**4.1 Expression and significance of peritoneal fluid protein in patients with endometriosis**

In 2003, Tabibzadeh et al. [88] used two-dimensional gel electrophoresis to analyze the protein profile of peritoneal fluid in 12 patients with EMs (6 cases were mild and 6 cases were severe degree). However, 12 cases of non-EMs ascites were analyzed as control (6 cases of infertility, 6 cases of normal fertile). There was no significant difference between the infertile controls and the normal fertile control group. However, the patients with mild EMs had protein reductions associated with several peritoneal protein spots of approximate molecular weights of 35–40 kD and pI close to 5.7–6.0. and the reduction in severe EMs cases was more markedly apparent. Consistent with these data, enzyme-linked immunosorbent assay showed that severe endometriosis was associated with markedly elevated levels of IL-10 in the peritoneal fluid. Endometriosis maybe associated with disturbed secretion of proteins into the peritoneal cavity and with an elevated level of IL-10 in the peritoneal fluid. Most of these proteins have not been further described in the existing literatures, so it is still unclear whether the aforementioned results can be used as diagnostic markers for EMs.

Ferrero et al. [89] used two-dimensional gel electrophoresis, silver stained, semiquantitative computerized analysis the changes of protein expression profile in the peritoneal fluid and plasma of 72 patients with EMs and 35 infertile control patients. Compared with the controls, one beta chain isoform (HpbetaE; molecular weight 38.40 ± 0.94 kD; and isoelectric point, 5.63 ± 0.17) had significantly higher expression in women with endometriosis. HpbetaE level was found no significant difference between mild endometriosis (rAFS, stage I-II) and severe endometriosis (rAFS, stage III-IV). But the expression of HpbetaE in the control group was obtained to be related to the stage of menstrual cycle. The above studies indicate that changes in the protein expression profile of patients with endometriosis. In 2007, Liu et al. [90] used SELD I-TOF-MS technology and its associated protein chip to detect the plasma protein profiles from 36 patients of endometriosis and 35 healthy individuals. 21 differentially expressed protein peaks were found and three protein peaks were established. The endometriosis diagnostic model had a sensitivity of 91.7% and a specificity of 82.9%, and was performed on 16 healthy subjects and 15 patients. The sensitivity was 87.5% and the specificity was 80%. It provides an approach for screening the plasma markers of endometriosis. In 2007, Ferrero et al. [91] used two-dimensional gel electrophoresis; protein spots of interest were identified by liquid chromatography tandem mass spectrometry to study the differential expression of peritoneal fluid proteins in patients with and without endometriosis. Several molecules had aberrant expression in peritoneal fluid of women with endometriosis may be useful for a better understanding of the pathogenesis of this disease.

In 2006, Zhang et al. [92] applied two-dimensional gel electrophoresis (2-DE), Western blotting, and mass spectrometry (MS) technology to study proteins in endometriosis and normal controls, and analyzed differences using Western blots. The normal human serum and patient serum were compared with the total protein of endometriosis. In patients with endometriosis, 13 protein spots were associated with 11 known proteins, while 11 protein spots were found differently expressed in the endometrium of patients with and without endometriosis. Some proteins may be cytoskeleton, some may regulate in cell cycle, signal transduction or immune function participation. The hybridization of vimentin, beta-actin and ATP synthase beta subunit in serum of patients with endometriosis was significantly different from that of normal serum. Three different points were used to determine the protein expression profile, vimentin, β-actin, and ATP synthase β subunits respectively. ATP synthase may play an important role in ectopic endometrium as it needs invasive, and cell adhesion and cytoskeletal remodeling. Vimentin and β-actin is a cytoskeletal protein. Studies have shown that the expression of these proteins is upregulated in the endometrium in patients with endometriosis. These proteins have a certain effect on the formation of endometriotic lesions. Given that the occurrence of endometriosis may be due to an abnormality of eutopic endometrium itself. In 2007 and 2008, Liang [93] and others used surface-enhanced laser desorption/ ionization time-of-flight mass spectrometry (SELDI-TOF-MS) technology to study serum protein expression in patients with endometriosis and healthy controls. A diagnostic model consisting of 5 protein peaks was established with a sensitivity of 91.7% and a specificity of 90.0% provides new prospect for screening endometriosis markers. In 2007, Liu et al. [90] also used SELDI-TOF-MS technology to study plasma protein expression in patients with endometriosis and healthy controls. It was found that 20 protein peaks were elevated or decreased in both of them. The sensitivity was 87.5% and the specificity was 80.0%.
