Antibiotic Myths for the Infectious Diseases Clinician

Antimicrobials are commonly prescribed and often misunderstood. With more than 50% of hospitalized patients receiving an antimicrobial agent at any point in time, judicious and optimal use of these drugs is paramount to advancing patient care. This narrative will focus on myths relevant to nuanced consultation from infectious diseases specialists, particularly surrounding specific considerations for a variety of antibiotics.

Evaluation of an Opt-Out Protocol for Antibiotic De-Escalation in Patients With Suspected Sepsis: A Multicenter, Randomized, Controlled Trial

BACKGROUND

Sepsis guidelines recommend daily review to de-escalate or stop antibiotics in appropriate patients. This randomized, controlled trial evaluated an opt-out protocol to decrease unnecessary antibiotics in patients with suspected sepsis.

METHODS

We evaluated non-intensive care adults on broad-spectrum antibiotics despite negative blood cultures at 10 US hospitals from September 2018 through May 2020. A 23-item safety check excluded patients with ongoing signs of systemic infection, concerning or inadequate microbiologic data, or high-risk conditions. Eligible patients were randomized to the opt-out protocol vs usual care. Primary outcome was post-enrollment antibacterial days of therapy (DOT). Clinicians caring for intervention patients were contacted to encourage antibiotic discontinuation using opt-out language. If continued, clinicians discussed the rationale for continuing antibiotics and de-escalation plans. To evaluate those with zero post-enrollment DOT, hurdle models provided 2 measures: odds ratio of antibiotic continuation and ratio of mean DOT among those who continued antibiotics.

RESULTS

Among 9606 patients screened, 767 (8%) were enrolled. Intervention patients had 32% lower odds of antibiotic continuation (79% vs 84%; odds ratio, 0.68; 95% confidence interval [CI], .47-.98). DOT among those who continued antibiotics were similar (ratio of means, 1.06; 95% CI, .88-1.26). Fewer intervention patients were exposed to extended-spectrum antibiotics (36% vs 44%). Common reasons for continuing antibiotics were treatment of localized infection (76%) and belief that stopping antibiotics was unsafe (31%). Thirty-day safety events were similar.

CONCLUSIONS

An antibiotic opt-out protocol that targeted patients with suspected sepsis resulted in more antibiotic discontinuations, similar DOT when antibiotics were continued, and no evidence of harm.

CLINICAL TRIALS REGISTRATION

NCT03517007.

Effects of a Collaborative, Community Hospital Network for Antimicrobial Stewardship Program Implementation

BACKGROUND

Individual hospitals may lack expertise, data resources, and educational tools to support antimicrobial stewardship programs (ASP).

METHODS

We established a collaborative, consultative network focused on hospital ASP implementation. Services included on-site expert consultation, shared database for routine feedback and benchmarking, and educational programs. We performed a retrospective, longitudinal analysis of antimicrobial use (AU) in 17 hospitals that participated for at least 36 months during 2013-2018. ASP practice was assessed using structured interviews. Segmented regression estimated change in facility-wide AU after a 1-year assessment, planning, and intervention initiation period. Year one AU trend (1 to 12 months) and AU trend following the first year (13 to 42 months) were compared using relative rates (RR). Monthly AU rates were measured in days of therapy (DOT) per 1,000 patient days for overall AU, specific agents, and agent groups.

RESULTS

Analyzed data included over 2.5 million DOT and almost 3 million patient-days. Participating hospitals increased ASP-focused activities over time. Network-wide overall AU trends were flat during the first 12 months after network entry but decreased thereafter (RR month 42 vs month 13, 0.95, 95% Confidence Interval (CI) 0.91-0.99.) Large variation was seen in hospital-specific AU. Fluoroquinolone use was stable during year one, then dropped significantly. Other agent groups demonstrated a non-significant downward trajectory after year one.

CONCLUSIONS

Network hospitals increased ASP activities and demonstrated decline in AU over a 42-month period. A collaborative, consultative network is a unique model in which hospitals can access ASP implementation expertise to support long-term program growth.

Development of an electronic definition for de-escalation of antibiotics in hospitalized patients

BACKGROUND

Antimicrobial stewardship programs (ASPs) promote the principle of de-escalation: moving from broad to narrow spectrum agents and stopping antibiotics when no longer indicated. A standard, objective definition of de-escalation applied to electronic data could be useful for ASP assessments.

METHODS

We derived an electronic definition of antibiotic de-escalation and performed a retrospective study among five hospitals. Antibiotics were ranked into 4 categories: narrow spectrum, broad spectrum, extended spectrum, and agents targeted for protection. Eligible adult patients were cared for on inpatient units, had antibiotic therapy for at least 2 days, and were hospitalized for at least 3 days after starting antibiotics. Number of antibiotics and rank were assessed at two time points: day of antibiotic initiation and either day of discharge or day 5. De-escalation was defined as reduction in either the number of antibiotics or rank. Escalation was an increase in either number or rank. Unchanged was either no change or discordant directions of change. We summarized outcomes among hospitals, units, and diagnoses.

RESULTS

Among 39,226 eligible admissions, de-escalation occurred in 14,138 (36%), escalation in 5,129 (13%), and antibiotics were unchanged in 19,959 (51%). De-escalation varied among hospitals (median 37%, range 31-39%, p<.001). Diagnoses with lower de-escalation rates included intra-abdominal (23%) and skin and soft tissue (28%) infections. Critical care had higher rates of both de-escalation and escalation compared with wards.

CONCLUSIONS

Our electronic de-escalation metric demonstrated variation among hospitals, units, and diagnoses. This metric may be useful for assessing stewardship opportunities and impact.

Is increased screening and early antiretroviral treatment for HIV-1 worth the investment? An analysis of the public health and economic impact of improvement in the UK

OBJECTIVES

Early treatment of HIV-1 infection at all CD4 levels has demonstrated clinical and public health benefits. This analysis examined the costs, health outcomes, and cost-effectiveness of increased HIV-1 screening and early treatment initiation in the UK.

