The impact of metformin exposure on placental ageing, metabolism, and mitochondrial function

Metformin is a commonly prescribed medication in pregnancy across many global settings. Over the past 5 years, metformin has been endorsed as an acceptable and economic alternative to insulin for treatment of gestational diabetes (GDM) by national bodies in countries including UK, US, and New Zealand. Metformin has also been trialled for other indications during pregnancy, for example maternal obesity and polycystic ovaries. With risk factors for GDM (for example obesity and maternal age) increasing globally, the proportion of pregnant women prescribed metformin is likely to rise. Moreover, new trials of metformin in pregnancy are planned in low-resource settings, particularly in Asia and Africa.

Trials show that metformin limits maternal weight gain during pregnancy and stabilises blood sugar. However it is not known how metformin could affect placental function or impact on the baby's growth in the longer term. Our meta-analysis of trials of metformin treatment for GDM shows that babies are born smaller after metformin compared to insulin treatment but then catch-up in growth after birth, suggesting that metformin may restrict fetal growth during pregnancy. During late pregnancy, the growth of the fetus is highly dependent on the placenta. The placenta has key roles in nutrient-sensing, energy regulation, and metabolism, all of which are crucial for a normal pattern of fetal growth and development. In this project we will investigate the impact of metformin on placental function in human pregnancy, which has potential important consequences for long-term fetal growth and cardio-metabolic outcomes.

We will use placentas donated from two previous landmark human studies where mothers were treated with metformin during pregnancy. We will assess markers of cellular ageing (for example measuring telomere length, ageing-associated gene expression, and oxidative stress) in placentas treated with metformin compared to controls to determine whether metformin causes the normal placental ageing process to accelerate. We will also measure placental processing and transfer of key nutrients. We will look for differences in the profiles of metabolic products and lipids in metformin-exposed compared to control placentas, which could have critical long-term effects on fetal growth.

We will also test how placental cells from normal healthy pregnancies respond directly to physiologically-relevant concentrations of metformin. We will examine how efficiently metformin-exposed placental cells produce energy via mitochondria compared to controls. We will also measure placental oxygen utilisation and assess the leakage of potentially damaging free radicals. We hypothesise that placental cells exposed to metformin will have inefficient energy production compared to the same cells without added metformin. This experiment will test whether metformin has direct effects on the placental cells themselves (rather than acting indirectly via an effect on the mother's physiology) and also whether energy production might account for the differences that we see in the growth patterns of babies whose mothers are treated with metformin during pregnancy.

If metformin adversely impacts on the human placenta, then this study will provide crucial information for pregnant women and their doctors in decision-making regarding metformin treatment in pregnancy. These results are also likely to be of interest to public health policy-makers, particularly as UK NICE guidelines currently recommend metformin as a first-line drug treatment for GDM. The impact of metformin on the placenta will also be of interest and relevance to reproductive biologists, placental physiologists, and other scientists in the field of fetal growth and developmental programming. If these results are reassuring regarding the impact of metformin-exposure on the placenta, then our study will be useful in adding to the body of evidence regarding metformin safety during pregnancy.

The project aim is to evaluate the impact of metformin (N,N-dimethylbiguanide) on the human placenta. There is strong evidence from both meta-analysis of human trial data and from animal models that intrauterine metformin results in a pattern of low birth-weight and post-natal catch-up growth in metformin-exposed offspring. Metformin has multiple targets within metabolically active cells and is actively transported across the placenta via organic cation transporters. We hypothesise that reduced fetal growth in metformin-exposed pregnancies may be a result of accelerated placental ageing, metabolism, and mitochondrial function.

