Arbutin: mechanism of its depigmenting action in human melanocyte culture

Arbutin, a naturally occurring beta-D-glucopyranoside of hydroquinone, is effective in the topical treatment of various cutaneous hyperpigmentations characterized by hyperactive melanocyte function. We examined the mechanism of its depigmenting action in human melanocyte cultures. Arbutin inhibited the tyrosinase activity of cultured human melanocytes at noncytotoxic concentrations. It did not affect the expression of tyrosinase mRNA. Melanin production was inhibited significantly by arbutin, as determined by measuring eumelanin radicals with an electron spin resonance spectrometer. The study of the kinetics and mechanism for inhibition of tyrosinase confirms the reversibility of arbutin as a competitive inhibitor of this enzyme. The utilization of L-tyrosine or L-dopa as the substrate suggests a mechanism involving competition with arbutin for the L-tyrosine binding site at the active site of tyrosinase. These results suggest that the depigmenting mechanism of arbutin in humans involves inhibition of melanosomal tyrosinase activity, rather than suppression of the expression and synthesis of tyrosinase.

Fibronectin in the tear film

PURPOSE

Fibronectin plays an important role in corneal healing and has been detected previously in the tear film. To investigate the levels of fibronectin in normal human tears, the authors measured and compared fibronectin concentration in open-eye, closed-eye, and reflex tear fluid. The origin of fibronectin in the tear film was investigated by comparing fibronectin concentration in sequentially collected reflex tear samples with the concentrations of total protein and albumin in the same samples.

METHODS

Open-eye and closed-eye tears were collected from 11 noncontact lens wearers. From 7 subjects, 20 uninterrupted reflex tear samples (10 microliters each) subsequently were collected, using the sneeze reflex method of stimulation, followed by an additional 10 nonstimulated tear samples (3 microliters each) immediately after cessation of stimulus. Enzyme-linked immunosorbent assays were used to determine fibronectin and albumin concentrations, and bicinchoninic acid protein assays were used to determine total protein concentration in each sample.

RESULTS

Fibronectin concentration in open-eye tears (19 +/- 24 eta g/ml, range 3 to 78 eta g/ml) was significantly different (P = 0.004) from that in closed-eyes tears (4127 +/- 3222 eta g/ml, range 1177 to 11384 eta g/ml). In the first 50 microliters of reflex tears, fibronectin concentrations were low (10 +/- 23 eta g/ml), but they increased significantly (P = 0.028) after 100 microliters of reflex tears had been collected (220 +/- 126 eta g/ml). There was a further marked transient increase (767 +/- 946 eta g/ml) after cessation of stimulus. Total protein concentration in the same samples decreased significantly during reflex tear collection compared to open-eye tears, and it increased gradually after cessation of stimulus. Albumin concentration in the same samples, analyzed for two subjects only, showed a pattern similar to that for fibronectin. Dilation of conjunctival blood vessels was noted in all subjects after reflex tear collection. Administration of a topical vasoconstrictor in two subjects eliminated the increase in fibronectin concentration during reflex tearing but did not affect total protein concentration. Under reducing conditions, the molecular mass of fibronectin in open-eye and reflex tears was 240 kDa, identical to commercially available purified plasma fibronectin, whereas fibronectin in closed-eye tears was degraded into small molecular mass fragments.

CONCLUSIONS

These findings suggest that fibronectin in tear fluid is derived from plasma and that the increase in concentration in closed-eye and reflex tear fluid is caused by leakage from dilated conjunctival blood vessels.

