The complementarity of DDR, nucleic acids and anti-tumour immunity

Immune checkpoint blockade (ICB) immunotherapy is a first-line treatment for selected cancers, yet the mechanisms of its efficacy remain incompletely understood. Furthermore, only a minority of patients with cancer benefit from ICB, and there is a lack of fully informative treatment response biomarkers. Selectively exploiting defects in DNA damage repair is also a standard treatment for cancer, spurred by enhanced understanding of the DNA damage response (DDR). DDR and ICB are closely linked-faulty DDR produces immunogenic cancer neoantigens that can increase the efficacy of ICB therapy, and tumour mutational burden is a good but imperfect biomarker for the response to ICB. DDR studies in ICB efficacy initially focused on contributions to neoantigen burden. However, a growing body of evidence suggests that ICB efficacy is complicated by the immunogenic effects of nucleic acids generated from exogenous DNA damage or endogenous processes such as DNA replication. Chemotherapy, radiation, or selective DDR inhibitors (such as PARP inhibitors) can generate aberrant nucleic acids to induce tumour immunogenicity independently of neoantigens. Independent of their functions in immunity, targets of immunotherapy such as cyclic GMP-AMP synthase (cGAS) or PD-L1 can crosstalk with DDR or the DNA repair machinery to influence the response to DNA-damaging agents. Here we review the rapidly evolving, multifaceted interfaces between DDR, nucleic acid immunogenicity and immunotherapy efficacy, focusing on ICB. Understanding these interrelated processes could explain ICB treatment failures and reveal novel exploitable therapeutic vulnerabilities in cancers. We conclude by addressing major unanswered questions and new research directions.

DNA binding and RAD51 engagement by the BRCA2 C-terminus orchestrate DNA repair and replication fork preservation

The tumor suppressor BRCA2 participates in DNA double-strand break repair by RAD51-dependent homologous recombination and protects stressed DNA replication forks from nucleolytic attack. We demonstrate that the C-terminal Recombinase Binding (CTRB) region of BRCA2, encoded by gene exon 27, harbors a DNA binding activity. CTRB alone stimulates the DNA strand exchange activity of RAD51 and permits the utilization of RPA-coated ssDNA by RAD51 for strand exchange. Moreover, CTRB functionally synergizes with the Oligonucleotide Binding fold containing DNA binding domain and BRC4 repeat of BRCA2 in RPA-RAD51 exchange on ssDNA. Importantly, we show that the DNA binding and RAD51 interaction attributes of the CTRB are crucial for homologous recombination and protection of replication forks against MRE11-mediated attrition. Our findings shed light on the role of the CTRB region in genome repair, reveal remarkable functional plasticity of BRCA2, and help explain why deletion of Brca2 exon 27 impacts upon embryonic lethality.

Tumor Intrinsic PD-L1 Promotes DNA Repair in Distinct Cancers and Suppresses PARP Inhibitor-Induced Synthetic Lethality

BRCA1-mediated homologous recombination is an important DNA repair mechanism that is the target of FDA-approved PARP inhibitors, yet details of BRCA1-mediated functions remain to be fully elucidated. Similarly, immune checkpoint molecules are targets of FDA-approved cancer immunotherapies, but the biological and mechanistic consequences of their application are incompletely understood. We show here that the immune checkpoint molecule PD-L1 regulates homologous recombination in cancer cells by promoting BRCA1 nuclear foci formation and DNA end resection. Genetic depletion of tumor PD-L1 reduced homologous recombination, increased nonhomologous end joining, and elicited synthetic lethality to PARP inhibitors olaparib and talazoparib in vitro in some, but not all, BRCA1 wild-type tumor cells. In vivo, genetic depletion of tumor PD-L1 rendered olaparib-resistant tumors sensitive to olaparib. In contrast, anti-PD-L1 immune checkpoint blockade neither enhanced olaparib synthetic lethality nor improved its efficacy in vitro or in wild-type mice. Tumor PD-L1 did not alter expression of BRCA1 or its cofactor BARD1 but instead coimmunoprecipitated with BARD1 and increased BRCA1 nuclear accumulation. Tumor PD-L1 depletion enhanced tumor CCL5 expression and TANK-binding kinase 1 activation in vitro, similar to known immune-potentiating effects of PARP inhibitors. Collectively, these data define immune-dependent and immune-independent effects of PARP inhibitor treatment and genetic tumor PD-L1 depletion. Moreover, they implicate a tumor cell-intrinsic, immune checkpoint-independent function of PD-L1 in cancer cell BRCA1-mediated DNA damage repair with translational potential, including as a treatment response biomarker.

SIGNIFICANCE

PD-L1 upregulates BRCA1-mediated homologous recombination, and PD-L1-deficient tumors exhibit BRCAness by manifesting synthetic lethality in response to PARP inhibitors, revealing an exploitable therapeutic vulnerability and a candidate treatment response biomarker. See related commentary by Hanks, p. 2069.

In Vitro Reconstitution of BRCA1-BARD1/RAD51-Mediated Homologous DNA Pairing

RAD51-mediated homologous recombination (HR) is a conserved mechanism for the repair of DNA double-strand breaks and the maintenance of DNA replication forks. Several breast and ovarian tumor suppressors, including BRCA1 and BARD1, have been implicated in HR since their discovery in the 1990s. However, a holistic understanding of how they participate in HR has been hampered by the immense challenge of expressing and purifying these large and unstable protein complexes for mechanistic analysis. Recently, we have overcome such a challenge for the BRCA1-BARD1 complex, allowing us to demonstrate its pivotal role in HR via the promotion of RAD51-mediated DNA strand invasion. In this chapter, we describe detailed procedures for the expression and purification of the BRCA1-BARD1 complex and in vitro assays using this tumor suppressor complex to examine its ability to promote RAD51-mediated homologous DNA pairing. This includes two distinct biochemical assays, namely, D-loop formation and synaptic complex assembly. These methods are invaluable for studying the BRCA1-BARD1 complex and its functional interplay with other factors in the HR process.

