A Systematic Review of Warfarin Use in Post-Bariatric Surgery Patients: Cases Compiled From a Literature Review

OBJECTIVE

The objective of this review was to provide dosing recommendations for percentage change in weekly warfarin dose and rates of thrombotic and bleeding events in patients requiring long-term warfarin therapy after bariatric surgery.

DATA SOURCES

A comprehensive literature search of PubMed (through April 5, 2021), Cochrane Library, and Google Scholar (through April 5, 2021) databases was completed using the keywords warfarin OR vitamin k antagonist AND bariatric surgery.

STUDY SELECTION AND DATA EXTRACTION

Retrospective studies and matched-cohort studies evaluating preoperative and postoperative use of warfarin after bariatric surgery for obesity were considered. Weekly dose defined as sum of daily doses of warfarin for 7 consecutive days was a required outcome to be considered in this review. Patients were excluded from review if post-operative dosage change was not reported.

DATA SYNTHESIS

Six studies were included with a total of 160 patients who met the criteria. A decrease in average warfarin dose was seen in all studies, with the largest decrease occurring at 1 month postsurgery followed by an upward trend toward baseline about 90 days postsurgery. While thrombotic events were observed in none of the patients, there was an increased risk of bleeding in patients, particularly in those who underwent roux-en-y gastric bypass (RYGB) surgery.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

The study provides a specific warfarin dosing titration regimen, as well as embolic and bleed risk in post-bariatric surgery population.

CONCLUSIONS

Clinicians may consider lowering warfarin weekly dose by about 25% immediately postsurgery, with doses approaching closer to baseline about 90 days postsurgery.

Drug-Induced Hyperthermia Review

Humans maintain core body temperature via a complicated system of physiologic mechanisms that counteract heat/cold fluctuations from metabolism, exertion, and the environment. Overextension of these mechanisms or disruption of body temperature homeostasis leads to bodily dysfunction, culminating in a syndrome analogous to exertional heat stroke (EHS). The inability of this thermoregulatory process to maintain the body temperature is caused by either thermal stress or certain drugs. EHS is a syndrome characterized by hyperthermia and the activation of systemic inflammation. Several drug-induced hyperthermic syndromes may resemble EHS and share common mechanisms. The purpose of this article is to review the current literature and compare exertional heat stroke (EHS) to three of the most widely studied drug-induced hyperthermic syndromes: malignant hyperthermia (MH), neuroleptic malignant syndrome (NMS), and serotonin syndrome (SS). Drugs and drug classes that have been implicated in these conditions include amphetamines, diuretics, cocaine, antipsychotics, metoclopramide, selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants (TCAs), and many more. Observations suggest that severe or fulminant cases of drug-induced hyperthermia may evolve into an inflammatory syndrome best described as heat stroke. Their underlying mechanisms, symptoms, and treatment approaches will be reviewed to assist in accurate diagnosis, which will impact the management of potentially life-threatening complications.

Student perceptions of non-technical skills development during advanced pharmacy practice experiences

INTRODUCTION

In today's workforce, non-technical skills (NTS) are essential in determining an employee's ability to fit into an organization. However, it is unknown whether pharmacy students consider these skills essential to their future work or believe they are sufficiently trained. Therefore, this study evaluated student perceptions of the value of NTS as a pharmacist and their satisfaction with NTS training.

METHODS

A 45-item survey was distributed to 111 fourth-year pharmacy students at Texas A&M College of Pharmacy in March 2019. Given the diverse nature of NTS, this study collected student perceptions about the 2016 Accreditation Council for Pharmacy Education Standard 4 Key Elements: self-awareness, leadership, innovation, and professionalism. Results were analyzed utilizing descriptive statistics.

RESULTS

Approximately 84% (n = 93) of students completed the survey. More students perceived professionalism as an important skill to have, followed by leadership, self-awareness, and innovation. Similar results were shown with students' satisfaction with NTS training. Also, results highlighted that students' satisfaction level with their NTS training and their belief regarding their strengths relied on two factors: the number of advanced pharmacy practice experiences (APPEs) where NTS training occurred and the amount of time spent practicing the NTS.

CONCLUSION

These data add to the existing literature to support NTS training in experiential pharmacy education. While APPEs should not be the only setting where these skills are practiced in the curriculum, our study's findings may further guide curricular priorities and assessment strategies for NTS in the experiential setting.

