B-535a, b and c, new sphingosine kinase inhibitors, produced by a marine bacterium; taxonomy, fermentation, isolation, physico-chemical properties and structure determination

In the course of our screening for inhibitors of sphingosine kinase, we found a series of active compounds in a culture broth of a novel marine bacterium, SANK 71896. The structures of the compounds, named B-5354a, b and c, were elucidated by a combination of spectroscopic analyses to be new esters of 4-amino-3-hydroxybenzoic acid with long-chain unsaturated alcohols. B-5354a, b and c inhibit sphingosine kinase activity with IC50 values of 21, 58 and 38 microm, respectively.

High frequency of c-Met expression in gastric cancers producing alpha- fetoprotein

Gastric cancers producing alpha-fetoprotein (AFP) have a poor prognosis and a high incidence of liver metastasis. Hepatocyte growth factor (HGF) and its receptor, c-Met, are known to induce mitosis and cell movement and to promote tumor progression. In the present study, c-Met and HGF expression in AFP-producing gastric cancer was compared with those gastric cancers that do not produce AFP. Twenty-six patients with AFP-producing gastric cancers [AFP(+)] and 26 patients stage-matched gastric cancers without AFP production [AFP(-)] were evaluated for c-Met and HGF expression and proliferating cell nuclear antigen-labelling index using immunohistochemical analysis. A higher frequency of c-Met expression was observed in the AFP(+) group than in the AFP(-) group (p < 0.01). A higher expression of c-Met might be one explanation for the poorer prognosis of AFP-producing gastric cancers.

The efficacy of conventional radiation therapy in the management of pituitary adenoma

PURPOSE

To evaluate the efficacy of conventional radiotherapy for reducing tumor size and endocrine hypersecretion of pituitary adenomas.

METHODS AND MATERIALS

We reviewed the records of 91 patients with pituitary adenoma, who were first treated between 1969 and 1994 and had been followed for more than 2 years (median, 8.2 years.) Of these patients, 86 had received postoperative radiotherapy, and 5 had received radiotherapy alone. The median total dose was 51 Gy. Clinical symptoms related to mass effects or endocrine hypersecretion were assessed. The efficacy of radiotherapy was evaluated before treatment and during the follow-up period (1-14 years; median, 3 years) by estimating tumor size on computed tomography or magnetic resonance imaging in 56 patients, as well as by endocrine testing in the 22 patients who had secreting adenomas. Local control rate, prognostic factors, and side effects were analyzed.

RESULTS

Mass-effect symptoms improved in 72% and 79% of patients who had such symptoms due to nonsecreting adenomas and secreting adenomas, respectively. Symptoms of endocrine hypersecretion abated in 67% of patients who had such symptoms. Excessive hormone levels normalized in 74% of patients who showed endocrine hypersecretions. The greatest size reduction was seen 3 years after the completion of radiotherapy (24% CR, 62% PR, 12% NC, and 3% PD in nonsecreting adenomas, and 32% CR, 36% PR, 27% NC, and 5% PD in secreting adenomas). Three patients with secreting adenomas (2 with prolactinoma and 1 with Cushing's disease) showed a mismatch between reduction in tumor size and normalization of endocrine hypersecretion. The 10-year local control rates were 98%, 85%, 83%, and 67% for nonsecreting adenoma, growth-hormone-secreting adenoma, prolactinoma, and Cushing's disease, respectively. Univariate analyses showed that disease type and radiation field size were significant prognostic factors. Brain necrosis occurred in 1 patient who received a 60-Gy dose of irradiation.

CONCLUSION

We conclude that conventional external radiotherapy with 50 Gy is safe and sufficient to control pituitary adenoma. Careful observation is required in the management of secreting adenomas because the effects on tumor size and endocrine hypersecretion may be mismatched in some secreting adenomas.

