Is ultraviolet light disinfection fit to be the future standard for the disinfection of flexible endoscopes without a working channel?

OBJECTIVE

To investigate colony-forming unit (CFU) reduction on contaminated flexible endoscopes (FEs) without a working channel after UV-C light disinfection, compared to the current disinfection method with the endoscope washer disinfector (EWD).

DESIGN, SETTING AND PARTICIPANTS

After pharyngolaryngoscopy, a manual pre-cleaning with tap water was performed. A culture was then collected by rolling the distal 8-10 cm of the FE over an Agar plate. The FE was disinfected using the D60 (60-s disinfection process with UV-C light) or the EWD (gold standard reprocessing process with water and chemicals). Another culture was then taken. After incubation, a CFU count was performed.

RESULTS

A total of 200 FEs without a working channel were divided equally between the two disinfection groups. After clinical use and manual pre-cleaning, 84 of the 100 (84.0%) (UV-C light group) and 79 of the 100 (79.0%) (EWD) FEs were contaminated with at least 1 CFU. FEs that showed no contamination after use were excluded from further analysis. After disinfection with UV-C light, 72 (85.7%) FEs showed no contamination (i.e., 0 CFUs) versus 66 (83.5%) FEs after reprocessing with the EWD.

CONCLUSION

There is no difference in CFUs reduction on contaminated FEs without a working channel between UV-C light disinfection and the current gold standard, the EWD.

A multi-center assessment to compare residual allergenicity of partial hydrolyzed whey proteins in a murine model for cow's milk allergy - Comparison to the single parameter guinea pig model

INTRODUCTION

This 4-center study is part of a project to validate a food allergy murine model for safety testing of hydrolyzed infant formulas.

AIM

The aim of the current multi-center experiment was to evaluate the residual allergenicity of three partial hydrolyzed whey proteins (pWH) in a multiple-parameter cow's milk allergy murine model and to compare to the classically used guinea pig model. Previous work showed differences in the magnitude of the allergic response to whey between centers. To get a first insight in the effect of housing on the robustness of the mouse model, microbiota composition of non-sensitized mice was analyzed and compared between centers.

METHODS

Mice were sensitized intragastrically (i.g.) with whey, pWH or eWH using cholera toxin as an adjuvant. In mice, whey-IgE/IgG1, acute allergic symptoms were determined upon whey challenge. Guinea pigs were orally sensitized ad libitum via the drinking water (day 0-37) and challenged intravenously with whey on day 49. The microbial composition in fecal samples was determined in non-sensitized mice in all 4 research centers before and after conduct of the study.

RESULTS

Elevated levels of whey-IgG1 were detected in whey-sensitized mice in all centers. Except for pWH-A in center 4, we observed elevated levels of whey-IgE in whey-sensitized mice and mice sensitized with pWH-A, -B, -C. Center 2 was excluded from further analysis because of non-significant IgE levels in the positive control. In contrast to whey-mice, pWH-A treated mice showed no acute skin response, mMCP-1 release or change in body temperature upon whey challenge in all centers, which corresponds with the absence of anaphylactic shock symptoms in both the mouse and guinea pig model. pWH-B and -C induced anaphylactic shock symptoms in the guinea-pig and mice whereas results on the remaining allergic outcomes in mice were inconclusive. No differences in microbiota composition were measured in response to the challenge and Microbiota composition depended on the location of the centers.

CONCLUSIONS

Both animal models showed comparable results on the residual allergenicity of partial hydrolyzed whey proteins, but none of the centers was able to differentiate between the residual sensitizing capacities of the pWH-B and -C based on a single elicitation parameter in the murine model. Differences in microbiota composition might contribute to the robustness of the food allergy murine model. For a well-balanced prediction on the potential allergenicity of hydrolyzed infant formulas a multiple murine parameter model is suggested to decrease the risk of false positive or false negative results. A future challenge is to develop an overall scoring system for proper risk assessment, taking all parameters into account.

The mycotoxin deoxynivalenol facilitates allergic sensitization to whey in mice

Intestinal epithelial stress or damage may contribute to allergic sensitization against certain food antigens. Hence, the present study investigated whether impairment of intestinal barrier integrity by the mycotoxin deoxynivalenol (DON) contributes to the development of whey-induced food allergy in a murine model. C3H/HeOuJ mice, orally exposed to DON plus whey once a week for 5 consecutive weeks, showed whey-specific IgG1 and IgE in serum and an acute allergic skin response upon intradermal whey challenge, although early initiating mechanisms of sensitization in the intestine appeared to be different compared with the widely used mucosal adjuvant cholera toxin (CT). Notably, DON exposure modulated tight-junction mRNA and protein levels, and caused an early increase in IL-33, whereas CT exposure affected intestinal γδ T cells. On the other hand, both DON- and CT-sensitized mice induced a time-dependent increase in the soluble IL-33 receptor ST2 (IL-1R1) in serum, and enhanced local innate lymphoid cells type 2 cell numbers. Together, these results demonstrate that DON facilitates allergic sensitization to food proteins and that development of sensitization can be induced by different molecular mechanisms and local immune responses. Our data illustrate the possible contribution of food contaminants in allergic sensitization in humans.

The aryl hydrocarbon receptor and food allergy

The immune system is important for protection against pathogens and malignant cells. However, malfunction of the immune system can also result in detrimental auto-immune diseases, inflammatory diseases, cancers and allergies. The aryl hydrocarbon receptor (AhR), present in numerous tissues and cell subsets, including cells of the immune system, plays an important role in the functioning of the immune system. Activation of the AhR is for example associated with various effects on dendritic cells (DCs), regulatory T cells and the Th1/Th2 cell balance. These cells play a major role in the development of food allergy. Food allergy is an increasing health problem in both humans and animals. Despite the knowledge in risk factors and cellular mechanisms for food allergy, no approved treatments are available yet. Recently, it has been shown that activation of the AhR by dioxin-like compounds suppresses allergic sensitization by suppressing the absolute number of precursor and effector T cells, by preserving CD4(+)CD25(+)Foxp3(+) Treg cells and by affecting DCs and their interaction with effector T cells. Future research should elucidate whether and how AhR activation can be used to interfere in food allergic responses in humans and in animals. This may lead to new prevention strategies and therapeutic possibilities for food allergy.

