Evaluation of medical decision support systems (DDX generators) using real medical cases of varying complexity and origin.

BACKGROUND: Medical decision support systems (CDSSs) are increasingly used in medicine, but their utility in daily medical practice is difficult to evaluate. One variant of CDSS is a generator of differential diagnoses (DDx generator). We performed a feasibility study on three different, publicly available data sets of medical cases in order to identify the frequency in which two different DDx generators provide helpful information (either by providing a list of differential diagnosis or recognizing the expert diagnosis if available) for a given case report. METHODS: Used data sets were n = 105 cases from a web-based forum of telemedicine with real life cases from Afghanistan (Afghan data set; AD), n = 124 cases discussed in a web-based medical forum (Coliquio data set; CD). Both websites are restricted for medical professionals only. The third data set consisted 50 special case reports published in the New England Journal of Medicine (NEJM). After keyword extraction, data were entered into two different DDx generators (IsabelHealth (IH), Memem7 (M7)) to examine differences in target diagnosis recognition and physician-rated usefulness between DDx generators. RESULTS: Both DDx generators detected the target diagnosis equally successfully (all cases: M7, 83/170 (49%); IH 90/170 (53%), NEJM: M7, 28/50 (56%); IH, 34/50 (68%); differences n.s.). Differences occurred in AD, where detection of an expert diagnosis was less successful with IH than with M7 (29.7% vs. 54.1%, p = 0.003). In contrast, in CD IH performed significantly better than M7 (73.9% vs. 32.6%, p = 0.021). Congruent identification of target diagnosis occurred in only 46/170 (27.1%) of cases. However, a qualitative analysis of the DDx results revealed useful complements from using the two systems in parallel. CONCLUSION: Both DDx systems IsabelHealth and Memem7 provided substantial help in finding a helpful list of differential diagnoses or identifying the target diagnosis either in standard cases or complicated and rare cases. Our pilot study highlights the need for different levels of complexity and types of real-world medical test cases, as there are significant differences between DDx generators away from traditional case reports. Combining different results from DDx generators seems to be a possible approach for future review and use of the systems.

Electrode Surface Potential-Driven Protein Adsorption and Desorption through Modulation of Electrostatic, van der Waals, and Hydration Interactions.

When proteins in aqueous solutions are exposed to solid substrates, they adsorb due to the dynamic interplay of electrostatic, van der Waals, and hydration interactions and do so in a rather irreversible fashion, which makes protein recovery troublesome. Here, we use a gold electrode as the solid substrate and modulate the surface potential to systematically induce protein adsorption as well as partial desorption. We use different methods such as surface plasmon resonance, atomic force microscopy, and electrowetting and show that biasing the electrode to more negative potentials (by -0.4 V compared to the open-circuit potential at pH 6) results in an increased adsorption barrier of 6 kJ mol-1 for the negatively charged protein ß-lactoglobulin. Further, we clearly demonstrate that this is due to an increased double layer potential of -0.06 V and an increase in hydration repulsion. This indicates that an electric potential can directly influence surface interactions and thus induce partial ß-lactoglobulin desorption. These observations can be the basis for biosensors as well as separation technologies that use only one trigger to steer protein ad- and desorption, which is low in energy requirement and does not generate large waste streams, as is the case for standard protein separation technologies.

Clinical outcome and global gene expression data support the existence of the estrogen receptor-negative/progesterone receptor-positive invasive breast cancer phenotype.

The presence or absence of estrogen and progesterone steroid hormone receptor expression (ER, PR) is an essential feature of invasive breast cancer and determines prognosis and endocrine treatment decisions. Among the four ER/PR receptor phenotypes, the ER-/PR+ is infrequent, and its clinical relevance has been controversially discussed. Thus, we investigated its clinical significance and gene expression pattern in large datasets. In a retrospective clinical study of 15,747 breast cancer patients, we determined the ER/PR subtype survival probabilities using Kaplan-Meier and Cox regression analyses. From The Cancer Genome Atlas (TCGA) breast cancer dataset, PAM50 expression signature and pathway analyses were performed to test for distinct molecular features. In our cohort, the ER-/PR+ phenotype has been observed at a frequency of 4.1 % and was associated with an improved 10-year survival for stage I cancers compared to the ER+/PR+ reference subtype (median; 95 % CI 88.1 %; 83-93 vs. 84.3 %; 82-86 %, P = 0.024) as was confirmed by multivariate analysis over the entire follow-up (HR 0.59, 95 % CI 0.38-0.92, P = 0.021). This association lacked significance when including all stages. ER-/PR+ patients treated with antihormonal agents (34.5 %) had shorter survival compared to their non-treated counterparts (Log-rank P = 0.0001). PAM50 signatures suggest a distinct configuration for the ER-/PR+ phenotype. This specific phenotype has been further separated by a set of 59 uniquely expressed genes. Our study supports the notion of the existence of an ER-/PR+ phenotype with clinical and molecular features distinct from the large group of ER+/PR+ patients.

