Percutaneous transhepatic portal catheterization guided by ultrasound technology for islet transplantation in rhesus monkey

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

Pancreatic islet transplantation has been validated as a valuable therapy for type 1 diabetes mellitus patients with exhausted insulin treatment. However, this therapy remains limited by the shortage of donor and the requirement of lifelong immunosuppression. Islet encapsulation, as an available bioartificial pancreas (BAP), represents a promising approach to enable protecting islet grafts without or with minimal immunosuppression and possibly expanding the donor pool. To develop a clinically implantable BAP, some key aspects need to be taken into account: encapsulation material, capsule design, and implant site. Among them, the implant site exerts an important influence on the engraftment, stability, and biocompatibility of implanted BAP. Currently, an optimal site for encapsulated islet transplantation may include sufficient capacity to host large graft volumes, portal drainage, ease of access using safe and reproducible procedure, adequate blood/oxygen supply, minimal immune/inflammatory reaction, pliable for noninvasive imaging and biopsy, and potential of local microenvironment manipulation or bioengineering. Varying degrees of success have been confirmed with the utilization of liver or extrahepatic sites in an experimental or preclinical setting. However, the ideal implant site remains to be further engineered or selected for the widespread application of encapsulated islet transplantation.

Comparison of physical parameter measurements between peripheral and portal blood samples in patients with portal hypertension

BACKGROUND

Measuring portal venous pressure is necessary to examine, diagnose, and treat portal hypertension, but current methods are invasive.

OBJECTIVE

This study aimed to determine whether a noninvasive peripheral blood measurement could be used to estimate portal venous pressure by investigating correlations between certain physical parameter measurements in the peripheral blood with those obtained in portal blood samples.

METHODS

A total of 128 peripheral and portal blood samples from patients (n= 128) were analyzed for blood rheology and routine blood parameters.

RESULTS

The mean peripheral and portal whole blood viscosities under the shear rates of 200 s-1 (BV 200 s-1) were 2.97 ± 0.50 mPa.s and 3.06 ± 0.39 mPa.s. The mean peripheral and portal BV 30 s-1 values were 3.96 ± 0.79 mPa.s and 4.16 ± 0.64 mPa.s. We observed strong correlations between peripheral and portal blood measurements of BV 200 s-1 (r2= 0.9649), BV 30 s-1 (r2= 0.9622), BV 5 s-1 (r2= 0.9610), and BV 1 s-1 (r2= 0.9623).

CONCLUSIONS

Our results indicate that peripheral blood can be used to evaluate certain parameters in portal blood for use in biofluid mechanics studies, and to provide noninvasive measurement of portal venous pressure.

Anatomically Realistic Simulations of Liver Ablation by Irreversible Electroporation: Impact of Blood Vessels on Ablation Volumes and Undertreatment

Irreversible electroporation is a novel tissue ablation technique which entails delivering intense electrical pulses to target tissue, hence producing fatal defects in the cell membrane. The present study numerically analyzes the potential impact of liver blood vessels on ablation by irreversible electroporation because of their influence on the electric field distribution. An anatomically realistic computer model of the liver and its vasculature within an abdominal section was employed, and blood vessels down to 0.4 mm in diameter were considered. In this model, the electric field distribution was simulated in a large series of scenarios (N = 576) corresponding to plausible percutaneous irreversible electroporation treatments by needle electrode pairs. These modeled treatments were relatively superficial (maximum penetration depth of the electrode within the liver = 26 mm) and it was ensured that the electrodes did not penetrate the vessels nor were in contact with them. In terms of total ablation volume, the maximum deviation caused by the presence of the vessels was 6%, which could be considered negligible compared to the impact by other sources of uncertainty. Sublethal field magnitudes were noticed around vessels covering volumes of up to 228 mm³. If in this model the blood was substituted by a liquid with a low electrical conductivity (0.1 S/m), the maximum volume covered by sublethal field magnitudes was 3.7 mm³ and almost no sublethal regions were observable. We conclude that undertreatment around blood vessels may occur in current liver ablation procedures by irreversible electroporation. Infusion of isotonic low conductivity liquids into the liver vasculature could prevent this risk.

Strategy for clinical setting in intramuscular and subcutaneous islet transplantation

Intraportal islet transplantation has a long history as a procedure for clinical islet transplantation. However, many recent studies revealed that the intraportal procedure has some disadvantages in transplant efficiency and safety. Many candidates as an optimal transplant site for islets have been assessed, but further studies and clinical trials are still necessary. Intramuscular and subcutaneous spaces are important candidates, because the transplant and biopsy procedures are simple approaches with minimal invasion and few complications. Although they are sites with hypovascularity and hypoxia, which contribute to the poor transplant efficiency, many experimental trials for improving the outcome in intramuscular and subcutaneous islet transplantations have been performed, focusing on early angiogenesis and scaffolds for engrafting transplanted islets. We review current progress in intramuscular and subcutaneous islet transplantations and discuss ways to develop them as optimal transplant sites for islets.