Identification of potent and selective inhibitors of PKR via virtual screening and traditional design

Protein Kinase RNA-activated (PKR) inhibition is thought to be relevant for immunology due to the potential to reduce macrophage and dendritic cell responses to bacteria and its signaling downstream of TNFα. PKR is also associated with neuroscience indications such as Alzheimer's disease due to its activation by the double stranded DNA (dsDNA) virus HSV1, a virus suggested to be important in the development of AD. Studies exploring the mechanistic role of PKR with existing tool molecules such as the tricyclic oxindole C16 are clouded by the poor selectivity profile of this ATP-competitive, Type I kinase inhibitor. Type II kinase leads such as the benzothiophene or pyrazolopyrimidine scaffolds from literature are equally poor in their selectivity profiles. As such, it became necessary to identify more potent and selective chemical matter to better understand PKR biology. A dual approach was taken. The first step of the strategy included virtual screening of the AbbVie compound collection. A combination of pharmacophore-based and GPU shape-based screening was pursued to identify selective chemical matter from promiscuous leads. The second step of the strategy followed traditional compound design. This step initiated from a literature lead with PKR cross reactivity. Combined, the two parallel efforts led to identification of more selective leads for investigation of PKR biology.

Examining change in social support and fruit and vegetable consumption in African American adults

OBJECTIVE

To examine (a) inter-individual variation in African Americans' fruit and vegetable social support, behavior, and consumption trajectories by estimating latent growth curves (LGCs) and (b) the associations between these trajectories over time.

DESIGN

As part of a larger intervention study, data were collected from mid-life and older African Americans yearly for three years. The study incorporated a quasi-experimental design with random selection of participants, stratifying for age and gender.

SETTING

Six churches in North Florida.

PARTICIPANTS

Two hundred and thirty one (73% women; median age range of 57-63) older African Americans.

MEASUREMENTS

A structured questionnaire elicited personal data as well as information on dietary social support, eating-related behaviors, and fruit and vegetable dietary intake.

RESULTS

Age was positively associated with initial social support but negatively associated with the rate of change in social support. More important, the rate of change in dietary social support predicted eating-related behavior trajectories, which influenced the rate of change in fruit and vegetable consumption over time after controlling for the intervention.

CONCLUSION

These findings illustrate the mediating role of eating-related behaviors and the inter-locking nature of social support, behavior and consumption trajectories. This research has implications for future research as well as community interventions and programs.

Life dissatisfaction and eating behaviors among older African Americans: the protective role of social support

OBJECTIVES

To examine (a) the influences of life dissatisfaction and dietary social support on eating behaviors (a high-fat diet and fruit/vegetable consumption) of older African Americans and (b) the moderating role of perceived dietary social support on the association between their life dissatisfaction and unhealthy eating behaviors.

DESIGN

Baseline data from a larger intervention study of mid-life and older African Americans. The study incorporated a quasi-experimental design with random selection of participants, stratifying for age and gender.

SETTING

Six churches in North Florida.

PARTICIPANTS

One hundred and seventy-eight (132 females and 46 males with a median age of 60) older African Americans.

MEASUREMENTS

A structured questionnaire elicited personal data as well as information on eating behaviors, life dissatisfaction, and perceived dietary social support.

RESULTS

Older African Americans with more cumulative life adversity, as reflected by high life dissatisfaction, had significantly poorer eating behaviors including the consumption of a high-fat diet and low intake of fruits and vegetables. Older African Americans' dietary choices were also associated with their perceived social support. More importantly, perceived social support acted as a buffer to mitigate the influence of life dissatisfaction on older African Americans' eating behaviors.

CONCLUSION

Life dissatisfaction places older African Americans at risk for unhealthy eating behaviors. However, high levels of dietary social support can protect older African Americans from the influence of life dissatisfaction on unhealthy eating behaviors. There are practical implications of this research for health interventions and programming.

Web-based self-management for patients with multiple sclerosis: a practical, randomized trial

OBJECTIVE

No studies have addressed the use of electronic personal health records (e-PHRs) for self-management in complex neurological disorders. We assessed and tested an Internet-based self-management system that utilized the e-PHR and determined its impact on self-assessed well-being, clinician-assessed well-being, and healthcare utilization in patients with multiple sclerosis (MS).

MATERIALS AND METHODS

Subjects were randomized to usual care (a secure Web-based messaging system) or active intervention, which included secure messaging, self-monitoring, self-management of MS symptoms, and communication about upcoming clinic visits. Computers and Internet access were provided. Subjects were included if they had MS, lived within the county or region surrounding our MS center, had at least two appointments at our center in the previous 12 months, and demonstrated basic typing and computer skills. Study duration was 12 months.

RESULTS

Of 220 subjects completing informed consent, 206 met the inclusion criteria. At the study's end, 83 subjects remained in the usual care group and 84 in the enhanced care group. Both groups used the available system components. The groups did not significantly differ on the primary endpoints or healthcare utilization.

