Effect of microstructure upon elastic behaviour of human tooth enamel

Tooth enamel is the stiffest tissue in the human body with a well-organized microstructure. Developmental diseases, such as enamel hypomineralisation, have been reported to cause marked reduction in the elastic modulus of enamel and consequently impair dental function. We produce evidence, using site-specific transmission electron microscopy (TEM), of difference in microstructure between sound and hypomineralised enamel. Built upon that, we develop a mechanical model to explore the relationship of the elastic modulus of the mineral-protein composite structure of enamel with the thickness of protein layers and the direction of mechanical loading. We conclude that when subject to complex mechanical loading conditions, sound enamel exhibits consistently high stiffness, which is essential for dental function. A marked decrease in stiffness of hypomineralised enamel is caused primarily by an increase in the thickness of protein layers between apatite crystals and to a lesser extent by an increase in the effective crystal orientation angle.

Alterations of fibrinogen structure in human disease

Products of normal and pathologic metabolism can react with proteins to cause covalent modification. When such modifications affect fibrinogen they can potentially alter fibrinogen function. Those that have been best studied are oxidation, nitration, homocysteinylation and glycation. It appears that the clottability of fibrinogen is maintained unless the degree of modification is extensive. However, modest degrees of fibrinogen modification can alter the rate of assembly of fibrin monomers into a fibrin clot and the fiber structure and packing. In addition, some types of modification affect lysine residues that are critical to binding, activation and activity of fibrinolytic enzymes. Any of these alterations could potentially affect the susceptibility of fibrin clots to fibrinolysis, and have been shown to do so in vitro. In the case of homocysteinylation and glycation, good evidence exists that fibrinogen modification affects clot stability in vivo. However, direct evidence is still lacking that these modifications contribute to the increased atherothrombotic risk associated with hyperhomocysteinemia and diabetes.

Formulation of Insulin-Loaded Polymeric Nanoparticles Using Response Surface Methodology

The objective of this work was to formulate new oral insulin-loaded nanoparticules using the response surface methodology. The insulin nanoparticles were prepared by a water-in-oil-in-water emulsification and evaporation method. The polymers used for the encapsulation were blends of biodegradable poly-epsilon-caprolactone (PCL) and of positively-charged, nonbiodegradable polymer (Eudragis RS). A central composite design has been built to investigate the effects of three controlled variables: ratio of polymers (PCL/RS ratio), volume, and pH of the aqueous solution of polyvinyl alcohol. The nanoparticles were characterized by measuring the amount of entrapped insulin, the particle size, the polydispersity of the obtained particles, the zeta potential, and the amount of insulin released after 7 hours. A second-order model was evaluated by multiple regression and was statistically tested for each of the studied controlled variable. The obtained polynomials proved efficient to localize an optimal operating area highlighted by the use of three-dimensional response surfaces and their corresponding isoresponse curves. An interesting formulation given by the models was selected, prepared, and evaluated. The corresponding quantity of entrapped insulin was 25 IU per 100 mg of polymer, and the particle size was 350 nm with a polydispersity of 0.21. The quantity of released insulin was 4.8 IU per 100 mg of polymer after 7 hours and the zeta potential was +44 mV. All these collected values were in perfect accordance with values estimated by the models. Finally, the results suggested that PCL/RS 50/50 nanoparticles might represent a promising formulation for oral delivery of insulin.