Superheavy element flerovium (element 114) is a volatile metal.

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Experimental gas-solid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction (244)Pu((48)Ca, 3-4n)(288,289)Fl and was isolated in-flight from the primary (48)Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

Discovery of the heaviest elements.

The search for new superheavy elements (SHEs) is at present one of the most exciting adventures in nuclear physics. Thanks to enhanced experimental techniques, the synthesis of elements Z=113 to 118 in reactions using (48)Ca projectiles and targets made of isotopes of the elements neptunium to californium has been claimed. Discovery of the elements Z=114 (named flerovium) and Z=116 (named livermorium) has been accepted by the IUPAC. The others are waiting. The situation for element 113 is particular; here claims on discovery come from groups from RIKEN, Wako, Saitama, Japan and FLNR-JINR, Dubna, Russia.

Cryobiopsy increases the diagnostic yield of endobronchial biopsy: a multicentre trial.

Forceps, brushes or needles are currently the standard tools used during flexible bronchoscopy when diagnosing endobronchial malignancies. The new biopsy technique of cryobiopsy appears to provide better diagnostic samples. The aim of this study was to evaluate cryobiopsy over conventional endobronchial sampling. A total of 600 patients in eight centres with suspected endobronchial tumours were included in a prospective, randomised, single-blinded multicentre study. Patients were randomised to either sampling using forceps or the cryoprobe. After obtaining biopsy samples, a blinded histological evaluation was performed. According to the definitive clinical diagnosis, the diagnostic yield for malignancy was evaluated by a Chi-squared test. A total of 593 patients were randomised, of whom 563 had a final diagnosis of cancer. 281 patients were randomised to receive endobronchial biopsies using forceps and 282 had biopsies performed using a flexible cryoprobe. A definitive diagnosis was achieved in 85.1% of patients randomised to conventional forceps biopsy and 95.0% of patients who underwent cryobiopsy (p<0.001). Importantly, there was no difference in the incidence of significant bleeding. Endobronchial cryobiopsy is a safe technique with superior diagnostic yield in comparison with conventional forceps biopsy.

Rabbit lactate dehydrogenase isozymes: effect of pH on activity.

The ability of lactate dehydrogenase isozyme five from rabbit skeletal muscle to catalyze pyruvate reduction is extremely sensitive to changes of pH within the range of 6.2 to 7.8. The activity of lactate dehydrogenase isozyme one from rabbit heart is virtually unaffected by changes of pH within the same range. Isozyme five is activated by low concentrations of oxalacetate and inhibited by higher concentrations, but other substrates of the citric acid cycle have no effect.

Strontium Uptake in Shell Aragonite from the Freshwater Gastropod Limnaea stagnalis.

Shell aragonite from 96 specimens of the freshwater gastropod Limnaea stagnalis grown in laboratory tanks at different temperatures in water with variable strontium/calcium ratios have been analyzed for its strontium content in order to evaluate the mechanisms of strontium uptake in molluskan aragonite. Within the limits defined by natural freshwater environments, the strontium/calcium ratio in the aragonite was found to be linearly related to the strontium/calcium ratio in the water. A distribution coefficient k(A)(Sr) = 0.237 +/- 0.029, unaffected by variations in temperature and growth rate, has been found. This finding substantiates the existence of a strontium-discriminating effect in aragonite precipitated by mollusks as compared to the case for nonbiogenic aragonite which contains about five times as much strontium when precipitated under the same conditions.

Carbon-13 and oxygen-18 in dinosaur, crocodile, and bird eggshells indicate environmental conditions.

We have gathered, from the nests of dinosaurs, and living and fossil birds, some evidence of the environment in which these creatures lived. However, our isotope determinations suggest it will be impossible to resolve the problem as to whether the dinosaurs were warm-or cold-blooded from the oxygen and carbon isotopes content of their shells.

