Synthesis of pyrophosphate-containing compounds that stimulate Vgamma2Vdelta2 T cells: application to cancer immunotherapy.

Human Vgamma2Vdelta2 T cells recognize nonpeptide antigens, such as isoprenoid pyrophosphomonoester intermediates, alkylamine compounds, and bisphosphonate drugs, as well as some tumor cells. Although attempts have been made to derive novel cancer immunotherapies based on the discovery of these unconventional antigens, effective therapies remain to be developed. Here, we synthesized a series of pyrophosphate-containing compounds and examined the chemical requirements for the recognition of pyrophosphomonoester antigens by gammadelta T cells. The structural analysis clearly demonstrated that a proximal methylene moiety plays a crucial role in the stimulatory activity of the antigens. For optimal gammadelta T cell proliferation, we find that the use of human serum albumin was preferred and that pyrophosphomonoesters were superior to nitrogen-containing bisphosphonate compounds. Using these techniques, we have successfully expanded gammadelta T cells from healthy donors as well as from cancer patients using one of the most active compounds, 2-methyl-3-butenyl-1-pyrophosphate (2M3B1PP). The resulting expanded gammadelta T cells exhibited potent, cytotoxic activity against a wide variety of tumor cell lines. Even gammadelta T cells from a patient with advanced liver carcinoma efficiently responded to 2M3B1PP and exhibited strong cytotoxic activity against tumor cells. The pretreatment of tumor cells with nonpeptide antigens was essential for efficient cytotoxicity via TCR-gammadelta. The present study suggests a novel strategy for cancer immunotherapy using synthetic small pyrophosphate-containing compounds and nitrogen-containing bisphosphonates.

Mechanism of the linkage between te electrophoretic mobility and oxygen uptake of ascites tumor cells.

Electrophoretic mobility, glucose metabolism, and oxygen uptake were studied in three leukemic and in four nonleukemic strains of ascites tumor cells. The cells differed markedly in mobility. This variation was related neither to cell growth nor to rates of endogenous respiration and aerobic glycolysis. The nonleukemic tumor cells showed higher mobility than did the leukemic cells. Additional increases in mobility appear to be related to suppressed oxygen uptake, which results from the addition of glucose or 0.05 mM 2,4-dinitrophenol. The augmented negative surface charge does not seem to be related to those ionogenic sites susceptible to neuraminidase. However, RNase treatment of the nonleukemic tumor cell does reveal the presence in their surface membrane of negatively charged sites susceptible to this enzyme. Such RNase-susceptible ionogenic sites presumably redistribute at the cell surface membrane from the inner sites as a response to suppressed oxygen uptake. This results in a higher negative surface charge and increased mobility. The leukemic cells, on the other hand, did not show any change in oxygen uptake or mobility in the presence of glucose. Moreover, the reduced rate of oxygen uptake induced by the addition of 0.05 mM 2,4-dinitrophenol did not result in any significant alterations in mobility. This is consistent with the observation that the ionogenic sites susceptible to RNase do not appear at the surface of the leukemic cells upon suppressed oxygen uptake. The leukemic cells have thus been shown to differ from the nonleukemic tumor cells in certain aspects of their glucose metabolism as well as in the electrophoretic properties of their surface.

Isolation and sequence analysis of human cadherin-6 complementary DNA for the full coding sequence and its expression in human carcinoma cells.

