Successful desensitization with cetuximab after an infusion reaction to panitumumab in patients with metastatic colorectal cancer.

BACKGROUND: Cetuximab and panitumumab are chimeric and fully human monoclonal antibodies, respectively, against epidermal growth factor receptor used in the treatment of metastatic colorectal cancer (mCRC). Incidence of documented infusion reaction (IR) is more common with cetuximab (all grades [g]: 15-21%, g 3/4: 2-5%) than panitumumab (all g: 4%, g 3/4: 1%). Anecdotal reports suggest successful challenge with panitumumab following IR with cetuximab (Saif et al. in Cancer Chemother Pharmacol 63(6):1017-1022, 2009). However, safety of cetuximab after IR with panitumumab is not known. We report two patients successfully desensitized with cetuximab after IR with panitumumab. PATIENTS AND METHODS: A 42-year-old female with mCRC received panitumumab as a third-line agent. She developed severe chest tightness, pain, and shortness of breath (SOB), 5 min after first panitumumab infusion. A second 70-year-old male with mCRC developed severe facial flushing, back pain, SOB, tachycardia and hypotension, 5 min after second dose of panitumumab plus irinotecan as a second-line therapy. These two patients received desensitization protocol for cetuximab after a test dose of 20 mg IV over 10 min followed by a slow infusion 10% of original rate in 0-2 h, 25% of original rate in 2-2.5 h, 50% reduced rate in 2.5-3 h, and then 100% infusion rate after 3 h. Patients were observed 4 h after completion of infusion. RESULTS: First patient received a total of 12 cycles of cetuximab with stable disease, no recurrence of IR, and grade 1-2 acniform rash that first developed after third cycle. Second patient received a total of eight cycles uneventfully without IR. CONCLUSIONS: To our knowledge, this is the first report of two patients with documented IR with panitumumab being desensitized successfully with cetuximab. Though anecdotal reports suggest safety of panitumumab in patients following IR with cetuximab, panitumumab can also cause severe IR. Our experience suggests that in case of limited options, such patients can be successfully challenged with cetuximab in a hospital after appropriate desensitization and premedication. Further studies focusing on desensitization and identifying hypersensitivity profile of different anti-epidermal growth factor receptor antibodies are warranted.

Intermittent dislocation flow in viscoplastic deformation.

The viscoplastic deformation (creep) of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Analytical methods and sophisticated 'dislocation dynamics' simulations have proved very effective in the study of dislocation patterning, and have led to macroscopic constitutive laws of plastic deformation. Yet, a statistical analysis of the dynamics of an assembly of interacting dislocations has not hitherto been performed. Here we report acoustic emission measurements on stressed ice single crystals, the results of which indicate that dislocations move in a scale-free intermittent fashion. This result is confirmed by numerical simulations of a model of interacting dislocations that successfully reproduces the main features of the experiment. We find that dislocations generate a slowly evolving configuration landscape which coexists with rapid collective rearrangements. These rearrangements involve a comparatively small fraction of the dislocations and lead to an intermittent behaviour of the net plastic response. This basic dynamical picture appears to be a generic feature in the deformation of many other materials. Moreover, it should provide a framework for discussing fundamental aspects of plasticity that goes beyond standard mean-field approaches that see plastic deformation as a smooth laminar flow.

Patient falls from bed and the role of bedrails in the acute care setting.

The use of bedrails in preventing patient falls from bed remains highly controversial and has received only limited research attention throughout the last decade. The present study questioned the relationship between bedrail use and patient falls from bed particularly in terms of age-gender characteristics, mental status and the severity of injuries sustained. A retrospective, cross-sectional analysis was conducted of 419 patient falls occurring in an urban, acute care hospital from 1993-2000. This audit identified 136 falls from bed. It was found that for all age-gender groups the incidence of falls from bed with bedrails elevated was equal to or higher than when bedrails were not elevated. Patients in a 'non rational' state at the time of falling were significantly more likely to have fallen with the bedrails elevated (chi 2 = 19.463, p < 0.001). Whilst there was no statistically significant relationship between the position of bedrails and the severity of injuries sustained (chi 2 = 1.088, p = 0.780) the fact that there was a patient death resulting from a fall from bed over elevated bedrails was considered to be of particular clinical significance. Thus the role of bedrails as protective or safety devices was challenged and an urgent re-evaluation of current practices recommended.

The effect of denture adhesive on mandibular movement during chewing.

