Improved Assessment of Isolated Islet Tissue Volume Using Digital Image Analysis

Accurate and consistent measurement of tissue volume is critical to performing many types of islet research; however, conventional visual determination of isolated islet yields through a microscope is heavily operator dependent. An improved method of islet volume determination using digital image analysis (DIA) was developed to remove operator bias and automate the islet counting process. A series of 140 porcine islet isolations were used to evaluate the DIA method in three separate stages. In Stage 1 ( n = 29 isolations), the conventional and DIA methods were correlated with two other independent islet quantitation methods: insulin extraction, and DNA extraction. It was found that volumes determined by DIA correlated more closely with insulin content and DNA content than did conventionally determined volumes. In Stages 2 and 3 ( n = 54 and 57 isolations, respectively), it was shown that an increase in the number of fields analyzed by DIA did not significantly improve the quality of the correlations. Inclusion of very small tissue (<50 fun in diameter), which is ignored in the conventional protocol affected yields by less than 10% and did not significantly improve the correlation with insulin or DNA content. Quantitation of isolated islet tissue volume using DIA has been shown to be rapid, consistent, and objective. In the laboratory, use of this method as the standard for islet volume measurement will allow more meaningful comparison of experimental results between centers. In the clinic, its use will allow more accurate dosing of transplanted tissue. © 1998 Elsevier Science Inc.

A Simple and Cost-Effective Method for the Isolation of Islets from Nonhuman Primates

Recent advances in islet cell transplantation have led to insulin independence in a majority of islet transplant recipients. However, there exists a need to overcome the shortage of donor tissue and the necessity for lifelong immunosuppression. Preclinical studies in large animal models are necessary to evaluate the safety and efficacy of alternative approaches for clinical islet transplantation. The nonhuman primate serves as an appropriate animal model for such investigations; however, a major impediment in performing such preclinical research has been the difficulty in isolating islets of sufficient quantity and quality. The current study describes a simple and cost-effective method to isolate nonhuman primate islets to support preclinical islet transplantation research. The results of islet isolations from 54 cynomolgus monkeys and 4 baboons are reported. The pancreas was infused with Liberase HI and subjected to static digestion. The digested tissue was shaken, filtered through a mesh screen, applied to a discontinuous gradient, and centrifuged in much the same manner as with conventional rodent islet isolations. Islets were collected from the two interfaces, washed, and transplanted. Following purification, cynomolgus monkey islet isolation yields were 50,100 ± 3120 IE total or 8760 ± 420 IE/g pancreas with the percent purity and viability of 90.8 ± 0.9 and 90.7 ± 0.7, respectively. Total insulin content of the isolated islets was 405 ± 53 μg insulin with DNA content being and 976 ± 117 μg DNA, corresponding to a ratio of 0.57 μg insulin/μg DNA. STZ-induced diabetes was reversed in both mouse and nonhuman primate recipients, which possessed significant levels of c-peptide following transplantation and well-granulated islet grafts. The technique yields sufficient numbers of pure and viable islets to support preclinical research to develop improved strategies to prevent the immune destruction of the transplanted islet graft.

Kidney Versus Islet Allograft Survival After Induction of Mixed Chimerism With Combined Donor Bone Marrow Transplantation

We have previously reported successful induction of transient mixed chimerism and long-term acceptance of renal allografts in MHC mismatched nonhuman primates. In this study, we attempted to extend this tolerance induction approach to islet allografts. A total of eight recipients underwent MHC mismatched combined islet and bone marrow (BM) transplantation after induction of diabetes by streptozotocin. Three recipients were treated after a nonmyeloablative conditioning regimen that included low-dose total body and thymic irradiation, horse Atgam (ATG), six doses of anti-CD154 monoclonal antibody (mAb), and a 1-month course of cyclosporine (CyA) (Islet A). In Islet B, anti-CD8 mAb was administered in place of CyA. In Islet C, two recipients were treated with Islet B, but without ATG. The results were compared with previously reported results of eight cynomolgus monkeys that received combined kidney and BM transplantation (Kidney A) following the same conditioning regimen used in Islet A. The majority of kidney/BM recipients achieved long-term renal allograft survival after induction of transient chimerism. However, prolonged islet survival was not achieved in similarly conditioned islet/BM recipients (Islet A), despite induction of comparable levels of chimerism. In order to rule out islet allograft loss due to CyA toxicity, three recipients were treated with anti-CD8 mAb in place of CyA. Although these recipients developed significantly superior mixed chimerism and more prolonged islet allograft survival (61, 103, and 113 days), islet function was lost soon after the disappearance of chimerism. In Islet C recipients, neither prolonged chimerism nor islet survival was observed (30 and 40 days). Significant improvement of mixed chimerism induction and islet allograft survival were achieved with a CyA-free regimen that included anti-CD8 mAb. However, unlike the kidney allograft, islet allograft tolerance was not induced with transient chimerism. Induction of more durable mixed chimerism may be necessary for induction of islet allograft tolerance.

Enrichment of human embryonic stem cell-derived NKX6.1-expressing pancreatic progenitor cells accelerates the maturation of insulin-secreting cells in vivo

Human embryonic stem cells (hESCs) are considered a potential alternative to cadaveric islets as a source of transplantable cells for treating patients with diabetes. We previously described a differentiation protocol to generate pancreatic progenitor cells from hESCs, composed of mainly pancreatic endoderm (PDX1/NKX6.1-positive), endocrine precursors (NKX2.2/synaptophysin-positive, hormone/NKX6.1-negative), and polyhormonal cells (insulin/glucagon-positive, NKX6.1-negative). However, the relative contributions of NKX6.1-negative versus NKX6.1-positive cell fractions to the maturation of functional β-cells remained unclear. To address this question, we generated two distinct pancreatic progenitor cell populations using modified differentiation protocols. Prior to transplant, both populations contained a high proportion of PDX1-expressing cells (~85%-90%) but were distinguished by their relatively high (~80%) or low (~25%) expression of NKX6.1. NKX6.1-high and NKX6.1-low progenitor populations were transplanted subcutaneously within macroencapsulation devices into diabetic mice. Mice transplanted with NKX6.1-low cells remained hyperglycemic throughout the 5-month post-transplant period whereas diabetes was reversed in NKX6.1-high recipients within 3 months. Fasting human C-peptide levels were similar between groups throughout the study, but only NKX6.1-high grafts displayed robust meal-, glucose- and arginine-responsive insulin secretion as early as 3 months post-transplant. NKX6.1-low recipients displayed elevated fasting glucagon levels. Theracyte devices from both groups contained almost exclusively pancreatic endocrine tissue, but NKX6.1-high grafts contained a greater proportion of insulin-positive and somatostatin-positive cells, whereas NKX6.1-low grafts contained mainly glucagon-expressing cells. Insulin-positive cells in NKX6.1-high, but not NKX6.1-low grafts expressed nuclear MAFA. Collectively, this study demonstrates that a pancreatic endoderm-enriched population can mature into highly functional β-cells with only a minor contribution from the endocrine subpopulation.

Maturation and function of human embryonic stem cell-derived pancreatic progenitors in macroencapsulation devices following transplant into mice

AIMS/HYPOTHESIS

Islet transplantation is a promising cell therapy for patients with diabetes, but it is currently limited by the reliance upon cadaveric donor tissue. We previously demonstrated that human embryonic stem cell (hESC)-derived pancreatic progenitor cells matured under the kidney capsule in a mouse model of diabetes into glucose-responsive insulin-secreting cells capable of reversing diabetes. However, the formation of cells resembling bone and cartilage was a major limitation of that study. Therefore, we developed an improved differentiation protocol that aimed to prevent the formation of off-target mesoderm tissue following transplantation. We also examined how variation within the complex host environment influenced the development of pancreatic progenitors in vivo.

