The molecular dissociation constant, K_d, is a well-established parameter to quantitate the affinity of protein-protein or other molecular interactions. Recently, we reported the theoretical basis and experimental procedure for K_d determination using a quantitative FRET method. Here we report a new development of K_d determination by measuring the reduction in donor fluorescence due to acceptor quenching in FRET. A new method of K_d determination was developed from the quantitative measurement of donor fluorescence quenching. The estimated K_d values of SUMO1-Ubc9 interaction based on this method are in good agreement with those determined by other technologies, including FRET acceptor emission. Thus, the acceptor-quenched approach can be used as a complement to the previously developed acceptor excitation method. The new methodology has more general applications regardless whether the acceptor is an excitable fluorophore or a quencher. Thus, these developments provide a complete methodology for protein or other molecule interaction affinity determinations in solution.

Acute liver failure (ALF) is associated with high mortality, and a poor understanding of the underlying pathophysiology has resulted in a lack of effective treatments so far. Here, using an amatoxin-induced rhesus monkey model of ALF, we panoramically revealed the cellular and molecular events that lead to the development of ALF. The challenged monkeys with toxins underwent a typical course of ALF including severe hepatic injury, systemic inflammation and eventual death. Adaptive immune was not noticeably disturbed throughout the progress of ALF. A systematic examination of serum factors and cytokines revealed that IL-6 increase was the most rapid and drastic. Interestingly, we found that IL-6 was mainly produced by circulating monocytes. Furthermore, ablation of monocyte-derived IL-6 in mice decreased liver injury and systemic inflammation following chemical injection. Our findings reveal a critical role of circulating monocytes in initiating and accelerating ALF, indicating a potential therapeutic target in clinical treatment for ALF.

Background

Acute liver failure (ALF) is a complicated clinical syndrome associated with high mortality, with liver transplantation as the only treatment option. Treatment of mesenchymal stem cells has shown a potential therapeutic option for acute liver failure. However, the lack of random clinical trials and large non-human primate studies makes it necessary to assess the efficacy and safety in the clinic.

Methods

We treated the monkeys with peripheral delivery of human umbilical MSCs (hUC-MSCs) and investigated the role of hUC-MSCs in modulating the progress of acute liver failure.

Results

The use of early peripheral infusion of human umbilical cord MSC infusion did not improve liver regeneration or modulate adaptive immunity. However, it significantly suppressed the hepatic aggregation and maturation of circulating monocytes and their IL-6 secretion, greatly improving liver histology, systemic homeostasis, and survival.

Conclusions

Our study reveals the critical role of monocyte-derived IL-6 in initiating and accelerating acute liver failure and hUC-MSC treatment can disrupt the development of the inflammatory cascade by inhibiting monocyte activation. Early hUC-MSC treatment disrupts the development of the inflammatory cascade, indicating a potential clinical solution for acute liver failure.