Efficacy of local dipyridamole therapy in a porcine model of arteriovenous graft stenosis

Perivascular delivery of antiproliferative drugs has been proposed as an approach to prevent neointimal hyperplasia associated with hemodialysis polytetrafluoroethylene (PTFE) grafts. We examined this approach to deliver dipyridamole in a porcine graft model. PTFE grafts were implanted between the carotid artery and external jugular vein bilaterally in pigs. During the surgery or 1 week post-graft placement, dipyridamole (0.26-52 mg) alone or incorporated in microspheres was mixed with an injectable polymeric gel and applied to the graft-arterial and graft-venous anastomoses on one side, whereas the contralateral control graft received no treatment. Three or four weeks after operation, the grafts and adjacent vessels were explanted en bloc and cross-sections of the anastomoses were examined histologically. The degree of neointimal hyperplasia was quantified by planimetry. In separate experiments, dipyridamole was extracted from the explanted tissues and assayed by spectrofluorometry. The normalized median hyperplasia areas of the treated and control graft-venous anastomoses were 0.45 (25th-75th percentile, 0.30-0.86) and 0.24 (0.21-0.30), respectively (N=7; P=0.08). The median hyperplasia areas of the treated and control graft-arterial anastomoses were 0.12 (0.07-0.39) and 0.11 (0.09-0.13), respectively (N=7; P=0.31). The dipyridamole levels in the vascular walls around the anastomoses were at or above the in vitro inhibitory concentrations for approximately 3 weeks. These results suggest that the local perivascular sustained delivery of dipyridamole, even at high dosages, was ineffective in inhibiting neointimal hyperplasia associated with PTFE grafts in a porcine model.

Regeneration of the replication-associated proteins tandem direct repeat recognition nucleotide sequence at the origin of DNA replication of porcine circovirus type 1

Four copies of a hexanucleotide (H) sequence are located to the right of the palindrome at the origin of DNA replication of the porcine circovirus type 1 (PCV1) genome. These sequences are organized in two direct tandems, the proximal H1/H2 and the distal H3/H4 repeats, and they have been shown to be binding sites for the essential Rep and Rep' proteins. Previous work demonstrated that infectious PCV1 virion can accommodate a variable number of H sequences at the origin of DNA replication. In this work, mutational analysis was conducted to elucidate the critical core element within the hexanucleotide with respect to self-DNA replication and progeny virus synthesis. It was found that while a single H sequence abutting the palindrome is sufficient for PCV1 viability, a tandem repeat arrangement is the more stable and thus preferred configuration. Within the H sequence, selected nucleotides at specific positions are critical for Rep-associated protein recognition and for viral DNA replication.

Mutational analysis of the direct tandem repeat sequences at the origin of DNA replication of porcine circovirus type 1

Mutational analysis was conducted to investigate the role of the nucleotide sequences flanking the stem-loop palindromic structure at the origin of DNA replication of porcine circovirus type 1 (PCV1) with respect to self-DNA replication and progeny virus generation. The results demonstrated that the A-rich sequence to the left of the palindrome is non-essential for virus replication. Although a set of four hexanucleotide (H) sequences to the right of the palindrome (organized in two tandem repeats: the proximal H1/H2 and the distal H3/H4) are binding sites for the viral Rep-associated proteins in vitro, only a proximal tandem (H/H or h-like/H) is essential for PCV1 DNA replication. In the presence of H1/H2, mutations engineered into H3/H4 were preserved in the progeny viruses. Mutations engineered into H1/H2 were invariably deleted so that the downstream H3/H4 was placed next to the palindrome. Viral genome with mutations engineered into both H1/H2 and H3/H4 underwent extensive nucleotide reorganization to yield progeny viruses containing either H3/H4, h-like/H4, or h-like/H3/H4 sequences.

Detection of rampant nucleotide reversion at the origin of DNA replication of porcine circovirus type 1

Mutational analysis was conducted to investigate the involvement of the "loop-sequence" (which is flanked by a pair of 11-nucleotide inverted repeats) at the origin of DNA replication of porcine circovirus type 1 with respect to viral protein synthesis, DNA self-replication and progeny virus production. The results demonstrated that an octanucleotide (A1G2T3A4T5T6A7C8) embedded in the loop is essential for viral DNA replication. Similar to previous work with porcine circovirus type 2, this octanucleotide can be further condensed to an essential core element represented by AxTAxTAC. After transfection, mutations introduced into the positions indicated by x (positions 2 and 5) were retained in the progeny viruses, while mutations engineered into the positions specified by the indicated nucleotides either did not yield any progeny virus (positions 6, 7, and 8) or they reverted back to wild-type nucleotide to generate infectious progeny viruses (positions 1, 3, and 4). In comparison to porcine circovirus type 2, porcine circovirus type 1 mutant genomes with perturbed octanucleotide sequences exhibited higher propensity to revert to wild-type under similar experimental conditions. The rate and frequency at which some of the nucleotide reversions occurred suggest that base complementarity may not be the governing factor for nucleotide incorporation at the porcine circovirus origin of DNA replication, and that the Rep-associated protein(s) may play a critical role in this process.

