in the von Ebner's glands in rat tongue (5),rabbit stom ach mucosa (6)and human gastric juice (7)were purified to homogeneity, and various molecular and ...
Lipids
Adaptation of Lingual Lipase to Dietary Fat in Rats MARTINEARMAND, PATRICK.BOREI, LOUIS CARA, MICHELESENFT, MAGALI CHAÜTAN,HUGÜETTE LAFONT ANDDENIS LA1ROH Unité130 (Unité de Recherches sur le Transport des Lipides), Institut National de la Santéet de la Recherche Médicale (IHSERM), 13009 Marseille, France
ABSTRACT To study the adaptive response of lingual Upase and pancreatic lipase to dietary fat, three sets of experiments were performed in adult male rats. In the first experiment, rats were fed for 3 wk a low fat diet (4.5% fat) or a 10, 20 or 30% fat diet. In the second, rats were fed a 4.5% fat diet for 4 wk or a 20% fat diet for 1, 2 or 4 wk. In the third, rats were fed for 3 wk a 10% fat diet with various sources of fat (lard, sunflower oil, olive oil, peanut oil, butter, soybean oil, corn oil or salmon oil). The results demonstrated that 10% dietary fat was sufficient to promote a maximum significant increase in lingual lipase activity (expressed in units/g tissue and in units/mg protein), whereas pancreatic lipase responded steadily to 20 and 30% fat diets. After 1 wk of feeding 20% dietary fat, both enzyme specific activities had reached their maximum values. The fatty acid composition of dietary triglycér ide molecules (chain length, number and location of double bonds) had no specific effect on the adaptation of lingual lipase. The physiological implications of these findings are discussed in regard to the role of intragastric lipolysis in fat digestion. J. Nutr. 120:1148-1156, 1990. INDEXING KEY WORDS:
•rat •lipase •dietary fat
•tongue
pancreas
The presence of pre-duodenal Upases is now clearly established in various species (1-4). The Upases present in the von Ebner's glands in rat tongue (5),rabbit stom ach mucosa (6)and human gastric juice (7)were purified to homogeneity, and various molecular and kinetic pa rameters were determined in recent years. The tissue localization of the enzyme depends on the species con cerned. Although lipase activity is measurable in all species studied either in tongue or gastric mucosa homogenates, three recent studies clearly established that the essential source of pre-duodenal lipase in rats, mice and sheep is the tongue, whereas in rabbits, pigs, ba boons and humans the gastric enzyme is predominant
MATERIALS AND METHODS Animals and diets. French official regulations (no. 87-849 of 19 October 1987) for the care and use of laboratory animals were followed. Seventeen groups of eight male Wistar rats, which weighed about 260 g (IFFA
0022-3166/90 $3.00 ©1990 American Institute of Nutrition. Received 15 August 1989. Accepted 2 April 1990.
1148
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(2-4). In both cases, the enzyme begins the hydrolysis of dietary triglycéridesin the acidic environment of the stomach. This process is assumed to be important for promoting the action of pancreatic lipase on complex lipid emulsions in the small intestine (8-12) and, thus, for enabling an almost complete assimilation of dietary fat. More important is the finding that pre-duodenal lipase can play a key role in fat assimilitation in preterm infants, children suffering from cystic fibrosis and patients with pancreatic insufficiency (9, 13, 14). There is evidence that the lipase of pancreatic origin adapts to dietary fat in a number of species, such as rats (15-21),hogs (9),dogs and chickens. In rats, most studies show that the lipase content in the pancreas is signifi cantly increased when the fat content of the diet is about 20% of the solids or more. Only one paper about pre-duodenal lipases describes a limited experiment in which lingual lipase activity is shown to increase by 45% when the fat content of the diet varies from 4 to 22% for 2 wk (23).Thus, it has not yet been clearly demonstrated whether pre-duodenal lipases have the ability to adapt to the dietary fat con tent. We therefore performed the present study in adult rats to determine whether the lingual lipase adaptation depends on the amount of dietary fat, the duration of fat feeding or the type of dietary fat. Lingual lipase adapta tion was compared in the same animals to the adaptive response of lipase from the pancreatic gland. The results demonstrate for the first time that the level of activity of rat lingual lipase increases significantly after 1 wk of feeding a diet containing at least 10% fat.
