Recombinant Human FGF-18

Recombinant Human FGF-18 (rhFGF-18) is widely used in research due to its potent roles in tissue regeneration, especially for cartilage repair, skeletal development, and modulation of cell proliferation and differentiation. Its applications are supported by robust preclinical and in vitro evidence.

Key scientific reasons to use rhFGF-18 in research applications:

• Cartilage Regeneration and Repair:
  rhFGF-18 significantly enhances cartilage healing after injury or surgical procedures such as microfracture or osteochondral defect repair. Preclinical studies in large animal models show that rhFGF-18 improves both the quality and quantity of repair tissue, increases chondrocyte proliferation, boosts proteoglycan and collagen synthesis, and preserves cartilage phenotype, with no reported short-term adverse effects. This makes it a valuable tool for studying cartilage biology, osteoarthritis, and regenerative medicine.

• Maintenance of Cartilage Mechanical Properties:
  In long-term in vitro culture, rhFGF-18 (also known as sprifermin) helps preserve the depth-dependent mechanical properties of articular cartilage, maintaining tissue integrity and function over time.

• Skeletal Development:
  FGF-18 is essential for normal skeletal development, recruiting osteoclasts and osteoblasts to the growth plate and promoting bone remodeling processes.

• Cell Proliferation and Tissue Repair:
  FGF-18 acts as a pleiotropic growth factor, stimulating proliferation in various cell types, including fibroblasts, epithelial, and mesenchymal cells. It is involved in tissue repair and wound healing, making it relevant for studies in regenerative biology and disease models.

• Lung and Organ Development:
  FGF-18 promotes lung branching morphogenesis by increasing epithelial proliferation and maintaining progenitor cell populations, supporting its use in developmental biology and organoid research.

• Cancer Research:
  FGF-18 is implicated in tumor progression, angiogenesis, and modulation of the tumor microenvironment. It is studied as a potential therapeutic target and biomarker in various cancers, including ovarian and breast cancer.

• Molecular Mechanism Studies:
  Using recombinant protein allows for controlled, reproducible studies of FGF-18’s signaling pathways, receptor interactions, and downstream effects in diverse biological systems.

Summary of research applications:

• Cartilage and bone regeneration models
• Osteoarthritis and joint disease studies
• Tissue engineering and organoid systems
• Developmental biology (lung, skeletal, liver, intestine)
• Cancer biology and therapeutic target validation
• Mechanistic studies of growth factor signaling

Best practices:
Use rhFGF-18 at concentrations and delivery methods validated in the literature for your specific model system. Monitor for cell-type specific responses and consider its pleiotropic effects when interpreting results.

In conclusion, rhFGF-18 is a versatile and well-characterized growth factor for research in regenerative medicine, developmental biology, and disease modeling, with strong evidence supporting its efficacy and safety in preclinical settings.

Recombinant Human FGF-18 can be used as a standard for quantification or calibration in ELISA assays, provided it is validated for this purpose and matches the native protein in terms of immunoreactivity and structure.

Most commercial ELISA kits for Human FGF-18 use recombinant FGF-18 as their standard for generating calibration curves, which are essential for quantifying FGF-18 concentrations in biological samples. The standard curve is constructed by measuring the optical density (OD) of wells containing known concentrations of recombinant FGF-18 and comparing sample OD values to this curve.

Key considerations for using recombinant FGF-18 as an ELISA standard:

• Immunoreactivity: The recombinant FGF-18 must be recognized by the capture and detection antibodies used in your ELISA. Most sandwich ELISA kits are designed to detect both native and recombinant forms, but this should be confirmed in your assay documentation.
• Purity and Structure: The recombinant protein should be highly pure and correctly folded, as antibody binding often depends on the native conformation. Misfolded or degraded protein may not be detected efficiently.
• Validation: Ideally, the recombinant standard should be validated for equivalence to native FGF-18 in your specific assay system. This can be done by spike-and-recovery experiments or parallelism testing, ensuring that the standard curve accurately reflects sample quantification.
• Concentration Range: The standard should cover the expected concentration range of your samples. Commercial kits typically provide standards from ~7.8 pg/mL up to 1000 pg/mL.
• Matrix Effects: If you are preparing your own standards, dilute recombinant FGF-18 in a matrix similar to your samples (e.g., serum, plasma, or assay buffer) to minimize matrix effects and improve accuracy.

Protocol best practices:

• Prepare serial dilutions of recombinant FGF-18 to generate a standard curve for each assay run.
• Include quality controls and replicate standards to assess intra- and inter-assay precision.
• Confirm recovery and linearity by spiking recombinant FGF-18 into representative sample matrices.

