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Biomedical subjects

P Mack

Publications and source records attributed to P Mack.

At least 19 recordsLinked to original sources
PubMed2005

Whole genomewide linkage screen for neural tube defects reveals regions of interest on chromosomes 7 and 10.

Neural tube defects (NTDs) are the second most common birth defects (1 in 1000 live births) in the world. Periconceptional maternal folate supplementation reduces NTD risk by 50-70%; however, studies of folate related and other developmental genes in humans have failed to definitively identify a major causal gene for NTD. The aetiology of NTDs remains unknown and both genetic and environmental factors are implicated. We present findings from a microsatellite based screen of 44 multiplex pedigrees ascertained through the NTD Collaborative Group. For the linkage analysis, we defined our phenotype narrowly by considering individuals with a lumbosacral level myelomeningocele as affected, then we expanded the phenotype to include all types of NTDs. Two point parametric analyses were performed using VITESSE and HOMOG. Multipoint parametric and nonparametric analyses were performed using ALLEGRO. Initial results identified chromosomes 7 and 10, both with maximum parametric multipoint lod scores (Mlod) >2.0. Chromosome 7 produced the highest score in the 24 cM interval between D7S3056 and D7S3051 (parametric Mlod 2.45; nonparametric Mlod 1.89). Further investigation demonstrated that results on chromosome 7 were being primarily driven by a single large pedigree (parametric Mlod 2.40). When this family was removed from analysis, chromosome 10 was the most interesting region, with a peak Mlod of 2.25 at D10S1731. Based on mouse human synteny, two candidate genes (Meox2, Twist1) were identified on chromosome 7. A review of public databases revealed three biologically plausible candidates (FGFR2, GFRA1, Pax2) on chromosome 10. The results from this screen provide valuable positional data for prioritisation of candidate gene assessment in future studies of NTDs.

Chromosomes, Human, Pair 10↗
PubMed2003

Electron probe and auger electron microprobe characterization of modified Cu-based amorphous alloys.

Changes in morphology and local chemical composition due to various methods of modification of surfaces of Cu-Zr, Cu-Hf, and Cu-Ti amorphous alloys (caused by aging in air/dry corrosion or hydrogen charging) were investigated. These modification/activation procedures transform the original amorphous ribbons of low surface area into efficient and stable catalysts, due to the segregation of a distinct amount of Cu and the development of a large specific surface area of Cu on a ZrO x or HfO x support. It was found that aging in air resulted in the formation of a bilayer of rough copper (containing small Cu particles indispensable for catalysis) on top of a rather smooth oxide underlayer (ZrO x, HfO x ). Careful examination of the cross sections of the modified Cu-based ribbons revealed that, even after prolonged aging in air, only the first few microns of the surface layer was modified. Cu-Ti alloy was stable in air and did not undergo the expected modification. Hydrogenation followed by air exposure resulted in a disintegration of the ribbons into small pieces. Each piece was covered with many small Cu clusters 0.1-0.5 microm in diameter formed on an oxide underlayer. High-energy resolution Auger spectroscopy allowed identification of the underlayers (ZrO2, HfO2, or TiO x ), identification of small Cu clusters, determination of the degree of surface oxidation of them, and mapping of the surface to identify the Cu-covered and "naked" heavy metal.

Journal Article↗
PubMed2001

Inhibition of epidermal growth factor receptor tyrosine kinase by chalcone derivatives.

In our previous study, butein, a chalcone derivative, was found to be an inhibitor of tyrosine kinases and the inhibition was ATP-competitive. In this work, chalcone and seven chalcone derivatives were used to analyse the relationship between the structure of these compounds and their inhibition of tyrosine kinase activity. Three of chalcone derivatives, including butein, marein and phloretin, were found to have an ability to inhibit the tyrosine kinase activity of epidermal growth factor receptor (EGFR) in vitro. IC(50) was 8 microM for butein, 19 microM for marein and 25 microM for phloretin. The structural characterisations of these inhibitors suggest that the hydroxylations at C4 and C4' of these molecules may be required for them to act as EGFR tyrosine kinase inhibitors. The inhibition of EGF-induced EGFR tyrosine phosphorylation by butein was also observed in human hepatocellular carcinoma HepG2 cells, while marein and phloretin were inactive at the doses tested. Molecular modelling suggests that butein, marein and phloretin can be docked into the ATP binding pocket of EGFR. Hydrogen bonds and hydrophobic interaction appear to be important in the binding of these inhibitors to EGFR.