Palindrome regeneration by template strand-switching mechanism at the origin of DNA replication of porcine circovirus via the rolling-circle melting-pot replication model

Palindromic sequences (inverted repeats) flanking the origin of DNA replication with the potential of forming single-stranded stem-loop cruciform structures have been reported to be essential for replication of the circular genomes of many prokaryotic and eukaryotic systems. In this study, mutant genomes of porcine circovirus with deletions in the origin-flanking palindrome and incapable of forming any cruciform structures invariably yielded progeny viruses containing longer and more stable palindromes. These results suggest that origin-flanking palindromes are essential for termination but not for initiation of DNA replication. Detection of template strand switching in the middle of an inverted repeat strand among the progeny viruses demonstrated that both the minus genome and a corresponding palindromic strand served as templates simultaneously during DNA biosynthesis and supports the recently proposed rolling-circle "melting-pot" replication model. The genome configuration presented by this model, a four-stranded tertiary structure, provides insights into the mechanisms of DNA replication, inverted repeat correction (or conversion), and illegitimate recombination of any circular DNA molecule with an origin-flanking palindrome.

Identification of an octanucleotide motif sequence essential for viral protein, DNA, and progeny virus biosynthesis at the origin of DNA replication of porcine circovirus type 2

A plasmid-based transfection system capable of generating infectious porcine circovirus type 2 (PCV2) was established. This system was then used in mutagenesis studies to investigate the involvement of a "conserved" nonanucleotide (which constitutes a portion of the loop sequence) located at the origin of DNA replication of PCV2 with respect to viral protein synthesis, DNA self-replication, and progeny virus production. The results demonstrated that an octanucleotide (AGTATTAC) embedded in the loop sequence is essential for virus replication. This octanucleotide can be further condensed to an essential core element (ECE) represented by AxTAxTAC. The positions specified by the indicated nucleotides are critical for viral DNA replication and stable infectious virus production, and they cannot be substituted by other bases, while the positions indicated by x can accept variable bases and yield stable progeny viruses.

Detection of template strand switching during initiation and termination of DNA replication of porcine circovirus

Nucleotide substitution mutagenesis was conducted to investigate the importance of the inverted repeats (palindrome) at the origin of DNA replication (Ori) of porcine circovirus type 1 (PCV1). Viral genomes with engineered mutations on either arm or both arms of the palindrome were not impaired in protein synthesis and yielded infectious progeny viruses with restored or new palindromes. Thus, a flanking palindrome at the Ori was not essential for initiation of DNA replication, but one was generated inevitably at termination. Among the 26 viruses recovered, 16 showed evidence of template strand switching, from minus-strand genome DNA to palindromic strand DNA, during biosynthesis of the Ori. Here I propose a novel rolling-circle "melting-pot" model for PCV1 DNA replication. In this model, the replicator Rep protein complex binds, destabilizes, and nicks the Ori sequence to initiate leading-strand DNA synthesis. All four strands of the destabilized inverted repeats exist in a "melted" configuration, and the minus-strand viral genome and a palindromic strand are available as templates, simultaneously, during initiation or termination of DNA replication. Inherent in this model is a "gene correction" or "terminal repeat correction" mechanism that can restore mutilated inverted-repeat sequences to a palindrome at the Ori of circular DNAs or at the termini of circularized linear DNAs. Potentially, the melted state of the inverted repeats increases the rate of noncomplementary or illegitimate nucleotide incorporation into the palindrome. Thus, this melting-pot model provides insight into the mechanisms of DNA replication, gene correction, and illegitimate recombination at the Ori of PCV1, and it may be applicable to the replication of other circular DNA molecules.