Summary Table: Use of Recombinant FGF-18 as ELISA Standard

If your recombinant Human FGF-18 meets these criteria, it is suitable for use as a standard in ELISA quantification and calibration. Always refer to your specific assay protocol and validate the standard in your experimental context.

Recombinant human FGF-18 has been validated for several significant applications across both preclinical and clinical research contexts:

Cartilage Repair and Regeneration

The most extensively validated application is cartilage healing and regeneration. In preclinical large animal models, recombinant human FGF-18 (rhFGF-18) has demonstrated significant improvements in cartilage defect repair when used as an augmentation to microfracture or osteochondral defect repair procedures. The protein has been shown to improve cartilage quality and quantity at 6 months postoperatively, with positive outcomes measured by International Cartilage Repair Society (ICRS) scores, modified O'Driscoll scores, tissue infill, and collagen type II expression.

In vitro studies have confirmed that FGF-18 increases chondrocyte proliferation, enhances proteoglycan and collagen synthesis, preserves cartilage phenotype, and promotes cartilage thickness. The protein also preserves depth-dependent mechanical properties in articular cartilage, making it particularly valuable for maintaining functional tissue characteristics.

Osteoarthritis Treatment

Recombinant human FGF-18 has been validated for osteoarthritis applications through both preclinical and clinical studies. In animal models, intra-articular injection has reduced cartilage degeneration and induced new cartilage formation. Clinical trials, including the FORWARD (FGF-18 Osteoarthritis Randomized Trial with Administration of Repeated Doses) study, have demonstrated that repeated doses increase cartilage thickness and reduce cartilage loss over extended periods. The protein stimulates matrix-producing chondrocytes and increases the collagen type II to type I ratio while upregulating SOX9, a critical transcription factor in cartilage development.

Hepatic Protection

Recombinant FGF-18 has been validated for protecting liver tissue against ischemia-reperfusion injury (IRI). Exogenous FGF-18 administration reduces liver damage, decreases hepatocyte apoptosis, reduces reactive oxygen species levels, and minimizes necrosis and inflammation through the USP16/KEAP1/Nrf2 signaling pathway.

Functional Assays

The protein has been validated for use in functional bioactivity assays, where it induces cell proliferation in transfected cell lines with effective concentrations in the range of 4-24 ng/mL. It has also been validated for standard molecular biology applications including Western blotting, ELISA, and immunohistochemistry.

Lung Development

Recent research has validated FGF-18 for promoting human lung branching morphogenesis, demonstrating increased epithelial proliferation and maintenance of branching architecture in explant cultures.

No adverse events have been reported with intra-articular administration of recombinant human FGF-18 at the doses and timeframes evaluated in preclinical studies, supporting its safety profile for therapeutic applications.

To properly reconstitute and prepare Recombinant Human FGF-18 protein for cell culture experiments, follow these best practices based on manufacturer guidelines and scientific protocols:

1. Reconstitution

• Centrifuge the vial briefly before opening to ensure all lyophilized powder is at the bottom.
• Reconstitute the protein in sterile distilled water or sterile PBS (pH 7.4). Most manufacturers recommend a concentration between 0.1–1.0 mg/mL (commonly 0.1–0.5 mg/mL or 500 µg/mL).
• Gently mix after adding the solvent. Avoid vortexing or vigorous pipetting to prevent protein denaturation.

2. Sterility and Endotoxin

• Filter sterilize the reconstituted solution using a 0.22 µm filter before use in cell culture, especially if the protein is not guaranteed sterile.
• If using for sensitive cell types, consider testing for endotoxin levels or request low-endotoxin preparations.

3. Working Dilutions

• For cell culture, further dilute the reconstituted stock in culture medium or buffer containing a carrier protein (e.g., 0.1–1.0% BSA) to minimize non-specific binding and stabilize the protein.
• Typical working concentrations for bioactivity range from 4–24 ng/mL, depending on the cell type and experimental design.

4. Storage

• Aliquot the reconstituted protein and store at –80°C to avoid repeated freeze-thaw cycles.
• For short-term use, keep at 4°C for up to a week, but avoid prolonged storage at this temperature.

5. Additional Notes

• Some formulations may include stabilizers like trehalose or mannitol; these are compatible with cell culture.
• Always refer to the specific product datasheet for exact buffer composition and recommended concentrations.

Summary Protocol:

1. Centrifuge vial briefly.
2. Reconstitute in sterile water or PBS to 0.1–1.0 mg/mL.
3. Gently mix; do not vortex.
4. Filter sterilize (0.22 µm).
5. Dilute in culture medium with carrier protein (e.g., 0.1% BSA).
6. Aliquot and store at –80°C.

This approach ensures optimal protein stability, activity, and sterility for cell culture applications.