Role of CFTR in epithelial physiology.

Salt and fluid absorption and secretion are two processes that are fundamental to epithelial function and whole body fluid homeostasis, and as such are tightly regulated in epithelial tissues. The CFTR anion channel plays a major role in regulating both secretion and absorption in a diverse range of epithelial tissues, including the airways, the GI and reproductive tracts, sweat and salivary glands. It is not surprising then that defects in CFTR function are linked to disease, including life-threatening secretory diarrhoeas, such as cholera, as well as the inherited disease, cystic fibrosis (CF), one of the most common life-limiting genetic diseases in Caucasian populations. More recently, CFTR dysfunction has also been implicated in the pathogenesis of acute pancreatitis, chronic obstructive pulmonary disease (COPD), and the hyper-responsiveness in asthma, underscoring its fundamental role in whole body health and disease. CFTR regulates many mechanisms in epithelial physiology, such as maintaining epithelial surface hydration and regulating luminal pH. Indeed, recent studies have identified luminal pH as an important arbiter of epithelial barrier function and innate defence, particularly in the airways and GI tract. In this chapter, we will illustrate the different operational roles of CFTR in epithelial function by describing its characteristics in three different tissues: the airways, the pancreas, and the sweat gland.

Relationships among CFTR expression, HCO3- secretion, and host defense may inform gene- and cell-based cystic fibrosis therapies.

Cystic fibrosis (CF) is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. Airway disease is the major source of morbidity and mortality. Successful implementation of gene- and cell-based therapies for CF airway disease requires knowledge of relationships among percentages of targeted cells, levels of CFTR expression, correction of electrolyte transport, and rescue of host defense defects. Previous studies suggested that, when ∼10-50% of airway epithelial cells expressed CFTR, they generated nearly wild-type levels of Cl(-) secretion; overexpressing CFTR offered no advantage compared with endogenous expression levels. However, recent discoveries focused attention on CFTR-mediated HCO3 (-) secretion and airway surface liquid (ASL) pH as critical for host defense and CF pathogenesis. Therefore, we generated porcine airway epithelia with varying ratios of CF and wild-type cells. Epithelia with a 50:50 mix secreted HCO3 (-) at half the rate of wild-type epithelia. Likewise, heterozygous epithelia (CFTR(+/-) or CFTR(+/∆F508)) expressed CFTR and secreted HCO3 (-) at ∼50% of wild-type values. ASL pH, antimicrobial activity, and viscosity showed similar relationships to the amount of CFTR. Overexpressing CFTR increased HCO3 (-) secretion to rates greater than wild type, but ASL pH did not exceed wild-type values. Thus, in contrast to Cl(-) secretion, the amount of CFTR is rate-limiting for HCO3 (-) secretion and for correcting host defense abnormalities. In addition, overexpressing CFTR might produce a greater benefit than expressing CFTR at wild-type levels when targeting small fractions of cells. These findings may also explain the risk of airway disease in CF carriers.

Immunoreactivity to a monoclonal antibody (OS-3) is shared by osteoclasts and bicarbonate-secreting cells.

OS-3, a monoclonal antibody raised against macrophagic cells derived from cultured rat glomeruli, reacts with the plasma membrane of various bicarbonate-secreting cells such as epithelial cells of the pancreatic excretory duct and type B intercalated cells of the kidney, suggesting that the antigenic molecule of OS-3 is involved in bicarbonate production and/or secretion. Since osteoclasts must vigorously extrude bicarbonate to maintain cytoplasmic pH in a physiologic range during proton secretion, we examined the localization of OS-3 immunoreactivity in the bone tissue to determine the involvement of the detected molecule in the transmembrane transport of bicarbonate in osteoclasts. The OS-3 selectively stained the basolateral plasma membrane of osteoclasts. Ultrastructurally, the immunoreactivity with OS-3 was associated with small cytoplasmic projections and microplicae of the basolateral plasma membrane. This finding suggests that osteoclasts express the molecule common to bicarbonate-secreting cells to utilize it for bicarbonate transport during bone resorption.

A modified Shigella volunteer challenge model in which the inoculum is administered with bicarbonate buffer: clinical experience and implications for Shigella infectivity.

