K. Papas - Academia.edu (original) (raw)
Papers by K. Papas
Transplantation Journal, 2010
Benign encapsulation of living cells within stable, permselective materials holds exciting prospe... more Benign encapsulation of living cells within stable, permselective materials holds exciting prospects for implantable autonomous therapeutics, but is challenged by the demand by such applications for materials bearing an optimal combination of microstructure, stability, and functionality. The ideal capsule would simultaneously protect the cell from immunological attack, efficiently transport nutrients, and rapidly release therapeutic cell metabolites. Recently, we have developed a benign and controllable method for synthesizing stable silica nanoparticles (Lys-Sil) from 10 to 50 nm, and their in situ and ex situ ordering into colloidal crystal arrays and thin films1. Encapsulating living cells within nanoparticle films of controllable thickness (i.e., tens of nanometers) will translate to higher flux of chemical species2. In addition, the porosity of such ordered nanoparticle films, imparted by the interstitial spacing between particles, can be tuned through particle size control and...
American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons, 2014
The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and... more The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and transplants. This retrospective report analyzed 1017 islet isolation procedures performed for 537 recipients of allogeneic clinical islet transplantation in 1999-2010. This study describes changes in donor and islet isolation variables by era and factors associated with quantity and quality of final islet products. Donor body weight and BMI increased significantly over the period (p<0.001). Islet yield measures have improved with time including islet equivalent (IEQ)/particle ratio and IEQs infused. The average dose of islets infused significantly increased in the era of 2007-2010 when compared to 1999-2002 (445.4±156.8 vs. 421.3±155.4×0(3) IEQ; p<0.05). Islet purity and total number of β cells significantly improved over the study period (p<0.01 and <0.05, respectively). Otherwise, the quality of clinical islets has remained consistently very high through this period, and d...
Transplantation Journal, 2010
Xenotransplantation
Paramagnetic microparticles (MPs) may be useful in pancreatic islet purification, in particular p... more Paramagnetic microparticles (MPs) may be useful in pancreatic islet purification, in particular purification of porcine islets as a potential xenotransplantation product. We assessed whether MPs affect islet function or induce an adverse effect following implantation. Porcine islets were co-cultured with 0, 500, and 1500 MPs per islet equivalent (IE) for 1 day and with 0 and 1500 MPs/IE for 7 days. Fractional viability was assessed using oxygen consumption rate normalized to DNA content (OCR/DNA) and after 7-day co-culture by perifusion glucose-stimulated insulin secretion (GSIS) and by transplantation under the renal capsule of diabetic nude mice. To assess an inflammatory response or immune reaction, MPs (∼10(7)) were implanted under the renal capsule of C57BL/6 mice. No statistically significant differences were measured in OCR/DNA (mean ± SE) following 1-day co-culture with 0, 500, or 1500 MPs/IE (243.3 ± 4.5, 211.3 ± 8.1, or 230.6 ± 11.3 nmol/min·mgDNA, respectively) or followi...
Transplantation Proceedings, 2010
Introduction. Despite significant advances, widespread applicability of islet cell transplantatio... more Introduction. Despite significant advances, widespread applicability of islet cell transplantation remains elusive. Refinement of current islet isolation protocols may improve transplant outcomes. Islet purification by magnetic separation has shown early promise. However, surgical protocols must be optimized to maximize the incorporation of paramagnetic microparticles (MP) within a greater number of islets. This study explores the impact of MP concentration and infusion method on optimizing MP incorporation within islets. Methods. Five porcine pancreata were procured from donors after cardiac death. Splenic lobes were isolated and infused with varying concentrations of MP (8, 16, and 32 ϫ 10 8 MP/L of cold preservation solution) and using one of two delivery techniques (hanging bag versus hand-syringe). After procurement and infusion, pancreata were stored at 0°C to 4°C during transportation (less than 1 hour), fixed in 10% buffered formalin, and examined by standard magnetic resonance imaging (MRI) and histopathology. Results. T2*-weighted MRI showed homogeneous distribution of MP in all experimental splenic lobes. In addition, histologic analysis confirmed that MP were primarily located within the microvasculature of islets (82% to 85%), with few MP present in acinar tissue (15% to 18%), with an average of five to seven MP per islet (within a 5-m thick section). The highest MP incorporation was achieved at a concentration of 16 ϫ 10 8 MP/L using the hand-syringe technique. Conclusion. This preliminary study suggests that optimization of a surgical protocol, MP concentrations, and applied infusion pressures may enable more uniform distribution of MP in the porcine pancreas and better control of MP incorporation within islets. These results may have implications in maximizing the efficacy of islet purification by magnetic separation.