On the structure-property relationship of sound and hypomineralized enamel

Developmental defects in dental enamel pose significant clinical challenges which have highlighted our limited understanding of the structure and properties of this tissue. In this study, we first investigated the contact-size dependence of the physical properties of sound and hypomineralized enamel, and then examined the microstructure to establish a structural basis for their differing properties. Depth-sensing indentation tests were carried out over a wide range of peak loads in a direction perpendicular to the enamel prisms. Hypomineralized enamel demonstrated stronger penetration dependence for measured hardness and elastic modulus than sound enamel. The microstructure of sound and hypomineralized enamel was observed using field emission scanning electron microscopy and transmission electron microscopy with support of a focused ion beam milling system. Images of sound enamel showed barely distinguishable sheath regions with minimal organic presence. In contrast, hypomineralized enamel showed thicker sheath structures surrounding the prisms and higher levels of organic content within both the prisms and the sheath regions. It is argued that the higher organic content within prism structure was responsible for an initial lower hardness and elastic modulus of hypomineralized enamel under low-load indentation. As the indentation depth increased, the thicker organic-rich sheath regions played a more important role in reducing the mechanical properties of the hypomineralized enamel. On the basis of Spears finite element model [Spears IR. A three-dimensional finite element model of prismatic enamel: a re-appraisal of the data on the Young's modulus of enamel. J Dental Res 1997; 76(10):1690-97], elastic moduli of sound and hypomineralized enamel were predicted, which matched experimental results.

Effect of the microencapsulation of nanoparticles on the reduction of burst release

The initial burst release is one of the major problems in the development of controlled release formulations including drug-loaded micro- and nanoparticles, especially with low molecular weight drugs. The objective of the present work was to encapsulate, by the W/O/W emulsion, polymeric nanoparticles into polymeric microparticles by using non-water soluble polymers and appropriate organic solvents for the preparation of these composite microparticles. They were characterized in vitro (encapsulation efficiency, mean diameter and release kinetics) and compared with nanoparticles and classical microparticles prepared by the same method. Poly-epsilon-caprolactone (PCL) dissolved in methylene chloride was used to make nanoparticles, whereas ethylcellulose and Eudragit RS dissolved in ethyl acetate, a non-solvent of poly-epsilon-caprolactone, were used for the preparation of microparticles. Ibuprofen and triptorelin acetate were chosen as lipophilic and hydrophilic model drugs, respectively. High entrapment efficiencies were obtained with ibuprofen whereas lower amounts of triptorelin acetate were encapsulated, mainly with formulations prepared with poly-epsilon-caprolactone and Eudragit RS used alone or blended with ethylcellulose. The burst was significantly lower with composite microparticles and may be explained by the slower diffusion of the drugs through the double polymeric wall formed by the nanoparticle matrix followed by another diffusion step through the microparticle polymeric wall.

Development of graded hydroxyapatite/CaCO(3) composite structures for bone ingrowth

Ceramic composites composed of constituents with different bone cell reactions present an interesting consideration for a new bone replacement material. The first component of the composite used in this study, hydroxyapatite, is known to be replaced by natural tissue significantly slower than the second, calcium carbonate, which has limited structural stability. A graded hydroxyapatite/calcium carbonate composite with bimodal component distribution was developed using a combined slip infiltration and dip-coating technique from a porous polyurethane sponge replica. A graded hydroxyapatite scaffold with porosities from 5 to 90% was produced and then infiltrated with a calcium carbonate slip and sintered. The resultant composite had improved mechanical properties compared with the monolith as measured by crushing and moduli tests.

Restoring hemostatic thrombin generation at the time of cutaneous wounding does not normalize healing in hemophilia B

BACKGROUND

We recently reported that wound healing is abnormal in hemophilia B (HB) mice [1]. The wounds show abnormal histology: s.c. hematoma formation; delayed re-epithelialization; delayed macrophage influx; and an increase in wound site angiogenesis.

OBJECTIVE

To test the hypothesis that restoring a hemostatic level of thrombin generation at the time of wounding would allow formation of an adequate platelet/fibrin plug and correct abnormalities of wound healing in HB.

METHODS

We placed a 3-mm cutaneous wound on the back of each HB or wild-type (WT) mouse. Some HB mice were treated just prior to wounding with either human factor IX (FIX) or FVIIa in a dose sufficient to normalize bleeding in a tail bleed model.

RESULTS

The average wound size over time in treated HB animals was intermediate between those in WT and untreated HB mice. However, the time to complete skin closure was not improved by treatment. Hematoma formation was decreased and macrophage influx began earlier in treated than in untreated HB animals. However, treated HB mice had evidence of ongoing low-level bleeding near the wound site, even after closure of the skin defect. Treatment also did not normalize the increased angiogenesis observed in HB mice.

