Early clamping of umbilical cord blood and foetal CD34 enrichment

We describe the relation between clamping time and blood volume collected, and two enrichment systems of CD34+ stem cells from umbilical cord blood, in order to determine the criteria for an excellent recovery with high proliferative ability and bone marrow reconstitution. After an obstetrician-based cord blood collection, the purification of stem cells was performed either with a combination of monoclonal antibodies, negative selections, using the Stem Sep method, or with a positive cells selection owing to their surface CD34 antigens, using the Mini Macs system. An excellent recovery of haematopoietic progenitors--burst forming unit erythroid; colony-forming unit granulocyte and macrophage; and colony-forming unit granulocyte, erythroid, monocyte, and macrophage--inversely related to an increase in clamping time, was achieved using the Mini Macs system (54% of colonies with a 90% purity), while the recovery of haematopoietic progenitors was 35% (with a 80% purity) using the Stem Sep method. By clamping umbilical cord blood at an early stage, we obtained a greater number of CD34+ cells, and their clonogenic activity increased with enrichment. This is particularly useful considering that the number of CD34+ stem cells contained in a unit of placental blood is sufficient for transplanting into a child but not for an adult engraftment. Thus, using these methods, we obtain a larger number of CD34+ stem cells. This increases the possibility of reducing graft versus host disease in adult patients and produces survival rates similar to the ones we observed in transplantation of bone marrow from unrelated donors.

Two enrichment methods to obtain CD34+ stem cells from umbilical cord blood

We describe the relation between umbilical cord clamping time and two different enrichment system of CD34+ stem cells from umbilical cord blood with the proliferative ability and bone marrow reconstitution of the stem cells obtained. After an obstetrician performed the cord blood collection, the purification of stem cells was performed either with a combination of monoclonal antibodies (negative selections) using the Stem Sep method, or with a positive cells selection based on their surface CD34 antigens using the Mini Macs system. An excellent recovery of haematopoietic progenitors (Burst Forming Unit Erythroids (BFUE); Colony Forming Unit Granulocytes and Macrophages (CFU-GM); and Colony Forming Unit Granulocytes, Erythroids, Monocytes and Macrophages (CFU-GME)), inversely related to the increase in clamping time, was performed with the Mini Macs system (54% of colonies, with a 90% purity). With Stem Sep method, haematopoietic progenitors recovery was 35% (with a 80% purity). By applying early clamping of umbilical cord blood we obtained a greater number of CD34+ cells and their clonogenic activity was increased with enrichment. This is a useful technique considering that the number of CD34+ stem cells usually contained from a unit of placental blood is enough for the transplant to a child, but not for an adult. Thus, using these methods, we can get a larger number of CD34+ stem cells which reduces the risk of Graft versus Host Disease also in adult patients, producing survival rates similar to the those obtained with transplantation of bone marrow from unrelated donors.

Reconstruction of the anterior column of the thoracic and lumbar spine with a carbon fiber stackable cage system

A carbon fiber stackable cage system is presented to promote the reconstruction of the anterior column after vertebrectomy or corpectomy in tumor and trauma surgery. Modularity, immediate stability, early fusion of the graft, radiolucency, and no risk of disease transmission are the main advantages of this system.

Symptomatic vertebral hemangioma: the treatment of 23 cases and a review of the literature

It is the purpose of this study to analyze a group of 23 patients affected with hemangioma in one or more metameres of the vertebral column. On the basis of clinical examination and instrumental testing in time (minimum follow-up 12 months, maximum 217 months) the following treatment options are discussed: medical treatment and clinical monitoring closer in time; palliative surgical treatment whether or not associated with embolization of vascular afferences of the lesion and adjuvant treatment; intralesional surgical treatment whether or not associated with embolization of the vascular afferences of the lesion and adjuvant treatment. Skeletal hemangioma is a hamartomatous proliferation of vascular tissue, more precisely of endothelial tissue. This is demonstrated by its anatomical identity with other tissues and the existence of exceptional skeletal and multiple tissue hemangiomatosis that begin during childhood. Hemangioma is the benign tumor that is most frequently localized in the spine, involving about 10% of the world population, as reported in the literature on autoptic studies. It is often a solitary lesion, usually localized in the vertebral body, although it may extend to the posterior arch. There is predilection for the thoracic region of the spine, while it less frequently occurs in the cervical and lumbar spines. Generally, it remains asymptomatic throughout the entire life of the subject, so much so that it is often difficult to establish the onset of the lesion. Symptomatic hemangiomas (less than 1% of all hemangiomas) are those that are accidentally discovered via radiograms; they are most often observed during adult age. The most common treatment used for vertebral hemangioma associated with pain is radiotherapy, even if clinical observation represents a reasonable choice. Surgical treatment, preceded when possible by embolization of the vascular afferences of the lesion, is often associated with radiation therapy in cases where there is neurologic compression in addition to pain. It was the purpose of this study to analyze the long-term results obtained in a group of 23 patients affected with symptomatic vertebral hemangioma.

Placing the newborn on the maternal abdomen increases the volume of umbilical cord blood collected

Haematopoietic stem cell transplantation is an important therapy for certain haematological and malignant disorders. Umbilical cord blood contains a high proportion of potentially transplantable haematopoietic progenitor cells. However, the use of cord blood stem cell transplantation is limited by the low number of stem cells obtainable from a single cord blood donor. The aim of our study was to investigate the possibility that procedures during delivery might influence the number of umbilical cord blood haematopoietic progenitor cells available for transplantation. We assessed the effects of upper and lower positions of the newborn infant on the yield of cord blood stem cells in 51 vaginal deliveries. Neonates in the upper position group were placed by the midwife on the maternal abdomen immediately after birth, while those in the lower position group were placed on the delivery table, below the maternal introitus. The total volume of cord blood and the total number of CD34+ cells collected from babies in the upper position group were significantly higher than those from babies in the lower position group. There were no significant differences in cord blood haemoglobin levels and white blood cell counts between the two groups, nor were there any adverse effects in the newborn infants. The simple manoeuvre of placing the newborn on the maternal abdomen after delivery may thus increase the yield of transplantable haematopoietic progenitor cells in cord blood.

Annexin 1 peptides protect against experimental myocardial ischemia-reperfusion: analysis of their mechanism of action

Myocardial reperfusion injury is associated with the infiltration of blood-borne polymorphonuclear leukocytes. We have previous described the protection afforded by annexin 1 (ANXA1) in an experimental model of rat myocardial ischemia-reperfusion (IR) injury. We examined the 1) amino acid region of ANXA1 that retained the protective effect in a model of rat heart IR; 2) changes in endogenous ANXA1 in relation to the IR induced damage and after pharmacological modulation; and 3) potential involvement of the formyl peptide receptor (FPR) in the protective action displayed by ANXA1 peptides. Administration of peptide Ac2-26 at 0, 30, and 60 min postreperfusion produced a significant protection against IR injury, and this was associated with reduced myeloperoxidase activity and IL-1beta levels in the infarcted heart. Western blotting and electron microscopy analyses showed that IR heart had increased ANXA1 expression in the injured tissue, associated mainly with the infiltrated leukocytes. Finally, an antagonist to the FPR receptor selectively inhibited the protective action of peptide ANXA1 and its derived peptides against IR injury. Altogether, these data provide further insight into the protective effect of ANXA1 and its mimetics and a rationale for a clinical use for drugs developed from this line of research.

At term pregnancies in transfusion-dependent beta-thalassemic women

The health background management and outcome of five pregnancies in women affected by Cooley Disease are described and the preconceptual guidance and care are considered. The patients were selected from a group of 103 thalassemic women divided into three subgroups according to their first and successive menstruation characteristics. Only one woman needed induction of ovulation. A precise and detailed pre-pregnancy assessment was done before each conception. All the women were in labour at 38 weeks' gestation, and five healthy babies were born at term, weighing between 2,600 and 3,200 g. The improvement in current treatments will result in a continuous increase in pregnancies in thalassemic women, making pregnancy a real eventuality for them. Furthermore, we are studying the possibility of collecting foetus umbilical cord blood after delivery, with the aim of obtaining complete marrow reconstitution in an attempt at heterologous transplantation to the mother.

