Brief Report: Consecutive Alendronate Administration-Mediated Inhibition of Osteoclasts Improves Long-Term Engraftment Potential and Stress Resistance of HSCs

Exposure of newborns to atmospherically relevant artificial particulate matter induces hematopoietic stem cell senescence

Research on the negative impacts of PM_2.5 have been focused on lung, brain, immune, and metabolism-related diseases. However, little is known about the mechanism underlying the effects of PM_2.5 on the modulation of hematopoietic stem cell (HSC) fate. Maturation of the hematopoietic system and differentiation of hematopoietic stem progenitor cells (HSPCs) occurs soon after birth when infants are susceptible to external stresses. We investigated how exposure to atmospherically relevant artificial particulate matter of diameter < 2.5 µm (termed, PM_2.5) affects HSPCs in newborns. The lungs of newborn mice exposed to PM_2.5 exhibited higher levels of oxidative stress and inflammasome activation, which continued during aging. PM_2.5 also stimulated oxidative stress and inflammasome activation in bone marrow (BM). PM_2.5-exposed infant mice at 12 months but not at 6 months displayed progressive senescence of HSCs accompanied by preferential impairment of the BM microenvironment with age-related phenotypes, as evidenced by colony-forming assay and serial transplantation and animal survival experiments. Further, PM_2.5-exposed middle-aged mice did not exhibit radioprotective potential. Collectively, exposure of newborns to PM_2.5 causes progressive senescence of HSCs. These findings revealed a novel mechanism by which PM_2.5 affects the fate of HSCs, highlighting the crucial role of early life exposure to air pollution in determining human health outcomes.

Reactive Oxygen Species and Nrf2: Functional and Transcriptional Regulators of Hematopoiesis

Hematopoietic stem cells (HSCs) are characterized by self-renewal and multilineage differentiation potentials. Although they play a central role in hematopoietic homeostasis and bone marrow (BM) transplantation, they are affected by multiple environmental factors in the BM. Here, we review the effects of reactive oxygen species (ROS) and Nrf2 on HSC function and BM transplantation. HSCs reside in the hypoxic microenvironment of BM, and ROS play an important role in HSPC regulation. Recently, an extraphysiologic oxygen shock/stress phenomenon was identified in human cord blood HSCs collected under ambient air conditions. Moreover, Nrf2 has been recently recognized as a master transcriptional factor that regulates multiple antioxidant enzymes. Since several years, the role of Nrf2 in hematopoiesis has been extensively studied, which has functional similarities of cellular oxygen sensor hypoxia-inducible factor-1 as transcriptional factors. Increasing evidence has revealed that abnormally elevated ROS production due to factors such as genetic defects, aging, and ionizing radiation unexceptionally resulted in lethal impairment of HSC function and hematopoiesis. Both experimental and clinical studies have identified elevated ROS levels as a major culprit of ineffective BM transplantation. Lastly, we discuss the possibility of using small molecule antioxidants, such as N-acetyl cysteine, resveratrol, and curcumin, to augment HSC function and improve the therapeutic efficacy of BM transplantation. Further research on the function of ROS levels and improving the efficacy of BM transplantation may have a great potential for broad clinical applications of HSCs.

Quercetin and alendronate multi-functionalized materials as tools to hinder oxidative stress damage

In spite of its remarkable anti-oxidant, anti-inflammatory, anti-cancer properties and its possible inhibition activity towards bone resorption, quercetin therapeutic use is limited by its poor bioavailability. Herein we developed a new multifunctionalized system for the local administration of quercetin and alendronate, one of the most potent anti-osteoporotic drugs, with the aim to get a material with enhanced properties. To this purpose we loaded quercetin on hydroxyapatite functionalized with alendronate, as well as on hydroxyapatite. Characterization was performed by means of X-ray diffraction, FT-IR and Raman spectroscopies, thermogravimetric and spectrophotometric analyses. Loading of quercetin from hydro-alcoholic solution increased with time and reached a constant value of about 5 weight% on both substrates, without causing significant structural and morphological modifications. Quercetin functionalized materials exhibit relevant anti-oxidant properties, in agreement with their high radical scavenging activity, and a quercetin sustained release in phosphate buffer. In vitro osteoblast and osteoclast co-culture in a microenvironment altered by oxidative stress shows that both alendronate and quercetin significantly reduce osteoclast viability, whereas they are able to counteract the negative effect of oxidative stress on osteoblast viability and differentiation, suggesting that their relative amount in the functionalized materials can be utilized to tailor bone cells response. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3293-3303, 2017.