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Press play: power of podcasts in medical education
No full textDetailed formal protocol with illustrations and extensive bibliography.A recording of the protocol presentation is available on UT Southwestern’s Mediasite. Note: Access to the video is restricted to authorized UT Southwestern users only.UT Southwestern--Internal Medicin
Antioxidant Programs Are Essential for Enzalutamide-Resistant Prostate Cancer
Full text linkTherapy resistance to second generation androgen receptor (AR) antagonists, such as enzalutamide, is common in patients with advanced prostate cancer (PCa). In order to identify which patients will develop therapy resistance and the underlying cause, it is critical to characterize detailed mechanisms of resistance to improve patient outcomes. To identify the metabolic alterations involved in enzalutamide resistance, we performed metabolomic, transcriptomic, and cistromic analyses of enzalutamide-sensitive and -resistant PCa cells, xenografts, patient-derived organoids, patient-derived explants, and tumors. We noted that enzalutamide-resistant PCa cells and castration-resistant PCa (CRPC) tumors had dramatically higher levels of both basal and inducible levels of reactive oxygen species (ROS) than either enzalutamide-sensitive PCa cells or primary therapy-naïve tumors, respectively. Unbiased metabolomic evaluation identified that glutamine metabolism was consistently upregulated in enzalutamide-resistant PCa cells and CRPC tumors. Stable isotope tracing studies suggest that this enhanced glutamine metabolism drives an antioxidant program that allows these cells to tolerate higher basal levels of ROS. Inhibition of glutamine metabolism with either a small-molecule glutaminase inhibitor or genetic knockout blocked this antioxidant pathway, further enhanced ROS levels, and blocked the growth of enzalutamide-resistant PCa. The critical role of the compensatory antioxidant pathways in maintaining enzalutamide-resistant PCa cells was further validated by targeting another antioxidant program driver, ferredoxin 1. Taken together, our data identify a metabolic need to maintain antioxidant programs and a potentially targetable metabolic vulnerability in enzalutamide-resistant PCa
Single-Center Experience of Providing Congenital Heart Surgery to Low- and Middle-Income Countries
Full text linkOBJECTIVE: The objective of this study is to analyze the demographics of congenital heart disease (CHD) patients from over 50 low- and middle-income countries (LMICs) who received care at Frontier Lifeline Hospital (FLL), a specialty cardiac center in Chennai, India, and identify the barriers and limitations they faced.
METHODS: This two-part retrospective study analyzed International Quality Improvement Collaborative (IQIC) data from Boston Children's hospital and FLL data of CHD patients who received cardiac surgery from 2008 to 2020. The first part collected demographic and clinical data. The second part included interviews with organizations and physicians to identify the barriers to cardiac care faced by patients from LMICs.
RESULTS: A total of 3002 patients from various LMICs received care at FLL during this period (2008-2020). Of these patients, 2087 (81%) patients received their first cardiac surgery at FLL. Majority of patients came from the following countries: Fiji (201), Uganda (194), Bahrain (185), Sri Lanka (147), and Kenya (126). Of the total, 1801 (60%) patients were 1 to 18 years old, 975 (32%) were infants, 118 (4%) were neonates, and 108 (4%) were adult congenital, with a median age of 5 years. Common procedures included ventricular septal defect closure (787; 26%) and atrial septal defect repair (700; 23%). Of the total patients, 2950 cases were assigned a Risk adjustment for congenital heart surgery (RACHS-1) score, of which RACHS-1 categories 2 (1146; 39%) and 3 (1033; 35%) comprised the majority.
