Optimal conditions for the fluorometric determination of DNA

The Effect of Antiseptics and the Moist Wound Environment on Ulcer Healing: An Experimental and Biochemical Study

The effect of topical aqueous chlorhexidine (0.5% and 5%) and Eusol has been studied on the healing of 2 cm skin defects in rats, with measurements of DNA and collagen synthesis as biochemical markers. Healing was also compared under an occlusive dressing (Comfeel Ulcer Dressing, Coloplast) and a non-occlusive dressing (Jelonet, Smith and Nephew).

Healing was significantly delayed under Jelonet dressings compared with the Comfeel groups. The hydroxyproline levels, 4 d after wounding were: chlorhexidine 5% 1.82 μg mg−1 (1.46–11.57), Eusol 1.78 (1.13–3.52), Jelonet 2.04 (1.89–3.91), Comfeel 3.21 (1.99–3.46), Comfeel–saline 3.09 (1.99–3.46), chlorhexidine 5% 3.61 (1.47–6.28). The moist wound environment provided by the Comfeel dressings was the most conducive to healing in this study. Chlorhexidine, at a recommended strength of 0.5% (or less), did not impair healing and can safely be used if an antimicrobial is required.

Attenuation and loss of hormonal modulation of KGF (FGF-7)/KGF receptor expression and mitogenesis during mammary tumor progression

Keratinocyte growth factor (KGF), alone and in synergism with progesterone (P) and prolactin (PRL), is mitogenic for normal mammary epithelium (ME) in vitro. In addition, P can upregulate ME sensitivity to KGF by slowing KGF receptor (KGFR) mRNA turnover in vitro. These hormonal interactions with KGF in vitro raise the possibility that alterations in these interactions can play a role in hormone-dependent mammary tumor growth and progression. The effect of hormones on KGF mitogenesis and the regulation of KGFR expression was examined in pregnancy-dependent (PDT) and ovarian-independent (OIT) mouse mammary tumors. In serum-free, collagen gel cell culture, dose/response (2-20 ng/ml) and time course studies showed that KGF stimulated the proliferation of PDT (not OIT) cells but synergism with P or PRL was not observed. The level of KGFR mRNA in PDT cells was not significantly different from normal ME but in OIT it was reduced more than 90%. P did not affect KGFR mRNA turnover in cultured PDT cells. However, KGFR mRNA was more stable in PDT cells compared to normal ME; after 6 days culture in basal medium, KGFR mRNA levels declined 40% vs. 85% previously shown for normal ME. Determination of KGF mRNA levels in tissues showed that it was lower in PDT compared to normal mammary gland and not detectable in OIT. These data show that in PDT both KGF-stimulated mitogenesis and the regulation of KGFR expression are independent of hormones. OIT has progressed to independence from any KGF influence. Thus, a subset of hormonally regulated pathways related to epithelial/stromal cell interactions can be lost in hormone-dependent mammary tumors during tumor progression.

Adenosine-mediated inhibition of casein production by mouse mammary glands in culture

The present study was carried out to examine whether activation of adenosine receptors by adenosine analogues will affect casein production by mouse mammary epithelial cells. The morphogenesis and functions of epithelial tissue in the mammary gland are influenced by their surrounding adipocytes. Adipocytes are known to release adenosine into the extracellular fluid which can modulate cyclic-AMP levels in surrounding cells through binding to their adenosine receptors. To examine a possible paracrine effect of adenosine, the modulation of casein production in mammary explant culture and mammary epithelial cell (MEC) culture by adenosine receptor agonists has been investigated. We have observed that activation of the A1-adenosine receptor subtype in mammary tissue by an adenosine analogue (-)N6-(R-phenyl-isopropyl)-adenosine (PIA) raised cAMP levels. PIA and another adenosine receptor agonist, isobutylmethylxanthine (IBMX), inhibited casein accumulation both in explants and in MEC cultures in the presence of lactogenic hormones, which suggests that PIA or adenosine can act directly on the epithelial cells. This inhibition does not appear to be caused by elevation of cAMP levels or phosphodiesterase activity. The inhibition of intracellular casein accumulation by PIA and IBMX in explant cultures can be reversed via treatment of pertussis toxin which is known to ADP-ribosylate GTP-binding G alpha i-proteins, indicating that a Gi-protein-dependent pathway may be involved in this inhibition. The results also suggest that local accumulation of adenosine in the extracellular fluids of mammary glands is likely to inhibit the lactogenic response of mammary epithelial cells.

