A model and diagnostic measures for response time series on tests of concentration: historical background, conceptual framework, and some applications

Based upon classical hypotheses about accumulating mental fatigue and distraction and its effect on response times, put forward in late 19th and early 20th century papers, a mathematical model is proposed for response times on tests of speed and concentration. The model assumes the random occurrence of very short distractions during information processing. It explains fluctuation and the increasing trend in response times on successive equivalent task units and leads to some simple diagnostic RT measures of speed and concentration as alternatives to the mean RT. A review is given of several experimental applications of the model, with subjects with and without concentration problems, using cancellation and digit addition tasks. The results demonstrate the potential usefulness of the model and the diagnostic measures derived from it. As predicted by the model, prolonged task performance yields an increasing trend in RT mean and variance that can be strongly reduced by giving very short resting periods very frequently, and to a lesser extent also by task alternation, but not by simply motivating the subjects to concentrate. Some practical implications for the administration and scoring of tests of speed and concentration are discussed, as well as limitations of the present results and the complementary relation of our approach to popular ones such as "stage analysis."

Postprandial hypotension: epidemiology, pathophysiology, and clinical management

OBJECTIVE

To show the clinical relevance of postprandial hypotension and to review its pathophysiology and management.

DATA SOURCES

Articles on postprandial hypotension were identified through MEDLINE and bibliographies of relevant articles.

STUDY SELECTION

All articles and case reports describing meal-related hypotension in the elderly and in patients with autonomic failure.

DATA SYNTHESIS

Postprandial hypotension, defined as a decrease in systolic blood pressure of 20 mm Hg or more, may result in syncope, falls, dizziness, weakness, angina pectoris, and stroke. Postprandial hypotension is distinct from and probably more common than orthostatic hypotension. Because meal-related hypotension is particularly common in older hypertensive patients, it has important implications for the evaluation and management of hypertension. The mechanism of postprandial hypotension is not fully understood. Possible contributors include inadequate sympathetic nervous system compensation for meal-induced splanchnic blood pooling; impairments in baroreflex function; inadequate postprandial increases in cardiac output; and impaired peripheral vasoconstriction, insulin-induced vasodilation, and release of vasodilatory gastrointestinal peptides. Although caffeine is often recommended as treatment for postprandial hypotension, available data do not support its use. Octreotide, a somatostatin analog, has been shown to be effective, but it is expensive and must be given parenterally.

CONCLUSION

All physicians caring for elderly patients should be aware of the hypotensive effects of food intake and should consider postprandial hypotension in the evaluation of syncope, falls, dizziness, and other cerebral ischemic symptoms.

Inhibition of hepatitis B virus in tissue culture by alpha interferon

Alpha-n1 interferon (Wellferon), alpha-2a interferon (Roferon), and alpha-2b interferon (Intron-A) inhibited accumulation of intracellular replicative forms of hepatitis B virus (HBV) in chronic producer cells by inhibiting accumulation of RNase-resistant HBV RNA. In contrast, the nucleoside analog FTC (cis-5-fluoro-1- [2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine) inhibited the accumulation of HBV DNA.

Haemodynamic and neurohumoral effects of caffeine in elderly patients with symptomatic postprandial hypotension: a double-blind, randomized, placebo-controlled study

