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W L Chick

Publications and source records attributed to W L Chick.

At least 37 records · Page 2Linked to original sources
PubMed1993

Biohybrid artificial pancreas. Long-term function of discordant islet xenografts in streptozotocin diabetic rats.

Long-term function of canine, bovine, and porcine islet xenografts implanted in streptozotocin-induced diabetic rats has been achieved by islet encapsulation within permselective acrylic membrane chambers. Intraperitoneal implants of 1 x 10(4) (n = 11) or 2 x 10(4) (n = 2) encapsulated canine islets reversed the diabetic state of the recipients within 24 hr, with plasma glucose levels dropping from a preimplantation level of 480 +/- 26 (mean +/- SEM) to 97 +/- 4 mg/dl during the first month. Chambers from 2 of the animals were removed, bisected, and reimplanted at 1 week and 2 months; both animals reverted to hyperglycemia (glucose, > 200 mg/dl) in < 2 weeks. The remaining implants maintained function for a mean time of 138 +/- 16 days, whereas the 2 animals that received the higher islet dose maintained function for > 260 days. Membranes containing 2 x 10(4) bovine (n = 6) or porcine (n = 10) islets also normalized glucose concentrations, with plasma glucose levels dropping from 468 +/- 61 to 91 +/- 10 (bovine) and 97 +/- 11 (porcine) mg/dl during the first month (vs. 94 +/- 3 mg/dl for nondiabetic control rats). Three of the latter implants were removed at 1 month. All 3 animals promptly reverted to diabetes. The 3-, 6-, 9-, and 12-month graft survival rates for the remaining animals were 100%, 100%, 60%, and 40%, and 100%, 75%, 50%, and 25%, respectively. The transplant recipients showed an approximately 38-54% gain in body weight during the first 100 days after implantation, compared with < 1% (P < 0.001) and 86% (P < 0.001) for the untreated diabetic (n = 5) and normal control (n = 6) groups. Immunohistochemical staining of long-term grafts (1-20 months) revealed varying degrees of alpha-, beta-, and delta-cell granulation; the external membrane surfaces were generally free of fibrotic overgrowth and exhibited only occasional host cell adherence. Despite a problem of membrane breakage in long-term implants, these results suggest that prolonged survival of discordant transplants of porcine, bovine, and canine islets in diabetic rats can be achieved without immunosuppression.

Animals↗
PubMed1992

Transplantation of encapsulated canine islets into spontaneously diabetic BB/Wor rats without immunosuppression.

Extended survival of canine islet xenografts implanted in spontaneously diabetic BB/Wor rats has been achieved by islet encapsulation inside cylindrical chambers fabricated from permselective acrylic membranes. Intraperitoneal implantation of the encapsulated islets reversed the diabetic state of the 10 recipients within 24 h. Plasma glucose levels declined from a preimplantation level of 459 +/- 30 to 102 +/- 14 mg/dl during the first 10 days. All of the animals sustained these levels for at least 1 month, and 2 animals for at least 2 and 8 months, respectively. To confirm that glucose homeostasis resulted from the encapsulated islet grafts, the implants were removed from 2 rats 1 month postimplantation, whereas a third was removed at 2 months. Hyperglycemia was observed immediately in all 3 animals, with glucose levels rising from 100 +/- 3 to 510 +/- 43 mg/dl within 1 day. In contrast, diabetic control rats (n = 4) receiving nonencapsulated islets became hyperglycemic in less than 1 week. The iv glucose tolerance test K value (decline in glucose levels, percent per min) at 10 days was 2.3 +/- 0.4 compared with 0.6 +/- 0.1 (P less than 0.005) and 3.1 +/- 0.1 (P less than 0.02) for untreated diabetic (n = 4) and normal control (n = 4) groups. Histological analyses and electron microscopy of long term functioning grafts revealed well preserved islets, with hormone-producing alpha-, beta-, and delta-cells; the membranes were generally free of fibrosis and host cell adherence. These results demonstrate that permselective artificial membranes can protect discordant islet xenografts from both graft rejection and autoimmune destruction for more than 1 month in an animal model that is similar in several respects to human type I diabetes.

Animals↗
PubMed1992

Perspectives in diabetes. Islet transplantation with immunoisolation.

