Impact of breath hold on regional nodal irradiation and heart volume in field in left breast cancer adjuvant irradiation

PURPOSE

Compared to the free-breathing technique, adjuvant left breast irradiation after breast-conserving surgery or mastectomy using the breath-hold method significantly reduces the heart mean dose, Left anterior descending artery, and ipsilateral lung doses. Movement with deep inspiration may also reduce heart volume in the field and regional node doses.

MATERIALS AND METHODS

Pre-radiotherapy planning CT was performed in the free-breathing, and breath-hold techniques using RPM, demographic information, clinicopathological data, heart volume in the field, heart mean dose, LAD mean dose, and regional nodal doses were calculated in both free breathing and DIBH. Fifty patients with left breast cancer receiving left breast adjuvant radiation were enrolled.

RESULTS

There was no significant difference in axillary LN coverage between the two techniques, except for SCL maximum dose, Axilla I node maximum dose, and Axilla II minimum dose in favor of the breath hold technique. The mean age was 47.54 years, 78% had GII IDC, 66% had positive LVSI results, and 74% of patients had T2. The breath hold strategy resulted in considerably decreased mean heart dose (p = 0.000), LAD dose (p = 0.000), ipsilateral lung mean dose (p = 0.012), and heart volume if the field (p = 0.013). The mean cardiac dosage and the dose of the LAD were significantly correlated (p = 0.000, R = 0.673). Heart volume in the field and heart mean dosage was not significantly correlated (p = 0.285, r = - 0.108).

CONCLUSION

When compared to free breathing scans, DIBH procedures result in considerably reduced dosage to the OAR and no appreciable changes in dose exposure to regional lymph node stations in patients with left-sided breast cancer.

Optimized Conformal Total Body Irradiation with VMAT Using a Linear-Accelerator-Based Radiosurgery Treatment System in Comparison to the Golden Standard Helical TomoTherapy

Modern irradiation techniques for optimized conformal TBI can be realized by Helical Tomotherapy (HT) or Volumetric Modulated Arc Therapy (VMAT), depending on the availability of suitable specialized equipment. In this dosimetric planning study, we compared both modalities and addressed the question of whether VMAT with small field sizes is also suitable as a backup in case of HT equipment malfunctions. For this purpose, we retrospectively used planning computed tomography (CT) data from 10 patients treated with HT with a total dose of 8 Gy (n = 5) or 12 Gy (n = 5) for treatment planning for VMAT with a small field size (36 × 22 cm). The target volume coverage, dose homogeneity at target volume, and dose reduction in organs at risk (OAR) (lungs, kidneys, lenses) were analyzed and compared. One patient was irradiated with both modalities due to a device failure of the HT equipment during the study, which facilitated a comparison in a real clinical setting. The findings indicate that in addition to a higher mean dose to the lenses in the 12 Gy group for VMAT and a better dose homogeneity in the target volume for HT, comparably good and adequate target dose coverage and dose reduction in the other OAR could be achieved for both modalities, with significantly longer treatment times for VMAT. In conclusion, after appropriate optimization of the treatment times, VMAT using linear accelerator radiosurgery technology can be used both as a backup in addition to HT and in clinical routines to perform optimized conformal TBI.

Analytical dosimetric study of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) for prostate cancer

PURPOSE

The study aimed to compare the dosimetric results and treatment delivery efficiency among four techniques to explore the preferred technique in prostate treatment.

MATERIALS AND METHODS

7 IMRT, 9 IMRT, 1 ARC, and 2 ARC plans were created for 30 prostate cancer patients using the Eclipse™ treatment planning system (Varian Medical Systems). All the plans were designed to deliver 80.0 Gy in 40 fractions to the prostate planning target volume (PTV). Target coverage, organs at risk (OARs), number of monitor units, homogeneity, and conformity were compared across the four techniques to assess the quality of the plans.