Activation of the aryl hydrocarbon receptor reduces the number of precursor and effector T cells, but preserves thymic CD4+CD25+Foxp3+ regulatory T cells

Aryl hydrocarbon receptor (AhR) activation suppresses immune responses, including allergic sensitization, by increasing the percentage of regulatory (Treg) cells. Furthermore, AhR activation is known to affect thymic precursor T cells. However, the effect of AhR activation on intrathymic CD4+CD25+Foxp3+ Treg cells is unknown. Therefore, we investigated the effect of AhR activation on the percentage and number of CD4+CD25+Foxp3+ Treg cells during allergic sensitization in relevant immunological organs. C3H/HeOuJ mice were treated on day 0 with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and subsequently sensitized to peanut. On day 8, mice were sacrificed and thymus, spleen and mesenteric lymph nodes (MLN) were isolated. TCDD treatment decreased the number of CD4-CD8-, CD4+CD8+, CD4+CD8- and CD4-CD8+ precursor T cells, but not the number of thymic CD4+CD25+Foxp3+ Treg cells. TCDD treatment increased the number of splenic CD4+CD25+Foxp3+ Treg cells and decreased Th1, Th2 and cytotoxic T cells in the spleen. This appeared to be independent of allergic sensitization. In MLN, TCDD treatment suppressed the increase of the number of CD4+CD25+Foxp3+ Treg cells, Th1, Th2 and cytotoxic T cells induced by peanut sensitization. Together, TCDD treatment preserves thymic CD4+CD25+Foxp3+ Treg cells and decreases peripheral T helper and cytotoxic T cells. This effect of TCDD may contribute to the increased influence of CD4+CD25+Foxp3+ Treg cells on immune mediated responses and to the understanding of how AhR activation modulates immune mediated diseases, including food allergy.

Activation of the aryl hydrocarbon receptor suppresses sensitization in a mouse peanut allergy model

Food allergy is an increasing health problem in Western countries. Previously, it has been shown that the intensity of food allergic reactions can be regulated by regulatory T (T(reg)) cells. In addition, it has been shown that activation of the aryl hydrocarbon receptor (AhR) regulates T-cell responses by induction of T(reg) cells. Therefore, we hypothesized that activation of the AhR pathway can suppress development of food allergic responses through the induction of T(reg) cells. This was investigated by using a mouse model for peanut allergy. C3H/HeOuJ mice (AhR(b)(-2)) were sensitized to peanut by administering peanut extract (PE) by gavage in the presence of cholera toxin and were treated with the prototypical AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.6, 1.7, 5, and 15 μg/kg body weight) on days 3 and 11 orally. The functional role of CD4(+)CD25(+)Foxp3(+) T(reg) cells was investigated by depleting these cells with anti-CD25 mAb during sensitization to PE. TCDD treatment dose dependently suppressed sensitization to peanut (PE-specific IgE, IgG1, and IgG2a and PE-induced IL-5, IL-10, and IL-13, respectively). The percentage, but not the number, of CD4(+)CD25(+)Foxp3(+) T(reg) cells dose dependently increased by AhR activation in both spleen and mesenteric lymph nodes. Depletion of CD4(+)CD25(+)Foxp3(+) T(reg) cells markedly reversed the suppressive effect of TCDD on PE-specific antibody levels and PE-induced IL-5, IL-10, and IL-13 cytokine production. Present data demonstrate for the first time that activation of the AhR by TCDD suppressed the development of Th2-mediated food allergic responses. A functional shift within the CD4(+) cell population toward CD4(+)CD25(+)Foxp3(+) T(reg) cells appeared to underlie this effect. This suggests that the AhR pathway might provide potential therapeutic targets to treat food allergic diseases.

The role of intestinal dendritic cells subsets in the establishment of food allergy

BACKGROUND

Food allergy affects approximately 6% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. Crucial in the establishment of allergy is the activation of dendritic cells (DC) leading to T helper 2-mediated responses.

OBJECTIVE

We, therefore, investigated whether changes in DC subsets precede the establishment of food allergy, and which DC subsets have functional relevance during allergic sensitization in a mouse model.

METHODS

Changes in DC populations in the intestine were analysed after exposure to cholera toxin alone and in combination with peanut extract (PE) as an allergen. To study the functional role of DC subsets in relation to food allergy, we used expansion of DC in vivo by treatment with Flt3L.

RESULTS

Sensitization to PE in this mouse model was accompanied by a shift in DC subsets in intestinal tissues towards more CD11b(+) DC and less CD103(+) DC. No significant changes in the plasmacytoid DC (pDC) numbers were observed. Flt3L treatment, resulting in the expansion of all DC subtypes, inhibited allergic manifestations in our model, including Th2 cytokine production, PE-specific IgE and PE-induced mast cell degranulation. pDC depletion reversed Flt3L-induced inhibition of IgE responses and mast cell degranulation. conclusions and clinical relevance: The establishment of food allergy is accompanied by profound changes in DC subsets in the intestine towards more inflammatory CD11b(+) DC. In addition, expansion of DC numbers by Flt3L, in particular pDC, inhibits the establishment of allergic manifestations in the intestine. These findings are of relevance for understanding the role of DC subsets early during the process of allergic sensitization, and may lead to new therapeutic or prophylactic opportunities to prevent food allergy.

Regulation by intestinal γδ T cells during establishment of food allergic sensitization in mice

BACKGROUND

Food allergy affects approximately 5% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. The mucosal adjuvant cholera toxin induces allergic sensitization to co-administered proteins in mice, while feeding the protein alone induces oral tolerance. Intestinal γδ T cells could be of importance in the induction of oral tolerance. This study aims to investigate whether γδ T cells have functional relevance in food allergic sensitization.

