Discontinuation of potent antiretroviral therapy: predictive value of and impact on CD4 cell counts and HIV RNA levels

OBJECTIVE

To characterize predictors and consequences of discontinuing antiretroviral therapy (ART) in terms of CD4 cell count, HIV RNA, and reported side-effects in a large cohort of HIV-infected women.

DESIGN

Cohort study.

METHODS

A total of 1058 HIV-infected women initiated potent ART before September 1999. For each 6 month period after October 1996 we determined the proportion of potent ART users who downshifted to non-potent ART and who discontinued all ART. We examined the role of CD4 cell count and HIV RNA with regard to ART discontinuation.

RESULTS

Between October 1996 and September 1999, 1058 individuals contributed 3362 visits at which potent ART was reported in the previous 6 months. Overall rates of 6 month downshifting and discontinuation were 10.0% and 6.7%. The proportion of individuals discontinuing all ART increased from 2.9% in late 1996 to 9.1% in mid 1999 (P < 0.001). Individuals with high HIV RNA levels were more likely to discontinue (P < 0.05). Compared to those who continued on potent ART, individuals who discontinued experienced large declines (P < 0.001) in CD4 cell counts and were more than three times more likely (P < 0.001) to experience HIV RNA increases. However, over one-third of those discontinuing ART reported side-effects and this subset had smaller CD4 cell count declines as compared to discontinuers not reporting side-effects (P = 0.147).

CONCLUSIONS

In a large cohort of HIV-infected women, an increasing proportion of potent ART users discontinued ART over 3 years. Higher HIV RNA levels predicted discontinuation. Immediate immunological/virological deleterious consequences were observed. Side-effects were the most common reason for discontinuation and CD4 cell count declines were larger among those who did not cite side-effects as the reason for discontinuation.

Molecular dynamics simulation reveals sequence-intrinsic and protein-induced geometrical features of the OL1 DNA operator

We have carried out molecular dynamics simulation of the lambda OL1 DNA operator on the free and the protein-bound forms. Our results lead us to conclude that the binding of the repressor actually makes the N-7 atom of Gua8' more solvent exposed, thereby enhancing its reactivity to chemical methylation. This increase in solvent accessibility surface area occurs simultaneously with the formation of hydrogen bonds between Lys-4 of the nonconsensus flexible N-terminal arm and Gua6' of the nonconsensus half-site operator DNA. Calculations of protein--DNA interaction energies reveal that among the residues of the arm, Lys-4 contributes the most favorably to the interaction energies. This result is consistent with mutagenesis studies that established that lysine at position 4 is absolutely required for tight binding. We find that the nonconsensus arm and the nonconsensus monomer interacts less favorably with DNA than do their respective counterparts of the consensus monomer. Moreover, the six-residue flexible arm accounts for at least half the total protein--DNA interactions energy. These results are in agreement with previous experimental studies. In accord with the diffuse electron density map observed in crystallographic studies of the nonconsensus flexible arm, we find that our model built for this region is more flexible and exhibits more conformations than its consensus counterpart. The simulation also reveals that DNA bending observed near the outer edge of the operator site is an intrinsic sequence-dependent property. By contrast, the DNA-bending features observed toward the center of the operator are induced by the protein. On the whole, stepwise protein-induced bending is more pronounced in the consensus half-site operator. We also find that the unusually large helical twist (49 degrees ) observed in the protein-bound form near the center of the operator results from the binding of the protein at a base step with some propensity for high twists.

Chronic inflammation with increased human immunodeficiency virus (HIV) RNA expression in the vaginal epithelium of HIV-infected Thai women

Thai residents have a greater risk of heterosexual transmission of human immunodeficiency virus (HIV) than do US residents. To analyze host factors associated with heterosexual transmission, vaginal epithelial biopsies from HIV-seropositive Thai and US women were evaluated for tissue virus load and histologic makeup. In all, 84% of Thai and 14% of US women exhibited a chronic inflammatory T cell infiltrate in the vaginal epithelium. In Thai tissue, the infiltrate was associated with elevated levels of HIV RNA in the epidermis. Uninfected Thai women also had vaginal epithelial inflammation. Inflammation did not correlate with sexually transmitted diseases or HIV disease stage. The higher rates and increased risk of heterosexual transmission in Thailand may be due to chronic inflammation at the site where the virus is transmitted, which leads to the accumulation of activated T cells. Such cells might act as targets for initial viral infection and subsequently as reservoirs that support efficient transmission.