The expression pattern of E- and P-cadherin in human carcinomas has been reported by many laboratories. However, little is known about the involvement of other cadherin types in human carcinomas. cDNA clones for a cadherin molecule were isolated from a cDNA library of human hepatocellular carcinoma cells which lacked E- and P-cadherin expression but exhibited cell aggregation activity mediated by an unknown cadherin, and they were subjected to sequence analysis. The overlapped clones covered 4315 nucleotides and were found to encode a typical cadherin molecule consisting of 790 amino acids. Since the deduced amino acid sequence was identical to a partially available human cadherin-6 sequence except for two amino acid residues, the clones were considered to be human cadherin-6 cDNAs encoding the entire open reading frame. The deduced amino acid sequence also showed extremely high homology with recently reported rat K-cadherin, 97% for the putative mature protein, suggesting that cadherin-6 is the human counterpart of rat K-cadherin. Expression of cadherin-6 in various human normal tissues and carcinoma cells was examined by Northern blot analysis using a specific probe corresponding to the signal and precursor sequence. Among normal tissues examined, brain, cerebellum, and kidney showed strong expression of cadherin-6, whereas lung, pancreas, and gastric mucosa showed weak expression. Transcripts of cadherin-6 were not detected in normal liver, whereas four of six hepatocellular carcinoma cell lines examined expressed cadherin-6 abundantly. As reported for rat K-cadherin, three renal carcinoma cell lines also expressed cadherin-6 strongly. The most interesting finding was obtained for small cell lung carcinoma lines. Among 15 of such cell lines examined, all of 11 cadherin-6-positive lines were classified into the classic type, whereas the negative cell lines were all of the variant type. The present results suggest that besides E- and P-cadherin, other cadherin molecules are expressed in human cancers and are responsible for additional biological properties of the carcinoma cells.

Reversible squamous cell characteristics induced by vitamin A deficiency in a small cell lung cancer cell line.

A cultured small cell lung cancer cell line (Lu-134-B-S) established from a xenotransplanted tumor in a nude mouse, which had originated from a primary focus of small cell lung cancer, showed morphological changes when the medium was changed from RPMI 1640 supplemented with 10% fetal calf serum to RPMI 1640 supplemented with 10% delipidized fetal calf serum. That is, it consisted of "classic" small cells in the former medium, but after eight passages in the latter medium many cells became squamous cells, possessing abundant eosinophilic cytoplasm and intercellular bridges. Immunohistochemically, they reacted to antikeratin and antiinvolucrin antibodies. Electron microscopically, well developed desmosomes and associated tonofibrils were noted, and electrophoretically, the amount of medium (Mr 57,000 and 59,000) and large-sized (Mr 67,000) keratins were found to increase with the change of the medium. These changes reversed to the original small cell morphology within 4 weeks after addition of vitamin A (retinoic acid) to the medium. These findings suggested that deficiency of vitamin A caused the change of the cell from small to squamous cell and vice versa.

Heterogeneity of lung cancer cells with respect to the amplification and rearrangement of myc family oncogenes.

Seventy lung tumors from 53 patients were analysed for alterations of myc family oncogenes, c-myc, N-myc and L-myc, to evaluate when activation of these genes occurs during tumor development. The 53 cases were 17 small cell carcinomas (SCCs), 18 adenocarcinomas, 12 squamous cell carcinomas (SqCs), 4 large cell carcinomas and 2 adenosquamous carcinomas. Either N-myc or L-myc was amplified in 4 of the 17 (one N-myc and 3 L-myc) SCCs (24%), while c-myc was amplified in 3 of the 12 SqCs (25%). In one SCC, amplification of N-myc was found in the primary tumor, a pulmonary hilar lymph node metastasis and a pleural metastasis, but not in a liver metastasis or a para-aortic lymph node metastasis. In one SqC, c-myc was amplified in a pleural metastasis and a lymph node metastasis, but not in the primary tumor. In 2 cases of SCCs, amplification or rearrangement of c-myc was detected only in the cell lines, but not in the original tumors taken from the same individuals. These results indicate that tumor cells were heterogeneous for amplification and rearrangement of myc family oncogenes, and suggest that activation of these oncogenes in SCCs and SqCs occurs not at the time of malignant transformation but during tumor progression.

Altered expression of the retinoblastoma (RB) gene in small-cell carcinoma of the lung.

Nine lung small-cell carcinoma (SCC) cell lines and 9 lung non-SCC cell lines were examined for structural changes of the retinoblastoma (RB) gene as well as its expression using a complementary DNA probe. The RB protein product was investigated using an anti-RB antibody which we produced. Although homozygosity or hemizygosity of the RB gene was suggested in 8 of 9 SCCs and one of 2 large cell carcinomas (LCCs) by Southern blot analysis using an RB cDNA probe and polymorphic DNA markers for chromosome 13, no obvious structural changes of the RB gene were detected in these 18 cell lines. However, RB transcripts were either markedly reduced in quantity or abnormal in length in 3 of 9 SCCs. The specific 115 kD protein was not immunoprecipitated by the anti-RB antibody in all 9 SCCs with either normal or abnormal size RB mRNA. Three of 4 adenocarcinomas (AdCs), all 3 squamous cell carcinomas, and one of 2 LCCs expressed normal size RB mRNA, and the 115 kD protein was immunoprecipitated by the anti-RB antibody. The 115 kD protein was also absent in one of 2 LCCs with shortened RB mRNA and in one of 4 AdCs with low level of RB mRNA expression. These results strongly suggest that inactivation of the RB gene might be involved in the development of lung cancers, especially of SCCs.

