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PubMed2002

mbgA-dependent lactose utilization by Bacillus megaterium.

The beta-galactosidase-encoding mbgA gene has recently been cloned from Bacillus megaterium. We now report that disruption of the chromosomal mbgA rendered B. megaterium unable to utilize lactose as a sole carbon source. Complementation of the mbgA mutant with a multicopy plasmid carrying intact mbga restored the ability to utilize lactose for cell growth. Crude extracts from the wild-type B. megaterium cells grown in the presence of lactose exhibited a significant level of lactose-hydrolyzing activity, whereas no activity was observed in crude extracts of the mbgA mutant grown under the same condition. The mbgA gene could also confer the ability of lactose utilization on a lacZ deletion mutant of Escherichia coli. Lactose-hydrolyzing activity was also observed in crude extracts of the lacZ deletion mutant carrying mbgA on a multicopy plasmid. In addition, inactivation of the chromosomal mbgA did not affect lactose induction of expression of the mbgA promoter-xylE transcriptional fusion. Taken together, these results suggest that mbgA is essential for lactose utilization by B. megaterium, but is not involved in generation of the intracellular inducer for lactose induction of mbgA expression.

Bacillus megaterium↗
PubMed1978

Metabolic control of lactose entry in Escherichia coli.

A general method has been developed for determining the rate of entry of lactose into cells of Escherichia coli that contain beta-galactosidase. Lactose entry is measured by either the glucose or galactose released after lactose hydrolysis. Since lactose is hydrolyzed by beta-galactosidase as soon as it enters the cell, this assay measures the activity of the lactose transport system with respect to the translocation step. Using assays of glucose release, lactose entry was studied in strain GN2, which does not phosphorylate glucose. Lactose entry was stimulated 3-fold when cells were also presented with readily metabolizable substrates. Entry of omicron-nitrophenyl-beta-D-galactopyranoside (ONPG) was only slightly elevated (1.5-fold) under the same conditions. The effects of arsenate treatment and anaerobiosis suggest that lactose entry may be limited by the need for reextrusion of protons which enter during H+/sugar cotransport. Entry of omicron-nitrophenyl-beta-D-galactopyranoside is less dependent on the need for proton reextrusion, probably because the stoichiometry of H+/substrate cotransport is greater for lactose than for ONPG.

Arsenates↗
PubMed2004

Functionality testing of inhalation grade lactose.

Lactose monohydrate for inhalation is commonly produced by sieving out customer-specific size fractions of a crystallized bulk material of lactose. It was the aim of this study to investigate the influence of the raw material on the physico-chemical properties of the inhalation grade lactose and on the efficacy of powders for inhalation produced from these batches. The selected raw material lactose batches differed in the size distribution characteristics, the fines and the agglomerate content. These differences in the raw material could also be found to a smaller extent in the intermediate products and could not be completely levelled out in the final inhalation grade lactose. Efficiency testing was done using salbutamol sulphate in two different concentrations (drug-to-carrier ratio of 1:36 and 1:400) as a model drug; the powder blends were delivered using the Aerolizer and the Easyhaler device. With the high drug load, nearly no differences could be observed between both the delivery systems and the different produced lactose batches. The fine particle fraction (FPF) (%<5 microm) was on a high level of >39% in all cases. With the low drug load significant differences between the devices and the lactose batches were found. The FPF was distinctly reduced to 15-30%, with the Easyhaler generating a higher fraction of fine particles than the Aerolizer device. Although the observed differences between the lactose batches could not be linked to one specific physico-chemical parameter determined for the carrier, they led to the conclusion that the differences between the test batches of inhalation grade lactose especially manufactured for this study can affect the functionality of an inhalation powder. The effects are significantly smaller with high drug load formulations than using a low drug concentration.

Administration, Inhalation↗
PubMed2004

Single-step granulation/tabletting of different grades of lactose: a comparison with high shear granulation and compression.