CONCLUSIONS

Restoring initial hemostasis can modulate some of the parameters of wound healing. However, an extended period of adequate hemostatic function is necessary to achieve normal healing, probably because the risk of hemorrhage is increased by vascular remodeling and angiogenesis during the healing process.

No relationship observed between human p53 codon-72 genotype and HPV-associated cervical cancer in a population group with a low arginine-72 allele frequency

Infection with high-risk human papillomavirus (HR-HPV) is a necessary but not a sufficient event in the development of cervical cancer, as most infections regress without intervention. Thus, genetic host factors and cellular immune responses could be potential modifiers for the risk of developing cervical cancer. In particular, p53 is considered as the most critical tumour suppressor gene and is involved in regulating cell division. The polymorphism on p53, which encodes either a proline or an arginine amino acid residue at codon 72, has been reported as a possible risk factor for cervical disease. This polymorphism has been shown to differentially affect the efficiency of degradation of p53 protein mediated by HR-HPV E6 oncoprotein. Women with histologically proven cancer of the cervix (n = 111) and hospital-based controls (n = 143) were included in this study. The patients and controls were from the Western Cape Province in South Africa. Genotyping of the p53 polymorphism was conducted using polymerase chain reaction and restriction fragment-length polymorphism method. The distributions of the allelic frequencies were stratified in both patients and controls into two South African ethnic population groups. In this study, we observed no association between the distribution of p53 polymorphism and susceptibility to cervical cancer in the Western Cape Province populations (P = 0.466). However, the frequency of the Pro/Pro residue at codon 72 was increased in the South African population when compared to Caucasians, Indians and Portuguese population groups. Notably, as the distribution of the Pro/Pro at codon 72 of p53 gene was significantly different (P < 0.05) between the control groups of South Africa and other population groups. This result suggests that ethnic disparity may influence the levels of p53 produced.

Review article: the prothrombin time test as a measure of bleeding risk and prognosis in liver disease

BACKGROUND

Prothrombin time (PT)-derived international normalized ratio (INR) is used to assess bleeding risk and prognosis in cirrhosis, and to guide management of associated coagulation disturbances. Recent studies cast doubt on the validity of the assumptions that form the basis for these applications.

AIMS

To review and critique the use of the PT-INR in cirrhosis.

METHODS

Search of the literature.

RESULTS

In cirrhosis, there is a decrease in both pro- and anti-coagulants. The PT-INR measures only the activity of procoagulants and fails to capture changes in anticoagulants. It is therefore not surprising that the PT does not predict the bleeding risk. The PT-INR provides a robust measure of liver function but recent data showed INR inter-laboratory variability in this setting. This is not surprising as the INR was validated to normalize results for patients on vitamin-K antagonists, not for cirrhosis. This limitation was not appreciated, but the INR is used to construct the model for end-stage liver disease score to prioritize patients for liver transplantation. Reports showed that model for end-stage liver disease is modified by the thromboplastin used for testing.

CONCLUSIONS

Alternate tests to predict bleeding risk should be developed. The potential for misuse of the PT-INR should drive the development of alternate algorithms for organ allocation.

Tissue factor around dermal vessels has bound factor VII in the absence of injury

BACKGROUND

'Idling' or ongoing low-level activity of the tissue factor (TF) pathway is a postulated mechanism by which the coagulation process can become active without a lag period at sites of injury.

OBJECTIVE

To determine whether TF around cutaneous vessels has bound factor VIIa in the absence of injury, and thus could participate in the idling process.

METHODS

Immunostaining of mouse skin with antibodies against a 15-residue peptide from the sequence of mouse TF, and against the whole extracellular portion of TF.

