Epigenetic Modulation of Intestinal Cholesterol Transporter Niemann-Pick C1-like 1 (NPC1L1) Gene Expression by DNA Methylation

Intestinal NPC1L1 transporter is essential for cholesterol absorption and the maintenance of cholesterol homeostasis in the body. NPC1L1 is differentially expressed along the gastrointestinal tract with very low levels in the colon as compared with the small intestine. This study was undertaken to examine whether DNA methylation was responsible for segment-specific expression of NPC1L1. Treatment of mice with 5-azacytidine (i.p.) resulted in a significant dose-dependent increase in NPC1L1 mRNA expression in the colon. The lack of expression of NPC1L1 in the normal colon was associated with high levels of methylation in the area flanking the 3-kb fragment upstream of the initiation site of the mouse NPC1L1 gene in mouse colon as analyzed by EpiTYPER® MassARRAY®. The high level of methylation in the colon was observed in specific CpG dinucleotides and was significantly decreased in response to 5-azacytidine. Similar to mouse NPC1L1, 5-azacytidine treatment also increased the level of human NPC1L1 mRNA expression in the intestinal HuTu-80 cell line in a dose- and time-dependent manner. Silencing the expression of DNA methyltransferase DNMT1, -2, -3A, and -3B alone by siRNA did not affect NPC1L1 expression in HuTu-80 cells. However, the simultaneous attenuation of DNMT1 and -3B expression caused a significant increase in NPC1L1 mRNA expression as compared with control. Also, in vitro methylation of the human NPC1L1 promoter significantly decreased NPC1L1 promoter activity in human intestinal Caco2 cells. In conclusion, our data demonstrated for the first time that DNA methylation in the promoter region of the NPC1L1 gene appears to be a major mechanism underlying differential expression of NPC1L1 along the length of the gastrointestinal tract.     

Understanding and modeling alternating tangential flow filtration for perfusion cell culture

Alternating tangential flow (ATF) filtration has been used with success in the Biopharmaceutical industry as a lower shear technology for cell retention with perfusion cultures. The ATF system is different than tangential flow filtration; however, in that reverse flow is used once per cycle as a means to minimize fouling. Few studies have been reported in the literature that evaluates ATF and how key system variables affect the rate at which ATF filters foul. In this study, an experimental setup was devised that allowed for determination of the time it took for fouling to occur for given mammalian (PER.C6) cell culture cell densities and viabilities as permeate flow rate and antifoam concentration was varied. The experimental results indicate, in accordance with D'Arcy's law, that the average resistance to permeate flow (across a cycle of operation) increases as biological material deposits on the membrane. Scanning electron microscope images of the post‐run filtration surface indicated that both cells and antifoam micelles deposit on the membrane. A unique mathematical model, based on the assumption that fouling was due to pore blockage from the cells and micelles in combination, was devised that allowed for estimation of sticking factors for the cells and the micelles on the membrane. This model was then used to accurately predict the increase in transmembane pressure during constant flux operation for an ATF cartridge used for perfusion cell culture. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1291–1300, 2014     

Reduction of the C2 and C4 vinyl groups of Sn-protoporphyrin to form Sn-mesoporphyrin markedly enhances the ability of the metalloporphyrin to inhibit in vivo heme catabolism

Sn (tin)-mesoporphyrin (Sn-protoporphyrin in which the vinyl groups at C2 and C4 have been reduced to ethyl groups) when incubated with rat splenic microsomal heme oxygenase proved to be a potent competitive inhibitor of enzyme activity in vitro, with a Ki of 0.014 microM. Sn-mesoporphyrin (1 mumol/kg body wt) also inhibited hepatic, renal, and splenic heme oxygenase activity in vivo in adult animals for extended periods of time. Sn-mesoporphyrin (1 mumol/kg body wt) prevented the transient increase in serum bilirubin 24 h after birth in the rat neonate and substantially reduced the levels of serum bilirubin in ALA (delta-aminolevulinic acid) induced hyperbilirubinemia in the 7-day-old suckling neonate. Tissue heme oxygenase activity was decreased in both animal models of hyperbilirubinemia. Sn-mesoporphyrin administration led to a prolonged increase in the heme saturation of hepatic tryptophan pyrrolase indicating an increase in the "heme pool" related to tryptophan pyrrolase and the compound also suppressed chemically induced hepatic porphyria. The administration of Sn-mesoporphyrin to bile duct-cannulated rats was followed by a prompt and sustained decrease in bilirubin output in bile. In addition the excretion of heme in bile was enhanced in these animals. These studies indicate that Sn-mesoporphyrin, like Sn-protoporphyrin, decreases serum bilirubin by inhibiting the production of bilirubin in vivo and its mode of action is through a sustained competitive inhibition of heme oxygenase. However, when a direct comparison of Sn-protoporphyrin and Sn-mesoporphyrin was made, these studies clearly established that the reduction of the C2 and C4 vinyl groups of the porphyrin macrocycle to ethyl groups increases the effectiveness of the Sn-mesoporphyrin derivative 10-fold or more as compared with Sn-protoporphyrin in inhibiting heme catabolism in the animal model systems examined. Thus alterations in the side chain substituents as well as of the central metal atom can influence in a significant manner the potency of the resultant synthetic heme analog as an agent capable of inhibiting heme degradation in vivo.     

