Protein unfolding during reversed-phase chromatography: I. Effect of surface properties and duration of adsorption.

Residue-level features of bovine pancreatic trypsin inhibitor (BPTI) unfolding on reversed-phase chromatography (RPC) surfaces were investigated using hydrogen-deuterium exchange labeling and NMR. A set of silica-based RPC surfaces was used to examine the influence of alkyl chain length and media pore size on adsorbed BPTI conformation. In all cases there was substantial unfolding in the adsorbed state; however, residual protection from exchange was consistently observed. Particle pore size did not influence conformation substantially for C4-alkyl modified silica; however, 120 A pore C18 media produced more hydrogen exchange than any other surface examined. In this case, the radius of curvature inside the pore approaches the size of the BPTI molecule. Generally, the pattern of hydrogen exchange protection was uniform; however, the beta-sheet region was selectively protected on the large-pore C18 media. The beta-sheet region forms a hydrophobic core that forms early when BPTI folds in solution. This suggests that partially unfolded states possessing a native-like structure play an important role in adsorption and elution in RPC. Finally, increased contact time with the surface before elution fostered unfolding and altered chromatographic behavior considerably.

Protein unfolding during reversed-phase chromatography: II. Role of salt type and ionic strength.

While reversed-phase chromatography (RPC) may be a powerful method for purification of proteins at the analytical scale, both preparative and analytical applications have been hindered by the complex chromatographic behavior of proteins compared to small molecules. Further, preparative applications have been limited because of poor yields caused by the denaturing conditions involved. One means for modulating both the stability and chromatographic behavior of proteins is through the use of added salt. In this investigation, we show how salt type and ionic strength affect protein conformation on RPC surfaces. Exposure of amide groups of adsorbed BPTI was monitored using nuclear magnetic resonance (NMR) spectroscopy and hydrogen-deuterium isotope exchange. Sodium chloride, sodium acetate, and ammonium sulfate were studied at ionic strengths up to I = 0.375, with adsorption hold times being 5 min and 2 h. We found that increasing ionic strength decreased exposure of the exchange reporter groups in essentially all cases. However, even at the same ionic strength the level and distribution of residue protection varied with salt type and hold time. NaCl does not protect certain reporter groups at all, while those that it does protect to some degree at short hold times can exchange slightly more at longer times. The pattern and level of protection for NaAc at short times is similar to that for NaCl, but at longer times more uniform protection is seen as the reporter groups completely exposed at short times become more protected. For (NH(4))(2)SO(4) the pattern of protection at short hold time is similar to those of the other salts, although it protects all groups much more. This would be expected from the Hofmeister series. However, at longer times the level of protection with (NH(4))(2)SO(4) decreases below that of the other salts, while it uniquely protects all groups to nearly the same level. Such subtle variations in the protein structure would not have been detected without the measurements and analysis used here. Chromatographic retention times and peak shapes were obtained for the above systems. Variations of behavior were seen that could not be correlated with any of the above protection patterns and levels or even with heuristics such as the Hofmeister series. This suggests further conformational changes upon elution may be critical to the retention process. However, an excellent correlation was found between peak width at half-height and the average degree of unfolding, as indicated by the average level of isotopic exchange. Thus, while further studies are needed to definitively determine the connection between protein unfolding and retention, use of this correlation may improve designing and screening for chromatographic conditions that minimize protein unfolding.

Pharmacodynamic models for the cardiovascular effects of moxonidine in patients with congestive heart failure.

AIMS: To assess the pharmacodynamics of moxonidine in patients with functional NYHA Class II-III congestive heart failure (CHF). METHODS: A parallel population pharmacokinetic/pharmacodynamic (PK/PD) analysis was performed to assess the effect of moxonidine (0.1, 0.2, 0.3 mg twice daily) and placebo treatment on plasma noradrenaline (NA) levels, standing systolic blood pressure (SBP), and heart rate (HR) over 12 weeks in 97 patients with CHF using a parallel group design with dose escalation. A sequential analysis was also developed, where the relative changes in NA concentration were related to both SBP and HR. RESULTS: In the parallel PD analysis, an effect delay was shown for all three end points (NA, SBP, and HR). An inhibitory Emax model was used to characterize the concentration-effect relationships. For SBP and HR, the EC50 value increased over time. For NA, there was a positive baseline drift over the 12 weeks; this was interpreted as disease progression. Moxonidine delayed this increase by 9.8 weeks. For SBP, there was a circadian pattern at baseline. In the sequential PD analysis, the relationship between the drug response (NA) and SBP or HR was best described by an inhibitory Emax model. No effect delays between the response and effects were found. CONCLUSIONS: Effects of moxonidine on NA, SBP, and HR could be quantified by an effect compartment model in the presence of disease progression and circadian variations. Disease progression, as judged by increasing NA levels with time, was delayed by moxonidine. A direct relationship was found between NA and SBP/HR.