1. The aim of this study was to determine the effects of caffeine on haemodynamic and neurohumoral responses to meal ingestion in elderly patients with a history of symptomatic postprandial hypotension. 2. Postprandial hypotension is a common disorder of blood pressure regulation in the elderly, associated with falls and syncope. The pathophysiological mechanism is thought to be related to impaired vascular compensation for splanchnic blood pooling after a meal. Since caffeine inhibits vasodilatory adenosine receptors in the splanchnic circulation, we postulated that caffeine would reduce splanchnic blood pooling and prevent the development of postprandial hypotension. 3. We conducted a randomized, double-blind, placebo-controlled, cross-over study in nine elderly patients [age 76 +/- 9 (SD) years] with histories of symptomatic postprandial hypotension. Standardized 1674kJ liquid meals with 250 mg of caffeine or placebo were given on two occasions, at least 1 week apart. Blood pressure, heart rate, forearm vascular resistance (by venous occlusion plethysmography), and plasma caffeine and catecholamine levels were measured. Cardiac and splanchnic blood volume were determined by radionuclide scans. 4. By 30 min after both caffeine and placebo meal studies, supine mean arterial blood pressure fell significantly (P = 0.006) by 31 +/- 7 and 19 +/- 6 mmHg, respectively (mean +/- SEM, between group difference was not significant). Heart rate, cardiac output and splanchnic blood volume increased significantly, but to a similar extent, after caffeine and placebo. Forearm vascular resistance was unchanged after both meals. 5. Oral caffeine given with a meal does not reduce splanchnic blood pooling nor prevent postprandial hypotension in symptomatic elderly patients.

Evaluation of the potent anti-hepatitis B virus agent (-) cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine in a novel in vivo model

A murine model was developed to investigate the in vivo activity of anti-hepatitis B virus (HBV) agents. Mice with subcutaneous tumors of HBV-producing 2.2.15 cells showed reductions in levels of HBV in serum and in intracellular levels of HBV when the mice were orally dosed with (-) cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine (FTC). No effects on tumor size or alpha-fetoprotein levels were observed. FTC can selectively inhibit HBV replication at nontoxic doses.

Novel, negatively charged, human serum albumins display potent and selective in vitro anti-human immunodeficiency virus type 1 activity

We prepared a series of modified proteins and peptides by derivatizing the positively charged epsilon-amino groups of the lysine amino acids through reaction with anhydrides of succinic acid (Suc) and aconitic acid (Aco). Human serum albumin (HSA) was modified by introduction of a single carboxylic group (Suc-HSA) or two carboxylic groups (Aco-HSA) per amine function, yielding strongly negatively charged compounds. The in vitro anti-human immunodeficiency virus (HIV)-1 IC50 of Suc-HSA was about 1 microgram/ml, and the most polyanionic modified albumin of the series (Aco-HSA) exhibited an IC50 as low as 0.02 microgram/ml. Similar derivatization of the plasma protein orosomucoid or the synthetic polypeptide polylysine did not produce compounds with significant anti-HIV-1 activity, indicating an HSA-specific effect. The mechanism of action of Suc-HSA was reported to be the inhibition of a post-binding virus-cell fusion event, probably due to interference with the gp41-mediated fusion process. In the present study we demonstrate that the more potent Aco-HSA also interferes with this fusion process but, additionally, this compound inhibits (i) the binding of soluble CD4 to HIV-infected cells, (ii) the binding of HIV particles to MT-4 cells, and (iii) the binding of anti-gp120 monoclonal antibody to the gp120 molecule. This indicates that Aco-HSA, apart from post-binding fusion, also inhibits virus-cell binding by shielding viral gp120. The simultaneous inhibition of binding and fusion may lead to a synergistic effect, explaining the extreme potency of Aco-HSA. The polyanionic HSAs are significantly less active against HIV-2 and do not interfere with the replication of feline immunodeficiency virus or 12 other DNA or RNA viruses, indicating a HIV-1-specific effect. In contrast, another polyanionic compound, the sulfated polysaccharide dextran sulfate, inhibits the replication of various viruses in a more nonspecific way, as a general polyanion. Dextran sulfate also exhibits strong anticoagulant activity, whereas Suc-HSA and Aco-HSA do not show this unwanted side effect.