METHODS

The hESCs were differentiated for 14 days into pancreatic progenitor cells and transplanted either under the kidney capsule or within Theracyte (TheraCyte, Laguna Hills, CA, USA) devices into diabetic mice.

RESULTS

Our revised differentiation protocol successfully eliminated the formation of non-endodermal cell populations in 99% of transplanted mice and generated grafts containing >80% endocrine cells. Progenitor cells developed efficiently into pancreatic endocrine tissue within macroencapsulation devices, despite lacking direct contact with the host environment, and reversed diabetes within 3 months. The preparation of cell aggregates pre-transplant was critical for the formation of insulin-producing cells in vivo and endocrine cell development was accelerated within a diabetic host environment compared with healthy mice. Neither insulin nor exendin-4 therapy post-transplant affected the maturation of macroencapsulated cells.

CONCLUSIONS/INTERPRETATION

Efficient differentiation of hESC-derived pancreatic endocrine cells can occur in a macroencapsulation device, yielding glucose-responsive insulin-producing cells capable of reversing diabetes.

The use of an approved biodegradable polymer scaffold as a solid support system for improvement of islet engraftment

The aim of this study was to investigate whether the use of a medically approved biodegradable scaffold as a solid support system would enhance graft survival following transplantation into the omental pouch in a preclinical large animal model. Six beagle dogs underwent total pancreatectomy followed by islet autotransplantation into the omental pouch. Four dogs received islets seeded in a biodegradable polymer scaffold and two received free islets without a scaffold. All four animals that received islets in the scaffold became normoglycemic without exogeneous insulin injection. One dog, transplanted with the largest number of islets, maintained a normal metabolic state until the graft was removed at 5 months posttransplant. In two out of the three that received a marginal islet mass, insulin independence was sustained up to 2 months. In contrast, two dogs transplanted with a similar marginal mass without the scaffold never became normoglycemic. Histological examination of the grafts in the scaffold showed numerous well-granulated, insulin-containing cells as well as glucagon-positive cells. These results indicate that biodegradable scaffolds may enhance survival and function of islet grafts. Manipulation of the microenvironment of transplanted islets may constitute the basis for new approaches to enhance islet engraftment.

Interference with tissue factor prolongs intrahepatic islet allograft survival in a nonhuman primate marginal mass model

BACKGROUND

Tissue factor (TF) expression on islets can result in an instant blood-mediated inflammatory reaction (IBMIR) that contributes to early islet loss. We tested whether peritransplant protection of islets from IBMIR with a monoclonal anti-TF antibody (CNTO859) would enhance engraftment in our nonhuman primate marginal mass model.

METHODS

Each of six pairs of cynomolgus monkeys (CM) with streptozotocin-induced diabetes was closely matched for metabolic control and was transplanted with 5,000 IEQ/kg allogeneic, ABO-compatible islets from the same donor under the cover of steroid-free immunosuppression. For each pair, experimental animals received islets cultured with 20 microg/mL anti-TF and were dosed with 6 mg/kg anti-TF intravenously, 10-25 min before islet infusion; control monkeys received an equal number of islets from the same preparation cultured without anti-TF and no in vivo treatment.

RESULTS

Early fasting C-peptide (CP) values were different between (P<0.01), but not within, pairs and correlated with in vitro functional capacity of islets as assessed by perifusion (r=0.60; P=0.022). Compared to their matched controls, experimental animals had decreased posttransplant markers of coagulation, higher fasting CP levels (1 month posttransplant and end of study) and prolonged graft function.

CONCLUSIONS

These data suggest that pretreatment of islets and the recipient with anti-TF may limit the effects of IBMIR, thereby enhancing islet engraftment and survival.

Effective islet isolation method with extremely high islet yields from adult pigs

Achieving good islet isolation is one of the most important factors for successful islet transplantation. Porcine pancreas is suitable for islet isolation research due to its anatomical and physiological similarities to human pancreas. In this study, we evaluated a new porcine islet isolation method designed to maximize islet yield and compared it with our previous open pan method and the standard method using a Ricordi chamber (Ricordi method). We performed 15 porcine islet isolations, five each with the new method, the open pan method, and the Ricordi method. The new method features several important improvements. Pancreata remain uncut and are kept intact during collagenase intraductal injection, a large filtration chamber to handle whole pancreata, low concentration of collagenase (Liberase HI) for digestion, and large plastic containers for large-scale islet purification. All isolated islets were assessed for yield, purity, viability and in vitro function. Islets isolated with this new method were transplanted under the kidney capsules of SCID mice with chemically induced diabetes for in vivo functional assessment (n = 8). With the new method, we obtained on average more than 1,000,000 islet equivalents (IE) (1,236,266 +/- 213,486 IE) (mean +/- SE) before purification and 800,000 IE (879,815 +/- 222,729 IE) after purification from one adult pig. Islet yield per pancreas was significantly higher compared with our previous open pan method (30,666 +/- 11,532 IE, p < 0.01) and the Ricordi method (317,073 +/- 86,093 IE, p < 0.05). All mice, transplanted with 1000 islets from the new method, returned to normoglycemia within 4 days after transplantation. Our new method makes it possible to obtain extremely high porcine islet yield with good function. It should produce useful information for human islet isolation and transplantation, and might be applied to single donor clinical xenogeneic transplantation.

Survival of microencapsulated adult pig islets in mice in spite of an antibody response

The aim of this study was to assess the capacity of simple alginate capsules to protect adult pig islets in a model of xenotransplantation. Adult pig islets were microencapsulated in alginate, with either single alginate coats (SAC) or double alginate coats (DAC), and transplanted into the streptozotocin-induced diabetic B6AF1 mice. Normalization of glucose levels was associated with an improvement of the glucose clearance during intravenous glucose tolerance tests. After explantation, all mice became hyperglycemic, demonstrating the efficacy of the encapsulated pig islets. Explanted capsules were mainly free of fibrotic reaction and encapsulated islets were still functional, responding to glucose stimulation with a 10-fold increase in insulin secretion. However, a significant decrease in the insulin content and insulin responses to glucose was observed for encapsulated islets explanted from hyperglycemic mice. An immune response of both IgG and IgM subtypes was detectable after transplantation. Interestingly, there were more newly formed antibodies in the serum of mice transplanted with SAC capsules than in the serum of mice transplanted with DAC capsules. In conclusion, alginate capsules can prolong the survival of adult pig islets transplanted into diabetic mice for up to 190 days, even in the presence of an antibody response.

Vascularized islet-cell transplantation in miniature swine. I. Preparation of vascularized islet kidneys

BACKGROUND

Whereas clinical pancreatic transplantation has been highly successful in correcting the hyperglycemia of insulin-dependent diabetes mellitus (type 1), the results of islet transplantation have been disappointing. This discrepancy may be because of, at least in part, nonspecific loss of islets during the time required for revascularization. To test this hypothesis, we have designed composite kidney grafts containing vascularized autologous islets that can be used to compare the engraftment potential of vascularized versus nonvascularized islet tissue.

METHODS

(1) Islet-cell isolation: miniature swine underwent either partial pancreatectomy to isolate autologous islets or total pancreatectomy to isolate minor antigen-mismatched islets. Islets were purified from excised pancreatic tissue by enzymatic digestion and discontinuous density gradient purification. Isolated islets were cultured for 3 days before transplant. (2) Creation of vascularized islet kidneys (IK): autologous islets alone (n=6), minor-mismatched islets alone (n=3), and minor-mismatched islets plus simultaneous autologous thymic tissue (n=3) were transplanted beneath the renal capsule of juvenile miniature swine. Minor antigen-mismatched islets were also transplanted into both the vascularized thymic graft of a thymokidney (to produce a thymo-islet kidney [TIK]) and the contralateral native kidney (n=3) and both the host thymus and beneath the renal capsule (n=2). All recipients receiving minor-mismatched islets were treated with a 12-day intravenous (IV) course of either cyclosporine A (CsA) at 10 mg/kg per day or FK506 at 0.15 mg/kg per day. (3) Assessment of Function: to evaluate the function of the transplanted islets, three animals bearing TIK and IK underwent total pancreatectomy 3 months following islet transplantation.

