Evaluation of the wear and retention performance of a shape-memory alloy abutment system after 6 months of clinical use.

STATEMENT OF PROBLEM: A nitinol sleeve that uses shape memory to rapidly unlock dental restorations from implant abutments has been developed to allow prosthesis removal for assessment and maintenance, and clinical treatment has been promising. However, objective studies that evaluate the wear and retention performance after short-term clinical use are lacking. PURPOSE: The purpose of this clinical study was to evaluate the wear and retention performance of a shape-memory abutment system after 6 months of clinical use. MATERIAL AND METHODS: Shape-memory alloy sleeves on posterior osseointegrated implants were retrieved after 6 months of clinical use. Scanning electron microscopy (SEM) was used to evaluate the surfaces of the retention sleeve's arms for wear. Uniaxial tensile testing was performed to measure the change in retention force after clinical use. Average retention values of the shape-memory abutment system were compared with previously reported in vitro retention values for definitive and interim cements used in titanium abutment and coping assemblies by using the Welch t test. RESULTS: No evidence of wear, fracture, or chipping was observed during SEM analysis on the shape-memory alloy sleeves. Additionally, no statistically significant difference was found in the median retention force for new (484.5 N) and clinically retrieved (476 N) nitinol sleeve specimens. Compared with a commercially available resin cement, the mean retention force for the control sleeves (480 ±37 N) was higher than that for the freshly cemented specimens (336.3 ±188 N). After 5000 cycles of compressive loads, the mean retention force for cement specimens decreased (209.4 ±83 N), while the clinical sleeves (476 ±50 N) remained unchanged. CONCLUSIONS: According to the results of this study, after 6 months of clinical use, the engaging surfaces of the shape-memory alloy sleeve did not show signs of wear, and the retention force was unchanged.

Clinical application of a shape memory implant abutment system.

An innovative abutment system has recently been developed to address the well-known limitations of screw- and cement-retained implant restorations. This abutment system offers retrievability by replacing the cement layer with a precision-engineered nickel-titanium sleeve that switches between shapes that lock and unlock the prosthesis. The avoidance of cement precludes cement-related periimplant complications, while the elimination of occlusal screw access holes may enable predictable control over occlusion and improve the structural integrity of the prosthesis. By eliminating the need for cement clean up, occlusal access closure, and occlusal adjustments after insertion, the dentist is afforded more time to attend to the patient's general needs. This paper describes the design rationale for and clinical treatment using this novel abutment system.

Imbalancing the DNA base excision repair pathway in the mitochondria; targeting and overexpressing N-methylpurine DNA glycosylase in mitochondria leads to enhanced cell killing.

The DNA base excision repair (BER) pathway is responsible for the repair of alkylation and oxidative DNA damage. The short-patch BER pathway, beginning with the simple glycosylase N-methylpurine DNA glycosylase (MPG), is responsible for the removal of damaged bases such as 3-methyladenine and 1,N(6)-ethenoadenine from the DNA after alkylation or oxidative DNA damage. The resulting apurinic site is further processed by the other members in the pathway, resulting in the insertion of the correct nucleotide. If apurinic sites accumulate, they are mutagenic and cytotoxic to the cell. To evaluate its efficacy in sensitizing breast cancer cells to chemotherapy, MPG has been overexpressed in the breast cancer cell line, MDA-MB231. With MPG overexpression, an increase in DNA damage and increased cytotoxicity to methyl methanesulfonate as well as increased apoptosis levels was observed in these cells. Because mitochondrial DNA has been shown to be more sensitive to DNA damage than nuclear DNA, a construct containing mitochondrial-targeted MPG using the human manganese superoxide dismutase mitochondrial-targeting sequence was made. Overexpression of the mitochondrially targeted MPG dramatically increased the breast cancer cells' sensitivity to methyl methanesulfonate. In conclusion, we believe that the increase in sensitivity to DNA damage by overexpression of nuclear MPG is because of an imbalance in the BER pathway, and an even greater increase in cell sensitivity is observed when mitochondrial DNA is targeted.

Selenomethionine induction of DNA repair response in human fibroblasts.

Selenium compounds have a long history in chemoprevention of mammary and colon cancers in rodent models. Selenium compounds are in current clinical trials, having shown promise in prevention of prostate and other human cancers. In human tissues, it has been estimated that each cell sustains approximately 10 000 potentially mutagenic (if not repaired) lesions per day due to endogenous DNA damage. Almost no studies have addressed the potential for selenium compounds to induce DNA repair, a potential mechanism for their cancer-preventive actions. We show that selenium in the form of selenomethionine induces a DNA repair response in normal human fibroblasts in vitro, and protects cells from DNA damage. We show a possible mechanism for the inducible DNA repair response, in which enhanced repair complex formation was observed in selenomethionine-treated cells.

Implication of p53 in base excision DNA repair: in vivo evidence.

