Hydroxylapatite growth on single-crystal rutile substrates

Titanium is widely used as an implant material. In addition to the bulk properties of titanium, the biological response is to a large degree controlled via the surface. The native amorphous titanium oxide that forms spontaneously on the surface gives a very good biological response. Lately it has been shown that crystalline titanium oxides (rutile and anatase) have in vitro bioactive properties. In addition to its potential for new materials development, this finding also opens up for the possibility of studying the mechanisms of bioactivity on materials with strictly controlled surfaces. In this paper the mechanisms behind the in vitro bioactivity are studied, using rutile single crystals. Three single-crystal rutile substrates: (100), (110), and (001), and a polycrystalline rutile substrate obtained by physical vapour deposition were soaked in a phosphate buffered saline solution for up to 4 weeks. The hydroxylapatite films that formed were analysed by X-ray diffraction, scanning electron microscopy, focused ion beam, and transmission electron microscopy. The hydroxylapatite grew faster on the (001) surface than on the other two. It was also found that on the (001) surface the direction of fast growth in hydroxylapatite was aligned parallel to the surface. This is in contrast to the (110) rutile surface where the fast growth of the hydroxylapatite crystal was directed outwards from the surface. The (100) face had poor adhesion at the interface. The orientations of the precipitated crystallites play a significant role in the faster coverage of the (001) rutile face. Based on the experimental results, a model for the hydroxylapatite growth process is given.     

Role of polymorphic residues of human leucocyte antigen-DR molecules on the binding of human immunodeficiency virus peptides.

A study was made of the binding properties of 96 human immunodeficiency virus peptides to human leucocyte antigen (HLA)-DR1 and HLA-DR103 molecules, which differ by three amino acids at positions 67, 70 and 71 in the beta chains. The affinity of the peptides was characterized by their inhibitory concentrations in competitive binding assays which displace half of the labelled influenza haemagglutinin peptide HA306-318 (IC50). Among the high-affinity peptides (IC50 < or = 1 microM), seven bound to DR1, three to DR103 and five equally well to both alleles (promiscuous peptides). Thirty-two other peptides showed medium or low affinity for DR molecules. The role of polymorphic residues was analysed using six mutated DR molecules, intermediates between DR1 and DR103 and differing by one or two substitutions at positions 67, 70 or 71. We reached the same conclusions when using DR1-specific or DR103-specific peptides: modification of residue 70 had no effect on peptide affinity, but single substitution at positions 67 or 71 decreased the allele specificity of the peptides while double substitution at 67 and 71 completely reversed the peptide specificity. In functional assays, DR-binding peptides are able to outcompete specific T-cell proliferation. Furthermore, modification at position 67 or 70 significantly affects the T-cell response and mutation at position 71 abolishes completely the T-cell proliferation. Thus, the polymorphic positions 67 and 71 contributed to the peptide binding with direct effects on T-cell receptor (TCR) recognition while position 70 seems to be mostly engaged in TCR interactions. Furthermore, our results suggest that polymorphic residues may select allele-specific peptides and also influence the conformation of promiscuous peptides.     

Highly packed and aligned fluoride substituted hydroxyapatite via a surfactant-free process

Biomolecules and surfactants are believed to be the key factors for reconstruction of tooth enamel and preparation of fluoride hydroxyapatite coating with enamel-like structure on dental implants. We have developed an alternative surfactant-free biomimetic method to stimulate growth of fluoride substituted hydroxyapatite coatings with highly packed and aligned structure on metallic substrates. Oxidized titanium plates were chosen as the substrates. The biomimetic fluoride hydroxyapatite was prepared by immersing the pretreated Ti plates into the phosphate-buffered solution with Ca(2+), H(2)PO(4)(-), HPO(4)(2-), and F(-). The pH value was controlled at 7.4 at the beginning. Every titanium plate (10 mm × 10 mm × 1 mm) was soaked into 20 mL of ion doped phosphate buffered solution in sealed plastic bottles, kept at 37°C or 60°C without stirring for time periods of 1 day to 2 weeks. After immersion, the samples were removed from the solution, rinsed with deionized water and allowed to dry in air. The fluoride substituted hydroxyapatite layer, composed of needle-like crystallites with the diameter of 10-20 nm, was well-organized and tightly packed. XRD results showed a sharper and stronger (002) peak, which could be used to explain that there was a preferable orientation along the c axis. The coating could be reconstructed on the former layer if the mineralization process was repeated, and the structure of the coating could be preserved. The method could be used to construct well organized fluoride substitute hydroxyapatite coating on metal implants.     

Baseline C-reactive protein level as a predictor of mortality in bacteraemia patients: a population-based cohort study

We examined the association between C-reactive protein (CRP) level at time of blood culture (BC) draw and mortality following bacteraemia. Our population-based cohort study comprised all first-time monomicrobial bacteraemia episodes in adults in a Danish county during 1996–2004 (n = 5267). CRP was measured within 24 h of the first positive BC draw. Cox regression was used to compute mortality rate ratios (MRRs) associated with CRP level quartiles (10–64 (reference), 65–143, 144–240 and 241–688 mg/L), controlling for age, gender, comorbidity, specialty, acquisition of infection, and infection focus. We also looked for a biological interaction between CRP level and high magnitude of bacteraemia (three of three culture bottles positive). Thirty-day mortality increased with higher CRP level: adjusted 0–30-day MRRs for patients in the second, third and fourth CRP quartiles were 1.38 (95% CI 1.13–1.69), 1.70 (95% CI 1.40–2.06), and 2.38 (95% CI 1.96–2.87), respectively (p for trend <10⁾⁴). In contrast, mortality associations with CRP during 31–365 days of follow-up were weak (adjusted MRRs for the second to fourth quartiles ranged from 1.18 to 1.28). A high magnitude of bacteraemia strengthened the association between high CRP level and 30-day mortality. We conclude that the CRP level, measured concurrently with the first positive BC, independently predicted 30-day mortality in adult bacteraemia patients.     

