Multiple pathways are involved in protection of MCF-7 cells against death due to protein synthesis inhibition

Previously we have shown that IGF-I protected MCF-7 cells against death induced by the protein synthesis inhibitor cycloheximide (CHX). In the present study we investigated the ability of protein kinase C activator 12-0-tetradecanoyl-phorbol-13-acetate (TPA), the protein kinase A activator 8-bromoadenosine 3'5'-cyclic monophosphate (Br-cAMP), and the enzyme inhibitor aurintricarboxylic acid (ATA) to protect MCF-7 cells against death, due to a continuous presence of CHX. Cell death was evaluated after 48 h of incubation by several techniques (trypan blue staining, release of lactic dehydrogenase, cellular ATP content, transmission electron microscopy, and DNA fragmentation). Apoptosis which terminates in necrosis, characterized this mode of cell death. TPA and ATA at optimal concentrations of 40 ng/ml and 100 micrograms/ml, respectively, reduced cell death to the control level (without CHX), while Br-cAMP at an optimal concentration of 650 micrograms/ml reduced cell death only partially. IGF-1, TPA, and ATA, which stimulated protein synthesis in the control MCF-7 cells, had no effect on protein synthesis in the CHX-treated cells, indicating that the survival effect is not due to new protein synthesis. The protein kinase C inhibitor staurosporine blocked the survival effect of TPA and IGF-1 in a dose-dependent manner, however did not affect the survival effect of ATA. The tyrosine kinase inhibitor genistein blocked the survival effect of IGF-1, but not that of TPA and ATA. Our results provide evidence for several distinctive pathways, the activation of which protects MCF-7 cells against death, due to protein synthesis inhibition.

Restrictin-P/stromal activin A, kills its target cells via an apoptotic mechanism

We have recently found that the inhibitor of plasmacytoma cell growth, restrictin-P, is a stroma derived activin A and that it is an antagonist of interleukin-6 and interleukin-11. The present study was aimed at determining the mode by which this cytokine kills its target cells. On addition of the cytokine there was little or no net increase in cell number, depending on the specific target cells. All plasmacytoma cell lines tested exhibited a similar time dependent inhibition of DNA synthesis and a G0/G1 shift in the cell cycle. Electron microscope examination revealed classical apoptotic features i.e. chromatin condensation and membrane blebbing. DNA fragmentation, measured qualitatively and quantitatively, occurred in all cytokine treated plasmacytoma cell lines. Bovine activin A had an identical capacity to reduce cell viability, to induce G0/G1 shift and to cause DNA fragmentation. X-ray microanalysis of intracellular ions revealed an increase in calcium ions, following exposure of plasmacytoma cells to restrictin-P, accompanied by a decrease in phosphor ions. The cytotoxicity of the inhibitor was augmented in an additive manner by cycloheximide (CHX) indicating that the process did not require de novo protein synthesis. This study thus shows that restrictin-P/stromal activin A kills its target cells by inducing apoptosis. This effect was mediated by subnanogram concentrations and therefore may represent one physiological function of this pleiotropic cytokine.

Epidermal growth factor, phorbol esters, and aurintricarboxylic acid are survival factors for MDA-231 cells exposed to adriamycin

The ability of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), insulin, 12-O-tetradecanoylphorbol-13-acetate (TPA), and aurintricarboxylic acid (ATA) to protect the human breast cancer cell line MDA-231 from death induced by the anticancer drug adriamycin was investigated. Cell death was induced in the MDA-231 cells either by a short-time exposure to a high dose of adriamycin (2 micrograms.ml-1.1h-1) and further culturing in the absence of the drug, or by continuous exposure to a low dose of adriamycin (0.3 micrograms/ml). Cell death was evaluated after 48 h of incubation by several techniques (trypan blue dye exclusion, lactic dehydrogenase activity, cellular ATP content, transmission electron microscopy, and DNA fragmentation). EGF, TPA, and ATA, each at an optimal concentration of 20 ng/ml, 5 ng/ml, and 100 micrograms/ml respectively, substantially enhanced survival of cells exposed either to a high or low dose of adriamycin. Neither IGF-1 nor insulin, each at concentrations of 20 ng/ml, had an effect on cell survival. The three survival factors enhanced protein synthesis in the untreated cells and attenuated the continuous decrease in protein synthesis in the adriamycin-treated cells. Moreover, the three survival factors protected the MDA-231 cells from death in the absence of protein synthesis (cycloheximide 30 micrograms/ml). These results suggest that EGF, TPA, and ATA promote survival of adriamycin pretreated cells by at least two mechanisms: enhancement of protein synthesis and by a protein synthesis independent process, probably a posttranslational modification effect.

