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PubMed1997

Topology of allosteric regulation of lactose permease.

Sugar transport by some permeases in Escherichia coli is allosterically regulated by the phosphorylation state of the intracellular regulatory protein, enzyme IIAglc of the phosphoenolpyruvate:sugar phosphotransferase system. A sensitive radiochemical assay for the interaction of enzyme IIAglc with membrane-associated lactose permease was used to characterize the binding reaction. The binding is stimulated by transportable substrates such as lactose, melibiose, and raffinose, but not by sugars that are not transported (maltose and sucrose). Treatment of lactose permease with N-ethylmaleimide, which blocks ligand binding and transport by alkylating Cys-148, also blocks enzyme IIAglc binding. Preincubation with the substrate analog beta-D-galactopyranosyl 1-thio-beta-D-galactopyranoside protects both lactose transport and enzyme IIAglc binding against inhibition by N-ethylmaleimide. A collection of lactose permease replacement mutants at Cys-148 showed, with the exception of C148V, a good correlation of relative transport activity and enzyme IIAglc binding. The nature of the interaction of enzyme IIAglc with the cytoplasmic face of lactose permease was explored. The N- and C-termini, as well as five hydrophilic loops in the permease, are exposed on the cytoplasmic surface of the membrane and it has been proposed that the central cytoplasmic loop of lactose permease is the major determinant for interaction with enzyme IIAglc. Lactose permease mutants with polyhistidine insertions in cytoplasmic loops IV/V and VI/VII and periplasmic loop VII/VIII retain transport activity and therefore substrate binding, but do not bind enzyme IIAglc, indicating that these regions of lactose permease may be involved in recognition of enzyme IIAglc. Taken together, these results suggest that interaction of lactose permease with substrate promotes a conformational change that brings several cytoplasmic loops into an arrangement optimal for interaction with the regulatory protein, enzyme IIAglc. A topological map of the proposed interaction is presented.

Allosteric Regulation↗
PubMed1966

Delayed lactose fermentation by enterobacteriaceae.

Goodman, R. E. (University of California, Los Angeles), and M. J. Pickett. Delayed lactose fermentation by Enterobacteriaceae. J. Bacteriol. 92:318-327. 1966.-When 171 Citrobacter freundii strains and 14 Paracolobactrum arizonae strains examined, 51 of the C. freundii strains and 13 of the P. arizonae strains were found to be delayed or negative lactose fermenters. Of the slow fermenters, 65% yielded rapidly fermenting mutants in cultures undergoing delayed fermentation. Lactose fermentation could generally be hastened by increasing lactose concentrations. Many organisms which fermented lactose slowly grew readily on a medium containing lactose as the sole carbon source. Regardless of their ability to ferment lactose, all strains of C. freundii and P. arizonae investigated could be shown to possess beta-galactosidase. Delayed fermenters failed to take up lactose from the culture medium, whereas prompt fermenters did so readily. The beta-galactosidases of 12 strains of enteric bacteria were studied in crude cell extracts with respect to specific activity, stability, and activity at varying substrate (o-nitrophenyl-beta-d-galactopyranoside) concentrations, at varying pH, and in the presence of sodium, potassium, and magnesium. The widely varying specific activities and the approximate similarity of the Michaelis constants (about 2 x 10(-4)m) suggested that the strains investigated produced differing amounts of beta-galactosidase. Moreover, qualitative differences in the enzymes provided evidence that these strains synthesized different molecular forms of beta-galactosidase. The results suggested that organisms which ferment lactose only after a prolonged delay do so because they possess multiple defects in their lactose-metabolizing machinery.

Journal Article↗
PubMed2002

Lactose intolerance: a risk factor for reduced bone mineral density and vertebral fractures?

