Inverse electron demand Diels-Alder reactions in chemical biology

The emerging inverse electron demand Diels-Alder (IEDDA) reaction stands out from other bioorthogonal reactions by virtue of its unmatchable kinetics, excellent orthogonality and biocompatibility. With the recent discovery of novel dienophiles and optimal tetrazine coupling partners, attention has now been turned to the use of IEDDA approaches in basic biology, imaging and therapeutics. Here we review this bioorthogonal reaction and its promising applications for live cell and animal studies. We first discuss the key factors that contribute to the fast IEDDA kinetics and describe the most recent advances in the synthesis of tetrazine and dienophile coupling partners. Both coupling partners have been incorporated into proteins for tracking and imaging by use of fluorogenic tetrazines that become strongly fluorescent upon reaction. Selected notable examples of such applications are presented. The exceptional fast kinetics of this catalyst-free reaction, even using low concentrations of coupling partners, make it amenable for in vivo radiolabelling using pretargeting methodologies, which are also discussed. Finally, IEDDA reactions have recently found use in bioorthogonal decaging to activate proteins or drugs in gain-of-function strategies. We conclude by showing applications of the IEDDA reaction in the construction of biomaterials that are used for drug delivery and multimodal imaging, among others. The use and utility of the IEDDA reaction is interdisciplinary and promises to revolutionize chemical biology, radiochemistry and materials science.

Direct fluorescence analysis of genetic polymorphisms by hybridization with oligonucleotide arrays on glass supports

A simple and rapid method for the analysis of genetic polymorphisms has been developed using allele-specific oligonucleotide arrays bound to glass supports. Allele-specific oligonucleotides are covalently immobilized on glass slides in arrays of 3 mm spots. Genomic DNA is amplified by PCR using one fluorescently tagged primer oligonucleotide and one biotinylated primer oligonucleotide. The two complementary DNA strands are separated, the fluorescently tagged strand is hybridized to the support-bound oligonucleotide array, and the hybridization pattern is detected by fluorescence scanning. Multiple polymorphisms present in the PCR product may be detected in parallel. The effect of spacer length, surface density and hybridization conditions were evaluated, as was the relative efficacy of hybridization with single or double-stranded PCR products. The utility of the method was demonstrated in the parallel analysis of 5 point mutations from exon 4 of the human tyrosinase gene.

Head injury and the risk of AD in the MIRAGE study

OBJECTIVES

It has been suggested in some studies that head injury is a risk factor for AD, and that this risk is heightened among carriers of the APOE-epsilon4 allele. We examined the effects of head injury and APOE genotype on AD risk in a large family study.

SUBJECTS

A total of 2,233 probands who met criteria for probable or definite AD and their 14,668 first-degree family members (4,465 parents, 7,694 siblings, and 2,509 spouses) were ascertained at 13 centers in the United States, Canada, and Germany participating in the MIRAGE (Multi-Institutional Research in Alzheimer Genetic Epidemiology) project. Information on head injury was collected by interview of multiple informants and review of medical records. Nondemented relatives and spouses served as control subjects for this study.

METHODS

Odds of AD for head trauma with or without loss of consciousness were computed by comparing probands with unaffected spouses using conditional logistic regression analysis. To account for the unique biologic relationship between probands and their parents and siblings, odds of AD were computed using a generalized estimating equation (GEE) Poisson regression approach. GEE logistic regression was used to examine the joint effects of APOE genotype and head injury on the odds of AD in probands and a control group comprised of unaffected siblings and spouses.

RESULTS

Comparison of probands with their unaffected spouses yielded odds ratios for AD of 9.9 (95% CI, 6.5 to 15.1) for head injury with loss of consciousness and 3.1 (2.3 to 4.0) for head injury without loss of consciousness. The corresponding odds derived from the comparison of probands with their parents and sibs were 4.0 (2.9 to 5.5) for head injury with loss of consciousness and 2.0 (1.5 to 2.7) for head injury without loss of consciousness. Head injury without loss of consciousness did not significantly increase the risk of AD in spouses (OR = 1.3; 95% CI, 0.4 to 4.1). The joint effects of head injury and APOE genotype were evaluated in a subsample of 942 probands and 327 controls (spouses and siblings). Head injury increased the odds of AD to a greater extent among those lacking epsilon4 (OR = 3.3) than among epsilon4 heterozygotes (OR = 1.8) or homozygotes (OR = 1.3).

