A Pyrazolate Osmium(VI) Nitride Exhibits Anticancer Activity through Modulating Protein Homeostasis in HepG2 Cells

Interest in the third-row transition metal osmium and its compounds as potential anticancer agents has grown in recent years. Here, we synthesized the osmium(VI) nitrido complex Na[Os^VI(N)(tpm)₂] (tpm = [5-(Thien-2-yl)-1H-pyrazol-3-yl]methanol), which exhibited a greater inhibitory effect on the cell viabilities of the cervical, ovarian, and breast cancer cell lines compared with cisplatin. Proteomics analysis revealed that Na[Os^VI(N)(tpm)₂] modulates the expression of protein-transportation-associated, DNA-metabolism-associated, and oxidative-stress-associated proteins in HepG2 cells. Perturbation of protein expression activity by the complex in cancer cells affects the functions of the mitochondria, resulting in high levels of cellular oxidative stress and low rates of cell survival. Moreover, it caused G2/M phase cell cycle arrest and caspase-mediated apoptosis of HepG2 cells. This study reveals a new high-valent osmium complex as an anticancer agent candidate modulating protein homeostasis.

Highly Cytotoxic Osmium(II) Compounds and Their Ruthenium(II) Analogues Targeting Ovarian Carcinoma Cell Lines and Evading Cisplatin Resistance Mechanisms

(1) Background: Ruthenium and osmium complexes attract increasing interest as next generation anticancer drugs. Focusing on structure-activity-relationships of this class of compounds, we report on 17 different ruthenium(II) complexes and four promising osmium(II) analogues with cinnamic acid derivatives as O,S bidentate ligands. The aim of this study was to determine the anticancer activity and the ability to evade platin resistance mechanisms for these compounds. (2) Methods: Structural characterizations and stability determinations have been carried out with standard techniques, including NMR spectroscopy and X-ray crystallography. All complexes and single ligands have been tested for cytotoxic activity on two ovarian cancer cell lines (A2780, SKOV3) and their cisplatin-resistant isogenic cell cultures, a lung carcinoma cell line (A549) as well as selected compounds on three non-cancerous cell cultures in vitro. FACS analyses and histone γH2AX staining were carried out for cell cycle distribution and cell death or DNA damage analyses, respectively. (3) Results: IC50 values show promising results, specifically a high cancer selective cytotoxicity and evasion of resistance mechanisms for Ru(II) and Os(II) compounds. Histone γH2AX foci and FACS experiments validated the high cytotoxicity but revealed diminished DNA damage-inducing activity and an absence of cell cycle disturbance thus pointing to another mode of action. (4) Conclusion: Ru(II) and Os(II) compounds with O,S-bidentate ligands show high cytotoxicity without strong effects on DNA damage and cell cycle, and this seems to be the basis to circumvent resistance mechanisms and for the high cancer cell specificity.

Osmium(VI) nitride triggers mitochondria-induced oncosis and apoptosis

We report a new osmium(VI) nitrido complex bearing a nonplanar tetradentate ligand with potent anticancer activity. This complex causes mitochondrial damage, which induces liver cancer cell death via oncosis and apoptosis. This is the first osmium-based anticancer candidate that induces oncosis.

Os(II)-Bridged Polyarginine Conjugates: The Additive Effects of Peptides in Promoting or Preventing Permeation in Cells and Multicellular Tumor Spheroids

The preparation of two polyarginine conjugates of the complex Os(II) [bis-(4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine)] [Os-(Rn)2]x+ (n = 4 and 8; x = 10 and 18) is reported, to explore whether the R8 peptide sequence that promotes cell uptake requires a contiguous amino acid sequence for membrane permeation or if this can be accomplished in a linearly bridged structure with the additive effect of shorter peptide sequences. The conjugates exhibit NIR emission centered at 754 nm and essentially oxygen-insensitive emission with a lifetime of 89 ns in phosphate-buffered saline. The uptake, distribution, and cytotoxicity of the parent complex and peptide derivatives were compared in 2D cell monolayers and a three-dimensional (3D) multicellular tumor spheroid (MCTS) model. Whereas, the bis-octaarginine sequences were impermeable to cells and spheroids, and the bis-tetraarginine conjugate showed excellent cellular uptake and accumulation in two 2D monolayer cell lines and remarkable in-depth penetration of 3D MCTSs of pancreatic cancer cells. Overall, the data indicates that cell permeability can be promoted via non-contiguous sequences of arginine residues bridged across the metal centre.

Tracking Reactions of Asymmetric Organo-Osmium Transfer Hydrogenation Catalysts in Cancer Cells

Most metallodrugs are prodrugs that can undergo ligand exchange and redox reactions in biological media. Here we have investigated the cellular stability of the anticancer complex [OsII [(η6 -p-cymene)(RR/SS-MePh-DPEN)] [1] (MePh-DPEN=tosyl-diphenylethylenediamine) which catalyses the enantioselective reduction of pyruvate to lactate in cells. The introduction of a bromide tag at an unreactive site on a phenyl substituent of Ph-DPEN allowed us to probe the fate of this ligand and Os in human cancer cells by a combination of X-ray fluorescence (XRF) elemental mapping and inductively coupled plasma-mass spectrometry (ICP-MS). The BrPh-DPEN ligand is readily displaced by reaction with endogenous thiols and translocated to the nucleus, whereas the Os fragment is exported from the cells. These data explain why the efficiency of catalysis is low, and suggests that it could be optimised by developing thiol resistant analogues. Moreover, this work also provides a new way for the delivery of ligands which are inactive when administered on their own.

