Simvastatin and Emotional Processing (OxSTEP)

Depression is common and associated with considerable disability (James-2018). Furthermore, the impact of the current Covid-19 pandemic on the mental health of the general population, especially in terms of depression, anxiety, and stress is proving enormous (Vindegaard-2020). Such effect is likely due to an intricate combination of biological factors (potentially neuroimmune [Troyer-2020]) as well as psychosocial aspects (such as self-isolation and loneliness [Blanco-2020]) - the latter significantly associated with worse mental health outcomes (Leigh-Hunt-2017). In particular, an important factor associated with increased vulnerability to depression is social isolation and loneliness, both of which are exacerbated by the measures needed to control the Covid-19 pandemic. Within this context, there is a need to identify factors that may be protective against the negative mental health consequences of such psychosocial stressors.

There is increasing evidence that low-level inflammation is an important mechanism by which psychosocial stress, including loneliness, predisposes to depressive symptomatology (Nersesian-2018). Consistent with this, a recent observational study conducted by our group in the context of the COVID-19 pandemic found that people who were taking a statin (which have broad anti-inflammatory properties) had a relatively increased positive bias on measures of emotional processing that are known to be associated with psychological vulnerability to depression (COSIE study, R69299/RE001). This raises the interesting possibility that reduced levels of inflammation have a protective effect within the current context of the high levels of psychosocial stress associated with the pandemic. This is consistent with a wealth of epidemiological studies showing that, at a population level, prescription of statins is associated with decreased rates of anxiety and depression (Parsaik-2014).

The aim of the current study is to extend these observational studies and experimentally test in a prospective double-blind controlled design whether reducing inflammation by administering a statin lowers vulnerability to depression in at-risk individuals, as measured by well-established cognitive biomarkers.

Patients with depression and people vulnerable to depression consistently show negative biases in emotional processing, which are believed to play a key role in the development and maintenance of clinical depressive symptoms (Roiser-2013). Overall, evidence suggests that early changes in emotional processing can serve as valid surrogate markers of antidepressant efficacy (Harmer-2017). Intriguingly, our previous study showed that patients on statins were less likely to show negative cognitive biases (COSIE study, R69299/RE001): this observation provides a potential cognitive biomarker of the ability of statins to prevent depression. We and others have also shown that induction of inflammation in healthy participants is associated with negative cognitive biases and deficits in reward learning (Cooper-2017; Miller-2017). In addition, inflammation is associated with impairment in tests of learning and memory (Gorelick-2010). This could add to the likelihood of inflammation leading to depression through compromise of problem-solving skills.

While the COSIE study suggests that statin treatment is associated with decreased negative emotional processing in an at-risk population, such observational studies are subject to confounders and require prospective controlled investigations for confirmation. In the present study therefore we propose to assess the effect of 28-days administration of statin treatment compared to placebo on emotional processing, reward learning, and working memory, in 100 healthy volunteers at-risk for depression due to loneliness in the context of the Covid-19 pandemic. We will also measure waking salivary cortisol as an index of the effect of inflammation to activate the hypothalamic-pituitary-adrenal (HPA) axis. The statin we have selected is simvastatin in view of its widespread use and safety. Our prediction is that, relative to placebo, in this at-risk group, simvastatin will lead to positive effects on emotional processing, reward learning, working memory, and will also lower waking salivary cortisol.