BACKGROUND: The authors conducted a study to determine if reducing mandibular denture movement through the use of a denture adhesive improves chewing function in edentulous patients. METHODS: The authors compared the mean chewing rates of 10 denture wearers who used and did not use a denture adhesive with that of a control group of 10 dentate people. The authors recorded mandibular movements using a multichannel magnetometer tracking system while the subjects chewed standardized pieces of dried apricots and fresh white bread. They made recordings for the test subjects without the use of denture adhesive and at zero, two and four hours after Fixodent denture adhesive cream (Procter & Gamble Co.) was applied to the mandibular denture. RESULTS: The mean chewing rate for the control group was significantly faster than that of the test group at baseline (P < .01). The authors found statistically significant increases in the mean chewing rates for the test group after the denture adhesive was applied at all time points for both foods. None of the after--adhesive-application rates were significantly different from the control group's rate (P > .05). CONCLUSIONS: Use of denture adhesive increased the mean chewing rate in test subjects immediately after and at two and four hours after denture adhesive was applied to a rate that approximated that observed in control subjects (P > .05). CLINICAL IMPLICATIONS: These findings show that using a denture adhesive promotes a faster and more natural rate of chewing.

Effect of denture adhesive on retention of the mandibular and maxillary dentures during function.

The purpose of this study was to determine the effect of denture adhesive on retention of mandibular and maxillary dentures over a four-hour period. Denture movements were measured using an alternating magnetic field tracking device that determines the position of magnetic receiver coils relative to a transmitter coil positioned over the head. Ten adults with complete maxillary dentures and complete mandibular implant overdentures were enrolled in the study. Specially fabricated mandibular dentures contained a relief area that exposed the implant post which no longer anchored the denture, but now served as an attachment point for a receiver coil that measured mandibular movement. The denture coil was attached lateral to the post coil on a shelf cut into the denture. Mandibular denture movements were recorded as the difference between the mandible movement signal and the mandible + mandibular denture signals. Measurements of denture movements were made at baseline (no adhesive) and at 0, 2, 4 hours post-adhesive application with Fixodent cream for standardized chewing and biting. The MoveTrack signals were recorded on a digital data cassette recorder for subsequent computer analysis. The results of the measurements were analyzed using paired sample t-tests. Specifically, the following comparisons of movement means were made: mandibular vs. maxillary, baseline vs. post-baseline and successive changes (e.g., baseline vs. hour 0, hour 0 vs. hour 2, etc.). Results of these analyses showed that: 1) mandibular denture movements under both adhesive and non-adhesive conditions were significantly greater than maxillary denture movements; 2) the adhesive significantly reduced movement of the maxillary and mandibular dentures during both chewing and biting; and 3) the improvement occurred immediately post-application of the adhesive and was maintained for the four hours of follow-up.

Professional attitudes toward denture adhesives: A Delphi technique survey of academic prosthodontists.

STATEMENT OF PROBLEM: The use of denture adhesives and their role in prosthodontics has been an intriguing and conflicted topic, both in clinical practice and dental education. PURPOSE: This study generated discussion, and if possible, obtained a consensus on a series of issues related to denture adhesives among a group of leading academic prosthodontists. MATERIAL AND METHODS: The Delphi Technique survey method was used. It consists of a series of survey questionnaire rounds to a panel of experts to either develop a consensus (>70% agreement) or to clarify the reasons for multiple schools of thought on a topic. A 24-item Delphi questionnaire was sent to an expert panel that consisted of a 33% regionally stratified random sample of program directors of undergraduate complete denture courses in US dental schools. The 5 major topic areas on denture adhesives addressed by the questionnaire items were (1) general perceptions, (2) specific clinical uses/misuses, (3) patient education, (4) inclusion in dental curricula, and (5) overall opinions of utility. RESULTS: Of the 18 randomly selected panelists, 94% (n = 17) agreed to participate, with either 16 or 17 fully participating in each of the 3 survey rounds. The panel achieved consensus and clearly concluded that denture adhesives: (1) are a useful adjunct in denture prosthesis services, having specific roles in both the fabrication and postinsertion phases; (2) had the potential for misuse, both by dentists and by patients; and (3) should be an integral part of patient education for all denture patients and of the undergraduate dental curriculum. However, the panel was unable to achieve consensus on whether denture adhesives should be used at the postinsertion phase for immediate denture patients and whether, on the whole, they were a beneficial adjunct in denture patient management (59% agreed they were). The panelists also clearly expressed their concerns that neither dentists nor patients should use denture adhesives as a substitute for either good clinical practices or proper denture maintenance routines. CONCLUSIONS: This panel of leading academic prosthodontists concluded that denture adhesives are a useful adjunct in denture prosthesis services, with specific roles in both fabrication and postinsertion phases. They also indicated that only through education, for dentists and patients, would the dual goals of maximizing the beneficial aspects of denture adhesive use while minimizing the misuse of denture adhesives be achieved.