RESULTS

The study revealed better Planning Target Volume (PTV) dose coverage in the VMAT-2A than in the other plans. At the same time, VMAT-2A plans were found to be significantly lower in terms of Bladder and rectum doses than other techniques. In addition, VMAT has the advantage of considerably reducing the number of monitor units and treatment time.

CONCLUSION

For prostate cancer, VMAT may offer a favorable dose gradient profile, conformity, and MU and treatment time compared to IMRT.

A single-institution retrospective analysis of intraoperative radiation boost during breast-conservation treatment for breast cancer

BACKGROUND

As part of a breast-conservation strategy for breast cancer, there are presently no data from randomized controlled studies on the use of intraoperative radiation (IORT) as a tumor bed boost. The effectiveness and safety of IORT as a boost therapy at a tertiary cancer center were retrospectively reviewed in this study.

METHODS

Patients had breast-conserving surgery from 2012 to 2016 that included staging of the axillary lymph nodes, a single dose of 20 Gy IORT with 50-kV photons, whole-breast irradiation (WBI), and (neo-)adjuvant systemic treatment (if applicable). During the follow-up patients were monitored for the assessment of acute and late toxicities (using the Common Terminology Criteria for Adverse Events version 4.03). Results included ipsilateral (IBTR), contralateral (CBE), and distant metastasis-free (DMFS) breast progression-free survival, as well as overall survival (OS).

RESULTS

The 68 patients had a median follow-up of 91.5 months (with a range of 9-125). Most patients (n = 51) had T1 disease and were clinically node negative. Only a small number of individuals had triple negative or high-grade illness. The majority of patients had sentinel node biopsy, and three (4.4%) had to have their tumors removed again since their original margins were positive. Finally, there were no distinct tumor bed margins. Neoadjuvant chemotherapy was administered to ten (14.7%). The median duration from BCS to WBI was 54.5 days, and conventionally fractionated WBI was used to accomplish WBI most frequently (n = 57, 96.6%). IORT was administered in a single 20 Gy dosage. 50 Gy was the median WBI dosage (range 40.05-50.4 Gy). There were no grade 4 adverse events for any patients in. Toxicities following surgery were minimal. There were only one patient with grade 3 toxicity (radiation dermatitis) to observe. Five tumor bed recurrences and two contralateral breast incident each occurred.

CONCLUSION

This work adds to the preliminary evidence already in the literature and supports the use of IORT in boost settings. When randomized trials like TARGIT-B are eventually published, these hopeful findings should be prospectively evaluated.

Metabolic response after 68Ga-PSMA-PET/CT-directed IGRT/SBRT for oligometastases prostate cancer

BACKGROUND

We used 68Ga PSMA PET/CT in the current investigation to assess the metabolic response and local control of metastasis in patients with oligometastatic prostate cancer receiving SBRT.

MATERIALS AND PROCEDURES

We performed a retrospective evaluation of the medical data of all patients with oligometastatic prostate cancer who underwent stereotactic body radiation therapy (SBRT) between 2017 and 2021. Our analysis only included medical records of patients who had SBRT for oligometastatic prostate cancer and had pre and post-SBRT 68Ga PSMA PET/CT images. Patient-related (age), disease-related (Gleason score, location of metastases), and treatment-related (factors and outcomes) data were collected from the medical files.

RESULTS

A total of 17 patients (28 lesions) with a median age of 69 years were included in the research. A median follow-up of 16.6 months was used (range 6-36 months). The median follow-up period for 68 Ga PSMA PET/CT was 8 months (the range was 5-24 months). The median pre-treatment PSA level was 1.7 ng/mL (range 0.39-18.3 ng/mL) compared to the post-treatment PSA nadir of 0.05 ng/mL (0.02-4.57). During the follow-up period, local control was 96%, and there was a link between PSMA avidity on PET. In the treated lesions, there were no recurrences. During follow-up, none of the patients experienced toxicities of grade 3 or above.

CONCLUSIONS

SBRT is a highly successful and safe way of treating patients with oligometastatic prostate cancer. Additional research is needed to examine 68Ga PSMA PET/CT to assess further for demarcation and follow-up.

