Investigational new drug enabling angiotensin oral-delivery studies to attenuate pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a deadly and uncurable disease characterized by remodeling of the pulmonary vasculature and increased pulmonary artery pressure. Angiotensin Converting Enzyme 2 (ACE2) and its product, angiotensin-(1-7) [ANG-(1-7)] were expressed in lettuce chloroplasts to facilitate affordable oral drug delivery. Lyophilized lettuce cells were stable up to 28 months at ambient temperature with proper folding, assembly of CTB-ACE2/ANG-(1-7) and functionality. When the antibiotic resistance gene was removed, Ang1-7 expression was stable in subsequent generations in marker-free transplastomic lines. Oral gavage of monocrotaline-induced PAH rats resulted in dose-dependent delivery of ANG-(1-7) and ACE2 in plasma/tissues and PAH development was attenuated with decreases in right ventricular (RV) hypertrophy, RV systolic pressure, total pulmonary resistance and pulmonary artery remodeling. Such attenuation correlated well with alterations in the transcription of Ang-(1-7) receptor MAS and angiotensin II receptor AGTRI as well as IL-1β and TGF-β1. Toxicology studies showed that both male and female rats tolerated ~10-fold ACE2/ANG-(1-7) higher than efficacy dose. Plant cell wall degrading enzymes enhanced plasma levels of orally delivered protein drug bioencapsulated within plant cells. Efficient attenuation of PAH with no toxicity augurs well for clinical advancement of the first oral protein therapy to prevent/treat underlying pathology for this disease.

Oral delivery of novel human IGF-1 bioencapsulated in lettuce cells promotes musculoskeletal cell proliferation, differentiation and diabetic fracture healing

Human insulin-like growth factor-1 (IGF-1) plays important roles in development and regeneration of skeletal muscles and bones but requires daily injections or surgical implantation. Current clinical IGF-1 lacks e-peptide and is glycosylated, reducing functional efficacy. In this study, codon-optimized Pro-IGF-1 with e-peptide (fused to GM1 receptor binding protein CTB or cell penetrating peptide PTD) was expressed in lettuce chloroplasts to facilitate oral delivery. Pro-IGF-1 was expressed at high levels in the absence of the antibiotic resistance gene in lettuce chloroplasts and was maintained in subsequent generations. In lyophilized plant cells, Pro-IGF-1 maintained folding, assembly, stability and functionality up to 31 months, when stored at ambient temperature. CTB-Pro-IGF-1 stimulated proliferation of human oral keratinocytes, gingiva-derived mesenchymal stromal cells and mouse osteoblasts in a dose-dependent manner and promoted osteoblast differentiation through upregulation of ALP, OSX and RUNX2 genes. Mice orally gavaged with the lyophilized plant cells significantly increased IGF-1 levels in sera, skeletal muscles and was stable for several hours. When bioencapsulated CTB-Pro-IGF-1 was gavaged to femoral fractured diabetic mice, bone regeneration was significantly promoted with increase in bone volume, density and area. This novel delivery system should increase affordability and patient compliance, especially for treatment of musculoskeletal diseases.

Platelet Shape Change and Cytoskeletal Assembly: Effects of pH and Monovalent Cation lonophores

The monovalent cation ionophores monensin and nigericin cause platelet shape change at a rate of approximately 1/20 of that caused by ADP. The effect of monensin was studied further. Shape change caused by monensin is pH dependent, increasing in rate as extracellular pH increases. Monensin induced shape change is not blocked by 30 μM cinanserin which completely inhibits serotonin induced shape change. Also, the amount of serotonin secreted by monensin treated platelets is below the threshold required to induce shape change. 100 μM ATP which inhibits ADP induced shape change does not affect monensin induced shape change. Amiloride, a sodium transport blocker, inhibits both the rate of ADP induced shape change and platelet spreading on poly-lysine coated glass. Amorphous platelet cyto-skeletons isolated from resting platelets at pH 6.8 with Mg+ + but not Ca++ can be transformed into filament bundles by subsequent incubation at pH 7.6. We conclude that platelet shape change is at least in part triggered by changes in cellular Na+ and pH

