Bruce D. Wigness

Nonenzymatic Glycation of Fibronectin and Alterations in the Molecular Association of Cell Matrix and Basement Membrane Components in Diabetes Mellitus

This study reports the nonenzymatic glycation of plasma fibronectin in vivo in diabetic dogs and also in vitro by incubation of human plasma fibronectin with excess glucose. Although no difference is observed in the total plasma fibronectin level, the nonenzymatic glycation of fibronectin is increased 2.3-fold in inbred male beagle dogs made diabetic with alloxan in comparison with age-matched controls. The extent of nonenzymatic glycation of fibronectin is shown to be proportional to blood glucose levels. HPLC reverse-phase analysis of the hydrolyzed amino acids and glycoamino acids from plasma fibronectin samples of normal and diabetic dogs show that nonenzymatic glycation occurs only on lysine residues. When purified human plasma fibronectin was incubated in vitro with 500 mM glucose, the extent of nonenzymatic glycation of fibronectin was observed to increase proportionately with time. Ligand binding assays conducted in solution with varying concentrations of 3H-heparin in the presence of a constant amount of normal or nonenzymatically glycated human plasma fibronectin gave virtually identical binding curves. However, the binding of 3H-heparin to normal fibronectin could be increased fourfold by the concomitant addition of normal gelatin (denatured calfskin collagen). If in vitro glycated fibronectin and/or in vitro glycated gelatin are added under this latter condition with 3H-heparin, there is a tremendous decrease in the expected heparin binding seen with normal levels of nonenzymatic glycation. Other experiments were performed to quantitate the binding of 3H-labeled fibronectin to gelatin-coated nitrocellulose filters. Nonenzymatic glycation of fibronectin in vitro resulted in markedly decreased binding of 3H-fibronectin to collagen. Enhanced nonenzymatic glycation of fibronectin in vivo and alterations in the molecular association of fibronectin, gelatin, and heparin brought about by nonenzymatic glycation are discussed relevant to the pathophysiology of the complications of diabetes.

A Totally Implantable Drug Infusion Defice: Laboratory and Clinical Experience Using a Model with Single Flow Rate and New Design for Modulated Insulin Infusion

The Infusaid implantable infusion pump with a single delivery rate has maintained chronic intravenous heparin infusion in man for greater than 35 mo and for greater than 5 yr in the dog. Intra-arterial infuson of fluorodeoxyuridine has been maintained for greater than 8 mo in man. In a pilot study using a commercially available, transcutaneously controllable, magnetically activated valve for baseline superimposed bolus insulin infusion, the feasibility of maintaining near normal serum glucose in diabetic dogs was demonstrated. The effect of long-term intravenous cannulation was investigated; it was found that the intimal tissues of the vena cava surrounding the cannulae were largely unaltered and microemboli could not be detected in the lungs of the animals studied. Cannula plugging, which occurred on several occasions due to thrombus formation in the final centimeter of the cannula, has been solved by changes in pump design and refilling procedures. The problem of insulin precipitation in flow passages of the pump remains unsolved, but there are indications that substances entering the cannula from the blood may be involved. A new pump design for modulated insulin infusion is described.

Glycerol Prevents Insulin Precipitation and Interruption of Flow in an Implantable Insulin Infusion Pump

Insulin precipitation is a major obstacle to the use of implantable insulin infusion pumps. In one such pump (Infusaid, Infusaid Corporation, Norwood, Massachusetts), unprotected insulin precipitated and occluded nine pumps implanted in normal dogs within 43 days. In contrast, two similar pumps containing insulin mixed with 80% glycerol functioned normally for more than 250 days. In human studies, a similar mixture allowed insulin to be delivered to nine diabetic subjects for more than 6 mo in each case; total fluid flow rates from the pump were essentially unchanged after 460 patients-weeks of insulin infusion. A possible drawback of the mixture is a time- and temperature-dependent propensity to cause the formation of soluble, higher-molecular-weight insulin polymers, which apparently have lower biologic activity. Formation of such polymers and maintenance of biologic activity were largely prevented by the addition of phosphate buffer at neutral pH.