INTS11 regulates hematopoiesis by promoting PRC2 function

INTS11, the catalytic subunit of the Integrator (INT) complex, is crucial for the biogenesis of small nuclear RNAs and enhancer RNAs. However, the role of INTS11 in hematopoietic stem and progenitor cell (HSPC) biology is unknown. Here, we report that INTS11 is required for normal hematopoiesis and hematopoietic-specific genetic deletion of Ints11 leads to cell cycle arrest and impairment of fetal and adult HSPCs. We identified a novel INTS11-interacting protein complex, Polycomb repressive complex 2 (PRC2), that maintains HSPC functions. Loss of INTS11 destabilizes the PRC2 complex, decreases the level of histone H3 lysine 27 trimethylation (H3K27me3), and derepresses PRC2 target genes. Reexpression of INTS11 or PRC2 proteins in Ints11-deficient HSPCs restores the levels of PRC2 and H3K27me3 as well as HSPC functions. Collectively, our data demonstrate that INTS11 is an essential regulator of HSPC homeostasis through the INTS11-PRC2 axis.

A deep dive into the RecQ interactome: something old and something new

RecQ family helicases are found in all domains of life and play roles in multiple processes that underpin genomic integrity. As such, they are often referred to as guardians or caretakers of the genome. Despite their importance, however, there is still much we do not know about their basic functions in vivo, nor do we fully understand how they interact in organisms that encode more than one RecQ family member. We recently took a multi-omics approach to better understand the Saccharomyces cerevisiae Hrq1 helicase and its interaction with Sgs1, with these enzymes being the functional homologs of the disease-linked RECQL4 and BLM helicases, respectively. Using synthetic genetic array analyses, immuno-precipitation coupled to mass spectrometry, and RNA-seq, we found that Hrq1 and Sgs1 likely participate in many pathways outside of the canonical DNA recombination and repair functions for which they are already known. For instance, connections to transcription, ribosome biogenesis, and chromatin/chromosome organization were uncovered. These recent results are briefly detailed with respect to current knowledge in the field, and possible follow-up experiments are suggested. In this way, we hope to gain a wholistic understanding of these RecQ helicases and how their mutation leads to genomic instability.

The Genetic and Physical Interactomes of the Saccharomyces cerevisiae Hrq1 Helicase

The human genome encodes five RecQ helicases (RECQL1, BLM, WRN, RECQL4, and RECQL5) that participate in various processes underpinning genomic stability. Of these enzymes, the disease-associated RECQL4 is comparatively understudied due to a variety of technical challenges. However, Saccharomyces cerevisiae encodes a functional homolog of RECQL4 called Hrq1, which is more amenable to experimentation and has recently been shown to be involved in DNA inter-strand crosslink (ICL) repair and telomere maintenance. To expand our understanding of Hrq1 and the RecQ4 subfamily of helicases in general, we took a multi-omics approach to define the Hrq1 interactome in yeast. Using synthetic genetic array analysis, we found that mutations of genes involved in processes such as DNA repair, chromosome segregation, and transcription synthetically interact with deletion of HRQ1 and the catalytically inactive hrq1-K318A allele. Pull-down of tagged Hrq1 and mass spectrometry identification of interacting partners similarly underscored links to these processes and others. Focusing on transcription, we found that hrq1 mutant cells are sensitive to caffeine and that mutation of HRQ1 alters the expression levels of hundreds of genes. In the case of hrq1-K318A, several of the most highly upregulated genes encode proteins of unknown function whose expression levels are also increased by DNA ICL damage. Together, our results suggest a heretofore unrecognized role for Hrq1 in transcription, as well as novel members of the Hrq1 ICL repair pathway. These data expand our understanding of RecQ4 subfamily helicase biology and help to explain why mutations in human RECQL4 cause diseases of genomic instability.

Fanconi anemia-independent DNA inter-strand crosslink repair in eukaryotes

DNA inter-strand crosslinks (ICLs) are dangerous lesions that can be caused by a variety of endogenous and exogenous bifunctional compounds. Because covalently linking both strands of the double helix locally disrupts DNA replication and transcription, failure to remove even a single ICL can be fatal to the cell. Thus, multiple ICL repair pathways have evolved, with the best studied being the canonical Fanconi anemia (FA) pathway. However, recent research demonstrates that different types of ICLs (e.g., backbone distorting vs. non-distorting) can be discriminated by the cell, which then mounts a specific repair response using the FA pathway or one of a variety of FA-independent ICL repair pathways. This review focuses on the latter, covering current work on the transcription-coupled, base excision, acetaldehyde-induced, and SNM1A/RecQ4 ICL repair pathways and highlighting unanswered questions in the field. Answering these questions will provide mechanistic insight into the various pathways of ICL repair and enable ICL-inducing agents to be more effectively used as chemotherapeutics.

The yeast Hrq1 helicase stimulates Pso2 translesion nuclease activity and thereby promotes DNA interstrand crosslink repair

DNA interstrand crosslink (ICL) repair requires a complex network of DNA damage response pathways. Removal of the ICL lesions is vital, as they are physical barriers to essential DNA processes that require the separation of duplex DNA, such as replication and transcription. The Fanconi anemia (FA) pathway is the principal mechanism for ICL repair in metazoans and is coupled to DNA replication. In Saccharomyces cerevisiae, a vestigial FA pathway is present, but ICLs are predominantly repaired by a pathway involving the Pso2 nuclease, which is hypothesized to use its exonuclease activity to digest through the lesion to provide access for translesion polymerases. However, Pso2 lacks translesion nuclease activity in vitro, and mechanistic details of this pathway are lacking, especially relative to FA. We recently identified the Hrq1 helicase, a homolog of the disease-linked enzyme RecQ-like helicase 4 (RECQL4), as a component of Pso2-mediated ICL repair. Here, using genetic, biochemical, and biophysical approaches, including single-molecule FRET (smFRET)- and gel-based nuclease assays, we show that Hrq1 stimulates the Pso2 nuclease through a mechanism that requires Hrq1 catalytic activity. Importantly, Hrq1 also stimulated Pso2 translesion nuclease activity through a site-specific ICL in vitro We noted that stimulation of Pso2 nuclease activity is specific to eukaryotic RecQ4 subfamily helicases, and genetic and biochemical data suggest that Hrq1 likely interacts with Pso2 through their N-terminal domains. These results advance our understanding of FA-independent ICL repair and establish a role for the RecQ4 helicases in the repair of these detrimental DNA lesions.

