Biocompatibility evaluation of densified bacterial nanocellulose hydrogel as an implant material for auricular cartilage regeneration

Bacterial nanocellulose (BNC), synthesized by the bacterium Gluconacetobacter xylinus, is composed of highly hydrated fibrils (99 % water) with high mechanical strength. These exceptional material properties make BNC a novel biomaterial for many potential medical and tissue engineering applications. Recently, BNC with cellulose content of 15 % has been proposed as an implant material for auricular cartilage replacement, since it matches the mechanical requirements of human auricular cartilage. This study investigates the biocompatibility of BNC with increased cellulose content (17 %) to evaluate its response in vitro and in vivo. Cylindrical BNC structures (Ø48?×?20 mm) were produced, purified in a built-in house perfusion system, and compressed to increase the cellulose content in BNC hydrogels. The reduction of endotoxicity of the material was quantified by bacterial endotoxin analysis throughout the purification process. Afterward, the biocompatibility of the purified BNC hydrogels with cellulose content of 17 % was assessed in vitro and in vivo, according to standards set forth in ISO 10993. The endotoxin content in non-purified BNC (2,390 endotoxin units (EU)/ml) was reduced to 0.10 EU/ml after the purification process, level well below the endotoxin threshold set for medical devices. Furthermore, the biocompatibility tests demonstrated that densified BNC hydrogels are non-cytotoxic and cause a minimal foreign body response. In support with our previous findings, this study concludes that BNC with increased cellulose content of 17 % is a promising non-resorbable biomaterial for auricular cartilage tissue engineering, due to its similarity with auricular cartilage in terms of mechanical strength and host tissue response.     

DNA Methylation Signature Analysis: How Easy Is It to Perform?

Epigenetic changes, or heritable alterations in gene function that do not affect DNA sequence, are rapidly gaining acceptance as co-conspirators in carcinogenesis. Although DNA methylation signature analysis by methylation-specific polymerase chain reaction has been a breakthrough method in speed and sensitivity for gene methylation studies, several factors still limit its application as a routine diagnostic and prognostic test.     

Use of forest canopy by European red squirrelsSciurus vulgaris in Northern Greece: claws and the small branch niche

Moving and standing in trees impose multiple problems to arboreal mammals. Among them, the major ones are the negotiation of slender terminal branches and of large vertical supports. Both microhabitats are important as they have been linked alternatively to the evolutionary loss of claws in early primates. Therefore, rates of use of these different supports by claw-bearing arboreal mammals may offer insights to their actual significance in the adaptive evolution of early primates. In this context, canopy, tree crown, branch size, inclination, and texture use were recorded on four adult free ranging European red squirrelsSciurus vulgaris Linnaeus, 1758 in a mixed coniferous forest in northern Greece.S. vulgaris was mainly arboreal, exploiting the terminal branch zone, using frequently oblique and intermediately textured supports<5 cm and moderately large vertical branches. Furthermore, comparative data from other sciurid species and clawed primates showed positive correlations of small and horizontal support use, and negative ones of vertical support use to body mass. These findings show that keeled functional claws do not impede habitual use of slender branches and may not facilitate efficient climbing on large vertical trunks. These observations partly question the association between habitual use of the small branch niche and primate adaptations and lend support to alternative hypotheses, underscoring the importance of inquiring for more complex mechanisms that lead to the evolution of the unique set of primate morphological adaptations.     

The absence or presence of a lytic coliphage affects the response of <Emphasis Type="Italic">Escherichia coli</Emphasis> to heat,chlorine, or UV exposure

Disinfection aims at maximal inactivation of target organisms and the sustainable suppression of their regrowth. Whereas many disinfection efforts achieve efficient inactivation when the effect is measured directly after treatment, there are questions about the sustainability of this effect. One aspect is that the treated bacteria might recover and regain the ability to grow. In an environmental context, another question is how amenable surviving bacteria are to predation by omnipresent bacteriophages. Provisional data suggested that bacteria when subjected to sublethal heat stress might develop a phage-resistant phenotype. The result made us wonder about the susceptibility to phage-mediated lysis for bacteria exposed to a gradient of chlorine and UV-LED disinfection strengths. Whereas bacteria exposed to low sublethal chlorine doses still underwent phage-mediated lysis, the critical chlorine Ct of 0.5 mg min/L eliminated this susceptibility and induced phage resistance in the cells that survived treatment. In the case of UV, even the smallest tested dose of 2.8 mJ/cm² abolished phage lysis leading to direct regrowth. Results suggest that bacteria surviving disinfection might have higher environmental survival chances directly after treatment compared to non-treated cells. A reason could possibly lie in their compromised metabolism that is essential for phage replication.     

Conformationally constrained human calcitonin (hCt) analogues reveal a critical role of sequence 17-21 for the oligomerization state and bioactivity of hCt.

Calcitonin (Ct) is a 32-residue peptide hormone that is mainly known for its hypocalcemic effect and the inhibition of bone resorption. Our previous studies have led to potent, side-chain lactam-bridged human Ct (hCt) analogues [Kapurniotu, A. Kayed, R., Taylor, J.W. & Voelter W. (1999) Eur. J. Biochem. 265, 606-618; Kapurniotu, A. & Taylor, J.W. (1995) J. Med. Chem. 38, 836-847]. We have hypothesized that a possibly type I beta turn/beta sheet conformation in the region 17-21 may play an important role in hCt bioactivity. To investigate this hypothesis, analogues of the potent hCt agonist cyclo17,21-[Asp17,Lys21]hCt (1) bearing type I (and II') or II beta turn-promoting substituents at positions 18 and 19 were designed, synthesized and their solution conformations, human Ct receptor binding affinities and in vivo hypocalcemic potencies were assessed. The novel analogues include cyclo17,21-[Asp17,D-Phe19, Lys21]hCt (2), cyclo17,21-[Asp17,Aib18,Lys21]hCt (3), cyclo17,21-[Asp17,D-Lys18,Lys21]hCt (4), corresponding partial sequence peptides containing the lactam-bridged region 16-22, and nonbridged control peptides. Only 1 showed a higher Ct receptor binding affinity than hCt, whereas analogues 2-4 had similar receptor affinities to hCt. In the in vivo hypocalcemic assay, 3 and 4 were as potent as 1, whereas 2 completely lost the high potency of 1, suggesting that type I (and II') beta turn-promoting substituents are fully compatible with in vivo bioactivity. CD spectroscopy showed that analogues 1-4 were markedly beta sheet-stabilized compared to hCt and indicated the presence of distinct beta turn conformeric populations in each of the analogues. Unexpectedly, the D-amino acid- or Aib-containing cyclic analogues 2-4 but not 1 or hCt self-associated into SDS denaturation-stable dimers. Our results demonstrate a crucial role of the conformational and topological features of the residues in sequence 17-21 and in particular of residues 18 and 19 for human Ct receptor binding and in vivo bioactivity and also for the self association state of hCt. These results may assist to delineate the structure-function relationships of hCt and to design novel hCt agonists for the treatment of osteoporosis and other bone-disorder-related diseases.