CONCLUSIONS

Self-management support is an emerging aspect of chronic care management. We established the feasibility of conducting a randomized, controlled trial using e-PHRs for patient self-management. We did not find that e-PHR-enabled self-management augmented multidisciplinary MS center-based care, possibly because the differences between interventions were not great enough.

Satisfaction with web-based training in an integrated healthcare delivery network: do age, education, computer skills and attitudes matter?

BACKGROUND

Healthcare institutions spend enormous time and effort to train their workforce. Web-based training can potentially streamline this process. However the deployment of web-based training in a large-scale setting with a diverse healthcare workforce has not been evaluated. The aim of this study was to evaluate the satisfaction of healthcare professionals with web-based training and to determine the predictors of such satisfaction including age, education status and computer proficiency.

METHODS

Observational, cross-sectional survey of healthcare professionals from six hospital systems in an integrated delivery network. We measured overall satisfaction to web-based training and response to survey items measuring Website Usability, Course Usefulness, Instructional Design Effectiveness, Computer Proficiency and Self-learning Attitude.

RESULTS

A total of 17,891 healthcare professionals completed the web-based training on HIPAA Privacy Rule; and of these, 13,537 completed the survey (response rate 75.6%). Overall course satisfaction was good (median, 4; scale, 1 to 5) with more than 75% of the respondents satisfied with the training (rating 4 or 5) and 65% preferring web-based training over traditional instructor-led training (rating 4 or 5). Multivariable ordinal regression revealed 3 key predictors of satisfaction with web-based training: Instructional Design Effectiveness, Website Usability and Course Usefulness. Demographic predictors such as gender, age and education did not have an effect on satisfaction.

CONCLUSION

The study shows that web-based training when tailored to learners' background, is perceived as a satisfactory mode of learning by an interdisciplinary group of healthcare professionals, irrespective of age, education level or prior computer experience. Future studies should aim to measure the long-term outcomes of web-based training.

Bone conduction auditory brainstem responses in infants

The contribution of air conduction auditory brainstem response (AC-ABR) testing in the paediatric population is widely accepted in clinical audiology. However, this does not allow for differentiation between conductive and sensorineural hearing loss. The purpose ofthis paper is to review the role of bone conduction auditory brainstem responses (BC-ABR). It is argued that despite such technical difficulties as a narrow dynamic range, masking dilemmas, stimulus artifact and low frequency underestimation of hearing loss, considerable evidence exists to suggest that BC-ABR testing provides an important contribution in the accurate assessmentof hearing loss in infants. Modification of the BC-ABR protocol is discussed and the technical difficulties that may arise are addressed, permitting BC-ABR to be used as a tool in the differential diagnosis between conductive and sensorineural hearing. Two relevant case studies are presented to highlight the growing importance of appropriate management in early identification of hearing loss. It can be concluded that BC-ABR should be adopted as a routine clinical diagnostic tool.

Sildenafil (Viagra) corrects DeltaF508-CFTR location in nasal epithelial cells from patients with cystic fibrosis

BACKGROUND

Most patients with cystic fibrosis (CF) have a DeltaF508 mutation resulting in abnormal retention of mutant gene protein (DeltaF508-CFTR) within the cell. This study was undertaken to investigate DeltaF508-CFTR trafficking in native cells from patients with CF with the aim of discovering pharmacological agents that can move DeltaF508-CFTR to its correct location in the apical cell membrane.

METHOD

Nasal epithelial cells were obtained by brushing from individuals with CF. CFTR location was determined using immunofluorescence and confocal imaging in untreated cells and cells treated with sildenafil. The effect of sildenafil treatment on CFTR chloride transport function was measured in CF15 cells using an iodide efflux assay.

RESULTS

In most untreated CF cells DeltaF508-CFTR was mislocalised within the cell at a site close to the nucleus. Exposure of cells to sildenafil (2 hours at 37 degrees C) resulted in recruitment of DeltaF508-CFTR to the apical membrane and the appearance of chloride transport activity. Sildenafil also increased DeltaF508-CFTR trafficking in cells from individuals with CF with a single copy DeltaF508 (DeltaF508/4016ins) or with a newly described CF trafficking mutation (R1283M).

CONCLUSIONS

The findings provide proof of principle for sildenafil as a DeltaF508-CFTR trafficking drug and give encouragement for future testing of sildenafil and related PDE5 inhibitors in patients with CF.