Biochemical and morphological changes in rat muscle cultures caused by 28,000 mol. wt toxin of Bacillus thuringiensis israelensis

The 28,000 mol. wt protein of Bacillus thuringiensis israelensis showed a high degree of toxicity to rat muscle in culture. Application of 1 microgram/ml to the culture medium completely inhibited cell fusion. Reversibility of this effect was demonstrated by replacement of the culture medium with fresh medium, and the consequence was that cell fusion was resumed. When differentiated myotubes were treated with 1 microgram/ml of the toxin, the spontaneous contractile activity was abolished within 20 min. Cytotoxic effects were observed 1 hr after treatment was initiated, as manifested by creatine kinase (CK) release to the medium. Two hours after toxin was applied to the muscle culture, the myotubes were deteriorated whereas the mononucleated cells were not affected. Six or 7-day-old cultures which were treated by 1 microgram/ml of 28,00 mol. wt toxin revealed a change in the levels of Na+ and K+ within the fibres as analysed by X-ray microanalysis (XRMA). Preincubation of the toxin for 20 min with phospholipids before application to the cells reduced the cytotoxic effect. Phosphatidylinositol and phosphatidylserine were the most efficient inhibitors, whereas phosphatidylcholine, sphingomyelin and phosphatidylethanolamine were less effective in protecting cultures from the cytotoxic effects of the 28,000 mol. wt protein.

New phthalocyanines for photodynamic virus inactivation in red blood cell concentrates

Cationic phthalocyanines with either aluminum or silicon as the central metal were evaluated for their ability to inactivate viruses in red blood cell concentrates (RBCC) photodynamically. In addition, the virucidal potential of a substituted anionic phthalocyanine, aluminum dibenzodisulfophthalocyanine hydroxide (A1N2SB2POH) was evaluated and compared with that of the much studied anionic aluminum tetrasulfophthalocyanine hydroxide (A1PcS4OH). Based on the rate of inactivation of the lipid-enveloped vesicular stomatitis virus (VSV), the virucidal potential of these phthalocyanines was: HOSiPcOSi(CH3)2(CH2)3N+(CH3)3I- (Pc 5) = SiPc[OSi(CH3)2-(CH2)3N+(CH3)3I-]2 (Pc 6) > A1PcOSi(CH3)2(CH2)3N+(CH3)2(CH2)11CH3I- (Pc 21) = A1N2SB2POH = A1PcS4 > HOSiPc[OSi(CH3)2(CH2)3N+(CH3)2(CH2)11CH3I-]2 (Pc 14) > A1PcOSi(CH3)2(CH2)3N+(CH3)3I- (Pc 2). Phthalocyanine ligand 14 and Pc 21 are new phthalocyanines, made by quaternizing known amino analogues. Compared to VSV, the rate of inactivation of Sindbis virus (another model lipid-enveloped virus) was identical when treated in red blood cells (RBC) with Pc 5 and slightly higher when treated with Pc 6 and A1PcS4OH. Treatment of RBCC containing cell-free human immunodeficiency virus (HIV-1) with Pc 5 or A1PcS4OH required 15 min of irradiation to inactivate (> 5 log10 reduction) the virus. The extent of HIV-1 inactivation with A1N2SB2POH was 3.7 log10 after 60 min of red light exposure. The RBC integrity after photosensitization was measured by the ability of the cells to bind to plates coated with poly-L-lysine, (which reflects the retention of the RBC surface negative charges) and hemolysis of the cells over a 7 day storage period.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of virus production and induction of self-syncytium formation in human T-cell leukemia virus type I- and type II-infected T cells by 12-O-tetradecanoylphorbol-13-acetate

