Stroke Classification with Microwave Signals using Explainable Wavelet Convolutional Neural Network

Stroke is one of the leading causes of death and disability. To address this challenge, microwave imaging has been proposed as a portable medical imaging modality. However, accurate stroke classification using microwave signals is still an open challenge. In addition, identified features of microwave signals used for stroke classification need to be linked back to the original data. This work attempts to address these issues by proposing a wavelet convolutional neural network (CNN), which combines multiresolution analysis and CNN to learn distinctive patterns in the scalogram for accurate classification. A game theoretic approach is used to explain the model and indicate distinctive features for discriminating stroke types. The proposed algorithm is tested in simulation and experiments. Different types of noise and manufacturing tolerances are modeled using data collected from healthy human trials and added to the simulation data to bridge the gap between the simulation and real-life data. The achieved classification accuracy using the proposed method ranges from 81.7% for 3D simulations to 95.7% for lab experiments using simple head phantoms. Obtained explanations using the method indicate the relevance of wavelet coefficients on frequencies 0.95-1.45 GHz and the time slot of 1.3 to 1.7 ns for distinguishing ischemic from hemorrhagic strokes.

Calibrated Frequency-Division Distorted Born Iterative Tomography for Real-Life Head Imaging

The clinical use of microwave tomography (MT) requires addressing the significant mismatch between simulated environment, which is used in the forward solver, and real-life system. To alleviate this mismatch, a calibrated tomography, which uses two homogeneous calibration phantoms and a modified distorted Born iterative method (DBIM), is presented. The two phantoms are used to derive a linear model that matches the forward solver to real-life measurements. Moreover, experimental observations indicate that signal quality at different frequencies varies between different antennas due to inevitably inconsistent manufacturing tolerance and variances in radio-frequency chains. An optimum frequency, at which the simulated and measured signals of the antenna present maximum similarity when irradiating the calibrated phantoms, is thus calculated for each antenna. A frequency-division DBIM (FD-DBIM), in which different antennas in the array transmit their corresponding optimum frequencies, is subsequently developed. A clinical brain scanner is then used to assess performance of the algorithm in lab and healthy volunteers' tests. The linear calibration model is first used to calibrate the measured data. After that FD-DBIM is used to solve the problem and map the dielectric properties of the imaged domain. The simulated and experimental results confirm validity of the presented approach and its superiority to other tomographic method.

Developmental expression of ACE2 in the SHR kidney: a role in hypertension?

The abnormal development of the intrarenal renin-angiotensin system (RAS) is thought contribute to adult-onset hypertension in the spontaneously hypertensive rat (SHR). Angiotensin-converting enzyme 2 (ACE2) is a novel enzyme with complementary actions to that of ACE. Recent studies have shown that ACE2 expression is reduced in the adult SHR. However, its regulation in pre-hypertensive animals is unknown. In this study, we examine the developmental expression of ACE2 in the rodent kidney and its temporal expression, as it relates to the development of hypertension in the SHR model. Kidneys from SHR and normotensive Wistar Kyoto (WKY) rats (n=8-12/group) at birth, 6 weeks of age, and adulthood (80 days) were examined. Gene expression and activity of ACE2 were determined by real-time reverse transcription-polymerase chain reaction and quenched fluorescence assays, respectively. Renal expression was localized by in situ hybridization and immunohistochemistry. The expression and ACE2 activity are significantly increased in the SHR kidney at birth. With the onset of hypertension, the tubular expression of ACE2 falls in SHR compared to WKY and remains reduced in the adult SHR kidney. Glomerular expression is paradoxically increased in the SHR glomerulus. The overall developmental pattern of ACE2 expression in the SHR kidney is also modified, with declining expression over the course of renal development. The developmental pattern of ACE2 expression in the SHR kidney is altered before the onset of hypertension, consistent with the key role of the RAS in the pathogenesis of adult-onset hypertension. Further research is required to distinguish the contribution of these changes to the development and progression of hypertension in this model.

