Effect of Artificial Aging on Translucency of Zirconia Reinforced Lithium Silicate and Lithium Disilicate Ceramics: A Systematic Review

INTRODUCTION

Digital dentistry and advanced ceramic materials have been widely used but which material has a better esthetically durable outcome needs to be evaluated. The purpose of this systematic review and meta-analysis was to evaluate the difference in the translucency of CAD zirconia-reinforced lithium silicate and CAD lithium disilicate glass ceramics after being subjected to artificial aging.

MATERIAL AND METHODS

Two independent reviewers searched the MEDLINE/ PubMed, Embase, and EBSCO databases and the Google Scholar search engine for in-vitro studies published from January 2010 to May 2023 to identify relevant studies measuring the translucency of CAD ZLS and CAD lithium disilicate glass ceramics after being subjected to different artificial aging conditions using the coffee solution, 4% acetic acid, distilled water and UV aging.

RESULTS

For qualitative synthesis, 10 studies were included. A statistically significant difference was observed between CAD zirconia-reinforced lithium silicate and CAD lithium disilicate glass ceramics (P⟨0.05, mean difference=-0.25 [-0.38,-0.11]). Translucency of CAD ZLS was less than CAD lithium disilicate glass ceramics.

CONCLUSIONS

Artificial aging has decreased the translucency of glass ceramics. For fixed prosthetic rehabilitation clinicians can opt for CAD lithium disilicate glass-ceramic as a more esthetically pleasing and durable material in oral environment.

Abstract 195: A focused ultrasound blood brain barrier disruption model to test the influence of tight junction genes to treat brain tumors

A major hindrance to advances in the care of patients with malignant gliomas is the presence of the blood brain barrier (BBB) and blood-brain tumor barrier (BBTB) that greatly restricts drug access from the plasma to the tumor cells. Bubble-assisted Focused Ultrasound (BAFUS) has proven effective in opening the BBB for treatment of glial tumors in adults and pediatric cases. BAFUS has been previously shown to disrupt noninvasively, selectively, and transiently the BBB in small animals in vivo. However, there is a lack of an in vitro preclinical model suitable for testing the genetic determinants of endothelial cell tight junction integrity and vulnerability to the physical disruption. Our BBB organ-on-chip platform will enable precision medicine of brain cancers through identifying patient-specific parameters by which to open the BBB allowing use of drugs and drug combinations otherwise unsuitable. We intend to sequence these in vitro models to verify that the genotype (alleles/SNPs) of tight junction proteins contribute to BBB structure and integrity. To initiate this effort, we report the development of an ultrasound transparent organ-on-chip model populated by iPSC-derived endothelial cells (iPSC-EC) co-cultured with astrocytes. Western blot, immunocytochemistry, permeability, and transelectrical endothelial resistance (TEER) studies all convey expression of key EC proteins and marked barrier integrity. Further benchmarking of device-ultrasound interactions, successful iPSC differentiation, tight junction formation, and fabrication of nanobubbles and their assistance in ultrasound BBB disruption will be presented. Efforts are underway to analyze nine characteristic BBB tight junction genes from WGS data to determine associations between iPSC-EC genotype and phenotype.

Citation Format: Jayashree Iyer, Adam Akkad, Nanyun Tang, Sen Peng, Michael Berens, Frederic Zenhausern, Jian Gu. A focused ultrasound blood brain barrier disruption model to test the influence of tight junction genes to treat brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 195.

EXTH-17. A FOCUSED ULTRASOUND BLOOD BRAIN BARRIER DISRUPTION MODEL TO TEST THE INFLUENCE OF TIGHT JUNCTION GENES TO TREAT BRAIN TUMORS

Treating primary or metastatic tumors in the brain (glioblastomas, melanoma, lung cancer, breast cancer) proves challenging by virtue of the protective function of the blood brain barrier (BBB). The tight junction proteins (TJPs) binding the specialized endothelial cells of the BBB largely contribute to the limited permeability of cancer-therapeutic drugs. In both preclinical and clinical models, low intensity focused ultrasound (LIFU) coupled with microbubbles has been proven to safely and transiently open the BBB. Despite this method being established, potential genetic influences on the durability and vulnerability of tight junctions to LIFU have not been elucidated, nor have the determinants of tight junction repair post LIFU been thoroughly investigated. We report the development of an ultrasound transparent organ-on-chip model populated by iPSC-derived endothelial cells (iPSC-EC) co-cultured with astrocytes. We aim to probe the contributions of various tight junction genes to barrier integrity along with the subsequent protein topology involved in reassembly post ultrasound. Thus, this model serves to determine parameters for ultrasound disruption for precision opening of the BBB. The BBB-On-Chip was successfully fabricated and assembled with an optimized technique that has an 80% yield of leak-free devices, with stable cavitation post nanobubble injection. Furthermore, Western blots show expression of claudin-5, a key TJP, in our iPSC-ECs. We have also demonstrated by confocal microscopy that another component of the TJP complex, ZO-1, can be visualized at iPSC-derived cell junctions. Further benchmarking of device-ultrasound interactions, successful iPSC differentiation, tight junction formation, and fabrication of nanobubbles and their assistance in ultrasound BBB disruption will be presented. Efforts are underway to characterize the contributions of tight junction genes and their variations to the integrity and disruption of the BBB.

