Assessment of DNA damage in postmenopausal women under osteoporosis therapy

GDF15 Modulates the Zoledronic-Acid-Induced Hyperinflammatory Mechanoresponse of Periodontal Ligament Fibroblasts

Orthodontic tooth movement (OTM) is thought to be impeded by bisphosphonate (BP) therapy, mainly due to increased osteoclast apoptosis and changes in the periodontal ligament (PdL), a connecting tissue between the alveolar bone and teeth. PdL cells, mainly fibroblasts (PdLFs), are crucial regulators in OTM by modulating force-induced local inflammatory processes. Recently, we identified the TGF-β/BMP superfamily member GDF15 as an important modulator in OTM, promoting the pro-inflammatory mechanoresponses of PdLFs. The precise impact of the highly potent BP zoledronate (ZOL) on the mechanofunctionality of PdLFs is still under-investigated. Therefore, the aim of this study was to further characterize the ZOL-induced changes in the initial inflammatory mechanoresponse of human PdLFs (hPdLFs) and to further clarify a potential interrelationship with GDF15 signaling. Thus, two-day in vitro treatment with 0.5 µM, 5 µM and 50 µM of ZOL altered the cellular properties of hPdLFs partially in a concentration-dependent manner. In particular, exposure to ZOL decreased their metabolic activity, the proliferation rate, detected using Ki-67 immunofluorescent staining, and survival, analyzed using trypan blue. An increasing occurrence of DNA strand breaks was observed using TUNEL and an activated DNA damage response was demonstrated using H2A.X (phosphoS139) staining. While the osteogenic differentiation of hPdLFs was unaffected by ZOL, increased cellular senescence was observed using enhanced p21Waf1/Cip1/Sdi1 and β-galactosidase staining. In addition, cytokine-encoding genes such as IL6, IL8, COX2 and GDF15, which are associated with a senescence-associated secretory phenotype, were up-regulated by ZOL. Subsequently, this change in the hPdLF phenotype promoted a hyperinflammatory response to applied compressive forces with an increased expression of the pro-inflammatory markers IL1β, IL6 and GDF15, as well as the activation of monocytic THP1 cells. GDF15 appeared to be particularly relevant to these changes, as siRNA-mediated down-regulation balanced these hyperinflammatory responses by reducing IL-1β and IL-6 expression (IL1B p-value < 0.0001; IL6 p-value < 0.001) and secretion (IL-1β p-value < 0.05; IL-6 p-value < 0.001), as well as immune cell activation (p-value < 0.0001). In addition, ZOL-related reduced RANKL/OPG values and inhibited osteoclast activation were enhanced in GDF15-deficient hPdLFs (both p-values < 0.0001; all statistical tests: one-way ANOVA, Tukey's post hoc test). Thus, GDF15 may become a promising new target in the personalized orthodontic treatment of bisphosphonatepatients.

Comparison of genotoxic effect between smokeless tobacco (Maras powder) users and cigarette smokers by the alkaline comet assay

Maras powder (MP) is a kind of smokeless tobacco used in the south-eastern region of Turkey and in several other countries of Middle and Far East. The present study was performed to assess the impacts of MP and cigarette smoking on the possible DNA damaging effect. Alkaline comet assay, which is a reliable and an important tool in human biomonitoring studies in the area of genetic toxicology, was used in peripheral lymphocytes of MP users, cigarette smokers, and non-smokers while their frequencies of total comet scores (TCS) were evaluated. The mean TCS (+/-SD) frequency in the peripheral lymphocytes was 14.4 (+/-10.04) for MP users and 8.26 (+/-5.38), 5.94 (+/-3.87) for cigarette smokers (P < 0.05) and non-smoking control subjects, respectively (P < 0.001). There was no significant effect of daily consumption of MP and the duration of MP usage on comet frequencies. In reply to a wrong belief among MP users ("the use of smokeless tobacco product is substantially less hazardous than cigarettes"), the present study shows that the oral use of smokeless tobacco represents a genotoxic hazard which is even higher than the DNA damage observed in cigarette smokers. Therefore, habitual use of MP should be taken into account and could be considered unsafe, equally harmful, and it should not be viewed as a safe alternative to cigarettes.