Thin-Layer Chromatography and Real-Time Coupled Assays to Measure ATP Hydrolysis

Many chemical reactions in the cell are thermodynamically unfavorable. To overcome this barrier, the energy released from the hydrolysis of adenosine triphosphate (ATP) is coupled to these reactions via ATP hydrolyzing enzymes known as ATPases. These enzymes are ubiquitous in nature and frequently act as molecular motors in processes ranging from DNA replication to protein degradation. Assays that characterize ATPase activity in vitro are important tools to gain insight into their functions in vivo. Here, we describe a direct and flexible thin-layer chromatography method for detecting ATPase activity using radiolabeled ATP. Additionally, we describe a high-throughput coupled reaction assay pairing ATP hydrolysis with nicotinamide adenine dinucleotide (NADH) oxidation to monitor ATP hydrolysis in real time.

Toward the improvement of total nitrogen deposition budgets in the United States

Frameworks for limiting ecosystem exposure to excess nutrients and acidity require accurate and complete deposition budgets of reactive nitrogen (Nr). While much progress has been made in developing total Nr deposition budgets for the U.S., current budgets remain limited by key data and knowledge gaps. Analysis of National Atmospheric Deposition Program Total Deposition (NADP/TDep) data illustrates several aspects of current Nr deposition that motivate additional research. Averaged across the continental U.S., dry deposition contributes slightly more (55%) to total deposition than wet deposition and is the dominant process (>90%) over broad areas of the Southwest and other arid regions of the West. Lack of dry deposition measurements imposes a reliance on models, resulting in a much higher degree of uncertainty relative to wet deposition which is routinely measured. As nitrogen oxide (NOx) emissions continue to decline, reduced forms of inorganic nitrogen (NHx = NH3 + NH4+) now contribute >50% of total Nr deposition over large areas of the U.S. Expanded monitoring and additional process-level research are needed to better understand NHx deposition, its contribution to total Nr deposition budgets, and the processes by which reduced N deposits to ecosystems. Urban and suburban areas are hotspots where routine monitoring of oxidized and reduced Nr deposition is needed. Finally, deposition budgets have incomplete information about the speciation of atmospheric nitrogen; monitoring networks do not capture important forms of Nr such as organic nitrogen. Building on these themes, we detail the state of the science of Nr deposition budgets in the U.S. and highlight research priorities to improve deposition budgets in terms of monitoring and flux measurements, leaf- to regional-scale modeling, source apportionment, and characterization of deposition trends and patterns.

Gel-Based Assays for Measuring DNA Unwinding, Annealing, and Strand Exchange

Efficient replication and repair of the genome requires a multitude of protein-DNA transactions. These interactions can result in a variety of consequences for DNA such as the unwinding of double-stranded DNA (dsDNA) into single-stranded DNA (ssDNA), the annealing of complementary ssDNAs, or the exchange of ssDNA with one strand of a dsDNA duplex. Some DNA helicases possess all three activities, but many DNA-interacting proteins can also catalyze one or more of these reactions. Assays that quantify these activities are an important first step in characterizing these protein-DNA interactions in vitro. Here, we describe methods for the formation of dsDNA substrates and the assays that can be used to biochemically characterize proteins that can unwind, anneal, and/or exchange DNA strands.

The Saccharomyces cerevisiae Hrq1 and Pif1 DNA helicases synergistically modulate telomerase activity in vitro

Telomere length homeostasis is vital for maintaining genomic stability and is regulated by multiple factors, including telomerase activity and DNA helicases. The Saccharomyces cerevisiae Pif1 helicase was the first discovered catalytic inhibitor of telomerase, but recent experimental evidence suggests that Hrq1, the yeast homolog of the disease-linked human RecQ-like helicase 4 (RECQL4), plays a similar role via an undefined mechanism. Using yeast extracts enriched for telomerase activity and an in vitro primer extension assay, here we determined the effects of recombinant WT and inactive Hrq1 and Pif1 on total telomerase activity and telomerase processivity. We found that titrations of these helicases alone have equal-but-opposite biphasic effects on telomerase, with Hrq1 stimulating activity at high concentrations. When the helicases were combined in reactions, however, they synergistically inhibited or stimulated telomerase activity depending on which helicase was catalytically active. These results suggest that Hrq1 and Pif1 interact and that their concerted activities ensure proper telomere length homeostasis in vivo We propose a model in which Hrq1 and Pif1 cooperatively contribute to telomere length homeostasis in yeast.

Clinical Neuroscience in Practice: An Experiential Learning Course for Undergraduates Offered by Neurosurgeons and Neuroscientists

Many pre-health students pursue extracurricular shadowing opportunities to gain clinical experience. The Virginia Tech School of Neuroscience introduced a formal course that provides a clinical experience superior to that received by many medical students. This course is composed of weekly 75-minute seminars that cover diseases affecting the nervous system, their diagnosis and treatment, complemented by weekly half-day intensive clinical experiences with unprecedented access to a team of neurosurgeons (in hospital operating rooms, Intensive Care Units, emergency room, angiographic suites, and wards). In the operating rooms, students routinely "scrub-in" for complex surgeries. On hospital rounds, students experience direct patient care and receive in-depth exposure to modern nervous system imaging. Students participate in two 24-hour "on-call" experiences with team providers. After call, students participate in cognitive and psychological studies to assess physiological and psychological effects of call-related sleep deprivation. Students prepare weekly essays on challenging socioeconomic and ethical questions, exploring subjects such as the cost of medicine and inequalities in access to health care. Towards the end of the course, students meet with the admission dean of the Virginia Tech Carilion medical school; they prepare a personal statement for medical school/graduate school applications, and attend a half-day block of mock medical school/graduate school interviews delivered by experienced clinicians. In lieu of a final exam, each student presents to the entire neurosurgery department, an in-depth clinical analysis of a case in which they participated. We provide details on implementation, challenges and outcomes based on experiences from three semesters with a total enrollment of approximately 60 students.