RESULTS

(1) Islet-cell yields: an average of 254,960+/-51,879 (4,452+/-932 islet equivalents [IEQ]/gram of pancreas) and 374,410+/-9,548 (4,183+/-721 IEQ/gram of pancreas) viable islets were obtained by partial pancreatectomy and complete pancreatectomy, respectively. (2) Creation of IK: autologous islets engrafted indefinitely, whereas recipients of minor-mismatched islets alone rejected the islets within 2 months. However, when minor-mismatched islets were implanted into both the thymokidney and the contralateral kidney of animals bearing a thymokidney, the islets engrafted indefinitely in both sites (>3 months). Simultaneous implantation of islets into the host thymus and under the renal capsule also led to permanent engraftment of minor-mismatched islets. (3) Function of vascularized islets: three animals with both a TIK and an IK in place for 3 months underwent total pancreatectomy. All three animals maintained normoglycemia thereafter. In two of these animals, the IKs were removed 2 months after the pancreatectomy, and in both cases normoglycemia was maintained thereafter by the TIK.

CONCLUSIONS

The implantation of islets beneath the autologous renal capsule permitted the establishment of a vascular supply and thereby supported normal islet-cell growth and function. The presence of thymic tissue beneath the autologous renal capsule facilitated the engraftment of minor-mismatched islets, and such grafts achieved results similar to autologous islet transplants. Therefore, the ability to create vascularized islet grafts may provide a strategy for successful islet transplantation across allogeneic and potentially across xenogeneic barriers.

Vascularized islet cell transplantation in miniature Swine: islet-kidney allografts correct the diabetic hyperglycemia induced by total pancreatectomy

We have previously reported the preparation of vascularized islet-kidneys (IKs) by transplantation of islets under the autologous kidney capsule. Here, we compare the efficacy of transplanting vascularized versus nonvascularized islets into diabetic allogeneic swine recipients. In the vascularized islet transplantation (5,000 islet equivalents [IE]/kg), recipients received minor-mismatched (n = 4) or fully-mismatched (n = 2) IKs after pancreatectomy, with a 12-day course of cyclosporine A (CyA) or FK506, respectively. For the nonvascularized islet transplantation (7,000 IE/kg), three recipients received minor-mismatched islets alone and two recipients received minor-mismatched donor islets placed in a donor kidney on the day of transplantation. All recipients of nonvascularized islets were treated with a 12-day course of CyA. With vascularized islet transplantation, pancreatectomized recipients were markedly hyperglycemic pretransplant (fasting blood glucose >300 mg/dl). After composite IK transplantation, all recipients developed and maintained normoglycemia (<120 mg/dl) and stable renal function indefinitely (>3 months), and insulin therapy was not required. Major histocompatibility complex-mismatched recipients demonstrated in vitro donor-specific unresponsiveness. In contrast, recipients of nonvascularized islets remained hyperglycemic. In conclusion, IK allografts cured surgically induced diabetes across allogeneic barriers, whereas nonvascularized islet transplants did not. These data indicate that prevascularization of islet allografts is crucial for their subsequent engraftment and that composite IKs may provide a strategy for successful islet transplantation.

The isolation and function of porcine islets from market weight pigs

The efficacy of clinical islet transplantation has been demonstrated with autografts, and although islet allografts have established insulin independence in a small number of IDDM patients, the treatment is confounded by the necessity of immunosuppression. the lack of donor tissue, and recurring islet immunogenicity. These limitations underscore a need to develop therapies to serve the large population of diabetic patients. Porcine islet xenotransplantation, together with a successful immune intervention strategy, may provide the necessary clinical alternative. However, a major obstacle in evaluating this approach has been the difficulty of obtaining adequate volumes of functional islet tissue from pigs. Donors of market weight are preferable to retired breeders due to their abundance, lower animal and husbandry costs. and are more suitable to meet regulatory guidelines for donor tissue for xenotransplantation. We describe a simple isolation procedure that following purification yields a mean of 350,000 IE, corresponding to 179 units of insulin and 1.8 mg of DNA with an islet purity and viability in excess of 85% (n = 317 isolations). In both short- and long-term cell cultures, porcine islets demonstrated glucose-responsive insulin secretion. However, this secretion is density dependent, which may have significant consequences in the development of immunoisolation technologies to support porcine islet xenotransplantation. Following implantation into diabetic nude mice, porcine islets remained functional in excess of 1 year. Implantation of a bioartificial pancreas containing porcine islets into pancreatectomized dogs provided significant clinical benefit with an improved diabetic condition. Finally, secretagogue-induced insulin release was demonstrated in vitro from these devices after removal from immunocompetent recipients. Immunohistochemical staining identified well-granulated islets following long-term implantation in both the rodent and canine models. This study demonstrates the ability to isolate porcine islets in clinically relevant numbers from market animals, which survive and remain functional for prolonged periods of time in an immune-deficient or immunoprotected environment.

Complete protection of islets against allorejection and autoimmunity by a simple barium-alginate membrane

We describe a new technique for microencapsulation with high-mannuronic acid (high-M) alginate crosslinked with BaCl(2) without a traditional permselective component, which allows the production of biocompatible capsules that allow prolonged survival of syngeneic and allogeneic transplanted islets in diabetic BALB/c and NOD mice for >350 days. The normalization of the glycemia in the transplanted mice was associated with normal glucose profiles in response to intravenous glucose tolerance tests. After explantation of the capsules, all mice became hyperglycemic, demonstrating the efficacy of the encapsulated islets. The retrieved capsules were free of cellular overgrowth and islets responded to glucose stimulation with a 5- to 10-fold increase of insulin secretion. Transfer of splenocytes isolated from transplanted NOD mice to NOD/SCID mice adoptively transferred diabetes, indicating that NOD recipients maintained islet-specific autoimmunity. In conclusion, we have developed a simple technique for microencapsulation that prolongs islet survival without immunosuppression, providing complete protection against allorejection and the recurrence of autoimmune diabetes.

Long-term islet allograft function in the absence of chronic immunosuppression: a case report of a nonhuman primate previously made tolerant to a renal allograft from the same donor

Development of mixed chimerism by donor bone marrow transplantation (DBMT) has led to long-term tolerance of solid organ allografts in nonhuman primates. As an initial attempt to extend this approach to cellular transplant, islet transplant from the same donor was attempted in the recipient previously made tolerant to a kidney allograft.

METHODS

After the conditioning with ATG, total body irradiation, thymic irradiation, and splenectomy, DBMT was performed followed by 4 weeks of cyclosporine. Kidney transplantation and native nephrectomies were subsequently performed on day 89. After 2.8 years of DBMT, diabetes was induced by streptozocin (STZ) and islets from bone marrow and kidney donor were transplanted without immunosuppression.

RESULTS

After DBMT, the recipient developed chimerism and no evidence of kidney rejection for more than 1000 days. STZ induced diabetes was reversed after the islet transplantation. Islet biopsies demonstrated insulin staining without rejection. Although the recipient became diabetic 300 days after islet transplantation, viable transplanted islets were found in the liver and under the kidney capsule without any evidence of rejection.

CONCLUSION

Tolerance with a nonmyeloablative conditioning can allow successful pancreatic islet transplantation without immunosuppression. Because no histological evidence of rejection was identified, recurrent diabetes is presumed to be inadequate islet mass.

