Byoung Hyun Min

Hypoxia-inducible factor-2α is a catabolic regulator of osteoarthritic cartilage destruction

Osteoarthritic cartilage destruction is caused by an imbalance between anabolic and catabolic factors. Here, we show that hypoxia-inducible factor-2α (HIF-2α, encoded by EPAS1) is a catabolic transcription factor in the osteoarthritic process. HIF-2α directly induces the expression in chondrocytes of genes encoding catabolic factors, including matrix metalloproteinases (MMP1, MMP3, MMP9, MMP12 and MMP13), aggrecanase-1 (ADAMTS4), nitric oxide synthase-2 (NOS2) and prostaglandin-endoperoxide synthase-2 (PTGS2). HIF-2α expression was markedly increased in human and mouse osteoarthritic cartilage, and its ectopic expression triggered articular cartilage destruction in mice and rabbits. Moreover, mice transgenic for Epas1 only in chondrocytes showed spontaneous cartilage destruction, whereas heterozygous genetic deletion of Epas1 in mice suppressed cartilage destruction caused by destabilization of the medial meniscus (DMM) or collagenase injection, with concomitant modulation of catabolic factors. Our results collectively demonstrate that HIF-2α causes cartilage destruction by regulating crucial catabolic genes.

A biodegradable, injectable, gel system based on MPEG-b-(PCL-ran-PLLA) diblock copolymers with an adjustable therapeutic window.

In situ-forming gel systems have drawn increasing attention for their potential use in a variety of biomedical applications. Here, we examined an in situ-forming gel system comprised of MPEG-b-PCL and MPEG-b-(PCL-ran-PLLA) diblock copolymers with different PLLA contents (0-10 mol%) in the PCL segment. The crystalline region of the PCL-ran-PLLA segment decreased with increasing PLLA content. The MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions were liquid at room temperature and only MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions with a PLLA content < or = 5 mol% in the PCL segment showed a sol-to-gel transition as the temperature was increased. The viscosity change associated with sol-to-gel phase transition depended on the PLLA content in the PCL segment. A MPEG-b-PCL diblock copolymer solution incubated in vitro showed increasing viscosity without degradation, whereas the viscosity of MPEG-b-(PCL-ran-PLLA) diblock copolymer solutions continuously and sharply decreased with increasing PLLA content in the PCL segment. As the amount of PLLA increased, the size of in vivo-formed MPEG-b-(PCL-ran-PLLA) gels after initial injection tended to gradually decrease because of hydrolytic degradation of the PLLA in the PCL-ran-PLLA segment. An immunohistochemical examination showed that in vivo MPEG-b-(PCL-ran-PLLA) diblock copolymer gels provoked only a modest inflammatory response. Collectively, our results show that the MPEG-b-(PCL-ran-PLLA) diblock copolymer gel described here could serve as a minimally invasive, therapeutic, in situ-forming gel system that offers an experimental window adjustable from a few weeks to a few months.

In vivo efficacy of paclitaxel-loaded injectable in situ-forming gel against subcutaneous tumor growth.

Injectable in situ-forming gels have received considerable attention as localized drug delivery systems. Here, we examined a poly(ethylene glycol)-b-polycaprolactone (MPEG-PCL) diblock copolymer gel as an injectable drug depot for paclitaxel (Ptx). The copolymer solution remained liquid at room temperature and rapidly gelled in vivo at body temperature. In vitro experiments showed that Ptx was released from MPEG-PCL copolymer gels over the course of more than 14 days. Experiments employing intratumoral injection of saline (control), gel-only, Taxol, or Ptx-loaded gel into mice bearing B16F10 tumor xenografts showed that Ptx-loaded gel inhibited the growth of B16F10 tumors more effectively than did saline or gel alone. Further, intratumoral injection of Ptx-loaded gel was more efficacious in inhibiting the growth of B16F10 tumor over 10 days than was injection of Taxol. A histological analysis demonstrated an increase in necrotic tissue in tumors treated with Ptx-loaded gel. In conclusion, our data show that intratumoral injection of Ptx-loaded MPEG-PCL diblock copolymer yielded an in situ-forming gel that exhibited controlled Ptx release profile, and that was effective in treating localized solid tumors.

