The role of circulating DNA in sepsis

Introduction

The identification of the early steps of the response trigged by free DNAs on normal cells may elucidate questions concerning the pathophysiology of some diseases. Small amounts of plasma free DNA have been observed both in healthy individuals and in patients with various diseases such as systemic lupus erythematosus, viral hepatitis and cancer. This study demonstrates that septic patients also release DNA in plasma at levels higher than polytraumatic patients, who also have an inflammatory response to trauma. In vitro studies of protein profile of normal leukocytes in response to a short exposure to DNA purified of bacteria, protozoa (Tcruzi), human DNA (HeLa cells) and to a synthetic unmethylated CpG motif, demonstrated that free DNA is able to modify the protein profile of the blood cells. Understanding how free DNA act as a signal between cells is important for knowing how DNA orchestrates immune responses in sepsis and other diseases. The role of lipopolysaccharide in the physiopathology of sepsis is clearly recognized, but additional effort will be needed to clarify the sepsis puzzle.

Methods

The study sample included 19 patients with pulmonary sepsis; eight critically ill patients suffering from major tissue injury due to polytrauma, admitted in the medical intensive care unit; and 16 healthy controls. The criteria for inclusion in the group with sepsis were according to criteria of American College of Chest Physicians/Society of Critical Care Medicine Consensus. This study was approved by the ethical council of the Hospital. Informed consent was obtained from all patients or next-of-kin. The samples were obtained in the Hospital Municipal Miguel Couto and the Hospital Universitário Clementino Fraga Filho (HUCFF).

Plasma DNA purification

DNA was extracted from plasma by a method adapted from Federov et al [1] and amplified by PCR of K-ras. Quantification of the amount of DNA was estimated with ethidium bromide fluorescence.