The effect of glucosamine and N-acetylglucosamine on aggregation and energy metabolism was investigated over an 8-h period in cells dissociated by 0.25% (w/v) trypsin from the skeletal muscle of 9-day-old chick embryos. At 8 h, 0.023 M glucosamine and N-acetylglucosamine inhibited the aggregation of cells suspended in Eagle's minimal essential medium by 18.9% and 16.4% respectively, as judged on a basis of aggregate size.
Glucosamine and N-acetylglucosamine reduced the cellular ATP level by a mean of 36% and 27% respectively; values reflected in the 32% and 19% loss of total adenine nucleotides caused by these sugars. The adenine nucleotide balance was also changed from a mean control ATP/AMP ratio of 13.7 to 8.75 by N-acetylglucosamine and to 8.0 by glucosamine.
Intracellular lactate/pyruvate ratios were similarly disrupted in cells incubated with 0.023 M hexosamine. Although the hourly values fluctuated, it was seen that the amount of lactic acid relative to pyruvic acid, considered as an average for the 8-h period, was raised from 6:1 in controls to 8:1 in N-acetylglucosamine-treated and to 10:1 in glucosamine-treated cell preparations. Compared to controls at 8 h, glucosamine enhanced the production of lactate into the suspension medium by 99%. The N-acetyl analogue caused cells to produce more lactic acid than did controls for 4-5 h only, for by 8 h 25% less of this metabolite was assayed in the culture medium.
The incorporation of D-[U-14C]glucose into glycogen paralleled the results of extracellular lactic acid assays. N-acetylglucosamine inhibited the incorporation by 30% at 4 h, although by 6 h, and for the remainder of the experimental period, there was more 14C-labelled glycogen in these cells than in controls. By contrast, glucosamine inhibited the incorporation of radioactive glucose into glycogen by 42% at 4 h and, unlike N-acetylglucosamine, consistently thereafter.
Glucosamine also enhanced cellular oxygen uptake throughout the experimental period, to the extent of 59% at 8 h. The oxygen uptake of N-acetylglucosamine-treated cells was similar to controls until about the 5th hour, when there was a subsequent inhibition which had accumulated to 13% by the end of the experiment.
The release of 14CO2 by cells was inhibited by glucosamine. This hexosamine depressed production by 19% at 12 h whereas N-acetylglucosamine inhibited this evolution by 9% at this time.
The metabolic effects of these hexosamines on chick muscle cells in vitro are mainly attributed to a central alteration of the adenine nucleotide balance although certain other documented effects of glucosamine are considered to be involved. An inhibition of cell aggregation by glucosamine and N-acetylglucosamine is discussed in terms of a depressed cellular metabolic economy.