Fig. 1 | npj Biofilms and Microbiomes

Fig. 1

From: New melanocortin-like peptide of E. coli can suppress inflammation via the mammalian melanocortin-1 receptor (MC1R): possible endocrine-like function for microbes of the gut

Fig. 1

MECO-1 attenuates HMGB1-induced TNF release by macrophages in culture. Murine macrophage-like RAW 264.7 cells were incubated for up to 24 h with purified recombinant HMGB1 (0.1 mg/ml) in the absence or presence of MECO-1 (Panel a), or alpha-MSH (Panel b), at 10−10 and 10−12 M. The levels of TNF in the culture medium were determined by ELISA and expressed as mean ± SEM of two independent experiments (in duplicate). *p < 0.05, **p < 0.01 vs. control (“HMGB1 alone”). [In a third experiment (not shown), very similar results were obtained except that the maximum TNF release was observed at 16–24 h, similar to results of others with human endothelial cells]. In panels c and d, cells were incubated with HMGB1 for 6 h with or without MECO-1 or alpha-MSH (10−16–10−6 M). Data represent mean ± SEM of three independent experiments performed in duplicate. With 10−14 M peptide, results were significant at *p < 0.05, and at 10−12 M or more were typically **p < 0.01. In our experiments, at concentrations of MECO-1, alpha-MSH, and ACTH of around 1 nM and higher, dose response curves often reverse direction, i.e., turn upward. The reversal is more clearly seen in Fig. 2. The mechanism of the reversal is not known. (Desensitization, receptor inactivation, receptor internalization, and dissociation of dimeric receptors are all plausible candidates.) As a result, the shape of the lower part of the curve and the actual inflection point may vary from experiment to experiment. This feature may be missed when results of several experiments are combined

Back to article page