An investigation of the disabled elderly in a geriatric health services facility in an urban area of Japan and attitudes of their family caregiver

We investigated characteristics of 72 clients in a geriatric health services facility (hereafter called GHSF), conditions of their family caregivers, and the factors associated with the caregivers choice of discharge destination. Most of the clients were elderly females with a low degree of independence, and dementia was observed in about 60% of them. The clients had children, but many of them lived alone before admission to the GHSF. The rate of admission from hospitals was high (54%), and that of discharge to hospitals was also high (50%). Sixty-seven percent of the clients stayed in for a period of over six months. Most of the family caregivers were daughters or daughters-in-law, and considered themselves to be healthy. Sixty-three percent of them had jobs, and most of the caregivers had no sub-caregiver to assist them. The family caregivers desired the client's home (19.4%), hospital or another GHSF (54.2%), or nursing home (26.4%) as the discharge destination from the GHSF. According to Hayashi's quantification theory type II, the factors related to the home as the discharge destination desired by client's family caregivers are as follows; caregivers used formal home public health nursing visit service before entering the GHSF, the job of the caregiver was a part-time job, the client did not show dementia, the period of care experience was shorter than one year.

Comparison of expressed sequence tags from male and female sexual organs of Marchantia polymorpha

A total of 935 expressed sequence tags (ESTs) from male immature sexual organ were determined, of which 600 ESTs were assembled into 110 non-redundant groups, resulting in 445 unique EST sequences. Of these, 244 sequences shared significant similarities to known nucleotide or amino acid sequences in other organisms. The remaining 201 unique sequences showed no significant matches and thus are likely to be novel transcripts. ESTs from male and female immature sexual organs of a liverwort, Marchantia polymorpha, were compared to characterize gene expression patterns during sex differentiation. Ninety-nine male ESTs turned out to be common genes found also in the female library. Interestingly, one of the ESTs found only in male shows a significant similarity to the transformer-2 gene involved in sex determination in Drosophila. In female, several unique lectin ESTs were found that are not present in the male library.

Molecular cloning and functional characterization of a novel mammalian sphingosine kinase type 2 isoform

Sphingosine-1-phosphate (SPP) has diverse biological functions acting inside cells as a second messenger to regulate proliferation and survival, and extracellularly, as a ligand for G protein-coupled receptors of the endothelial differentiation gene-1 subfamily. Based on sequence homology to murine and human sphingosine kinase-1 (SPHK1), which we recently cloned (Kohama, T., Oliver, A., Edsall, L. , Nagiec, M. M., Dickson, R., and Spiegel, S. (1998) J. Biol. Chem. 273, 23722-23728), we have now cloned a second type of mouse and human sphingosine kinase (mSPHK2 and hSPHK2). mSPHK2 and hSPHK2 encode proteins of 617 and 618 amino acids, respectively, both much larger than SPHK1, and though diverging considerably, both contain the conserved domains found in all SPHK1s. Northern blot analysis revealed that SPHK2 mRNA expression had a strikingly different tissue distribution from that of SPHK1 and appeared later in embryonic development. Expression of SPHK2 in HEK 293 cells resulted in elevated SPP levels. d-erythro-dihydrosphingosine was a better substrate than d-erythro-sphingosine for SPHK2. Surprisingly, d, l-threo-dihydrosphingosine was also phosphorylated by SPHK2. In contrast to the inhibitory effects on SPHK1, high salt concentrations markedly stimulated SPHK2. Triton X-100 inhibited SPHK2 and stimulated SPHK1, whereas phosphatidylserine stimulated both type 1 and type 2 SPHK. Thus, SPHK2 is another member of a growing class of sphingolipid kinases that may have novel functions.

