Biomedical subjects

R Tien

Publications and source records attributed to R Tien.

At least 19 recordsLinked to original sources

PubMed2002

Structural and guanosine triphosphate/diphosphate requirements for transit peptide recognition by the cytosolic domain of the chloroplast outer envelope receptor, Toc34.

Toc34 is a transmembrane protein located in the outer envelope membrane of chloroplasts and involved in transit peptide recognition. The cytosolic region of Toc34 reveals 34% alpha-helical and 26% beta-strand structure and is stabilized by intramolecular electrostatic interaction. Toc34 binds both chloroplast preproteins and isolated transit peptides in a guanosine triphosphate- (GTP-) dependent mechanism. In this study we demonstrate that the soluble, cytosolic domain of Toc34 (Toc34deltaTM) functions as receptor in vitro and is capable to compete with the import of the preprotein of the small subunit (preSSU) of ribulose-1,5-bisphosphate carboxylase-oxygenase into chloroplasts in a GTP-dependent manner. We have developed a biosensor assay to study the interaction of Toc34deltaTM with purified preproteins and transit peptides. The results are compared with the interactions of both a full-size preprotein and the transit peptide of preSSU with the translocon of the outer envelope of chloroplasts (Toc complex) in situ. Several mutants of the transit peptide of preSSU were evaluated to identify amino acid segments that are specifically recognized by Toc34. We present a model of how Toc34 may recognize the transit peptide and discuss how this interaction may facilitate interaction and translocation of preproteins via the Toc complex in vivo.

Amino Acid Sequence↗

PubMed2001

Lipid composition of outer leaflet of chloroplast outer envelope determines topology of OEP7.

OEP7, a 6.7-kDa outer envelope protein of spinach chloroplasts inserts into the outer envelope of the organelle independent of a classical cleavable targeting signal. The insertion of OEP7 was studied to describe the determinants for association with, integration into, and orientation of the protein in the outer envelope of chloroplasts. The insertion of OEP7 into the membrane is independent of outer membrane channel proteins and can be reconstituted with the use of protein-free liposomes. In situ, the binding of OEP7 to the membrane surface is not driven by electrostatic interaction because reduction of phosphatidylglycerol or phosphatidylinositol did not reduce the association with the liposomes. The positively charged amino acids flanking the transmembrane domain at the C terminus are essential to retain the native N(in)-C(out) orientation during insertion into chloroplasts. OEP7 inserts with reversed orientation into liposomes containing the average lipid composition of the outer envelopes. The native like N(in)-C(out) orientation is achieved by reduction of the phoshpatidylglycerol concentration mimicking the composition of the outer leaflet of the outer envelope of chloroplasts. We conclude that the unique lipid composition of the outer leaflet due to lipid asymmetry of the outer envelope is essential for the correct topology of OEP7.

Chloroplasts↗

PubMed1998

Activity of high-dose cyclophosphamide in the treatment of childhood malignant gliomas.

Seventeen patients less than or equal to 20 years of age with newly diagnosed (n = 10) or recurrent (n = 7) malignant gliomas (anaplastic astrocytoma and glioblastoma multiforme) were treated with cyclophosphamide in association with hematopoietic cytokines (GM-CSF or G-CSF). Cyclophosphamide was given at a dose of 2 g/m2 daily for 2 days at 4-week intervals. Toxicity consisted of grade IV neutropenia and thrombocytopenia in 95% and 48% of cycles, respectively. There were no cyclophosphamide-related cardiac, pulmonary, or urothelial toxicities observed. Four of 10 patients with newly diagnosed disease demonstrated responses (three complete and one partial responses; one CR was only of 2 months duration). None of the seven patients with recurrent tumors demonstrated a response. We conclude that high-dose cyclophosphamide warrants further evaluation in children with newly diagnosed malignant glioma.

Adolescent↗

PubMed1998

Protein translocation into and across the chloroplastic envelope membranes.

Post-translational protein import into chloroplasts follows a common route characterised by the need for nucleoside-triphosphates at various steps and two distinct protein import machineries at the outer and inner envelope membrane, respectively. Several subunits of these complexes have been elucidated. In contrast, protein translocation into the chloroplastic outer envelope uses distinct and various but poorly characterised insertion pathways. A topological framework for single-membrane spanning proteins of the chloroplastic outer envelope is presented.

