Predicting Deformity Correction of Growth Modulation in Late-onset Tibia Vara

BACKGROUND

Growth modulation in late-onset tibia vara (LOTV) has been reported to yield variable results. We hypothesized that parameters of deformity severity, skeletal maturity, and body weight could predict the odds of a successful outcome.

METHODS

A retrospective review of tension band growth modulation for LOTV (onset ≥8 y) was performed at 7 centers. Tibial/overall limb deformity and hip/knee physeal maturity were assessed on preoperative anteroposterior standing lower-extremity digital radiographs. Tibial deformity change with first-time lateral tibial tension band plating (first LTTBP) was assessed by medial proximal tibia angle (MPTA). Effects of a growth modulation series (GMS) on overall limb alignment were assessed by mechanical tibiofemoral angle (mTFA) and included changes from implant removal, revision, reimplantation, subsequent growth, and femoral procedures during the study period. The successful outcome was defined as radiographic resolution of varus deformity or valgus overcorrection. Patient demographics, characteristics, maturity, deformity, and implant selections were assessed as outcome predictors using multiple logistic regression.

RESULTS

Fifty-four patients (76 limbs) had 84 LTTBP procedures and 29 femoral tension band procedures. For each 1-degree decrease in preoperative MPTA or 1-degree increase in preoperative mTFA the odds of their successful correction decreased by 26% in the first LTTBP and 6% by GMS, respectively, controlling for maturity. The change in odds of success for GMS assessed by mTFA was similar when controlling for weight. Closure of a proximal femoral physis decreased the odds of success for postoperative-MPTA by 91% with first LTTBP and for final-mTFA by 90% with GMS, controlling for preoperative deformity. Preoperative weight ≥100 kg decreased the odds of success for final-mTFA with GMS by 82%, controlling for preoperative mTFA. Age, sex, race/ethnicity, type of implant, and knee center peak value adjusted age (a method for bone age) were not predictive of outcome.

CONCLUSIONS

Resolution of varus alignment in LOTV using first LTTBP and GMS, as quantified by MPTA and mTFA, respectively, is negatively impacted by deformity magnitude, hip physeal closure, and/or body weight ≥100 kg. The presented table, utilizing these variables, is helpful in the prediction of the outcome of the first LTTBP and GMS. Even if complete correction is not predicted, growth modulation may still be appropriate to reduce deformity in high-risk patients.

LEVEL OF EVIDENCE

Level III.

Predicting Success of Deformity Correction With Tension Band Plating in Early-Onset Tibia Vara

BACKGROUND

Angular deformity correction with tension band plating has not been as successful in early-onset tibia vara (EOTV) as it has been in other conditions. Our hypothesis is that perioperative factors can predict the success of lateral tibial tension band plating (LTTBP) in patients with EOTV.

METHODS

A retrospective review was performed at 7 centers evaluating radiographic outcomes of LTTBP in patients with EOTV (onset <7 y of age). Single-event tibial LTTBP outcome was assessed through medial proximal tibial angle (MPTA). The final limb alignment following comprehensive limb growth modulation (CLGM), which could include multiple procedures, was assessed by mechanical axis zone (MAZone), mechanical tibio-femoral angle (mTFA), and mechanical axis deviation (MAD). Preoperative age, weight, deformity severity, medial physeal slope, and Langenskiöld classification +/- modification were investigated as predictors of outcome. Success was defined as the correction or overcorrection to normal age-adjusted alignment. The minimum follow-up was 2 years except when deformity correction, skeletal maturity, or additional surgery occurred.

RESULTS

Fifty-two patients with 80 limbs underwent 115 tibial LTTBP procedures at a mean age of 5.3 y, including 78 primary, 21 implant revisions, and 15 reimplantations for recurrence. Tibial LTTBP resulted in a mean change of +8.6 o in MPTA and corrected 53% of tibias. CLGM resulted in MAD correction for 54% of limbs.Univariate analysis showed that success was best predicted by preoperative age, weight, MPTA, and MAD. Multivariate analysis identified that preoperative-MPTA/MAD and preoperative-weight<70 kg were predictive of MPTA and MAD correction, respectively. The probability of success tables are presented for reference.

