8q24.12

OCIF,OPG,PDB5,TR1

Cancer

A potential role of full-lenght OPG in tumor cell biology is supported by different studies that have investigated the OPG serum levels, OPG tissue expression and OPG polymorphisms in cancer patients. In fact, it has been shown that the serum levels of OPG are elevated in a variety of human malignancies, in particular in patients with more advanced cancer. Of note, OPG levels were increased in the serum of patients with prostate or breast cancer metastatized to the bone (Lipton et al., 2001). Surprisingly, OPG serum levels were elevated also in other types of tumors, which do not show a preferential tropism for bone, such as B cell lymphomas (Lipton et al., 2001), but also in patients with bladder carcinoma (Mizutani et al., 2004), where OPG levels were found to be associated with high tumour stage and grade. After a follow up period of 5 years, patients who had low serum OPG levels had a longer post-operative tumour-free interval and increased survival compared with patients with high levels of serum OPG (Mizutani et al., 2004), suggesting that serum OPG correlates with tumour stage and is also predictive of early recurrence of bladder carcinoma.
Moreover, in different studies, it was shown that OPG is overexpressed in epithelial carcinomas of the gastroenteric tract (Ito et al., 2003; Pettersen et al., 2005). In particular, it was reported a significant correlation between OPG expression and tumor stage, suggesting that OPG expression may be a marker of aggressive gastric carcinomas. In addition, investigation of various human cancers demonstrated that OPG is highly expressed by endothelial cells in the majority of malignant tumors examined (60% of malignant tumors), although endothelial cells in benign tumors do not express high levels of OPG. In particular, in breast cancers endothelial expression of OPG seems to be associated with increasing tumor grade (Cross et al., 2006). Taken together, these observations suggest that the increased levels of OPG expression may be associated with tumor development and/or progression.
Finally, a recent study has addressed the possible role of OPG promoter polymorphisms as genetic modifiers in the etiology of prostate cancer and disease progression (Narita et al., 2008). Patients affected by prostate cancer with TC and TT genotypes in the 950 T/C polymorphism had a significantly increased risk of extraprostatic and metastatic disease compared with those with the CC genotype. In addition, analysis of the metastatic prostatic cancer patients showed that the presence of the T allele of the OPG 950 T/C polymorphism was an independent risk factor, predicting survival by Cox proportional hazard regression analyses (Narita et al., 2008).

Vascular diseases

A growing number of experimental data have demonstrated that the serum levels of OPG are significantly increased in both diabetic and non-diabetic patients affected by coronary artery disease (Jono et al., 2002; Schoppet et al., 2003; Avignon et al., 2005; Rasmussen et al., 2006), with a strong association between levels of OPG and the presence and severity of coronary artery disease (Browner et al., 2001). Serum OPG levels have shown to have prognostic value in heart failure after acute myocardial infarction as well as in patients affected by abdominal aortic aneurysm and peripheral artery disease (Karan et al., 2005; Ziegler et al., 2005). Remarkably, two OPG genetic polymorphisms have been associated with an increased risk of coronary artery disease in Caucasian men, and serum OPG levels correlated with one of these polymorphisms (Soufi et al., 2004). Thus, these studies strongly indicate that serum OPG levels frequently rise in clinical conditions that favor vascular dysfunction or atherosclerosis. In this respect, the presence of OPG has been documented in atherosclerotic lesions (Schoppet et al., 2004). Moreover, in a large observational study, plasma concentrations of OPG were higher in diabetic than in non-diabetic subjects, in particular in diabetic patients with vascular complications (Knudsen et al., 2003), suggesting that elevated levels of OPG may reflect vascular damage among patients with diabetes rather than the diabetic state per se.
At present it is unclear whether OPG plays a pathogenetic or compensatory role in the vascular dysfunction and atherosclerosis. However, the ability of recombinant OPG to enhance the recruitment and infiltration of monocyte/macrophages ( Mosheimer et al., 2005) is particularly noteworthy in the hypothesis that an abnormal and prolonged elevation of OPG levels may be involved in the devolopment of vascular dysfunction.