Immunoisolation is a potentially important approach to transplanting islets without need for immunosuppressive drugs. Immunoisolation systems have been conceived in which the transplanted tissue is separated from the immune system of the host by an artificial barrier. These systems offer a solution to the problem of human islet procurement by permitting use of islets isolated from animal pancreases. The devices used are referred to as biohybrid artificial organs because they combine synthetic, selectively permeable membranes that block immune rejection with living transplants. Three major types of biohybrid pancreas devices have been studied. These include devices anastomosed to the vascular system as AV shunts, diffusion chambers, and microcapsules. Results in diabetic rodents and dogs indicate that biohybrid pancreas devices significantly improve glucose homeostasis and can function for more than a year. Recent progress made with this approach is discussed, and some of the remaining problems that must be resolved to bring this technology to clinical reality are addressed.

Animals↗
PubMed1992

Treatment of severely diabetic pancreatectomized dogs using a diffusion-based hybrid pancreas.

Long-term survival of dog islet allografts implanted in diabetic pancreatectomized dogs was achieved by islet encapsulation inside cylindrical chambers fabricated from permselective acrylic membranes (nominal M(r) exclusion of 50,000-80,000). Dog islets were isolated from the pancreases of outbred mongrel dogs by collagenase digestion. Chambers containing mean +/- SE 316 +/- 63K islet equivalents (mean islet volume, 558 +/- 111 mm3, purity 90-95%) were peritoneally implanted into six totally pancreatectomized dogs. The dogs were monitored for glycemic control by fasting and postprandial blood glucose determinations, and responses to both intravenous glucose (intravenous glucose tolerance test 0.5 g/kg) and oral glucose (oral glucose tolerance test 1 g/kg). All of the dogs required appreciably lower dosages of exogenous insulin therapy for control of fasting blood glucose levels, with the mean daily insulin dose dropping from 38 +/- 7 to 5 +/- 1 U/day during the 1st wk. Three recipients required no insulin for greater than 82, greater than 68, and 51 days. Intravenous glucose tolerance test K values (decline in glucose levels, %/min) at 1 and 2 mo postimplantation were 2.7 +/- 0.4 and 2.0 +/- 0.5, respectively compared with 3.5 +/- 0.5 before pancreatectomy. The glucose values during oral glucose tolerance tests at 2 wk, although returning to less than 125 mg/dl (less than 7.0 mM) by 2 h, exceeded the normal range, with peak values of 174 to 202 mg/dl (9.7 to 11.3 mM). These preliminary results are encouraging, and represent an important step in determining the feasibility of using this type of diffusion-based hybrid artificial pancreas as treatment for diabetes mellitus in humans.

Animals↗
PubMed1991

Biohybrid artificial pancreas: long-term implantation studies in diabetic, pancreatectomized dogs.

Diabetic complications such as neuropathy, retinopathy, and renal and cardiovascular disease continue to pose major health risks for diabetic patients. Consequently, much effort has focused on approaches that could replace conventional insulin therapy and provide more precise regulation of blood glucose levels. The biohybrid perfused artificial pancreas was designed to incorporate islet tissue and a selectively permeable membrane that isolates this tissue from the immune system of the recipient. Biohybrid pancreas devices containing canine islet allografts were implanted in ten pancreatectomized dogs requiring 18 to 32 units of injected insulin daily. These implants resulted in good control of fasting glucose levels in six of these animals without further exogenous insulin for periods of up to 5 months.

Animals↗
PubMed1991

Transplantation of islet allografts and xenografts in totally pancreatectomized diabetic dogs using the hybrid artificial pancreas.

Previously the authors reported on a Hybrid Artificial Pancreas device that maintained patent vascular anastomoses in normal dogs and, when seeded with allogeneic canine islets, maintained normal fasting blood sugars (FBS) in diabetic pancreatectomized dogs. Eventual failure of these devices was believed to be related to loss of islet viability and/or insufficient islet mass. The current study evaluates the effect of increased islet mass produced by implantation of two islet-seeded devices in pancreatectomized dogs and compares the results with those from dogs that received a single device. Twelve of fifteen dogs receiving single devices showed initial function as determined by elimination or reduction of exogenous insulin requirement; four showed initial function and seven showed extended function (100 to 284 days). Excessive weight loss (more than 20%), despite normal FBS and insulin dependence, required that four animals in this latter group be killed. Devices seeded with xenogeneic islets have met with limited success. One dog that received two bovine islet-seeded devices achieved function for more than 100 days; the remaining bovine-seeded devices (n = 8) functioned for only 3 to 16 days. Porcine islet-seeded devices were assessed by intravenous glucose tolerance tests (IVGTT). Recipients of two devices seeded with allogeneic islets demonstrated improved IVGTT results when compared to those from pancreatectomized dogs and recipients of single devices but were abnormal when compared to intact animals. Histologic examination of device and autopsy material from all failed experiments was performed and showed no mononuclear cell infiltration of the islet chamber or vascular graft material, only a few incidence of device thrombosis, and varying degrees of islet viability as judged by morphologic and immunohistochemical evaluation. The authors believe they have demonstrated progress toward the development and clinical applicability of the Hybrid Artificial Pancreas.

