AG-041R, a cholecystokinin-B/gastrin receptor antagonist, stimulates the repair of osteochondral defect in rabbit model

Articular cartilage regeneration and tissue engineering models: a systematic review

INTRODUCTION

Cartilage regeneration and restoration is a major topic in orthopedic research as cartilaginous degeneration and damage is associated with osteoarthritis and joint destruction. This systematic review aims to summarize current research strategies in cartilage regeneration research.

MATERIALS AND METHODS

A Pubmed search for models investigating single-site cartilage defects as well as chondrogenesis was conducted and articles were evaluated for content by title and abstract. Finally, only manuscripts were included, which report new models or approaches of cartilage regeneration.

RESULTS

The search resulted in 2217 studies, 200 of which were eligible for inclusion in this review. The identified manuscripts consisted of a large spectrum of research approaches spanning from cell culture to tissue engineering and transplantation as well as sophisticated computational modeling.

CONCLUSIONS

In the past three decades, knowledge about articular cartilage and its defects has multiplied in clinical and experimental settings and the respective body of research literature has grown significantly. However, current strategies for articular cartilage repair have not yet succeeded to replicate the structure and function of innate articular cartilage, which makes it even more important to understand the current strategies and their impact. Therefore, the purpose of this review was to globally summarize experimental strategies investigating cartilage regeneration in vitro as well as in vivo. This will allow for better referencing when designing new models or strategies and potentially improve research translation from bench to bedside.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

AG-041R, a novel indoline-2-one derivative, stimulates chondrogenesis in a bipotent chondroprogenitor cell line CL-1

OBJECTIVE

To examine the chondrogenic activity of AG-041R and its mode of action in a bipotent chondroprogenitor cell line CL-1.

DESIGN

Chondrogenic activity of AG-041R in CL-1 was examined by histology, alcian blue pH 1.0 intensity and mRNA expression of cartilage matrix proteins (collagen type II, aggrecan). Chondrogenic activities of other CCK2/gastrin receptor antagonists were also examined. Since TGF-beta1 induces dominant chondrogenesis and suppressed adipogenesis in CL-1, induction of TGF-beta by AG-041R was examined by enzyme linked immunosorbent assay. Involvement of MAP kinases in the chondrogenic effect of AG-041R in CL-1 was examined by Western blotting and MAP kinase inhibitors.

RESULTS

AG-041R induced dominant chondrogenesis and marked suppression of adipogenesis in CL-1. Neither of the other CCK2/gastrin receptor antagonists tested showed chondrogenic activity in CL-1. AG-041R increased alcian blue pH 1.0 intensity and mRNA expression of collagen type II and aggrecan. TGF-beta1 and -beta2 proteins were increased by AG-041R. The chondrogenic activity of AG-041R in CL-1 was blocked by TGF-beta neutralizing antibody or inhibitors for activation of latent TGF-beta. AG-041R activated both Erk (p44/42) and p38 MAP kinases in CL-1. Inhibition of Erk (p44/42) by PD98059 canceled the adipogenesis suppression by AG-041R in CL-1. Inhibition of p38 by SB202190 completely canceled the chondrogenic activity of AG-041R in CL-1.

CONCLUSION

AG-041R has chondrogenic activity in CL-1 not related to CCK2/gastrin receptor antagonism. It is suggested that TGF-beta induction and the activation of MAP kinases mediate the chondrogenic activity of AG-041R in CL-1.

Cholecystokinin antagonists: pharmacological and therapeutic potential

Cholecystokinin (CCK) is a regulatory peptide hormone, predominantly found in the gastrointestinal tract, and a neurotransmitter present throughout the nervous system. In the gastrointestinal system CCK regulates motility, pancreatic enzyme secretion, gastric emptying, and gastric acid secretion. In the nervous system CCK is involved in anxiogenesis, satiety, nociception, and memory and learning processes. Moreover, CCK interacts with other neurotransmitters in some areas of the CNS. The biological effects of CCK are mediated by two specific G protein coupled receptor subtypes, termed CCK(1) and CCK(2). Over the past fifteen years the search of CCK receptor ligands has evolved from the initial CCK structure derived peptides towards peptidomimetic or non-peptide agonists and antagonists with improved pharmacokinetic profile. This research has provided a broad assortment of potent and selective CCK(1) and CCK(2) antagonists of diverse chemical structure. These antagonists have been discovered through optimization programs of lead compounds which were designed based on the structures of the C-terminal tetrapeptide, CCK-4, or the non-peptide natural compound, asperlicin, or derived from random screening programs. This review covers the main pharmacological and therapeutic aspects of these CCK(1) and CCK(2) antagonist. CCK(1) antagonists might have therapeutic potential for the treatment of pancreatic disorders and as prokinetics for the treatment of gastroesophageal reflux disease, bowel disorders, and gastroparesis. On the other hand, CCK(2) antagonists might have application for the treatment of gastric acid secretion and anxiety disorders.

AG-041R stimulates cartilage matrix synthesis without promoting terminal differentiation in rat articular chondrocytes

OBJECTIVE

AG-041R, a novel indolin-2-one derivative, has recently been demonstrated to induce systemic hyaline cartilage hyperplasia in rats. The aim of this study was to characterize its anabolic actions on chondrocytes.

DESIGN

Chondrocytes were isolated from knee joints of 5-week-old SD rats. Effects of AG-041R on cartilage matrix synthesis were examined by measuring [(35)S]sulfate incorporation into proteoglycans, Alcian blue staining, and Northern blotting of cartilage matrix genes. ALP activity, mineral deposition and the expression of markers for hypertrophic chondrocytes, were assessed for terminal differentiation of chondrocytes. Roles of endogenous TGF-beta/BMPs and MEK1/Erk signaling in the action of AG-041R were investigated using the neutralizing soluble receptors and the MEK1 inhibitor.

RESULTS

AG-041R accelerated proteoglycan synthesis assessed by both [(35)S]sulfate incorporation and Alcian blue stainable extracellular matrix accumulation. It also up-regulated the gene expression of type II collagen and aggrecan, as well as tenascin, a marker for articular cartilage. In contrast, AG-041R suppressed ALP activity, mineralization, and the gene expression of type X collagen and Cbfa1, indicating that AG-041R prevents chondrocyte terminal differentiation. AG-041R increased in BMP-2 mRNA, and the neutralizing soluble receptor for BMPs reversed the stimulatory effects of AG-041R on cartilage matrix synthesis. Moreover, AG-041R activated MEK1/Erk pathway, which was revealed to prevent chondrocyte terminal differentiation.

CONCLUSION

AG-041R stimulates cartilage matrix synthesis without promoting terminal differentiation in rat articular chondrocytes, which is mediated at least in part by endogenous BMPs and Erk. The data demonstrates that AG-041R has a potential to be a useful therapeutic agent for articular cartilage disorders.