BACKGROUND: The purpose of the present study was to determine differences, if any, in bone mineral density, the risk of fracture, and clinical behavior in patients with lactose intolerance investigated by hydrogen breath test. METHODS: The study population (n = 218; age, mean +/- SD, 58.2 +/- 11.5 years) consisted of 103 healthy individuals negative hydrogen breath test (Delta H2 0-20 ppm; group I), and 115 individuals with evidence of lactose intolerance according to the hydrogen breath test (Delta H2 > 20 ppm), of whom 40 individuals had test results of 20 ppm < Delta H2 < 59 ppm (group II). The remaining 75 individuals were strongly positive on the hydrogen breath test (Delta H2 > 60 ppm; group III). The entire study population was measured for bone mineral density in the nondominant forearm and in the vertebra (quantitative computed tomography [qCT]). Radiographs of the spine were studied for fractures. RESULTS: In healthy individuals, bone mineral density in the vertebra assessed by qCT (mean +/- SD, 111.2 +/- 31 mg/cc) did not significantly differ between those with mild (qCT, mean +/- SD, 109.8 +/- 35 mg/cc) and those with severe (qCT, mean +/- SD, 107.7 +/- 36 mg/cc) lactose intolerance. Lactose-intolerant individuals had more vertebral fractures per patient when compared with those with mild lactose intolerance or controls ( P < 0.05). Considering vertebral and self-reported non-vertebral fractures, no statistically significant differences were found. In the entire group, the overall occurrences of fracture in the presence of lactose intolerance and in controls were comparable after correction for age and body mass index (BMI). CONCLUSIONS: Individuals with lactose intolerance verified by the hydrogen breath test appear not to be at risk for accelerated bone loss. Nevertheless, a relationship between vertebral fractures and an apparent lactose intolerance cannot be excluded, as a few individuals with severe lactose intolerance had a large number of vertebral fractures.

Absorptiometry, Photon↗
PubMed2001

Nutritional supplements used in weight-reduction programs increase intestinal gas in persons who malabsorb lactose.

OBJECTIVE: To determine if ingestion of 2 doses of milk-based dietary supplements produce gaseous symptoms in subjects who malabsorb lactose. DESIGN: Randomized, controlled, crossover trial. SUBJECTS/SETTING: Ten community-based subjects who malabsorb lactose. INTERVENTION: Ingestion of 2 standard servings of milk-based supplements (a powder reconstituted in fat-free milk or a ready-to-drink preparation) or low-lactose control preparations. MAIN OUTCOME MEASURES: Frequency of flatus passage and subjective impression of bloating, flatulence, and abdominal discomfort. STATISTICAL ANALYSIS: Wilcoxon signed-rank test. RESULTS: The high lactose content (27 g) of 2 servings of the powder-based supplement ingested without other food resulted in a marked increase in daily flatus passages from the basal level of 9.7+/-8.2 to 30+/-14 (mean+/-SD), and a significant increase in the subjects' perception of gas. In contrast, the lower lactose content (18.4 g) of 2 servings of a ready-to-drink supplement resulted in a flatus frequency of 17+/-10 (P=.14 vs baseline) and no significant increase in the perception of increased gas. Neither supplement resulted in a significant increase in bloating, abdominal pain, or diarrhea. The lactose content of the liquid supplement was reduced by 80% following overnight incubation with an over-the-counter lactase preparation. APPLICATIONS/CONCLUSIONS: Persons who malabsorb lactose should be aware that sizable increases in rectal gas commonly occur when milk-based powders reconstituted in milk are used as meal replacements. In contrast, gas problems probably will be minor following ingestion of 2 doses of a ready-to-drink, milk-based supplement. The lactose content of these supplements can be markedly reduced by overnight incubation with over-the-counter lactase preparations, and this manipulation should be beneficial for subjects troubled by the increased gas caused by the consumption of lactose-containing supplements.

Abdominal Pain↗
PubMed1998

Allaying fears and fallacies about lactose intolerance.

Public awareness and misunderstandings of lactose intolerance are at an all-time high. Many people erroneously believe they are lactose intolerant or develop gastrointestinal symptoms after intake of lactose. Consequently, lactose-containing foods such as milk and other dairy foods may be eliminated unnecessarily from the diet. Because these foods are a major source of calcium, low intake of them can compromise calcium nutriture. This, in turn, can increase the risk of major chronic diseases such as osteoporosis (porous bones) and hypertension. This review is intended to help dietetics professionals alleviate clients' fears about lactose intolerance and recommend dietary strategies to improve tolerance to lactose. Scientific findings indicate that the prevalence of lactose intolerance is grossly overestimated. Other physiologic and psychologic factors can contribute to gastrointestinal symptoms that mimic lactose intolerance. Scientific findings also indicate that people with laboratory-confirmed low levels of the enzyme lactase can consume 1 serving of milk with a meal or 2 servings of milk per day in divided doses at breakfast and dinner without experiencing symptoms. Several dietary strategies are available to help lactose maldigesters include milk and other dairy foods in their diet without experiencing symptoms.