Oxidative DNA damage in fetal tissues after transplacental exposure to 3'-azido-3'-deoxythymidine (AZT)

The nucleoside analogue 3'-azido-3'-deoxythymidine (AZT) has been used successfully to reduce the incidence of transplacental and perinatal transmission of the HIV virus. However, prolonged treatment with high doses of AZT is utilized in this therapy, and AZT has been found to be a perinatal carcinogen in mice. Any possible perinatal carcinogenic side effects in the human can best be managed if the mechanism is understood. AZT targets mitochondria and might cause increased intracellular production of reactive oxygen species (ROS). We tested whether transplacental AZT may cause oxidative damage in nuclear DNA of fetal tissues. CD-1 Swiss pregnant mice were treated with the transplacental carcinogenesis regimen (25 mg/day AZT, for gestation days 12-18) and tissues collected on the day of birth. Significant increases in 8-oxo-2'-deoxyguano- sine (8-oxo-dG) were found in the livers, a target tissue for transplacental carcinogenesis, and in the kidneys. A non-significant increase occurred in brain, with no change in lung. Tissues were also obtained from fetal patas monkeys (Erythrocebus patas), whose mothers had received 10 mg AZT/day during the last half of gestation. Although limited numbers of samples were available, possible increases in 8-oxo-dG were noted, relative to controls, for placenta and for fetal lung and brain (P = 0.055 for treatment-related increases in these tissues). These results suggest that an increase in reactive oxygen species could contribute to the mechanism of transplacental carcinogenesis by AZT in mice, and that this may also occur in primates.

Inhibition of antimutagenic enzymes, 8-oxo-dGTPases, by carcinogenic metals. Recent developments

Nickel, cadmium, cobalt, and copper are carcinogenic to humans and/or animals, but the underlying mechanisms are poorly understood. Our studies have been focused on one such mechanism involving mediation by the metals of promutagenic oxidative damage to DNA bases. The damage may be inflicted directly in DNA or in the deoxynucleotide pool, from which the damaged bases are incorporated into DNA. Such incorporation is prevented in cells by 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphatases (8-oxo-dGTPases). Thus, inhibition of these enzymes should enhance carcinogenesis. We have studied effects of Cd(II), Cu(II), Co(II), and Ni(II) on the activity of isolated bacterial and human 8-oxo-dGTPases. Cd(II) and Cu(II) were strongly inhibitory, while Ni(II) and Co(II) were much less suppressive. After developing an assay for 8-oxo-dGTPase activity, we confirmed the inhibition by Cd(II) in cultured cells and in the rat testis, the target organ for cadmium carcinogenesis. 8-Oxo-dGTPase inhibition was accompanied by an increase in the 8-oxo-dG level in testicular DNA.

Activity of the antimutagenic enzyme 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) in cultured chinese hamster ovary cells: effects of cell cycle, proliferation rate, and population density

Mammalian 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolases (8-oxo-dGTPases), such as MTH1, are believed to play the same antimutagenic role as their bacterial homologues, like MutT. Both decompose promutagenic 8-oxo-dGTP, a product of active oxygen's attack on dGTP. It is not known how 8-oxo-dGTPase expression and function are regulated. Therefore, we investigated the effect of cell population density, proliferation rate, and cell cycle phase on 8-oxo-dGTPase specific activity in cultured Chinese hamster ovary K1-BH4 (CHO) cells. With increasing cell population density (from 30 to 95% confluence), the activity of 8-oxo-dGTPase per milligram protein decreased by 33% (p =.007 by ANOVA) while cells shifted by 9% into the G(0)/G(1) phase, with a 5% drop in cells in S phase. Importantly, inhibition of the cells' proliferation rate by calf serum deprivation caused a more dramatic 23% shift toward the G(0)/G(1) phase and a 25% drop in S phase, but had no effect on 8-oxo-dGTPase activity. Likewise, no differences in the enzyme activity were observed within cell populations of different cell cycle phases separated by centrifugal elutriation. Thus, the present results exclude cell cycle-dependent regulation of 8-oxo-dGTPase activity in CHO cells or its simple dependence on proliferation rate. The observed decrease of 8-oxo-dGTPase activity with increasing cell population density might be related to augmentation of cell-to-cell contact.