Amino Acid Sequence↗

PubMed1997

False positive images in the follow-up of patients with brain tumors.

In recent years, major advances in the diagnosis and treatment of patients with brain tumors have been seen. Today, evaluation of the central nervous system almost always includes magnetic resonance imaging (MRI). The appearance of a new lesion on the MRI scan of a patient previously treated for a central nervous system (CNS) tumor raises concern for recurrent disease with the need for selection of new, potentially toxic therapy. However, the sensitivity of MRI may allow demonstration of new lesions which are not due to tumor. We now report three patients with medulloblastoma who demonstrated new enhancing lesions on MRI following treatment of their tumors with surgery (3 patients), chemotherapy (2 patients), and radiotherapy (2 patients). Two patients underwent resection of the lesion revealing gliosis. One patient had serial imaging that showed disappearance of the lesions. This suggests that not all new enhancing lesions in previously treated brain tumor patients represent tumor. Histologic proof of a suspicious lesion should be demonstrated prior to initiation of new therapy.

Brain Neoplasms↗

PubMed1996

Treatment of patients with pineoblastoma with high dose cyclophosphamide.

The outcome for patients with pineoblastoma has historically been very poor, with most patients dying of disseminated disease despite irradiation. Furthermore, the low incidence of this tumor has hindered progress toward defining better treatment strategies. Here we report the activity and toxicity of cyclophosphamide administered as a single agent at a dose schedule of 2 g/m2/day for 2 successive days at monthly intervals for a maximum of four courses. Eight patients were evaluated, six newly diagnosed and two recurrent. Amongst the six newly diagnosed patients, there were three patients demonstrating partial responses, and three had stable disease throughout the cyclophosphamide treatment period. All six patients are alive and disease free after further therapy. One patient with recurrent disease demonstrated tumor progression on cyclophosphamide, and the other had stable disease throughout the cyclophosphamide treatment period. Both patients subsequently died of progressive disease. The major toxicity of high dose cyclophosphamide was hematopoietic, with one patient requiring a dose reduction after three courses due to prolonged thrombocytopenia. One patient was also withdrawn from treatment with cyclophosphamide due to impaired pulmonary function. This study demonstrates the activity of high dose cyclophosphamide in the treatment of pineoblastoma and may serve as basis for the design of future studies of this tumor.

Adolescent↗

PubMed1996

Successful treatment of childhood pilocytic astrocytomas metastatic to the leptomeninges with high-dose cyclophosphamide.

Leptomeningeal dissemination of childhood pilocytic astrocytoma (PA) is a rare event with little information available regarding therapy. We report here four children with disseminated PA whom we treated with high doses of cyclophosphamide with clinical benefit. The patients were aged 2.5 to 8 years. Three patients presented with PA localized in the posterior fossa, initially treated with surgical resection (n = 3) and radiotherapy (n = 1). Leptomeningeal dissemination occurred at 32, 44, and 8 months from diagnosis, respectively. The fourth patient presented with an optic pathway tumor with leptomeningeal dissemination at diagnosis. At commencement of cyclophosphamide therapy, disease was present in the subarachnoid space (intracranial, n = 2; spinal, n = 4), cerebral ventricles (n = 2), and primary site (n = 3). Histology was identical at diagnosis and recurrence in the two biopsied cases and cerebrospinal fluid was negative in all cases. Treatment was with cyclophosphamide 4-5 g/m2/cycle given every 4 weeks for a total of two cycles (n = 1) and four cycles (n = 3). One patient achieved disease stabilization (duration 27 months at the time of publication) and three patients experienced significant reductions in tumor burden. Subsequent intrathecal therapy was administered to two patients. Two patients developed disease progression at 10 and 9 months from cessation of chemotherapy. The one re-treated patient responded to further, lower dose, cyclophosphamide. This is the first report of the use of high dose cyclophosphamide for disseminated PA. The recurrence of disease in two cases with a further response to lower dose cyclophosphamide has implications for the optimal duration of therapy for these low grade, aggressive tumors.

Antineoplastic Agents, Alkylating↗

PubMed1996

Imaging in acquired immune deficiency syndrome dementia complex (AIDS dementia complex): a review.

