Effects of sugars on the physiology of cultured fibroblasts

Fructose-induced enhanced mitogenicity of diploid human cells: possible relationship with cell differentiation

Fructose strongly stimulates the growth of normal diploid human skin fibroblasts (SFs) and induces marked changes in their morphology and lipid accumulation. This mitogenic effect occurs despite very low fructose consumption and depends on the presence of glutamine. The cell kinetics of cultured fructose-fed human skin fibroblasts were different from those fed on glucose: in the presence of fructose a high proliferative index persisted at Day 14 of culture and the duration of the total cell cycle and of the G1 + 1/2 M and S phases was slightly shorter. The mitogenic effect of fructose on SF was largest in the presence of human serum: it was small or undetectable when fibroblasts were cultured in media supplemented with dialyzed human serum, fetal bovine serum, or serum substitutes. This suggests that serum growth factor(s) mediate the mitogenic effect of fructose. Only normal diploid human cells seem to be sensitive to this mitogenic effect of fructose: the long-term growth of normal human liver cells on fructose was slightly better or similar to that on glucose. In contrast, fructose could only support limited growth of hamster fibroblastic Nil cells and of a transformed human fibroblastic line, which grew better with glucose.

DNA binding of histone H1 is modulated by nucleotides

Histone H1 acts as a general repressor of transcription in eukaryotes by organizing nucleosomes into inaccessible condensed forms of chromatin. The capability of H1 to bind to DNA with some sequence specificity is likely to be critical in the control of these processes. We show here that ATP and several other nucleotides, including non-hydrolyzable derivatives, can inhibit DNA binding of H1. The results also show that ATP differentially affects binding of H1 to DNA in a fashion enhancing nucleotide sequence specificity of the binding. The study suggests a novel mechanism of modulation of H1 activity that has important implications for the role of H1 as a transcriptional regulator.

Production of recombinant protein C in serum-containing and serum-free perfusion culture

For the development of a perfusion culture producing recombinant human protein C, the effects of fetal calf serum and growth factors on cell growth and recombinant protein production were investigated. Although the growth of recombinant cells was stimulated by serum in a dose-dependent manner, a lower concentration of serum (2%) could support both synthesis and post-translational modification of protein C as efficiently as 10% serum. Among the growth factors tested, transferrin enhanced protein C production to the level comparable with 10% serum, while insulin was effective in maintaining cellular metabolism. Based on these results, a perfusion culture for a scale-up production of recombinant protein C was done using an Opticell culture system. A good productivity of the recombinant protein was obtained in low serum or serum-free medium for more than one month.

Biocompatibility of wound management products: the effect of various monosaccharides on L929 and 2002 fibroblast cells in culture

The effects of various monosaccharides on the growth of human 2002 and mouse L929 fibroblast cultures have been investigated. Eleven monosaccharides having acidic, neutral, and basic characteristics were evaluated in a bioassay procedure developed for the investigation of biocompatibility of wound management materials. Rate of growth in both cell lines was inhibited by D-galacturonic acid and by D-glucuronic acid. Although most neutral sugars produced no significant change in the growth rate or in the morphology of the cells, galactose produced a significant increase in the growth rate of both cell lines whilst L-fucose caused a significant decrease in growth of the L929 cells but did not significantly affect the growth of 2002 cells; xylose increased the growth rate of L929 but not 2002 cells. D-Glucosamine, a basic sugar, produced inhibition of growth which followed a different pattern from that produced by the acidic sugars; N-acetylglucosamine produced a species specific increase in cell growth of L929 cells. The results show that the effects produced by the monosaccharides on the cultured fibroblasts are related to their chemical structure and to cell line, and suggest that the use of galactose as a possible aid to wound healing should be investigated.

Comparative metabolic effects of fructose and glucose in human fibroblast cultures

The comparative metabolic effects of fructose and glucose were determined in human fibroblast cultures. Cells were grown in four different media containing 5.5 and 27.5 mM of glucose and fructose, respectively. For these two hexoses, we compared their uptake, consumption, and conversion into 14CO2 and 14C-lipids. D-Fructose was taken up in fibroblasts by an unsaturable process and its consumption was much smaller than that of D-glucose. Whatever the experimental procedure, the glycogen content of cells grown in fructose media was significantly lower than of those grown in glucose media. Labeling of fructose and glucose with 14C showed that more carbon from fructose than from glucose was incorporated into CO2 and glycerolipids. The relative distribution of 14C in the different lipid fractions was similar for both hexoses. These results indicated that the pathways of intermediary metabolism in fibroblast cultures were influenced by the nature of the carbohydrate present in the culture medium and that fructose was a better lipogenic substrate than glucose in human fibroblast cultures.