Pharmacokinetics and effects after intravenous administration of high-dose boron to rat

Boron (B) compounds have been widely used in the chemical industry, agriculture, and environmental science. The kinetics and toxicity of B were studied by analyzing several serum and urine parameters after a single intravenous injection of sodium tetraborate solution (B: 85.7 mg/kg) in Wistar male rats. Blood samples were removed at 0, 1, 2, 4, and 6 h after injection. The serum parameters studied included: B, Na, Ca, K, P, Mg, gamma-GTP, AST, ALT, BUN, Cr, CK, LDH and ALD. Plasma concentration-time profiles of B were evaluated by a nonlinear least-squares method for fitting data to polyexponential equations and calculation of relevant pharmacokinetic parameters. Urine samples were collected from the bladder following infusion. The urinary parameters that were studied included urine volume and excretion of B, Cr and NAG. Results indicated that a two-compartment model could describe the elimination of B from plasma after intravenous administration. Urine volume significantly increased. A diuretic effect of B was noted.

Body height correction in scoliosis patients for pulmonary function test

We studied standing anteroposterior roentgenograms from 140 scoliosis patients and obtained a correction equation for body height by Cobb angle. This equation is applicable to patients with a double curve or special curve pattern as well as patients with a single curve. The repeatability of the method examined with this equation was higher than that with the previous correction method for body height by Cobb angle, and the difference between the corrected values and the measured values was small. Therefore, this method is considered to be more reliable.

Successful treatments of lung injury and skin burn due to hydrofluoric acid exposure

Recent growth in the electronics and chemical industries has brought about a progressive increase in the use of hydrofluoric acid (HF), along with the concomitant risk of acute poisoning among HF workers. We report severe cases of inhalation exposure and skin injury which were successfully treated by administering a 5% calcium gluconate solution with a nebulizer and applying 2.5% calcium gluconate jelly, respectively. Case 1: A 52-year old worker used HF for surface treatment after welding stainless steel, and was hospitalized with rapid onset of severe dyspnea. On admission to the critical care medical center he had widespread wheezing and crackles in his lungs. Chest radiograph showed a fine diffuse veiling over both lower pulmonary fields. Severe hypocalcemia with high concentrations of F in serum and urine were disclosed. He was immediately given 5% calcium gluconate solution by intermittent positive-pressure breathing (IPPB), utilizing a nebulizer. On the 21st hospital day, chest film and CT scan did not demonstrate any abnormality. He was discharged very much improved on the 22nd hospital day. Case 2: A 35-year old worker at an electronics factory was admitted to his local hospital with severe skin burn on his face and neck after exposure to 100% HF. Treatment began with immediate copious washing with water for 20 min. Calcium gluconate 2.5% gel (HF burn jelly) was applied to the area as a first-aid measure. Persistent high concentrations of serum and urinary F were disclosed for 2 weeks. After treatment with applications of HF burn jelly, he was confirmed as being completely recovered. The present cases and a review of published data suggest that an adequate method of emergency treatment for accidental HF poisoning is necessary.

Toxicokinetics of intravenous fluoride in rats with renal damage caused by high-dose fluoride exposure

Fluoride (F) complexes are used in some fields of industry and medicine. F excretion mainly depends on kidney function. Urinary F concentration is measured to monitor the health of workers exposed to F. The toxicokinetics of F were studied by analyzing plasma concentration of F after intravenous injection of 2.86, 5.71 and 8.57 mg/kg into male Wistar rats. A dose-response relationship was recognized between these F doses and renal tissue injury. Blood samples were removed at 0, 10, 20, and 30 min, and after 1, 2, 3, 4, 5, and 6 h after injection. Plasma concentration-vs-time profiles were evaluated by a nonlinear least-squares method for fitting data to polyexponential equations and calculation of relevant pharmacokinetic parameters. Results indicated that a two-compartment model could describe the elimination of F from plasma. The beta rate constant, total plasma clearance (C1) and first-order rate constants (K21, Kel) decreased, and the half-time of the beta-phase (t1/2beta) was significantly prolonged with increasing dose. The kidney is the main target organ for F toxicity. Acute exposure to high doses of F damages renal tissue and causes renal dysfunction. The C1 of F is mainly dependent on renal F excretion. Since severe kidney damage markedly affected the toxicokinetics of F and decreased its elimination, other nephrotoxic indicators and measurement of plasma F concentration are necessary for monitoring high-dose F exposure.