1149
LINGUAL LIPASE AND DIETARY FAT
Credo, L'arbresle, France) and were 2 mo old at the beginning of the experiment, were used. The animals were housed individually in wire-bottomed cages at 21"C with a 12 h light/12 h dark cycle, and they had free Constituent
Low fat Low fat High fat High fat High fat diet I diet ^ diet 1 diet 2 diet 3 g/100 g food
Protein (casein)
25
40
25
25
25
Carbohydrate Starch Sucrose
42 18
32 13
39 15.5
32 12.5
24 11.5
10 10
15 15
Fat Sunflower oil Lard Cellulose Vitamins2 Minerals3 Energy,kj/100 g
2.3 2.2
23 2.2
5 5
4.5
4.5 1 5
4.5 1 5
4.5 1 5
4.5 1 5
1590.5
1705.4
1914.4
2140.2
1
5 1590.5
'Casein, wheat starch, sucrose, lard, cellulose, vitamins and min erals were purchased from UAR, Villemoison sur Orge, France. Sun flower oil was purchased from Lessieur, Coudekerke-Branche, France. 2Vitamins,given in g/kg diet (unless otherwise noted): retinol, 19.8 IU; cholecalciferol, 61 u; thiamin, 0.02; riboflavin, 0.015; nicotinamide, 0.035; pyridoxine, 0.01; carnitine, 0.15; cyanocobalamin, 5 x IO"5;ascorbic acid, 0.8; a-tocopherol, 0.17; menadione, 0.04; nicotinic acid, 0.10; choline, 1.36; pteroylmonoglutamic acid, 5 x 10^; p-aminobenzoic acid, 0.05; biotin, 3 x 10^*. 'Minerals, given in g/kg diet: CaHPO4, 21.5; KC1, 5; NaCl, 5; MgSO4/ 2.50; Fe2O3/ 0.15; FeSO4-7H2O,0.25; MnSO4H2O, 0.12; CuSO4-5H2O,0.025; CoSO47H2O, 2 x I0r*,ZnSO4 7H2O, 0.1; stabi lized KI,4 x 10-";NaF, 0.012.
after a careful removal of mesenteric fat, each pancreas was weighed and homogenized for three 10-sbursts with a Kinematica apparatus in ice-cold distilled water (10 mL/g tissue). Aliquots of the homogenates were frozen and stored at -80°Cuntil analysis. Assays. Aliquots of 200 |J.Lwere used fordetermina tion of lingual lipase activity. The enzyme activity was measured with a pH stat Titrator (Metrohm, Herisau, Switzerland) at pH 5.4 and 37°C, with tributyrin as the substrate (0.5 mL), in the presence of 14.5 mL of a solution containing 150 mmol/L NaCl, 6 mmol/L CaCl2, 8 mmol/L mixed conjugated bile salts (Calbiochem, LaJolla, CA) and 30 umol/L fatty acid-free bovine serum albumin (Sigma, La Verpilliere, France), as pre viously described (3,26). At the end of the reaction time, the pH of the medium was quickly raised to pH 9.5 to allow the complete titration of ionized butyric acid (3). Controls lacked an enzyme source. The total pancreatic lipase activity of a homogenate (20 uL of the homogenate diluted 20 times) was assayed as previously described (21) at pH 7.5 with a pH stat Titrator and tributyrin as the substrate, in the presence
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access to water. In the first set of experiments (adaptation according to fat level), the rats were fed for 3 wk the five diets described in Table 1. The effects of two low fat diets (4.5% fat) with different protein content (25 or 40%) were compared with those of three high fat diets with a given amount of protein (25%)and a variable fat content (10, 20 or 30% fat). Fat was composed of a mixture of half sunflower oil and half lard with the fatty acid composition given in Table 2. In the second set of experiments (adaptation accord ing to duration of feeding), the rats were fed either low fat diet 1 (4.5% fat, 25% protein) for 4 wk or high fat diet 2 (20% fat, 25% protein) for 1, 2 or 4 wk (Table 1). Fat was a mixture of half sunflower oil and half lard. In the third set of experiments (adaptation according to type of fat), eight groups of rats were fed for 3 wk high fat diet 1 (10% fat, 25% protein), in which fat was only lard, sunflower oil, olive