Receptor-mediated endocytosis of A14-125I-insulin by the nonfiltering perfused rat kidney.

The mechanism of insulin uptake and/or degradation in the peritubular circulation of the kidney was investigated using nonfiltering perfused rat kidneys, in which glomerular filtration was sufficiently reduced. After perfusion of A14-125I-insulin in the nonfiltering kidney for designated intervals, the acid-wash technique was employed to separately measure the acid-extractable and acid-resistant A14-125I-insulin, which were quantitated by HPLC and TCA-precipitability. HPLC profiles showed that the nonfiltering kidney metabolizes A14-125I-insulin only to a small extent during 1-h perfusion, suggesting that the peritubular clearance of A14-125I-insulin was not due to extracellular degradation but for the most part to uptake by the kidney. Acid-extractable A14-125I-insulin rapidly increased with time and reached pseudo-equilibrium with perfusate at approx. 10 min, whereas acid-resistant A14-125I-insulin increased continuously. An endocytosis inhibitor, phenylarsine oxide, inhibited significantly the acid-resistant A14-125I-insulin with no change in acid-extractable A14-125I-insulin, suggesting that the peritubular uptake of A14-125I-insulin largely represents endocytosis of the peptide into the intracellular space. Moreover, both the acid-extractable and acid-resistant A14-125I-insulin were significantly decreased in the presence of unlabeled insulin (1 microM). These lines of evidence suggest that insulin is taken up by the nonfiltering perfused kidney via receptor-mediated endocytosis (RME), which possibly occurs at the basolateral side of renal tubular cells, and that the peritubular clearance of insulin is largely accounted for by this mechanism.

In vitro models for the blood-brain barrier.

The aim of the present study was to identify a model for the blood-brain barrier based on the use of a continuous cell line, and to investigate the specificity of this model. A set of test compounds, reflecting different transport mechanisms and different degrees of permeability, as well as different physiochemical properties was selected. In vivo data for transport across the blood-brain barrier of this set of test compounds was generated as part of the study using two different in vivo models. A computational prediction model was also developed, based on 74 proprietary Pharmacia compounds, previously tested in one of the in vivo models. Molsurf descriptors were calculated and 21 descriptors were correlated with log(Brain(conc.)/Plasma(conc.)) using partial least squares projection to latent structures (PLS). However, the correlation between predicted and measured values was found to be rather low and differed between one and two log units for several of the compounds. The test compounds were analyzed in vitro using primary bovine and human brain endothelial cells co-cultured with astrocytes, and also using two different immortalized brain endothelial cell lines, one originating from rat and one from mouse. Cell models using cells not derived from the blood-brain barrier, ECV/C6, MDCK and Caco-2 cell lines, were also used. No linear correlation between in vivo and in vitro permeability was found for any of the in vitro models when all compounds were included in the analysis. The highest r2 values were seen in the bovine brain endothelial cells (r2=0.43) and MDCKwt (r2=0.46) cell models. Higher correlations were seen when only passively transported compounds were included in the analysis, bovine brain endothelial cells (r2=0.74), MDCKwt (r2=0.65) and Caco-2 (r2=0.86). By plotting in vivo Papp values against logDpH7.4 it was possible to classify compounds into four different classes: (1) compounds crossing the blood-brain barrier by passive diffusion, (2) compounds crossing the blood-brain barrier by blood-flow limited passive diffusion, (3) compounds crossing the blood-brain barrier by carrier mediated influx, and (4) compounds being actively excreted from the brain by active efflux. Papp and Pe values obtained using the different in vitro models were also plotted against logDpH7.4 and compared to the plot obtained when in vivo Papp values were used. Several of the in vitro models could distinguish between passively distributed compounds and efflux substrates. Of the cell lines included in the present study, the MDCKmdr-1 cell line gave the best separation of passively and effluxed compounds. Ratios between AUC in brain and AUC in blood were also calculated for six of the compounds and compared to ratios between Pe or Papp for transport in the apical to basolateral and basolateral to apical direction. Again the MDCKmdr-1 cell line gave the best correlation with only one compound (AZT) giving large discrepancy between in vitro and in vivo data. None of the in vitro models could identify compounds known to be substrates for carrier mediated influxed as such, and the results indicate that a tighter in vitro blood-brain barrier model probably is needed in order to facilitate studies on carrier mediated influx. The findings presented also indicate that identification of "batteries" of in vitro tests are likely to be necessary in order to improve in vitro-in vivo correlations and to make it possible to perform acceptable predictions of in vivo brain distributions from in vitro data.