Polymeric Scaffolds for Regenerative Medicine

Regenerative medicine, one of the most exciting and dynamic life science fields, is an emerging biomedical technology for assisting and accelerating the regeneration and repair of lost or damaged organs or body parts. Modern regenerative medicine is increasingly using three-dimensional structured scaffolds because they represent a wide range of morphological and geometric in vivo possibilities that can be tailored for each specific regenerative medicine application. This review focuses on polymeric scaffolds, a highly promising regenerative medicine strategy, summarizing some important issues related to various natural and synthetic scaffolding biomaterials, techniques on the design and fabrication of three-dimensional polymeric scaffolds to mimic the properties of the extracellular matrix, and clinical applications of polymeric scaffolds for tissue regeneration.

Tissue engineered regeneration of completely transected spinal cord using human mesenchymal stem cells

The present study employed a combinatorial strategy using poly(D,L-lactide-co-glycolide) (PLGA) scaffolds seeded with human mesenchymal stem cells (hMSCs) to promote cell survival, differentiation, and neurological function in a completely transected spinal cord injury (SCI) model. The SCI model was prepared by complete removal of a 2-mm length of spinal cord in the eighth-to-ninth spinal vertebra, a procedure that resulted in bilateral hindlimb paralysis. PLGA scaffolds 2 mm in length without hMSCs (control) or with different numbers of hMSCs (1 × 10(5), 2 × 10(4), and 4 × 10(3)) were fitted into the completely transected spinal cord. Rats implanted with hMSCs received Basso-Beattie-Bresnahan scores for hindlimb locomotion of about 5, compared with ~2 for animals in the control group. The amplitude of motor-evoked potentials (MEPs) averaged 200-300 μV in all hMSC-implanted SCR model rats. In contrast, the amplitude of MEPs in control group animals averaged 135 μV at 4 weeks and then declined to 100 μV at 8 weeks. These results demonstrate functional recovery in a completely transected SCI model under conditions that exclude self-recovery. hMSCs were detected at the implanted site 4 and 8 weeks after transplantation, indicating in vivo survival of implanted hMSCs. Immunohistochemical staining revealed differentiation of implanted hMSCs into nerve cells, and immunostained images showed clear evidence for axonal regeneration only in hMSC-seeded PLGA scaffolds. Collectively, our results indicate that hMSC-seeded PLGA scaffolds induced nerve regeneration in a completely transected SCI model, a finding that should have significant implications for the feasibility of therapeutic and clinical hMSC-delivery using three-dimensional scaffolds, especially in the context of complete spinal cord transection.

An injectable biodegradable temperature-responsive gel with an adjustable persistence window

ɛ-Caprolactone (CL) and 3-benzyloxymethyl-6-methyl-1,4-dioxane-2,5-dion (fLA), with a benzyloxymethyl group at the 3-position of the lactide, were randomly copolymerized. The methoxy polyethylene glycol (MPEG)-b-[poly(ɛ-caprolactone)-ran-poly(3-benzyloxymethyl lactide) (PCL-ran-PfLA)] diblock copolymers were designed such that the PfLA content (0-15 mol%) in the PCL segment was varied. The MPEG-b-(PCL-ran-PfLA) diblock copolymers were derivatized by introducing a pendant benzyl group (MC(x)L(y)-OBn), hydroxyl group (MC(x)L(y)-OH), or carboxylic acid group (MC(x)L(y)-COOH) at the PfLA segment. The derivatized MPEG-b-(PCL-ran-PfLA) diblock copolymer solutions exhibited sol-to-gel phase transitions upon a temperature increase. The sol-to-gel phase transition depended on both the type of functional pendant group on the PfLA and the PfLA content in the PCL segment. MC(x)L(y)-COOH diblock copolymer solutions formed gels immediately after injection into Fischer rats. The gels gradually degraded over a period of 0-6 weeks after the initial injection, and the rate of degradation increased for higher concentrations of PfLA. Immunohistochemical characterization showed that the in vivo MPEG-b-(PCL-ran-PfLA) diblock copolymer gels provoked only a modest inflammatory response. These results show that the MPEG-b-(PCL-ran-PfLA) diblock copolymer gel described here may serve as a minimally invasive therapeutic, in situ-forming gel system with an adjustable temperature-responsive and in vivo biodegradable window.

