Inducible Nitric Oxide Synthase in Circulating Microvesicles: Discovery, Evolution, and Evidence as a Novel Biomarker and the Probable Causative Agent for Sepsis

Abstract

Background: The sepsis pathology remains an enormous medical problem globally because morbidity and mortality remain unacceptably high in septic patients despite intense research efforts. The economic and societal burden of sepsis makes it the most pressing patient care issue in the United States and worldwide. Sepsis is a dysregulated immune response normally initiated by an infection. The need for an early, accurate, and reliable biomarker test to detect the onset of sepsis and for a targeted sepsis therapy are widely recognized in the biomedical community.

Content: This report reviews the published findings relevant to microvesicle-associated inducible nitric oxide synthase (MV-A iNOS) as a novel plasma biomarker for the onset of sepsis including human clinical studies and animal studies. Plasma iNOS as a standalone test and as one of the components of a novel panel of biomarkers to stage the progression of sepsis are presented and discussed in comparison to other biomarkers and other proposed panels of biomarkers for sepsis.

Summary: The data strongly support the concept that extracellular plasma MV-A iNOS in circulating microvesicles is centrally involved in the initiation of sepsis, and a diagnostic test based upon plasma iNOS can serve as an early pre-symptomatic warning signal for the onset of sepsis. A novel panel of plasma biomarkers comprised of iNOS, pro-IL-18, pro-IL-33, and Reg-1α is proposed as a multianalyte pre-symptomatic method to stage the onset of sepsis for improved prompt data driven patient care.

Keywords: biomarker; blood; iNOS; inducible nitric oxide synthase; microvesicle-associated; microvesicles; plasma; sepsis.

Figures

Figure 1:. Discovery of iNOS in Plasma

A. Western immunoblots of immunoprecipitated iNOS from Patient #7 Day 0, 1, 2 and 4 plasma in the first ICU study. B. Concentration of iNOS measured by the EIA in plasma from Patients #7 (light bars) and #8 (dark bars) on Days 0, 1, 2 and 4 of the study (27,28). * denotes the day the Intensivists first suspected sepsis

Figure 2:. Discovery of Microvesicle-Associated in iNOS

Microvesicle-associated iNOS in a peripheral blood mononuclear cell (PBMC) preparation from a septic patient immunostained with FITC-labeled anti-iNOS monoclonal antibody (28,38). The arrows are pointing to fluorescently immunostained, extracellular microvesicle-associated iNOS in a field containing both immunostained and unstained blood cells. These iNOS-containing microvesicles are only found in septic patients. The PBMC preparation was isolated by density gradient centrifugation.

Figure 3:. Microvesicle-Associated iNOS Role in the Sepsis Cascade

This diagram illustrates the role microvesicle-associated iNOS (MV-A iNOS), shown as green balls, plays in the sepsis cascade (38,40). Once the MV-A iNOS is delivered to susceptible cells, it is internalized, produces toxic quantities of nitric oxide and peroxynitrite inside the vulnerable receiver cell. This can kill the cell, produce microperforations in barrier structures, and lead to hemodynamic collapse.