LCT is the gene encoding for lactase, the enzymes needed to digest lactose, and therefore milk. In nature, most mammals loose the ability of digesting lactose after a certain age, but some human populations have evolve the ability of maintaining this enzyme even in adult age. It has been proposed that this adaptation is caused by a selective advantage to the early cattle breeded, who, thanks to the lactose mutation, were able to digest an additional source of protein. Recent studies have also confirmed genetical evidences for a selective sweep on this gene - e.g. (Bersaglieri et al 2004) found the presence of a extremely long homozygote haplotype in most north-european people, containing alleles that have been clinically demonstrated to be associated to the ability of digesting milk.

Disease relevance of LCT

• However, the subjects in group 2 (MCT) demonstrated an increase in glucose requirement to maintain euglycemia during the clamp after weight loss (delta 0.18 +/- 0.13 mmol.m-2.min-1) whereas subjects in group 1 (LCT) had a diminished requirement (delta -0.12 +/- 0.10, p = 0.036) [1].
• Elimination and hydrolysis of fat emulsions containing long-chain (LCT) or long- and medium-chain triglycerides (MCT, 50:50) were compared in eight patients with advanced chronic hepatic failure (CHF) and six healthy control subjects by using a two-stage constant infusion protocol [2].
• Elimination and hydrolysis of fat emulsions containing long-chain (LCT; Intralipid) or long- and medium-chain triglycerides (MCT; Lipofundin MCT) were compared in seven patients with acute renal failure (ARF) and six healthy control subjects [3].
• Because metabolic acidosis occurred with the LCT formula, the chloride content was adjusted to that of the MCT were confirmed and, in addition, there was a higher (P smaller than .01) percent retention of nitrogen (67.3 leads to 82.1) [4].
• CONCLUSION: LCT/MCT 1:1 mixtures are recommended in cases of acute pancreatitis and ARDS, even though infusion over a short period increases the metabolic demand [5].
• Our study demonstrate conclusively that the impairment of lactase enzymatic activity at the BBM of the enterocyte-like Caco-2 cells observed during rotavirus infection results from an inhibitory action of the secreted non-structural rotavirus protein NSP4 [6].

Psychiatry related information on LCT

• CONCLUSIONS: The satiation induced by intraduodenal LCT infusion seems to involve changes in gastric tone and plasma gut hormone levels [7].
• 2. Distortions in the EMG and motor activity pattern after LCT injection indicated venom effects on the crayfish nervous system [8].
• Breath hydrogen excretion in normal newborn infants in response to usual feeding patterns: evidence for "functional lactase insufficiency" beyond the first month of life [9].
• Mean plasma levels of beta-endorphin (beta EP), beta-lipotropin (beta LPH) and ACTH were significantly higher in 22 patients with primary affective disorders (PAD) and in 2 schizoaffective subjects off therapy since 10 days than in 22 age- and sex-matched healthy controls [10].

High impact information on LCT

• We conducted a genotype-phenotype association study in 470 Tanzanians, Kenyans and Sudanese and identified three SNPs (G/C-14010, T/G-13915 and C/G-13907) that are associated with lactase persistence and that have derived alleles that significantly enhance transcription from the LCT promoter in vitro [11].
• LPH hydrolyzes lactose into glucose and galactose [12].
• Sequence analyses of the coding and promoter regions of LCT, the gene encoding LPH, has revealed no DNA variations correlating with lactase non-persistence [12].
• An associated haplotype spanning LCT, as well as a distinct difference in the transcript levels of 'non-persistence' and 'persistence' alleles in heterozygotes, suggest that a cis-acting element contributes to the lactase non-persistence phenotype [12].
• When lactose and ethanol were given together, the rise in plasma galactose remained less than 5 mg per deciliter in 24 of the lactase-deficient subjects [13].

Chemical compound and disease context of LCT

• Medium-chain (MCT) and long-chain (LCT) triglyceride diets were compared during and after 4 or 12 wk of hypocaloric feeding in obese women to determine the effects on weight loss, ketones, nitrogen balance, and insulin action [1].
• CONCLUSIONS: The administration of LCT emulsion given at a slow rate did not alter arterial oxygenation because of the beneficial effect of a high cardiac output, hence offsetting the detrimental effect of increased O2 consumption [14].
• To evaluate clinical benefits either by a combination of carbohydrates and a medium-chain/long-chain triglyceride (MCT/LCT) lipid emulsion versus carbohydrates as the sole energy donor, 24 ventilated patients with multiple injuries and major head trauma were investigated [15].
• Lipid emulsions containing a physical mixture of medium and long chain triglycerides (MCT/LCT) are a well-proven concept in parenteral nutrition of critically ill patients [16].
• The diagnostic value of 1-14C-lactose breath test was compared with the standard lactose tolerance test and lactase assay in jejunal biopsies in 16 control subjects, 14 patients with lactase deficiency (LD) proven by lactase assay and 20 patients with irritable bowel syndrome (IBS) [17].