A model of neuronopathic Gaucher disease

Gaucher disease (GD) is a lysosomal disorder involving the accumulation of glucocerebroside in the liver, spleen, bones and brain. Some patients exhibit only systemic disease (type I), but others have additional neurological signs which may lead to rapid neurodegeneration in infancy (type II) or take a more intermediate course (type III). Types II and III are collectively known as neuronopathic Gaucher disease (NGD). Systemic disease can now be treated by enzyme replacement therapy (ERT), but its efficacy in NGD is limited. Two infants who presented with bulbar palsy and failure to thrive were enzymatically diagnosed at 8 months with NGD. They were started on high-dose ERT (120 IU/kg every 2 weeks). Both underwent serial oculomotor assessment and an audiological battery, including visual reinforcement audiometry, otoacoustic emissions, and the auditory brain stem response (ABR). Biochemical markers showed an incomplete systemic response to ERT, but neurological deterioration was relentless, leading to death at 16 and 25 months. Oculomotor testing revealed a complete absence of saccadic eye movements and progressive bilateral sixth nerve palsy in one. Audiological assessment revealed progressive deterioration of ABRs, but with normal peripheral hearing and otoacoustic emissions. Both infants showed neurological deterioration in spite of high-dose ERT. The audiological findings suggested a loss of inner hair cell pathway function with preserved outer hair function, similar to what is seen in auditory neuropathy. The unusual pattern of audiological and oculomotor abnormalities is consistent with an excitotoxic mechanism predisposing nerve cells to glucocerebroside toxicity. Such excitotoxic damage may be amenable to direct therapeutic intervention.

Familial vestibulocerebellar disorder maps to chromosome 13q31-q33: a new nystagmus locus

PURPOSE

To determine a gene locus for a family with a dominantly inherited vestibulocerebellar disorder characterised by early onset, but not congenital nystagmus.

DESIGN

Observational and experimental study.

METHODS

We carried out a phenotypic study of a unique four generation family with nystagmus. We performed genetic linkage studies including a genome wide search.

RESULTS

Affected family members developed vestibulocerebellar type nystagmus in the first two years of life. A higher incidence of strabismus was noted in affected members. Haplotype construction and analysis of recombination events linked the disorder to a locus (NYS4) on chromosome 13q31-q33 with a lod score of 6.322 at theta=0 for D13S159 and narrowed the region to a 13.8 cM region between markers D13S1300 and D13S158.

CONCLUSIONS

This study suggests that the early onset acquired nystagmus seen in this family is caused by a single gene defect. Identification of the gene may hold the key to understanding pathways for early eye stabilisation and strabismus.

Comparison of the main sequence of reflexive saccades and the quick phases of optokinetic nystagmus

BACKGROUND/AIMS

Abnormalities in the saccadic main sequence are an important finding and may indicate pathology of the ocular motor periphery or central neurological disorders. In young or uncooperative patients it can be difficult eliciting a sufficient number of saccades to measure the main sequence. It is often assumed that the quick phases of optokinetic nystagmus (OKN) are identical to saccades. If this were the case, it would be feasible to use OKN, an involuntary response that is easily evoked, as a simple way of eliciting many saccades. The aim of this study was to determine whether reflexive saccades and the quick phases of OKN are indeed identical, and whether OKN quick phases could have a clinical role in identifying patients with slow saccades.

METHODS

OKN and reflexive saccades were recorded from 10 healthy adults using an infrared limbus eye tracker and bitemporal DC electro-oculography simultaneously. OKN was stimulated by rotating a full field patterned curtain around the subject at 10-50 degrees /s. Reflexive saccades were elicited to red LED targets at 5-20 degrees eccentricity.

RESULTS

OKN quick phases tended to have a longer duration compared to saccades, but these differences were not significant. OKN quick phases had a slightly lower peak velocity compared to saccades, which was statistically significant (p<0.05).

CONCLUSION

The main sequence for duration is the same for reflexive saccades and OKN quick phases. The main sequence for peak velocity is slightly faster for reflexive saccades than OKN quick phases, but the difference is unlikely to be of clinical significance. As an illustration of the potential of this technique, the authors demonstrate that OKN quick phases show similar slowness to saccades in a child with brainstem pathology caused by Gaucher disease type III. It is concluded that recording OKN may be a simple clinical means for approximating the main sequence.

Identification and role of ionizing functional groups at the active center of Rhodotorula gracilis D-amino acid oxidase

D-Amino acid oxidase (DAAO) is a flavoprotein oxidase that catalyzes the oxidation of amino acids and produces ketoacids and H(2)O(2). The rate of product release from reduced DAAO from Rhodotorula gracilis is pH dependent and reflects a pK(a) of approximately 9.3. Binding of benzoate and 3,3,3-trifluoro-D-alanine to wild-type and Y238F-DAAO is also pH dependent (pK(a)=9.8+/-0.1 and 9.05+/-0.1, respectively for benzoate binding). However, binding of benzoate to Y223F-DAAO is pH independent, indicating the pK(a) is due to Y223-OH. This latter residue is thus involved in substrate binding, and probably is the group that governs product release. In contrast to this, the second active site tyrosine, Y238, has little influence on ligand binding.

