Osteochondral defect repair using bilayered hydrogels encapsulating both chondrogenically and osteogenically pre-differentiated mesenchymal stem cells in a rabbit model.

OBJECTIVE: To investigate the ability of cell-laden bilayered hydrogels encapsulating chondrogenically and osteogenically (OS) pre-differentiated mesenchymal stem cells (MSCs) to effect osteochondral defect repair in a rabbit model. By varying the period of chondrogenic pre-differentiation from 7 (CG7) to 14 days (CG14), the effect of chondrogenic differentiation stage on osteochondral tissue repair was also investigated. METHODS: Rabbit MSCs were subjected to either chondrogenic or osteogenic pre-differentiation, encapsulated within respective chondral/subchondral layers of a bilayered hydrogel construct, and then implanted into femoral condyle osteochondral defects. Rabbits were randomized into one of four groups (MSC/MSC, MSC/OS, CG7/OS, and CG14/OS; chondral/subchondral) and received two similar constructs bilaterally. Defects were evaluated after 12 weeks. RESULTS: All groups exhibited similar overall neo-tissue filling. The delivery of OS cells when compared to undifferentiated MSCs in the subchondral construct layer resulted in improvements in neo-cartilage thickness and regularity. However, the addition of CG cells in the chondral layer, with OS cells in the subchondral layer, did not augment tissue repair as influenced by the latter when compared to the control. Instead, CG7/OS implants resulted in more irregular neo-tissue surfaces when compared to MSC/OS implants. Notably, the delivery of CG7 cells, when compared to CG14 cells, with OS cells stimulated morphologically superior cartilage repair. However, neither osteogenic nor chondrogenic pre-differentiation affected detectable changes in subchondral tissue repair. CONCLUSIONS: Cartilage regeneration in osteochondral defects can be enhanced by MSCs that are chondrogenically and osteogenically pre-differentiated prior to implantation. Longer chondrogenic pre-differentiation periods, however, lead to diminished cartilage repair.

Reversal of in vitro hepatic insulin resistance in chronic pancreatitis by pancreatic polypeptide in the rat.

In vitro isolated liver perfusion in a rat model of chronic pancreatitis (CP) has been shown to demonstrate hepatic resistance to insulin. The ability of pancreatic polypeptide (PP) to reverse the resistance to insulin on glucagon-stimulated hepatic glucose production was therefore investigated in this model. CP was induced in 250 to 300 gm Sprague-Dawley rats by infusion of 50 microliters of 99% oleic acid into the pancreas via the common bile duct. After 6 to 8 weeks, isolated liver perfusion was performed on livers from both CP rats and sham-operated control animals (n = 12, 14), both with and without PP administration. Glucagon infusion (100 pg/ml for 30 minutes) produced a five- to sixfold increase in hepatic glucose production. The integrated hepatic glucose output (IHGO) response to glucagon alone was comparable in pancreatic and sham-operated animals; during period 1 (0 to 10 minutes) IHGO was 7.1 +/- 0.5 mg/gm-min for sham-operated controls (n = 8) and 7.1 +/- 0.4 mg/gm-min for pancreatitic animals (n = 6) without PP treatment. Animals that received PP (100 ng intraperitoneally 5 hours before liver harvest and perfusion with 4.2 ng/ml from 10 to 30 minutes) demonstrated an IHGO for period 1 for the sham (n = 6) and pancreatitic animals (n = 6) of 5.6 +/- 0.6 and 4.8 +/- 0.8 mg/gm-min, respectively. Insulin infusion (100 microU/ml added to perfusate from 10 to 30 minutes) in CP livers without PP revealed impaired responsiveness to insulin; the ratio of period 3 (20 to 30 minutes)/period 1 IHGO was 110% +/- 5% in CP livers compared with 77% +/- 5% in sham controls (p less than 0.01). In contrast, PP treatment restored hepatic responsiveness to insulin to control levels; the period 3/period 1 IHGO was 75% +/- 13% in CP livers treated with PP, which was indistinguishable from the 67% +/- 9% response seen in sham-operated control animals. These data provide the first in vitro evidence of a primary hepatic glucoregulatory role of PP. Therefore PP deficiency may contribute to altered glucose metabolism through the induction of a reversible hepatic resistance to insulin.