver slices from the freeze-tolerant frog Rana sylvatica. Micrographs of liver slices from 5 degrees C-acclimated frogs frozen on the directional stage to -7 degrees C showed continuous ice formed along an expanded vasculature with hepatocytes that were shrunken and virtually dehydrated. However, when frogs were given a survivable freezing exposure at -4 degrees C for 24 h, liver slices subsequently frozen in vitro at -7 degrees C were much less shrunken and the presence of intracellular ice crystals (formed when samples were plunged into liquid N2 before microscopy) demonstrated that ample free water remained in these hepatocytes at -7 degrees C. This reduced level of cell dehydration was correlated with the buildup of 280 +/- 61 mumol/g wet wt glucose as a cryoprotectant in liver during the -4 degrees C exposure in vivo. The study provides the first direct cytological analysis of the freezing process in an organ of a freeze-tolerant vertebrate and the first confirmation of the relationship between maintenance of a critical minimum cell volume and freezing survival by these animals.

Acclimatization↗
PubMed1991

Hypothermic protection--a fundamental property of "antifreeze" proteins.

For the last two decades fish antifreeze proteins have been considered to function exclusively in conferring freeze-resistance to fish by binding to ice crystals and thereby depressing blood plasma freezing points non-colligatively. We report here the discovery of a second fundamental property of antifreeze proteins, the ability to protect cells and their membranes from hypothermic damage. Experiments were carried out exposing immature bovine oocytes to 4 degrees C for 24 h in the presence of type I alanine rich alpha helical antifreeze polypeptides (AFP) from winter flounder, type II cysteine-rich AFP from sea raven or type III AFP from ocean pout. The presence of AFP in the incubation medium resulted in an approximate four fold increase in the number of oocytes retaining an intact oolemma and a three fold increase in the number of oocytes able to undergo in vitro maturation. None of the control oocytes could be fertilized, whereas, of those incubated in AFP, the percentage which developed normally following fertilization was comparable to that observed for fresh oocytes. These results indicate that cold-sensitive mammalian cells can be rendered cold-tolerant through the addition of "antifreeze" proteins.

Animals↗
PubMed1991

Ultrasound-guided hepatic cryosurgery in the treatment of metastatic colon carcinoma. Preliminary results.

Cryosurgery, the in situ freezing of cancer, has been proposed in the past as a possible treatment for unresectable hepatic tumors. Its advantage lies in the fact that it is a very focal treatment sacrificing less normal tissue than surgical resection, allowing treatment of multiple lobes. Because cryosurgery does not affect large vessels, tumors in difficult locations, such as adjacent to the inferior vena cava (IVC), can be treated. With the use of intraoperative ultrasound to place the cryoprobes and monitor the freezing process, 18 patients with unresectable metastatic colon carcinoma confined to the liver were treated. Of the 18 patients treated, 4 (22%) are in complete remission as determined by computed tomography (CT) scans and carcinoembryonic antigen (CEA) levels, with a mean follow-up of 28.8 months. Four patients (22%) were not adequately treated at the time of cryosurgery. The number of lesions frozen in each patient ranged from 1 to 12, with a mean of 6 lesions. Fourteen patients had bilobar disease; three patients had previous right lobectomies with recurrences in their remaining left lobes prior to cryosurgery, and one patient had unilobar disease. Mean survival of the 14 cases with recurrence was 21.4 months, with 2 of the 14 still alive. Ultrasound-guided hepatic cryosurgery appears to be an effective treatment for metastatic colon carcinoma to the liver that is unresectable (including patients with bilobar and multiple lesions). These preliminary results indicate that the procedure warrants further study.

Adult↗
PubMed1991

Percutaneous transperineal prostate cryosurgery using transrectal ultrasound guidance: animal model.

Cryosurgery has previously been used successfully to treat prostatic carcinoma. Inability to monitor the freezing led to local complications that limited the use of this modality. Recent studies have shown that monitoring of the freezing process can be accomplished using real-time ultrasound. In this study, transrectal ultrasound guidance was used to guide a cryoprobe percutaneously, using a transperineal approach, into the prostate. The extent of freezing was then monitored using ultrasound, taking care not to freeze the urethra or the rectum. Six dogs had the procedure without any complications. This study demonstrates the feasibility of a noninvasive treatment for prostatic carcinoma.

Animals↗
PubMed1990

The effect of antifreeze glycopeptides on membrane potential changes at hypothermic temperatures.

