The present study was designed to determine the cause of early hepatocellular injury during liver resection. Previous publications already showed elevated plasma levels of markers of liver damage prior to liver transection and hepatic inflow occlusion [3, 6]. These observations suggested that mechanisms other than ischemia-reperfusion injury could contribute to peri- and postoperative cell death and organ dysfunction. We showed that direct manipulation of the liver during surgery is a leading cause of hepatocellular injury.
Arterial L-FABP and GSTα plasma levels increased following the start of the operation and reached a plateau before liver transection and ischemia-reperfusion. Surprisingly, we found no additional effect of organ transection or intermittent Pringle maneuver on these increased L-FABP and GSTα plasma levels. The apparent resistance of the liver to an ischemic insult however, is in line with previous data by Figueras et al. [13] who showed no effect of the extent of inflow occlusion in patients with a normal liver, although in their study livers of patients with cirrhosis appeared to be more vulnerable to hepatic inflow occlusion. In addition, other authors who showed a progressive release of GSTα following a Pringle maneuver applied prolonged and continuous inflow occlusion [6], which is known to aggravate hepatocellular injury compared to the intermittent Pringle maneuver [14].
Previous authors who observed an early increase in plasma concentrations of transaminases and GSTα have ascribed this phenomenon to the hepatotoxic effects of anesthesia [4], systemic inflammation after intestinal manipulation [5], and the effects of manipulation of the liver itself during perihepatic dissection and mobilization [6]. We were able to rule out the first two factors as potential causes of early hepatocyte injury since a similar increase of L-FABP plasma concentrations did not occur in patients undergoing lower intestinal surgery. These patients were anesthetized in a similar manner as the patients undergoing liver resection and underwent extensive intestinal manipulation.
By elimination of other potential causes, it thus must be concluded that increasing L-FABP levels occurs during and due to liver manipulation in patients undergoing liver resection. By measuring concentration gradients across the intestines and the liver, we were able to show that the increased L-FABP levels during liver manipulation are exclusively due to L-FABP release from the liver. Some intestinal L-FABP release could have been expected when L-FABP, which is also expressed by the intestines, would have been released from injured enterocytes, but the absence of intestinal L-FABP release clearly indicates that organ manipulation during liver resection results in hepatocellular injury without causing intestinal injury.
Finally, we were able to rule out systemic inflammation as a leading cause of hepatocellular injury since L-FABP peak levels were reached already before the onset of the inflammatory response. Arterial IL-6 plasma levels increased between 90 and 125 min after laparotomy, which approximates the established time lag between an inflammatory stimulus and IL-6 release [15]. This suggests that the inflammatory response is triggered by an early event during the operation.
According to the “danger model” hypothesis of Matzinger [16], cell injury leads to the release of immunostimulatory proteins or nucleotides, so-called danger signals, that activate the immune system and induce systemic inflammation [17]. In line with this theory, we consider that early hepatocyte damage due to liver manipulation could give rise to the release of such “danger signals” and contribute to systemic inflammation. Consequently, liver manipulation-induced hepatocyte injury may be a trigger for the inflammatory response to surgery. Mechanistic proof for this theory, however, is difficult to obtain in vivo.
Both L-FABP and GSTα decreased immediately following surgery, in contrast to the more classic marker of hepatocyte injury, AST. The ongoing increase of plasma levels of such markers following liver surgery has been regarded as a sign of ongoing hepatocellular injury and impending liver failure [18]. Our study shows that the late postoperative peak of AST is more likely to be a reflection of slow leakage than of ongoing injury, since the leakage of small-molecular proteins L-FABP and GSTα decreased within 90 min. As a consequence, L-FABP and GSTα are probably more sensitive for detecting ongoing hepatocyte injury and impending liver failure than AST. To prove this assumption, however, a large prospective study is needed. The rapid decline of L-FABP and GSTα is a result of their rapid renal clearance. Arterial renal venous concentration gradients showed that the kidneys remove approximately 30% of L-FABP in a single pass, leading to a calculated L-FABP half-life of 11 min.
We did not explore potential mechanisms of liver manipulation-induced cell injury. Earlier studies showed that liver mobilization and assessment of resectability significantly reduced hepatic venous oxygen saturation [19, 20]. This could also be a cause of hepatocyte damage in our case, although we did not measure hepatic oxygen saturation. It is not clear whether hepatic oxygen saturation decreased due to physical obstruction of the blood stream or whether it decreased secondary to other processes [21, 22]. Alternatively, cell damage may occur as a direct consequence of mechanical impact [23].
In summary, it was previously believed that vascular occlusion and parenchymal transection were the major reasons for hepatocyte injury during liver surgery. This study demonstrates that liver manipulation is a leading cause of hepatocyte injury during liver surgery. A potential causal relation between liver manipulation and systemic inflammation remains to be established. However, since the inflammatory cascade is apparently initiated early during major abdominal surgery, interventions aimed at reducing postoperative inflammation and related complications should be started early during surgery or beforehand.