Increase in beta-cell mass in transplanted porcine neonatal pancreatic cell clusters is due to proliferation of beta-cells and differentiation of duct cells

A 20-fold increase in beta-cell mass has been found after transplantation of porcine neonatal pancreatic cell clusters (NPCCs). Here the mechanisms leading to this increased beta-cell mass were studied. NPCCs (4000 islet equivalents) generated after 8 days culture of digested neonatal pig pancreas were transplanted beneath the renal capsule of streptozotocin (STZ) diabetic and normoglycemic nude mice. Grafts were removed at 10 days, 6 weeks, and 20 weeks after transplantation for immunostaining and insulin content. Proliferation of beta-cells and duct cells was assessed morphometrically using double immunostaining for Ki-67 with insulin or cytokeratin 7 (CK7). Graft maturation was assessed with double immunostaining of CK7 and insulin. Apoptosis was determined using propidium iodide staining. beta-cell proliferation in NPCCs was higher after 8 days of culture compared with that found in neonatal pig pancreas. After transplantation, beta-cell proliferation remained high at 10 days, decreased somewhat at 6 weeks, and was much lower 20 weeks after transplantation. Diabetic recipients not cured at 6 weeks after transplantation had significantly higher beta-cell proliferation compared with those cured and to normoglycemic recipients. The size of individual beta-cells, as determined by cross-sectional area, increased as the grafts matured. Graft insulin content was 20-fold increased at 20 weeks after transplantation compared with 8 days cultured NPCCS: The proliferation index of duct cells was significantly higher in neonatal pig pancreas than in 8 days cultured NPCCs and in 10-day-old grafts. The incidence of apoptosis in duct cells appeared to be low. About 20% of duct cells 10 days post transplantation showed costaining for CK7 and insulin, a marker of protodifferentiation. In conclusion, the increase in beta-cell mass after transplantation of NPCCs is due to both proliferation of differentiated beta-cells and differentiation of duct cells into beta-cells.

In vitro cultivation of human islets from expanded ductal tissue

A major obstacle to successful islet transplantation for both type 1 and 2 diabetes is an inadequate supply of insulin-producing tissue. This need for transplantable human islets has stimulated efforts to expand existing pancreatic islets and/or grow new ones. To test the hypothesis that human adult duct tissue could be expanded and differentiated in vitro to form islet cells, digested pancreatic tissue that is normally discarded from eight human islet isolations was cultured under conditions that allowed expansion of the ductal cells as a monolayer whereupon the cells were overlaid with a thin layer of Matrigel. With this manipulation, the monolayer of epithelial cells formed three-dimensional structures of ductal cysts from which 50-to 150- micrometer diameter islet-like clusters of pancreatic endocrine cells budded. Over 3-4 weeks culture the insulin content per flask increased 10- to 15-fold as the DNA content increased up to 7-fold. The cultivated human islet buds were shown by immunofluorescence to consist of cytokeratin 19-positive duct cells and hormone-positive islet cells. Double staining of insulin and non-beta cell hormones in occasional cells indicated immature cells still in the process of differentiation. Insulin secretion studies were done over 24 h in culture. Compared with their basal secretion at 5 mM glucose, cysts/cultivated human islet buds exposed to stimulatory 20 mM glucose had a 2.3-fold increase in secreted insulin. Thus, duct tissue from human pancreas can be expanded in culture and then be directed to differentiate into glucose responsive islet tissue in vitro. This approach may provide a potential new source of pancreatic islet cells for transplantation.

Evaluating the effectiveness of 2 educational interventions in family practice

BACKGROUND

Structured feedback of information can produce change in physician behaviour. The objective of this study was to assess the effectiveness of 2 educational interventions for improving the quality of care provided by family physicians in Ontario: the Practice Assessment Report (PAR) and the Continuing Medical Education Plan (CMEP) with a follow-up visit by a mentor.

METHODS

The study was a randomized controlled trial. Physicians in the control group received only the PAR, whereas those in the experimental group received the PAR, CMEP and mentor interventions. The participants were 56 family physicians and general practitioners (27 in the PAR group and 29 in the CMEP group) in southern Ontario who agreed to participate in the interventions and provide data. A total of 2395 patients randomly sampled from the practices returned questionnaires and consented to have their medical records abstracted. The outcome measures were global scores in 4 areas--quality of care, charting, prevention and overall use of medications--and patient ratings of satisfaction with care and preventive practices. The measures were applied at the beginning (phase 1) and end (phase 2) of the study.

RESULTS

The mean global scores at the end of the study for the PAR group were 70.1% for quality of care, 84.7% for prevention, 77.7% for charting and 82.2% for overall use of medications. The corresponding scores for the CMEP group were 68.3%, 82.1%, 76.4% and 83.2%. In the patient satisfaction component, the personal care scores at phase 2 were 93.6% for the PAR group and 94.6% for the CMEP group. Examples of the scores for prevention for the PAR group were 98.3% for children's current immunization, 96.6% for blood pressure measured within the previous 5 years, 79.4% for referral of women of the appropriate age for mammography within the previous 2 years, and 58.4% for discussion about alcohol use. The corresponding scores for the CMEP group were 95.8%, 97.6%, 77.6% and 64.6%. The changes in mean scores between phase 1 and phase 2 ranged from -1.9 to 2.3 points. There were no significant differences between the 2 groups in phase 1 or phase 2 scores or in change in scores. A total of 64.3% of the physicians rated the PAR as useful, 26.5% found the CMEP to be useful, and 41.0% considered the mentor strategy to be a useful form of continuing medical education. Although changes in practice related to the PAR, CMEP or mentor were reported by some physicians, they were not related to chart audit or patient scores.

INTERPRETATION

Educational interventions based on quality-of-care assessments and directed to global improvements in quality of care did not result in improvements in the outcome measures. Educational interventions may have to be targeted to specific areas of the practice, with physicians being monitored and receiving ongoing feedback on their performance.

Resistance of established porcine islet xenografts to humoral rejection by hyperimmune sera

BACKGROUND

Although preformed natural antibodies cause hyperacute rejection of primarily vascularized xenografts, tissue grafts such as skin or islets are revascularized by in-growth of host capillaries and therefore might be resistant to circulating antibodies. We examined the effect of hyperimmune serum and primed T cells on the survival of long-term porcine islet xenografts in diabetic nude mice.

METHODS

Porcine islets were transplanted beneath the kidney capsule of streptozotocin-induced diabetic BALB/c athymic mice. Hyperimmune serum and sensitized splenocytes were prepared by repeated immunization of BALB/c mice with porcine lymph node cells. Splenic T cells were enriched by nylon wool column separation. Tissues were examined by immunohistology using murine- and porcine-specific monoclonal antibodies.

RESULTS

Porcine islets survived in nude mice for > 100 days with high levels of circulating porcine C-peptide and maintenance of normoglycemia. Injection of the hyperimmune sera (IgG) into normoglycemic nude mice bearing porcine islets for > 70 days failed to induce rejection despite the continued presence of circulating anti-porcine cytotoxic antibody. Injection of sensitized T cells caused acute rejection of long-term (>140 days) porcine islets, whereas injection of naive T cells had no effect. Histologically, porcine islets removed from mice treated with hyperimmune serum showed no staining for IgG. Long-surviving porcine islet grafts showed strong staining for interleukin (IL)-10 and a lesser amount of IL-4 but no staining for IL-2 or interferon-gamma. Although fresh porcine islets were positive for swine leukocyte antigen class 1 antigen and intercellular adhesion molecule (ICAM)-1 but negative for mouse platelet endothelial cell adhesion molecule and ICAM-2, long-surviving porcine islets showed positive endothelial staining for mouse platelet endothelial cell adhesion molecule and ICAM-2.

CONCLUSIONS

Established islet xenografts are resistant to hyperimmune serum as a result of a lack of target endothelial antigens, whereas they remain susceptible to rejection caused by primed T cells. Local production of Th2 cytokines may explain the inability of long-surviving islet xenografts to activate injected naive T cells.

