Vitamin D, Testosterone, Epigenetics and Pain an Evolving Concept of Neurosignaling, Neuroplasticity and Homeostasis

摘要

The thought of exploring a possible relationship between the broad systems of steroid hormone physiology (specifically vitamin D and testosterone) and nocioception was prompted by an unexpectedly frequent personal clinical observation. Patients with chronic pain syndromes or chronic musculoskeletal pain often have low serum levels of vitamin D and testos-terone. Mining for relevant information in Pub Med, Medline and Cochrane Systems Review, three concepts repeatedly emerge that provide a common context for understanding the mechanics of these diverse sys-tems—epigenetic, homeostasis and neuroplasticity. Viewing homeostasis within the framework of epigenetics allows reasoned speculation as to how various human systems interact to maintain integrity and function, while simultaneously responding in a plastic manner to external stimuli. Cell signaling supports normal function by regulating synaptic activity, but can also effect plastic change in the central and peripheral nervous system. This is most commonly achieved by post-translational remodeling of chromatin. There is thus persistent epigenetic change in protein synthesis with all the related downstream effects but without disruption of normal DNA se-quencing. In itself, this may be considered an example of genomic homeo-stasis. Epigenetic mechanisms in nociception and analgesia are active in the paleospinothalamic and neospinothalamic tracts at all levels. Physiologic response to a nociceptive insult, whether mechanical, inflammatory or ischemic, is provided by cell signaling that is significantly enhanced through epigenetic mechanisms at work in nociceptors, Gamma-Aminobutyric Acid (GABA) and glutamate receptors, voltage gated receptors, higher order neurons in the various dorsal horn laminae and proximal nociceptive pro-cessing centers in the brainstem and cortex. The mediators of these direct or epigenetic effects are various ligands also active in signaling, such as free radicals, substance P, a variety of cytokines, growth factors and G proteins, stress responsive proteins, matrix and structural proteins such as reelin and the Jmjd3 gene/enzyme. Calcitriol, the vitamin D receptor and vitamin D Responsive Elements collectively determine regulatory effects of this secosteroid hormone. Agents of homeostasis and plasticity include various D-system specific cytochrome enzymes (CYP 24, CYP 27 A1, B1), as well as more widely active enzymes and protein cell signalers (Jmjd3, Calbindin, BMP), many of which play a role in the nociceptive system. While the highlighted information represents an understanding of complex systems that is currently in its infancy, there are clear results from reliable research at a foundational level. These results are beginning to tell a compelling tale of the homeostasis and plasticity inherent in vitamin D and nociception systems.