Adenomyosis and uterus rupture during labor

A spontaneous uterus rupture occurred during the labour of a 37-week-pregnant woman showing a precocious rupture of membranes. It appeared enlarged and the cut surface of the myometrium showed coarse trabeculations. The histological examination showed a hypertrophic gravidic myometrium with heterogeneous areas of fibrosis and adenomyosis, necrotic decidual foci and hyperplastic cervical canal glands. Our experience suggests that a silent and spontaneous uterine rupture, is possible even in the absence of the principal risk factors.

Reasons to Eliminate Umbilical Cord Blood Units before Cryopreservation

Hematopoietic stem cells collected from umbilical cord blood (UCB) are widely considered a potential alternative to bone marrow. Research on UCB has now developed with the establishment of cord blood banks throughout the world. The aim of our study is to improve the efficiency of our bank because of the high cost and the administrative effort involved in its organization, finding a correlation between the terms of UCB units discarding, such as the low volume and for the low cell counts, and the obstetrics causes. This process has been made to cut the cost of the research and to improve the final result of each bank. We obtained, in 15 months, 683 cord blood units by blood withdrawal from the placenta. The units were cryopreserved within 24 h of collection, in a volume of at least 60 ml with a nucleated cells total of more than 800 per 10(6). Specific analyses of the unit blood to exclude bacterial contamination were undertaken. Of the 683 bags collected, 340 (49.75%) were discarded, and 343 were banked. The main reasons for rejecting the UCB units were: low volume; low cell counts; clinical history; bacterial contamination; freezing problems; unit misidentification; and no informed consent. We suggest that regular monitoring of the reasons for the rejection of the UCB units could give a significant effort to the bank organization, and identifying those units that are suitable before the cryopreservation could save precious resources.

Aneurysmal bone cyst of the mobile spine: report on 41 cases

STUDY DESIGN

Forty-one cases of aneurysmal bone cyst of the mobile spine were retrospectively reviewed.

OBJECTIVES

To evaluate the role of surgical and nonsurgical treatment of aneurysmal bone cyst of the spine.

SUMMARY OF BACKGROUND DATA

Ten to 30% of aneurysmal bone cysts arise from the mobile spine, frequently occurring in pediatric patients. The course of the disease depends on the aggressiveness of the tumor, as well as the treatment. Intralesional surgery seems to be an effective treatment, as well as radiotherapy and embolization.

METHODS

All charts, radiographs, and images were reviewed. The composite information provided by this review allowed for oncologic and surgical staging of these cases. Thirty-two patients underwent curettage (14 of them followed by radiotherapy), four were submitted to selective arterial embolization, three received radiotherapy alone, and two underwent en bloc-excision.

RESULTS

All patients were found alive and disease free at final follow-up evaluation. Two recurrences followed one incomplete curettage and one embolization. The combination of curettage and radiotherapy, although effective, showed the greatest incidence of late axial deformity. Selective arterial embolization was curative in three of four cases and did not affect the possibility of surgery in case of local recurrence.

CONCLUSIONS

If confirmed on larger series, selective arterial embolization seems to be the first treatment option for spine aneurysmal bone cyst, because of the low cost-to-benefit ratio. Diagnosis must be certain, based on pathognomonic radiographic pattern or on histologic study.- In case of neurologic involvement, pathologic fracture, technical impossibility of performing embolization, or local recurrence after at least two embolization procedures, complete intralesional excision would be the therapy of choice.

Pregnancy outcome of a transfusion-dependent thalassemic woman

A clinical case concerning a normal pregnancy outcome in a transfusion-dependent woman affected by homozygous beta thalassemia, whose partner was negative with regard to the "thalassemic trait", was reported. The patient showed no iron deposit problems, viral diseases that could have made the pregnancy management difficult or any complications during the gestation. Blood transfusion was not necessary during the following caesarean delivery. The outcome was a healthy female child, born at a gestational age of 38 weeks, showing neither malformations nor problems. This was possible due to a detailed preconceptual guidance and a pre-pregnancy assessment. The patient normally would have had a blood transfusion every 20 days and a strict desferrioxamine chelating therapy; however, this treatment was suspended during her pregnancy because of the well-recognised teratogenic effects of the drug. The average values of ferritin were just a little higher than before being pregnant. The foetus, due to her particular chelating activity, probably maintained these ferritin levels. A sample of 95 ml umbilical cord blood was taken during the delivery. It is well known that umbilical cord blood contains a good quantity of CD34+ stem cells, the haematopoietic progenitors. It was therefore collected for transplanting to the mother and for bone marrow reconstitution. Moreover, our experience suggests that desferrioxamine therapy during lactation does not alter iron excretion in breast milk. Therefore, women now affected by Cooley disease may possibly have a normal pregnancy without ovulation induction, intrauterine growth retardation, foetal loss and preterm labour.

The use of the carbon-fiber reinforced modular implant for the reconstruction of the anterior column of the spine. A clinical and experimental study conducted on 42 cases

The conservative treatment of neoplasms of the locomotor apparatus means the production of bone defects that may be filled with prostheses, bone grafts, systems of osteosynthesis. In the vertebral column, reconstruction of the resected elements--in the case of total vertebrectomy--requires the combination of anterior and posterior implants. It is the purpose of this study to analyze a group of 42 patients who, after accurate and uniform oncological (Enneking) and surgical (Weinstein-Boriani-Biagini) staging, were submitted to excision of one or more vertebral bodies for the treatment of neoplastic pathology, with reconstruction by prosthetic carbon fiber modular implant in order to obtain immediate stability, and to stimulate solid intervertebral fusion by bone grafts introduced inside the prosthesis. Thirty of the 42 patients presented with primary malignant tumor, 3 with benign tumor, 6 with solitary metastases, and 3 with plasmacytoma. In 32 cases, en bloc resection of the vertebral body was carried out (vertebrectomy) with combined anterior and posterior access in 29 patients (69.0%), and by posterior approach alone in 3 cases (7.1%). Ten intralesional corporectomies were carried out, 8 by anterior approach, 2 by posterior approach. The carbon prosthesis was filled with cortical and cancellous bone grafts in 38 cases. At a mean clinical and instrumental follow-up obtained 26 months after surgery for all of the patients, the use of a carbon prosthesis did not cause short- or long-term mechanical complications. The results of our study tend to affirm that the use of a carbon fiber modular implant may fill any loss of bone substance of the vertebral column, that it allows for immediate weight-bearing, and that if favors bone fusion. Some particular features of the carbon prosthesis favorably adapt to the surgical method of vertebrectomy: 1. The various components of the prosthesis may adapt to any type of bone resection of the vertebral body, even in unexpected situations; 2. Connection to posterior instrumentation in total vertebrectomies avoids the use of an anterior plate, thus reducing the time required for reconstruction of the anterior column, eliminating necessary surgical procedures in the segmental vascular structures. Finally, the radiolucency of the prosthesis allows for an easy evaluation of the formation of bone within and around the implant up to definitive anterior fusion and, of no less importance, early diagnosis of any local recurrence.

Collection of fetal stem cells and newborn effects

The aim of this work was to test fetal stem cells (FSC) number modification in relation to clamping time and newborn effect. The results show that a fast sample, between 20 and 40 seconds, from umbilical cord after fetus birth and before placental detachment assured a greater quantity of blood useful for the transplants; and that it was necessary to enrich the collected blood in CD34+ cells with specific clonogenic culture, as this is otherwise a small number for a donation to an adult. In the "new donors" the effects of the unconscious donation always depend on the clamping time, which should be the shortest possible to avoid blood overload, which is very dangerous in the presence of heart malformation.

Chondrosarcoma of the mobile spine: report on 22 cases

STUDY DESIGN

A retrospective review of 22 cases of chondrosarcoma arising from the mobile spine.

OBJECTIVE

To evaluate the role of oncologic and surgical staging in correlating management and outcome of chondrosarcoma involving the spine.

SUMMARY OF BACKGROUND DATA

Approximately 10% of chondrosarcomas arise from the mobile spine, occurring mainly in adults, particularly elderly men. The course of the disease depends on the aggressiveness of the tumor, but also is influenced by the management. Intralesional surgery is followed almost constantly by local recurrence even with adjuvant therapy.

