Chenodeoxycholic acid stimulated fibroblast growth factor 19 response - a potential biochemical test for bile acid diarrhoea

BACKGROUND

Bile acid diarrhoea is underdiagnosed and better diagnostic tests are needed. Fasting serum fibroblast growth factor-19 (FGF19) has insufficient diagnostic value, but this may be improved by stimulation.

AIM

To explore if an impaired FGF19 response identifies primary bile acid diarrhoea.

METHODS

Eight patients with primary bile acid diarrhoea and eight healthy volunteers ingested (i) a meal plus 1250 mg chenodeoxycholic acid (CDCA), (ii) 1250 mg CDCA or (iii) the meal. Blood was sampled at fasting and repeatedly after stimulation. We analysed FGF19 by enzyme-linked immunosorbent assay and bile acids including 7α-hydroxy-4-cholesten-3-one by liquid chromatography-tandem mass spectrometry.

RESULTS

Stimulation with the meal plus CDCA increased median FGF19 in healthy volunteers from fasting 62 pg/mL [interquartile range (IQR): 41-138] to 99 pg/mL (IQR: 67-147; P = 0.012) after 90 min and peaked after 150 min at 313 pg/mL (IQR: 54-512). This response was impaired in primary bile acid diarrhoea patients [fasting 56 pg/mL (IQR: 42-79); 90 min: 48 pg/mL [IQR: 37-63); 150 min: 57 pg/mL (48-198)]. Receiver operating characteristics (ROC_AUC ) for fasting FGF19 was 0.55 (P = 0.75) and at 90 min 0.84 (P = 0.02). The difference in FGF19 from fasting to 90 min after the meal plus CDCA separated the groups (ROC_AUC 1.0; P = 0.001). 7α-hydroxy-4-cholesten-3-one was elevated in primary bile acid diarrhoea (P = 0.038) and not significantly affected by stimulation.

CONCLUSIONS

The FGF19 response following chenodeoxycholic acid plus meal is impaired in primary bile acid diarrhoea. This may provide a biochemical diagnostic test.

The gut microbiota, bile acids and their correlation in primary sclerosing cholangitis associated with inflammatory bowel disease

Background

Patients with primary sclerosing cholangitis associated with inflammatory bowel disease (PSC-IBD) have a very high risk of developing colorectal neoplasia. Alterations in the gut microbiota and/or gut bile acids could account for the increase in this risk. However, no studies have yet investigated the net result of cholestasis and a potentially altered bile acid pool interacting with a dysbiotic gut flora in the inflamed colon of PSC-IBD.

Aim

The aim of this study was to compare the gut microbiota and stool bile acid profiles, as well as and their correlation in patients with PSC-IBD and inflammatory bowel disease alone.

Methods

Thirty patients with extensive colitis (15 with concomitant primary sclerosing cholangitis) were prospectively recruited and fresh stool samples were collected. The microbiota composition in stool was profiled using bacterial 16S rRNA sequencing. Stool bile acids were assessed by high-performance liquid chromatography tandem mass spectrometry.

Results

The total stool bile acid pool was significantly reduced in PSC-IBD. Although no major differences were observed in the individual bile acid species in stool, their overall combination allowed a good separation between PSC-IBD and inflammatory bowel disease. Compared with inflammatory bowel disease alone, PSC-IBD patients demonstrated a different gut microbiota composition with enrichment in Ruminococcus and Fusobacterium genus compared with inflammatory bowel disease. At the operational taxonomic unit level major shifts were observed within the Firmicutes (73%) and Bacteroidetes phyla (17%). Specific microbiota-bile acid correlations were observed in PSC-IBD, where 12% of the operational taxonomic units strongly correlated with stool bile acids, compared with only 0.4% in non-PSC-IBD.

Conclusions

Patients with PSC-IBD had distinct microbiota and microbiota-stool bile acid correlations as compared with inflammatory bowel disease. Whether these changes are associated with, or may predispose to, an increased risk of colorectal neoplasia needs to be further clarified.

Interplay between bile acid metabolism and microbiota in irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) physiopathology is multifactorial and roles for both microbiota and bile acid (BA) modifications have been proposed. We investigated role of dysbiosis, transit pattern and BA metabolism in IBS.