METHODS

Changes in γδ T cells on days 1, 2, 3, and 7 after initiation of food allergy were evaluated using flowcytometry. Furthermore, the anti-γδ T-cell receptor (TCR) antibody UC7 was used to block the γδ TCR in mice in vivo, followed by sensitization to peanut. After 4 weeks, peanut-specific antibodies in serum and cytokine production in spleen were measured.

RESULTS

Induction of food allergy resulted in a profound decrease in the percentage of γδ T cells in intestinal tissues and Peyer's Patches, but not in mesenteric lymph nodes or spleen. This decrease could be detected from days 1 to 2 after the initiation of food allergy and the number of γδ T cells returned to normal on day 7. Blockade of the γδ TCR resulted in elevated food allergic responses upon sensitization with peanut characterized by increased IgE and Th2 cytokine production in splenocytes.

CONCLUSION

These results demonstrate a unique regulatory role of γδ T cells, suggesting that targeting γδ T cells in the intestine may contribute to strategies to prevent and possibly treat food allergy.

Mycobacterium vaccae administration during allergen sensitization or challenge suppresses asthmatic features

BACKGROUND AND OBJECTIVE

The hygiene hypothesis suggests that a lack of bacterial infections would favour the development of allergic disease. For this reason, bacteria or their components can be used as potential treatment for allergic asthma. We investigated whether heat-killed Mycobacterium vaccae is either able to suppress the induction of allergic asthma or able to suppress already established allergic asthma.

METHODS

Mice were sensitized with ovalbumin (OVA)/alum on days 0 and 14. Thereafter, mice were challenged on days 35, 39 and 42 by inhalation of either OVA or saline aerosols. M. vaccae-treated mice received an injection with 106, 107 or 108 CFU heat-killed M. vaccae on days 0 and 14 or 107 CFU on days 35 and 39. On day 43, the airway responsiveness of the mice to increasing concentrations of methacholine was assessed, blood was withdrawn to measure serum parameters, and lung lavage was performed to detect cytokines and inflammatory cell number.

RESULTS

Treatment of OVA-sensitized mice with 107 CFU M. vaccae either during sensitization or challenge suppresses airway hyper-responsiveness, airway eosinophilia and IL-5 production after OVA challenge. The increases in OVA-specific serum IgE and in IL-4 by respiratory challenges with OVA were only diminished after M. vaccae treatment (107 CFU) during sensitization.

CONCLUSIONS

Heat-killed M. vaccae prevents allergic and asthmatic manifestations in a mouse model and, more importantly, M. vaccae treatment during challenge suppresses features of asthma, which opens up possibilities for new therapeutic interventions.

Filtration of activated granulocytes during cardiopulmonary bypass surgery: a morphologic and immunologic study to characterize the trapped leukocytes

Cardiopulmonary bypass surgery induces an inflammatory reaction among others by activation of granulocytes. Leukocyte filtration has been shown to reduce the postoperative morbidity mediated by activated granulocytes. However, little is known about the mechanism of filter-leukocyte interaction. This study examines whether a leukocyte filter removes activated granulocytes or a general leukocyte population. Eleven patients undergoing cardiopulmonary bypass surgery were included in this study. Leukocyte filtration was achieved before the reperfusion phase with a Pall non-woven polyester filter located at the venous side of the heart-lung machine. After filtration, the trapped granulocytes inside the filter were examined morphologically with light and scanning electron microscopy and immunologically by CD45RO antigen binding to the filter material. Furthermore, leukocyte release markers were measured to determine whether cells were activated during filtration. Microscopic evaluation revealed 84% granulocytes and 14% lymphocytes trapped in the filter, compared with 78% granulocytes and 22% lymphocytes in the blood before filtration. Granulocytes were trapped significantly more in the first blood contact layer of the filter material than in the middle layer and last layer, whereas lymphocytes trapped slightly more in the middle layer. The near maximum level of CD45RO expression was measured on granulocytes trapped inside the filter material, whereas CD2 and CD19 measured on lymphocytes were bound to a minor extent. Beta-glucuronidase concentration did not increase after filtration, suggesting the absence of activation of granulocytes by filtration. A leukocyte filter made of non-woven polyester material removes the activated granulocytes rather than leukocytes at random. This implies that this particular type of leukocyte removal filter is suitable for use in cardiopulmonary bypass patients whose granulocytes in the circulation are activated. Furthermore, measurement of activated granulocytes instead of total leukocyte count is likely preferable for functional assessment of leukocyte removal devices.

Transient lowering of plasma vitamin B12 concentrations in Ouessant sheep fed on a potassium-rich ration

The hypothesis tested was that a high intake of potassium (K) interferes with cobalt (Co)-vitamin B12 metabolism in ruminants. Ouessant sheep were fed either a low- (8 g K/kg dry matter) or high-K diet (43 g K/kg dry matter) with an adequate amount of Co (124 micrograms Co/kg dry matter). Plasma vitamin B12 concentrations were measured. Sheep fed a low-K diet, but containing only 70 micrograms Co/kg dry matter, served as positive controls. Feeding the low-Co ration produced a significant decrease in plasma vitamin B12 concentrations. The high- versus low-K ration induced a significant decrease in plasma vitamin B12 during the first 6 weeks, but thereafter the values in the high-K group rose to those seen in the low-K group. The mechanism by which dietary K may interact with Co-vitamin B12 metabolism in sheep is unknown.

Efficiency and safety of leukocyte filtration during cardiopulmonary bypass for cardiac surgery

BACKGROUND

Leukocyte filtration of systemic blood during cardiopulmonary bypass surgery to reduce post-operative morbidity has not yet been established because of the enormous leukocyte release from the third space. This study was designed to examine the efficiency and safety of leukocyte filtration by a new prototype large capacity leukocyte filter.