METHODS

All charts, radiographs, and images were reviewed. The composite information provided by this review allowed for oncologic and surgical staging of the reviewed cases. According to Enneking criteria, the surgical procedures were defined as curettage (piecemeal excision) or en blocexcision. The margins were submitted to histologic study and reported as intralesional, marginal, or wide. - As primary management, 10 intralesional curettages (follow-up period, 2-119 months; average, 61 months) and 12 en bloc excisions (follow-up period, 39-207 months; average, 97 months) were performed. A total of 33 procedures were performed, including the management of the recurrences (18 curettages and 15 en bloc excisions: one for soft tissue recurrence). A clinical and radiographic follow-up period of of 2 to 236 months (average, 81 months; minimal follow-up period for survivors, 30 months; average follow-up period for survivors, 115 months) was available for all the patients.

RESULTS

Three recurrences occurred in 14 patients treated by en bloc excision at onset or for recurrence, two in cases of histologically proven contaminated or intralesional margins. All but one patient were alive at final follow-up evaluation. Conversely, all the patients treated by one or more curettages (with or without adjuvant radiation therapy) had at least one recurrence, and 8 of 10 of these patients died of the disease. At final follow-up evaluation, nine patients had died of the disease; nine were continuously disease free (but one had died of another unrelated malignancy); and four were symptom free after management for recurrences (one was found alive 155 months after a soft-tissue metastasis en-bloc excision).

CONCLUSIONS

En bloc excision, with wide or marginal histologic margins, is the suggested management for chondrosarcomas of the spine. Early diagnosis and careful surgical staging and planning are necessary for conducting adequate management. However, tumor contamination of the specimen margins, even in a small area, or spreading of the tumor myxoid content can worsen the prognosis.

The treatment of thoracic and lumbar spine fractures: a study of 123 cases treated surgically in 101 patients

For a total of 123 thoracolumbar traumatic lesions treated surgically in 101 patients over approximately 2 years (all monitored clinically and radiographically up to consolidation by follow-ups after from 6 to 26 months, mean 10 months) the technique used, complications and treatment are reported. The treatment procedure included: emergency surgery decompression, osteosynthesis, and fusion (posterior and possibly intersomatic); immediate recovery of function and loading; clinical and radiographic monitoring within 4-6 weeks, and possible anterior fusion in case of insufficient reconstruction of the anterior column. The complications observed out of 123 fractures were: collapse of the implant (4 cases), infection (5 cases), liquoral fistula (1 case), transitory paralysis of the abdominal muscles homolateral to the lombotomic incision (1 case), TVP (2 cases), bronchial pneumonia (2 cases), paralytic ileum (1 case). There was no sagittal deformity (secondary kyphosis) except for 5 cases of mechanical collapse that were resolved with a new operation. Neurologic deficit was caused by fracture in 49 patients (40% of the fractures or 48% of the patients). Six patients out of 30 affected with spinal cord lesion (20%) and 15 out of 19 affected with cone and/or cauda lesion (79%) improved. There was no progression of the neurologic findings after surgery. The authors conclude by proposing a protocol of posterior osteosynthesis for the use of a system in titanium made up of pedicle screws and hooks connected to a pair of cylindrical bars joined together.

Hemorrhagic synovial lumbar cyst: a case report and review of the literature

The authors report a case of an 81-year-old woman affected by a synovial cyst arising from the left facet joint of L3. The patient presented with severe pain and claudicatio spinalis. Diagnosis was based upon standard x-rays and MRI; the patient was operated on and the histology of the lesion confirmed the pre-operative diagnosis. On MRI images the lesion appeared as a roundish extradural mass arising from the left facet joint of L3, compressing the cauda equina posteriorly, and it appeared with an increased heterogeneous signal, consistent with a high quantity of fluid and hemosiderin within the cyst. A communication between the lesion and the joint space was evident on the MRI sagittal reconstruction. Grossly the cut surface of the mass had a cystic aspect, with some hemorrhagic areas between whitish myxoid tissue. Histologically the lesion was formed by fibrous connective tissue covered by synovium; focal inflammation and hemosiderin-laden macrophages were also present in some areas. At one year follow-up the patient is symptom-free.

Bizarre parosteal osteochondromatous proliferation of bone

A 47-year-old man presented with a painless mass of 7 months' duration, on the plantar aspect of the great toe of the right foot. Radiographs and CT images initially suggested an osteochondroma arising from the proximal phalanx of the great toe but there was no continuity between the medullary canal of the phalanx and the lesion. The mass was excised and a histological diagnosis of bizarre parosteal osteochondromatous proliferation of bone (Nora's disease) was made. The aggressive growth of this lesion may clinically suggest a neoplasm. Histological features, however, are those of a reactive lesion.

Resection surgery in the treatment of vertebral tumors

With the purpose of clarifying the limits of resection surgery (en bloc excision) for the treatment of bone tumors of the spine, the authors report the indications and results of 43 operations. This series was homogeneous in terms of oncological and surgical staging, as well as with regard to surgical method used and anaesthesiology. Three different types of surgery were performed: en bloc resection of tumors of the body (sectors 5-9 or 4-8 depending on the WBB staging system), of the posterior arch (sectors 10-3) or characterized by eccentric growth (sectors 2-5 or 8-11). The surgical margins were histologically studied in all of the cases: based on the evaluation and on histological diagnosis further chemo- and/or radiation therapy were decided on. Long-term follow-up was obtained for all of the cases (from 6 to 153 months, mean 30 months; 26 cases followed for more than 24 months). Six of the patients died as a result of the disease from 10 to 28 months after resection. There were 4 local recurrences, 4 pulmonary metastases, and 5 metastatic disseminations to the skeleton and to other tissues observed in 11 patients. At final follow-up 33 patients (77%) were thus disease-free (32 continually), in excellent condition, and capable of living a normal life. Complications and treatment are also reported. A careful study of the neoplasm, an appropriate selection of the patients based on diagnosis and histological staging, a knowledge of the natural progression of bone neoplasms and of the surgical anatomy of the vertebral column, the application of suitable measures of anaesthesiological control, allow for a correct cost/benefit evaluation of this type of surgery as compared to oncological methods that are less effective but more diffused. On the basis of these considerations indications for en bloc resection in tumors of the spine are defined.

Reconstruction techniques in the treatment of vertebral neoplasms

The authors present a new system for the topographical description of vertebral neoplasms. The general criteria of reconstruction after curettage or vertebral resection are evaluated. The literature is reviewed in terms of the use of prostheses, bone grafts, cement and stabilization systems in the treatment of tumors of the spine. Indications for the different methods are discussed.

The sitting position in posterior access to the cervical spine for the treatment of neoplasm

The authors evaluate the posterior approach to the cervical spine with the patient in a sitting position for the surgical treatment of neoplasms of the vertebral arch. Advantages and risks, particularly those related to anesthesia, are examined. Two cases in which the sitting position was advantageous are reported.

Congenital and acquired syphilis of bone: pathologic fracture with hyperplastic callus. A description of two cases and a review of the literature

The authors describe two cases of syphilis of bone with multiple pathologic fractures. Healing of the fractures occurred over a normal period of time, with the production of hyperplastic callus. Differential diagnosis with tumorous and pseudotumorous lesions is possible based on clinical data and a history of the patient, as well as specific laboratory tests for syphilis; occasionally, biopsy is required.

Monoclonal antibodies of differentiating specificities as probes of cytochrome P450h (2C11)

A panel of 30 monoclonal antibodies against rat hepatic microsomal cytochrome P450h (2C11) has been produced, purified, and characterized. A broad range of reactivities was observed when 13 purified rat cytochrome P450 isozymes were tested for epitope relatedness in a noncompetitive enzyme-linked immunosorbent assay or on immunoblots. Several antibodies were antigen-specific, others reacted with additional members of the 2C subfamily, and other monoclonal antibodies recognized cytochromes P450 from the 2E, 2B, 2A, and 1A subfamilies. Cytochromes P450p (3A1) and P4501 (3A2) did not react with any of the antibodies. A minimum of seven spatially distinct epitopes on cytochrome P450h were defined by the panel of antibodies. Immunoblot analysis of rat microsomes illustrated the male specificity of cytochrome P450h expression which extended to extrahepatic tissues including kidney and lung. A survey of various species by immunoblot analysis with several antibodies revealed little if any epitope relatedness among microsomal proteins from rats, mice, rabbits, hamsters, squirrel monkeys, guinea pigs, or humans. All of the antibodies were screened as potential inhibitors of cytochrome P450h-mediated testosterone hydroxylation in a reconstituted system. Although most of the antibodies were noninhibitory, greater than 70% inhibition of 2 alpha- and 16 alpha-hydroxylation of testosterone was observed with selected antibodies. These inhibitory antibodies gave similar results when benzphetamine N-demethylation was evaluated in the reconstituted system. The inhibitory antibodies were then used to assess the role of cytochrome P450h in microsomal benzphetamine N-demethylation, since this isozyme exhibits high catalytic activity for this substrate. Only 20-25% inhibition of benzphetamine metabolism was attained in microsomal preparations from adult male rats, and the antibodies did not influence the microsomal catalytic activity of immature males or females or adult females. Thus, despite the high level of expression of cytochrome P450h in microsomes from adult male rats and the high catalytic activity of the purified protein for benzphetamine, this isozyme contributes only a small portion of the metabolism of this substrate in microsomes.

