Publications

BACKGROUND

It has recently been recognized that atrial fibrillation can originate from focal sources in the pulmonary veins (PVs). However, the mechanisms of focal atrial fibrillation have not been well characterized. We assessed the electrophysiological characteristics of the PVs using high-resolution optical mapping.

METHODS AND RESULTS

Coronary-perfused, isolated whole-atrial preparations from 33 normal dogs were studied. Programmed electrical stimulation was performed, and a 4-cm2 area of the PV underwent optical mapping of transmembrane voltage to obtain 256 simultaneous action potentials. Marked conduction slowing was seen at the proximal PV, compared with the rest of the vein, on both the epicardial (31.3+/-4.47 versus 90.2+/-20.7 cm/s, P=0.001) and endocardial (45.8+/-6.90 versus 67.6+/-10.4 cm/s, P=0.012) aspects. Pronounced repolarization heterogeneity was also noted, with action potential duration at 80% repolarization being longest at the PV endocardium. Nonsustained reentrant beats were induced with single extrastimuli, and the complete reentrant loop was visualized (cycle length, 155+/-30.3 ms); reentrant activity could be sustained with isoproterenol. Sustained focal discharge (cycle length, 330 to 1100 ms) was seen from the endocardial surface in the presence of isoproterenol; each focus was localized near the venous ostium.

CONCLUSIONS

The normal PV seems to have the necessary substrate to support reentry as well as focal activity. Although reentry occurred more distally in the vein, focal activity seemed to occur more proximally.

PURPOSE

To select a daily dose of arzoxifene (LY353381), a selective estrogen receptor modulator, for use in future studies in women with locally advanced or metastatic breast cancer who are either potentially tamoxifen sensitive (TS) or tamoxifen refractory (TR).

PATIENTS AND METHODS

This trial was a randomized, double-blind, phase II study of arzoxifene 20 mg (n = 55) and 50 mg (n = 57) in women with advanced or metastatic breast cancer. Patients were randomly assigned to balance for number of metastatic disease sites, prior tamoxifen therapy, and estrogen receptor status. The primary end point was tumor response rate (RR). Secondary end points included clinical benefit rate (CBR), time to progression (TTP), and toxicity.

RESULTS

Forty-nine patients were TS and 63 were TR. According to independent review, among TS patients, RR was higher in the 20-mg arm than the 50-mg arm (26.1% v 8.0%), with a longer TTP (8.3 v 3.2 months; P >.05). Among the TR patients, response rate was the same in the 20-mg and 50-mg arms (10.3%) with similar TTP (2.7 and 2.8 months, respectively; P >.05). CBR was higher in the 20-mg arm than in the 50-mg arm among TS patients (39.1% v 20.0%) and TR patients (13.8% v 10.3%). Arzoxifene was well tolerated. Dose-dependent toxicity was not demonstrated. There were no deaths during study.

CONCLUSION

Arzoxifene is effective in the treatment of TS and TR patients with advanced or metastatic breast cancer at the 20-mg and 50-mg dose levels. Toxicities are minimal, and the therapy is tolerated. The 20-mg dose seems to be at least as effective as the 50-mg dose. Accordingly, arzoxifene 20 mg/d was selected for further study in patients with breast cancer.

Integrins are heterodimeric cell-surface proteins that regulate cell growth, migration and survival. We have shown previously that the epithelial-restricted integrin alpha(v)beta6 has another critical function; that is, it binds and activates latent transforming growth factor-beta (TGF-beta). Through a global analysis of pulmonary gene expression in the lungs of mice lacking this integrin (Itgb6 null mice) we have identified a marked induction of macrophage metalloelastase (Mmp12)--a metalloproteinase that preferentially degrades elastin and has been implicated in the chronic lung disease emphysema. Here we report that Itgb6-null mice develop age-related emphysema that is completely abrogated either by transgenic expression of versions of the beta6 integrin subunit that support TGF-beta activation, or by the loss of Mmp12. Furthermore, we show that the effects of Itgb6 deletion are overcome by simultaneous transgenic expression of active TGF-beta1. We have uncovered a pathway in which the loss of integrin-mediated activation of latent TGF-beta causes age-dependent pulmonary emphysema through alterations of macrophage Mmp12 expression. Furthermore, we show that a functional alteration in the TGF-beta activation pathway affects susceptibility to this disease.