A human polysialyltransferase directs in vitro synthesis of polysialic acid

Polysialic acid (PSA) is a linear homopolymer of alpha-2,8-linked sialic acid residues whose expression is developmentally regulated and modulates the adhesive property of the neural adhesion molecule, N-CAM. Recently, hamster and human cDNAs encoding polysialyltransferase (PST-1 for the hamster enzyme and PST for the human enzyme) were cloned, and by using the human cDNA it was demonstrated that the expression of PSA in N-CAM facilitates neurite outgrowth (Nakayama, J., Fukuda, M.N., Fredette, B., Ranscht, B., and Fukuda, M. (1995) Proc. Natl. Acad. Sci. U.S.A., 92, 7031-7035; Eckhardt, M.A., Mühlenhoff, M., Bethe, A., Koopman, J., Frosch, M., and Gerardy-Schahn, R. (1995) Nature 373, 715-718.) Although these studies demonstrated that PST-1 and PST synthesize PSA in cultured cells, it was not shown that they could catalyze the polycondensation of alpha-2,8-linked sialic acid on a glycoconjugate template containing alpha-2,3-linked sialic acid. Here we demonstrate that PSA formation by PST is independent from the presence of N-CAM in vivo. We then develop an in vitro assay of PSA synthesis using glycoproteins other than N-CAM as acceptors and a soluble PST as an enzyme source. The soluble PST, produced as a chimeric protein fused with protein A, was incubated with rat alpha 1-acid glycoprotein, fetuin or human alpha 1-acid glycoprotein as acceptors together with the donor substrate CMP-[14C]NeuNAc. Incubation of fetuin with the soluble PST, in particular, resulted in a high molecular weight product that was susceptible to PSA-specific endoneuraminidase. Polysialylated products were not formed when alpha-2,3-linked sialic acid was removed from the acceptor fetuin before incubation. These results establish that a single enzyme, PST, alone can catalyze both the addition of the first alpha-2,8-linked sialic acid to alpha-2,3-linked sialic acid and the polycondensation of all alpha-2,8-linked sialic acids, yielding PSA.

Postsynaptic calcium and calcium-dependent processes in synaptic plasticity in the developing visual cortex

In this paper we describe some of the results obtained from recent experiments on mechanisms underlying long-term potentiation (LTP) and long-term depression (LTD) in the visual cortex of young rats. In particular, we focus on experiments which tested the hypotheses that the induction of LTP in the visual cortex is of Hebbian type and that an input-associated Ca2+ rise at postsynaptic sites and subsequent activation of protein kinases or protein phosphatases may play roles in the induction of LTP or LTD in the developing visual cortex.

Detection of lysyl oxidase gene expression in rat skin during wound healing

Lysyl oxidase (LOX) initiates the crosslinking of the lysine-derived aldehyde and plays an essential role in maturation of collagen, for example in wound healing. Although the activity of this enzyme has been examined in various disorders, and a further intriguing aspect of the relationship between LOX and tumorigenesis has recently emerged, its gene expression pattern in tissues is still unknown. We examined LOX gene expression during wound healing in rat skin. In addition, type III collagen gene expression was studied to determine the formation of fibrils. The LOX mRNA level reached a peak by day 3 after injury, which was earlier than that of type III collagen, and continued at a high level until day 22. The type III collagen mRNA level began to rise from day 3 and had increased intensely by day 22. In situ hybridization revealed grains corresponding to LOX mRNA in the fibroblasts of the granulomatous tissue. These results suggest that LOX is produced before collagen synthesis in preparation for crosslinking in the early phase of wound healing.

Topical aldose reductase inhibitor for correcting corneal endothelial changes in diabetic patients

BACKGROUND

Marked variations in cell size (polymegethism) and shape (pleomorphism) are characteristic of the corneal endothelium in diabetic patients and animals.

METHOD

Wide field specular microscopy was used to evaluate the clinical efficacy of treating the diabetic corneal endothelium with topical instillation of 0.5% aldose reductase inhibitor, CT-112.

RESULTS

Morphological variations (polymegethism and pleomorphism) of the endothelium in eight eyes from eight patients receiving CT-112 resolved within 3 months after initiation of treatment. In contrast, no change in endothelial morphology was noted in five eyes from five patients who received placebo.

CONCLUSION

These observations suggest that aldose reductase may be involved in the aetiology of corneal endothelial variations in diabetic patients.

A common-source outbreak of fulminant hepatitis B in hemodialysis patients induced by precore mutant

From September 9 to October 3, 1994, five patients on maintenance hemodialysis in a dialysis unit in Tokyo contracted hepatitis B virus (HBV) infection successively, and four of them died of fulminant hepatitis. The unit treated 181 patients three times a week on eight shifts, and all five afflicted patients were on the same shift along with 27 other patients. HBV DNA clones from the hepatitis patients had a point mutation converting codon 28 in the precore region to a stop codon, which aborts the synthesis and secretion of hepatitis B e antigen, and showed a sequence similarity of > 99.5% within 645 base pairs covering the X gene and precore region. There were two HBV carriers with antibody to hepatitis B e antigen who were receiving hemodialysis on the same shift. HBV DNA clones from one of them had the stop codon 28 in the precore region, and a sequence similarity of > 99.7% to those from the five patients. Based on these results, it was deduced that the fulminant HBV strain was transmitted from the carrier to five patients, and resulted in the death of four. The outbreak indicates that immunocompromised hosts like hemodialysis patients can develop fulminant hepatitis B if and when they are infected with extremely virulent HBV strains.