Minimally Invasive Surgical Approach for Esophageal Adenocarcinoma in a Patient with Previous Belsey Mark IV Fundoplication: A Case Report

Background: Historically, the management for recurrent or persistent Gastro-esophageal reflux disease included selective vagotomy and fundoplication. Despite these surgical interventions, the risk of Barrett’s esophagus (BE) and subsequent malignant transformation remains, requiring cancer resection surgery. We present a case of a patient with a gastro-esophageal junction (GEJ) adenocarcinoma, who underwent a pediatric thoracotomy and Belsey Mark IV fundoplication, and was successfully treated by Laparoscopic Ivor-Lewis Esophagectomy (LILE). Case Presentation: This 64-year-old gentleman with BE and GEJ adenocarcinoma was previously deemed unsuitable for curative surgery due to clinical staging indicating a tumor length of 10cm and suspected invasion of the left pleura. Further staging by Endoscopic ultrasound indicated no evidence of pleural invasion with the distal esophageal thickening in keeping with his previous Belsey Mark IV fundoplication. He underwent neo-adjuvant chemotherapy and a subsequent LILE with complete laparoscopic reversion of the gastric fundoplication without injury to the gastroepiploic artery or fundus. There was sufficient preservation of conduit length to enable a tension free hand-sewn anastomosis with an uneventful post-operative recovery. Final histopathology confirmed ypT1 ypN0 moderately differentiated adenocarcinoma with R0 resection margins. The patient has completed 24 months of cancer recurrence free surveillance. Conclusion: We describe the successful management of a patient by LILE on a background of previous hiatal fundoplication surgery, previously refused curative surgery. We highlight the importance of EUS as a staging modality for such cases showing invasive disease to increase the final clinical staging accuracy. We suggest a minimally invasive approach may be utilized for successful re-do hiatal dissection as an alternative to a conventional open surgery.

Agricultural workers in meatpacking plants presenting to an emergency department with suspected COVID-19 infection are disproportionately Black and Hispanic

Objective

Facilities that process and package meat for consumer sale and consumption (meatpacking plants) were early sites of coronavirus disease 2019 (COVID‐19) outbreaks. The aim of this study was to characterize the association between meatpacking plant exposure and clinical outcomes among emergency department (ED) patients with COVID‐19 symptoms.

Methods

This was a retrospective cohort study of patients presenting to a single ED, from March 1 to May 31, 2020, who had: 1) symptoms consistent with COVID‐19 and 2) a COVID‐19 test performed. The primary outcome was COVID‐19 positivity, and secondary outcomes included hospital admission from the ED, ventilator use, intensive care unit (ICU) admission, hospital length of stay (LOS; <48 or ≥48 h), and mortality.

Results

Patients from meatpacking plants were more likely to be Black or Hispanic than the ED patients without this occupational exposure. Patients with a meatpacking plant exposure were more likely to test positive for COVID‐19 (adjusted relative risk [aRR] = 2.37, 95% confidence interval [CI] = 1.59 to 3.53) but had similar rates of hospital admission (aRR = 0.94, 95% CI = 0.82 to 1.07) and hospital LOS (aRR = 0.76, 95% CI = 0.45 to 1.23). There was no significant difference in ventilator use among patients with meatpacking and nonmeatpacking plant exposure (8.2% vs. 11.1%, p = 0.531), ICU admissions (4.1% vs. 12.0%, p = 0.094), and mortality (2.0% vs. 4.1%, p = 0.473).

Conclusions

Workers in meatpacking plants in Iowa had a higher rate of testing positive for COVID‐19 but were not more likely to be hospitalized for their illness. These patients were disproportionately Black and Hispanic.

OPA1 deletion in brown adipose tissue improves thermoregulation and systemic metabolism via FGF21

Adrenergic stimulation of brown adipocytes alters mitochondrial dynamics, including the mitochondrial fusion protein optic atrophy 1 (OPA1). However, direct mechanisms linking OPA1 to brown adipose tissue (BAT) physiology are incompletely understood. We utilized a mouse model of selective OPA1 deletion in BAT (OPA1 BAT KO) to investigate the role of OPA1 in thermogenesis. OPA1 is required for cold-induced activation of thermogenic genes in BAT. Unexpectedly, OPA1 deficiency induced fibroblast growth factor 21 (FGF21) as a BATokine in an activating transcription factor 4 (ATF4)-dependent manner. BAT-derived FGF21 mediates an adaptive response by inducing browning of white adipose tissue, increasing resting metabolic rates, and improving thermoregulation. However, mechanisms independent of FGF21, but dependent on ATF4 induction, promote resistance to diet-induced obesity in OPA1 BAT KO mice. These findings uncover a homeostatic mechanism of BAT-mediated metabolic protection governed in part by an ATF4-FGF21 axis, which is activated independently of BAT thermogenic function.