Yeast Hrq1 shares structural and functional homology with the disease-linked human RecQ4 helicase

The five human RecQ helicases participate in multiple processes required to maintain genome integrity. Of these, the disease-linked RecQ4 is the least studied because it poses many technical challenges. We previously demonstrated that the yeast Hrq1 helicase displays similar functions to RecQ4 in vivo, and here, we report the biochemical and structural characterization of these enzymes. In vitro, Hrq1 and RecQ4 are DNA-stimulated ATPases and robust helicases. Further, these activities were sensitive to DNA sequence and structure, with the helicases preferentially unwinding D-loops. Consistent with their roles at telomeres, telomeric repeat sequence DNA also stimulated binding and unwinding by these enzymes. Finally, electron microscopy revealed that Hrq1 and RecQ4 share similar structural features. These results solidify Hrq1 as a true RecQ4 homolog and position it as the premier model to determine how RecQ4 mutations lead to genomic instability and disease.

Saccharomyces cerevisiae Hrq1 helicase activity is affected by the sequence but not the length of single-stranded DNA

Mutations in the human RecQ4 DNA helicase are associated with three different diseases characterized by genomic instability. To gain insight into how RecQ4 dysfunction leads to these pathologies, several groups have used the Saccharomyces cerevisiae RecQ4 homolog Hrq1 as an experimental model. Hrq1 displays many of the same functions as RecQ4 in vivo and in vitro. However, there is some disagreement in the literature about the effects of single-stranded DNA (ssDNA) length on Hrq1 helicase activity and the ability of Hrq1 to anneal complementary ssDNA oligonucleotides into duplex DNA. Here, we present a side-by-side comparison of Hrq1 and RecQ4 helicase activity, demonstrating that in both cases, long random-sequence 3' ssDNA tails inhibit DNA unwinding in vitro in a length-dependent manner. This appears to be due to the formation of secondary structures in the random-sequence ssDNA because Hrq1 preferentially unwound poly(dT)-tailed forks independent of ssDNA length. Further, RecQ4 is capable of ssDNA strand annealing and annealing-dependent strand exchange, but Hrq1 lacks these activities. These results establish the importance of DNA sequence in Hrq1 helicase activity, and the absence of Hrq1 strand annealing activity explains the previously identified discrepancies between S. cerevisiae Hrq1 and human RecQ4.

Regulation of the pharynx of Caenorhabditis elegans by 5-HT, octopamine, and FMRFamide-like neuropeptides

More than fifty FMRFamide-like neuropeptides have been identified in nematodes. We addressed the role of a subset of these in the control of nematode feeding by electrophysiological recording of the activity of C. elegans pharynx. AF1 (KNEFIRFamide), AF2 (KHEYLRFamide), AF8 (KSAYMRFamide), and GAKFIRFamide (encoded by the C. elegans genes flp-8, flp-14, flp-6, and flp-5, respectively) increased pharyngeal action potential frequency, in a manner similar to 5-HT. In contrast, SDPNFLRFamide, SADPNFLRFamide, SAEPFGTMRFamide, KPSVRFamide, APEASPFIRFamide, and AQTVRFamide (encoded by the C. elegans genes flp-1; flp-1; flp-3; flp-9; flp-13, and flp-16, respectively) inhibited the pharynx in a manner similar to octopamine. Only three of the neuropeptides had potent effects at low nanomolar concentrations, consistent with a physiological role in pharyngeal regulation. Therefore, we assessed whether these three peptides mediated their actions either directly on the pharynx or indirectly via the neural circuit controlling its activity by comparing actions between wild-type and mutants with deficits in synaptic signaling. Our data support the conclusion that AF1 and SAEPFGTMRFamide regulate the activity of the pharynx indirectly, whereas APEASPFIRFamide exerts its action directly. These results are in agreement with the expression pattern for the genes encoding the neuropeptides (Kim and Li, 1999) as both flp-8 and flp-3 are expressed in extrapharyngeal neurons, whereas flp-13 is expressed in I5, a neuron with synaptic output to the pharyngeal muscle. These results provide the first, direct, functional information on the action of neuropeptides in C. elegans. Furthermore, we provide evidence for a putative inhibitory peptidergic synapse, which is likely to have a role in the control of feeding.

Differential sensitivity to calciseptine of L-type Ca(2+) currents in a 'lower' vertebrate (Scyliorhinus canicula), a protochordate (Branchiostoma lanceolatum) and an invertebrate (Alloteuthis subulata)

Voltage-dependent calcium currents in vertebrate (Scyliorhinus canicula), protochordate (Branchiostoma lanceolatum), and invertebrate (Alloteuthis subulata) skeletal and striated muscle were examined under whole-cell voltage clamp. Nifedipine (10 microM) suppressed and cobalt (5 mM) blocked striated/skeletal muscle calcium currents in all of the animals examined, confirming that they are of the L-type class. Calciseptine, a specific blocker of vertebrate cardiac muscle and neuronal L-type calcium currents, was applied (0.2 microM) under whole-cell voltage clamp. Protochordate and invertebrate striated muscle L-type calcium currents were suppressed while up to 4 microM calciseptine had no effect on dogfish skeletal muscle L-type calcium currents. Our results demonstrate the presence of at least two sub-types of L-type calcium current in these different animals, which may be distinguished by their calciseptine sensitivity. We conclude that the invertebrate and protochordate L-type current sub-type that we have examined has properties in common with vertebrate 'cardiac' and 'neuronal' current sub-types, but not the skeletal muscle sub-type of the L-type channel.

Epithelial ingrowth: causes, prevention, and treatment in 5 cases

PURPOSE

To examine the clinical course, treatment, and outcome in 5 cases of epithelial ingrowth following laser in situ keratomileusis (LASIK).

SETTING

The Eye Institute, Sydney, Australia.

METHODS

Five patients with adequate follow-up were selected. Each patient had developed epithelial ingrowth as a consequence of LASIK, and each represented a different clinical course in terms of severity, time, and treatment of the epithelial ingrowth.

RESULTS

Treatment ranged from observation, lifting and manual removal, phototherapeutic keratectomy, alcohol application, removal of the corneal cap, and penetrating keratoplasty (PKP). Outcomes ranging from retention of preoperative best corrected visual acuity to the need for PKP reflect the wide disparity in the severity of this complication and the therapeutic interventions required.

