Demonstration of lipids in plastic resin-embedded sections of skin material

Two different fluorescence stains, green: 5-hexadecanoylaminofluorescein, and red: BODIPY(R) 665/676 [(E,E)-3, 5-bis-(4-phenyl-1,3-butadienyl)-4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene, produced good results regarding the demonstration of glycolipids, free fatty acids and triglycerides in mammalian skin material that had been embedded in a water miscible plastic resin (Technovit(R) 7100). In this way, functional aspects of specific structures (epidermal barrier region, sebaceous glands) could be characterized histochemically in the integument of five mammalian species with sparse or dense hair coats.

Chemistry and the biological response against immunoisolating alginate–polycation capsules of different composition

Implantation of microencapsulated cells has been proposed as a therapy for a wide variety of diseases. An absolute requirement is that the applied microcapsules have an optimal biocompatibility. The alginate-poly-L-lysine system is the most commonly applied system but is still suffering from tissue responses provoked by the capsule materials. In the present study, we investigate the biocompatibility of microcapsules elaborated with two commonly applied alginates, i.e. an intermediate-G alginate and a high-G alginate. These alginates were coated with poly-L-lysine (PLL), poly-D-lysine (PDL) and poly-L-ornithine (PLO). The main objective of this study is to determine the interaction of each alginate matrix with the different polycations and the potential impact of these interactions in the modulation of the host's immune response. To address these issues the different types of microcapsules were implanted into the peritoneal cavity of rats for I month. After this period the microcapsules were recovered and they were evaluated by different techniques. Monochromatised X-ray photoelectron spectroscopy (XPS) was performance and the degree of capsular recovery, overgrowth on each capsule, and the cellular composition of the overgrowth were evaluated by histology. Our results illustrate that the different observed immune responses are the consequence of the variations in the interactions between the polycations and alginates rather than to the alginates themselves. Our results suggest that PLL is the best option available and that we should avoid using PLO and PDL in its present form since it is our goals to produce capsules that lack overgrowth and do not induce an immunological response as such.

Efficacy of a prevascularized expanded polytetrafluoroethylene solid support system as a transplantation site for pancreatic islets

An intraperitoneally located and prevascularized expanded polytetrafluoroethylene solid support is potentially a suitable transplantation site for encapsulated pancreatic islets, because it allows for both the implantation of a large volume islet graft in the immediate vicinity of blood vessels, and its complete removal. The present study investigates the efficacy of such solid supports for the implantation of nonencapsulated islet isografts in streptozotocin diabetic rat recipients. These solid supports were always coated with acidic fibroblast growth factor, because we found that this growth factor enhances the neovascularization. The success rates of 5-microl (group A) and 10-microl (group B) islet isografts in solid supports were compared with the success rates of 5-microl (group C) and 10-microl (group D) islet isografts implanted in the unmodified peritoneal cavity. Four of seven rats in group A and all seven rats in group B became normoglycemic for at least 6 months. Only two of eight rats in group C and four of eleven rats in group D showed normoglycemia. The normoglycemia lasted for at least 6 months in zero of two animals in group C and in three of four animals in group D. Because of the low success rates in groups C and D, intravenous and oral glucose testing were restricted to the successful recipients in groups A and B. Glucose tolerance was found to be proportional to the grafted islet volume but, expectedly, in both groups the glucose tolerance and the insulin responses were somewhat lower than in controls. Thus, the prevascularized expanded polytetrafluoroethylene solid support, rather than the unmodified peritoneal cavity, is an efficacious transplantation site, potentially suitable for encapsulated islets.

Effect of the alginate composition on the biocompatibility of alginate-polylysine microcapsules

Alginate-polylysine (PLL) capsules are commonly applied for immunoprotection of endocrine tissues. Alginate is composed of mannuronic acid (M) and guluronic acid (G). Different types of alginate have different ratios of G to M, but little is known of the influence of these differences on biocompatibility. Therefore, we have investigated in vivo the effect of the G-content of the alginate on the biocompatibility of the capsules. Capsules prepared of commercially available alginates with either a high or an intermediate G-content were implanted in the peritoneal cavity of rats and retrieved one month later for histological evaluation. The fibrotic reaction was more severe against high-G alginate capsules than to intermediate-G alginate capsules. The majority of the high-G capsules proved to be overgrown and adherent to the abdominal organs whereas with intermediate-G alginate most capsules were found freely floating in the peritoneal cavity and free of any adhesion of cells. This was not caused by the alginate as such but rather by inadequate binding of high-G alginate to PLL since in the absence of PLL, i.e. with beads instead of capsules, no fibrotic reaction was observed. As high-G alginates have beneficial effects for islet encapsulation, efforts should be made to apply polycations which more effectively interact with high-G alginate than PLL.