PATIENTS AND METHODS

Patients undergoing cardiopulmonary bypass surgery were prospectively divided into two groups: a leukocyte removal group (n = 11) receiving leukocyte filtration during cardiopulmonary bypass and a control group (n = 20) with no filtration. The filtration efficiency was indicated by electronic leukocyte counts before and after filtration and the clinical efficiency to reduce post-operative morbidity was indicated by PaO2. Safety was indicated by monitoring the filtration pressure and leukocyte release products across the filter, as well as by examining the post-filtration filter by light and electron microscopy.

RESULTS

On an average, 75% of all entering leukocytes were removed by the filter. The post-operative PaO2 showed a tendency to improve after filtration. During filtration, the pressure across the filter material increased in five cases, accompanied by an increase in post-filter plasma hemoglobin and beta-glucoronidase. Within these filters accumulations of fibrin network with many trapped leukocytes were discovered microscopically.

CONCLUSIONS

The filter was efficient in filtering leukocytes, but the filtration efficiency slowed at the end of filtration. Furthermore, the patients' post-operative parameters showed a tendency to improve after filtration. However, flow obstruction by means of clotting seems to be an important issue of safety involved in the filtration of large numbers of leukocytes for cardiopulmonary surgical patients.

Immune-mediated effects upon oral challenge of ovalbumin-sensitized Brown Norway rats: further characterization of a rat food allergy model

Although several in vivo antigenicity assays using parenteral immunization are operational, no full validated enteral models are available to study food allergy and allergenicity of food proteins. To further validate a developed enteral Brown Norway (BN) rat food allergy model, systemic and local immune-mediated reactions were studied upon oral challenges. The animals were exposed to ovalbumin (OVA) by daily gavage dosing (1 mg OVA/rat/day) for 6 weeks, without the use of an adjuvant, or by intraperitoneal injections with OVA together with AL(OH)3. Subsequently, effects on breathing frequency, blood pressure, and gastrointestinal permeability were investigated upon an oral challenge with 10 to 100 mg OVA in vivo. In both parenterally and orally sensitized rats, an increase in gut permeability (increased passage of beta-lactoglobulin as bystander protein) was determined between 0.5 and 1 h after an oral OVA challenge was given. An oral challenge with OVA did not induce a clear effect on the respiratory system or blood pressure in the majority of the animals. However, some animals demonstrated a temporary decrease in breathing frequency or systolic blood pressure. Upon oral challenge with OVA of orally and parenterally sensitized animals, local effects were observed in all animals whereas systemic effects were observed at a low frequency, which reflects the situation in food allergic patients after an oral challenge. These studies show that the BN rat provides a suitable animal model to study oral sensitization to food proteins as well as immune-mediated effects after oral challenge with food proteins.

Normal viability and altered pharmacokinetics in mice lacking mdr1-type (drug-transporting) P-glycoproteins

The mdr1-type P-glycoproteins (P-gps) confer multidrug resistance to cancer cells by active extrusion of a wide range of drugs from the cell. To study their physiological roles, we have generated mice genetically deficient in the mdr1b gene [mdr1b (-/-) mice] and in both the mdr1a and mdr1b genes [mdr1a/1b (-/-) mice]. In spite of the host of functions speculatively attributed to the mdrl-type P-gps, we found no physiological abnormalities in either strain. Viability, fertility, and a range of histological, hematological, serum-chemical, and immunological parameters were not abnormal in mdr1a/1b (-/-) mice. The high level of mdrlb P-gp normally present in the pregnant uterus did not protect fetuses from a drug (digoxin) in the bloodstream of the mother, although the protein did reduce drug accumulation in the adrenal gland and ovaries. Pharmacologically, mdr1a/1b (-/-) mice behaved similarly to the previously analyzed mdr1a (-/-) mice, displaying, for instance, increased brain penetration and reduced elimination of digoxin. However, both mdr1a and mdr1b P-gps contributed to the extrusion of rhodamine from hematopoietic progenitor cells, suggesting a potential role for the endogenous mdr1-type P-gps in protection of bone marrow against cytotoxic anticancer drugs. This, and the normal viability of mdr1a/1b (-/-) mice, has implications for the use of P-gp-blocking agents in cancer and other chemotherapy. mdr1a/1b (-/-) mice should provide a useful model system to further test the pharmacological roles of the drug-transporting P-gps and to analyze the specificity and effectivity of P-gp-blocking drugs.

Peripheral neuropathy in mice transgenic for a human MDR3 P-glycoprotein mini-gene

We have generated mice transgenic for a human MDR3 mini-gene, under control of a hamster vimentin promoter. Expression of the MDR3 transgene was found in mesenchymal tissues, peripheral nerves, and the eye lens. These MDR3 transgenic mice have a slowed motor nerve conduction and dysmyelination of their peripheral nerves. An extensive dysmyelination in some transgenic strains results in a severe peripheral neuropathy with paresis of the hind legs. How expression of the MDR3 transgene causes these abnormalities is unknown. The MDR3 gene encodes a large glycosylated plasma membrane protein with multiple transmembrane spanning domains, which are involved in the translocation of the phospholipid phosphatidylcholine through the hepatocyte canalicular membrane. The ability of the MDR3 P-glycoprotein to alter phsopholipid distribution in the plasma membrane of Schwann cells may cause the damage. It is also possible, however, that the presence of a large glycoprotein in the cell membrane may be sufficient to severely disturb myelination of peripheral nerves.

Human multidrug resistance 3-P-glycoprotein expression in transgenic mice induces lens membrane alterations leading to cataract

We have generated mice transgenic for a human multidrug resistance (MDR)3 mini-gene driven by a hamster vimentin promoter. The MDR3 gene encodes a P-Glycoprotein that resembles the mouse multidrug resistance 2 P-Glycoprotein shown to be involved in the translocation of the phospholipid phosphatidylcholine through the hepatocyte canalicular membrane (Smit et al., 1993. Cell. 75:451-462). The vimentin promoter drives expression of the MDR3 transgene in mesenchymal tissues and in the eye lens. We show here that the presence of human multidrug resistance 3 P-Glycoprotein in the lens results in a severe lenticular pathology. Lens structural abnormalities initiate at a late embryonic stage and increase during postnatal lens development. Differentiation of the primary fibers is affected, and the terminal differentiation of the lens epithelium into secondary fibers is also perturbed. The ultrastructural alterations, particularly of the lens plasma membranes, resemble those identified in congenital mouse osmotic cataract.

