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Literature Review | Could There Be New Hope for Osteoarthritis Treatment? Biodegradable HMBP Enzyme Shows Great Potential!

Introduction

October 12 is World Arthritis Day. There are 355 million people with arthritis worldwide. In Asia, one in six individuals will develop arthritis at some point in their lives—a condition that ranks as the leading cause of disability globally.

Osteoarthritis, one of the most common degenerative diseases, affects approximately 18% of women and 9.6% of men aged 60 and older worldwide.

This issue’s literature review presents treatment-related articles from the Sixth People’s Hospital of Shanghai Jiao Tong University on osteoarthritis research.

 

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Osteoarthritis causes knee pain and joint dysfunction, imposing a substantial medical and economic burden. It is characterized by pathological changes, including cartilage degeneration, synovial inflammation, and subchondral bone remodeling.

Recent studies have demonstrated that the severity of osteoarthritis is associated with synovial inflammation. An increasing body of research indicates that macrophages proliferate and infiltrate the synovium during the progression of OA, suggesting that these cells play a critical role in the pathogenesis of the disease.

Macrophages exhibit distinct subtypes at different stages of inflammation. They can be phenotypically polarized in various microenvironments and are broadly classified into two categories: M1 and M2, which are described below.

 

LPS induces M1 macrophages to secrete a variety of pro-inflammatory cytokines, including IL‑1, IL‑6, and TNF‑α, thereby promoting chondrocyte degeneration and amplifying inflammation. In contrast, M2 macrophages exert anti-inflammatory effects and facilitate tissue repair.

Therefore, inducing the phenotypic conversion of synovial macrophages from the M1 to the M2 subtype may represent another therapeutic strategy for osteoarthritis.

 

Construction and Identification of hmpb Enzyme

Previous research has found that, Nanoenzymes possess abundant low reduction potentials and variable oxidation states, endowing them with robust reactive oxygen species (ROS) scavenging capabilities. This suggests that the manganese–Prussian blue nanozyme may exhibit pH‑responsive degradation properties. Accordingly, leveraging the multivalent states of manganese and iron ions in the Fe–CN–Mn framework, along with their low reduction potentials and pH‑dependent decomposition characteristics, the researchers selected manganese chloride and potassium ferrocyanide as precursors to synthesize the BMPB enzyme. Bovine serum albumin (BSA) plays a crucial role in the synthesis of the hollow‑structured HMPB enzyme.

(Figure 1)

Scanning electron microscopy and transmission electron microscopy (TEM) results show that the prepared HMP@mpb enzyme consists of Prussian blue manganese nanoparticles with a size of approximately 145 nm. Hollow structure 。

(Figure 2)

 

 

ROS-scavenging properties and pH-responsive degradability of hmpb enzyme

We investigated the ROS-scavenging activity and pH‑responsive degradation of the prepared hmpb enzyme. Changes in hydroxyl radicals and superoxide anions were monitored using electron spin resonance (ESR) spectroscopy. HMPB enzyme exhibits concentration-dependent scavenging of hydroxyl radicals within a certain range; within a specific concentration range, the superoxide anion‑scavenging activity of HMPB enzyme also shows concentration dependence; at a pH of 6.5, HMPB enzyme is degraded. 。

(Figure 3)

 

In vitro ROS-scavenging capacity, hypoxia‑inhibitory effects, and therapeutic efficacy of hmpb enzyme

The ROS-scavenging capacity of the hmpb enzyme was assessed in vitro using bone marrow–derived macrophages (BMDMs). The researchers employed the DCFH-DA probe to measure intracellular oxidative stress in BMDMs following treatment with hmpb enzyme and/or LPS. The DCFH‑DA dye permeates the cell membrane and is cleaved into DCFH, which is then oxidized to DCF—a fluorescent compound suitable for imaging. Fluorescence intensity was analyzed by flow cytometry (Fig. 4a,b). It was found that… hmpb enzyme It possesses excellent ROS-scavenging ability. ， This is consistent with the intracellular results.

(Figure 4)

To evaluate the hypoxia‑induced inhibitory effect of hmpb enzyme, immunofluorescence staining was used to assess HIF‑1α expression levels (Fig. 4d; Fig. S3c, Supplementary Information), and the results showed In the hmpb enzyme group, the inhibition of HIF‑1α expression was more pronounced, suggesting that hmpb exerts a hypoxia‑induced inhibitory effect. . qRT-PCR results showed that, HMPB enzyme markedly suppresses in vitro inflammatory responses, promotes anabolic processes, and inhibits catabolic activity in chondrocytes treated with IL‑1β. 。

 

HMPB enzyme induces the phenotypic conversion of M1 to M2 and attenuates hypoxia both in vitro and in vivo.