METHODS

Clinical data, serum, and stool samples were collected in 15 healthy subjects (HS), 16 diarrhea-predominant (IBS-D) and 15 constipation-predominant IBS (IBS-C). Fecal microbiota composition was analyzed by real-time PCR. Sera and fecal BA profiles, 7α-C4 levels, and in vitro BA transformation activity by fecal microbiota were measured by mass spectrometry. Serum Fibroblast Growth Factor 19 (FGF19) was assayed by ELISA.

KEYS RESULTS

Dysbiosis was present in IBS patients with an increase in Escherichia coli in IBS-D patients (p = 0.03), and an increase in Bacteroides (p = 0.01) and Bifidobacterium (p = 0.04) in IBS-C patients. Sera primary and amino-conjugated BA were increased in IBS-D (63.5 ± 5.5%, p = 0.01 and 78.9 ± 6.3%, p = 0.03) and IBS-C patients (55.9 ± 5.5%, p = 0.04 and 65.3 ± 6.5%, p = 0.005) compared to HS (37.0 ± 5.8% and 56.7 ± 8.1%). Serum 7α-C4 and FGF19 levels were not different among all three groups. Fecal primary BA were increased in IBS-D patients compared to HS, including chenodeoxycholic acid which has laxative properties (25.6 ± 8.5% vs 3.5 ± 0.6%, p = 0.005). Bile acid deconjugation activity was decreased in IBS-D (p = 0.0001) and IBS-C (p = 0.003) feces. Abdominal pain was positively correlated with serum (R = 0.635, p < 0.001) and fecal (R = 0.391, p = 0.024) primary BA.

CONCLUSIONS & INFERENCES

Different sera and fecal BA profiles in IBS patients could be secondary to dysbiosis and further differences between IBS-C and IBS-D could explain stool patterns. This study opens new fields in IBS physiopathology and suggests that modification of BA profiles could have therapeutic potential.

Identification of an anti-inflammatory protein from Faecalibacterium prausnitzii, a commensal bacterium deficient in Crohn's disease

BACKGROUND

Crohn's disease (CD)-associated dysbiosis is characterised by a loss of Faecalibacterium prausnitzii, whose culture supernatant exerts an anti-inflammatory effect both in vitro and in vivo. However, the chemical nature of the anti-inflammatory compounds has not yet been determined.

METHODS

Peptidomic analysis using mass spectrometry was applied to F. prausnitzii supernatant. Anti-inflammatory effects of identified peptides were tested in vitro directly on intestinal epithelial cell lines and on cell lines transfected with a plasmid construction coding for the candidate protein encompassing these peptides. In vivo, the cDNA of the candidate protein was delivered to the gut by recombinant lactic acid bacteria to prevent dinitrobenzene sulfonic acid (DNBS)-colitis in mice.

RESULTS

The seven peptides, identified in the F. prausnitzii culture supernatants, derived from a single microbial anti-inflammatory molecule (MAM), a protein of 15 kDa, and comprising 53% of non-polar residues. This last feature prevented the direct characterisation of the putative anti-inflammatory activity of MAM-derived peptides. Transfection of MAM cDNA in epithelial cells led to a significant decrease in the activation of the nuclear factor (NF)-κB pathway with a dose-dependent effect. Finally, the use of a food-grade bacterium, Lactococcus lactis, delivering a plasmid encoding MAM was able to alleviate DNBS-induced colitis in mice.

CONCLUSIONS

A 15 kDa protein with anti-inflammatory properties is produced by F. prausnitzii, a commensal bacterium involved in CD pathogenesis. This protein is able to inhibit the NF-κB pathway in intestinal epithelial cells and to prevent colitis in an animal model.

Increase in fecal primary bile acids and dysbiosis in patients with diarrhea-predominant irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a multifactorial disease for which a dysbiosis of the gut microbiota has been described. Bile acids (BA) could play a role as they are endogenous laxatives and are metabolized by gut microbiota. We compared fecal BA profiles and microbiota in healthy subjects (HS) and patients with diarrhea-predominant IBS (IBS-D), and we searched for an association with symptoms.

METHODS

Clinical features and stool samples were collected in IBS-D patients and HS. Fecal BA profiles were generated using HPLC coupled to tandem mass spectrometry. The fecal microbiota composition was assessed by q-PCR targeting dominant bacterial groups and species implicated in BA transformation.

KEY RESULTS

Fourteen IBS-D patients and 18 HS were included. The two groups were comparable in terms of age and sex. The percentage of fecal primary BA was significantly higher in IBS-D patients than in HS, and it was significantly correlated with stool consistency and frequency. Fecal counts of all bacteria, lactobacillus, coccoides, leptum and Faecalibacterium prausnitzii were similar. There was a significant increase of Escherichia coli and a significant decrease of leptum and bifidobacterium in IBS-D patients.