Molecular pathologic analysis enhances the diagnosis and management of Muir-Torre syndrome and gives insight into its underlying molecular pathogenesis

The Muir-Torre syndrome (MTS) is an autosomal dominantly inherited disorder, characterized by visceral malignancies and sebaceous skin lesions. In a subset of MTS families the disease is due to an underlying DNA mismatch-repair defect. We have identified a MTS family whose spectrum of reported neoplasia included adenocarcinomas of numerous gastrointestinal sites, carcinomas of the endometrium, ovary and breast, papillary transitional cell carcinoma of the ureter, a range of cutaneous tumors, as well as keratoacanthomas. All tumors were tested for microsatellite instability and immunohistochemically stained for expression of MLH1 and MSH2 proteins. All tumors were found to be microsatellite unstable and lacking in MSH2 protein expression. The subsequent mutation detection focused on hMSH2, and a germline mutation was identified (CAA-->TAA, Gln-->STOP, codon 337). This mutation was subsequently found in a family member with a single skin lesion only. We propose that the combination of immunohistologic and microsatellite instability analysis can be exploited to screen individuals with characteristic skin lesions even before development of visceral tumors and to direct the subsequent germline mutation search. The profile of microsatellite instability and the genes rendered dysfunctional differed between tumor samples, suggesting that the molecular pathogenesis varied between lesions, despite a common germline mutation.

Dynamic coupling between the SH2 and SH3 domains of c-Src and Hck underlies their inactivation by C-terminal tyrosine phosphorylation

The effect of C-terminal tyrosine phosphorylation on molecular motions in the Src kinases Hck and c-Src is investigated by molecular dynamics simulations. The SH2 and SH3 domains of the inactive kinases are seen to be tightly coupled by the connector between them, impeding activation. Dephosphorylation of the tail reduces the coupling between the SH2 and SH3 domains in the simulations, as does replacement of connector residues with glycine. A mutational analysis of c-Src expressed in Schizosaccharomyces pombe demonstrates that replacement of residues in the SH2-SH3 connector with glycine activates c-Src. The SH2-SH3 connector appears to be an inducible "snap lock" that clamps the SH2 and SH3 domains upon tail phosphorylation, but which allows flexibility when the tail is released.

Human herpesvirus 8 infection and Kaposi's sarcoma among human immunodeficiency virus-infected and -uninfected women

Little is known about the epidemiology of human herpesvirus 8 (HHV-8) infections among women. A cross-sectional study was conducted of HHV-8 infection among human immunodeficiency virus (HIV)-infected and high-risk HIV-uninfected women. Serological tests with noninduced (latent) and induced (lytic) HHV-8 antigens were used to detect infection among 2483 participants of a multisite cohort. Reactivity to latent antigen was present in 4.1% and to induced antigens in 12.0% of women. Seven of 8 women who reported Kaposi's sarcoma had HHV-8 antibodies. Among HIV-positive women, HHV-8 infection was associated with use of crack, cocaine, or heroin (76% vs. 65%; P<.001), past syphilis (29% vs. 20%; P<.001), an injection drug-using male sex partner (61% vs. 53%; P=.014), black race (P=.010), and enrollment site (P=.015). In multivariate analysis, HIV infection, older age, past syphilis, black race, and enrollment site were independently associated with HHV-8 infection. In this cohort of North American women, HHV-8 infection was associated with HIV infection, drug use, and risky sexual behavior.

Blocking chloride channels in the rat lens: localized changes in tissue hydration support the existence of a circulating chloride flux

PURPOSE

To investigate the effects of inhibitors of chloride channels on lens volume and tissue architecture under isotonic conditions.

METHODS

Rat lenses were maintained in organ culture under isotonic conditions in the presence of various putative chloride channel inhibitors. The effect of an inhibitor on lens wet mass and tissue morphology was determined by weighing and histologic examination, respectively.