Omecamtiv Mecarbil: A Novel Mechanistic and Therapeutic Approach to Chronic Heart Failure Management

Heart failure (HF) is a major public health problem in the United States as well as worldwide. Chronic heart failure is a syndrome of reduced cardiac output resulting from impaired ventricular function, impaired filling, or a combination of both. Associated symptoms include dyspnea, fatigue, and decreased exercise tolerance. HF has a marked effect on morbidity and mortality, given limited therapeutic choices. The first line of therapeutic agents indicated in heart failure are beta-blockers. Other drugs and therapeutic modalities employed in HF treatment include angiotensin-receptor blockers (ARBs), sacubitril (neprilysin inhibitor) combination with the ARB, valsartan, small doses of aldosterone receptor antagonists (ARAs) in the setting of angiotensin-converting enzyme (ACE) inhibitors, and beta-blockers. Additionally, the sodium-glucose transporter-2 inhibitor, dapagliflozin in the setting of ACE inhibitors, ARBs, or sacubitril-valsartan plus beta-blocker have been employed. Other therapeutic modalities have included loop diuretics, digoxin, the hydralazine-isosorbide dinitrate combination, ivabradine, the inotropes, dobutamine, milrinone, and dopamine. Decreased cardiac contractility is central to the systolic HF. Therapeutic agents employed to increase cardiac contractility in HF are limited because of their mechanistic-related adverse effect profiles. Omecamtiv mecarbil (OM) is a first of its class cardiac myosin activator that increases the cardiac contractility by specifically binding to the catalytic S1 domain of cardiac myosin, to be employed in heart failure treatment. This agent has demonstrated benefit in reducing heart rate, peripheral vascular resistance, mean left arterial pressure, and left ventricular end-diastolic pressure in the animal models. Additionally, OM is known to improve systolic wall thickening, stroke volume (SV), and cardiac output (CO). OM increases systolic ejection time (SET), cardiac myocyte fractional shortening without significant increase of LV dP/dtmax, myocardial oxygen consumption, and myocyte intracellular calcium. The benefits of OM have been demonstrated through key trials, as (i) The Acute Treatment with Omecamtiv mecarbil to Increase Contractility in Acute Heart Failure (ATOMIC-AHF), and (ii) The Chronic Oral Study of Myosin Activation to Increase Contractility in Heart Failure (COSMIC-HF). The Global Approach to Lowering Adverse Cardiac Outcomes Through Improving Contractility in Heart Failure (GALACTIC-HF) trial is ongoing and can help provide further clinical data. OM provides a novel mechanism and therapeutic approach to managing patients with HF. Preclinical and clinical data suggest that OM capability can improve cardiac function, decrease ventricular wall stress, reverse ventricular remodeling, and promote sympathetic withdrawal.

The Dandelion Dilemma Revisited for Oligoprogression: Treat the Whole Lawn or Weed Selectively?

Oligoprogressive disease is a relatively new clinical concept describing progression at only a few sites of metastasis in patients with otherwise controlled widespread disease. In the era of well-tolerated targeted treatments, resistance inevitably occurs and overcoming this is a challenge. Local ablative therapy for oligoprogressive disease may allow the continuation of systemic treatments by overcoming the few sub-clones that have developed resistance. Stereotactic body radiotherapy is now frequently used in treating oligometastatic disease using ablative doses with minimally invasive techniques and acceptable toxicity. We discuss the current retrospective clinical evidence base supporting the use of local ablative therapy for oligoprogression in metastatic patients on targeted treatments within multiple tumour sites. As there is currently a lack of published prospective data available, the best management for these patients remains unclear. We discuss current trials in recruitment and the potential advancements in treating this group of patients with stereotactic radiotherapy.

Impact of the Implementation of Project Re-Engineered Discharge for Heart Failure patients at a Veterans Affairs Hospital at the Central Arkansas Veterans Healthcare System

Background: Hospitalizations due to chronic diseases such as heart failure (HF) continue to increase worldwide. Fragmentation of care while transitioning from one care setting to another is an important factor contributing to hospitalizations. Fragmented discharge tools have been implemented; however, the impact of a comprehensive interdisciplinary discharge tool has not been previously studied. Objective: The goal of this study is to assess the impact of the implementation of Project Re-Engineered Discharge (RED) on the incidence of hospital readmissions, all-cause mortality, primary care physician follow-up rate, and cost savings for patients with HF. Methods: This was a single-center, retrospective, cohort study of patients admitted with HF exacerbation at the Central Arkansas Veterans Healthcare System (CAVHS). A random sample of 100 patients admitted prior to implementation of Project RED and 50 patients after Project RED intervention were included in the study. The primary end point was 30-day hospital readmission for HF exacerbation. The co-secondary end points were all-cause mortality, cost savings, and rate of primary care physician appointments scheduled as well as attended per postdischarge recommendations. Results: The 30-day hospital readmission rate was 28% in the pre-Project RED group, and it was 18% in the post-Project RED group (P = .18). The all-cause mortality was significantly lower in the post-Project RED group as compared with the pre-Project RED group (18% vs 41%, P = .04). More patients in the post-Project RED group attended an outpatient primary care appointment as recommended per postdischarge instructions (40% vs 19%, P = .006). In addition, with the decrease in hospital 30-day readmission rate in the post-Project RED group, there was a cost savings of $1453 per patient visit for HF exacerbation. Conclusions: Coordination of care using a discharge tool like Project RED should be utilized in institutions to improve patient outcomes as well as patient safety while decrease the overall health care cost.

