Dietary zinc restriction induces nociceptive pain with reduced inflammation in mice

Zinc (Zn) is an essential micronutrient involved in a large diversity of cellular metabolism, included in the physiology of nervous system and pain modulation. There is little evidence for the role of Zn nutritional alternations to the onset and progression of neuropathic and inflammatory pain. We investigate the effects of a zinc restricted diet on the development of pain. Weaned mice were submitted to different diets: AIN-93 (38mg/kg of Zn) and Zn-deficient (AIN-93 with 11mg/kg of Zn), during four weeks. Mechanical allodynia was measured weekly using Von Frey hairs. Plantar assays for cold and heat allodynia, formalin-induced nociception and carrageenan-induced mechanical allodynia were performed at the 4th week. Plasma, DRG and livers samples were obtained for biochemical and metabolomics analysis. Zn deficient diet completely changed mice sensitivity pattern, inducing an intense allodynia evoked by mechanical, cold and heat stimulus since weaning and during four weeks. Showed also an increased sensitivity of neurogenic phase of formalin test but the inflammatory pain behavior was drastically reduced. Zn restriction increased the ATF-3 and SOD-1 levels at DRG and reduced that of GFAP, leading an increase of neuronal activation and oxidative stress, and reduced neuroimmune activity. Plasma TNF was also reduced and metabolomics analyses suggest a downregulation of lipid metabolism of arachidonic acid, reinforcing the impact of Zn restriction to the inflammatory response. Reduction of Zn intake interferes in pain circuits, reducing inflammatory pain, however enhancing nociceptive pain. Accordingly, Zn imbalance could be predisposing factor for NP development. Therefore, dietary zinc supplementation and its monitoring present clinical relevance.