The influence of the particle size, particle morphology and crystallinity of lactose on the extrusion properties and on the quality of tablets were investigated using single-step granulation/tabletting as a tabletting technique. Results showed that particle size and type of lactose (alpha-lactose monohydrate, anhydrous beta-lactose and spray dried lactose) affected the powder feeding, the process performance as well as the process capacity. Different grades of lactose yielded tablets with similar tensile strength, but significantly different disintegration time. Single-step granulation/tabletting always yielded tablets with a significantly higher tensile strength and similar or significantly lower disintegration time compared to high shear granulation and compression. The tensile strength of alpha-lactose monohydrate tablets (without and with PVP) did not change during one year of storage at 60% RH-25 degrees C and at 75% RH-40 degrees C, whereas a significant increase in disintegration time was observed. It can be concluded that although the lactose grade affected the performance and the optimal parameters of single-step granulation/tabletting, all lactose grades can be efficiently processed using this technique.

Compressive Strength↗
PubMed2002

Lactose modifications enhance its drug performance in the novel multiple dose Taifun DPI.

Drug-carrier particle interactions greatly affect the detachment of drug from the carrier in inhalation powders. In this study, a novel multiple dose, reservoir-based Taifun was used as a dry powder inhaler, and the effects of carrier physical properties were evaluated on the pulmonary deposition of budesonide, along with physical stability of the inhalation powder. In this study, untreated commercial preparation of alpha-lactose monohydrate, highly amorphous spray dried lactose, crystallized spray dried lactose, Flowlac-100 and Flowlac-100 mixed with crystalline micronized lactose were used as carriers. Dry powder formulations were prepared by the suspension method, where the budesonide-carrier ratio was 1:15.1 (w/w). Carriers and formulations were initially characterized, and again after 1 month's storage at 40 degrees C/75% RH. The physical properties of the carriers strongly affected the pulmonary deposition of budesonide and the physical stability of the inhalation powder. Initially, amorphous contents of the carriers were 0-64%, but spontaneous crystallisation of the amorphous lactose occurred during storage and, thus all carriers were 100% crystalline after storage. When compared to an untreated alpha-lactose monohydrate, the highly amorphous spray dried lactose and Flowlac-100 did not improve aerosol performance of the inhalation powder. When crystalline spray dried lactose was used as a carrier, the highest RF% values were achieved, and RF % values did not alter during storage but the emitted budesonide dose was lower than the theoretical dose. When Flowlac-100 mixed with crystalline micronized lactose was used as a carrier, the emitted budesonide dose was close to the theoretical dose, and high RF % values were achieved but these changed during storage.

Budesonide↗
PubMed1998

Stability of a hydrophobic drug in presence of hydrous and anhydrous lactose.

The chemical stability of a hydrophobic Leukotriene receptor antagonist drug was investigated in the presence of lactose (both hydrous and anhydrous) under various humidity and temperature conditions. The effect of wet-granulation and direct-mixing on the stability of the drug was also studied. Mixtures of drug:lactose in the ratio 1:25, 1:50 and 1:100 were prepared and analyzed over a 6 week period after storage at 40, 83 and 97% RH (all at 25 degreesC) and 75% RH at 40 degreesC. The mixtures were subjected to LOD, Karl--Fischer titrimetry, HPLC and DSC analysis to evaluate the amount of moisture pickup, percent potency and presence of drug-moisture-lactose interaction. Mixtures containing lactose anhydrous picked up more moisture and exhibited greater drug degradation than those containing lactose hydrous. Also, mixtures stored under high temperature and humidity condition showed greater moisture uptake than those stored at high humidity alone. Lactose anhydrous becomes hydrated on exposure to high humidity/temperature and storage conditions. The transition state of lactose and not its stable state may be responsible for its greater interaction and subsequent degradation of the drug. Therefore, the normal belief that lactose anhydrous, which has less than 0.5% moisture, should provide greater stability as compared to lactose hydrous, needs to be properly evaluated.

Calorimetry, Differential Scanning↗
PubMed1976

A quantitation of the factors which affect the hydrolase and transgalactosylase activities of beta-galactosidase (E. coli) on lactose.

