The role of leptin in HIV associated pre-eclampsia.
HIV and hypertensive disorders in pregnancy, in particular pre-eclampsia, are the main causes of maternal mortality in South Africa. In HIV associated pre-eclampsia, it is biologically plausible that the immune activation associated with pre-eclampsia may be neutralised by the immune suppression of HIV infection. The precise aetiology of pre-eclampsia is unknown, however leptin has been implicated in its development. Leptin is an adipocyte hormone, also produced by the placenta. It has a role in the development of inflammation. Adipose tissue is reduced in HIV infected individuals, resulting in lower leptin levels with consequent impaired immune function. This study aimed to compare serum and placental leptin levels in HIV infected and uninfected normotensive and pre-eclamptic pregnancies. Since insulin levels may affect the secretion of leptin, the study also compared insulin levels in these pregnancies. Following ethical clearance and hospital permission, 180 participants were recruited during their antenatal period. The groups were HIV- normotensive (n = 30), HIV+ normotensive (n = 60), HIV– pre-eclamptic (n = 30) and HIV+ pre-eclamptic (n = 60). Blood samples were collected ante-natally and placental samples post delivery. Serum leptin and insulin levels were determined by ELISA. Placental leptin levels were determined by ELISA and immunohistochemistry with morphometric image analysis. The placental production of leptin was determined by RT PCR. There was a non-significant increase in serum leptin levels in HIV- pre-eclampsia compared to HIV- normotensive pregnancies (p = 0.42). However leptin was decreased significantly in HIV+ pre-eclampsia compared to HIV- normotensive (p = 0.03). Based on HIV status leptin levels were decreased in HIV+ groups compared to HIV- groups in both pre-eclamptic (p < 0.01) and normotensive pregnancies (p < 0.01). Insulin levels of the HIV positive groups were lower than those of the HIV negative groups (p < 0.001). Insulin levels were also decreased in pre-eclampsia compared to normotensive pregnancies, irrespective of HIV status (p = 0.02). Immunohistochemistry demonstrated an increase in immuno-reactivity of leptin in the exchange villi of pre-eclamptic compared to normotensive placentae, irrespective of HIV status (p < 0.001). Supporting this finding, ELISA also demonstrated elevated leptin levels in the placenta of pre-eclamptic compared to normotensive pregnancies (p < 0.001). Placental leptin levels were similar in both HIV positive and negative pregnancies (p = 0.36). However, the placental leptin mRNA expression was up-regulated in HIV negative pre-eclampsia (p = 0.04) but not in HIV positive pre-eclampsia (p = 1.00). In conclusion, the elevated placental leptin in pre-eclampsia, irrespective of HIV status, is consistent with hypoxia. These elevated levels are not reflected in the maternal serum which raises the possibility of decreased leptin expression by adipose tissue especially in HIV infection where serum leptin levels are decreased. This would negate the increased placental leptin expression in pre-eclampsia. Furthermore, the elevated placental leptin levels are suggestive of an autocrine role of leptin in the placenta.