Canagliflozin triggers the FGF23/1,25-dihydroxyvitamin D/PTH axis in healthy volunteers in a randomized crossover study

Abstract

Background: Sodium glucose cotransporter-2 (SGLT2) inhibitors are the most recently approved class of drugs for type 2 diabetes and provide both glycemic efficacy and cardiovascular risk reduction. A number of safety issues have been identified, including treatment-emergent bone fractures. To understand the overall clinical profile, these safety issues must be balanced against an attractive efficacy profile. Our study was designed to investigate pathophysiological mechanisms mediating treatment-emergent adverse effects on bone health.

Methods: We conducted a single-blind randomized crossover study in hospitalized healthy adults (n = 25) receiving either canagliflozin (300 mg/d) or placebo for 5 days. The primary end-point was the drug-induced change in AUC for plasma intact fibroblast growth factor 23 (FGF23) immunoactivity between 24 and 72 hours.

Results: Canagliflozin administration increased placebo-subtracted mean levels of serum phosphorus (+16%), plasma FGF23 (+20%), and plasma parathyroid hormone (PTH) (+25%), while decreasing the level of 1,25-dihydroxyvitamin D (-10%). There was substantial interindividual variation in the magnitude of each of these pharmacodynamic responses. The increase in plasma FGF23 was correlated with the increase in serum phosphorus, and the decrease in plasma 1,25-dihydroxyvitamin D was correlated with the increase in plasma FGF23.

Conclusions: Canagliflozin induced a prompt increase in serum phosphorus, which triggers downstream changes in FGF23, 1,25-dihydroxyvitamin D, and PTH, with potential to exert adverse effects on bone health. These pharmacodynamic data provide a foundation for future research to elucidate pathophysiological mechanisms of adverse effects on bone health, with the objective of devising therapeutic strategies to mitigate the drug-associated fracture risk.

Trial registration: ClinicalTrial.gov (NCT02404870).

Funding: Supported by the Intramural Program of NIDDK.

Keywords: Bone Biology; Bone disease; Diabetes; Endocrinology.

Figure 1. Trial enrollment details.

A total of 67 healthy volunteers were assessed for eligibility based on inclusion/exclusion criteria (see Supplemental Methods for complete list). A total of 29 subjects were randomized for the cross-over study (canagliflozin vs. placebo [BPO]). Four subjects withdrew from the study after randomization. Therefore, data were collected and analyses performed on 25 subjects.

Figure 2. Canaglifozin-induced changes in urinary excretion of glucose, sodium, and phosphate.

Research subjects (n = 25) received canaglifozin (Cana) (300 mg/d) for 5 days starting at 0 hours. Urinary excretion of glucose (g/d), sodium (mmol/d), creatinine (g/d), and phosphate (g/d) were collected over 24-hour periods. Ratios of glucose (g)/creatinine (g) excretion (A) and sodium (mmol)/creatinine (g) excretion (B) were plotted as means ± SEM at time points corresponding to the ends of the collection periods. (C) Drug-induced increase in urinary sodium/creatinine ratio as a function of baseline urinary sodium excretion. (D) Percent urinary phosphate excretion on the left axis and % urinary phosphorus absorption on the right axis. Note that the sum of excretion and absorption equals 100% at all time points. Urinary excretion (left axis) is plotted with values increasing, whereas transtubular reabsorption of phosphate (TRP; right axis) is plotted with values decreasing. Daily timed urine specimens were collected at 0, 2, 4, and 12 hours. Aliquots (10 ml) were analyzed to generate data for D, and the remainder of the urine specimen was added to the 24-hour urine collection. (E) Twenty-four–hour urinary calcium excretion (mmol/24 hr)/creatinine (g) excretion as a function of the day on which the urine was collected. In B, D, and E, *P < 0.0001 and ^ǂP < 0.05 by 2-tailed t test, respectively. Data for placebo and canagliflozin are represented in blue and red, respectively.

Figure 3. Effect of canagliflozin on serum phosphorus and hormones of mineral metabolism.