Phosphodiesterase 4 Inhibitors Attenuate the Asthma Phenotype Produced by β2-Adrenoceptor Agonists in Phenylethanolamine N-Methyltransferase-Knockout Mice

Mice lacking the endogenous β2-adrenoceptor (β2AR) agonist epinephrine (phenylethanolamine N-methyltransferase [PNMT]-knockout mice) are resistant to developing an "asthma-like" phenotype in an ovalbumin sensitization and challenge (Ova S/C) model, and chronic administration of β2AR agonists to PNMT-KO mice restores the phenotype. Based on these and other studies showing differential effects of various β2AR ligands on the asthma phenotype, we have speculated that the permissive effect of endogenous epinephrine and exogenous β2AR agonists on allergic lung inflammation can be explained by qualitative β2AR signaling. The β2AR can signal through at least two pathways: the canonical Gαs-cAMP pathway and a β-arrestin-dependent pathway. Previous studies suggest that β-arrestin-2 is required for allergic lung inflammation. On the other hand, cell-based assays suggest antiinflammatory effects of Gαs-cAMP signaling. This study was designed to test whether the in vitro antiinflammatory effects of phosphodiesterase 4 inhibitors, known to increase intracellular cAMP in multiple airway cell types, attenuate the asthma-like phenotype produced by the β2AR agonists formoterol and salmeterol in vivo in PNMT-KO mice, based on the hypothesis that skewing β2AR signaling toward Gαs-cAMP pathway is beneficial. Airway inflammatory cells, epithelial mucus production, and airway hyperresponsiveness were quantified. In Ova S/C PNMT-KO mice, formoterol and salmeterol restored the asthma-like phenotype comparable to Ova S/C wild-type mice. However, coadministration of either roflumilast or rolipram attenuated this formoterol- or salmeterol-driven phenotype in Ova S/C PNMT-KO. These findings suggest that amplification of β2AR-mediated cAMP by phosphodiesterase 4 inhibitors attenuates the asthma-like phenotype promoted by β-agonists.

Oral tolerization with cardiac myosin peptide (614-629) ameliorates experimental autoimmune myocarditis: role of STAT 6 genes in BALB/CJ mice

INTRODUCTION

Experimental autoimmune myocarditis (EAM) is mediated by myocardial infiltration by myosin-specific T cells secreting inflammatory cytokines.

MATERIALS AND METHODS

To clarify the role of cytokines in EAM, we compared STAT 6-deficient ((-/-)) with STAT 4(-/-) and wild-type (BALB/CJ) mice following immunization with cardiac myosin peptide (614-629).

RESULTS

Wild-type mice developed severe disease with a small increase in severity in STAT 6(-/-) mice, while STAT 4(-/-) mice were resistant to EAM. STAT 6(-/-) mice had increased splenocyte proliferation and INF-gamma production versus wild type, while STAT 4(-/-) mice had decreased proliferation and INF-gamma. Following oral administration of myosin (614-629), tolerization was induced in wild-type mice evidenced by amelioration of myocarditis and up-regulation of IL-4. Adoptive transfer of splenocytes from orally tolerized mice resulted in inhibition of disease in STAT 6(-/-) mice.

CONCLUSION

These results demonstrate that oral tolerization ameliorates EAM in BALB/CJ mice and indicate a down-regulatory role for STAT 6 genes.

Induction of oral tolerization in CD86 deficient mice: a role for CD86 and B cells in the up-regulation of TGF-beta