Improved assessment of isolated islet tissue volume using digital image analysis

Accurate and consistent measurement of tissue volume is critical to performing many types of islet research; however, conventional visual determination of isolated islet yields through a microscope is heavily operator dependent. An improved method of islet volume determination using digital image analysis (DIA) was developed to remove operator bias and automate the islet counting process. A series of 140 porcine islet isolations were used to evaluate the DIA method in three separate stages. In Stage 1 (n = 29 isolations), the conventional and DIA methods were correlated with two other independent islet quantitation methods: insulin extraction, and DNA extraction. It was found that volumes determined by DIA correlated more closely with insulin content and DNA content than did conventionally determined volumes. In Stages 2 and 3 (n = 54 and 57 isolations, respectively), it was shown that an increase in the number of fields analyzed by DIA did not significantly improve the quality of the correlations. Inclusion of very small tissue (<50 microm in diameter), which is ignored in the conventional protocol affected yields by less than 10% and did not significantly improve the correlation with insulin or DNA content. Quantitation of isolated islet tissue volume using DIA has been shown to be rapid, consistent, and objective. In the laboratory, use of this method as the standard for islet volume measurement will allow more meaningful comparison of experimental results between centers. In the clinic, its use will allow more accurate dosing of transplanted tissue.

Porcine islets for xenotransplantation

Long-term function of isolated porcine islets was investigated in diabetic nude mice. Seven of eight mice that received transplants of porcine islets remained normoglycemic for 1 year with progressive weight gain. Circulating porcine C-peptide was detected throughout the study period. Intravenous glucose tolerance tests showed a rapid glucose clearance rate. Together with our recent finding that porcine islets contained within an immunoexclusion device achieved glycemic control in a totally pancreatectomized dog, these results clearly demonstrate that isolated porcine islets are capable of functioning for prolonged periods in xenogeneic hosts and are suitable for long-term use in an immunoexclusion device in a discordant host.

Treatment of diabetes by xenogeneic islets without immunosuppression. Use of a vascularized bioartificial pancreas

Tight glycemic control by intensive insulin therapy effectively delays the onset and slows the progression of diabetic complications but is associated with frequent dose adjustments and a high incidence of hypoglycemia. Successful pancreas transplantation corrects abnormal glucose metabolism but subjects patients to morbidity and mortality associated with chronic immunosuppression. A vascularized artificial pancreas device containing pancreatic islets is designed to provide glycemic control without immunosuppression. We report here that devices seeded with porcine islets implanted into pancreatectomized severely diabetic dogs maintained a marked improvement in glycemic control with reduced exogenous insulin requirements for up to 9 months with improved glucose tolerance and a reduction in glycosylated hemoglobin levels. No immunosuppression was used. Thus, use of a vascularized artificial pancreas containing xenogeneic porcine islets could be an alternative to intensive insulin therapy and pancreatic transplantation in treating diabetic patients before the development of severe diabetic complications.

Multiple TCR V beta usage by infiltrates of young NOD mouse islets of Langerhans. A polymerase chain reaction analysis

Because a restricted repertoire of T-cell receptor (TCR) V beta gene expression has been reported in other autoimmune diseases, the possibility of similarly restricted V beta gene expression by T-cell infiltrates of NOD mouse islets was examined. With isolated islets from 4- to 12-wk-old NOD mice, a prospective polymerase chain reaction analysis with 18 V beta-specific oligonucleotide primers was performed on the noncloned and unexpanded islet-infiltrating T cells. The methodology used permitted the detection of a minimum of 50 T cells. In contrast to the restricted TCR V beta gene usage reported for other autoimmune diseases, infiltrates of even the youngest mice were characterized by expression of multiple V beta gene segments.

Respiratory response of humans exposed to low levels of ozone for 6.6 hours

Recent evidence suggests that prolonged exposures of exercising men to 0.08 ppm ozone (O3) result in significant decrements in lung function, induction of respiratory symptoms, and increases in nonspecific airway reactivity. The purpose of this study was to confirm or refute these findings by exposing 38 healthy young men to 0.08 ppm O3 for 6.6 h. During exposure, subjects performed exercise for a total of 5 h, which required a minute ventilation of 40 l/min. Significant O3-induced decrements were observed for forced vital capacity (FVC, -0.25 l), forced expiratory volume in 1 s (FEV1.0, -0.35 l), and mean expiratory flow rate between 25% and 75% of FVC (FEF25-75, -0.57 l/s), and significant increases were observed in airway reactivity (35%), specific airway resistance (0.77 cm H2O/s), and respiratory symptoms. These results essentially confirm previous findings. A large range in individual responses was noted (e.g., percentage change in FEV1.0; 4% increase to 38% decrease). Responses also appeared to be nonlinear in time under these experimental conditions.

Effects of 4 percent and 6 percent carboxyhemoglobin on arrhythmia production in patients with coronary artery disease

In this study, we assessed the effects of exposure to 4 percent and 6 percent carboxyhemoglobin on ventricular arrhythmias in 41 subjects (nonsmokers) with documented coronary artery disease. We used a randomized, double-blind, crossover design. On day 1, a training session with no exposure, the baseline carboxyhemoglobin level was measured, and a supine bicycle exercise test was done. On days 2 through 4, subjects were exposed to room air, 100 parts per million (ppm)2 carbon monoxide (target, 4 percent blood carboxyhemoglobin), or 200 ppm carbon monoxide (target, 6 percent blood carboxyhemoglobin), and they then did a supine bicycle exercise test. Radionuclide ventriculography was performed at rest and during exercise. Ambulatory electrocardiogram recordings were made during the four consecutive days to determine the frequency of premature ventricular contractions at various intervals. The frequency of single premature ventricular contractions per hour during exercise was significantly greater on the 6 percent carboxyhemoglobin day than on the room air day (167.72 +/- 37.99 for 6 percent carboxyhemoglobin compared with 127.32 +/- 28.22 for room air, p = 0.03). The frequency of multiple premature ventricular contractions per hour was also significantly greater during exercise on the 6 percent carboxyhemoglobin day compared with the room air day (9.59 +/- 3.70 for the 6 percent carboxyhemoglobin day compared with 3.18 +/- 1.67 for the room air day, p = 0.02). Patients who developed increased arrhythmias during exercise on the 6 percent carboxyhemoglobin day were significantly older than those who had no increased arrhythmia, and, in addition, exercised longer and had a higher peak workload during exercise. No effect of carbon monoxide exposure was seen on the 4 percent carboxyhemoglobin day.

Production of arrhythmias by elevated carboxyhemoglobin in patients with coronary artery disease

OBJECTIVE

To assess the effects of exposure to 4% and 6% carboxyhemoglobin on ventricular arrhythmias in patients with coronary artery disease.

DESIGN

Randomized, double-blind, crossover design.

SETTING

Exercise laboratory with an environmentally controlled exposure.

PATIENTS

Forty-one nonsmokers with documented coronary artery disease.

INTERVENTION

On day 1, a training session with no exposure, the baseline carboxyhemoglobin level was measured, and a supine bicycle exercise test was done. On days 2 to 4, patients were exposed to room air, 100 ppm carbon monoxide (target, 4% carboxyhemoglobin) or 200 ppm carbon monoxide (target, 6% carboxyhemoglobin), and they then did supine bicycle exercise with radionuclide ventriculography. Ambulatory electrocardiogram recordings were made during the 4 consecutive days to determine the frequency of ventricular premature depolarization (VPD) at various intervals.

MEASUREMENTS AND MAIN RESULTS

The frequency of single VPD/h was significantly greater on the 6% carboxyhemoglobin day than on the room air day during the exercise period (167.72 +/- 37.99 for 6% carboxyhemoglobin compared with 127.32 +/- 28.22 for room air, P = 0.03). During exercise, the frequency of multiple VPD/h was greater on the 6% carboxyhemoglobin day compared with room air (9.59 +/- 3.70 on the 6% carboxyhemoglobin compared with 3.18 +/- 1.67 on room air, P = 0.02). Patients who developed increased single VPD during exercise on the 6% carboxyhemoglobin day were significantly older than those who had no increased arrhythmia, whereas patients who developed complex arrhythmias were also older and, in addition, exercised longer and had a higher peak workload during exercise.