A study was implemented to quantitate the hydrolase and transgalactosylase activities of beta-galactosidase (E. coli) with lactose as the substrate and to investigate various factors which affect these activities. At low lactose concentrations the rate of galactose production was equal to the rate of glucose production. The rate of galactose production relative to glucose, however, dropped dramatically at lactose concentrations higher than 0.05 M and production of trisaccharides and tetrasaccharides began (galactose/glucose ratios of about 2:1 and 3:1, respectively, were found for these two types of oligosaccharides). At least five different trissacharides were formed and their patterns of formation showed that they probably utilized both lactose and allolactose as galactosyl acceptors. Allolactose was produced in amounts proportional to glucose at all lactose concentrations (ratios of allolactose/glucose were about 0.88). Analyses of various data, including a reaction analyzed at very early times, showed that the major means of production of allolactose (and the only means initially) was the direct enzymatic transfer of galactose from the 4 position to the 6 position of the glucose moiety of lactose without prior release of glucose from the enzyme. It was shown, however, that allolactose could also be formed in significant quantities by the transfer of galactose to the 6 position of free glucose, and also by hydrolysis of preformed trisaccharide. A mechanism which fits the initial velocity data was proposed in which the steps involving the formation of an enzyme-gallactose-glucose complex, the formation and breakage of allolactose on the enzyme, and the release of glucose all seem to be of roughly equal magnitude and rate determining. Various factors affected the amounts of transgalactosylase and hydrolase activities occurring. At high pH values (greater than 7.8) the transgalactosylase/hydrolyase activity ratio increased dramatically while it decreased at low pH values (less than 6.0). At mid pH values the ratio was essentially constant. The absence of Mg2+ caused a large decrease in the transgalactosylase/hydrolase activity ratio while the absence of all but traces of Na+ or K+ had no effect. The anomeric configuration of lactose altered the transgalactosylase/hydrolase activity ratios, alpha-Lactose resulted in a decrease of allolactose production (transgalactosylase activity) relative to hydrolase activities (glucose production) while beta-lactose had the opposite effect.

Chromatography, Gas↗
PubMedDate not supplied

Quantitative comparison of lactose and glucose utilization in Bifidobacterium longum cultures.

In batch cultures, Bifidobacterium longum SH2 has a higher final cell concentration and greater substrate consumption when grown on lactose versus glucose. Continuous cultures were used to compare lactose and glucose utilization by B. longum quantitatively. In the continuous culture, the estimated maintenance coefficients (m) were similar when on lactose and glucose; the maximum cell yield coefficient (Y(X/S)(max)) was higher on lactose; and the specific consumption rate of lactose (q(S)) was lower than that of glucose. Assuming that cell growth followed the Monod model, the maximum specific growth rates (mu(max)) and saturation constants (K(S)) in lactose and glucose media were determined using the Hanes-Woolf plots. The respective values were 0.40 h(-)(1) and 78 mg/L for lactose and 0.46 h(-)(1) and 697 mg/L for glucose. The kinetic parameters of the continuous cultures showed that B. longum preferred lactose to glucose, although the specific consumption rate of glucose was higher than that of lactose.

Bifidobacterium↗
PubMed1997

Determinants of lactose digestion in the miniature pig.

Although lactose is an important nutrient in the diet of the infant and child, the factors contributing to its digestion have not been clarified adequately. We sought to determine the degree to which lactase activity and small intestinal transit explain lactose digestion, the average error (SEE) in estimating lactose digestion using these parameters, and the effect of age. We compared lactose digestion from both a 7% lactose-containing formula and a solution by determining lactose in ileostomy output in pig littermates at 10 days, 4 weeks, and 10 weeks of age. The entire small intestinal mucosa was assayed for lactase specific activity (micromol x min-1 x g protein-1), total activity (micromol x min-1), and whole-villus lactase activity. Transit time (min), and transit rate (cm/min) were measured. Meal type did not affect lactose digestion. Lactose digestion was explained best by lactase specific activity (formula, R2 = 0.73, SEE = 1.1; solution, R2 = 0.69, SEE = 1.0; P < 0.001). The next best parameter was total transit rate (formula, R2 = 0.69, SEE = 2.0; solution, R2 = 0.46, SEE = 1.3). The relationship with lactase specific activity was age related and there appeared to be a critical value of lactase specific activity above which essentially all the lactose was digested.

Aging↗
PubMed2001

The effect of different concentrations of lactose powder on the airway function of adult asthmatics.