A single-center experience with linear accelerator-based stereotactic radiotherapy for meningiomas: hypofractionation and radiosurgery

PURPOSE

Meningioma is a common type of benign tumor that can be managed in several ways, ranging from close observation, surgical resection, and various types of radiation. We present here results from a 10 year experience treating meningiomas with a hypofractionated approach.

MATERIALS AND METHODS

To define the rate of tumor control and factors associated with the relief of symptoms and radiation-related complications after radiosurgery and hypofractionated radiosurgery for patients with imaging-defined intracranial meningiomas. We reviewed the charts of 48 patients treated with stereotactic radiosurgery (SRS) or hypofractionated stereotactic radiotherapy (SRT) from 2002 to 2018. A total of 37 (82%) patients had WHO Grade 1 disease, and 11 (22%) had Grade 2. Outcomes that were analyzed included local control rates and the rate and grade of any reported toxicity.

RESULTS

Only 36 patients with 38 lesions, who underwent the follow-up regime, were enrolled in the retrospective analysis. The follow-up mean was 40 months (12-120 months). 25/34 patients had surgery before the radiotherapy. Sixteen underwent SRS with a median dose of 13, 5, and 20 received hypofractionated SBRT with a median dose of 26.9 (22-45 Gy) in median six fractions (5-13 fractions). Local control at 2 and 5 years for all patients was 90 and 70%, respectively. No patient suffered from toxicity > 2 CTC. 21/36 patients showed stable disease, while 8/36 patients showed partial Remission. 7/36 developed recurrent meningioma (five in-field), only one patient with grade 1 meningioma, in a median of 22 months (13-48 months).

CONCLUSION

SFRT was superior to SRS for local control in our analysis of Grade I meningiomas. This might be due to a tendency for higher EQD2 in the PTV with SFRT compared to SRS, which was reduced to avoid brain necrosis in large PTVs. Therefore, SFRT appears preferable for typical meningioma PTVs.

Impact of breath-hold technique on incidence of cardiac events in adjuvant left breast cancer irradiation

BACKGROUND

This study aims to compare the incidence of cardiac events and to identify its predictors in left breast cancer patients receiving adjuvant radiotherapy using breath-hold technique (DIBH) versus free breathing technique (FB).

METHODS

We conducted a retrospective multi-center study of two arms; the free breathing arm included 208 patients who were treated with traditional radiotherapy treatment technique, while DIBH arm included 224 patients who were treated with breath-hold technique using The Varian Real-time Position Management (RPM). We retrospectively reviewed the medical records of the patients from January 2010 to December 2017.

RESULTS

The mean dose to the heart and left anterior descending artery were significantly lower in the DIBH arm (2.10 ± 0.39 and 6.16 ± 0.18 Gy) compared with (4.29 ± 0.60 Gy and 12.69 ± 0.93 Gy, respectively) in the FB arm. The incidence of cardiac events was higher in the FB arm than in the DIBH arm, but it was not statically significant. Our analysis revealed that age, diabetes, hypertension, smoking, mean LAD dose, and heart mean dose were significant prognostic factors for the occurrence of cardiac events in the breath-hold arm. Hypertension, smoking, as well as heart mean dose were independent risk factors for the occurrence of cardiac events.

CONCLUSION

Use of the DIBH technique resulted in a significant reduction in doses to the heart, LAD and lesser cardiac events incidence compared to free breathing.

Can alternative liver function scores facilitate the establishment of an indication for radioablative therapy in patients with hepatocellular carcinoma?

Background and purpose

ALBI and IBI are new scores to evaluate the liver function in patients with hepatocellular carcinoma (HCC). The purpose of this study was to evaluate the prognostic abilities of those scores in patients treated with interstitial brachytherapy (iBT).