CONCLUSION

The number and complexity of ventricular arrhythmias increases significantly during exercise after carbon monoxide exposure producing 6% carboxyhemoglobin compared with room air but not after exposure producing 4% carboxyhemoglobin.

The influence of fentanyl upon cerebral high-energy metabolites, lactate, and glucose during severe hypoxia in the rat

The effects of intravenous administration of high-dose fentanyl (100 micrograms.kg-1, loading dose followed by an infusion of 200 micrograms.kg-1.h-1) were compared with those of a barbiturate (pentobarbital sodium 25 mg.kg-1, intraperitoneal) or hypothermia (rectal temperature 32 degrees C) on changes in cerebral cortical tissue levels of adenosine triphosphate (ATP), phosphocreatine (PCr), lactate, and glucose in severely hypoxemic rats (PaO2 13-23 mmHg for 20 min) with unilateral (left side) carotid ligation (10-12 animals in each group). Ligation of the carotid artery alone produced no change in brain high-energy metabolites, lactate, or glucose. The control values on the ligated side (nitrous oxide, 70%, + normoxia group) for cortical ATP, PCr, lactate, and glucose were 2.86 +/- 0.09 (mumol.g-1 wet weight, mean +/- 1 SE), 3.83 +/- 0.11, 1.68 +/- 0.21, and 3.29 +/- 0.47, respectively. Hypoxia (nitrous oxide, 70%, + hypoxia group) produced a significant (P less than 0.05) decrease in ATP (1.83 +/- 0.37) and PCr (1.93 +/- 0.48) and an increase in lactate (15.8 +/- 1.77) compared with the normoxic group, whereas brain glucose was not significantly changed (1.97 +/- 0.65). Fentanyl (fentanyl + hypoxia group) did not prevent the deleterious effects of hypoxia on cortical high energy metabolites (ATP, 2.0 +/- 0.27; PCr, 2.24 +/- 0.3) or lactate (19.33 +/- 3.16); however, fentanyl caused no alteration in high-energy cerebral metabolite concentrations in normoxic rats, nor did fentanyl produce a significant difference in brain tissue glucose or lactate.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute elevation of blood carboxyhemoglobin to 6% impairs exercise performance and aggravates symptoms in patients with ischemic heart disease

Acute exposure to carbon monoxide has the potential to impair exercise capacity in patients with ischemic heart disease. The effect of sufficient inhalation of this compound to gradually produce a level of 6% carboxyhemoglobin was studied in 30 nonsmoking patients with obstructive coronary artery disease and evidence of exercise-induced ischemia. After an initial training session, subjects were exposed to air or carbon monoxide on successive days in a randomized double-blind crossover fashion. Cardiac function and exercise capacity were assessed during symptom-limited supine radionuclide ventriculography. On the carbon monoxide day, mean postexposure carboxyhemoglobin was 5.9 +/- 0.1% compared with 1.6 +/- 0.1% (p less than 0.01) after air exposure. The mean duration of exercise was significantly longer after air compared with carbon monoxide exposure (626 +/- 50 s for air versus 585 +/- 49 s for carbon monoxide, p less than 0.05). Actuarial methods suggested that subjects were likely to experience angina earlier during exercise on the day of carbon monoxide exposure (p less than 0.05). Both the level (62 +/- 2.4 versus 60 +/- 2.4%, p = 0.05) and change in left ventricular ejection fraction at submaximal exercise (1.6 +/- 1.6 versus -1.2 +/- 1.6%, p = 0.05) were greater on the air exposure day compared with the carbon monoxide day. The peak exercise left ventricular ejection fraction was not different for the two exposures (57 +/- 2.5% for both). These results demonstrate earlier onset of ventricular dysfunction, angina and poorer exercise performance in patients with ischemic heart disease after acute carbon monoxide exposure sufficient to increase blood carboxyhemoglobin to 6%.

Extrathoracic and intrathoracic removal of O3 in tidal-breathing humans

We measured the efficiency of O3 removal from inspired air by the extrathoracic and intrathoracic airways in 18 healthy, nonsmoking, young male volunteers. Removal efficiencies were measured as a function of O3 concentration (0.1, 0.2, and 0.4 ppm), mode of breathing (nose only, mouth only, and oronasal), and respiration frequency (12 and 24 breaths/min). Subjects were placed in a controlled environmental chamber into which O3 was introduced. A small polyethylene tube was then inserted into the nose of each subject, with the tip positioned in the posterior pharynx. Samples of air were collected from the posterior pharynx through the tube and into a rapidly responding O3 analyzer yielding inspiratory and expiratory O3 concentrations in the posterior pharynx. The O3 removal efficiency of the extrathoracic airways was computed with the use of the inspiratory concentration and the chamber concentration, and intrathoracic removal efficiency was computed with the use of the inspiratory and expiratory concentrations. The mean extrathoracic removal efficiency for all measurements was 39.6 +/- 0.7% (SE), and the mean intrathoracic removal efficiency was 91.0 +/- 0.5%. Significantly less O3 was removed both extrathoracically and intrathoracically when subjects breathed at 24 breaths/min compared with 12 breaths/min (P less than 0.001). O3 concentration had no effect on extrathoracic removal efficiency, but there was a significantly greater intrathoracic removal efficiency at 0.4 ppm than at 0.1 ppm (P less than 0.05). Mode of breathing significantly affected extrathoracic removal efficiency, with less O3 removed during nasal breathing than during either mouth breathing or oronasal breathing (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Both the Lyt-2+ and L3T4+ T cell subsets are required for the transfer of diabetes in nonobese diabetic mice

The nonobese diabetic mouse is a model of spontaneous type I diabetes mellitus. It is possible to induce diabetes in young, irradiated nonobese diabetic mice by using adoptive transfer of splenocytes or splenic T cells obtained from diabetic donors. This study demonstrates that the induction of diabetes in the adoptive transfer system is dependent on both the L3T4+ and Lyt-2+ subsets of T cells. Neither of these T cell subsets alone mediates the development of severe insulitis or diabetes when adoptively transferred to young, irradiated recipients. In addition, we show that both the L3T4+ and Lyt-2+ subsets must be obtained from diabetic donors in order to transfer diabetes; neither subset can be replaced with cells obtained from young, nondiabetic donors.

Both the Lyt-2+ and L3T4+ T cell subsets are required for the transfer of diabetes in nonobese diabetic mice

The nonobese diabetic mouse is a model of spontaneous type I diabetes mellitus. It is possible to induce diabetes in young, irradiated nonobese diabetic mice by using adoptive transfer of splenocytes or splenic T cells obtained from diabetic donors. This study demonstrates that the induction of diabetes in the adoptive transfer system is dependent on both the L3T4+ and Lyt-2+ subsets of T cells. Neither of these T cell subsets alone mediates the development of severe insulitis or diabetes when adoptively transferred to young, irradiated recipients. In addition, we show that both the L3T4+ and Lyt-2+ subsets must be obtained from diabetic donors in order to transfer diabetes; neither subset can be replaced with cells obtained from young, nondiabetic donors.

