A Comparative Study of the Resorption and Immune Response for Two Starch-Based Hemostat Powders

INTRODUCTION

Powder hemostats are valuable adjuncts to minimize intraoperative and postoperative complications. In addition to promotion of rapid coagulation, resorption, and biocompatibility are desirable attributes. Plant starch-based polysaccharide hemostat powders are effective and widely used hemostatic agents, however their source and/or processing can affect characteristics such as in vivo degradability. For example, Arista is a purified/hydrolyzed starch powder that is rapidly resorbed in vivo; whereas PerClot shows slow resorption and preservation of a crystalline form.

MATERIALS AND METHODS

In the present study, we compared the cellular response to the hemostatic agents PerClot and Arista both in vitro and in vivo, and used potato starch and urinary bladder extracellular matrix (UBM-ECM) as high crystallinity/slowly resorbable and prohealing controls, respectively.

RESULTS

All test articles and their degradation products were cytocompatible in vitro as measured by cell viability and metabolic activity of bone-marrow macrophages. PerClot induced a stronger proinflammatory, M1-like macrophage response in vitro (P < 0.001) than Arista, likely due to differences in source composition. Histologic examination of the in vivo surgical site showed the almost complete degradation of Arista after 12 h (day 0), whereas both PerClot and potato starch were still present at 28 d with crystals identifiable with polarized light microscopy and periodic acid Schiff (PAS) staining. Macrophage phenotype in vivo showed no differences between PerClot and Arista. Collagen deposition and mononuclear cell accumulation consistent with an early foreign body response were present around PerClot and potato starch crystals, whereas no such cell or connective tissue deposition was noted at the site of Arista or UBM-ECM placement.

The Physical Properties of a Hyaluronic Acid Based Bioresorbable Membrane for the Prevention of postsurgical Adhesions

We have evaluated the physical properties and animal efficacy of a hyaluronic acid (HA) based bioresorbable membrane for the prevention of post-surgical adhesions. Test methods were developed to measure the dry and wet tensile properties and ia Xilm tissue adhesiveness of the membranes. The thin membranes were found to have sufficient strength and flexibility in the dry state for surgical handling. When hydrated in buffered saline, the membranes became weaker and more elastic. The membranes exhibited a high degree of tissue adhesiveness and significantly reduced adhesion formation in a rat cecal abrasion model.

Enhancement of the gluconeogenic flux of hepatic glycogen repletion by a phenacyl imidazolium compound in vivo

The effect of a phenacyl imidazolium compound (LY177507 or Proglycosyn, Eli Lilly) on the direct (glucose-->glucose-6-phosphate-->glycogen) and indirect (three-carbon compounds-->glucose-6-phosphate-->glycogen) pathways of liver glycogen synthesis was studied in conscious rats. [1-13C]Glucose (99% enriched) was infused intraduodenally into chronically catheterized Proglycosyn-treated (n = 7) and saline-treated (n = 7) rats for 120 min. Net hepatic glycogen synthetic rates were increased twofold in drug-treated rats compared with saline-treated controls. The percentage of liver glycogen synthesized by the direct pathway was calculated by comparing the 13C isotopic enrichment in the C1 and C6 positions of hepatic glycogen and plasma glucose using 13C nuclear magnetic resonance spectroscopy and gas chromatography-mass spectroscopy techniques and was found to be 59 +/- 5% and 39 +/- 2% (P < 0.05) in the saline treated and Proglycosyn-treated groups, respectively. Net flux rates for the direct and indirect pathways were calculated to be 0.24 +/- 0.04 and 0.17 +/- 0.03 mumol/g liver per min, respectively, in the saline-treated group and 0.30 +/- 0.04 (P = NS) and 0.46 +/- 0.06 (P < 0.05) mumol/g liver per min, respectively, in the Proglycosyn-treated group. Thus, Proglycosyn increases net hepatic glycogen synthesis in vivo exclusively through augmentation of the indirect pathway.

Immunocytochemical localization of alpha-protein kinase C in rat pancreatic beta-cells during glucose-induced insulin secretion

To investigate the role of protein kinase C (PKC) in the regulation of insulin secretion, we visualized changes in the intracellular localization of alpha-PKC in fixed beta-cells from both isolated rat pancreatic islets and the pancreas of awake unstressed rats during glucose-induced insulin secretion. Isolated, perifused rat islets were fixed in 4% paraformaldehyde, detergent permeabilized, and labeled with a mAb specific for alpha-PKC. The labeling was visualized by confocal immunofluorescent microscopy. In isolated rat pancreatic islets perifused with 2.75 mM glucose, alpha-PKC immunostaining was primarily cytoplasmic in distribution throughout the beta-cells. In islets stimulated with 20 mM glucose, there was a significant redistribution of alpha-PKC to the cell periphery. This glucose-induced redistribution was abolished when either mannoheptulose, an inhibitor of glucose metabolism, or nitrendipine, an inhibitor of calcium influx, were added to the perifusate. We also examined changes in the intracellular distribution of alpha-PKC in the beta-cells of awake, unstressed rats that were given an intravenous infusion of glucose. Immunocytochemical analysis of pancreatic sections from these rats demonstrated a glucose-induced translocation of alpha-PKC to the cell periphery of the beta-cells. These results demonstrate that the metabolism of glucose can induce the redistribution of alpha-PKC to the cell periphery of beta-cells, both in isolated islets and in the intact animal, and suggest that alpha-PKC plays a role in mediating glucose-induced insulin secretion.

Simultaneous insulinlike growth factor I and insulin resistance in obese Zucker rats

It has recently been shown that the ability of insulinlike growth factor I (IGF-I) to stimulate glucose uptake and to lower circulating amino acid levels is retained in insulin-resistant diabetic BB rats. To examine in vivo effects of IGF-I in obese Zucker rats (another model of insulin resistance) 6 obese and 6 lean rats received euglycemic IGF-I infusions (0.65 nmol.kg-1.min-1). IGF-I-stimulated glucose uptake in obese rats was 50% lower than lean control rats (45.0 +/- 2.8 vs. 92.2 +/- 6.1 mumol.kg-1.min-1, respectively), even though the rise in circulating IGF-I levels was greater in the obese group during IGF-I infusion. In addition, branched chain amino acid concentrations that declined by 45% in lean controls were not suppressed significantly in obese rats (392 +/- 33 basal vs. 327 +/- 29 microM at 90 min). Equivalent results were observed during euglycemic insulin clamps (12 pmol.kg-1.min-1) in 7 obese and 11 lean rats. These studies demonstrate that obese Zucker rats are resistant to the effects of IGF-I and insulin on glucose and amino acid metabolism.

Ventilatory responses to inspiratory threshold loading in humans

Normal alveolar ventilation tends to be maintained during external mechanical loading. The precise manner by which this occurs is unclear but may involve intrinsic mechanisms related to the muscular pump, neural influences, and chemoreceptor control. Recent observations suggest that submaximal threshold loads may result in hyperventilation. In this study we explicitly examined the respiratory effects of sustained threshold loading in normal subjects. We found that sustained threshold loading resulted in hyperventilation associated with high P100's (mouth pressure 100 ms after the start of an occluded breath) and increased tidal volumes but with little effect on duty cycle or respiratory rate. In addition, this increased respiratory motor output was sustained for 30-60 s after the load was removed. At very high threshold loads, hyperventilation failed to occur, despite increased P100's. We conclude that threshold loading results in increased respiratory motor output and hyperventilation, a response that is different from that observed with either resistive or elastic loads, and that the failure to hyperventilate at the higher loads may be the result of mechanical limitation.