Lipid Digestion in Cystic Fibrosis: Comparison of Conventional and High-Lipase Enzyme Therapy Using the Mixed-Triglyceride Breath Test

Background: Fat maldigestion occurs in most patients with cystic fibrosis. Conventional pancreatic enzyme replacement therapy partially corrects this defect. In this study, the mixed-triglyceride breath test was used to evaluate whether high-lipase enzymes are equivalent to conventional enzymes in improving fat maldigestion in children with cystic fibrosis.

Cited Here... Fat digestion was studied in 11 patients with a mean age of 10.5 years. The mean intake of conventional enzyme capsules a day was 19. Four ¹³C mixed-triglyceride tests were performed on separate days and in random order. One test was taken without enzyme substitution, one with three capsules of 8,000 FIP units Creon (pancreatinum, Kali-chemie Pharma, Hannover, Germany) and one with one capsule of 25,000 FIP units. The fourth test was made with¹³ C octanoic acid to study gastric emptying time.

Cited Here... Without enzyme intake, the mean cumulative percentage of ¹³C dose exhaled after 6 hours was 7.2 ± 3.7%. This increased to 14.4 ± 4% with intake of conventional pancreatinum and to 14.3 ± 5.1% with intake of high-lipase pancreatinum (p = 0.0008 for both; pairedt-test). There was no difference between both treatments. Also, the time course of ¹³C exhalation measured by percentage of¹³ CO₂ exhaled per hour did not differ between enzyme treatments.

Conclusions: The ¹³C mixed-triglyceride test is noninvasive and documents improved lipid digestion with pancreatic enzyme replacement therapy. If the lipase dose is kept constant, results obtained with high-lipase preparations are equivalent to those obtained with conventional preparations.

In approximately 85% of cystic fibrosis (CF) patients, exocrine pancreatic insufficiency is present from birth. The presence of steatorrhea correlates in general with a pancreatic enzyme output less than 10% of normal⁽¹⁾.

Treatment of pancreatic insufficiency in CF patients is based on oral replacement with pancreatic enzymes. Enteric-coated tablets that prevent gastric acid denaturation are commonly used. Pancreatinum capsules contain 8,000 FIP units lipase per capsule. Recently, so-called high-lipase preparations have been developed. These may prove advantageous in patients with persistent steatorrhea ⁽²⁾. For some of these preparations, a possible correlation with colonic strictures has been reported⁽³⁾. Therefore, adequate documentation of equivalence or benefit in comparison with conventional capsules is important.

The definitive test for exocrine pancreatic function in CF remains duodenal intubation with the secretin-pancreozymin stimulation test⁽⁴⁾, but the test is invasive and difficult to perform. Nonspecific evidence of pancreatic insufficiency is provided by demonstration of unsplit fat globules in stools or by increased 3-day fecal fat excretion. Because these tests are complex and cumber-some, the ¹³C mixed-triglyceride (MTG) breath test has been introduced as a noninvasive, simple test for studying lipid digestion ⁽⁵⁾. The formation of free fatty acids and monoglyceride after lipase hydrolysis of the test substance-1,2 distearyl, ¹³C octanoyl glycerol (referred to as¹³ C mixed-triglyceride)-mainly quantitates lipase activity. In adults, the result of this test correlates with lipase activity. Lipase activity is the rate-limiting step for the presence of CO₂ in exhaled air. Normal values in adults ⁽⁵⁾ and in children⁽⁶⁾ have been reported.

Gastric emptying time is a factor known to influence fat digestion. Rapid gastric emptying may worsen maldigestion, because the limited pancreatic enzyme stores are overwhelmed ⁽⁷⁾. Conversely, many patients with CF have delayed gastric emptying ⁽⁸⁾. The¹³ C octanoic acid breath test can be used to determine gastric emptying time ⁽⁹⁾ in adults and in children⁽¹⁰⁾.

