Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Comparison of PvLAP5 and Pvs25 qRT-PCR assays for the detection of Plasmodium vivax gametocytes in field samples preserved at ambient temperature from remote malaria endemic regions of Panama

BACKGROUND

As the elimination of malaria in Mesoamerica progresses, detection of Plasmodium vivax using light microscopy (LM) becomes more difficult. Highly sensitive molecular tools have been developed to help determine the hidden reservoir of malaria transmission in low transmission settings. In this study we compare the performance of PvLAP5 and Pvs25 qRT-PCR assays to LM for the detection of Plasmodium vivax gametocytes in field samples preserved at ambient temperature from malaria endemic regions of Panama.

METHODS

For this purpose, we collected a total of 83 malaria field samples during 2017-2020 preserved in RNAprotect (RNAp) of which 63 (76%) were confirmed P. vivax by LM and selected for further analysis. Additionally, 16 blood samples from local healthy malaria smear negative volunteers, as well as, from 15 malaria naïve lab-bred Aotus monkeys were used as controls. To optimize the assays, we first determined the minimum blood volume sufficient for detection of PvLAP5 and Pv18SrRNA using P. vivax infected Aotus blood that was preserved in RNAp and kept either at ambient temperature for up to 8 days before freezing or was snap-frozen at -80° Celsius at the time of bleeding. We then compared the mean differences in gametocyte detection rates of both qRT-PCR assays to LM and performed a multivariate correlation analysis of study variables. Finally, we determined the sensitivity (Se) and specificity (Sp) of the assays at detecting gametocytes compared to LM.

RESULTS

Blood volume optimization indicated that a blood volume of at least 60 μL was sufficient for detection of PvLAP5 and Pv18SrRNA and no significant differences were found between RNA storage conditions. Both PvLAP5 and Pvs25 qRT-PCR assays showed a 37-39% increase in gametocyte detection rate compared to LM respectively. Strong positive correlations were found between gametocytemia and parasitemia and both PvLAP5 and Pvs25 gametocyte markers. However, no significant differences were detected in the Se and Sp of the Pvs25 and PvLAP5 qRT-PCR assays, even though data from control samples suggested Pvs25 to be more abundant than PvLAP5.

CONCLUSIONS

This study shows that the PvLAP5 qRT-PCR assay is as Se and Sp as the gold standard Pvs25 assay and is at least 37% more sensitive than LM at detecting P. vivax gametocytes in field samples preserved in RNAp at ambient temperature from malaria endemic regions of Panama.

AUTHOR SUMMARY

Plasmodium vivax is one of the five species of malaria (P. falciparum, P. malariae, P. ovale and P. knowlesi) that are transmitted to man by the bite of female anopheles mosquitoes. It causes ~14.3 million cases mainly in Southeast Asia, India, the Western Pacific and the Americas annually. In the Americas, malaria remains a major problem in underdeveloped areas and indigenous communities in the Amazon region and eastern Panama, where it is endemic and difficult to eliminate. As malaria elimination progresses, detection of P. vivax by light microscopy (LM) becomes more difficult. Therefore, highly sensitive molecular tools have been developed that use genetic markers for the parasite to help determine the hidden reservoir of malaria transmission. This study compares the performance of two molecular assays based on the genetic markers of mature gametocytes PvLAP5 and Pvs25 with LM. The study shows that the PvLAP5 qRT-PCR assay is as sensitive and specific as the gold standard Pvs25 assay and is at least 37% more sensitive than LM at detecting P. vivax gametocytes. These data suggest that the PvLAP5 qRT-PCR assay can be a useful tool to help determine the hidden reservoir of transmission in endemic foci approaching elimination.

Population genomics of Plasmodium vivax in Panama to assess the risk of case importation on malaria elimination