The effects of chronic, sustained-release moxonidine therapy on clinical and neurohumoral status in patients with heart failure.

AIMS: Congestive heart failure (CHF) is characterized by elevated plasma norepinephrine (PNE) associated with a poor prognosis. Moxonidine selectively stimulates medullary imidazoline receptors which centrally inhibit sympathetic outflow and potently suppress levels of circulating PNE. This study was designed to evaluate the effects of central sympathetic inhibition on clinical and neurohumoral status in patients with CHF. METHODS AND RESULTS: This study evaluated 25 patients (age=69+/-7 years, 20 males) with symptomatic CHF (NYHA II-III), stabilized on standard therapy. The mean ejection fraction was 28+/-7% at baseline. Patients were titrated in a double-blind fashion to 11 weeks of oral therapy with placebo (n=9) or sustained-release (SR) moxonidine 0.9 mg bid (n=16). Clinical and neurohumoral status were evaluated at baseline, on chronic therapy at the target dose, and during cessation of therapy. All patients completed the trial and reached the target dose. Dry mouth, symptomatic hypotension, and asthenia were more frequent in the moxonidine SR-treated group. PNE was substantially reduced after 6 weeks at the maximum dose (0.9 mg bid) by 50% vs. placebo (P<0. 0005). A reduction in 24-h mean heart rate (P<0.01) was correlated to the reduction in PNE (r=0.70, P<0.05). A 36% increase in the standard deviation of normal-to-normal intervals (SDNN) was observed in the moxonidine SR group vs. a 2% decrease for placebo (P=0.06); for the root mean square of successive differences (rMSSD), there was a 21% increase for moxonidine SR vs. a 19% decrease for placebo (P<0.05). Abrupt cessation of chronic therapy resulted in substantial increases in PNE, blood pressure, and heart rate. CONCLUSIONS: Chronic therapy with a sustained-release formulation of moxonidine in patients with CHF was well tolerated, with substantial and sustained reductions in PNE. The tachyarrhythmias were attenuated, with evidence of improved autonomic tone. Due to the observed effects following moxonidine discontinuation, tapering of therapy is recommended.

The effects of moxonidine, a novel imidazoline, on plasma norepinephrine in patients with congestive heart failure. Moxonidine Investigators.

OBJECTIVE: To evaluate the dose response relationship of moxonidine on plasma concentration of norepinephrine during acute and chronic administration in patients with congestive heart failure (CHF). BACKGROUND: Sympathetic activation is increased in heart failure. Moxonidine is an imidazoline ligand acting on the central nervous system (CNS) receptors to decrease sympathetic activation. METHODS: Ninety-seven patients with heart failure and New York Heart Association class II-III symptoms and ejection fraction <40% were randomized to placebo or one of three target doses of moxonidine, 0.1, 0.2 or 0.3 mg administered twice daily. An initial dose of moxonidine 0.1 mg twice a day (b.i.d.) was followed by weekly increments of 0.1 mg b.i.d. until target dose. The second and third study days occurred after four weeks (at target dose) and after 12 weeks, respectively. At each study day, repeated blood samples were drawn. RESULTS: There was a significant dose-related decrease of systolic blood pressure across all three study days. Heart rate decreased significantly on study day 3 in a dose-related manner. The acute 2 h decrease in plasma norepinephrine in response to all three doses of moxonidine was significantly different compared with placebo after four and 12 weeks. There was a significant linear relation between dose and plasma norepinephrine after four and 12 weeks in both 2 h peak and the time averaged effect (>8 h). The number of adverse events was similar in the moxonidine and placebo groups. CONCLUSIONS: The increased sympathetic activation in CHF can be reduced by moxonidine through CNS inhibition.