The objective of the current study was to evaluate by means of the¹³ C MTG breath test whether high-lipase enzymes are equivalent or superior to conventional enzymes in correcting fat maldigestion in children with CF. To assess the possible influence of gastric emptying time on fat digestion, a ¹³C octanoic acid test was also obtained.

PATIENTS AND METHODS

Inclusion criteria were a diagnosis of CF established by at least two sweat chloride values more than 60 mEq/l determined according to the method described by Gibson and Cooke ⁽¹¹⁾, age more than 5 years, and evidence of pancreatic insufficiency by 3-day fat collection (fat loss >10% of intake). Exclusion criteria were intake of antacids, prokinetic drugs, a semielemental diet, or antibiotics within 14 days of the study and the presence of a gastrostomy. Oral informed consent was obtained from the patients' legal guardians.

All patients underwent three ¹³C MTG breath tests on separate days. One test was taken without enzyme substitution, one with three capsules of conventional enzymes (Creon, 3 × 8,000 FIP units lipase) and one with one capsule of high-enzyme lipase (Creon, 25,000 FIP units lipase). Enzymes were taken immediately before the test meal. A fourth test was obtained with¹³ C octanoic acid to study gastric emptying time. Tests were administered in random order.

The test meal consisted of 240 mg of ¹³C MTG baked into a regular pancake containing 18 g of fat, 18 g of carbohydrate, and 12 g of protein. After an overnight fast, the pancake was eaten in a maximum of 10 minutes. Exhaled breath was sampled before and every 15 minutes after the meal for up to 6 hours. Further eating and drinking were prohibited, and patients were kept at rest throughout the test, reading or watching television.

Breath samples were collected in an evacuated Becton-Dickinson tube(Franklin Lakes, NJ, U.S.A.) and measured for ¹³C content by isotope ratio mass spectrometer (Finnigan MAT, Delta S, Bremen, Germany). CO₂ production used in calculation of test results was 300 mmol/m² per hour as reported in the literature ⁽¹²⁾. Test results are expressed in percentage of ¹³C dose per hour and in cumulative percentage of ¹³C excretion in 6 hours. In normal adults, 23% is the lowest normal value for cumulative percentage of ¹³C dose exhaled in 6 hours. Normal values for various pediatric age groups were recently reported⁽⁶⁾. Twenty-two percent is the lower limit of normal in children 6 to 15 years old. Gastric emptying was expressed as half-emptying time ⁽⁹⁾.

Normal distribution of test results was checked by a normal-probability plot program. (Excel 4.0, Microsoft Corp., Redmond, WA, U.S.A.) Results were evaluated by analysis of variance and Duncan test (SAS, Proc anova).

RESULTS

One patient was unable to eat the test meal within the allotted time. One patient did not complete all tests. All four breath tests were performed by 11 patients, 7 girls and 4 boys. Their ages ranged from 6 years to 15 years(mean, 10.5 years), heights from 120 to 167 cm (mean, 136 cm), and weights from 21 to 57 kg (mean, 32 kg). Weight was below the 25th percentile in 3 patients, and weight-for-height was below the 50th percentile in 4 patients. All patients received pancreatic enzyme replacement therapy. The daily intake of conventional pancreatic enzyme ranged from 6 to 45 capsules (mean, 19).

The individual patient values for cumulative percentage of ¹³C dose exhaled after 6 hours in the three test situations are given inTable 1. These values were normally distributed. The mean cumulative percentage of ¹³C exhaled after 6 hours without enzyme intake was 7.1 ± 3.7%; it increased significantly to 14.4 ± 4.9% with intake of three capsules of conventional Creon or to 14.3 ± 5.1% with intake of one capsule of high-lipase Creon (p = 0.0008 for both; paired t-test). The time course of ¹³C exhalation measured by percentage of dose exhaled per hour did not differ between the two enzyme treatments. As an example, the three curves for one of the patients are shown (Fig 1).