Malaria incidence in Panama has plateaued in recent years in spite of elimination efforts, with almost all cases caused by Plasmodium vivax. Notwithstanding, overall malaria prevalence remains low (fewer than 1 case per 1000 persons). We used selective whole genome amplification to sequence 59 P. vivax samples from Panama. The P. vivax samples were collected from two periods (2007-2009 and 2017-2019) to study the population structure and transmission dynamics of the parasite. Imported cases resulting from increased levels of human migration could threaten malaria elimination prospects, and four of the samples evaluated came from individuals with travel history. We explored patterns of recent common ancestry among the samples and observed that a highly genetically related lineage (termed CL1) was dominant among the samples (47 out of 59 samples with good sequencing coverage), spanning the entire period of the collection (2007-2019) and all regions of the country. We also found a second, smaller clonal lineage (termed CL2) of four parasites collected between 2017 and 2019. To explore the regional context of Panamanian P. vivax we conducted principal components analysis and constructed a neighbor-joining tree using these samples and samples collected worldwide from a previous study. Three of the four samples with travel history clustered with samples collected from their suspected country of origin (consistent with importation), while one appears to have been a result of local transmission. The small number of Panamanian P. vivax samples not belonging to either CL1 or CL2 clustered with samples collected from Colombia, suggesting they represent the genetically similar ancestral P. vivax population in Panama or were recently imported from Colombia. The low diversity we observe in Panama indicates that this parasite population has been previously subject to a severe bottleneck and may be eligible for elimination. Additionally, while we confirmed that P. vivax is imported to Panama from diverse geographic locations, the lack of impact from imported cases on the overall parasite population genomic profile suggests that onward transmission from such cases is limited and that imported cases may not presently pose a major barrier to elimination.

Sexual Risk Behaviors Associated with Sexually Transmitted Infections in a US Military Population Living with HIV After the Repeal of "Don't Ask, Don't Tell"

Risk behaviors associated with sexually transmitted infections (STIs) among people living with HIV (PLWH) have not been well characterized in the US military. We identified risk behaviors associated with a new STI in this population after the repeal of "Don't Ask, Don't Tell." US Military HIV Natural History Study participants who completed the risk behavior questionnaire (RBQ) between 2014 and 2017 and had at least 1 year of follow-up were included (n = 1589). Logistic regression identified behaviors associated with incident STI in the year following RBQ completion. Overall, 18.9% acquired an STI and 52.7% reported condom use at last sexual encounter. Compared with those with no new sex partners, participants with between one and four or five or more new partners were 1.71 [1.25-2.35] and 6.12 [3.47-10.79] times more likely to get an STI, respectively. Individuals reporting low or medium/high perceived risk of STI were 1.83 [1.23-2.72] and 2.65 [1.70-4.15] times more likely to acquire a new STI than those reporting no perceived risk, respectively. Participants who preferred not to answer about sexual preference, number of new partners, or perceived STI risk were also more likely to acquire a new STI. Our study illustrates that despite regular access to health care and accurate perceptions of risk, rates of STI among PLWH remain high in the US military setting, as in others. Given the potential individual and public health consequences of STI coinfection after HIV, more work is needed to assess interventions aimed at sexual behavior change for PLWH.

Suitability of 3D printed pieces of nanocrystalline zirconia for dental applications

OBJECTIVES

The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications.

METHODS

The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating.

RESULTS

AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps' wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples.

SIGNIFICANCE

Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.

Known heat-shock proteins are not responsible for stress-induced rapid degradation of ribosomal protein mRNAs in yeast

We have previously shown that the heat-induced enhanced decay of yeast mRNAs encoding ribosomal proteins (rp-mRNAs) requires ongoing transcription during the heat treatment [Herruer et al. (1988) Nucl. Acids Res. 16, 7917]. In order to determine whether this requirement reflects the need for heat-shock protein (hsp), we analysed the effect of heat shock on rp-mRNA levels in several yeast strains in which each of the heat-shock genes encoding hsp26, hsp35 or hsp83 had been individually disrupted. In all three strains we still observed increased degradation of rp-mRNAs immediately after the temperature shift, demonstrating that hsp26, hsp35 and hsp83 are not required for this effect. Accelerated turnover of rp-mRNA was also found to occur upon raising the growth temperature of a mutant strain that contains a disruption of the gene specifying the heat-shock transcription factor and in wild-type yeast cells treated with canavanine, an arginine analogue that will be incorporated into all known hsps and that is known to cause misfolding of the polypeptide chain. Latter observation suggests that enhanced rp-mRNA decay is a more general stress-related phenomenon. Taken together, these data strongly indicate that the trans-acting factor required for the increase in the rate of degradation of rp-mRNAs upon stress is not one of the known yeast hsps.