Hyaluronic acid substantially increases the retention of motility in cryopreserved/thawed human spermatozoa.

We have demonstrated previously that hyaluronic acid (HA) improves the velocity and the retention of motility in freshly ejaculated human spermatozoa. In the present work, we examined the effect of HA on cryopreserved/ thawed spermatozoa in four paradigms: (i) effect of HA on sperm motility and velocity in semen; (ii) stabilizing effect of HA after 4 h of incubation when the decline of sperm motility is already detectable; (iii) the duration of improved motility after the separation of spermatozoa from HA by Percoll gradient centrifugation; and (iv) motility of sperm cryopreserved in the presence of HA. HA improved the retention of sperm motility in thawed spermatozoa. Indeed, the motility values after 30 h were approximately 100% higher in the HA compared with the control samples. This effect of HA was also evident in the stabilization of spermatozoa with already declining motility. After removal of the HA from the incubation medium, significantly increased motility in the HA-exposed spermatozoa was still detectable for at least 4 h. Cryopreservation of spermatozoa in the presence of HA did not improve the recovery of motility. The data indicate that HA improves the retention of motility of cryopreserved/thawed spermatozoa, even after the removal of HA from the incubation medium. The utilization of HA will probably prove beneficial in assisted reproduction: in intrauterine insemination and in in-vitro fertilization (IVF), the extended sperm motility and velocity will enhance the fertilizing efficiency; in intracytoplasmic sperm injection (ICSI), the improved motility will facilitate the identification of viable spermatozoa. Because HA is a physiological component of the cumulus and of the female and male reproductive tracts, administration of HA should not cause ethical concerns.

Differential expression of IGF-I and IGF-II in eutopic and ectopic endometria of women with endometriosis and in women without endometriosis.

PROBLEM: Factors regulating the development, growth, and differentiation of endometrial cells of endometriotic lesions are poorly understood. To investigate the paracrine-autocrine regulation of ectopic endometrial cell growth, the expression of IGF-I and IGF-II were studied. METHOD: Tissue specimens of eutopic and ectopic endometria were obtained from eight patients with endometriosis at laparoscopy and from the endometria of 14 women without endometriosis as controls. They were tested for the expression of IGF-I and IGF-II by immunohistochemical analysis. RESULTS: Immunohistochemical study for IGF-I in controls showed a more intense staining during the proliferative phase both in stromal and epithelial cells. In eutopic endometria of women with endometriosis a reduction in the staining was observed, whereas in epithelial cells of fibrotic peritoneal adhesions an intense immunostaining for IGF-I was observed. Immunohistochemical study of IGF-II in controls showed a more intense staining during secretory phase both in stromal and epithelial cells. In eutopic endometria of women with endometriosis, a reduction in the staining was observed, whereas in epithelial cells of fibrotic peritoneal adhesions an intense immunostaining for IGF-I was observed. Immunohistochemical study of IGF-II in controls showed a more intense staining during secretory phase both in stromal and epithelial cells. In eutopic endometria of women with endometriosis, a reduction in the staining was observed, whereas in epithelial cells of ovarian lesions and fibrotic peritoneal adhesions, no immunostaining for IGF-II was observed. CONCLUSIONS: In endometriosis there is an alteration of mechanisms regulating cell proliferation and differentiation.

Bend testing of wrought wire removable partial denture alloys.

The flexibility of the wrought wire clasp is related to a number of factors, including the type and gauge of the alloy. The purpose of this study was to compare the bend behavior of five wrought wire alloys used in removable partial dentures. The alloys and their gauge diameters (in millimeters) were Ticonium (18, 19, 20), platinum-gold-palladium (18, 19), Wironium (18, 20), Jelenko Standard (18, 19, 20), and Denture Clasp (18, 19, 20). A total of 12 to 15 samples of each dental alloy were tested. Three-point bending was performed on a servohydraulic testing system controlled by a computer at 1.00 mm/sec until fracture or actuator contact occurred. Maximum stress and elastic modulus in bending were determined for each gauge diameter. Analysis of variance and post hoc Scheffe statistical analyses revealed significant maximum stress and elastic modulus in bending differences for different alloys of the same gauge and for different gauges of the same alloy. The choice of material and the gauge diameter significantly influenced the mechanical property of bending for wrought wire removable partial denture alloys. The Ticonium alloy had the greatest elastic modulus (stiffest) at all levels and the Denture Clasp and the Jelenko Standard alloys had the lowest elastic modulus (most flexible). These data indicate that knowledge of the bending properties of an alloy is equally as important as the gauge size when selecting a wire clasp.