CONCLUSIONS & INFERENCES

We report an increase of primary BA in the feces of IBS-D patients compared to HS, correlated with stool consistency and frequency. A dysbiosis of different bacterial groups was detected, some of them involved in BA transformation. As the gut microbiota is the exclusive pathway to transform primary into secondary BA, this suggests a functional consequence of dysbiosis, leading to lower BA transformation.

Lipidomics of the red cell in diagnosis of human disorders

Applications of tandem mass spectrometry in the field of lipid clinical chemistry are considered. Haemato-logical and biochemical advantages are presented favoring the choice of red blood cell membranes as a starting material in a wide variety of biomedical fields. Practical considerations are discussed with respect to methods of sampling, storage, and lipid extraction of red blood cells. The chapter describes the capabilities of a direct infusion of raw lipid extracts in the electro-spray ionization source compared with the more sophisticated method of high-performance liquid chromatography coupled with hybrid tandem mass spectrometry. Both methods have been evaluated and have been shown to be suitable for diagnosis and/or monitoring for a variety of human disorders.

Building up of the liquid-ordered phase formed by sphingomyelin and cholesterol

The long-range and molecular orders and dynamics in codispersions of egg sphingomyelin-cholesterol have been investigated by synchrotron x-ray diffraction and electron spin resonance using phosphatidylcholine spin-labeled at several positions on the sn-2 chain. Mixtures containing 0, 17, 33, 41, 50 mol% cholesterol exhibited a single phase by x-ray diffraction methods. The temperature dependence of the d-spacing between 20 and 50 degrees C is attenuated with increasing proportions of cholesterol, becoming invariant for cholesterol contents of 41 and 50 mol% on completion of the liquid-ordered phase. Electron spin resonance revealed two sites for 17 and 33 mol% cholesterol. One site is highly ordered and the other is less ordered than the fluid phase of pure sphingomyelin as shown by the molecular and the intramolecular order parameters reflecting the segmental motions of the probe. The two-sites exchange rate indicates a mean lifetime of the sites of approximately 0.1 micros during which the lipid displacement is approximately 1 nm. The short lifetime of the sites probed by ESR and the single phase detected by x-ray diffraction support in this binary mixture, the building up of the Lo phase by a progressive accumulation of randomly distributed sphingomyelin-cholesterol condensed complexes rather than by diffusional exchange between extended domains.

Establishment of plasma membrane polarity in mammary epithelial cells correlates with changes in prolactin trafficking and in annexin VI recruitment to membranes

Mammary epithelial cells (MEC) of lactating animals ferry large amounts of milk constituents in vesicular structures which have mostly been characterized by morphological approaches (Ollivier-Bousquet, 1998). Recently, we have shown that under conditions of lipid deprivation, perturbed prolactin traffic paralleled changes in the membrane phospholipid composition and in the cytosol versus membrane distribution of annexin VI (Ollivier-Bousquet et al., 1997). To obtain additional information on the membrane events involved in the vesicular transport of the hormone to the apical pole of the cell, we conducted a biochemical study on prolactin-containing vesicles in MEC at two different stages of differentiation. We first showed that MEC of pregnant and lactating rabbits exhibited membrane characteristics of non-polarized and polarized cells respectively, using annexin IV and the alpha-6 subunit of integrin as membrane markers. Incubation of both cell types with biotinylated prolactin for 1 h at 15 degrees C, followed by a 10-min chase at 37 degrees C revealed that prolactin transport was activated upon MEC membrane polarization. This was confirmed by subcellular fractionation of prolactin-containing vesicles on discontinuous density gradients. In non-polarized MEC, (125)I-prolactin was mainly recovered in gradient fractions enriched with endocytotic vesicles either after incubation at 15 degrees C or after a 10-min chase at 37 degrees C. In contrast, in polarized MEC, the hormone switched from endocytotic compartments to a fraction enriched in exocytotic clathrin-coated vesicles during the 10-min chase at 37 degrees C. Association of annexin VI to prolactin carriers was next studied in both non-polarized and polarized cells. Membrane compartments collected at each gradient interface were solubilized under mild conditions by Triton X-100 (TX100) and the distribution of annexin VI in TX100-insoluble and TX100-soluble fractions was analyzed by Western blotting. Upon MEC polarization, the amount of annexin VI recovered in TX100-insoluble fractions changed. Quite interestingly, it increased in a membrane fraction enriched with endocytotic clathrin-coated vesicles, suggesting that annexin VI may act as a sorting signal in prolactin transport.