Intramural Purkinje fibers facilitate rapid ventricular activation in the equine heart

Background

The Purkinje fibers convey the electrical impulses at much higher speed than the working myocardial cells. Thus, the distribution of the Purkinje network is of paramount importance for the timing and coordination of ventricular activation. The Purkinje fibers are found in the subendocardium of all species of mammals, but some mammals also possess an intramural Purkinje fiber network that provides for relatively instantaneous, burst-like activation of the entire ventricular wall, and gives rise to an rS configuration in lead II of the ECG.

Aim

To relate the topography of the horse heart and the distribution and histology of the conduction system to the pattern of ventricular activation as a mechanism for the unique electrical axis of the equine heart.

Methods

The morphology and distribution of the cardiac conduction system was determined by histochemistry. The electrical activity was measured using ECG in the Einthoven and orthogonal configuration.

Results

The long axis of the equine heart is close to vertical. Outside the nodal regions the conduction system consisted of Purkinje fibers connected by connexin 43 and long, slender parallel running transitional cells. The Purkinje fiber network extended deep into the ventricular walls. ECGs recorded in an orthogonal configuration revealed a mean electrical axis pointing in a cranial-to-left direction indicating ventricular activation in an apex-to-base direction.

Conclusion

The direction of the mean electrical axis in the equine heart is determined by the architecture of the intramural Purkinje network, rather than being a reflection of ventricular mass.     

The role of whole blood in thrombin generation in contact with various titanium surfaces

Understanding of the thrombotic response (activation of the intrinsic coagulation system followed by platelet activation) from blood components upon contact with a titanium dental implant is important and not fully understood. The aims of this study were to evaluate: (1) the thrombogenic response of whole blood, platelet-rich plasma (PRP) and platelet-poor plasma (PPP) in contact with a highly thrombogenic surface as titanium, (2) the thrombogenic response of clinically used surfaces as hydroxyapatite (HA), machined titanium (mTi), TiO2 grit-blasted titanium (TiOB) and fluoride ion-modified grit-blasted titanium (TiOB-F). An in vitro slide chamber model, furnished with heparin, was used in which whole blood, PRP or PPP came in contact with slides of the test surfaces. After incubation (60 min rotation at 22 rpm in a 37 degrees C water bath), blood/plasma was mixed with EDTA or citrate, further centrifuged at +4 degrees C (2200 g at 10 min). Finally, plasma was collected pending analysis. Whole blood in contact with Ti alloy resulted in the binding of platelets to the material surface and in the generation of thrombin-antithrombin (TAT) complexes. With whole blood TAT levels increased 1000-fold compared with PRP and PPP, in which both almost no increase of TAT could be detected. In addition, the platelet activation showed a similar pattern with a 15-fold higher release of beta-TG in whole blood. In the in vitro chamber model with the clinically relevant materials, the fluoride-modified surface (TiOB-F) showed pronounced TAT generation compared with TiOB, mTi and HA. Similar results were achieved for platelet consumption and activation markers of the intrinsic coagulation system. Taken together these results implicate first that whole blood is necessary for sufficient thrombin generation and platelet activation during placement of implants. Second, a fluoride ion modification seems to augment the thrombogenic properties of titanium.     

CCR2+ and CCR5+ CD8+ T cells increase during viral infection and migrate to sites of infection

Chemokines and their receptors play a critical role in the selective recruitment of various leukocyte subsets. In this study, we correlated the expression of multiple chemokine and CC chemokine receptor (CCR) genes during the course of intracerebral (i.c.) infection with lymphocytic choriomeningitis virus (LCMV) and vesicular stomatitis virus (VSV), which are prototypic of a noncytopathic and a cytopathic virus, respectively. Infection of mice with either virus resulted in rapid activation and overlapping cerebral expression of a number of chemokine genes. Infection with VSV i.c. causes a rapidly lethal, T cell-independent encephalitis, and infection resulted in a dramatic early up-regulation of chemokine gene expression. Similar marked up-regulation of chemokine expression was not seen until late after LCMV infection and required the presence of activated T cells. Cerebral CCR gene expression was dominated by CCR1, CCR2 and CCR5. However, despite a stronger initial chemokine signal in VSV-infected mice, only LCMV-induced T cell-dependent inflammation was found to be associated with substantially increased expression of CCR genes. Virus-activated CD8+ T cells were found to express CCR2 and CCR5, whereas activated monocytes/macrophages expressed CCR1 in addition to CCR2 and CCR5. Together, these CCR profiles readily account for the CCR profile prominent during CD8+-dependent CNS inflammation.     

Combined MR examination of prostate: is it reliable?

A combination of magnetic resonance (MR) methods (T2-weighted MRI, proton MR spectroscopy, and dynamic contrast enhancement) gives the highest sensitivity and specificity for identification of prostate cancer by MRI. The prostate MR findings of a patient with a congenital cystic disease of seminal vesicle are presented. To our knowledge, this is the only case described in the literature. The MR examination resulted in a false-positive indication of prostate cancer.