The project aims are (i) to investigate the impact of maternal metformin exposure during pregnancy on placental ageing and metabolism, and (ii) to determine the direct effects of metformin on mitochondrial function in human primary trophoblast cells. A unique resource of placental tissue collected during two landmark studies: Efficacy of Metformin in Obese Pregnant Women, a Randomised controlled (EMPOWaR) trial and the Pregnancy Outcome Prediction (POP) study will be used to address the first aim. Placental ageing will be assessed by measuring telomere length, expression of ageing-associated genes, and end-products of oxidative stress. Detailed deep-phenotyping using multiomics techniques (RNAseq, lipidomics, metabolomics) will be performed to test the impact of metformin on lipidomic profiles and 1-carbon metabolism. The second aim will be addressed using direct metformin administration to in vitro isolated primary trophoblast cells isolated from donated healthy human placentas. We will thus test whether metformin acts directly on trophoblast through assaying cellular oxygen consumption rate and respiratory chain complex activities.

The project results will add to current knowledge regarding energy production and nutrient transfer late in pregnancy, and will provide important new data to help guide safe use of metformin during pregnancy

Who might benefit from this research?
Gestational diabetes mellitus (GDM) currently affects between 3-25% of pregnancies worldwide, constituting a significant global health-care burden. Moreover the incidence of gestational diabetes continues to rise, as do population risk factors for developing GDM such as obesity and advanced maternal age. The new knowledge generated by this research will be of direct benefit to clinicians, academics, and health policy-makers developing guidelines and national recommendations regarding optimal treatment strategies for gestational diabetes and appropriate drug use in pregnancy. Insight into how metformin affects the placenta will provide a mechanistic framework to interpret fetal and offspring growth outcomes observed in human trials of metformin use in pregnancy. A greater understanding of the placental effects of metformin will be highly informative for clinicians (obstetricians and endocrinologists) who, together with their patients, weigh the risks and benefits of various treatment options for gestational diabetes and other metabolic conditions (PCOS, obesity) during pregnancy. Our results will be of relevance to improving the pregnancy outcomes and optimising treatment for the 1 in 20 pregnant women in the UK who develop GDM, and the 1 in 7 who are affected worldwide. In addition, because the project will shed light on the potential long-term effects of intrauterine metformin, our results will be of interest and potential impact for families with children who have previously been exposed to metformin during their development in the womb. Because the effects of a sub-optimal intrauterine environment on offspring can be life-long, there will be significant health, economic, and societal benefits to optimising GDM treatment. We expect new knowledge of how metformin affects the placenta to advance the work of scientists with interests in placental biology, fetal growth, pregnancy outcomes, and gestational diabetes.

How might they benefit from this research?
Untreated, GDM poses significant risks to the immediate and long-term health of the mother and fetus. Hence it is essential to implement effective clinical interventions to maintain glycaemic control and limit fetal growth during GDM-affected pregnancies. Metformin offers important pragmatic advantages of being cheap to produce, convenient to take, and easy to store, particularly in low and middle development index (LMDI) settings, where highest incidences of GDM currently occur (>25% in some south-east Asian settings). Metformin is currently offered as first-line drug treatment in many global settings, including the UK, US and New Zealand. However, recent worrying follow-up data from clinical trials suggest that it may increase the risk of obesity and adverse metabolic outcomes in children. Hence there is an urgent unmet need to understand the long-term impact of maternal metformin treatment. Our results will fill this knowledge gap by determining the impact of metformin treatment on the placenta's ability to support fetal growth and by testing the direct effect of metformin on placental energy production. There will thus be direct benefit to scientists, clinicians, health-policy makers, and patients through providing much-needed insight into the placental impact of metformin treatment during pregnancy. For women who are pregnant and diagnosed with GDM that requires drug treatment (~1:50 pregnant women in the UK), our data will be invaluable in helping them, with their clinicians, to make informed choices about care.

For scientists working in the field of placental biology and fetal growth, our results will give new insight into mechanisms of placental energy production and mitochondrial function in late pregnancy. Establishing a paradigm and workable schema for comprehensive placental drug testing would be of immense value in the future in helping to develop safe and effective treatments for medical conditions in pregnancy