In the absence of a definitive immunologic correlate of protection against shigellosis, promising Shigella vaccine candidates have been selected based on their ability to confer resistance against experimental challenge with wild-type Shigella in healthy adult volunteers. A limitation of this model has been the low and often variable attack rate of illness among controls, necessitating repeated inpatient studies to demonstrate statistically significant results. In this study, the Shigella challenge model was modified by using bicarbonate buffer instead of skimmed milk as the delivery vehicle to enhance survival of the ingested challenge inoculum. To determine the ability of the modified model to detect protective efficacy, 11 veteran volunteers (previously challenged with S. flexneri 2a in bicarbonate buffer) and 12 immunologically naive control subjects were challenged with 1.4 x 10(3) c.f.u. S. flexneri 2a. Shigellosis occurred in 3 veterans and 11 control subjects (27 vs 92%, p = 0.003), yielding a protective efficacy of 70%. Dose response was evaluated in an additional seven naive subjects who were inoculated with a log lower (1.4 x 10(2) c.f.u.) S. flexneri 2a and had a significantly diminished attack rate of shigellosis (317 (43%) vs 11/12 (92%), p = 0.04). These findings indicate that the modified bicarbonate challenge model using an inoculum of 10(3) c.f.u. is a safe, repeatable, and valid method of selecting Shigella vaccines and other immunoprophylactic agents that are likely to confer protection against natural shigellosis.

Efecto del bicarbonato de sodio sobre la actividad colinesterasa en cerebro, eritrocitos, plasma e higado de ratas intoxicadas con paratión

El presente trabajo se realizó con la finalidad de evaluar el efecto que tiene el bicarbonato sobre la actividad de la acetil colinesterasa de diversos tejidos, en animales de experimentación intoxicados con paratión. Para ello se formaron cuatro grupos de diez ratas cada uno. El grupo A sirvió de control . Los grupos B y C recibieronm por vía intraperitoneal paratión y además este último recibió bicarbonato de sodio luego de quine minutos de ser administrado el organofosforado. El grupo D recibió únicamente bicarbonato de sodio. Se dosaron las actividades colinesterásicas de los cuatro grupos en plasma , eritrocito, cerebro e hígado, por el método de Ellman modificado, y se compararon las actividades en los diferentes tejidos entre los grup[os de estudio con el fin de ver como variaba la actividad de la enzima inhibida por el paratión, por efecto del bicarbonato. Se encontró que la inhibición de la actividad colinesterásica, por el efecto del paratión, era significativa a nivel plasmático, cerebral y hepático, mas no a nivel eritrocítico; además se vió que el bicarbonato por si solo inhibia la actividad de la enzima en los mismos tejidos, de manera significativa. Por otro lado se encontró que la actividad colinesterásica inhibida por el órgano fosforado, se recuperó luego de la administración del bicarbonato de sodio. Con los resultados obtenidos se propone que la acción del bicarbonato sería desactivando al insecticida mismo y no sobre la colinesterasa.

Host metabolites that phenotypically increase the resistance of Haemophilus influenzae type b to clearance mechanisms.

Unidentified low-molecular-weight factor(s) in serum or nasopharyngeal secretions were known to phenotypically increase the resistance of Haemophilus influenzae type b (Hib) to bactericidal and opsonic antibodies, and resistance was attributed to two hypothetical mechanisms. Serum components generating resistance were studied. Mechanism 1, present in some Hib strains and their capsule-deficient mutants and accompanied by apparent increases in lipopolysaccharide content, was reproduced with a mixture of glucose, lactate, urea, and bicarbonate. Mechanism 2, present only in capsulated Hib and accompanied by increased capsulation, was reported with a mixture of Ca++ and lactate. Hib incubated with these compounds in buffer or grown in serum filtrate was resistant, but Hib grown in conventional media containing the metabolites in serum filtrate was resistant, but Hib grown in conventional media containing the metabolites was not. The resistant phenotype, which resembles Hib in vivo, may depend on nutrient balance as well as the specific factors. Lactate apparently is an important energy source for Hib.