Robust Dipolar Layers between Organic Semiconductors and Silver for Energy-Level Alignment.

The interface between a metal electrode and an organic semiconductor (OS) layer has a defining role in the properties of the resulting device. To obtain the desired performance, interlayers are introduced to modify the adhesion and growth of OS and enhance the efficiency of charge transport through the interface. However, the employed interlayers face common challenges, including a lack of electric dipoles to tune the mutual position of energy levels, being too thick for efficient electronic transport, or being prone to intermixing with subsequently deposited OS layers. Here, we show that monolayers of 1,3,5-tris(4-carboxyphenyl)benzene (BTB) with fully deprotonated carboxyl groups on silver substrates form a compact layer resistant to intermixing while capable of mediating energy-level alignment and showing a large insensitivity to substrate termination. Employing a combination of surface-sensitive techniques, i.e., low-energy electron microscopy and diffraction, X-ray photoelectron spectroscopy, and scanning tunneling microscopy, we have comprehensively characterized the compact layer and proven its robustness against mixing with the subsequently deposited organic semiconductor layer. Density functional theory calculations show that the robustness arises from a strong interaction of carboxylate groups with the Ag surface, and thus, the BTB in the first layer is energetically favored. Synchrotron radiation photoelectron spectroscopy shows that this layer displays considerable electrical dipoles that can be utilized for work function engineering and electronic alignment of molecular frontier orbitals with respect to the substrate Fermi level. Our work thus provides a widely applicable molecular interlayer and general insights necessary for engineering of charge injection layers for efficient organic electronics.

ProLEED Studio: software for modeling low-energy electron diffraction patterns.

Low-energy electron diffraction patterns contain precise information about the structure of the surface studied. However, retrieving the real space lattice periodicity from complex diffraction patterns is challenging, especially when the modeled patterns originate from superlattices with large unit cells composed of several symmetry-equivalent domains without a simple relation to the substrate. This work presents ProLEED Studio software, built to provide simple, intuitive and precise modeling of low-energy electron diffraction patterns. The interactive graphical user interface allows real-time modeling of experimental diffraction patterns, change of depicted diffraction spot intensities, visualization of different diffraction domains, and manipulation of any lattice points or diffraction spots. The visualization of unit cells, lattice vectors, grids and scale bars as well as the possibility of exporting ready-to-publish models in bitmap and vector formats significantly simplifies the modeling process and publishing of results.

How the Support Defines Properties of 2D Metal-Organic Frameworks: Fe-TCNQ on Graphene versus Au(111).

The functionality of 2D metal-organic frameworks (MOFs) is crucially dependent on the local environment of the embedded metal atoms. These atomic-scale details are best ascertained on MOFs supported on well-defined surfaces, but the interaction with the support often changes the MOF properties. We elucidate the extent of this effect by comparing the Fe-TCNQ 2D MOF on two weakly interacting supports: graphene and Au(111). We show that the Fe-TCNQ on graphene is nonplanar with iron in quasi-tetrahedral sites, but on Au(111) it is planarized by stronger van der Waals interaction. The differences in physical and electronic structures result in distinct properties of the supported 2D MOFs. The dz2 center position is shifted by 1.4 eV between Fe sites on the two supports, and dramatic differences in chemical reactivity are experimentally identified using a TCNQ probe molecule. These results outline the limitations of common on-surface approaches using metal supports and show that the intrinsic MOF properties can be partially retained on graphene.

Visualization of molecular stacking using low-energy electron microscopy.

The design of metal-organic interfaces with atomic precision enables the fabrication of highly efficient devices with tailored functionality. The possibility of fast and reliable analysis of molecular stacking order at the interface is of crucial importance, as the interfacial stacking order of molecules directly influences the quality and functionality of fabricated organic-based devices. Dark-field (DF) imaging using Low-Energy Electron Microscopy (LEEM) allows the visualization of areas with a specific structure or symmetry. However, distinguishing layers with different stacking orders featuring the same diffraction patterns becomes more complicated. Here we show that the top layer shift in organic molecular bilayers induces measurable differences in spot intensities of respective diffraction patterns that can be visualized in DF images. Scanning Tunneling Microscopy (STM) imaging of molecular bilayers allowed us to measure the shift directly and compare it with the diffraction data. We also provide a conceptual diffraction model based on the electron path differences, which qualitatively explains the observed phenomenon.

Endovascular treatment for acute ischemic stroke in patients with tandem lesion in the anterior circulation: analysis from the METRICS study.