Identification of the essential and non-essential transcription units for protein synthesis, DNA replication and infectious virus production of Porcine circovirus type 1

A plasmid-based transfection system capable of yielding infectious Porcine circovirus type 1 (PCV1) was established and mutational analysis was conducted to investigate the involvement of each viral transcription unit in protein synthesis, DNA replication and progeny virus production. During PCV1 replication in PK15 cells, twelve viral-specific RNAs are synthesized. They include the capsid protein RNA ( CR), eight Rep-associated RNAs ( Rep, Rep', Rep3a, Rep3b, Rep3c-1, Rep3c-2, Rep3c-3 and Rep3c-4), and three NS-associated RNAs ( NS462, NS642 and NS0). A stop codon introduced at the 5'-end of CR did not affect Rep-associated antigens or viral DNA synthesis. Altering the consensus dinucleotide at the splice junctions of the Rep3 RNAs and NS462 or introducing an early termination codon in Rep3c-4 and NS0 also did not have any affect on virus replication. However, mutations in Rep and Rep' caused greater than 99% reduction of protein synthesis and complete shut down of viral DNA replication. NS642 could not be assayed in this study because silent mutation at the splice junction was not possible. However, it is probably equivalent to the non-essential RNA ( NS672) of PCV type 2. Thus, only two proteins, Rep and Rep', are essential for PCV1 protein, DNA and infectious virus biosynthesis.

The essential and nonessential transcription units for viral protein synthesis and DNA replication of porcine circovirus type 2

During porcine circovirus (PCV) replication in PK15 cells, nine PCV type 2 (PCV2)-specific RNAs are synthesized. They include the capsid RNA (CR), five Rep-associated RNAs (Rep, Rep', Rep3a, Rep3b, and Rep3c), and three NS-associated RNAs (NS515, NS672, and NS0). In this work, mutational analyses were conducted to investigate the involvement of each PCV2 transcription unit in viral protein synthesis and DNA replication. The results demonstrated that a stop codon introduced at the very 5'-end of CR did not affect Rep-associated antigens or viral DNA synthesis. Altering the consensus dinucleotides at the splice junctions of the minor RNAs (Rep3a, Rep3b, Rep3c, NS515, and NS672) or introducing a stop codon in the abundant NS0 RNA also did not have any effect on viral protein synthesis or DNA replication. However, mutations that resulted in truncated Rep or Rep' proteins caused greater than 99% reduction of viral protein synthesis and complete shut down of viral DNA replication. These results demonstrated that both Rep and Rep' are absolutely essential for PCV2 replication.

Comparative analysis of the transcriptional patterns of pathogenic and nonpathogenic porcine circoviruses

The RNAs of porcine circovirus type 1 (PCV1) synthesized in PK15 cells were characterized. A total of 12 RNAs were detected. They include the viral capsid protein RNA (CR), a cluster of eight Rep-associated RNAs (designated Rep, Rep', Rep3a, Rep3b, Rep3c-1, Rep3c-2, Rep3c-3, and Rep3c-4), and three NS-associated RNAs (designated NS462, NS642, and NS0). Members of the Rep-associated RNA cluster all share common 5'- and 3'-nucleotide sequences and they share common 3'-nucleotide sequence with the NS-associated RNAs. Rep, capable of coding for the full-length replication-associated protein, appears to be the primary transcript that gives rise to the other seven Rep-associated RNAs by alternate splicing. NS462, NS642, and NS0 appear to have been transcribed from three different promoters present inside ORF1, independent from the Rep promoter. Based on sequence alignment analysis, both the nonpathogenic PCV1 and the pathogenic porcine circovirus type 2 (PCV2) (with nine RNAs: Rep, Rep', Rep3a, Rep3b, Rep3c, NS515, NS672, and NS0) utilize comparable genetic elements similarly located along the genome for viral gene expression. The Rep, Rep', Rep3a, Rep3b, and NS0 of PCV1 and PCV2 are considered equivalent entities in their respective systems. However, quantitative and qualitative differences (splice junction variation) were observed among the Rep3c- and NS-associated RNAs. This work provides a general framework and genetic basis to investigate the biologic properties (and differences) of PCV1 and PCV2.

Transcriptional analysis of porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is the causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome. In this work, the RNAs of PCV2 synthesized during productive infection in porcine kidney cells were characterized. A total of nine RNAs were detected. They include the viral capsid protein RNA (CR), a cluster of five Rep-associated RNAs (designated Rep, Rep', Rep3a, Rep3b, and Rep3c), and three NS-associated RNA (designated NS515, NS672, and NS0). Members of the Rep-associated RNA cluster all share common 5' and 3' nucleotide sequences and they also share 200 common 3' nucleotides with the NS-associated RNAs. Rep, capable of coding for the replication-associated-protein (RepP), appears to be the primary transcript that gives rise to Rep', Rep3a, Rep3b, and Rep3c by alternate splicing. Protein sequence alignment showed that RepP and the Rep' protein of PCV2 are equivalent to those described for PCV type 1 (PCV1) (a nonpathogenic virus), which had been shown to be essential for viral DNA replication. The results also suggest that NS515, NS672, and NS0 are transcribed from three different promoters inside ORF1 downstream of the Rep promoter. To date, only three RNAs (CR, Rep, and Rep') have been reported for PCV1-infected porcine kidney cells. Therefore, it is important to apply similar strategies from this study to reexamine the transcription pattern of PCV1.

