• Oxidation of Dietary Amino Acids Disrupts their Anabolic Effects on Bone Marrow-Derived Mesenchymal Stem Cells

      El Refaey, Mona M.; Department of Cellular Biology and Anatomy (2016-07)
      Age-dependent bone loss has been well documented in both human and animal models. Since it has been proposed that aging is associated with an increase in the generation of damaging reactive oxygen species (ROS), our hypothesis was that the oxidized products of dietary amino acids could play a role in age-induced bone loss by altering osteoprogenitor cell differentiation and function or activating osteoclastic activity. We first examined the effects of the oxidized nutrients on the bone marrow-derived mesenchymal stem cells and our data showed a decrease in the protein and gene expression of osteogenic markers normally stimulated by nutrients. Aromatic amino acids activated signaling pathways involved in protein synthesis in vitro, and thus, in contrast, the oxidized metabolites of these aromatic amino acids had no effect on the activation of these anabolic pathways. We then examined the bone marrow concentration of the oxidized aromatic amino acids in mature (12 months) vs. aged (24 months) C57BL/6 mice and found that kynurenine, the oxidized product of the aromatic amino acid tryptophan, was found in the highest concentration in 12 months mice. Thus, we tested the effects of kynurenine, fed as a dietary supplement, on the bone mass of twelve-month-old C57BL/6 mice compared to a normal protein diet to see if the oxidized amino acid would induce a pattern consistent with age-related bone loss. Twelve-month-old, male C57BL/6 mice were fed one of four diets; 18% protein diet (normal protein diet); 8% protein diet + tryptophan; 8% protein diet + kynurenine (50 μM) and 8% protein diet + kynurenine (100 μM) for 8 wks. Bone densitometry and micro-CT analyses demonstrated bone loss following the kynurenine diet. Histological and histomorphometric studies showed a decreased bone formation and an increased MONA M. EL REFAEY Oxidation of Dietary Amino Acids Disrupts Their Anabolic Effects on Bone Marrow-Derived Mesenchymal Stem Cells (Under the direction of DR. CARLOS M. ISALES) osteoclastic activity in the kynurenine groups; these animals also exhibited an increase in serum pyridinoline, a marker of bone breakdown. Thus, these data demonstrate that feeding an oxidized product of an essential amino acid induces bone loss in a pattern consistent with accelerated aging, and we propose that one of the mechanisms involved in age-induced bone loss may be from alterations of dietary nutrients by the increased generation of ROS associated with aging.
    • Role of NADPH Oxidase following Traumatic Brain Injury

      Ma, Merry Wenlan; Department of Neuroscience and Regenerative Medicine (5/22/2018)
      Traumatic brain injury (TBI) is a major cause of death and disability worldwide. Despite intense investigation, no neuroprotective agents for TBI have yet translated to the clinic. Recent efforts have focused on identifying potential therapeutic targets that underlie the secondary TBI pathology that evolves minutes to years following the initial injury. Oxidative stress is a key player in this complex cascade of secondary injury mechanisms and prominently contributes to neurodegeneration and neuroinflammation. In addition, the NLRP3 inflammasome, which produces pro-inflammatory signals, can become activated in response to oxidative stress and may exacerbate secondary pathology. NADPH oxidase (NOX) is a unique family of enzymes whose primary function is to produce reactive oxygen species (ROS). Human post-mortem and animal studies have identified elevated NOX2 and NOX4 levels in the injured brain, suggesting that NOX is involved in the pathogenesis of TBI. Our experiments demonstrate that targeting NOX, specifically NOX2 and NOX4, can reduce oxidative stress, attenuate neuroinflammation, reduce lesion size, and promote neuronal survival following TBI. In particular, deletion of NOX2 or inhibition of NOX can attenuate the increased expression and activation of the NLRP3 inflammasome via TXNIP- mediated pathway and decrease the production of pro-inflammatory factors, such as caspase-1 and IL-1β. We also demonstrate the novel findings that deletion of NOX4 can reduce neuronal oxidative damage evidenced by decreased DNA oxidation, lipid peroxidation, and protein nitration in the injured cerebral cortex. Mice lacking NOX4 also showed reduced cell death and neurodegeneration following TBI. Collectively, our results support the notion that targeting NOX enzymes can suppress neuroinflammatory secondary TBI pathology in addition to alleviating oxidative damage following injury. In addition, our inhibitor studies extend the critical window of efficacious TBI treatment, which further supports the pursuit of NOX as therapeutic targets.