Lipid-depleted diet perturbs membrane composition and intracellular transport in lactating mammary cells

When rats were fed a control or a lipid-depleted diet for five generations, reproduction was not disturbed but pup growth was affected. The membrane organization and the secretory activity of mammary epithelial cells from these lactating rats were investigated. This diet induced a large decrease in the level of polyunsaturated fatty acids of membrane phospholipids (26.6% versus 44.0%). The level of 20:4 (n-6) was strongly decreased, mainly in phosphatidylethanolamine. Annexin VI, which interacts preferentially with this phospholipid, accumulated at the periphery of the cell and was largely associated to the hydrophobic region of the bilayer as compared to control membranes. Casein synthesis and casein secretion measured in incubated explants, after pulse-chase metabolic labeling, were both reduced by about 60% in lipid-deprived cells. The secretory ratio (radioactive secreted caseins in %) was not modified, suggesting that the mechanism of basal secretion was not mainly affected. On the contrary, the secretagogue effect of prolactin disappeared. The intracellular transport of the hormone was considerably slowed down by the diet and prolactin did not reach the lumen of the acini after 1 h of chase, in contrast to what occurred in control cells. Addition of 20:4 (n-6), in vitro, to mammary fragments from lipid-deprived rats restored the localization of annexin VI, increased synthesis and secretion of caseins as well as intracellular transport of PRI. Together, these data underline the importance of the level of 20:4 (n-6) in membrane phospholipids for exocytic and endocytic transport in lactating mammary epithelial cells.

Characterization and ultrastructural localization of annexin VI from mitochondria

Annexin VI, a member of a family of related intracellular proteins that associate reversibly with membrane phospholipids in a Ca(2+)-dependent manner, has been purified from bovine liver mitochondria and characterized. Moreover, biochemical and immunocytochemical lines of evidence are presented which strongly suggest that annexin VI is closely associated with the cristae in the inner membrane of mitochondria. These findings are consistent with a calcium channel activity of annexin VI in mitochondria.

Annexins from bovine adrenal cortex exhibit specific cytosol/membrane solvation

Cytosol/membrane localization of annexins I to VI was analyzed in tissue extracts from bovine adrenal cortex. Based on their solubility in either aqueous or detergents solutions, they were subfractionated in three groups named cytosolic (C), membrane-bound (MB) and membrane-inserted (MI). Less than 1% of the total annexins present in the tissue were recovered in the C fraction when as much as 76.5 and 22.5% were obtained respectively in the MB and the MI fractions. By immunoblotting after SDS-PAGE, it was shown that the various members of the annexin family were not equally recovered in the different fractions. A-V and A-VI were found present in the three fractions whereas the distribution of A-I, A-II, A-III and A-IV was distinct, suggesting different cellular functions.

Localization of calmodulin in perinuclear structures of spermatids and spermatozoa: a comparison of six mammalian species

The distribution of Calmodulin was examined during spermiogenesis and sperm epididymal maturation in rabbit, hamster, mouse, rat, monkey, and human. An affinity-purified antibody to Calmodulin was used to characterize this protein in sperm extracts by immunoblot analysis. Post-embedding immunogold procedures were used to localize Calmodulin at the ultrastructural level. The pattern of Calmodulin distribution was similar in the six species studied. A diffuse labeling was observed in round spermatids. Gold particles accumulated first in the subacrosomal layer of elongating spermatids. The perinuclear ring was also labeled. During the maturation phase of spermatids, Calmodulin labeling extended to the postacrosomal sheath. Dramatic changes occurred at spermiation so that in testicular sperm Calmodulin immunostaining was predominant in the postacrosomal sheath. Some labeling was still detected in restricted areas of the subacrosomal layer. This feature varied from species to species. Calmodulin location did not change during sperm epididymal maturation. A role for Calmodulin in the control of manchette development and regulation of subacrosomal actin aggregation state during spermiogenesis is proposed. The unique location of Calmodulin in the postacrosomal sheath of all species that have been studied in this work, together with the known presence of calcium in this area suggest a pivotal role for Calmodulin in sperm-egg fusion process.