METHODS

A Markov model followed theoretical cohorts of men who have sex with men (MSM), heterosexuals, and people who inject drugs (PWID) with initially undiagnosed HIV-1 infection over their remaining lifetimes. The analysis examined increased HIV-1 screening (resulting in 10-50% improvements in diagnosis rates) versus current screening in sexual health services (SHS) and other settings, with all individuals initiating treatment within 3 months of diagnosis. Health status was modelled by viral load and CD4 cell count as individuals progressed to diagnosis and treatment. Individuals accrued quality-adjusted life-years (QALYs), incurred costs for screening and HIV-related clinical management, and were at risk of transmitting HIV-1 infection to their partners. Input parameter data were taken primarily from UK-specific published sources. All outcomes were discounted at 3.5% annually.

RESULTS

The model estimated that increased screening and early treatment resulted in fewer onward HIV transmissions, more QALYs, and higher total costs. For SHS, incremental cost-effectiveness ratios (ICERs) for heterosexuals (~£22 000/QALY gained) were within typical UK willingness-to-pay thresholds and were well below these thresholds for MSM (~£9500/QALY gained) and PWID (~£6500/QALY gained). Sensitivity analysis showed that model results were robust.

CONCLUSIONS

Increased HIV-1 screening and early treatment initiation may be a cost-effective strategy to reduce HIV transmission and improve health for MSM, heterosexuals, and PWID in the UK.

C5a is important in the tubulointerstitial component of experimental immune complex glomerulonephritis

Interstitial injury is the hallmark of glomerulonephritis which is progressing to end-stage renal disease (ESRD). In humans and experimental animals, we have shown that interstitial disease is accompanied by up-regulation of complement components in tubular epithelial cells. Glomerulonephritis was induced in mice by the intraperitoneal injection of horse spleen apoferritin (HSA) and lipopolysaccharide (LPS). In addition to wild-type C57/B6 mice, animals in which the C5a receptor had been deleted (C5aR KO) were used. Animals were killed after 3 or 6 weeks, and kidneys harvested. At three weeks, both groups had evidence of mild mesangial matrix expansion and increased cellularity; there were no crescents, sclerotic lesions, or interstitial disease. At six weeks, glomerular lesions were advanced, but identical in the two groups. Both groups had evidence of an identical pattern of C3 gene expression in the tubular epithelium by in situ hybridization. There was a marked difference, however, in the extent of interstitial injury. Wild-type animals had significantly greater numbers of infiltrating interstitial cells, greater expansion of the peritubular space, more tubular atrophy, and more apoptotic tubular cells than did C5aR KOs. The anaphylotoxic fragment of C5, C5a, is not likely to be important in the glomerular component of this model of progressive glomerulonephritis. On the other hand, the interstitial component is markedly attenuated in knockout animals. These data support a role for complement in the interstitial component of this glomerulonephritis model. They are consistent with our hypotheses of a role for complement in the progression of some forms of glomerulonephritis to ESRD.

C1 inhibitor: analysis of the role of amino acid residues within the reactive center loop in target protease recognition

Previous analysis of a naturally occurring C1 inhibitor P2 mutant (Ala(443)-->Val) indicated a role for P2 in specificity determination. To define this role and that of other reactive center loop residues, a number of different amino acids were introduced at P2, as well as at P6 (Ala(439)) and P8'/9' (Gln(452)Gln(453)). Ala(439)-->Val is a naturally occurring mutant observed in a patient with hereditary angioedema. Previous data suggested that Gln(452)Gln(453) might be a contact site for C1s. Reactivity of the inhibitors toward target (C1s, C1r, kallikrein, beta factor XIIa, and plasmin) and nontarget proteases (alpha-thrombin and trypsin) were studied. Substitution of P2 with bulky or charged residues resulted in decreased reactivity with all target proteases. Substitution with residues with hydrophobic or polar side chains resulted in decreased reactivity with some proteases, but in unaltered or increased reactivity with others. Second order rate constants for the reaction with C1s were determined for the mutants with activities most similar to the wild-type protein. The three P2 mutants showed reductions in rate from 3.35 x 10(5) M(-1)s(-1) for the wild type to 1.61, 1.29, and 0.63 x 10(5) for the Ser, Thr, and Val mutants, respectively. In contrast, the Ala(439)-->Val and the Gln(452)Gln(453)-->Ala mutants showed little difference in association rates with C1s, in comparison with the wild-type inhibitor. The data confirm the importance of P2 in specificity determination. However, the P6 position appears to be of little, if any, importance. Furthermore, it appears unlikely that Gln(452)Gln(453) comprise a portion of a protease contact site within the inhibitor.

Effects of entorhinal cortex lesions on sensory integration and spatial learning

BACKGROUND

The entorhinal cortex provides sensory information to the hippocampus for memory and learning. Damage to the entorhinal cortex is common in patients who experience traumatic brain injury, stroke, and Alzheimer's disease. Entorhinal damage is assumed to interfere with sensory integration; however, substantive knowledge of behavioral patterns is lacking.

OBJECTIVES

To describe specific behavioral deficits associated with entorhinal cortex injury related to special senses identification, sensory integration, and spatial learning.

METHOD

Adult male rats received bilateral entorhinal cortex damage (n = 19) or sham surgery (n = 11) with a subset randomized to participate in special senses identification, exploration, and sensory integration testing. Spatial learning was examined using a water maze.

RESULTS

Lesion and control animals were similar in special senses identification testing. Sensory integration was markedly impaired in lesion animals over 3 days for all integration tasks; however, travel deficit persisted for 4 days. By day 5 sensory integration ability was equal. Lesion animals were significantly impaired across all days of spatial learning for swim time (p = .0001) and directional heading error (p = .03). Control animals exposed to sensory testing demonstrated significantly more efficient learning (p = .005) on swim days 2 and 3 versus control animals not exposed to sensory testing.

CONCLUSIONS

Early and prolonged behavioral changes are evident following entorhinal cortex damage including sensory integration deficits and persistent spatial learning impairment.

Cognitive impairments following traumatic brain injury. Etiologies and interventions

Brain injury is a dynamic process that continues for weeks. Recovery is also a lengthy process, proceeding in overlapping stages along with injury. The outcome for many patients with TBI is an inability to fully participate in life events because of cognitive impairments. Physiologic responses throughout the injury and recovery are punctuated by neuroprotective and neuroplastic events. The time course of these injury and recovery activities requires that medical and nursing therapies are targeted across the trajectory of injury as damage and recovery processes are occurring. Prevention of secondary injury using medical and nursing strategies should be of paramount importance. Altering the environment by providing meaningful yet novel sensory stimulation may enhance plasticity and lead to reorganization of structures that support cognitive processes. Administration of neuroprotective agents in an effort to control damage from neurochemical processes should proceed as these agents become approved for clinical use. Active participation in rehabilitation programs and neuropsychologic testing provide additional avenues for identifying and addressing cognitive impairments. The complex relationship between injury and cognitive impairment is slowly being unraveled. Through an understanding of the brain structures and networks associated with information processing as well as the pathophysiologic consequences of brain injury, critical care nurses can design evidence-based regimens of care that preserve cognitive function and result in improvement of long-term cognitive outcomes and fuller participation in everyday life activities.