Regulation of two members of the steroid-inducible cytochrome P450 subfamily (3A) in rats

Monoclonal antibodies have been successfully isolated which are isozyme-specific for cytochrome P450p (3A1) or P4501 (3A2), two members of the steroid-inducible cytochrome P450 subfamily exhibiting 89% amino acid sequence homology, and these antibodies show less than 5% cross-reaction with 11 other cytochromes P450 (P450a-P450k). A library of 28 purified monoclonal antibodies was established and characterized as to epitope specificity. Appropriate antibodies were selected and utilized to investigate the regulation of expressed cytochrome P450p and P4501 proteins as a function of age, sex, and treatment of rats with various inducing agents. Cytochrome P450p is not detectable in hepatic microsomes from untreated immature or adult male and female rats. Following dexamethasone treatment, expression of cytochrome P450p is observed in all groups with the levels reaching 30-37% of total microsomal cytochrome P450. Administration of other inducers such as pregnenolone 16 alpha-carbonitrile also yield enhanced levels of cytochrome P450p. Measurable amounts of constitutive cytochrome P4501 were detected in hepatic microsomes from immature and adult males as well as immature females but not in adult females. Cytochrome P4501 expression is inducible by dexamethasone in immature rats of both sexes and adult males, although dexamethasone is more effective as an inducer of cytochrome P450p than cytochrome P4501. Hence, not only is cytochrome P4501 protein expressed in immature animals of both sexes, it is also inducible in both sexes. These studies show that constitutive expression and induction of steroid-inducible cytochrome P450s may vary as a function of age.

Effects of testosterone and estrogen on hepatic levels of cytochromes P450 2C7 and P450 2C11 in the rat

The effects of exogenous hormone treatment on the expression of cytochromes P450 2C7 and P450 2C11 were studied in neonatally gonadectomized and sham-operated male and female rats. Hepatic levels of cytochrome P450 2C7 were found to be two- to threefold higher in intact adult female versus male rats. Neonatal gonadectomy resulted in a reversal of the relative cytochrome P450 2C7 levels in male and female animals at maturity. Expression of this isozyme was restored in ovariectomized females by estradiol treatment. Furthermore, neonatal and/or pubertal administration of estradiol to intact male rats induced cytochrome P450 2C7 to adult female levels. On the other hand, administration of testosterone at all times examined had no effect in intact female rats, but decreased cytochrome P450 2C7 to normal levels in neonatally castrated males treated during adulthood. Neonatal testosterone treatment also increased hepatic cytochrome P450 2C7 content in both ovariectomized females and intact males. These results indicate that estrogen is required for full expression of cytochrome P450 2C7 while the effect of testosterone is ambiguous. In comparison, neonatal gonadectomy of male rats abolished the adult expression of cytochrome P450 2C11. Normal levels were restored only by treatment with testosterone during adulthood. Neonatal testosterone treatment did not induce cytochrome P450 2C11 levels in gonadectomized rats of either sex. In contrast, neonatal estrogen treatment suppressed cytochrome P450 2C11 expression in intact adult male rats to the same extent as neonatal castration. These results indicate that androgen exposure during the adult, and not the neonatal, phase is essential for full expression of cytochrome P450 2C11.

Imprinting of hepatic microsomal cytochrome P-450 enzyme activities and cytochrome P-450IIC11 by peripubertal administration of testosterone in female rats

The influence of peripubertal exposure to physiological doses of testosterone on the adult androgen responsiveness of hepatic microsomal cytochrome P-450 was investigated. Male and female Sprague-Dawley rats were sham-operated or gonadectomized before puberty, at 25 days of age. They were injected subcutaneously with testosterone enanthate (5 mumol/kg/day) during the pubertal time period, on days 35-49. Responsiveness to this same dose of testosterone was tested by administering the compound during adulthood, on days 81-89. The females provided a model that had not been exposed to neonatal androgen imprinting, in contrast to the males. Testosterone 2 alpha-hydroxylase activity and cytochrome P-450IIC11, which are normally expressed only in adult males, were expressed in the gonadectomized females administered testosterone during puberty with no further exposure to the hormone for the next 40 days. The levels found were similar to those in the gonadectomized male group. When the combined pubertal and adult testosterone regimen was used, a synergistic effect was produced; the 2 alpha-hydroxylase activity reached control male levels in both gonadectomized and sham-operated females and, in addition, cytochrome P-450IIC11 attained control male levels in the gonadectomized females. Testosterone 6 beta-hydroxylase and erythromycin N-demethylase activities were used as indicators of the cytochrome P-450IIIA subfamily. These activities were significantly increased only in the females treated with testosterone during both the pubertal and adult periods, reaching control male levels of 6 beta-hydroxylation. A similar effect, but in the opposite direction, was found with testosterone 7 alpha-hydroxylase, an enzyme activity indicative of cytochrome P-450IIA1. A decrease in this enzyme was produced in the females administered testosterone during both time periods, resulting in levels equivalent to those found in control males. In general, a highly significant interaction was found between the pubertal and adult treatment periods for the females, indicating a chronic effect of the pubertal exposure. The experiments with castrated males did not result in synergistic interactions, although there was some evidence of an additive effect. The results of this study support the hypothesis that the peripubertal period is a time during which testosterone imprinting of both increased basal levels and adult androgen responsiveness of some hepatic cytochrome P-450 enzymes can occur in the female rat.

Expression and catalysis of sex-specific cytochrome P450 isozymes in rat liver

Research interest in the study of cytochromes P450 has recently been shifting to the characterization of "constitutively" expressed isozymes from that of the inducible forms. Several "constitutive" cytochrome P450 isozymes have been purified from rat liver including five immunochemically related proteins designated cytochromes P450f, P450g, P450h, P450i, and P450k. These hemoproteins have been identified as distinct isozymes on the basis of spectral, electrophoretic, and catalytic properties and NH2-terminal sequence analysis. Purification and immunoquantitation studies have indicated that these isozymes are expressed in a developmental as well as sex-related manner, and are relatively refractory to induction by xenobiotics. Cytochromes P450h and P450g are male-specific proteins, cytochrome P450i is a female-specific isozyme, while cytochromes P450f and P450k are present in both male and female adult rats. In addition, the expression of cytochrome P450g was shown to segregate into two phenotypes in outbred rats. Genetic studies utilizing inbred strains have indicated that the gene responsible for inheritance of high levels of cytochrome P450g is autosomal. Although considerable progress has been made in understanding the role of gonadal hormones and growth hormone in the hepatic regulation of cytochromes P450g, P450h, and P450i in particular, the physiological significance of the "constitutive" isozymes in the liver remains largely unresolved.

A simple, non-chromatographic purification procedure for monoclonal antibodies. Isolation of monoclonal antibodies against cytochrome P450 isozymes

A simple, non-chromatographic purification procedure for monoclonal antibodies from mouse ascites fluid is described. This procedure, which is rapid, inexpensive, and has high capacity involves the precipitation of contaminating proteins with caprylic acid followed by precipitation of immunoglobulin using ammonium sulfate. This two-step procedure is shown to be effective for the purification of various immunoglobulins including IgG1, IgG2a and IgG2b. In the present report, more than 30 monoclonal antibodies directed against cytochrome P450 isozymes have been purified by this method and characterized.