BACKGROUND: Acute ischemic stroke (AIS) due to anterior circulation tandem lesion (TL) remains a technical and clinical challenge for endovascular treatment (EVT). Conflicting results from observational studies and missing evidence from the randomized trials led us to report a recent real-world multicenter clinical experience and evaluate possible predictors of good outcome after EVT. METHODS: We analyzed all AIS patients with TL enrolled in the prospective national study METRICS (Mechanical Thrombectomy Quality Indicators Study in Czech Stroke Centers). A good 3-month clinical outcome was scored as 0-2 points in modified Rankin Scale (mRS), achieved recanalization using the Thrombolysis In Cerebral Infarction (TICI) scale and symptomatic intracerebral hemorrhage (sICH) according to the Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST) criteria. RESULTS: Of 1178 patients enrolled in METRICS, 194 (19.2%) (59.8% males, mean age 68.7±11.5 years) were treated for TL. They did not differ in mRS 0-2 (48.7% vs 46.7%; p=0.616), mortality (17.3% vs 22.7%; p=0.103) and sICH (4.7% vs 5.1%; p=0.809) from those with single occlusion (SO). More TL patients with prior intravenous thrombolysis (IVT) reached TICI 3 (70.3% vs 50.8%; p=0.012) and mRS 0-2 (55.4% vs 34.4%; p=0.007) than those without IVT. No difference was found in the rate of sICH (6.2% vs 1.6%; p=0.276). Multivariate logistic regression analysis showed prior IVT as a predictor of mRS 0-2 after adjustment for potential confounders (OR 3.818, 95% CI 1.614 to 9.030, p=0.002). CONCLUSION: Patients with TL did not differ from those with SO in outcomes after EVT. TL patients with prior IVT had more complete recanalization and mRS 0-2 and IVT was found to be a predictor of good outcome after EVT.

Remarkably stable metal-organic frameworks on an inert substrate: M-TCNQ on graphene (M = Ni, Fe, Mn).

Potential applications of 2D metal-organic frameworks (MOF) require the frameworks to be monophase and well-defined at the atomic scale, to be decoupled from the supporting substrate, and to remain stable at the application conditions. Here, we present three systems meeting this elusive set of requirements: M-TCNQ (M = Ni, Fe, Mn) on epitaxial graphene/Ir(111). We study the systems experimentally by scanning tunneling microscopy, low energy electron microscopy and X-ray photoelectron spectroscopy. When synthesized on graphene, the 2D M-TCNQ MOFs are monophase with M1(TCNQ)1 stoichiometry, no alternative structure was observed with slight variation of the preparation protocol. We further demonstrate a remarkable chemical and thermal stability of TCNQ-based 2D MOFs: all the studied systems survive exposure to ambient conditions, with Ni-TCNQ doing so without any significant changes to its atomic-scale structure or chemical state. Thermally, the most stable system is Fe-TCNQ which remains stable above 500 °C, while all the tested MOFs survive heating to 250 °C. Overall, the modular M-TCNQ/graphene system combines the atomic-scale definition required for fundamental studies with the robustness and stability needed for applications, thus we consider it an ideal model for research in single atom catalysis, spintronics or high-density storage media.

Mechanical Thrombectomy Quality Indicators Study in Czech Stroke Centers: Results of the METRICS Study.

BACKGROUND AND PURPOSE: Rigorous and regular evaluation of defined quality indicators is crucial for further improvement of both technical and clinical results after mechanical thrombectomy (MT) for acute ischemic stroke (AIS). Following the recent international multi-society consensus quality indicators, we aimed to assess trend in these indicators on national level. MATERIAL AND METHODS: The prospective multicenter study (METRICS) was conducted in Czech Republic (CR) in year 2019. All participating centers collected technical and clinical data including defined quality indicators and results were subsequently compared with those from year 2016. RESULTS: In the 2019, 1375 MT were performed in the CR and 1178 (86%) patients (50.3% males, mean age 70.5 ± 13.0 years) were analyzed. Recanalization (TICI 2b-3) was achieved in 83.7% of patients and 46.2% of patients had good 3-month clinical outcome. Following time intervals were shortened in comparison to 2016: "hospital arrival - GP" (77 vs. 53 min; p<0.0001), "hospital arrival - maximal achieved recanalization" (122 vs. 93 min; p<0.0001), and "stroke onset - maximal achieved recanalization" (240 vs. 229 min; p p<0.0001). More patients with tandem occlusion were treated in 2019 (7.8 vs. 16.5%; p<0.0001) and more secondary transports were in 2019 (31.3 vs. 37.8%; p=0.002). No difference was found in 3-month clinical outcome and in the rate of periprocedural complications. Results of the METRICS study met all criteria of multi-society consensus quality indicators. CONCLUSION: Nationwide comparison between 2016 and 2019 showed improvement in the key time intervals, but without better overall clinical outcomes after MT.