A cytotoxic nitrido-osmium(VI) complex induces caspase-mediated apoptosis in HepG2 cancer cells

The osmium(vi) nitrido complex [OsVI(N)(sap)(py)Cl] is a potential anti-cancer drug with promising in vitro antiproliferative activities toward a panel of cancer cell lines, including cisplatin-resistant cells (IC50 values of 2.8-13.8 μM). This drug targets DNA and changes its conformation via covalent binding and insertion. In vitro studies indicate that the drug induces HepG2 cells G2/M phase arrest, disrupts the mitochondrial membrane potential and causes caspase-mediated apoptosis. Further in vivo studies using HepG2-bearing nude mice reveal that this drug not only shows good antitumor efficacy of inhibiting tumor growth, but also does not show the side effect of weight loss.

Os(II) Oligothienyl Complexes as a Hypoxia-Active Photosensitizer Class for Photodynamic Therapy

Hypoxia presents a challenge to anticancer therapy, reducing the efficacy of many available treatments. Photodynamic therapy is particularly susceptible to hypoxia, given that its mechanism relies on oxygen. Herein, we introduce two new osmium-based polypyridyl photosensitizers that are active in hypoxia. The lead compounds emerged from a systematic study of two Os(II) polypyridyl families derived from 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb) as coligands combined with imidazo[4,5-f][1,10]phenanthroline ligands tethered to n = 0-4 thiophenes (IP-nT). The compounds were characterized and investigated for their spectroscopic and (photo)biological activities. The two hypoxia-active Os(II) photosensitizers had n = 4 thiophenes, with the bpy analogue 1-4T being the most potent. In normoxia, 1-4T had low nanomolar activity (half-maximal effective concentration (EC50) = 1-13 nM) with phototherapeutic indices (PI) ranging from 5500 to 55 000 with red and visible light, respectively. A sub-micromolar potency was maintained even in hypoxia (1% O2), with light EC50 and PI values of 732-812 nM and 68-76, respectively -currently among the largest PIs for hypoxic photoactivity. This high degree of activity coincided with a low-energy, long-lived (0.98-3.6 μs) mixed-character intraligand charge-transfer (3ILCT)/ligand-to-ligand charge-transfer (3LLCT) state only accessible in quaterthiophene complexes 1-4T and 2-4T. The coligand identity strongly influenced the photophysical and photobiological results in this study, whereby the bpy coligand led to longer lifetimes (3.6 μs) and more potent photo-cytotoxicity relative to those of dmb. The unactivated compounds were relatively nontoxic both in vitro and in vivo. The maximum tolerated dose for 1-4T and 2-4T in mice was greater than or equal to 200 mg kg-1, an excellent starting point for future in vivo validation.

In-Cell Activation of Organo-Osmium(II) Anticancer Complexes

The family of iodido OsII arene phenylazopyridine complexes [Os(η6 -p-cym)(5-R1 -pyridylazo-4-R2 -phenyl))I]+ (where p-cym=para-cymene) exhibit potent sub-micromolar antiproliferative activity towards human cancer cells and are active in vivo. Their chemical behavior is distinct from that of cisplatin: they do not readily hydrolyze, nor bind to DNA bases. We report here a mechanism by which they are activated in cancer cells, involving release of the I- ligand in the presence of glutathione (GSH). The X-ray crystal structures of two active complexes are reported, 1-I (R1 =OEt, R2 =H) and 2-I (R1 =H, R2 =NMe2 ). They were labelled with the radionuclide 131 I (β- /γ emitter, t1/2 8.02 d), and their activity in MCF-7 human breast cancer cells was studied. 1-[131 I] and 2-[131 I] exhibit good stability in both phosphate-buffered saline and blood serum. In contrast, once taken up by MCF-7 cells, the iodide ligand is rapidly pumped out. Intriguingly, GSH catalyzes their hydrolysis. The resulting hydroxido complexes can form thiolato and sulfenato adducts with GSH, and react with H2 O2 generating hydroxyl radicals. These findings shed new light on the mechanism of action of these organo-osmium complexes.

Similar biological activities of two isostructural ruthenium and osmium complexes

In this study, we probe and verify the concept of designing unreactive bioactive metal complexes, in which the metal possesses a purely structural function, by investigating the consequences of replacing ruthenium in a bioactive half-sandwich kinase inhibitor scaffold by its heavier congener osmium. The two isostructural complexes are compared with respect to their anticancer properties in 1205 Lu melanoma cells, activation of the Wnt signaling pathway, IC(50) values against the protein kinases GSK-3beta and Pim-1, and binding modes to the protein kinase Pim-1 by protein crystallography. It was found that the two congeners display almost indistinguishable biological activities, which can be explained by their nearly identical three-dimensional structures and their identical mode of action as protein kinase inhibitors. This is a unique example in which the replacement of a metal in an anticancer scaffold by its heavier homologue does not alter its biological activity.