Kinetics of porcine circovirus type 2 replication

The kinetics of porcine circovirus type 2 (PCV2) replication in PK15 cells was examined. During productive infection, viral antigens, RNA transcripts and progeny viruses all increased in a time dependent manner. Viral antigens were observed in a few cells at 18 hour postinfection (h p.i.) and cell-free progeny viruses began to appear at about 30 h p.i. Viral transcripts were detected by 18 h p.i. and the capsid protein RNA of 950 nucleotides (nt) was the most abundant RNA species. Two other RNAs of sizes 750 and 450 nt, derived from the predicted replication associated protein (Rep) gene region, were also detected. These two RNAs share 3' common nucleotide sequences and they are transcribed in the same orientation as the proposed unspliced Rep RNA or the recently described Rep' RNA. The 35 kD capsid protein was observed at 30 h p.i. by Western blot analysis and it appeared to be the most immunodominant protein in swine exposed to PCV2. The capsid proteins of PCV type 1 and PCV2 each contain a nuclear localization signal sequence capable of targeting a reporter protein to the nucleoli of transfected cells when the capsid proteins were expressed as 3' fusion polypeptides. Although previous reports indicated that PCV2 capsid proteins localized predominantly in the nuclei of infected cells, we observed an abundant amount of PCV2 capsid proteins in the cytoplasm of many cells of the infected cultures. The cells that exhibited cytoplasmic capsid proteins also contained virus nucleic acids, indicating that these proteins were synthesized by the infected cells and not through uptake from the culture medium. Elucidation of the changes that affect the localization pattern of PCV2 capsid proteins, nuclear versus cytoplasmic, requires further investigation.

Increases in mass transfer-area coefficients and urea Kt/V with increasing dialysate flow rate are greater for high-flux dialyzers

The hemodialyzer mass transfer-area coefficient (K(o)A) for urea increases with increasing dialysate flow rate (Q(d)). The magnitude of the increase in K(o)A varies depending on the particular dialyzer under consideration; however, dialyzer properties that govern this phenomenon have not been established. We hypothesized that Q(d)-dependent increases in K(o)As are influenced by the water permeability of the dialysis membrane. We evaluated in vitro the effect of blood flow rate (Q(b)) and Q(d) on urea and creatinine K(o)As for two low-flux (Polyflux 6L and 8L) and two high-flux (Polyflux 14S and 17S) dialyzers containing Polyamide S membranes with similar membrane surface areas. Additional experiments were also performed on high-flux dialyzers containing Polyamide S membranes with very large surface areas (Polyflux 21S and 24S). K(o)As, calculated from the mean of blood- and dialysate-side clearances, were determined at zero net ultrafiltration for three different Q(b) and Q(d) combinations: Q(b) of 300 mL/min and Q(d) of 500 mL/min; Q(b) of 450 mL/min and Q(d) of 500 mL/min; and Q(b) of 450 mL/min and Q(d) of 800 mL/min. Urea and creatinine K(o)As were independent of the Q(b) but increased when Q(d) was increased from 500 to 800 mL/min. These increases in both urea and creatinine K(o)As were greater for high-flux than low-flux dialyzers (P < 0.0001). As expected, urea and creatinine K(o)As also increased with increasing membrane surface area. We conclude that dialysis membrane water permeability (or flux) is a dialyzer property that influences the dependence of small-solute K(o)As and clearance on Q(d). Whether this phenomenon is caused by enhanced internal filtration for dialyzers containing high-flux membranes requires further study.

Quantification of middle molecular weight solute removal in dialysis

The pioneering work of Gotch emphasized the critical need to be quantitative with respect to treatment prescription. Through his meticulous derivations and analyses regarding Kt/V(urea), he has provided powerful insight into the standard therapy prescriptions that we now employ clinically. However, time has seen the proliferation of treatment techniques, most of which are too "young" to have been characterized with respect to clinical outcomes. Further, the relationship between removal of urea and removal of middle molecular size solutes associated with these newer techniques deviates from that associated with conventional, clinically qualified techniques. In this article we examine the solute clearance profile of some of these new methodologies and their relationship to current criteria for treatment adequacy. Our approach is to discuss components of the overall transport process and then utilize modeling of surrogate molecules over the size range of interest whose transport characteristics are known. Alteration in the solute clearance profile of these surrogate markers in response to changes in prescription variables will thus offer insight into the spectrum of toxic middle molecules that are removed when size, space of distribution, and generation rate are known.