Multifunctional phosphatidic acid signaling in mammary epithelial cells: stimulation of phosphoinositide hydrolysis and conversion to diglyceride

We have shown previously that phosphatidic acid esterified to polyunsaturated fatty acids is mitogenic for primary cultures of mouse mammary epithelial cells embedded within collagen gels. We hypothesized that this mitogenic competence resulted from the ability of this phospholipid to activate multiple signal transduction pathways in mammary epithelium. A closer examination of this hypothesis was undertaken by examining the effect of exogenous phosphatidic acid on phosphoinositide (PI) hydrolysis and its intracellular metabolism to diglyceride, an activator of protein kinase C. For assays of phosphoinositide-specific phospholipase C activation, mammary epithelial cells from virgin Balb/c mice were isolated by collagenase dissociation of mammary glands and cultured on the surface of Type I collagen-coated culture dishes. Phosphatidic acid (PA) stimulated a sustained increase in inositol phosphates and caused inositol phospholipid depletion when added to cells in which inositol phospholipids were prelabeled with 3H-myoinositol. This effect was specific for PA among phospholipids tested. Neither lineoleic acid, that can be released from PA, nor prostaglandin E2 affected PI hydrolysis. When mammary epithelial cells were cultured inside collagen gels in the presence of exogenous PA or phosphatidylcholine (PC) radiolabeled with 3H-glycerol, PA was found to persist intracellularly and be dephosphorylated to diglyceride (an activator of protein kinase C) to a greater extent than PC, a nonmitogenic phospholipid. In contrast to PA, epidermal growth factor (EGF) only slightly stimulated PI hydrolysis, showing that these two different growth-promoting factors do not actively couple to the same signal transduction pathways in mammary epithelial cells. These results show that PA may activate multiple pathways in mammary epithelial cells either directly or via its metabolism to diglyceride.

Growth stimulation by PGE2 and EGF activates cyclic AMP-dependent and -independent pathways in primary cultures of mouse mammary epithelial cells

Mammary epithelial cells from virgin Balb/c mice were isolated by collagenase digestion and cultured within collagen gels in serum-free basal medium containing insulin (10 micrograms/ml). Previous work has shown that linoleate or its metabolite, prostaglandin E2 (PGE2), stimulate the growth of these cells only in the presence of a growth stimulant such as epidermal growth factor (EGF). Since PGE2 can stimulate cyclic AMP (cAMP) production, the role of cAMP in linoleate and EGF-stimulated growth was examined. The cAMP phosphodiesterase inhibitor, IBMX (0.1 mM), was found to augment growth when cells were cultured in the presence of both EGF and linoleate or PGE2, but not either factor alone. These results indicated that EGF does not stimulate proliferation via cyclic AMP mediated events but could synergize with cAMP events if cAMP levels were elevated by PGE2. When assayed in cells plated on top of collagen-coated culture dishes, cellular cyclic AMP levels were stimulated by PGE2, but only marginally by EGF. Although the stimulation of endogenous cAMP by PGE2 and IBMX was insufficient to stimulate growth in the absence of EGF, exogenous dibutyryl-cAMP (greater than 100 micrograms/ml) was able to do so showing that a sustained, and high level of cAMP (greater than 100 micrograms/ml) could stimulate growth in insulin-containing basal medium. EGF was capable of enhancing the cellular sensitivity to dibutyryl-cAMP but the converse was not observed. cAMP stimulation of growth was dependent upon a superphysiological concentration of insulin (10 micrograms/ml) or a physiological concentration of somatomedin-C. These results indicate that the proliferation of mouse mammary epithelial cells can be stimulated separately or in synergism by cAMP-dependent or -independent events.

