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We investigated whether the phosphate (Pi) load in the circulation causes renal damage in non-CKD women. This cross-sectional study included 1,094 non-CKD Japanese women. Fibroblast growth factor (FGF)-23 as a parameter for the Pi load, bone alkaline phosphatase (BAP) as a bone metabolic marker, and the urinary albumin-to-creatinine ratio (UACR) as an early marker for renal damage were measured. Postmenopausal women exhibited significantly higher levels of serum Pi, FGF-23, BAP, and UACR and significantly lower eGFR than premenopausal women. In postmenopausal women, a multiple regression analysis confirmed a correlation between serum BAP and log UACR. In premenopausal women, although serum FGF-23 did not correlate with log UACR, a multiple regression analysis revealed that FGF-23 correlated with log UACR. Based on the i ncrease observed in BAP and its close relationship with log UACR in postmenopausal women, the release of Pi from bone may be linked to the systemic circulation of Pi, which has the potential to induce renal and vascular damage. Therefore, serum FGF-23 may be a useful marker for renal and vascular damage in premenopausal women; however, it currently remains unclear whether FGF-23 by itself or as a surrogate marker for the Pi load induces damage in the kidney and/or vasculature.

Urinary human intestinal alkaline phosphatase (IAP), beta 2-microglobulin (beta 2-MG) and N-acetyl-beta-D-glucosaminidase (NAG) were analyzed in 40 Japanese environmental-cadmium (Cd)-exposed and 40 non-exposed subjects to evaluate early biological markers for Cd-induced renal damage. All urinary indicators were significantly higher in the Cd-exposed subjects than non-exposed subjects. A fourth-order function was fitted for the relationship between beta 2-MG and IAP or NAG. The beta 2-MG concentration corresponding to the inflexion point for IAP was smaller than that for NAG. This result may support the contention that the cells containing IAP are damaged earlier than those containing NAG, and that IAP is a useful marker for detecting renal tubular dysfunction in people moderately exposed to Cd. However, in the stage of severe renal damage, the combination of IAP and beta 2-MG is considered to be more useful.