Direct toxicity of insulin on the human placenta and protection by metformin.

Objective: To study the effects of insulin and metformin on primary trophoblasts from early pregnancies.

Design: Experimental in vitro study.

Setting: Academic research institute.

Patient(s): Trophoblasts from healthy patients undergoing first trimester elective termination of pregnancy and primary lung fibroblasts (IMR-90).

Intervention(s): Culture and treatment with insulin and metformin of primary trophoblasts and primary lung fibroblasts (IMR-90).

Main Outcome Measure(s): DNA damage measured by expression of γ-H2AX with immunofluorescence and Western blot. Apoptosis measured by expression of cleaved caspase-3 by Western blot. Cell survival measured by cell proliferation assay.

Result(s): Culture of purified primary trophoblast cells in the presence of insulin at levels as low as 1 nM resulted in a 386% increase in the number of cell with elevated γ-H2AX expression, a 66% reduction in cell survival and a marked increase of cleaved caspase-3 expression. Pretreatment of trophoblasts with therapeutic doses of metformin prevented the detrimental effects of insulin. Treatment with insulin and/or metformin had no effects on primary fibroblasts.

Conclusion(s): Elevated insulin levels are directly toxic to first trimester trophoblasts and result in increased DNA damage, apoptosis, and decreased cell survival. These effects are prevented by metformin. Trophoblast cells from early pregnancy are uniquely vulnerable to elevated levels of insulin. These findings, if confirmed in vivo, suggest that there may be a role for insulin resistance screening before attempting pregnancy and for focusing on prevention of hyperinsulinemia during early pregnancy.