We have shown that the commercially available TZD, ciglitazone, significantly decreased VEGF production by human granulosa cells in an in vitro
model. The greatest inhibitory response was observed when using a 40 uM dose of ciglitazone. Our findings were consistent with existing data that demonstrated inhibition of VEGF expression by PPARγ ligands in a variety of other cell types (11
). Given VEGF’s pivotal role in the pathogenesis of OHSS, our findings suggest a theoretical role for PPARγ ligands in prevention of this condition.
Data accumulated over the past decade strongly implicates VEGF as the primary promoter of vascular permeability in OHSS (17
). Subsequent studies have focused on identifying the cell types in which VEGF is produced and examining its expression during ovarian stimulation. VEGF expression has been confirmed in human granulosa cells, (4
) where it has been shown to increase in response to administration of hCG (20
). Recent work has also identified elevated levels of VEGF in circulating peripheral blood mononuclear cells in women with OHSS, suggesting a role for immune cells in the pathogenesis of the disease (22
Comparatively little is known about the mechanism by which VEGF exerts its clinical effects, and studies examining prevention of OHSS via inhibition of VEGF production have frequently suffered from a lack of mechanistic support. Endothelial adherens junctions and the adhesion molecule vascular endothelial (VE)-cadherin have recently been investigated as downstream targets for VEGF signaling (23
), although potential applications of this pathway in the clinical setting have not been explored. The specific VEGFR-2 inhibitor SU5416 (Z-3-[(2,4-dimethylpyrrol-5-yl)methylidenyl]-2-indolinone) has been shown to decrease vascular permeability following hCG stimulation in a rodent model of OHSS (18
), but its side effect profile and interference with early pregnancy development limit its clinical utility (24
). The use of low-dose dopamine agonists to block VEGF mediated vascular permeability without altering VEGFR-2 dependent angiogenesis is emerging as a potential means of preventing OHSS in a clinical setting (25
). Our data indicated that TZDs decreased VEGF production by cultured granulosa cells, and treatment with FDA-approved pioglitazone did not adversely impact the morphologic development of cultured murine embryos in vivo.
Given the widespread use of orally administered TZDs in clinical practice, we propose these PPARγ ligands as an alternate and novel means of inhibiting VEGF production and perhaps abrogating the clinical syndrome of OHSS.
It should be mentioned that ciglitazone, the compound used in our granulosa cell experiments, is a commercially available TZD that is not in clinical use. Secondary to its ease of availability, however, ciglitazone is widely used as an index drug for this class in the scientific literature investigating actions of PPARγ (16
), thus prompting its use in our initial studies. During the time period that we conducted our experiments, new evidence emerged that raised concern about differential safety profiles between various TZDs. The widely publicized 2007 meta-analysis implicating rosiglitazone as posing an increased cardiac ischemic risk for type 2 diabetics (28
) prompted us to conduct the remainder of our murine embryo experiments using pioglitazone, a clinically utilized TZD that has been shown to have a favorable safety profile with respect to cardiovascular health (29
). As existing literature suggests that all members of the TZD drug class appear to share a common mechanism of action via PPARγ (30
), we can postulate that pioglitazone and ciglitazone would have similar inhibitory effects on VEGF production in granulosa cells. Subsequent experiments would have to confirm this assumption.
Earlier studies have demonstrated a two to three-fold increase in VEGF production by granulosa cells cultured in the presence of hCG (3
). There seems to be disagreement on the time course of this effect, with some groups noting maximal increase in VEGF secretion after 3 hours of exposure to hCG (21
) and others noting no increase prior to day 4 of culture (3
). Our data demonstrate a significant increase in VEGF secretion by granulosa cells cultured in the presence of hCG, but the effect is of a smaller magnitude than previously reported. This difference is most likely attributable to the timing of our VEGF measurements, which were performed at 24 and 48 hours of culture following an initial 48 hour acclimation period. Our previous studies have shown that luteinized granulosa cells require 48 hours to recover from the initial downregulation of the LH receptor following exogenous hCG administration (13
). As the granulosa cells were cultured for an additional 2 days, we attribute the minimal hCG response to decreased levels of LH receptors in these cells secondary to the prolonged duration of culture.
At the present time, no mechanistic evidence has been provided by our study. Follow up experiments will need to thoroughly explore the mechanisms by which TZDs exert their inhibitory effect on VEGF and whether TZDs have any effect on granulosa cell steroidgenesis.
The safety of TZDs in early pregnancy has been suggested by the literature. Murine studies have demonstrated that rosiglitazone does not adversely impact embryo or neonatal development (32
) and may even exert positive effects on blastocyst quality in female mice with diet-induced obesity (33
). First-trimester use of rosiglitazone in a small case series of pregnant women with polycystic ovary syndrome demonstrated no evidence of developmental or congenital abnormalities (34
). The clinical utility of TZDs in ameliorating OHSS may be best initially studied in a population of oocyte donors until the long term safety of the compounds in fetal development can be further established in human studies.
This study is the first to our knowledge to identify PPARγ ligands as inhibitors of VEGF production by luteinized granulosa cells. Our data indicates that TZDs are not cytotoxic to granulosa cells, and do not adversely impact the morphologic development of cultured murine embryos. These findings suggest a potential role for TZDs in the amelioration or prevention of OHSS.