Polyclonal and monoclonal antibodies as probes of rat hepatic cytochrome P-450 isozymes

Cytochrome P-450 is the terminal oxidase of an electron transport system that is responsible for the oxidative metabolism of a large variety of endogenous and exogenous compounds. This broad substrate selectivity is caused by multiple isozymes of cytochrome P-450 and the wide substrate selectivity of many of these isozymes. We have isolated 11 isozymes of cytochrome P-450 from the livers of rats (cytochromes P-450a-P-450k). We have found both polyclonal and monoclonal antibodies increasingly useful to distinguish among these isozymes and to quantitate enzyme levels in liver microsomal preparations where as many as 15 or more cytochrome P-450 isozymes are present. Several of these isozymes show considerable immunochemical relatedness to each other, and operationally they can be grouped into families of immunochemically related isozymes that include cytochromes P-450b and P-450e in one family, cytochromes P-450c and P-450d in another, and cytochromes P-450f-P-450i, and P-450k in a third family. Immunoquantitation of some of these isozymes has revealed dramatic increases of over 50-fold in the levels of certain of these isozymes when exogenous compounds are administered to rats.

Regulation of cytochrome P-450j, a high-affinity N-nitrosodimethylamine demethylase, in rat hepatic microsomes

Polyclonal antibodies were produced in rabbits against purified cytochrome P-450j isolated from isoniazid-treated adult male rats. The monospecificity of immunoadsorbed antibody to cytochrome P-450j was demonstrated by Ouchterlony double diffusion analyses, enzyme-linked immunosorbent assays, and immunoblots. Immunoquantitation results indicated that rat liver microsomal cytochrome P-450j content decreases between 3 and 6 weeks of age in both the male and female animal. Several xenobiotics, such as Aroclor 1254, mirex, and 3-methylcholanthrene, repressed cytochrome P-450j levels when administered to male rats. Isoniazid, dimethyl sulfoxide, pyrazole, 4-methylpyrazole, and ethanol were inducers of cytochrome P-450j in rat liver although these compounds showed different inducing potencies. Microsomes from adult male rats with chemically induced diabetes also contained elevated levels of cytochrome P-450j compared to untreated animals. Cytochrome P-450j levels were measurable in kidney, whereas this isozyme was barely detectable in lung, ovaries, and testes; however, extrahepatic cytochrome P-450j was inducible by isoniazid. Approximately 80-90% of microsomal N-nitrosodimethylamine demethylation was inhibited by antibody to cytochrome P-450j whether the microsomes were isolated from untreated rats or animals administered inducers or repressors of cytochrome P-450j. The residual catalytic activity resistant to antibody inhibition may be a reflection of the inaccessibility of a certain amount of cytochrome P-450j due to interference by NADPH-cytochrome P-450 reductase based on results obtained with the reconstituted system. There was a good correlation (r2 = 0.87) between cytochrome P-450j content and N-nitrosodimethylamine demethylase activity in microsomes from rats of different ages and treated with various xenobiotics. The evidence presented indicates that cytochrome P-450j is the primary, and perhaps sole, microsomal catalyst of N-nitrosodimethylamine demethylation at substrate concentrations relevant to hepatocarcinogenesis induced by N-nitrosodimethylamine.

A regulatory polymorphism for rat hepatic cytochrome P-450g

Rat hepatic cytochrome P-450g is a male-specific hemoprotein found at significant levels only in adult animals. In the present study, two-dimensional gel electrophoretic and immunochemical methods were used to study a polymorphism of this isozyme and its ontogenetic regulation. Inbred ACI/Hsd and WF/Hsd rats were found to express high and low levels of cytochrome P-450g, respectively. F1 hybrids of these strains showed additive inheritance for this trait and the responsible gene was found to be autosomal. Cytochrome P-450g and another male-specific form of the enzyme, cytochrome P-450h, were characterized by a similar time-course for their ontogenetic expressions. However, unlike cytochrome P-450g, the level of cytochrome P-450h was indistinguishable in hepatic microsomes from mature ACI/Hsd and WF/Hsd rats. Considering these results, we tentatively conclude that the gene regulating the level of cytochrome P-450g is Cis-acting.

Age- and sex-related expression of cytochromes p450f and P450g in rat liver

We have previously shown that rat hepatic cytochromes P450f, P450g, P450h, and P450i possess a high degree of immunochemical and, presumably, structural relatedness. Polyclonal antibodies directed against cytochromes P450f and P450g were made monospecific by immunoabsorption against the cross-reactive proteins. The specificity of the immunoabsorbed antibodies was established by using Ouchterlony double diffusion analyses, enzyme-linked immunosorbent assays (ELISA), and immunoblots. Since factors regulating the expression of cytochromes P450f and P450g are unknown, a competitive ELISA employing the monospecific antibodies was developed to quantitate each of these isozymes in hepatic microsomes from control and treated rats. The results obtained showed that expression of cytochrome P450f is developmentally regulated in both male and female rat liver. Cytochrome P450f levels rise from less than 1% in young animals to approximately 7 and 14% of total cytochrome P450 in adult male and female rats, respectively. Cytochrome P450g is sex-specific since it is expressed only in male rat liver where it also is developmentally regulated. Levels of cytochrome P450g rise from less than 1% in 3-week-old male rats to an average value of 17% of total cytochrome P450 in 6-week-old adult animals. However, there appear to be at least two subpopulations of adult male Long Evans rats, one of which expresses low levels (less than 1%) of cytochrome P450g and the other high levels (greater than or equal to 10%). This expression appears to be independent of serum testosterone levels. Treatment of immature and adult male rats with 20 xenobiotics that are known inducers of certain cytochrome P450 isozymes revealed that cytochromes P450f and P450g are relatively refractory to induction, although Kepone appears to be a weak inducer of cytochrome P450f.

Polychlorinated dibenzofurans (PCDFs): correlation between in vivo and in vitro structure-activity relationships

Fifteen polychlorinated dibenzofuran (PCDF) congeners were administered in a dose-response fashion to immature male Wistar rats and ED50 values for body weight loss, thymic atrophy and the induction of the hepatic microsomal cytochrome P-448-dependent monooxygenases, aryl hydrocarbon hydroxylase (AHH) and 4-chlorobiphenyl hydroxylase were determined. There was an excellent correlation between the in vivo quantitative structure-activity relationships for these PCDFs and their in vitro activities as AHH inducers in rat hepatoma H-4-II E cells and as ligands for the 2,3,7,8-TCDD receptor protein. A comparison of isomers which differ at all 4 positions in the dibenzofuran ring system indicated that chlorine substitution at each position contributed differentially to the overall molecular activity [C-3 (or C-7) greater than C-2 (or C-8) greater than C-4 (or C-6) greater than C-1 (or C-9)]. There was also an excellent linear correlation between a plot of the -log ED50 for body weight loss vs. -log EC50 for in vitro AHH induction (correlation coefficient, r = 0.96) and -log ED50 for thymic atrophy vs. -log EC50 for in vitro AHH induction (correlation coefficient, r = 0.88). Since body weight loss and thymic atrophy in the rat are representative toxic responses to PCDFs and related toxic halogenated aryl hydrocarbons, the correlations noted above support the use of the in vitro AHH induction assay as a short term quantitative test system for this class of toxic halogenated aryl hydrocarbons.

Effects of structure on binding to the 2,3,7,8-TCDD receptor protein and AHH induction--halogenated biphenyls

The quantitative structure-activity relationships (QSARs) for polychlorinated biphenyl (PCB) congeners have been determined by comparing the EC50 values for three in vitro test systems, namely, aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) induction in rat hepatoma H-4-II-E cells and competitive binding avidities to the rat cytosolic receptor protein (using 2,3,7,8-tetrachlorodibenzo-p-dioxin as a radioligand). For several PCB congeners that are in vivo inducers of rat hepatic microsomal AHH, there was a linear correlation between the -log EC50 values for receptor and the -log EC50 values for AHH (or EROD) induction; moreover, a comparable linear relationship was observed between the -log EC50 values for AHH and EROD induction. Previous in vivo studies have shown that the most active PCB congeners 3,3',4,4'-tetra-, 3,4,4',5-tetra-, 3,3',4,4',5-penta-, and 3,3',4,4',5,5'-hexachlorobiphenyl, cause many of the biologic and toxic effects reported for the highly toxic halogenated aryl hydrocarbon, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Moreover, the monoortho-substituted homologs of the four coplanar PCBs also elicit comparable in vivo biologic and toxic responses. It was evident from the QSARs for PCBs that there was an excellent correspondence between the in vivo and in vitro potencies of the individual PCB congeners. The effects of substituents on both receptor binding and AHH/EROD induction was determined for a series of 4'-substituted (X)-2,3,4,5-tetrachlorobiphenyls (where X = H, Cl, Br, I, OH, OCH3, NO2, COCH3, F, CF3, CH3, C2H5, i-C3H7, n-C4H9 and t-C4H9). Not unexpectedly, there was a linear relationship between the -log EC50 values for AHH and EROD induction, and these results confirm that both enzymatic oxidations are catalyzed by the same cytochrome P-450 isozyme(s). The effects of substituent structure on receptor binding for 12 substituents was subjected to multiple regression analysis which correlates the relative binding affinities of the compounds with the physical chemical characteristics of the substituents. The analysis gave the following equation: log (1/EC50) = 1.53 sigma + 1.47 pi + 1.09 HB + 4.08 for n = 12, s = 0.18, r = 0.978; where n is the number of substituents, s is the standard deviation, r is the correlation coefficient, and sigma = electronegativity, pi = hydrophobicity (log P) and HB = hydrogen bonding capacity for the substituent groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for a family of four immunochemically related isozymes of cytochrome P-450 purified from untreated rats