RESULTS

Exposure to 100 microM of either 5-nitro-2- (3-phenylpropylamino) benzoic acid (NPPB) or 4, 4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) caused an increase in wet mass and severe tissue disruption in the lens equatorial region. Two distinctly different zones of tissue damage were evident: a peripheral zone of fiber cell swelling and an inner zone of extensive tissue breakdown. Extracellular space dilations caused the extensive tissue damage in the inner zone and preceded the peripheral fiber cell swellings. That the observed effects were a consequence of the inhibition of chloride channels was supported by (1) the effectiveness of NPPB at the lower dose of 10 microM, (2) the absence of any NPPB effect in chloride-free medium, and (3) an identical effect after exposure to tamoxifen, an inhibitor of the chloride channel regulator p-glycoprotein.

CONCLUSIONS

Study results indicate that chloride channels are active in the lens under isotonic conditions. The spatial and temporal pattern of morphologic changes that was observed is consistent with a steady state efflux of chloride ions and water from peripheral fiber cells and a corresponding influx into fiber cells deeper in the lens. These observations may therefore represent the first visualization of the chloride flux postulated by others to be a component of the lens internal circulation system.

One nanosecond molecular dynamics simulation of the N-terminal domain of the lambda repressor protein

We have carried out molecular dynamics simulation of the N-terminal domain of the lambda repressor protein in a surrounding environment including explicit waters and ions. We observe two apparent dynamics substates in the nanosecond protein simulation, the transition occurring around 500 ps. The existence of these two apparent substates results from a high flexibility of the arm in each monomer, a relative flexibility of both arms with respect to each other, and a relative displacement of the recognition helices from 30 to 40 A of interhelical distance. Many amino acid residues, including those involved in DNA recognition, undergo a simultaneous transition in their side-chain conformations, consistent with the relationship between side-chain conformation and secondary structural elements, as observed in protein crystal structures. This result suggests plausible conformational changes experienced by the protein upon DNA binding. On the whole, the non-consensus monomer appears to be more flexible than its consensus counterpart.

Molecular dynamics simulation accurately predicts the experimentally-observed distributions of the (C, N, O) protein atoms around water molecules and sodium ions

A molecular dynamics simulation of the operator binding domain of the lambda repressor protein has been carried out. The protein was embedded in explicit waters, Na(+) and CL(-) ions. The Amber 4.1 computer package and the Cornell et al. Force field were used for energy-minimization and molecular dynamics simulation. We find that the atoms distributions in the environment of waters and Na(+) ions are in excellent agreement with those derived from the analysis of water molecules in crystal structures and ion-binding proteins. We also find that, on the whole, both distributions are similar to each other.

Effect of HIV infection on menstrual cycle length

HIV serostatus and menstrual function were examined using prospectively collected menstrual data from 802 HIV-seropositive and 273 HIV-seronegative women, ages 20 to 44, enrolled in two cohort studies of HIV infection in North American women. The associations between HIV serostatus and the probabilities of having a cycle lasting >40 days (n = 541 cycles), >90 days (n = 67 cycles), <18 days (n = 316 cycles) and mean length and variability of 18 to 40 day cycles (n = 3,634) were assessed. After adjustment for demographic characteristics, body mass index, and substance use, seropositivity increased the odds of having a very short cycle (< 18 days, odds ratio [OR], 1.45; 95% confidence interval [CI], 1.00-2.11) and a very long cycle (>90 days, OR, 1.32; 95% CI, 0.68-2.58) slightly, although the latter CIs include one. Seropositivity did not increase the odds of having a moderately long cycle (>40 days, OR, 1.14) or affect mean cycle length or variability (beta, 0.30 +/- 0.20; between-woman standard deviation [SD], 2.2 days [HIV-seronegative] and 1.9 days [HIV-seropositive]; within-woman SD, 3.5 days for both). Although seropositivity may slightly increase the probability of very short cycles, HIV serostatus has little overall effect on amenorrhea, menstrual cycle length, or variability. Among HIV-seropositive women, higher viral loads and lower CD4+ counts were associated with increased cycle variability and polymenorrhea.

The short- and long-term efficacy of empirical esophageal dilation in patients with nonobstructive dysphagia: a prospective, randomized study

OBJECTIVE

The efficacy of empirical esophageal dilation for nonobstructive dysphagia (NOD) is unknown. Our aim was to assess the efficacy and safety of empirical dilation with a large bougie in patients with NOD.

