Enhancement of implant osseointegration by high-frequency low-magnitude loading

Background

Mechanical loading is known to play an important role in bone remodelling. This study aimed to evaluate the effect of high- and low-frequency axial loading, applied directly to the implant, on peri-implant bone healing and implant osseointegration.

Methodology

Titanium implants were bilaterally installed in rat tibiae. For every animal, one implant was loaded (test) while the other one was not (control). The test implants were randomly divided into 8 groups according to 4 loading regimes and 2 experimental periods (1 and 4 weeks). The loaded implants were subject to an axial displacement. Within the high- (HF, 40 Hz) or low-frequency (LF, 8 Hz) loading category, the displacements varied 2-fold and were ranked as low- or high-magnitude (LM, HM), respectively. The strain rate amplitudes were kept constant between the two frequency groups. This resulted in the following 4 loading regimes: 1) HF-LM, 40 Hz-8 µm; 2) HF-HM, 40 Hz-16 µm; 3) LF-LM, 8 Hz-41 µm; 4) LF-HM, 8 Hz-82 µm. The tissue samples were processed for resin embedding and subjected to histological and histomorphometrical analyses. Data were analyzed statistically with the significance set at p<0.05.

Principal Findings

After loading for 4 weeks, HF-LM loading (40 Hz-8 µm) induced more bone-to-implant contact (BIC) at the level of the cortex compared to its unloaded control. No significant effect of the four loading regimes on the peri-implant bone fraction (BF) was found in the 2 experimental periods.

Conclusions

The stimulatory effect of immediate implant loading on bone-to-implant contact was only observed in case of high-frequency (40 Hz) low-magnitude (8 µm) loading. The applied load regimes failed to influence the peri-implant bone mass.     

Oxidative effects of inorganic and organic contaminants on haemolymph of mussels

We applied a newly-established method in haemolymph of mussels, Mytilus galloprovincialis, exposed to different concentrations of heavy metals, such as zinc and cadmium and organic pollutants, such as PAHs and lindane, for the detection of total antioxidant capacity (TAC). The susceptibility of exposed mussels was increased in relation to oxidative stress induced by contaminants tested. Oxidative modifications of proteins were estimated by measuring protein carbonyl content (PCC) and malondialdehyde levels (MDA). For PCC measurement, a highly sensitive and accurate ELISA method, which requires only 5 µg of protein, was used. The significant increase of PCC and MDA in haemolymph of exposed mussels reinforces its role as biomarkers of oxidative stress. Significant correlation of TAC assay, PCC and MDA was conducted in order to evaluate the utility of PCC and TAC assay, used in the present study, as tools for determining oxidative effects of pollutants in mussels. The results reinforce the application of PCC method as useful tool for the determination of PCC alterations in haemolymph of mussels exposed to different levels of contaminants. In addition, the TAC method gives encouraging results, concerning its ability to predict antioxidant efficiency in haemolymph of mussels exposed to inorganic and organic contaminants.     

Align-m--a new algorithm for multiple alignment of highly divergent sequences

MOTIVATION: Multiple alignment of highly divergent sequences is a challenging problem for which available programs tend to show poor performance. Generally, this is due to a scoring function that does not describe biological reality accurately enough or a heuristic that cannot explore solution space efficiently enough. In this respect, we present a new program, Align-m, that uses a non-progressive local approach to guide a global alignment. RESULTS: Two large test sets were used that represent the entire SCOP classification and cover sequence similarities between 0 and 50% identity. Performance was compared with the publicly available algorithms ClustalW, T-Coffee and DiAlign. In general, Align-m has comparable or slightly higher accuracy in terms of correctly aligned residues, especially for distantly related sequences. Importantly, it aligns much fewer residues incorrectly, with average differences of over 15% compared with some of the other algorithms. AVAILABILITY: Align-m and the test sets are available at http://bioinformatics.vub.ac.be     

Seasonal and Habitat Variability in the Fungal Pathogens, Neozygites cf. floridana and Hirsutella thompsonii, Associated with Cassava Mites in Benin, West Africa