Tuning the Hydrolytic Aqueous Chemistry of Osmium Arene Complexes with N,O-Chelating Ligands to Achieve Cancer Cell Cytotoxicity

Potential biological and medical applications of organometallic complexes are hampered by a lack of knowledge of their aqueous solution chemistry. We show that the hydrolytic and aqueous solution chemistry of half-sandwich OsII arene complexes of the type [(eta6-arene)Os(XY)Cl] can be tuned with XY chelating ligands to achieve cancer cell cytoxicity comparable to carboplatin. Complexes containing arene = p-cymene, XY = N,O-chelating ligands glycinate (1), L-alaninate (2), alpha-aminobutyrate (3), beta-alaninate (4), picolinate (5), or 8-hydroxyquinolinate (7) were synthesized. Although, 1-4 and 7 hydrolyzed rapidly (<min), complexes with pi-acceptor pyridine as N-donor and carboxylate as O-donor (5 and 6) hydrolyzed much more slowly (t1/2 = 0.20 and 0.52 h, 298 K). The aqua picolinate complexes were more acidic (pKa* = 6.67, 6.33) than the other aqua adducts (pKa* = 7.17-7.71). At biological test concentrations (micromolar), the chelating ligands dissociated from complexes 1-4 to give the inert hydroxo-bridged dinuclear species [(eta6-arene)Os(mu-OH)3Os(eta6-arene)]+ (8), and these complexes were inactive toward human lung A549 and ovarian A2780 cancer cells. In contrast, 5-7 were cytotoxic, especially 6 (IC50 values of 8 and 4.2 microM). The X-ray structures of 9-ethylguanine, [(eta6-p-cym)Os(pico)(9EtG-N7)]PF6, and 9-ethyladenine, [(eta6-p-cym)Os(pico)(9EtA-N7)]PF6, adducts of 5 are reported (the first reported for G or A adducts of OsII). Crystals of the 9EtA complex contain homoadenine base pairing. The 9EtG adduct in particular exhibits remarkable aqueous kinetic stability. This work shows how the rational control of chemical reactivity (hydrolysis, acidity, formation of hydroxo-bridged dinuclear species) can allow the design of cytotoxic anticancer OsII arene complexes.

Oocyte–follicle cell interactions during ovarian follicle development, as seen by high resolution scanning and transmission electron microscopy in humans

The aim of this article is to summarize and update, through an integrated analysis by transmission electron microscopy (TEM) and high resolution scanning electron microscopy (SEM) after osmium-dimethyl sulfoxide-osmium (ODO) maceration, the studies of our research group on the morphodynamics of oocyte-follicle cell associations during follicle development in humans. In resting oocytes, follicular cells project few and short cytoplasmic processes in the perioocytic space. They often form bulbous terminals very close to the oolemma where zonulae adherentes, maculae adherentes, and gap junctions are present. The oolemma mostly appears smooth with short and scanty microvilli. In early growing follicles, follicular cell projections appear as (a) long and tortuous microvilli or (b) large and short extensions. The oolemma shows numerous short microvilli. By TEM, long and thin follicular "intraooplasmic processes" have been seen to penetrate deeply into some oolemma invaginations. In macerated samples, they are observed by SEM to come very close to the nucleus and contact different oocyte organelles. These processes are more likely involved in early oocyte growth. In late growing follicles, oocyte-somatic cell interactions-now established through the interposition of the zona pellucida (ZP)-preserve the general features of early growth stage, with the exceptions of "intraooplasmic processes," which are no more present. In mature follicles subjected to a long ODO maceration, corona cells appear to contact the oocyte through an apical plume of numerous very long "curly hair-like microvilli." Corona cell microvilli, quite likely provide a sort of cytoplasmic skeleton for the ZP and they are possibly involved in (a) release of nutrients or removal catabolites to/from oocyte and vice versa and (b) transfer of substances to build up ZP. In conclusion, among oocyte and somatic cells a structural and functional association is revealed. This association, certainly highly dynamic in vivo, plays a key role in regulating the healthy folliculogenesis to assure a correct and timed oocyte maturation and ovulation.

Low-potential cyclometalated osmium(II) mediators of glucose oxidase

The osma(II)cycles [Os(phpy)(LL)(2)]PF(6) (LL = 1,10-phen (3a) and 4,4'-Me(2)-2,2'-bpy (3b)) are made from [(eta(6)-C(6)H(6))Os(micro-Cl)Cl](2) (1) either via transmetalation using the [Hg(phpy)(2)] organomercurial in MeOH or via the sp(2)-C-H bond cleavage of 2-phenylpyridine (phpyH) in MeCN to afford [(eta(6)-C(6)H(6))Os(phpy)Cl] or [(eta(6)-C(6)H(6))Os(phpy)(MeCN)]PF(6), respectively. The latter two react cleanly with LL to give 3a and 3b, the M(II/III) redox potentials of which equal 30 and -100 mV (vs Ag/AgCl), respectively. The electrochemically made Os(III) species oxidize rapidly reduced glucose oxidase. The second-order rate constant equals 1.1 x 10(7) M(-)(1) s(-)(1) for 3a at 25 degrees C, pH 7.

Preparation of crystalline p-nitrobenzyl 2-formyl carbapenems by oxidative cleavage

Crystalline 1beta-methyl-2-formyl carbapenem pNB esters were prepared by osmium-mediated oxidative cleavage of the corresponding 2-vinyl derivatives. Reduction of the 2-formyl compounds gave the corresponding 2-hydroxymethyl derivatives, which are key intermediates for the anti-MRS carbapenem candidate (1).

