Liver Dysfunction and Phosphatidylinositol-3-Kinase Signalling in Early Sepsis: Experimental Studies in Rodent Models of Peritonitis

Abstract

Hepatic dysfunction and jaundice are traditionally viewed as late features of sepsis and portend poor outcomes. We hypothesized that changes in liver function occur early in the onset of sepsis, yet pass undetected by standard laboratory tests. In a long-term rat model of faecal peritonitis, biotransformation and hepatobiliary transport were impaired, depending on subsequent disease severity, as early as 6 h after peritoneal contamination. Phosphatidylinositol-3-kinase (PI3K) signalling was simultaneously induced at this time point. At 15 h there was hepatocellular accumulation of bilirubin, bile acids, and xenobiotics, with disturbed bile acid conjugation and drug metabolism. Cholestasis was preceded by disruption of the bile acid and organic anion transport machinery at the canalicular pole. Inhibitors of PI3K partially prevented cytokine-induced loss of villi in cultured HepG2 cells. Notably, mice lacking the PI3Kγ gene were protected against cholestasis and impaired bile acid conjugation. This was partially confirmed by an increase in plasma bile acids (e.g., chenodeoxycholic acid [CDCA] and taurodeoxycholic acid [TDCA]) observed in 48 patients on the day severe sepsis was diagnosed; unlike bilirubin (area under the receiver-operating curve: 0.59), these bile acids predicted 28-d mortality with high sensitivity and specificity (area under the receiver-operating curve: CDCA: 0.77; TDCA: 0.72; CDCA+TDCA: 0.87). Liver dysfunction is an early and commonplace event in the rat model of sepsis studied here; PI3K signalling seems to play a crucial role. All aspects of hepatic biotransformation are affected, with severity relating to subsequent prognosis. Detected changes significantly precede conventional markers and are reflected by early alterations in plasma bile acids. These observations carry important implications for the diagnosis of liver dysfunction and pharmacotherapy in the critically ill. Further clinical work is necessary to extend these concepts into clinical practice. Please see later in the article for the Editors' Summary Sepsis (blood poisoning)—a life-threatening condition caused by an inappropriate immune response to an infection—is a major global cause of death. Normally, when bacteria or other microbes enter the human body, the immune system efficiently destroys the invaders. In sepsis the immune system goes into overdrive, and the chemicals it releases into the blood to combat the infection trigger widespread inflammation (swelling). This leads to the formation of small blood clots and leaky blood vessels that block the flow of blood to vital organs such as the kidneys and liver. In the most severe cases, multiple organs fail and the patient dies. Anyone can get sepsis, but people with weakened immune systems, the very young, and the elderly are most vulnerable. Symptoms of sepsis include fever, chills, rapid breathing, a fast heart rate, and confusion. In its early stages, sepsis can be treated with antibiotics alone, but people with severe sepsis need to be admitted to an intensive care unit where the vital organs can be supported while the infection is treated. Thirty to fifty percent of people who develop severe sepsis die. If sepsis could be diagnosed in its early stages, it might be possible to save more people. Unfortunately, the symptoms of sepsis mimic those of other conditions, and, because sepsis tends to develop very quickly, it is often not diagnosed until it is too late to save the patient's life. The development of liver (hepatic) dysfunction and jaundice are both regarded as late features of sepsis (jaundice is yellowing of the skin and eyes caused by a build-up of bilirubin in the blood). However, the researchers hypothesized that changes in liver function occur early in sepsis and could, therefore, be used to improve the diagnosis and management of sepsis. The researchers induced sepsis in rats by injecting bacteria into the peritoneal cavity (the gap between the abdominal wall and the abdominal organs), separated the infected animals into predicted survivors and non-survivors based on their heart stroke volume measured using cardiac ultrasound, and then examined their liver function. The expression of genes encoding proteins involved in “biotransformation” and “hepatobiliary transport” (the processes that convert waste products and toxic chemicals into substances that can be conjugated to increase solubility and then excreted) was down-regulated within six hours of sepsis induction in the predicted non-survivors compared to the predicted survivors. Functional changes such as bilirubin and bile acid accumulation in the liver (cholestasis), poor excretion of xenobiotics (molecules not usually found in the body such as antibiotics), and disturbed bile acid conjugation were also seen in predicted non-survivors but not in survivors. Moreover, phosphatidylinositol-3-kinase (PI3K) signaling (which is involved in several immune processes) increased soon after sepsis induction in non-survivor but not in survivor animals. Notably, mice lacking the PI3Kγ gene did not develop cholestasis or show impaired bile acid conjugation after induction of sepsis. Finally, in human patients, plasma bile acids were increased in 48 patients on the day that severe sepsis was diagnosed, and these increases accurately predicted death in these patients. These findings show that liver dysfunction is an early event in animal models of sepsis and that PI3K signalling plays a crucial role in the development of liver dysfunction. They show that all aspects of liver biotransformation are affected during sepsis and suggest that outcomes are related to the severity of these changes. The limited clinical data included in this study also support the hypothesis that changes in liver function occur early in sepsis, although these data need confirming and extending. Taken together, these findings suggest that liver function tests might aid early diagnosis of sepsis and might also provide information about likely outcomes. They also have important implications for the use of drugs in patients who are critically ill with sepsis, in that some of the drugs routinely administered to such patients may not be adequately detoxified and may, therefore, contribute to organ injury. Finally, these findings suggest that inhibition of PI3Kγ may alleviate sepsis-associated cholestasis. Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001338.