Introduction

Impaired brain energy metabolism is a common feature of neurodegenerative diseases such as Parkinson’s disease (PD) and Huntington's disease (HD). Recently, Terazosin (TZ), an FDA-approved medicine that is used to treat benign prostate hypertrophy, was found to increase brain ATP levels by stimulating phosphoglycerate kinase 1 (PGK1) activity, an ATP-generating enzyme in glycolysis¹. Human clinical databases also reveal that TZ may be neuroprotective in PD¹. However, the current TZ dose was based on treating benign prostatic hypertrophy, the optimal TZ dose to increase brain ATP in both sexes is still unknown². ³¹P MRS has the unique advantage of directly monitoring precise details of energetic metabolites like ATP and inorganic phosphate (Pi). Here we assessed the target engagement of TZ of both sexes in mice and humans at varying doses by ³¹P MRS at 7T.

Methods

Mice: 30 mice were divided into 6 groups and treated with varying TZ doses (0, 0.1, 1, 10, 100, 1000 μg/kg/d) by IP injection. Mice were scanned before and after receiving their respective dose of TZ for 14 days. During scanning, the mice were anesthetized with isoflurane. The body temperature of the mice was maintained with heated air, and respiration rate was monitored. The mice MRS were collected on a GE 7T small animal scanner (MR901) with a ¹H/³¹P dual tuned RAPID biomedical surface coil. The animal studies were approved by the IACUC of our institution. Human: 34 participants (age: 58±15 years) were recruited for both MRI and blood draws. 14 patients with neurodegenerative diseases (9 HD, 5 PD) and 20 sex- and age-matched healthy controls were imaged on a GE MR950 7T scanner. The MR session included the following scans: 1) a localizer, 2) ¹H anatomical image, 3) high order B₀ shimming including three linear and five second-order terms, 4) Bloch-Siegert estimation of center frequency and transmitter gain, and 5) quantitative non-localized ³¹P MRS using a free induction decay (FID) sequence. The metabolites of interest were defined with AMARES and fixed boundaries^2,3. The peak area was calculated simply as the summation of all data points within the boundaries. The defined ranges were sufficiently broad that the peak area could be reliably calculated even with variations in peak locations due to differences in pH^2,3. The human scan was approved by the IRB of our institution.

Results

We compared the TZ-induced ³¹P MRS metabolite ratios to the whole blood ATP levels from the same participants and found that the changes in the two assays were correlated (Fig. 2). Data from the mouse study suggests that the optimal TZ dose to increase brain ATP levels is 1.0 μg/kg/d for males, but 0.1 μg/kg/d for females. The sex difference in TZ dose-response is also observed in human participants. As shown in Fig. 4, the 14 patients with PD or Huntington’s disease (HD) respond differently to TZ (p=0.08). The female participants had a greater ATP response to a dose of 1.0 mg while the male greatest increase in ATP levels was at 5.0 mg (p=0.02). We did not observe a significant increase in ATP levels at either TZ dose in the control subjects.

Discussion

TZ is a drug that has been used primarily for men and data from women are missing. For the first time, we assessed the target engagement of TZ for both sexes with animal and human models. We found the non-invasive brain ³¹P MRS significantly correlates with the whole blood ATP assay. This correlation suggests that 1) both assays may capture TZ-induced ATP changes; 2) The TZ-induced changes cross the blood-brain barrier; 3) ³¹P MRS metabolite ratios can be used as biomarkers for assessing target assessment of TZ. We chose the βATP/Pi ratio as a biomarker of ATP levels to exclude possible contaminations from ADP or NADH signals. We observed similar sex differences in the response to TZ dose in both mouse and human models. We found male participants with a neurodegenerative disorder had the greatest ATP increase with a 5 mg TZ dose, which is consistent with the previous finding that PD patients taking TZ to treat enlarged prostate had slower PD progression and reduced PD complications¹. However, the female participants with a neurodegenerative disorder had a larger response at a dose of 1 mg. It is possible that this difference is due to body mass differences between the sexes. A major limitation of this ongoing project is the small sample size: there are only 2 or 3 mice for each sex at each dose, and there are only 14 patients and 20 healthy controls. Despite this limitation, our data provide useful information that may help to guide dose selection for future clinical trials.

Conclusion

We found the dose-response to TZ was different in males as compared to females. The optimal dose of TZ to increase brain ATP levels are 5 mg for male participants with a neurodegenerative disorder. In contrast, the female participants with a neurodegenerative disorder had a greater increase in ATP levels at 1.0 mg. It is possible that this difference is due to body mass differences between the sexes.

Acknowledgements

This work is supported by Michael J. Fox Foundation, the National Institutes of Health (UL1TR002537), and the Carver Foundation. Imaging in this study was conducted on equipment supported by S10RR028821.