Mechanisms of traumatic brain injury: biomechanical, structural and cellular considerations

Traumatic brain injury (TBI) is a public health problem of great concern, because it affects more than 2 million individuals each year. TBI occurs as a result of motor vehicle crashes, falls, and sports-related events. Biomechanical mechanisms occurring at the time of the injury initiate primary and secondary injuries that evolve over several days. In this article the relationship between an blunt injury event and the subsequent damage produced is addressed. Mechanisms of brain injury from biomechanics to cellular pathobiology are presented. Primary and secondary injuries are differentiated, and specific focal and diffuse clinical syndromes are described. Cellular mechanisms responsible for injury are also addressed, because they provide the unifying concepts across the many clinical syndromes so often discussed separately in reviews of traumatic brain injury.

The C5a receptor is expressed by human renal proximal tubular epithelial cells

The C5a receptor is expressed by a variety of cell types. These studies demonstrate by immunohistochemistry that the receptor is present on the surface of proximal and distal tubular epithelial cells from normal kidney. In addition, the receptor was detected on transitional epithelial cells of the ureter and bladder. Primary proximal tubular cultures and a proximal tubular cell line both also expressed the C5a receptor, as demonstrated by immunofluorescence and by FACS analysis. The presence of mRNA encoding the receptor was confirmed by reverse transcriptase-polymerase chain reaction analysis. As opposed to its effect on glomerular mesangial cells, the receptor did not mediate a proliferative response by the proximal tubular cells. C5a also did not enhance the synthesis/secretion of transforming growth factor-beta 1, monocyte chemoattractant protein-1, platelet-derived growth factor-AB or tumour necrosis factor-alpha by cultured proximal tubular cells. Therefore, although the C5a receptor clearly is expressed by proximal tubular cells, clarification of its functional relevance on this cell type awaits further studies.

Neck mass caused by an intraluminal jugular paraganglioma

Paragangliomas can develop in a number of head and neck sites, the most common being the carotid body paragangliomas and glomus jugulare tumours. This is a case of a paraganglioma confined entirely within the lumen of the jugular vein.

The promoter of the C1 inhibitor gene contains a polypurine.polypyrimidine segment that enhances transcriptional activity

The C1 inhibitor (C1INH) promoter is unusual in two respects: 1) It contains no TATA sequence, but instead contains a TdT-like initiator element (Inr) at nucleotides -3 to +5; 2) it contains a polypurine.polypyrimidine tract between nucleotides -17 and -45. Disruption of the Inr by the introduction of point mutations reduced promoter activity by 40%. A TATA element inserted at nucleotide -30 in the wild-type promoter and in promoter constructs containing the mutated Inr led to a 2-fold increase in basal promoter activity. Previous studies suggested that the potential hinged DNA-forming polypurine.polypyrimidine tract might be important in the regulation of C1INH promoter activity. The present studies indicate that this region is capable of such intramolecular triple helix formation. Disruption of the polypurine.polypyrimidine sequence by substitution of 5 of the 23 cytosine residues with adenine prevented triple helix formation. Site-directed mutagenesis experiments demonstrate that the regulation of promoter activity is independent of hinged DNA-forming capacity but requires an intact AC box (ACCCTNNNNNACCCT) or the overlapping PuF binding site (GGGTGGG). The C1INH gene also contains a number of potential regulatory elements, including an Sp-1 and an hepatocyte nuclear factor-1 binding site and a CAAT box. The role of these elements in regulation of the C1INH promoter was examined. Elimination of the hepatocyte nuclear factor-1 site at nucleotides -94 to -81 by truncation reduced the activity of the promoter by approximately 50%. Similarly, site-directed mutations that disrupt this site reduce promoter activity by 70%.

Cultured human glomerular mesangial cells express the C5a receptor

BACKGROUND

While the association of complement activation and glomerulonephritis has been recognized for decades, the pathogenic mechanisms of complement-mediated glomerular damage are incompletely understood. Expression of the C5a receptor in the kidney suggests that C5a could play a direct role in initiating or promoting glomerulonephritis.

METHODS

Expression of the C5a receptor by cultured human glomerular mesangial cells (HGMC) was examined by immunofluorescence, by FACS analysis and by reverse transcriptase-polymerase chain reaction (RT-PCR). Potential mitogenic effects were examined by analysis of neutral red dye uptake after treatment with recombinant C5a (rC5a). The production of cytokines [interleukin-1 (IL-1), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1)] and growth factors [transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF-AB)] by mesangial cells stimulated with rC5a was examined by ELISA of cell culture supernatants.

RESULTS

Expression of the C5a receptor by the cultured HGMC was demonstrated by both immunofluorescence and FACS. The presence of mRNA encoding the receptor was confirmed by RT-PCR. Treatment of HGMC in vitro with rC5a resulted in mild cellular proliferation. No IL-1 was detected despite stimulation with up to 100 nM rC5a. Concentrations of IL-8 and TGF-beta did not increase beyond basal levels in control samples at any level of stimulation. Mean MCP-1 concentrations and PDGF-AB concentrations increased by 40% and 70% above control values 48 hours post-stimulation (P = 0.01 and P = 0.003, respectively).

CONCLUSIONS

These data indicate that the C5a receptor is expressed on HGMC in vitro, and may play a role in mediating glomerular injury by promoting cellular proliferation and the production of cytokines and growth factors.

