Credit:Suppression of local inflammation via galectin-anchored indoleamine 2,3-dioxygenase.

IDO-Gal3 suppresses inflammation.a,b, Schematic representation of the IDO-Gal3 fusion protein (a) and the concept of anchoring IDO at different tissue locations through Gal3-mediated recognition of tissue glycans (b). c,d, Characterization of IDO-Gal3 enzymatic activity (c), plotted as initial rate (V0) vs substrate concentration, where initial and maximum rate (Vmax) are expressed in units, U (pmol(n-formyl kynurenine) min−1 pmol−1(IDO)), and binding to immobilized lactose (d). e, Schedule to evaluate anchored IDO suppression of inflammation resulting from local LPS injection. f,g, Histological evaluation (f) of IDO-Gal3 suppression of inflammation induced by injected LPS by enumeration of cell infiltration (g). Scale bar, 50 microns. h–k, Relative quantification (RQ) values of inflammatory gene (IL-6, IFN-γ, IL-12, IL-1β) expression in tissues treated with anchored IDO before challenge with LPS. l,m, Schedule (l) and psoriatic area severity index (m) to evaluate anchored IDO suppression of inflammation induced by topical imiquimod. The Gal3-containing protein, NanoLuc® luciferase fusion with Gal3 (NL-Gal3) and lacking the IDO domain, is included as a control. Data shown as mean ± s.e.m. in c, and mean ± s.d. in g and m. Statistical analysis: (g–k) one-way analysis of variance (ANOVA) with Tukey’s post-hoc. NS indicates no difference compared to vehicle, ns indicates no difference compared to LPS positive control, bar denotes P value relative to LPS positive control; n = 6. For g, P = 0.0054, F = 6.200. For h, P = 0.0040, F = 6.630. For i, P = 0.0006, F = 10.15. For j, P = 0.0898, F = 2.579. For m, Mann-Whitney U-test with alpha = 0.05, ****P < 0.0001, n = 12.

Chronic inflammation, resulting from interactions between immune cells and tissue cells, often leads to irreversible tissue damage and serves as a central pathological process in various diseases, including cardiovascular diseases, diabetes, cancer, and autoimmune disorders. Effective control of chronic inflammation is crucial for reducing the incidence and mortality associated with these conditions. However, systemic administration of anti-inflammatory drugs can cause a range of side effects, and the effects of locally injected anti-inflammatory agents are typically short-lived. This short duration is due to the rapid diffusion and metabolism of the drugs, necessitating frequent administration, which is not conducive to long-term management. Additionally, traditional local anti-inflammatory drugs lack targeting specificity and may impact the function of normal tissues. Consequently, current treatment methods have significant limitations.

Indoleamine 2,3-dioxygenase (IDO) is a key immunomodulatory enzyme that can inhibit T cell activation and proliferation by catalyzing the metabolism of tryptophan to kynurenine and promote the generation of regulatory T cells (Tregs), thereby exerting anti-inflammatory and immunosuppressive effects. In contrast, Galectin-3 (Gal3) is a glycoprotein that binds to glycans on cell surfaces. Through its glycan-binding ability, Gal3 can anchor bound molecules to tissues, preventing their diffusion.

Recently, Bracho-Sanchez et al. developed a novel anti-inflammatory therapeutic strategy by leveraging the anti-inflammatory properties of IDO and the glycan-binding characteristics of Gal3. This strategy involves fusing IDO with Gal3 to create the IDO-Gal3 fusion protein, which aims to achieve localized anti-inflammatory effects. The efficacy of IDO-Gal3 was validated through various inflammation models, including endotoxin-induced inflammation, psoriasis, periodontal disease, and osteoarthritis.

First, the research team analyzed the effects of IDO-Gal3 on local inflammation in different animal models. In the subcutaneous inflammation model induced by lipopolysaccharide (LPS) in mice, injection of IDO-Gal3 significantly suppressed the inflammatory response. Histological analysis showed a marked reduction in cellular infiltration in the IDO-Gal3 pre-treatment group. Compared to the control group, the expression of inflammatory cytokines such as IL-6, IFN-γ, and IL-12p35 was significantly decreased. In the psoriasis model, subcutaneous injection of IDO-Gal3 resulted in a substantial reduction in psoriasis severity scores, which remained low until the end of the experiment. In the periodontal disease model, submandibular injection of IDO-Gal3 significantly inhibited gingival inflammation and bone loss. Micro-CT analysis revealed that both prophylactic and therapeutic injections of IDO-Gal3 prevented further loss of alveolar bone and reduced the expression of inflammatory cytokines such as IL-6, IL-1β, and MCP1, while maintaining IL-10 levels. In the post-traumatic osteoarthritis model, intra-articular injection of IDO-Gal3 significantly reduced joint tissue damage and inflammation caused by mechanical loading. The expression levels of matrix metalloproteinase 13 (MMP13) and tumor necrosis factor-α (TNF-α) were notably lower in the IDO-Gal3 treated group.

Bioluminescence imaging revealed that injected IDO-Gal3 remained at the site of inflammation for more than a week, whereas unanchored IDO diffused rapidly. This indicates that IDO-Gal3 has stronger retention and functional activity at local inflammation sites. Additionally, the glycan-binding ability of Gal3 effectively prolonged the retention time of IDO-Gal3 in tissues, enhancing its local anti-inflammatory effects. Unlike traditional systemic anti-inflammatory drugs, IDO-Gal3 exerts its effects locally without causing systemic immune suppression, making it a safer option for anti-inflammatory therapy.

This study utilized genetic engineering techniques to fuse IDO with Gal3, creating the novel fusion protein IDO-Gal3. Through Gal3's anchoring mechanism, the study innovatively achieved efficient retention and functionality of the anti-inflammatory drug in local tissues, addressing the side effects associated with systemic administration of traditional anti-inflammatory drugs.

In summary, compared to traditional anti-inflammatory drugs, IDO-Gal3 demonstrates significant advantages in extending drug retention time, reducing systemic side effects, improving therapeutic efficacy, and having broad applicability. This research not only provides a new theoretical approach for treating chronic inflammation but also shows great potential in practical applications.

However, while the study demonstrated the significant effects of IDO-Gal3 in local anti-inflammatory therapy, there are still some limitations and challenges related to experimental design, long-term effects, safety, and clinical translation. The specific molecular processes underlying the potential mechanisms of IDO-Gal3's anti-inflammatory action at the local level have not been fully elucidated.

Future research needs to focus on further investigating the detailed mechanisms of action of IDO-Gal3 at both cellular and molecular levels. Additionally, it is crucial to validate these findings across different species, conduct long-term safety assessments, and develop personalized treatment strategies to ensure the broad applicability and successful clinical translation of IDO-Gal3.

Reference:

Bracho-Sanchez, Evelyn, et al. "Suppression of local inflammation via galectin-anchored indoleamine 2, 3-dioxygenase." Nature biomedical engineering 7.9 (2023): 1156-1169.