The scientific rationale rests on a hormone loop with remarkable reach. FGF23 is a bone-derived hormone secreted mainly by osteoblasts and osteocytes that travels through the circulation to the kidney, where it binds a receptor complex of FGF receptor 1 and the co-receptor α-Klotho on renal tubular cells. Klotho, expressed predominantly in renal tubular cells, is often described as an anti-ageing protein: animals deficient in Klotho develop a syndrome resembling accelerated human ageing, with vascular calcification, skin atrophy and osteoporosis. Through the α-Klotho-FGFR1 complex, FGF23 downregulates the sodium-phosphate cotransporter NaPi-IIa to promote phosphaturia and suppresses the vitamin D-activating enzyme 1α-hydroxylase, or Cyp27b1, thereby lowering circulating 1,25-dihydroxyvitamin D3. This loop protects the organism from vitamin D excess and couples renal phosphate handling to bone mineralization and turnover, making it a plausible target in a disease characterized by deteriorating bone mineral balance.

To test the formula, the researchers randomly divided forty specific pathogen-free female Sprague-Dawley rats into four groups of ten: a sham-operated control group, an ovariectomized model group, a BSJPHXF treatment group and a group receiving Liuwei Dihuang Wan, a classical kidney-tonifying Chinese formula used as a positive control. After a twelve-week recovery period following surgery, the treatment groups received their assigned formula by gavage once daily for four weeks, while the sham and model groups received an equal volume of saline. The BSJPHXF dose of 2.979 grams per kilogram per day was converted from a clinical adult dose by body-surface-area scaling, and the Liuwei Dihuang Wan dose was adopted from a published ovariectomized-rat study. Three rats died during the study from postoperative infection or improper gavage technique and were excluded because no endpoint data could be obtained, leaving nine animals per group for analysis.

The measurements spanned several levels of biology. Serum calcium and phosphorus were quantified by automated biochemical analysis, while circulating FGF23, parathyroid hormone and 1,25-dihydroxyvitamin D3 were measured by ELISA in nine animals per group. Renal protein expression of Klotho, NaPi-IIa and Cyp27b1 was assessed by Western blot, trabecular bone microstructure of the distal femoral metaphysis was scanned by Micro-CT, and kidney histopathology was examined by haematoxylin and eosin staining. Here the study’s two-tier evidence structure becomes important: the Western blot, Micro-CT and histological endpoints rested on only three animals per group, a sample the authors themselves flag as a major limitation, at which statistical power is limited and a single outlier can shift the group mean. Serum oestradiol was not measured, so confirmation of ovariectomy rested on the surgical procedure and daily vaginal cytology rather than hormonal confirmation.

The biochemical results were striking. Compared with sham animals, ovariectomized rats had lower serum calcium, 1.997 versus 2.547 millimoles per litre, and lower 1,25-dihydroxyvitamin D3, 102.21 versus 201.74 picograms per millilitre, alongside higher serum phosphorus, 2.019 versus 1.355 millimoles per litre, higher FGF23, 366.82 versus 159.52 picograms per millilitre, and higher parathyroid hormone, 141.63 versus 33.91 picograms per millilitre, with all differences significant at P<0.001. BSJPHXF attenuated every one of these disturbances relative to the untreated model group. The rise in parathyroid hormone is particularly telling, the authors argue, because three signals in the ovariectomized animals favour its secretion: hypocalcaemia, hyperphosphataemia and the fall in active vitamin D, which releases vitamin D receptor-mediated inhibition of parathyroid hormone gene transcription. Its normalization after treatment is consistent with secondary hyperparathyroidism arising from a state of relative FGF23 resistance.

That resistance interpretation carries an important mechanistic puzzle. Physiologically, FGF23 suppresses parathyroid hormone secretion and promotes urinary phosphate excretion, yet in the ovariectomized rats the rise in FGF23 was accompanied by hyperphosphataemia and increased renal NaPi-IIa rather than the phosphaturia expected from an intact FGF23 effect. The authors suggest that when renal and parathyroid α-Klotho availability falls, the suppression of parathyroid hormone is attenuated and the kidney becomes less responsive to circulating FGF23. However, they are careful to note that urinary phosphate excretion, renal Cyp24a1 expression and downstream FGFR signalling were not measured, so FGF23 resistance cannot be formally demonstrated and the direction of causality remains to be established. The renal changes may equally reflect downstream consequences of altered bone turnover and elevated bone-derived FGF23 rather than a primary renal disorder, a possibility the data cannot distinguish.