Evaluating Retention of Skin Cancer Education in Kidney Transplant Recipients Reveals a Window of Opportunity for Re-education

BACKGROUND

Skin cancer is the most common malignancy after solid organ transplant and can lead to significant morbidity. The likelihood of developing squamous cell carcinomas and melanomas is 100 and 2.4 times more likely, respectively, in kidney transplant recipients when compared with the general population. There are few data regarding the assessment and influence of solid organ transplant recipient (SOTR) knowledge of skin cancer and its effect on short- and long-term awareness and behavior.

METHODS

The purpose of this study was to assess the baseline knowledge of SOTR immediately after transplantation, and then to reassess their knowledge following a 5-minute educational video. We also wanted to determine whether lifestyle modifications had been implemented 4 to 8 months after the intervention.

RESULTS

Forty patients were enrolled within 2 months of transplantation. Eighty-seven percent of patients were renal transplant recipients, and 75% of patients were available for long-term follow-up. There was a significant increase in knowledge in the immediate postintervention period, which was sustained at 4- to 8-month follow-up, as assessed by patient questionnaire. Patients appeared to be applying this knowledge by participating in lifestyle risk modification and positive sun-protective behavior.

CONCLUSIONS

Our study suggests that incorporating additional skin cancer education into the early transplant timeline (perhaps in the first one or two outpatient follow-up visits) with an easy to administer educational video and question and answer form increases patient knowledge and influences positive sun-protective behavior.

Ivemark syndrome: bronchial compression from anomalous pulmonary venous anatomy

Ivemark syndrome is a heterotaxy syndrome which affects multiple organs and affects roughly 1 in every 6000 deliveries. Specifically, it can cause total anomalous pulmonary venous return and cardiac defects, which ultimately lead to decreased life expectancy. In order to better understand the nature of cardiac structures, CT angiogram has been heavily relied upon as it also allows for 3D reconstruction and optimal visualization of those features. This specific case presents with an anomalous venous return accompanied by multi-organ right isomerism that was reconstructed with 3D CT angiogram to better visualize and understand the cardiopulmonary system, as well as contribute to a fund of knowledge in hopes of discovering a solution to this condition.

Abstract OT1-03-09: FAIRLANE: A phase II randomized, double-blind, study of the Akt inhibitor ipatasertib (Ipat, GDC-0068) in combination with paclitaxel (Pac) as neoadjuvant treatment for early stage triple-negative breast cancer (TNBC)

Background: TNBC often exhibits activation of PI3K/Akt signaling, associated with loss of PTEN expression, low INPP4B expression, and/or increased AKT3 amplification. Inhibition of the PI3K/Akt pathway in diverse cancers leads to radiosensitization and/or chemosensitization. Ipat is an oral, potent ATP-competitive small molecule inhibitor of all three isoforms of Akt. The combination of ipat with taxanes in preclinical models resulted in enhanced efficacy relative to either ipat or chemotherapy alone. In a Phase Ib clinical study, the combination of ipat with diverse chemotherapy regimens was well-tolerated and resulted in RECIST responses, particularly pts with tumors having PI3K/Akt activation.

Methods: FAIRLANE is a randomized, double-blind, placebo controlled, multicenter, neoadjuvant Phase II study designed to estimate the efficacy of ipat combined with pac versus placebo combined with pac in women with Stage Ia  IIIa TNBC. Approximately 150 pts (Pts) will be enrolled, randomized in a 1:1 ratio, and stratified by PTEN status, node involvement, and tumor size. Pts will receive 3 cycles of ipat 400 mg or placebo orally once daily on Days 1 to 21 of each 28-day cycle, along with pac 80 mg/m2 every 7 days for a total of 12 doses. All pts will undergo pretreatment and Day 8 tumor tissue acquisition to evaluate pathway biomarkers. Following three cycles of treatment, pts will undergo surgery. The primary efficacy endpoint, pCR within the breast and axilla (ypT0/Tis ypN0) in all pts and in pts with PTEN low tumors, will be assessed by local pathology evaluation following completion of neoadjuvant therapy and surgery. Additional endpoints include objective response rate, safety, BCS rate, pharmacokinetics, and pathway biomarkers. Following surgical resection of primary tumor, pts are expected to continue post-operative treatment with a standard adjuvant chemotherapy regimen at physician's discretion. The study is open for accrual. Clinical trial information: NCT02301988.