Cadmium(II), unlike nickel(II), inhibits 8-oxo-dGTPase activity and increases 8-oxo-dG level in DNA of the rat testis, a target organ for cadmium(II) carcinogenesis

8-Oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) is an enzyme which prevents incorporation into DNA of promutagenic 8-oxo-2'-deoxyguanosine (8-oxo-dG) from a deoxynucleotide pool damaged by endogenous oxidants. Its inhibition may thus be carcinogenic. We previously found that Cd(II) inhibited 8-oxo-dGTPase in both cell free systems and cultured cells. To verify this finding in a relevant animal model, we investigated the effects of Cd(II) on cellular 8-oxo-dGTPase activity and nuclear DNA 8-oxo-dG levels in the rat testis, a target organ for Cd(II) carcinogenesis. Ni(II), which does not induce testicular tumors in rats and is a weaker in vitro inhibitor of 8-oxo-dGTPase than Cd(II), was investigated as a comparison. Male F344/NCr rats were given a single s.c. dose of 20 micromol Cd(II) acetate, 90 micromol Ni(II) acetate or 180 micromol sodium acetate (controls) per kg body wt and killed 2, 8, 24 or 48 h later (three rats/time point). Cd(II) caused a gradual decrease in testicular 8-oxo-dGTPase activity with time. It became significant only after 8 h post-injection (P < 0.05) and resulted in a final 50% loss of the enzyme activity at 48 h (P < 0. 01). Although the results for Ni(II) at 8 h and later were apparently lower than the controls, the decrease did not reach statistical significance. Treatment of rats with Cd(II) led to an early and progressive increase (from 130% at 2 h to 200% at 48 h versus the controls) of the 8-oxo-dG level in testicular DNA (P < 0. 05 or better). Ni(II) acetate also tended to raise the testicular 8-oxo-dG level, but the increase was transient, with an apparent maximum at 8 h, and did not approach statistical significance (P < 0. 2). Thus, Cd(II), unlike Ni(II), is able to inhibit 8-oxo-dGTPase activity and to raise 8-oxo-dG levels in rat testicular DNA. However, the time course of both effects indicates that 8-oxo-dGTPase inhibition is most likely not the sole cause of the increase in 8-oxo-dG.

Higher activity of 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) coincides with lower background levels of 8-oxo-2'-deoxyguanosine in DNA of fetal compared with maternal mouse organs

Mammalian homologues of Escherichia coli MutT, a protein having 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) activity, are thought to play the same role in preventing the incorporation of promutagenic 8-oxo-2'-deoxyguanosine (8-oxo-dG) into DNA. One could thus expect that higher activity of 8-oxo-dGTPase should correlate with a lower background level of 8-oxo-dG in nuclear DNA. During transplacental carcinogenesis experiments, in control healthy Swiss mice on day 18 of gestation we found consistently lower levels of 8-oxo-dG in DNA in fetal livers and lungs (1.74+/-0.04 SE and 1.49+/-0.08 SE 8-oxo-dG/10(5) dG, respectively; pooled organs of fetuses of 8 dams) as compared with maternal organs (3.05+/-0.20 SE and 3.08+/-0.17 SE 8-oxo-dG/10(5) dG, respectively; n = 8). The 8-oxo-dGTPase activity determination in the same organs revealed that the lower levels of 8-oxo-dG in fetal DNA did, indeed, coincide with higher 8-oxo-dGTPase activity (48.8+/-2.6 SE and 52.5+/-2.5 SE U/mg protein in livers and lungs, respectively); and vice versa, higher 8-oxo-dG levels in DNA of maternal organs were associated with lower levels of 8-oxo-dGTPase activity (24.3+/-1.3 SE and 4.7+/-0.6 SE U/mg protein, as above). Without excluding other reasons for the relatively low 8-oxo-dG background in DNA of fetal tissues (e.g., higher level of antioxidants and antioxidative enzymes; more efficient DNA repair), this inverse relationship may support or at least does not contradict the concept of a guardian role of 8-oxo-dGTPase against 8-oxo-dGTP mutagenicity in mammalian cells.