Feeding myelin oligodendrocyte glycoprotein (MOG) followed by immunization results in induction of oral tolerance evidenced by the amelioration of experimental autoimmune encephalomyelitis (EAE). Oral tolerization is characterized by the suppression of Th1 responses and up-regulation of Th2 responses and TGF-beta. To identify the costimulatory molecules and cell types involved in cytokine-mediated suppression we examined wild type mice and mice deficient for either CD86 (CD86-/-) or B cells (muMT). Oral tolerance was found in CD86-/- mice evidenced by amelioration of disease severity, decreased proliferative responses and IFN-gamma production and increased IL-4. TGF-beta was not up-regulated in CD86-/- or muMT mice but was increased in wild type mice. Analysis of the gut associated lymphoid tissue (GALT) of different mouse strains (C57BL/6 and PLJxSJL F1) fed distinct myelin antigens (MOG and myelin basic protein, MBP) showed that TGF-beta was increased in wild type mice of both strains by 3 days post-immunization and further increased with time. In contrast, no up-regulation of TGF-beta was found in the GALT of CD86-/- or muMT mice. These results demonstrate that CD86 is not required for oral tolerization and that both CD86 and B cells are important for the up-regulation of TGF-beta following oral antigen.

Induction of low dose oral tolerance in IL-10 deficient mice with experimental autoimmune encephalomyelitis

IL-10 has been shown to be an important anti-inflammatory mediator that has both down-regulatory and immunomodulatory effects. Utilizing IL-10(-/-) mice we demonstrate the induction of low dose oral tolerance characterized by the up-regulation of TGF-beta and IL-4 and the suppression of Ag specific proliferation with little suppression of INF-gamma. More severe EAE was found in IL-10(-/-) mice than in wild type controls, however, feeding resulted in amelioration of disease severity in both groups. Orally tolerized IL-10(-/-) mice had greater disease severity compared to orally tolerized wild type mice. IL-4 was present in the GALT of IL-10(-/-) mice and up-regulation of TGF-beta was detected in the lamina propria of fed mice. These results demonstrate that IL-10 is not required for the induction of low dose oral tolerance but is required for the regulation of INF-gamma which affects severity of disease in tolerized mice.

Induction of low dose oral tolerance in monocyte chemoattractant protein-1- and CCR2-deficient mice

The chemokine monocyte chemoattractant protein-1 (MCP-1) and its receptor CCR2 have been shown to play an important role in the migration and trafficking of macrophages and Th1 effector cells in experimental autoimmune encephalomyelitis. Also, MCP-1 has been reported to regulate oral tolerance induction by inhibition of Th1 cell-related cytokines and by the ability of Abs to MCP-1 to inhibit oral tolerance. This study demonstrates that neither MCP-1 nor its receptor CCR2 is required for the induction of oral tolerance. Mice deletional for either MCP-1 or CCR2 had suppressed cell-proliferative and Th1 responses following oral administration and immunization with myelin oligodendrocyte glycoprotein (MOG(35-55)). TGF-beta was up-regulated in fed and immunized deletional mice, while IL-4 was absent from deletional mice, but up-regulated in controls. Decreased experimental autoimmune encephalomyelitis severity was found in MOG(35-55)-fed MCP-1 deletional mice, indicating induction of oral tolerance. These results demonstrate that MCP-1 is not required for induction of oral tolerance and that MCP-1 and CCR2 are essential for up-regulation of IL-4 in tolerized mice.

B cell-deficient (mu MT) mice have alterations in the cytokine microenvironment of the gut-associated lymphoid tissue (GALT) and a defect in the low dose mechanism of oral tolerance

Peripheral immune tolerance following i.v. administration of Ag has been shown to occur in the absence of B cells. Because different mechanisms have been identified for i.v. vs low dose oral tolerance and B cells are a predominant component of the gut-associated lymphoid tissue (GALT) they may play a role in tolerance induction following oral Ag. To examine the role of B cells in oral tolerance we fed low doses of OVA or myelin oligodendrocyte glycoprotein to B cell-deficient ( microMT) and wild-type C57BL/6 mice. Results showed that the GALT of naive wild-type and microMT mice was characterized by major differences in the cytokine microenvironment. Feeding low doses of 0.5 mg OVA or 250 microg myelin oligodendrocyte glycoprotein resulted in up-regulation of IL-4, IL-10, and TGF-beta in the GALT of wild-type but not microMT mice. Upon stimulation of popliteal node cells, in vitro induction of regulatory cytokines TGF-beta and IL-10 was observed in wild-type but not microMT mice. Greater protection against experimental autoimmune encephalomyelitis was found in wild-type mice. Oral tolerance in microMT and wild-type mice was found to proceed by different mechanisms. Anergy was observed from 0.5 mg to 250 ng in microMT mice but not in wild-type mice. Increased Ag was detected in the lymph of microMT mice. No cytokine-mediated suppression was found following lower doses from 100 ng to 500 pg in either group. These results demonstrate the importance of the B cell for the induction of cytokine-mediated suppression associated with low doses of Ag.