Amino Acid Sequence↗
PubMed2001

Structure-activity relationships of neurokinin A (4-10) at the human tachykinin NK(2) receptor: the role of natural residues and their chirality.

A structure-activity study of neurokinin A (NKA) (4-10) was performed to investigate the importance of residue and chirality for affinity and efficacy at the NK(2) receptor in human colon circular muscle. Two series of NKA(4-10) analogues were produced with either L-alanine or the D-enantiomer substituted. Their activities were determined in vitro by means of radioligand binding and isolated smooth muscle pharmacology. NKA was more potent than NKA(4-10) at the human, unlike the rabbit, NK(2) receptor. The contractile response of NKA(4-10) was unaffected by N-terminal acetylation. L-Ala substitution of Asp(4), Val(7), Leu(9), and Met(10) caused an 8- to 80-fold decrease, and substitution of Phe(6) caused a 5000-fold decrease in binding affinity (P < 0.01). Positions Ser(5) and Gly(8) were not significantly affected. In functional studies, a similar pattern was observed. The replacement of residues with their respective D-enantiomer drastically reduced binding affinity and functional potency, particularly at positions 6 and 7 (P < 0.05). NKA(4-10) analogues L-Ala(6), L-Ala(8), D-Phe(6), D-Val(7), and D-Met(10) were partial agonists. An excellent correlation was observed between binding and functional data (r = 0.95). A retro-inverso analogue of NKA(4-10) was inactive. In conclusion, the side chains of Asp(4), Phe(6), Val(7), Leu(9), and Met(10) are structurally important features of NKA(4-10) for agonist activity, and changes in amino acid chirality are detrimental to binding affinity and functional activity. Overall, our data are broadly similar to those of previous studies in the rat. However, at the human NK(2) receptor, unlike the rat, [Ala(8)]NKA(4-10) was an antagonist.

Aged↗
PubMed2001

Modulation of cisplatin cytotoxicity and cisplatin-induced DNA cross-links in HepG2 cells by regulation of glutathione-related mechanisms.

Glutathione (GSH), glutathione S-transferase (GST), and glutathione conjugate export pump (GS-X pump) have been shown to participate collectively in the detoxification of many anticancer drugs, including cisplatin. Identification and regulation of the rate-limiting step in the overall system for cisplatin detoxification is of crucial importance for sensitization of human tumor cells to cisplatin. In this study, the GSH content, GST activity, and GS-X pump activity were regulated separately to examine effects of the regulation on cisplatin cytotoxicity and cisplatin-induced DNA interstrand cross-links (ICL) in HepG2 cells. Seventy-percent depletion of GSH by buthionine sulfoximine (BSO) and 50% increase of GSH by monoethyl GSH ester (GSHe) potentiated and decreased cisplatin cytotoxicity, respectively. This was reflected by a significant decrease and increase of their respective IC(50) values by 62 and 107%. Cisplatin-induced ICL was also potentiated by depletion of GSH by BSO and decreased by enrichment of GSH by GSHe, as shown by a 125% increase and a 34% decrease of cross-linked DNA compared with control samples exposed to cisplatin alone (p = 0.008 and 0.03, respectively). On the other hand, inhibition of GST and GS-X pump by ethacrynic acid, quercetin, tannic acid, and indomethacin at concentrations that inhibited activities of GST and GS-X pump by more than 50% had no significant effects on cisplatin cytotoxicity and cisplatin-induced DNA ICL in these cells. The results showed that of the parameters measured, intracellular GSH seems to be the rate-limiting factor, and its regulation would provide a more promising strategy for sensitization of human liver tumor cells to cisplatin.

Biological Transport↗
PubMed2001

Microsatellite alterations in human hepatocellular carcinoma infected with hepatitis B virus: associated with the elevation of serum alpha-fetoprotein.