oil, peanut oil, soybean oil, corn oil, salmon oil or butter. The fatty acid composi tions of these fat sources as determined by gas-liquid chromatography are given in Table 2. The food intake was measured each day for three consecutive days and was given as the mean ±SEM(g/d and kj/d). Preparation of tissue samples. After an overnight fast, the rats were anesthetized with diethyl ether be tween 0800 and 1000 h. The tongue was carefully cut with special attention to remove the posterior part of the organ, which is assumed to contain most of the lipase activity (3, 24). The tongue was weighed, cut into small pieces with surgical scissors and homogenized by using a Kinematica apparatus (Lucerne, Switzerland) with a PT 10 probe, at speed level 6, for 1 min in an ice-cold solution containing 150 mmol/L NaCl and 6 mmol/L CaCl2 (4 mL/g tissue). The homogenates were kept on ice until use on the same day for the assay of lipase activity and proteins. Preliminary investigations were made to compare different methods of sample preparation prior to enzyme assay. Homogenates of tongue tissue were previously prepared either in 0.9% NaCl or phosphate buffer containing 0.9% NaCl (25)or in the presence of 0.5% Triton X 100 (3).In both meth ods, the homogenates were centrifuged, and the result ing supernatants were used as an enzyme source. In our hands, almost all lipase activity was recovered in such supernatants (95%), but only 64-67% of the tissue pro teins were found in this soluble fraction. Thus, to allow the accurate measurement of the specific activity of lingual lipase (units/mg protein), lipase activity and protein concentration were determined in the present study on the whole tongue homogenates. The pancreas was rapidly removed from each rat;
TABLE 1 Composition of experimental diets1
1150
ARMAND ET AL. TABLE2 Fatty acid composition of the diets1
Fatty acid
Sunflower oil/lard ISO/50)2
Lard
Sunflower oil
Olive oil
Peanut oil
Soybean oil
Butter3
Corn oil
Salmon oil
% of total fatty acids 14:0 14:1 16:0 16:l( 18:0 18:2(n-6) 18:3(n-3) 18:4(n-3) 20:0 20:l(n-9)
Saturated (S) Polyunsaturated (P)P/S (n-6)/(n-3)25.11
12.37 1.06 3.13 75.18
10.37 0.14 3.79 56.70
36.84 0.05
68.68 0.11
6.99 0.60
21.29 0.10
0.15 0.08
0.31 0.16
0.33 0.20
1.58 1.15
17.38 1.05 6.60 36.73
28 2 8 56
4.6 0.3
10.49 0.11 4.05 23.67
0.2 26.8
0.3
53.15 6.98
60.0 0.8
0.6 1.1
0.38 0.29
0.4
1.6
11.6
0.1
0.77
0.38
—
2.86
12.6 5.4 1.8 14.8 2.6 16.9 0.6 2.0 0.3 2.6 7.8 0.4 0.6 9.8
0.47
6.6 0.6 1.2 7.2 0.20
0.10
—
1.48
—
0.16 0.4
36.891.47
73737.0
5.00.13
> 100013.25
68.795.19
62415.83
7.590.48
11.6520.08
21.391.06
21369.5
1.90.03
5.3315.55
60.133.86
60.95.075.019.3 38.72.0
7.6112.2
0.80
'Sunflower oil, olive oil, peanut oil and soybean oil were purchased from Lessieur, Coudekerke-Branche, France. Lard was from UAR, Villemoison sur Orge, France. Corn oil was purchased from Delta GMH, Marseille, France. Butter was from LEB, Retiers, France. Salmon oil was from Arko-pharma, Carros, France. Values are expressed as a percentage of total fatty acids. If a value is missing, the fatty acid was not detectable (limit of detection: 0.05%). The fatty acid composition was determined after extraction of fats in organic solvents, saponification and methylation; the fatty acid methyl esters were separated and quantified by gas-liquid chromatography on a capillary column (length: 50 m, i.d. 0.32 mm, Carbowax 20 mol/L) with a flame ionization detector. 2Mixed fats in low fat diet 1 and high fat diets 1, 2 and 3 as described in Table 1. 3The sum of fatty acids between C4 and Ci2 amounts to 17.1%.
