Growth Hormone-Fc Fusion Protein Sped Fracture Healing in Rats, Metabolomics Study Finds

A long-acting fusion of human growth hormone accelerated the healing of broken tibias in rats, and a detailed scan of the animals’ blood chemistry now offers clues about how the effect may arise. In a study published in Frontiers in Molecular Biosciences, researchers report that a growth hormone fused to a human antibody fragment known as Fc shortened the healing period of a rat tibial fracture model by more than a week compared with teriparatide, a bone-building drug used as the positive control. The work, led by Jianyang Gu, Ping Gong and Han Liu of Changchun University of Science and Technology together with colleagues at Changchun Institute of Biological Products Co., Ltd., combined imaging, histology, hormone measurements and untargeted serum metabolomics to trace the biological signature left behind by the treatment.

Growth hormone is not a new player in bone biology. It acts largely through insulin-like growth factor-1, or IGF-1, which is produced mainly by the liver and supports bone growth, and through IGF binding protein-3, or IGFBP-3, which carries roughly three quarters of the IGF-1 circulating in plasma. Previous research has linked both factors to fracture risk and to the healing process itself. The catch with ordinary growth hormone is practical rather than biological: the molecule has a short half-life in the body, which has driven efforts to extend its duration of action. PEGylated growth hormone achieves this but carries side effects, while an albumin-fused version prolongs exposure at the cost of reduced bioactivity. The team’s earlier work suggested that fusing growth hormone to naturally occurring human Fc protein could lower the risk of immune reactions and markedly extend how long the hormone stays active, while still powerfully stimulating IGF-1 and IGFBP-3.

To test whether that extended-action hormone could help broken bones, the researchers turned to a standard rodent injury model. They used 102 four-week-old male Sprague-Dawley rats weighing about 200 grams, housed under specific pathogen-free conditions. Surgeons exposed the midshaft of the tibia, transected it horizontally with a fine-toothed steel saw to create a standardized transverse fracture, and stabilized the broken ends by threading a Kirschner wire through the tibial marrow cavity. In the first phase, 72 rats were randomly divided into six groups of twelve: an uninjured-style control group, a fracture model group receiving only saline, a group treated daily with teriparatide injection, and three groups receiving subcutaneous injections of the FcGH fusion protein at low, medium and high doses of 0.45, 0.9 and 1.8 milligrams per milliliter respectively. Doses were calculated from the clinical growth hormone dose using a rat conversion coefficient of 0.63. The FcGH groups received weekly injections of 0.2 milliliters, while the teriparatide group received daily treatment at 2.1 micrograms per kilogram.

Healing was tracked at two, three and four weeks after dosing began, using micro-computed tomography and Safranin O-fast green histological staining. At two weeks, every treatment group showed obvious callus formation, and the drug-treated groups displayed more pronounced red cartilage tissue around the fracture gaps than the untreated model group, a sign that cartilage-driven repair was underway. The picture diverged sharply at three weeks: the high-dose FcGH group no longer showed a visible fracture line, and its cartilage tissue had disappeared, while the teriparatide group, though free of a fracture gap, still retained some cartilage, and the other groups still had clearly visible fracture lines. By four weeks, the teriparatide group and both the medium- and high-dose FcGH groups showed no obvious fracture line, thickened callus and dense, well-organized osteocytes. In the high-dose group the callus had even begun to shrink, indicating near-complete healing, whereas the model and low-dose groups still showed prominent fracture lines and noticeable cartilage. Taken together, the authors concluded that the effect was dose-dependent and that the high-dose group’s healing period was shortened by more than one week compared with teriparatide, and by roughly a week or more relative to healing times reported in preliminary experiments and the literature.

The hormone measurements supported the imaging story. Four weeks after dosing, blood levels of IGF-1 and IGFBP-3 differed significantly between the fracture model group and the uninjured control group, and the three FcGH dose groups each differed significantly from the model group. In the discussion, the authors note that these differences were dose-dependent, and that the model group showed no significant differences from the teriparatide group on these markers. Because IGF-1 and IGFBP-3 are considered important indicators for predicting fracture risk and play roles in the healing process, the team argues that the fusion protein may promote repair by lifting the levels of these two growth hormone effectors.

The more novel half of the study asked what the treatment does to metabolism. In a second experiment, 30 additional rats were randomized into model, control and high-dose FcGH groups of ten animals each, with the same fracture surgery and dosing regimen. All were sacrificed at week four, and their blood serum was analyzed on an AB Triple TOF 6600 mass spectrometer coupled to an Agilent 1290 Infinity liquid chromatography system, using both positive and negative electrospray ionization modes. Quality control samples showed strong analytical performance: chromatographic peaks overlapped closely, Pearson correlation coefficients among QC samples exceeded 0.9, and more than 70 percent of ion peaks had a relative standard deviation at or below 30 percent, indicating the instrument system was stable enough for downstream analysis.