Pharmacokinetic analysis and cellular distribution of the anti-HIV compound succinylated human serum albumin (Suc-HSA) in vivo and in the isolated perfused rat liver

After intravenous injection of a low dose (25 micrograms/kg) in rats, the anti HIV-1 compound succinylated human serum albumin (Suc-HSA) is taken up mainly in the liver and spleen and is proteolytically degraded. Ten minutes after injection of 125I-Suc-HSA, 72 and 14% of the dose were found in the liver and spleen, respectively. With immunohistochemistry we demonstrated that in both organs, Suc-HSA was specifically endocytosed in endothelial cells. In the isolated perfused rat liver preparation, liver uptake was shown to be saturable, with a Km of 2.9 10(-8) M and a Vmax of 2.4 micrograms/min/100 g body weight. The apparent Km and Vmax in vivo were 2.2 10(-7) M and 10.3 micrograms/min/100 g, respectively. Uptake in liver and spleen was inhibited by preadministration of an excess of formaldehyde-treated albumin and with polyinosinic acid, indicating the involvement of the scavenger receptor, as anticipated for such polyanionic compounds. Suc-HSA is not absorbed intact from the colon and the ileum. After injecting (i.v.) rats with a high dose of Suc-HSA (10 mg/kg), the elimination t1/2 was 3 hr, and therefore, sustained plasma levels above the concentration needed for in vitro anti-HIV-1 activity can be achieved.

Coupling of the antiviral drug ara-AMP to lactosaminated albumin leads to specific uptake in rat and human hepatocytes

We covalently coupled 9-beta-D-arabinofuranosyladenine 5'-monophosphate (ara-AMP) to the carrier molecule lactosaminated human serum albumin using a water-soluble carbodiimide with a two-step conjugation method (pH 4.5 and pH 7.5) instead of the commonly used single-step conjugation at pH 7.5. This resulted in a predominantly monomeric conjugate (lac27-HSA-ara-AMP9). The conjugate was stable in buffer (pH 7.4) and blood plasma. After in vivo injection, the carrier and the monomeric conjugate were subjected to selective endocytosis in rat hepatocytes, as shown on immunohistochemical study and cell-separation techniques using 125I-labeled material. In competition experiments with other ligands for the asialoglycoprotein receptor N-acetylgalactosamine and asialofetuin, we showed that both lactosaminated human serum albumin and lac27-HSA-ara-AMP9 are subject to endocytosis by this receptor system. Although the coupling of ara-AMP significantly increased the net negative charge of the conjugate compared with the native carrier, liver uptake was not affected by coadministration of an excess of succinylated human serum albumin (suc-HSA), a negatively charged ligand for the scavenger receptor. Incubation studies with purified rat liver lysosomes showed that in this acidic and proteolytic environment, mainly ara-AMP and, to a much lesser extent, ara-A itself were released from the carrier. After injection into the rat in vivo and in isolated perfused rat liver, no free ara-AMP or 9-B-D-arabinofuranosyladenine (ara-A) could be detected in plasma and perfusate, respectively, indicating proper retention of the virally active components in hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic and intrahepatic targeting of an anti-inflammatory agent with human serum albumin and neoglycoproteins as carrier molecules