1. Since 1986, the AIDS dementia complex has been recognized increasingly as a significant sequela of HIV infection. Though the pathogenesis remains poorly characterized and the diagnosis is one of exclusion, research utilizing various imaging techniques has resulted in greater understanding of the progressive character of ADC. 2. CT and MR studies have revealed general atrophy, atrophy of the basal ganglia, and white matter lesions that appear to increase in severity with progression of HIV infection. 3. CT and MR are relatively insensitive to the presence of clinical dementia, neurological signs, or positive findings on neuropsychological tests. In addition, they show poor correlation with histopathologic findings. 4. PET, SPECT, and MRS show the greatest sensitivity to changes wrought by primary HIV infection of the CNS and thus the greatest potential for early diagnosis of ADC. 5. PET, SPECT, and MRS show involvement of the basal ganglia, bloodflow abnormalities, and metabolite disturbances in HIV-seropositive subjects without findings on examination or neuropsychological tests.

AIDS Dementia Complex↗

PubMed1995

Dose escalation trial of cyclophosphamide with Sargramostim in the treatment of central nervous system (CNS) neoplasms.

We conducted a dose escalation trial of cyclophosphamide plus Sargramostim in the therapy of patients with newly diagnosed or recurrent central nervous system tumors. Cyclophosphamide was administered at doses ranging between 1.0 and 2.5 g/m2 daily for two doses. Sargramostim was administered at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the absolute neutrophil count (ANC) was > 1,000 cells/microliters for two consecutive days. The MTD for patients who had not received any prior chemotherapy and who had received either no radiotherapy or radiotherapy confined to the cranium was 2.0 g/m2 daily for two doses. The MTD for patients previously treated with chemotherapy or neuraxis radiotherapy was also 2.0 g/m2 daily for two doses. Responses were seen in patients with medulloblastoma (8/9), glioblastoma multiforme (2/13), germinoma (1/1), and pineoblastoma (1/2).

Adolescent↗

PubMed1995

Cyclophosphamide in combination with sargramostim for treatment of recurrent medulloblastoma.

Thirteen patients with recurrent medulloblastoma were treated with cyclophosphamide in association with Sargramostim. Cyclophosphamide was given at doses ranging between 1.0-2.5 g/m2 daily for two doses. Sargramostim was given at a fixed dose of 250 micrograms/m2 subcutaneously twice a day beginning 24 hours after the second cyclophosphamide dose and continuing through the leukocyte nadir until the ANC was more than 1,000 cells/microliters for two consecutive days. A total of 33 courses were given with toxicity consisting of grade 4 neutropenia in all courses and grade 3-4 thrombocytopenia in 10 of 13 patients. There were no deaths related to infection or bleeding. Four patients were taken off study because of prolonged myelosuppression. Three of these patients were at the 2.5 g/m2 level, and of these three, two developed lung toxicity (grades 2 and 4, respectively). One patient developed an allergic reaction following the first injection of Sargramostim and was also taken off study. Of 10 evaluable patients, there were 9 PR and 1 SD. We conclude that cyclophosphamide at a dose of 2.0 g/m2/day x 2 days q 4 weeks in association with Sargramostim demonstrates marked activity with acceptable toxicity in patients with recurrent medulloblastoma.

Adolescent↗

PubMed1995

Neuro-Behçet's disease: factors hampering proper diagnosis.

We reviewed the clinical course of nine patients with neuro-Behçet's disease to assess difficulties in making this diagnosis. Factors delaying proper diagnosis included lack of accurate history and physical examination, lack of recognition of an underlying systemic syndrome and its relationship to the neurologic symptoms, presence of intermittently normal CSF studies, and use of noncontrasted neuroimaging techniques.

Adolescent↗

PubMed1995

Gd-DPTA enhanced MRI in Bell's palsy and herpes zoster oticus: an overview and implications for future studies.