CONCLUSION

Epithelial ingrowth is a relatively uncommon complication following LASIK. Suggestions for prevention and treatment are made.

Recutting the Cornea Versus Lifting the Flap: Comparison of Two Enhancement Techniques Following Laser in situ Keratomileusis

PURPOSE

To evaluate enhancement techniques following laser in situ keratomileusis (LASIK).

METHODS

Recutting was performed on 263 eyes and the flap was lifted in 55 eyes that had LASIK for simple myopia or myopic astigmatism. The time interval between LASIK and retreatment was 340+/-46 days (range, 270 to 892 days) in the recutting group and 215+/-36 days (range, 53 to 617 days) in the flap lifting group. Mean spherical equivalent refraction, refractive cylinder, uncorrected and best spectacle-corrected visual acuity were examined prior to, and 1, 3, and 6 months after retreatment.

RESULTS

Seventeen eyes were lost to follow-up in the lifting group and 53 eyes in the recutting group. In the recutting group, mean spherical equivalent refraction improved from -1.48+/-1.25 D to -0.49+/-0.88 D at 6 months. In the flap lifting group, mean spherical equivalent refraction improved from -1.05+/-1.49 D to -0.45+/-0.39 D at 6 months. Refractive cylinder did not change significantly in either group (P = .2). There was a significant increase in uncorrected visual acuity (UCVA) of 6/6 in each group. In the recutting group, UCVA of 6/6 increased from 3.8% to 65.2% at 6 months, and in the lifting group from 3.6% to 71.1% at 6 months. In the recutting group, seven free flaps and three macerated flaps that required removal occurred. One eye in the recutting group and two in the lifting group developed significant epithelial ingrowth. No patient lost more than one line of best spectacle-corrected visual acuity (BSCVA).

CONCLUSION

Both procedures were safe, effective, and highly predictable for enhancements, but flap complications may be more likely with recutting.

Corneal deposition after high-dose chlorpromazine hydrochloride therapy

PURPOSE

To report a case of dermal and ocular changes after prolonged use of high-dose chlorpromazine hydrochloride therapy.

METHOD

This case report includes clinical history, clinical findings, and photographic images of ocular and dermal changes. RESULTS. Chlorpromazine therapy in a cumulative dosage exceeding 1,100 g resulted in dramatic skin discoloration and multiple crystalline deposits in both corneas. Anterior capsular opacities were binocularly present. These changes were sufficient to cause reduction in visual acuity.

CONCLUSIONS

Chlorpromazine deposition at high levels can cause reduction in visual acuity and significant skin discoloration.

Successful treatment of Paecilomyces lilacinus endophthalmitis after foreign body trauma to the cornea

PURPOSE

To report the successful treatment of a patient with Paecilomyces lilacinus endophthalmitis infection after foreign body (FB) trauma to the cornea.

METHODS

A 30-year-old man presented to us with a corneal abscess and iritis 2 months after removal of a metal corneal FB. Initial corneal biopsy culture was negative. Treatment with topical 5% natamycin, 0.9% fortified gentamycin, and 5% cephalothin hourly was commenced. As a result of developing signs of endophthalmitis, two more biopsies were taken, a week apart, from the vitreous and anterior chamber, successively. The last biopsy yielded positive microbiologic results of the specious Paecilomyces lilacinus. Intravitreal injection of 50 microg/0.5 mL of amphotericin was administered during the vitreal biopsy. Soon after isolating the specious Paecilomyces lilacinus, the following treatment was administered: 200 mg of itraconazole bd by mouth, 5% topical natamycin every hour, 2 mg/mL of topical fluconazole every 2 hours, three anterior chamber injections of 0.35 mL of 0.1% fluconazole and two amphotericin B injections to the anterior chamber of 50 microg/0.5 mL each.

RESULTS

There appeared to be no sign of infection 6 months after initial treatment. A large, dense scar existed in the medial part of the cornea only. The pupil was secluded. The patient's visual acuity was 6/21. The eye was comfortable and all topical antifungal medication was ceased.

Ring keratitis from topical anaesthetic misuse

BACKGROUND

Topical anaesthetic abuse is now an established differential diagnosis of ring keratitis. Published evidence suggests that this condition often has a poor prognosis, with the eyes sometimes requiring penetrating keratoplasty or the patient becoming blind.

METHOD

A case of topical anaesthetic abuse and its subsequent management is presented. Ocular examination including pachymetry and specular microscopy is reported.

RESULTS

The cornea made an excellent recovery, allowing a visual acuity of 6/6. Pachymetry showed corneal thickening and specular microscopy demonstrated a decreased cell count in the affected eye.

CONCLUSIONS

With prompt recognition and appropriate treatment the prognosis for these cases can be excellent. However, there is evidence to suggest permanent cellular damage to the endothelium.

LASIK for post penetrating keratoplasty astigmatism and myopia

AIMS

To report the results of a series of patients who were treated with LASIK to correct post penetrating keratoplasty ametropia.

METHODS

26 eyes of 24 patients underwent LASIK to correct astigmatism and myopia after corneal transplantation; 14 eyes also received arcuate cuts in the stromal bed at the time of surgery. The mean preoperative spherical equivalent was -5.20D and the mean preoperative astigmatism was 8.67D.

RESULTS

The results of 25 eyes are reported. The mean 1 month values for spherical equivalent and astigmatism were -0.24D and 2.48D respectively. 18 eyes have been followed up for 6 months or more. The final follow up results for these eyes are -1.91D and 2.92D for spherical equivalent and astigmatism. The patients undergoing arcuate cuts were less myopic but had greater astigmatism than those not. The patients receiving arcuate cuts had a greater target induced astigmatism, surgically induced astigmatism, and astigmatism correction index than those eyes that did not. One eye suffered a surgical complication. No eyes lost more than one line of BSCVA and all eyes gained between 0 and 6 lines UCVA.

CONCLUSIONS

LASIK after penetrating keratoplasty is a relatively safe and effective procedure. It reduces both the spherical error and the cylindrical component of the ametropia. Correction of high astigmatism may be augmented by performing arcuate cuts in the stromal bed.