Functional characterization of human sphingosine kinase-1

Sphingosine kinase catalyzes the phosphorylation of sphingosine to form sphingosine 1-phosphate (SPP), a novel lipid mediator with both intra- and extracellular functions. Based on sequence identity to murine sphingosine kinase (mSPHK1a), we cloned and characterized the first human sphingosine kinase (hSPHK1). The open reading frame of hSPHK1 encodes a 384 amino acid protein with 85% identity and 92% similarity to mSPHK1a at the amino acid level. Similar to mSPHK1a, when HEK293 cells were transfected with hSPHK1, there were marked increases in sphingosine kinase activity resulting in elevated SPP levels. hSPHK1 also specifically phosphorylated D-erythro-sphingosine and to a lesser extent sphinganine, but not other lipids, such as D,L-threo-dihydrosphingosine, N, N-dimethylsphingosine, diacylglycerol, ceramide, or phosphatidylinositol. Northern analysis revealed that hSPHK1 was widely expressed with highest levels in adult liver, kidney, heart and skeletal muscle. Thus, hSPHK1 belongs to a highly conserved unique lipid kinase family that regulates diverse biological functions.

Serum level of HER-2/neu in patients with gastric cancer: correlation with HER-2/neu overexpression in gastric carcinoma tissue

Serum HER-2/neu (c-erbB-2) levels in patients with gastric cancer were evaluated by an enzyme-linked immunosorbent assay and tissue levels of HER-2/neu in the same cohort were determined by immunohistochemistry. Nine (16%) of 57 gastric carcinomas had an overexpression of HER-2/neu detected immunohistochemically. Of these 9 patients, 6 had elevated serum HER-2/neu levels, while 45 of 48 tissue samples with negative staining exhibited normal serum HER-2/neu levels. These results indicated that overall accuracy, positive predictive value, and negative predictive values of their serum measurements were 89, 67 and 94%, respectively. Serum levels of HER-2/neu were correlated with tissue overexpression of HER-2/neu in patients with gastric cancer.

F-12509A, a new sphingosine kinase inhibitor, produced by a discomycete

In the course of our screening for inhibitors of sphingosine kinase, we found an active compound from a culture broth of a discomycete, Trichopezizella barbata SANK 25395. The structure of the compound, named F-12509A, was elucidated by a combination of spectroscopic analyses, to be a new sesquiterpene quinone consisting of a drimane moiety and a dihydroxybenzoquinone. Enzyme kinetic analyses showed that F-12509A inhibits sphingosine kinase activity in a competitive manner with respect to sphingosine, with a Ki value of 18 microM.

Epidemiological study of methicillin-resistant Staphylococcus aureus at Fukuoka University Hospital

To clarify what types of methicillin-resistant Staphylococcus aureus (MRSA) strains were easily transmitted and colonized in the inpatients of the emergency center and the neonatal intensive-care unit (NICU) at Fukuoka University Hospital, 70 MRSA isolates obtained from February to November 1995 (the first survey) and from November 1996 to March 1997 (the second survey) were investigated biologically and genetically. Pulsed-field gel electrophoresis (PFGE) showed 12 types (PFGE types A-L) of DNA patterns for the MRSA isolates. At the emergency center, the PFGE types A and B strains were isolated from 40.9% and 27.2% of the MRSA-excreting patients in the first survey, respectively, while type E was isolated from 66.7% in the second survey. At the NICU, type A and J strains were isolated from 33.3% and 55.6% of the MRSA-excreting patients in the first survey, while the types A and B were isolated from 25% and 50%, respectively, in the second survey. Type A-D strains were isolated in both wards, while other epidemic types strains were isolated in only one ward. These results suggest that the type A and B strains have been colonized in the two wards for a long time and these strains might spread and colonize easily in the patients. Type C and D strains have also been colonized, but only in a small population over the two wards.