In recent studies we demonstrated that the analgesic effect of the kappa-like opioids is significantly greater in women, that low dose nalbuphine (5 mg) produces profound anti-analgesia (i.e. enhances pain) in men, and that addition of a low dose of the non-selective opioid receptor antagonist naloxone (0.4 mg) to nalbuphine (5 mg) abolishes the sex difference and results in significantly enhanced analgesia in both sexes. To further delineate the dose-dependent analgesic and anti-analgesic effects of nalbuphine, the present study evaluated the effect of a lower dose of nalbuphine (2.5 mg), with and without naloxone, on dental postoperative pain. In women, nalbuphine alone induced modest, short duration analgesia, which was antagonized rather than enhanced by the addition of naloxone (0.4 mg). In men, this dose of nalbuphine alone did not produce analgesia or anti-analgesia, and naloxone (0.4 mg) did not alter the response to nalbuphine. Thus, the anti-analgesic effect of nalbuphine, present in both sexes at the 5 mg dose disappears at the lower dose of nalbuphine. In addition, the mild analgesia in women produced by this lower dose of nalbuphine is antagonized by naloxone.

Human chymase is a protease involved in physiological processes ranging from inflammation to hypertension. As are all proteases of the trypsin fold, chymase is synthesized as an inactive "zymogen" with an N-terminal pro region that prevents the transition of the zymogen to an activated conformation. The 1.8 A structure of pro-chymase, reported here, is the first zymogen with a dipeptide pro region (glycine-glutamate) to be characterized at atomic resolution. Three segments of the pro-chymase structure differ from that of the activated enzyme: the N-terminus (Gly14-Gly19), the autolysis loop (Gly142-Thr154), and the 180s loop (Pro185A-Asp194). The four N-terminal residues (Gly14-Glu15-Ile16-Ile17) are disordered. The autolysis loop occupies a position up to 10 A closer to the active site than is seen in the activated enzyme, thereby forming a hydrogen bond with the catalytic residue Ser195 and occluding the S1' binding pocket. Nevertheless, the catalytic triad (Asp102-His57-Ser195) is arrayed in a geometry close to that seen in activated chymase (all atom rmsd of 0.52 A). The 180s loop of pro-chymase is, on average, 4 A removed from its conformation in the activated enzyme. This conformation disconnects the oxyanion hole (the amides of Gly193 and Ser195) from the active site and positions only approximately 35% of the S1-S3 binding pockets in the active conformation. The backbone of residue Asp194 is rotated 180 degrees when compared to its conformation in the activated enzyme, allowing a hydrogen bond between the main-chain amide of residue Trp141 and the carboxylate of Asp194. The side chains of residues Phe191 and Lys192 of pro-chymase fill the Ile16 binding pocket and the base of the S1 binding pocket, respectively. The zymogen positioning of both the 180s and autolysis loops are synergistic structural elements that appear to prevent premature proteolysis by chymase and, quite possibly, by other dipeptide zymogens.

Granzyme A (GzmA) induces a caspase-independent cell death pathway characterized by single-stranded DNA nicks and other features of apoptosis. A GzmA-activated DNase (GAAD) is in an ER associated complex containing pp32 and the GzmA substrates SET, HMG-2, and Ape1. We show that GAAD is NM23-H1, a nucleoside diphosphate kinase implicated in suppression of tumor metastasis, and its specific inhibitor (IGAAD) is SET. NM23-H1 binds to SET and is released from inhibition by GzmA cleavage of SET. After GzmA loading or CTL attack, SET and NM23-H1 translocate to the nucleus and SET is degraded, allowing NM23-H1 to nick chromosomal DNA. GzmA-treated cells with silenced NM23-H1 expression are resistant to GzmA-mediated DNA damage and cytolysis, while cells overexpressing NM23-H1 are more sensitive.