In situ immune response in gut-associated lymphoid tissue (GALT) following oral antigen in TCR-transgenic mice

Oral administration of Ag results in systemic hyporesponsiveness termed oral tolerance. The regulatory cells induced by oral Ag are effective in the suppression of Th1-type autoimmune diseases. We examined the cytokine microenvironment in gut-associated lymphoid tissue in response to orally administered OVA in OVA TCR-transgenic mice. Mice were fed a low (0.5 mg) or high (500 mg) dose of OVA one time or five times. Immunohistochemical analysis demonstrated increased IL-4, IL-10, and TGF-beta in the gut within 6 h of a low-dose feeding and after five low-dose or high-dose feedings. IFN-gamma and IL-2 either decreased or showed no change, with the exception of a small transient increase in IL-2 at 6 h after a low dose. Increases in IL-4 and IL-10 were found in the dome of the Peyer's patch, and increases in TGF-beta were observed in the interfollicular region and the villi. IL-10 was also substantially increased in the villi. IL-4 and IL-10 were produced predominately by CD4+ T cells. TGF-beta was found predominately in macrophages and CD4+ T cells. Peyer's patches had a marked up-regulation of TGF-beta mRNA as measured by RT-PCR. These results demonstrate the differential activation of cytokine production in discrete regions of gut-associated lymphoid tissue. The induction of cytokines known to inhibit autoimmune disease at the site of Ag absorption indicates an important role for the mucosal immune system in the establishment of oral tolerance.

In Situ Immune Response in Gut-Associated Lymphoid Tissue (GALT) Following Oral Antigen in TCR-Transgenic Mice

Oral administration of Ag results in systemic hyporesponsiveness termed oral tolerance. The regulatory cells induced by oral Ag are effective in the suppression of Th1-type autoimmune diseases. We examined the cytokine microenvironment in gut-associated lymphoid tissue in response to orally administered OVA in OVA TCR-transgenic mice. Mice were fed a low (0.5 mg) or high (500 mg) dose of OVA one time or five times. Immunohistochemical analysis demonstrated increased IL-4, IL-10, and TGF-β in the gut within 6 h of a low-dose feeding and after five low-dose or high-dose feedings. IFN-γ and IL-2 either decreased or showed no change, with the exception of a small transient increase in IL-2 at 6 h after a low dose. Increases in IL-4 and IL-10 were found in the dome of the Peyer’s patch, and increases in TGF-β were observed in the interfollicular region and the villi. IL-10 was also substantially increased in the villi. IL-4 and IL-10 were produced predominately by CD4+ T cells. TGF-β was found predominately in macrophages and CD4+ T cells. Peyer’s patches had a marked up-regulation of TGF-β mRNA as measured by RT-PCR. These results demonstrate the differential activation of cytokine production in discrete regions of gut-associated lymphoid tissue. The induction of cytokines known to inhibit autoimmune disease at the site of Ag absorption indicates an important role for the mucosal immune system in the establishment of oral tolerance.