CONCLUSION

Successful correction of MPTA to age-adjusted norms following a single-event LTTBP occurred in 53% of tibias and was best predicted by preoperative-MPTA and preoperative body weight <70 kg. Comprehensive growth modulation corrected limbs in 54%. The probability of correction to age-adjusted MAD is best estimated by preoperative-MAZone 1 or 2 (MAD ≤40 mm). Limbs with preoperative-MAD>80 mm improved, but ultimately all failed to correct completely with CLGM. Osteotomy may need to be considered with these severe deformities. While modified Langenskiöld classification and medial physeal slope have been shown to predict the outcome of osteotomy, they were not predictive for LTTBP. Change in MPTA was common after physeal untethering.

LEVEL OF EVIDENCE

Level-III.

Femoral Deformity in Tibia Vara and Its Response to Growth Modulation

BACKGROUND

While tibia vara is a disorder of the proximal tibial physis, femoral deformity frequently contributes to the overall limb malalignment. Our purpose was to determine how femoral varus deformity in tibia vara responds to growth modulation, with/without lateral tension band plating (LTBP) to the femur.

METHODS

One-hundred twenty-seven limbs undergoing LTBP for tibia vara were reviewed. All had tibial LTBP and 35 limbs also had femoral LTBP for varus. Radiographs were measured for correction of the mechanical lateral distal femoral angle (mLDFA) and mechanical axis deviation (MAD). Preoperative-femoral varus was defined with an age-adjusted guide: mLDFA >95 degrees for 2 to below 4 years and mLDFA >90 degrees for 4 to 18 years. The 35 limbs having femoral LTBP were compared with 50 limbs with femoral varus and no femoral LTBP. In addition, 42 limbs that did not have preoperative-femoral varus were followed. Patients with early-onset (below 7 y) tibia vara were compared with those with late-onset (≥8 y). Outcome success was based on published age-adjusted mLDFA and MAD norms.

RESULTS

Following femoral LTBP, the mean mLDFA decreased from 98.0 to 87.1 degrees. All femurs had some improvement, with 28/35 femurs (80%) achieving complete correction. One limb, with late follow-up, overcorrected, requiring reverse (medial) femoral tension band plating.For the 50 limbs with femoral varus and only tibial LTBP, 16/22 limbs (73%) with early-onset and 11/28 limbs (39%) with late-onset completely corrected their femoral deformities. If the limb had preoperative-femoral varus, femoral LTBP statistically correlated with successful mLDFA correction and improvement of MAD, only in the late-onset group.Forty-two limbs, without preoperative-femoral varus, had no change in their mean mLDFA of 87 degrees. However, 4 femurs (10%) ended with posttreatment varus.

CONCLUSIONS

Femoral LTBP is effective in correcting femoral varus deformity in the tibia vara. For femoral varus associated with late-onset tibia vara, femoral LTBP should be considered. Those that had femoral LTBP had statistically more successful femoral and overall limb varus correction. However, in early-onset tibia vara, with associated femoral varus, observation is warranted because 73% of femurs are corrected without femoral intervention. This study was underpowered to show additional improvement with femoral LTBP in the early-onset group. Even limbs with normal femoral alignment, should be observed closely for the development of femoral varus, during tibial LTBP treatment for tibia vara.

LEVEL OF EVIDENCE

Level III.

Guided Growth for Varus Deformity Following Early Tibial Osteotomy in Infantile Tibia Vara-A Multi-Center Study

BACKGROUND

Despite early osteotomy, many patients with infantile tibia vara (ITV) have persistent or recurrent varus deformity and disordered growth at the medial proximal tibial physis. Our hypothesis was that lateral tibial tension band plating (LTTBP) could guide correction.

METHODS

A retrospective review at 6 centers of 15 patients (16 extremities) was performed of LTTBP for varus deformity following early osteotomy in ITV, diagnosed≤4years of age. Correction of deformity parameters on digital standing anteroposterior lower extremity radiographs determined outcome.