Transplantation Proceedings, 2010
Islet transplantation is emerging as a promising treatment for patients with type 1 diabetes. It ... more Islet transplantation is emerging as a promising treatment for patients with type 1 diabetes. It is important to maximize viable islet yield for each organ due to scarcity of suitable human donor pancreata, high cost, and the large dose of islets required for insulin independence. However, organ transport for 8 hours using the two-layer method (TLM) frequently results in low islet yields. Since efficient oxygenation of the core of larger organs (eg, pig, human) in TLM has recently come under question, we investigated oxygen persufflation as an alternative way to supply the pancreas with oxygen during preservation. Porcine pancreata were procured from donors after cardiac death and preserved by either TLM or persufflation for 24 hours and subsequently fixed. Biopsies collected from several regions of the pancreas were sectioned, stained with hematoxylin and eosin, and evaluated by a histologist. Persufflated tissues exhibited distended capillaries and significantly less autolysis/cell death relative to regions not exposed to persufflation or to tissues preserved with TLM. The histology presented here suggests that after 24 hours of preservation, persufflation dramatically improves tissue health when compared with TLM. These results indicate the potential for persufflation to improve viable islet yields and extend the duration of preservation, allowing more donor organs to be utilized.
Transplantation Proceedings, 2010
Transplantation Journal, 2010
American Journal of Transplantation, 2008
We sought to determine the long-term outcomes in type 1 diabetic recipients of intraportal allois... more We sought to determine the long-term outcomes in type 1 diabetic recipients of intraportal alloislet transplants on a modified immunosuppressive protocol. Six recipients with hypoglycemia unawareness received one to two islet infusions. Induction therapy was with antithymocyte globulin (ATG) plus etanercept for tumor necrosis factor-a blockade. Recipients received cyclosporine and everolimus for maintenance immunosuppression for the first year posttransplant, with mycophenolic acid or mycophenolate mofetil subsequently substituted for everolimus. Recipients have been followed for 1173 ± 270 days since their last infusion for islet graft function (insulin independence, hemoglobin A 1c levels and C-peptide production) and for adverse events associated with the study protocol. Of the six recipients, five were insulin-independent at 1 year, and four continue to be insulin-independent at a mean of 3.4 ± 0.4 years posttransplant. None of the six recipients experienced recurrence of severe hypoglycemia. Measured glomerular filtration rate decreased from 110.5 ± 21.2 mL/min/1.73 m 2 pretransplant to 82.6 ±19.1 mL/min/1.73 m 2 at 1 year posttransplant. In conclusion, islet transplants restored insulin independence for a mean of >3 years in four of six recipients treated with ATG and etanercept induction therapy and with cyclosporine and, initially, everolimus for maintenance. Our results suggest this immunosuppressive protocol may allow long-term graft survival.
Transplantation Journal, 2010
Benign encapsulation of living cells within stable, permselective materials holds exciting prospe... more Benign encapsulation of living cells within stable, permselective materials holds exciting prospects for implantable autonomous therapeutics, but is challenged by the demand by such applications for materials bearing an optimal combination of microstructure, stability, and functionality. The ideal capsule would simultaneously protect the cell from immunological attack, efficiently transport nutrients, and rapidly release therapeutic cell metabolites. Recently, we have developed a benign and controllable method for synthesizing stable silica nanoparticles (Lys-Sil) from 10 to 50 nm, and their in situ and ex situ ordering into colloidal crystal arrays and thin films1. Encapsulating living cells within nanoparticle films of controllable thickness (i.e., tens of nanometers) will translate to higher flux of chemical species2. In addition, the porosity of such ordered nanoparticle films, imparted by the interstitial spacing between particles, can be tuned through particle size control and...
American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons, 2014
The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and... more The Collaborative Islet Transplant Registry (CITR) collects data on clinical islet isolations and transplants. This retrospective report analyzed 1017 islet isolation procedures performed for 537 recipients of allogeneic clinical islet transplantation in 1999-2010. This study describes changes in donor and islet isolation variables by era and factors associated with quantity and quality of final islet products. Donor body weight and BMI increased significantly over the period (p<0.001). Islet yield measures have improved with time including islet equivalent (IEQ)/particle ratio and IEQs infused. The average dose of islets infused significantly increased in the era of 2007-2010 when compared to 1999-2002 (445.4±156.8 vs. 421.3±155.4×0(3) IEQ; p<0.05). Islet purity and total number of β cells significantly improved over the study period (p<0.01 and <0.05, respectively). Otherwise, the quality of clinical islets has remained consistently very high through this period, and d...
Transplantation Journal, 2010
Xenotransplantation
Paramagnetic microparticles (MPs) may be useful in pancreatic islet purification, in particular p... more Paramagnetic microparticles (MPs) may be useful in pancreatic islet purification, in particular purification of porcine islets as a potential xenotransplantation product. We assessed whether MPs affect islet function or induce an adverse effect following implantation. Porcine islets were co-cultured with 0, 500, and 1500 MPs per islet equivalent (IE) for 1 day and with 0 and 1500 MPs/IE for 7 days. Fractional viability was assessed using oxygen consumption rate normalized to DNA content (OCR/DNA) and after 7-day co-culture by perifusion glucose-stimulated insulin secretion (GSIS) and by transplantation under the renal capsule of diabetic nude mice. To assess an inflammatory response or immune reaction, MPs (∼10(7)) were implanted under the renal capsule of C57BL/6 mice. No statistically significant differences were measured in OCR/DNA (mean ± SE) following 1-day co-culture with 0, 500, or 1500 MPs/IE (243.3 ± 4.5, 211.3 ± 8.1, or 230.6 ± 11.3 nmol/min·mgDNA, respectively) or followi...