Identification of functional elements of the chicken epsilon-globin promoter involved in stage-specific interaction with the beta/epsilon enhancer.

Expression of the chicken globin genes is regulated in part by competition between the betaA-globin and epsilon-globin promoters for the enhancer found between the genes. To understand the determinants of the enhancer-promoter interaction in stage-specific regulation, the functional elements of the embryonic chicken epsilon-globin promoter were characterized. In vitro assays demonstrated that: (a) the TATA motif at -30 bound GATA-1, (b) Sp1 bound to an element centered at -54, and (c) both Sp1 and another factor, designated CACCC (which appears related to erythroid Krüppel-like factor, EKLF) bound in the -120 to -128 region. The functions of these motifs were tested using transient expression in embryonic erythroid cells. In the absence of the enhancer, promoter point mutants showed that the TATA, Sp1, and CCAAT motifs (but not the CACCC motif) contributed to promoter activity. In contrast, in the presence of the enhancer, all four motifs (including the CACCC motif) contributed to transcription. Developmental regulation of the enhancer activity was observed, with enhancement decreasing sharply from 185-fold at 4 days (cells expressing epsilon-globin) to 16-fold at 10 days (when epsilon-globin is no longer expressed). Taken together, the data suggest that multiple transcription factors contribute to promoter-enhancer interaction and the developmental regulation of epsilon-globin expression, with EKLF-like factors having an especially important role. Regulation of stage specificity occurs at the level of enhancer/epsilon-promoter interaction, even in the absence of competition, and is not simply a property of the enhancer or promoter in isolation.

HLA antigen sharing in Italian couples in which women were affected by gestational trophoblastic tumors.

PROBLEM: The development of gestational trophoblastic tumors (GTT), in which genetic factors are strongly involved, is a rare event. To test the possibility that gene(s) linked to the Major histocompatibility Complex (MHC) may have a role in both embryo growth and tumor development, the HLA typing was performed on patients affected by GTT and on their partners. METHOD: The study group of sixteen couples, in which the women were affected by an invasive mole or choriocarcinoma, and the control group of thirty normal fertile couples without history of spontaneous abortion or GTT were typed for class I and class II HLA antigen. RESULTS: The results showed no differences in single HLA-A and B antigen frequency between GTT couples and controls. In HLA-DR, locus an increased frequency of DR-6 antigen was observed (p < 0.05). No differences were observed in the frequency of number of antigens shared. When considering the single locus no differences were found in the sharing of the antigens of the A and B locus, while the frequency of antigenic sharing for DR locus was significantly higher in GTT couples with respect to controls (p < 0.025). Furthermore a higher frequency of Bw35-DR5 antigenic combination was found in GTT partners than in controls (P < 0.02). CONCLUSIONS: These data represent a confirmation of the existence of a MHC linked gene(s) influencing the GTT development.

Influence of histocompatibility antigens in recurrent spontaneous abortion couples and on their reproductive performances.

PROBLEM: To determine if human leukocyte antigens (HLA) play any role in the aetiology of recurrent spontaneous abortion (RSA), a substantial group of RSA couples were studied, and their reproductive performances in a 3-year follow-up recorded. METHODS: HLA typing was performed for HLA-A, -B, and DR antigens in both partners of 75 couples with unexplained RSA, and compared with a control group of 30 fertile couples that never experienced abortion. A further 57 couples of this group were studied for their reproductive performance in a 3-year follow-up, and subdivided into three subgroups: 1) couples that achieved successful pregnancy during the follow-up, and subdivided into three subgroups: 1) couples that achieved successful pregnancy during the follow-up; 2) couples that experienced abortion and no livebirth during the follow-up; and 3) couples that experienced infertility during the follow-up. RESULTS: There were no significant differences for antigen frequency in all the different HLA loci, and HLA antigen sharing between all the RSA couples and controls. Significant increase of sharing for HLA-DR locus was observed in the couples that aborted during the follow-up with respect to the couples that achieved livebirth and controls (P < 0.03 and P < 0.02 respectively), and significantly increased frequency of B44, DR5 antigen combination in the same comparison (P < 0.03). No significant differences were observed in terms of the interval between conceptions in couples without antigen sharing with respect to couples with 1, 2 or more antigens shared, and antigen sharing in Locus A, B or DR. CONCLUSIONS: The results suggest that gene(s) disadvantageous for reproduction may exist between the HLA-B and -DR chromosomal region which influences the pregnancy outcome in RSA couples, and that HLA-antigen sharing itself does not influence the outcome.