RESULTS

Twenty-two LTTBP procedures were performed at mean age of 7.5 years, including 4 revisions for implant failure and 2 reimplantations for recurrence. Single event LLTBP, improved the medial proximal tibial angle with a mean change of 13.4 degrees (0.39 degrees/month). Eleven limbs had preoperative mechanical lateral distal femoral angle (mLDFA)>90 degrees. While n degree femoral procedures were performed, at study end, 11 femurs had mechanical lateral distal femoral angle≤90°. Pretreatment, 13 extremities had mechanical axis zone (MAZone) III varus (81%) and 3 had MAZone II varus (19%). LTTBP's were able to initially correct 13 limbs to MAZone I or valgus but 4 limbs rebounded to MAZone II varus after implant removal. Final limb alignment, after all surgeries and rebound, included 9 in MAZone I, 5 in MAZone II varus and 2 in MAZone III varus. Average follow-up was 3.0 years at mean 10.7 years of age. Fifteen procedures resulted in improvement in MAZone and 7 had no change. On average, those that improved were younger (7.3 vs. 8.0 y), weighed less (45.5 kg with body mass index 26.5 kg/m 2 vs. 67.8 kg and body mass index 35.7 kg/m 2 ), had lower mechanical axis deviation (37.1 mm vs. 43.9 mm), lower medial physeal slope (61.7 vs. 68.7 degrees) and had a higher percentage of open triradiate phases (87 vs. 57%).

CONCLUSIONS

LTTBP for residual varus, after initial osteotomy in ITV, resulted in 81% of limbs initially achieving MAZone I or valgus with implant failure revisions and femoral remodeling. Rebound after implant removal reduced the corrected rate to 56%. Ninety-four percent avoided osteotomy during the study period.

LEVEL OF EVIDENCE

IV.

Limited evidence for graft selection in pediatric ACL reconstruction: a narrative review

Anterior cruciate ligament reconstruction is the preferred treatment to anterior cruciate ligament injury. With the increase in anterior cruciate ligament injuries in both adults and skeletally immature patients comes the need for individualized anterior cruciate ligament reconstruction graft selection whether it is the type of graft (auto vs. allograft) or the harvesting site (hamstrings, iliotibial band, quadriceps, patella). Several factors need to be considered preoperatively in order to optimize the patients’ recovery and restore anterior cruciate ligament strength and function. These include age and bone maturity, preoperative knee flexor/extensor strength, sport participation, patient’s needs and anatomical characteristics. This paper aims at bringing evidence supporting the use of a personalized approach in graft selection for faster and more efficient return to sport and propose a theoretical framework to support the approach.

Increasing hospital admissions for patellar instability: a national database study from 2004 to 2017

Objectives: Epidemiology of patellar instability is not fully characterized, as some studies have produced conflicting information or been drawn from limited populations. In this study, we used the Pediatric Health Information System (PHIS) database to examine trends in admissions for patellar instability throughout the United States. We hypothesized that there would be an increasing rate of patellar instability admissions in recent years. Secondarily, we examined how demographic factors and insurance status relate to admissions for patellar instability.Methods: This study queried the Pediatric Health Information System (PHIS). Patients with ICD 9 & 10 codes 8363, 8364, 71,785, M221.0, S83.001, S83.002, S83.003, S83.004, S83.005, and S83.006, were abstracted from PHIS. We included all patients admitted with patellofemoral dislocations that were reported in the PHIS database between 1 January 2004 and 30 April 2017. The rate of patellar instability admissions was examined as well as demographic factors and insurance status.Results: An estimated total of 25,413 admissions for patellar instability were identified by the search of the PHIS database; 15,444 (60.8%) were female patients and 9,966 (39.2%) were male. The adjusted number of admissions per reporting hospital significantly increased over the years studied (r = 0.775, p < 0.001), from 14.5 admissions per reporting hospital in 2004 to 86.0 admissions per reporting hospital in 2016. Of all patellar instability admissions, 55.0% were white, 20.4% were black, 1.7% were Asian, and 22.9% were unknown race. A larger number of admissions occurred in patients with insurance status other than Medicaid in every year data were collected.Conclusions: Based on a PHIS database search, pediatric hospital admissions for patellar instability are steadily increasing. The majority of patients admitted for patellar instability are female, white, and have insurance other than Medicaid. Males admitted for patellar instability tended to be older than females admitted for the same.Level of evidence: II.