Treatment of human T-cell leukemia virus type I (HTLV-I)- and HTLV-II-infected T-cell lines with 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulated virus release. However, this stimulation was mainly detected at 42 to 48 h of treatment, whereas later virus release declined rapidly. During the first 48 h, TPA had no effect on cell growth, but later, the number of viable cells was profoundly lower in the TPA-treated than in the untreated cultures. This shift in virus release and cell number resulted from self-fusion of a large proportion of the virus-producing cells, which seemed to consequently enter into a dying process. This fusion, which resulted in syncytium formation, was strongly inhibited by anti-HTLV-I env monoclonal antibodies. Furthermore, no self-fusion was detected in three different uninfected T-cell lines similarly treated with TPA. On the other hand, stimulation of virus production by 3-methylcholanthrene (3-MC) treatment failed to induce self-fusion in the infected cells. Moreover, no syncytium was detected when these 3-MC-treated infected cells were cocultured with any of the TPA-treated uninfected cells. The effects of TPA on virus production and syncytium formation were both abolished by three different protein kinase C inhibitors. Taken together, these data suggest that the self-fusion observed in these experiments required both enhanced virus production and protein kinase C-phosphorylated viral or/and virally induced cellular component(s).

Epidermal growth factor and insulin-like growth factor-1 protect MDA-231 cells from death induced by actinomycin D: the involvement of growth factors in drug resistance

In the present study, we investigated the ability of epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and insulin to protect the human breast cancer cell line MDA-231 from death induced by the antitumor drug actinomycin D (ACT-D). ACT-D is an inhibitor of RNA and protein synthesis, and its cytotoxicity may result due to continuous depletion in some vital protein molecules. Cell death was induced in the MDA-231 cells by either continuous exposure to a low dose of ACT-D (0.2 microgram/ml), or by a short-time exposure to a high dose of ACT-D (2 micrograms/ml) and further culturing in the absence of the drug. Cell death was evaluated by the trypan blue dye exclusion test, the release of lactic dehydrogenase into the culture medium, and the depletion in the cellular ATP content. EGF and IGF-1, each at an optimal concentration of 20 ng/ml, enhanced substantially survival of cells exposed either to a low or a high dose of ACT-D. The combination of EGF (10 ng/ml) and IGF-1 (10 ng/ml) had an additive survival effect, which proposes that each of the growth factors enhanced survival by a distinct pathway. Insulin up to 40 ng/ml had no effect on cell survival. Pretreatment of the cells for 1 to 5 h with EGF and IGF-1 protected cells from the cytotoxic effect of ACT-D. Exposure of the cells to 2 micrograms/ml of ACT-D for 1 h resulted in a drastic inhibition in uridine incorporation and only in a slight inhibition in leucine incorporation.(ABSTRACT TRUNCATED AT 250 WORDS)

Protoporphyrin biosynthesis in melanoma B16 cells stimulated by 5-aminolevulinic acid and chemical inducers: characterization of photodynamic inactivation