Co-distribution of annexin VI and actin in secretory ameloblasts and odontoblasts of rat incisor

Annexin VI and actin were detected by immunoblot analysis in the enamel- and dentin-related portions of dental tissues. Annexin VI was found mainly in the particulate fraction whereas actin was detected in both the soluble and particulate fractions. By immunoelectron microscopy, annexin VI antibodies conjugated with colloidal gold were seen to label the mitochondria, the cytosol and the nucleus of secretory ameloblasts and odontoblasts of rat incisor. In the processes of these cells, the plasmalemmal undercoat was labeled. Anti-actin antibodies labeled the desmosome-like junctions, the cytosol, and the mitochondria of the cell bodies. Extensive labeling was seen at the periphery of the Tomes' processes and odontoblast processes. These results suggest that annexin VI may play a role in Ca2(+)-regulation in the cell bodies, especially as a calcium receptor protein in the mitochondria. Moreover, annexin VI and actin seem to be co-distributed in secretory processes. Thus, these proteins might be both involved in exocytotic and endocytotic events.

Annexins I-VI in secretory ameloblasts and odontoblasts of rat incisor

Immunoblot analyses and ultrastructural immunogold studies have been conducted on annexins in the secretory ameloblasts and odontoblasts of the rat incisor. Annexins I and II were seen in the soluble and particulate fractions of the enamel-related portion but not in the dentin-related portion. These proteins were visualized in the cytosol, near to the plasma membrane of Tomes' processes and in secretory vesicles in the ameloblasts. The forming enamel was also labeled. Annexins III, VI an V were detected in both the soluble and particulate fractions of the enamel-and dentin-related portions. Annexin IV was mainly localized in the proximal and distal areas of the secretory ameloblasts and virtually absent from in the supranuclear area. Annexin V was mainly detected in the cytosol of the cells and to a lesser extent near the plasma membrane. Annexin VI was mainly detected in the particulate fraction of enamel- and dentin-related portions. It was seen in the mitochondria and in the subplasmalemmal undercoat. All these proteins may play a role in exocytosis and endocytosis. They are implied in the regulation of cell calcium, but not in the transfer of calcium through the cells in the direction of the forming enamel and dentin, except annexins I and II since they are both present in the secretory vesicles and in the forming enamel.

Effects of calcium and calcium analogs on calmodulin: a Fourier transform infrared and electron spin resonance investigation

Fourier transform infrared (FTIR) and electron spin resonance (ESR) spectroscopies have been used to monitor changes in the conformation of calmodulin induced by Ca2+ and Ca2+ analogs. Using FTIR spectroscopy we observe that Ca2+: (i) favors the alpha-helical conformation and decreases the flexibility of the molecule; (ii) multiplies the intramolecular hydrogen bonds (the ratio of freely vibrating NH/hydrogen bound NH groups decreases); (iii) induces changes in the C-terminal tyrosine environment; and (iv) increases compactness of the molecule (less NH groups in the peptide bonds can be deuterated). As proved by ESR, Ca2+ binding induces exposure of hydrophobic domains allowing binding of a spin-labelled phenothiazine on calmodulin. When the experiments are performed in the presence of increasing amounts of Ca2+, both ESR and FTIR provide evidence that major conformational changes result after the filling of only two Ca2+-binding sites. But achievement of the spectroscopical changes is only observed when the four binding sites are filled (Ca2+/calmodulin = 4). The effects of analogs are monitored with the same spectroscopical parameters. Zn+ does not induce structural modifications of calmodulin but all other analogs studied mimic the calcium effects to some extent. As regards the amplitude of the spectroscopical effects, analogs rank in the following order: Ca2+ greater than Cd2+ greater than Tb3+ = Eu3+ greater than Gd3+ greater than La3+ greater than Zn2+ = cation depleted. Except for Zn2+, ranking for their activating potency of MLCK, the analogs can be arranged in a similar order.

Calmodulin in lymphocyte mitogenic stimulation and in lymphoid cell line growth

Calmodulin levels are elevated three- to fourfold in the dividing cells, resulting from the lectin-induced stimulation of fresh human lymphocytes. This increase in calmodulin appears to be related mainly to progression into S phase and supports the hypothesis that calmodulin might be crucial in regulating the progression of lymphoblasts through their division cycle. Calmodulin levels are higher in a lymphoid cell line derived from human acute lymphoblastic leukemia blood cells than in a lymphoid cell line derived from normal human blood cells, suggesting that calmodulin could be an important mediator of the leukemogenetic process.

