The influence of porcine pancreas digestion parameters and islet histomorphology on islet isolation outcome

Adult porcine islet isolation using a ductal preservation method and purification with a density gradient composed of histidine-tryptophan-ketoglutarate solution and iodixanol

BACKGROUND

Given the fragility of adult porcine islets, reduction of shearing stress in islet purification using histidine-tryptophan-ketoglutarate (HTK) solution and iodixanol could be an effective strategy. We examined the effect of ductal preservation with HTK solution and an islet purification protocol that utilizes HTK solution and iodixanol in adult porcine islet isolation.

METHODS

Islets were isolated with a modified Ricordi method using adult Prestige World Genetics (PWG) and Yucatan pigs. The discontinuous density gradient was composed of either HTK solution/iodixanol (n = 23, iodixanol group) or Hank's balanced salt solution (HBSS)/Ficoll (n = 17, Ficoll group). In the iodixanol group, ductal injection of HTK solution was performed before purification.

RESULTS

In PWG pigs, significantly higher islet yield after purification (3480 ± 214.2 islet equivalent [IEQ]/g, P = .003) and higher recovery rate (85.45% ± 3.49%, P = .0043) were obtained from the HTK/iodixanol group as compared to the HBSS/Ficoll group (1905 ± 323.2 IEQ/g, and 67.22% ± 4.77%, respectively). Similar results were obtained in Yucatan pigs with greater body weight.

CONCLUSION

Ductal preservation and iodixanol-based islet purification using HTK solution improved the yield of adult porcine islet isolation compared to the conventional method using HBSS and Ficoll. The results of this study support the feasibility of an adult porcine islet isolation protocol using HTK solution and iodixanol, which have the favorable physical properties.

In Vitro Maturation of Viable Islets from Partially Digested Young Pig Pancreas

Isolation of islets from market-sized pigs is costly, with considerable islet losses from fragmentation occurring during isolation and tissue culture. Fetal and neonatal pigs yield insulin unresponsive islet-like cell clusters that become glucose-responsive after extended periods of time. Both issues impact clinical applicability and commercial scale-up. We have focused our efforts on a cost-effective scalable method of isolating viable insulin-responsive islets. Young Yorkshire pigs (mean age 20 days, range 4–30 days) underwent rapid pancreatectomy (<5 min) and partial digestion using low-dose collagenase, followed by in vitro culture at 37°C and 5% CO2 for up to 14 days. Islet viability was assessed using FDA/PI or Newport Green, and function was assessed using a glucose-stimulated insulin release (GSIR) assay. Islet yield was performed using enumeration of dithizonestained aliquots. The young porcine (YP) islet yield at dissociation was 12.6 ± 2.1 × 103 IEQ (mean ± SEM) per organ and increased to 33.3 ± 6.4 × 103 IEQ after 7 days of in vitro culture. Viability was 97.3 ± 7% at dissociation and remained over 90% viable after 11 days in tissue culture ( n = ns). Glucose responsiveness increased throughout maturation in culture. The stimulation index (SI) of the islets increased from 1.7 ± 2 on culture day 3 to 2.58 ± 0.5 on culture day 7. These results suggest that this method is both efficient and scalable for isolating and maturing insulin-responsive porcine islets in culture.