Pseudomonas aeruginosa and the Airways Disease of Cystic Fibrosis

Action of natural products on p2 receptors: a reinvented era for drug discovery

Natural products contribute significantly to available drug therapies and have been a rich source for scientific investigation. In general, due to their low cost and traditional use in some cultures, they are an object of growing interest as alternatives to synthetic drugs. With several diseases such as cancer, and inflammatory and neuropathic diseases having been linked to the participation of purinergic (P2) receptors, there has been a flurry of investigations on ligands within natural products. Thirty-four different sources of these compounds have been found so far, that have shown either agonistic or antagonistic effects on P2 receptors. Of those, nine different plant sources demonstrated effects on P2X2, P2X3, P2X7, and possibly P2Y12 receptor subtypes. Microorganisms, which represent the largest group, with 26 different sources, showed effects on both receptor subtypes, ranging from P2X1 to P2X4 and P2X7, and P2Y1, P2Y2, P2Y4, and P2Y6. In addition, there were seventeen animal sources that affected P2X7 and P2Y1 and P2Y12 receptors. Natural products have provided some fascinating new mechanisms and sources to better understand the P2 receptor antagonism. Moreover, current investigations should clarify further pharmacological mechanisms in order to consider these products as potential new medicines.

Improvement of cystic fibrosis during treatment with isotretinoin

A 15-year-old boy with a history significant for multiple respiratory infections since birth presented for evaluation of acne vulgaris. He was initially prescribed doxycycline, topical tretinoin, and topical clindamycin solution, with the later addition of a benzoyl peroxide preparation to his regimen. The patient returned 6 months later after having been diagnosed with CF (cystic fibrosis) by sweat testing and genetic testing. His skin condition had not responded adequately to prior therapy, so all acne medications were discontinued. The 84-kg patient was started on 80 mg (0.95 mg/kg/d) of isotretinoin (13-cis-retinoic acid) daily. The patient's dose was decreased to 40 mg/d 2 weeks later following an episode of blood in his stool and epistaxis. At the 1- and 2-month follow-up visits, the patient reported improvement in his acne and mentioned that his lung secretions seemed reduced. His acne cleared after 4 months of therapy, so the isotretinoin was discontinued. The patient and his mother noted that no respiratory infections had occurred during the course of therapy. The patient's acne relapsed nearly 2 years later, so isotretinoin was restarted at 60 mg/d. During the next 7 months while on the drug, he experienced no further episodes of epistaxis or bloody stools and his acne had resolved by the end of therapy. The patient and his mother again reported fewer bronchopulmonary secretions and no infections requiring antibiotics during treatment with isotretinoin. This was unusual because he had experienced numerous respiratory infections requiring antibiotics during the prior 2 years. Since discontinuing the drug, the patient has had intermittent pulmonary infections and exacerbations in the symptomatology of his CF.

Pseudomonas aeruginosa quorum-sensing signal molecule N-(3-oxododecanoyl)-L-homoserine lactone inhibits expression of P2Y receptors in cystic fibrosis tracheal gland cells

ATP and UTP have been proposed for use as therapeutic treatment of the abnormal ion transport in the airway epithelium in cystic fibrosis (CF), the most characteristic feature of which is permanent infection by Pseudomonas aeruginosa. As for diverse gram-negative bacteria, this pathogenic bacterium accumulates diffusible N-acylhomoserine lactone (AHL) signal molecules, and when a threshold concentration is reached, virulence factor genes are activated. Human submucosal tracheal gland serous (HTGS) cells are believed to play a major role in the physiopathology of CF. Since ATP and UTP stimulate CF epithelial cells through P2Y receptors, we sought to determine whether CF HTGS cells are capable of responding to the AHLs N-butanoyl-L-homoserine lactone (BHL), N-hexanoyl-L-homoserine lactone (HHL), N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), and N-(3-oxohexanoyl)-L-homoserine lactone (OHHL), with special reference to P2Y receptors. All AHLs inhibited ATP- and UTP-induced secretion by CF HTGS cells. The 50% inhibitory concentrations were as high as 10 and 5 microM for BHL and HHL, respectively, but were only 0.3 and 0.4 pM for OdDHL and OHHL, respectively. Furthermore, all AHLs down-regulated the expression of the P2Y2 and P2Y4 receptors. Ibuprofen and nordihydroguaiaretic acid were able to prevent AHL inhibition of the responses to nucleotides, but neither dexamethasone nor indomethacin was able to do this. These data indicate that AHLs may alter responsiveness to ATP and UTP by CF HTGS cells and suggest that, in addition to ATP and/or UTP analogues, ibuprofen may be of use for a combinational pharmacological therapy for CF.