of 8 mmol/L sodium taurodeoxycholate (Calbiochem) and excess porcine pancreatic colipase (Boehringer Mannheim GmbH, Mannheim, FRG). In both cases (lingual or pancreatic enzyme), one lipase unit was defined as 1 umol fatty acid titrated per minute. Protein concentrations in tongue and pancreas homogenates (400 uL homogenate diluted 200 times) were measured by the method of Lowry et al. (27) using bovine serum albumin as the standard. All measure ments of lipase activity and protein concentration were conducted in duplicate. Statìstica! analysis. The statistical significance of the results was analyzed by one-way analysis of variance (ANOVA), and the differences among treatment groups
were assessed by Fisher's test (28); differences associated with a p value of < 0.05 were considered significant.
statistically
RESULTS Effect of various levels of dietary fat and protein. As shown in Table 3, feeding the rats for 3 wk diets with increased levels of protein (40%) or fat (10 or 20%) did not significantly affect body weight change whereas feeding the diet containing 30% fat resulted in signifi cantly higher weight gain. Feeding the rats 20 or 30% fat diets decreased food intake relative to that in the other groups. Rats fed the low fat, high protein diet had
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20:4(n-6) 20:4(n-3) 20:5(n-3) 22:0 22:l(n-ll) 22:l(n-3) 22:5(n-3) 22:6(n-3) 24:0 24:l(n-9)
6.76 0.10 5.21 17.47
12.4 1.0 27.6 1.8 12.2 20.3
0.5
1151
LINGUAL LIPASE AND DIETARY FAT TABLES food intake and weight of rats fed low fat diets or high fat diets for 3 weeks1 Low fat diet 1 4.5% fat, 25% protein
Measure Initial weight, g Final weight, g Weight g/dFood gain,
intake latidg/d kj/d267
Low fat diet 2 4.5% fat, 40% protein
High fat diet 1 10% fat, 25% protein
High fat diet 2 20% fat, 25% protein
High fat diet 3 30% fat, 25% protein
± 2.1a 378 ± 6.8a 5.4 0.4a1.65 ±
±2.0b 364 ±7.4b 5.0 0.3a1.97 ±
±1.7ac 376 ±4.4a 0.2a3.54 5.3 ±
± 1.3* 385 ± 5.0° 5.8 0.3"5.88 ±
1.3'402 ± ± 7.4d 6.4 0.3*7.32 ±
± 0.06a 36.6 ± 1.2a 582.12 ±19.09a258
±0.08a 43.8 ±0.5b 687.09 ±7.95b265
±0.05b 35.4 ±0.5a 603.71 ±8.53a262
± 0.13C 29.4 ± 0.6° 562.83 ±11.49e268
± 0.38d 24.4 ± 1.3d 522.21 ±27.82d
'Adult rats were fed low fat diets or high fat diets for 3 wk. Low fat diets 1 and 2 contained 25% and 40% casein, respectively. High fat diets 1, 2 and 3 contained a fixed amount of casein (25%) and variable amounts of fat (10, 20 and 30%, respectively). Fats were provided in the form of a mixture (50/50) of sunflower oil and lard. Values are means ±SEMfor eight determinations. Values bearing different superscript letters (a, b, c, d) in the same row are significantly different (ANOVA and Fisher's test, p < 0.05).