Stereospecificity of triiodothyronine transport into brain, liver, and salivary gland: role of carrier- and plasma protein-mediated transport.

The stereospecificity of T3 transport through the walls of the brain capillary, i.e. the blood-brain barrier (BBB), and the salivary gland capillary and through the hepatocyte plasma membrane was studied with a tissue-sampling single injection technique in rats. In the absence of plasma proteins, the ED50 of inhibition of the saturable transport of [125I]L-T3 through the BBB was 1 microM for unlabeled L-T3 and 9 microM for unlabeled D-T3. The brain extraction of [125I]D-T3, 5.9 +/- 0.1% (+/- SE), was about one third that of [125I]L-T3. Conversely, no saturable and no stereospecific T3 transport was observed for the salivary gland capillary, which, unlike the brain capillary, is porous. The hepatic extraction of T3 was minimally stereospecific in the absence of plasma proteins. In the presence of 5 g/dl bovine albumin, the fraction of circulating D- or L-T3 that was available for transport into liver (50-100%) was many-fold greater than the fraction that was free in vitro (approximately 2%); therefore, both D-T3 and L-T3 were available for uptake by liver from the circulating albumin-bound pool. This plasma protein-mediated transport of T3 is believed to represent a process of enhanced dissociation of T3 from the albumin-binding site, since the plasma protein per se is not significantly taken up by liver on a single pass. However, in the presence of 5 g/dl bovine albumin, the extravascular hepatic extraction of [125I]D-T3 (50 +/- 2%) was nearly half that for [125I]T3 (93 +/- 12%), although no significant difference in the in vitro binding of [125I]D-T3 and [125I]L-T3 to 5 g/dl bovine albumin was found with equilibrium dialysis. In addition, the isoelectric point of bovine albumin bound to [125I] L-T3 (5.1) was higher than that of bovine albumin bound to [125I] D-T3 (5.0), as determined by isoelectric focusing, which indicates that the surface of the bovine albumin molecule is slightly more positive when the protein binds L-T3 as opposed to D-T3. The isoelectric focusing and in vivo transport data together suggest that the interaction between the surfaces of the plasma protein and the hepatic microcirculation that is presumed to cause enhanced hormone dissociation from the protein-binding site is electrostatic in nature. These studies (1) show that the BBB thyroid hormone transport system is sharply stereospecific, and this property is probably a major factor underlying the low biological potency of D-T3 in brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential binding of testosterone and estradiol to isoforms of sex hormone-binding globulin: selective alteration of estradiol binding in cirrhosis.

The MCR of testosterone is decreased but the MCR of estradiol is unchanged in men with cirrhosis and elevated serum sex hormone-binding globulin (SHBG) concentrations. Previous studies indicated that SHBG from cirrhotic men selectively delivers estradiol, but not testosterone, to peripheral tissues of rats in vivo. These results suggest that estradiol and testosterone may bind to different SHBG isoforms in serum and that the estradiol-binding isoforms may be selectively altered in cirrhosis. This hypothesis was tested by polyacrylamide gel isoelectric focusing and fast protein liquid chromatography chromatofocusing. After Concanavalin-A affinity purification of serum glycoproteins from pregnant women, normal men, normal women, and cirrhotic men, the glycoprotein fraction was reconstituted, labeled with [3H]testosterone or [3H]estradiol, and applied to isoelectric focusing gels. Testosterone was bound selectively by the most acidic isoforms of SHBG, pI 4.5-5.4, and there was a significant anodal shift of the estradiol-binding isoforms in serum from cirrhotic men compared to that in serum from normal men. The selective binding of testosterone to the most acidic isoforms of SHBG was confirmed by fast protein liquid chromatography chromatofocusing, wherein the binding reactions were measured at neutral pH after separation of the isoforms. These biochemical studies and previous physiological experiments question the conventional view that testosterone and estradiol bind to a single competitive binding site on SHBG. Rather, testosterone is selectively bound by the most acidic SHBG isoforms. The estradiol-binding isoforms undergo a significant anodal shift in cirrhosis; this abnormality may result in the lack of decrease in estradiol MCR in cirrhosis.

