Defining mechanisms of lymphocyte inhibition by Glycerol Monolaurate

Glycerol monolaurate (GML) is a naturally occurring monoglyceride with a 12-carbon acyl chain attached to a glycerol head group via an ester linkage. GML functions as both an anti-microbial agent and an immunosuppressive compound. To the best of my knowledge, this is the only pharmaceutical agent in use today that has both functions. However, a better understanding of GML’s mechanism of action is required to find the best clinical applications. The following chapters will address the broader impact GML has on the adaptive immune system, investigate inhibitory components of the GML molecule, and address additional mechanisms of GML inhibition.
In Chapter 3, we explore how GML impacts the adaptive immune system by examining the effect of GML on B cell activation. B cells signal in a similar manner to T cells, both heavily impacted by lipid membrane dynamics. Interestingly, while GML does inhibit B cell activation, there were distinct differences seen in GML-mediated inhibition of B cells that were not seen in T cells. These data presented in this chapter demonstrate that GML can impact the activation of multiple immune cell types but that the mechanism of inhibition may be cell type specific.
In addition to understanding how GML affects various immune cell types, it is also important to understand what components of GML are necessary for its inhibitory activity. This thought-provoking information is needed not only to better comprehend its mechanism of action but also for developing similar compounds that may be more effective as therapeutic agents. In Chapter 4, I describe studies investigating the components of GML required for its inhibitory function. Human primary T cells were treated with structural analogs of GML with variable chain length, linkage, head group, position, and number of laurate groups. Surprisingly, small changes to its structure can eliminate GML’s inhibitory effects. A single carbon chain of at least 12 carbons with an ester linkage to a polar head group is necessary for GML’s inhibitory effects. Altering these components results in a compound that no longer inhibits T cell activation.
Interestingly, while testing these analogs we observed that some analogs did not inhibit early signaling events but still inhibited cytokine production. These data support a secondary mechanism of GML acting upon later signaling events. In Chapter 5, we hypothesize that GML is disrupting mitochondrial function leading to dysregulated T cell metabolism as a secondary mechanism of GML inhibition. GML treatment resulted in loss of mitochondrial membrane potential, increased ROS production, and significantly decreased ATP concentration. Furthermore, Seahorse analysis showed significant changes in ATP-linked respiration and maximum respiratory capacity. Finally, GML treated cells had notable changes in key tricarboxylic acid cycle metabolites and amino acid levels. Overall, these data support the conclusions that GML treatment disrupts T cell metabolism, thereby inhibiting T cell activation and function. These data suggest a second mechanism used by GML to alter cellular function.
Overall, these studies expand our understanding of how GML impacts the adaptive immune response via altered early signaling and cellular metabolism. These studies broaden our understanding and applications of immune modulating monoglycerides.