Multivariate statistics separated the groups cleanly. Principal component analysis placed the control, model and FcGH groups in distinct regions of the metabolic space, and an orthogonal partial least squares discriminant model showed clear separation between the model and FcGH groups, with explanatory and predictive parameters both close to 1 and validation by 200 permutation tests. Applying thresholds of a fold change of 2 or greater or 0.5 or less, a variable importance in projection score above 1 and a p-value below 0.05, the researchers identified 17 differential metabolites. Every one of them achieved an area under the receiver operating characteristic curve greater than 0.8 with p-values below 0.05 in comparisons of the model group against both the control group and the FcGH group, which the authors interpret as evidence that all 17 are associated with fracture healing and that FcGH acts on healing by influencing them.

The metabolite list is chemically diverse. It includes the sugars D-glucose, alpha-D-glucose, D-fructose and D-galactose, along with D-mannose; the amino acid derivatives sarcosine, creatine and hydroxypyruvic acid; the lipid species PC(32:0), phosphatidylethanolamine PE(24:1/15:0), lysoPC(18:1/0:0) and glycerophosphocholine; the terpenoid precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate; the vitamin A storage form retinyl ester; and myo-inositol. Several sugars and the amino acid derivatives were elevated in the fracture model and reduced by FcGH treatment, while isopentenyl pyrophosphate, retinyl ester, lysoPC and glycerophosphocholine were depleted in the model and restored by the drug. Pathway enrichment analysis on the MetaboAnalyst 6.0 platform mapped these compounds onto eight pathways with impact values above 0.1: starch and sucrose metabolism, galactose metabolism, glycerophospholipid metabolism, terpenoid backbone biosynthesis, glyoxylate and dicarboxylate metabolism, retinol metabolism, glycine, serine and threonine metabolism, and inositol phosphate metabolism.

The authors connect each pathway to bone biology through prior literature. Galactose metabolism feeds the synthesis of keratan sulfate and the glycosylation of collagen, directly affecting bone development, and supplies energy for healing by enhancing the oxidation of glucose and fatty acids. Inositol phosphate is a precursor of inositol hexaphosphate, which influences the body’s absorption of bone minerals. Glyoxylate and dicarboxylate metabolism has been linked to bone density in clinical studies, while glycine and serine are described as important risk factors for fractures. Retinyl ester is the main storage form of vitamin A, whose levels affect bone quality, with both excess and deficiency raising fracture risk. Cholesterol made through the mevalonate pathway, a terpenoid product, participates directly in bone remodeling, and the membrane phospholipids phosphatidylcholine and phosphatidylethanolamine influence the formation of osteocytes. The team proposes that FcGH promotes healing, at least in part, by correcting the metabolic disturbances that fracture induces across these interconnected pathways.

The findings remain firmly preclinical, and the authors are explicit about the limits. The experiment was single-center, with a limited sample size, and metabolomics itself carries inherent constraints: databases cannot annotate every metabolite, many metabolic pathways remain incompletely characterized, and metabolic interactions can bias detection. The study also involved young male rats with a standardized transverse fracture, so translation to older patients with comminuted fractures is untested. Still, the convergence of imaging, histology, hormone data and metabolic profiling gives the result an unusually complete internal picture, and the authors frame the work as a foundation for larger, multicenter animal experiments and, eventually, clinical translational research on FcGH as a fracture treatment. If those steps succeed, a single weekly injection that outpaces a daily bone-building drug in healing speed would represent a meaningful shift in how fractures are managed, though the leap from rat tibia to human bone is long and, on this evidence, far from made.

Subject of Research: Effects of a long-acting human growth hormone-Fc fusion protein on tibial fracture healing in a rat model, examined with micro-CT, histology, hormone assays and serum metabolomics

Article Title: Elucidation of the mechanism of human growth hormone-Fc fusion protein in accelerating tibial fracture healing in rats via untargeted metabolomics

Article References: Gu, J., Liu, J., Peng, B., Zhou, B., Li, Z., Zhang, H., Zhang, T., Jiang, H., Sun, R., Gong, P., & Liu, H. (2026). Elucidation of the mechanism of human growth hormone-Fc fusion protein in accelerating tibial fracture healing in rats via untargeted metabolomics. Frontiers in Molecular Biosciences, 13, Article 1971992. https://doi.org/10.3389/fmolb.2026.1971992

Image Credits: AI Generated

DOI: 10.3389/fmolb.2026.1971992

Keywords: fracture healing, growth hormone, Fc fusion protein, IGF-1, IGFBP-3, metabolomics, rat model, tibia, teriparatide, bone remodeling, micro-CT, Frontiers in Molecular Biosciences