Regulation of protein secretion into bile: studies in mice with a disrupted mdr2 p-glycoprotein gene

BACKGROUND & AIMS

Protein is secreted into bile via several independent pathways. The aim of this study was to investigate whether these pathways are influenced by secretion of biliary lipid.

METHODS

Protein secretion and biliary lipid output were studied in wild-type mice (+/+), heterozygotes (+/-), and homozygotes (-/-) for mdr2 gene disruption. Biliary lipid and protein output were varied by infusion with taurocholate (TC) and tauroursodeoxycholate (TUDC).

RESULTS

Exocytosis and transcytosis were unaltered in (-/-) mice. Infusion with TC strongly induced secretion of alkaline phosphatase in (-/-) mice but had little effect in (+/-) and (+/+) mice. Infusion with TUDC had little effect on alkaline phosphatase output. In contrast, both TUDC and TC strongly stimulated secretion of aminopeptidase N and lysosomal enzymes in (+/+) mice but had no effect in (-/-) animals. Aminopeptidase N secretion correlated with phospholipid output, but only at high flux. At low flux, aminopeptidase N was secreted independently from both phospholipid and bile salts.

CONCLUSIONS

The canalicular membrane enzymes alkaline phosphatase and aminopeptidase N are secreted via separate pathways. Part of alkaline phosphatase output is controlled by bile salt hydrophobicity, whereas at high lipid flux, aminopeptidase N secretion seems to be coupled to phospholipid output. Lysosomal enzymes follow the latter pathway.

Multidrug resistance and the role of P-glycoprotein knockout mice

Drug resistance, be it intrinsic or acquired, is a major problem in cancer chemotherapy. In vitro, one well characterised form of resistance against many different cytotoxic drugs is caused by the MDR1 P-glycoprotein, a large plasma membrane protein that protects the cell by actively pumping substrate drugs out. Available evidence suggests that this protein may cause drug resistance in at least some clinical tumours. Drugs inhibiting the MDR1 P-glycoprotein activity are, therefore, co-administered during chemotherapy of these tumours. To predict the biological and pharmacological effects of the blocking of this protein, we have generated mice with a genetic disruption of the drug-transporting mdr1a P-glycoprotein. These mice are overall healthy, but they accumulate much higher levels of substrate drugs in the brain, and have markedly slower elimination of these drugs from the circulation. For some drugs, this leads to dramatically increased toxicity, indicating that P-glycoprotein inhibitors should be used with caution in patients.

Characterization of the promoter region of the human MDR3 P-glycoprotein gene

The human MDR3 (or MDR2) P-glycoprotein is probably involved in the transport of phospholipids from liver hepatocytes into bile (Smit et al. (1993) Cell 75, 451-462). In accordance with this function, MDR3 is highly expressed in human liver, but lower mRNA levels were also found in adrenal, heart, muscle and cells of the B-cell compartment. We have cloned and analyzed the MDR3 promoter region. It is GC-rich, and contains neither a TATA nor a CAAT box, but it does contain multiple putative SP1 binding sites, features also found in so-called housekeeping genes. RNase protection and primer extension analyses indicate that the MDR3 gene has multiple transcription start sites in a GC-rich region with considerable homology to the putative mouse mdr2 promoter. A 3 kb genomic fragment containing the MDR3 start sites directs transcription of a chloramphenicol acetyltransferase (CAT) reporter gene upon transient transfection in the human hepatoma cell line HepG2. This transcription is orientation dependent, and stimulated by a SV40 enhancer, indicating that the 3 kb insert contains the core promoter elements of the MDR3 gene. The promoter region contains several consensus sequences where known or putative liver-specific (C/EBP, HNF5) or lymphoid specific (Pu.1, ets-1) transcription factors may bind.

Regulation of biliary lipid secretion by mdr2 P-glycoprotein in the mouse

Disruption of the mdr2 gene in mice leads to a complete absence of phospholipid from bile (Smit, J. J. M., et al. 1993. Cell. 75:451-462). We have investigated the control of both mdr2 P-glycoprotein (Pgp) expression and bile salt secretion on biliary lipid secretion in the mouse. Lipid secretion was monitored at various bile salt output rates in wild-type mice (+/+), heterozygotes (+/-), and homozygotes (-/-) for mdr2 gene disruption. In (-/-) mice, phospholipid secretion was negligible at all bile salt output rates. In (+/-) mice, a curvilinear relation between bile salt and phospholipid secretion was observed similar to that in (+/+) mice; however, at all bile salt secretion rates phospholipid secretion was reduced compared to (+/+) mice, indicating that mdr2 Pgp exerts a strong control over secretion. Infusion of increasing amounts of taurocholate up to maximal secretory rate led to a decline in the phospholipid and cholesterol secretion in both (+/+) and (+/-) mice in accordance to what has been observed in other species. In contrast, in (-/-) mice cholesterol secretion increased under these conditions while phospholipid output remained extremely low. The increased cholesterol secretion may represent extraction of cholesterol from the canalicular plasma membrane by taurocholate micelles as opposed to the concomitant secretion of both phospholipid and cholesterol in the presence of a functional mdr2 Pgp. Increased bile flow in (-/-) mice could be attributed completely to an increase in the bile salt-independent fraction and may therefore be caused by the bile duct proliferation in these mice.