T-cell dysfunction in a patient with short bowel syndrome: report of a case

We describe herein the case of a 48-year-old man who underwent emergency massive resection of the small intestine due to strangulated ileus, which led to short bowel syndrome (SBS) as he was left with 7 cm of jejunum and 8 cm of ileum. We evaluated the immune function in this patient, focusing particular attention on T-cell-mediated immunity. Biochemical and nutritional parameters, including minerals and trace elements, indicated that the patient was in relatively good health; however, the proliferative response to mitogen and tumor necrosis factor-alpha production in response to the anti-CD3 monoclonal antibody in peripheral blood lymphocytes (PBL) were impaired compared with age-matched postgastrectomy patients and healthy donors. Moreover, the expression of T-cell receptor (TCR) zeta, which is involved in signal transduction and the subsequent activation of T cells, was downregulated in this patient compared with that in the age-matched postgastrectomy patients and healthy donors. These observations suggest that T-cell function was disturbed in our patient, and that this dysfunction was associated with the decreased expression of TCR zeta molecules.

Water-soluble dendritic unimolecular micelles: their potential as drug delivery agents

To explore the potential of dendritic unimolecular micelles in drug delivery systems, dendritic unimolecular micelles with a hydrophobic core surrounded by a hydrophilic shell were prepared by coupling dendritic hypercores with poly(ethylene glycol) [PEG] mesylate. The monomer selected to build the dendritic cores was 4, 4-bis(4'-hydroxyphenyl) pentanol as this large monomer unit provides flexibility to the dendritic structure while contributing to the "container" capacity of the overall structure. Four generations of dendritic hypercores with six, 12, 24, and 48 phenolic end groups were prepared. Subsequent coupling reactions with PEG mesylate afforded four generations of dendritic unimolecular micelles. The micelles were characterized by Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS), 1H-NMR and Gel Permeation Chromatography (GPC). The "container" property of micelles was demonstrated by solubilizing pyrene in aqueous solution. Entrapment of the model drug indomethacin in the dendritic micelles was achieved at 11 wt.% loading level, and preliminary in vitro release tests showed that sustained release characteristics were achieved.

[Complications of percutaneous endoscopic gastrostomy in the elderly: local skin infection and respiratory infection]

We investigated post-operative management of acute complications of percutaneous endoscopic gastrostomy (PEG) which often caused respiratory infections and local skin infections. The subjects were a total of 341 patients (male 131, female 210, and the mean age was 80.3), they were classified into six groups by method of feeding and use of antibiotics. Patients were divided into three groups based on the time that feeding was started. In Group I, enteral feeding was not started within the first five days. In Group II, sterilized enteral feeding (lactated Ringer's solution for intravenous infusion) using sterilized intravenous infusion kit started within 24 hours after the procedure, and in Group III, feeding of the usual enteral formula started within 24 hours after the procedure. And as for the using of antibiotics, they were also divided into two groups, antibiotics administered[AB (+)] and no antibiotics administered[AB (-)]. Thus, the patients were divided into six groups according to the time of starting nutrition and the use of antibiotics. The rates of incidence of acute respiratory infections and local skin infections in the six groups were compared by the chi-square test and differences in the rates of incidence of complication were also compared between two PEG methods; the Pull/Push method and the Introducer method. The frequency of local skin infection in Group III was significantly higher than in Group I and Group II. As for the PEG methods, the frequency of local skin infection in the Pull/Push method was significantly higher than Introducer methods. Acute respiratory infections occurred significantly less in the AB (+) group than in the AB (-) group. Postoperative administration of antibiotics would seem to be appropriate for prophylaxis of respiratory infection in elderly patients after PEG. On the other hand, local skin infections are not related to administration of antibiotics, and are highly related to the method of feeding. We concluded that nutrition of sterilized enteral feeding immediately after operation using a sterilized intravenous infusion kit and administration of antibiotics are advisable to prevent major complications in elderly patients.