The tumor suppressor p53 plays an important role in response to DNA damage, including DNA repair. One DNA repair pathway, nucleotide excision repair (NER), has been well-documented to be regulated by p53. It seemed probable that p53 may affect other DNA repair pathways. We employed matched isogenic pairs of cell lines, wild-type or p53-deficient, to investigate this question using methyl methanesulfonate (MMS), a base-damaging agent. Alkylation damage induced by MMS is repaired exclusively by the base excision repair (BER) pathway. Cells carrying mutant or no p53 genes exhibited slow BER of MMS-induced DNA damage, and exhibited MMS-sensitivity. One contributing factor is the abundance of DNA polymerase beta (beta-pol), an enzyme required for BER, which was almost absent in p53 mutant and p53-null cells. Our findings demonstrate an in vivo requirement for p53 in regulating the base excision repair response, a novel finding of great potential importance in understanding the DNA repair branch of the p53 pathway.

Characterization of a novel repetitive secretory protein specifically expressed in the modified salivary gland of Hydropsyche sp. (Trichoptera; Hydropsychidae).

Here, we report the cloning and characterization of a common salivary gland-specific gene, Nf-1, from late instar Hydropsyche sp. larvae, and show that the corresponding gene product is translated in the gland and secreted to the gland lumen. The deduced Nf-1 protein is primarily composed of five repetitive sequence units of 63-65 amino acids, and contains a putative signal sequence composed of 19 amino acids. Secreted Nf-1 (approximately 37 kDa) was localized to the gland lumen by Western blotting of gland and lumen fractions. Together, the structure, expression pattern and protein localization of Nf-1 indicate that this protein is likely to be a major component of the silk shields and nets produced by the aquatic insect, Trichoptera.

Current issues of selenium in cancer chemoprevention.

The element selenium (Se) was identified, nearly 40 years ago, as being essential in the nutrition of animals and humans. In addition, antitumorigenic effects of Se compounds have been described in a variety of in vitro and animal models, suggesting that supplemental Se in human diets may reduce cancer risk. Apparent mechanisms underlying the potential of Se compounds as cancer chemopreventive agents have been suggested. Some recent clinical trials, however, have shed doubt on the anticancer effects of Se. The contradictory findings and consequent controversy might be due to the lack of understanding of the mechanisms underlying Se biology. This article reviews current knowledge on this topic and addresses the disparate viewpoints on the chemopreventive effects of Se, the human populations.

Enhancement of methyl methanesulfonate-induced base excision repair in the presence of selenomethionine on p53-dependent pathway.

Selenomethionine (SeMet) has been identified as a chemopreventive antioxidant to activate p53-mediated nucleotide excision repair. In this study, we examined whether p53-mediated base excision repair (BER) might be induced by SeMet. When methyl methanesulfonate, a BER-inducing agent, was treated in the cells, DNA damage was rapidly decreased in the presence of SeMet. In addition, our data showed that the removal of apurinic/apyrimidinic sites was significantly enhanced in the presence of SeMet. Furthermore, we observed that the expression of gadd45a, known to involve BER as one of the p53 downstream genes, was increased by SeMet in p53 wild-type RKO cells. Those results supported the proposal that BER activity might be dependent on wild-type p53 under the modulation of gadd45a expression in response to SeMet. We suggested that p53-dependent BER activity as a distinct mechanism of SeMet might play an important role to prevent cancer caused by various oxidative stresses.

Protective effects of selenomethionine against ionizing radiation under the modulation of p53 tumor suppressor.

Ionizing radiation (IR) therapy has been widely employed in the treatment of cancer. However, certain issues, including toxicity, have been raised in conjunction with IR therapy for cancer. Recently, selenomethionine (SeMet) as an antioxidant has been the subject of a great deal of attention for its chemopreventive effects. In this study, we found that DNA repair activity has been enhanced in response to SeMet against IR. In addition, our data showed that p53 functional activity was significantly reduced against IR in the cells expressing a mutant form of redox factor 1 (Ref-1) contrast with Ref-1 wild-type cells treated with SeMet, suggesting that p53 activation under the modulation of Ref-1 might play an important role in IR-treated cells in the presence of SeMet. Furthermore, IR-induced micronuclei numbers were also reduced after treatment with SeMet, strongly implicating protection by SeMet in genomic stability against IR-induced genotoxicity. From this study, we suggest that the p53-mediated protective mechanism of SeMet might provide clues for reducing side effects of IR therapy.

Identification of up-regulated proteins in the hemolymph of immunized Bombyx mori larvae.

Insects defend themselves against foreign invaders via both a cellular response and a humoral response. The objective of this study was to identify proteins which were differently regulated in the immunized Bombyx mori larvae. Heat-inactivated bacteria (Bacillus megaterium) were injected into B. mori larvae, 4 days after final ecdysis. After 6 h, we identified the immune proteins in the hemolymph which had been differentially regulated in the immune-challenged larvae, using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and quadrupole time-of-flight (Q-TOF) tandem mass spectrometry (MS). After the bacterial injection, more than 30 spots determined to have been up-regulated, and 11 spots were down-regulated. The heat shock 70 kDa protein cognate was one of the up-regulated hemocytic proteins, and peptidoglycan recognition protein, antichymotrypsin precursor, and gloverin-like protein 1 approximately 4 were newly synthesized in the plasma. Antennal binding protein 7 was up-regulated in the plasma. Our results indicated that these immune response proteins were involved with the carrying out of innate immune responses.

p53 regulation of DNA excision repair pathways.