pH and kinetic isotope effects in d-amino acid oxidase catalysis

The effects of pH, solvent isotope, and primary isotope replacement on substrate dehydrogenation by Rhodotorula gracilis d-amino acid oxidase were investigated. The rate constant for enzyme-FAD reduction by d-alanine increases approximately fourfold with pH, reflecting apparent pKa values of approximately 6 and approximately 8, and reaches plateaus at high and low pH. Such profiles are observed in all presteady-state and steady-state kinetic experiments, using both d-alanine and d-asparagine as substrates, and are inconsistent with the operation of a base essential to catalysis. A solvent deuterium isotope effect of 3.1 +/- 1.1 is observed on the reaction with d-alanine at pH 6; it decreases to 1.2 +/- 0.2 at pH 10. The primary substrate isotope effect on the reduction rate with [2-D]d-alanine is 9.1 +/- 1.5 at low and 2.3 +/- 0.3 at high pH. At pH 6.0, the solvent isotope effect is 2.9 +/- 0.8 with [2-D]d-alanine, and the primary isotope effect is 8.4 +/- 2.4 in D2O. Thus, primary and solvent kinetic isotope effects (KIEs) are independent of the presence of the other isotope, i.e. the 'double' kinetic isotope effect is the product of the individual KIEs, consistent with a transition state in which rupture of the two bonds of the substrate to hydrogen is concerted. These results support a hydride transfer mechanism for the dehydrogenation reaction in d-amino acid oxidase and argue against the occurrence of any intermediates in the process. A pKa,app of approximately 8 is interpreted to arise from the microscopic ionization of the substrate amino acid alpha-amino group, but also includes contributions from kinetic parameters.

Interchain cross-linking of DNA mediated by the principal adduct of acrolein

A DNA duplex containing the primary acrolein adduct, 3-(2-deoxy-beta-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a]purin-10(3H)-one (2), of deoxyguanosine in a 5'-CpG sequence context spontaneously but reversibly formed an interchain cross-link with the exocyclic amino group of deoxyguanosine in the opposing chain. The linkage was sufficiently stable that the cross-linked duplex could be isolated by HPLC and characterized by MALDI-TOF mass spectrometry. Enzymatic degradation gave bis-nucleoside 6, which was independently prepared by direct reaction of 2 with dGuo.

Stereospecific synthesis of oligonucleotides containing crotonaldehyde adducts of deoxyguanosine

Crotonaldehyde reacts with DNA to form two diastereomeric 1,N(2) cyclic adducts of deoxyguanosine. A synthesis of the two diastereomeric deoxynucleosides has been achieved by reaction of mixed diastereomers of 4-amino-1,2-pentanediol with 2-fluoro-O(6)-(trimethylsilylethyl)-deoxyinosine. The resulting N(2)-(1-methyl-3,4-dihydroxybutyl)-deoxyguanosine was treated with NaIO(4), cleaving the vicinal diol to the aldehyde. Spontaneous cyclization gave the two diastereomers of the crotonaldehyde-adducted nucleoside that were readily separated by HPLC. The absolute configurations were assigned by an enantiospecific synthesis of one diastereomer from (S)-3-aminobutanoic acid. The synthetic strategy has been extended to preparation of a site-specifically adducted oligonucleotide by reaction of the mixed diastereomers of 4-amino-1,2-pentanediol with an 8-mer oligonucleotide containing 2-fluoro-O(6)-(trimethylsilylethyl)-deoxyinosine. The diastereomeric oligonucleotides were separated by HPLC and absolute configurations of the adducts were established by enzymatic digestion to the adducted nucleosides.

Synthesis and characterization of nucleosides and oligonucleotides with a benzo[a]pyren-6-ylmethyl adduct at adenine N6 or guanine N2

Benzo[a]pyrene (1) can be converted to reactive electrophilic species by a number of metabolic pathways, of which the route to the mutagenic and carcinogenic diol epoxide(s) is the best studied. An alternative and interesting pathway to a highly genotoxic electrophile is through alkylation at the 6 position to 6-methylbenzo[a]pyrene (2) followed by oxidation of the methyl group to give 6-hydroxymethylbenzo[a]pyrene (3). Esterification of 3, especially to sulfate ester 4, gives compounds which are both mutagenic and carcinogenic. The major DNA adduct identified from exposure of rats and mice to 4 is the guanine N(2) adduct [2'-deoxy-N(2)-(benzo[a]pyren-6-ylmethyl)guanosine, 5] which is also formed via activation of 2 to a radical cation species by horseradish peroxidase/H(2)O(2) or iodine. To study the biological and structural properties of this adduct and the analogous adenine N(6) adduct (6), a nonbiomimetic synthesis of the adducted nucleosides 5 and 6 has been developed and has been extended to preparation of oligonucleotides containing 5 or 6 at a single site.