Table 1

Fig. 1

Gastric emptying measured with the ¹³C octanoic acid test showed a large intersubject variability. The gastric half-emptying time ranged from 20 minutes to more than 200 minutes, with a median of 87 minutes. Only one of the patients with prolonged gastric emptying (174 minutes) failed to show an increase in ¹³CO₂ exhalation with enzymes substitution, indicating no improvement in fat digestion. For all other patients, even in the remaining patients with gastric emptying times of more than 120 minutes, the cumulative ¹³CO₂ exhaled after 6 hours indicates a therapeutic effect of enzyme substitution.

DISCUSSION

In CF, pancreatic enzyme replacement therapy is known to improve fat digestion substantially when evaluated in fat balance studies⁽²⁾. The current results show that this positive effect of pancreatic enzymes on fat digestion can also be demonstrated, using the¹³ C MTG breath test. In addition, it can be seen that replacement therapy significantly improves but does not normalize fat digestion and that in this respect, high-lipase products are not superior to conventional preparations. Indeed, the results clearly show equivalence of the two enzyme treatments.

A difference in enteric-coated granule size or a difference in the coating's pH stability or solubility could be responsible for differences in enzyme efficacy. Meyer ⁽¹³⁾ reported that 93% of granules in conventional Creon measure between 1.2 and 2 mm and 5% are smaller than 1.2 mm. High-lipase Creon contains 79% of particles between 1.2 and 2 mm and 14% smaller than 1.2 mm (Solvay, Pharma, Dr. Ceuppens, personal communication). In healthy volunteers, particles of 1 mm most consistently empty together with the test meal ⁽¹³⁾. Despite this size distribution difference between the formulations, improved fat digestion was not documented.

Only the equivalence of high-lipase products and conventional products could be demonstrated. The most significant advantage of high-lipase products is thus the need to take a reduced number of pills, which may improve compliance. The side effect of colonic strictures with porcine enzyme substitution is dose dependent ⁽¹⁵⁾. The most appropriate action at present is thus to avoid exceeding the current dosage recommendations.

Differences in results between fat balance studies that often show normalization of fat excretion and ¹³C MTG tests as shown here, can be easily explained. Fat excretion is normal when 10% of pancreatic enzyme secretion is present ⁽¹⁾ and ¹³C MTG breath tests even detect subclinical pancreatic insufficiency.

Factors other than lipolysis are known to influence fat digestion-i.e., gastric emptying time, duodenal acidity leading to enzyme inactivation, lipid micelle formation, and bile acid pool. In three patients, the delayed gastric emptying could influence the lipid digestion measured by the ¹³C MTG test. Still, in two of them a normal increase in fat absorption after enzyme substitution was measured.

In the current study, interindividual errors were avoided by using each patient as his or her own control. To normalize for CO₂ production, 300 mmol/m² per hour is used, according to Schreeve et al⁽¹²⁾. CO₂ production at rest was measured in 21 CF patients with different disease severity, using the Sensormedics 2800 (Yorba Linda, CA, U.S.A.) ergospirometry set-up. Their mean CO₂ production was 402 ± 128 mmol/m² per hour (data not shown)-i.e., higher than the values used by Schreeve. This is in agreement with the data of Tomezsko et al. ⁽¹⁴⁾, who reported a higher basic metabolic rate in patients with CF when compared with that in control subjects. Because each patient was used as his or her own control, the absolute values were different but the relative changes and the conclusion remained the same. Still, because of a large intersubject variability in CO₂ production in patients with different disease severity, it may be better to determine the CO₂ production at rest in individual patients rather than to use one, set average value in the calculation of the results.

In conclusion, the ¹³C MTG breath test may be used to document the improved fat digestion that occurs with pancreatic enzyme replacement therapy in CF patients. When using equal amounts of FIP lipases, conventional and high-lipase preparations lead to a similar improvement in fat digestion.