Effect of oral beta interferon on subsequent immune responsiveness

Oral administration of myelin antigens reduces the incidence and severity of EAE in rat and mouse models and decreases the frequency of MBP-reactive cells and the frequency of attacks in some patients with multiple sclerosis. Low-dose oral tolerance has been shown to be mediated by Th2-type regulatory cells that secrete TGFbeta and IL-4/IL-10. Adjuvants and cytokines may modulate oral tolerance. The addition of betaIFN to the experimental therapy regimen, either orally or by intraperitoneal injection, has been shown to enhance the suppressive effects of oral myelin antigens when either are fed the suboptimal dosing regimen to suppress EAE. The current studies were conducted to elucidate the mechanism of the observed in vivo synergy of betaIFN and antigen feeding. Analysis of the in vitro proliferative response and cytokine production by lymphocytes from fed animals in response to specific antigen in culture shows that the synergistic effect may be related to both independent suppression of the immune response by oral betaIFN and enhanced production of TGFbeta and IL-4/IL-10. There was an unexpected increase in the production of gammaIFN by lymphocytes in vitro after three doses of oral betaIFN in vivo. These observations have important implications for the use of cytokines to modulate oral tolerance.

Induced hyporesponsiveness in rat Kupffer cells is not specific for lipopolysaccharide

The phenomenon of lipopolysaccharide (LPS)-induced hyporesponsiveness has been reported to occur in macrophage cell lines and primary cells. Hyporesponsiveness was evidenced by a diminution or lack of production of tumour necrosis factor-alpha (TNF-alpha) after sequential doses of LPS. In order to characterize the hyporesponsive state in Kupffer cells, the production of TNF-alpha was quantified after varying the concentration of a primary low dose of LPS prior to a challenge with a high, normally stimulatory dose of LPS. The kinetics of establishment of the hyporesponsive state and the effect of varying the bacterial serotype and genus of the challenge dose were determined. The specificity of the hyporesponsive state for LPS was examined. Our results demonstrate that complete hyporesponsiveness with no detectable production of TNF-alpha (< 30 pg/ml) was achieved after a primary dose > or = 10 ng/ml. Establishment of the hyporesponsive state took place within 6 hr. Induction of hyporesponsiveness was not dependent upon the serotype or genus of the challenge dose of LPS and was not specific for LPS. Complete hyporesponsiveness was induced after a primary dose (10 micrograms/ml) of the Gram-positive bacterium Corynebacterium parvum (Cp) and was evident upon challenge with 100 micrograms/ml Cp. The data indicate that the mechanisms by which LPS and Cp induce hyporesponsiveness are not identical in that a primary dose of LPS (10 ng/ml) induced only partial hyporesponsiveness upon challenge with Cp (100 micrograms/ml). These studies improve our understanding of Kupffer cell function.

Co-localization of class II antigen and exogenous antigen in the rat enterocyte

The role of class II major histocompatibility antigens in classical antigen-presenting cells has been described (Unanue (1984) Annu. Rev. Immunol. 2, 395–428; Watts and McConnell (1987) Rev. Immunol. 5, 461–475). Whether enterocytes, which also express class II antigens, can act as antigen-presenting cells in vivo is not known. One pre-requisite for a role for enterocytes in antigen presentation is an interaction between exogenous antigen and class II antigens. Our results demonstrate that class II antigen and exogenous antigen absorbed from the gastrointestinal tract are co-localized within endocytic compartments and along the basolateral membranes of enterocytes.

Divalent hapten-induced intestinal anaphylaxis in the mouse enhances macromolecular uptake from the stomach

The capacity of the stomach to participate in anaphylaxis induced by the hapten N,N'-di-2,4,dinitrophenyllysine (di-DNP-lysine) was examined in BDF1 female mice immunized with dinitrophenylated Ascaris suum extract. Immunized animals underwent laparotomy and nontraumatic pyloric occlusion using a microvascular clamp. Following wound closure, animals were gavage-fed ovalbumin together with di-DNP-lysine. Other mice were subjected to systemic anaphylaxis by intravenous injection of di-DNP-lysine administered 1 min after gavage feeding of ovalbumin. The intravenous and intragastric administration of di-DNP-lysine led to a sixfold or greater increase in serum immunoreactive ovalbumin. Examination of 1-micron sections of gastric tissue from DNP-Asc-immunized and unimmunized mice showed an intact mucosal and submucosal architecture. A 75% increase in the number of mast cells below the muscularis mucosa was seen in immunized compared with unimmunized BDF1 mice. Gastric tissue sections from immunized mice challenged orally or intravenously with di-DNP-lysine showed compaction of erythrocytes in blood vessels, degranulation of mast cells, degenerative changes in the gastric epithelium, expulsion of mucus from gastric glands, and edema in the lamina propria. The present model may be useful for further defining the consequences of anaphylaxis on the development of immune responses to dietary antigens.