Evaluation of 8-oxodeoxyguanosine, typical oxidative DNA damage, in lymphocytes of ozone-treated arteriosclerotic patients

In the present study we measured the amount of 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA isolated from lymphocytes of arteriosclerotic patients undergoing ozonetherapy. Treatment of the patients with therapeutic concentration of ozone caused a significant increase over the control value in the amount of 8-oxo-dG of DNA isolated from their lymphocytes. However, only three out of six patients examined responded positively to the treatment in terms of the base damage. The increases varied among patients, and were in the range of 100-450%. This interindividual difference may at least be partly explained by recently demonstrated heritable susceptibility to ozone.

Interactions of Nickel(II) with histones: interactions of Nickel(II) with CH3CO-Thr-Glu-Ser-His-His-Lys-NH2, a peptide modeling the potential metal binding site in the "C-Tail" region of histone H2A

A combined pH-metric and spectroscopic (UV/vis, CD, NMR) study of the Ni(II) binding to CH3CO-Thr-Glu-Ser-His-His-Lys-NH2 (AcTESHHKam), a blocked hexapeptide modeling a part of the C-terminal sequence of the major variant of histone H2A (residues 120-125), revealed the formation of a pseudo-octahedral NiHL complex in weakly acidic and neutral solutions. Ni(II) is bound to the peptide through imidazole nitrogens on both of its histidine residues and the carboxylate of the side chain of glutamic acid. At higher pH, a series of square-planar complexes are formed. This process is accompanied by hydrolytic degradation of the peptide. At pH 7.4, the peptide hydrolyzes in a Ni(II)-assisted fashion, yielding the square-planar Ni(II) complex of SHHKam as the sole product detected by CD, MALDI-TOF MS, and HPLC. Quantitative analysis of complex stabilities indicates that the -TESHHK- motif is a very likely binding site for carcinogenic Ni(II) ions in the cell nucleus. The Ni(II)-assisted hydrolysis of the C-terminal chain of histone H2A may provide a novel mechanism of genotoxicity combining the damage to the nucleosome with the generation of further toxic Ni(II) species.

A novel assay of 8-oxo-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase (8-oxo-dGTPase) activity in cultured cells and its use for evaluation of cadmium(II) inhibition of this activity

8-Oxo-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is a product of oxidative modification of dGTP, thatcan be misincorporated into DNA, causing AT-->CG mutations. Cells are protected against 8-oxo-dGTP by 8-oxo-dGTP 5'-pyrophosphohydrolases (8-oxo-dGTP-ases) that convert it to 8-oxo-dGMP. Thus, inhibition of 8-oxo-dGTPases may lead to cancer. To elucidate the involvement of 8-oxo-dGTPases in carcinogenesis, an assay of the 8-oxo-dGTPase activity is required. This paper presents such an assay developed for Chinese hamster ovary (CHO) cells that can be applied to any biological material. It includes: (i) a convenient method for preparing 8-oxo-2'-deoxyguanosine 5'-phosphates; (ii) an HPLC/UV quantification of 8-oxo-dGTP hydrolysis products and (iii) separation of 8-oxo-dGTPase activity from interfering 8-oxo-dGTP phosphatase(s). The 8-oxo-dGTPase activity of CHO cells depends on magnesium, has a pH optimum of 8.5, Km for 8-oxo-dGTP of 9.3 microM, and is inhibited by 8-oxo-dGDP, the product of interfering 8-oxo-dGTP phosphatases. The latter must be removed from the assayed samples by ultrafiltration through 30 kDa cut-off membranes. The method was used to test the inhibition by cadmium ions of the activity of 8-oxo-dGTPase in CHO cells. The cells cultured with 0.3-3 microM cadmium(II) acetate for up to 24 h had their 8-oxo-dGTPase activity suppressed in a Cd(II) concentration-dependent manner, down to 70% of the control value.