Staphylococcal infection under a LASIK flap

PURPOSE

To report a staphylococcal infection under a laser in situ keratomileusis (LASIK) flap and to discuss the management of this rare and potentially devastating complication.

METHODS

A patient was referred to our practice having had bilateral LASIK. She was found to have abscesses under the left corneal flap. Staphylococcus aureus was identified as the infecting organism by corneal scrape and treated with appropriate antibiotics. The cornea improved, and then the abscess recurred. The abscess was again scraped and intensive treatment reinstituted.

RESULTS

After successful treatment, the patient recovered excellent visual acuity with only a minimal astigmatic error.

CONCLUSION

The possible reasons for the apparent improvement and then recurrence of the abscess are discussed. The management of this case including the need for corneal scrape and antibiotic prophylaxis is discussed in relation to previously reported cases.

Toric laser in situ keratomileusis for myopic astigmatism using an ablatable mask

BACKGROUND

To assess the results of toric laser in situ keratomileusis (LASIK) correction of myopic astigmatism.

METHODS

A prospective study was performed over a 20 week period for consecutive patients treated for myopic astigmatism. Spectacle-corrected visual acuity, uncorrected visual acuity, spectacle refraction, videokeratography, and complications were recorded. Vector analysis was performed by the ASSORT program.

RESULTS

Sixty-five eyes of 42 patients underwent toric LASIK with a Summit Technologies Apex Plus excimer laser. Mean preoperative spherical equivalent refraction at the spectacle plane was -6.24 +/- 2.42 D (range, -1.63 to -14.63 D) and mean pre-operative refractive cylinder magnitude was 1.99 +/- 1.35 D (range, 0.75 to 7.00 D); mean attempted refractive cylinder correction was 1.90 +/- 1.00 D. Six months after LASIK (43 eyes followed), mean spherical equivalent refraction at the spectacle plane was -0.40 +/- 0.55 D and 31 eyes (72.1%) were within +/- 0.50 D of emmetropia. At 6 months, mean refractive cylinder magnitude was 0.74 +/- 0.70 D, mean surgically induced astigmatism was 1.46 +/- 0.86 D, mean absolute angle of error was 10.33 degrees, mean astigmatic correction index was 0.93 +/- 0.36 D, and mean index of success was 0.46 +/- 0.39. Uncorrected visual acuity was 6/12 or better in 34 eyes (79.1%) and 6/6 in 15 eyes (35%); spectacle- corrected visual acuity was 6/9 or better in 41 eyes (95.35%). Six eyes (14.0%) lost 1 line of spectacle-corrected visual acuity at 6 months and one eye (2.3%) lost 2 lines. Ten eyes (23.3%) gained 1 line at 6 months.

CONCLUSION

Toric LASIK with an ablatable mask using the Summit Apex Plus excimer laser is a safe and relatively accurate procedure for the correction of myopic astigmatism.

Central Focal Interface Opacity After Laser in situ Keratomileusis

BACKGROUND

The acute onset of a focal central interface opacity with visual loss following LASIK has not been described in the peer reviewed literature. Non-peer reviewed reports of various inflammatory lesions have been recorded.

METHODS

We describe three cases in which an acute focal stromal interface opacification was identified within 1 week of laser in situ keratomileusis (LASIK). Each case was performed by a different surgeon on a different day, but using the same method, materials, and the Summit Apex Plus excimer laser. Immediately after surgery, all eyes were normal with good unaided vision. The appearance of the central stromal opacity was associated with acute visual deterioration. Preoperative and postoperative cycloplegic refractions, videokeratography, and postoperative slit-lamp biomicroscopy were performed. Each case was treated with intensive topical corticosteroids.

RESULTS

Each case demonstrated a central circular opacity in the interface between corneal flap and stromal bed, with associated variable stromal thinning. Resolution of the pathological process followed 2 to 4 weeks of treatment with topical corticosteroids and subsequent improvement in slit-lamp biomicroscopy, corneal topography, and vision. Etiology was uncertain.

CONCLUSION

Central interface opacification is a rare but visually important inflammatory complication of LASIK.

Different excitation-contraction coupling mechanisms exist in squid, cuttlefish and octopod mantle muscle

Excitation-contraction (EC) coupling was studied in central zone mantle muscle fibres of a squid (Alloteuthis subulata), a cuttlefish (Sepia officinalis) and an octopod (Eledone cirrhosa). Thin slices of muscle were used for twitch experiments and enzymatic isolation of single fibres for whole-cell patch-clamp studies. The current required for a supramaximal twitch response during direct stimulation of muscle slices was lower for squid than for cuttlefish. In squid, but not in cuttlefish, the current-response relationship was independent of slice thickness (range 0.1-0.5 mm). Twitches of squid and cuttlefish slices were reversibly abolished by removal of extracellular Ca2+. In squid, but not in cuttlefish, the current-response relationship was Na+-dependent, and in the absence of Na+ higher current strengths were required to generate a supramaximal response. In whole-cell voltage-clamp experiments on isolated muscle fibres from squid, cuttlefish and Eledone cirrhosa, a sustained inward current was recorded upon depolarisation. This current was blocked by 5 mmol l-1 Co2+ and suppressed by 10 micromol l-1 nifedipine. In squid, an additional inward fast-activating transient current was seen which was blocked by 2 micromol l-1 tetrodotoxin and depolarised holding potentials. The fast current represents a voltage-activated Na+ channel, and the slow currents represent L-type Ca2+ channels. We conclude that squid possess a specialised rapid EC coupling mechanism in central zone fibres that is absent in cuttlefish and Eledone cirrhosa.

Retreatment of undercorrected photorefractive keratectomy for myopia

Fourteen eyes treated by photorefractive keratectomy (PRK) for myopia required retreatment because of undercorrection. The mean preoperative refraction of these eyes had been -9.82 D (range 5.25 to 17.13). No eyes before photorefractive keratectomy had low myopia, three eyes had myopia between -3.10 and -6.00 D, four were between -6.10 and -10.00 D, and seven had more than -10.00 D of myopia. Retreatment was required for manifest scars in association with regression, unresponsive to topical corticosteroids. The retreatments were performed using a Summit ExciMed UV200LA excimer laser with a dual ablation technique utilizing a phototherapeutic keratectomy followed by a photorefractive keratectomy. Follow-up ranged from 1 to 9 months. Eight eyes followed more than 3 months had a mean spherical equivalent refraction of -0.58 D (range -7.35 to +1.25).