Multiscale Analysis of Phase Transformations in Self-Assembled Layers of 4,4'-Biphenyl Dicarboxylic Acid on the Ag(001) Surface.

Understanding the nucleation and growth kinetics of thin films is a prerequisite for their large-scale utilization in devices. For self-assembled molecular phases near thermodynamic equilibrium the nucleation-growth kinetic models are still not developed. Here, we employ real-time low-energy electron microscopy (LEEM) to visualize a phase transformation induced by the carboxylation of 4,4'-biphenyl dicarboxylic acid on Ag(001) under ultra-high-vacuum conditions. The initial (α) and transformed (ß) molecular phases are characterized in detail by X-ray photoemission spectroscopy, single-domain low-energy electron diffraction, room-temperature scanning tunneling microscopy, noncontact atomic force microscopy, and density functional theory calculations. The phase transformation is shown to exhibit a rich variety of phenomena, including Ostwald ripening of the α domains, burst nucleation of the ß domains outside the α phase, remote dissolution of the α domains by nearby ß domains, and a structural change from disorder to order. We show that all phenomena are well described by a general growth-conversion-growth (GCG) model. Here, the two-dimensional gas of admolecules has a dual role: it mediates mass transport between the molecular islands and hosts a slow deprotonation reaction. Further, we conclude that burst nucleation is consistent with a combination of rather weak intermolecular bonding and the onset of an additional weak many-body attractive interaction when a molecule is surrounded by its nearest neighbors. In addition, we conclude that Ostwald ripening and remote dissolution are essentially the same phenomenon, where a more stable structure grows at the expense of a kinetically formed, less stable entity via transport through the 2D gas. The proposed GCG model is validated through kinetic Monte Carlo (kMC) simulations.

Complex k-uniform tilings by a simple bitopic precursor self-assembled on Ag(001) surface.

The realization of complex long-range ordered structures in a Euclidean plane presents a significant challenge en route to the utilization of their unique physical and chemical properties. Recent progress in on-surface supramolecular chemistry has enabled the engineering of regular and semi-regular tilings, expressing translation symmetric, quasicrystalline, and fractal geometries. However, the k-uniform tilings possessing several distinct vertices remain largely unexplored. Here, we show that these complex geometries can be prepared from a simple bitopic molecular precursor - 4,4'-biphenyl dicarboxylic acid (BDA) - by its controlled chemical transformation on the Ag(001) surface. The realization of 2- and 3-uniform tilings is enabled by partially carboxylated BDA mediating the seamless connection of two distinct binding motifs in a single long-range ordered molecular phase. These results define the basic self-assembly criteria, opening way to the utilization of complex supramolecular tilings.

Ambipolar remote graphene doping by low-energy electron beam irradiation.

We employ low-energy electron beam irradiation to induce both n- and p-doping in a graphene layer. Depending on the applied gate voltage during the irradiation, either n- or p-doping can be achieved, and by setting an appropriate irradiation protocol, any desired doping levels can be achieved.

Kelvin Probe Force Microscopy and Calculation of Charge Transport in a Graphene/Silicon Dioxide System at Different Relative Humidity.

The article shows how the dynamic mapping of surface potential (SP) measured by Kelvin probe force microscopy (KPFM) in combination with calculation by a diffusion-like equation and the theory based on the Brunauer-Emmett-Teller (BET) model of water condensation and electron hopping can provide the information concerning the resistivity of low conductive surfaces and their water coverage. This is enabled by a study of charge transport between isolated and grounded graphene sheets on a silicon dioxide surface at different relative humidity (RH) with regard to the use of graphene in ambient electronic circuits and especially in sensors. In the experimental part, the chemical vapor-deposited graphene is precisely patterned by the mechanical atomic force microscopy (AFM) lithography and the charge transport is studied through a surface potential evolution measured by KPFM. In the computational part, a quantitative model based on solving the diffusion-like equation for the charge transport is used to fit the experimental data and thus to find the SiO2 surface resistivity ranging from 107 to 1010 Ω and exponentially decreasing with the RH increase. Such a behavior is explained using the formation of water layers predicted by the BET adsorption theory and electron-hopping theory that for the SiO2 surface patterned by AFM predicts a high water coverage even at low RHs.