the concentration (units/g tongue) of lingual lipase and the specific activity of the enzyme significantly in creased by 28.6 and 23.2%, respectively. The maximum increases observed after feeding the rats the 20% fat diet were 35.9 and 30.5%, respectively, greater than the values obtained with the 4.5% fat diet. Adding more fat in the diet up to 30% induced no further increase of the lingual lipase activity. The activity of lipase in the pancreas (Table 4) showed no significant change when the diet contained only 10% fat but was significantly enhanced after feeding the rats a 20% fat diet and again after feeding them a 30% fat diet. The specific activity of pancreatic lipase rose by 19.8, 89.6 and 115.9% after feeding 10, 20 and 30% fat
TABLE4 Protein and lipase contents of tongues and pancreas of rats fed low fat diets or high fat diets for 3 weeks1
MeasureLow Tongue Weight, Protein, Lipase, Lipase,
g mg/g tongue u/g tongue2 u/mg protein
Pancreas Weight, g Protein, mg/g pancreas Lipase, Itf u/g pancreas1 Lipase, u/mg protein1.004±
fat diet 1 4.5% fat, 25% proteinLow 0.855 ±0.02a 132 ±6.8 231 ±9.5a 1.77 ±0.09a
185 2.36 126
fat diet 2 4.5% fat, 40% proteinHigh 0.808 ± 0.02ab 124 ± 3.2 220 ± 7.1a 1.78 ± 0.07a
0.09 ±7.3 179 ±0.16a 2.48 ±5.66a0.982 134
fat diet 1 10% fat, 25% proteinHigh
0.866 137 279 2.18
± 0.04 ±10.1 190 ± 0.31a 2.87 ±10.25a0.922 151
± 0.16ab ± 3.7 ±17.9b ± 0.1 lb
fat diet 2 20% fat, 25% proteinHigh 0.903 ± 0.01ab 138 314 2.31
± 0.03 ± 8.30 183 ± 0.27a 4.36 ±11.28a0.988 239
± 7.3 ±22.6b ± 0.21b
fat diet 3 30% fat, 25% protein 0.840 ± 0.19a 140 276 2.01
± 4.9 ±12.5b ± 0.10'*
± 0.04 ± 9.8 190 ± 0.26b 5.15 ±10.86b0.958 272
± 0.02 ±12.7 ± 0.29e ±21.18C
'Adult rats were fed low fat diets or high fat diets for 3 wk. Low fat diets 1 and 2 contained 25% and 40% casein, respectively. High fat diets 1, 2 and 3 contained a fixed amount of casein (25%) and variable amounts of fat (10, 20 and 30%, respectively). Fats were provided in the form of a mixture (50/50) of sunflower oil and lard. Tissues were collected from anesthetized animals after an overnight fast. Values are means ±SEMfor eight determinations. Values bearing different superscript letters (a, b, c) in the same row are significantly different (ANOVA and Fisher's test, p < 0.05). 2One lipase unit (u) was defined as 1 umol fatty acid liberated per minute in the assay conditions (for details, see Materials and Methods).
