In this study, we observed that infertile women with PCOS undergoing IVF showed higher serum and follicular fluid tumor necrosis factor–α and interleukin-6 levels than the control subjects. Moreover, we demonstrated that follicular fluid concentrations of tumor necrosis factor–α were significantly and inversely correlated to follicular fluid E2 levels.
The role of the cytokines in PCOS has been investigated, with controversial results in relation to the different analysis procedures and the different study populations. 17,20–23 We choose to evaluate the tumor necrosis factor–α and interleukin-6 values in infertile PCOS women undergoing IVF. This study model was suggested by the need to recognize the different phases of the folliculogenesis that have been shown to markedly influence cytokine production. Previous studies reported high serum tumor necrosis factor–α concentrations in nonstimulated PCOS women. 21,22 In the present study we confirmed this finding, and we found a strict correlation between tumor necrosis factor–α and interleukin-6 values. These findings disagree with previous observations that do not demonstrate any significant increase of the latter cytokine in PCOS patients in the course of spontaneous cycles. 17,20 Furthermore, we demonstrated that such difference was evident both in the early phase of the folliculogenesis and at the time of ovulation. The gonadotropin stimulation, however, induced a significant and comparable increase of interleukin-6 and tumor necrosis factor–α either in the patients with PCOS or in the normal group. This finding is suggestive for a physiologic modulation of cytokine secretion by these pituitary hormones, although in our study protocol the gonadotropin stimulation was performed with pharmacological doses. Indeed, previous studies demonstrated that FSH was able to induce interleukin-6 expression from granulosa cells, 10 and a possible regulation of interleukin-6 expression by luteinizing hormone (LH) was also suggested. 29 The rise of interleukin-6 levels could be in relation to the angiogenesis occurring during the ovarian follicular development. 12
In our PCOS patients, the intrafollicular interleukin-6 and tumor necrosis factor–α concentrations were higher than those found in the serum, suggesting a local production for these cytokines. Indeed, even if both cytokines are mainly produced by white blood cells, they can be also elaborated by granulosa cells. 30 Besides the source of production, however, the high intrafollicular levels of tumor necrosis factor–α and interleukin-6, as well as the inverse correlation between the tumor necrosis factor–α and E2 values, could be suggestive of an involvement of these cytokines in the pathophysiology of PCOS. This conclusion follows the hypothesis of the existence of a relationship between the endocrine and immune systems in such disease, 4 as demonstrated in other pathologic diseases of the reproductive system. 31,32 Because the present study was performed in a homogeneous group of PCOS patients undergoing stimulation, we cannot demonstrate either the pathophysiologic mechanisms or the eventual involvement of the above cytokines in all pathologic aspects of the syndrome. Actually, both interleukin-6 and tumor necrosis factor–α seem to exert many effects at the reproductive axis. In particular, interleukin-6 has a stimulatory effect on LH secretion, 29,33 which pulse secretion is impaired in the patients with PCOS. 34 Also, tumor necrosis factor–α has been shown to influence folliculogenesis, follicular maturation, 7,9,10 and gonadotropin-induced steroidogenesis by stimulating the proliferation of theca-luteinized and interstitial cells, 35 androgen synthesis, 36 and inhibition of differentiation of cultured granulosa cells. 37 Moreover, high tumor necrosis factor–α concentrations in follicular fluid were linked to a poor quality of oocytes, 31,32,38 and some evidence suggests that tumor necrosis factor–α could mediate insulin resistance, 39 which is a common finding in patients with PCOS. In addition to these effects, the immunological properties of tumor necrosis factor–α should be considered in this physiopathologic context. Tumor necrosis factor–α is a proinflammatory cytokine associated with the Th1 immune response. 40 As a Th1-inducing factor, tumor necrosis factor–α seems to play a critical role in modulating the apoptotic process in experimental models of autoimmune diseases. 41 Abnormality in apoptotic process has been described in PCOS, 42 and the modulatory role of type 1 cytokines has been investigated. 43 The results of our study suggest an involvement of the immune system in the pathogenesis of disease. 3 The future characterization of these physiopathologic aspects might favor new diagnostic and therapeutic perspectives in the management of patients with PCOS.
Our study demonstrated that in infertile women with PCOS in the course of IVF, 1) serum interleukin-6 and tumor necrosis factor–α levels were higher than those found in control women, 2) the cytokine concentrations were higher in the follicular fluid than in the serum, and 3) the intrafollicular tumor necrosis factor–α concentrations were significantly and inversely correlated to the E2 levels. Further studies are needed to clarify both the specific role of these cytokines in the disease and the eventual application of cytokine measurement, as well as the anticytokine treatment, in the management of patients with PCOS.
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