Citation Format: Saura C, Isakoff SJ, Calvo I, Patt D, Andersen J, Gonzalez-Martin A, Fisher J, Ciruelos E, Gil-Gil M, De la Peña L, Choi Y, Jia S, Singel S, Patel PH, Baselga J, Oliveira M. FAIRLANE: A phase II randomized, double-blind, study of the Akt inhibitor ipatasertib (Ipat, GDC-0068) in combination with paclitaxel (Pac) as neoadjuvant treatment for early stage triple-negative breast cancer (TNBC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT1-03-09.

Development and Validation of a Simple Isocratic HPLC Method for Simultaneous Estimation of Phytosterols in Cissus quadrangularis

Cissus quadrangularis L. is a promising remedy prescribed in the ancient Ayurvedic literature for bone fracture healing properties. As this activity has been extensively investigated and well established, a range of formulations containing C. quadrangularis has been marketed. This work reports the development and validation of a reliable RP-HPLC method for the analysis of phytosterols in the various extracts of the plant. The proposed method utilizes a Cosmosil C₈ column (250 ΄ 4.6 mm) with a compatible Phenomenex C₈ guard column with isocratic elution of acetonitrile and water (95:5 v/v) at 25°. An effluent flow rate of 2 ml/min and UV detection at 202 nm was used for the analysis of phytosterols. The described method was linear in the range of 1–500 μg/ml, with excellent correlation coefficients. The precision, robustness and ruggedness values were also within the prescribed limits (less than 2%). The recovery values were within the range, which indicates that the accuracy of the analysis was good and that the interference of the matrix with the recovery of phytosterols was low. The phytosterols were found to be stable in a stock solution for 48 h (% RSD was below 2%) and no interfering extra peaks were observed under controlled stress conditions. The proposed method is simple, specific, precise, accurate, and reproducible and thus can be used for routine analysis of C. quadrangularis phytosterols in quality control laboratories.

Striatal leucine-rich repeat kinase 2 mRNA is increased in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned common marmosets (Callithrix jacchus) with L-3, 4-dihydroxyphenylalanine methyl ester-induced dyskinesia

The level of leucine-rich repeat kinase 2 (Lrrk2) mRNA expression was measured by reverse transcription-polymerase chain reaction in anterior striatum from normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets (Callithrix jacchus) that had L-3,4-dihydroxyphenylalanine methyl ester (L-DOPA)-induced dyskinesia. The level of striatal Lrrk2 mRNA was increased in MPTP-treated common marmosets that had L-DOPA-induced dyskinesia compared with normal animals that did not receive l-DOPA. Marmosets that exhibited higher levels of dyskinesia had the greatest increase in striatal Lrrk2 mRNA. Lrrk2 mRNA expression was also measured in human striatum and substantia nigra from control subjects and patients dying with Parkinson's disease. In contrast to marmoset tissue, no alteration in Lrrk2 mRNA expression was found in parkinsonian human brain. However, the brain was from patients who had an overall low level of dyskinesia. The correlation between striatal Lrrk2 mRNA levels in MPTP-treated common marmoset striatum and L-DOPA-induced dyskinesia indicates that LRRK2 may have a role in the molecular alterations that cause L-DOPA-induced dyskinesia.

Targeted therapy for metastatic renal cell carcinoma

Metastatic renal cell carcinoma (RCC) has historically been refractory to cytotoxic and hormonal agents; only interleukin 2 and interferon alpha provide response in a minority of patients. We reviewed RCC biology and explored the ways in which this understanding led to development of novel, effective targeted therapies. Small molecule tyrosine kinase inhibitors, monoclonal antibodies and novel agents are all being studied, and phase II studies show promising activity of sunitinib, sorafenib and bevacizumab. The results of phase III studies will determine the role of these agents in metastatic RCC.

Prokaryotic DNA polymerase I: evolution, structure, and "base flipping" mechanism for nucleotide selection

Accurate transmission of DNA material from one generation to the next is crucial for prolonged cell survival. Following the discovery of DNA polymerse I in Escherichia coli, the DNA polymerase I class of enzymes has served as the prototype for studies on structural and biochemical mechanisms of DNA replication. Recently, a series of genomic, mutagenesis and structural investigations have provided key insights into how Pol I class of enzymes function and evolve. X-ray crystal structures of at least three Pol I class of enzymes have been solved in the presence of DNA and dNTP, thus allowing a detailed description of a productive replication complex. Rapid-quench stop-flow studies have helped define individual steps during nucleotide incorporation and conformational changes that are rate limiting during catalysis. Studies in our laboratory have generated large libraries of active mutant enzymes (8000) containing a variety of substitutions within the active site, some of which exhibit altered biochemical properties. Extensive genomic information of Pol I has recently become available, as over 50 polA genes from different prokaryotic species have been sequenced. In light of these advancements, we review here the structure-function relationships of Pol I, and we highlight those interactions that are responsible for the high fidelity of DNA synthesis. We present a mechanism for "flipping" of the complementary template base to enhance interactions with the incoming nucleotide substrate during DNA synthesis.