Effects of low-intensity ultrasound (LIUS) stimulation on human cartilage explants

Objective: To evaluate the effects of low‐intensity ultrasound (LIUS) stimulation on the anabolic state of human cartilage from patients with osteoarthritis (OA). Methods: Explant cultures of human OA cartilage were stimulated for 10 min every day for 7 consecutive days using continuous‐wave sonication at a frequency of 1 MHz with spatial and temporal average intensities of 0 (control), 40, 200, 500, or 700 mW/cm2. The effects of LIUS on cell proliferation were evaluated by 3H‐thymidine incorporation. Proteoglycan synthesis was evaluated by the incorporation of 35S‐sulfate and by Safaranin O staining. Collagen synthesis was evaluated by 3H‐proline incorporation and immunohistochemistry. Results: At an intensity of 200 mW/cm2, LIUS treatment induced the expression of collagen type II and proteoglycan measured by the incorporation of radioactivity and specific staining of the cartilage explants. However, the expression decreased again at the higher intensities of 500 or 700 mW/cm2. Ultrasound had no stimulatory effect on cell proliferation at any intensity. Conclusion: LIUS has anabolic effects on human cartilage in explant cultures, indicating a potentially important method for the repair of osteoarthritic cartilage.

Injectable intratumoral hydrogel as 5-fluorouracil drug depot

The effectiveness of systemically administered anticancer treatments is limited by difficulties in achieving therapeutic doses within tumors, a problem that is complicated by dose-limiting side effects to normal tissue. To increase the efficacy and reduce the toxicity of systemically administered anticancer 5-fluorouracil (5-Fu) treatments in patients, intratumoral administration of an injectable hydrogel has been evaluated in the current work. The MPEG-b-(PCL-ran-PLLA) diblock copolymer (MCL) containing 5-Fu existed in an emulsion-sol state at room temperature and rapidly gelled in vivo at the body temperature. MCL acted as in vivo biodegradable drug depot over a defined experimental period. A single injection of 5-Fu-loaded MCL solution resulted in significant suppression of tumor growth, compared with repeated injection of free 5-Fu as well as saline and MCL alone. For both repeated injections of free 5-Fu and single injection of 5-Fu-loaded MCL, most of the 5-Fu was found in the tumor, indicating the maintenance of therapeutic concentrations of 5-Fu within the target tumor tissue and the prevention of systemic toxicity associated with 5-Fu in healthy normal tissues. In conclusion, this work demonstrated that intratumoral injection of 5-Fu-loaded MCL may induce significant suppression of tumor growth through effective accumulation of 5-Fu in the tumor.

Annulus fibrosus tissue engineering using lamellar silk scaffolds

Degeneration of the intervertebral disc (IVD) represents a significant muscular skeletal disease. Recently, scaffolds composed of synthetic, natural and hybrid biomaterials have been investigated as options to restore the IVD; however, they lack the hallmark lamellar morphological features of annulus fibrosus (AF) tissue. The goal of regenerating the disc is to achieve anatomical morphology as well as restoration of mechanical and biological function. In this study, two types of scaffold morphology formed from silk fibroin were investigated towards the goal of AF tissue restoration. The first design mimics the lamellar features of the IVD that are associated with the AF region. The second is a porous spongy scaffold that serves as a control. Toroidal scaffolds were formed from the lamellar and porous silk material systems to generate structures with an outer diameter of 8 mm, inner diameter of 3.5 mm and a height of 3 mm. The inter‐lamellar spacing in the lamellar scaffold was 150–250 µm and the average pore sizes in the porous scaffolds were 100–250 µm. The scaffolds were seeded with porcine AF cells and, after growth over defined time frames in vitro, histology, biochemical assays, mechanical testing and gene expression indicated that the lamellar scaffold generated results that were more favourable in terms of ECM expression and tissue function than the porous scaffold for AF tissue. Further, the seeded porcine AF cells supported the native shape of AF tissue in the lamellar silk scaffolds. The lamellar silk scaffolds were effective in the formation of AF‐like tissue in vitro. Copyright

Stimuli-Responsive Injectable In situ-Forming Hydrogels for Regenerative Medicines

Research on injectable in situ-forming hydrogels has been conducted in diverse biomedical applications for a long period. These hydrogels exhibit sol-to-gel phase transition in accordance with the external stimuli such as temperature change. Also, unlike the traditional surgical procedures the hydrogels have the distinct properties of easy management and minimal invasiveness via simple aqueous state injections at target sites. Currently, numerous polymer materials have been reported as potential stimulus-induced in situ–forming hydrogels. In this review, a comprehensive overview of the state-of-the-art of these rapidly developing materials has been outlined. In situ–forming hydrogels formed by electrostatic and hydrophobic interactions as well as their mechanistic characteristics and biomedical applications in regenerative medicine have also been discussed. The review concludes with perspectives on the future of stimulus-induced in situ–forming hydrogels.