Pathophysiological responses in a tissue, no matter the cause, are characterized by dramatic changes of bio-molecular activity in the local tissue microenvironment. Our understanding of disease development and ability to administer critical treatment depends heavily on the amount of accurate information we can collect from the molecular tissue microenvironment at any time. To date, however, no sensing platform has been able to achieve this on a molecular level.
In research published at the beginning of April, a team mimicked the in vitro conditions that occur during the progression of inflammation/infection on a sensing platform in order to investigate how bio-molecular dynamics changes in the local microenvironment. They used a novel engineered cell-membrane-mimetic surface, where a custom polymer mimics phosphorylcholine (PC) as an alternative receptor for the human acute phase protein C-reactive protein (CRP) on the eukaryotic cell-membrane. The role of CRP is to bind to damaged host cells or invading microbes at the site of inflammation, thus activating the complement pathway, leading to clearance by innate-immune cells.
To further replicate the local ionic microenvironment of a pathogenic site, a conducting-polymer-based organic bioelectronic ion pump (OEIP) delivering [Ca2+] and [H+] with well-defined, spatio-temporal control was integrated with the sensing platform. Since Ca2+-dependent binding of CRP to the engineered PC surface models the interactions occurring between systemic CRP and cell membrane-bound CRP receptors, the biomimetic interface allows for the the binding constants (kon, koff, and Kd) of CRP to PC to be determined. These values are important to understand the binding affinity of CRP to the receptor on cell membrane and why the serum CRP level needs to be elevated 100- to 1000-fold in acute-phase.
Moreover, the study revealed the local ionic microenvironment to be an essential parameter in transforming CRP binding kinetics, indicating a hidden mechanism on site-selective activation of circulating CRP in damaged tissue. At conditions promoting active binding of CRP, it is further shown that both complement component 1q (C1q) and the tissue-constructing protein fibronectin (FN) is recruited to the site in a local pH-dependent manner.
Taken together, this manuscript illustrates a novel approach to detect CRP by using a robust cell-membrane-mimetic surface sensor with an advanced feature of repeated uses (over 200 times). From a clinical perspective, such intricate dynamics in the binding affinity imply a mechanism of site-selective binding of circulating CRP at the local ionic microenvironment, a common situation in damaged tissue. Furthermore, the high specificity of the biomimetic interface for CRP enables label-free sensing of CRP in sampled serum, ranging from physiological plasma concentrations to pathophysiological acute phase conditions. By presenting a more coherent picture of the host response in which the active local form of CRP is obviously different from measuring systemic CRP level, the biomimetic interface emerge as a powerful tool in revealing the whole picture of well-organized acute phase responses at molecular resolution.