Anxiety↗
PubMed1995

Lactose intolerance and bone mass in postmenopausal Italian women.

Previous studies on the role of lactose malabsorption in the pathogenesis of postmenopausal osteoporosis have yielded conflicting results and further information is needed. To date, all studies have been carried out on populations with a low prevalence of lactose malabsorption and the lactose intestinal absorptive capacity was tested using a non-physiological dose of lactose. In fifty-eight Italian postmenopausal women (mean age 57 (SD 7) years), bone mineral density (BMD) at lumbar spine, H2 breath response after ingestion of 20 g lactose, intensity of symptoms of intolerance after a lactose load and daily Ca intake were evaluated. No differences were found between women with or without a positive H2 breath test with regard to BMD (-1.2 (SD 0.9) v. -0.9 (SD 0.8)) and Ca intake (509 (SD 266) v. 511 (SD 313) mg/d). On the contrary, both BMD and Ca intake were significantly lower in women with lactose malabsorption and symptoms of intolerance (-1.5 (SD 0.7) and 378 (SD 220) mg/d) than in those with malabsorption without symptoms (-0.9 (SD 0.9) and 624 (SD 254) mg/d). Moreover, in lactose malabsorbers Ca intake was correlated inversely with symptom score (rs -0.31, P < 0.05) and positively with BMD (rs 0.42, P < 0.005). Our results show that in Italian postmenopausal women Ca intake and BMD are not influenced directly by lactose malabsorption; the appearance of symptoms of intolerance seems to influence BMD unfavourably through a reduced Ca intake.

Bone Density↗
PubMed2000

Temperature of a test solution influences abdominal symptoms in lactose tolerance tests.

In lactose maldigesters, retarding gastric emptying (food/pharmaceuticals) improves tolerance to lactose. The role of temperature of test solution on the indicators of lactose intolerance was studied. After an overnight fast, 10 lactose maldigesters ingested, in three sessions, 50 g lactose in a randomized cross-over trial. The solutions were at temperatures of 20-21 degrees C (room temperature), 2-3 degrees C (cold) and 55-58 degrees C (hot). Gastrointestinal symptoms and indicators measuring lactose absorption were recorded. Abdominal pain was noticeably increased by the modification of temperature. The cold solution reduced flatulence and abdominal bloating, whereas the hot solution increased bloating and borborygmi. Breath hydrogen excretion tended to be augmented and retarded after cold solution. The temperature of the solution used in a lactose tolerance test affects the gastrointestinal symptoms, but has only minor effects on the other indicators of lactose maldigestion. The constant tendencies observed suggest that a room temperature solution is to be recommended for testing lactose digestion.

Abdomen↗
PubMed1978

Respiratory hydrogen excretion as a parameter for lactose malabsorption in children.

Respiratory hydrogen excretion was measured during tolerance tests with lactose, glucose plus galactose, and skim milk in 52 children, 4 to 15 years of age. Ten children appeared to be lactose-malabsorbers, as reflected by increased respiratory hydrogen excretion after administration of 2 g lactose per kilogram, maximum 50 g. Skim milk, equivalent to 0.5 g lactose per kilogram was administered to all lactose-malabsorbers. Eight children were tolerant and two children were "intolerant" for this physiological amount of lactose when administered as skim milk. Disaccharidase activities of jejunal biopsies were determined in all 10 children with lactose malabsorption. Lactase activity was deficient in nine children and normal in one child. The increase of blood glucose during the lactose tolerance test did reflect lactose malabsorption less accurately than the respiratory hydrogen excretion.

Adolescent↗
PubMed1985

Dietary manipulation of postprandial colonic lactose fermentation: I. Effect of solid foods in a meal.

