Hema J. Patel

Activation of Peroxisome Proliferator-Activated Receptors in Human Airway Smooth Muscle Cells Has a Superior Anti-inflammatory Profile to Corticosteroids: Relevance for Chronic Obstructive Pulmonary Disease Therapy

Airway smooth muscle is actively involved in the inflammatory process in diseases such as chronic obstructive pulmonary disease and asthma by 1) contributing to airway narrowing through hyperplasia and hypertrophy and 2) the release of GM-CSF and G-CSF, which promotes the survival and activation of infiltrating leukocytes. Thus, the identification of novel anti-inflammatory pathways in airway smooth muscle will have important implications for the treatment of inflammatory airway disease. This study identifies such a pathway in the activation of peroxisome proliferator-activated receptors (PPARs). PPAR ligands are known therapeutic agents in the treatment of diabetes; however, their role in human airway disease is unknown. We demonstrate, for the first time, that human airway smooth muscle cells express PPARα and -γ subtypes. Activation of PPARγ by natural and synthetic ligands inhibits serum-induced cell growth more effectively than does the steroid dexamethasone, and induces apoptosis. Moreover, PPARγ activation, like dexamethasone, inhibits the release of GM-CSF. However, PPARγ ligands, but not dexamethasone, similarly inhibits G-CSF release. These results reveal a novel anti-inflammatory pathway in human airway smooth muscle, where PPARγ activation has additional anti-inflammatory effects to those of steroids. Hence, PPAR ligands might act as potential treatments in human respiratory diseases.

Theobromine inhibits sensory nerve activation and cough

Cough is a common and protective reflex, but persistent coughing is debilitating and impairs quality of life. Antitussive treatment using opioids is limited by unacceptable side effects, and there is a great need for more effective remedies. The present study demonstrates that theobromine, a methylxanthine derivative present in cocoa, effectively inhibits citric acid‐induced cough in guinea‐pigs in vivo. Furthermore, in a randomized, double‐blind, placebo‐controlled study in man, theobromine suppresses capsaicin‐induced cough with no adverse effects. We also demonstrate that theobromine directly inhibits capsaicin‐induced sensory nerve depolarization of guinea‐pig and human vagus nerve suggestive of an inhibitory effect on afferent nerve activation. These data indicate the actions of theobromine appear to be peripherally mediated. We conclude theobromine is a novel and promising treatment, which may form the basis for a new class of antitussive drugs.

Naloxone‐insensitive inhibition of acetylcholine release from parasympathetic nerves innervating guinea‐pig trachea by the novel opioid, nociceptin

The novel peptide, nociceptin and the μ‐opioid agonist [d‐Ala2, N‐Me‐Phe4, Gly5‐ol]‐enkephalin (DAMGO) produced a concentration‐dependent inhibition of electrical field stimulation (EFS)‐evoked release of acetylcholine (ACh) from cholinergic nerves innervating guinea‐pig trachea. The non‐selective opioid receptor antagonist, naloxone, did not antagonize the inhibitory action of nociceptin under conditions where the inhibition of ACh release evoked by DAMGO was completely reversed. It is suggested that DAMGO and nociceptin can inhibit cholinergic, parasympathetic neurotransmission to the airways via the activation of classical (naloxone‐sensitive) and novel (naloxone‐insensitive) opioid receptors, respectively.

Constitutive expressions of type I NOS in human airway smooth muscle cells: evidence for an antiproliferative role

In airway diseases, smooth muscle cells can proliferate at exaggerated rates; thus, the identification of endogenous pathways that limit proliferative responses is important. Here we show that human airway smooth muscle express type I nitric oxide synthase (NOS), which results in inhibition of DNA synthesis and cell proliferation. In addition, superoxide dismutase (SOD), a cell‐permeable mimetic that increases the biological half‐life and therefore enhances the biological activity of endogenously released nitric oxide (NO), or NO‐releasing drugs also greatly reduce DNA synthesis and cell proliferation. Observations in this study have important clinical implications: 1) NOS inhibition may exacerbate airway disease and 2) inhaled SOD/mimetics or NO/nitrovasodilators may be therapies for the treatment of asthma or chronic obliterative pulmonary disease.—Patel, H. J., Belvisi, M. G., Donnelly, L. E., Yacoub, M. H., Chung, K. F., Mitchell, J. A. Constitutive expressions of type I NOS in human airway smooth muscle cells: evidence for an antiproliferative role. FASEB J. 13, 1810–1816 (1999)

Pharmacological characterization of the muscarinic receptor antagonist, glycopyrrolate, in human and guinea‐pig airways

