2-Butoxyethanol model of haemolysis and disseminated thrombosis in female rats: a preliminary study of the vascular mechanism of osteoarthritis in the temporomandibular joint

Female rats develop haemolytic anaemia and disseminated thrombosis and infarction in multiple organs, including bone, when exposed to 2-butoxyethanol (BE). There is growing evidence that vascular occlusion of the subchondral bone may play a part in some cases of osteoarthritis. The subchondral bone is the main weight bearer as well as the source of the blood supply to the mandibular articular cartilage. Vascular occlusion is thought to be linked to sclerosis of the subchondral bone associated with disintegration of the articular cartilage. The aim of this study was to find out whether this model of haemolysis and disseminated thrombosis supports the vascular hypothesis of osteoarthritis. Six female rats were given BE orally for 4 consecutive days and the two control rats were given tap water alone. The rats were killed 26 days after the final dose. The mandibular condyles showed histological and radiological features consistent with osteoarthritis in three of the four experimental rats and in neither of the control rats. These results may support the need to explore the vascular mechanism of osteoarthritis further.     

The process of lubrication impairment and its involvement in temporomandibular joint disc displacement: a theoretical concept.

PURPOSE: This article re-evaluates the chain of events leading to temporomandibular joint (TMJ) disc displacement. The joint lubrication system and the process of its breakdown are clarified and an attempt is made to evaluate the possible effect of increased friction between the disc and fossa on the anterior displacement of the disc. MATERIALS AND METHODS: The study is based on the author's accumulated clinical data and results obtained from laboratory investigations regarding TMJ lubrication and its possible breakdown, coupled with pertinent information culled from the literature. RESULTS: Translation of the disc in the TMJ is enabled due to the presence of phospholipids and hyaluronic acid, which constitute an efficient lubrication system. This system may break down in the presence of uncontrolled free radicals. In the absence of lubricants, the articular surfaces are smooth, elastic in texture, and possess strong surface energy. Such opposing planes, especially in the presence of a thin fluid film (sub-boundary lubrication) tend to generate high friction while the disc is sliding against the fossa. Such friction is probably the prime mover in loosening the disc attachments to the condyle, with subsequent disc displacement. CONCLUSIONS: Increased friction of the contiguous parts may well be a major causative factor in displacement of the articular disc. This should be taken into account in considering the appropriate treatment approach. It also raises some doubts regarding the validity of using repositioning techniques.     

Electron microscope and biochemical observations of the surface active phospholipids on the articular surfaces and in the synovial fluid of the temporomandibular joint: a preliminary investigation.

PURPOSE: The goal of this article is to investigate the surface-active phospholipids located on the articular surfaces and in the temporomandibular joint (TMJ) synovial fluid (SF) by means of electron microscopy and biochemical analysis. MATERIALS AND METHODS: Synovial fluids and articular cartilage samples taken from 6 normally functioning TMJs were studied. The osmiophilic lining of human TMJ articular surfaces has been studied by using special nondestructive fixation procedures. To study the SF, negative staining technique has been used. In addition, thin-layer chromatography has been used to identify the phospholipids extracted from synovial fluid of human TMJs. RESULTS: In the SF, granular bodies were identified with diameter of between 170 and 280 nm. Their diameter decreased dramatically when exposed to phospholipase-A(2). The amorphous and highly osmophilic material on the articular surface include membrane-bound vesicles (270 nm in diameter) with lamellated pattern surrounding the amorphous-dense core. Biochemical extraction revealed phosphatidylcholine as the major component of the polar lipids. CONCLUSIONS: This preliminary study presents findings that suggest that phospholipids present in the TMJ may provide an efficient boundary lubrication that enables the disc to slide down the slope of the eminence on joint function.     

Ubiquitin degradation with its substrate,or as a monomer in a ubiquitination-independent mode,provides clues to proteasome regulation

The mechanisms that regulate the ubiquitin (Ub)-proteasome system''s own components, although critically important, are largely unknown. Ub, a principal component of the system, must be maintained at adequate levels to support cellular homeostasis under basal and stressed conditions. It was suggested that Ub is degraded as part of the polyubiquitin chain along with its substrate. Here, we demonstrate in a direct manner that Ub is indeed degraded in a “piggyback” mechanism. Also, it has been shown that monomeric Ub can be rapidly degraded when a C-terminal tail of a minimal length is fused to it. The tail, which may represent the substrate or part of it, or a naturally occurring extended form of Ub, probably allows entry of the protein into the 20S catalytic chamber, while Ub serves as an anchor to the 19S complex. Here, we show that shorter-tailed Ubs, such as UBB⁺¹, bind to the proteasome but because they cannot be efficiently degraded, they inhibit the degradation of other Ub system''s substrates such as Myc, p21, Mdm2, and MyoD. The inhibition depends on the ability of the tailed Ubs to be ubiquitinated: their mere binding to the proteasome is not sufficient. Interestingly, the inhibition affects only substrates that must undergo ubiquitination for their degradation: ornithine decarboxylase that is targeted by the proteasome in a Ub-independent manner, is not affected by the short-tailed ubiquitinated Ubs, suggesting it binds to the 19S complex in a site different from that to which ubiquitinated substrates bind.     

Pericoronitis: a reappraisal of its clinical and microbiologic aspects

Pericoronitis is an infectious disease of the operculum overlying an erupting or semi-impacted tooth. It manifests itself mainly in late adolescence and young adulthood and nearly always occurs around the lower third molar. The distinctive location, age, clinical picture, and link with predisposing factors warranted a reappraisal of pericoronitis and its etiology. Spirochetes and fusobacteria proved prevalent at all stages of the disease. The presence of these microbacteria may provide a clue as to the late appearance, particular location, and singular clinical picture of pericoronitis. The fact that spirochetes and fusobacteria are also found in acute necrotizing ulcerative gingivitis, and have been associated with alveolar osteitis, indicates a possible relationship between these disorders and pericoronitis.