Magdalena Kamińska

13C-methacetin breath test reproducibility study reveals persistent CYP1A2 stimulation on repeat examinations

AIM To find the most reproducible quantitative parameter of a standard (13)C-methacetin breath test ((13)C-MBT). METHODS Twenty healthy volunteers (10 female, 10 male) underwent the (13)C-MBT after intake of 75 mg (13)C-methacetin p.o. on three occasions. Short- and medium-term reproducibility was assessed with paired examinations taken at an interval of 2 and 18 d (medians), respectively. RESULTS The reproducibility of the 1-h cumulative (13)C recovery (AUC(0-60)), characterized by a coefficient of variation of 10%, appeared to be considerably better than the reproducibility of the maximum momentary (13)C recovery or the time of reaching it. Remarkably, as opposed to the short gap between consecutive examinations, the capacity of the liver to handle (13)C-methacetin increased slightly but statistically significantly when a repeat dose was administered after two to three weeks. Regarding the AUC(0-60), the magnitude of this fixed bias amounted to 7.5%. Neither the time gap between the repeat examinations nor the gender of the subjects affected the (13)C-MBT reproducibility. CONCLUSION (13)C-MBT is most reproducibly quantified by the cumulative (13)C recovery, but the exactitude thereof may be modestly affected by persistent stimulation of CYP1A2 on repeat examinations.

Interference of acute cigarette smoking with [13C]methacetin breath test

It is essential to establish whether and how environmental factors affect the reliability of [13C]methacetin breath test (13C-MBT). In 12 healthy volunteers (smokers), a standard 13C-MBT with 75 mg [13C]methacetin was performed twice in random order: on a control day without smoking and on another day with smoking two cigarettes antecedently. A considerable flattening of the curve of the momentary 13C recovery within the expiratory air was observed when the 13C-MBT was performed after smoking. The maximum of the momentary 13C recovery, D max, decreased from 37.20±2.58 to 25.39±2.29% dose/h (p=0.00052). Moreover, the time to reach D max was prolonged after cigarette smoking (26.5±3.1 vs. 16.5±1.9 min, p=0.0199). The curve of the cumulative 13C recovery on the cigarette smoking day appeared to be shifted downwards, and statistically significant differences relative to the control situation were found between the 24th and 75th minute following [13C]methacetin administration. Smoking cigarettes immediately prior to the 13C-MBT diminishes the ability of the liver to handle methacetin, and hence a possibility of such an interaction should be excluded in order to interpret the results of the test correctly.

Long-term effects of lipase inhibition by orlistat on gastric emptying and orocecal transit time of a solid meal

BackgroundWe assessed the impact of a prolonged lipase inhibition upon gastric emptying (GE) and orocecal transit time (OCTT) of a 355-kcal low-fat solid meal.MethodsIn double-blind manner, 40 obese women BMI > 30 kg/m2, randomly allocated into two equal groups, took orally t.i.d. 120 mg orlistat or placebo during 8 weeks of a weight-reducing management. At randomization and after 2 months, GE was measured simultaneously with OCTT by means of a 13C-octanoic acid and a hydrogen breath test, respectively. Lipolytic activity was evaluated with a 13C-mixed triglyceride breath test (13C-MTGBT).ResultsA profound lipase inhibition by orlistat was confirmed by a 79.5% ± 16.9% reduction of the cumulative 6-h 13C recovery with 13CMTGBT. GE remained unchanged either in the orlistat (T1/2, 188 ± 35 min start versus 198 ± 36 min end) or the placebo (T1/2, 191 ± 35 min start versus 180 ± 39 min end) group. OCTT increased from 208 ± 54 min to 271 ± 64 min (P < 0.01) after orlistat treatment and did not change significantly (216 ± 76 vs. 234 ± 72 min) in the placebo group.ConclusionsNo adverse effect on the GE and a moderate prolongation of the OCTT of a low-fat solid meal is to be expected under a prolonged treatment with orlistat at a typical dosage regimen.

Impact of combined oral contraceptives containing ethinylestradiol on the liver microsomal metabolism

Abstract Objectives To check whether currently used combined oral contraceptives (COCs) containing ethinylestradiol (EE) affect the liver microsomal metabolism. Methods 13C-methacetin breath test (13C-MBT) – a sensitive non-invasive probe of cytochrome P-450 1A2 activity – was performed in 15 women on day 14, 15, 16, 17 or 18 of intake of their COC (containing EE), and between day 1 and 5 during the withdrawal bleeding, as well as in nine women not using hormonal contraception during the luteal phase of their cycle (between the 17th and the 23rd day), and between day 1 and 5 during menstruation. Results The maximum breath 13C elimination was significantly lower during the phase of intake of contraceptive pills than during withdrawal bleeding: 31.5 ± 2.2 %/h vs. 38.2 ± 1.9 %/h (p = 0.0045), whereas the time to reach it was similar on the two study days: 21.2 ± 1.2 min vs. 21.0 ± 1.1 min. Between the 27th and the 180th min of observation the cumulative breath 13C elimination was statistically significantly lower during intake of the pill than during withdrawal bleeding. No significant menstrual cycle phase-dependent fluctuations in the results of the 13C- methacetin breath test were observed in the control group. Conclusion COCs containing EE markedly inhibit hepatic microsomal function. This phenomenon must be taken into consideration when interpreting results of 13C-MBT.