The stimulation of protoporphyrin (PP) biosynthesis in B16 melanoma cells in order to facilitate photodynamic cell killing was studied. Biosynthesis and accumulation of PP in the melanoma cells was increased from 8 to 15 pmol/mg protein by the use of dimethyl-sulfoxide (DMSO), a differentiation-inducer. Treatment of the cells with the porphyrogenic agent allylisopropyl-acetamide (AIA) stimulated an additional PP increase. The most remarkable enhancement of intracellular PP was achieved by the supplementation of 5-aminolevulinic acid (5-ALA) to the growth medium following the addition of DMSO and AIA during the induction phase. The intracellular concentration of PP exceeded 21,950 pmol/mg protein following combined stimulation by DMSO/AIA and 5-ALA. The porphyrins produced in the incubated cells, in serum-depleted medium, consisted of 95% PP; 88% of it was recovered from the cells and only 7% was excreted into the medium. Photosensitization of the B16 melanoma cells containing high PP concentrations was effective even at low light doses. Potassium (K) efflux was the first measurable sign of cell damage determined by X-ray microanalysis (XRMA) following fast liquid-nitrogen fixation. During a 1 min interval, 70% of cellular K was lost. After 5 min illumination, complete cell destruction was detected by scanning electron microscopy (SEM) and XRMA. The photodamaged cells showed influx of Na, Cl and Ca ions accompanying the immediate K losses. Ultrastructural cell damage was manifested by disintegration of the outer membrane. Total cell death of B16 melanoma cells was achieved by chemical induction of endogenous PP and photosensitization.

Photodynamic inactivation of herpes viruses with phthalocyanine derivatives

The antiviral photosensitization capacity of 11 different phthalocyanine (Pc) derivatives was examined using herpes simplex virus-1, herpes simplex virus-2 and varicella zoster virus in the search for the most potent sensitizers for viral decontamination of blood. The kinetics of viral photoinactivation were resolved during the stages of viral adsorption and penetration into the host cells. The capacity of Pc in the photodynamic inactivation of viruses was compared with that of merocyanine 540 (MC540), another widely studied photosensitizer. Sensitivity to photoinactivation decreased progressively with time after addition of viruses to their host cells. The viruses were most sensitive to photodynamic inactivation up to 30 min from the initiation of adsorption. Cell-associated viruses, 45-60 min after the onset of adsorption, are highly resistant to photodynamic treatment by most photosensitizers, with the exception of amphiphilic Pc derivatives. Thus the mixed sulfonated Pc-naphthalocyanine derivatives AlNSB3P and AlN2SB2P demonstrated a remarkable decontamination activity even 60 min after the onset of adsorption. Ultrastructural examination of these photosensitized viruses demonstrated damage to the viral envelope which prevented viral adsorption and/or penetration. The non-enveloped adenovirus was found to be resistant to all the dyes tested.

Collapse of K+ and ionic balance during photodynamic inactivation of leukemic cells, erythrocytes and Staphylococcus aureus

1. The immediate and fast ionic fluxes in Friend erythroleukemic cells (FELC), erythrocytes and Staphylococcus aureus during short intervals of porphyrin mediated photosensitization were determined uniquely by X-ray microanalysis (XRMA) combined with electron microscopy. 2. Photodynamic inactivation of FELC was mediated by either endogenous protoporphyrin induced by 5-amino levulinic acid (5-ALA), or Photofrin-II. We describe the predominant phenomena of > 85% K-loss within 2-10 min of photoactivation. However the accompanied Na inflow and the collapse of the cellular balance of elemental-composition were inconsistent and acted as a function of cell damage. 3. Erythrocytes treated with hematoporphyrin (HP) lost most of their intracellular K yet instantly gained Na. Nevertheless the K/Na molar ratio of the control erythrocytes was nearly 12/1 while after photosensitization and K loss it changed to 1/1. 4. The S. aureus bacteria photosensitized with HP showed entire K-loss as well as marked Na efflux which increased with irradiation time; this was accompanied by the decline of other cell elements. 5. The prevailing K loss in FELC, erythrocytes and bacteria during the first minutes of photosensitization is deduced to be an immediate primary consequence of the photodynamic effect, while other ionic changes are joined in order with the development of cellular damage.

Electric depolarization of photosensitized cells: lipid vs. protein alterations

We have monitored several photosensitized reactions in proteins, liposomes and cells under similar conditions. We found that the depolarization of K(+)-diffusion potential of liposomes or the leakage of an entrapped molecule, calcein, progress at a much slower rate than the photosensitized damage to proteins and the photosensitized killing of bacterial and leukemic cells. X-ray microanalysis revealed that upon light exposure of HP-treated leukemic cells and bacteria, they totally lost their cellular potassium. We deduce that the direct photosensitized oxidation of lipid components cannot cause the depolarization of cells, which in turn could be responsible for their death. A photosensitized damage to protein sites in the cell, probably in the membrane, is a more likely reason for the depolarization, the loss of potassium ions and cell death that is caused in light-activated photodynamic processes.