Risk factors for hypertension in chronic hemodialysis patients: baseline data from the HEMO study

A cross-sectional analysis was performed to determine risk factors associated with hypertension in 1,238 chronic hemodialysis patients upon enrollment into the HEMO Study. The mean pre- and post-dialysis systolic blood pressure were 152.4 +/- 25.0 (mean +/- SD) and 137.8 +/- 24.6 mm Hg, respectively. The mean pre- and post-dialysis diastolic blood pressures were 82.1 +/- 14.8 and 74.7 +/- 13.8 mm Hg, respectively. Less than 30% of the study cohort had blood pressures that were normotensive by JNC VI guidelines. Risk factors associated with higher pre- and post-dialysis systolic blood pressures included the presence of diabetes mellitus, older age, increased number of prescribed antihypertensive medications, lower hematocrit, and absence of arrhythmias. Variables associated with higher pre- and post-dialysis diastolic blood pressures included younger age, increased number of prescribed anti-hypertensive medications and absence of arrhythmias. There was also a nonlinear relationship between blood pressure and prescribed total ultrafiltration volume. A total ultrafiltration volume of >2.5 kg was associated with an elevation in pre-dialysis systolic and diastolic blood pressures. A total ultrafiltration volume of < or =2.5 kg was associated with an elevation in post-dialysis systolic and diastolic blood pressures. These data on ultrafiltration volume suggest that higher pre-dialysis blood pressures may be associated with excessive interdialytic weight gains due to patient noncompliance with fluid restriction and that higher post-dialysis blood pressures may be associated with a prescribed dry weight that is higher than the patient's true dry weight. Better management of these parameters may improve the prevalence and severity of hypertension in this population.

Effect of indomethacin on peritoneal protein loss in a rabbit model of peritonitis

BACKGROUND

Although various inflammatory mediators have been previously shown to be released into the peritoneal cavity during peritonitis in peritoneal dialysis patients, those that are involved in governing changes in peritoneal permeability to small solutes and protein remain incompletely defined.

METHODS

We determined the importance of prostanoid production in the enhanced protein loss observed during acute peritonitis by inhibition experiments using indomethacin, an inhibitor of cyclooxygenase activity. The association between changes in peritoneal permeability and the generation of inflammatory mediators after adding Escherichia coli to peritoneal dialysate was first examined in series 1 experiments. Series 2 experiments then determined the effect of intraperitoneal administration of indomethacin (75 microg/mL) on changes in peritoneal permeability after adding E. coli to peritoneal dialysate. All experiments were performed in male New Zealand White rabbits (2.6 to 3.4 kg body weight) using an eight-hour dwell of dialysate containing 2.5% glucose. Peritoneal permeability to creatinine and protein was assessed by time-dependent changes in the dialysate to plasma concentration ratios of these solutes.

RESULTS

Series 1 experiments showed enhanced leukocyte migration into the peritoneal cavity and increased peritoneal permeability to protein during bacterial challenge that was accompanied by an increase in the dialysate concentrations of prostaglandin E2 (PGE2), 6-keto-PGF1alpha, and interleukin-8, but not nitrate + nitrite (a measure of local nitric oxide production). Inhibition of prostanoid production by intraperitoneal administration of indomethacin in series 2 experiments resulted in lower dialysate concentrations of PGE2 and 6-keto-PGF1alpha and in lower peritoneal permeability to protein, both to control levels. No effect of indomethacin on transperitoneal migration of leukocytes or the generation of interleukin-8 was observed.

CONCLUSIONS

Enhanced production of prostanoids likely plays an important role in governing the increase in peritoneal permeability to protein during acute, bacterial peritonitis in the rabbit.

Atherosclerotic cardiovascular disease risks in chronic hemodialysis patients

BACKGROUND

Cardiovascular diseases are the most common causes of death among chronic hemodialysis patients, yet the risk factors for these events have not been well established.

METHODS

In this cross-sectional study, we examined the relationship between several traditional cardiovascular disease risk factors and the presence or history of cardiovascular events in 936 hemodialysis patients enrolled in the baseline phase of the Hemodialysis Study sponsored by the U.S. National Institutes of Health. The adjusted odds ratios for each of the selected risk factors were estimated using a multivariable logistic regression model, controlling for the remaining risk factors, clinical center, and years on dialysis.