Antimicrobial activities in vitro and in vivo of transition element complexes containing gold(I) and osmium(VI)

Metal compounds have been used as antibacterial agents for centuries. The in-vitro activity of two metal containing complexes, one gold, the other osmium, was investigated using a panel of clinically isolated bacteria and Candida albicans. Twenty strains of each organism were used and MIC and MBC values determined using the agar plate dilution method. Protein binding effects on the activity of the compounds were also investigated using media supplemented with 5% human blood. In-vivo activity of the two compounds was subsequently determined in a hairless-obese mouse skin-surface activity model. Both compounds were highly active against the Gram-positive organisms and Candida albicans in vitro. The gold compound had some Gram-negative activity but the osmium complex was inactive against these organisms. Both were extensively protein bound. In the in-vivo experiment the gold compound achieved a 2-3 log reduction for all the test organisms and was at least as good as or superior to mupirocin in its eradication rate. The osmium compound was inactive.

Cholesterol and 25-hydroxycholesterol retention in specimens of liver and aorta prepared for electron microscopy. II. Effect of filipin, osmium, digitonin and saponin

Sprague-Dawley rats were injected intraperitoneally with [1 alpha, 2 alpha(n)-3H]cholesterol or 25-hydroxy-[26,27-3H]cholesterol, and one and five days later liver and aortic tissues were fixed. The extent to which these sterols were lost from the tissues during preparation for electron microscopy (EM) was examined utilizing different fixation procedures and various protective agents. Radioactive tracers, scintillation counting and standard EM techniques were used. Although most of the procedures examined caused major lipid losses, useful fixation procedures that allow retention of cholesterol or 25-hydroxy-cholesterol in liver and aortic tissues were found and are described here.

The activity of metal compounds against aerobic and anaerobic bacteria

We evaluated the antimicrobial activity of two metal compounds, JM-1397 (OsO2[xylyl]2) and JM-2469 (AuCl[S2CPEt3]). Both inhibited methicillin-susceptible and methicillin-resistant Staphylococcus aureus at concentrations of 0.5-2 micrograms/ml, with a minimum inhibitory concentration (MIC90) of 1 microgram/ml for JM-1397 and 0.5 microgram/ml for JM-2469. Similar concentrations inhibited methicillin-susceptible and -resistant coagulase-negative staphylococci (S. epidermidis, S. haemolyticus, and S. saprophyticus). JM-2469 inhibited group A, B, C, F, and G beta-hemolytic streptococci and viridans group streptococci at 1-8 micrograms/ml (MIC90 4 micrograms/ml) but Enterococcus faecalis and E. faecium had MICs of 8-16 micrograms/ml. JM-1397 had MICs for these organisms of greater than 64 micrograms/ml. Bacteroides fragilis, other Bacteroides, and Clostridium species were inhibited by less than or equal to 0.12-4 micrograms/ml (MIC90, 0.5 microgram/ml). MICs of both compounds for Enterobacteriaceae and Pseudomonas spp. were greater than 64 micrograms/ml. These studies show that osmium and gold compounds have potential as topical agents against Gram-positive and anaerobic species.

Pharmacomodulations on new organometallic complexes of Ir, Pt, Rh, Pd, Os: in vitro and in vivo trypanocidal study against Trypanosoma brucei brucei

New organometallic complexes have been synthesized by association of an active organic molecule with a metallic element such as Pt, Rh, Ir, Pd, Os. Their trypanocidal activity was studied in vitro and in vivo against T. b. brucei. The more active compounds were pentamidine derivatives. The Ir- COD-pentamidine complex, and Iridium (I) cationic and organometallic complex showed and in vitro activity at 60 micrograms/l. Moreover, all infected mice were cured by this compound subcutaneously administered in a single dose at 0.5 mg/kg (0.317 mumol/kg). In the same conditions, pentamidine cured all the mice at 5 mumol/kg. Ir-COD-pentamidine (or P1995) was 16 fold more efficient than pentamidine. Since the chemotherapeutic index of this molecule was 7.5 fold higher than those of pentamidine, P1995 can be considered as a potential trypanocidal drug of the future.

Site-directed chemical modification for probing DNA-protein interactions. Osmium tetroxide modification of the -10 site of the lacUV5 promoter enhances open complex formation

A new experimental approach, site-directed chemical modification, was used to explore relationships between RNA polymerase-promoter interactions and function. For this study, the lacUV5 promoter with an exposed -10 thymine on the non-template strand was constructed. Osmium tetroxide was selected as the thymine modifying reagent. Modification occurred predominantly at the exposed -10 T with 5-fold less reactivity at the -12 T residue. The isolated modified strand was used to reconstitute a lacUV5 promoter with -10 (-12) adducts. OsO4 modification at both the -10 and -12 positions of the lacUV5 promoter significantly enhances Escherichia coli RNA polymerase-promoter open complex formation relative to the unmodified promoter. DNase I cleavage sites at -7, -8, and -10 of the unmodified promoter were rendered insusceptible to scission in the modified promoter. However, no difference can be detected in the RNA polymerase footprints for unmodified versus modified open complexes. The latter are fully capable of productive transcription with comparable amounts of identical run-off transcripts to unmodified open complexes. A 16 degrees C reduction in Tm was found for a 14-base pair oligonucleotide duplex containing a single OsO4-bispyridine adduct. The latter result suggests that open complex formation appears to be enhanced due to promoter unpairing at the -10 (-12) adduct sites.