The anti-inflammatory agent naproxen (Nap) was covalently coupled to human serum albumin (HSA) and to the neoglycoproteins, galactose and mannose terminated HSA, to deliver this drug selectively to different cell types of the liver. Disposition of Nap20-HSA was studied in rats and compared to that of equivalent doses of mixtures of uncoupled drug and protein. The liver to kidney ratios of the drug (L/K-Nap) and the protein (L/K-prot.) were increased, indicating an improved delivery of both protein and drug to the target site. After injection of 10 micrograms Nap20-HSA the L/K-prot. was increased 15.0 +/- 0.21-fold as measured 1 hr after injection. Even after injection of 5 mg of the conjugate, the L/K-prot. was enhanced 5.6 +/- 0.34-fold and the L/K-Nap 4.6 +/- 0.23-fold as measured 1 hr after injection. Immunohistochemical staining of liver slices revealed that the endothelial cells were the main sites for hepatic uptake. Further pharmacokinetic studies of Nap20-HSA in isolated perfused rat livers showed a saturable uptake process (Vmax = 2.46 micrograms/min/10.0 g liver and Km = 4.27 x 10(-6) M). The uptake in the liver could be inhibited by various polyanionic probes, indicating the major involvement of a scavenger receptor system in the internalization mechanism of Nap20-HSA. This endothelial uptake via the scavenger receptor system is likely to be related to the increased negative charge of the Nap-albumin conjugate as was revealed by anion exchange chromatography. Studies in the intact organ and in purified liver lysosomal lysates indicate that after internalization of Nap20-HSA the conjugate is proteolytically degraded leading to the formation of the lysine conjugate of Nap. This amino acid conjugate of Nap was shown in a previous study by us to be equipotent to Nap itself with regard to prostaglandin-E2 synthesis inhibition. A pronounced altered intrahepatic distribution was observed when Nap was coupled to lactosaminated and mannosylated HSA (Lact-HSA and Man-HSA, respectively). Coupling of Nap to Lact27-HSA and Man10-HSA resulted in a major shift in intrahepatic distribution from endothelial cells to the hepatocytes and Kupffer cells, respectively. We conclude that conjugation of Nap to HSA itself results in a selective delivery to endothelial cells and that the local proteolysis of the conjugate produces an active catabolite. Selective delivery to other cell types of the liver can be achieved by attaching naproxen to neoglycoproteins with an appropriate type and number of sugar groups.

High-capacity in vitro assessment of anti-hepatitis B virus compound selectivity by a virion-specific polymerase chain reaction assay

An integrated assessment system specific for hepatitis B virus (HBV) Dane particle DNA was developed to examine the activity of potential anti-HBV compounds in chronic HBV-producing HepG2-derived 2.2.15 cells. Cell culture, immunoaffinity purification, polymerase chain reaction, and hybrid-capture detection were performed in the microtiter format to facilitate increased throughput by automation. The high sensitivity afforded by the assay provided quantitative detection of less than 0.5 fg of extracellular HBV DNA from 25 microliters of cell culture supernatants, and drug-induced reductions in HBV titers greater than 100-fold were easily measured. Fluorometric determination of total cellular DNA from the same 96-well proliferating cell cultures allowed simultaneous evaluation of inhibition of cell growth, thus providing the ability to assess the overall selectivities of candidate compounds in a single experiment. The potent activities of three anti-HBV compounds, the (+) and (-) enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxythiolane-5-yl]cytosine (FTC) and D-carbocyclic-2'-deoxyguanosine (CDG), were confirmed by this method. (-)-FTC was more active than its (+) enantiomer (50% inhibitory concentrations, 0.033 +/- 0.006 and 0.723 +/- 0.160 microM [standard error of the mean; SEM], respectively), while both enantiomers demonstrated a lack of cytotoxicity at 200 microM. CDG was more potent (50% inhibitory concentration, 0.0063 +/- 0.0007 microM [SEM]) but was also significantly more toxic, inhibiting cell growth by 50% at 32 +/- 6 microM (SEM). These results demonstrate the usefulness of this immunoaffinity-based, quantitative polymerase chain reaction system as a high-capacity in vitro tool for assessment of anti-HBV compound selectivity.

Reproducibility of the finger cooling test

A finger cooling test is used to objectify Raynaud's phenomenon and to assess its severity. For this purpose, finger skin temperature (FST) and laser Doppler flux (LDF) are measured on the fingertips before and during cooling of the hand (16 degrees water bath for 5 min) and a subsequent recovery period (20 min). To study reproducibility, this test was performed twice within 3 months in 34 healthy subjects and in 56 Raynaud patients. Three test parameters were used in the analysis: the baseline value, the value after 12 min of recovery, and the mean level during recovery. We determined the limits of agreement (mean differences between the first and the second test +/- 2SD) and the coefficients of variation. No systematic differences between the first and the second test were found. Outside temperature did not influence FST or LDF. FST was shown to have a better reproducibility than LDF. For the baseline value in the total group the coefficient of variation was 3.3% for FST and, rather high, 21.6% for LDF. The limits of agreement for the baseline value in the total group were -4.8 to 4.2 degrees for FST and -25.2 to 22.2 arbitrary units for LDF. In conclusion, the applied cooling test has limited value in individual cases, but can be useful when comparing large groups in pathophysiologic or therapeutic studies.