Different patterns of expression of beta-tubulin genes in Tetrahymena pyriformis during reciliation

The ciliate Tetrahymena pyriformis contains one alpha-tubulin (alpha TT) and two beta-tubulin (beta TT1 and beta TT2) genes. The specific expression of these genes was investigated by Northern blot hybridization using oligonucleotide probes complementary to beta TT1 and beta TT2 genes and the coding region of the alpha-tubulin gene. The three genes are expressed producing 1.8-kb mRNAs but the level of beta TT1 mRNA is much higher than that of beta TT2 mRNA. During cilia regeneration, we found that the expression patterns of the alpha TT and beta TT1 genes are similar whereas that of the beta TT2 gene is different. The alpha TT and beta TT1 transcripts reached higher values between 60-120 min after the onset of reciliation than in exponentially growing cells, while beta TT2 transcripts were maintained at low levels during the whole period. The differences in the amounts of steady-state populations of the both beta-tubulin mRNAs do not correspond to the copy number per haploid genome. These differences could result from the fact that the promoter region of beta TT2 may contain highly structured sequences which would affect the binding of the respective trans-acting factor(s). The apparent transcription rate revealed a significant increase at 15 min of reciliation which could be responsible for the high levels of alpha TT and beta TT1 transcripts in the cytoplasm between 60-120 min of reciliation. This coordinated response to cilia regeneration of the alpha TT and beta TT1 tubulin genes is also a relevant aspect of our findings. Several conserved motifs found in their promoter regions led us to think that some of them may function as cis-elements in the specific binding of nuclear protein factor(s).

Ubiquitin genes in Tetrahymena pyriformis and their expression during heat shock

The genome of Tetrahymena pyriformis was shown to contain a ubiquitin multigene family consisting of at least four polyubiquitin genes. Three genomic clones with different ubiquitin-coding sequences, were isolated and partially characterized. The complete nucleotide sequence of one of these clones (pTU2) was determined and showed two open reading frames (ORFs) at opposite ends of the cloned DNA insert. A comparison of the predicted amino acid (aa) sequence of T. pyriformis ubiquitin-coding unit with those from other organisms indicated a high degree of homology. However, Tetrahymena ubiquitin contained two aa substitutions at positions 16 (Asp) and 19 (Ala). Interestingly, the first pTU2 ORF showed two extra triplets coding for Ser and Gln, upstream from TGA. This feature is different from all the polyubiquitin genes thus far sequenced. Regions flanking the 3' and 5' ubiquitin-coding sequences presented several conserved motifs. The 5' flanking sequence of the second ORF of pTU2 contained one heat-shock element. We therefore studied the expression of the ubiquitin genes under stress conditions. The results showed that they are heat-inducible and that a new specific 1.6-kb mRNA appeared. These results suggest that the regulation of ubiquitin genes is important in T. pyriformis under thermal stress conditions.

Destabilization of tubulin mRNA during heat shock in Tetrahymena pyriformis

The regulation of tubulin gene expression was studied in Tetrahymena pyriformis cells during heat shock (shift from 28 degrees C to 34 degrees C). Fluorograms of two-dimensional gels of radiolabelled proteins synthesized during thermal stress revealed that tubulin synthesis is highly repressed when compared with that of exponentially growing cells. The variation in the levels of alpha and beta-tubulin mRNAs was analyzed by Northern-blot hybridization using homologous genomic probes (alpha TT and beta TT1). The results obtained show that heat shock induces a drastic and coordinate reduction in the amount of alpha and beta-tubulin mRNAs isolated from polysomes. This decrease is not due to a shift from the polysomes to the post-polysomal fraction because it was also observed when total cytoplasmic mRNAs were analyzed. Run-on transcription experiments were performed in order to examine whether repression of transcription in heat-shocked cells could explain that reduction. The results obtained show that the apparent rates of tubulin gene transcription are not significantly modified, but on the contrary increase slightly in cells heat-shocked for 15 min and 30 min. The effects of inhibitors of protein synthesis, cycloheximide and pactamycin, on the destabilization of tubulin mRNAs were tested in heat-shocked Tetrahymena cells. Our results revealed that in the presence of these inhibitors, tubulin mRNAs become more stable thus suggesting that an induced factor may be involved in the degradation of alpha and beta-tubulin mRNAs during heat shock.

Sequence of one alpha- and two beta-tubulin genes of Tetrahymena pyriformis. Structural and functional relationships with other eukaryotic tubulin genes

Macronuclear DNA of the ciliate Tetrahymena pyriformis contains only one size class of fragments coding for alpha-tubulin, alpha TT. We have isolated alpha TT from a partial plasmid library, using Chlamydomonas reinhardtii alpha-tubulin gene as a probe. This gene as well as the two beta-tubulin genes, beta TT1 and beta TT2, have been sequenced. None of these genes contains introns and all use TGA as the stop codon. In the coding region of the two beta-tubulin genes, there are several TAA and TAG stop codons that probably code for glutamine. The codon usage is very biased. Regions flanking the tubulin coding sequences are A + T-rich (75%) and quite different among themselves. In these regions there are several putative transcription-regulatory sequences. Nuclear transcripts begin and terminate at multiple sites. The beta-tubulin proteins differ only in two amino acid residues. Primary structure of Tetrahymena tubulins as well as their hydropathy indexes show a high degree of homology with tubulins from other organisms. Two-dimensional electrophoretic analysis of the ciliary tubulins shows the presence of eight alpha-tubulins and four beta-tubulins. The alpha-tubulins migrate faster than the beta-tubulins, in contrast with what happens with brain tubulins. We suggest that there are several alpha- and beta-tubulin isoforms and the migratory inversion observed may be due to post-translational modifications.

