Lithium reduces orthodontically induced root resorption by suppressing cell death, hyalinization, and odontoclast formation in rats

Early-stage periodontal ligament compression predicts orthodontically induced root resorption in rats

OBJECTIVES

To determine the effect of orthodontic pressure on periodontal ligament (PDL) compression in rats and assess correlation between PDL compression and orthodontically induced root resorption (OIRR).

MATERIALS AND METHODS

Eight female Wistar rats aged 10 weeks underwent surgery to place 2 mini-screws at the center of the palatal plate. 25 cN coil springs connecting the maxillary first molars and mini-screws were applied bilaterally to generate mesial force. Maxillary first molars were assigned to undergo either bodily or tipping movements. Micro-computed tomography (μCT) scans were taken on days 0, 3, 7, and 14, and histological sections were taken on day 14. OIRR was measured from histological sections, and the corresponding PDL compression ratio was quantified using μCT images.

RESULTS

The PDL was compressed by approximately 76% in tipping movement and 55% in bodily movement after 3 days, and by approximately 47% in bodily and tipping movements after 7 days of orthodontic force application. The extent of OIRR in tipping movement was significantly greater than that in bodily movement. A strong positive correlation between OIRR and PDL compression ratio was observed on day 3; however, no correlation was observed on day 7.

CONCLUSIONS

A strong correlation between PDL compression ratio and OIRR was observed at an early stage after the application of orthodontic force regardless of the tooth movement type (bodily or tipping), implying the importance of early stage PDL compression in the induction of OIRR.

Exploring the Neuroprotective Effects of Lithium in Ischemic Stroke: A literature review

Ischemic stroke ranks among the foremost clinical causes of mortality and disability, instigating neuronal degeneration, fatalities, and various sequelae. While standard treatments, such as intravenous thrombolysis and endovascular thrombectomy, prove effective, they come with limitations. Hence, there is a compelling need to develop neuroprotective agents capable of improving the functional outcomes of the nervous system. Numerous preclinical studies have demonstrated that lithium can act in multiple molecular pathways, including glycogen synthase kinase 3(GSK-3), the Wnt signaling pathway, the mitogen-activated protein kinase (MAPK)/ extracellular signal-regulated kinase (ERK) signaling pathway, brain-derived neurotrophic factor (BDNF), mammalian target of rapamycin (mTOR), and glutamate receptors. Through these pathways, lithium has been shown to affect inflammation, autophagy, apoptosis, ferroptosis, excitotoxicity, and other pathological processes, thereby improving central nervous system (CNS) damage caused by ischemic stroke. Despite these promising preclinical findings, the number of clinical trials exploring lithium's efficacy remains limited. Additional trials are imperative to thoroughly ascertain the effectiveness and safety of lithium in clinical settings. This review delineates the mechanisms underpinning lithium's neuroprotective capabilities in the context of ischemic stroke. It elucidates the intricate interplay between these mechanisms and sheds light on the involvement of mitochondrial dysfunction and inflammatory markers in the pathophysiology of ischemic stroke. Furthermore, the review offers directions for future research, thereby advancing the understanding of the potential therapeutic utility of lithium and establishing a theoretical foundation for its clinical application.

Force-Loaded Cementocytes Regulate Osteoclastogenesis via S1P/S1PR1/Rac1 Axis

Orthodontically induced inflammatory root resorption (OIIRR) is the major iatrogenic complication of orthodontic treatment, seriously endangering tooth longevity and impairing masticatory function. Osteoclasts are thought to be the primary effector cells that initiate the pathological process of OIIRR; however, the cellular and molecular mechanisms responsible for OIIRR remain unclear. Our previous studies revealed that cementocytes, the major mechanically responsive cells in cementum, respond to compressive stress to activate and influence osteoclasts locally. For this study, we hypothesized that the sphingosine-1-phosphate (S1P) signaling pathway, a key mechanotransduction pathway in cementocytes, may regulate osteoclasts under the different magnitudes of either physiologic compressive stress that causes tooth movement or pathologic stress that causes OIIRR. Here, we show a biphasic effect of higher compression force stimulating the synthesis and secretion of S1P, whereas lower compression force reduced signaling in IDG-CM6 cementocytes. Using conditioned media from force-loaded cementocytes, we verified the cell-to-cell communication between cementocytes and osteoclasts and show that selective knockdown of S1PR1 and Rac1 plays a role in cementocyte-driven osteoclastogenesis via the S1P/S1PR1/Rac1 axis. Most importantly, the use of inhibitors of this axis reduced or prevented the pathological process of OIIRR. The intercellular communication mechanisms between cementocytes and osteoclasts may serve as a promising therapeutic target for OIIRR.