Biological context of LCT

• Two phenotypes exist in the human population with regard to expression of lactase in adults [18].
• Expression of Oct-1 stimulates reporter gene expression from the T and the C-13,910 variant/LPH promoter constructs only when it is co-expressed with HNF1alpha [18].
• Regional localization of the lactase-phlorizin hydrolase gene, LCT, to chromosome 2q21 [19].
• LCT is closely linked to D2S44, with a lod score of 30.6 at theta = 0.10 [19].
• RESULTS: LCT-MUFA (3 mmol/L) did not alter the N-formyl-Met-Leu-Phe (FMLP)-induced rise in [Ca(2+)](i), oxidative burst, chemotaxis, and elastase release, whereas LCT-MCT decreased [Ca(2+)](i) and chemotaxis and increased oxidative burst [20].

Anatomical context of LCT

• The gene LCT which codes for the intestinal disaccharidase lactase-phlorizin hydrolase has previously been mapped, using somatic cell hybrids and linkage analysis, using the CEPH families, to chromosome 2 [19].
• CONCLUSIONS: LCT-MUFA showed lower in vitro and in vivo impact on neutrophil function compared with LCT and LCT-MCT [20].
• LPS (1 mug/mL)-induced increase in leukocyte rolling flux, adhesion, and emigration was inhibited by LCT and LCT-MCT but unaffected in LCT-MUFA-treated rats [20].
• Transcription of the lactase gene is activated during enterocyte differentiation [21].
• We report the primary structures of human and rabbit brush border membrane beta-glycosidase complexes (pre-pro-lactase-phlorizin hydrolase, or pre-pro-LPH, EC 3.2.1.23-62), as deduced from cDNA sequences [22].

Associations of LCT with chemical compounds

• Lactase non-persistence (adult-type hypolactasia and lactose intolerance) is characterized by a decline in the expression of lactase-phlorizin hydrolase (LPH) after weaning [18].
• Immunohistochemistry showed LPS-induced increase in P-selectin expression attenuated by LCT and LCT-MCT but not LCT-MUFA [20].
• LPH alpha, which is rich in cysteine and hydrophobic amino acid residues, may fold rapidly into a tight and rigid globular domain in which carbohydrate attachment sites are no longer accessible to glycosyltransferases [23].
• During infusion of THL or SPE, the effects were smaller than during LCT or MCT [24].
• The different effects of long chain (LCT) and medium chain (MCT) triglyceride ingestion on perception, gastric relaxation, and hormonal release may help to elucidate the mechanisms underlying nutrient induced sensations [7].

Physical interactions of LCT

• T-13910 DNA variant associated with lactase persistence interacts with Oct-1 and stimulates lactase promoter activity in vitro [18].
• EMSAs demonstrated that PDX-1 can interact with the lactase promoter binding site but not with a site in which the core PDX-1 binding sequence TAAT is mutated [25].
• The LPH promoter contains binding sites that mediate activation by members of the GATA-4, -5, and -6 subfamily, but little is known about their individual contribution to LPH regulation in vivo [26].

Regulatory relationships of LCT

• This study aimed to determine the role of PDX-1 in regulating lactase gene promoter activity in intestinal epithelial cells [25].
• The D3 clone and other sublines with intrinsic lactase activities greater than 100 nmol/mg/min expressed a class of high-affinity EGF receptors (e.g., D3 cells had 3.48 X 10(4) EGF receptors/cell with a kd of 0.61 nM) [27].

Other interactions of LCT

• The data suggest that the binding of Oct-1 to the T-13,910 variant directs increased lactase promoter activity and this might provide an explanation for the lactase persistence phenotype in the human population [18].
• In the human LPH promoter, an intact HNF-1 binding site was required for functional synergy [28].
• Given the contrasting spatial expression pattern, PDX-1 may function to specify the anterior boundary of lactase expression in the small intestine and is thus a candidate regulator of anterior spatial restriction in the gut [25].
• LCT-MUFA did not alter apoptosis, but LCT increased apoptosis in absence and presence of GM-CSF [20].
• This analysis placed DPP4 between LCT and GAD in bands q21 to q31 [29].

Analytical, diagnostic and therapeutic context of LCT

• Sequence analysis of the complete region and subsequent association analyses revealed that a DNA variant, C/T-13910, roughly 14 kb upstream from the LCT locus, completely associates with biochemically verified lactase non-persistence in Finnish families and a sample set of 236 individuals from four different populations [12].
• We describe here the regional localization of LCT to chromosome 2q21 by polymerase chain reaction (PCR) analysis of somatic cell hybrids and in situ hybridization [19].
• We further examined the LPH mRNA of a hypolactasic subject by S1 mapping and by sequencing a set of overlapping PCR products produced from cDNA templates [30].
• Site-directed mutagenesis of the PDX-1 core binding site in the lactase promoter-reporter construct suggests that PDX-1 can function independently of DNA binding to its consensus binding site [25].
• METHODS: In a double-blind study, 15 healthy subjects were studied on 5 occasions during which LCT or MCT emulsions (2 kcal/min), with or without 120 mg tetrahydrolipstatin (THL, lipase inhibitor), or sucrose polyester (SPE, nondigestible fat) were infused intraduodenally in randomized order [24].

References