METHODS

Patients with NOD (normal barium swallow, free passage of a 13-mm barium pill, and normal esophagogastroduodenoscopy) were randomized to dilation with either a 50-Fr (Group A) or 26-Fr (Group B) Maloney dilator. Before dilation, the dysphagia (DyspSC) and diet (DietSc) scores were recorded and an esophageal manometry performed. Both scores were reassessed at 1, 3, 7, and 14 days after dilation. Success was defined at day 14 as an improvement in the DietSc of at least 25% from baseline, or a DyspSc of < or =3. Nonresponders were crossed-over to the alternate dilator and restudied.

RESULTS

Twenty-three patients (58.7+/-1.9 yr) were enrolled: 13 in Group A and 10 in Group B. Both groups were matched for age, baseline DyspSc (4.2+/-0.6 vs 3.8+/-0.5), baseline DietSc (13.3+/-1.7 vs 12.0+/-1.9), and manometric findings. A nonspecific motility disorder was seen in 43.4% patients. Group A had an initial response rate significantly greater (84.6%) than Group B (40%) (p = 0.03; odds ratio [OR] = 8.25). The DyspSc and DietSc were better than baseline with both dilators, but only the DietSc improved significantly in patients dilated with the 50-Fr dilator (5.3+/-1.9 vs 12.3+/-1.4; p = 0.004). At 2 yr, 80% of the patients responding to the 50-Fr Maloney had a sustained response.

CONCLUSION

Empirical dilation with a large (50-Fr) bougie is safe, effective, and long-lasting in improving nonobstructive dysphagia.

Molecular dynamics studies of axis bending in d(G5-(GA4T4C)2-C5) and d(G5-(GT4A4C)2-C5): effects of sequence polarity on DNA curvature

Gel retardation studies and other experiments indicate that DNA sequences containing the d(GA4T4C)n motif are curved, whereas those of identical composition but with a reverse sequence polarity, the d(GT4A4C)n motif, are straight. Hydroxyl radical cleavage experiments show that d(GA4T4C)n shows a unique signature, whereas d(GT4A4C)n behaves normally. To explain these results at a molecular level, molecular dynamics (MD) simulations were performed on the DNA duplexes d(G5-(GA4T4C)2-C5) and d(G5-(GT4A4C)2-C5) to 3.0 and 2.5 ns, respectively. The MD simulations are based on the Cornell force field implemented in the AMBER 4.1 modeling package and performed in a neutral solution of anionic DNA with K+, Cl- and Mg2+ at concentrations roughly comparable to a ligase buffer. Long range interactions were treated by the particle mesh Ewald method. Analysis of the results shows that the calculated dynamical structure of d(G5-(GA4T4C)2-C5) exhibits strong gross curvature, consistent with the observed behavior. The most significant locus of curvature in the MD structure is found at the central C15-G16 step, with an average roll angle of 12.8(+/-6.40)deg. The d(G5-(GT4A4C)2-C5) MD structure exhibited significantly less gross curvature. Analysis of results indicates that the reduction in gross curvature in the d(G5-(GT4A4C)2-C5) trajectory originates from the effect of the T10-A11 and T20-A21 steps, which showed average roll angles of 12.5(+/-5)deg. These three steps, T10-A11, C15-G16 and T20-A21, are half-helix turns away from one another, and their contributions to concerted bending cancel out. The A-tracts in the MD structure are essentially straight. The dynamical structure of d(G5-(GA4T4C)2-C5) exhibited minor groove deformation comprised of expansion at the 5' end of A-tracts and progressive narrowing towards the 3' end, consistent with and elaborating the interpretation of hydroxyl radical chemical probing results.

Limited access to a dietary fat option affects ingestive behavior but not body composition in male rats

Restricting access to high-fat foods is a common strategy utilized to promote health. This strategy may contribute to episodes of overconsumption, however, when the restricted foods subsequently become available. The present study utilized a rat feeding procedure to determine if restricting access to an optional source of dietary fat would increase later consumption of that food under nonenergy-deprived conditions. Five groups of male Sprague-Dawley rats were used, all of which had continuous access to a standard rodent diet and water. The control group had no access to shortening. The low-restriction group had 2-h access to shortening every day. The high-restriction group had 2-h access to shortening on Monday, Wednesday, and Friday. Two additional groups were switched between the high and low conditions. Two-hour and 24-h food intakes were measured every day for 6 weeks. At the end of the study rats were sacrificed and carcass composition determined. As access to the shortening decreased, consumption during the 2-h access period increased. Rats compensated for the increased shortening consumption by decreasing intake of the standard diet. Thus, cumulative energy consumption did not differ among the groups. When switched between the high and low conditions, rats rapidly adjusted to the change in shortening availability. There were no effects of access schedule on carcass composition. These results indicate that restricting access to an optional high-fat food, even under nonenergy-deprived conditions, can promote significant increases in the consumption of that food when it subsequently becomes available.