Animals↗
PubMed1991

Successful treatment of diabetes with the biohybrid artificial pancreas in dogs.

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

Animals↗
PubMed1991

Expression of functional human Epstein-Barr virus/C3d receptor ([CR2] CD21) on insulinoma cell line. Induction of tumor rejection but not diabetes in syngeneic rats.

We stably expressed human complement receptor 2 ([CR2] CD21 C3d/Epstein-Barr virus [EBV] receptor) on the rat insulinoma cell line RINm5F with a recombinant retroviral vector. CR2-expressing RINm5F cells secreted 78-33% less insulin than parental cells or cells transduced with an antisense vector and could be infected with high-titer EBV. We tested whether human CR2 expression on RINm5F cells would affect tumorigenesis after transplantation to syngeneic New England Deaconess Hospital rats. Non-CR2-expressing antisense-transduced RINm5F cells rapidly grew tumors and caused hypoglycemia, hyperinsulinemia, and the death of the animals after 15.7 +/- 0.7 days. CR2-expressing RINm5F cells were infiltrated by mononuclear cells at an early stage and eventually caused noninfiltrated tumors and the death of the animals after 33.0 +/- 0.4 days. These tumors were CR2- and are believed to have arisen from a minor CR2- population of tumor cells. The pancreatic islets were histologically normal at all time points. We conclude that expression of a xenoantigen on a rat insulinoma cell line induces an immune response in syngeneic rats but does not result in breakage of tolerance to parental or revertant cells.

Animals↗
PubMed1990

Islet cell culture in defined serum-free medium.

A serum-free, hormone- and factor-supplemented, defined medium was developed which maintains functional activity of primary cultures of adult islet cells and continuous islet cell lines. Medium supplements examined included proteose peptone (PP), transferrin (TrFe), insulin-like growth factor-I (IGF-I), an insulinotropic fragment of human GH [hGH-(6-13)], ethanolamine (EA), phosphoethanolamine (PEA), and human serum albumin (HSA). Glucose-stimulated insulin secretion from islet monolayers was determined after culture in serum-free supplemented medium by either 2- to 3-h static incubations or in a superfusion system with either low (2.8-8.3 mM) or stimulatory (16.7-19.4 mM) glucose concentrations. Glucose-induced secretion was not sustained after 3-4 days of culture in medium supplemented with PP (0.5 mg/ml) and TrFe (10 micrograms/ml) alone. Addition of T3 did not restore glucose-induced secretion, although a combination of T3 and IGF-I or of T3, IGF-I, and PRL (10(-10)-10(-9) M) maintained glucose-induced insulin secretion for 1 month. No beneficial effects were noted with hGH-(6-13). The beta-cell lines HIT-T15 and RINr 1046-38 were used to screen for a potential replacement for PP, the undefined component of the serum-free medium. A combination of HSA (1 mg/ml), EA (50 microM), and PEA (50 microM) provided a replacement for PP. In fact, insulin secretion from HIT-T15 cells was significantly better after culture in medium supplemented with HSA, EA, PEA, TrFe, T3, IGF-I, and PRL than in medium with PP, TrFe, T3, IGF-I, and PRL. HSA (1 mg/ml), EA (50 microM), and PEA (50 microM) in combination with TrFe (10 micrograms/ml), T3 (0.1 nM), IGF-I (0.65 nM), and PRL (1 nM) were used in studies with primary islet monolayers. After 3 weeks of culture islet monolayers were superfused, and the biphasic glucose-induced insulin secretion of cells maintained in defined medium was indistinguishable from the insulin secretion of cells maintained in medium with 5% fetal bovine serum. These studies indicate that adult rat beta-cells retain biphasic glucose-induced insulin secretion after extended culture in defined serum-free medium. The defined medium was also useful for cultures of RINr 1046-38 and HIT-T15 cells and should provide a basis for formulating media for islet cells from higher mammals, including man.