The effect of adding solid foods--cornflakes, banana and hard-boiled egg--to a meal with 360 ml of intact milk containing 18 g of lactose was investigated in 13 lactose-malabsorbers and 10 lactose-absorbers chosen from 36 Guatemalan adults screened for their capacity to digest and absorb completely the lactose in this volume of milk. A six-hour hydrogen breath test was used as the index of carbohydrate absorption. Minimal breath H2 was excreted by lactose-absorbers with either the intact milk alone, the intact milk with solid foods, or lactose-prehydrolyzed milk with solids. In lactose-malabsorbers, however, the 6-h excretion of H2 with intact milk plus solid food was intermediary between milk alone and prehydrolyzed milk with solids. A relative net reduction of 47% in lactose malabsorption was produced by adding food, and the peak-rise in breath H2 was delayed by 2 hours. A physiological consequence of taking solid foods along with milk is a slower rate of colonic fermentation, and this may be the basis for reducing gastro-intestinal symptoms in lactose-intolerant malabsorbers.

Adult↗
PubMed2006

Lactose intolerance symptoms assessed by meta-analysis: a grain of truth that leads to exaggeration.

A meta-analysis was conducted to compare the lactose intolerance symptoms of lactose maldigesters after consuming lactose (as milk, lactose dissolved in water, milk products, or commercial product) with responses after a placebo under masked conditions. An English language MEDLINE search was conducted using the medical subject heading of "lactose intolerance" from 1966 to January 2002. From an initial 1,553 citations, 2 independent reviewers selected 21 studies based on study design (randomized, crossover, blind) and use of an amount of lactose likely to be found in a meal (7-25 g) and a placebo among subjects free of gastrointestinal problems and >4 years old. Mean severity of symptom responses were analyzed as standardized differences, and the presence or absence of a symptom was estimated as pooled incidence differences (ID). For severity of flatulence, the standardized difference was 0.18 (95% confidence interval [CI] -0.16 to +0.52). The CIs for abdominal bloating and pain, degree of diarrhea, frequency of bowel movements per day, and frequency of diarrhea per day also included 0. For abdominal bloating, the ID was 5.9 more people per 100 with symptoms after lactose than placebo (CI -0.07 to +0.19). This same nonsignificant relationship was found for abdominal pain. The ID for diarrhea or loose stools was 0.15 (CI 0.03 to 0.28). Although the incidence of diarrhea was significantly higher, the size of the effect was very small. The results indicate that lactose is not a major cause of symptoms for lactose maldigesters following usual intakes of dairy foods, that is, 1 cup.

Abdominal Pain↗
PubMed1984

Calcium absorption and acceptance of low-lactose milk among children with primary lactase deficiency.

A calcium absorption investigation was carried out with the purpose of determining whether lactose-hydrolyzed milk facilitates calcium absorption in subjects with lactose malabsorption. Nine children participated in the study, which was divided into two investigation periods separated by at least 1 week. During the first period the children were given a lactose-free diet, whereas during the second period their diet contained lactose-hydrolyzed milk. The amount of calcium, number of calories, and rotation of specifically defined meals in the diet during the two periods were identical, and the children functioned as their own controls. We found calcium absorption to be significantly higher with the diet containing hydrolyzed milk than with the lactose-free diet supplemented with extra calcium (p less than 0.05). During the study a double-blind lactose intolerance test was performed. The children had significantly fewer clinical symptoms and signs, such as abdominal pain, borborygmus, meteorism, and defecations, within 24 h after drinking 0.5 L of lactose-hydrolyzed milk as compared with drinking ordinary milk (25 g of lactose). None of the children experienced any unpleasant side effects when consuming the lactose-hydrolyzed milk (approximately 94% degree of hydrolysis) during the study period. All the children liked the hydrolyzed milk because it had a pleasant, sweet flavor as a result of the increased content of glucose.

Adolescent↗
PubMed2004

Deadaption and readaptation with lactose, but no cross-adaptation to lactulose: a case of occult colonic bacterial adaptation.