The acid instability of myelin. A model for myelin degeneration in multiple sclerosis

Electron micrographs of samples of bovine spinal cord which have been briefly acidified (10 mM lactate buffer, pH 5.5, 25 degrees C, 15 minutes) prior to being fixed for EM examination, reveal extensive vesicular disruption of the myelin lamellae; micrographs of control samples incubated under identical conditions at pH 7.0, show normal compact lamellae. Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in the secretion of lactic acid and the acidification of the culture medium to levels which are comparable to those which cause lamellae disruption in the tissue slices. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Secretion of lactic acid by peritoneal macrophages during extracellular phagocytosis. The possible role of local hyperacidity in inflammatory demyelination

Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in a release of the lysosomal marker enzyme beta-glucuronidase that is both dose- and time-dependent. Concomitant with enzyme secretion, lactic acid is secreted in a manner that is also dose- and time-dependent. The secretion of lactic acid represents an increased dependence on anaerobic glycolysis by the aerobic phagocyte cultures and is paralleled by an increase in cytoplasmic lactate dehydrogenase. When unbuffered media are used, the secretion of lactic acid is accompanied by a drop in the pH of the culture medium. Culture of the cells in the presence of the pyruvate dehydrogenase stimulator, dichloroacetate, inhibits the formation of lactic acid and the resulting drop in pH. Suspensions of multilamellar myelin undergo turbidity changes and aggregation in acidic media. Initial rates of turbidity changes follow a titration curve with an apparent pKa of 6.0. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics, such as dichloroacetate, may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Oestradiol-receptor complexes in subnuclear fractions of rat uterine tissue

The subnuclear distribution of 3H-oestradiol-receptor complexes was studied in uterine tissue of ovariectomized adult rats. Nuclei were sonically disrupted and 8 different subnuclear fractions were isolated by discontinuous sucrose density gradient centrifugation. 3H-Oestradiol-receptor complexes, measured by hydroxylapatite column chromatography, were localized in a light chromatin fraction as well as in a heavy chromatin fraction. Using the hydroxylapatite chromatography technique it was possible to demonstrate three classes of oestradiol-receptor complexes which differ in affinity for the chromatin. Oestradiol-receptor complexes with a high affinity for the chromatin were predominantly localized in the heavy chromatin fraction, whereas complexes with a lower affinity for their acceptor sites were present in the lighter chromatin fraction.

Ribonucleic acid synthesis in vitro in primary spermatocytes isolated from rat testis

The incorporation of [(3)H]uridine into RNA was studied quantitatively (by incorporation of [(3)H]uridine into acid-precipitable material) and qualitatively (by phenol extraction and electrophoretic separation of RNA in polyacrylamide gels) in preparations enriched in primary spermatocytes, obtained from testes of rats 26 or 32 days old. The rate of incorporation of [(3)H]uridine into RNA of isolated spermatocytes was constant during the first 8h of incubation, after which it decreased, but the decreased rate of incorporation was not reflected in a marked change in electrophoretic profiles of labelled RNA. In isolated spermatocytes, [(3)H]uridine was incorporated mainly into heterogeneous RNA with a low electrophoretic mobility. Most of this RNA was labile, as shown when further RNA synthesis was inhibited with actinomycin D. Spermatocytes in vivo also synthesized heterogeneous RNA with a low electrophoretic mobility. A low rate of incorporation of [(3)H]uridine into rRNA of isolated spermatocytes was observed. The cleavage of 32S precursor rRNA to 28S rRNA was probably retarded in spermatocytes in vitro as well as in vivo. RNA synthesis by preparations enriched in early spermatids or Sertoli cells was qualitatatively different from RNA synthesis by the spermatocyte preparations. It is concluded that isolated primary spermatocytes maintain a specific pattern of RNA synthesis, which resembles RNA synthesis in spermatocytes in vivo. Therefore isolated spermatocytes of the rat can be used for studying the possible regulation of RNA synthesis during the meiotic prophase.