Isolation and characterization of a pseudogene related to human core 2 beta-1,6-N-acetylglucosaminyl-transferase

In a previous study, we isolated genomic clones encoding core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) and blood group IGnT and proposed that these two genes were produced from a common ancestral gene by duplication, diversion and intron insertion. In the present study, we have isolated a pseudogene which is highly related to the gene of C2GnT. The sequence analysis of this pseudogene indicated that the pseudogene was produced by duplication of a common precursor gene for C2GnT. These results taken together strongly suggest that the ancestral gene was first duplicated and one of the duplicated genes directly evolved into the IGnT gene. The other duplicated gene was further duplicated to produce the C2GnT gene and the pseudogene.

Role of the C2B domain of synaptotagmin in vesicular release and recycling as determined by specific antibody injection into the squid giant synapse preterminal

Synaptotagmin (Syt) is an inositol high-polyphosphate series [IHPS inositol 1,3,4,5-tetrakisphosphate (IP4), inositol 1,3,4,5,6-pentakisphosphate, and inositol 1,2,3,4,5,6-hexakisphosphate] binding synaptic vesicle protein. A polyclonal antibody against the C2B domain (anti-Syt-C2B), an IHPS binding site, was produced. The specificity of this antibody to the C2B domain was determined by comparing its ability to inhibit IP4 binding to the C2B domain with that to inhibit the Ca2+/phospholipid binding to the C2A domain. Injection of the anti-Syt-C2B IgG into the squid giant presynapse did not block synaptic release. Coinjection of IP4 and anti-Syt-C2B IgG failed to block transmitter release, while IP4 itself was a powerful synpatic release blocker. Repetitive stimulation to presynaptic fiber injected with anti-Syt-C2B IgG demonstrated a rapid decline of the postsynaptic response amplitude probably due to its block of synaptic vesicle recycling. Electron microscopy of the anti-Syt-C2B-injected presynapse showed a 90% reduction of the numbers of synaptic vesicles. These results, taken together, indicate that the Syt molecule is central, in synaptic vesicle fusion by Ca2+ and its regulation by IHPS, as well as in the recycling of synaptic vesicles.

Role of the C2A domain of synaptotagmin in transmitter release as determined by specific antibody injection into the squid giant synapse preterminal

Squid synaptotagmin (Syt) cDNA, including its open reading frame, was cloned and polyclonal antibodies were obtained in rabbits immunized with glutathione S-transferase (GST)-Syt-C2A. Binding assays indicated that the antibody, anti-Syt-C2A, recognized squid Syt and inhibited the Ca(2+)-dependent phospholipid binding to the C2A domain. This antibody, when injected into the preterminal at the squid giant synapse, blocked transmitter release in a manner similar to that previously reported for the presynaptic injection of members of the inositol high-polyphosphate series. The block was not accompanied by any change in the presynaptic action potential or the amplitude or voltage dependence of the presynaptic Ca2+ current. The postsynaptic potential was rather insensitive to repetitive presynaptic stimulation, indicating a direct effect of the antibody on the transmitter release system. Following block of transmitter release, confocal microscopical analysis of the preterminal junction injected with rhodamine-conjugated anti-Syt-C2A demonstrated fluorescent spots at the inner surface of the presynaptic plasmalemma next to the active zones. Structural analysis of the same preparations demonstrated an accumulation of synaptic vesicles corresponding in size and distribution to the fluorescent spots demonstrated confocally. Together with the finding that such antibody prevents Ca2+ binding to a specific receptor in the C2A domain, these results indicate that Ca2+ triggers transmitter release by activating the C2A domain of Syt. We conclude that the C2A domain is directly related to the fusion of synaptic vesicles that results in transmitter release.