Immunoelectron microscopic localization of calmodulin and phospholipase A2 in spermatozoa. I

Using the Lowicryl K4M embedding technique, together with indirect immunoferritin or immunogold labeling on ultra-thin sections, tubulin, calmodulin and phospholipase A2 were distinctly localized in ejaculated bull spermatozoa. Calmodulin was concentrated on the plasma membrane, nucleus, post-acrosomal substance, and, in lesser amounts, between coarse fibers and axonemal microtubules of the flagellum. Phospholipase A2 was distributed evenly along the plasma membrane, nucleus, acrosome, post-acrosomal substance, and in the flagellum, on mitochondria, fibrous sheath, coarse fibers, between coarse fibers and axonemal microtubules. Antibodies to tubulin labeled only axonemal microtubules, including the central pair of microtubules. Patterns of tubulin labeling were identical when ferritin granule- or gold particle-conjugated antibodies were tested. In agreement with our previous biochemical studies demonstrating calmodulin binding to phospholipase A2, concomitant with enhancement of phospholipase A2 activity (Arch Biochem Biophys 241:413, 1985), the overlapping distribution of calmodulin and phospholipase A2 in several parts of the sperm suggests that these proteins may play a concerted role in male gamete function in preparation for or during fertilization. The distinct distribution of tubulin along flagellum microtubules indicates their special function in sperm mobility.

Interaction between calmodulin and five different spin-labelled chlorophenothiazines

The binding to purified calmodulin of five spin-labelled derivatives of chlorophenothiazine was investigated by e.s.r. spectrometry and by the antagonizing potency on the calmodulin-dependent activation of myosin light chain kinase. The results of a comparative study and the influence of pH and ionic strength on the binding support the occurrence of an electrostatic binding involving the terminal amino group of the side-chain of the chlorophenothiazine. These results are discussed in relation to the specificity of the interaction that holds the antipsychotic drug-calmodulin complex together.

Changes in calmodulin level after fertilization and during first cleavage in the egg of the urodelan amphibian Pleurodeles waltlii

We report three significant calmodulin rises related to Pleurodeles waltlii egg fertilization and following developmental events. These elevations are correlated to the major obvious Ca2+-dependent events: Na+-H+ exchange, activation of NAD kinase, triggering of cortical reaction, resumption of meiotic division II, initiation of DNA synthesis and regulation of cell division. Therefore, it is suggested that alterations in calmodulin level in fertilized egg may be part of the Ca2+-dependent regulatory mechanisms which turn on metabolisms, initiate development and govern cell cleavages.

Effects of AY 9944 on low density lipoprotein metabolism in cultured human fibroblasts

Treatment of cultured human fibroblasts with the hypocholesterolemic drug AY 9944 resulted in a marked increase in low density lipoprotein internalization and degradation for concentrations up to 5 X 10(-6)M. Low density lipoprotein binding was less affected. Concentrations above 5 X 10(-6)M resulted in a relative decrease in low density lipoprotein degradation, whereas binding and internalization plateaued. The stimulation of low density lipoprotein internalization took place within the first hours of incubation of cells with the drug, which suggests a direct effect on the cell membrane. Such phenomenon could account at least partially for the hypocholesterolemic effect of the drug, besides its inhibitory effect on 7-dehydrocholesterol reductase.

Binding of a spin-labelled chlorpromazine analogue to calmodulin

The binding of a spin-labelled derivative of chlorpromazine to calmodulin was investigated by e.s.r. spectrometry. The completion of the spectroscopic changes requires the presence of 4 Ca2+ ions per calmodulin molecule. The influences of various physicochemical factors (pH, ionic strength) are discussed in relation to the nature (hydrophobic and polar) of the interactions that hold the drug-calmodulin complex together.

Effects of phenothiazines on low density lipoprotein metabolism in cultured human fibroblasts

Treatment of cultured human fibroblasts with trifluoperazine or chlorpromazine resulted in a biphasic effect on low density lipoprotein (LDL) catabolism, depending upon the dose. At up to 10(-5) M, a marked increase in LDL binding, internalization and degradation was observed. This phenomenon took place within the first hours of incubation with the drugs, suggesting a direct effect on cell membrane physical characteristics, probably related to the lipophilic properties of phenothiazines. Concentrations above 2 X 10(-5) M resulted in a relative decrease in LDL binding and internalization, and in a dramatic decrease in LDL degradation, which may be related to an inhibition of calmodulin-dependent processes.