Ozone exposure increases respiratory epithelial permeability in humans

Ozone is a respiratory irritant that has been shown to cause an increase in the permeability of the respiratory epithelium in animals. We used inhaled aerosolized 99mTc-labeled diethylene triamine pentacetic acid (99mTc-DTPA) to investigate whether human respiratory epithelial permeability is similarly affected by exposure to ozone. In a randomized, crossover double-blinded study, 8 healthy, nonsmoking young men were exposed for 2 h to purified air and 0.4 ppm ozone while performing intermittent high intensity treadmill exercise (minute ventilation = 66.8 L/min). SRaw and FVC were measured before and at the end of exposures. Seventy-five minutes after the exposures, the pulmonary clearance of 99mTc-DTPA was measured by sequential posterior lung imaging with a computer-assisted gamma camera. Ozone exposure caused respiratory symptoms in all 8 subjects and was associated with a 14 +/- 2.8% (mean +/- SEM) decrement in FVC (p less than 0.001) and a 71 +/- 22% increase in SRaw (p = 0.04). Compared with the air exposure day, 7 of the 8 subjects showed increased 99mTc-DTPA clearance after the ozone exposure, with the mean value increasing from 0.59 +/- 0.08 to 1.75 +/- 0.43%/min (p = 0.03). These data show that ozone exposure sufficient to produce decrements in the pulmonary function of human subjects also causes an increase in 99mTc-DTPA clearance.

Lack of effect of low levels of carboxyhemoglobin on cardiovascular function in patients with ischemic heart disease

We studied 30 patients 38-75 yr of age who had ischemic heart disease to assess the effect of acute elevation of carboxyhemoglobin (COHb) concentration. Patients were nonsmokers with ischemia defined by exercise-induced ST depression (ST decreases)--25/30, angina--23/30, or abnormal ejection fraction (EF) response--18/30. After an initial familiarization and exercise session patients were exposed to air (carboxyhemoglobin [COHb] = 1.5 +/- 0.05%) and to carbon monoxide (CO) (100 ppm-COHb-average = 3.8 +/- 0.1%) on successive days in a double blind, randomized fashion. There was no significant difference in time to onset of angina (air = 312 sec, CO = 306 sec), maximal exercise time (air = 711 sec, CO = 702 sec), maximal ST decreases (1.5 mm for both), or time to significant ST decreases (air = 474 sec, CO = 475 sec). Double product at ST decreases and maximal double products were similar for both conditions. Resting ejection fraction was slightly but nonsignificantly higher after CO exposure (air = 53.9%, CO = 55.2%). Maximal ejection fraction was similar for both conditions (air = 57.4%, CO = 57.1%). Change in ejection fraction was slightly lower for CO exposure (air = 3.5%, CO = 2%), p = .049. In conclusion, there is no clinically significant effect of 3.8% COHb (representing a 2.2% increase from resting values) on the cardiovascular system in this study.

Differential regulation of glucokinase activity in pancreatic islets and liver of the rat

The differential tissue-specific regulation of glucokinase activity in liver and pancreatic islet cells was investigated in the insulinoma-bearing rat. A transplantable insulinoma caused hyperinsulinemia and hypoglycemia in the host by 2-3 months after implantation. Suppression of the pancreatic B-cells by the high insulin and/or low glucose manifested itself by a decrease of insulin in islet tissue. Removal of the tumor initiated transient insulin deficiency and hyperglycemia with extremes of these changes at 24 h after tumor resection. These conditions markedly affected glucose phosphorylation in the islet cells: glucokinase activity was reduced 71% in islet samples from insulinoma-bearing rats, and the enzyme fully recovered within 24 h after tumor resection. Hexokinase activity, by contrast, was not affected by these manipulations. To evaluate the relative contributions of hypoglycemia and hyperinsulinemia in islet glucokinase adaptation, glucose was intravenously infused to insulinoma-bearing rats; glycemia in excess of 150 mg/100 ml combined with excessive hyperinsulinemia resulted in a partial recovery of islet glucokinase activity, first apparent after 9 h of glucose infusion and with doubling of the activity after 24 h after glucose loading. In contrast, liver glucokinase was increased nearly 4-fold at the time of extreme hypoglycemia and hyperinsulinemia and rapidly fell to control rates following tumor removal. Intravenous infusion of glucose for 24 h into the tumor-bearing rat (i.e. hyperglycemia combined with excessive plasma insulin) had no influence on liver glucokinase activity. Liver hexokinase was not influenced by any of these experimental manipulations. The data indicate that the activities of pancreatic islet and liver glucokinase are regulated in a differential manner. Insulin is apparently the primary determinant of liver glucokinase and glucose seems to control islet glucokinase. Biochemical mechanisms for differential organ-specific regulation of glucokinase activity seem to have evolved such that this enzyme may play a dual role in glucose homeostasis, namely to serve as insulin-dependent glucose sensor in the B-cells and as insulin-sensitive determinant of hepatic glucose use.

Tissue slices in the study of lung metabolism and toxicology

Lung tissue slices are model systems for the study of pulmonary metabolism. Because of the speed and simplicity of slice preparation, lung slices have been used in studies of oxygen, amino acid, carbohydrate and lipid utilization and adenine nucleotide metabolism. Dose-response characteristics for toxicants are readily described because multiple lung samples can be studied from the same animal or a population of animals. Lung slices prepared from animals exposed to oxidant air pollutants exhibit alterations in respiration, glucose consumption and lipid metabolism. These studies have indicated both direct toxic effects of air pollutants on enzyme systems and also air pollutant-induced changes in the cellularity of lungs.

Pulmonary function testing in small laboratory mammals

The lung is the primary organ likely to be exposed by inhalation studies and, therefore, measurement of changes in lung function are of particular interest to the pulmonary physiologist and toxicologist. Tests of pulmonary function have been developed which can be used with small animals to measure spirometry (lung volumes), mechanics, distribution of ventilation, gas exchange or control of ventilation. These tests were designed on the basis of similar tests which are used in humans to diagnose and manage patients with lung disease. A major difference is that many of the measurements are performed in anesthetized animals, while human pulmonary function is usually measured in awake cooperating individuals. In addition, the measurement of respiratory events in small animals requires sensitive and rapidly responding equipment, because signals may be small and events can occur quickly. In general, the measurements described provide information on the change in normal lung function which results primarily from structural changes. These tests of pulmonary function can be repetitively and routinely accomplished and the results appear to be highly reproducible. Although some are quite sophisticated, many can be undertaken with relatively inexpensive equipment and provide useful information for toxicological testing.

Maximal oxygen consumption and pulmonary diffusing capacity: a direct comparison of physiologic and morphometric measurements in canids

The purpose of this study was to check the validity of the morphometric model for estimating physiological conductances for gases, DL. We make a direct comparison between the lung's conductance for carbon monoxide, measured physiologically using the single breath method, DLCO (sb), and that measured morphometrically using the previously published model, DLCO(mm). We also make a direct comparison between the maximum rate of oxygen uptake by the lung during exercise, VO2max, and the lung's conductance for oxygen DLO2(mm). We made these measurements on four species of canids (foxes, coyotes, dogs and wolves). We find a direct proportionality between morphometric and physiologic DLCO measurements, the morphometric being consistently larger by a factor of two. We also find that both DLCO and DLO2 increase more steeply with body mass than VO2max, the difference between the allometric slopes being the same as we had found previously in a wide range of mammalian species ranging from 2 g to 700 kg, although the slopes themselves were different. We conclude that the discordant scaling of DLO2 and VO2max with respect to body mass is not an artifact of the model for calculating DLO2 from morphometric data.

Can animal pulmonary function testing provide data for regulatory decision making?

The process of setting health standards requires rigorous, scientifically sound data that relate to man's interaction with his environment. Tests of pulmonary function are especially useful, since they may permit some direct comparisons between animals and man. The development of tests to measure pulmonary function in small animals has been important, and research into the health effects of air pollution may be greatly strengthened with the use of data from such measurements.