CONCLUSION

Head injury is a risk factor for AD. The magnitude of the risk is proportional to severity and heightened among first-degree relatives of AD patients. The influence of head injury on the risk of AD appears to be greater among persons lacking APOE-epsilon4 compared with those having one or two epsilon4 alleles, suggesting that these risk factors may have a common biologic underpinning.

Repair of tobacco carcinogen-induced DNA adducts and lung cancer risk: a molecular epidemiologic study

BACKGROUND

Only a fraction of cigarette smokers develop lung cancer, suggesting that people differ in their susceptibility to this disease. We investigated whether differences in DNA repair capacity (DRC) for repairing tobacco carcinogen-induced DNA damage are associated with differential susceptibility to lung cancer.

METHODS

From August 1, 1995, through April 30, 1999, we conducted a hospital-based, case-control study of 316 newly diagnosed lung cancer patients and 316 cancer-free control subjects matched on age, sex, and smoking status. DRC was measured in cultured lymphocytes with the use of the host-cell reactivation assay with a reporter gene damaged by a known activated tobacco carcinogen, benzo[a]pyrene diol epoxide. Statistical tests were two-sided.

RESULTS

Overall, lower DRC was observed in case patients than in control subjects (P:<.001) and was associated with a greater than twofold increased risk of lung cancer. Compared with the highest DRC quartile in the control subjects and after adjustment for age, sex, pack-years of smoking, family history of cancer, and other covariates, reduced DRC was associated with increased risk of lung cancer in a dose-dependent fashion (odds ratio [OR] = 1.8 with 95% confidence interval [CI] = 1.1-3.1, OR = 2.0 with 95% CI = 1.2-3.4, and OR = 4. 3 with 95% CI = 2.6-7.2 for the second, third, and fourth quartiles, respectively; P:(trend)<.001). Case patients who were younger at diagnosis (<60 years old), female, or lighter smokers or who reported a family history of cancer exhibited the lowest DRC and the highest lung cancer risk among their subgroups, suggesting that these subgroups may be especially susceptible to lung cancer.

CONCLUSION

The results provide evidence that low DRC is associated with increased risk of lung cancer. The findings from this hospital-based, case-control study should be validated in prospective studies.

Requirement for Atr in phosphorylation of Chk1 and cell cycle regulation in response to DNA replication blocks and UV-damaged DNA in Xenopus egg extracts

The checkpoint kinase Xchk1 becomes phosphorylated in Xenopus egg extracts in response to DNA replication blocks or UV-damaged DNA. Xchk1 is also required for the cell cycle delay that is induced by unreplicated or UV-damaged DNA. In this report, we have removed the Xenopus homolog of ATR (Xatr) from egg extracts by immunodepletion. In Xatr-depleted extracts, the checkpoint-associated phosphorylation of Xchk1 is abolished, and the cell cycle delay induced by replication blocks is strongly compromised. Xatr from egg extracts phosphorylated recombinant Xchk1 in vitro, but not a mutant form of Xchk1 (Xchk1-4AQ) containing nonphosphorylatable residues in its four conserved SQ/TQ motifs. Recombinant human ATR, but not a kinase-inactive mutant, phosphorylated the same sites in Xchk1. Furthermore, the Xchk1-4AQ mutant was found to be defective in mediating a checkpoint response in egg extracts. These findings suggest that Xchk1 is a functionally important target of Xatr during a checkpoint response to unreplicated or UV-damaged DNA.

The essential role of MEKK3 in TNF-induced NF-kappaB activation

Activation of IkappaB kinase (IKK) is the key step in stimulation of the transcription factor NF-kappaB, which regulates many genes in the inflammatory response pathway. The molecular mechanism that underlies IKK activation in response to tumor necrosis factor (TNF) is still unknown. Using mitogen-activated protein kinase kinase kinase 3 (MEKK3)-deficient fibroblast cells, we found that MEKK3 plays a critical role in TNF-induced NF-kappaB activation. We have shown that MEKK3 is required for IKK activation and functions downstream of receptor-interacting protein (RIP) and TNF receptor- associated factor 2. We have also shown that MEKK3 interacts with RIP and directly phosphorylates IKK. The kinase activity of MEKK3 is pivotal to its function and, therefore, MEKK3 links RIP and IKK in TNF-induced NF-kappaB activation.

