ROLE OF MELATONIN ON PULMONARY FIBROSIS AND LUNG ASSOCIATED IMMUNITY IN ALBINO RAT

Melatonin’s Role in Pulmonary Fibrosis and Lung Immunity | PDF

Introduction

This blog post summarizes the doctoral thesis “ROLE OF MELATONIN ON PULMONARY FIBROSIS AND LUNG ASSOCIATED IMMUNITY IN ALBINO RAT” submitted in 2020 by Manish Kumar Sonker under the supervision of Dr. Devbrat Mishra at Veer Bahadur Singh Purvanchal University, Jaunpur. The thesis investigates how **melatonin** influences experimentally induced pulmonary fibrosis and the lung-associated immune system (LAIS) using the bleomycin (BLM) model in albino rats. This summary highlights context, methods, core findings, and translational implications—written to be accessible to researchers, clinicians, and informed readers searching for reliable information on **melatonin pulmonary fibrosis**.

Background and problem statement

**Pulmonary fibrosis** is a progressive lung disorder characterized by scarring and stiffening of lung tissue that impairs gas exchange. Chemotherapeutic agent **bleomycin (BLM)** is widely used in research to induce experimental pulmonary fibrosis because it reproduces key pathological changes such as excess extracellular matrix and collagen deposition. The thesis addresses two related gaps: first, the interaction between fibrosis and the lung-associated immune system (LAIS); second, whether **melatonin**—a multifunctional neurohormone produced by the pineal gland—can modulate fibrotic progression and immune responses in the lung.

Objectives and research questions

• To evaluate **sex-dependent differences** in lung immune response during BLM-induced fibrosis.
• To map expression of melatonin receptors MT1 and MT2 in fibrotic lung tissue.
• To test whether exogenous **melatonin** regulates LAIS and macrophage-driven biomarkers of fibrosis.
• To examine melatonin’s effect on alveolar epithelial cells (Type I and II) and on signaling pathways (including Hippo/YAP1).
• To compare the anti-fibrotic effects of melatonin with approved antifibrotic drugs **nintedanib (Ofev)** and **pirfenidone (Esbriet)** and correlate tissue changes with blood biomarkers.

Methods — experimental design and assays

The study used four-month-old albino rats (≈120 ± 10 g) acclimatized to laboratory conditions. Pulmonary fibrosis was induced using **bleomycin (BLM)**. Key experimental elements included:

• Histology and morphometric analysis to quantify collagen deposition and architectural changes.
• Immunohistochemistry to detect **MT1/MT2** receptor expression and immune markers.
• Biochemical assays such as **hydroxyproline** measurement as a surrogate of collagen content.
• Functional and behavioral tests (e.g., sucrose preference, NSF) to assess systemic effects where relevant.
• In vitro culture of rat lung fibroblasts to probe estradiol and melatonin effects on fibroblast behavior.
• Comparative pharmacology: melatonin vs. **nintedanib** and **pirfenidone**, with correlation to blood biomarkers (e.g., cytokines, estradiol).

Key findings

1. Sex-based differences in BLM-induced fibrosis

One of the thesis’s strongest contributions is rigorous documentation of sex-dependent responses. Male and female rats showed differential morbidity/mortality and collagen expression after BLM. The author reports that sex hormones (e.g., estradiol) modulate fibrotic outcomes: ovariectomy and estradiol supplementation experiments altered both fibrosis severity and immune marker profiles—implicating endocrine-immune crosstalk in pulmonary fibrosis pathology.

2. Expression of melatonin receptors in fibrotic lung

Immunohistochemistry revealed altered expression of MT1 and **MT2** receptors in fibrotic lung tissue. The findings suggest that lung cells, including epithelial cells and immune cells, retain melatonin receptor expression during fibrosis—providing a mechanistic basis for melatonin’s modulatory effects.

3. Melatonin attenuates fibrosis and regulates LAIS

Treated animals receiving melatonin displayed reduced collagen accumulation (lower hydroxyproline), improved histological scores, and shifted immune marker profiles consistent with attenuation of pro-fibrotic signaling. **Melatonin** modulated macrophage-associated biomarkers and affected neutrophil (PMN) activity and chemotactic mediators (e.g., LTB4), indicating broad immunomodulatory activity within the lung microenvironment.

