Molekularbiologische und immunhistologische Leberveränderungen beim Mausmodell eines Kachexie-induzierenden Pankreas-Karzinoms: Effekte einer Monoaminoxidase-A-Inhibition

Background: Cancer cachexia represents a multisystem disease affecting more than 50 % of cancer patients and is associated with a worsened prognosis and quality of life. Cancer cachexia is characterized by a symptom complex of weight loss, muscle wasting and inflammation. As the exact mechanisms are not completely understood, early cachexia markers are missing, and no effective therapy is available, cancer cachexia is often diagnosed too late and not treated effectively. In particular, the altered liver metabolism associated with negative nitrogen balance is poorly understood. This work explores the hypothesis that there is tumor cachexia-induced, possibly inflammatory, damage to the perivenous glutamine synthetase (GS)-expressing cell layers of the liver. This may contribute to the negative nitrogen balance in cancer cachexia by limiting perivenous ammonia scavenging. Also, the mitochondrial enzyme monoamine oxidase A (MAO-A) might contribute to liver injury through formation of reactive oxygen species, thus representing a potential therapeutic target in cancer cachexia. Methods: Untreated mice with pancreatic cancer (CA n=11) of the 3x transgenic LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx-1-Cre murine model of pancreatic cancer (PDAC) were first compared with wild-type control animals (WT n=13). In addition, the effect of MAO-A inhibition was studied in 3x transgenic mice with pancreatic cancer (CA HH n=7) and wild-type control animals (WT HH n=11). To this end, these mice were intraperitoneally administered 0.6 mg harmine hydrochloride (HH) daily for a period of two months starting from the third month of life. In these four groups, the liver was examined by immunohistochemistry using 6 µm cryosections for protein expression and zonal distribution of GS, MAO-A and inflammation markers (IL-1β, COX-2, CD68) as well as liver glycogen content (PAS reaction). Furthermore, relative gene expression of GS, factors of hepatic amino acid transport (FXR, RhBG, SLC1A2, SLC1A4, SLCA1A5), inflammation (IL-1β, IL-6, TNF-α, COX-1, CD68, SOCS-3, MIF), apoptosis (BAX, BCL-2, Caspase-3) and proliferation (PCNA) markers, as well as MAO-A and MAO-B were analyzed by qRT-PCR on liver homogenate. Results: In the CA group, a significant reduction in strictly perivenous GS protein expression was shown as an important cancer cachexia effect compared to WT. In contrast to that, an increase in GS mRNA was shown in the CA group, suggesting a posttranscriptional effect by PDAC. The examined inflammation markers were significantly increased at both the protein and mRNA levels in the CA group compared to WT. Contrary to the hypothesis of cancer cachexia-induced MAO-A upregulation, this was not detectable at either the protein or mRNA level. This, however, does not allow conclusions about a possible increased MAO-A enzyme activity. MAO-A inhibition with HH reversed the reduction of GS protein expression in the CA group. Similarly, protein expression of the inflammatory markers IL-1β and CD68 in the CA group was decreased by HH treatment. However, a positive effect on body weight by HH treatment was not detectable. Conclusion: The present work confirms previous findings and provides new evidence for the importance of early changes in liver metabolism in cancer cachexia. Significantly decreased GS protein expression suggests damage to the perivenous zone. Reduction of glutamine synthesis and ammonia scavenging may explain cachexia-typical metabolic changes such as decreased glutamine and increased glutamate levels and hyperammonemia. The increased expression of inflammatory markers in CA animals supports the hypothesis of inflammation-related liver injury as a cachexia-promoting alteration. Regarding the anticachectic therapeutic potential of the MAO-A inhibitor HH, a conflicting picture emerges. Although HH seems to effectively counteract GS reduction, perivenous zone damage, and hepatic inflammatory response, this was not associated with a positive effect on body weight. Further research on this subject is necessary.