Transplantation Proceedings, 2010
Introduction. Despite significant advances, widespread applicability of islet cell transplantatio... more Introduction. Despite significant advances, widespread applicability of islet cell transplantation remains elusive. Refinement of current islet isolation protocols may improve transplant outcomes. Islet purification by magnetic separation has shown early promise. However, surgical protocols must be optimized to maximize the incorporation of paramagnetic microparticles (MP) within a greater number of islets. This study explores the impact of MP concentration and infusion method on optimizing MP incorporation within islets. Methods. Five porcine pancreata were procured from donors after cardiac death. Splenic lobes were isolated and infused with varying concentrations of MP (8, 16, and 32 ϫ 10 8 MP/L of cold preservation solution) and using one of two delivery techniques (hanging bag versus hand-syringe). After procurement and infusion, pancreata were stored at 0°C to 4°C during transportation (less than 1 hour), fixed in 10% buffered formalin, and examined by standard magnetic resonance imaging (MRI) and histopathology. Results. T2*-weighted MRI showed homogeneous distribution of MP in all experimental splenic lobes. In addition, histologic analysis confirmed that MP were primarily located within the microvasculature of islets (82% to 85%), with few MP present in acinar tissue (15% to 18%), with an average of five to seven MP per islet (within a 5-m thick section). The highest MP incorporation was achieved at a concentration of 16 ϫ 10 8 MP/L using the hand-syringe technique. Conclusion. This preliminary study suggests that optimization of a surgical protocol, MP concentrations, and applied infusion pressures may enable more uniform distribution of MP in the porcine pancreas and better control of MP incorporation within islets. These results may have implications in maximizing the efficacy of islet purification by magnetic separation.
Transplantation Proceedings, 2010
Islet transplantation is emerging as a promising treatment for patients with type 1 diabetes. It ... more Islet transplantation is emerging as a promising treatment for patients with type 1 diabetes. It is important to maximize viable islet yield for each organ due to scarcity of suitable human donor pancreata, high cost, and the large dose of islets required for insulin independence. However, organ transport for 8 hours using the two-layer method (TLM) frequently results in low islet yields. Since efficient oxygenation of the core of larger organs (eg, pig, human) in TLM has recently come under question, we investigated oxygen persufflation as an alternative way to supply the pancreas with oxygen during preservation. Porcine pancreata were procured from donors after cardiac death and preserved by either TLM or persufflation for 24 hours and subsequently fixed. Biopsies collected from several regions of the pancreas were sectioned, stained with hematoxylin and eosin, and evaluated by a histologist. Persufflated tissues exhibited distended capillaries and significantly less autolysis/cell death relative to regions not exposed to persufflation or to tissues preserved with TLM. The histology presented here suggests that after 24 hours of preservation, persufflation dramatically improves tissue health when compared with TLM. These results indicate the potential for persufflation to improve viable islet yields and extend the duration of preservation, allowing more donor organs to be utilized.
Transplantation Proceedings, 2010
Transplantation Journal, 2010
American Journal of Transplantation, 2008
We sought to determine the long-term outcomes in type 1 diabetic recipients of intraportal allois... more We sought to determine the long-term outcomes in type 1 diabetic recipients of intraportal alloislet transplants on a modified immunosuppressive protocol. Six recipients with hypoglycemia unawareness received one to two islet infusions. Induction therapy was with antithymocyte globulin (ATG) plus etanercept for tumor necrosis factor-a blockade. Recipients received cyclosporine and everolimus for maintenance immunosuppression for the first year posttransplant, with mycophenolic acid or mycophenolate mofetil subsequently substituted for everolimus. Recipients have been followed for 1173 ± 270 days since their last infusion for islet graft function (insulin independence, hemoglobin A 1c levels and C-peptide production) and for adverse events associated with the study protocol. Of the six recipients, five were insulin-independent at 1 year, and four continue to be insulin-independent at a mean of 3.4 ± 0.4 years posttransplant. None of the six recipients experienced recurrence of severe hypoglycemia. Measured glomerular filtration rate decreased from 110.5 ± 21.2 mL/min/1.73 m 2 pretransplant to 82.6 ±19.1 mL/min/1.73 m 2 at 1 year posttransplant. In conclusion, islet transplants restored insulin independence for a mean of >3 years in four of six recipients treated with ATG and etanercept induction therapy and with cyclosporine and, initially, everolimus for maintenance. Our results suggest this immunosuppressive protocol may allow long-term graft survival.