The human MDR3 P-glycoprotein promotes translocation of phosphatidylcholine through the plasma membrane of fibroblasts from transgenic mice

The mouse mdr2 P-glycoprotein (P-gp) and its human MDR3 homologue are present in high concentrations in the canalicular membrane of hepatocytes. Mice lacking this protein are unable to secrete phosphatidylcholine (PC) into bile, suggesting that this P-gp is a PC translocator. We have tested this in fibroblasts from transgenic mice expressing the MDR3 gene under a vimentin promoter. Transgenic and control fibroblasts were incubated with [14C]choline to label PC. When the labeled cells were incubated with a PC transfer protein and acceptor liposomes, transfer of radioactive PC was enhanced in transgenic cells relative to the wild type controls. We conclude that the MDR3 P-glycoprotein is able to promote the transfer of PC from the inner to the outer leaflet of the plasma membrane, supporting the idea that this protein functions as a PC flippase.

Tissue distribution of the human MDR3 P-glycoprotein

BACKGROUND

P-glycoproteins (Pgps) belong to a family of well conserved plasma membrane proteins with two members in humans: MDR1 and MDR3. The MDR1 Pgp can transport drugs; the murine homologue of MDR3, mdr2, was recently shown by us to be involved in transport of the phospholipid phosphatidylcholine (lecithin) into bile.

EXPERIMENTAL DESIGN

We have determined the MDR3 mRNA levels in a panel of human tissues by RNase protection. We have also generated polyclonal antibodies specific for the MDR3 Pgp. Detection of the MDR3 Pgp in human tissues with these antibodies was by a streptavidin-ABC procedure.

RESULTS

The RNase protection results show that expression of the MDR3 gene has a more restricted distribution than that of MDR1. A high level of MDR3 mRNA was detected in the liver and in low levels in the adrenal gland, heart, striated muscle, spleen, and tonsil. In all of these tissues, some of the previously described splice variants of MDR3 were abundantly expressed. No indications were found for a tissue-specific regulation of alternative splicing of the MDR3 pre-mRNA. Two MDR3 Pgp-specific antibodies stained the bile canalicular membrane of hepatocytes across the entire liver lobule. No staining was found in the epithelial cells of the bile ductules and gall bladder, indicating that the staining at these sites with C219, a monoclonal antibody that recognizes both MDR1 and MDR3 Pgp, (mainly) represents the MDR1 Pgp. No MDR3 was detected by specific antibodies in the adrenal gland, spleen, and muscle. Since no staining was reported with MDR1-specific antibodies in muscle either, our results indicate that the C219 staining in some fibers of striated muscle represents a cross-reaction with another protein. One of the human MDR3-specific antibodies cross-reacted with the highly homologous mouse mdr2 Pgp. Staining with this antibody showed that the distribution of this protein in mouse liver and striated muscle is very similar to that of MDR3 Pgp in human tissues.

CONCLUSIONS

The highest expression of the MDR3 Pgp was found in liver in the canalicular membranes of hepatocytes. This is in agreement with a role for MDR3 in the transport of phospholipid into bile.

Mice with homozygous disruption of the mdr2 P-glycoprotein gene. A novel animal model for studies of nonsuppurative inflammatory cholangitis and hepatocarcinogenesis

The mouse mdr2 gene (and its human homologue MDR3, also called MDR2) encodes a P-glycoprotein that is present in high concentration in the bile canalicular membrane of hepatocytes. The 129/OlaHsd mice with a homozygous disruption of the mdr2 gene (-/- mice) lack this P-glycoprotein in the canalicular membrane. These mice are unable to secrete phospholipids into bile, showing an essential role for the mdr2 P-glycoprotein in the transport of phosphatidylcholine across the canalicular membrane. The complete absence of phospholipids from bile leads to a hepatic disease, which becomes manifest shortly after birth and shows progression to an end stage in the course of 3 months. The liver pathology is that of a nonsuppurative inflammatory cholangitis with portal inflammation and ductular proliferation, consistent with toxic injury of the biliary system from bile salts unaccompanied by phospholipids. Thus, the mdr2 (-/-) mice can serve as an animal model for studying mechanisms and potential interventions in nonsuppurative inflammatory cholangitis (in a generic sense) in human disease, be it congenital or acquired. When the mice are 4 to 6 months of age, preneoplastic lesions develop in the liver, progressing to metastatic liver cancer in the terminal phase. The mdr2 (-/-) mice therefore also provide a tumor progression model of value for the study of hepatic carcinogenesis. Interestingly, also in this regard, the model mimicks human disease, because chronic inflammation of the biliary system in humans may similarly carry increased cancer risk.

Traditional birth attendants in Malawi

Traditional Birth Attendants (TBAs) and traditional healers form an important link in the chain of health personnel providing primary health care in Malawi. In spite of the establishment of hospitals and health centres, it is to these traditional healers and TBAs that the majority of people turn in times of sickness and child-birth. Approximately 60 per cent of all deliveries in Malawi occur in the villages. It is therefore important that due regard be paid to the activities of these traditional practitioners in order to ensure the achievement of the goal--"Health for all by the year 2000". The training of TBAs is seen as part of the Maternal and Child Health Services in the country. The Ministry of Health is responsible for the training and control of Traditional Birth Attendants and in 1976 opened a register in order to list all those trained. In early 1978 a training course for selected TBAs was conducted at the Kamuzu Central Hospital, Lilongwe and from 1982 the training programme evolved into a national training programme for TBAs. By February 1987, a total of 841 Traditional birth Attendants had been trained and the programme is still continuing.

Disruption of the mouse mdr1a P-glycoprotein gene leads to a deficiency in the blood-brain barrier and to increased sensitivity to drugs

We have generated mice homozygous for a disruption of the mdr1a (also called mdr3) gene, encoding a drug-transporting P-glycoprotein. The mice were viable and fertile and appeared phenotypically normal, but they displayed an increased sensitivity to the centrally neurotoxic pesticide ivermectin (100-fold) and to the carcinostatic drug vinblastine (3-fold). By comparison of mdr1a (+/+) and (-/-) mice, we found that the mdr1a P-glycoprotein is the major P-glycoprotein in the blood-brain barrier and that its absence results in elevated drug levels in many tissues (especially in brain) and in decreased drug elimination. Our findings explain some of the side effects in patients treated with a combination of carcinostatics and P-glycoprotein inhibitors and indicate that these inhibitors might be useful in selectively enhancing the access of a range of drugs to the brain.