Materials and methods

190 patients treated with iBT between 01.01.2006 and 01.01.2018 were included in this study. The clinical target dose was 15 Gy. The patients were all in Child–Pugh stadium A or B and across the Barcelona Clinic Liver Cancer (BCLC) Stages 0–C. Retrospectively ALBI and IBI were calculated pre- and post-therapeutic until 6 months after iBT. Hazards ratios were calculated, and p values corrected using the false discovery rate according to Benjamini and Hochberg.

Results

The median overall survival was 23.5 months (CI 19–28.5 months), and the median progression-free survival was 7.5 months (CI 6–9 months). Elevated ALBI showed a significantly higher risk to die with a hazard ratio (HR) of 2.010 (ALBI 2 vs. 1) and 4082 (ALBI 3 vs. 1), respectively. The IBI did also show a higher risk with an HR of 1.816 (IBI 1 vs. 0) and 4608 (IBI 2 vs. 0), respectively. Even 3 months after therapy elevated ALBI and IBI showed poor overall survival. Concerning progression-free survival, ALBI and IBI could not provide any relevant additional information.

Conclusion

ALBI and IBI are useful tools to predict the overall survival in patients treated with iBT and might be helpful to assign the patients to the appropriate therapy.

125 years of head and neck radiotherapy: could organ-sparing radiotherapy of larynx cancer have prevented World War I?

PURPOSE

We aim to recapitulate the rapid development of head and neck radiotherapy in the context of otorhinolaryngology (ORL) medicine starting 125 years ago. This is put into context with the unsuccessful treatment of the laryngeal cancer (LC) of the German emperor Frederick III and its historical consequences.

METHODS

The three-step process consisted in the analysis of (1) historical sources of the development of ORL radiotherapy from the discovery of x‑rays and radioactivity until World War I, (2) course and treatment of Frederick's III LC, (3) political context with a special focus on the escalation towards World War I. Pertinent historical illustrations of technical developments of radiotherapy were summarized in a video.

RESULTS

ORL radiotherapy initiated on 03 February 1896, only 65 days after the discovery of X‑rays. By 1914, organ-sparing LC radiotherapy was established with a predominance of curietherapy over roentgentherapy. Correct diagnosis of Frederick III's primarily radiocurable cT1a glottic LC was delayed by one year, which resulted in advancement to a fatal pT4 pN1 Mx tumour stage. Historically, his successor, William II, was assumed to have contributed to the causes of World War I.

CONCLUSION

ORL radiotherapy came only eight years late to treat Frederick III who might have impeded World War I. This illustrates the potential impact of modern curative radiotherapy on the future course of public life beyond the personal fate of the patient himself.

Seroprevalence of camel brucellosis in Qatar

Brucellosis is a significant zoonotic disease and one of the most common neglected diseases worldwide. It can infect a wide range of domestic and wild animal species. Infected animals are usually culled, causing substantial economic losses to animal owners and the country's economy in general. The disease is endemic among cattle, sheep, and goats in many countries around the Middle East and prevalent in most Gulf Cooperation Council countries, comprising a significant public health risk in the region. This study investigated the seroprevalence of brucellosis among camels in Qatar. Two hundred and forty-eight samples were collected from dromedary camels from 28 farms across the entire country. Each sample was tested for Brucella antibodies with both Rose Bengal and competitive enzyme-linked immunosorbent assay. Only samples that tested positive by both tests were considered seropositive for brucellosis. The overall prevalence was (20.6%, 95% CI, 15.7-26.1). The association between sex and seropositivity was slightly significant (Χ² = 4.32, P = 0.04), with higher seroprevalence in females. Camels below breeding age (i.e., < 4 years old) showed decreased seropositivity (3.4%, 95% CI, 0.1-17.8), compared to (22.8%, 95% CI, 17.4-29.0) seropositivity in camels ≥ 4 years of age, with a significant association between age groups and seropositivity (P = 0.02). Our results indicate that the seroprevalence of brucellosis in Qatar's camels is alarming, mandating more efforts to control the disease. The findings of this study will aid in selecting better effective measures to control camel brucellosis in Qatar. Further studies need to be conducted on Brucella infection among camels to determine the predisposing risk factors and the steps that should be followed to control brucellosis.