Differential display using one-base anchored oligo-dT primers

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A synthetic inhibitor of p53 protects neurons against death induced by ischemic and excitotoxic insults, and amyloid beta-peptide

The tumor suppressor protein p53 is essential for neuronal death in several experimental settings and may participate in human neurodegenerative disorders. Based upon recent studies characterizing chemical inhibitors of p53 in preclinical studies in the cancer therapy field, we synthesized the compound pifithrin-alpha and evaluated its potential neuroprotective properties in experimental models relevant to the pathogenesis of stroke and neurodegenerative disorders. Pifithrin-alpha protected neurons against apoptosis induced by DNA-damaging agents, amyloid beta-peptide and glutamate. Protection by pifithrin-alpha was correlated with decreased p53 DNA-binding activity, decreased expression of the p53 target gene BAX and suppression of mitochondrial dysfunction and caspase activation. Mice given pifithrin-alpha exhibited increased resistance of cortical and striatal neurons to focal ischemic injury and of hippocampal neurons to excitotoxic damage. These preclinical studies demonstrate the efficacy of a p53 inhibitor in models of stroke and neurodegenerative disorders, and suggest that drugs that inhibit p53 may reduce the extent of brain damage in related human neurodegenerative conditions.

A review of electrical impedance techniques for breast cancer detection

Some evidence has been found that malignant breast tumors have lower electrical impedance than surrounding normal tissues. Although the separation of malignant tumors from benign lesions based on impedance measurements needs further investigation, electrical impedance could be used as an indicator for breast cancer detection. In this paper, we provide a systematic technical review of the existing electrical impedance techniques proposed for breast cancer detection, with an emphasis on noninvasive impedance imaging techniques. The electrical impedance of human breast tissue is first introduced, with tabulation of previous in vitro impedance measurement results on cancerous and normal breast tissues, and a brief description on the limited in vivo impedance measurements completed with invasive, or noninvasive, non-imaging techniques. A detailed review on noninvasive impedance imaging techniques for breast cancer detection, such as electrical impedance tomography (EIT) and electrical impedance mapping (EIM), is then presented. We suggest that for better breast cancer detection, an invasive impedance technique may be enhanced by combination with other cancer indicators. 3D EIT should be improved through collective efforts. EIM using a pair of electrode arrays is a viable method with great potential. Magnetic induction tomography and other magnetic induction based impedance imaging for breast cancer detection are promising and merit further exploration as well.

Hydrolysis theory for cisplatin and its analogues based on density functional studies

Hydrolysis of cisplatin, the most widely used anticancer drug in the world, is believed to be the key activation step before the drug reaching its intracellular target DNA. To obtain an accurate hydrolysis theory for this important class of square-planar Pt(II) complexes, three typical reactions, i.e., the first and second hydrolyses of cisplatin and the hydrolysis of [Pt(dien)Cl](+) (dien = diethylenetriamine), were studied at the experimental temperature with the solvent effect using mPW1PW91/SDD from a comprehensive methodological study on the Hartree-Fock (HF) ab initio method, electron correlation methods, pure density functional theory (DFT) methods, and hybrid HF-DFT methods with several basis sets. The true five stationary states in the second-order nucleophilic substitution (S(N)2) pathway for the hydrolysis process, namely, reactant (R) --> intermediate 1 (I1) --> TS --> intermediate 2 (I2) --> product (P) were obtained and characterized theoretically for the first time. The most remarkable structural variations and the associated atomic charge variations in the hydrolysis process were found to occur in the equatorial plane of the five-coordinate trigonal-bipyramidal (TBP)-like structures of I1, TS, and I2. The reaction with the TS structure of smaller L-M-E angle and more lengthened M-L and M-E bonds was found to have a smaller Gibbs free energy change and accordingly the better hydrolysis yield. It is found that the sum of the three concentric angles in the TBP's equator is near 360 degrees in I1 and I2 and is almost 360 degrees in TS in each reaction. The associated energy profiles again demonstrated a typical S(N)2 reaction curve. The computed forward and backward reaction enthalpy (Delta H(++)) and reaction entropy (Delta S(++)) in the rate-determining step I1 --> TS --> I2 are in good agreement with the experiments. Natural bonding orbital population analysis shows that the charge-separating extent follows the same order of Delta G in studied reactions. Comparing with the computational results of gas-phase reactions, it can be concluded that the solvent effect should be considered to obtain an accurate hydrolysis picture. The most affected structural parameters after solvation are related to the equatorial plane of the TBP-like geometry. The results provide theoretical guidance on detailed understanding on the mechanism of the hydrolysis of cisplatin, which could be useful in the design of novel Pt-based anticancer agents.

