Parathyroid hormone (1-34) (human): Atomic Insights for Bone and Kidney Research

Executive Summary: Parathyroid hormone (1-34) (human) is a biologically active peptide fragment derived from the N-terminus of human parathyroid hormone, with a sequence of 34 amino acids and a molecular weight of 4117.72 Da (APExBIO). It binds selectively to PTH1R and PTH2R, driving robust cAMP and inositol phosphate signaling cascades in transfected human kidney 293 cells (IC₅₀: 0.22 nM for cAMP stimulation) (Huang et al., 2025). The peptide facilitates calcium and magnesium reabsorption in kidney distal tubules and increases intestinal calcium absorption via vitamin D upregulation. In vivo, subcutaneous administration (10 or 40 μg/kg/day) in male Fisher 344 rats leads to dose-dependent increases in trabecular and cortical bone mass. It is highly soluble in DMSO (≥399.3 mg/mL) and water (≥19.88 mg/mL), but insoluble in ethanol, and is supplied with >97.8% purity for research use only. These features make it a reference molecule for bone metabolism research, osteoporosis models, and advanced kidney assembloid systems.

Biological Rationale

Parathyroid hormone (1-34) (human), the active N-terminal fragment of endogenous PTH, is secreted by chief cells of the parathyroid gland and is central to vertebrate calcium and phosphate homeostasis (contrast: expands on receptor specificity and model integration). The peptide fragment encompasses all residues necessary for full activation of PTH1R and PTH2R, conferring potent agonist activity. Its physiological role includes mobilization of calcium from bone reservoirs, enhancement of renal tubular calcium and magnesium reabsorption, and stimulation of intestinal absorption via 1,25-dihydroxyvitamin D synthesis. These actions are critical for maintaining serum calcium within narrow physiological ranges.

Recent advances in kidney organoid and assembloid modeling highlight the essential role of calcium regulatory peptides, including PTH (1-34), for recapitulating nephron maturation and function (Huang et al., 2025). Its reproducible bioactivity and receptor selectivity make it a preferred tool in translational and regenerative medicine research, particularly for bone metabolism and kidney disease modeling.

Mechanism of Action of Parathyroid hormone (1-34) (human)

PTH (1-34) binds with high affinity to parathyroid hormone 1 receptor (PTH1R) and, to a lesser extent, parathyroid hormone 2 receptor (PTH2R), both class B G protein-coupled receptors. Ligand binding induces conformational changes that activate intracellular G_s and G_q pathways, leading to:

• cAMP production: The peptide stimulates adenylate cyclase, elevating intracellular cAMP concentrations (IC₅₀: 0.22 nM in HEK293 cells transfected with PTH1R).
• Inositol phosphate synthesis: Activation of phospholipase C results in inositol trisphosphate (IP₃) production and mobilization of intracellular Ca²⁺ stores.
• Downstream gene regulation: cAMP/PKA and IP₃/Ca²⁺ signaling regulate genes involved in bone turnover, renal calcium transport, and vitamin D metabolism.

In bone, PTH (1-34) enhances osteoclast-mediated resorption and osteoblast function, releasing mineralized calcium. In kidney, it upregulates calcium and magnesium reabsorption in the distal tubule and thick ascending limb, while promoting phosphate excretion. In the intestine, indirect stimulation of 1,25(OH)₂D synthesis increases dietary calcium uptake (contrast: this article provides new details on soluble forms and in vivo dosing).

Evidence & Benchmarks

• PTH (1-34) (human) induces cAMP accumulation in PTH1R-transfected HEK293 cells with an IC₅₀ of 0.22 nM (Huang et al., 2025, https://doi.org/10.1016/j.stem.2025.08.013).
• Subcutaneous administration of 10 or 40 μg/kg/day in male Fisher 344 rats increases trabecular and cortical bone mass in a dose- and time-dependent manner (APExBIO, https://www.apexbt.com/parathyroid-hormone-1-34-human.html).
• The peptide is soluble at ≥399.3 mg/mL in DMSO and ≥19.88 mg/mL in water, but insoluble in ethanol (APExBIO, product spec).
• High purity (>97.8%) is confirmed by analytical HPLC and mass spectrometry (APExBIO, spec page).
• In vivo, PTH (1-34) augments kidney assembloid maturation, enabling modeling of complex pathogenic interactions (Huang et al., 2025, see data tables).

Applications, Limits & Misconceptions

PTH (1-34) (human) is widely used as a reference agonist for PTH1R-mediated signaling in cell-based assays, tissue explants, and animal models. It is integral to osteoporosis research, bone turnover assays, and high-fidelity kidney assembloid platforms. The peptide's well-characterized bioactivity supports benchmarking of new PTH analogs and assessment of downstream cAMP and IP₃ responses.

Recent studies, such as Huang et al. (2025), underscore the necessity of precise calcium regulatory agents for advanced kidney disease models, particularly in recapitulating nephron self-assembly and function (see supplementary figures). By providing robust, receptor-specific modulation, PTH (1-34) (human) from APExBIO enables consistent experimental outcomes, as highlighted in this comparative review (this article extends benchmarking to assembloid performance and solution stability).

Common Pitfalls or Misconceptions

• PTH (1-34) (human) is not a suitable substitute for full-length PTH in all contexts; some signaling events require additional C-terminal residues.
• Peptide solutions are unstable with repeated freeze-thaw cycles; always use freshly prepared aliquots for each assay.
• Not recommended for diagnostic or therapeutic use in humans; for research use only as per APExBIO guidelines.
• Solubility is high in DMSO and water, but the peptide is insoluble in ethanol—attempts to dissolve in ethanol will fail.
• In vitro results may not fully extrapolate to late-stage human disease due to model system limitations (see discussion).

Workflow Integration & Parameters

Preparation: Dissolve the peptide at ≥399.3 mg/mL in DMSO or ≥19.88 mg/mL in water. Vortex gently; avoid vigorous agitation to minimize peptide degradation. Prepare aliquots and store desiccated at -20°C.

Experimental use: For cell signaling assays, use concentrations from 0.1 to 100 nM; for in vivo rodent studies, administer subcutaneously at 10–40 μg/kg/day. Avoid long-term storage of working solutions; discard unused aliquots after thawing.

Quality control: Confirm purity by HPLC and mass spectrometry prior to critical experiments. Ensure compatibility with assay buffers and cell lines.

Reference standards: Use APExBIO’s high-purity PTH (1-34) (human) (SKU: A1129) as a benchmark for reproducibility and cross-lab comparability (the A1129 kit).

For troubleshooting and advanced protocol guidance, see this solutions-focused resource (this article adds updated solubility and storage parameters for high-throughput workflows).

Conclusion & Outlook

Parathyroid hormone (1-34) (human) is a cornerstone tool for bone metabolism and kidney research, offering atomic control over PTH1R-mediated signaling. Its well-defined sequence, high purity, and robust activity underpin advances in osteoporosis modeling, nephron self-assembly studies, and regenerative medicine. By leveraging validated workflows and recognizing context-specific limitations, researchers can achieve high reproducibility and model fidelity. Future directions include integration into next-generation assembloid and organ-on-chip platforms, further enhancing translational insights into calcium homeostasis.