Regulation of C1 inhibitor synthesis

The primary biologic roles of C1 inhibitor (C1-INH) are the regulation of activation of the classical complement pathway and of the contact system of kinin formation. Heterozygosity for deficiency or dysfunction of C1-INH results in hereditary angioedema (HAE). This deficiency results in loss of homeostasis with unregulated complement and contact system activation. Due to the consequent C1-INH consumption, plasma levels of C1-INH in patients with HAE are decreased below 50% of normal. In addition, diminished synthesis contributes to the lowered levels in some patients. The hepatocyte is the primary source of C1-INH, although a number of other cell types, including peripheral blood monocytes, microglial cells, fibroblasts, endothelial cells, the placenta, and megakaryocytes also synthesize and secrete the protein both in vivo and in vitro. Interferon-gamma and alpha (IFN), colony stimulating factor-1, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) all induce C1-INH synthesis in a variety of cell types. The IFN-response elements in the 5'-flanking region and in the first intron have been partially characterized, as have several of the promoter elements that direct basal transcription of the gene. However, although androgen therapy, in vivo, results in an increase in C1-INH plasma levels, a direct effect of androgens on C1-INH synthesis has not been convincingly demonstrated. Although the C1-INH gene contains a potential glucocorticoid/androgen response element, this element does not appear to respond to androgen. Continued analysis of the transcriptional regulation of the C1-INH gene may lead to new approaches to therapy of HAE.

Characterization of the IFN-gamma-responsive element in the 5' flanking region of the C1 inhibitor gene

Treatment of a variety of cell lines with IFN-gamma leads to enhanced synthesis and secretion of C1 inhibitor (C1inh). The induction of C1inh synthesis by IFN-gamma is primarily regulated at the transcriptional level, and is controlled by elements in the 5' flanking region and the first intron of the C1inh gene. Hep3B cells transfected with reporter constructs containing truncated segments between -738 and -81 of the 5' flanking region and stimulated with IFN-gamma expressed increased levels of chloramphenicol acetyl transferase. These data as well as the data obtained from studies using constructs with mutated IFN-gamma-activated sequence (GAS) indicate that the most proximal GAS element (GAS 4) that mapped to nucleotides -126 to -118 is responsible for this IFN-gamma responsiveness. Electrophoretic mobility shift assays using GAS 4 yielded a single band that appeared within 5 min after stimulation with IFN-gamma. In competition experiments, both GAS 4 and consensus GAS probes, but not a mutated GAS probe, competed for the GAS binding protein present in Hep3B and U-937 cell extracts. The identity of the GAS binding protein was confirmed using anti-STAT-1alpha Abs in supershift assays. The results indicate that STAT-1alpha binds to GAS 4, which is the primary element in the 5' flanking region responsible for IFN-gamma induction of the C1inh gene.

Characterization of the IFN-gamma-responsive element in the 5' flanking region of the C1 inhibitor gene

Treatment of a variety of cell lines with IFN-gamma leads to enhanced synthesis and secretion of C1 inhibitor (C1inh). The induction of C1inh synthesis by IFN-gamma is primarily regulated at the transcriptional level, and is controlled by elements in the 5' flanking region and the first intron of the C1inh gene. Hep3B cells transfected with reporter constructs containing truncated segments between -738 and -81 of the 5' flanking region and stimulated with IFN-gamma expressed increased levels of chloramphenicol acetyl transferase. These data as well as the data obtained from studies using constructs with mutated IFN-gamma-activated sequence (GAS) indicate that the most proximal GAS element (GAS 4) that mapped to nucleotides -126 to -118 is responsible for this IFN-gamma responsiveness. Electrophoretic mobility shift assays using GAS 4 yielded a single band that appeared within 5 min after stimulation with IFN-gamma. In competition experiments, both GAS 4 and consensus GAS probes, but not a mutated GAS probe, competed for the GAS binding protein present in Hep3B and U-937 cell extracts. The identity of the GAS binding protein was confirmed using anti-STAT-1alpha Abs in supershift assays. The results indicate that STAT-1alpha binds to GAS 4, which is the primary element in the 5' flanking region responsible for IFN-gamma induction of the C1inh gene.

Syncytium formation induced by human immunodeficiency virus type 1 isolates correlates with affinity for CD4

Different strains of human immunodeficiency virus type 1 (HIV-1) show considerable divergence in genetic content and biological properties. One property that has been closely correlated with clinical prognosis is the ability to induce syncytia formation in susceptible cells. This ability had been correlated with the V3 loop sequence of major envelope glycoprotein, gp120, but recent reports have questioned this connection. We investigated the contributions of different regions of the env gene to syncytia induction using chimeric viruses that contain part of the genome of a strain that lacks this ability (HIV-1(Ba-L)) within the genome of a virus that can form syncytia (HIV-1(HXB-2)). When tested in two cell lines susceptible to both parental viruses, as well as in primary cells, these chimeric viruses demonstrated that the ability to induce syncytia formation was determined by regions of env outside the V3 loop, which encompass residues that contribute to the binding of CD4 by gp120. Further investigation failed to show any difference in the expression of gp120 on the cell surface or cell adhesion molecules by cells infected with SI or NSI variants that would explain the observed differences in the ability to form syncytia. Assays of relative affinity for CD4 indicated that gp120 from SI variants showed a significantly higher affinity for CD4 than gp120 from NSI variants. These observations suggest that areas of the HIV-1 env gene contributing to the CD4 binding site may also contribute to the determination of syncytium-inducing (SI) and non-syncytium-inducing (NSI) phenotypes.

Role of the P2 residue of complement 1 inhibitor (Ala443) in determination of target protease specificity: inhibition of complement and contact system proteases

A dysfunctional C1 inhibitor (C1 INH) from a family in whom the propositus presented with systemic lupus erythematosus but without angioedema previously was shown to have diminished inhibitory activity toward isolated C1r and C1s, and intact C1. The mutation was identified as replacement of Ala443 (P2) with Val. This study further analyzed the reactivity of this mutant and characterized two mutants with Ser or Asp at this position. Ser at P2 does not interfere with binding of target proteases. However, the mutant with Asp at this position is unable to bind C1r and beta factor XIIa, and also has a decreased rate of reaction with C1s and kallikrein. Therefore, alteration of polarity alone had no effect on binding, while a bulky and/or charged side chain was not tolerated. Although defective in inhibition of C1r and C1s, the P2 A--&gt;V mutant had acquired the ability to complex with trypsin. It also completely retained the ability to complex with kallikrein and factor XIIa. None of the 10 individuals expressing this mutant protein has ever had angioedema. This observation, combined with normal inhibition of contact system proteases and defective inhibition of complement proteases, suggests that angioedema is caused by bradykinin generated from contact system activation.