Lactose is widely used as a carrier of drugs in inhalation devices for asthmatic patients, but some clinicans have suspected that it may cause bronchoconstriction. Only a few studies have been done to examine this and the results are not uniform. This study was conducted to determine the effects of inhalation grade lactose delivered by Diskhaler on lung function and airway conductance in asthmatic subjects. The effect of five doses of lactose ranging from 6.25 mg to 100 mg and placebo were investigated using spirometry and constant volume plethysmography. Nineteen subjects (nine females) with stable asthma and a proven reversibility of at least 12% in forced expiratory volume in 1 sec (FEV) (compared to baseline) in the last 6 months, were included in this single-centre, randomized, placebo-controlled, double-blind, cross-over study. The subjects received placebo plus five doses of lactose on one study day and six doses of placebo on another study day. Both doses and study days were assigned in a random order, and intervals of 1 h were allowed between each dose and at least 36 h between study days. Specific airways conductance (sGaw) and FEV were measured periodically over the course of 1 h after each dose of lactose or placebo. Administration of lactose at four or eight times the concentration in the Diskus and Diskhaler dry powder inhalers did not result in any statistically significant changes in FEV1. sGaw also showed no statistical difference between lactose and placebo at 1 or 3 min post-dosing. Both placebo and lactose produced both dilatation and constriction of the airways in the same patients, with no consistency in direction and no dose-response relationship. No adverse effect of lactose on a rways conductance or FEV1 of stable asthmatic patients was found in this study when given at higher than normal clinical doses.

Adolescent↗
PubMed1993

Ileal pH and apparent absorption of magnesium in rats fed on diets containing either lactose or lactulose.

The hypothesis was tested that dietary lactose v. glucose stimulates Mg absorption in rats because lactose lowers pH of the ileal lumen, which improves Mg solubility which in turn enhances Mg availability for transport across the ileal epithelium. For comparison, the effects of lactulose were studied because it shares with lactose the characteristic of being poorly digestible. Replacement of glucose by lactose (100 g/kg) significantly stimulated apparent absorption of Mg. Apart from Mg absorption, lactulose also significantly enhanced absorption of Ca and phosphate. Lactose v. glucose lowered the pH of the ileal lumen from 7.5 to 7.2, whereas lactulose significantly reduced it to 7.0. In in vitro incubations a decrease in pH within the range of fluctuation in vivo was found to cause an improved solubility of Mg, and to a lesser extent also of Ca and phosphate. The smaller fall of ileal pH induced by feeding lactose instead of lactulose may explain why lactose improved Mg absorption only. For all individual rats combined there were negative relationships between ileal pH and apparent absorption of minerals, the relationship being strongest for Mg. Neither lactose nor lactulose was found to raise ileal solubility of minerals, which could relate to the possibility that the time of sampling was not appropriate. It is suggested that lactose-induced stimulation of Mg absorption in rats is caused by a lowering of ileal pH.

Animals↗
PubMed2000

13C-carbohydrate breath tests: impact of physical activity on the rate-limiting step in lactose utilization.

BACKGROUND: 13CO2 breath tests can be used to monitor carbohydrate digestion in the small intestine. However, after ingestion of 13C-substrates, 13CO2 excretion in breath originates from two sources: a digestive/oxidative fraction, derived from the small intestine, and a fermentation fraction, derived from undigested substrate spill-over in the colon. In this study, the determinants of the digestive/oxidative fraction were analysed in order to improve the sensitivity/specificity of the 13C-carbohydrate breath tests. METHODS: 13C-carbohydrate breath tests were performed in healthy adults using 13C-lactose, pre-digested 13C-lactose, 13C-glucose, and 13C-galactose as substrates. The effect of exercise (bicycling, 50 W), increasing the metabolism of digested/absorbed substrate, on the outcome of the test was analysed. RESULTS: In rest, no difference was observed in the 4-h cumulative percentage dose recovered in breath (4-h cPDR) after administration of glucose, pre-digested lactose, and lactose, which were 20.3 +/- 4.5%, 19.2 +/- 5.5%, and 19.9 +/- 4.9%, respectively. The 13CO2 excretion rate after 13C-galactose consumption was significantly slower than after 13C-glucose consumption. Exercise increased 4-h cPDR of 13C-glucose significantly: 76.0 +/- 1.0% vs. 22.7 +/- 2.3%. This effect was also observed using 13C-lactose as substrate: 66.1 +/- 6.2% vs. 19.6 +/- 3.9%. One subject had non-symptomatic lactose maldigestion indicated by a positive H2 breath test. The 13CO2 breath test of this subject in rest was indistinguishable from that of the others (4-h cPDR 16.6 vs. 19.6 +/- 3.9%), whereas the test was clearly indicative during exercise (4-h cPDR 20.5 vs. 66.1 +/- 6.2%). CONCLUSION: In healthy volunteers in rest, glucose oxidation is the rate-limiting step in lactose conversion into 13CO2. Increase of metabolism (for instance, by exercise) can shift this step to intestinal hydrolysis of lactose, making the 13C-lactose breath test more sensitive.