Denture adhesives: changing attitudes.

Since people began using denture adhesives more than 200 years ago, dentists have been slow to acknowledge their place in prosthetic dentistry. The author maintains that if properly used, denture adhesives can be an asset to the dentist's armamentarium. This article reviews much of the recent research on adhesives and outlines the conditions under which they should be used.

Sperm function and choice of preparation media: comparison of Percoll and Accudenz discontinuous density gradients.

We compared the sperm populations prepared by Accudenz (35-65%) and Percoll (40-80%) density gradients in 21 normospermic specimens (concentration, 53.6 +/- 3.8 x 10(6) sperm/ml; motility, 44.5 +/- 3.5%). Accudenz facilitated a higher recovery of sperm and motile sperm (68.4 +/- 6.6% vs. 49.3 +/- 4.9%, P < 0.001, and 87.8 +/- 4.1% vs. 77.8 +/- 3.7%, P < 0.01, respectively). Sperm motility was lower in the Accudenz compared to the Percoll pellets; thus the values of total motile sperm recovered were not different (17.1 +/- 2.4 vs. 15 + /- 1 2.2 x 10(6) sperm/ml). The long term retention of sperm motility was substantially improved in Accudenz (at 24 hours, 34.9 +/- 2.8% vs. 26.3 +/- 1.5%; 60% vs. 40% of the initial motility, P < 0.001), and the Accudenz vs. Percoll samples also exhibited a higher retention of total motile sperm (at 24 hours, 9.8 +/-.2 vs. 6.1 = 0.5 x 10(6) motile sperm/ml, P < 0.05). The sperm motility index, a multiple of velocity and motility in the sample that reflects the efficiency of the sperm population in sperm-oocyte interaction, was 75% higher in the Accudenz samples at 24 hours (3.6 +/- 0.4 vs. 2.1 +/- 0.2, mu m/second, P < 0.01). Sperm cellular maturity by the creatine phosphokinase (CK) activity and CK-M to CK-B isoform ratio parameters (in the original samples 0.14 +/- 0.02 lU CK/100 x 10(6) sperm and 57.9 +/- 3.7%, respectively) were improved in both the Accudenz and Percoll pellets (P < 0.001), with no difference between the two sperm fractions. Sperm activation status monitored by chlortetracycline fluorescence indicated that after 4 hours of incubation the incidence of fully acrosome-reacted spermatozoa in the Accudenz versus Percoll pellets was 6.2 +/- 0.3% versus 13.1 +/- 1.0% (P < 0.001), a 100% increase in Percoll. We can conclude that Accudenz yields a higher concentration of motile spermatozoa, with improved retention of motility, velocity, and acrosomal integrity and without an increase of sperm with diminished cellular maturity. Thus, in sperm preparation for intrauterine insemination, in which the timing of ovulation and insemination frequently do not correspond, Accudenz-prepared sperm, with a better retention of motility/velocity and acrosomal integrity and with a consequential higher resistance to activation by the female reproductive tract, are expected to be more effective.

Semen parameters and sperm morphology in men in unexplained recurrent spontaneous abortion, before and during a 3 year follow-up period.

To investigate the role of the 'male factor' in the pathogenesis of recurrent spontaneous abortion (RSA), especially sperm morphology abnormalities, 120 previously selected couples with unexplained RSA were studied for sperm parameters retrospectively and prospectively. The patients were subdivided into three subgroups, depending on their reproductive outcome during the 3 years of follow-up study: (i) 48 RSA couples who achieved a successful pregnancy; (ii) 39 RSA couples who experienced further abortions, and (iii) 33 RSA couples who experienced infertility during the follow-up period. A semen analysis was performed twice at the time of inclusion in this study, and twice again during the 3 year follow-up period. No significant differences in semen parameters were observed between RSA males and fertile controls. Instead, significant differences were observed between the group of RSA couples who experienced infertility during the follow-up and the other two groups (RSA couples who achieved successful pregnancy and RSA couples who experienced miscarriages and no live birth during the follow-up) for sperm concentration (P < 0.01 and P < 0.01 respectively), sperm motility (P < 0.01 and P < 0.01 respectively) and sperm morphology abnormalities (P < 0.01 and P < 0.01 respectively). Sperm morphology abnormalities do not seem to be involved in determining RSA; instead, they are an aetiological factor in determining infertility in patients, along with the other semen parameters, in the RSA couple's subsequent reproductive life. Semen analysis is an important test in the clinical management of RSA couples.

