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The local anesthetic lidocaine, which has been used extensively during liposuction, has been
reported to have cytotoxic effects and therefore would be unsuitable for use in autologous lipotransfer.
We evaluated the effect of lidocaine on the distribution, number, and viability of adipose-derived stem
cells (ASCs), preadipocytes, mature adipocytes, and leukocytes in the fatty and fluid portion of the
lipoaspirate using antibody staining and flow cytometry analyses. Adipose tissue was harvested from
11 female patients who underwent liposuction. Abdominal subcutaneous fat tissue was infiltrated
with tumescent local anesthesia, containing lidocaine on the left and lacking lidocaine on the right
side of the abdomen, and harvested subsequently. Lidocaine had no influence on the relative
distribution, cell number, or viability of ASCs, preadipocytes, mature adipocytes, or leukocytes in the
stromal-vascular fraction. Assessing the fatty and fluid portions of the lipoaspirate, the fatty portions
contained significantly more ASCs (p < 0.05), stem cells expressing the preadipocyte marker Pref-1
(p < 0.01 w/lidocaine, p < 0.05 w/o lidocaine), and mature adipocytes (p < 0.05 w/lidocaine, p < 0.01
w/o lidocaine) than the fluid portions. Only the fatty portion should be used for transplantation. This
study found no evidence that would contraindicate the use of lidocaine in lipotransfer. Limitations of
the study include the small sample size and the inclusion of only female patients.
Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO2) are the key enzymes of tryptophan (TRP) metabolism in the kynurenine pathway (KP). Both enzymes function as indicators of immunosuppression and poor survival in cancer patients. Direct or indirect targeting of either of these substances seems thus reasonable to improve therapy options for patients. In this study, glioblastoma multiforme (GBM) as well as head and neck squamous cell carcinomas (HNSCC) were examined because of their different mechanisms of spontaneous and treatment-induced immune escape. Effects on gene expression and protein levels were examined. Accompanying assessment of TRP metabolites from treated GBM cell culture supernatants was conducted. Our results show a heterogeneous and inversely correlated expression profile of TRP-metabolizing genes among GBM and HNSCC cells, with low, but inducible IDO1 expression upon IFNγ treatment. TDO2 expression was higher in GBM cells, while genes encoding kynurenine aminotransferases were mainly confined to HNSCC cells. These data indicate that the KP is active in both entities, with however different enzymes involved in TRP catabolism. Upon treatment with Temozolomide, the standard of care for GBM patients, IDO1 was upregulated. Comparable, although less pronounced effects were seen in HNSCC upon Cetuximab and conventional drugs (i.e., 5-fluorouracil, Gemcitabine). Here, IDO1 and additional genes of the KP (KYAT1, KYAT2, and KMO) were induced. Vice versa, the novel yet experimental cyclin-dependent kinase inhibitor Dinaciclib suppressed KP in both entities. Our comprehensive data imply inhibition of the TRP catabolism by Dinaciclib, while conventional chemotherapeutics tend to activate this pathway. These data point to limitations of conventional therapy and highlight the potential of targeted therapies to interfere with the cells' metabolism more than anticipated.
The Immunomodulator 1-Methyltryptophan Drives Tryptophan Catabolism Toward the Kynurenic Acid Branch
(2020)
Background: Animal model studies revealed that the application of 1-methyltryptophan (1-MT), a tryptophan (TRP) analog, surprisingly increased plasma levels of the TRP metabolite, kynurenic acid (KYNA). Under inflammatory conditions, KYNA has been shown to mediate various immunomodulatory effects. Therefore, the present study aims to confirm and clarify the effects of 1-MT on TRP metabolism in mice as well as in humans.
Methods: Splenocytes from Balb/C or indoleamine 2,3-dioxygenase knockout (IDO1−/−) mice or whole human blood were stimulated with 1-MT for 6, 24, or 36 h. C57BL/6 mice received 1-MT in drinking water for 5 days. Cell-free supernatants and plasma were analyzed for TRP and its metabolites by tandem mass spectrometry (MS/MS).
Results: 1-MT treatment induced an increase in TRP and its metabolite, KYNA in Balb/C, IDO−/− mice, and in human blood. Concurrently, the intermediate metabolite kynurenine (KYN), as well as the KYN/TRP ratio, were reduced after 1-MT treatment. The effects of 1-MT on TRP metabolites were similar after the in vivo application of 1-MT to C57BL/6 mice.
Conclusions: The data indicate that 1-MT induced an increase of KYNA ex vivo and in vivo confirming previously described results. Furthermore, the results of IDO−/− mice indicate that this effect seems not to be mediated by IDO1. Due to the proven immunomodulatory properties of KYNA, a shift toward this branch of the kynurenine pathway (KP) may be one potential mode of action by 1-MT and should be considered for further applications.