Gut Microbiome Identifies Risk Factors for Depression, High Blood Pressure

Bruce R. Stevens, PhD

Gut bacteria could help identify the risk factors for comorbid hypertension with depression, without depression, as well as depression without hypertension.

A team led by Bruce R. Stevens, PhD, professor of physiology & functional genomics, medicine and psychiatry at the University of Florida College of Medicine, collected stool samples using 16S rRNA gene amplicon sequence analyses followed by extensive whole genome metagenomics shotgun sequencing analyses from volunteers diagnosed with hypertension and/or met the DSM-5 criteria for a depressive disorder.

They also collected samples from healthy volunteers that were not diagnosed with either hypertension or a mental illness. A total of 105 people participated in the study.

The team found KEGG ortholog metabolic pathways and gene analyses relating to systemic inflammasome induction and gut wall ACE components, multivariate PCA ordination, linear discriminant analysis effect size assessments, and network distance analyses collectively showed substantially different (P <.05) microbiome taxa and metabolic pathway patterns that differentiated the risk interactions.

According to Stevens, different medical mechanisms for high blood pressure likely correlate with signature molecules produced by gut bacteria that are thought to impact the cardiovascular system, metabolism, hormones, and the nervous system.

"We believe we have uncovered new forms of high blood pressure: 'Depressive Hypertension' (high blood pressure with depression), which may be a completely different disease than 'Non-Depressive Hypertension' (high blood pressure without depression), which are each different from 'Non-Hypertensive Depression,'" Stevens said.

Human gut microbiome dysbiosis and attending pathologic metabolic pathways yielded discrete risk factors that discriminate patients comorbid with hypertensions with or without depression, as well as depression without hypertension, in comparison with healthy subjects.

"People are 'meta-organisms' made up of roughly equal numbers of human cells and bacteria. Gut bacteria ecology interacts with our bodily physiology and brains, which may steer some people towards developing high blood pressure and depression," Stevens said in a statement. "In the future, health professionals may target your gut in order to prevent, diagnose and selectively treat different forms of high blood pressure."

In the past, investigators have found that high blood pressure drugs affect mood disorders including depression and bipolar disorder, with evidence suggesting that the pathways that high blood pressure drugs target plays a role in the development of the mood disorders.

In a 2015 comprehensive study, investigators also found the observed heterogeneity in depression prevalence of hypertension may be attributed to differences in method of evaluation and self-report scales should be cautious of estimating the presence of depression.

The investigators concluded after identifying 41 studies involving 30,796 participants that interview-defined depression affects approximately 33% of hypertensive patients.

Depression is a significant contributor to the global burden of disease. The World Mental Health Survey conducted in 17 countries in 2012 found that on average about 1 in 20 people reported having an episode of depression in the previous experience. It is estimated that depression affects 350 million people around the world, with a lifetime risk of 7%.