Methicillin-resistant Staphylococcus aureus (MRSA) isolated at Fukuoka University Hospital and hospitals and clinics in the Fukuoka city area

Bacteriological and epidemiological studies were carried out on 106 isolates of methicillin-resistant Staphylococcus aureus (MRSA) isolated at our hospital (56 isolates) and from 15 other hospitals and clinics (50 isolates) in the Fukuoka city area. Strains were studied regarding coagulase-type, beta-lactamase production, and antimicrobial susceptibility; genotype studies used pulsed-field gel electrophoresis (PFGE) with cluster analysis. The majority of isolates produced coagulase type II (75.5%) and beta-lactamase (72. 6%); there was high susceptibility to arbekacin (84.9%) but no resistance to vancomycin. Dendrogram analysis of PFGE patterns identified five major clusters that generally correlated with coagulase-type and beta-lactamase production. Though isolates of two clusters were both coagulase type II and beta-lactamase producing, which was the most common circulating strain both in our hospital and other hospitals and clinics, dendrogram analysis of PFGE patterns showed that they were heterogeneous. Four genetically identical isolates from the same hospital suggested the existence of hospital-specific strains. Nine genetically identical isolates from intensive care units (ICU) in our hospital suggested that a unique strain of MRSA was found there. It had not been transmitted from another area. PFGE with cluster analysis seemed to be an essential tool to detect area-specific or hospital-specific strains undifferentiated by phenotyping. These findings confirmed that a combination of PFGE, including cluster analysis along with coagulase-type and beta-lactamase production may provide more detailed information for the epidemiological study of MRSA.

Design of dendritic macromolecules containing folate or methotrexate residues

Polyether dendritic compounds bearing folate residues on their surface were prepared as model drug carriers with potential tumor cell specificity. Starting from ester-terminated polyether dendrimers, hydrazide groups were easily introduced to the surface of the dendrimers by reaction with hydrazine. Folate residues were then conjugated to the hydrazide chain ends of the dendrimers by direct condensation with folic acid in the presence of a condensing agent or by reaction with an active ester derivative of folic acid. Essentially complete functionalization of the terminal hydrazide groups was achieved for both the first and the second generation dendrimers with four and eight hydrazide groups. For the G-2 dendrimer with 16 hydrazide groups, an average number of only 12.6 folate residues were attached to each dendrimer. The conjugates are soluble in aqueous medium above pH 7.4. In addition, a similar conjugation of the antitumor drug methotrexate to the dendrimer was also investigated. Once optimized, these molecules may form the basis for a novel family of multivalent drug carriers.

Case report of 14-year survival after radiotherapy for clinical T3 esophageal carcinoma, with local recurrence finally rescued by surgery

A 51-year-old man with increasing dysphasia was admitted to our hospital on March 18, 1985. Several examinations revealed thoracic esophageal squamous cell carcinoma 11 cm in length staged T3N0M0 (stage IIA) by UICC 1987. As he rejected our proposal of surgery, definitive radiotherapy (60 Gy) was delivered, and complete response was obtained. The patient had been doing well for 5 years after radiotherapy until superficial local recurrence was discovered at a periodic endoscopic examination. High-dose-rate intraluminal brachytherapy (10 Gy/2 Fr) was administered. After a 3-year disease-free interval, superficial recurrence developed in the same location, and early gastric cancer was detected as a secondary cancer. Radical salvage surgery was performed. The patient was alive and disease free 5 years and 5 months after surgery. We present this rare case of a patient who survived 14 years after the initial radiotherapy. The present case demonstrated the importance of long-term follow-up after radiotherapy, long-term local controllability of relatively low doses of intraluminal brachytherapy after superficial recurrence, and the feasibility of salvage surgery as long as local recurrence is limited to within the mucosal layer.