Magnetic resonance imaging (MRI) is a new and important tool for use in diagnosing and investigating diseases affecting the facial nerve. In recent gadolinium-DTPA enhanced MRI (Gd-MRI) studies it has unequivocally been demonstrated that ipsilateral facial nerve contrast enhancement, predominantly in the meatal portion, is present in both Bell's palsy and herpes zoster oticus. In this overview, the results of MRI studies performed on patients with acute peripheral facial palsy, especially Bell's palsy and herpes zoster oticus, are discussed. The Gd-MRI pattern in Bell's palsy is very similar to that seen in herpes zoster oticus, and the findings reported so far support the theory that an inflammation may be the cause of the nerve injury in both cases. So far, however, Gd-MRI has not been helpful in evaluating the severity and/or prognosis of the facial palsy. Further studies employing improved techniques, including three-dimensional fast (or turbo) spin echo (3DFSE) MRI with heavily T2-weighted sections and high resolution three-dimensional Fourier transform (3DFT) MRI, need to be conducted in order to determine whether it is possible to follow the course of the disease and whether MRI and/or Gd-MRI are useful prognostic tools in the early stages of palsy.

Contrast Media↗

PubMed1995

Detection of cerebrospinal fluid metastasis: CT myelography or MR?

PURPOSE: To determine the sensitivity of contrast MR versus myelography followed by CT in the detection of cerebrospinal fluid metastases in children with primary central nervous system tumors. METHODS: Thirty-three patients who had primary central nervous system malignancies had spinal MR with gadolinium within 2 weeks of a myelogram followed by CT. MR technique included T1-weighted image sequences of the entire spine with and without gadolinium. CT scans were routinely performed at T-12 to L-2, L-4 to S-1, and foramen magnum to C-2. All studies were reviewed blindly; the number, character, and location of all metastases was recorded and the results of the two studies compared. Cerebrospinal fluid cytologic findings were recorded for each patient, and compared with the results of the imaging studies. RESULTS: Seven of the 33 patients had metastases detected; metastases were seen on both MR and myelography followed by CT. However, MR showed 24 lesions and myelography followed by CT showed only 15. When a lesion was seen on both MR and myelography followed by CT, the MR was usually more convincing. Superficial lesions seen on MR sometimes would be missed on myelography followed by CT. Both MR and myelography followed by CT were quite sensitive in the detection of small lesions (2 to 3 mm) when present on spinal nerve roots. Whereas MR showed multiple lesions not seen on myelography followed by CT, CT failed to show any metastases not seen on MR. Imaging studies showed metastases in 3 patients who had normal cytologic findings. CONCLUSIONS: MR shows significantly more cerebrospinal fluid metastases than myelography followed by CT.

Adolescent↗

PubMed1994

Management of pineal non-germinoma germ cell tumor with residual teratoma and normal alpha-fetoprotein.

A 16-year-old white male presented with multiple abnormal extraocular movements secondary to an enhancing pineal tumor. Subtotal resection of the lesion revealed a mixed malignant germ cell tumor. The preoperative serum alpha-fetoprotein (AFP) was markedly elevated at 155 IU/L. The patient subsequently received radiotherapy and adjuvant chemotherapy consisting of cisplatin rotating monthly with vincristine and cyclophosphamide, with dramatic tumor regression and return of AFP to normal. Eighteen months later the persistence of a substantial tumor mass despite a normal AFP raised concern for residual active tumor. Histological examination of the resected lesion revealed benign teratoma and fibrous tissue. Repeat management of mixed malignant germ cell tumors, which demonstrate a persistent mass following an initial response to treatment.

Adolescent↗

PubMed1994

Cerebral atrophy in an infant following treatment with ifosfamide.

Ifosfamide, a nitrogen mustard derived alkylating agent commonly used in the treatment of solid tumors, has been associated with neurotoxicity in 5-33% of treated patients. Encephalopathy most often occurs during or shortly following drug administration, with increased drowsiness or irritability, confusion, hallucinations, visual blurring, extrapyramidal dysfunction, cranial nerve abnormalities, incontinence, generalized muscle twitching, seizures, and coma reported in infants, children, and older adults. While most reported neurologic abnormalities associated with ifosfamide have been reversible, encephalopathy resulting in death has occurred. We now report an infant who developed ifosfamide-induced encephalopathy, loss of developmental milestones, progressive brain atrophy, and cessation of cranial growth. This is the first case of cerebral atrophy and loss of developmental milestones that has been reported in a pediatric patient treated with ifosfamide. Given the efficacy of this anti-neoplastic agent and its increasing use in pediatrics, further investigation is indicated, especially in infants where brain growth is ongoing.

