Thymalin

Thymulin Research

What is the research background of Thymulin?  

Research on Thymulin began with scientists' exploration of immunocompetent components in thymic extracts. In the 1970s, this small polypeptide composed of 43 amino acids was isolated from bovine thymus, and it was discovered to play an important role in immune cell differentiation, particularly in regulating T cell development, thus initiating in-depth research on Thymulin.  

With advancing research, the functions of Thymulin have been gradually expanded. It not only demonstrates prominence in immune regulation but also exhibits significant potential in tissue repair, anti-inflammation, and anti-fibrosis. These findings have prompted Thymulin research to span multiple disciplines, with scientists exploring its therapeutic roles in inflammatory diseases such as asthma and multiple sclerosis, as well as conditions like myocardial injury and COVID-19 complications, laying a theoretical foundation for its clinical applications.  

What is the mechanism of action of Thymulin?  

Anti-Inflammatory Mechanism  

Inhibition of Inflammatory Mediator Release: Thymulin can downregulate the release of inflammatory mediators such as cytokines and chemokines. During inflammatory responses, these mediators are abundantly released, triggering inflammatory symptoms. For example, in a rat model of inflammation induced by complete Freund's adjuvant (CFA), Thymulin treatment reduced the production of spinal pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), thereby alleviating the inflammatory response^[1].  

Upregulation of Anti-Inflammatory Factors: It can also upregulate anti-inflammatory factors such as interleukin-10 (IL-10). IL-10 is a critical anti-inflammatory cytokine that inhibits the activity of inflammatory cells and reduces inflammation. By upregulating IL-10, Thymulin helps maintain the body's inflammatory balance and prevents tissue damage from excessive inflammation^[2].  

Regulation of Transcription Factors and Mediators: Thymulin achieves molecular control of inflammation through regulating transcription factors and mediators. Transcription factors govern the expression of inflammation-related genes, and Thymulin can influence the activity of these factors, thereby reducing the synthesis of inflammation-related proteins and achieving anti-inflammatory effects^[2].  

Antihyperalgesic Mechanism  

Effects on Spinal Microglia: In inflammatory pain models, Thymulin inhibits the activation of spinal microglia. Microglia become activated by inflammatory stimuli, releasing multiple inflammatory mediators that exacerbate pain perception. Thymulin reduces the release of these mediators by decreasing microglial activation, thereby alleviating hyperalgesia. In a CFA-induced inflammatory rat model, Thymulin treatment significantly reduced thermal hyperalgesia and paw edema while decreasing CFA-induced microglial activation^[1] .

Role in the p38 MAPK Signaling Pathway: Thymulin decreases the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK). The p38 MAPK signaling pathway is crucial in inflammatory and pain signaling; its phosphorylation activates a series of downstream signaling molecules, leading to the production of inflammatory mediators and hyperalgesia. Thymulin alleviates inflammatory pain by inhibiting p38 MAPK phosphorylation and blocking this signaling pathway^[1].  

Immunomodulatory Mechanism  

T Lymphocyte Differentiation: Thymulin is a hormone essential for T lymphocyte differentiation, critical for the normal development and functional maintenance of T lymphocytes. It participates in regulating the ratio of T helper cells to suppressor cells, contributing to the balance and stability of the immune system. Abnormal Thymulin levels may lead to T lymphocyte dysfunction and immune-related diseases.  

Regulation of Immune Cell Function: In a mouse granuloma model induced by bacille Calmette-Guérin (BCG), a 5CH dilution of Thymulin regulated the differentiation of local and systemic phagocytes, promoted the differentiation of B1 peritoneal stem cells into phagocytes, and increased the number of CD4⁺ and CD8⁺ T lymphocytes in local lymph nodes, improving the granulomatous inflammation process. This indicates that Thymulin regulates the function of immune cells^[2] .  

Mechanism of Action on the Neuroendocrine System  

Bidirectional Regulation: The production and secretion of Thymulin are significantly influenced by the neuroendocrine system, and it can also act as a hypophysiotropic peptide on the neuroendocrine system. This bidirectional regulatory relationship indicates that Thymulin plays a key role in the interaction between the neuroendocrine and immune systems, helping maintain overall physiological balance in the body^[3].  

What are the applications of Thymulin?  

Anti-Inflammatory Effects  

Relief of Inflammatory Pain: In rat inflammation models (such as the CFA-induced inflammation model), intraperitoneal injection of Thymulin significantly alleviated CFA-induced thermal hyperalgesia and paw edema. Molecular mechanism studies showed that Thymulin reduced CFA-induced microglial activation, p38 MAPK phosphorylation, and spinal pro-inflammatory cytokine (e.g., TNF-α, IL-6) production, thereby mitigating inflammation and relieving pain symptoms ^[1].  

Improvement of Airway Inflammation: In an experimental mouse model of allergic asthma, Thymulin gene therapy mediated by DNA nanoparticles prevented pulmonary inflammation. A single dose of DNA nanoparticles carrying the Thymulin plasmid blocked inflammatory responses in the lungs of ovalbumin-challenged allergic asthma mice, including reducing inflammatory cell infiltration and improving lung mechanics^[4] (Da S A, 2014). Additionally, intratracheal treatment of fully established asthma with Thymulin-expressing plasmid delivered via nanoparticles normalized key pathological features of chronic inflammation in asthmatic lungs after 20 days, mediated by the therapy’s combined anti-inflammatory and anti-fibrotic effects^[4].  