Comparative use of glucose and fructose in cultured fibroblasts from patients with hereditary fructose intolerance

The utilization of fructose and glucose by fibroblast cultures obtained from patients with hereditary fructose intolerance (HFI) was studied in comparison with fibroblast controls. The cell growth, the time course of D-glucose or D-fructose uptake and the consumption of fructose were similar for both HFI and control cells. Some results showed significant differences between these two cell types: HFI cells consumed less glucose, produced less lactate and contained less glycogen than control cells. Furthermore, significantly less [U-14C]D-glucose and [U-14C]D-fructose was incorporated into lipids in HFI cells than in control cells. The mechanisms responsible for these differences observed between the two cell types are not known.

Comparative use of fructose and glucose in human liver and fibroblastic cell cultures

The effect of fructose as a substitute for glucose in cell culture media was investigated in human skin fibroblast and liver cell cultures. Cells were grown for between 2 and 10 days in identical flasks in four different media, containing 5.5 mmol X 1-1 and 27.5 mmol X 1-1 glucose and fructose, respectively. In the presence of fructose, cell growth was stimulated, but less in liver cells than fibroblasts. At Day 6, increases were observed in [3H]thymidine incorporation, protein levels, and amino acid consumption, and a reduction was noted in ATP levels. In media containing 5.5 mmol X 1-1 glucose or fructose, consumption of fructose was four times lower than that of glucose at Day 3 and did not rise until Day 6. In fructose media, the lactate production was very low (four to five times less than that of glucose) and the pH values were always higher. Some findings were different for the fibroblasts and liver cells, owing to the specific characteristics of these two cell types in culture; this applied especially to the effects of glucose and fructose concentrations of 27.5 mmol X 1-1. Several possible explanations for the stimulation of cell growth in fructose medium were discussed.

Comparative effects of glucose and fructose on growth and morphological aspects of cultured skin fibroblasts

The growth rate of human skin fibroblasts was evaluated when glucose was replaced by fructose in the culture medium. Four mediums containing respectively 5.5 mmol/l glucose (G1), 27.5 mmol/l glucose (G5), 5.5 mmol/l fructose (F1), and 27.5 mmol/fructose (F5) were used. Skin fibroblasts from fourteen subjects were continuously cultured for 20 days and the number of cells was counted at days 1, 3, 7, 10, 15 and 20 after plating. The morphological patterns were observed and compared, the pH values of the medium were calculated, as were hexose consumption and lactate production. The results established clear differences in cell growth, pH and morphology: up to day 7, the growth rate was lower in fructose than in glucose medium, and the pH values were higher. In addition, marked steatosis appeared, with increased pyruvate dehydrogenase (PDH) activity. After day 10, the mean values gave a significant increase in the number of cells grown in fructose mediums, even if variations occurred between different cell strains. This increase was accompanied by loss of density-dependent growth inhibition and a reduction in the quantity and size of the vacuoles caused by steatosis. These findings were also established for other cell types, like aponeurosis fibroblasts. In addition, the longevity of the strains increased. These observations indicate that intermediary metabolism is considerably influenced by the carbohydrate present in the cell culture medium and that there are also repercussions on the growth rate. Under our experimental conditions, metabolism pathways seemed to differ on day 7 and on day 20. The various metabolic events suggested by the differences in the pH values are now being studied in our laboratory.

Reactivation of NAD(H) biosynthetic pathway by exogenous NAD+ in Nil cells severely depleted of NAD(H)

The culture of Nil hamster fibroblasts in MEM lacking nicotinamide (NAm-MEM) leads to: (1) the rapid loss of intracellular total nicotinamide adenine dinucleotide (NAD(H)) content in these cells from a level of 150-200 pmoles/10(5) cells to less than 20 pmoles/10(5) cells; (2) the cessation of cell division and inhibition of DNA synthesis; and (3) a reduction of glucose consumption and lactic acid production. In most situations, following nicotinamide starvation, the restoration of intracellular NAD(H) follows rapidly the readdition of NAD+ (oxidized), nicotinamide mononucleotide (NMN), nicotinamide, or nicotinic acid. Resumption of cell division occurs after only a lag of about 24 hours. Nil cells subcultured for three consecutive times in the absence of nicotinamide (3(0) NAm- cells) exhibit different behavior. These severely starved cells are incapable of quickly restoring their intracellular NAD(H) content to normal levels when provided with any pyridine ring compound except NAD+. One-hour exposure of such cells to NAD+ allows utilization of nicotinamide to rapidly restore intracellular NAD(H). This short incubation with NAD+ does not result in any significant restoration of intracellular NAD(H) or lead to the accumulation of an intracellular pool of some precursor. This function of NAD+ as a stimulatory signal to the NAD(H)-biosynthetic pathway in severely starved Nil cells is a previously unreported role of NAD+, and does not require protein synthesis.