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a significantly greater daily food intake than rats fed the low fat, low protein diet. The fat intake (g/d) signifi cantly increased when the fat content of the diet was increased from 4.5 to 10%, from 10 to 20% and from 20 to 30%. The data presented in Table 4 demonstrate that the tongue and pancreas weights and the protein concentra tions in both tissues generally were not affected by the protein or the fat content of the diet. Increasing the amount of protein in the low fat diet (from 25 to 40%) did not modify the lipase activity level in the tongue or the pancreas (Table 4). Conversely, when the amount of fat (mixture of half sunflower oil and half lard) present in the diet was approximately doubled (from 4.5 to 10%),
1152
ARMANDETAL. TABLES Body weights, tongue and pancreas weights and protein contents of rats fed a low fat diet or a high fat diet for 1,2 or 4 weeks1
1MeasureInitial
Low fat diet
2wk±±±±±±2.5«2.5b0.03'"4.6b0.06"18.82823712wk± fat diet
3.6'b± gFinal weight, 4.8C0.823 gTongue weight, 0.01"1330171± ± gTongue weight, ±±.0701±7.2'7.1*0.03"k6.8«0.04a8.112773200.7501140.822190High ±1531.166±138 2.7e879 tonguePancreas protein, mg/g 0.05b± ± ±±5.3b10.18d0.02e4.8'0.0 gPancreas weight, proteins, mg/g pancreas4wk27642001501185±±.779 6.24wk294455±±0.872 'Adult rats were fed a low fat diet (25% casein, 4.5% fat) for 4 wk or a high fat diet (25% casein, 20% fat) for 1, 2 or 4 wk. Fats were provided in the form of a mixture (50/50) of sunflower oil and lard. Tissues were collected from anesthetized animals after an overnight fast. Values are means ±SEMfor eight determinations. Values bearing different superscript letters (a, b, c, d) in the same row are significantly different (ANOVA and Fisher's test, p < 0.05).
diet (mixture of half sunflower oil and half lard). As shown in Table 6, the body weight gains after 3 wk of feeding were highest in the groups fed lard, sunflower oil or salmon oil diets, and the food intakes were lowest in the groups fed the corn oil or salmon oil diets. The protein concentration in the tongue tissue was compa-
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FIGURE 1 Effect on the activity of lingual lipase of feeding rats a diet [high fat (HF) 2] containing 20% fat and 25% protein for 1, 2 or 4 wk. Control rats were fed for 4 wk a low fat (LF) diet containing 4.5% fat and 25% protein. Fat was a mixture of half sunflower oil and half lard. One lipase unit was defined as 1 umol fatty acid titrated per minute. Columns bearing different letters represent significantly different mean values (ANOVA and Fisher's test, p < 0.05).
Downloaded from jn.nutrition.org by guest on July 10, 2011
diets, respectively, with a linear relationship (r = 0.95, p < 0.05). Effect of duration of fat feeding. The data obtained after feeding rats a diet containing 20% fat (mixture of half sunflower oil and half lard) for 1,2 or 4 wk are shown in Table 5. Compared to rats fed a 4.5% fat diet, those fed the 20% fat diet had a significantly greater body weight after 4 wk. The tongue weights were signifi cantly greater after feeding a 20% fat diet than after feeding a 4.5% fat diet for 4 wk. Pancreas weights in the two groups were comparable after 4 wk. The tongue protein concentration changed over the experimental period, but it did not seem to be specific ally affected by the dietary fat content (Table 5). Tongue protein concentrations were comparable in both groups after 4 wk of dietary treatment. The protein concentra tion in the pancreas of rats fed a 20% fat diet for 1, 2 or 4 wk did not change (Table 5). The level of lipase activity in both tissues varied markedly. As shown in Figure 1, the lipase activity in the tongue and the specific activity of the enzyme were significantly increased by 12.6 and 46.9%, respectively, after feeding the rats for 1 wk a 20% fat diet. The lipase activity in the tongue was further enhanced (24.8%) after feeding this diet for 2 wk. Feeding rats a 20% fat diet for 4 wk did not result in an additional change of the lingual lipase activity. The pattern shown by pan creatic lipase is presented in Figure 2. As observed for the lingual enzyme, the activity of lipase in the pancreas and the specific activity of the enzyme were signifi cantly increased by 56.3 and 52.9%, respectively, after feeding a 20% fat diet for 1 wk. Feeding this diet for 2 or 4 wk did not lead to an additional significant increase of the activity of pancreatic lipase. Effect of type of dietary fat. In this set of experi ments, eight groups of rats were fed for 3 wk a diet containing 10% of one of the following fats: sunflower oil, olive oil, peanut oil, butter, soybean oil, corn oil or salmon oil. Rats of a control group were fed a 4.5% fat
1153
LINGUAL LIPASE AND DIETARY FAT
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