Photorefractive keratectomy for myopia of more than -10 diopters

Twenty-seven consecutive eyes of 18 patients with myopia of more than -10.00 diopters (D) were treated by photorefractive keratectomy (PRK) using the ExciMed UV200LA excimer laser and a double ablation technique in an attempt to achieve a refraction of plano. The preoperative mean spherical equivalent refraction was -13.32 D (standard deviation 2.54, range -10.25 to -20.50). Preoperative spectacle corrected visual acuity ranged from 6/6 to 6/60 and one eye had had two previous refractive keratotomies. Follow up ranged from 3 to 15 months (mean 8.9). At 6 months after surgery, the mean change in refraction was 11.03 D, from a preoperative mean of -13.32 D to a postoperative mean of -2.29 D. The mean keratometric flattening was 5.83 D, from a preoperative mean of 42.92 D to a postoperative mean of 39.09 D. The reason for this large difference is uncertain. At three months the mean spherical equivalent refraction was +0.07 D (SD 2.94, range -10.50 to +3.25). The 14 eyes that had achieved 12 months follow up had a mean spherical equivalent of -1.91 D (SD 3.87, range -11.00 to +2.50). Seven of these 14 eyes have been reablated for manifest scars in association with regression. All 14 eyes had best spectacle corrected visual acuity at or better than their preoperative level.

Localisation of the mitogenic epitope of staphylococcal enterotoxin B

Limited digestion of staphylococcal enterotoxin B (SEB) with trypsin resulted in the generation of a 12-Kda amino-terminal fragment and a 17-Kda carboxy-terminal fragment which were isolated by preparative iso-electric focusing. The carboxy-terminal fragment exhibited significant mitogenic activity for murine splenocytes, whereas the isolated amino-terminal fragment possessed little detectable mitogenic activity. Monoclonal antibodies (MAbs) specific for the carboxy-terminal fragment neutralised most of the mitogenic activity of both the intact toxin and the carboxy-terminal fragment. MAbs specific for the amino-terminal fragment had no detectable neutralising activity. These results support the hypothesis that the epitope(s) responsible for mitogenic activity is located in the carboxy-terminal region of SEB.

Calmodulin is associated with microtubules forming in PTK1 cells upon release from nocodazole treatment

To investigate the association of calmodulin (CaM) with microtubules (MTs) in the mitotic apparatus (MA), the distributions of CaM and tubulin were examined in cells in which the normal spindle organization had been altered. A fluorescent CaM conjugate with tetramethylrhodamine isothiocyanate (CaM-TRITC) and a dichlorotriazinyl aminofluorescein conjugate with tubulin (tubulin-DTAF) were injected into cells that had been treated with the MT inhibitor nocodazole. With moderate nocodazole concentration (0.3 micrograms/ml, 37 degrees C, 4 h) in live cells, CaM-TRITC and tubulin-DTAF concentrated identically on or near the centrosomes and kinetochores. In serial sections of these cells, small MT segments were observed by transmission electron microscopy (TEM) in the regions where fluorescent protein had concentrated. When a higher drug concentration was used (3.0 micrograms/ml, 37 degrees C, 4 h), no regions of CaM-TRITC or tubulin-DTAF localization were observed, and no MTs were observed when serial sections were examined by TEM. However, following release from the high-concentration nocodazole block, CaM-TRITC colocalized with newly formed MTs at the kinetochores and centrosomes. Later in the recovery period, when chromosome-to-pole fibers had formed, CaM association with kinetochores diminished, ultimately attaining its normal pole-proximal association with kinetochore MTs in cells that progressed through mitosis. We interpret these observations as supporting the hypothesis that in the MA, CaM attains a physical association with kinetochore MTs and suggest that CaM-associated MTs may be inherently more stable.

Calmodulin stabilization of kinetochore microtubule structure to the effect of nocodazole

To investigate the function of calmodulin (CaM) in the mitotic apparatus, the effect of microinjected CaM and chemically modified CaMs on nocodazole-induced depolymerization of spindle microtubules was examined. When metaphase PtK1 cells were microinjected with CaM or a CaM-TRITC conjugate, kinetochore microtubules (kMTs) were protected from the effect of nocodazole. The ability of microinjected CaM to subsequently protect kMTs from the depolymerizing effect of nocodazole was dose dependent, and was effective for approximately 45 min, with protection decreasing if nocodazole treatment was delayed for more than 60 min after injection of CaM. The CaM-TRITC conjugate, similar to native CaM, displayed the ability to activate bovine brain CaM-dependent adenylate cyclase in a Ca++-dependent manner and showed a Ca++-dependent mobility shift when subjected to PAGE. A heat-altered CaM-TRITC conjugate also protected kMTs from the effect of nocodazole. However, this modified CaM was not able to activate adenylate cyclase nor did it display a Ca++-dependent mobility shift when electrophoresed. In a permeabilized cell model system, both CaM analogs were observed to bind to the spindle in a Ca++-independent manner. In contrast, a performic acid-oxidized CaM did not have a protective effect on spindle structure when microinjected into metaphase cells before nocodazole treatment. The oxidized CaM did not activate adenylate cyclase and did not exhibit Ca++-dependent mobility on polyacrylamide gels. These results are interpreted as supporting the hypothesis that CaM binds to the mitotic spindle in a Ca++-independent manner and that CaM may serve in the spindle, at least in part, to stabilize kMTs.

Macular suprastructure, stereociliary bonding and kinociliary/stereociliary coupling in rat utricular macula

This report considers rat utricular macular suprastructure after chemical treatment with the sodium salt of N,N-Naphthaloylhydroxylamine (NHA), used alone or in combination with tannic acid (TA). NHA and TA preserve calcium and complex carbohydrate-protein molecules, respectively. Macromolecules of supramacular substance appear comparable morphologically to material of the external lamina of glycocalyx. Similar material crosslinks stereocilia with approximately equal to 58 nm periodicity and couples parts of kinocilia with specific stereocilia. Particles which occur within kinocilia at certain attachment sites connect to dynein arms of the kinocilia. Interstereociliary connections are aligned with internal linkers to actin. Thus, a basis for dynamic communication between kinocilia and stereociliary actin has been shown. The mechanism would appear to be calcium dependent. The findings support the concept that kinocilia are motile and lead to the stereociliary tuft in vestibular hair cells.