The regulation of DNA excision repair pathways by p53 and its downstream genes is an emerging body of literature, largely distinct and separable from the more-studied cell cycle arrest and apoptosis responses regulated by p53. Regulation of nucleotide excision repair of UV-damage by p53 and its downstream genes Gadd45 and p48XPE has been well-documented, but much remains to be done in elucidating mechanisms. Moreover, p53 also participates in base excision repair of hydrogen peroxide-induced damage, still at an early stage of investigation. In human cancers carrying inactivating mutations in p53, especially those wherein p53 mutation occurs early, accelerated mutagenesis by exogenous and endogenous DNA damage is predicted. At the same time, the excision repair pathways could provide a useful target for DNA-damaging chemotherapeutics against p53-defective cancers, having decreased ability to repair chemotherapeutic damage. To our knowledge, this is the first review to address this emerging field.

The protective effect of mild hyperthermia against UV-mimetic agent 4-nitroquinoline-1-oxide (4NQO) in human colon cells.

Hyperthermia-induced cellular response has been widely investigated for understanding cell physiology in stressful conditions as well as for therapeutic application using heat shock. In this study, the protective effect of mild hyperthermia-induced cellular response was investigated in RKO human colon cell lines, which harbor wild-type p53. Our data showed that the accumulation of p53 protein was induced without DNA damage in response to mild hyperthermia. Interestingly, the sub-lethal of heat shock at 40 degrees C for 30 minutes in RKO cells showed the protective effect against UV mimetic agent 4-nitroquinoline-1-oxide (4NQO) with the decrease in mitotic index, although other papers had shown the induction of apoptosis in RKO cells under the higher dose of heat stress. Thus, we suggest that the protective effect of sub-lethal heat shock might be applicable for a novel preventive approach to clinical applications of mild hyperthermia.

Elimination of methyl methanesulfonate (MMS)-induced micronuclei (MNS) under mild hyperthermia via p53-dependent pathway in human lymphoid cells.

P53-mediated cellular response has been known to play a crucial role in maintaining genomic stability of mammalian cells against genotoxic stresses. In our previous study, we showed that mild hyperthermia was sufficient to induce apoptosis on p53-dependent pathway in human lymphoid system (Seo et al., 1999), suggesting that mild hyperthermia might be useful for the reducing of genomic instability. However, there have been few reports to show the direct evidence on preventive role of p53 under mild hyperthermia against carcinogenic DNA damage. Here we first show the elimination of MMS-induced micronuclei (MN) as one of biomarkers of carcinogenic risk by p53 activation in human lymphoid cells in response to mild hyperthermia, strongly suggesting a possible protective role of mild hyperthermia in chromosomal stability against genotoxic stresses. Our data might support investigation of the clinical application of mild hyperthermia for the prevention of carcinogenesise in the human lymphoid system.

Selenomethionine regulation of p53 by a ref1-dependent redox mechanism.

The cancer chemopreventive properties of selenium compounds are well documented, yet little is known of the mechanism(s) by which these agents inhibit carcinogenesis. We show that selenium in the form of selenomethionine (SeMet) can activate the p53 tumor suppressor protein by a redox mechanism that requires the redox factor Ref1. Assays to measure direct reduction/oxidation of p53 showed a SeMet-dependent response that was blocked by a dominant-negative Ref1. By using a peptide containing only p53 cysteine residues 275 and 277, we demonstrate the importance of these residues in the SeMet-induced response. SeMet induced sequence-specific DNA binding and transactivation by p53. Finally, cellular responses to SeMet were determined in mouse embryo fibroblasts wild-type or null for p53 genes. The evidence suggests that the DNA repair branch of the p53 pathway was activated. The central relevance of DNA repair to cancer prevention is discussed.

Sensitivity of p53-deficient cells to oxaliplatin and thio-TEPA (N, N', N" triethylenethiophosphoramide).

P53 is known as a determinant of cellular responses to DNA damage, including apoptosis, cell cycle arrest, and DNA repair. Its role is most easily understood in the context of Burkitt lymphoma and other apoptosis-prone cell types. A number of epithelial cancer cell types, by contrast, exhibit a higher threshold for apoptosis induction in response to DNA damage. In fact, p53 mediates DNA repair and protective responses in the latter cell types, in some cases p53-deficient cells being more sensitive to DNA damage, antithetical to the situation in Burkitt lymphoma and other apoptosis-prone cell types. Ultraviolet light, cisplatin, and nitrogen mustards produce damage that is repaired by a p53-regulated pathway. Here, we explore the sensitivity of the platinum compound oxaliplatin and thio-TEPA (N, N', N", triethylenethiophosphoramide), a cancer chemotherapeutic agent that produces largely base damage, in p53-defective cells. This work demonstrates that the contribution of p53 temporally correlates with DNA repair pathways to produce a resistant phenotype, while the p53-defective cells are more sensitive to certain DNA-damaging chemotherapeutic agents.