Fig. 5. A: An outline of the gingival tissues is illustrated. A tooth is mechanically supported by alveolar bone, and the tooth and the alveolar bone are surrounded by gingiva. The tooth and the alveolar bone are tightly attached by the thin gingival membrane called periodontal ligament. On the top of the periodontal ligament, there is gingival crevice which is a small space between the tooth and gingival epithelia. Gingival crevicular fluid (GCF) is an exudate recovered from the crevice. When the tissue is injured from periodontitis, the alveolar bone and the periodontal ligament are reduced and the gingival crevice deepens. B: GCF is easily and safely recovered using a needleshaped filter paper called a paperpoint. When a peripheral nerve fiber is injured, the axon and myelin sheath are regenerated. In this process many types of cells are involved, including Schwann cells, macrophages and fibroblasts are involved. Macrophages are thought to have a scavenging role in which damaged cells and cell debris are recognized by scavenger receptors and cleared away by endocytosis. Oxidative modification of membranes could be involved in this cellular damage of nerve cells, since OxPC has been shown to accumulate in the sciatic nerve of CD36-knockoput mice after crush injury.(32) Lipid peroxidation can proceed not only in lipoproteins but a lipid environment, such as cellular membranes. The presence of OxPC in certain disease lesions suggests that either oxidative damage of cell components has occurred or oxidized materials such as OxLDL have accumulated in local tissues. It is thus a reasonable hypothesis that cellular membranes in the retina, chondrocytes and nerve cells are oxidized under certain patho- logical conditions. The Presence of OxLDL in the Oral Environment In developed countries, the number of patients with periodontitis has been increasing, and now periodontitis is the primary cause of tooth loss. Evidence has accumulated for a close relationship between atherosclerosis and periodontal diseases. For example, epidemiological studies have shown a significantly higher proba- bility of periodontitis in patients with hypercholesterolemia and cardiovascular disease.(33–35) The presence of Porphyromonas gingivalis in atherosclerotic lesions, one of the major culprit bacterial species of periodontitis, has been demonstrated.(36) When P. gingivalis was injected in apoE-KO mice, the aortic lesions increased significantly.(37,38) The gingiva is made up of the tissues surrounding the teeth and alveolar bones. Since these tissues are exposed to air and/or food essentially all the time, it is a front-line region of bacterial infection in oral tissue. Teeth are fixed by the alveolar bones together with the support of the periodontal ligament, which is attached to the gingival tissues (Fig. 5). Gingival crevicular fluid (GCF) is an exudate from gingival tissues that originates from H. Itabe plasma, so that many of the plasma proteins are detected in GCF in addition to certain gingival tissue proteins which are secreted.(39) For example, α-defensin, a potent anti-inflammatory peptide, has reportedly been found in GCF.(40) However, the information on GCF thus far is very limited. One interesting feature of GCF is that it can be easily and safely recovered from the gingival crevice, suggesting that it is poten- tially useful as a clinical target of biochemical evaluation. We collected GCF at the sites of healthy teeth from patients with dental problems but no evident systemic or other infection. The presence of apoB was demonstrated by Western blotting and the presence of OxLDL was observed using sandwich ELISA.(41) Interestingly, the OxLDL level in GCF from healthy subjects was 17 times higher than the plasma OxLDL levels in the same subjects on average, suggesting that LDL is oxidized in local gingival tissues (Fig. 6). The GCF OxLDL levels relatively large deviations, it did not reach significant difference. The GCF OxLDL levels might, therefore, be a useful marker of the oxidative status in our body. Since the relationship between periodontitis and metabolic disorders such as diabetic mellitus and atherosclerosis has come to be a focus of attention recently,(33–38) it is important to study the relative OxLDL levels in patients with these metabolic disorders so as to eventually obtain simple and effective clinical tests. OxLDL as an Inflammatory Stimulant in Oral Disease A number of studies have shown that OxLDL is a potent stimu- lant of various types of activity in vessel wall cells, for example, the proliferation of endothelial cells, smooth muscle cells and macrophages,(42,43) the production of cytokines and other media- tors,(44–46) platelet activation(47) and the induction of cell death.(48,49) However, the effects of OxLDL on other types of cells, such as epithelial cells, have not been well studied yet. There is a paper reporting the effects of OxLDL on NRK52E proximal tubule epithelial cells, in which the up-regulation of ICAM-1 and focal adhesion kinase was observed.(50) We thought that the OxLDL identified in GCF might be actively J. Clin. Biochem. Nutr. | July 2012 | vol. 51 | no. 1 | 5 ©2012 JCBN