RESULTS

Forty percent of the patients had coronary heart disease. Nineteen percent had cerebrovascular disease, and 23% had peripheral vascular disease. As expected, diabetes and smoking were strongly associated with cardiovascular diseases. Increasing age was also an important contributor, especially in the group less than 55 years and in nondiabetic patients. Black race was associated with a lower risk of cardiovascular diseases than non-blacks. Interestingly, neither serum total cholesterol nor predialysis systolic blood pressure was associated with coronary heart disease, cerebrovascular disease, or peripheral vascular disease. Further estimation of the coronary risks in our cohort using the Framingham coronary point score suggests that traditional risk factors are inadequate predictors of coronary heart disease in hemodialysis patients.

CONCLUSIONS

Some of the traditional coronary risk factors in the general population appear to be also applicable to the hemodialysis population, while other factors did not correlate with atherosclerotic cardiovascular diseases in this cross-sectional study. Nontraditional risk factors, including the uremic milieu and perhaps the hemodialysis procedure itself, are likely to be contributory. Further studies are necessary to define the cardiovascular risk factors in order to devise preventive and interventional strategies for the chronic hemodialysis population.

Cardiopulmonary events during hemodialysis: effects of dialysis membranes and dialysate buffers

Adverse cardiac and pulmonary events are frequently observed during hemodialysis and contribute to significant morbidity and mortality. The temporal relationship between these events during the intradialytic period has not been well defined. To examine the event rate and timing of silent ischemia, cardiac ectopy, and hypoxemia, we conducted a prospective, single-blind, randomized study of 10 subjects undergoing maintenance hemodialysis with four contiguous combinations of dialysis membranes (cuprammonium or polysulfone) and dialysates (acetate or bicarbonate). The frequency of oxygen desaturation events peaked during the first 2 hours, whereas silent myocardial ischemia and supraventricular ectopies occurred more often in the later hours. Ventricular ectopy occurred steadily throughout the intradialytic period. The combination of acetate dialysis and cuprammonium membrane is associated with the most frequent events. We conclude that cardiopulmonary events can occur frequently during hemodialysis, and the frequency is dependent on the type of dialysis membrane and dialysate buffer used.

Increased protein loss during peritonitis associated with peritoneal dialysis is neutrophil dependent

BACKGROUND

Peritonitis in peritoneal dialysis patients is accompanied by an enhanced migration of neutrophils (PMNs) and increased protein loss into the peritoneal cavity; however, the role of PMNs in governing increased protein loss during peritonitis associated with peritoneal dialysis is unknown.

METHODS

We determined the importance of PMNs in governing changes in peritoneal permeability to protein in New Zealand White rabbits in which acute peritonitis was induced by adding 4 x 106 colony-forming units of Escherichia coli to 35 mL/kg of 0.9% saline dialysate. The total leukocyte and PMN migration into the peritoneal cavity was assessed by differential cell counts in the dialysate, and peritoneal permeability to protein was evaluated by calculating the dialysate to plasma concentration ratio for total protein as a function of time during a six- or eight-hour dwell. In series 1 experiments, leukocytes were depleted from the rabbit circulation by an intravenous injection of mustine (1.2 mg/kg) three days before the experiment; in series 2 experiments, integrin-dependent PMN migration into the peritoneal cavity was inhibited by an intravenous injection of monoclonal antibody (mAb) 60.3 (2 mg/kg) directed against the integrin CD18 on leukocytes five minutes before the experiment.

RESULTS

In series 1 experiments, mustine decreased circulating leukocytes by 82 +/- 5% (mean +/- SEM) and circulating PMNs by 93 +/- 3%. Total leukocyte and PMN migration into the peritoneal cavity and peritoneal permeability to protein were decreased in mustine-treated rabbits after exposure to E. coli in the dialysate to levels similar to those found in rabbits without bacterial peritonitis. In series 2 experiments, an intravenous injection of anti-CD18 antibody also abrogated both the enhanced PMN migration into the peritoneal cavity and the increased peritoneal permeability to protein after exposure to E. coli in the dialysate.

CONCLUSIONS

PMN migration into the peritoneal cavity is integrin dependent. Increased protein loss during acute, gram-negative bacterial peritonitis in a rabbit model of peritoneal dialysis is PMN dependent.