Epirubicin-induced oxidative DNA damage and evidence for its repair in lymphocytes of cancer patients who are undergoing chemotherapy

Anthracycline derivatives have been widely used in the treatment of several types of human malignancies. Cytotoxicity of these drugs has been attributed to inhibition of topoisomerase II as well as intracellular production of free radicals. In our work we used a gas chromatography/mass spectrometry technique to study free radical-induced DNA base modifications in chromatin isolated from lymphocytes of cancer patients who received chemotherapy with epirubicin (one of anthracycline's antitumor derivatives). The anticancer therapy caused significant increases in the amount of all four DNA base modifications over control levels in the lymphocytes of most of the patients. For the majority of the cases the base products returned to the control value 24 hr after the infusion of the drug, which suggests the removal of these lesions by cellular repair processes. However, some of the modified bases escaped repair. Because part of these modifications may possess premutagenic properties, they may be responsible for secondary cancers induced by chemotherapy.

Improved high-performance liquid chromatographic method for N-acetylgalactosamine-4-sulfate sulfatase (arylsulfatase B) activity determination using uridine diphospho-N-acetylgalactosamine-4-sulfate

UDP-N-acetylgalactosamine-4-sulfate (UDP-GalNAc-4-S) was isolated from hen oviduct (isthmus) with a yield of 31 mumol per 100 g of wet tissue and used for arylsulfatase B (ASB) activity determination. Two HPLC methods of separation and quantitation of the reaction product were described: (1) an original gradient elution method which makes it possible to determine the reaction product when only partially purified ASB was used and additional uridine derivatives were formed during incubation; (2) an improved, fast isocratic elution method which may be used in the case of purified ASB preparations, devoid of other nucleotide hydrolysing enzymes. For both methods the detection limit was 0.1 nmol of product with standard error of determination < or = 3%. Using the gradient elution method we have found that UDP-GalNAc-4-S was hydrolysed by bovine arylsulfatase B1 most efficiently at pH 5.0 and concentration 0.5 mM with K(m) = 85 microM.

8-Oxo-2'-deoxyguanosine level in lymphocytes DNA of cancer patients undergoing radiotherapy

We analyzed the level of 8-oxo-2'-deoxyguanosine in lymphocytes DNA of cancer patients undergoing radiotherapy. The results of this work indicate that exposure of cancer patients to therapeutic doses of ionizing radiation causes significant increase of the amount of 8-oxo-dG in DNA isolated from their lymphocytes.

Effect of 2'-deoxyguanosine oxidation at C8 position on N-glycosidic bond stability

The influence of 2'-deoxyguanosine (dG) oxidation at the C-8 position on N-glycosidic bond stability was investigated. A kinetic analysis of dG and 8-oxo-2'-deoxyguanosine (8-oxodG) depurination reactions was carried out in water solutions at pH ranging from 2 to 7.4 and temperature of 100 degrees C. The results indicate that N-glycosidic bond of 8-oxodG is significantly more stable in comparison with dG at any pH applied. At pH 5.1 hydrolysis rate of dG is 4.5-fold higher than that for 8-oxodG. The chemical stability of the modified nucleoside in oxidatively damaged DNA is one of important factors contributing to its mutagenic potential. Results of our experiments indicate that 8-oxodG, potentially mutagenic and carcinogenic nucleoside, is hardly susceptible to spontaneous depurination and its removal from cellular DNA depends mostly on the activity of DNA repair enzymes.