RESUMO
BACKGROUND: Epidemiological studies suggest that smokeless tobacco in the form of Swedish snus has been used by many smokers in Scandinavia to quit smoking, but the efficacy of snus has so far not been evaluated in controlled clinical trials. METHODS: We conducted a randomized, double-blind, placebo-controlled, clinical trial aimed at assessing the efficacy of snus to help adult cigarette smokers in Serbia to substantially reduce, and, eventually, completely stop smoking. The study enrolled 319 healthy smokers aged 20-65 years at two occupational health centers in Belgrade, Serbia. Most of them (81%) expressed an interest to quit rather than just reduce their smoking. Study products were used ad libitum throughout the 48-week study period. The main study objective during the first 24 weeks was smoking reduction. The primary end-point was defined as a biologically verified reduction of ≥ 50% in the average number of smoked cigarettes per day during week 21-24 compared to baseline. During week 25-48 participants were actively instructed to stop smoking completely. Outcome measures of biologically verified, complete smoking cessation included 1-week point prevalence rates at clinical visits after 12, 24, 36, and 48 weeks, as well as 4-, 12- and 24-week continued cessation rates at the week 36 and 48 visits. RESULTS: At the week 24 visit, the proportion of participants who achieved the protocol definition of a ≥ 50% smoking reduction was similar in the two treatment groups. However, the proportion that reported more extreme reductions (≥ 75%) was statistically significantly higher in the snus group than in the placebo group (p < 0.01). The results for biologically verified complete cessation suggested that participants in the snus group were more likely to quit smoking completely than the controls; the odds ratio (snus versus placebo) for the protocol estimates of cessation varied between 1.9 to 3.4, but these ratios were of borderline significance with p-values ranging from 0.04-0.10. Snus was well tolerated and only 2/158 (1.3%) participants in the snus group discontinued treatment due to an adverse event (in both cases unrelated to snus). CONCLUSIONS: Swedish snus could promote smoking cessation among smokers in Serbia, that is, in a cultural setting without traditional use of oral, smokeless tobacco. TRIAL REGISTRATION: www.clinicaltrials.gov, identifier: NCT00601042.
RESUMO
Inhibition of Na+/K+-ATPase activity from human erythrocyte membranes and commercial porcine cerebral cortex by in vitro single and simultaneous exposure to digoxin and gitoxin was investigated to elucidate the difference in the mechanism of the enzyme inhibition by structurally different cardiac glycosides. The drugs exerted a biphasic dose-dependent inhibitory effect on the enzyme activity in both tissues, supporting the existence of two sensitive Na+/K+-ATPase isoforms. The IC50 values for the low and high affinity isoforms were calculated from the inhibition curves using mathematical analysis. The Hill coefficient (n) fulfilled the relationship 1 < n < 3, suggesting cooperative binding of inhibitors to the enzyme. Kinetic analysis showed that digoxin and gitoxin inhibited Na+/K+-ATPase by reducing the maximum enzymatic velocity (Vmax) and Km, implying an uncompetitive mode of interaction. Both the isoforms were always more sensitive to gitoxin. The erythrocyte enzyme was more sensitive to the inhibitors in the range of low concentrations but the commercial cerebral cortex enzyme exerted a higher sensitivity in high inhibitors affinity concentration range. By simultaneous exposure of the enzyme to digoxin and gitoxin in combinations a synergistic effect was achieved by low inhibitor concentrations. An antagonistic effect was obtained with erythrocyte membrane enzyme at high inhibitors concentration.