Identification of the basic genetic changes in human hepatocellular carcinoma (HCC) is very important for the understanding of this cancer. In this study, genomic DNA from 29 pairs of HCC and corresponding non-tumour tissues infected with hepatitis B virus (HBV) was prepared. Five CA-repeated microsatellite markers, including D8S277, D3S1029, D5S409, D2S123, and TP53, were used to analyse microsatellite alterations and their subtypes in these patients by polymerase chain reaction (PCR) amplification and denatured polyacrylamide gel electrophoresis. Microsatellite alterations were found in 15 of the 29 HCC patients (51.72%), implying that microsatellites are unstable in genomic DNA of HBV-infected HCC. It was found that frequency of microsatellite alterations in these HCC patients was not associated with patients' age, sex, status of tumour differentiation, and tumour size. Frequency of microsatellite alterations in HCC patients with cirrhosis tended to be less than that in patients without cirrhosis, but Fisher's exact test, 2-tailed, showed that this difference was not significant. Significantly more microsatellite alterations in serum alpha-fetoprotein (AFP)-positive cases were observed than those in serum AFP-negative ones, implying that the elevation of AFP in HBV-infected HCC may be associated with microsatellite stability.

Adult↗
PubMed2001

Follow-up of breast cancer: time for a new approach?

After treatment for breast cancer women are monitored for recurrent disease by means of routine hospital-based follow-up appointments. The aim of this study is to determine the efficiency of this system, by establishing how recurrence presents to our hospital. The study comes at a time of increasing pressure on breast clinics from new patient referrals and the need, since April 1999, to see all cases classified as urgent within two weeks of referral. A consecutive series of 643 patients who presented with operable breast cancer between 1992 and 1998 were reviewed. Details about the 108 patients who had locoregional or metastatic relapse were obtained from our breast cancer database and their clinical records. Full data were available on 104 patients: 77 (74%) were seen at expedited (interval) appointments and a further 18 (17.3%) drew attention to symptoms at a routine visit. Two cases of locoregional recurrence were revealed by surveillance imaging. Unsuspected disease, locoregional in all cases, was detected on examination in 7 (6.7%) patients. The median time to presentation of recurrence was 19 months for metastatic and 18 months for locoregional disease. Breast cancer recurrence usually presents to an interval clinic. Most cases that are confirmed following a routine review are already symptomatic. Long-term routine hospital follow-up after treatment for breast cancer appears inefficient and unnecessary. Following liaison with local general practitioners we propose to discharge patients from routine review after two years. Thereafter they will have scheduled appointments with their GPs with immediate access to specialist review in the breast care unit if required.

Breast Neoplasms↗
PubMed2000

Glutathione-related factors are not correlated with sensitivity of human tumour cells to actinomycin D.

Glutathione (GSH) contents and activities of glutathione S-transferases (GST), glutathione reductase (GSH-RD), glutathione peroxidase (GSHpx) and glutathione conjugate export pump (GS-X pump) were determined in eight human tumour cell lines with different sensitivities to melphalan, a substrate of glutathione conjugation, and actinomycin D which has not been shown to be detoxified by glutathione-related mechanisms. Chang liver cells with highest GSH content and highest activities of GST, GSH-RD, GSHpx and GS-X pump were found to be most resistant to melphalan. Statistical analysis showed significant correlations between sensitivities of the human tumour cells to melphalan and the glutathione-related factors (r = 0.72-0.79; except for GST, r = 0.65, P = 0.08), while there were no significant correlations observed between sensitivities of the human tumour cells to actinomycin D and all the glutathione-related factors tested (r = -0.25-0.14). Significant correlations of the glutathione-related factors to resistance of human tumour cells to melphalan, a substrate of glutathione conjugation, but not to resistance of the human tumour cells to actinomycin D which has not been shown to be detoxified by glutathione-related mechanisms suggested that glutathione-related mechanisms contribute to drug resistance by increased detoxification of the drugs involved.

Antibiotics, Antineoplastic↗
PubMed1999

Daphnetin, one of coumarin derivatives, is a protein kinase inhibitor.