The nonmutagenic (R)- and (S)-beta-(N(6)-adenyl)styrene oxide adducts are oriented in the major groove and show little perturbation to DNA structure

Conformations of (R)-beta-(N(6)-adenyl)styrene oxide and (S)-beta-(N(6)-adenyl)styrene oxide adducts at position X(6) in d(CGGACXAGAAG).d(CTTCTTGTCCG), incorporating codons 60, 61 (underlined), and 62 of the human N-ras protooncogene, were refined from (1)H NMR data. These were designated as the beta-R(61,2) and beta-S(61,2) adducts. A total of 533 distance restraints and 162 dihedral restraints were used for the molecular dynamics calculations of the beta-S(61,2) adduct, while 518 distances and 163 dihedrals were used for the beta-R(61,2) adduct. The increased tether length of the beta-adducts results in two significant changes in adduct structure as compared to the corresponding alpha-styrenyl adducts [Stone, M. P., and Feng, B. (1996) Magn. Reson. Chem. 34, S105-S114]. First, it reduces the distortion introduced into the DNA duplex. For both the beta-R(61,2) and beta-S(61,2) adducts, the styrenyl moiety was positioned in the major groove of the duplex with little steric hindrance. Second, it mutes the influence of stereochemistry at the alpha-carbon such that both the beta-R(61,2) and beta-S(61,2) adducts exhibit similar conformations. The results were correlated with site-specific mutagenesis experiments that revealed the beta-R(61,2) and beta-S(61,2) adducts were not mutagenic and did not block polymerase bypass.

Intercalation of the (1R,2S,3R,4S)-N6-[1-(1,2,3,4-tetrahydro-2,3,4-trihydroxybenz[a]anthracenyl)]-2'-deoxyadenosyl adduct in the N-ras codon 61 sequence: DNA sequence effects

The structure of the bay region (1R,2S,3R,4S)-N6-[1-(1,2,3,4-tetrahydro-2,3,4-trihydroxybenz[a]anthracenyl)]-2'-deoxyadenosyl adduct at X(7) of 5'-d(CGGACAXGAAG)-3'.5'-d(CTTCTTGTCCG)-3', incorporating codons 60, 61 (underlined), and 62 of the human N-ras protooncogene, was determined by NMR. This was the bay region benz[a]anthracene RSRS (61,3) adduct. The BA moiety intercalated above the 5'-face of the modified base pair. NOE connectivities between imino protons were disrupted at T16 and T17. Large chemical shifts at the lesion site were consistent with ring current shielding arising from the BA moiety. A large chemical shift dispersion was observed for the BA aromatic protons. An increased rise of 8.17 A was observed between base pairs A6 x T17 and X7 x T(16). The PAH moiety stacked with the purine ring of A6, the 5'-neighbor nucleotide. This resulted in buckling of the 5'-neighbor A6 x T17 base pair, evidenced by exchange broadening for the T17 imino resonance. It also interrupted sequential NOE connectivities between nucleotides C5 and A6. The A6 deoxyribose ring showed an increased percentage of the C3'-endo conformation. This differed from the bay region BA RSRS (61,2) adduct, in which the lesion was located at position X6 [Li, Z., Mao, H., Kim, H.-Y., Tamura, P. J., Harris, C. M., Harris, T. M., and Stone, M. P. (1999) Biochemistry 38, 2969-2981], but was similar to the benzo[a]pyrene BP SRSR (61,3) adduct [Zegar I. S., Chary, P., Jabil, R. J., Tamura, P. J., Johansen, T. N., Lloyd, R. S., Harris, C. M., Harris, T. M., and Stone, M. P. (1998) Biochemistry 37, 16516-16528]. The altered sugar pseudorotation at A6 appears to be common to both bay region BA RSRS (61,3) and BP SRSR (61,3) adducts. It could not be discerned if the C3'-endo conformation at A6 in the BA RSRS (61,3) adduct altered base pairing geometry at X7 x T16, as compared to the C2'-endo conformation. The structural studies suggest that the mutational spectrum of this adduct may be more complex than that of the BA RSRS (61,2) adduct.

Synthesis and characterization of oligodeoxynucleotides containing an N1 beta-hydroxyalkyl adduct of 2'-deoxyinosine

Hydroxyethyl adducts arising by the reactions of simple epoxides at the N1 position of adenine nucleosides can deaminate to give the inosine analogues which, if formed in DNA, are suspected of being highly mutagenic. A method has been developed for synthesis of oligonucleotides containing N1-adducted 2'-deoxyinosines. The 2'-deoxyinosine adduct of 3,4-epoxy-1-butene was prepared from (+/-)-4-acetoxy-3-bromo-1-butene and tetraisopropyldisiloxanediyl-protected 2'-deoxyinosine with base. The 2'-deoxyinosine derivative was then incorporated into the oligodeoxynucleotide sequence 5'-d(CGGACXAGAAG)-3' (X = N1-(1-hydroxy-3-buten-2-yl)-2'-deoxyinosine).