Respiratory complications of gastrointestinal diseases

Further advances in the ability to diagnose GER disease by use of ambulatory pH monitoring have unveiled a host of extraesophageal manifestations of GERD. These include pulmonary symptoms of asthma, recurrent pneumonia, cough or bronchitis, and infant apnea. Many of these symptoms may be the sole presentations of GER in these patients. It is important that the clinician is aware of these atypical presentations of GERD. The expanding use of ambulatory pH monitoring is helping to clarify the underlying pathophysiology of these disorders as well as to improve the ability to diagnose the atypical manifestations of GERD.

Extended confocal microscopy of myocardial laminae and collagen network

Ventricular myocardium has a complex three-dimensional structure which has previously been inferred from two-dimensional images. We describe a technique for imaging the 3D organization of myocytes in conjunction with the collagen network in extended blocks of myocardium. Rat hearts were fixed with Bouin's solution and perfusion-stained with picrosirius red. Transmural blocks from the left ventricular free wall were embedded in Agar 100 resin and mounted securely in an ultramicrotome chuck. Confocal fluorescence laser scanning microscopy was used to obtain 3D images to a depth of 60 microns in a contiguous mosaic across the surface. Approximately 50 microns was then cut off the surface of the block with an ultramicrotome. This sequence was repeated 20 times. Images were assembled and registered in 3D to form an extended volume 3800 x 800 x 800 microns 3 spanning the heart wall from epicardium to endocardium. Examples are given of how digital reslicing and volume rendering methods can be applied to the resulting dataset to provide quantitative structural information about the 3D organization of myocytes, extracellular collagen matrix and blood vessel network of the heart.

Bright light treatment of winter depression: a placebo-controlled trial

BACKGROUND

Bright light therapy is the recommended treatment for winter seasonal affective disorder (SAD). However, the studies with the best placebo controls have not been able to demonstrate that light treatment has a benefit beyond its placebo effect.

METHODS

Ninety-six patients with SAD completed the study. Patients were randomly assigned to 1 of 3 treatments for 4 weeks, each 1.5 hours per day: morning light (average start time about 6 AM), evening light (average start about 9 PM), or morning placebo (average start about 6 AM). The bright light (approximately 6000 lux) was produced by light boxes, and the placebos were sham negative-ion generators. Depression ratings using the Structured Interview Guide for the Hamilton Depression Rating Scale, SAD version (SIGH-SAD) were performed weekly.

RESULTS

There were no differences among the 3 groups in expectation ratings or mean depression scores after 4 weeks of treatment. However, strict response criteria revealed statistically significant differences; after 3 weeks of treatment morning light produced more of the complete or almost complete remissions than placebo. By 1 criterion (24-item SIGH-SAD score <50% of baseline and < or =8), 61% of the patients responded to morning light, 50% to evening light, and 32% to placebo after 4 weeks of treatment.

CONCLUSIONS

Bright light therapy had a specific antidepressant effect beyond its placebo effect, but it took at least 3 weeks for a significant effect to develop. The benefit of light over placebo was in producing more of the full remissions.

Neurologic complications after coronary artery bypass grafting

Although outcomes from coronary artery bypass grafting (CABG) surgery have improved in general, there has been little or no improvement in the incidence of postoperative stroke or neurologic dysfunction. Several studies have identified factors that increase the CABG patient's risk for developing a stroke and neurologic complications. It is important to identify those patients at increased risk and differentiate among stroke, delirium, and seizures. Post-CABG patients need to be monitored for neurological dysfunction with appropriate assessments. Neurologic complications must be appropriately managed to optimize patient recovery.