Correlation between growth rate, cell density, and intracellular concentrations of cyclic nucleotides in chemostat cultures of mouse L1210 cells

Constant intracellular concentrations of both adenosine 3',5' cyclic monophosphate (cyclic AMP) and guanosine 3',5' cyclic monophosphate (cyclic GMP) were obtained when mouse leukemia L1210 cells were cultivated under steady-state conditions in the chemostat. When L1210 cells were maintained at a constant growth rate in the chemostat, the mean steady-state intracellular concentration of cyclic AMP decreased with increasing cell density, while the concentration of cyclic GMP remained unchanged. When cell growth rate was increased by three-fold, independently of cell density, in the chemostat, then the mean steady-state intracellular concentration of cyclic GMP increased by 3.6-fold, whereas that of cyclic AMP increased by only 22%. The ratio of cyclic AMP to cyclic GMP was found to decrease with increasing cell growth rate in the chemostat. Our results show that a close correlation exists between the steady-state intracellular concentrations of cyclic nucleotides and changes in both cell growth rate and cell density in chemostat cultures of L1210 tumour cells.

Effect of carcinogenic polycyclic aromatic hydrocarbons on mouse embryonic cells in culture: induction of spindle-shaped cells

In cultured mouse embryonic cells (MECs) treated with benzo[a]pyrene (B[a]P), there appeared unusual type of fibroblasts, spindle-shaped cells (SP cells), which were characterized by their narrow bipolar shape, long cellular processes and optically distinct cell borders. Appearance of SP cells was massive and irreversible. The amount of SP cells increased with increasing concentrations of B[a]P, while early cytotoxicity did not. In various polycyclic aromatic hydrocarbons (PAHs) tested, only potent carcinogens (7,12-dimethylbenz[a]anthracene (DMBA), 3-methylcholanthrene (MCA), B[a]P, and dibenz[a,e]pyrene (DB[a,e]P) induced SP cells. Among them, PAH having higher Iball's index induced SP cells at lower concentration and at an earlier time. Weak or non-carcinogenic PAHs including 3-hydroxybenzo[a]-pyrene (3-OH-B[a]P) did not induce SP cells. alpha-Napthoflavon (alpha NF) suppressed the induction of SP cell by carcinogenic PAH. SP cells did not appear spontaneously under various abnormal culture conditions. These results indicate that carcinogenic PAHs induce the appearance of a specific type of fibroblast, SP cells in MEC cultures in accordance with their carcinogenicity.

Selective high metabolic lability of uridine, guanosine and cytosine triphosphates in response to glucose deprivation and refeeding of untransformed and polyoma virus-transformed hamster fibroblasts

Sugar deprivation of hamster fibroblasts (NIL) affected the steady state levels (pool sizes) of cellular acid soluble nucleotides in the folloing fashion: the pools of UTP, GTP and CTP decreased to a much greater extent than the cellular ATP pools, with the UTP pools undergoing the most dramatic reduction. Sugar deprivation of polyoma-transformed NIL cells (PyNIL) yielded even sharper decreases in the nucleoside triphosphate pools with relative changes similar to those of the untransformed cells. Inhibition of protein synthesis by cycloheximide, initiated at the onset of (and continued during) sugar deprivation, prevented the reduction in pool sizes and yielded values slightly higher than those observed for pool sizes in cells cultured in sugar-supplemented medium. Refeeding glucose to sugar-depleted hamster fibroblasts led to rapid increases (within 1 hour) in the UTP and CTP pools to levels well above the pool sizes observed in cells which were continuously cultured (16 hours) in sugar supplemented medium. Feeding NIL or PyNIL cells with fructose instead of glucose as the only hexose source did not appreciably affect any of the ribonucleoside triphosphate pool sizes. Measurements of hexose uptake by NIL and PyNIL cells under a variety of conditions suggest that hexose transport is not regulated by the total cellular pools of ATP or any of the other ribonucleoside triphosphates.

Cyclic nucleotide metabolism in tumours

Many hormones act by combining with cell surface receptors and stimulating adenylate cyclase activity. The cyclic AMP generated is the mediator of a number of cellular metabolic processes. Other processes may be influenced by changes in cyclic GMP levels. Although much evidence from cultured cells suggested that low cellular levels of cyclic AMP and high levels of cyclic GMP are a feature of rapid cell growth and of malignant transformation, review of the data reveals many inconsistencies. Thus in established tumours growing in vivo, for example, cyclic AMP levels appear to be unrelated to tumour growth rates. It seems that tumour cell cyclic AMP is more likely concerned with the regulation of tumour cell function than of growth. This would have implications for therapy, in that drugs which influence cyclic nucleotide metabolism could influence tumour cell function. The control of cyclic nucleotide production in normal and tumour cells is discussed, together with the possible ways in which abnormalities of this may occur.

Pentose utilizing variants of Novikoff hepatoma cells: modification of growth and morphological properties

A series of variant lines that utilize multiple pentoses for growth in place of glucose have been isolated from an 8-azaguanine resistant line of Novikoff hepatoma cells (N1S167). These variants utilize for growth ribose, xylose, arabinose, and/or deoxyribose. The variants growing on pentose containing medium (a) exhibit a density dependent cessation of growth, (b) have a morphology change to a more flattened cell type, (c) become binucleated in the presence of cyto chalasin B, and (d) show an altered sensitivity to trypsin treatment.