Homozygous disruption of the murine mdr2 P-glycoprotein gene leads to a complete absence of phospholipid from bile and to liver disease

Two types of P-glycoprotein have been found in mammals: the drug-transporting P-glycoproteins and a second type, unable to transport hydrophobic anticancer drugs. The latter is encoded by the human MDR3 (also called MDR2) and the mouse mdr2 genes, and its tissue distribution (bile canalicular membrane of hepatocytes, B cells, heart, and muscle) suggests a specialized metabolic function. We have generated mice homozygous for a disruption of the mdr2 gene. These mice develop a liver disease that appears to be caused by the complete inability of the liver to secrete phospholipid into the bile. Mice heterozygous for the disrupted allele had no detectable liver pathology, but half the level of phospholipid in bile. We conclude that the mdr2 P-glycoprotein has an essential role in the secretion of phosphatidylcholine into bile and hypothesize that it may be a phospholipid transport protein or phospholipid flippase.

Classical and novel forms of multidrug resistance and the physiological functions of P-glycoproteins in mammals

In this paper, we review recent work on multidrug resistance (MDR) in Amsterdam. We have generated mice homozygous for a disruption of one of their P-glycoprotein (Pgp) genes. The mutations do not interfere with viability or fertility, showing that these Pgps have no indispensable role in early development or metabolism. Mice homozygous for a disruption of their mdr2 gene, however, develop liver disease and this appears to be due to their complete inability to secrete phospholipids into bile. This suggests that the mdr2 Pgp (and, by inference, its human MDR3 homologue) is essential for translocating phospholipids through the hepatocyte canalicular membrane in which this Pgp is located. These and other results show the importance of the genetic approach for studying drug metabolism. MDR is not only caused by increased activity of Pgps. When the human non-small cell lung carcinoma cell line SW-1573 is selected in vitro for low level doxorubicin resistance, the resistant variants are nearly always multidrug resistant, but this is not due to increased Pgp activity. Only when resistance is pushed to higher levels does activation of the MDR1 Pgp gene occur. This suggests that clinically relevant levels of drug resistance in some cells may be caused predominantly by non-Pgp-mediated drug resistance mechanisms. The protein responsible for MDR in the SW-1573 cells has not yet been identified and experiments are in progress to find the gene encoding it.

Binding properties of monoclonal antibodies recognizing external epitopes of the human MDR1 P-glycoprotein

Monoclonal antibodies (MAbs) recognizing external epitopes of the human MDR1 P-glycoprotein have been used both for the detection of multidrug-resistant cells and as specific inhibitors of P-glycoprotein-mediated multidrug resistance. Using a panel of recently developed transfected or transgenic cell lines containing variants of the human MDR1 and MDR3 P-glycoproteins, we have compared the specificity and binding properties of the previously isolated MAbs MRK16, HYB-241, UIC2 and 4E3, and of the newly isolated MAb 7G4. The removal of 1, 2 or all 3 of the N-glycosylation sites present in the first extracellular loop of MDR1 P-glycoprotein did not significantly affect the binding of these MAbs. In contrast, 20 amino acid deletion in the first extracellular loop of MDR1 P-glycoprotein completely abolished binding of UIC2, whereas the binding of all other MAbs was hardly affected. None of the MAbs tested bound detectably to cell lines containing a high level of the human MDR3 P-glycoprotein. The differences in the binding specificity between UIC2 and the other tested antibodies parallel the reported functional differences in the ability of these antibodies to inhibit P-glycoprotein-mediated drug efflux.

Analysis of the expression of MRP, the gene for a new putative transmembrane drug transporter, in human multidrug resistant lung cancer cell lines

Human cells can become multidrug resistant (MDR) by an increase in the activity of the MDR1 P-glycoprotein or by other, as yet unknown mechanisms, referred to as non-P-glycoprotein mediated MDR (non-Pgp MDR). S. P. C. Cole et al. [Science (Washington DC), 258: 1650-1654, 1992] recently reported that in two cell lines non-Pgp MDR was associated with the overexpression of a new putative membrane transporter gene, MRP. Using an RNase protection assay we have analyzed the expression of MRP in non-Pgp MDR sublines of the human lung cancer cell lines SW-1573 (non-small cell lung cancer) and GLC4 (small cell lung cancer). In all of ten SW-1573 derived lines examined the MRP mRNA level was equal to that in the parental line, whereas MRP was 25-fold overexpressed in a resistant subline of GLC4. We conclude that overexpression of MRP cannot account for all forms of non-Pgp MDR.

Amino acid release from cerebral cortex in experimental acute liver failure, studied by in vivo cerebral cortex microdialysis

Both increased gamma-aminobutyric acid (GABA)-ergic and decreased glutamatergic neurotransmission have been suggested relative to the pathophysiology of hepatic encephalopathy. This proposed disturbance in neurotransmitter balance, however, is based mainly on brain tissue analysis. Because the approach of whole tissue analysis is of limited value with regard to in vivo neurotransmission, we have studied the extracellular concentrations in the cerebral cortex of several neuroactive amino acids by application of the in vivo microdialysis technique. During acute hepatic encephalopathy induced in rats by complete liver ischemia, increased extracellular concentrations of the neuroactive amino acids glutamate, taurine, and glycine were observed, whereas extracellular concentrations of aspartate and GABA were unaltered and glutamine decreased. It is therefore suggested that hepatic encephalopathy is associated with glycine potentiated glutamate neurotoxicity rather than with a shortage of the neurotransmitter glutamate. In addition, increased extracellular concentration of taurine might contribute to the disturbed neurotransmitter balance. The observation of decreasing glutamine concentrations, after an initial increase, points to a possible astrocytic dysfunction involved in the pathophysiology of hepatic encephalopathy.