Phthalocyanine-induced photohemolysis: structure-activity relationship and the effect of fluoride

Phthalocyanine (Pc) containing A1, Ga or Zn as central metal ligand and substituted with a varying number of sulfonic acid residues as well as additional benzene rings were synthesized and their photodynamic activity was assayed using photohemolysis of human erythrocytes as an endpoint. The Pc derivatives varied > 300-fold in their photodynamic activity. Activity correlated with binding of the dye to the cell, with the exception of some of the amphiphilic dyes where cell uptake was an order of magnitude higher than expected from the observed activity. Fluoride was shown to inhibit A1PcSn-induced photohemolysis. This effect occurred also with other A1Pc and GaPc derivatives, but the concentration of F- required to slow photohemolysis by a factor of two (Ki) varied between 4 microM and 10 mM. Fluorescence spectral studies indicated complex formation between F- and the dye, which was stronger for A1Pc than GaPc derivatives. Ultrastructural studies using scanning electron microscopy showed that the photosensitized cells were converted to spherocytes and that F- prevented this to a large extent.

The antibacterial activity of haemin compared with cobalt, zinc and magnesium protoporphyrin and its effect on potassium loss and ultrastructure of Staphylococcus aureus

The unique antibacterial properties of Fe-protoporphyrin (haemin) on Staphylococcus aureus, compared to Co-protoporphyrin (Co-PP), Mg-protoporphyrin (Mg-PP) and Zn-protoporphyrin (Zn-PP) are described. Only haemin (20 microM) exhibits a strong light-independent antibacterial effect on S. aureus; the other metalloporphyrins, Co-PP, Mg-PP or Zn-PP, have no antibacterial effect in the dark. Only light photosensitization of Mg-PP-treated cells resulted in the inhibition of the bacterial growth, while Co-PP or Zn-PP were photodynamically inactive. A notable effect of haemin on inactivation of S. aureus was the induction of immediate ion fluxes as determined by X-ray microanalysis (XRMA) of fast-frozen cells. A marked efflux of K (96%) and Cl (94%) was expressed immediately as determined by X-ray microanalysis of S. aureus cells treated with haemin for 5 min. Only 48% loss of Na was detected in the cells under these treatment conditions, while P content was increased by 150%. Electron microscopy analysis revealed the appearance of a mesosome-like structure connected to the new septa, filamentous chromosome and arrays of aggregated ribosomes in the cytoplasm. We propose that haemin has multiple cellular targets for its oxidative effect in S. aureus.

The effect of EDTA and serum on endogenous porphyrin accumulation and photodynamic sensitization of human K562 leukemic cells

The interrelationship between the effect of serum on the induction of porphyrin synthesis, intracellular porphyrin accumulation and photodynamic sensitization of human K562 cells is described. Endogenous porphyrins, synthesized from supplemented 5-amino levulinic acid (5-ALA), were shown to accumulate in the cells, while an addition of serum triggered porphyrin translocation from the cell to the serum. In order to enhance porphyrin accumulation in the cells themselves, they were further stimulated by EDTA, which in combination with 5-ALA reduces Fe++ cellular content. The higher porphyrin cellular content under EDTA and 5-ALA induction was exploited to photoinactivate the human leukemic cells by more then 3 orders of magnitude.