The conserved active site motif A of Escherichia coli DNA polymerase I is highly mutable

Escherichia coli DNA polymerase I participates in DNA replication, DNA repair, and genetic recombination; it is the most extensively studied of all DNA polymerases. Motif A in the polymerase active site has a required role in catalysis and is highly conserved. To assess the tolerance of motif A for amino acid substitutions, we determined the mutability of the 13 constituent amino acids Val(700)-Arg(712) by using random mutagenesis and genetic selection. We observed that every residue except the catalytically essential Asp(705) can be mutated while allowing bacterial growth and preserving wild-type DNA polymerase activity. Hence, the primary structure of motif A is plastic. We present evidence that mutability of motif A has been conserved during evolution, supporting the premise that the tolerance for mutation is adaptive. In addition, our work allows identification of refinements in catalytic function that may contribute to preservation of the wild-type motif A sequence. As an example, we established that the naturally occurring Ile(709) has a previously undocumented role in supporting sugar discrimination.

A single highly mutable catalytic site amino acid is critical for DNA polymerase fidelity

DNA polymerases contain active sites that are structurally superimposable and conserved in amino acid sequence. To probe the biochemical and structure-function relationship of DNA polymerases, a large library (200,000 members) of mutant Thermus aquaticus DNA polymerase I (Taq pol I) was created containing random substitutions within a portion of the dNTP binding site (Motif A; amino acids 605-617), and a fraction of all selected active Taq pol I (291 out of 8000) was tested for base pairing fidelity; seven unique mutants that efficiently misincorporate bases and/or extend mismatched bases were identified and sequenced. These mutants all contain substitutions of one specific amino acid, Ile-614, which forms part of the hydrophobic pocket that binds the base and ribose portions of the incoming nucleotide. Mutant Taq pol Is containing hydrophilic substitution I614K exhibit 10-fold lower base misincorporation fidelity, as well as a high propensity to extend mispairs. In addition, these low fidelity mutants containing hydrophilic substitution for Ile-614 can bypass damaged templates that include an abasic site and vinyl chloride adduct ethenoA. During polymerase chain reaction, Taq pol I mutant I614K exhibits an error rate that is >20-fold higher relative to the wild-type enzyme and efficiently catalyzes both transition and transversion errors. These studies have generated polymerase chain reaction-proficient mutant polymerases containing substitutions within the active site that confers low base pairing fidelity and a high error rate. Considering the structural and sequence conservation of Motif A, it is likely that a similar substitution will yield active low fidelity DNA polymerases that are mutagenic.

Multiple amino acid substitutions allow DNA polymerases to synthesize RNA

DNA and RNA polymerase exhibit similarities in structures and catalytic mechanisms, suggesting that both classes of enzymes are evolutionarily related. To probe the biochemical and structure-function relationship between the two classes of polymerases, a large library (200,000 members) of mutant Thermus aquaticus DNA polymerase I (Taq pol I) was created containing random substitutions within a portion of the dNTP binding site (motif A; amino acids 605-617), and a fraction of all selected active Taq pol I (291 of 8000) was tested for the ability to incorporate successive ribonucleotides; 23 unique mutants that added rNTPs into a growing polynucleotide chain were identified and sequenced. These mutants, each containing one to four substitutions, incorporate ribonucleotides at a efficiency approaching 10(3)-fold greater than that of wild type Taq pol I. Several mutants added successive ribonucleotides and thus can catalyze the synthesis of RNA. Sequence analysis of these mutants demonstrates that at least two amino acid residues are involved in excluding ribonucleotides from the active site. Interestingly, wild type DNA polymerases from several distinct families selectively discriminate against rUTP. This study suggests that current DNA and RNA polymerases could have evolved by divergent evolution from an ancestor that shared a common mechanism for polynucleotide synthesis.