Echinomycin-induced hypersensitivity to osmium tetroxide of DNA fragments incapable of forming Hoogsteen base pairs

To show conclusively that the critical structural deformation of double-helical DNA that is induced by the binding of quinoxaline antibiotics does not involve the formation of Hoogsteen base pairs, we have prepared a DNA fragment containing the nucleoside analog 7-deaza-2'-deoxyadenosine in one of the two strands. This DNA fragment was subjected to treatment with the thymidine-specific reagent osmium tetroxide and to DNase I "footprinting" in the presence or absence of micromolar concentrations of echinomycin. We report that this anti-tumor antibiotic binds to DNA containing the nucleoside analog as well as to natural DNA and that the previously reported hypersensitivity to osmium tetroxide of certain thymidine residues adjacent to echinomycin binding sites is maintained in analog-containing DNA. Since these thymidines are rendered incapable of participating in Hoogsteen base pairs by the incorporation of 7-deaza-2'-deoxyadenosine, we conclude that this unusual base-pairing scheme is not the cause of the observed hypersensitivity to osmium tetroxide and that it therefore results from a large local unwinding of the DNA in the presence of the antibiotic. Moreover, preventing the possibility of Hoogsteen base pairing does not preclude echinomycin binding.

Characterization of damage in gamma-irradiated and OsO4-treated DNA using methoxyamine

Unlabelled and radiolabelled methoxyamine have been used to characterize DNA damage caused by gamma-rays or by the chemical reagent osmium tetroxide (OsO4). Both treatments introduce in DNA a number of methoxyamine-binding sites proportional to the dose. Whereas the number of these sites remains constant after the OsO4 treatment it increases during postirradiation incubation; the postirradiation appearance of methoxyamine-binding sites is enhanced by the presence of methoxyamine. OsO4 treatment and gamma-irradiation also induce the formation of alkali-labile sites in DNA. Whereas the number of these sites remains constant after OsO4 treatment, it increases during postirradiation incubation and an alkaline medium accelerates their formation. A fraction of the alkali-labile sites found in gamma-irradiated DNA is methoxyamine-labile; by contrast, the OsO4-treated DNA is stable in the presence of methoxyamine.

Reactivity of cytosine and thymine in single-base-pair mismatches with hydroxylamine and osmium tetroxide and its application to the study of mutations

The chemical reactivity of thymine (T), when mismatched with the bases cytosine, guanine, and thymine, and of cytosine (C), when mismatched with thymine, adenine, and cytosine, has been examined. Heteroduplex DNAs containing such mismatched base pairs were first incubated with osmium tetroxide (for T and C mismatches) or hydroxylamine (for C mismatches) and then incubated with piperidine to cleave the DNA at the modified mismatched base. This cleavage was studied with an internally labeled strand containing the mismatched T or C, such that DNA cleavage and thus reactivity could be detected by gel electrophoresis. Cleavage at a total of 13 T and 21 C mismatches isolated (by at least three properly paired bases on both sides) single-base-pair mismatches was identified. All T or C mismatches studied were cleaved. By using end-labeled DNA probes containing T or C single-base-pair mismatches and conditions for limited cleavage, we were able to show that cleavage was at the base predicted by sequence analysis and that mismatches in a length of DNA could be readily detected by such an approach. This procedure may enable detection of all single-base-pair mismatches by use of sense and antisense probes and thus may be used to identify the mutated base and its position in a heteroduplex.

Probing of DNA polymorphic structure in the cell with osmium tetroxide

It is shown that osmium tetroxide, 2,2'-bipyridine can be applied as a probe of DNA structure in a bacterial cell. Using this probe we demonstrate (a) presence of structural distortions at the junctions between the right-handed B and left-handed Z DNA in a recombinant plasmid pRW751 and (b) unusual structure of the d(A-T)16 insert in pAT32 plasmid in E. coli cells and in in vitro.

Site-specific OsO4 modification of the B-Z junctions formed at the (dA-dC)32 region in supercoiled DNA

OsO4 in the presence of pyridine specifically modifies the structural distortions of the primary helix of supercoiled pRW777 near the (dA-dC)32 sequence. Modification occurs at the same negative superhelix density value as required for formation of the Z-helix within the polymer block. Fine mapping of the distorted regions, which are probably the B-Z junctions, is presented. OsO4 reactions provide a powerful and sensitive chemical approach to study DNA polymorphism in solution.

Formation of cytosine glycol and 5,6-dihydroxycytosine in deoxyribonucleic acid on treatment with osmium tetroxide

OsO4 selectively forms thymine glycol lesions in DNA. In the past, OsO4-treated DNA has been used as a substrate in studies of DNA repair utilizing base-excision repair enzymes such as DNA glycosylases. There is, however, no information available on the chemical identity of other OsO4-induced base lesions in DNA. A complete knowledge of such DNA lesions may be of importance for repair studies. Using a methodology developed recently for characterization of oxidative base damage in DNA, we provide evidence for the formation of cytosine glycol and 5,6-dihydroxycytosine moieties, in addition to thymine glycol, in DNA on treatment with OsO4. For this purpose, samples of OsO4-treated DNA were hydrolysed with formic acid, then trimethylsilylated and analysed by capillary gas chromatography-mass spectrometry. In addition to thymine glycol, 5-hydroxyuracil (isobarbituric acid), 5-hydroxycytosine and 5,6-dihydroxyuracil (isodialuric acid or dialuric acid) were identified in OsO4-treated DNA. It is suggested that 5-hydroxyuracil was formed by formic acid-induced deamination and dehydration of cytosine glycol, which was the actual oxidation product of the cytosine moiety in DNA. 5-Hydroxycytosine obviously resulted from dehydration of cytosine glycol, and 5,6-dihydroxyuracil from deamination of 5,6-dihydroxycytosine. This scheme was supported by the presence of 5-hydroxyuracil, uracil glycol and 5,6-dihydroxyuracil in OsO4-treated cytosine. Treatment of OsO4-treated cytosine with formic acid caused the complete conversion of uracil glycol into 5-hydroxyuracil. The implications of these findings relative to studies of DNA repair are discussed.