Acute hemodynamic and neurohumoral effects of moxonidine in congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy.

Elevated plasma norepinephrine (PNE) has been shown to be an important predictor of morbidity and mortality in patients with congestive heart failure (CHF). Moxonidine selectively stimulates imidazoline receptors located in the medulla, which centrally inhibit sympathetic outflow. PNE is suppressed and peripheral vasodilation reduces systemic blood pressure. This study evaluated the acute neurohumoral and hemodynamic effects of a single dose of oral moxonidine in 32 patients (22 men, mean +/- SD age 66 +/- 10 years) with CHF. All patients were in New York Heart Association functional class III and stabilized on chronic therapy with diuretics, digitalis, and angiotensin-converting enzyme inhibitors. The mean PNE concentration was 509 +/- 304 pg/ml at baseline. Patients underwent invasive hemodynamic monitoring after double-blind randomization to either placebo (n = 12), moxonidine 0.4 mg (n = 9), or moxonidine 0.6 mg (n = 11). Moxonidine produced a dose-dependent, vasodilator response compared with placebo. Analysis of the time-averaged change from baseline over 6 hours demonstrated that moxonidine 0.6 mg caused significant reductions in mean systemic arterial pressure (p <0.0001), mean pulmonary arterial pressure (p <0.005), systemic vascular resistance (p <0.05), pulmonary vascular resistance (p <0.01), and heart rate (p <0.05). Stroke volume was unchanged. PNE was reduced substantially (-180 pg/ml at 4 hours, p <0.005) and the reduction was highly correlated with the baseline level (r = -0.968). Moxonidine was well tolerated in this single-dose study and resulted in a modest, dose-dependent, vasodilator response, with substantial reductions in systemic and pulmonary arterial blood pressure. Trials designed to evaluate the clinical efficacy of chronic moxonidine therapy in CHF added to conventional therapy would be appropriate.

Population pharmacokinetic-pharmacodynamic modeling of moxonidine using 24-hour ambulatory blood pressure measurements.

OBJECTIVES: To develop a model for 24-hour ambulatory blood pressure measurements (ABPM) that can be applied in a pharmacokinetic-pharmacodynamic model. METHODS: Four different data sets were prepared from 2 studies to accommodate different modeling strategies. In study A, a double-blind placebo-controlled study in 47 patients, 24-hour ABPM profiles (74 to 99 measurements per profile) were obtained during the placebo run-in phase and after 3, 5, and 11 weeks during the treatment. Three to 5 plasma samples were taken. Cosine and polynomial models were evaluated to describe the circadian rhythm in blood pressure based on 3 data sets (1: only run-in data; 2: only placebo data; 3: all data). In study B, a double-blind placebo-controlled study in 94 patients, two 24-hour ABPM profiles per patient (during placebo run-in and after 8 weeks) were recorded and randomly reduced to 15 measurements per profile to evaluate the robustness of the baseline model. RESULTS: The mean moxonidine clearance was 35 L/h, and the volume of distribution was 132 L. The final baseline model consisted of 2 cosine terms with fixed-effect parameters for rhythm-adjusted 24-hour mean blood pressure, amplitude, phase, and period; random-effect parameters for interindividual variability in rhythm-adjusted 24-hour mean, amplitude, and clock time; and interoccasion variability in rhythm-adjusted 24-hour mean and clock time. The final baseline model was combined with an Emax model for the drug effect. An effect compartment was used (kco = 0.198 h-1). The maximum decrease in diastolic blood pressure (Emax) was 16.7%, and EC50 was 0.945 microgram/L. CONCLUSION: The pharmacokinetic-pharmacodynamic model for 24-hour ABPM can be used to estimate the concentration-effect relationship of antihypertensive drugs.

Effect of tibenelast (a phosphodiesterase inhibitor) and theophylline on isoproterenol-stimulated heart rate, cyclic AMP and norepinephrine levels.