Role of the P2 residue of complement 1 inhibitor (Ala443) in determination of target protease specificity: inhibition of complement and contact system proteases

A dysfunctional C1 inhibitor (C1 INH) from a family in whom the propositus presented with systemic lupus erythematosus but without angioedema previously was shown to have diminished inhibitory activity toward isolated C1r and C1s, and intact C1. The mutation was identified as replacement of Ala443 (P2) with Val. This study further analyzed the reactivity of this mutant and characterized two mutants with Ser or Asp at this position. Ser at P2 does not interfere with binding of target proteases. However, the mutant with Asp at this position is unable to bind C1r and beta factor XIIa, and also has a decreased rate of reaction with C1s and kallikrein. Therefore, alteration of polarity alone had no effect on binding, while a bulky and/or charged side chain was not tolerated. Although defective in inhibition of C1r and C1s, the P2 A-->V mutant had acquired the ability to complex with trypsin. It also completely retained the ability to complex with kallikrein and factor XIIa. None of the 10 individuals expressing this mutant protein has ever had angioedema. This observation, combined with normal inhibition of contact system proteases and defective inhibition of complement proteases, suggests that angioedema is caused by bradykinin generated from contact system activation.

Molecular defects in hereditary angioneurotic edema

Thirty-eight previously unreported, unrelated patients with hereditary angioneurotic edema were studied, and each was found to have a single mutation in the C1 inhibitor gene. On the basis of serine protease inhibitor crystal structure, these and published mutations affect critical domains in the reactive center loop, alpha-helices A, B, C, E, and F, and beta-sheets A and C. Almost all mutations, other than in the reactive center loop, occur at residues that are highly conserved among serine protease inhibitors, and the others are likely to interfere with molecular movement. These mutations begin to identify residues critical for molecular function of the C1 inhibitor molecule.

Retinoic acid increases cellular retinol binding protein II mRNA and retinol uptake in the human intestinal Caco-2 cell line

Cellular retinol binding protein II (CRBPII) is an abundant small intestinal protein that facilitates vitamin A trafficking and metabolism. The magnitude of retinol uptake and metabolism correlate to CRBPII levels in the human intestinal Caco-2 cell line. To investigate the importance of retinoic acid receptor response elements in the promoter of the CRBPII gene, retinoic acid regulation of CRBPII expression and vitamin A absorption was studied in differentiated Caco-2 cells. All-trans- or 9-cis-retinoic acid increased CRBPII mRNA levels two- to threefold. This was associated with a 50% increase in retinol absorption. Retinoic acid receptor beta and apolipoprotein A1 regulatory protein-1, two nuclear receptors that bind to the CRBPII promoter, were also induced, whereas other retinoid and orphan receptors were not. Thus, retinoic acid may regulate CRBPII expression directly or by selectively changing levels of nuclear receptors or other factors. These studies are the first to demonstrate that retinoic acid can modulate endogenous CRBPII mRNA levels and retinol absorption in Caco-2 cells and suggest that human intestinal vitamin A absorption may be regulated by retinoids.

Resistance of human immunodeficiency virus type 1 to neutralization by natural antisera occurs through single amino acid substitutions that cause changes in antibody binding at multiple sites

The ability of human immunodeficiency virus type 1 (HIV-1) to replicate in the presence of strong immune responses to the virus may be due to its high mutation rate, which provides envelope gene variability for selection of neutralization-resistant variants. Understanding neutralization escape mechanisms is therefore important for the design of HIV-1 vaccines and our understanding of the disease process. In this report, we analyze mutations at amino acid positions 281 and 582 in the HIV-1 envelope, where substitutions confer resistance to broadly reactive neutralizing antisera from seropositive individuals. Neither of these mutations lies within an antibody-binding site, and therefore the mechanism of immune escape in both cases is by alteration of the shape of the envelope proteins. The conformation of the CD4-binding site is shown to be critical with regard to presentation of other discontinuous epitopes. From our analysis of the neutralization of these variants, we conclude that escape from polyclonal sera occurs through alterations at several different epitopes, generally resulting from single amino acid substitutions which influence envelope conformation. Experiments on a double mutant showed that the combination of both mutations is not additive, suggesting that these variants utilized alternate pathways to elicit similar alterations of the HIV-1 envelope structure.

Antibody to C1-inhibitor in a patient receiving C1-inhibitor infusions for treatment of hereditary angioneurotic edema with systemic lupus erythematosus reacts with a normal allotype of residue 458 of C1-inhibitor

Patients with hereditary C4 deficiency are likely to have severe lupus erythematosus. A patient with hereditary angioneurotic edema (HANE) and systemic lupus erythematosus (SLE) had a chronic deficiency in C4 because the hereditary deficiency in C1-inhibitor allowed the C1 in her serum to become activated and then inactivate C4. An attempt was made to repair the C4 deficiency as well as the deficiency in C1-inhibitor by giving infusions of human C1-inhibitor in the hope of inducing remissions of both HANE and SLE. During treatment, antibody to C1-inhibitor developed in the patient; this cleared when the infusions were stopped. During subsequent treatment with danazol alone, measurable C1-inhibitor developed in the patient's serum, but levels of C4 were never significantly increased. Antibody to normal C1-inhibitor was not expected to develop in the patient because she is heterozygous for this autosomal dominant trait. A normal allotype (VAL or MET 458), which would have been in the preparation used but which the patient does not synthesize because she can produce only one allotype (MET 458), appears to have been immunogenic. The antibody isolated from the patient's serum reacted with C1-inhibitor from a normal individual known to be homozygous for 458-VAL but not with one from a homozygote for MET-458.

Expression of CD26 does not correlate with the replication of macrophage-tropic strains of HIV-1 in T-cell lines

Strains of human immunodeficiency virus type 1 (HIV-1) differ significantly in both genetic content and biological properties. One of the earliest discovered differences between HIV-1 strains was divergence in the relative ability of different strains to replicate in either T-cell lines or monocytes/macrophages. This observation has led to the suggestion that molecules present on the surface of HIV-susceptible cells other than CD4 may interact with gp120 in facilitating the entry of HIV-1 into host cell populations. Several reports have suggested that CD26, a cell surface protease expressed on many cells of the immune system including some CD4+ T-cells and macrophage, may be an accessory molecule for HIV-1 entry. Recently, it has also been reported that the expression of high levels of CD26 correlates with the entry and replication of macrophage-tropic strains of HIV-1 in a T-cell line. In this report, we demonstrate that replication of macrophage-tropic strains of HIV-1 in T-cell lines is independent of CD26 expression. From this observation, we conclude that CD26 plays no role in the entry of HIV-1 into these cells.