Simultaneous analysis of azidothymidine and its mono-, di- and triphosphate derivatives in biological fluids, tissue and cultured cells by a rapid high-performance liquid chromatographic method

A rapid high-performance liquid chromatographic (HPLC) method for the simultaneous analysis of the antiviral drug azidothymidine (AZT), AZT monophosphate, AZT diphosphate and AZT triphosphate, with ultraviolet detection in the nanomolar range, is described. Determination of these compounds in vitro in the human MT-4 lymphocyte cell line did not require a prior extraction, and AZT and its phosphorylated derivatives could be accurately analysed in one HPLC run. However, plasma, bile, liver homogenate and urine samples could not be injected directly into the chromatograph. Therefore, a solid-phase extraction procedure was developed, using azidodideoxyinosine as internal standard. The extractions of the compounds of interest from all but urine samples were reproducible, with recoveries between 65% (AZT triphosphate from plasma) and 100% (AZT from plasma).

Genetic relatedness of hepatitis A virus strains recovered from different geographical regions

A pairwise comparison of the nucleic acid sequence of 168 bases from 152 wild-type or unique cell culture-adapted strains of hepatitis A virus (HAV) revealed that HAV strains can be differentiated genetically into seven unique genotypes (I to VII). In general, the nucleotide sequence of viruses in different genotypes differs at 15 to 25% of positions within this segment of the genome. Viruses from four of the genotypes (I, II, III and VII) were recovered from cases of hepatitis A in humans, whereas viruses from the other three genotypes (IV, V and VI) were isolated only from simian species developing a hepatitis A-like illness during captivity. Among non-epidemiologically related human HAV strains, 81 were characterized as genotype I, and 19 as genotype III. Within each of these major genotypes, there were two distinct groups (subgenotypes), which differed in sequence at approximately 7.5% of base positions. Each genotype and subgenotype has a characteristic amino acid sequence in this region of the polyprotein, with the most divergent genotypes differing at 10 of 56 residues. Strains recovered from some geographical regions belonged to a common (endemic) genotype, whereas strains from other regions belonged to several, probably imported, genotypes. Thus, HAV strains recovered in North America were for the most part closely related at the nucleotide sequence level, whereas in other regions, such as Japan and Western Europe, HAV strains were derived from multiple genotypes or sub-genotypes. These data indicate that patterns of endemic transmission can be differentiated from situations in which infections are imported due to travel.

Genetic, antigenic and biological differences between strains of hepatitis A virus

Recent studies have documented a considerable degree of genetic divergence among wild-type hepatitis A virus (HAV) strains recovered from different geographical locations. Human HAV strains can be grouped into four genotypes (I, II, III and VII) and unique simian strains belong to three additional genotypes (IV, V and VI). Between each of these genotypes, the nucleotide sequence varies at 15-25% of base positions in the P1 region. Despite this, there is good evidence that most, if not all, human strains of HAV are closely related antigenically. In contrast, although simian strains recovered from Old World monkeys are cross-reactive in immunoassays employing polyclonal antibodies, these strains have significant antigenic differences from human HAV strains. Nonetheless, because biological differences in the host range of these strains apparently preclude significant human infection, this is unlikely to pose a problem in controlling HAV infections with active immunization. Inactivated and attenuated vaccines produced from genotype I human strains (HM175 or CR326) are likely to provide protection against all relevant human HAV strains.

