The Impact of Electrical Stimulation of the Brain and Spinal Cord on Iron and Calcium-Phosphate Metabolism

Background: Deep-brain stimulation (DBS) electrically modulates the subcortical brain regions. Under conditions of monopolar cerebral stimulation, electrical current flows between electrode's contacts and an implantable pulse generator, placed in the subclavicular area. Spinal cord stimulation (SCS) delivers an electrical current to the spinal cord. Epidural electrical stimulation is associated with the leakage of current, which can cause a generalized reaction. The aim of our study was to investigate whether the electrical stimulation of the cerebrum and spinal cord could have generalized effects on biochemical parameters.

Materials and methods: A total of 25 patients with Parkinson's disease (PD, n = 21) and dystonia (n = 4), who underwent DBS implantation, and 12 patients with chronic pain, who had SCS, received electrical stimulation. The blood levels of selected biochemical parameters were measured before and after overnight stimulation.

Results: After DBS, the mean ± interquartile range (IQR) values for iron (off 15.6 ± 13.53 µmol/L; on: 7.65 ± 10.8 µmol/L; p < 0.001), transferrin (off: 2.42 ± 0.88 g/L; on: 1.99 ± 0.59 g/L; p < 0.001), transferrin saturation (off: 23.20 ± 14.50%; on: 10.70 ± 11.35%; p = 0.001), phosphate (off: 1.04 ± 0.2 mmol/L; on: 0.83 ± 0.2 mmol/L; p = 0.007), and total calcium (off: 2.39 ± 0.29 mmol/L; on: 2.27 ± 0.19 mmol/L; p = 0.016) were significantly reduced, whereas ferritin (off: 112.00 ± 89.00 ng/mL; on: 150.00 ± 89.00 ng/mL; p = 0.003) and C-reactive protein (off: 0.90 ± 19.39 mg/L; on: 60.35 ± 35.91 mg/L; p = 0.002) were significantly increased. Among patients with SCS, significant differences were observed for ferritin (off: 35 ± 63 ng/mL; on: 56 ± 62 ng/mL; p = 0.013), transferrin (off: 2.70 ± 0.74 g/L; on: 2.49 ± 0.69 g/L; p = 0.048), and C-reactive protein (off: 31.00 ± 36.40 mg/L; on: 36.60 ± 62.030 mg/L; p = 0.018) before and after electrical stimulation. No significant changes in the examined parameters were observed among patients after thalamotomy and pallidotomy.

Conclusions: Leaking electric current delivered to the subcortical nuclei of the brain and the dorsal column of the spinal cord exposes the rest of the body to a negative charge. The generalized reaction is associated with an inflammatory response and altered iron and calcium-phosphate metabolism. Alterations in iron metabolism due to electrical stimulation may impact the course of PD. Future research should investigate the influence of electric current and electromagnetic field induced by neurostimulators on human metabolism.