Characterization of C1 inhibitor-Ta. A dysfunctional C1INH with deletion of lysine 251

Dysfunctional C1 inhibitor (C1INH)-Ta is a naturally occurring mutant from a patient with type II hereditary angioedema. This mutant has a deletion of the codon for Lys-251, which is located in the connecting strand between helix F and strand 3A, overlying beta sheet A. Deletion of this Lys modifies the amino acid sequence at this position from Asn-Lys-Ile-Ser to Asn-Ile-Ser and creates a new glycosylation site. To further characterize the mechanism of dysfunction, we have analyzed the recombinant normal and Ta proteins expressed by COS cells in addition to the proteins in serum and isolated from serum. Recombinant C1INH-Ta revealed an intermediate thermal stability in comparison with the intact and reactive center cleaved normal proteins. Analysis of the reactivity of this recombinant protein with target proteases demonstrated no complex formation with C1s, C1r, or kallikrein. Inefficient complex formation was, however, clearly detectable with beta-factor XIIa. Each protease produced partial cleavage of the recombinant mutant inhibitor. Recombinant C1INH-Ta, on 7.5% SDS-polyacrylamide gel electrophoresis and by size fractionation on Superose 12, showed a higher molecular weight fraction that was compatible in size with dimer formation. However, no multimerization of C1INH-Ta isolated from serum or of C1INH-Ta in serum, was observed. The C1INH-Ta dimer expressed the epitopes that normally are expressed only on the protease complexed or the cleaved inhibitor. These epitopes were not expressed on the monomeric inhibitor. The data suggest that the mutation in C1INH-Ta results in a folding abnormality that behaves as if it consists of two populations of molecules, one of which is susceptible to multimerization and one of which is converted to a substrate, but which retains residual inhibitory activity.

Primary care management of chronic musculoskeletal pain

Chronic musculoskeletal pain, a common problem seen in the primary care setting, is often frustrating for both the patient and the clinician. Despite its prevalence, chronic pain is often poorly understood and inconsistently managed by health care providers. Unlike acute pain, chronic pain serves no biologic function and persists long after the tissue has healed from injury. Patients with chronic pain may become isolated from friends and family, lose their jobs, and develop depression. Nonpharmacologic techniques such as acupuncture, massage, and relaxation may be helpful to the patient with chronic pain. In addition to nonsteroidal antiinflammatory drugs, antidepressants and opioid analgesics are useful for treating chronic musculoskeletal pain. This article explains that pathophysiology of chronic pain, lists aspects of chronic pain that distinguish it from acute pain, and develops a general primary care plan for patients with chronic musculoskeletal pain.

The catabolism of intact, reactive centre-cleaved and proteinase-complexed C1 inhibitor in the guinea pig

Clearance rates in the guinea pig were determined for intact guinea pig and human C1 inhibitor, the complexes of both inhibitors with human Cls, beta factor XIIa and kallikrein, and for each inhibitor cleaved at its reactive centre with trypsin. Intact human and guinea pig C1 inhibitor were cleared from the circulation more slowly (t1/2s of 9-7 h and 12.1 h and fractional catabolic rates (FCRs) of 0.09 and 0.117) than any of their cleaved or complexed forms. The reactive centre-cleaved inhibitors were cleared with half-lives of 6.75 h for humans and 10.1 h for the guinea pig. The complexes with target proteases were catabolized much more rapidly, with half-lives ranging from 3-08 h to 4.3 h. The complexes with kallikrein were cleared more slowly than those with Cls and beta factor XIIa. Complexes prepared with the guinea pig and human inhibitors were cleared at equivalent rates. The free inactivated proteases were cleared at rates similar to the equivalent complexes, except for kallikrein, which was cleared more rapidly than its complex. The fact that the complexes with different target proteases differed in their catabolism and that protease and complex catabolism were similar suggests that protease may play a direct role in clearance.

Impaired production of both normal and mutant C1 inhibitor proteins in type I hereditary angioedema with a duplication in exon 8

In the autosomal dominant disorder type I hereditary angioedema, reduced levels of C1 inhibitor may be due in part to increased turnover and decreased synthesis of normal C1 inhibitor protein. A type I hereditary angioedema patient was recently described in whom the C1 inhibitor mutation consisted of a 20-bp duplication of nucleotides 1414 to 1433 in exon 8 that introduced a frame shift predicting the loss of a normal stop codon and the translation of a protein 52 amino acids longer than normal. In this study, we analyzed the expression of C1 inhibitor in fibroblasts obtained from a skin biopsy of this patient. Two proteins of approximately 78 and 94 kDa were found intracellularly, corresponding to the products of normal and mutated alleles, respectively. Pulse-chase analysis showed a complete lack of secretion of the mutated form. In addition, there was decreased extracellular production of the normal C1 inhibitor, suggesting either decreased secretion or increased intracellular catabolism of the normal protein because of the presence of the mutant allele. The production of other complement proteins was normal. This study provides a model for further analysis of autosomal dominant genetic disorders in which production of the functional protein may be affected by the product of the mutated allele.

Impaired production of both normal and mutant C1 inhibitor proteins in type I hereditary angioedema with a duplication in exon 8

In the autosomal dominant disorder type I hereditary angioedema, reduced levels of C1 inhibitor may be due in part to increased turnover and decreased synthesis of normal C1 inhibitor protein. A type I hereditary angioedema patient was recently described in whom the C1 inhibitor mutation consisted of a 20-bp duplication of nucleotides 1414 to 1433 in exon 8 that introduced a frame shift predicting the loss of a normal stop codon and the translation of a protein 52 amino acids longer than normal. In this study, we analyzed the expression of C1 inhibitor in fibroblasts obtained from a skin biopsy of this patient. Two proteins of approximately 78 and 94 kDa were found intracellularly, corresponding to the products of normal and mutated alleles, respectively. Pulse-chase analysis showed a complete lack of secretion of the mutated form. In addition, there was decreased extracellular production of the normal C1 inhibitor, suggesting either decreased secretion or increased intracellular catabolism of the normal protein because of the presence of the mutant allele. The production of other complement proteins was normal. This study provides a model for further analysis of autosomal dominant genetic disorders in which production of the functional protein may be affected by the product of the mutated allele.

