Characterization of sulfidopeptide leukotriene responses in sheep tracheal smooth muscle in vitro

Hyaluronic acid blocks porcine pancreatic elastase (PPE)-induced bronchoconstriction in sheep

We previously showed that inhaled porcine pancreatic elastase (PPE) causes bronchoconstriction in sheep via a bradykinin-mediated mechanism. Hyaluronic acid (HA), in vitro, binds and inactivates airway tissue kallikrein (TK), the enzyme responsible for kinin generation. Therefore, we hypothesized that in vivo, HA should prevent PPE-induced bronchoconstriction by binding and inactivating TK. To test this, we measured pulmonary resistance (RL) in allergic sheep before and after inhalation of PPE alone (500 microg) and after pretreatment with either inhaled HA at 70 kD, designated low molecular weight (LMW)-HA or 200 kD, designated high molecular weight (HMW)-HA at different concentrations. Inhaled PPE increased RL 147 +/- 8% over baseline values and this effect was associated with a 111 +/- 28% increase in bronchoalveolar lavage fluid (BALF) TK activity. HA blocked the PPE-induced bronchoconstriction and the increase in BALF TK activity in a dose- dependent and molecular weight-dependent fashion. HA alone had no effect on RL. Instillation of PPE in the lung increased kinin concentrations in BALF, a result consistent with the PPE-induced increase in BALF TK activity. Our findings show that HA blocks PPE-induced bronchoconstriction in a dose-dependent and molecular weight-dependent fashion by a mechanism that may, in part, be related to inhibition of TK activity and the formation of kinins.

An alternative pathway for metabolism of leukotriene D(4): effects on contractions to cysteinyl-leukotrienes in the guinea-pig trachea

Contractions of guinea-pig tracheal preparations to cysteinyl-leukotrienes (LTC(4), LTD(4) and LTE(4)) were characterized in organ baths, and cysteinyl-leukotriene metabolism was studied using radiolabelled agonists and RP-HPLC separation. In the presence of S-hexyl GSH (100 microM) the metabolism of [(3)H]-LTC(4) into [(3)H]-LTD(4) was inhibited and the LTC(4)-induced contractions were resistant to CysLT(1) receptor antagonism but inhibited by the dual CysLT(1)/CysLT(2) receptor antagonist BAY u9773 (0.3 - 3 microM) with a pA(2)-value of 6.8+/-0.2. In the presence of L-cysteine (5 mM), the metabolism of [(3)H]-LTD(4) into [(3)H]-LTE(4) was inhibited and the LTD(4)-induced contractions were inhibited by the CysLT(1) receptor antagonist ICI 198,615 (1 - 10 nM) with a pA(2)-value of 9.3+/-0.2. However, at higher concentrations of ICI 198,615 (30 - 300 nM) a residual contraction to LTD(4) was unmasked, and this response was inhibited by BAY u9773 (1 - 3 microM). In the presence of the combination of S-hexyl GSH with L-cysteine, the LTD(4)-induced contractions displayed the characteristics of the LTC(4) contractile responses, i.e. resistant to CysLT(1) receptor antagonism, increased maximal contractions and slower time-course. This qualitative change of the LTD(4)-induced contraction was also observed in the presence of S-decyl GSH (100 microM), GSH (10 mM) and GSSG (10 mM). S-hexyl GSH, S-decyl GSH, GSH and GSSG all stimulated a formation of [(3)H]-LTC(4) from [(3)H]-LTD(4). In conclusion, GSH and GSH-related compounds changed the pharmacology of the LTD(4)-induced contractions by stimulating the conversion of LTD(4) into LTC(4). Moreover, the results indicate that, in addition to the metabolism of LTC(4) into LTD(4) and LTE(4), also the formation of LTC(4) from LTD(4) may regulate cysteinyl-leukotriene function.

Agonist and antagonist activities of the leukotriene analogue BAY u9773 in guinea pig lung parenchyma

BAY u9773(6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11( Z),14(Z)-eicosatetraenoic acid) is a leukotriene E4 analogue used to define 'atypical' receptors for cysteinyl-leukotrienes. The aims of this study were first to characterise the intrinsic properties of BAY u9773 in guinea-pig lung parenchyma in vitro and second to study the influence of BAY u9773 on the concentration-response relation for leukotriene D4 in the same preparation. BAY u9773 in itself caused a concentration-dependent contraction, which was not inhibited by the cyclooxygenase inhibitor indomethacin nor by the 5-lipoxygenase inhibitor zileuton (N-(1-benzo-(12)-thien-2-ylethyl)-N-hydroxyurea). The CysLT1 receptor antagonist ICI 198,615 [(1-((2-methoxy-4-(((phenylsulfonyl)amino) carbonyl)phenyl)methyl)-1H-indazol-6-yl)carbamic acid cyclopentyl ester] alone blocked the contractile response to BAY u9773 1 microM, whereas a combination of the TP receptor antagonist BAY u3405 ((3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz olepropanoic acid) and ICI 198,615 was required to block the contraction induced by BAY u9773 10 microM. Together the findings suggest that BAY u9773 acted as a CysLT1 receptor agonist and in the higher concentration also as a TP receptor agonist. The CysLT1 receptor antagonist ICI 198,615 partly inhibited the contractile response to leukotriene D4. Pretreatment with BAY u9773 or leukotriene D4, caused concentration-dependent rightward displacement of the concentration-response curve for leukotriene D4. The inhibition by BAY u9773 was partial, and not greater than that produced by ICI 198,615. Combination of BAY u9773 and ICI 198,615 did not produce additive inhibition, suggesting that the major part of the leukotriene D4 induced contraction in guinea pig lung parenchyma is mediated by a CysLT receptor with properties distinct from those of previously described CysLT1 and CysLT2 receptors.