Role of REM sleep and dream variables in the prediction of remission from depression

To test the hypothesis that REM sleep and/or dreams contribute to overnight mood regulation, 61 subjects were tested on the Beck Depression Inventory (BDI), and for 3 nights of monitored sleep on two occasions, once close to, and 1 year after, a marital separation. Forty-nine percent of the variance in the follow-up BDI could be accounted for by the initial BDI score, and three sleep and dream variables associated with the mood regulatory hypothesis: eye movement density in the first REM, strength of the affect in the first dream and total number of negative dreams recalled from REM awakenings. Among the 39 who met BDI depression criteria initially, 71.8% could be classified correctly as remitted or not remitted at follow-up by discriminant function analysis based on the presence of negative dreams the first vs. second half of the night. Subjects reporting more negative dreams at the beginning and fewer at the night's end were more likely to be in remission 1 year later than were those with fewer negative dreams at the beginning and more at the end of the night. Early negative dreams may reflect a within-sleep mood regulation process taking place, while those that occur later may indicate a failure in the completion of this process.

Coadministration of acetaminophen and troglitazone: pharmacokinetics and safety

Troglitazone, a PPAR-gamma agonist, enhances the actions of insulin on muscle and liver. It is metabolized predominantly in the liver to a sulfate conjugate and a quinone metabolite. Acetaminophen also undergoes metabolism by conjugation. This three-way crossover study in 12 healthy male volunteers was conducted to investigate the effects of acetaminophen on the metabolism of troglitazone and vice versa. No statistically or clinically relevant differences in area under the concentration-time curve extrapolated to infinity (AUCinfinity) were observed for troglitazone, its quinone metabolite, or acetaminophen. A statistically significant decrease in troglitazone sulfate conjugate during administration with acetaminophen was not clinically relevant. No statistically or clinically relevant differences were observed in maximum concentration (Cmax), time to Cmax (tmax), or elimination half-life of troglitazone, its two main metabolites, and acetaminophen or in acetaminophen urinary sulfate excretion, although there was a slight decrease in acetaminophen glucuronide excretion during administration with troglitazone. Adverse events were minor and similar between treatments. These findings suggest that troglitazone and acetaminophen can be coadministered without adverse clinical consequences.

Gastrointestinal manifestations of scleroderma

Gastrointestinal involvement is commonly found in scleroderma. Gastrointestinal symptoms may be the presenting symptoms for the diagnosis and may precede the actual diagnosis by months to years. The esophagus is the most frequently affected, but functional problems of the anorectum, small bowel, colon, and stomach may occur. The pathophysiologic mechanism appears to be one of smooth muscle atrophy and, to a lesser degree, fibrosis. These changes result in gastrointestinal motility disturbances and may cause GERD, pseudo-obstruction, bacterial overgrowth, and defecatory disorders. Malnutrition may be a serious consequence. The evaluation of a particular symptom in a patient with scleroderma may lead to treatment strategies that improve the patient's sense of well-being and quality of life.

Pharmacokinetics of troglitazone, a PPAR-gamma agonist, in patients with hepatic insufficiency

OBJECTIVE

Troglitazone is an agonist of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma), which has been shown to improve the metabolic control of type 2 diabetes. Troglitazone undergoes hepatic metabolism to an inactive sulphate conjugate and an oxidative quinone metabolite with minor activity. The objective of this study was to compare the pharmacokinetics of troglitazone in patients with hepatic insufficiency and normal subjects.

METHODS

Three groups of eight subjects with normal liver function and moderate or severe hepatic impairment (Pugh-Child classification) completed this open study. Subjects received a single 400-mg dose of troglitazone 30 min after breakfast. Plasma concentrations of troglitazone and its metabolites were measured and standard pharmacokinetic parameters derived.

RESULTS

A 46% increase in area under the plasma concentration-time curve (AUClast) was observed for troglitazone, together with a 154% increase for the quinone metabolite in the patients with moderate hepatic impairment compared with normal subjects, but these did not reach statistical significance. Corresponding increases of 18% and 53% in the severe group also failed to reach statistical significance. For the sulphate conjugate, the AUClast values for both moderate and severe hepatic impairment were in the order of fourfold higher than those in the normal group. There were reductions in the maximum observed plasma concentration (Cmax) of troglitazone to 61% of the normal group in the severe group for troglitazone, and twofold increases in sulphate metabolite Cmax in the moderate and severe groups. There was an approximately threefold increase in the half-life of the sulphate conjugate in subjects with both moderate and severe impairment of liver function compared with normal individuals. First times to maximum concentrations of troglitazone, its sulphate conjugate and the quinone metabolite were significantly longer in all severely impaired subjects compared with those with normal hepatic function, although the range was wide in all cases. Plasma protein binding was high in all subjects measured (mean unbound fraction range 0.7-5.1%), but there were insufficient samples to compare across groups.