The effect of the phosphodiesterase inhibitors (tibenelast, theophylline) and placebo on isoproterenol-induced changes in heart rate, cAMP and norepinephrine levels in normal male volunteers was studied. Heart rates in response to isoproterenol dosing were fitted by linear regression, and horizontal shifts in the regression lines were examined between the three treatments. The shift of the regression line after placebo compared to the preplacebo line was to the right by 2.6 +/- 2.2 ng ISO/kg/min, theophylline pretreatment shifted this line to the left by 2.4 +/- 1.8 ng/kg/min (p < 0.05) and tibenelast by 3.7 +/- 1.9 ng/kg/min (p < 0.02). Both tibenelast and theophylline increased the heart rate response to isoproterenol infusion, whereas norepinephrine and cAMP levels were not different in any treatment.

Transmission of the apomictic mode of reproduction in Pennisetum: co-inheritance of the trait and molecular markers.

Apomixis, asexual reproduction through seed, is an obligate mode of reproduction in several species from the genus Pennisetum. Transfer of apomixis to sexual, cultivated pearl millet (P. glaucum) from a wild species P. squamulatum has resulted in an obligate apomictic backcross line with a low, but unknown number, of chromosomes from the wild species. Molecular markers (restriction fragment length polymorphisms and random amplified polymorphic DNAs) have been identified that unequivocally demonstrate the presence of P. squamulatum DNA in BC3. Three of the informative RFLP clones have been sequenced and converted to sequence-tagged sites that can be amplified by the polymerase chain reaction. Molecular genetic analysis of more advanced back-cross individuals, using the two types of polymerase chain reaction-based molecular markers, has demonstrated co-inheritance of apomictic reproduction and two of the molecular markers. The remaining five molecular markers generally co-segregate with each other but are not linked with the mode of reproduction. These results suggest that genes for apomixis apparently can be transmitted by a single chromosome. Chromosome-specific markers will provide a starting point for the mapping of this genetically intractable reproductive trait.

Translocation of the MOS gene in a rare t(8;16) associated with acute myeloblastic leukemia and Down syndrome.

Cytogenetic analysis of an infant with Down syndrome with concomitant acute myelogenous leukemia revealed a unique t(8;16)(q22;q24). In situ chromosomal hybridization was used to demonstrate that the protooncogene MOS was translocated from chromosome 8 to chromosome 16. This is the first report of the transposition of MOS in association with acute leukemia.

Translocation (8;16)(p11;p13) in patients with acute monocytic leukemias. An evolving syndrome?

The case of a patient with a t(8;16)(p11;p13) chromosomal abnormality and acute myelomonocytic leukemia is described. Review of cases with this translocation showed that 11 of 13 patients had acute monocytic or myelomonocytic leukemia with a high frequency of extramedullary disease and phagocytosis of normal blood cells by the malignant cells. While these patients are not clinically distinct from others with acute monocytic leukemia, the characteristic features of this subset of patients will certainly evolve.

Captopril modifies the hemodynamic and neuroendocrine responses to sodium nitroprusside in hypertensive patients.

To determine if clinically effective doses of the antihypertensive agent captopril affected the neuronal release of norepinephrine or baroreflex sensitivity, changes in plasma norepinephrine concentration and heart rate were related to the changes in mean arterial pressure seen during the intravenous infusion of stepwise incremental doses of sodium nitroprusside before and during captopril treatment in eight hypertensive men with normal or low plasma renin activity. At all times, significant linear correlations were found between the decrease in mean arterial pressure and the dose of sodium nitroprusside, the increase in heart rate and the decrease in mean arterial pressure, and the increase in plasma norepinephrine concentration and the decrease in mean arterial pressure. When the subjects were treated with captopril (25 mg t.i.d.) for 2 to 4 weeks, supine mean arterial pressure decreased from 130 to 114 mm Hg (-12%; p less than 0.05), heart rate did not change, supine and upright plasma renin activity increased, while supine plasma norepinephrine and epinephrine concentration decreased slightly. Therapy with captopril (25 mg t.i.d.) increased baroreflex sensitivity, as assessed by the slope of the regression line relating the increase in heart rate to the decrease in mean arterial pressure, and increased the responsiveness of the sympathetic nervous system, as assessed by the slope of the regression line relating the increase in plasma norepinephrine concentration to the decrease in mean arterial pressure. These increases were accompanied by a decrease in the slope of the regression line relating the decrease in mean arterial pressure to the dose of sodium nitroprusside and thus were associated with a decreased sensitivity to the vasodepressor effects of sodium nitroprusside.(ABSTRACT TRUNCATED AT 250 WORDS)

Fertility restoration and mitochondrial nucleic acids distinguish at least five subgroups among cms-S cytoplasms of maize (Zea mays L.).