Pharmacokinetics of antituberculosis drugs in patients

The pharmacokinetics of rifampin, isoniazid, and ethambutol were determined in 26 ambulatory male patients (aged 49.5 +/- 9.9 yr) with tuberculosis. Rifampin and isoniazid were given individually or together, with or without ethambutol; studies were done after a single dose and after chronic administration. Under the study conditions, with large variability in the extent of disease and physical status and history of alcohol and tobacco abuse and narrow age range, the pharmacokinetics of these three antituberculosis drugs were not modified significantly by patient age. Furthermore, appreciable drug-drug interactions did not occur when the three drugs were administered concurrently. Self-induction of rifampin clearance by chronic dosing with the drug may lead to subtherapeutic levels of rifampin. Administration of isoniazid and ethambutol in two divided doses resulted in peak plasma concentrations below the accepted therapeutic levels of the two drugs. Our findings indicate that at least in the middle-aged patients with tuberculosis, the current single daily dose, multiple-drug regimen is therapeutically sound pharmacokinetically, and clinicians do not have to make adjustments in dosages of these drugs for age and the extent of disease.

Innervation patterns in rat saccular macula. A structural basis for complex sensory processing

Serial sections through the anterior part of rat saccular macula were reconstructed as montages. Findings are that type II hair cells are integrated into the neural circuitry of type I cells, chiefly by synapses with neighboring calyces and their collaterals; and that complex interactions between afferent- and efferent-type nerve elements take place. Three basic types of nerve/calyx pattern are present: U-type nerves lose their myelin before they enter the macula and have complex calyces with several collaterals; M-type nerves are myelinated up to the calyx, which lacks collaterals; and M/U-type nerves have short, unmyelinated segments proximal to their calyces, which have few collaterals. Both afferent- and efferent-type collaterals spring from calyces, chiefly from those of U-type nerves. Type II cells are presynaptic both to electron-lucent and to vesiculated terminals; some synapses are reciprocal. Electron-lucent boutons sometimes are presynaptic to calyces and to type II hair cells; and morphologically afferent-to-afferent kinds of synapses occur in the neuroepithelium. The anatomical findings indicate that complex information processing must occur in mammalian gravity receptors.

Induction of suppressor cells in vitro by Candida albicans

Normal splenocytes cultured with Formalin-killed Candida albicans were shown to acquire significant suppressor cell activity in a period of 3 days. These cells were found to suppress both the phytohemagglutinin-induced mitogen response as well as the anti-sheep erythrocyte antibody response. Experiments were carried out to determine the nature of the suppressor cell population. Results showed that these cells were not susceptible to treatment with anti-Thy 1 antibody and complement. Panning experiments showed that the suppressor cells were not plastic-adherent or Mac-1 antigen-positive. The suppressor cells were, however, adherent to anti-mouse immunoglobulin (F(ab')2-fragment)-coated dishes. Additional experiments showed that the suppressor cell activity was susceptible to treatment with monoclonal anti-Lyb 2.1 antibody and complement. These results suggest that the suppressor cell induced in vitro by Candida is a member of the B-lymphocyte lineage.

Microinjected ras family oncogenes stimulate DNA synthesis in quiescent mammalian cells

Oncogenes of the ras family stimulate DNA synthesis when microinjected into quiescent mouse and hamster fibroblasts, as detected by in situ autoradiography. The molecularly cloned genomes of Harvey and Kirsten sarcoma viruses, the cloned Harvey ras gene, and the product of the v-ras gene, the p21v-rasH protein, stimulate DNA synthesis in quiescent cells. This stimulation is comparable to the stimulatory activity of the microinjected SV40 T-antigen-coding gene. The demonstration that these oncogenes can stimulate transient DNA synthesis in quiescent cells is relevant to understanding the mechanism by which these genes are able to transform cells in vitro and induce tumors in animals.

Effects of Wy-18,251 (3-p-chlorophenyl)thiazolo[3,2-a]benzimidazole- 2-acetic acid), levamisole and indomethacin on the generation of murine T suppressor cells in vitro

In vitro culture of normal BALB/c spleen cells with staphylococcal enterotoxin B (SEB) activates antigen non-specific suppressor T cells (Ts) which can be assayed by their ability to suppress antibody production in a plaque assay. Addition of the experimental immunomodulatory drug Wy-18,251 (10-100 microM) to cultures of spleen cells plus SEB significantly increased Ts activity relative to cultures without the drug. Similar results were obtained with levamisole, but, in contrast, indomethacin (0.1-10 microM) inhibited SEB-induced suppressor cell activity. The ability of Wy-18,251 to augment Ts activity could be therapeutically useful in the treatment of those autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, in which hyperactive B cell function is a characteristic feature.

T4 phage-coded dihydrofolate reductase. Subunit composition and cloning of its structural gene

The structures of phage-coded dihydrofolate reductases are of interest because of 1) possible relationship to plasmid-coded dihydrofolate reductases; 2) unusual regulation of enzyme synthesis; and 3) multiple roles and intermolecular interactions involving the protein. To prepare for primary structural studies, we have cloned the T4 frd gene, which codes for dihydrofolate reductase, and we have determined for redetermined some physical properties of the enzyme. The native enzyme has a molecular weight of about 44,500, as determined by sedimentation velocity and gel filtration, and a subunit molecular weight of about 23,000, as determined by aminopterin titration and denaturing gel electrophoresis. We conclude that the enzyme is a dimer, with each subunit containing one methotrexate-binding site. A 1.1-kilobase pair fragment from a HindIII restriction digest of cytosine-substituted T4 DNA was cloned into pBR322, and recombinants were identified by trimethoprim resistance. Cells carrying this recombinant plasmid produce both the host cell and phage-coded dihydrofolate reductases.