[Optimal thoracic irradiation for stage IV lung cancer]

To investigate optimal thoracic irradiation (TI) for stage IV lung cancer, we retrospectively reviewed 150 patients. In all, 101 patients underwent radiotherapy for the primary lesion, and 130 had radiotherapy for metastasized sites. TI fields were basically divided into two groups; whole thoracic lesion irradiation (WTLI) and partial thoracic lesion irradiation (PTLI). Overall survival rates at 6 months, 1 year and 2 years were 58%, 27% and 11%, respectively, and MST was 7.1 months. There was no difference in survival according to histological type. On univariate analysis, the factors of good prognosis included good PS, free of bone metastasis, metastasis limited to a single organ, TI, chemotherapy, age (less than or equal to 75 years), and TN factors (T0-2 and N0-1). Multivariate analysis showed PS was the predominant factor. Among the patients treated with TI, survival rates of patients with PS 0-1 were superior to those of patients with PS 2-4. Radiation pneumonitis was more frequent in WTLI than in PTLI. The rates of thoracic failure death were 31.7% in patients treated with TI and 63.3% without TI. However, the size of the thoracic radiation field did not affect the rates of thoracic failure death. We concluded that TI for stage IV patients could reduce thoracic symptoms and increase the survival rate in the subgroup with good PS. Furthermore, we considered PTLI was worth while in the subgroup with poor PS.

Temperature-controlled interaction of thermosensitive polymer-modified cationic liposomes with negatively charged phospholipid membranes

To obtain cationic liposomes of which affinity to negatively charged membranes can be controlled by temperature, cationic liposomes consisting of 3beta-[N-(N', N'-dimethylaminoethane)carbamoyl]cholesterol and dioleoylphosphatidylethanolamine were modified with poly(N-acryloylpyrrolidine), which is a thermosensitive polymer exhibiting a lower critical solution temperature (LCST) at ca. 52 degrees C. The unmodified cationic liposomes did not change its zeta potential between 20-60 degrees C. The polymer-modified cationic liposomes revealed much lower zeta potential values below the LCST of the polymer than the unmodified cationic liposomes. However, their zeta potential increased significantly above this temperature. The unmodified cationic liposomes formed aggregates and fused intensively with anionic liposomes consisting of egg yolk phosphatidylcholine and phosphatidic acid in the region of 20-60 degrees C, due to the electrostatic interaction. In contrast, aggregation and fusion of the polymer-modified cationic liposomes with the anionic liposomes were strongly suppressed below the LCST. However, these interactions were enhanced remarkably above the LCST. In addition, the polymer-modified cationic liposomes did not cause leakage of calcein from the anionic liposomes below the LCST, but promoted the leakage above this temperature as the unmodified cationic liposomes did. Temperature-induced conformational change of the polymer chains from a hydrated coil to a dehydrated globule might affect the affinity of the polymer-modified cationic liposomes to the anionic liposomes.

Temperature-dependent interaction of thermo-sensitive polymer-modified liposomes with CV1 cells

Egg yolk phosphatidylcholine liposomes modified with a copolymer of N-acryloylpyrrolidine and N-isopropylacrylamide having a lower critical solution temperature at ca. 40 degrees C were prepared and an effect of temperature on their interaction with CV1 cells was investigated. The unmodified liposomes were taken up by the cells approximately to the same extent after 3 h incubation at 37 and 42 degrees C. In contrast, uptake of the polymer-modified liposomes by CV1 cells decreased slightly at 37 degrees C but increased greatly at 42 degrees C, compared to the unmodified liposomes. Proliferation of the cells was partly prohibited by the incubation with the unmodified liposomes encapsulating methotrexate at 37 and 42 degrees C. The treatment with the polymer-modified liposomes containing methotrexate at 37 degrees C hardly effected the cell growth. However, the treatment at 42 degrees C inhibited the cell growth completely. It is considered that the highly hydrated polymer chains attached to the liposome surface suppressed the liposome-cell interaction below the lower critical solution temperature of the polymer but the dehydrated polymer chains enhanced the interaction above this temperature. Because interaction of the polymer-modified liposomes with cells can be controlled by the ambient temperature, these liposomes may have potential usefulness as efficient site-specific drug delivery systems.