Functional diversity of C2 domains of synaptotagmin family. Mutational analysis of inositol high polyphosphate binding domain

Synaptotagmins I and II are inositol high polyphosphate series (inositol 1,3,4,5-tetrakisphosphate (IP4), inositol 1,3,4,5,6-pentakisphosphate, and inositol 1,2,3,4,5,6-hexakisphosphate) binding proteins, which are thought to be essential for Ca(2+)-regulated exocytosis of neurosecretory vesicles. In this study, we analyzed the inositol high polyphosphate series binding site in the C2B domain by site-directed mutagenesis and compared the IP4 binding properties of the C2B domains of multiple synaptotagmins (II-IV). The IP4 binding domain of synaptotagmin II is characterized by a cluster of highly conserved, positively charged amino acids (321 GKRLKKKKTTVKKK 324). Among these, three lysine residues, at positions 327, 328, and 332 in the middle of the C2B domain, which is not conserved in the C2A domain, were found to be essential for IP4 binding in synaptotagmin II. When these lysine residues were altered to glutamine, the IP4 binding ability was completely abolished. The primary structures of the IP4 binding sites are highly conserved among synaptotagmins I through IV. However, synaptotagmin III did not show significant binding ability, which may be due to steric hindrance by the C-terminal flanking region. These functional diversities of C2B domains suggest that not all synaptotagmins function as inositol high polyphosphate sensors at the synaptic vesicle.

Splenic metastasis from lung cancer

Splenic metastasis from lung cancer is a rare clinical event, most often diagnosed at the time of autopsy. We report 2 cases of splenic metastasis with a primary lung cancer. The first case was a 76-year-old man presenting with a recurrent solitary splenic metastasis 14 months after surgical removal of a squamous cell carcinoma of the lung. The second patient was a 72-year-old woman who had a poorly differentiated carcinoma of the lung and multiple abdominal metastasis. We also investigated 267 autopsy cases of lung cancer from 1975 to 1992. Histologically, there were 73 cases of squamous cell carcinoma, 123 adenocarcinoma, 29 large cell carcinoma, 36 small cell carcinoma, and 7 other miscellaneous tumours. The number of splenic metastasis from lung cancer in these cases was 15 (5.6%). Splenic metastasis from a primary cancer of the left lung was more frequent than that from the right lung. Nine of 15 splenic metastases were smaller than 1 cm in size. Splenic metastasis was associated with liver and pancreas metastasis. All 15 autopsy cases with splenic metastasis from lung cancer had other abdominal organ metastasis. Our analysis indicates that a solitary splenic metastasis is rare. Selection of a suitable therapeutic approach is important.

[Intratumoral pharmacokinetics following intraarterial administration of MCNU in patients with malignant gliomas]

This clinical study was undertaken to examine intratumoral (i.t.) pharmacokinetics after intraarterial (i.a.) administration of MCNU (80mg/m2) in 5 patients with glioblastoma (GB) and 2 with anaplastic astrocytoma (AA). After resection or stereotactic biopsy of the cystic lesion, an Ommaya reservoir was placed into the tumor cavity in all patients. The distribution of MCNU in blood was compatible with a two-compartment model, and the half life of the alpha-phase and beta-phase was 4.1 minutes and 160.4 minutes, respectively. MCNU was detected in the i.t. fluid in 5 cases, 4 of GB and 1 of AA. The concentration of i.t. MCNU gradually increased during the 5 to 30 minutes after i.a. injection to a level about 20.0% of its blood concentration. However, no MCNU was detected in patients showing partial response (3 of GB and 1 of AA) or no change (1 of GB) after the i.a. infusion of MCNU during maintenance chemotherapy. These results suggests that MCNU may transfer into the tumor tissues. Further investigation is warranted.

Benefits of Medroxyprogesterone Acetate (MPA) in Advanced or Recurrent Breast Cancer with Higher Serum Concertration

The efficacy of medroxyprogesterone acetate (MPA) therapy in controlling progressive measurable metastatic breast cancer was assessed in 61 patients. In addition serum MPA concentrations were measured by high performance liquid chromatography (HPLC) and subjective effects of treatment were monitored. Overall 24 patients (39.3%) achieved an objective response(2 complete responses [ CR ] and 22 partial responses [ PR ]). There was no significant relationships between response to therapy and menopausal status, metastatic sites, previous therapy, histological type, or disease-free interval. Patients with estrogen (ER) and progesterone (PgR) receptor-positive tumors responded more frequently. Significant differences in serum MPA concentrations were seen between responders and non-responders, objective tumor shrinkage being seen in patients with serum levels in excess of 55 ng/ml. There were few cases responding to the therapy with serum MPA concentrations lower than 25 ng/ml. The serum MPA levels significantly correlated with an improvement in the performance status and survival. Patients with serum MPA concentrations lower than 25 ng/ml had significantly poorer survival. There was a significant relationship between MPA level and dose per area of boby surface (mg/ m(2)) in cases with CR or PR or no change (NC). However, the serum levels of patients with progressive disease despite therapy were lower than the expected levels based on the body surface area. This study demonstrated that serum MPA concentration is a determining factor for therapeutic benefit in advanced or recurrent breast cancer.