Uptake and transport of epidermal growth factor by the small intestinal epithelium of the fetal rat

Epidermal growth factor may play an important part in postnatal gastrointestinal development. However, little is known of its role prenatally. The aim of this study was to detect epidermal growth factor in amniotic fluid and to study its uptake and transfer across the epithelium of fetal rat small intestine. Anesthetized 20-day gestation rats underwent caesarean section. Three fetuses were exteriorized, their abdomens were opened, and ligated loops of proximal and distal small intestine were infused with 100 micrograms epidermal growth factor. Infused segments were removed 30 min later and processed for electron microscopy, and tissue was embedded in LR gold resin. Sections were treated with rabbit anti-rat epidermal growth factor antibody, followed by 5 nm gold-labeled goat anti-rabbit immunoglobulin before staining. Epidermal growth factor was measured in amniotic fluid by radioimmunoassay. In the proximal and distal small intestine epidermal growth factor was found membrane-associated along the luminal surface of microvilli, within apical invaginations and endosomal compartments, free from the membrane in multivesicular bodies, within large clear vesicles, basal vesicles and in association with the basolateral membrane and beyond. Epidermal growth factor was found in amniotic fluid at a concentration of 0.38 +/- 0.07 (SD) ng/ml. This study shows that epidermal growth factor is present in amniotic fluid and is transported across the epithelium of fetal rats by an endocytotic process in both the upper and lower small intestine. It is likely that amniotic fluid epidermal growth factor plays a part in intestinal mucosal development, and may be active systemically after transepithelial passage in utero.

Prolactin is transported across the epithelium of the jejunum and ileum of the suckling rat

Milk prolactin is transferred from the gastrointestinal tract to the circulation of the suckling rat. To identify the site of prolactin penetration and to determine the mechanism by which the hormone traverses the mucosal barrier, we followed the uptake of prolactin from ligated loops of jejunum or ileum in vivo by three methods: autoradiography, transport of prolactin-gold conjugates, and immunocytochemistry. Autoradiographic studies demonstrated specific binding sites for 125I-prolactin on apical membranes of the jejunum and ileum. Excess cold prolactin reduced radiolabel in apical and basal compartments. Gel autoradiography of portal sera showed the presence of intact prolactin and a prolactin fragment following jejunal transport but only a prolactin fragment following ileal transport. Uptake of prolactin-gold conjugates demonstrated that, in the jejunum, label was present at the luminal surface, within endosomal compartments and lysosomes, in basal coated and smooth vesicles, within basal coated pits, and beyond the basolateral surface. In the ileum, label was found at the luminal surface; within the tubulocisternae, endosomal vesicles, lysosomes, and basal smooth vesicles; and beyond the basolateral surface. Immunoreactive prolactin was present throughout the transepithelial pathways. This study demonstrates that prolactin is selectively and nonselectively absorbed in the jejunum and ileum and that the hormone is directed either to the lysosome for degradation or across the epithelium by means of a transcellular pathway.

Transepithelial transport of epidermal growth factor by absorptive cells of suckling rat ileum

Epidermal growth factor (EGF), an acid-stable peptide present in rodent and human milk, is absorbed and promotes intestinal growth when fed to suckling rats. To determine whether absorptive cells of suckling rat ileum conduct selective transepithelial transport of EGF, we followed uptake of 125I-EGF from ileal loops by autoradiography and biochemical methods. Specific binding sites for 125I-EGF were localized by electron microscope autoradiography on apical membranes of ileal epithelial sheets in vitro. During uptake in vivo, radiolabeled molecules were concentrated in apical endosomal compartments and were also associated with lysosomal vacuoles, basolateral cell surfaces, and lamina propria. Excess cold EGF reduced basolateral label by 44% and TCA precipitable serum label by 38%. After 30 and 60 min of continuous uptake, radiolabeled molecules in epithelium, denuded mucosa, blood, and liver were analyzed under reducing conditions by reversed-phase high-pressure liquid chromatography (HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Although considerable degradation of 125I-EGF occurred after uptake from the lumen, a portion of radiolabel in epithelium and mucosa represented 125I-EGF which eluted somewhat more rapidly from C18 HPLC columns and showed a slight decrease in apparent molecular weight by SDS-PAGE. All radiolabel in blood and liver represented breakdown products. Thus, EGF is selectively transported across the ileal epithelium in suckling rats but is modified during transport. Milk EGF may accumulate in the lamina propria where it could influence growth and maturation of the suckling intestine.