GAT2/BGT-1 as a system responsible for the transport of gamma-aminobutyric acid at the mouse blood-brain barrier.

In this study, the gamma-aminobutyric acid (GABA) transporter at the blood-brain barrier (BBB) was identified by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunostaining analysis, and the transport mechanism was characterized using a conditionally immortalized mouse brain capillary endothelial cell line (TM-BBB) as an in vitro model of the BBB. gamma-Aminobutyric acid transport was studied by the cellular uptake of [ 3 H]GABA. [3H]GABA uptake by TM-BBB cells was Na (+)-, Cl(-)-, and concentration-dependent. The corresponding Michaelis-Menten constant was 679 +/- 80 micromol/L and the maximal uptake rate was 4,790 +/- 494 pmol/(mg protein x 5 minutes). [3H]GABA uptake by TM-BBB cells was significantly inhibited by betaine, beta-alanine, nipecotic acid, taurine, and quinidine, whereas probenecid, L-proline, creatine, and glycine had no effect. This type of inhibition is consistent with the predominant involvement of the GAT2/BGT-1 transporter in TM-BBB cells. RT-PCR analysis showed that GAT2/BGT-1 mRNA was expressed in TM-BBB cells, whereas Western blot analysis showed that TM-BBB cells and mouse brain capillaries express GAT2/BGT-1 protein. Moreover, confocal immunofluorescent microscopy of dual-labeled mouse brain sections demonstrated the colocalization of GAT2/BGT-1 and P-glycoprotein, a BBB-specific marker, on brain capillaries labeled with anti-GAT2/BGT-1 antibody and anti-P-glycoprotein antibody, respectively. These results are evidence that GAT2/BGT-1 is expressed at the BBB and is involved in GABA transport across the BBB.

Brain-to-blood active transport of beta-alanine across the blood-brain barrier.

A high-affinity antiluminal uptake system for beta-alanine was demonstrated in primary cultured bovine brain capillary endothelial cells (BCEC) for which K(t) is 66.9 microM. beta alanine uptake was energy-, sodium- and chloride ion-dependent. beta-amino acids strongly inhibited the uptake, while alpha- and gamma-amino acids had a little or no inhibitory effect. In ATP-depleted cells, the uptake was stimulated by preloading beta-alanine or taurine but not by L-leucine. These results suggest that beta-alanine is actively transported across the antiluminal membrane of BCECs that is common to beta-amino acids. The system may function for the efflux from the brain to blood.

Presenile-onset cerebral adrenoleukodystrophy presenting as Balint's syndrome and dementia.

We describe a patient with presenile-onset cerebral adrenoleukodystrophy presenting as Balint's syndrome and dementia. There were demyelinating MRI changes in the parieto-occipital white matter bilaterally, including the splenium of the corpus callosum. Therapeutic trials using 1-deamino-(8-D-arginine)-vasopressin, very long-chain fatty acid-free diet, and gamma-globulin were of no benefit.

Decreased plasma tissue factor pathway inhibitor activity in ischemic stroke patients.

Although tissue factor pathway inhibitor (TFPI) plays an essential role in the regulation of blood coagulation, the quantitative changes in its levels in thrombotic disease are still undefined. We compared TFPI activity in ischemic stroke patients and control subjects matched for age and cholesterol level to determine whether TFPI activity is changed in the disease. TFPI activity was significantly lower in the stroke patients (1.01 +/- 0.24 U/ml) than in the control subjects (1.10 +/- 0.16 U/ml). In relation to clinical subtypes of stroke, TFPI activity in atherothrombotic infarction (0.93 +/- 0.19 U/ml) and lacunar infarction (0.99 +/- 0.23 U/ml) was significantly lower than in the control subjects, whereas the level in cardioembolic infarction (1.16 +/- 0.31 U/ml) was not. No relationship could be established between TFPI activity and other haemostatic parameters reflecting the production of thrombin/fibrin and the activation of fibrinolysis. These results may suggest that the moderately lower TFPI activity in stroke patients could be due to atherosclerotic changes rather than to consumptive coagulopathy.