Synthesis and characterization of nucleosides and oligonucleotides bearing adducts of butadiene epoxides on adenine n(6) and guanine n(2)

Butadiene is a major industrial chemical whose genotoxic effects are attributed to the reaction of its oxidized metabolites, butadiene monoepoxide (BDO) and butadiene diepoxide (BDO2), with DNA. Nucleosides and oligonucleotides containing regio- and stereochemically specific adducts of BDO and the BDO2-related compound, butene 3,4-diol 1,2-epoxide (BDE), on guanine [(2R)- and (2S)-N(2)-(1-hydroxy-3-buten-2-yl) and (2R,3R)- and (2S,3S)-N(2)-(2,3,4-trihydroxybut-1-yl), respectively] and on adenine [(2R)- and (2S)-N(6)-(1-hydroxy-3-buten-2-yl) and (2R,3R)- and (2S,3S)-N(6)-(2,3,4-trihydroxybut-1-yl), respectively] have been prepared by nonbiomimetic routes. For guanine adducts, 2-fluoro-O(6)-(trimethylsilylethyl)-2'-deoxyinosine was treated with (2R)- and (2S)-2-amino-3-buten-1-ol to give the BDO adducts and with (2R,3R)- and (2S,3S)-1-amino-2,3,4-butanetriol to produce the BDE adducts; the adducted oligonucleotides were prepared from 11-mer oligonucleotides containing the halopurine. Adenine adducts were prepared in a similar fashion using 6-chloropurine 2'-deoxyriboside as the reactive purine component.

Spontaneous reversal of nystagmus in the dark

AIM

To report five children with horizontal jerk nystagmus in whom eye movement recordings in the dark revealed a spontaneous reversal in the direction of the nystagmus beat. Three patients were blind in one eye and were diagnosed as having a manifest latent nystagmus (MLN), and two patients had strabismus and congenital nystagmus (CN).

METHODS

Eye movements were recorded using DC electro-oculography with simultaneous video recording, including infrared recording in total darkness.

RESULTS

Four patients had decelerating velocity slow phase jerk nystagmus when recorded under natural lighting conditions; the fifth case had accelerating velocity and linear slow phase jerk nystagmus. Under absolute darkness, nystagmus reversed in direction of beat with a mixture of linear and decelerating velocity slow phase waveforms. One child with unilateral anophthalmos could wilfully reverse the beat direction of his nystagmus by trying to look with his blind eye in the light and dark.

CONCLUSIONS

These observations support the theory that LN/MLN beat direction is determined by the "presumed" viewing eye and may be consciously controlled. The spontaneous reversal of beat direction in the dark suggests eye dominance is predetermined. Eye movement recordings identified mixed nystagmus waveforms indicating that CN (accelerating velocity slow phases) and LN/MLN (linear/decelerating velocity slow phases) coexist in these subjects.

Evaluation of the mutagenic potential of the principal DNA adduct of acrolein

Acrolein is produced extensively in the environment by incomplete combustion of organic materials, and it arises endogenously in humans as a metabolic by-product. Acrolein reacts with DNA at guanine residues to form the exocyclic adduct, 8-hydroxypropanodeoxyguanosine (HOPdG). Acrolein is mutagenic, and a correlation exists between HOPdG levels in Salmonella typhimurium treated with acrolein and a resultant increase in mutation frequency. Site-specifically modified oligonucleotides were used to explore the mutagenic potential of HOPdG in Escherichia coli strains that were either wild-type for repair or deficient in nucleotide excision repair or base excision repair. Oligonucleotides modified with HOPdG were inserted into double-stranded bacteriophage vectors using the gapped-duplex method or into single-stranded bacteriophage vectors and transformed into SOS-induced E. coli strains. Progeny phage were analyzed by oligonucleotide hybridization to establish the mutation frequency and the spectrum of mutations produced by HOPdG. The correct base, dCMP, was incorporated opposite HOPdG in all circumstances tested. In contrast, in vitro lesion bypass studies showed that HOPdG causes misincorporation opposite the modified base and is a block to replication. The combination of these studies showed that HOPdG is not miscoding in vivo at the level of sensitivity of these site-specific mutagenesis assays.

Structural studies of an oligodeoxynucleotide containing a trimethylene interstrand cross-link in a 5'-(CpG) motif: model of a malondialdehyde cross-link

Malondialdehyde (MDA), a known mutagen and suspected carcinogen, is a product of lipid peroxidation and byproduct of eicosanoid biosynthesis. MDA can react with DNA to generate potentially mutagenic adducts on adenine, cytosine, and particularly guanine. In addition, repair-dependent frame shift mutations in a GCGCGC region of Salmonella typhimurium hisD3052 have been attributed to formation of interstrand cross-links (Mukai, F. H. and Goldstein, B. D. Science 1976, 191, 868--869). The cross-linked species is unstable and has never been characterized but has been postulated to be a bis-imino linkage between N(2) positions of guanines. An analogous linkage has now been investigated as a stable surrogate using the self-complementary oligodeoxynucleotide sequence 5'-d(AGGCG*CCT)(2,) in which G* represents guanines linked via a trimethylene chain between N(2) positions. The solution structure, obtained by NMR spectroscopy and molecular dynamics using a simulated annealing protocol, revealed the cross-link only minimally distorts duplex structure in the region of the cross-link. The tether is accommodated by partially unwinding the duplex at the lesion site to produce a bulge and tipping the guanine residues; the two guanines and the tether attain a nearly planar conformation. This distortion did not result in significant bending of the DNA, a result which was confirmed by gel electrophoresis studies of multimers of a 21-mer duplex containing the cross-link.