The effects of heparin, protamine, and heparinase 1 on platelets in vitro using whole blood flow cytometry

The effects of heparinization and the reversal of heparin activity on platelet function after cardiopulmonary bypass have not been well defined. Flow cytometry has become a convenient and powerful technique for characterizing platelets. We examined the expression of a secretion marker (P-selectin) and an aggregation marker (activated fibrinogen receptor GP IIb-IIIa) on normal platelets in response to heparin, heparinase 1, and protamine in vitro using whole blood flow cytometry. Unfractionated heparin increased adenosine diphosphate-induced expression of P-selectin and GP IIb-IIIa in a dose-dependent manner. Heparinase 1 alone decreased both markers of platelet activation. Protamine alone increased P-selectin expression but had no effect on GP IIb-IIIa expression. Heparinase 1 antagonized the stimulatory effect of heparin on both markers. In contrast, protamine antagonized the effect of heparin on GP IIb-IIIa expression but potentiated the effect of heparin on P-selectin expression. These in vitro observations suggest that 1) both heparin and its reversal agents affect platelet secretion and aggregation, and 2) heparinase 1 reverses heparin-induced platelet preactivation more effectively than protamine.

IMPLICATIONS

This experimental in vitro study demonstrates that heparin and its reversal agents affect platelet secretion and aggregation.

The effects of aprotonin on platelets in vitro using whole blood flow cytometry

We sought to evaluate the effects of aprotinin on the number and function of the platelet glycoprotein (GP) IIb-IIIa receptor and on the expression of P-selectin in vitro in order to gain insight into the potential mechanisms involved in the platelet-protective action of aprotinin during cardiopulmonary bypass. Aprotinin at 50 to 200 kallikrein inhibiting units/mL decreased the expression of activated GP IIb-IIIa complex in response to adenosine diphosphate or thrombin receptor activator peptide 6 in a dose-dependent manner in both citrated and heparinized whole blood experiments. Aprotinin inhibited adenosine diphosphate-induced platelet aggregation, but it exhibited no effect on the expression of GP IIIa and P-selectin. These results indicate that aprotinin interferes with the platelet fibrinogen receptor function during pharmacological activation. Reduced aggregability and platelet adhesion to fibrinogen adsorbed to synthetic surfaces in the presence of aprotinin may prevent platelet consumption during clinical cardiopulmonary bypass. This in vitro study demonstrates that aprotinin decreases the agonist-induced expression of activated GP IIb-IIIa receptors that play a major role in platelet aggregation and adhesion to biomaterial surfaces.

IMPLICATIONS

This in vitro study demonstrates that aprotinin decreases the agonist-induced expression of activated glycoprotein IIb-IIIa receptors that play a major role in platelet aggregation and adhesion to biomaterial surfaces.

Pseudorabies virus induces apoptosis in tissue culture cells

The process of cell death as a result of exposure to pseudorabies virus (PRV) in cultured cells was examined and specific features characteristic of apoptosis were observed. At early times of infection, externalization of membrane phospholipid phophatidylserine was detected by flow cytometry analysis. During the infection process, caspase 3-like protease activity was induced and the activity increased in a time dependent manner. Cellular DNA degradation was demonstrated by agarose gel electrophoresis. Morphologic changes of the nucleus that included chromatin condensation and margination to the periphery of the nucleus were evident in electron microscopy analysis. These biochemical and morphologic changes demonstrated that, during PRV replication, the host cell was induced to undergo apoptosis.

Rebound kinetics of beta2-microglobulin after hemodialysis

BACKGROUND

Evaluation of beta2-microglobulin (beta2m) removal during hemodialysis using predialysis and immediate postdialysis plasma concentrations is only valid in the absence of postdialysis rebound. Postdialysis rebound of beta2m has not been studied extensively, and its importance in the determination of beta2m clearance is unknown.

METHODS

We evaluated the kinetics of urea and beta2m in a crossover study of 10 chronic hemodialysis patients using dialyzers with similar urea mass transfer-area coefficients containing either low-flux cellulose acetate or high-flux cellulose triacetate membranes. Kinetics were examined during and following a 210 minute treatment by measuring plasma concentrations predialysis at regular intervals during therapy and at 0, 2, 10, 20, 30, and 60 minutes postdialysis. Clearances of urea and beta2m were also determined directly from the arterial and venous concentration differences across the dialyzer at 60 minutes after starting dialysis.