A Promising Platform of Magnetic Nanofluid and Ultrasonic Treatment for Cancer Hyperthermia Therapy: In Vitro and in Vivo Study

Localized hyperthermia is a very promising cancer therapy approach especially when stimulated by the exceptional properties of iron oxide magnetic nanoparticles (MNPs). This approach is a highly site-specific method for localized heating of bodily tissue without any harmful side effects that could revolutionize the practice of cancer therapy. The main objective of this study was to evaluate the cancer cell-destroying capability of MNPs in combination with ultrasound treatment as an innovative sonomagnetic cancer therapy. Magnetic nanofluids (MNFs) were synthesized by co-precipitation/sonochemical techniques in an aqueous medium without any surfactant and/or capping agent. The physicochemical characteristics of the prepared MNFs were investigated with scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, Fourier transform infrared and vibrating sample magnetometry. The MNFs was used as a mediator and sonosensitizer to destroy tumor tissue when irradiated by ultrasound waves. The antitumor efficiency of MNFs in combination with pulsed ultrasound (1.5 W/cm², 1 MHz) was evaluated in vitro and in vivo. In vitro efficacy was estimated by determining the cell viability of Ehrlich ascites carcinoma cells. For in vivo experiments, female mice were inoculated subcutaneously with Ehrlich carcinoma cells to establish solid Ehrlich carcinoma. The cytotoxic concentration of MNFs (400 µg/mL) was injected intratumorally and exposed to pulsed ultrasound (1.5 W/cm², 1 MHz). The cytotoxic effect was determined in terms of tumor growth rate, apoptosis and necrosis. Our results revealed that MNFs in the presence of pulsed ultrasound cause a significant increase in the cytotoxicity effect on tumor cells. This study illustrates the high efficiency of cancer therapy as assisted by both ultrasound and magnetic nanofluid.

Changing Patterns of Hepatocellular Carcinoma after Treatment with Direct Antiviral Agents

Introduction

The impact of direct antiviral agents (DAAs) on the development of hepatocellular carcinoma (HCC) is controversial. One important aspect of this controversy is the changing pattern of HCC.

Objective

In this study, we attempted to assess the changes in the pattern of HCC after treatment with DAAs.

Methods

A total of 51 HCC patients after DAA treatment and 54 HCC patients without DAA treatment were included. The diagnosis of HCC was based on typical dynamic CT and/or MRI criteria in both groups. Liver status was assessed by means of the fibrosis 4 index (Fib-4), Child-Pugh classification, and model for end-stage liver disease (MELD). HCC infiltrative pattern, portal vein thrombosis (PVT), local and distant metastases, and α-fetoprotein (AFP) level were compared in the 2 groups. The staging of HCC and treatment decisions were made in both groups following the Milan criteria, Barcelona Clinic Liver Cancer staging, tumor-node-metastasis staging, and Cancer of the Liver Italian Program categorization.

Results

The mean age of the HCC patients after DAA treatment (59.1± 7.4 years) was older than that of the HCC patients without DAA treatment. There was no significant difference between groups regarding sex distribution. The mean Fib-4 score (4.84 ± 3.53) was significantly lower in HCC patients after DAA treatment than in those without DAA treatment. The frequency of the infiltrative HCC pattern, PVT, and regional lymph node metastasis was significantly higher in HCC patients after DAA treatment than in those without DAA treatment (p ≤ 0.05); mean AFP level (5,085.2 ± 11,883.2 ng/mL) was also significantly higher. HCC patients after DAA treatment had significantly advanced stages and limited treatment options (p ≤ 0.05).

Conclusion

The changing HCC pattern after DAA treatment may suggest the need for new HCC staging and treatment protocols.

Dosimetric and volumetric effects in clinical target volume and organs at risk during postprostatectomy radiotherapy

PURPOSE

To assess the reproducibility of the dose-volume distribution of the initial simulation CT, generated using volumetric modulated arc therapy (VMAT) planning, during the radiotherapy of the prostatic bed based on weekly cone beam CTs (CBCT).