Retention and stability of the maxillary denture during function.

The objectives of this study were to provide a quantitative account of the extent to which the maxillary complete denture moves during function (chewing, swallowing, and speech production) and to determine whether differences in movement occur as a function of denture fit. A total of 24 patients were studied, 12 with poorly fitting dentures and 12 with well-fitting dentures. Denture movements were measured with a Myotronics kinesiograph that tracked the movements of a small magnet attached to the inferior surface of the denture. Results indicated that denture movement was greatest for the two chewing activities; varied extensively from individual to individual; and that there were no statistically significant overall movement effects as a function of fit. It was concluded that all maxillary dentures are subject to movements in all directions, but that the degree of movement is related more to the individual denture wearer than it is to the fit of the denture.

Effect of denture adhesive on the retention and stability of maxillary dentures.

This study used quantitative methods to measure the effects of a denture adhesive on the retention and stability of the maxillary denture. Denture movements were measured on 20 patients during standardized chewing, swallowing, and speaking activities, first with no adhesive, and then at 0, 2, 4, 6, and 8 hours after application of an over-the-counter cream adhesive. The major findings were that the denture adhesive produced a statistically significant improvement in the retention and stability of the maxillary denture during the various chewing, swallowing, and speaking activities, for up to 8 hours; there were no statistically significant differences in improvement between a poorly fitting and well-fitting denture; and patients were able to produce significantly greater levels of incisal bite force with the use of the adhesive.

Primary sequence, evolution, and repetitive elements of the Gallus gallus (chicken) beta-globin cluster.

The DNA sequence of the Gallus gallus (chicken) beta-globin cluster was completed and analyzed. This G + C-rich region is 23.7 kb in length and includes the rho-, beta H-, beta A-, and epsilon-globin genes, the enhancer found between the beta A and epsilon genes, and three upstream DNase I hypersensitive sites. The CpG dinucleotides are nonrandomly distributed, being present at an increased relative frequency near the promoters and upstream hypersensitive sites. The cluster has an unusually low TA dinucleotide frequency. The upstream hypersensitive sites (5'HS1, 5'HS2, and 5'HS3) contain DNA sequence motifs recognized by erythroid transcription factors. However, no significant sequence similarity was found among the upstream hypersensitive sites and the beta A/epsilon enhancer. The G. gallus upstream site sequences were not similar to the upstream sites of the mammalian globin clusters, probably due to the small size of the functional regions and large evolutionary distance between the classes. The avian cluster evolved by gene duplication from an ancestor beta-globin gene, first producing the epsilon and the rho/beta H/beta A ancestor genes, then the rho and the beta H/beta A ancestor genes, and finally the beta H- and beta A-globins. Four probable gene conversions can be documented: beta A to beta H, epsilon to beta H, and rho/epsilon (twice). The cluster shows a massive overrepresentation of a non-LTR retrotransposon, CR1, which accounts for 16% of the DNA. We suggest that the locus is a preferred site for CR1 insertion.

Iron distribution in Belgrade rat reticulocytes after inhibition of heme synthesis with succinylacetone.

We have used succinylacetone (4,6-dioxoheptanoic acid), a specific inhibitor of delta-aminolevulinic acid dehydrase, to gain insight into the defect in iron metabolism in the Belgrade anemia. The Belgrade rat has an inherited microcytic, hypochromic anemia associated with poor iron uptake into developing erythroid cells. Succinylacetone inhibits heme synthesis, leading to nonheme iron accumulation in mitochondria and cytosol of normal reticulocytes. When succinylacetone is used to inhibit Belgrade heme synthesis, iron from diferric transferrin does not accumulate in the stromal fraction that contains mitochondria, nor does 59Fe accumulate in the nonheme cytosolic fraction. Hence, the defect in the Belgrade rat reticulocyte occurs in the endocytic vesicle or in a step subsequent to iron transit from the vesicle but before the nonheme cytosolic or mitochondrial iron fractions. Therefore, the mutation affects either the release of iron from transferrin or iron transport from the vesicle to the mitochondrion.