Ultrastructural damage in photosensitized endothelial cells: dependence on hematoporphyrin delivery pathways

The subcellular photodamage to endothelial cells in culture, revealed by transmission electron microscopy, was correlated with discrete delivery pathways of hematoporphyrin (HP). Cell detachment from the extracellular matrix, prominent water influx starting at the outer membrane and formation of blebs followed by cell death were the result of photodynamic damage induced by aqueous HP. Serum-bound HP was internalized by endocytosis and accumulated in lysosomal compartments as located after photosensitization. Obstructed lysosomal membranes, degradation of chromatin and swelling of endoplasmic reticulum were revealed in these cells. Red blood cells (RBCs), preincubated with HP, delivered low amounts of the drug to endothelial cells. The photodamage was limited to the nucleus and nucleolus. The role of photosensitizer delivery pathways in cancer cell damage is discussed.

Inactivation of gram-negative bacteria by photosensitized porphyrins

Photosensitization of Escherichia coli and Pseudomonas aeruginosa cells by deuteroporphyrin (DP) is shown to be possible in the presence of the polycationic agent polymyxin nonapeptide (PMNP). Previous studies established complete resistance of Gram-negative bacteria to the photodynamic effects of porphyrins. The present results show that combined treatment of E. coli or P. aeruginosa cultures with DP and PMNP inhibit cell growth and viability. No antibacterial activity of PMNP alone could be demonstrated and cell viability remained unchanged. Spectroscopically, PMNP was found to bind DP, a mechanism which probably assists its penetration into the cell's membranes. Insertion of DP into the cells was monitored by the characteristic fluorescence band of bound DP at 622 nm. Binding times were 5-40 min and the extent of binding increased with decreasing the pH from 8.5 to 6.5. DP binding constants, as well as the concentrations of PMNP which were required for maximal effect on the various Gram-negative bacteria, were determined fluorometrically. By the treatment of DP, PMNP and light the growth of E. coli and P. aeruginosa cultures was stopped and the viability of the culture was dramatically reduced. Within 60 min of treatment the survival fraction of E. coli culture was 9 x 10(-6) and that of P. aeruginosa was 5.2 x 10(-4). Electron microscopy depicted ultrastructural alterations in the Gram-negative cells treated by DP and PMNP. The completion of cell division was inhibited and the chromosomal domain was altered markedly.

In vivo effects of porphyrins on bacterial DNA

The DNA damage in intact Staphylococcus aureus and E. coli cells induced by photosensitized deuteroporphyrin or hemin is described. Treatment of S. aureus cultures with hemin or photosensitized deuteroporphyrin (Dp) caused time-dependent changes in the plasmidial DNA profiles. The major observation was the disappearance of the plasmid supercoiled fraction. The chromosomal DNA was also affected by hemin and by photosensitized Dp, since its degradation products were detected after exposing the bacterial cells to the porphyrin drugs. Photosensitization of E. coli cells, pretreated with Dp and polymyxin B nonapeptide (PMBNP), also resulted in plasmidial damage. No such damage occurred when E. coli cultures were treated with hemin and PMBNP. The above results can be tightly correlated with the antimicrobial action of porphyrins. Their damage to the bacterial DNA seems to reflect one of the in vivo effects of these porphyrins.

The bactericidal activity of a deuteroporphyrin-hemin mixture on gram-positive bacteria. A microbiological and spectroscopic study

The combined antibacterial activity of various porphyrins with hemin on Gram-positive bacteria was studied. Protoporphyrin, hematoporphyrin derivative and deuteroporphyrin show only a marginal inhibitory effect in the dark. However, hemin has a strong cytotoxic effect which is independent of illumination and is equally strong in the dark. The disadvantage of hemin treatment is that it is temporary. In this study, we have demonstrated that a combination of deuteroporphyrin and hemin has a unique cytotoxic activity on Staphylococcus aureus, Streptococcus faecalis and Bacillus cereus. The effect of the combined compound is stronger than that of the separate constituents, and is as strong in the dark as in the light. Only 0.005% of the initial S. aureus population survive after a 2 h treatment. Absorption and fluorescence spectra of hemin-deuteroporphyrin mixtures in water and liposomes suggest the formation of a species with spectroscopic properties which are different from those of the two constituents.