The 5' nontranslated region of hepatitis A virus RNA: secondary structure and elements required for translation in vitro

Although the lengthy 5' nontranslated regions (5'NTRs) of other picornaviral RNAs form highly ordered structures with important functions in viral translation, little is known about the 5'NTR of hepatitis A virus (HAV). We determined the nearly complete 5'NTR nucleotide sequences of two genetically divergent HAV strains (PA21 and CF53) and included these data in a comparative phylogenetic analysis of the HAV 5'NTR. We identified covariant nucleotide substitutions predictive of conserved secondary structures and used this information to develop a model of the 5'NTR secondary structure, which was further refined by thermodynamic predictions and nuclease digestion experiments. According to this model, the 5'NTR comprises six major structural domains. Domains I and II (bases 1 to 95) contain a 5'-terminal hairpin and two stem-loops followed by a single-stranded and highly variable pyrimidine-rich tract (bases 96 to 154). The remainder of the 5'NTR (domains III to VI, bases 155 to 734) contains several complex stem-loops, one of which may form a pseudoknot, and terminates in a highly conserved region containing an oligopyrimidine tract preceding the putative start codon by 13 bases. To determine which structural elements might function as an internal ribosome entry site, RNA transcripts representing the HAV 5'NTR with progressive 5' deletions were translated in rabbit reticulocyte lysates. The translation product was truncated, unprocessed P1 polyprotein. Removal of the 5'-terminal 354 bases of the 5'NTR had little effect on translation. However, deletion to base 447 slightly decreased translation, while deletion to base 533 almost completely abolished it. These data indicate that sequences 3' of base 355 play an important role in the translation mechanism utilized by genomic-length HAV RNA. Significantly, this region shares several conserved structural features with the internal ribosome entry site element of murine encephalomyocarditis virus.

Formaldehyde treated albumin contains monomeric and polymeric forms that are differently cleared by endothelial and Kupffer cells of the liver: evidence for scavenger receptor heterogeneity

Formaldehyde treated albumin (F-HSA) was found to consist of a monomeric and a polymeric fraction. Both fractions were primarily endocytosed by rat liver sinusoidal cells. However, immunohistochemical staining of endocytosed material showed that the relative contribution of the endothelial and Kupffer cells in uptake of the monomer and the polymer differed significantly, with the monomer mainly having an endothelial cell- and the polymer predominantly having a Kupffer cell pattern of distribution. To directly confirm these heterogeneous patterns, we injected in vivo the 125I-labeled F-HSA fractions and isolated the endothelial and Kupffer cells by centrifugal elutriation. 73.7% of the monomeric F-HSA was found in endothelial cells and only 14.9% was found in Kupffer cells. In contrast, the polymeric F-HSA (1500 kD) was mainly endocytosed by Kupffer cells (71%), whereas the endothelial cells contributed only for 24% in hepatic uptake. In vivo studies and isolated perfused rat liver experiments showed that endocytosis of both monomer and polymer was inhibited by co-administration of polyinosinic acid, a well known inhibitor for scavenger receptors, indicating that these receptors on endothelial and Kupffer cells are mainly involved in this uptake process.

Mild dehydration and atrial natriuretic peptide in young and elderly subjects

The influence of mild dehydration on plasma levels of atrial natriuretic peptide (ANP) was studied in both young (aged 18 to 25 years) and elderly (aged 72 to 86 years) subjects. We expected that dehydration would lower ANP concentrations due to the ensuing volume contraction. A different response of the ANP hormonal system in the elderly might help to explain the observation that elderly subjects are more predisposed to dehydration as compared to young subjects. Dehydration was induced by restriction of fluid intake to 25% of normal for one day. During the study, urinary osmolality increased while osmolar clearance and body weight decreased. Basal ANP concentrations were higher in the elderly subjects. However, these levels did not change during the dehydration study neither in the young nor in the elderly subjects. This may be explained by the activation of counter-regulatory systems preventing a decrease in central blood volume and hence a decrease in ANP concentration.