Instrument development: getting started

The four steps involved in instrument development are: concept identification; item construction; validity testing and reliability testing. The clinician who has begun to identify characteristics associated with a patient group has in reality begun the process of instrument development. The challenge for clinicians and researchers is to transform those observable phenomena into a instrument that measures the attribute of the group. Only with reliable and valid measures can true relationships and differences be determined and effective intervention programs be formulated.

Evidence for distinct contributions of heavy and light chains to restriction of antibody recognition of the HIV-1 principal neutralization determinant

We have used phage Ab display technology to analyze two mAbs to HIV-1 envelope proteins gp120 and gp41. From the data obtained we are able to demonstrate that the recognition of the principal neutralization determinant of different strains of HIV-1 by neutralizing mAb M77 is restricted by its heavy and light chains in different ways. Native M77 is able to recognize and neutralize HIV-1 strain IIIB through binding to the gp120 V3 loop. M77 is unable to recognize strains of HIV-1 that differ on either the left or right side of the V3 loop tip. A chain-switched Fab fragment containing the M77 Fd fragment and a different light chain was able to recognize HIV-1 strains that differ from IIIB on the left side but not the right side of the V3 loop tip.

Evidence for distinct contributions of heavy and light chains to restriction of antibody recognition of the HIV-1 principal neutralization determinant

We have used phage Ab display technology to analyze two mAbs to HIV-1 envelope proteins gp120 and gp41. From the data obtained we are able to demonstrate that the recognition of the principal neutralization determinant of different strains of HIV-1 by neutralizing mAb M77 is restricted by its heavy and light chains in different ways. Native M77 is able to recognize and neutralize HIV-1 strain IIIB through binding to the gp120 V3 loop. M77 is unable to recognize strains of HIV-1 that differ on either the left or right side of the V3 loop tip. A chain-switched Fab fragment containing the M77 Fd fragment and a different light chain was able to recognize HIV-1 strains that differ from IIIB on the left side but not the right side of the V3 loop tip.

An autoantibody to C1-inhibitor recognizes the reactive center of the inhibitor

An autoantibody to C1-inhibitor produced a clinical disorder resembling that of patients with hereditary angioneurotic edema. The antibody could not interact with C1-inhibitor after exposure to synthetic peptides representing the primary structure of the reactive center region of the protein. Therefore the antibody recognized this domain of the inhibitor, and it probably impaired the function of C1-inhibitor by altering its conformational properties.

V-region and class specific RT-PCR amplification of human immunoglobulin heavy and light chain genes from B-cell lines

We have designed and tested primers that amplify complete human kappa and lambda light chain genes, and human Fd fragments from gamma, mu and alpha heavy chain genes. These primers were tested for efficiency and specificity on monoclonal sources of human immunoglobulin RNA, obtained from human B-cell lines of known immunoglobulin gene expression. Analysis of the sequences derived from these B-cells confirms the specificity of the PCR primers and the extent of somatic mutation seen in different B-cell malignancies supports existing concepts for differing aetiologies in the tumours concerned.

Innovative sensory input for the comatose brain-injured patient

Coma following brain injury may last days or months and is associated with decreased quality of life for survivors and families. One intervention postulated to improve coma recovery is sensory stimulation. This article critically examines current theoretical perspectives and empirical data related to sensory stimulation, discusses the usefulness of sensory stimulation programs (SSP) in critical care settings, and poses strategies for implementation of an SSP. Future directions for nursing practice and research also are addressed.

Preventing feeding-associated aspiration

Aspiration and its sequela aspiration pneumonia are frequent complications associated with enteral feeding. The purpose of this article is to provide a framework for recognizing aspiration events, identifying at-risk patients, and developing research-based strategies to prevent aspiration.

Unique C1 inhibitor dysfunction in a kindred without angioedema. II. Identification of an Ala443-->Val substitution and functional analysis of the recombinant mutant protein

We have determined the cause of an unusual C1 inhibitor abnormality in a large kindred. We previously found that half of serum C1 inhibitor molecules in affected kindred members are normal. The other half complexed with C1s but showed little complex formation with C1r. These molecules also appeared to be relatively resistant to digestion by trypsin. Taken together, the findings suggested that members of this kindred are heterozygous for an unusual C1 inhibitor mutation. Sequencing of genomic DNA from the kindred revealed that thymine has replaced cytosine in the codon for Ala443 (P2 residue) in one C1 inhibitor allele, resulting in substitution with a Val residue. To test the effect of this substitution, a mutant C1 inhibitor containing Ala443-->Val was constructed by site-directed mutagenesis and expressed in COS-1 cells. Both the Ala443-->Val mutant and the wild-type C1 inhibitor complexed completely with C1s, kallikrein, and coagulation Factor XIIa after incubation at 37 degrees C for 60 min. In contrast, the mutant inhibitor failed to complex completely with C1r under the same conditions. Time course analysis showed that the ability of the mutant to complex with C1s is also impaired: although it complexed completely in 60 min, the rate of complex formation during a 0-60-min incubation was decreased compared with wild-type C1 inhibitor. The mutant inhibitor also formed a complex with trypsin, a serine protease that cleaves, and is not inhibited by, wild-type C1 inhibitor. The Ala443-->Val mutation therefore converts C1 inhibitor from a substrate to an inhibitor of trypsin. These studies emphasize the role of the P2 residue in the determination of target protease specificity.

Vitamin A trafficking in Caco-2 cells stably transfected with cellular retinol binding proteins

During intestinal vitamin A absorption, retinol is esterified by long-chain fatty acids and secreted in chylomicron particles. Stable transfectants of the human intestinal Caco-2 cell line overexpressing cellular retinol binding protein II (CRBP II) or coexpressing CRBP II and CRBP were established to study their role in intestinal vitamin A trafficking. Compared with control cell lines, retinol uptake increased up to twofold by overexpression of CRBP II and up to 2.9-fold by coexpression of CRBP and CRBP II. Retinyl ester synthesis was increased proportionate to the increase in retinol absorption in all cell lines. Retinyl ester secretion was directly correlated with retinyl ester synthesis in control and CRBP II-transfected cell lines. However, transfection with CRBP increased the proportion secreted. Expression of CRBP and CRBP II also affected the polarity of retinyl ester secretion by increasing the proportion secreted basolaterally. Thus these studies provide evidence that intestinal retinol uptake, retinyl ester synthesis, and retinyl ester secretion are correlated with levels of CRBP and CRBP II and that the effects of CRBP on retinyl ester secretion can be distinguished from those of CRBP II.