Tachykinin NK2 receptors predominantly mediate tachykinin-induced contractions in ovine trachea

In vitro studies were conducted to characterize the contractile effects of tachykinins in normal ovine trachea with a view in the future to compare tachykinin contractile responses in allergic tissue. Tracheal smooth muscle strips were prepared for in vitro studies of isometric contraction in response to cumulative addition of carbachol, acetylcholine, histamine, neuropeptide gamma, substance P, neurokinin A, neurokinin B, [Sar9, Met(O2)11]substance P, [Nle10]neurokinin A-(4-10), and [Succinyl-Asp6, Me-Phe8]substance P-(6-11) (senktide). The rank order of potency was neuropeptide gamma > carbachol > neurokinin A > or = [Nle10]neurokinin A-(4-10) > acetylcholine > or = histamine. Phosphoramidon enhanced the contractile response to neurokinin A and substance P, but not to neuropeptide gamma, [Sar9, Met(O2)11]substance P or senktide. Repeated cumulative concentration responses for acetylcholine, substance P, neurokinin A, [Sar9, Met(O2)11]substance P and histamine were also conducted to test for tachyphylaxis. No tachyphylaxis to acetylcholine, substance P, or neurokinin A was observed, however, [Sar9, Met(O2)11]substance P and histamine did exhibit tachyphylaxis. Atropine had no effect on tracheal contractions to neurokinin A and substance P, while [Sar9, Met(O2)11]substance P contractions were atropine sensitive. Pyrilamine did not affect substance P-induced tracheal smooth muscle contractions, indicating that the response to substance P was not mediated by histamine release. These results show that, in vitro, natural tachykinins induce tracheal smooth muscle contraction predominantly by a direct effect mediated by tachykinin NK2 receptors, and a small tachykinin NK1 receptor mediated cholinergic mechanism.

Leukotriene receptors

The current challenge in research on leukotriene receptors is to clone these molecules. Traditional protein purification approaches have not been successful in providing sequence information. Solubilization of cys-LT1 has been achieved but results in the dissociation of G-proteins and the loss of high affinity binding (Mong et al., 1986b; Mong and Sarau, 1990), while cys-LT2 activity cannot be monitored by other than functional assays and there have not been any purification attempts. Partial purification of B-LT has been reported but has not been continued to homogeneity (Sherman et al., 1992; Votta et al., 1990; Miki et al., 1990). Nor have attempts to clone these receptors through either homology screening or expression cloning been successful. The cloning of the prostanoid receptors, described in detail elsewhere in this volume, has shown that these receptors belong to a distinct family within the G-protein-coupled receptor superfamily. It is probable, therefore, that the leukotriene receptors will also belong to a separate group within this superfamily since phylogenic comparisons have shown that receptors displaying high affinity for structurally related ligands exist as discrete families. Recently, a human cDNA encoding an orphan FMLP-related receptor cloned from HL60 cells of myeloid lineage was identified as the receptor for another eicosanoid, lipoxin A (Fiore et al., 1994). FMLP has a similar profile of biological actions to LTB4. Moreover, LTD4 showed a high degree of cross-reactivity with this receptor with an affinity only 20-fold less that of lipoxin A, although LTB4 was inactive. It remains to be determined whether the leukotriene receptors will fall into this class of receptors. The cloning of the leukotriene receptors will allow identification of the different receptor types and subtypes and potentially splice variants. Evaluation of currently developed antagonists at these receptor types could also open the way for novel therapies for inflammatory conditions.

Carbonate inhibition of leukotriene D4-dipeptidase in human serum

Human serum contains an inhibitor of leukotriene D4 (LTD4) dipeptidase which was separated from the enzyme by ultrafiltration (Amicon, YM-10). Removal of the inhibitor resulted in a 3- to 5-fold increase in total LTD4-dipeptidase activity in the material retained by the filter. Inhibitor activity (which was assayed with a partially purified LTD4-dipeptidase) was recovered in the filtrate. Ultrafiltration of serum using YM-3, YM-1, and YC-05 membranes suggested an inhibitor molecular weight of less than 500. Elution of inhibitor activity from a Bio Gel P2 gel filtration column was identical to the elution pattern of pure carbonate. The inhibitor was heat stable (95 degrees C, 30 min), stable in 0.1 N NaOH, but rapidly inactivated by 0.1 N HCl at both 4 degrees C and 30 degrees C. Partially purified LTD4-dipeptidase was inhibited by carbonate and phosphate but not by nitrate, sulfate, or chloride. Based on these observations it was concluded that the inhibitor of LTD4-dipeptidase in human serum either was carbonate or required carbonate. The relative concentrations of LTC4, LTD4, and LTE4 appear to be important parameters in determining the duration and intensity of LT mediated reactions. The relative concentration of carbonate in serum or extracellular fluids might, therefore, be a factor in modulating localized LT mediated responses.