Combined oral contraceptives affect liver mitochondrial activity

Abstract Objectives To examine liver mitochondrial function in women using combined oral contraceptives (COCs) containing ethinylestradiol. Methods A breath test after oral administration of 1 mg/kg 13C-alpha-ketoisocaproic acid (13C-KICA) and 20 mg/kg L-leucine was performed twice: (i) in 15 women on day 14, 15, 16, 17 or 18 of COC intake, and between day 1 and 5 of the withdrawal bleeding; and (ii) in 15 regularly menstruating females not taking hormonal contraceptives: during the luteal phase, between the 18th and the 22nd day of the cycle, and again between day 1 and 5 of the menstruation. Results In women on COCs the maximum 13C elimination in breath air (Dmax) was higher (26.8 ± 1.6%/h) than during withdrawal bleeding (23.5 ± 1.2%/h; p = 0.012). The time to reach the Dmax was similar on the two study days: 33.3 ± 2.4 min during the phase of pill intake vs. 37.0 ± 2.5 min during the pill-free interval. The one-hour cumulative breath 13C elimination was greater after two weeks of COC intake than during the withdrawal bleeding: 17.49 ± 1.03% vs. 15.32 ± 0.85% (p = 0.024). In the control group no menstrual cycle phase-dependent fluctuations in the results of the 13C-KICA breath test were observed. Conclusion The metabolism of 13C-alpha-ketoisocaproic acid augments during the intake of COCs containing ethinylestradiol, reflecting enhanced liver mitochondrial metabolic activity.

Scrutiny of 13C-phenylalanine breath test reproducibility

ABSTRACT We evaluated the reproducibility of the 13C-phenylalanine breath test (13C-PheBT). On three separate days, 21 healthy volunteers (11 F and 10 M) underwent 13C-PheBT with 100 mg l-[1-13C]phenylalanine taken orally. Short-term reproducibility was evaluated with paired examinations taken 3 days apart; paired examinations separated by 23 days (median) served for the medium-term reproducibility assessment. Expiratory air was sampled at 19 points throughout 3 h. Determined limited reproducibility of the 13C-PheBT must be taken into consideration while interpreting the results of this diagnostic tool. The results of this study imply the following conclusions: (i) From among the three parameters examined, the cumulative 13C recovery area under the curve (AUC) offers much better reproducibility than the maximum momentary 13C recovery in the expiratory air (Dmax) or the time to reach the maximum momentary 13C recovery (Tmax) (ii) Collection of the breath air samples for 2 h results in a much better reproducibility of AUC, than for 1 h only; (iii) Reproducibility of 13C-PheBT is affected neither by the duration of the time gap between repeated tests nor by gender; (iv) Comparison with data obtained formerly reveals that reproducibility of the 13C-PheBT is worse than either that of of the 13C-methacetin (13C-MBT) or the 13C-alpha-ketoisocaproic acic (13C-KICA-BT) breath tests. This finding will have to be taken into consideration while interpreting the results of this diagnostic tool.

Reproducibility of two ¹³CO₂ breath tests dedicated to assess pancreatic exocrine function.

The aim of this study was to check on the reproducibility of two breath tests intended to test the pancreatic exocrine function accomplished with 13C-mixed triglyceride (13C-MTG) or cornflakes naturally enriched in 13C (13C-CF). The 13CO2 content within breath samples was determined with isotope-selective non-dispersive infrared spectrometry. A 72-h monitoring performed in healthy subjects revealed that a statistically significant rise in breath 13CO2 occurs between the 1st and the 9th hour and between the 1st and the 24th hour after intake of a test meal containing 300 mg 13C-MTG (n=10) or 100 g 13C-CF (n=12), respectively. In another two groups of 12 healthy volunteers each, short-term reproducibility of the two tests was assessed with paired examinations taken at a median interval of two days, whereas paired examinations separated by a median of 20 days served for the medium-term reproducibility assessment. In the case of either test, the medium-term reproducibility was not any worse than the short-term one. The reproducibility of the 13C-CF breath test tended to be slightly worse than that of the 13C-MTG breath test: a least detectable difference in 6-h cumulative 13C breath excretion (which is expressed as the percentage of the administered dose of the substrate) amounted to 2.7 and 4.4 % (short-term reproducibility) and to 3.5 and 4.4 % (medium-term reproducibility) in the case of the 13C-MTG breath test and the 13C-CF breath test, respectively. It is concluded that both tests offer a satisfactory reproducibility for use within a clinical setting. In case the lipolytic and the amylolytic activity would be required to be examined in the same patient, the 13C-CF breath test can be executed on the next day following the 13C-MTG breath test, whereas reciprocally, a 1-day break is recommended before accomplishment of a 13C-MTG breath test following a 13C-CF breath test.