Point mutations induced by 1,2-epoxy-3-butene N1 deoxyinosine adducts

The National Toxicology Program has recently classified 1,3-butadiene (BD) as a human carcinogen. BD is metabolized to the intermediates 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB), and 1,2-dihydroxy-3,4-epoxybutane. All three metabolites have been implicated in producing specific types of DNA damage and as genotoxic agents in mice, rat, and human cells. This study has focused on EB-induced N1 deoxyinosine lesions that are formed by deamination of deoxyadenosine following reaction of the epoxide at the N(1) position. The R and S stereoisomers of this lesion were incorporated site-specifically within the context of an 11-mer oligodeoxynucleotide, incorporated into M13mp7L2 single-stranded DNA, and transfected into E. coli. Both stereoisomers modestly reduced plaque-forming ability, indicating that neither lesion presents a base modification that cannot be bypassed. The resulting plaques were assessed for point mutations using differential hybridization and DNA sequence analyses. The overall mutagenic spectrum revealed that the N1 adducts were highly mutagenic (approximately 90% per replication cycle), causing a predominance of A --> G transitions.

Studies of the mechanisms of adduction of 2'-deoxyadenosine with styrene oxide and polycyclic aromatic hydrocarbon dihydrodiol epoxides

The mechanism of adduction of 2'-deoxyadenosine by styrene oxide and polycyclic aromatic hydrocarbon dihydrodiol epoxides has been explored using (15)N(6)-labeled adenine nucleosides. The extent of reaction at N1 versus N(6) was evaluated by (1)H NMR of the N(6) adducts after allowing Dimroth rearrangement to occur. Products arising from attack at N1 followed by Dimroth rearrangement exhibited a small two-bond (1)H-(15)N coupling constant (N1-H2 J approximately 13 Hz); products from direct attack exhibited a much larger one-bond (1)H-(15)N coupling constant (J approximately 90 Hz). In the case of styrene oxide, all of the N(6) beta adduct arose by initial attack at N1, whereas the majority (70-80%) of the N(6) alpha adducts came from direct attack. The styrene oxide reaction was also studied with a self-complementary oligodeoxynucleotide (24-mer) containing nine (15)N(6)-labeled adenine residues. NMR examination of the N(6) alpha- and beta-styrene oxide adducts isolated after enzymatic degradation of the 24-mer gave very similar results, indicating that N1 attack can occur readily even with a duplexed oligonucleotide. With the PAH dihydrodiol epoxides, only naphthalene dihydrodiol epoxide exhibited significant initial reaction at N1 (50%). No detectable rearranged product was seen in reactions with benzo[a]pyrene dihydrodiol epoxide or non-bay or bay region benz[a]anthracene dihydrodiol epoxide; interestingly, a small amount of N1 attack (5-7%) was seen in the case of benzo[c]phenanthrene dihydrodiol epoxide. It appears that initial attack at N1 is only a significant reaction pathway for epoxides attached to a single aromatic ring.

Butadiene-induced intrastrand DNA cross-links: a possible role in deletion mutagenesis

To initiate studies designed to identify the mutagenic spectrum associated with butadiene diepoxide-induced N(2)-N(2) guanine intrastrand cross-links, site specifically adducted oligodeoxynucleotides were synthesized in which the adducted bases were centrally located within the context of the human ras 12 codon. The two stereospecifically modified DNAs and the corresponding unmodified DNA were ligated into a single-stranded M13mp7L2 vector and transfected into Escherichia coli. Both stereoisomeric forms (R, R and S,S) of the DNA cross-links resulted in very severely decreased plaque-forming ability, along with an increased mutagenic frequency for both single base substitutions and deletions compared with unadducted DNAs, with the S,S stereoisomer being the most mutagenic. Consistent with decreased plaque formation, in vitro replication of DNA templates containing the cross-links by the three major E. coli polymerases revealed replication blockage by both stereoisomeric forms of the cross-links. The same DNAs that were used for replication studies were also assembled into duplex DNAs and tested as substrates for the initiation of nucleotide excision repair by the E. coli UvrABC complex. UvrABC incised linear substrates containing these intrastrand cross-links with low efficiency, suggesting that these lesions may be inefficiently repaired by the nucleotide excision repair system.

Abnormal vertical optokinetic nystagmus in infants and children

AIMS

To determine if testing vertical optokinetic nystagmus (VOKN) has a role in the clinical assessment of infants and children.