Fibrogenic growth factors in encapsulating peritoneal sclerosis.

BACKGROUND: Increased local levels of fibrogenic growth hormones contribute substantially to the process of encapsulating peritoneal sclerosis (EPS) in animal models. METHODS: We analyzed probes from patients with normal kidney function (n = 10), with normal kidney function and inflammation (n = 10), on PD without (n = 10) and with EPS (n = 9). We investigated the degree of fibrosis and the number of vessels and vasculopathy. Additionally, we investigated the expression of NFkappaB, TGFbeta1, TGFbeta1 receptor, TGFbeta2, TGFbeta2 receptor, FGF-BP, CTGF and VEGF by immunohistochemistry. RESULTS: In EPS, we found an exclusive upregulation of VEGF (normal 0, appendicitis 1.0 +/- 1.2, PD 1.7 +/- 1.8 and EPS 5.7 +/- 4.4; p < 0.0001), whereas in PD, CTGF was significantly increased (normal 6.0 +/- 2.8, appendicitis 7.3 +/- 2.5, PD 10.0 +/- 1.8 and EPS 7.3 +/- 2.1; p = 0.0059). The results for the TGFbeta system and NFkappaB were not uniform, in EPS no increases were demonstrable. Vasculopathy was significantly more pronounced in EPS (normal 0.4 +/- 0.5, appendicitis 0.2 +/- 0.3, PD 1.0 +/- 0.7 and EPS 1.6 +/- 1.2; p < 0.0001) than in PD or inflammation (normal 30 +/- 16, appendicitis 82 +/- 48, PD 1,936 +/- 952 and EPS 2,613 +/- 1,209; p < 0.0001), whereas the density of vessels were decreased (normal 125 +/- 114, appendicitis 817 +/- 347, PD 81 +/- 57 and EPS 36 +/- 33; p < 0.0001). CONCLUSIONS: The process of EPS was associated with increased VEGF in the peritoneum. The reduced density of vessels compared with marked fibrosis could point to hypoxia as an inducer.

The role of intestinal P-glycoprotein in the interaction of digoxin and rifampin.

Recent data point to the contribution of P-glycoprotein (P-gp) to digoxin elimination. On the basis of clinical observations of patients in whom digoxin levels decreased considerably when treated with rifampin, we hypothesized that concomitant rifampin therapy may affect digoxin disposition in humans by induction of P-gp. We compared single-dose (1 mg oral and 1 mg intravenous) pharmacokinetics of digoxin before and after coadministration of rifampin (600 mg/d for 10 days) in 8 healthy volunteers. Duodenal biopsies were obtained from each volunteer before and after administration of rifampin. The area under the plasma concentration time curve (AUC) of oral digoxin was significantly lower during rifampin treatment; the effect was less pronounced after intravenous administration of digoxin. Renal clearance and half-life of digoxin were not altered by rifampin. Rifampin treatment increased intestinal P-gp content 3.5 +/- 2.1-fold, which correlated with the AUC after oral digoxin but not after intravenous digoxin. P-gp is a determinant of the disposition of digoxin. Concomitant administration of rifampin reduced digoxin plasma concentrations substantially after oral administration but to a lesser extent after intravenous administration. The rifampin-digoxin interaction appears to occur largely at the level of the intestine. Therefore, induction of intestinal P-gp could explain this new type of drug-drug interaction.

Hepatic expression of galectin-3 and receptor for advanced glycation end products in patients with liver disease.

BACKGROUND: Advanced glycation end products (AGEs) are a heterogeneous group of glycosylated proteins (of which carboxymethyl-lysine (CML) is the most common) which accumulate during ageing processes and play an important role in the pathogenesis of a variety of chronic diseases. Impaired hepatic function might result in elevated levels of AGEs, as the liver represents the major site of AGE metabolism. The actions of AGEs are mediated by various receptors, among which the AGE-receptor complex (including galectin-3 as an essential part) is thought to have a cytoprotective effect, and receptor for advanced glycation end product (RAGE) a cytotoxic effect. AIM: To assess the relationship between CML and expression of galectin-3 and RAGE in different histological structures in biopsy specimens from patients with varying degrees of liver impairment. METHOD: Immunohistochemical staining of 164 biopsies from patients with varying degrees of liver impairment was performed to determine the levels of CML, galectin-3 and RAGE in hepatocytes, Kupffer cells and bile ducts by a semiquantative score. RESULTS: Independent of diagnosis, CML and RAGEs were detected in hepatocytes, whereas galectin-3 was present only in hepatocytes of cirrhotics. By contrast, CML and galectin-3 were highly expressed in Kupffer cells (well correlating levels, highest scores in cholestasis) whereas expression of RAGEs was not significant. All three assessed biochemical markers showed their highest levels of expression/detection in bile ducts. CONCLUSION: These findings indicate an increased susceptibility of hepatocytes to the detrimental effects of AGEs and underline the protective function of Kupffer cells. Furthermore, the biliary system seems to play an important role in the disposition of AGEs.