RESULTS

The whole TF antibody recognized TF in squamous epithelium and around vessels in the dermis. By contrast, the monospecific antibody only recognized TF in the squamous epithelium, but not around vessels. We also found that biotinylated, active site-inhibited FVIIa (FVIIai) bound to tissue sections in the same areas in which TF was recognized by the monospecific antibody (squamous epithelium), but did not bind around vessels. Molecular modeling revealed that FVIIa and FX binding to TF masked a significant part of the surface of the target peptide.

CONCLUSIONS

In the aggregate, these data are most consistent with the interpretation that TF in perivascular sites has bound FVIIa, even in the absence of any injury. The presence of endogenously bound FVIIa prevents the subsequent binding of the monospecific antibody or exogenous FVIIai to perivascular TF.

First pulmonary case reported in Argentina of infection with mycobacterium szulgai, a rare pathogen

Mycobacterium szulgai is a rare pathogen. Nontuberculous mycobacteria usually produce disease in people with some kind of immunosuppression or another predisposing condition. A case of pulmonary Mycobacterium szulgai infection is described.

Omission of radiotherapy after breast conserving surgery among elderly women with favorable prognosis tumors

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Background: Adjuvant radiotherapy after breast-conserving surgery is a standard therapy for invasive breast carcinoma. Controversy exists regarding the benefit of adjuvant radiotherapy for elderly women with favorable prognosis tumors. Methods: Using data from the Surveillance Epidemiology and End Results (SEER) registry, data were analyzed for 28,808 women ages = 65 years, with stage I and II, who underwent breast conservation therapy between 1998 and 2002. Relative survival rates (observed survival/expected survival) were calculated using Kaplan-Meier method for women who underwent radiotherapy and those for whom radiotherapy was omitted. Results: Among women = 65 years with stage I breast cancer who underwent breast conserving surgery (n = 20,400), 71.7% received adjuvant radiotherapy. Among those with stage II breast cancer (n = 8,408), 66.0% received adjuvant radiotherapy. Five-year relative survival rates among stage I patients were 1.000 (95% CI: 0.990, 1.010) for those receiving adjuvant radiotherapy, and 0.959 (95% CI: 0.932, 0.986) for those without adjuvant radiotherapy. Among stage II patients, the 5-year survival rates were 0.998 (95% CI: 0.978, 1.018) for those receiving adjuvant radiotherapy, and 0.832 (95% CI: 0.791, 0.873) for those without adjuvant radiotherapy. Conclusions: Adjuvant radiotherapy following breast conserving surgery may be safely omitted for elderly women with stage I breast carcinoma, especially for women ages 85–94 years.

[Table: see text]

No significant financial relationships to disclose.

[Cerebral creatine transporter deficiency: an infradiagnosed neurometabolic disease]

INTRODUCTION

Brain creatine deficiencies are a group of inborn errors of metabolism recently recognized which are caused by arginine: glycine amidinotransferase (AGAT) deficiency, guanidinoacetate metiltransferase (GAMT) deficiency and defects in creatine transporter (CRTR). Although all of them are characterized by a brain creatine deficiency, clinical and biochemical features are different.

CASE REPORTS

We present a retrospective study about four patients of masculine sex affected of creatine transporter defects who were recently diagnosed in our centre. We describe the clinical presentation features, the different tests that we used in the diagnosis process (brain magnetic resonance spectroscopy, biochemical analysis of guanidinoacetate and creatine/creatinine ratio in urine), evolution aspects and the response to treatment. The most significative clinical feature was developmental delay mainly in expressive speech, they also presented epilepsy (three cases), autism (three cases), hypotonia (one case) and microcephalia (one case). Brain magnetic resonance spectroscopy showed a low (three cases) or an absence (one case) of creatine level. To confirm the defect we studied the creatine uptake in fibroblasts and molecular analysis of the SLC6A8/creatine transporter gene. Patients with creatine transporter deficiency are being treated with arginine, because a lack of response to creatine.

CONCLUSION

Cerebral creatine transporter deficiency can present with different neurological symptoms but developmental and language delay and epilepsy are the most significative; diagnosis is easy and there are some therapeutical options.