CONCLUSION

The formation of metabolites of troglitazone following a single dose is not impaired in the presence of reduced liver function although the capacity to eliminate the metabolites is altered. The clinical significance of the effect of liver disease on the conjugates is not clear.

Molecular dynamics simulations of an oligonucleotide duplex with adenine tracts phased by a full helix turn

A theoretical model of a DNA oligonucleotide duplex featuring A-tracts phased by a full helix turn is developed based on molecular dynamics computer simulation. The extent to which this model agrees with relevant experimental data on axis bending and the relationship of A-tracts to bending and other aspects of helix morphology is investigated. Specifically, a series of nanosecond-level molecular dynamics (MD) simulations have been carried out for the 25 bp duplex d(ATAGGCAAAAAATAGGCAAAAATGG) at various concentrations of saline solution. A 30 base-pair sequence composed of three 10 bp repeats of the BamHI recognition sequence ligated together, d(CGGGATCCCG. CGGGATCCCG.CGGGATCCCG), was simulated as a control. The MD was carried out using the AMBER 4.1 suite of programs, and utilized the Cornell et al. force-field with the electrostatic boundary conditions treated by the particle-mesh Ewald summation protocol. The MD results show that at a concentration of 60 mM KCl, 10 mM MgCl2 added salt plus minimal neutralizing cations, the MD model exhibits concerted axis bending to the extent of 15.5 degrees per A-tract. This compares favorably with the bending per turn of 17 to 21 degrees inferred from cyclization experiments. The MD model also exhibits a progressive 5' to 3' narrowing of the minor-groove region of A-tracts, a feature inferred from DNA footprinting experiments. Analysis of the dynamic structure of the MD models shows that the origin of the bending follows a junction-type bending model with an admixture of mixed sequence effects, with A-tracts relatively straight, as in oligonucleotide crystal structures of sequences containing A-tracts. The results are shown to be sensitive to environmental conditions: MD on d(ATAGGCAAAAAATAGGCAAAAATGG) in neutralizing Na+ buffer results in markedly reduced curvature, and the removal of Mg2+ measurably affects bending. Carrying out the simulations at experimental salt conditions appears to be essential to obtain an accurate account of the experimentally observed bending.

Measuring pre-hepatic insulin secretion using a population model of C-peptide kinetics: accuracy and required sampling schedule

The accuracy of calculations of pre-hepatic insulin secretion were investigated, to provide independent validation of a population model of C-peptide kinetics. The effects of sampling frequency were also assessed. Five normal subjects (aged 28 to 43 years; BMI (kg/m2) 20.5 to 24.5) and five subjects with non-insulin-dependent diabetes mellitus (NIDDM) treated by diet alone (aged 34 to 57 years; BMI 22.6 to 25.6) were given a variable intravenous infusion of biosynthetic human C-peptide (BHCP) (t=-60 to 240 min) mimicking meal stimulated C-peptide secretion, with short-term oscillations (peak approximately every 12 min) superimposed on the infusion profile. Plasma C-peptide was measured every 5 min (t=0 to 240 min). The BHCP infusion was reconstructed from C-peptide measurements using a population model of C-peptide kinetics and a deconvolution method. Bias, defined as the percentage difference between the total amount of calculated BHCP and the total amount of infused BHCP (t=0 to 240 min), indicated that overall C-peptide secretion can be measured with 14% [95% confidence interval (CI) -11 to 39%] and 21% (95% CI -3 to 45%) accuracy in normal subjects and subjects with NIDDM respectively. Accuracy was not reduced by reducing the sampling frequency to every 30 min. The root mean square error, measuring the average deviation between the infused and normalised calculated BHCP profiles, was also independent of the sampling frequency [mean (95% CI) 0.9 (0.3 to 1.6) pmol/kg per min in normal subjects; 1.0 (0.9 to 1.1) pmol/kg per min in subjects with NIDDM]. Deconvolution employing a population model of C-peptide kinetics can be used to estimate postprandial total C-peptide secretion with biases of 14% and 22% respectively in normal subjects and subjects with NIDDM. Plasma C-peptide samples need only be drawn every 30 minutes.