DNA polymerase active site is highly mutable: evolutionary consequences

DNA polymerases contain active sites that are structurally superimposable and highly conserved in sequence. To assess the significance of this preservation and to determine the mutational burden that active sites can tolerate, we randomly mutated a stretch of 13 amino acids within the polymerase catalytic site (motif A) of Thermus aquaticus DNA polymerase I. After selection, by using genetic complementation, we obtained a library of approximately 8, 000 active mutant DNA polymerases, of which 350 were sequenced and analyzed. This is the largest collection of physiologically active polymerase mutants. We find that all residues of motif A, except one (Asp-610), are mutable while preserving wild-type activity. A wide variety of amino acid substitutions were obtained at sites that are evolutionarily maintained, and conservative substitutions predominate at regions that stabilize tertiary structures. Several mutants exhibit unique properties, including DNA polymerase activity higher than the wild-type enzyme or the ability to incorporate ribonucleotide analogs. Bacteria dependent on these mutated polymerases for survival are fit to replicate repetitively. The high mutability of the polymerase active site in vivo and the ability to evolve altered enzymes may be required for survival in environments that demand increased mutagenesis. The inherent substitutability of the polymerase active site must be addressed relative to the constancy of nucleotide sequence found in nature.

Evaluation of an unused 1952 Ridley intraocular lens

PURPOSE

To evaluate an unused 1952 historic Ridley intraocular lens (IOL) brought to Bombay, India, in 1952 from an Oxford Ophthalmologic Conference in England and given to 1 of the authors during his residency.

SETTING

Alcon Laboratories, Fort Worth, Texas, USA.

METHODS

The Ridley IOL was evaluated at Alcon Laboratories, Inc., using the established procedures of its Intraocular R&D Laboratories. Various optical and physical aspects of the Ridley lens were evaluated including (1) dimensions, (2) weight, (3) power, (4) resolution efficiency and modulation transfer function (MTF), (5) surface sphericity by interferometry, (6) ultraviolet (UV)-visible transmission characteristic, (7) attenuated total reflectance (ATR)-Fourier transform infrared reflectance spectrum, and (8) cosmetics by visual inspection using light microscopy.

RESULTS

This 8.5 mm diameter, 2.4 mm thick, 23 diopter biconvex IOL weighed 108 mg. The ATR spectrum, UV-visible transmission, and refractive index confirmed its poly-(methyl methacrylate) material. The 0.56 MTF value at 100 line pairs/mm, per the International Standards Organization--IOL Optics Standard, and 93% resolution efficiency in water, per the American National Standard Institute IOL Optics Standard, revealed the IOL's excellent optics. This was confirmed by 0.278 wave root mean square surface figure as measured by Zygo interferometer using a 633 nm wavelength. Visual inspection revealed rough edges with sharp corners and some surface scratches. Early clinical experience with Ridley IOLs in Bombay, India, is briefly given.

CONCLUSION

The Ridley IOL had excellent optical quality, meeting the requirements of current IOL optics standards. The selection of its dimensions was guided by the human crystalline lens, and the Ridley IOL was half as bulky. Although its clinical results were mixed, successful cases inspired subsequent improvements, leading to modern, highly satisfactory IOLs. This IOL represented a revolutionary innovation in ophthalmology.

Insights into DNA polymerization mechanisms from structure and function analysis of HIV-1 reverse transcriptase

When the single-stranded RNA genome of HIV-1 is copied into double-stranded DNA, the viral enzyme reverse transcriptase (RT) catalyzes the addition of approximately 20,000 nucleotides; however, the precise mechanism of nucleotide addition is unknown. In this study, we attempt to integrate the genetic data and biochemical mechanism of DNA polymerization with the structure of HIV-1 RT complexed with a dsDNA template-primer. The first step of polymerization involves the physical association of a polymerase with its nucleic acid substrate. A comparison of the structures of HIV-1 RT in the presence and absence of DNA indicates that the tip of the p66 thumb moves approximately 30 A upon DNA binding. This conformational change permits numerous interactions between residues of alpha-helices H and I in the thumb subdomain and the DNA. Measurements of DNA binding affinity for nucleic acids with double-stranded DNAs that have an increasing number of bases in the template overhang and molecular modeling suggest that portions of beta 3 and beta 4 within the fingers subdomain bind single-stranded regions of the template. Measurements of nucleotide incorporation efficiency (kcat/Km) show that the binding and incorporation of the next complementary nucleotide are not dependent on the length of the template overhang. Molecular modeling of an incoming nucleotide triphosphate (dTTP), based in part on the position of mercury atoms in a RT/DNA/Hg-UTP/Fab structure, suggests that portions of secondary structural elements alpha C-beta 6, alpha E, beta 11b, and beta 9-beta 10 determine the topology of the dNTP-binding site. These results also suggest that nucleotide incorporation is accompanied by a protein conformational change that positions the dNTP for nucleophilic attack. Nucleophilic attack by the oxygen atom of the 3'-OH group of the primer strand could be metal-mediated, and Asp185 may be directly involved in stabilizing the transition state. The translocation step may be characterized by rotational as well as translational motions of HIV-1 RT relative to the DNA double helix. Some of the energy required for translocation could be provided by dNTP hydrolysis and could be coupled with conformational changes within the nucleic acid. A structural comparison of HIV-1 RT, Klenow fragment, and T7 RNA polymerase identified regions within T7 RNA polymerase which are not present in the other two polymerases that might help this polymerase to remain bound with nucleic acids and contribute to the ability of the T7 RNA polymerase to polymerize processively.