Figure 1 Quantification of asthma-related mediators in the BALF. The levels of pro-inflammatory TH2 cytokines, including (A) IL-4 and (B) IL-13, (C) an anti-inflammatory cytokine, IL-10, and profibrotic cytokines, including (D) VEGF and (E) TGF-β, were quantified by ELISA (n = 6 mice per group).  

Source: PubMed ^[4]

Immunomodulatory Effects  

Regulation of Granulomatous Inflammation Processes: In a BCG-induced mouse granuloma model, homeopathic 5CH-diluted Thymulin regulated the differentiation of local and systemic phagocytes and T cell migration to local lymph nodes, thereby improving the granulomatous inflammation process. Specifically, after 21 days of infection, Thymulin-treated mice exhibited a higher peak in the differentiation of B1 peritoneal stem cells into phagocytes, reduced numbers of infected phagocytes in lesions (indicating alleviated infection), and increased numbers of B1-derived phagocytes, CD4⁺, and CD8⁺ T lymphocytes in local lymph nodes ^[4].

Relief of Experimental Autoimmune Encephalomyelitis Symptoms: In a mouse model of relapsing-remitting experimental autoimmune encephalomyelitis (rEAE), Thymulin bound to polybutylcyanoacrylate (PBCA) nanoparticles significantly alleviated rEAE symptoms, reduced plasma cytokine levels, and decreased NF-κB and SAPK/JNK cascade activation. Thymulin regulates NF-κB pathway activity through site-specific phosphorylation of RelA/p65 protein (at Ser276 and Ser536 sites), and nanoparticle-bound Thymulin was more effective than free Thymulin, holding promise as a prospective treatment for this disease^[5].  

Anti-Fibrotic Effects: In allergic asthma models, Thymulin not only reduced inflammation but also inhibited pulmonary fibrosis. For example, DNA nanoparticle-mediated Thymulin gene therapy prevented collagen deposition and smooth muscle hypertrophy in mouse lungs, and treating established asthma with Thymulin-expressing plasmid delivered via nanoparticles normalized pulmonary fibrosis, indicating that Thymulin inhibits tissue fibrosis and helps improve tissue structure and function^{[4, 6]}.

Potential Application in COVID-19 Treatment: During the COVID-19 pandemic, studies proposed that Thymulin might be a treatment for severe COVID-19 cases. Cytokine storm syndrome due to immune dysregulation is one of the most critical mechanisms leading to death in severe COVID-19 patients, and immune system regulation may reduce mortality. As a thymic peptide, Thymulin is promising for treating severe COVID-19 cases by controlling cytokine storms^[7].  

Conclusion 

Thymulin exhibits anti-inflammatory, immunomodulatory, and anti-fibrotic effects, capable of reducing inflammatory pain, improving airway inflammation and pulmonary fibrosis, alleviating rEAE symptoms, and regulating immune cell differentiation in granulomas. Applied via nanoparticle delivery and other methods, it has demonstrated efficacy in diseases such as allergic asthma and holds potential for treating COVID-19 cytokine storms.

Relevant Citations

[1]   Nasseri B, Zaringhalam J, Daniali S, et al. Thymulin treatment attenuates inflammatory pain by modulating spinal cellular and  molecular signaling pathways[J]. International Immunopharmacology, 2019,70:225-234.DOI:10.1016/j.intimp.2019.02.042.

[2]   Haddad J J E, E N E S, Garabedian B S. Thymulin: An Emerging Anti-Inflammatory Molecule[J]. Current Medicinal Chemistry - Anti-Inflammatory \& Anti-Allergy Agents, 2005,4:333-338. https://api.semanticscholar.org/CorpusID:55757311.

[3]   Bonamin L, Sato C, Santana F, et al. Differentiation and modulation of phagocyte activity in murine granuloma after treatment with thymulin 5cH[J]. International Journal of High Dilution Research - ISSN 1982-6206, 2021,11:148.DOI:10.51910/ijhdr.v11i40.580.

[4]   Da S A, Martini S V, Abreu S C, et al. DNA nanoparticle-mediated thymulin gene therapy prevents airway remodeling in  experimental allergic asthma[J]. Journal of Controlled Release, 2014,180:125-133.DOI:10.1016/j.jconrel.2014.02.010.

[5]   Lunin S M, Khrenov M O, Glushkova O V, et al. Protective Effect of PBCA Nanoparticles Loaded with Thymulin Against the  Relapsing-Remitting Form of Experimental Autoimmune Encephalomyelitis in Mice[J]. International Journal of Molecular Sciences, 2019,20(21).DOI:10.3390/ijms20215374.

[6]   Da S A, de Oliveira G P, Kim N, et al. Nanoparticle-based thymulin gene therapy therapeutically reverses key pathology  of experimental allergic asthma[J]. Science Advances, 2020,6(24):eaay7973.DOI:10.1126/sciadv.aay7973.

[7]   Vishal C, Ajay K, Tech K R M. Thymulin—a hope out of the box in the COVID-19 disaster, 2020[C]. https://api.semanticscholar.org/CorpusID:231646690