METHODS

A large field projection system was developed with which optokinetic nystagmus (OKN) could be stimulated in any direction. Gross abnormalities in the response were detected simply by observation.

RESULTS

VOKN was tested in 144 children using this OKN projection system. 26 of these children had abnormal VOKN; 13 had a vertical saccade initiation failure "ocular motor apraxia" (in either direction, up/down, or in both) and 13 had absent VOKN (in either direction, up/down, or in both). Nine of the children with an up and/or down vertical saccade initiation failure (VSIF) had a neurometabolic disease (two had Niemann-Pick disease type C, five had Gaucher disease type III, one had Gaucher disease type II, and one had Gaucher disease type I). Five children with a VSIF had an abnormality identified by a magnetic resonance imaging (MRI) scan of the brain. In two of these children there was a focal lesion of the rostral midbrain. In 11 of the children with absent up and/or down VOKN an MRI scan revealed an abnormality. This involved the brainstem and/or the cerebellum in 10. Absent up and/or down VOKN was found in association with Joubert syndrome, Leigh disease, and cerebral palsy.

CONCLUSION

VOKN testing has a useful role in detecting neurological abnormalities in infants and children. Detection of abnormal VOKN should indicate further investigations for a neurometabolic disease or an abnormality involving the cortex, brainstem, and/or cerebellum. Abnormal VOKN but normal horizontal OKN is highly suggestive of a rostral midbrain lesion.

Synthesis of nucleosides and oligonucleotides containing adducts of acrolein and vinyl chloride

Vinyl chloride and acrolein are important industrial chemicals. Both form DNA adducts, vinyl chloride after enzymatic oxidation to chlorooxirane and acrolein by direct reaction. Reaction at the N(2) position of guanine is a major pathway. The resulting 2-oxoethyl and 3-oxopropyl adducts cyclize spontaneously to hydroxyethano and hydroxypropano derivatives, respectively. The two cyclic adducts have been detected in DNA exposed to these mutagens. A new method has been developed for the synthesis of deoxyguanosine adducts of chlorooxirane and acrolein, as well as oligonucleotides containing these adducts. Reaction of O(6)-[(trimethylsilyl)ethyl]-2-fluoro-2'-deoxyinosine with the appropriate aminodiol followed by oxidative cleavage of the diol with NaIO(4) gave the adducts in excellent yields. Reaction of oligonucleotides containing the halonucleoside with the aminodiols followed by NaIO(4) efficiently created the nucleosides in the oligonucleotides. Deoxyadenosine adducts were created similarly using 6-chloropurine 9-(2'-deoxyriboside).

Sequence- and stereospecific conformational rearrangement of styrene oxide adducts located at A x C mismatched base pairs

The solution structures of R- and S-alpha-(N(6)-adenyl)-styrene oxide adducts mismatched with cytosine at position X(7) in d(CGGACAXGAAG) x d(CTTCCTGTCCG), incorporating codons 60, 61 (underlined), and 62 of the human N-ras protooncogene, were determined. These were the R- and S(61,3)C adducts. The structures for these mismatched adducts differed from the sequence isomeric R- and S(61,2)C adducts [Painter, S. L., Zegar, I. S., Tamura, P. J., Bluhm, S., Harris, C. M., Harris, T. M., and Stone, M. P. (1999) Biochemistry 38, 8635-8646]. The results reveal that the structural consequences of cytosine mispairing opposite the R- and S-alpha-SO adducts differ as a function of DNA sequence. The thermodynamic stability of both the R- and S(61,3)C mismatched adducts was dependent upon pH. At neutral pH, the R- and S(61,3)C adducts exhibited significant structural perturbation and had lower T(m) values, as compared to the R- and S(61,2)C adducts. In both instances, this was attributed to reorientation about the C6-N(6) bond, such that the N(6)H proton faced away from the Watson-Crick face of the purine base and into the major groove. The conformation about the N(6)-C(alpha)-C(beta)-O torsion angle was predicted from rMD calculations to be stabilized by a N/O gauche-type interaction between the styrenyl hydroxyl moiety and adenine N(6) at the lesion site. For the R(61,3)C adduct, the styrenyl moiety remained oriented in the major groove and faced in the 3'-direction. In the properly base-paired R(61,3) adduct, it had faced in the 5' direction. For the S(61,3)C adduct, the styrene ring was inserted into the duplex, approximately perpendicular to the helical axis of the DNA. It faced in the 5'-direction. In the properly base-paired S(61,3) adduct, it had faced in the 3'-direction. The results were correlated with site-specific mutagenesis experiments in vivo. The latter revealed that the R- and S(61,3)-alpha-styrene oxide adducts were nonmutagenic. This may be a consequence of the greater structural perturbation associated with formation of the cytosine mismatch at neutral pH for the R- and S(61,3) adducts as compared to the S(61,2) adduct that exhibited low levels of A --> G mutations.