Glycoconjugate distribution and mobility on apical membranes of absorptive cells of suckling rat ileum in vivo

The luminal membrane of ileal absorptive cells in suckling rats includes two domains: microvillar membranes and deep invaginations between microvilli. We examined the fates of foreign macromolecules that bind to anionic or saccharide sites on these domains after infusion into ligated loops in vivo. Cationized ferritin (CF) and ferritin-RCAI (beta-galactosyl) binding sites were distributed over the entire apical membrane. Ligands bound to apical invaginations were rapidly endocytosed, but ligands on microvilli were not. After CF binding, anionic sites on microvilli were mobile in the plane of the membrane and formed CF clusters at the tip and base of each microvillus. RCAI binding sites did not cluster. Wheat germ agglutinin (WGA, sialic acid) labeling was restricted to microvillus tips of mature cells but was dispersed over the microvillar surfaces of lower villus cells. Ferritin conjugates of Concanavalia ensiformis (Con A), Ulex europaeus agglutinin (UEA), and Dolichos biflorus agglutinin (DBA) did not bind to cell surfaces in vivo. Aldehyde fixation dramatically altered lectin binding patterns, resulting in unmasking and labeling of Con A, WGA, and DBA binding sites that were unavailable in vivo.

Membrane-bound and fluid-phase macromolecules enter separate prelysosomal compartments in absorptive cells of suckling rat ileum

The absorptive cell of the suckling rat ileum is specialized for the uptake and digestion of milk macromolecules from the intestinal lumen. The apical cytoplasm contains an extensive tubulocisternal system, a variety of vesicles and multivesicular bodies (MVB), and a giant phagolysosomal vacuole where digestion is completed. To determine if sorting of membrane-bound and fluid-phase macromolecules occurs in this elaborate endocytic system, we infused adsorptive and soluble tracers into ligated intestinal loops in vivo and examined their fates. Lysosomal compartments were identified by acid phosphatase histochemistry. Native ferritin and two ferritin-lectin conjugates that do not bind to ileal membranes (Con A, UEAI) served as soluble tracers. Horseradish peroxidase binds to ileal membranes and thus was not useful as a fluid-phase tracer in this system. Cationized ferritin and a lectin that binds to terminal B-D-galactosyl sites on ileal membranes (Ricinus communis agglutinin [RCAI]-ferritin) were used as tracer ligands. All tracers entered the wide apical invaginations of the luminal cell surface and were transported intracellularly. Membrane-bound tracers were found in coated pits and vesicles, and throughout the tubulocisternal system (where cationized ferritin is released from the membrane) and later, in large clear vesicles and MVB. In contrast, fluid-phase tracers appeared within 5 min in vesicles of various sizes and were not transported through the tubulocisternae, rather, they were concentrated in a separate population of vesicles of increasing size that contained amorphous dense material. Large clear vesicles, large dense vesicles, and MVB eventually fused with the giant supranuclear vacuole. Acid phosphatase activity was present in MVB and in the giant vacuole but was not present in most large vesicles or in the tubulocisternae. These results demonstrate that membrane-bound and soluble protein are transported to a common lysosomal destination via separate intracellular routes involving several distinct prelysosomal compartments.