Relocation of the t-SNARE SNAP-23 from lamellipodia-like cell surface projections regulates compound exocytosis in mast cells

For regulated secretion, mast cells and several other cell types utilize compound exocytosis, a combination of granule-plasma membrane and granule-granule fusions. The molecular machinery that controls this massive export process has not been identified. We report that SNAP-23, a t-SNARE related to SNAP-25, relocates in response to stimulation from plasma membrane lamellipodia-like projections to granule membranes in permeabilized mast cells. While relocation is a prerequisite for secretion, it can occur without membrane fusion and will expedite a subsequent secretory response. After relocation, SNAP-23 is required for exocytosis, implying a crucial role in promoting membrane fusion. Thus, relocation of this SNARE regulates compound exocytosis and links granule-plasma membrane and granule-granule fusions.

Low blood pressure and dementia in elderly people: the Kungsholmen project

OBJECTIVE

To examine the relation between blood pressure and dementia in elderly people.

DESIGN

Cross sectional, population based study.

SETTING

Kungsholmen district of Stockholm, Sweden.

SUBJECTS

1642 subjects aged 75-101 years.

MAIN OUTCOME MEASURES

Prevalence and adjusted odds ratio of dementia by blood pressure.

RESULTS

People with systolic pressure < or = 140 mm Hg were more often diagnosed as demented than those with systolic pressure >140 mm Hg: odds ratios (95% confidence interval) adjusted for age, sex, and education were 2.98 (2.17 to 4.08) for all dementias, 2.91 (1.93 to 4.38) for Alzheimer's disease, 2.00 (1.09 to 3.65) for vascular dementia, and 5.07 (2.65 to 9.70) for other dementias. Similar results were seen in subjects with diastolic pressure < or = 75 mm Hg compared with those with higher diastolic pressure. When severity and duration of dementia were taken into account, only moderate and severe dementia were found to be significantly related to relatively low blood pressure, and the association was stronger in subjects with longer disease duration. Use of hypotensive drugs and comorbidity with cardiovascular disease did not modify the results for all dementias, Alzheimer's disease, and other dementias but slightly reduced the association between vascular dementia and diastolic blood pressure.

CONCLUSIONS

Both systolic and diastolic blood pressure were inversely related to prevalence of dementia in elderly people. We think that relatively low blood pressure is probably a complication of the dementia process, particularly Alzheimer's disease, although it is possible that low blood pressure may predispose a subpopulation to developing dementia.

Dementia is the major cause of functional dependence in the elderly: 3-year follow-up data from a population-based study

OBJECTIVES

The purpose of this investigation was to study the role of dementia and other common age-related diseases as determinants of dependence in activities of daily living (ADL) in the elderly.

METHODS

The study population consisted of 1745 persons, aged 75 years and older, living in a district of Stockholm. They were examined at baseline and after a 3-year follow-up interval. Katz's index was used to measure functional status. Functional dependence at baseline, functional decline, and development of functional dependence at follow-up were examined in relation to sociodemographic characteristics and chronic conditions.

RESULTS

At baseline, factors associated with functional dependence were age, dementia, cerebrovascular disease, heart disease, and hip fracture. However, only age and dementia were associated with the development of functional dependence and decline after 3 years. In a similar analysis, including only nondemented subjects. Mini-Mental State Examination scores emerged as one of the strongest determinants. The population attributable risk percentage of dementia in the development of functional dependence was 49%.

CONCLUSIONS

In a very old population, dementia and cognitive impairment make the strongest contribution to both the development of long-term functional dependence and decline in function.