Percutaneous Mechanical Thrombectomy Using Rotarex® S Device in Acute Limb Ischemia in Infrainguinal Occlusions.

PURPOSE: To evaluate the effectiveness of percutaneous mechanical thrombectomy using Rotarex S in the treatment of acute limb ischemia (ALI) in infrainguinal occlusions in a retrospective study of patients treated in our institution. METHODS: In this study, we identified a total of 147 ALI patients that underwent mechanical thrombectomy using Rotarex S at our institution. In 82% of the cases, percutaneous thrombectomy was used as first-line treatment, and for the remainder of the cases, it was used as bailout after ineffective aspiration or thrombolysis. Additional fibrinolysis and adjunctive aspirational thrombectomy were utilized for outflow occlusion when required. Procedural outcomes, amputation rate, and mortality at 30 days were evaluated. RESULTS: Of the 147 patients treated with mechanical thrombectomy, Rotarex S was used as first-line treatment in 120 cases and as second-line treatment in 27 cases. Overall, we achieved 90.5% procedural revascularization success rate when combining mechanical thrombectomy with limited thrombolysis for severe outflow obstruction, and 1 death and 3 amputations were observed. We achieved primary success in 68.7% of the patients with the mechanical thrombectomy only, and in 21.8% of the patients, we successfully used additional limited thrombolysis in the outflow. The overall mortality was 0.7% and amputation rate was 2% at 30 days. CONCLUSION: Percutaneous mechanical thrombectomy as first-line mini-invasive treatment in infrainguinal ALI is safe, quick, and effective, and the performance outcomes can be superior to that of traditional surgical embolectomy.

X-ray induced electrostatic graphene doping via defect charging in gate dielectric.

Graphene field effect transistors are becoming an integral part of advanced devices. Hence, the advanced strategies for both characterization and tuning of graphene properties are required. Here we show that the X-ray irradiation at the zero applied gate voltage causes very strong negative doping of graphene, which is explained by X-ray radiation induced charging of defects in the gate dielectric. The induced charge can be neutralized and compensated if the graphene device is irradiated by X-rays at a negative gate voltage. Here the charge neutrality point shifts back to zero voltage. The observed phenomenon has strong implications for interpretation of X-ray based measurements of graphene devices as it renders them to significantly altered state. Our results also form a basis for remote X-ray tuning of graphene transport properties and X-ray sensors comprising the graphene/oxide interface as an active layer.

Valproic Acid Increases CD133 Positive Cells that Show Low Sensitivity to Cytostatics in Neuroblastoma.

Valproic acid (VPA) is a well-known antiepileptic drug that exhibits antitumor activities through its action as a histone deacetylase inhibitor. CD133 is considered to be a cancer stem cell marker in several tumors including neuroblastoma. CD133 transcription is strictly regulated by epigenetic modifications. We evaluated the epigenetic effects of treatment with 1mM VPA and its influence on the expression of CD133 in four human neuroblastoma cell lines. Chemoresistance and cell cycle of CD133+ and CD133- populations were examined by flow cytometry. We performed bisulfite conversion followed by methylation-sensitive high resolution melting analysis to assess the methylation status of CD133 promoters P1 and P3. Our results revealed that VPA induced CD133 expression that was associated with increased acetylation of histones H3 and H4. On treatment with VPA and cytostatics, CD133+ cells were mainly detected in the S and G2/M phases of the cell cycle and they showed less activated caspase-3 compared to CD133- cells. UKF-NB-3 neuroblastoma cells which express CD133 displayed higher colony and neurosphere formation capacities when treated with VPA, unlike IMR-32 which lacks for CD133 protein. Induction of CD133 in UKF-NB-3 was associated with increased expression of phosphorylated Akt and pluripotency transcription factors Nanog, Oct-4 and Sox2. VPA did not induce CD133 expression in cell lines with methylated P1 and P3 promoters, where the CD133 protein was not detected. Applying the demethylating agent 5-aza-2'-deoxycytidine to the cell lines with methylated promoters resulted in CD133 re-expression that was associated with a drop in P1 and P3 methylation level. In conclusion, CD133 expression in neuroblastoma can be regulated by histone acetylation and/or methylation of its CpG promoters. VPA can induce CD133+ cells which display high proliferation potential and low sensitivity to cytostatics in neuroblastoma. These results give new insight into the possible limitations to use VPA in cancer therapy.