Pulmonary function in normal and elastase-treated hamsters exposed to a complex mixture of olefin-ozone-sulfur dioxide reaction products

An elastase-induced emphysema model was utilized to determine if hamsters with preexisting lung disease were more susceptible to lung damage from air pollutant exposure. Male golden hamsters, divided into two treatment groups, were given a single intratracheal injection of either 6 units of porcine pancreatic elastase (EMP) or buffer (CNT). After a 4-week recovery period, equal numbers of each group were exposed 23 hr/day X 28 day to filtered air (AIR) or to the complex by-products from a dark phase reaction mixture of trans-2-butene, ozone, and sulfur dioxide (MIX). Lung function measurements on the elastase-treated groups showed changes consistent with mild emphysema. There were no significant differences in lung volumes or lung compliance between the AIR- and MIX-exposed animals. However, the nitrogen washout slope decreased (P less than 0.05), and the diffusing capacity for carbon monoxide increased (P less than 0.05) in both the CNT and EMP hamsters exposed to the MIX. The change in diffusing capacity was greater (P less than 0.05) in normal hamsters than in hamsters with emphysema, and it is hypothesized that animals with impaired lung function had a decreased ability to respond to a pulmonary insult from the mix.

Oxygen consumption measured with microcomputer-assisted Warburg manometry

We have developed and tested an automated system that measures in vitro oxygen consumption by Warburg manometry in as many as 16 units that are under the simultaneous control of a microcomputer which requires attention at the beginning of the study only. The all-glass Submarine Volumometers used are readily adapted to automation using a microcomputer that interacts with an infrared photodetector sensitive to manometric changes in the reaction vessel and a stepper motor that can advance the calibrated micrometer in response to these changes. The microcomputer interacts with the user at the start of the study during data entry and subsequently determines volume changes related to oxygen consumption, calculates respiration rates, and prints or graphs the results without further user interaction. We compared this automated system with manual methods by measuring the oxygen consumption of lung tissue slices and by determining the ability of the system to match known volumes entered manually. We found that the results obtained using the automated system were not significantly different from known manual methods (P less than 0.05).

Morphologic changes in the lung during the lifespan of Fischer 344 rats

Pulmonary structure and function were quantitatively investigated over the lifespan of the Fischer 344 rat by morphometric and physiologic techniques. Male animals 1 week, 6 weeks, 5 months, 14 months, and 26 months of age and female animals 5 months, 14 months, and 26 months of age were studied. All alveolar tissue compartments demonstrated significant increases in volume, surface area, and cell number during the first 5 months of life. From 5 to 26 months of age, remodelling in the epithelial and interstitial compartments continued to take place while the endothelial compartment remained relatively unchanged. In the epithelial compartment the ratio of type II cells to type I cells lining the alveolar surface decreased as age increased. In the interstitial compartment the volume of the noncellular components of the interstitium increased by 39% in males and by 89% in females from 5 to 26 months of age. Physiologic measurements of lung volumes in males at 6 weeks, 14 months, and 26 months demonstrated progressive increases in vital capacity (VC) and total lung capacity (TLC). Morphometric pulmonary-diffusion capacity (DLO2) increased in males from 1 week to 5 months of age and remained relatively unchanged from 5 to 26 months of age in both sexes.

Dose response of elastase-induced emphysema in hamsters

Elastase-induced emphysema in hamsters was studied using pulmonary function tests in an effort to develop techniques for determining the effects of air pollutants on the progression of this disease. Single intratracheal injections of 6, 12, or 24 units of porcine pancreatic elastase produced dose-related changes in pulmonary function after 4 wk when compared with sham-injected control animals. Boyle's law end-expiratory volume and residual volume, measured by gas dilution, increased (p less than 0.05) at 12 and 24 units, respectively, whereas vital capacity, determined plethysmographically, and total lung capacity wee increased (p less than 0.05) at all 3 elastase doses. Respiratory system compliance, calculated by a nonlinear least squares regression fit of the deflation pressure-volume curve, increased (p less than 0.05) at 24 units only. The multiple-breath nitrogen washout slope (N2 slope) and the single-breath diffusing capacity for carbon monoxide (DLCO) decreased (p less than 0.05) at all 3 doses of elastase. Both histologic and physiologic evaluation showed dose-related pulmonary impairment. It appears, therefore, that as little as 6 units of elastase produces mild emphysema in hamsters, which is detectable by pulmonary function testing. Of these tests, the DLCO and N2 slope were the most effective in detecting the degree of impairment.

Pulmonary injury in rats following continuous exposure to 60% O2 for 7 days

Morphological, biochemical, and physiological studies were done on rats exposed to 60% O2 for 7 days. This exposure did not induce O2 tolerance but instead caused a significant decrease in survival time of animals subsequently exposed to pure O2. The activity of lung superoxide dismutases and glucose-6-phosphate dehydrogenase were unchanged after exposure to 60% O2. A decrease in lung compliance was suggested by changes in the total lung capacity and in the pressure-volume curves of excised lungs. Ventilation of these animals with large tidal excursion resulted in pulmonary edema. Morphometric analyses revealed a significant decrease in alveolar air volume and an increase in the number of alveolar macrophages. The most significant lesions involved the pulmonary vascular bed. The volume and thickness of the capillary endothelium was decreased. There were focal areas of pericapillary fluid accumulations, and a number of the smaller vessels had perivascular edema. These findings suggest that significant pulmonary injury occurs in rats exposed to 60% O2 and that the primary site of injury is the pulmonary capillary endothelium.

Single-breath diffusing capacity and lung volumes in small laboratory mammals

We measured the single-breath diffusing capacity for carbon monoxide (DLCO), total lung capacity (TLC), functional residual capacity (FRC), and residual volume (RV) in anesthetized male hamsters, rats, guinea pigs, and rabbits whose weights varied from 40 to 3,500 g. TLC (defined as an airway pressure of 25 cmH2O) was calculated by neon dilution. The DLCO was estimated by a modification of the single-breath method. There was a high correlation between body weight and our measurement of both the diffusing capacity and the lung volumes. No significant difference in DLCO was observed in rats when measured in different body positions, at airway pressures of 10 or 20 cmH2O, from FRC or RV, in male or female rats, or following hyperventilation.

Factors determining degree of inflation in intratracheally fixed rat lungs

The total lung capacity (TLC) of rats was measured in vivo and was compared to the displacement volume of the lungs following intratracheal fixation with glutaraldehyde or formaldehyde solution. When glutaraldehyde was used the speed of infusion of the fixative was an important factor in the final degree of lung inflation achieved. With a low rate of fixative infusion and a final pressure of 20 cm of fixative the glutaraldehyde-fixed lungs inflated to 55% TLC. With a high initial flow of glutaraldehyde and a final pressure of 20 cm of fixative the lungs inflated to 84% TLC. Fixation of lungs inside the intact chest wall was found to result in a higher degree of inflation. With a reservoir height of 20 cm and a low rate of fixative infusion lungs fixed in situ reached 74% TLC, whereas lungs fixed in situ, but from animals that have been exsanguinated prior to fixation, inflated to only 58% TLC. This suggests that the volume of the blood in the lungs prior to infusion of glutaraldehyde influences the degree of inflation achieved. Formaldehyde-fixed lungs required 72 h to be completely fixed and they were inflated to 90% TLC when a reservoir height of 20 cm was used. Because of the slow rate of fixation using with formaldehyde solution the rate of infusion was found not to limit the degree of inflation that could be achieved.

Metabolism in rat lung tissue slices: technical factors

We compared several sets of conditions used to estimate metabolism in rat lung slices. 14CO2 production from [14C]glucose, oxygen consumption, lactate production, and glucose consumption were used as measures of metabolic activity. The calculated results differed when we used 1) different techniques for estimating tissue weight, 2) tissue slices of 0.3-, 0.5-, 0.7-, and 1.0-mm thickness, 3) 95% air or 95% oxygen with 5% CO2 4) a delay after slice preparation and 4 degrees C and room temperature or periods of anoxia before incubation, 5) shaking rates of 60, 90, 120, or 150/min, 6) phosphate or bicarbonate buffers. Conditions of maximal activity were found using 95% O2 with 1.0-mm tissue slices, shaking at 120/min in phosphate buffer without periods of hypoxia or undue delays before incubation. Tissue weight should be obtained without exposure to aqueous solutions or dehydration by contact with cotton gauze or filter paper.