Hepatic microsomal cytochromes P-450f, P-450g, P-450h, and P-450i have recently been purified to electrophoretic homogeneity from untreated adult rats and identified as distinct isozymes [Ryan et al. (1984) J. Biol. Chem. 259, 1239-1250; Haniu et al. (1984) Arch. Biochem. Biophys. 235, 304-311]. In Ouchterlony double-diffusion plates, as well as enzyme-linked immunosorbent assays and Western blots, purified immunoglobulin G (IgG) raised in rabbits against cytochromes P-450f or P-450g show strong cross-reactions with the heterologous protein, indicating apparent partial identity. Anti-P-450f and anti-P-450g also show strong cross-reactivity with cytochromes P-450h and P-450i but not with five previously characterized rat hepatic cytochromes, P-450 (i.e., P-450a-P-450e), indicating a high degree of immunochemical and structural relatedness among cytochromes P-450f, P-450g, P-450h, and P-450i.

PCBs: structure-function relationships and mechanism of action

Numerous reports have illustrated the versatility of polychlorinated biphenyls (PCBs) and related halogenated aromatics as inducers of drug-metabolizing enzymes and the activity of individual compounds are remarkably dependent on structure. The most active PCB congeners, 3,4,4',5-tetra-, 3,3',4,4'-tetra-, 3,3',4,4',5-penta- and 3,3',4,4',5,5'-hexachlorobiphenyl, are substituted at both para and at two or more meta positions. The four coplanar PCBs resembled 3-methylcholanthrene (3-MC) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) in their mode of induction of the hepatic drug-metabolizing enzymes. These compounds induced rat hepatic microsomal benzo(a)pyrene hydroxylase (aryl hydrocarbon hydroxylase, AHH) and cytochromes P-450a, P-450c and P-450d. 3,4,4',5-Tetrachlorobiphenyl, the least active coplanar PCB, also induced dimethylaminoantipyrine N-demethylase and cytochromes P-450b+e and resembled Aroclor 1254 as an inducer of the mixed-function oxidase system. Like Aroclor 1254, all the mono-ortho- and at least eight di-ortho-chloro analogs of the coplanar PCBs exhibited a "mixed-type" induction pattern and induced microsomal AHH, dimethylaminoantipyrine NM-demethylase and cytochromes P-450a-P-450e. Quantitative structure-activity relationships (QSARs) within this series of PCBs were determined by comparing their AHH induction potencies (EC50) in rat hepatoma H-4-II-E cells and their binding affinities (ED50) for the 2,3,7,8-TCDD cytosolic receptor protein. The results showed that there was an excellent correlation between AHH induction potencies and receptor binding avidities of these compounds and the order of activity was coplanar PCBs (3,3',4,4' -tetra-, 3,3',4,4',5-penta- and 3,3',4,4',5,5'-hexachlorobiphenyls) greater than 3,4,4',5-tetrachlorobiphenyl approximately mono-ortho coplanar PCBs greater than di-ortho coplanar PCBs. It was also apparent that the relative toxicities of this group of PCBs paralleled their biological potencies. The coplanar and mono-ortho coplanar PCBs also exhibit differential effects in the inbred C57BL/6J and DBA/2J mice. These compounds induce AHH and cause thymic atrophy in the former "responsive" mice whereas at comparable or higher doses none of these effects are observed in the nonresponsive DBD/2J mice. Since the responsiveness of these two mice strains is due to the presence of the Ah receptor protein in the C57BL/6J mice and its relatively low concentration in the DBA/2J mice, the results for the PCB cogeners support the proposed receptor-mediated mechanism of action.

Polychlorinated dibenzofurans (PCDFs): effects of structure on binding to the 2,3,7,8-TCDD cytosolic receptor protein, AHH induction and toxicity

The effects of structure on the activity of 26 polychlorinated dibenzofurans (PCDFs) as competitive ligands for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) rat hepatic cytosolic receptor protein were determined in a dose-response fashion. The ED50 values for these compounds varied 100 000-fold and the most active PCDFs were substituted in the 2,3,7 and 8 lateral positions; the ED50 for the most active PCDF, 2,3,4,7,8-pentachlorodibenzofuran was 1.5 X 10(-8) M which was only slightly less active than 2,3,7,8-TCDD (1.0 X 10(-8) M). A comparison of the binding affinities of several isomer pairs also indicated the relative importance of chlorine substitution at C-4 (or C-6) compared to C-1 (or C-9). Moreover, for some isomers it is apparent that C-4 (or C-6) substituents are more active than lateral substituents for facilitating ligand binding to the receptor protein. This is illustrated by the relative binding potencies of the following isomer pairs: 1,2,4,6,7-/1,2,4,7,8 = 19.2; 2,6,7-/2,3,8- = 2.2; 1,3,6-/1,3,8- = 19. Most of the PCDF structure-activity effects noted above were also observed for the induction of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II-E cells in culture. The most active compounds were also substituted in the lateral 2,3,7 and 8 positions and a comparison of C-4 (or C-6) vs. C-1 (or C-9) substituted PCDFs confirmed the higher induction potencies for most of the former group of compounds. The in vitro quantitative structure-activity data were complemented by in vivo studies which determined the relative activities of selected PCDFs as inducers of hepatic microsomal cytochrome P-448 dependent monooxygenases and their effects on body weight gain and thymus weights in immature male Wistar rats. The results indicated that for 2 series of isomers, namely the 2,3,4,7,8-, 1,2,4,7,8- and 1,2,4,7,9-pentachlorodibenzofurans and the 2,3,7,8-, 2,3,4,8- and 1,2,4,8-tetrachlorodibenzofurans, their biologic and toxic potencies were dependent on one major structural factor, the number of lateral chloro substituents. These results support the proposed role of the cytosolic receptor protein in mediating the biologic and toxic effects of the PCDFs.

PCBs and PBBs: biologic and toxic effects on C57BL/6J and DBA/2J inbred mice

Treatment of genetically inbred "responsive" C57BL/6J and "non-responsive" DBA/2J mice with Aroclor 1254 or fireMaster BP-6 resulted in the induction of hepatic microsomal benzo[a]pyrene hydroxylase only in the former mouse strain and aminopyrine N-demethylase in both strains of mice. In contrast, 3,3',4,4',5-pentachlorobiphenyl and 3,3',4,4'-tetrabromobiphenyl, induced benzo[a]pyrene hydroxylase in both C57BL/6J and DBA/2J but did not enhance aminopyrine N-demethylase in either strain of mouse. Both these coplanar halogenated biphenyls also caused thymic atrophy in the responsive and non-responsive mice and their effects resembled those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Treatment of the inbred mice with several mono-ortho substituted analogs of the coplanar halogenated biphenyls, including 2,3,3',4,4'-pentachloro-, 2,3',4,4',5-pentabromo-, 2,3,3',4,4',5-hexachloro- and 3',4'-dibromo-2,3,4,5-tetrachlorobiphenyl, gave hepatic enzyme-induction results similar to those observed for the commercial halogenated biphenyls. At dose levels of 1500 mumol/kg, most of these compounds caused thymic atrophy in C57BL/6J mice but not in DBA/2J mice. The structure-activity correlations in the mice complement similar studies with the halogenated biphenyls in rats and support the proposed receptor-mediated mechanism for the toxic halogenated aromatics.