Intensive chemotherapy with cisplatin, doxorubicin, cyclophosphamide, etoposide and granulocyte colony-stimulating factor for advanced thymoma or thymic cancer: preliminary results

A study was conducted to evaluate the impact of cisplatin, doxorubicin, cyclophosphamide and etoposide (PACE) with granulocyte colony-stimulating factor (G-CSF) on advanced thymoma or thymic cancer. Between August 1989 and December 1994, 14 patients with invasive, metastatic or recurrent thymoma or thymic cancer were treated with cisplatin (80 mg/m2, on day 1), doxorubicin (45 mg/m2, on day 1), cyclophosphamide (800 mg/m2, on day 1) and etoposide (80 mg/m2, on day 1-3) with G-CSF (90 micrograms/m2, on day 5-18) at the National Cancer Center Hospital, Tokyo. Courses were repeated every 3 or 4 weeks for a maximum of 4 cycles. Twelve patients were treated with 2 or more courses of PACE. Two patients were treated with only one course, one refused and another required emergency thoracic radiotherapy after one course of PACE. Six patients had partial responses (3 thymomas and 3 thymic cancers) but there were no complete remissions (response rates, 42.9%; 95% confidence interval, 17.7% to 71.1%). Moderate hematological toxicities were observed: grade 3 or 4 leukopenia, neutropenia, anemia and thrombocytopenia in 10, 13, 8 and 6 patients, respectively. Six patients developed infections that required antibiotics. Surgical resection or thoracic radiotherapy after PACE treatment was performed in 2 and 7 patients, respectively. The overall median survival time was 14.7 months (range, 5.9 to 59.7 months). For 9 patients who had received no prior treatment before chemotherapy, the median survival time was 8.9 months, and one patient survived for 4 years and is still alive. In conclusion, PACE with G-CSF frequently produces objective remissions in patients with advanced thymoma or thymic cancer. A large-scale intergroup study is necessary to determine the impact of this regimen on advanced thymoma and thymic cancer.

Autoantibodies against 70-kDa heat shock proteins (HSP70) in allogeneic bone marrow transplant recipients

We report that autoantibodies against the 70-kDa heat shock protein family (HSP70) were detected in allogeneic bone marrow transplant recipients. Antibodies to HSP70 family proteins were detected in three out of 14 recipients of an allogeneic marrow graft but in none of the seven patients receiving autologous peripheral blood stem cell transplant (PBSCT). Immunoblotting analysis combined with two-dimensional SDS-PAGE revealed that these patients had antibodies to a constitutive 73-kDa/pI 5.5 heat shock protein (HSP73) and to a stress-inducible 72-kDa/pI 5.6 protein (HSP72). This is the first report, to our knowledge, describing the presence of autoantibody against HSP73 in allogeneic marrow transplant recipients. Our results may provide additional insight into the etiology and the pathophysiology of allogeneic transplant-related disorders.

[Effects of the nitric oxide donor SIN-1 on the membrane potential of mouse neuroblastoma-rat glioma hybrid cells]

The effect of the nitric oxide donor SIN-1 on the membrane potential of cultured mouse neuroblastoma-rat glioma hybrid NG108-15 cells was investigated using the whole cell patch method. It has been reported that neurite formation can be induced in NG108-15 cells by adding of dibutyryl cyclic AMP to the culture medium. Using this system we found that SIN-1 has a selective inhibitory effect on the membrane potential of the calcium current which is concentration-dependent in the 1 mu M-100 microM range. This effect was transient and reversible, the same as seen with the calcium channel blocker nilvadipine at concentrations of 10 microM to 10 microM. At higher concentrations, ranging from 500 microM to 1 mM, however, SIN-1 also caused prolonged inhibition of the membrane potential of the sodium current. However, this effect was also reversible. These findings suggest that SIN-1 has a reversible inhibitory action on the membrane potentials of neurons.