The standard 3 h breath hydrogen (3hBH2) test distinguishes lactose maldigesters from lactose digesters. However, multiple factors impact on BH2 and care is needed to exclude a priori variables. When these factors are controlled, a negative BH2 test implies lactase persistent status or lactase nonpersistent status with colonic adaptation. A case of a Sicilian man who tested negative (lactase persistent status confirmed) on an initial 50 g lactose challenge is described. It was observed that he consumed 28.1 g lactose/day before testing. He subsequently underwent five additional challenge tests in the course of the next 10 months. In four tests the dose intake of lactose was varied upon instruction, and in the fifth test a 30 g lactulose challenge was carried out. It was demonstrated that on radically decreasing lactose intake, a full lactase nonpersistent status was unmasked. Output of 3hBH2 varied inversely with daily lactose intake. Finally, at a time when he was readapted to lactose, there was no discernible adaptation to lactulose challenge. It was concluded that 'occult' colonically adapted subjects may contribute to negative BH2 tests. There is a relationship between variation in lactose intake and the results of BH2 testing. Finally, there was no cross-adaptation to lactulose challenge when lactose was used as the adapting sugar.

Adaptation, Physiological↗
PubMedDate not supplied

Effect of a lactase preparation on lactose content and osmolality of preterm and term infant formulas.

Lactose intolerance due to lactase deficiency often follows acute gastroenteritis. In such situations, a lactose-free formula may be indicated for preterm infants. Therefore, the effect of addition of lactase on the lactose content and osmolality of preterm and term infant formulas was studied. Lactose content of formulas at room temperature was decreased by approximately 50% 1 hour after addition of lactase. Concentration of lactose was reduced by 70% or more after 2 hours in all formulas. Because of the higher initial lactose concentration in term formulas, it took 24 hours to reach the same absolute lactose concentration (10 g/kg formula) found in preterm formulas after 2 hours. There was a moderate increase in osmolality in preterm formulas. The increase was greater in term formulas because of the greater initial concentration of lactose. The addition of lactase appears to be a suitable method for reduction of lactose content of preterm and term formulas, although the increase in osmolality of term formulas may preclude their clinical use.

Diarrhea↗
PubMed1988

Incidence and clinical significance of lactose malabsorption in adult coeliac disease.

Fifty-one adult patients with coeliac disease, verified by a proximal small-intestinal biopsy, were investigated. Before treatment with a gluten-free and low-lactose diet 52% showed a slight rise in blood glucose during the lactose tolerance test. Seventy-nine per cent of these patients had watery stools, and 88% had three or more bowel movements a day--statistically significantly different from the coeliac patients with a normal lactose tolerance test. After treatment 12% had a flat lactose tolerance curve. Half of them (6%) had specific lactase deficiency. This is approximately the incidence of lactose malabsorption in the general Danish population. The small-intestinal disaccharidases and alkaline phosphatase levels were severely depressed before treatment. After treatment the activities increased, but not to normal. We conclude that lactose malabsorption is a clinically important condition in many patients with untreated coeliac disease, giving rise to more frequent and more watery stools. In well-treated coeliac disease lactose malabsorption is not commoner than in the general population. The lactose activity in a proximal intestinal biopsy specimen was found to be an unreliable indicator of lactose malabsorption in coeliac disease.

Adolescent↗
PubMedDate not supplied

[Lactose malabsorption diagnosis with H2 breath test].

One hundred and five healthy subjects under investigation for lactose malabsorption were enrolled in this prospective study. After an overnight fast, breath was collected immediately before and every 15 minutes for three hours after an oral administration of 50 g lactose dissolved in 200 mL of water (lactose overload). Blood samples were also collected before and 20, 40 and 60 minutes after the lactose overload for blood glucose determination. Expired H2 was measured by gas chromatography using a Quintron Microlyser and the maximum increase in H2 (delta-H2) was calculated. The area under the curve (ASC-H2) was also calculated using the trapezoid model. Lactose malabsorption was defined as a maximum increase in blood glucose (delta-G) under 18 mg%. The sensibility (S), specificity (E) and accuracy (A) of the H2 determination was analyzed using (a) linear regression [log (ASC-H2) = 4.034-0.029. delta-G], (b) receiver operating curve (ROC) and by (c) Q-Q plot of the cubit root transformation of the ASC-H2 values. Our results demonstrate that ASC-H2, but not delta-H2, correlates with delta-G, suggesting that the measurement of maximum increase in H2 expired following a lactose overload is not reliable for the diagnosis of lactose malabsorption. The cutoff value for the ASC-H2 using linear regression was 3260 (S = 89.3%, E = 80% and A = 86.7%), while using ROC it was 3353 (S = 88.0%, E = 80.0% and A = 85.7%) and while using Q-Q plot method it was 2936 (S = 92.0%, E = 80.0% and A = 88.6%). When the cutoff value was set to 3000, the sensibility, specificity and accuracy were 90.7%, 80.0% and 88.6%, respectively. We conclude that the calculation of the ASC-H2, but not delta-H2, following a lactose overload is reliable in detecting lactose malabsorption and can be used in the clinical practice.