Association between capsule diameter, adequacy of encapsulation, and survival of microencapsulated rat islet allografts

As a consequence of its large volume, a microencapsulated islet graft can be implanted only into the peritoneal cavity. The graft volume can be reduced by using small capsules. However, reduction of the diameter of the capsules holds a certain risk, because with smaller capsules, more islets may be found to protrude from the capsules. We have developed a lectin binding assay which, after encapsulation, specifically labels islets or parts of islets that are insufficiently immunoprotected as a consequence of inadequate, and particularly incomplete, encapsulation. With this assay, we found that a reduction of the capsule diameter from 800 micrometers to 500 micrometers was associated with an increase in the percentage of inadequately encapsulated islets from 6.3+/-1.2% to 24.2+/-1.5%. The in vivo significance of this finding was investigated by performing allotransplantations with large diameter (700-800 micrometers) and small diameter (400-500 micrometers) capsules. With large-capsule islet grafts, all recipients (n=5) became normoglycemic for 7-16 weeks, whereas with small-capsule islet grafts, only one of seven recipients became normoglycemic. The in vivo significance of inadequate encapsulation was further substantiated by our finding that most large capsules were floating freely in the peritoneal cavity without any cell adhesion, whereas the vast majority of small capsules was found to be adherent to the surface of intra-abdominal organs and infiltrated by immune cell elements characteristic of both an allograft reaction and a foreign body reaction. We conclude that successful use of capsules with small diameters requires further study to determine which factors in the encapsulation procedure should be modified to reduce the number of inadequate small capsules.

Immunohistochemical detection of epidermal growth factor in glycol methacrylate embedded tissue

This study addresses a variety of immunohistochemical conditions for detecting EGF in 3.5% paraformaldehyde fixed, glycol methacrylate embedded tissue including antigen unmasking with trypsin, dilution of primary antibody, and incubation time with primary antibody. Color development was achieved with a biotinylated secondary antibody linked to an avidin biotinylated peroxidase complex. Trypsinization and a 12 hr incubation with the primary antibody was essential to detect EGF in this system. Adequate staining could be achieved with a 1:100 dilution of the primary antibody.

The capsular overgrowth on microencapsulated pancreatic islet grafts in streptozotocin and autoimmune diabetic rats

This study investigates whether capsular overgrowth on alginate-polylysine microencapsulated islets is influenced by (1) the presence of islet tissue, (2) MHC incompatibility between donor and recipient, or (3) the presence of autoimmune diabetes. Encapsulated Albino Oxford (AO, n = 6, isografts) and Lewis (n = 6, allografts) rat islets, and encapsulated human islets (n = 5, xenografts) were implanted intraperitoneally into streptozotocin-diabetic AO rats. Also, encapsulated AO islets were implanted into autoimmune diabetic Bio Breeding/Organon (BB/O) rats (n = 5, allografts). Five isografts, five allografts, and three xenografts in AO recipients and five allografts in BB/O recipients resulted in normoglycemia. Two weeks after implantation, islets containing capsules were retrieved by peritoneal lavage, after which all animals that had become normoglycemic after transplantation returned to a state of hyperglycemia. Recovery rates of the capsules of these successful grafts, expressed as percentages of the initially implanted graft volume, varied from 72% +/- 7% to 80% +/- 9%. The associated pericapsular infiltrates (PCI) were similar in all groups and varied from 3.2% +/- 1.4% to 8.3% +/- 2.6%. Similar recovery rates and PCI were also found with empty capsules. However, the recovery rates of recipients with graft failures were lower and showed more PCI. Immunohistological staining of PCI showed no differences in the types of cells in the PCI on capsules with or without islets. We conclude that this early PCI is a capsule-induced foreign body reaction that is not influenced by MHC incompatibility or by the presence of autoimmune diabetes, and it should be avoided by improving the biocompatibility of the capsules.

