1,25(OH)2D3 in Brain Function and Neuropsychiatric Disease.

1,25(OH)2D3 (1,25-dihydroxy-vitamin D3 = calcitriol) is a powerful regulator of mineral metabolism. The hormone increases calcium and phosphate plasma concentrations in part by stimulation of intestinal absorption and renal reabsorption of calcium and phosphate. It is primarily, but not exclusively, produced in the kidney. Renal 1,25(OH)2D3 formation is stimulated by calcium and phosphate deficiency and by parathyroid hormone which is up-regulated by hypocalcemia. 1,25(OH)2D3 formation is inhibited by fibroblast growth factor FGF23, which is up-regulated by phosphate excess and requires Klotho to become effective. Klotho- or FGF23-deficiency leads to excessive plasma 1,25(OH)2D3-, Ca2+- and phosphate-concentrations with severe soft tissue calcification and accelerated aging. Tissue calcification and premature aging are prevented by NH4Cl without affecting 1,25(OH)2D3-formation. 1,25(OH)2D3 has powerful effects apparently unrelated to mineral metabolism, including anti-inflammatory actions and modification of multiple brain functions. Excessive 1,25(OH)2D3 formation in klotho-deficient NH4Cl-treated mice leads to an amazing surge of exploratory behavior, lack of anxiety and decreased depression, effects dissipated by low vitamin D diet. Conversely, vitamin D deficient mice display reduced explorative behavior, enhanced anxiety, aberrant grooming, submissive social behavior, social neglect and maternal cannibalism. 1,25(OH)2D3 is generated in human brain, and acts on diverse structures including prefrontal cortex, hippocampus, cingulate gyrus, thalamus, hypothalamus, and substantia nigra. In neurons 1,25(OH)2D3 suppresses oxidative stress, inhibits inflammation, provides neuroprotection, down-regulates a variety of inflammatory mediators and up-regulates a wide variety of neurotrophins. Diseases postulated to be favorably modified by 1,25(OH)2D3 include multiple sclerosis, Parkinson´s disease, Alzheimer´s disease, depression, bipolar disorder and schizophrenia. Clearly, substantial additional experimentation is required to fully understand the neuro-psycho-pathophysiological role of 1,25(OH)2D3 and to exploit 1,25(OH)2D3 or related agonists in the treatment of neuro-psychiatric disorders.