Researchers investigated the phenotypic reprogramming of bone marrow–derived macrophages (BMDMs) following treatment with hmpb enzyme under hypoxic and inflammatory conditions. Western blot analysis revealed that hypoxia and inflammation significantly upregulated the expression of HIF‑1α and iNOS in pro‑inflammatory M1 macrophages (Figure 5a; Figure S4d, Supplementary Information). Concurrent with the increased expression of HIF‑1α, iNOS expression was similarly elevated, suggesting that HIF‑1α plays a critical role in activating the M1 inflammatory macrophage phenotype. The results indicate that… ， HMPB enzyme induces the polarization of BMDMs from the M1 subtype to the M2 subtype by scavenging ROS and generating O2 (Fig. 5b–e). 。

(Figure 5)

To confirm the in vivo activity of hmpb enzyme, the researchers employed an MIA model. Twenty-four hours after intra-articular injection of FITC‑labeled hmpb enzyme, immunofluorescence staining was used to localize the enzyme (Figure S5, Supplementary Information). Fluorescence microscopy of synovial tissue revealed that, owing to the robust phagocytic capacity of macrophages for foreign particles, HMPB enzyme exhibits significant intracellular accumulation in synovial macrophages. 。

In the OA model, the hypoxic inhibitory effect of hmpb enzyme was evaluated. Fluorescence intensity of HIF‑1α in synovial tissue indicated that hmpb enzyme significantly suppressed HIF‑1α expression in synovial tissue (Figure S6, Supplementary Information). Therefore, in the OA model, HMPB enzyme significantly downregulates HIF‑1α by alleviating hypoxia, thereby inducing the phenotypic conversion of synovial macrophages from the M1 to the M2 subtype. 。

 

hmpb enzyme In vivo therapeutic efficacy

To assess the in vivo retention time of hmpb enzyme, rats were imaged using an in vivo imaging system (IVIS) on days 1, 3, and 7 after drug administration. In the left knee joint, a MIA‑induced inflammation model was established, while the right knee received PBS as a normal control. IVIS images revealed that, Over time, hmpb enzyme is gradually degraded; however, by day 7, sufficient hmpb enzyme remains in the tissue. 。

To evaluate the in vivo ROS-scavenging efficacy of hmpb enzyme, rats were divided into three groups, with the right knee receiving an injection of PBS, DEX‑P, or hmpb enzyme s, respectively (Figure 6a). Prior to euthanasia, inflammation‑associated ROS were quantified using the ROS‑specific bioluminescent probe L‑012 via IVIS imaging (Figures 6f and 6g). The PBS group exhibited a pronounced bioluminescent signal, indicating the generation of reactive oxygen species under OA conditions, suggesting that… HMPB enzyme plays a crucial role in scavenging ROS in the OA model. 。

(Figure 6)

Cartilage structure was assessed using the international Osteoarthritis Research Society (OARSI) scoring system (Fig. 6i, j) and the Mankin score (Fig. 6l). The results indicated that cartilage treated with hmpb enzyme exhibited the best structural integrity, consistent with previous findings. These findings suggest that hmpb enzyme exerts a favorable therapeutic effect on osteoarthritis.

 

Discussion

HMPB enzyme exhibits excellent biodegradability, biocompatibility, and multi‑enzyme activity—features that other nanoenzymes lack. Intra‑articular injection of HMPB enzyme generates O₂ via its catalase activity, oxygenating the inflamed rat joint, thereby reducing HIF‑1α expression and attenuating inflammation by promoting macrophage polarization from the M1 to the M2 phenotype. This study demonstrates that the biodegradable HMPB enzyme holds promise as a ROS scavenger, an anti‑inflammatory agent, and a stimulator of the M2 macrophage phenotype for the treatment of osteoarthritis and other hypoxia‑related inflammatory diseases.

This study lays a solid foundation for the design, construction, and biomedical applications of biodegradable nanozymes, thereby advancing their utilization in the biomedical field.

 

Source: DOI: 10.1002/smll.202203240

 

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