Mitochondrial granules: are they reliable markers for heavy metal cations?

Mitochondrial granules have been used as markers for heavy metal cations, but since such granules can also be found in tissues in the absence of such cations, an attempt was made to define conditions under which these different granules might be visualised. The tissue used was the smooth muscle of the central ear artery of the rabbit. In all studies, the presence or absence of mitochondrial granules was determined by several observers, using coded specimens so that the previous treatment of the specimens was not at the time known to the observers. Paired tissues were exposed for 30 or 90 minutes at 20, 30 or 39 degrees C to an incubate containing either 10 mmol/l barium or a control barium-free solution. After fixation in osmium tetroxide, there was no difference between the two groups; in both cases granules appeared more frequently the longer the time and the higher the temperature of incubation. In a further series where glutaraldehyde was the fixative, granules were identified in 23 out of 41 tissues incubated with barium, but in only 1 out of 41 control tissues (P less than 0.001). Electron probe microanalysis showed that granules in osmium-fixed tissues contained osmium as the main element, whereas granules in glutaraldehyde-fixed tissues which had been incubated with barium showed barium as the predominant cation. Thus mitochondrial granules can be reliable markers for heavy metal cations, but only under carefully controlled conditions.

Modification of ColE1 DNA with osmium tetroxide generates positively supercoiled molecules

Covalent binding of osmium tetroxide to negatively supercoiled DNA in vitro initially induces its relaxation, accompanied by a formation of a single denaturation "bubble" per molecule. Binding of further osmium results in DNA overwinding and the appearance of positive supercoils as demonstrated by gel electrophoresis and electron microscopy.

Ultrastructural demonstration of calcitonin in osmium-fixed human medullary carcinoma of thyroid by the protein A-colloidal gold technique

In two medullary carcinomas of the thyroid gland two types of secretory granules were found electron microscopically in the cytoplasm of the tumour cells. The sizes of the granules in one case ranged 103-345 nm in diameter; they were round in shape, and they co-existed in the same tumour cell. They could not, therefore, be distinctively subdivided into two types. In another case, secretory granules in the cytoplasm closely resemble EC granule in morphology. Using the protein A-colloidal gold (PAG) technique the content of secretory granules could be identified as calcitonin irrespective of their sizes or morphology. Immunoreactivity at the ultrastructural level was fairly well preserved even in the osmium-fixed tumour cells. The labelling index, expressed as a mean number of gold particles per unit square area of the secretory granule, was higher in the non-osmium-fixed tumour cells than in the osmium-fixed. Non-osmium-fixed tumour cells embedded either in epoxy or methacryl resin were almost equally labelled with gold particles. The result indicates that the PAG method is practicable to demonstrate the ultrastructural localization of calcitonin even in the osmium-fixed, epoxy resin embedded material.

[Demonstration of lipids by imidazole-buffered osmium tetroxide in the odontoblasts and cells of the enamel organ in the rat incisor]

Tissue post-fixation with imidazole buffered osmium tetroxide allows localization of lipids rich in unsaturated fatty acids (Angermüller and Fahimi, 1982). In odontoblasts, a positive reaction is observed in mitochondria, in membranous structures and in vesicles containing an osmiophilic and amorphous material. In odontoblastic processes, tubulo-vesicular structures and electron-dense coated vesicles seemed to be engaged in endocytosis and transfer processes towards lysosomial structures of the cell body. In the enamel organ, lipidic structures are observed in the stellate reticulum and the stratum intermedium. The plasma membrane of secretory ameloblasts as well as the content of some lysosomial structures are well contrasted. However the distal membranes of the Tomes processes showed weakly stained portions alternating with electron dense segments. Extracellular lipidic globules, sometimes associated with plasma membranes were also seen. These observations demonstrated the alternating weak and strong staining reactions in unsaturated fatty acids of plasma membrane areas of the cell processes, which contrasts with the continuous staining of the plasma membrane of the cell bodies. These observations could be related to functional differences.

Repair of the mouse synovial membrane after chemical synovectomy with osmium tetroxide

Repair of the synovium of the mouse knee joint following intra-articular injection with osmium tetroxide has been studied by light and electron microscopy. Within a first few days after osmium tetroxide injection complete necrosis of the synovial intima and inflammatory response in the subintimal connective tissue occurred. The resurfacing of the denuded synovium was performed by proliferation of immature synovioblasts which appeared to be derived from mesenchymal cells in the transition zone. The synovial intima completely restored the original structure, while repair of the subintimal tissue was accomplished by a scarring.