Erythropoietic protoporphyria: photodynamic transfer of protoporphyrin from intact erythrocytes to other cells

Erythrocytes in patients with erythropoietic protoporphyria (EPP) contain large amounts of protoporphyrin and are regarded as the main source of protoporphyrin in this disease. Cells in the skin of EPP patients accumulate protoporphyrin released from the erythrocytes and upon sun exposure endothelial cells are photodamaged. In the present study a light-induced transfer of protoporphyrin directly from EPP erythrocytes to cultured cells is demonstrated. Erythrocytes were layered upon cultured cells and irradiated. The nearness of erythrocyte and cultured cell membranes potentiated the transfer of protoporphyrin between these cells. This transfer was rapid and preceded the release of protoporphyrin to proteins in the medium. Further irradiation of the protoporphyrin-enriched cultured cells, after removal of the erythrocytes, caused severe photodamage to the cells and survival was dependent on both the amount of protoporphyrin transferred and on the light fluence. Clinical observations and the results of this study indicate that light energy may be involved in two steps in the pathophysiology of EPP: (A) light-induced release of protoporphyrin from erythrocytes to endothelial cells and (B) photodynamic damage to protoporphyrin-enriched endothelial cells.

Bactericidal effects of photoactivated porphyrins--an alternative approach to antimicrobial drugs

Photoactivated porphyrins display a potent cytotoxic activity towards a variety of Gram positive bacteria, mycoplasma and yeasts, but not Gram negative cells. The prerequisite for photosensitization of a microbial cell is the binding of porphyrin to the cytoplasmic membrane in a pH-dependent manner. On illumination, the membrane bound, and possibly, cytoplasmic porphyrin molecules generate singlet oxygen and radicals which sensitize biomolecules and lead to cell death. The immediate inhibition of cell growth on photodynamic treatment is accompanied by alterations in cell wall and membrane synthesis, leading to the formation of large mesosomes adjacent to the unaccomplished septa. Hemin bound to microbial cells exerts cytotoxic activity by peroxidative and oxidative reactions independent of light. Future research in the field may enhance the possibility of using porphyrin photosensitization for treatment of microbial infections. Such clinical use will be unrelated to the antibiotic resistance of the pathogen. Resistance of Gram negative bacteria to porphyrin photosensitization is the main impediment to its use as a broad spectrum antibacterial method.

Molecular biology of Crohn's disease mycobacteria

A Glasgow surgeon, T.K. Dalziel, published a detailed description of chronic enteritis in humans in 1913. He proposed that the disease was caused by the same organisms as those responsible for chronic enteritis, Johne's disease, in animals described a few years earlier (1895). Dalziel's dilemma was that he could see acid-fast bacilli in the diseased animal tissues but not in the diseased human tissues. Little real progress in the medical understanding of the causes of chronic enteritis in humans occurred over the next half a century or more. From 1978, a decade of research in many laboratories using improved methods for the culture of environmental mycobacteria showed that these could be grown in bacillary form from about one in five cases of Crohn's disease, from the same proportion of cases of ulcerative colitis, and from about one in ten control tissues. Spheroplasts were grown from two in five cases of Crohn's disease, one in five cases of ulcerative colitis, and rarely from control tissues. The nature of these agents was often uncertain. We describe work which began in 1985 and led rapidly to the identification of IS900, a DNA repetitive element in an uncharacterized Crohn's disease mycobacterial isolate. With other isolates, these were then shown by DNA fingerprinting to be indistinguishable from Mycobacterium paratuberculosis, Johne's bacillus. Similar techniques also demonstrated the wood-pigeon strain of M. avium in some Crohn's disease cultures. This bacillus can also cause chronic enteritis in calves. IS900 is the first of a family of unusual DNA insertion sequences which extend widely throughout environmental mycobacteria. Use of assays based on PCR amplification of highly specific DNA sequences from these insertional elements, and recombinant and synthetic peptides from their predicted proteins, will revolutionize the detection and characterization of these agents. These methods, applied to animal, human and environmental samples, will indicate new ways for the prevention and treatment of chronic enteritis, as well as other disorders associated with infections by environmental mycobacteria.