The Xenopus Chk1 protein kinase mediates a caffeine-sensitive pathway of checkpoint control in cell-free extracts

We have analyzed the role of the protein kinase Chk1 in checkpoint control by using cell-free extracts from Xenopus eggs. Recombinant Xenopus Chk1 (Xchk1) phosphorylates the mitotic inducer Cdc25 in vitro on multiple sites including Ser-287. The Xchk1-catalyzed phosphorylation of Cdc25 on Ser-287 is sufficient to confer the binding of 14-3-3 proteins. Egg extracts from which Xchk1 has been removed by immunodepletion are strongly but not totally compromised in their ability to undergo a cell cycle delay in response to the presence of unreplicated DNA. Cdc25 in Xchk1-depleted extracts remains bound to 14-3-3 due to the action of a distinct Ser-287-specific kinase in addition to Xchk1. Xchk1 is highly phosphorylated in the presence of unreplicated or damaged DNA, and this phosphorylation is abolished by caffeine, an agent which attenuates checkpoint control. The checkpoint response to unreplicated DNA in this system involves both caffeine-sensitive and caffeine-insensitive steps. Our results indicate that caffeine disrupts the checkpoint pathway containing Xchk1.

Testosterone signaling through internalizable surface receptors in androgen receptor-free macrophages

Testosterone acts on cells through intracellular transcription-regulating androgen receptors (ARs). Here, we show that mouse IC-21 macrophages lack the classical AR yet exhibit specific nongenomic responses to testosterone. These manifest themselves as testosterone-induced rapid increase in intracellular free [Ca(2+)], which is due to release of Ca(2+) from intracellular Ca(2+) stores. This Ca(2+) mobilization is also inducible by plasma membrane-impermeable testosterone-BSA. It is not affected by the AR blockers cyproterone and flutamide, whereas it is completely inhibited by the phospholipase C inhibitor U-73122 and pertussis toxin. Binding sites for testosterone are detectable on the surface of intact IC-21 cells, which become selectively internalized independent on caveolae and clathrin-coated vesicles upon agonist stimulation. Internalization is dependent on temperature, ATP, cytoskeletal elements, phospholipase C, and G-proteins. Collectively, our data provide evidence for the existence of G-protein-coupled, agonist-sequestrable receptors for testosterone in plasma membranes, which initiate a transcription-independent signaling pathway of testosterone.

Regional postprandial fatty acid metabolism in different obesity phenotypes

To examine if postprandial splanchnic/hepatic free fatty acid (FFA) delivery is increased in upper-body (UB) obesity, and to determine the adipose tissue depots responsible for the greater postprandial FFA availability, we measured systemic and regional uptake and release of FFAs ([1-(14)C]palmitate) before and during a 5-h frequent-feeding mixed meal in eight UB and eight lower-body (LB) obese women. Postabsorptive FFA flux and splanchnic FFA delivery were not different in UB and LB obese women; however, postprandial FFA concentrations (257 +/- 45 vs. 81 +/- 12 micromol/l, P < 0.0001), FFA flux (8.5 +/- 1.2 vs. 3.9 +/- 0.8 micromol x kg(-1) fat-free mass x min(-1), P < 0.0001), splanchnic FFA delivery (275 +/- 45 vs. 88 +/- 24 micromol/min, respectively, P < 0.005), and estimated hepatic FFA delivery were greater in UB than LB obese women. Nonsplanchnic UB adipose tissue FFA release was greater in UB than in LB obese women (276 +/- 71 vs. 97 +/- 37 micromol/min, respectively, P < 0.05) and accounted for the greater postprandial FFA availability in UB obesity. Postprandial leg glucose uptake was less in UB than in LB obese women (8.4 +/- 5.1 vs. 22.9 +/- 2.6 micromol x kg(-1) leg fat-free mass x min(-1), P < 0.05). We conclude that the elevated postprandial FFA release observed in UB obese women originates from the nonsplanchnic UB fat, not visceral fat. These results suggest that visceral fat may be a marker for, but not the source of, excess postprandial FFAs in obesity.

Knockout mice heterozygous for Sod2 show alterations in cardiac mitochondrial function and apoptosis

Heart mitochondria from heterozygous (Sod2(-/+)) knockout mice have a 50% reduction in manganese superoxide dismutase (MnSOD) activity. The decrease in MnSOD activity was associated with increased mitochondrial oxidative damage as demonstrated by a decrease in the activities of iron sulfhydryl proteins sensitive to oxygen stress (aconitase and reduced nicotinamide adenine dinucleotide-oxidoreductase). Mitochondrial function was altered in the Sod2(-/+) mice, as shown by decreased respiration by complex I and an increase in the sensitivity of the permeability transition to induction by calcium and t-butylhydroperoxide. The increased induction of the permeability transition in heart mitochondria from Sod2(-/+.)mice was associated with increased release of cytochrome c and an increase in DNA fragmentation. Cardiomyocytes isolated from neonatal Sod2(-/+) and Sod2(-/-) mice were more sensitive to cell death than cardiomyocytes from Sod2(+/+) mice after t-butylhydroperoxide treatment, and this increased sensitivity was prevented by inhibiting the permeability transition with cyclosporin A. These experiments demonstrate that MnSOD may play an important role in the induction of the mitochondrial pathway of apoptosis in the heart, and this appears to occur primarily through the permeability transition.