Osmium-induced alteration in DNA structure

In the presence of pyridine and other ligands osmium tetroxide binds covalently to pyrimidine bases in DNA. Properties of osmium-modified native and denatured calf thymus DNA, and plasmid Co1E1 DNA were investigated by means of differential pulse polarography, absorption spectrophotometry, circular dichroism, agarose gel electrophoresis, and nuclease S1 digestion. A great difference in the reaction kinetics of native and denatured DNAs with osmium, pyridine was observed. On the ground of the slow stepwise reaction kinetics of native DNA in the initial stage of its modification by osmium it has been suggested that the primary reaction sites do not include bases contained in the intact double helix. Osmium binding to sporadic primary reaction sites (represented e.g. by bases in the vicinity of a single-strand break) in native calf thymus DNA resulted in local changes in DNA conformation limited to a close neighbourhood of the binding site. At higher osmium/nucleotide ratios disordering of the DNA structure over a region extending beyond the immediate binding site was observed. With denatured DNA the same type of structure disordering was detected already in the initial stage of the reaction at osmium/nucleotide ratios as low as 0.01. Osmium binding to the supercoiled Co1E1 DNA resulted in its relaxation without nicking and it increased its sensitivity to linearization by cleavage with nuclease S1. The behaviour of Co1E1 DNA has been explained by the formation of a denatured region in the molecule (accompanied by a coupled loss of duplex and superhelical turns). It has been suggested that osmium can be used to label and to visualize distorted regions in the DNA double helix.

Osmium tetroxide: a new probe for site-specific distortions in supercoiled DNAs

Supercoiled plasmids Col E1 and cDm 506 (a Col E1 derivative carrying the D. melanogaster histone gene repeat) were treated with OsO4 in presence of pyridine and the reaction products were analyzed using different approaches. Gel electrophoresis showed that OsO4 binding to supercoiled DNA induced its relaxation without nicking. The amount of osmium bound to DNA (as determined electrochemically) increased with the extent of DNA relaxation. As a result of osmium modification of supercoiled cDm 506, a single denaturation "bubble" was observed in the electron microscope. Mapping of the osmium binding site by S1 nuclease cleavage followed by restriction enzyme digestion has revealed one major site in the intergenic spacer between the H1 and H3 histone genes of D. melanogaster. This site differs from the site cleaved by S1 nuclease in supercoiled DNA in the absence of osmium.

[Amanita virosa peptides: viroidin and viroisin are more effective than phalloidin for the in vitro protection of actin against the effects of osmic acid]

Virotoxins are a group of monocyclic peptides recently identified in the deadly mushroom Amanita virosa by Faulstich and coll. We found that two of these peptides, which have a methyl sulfonyl group, namely viroidin and viroisin are very effective to protect F-actin against oxidative degradation by osmium tetroxide in vitro. Their desoxo analogs, which have a methyl sulfoxyde group instead of methyl sulfonyl are less active, therefore there exists a relationship between the chemistry of the sulfur group and the activity of the peptides.

The effect of osmium postfixation and uranyl and lead staining on the ultrastructure of young enamel in the rat incisor

Enamel crystallites are electron opaque without osmium or heavy metal staining and give a crystalline electron diffraction pattern. Since the opacity and diffraction pattern are abolished from ultrathin sections of young enamel by floating on distilled water (Bishop and Warshawsky, 1982), the possibility that aqueous staining may also remove crystallites was tested. In addition, the effect of osmium postfixation on crystallite structure was examined. Rat incisors fixed by perfusion with a mixture of aldehydes were either nonosmicated or osmicated prior to dehydration. Incisor segments in the region of inner enamel secretion were embedded in the same Epon block to ensure reliable comparison. Osmicated enamel was more intensely stained with toluidine blue and more electron opaque than nonosmicated enamel. No other structural differences were seen. However, crystallites in osmicated enamel were more resistant to grid demineralization and electron beam damage. Routine staining was done by floating sections on solutions of uranyl acetate and lead citrate; sections were also floated on similar solutions from which the heavy metals were omitted. These solutions removed the electron opaque crystallites from the youngest enamel. Stained sections showed electron opaque crystallite-like structures similar to unstained enamel. When sections that were extracted by the solutions from which the metals were omitted were restained, they appeared identical to routinely stained enamel. It was concluded that staining of young enamel removes the crystallites and reveals only the organic matrix.

Variation in epidermal structure as function of different fixation methods. A stereological and morphological study

Ultrastructural and volume variations in intact human epidermis due to differences in composition of the fixative have been investigated by electron microscopy and stereology. It was found that with glutaraldehyde as fixative variations in buffer osmolality in the range of 120-390 mosmol caused readily detectable changes in volume of the intercellular space and keratinocyte morphology. Also the epidermal Langerhans' cell was effected by variations in buffer osmolality. Three commonly used fixatives (glutaraldehyde, glutaraldehyde + paraformaldehyde, and osmium tetroxide) were found to result in different morphological and volume relations.

The localisation of intracellular immunoglobulin and alpha-1-antitrypsin by immunoelectron staining of post-osmicated, resin-embedded tissue

An indirect immunoperoxidase method is described to demonstrate intracellular immunoglobulins and alpha-1-antitrypsin in semithin and ultrathin sections from human tissue. The tissue was primarily fixed in glutaraldehyde, post-osmicated and resin-embedded.

The effects of glutaraldehyde and osmium tetroxide on the erythrocyte membrane. A spin label study

A nitroxide spin label probe technique was applied to study the interaction between glutaraldehyde or osmium tetroxide (OsO4) amd the membranes of horse erythrocytes, ghosts and liposomes prepared from erythrocyte lipids. Two major conclusions have been established: (1) Reaction of the fixation reagents with the membrane is selective. OsO4 reacts predominantly with lipids and glutaraldehyde with membrane proteins. (2) The lipid-protein interactions change after pretreatment by OsO4 or glutaraldehyde.