Research subjects (n = 25) were treated with canagliflozin or placebo (Figure 2). Serial blood tests were obtained and analyzed for serum phosphorus (A) and plasma hormones (FGF23, 1,25-dihydroxyvitamin D, and PTH in B–D, respectively). Differences were statistically significant (P < 0.05, paired 2-tailed t tests) for phosphorus (4–76 hours), FGF23 (24–60 hours), 1,25-dihydroxyvitamin D (28–100 hours), and PTH (36 and 52–108 hours). Data are graphed as means ± 95% CIs. Two-tailed P value for PTH refers to the rate of change over time. Data for placebo and canagliflozin are represented in blue and red, respectively.

Figure 4. Circadian rhythm of levels of serum phosphorus and plasma hormones of mineral metabolism in placebo arm.

Mean values from days 1–5 (0–108 hours) of the subjects’ placebo visits (n = 25) are arranged from top to bottom: serum phosphorus, plasma FGF23, plasma 1,25-dihydroxyvitamin D, and plasma PTH. Arrows are placed at the peaks for serum phosphorus (8 pm), plasma FGF23 (8 am), and plasma PTH (8 pm) and the nadir for plasma 1,25-dihydroxyvitamin D (12 pm).

Figure 5. Interindividual variation in urinary glucose and sodium excretion and circulating biomarkers of mineral metabolism in response to canagliflozin.

We defined indices of the drug’s effects on serum phosphorus and plasma FGF23 as the mean changes in those parameters on day 2 (24, 26, 28, and 36 hours); plasma 1,25-dihydroxyvitamin D as the mean change on day 3 (48, 52, and 60 hours); and plasma PTH as the mean change on day 5 (96, 98, 100, and 108 hours). (A) Histogram distribution of the ratio of urinary excretions of glucose/creatinine in research subjects treated with canagliflozin (day 1; Figure 2). (B) A similar histogram distribution of the ratio of urinary excretions of sodium/creatinine (day 1; Figure 2). X axes of the histograms (A, B, D–F) depict the ratio of each index during the canagliflozin treatment period divided by the index during the placebo period (i.e., a ratio [canagliflozin/placebo] of ratios [sodium/creatinine or glucose/creatinine]). The x axis for C plots the absolute change in serum phosphorus level (canagliflozin treatment period minus placebo period). The y axes (A–F) depict the number of individuals with the drug responses indicated on the x axes. Bin widths are 6 (A), 0.3 (B), and 0.1 (C, D, F). Data in B include 24 research subjects because of missing data from 1 subject. Data in E include 22 research subjects because of missing data on 3 subjects (see Supplemental Methods). Data in the other 4 panels include all 25 research subjects.

Figure 6. Associations among pharmacodynamic changes in response to canagliflozin.

Scatterplots showing the relationships between urinary excretion of sodium versus urinary glucose excretion (A), mean serum phosphorus response versus urinary sodium excretion (B), mean serum phosphorus response versus urinary glucose excretion (C), ΔFGF23 versus mean serum phosphorus response (D), mean 1,25-dihydroxyvitamind D versus ΔFGF23 (E), and mean PTH response versus mean 1,25-dihydroxyvitamin D response. Dotted lines represent correlations with P > 0.05. In each case, the indices of drug-induced changes are defined in Figure 3’s legend. The analysis excludes patients with missing data, as explained in Figure 3’s legend.

Figure 7. Homeostatic mechanisms mediating the effects of SGLT2 inhibitors on hormonal regulation of bone and mineral metabolism.

SLGT2 inhibition increases serum phosphorus, which triggers an increase in FGF23. Increased FGF23 provides negative feedback in order to restore serum phosphorus toward baseline levels. FGF23 is also known to decrease levels of 1,25-dihydroxyvitamin D (1,25-VitD), which is predicted to decrease gastrointestinal Ca⁺ absorption, thereby stimulating an increase in PTH levels. PTH acts to restore 1,25-VitD levels toward normal by upregulating CYP27B1, while also decreasing serum phosphate. The observed increase in PTH combined with a decrease in 1,25-VitD levels would be predicted to adversely affect bone health.