Highly Sensitive Detection of Surface and Intercalated Impurities in Graphene by LEIS.

Low-energy ion scattering (LEIS) is known for its extreme surface sensitivity, as it yields a quantitative analysis of the outermost surface as well as highly resolved in-depth information for ultrathin surface layers. Hence, it could have been generally considered to be a suitable technique for the analysis of graphene samples. However, due to the low scattering cross section for light elements such as carbon, LEIS has not become a common technique for the characterization of graphene. In the present study we use a high-sensitivity LEIS instrument with parallel energy analysis for the characterization of CVD graphene transferred to thermal silica/silicon substrates. Thanks to its high sensitivity and the exceptional depth resolution typical of LEIS, the graphene layer closure was verified, and different kinds of contaminants were detected, quantified, and localized within the graphene structure. Utilizing the extraordinarily strong neutralization of helium by carbon atoms in graphene, LEIS experiments performed at several primary ion energies permit us to distinguish carbon in graphene from that in nongraphitic forms (e.g., the remains of a resist). Furthermore, metal impurities such as Fe, Sn, and Na located at the graphene-silica interface (intercalated) are detected, and the coverages of Fe and Sn are determined. Hence, high-resolution LEIS is capable of both checking the purity of graphene surfaces and detecting impurities incorporated into graphene layers or their interfaces. Thus, it is a suitable method for monitoring the quality of the whole fabrication process of graphene, including its transfer on various substrates.

Beneficial Effect of Human Induced Pluripotent Stem Cell-Derived Neural Precursors in Spinal Cord Injury Repair.

Despite advances in our understanding and research of induced pluripotent stem cells (iPSCs), their use in clinical practice is still limited due to lack of preclinical experiments. Neural precursors (NPs) derived from a clone of human iPSCs (IMR90) were used to treat a rat spinal cord lesion 1 week after induction. Functional recovery was evaluated using the BBB, beam walking, rotarod, and plantar tests. Lesion morphology, endogenous axonal sprouting, graft survival, and iPSC-NP differentiation were analyzed immunohistochemically. Quantitative polymerase chain reaction (qPCR) was used to evaluate the effect of transplanted iPSC-NPs on endogenous regenerative processes and also to monitor their behavior after transplantation. Human iPSC-NPs robustly survived in the lesion, migrated, and partially filled the lesion cavity during the entire period of observation. Transplanted animals displayed significant motor improvement already from the second week after the transplantation of iPSC-NPs. qPCR revealed the increased expression of human neurotrophins 8 weeks after transplantation. Simultaneously, the white and gray matter were spared in the host tissue. The grafted cells were immunohistochemically positive for doublecortin, MAP2, ßIII-tubulin, GFAP, and CNPase 8 weeks after transplantation. Human iPSC-NPs further matured, and 17 weeks after transplantation differentiated toward interneurons, dopaminergic neurons, serotoninergic neurons, and ChAT-positive motoneurons. Human iPSC-NPs possess neurotrophic properties that are associated with significant early functional improvement and the sparing of spinal cord tissue. Their ability to differentiate into tissue-specific neurons leads to the long-term restoration of the lesioned tissue, making the cells a promising candidate for future cell-based therapy of SCI.

A novel c. 204 Ile68Met germline variant in exon 2 of the mutL homolog 1 gene in a colorectal cancer patient.

Mutations in the mutL homolog 1 (MLH1) gene are frequent in patients with hereditary non-polyposis colorectal cancer (CRC). The MLH1 gene was screened for mutations in patients with sporadic CRC. The nucleotide sequences for all 19 exons of MLH1 were analyzed by high resolution melting and sequenced in a group of 104 sporadic CRC patients, and the results were verified in a replication group of 1,095 patients and 1,469 controls. Different melting profiles for exon 2 of the MLH1 gene were observed in the germline DNA of one patient. Sequencing of the patient's DNA resulted in the identification of a heterozygous C>G variant at c.204, which resulted in an Ile68Met change in the amino acid. A detailed search of the National Center for Biotechnology Information and the 1000 Genomes databases indicated that the detected variant was unique. According to the SIFT and PolyPhen-2 algorithms, the substitution of Ile to Met was predicted to decrease the activity of the MLH1 protein. The newly identified, functional germline variant was not present in any other CRC patient or control. Thus, a novel germline variant in the MLH1 gene was identified, representing a rare event in sporadic CRC. The occurrence and relevance of this mutation in other types of cancer requires additional investigation.