4. Cellular and molecular mechanisms — Hippo/YAP1 and epithelial responses

The thesis links melatonin activity to the **Hippo/YAP1 pathway**, showing that melatonin’s anti-fibrotic effect may in part be mediated by downregulating YAP1 activity. This action preserves alveolar epithelial cell phenotypes (Type I/II) and reduces fibroblast activation. The work also reports that YAP1 can counteract melatonin’s benefits—suggesting a complex balance between signaling pathways during fibrogenesis.

5. Comparative pharmacology: melatonin, nintedanib, pirfenidone

Melatonin’s protective effects were comparable in direction (if not magnitude) to those of established antifibrotic agents **nintedanib** and **pirfenidone** in tissue assays and blood biomarker correlations. The thesis suggests potential additive or synergistic benefits when melatonin is combined with these drugs—an idea worth exploring in translational studies.

Implications, strengths, and limitations

Implications: The study supports **melatonin** as a promising adjunctive therapy in pulmonary fibrosis, acting via receptor-mediated and signaling pathway mechanisms that influence both parenchymal and immune compartments of the lung. The sex-specific analyses highlight the need to consider hormonal status in preclinical and clinical designs.

Strengths: comprehensive multimodal approach (in vivo, ex vivo, in vitro), attention to sex differences, receptor mapping, and mechanistic signaling work (Hippo/YAP1).

Limitations: rodent BLM models do not capture all features of human idiopathic pulmonary fibrosis (IPF). Dose translation and long-term safety/efficacy of melatonin combined with antifibrotic drugs require clinical investigation.

Conclusion

This thesis provides a well-rounded, methodologically sound evaluation of **melatonin pulmonary fibrosis** interactions, demonstrating protective histological, biochemical, and immunological effects in BLM-induced pulmonary fibrosis in albino rats. It recommends follow-up translational research to evaluate dosing, combination therapy potential, and clinical endpoints—particularly keeping sex and hormonal status in mind.

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FAQ

Q1: What model was used to study pulmonary fibrosis?
A1: The thesis used the bleomycin (BLM)-induced pulmonary fibrosis model in albino rats (4 months old, ~120 ± 10 g).

Q2: How does melatonin reduce fibrosis?
A2: Melatonin reduced fibrosis by downregulating collagen deposition, modulating macrophage and neutrophil biomarkers, regulating MT1/MT2 receptor-mediated responses, and influencing the Hippo/YAP1 signaling pathway.

Q3: Were there sex differences in the response to bleomycin and melatonin?
A3: Yes. The thesis documents sex-dependent differences in morbidity, collagen expression, and cytokine profiles; estradiol altered fibrotic outcomes, highlighting hormonal influences.

Q4: Is melatonin as effective as approved antifibrotic drugs?
A4: Melatonin showed protective effects comparable in direction to nintedanib and pirfenidone in this preclinical model; however, direct clinical comparisons require human trials.

Q5: What are the next research steps suggested?
A5: Suggested steps include dose-optimization studies, combination therapy experiments with nintedanib/pirfenidone, long-term safety assessments, and translational clinical trials accounting for sex and hormonal status.

Thesis Title: ROLE OF MELATONIN ON PULMONARY FIBROSIS AND LUNG ASSOCIATED IMMUNITY IN ALBINO RAT
Researcher (Author): Manish Kumar Sonker
Guide (Supervisor): Dr. Devbrat Mishra
University: Veer Bahadur Singh Purvanchal University, Jaunpur
Year of Submission: 2020

Manish Kumar Sonker — Researcher (M.Sc. Zoology). Manish is a doctoral researcher who investigated neurohormonal regulation of lung pathology with a focus on melatonin’s immunomodulatory and anti-fibrotic potential. His work blends in vivo models, cellular assays, and translational pharmacology to explore novel adjunctive strategies for pulmonary fibrosis.