Enhanced delivery to target cells by heat-sensitive immunoliposomes.

Heat-sensitive immunoliposomes are capable of releasing the entrapped content at the target cell surface upon a brief heating to the phase transition temperature of the liposome membrane. In this study we have examined the delivery efficiency of drugs entrapped in heat-sensitive immunoliposomes. Immunoliposomes composed of dipalmitoyl phosphatidylcholine with entrapped [3H]uridine were incubated with target cells at 4 degrees C. The cell-liposome mixture was then heated to 41 degrees C and the uptake of [3H]uridine into the intracellular pool of phosphorylated uridine-containing molecules was measured. The immunoliposomes showed maximal release of the uridine at 41 degrees C, the phase transition temperature of dipalmitoyl phosphatidylcholine liposomes. The largest accumulation of [3H]uridine in the target cells also took place at 41 degrees C. The initial level of uptake of [3H]uridine released from immunoliposomes by heating was greatly enhanced over that observed for free [3H]uridine and [3H]uridine released from liposomes without attached antibody. The nucleoside uptake inhibitors nitrothiobenzylinosine, dipyridamole, and unlabeled uridine were able to inhibit uptake of [3H]uridine released from immunoliposomes. This supports the hypothesis that the enhanced uptake is due to a heat-induced release of [3H]uridine at the cell surface followed by transport and phosphorylation of [3H]uridine by the target cells. These results indicate the feasibility of using the heat-sensitive immunoliposomes as a target-specific drug delivery system.     

Effect of calcium channel blocking agents on infarct size after ischaemia-reperfusion in anaesthetised pigs: relationship between cardioprotection and cardiodepression.

We compared the abilities of verapamil and nicardipine to protect the porcine myocardium from the consequences of ischaemia-reperfusion in vivo. Infusion of verapamil (50 micrograms/kg) into the left anterior descending coronary artery LAD (i.c.a.), in 15 min immediately before ligation depressed regional contractile function, reduced infarct size by 80%, and enabled contractile function to recover partially during reperfusion. Verapamil (10 micrograms/kg i.c.a.) did not depress contractile function before ligation or permit its recovery during reperfusion, despite reducing infarct size by 80%. Lower doses of verapamil were not cardioprotective. Nicardipine (10 and 30 micrograms/kg i.c.a.) depressed contractile function before ligation but did not permit its recovery during reperfusion. Nicardipine did not reduce infarct size development. Thus, drug-induced negative inotropic activity (which presumably reflects myocardial calcium channel blockade) and cardioprotection are not linked. Verapamil can markedly reduce infarct size development at a dose that exerts no detectable negative inotropic activity. This cardioprotective effect of verapamil was greatly reduced by intravenous (i.v) pretreatment with aspirin (30 mg/kg), which alone did not alter infarct size development. Thus, the cardioprotective effect of verapamil (10 micrograms/kg i.c.a.) appears to be mediated by a cyclooxygenase product, possibly prostacyclin.     

Normal release from proactive interference in untreated patients with Parkinson's disease.

The relationship of release from proactive interference (PI) to set-shifting, explicit free recall and language remains controversial. We tested 56 patients with Parkinson's disease (PD) who had never received medication and 37 matched normal control subjects on a test of PI release based on semantic category. The PD group showed normal PI release but impaired word recall. PI release was independent of impaired Wisconsin card-sorting test performance, language production, explicit memory, overall cognitive status and severity of depression. The results indicate dissociation between ability to benefit from semantic stimulus properties and processes of explicit memory, set-shifting and expressive language.     

Successful treatment of diabetes with the biohybrid artificial pancreas in dogs

We have investigated a new hybrid artificial pancreas device to transplant islet allografts without immunosuppression. The device consists of a chamber through which passes a copolymer membrane connected to standard vascular grafts. Islets are placed inside the chamber but are outside of the blood stream. Nominal molecular porosity of 80,000 daltons permits free diffusion of nutrients and insulin across the membrane but inhibits the entry of immunoglobulins and immunocytes from the blood stream into the chamber. Initial studies focused on the technical feasibility of implanting the unseeded (no islets) devices. In 12 normal mongrel dogs, the arterial limb of the device was anastomosed end-to-end to the common iliac artery and the venous limb end-to-side to the common iliac vein. Vascular patency was monitored by an audible bruit over the device. Two devices currently remain patent at 388 and 421 days. The remaining experiments failed due to thrombosis and membrane rupture, with 2 failing as late as 170 and 279 days. In a second series, both arterial and venous anastomoses were done end-to-side and dogs were placed on low-dose aspirin therapy. All 8 dogs are currently maintaining patent unseeded devices (96-226 days postimplantation). Subsequent studies determined the function of devices seeded with isolated canine pancreatic islet allografts in totally pancreatectomized, severely diabetic dogs. Diabetes was controlled by once-a-day insulin injection. After 2-3 weeks of diabetic control, a seeded device was implanted. Diabetic control was monitored by fasting blood levels and postprandial and intravenous glucose tolerance tests, and vascular patency by the loudness of the bruit. In the first series of 6 dogs given seeded devices without aspirin, no significant function was discernible, with failure attributable to thrombosis, poor islet viability, and surgical complications. In the second series of 13 dogs given aspirin, 8 dogs have required an appreciably lower dose of injected insulin to maintain fasting blood glucose at acceptable levels. Of note are 4 dogs that required virtually no exogenous insulin for at least 3 weeks. One dog lost function on day 74 and another still requires no insulin at 267 days postimplantation. However, despite normal fasting glucose levels, the glucose tolerance tests showed delayed return to normal levels. Weight lost following pancreatectomy was rapidly regained in the presence of a functioning seeded device. Histologic examination of the removed devices revealed no signs of rejection.