Protein kinases play key roles in the control of cell proliferation, differentiation and metabolism. In this work, we studied the effect of coumarin and its derivatives, including daphnetin, esculin, 2-OH-coumarin, 4-OH-coumarin and 7-OH-coumarin, on the activity of protein kinases. It was found that, in these compounds, only daphnetin was a protein kinase inhibitor. This compound inhibited tyrosine-specific protein kinase, EGF receptor (IC(50) = 7.67 microM), and serine/threonine-specific protein kinases, including cAMP-dependent protein kinase (PKA) (IC(50) = 9.33 microM) and protein kinase C (PKC) (IC(50) = 25.01 microM) in vitro. The inhibition of EGF receptor tyrosine kinase by daphnetin was competitive to ATP and non-competitive to the peptide substrate. The inhibition of EGF-induced tyrosine phosphorylation of EGF receptor by daphnetin was not observed in human hepatocellular carcinoma HepG2 cells. The structural comparison of daphnetin with coumarin and other coumarin derivatives suggests that the hydroxylation at C8 may be required for daphnetin acting as a protein kinase inhibitor.

Adenosine Triphosphate↗
PubMed1999

Induction of neuronal and inducible nitric oxide synthase in the motoneurons of spinal cord following transient abdominal aorta occlusion in rats.

BACKGROUND: Motoneurons in the spinal cord are especially vulnerable to ischemic injury and selectively destroyed after transient ischemia. Nitric oxide (NO) has been implicated in both neurodegneration and neuroprotection to ischemic insult. To evaluate the role of NO in pathophysiology to spinal cord ischemia, the expression of neuronal and inducible nitric oxide synthase (n-NOS and i-NOS) and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) in the motoneurons of the lumbosacral spinal cord was examined in a rat model with transient abdominal aorta (TAA) occlusion. MATERIALS AND METHODS: Male Sprague-Dawley rats were divided into sham-operated (n = 12) and TAA occlusion (n = 24) groups. TAA occlusion was induced by placement of a microvascular clamp around the abdominal aorta for 20 min. Three sham-operated and six TAA occlusion animals were sacrificed at each time interval at 4, 24, and 48 h and 7 days after operation. Tissue sections obtained from the lumbosacral spinal cord were processed for n-NOS, i-NOS, NADPH-d, and hematoxylin-eosin (HE) staining. Histological changes of motoneurons in ventral horn were assessed by HE staining. RESULTS: In sham-operated control animals, n-NOS-, i-NOS-, and NADPH-d-positive neurons were barely detectable in the ventral horn of the spinal cord. At 4 h after TTA occlusion, n-NOS and NADPH-d expression became evident in the motoneurons and was markedly enhanced at 24 and 48 h. i-NOS expression was also induced in the ventral horn motoneurons of the lumbosacral spinal cord at the same time points. Enzymatic expression in the motoneurons was diminished 7 days after operation. Hyperchromatic neurons indicative of cell death were observed in HE-stained specimens 7 days following TAA occlusion. CONCLUSIONS: The rapid induction of n-NOS, i-NOS, and NADPH-d in the motoneurons of ventral horn suggests that NO may be involved in the selective and delayed neuronal death in the spinal cord to the ischemic insult.

Animals↗
PubMed1999

GSH, GSH-related enzymes and GS-X pump in relation to sensitivity of human tumor cell lines to chlorambucil and adriamycin.

Glutathione (GSH) contents and activities of glutathione S-transferase (GST), glutathione reductase (GSH-RD), glutathione peroxidase (GSHpx) and glutathione conjugate export pump (GS-X pump) were determined in eight human tumor cell lines with different sensitivities to adriamycin and chlorambucil. Correlations between sensitivities of the human tumor cells to adriamycin and chlorambucil and the glutathione related factors were analyzed statistically. Sensitivities of the human tumor cells to chlorambucil were found to be correlated to all the glutathione related factors tested (r=0.68-0.88). IC50 values of adriamycin were also positively correlated to GSH contents and activities of GSH-RD, GSHpx and GS-X pump with r values ranging from 0.66 to 0.77 but not to GST activity (r=0.25). Chang liver cells with highest GSH content and highest activities of GST, GSH-RD, GSHpx and GS-X pump were most resistant to both adriamycin and chlorambucil. These data suggested that glutathione related factors may work as an overall detoxification system participating in the detoxification of anticancer drugs such as adriamycin and chlorambucil, and to be involved in cellular resistance to these drugs.

Antineoplastic Agents↗
PubMed1998

Butein, a specific protein tyrosine kinase inhibitor.