Blood Glucose↗
PubMed1975

A genetic study of lactose digestion in Nigerian families.

The ability to digest orally administered lactose was determined in individuals representing a number of Nigerian ethnic groups. The data are mainly presented as family pedigrees. In those families where both parents were unable to digest lactose, all of the progeny were lactose nondigestors. If one parent, usually of Northern garopena origin or of the Fulani tribe, could digest lactose, then the progeny contained some or all individuals who were capable of digesting the disaccharide. There was no difference in the results when either the mother or the father was the lactose digestor. Ten families were studied where one parent was of Europena or Yoruba-European origin (lactose digestor) while the other was proper Yoruba 0lactose nondigestor). From these matings, there were 18 lactose digestors and 11 lactose nondigestors. We have concluded that the ability to digest lactose is transmitted as an autosomal dominant and represents the mutated gene or a polymorphism.

Adult↗
PubMed1999

[Effect of exogenous lactase on the absorption of lactose and its intolerance symptoms].

The objective of this study was to evaluate the effects of lactase on lactose malabsorption and its intolerance symptoms, as well as the available way to improve lactose absorption. Healthy adults with a history of lactose intolerance were screened by 25 g lactose tolerance test. The individuals with higher H2 expired and/or lactose intolerance symptoms were selected as the subjects. Subjects were challenged twice with "400 ml low fat milk" and "400 ml low fat milk + 9000Fcc lactase" separately in 3 days interval. The breath H2 concentration and intolerance symptoms were tested in 4 hours after the challenge. The results showed that exogenous lactase can significantly decrease the incidence of lactose malabsorption (the abnormal expiration of H2 decreased from 100% to 48.9%) and milk intolerance symptoms(from 51.1% to 13.3%). The results from this study demonstrate that lactose malabsorption and intolerance symptoms are resulted from the reduced enzyme activities of individuals, and the exogenous lactase can improve lactose absorption and intolerance symptoms. Lactose supplementation may be an available way to increase the dairy consumption and promote health of people.

Adolescent↗
PubMed1985

Lactose absorption and malabsorption in healthy Italian children: do the quantity of malabsorbed sugar and the small bowel transit time play roles in symptom production?

Using breath hydrogen analysis after an oral lactose load (2 g/kg; maximum 50 g), we investigated the prevalence of lactose malabsorption in 61 healthy Italian children aged 6-13 years. We also examined the relationship between symptoms and small bowel transit time and the degree of sugar malabsorption. Three of 61 subjects produced no H2 after both lactose and lactulose load and thus were eliminated at the outset. Lactose malabsorption was defined as excretion of greater than 20 ppm H2. Lactose intolerance was classified as mild (colicky pain, flatulence, abdominal distension, borborygmi) or severe (diarrhea). The frequency of lactose malabsorption in the children aged 6-8 years (group I) was 25%; in the children aged 8-11 years (group II), it was 35%, and in the children aged 11-13 years (group III) 56%. The differences in frequency between the first and the third groups were significant (p = 0.05). Three of 20 (15%) in group I, two of 20 (10%) in group II, and three of 18 (17%) in group III were classified not only as lactose malabsorbing, but also as lactose intolerant, with symptoms during and after the test. We found no difference in the small bowel transit times or in the quantities of malabsorbed lactose in symptomatic and asymptomatic malabsorbing subjects. Other factors that may play a role in symptom production are discussed.

Adolescent↗