# Distinct Osteogenic Profiles of Tetracyclines from Different Generations in an Ex Vivo Embryonic Chick Femur Model

## TL;DR

This study compares how different generations of tetracyclines affect bone growth in an ex vivo chick model, finding that lower doses of newer tetracyclines promote better bone development.

## Contribution

First tissue-level comparison of four tetracyclines' osteogenic effects in a chick femur model.

## Key findings

- At 1 µg/mL, tetracyclines increased collagen deposition, matrix maturation, and mineralization.
- Osteogenic stimulation decreased at 10 µg/mL across all tetracycline groups.
- Doxycycline, minocycline, and sarecycline showed stronger osteogenic activity than tetracycline at lower doses.

## Abstract

Tetracyclines are broad-spectrum bacteriostatic agents with well-established antimicrobial efficacy and a shared core chemical structure, differentiated by distinct functional substitutions across generations. Beyond their antibacterial action, tetracyclines also exhibit pleiotropic biological effects, including modulation of bone metabolism. Nevertheless, the selection of agents and dosing for local bone applications remains largely empirical. Therefore, this study compares the tissue-level osteogenic potential of four tetracyclines from distinct generations using a translational ex vivo embryonic chick femur model. Organotypic femur cultures were maintained for 11 days and exposed to tetracycline (TC), doxycycline (DC), minocycline (MC), or sarecycline (SC), at 1 and 10 µg/mL, concentrations corresponding to clinically relevant local and systemic exposures. Osteogenic outcomes included microcomputed tomography, histological analyses, and quantitative gene expression. At 1 µg/mL, tetracyclines promoted osteogenic effects, increasing collagen deposition by approximately 30%, enhancing matrix maturation by 100%, stimulating tissue mineralization by 20–50%, and upregulating osteogenic marker expression, with TC exhibiting weaker activity. At 10 µg/mL, osteogenic stimulation was notably reduced across all groups. This study provides the first tissue-level, head-to-head comparison of four tetracyclines and their effects on bone biology. The findings indicate that tetracycline-induced osteogenic activity is both agent-specific and concentration-dependent, underscoring the importance of using lower doses to maximize osteogenic responses and supporting the preferential use of DC, MC, and SC in bone regeneration and adjunctive therapeutic applications.