Technical note: gold marker implants and high-frequency jet ventilation for stereotactic, single-dose irradiation of liver tumors.

With reference to radiosurgery of the liver, we describe techniques designed to solve the methodological problem of striking targets subject to respiratory motion with the necessary precision. Implanting a gold marker in the vicinity of the liver tumor was the first step in ensuring the reproducibility of the isocenter's position. An 18-karat gold rod measuring 1.9 x 3 mm was implanted approximately 2 cm from the edge of the tumor as this was displayed in the spiral, thin-slice CT with contrast media. Both the implantation of the marker and the required, CT-controlled biopsy of the liver tumor can be achieved simultaneously with the same puncture needle. The efficiency of high-frequency jet ventilation (HFJV) in neutralizing the targeted organ's respiratory motion during stereotactic single-dose irradiation was evaluated. The procedure was carried out on ten patients without any complications. In the time between treatment planning and irradiation (3 days), no significant marker migration was observable. In all cases, the gold marker (volume: 7.5 mm(3)) was readily observable in the treatment beam using portal imaging. HFJV provided reliable immobilization. The liver motion in each anesthetized patient was limited to under 3.0 mm in all directions. Thus, the correct field settings and target reproducibility were able to be analyzed and documented during the irradiation. The combination of marker and HFJV enables the determination of stereotactic coordinates directly related to the liver itself and, in this way, stereotactic radiation treatment of liver tumors is freed from the uncertainties involved in orientation to bony landmarks, in respiratory motion, and in changes of position in the stereotactic body frame. The method is feasible and can improve the accuracy of stereotactic body radiation therapy.

Iatrogenically-related, fatal methotrexate intoxication: a series of four cases.

Since the early eighties, the folic antagonist methotrexate (MTX) has been used in long-term treatment of rheumatoid arthritis. Because of the high toxic potential clinical and laboratory controls at regular intervals and patient education in order to avoid misadventure is of overriding importance. We present four cases of fatal MTX intoxication due to medical malpractice from the Tübingen Institute of Forensic Medicine autopsy material, which show the severe consequences of MTX overdose. It becomes evident that among non-rheumatologists there still is need for information about toxicity and dose limitation in MTX low-dose treatment.

Transfer of adriamycin resistance by fusion of Mr 170,000 P-glycoprotein to the plasma membrane of sensitive cells.

One of the characteristics of multidrug-resistant mammalian cells is the presence of a glycoprotein of approximately Mr 170,000 in their cell membrane. Termed P-glycoprotein, this glycoprotein is thought to be the gene product of an amplified gene cloned and sequenced from a cell line (LZ) which is highly resistant to Adriamycin and cross-resistant to actinomycin D, colchicine, and vincristine. Resistance to Adriamycin has been induced in sensitive cells by chromosome or gene transfer. We now show that P-glycoprotein isolated from LZ cells and fused to sensitive V79 Chinese hamster cells renders the latter transiently resistant to Adriamycin. Incorporation of P-glycoprotein was confirmed by immunoperoxidase staining of fusion products following treatment with antibody to P-glycoprotein and by Western blots of membrane preparations from fusion products. These results suggest that P-glycoprotein is one of the important factors in the expression of Adriamycin resistance and provide added confirmation that it may be the important product of gene amplification in multidrug-resistant cells. The results also suggest that the cell membrane may be one of several targets for Adriamycin cytotoxicity and that P-glycoprotein may be a binding site for Adriamycin, rendering the latter ineffective in registering sufficient membrane damage for cell killing.

Enhanced uptake of doxorubicin into bronchial carcinoma: beta-glucuronidase mediates release of doxorubicin from a glucuronide prodrug (HMR 1826) at the tumor site.

