Protein expression alterations in blood plasma may lead to new targets for drug discovery and therapeutic intervention for people with concomitant stroke and patent foramen ovale. Patent foramen ovale (PFO) refers to a hole between the right and left atria in the heart. The hole exists pre-birth in all humans and closes soon after birth in around 75% of people, leaving between 20% and 30% with the hole.1 Of these, the majority do not develop any clinical challenges and lead normal lives with no medical intervention.
PFO has, however, been associated with stroke caused by blood clots. Clots developed in leg veins can pass directly from the heart to the brain, bypassing the lungs due to the hole between the atria. While not all people who have PFO develop stroke, 40% of people who have suffered a stroke of unknown origin also have PFO.1 As a result, for people who have PFO and developed stroke, clinicians have begun to recommend PFO closure as a step to preventing further stroke activity. The other common therapeutic is blood thinners. Studies have found that PFO closure does reduce risk2 and a meta-analysis of comparative studies and meta-regression analysis suggests that PFO closure might be superior to drug therapy.3
While clinical results show that PFO closure leads to risk reduction, there are few theories suggesting why PFO closure might impact stroke risk. One study, from the Clinical Proteomics Research Center in Cambridge, Massachusetts, took a “before and after” look at patients with stroke and PFO and then subsequent PFO closure operations using mass spectrometry to characterize blood plasma protein levels.4 Reasoning that PFO closure may lead to changes in protein expression, the team went in search of biomarkers. This “before and after” approach provided the perfect control because patients act as their own control.
To overcome the limitations of traditional tandem mass spectrometry, the team developed a new two-pass approach that allowed them to increase their ability to identify low-quantity proteins and reduce the overall time to analyze samples. The technique combines liquid chromatography tandem mass spectrometry (LC-MS/MS) with expression trend ratios and receiver operating characteristic analyses to evaluate and score potential biomarkers. After a very accurate full-scan quantification with tandem MS, they used the inclusion list generated by quantitative analysis of the first pass and MS again to “fractionate” samples, resulting in an increased ability to identify low-abundance proteins.4
The new two-pass workflow identified clear quantitative differences in circulatory protein expression in stroke patients after PFO closure. Some of these related to biological pathways implicated in stroke, including a reduction in pro-inflammatory and pro-coagulent proteins after closure. Serotonin (5-HT), serotransferin, apolipoprotein AI, β-globin, serum albumin, and α2-macroglobulin were all downregulated after PFO closure. Specific stroke-related signaling pathways implicated include the acute-phase response, Liver X Receptor-Retinoid X Receptor (LXR/RXR) activation and intrinsic and extrinsic prothrombin activation.4
The Massachusetts team had previously suggested that PFO may lead to harmful chemoactive factors escaping deactivation by bypassing the lungs due to atrial-atrial shunting. Or, the bypass may prevent lung blood vessels from detecting important vasoactive mediators leading to their deregulation.4 Either way, the two-pass MS approach showed clear alterations in protein expression after PFO closure, offering explanatory biology supplementing clinical evidence that closure reduces further stroke risk.
1 Casaubon, L., et al. (2007) ‘Recurrent stroke/TIA in cryptogenic stroke patients with patent foramen ovale‘, Canadian Journal of Neurological Science, 34 (1), (pp. 74-80)
2 Yoon, J.H., et al. (2011) ‘Intermediate and long-term results of transcatheter closure of patent foramen ovale using the amplatzer patent foramen ovale occluder: one case of pulmonary embolism irrespective of patent foramen ovale closure‘, Korean Circulatory Journal, 41 (7), (pp. 356-362)
3 Agarwal, S., et al. (2012) ‘Meta-analysis of transcatheter closure versus medical therapy for patent foramen ovale in prevention of recurrent neurological events after presumed paradoxical embolism‘, JACC Cardiovasc Interventions, 5 (7), (pp. 777-789)
4 Lopez, M.F., et al. (2012) ‘Heart-brain signaling in patent foramen ovale-related stroke: differential plasma proteomic expression patterns revealed with a 2-pass liquid chromatography-tandem mass spectrometry discovery workflow‘, Journal of Investigative Medicine, 60 (8), (pp. 1122-1130)