RESULTS

By design, urea removal was similar for both low-flux and high-flux dialyzers as assessed by the urea reduction ratio and Kt/V. Postdialysis urea rebound was similar for low- and high-flux dialyzers; the rebound in the plasma urea nitrogen concentration (expressed as a percentage of the intradialytic decrease in plasma concentration) was 9.2 +/- 1.9% (mean +/- SEM) at 30 minutes postdialysis and 13.0 +/- 1.4% at 60 minutes postdialysis for a single pool urea Kt/V of 1.16 +/- 0.05. The plasma beta2m concentration increased by 11.1 +/- 3.0% during the treatment using the low-flux dialyzer but decreased by 27.1 +/- 4.0% during the treatment using the high-flux dialyzer. When using the high-flux dialyzer, the rebound of beta2m was 44.8 +/- 21.4% at 30 minute postdialysis and 45.9 +/- 15.9% at 60 minutes postdialysis. The clearance of beta2m for the high-flux dialyzer calculated from predialysis and immediate postdialysis plasma concentrations using a single-compartment model (28.2 +/- 4.4 ml/min) was higher (P < 0.05) than that determined directly across the dialyzer (18.3 +/- 2.0 ml/min). If either the 30- or 60-minute postdialysis plasma beta2m concentration was used instead, the calculated beta2m clearance (16. 5 +/- 4.8 ml/min or 15.6 +/- 2.8 ml/min, respectively) was similar to that determined directly across the dialyzer.

CONCLUSIONS

Postdialysis rebound of beta2m when using high-flux dialyzers is substantial; neglecting postdialysis rebound results in an overestimation of beta2m clearance when calculated using a single-compartment model.

Analysis of the latency-associated transcript/UL1-3.5 gene cluster promoter complex of pseudorabies virus

During latency, pseudorabies virus (PRV) DNA is preferentially retained in the neurons of the trigeminal ganglion and a spliced 8.5-kilobase poly-A RNA, designated large latency transcript (LLT), is synthesized. Because LLT is the only transcript made during the latent phase, the LLT promoter may be unique among all other PRV promoters that are active in productive infections. Organization of the PRV LLT promoter is quite complex because it coincides with the UL1-3.5 gene cluster promoter, but in the opposite orientation. By conventional designation, LLT is transcribed in the rightward direction while the UL1-3.5 gene cluster is transcribed in the leftward orientation. In this work, activities of the LLT promoter and the UL1-3.5 gene cluster promoter were investigated by transient reporter gene expression assay in cells of neuronal and non-neuronal origins. There are two TATA boxes in this region. We examined the promoter activities of the first TATA box with its 5' sequence (LAP1) and the second TATA box with its 5' sequence (LAP2). The UL1-3.5 promoter driven constructs gave no reporter gene activity in any of the experiments. Reporter gene activity was detected with LAP2 gene constructs, but not with LAP1 constructs, in both neuronal and non-neuronal cells. This is surprising because transcription of PRV LLT in vivo has been attributed to LAP1 and the initiation site was mapped downstream of the LAP1 TATA box and upstream of the LAP2 TATA box. Although LAP1 was not active in these experiments, there was a 3- to 10-fold enhancement of activity when LAP1 and LAP2 were placed in tandem.

Ultrafiltration method for measuring vascular access flow rates during hemodialysis

BACKGROUND

The vascular access blood flow rate (QA) has been shown to be an important predictor of vascular access failure; therefore, the routine measurement of QA may prove to be a useful clinical method of vascular access assessment.

METHODS

We have developed a new ultrafiltration (UF) method for determining QA during HD from changes in arterial hematocrit (H) after abrupt changes in the UF rate with the dialysis blood lines in the normal (DeltaHn) and reverse (DeltaHr) configurations. This method accounts for cardiopulmonary recirculation and requires neither intravenous saline injections nor accurate knowledge of the dialyzer blood flow rate. Clinical studies were conducted in 65 chronic HD patients from three different dialysis programs to compare QA determined by the UF method with that determined by saline dilution using an ultrasound flow sensor.

RESULTS

Arterial H increased (P<0.0001) after abrupt increases in the UF rate when the lines were in the normal and reverse configurations. An increase in the UF rate from the minimum setting to 1.8 liter/hr resulted in a DeltaHn of 0.3+/-0.2 (mean +/- SD) H units and a DeltaHr of 1.6+/-1.0 H units. Q(A) values determined by the UF method (1050+/-460 ml/min) were 16+/-25% higher (P<0.001) than those determined by saline dilution (950+/-440 ml/min); the calculated QA values by the UF and saline dilution methods correlated highly with each other (R = 0.92, P<0.0001). The average coefficient of variation for duplicate measurements of QA determined by the UF method in a subset of these patients (N = 21) was approximately 10% when assessed in either the same dialysis session or consecutive sessions.

CONCLUSIONS

The results from this study show that changes in arterial H after abrupt changes in the UF rate can be used to assess Q(A).