Lack of tumor selectivity is a severe limitation of cancer chemotherapy. Consequently, reducing dose-limiting organ toxicities such as the cardiac toxicity of doxorubicin (Dox) is of major clinical relevance. Approaches that would facilitate a more tumor-selective anticancer therapy by using nontoxic prodrugs that are converted to active anticancer agents at the tumor site have been the subject of intensive research. One potential method to overcome the cardiac toxicity of Dox is to apply a nontoxic, glucuronide prodrug (HMR 1826) from which Dox is released by the action of beta-glucuronidase, an enzyme present at high levels in many tumors. Using a recently developed, isolated, perfused human lung model, we compared the uptake of Dox into normal lung and lung tumors after a 2.5-h lung perfusion with doxorubicin (n = 8) and with the novel doxorubicin glucuronide prodrug (n = 8). Dox showed a poor uptake into lung tumors as compared with normal lung [mean Dox concentration at the end of perfusion, 1.78 +/- 3.11 (median, 0.66) microg/g versus 22.03 +/- 10.4 (median, 18.5) microg/g; P < 0.001]. However, after perfusion with HMR 1826, the level of Dox in tumor tissue was about 7-fold higher than after perfusion with Dox itself [14.04 +/- 12.9 (median, 12.9) microg/g versus 1.78 +/- 3.11 (median, 0.66) microg/g, P < 0.05, n = 8]. In vitro experiments showed a significantly higher beta-glucuronidase expression and activity in the tumors. The extent of in vitro cleavage of HMR 1826 by homogenized lung tissue was closely related to the content of beta-glucuronidase (r = 0.9834, P < 0.0001). When D-saccharolactone, a specific inhibitor of beta-glucuronidase, was added to the perfusate containing HMR 1826, no accumulation of Dox in lung tissue was seen. These data indicate that the high Dox levels achieved in the tumors with HMR 1826 resulted from cleavage of the prodrug by beta-glucuronidase at the tumor site. Thus, the problem of poor Dox uptake into lung tumors could be circumvented by applying the doxorubicin glucuronide prodrug. Several lines of evidence based on both ex vivo and in vitro results indicate that the approach described using a glucuronide prodrug may be useful in facilitating more selective delivery of chemotherapy to tumors in humans.

Ribonuclease H activity in rat mammary gland during the lactation cycle and in R3230AC mammary adenocarcinoma.

RNAase H, which catalyzes the hydrolysis of the RNA moiety of an RNA-DNA hybrid, was measured in the mammary gland of virgin, pregnant, lactating, and weaning Fischer rats and in the R3230AC mammary tumor grown in the same animals. In the normal mammary gland when DNA levels were low, as in the virgin state or during involution, RNAase H activity was also low. During pregnancy and lactogenesis when DNA levels increased, RNAase H activity, either on the basis of mammary gland weight or DNA content, also increased. During lactation when cellular proliferation ceases but rates of RNA and protein synthesis continue to reach peak values, RNAase H activity decreased. Compared to the corresponding enzyme from host glands, RNAase H from the R3230AC mammary tumor grown in pregnant and lactating hosts changes similarly, but to a lesser extent. The RNAase H activity which, ona tissue weight basis, was higher than in normal tissue also increased during pregnancy and directly after parturition, but decreased during lactation. During pregnancy these changes were accompanied by an increase in tumor DNA values. During lactation the tumor DNA values returned to the level seen in virgin hosts. These results are consistent with a role for RNAase H in DNA replication in rat mammary gland and in R3230Ac mammary tumor.

Microsomal epoxide hydrolase expression as a predictor of tamoxifen response in primary breast cancer: a retrospective exploratory study with long-term follow-up.

PURPOSE: It has been suggested that estrogen receptor-independent high-affinity binding sites for antiestrogens could limit their local bioavailability and response. Microsomal epoxide hydrolase (mEH) was recently shown to be a component of the antiestrogen binding site complex. We investigated whether mEH expression in primary breast tumors is related to disease outcome and to the efficacy of tamoxifen treatment. PATIENTS AND METHODS: Expression of mEH was semiquantitatively assessed by immunohistochemistry in sections prepared from archival paraffin blocks of primary breast cancers from 179 patients with a mean follow-up time of 81 months. RESULTS: Expression of mEH was correlated with poor disease outcome in all patients (P: < .01; n = 179) and in patients receiving tamoxifen (P: < .01; n = 78), but not in patients not treated with tamoxifen. Moreover, mEH was an independent prognostic factor by Cox regression analysis. CONCLUSION: The results of this first exploratory study suggest that mEH expression in primary breast cancer could be of predictive value for response to tamoxifen treatment and/or may be a novel independent prognostic factor for survival. The results are in agreement with the model that mEH participates in an estrogen receptor-independent tamoxifen- binding complex.