On the bone side, the two formulae parted ways. Micro-CT of the distal femur showed that ovariectomy reduced trabecular bone volume fraction from 0.292 to 0.087, reduced trabecular number from 3.613 to 2.595 per millimetre and increased trabecular separation from 0.187 to 0.302 millimetres, all at P<0.001, while trabecular thickness did not differ among groups. BSJPHXF significantly reversed all three affected parameters, bringing them statistically indistinguishable from sham, whereas Liuwei Dihuang Wan did not significantly reverse any of them relative to the model group and remained significantly below sham. For all three parameters BSJPHXF was superior to the positive control, with pairwise P values of 0.004, 0.032 and 0.043. By contrast, where the circulating mineral parameters differed between treatments, the differences favoured Liuwei Dihuang Wan, which produced a greater reduction in serum phosphorus, P=0.0015, and a greater increase in 1,25-dihydroxyvitamin D3, P=0.0002, while the two formulae did not differ for serum calcium, FGF23 or parathyroid hormone.

This dissociation between systemic mineral handling and trabecular microarchitecture suggests that the two prescriptions are not interchangeable in this model and that BSJPHXF’s microarchitectural effect may not be fully explained by its systemic action on calcium-phosphorus metabolism. The authors propose at least two complementary mechanisms: modulation of renal α-Klotho-FGF23 signalling that affects mineral balance, and direct effects on bone cells through the Wnt/β-catenin and BMP pathways, mechanisms supported by previous pharmacological work showing that BSJPHXF promotes bone formation through PI3K/Akt/NF-κB, Wnt/β-catenin and OPG/RANKL/RANK signalling and enhances osteogenic activity by inhibiting Beclin-1-induced autophagy. Several constituent compounds act on related pathways, including psoralen through Wnt/β-catenin and oestrogen receptor activation, icariin through BMP signalling, and Astragalus membranaceus, which has been reported to regulate the vitamin D-FGF23-Klotho axis in osteoporotic mice. A systematic review and meta-analysis of Gukang Capsule reported improved bone mineral density and faster healing of osteoporotic fractures without increased adverse events.

The authors also draw a careful boundary around what the study does and does not address. The endocrine actions of FGF23 on mineral homeostasis should be distinguished from the cell-autonomous roles of locally acting FGF ligands in bone: FGF2, for example, acts directly on bone marrow mesenchymal stem cells to regulate proliferation, senescence and osteogenic differentiation, and disruption of nuclear FGF2 transport and FGF2-dependent chromatin architecture drives stem cell ageing and impairs bone regeneration. The present study addresses only the endocrine arm and provides no evidence on these cell-autonomous pathways. Likewise, the ovariectomized rat models the acute consequences of oestrogen withdrawal and is not a model of chronic kidney disease or renal osteodystrophy, in which the bone phenotype is driven by disturbed mineral metabolism rather than oestrogen loss. The absence of a statistically significant difference between the two formulae should not be read as evidence of equivalent efficacy, since the study was not powered for equivalence testing.

For all its suggestive patterns, the study’s limitations are substantial and the authors state them plainly. The mechanistically most important endpoints, the Western blot, Micro-CT and histological findings, rest on only three animals per group and must be regarded as preliminary and hypothesis-generating. Functional renal parameters such as serum creatinine, blood urea nitrogen or urinary protein were not measured, so renal structure cannot be linked to renal function, and the qualitative tubular alterations seen on staining were not scored semiquantitatively. Bone histomorphometry, bone turnover markers and mechanical testing were absent, preventing any conclusion that BSJPHXF promotes bone formation or inhibits resorption. No pathway-specific inhibitor experiments were performed to confirm the direct molecular targets of the formula, and the analyses, though controlled within each endpoint by Tukey’s honestly significant difference test, were not adjusted for multiplicity across endpoints. Adequately powered studies with functional renal and bone endpoints, hormonal confirmation and pathway-specific interventions will be needed to establish causality and clinical relevance. Until then, the work stands as a detailed, cautiously framed first look at how a ten-herb prescription might engage one of the body’s most influential bone-kidney hormone circuits.

Subject of Research: Effects of the traditional Chinese formula BSJPHXF on the FGF23-Klotho axis, calcium-phosphorus metabolism and trabecular bone in ovariectomized rats

Article Title: BSJPHXF modulates the FGF23-Klotho bone-kidney axis and calcium-phosphorus metabolism in ovariectomized rats with postmenopausal osteoporosis

Article References: Zhang, H., Zhang, Y., Ning, B., Lin, Y., Wang, P., Zhang, X., Guo, Z., & Zhu, G. (2026). BSJPHXF modulates the FGF23-Klotho bone-kidney axis and calcium-phosphorus metabolism in ovariectomized rats with postmenopausal osteoporosis. Frontiers in Endocrinology, 17, Article 1943198. https://doi.org/10.3389/fendo.2026.1943198

Image Credits: AI Generated

DOI: 10.3389/fendo.2026.1943198

Keywords: BSJPHXF, modulates, FGF23-Klotho, bone-kidney, axis, calcium-phosphorus, metabolism, ovariectomized, rats, postmenopausal, osteoporosis, scientific research