In this study we have evaluated the pharmacological profile of the muscarinic antagonist glycopyrrolate in guinea‐pig and human airways in comparison with the commonly used antagonist ipratropium bromide. Glycopyrrolate and ipratropium bromide inhibited EFS‐induced contraction of guinea‐pig trachea and human airways in a concentration‐dependent manner. Glycopyrrolate was more potent than ipratropium bromide. The onset of action (time to attainment of 50% of maximum response) of glycopyrrolate was similar to that obtained with ipratropium bromide in both preparations. In guinea‐pig trachea, the offset of action (time taken for response to return to 50% recovery after wash out of the test antagonist) for glycopyrrolate (t1/2 [offset]=26.4±0.5 min) was less than that obtained with ipratropium bromide (81.2±3.7 min). In human airways, however, the duration of action of glycopyrrolate (t1/2 [offset]>96 min) was significantly more prolonged compared to ipratropium bromide (t1/2 [offset]=59.2±17.8 min). In competition studies, glycopyrrolate and ipratropium bromide bind human peripheral lung and human airway smooth muscle (HASM) muscarinic receptors with affinities in the nanomolar range (Ki values 0.5–3.6 nM). Similar to ipratropium bromide, glycopyrrolate showed no selectivity in its binding to the M1–M3 receptors. Kinetics studies, however, showed that glycopyrrolate dissociates slowly from HASM muscarinic receptors (60% protection against [3H]‐NMS binding at 30 nM) compared to ipratropium bromide. These results suggest that glycopyrrolate bind human and guinea‐pig airway muscarinic receptors with high affinity. Furthermore, we suggest that the slow dissociation profile of glycopyrrolate might be the underlying mechanism by which this drug accomplishes its long duration of action.

Effect of dopamine receptor agonists on sensory nerve activity: possible therapeutic targets for the treatment of asthma and COPD.

Sensory nerves regulate central and local reflexes such as airway plasma leakage, and cough and their function may be enhanced during inflammation. Evidence suggests that dopamine receptor agonists may inhibit sensory nerve‐mediated responses. In this study dopamine inhibited vagal sensory nerve induced microvascular leakage in the rat. In order to characterize the receptor involved rat vagus preparations were utilized. Quinagolide (D2/3 agonist), ropinirole (D2/3/4 agonist), SKF 38393 (D1/5 agonist), AR‐C68397AA (Viozan™) (dual D2/B2 agonist) and dopamine inhibited hypertonic saline induced depolarization by approximately 50%. Data suggests that AR‐C68397AA and quinagolide also inhibited depolarization of the human vagus. The quinagolide response was blocked by sulpiride (D2/3 antagonist) but not SCH 23390 (D1/5 antagonist); ropinirole was partially blocked by sulpiride, totally blocked by spiperone (at a concentration that blocks all dopamine receptors) but not by SCH 23390. The response to SKF 38393 was not blocked by sulpiride but was by SCH 23390. The inhibition evoked by AR‐C68397AA was only partially blocked by SCH 23390 but not by sulpiride or spiperone whereas dopamine was blocked by spiperone. The effect of dopamine was not stimulus‐specific as it inhibited capsaicin‐induced depolarization of the rat vagus in a spiperone sensitive manner. In conclusion, dopamine receptor ligands inhibit depolarization of the rat and human vagus. These data suggest that dopamine receptor agonists may be of therapeutic benefit in the treatment of symptoms such as cough and mucus secretion which are evident in respiratory diseases such as asthma and chronic obstructive pulmonary disease.

Modulation of acetylcholine release from parasympathetic nerves innervating guinea-pig and human trachea by endomorphin-1 and -2.

Endomorphin-1 and -2 (mu-opioid receptor agonists) produced a concentration-dependent and naloxone-sensitive inhibition of cholinergic contractile responses in guinea-pig trachea (at 10 microM, 46.1 +/- 8.0% and 33.8 +/- 8.6%, respectively). Endomorphin-1 and -2 also inhibited electrically-evoked acetylcholine release from cholinergic nerves innervating guinea-pig (at 0.1 microM, 41.8 +/- 10.9%; at 1 microM 60.1 +/- 6.3%, respectively) and human trachea (at 10 microM, 76.2 +/- 18.1%, and 77.7 +/- 14.3%, respectively). Naloxone prevented the inhibition by endomorphin-1 and -2 in both guinea-pig and human trachea, suggesting that these peptides can inhibit cholinergic, parasympathetic neurotransmission to the airways via the activation of classical opioid receptors.

Anti-spasmogenic activity of isoenzyme-selective phosphodiesterase inhibitors in guinea-pig trachealis

The anti‐spasmogenic potential of SK&F 94120 (PDE3‐selective), rolipram (PDE4‐selective), zaprinast (PDE5‐selective), zardaverine (dual PDE3/4 inhibitor) and theophylline (non‐selective) was evaluated in guinea‐pig trachealis. SK&F 94120 or rolipram (10 and 100 μM) antagonized histamine‐induced tension generation in a concentration‐dependent and non‐competitive manner whereas ACh‐induced contractions were unaffected. Similarly, SK&F 94120 and rolipram in combination were anti‐spasmogenic with respect to both contractile agonists to an extent that was greater than the effect of either drug alone. Identical results were obtained with zardaverine (1, 10 and 100 μM) and theophylline (100 μM and 1 mM). Zaprinast protected guinea‐pig trachealis against histamine‐, but not ACh‐induced contractile responses in a manner that was indistinguishable from the results obtained with SK&F 94120. However, in contrast to the interaction between SK&F 94120 and rolipram, no further antagonism was seen when zaprinast and rolipram were used in combination. Pre‐treatment of tissues with SNP (10 and 100 μM) antagonized histamine‐induced tension generation in a concentration‐dependent and non‐competitive manner. However, no further antagonism was produced when SNP and rolipram were used concurrently. Likewise, the protection afforded by a combination SNP and SK&F 94120 was no greater than that produced by SNP alone. These results demonstrate that an inhibitor of PDE3 enhances the anti‐spasmogenic activity of rolipram but not drugs that elevate cyclic GMP mass. Moreover, the ability of SNP and zaprinast to protect guinea‐pig trachealis against histamine‐induced contractions apparently is not due to the inhibition of PDE3.