CONCLUSIONS: Though healthcare systems in LMICs see and acknowledge the magnitude of patients with CHD, there are many challenges for providing cardiac care locally. Often, other priorities such as communicable diseases, raging wars, and refugee crises preclude attention for children with CHD. Patients who have sought care at FLL face other difficulties, including lack of long-term commitment from foreign partners, short-term trips directed at treating "easier" cases, and logistics of continued care. While sustaining a cardiac surgical program locally in LMICs may be a worthy goal, overcoming the myriad of barriers including funding and training professionals is no easy feat. Efforts should focus on creating surgical programs that can triage patients to address RACHS-1 categories 1, 2, and 3 and centralizing programs in LMICs with referral networks (as noted in this study) to address the more complex RACHS-1 categories 4, 5, and 6
Uncovering the Role of 5'-Nucleotidases in Pyrimidine Metabolism in Trypanosoma brucei
Full text linkThe protozoal parasite Trypanosoma brucei causes the disease African trypanosomiasis in humans and nagana in cattle. Fifty-five million people in subtropical countries are at risk for contracting T. brucei through the tsetse fly vector, and infection is typically fatal if untreated. While recent interventions have reduced disease prevalence, current therapies are toxic or fail to target the substantial animal reservoir. A better understanding of parasite metabolism is necessary to address these issues in treatment and vector control. T. brucei generates nucleic acids and nucleotide sugars through two pathways: pyrimidine salvage or de novo synthesis using glutamine. However, T. brucei lacks several key pyrimidine transporters and enzymes found in mammals, creating an area of parasite vulnerability, especially in the ability to maintain balance between nucleotide pools. Previous work in our lab discovered that thymidine kinase (TK) is necessary to balance the activity of 5'-nucleotidases. I have characterized three proteins with 5'-nucleotidase activity in T. brucei belonging to the histidine-aspartate (HD) and haloacid dehalogenase (HAD) protein families. I found that HD 5'-nucleotidase (5'-HDNT) preferentially converts pyrimidine mononucleotides to nucleosides and was essential for parasite growth, while neither of the HAD enzymes was essential. Parasite viability was restored by expression of the human enzyme dCMP deaminase, which provides an alternate conversion path between cytosine and uracil pools. Metabolomics analysis revealed depletion of de novo pathway intermediates, including glutamine, UDP-sugars, and CDP-phospholipids, contributing to parasite death. Isotope uptake assays showed deficiency in glutamine uptake, and proteomics analysis identified two downregulated amino acid transporters. Finally, I used a PCR-based assay to study DNA strand breaks in cells lacking 5'-HDNT, and DNA damage was visualized using a comet assay. These results support the critical role of 5'-HDNT in facilitating interconversion between pyrimidine nucleotides and nucleosides, especially C and U. Disruption of this cycle leads to dNTP imbalance and DNA damage, which signals the downregulation of glutamine uptake. Through the study of 5'-HDNT, I have unmasked a potential cell death pathway that goes beyond de novo and salvage pathways to implicate cellular metabolism in T. brucei
Precision Gene Editing for Muscle Diseases
Full text linkMuscle, comprising both skeletal muscle and cardiac muscle, is integral to the human experience, allowing us to do the many incredible things. Consequently, genetic mutations that cause muscle disease can have a profound effect on the afflicted individual. Gene editing tools like base editors and prime editors enable us to target and correct the underlying genetic causes of these diseases. Base editors enable precise base pair transition edits, while prime editors offer even more versatility, allowing for base pair transition and transversion edits, as well as short insertions and deletions.
Duchenne muscular dystrophy (DMD), a fatal neuromuscular disease of progressive muscle weakness and wasting, is caused by mutations in the DMD gene on the X chromosome, resulting in a lack of dystrophin protein. Affected individuals typically do not survive beyond their thirties. Hypertrophic cardiomyopathy (HCM), on the other hand, is a disease characterized by abnormal thickening of the heart muscle that can progress to heart failure and sudden cardiac death. It is often caused by a dominant-negative mutation in a sarcomere protein, which leads to pathological augmentation of sarcomere contraction.
In this dissertation work, I demonstrate the efficacy of base editing and prime editing approaches in targeting a few DNA mutations associated with DMD and HCM. For DMD, I employ exon skipping, a technique that modifies the processing of mature mRNA to produce an internally truncated but functional dystrophin protein. This proof-of-concept approach holds great promise for the treatment of this X-linked recessive disease. For HCM, base editing allows us to correct the DNA point mutation responsible for the disease, converting the pathogenic peptide back to its healthy form.
Through in vitro and in vivo studies using models of DMD and HCM, I demonstrate highly efficient correction and rescue of the pathological features associated with these diseases. These findings highlight the potential of gene editing as a targeted and precise therapeutic approach for muscle diseases, and this work represents a significant step forward in developing potential cures for these debilitating muscle diseases
Metabolomic Approaches in Parasitology
Full text linkMetabolic pathways and networks are crucial for maintaining cellular functions and sustaining life. Understanding these pathways in parasites may reveal novel targets for therapeutic application if they are sufficiently different from mammalian systems. My work investigated two such pathways: pyrimidine biosynthesis and the impact of inhibiting the pathway enzyme dihydroorotate dehydrogenase (DHODH) and the polyamine biosynthesis pathway and routes to obtaining the pathway precursor L-ornithine.
DHODH has recently been validated as a therapeutic target for malaria through clinical studies on the triazolopyrimidine-based Plasmodium DHODH inhibitor DSM265. Selective toxicity towards Plasmodium species could be achieved because malaria parasites lack pyrimidine salvage pathways, and DSM265 selectively inhibits Plasmodium DHODH over the human enzyme. However, while DSM265 does not inhibit human DHODH, it inhibits DHODH from several preclinical species, including mice, suggesting that any toxicity observed in those species could result from on-target DHODH inhibition. To test this hypothesis, I validated the use of the reaction substrate dihydroorotate as a biomarker for DHODH inhibition in mammalian cells and mice treated with DHODH inhibitors and correlated the biomarker response to the degree of DHODH inhibition. This work represents an important advance to monitor for on-target effects in preclinical and clinical applications of DHODH inhibitors used to treat human disease.