Differences in fertility restoration and mitochondrial nucleic acids permitted division of 25 accessions of S-type male sterile cytoplasm (cms-S) of maize into five subgroups: B/D, CA, LBN, ME, and S(USDA). S cytoplasm itself (USDA cytoplasm) was surprisingly not representative of cms-S, since only two other accessions, TC and I, matched its mitochondrial DNA pattern. CA was the predominant subgroup, containing 18 of the 25 accessions. The B/D and ME subgroups were the most fertile and LBN the most sterile. The exceptional sterility of LBN cytoplasm makes it the most promising of the 25 cms-S accessions for the production of hybrid seed. The most efficient means of quantifying the fertility of the subgroups was analysis of pollen morphology in plants having cms-S cytoplasm and simultaneously being heterozygous for nuclear restorer-of-fertility (Rf) genes. This method took advantage of the gametophytic nature of cms-S restoration. The inbred NY821LERf was found to contain at least two restorer genes for cms-S. Fertility differences were correlated with mitochondrial nucleic acid variation in the LBN, ME, and S (USDA) subgroups.

Effect of oral dose size on hydralazine kinetics and vasodepressor response.

Levels of hydralazine in blood are log-linearly related to its vasodepressor effect. We examined the effect of oral dose size on the proportion of hydralazine that reaches systemic circulation. Nine subjects with hypertension were given hydralazine in oral doses in the therapeutic range. Blood hydralazine levels, effective liver blood flow, blood pressure, and heart rate were measured. As the hydralazine dose increased, the ratios of the AUC of hydralazine to hydralazine dose and of peak blood hydralazine concentration to hydralazine dose increased, indicating an increase in the proportion of the dose in blood. Liver blood flow tended to increase (maximum 40%) as dose increased above 0.5 mg/kg. Vasodepressor response and degree of tachycardia increased disproportionately with increasing hydralazine dose. There were strong log-linear relationships between peak hydralazine levels and both vasodepressor response and tachycardia that did not change with increasing hydralazine dose. Thus blood hydralazine and vasodepressor response increase disproportionately with increasing hydralazine doses in hypertension.

Additional evidence implicating Triticum searsii as the B-genome donor to wheat.

In vitro DNA:DNA hybridizations and hydroxyapatite thermal-elution chromatography were employed to identify the diploid wheat species ancestral to the B genome of Triticum turgidum. 3H-T. turgidum DNA was hybridized to the unlabeled DNAs of T. urartu, T. speltoides, T. sharonensis, T. bicorne, T. longissimum, and T. searsii. 3H-Labeled DNAs of T. monococcum and a synthetic tetraploid AADD were hybridized with unlabeled DNAs of T. urartu and T. searsii to determine the relationship of the A genome of polyploid wheat and T. urartu. The heteroduplex thermal stabilities indicated that T. searsii was most closely related to the B genome of T. turgidum (AB) and that the genome of T. urartu and the A genome have a great deal of base-sequence homology. Thus, it appears that T. searsii is the B-genome donor to polyploid wheat or a major chromosome donor if the B genome is polyphyletic in origin.

Activation of the renin-angiotensin system by sodium nitroprusside in essential hypertension.