Response of Tetrahymena pyriformis to stress induced by starvation

mRNA synthesis was studied in exponentially growing and starved Tetrahymena pyriformis. Poly(A)-containing RNAs separated from total RNA by affinity chromatography on oligo(dT)-cellulose were characterized by poly acrylamide gel electrophoresis; their template activity was assayed in a rabbit reticulocyte lysate system and their translation products were analysed using two-dimensional electrophoresis according to O'Farrell. Polysome profiles show that the bulk of ribosomes are in 80S monosomes in starved cells, whereas less than 8% are present in the form of monosomes in exponentially growing cells, the rest being engaged in polysomes. Polysomes are almost completely reformed 30 min after addition of enriched medium to suspensions of starved cells. This polysome reformation is dependent on mRNA synthesis since we have shown that it is inhibited by actinomycin D. Electrophoretic profiles of poly(A)-rich RNA isolated from cytoplasmic fractions of exponential and starved cells are indistinguishable except that in the latter state significant amounts of low-molecular-mass species are observed. Poly(A)-rich RNAs isolated from polysomal and non-polysomal (subpolysomal) fractions of exponential cells are equally able to promote protein synthesis. The corresponding poly(A)-rich RNAs isolated from starved cells also possess equal template activities which are, however, 15% lower than those of the poly(A)-rich RNAs of exponentially growing cells. We also present evidence that in the system used in vitro, polyadenylated RNA isolated from heavy polysomes of starved cells directs the synthesis of four sets of proteins with molecular masses around 100 kDa, 70 kDa, 50 kDa and 30 kDa. The former two groups of proteins are more abundant in the translation products of poly(A)-rich RNA of starved than of normal cells, whereas the latter two groups are present only in the translation products of poly(A)-rich RNA of starved Cells. The fluorograms of the translation products obtained in vitro from subpolysomal poly(A)-rich RNA are identical to those obtained from polysomal poly(A)-rich RNA. Studies on starved cells in vivo show that polypeptides of 100 kDa, 70 kDa and 38 kDa are more strongly labelled and also revealed the specific presence of 85 kDa, 55 kDa, 50 kDa and 25 kDa proteins. These results lead us to the conclusion that this microorganism responds to depleted environmental conditions by regulating gene expression at the transcriptional level, but also at the translational level.

Site of tubulin synthesis in Tetrahymena pyriformis

Free and membrane-bound polysomes were isolated from the protozoa Tetrahymena pyriformis, and the contribution of these two types of polysomes to tubulin synthesis were studied using immunoprecipitation of the 35S-translational products in a rabbit reticulocyte lysate. One-dimensional electrophoretic analysis shows that tubulin is synthesized by polyadenylated RNA isolated from free and membrane-bound polysomes. Non-polyadenylated RNAs of free polysomes are also able to direct tubulin synthesis. Two-dimensional electrophoretic analysis using O'Farrell's system confirms these results and also reveals the existence of the alpha- and beta-tubulin subunits.

Protein synthesis directed by polyadenylated and non-polyadenylated RNA isolated from membrane-bound and free polysomes of Tetrahymena pyriformis

Free and membrane-bound polysomes were prepared from the protozoa Tetrahymena pyriformis using a procedure which gives good recovery and practically no cross-contamination. Polysomes are intact as analysed by sedimentation analysis. Poly(A)-rich RNA and poly(A)-free RNA, isolated from both populations of polysomes, show similar electrophoretic patterns. These RNAs were translated in the rabbit reticulocyte lysate cell-free system and the translation products were analysed by one-dimensional and two-dimensional gel electrophoresis. The most striking differences were found in the two-dimensional electrophoretic analysis namely: (a) a group of polypeptides (10) is synthesized mainly on membrane-bound polysomes, (b) a second abundant group is synthesized mainly in free polysomes (c) and a third class of polypeptides is synthesized on both kinds of polysomes. Poly(A)-free RNAs, isolated from free polysomes, are also able to promote synthesis of some polypeptides. The results are discussed taking into account the fact that T. pyriformis is a non-secretory cell.