A survey of the pathogenic fungi associated with mites on cassava in Benin, West Africa, revealed both geographical and seasonal variation in the presence of Neozygites cf. floridana (Weiser and Muma) and Hirsutella thompsonii Fisher on Mononychellus tanajoa (Bondar) and Oligonychus gossypii (Zacher). Few dead and infected mites were found during the dry season, regardless of vegetation zone. In three of 30 surveyed sites, N. floridana was found infecting 1% of the dead M. tanajoa and 2% of the dead O. gossypii, while H. thompsonii was observed infecting 20% of the dead M. tanajoa in a single site. The frequency of sites having infected mites during the wet season was 3.5 times greater than that seen during the dry season. N. floridana infected 10% of the dead M. tanajoa and 19% of the dead O. gossypii on young leaves. Mites infected with N. floridana were found either in the coastal Southern Forest Mosaic (SFM) or in the Northern Guinea Savanna vegetation zones. N. floridana was rare in the low mite densities associated with mature leaves. H. thompsonii was found on 19% and 29% of the dead M. tanajoa on young and mature leaves respectively. All M. tanajoa infected with H. thompsonii on young leaves and mature leaves (75%) were found in the SFM. A single M. tanajoa was the only infected mite found in the Southern Guinea Savanna. Relatively few O. gossypii were infected with H. thompsonii. N. floridana and H. thompsonii were found together in three sites, but never on the same host. Phytoseiids were never found infected with either pathogen. In a regression analysis, the number of dead mites was significantly estimated from the total number of mites for both species, regardless of leaf age. The numbers of dead M. tanajoa on mature leaves were also estimated from the proportion infected with H. thompsonii. The numbers of infected mites on young leaves were estimated from their association with the SFM for M. tanajoa infected with H. thompsonii, and from total mites for O. gossypii infected with N. floridana. On mature leaves, infected mite numbers were estimated from the numbers of dead M. tanajoa infected with H. thompsonii. The merit of introducing more virulent or better adapted isolates of N. floridana to control M. tanajoa in Africa is discussed.     

Adipose tissue in offspring of Lepr(db/+) mice: early-life environment vs. genotype

Gravidas with obesity and diabetes ("diabesity") may transmit this syndrome to their children through genetic and nongenetic mechanisms. Here, we used the Lepr(db/+) diabese mouse to examine the magnitude of these transmission modes, focusing on adipose tissue (AT). We compared the following six groups: wild-type (+/+) offspring from +/+ or db/+ dams (different early life environment) and db/+ offspring from db/+ dams, fed a standard or high-fat diet. Weight gain (0-8 wk) was higher in +/+ offspring from db/+ vs. +/+ mothers, and even higher in db/+ vs. +/+ offspring from db/+ mothers. In addition, we observed a stepwise increase in AT and adipocyte size in +/+ from +/+ mice, +/+ from db/+ mice, and db/+ mice at 8 wk. Differences in weight and adiposity between +/+ offspring from db/+ vs. +/+ dams were more pronounced in males than in females. Leptin and apelin mRNA levels in white and brown AT were higher in +/+ offspring from db/+ vs. +/+ dams; however, leptin, apelin, and tumor necrosis factor-alpha expression were boosted more robustly in db/+ offspring. The high-fat diet amplified AT differences between db/+ vs. +/+ offspring from db/+ dams, but not between +/+ offspring from db/+ vs. +/+ dams. Moreover, db/+ but not +/+ offspring from db/+ mothers were insulin-resistant and hyperinsulinemic after a glucose challenge. In conclusion, the genetic transmission of the diabesity phenotype clearly prevailed, but the early-life diabesity environment had discernible effects on postnatal weight gain as well as on adipocyte size and adipokine expression at a postpubertal age.     

Spatial patterns of a savanna palm tree Borassus aethiopum and its temporal variability

The spatial distributions and associations of plant species in a stand can provide essential information about their dynamics. However, since tree spatial distribution and association depend on factors that operate at different scales, disentangling the effects of environmental heterogeneity and plant–plant interactions requires the choice of a suitable null model for spatial analysis. We analyzed the spatial distributions of the same savanna palm tree populations that were studied, the underlying hypothesis being that these distributions have changed in 20 years. To remove the effect of large-scale environmental heterogeneity, the inhomogeneous L-function under the heterogeneous Poisson null model was used. We showed: (i) unlike 20 years ago, adults had a regular distribution instead of an aggregated distribution in the grass savanna; (ii) although the spatial distribution of seedlings and juveniles was always aggregated, we observed a decrease in the size of the aggregates (intensities); (iii) except for juveniles, no other stages were associated with nutrient-rich patches, which was also different 20 years ago; (iv) we did not observe any particular difference in structure between two study sites, only that female palm trees were spatially associated with entire-leafed seedlings in the reserve while they were spatially independent in the rural area. Our study supports the hypothesis that the spatial distributions have partially changed, and that the management of spatial heterogeneity has improved and given more precision in the results.     

Transformation of Gram-positive microorganisms with the Gram-negative broad-host-range cosmid vector pJRD215

Abstract In an in vitro direct assay with tissue-type plasminogen activator (tPA), plasminogen and the chromogenic substrate S-2251, the ability of Mycoplasma fermentans KL4 to stimulate tPA-mediated activation of plasminogen to plasmin was studied. Mycoplasma cells markedly enhanced the activation of plasminogen by tPA in a concentration-, temperature- and pH-dependent manner. Nonidet P-40 (0.01%), sonication, and freezing and thawing of the cells substantially increased the stimulatory effect of mycoplasma on tPA activity. In contrast, the activation of plasminogen by urokinase was refractory to mycoplasma cells. The mycoplasma-mediated stimulation of tPA activity was prevented by ϵ-aminocaproic acid (EACA), a lysine analogue known to block lysine-binding sites (LBS) in plasminogen and tPA. Among several Mycoplasma fermentans strains tested, incognitus strain demonstrated the highest stimulation activity. These results suggest that mycoplasma cells interact with LBS in tPA and plasminogen to enhance plasminogen activation.