We previously have demonstrated that the sympathetic nervous system is activated proportionately to the degree of vasodepression induced in hypertensive patients. In the present study, the role of the renin-angiotensin system in modulating the vasodepressor response to sodium nitroprusside was examined. Nine hospitalized hypertensive patients receiving a diuretic were given serially incremental doses of sodium nitroprusside over a dose range of 0.05-4.8 micrograms/kg/min with each dose being infused for 10 min. Mean arterial pressure (MAP), heart rate (HR), plasma renin activity (PRA), and plasma norepinephrine (NE) concentration were measured prior to and during each dose level of sodium nitroprusside. Stepwise increments in PRA were seen in each patient as the dose of sodium nitroprusside was increased. The increase in PRA was proportional to the increase in plasma NE concentration and to the decrease in MAP in each patient. However, considerable intersubject variation was seen in these relationships. When examined by multiple linear stepwise regression analysis, the degree of vasodepression was found to be dependent on the baseline blood pressure and baroreflex sensitivity (r = 0.97). However, increment in PRA was not an independent determinant of the vasodepressor response. Thus, the renin angiotensin system may not be a significant component of the acute homeostatic response to vasodepression in these patients.

Molecular analysis of genomic stability of mitochondrial DNA in tissue cultured cells of maize.

Mitochondrial DNA (mtDNA) of the Black Mexican sweet line of maize isolated from tissue cultured cell suspension cultures and young seedlings was examined. Restriction fragments generated by two endonucleases were comparatively analyzed by visualization of ethidium bromide stained gels as well as by membrane hybridization with nick-translated DNA probes of plasmid-like S1 and S2 DNA. Although no major molecular alterations were seen in tissue cultured cells, the samples were clearly not identical. The variation was mainly in the stoichiometry of several restriction fragments. Hybridization analyses with S1 and S2 probes show no evidence of molecular rearrangement in this part of the genome in tissue cultured cells. Minor variations in restriction patterns could reflect alterations in frequency of circular mtDNA molecules, perhaps related to nuclear alterations during the extended period of culture.

The response of plasma catecholamines to intravenous labetalol: a comparison with sodium nitroprusside.

Changes in mean arterial pressure (MAP), heart rate (HR), and plasma concentrations of norepinephrine (NE) and epinephrine were measured in eight hypertensive patients in a supine position after stepwise infusion of incremental sodium nitroprusside doses and intravenous injection of cumulative labetalol doses. Both drugs induced rises in plasma NE concentration that were linearly related to reductions in MAP. For any reduction in blood pressure (BP), however, the rise in plasma NE concentration induced by labetalol was approximately four times that induced by sodium nitroprusside. The difference can be explained by two effects of labetalol: impairment of neuronal NE uptake and beta-adrenergic-receptor blockade, which are known to reduce NE clearance from plasma. After both drugs there was a correlation between changes in HR and changes in BP and a correlation between changes in HR and changes in plasma NE concentration. Slopes of the regression lines for both relationships were less after labetalol than after sodium nitroprusside, presumably because of the beta-adrenergic-blocking properties of labetalol. Multiple-regression analysis indicated that the plasma NE rise was an important determinant of the vasodepressor response to each drug. The greater plasma NE elevation after labetalol may limit its antihypertensive effect.

Effects of hydralazine and sodium nitroprusside on plasma catecholamines and heart rate.

Hydralazine and sodium nitroprusside induce different effects on systemic hemodynamics, but their effects on sympathetic neuronal activity have not been compared. Five hypertensive subjects receiving only hydrochlorothiazide were studied during two sessions. During one session, four doses of hydralazine, 0.1 to 0.6 mg/kg, were given intravenously at least 3 days apart, and during the other session, sodium nitroprusside was infused in stepwise doses, 0.05 to 4.8 micrograms/kg/min for 10 min per dose. Mean arterial pressure (MAP), heart rate (HR), and plasma norepinephrine (NE) and epinephrine concentrations were determined before and after dosing. The following correlated linearly for hydralazine and sodium nitroprusside: delta HR/delta MAP, delta NE/delta MAP, and delta HR/delta NE. Comparison of these relationships, however, indicated significant differences between the sympathetic neuronal and hemodynamic responses to hydralazine and sodium nitroprusside. Increase in HR relative to decrease in MAP was greater for hydralazine than for sodium nitroprusside. There were greater increases in plasma NE concentration relative to falls in MAP with sodium nitroprusside than with hydralazine, but increases in HR relative to increases in plasma NE concentration were smaller for sodium nitroprusside than for hydralazine. Such responses may reflect differential effects of hydralazine and sodium nitroprusside on the systemic clearance of NE or of the activity of cardiopulmonary baroreceptors.