Acetyl glyceryl ether phosphorylcholine (AGEPC). A putative mediator of cardiac anaphylaxis in the guinea pig

Platelet-activating factor is a novel phospholipid that has been implicated as an important mediator of acute allergic reactions. The intravenous administration of acetyl glyceryl ether phosphorylcholine, a pure, synthetic platelet-activating factor, causes electrocardiographic changes in the rabbit similar to those which are characteristic manifestations of systemic anaphylaxis. To determine whether platelet-activating factor contributes to anaphylactic cardiac dysfunction, we measured platelet-activating factor release from the sensitized guinea pig heart challenged in vitro with specific antigen and compared the resulting cardiac dysfunction with that induced by the injection of acetyl glyceryl ether phosphorylcholine into nonsensitized hearts. The results of these studies document that, during anaphylaxis in the isolated guinea pig heart, a platelet-activating factor is released into the coronary effluent that has physicochemical and functional properties similar to those of acetyl glyceryl ether phosphorylcholine. The intracardiac administration of acetyl glyceryl ether phosphorylcholine (10(-14) to 3 X 10(-9) mol) induced dose-related decreases in left ventricular contractile force (-5 to -85%) and coronary flow (-5 to -85%), as well as impaired atrioventricular conduction. The negative inotropic effect of acetyl glyceryl ether phosphorylcholine also was present in hearts perfused at constant flow. Although, in these hearts, acetyl glyceryl ether phosphorylcholine increased coronary resistance, which may have caused regional shunting and ischemia, it is unlikely that the negative inotropic effect of acetyl glyceryl ether phosphorylcholine was secondary to changes in coronary flow, since acetyl glyceryl ether phosphorylcholine also caused a dose-dependent negative inotropic effect in the electrically paced, noncoronary-perfused left atrium and right ventricular papillary muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of modified human cytochrome P450 1A2 in Escherichia coli: stabilization, purification, spectral characterization, and catalytic activities of the enzyme

A full-length human cytochrome P450 (P450) 1A2 cDNA clone and four derivatives in which the 5'-terminus was modified were inserted into the pCW vector and used to transform Escherichia coli cells. Low levels of expression were seen with most of the constructs but high expression levels (245 nmol membrane-bound P450 recovered per liter culture) were achieved when the N-terminus was MALLLAVFL, as reported earlier by Fisher et al. (C. W. Fisher, D. L. Caudle, C. Martin-Wixtrom, L. C. Quattrochi, R. H. Tukey, M. R. Waterman, and R. W. Estabrook, 1992, FASEB J. 6, 759-764). The expressed human P450 1A2 in bacterial membranes was rapidly denatured to cytochrome P420 in the presence of detergents. This denaturation was blocked by the inhibitory ligand alpha-naphthoflavone (alpha NF, 7,8-benzoflavone). Human P450 1A2 was solubilized using high concentrations of sodium cholate and Triton N-101 and could be purified to near homogeneity in high yield in two steps. alpha NF was included in the buffer in the first step and then removed in the second chromatography step along with the detergent. The purified human P450 1A2 was found to be almost completely in the high spin iron configuration, in contrast to P450 1A2 enzymes isolated from rats and rabbits. The enzyme was catalytically active toward the known substrates 7-ethoxyresorufin and phenacetin. The N-terminal appears to be blocked, as is the case for other P450s we have expressed that contain the sequence MALLLAVFL in E. coli. Previously this human P450 has only been available in limited amounts; the methods presented here should facilitate further biochemical and practical studies on this interesting enzyme.