Competitive binding to the cytosolic 2,3,7,8-tetrachlorodibenzo-p-dioxin receptor. Effects of structure on the affinities of substituted halogenated biphenyls--a QSAR analysis

The proposed mechanism of action of the toxic halogenated aromatics, typified by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), involves the initial binding to a high-affinity, low-capacity, cytosolic receptor protein. Previous studies have shown that several 4'-halo-2,3,4,5-tetrachlorobiphenyls bind to the TCDD receptor and that a lateral substituent on both phenyl rings is required for activity. Using an extended series of eighteen 4'-substituted-2,3,4,5-tetrachlorobiphenyls as probes, the effects of a variable lateral substituent on receptor binding affinity and the induction of aryl hydrocarbon hydroxylase (AHH) in vivo and in rat hepatoma H-4-II E cells have been determined. For most substituents, there was an excellent correlation between the rank-order potency for receptor binding and the rank-order potency for AHH induction. Based on in vitro binding affinities (EC50 values) of the 4'-substituted tetrachlorobiphenyls, a multiparameter regression equation was formulated correlating the binding constants to physicochemical substituent parameters. For thirteen compounds out of the present series, multiple regression analysis of the binding data led to the following equation: log(1/EC50) = 1.53 sigma + 1.47 pi + 1.09HB + 4.08, r = 0.978. The results suggest that halogen substitution on both phenyl rings is not a requirement for binding and that hydrophobic (pi) and electronic (sigma) substituent constants and a variable for hydrogen bond (HB) formation are significant parameters describing relative binding avidities of this series of substituted biphenyls for the TCDD receptor.

Polychlorinated biphenyls as phenobarbitone-type inducers of microsomal enzymes. Structure-activity relationships for a series of 2,4-dichloro-substituted congeners

Several polychlorinated biphenyl (PCB) isomers and congeners resemble phenobarbitone (PB) in their mode of induction of the hepatic drug-metabolizing enzymes; however, unlike PCBs which induce aryl hydrocarbon hydroxylase, no apparent structure-activity correlations have been reported. This study examines the effects of structure on the activity of a series of 2,4-dichloro-substituted biphenyls as inducers of several microsomal enzyme activities including dimethylaminoantipyrine N-demethylase, benzo[a]pyrene hydroxylase, aldrin epoxidase, and ethoxyresorufin O-deethylase. The results clearly illustrate a marked effect of structure on activity: all of the 2,4-dichloro-substituted PCBs resembled PB in their mode of induction. However, the potency of the induction response was dependent on the substitution pattern of the second phenyl ring (i.e. 2,3,4,5-tetrachloro greater than or equal to 2,3,4,5,6-pentachloro greater than 2,3,4,6-tetrachloro greater than 2,3,5,6-tetrachloro greater than 2,4,6-trichloro); the structure of the lower chlorinated ring also determined induction potency since the 2,4-dichloro-substituted PCBs were generally more active than their 4-chloro-substituted analogs, whereas the 2-substituted PCB homologs were inactive. The structural factors which typify the most active PB-type inducer, 2,2',3,4,4',5-hexachlorobiphenyl, include the presence of two para-, at least two meta- and two ortho-chloro substituents. In addition to the structure-activity correlations noted for PCBs, the 2,2',3,4,4',5-hexachlorobiphenyl congener also elicited a dose-response induction of two PB-inducible enzymes, aldrin epoxidase and dimethylaminoantipyrine N-demethylase.

The comparative biologic and toxic potencies of polychlorinated biphenyls and polybrominated biphenyls

Aroclor 1254 and fireMaster BP-6, two commercial polychlorinated biphenyl (PCB) and polybrominated biphenyl (PBB) preparations, exhibit comparable biologic and toxic effects. In the present study the commercial PBB was more active than Aroclor 1254 in causing thymic atrophy in male Wistar rats. However, a direct comparison of the relative effects of bromine vs chlorine substituents is not possible with the commercial PBB and PCB mixtures due to their complex congeneric composition. This study reports the synthesis and biologic and toxic effects of a series of laterally substituted 3,3',4,4'-tetrahalobiphenyls which contain the following variable molecular Cl/Br ratios; Br4, Br3Cl, Br2Cl2 (two isomers), BrCl3, and Cl4. 3,3',4,4'-Tetrabromobiphenyl and 3,4,4'-tribromo-3'-chlorobiphenyl (150 mumol/kg)-pretreated animals significantly inhibited the growth rate of and caused thymic atrophy in immature male Wistar rats whereas those isostereomers with reduced Br (and increased Cl) content were either less active or inactive. Pretreatment of male Wistar rats with 10 mumol/kg of the 3,3',4,4'-tetrahalobiphenyls and determination of their effects as inducers of the hepatic microsomal drug-metabolizing enzymes also illustrated the effects of the relative Cl/Br ratios on induction potencies. Both 3,3',4,4'-tetrabromo- and 3,4,4'-tribromo-3'-chlorobiphenyl maximally induced the cytochrome P-448-dependent monooxygenases, benzo[a]pyrene and 4-chlorobiphenyl hydroxylase; the order of potency of the other isostereomers was 4,4'-dibromo-3,3'-dichloro- congruent to 3,4-dibromo-3',4'-dichlorobiphenyl greater than 4-bromo-3,3',4'-trichloro- greater than 3,3',4,4'-tetrachlorobiphenyl. With few exceptions this order of potency was observed for the induction of benzo[a]pyrene hydroxylase and ethoxyresorufin O-deethylase in rat hepatoma cells in culture and for their relative binding affinities to the rat cytosolic receptor protein. The data clearly demonstrate that the biologic activities of this group of isosteric halogenated biphenyls are enhanced with increasing bromine substitution and also support the hypothesis that the activities of this class of chemicals are mediated through the receptor.

Hepta-, hexa-, tetra- and dichloronaphthalene congeners as inducers of hepatic microsomal drug-metabolizing enzymes

Pretreatment of immature male Wistar rats with 1,2,3,4,5,6,7-hepta-, 1,2,3,4,5,6,8-hepta- and 1,2,3,4,5,6-hexachloronaphthalene resulted in the induction of several hepatic microsomal drug-metabolizing enzymes. The enzymic activities, reduced cytochrome P-450:CO and ethylisocyanide binding difference spectra and electrophoretic mobilities of the induced microsomal proteins were comparable to those observed after administration of the classical inducer of microsomal aryl hydrocarbon hydroxylase, 3-methylcholanthrene. The 1,2,3,4,5,6,7-heptachloronaphthalene congener, which is fully substituted in the lateral 2,3,6 and 7 positions, was more potent than the 1,2,3,4,5,6,8-hepta- and the 1,2,3,4,5,6-hexachloronaphthalene congeners which contain only 3 lateral chloro substituents. 1,2,3,4-Tetra- and several lower chlorinated naphthalenes were inactive as inducers of microsomal aryl hydrocarbon hydroxylase. The effects of structure on the induction activities of the polychlorinated naphthalenes were similar to those observed for other halogenated aryl hydrocarbons.

Halogenated biphenyls as AHH inducers: effects of different halogen substituents

4'-Iodo-, 4'-bromo-, 4'-chloro- and 4'-fluoro-2,3,4,5-tetrachlorobiphenyl were administered to immature male Wistar rats and the effects of this homologous series of 4'-halo-2,3,4,5-tetrachlorobiphenyls on the microsomal drug-metabolizing enzymes were determined. All the halogenated biphenyls increased microsomal benzo[a]pyrene hydroxylase (or aryl hydrocarbon hydroxylase, AHH), ethoxyresorufin (ER) O-deethylase and dimethylaminoantipyrine (DMAP) N-demethylase. The effects of the 4'-halo-2,3,4,5-tetrachlorobiphenyls on the microsomal enzyme activities and on the relative peak intensities and spectral shifts of the reduced cytochrome P-450:CO and ethylisocyanide (EIC) binding difference spectra were similar to those observed after coadministration of phenobarbitone (PB) and 3-methylcholanthrene (MC). The relative activities of the halogenated biphenyls were determined using two in vitro assays; namely cytochrome P-448 associated induction in rat hepatoma H-4-II E cells in culture and competitive binding to the hepatic cytosolic Ah receptor protein from male Wistar rats. Dose-response experiments for the iodo, bromo, chloro and fluoro analogs gave EC50(M) values of 8.5 x 10(-9), 6.6 x 10(-8), 5.7 x 10(-7), and 3.3 x 10(-5), and 1.5 x 10(-6), 2.5 x 10(-6), 4.1 x 10(-6) and 2.5 x 10(-5) for the Er O-deethylase induction and receptor binding assays respectively. The relative potencies of the 4'-halo-2,3,4,5-tetrachlorobiphenyls followed the order I greater than Br greater than Cl greater than F for both assays and differences in the EC50 values for the iodo and fluoro analogs were greater than three orders of magnitude for ER O-deethylase induction in rat hepatoma cells in culture. One possible explanation for these effects may be associated with differences in the polarizability of the laterally substituted halogen groups. However, other differences in the physico-chemical properties of the halogen atoms may also be important.