Quantitative aspects of enzyme histochemistry on sections of freeze-substituted glycol methacrylate-embedded rat liver

Freeze-substituted rat liver embedded in glycol methacrylate (GMA) has been used to demonstrate the activities of several enzymes. The following enzymes could be detected in GMA-sections by the indicated histochemical procedure(s): 5'-nucleotidase (lead salt, cerium-diaminobenzidine), alkaline phosphatase (indoxyl-tetrazolium salt), catalase (diaminobenzidine), acid phosphatase (diazonium salt), lactate dehydrogenase (tetrazolium salt) and glutamate dehydrogenase (tetrazolium salt). The activities of all these enzymes were dramatically decreased compared with the activities demonstrated in unfixed cryostat sections, with the exception of catalase. The activities of the following enzymes could not be detected in GMA-sections: glucose-6-phosphate dehydrogenase (tetrazolium salt), xanthine oxidoreductase (tetrazolium salt), D-amino acid oxidase (cerium-diaminobenzidine-cobalt-hydrogen peroxide) and glucose-6-phosphatase (cerium-diaminobenzidine). The possible role of restricted penetration of reagents into the resin was studied by measuring cytophotometrically the enzyme activities in GMA-sections of 3 and 6 microns in thickness. For all the enzymes that could be detected, the 6 microns:3 microns ratio varied from 1.4 to 2.7. An eventual retarded penetration of reagents into the resin was investigated by measuring cytophotometrically the amount of final reaction product during incubation for acid phosphatase and glutamate dehydrogenase activities. In both cases linear relationships without a lag phase were found for the specific enzyme activities with incubation time. Chemical denaturation of proteins or masking of active sites in proteins due to embedding in the resin monomer may be considered to be the main cause of decreased enzyme activities.

A new polychrome stain and simultaneous methods of histological, histochemical and immunohistochemical stainings performed on semithin sections of Bioacryl-embedded human tissues

We describe a new polychrome stain and simultaneous methods of histological, histochemical and immunocytochemical staining performed on sections from human tissues embedded in the new hydrophilic resin Bioacryl. The polychrome stain involves the sequential use of Harris' Haematoxylin, silver methenamine, Light Green and Eosin or Safranin dyes and provides a highly specific visualization of the overall cytological tissue architecture. When histochemical, immunocytochemical, and polychrome stains are performed together on the same section, crisp images are obtained, yielding simultaneous data of histochemical and immunological reactivities with clear tissue architecture.

Staining myelin and myelin-like degradation products in the spinal cords of chronic experimental allergic encephalomyelitis (Cr-EAE) rats using Sudan black B staining of glycol methacrylate-embedded material

A high-resolution light-microscopical (HRLM) technique is described to visualize myelin, and macrophages containing degradation products of myelin, in the spinal cords of chronic relapsing experimental allergic encephalomyelitis (Cr-EAE) rats. This HRLM technique was developed to optimalize the correlation between nuclear magnetic resonance (NMR) characteristics and histopathological images in this well-established animal model for multiple sclerosis (MS). Spinal cords were fixed by perfusion with a combination of cacodylate-buffered glutaraldehyde and formaldehyde, post-fixed in Dalton's fixative (containing osmium tetroxide), rinsed in water, processed in ethanol, acetone, and embedded in glycol methacrylate resin (Technovit 7100/HistoResin). Semi-thin sections were stained with Sudan Black B and counterstained with Cresyl Fast Violet, resulting in black staining of myelin and its degradation products, with blue/violet staining of demyelinated axons and other tissue elements. These dyes were selected with the aid of a numerical model of staining, which took both access and lipophilicity into account. The staining procedure is simple and highly reproducible. The resulting images are contrast rich, and combine excellent morphology with a high degree of lipid retention.

Staining sections of water-miscible resins. 2. Effects of staining-reagent lipophilicity on the staining of glycol-methacrylate-embedded tissues

Glycol methacrylate (GMA) sections of animal tissues were stained with a group of twenty-seven reagents of very varied chemical characteristics. The artefactual background staining of the resin was found to be dependent on the hydrophilic/lipophilic character of the staining reagent, as estimated from the logarithm of its octanol-water partition coefficient (log P). Intense background staining occurred with lipophilic stains, whose log P greater than 2. In keeping with this, use of GMA semi-permeable membranes for enzyme histochemistry failed to give staining when using a lipophilic substrate, probably because the substrate was trapped in the membrane. An analysis of other routine histochemical stains--in terms of the probable occurrence of high resin background staining and low tissue sensitivity--is made. A numerical guide is provided to help avoid artefacts resulting from hydrophobic and size effects. Note: small, hydrophilic reagents (log P less than 0; molecular weight less than 550 Da) are least likely to show either type of artefact. Conversely, reagents which are lipophilic, or/and of intermediate size (log P greater than 2; 550 less than ionic weight less than 1000 Da), give strong background staining.