METHODS

Twenty-three patients, after radical prostatectomy were treated with adjuvant or salvage radiotherapy between July and December 2016 and considered for this evaluation. Weekly CBCT scans (n = 138) were imported into the treatment planning system, and the clinical tumor volume (CTV), the rectum and the bladder were contoured. The initially calculated dose distribution and the dose-volume histograms generated from weekly CBCTs were compared. The prostatic fossa dose coverage was assessed by the proportion of the CTV fully encompassed by the 95% and 98% isodose lines. Rectal and bladder volumes receiving 50, 60 and 65 Gy during the treatment were compared to the initial plan, with statistical significance determined using the one-sample t‑test.

RESULTS

Marked variations in the total organ volume of the rectum and the bladder were observed. The correlation between rectum volume and V₅₀ was not significant (p = 0.487), while the bladder volume and V₅₀ demonstrated a significant correlation. There was no correlation between urinary bladder volume and CTV. The change in rectal volume correlated significantly with CTV. The dose coverage (D_98% and D_95%) to the prostatic bed could be achieved for all patients due to the ventral shift in the volume differences of the rectum.

CONCLUSION

Weekly CBCTs can be considered as adequate verification tools to assess the interfractional variability of the CTV and organs at risk. The proven volume changes in the urinary bladder and the rectum do not compromise the final delivered dose in the CTV.

Hepatitis B Virus Genotype E Infection among Egyptian Health Care Workers

BACKGROUND AND OBJECTIVES

Health Care Workers (HCWs) are at a high risk of needle stick injuries and HBV infection in Egypt; this problem is further aggravated by low Hepatitis B (HB) vaccination coverage. Limited data are available on the prevalence of HBV infection in Egyptian HCWs. In this study, we aimed to assess the HBV infection rate and genotypes among Egyptian HCWs.

METHODS

Five hundred and sixty-four (564) HCWs were included. Of them, 258 (45.74%) were health care providers and 306 (54.25%) were non-health care providers. All HCWs completed both the study questionnaires and provided a blood sample for HBV testing. Indeed, all HCWs were tested for Hepatitis B surface antigen (HBsAg) and antibody to Hepatitis B core antigen (anti-HBc), by enzyme-linked immunosorbent assay. HBVDNA was checked for HCWs who tested positive for HBsAg and/or anti-HBc, by nested Polymerase Chain Reaction (PCR). HBVDNA positive HCWs were further subjected to HBV genotyping.

RESULTS

The mean age of included HCWs was 33.0 ± 9.8 years, of whom 319 (56.56%) were males. The mean duration of health care work was 9.3 ± 6.7 years. The frequency of HBsAg and anti-HBc were 1.4%, and 24.5%, respectively. Old age and prolonged duration of health care work were significantly associated with anti-HBc seropositivity. Among 140 HCWs positive for HBsAg and/or anti-HBc, 14 (10 %) had positive HBVDNA by PCR. HBV/E (n = 7), HBV/D (n = 3) and co-infection with E and D (n = 4) genotypes were detected.

CONCLUSION

Egyptian HCWs have a significantly high rate of HBV exposure. The detection of HBV/E genotype among Egyptian HCWs suggests prevalent transmission of HBV/E among Egyptian populations.

Renal allograft venous thrombosis is salvageable

BACKGROUND

Renal vein thrombosis (RVT) is an uncommon but serious complication. It usually occurs early after surgery. While compression of the renal vein is the most common cause, early rejection and hemostatic defects are other known causes. The symptoms are nonspecific and diagnosis is often delayed. Ultrasonography and renal isotope scan findings may resemble acute rejection or acute tubular necrosis.

PATIENTS AND METHODS

We retrospectively reviewed the records of 684 recipients who were transplated between November 1993 and May 2006. The diagnosis of RVT was suspected by an unexplained drop in urine output, rise in serum creatinine, or hematuria, and confirmed by Doppler ultrasound and isotope scanning. Urgent exploration was performed in all suspected cases.