Atrophy↗

PubMed1993

Pilocytic astrocytoma: correlation between the initial imaging features and clinical aggressiveness.

OBJECTIVE: Astrocytomas are classified as either fibrillary or pilocytic on the basis of their histologic appearance. The imaging features of the fibrillary astrocytoma correlate closely with the tumor's clinical aggressiveness and are, therefore, useful in predicting prognosis. Correlation between the imaging features and the clinical aggressiveness of the pilocytic astrocytoma, however, is not well established. Accordingly, we compared the initial MR and CT appearances of the lesion with tumor aggressiveness as seen clinically to determine if a correlation exists. MATERIALS AND METHODS: We retrospectively evaluated the initial MR images or CT scans of 32 consecutive patients who had a histologic diagnosis of pilocytic astrocytoma. The lesions were evaluated with regard to location, size, calcification, morphology, and degree of contrast enhancement. These initial imaging features were correlated with the aggressiveness of the tumor as seen clinically. Tumors were classified as aggressive or nonaggressive on the basis of their clinical manifestations. Patients with clinically aggressive lesions had progressive symptoms and radiologic evidence of tumor progression or recurrence within an unusually short period. Patients with clinically nonaggressive lesions had a more indolent course, either improving or remaining stable, on both clinical and radiologic evaluations. In 12 patients, the tumor was classified as aggressive clinically, either progressing or recurring within a median time of 7.5 months (range, 2.5-118 months) from the initial diagnosis. The remaining 20 patients had a clinically nonaggressive course. RESULTS: In our series of patients, lesion size and location were not significantly different between the nonaggressive and aggressive tumors, as noted clinically. Furthermore, the aggressive and nonaggressive tumors were similar with regard to the presence or absence of calcium. Most tumors in both groups showed either moderate or marked enhancement and were multilobular. CONCLUSION: The initial CT and MR features of pilocytic astrocytoma are unreliable for predicting which lesions will behave in a more aggressive manner clinically and have a poor prognosis.

Adolescent↗

PubMed1993

Carboplatin treatment of progressive optic pathway gliomas to delay radiotherapy.

Six patients with optic pathway gliomas who were previously managed with surgery and/or chemotherapy were treated with carboplatin (560 mg/sq m) after radiographic evidence of disease progression. The median age at diagnosis was 2 years (range 4 months to 7 years), and the interval between diagnosis and carboplatin therapy ranged between 7 months and 6.5 years (median 1.8 years). Treatment was given at 4-week intervals and continued until unacceptable toxicity supervened, the disease progressed, or the disease was stable for 12 months. All patients demonstrated disease stability at the outset of the third cycle and continued to do so at the time of this writing. Two patients are 16 and 32 months from initial carboplatin therapy and have been off treatment for 5 and 14 months, respectively; two patients are still receiving therapy at 7 and 11 months after their initial treatment. During the study, two patients developed hypersensitivity to the drug, requiring its discontinuation. Toxicity was minimal, consisting mainly of thrombocytopenia, requiring a one-dose reduction in four of the six treated patients. No platelet transfusions were needed. These results suggest that carboplatin can arrest growth of progressive optic pathway gliomas in children and can allow delay of radiotherapy. A larger trial will be required to define the optimal use of carboplatin in the treatment of low-grade gliomas in children.

Astrocytoma↗

PubMed1992

Successful therapy for trilateral retinoblastoma.

Trilateral retinoblastoma, the intracranial malignancy associated with bilateral retinoblastoma, is an uncommon and clinically aggressive malignancy with a uniformly fatal outcome. Three children with newly diagnosed trilateral retinoblastoma were treated with systemic (cyclophosphamide and vincristine) and intrathecal (methotrexate, hydrocortisone, and cytarabine) chemotherapy, as well as craniospinal irradiation (one patient) in addition to therapy of the eye lesions. All three patients have had partial or complete response of the pineal tumors to chemotherapy, with no active disease eight or more years, 33 or more months, and 12 or more months, respectively, after diagnosis of the lesions.

Antineoplastic Combined Chemotherapy Protocols↗