LC-MS/MS in the Clinical Laboratory – Where to From Here?

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has seen enormous growth in clinical laboratories during the last 10-15 years. It offers analytical specificity superior to that of immunoassays or conventional high performance/pressure liquid chromatography (HPLC) for low molecular weight analytes and has higher throughput than gas chromatography-mass spectrometry (GC-MS). Drug/Toxicology and Biochemical Genetics/Newborn Screening laboratories were at the vanguard of clinical LC-MS/MS use, but have been eclipsed by Endocrine laboratories. In USA reference/referral laboratories, most steroids and biogenic amines are now assayed by LC-MS/MS, and the technology has started to penetrate into smaller laboratories. Assays for mineralo- and gluco-corticoids and their precursors, sex steroids, metanephrines and 25-hydroxy vitamin D highlight the advantages of LC-MS/MS.However, several limitations of LC-MS/MS have become apparent, centring on the interacting triangle of sensitivity - specificity - throughput. While sample throughput is higher than for conventional HPLC or GC-MS, it lags behind automated immunoassays. Techniques which improve throughput include direct sample injection, LC-multiplexing and samplemultiplexing. Measures to improve specificity and sensitivity include sample clean-up and optimising chromatography to avoid interferences and ion suppression due to sample-matrix components. Next generation instrumentation may offer additional benefits.The next challenge for clinical LC-MS/MS is peptide/protein analysis. The quest for multi-biomarker profiles for various diseases has largely failed, but targeted peptide and protein testing by LC-MS/MS, directed at analytical and clinical questions that need to be answered, is proving highly successful. We anticipate that this will result in similar growth of clinical protein/peptide LC-MS/MS as has been seen for low molecular weight applications.     

Invertebrate aspartyl/asparaginyl beta-hydroxylase: potential modification of endogenous epidermal growth factor-like modules.

An invertebrate alpha-ketoglutarate-dependent aspartyl/asparaginyl beta-hydroxylase, which posttranslationally hydroxylates specific aspartyl or asparaginyl residues within epidermal growth factor-like modules, was identified, partially purified and characterized. Preparations derived from two insect cell lines catalyzed the hydroxylation of the expected asparaginyl residue within a synthetic epidermal growth factor-like module. This activity was found to be similar to that of the purified mammalian aspartyl/asparaginyl beta-hydroxylase with respect to cofactor requirements, stereochemistry and substrate sequence specificity. Furthermore, recombinant human C1r, expressed in an insect cell-derived baculovirus expression system, was also found to be hydroxylated at the expected asparaginyl residue. Thus, these results establish the potential for invertebrate aspartyl/asparaginyl hydroxylation. Since several invertebrate proteins known to be required for proper embryonic development contain a putative consensus sequence that may be required for hydroxylation, the studies presented here provide the basis for further investigations concerned with identifying hydroxylated invertebrate proteins and determining their physiologic function.     

Echistatin is a potent inhibitor of bone resorption in culture

The venom protein, s-echistatin, originally derived from the saw-scaled viper Echis carinatus, was found to be a potent inhibitor of bone resorption by isolated osteoclasts. This Arg24-Gly25-Asp26-(RGD)-containing protein inhibited the excavation of bone slices by rat osteoclasts (IC50 = 0.1 nM). It also inhibited the release of [3H]proline from labeled bone particles by chicken osteoclasts (IC50 = 100 nM). By comparison, the tetrapeptide Arg-Gly-Asp-Ser (RGDS) inhibited resorption by rat or chicken osteoclasts with an IC50 of 0.1 mM while ala24-echistatin was inactive. Video microscopy showed that rat osteoclast attachment to substrate was more sensitive to s-echistatin than was the attachment of mononuclear cells or chicken osteoclasts. The difference in sensitivity of rat and chicken osteoclasts to s-echistatin may be due to differences between receptors on rat and chicken osteoclasts for s-echistatin. Antibody localization of echistatin on these cells showed much greater echistatin binding to rat osteoclasts than to chicken osteoclasts. Laser scanning confocal microscopy after immunohistochemical staining showed that s-echistatin binds to osteoclasts, that s-echistatin receptors are most abundant at the osteoclast/glass interface, and that s-echistatin colocalizes with vinculin. Confocal interference reflection microscopy of osteoclasts incubated with s-echistatin, demonstrated colocalization of s-echistatin with the outer edges of clusters of grey contacts at the tips of some lamellipodia. Identification of the echistatin receptor as an integrin was confirmed by colocalization of echistatin fluorescence with staining for an alpha-like subunit. Attachment of bone particles labeled with [3H]proline to chicken osteoclasts confirmed that the mechanism of action of echistatin was to inhibit osteoclast binding to bone presumably by disrupting adhesion structures. These data demonstrate that osteoclasts bind to bone via an RGD-sequence as an obligatory step in bone resorption, that this RGD-binding integrin is at adhesion structures, and that it colocalizes with vinculin and has an alpha-like subunit.     

Cycloart-25-en-2β-ol from Euphorbia nivulia

A new tetracyclic triterpene cycloart-25-en-3β-ol (9β,19-cyclolanost-25-en-3β-ol) and cyclolaudenol, have been isolated from Euphorbia nivulia.