Molecular cloning of a high-affinity receptor for the growth factor-like lipid mediator lysophosphatidic acid from Xenopus oocytes

Lysophosphatidic acid (1-acyl-2-lyso-snglycero-3-phosphate, LPA) is a multifunctional lipid mediator found in a variety of organisms that span the phylogenetic tree from humans to plants. Although its physiological function is not clearly understood, LPA is a potent regulator of mammalian cell proliferation; it is one of the major mitogens found in blood serum. In Xenopus laevis oocytes, LPA elicits oscillatory Cl- currents. This current, like other effects of LPA, is consistent with a plasma membrane receptor-mediated activation of G protein-linked signal transduction pathways. Herein we report the identification of a complementary DNA from Xenopus that encodes a functional high-affinity LPA receptor. The predicted structure of this protein of 372 amino acids contains features common to members of the seven transmembrane receptor superfamily with a predicted extracellular amino and intracellular carboxyl terminus. An antisense oligonucleotide derived from the first 5-11 predicted amino acids, selectively inhibited the expression of the endogenous high-affinity LPA receptors in Xenopus oocytes, whereas the same oligonucleotide did not affect the low-affinity LPA receptor. Expression of the full-length cRNA in oocytes led to an increase in maximal Cl- current due to increased expression of the high-affinity LPA receptor, but activation of the low-affinity receptor was, again, unaffected. Oocytes expressing cRNA prepared from this clone showed no response to other lipid mediators including prostaglandins, leukotrienes, sphingosine 1-phosphate, sphingosylphosphorylcholine, and platelet-activating factor, suggesting that the receptor is highly selective for LPA.

Oxidation of benzo[a]pyrene by recombinant human cytochrome P450 enzymes

The oxidation of benzo[a]pyrene (B[a]P) was examined using reconstituted systems prepared with recombinant human cytochrome P450 (P450) enzymes 1A1, 1A2, 2C8, 2C10, 2E1, and 3A4 and with microsomes prepared from Saccharomyces cerevisiae expressing recombinant human P450s 2C8, 2C9, and 2C18. Products measured by HPLC included the 3- and 9-phenols, the 4,5-, 7,8-, and 9,10-dihydrodiols (detected in the presence of epoxide hydrolase), and products in the polar fraction eluting immediately after the void volume. The most active enzyme in all reactions was P450 1A1. P450 3A4 and P450 1A2 formed appreciable amounts of several of the products, including the 3-phenol. P450 2C enzymes and P450 2E1 formed relatively low amounts of all B[a]P products. Consideration of these patterns along with knowledge of levels of expression of the P450s in human tissues and previous results with microsomes leads to the conclusion that P450 1A1 should dominate the oxidation of B[a]P in tissues where it is present and inducible. In human liver the level of P450 1A1 is low and P450 3A4, P450 2C subfamily enzymes, and P450 1A2 probably all contribute. Of the human P450s considered here, P450 1A2 was the most active hepatic enzyme forming the 7,8-dihydrodiol. 7,8-Benzoflavone stimulated the oxidation of B[a]P by P450 3A4 and inhibited the oxidations catalyzed by P450 1A2. The extent of inhibition of P450 1A1 was less (than with P450 1A2), probably due to the rapid oxidation of 7,8-benzoflavone by P450 1A1. The major 7,8-benzoflavone product appears to be the 5,6-oxide.

A reliable assessment of 8-oxo-2-deoxyguanosine levels in nuclear and mitochondrial DNA using the sodium iodide method to isolate DNA

A major controversy in the area of DNA biochemistry concerns the actual in vivo levels of oxidative damage in DNA. We show here that 8-oxo-2-deoxyguanosine (oxo8dG) generation during DNA isolation is eliminated using the sodium iodide (NaI) isolation method and that the level of oxo8dG in nuclear DNA (nDNA) is almost one-hundredth of the level obtained using the classical phenol method. We found using NaI that the ratio of oxo8dG/10(5 )deoxyguanosine (dG) in nDNA isolated from mouse tissues ranged from 0.032 +/- 0.002 for liver to 0.015 +/- 0.003 for brain. We observed a significant increase (10-fold) in oxo8dG in nDNA isolated from liver tissue after 2 Gy of gamma-irradiation when NaI was used to isolate DNA. The turnover of oxo8dG in nDNA was rapid, e.g. disappearance of oxo8dG in the mouse liver in vivo after gamma-irradiation had a half-life of 11 min. The levels of oxo8dG in mitochondrial DNA isolated from liver, heart and brain were 6-, 16- and 23-fold higher than nDNA from these tissues. Thus, our results showed that the steady-state levels of oxo8dG in mouse tissues range from 180 to 360 lesions in the nuclear genome and from one to two lesions in 100 mitochondrial genomes.