Adult↗
PubMed1990

Lactose absorption and consumption in Curaçao schoolchildren.

As an initial step to evaluate the school additional-nourishment program, which provides milk to schoolchildren, a study was conducted in the fall of 1984 on 729 black schoolchildren (aged 8-10 y) in Curaçao, for whom lactose consumption and absorption were determined. A food frequency questionnaire was used to determine lactose consumption, and a breath-hydrogen test was used to determine lactose absorption after a physiological load of 0.5 g lactose/kg body wt was administered in the form of standardized irradiated whole milk. An increase in breath-hydrogen of 20 ppm indicated lactose malabsorption; 14% of the children were malabsorbers of lactose. No relationship was found between lactose malabsorption and lactose consumption, as estimated from the questionnaire. Possible reasons for the lower-than-expected prevalence of lactose malabsorption in this population are the use of a physiological dose of lactose, and the fact that this population is well nourished and free from significant parasitism and other endemic diseases.

Absorption↗
PubMed1993

Adaptation of lactose maldigesters to continued milk intakes.

Twenty-five lactose-maldigesting and lactose-intolerant African Americans, ranging in age from 13 to 39 y, were given gradually increasing amounts of lactose in milk over a period of time until the maximum lactose dose tolerated was determined. Seventeen (77%) of the 22 subjects who completed the study tolerated > or = 12 g lactose and 5 (23%) tolerated < 12 g. Breath-hydrogen tests done on each subject with the maximum dose of lactose tolerated showed that only four (18%) had a breath-hydrogen concentration < 5 ppm above fasting concentration. This study suggests that the majority of African-American young adults who claim intolerance to moderate amounts of milk can ultimately adapt and tolerate > or = 12 g lactose in milk (the equivalent of 8 oz of full-lactose milk) with minimal or no discomfort if milk is ingested in gradually increasing amounts. The mechanism of adaptation is assumed to be an increased tolerance to colonic lactose-fermentation products.

Adaptation, Physiological↗
PubMed1998

Lactose maldigestion is not an impediment to the intake of 1500 mg calcium daily as dairy products.

BACKGROUND: A National Institutes of Health consensus conference concluded that a daily calcium intake of 1500 mg reduces the severity of osteoporosis. Because dairy products are the main natural source of dietary calcium, a diet providing 1500 mg Ca must contain large quantities of dairy products. However, it is widely believed that the lactose content of these products will not be tolerated by persons with lactose maldigestion (approximately 30% of the adult US population). OBJECTIVE: We evaluated the symptoms of lactose maldigestion and digestion when the diet was supplemented with dairy products providing 1300 mg Ca/d. DESIGN: Sixty-two women (31 with lactose maldigestion and 31 without) were studied in a double-blind, randomized protocol. Symptoms were compared during 1-wk periods when the diet was supplemented with 480 mL (2 cups) milk, 56 g cheese, and 240 mL yogurt provided as conventional products (34 g lactose/d) or as lactose-hydrolyzed products (2 g lactose/d). RESULTS: Women who digested lactose reported no significant difference in symptoms between the 2 treatment periods. Women with lactose maldigestion reported significantly increased flatus frequency and subjective impression of rectal gas during the period of high lactose intake; however, bloating, abdominal pain, diarrhea, and the global perception of overall symptom severity were not significantly different between the 2 treatment periods. CONCLUSION: The symptoms resulting from lactose maldigestion are not a major impediment to the ingestion of a dairy-rich diet supplying approximately 1500 mg Ca/d.

Adult↗
PubMed1976

Effect of dietary lactose at levels comparable to human consumption on cholesterol and bile acid metabolism of conventional and germfree rats.