Trypanosoma brucei is a parasitic protozoan and the causative agent of human African trypanosomiasis. The polyamine biosynthesis pathway plays a critical role in cell survival by producing putrescine and spermidine, essential for various cellular processes. L-Ornithine, the precursor for putrescine biosynthesis, is believed to be obtained by uptake from the environment, as T. brucei lacks a functional arginase enzyme. I characterized a T. brucei protein, Tb927.4.1300, belonging to the amidinotransferase family, potentially involved in L-arginine to L-ornithine conversion. Knockout of Tb927.4.1300 resulted in a growth deficit without significant changes in intracellular L-arginine or L-ornithine levels. Recombinantly expressed Tb927.4.1300 failed to catalyze L-ornithine synthesis with the availability of various substrates. Structural modeling based on AlphaFold revealed that alteration of key catalytic residues in Tb927.4.1300 rendered them unsuitable for the catalytic mechanism. Using isotope tracing experiments, I confirmed the inability of T. brucei to convert L-arginine to L-ornithine, indicating the absence of this enzymatic pathway, and supporting the hypothesis that the parasite is an L-ornithine auxotroph. Taken together, these findings shed light on the metabolic requirements of L-ornithine in T. brucei and characterize Tb927.4.1300 as a catalytically dead homolog of the amidinotransferase family whose knockout results in a growth deficit of the parasite
Our Memory
Full text linkThe author submitted this entry in the Open Verse Poetry category (Amateur division) for the 2025 On My Own Time™ (OMOT) Art Show.Two lovebirds full of memories; one of them is flying away while the other tries to hold on
Neural control of somatic function: the future of physiology and medicine
Full text linkDetailed formal protocol with illustrations and extensive bibliography.A recording of the protocol presentation is available on UT Southwestern’s Mediasite. Note: Access to the video is restricted to authorized UT Southwestern users only.UT Southwestern--Internal Medicin
Integration of Information Rich High Throughput Screens for Characterization of Natural Products
Full text linkNatural products have played a major role in advancing drug discovery and human biology. While these molecules have been a major source of inspiration for developing therapeutics, identifying their mechanism of action remains a major challenge. This work will discuss novel high throughput screening strategies that can assist in rapidly assigning biological function for natural products and characterize bioactive molecules that can be used as drugs or chemical probes. This work demonstrates how the discovery of bioactive natural products can be enhanced by high-throughput information-rich screening
Using Pre-Op Rhythm Strips to Reduce Cardiac-Related OR Cancellations
Full text linkBACKGROUND: Same-day cancellations pose a significant financial burden to ambulatory surgical centers. Cardiac abnormalities comprise a small percentage of total cancellations, but these abnormalities are detected primarily once the patient is already in the OR and after standard ASA monitors are placed on the patient, which is particularly disruptive. Even so, 12-lead electrocardiograms (ECG) are not recommended as a pre-op test for low-risk surgeries and are not part of the standard vital signs required on the day of surgery. Thus, implementing a 3-lead ECG with rhythm strip analysis during pre-op on the day of surgery may allow for earlier detection of these cardiac abnormalities before the OR.
AIM STATEMENT: Between March 2021 to October 2022, all cardiac abnormalities that warrant a same-day surgical cancellation will be detected by our 3-lead ECGs prior to the patient entering the OR.
METHODOLOGY: This is an ongoing prospective quality improvement study at UT Southwestern Medical Center's University Hospital Outpatient Surgery Center. The study period is from March 15, 2021 to October 13, 2022. All patients arriving at the study site on the day of their surgery were included, irrespective of demographics or risk factors. Exclusion criteria included any patients under the age of eighteen, and those with missing or incomplete information documented. A 3-lead ECG test was performed in addition to the standard day-of-surgery vital signs (BP, pulse oximetry, heart rate, and temperature). An anesthetic pre-op evaluation, along with patient vital signs, was reviewed by anesthesiologists prior to admission into the operating room. For all cancellations, the primary reason, the scheduled date of surgery, and the scheduled service were recorded by hand. Plan-Do-Study-Act (PDSA) cycles were used to design and evaluate the success of interventions in each phase of this study.
RESULTS: Within the study period and site, a total of 254 surgical cancellations were identified with three distinct categories: patient-focused (113 cases, 44.5%), systemic/facility (46 cases, 18.1%), and medical (96 cases, 37.4%). Of the 96 cancellations due to medical reasons, 26 of those were detectable by an ECG. All 26 of these cancellations were detected from our rhythm strip analysis during pre-op; there were no cardiac cancellations in the OR.
CONCLUSIONS: Our findings suggest that the implementation of a 3-lead ECG was effective and allowed for earlier detection of cardiac abnormalities that would have not otherwise been discovered until the patient was in the OR. With respect to expenditure data specific to our study site, earlier detection allows for substantial cost savings. Limitations include the absence of data on total surgeries performed by specialty service and baseline cancellation rates prior to ECG implementation. In the next PDSA cycle, documentation of specific surgical procedures has been added to the cancellation intake template. With rates of cardiac abnormalities like atrial fibrillation rising and with the patient population for ambulatory surgeries becoming older, this study represents a feasible, low-cost intervention that addresses these trends