Animals↗
PubMed1990

Modulation of glucose-induced insulin secretion from a rat clonal beta-cell line.

The present studies demonstrate that the beta-cell line RINr1046-38 (RIN-38) retains the capability to secrete insulin in response to glucose. The maximal effect of glucose was a 5- to 9-fold stimulation of insulin secretion from RIN-38 cells. This glucose-induced insulin secretion was maximal at 0.6 mM and was modulated by other secretagogues. Potassium concentrations of 10 mM, adenylate cyclase activators (glucagon-like peptide-1 and forskolin), and a phosphodiesterase inhibitor (isobutylmethylxanthine) potentiated glucose-induced insulin secretion, but had little or no effect on insulin secretion in the absence of glucose. Potassium concentrations of 20 mM or more, glibenclamide, and carbachol (Cch) stimulated insulin secretion 8- to 12-fold in the absence of glucose, while only Cch potentiated the effect of glucose on insulin secretion. Amino acids (alanine, arginine, leucine, and ketoisocaproate) also stimulated insulin secretion. The alpha 2-adrenergic agonist clonidine (1 microM), low extracellular calcium (less than or equal to 0.5 mM), and extended culture of RIN-38 cells at low glucose concentrations (0.33 mM) inhibited the stimulatory effect of glucose on insulin secretion. Insulin secretion was retained in RIN-38 cells for up to 98 passages. However, extended passage was associated with a decline in cellular insulin content (83% decline over 89 passages). In addition, high passage cells lost the ability to secrete insulin in response to glucose, but continued to respond to other secretagogues (K+, alanine, and carbachol). In fact, in the absence of glucose the effect of Cch on insulin secretion was well maintained in high passage cells (8- and 9.9-fold increase in insulin secretion, passages 9 and 70, respectively). Thus, low passage RIN-38 cells secrete insulin in response to glucose and other insulin secretagogues. High passage cells do not respond to glucose, but continue to respond to other secretagogues. Based on these results we propose that high and low passage RIN-38 cells provide a model for examining molecular mechanisms of glucose-induced insulin secretion. In addition, these findings emphasize that passage information is essential for interpretation of secretion studies with RIN cell lines.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Glucagon-like peptide I stimulates insulin gene expression and increases cyclic AMP levels in a rat islet cell line.

Insulin secretion is controlled by a complex set of factors. Although blood glucose levels serve as the major stimulus of insulin secretion in mammals, insulin release is also modulated by amino acids, catecholamines, glucagon, and other, intestinal hormones. The identification of factors that modulate insulin production has engendered much interest because of their potential importance in the altered dynamics of insulin secretion in response to glucose characteristic of maturity-onset diabetes mellitus. Decoding of the glucagon gene has uncovered two additional glucagon-like peptides encoded in proglucagon, the polypeptide precursor of glucagon. One of these peptides, glucagon-like peptide I, is processed from proglucagon in two forms, of 31 and 37 amino acids. We report that the smaller of the two glucagon-like peptides potently increases cAMP levels, insulin mRNA transcripts, and insulin release in cultured rat insulinoma cells. These results indicate that glucagon-like peptide I may be a physiologic modulator of insulin gene expression.

Actins↗
PubMed1987

Transcriptional regulation of genes encoding insulin, glucagon, and angiotensinogen by sodium butyrate in a rat islet cell line.

The state of differentiation of various neoplastic cell lines is inversely correlated with the rate of cellular growth. To delineate the changes in hormone gene expression associated with an induced decrease in the growth rate of rat insulinoma cells, we studied the effects of sodium butyrate on the expression of the genes encoding insulin, glucagon, and angiotensinogen. Sodium butyrate inhibited cellular proliferation and decreased levels of c-myc mRNA. Concomitantly, steady-state levels of mRNAs encoding insulin and glucagon increased by 10- and 8.5-fold, respectively, as a result of a specific increase in the transcription of both genes. Sodium butyrate also inhibited angiotensinogen gene expression, which was ectopic in the insulinoma cells. These observations suggest that sodium butyrate induces a pattern of events leading to the differentiation of the rat insulinoma cells.

Angiotensinogen↗