Effects of glutaraldehyde or osmium tetroxide fixation on the osmotic properties of lung cells

The osmotic properties of lung cells have been tested before and after perfusion fixation of isolated, perfused lungs with either glutaraldehyde or osmium tetroxide. The testing procedure was to add hypertonic sucrose to the perfusate for several minutes and monitor the lung weight response (an 'osmotic transient'). Each lung was perfused with one or the other fixative solutions for 10 min, then the perfusate was changed back to Ringer-lactate before the post-fixation test was conducted. The results indicate that osmium tetroxide makes the cell membranes as permeable to sucrose as to water, and that sucrose thus causes no osmotic volume change. Glutaraldehyde, on the other hand, apparently preserves the impermeability of the cell membranes to sucrose, but the osmotic volume response is attenuated, indicating that significant changes in the cells have occurred.

[Phalloidin counteracts the destruction of F-actin by osmic acid. II. Protection by phalloidin of F-actin crosslinked with aldehydes (author's transl)]

We have studied by viscometry and spectrophotometry the effects of glutaraldehyde, acetaldehyde, acrolein and formaldehyde on F-actin in vitro. Pretreatment with acrolein and, to a lesser extent, with glutaraldehyde, results in increased destruction of F-actin during the subsequent degradation with osmic acid. Formaldehyde alone disintegrates actin filaments. Acetaldehyde gives the best results and does not seem to damage F-actin. Phalloidin protects F-actin against destruction by osmic acid and this protection is also observed in the F-actin which has been pretreated with the four aldehydes mentioned.

Effects of glutaraldehyde and osmium tetroxide on newborn rat epidermal keratin

The effects of glutaraldehyde and osmium tetroxide (OsO4) fixation on ultrastructural and biochemical changes of epidermal keratin were investigated. Morphometrically, the apparent size of keratohyalin granules was smallest when granular cells were fixed with OsO4, whereas those fixed with glutaraldehyde were larger, and those double-fixed with glutaraldehyde and OsO4 were largest. The ultrastructure of tonofilaments appeared different in each type of fixation. Biochemically, cross-linking glutaraldehyde with purified keratin from cornified cells formed a high molecular weight product with a blue shift of the absorption maximum and an increase in absorbance. Detection of the absorption spectra of OsO4- keratin reactions revealed that a new absorption maximum around 410 nm developed in glutaraldehyde-treated keratin, while one around 315 nm appeared in nontreated keratin. In addition, glutaraldehyde pretreatment increased by 40% the initial reaction rate and by 23% the total amount of OsO4 reduction. Sodium dodecyl sulfate gel electrophoresis demonstrated that degradation of keratin molecules occurred in both glutaraldehyde-treated and untreated keratin after 2 hr of exposure to OsO4. These findings indicate that keratin molecules are chemically modified by fixatives routinely used for electron microscopy. We consider that this chemical information plays an essential role in the appropriate interpretation of the ultrastructure of epidermal cells.

[Phalloidin counteracts the destructive effects of osmic acid and potassium permanganate on F-actin (author's transl)]

Osmium tetroxide and potassium permanganate destroy F-actin filaments in vitro, and split actin molecules into smaller peptides. It is shown by viscometry, spectrophotometry, electrophoresis and electron microscopy that the destruction of F-actin by these agents is inhibited by phalloidin. Other proteins are unprotected.

Use of osmium-ferrocyanide treatment for improved lysosomal acid trimetaphosphatase reaction and subcellular detail in thyroid follicular cells

The histochemical reaction for acid trimetaphosphatase in addition to secondary tissue treatment with an osmium-ferrocyanide mixture was used to study lysosomes and phagolysosomes in the mouse thyroid gland. The osmium-ferrocyanide postfixation enhanced reaction product localization, reduced diffuse reaction, and improved membrane contrast. In addition, the ultrathin tissue sections did not require heavy metal staining, thus eliminating potential stain artifacts due to precipitation. In view of the improved tissue preservation and enzyme localization, it is suggested that osmium-ferrocyanide postfixation be used after the acid trimetaphosphatase method.

A quantitative immunoperoxidase procedure employing energy dispersive x-ray analysis

A method is described for substituting gold for osmium as a marker in the unlabeled antibody technique. The gold marker can be detected in the light or electron microscope. The gold-labeled reaction product can be detected in lower concentrations than osmium and can be used as the basis for quantitating antigen concentrations in cells and tissues with the scanning electron microscope and energy dispersive x-ray analysis.

Ultrastructure of Bacteroides species: Bacteroides asaccharolyticus, Bacteroides fragilis, Bacteroides melaninogenicus subspecies melaninogenicus, and B. melaninogenicus subspecies intermedius

Representative strains of two subspecies of Bacteroides melaninogenicus (subspecies melaninogenicus and subspecies intermedius) and Bacteroides asaccharolyticus as well as B. asaccharolyticus strain 536B isolated from a human perirectal abscess and Bacteroides fragilis ATCC 25285 were examined by glutaraldehyde-osmium fixation, ruthenium red fixation and staining, and thorium hydroxyde staining as well as by the physical preparative techniques of critical point drying--transmission electron microscopy (CPD--TEM) and scanning electron microscopy (SEM). All strains, with the exception of B. fragilis 25285, possessed an electron-dense material external to their outer membranes. Ruthenium red staining further revealed a layer, external to the surface of the outer membrane, that was distinct for each species examined. Thorium hydroxide, as well as CPD--TEM and SEM, showed the cells to be interconnected by thin fibers that not only connected adjacent cells but also traversed several microns to connect cell aggregates.