Abstract 2984: Building an in vitro blood brain barrier model to test the influence of tight junction gene alleles on disruption by focused ultrasound to treat brain tumors

Treating primary or metastatic tumors in the brain (glioblastomas, melanoma, lung cancer, breast cancer) proves challenging by virtue of the protective function of the blood brain barrier (BBB). Recently, it has been shown that low intensity focused ultrasonic (LIFU) waves stably cavitate infused microbubbles which then mechanically disrupt the tight junctions of the BBB. This leads to temporary, recoverable opening of the BBB, and passage of otherwise disqualified cancer-therapeutic drugs at precise locations targeted by the focused ultrasound. To date, potential genetic influences on the durability and vulnerability of tight junctions to LIFU have not been elucidated, nor have the determinants of tight junction repair post LIFU been thoroughly investigated. We report the development of an ultrasound transparent organ-on-chip model to test LIFU with microbubble infusion treatment on a cell-engineered BBB. The BBB is developed using brain-specific endothelial cells derived from genomically characterized immortalized pluripotent stem cells (iPSC). Furthermore, to test genetic variation effects we propose that alleles coding for the proteins involved in tight junction assembly contribute to LIFU disruption variability. Developing preclinical models of the BBB to accommodate cell sources with tight junction genes of different allele makeup will shed light on how individuals will respond to different ultrasound frequencies. The in vitro BBB device is composed of two orthogonally stacked fluidic channels formed by top and bottom polydimethylsiloxane (PDMS) membranes and a middle polyester membrane with 3 µm pores. An ultrasound system is constructed with a waveform generator, amplifier, and 1MHz ultrasound transducer. A 0.5 MHz receiving transducer and a digital storage oscilloscope are used for stable cavitation monitoring. Nanobubbles (FUS Instruments) transduce the LIFU into a mechanical vibration force to disrupt the BBB. To deliver the ultrasonic waves, the device is submerged in degassed DI water in a custom tank. Fluid flow was achieved, and subharmonic ultrasound signal is observed using the digital oscilloscope with Fast Fourier Transform (FFT). Preliminary results convey stable cavitation with LIFU and the formation of tight junctions in a brain microvascular endothelial cell monolayer in the device, eventually leading to a versatile platform to evaluate genetic-based vulnerability of the BBB.

Citation Format: Jayashree Iyer, Adam Akkad, Nanyun Tang, Michael E. Berens, Frederic Zenhausern, Jian Gu. Building an in vitro blood brain barrier model to test the influence of tight junction gene alleles on disruption by focused ultrasound to treat brain tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2984.

An evaluation of assumptions underlying respondent-driven sampling and the social contexts of sexual and gender minority youth participating in HIV clinical trials in the United States

Introduction:

Respondent-driven sampling has been an effective sampling strategy for HIV research in many settings, but has had limited success among some youth in the United States. We evaluated a modified RDS approach for sampling Black and Latinx sexual and gender minority youth (BLSGMY) and evaluates how lived experiences and social contexts of BLSGMY youth may impact traditional RDS assumptions.

Methods:

RDS was implemented in three cities to engage BLSGMY in HIV prevention or care intervention trials. RDS was modified to include targeted seed recruitment from venues, internet, and health clinics, and provided options for electronic or paper coupons. Qualitative interviews were conducted among a sub-sample of RDS participants to explore their experiences with RDS. Interviews were coded using RDS assumptions as an analytic framework.

Results:

Between August 2017 and October 2019, 405 participants were enrolled, 1,670 coupons were distributed, with 133 returned, yielding a 0.079 return rate. The maximum recruitment depth was 4 waves among seeds that propagated. Self-reported median network size was 5 (IQR 2–10) and reduced to 3 (IQR 1–5) when asked how many peers were seen in the past 30 days. Qualitative interviews (n=27) revealed that small social networks, peer trust, and targeted referral of peers with certain characteristics challenged network, random recruitment, and reciprocity assumptions of RDS. HIV stigma and research hesitancy were barriers to participation and peer referral.