Butein, a plant polyphenol, was shown to be a specific protein tyrosine kinase inhibitor. This compound inhibited not only the epidermal growth factor (EGF)-stimulated auto-phosphotyrosine level of EGF receptor in HepG2 cells but also tyrosine-specific protein kinase activities of EGF receptor (IC50 = 65 microM) and p60c-src (IC50 = 65 microM) in vitro. The inhibition was competitive to ATP and non-competitive to the phosphate acceptor, poly (Glu, Ala, Tyr) 6:3:1 for EGF receptor tyrosine kinase. In contrast, butein non-significantly inhibited the activities of serine- and threonine-specific protein kinases, such as protein kinase C (PKC) and cAMP-dependent protein kinase (PKA).

CSK Tyrosine-Protein Kinase↗
PubMed1998

The thermal activity of normal and malignant tissues. Microcalorimetric response of liver cancer to hepatic artery ligation, cryosurgery, adriamycin and norcantharidin.

The usefulness of metabolic heat measurements in quantifying the response of a solid tumour to anticancer treatment was evaluated. The heat production characteristic of malignant tissues, as measured from human stomach, breast and liver cancer samples, was observed to be inconsistent, and its value could be higher or lower than that of its normal tissue of origin. The various thermal activity responses of an experimental rat hepatoma to hepatic artery ligation, cryotherapy, intra-arterial (i.a.) Adriamycin (2.4 mg/kg), i.a. Norcantharidin (0.5 mg/kg) were next studied. The tumour/liver (T/L) ratio of untreated tumour-bearing rats was 0.83 but this fell to a minimum at 24 h in both the hepatic artery ligation and the cryosurgery groups. In these two groups marked fluctuations in the heat production of normal liver occurred with poor recovery of the T/L ratio even at 2-3 weeks. In the Adriamycin group, the T/L ratio dropped to a minimum at 5 days, and in the Norcantharidin group, at 3 days. Minimal disturbances in the thermal activity of liver tissue occurred in these two chemotherapy groups and the T/L ratio recovered by 3 weeks. Norcantharidin appeared as efficacious as Adriamycin in the treatment of hepatoma when evaluated in terms of thermal activity.

Animals↗
PubMed1998

Glutathione-related mechanisms in cellular resistance to anticancer drugs.

Glutathione conjugation and transport of glutathione conjugates of anticancer drugs out of cells have been shown to work as a system in the detoxification of many anticancer drugs. The major components of this system include glutathione (GSH), GSH-related enzymes and glutathione conjugate export pump (GS-X pump). GSH can combine with anticancer drugs to form less toxic and more water soluble GSH conjugates, the conjugation reaction is catalysed by glutathione S-transferases (GSTs). The GSH conjugates of anticancer drugs can be exported from cells by GS-X pump or multidrug resistance-associated protein (MRP). GSH, glutathione-related enzymes and GS-X pump or MRP have been found to be increased or overexpressed in many drug resistant cells. Increased detoxification of anticancer drugs by this system may confer drug resistance. Inhibition of this detoxification system is a strategy for modulation of drug resistance.

ATP-Binding Cassette Transporters↗
PubMed1997

Inhibition of glutathione reductase by plant polyphenols.

The effects of forty-one plant polyphenols on the activity of glutathione reductase (GSH-RD) were studied. These polyphenols showed varying degrees of concentration-dependent inhibition on the enzyme, with IC50 values that varied from approximately 40 microM to 1 mM. 4'-Hydroxychalcone and tannic acid were among the more potent inhibitors, with IC50 values of 47.3 and 50.4 microM, respectively. Different classes of polyphenols varied in potency in the following order: chalcones > tannic acid > flavonoids > coumarins > catechins. Analysis of structure-activity relationships showed certain chemical structures to be important for the inhibition of GSH-RD: (a) C-5 and C-7 hydroxylations in the A-ring, a carbonyl group at C-4, and the B-ring attached to C-2 in flavonoids; (b) C-2' and C-4' hydroxylations in chalcones; and (c) C-6 and C-7 hydroxylations in coumarins. The inhibition of GSH-RD by tannic acid and quercetin was time dependent and irreversible, whereas that by 4'-hydroxychalcone and esculin was reversible but not time dependent. Enhanced inhibition of GSH-RD by the four polyphenols 4'-hydroxychalcone, quercetin, butein, and acacetin was observed in the presence of NADPH. Kinetic studies showed that both tannic acid and 4'-hydroxychalcone exhibited non-competitive inhibition on GSH-RD towards glutathione disulfide.

Drug Resistance↗