Biological, pathological and clinical features of small cell lung cancer.

Small cell lung cancer, which is not uncommon, and is one of the most malignant and relatively well investigated solid tumors of adults, has been reviewed concerning its biology, pathology and clinical aspects. Although it is histologically very simple, its poorly differentiated epithelial cell characteristics are complicated by features of neuroendocrine cells, such as amine and peptide hormone production and specific enzyme activities, some of which have been found to be good monitoring markers during and after treatment. Because of the relative ease of establishing cell lines in vitro, cell characteristics have been studied in detail. This has led to subtyping of cell lines and may further lead to subtyping of histology. However, accumulation of further evidence has disclosed exceptions and unclassifiable cell lines. The same can be said about chromosomal abnormality. The reactivity of monoclonal antibodies and also oncogenes supports the prevalent concept discriminating small cell cancer from non-small cell cancer. However, concepts concerning histogenesis are still changing. Although it is one of the solid tumors most sensitive to radiation and chemotherapy, the response rate of the tumor to non-surgical treatment appears to have reached a plateau. In order to make a breakthrough in the treatment, strategies based on biological findings must be applied.

Na(+)- and Cl(-)-dependent transport of taurine at the blood-brain barrier.

The characteristics of carrier-mediated transport of taurine at the blood-brain barrier (BBB) were studied by using primary cultured bovine brain capillary endothelial cells (BCECs), in situ brain perfusion and brain capillary depletion methods in rats. The uptake of [3H]taurine by cultured cells showed that the active transporter functions on both the luminal and antiluminal membranes of BCECs. The kinetic parameters for the saturable transport of taurine were estimated to be: for the luminal uptake, the Michaelis constant, Kt, was 12.1 +/- 0.5 microM, and the maximum uptake rate, Jmax, was 4.32 +/- 0.05 nmol/30 min/mg protein; for the antiluminal uptake, Kt was 13.6 +/- 2.4 microM and Jmax was 2.81 +/- 0.22 nmol/30 min/mg protein. The luminal and antiluminal uptakes of [3H]taurine were each dependent on both Na+ Cl-. Stoichiometric analyses suggest that two Na+ and one Cl- are associated with the luminal uptake of one taurine molecule. beta-Amino acids such as beta-alanine and hypotaurine strongly inhibited the uptake of [3H]taurine, whereas alpha- and gamma-amino acids had little or no effect. Furthermore, by in situ brain perfusion and in vivo brain capillary depletion methods, the carrier-mediated transport found by in vitro experiments was confirmed to function for the translocation of the taurine molecule from the vascular space into the brain. From these results, it was concluded that a Na+ and Cl- gradient-dependent transport (uptake) system for taurine exists in both the luminal and the antiluminal membranes of BCECs.

Restricted transport of cyclosporin A across the blood-brain barrier by a multidrug transporter, P-glycoprotein.

The blood-brain barrier permeability of cyclosporin A (CsA), an immunosuppressive cyclic peptide, is restricted despite its highly lipophilic nature. In this study, the uptake of CsA by primary cultured bovine brain capillary endothelial cells (BCEC) was investigated in order to clarify whether P-glycoprotein (P-gp), an ATP-dependent drug efflux pump expressed in the luminal surface of BCEC, causes the decreased transport of CsA into the brain. P-gp, having a molecular mass of 130-140 kDa, was detected with anti-P-gp monoclonal antibody, C219, using western blot analysis of the membrane fraction isolated from the bovine brain capillary. The uptake of CsA by primary cultured bovine BCEC was time-dependent, and the steady-state uptake of CsA was increased in the presence of several multidrug resistance reversing agents including verapamil and steroid hormones and the substrate of P-gp in BCEC, vincristine. The steady-stage uptake was increased significantly to approximately 4-fold when cellular ATP was depleted by treating with 2,4-dinitrophenol, suggesting that the efflux process is ATP dependent. Furthermore, in the presence of an anti-P-gp monoclonal antibody, MRK16, at a 10 micrograms/mL concentration, the uptake of CsA was increased approximately 3-fold. These results suggest that the low permeability of CsA into the brain is caused by the active efflux from BCEC by P-gp present in the luminal surface of cells.