The research on antifreeze glycopeptides (AFGPs) from Antarctic and Arctic fishes has focused primarily on their interaction with ice crystals. This study reports results of experiments in which pig oocytes, known to be sensitive to hypothermic temperatures, were exposed to 4 degrees C for various periods of time, in solutions of different molecular weight AFGPs from Antarctic nototheniid fishes. The membrane potential was measured across the oolemma following hypothermic exposure. The results show that a physiological combination of the different molecular weight AFGPs protects the structural integrity of the oolemma and inhibits ion leakage across the oolemma at hypothermic temperatures. The results also show that the hypothermic protection is nonlinearly dependent on concentration and that separately, the different molecular weight glycopeptides do not stop ion leakage even at very high concentration. The protection of membranes at hypothermic temperatures is a new property of AFGPs which was not known prior to our work.

Animals↗
PubMed1990

Effects of cooling rate and glycerol concentration on the structure of the frozen kidney: assessment by cryo-scanning electron microscopy.

An experimental technique, employing a directional solidification stage for controlled freezing of tissue samples and low-temperature scanning electron microscopy for observation of the structure of the frozen-hydrated samples, was used to study freezing processes in the kidney. Parametric studies in which the cooling rate during freezing and the concentration of glycerol in the tissue were varied confirmed the results of earlier freeze-substitution studies. The results suggest a mechanism for ice propagation in the kidney similar to that already proposed for the liver, in which ice originates in, and is subsequently propagated through, the peritubular vasculature. The ice front dehydrates the cells and tubular structures encountered in its path, thus preventing intraluminal freezing. At higher rates of cooling and increased concentrations of glycerol there is less dehydration of cortical structure and intraluminal freezing occurs.

Animals↗
PubMed1990

The process of freezing and the mechanism of damage during hepatic cryosurgery.

Experiments were performed to correlate the structures of liver tissue frozen during cryosurgery, liver frozen at various constant cooling rates, and unfrozen, dried normal liver. The results show that during freezing of tissue ice forms and propagates along the vascular system, expanding during freezing at low cooling rates. This expansion occurs over most of the region frozen during cryosurgery and may be one of the mechanisms of damage to tissue during cryosurgery.

Animals↗
PubMed1988

A mathematical model for the freezing process in biological tissue.

A mathematical model has been developed to study the process of freezing in biological organs. The model consists of a repetitive unit structure comprising a cylinder of tissue with an axial blood vessel (Krogh cylinder) and it is analysed by the methods of irreversible thermodynamics. The mathematical simulation of the freezing process in liver tissue compares remarkably well with experimental data on the structure of tissue frozen under controlled thermal conditions and the response of liver cells to changes in cooling rate. The study also supports the proposal that the damage mechanism responsible for the lack of success in attempts to preserve tissue in a frozen state, under conditions in which cells in suspension survive freezing, is direct mechanical damage caused by the formation of ice in the vascular system.

Animals↗
PubMed1987

Heat transfer during cryopreservation by perfusion through the vascular system.

An analytical study was performed to determine whether it is possible to uniformly freeze or thaw biological tissue by perfusion with a fluid that transfers heat along the vascular system. A simple criterion was developed to evaluate the thermal performance of heat transfer fluids. The results show that fluids that have been considered in the past for heating or cooling by perfusion are unable to transfer heat uniformly through the tissue.

Animals↗
PubMed1986

Analysis of the introduction and removal of glycerol in rabbit kidneys using a Krogh cylinder model.

In 1982, Rubinsky and Cravalho described a Krogh cylinder model for the analysis of cryoprotectant transport in a perfused organ. By application of the Kedem-Katchalsky equations, changes in tissue volume caused by movements of water and solute were used to predict changes in capillary radius (Cryobiology 19, 70-82, 1982). We have now measured the changes in vascular resistance that are produced when sucrose or glycerol is introduced into the perfusate flowing through rabbit kidneys at 10 degrees C, and have analyzed these data by means of the Rubinsky-Cravalho semiempirical model. The sucrose data provided an estimate of hydraulic conductivity and the dimensions of the Krogh tissue units. Three rates of addition of glycerol, 10, 30, and 90 mM/min to a final concentration of 3 M, were studied. The vascular resistance fell to approximately 40% of its initial value (radius approximately 128% of initial value) with all three rates of addition, and then returned toward its normal value while the glycerol concentration was still increasing. This behavior could be explained either by a sudden change in solute permeability at that capillary radius, or by an inverse dependence of reflection coefficient upon solute concentration. Evidence is presented that favors the latter interpretation. The best fits for the apparent hydraulic conductivity and apparent solute permeability for glycerol are 1 X 10(-6) cm/sec atm and 6 X 10(-8) cm/sec, respectively, with the reflection coefficient falling from 1.0 when the glycerol concentration is zero to 0.1 when it is 3 M. The model is used to predict tissue concentrations of glycerol throughout each experiment.