Marked infidelity of human immunodeficiency virus type 1 reverse transcriptase at RNA and DNA template ends

Human immunodeficiency virus type 1 (HIV-1) is genetically highly variable. This is attributed to the error-prone nature of HIV-1 replication and its proclivity for recombination. During replication and recombination, reverse transcriptase (RT) must polymerize DNA to the 5' ends of multiple RNA and DNA template termini while converting HIV-1 RNA to double-stranded DNA. We have determined the fidelity of HIV-1 RT in vitro during polymerization to the 5' ends of HIV-1 long terminal repeat DNA template sequences and to the end of a partial HIV-1 genomic RNA template that mimics a recombination intermediate. HIV-1 RT readily extended recessed DNA primers to form full-length blunt-end DNA-DNA and DNA-RNA duplexes. In addition, HIV-1 RT catalyzed high yields of products with one to four extra nucleotides at the 3' ends of the nascent DNAs. These products were formed processively via a nontemplated mechanism that is highly specific for the addition of purine nucleotides (A > G >> T > or = C). Thus, HIV-1 RT is extremely unfaithful at both DNA and RNA template ends, introducing errors (extra nucleotides) in one out of every two or three nascent strands processively polymerized. This error rate is 1000 times higher than for HIV-1 RT-catalyzed errors at internal template positions. Blunt-end additions were also catalyzed by other retroviral RTs at relative rates of HIV-1 approximately Moloney murine leukemia virus > avian myeloblastosis virus. These data suggest a potentially important mechanism for retroviral mutation mediated by nontemplated blunt-end addition of purines prior to forced copy-choice recombination.

Esophageal contribution to chest pain in patients with coronary artery disease

We conducted a prospective study to determine the role of the esophagus in causing chest pain in patients with established CAD on optimum therapy. Thirty-two men with documented CAD who complained of frequent and usually daily retrosternal chest pain were evaluated. Following a standard esophageal manometry and acid perfusion test, simultaneous two-channel ambulatory Holter monitor and esophageal pH record tests were performed for 24 hours. Fifty-three episodes of chest pain were documented in 20 patients; 11 patients were free of pain. Of the 20 patients who complained of chest pains, 17 (85 percent) demonstrated at least one episode of PPR, defined as a drop in distal esophageal pH to less than 4 within ten minutes before or after the onset chest pain. Episodes of asymptomatic GER were common. The correlation of PPR with chest pain was 70 percent (37/53 episodes) and of ischemic ECG changes with chest pain 13 percent (7/53); in the remaining, there was no correlation with either. Two patients demonstrated simultaneous PPR and ischemic ECG changes. Seventeen esophageal motility abnormalities were observed in 14 patients (45 percent). It is our conclusion that esophageal disorders contribute to chest pain in patients with documented CAD. In this group, GER plays a greater role than in those with normal coronary arteries. In addition, esophageal motility disorders are common in these patients. Esophageal testing can be undertaken safely in these patients.

The value of Chiba fine-needle aspiration biopsy in the diagnosis of hepatic malignancy: a comparison with Menghini needle biopsy

The detection or exclusion of metastatic liver involvement is critical in the management and prognosis of patients with malignant disease. Noninvasive imaging modalities such as computed tomography, ultrasound, and technetium colloid liver scan are highly sensitive but nonspecific. Serum alkaline phosphatase is of similar value. A blind liver biopsy by the Menghini technique is often done to confirm the diagnosis, but its yield is low. We prospectively evaluated 74 patients using blind Menghini needle biopsy and concurrent Chiba fine-needle aspiration biopsy (FNAB) techniques. A positive diagnosis of malignancy was made in 30 patients (41%). In only 25 (34%) was the diagnosis made by Menghini biopsy, while Chiba FNAB confirmed the diagnosis in all 30 patients. Thus, concurrent use of both needles increased the diagnostic accuracy by 7%. Seven additional patients, considered to have one or more contraindications for the Menghini biopsy, underwent Chiba FNAB alone; the diagnosis was confirmed in all without complication. We conclude that FNAB alone or in combination with Menghini biopsy is valuable and safe in the diagnosis of metastatic liver disease.

Condyloma acuminata presenting as rectal polyps in a heterosexual man: importance of CT scan of the pelvis

Condyloma acuminata generally occur in and outside the anal canal of young homosexual men who practice anal coitus. We report the occurrence of large condyloma acuminata in the rectum of an elderly heterosexual man. Its characteristic endoscopic, pathological and CT scan features are discussed. CT scan may be invaluable in assessing local infiltration.