Preparation of pure neuronal and non-neuronal cultures from embryonic chick sympathetic ganglia: a new method based on both differential cell adhesiveness and the formation of homotypic neuronal aggregates

A new method has been developed for the preparation of essentially pure primary cultures of neurons and non-neuronal cells from 11-day embryonic chick sympathetic ganglia. This method utilizes (1) differences in cell-to-substrate adhesiveness between neurons and non-neuronal cells and (2) the capacity of neurons to form homotypic aggragates. The maximum difference in adhesiveness between neuronal and non-neuronal cells occurred when the ganglia were dissociated with trypsin following collection in a salt solution lacking divalent cations. This difference allowed the preparation of highly purified non-neuronal cultures and 85-90% pure neuronal cultures. Intermittent agitation during the period of cell separation markedly increased the purity of the neuronal cultures by (1) inhibiting neuronal but not non-neuronal cell attachment and (2) facilitating the formation of homotypic neuronal aggregates in the supernatant. Neuronal and non-neuronal cultures prepared under these conditions were more than 99% pure on the basis of both morphological and biochemical analyses. Both cell types exhibited attachment efficiencies greater than 95% and have been maintained for several weeks in vitro. Thus, completely isolated neuronal and non-neuronal cultures can be prepared and maintained for prolonged periods in the absence of cells of the other type.

Synchronization of mitochondrial DNA synthesis in Chinese hamster cells (line CHO) deprived of isoleucine

Mitochondrial DNA (mit-DNA) synthesis was compared in suspension cultures of Chinese hamster cells (line CHO) whose cell cycle events had been synchronized by isoleucine deprivation or mitotic selection. At hourly intervals during cell cycle progression, synchronized cells were exposed to tritiated thymidine ([(3)H]TdR), homogenized, and nuclei and mitochondria isolated by differential centrifugation. Mit-DNA and nuclear DNA were isolated and incorporation of radioisotope measured as counts per minute ([(3)H]TdR) per microgram DNA. Mit-DNA synthesis in cells synchronized by mitotic selection began after 4 h and continued for approximately 9 h. This time-course pattern resembled that of nuclear DNA synthesis. In contrast, mit-DNA synthesis in cells synchronized by isoleucine deprivation did not begin until 9-12 h after addition of isoleucine and virtually all [(3)H]TdR was incorporated during a 3-h interval. We have concluded from these results that mit-DNA synthesis is inhibited in CHO cells which are arrested in G(1) because of isoleucine deprivation and that addition of isoleucine stimulates synchronous synthesis of mit-DNA. We believe this method of synchronizing mit-DNA synthesis may be of value in studies of factors which regulate synthesis of mit-DNA.

Fluorometric determination of deoxyribonucleic acid in bacteria with ethidium bromide

A simple, sensitive, and rapid method is presented for the determination of deoxyribonucleic acid (DNA) in both gram-positive and gram-negative bacteria. It is based upon the fluorometric determination of DNA with ethidium bromide after alkaline digestion of the bacteria to hydrolyze the interfering ribonucleic acid. The assay takes less than 2 hr. Its sensitivity is at least 0.2 mug of DNA in a final solution of 4 ml and it uses commonly available filter or double monochromator fluorometers. Judicious choice of light source and filters allows an additional 10-fold increase in sensitivity with a filter fluorometer. Turbidity caused by bacteria or insoluble polysaccharides does not interfere with the fluorescence measurements. There was no significant difference between the results obtained with this method and those obtained with the indole and diphenylamine methods when these assays were applied to Escherichia coli and sucrose- or glucose-grown Streptococcus mutans. The method was also tested by determining the specific growth rate of E. coli. This new procedure should be especially useful for the determination of bacterial DNA in dilute suspensions and for the estimation of bacterial growth or DNA replication where more conventional methods are not applicable or sensitive enough.