Stereotactic single-dose radiation therapy of liver tumors: results of a phase I/II trial.

PURPOSE: To investigate the feasibility and the clinical response of a stereotactic single-dose radiation treatment for liver tumors. PATIENTS AND METHODS: Between April 1997 and September 1999, a stereotactic single-dose radiation treatment of 60 liver tumors (four primary tumors, 56 metastases) in 37 patients was performed. Patients were positioned in an individually shaped vacuum pillow. The applied dose was escalated from 14 to 26 Gy (reference point), with the 80% isodose surrounding the planning target volume. Median tumor size was 10 cm(3) (range, 1 to 132 cm(3)). The morbidity, clinical outcome, laboratory findings, and response as seen on computed tomography (CT) scan were evaluated. RESULTS: Follow-up data could be obtained from 55 treated tumors (35 patients). The median follow-up period was 5.7 months (range, 1.0 to 26.1 months; mean, 9.5 months). The treatment was well tolerated by all patients. There were no major side effects. Fifty-four (98%) of 55 tumors were locally controlled after 6 weeks at the initial follow-up based on the CT findings (22 cases of stable disease, 28 partial responses, and four complete responses). After a dose-escalating and learning phase, the actuarial local tumor control rate was 81% at 18 months after therapy. A total of 12 local failures were observed during follow-up. So far, the longest local tumor control is 26.1 months. CONCLUSION: Stereotactic single-dose radiation therapy is a feasible method for the treatment of singular inoperable liver metastases with the potential of a high local tumor control rate and low morbidity.

External beam radiation after stent implantation increases neointimal hyperplasia by augmenting smooth muscle cell proliferation and extracellular matrix accumulation.

OBJECTIVES: We sought to examine the effects of high volume external beam radiation (EBR) after stent implantation on neointimal hyperplasia, smooth muscle cell (SMC) proliferation, presence of inflammatory cells and expression of extracellular matrix (ECM). BACKGROUND: Endovascular irradiation has been shown to reduce restenosis rates after angioplasty in preliminary trials, but conflicting results have been reported for the effects of external beam irradiation. METHODS: Forty-three Palmaz-Schatz stents were implanted into iliac arteries of New Zealand White rabbits. The arteries were externally irradiated after stent implantation with a single dose of 8 Gy (at day 3) or 16 Gy in two fractions (8 Gy at days 3 and 4) by means of a linear accelerator. In the control rabbits, no radiation was applied after stent implantation. Smooth muscle cells, macrophages and ECM were studied by immunohistochemistry at one and 12 weeks after stent implantation. Collagen type I and biglycan messenger ribonucleic acid (mRNA) levels were assessed by Northern blot analysis at one week. Neointimal cell densities and arterial lumen stenosis were measured by histomorphometry at 12 weeks. RESULTS: At 1 week, SMC proliferation at the site of stent implantation was increased after EBR with 8 and 16 Gy (26 +/- 5%, 32 +/- 3% vs. 17 +/- 8%; p < 0.01, 16 Gy vs. control). External beam radiation with 8 and 16 Gy augmented SMC proliferation proximal and distal to the angioplasty site (11 +/- 3%, 14 +/- 3 vs. 6 +/- 1%; p < 0.01, 16 Gy vs. control). Collagen type I and biglycan mRNA levels were elevated in stented arteries after EBR with 16 Gy. At 12 weeks, a marked decrease in neointimal cell density (248 +/- 97 vs. 498 +/- 117 SMCs/0.1 mm2 neointima; p < 0.005 vs. control) was noted after EBR with 16 Gy. Irradiation with 8 and 16 Gy increased arterial lumen stenosis compared with nonirradiated control rabbits (45 +/- 7%, 55 +/- 9% vs. 33 +/- 7%; p < 0.05, 8 Gy and p < 0.001, 16 Gy vs. control). CONCLUSIONS: High volume external beam radiation at doses of 8 or 16 Gy causes restenosis by augmenting proliferative activity at and adjacent to the site of stent implantation, and by dose-dependent up-regulation of extracellular matrix expression. The study suggests that excessive matrix accumulation is an important determinant of failure of radiation therapy to prevent restenosis.