Liver regeneration after partial hepatectomy in rats with defective bilirubin conjugation or biliary excretion

The role of conjugated bilirubin in liver regeneration after partial hepatectomy (PH) was studied in Gunn rats, in transport-mutant (TR-) rats, and in rats with extrahepatic biliary obstruction. Ornithine decarboxylase (ODC) and thymidine kinase (TK) activities in liver homogenates and immunohistochemistry of in vivo bromodeoxyuridine (BrdU) incorporation in hepatic DNA were followed as regeneration parameters at 24 and 48 hr after PH. The results relative to TK activity and BrdU incorporation were consistent with significantly delayed hepatic DNA synthesis in Gunn rats in comparison to control Wistar and TR- rats. This delay in DNA synthesis was not reflected in the hepatic ODC activity. After one week of complete common bile duct obstruction (CBO), an increased TK activity and BrdU incorporation was seen. PH following CBO resulted in a further increase in ODC activity and BrdU incorporation. TK activity did not change, however. These data relative to the regulation of hepatic DNA synthesis after PH in Gunn rats and in rats with extrahepatic biliary obstruction suggest a possible stimulatory role for conjugated bilirubin in hepatic regeneration; however, the normal hepatic DNA synthesis in TR- rats studied before PH and the subnormal DNA synthesis seen 24 hr after PH in TR- rats and in rats with CBO indicate that conjugated bilirubin does not stimulate hepatic DNA synthesis.

The relationship between plasma free fatty acids and experimentally induced hepatic encephalopathy in the rat

Two experimental models of hepatic encephalopathy in the rat have been investigated in order to study the postulated relationship between plasma free fatty acids concentration (C6 - C22:0) and the degree of hepatic encephalopathy. As a model of chronic hepatic encephalopathy, porta caval shunted rats were studied for 15 weeks, whereas rats with acute liver ischemia were used as a model for acute hepatic encephalopathy. In porta caval shunted rats only a minor degree of hepatic encephalopathy developed, whereas plasma ammonia concentration increased significantly (82 +/- 8 to +/- 440 +/- 32 mumol/l). Acute liver ischemia induced severe grades of hepatic encephalopathy associated with high levels of plasma ammonia (+/- 1 200 mumol/l). Since no significant changes in plasma free fatty acids were observed during both chronic and acute hepatic encephalopathy no correlation between plasma free fatty acids and the stage of hepatic encephalopathy was found. Our data do not support an important role of free fatty acids in the pathogenesis of acute or chronic hepatic encephalopathy in the rat.

Structure of the human MDR3 gene and physical mapping of the human MDR locus

Two genes, MDR1 and MDR3, constitute the human P-glycoprotein gene family. To examine the evolutionary relationship between the three known classes of mammalian P-glycoprotein genes, we have cloned the MDR3 gene and compared its structure with that of the human MDR1 and the mouse mdr1 (mdr1b) genes analyzed by other groups. The MDR3 gene contains 28 exons and 27 of these contain coding sequences for the two homologous halves of the protein that correlate with functional domains. This structure is virtually identical to that of the human MDR1 gene and the mouse mdr1 (mdr1b) gene, indicating that the exon/intron structure was fixed before the duplication events that generated different classes of P-glycoproteins, but after the P-glycoproteins diverged from related genes, like the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which has an entirely different exon/intron structure. The four alternatively spliced transcripts of the MDR3 gene arise from alternative splicing of exons 23 and 26. Our analysis of DNA clones covering about 120 kilobases (kb) of the human MDR locus, including the entire MDR3 gene (74 kb) and the intergenic region between both genes (34 kb), combined with pulsed-field gel electrophoresis data shows that the human MDR locus covers about 230 kb. In contrast to the mouse mdr genes, both human genes are transcribed in the same direction (MDR3 located downstream of MDR1). The CpG-rich sequences marking the 5' ends of both genes are hypomethylated to different extents in different cell lines. Hypomethylation roughly correlates with transcriptional activity.

Multidrug resistance phenotype of human BRO melanoma cells transfected with a wild-type human mdr1 complementary DNA

We have transfected a eukaryotic expression vector containing a mdr1 complementary DNA isolated from normal human liver into human BRO melanoma cells to study the drug-resistant phenotype produced by the exclusive overexpression of normal human mdr1 P-glycoprotein. The drug resistance pattern of mdr1-transfected clones includes relatively high resistance to gramicidin D (about 300-fold), vincristine (about 100-fold), and actinomycin D (about 100-fold) and a lower degree of resistance to doxorubicin (about 10-fold), VP16-213 (about 10-fold), and colchicine (about 6-fold). The transfectants did not exhibit resistance to trimetrexate, cis-platinum, mitomycin C, 1-beta-D-arabinofuranosylcytosine, bleomycin, G418, or magainin-2-amide; they were slightly more sensitive to verapamil (2-fold) but not to Triton X-100. As in other multidrug-resistant cell lines, resistance to vincristine could be reversed by verapamil and, more effectively, by cyclosporin A. Chloroquine only marginally increased drug sensitivity in mdr1-transfected cells. Gramicidin D resistance was also reversed by verapamil, suggesting that the mechanism of resistance to this polypeptide antibiotic is similar to that of other drugs transported by P-glycoprotein. Thus, expression of the wild-type mdr1 complementary DNA induces a drug-resistant phenotype similar to that induced by mdr1 complementary DNAs isolated from drug-resistant cell lines with relatively low colchicine resistance. As other cell lines may display a different pattern of drug resistance, it is clear that other resistance mechanisms or cell type-specific factors may modulate the resistance. mdr1-transfected cell lines provide a convenient tool for the identification of P-glycoprotein-mediated phenomena.

The nursing contributors to health services of the black states

The black population of South Africa consists of several different ethnic groups, each with its own historical identity. Seven of these groups have homelands, they are the Xhosa of Ciskei, the Zulu of KwaZulu, the Swazi of Kangwane, the Changana/Tonga of Gazankulu, the Basotho of Qwa- Qwa, the North Sotho of Lebowa, and the Venda of Venda.