Portable Data Acquisition and Control Apparatus for Implanted Drug Infusion Pump Interrogation

Now that implantable drug infusion pumps are well established clinically, methods for diagnosing suspected pump failures are needed. The authors previously constructed a benchtop data acquisition and control apparatus to assist our work in developing new pump technology. Although this device is technically capable of in vivo pump monitoring, it is cumbersome. Thus, they recently created a portable interrogation unit with more limited features. This portable pump interrogation apparatus consists of a 32 bit MS-DOS labtop computer, data acquisition software, an analog/ASCII interface, a pressure transducer, and appropriate fluid conduits. Communication between the device and the implanted pump is via a percutaneous needle puncture of the drug reservoir refill septum. This procedure is identical to that employed in a standard pump refill. Pump performance is evaluated by incrementally filling the pump reservoir while simultaneously measuring reservoir pressure. The resulting data are presented on the computer screen as a plot of pressure versus volume that quickly and simply either eliminates or confirms the reservoir pressure source as a failure mode. Diagnostic runs are saved on file for archival purposes. Their benchtop apparatus has been a valuable and reliable tool over many years of use. The authors believe that their portable apparatus will be equally beneficial.

Failure to find amyloidosis in dogs treated with long-term intravenous insulin delivered by a totally implantable pump

SummaryWe examined tissues of seven non-diabetic mongrel dogs and four diabetic beagle dogs treated with constant insulin infusion via totally implantable pumps for from 210 to 880 days. Kidney and skeletal muscle tissue from all dogs were stained with Congo Red and thioflavin-T and appropriately examined. Kidney tissues from the beagle dogs were examined by electron microscopy. No amyloid deposits were found in any of these tissues. Thus, we cannot confirm an earlier report of amyloid occurring in dogs given long-term intravenous insulin. It is concluded that amyloidosis is not a necessary complication of long-term intravenous insulin infusion in dogs.

Operating Principles and Clinical Implications of Constant Flow Pumps

Intrathecal drug therapy has become an indispensable tool in the treatment of many different neurologic disorders. It allows targeted infusion of small quantities of drugs, thereby increasing effectiveness while reducing unwanted side effects typically seen in oral drug administration. The following paper discusses the current technology in constant rate intrathecal drug‐infusion delivery systems and the effect of pressure and temperature on flow rate accuracy.

The spring-driven implantable pump. A low-cost alternative.

In the current era of cost containment in medicine, manufacturing economics have become increasingly important. The authors devised an implantable pump powered by spring force from an elastomeric Belleville washer, which is also the outer flexible wall of the drug reservoir. Use of formed and injection molded parts provides for low-cost manufacturing, in contrast to the precision welded alternative designs. Additional advantages include insensitivity to changes in ambient temperature and pressure. Finite element modeling of the elastomer spring allows prediction of the effects of parameter changes on performance, so that expansions and reductions of scale can be made without compromising the uniform spring rate of the device. A concern that subcutaneous fibrous encapsulation might markedly alter reservoir pressure was not supported by experimental data. In a unit implanted subcutaneously in a dog, reservoir pressures measured over a 4 year period were stable. This new, simple, implantable infusion pump can serve as an economical vehicle for prolonged parenteral drug treatment of ambulatory subjects in circumstances where continuous single-rate infusion is appropriate.

[40] Implantable infusion pumps: Practical aspects

Publisher Summary This chapter discusses the practical aspects of implantable infusion pumps. The chapter discusses the pump implantation in humans. As with the implantation of any foreign body, the development of an infection at the site of infusion pump implantation usually requires pump removal. Meticulous attention to surgical detail is of great help in avoiding such problems. The pump can be implanted in various areas of the body but is always placed subcutaneously, usually on the muscle fascia, to which it can be sutured at the time of implantation. This prevents excessive rotation or movement of the pump. Before implantation, the appropriate pump model, preferred flow rate, and appropriate connectors needed (if any) should be selected. The chapter also discusses the pump implantation and refill procedures in dogs. As use of implantable drug delivery systems increases, both in experimental applications in animals and in clinical use in patients, it becomes important that descriptions of correct surgical and refill procedures be readily available.

A new spring-driven implantable drug infusion pump

An implantable infusion pump which uses elastomer spring pressure to provide constant-rate drug delivery is described. Desirable features of the design are its low-cost construction, temperature and pressure insensitivity, high volumetric efficiency, and scale flexibility. Test results for prototype models are reported. Spring performance characteristics appear to be unaffected by long-term implantation. The results indicate that the pump is suitable for multiple-drug-delivery applications requiring more than an infusion port but needing a programmable device.<<ETX>>