Hip fractures in the elderly: surveillance methods and injury control

Injury is a major health problem in the United States that has been viewed primarily as a disease of the young. As a result, the devastating consequences of injury on the elderly population have not been sufficiently explored. Proximal femur fractures (hip fractures), common injuries in persons over the age of 65, carry a mild Injury Severity Score but are associated with high morbidity and mortality in the older population. The author provides a rationale based on clinical and research literature for increasing injury surveillance for hip fractures in the elderly in order that injury care and control can be improved.

C3-independent glomerulonephritis in guinea pigs: dependence upon primary humoral response

We used C3-deficient (C3D) guinea pigs to evaluate the role of C3 in an active model of experimental nephritis. Normal strain 2 (C3N, n = 13) and C3D (n = 6) guinea pigs were immunized with cationized bovine gamma-globulin (CBGG). Fourteen days later (Day 0), daily intravenous injections of CBGG were given for 3 to 7 days and the animals were sacrificed on Day 10 or 21. Immunofluorescence (IF) microscopy of renal tissue revealed two patterns of glomerular IgG deposition: granular loop (11/13 C3N, 3/6 C3D), and predominantly mesangial (2/13 C3N, 3/6 C3D). Codeposited C3 was seen in all C3N and in no C3D animals. Electron microscopy showed subepithelial deposits in all. A significant correlation (P < 0.005) was seen between an animal's IF pattern and its level of serum antibodies to CBGG; those with lower antibody levels exhibited the mesangial pattern. C3D animals had lower mean antibody levels than C3N (P < 0.01), but both IF patterns were represented. Urine protein concentration, which was increased relative to controls, did not differ between C3N and C3D groups, but was significantly greater in those with loop IF. Serum albumin was significantly reduced in animals with loop IF. C3N animals showed a significant reduction in mean serum C3. In this model, immune deposit location and degree of proteinuria are independent of C3 deposition and dependent upon the level of antibody response to CBGG. Induction of antibody to CBGG is impaired in the absence of C3.

Functional analysis of the serpin domain of C1 inhibitor

To analyze the role of the heavily glycosylated amino-terminal domain of C1 inhibitor in protease inhibitory activity, two truncated C1 inhibitor molecules were constructed. The abilities of the recombinant truncated inhibitors to complex with target proteases were compared with that of the wild-type recombinant protein. One recombinant truncated molecule consisted of amino acid residues 76 to 478 (C-serp(76)) and the other of residues 98 to 478 (C-serp(98)). The recombinant proteins were each expressed in similar quantities. The thermal denaturation profiles of the two truncated proteins were similar to that of the wild-type protein. Identical binding of C1s, C1r, kallikrein, and beta factor XIIa was observed with the three molecules. Furthermore, the truncated molecules also effectively inhibited C1 activity in hemolytic assays. These studies therefore clearly demonstrate that the amino-terminal domain of C1 inhibitor does not influence complex formation with target proteases.

Functional analysis of the serpin domain of C1 inhibitor

To analyze the role of the heavily glycosylated amino-terminal domain of C1 inhibitor in protease inhibitory activity, two truncated C1 inhibitor molecules were constructed. The abilities of the recombinant truncated inhibitors to complex with target proteases were compared with that of the wild-type recombinant protein. One recombinant truncated molecule consisted of amino acid residues 76 to 478 (C-serp(76)) and the other of residues 98 to 478 (C-serp(98)). The recombinant proteins were each expressed in similar quantities. The thermal denaturation profiles of the two truncated proteins were similar to that of the wild-type protein. Identical binding of C1s, C1r, kallikrein, and beta factor XIIa was observed with the three molecules. Furthermore, the truncated molecules also effectively inhibited C1 activity in hemolytic assays. These studies therefore clearly demonstrate that the amino-terminal domain of C1 inhibitor does not influence complex formation with target proteases.

A cluster of mutations within a short triplet repeat in the C1 inhibitor gene

Mutations in the C1 inhibitor gene that result in low functional levels of C1 inhibitor protein cause hereditary angioneurotic edema. This disease is characterized by episodic edema leading to considerable morbidity and death. Among 60 unreported kindred with the disease, four patients were discovered to have mutations clustered within a 12-bp segment of exon 5 from nucleotide 8449 to nucleotide 8460. This short segment of DNA contains three direct repeats of the triplet CAA and is immediately preceded by a similar adenosine-rich sequence (CAAGAACAC). These triplet repeats make this region susceptible to mutation by a slipped mispairing mechanism. There are two other short triplet repeat elements in the coding region for this gene, but they have not become mutated in any kindred examined. This suggests that the apparent enhanced mutation rate in this region of exon 5 may be influenced by DNA structural characteristics.

Aspirin reduces the incidence of colonic carcinoma in the dimethylhydrazine rat animal model

BACKGROUND

Epidemiological studies in humans suggest that regular use of non-steroidal anti-inflammatory drugs (NSAIDS) especially aspirin significantly decreases the risk of developing colorectal cancer.

AIMS

The purpose of this study was to investigate the effect of aspirin on colonic carcinogenesis using the dimethylhydrazine (DMH) colonic cancer model in rats.

METHODS

Groups of animals were given daily doses of aspirin either 0, 5, 30 or 60 mg/kg for 18 weeks. Half of each group also received 18 x 30 mg/kg/wk injections of DMH.

RESULTS

Aspirin at doses of 5, 30 or 60 mg/kg/dy had a progressive effect on the reduction of tumour numbers and the percentage of tumours greater or equal to 5 mm in diameter. Aspirin at doses of 30 and 60 mg/kg/dy significantly reduced tumour incidence.

CONCLUSION

These findings support the epidemiological studies in humans. The rat DMH model would appear to be suitable for investigating the mechanism of action of aspirin in reducing colonic tumour formation.