Ultrasmooth metallic foils for growth of high quality graphene by chemical vapor deposition.

Synthesis of graphene by chemical vapor deposition is a promising route for manufacturing large-scale high-quality graphene for electronic applications. The quality of the employed substrates plays a crucial role, since the surface roughness and defects alter the graphene growth and cause difficulties in the subsequent graphene transfer. Here, we report on ultrasmooth high-purity copper foils prepared by sputter deposition of Cu thin film on a SiO2/Si template, and the subsequent peeling off of the metallic layer from the template. The surface displays a low level of oxidation and contamination, and the roughness of the foil surface is generally defined by the template, and was below 0.6 nm even on a large scale. The roughness and grain size increase occurred during both the annealing of the foils, and catalytic growth of graphene from methane (≈1000 °C), but on the large scale still remained far below the roughness typical for commercial foils. The micro-Raman spectroscopy and transport measurements proved the high quality of graphene grown on such foils, and the room temperature mobility of the graphene grown on the template stripped foil was three times higher compared to that of one grown on the commercial copper foil. The presented high-quality copper foils are expected to provide large-area substrates for the production of graphene suitable for electronic applications.

Molecular characteristics of mismatch repair genes in sporadic colorectal tumors in Czech patients.

BACKGROUND: Mismatch repair (MMR) genes are known to be frequently altered in colorectal cancer (CRC). Both genetics and epigenetics modifications seems to be relevant in this phenomenon, however it is still not clear how these two aspects are interconnected. The present study aimed at characterizing of epigenetic and gene expression profiles of MMR genes in sporadic CRC patients from the Czech Republic, a country with one of the highest incidences of this cancer all over Europe. METHODS: Expression levels and CpG promoter methylation status of all MMR genes were evaluated in DNA from tumor and adjacent mucosal samples of 53 incident CRC patients. RESULTS: We have found significantly increased transcription levels in EXO1 gene in tumor tissues (P = 0.05) and significant over-expression of MSH3 gene in colon tumors when compared to adjacent mucosal tissues (P = 0.02). Interestingly, almost all MMR genes were differently expressed when localization of tumors was compared. In particular, colon tumors showed an up-regulation of EXO1, MSH2, MSH3, MSH6, and PMS2 genes in comparison to rectal tumors (P = 0.02). Expression levels of all MMR genes positively correlated between each other. The promoter methylation of MLH1 gene was observed in 9% of CRC tissues only. CONCLUSIONS: In our study, we have observed different pattern of MMR genes expression according to tumor localization. However, a lack of association between methylation in MMR genes and their corresponding expressions was noticed in this study, the relationship between these two aspects is worthy to be analyzed in larger population studies and in pre-malignant stages.

Evaluation of tumor suppressor gene expressions and aberrant methylation in the colon of cancer-induced rats: a pilot study.

Altered expression and methylation pattern of tumor suppressor and DNA repair genes, in particular involved in mismatch repair (MMR) pathway, frequently occur in primary colorectal (CRC) tumors. However, little is known about (epi)genetic changes of these genes in precancerous and early stages of CRC. The aim of this pilot study was to analyze expression profile and promoter methylation status of important tumor suppressor and DNA repair genes in the early stages of experimentally induced colorectal carcinogenesis. Rats were treated with azoxymethane (AOM), dextran sodium sulphate (DSS) or with their combination, and sacrificed 1 or 4 months post-treatment period. The down-regulation of Apc expression in left colon, detectable in animals treated with DSS-AOM and sacrificed 1 month after the end of treatment, represents most early marker of the experimental colorectal carcinogenesis. Significantly reduced gene expressions were also found in 5 out of 7 studied MMR genes (Mlh1, Mlh3, Msh3 Pms1, Pms2), regarding the sequential administration of DSS-AOM at 4 months since the treatment. Strong down-regulation was also discovered for Apc, Apex1, Mgmt and TP53. Tumors developed in rectum-sigmoid region displayed significantly lower Apc and Pms2 expressions. The decreased expression of studied genes was not in any case associated with aberrant methylation of promoter region. Present data suggest that down-regulation of Apc and MMR genes are prerequisite for the development of CRC. In this study we addressed for the first time early functional alterations of tumor suppressor genes with underlying epigenetic mechanisms in experimentally induced CRC in rats.