Conclusions:

Small social networks and varying relationships with peers among BLSGMY challenge assumptions that underlie traditional RDS. Modified RDS approaches, including those that incorporate social media, may support recruitment for community-based research but may challenge assumptions of reciprocal relationships. Research hesitancy and situational barriers must be addressed in recruitment and study designs.

The sacrospinous ligament: conveniently effective or effectively convenient?

The sacrospinous ligament has been used for over 50 years as a convenient structure for treating vaginal vault and more recently, uterine prolapse. The procedure has evolved over the years and its efficacy has been hotly debated with invariable comparisons made to abdominal sacral colpopexy. Mesh surgery has introduced a newer dimension to the debate. This review is an attempt to clarify the anatomy, reflect on various techniques and offer a critique on the current 'status' of the sacrospinous ligament.

Inhibition of N-myc expression and induction of apoptosis by iron chelation in human neuroblastoma cells

Neuroblastoma is the second most common solid malignancy of childhood. Enhanced expression of the amplified N-myc gene in the tumor cells may be associated with poor patient prognosis and may contribute to tumor development and progression. The use of deferoxamine mesylate (DFO), an iron chelator, to treat neuroblastoma is being investigated in national clinical studies. We show here by TUNEL assay and DNA laddering that DFO induces apoptosis in cultured human neuroblastoma cells, which is preceded by a decrease in the expression of N-myc and the altered expression of some other oncogenes (up-regulating c-fos and down-regulating c-myb) but not housekeeping genes. The decrease in N-myc expression is iron-specific but does not result from inhibition of ribonucleotide reductase, because specific inhibition of this iron-containing enzyme by hydroxyurea does not affect N-myc protein levels. Nuclear run-on and transient reporter gene expression experiments show that the decrease in N-myc expression occurs at the level of initiation of transcription and by inhibiting N-myc promoter activity. Comparison across neuroblastoma cell lines of the amount of residual cellular N-myc protein with the extent of apoptosis measured as pan-caspase activity after 48 h of iron chelation reveals no correlation, suggesting that the decrease in N-myc expression is unlikely to mediate apoptosis. In conclusion, chelation of cellular iron by DFO may alter the expression of multiple genes affecting the malignant phenotype by multiple pathways. Given the clinical importance of N-myc overexpression in neuroblastoma malignancy, decreasing N-myc expression by DFO might be useful as an adjunct to current

Versatile copurification procedure for rapid isolation of homogeneous RAR-RXR heterodimers

RAR-RXR heterodimeric complexes (RARalphaDeltaAB-RXRalphaDeltaAB) bound to cognate DR5 DNA response elements were purified to apparent structural and functional homogeneity using a novel versatile immobilized metal affinity chromatography (IMAC) copurification procedure. Dynamic light scattering studies indicated that the complexes were more than 85% monodisperse. By electron microscopy the negatively stained RAR-RXR-DNA complexes appeared homogeneous and corresponded to a dimeric arrangement of the molecules. Using heterodimers purified according to this procedure we demonstrate ligand binding of RXR in the context of the RAR-RXR heterodimer-DNA complex. The present copurification procedure is rapid and has yielded high quality heterodimer-DNA complexes suitable for both structural and biochemical studies.

Ligand- and DNA-induced dissociation of RXR tetramers

Unliganded bacterially expressed RXR alpha lacking the N-terminal region AB (apo-RXR alpha delta AB) was found in solution as an apparent mixture of 165 kDa tetramers and 42 kDa monomers which could be quantitatively separated by gel filtration and non-denaturing gel electrophoresis. Under identical conditions both liganded (holo-) and apo-RAR alpha delta AB were present as single monomeric species. apo-RXR alpha delta AB tetramers, as well as dimers of the apo-RXR ligand binding domain (apo-LBD), dissociated readily into monomers when exposed to their cognate ligand 9-cis retinoic acid (9c-RA). The apo-RXR alpha delta AB tetramer bound only transiently to a cognate DR1 response element, and was converted into DR1-apo-RXR alpha delta AB homodimer complexes indistinguishable from those generated by cooperative DNA binding of apo-RXR alpha delta AB monomers. In the absence of DNA, the addition of 9c-RA greatly accelerated the formation of heterodimers with the apo-RAR alpha delta AB heterodimerization partner. No RXR alpha delta AB or RAR alpha delta AB homodimers could be observed in solution, but upon mixing of the two receptor monomers stable heterodimers could be isolated which bound to DR5 response elements in a highly cooperative manner. In these heterodimers, RXR alpha delta AB interacted with its cognate ligand as efficiently as in RXR alpha delta AB homodimers. The presence of ligand did not alter the stability of RXR alpha delta AB homodimer or RXR alpha delta AB-RAR alpha delta AB heterodimer complexes on DR1 and DR5 response elements, respectively. These in vitro data support a model in which RXR tetramers could serve as an inactive pool with the dual function of: (i) rapidly supplying large amounts of RXR heterodimerization partners upon 9c-RA generation; and (ii) allowing RXR homodimer formation on "accessible" cognate response elements in the absence of 9c-RA. These events may represent a ligand-dependent regulatory mechanism controlling the availability of the promiscuous RXR dimerization partner that is engaged in multiple nuclear receptor signalling pathways.

