The comparative osmoregulatory ability of two water beetle genera whose species span the fresh-hypersaline gradient in inland waters (Coleoptera: Dytiscidae, Hydrophilidae).

A better knowledge of the physiological basis of salinity tolerance is essential to understanding the ecology and evolutionary history of organisms that have colonized inland saline waters. Coleoptera are amongst the most diverse macroinvertebrates in inland waters, including saline habitats; however, the osmoregulatory strategies they employ to deal with osmotic stress remain unexplored. Survival and haemolymph osmotic concentration at different salinities were examined in adults of eight aquatic beetle species which inhabit different parts of the fresh-hypersaline gradient. Studied species belong to two unrelated genera which have invaded saline waters independently from freshwater ancestors; Nebrioporus (Dytiscidae) and Enochrus (Hydrophilidae). Their osmoregulatory strategy (osmoconformity or osmoregulation) was identified and osmotic capacity (the osmotic gradient between the animal's haemolymph and the external medium) was compared between species pairs co-habiting similar salinities in nature. We show that osmoregulatory capacity, rather than osmoconformity, has evolved independently in these different lineages. All species hyperegulated their haemolymph osmotic concentration in diluted waters; those living in fresh or low-salinity waters were unable to hyporegulate and survive in hyperosmotic media (> 340 mosmol kg(-1)). In contrast, the species which inhabit the hypo-hypersaline habitats were effective hyporegulators, maintaining their haemolymph osmolality within narrow limits (ca. 300 mosmol kg(-1)) across a wide range of external concentrations. The hypersaline species N. ceresyi and E. jesusarribasi tolerated conductivities up to 140 and 180 mS cm(-1), respectively, and maintained osmotic gradients over 3500 mosmol kg(-1), comparable to those of the most effective insect osmoregulators known to date. Syntopic species of both genera showed similar osmotic capacities and in general, osmotic responses correlated well with upper salinity levels occupied by individual species in nature. Therefore, osmoregulatory capacity may mediate habitat segregation amongst congeners across the salinity gradient

Long term in-vivo studies of a photo-oxidized bovine osteochondral transplant in sheep

BACKGROUND: Articular cartilage has limited capacity to repair. Defects greater than 3 mm heal with formation of inferior fibrous cartilage. Therefore, many attempts have been made to find the ideal graft for larger cartilage lesions. Different grafts, such as untreated or cryopreserved osteochondral transplants, have been used with variable success. METHODS: Photo-oxidized osteochondral grafts were implanted in both femoral condyles of one ovine knee. Untreated xenogeneic and autogeneic grafts served as controls. Three groups of 8 sheep each were formed and they were sacrificed 6, 12 or 18 months after surgery. RESULTS: The macroscopic evaluation of the condyle and graft showed a well-maintained cartilage surface in most grafts at all time points. However, the host cartilage matrix deteriorated considerably in all xenogeneic, most autogeneic and fewer of the photo-oxidized grafts at 12 and 18 months, respectively. The blue colour of the photo-oxidized grafts resulting from the process of photo-oxidation was visible in all grafts at 6 months, had diminished at 12 months and had completely disappeared at 18 months after surgery. Histologically a loss of matrix staining was almost never noticed in untreated xenografts, transiently at 6 months in photo-oxidized grafts and increased at 12 and 18 months. Fusion between graft and host cartilage could be seen in photo-oxidized grafts at 12 and 18 months, but was never seen in autografts and xenografts. CONCLUSIONS: The photo-oxidation of osteochondral grafts and its use as transplant appears to have a beneficial effect on cartilage and bone remodelling. Osteochondral grafts pre-treated with photo-oxidation may be considered for articular cartilage replacement and therefore may delay artificial joint replacements in human patients

Changes in subchondral bone in cartilage resurfacing--an experimental study in sheep using different types of osteochondral grafts

OBJECTIVE: This article addresses the subchondral bone integrity in cartilage resurfacing by comparing fresh, untreated auto-, xeno-, and photooxidized osteochondral allo- and xenografts. Photooxidation was expected to improve mechanical stability of the osteochondral grafts through an improved linkage of the collagen fibers within the bone matrix. DESIGN: Untreated auto- and xenografts and with photooxidation pretreated allo- and xenografts were surgically implanted in femoral condyles of sheep (n=40). After 2, 6, 12 and 18 months results were evaluated histologically using non-decalcified bone embedded in acrylic resin. Qualitative evaluation was performed with emphasis on bone matrix, biomechanical stability of graft anchorage, formation of cystic lesions, and bone resorption and formation. Quantitative evaluation of the total subchondral bone area was conducted histomorphometrically. Statistical analysis (factorial ANOVA test) was used to compare differences between groups with respect to the percentage of bone matrix and fibrous tissue per section. RESULTS: Subchondral bone resorption was fastest in untreated, fresh autografts, followed by photooxidized allografts, untreated, fresh xenografts and last pretreated photooxidized xenografts. Cystic lesions were seen in all types of grafts, but were most pronounced at 6 months in autografts and least in photooxidized grafts. Cyst-like lesions had subsided substantially in the untreated auto- and photooxidized xenografts, if no graft dislocation occurred during the healing period. Mononuclear cell infiltration and an increase in the presence of multinuclear cells were observed at 2 months, mostly in untreated autografts, followed by photooxidized allo- and untreated xenografts. They were much higher in numbers compared to photooxidized grafts, at least in the early specimens at 2 months. Graft stability was linked to the rate of bone resorption. CONCLUSION: Substantial resorption of the subchondral bone, involving the development of cyst-like lesions, lead to dislocation and finally to cartilage matrix degradation of the grafts. The process of photooxidation decreased the speed of bone resorption in osteochondral grafts and, thus, improved graft stability and cartilage survival. These results suggest that the remodeling of the subchondral bone of the host and the graft within the first 6 months is an important factor in graft stability and overall results of cartilage resurfacing