Animals↗
PubMed1986

Ultrasound monitored hepatic cryosurgery: longevity study on an animal model.

Ultrasound imaging has been proposed to monitor the amount of frozen tissue during hepatic cryosurgery of primary and metastatic tumors. In this follow-up study, a cryolesion was produced in an adult pig under ultrasound monitoring. The animal was allowed to recuperate for 3 days before being sacrificed. Pathologic and histologic evaluation showed extremely close correlation with the ultrasound image. The necrotic region was clearly observable in the sonogram after 3 days. Ultrasonography can accurately represent the extent of the cryolesion both during as well as following cryosurgery.

Animals↗
PubMed1986

Society of Gastrointestinal Radiologists Roscoe E. Miller Award. Monitoring hepatic cryosurgery with sonography.

The intraoperative sonographic appearance of frozen hepatic tumors and frozen normal liver was correlated with the histologic appearance of pathologic specimens from six patients. Frozen tissue was visualized as a hyperechoic rim with posterior acoustic shadowing. Normal liver that was frozen and then thawed appeared hypoechoic when compared with normal unfrozen liver. These findings allowed visualization of the extent of freezing in relation to tumor margins. Pathologically, frozen tumors showed definite evidence of necrosis. Normal liver tissue was extremely sensitive to cold and was completely necrotic after freezing. The sonographic appearance of frozen and thawed liver correlated precisely with the gross morphologic and histologic changes seen in the cryolesion. It appears that intraoperative sonography allows accurate monitoring of hepatic cryosurgery.

Carcinoma↗
PubMed1985

Real time ultrasonic monitoring of hepatic cryosurgery.

Cryosurgery has a number of advantages that make it particularly appealing in the treatment of liver cancer. However, a major problem in the clinical application of hepatic cryosurgery is the lack of a precise means of monitoring the freezing process in situ. Preliminary investigations on simulated tissue have shown that standard ultrasonography is capable of accurately determining the amount of frozen material during a cryosurgical procedure. To extend these results to living tissue, cryosurgery was performed, in vivo, on the livers of four mongrel dogs. An ultrasound imaging device using a new intraoperative ultrasound transducer monitored the entire process in real time. The results indicate that the entire freezing and thawing cycle can be monitored easily using real time ultrasound. During freezing, the solidification interface can be seen to move through the tissue allowing clear imaging of the cryolesion. After complete thawing, the cryolesion became less echogenic than before freezing and was therefore distinguishable under ultrasound. Postsurgical pathologic examination showed excellent correlation between the lesion size and its ultrasonic image.

Animals↗
PubMed1985

Sonographic monitoring of hepatic cryosurgery in an experimental animal model.

Several cryosurgical techniques for freezing hepatic parenchyma have been developed. To assess the efficacy of sonographic monitoring of hepatic cryosurgery, an experimental animal model was devised. Real-time sonography was used to monitor the in vivo evolution of hypothermically induced hepatic cryolesions in four mongrel dogs. The results suggest that sonography is an effective and accurate means of monitoring the entire freezing and thawing cycle in hepatic cryosurgery.

Animals↗
PubMed1984

An analytical method to evaluate cooling rates during cryopreservation protocols for organs.

A simple, graphical procedure has been established to estimate the cooling rates at a specified location and temperature in a biological medium frozen by imposing a constant cooling rate at the outer surface. The graphical procedure also facilitates the determination of the outer surface temperature at the instant a given temperature has been attained in a specific location. The results obtained through a numerical study using finite elements can be applied to biological media with various chemical compositions including different concentrations of cryoprotective agents.

Freezing↗
PubMed1984

Ultrasonic characteristics of frozen liver.

The recent development of new ultrasound probes has made real-time intraoperative monitoring of cryosurgery, and thermocouple placement a possibility. It is shown that frozen tissue and thermocouple needles have acoustic characteristics that enable them to be easily visualized by ultrasound examination. Further in vivo animal studies are needed to examine temperature characteristics of visualized cryolesions, to develop scanning techniques, and to correlate ultrasonic findings with histologic changes in tissue.

Animals↗