In recent years, the use of milk products and the concomitant intake of lactose have been tentatively linked to the etiology of cardiovascular disease. An effect of lactose on the microbial modification of acid and neutral sterols has been suggested. In the present study lactose intake, ranging up to 30% of total diet increased beta-muricholic (beta-MC) but not cholic acid concentrations in conventional (CV) rat small intestine to the extent that at the 20% and 30% intake level, the intestinal cholic: beta-MC ratio approached that in germ-free (GF) rats. Total intestinal bile acid (BA) content increased by approximately 1/3, but remained at less than half the value found in GF rats. At lactose intake levels within a range corresponding to the consumption of dairy products often recommended for adult man (5% to 10%) only moderate changes in intestinal, and little change in fecal BA were found during and after the 3 months experimental period. Intestinal beta-MC was increased in the presence and in the absence of an intestinal microflora. Experiments with GF rats fed 10% lactose or 10% maltose indicated that this increase is evoked similarly by both carbohydrates. The slight increase in serum cholesterol levels seen with disaccharide feeding, which became evident only in the GF rats, was again not specific for lactose. No influence was found of lactose feeding on liver cholesterol values. Comparison of CV rats fed nonsterile and radiation-sterilized lactose-containing diets suggested that this mode of sterilization has only a minor influence on the resulting data. When GF experiments are to be incorporated, sterilazation of diet by irradiation with 3.5 to 4.0 X 10(6) Rad is preferable to autoclaving. The present data indicate that no major effect specifically related to a normal dietary intake of lactose on cholesterol and BA metabolism of the adult rat could be demonstrated for the duration of these experiments.

Animals↗
PubMed1998

In well-fed young rats, lactose-induced chronic diarrhea reduces the apparent absorption of vitamins A and E and affects preferentially vitamin E status.

To establish the effect of lactose-induced diarrhea on the apparent absorption and status of vitamins-A and E in well-fed young rats, we fed Sprague Dawley rats a balanced diet or a lactose diet (350 g/kg). A group of rats fed the control diet equal to the level measured in the lactose-fed rats (pair-fed) was also included. The experiment lasted 23 d and feces were collected on days 4-6, 10-12, 14-16 and 20-22. Samples of serum and tissues were taken on days 10 and 23. Lactose caused a significant reduction in food intake, had no effect on body weight and produced a diarrhea that persisted during the whole experiment. The severity of diarrhea decreased with time, indicating that the rats partially adapted to lactose feeding. At the onset of diarrhea, the apparent absorption of vitamins A and E in the rats with diarrhea was significantly lower than in the control or pair-fed rats, but the rats with diarrhea recovered gradually, and in the case of vitamin E was normalized by day 15. At day 10 the rats with lactose-induced diarrhea had serum and liver concentrations of vitamins A and E that did not differ from the control or pair-fed rats. However, at day 23 the lactose-fed rats with diarrhea had significantly lower serum and liver concentrations of vitamin E than the control or pair-fed rats. Measured at that time, diarrhea had no effect on liver vitamin A, but lower serum concentrations of this vitamin were detected in both the lactose-fed rats and in the pair-fed rats. In general, in well-nourished rats, the chronic diarrhea associated with excessive dietary lactose reduced the apparent absorption of vitamin A and E and particularly compromised the nutritional status of vitamin E.

Animals↗
PubMed1997

Measurement of the rate of entry of intact colon-derived lactose into the circulation: a model for assessing gut uptake of molecules not endogenously synthesized.

BACKGROUND: Results of in vitro studies have documented colonic absorption of lactose in the newborn. A stable isotope model was developed for assessing the entry rate of intact lactose into the portal circulation in newborn piglets. METHODS: In experiment 1, unlabeled and [D-1-(13C)]-lactose were infused into two separate mesenteric veins, and in experiment 2, labeled lactose was infused into a mesenteric vein and unlabeled lactose was infused into the colon. The 13C-enrichment of plasma lactose was assessed by high performance liquid chromatography gas chromatography combined with mass spectrometry. RESULTS: The isotopic estimate of the mesenteric venous infusion rate of lactose was 91% of the theoretical. In the second experiment 13% of the unlabeled lactose infused into the colon reached the portal circulation. CONCLUSIONS: The current study provides the first, direct, in vivo confirmation of colon absorption of intact lactose. The tracer model could be used to evaluate intestinal or colonic absorption of other organic compounds not endogenously synthesized, including vitamins or drugs.

Animals↗