RESULTS

Seven incidences of biopsy-proven RVT were encountered, including 3 associated with hematoma and 1 with rejection. Four grafts were from cadaveric donors. Three grafts were salvaged.

CONCLUSIONS

The incidence of RVT in the present series was 1%. All cases developed in the first 2 weeks after transplantation. It was more common in adults, in female recipients, and in cadaveric grafts. Early diagnosis and intervention were the keys to salvage.

Effect of oxidation on the properties of apolipoproteins A-I and A-II

Purified apolipoprotein A-I has been separated by reversed-phase high performance liquid chromatography (HPLC) into multiple peaks and these peaks have been characterized. One peak, apoA-Ib had a relatively longer retention time on HPLC but its retention time could be shortened by treatment by hydrogen peroxide. CNBr cleavage studies indicated that the differences in apoA-Ib and in its oxidation product, apoA-Ia, were due to the different oxidation states of methionine. This phenomenon was also observed in apoA-II, where methionine oxidation produced two more forms of this apolipoprotein in addition to the native form. These isomers were found to have different secondary structures and affinities for lipid. Model peptide analogs of the amphipathic helix with the same sequence but with methionine and methionine sulfoxide at the nonpolar face of the amphipathic helix were synthesized and studied. It was found that the lipid affinities of these synthetic peptide isomers were very different. They also differed in their secondary structures as studied by circular dichroism (CD). We propose that methionine oxidation introduces hydrophilic residues at the nonpolar face of the amphipathic helical domains of these apolipoproteins and, therefore, alters their secondary structure and lipid affinity.

Inhibition of chondroitin and heparan sulfate biosynthesis in Chinese hamster ovary cell mutants defective in galactosyltransferase I

We have isolated five Chinese hamster ovary cell mutants defective in galactosyltransferase I (UDP-D-galactose:xylose beta-1,4-D-galactosyltransferase) and studied the effect of p-nitrophenyl-beta-D-xyloside supplementation on glycosaminoglycan biosynthesis in the mutant cells. Assays of galactosyltransferase I showed that the mutants contained less than 2% of the enzyme activity present in wild-type cells, and enzyme activity was additive in mixtures of mutant and wild-type cell extracts, suggesting that the mutations most likely defined the structural gene encoding the enzyme. Cell hybridization studies showed that the mutations in all five strains were recessive and that the mutants belonged to the same complementation group. The mutants contained wild-type levels of xylosyltransferase (UDP-D-xylose:core protein (serine) beta-D-xylosyltransferase), lactose synthase (UDP-D-galactose:N-acetyl-glucosaminide beta-1,4-D-galactosyltransferase), and lactosylceramide synthase (UDP-D-galactose:glucosylceramide beta-1,4-D-galactosyltransferase). Their sensitivity to lectin-mediated cytotoxicity was virtually identical to that of the wild-type, indicating that there were no gross alterations in glycoprotein or glycolipid compositions. Anion-exchange high performance liquid chromatography of 35S-glycosaminoglycans from one of the galactosyltransferase I-deficient mutants showed a dramatic reduction in both heparan sulfate and chondroitin sulfate, demonstrating that galactosyltransferase I is responsible for the formation of both glycosaminoglycans in intact cells. Surprisingly, the addition of 1 mM-p-nitrophenyl-beta-D-xyloside, a substrate for galactosyltransferase I, restored glycosaminoglycan synthesis in mutant cells. This finding suggested that another galactosyltransferase, possibly lactose synthase, can transfer galactose to xylose in intact cells.