alpha-Actinin and vinculin in normal and thrombasthenic platelets

Recently, the contractile protein alpha-actinin was identified in normal human platelets by its antigenic cross-reaction with a monospecific antibody to purified muscle alpha-actinin. In this study, we extend that preliminary identification of platelet alpha-actinin. Amino acid analysis, one-dimensional peptide maps, and silver stain analysis on polyacrylamide gels demonstrate that human platelet alpha-actinin shows a greater degree of similarity to smooth muscle alpha-actinin than to striated muscle alpha-actinin. There is no evidence to suggest that alpha-actinin is a glycoprotein. In addition, we find that thrombasthenic platelets, which are deficient in glycoproteins IIb and IIIa (GPIIb and GPIIIa) contain normal amounts of alpha-actinin, confirming the recent finding that alpha-actinin and GPIIIa are different proteins in human platelets. We demonstrate that both normal and thrombasthenic platelets also contain vinculin, a 130,000-dalton polypeptide found in many cell types at sites of end-on attachment of microfilaments to the plasma membrane. Thus, the thrombasthenic defect in GPIIb and GPIIIa does not diminish the content of either alpha-actinin or vinculin.

Platelet shape change and cytoskeletal assembly: effects of pH and monovalent cation ionophores

The monovalent cation ionophores monensin and nigericin cause platelet shape change at a rate of approximately 1/20 of that caused by ADP. The effect of monensin was studied further. Shape change caused by monensin is pH dependent, increasing in rate as extracellular pH increases. Monensin induced shape change is not blocked by 30 microM cinanserin which completely inhibits serotonin induced shape change. Also, the amount of serotonin secreted by monensin treated platelets is below the threshold required to induce shape change. 100 microM ATP which inhibits ADP induced shape change does not affect monensin induced shape change. Amiloride, a sodium transport blocker, inhibits both the rate of ADP induced shape change and platelet spreading on poly-lysine coated glass. Amorphous platelet cytoskeletons isolated from resting platelets at pH 6.8 with Mg++ but not Ca++ can be transformed into filament bundles by subsequent incubation at pH 7.6. We conclude that platelet shape change is at least in part triggered by changes in cellular Na+ and pH.

alpha-Actinin and membrane glycoprotein IIIa are different proteins in human blood platelets

It has been suggested that a platelet protein that is very similar to muscle alpha-actinin is identical to the membrane glycoprotein IIIa (GPIIIa) of platelets and is responsible for anchoring actin filaments directly into the plasma membrane of platelets. To determine if alpha-actinin and GPIIIa are related in platelets, we analyzed the purified proteins on 5% sodium dodecyl sulfate/polyacrylamide gels. The two proteins differ in mobility in both the unreduced and reduced states, and they stain differently with silver stain. In addition, alpha-actinin is a prominent component of the detergent-insoluble cytoskeletons of platelets, whereas GPIIIa is absent from these structures. By using monospecific antisera to the individual proteins, it was demonstrated that alpha-actinin and GPIIIa are immunologically distinct. We conclude that alpha-actinin and GPIIIa are different proteins in human blood platelets and that it is unlikely that alpha-actinin is an integral membrane protein.

Platelet activation and microfilament bundling

Human platelets were obtained in the fully resting state by treating discoid populations with 1.5 mM tetracaine and in the activated state by treatment with 2 microM A-23187. After gel filtration or washing, respectively, platelet suspensions were lysed with 1% Triton X-100 at pH 6.8. The precipitates from resting platelets viewed by negative staining appeared predominantly granular with a few very short microfilaments. They contained polypeptides of 250, 100, 45, 38, 36.5, and 35 Kdaltons, and three small polypeptides including one with the mobility of profilin on SDS gels. Precipitates from activated platelets lacked this low molecular weight band and contained a major band at 200 Kdaltons with the mobility of myosin; these precipitates had significant K+, Ca++ ATPase activity absent from the precipitate of resting platelets. As seen in negative staining, precipitates from activated platelets contained microfilaments arranged as nets or bundles. The granular resting precipitates were transformed in vitro into microfilament bundles by washing the precipitates in buffer at higher pH (7.6) in the presence of 5 X 10(-5) M calcium chloride.