Uptake of benzylpenicillin, cefpiramide and cefazolin by freshly prepared rat hepatocytes. Evidence for a carrier-mediated transport system.

The kinetics and mechanism of the hepatic uptake of beta-lactam antibiotics were studied by using freshly prepared rat hepatocytes. The initial uptake rates of benzylpenicillin and cefpiramide represented both saturable and nonsaturable transport processes, whereas that of cefazolin showed an apparently nonsaturable uptake process within the concentration range below 4 mM. The apparent nonsaturable uptake rate constants for benzylpenicillin, cefpiramide and cefazolin were 0.580, 0.047 and 0.289 nmoles/min/mg protein/mM respectively. The apparent values of Kt and Vmax describing the saturable transport were 0.473 +/- 0.158 mM and 2.02 +/- 0.48 nmoles/min/mg protein for benzylpenicillin and 0.847 +/- 0.254 mM and 0.70 +/- 0.18 nmoles/min/mg protein for cefpiramide respectively. The Arrhenius plot of benzylpenicillin uptake of 200 microM presented a single straight line in the range of 22 degrees-37 degrees with an activation energy of 16.8 kcal/mole. An energy requirement was also demonstrated for benzylpenicillin uptake as metabolic inhibitors (antimycin A, NaCN, rotenone and 2,4-dinitrophenol) significantly reduced the initial uptake rate of benzylpenicillin (P less than 0.05). Uptake of benzylpenicillin (200 microM) was not inhibited by ouabain (1 mM). Benzylpenicillin uptake was inhibited competitively by phenoxymethylpenicillin, cefpiramide and cefazolin with the inhibition constants, Ki, of 0.680, 0.583 and 11.7 mM respectively. Benzylpenicillin also inhibited competitively the uptake of cefpiramide with a Ki of 0.655 mM. From these results it was considered that a carrier-mediated uptake system participates in the hepatic uptake of at least four of the beta-lactam antibiotics examined in this study.

Functional expression of intestinal dipeptide/beta-lactam antibiotic transporter in Xenopus laevis oocytes.

An intestinal active transport system specific to small peptides and peptide-like drugs such as beta-lactam antibiotics was functionally expressed in Xenopus laevis oocytes after microinjection of messenger RNA (mRNA) derived from rat intestinal mucosal cells. The transport activity was evaluated by measuring the uptake of a tripeptide-like cephalosporin antibiotic, ceftibuten, which has high affinity for the intestinal peptide/H+ co-transporter and is resistant to peptidases. Ceftibuten transport in mRNA-injected oocytes was pH dependent (a proton gradient is the driving force), stereo selective (uptake of the cis-isomer of ceftibuten was about 4-fold higher than that of the trans-isomer), saturable and temperature dependent. Furthermore, various dipeptides showed cis-inhibitory and trans-stimulatory effects on the uptake of ceftibuten by mRNA-injected oocytes, suggesting that ceftibuten and dipeptides are transported by a common carrier protein. These results are in accordance with the functional properties of native proton-coupled peptide transporter previously clarified by studies with isolated intestinal brush-border membrane vesicles and other experimental systems. A protein with a molecular mass of about 130 kDa expressed in the membrane of mRNA-injected oocytes was identified as the transport protein by specific labeling with a photoreactive beta-lactam antibiotic, [3H]benzylpenicillin, followed by SDS-PAGE analysis of the radiolabeled protein. Furthermore, an experiment with mRNA size-fractionated by sucrose density gradient centrifugation indicated that the peptide transporter is encoded by mRNA of between 1.8 and 3.6 kb. These results, obtained using a heterologous gene expression technique, confirm that intestinal absorption of beta-lactam antibiotics occurs through a carrier-mediated mechanism and show that biologically stable beta-lactam antibiotics can be useful probes for molecular analysis of intestinal peptide transporter.