Studies of synthetic peptide analogs of the amphipathic helix. Effect of charge distribution, hydrophobicity, and secondary structure on lipid association and lecithin:cholesterol acyltransferase activation

Four peptides capable of forming an amphipathic alpha-helix have been synthesized and their conformational and lipid-binding properties studied. These peptides have been designed to vary the alpha-helix-forming potential as well as the charge distribution of the model peptide. The resulting peptide analogs and their complexes with dimyristoyl phosphatidylcholine were studied by using right angle light scattering, negative stain electron microscopy, nondenaturing gradient gel electrophoresis, circular dichroism, intrinsic tryptophan fluorescence, and differential scanning calorimetry techniques. The four analogs, [Glu4,9, Leu11,17] (reverse-18A, [Glu4,9, Leu5,11,17] reverse-18A, [Glu1,8, Leu11,17] 18A, and [Glu1,8, Leu5,11,17] 18A were derived from a model amphipathic peptide Asp-Trp-Leu-Lys-Ala-Phe-Tyr-Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe (18A) whose lipid-associating properties strongly mimic apolipoprotein A-I or derived from Lys-Trp-Leu-Asp-Ala-Phe-Tyr-Lys-Asp-Val-Ala-Lys-Glu-Leu-Glu-Lys-Ala-Phe (reverse-18A), a peptide with little affinity for lipid and having a reversed charge distribution compared to the 18A peptide. We have shown that by substituting glutamic acid and leucine for aspartic acid and alanine, respectively, in a weak lipid-associating amphipathic helix peptide, the lipid-associating ability can be increased. Thus, peptides with both kinds of charge distribution can associate with the lipid. The ability of the peptide to disrupt phospholipid bilayers, however, is higher for 18A analogs compared to the reverse-18A analogs even after increasing the helix-forming potential and hydrophobicity. In addition to forming smaller lipoprotein particles, the modified 18A analogs were much superior to the modified reverse-18A analogs in their ability to activate the enzyme lecithin:cholesterol acyltransferase. This demonstrates that the positions of charged residues in the amphipathic helix play an important role in lecithin:cholesterol acyltransferase activation.

Structural and biological studies on synthetic peptide analogues of a low-affinity calcium-binding site of skeletal troponin C

We have synthesized four oligopeptides that are structural analogues of a low-affinity Ca2+-specific binding site (site II) of rabbit skeletal troponin C. One analogue (peptide 3) was a dodecapeptide with a sequence corresponding to the 12-residue Ca2+-binding loop (residues 63-74 in troponin C), two (peptides 4 and 5) were 23-residue in length, corresponding to residues 52-74 of the protein, and the fourth (peptide 6) was a 25-residue peptide corresponding to residues 50-74. All four peptides had one amino acid substitution within the 12-residue binding loop in which phenylalanine at position 10 was replaced by tyrosine to provide a marker for spectroscopic studies. In addition, peptides 3 and 4 each had a second substitution within the binding loop where glycine at position 6 was replaced by alanine. The second substitution was motivated by the conservation of glycine at the position in the Ca2+-binding loops of all four Ca2+-binding sites in troponin C. The peptides were characterized by their intrinsic fluorescence, ability to enhance the emission of bound Tb3+, affinity for Ca2+ and Tb3+, and circular dichroism. The affinity for Ca2+ was in the range 10-10(2) M-1, and the affinity for Tb3+ was in the range 10(4)-10(5) M-1. The binding constants of the longer peptides were several-fold larger than that of the dodecapeptide. With peptides 4 and 5, substitution of glycine by alanine at position 6 within the 12-residue loop decreased the affinity for Ca2+ by a factor of four, but had little effect on the affinity for Tb3+. However, the mean residue ellipticity of peptide 4 was substantially higher than that of peptide 5. Since peptide 4 differs from peptide 5 only in the substitution of glycine at position 6 in the loop segment, the conservation of glycine at that position may serve a role in providing a suitable secondary structure of the binding sites for interaction with troponin I. Peptides 4 and 6, when present in a large excess, mimic troponin C in regulating fully reconstituted actomyosin ATPase by showing partial calcium sensitivity and activation of the ATPase. Since these peptides are the smallest peptides containing the Ca2+-binding loop of site II, their biological activity suggests that a Ca2+-dependent binding site of troponin C for troponin I could be as short as the segment comprising residues 52-62.