Potent in vitro anti-human immunodeficiency virus-1 activity of modified human serum albumins

A series of neoglycoproteins was synthesized by coupling of thiophosgene-activated p-aminophenyl derivatives [Biol. Cell. 47:95-110 (1983); J. Histochem. Cytochem. 32:1091-1094 (1984)] of various sugars to human serum albumin. The compounds were evaluated for their in vitro activity against human immunodeficiency virus (HIV). Neoglycoproteins with the highest sugar content were found to be the most potent inhibitors of HIV-1-induced cytopathogenicity. However, this was not due to the nature of the sugar used but, rather, was related to the extra negative charge of the neoglycoproteins. To investigate whether the antiviral activity of the neoglycoproteins exhibited sugar specificity, increased with increasing negative charge, or depended on both sugar specificity and negative charge, we synthesized albumins and neoglycoproteins with an enhanced negative charge, by treatment with formaldehyde or succinic anhydride. Succinylated human serum albumin had the most pronounced net negative charge and had an IC50 of about 1 microgram/ml. No cytotoxicity was observed at concentrations up to 1 mg/ml, implicating a selectivity index (CC50/IC50) of at least 10(3). To elucidate the mechanism of action of these anionic albumins, we investigated whether they interfered with HIV-1 adsorption to the cells, binding of anti-OKT4A monoclonal antibody (mAb) to the CD4 receptor, binding of anti-gp120 mAb to gp120, or inhibition of syncytium formation in co-cultures of HIV-1-infected HUT-78 cells with MOLT-4 cells. From these experiments, we conclude that albumins with an increased negative charge (a) are potent and nontoxic anti-HIV-1 agents, (b) cause a 50% reduction of syncytium formation in the same concentration range as their IC50 in the antiviral assay, and (c) do not bind to the OKT4A epitope of the CD4 receptor and only partly inhibit anti-gp120 mAb-gp120 interaction and virus-cell binding at concentrations that are 100 times higher than their IC50 in the antiviral assay. Therefore, we conclude that the modified albumins interfere with a post-binding event, of which one of the potential mechanisms is an interaction with the gp41 fusion protein, which is necessary for syncytium formation but is not involved in initial virus binding.

Antigenic and genetic variation in cytopathic hepatitis A virus variants arising during persistent infection: evidence for genetic recombination

Variants of hepatitis A virus (pHM175 virus) recovered from persistently infected green monkey kidney (BS-C-1) cells induced a cytopathic effect during serial passage in BS-C-1 or fetal rhesus kidney (FRhK-4) cells. Epitope-specific radioimmunofocus assays showed that this virus comprised two virion populations, one with altered antigenicity including neutralization resistance to monoclonal antibody K24F2, and the other with normal antigenic characteristics. Replication of the antigenic variant was favored over that of virus with the normal antigenic phenotype during persistent infection, while virus with the normal antigenic phenotype was selected during serial passage. Viruses of each type were clonally isolated; both were cytopathic in cell cultures and displayed a rapid replication phenotype when compared with the noncytopathic passage 16 (p16) HM175 virus which was used to establish the original persistent infection. The two cytopathic virus clones contained 31 and 34 nucleotide changes from the sequence of p16 HM175. Both shared a common 5' sequence (bases 30 to 1677), as well as sequence identity in the P2-P3 region (bases 3249 to 5303 and 6462 to 6781) and 3' terminus (bases 7272 to 7478). VP3, VP1, and 3Cpro contained different mutations in the two virus clones, with amino acid substitutions at residues 70 of VP3 and 197 and 276 of VP1 of the antigenic variant. These capsid mutations did not affect virion thermal stability. A comparison of the nearly complete genomic sequences of three clonally isolated cytopathic variants was suggestive of genetic recombination between these viruses during persistent infection and indicated that mutations in both 5' and 3' nontranslated regions and in the nonstructural proteins 2A, 2B, 2C, 3A, and 3Dpol may be related to the cytopathic phenotype.