An 80,000-kd glycoprotein cell surface antigen found only on nonhematopoietic cells in human bone marrow

The murine IgG2a monoclonal antibody (MoAb) 6-19 binds to the surface of human nonhematopoietic cells but not to hematopoietic cells. As previously described, it can be used with complement to selectively kill nonhematopoietic cells prior to culture of human bone marrow. It is now shown that the 6-19 MoAb recognizes a specific antigenic determinant of apparent molecular mass 80 kd, detected by western blotting on nonhematopoietic tumor cell lines, endothelial cells, and bone marrow stromal cells. Mouse L cells were transfected with human DNA, and the 6-19 monoclonal antibody selected cells that expressed an antigen with similar characteristics. The antigenic determinant is absent in hematopoietic tumor cell lines, peripheral blood cells, and bone marrow hematopoietic cells. Investigation of the biochemical nature of the antigen, using various enzymes, lectin-binding studies, and western blotting suggests that the 6-19 epitope is at least partially carbohydrate and that the protein has N-linked sugars but not O-linked. The affinity (Ka approximately 10(9) M-1) of MoAb 6-19 binding is similar in tumor cells and normal fibroblasts and endothelial cells. The identification of a specific antigenic determinant of 80 kd may help to discriminate between hematopoietic and nonhematopoietic cells in human bone marrow.

Partial reversion of the transformed phenotype in HRAS-transfected tumorigenic cells by transfer of a human gene

The transformed phenotype of rat FE-8 cells transfected by an activated human HRAS gene was suppressed upon fusion with normal cells. An experimental approach was developed to identify and isolate a human gene capable of suppressing the transforming activity of the HRAS oncogene in FE-8 cells. Genomic DNA from human placenta was introduced into FE-8 cells by cotransfection with the plasmid pY3 conferring hygromycin B resistance. Transfectants were selected in medium containing hygromycin B. HRAS-transformed FE-8 cells showed an increased sensitivity toward ouabain when compared to their normal counterparts. Therefore, the population of transfected hygromycin B-resistant cells was treated with ouabain to eliminate cells with a transformed phenotype. Ouabain selection resulted in a small number of cell clones exhibiting a more normal phenotype. The clones had lost the morphology of transformed cells and required anchorage for growth. The tumorigenicity of transfectants in nude mice was reduced but not completely abolished. FE-8 revertants continued to express the p21 RAS protein. Human repetitive sequences contained in the DNA of a secondary transfectant were used for isolation of the suppressor gene from reverted FE-8 cells. The cloned DNA fragment was transfected into tumorigenic FE-8 cells and conferred a partial reversion of the transformed phenotype.

Production and characterization of monoclonal antibodies against human neuroblastoma

MAb were derived from mice immunized with cells of the human neuroblastoma line IMR-32. Five hybridomas were selected according to their selective binding to human cell lines, tumors and normal tissues. One of them, CE7, reacted with all sympatho-adrenomedullary cells (neuroblastoma, ganglioneuroblastoma, ganglioneuroma, pheochromocytoma, adrenal medulla, sympathetic ganglion cells). Weak cross-reactivities were observed with melanocytes and with some human melanoma and glioma cell lines. The antigen recognized by CE7 was markedly expressed on neuroblastoma tumors of all histological grades, independently of the adrenergic or cholinergic nature of these cells. MAb derived from clones AD2, BC1, BC4 and CB10 bound variably to some, but not to all, neuroblastoma cells. By using these MAb, 3 phenotypes of neuroblastoma lines could be distinguished. The binding profiles of these types, however, showed no correlation with origin of the cell lines or stage of the disease.