(1967) UNC, Chapel Hill, NC
(1971) UNC, Chapel Hill, NC
(1975) Duke U., Durham, NC
(1980) UNC, Chapel Hill, NC
Professor of Medicine
Office: 7017 Thurston-Bowles
The overall goal of research at the UNC Pulmonary and CF Research Center is to better understand key host defense mechanisms in the conducting airways, and disease mechanisms that play a role in the development of non-asthmatic airways disease. The clinical research group is involved in a broad range of studies in human subjects, which interfaces with the basic research efforts at the UNC Research Center. The clinical research effort continues to focus on human genetic models of disease, including cystic fibrosis (CF), primary ciliary dyskinesia (PCD), and more unusual genetic disorders, such as pseudohypoaldosteronism (PHA). In general terms, our clinical investigation relates to three major areas.
Pathophysiology of non-asthmatic airways diseaseThe long-standing hypothesis of our research group is that mucociliary and cough clearance are the dominant host defense mechanism in the airways. We recognize that abnormalities of salt and water metabolism, dysfunction of cilia, and abnormal mucus impairs these important defense mechanisms, and leads to disease. Three genetic models of human airways disease illustrate our strategic approach to better understand these host-defense systems.
Cystic FibrosisCF is the genetic model of human airways disease that illustrates the importance of salt (and water) transport for normal mucociliary (and cough) clearance. Specifically, CF reflects mutations in the CFTR gene, which regulates the volume and composition of airway surface liquid. In CF, excessive salt (and water) absorption (driven by active Na+ transport) leads to thickened mucus, which is not cleared by either mucociliary or cough clearance. Previous studies clearly confirm that the defect in CF airways reflects excessive isotonic volume absorption. Recent studies have focused on more subtle alterations in the ion composition of airway surface liquid, which may involve defective bicarbonate transport or abnormal regulation of pH. These possibilities are being tested with ion selective microelectrodes in vivo, using the nasal surface liquid as a model of lower respiratory epithelial function.
The poor clearance of airway secretions in CF also leads to chronic bacterial infection of the lower airways, usually with Pseudomonas aeruginosa or Staphylococcus aureus. Recent studies from UNC also indicate that nontuberculous mycobacteria (NTM) is recovered from the respiratory samples of ~15% of adult CF patients. The predominant NTM organisms are Mycobacterium Avian Complex (MAC) and Mycobacterium Abscessus. A multicenter study is currently underway to define the clinical impact of NTM in CF. Another study is focused on testing for genes (genetic alleles) that predispose non-CF (apparently "normal") subjects to pulmonary infection with NTM, which should identify genes that increase the risk to infection with NTM.
Primary ciliary dyskinesiaPCD is a recessive genetic disorder leading to "immotile" or dyskinetic ciliary function. We are characterizing a large number of PCD patients in North America and collaborative centers in Italy and Australia. To date, our clinical studies have focused on defining important clinical features, which include chronic airway infection that parallels the bacterial organisms seen in CF (Staphylococcus aureus and Pseudomonas aeruginosa), but which appear at an older age in PCD. We are also developing diagnostic markers for PCD, which include quantitative analysis of the dynein arms of cilia, and measurement of nasal NO, which is very low and appears linked to the genetic origin of the disease. The pathophysiologic mechanism whereby low nasal NO is linked to defects in the inner (and outer) dynein arms, and/or ciliary dysfunction, is not known.
Pseudohypoaldosteronism (PHA)These patients suffer from loss-of-function mutations in the epithelial sodium channel (ENaC), which leads to a build-up (increased volume) of airway surface liquid. Although these patients have recurrent respiratory illnesses as children, we were surprised to find the rates of mucociliary clearance are greatly accelerated in teenage and adult patients. This observation confirms the notion that conducting airways have compensatory mechanisms to increase the clearance of airway surface liquid, and supports the hypothesis that increasing the volume of airway surface liquid (see below, under clinical/therapeutic research) may be useful to treat CF lung disease.
Genetic/Molecular StudiesThe emergence of readily available genetic information and molecular technology is opening-the-door to rapid determination of the genetic etiology of disease. Studies in CF and PCD illustrate an approach that will move very rapidly in the near-future, as we see the rewards of the Human Genome Project.
Cystic FibrosisIn CF, it is clear that some of the clinical variability of disease relates to different mutations in CFTR. We continue to study patients who have unusual types of suppurative airways disease, and we continue to identify "variant" (mild) forms of CF in some of these patients. These genotype/phenotype studies show links between "mild" forms of genetic mutations in CFTR and clinical disease. Recently, we have seen CFTR mutations that cause congenital bilateral absence of the vas deferens (CBAVD), or idiopathic pancreatitis, but with little (or no) lung disease.
More recently, we have begun testing to see what other (non-CFTR) genes may contribute to the clinical expression of disease in CF. Specifically, different genetic alleles (at loci unlinked to CFTR) may affect the severity of CF lung disease. We are initiating a large multicenter study to test for genes that have a significant impact on phenotypic expression of lung disease in CF patients, with the rationale that these studies may identify new therapeutic targets. Initial studies will utilize a "candidate gene" approach, and subsequent studies will employ more broad-based techniques to test for associated loci across the human genome. You can learn more about this study at the Genetic Modifiers Study website.
Primary ciliary dyskinesia (PCD)
The identification of a large number of PCD patients, and rigorous characterization of their clinical features, nasal NO levels, and ultrastructural (dynein arm) abnormalities, have allowed us to search for mutations that cause this disease. We have recently identified mutations in an intermediate chain (IC78) gene, which is associated with defective dynein arm ultrastructure and ciliary dysfunction. These findings will ultimately allow us to test whether some of the mutations in these genes have residual (partial) function, and which might not be associated with "full-blown" PCD. These mutations with only partial loss of ciliary function will be "risk factors" (genetic predispositions) for the development of airway disease in response to inhaled pollutants.
Clinical/TherapeuticWe continue to pursue new therapeutic approaches to the treatment of airways disease, including cystic fibrosis, primary ciliary dyskinesia, and chronic bronchitis.
Triphosphate nucleotidesWe have previously demonstrated that extracellular nucleotides, such as ATP and UTP, can stimulate mucociliary clearance through the activation of extracellular P2Y2 receptors. Initial studies were performed in normal subjects, and CF and PCD patients, and demonstrated clear acute improvement in mucociliary and cough clearance. New congeners of P2Y2 agonists are being tested through the Cystic Fibrosis Foundation-sponsored Therapeutic Development Network, including the UNC site. These Phase I/Phase II studies will allow us to test the safety and short-term "biological efficacy" of these compounds.
Na+ conductance inhibitorsAccelerated sodium absorption from CF airways has been a focused interest of the lab for two decades, and work continues in this area. The striking observation of the very rapidly accelerated rate of mucociliary clearance in patients with pseudohypoaldosteronism (PHA) set the stage for recent studies of mucociliary clearance in normal subjects. These studies are designed to increase the volume of airway surface liquid by a combination of aerosolized hypertonic saline plus aerosolized amiloride, a blocker of Na+ channels. These maneuvers stimulated an increase in the rate of mucociliary clearance, which indicates that mucociliary clearance rates are not maximized under baseline conditions in normal humans. This observation further supports the general concepts that: 1) drugs to block sodium absorption from CF airways, and 2) maneuvers to add salt to the airway surface liquid, may have a therapeutic role in non-asthmatic airway disease. To that end, Dr. Scott Donaldson has initiated a clinical research protocol to test this approach in a cohort of CF patients at UNC, which will provide key preliminary data about this therapeutic approach.
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