Rho proteins play a critical role in cell migration during the early phase of mucosal restitution

In the intestine, several growth factors stimulate migration of epithelial cells, contributing to the maintenance of tissue integrity. The Ras-like GTPase Rho regulates a signal transduction pathway linking growth factor receptors to the formation of actin stress fibers and focal adhesions, presumed to be important for motility. Using an in vitro wound-induced migration assay, we have examined the role of Rho GTPases in the migration of IEC-6 and Caco-2 cells, and provide evidence that the Rho GTPases play an essential role in the initial phase of mucosal wound healing. Treatment of the cells with Clostridium difficile toxins A and B, inhibitors of the Rho family GTPases inhibited migration in a dose-dependent fashion. Microinjection of the inhibitory exchange factor Rho-guanine nucleotide dissociation inhibitor (GDI), or Clostridium botulinum C3 ADP-ribosyl transferase (C3) toxin, a Rho-ADP-ribosylating exoenzyme, potently inhibited migration. Microinjection of RhoT19N, a dominant negative form of RhoA, or in vitro ADP-ribosylated RhoA impaired the ability of cells to migrate. Rho-GDI and C3 exoenzyme also inhibited EGF-induced migration of IEC-6 cells. These results demonstrate that Rho is required for endogenous and EGF-induced migration of small intestinal crypt cells, and that Rho proteins are essential elements of a mechanism by which growth factors induce cell migration to restitute mucosal integrity.

Occurrence and progression of dementia in a community population aged 75 years and older: relationship of antihypertensive medication use

OBJECTIVE

To examine whether antihypertensive medication use can affect the occurrence and progression of dementia.

SUBJECTS AND METHODS

In a community cohort of 1810 persons aged 75 years and older, 225 prevalent cases of dementia were detected. Among the 1301 persons without dementia, 224 incident cases of dementia were identified during an average period of 3 years. Among the 225 prevalent cases of dementia, 79 were suitable for the analysis of cognitive decline. Information on drug use was collected for the 2 weeks preceding the baseline interview.

RESULTS

Subjects taking antihypertensive medication (n = 651, 83.9% of whom took diuretics) had a lower prevalence of dementia than those not taking antihypertensive medication (P<.001). Subjects without dementia who were taking antihypertensive medication at baseline (n = 584) had a reduced incidence of dementia (adjusted relative risk, 0.7; 95% confidence interval, 0.6-1.0; P = .03). Furthermore, subjects taking diuretics (n = 484) had an adjusted relative risk of 0.7 (95% confidence interval, 0.5-1.0; P = .02) for all dementia, and subjects taking diuretic monotherapy (n = 345) had an adjusted relative risk of 0.6 (95% confidence interval, 0.4-0.9; P = .006). The use of other antihypertensive medication (calcium antagonists or beta-blockers), however, was related to a reduced risk of Alzheimer disease (adjusted relative risk, 0.6; 95% confidence interval, 0.3-1.2) only in the subpopulation with a higher baseline blood pressure (n = 458). Patients with dementia at baseline who were not taking diuretics had a 2-fold faster rate of decline in the score on the Mini-Mental State Examination than those taking diuretics.

CONCLUSION

The use of diuretics may protect against dementia in elderly persons.

Exploring the folding free energy surface of a three-helix bundle protein

The multidimensional free energy surface for a small fast folding helical protein is explored based on first-principle calculations. The model represents the 46-residue segment from fragment B of staphylococcal protein A. The relationship between collapse and tertiary structure formation, and the order of collapse and secondary structure formation, are investigated. We find that the initial collapse process gives rise to a transition state with about 30% of the native tertiary structure and 50-70% of the native helix content. We also observe two distinct distributions of native helix in this collapsed state (Rg approximately 12 A), one with about 20% of the native helical hydrogen bonds, the other with near 70%. The former corresponds to a local minimum. The barrier from this metastable state to the native state is about 2 kBT. In the latter case, folding is essentially a downhill process involving topological assembly. In addition, the order of formation of secondary structure among the three helices is examined. We observe cooperative formation of the secondary structure in helix I and helix II. Secondary structure in helix III starts to form following the formation of certain secondary structure in both helix I and helix II. Comparisons of our results with those from theory and experiment are made.