HLA class II polymorphism in cystic fibrosis. A possible modifier of pulmonary phenotype

Evolution of lung damage is highly variable in cystic fibrosis (CF) even in patients with the same cystic fibrosis transmembrane conductance regulator (CFTR) mutations. The analysis of genetic factors other than CFTR may help our understanding of genotype-phenotype relationships in CF. As human leukocyte antigen (HLA) class II polymorphism has been associated with a number of diseases including autoimmune and inflammatory diseases, asthma, and allergy, we investigated the possibility that HLA polymorphism contributes to CF-associated pulmonary inflammation. Among the 98 adult CF patients tested, the genotypic frequencies of DR4 and DR7 alleles (serologic group DR53) and DR7/ DQA*0201 haplotype were higher than in 39 selected control subjects without atopy (p </= 10(-)6, relative risk [RR] = 22, and p </= 5.10(-)4, RR = 27, respectively) and in a random population. No significant difference of these allelic distributions was found according to the CFTR genotype. In the CF patients, the DR7 allele was significantly associated with an increase in total IgE and with chronic Pseudomonas aeruginosa colonization (100% of DR7 versus 83% of non-DR7 patients being colonized, p < 0.05). Our results suggest that genetic factors known to modulate the immune response might contribute to chronic infection with Pseudomonas, increased total IgE, and pulmonary outcome in CF.

Altered cytokine production by cystic fibrosis tracheal gland serous cells

Human submucosal tracheal glands are now believed to play a major role in the physiopathology of cystic fibrosis (CF). We successfully developed techniques for culturing human tracheal gland serous cells from normal individuals (HTGS cells) and from CF patients (CF-HTGS cells) and have shown that the cultured cells have retained most of their in vivo epithelial and secretory characteristics. In order to determine to what extent the serous cells may participate in the lung defense against infection, we examined the effects of the lipopolysaccharide (LPS) of Pseudomonas aeruginosa on HTGS and CF-HTGS cells, with special reference to tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), and IL-8 secretion. HTGS cells showed a daily basal secretion of IL-6 (1.68 +/- 0.14 ng/10(6) cells) and IL-8 (9.6 +/- 1.3 ng/10(6) cells) and no constitutive secretion of TNF-alpha. Treatment with P. aeruginosa LPS resulted in a significant increase in the basal production of IL-6 (increase of 200% +/- 12%) and IL-8 (525% +/- 40%) as well as a rapid production of TNF-alpha (250 +/- 38 pg/10(6) cells). The LPS-induced secretion of IL-6 and IL-8, but not that of TNF-alpha, was inhibited by glucocorticoids. CF-HTGS cells showed a much higher basal secretion of IL-6 (13.2 +/- 0.5 ng/10(6) cells) and IL-8 (45.6 +/- 7.2 ng/10(6) cells) than normal cells. Treatment with the LPS of P. aeruginosa induced increased production of IL-6 (increase of 100% +/- 8%) and IL-8 (55% +/- 18%) but did not induce the secretion of TNF-alpha. Neither intracellular TNF-alpha nor TNF-alpha transcripts were found in CF-HTGS cells, whereas they were found in normal HTGS cells. In addition, dexamethasone was found to stimulate IL-6 and IL-8 secretion (in the presence or absence of LPS) but did not induce any secretion of TNF-alpha. All these data indicate that HTGS cells are responsive to P. aeruginosa LPS, which results in an increased secretion of IL-6, IL-8, and TNF-alpha, the secretion of which appeared to be impaired in CF-HTGS cells.