Halogenated biphenyls: molecular toxicology

The biologic and toxic effects of polychlorinated biphenyls (PCBs) are remarkably dependent on their structure. The most toxic PCBs, namely 3,3',4,4'-tetra-, 3,3',4,4',5-penta- and 3,3',4,4',5,5'-hexachlorobiphenyl are substituted in at least one meta and para position on both phenyl rings (i.e., the lateral positions) and contain no ortho-chloro substituents. These three congeners and a fourth PCB, namely 3,4,4',5-tetrachlorobiphenyl, are approximate isostereomers of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and, in common with TCDD, induce hepatic microsomal benzo[a]pyrene or aryl hydrocarbon hydroxylase (AHH) in rats and rat hepatoma cells in culture. The mono-ortho substituted analogs of the four laterally substituted PCBs also induce microsomal AHH activity and simultaneously enhance microsomal enzyme activities which are inducible by phenobarbitone (PB). This group of PCBs exhibits many of the properties of 2,3,7,8-TCDD and related polychlorinated dibenzo-p-dioxins; there is a close parallel in the relative potencies of these PCBs for AHH induction and their binding affinities for the Ah receptor protein and some of these PCBs are also toxic. Preliminary studies on other halogenated biphenyls confirm that the polarizability of a lateral substituent is an important factor in their activity as AHH inducers (i.e., I greater than Br greater than Cl greater than F). However, preliminary results with other substituted halogenated biphenyls suggest that additional structural factors are also important in determining the activity of these compounds.

Binding of polychlorinated biphenyls classified as either phenobarbitone-, 3-methylcholanthrene- or mixed-type inducers to cytosolic Ah receptor

It has been postulated that reversible, high-affinity binding of 3-methylcholanthrene(MC)-type inducers to a receptor protein (the Ah receptor) in hepatic cytosol is essential for induction of aryl hydrocarbon hydroxylase (AHH) enzymic activity. To test this postulate, the binding affinities of 16 highly-purified, synthetic chlorinated biphenyl (PCB) congeners, which have been categorized either as phenobarbitone(PB)-, MC- or mixed (PB + MC)-type inducers of cytochrome P-450-dependent monooxygenase have been examined. The affinity of individual biphenyl congeners for the receptor was determined by their competition with 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin ([3H]TCDD) for specific cytosolic binding sites as measured by sucrose density gradient analysis following dextran-charcoal treatment. This assay demonstrates (a) that the receptor binds with highest affinity to 3,3', 4,4',5-pentachlorobiphenyl and 3,3',4,4'-tetrachlorobiphenyl ('pure MC-like' inducers); (b) mixed-type PCB inducers also bind to the receptor but with an affinity (average EC50-value of 8.6 microM) lower than that for 3,3',4,4',5-pentachlorobiphenyl; this corresponds with their relatively lower potencies as AHH inducers; (c) the receptor binds 2,2',4,4'-tetra-, 2,3,4,5-tetra-, 2,2',4,4',5,5'-hexa- and 2,3',4,4',5',6-hexachlorobiphenyl at high concentrations (0.1 mM), whereas PB fails to bind, even at a concentration of 10 mM. All PCBs tested competed with [3H]TCDD for Ah receptor, but there was a great variation in their relative binding affinities. The fact that two chlorinated biphenyls classed as 'PB-like' inducers and two chlorinated biphenyls which are neither 'PB- nor MC-type' inducers competed, coupled with the fact that PB did not bind to the receptor suggest that chemicals other than "pure MC-type' inducers can bind to the cytosolic receptor. Affinity of the binding dictates the relative potency of given PCB congeners as inducers of cytochrome P-448.

Potent induction of rat liver microsomal, drug-metabolizing enzymes by 2,3,3',4,4',5-hexabromobiphenyl, a component of fireMaster

The multistep synthesis and purification of 2,3,3',4,4',5-hexabromobiphenyl (HBBp) is described. Capillary gas chromatography revealed that HBBp comprises 0.05% of the industrial polybrominated biphenyl (PBB) mixture, fireMaster BP-6 (lot 7062). When administered to immature male Wistar rats, HBBp caused a dose-dependent increase in (a) the activity of benzo[a]pyrene (B[a]P) hydroxylase (AHH) and 4-chlorobiphenyl (4-CBP) hydroxylase and (b) the concentration of cytochrome P-450. Sodium dodecyl sulfate (SDS)-gel electrophoresis indicated that these increases in cytochrome P-450 and cytochrome P-450-dependent monooxygenase activities were accompanied by a dose-dependent intensification of a protein of relative molecular weight (Mr) 55 000 which comigrated with the major 3-methylcholanthrene(MC)-inducible form of cytochrome P-450 (i.e., cytochrome P-448). Like MC, but in contrast to phenobarbitone (PB), HBBp competitively displaced 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin ([3H]-TCDD) from the cytosolic protein thought to be the receptor for cytochrome P-448 induction. The results indicate that HBBp is a potent inducer of cytochrome P-448 and as such is the third MC-type inducer identified in fireMaster BP-6.

Aryl hydrocarbon hydroxylase (AHH) induction by polybrominated biphenyls (PBBs): enchancement by photolysis

Irradiation of the commercial polybrominated biphenyl (PBB( mixture, fireMaster BP-6, in cyclohexane solution at 300 nm for 930 min resulted in a marked diminution of the major components of the mixture. Administration of the photolyzed PBB mixture of fireMaster BP-6 to immature male Wistar rats caused both dose-related decreases in thymus weight and increase in hepatic microsomal benzo[a]pyrene hydroxylase (AHH), 4-dimethylaminoantipyrine N-demethylase and NADPH-cytochrome c reductase activities and cytochrome P-450 content. The dose effecting half-maximal AHH induction for the photolyzed PBBs (9 mg . KG-1) was approximately 6 times lower than that of fireMaster BP-6 (50 mg. kg-1). Furthermore, the concentration of photolyzed PBBs (2 micrometers) required to displace 50% of the specifically-bound [3H] TCDD from its high-affinity cytosolic Ah receptor was approximately 150 times lower than that required for fireMaster BP-6 (300 micrometers), as measured by sucrose density gradient centrifugation analysis. The results suggest that the photolysis of the commercial PBB mixture yields products which possess increased biologic activity.

Octachloronaphthalene induction of hepatic microsomal aryl hydrocarbon hydroxylase activity in the immature male rat

Administration of octachloronaphthalene to immature male Wistar rats resulted in a dose-dependent increase in several enzymic, electrophoretic and spectral parameters associated with induction of the hepatic microsomal enzymes. Compared to corn-oil (control)treated animals octachloronaphthalene (150 mumol . kg-1) induced hepatic cytochrome P-450 (1.5-fold), benzo [alpha] pyrene hydroxylase (18-fold) and 4-chlorobiphenyl hydroxylase (18-fold) enzyme activities. In addition to increases in the relative peak intensities of the reduced microsomal cytochrome P-450 : CO and ethylisocyanide (EIC) difference spectra the peak maxima were observed at 448.5 and 452.2/428.0 nm, respectively. The effects of administering octachloronaphthalene to the rat were similar to those observed after pretreatment with 3-methylcholanthrene (MC) and electrophoresis of the induced microsomal proteins showed that both compounds enhance heme-staining peptides with comparable electrophoretic mobilities. Moreover coadministration of MC (3 x 100 mumol . kg-1) and octachloronaphthalene (2 x 150 mumol . kg-1) indicated that their inductive effects were not additive. It was concluded that octachloronaphthalene was an MC-type inducer of hepatic microsomal enzymes.