Age-Appropriate Pediatric Sports Patient-Reported Outcome Measures and Their Psychometric Properties: A Systematic Review

BACKGROUND

Phenomena including early sport specialization and year-round training and competition have contributed to an increase in pediatric sports injuries. There has been a concomitant increase in clinical studies focusing on physically active children and adolescents. These studies include investigations of patient-reported outcome measures (PROMs). While the use of PROMs in pediatric orthopaedics has been increasing, PROMs are often inappropriately applied to study populations for whom they are not specifically validated.

PURPOSE

The purpose of this study was to establish a comprehensive list of pediatric- and adolescent-validated PROMs and catalog their psychometric properties as a resource for clinicians and researchers.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A systematic review of articles in PubMed, Embase, and the Cochrane library was performed to identify articles developing and validating PROMs appropriate for use in pediatric sports medicine research. The inclusion criteria were as follows: age <18 years, the use of surveys and questionnaires, and the presence of sports-related injuries. The psychometric properties of included PROMs were entered into an electronic database.

RESULTS

Our search strategy identified 14,708 unique articles, among which 139 studies (0.9%) were included in the final data analysis. Forty-seven distinct PROMs were identified, as well as 160 cross-cultural adaptations. While all identified PROMs were validated in physically active young participants, only 12 (26%) were specifically created initially for active children. Thirty (64%) PROMs were health-related quality-of-life measures; 13 (28%) were psychosocial measures; and 4 (9%) were activity scales. No studies validated PROMs for use with wrist/hand injuries, and only 1 PROM each was valid for hip, back/spinal, and foot/ankle injuries in pediatric sports.

CONCLUSION

This systematic review yielded 47 unique PROMs reliable and valid for use in pediatric and adolescent sports medicine. This list will unify clinicians and researchers in using these age-appropriate measures while identifying areas that are still in need of appropriate PROMs for young athletes.

Anterior cruciate ligament tears in children and adolescents: a meta-analysis of nonoperative versus operative treatment

BACKGROUND

Debate regarding the optimal initial treatment for anterior cruciate ligament (ACL) injuries in children and adolescents has not resulted in a clear consensus for initial nonoperative treatment or operative reconstruction.

HYPOTHESIS/PURPOSE

The purpose of this meta-analysis was to systematically analyze aggregated data from the literature to determine if a benefit exists for either nonoperative or early operative treatment for ACL injuries in the pediatric patient. The hypothesis was that combined results would favor early operative reconstruction with respect to posttreatment episodes of instability/pathological laxity, symptomatic meniscal tears, clinical outcome scores, and return to activity.

STUDY DESIGN

Meta-analysis.

METHODS

A literature selection process included the extraction of data on the following clinical variables: symptomatic meniscal tears, return to activities, clinical outcome scores, return to the operating room, and posttreatment instability/pathological laxity. A symptomatic meniscal tear was defined as occurring after the initial presentation, limiting activity, and requiring further treatment. Instability/pathological laxity was defined for the sake of this study as having an episode of giving way, a grade ≥2 Lachman/pivot-shift test result, or a side-to-side difference of >4 mm as measured by the KT-1000 arthrometer. All studies were evaluated using a formal study quality analysis. Meta-analysis was conducted for aggregated data in each category.

RESULTS

Six studies (217 patients) comparing operative to nonoperative treatment and 5 studies (353 patients) comparing early to delayed reconstruction were identified. Three studies reported posttreatment instability/pathological laxity; 13.6% of patients after operative treatment experienced instability/pathological laxity compared with 75% of patients after nonoperative treatment (P < .01). Two studies reported symptomatic meniscal tears; patients were over 12 times more likely to have a medial meniscal tear after nonoperative treatment than after operative treatment (35.4% vs 3.9%, respectively; P = .02). A significant difference in scores between groups was noted in 1 of 2 studies reporting International Knee Documentation Committee (IKDC) scores (P = .002) and in 1 of 2 studies reporting Tegner scores (P = .007). Two studies reported return to activity; none of the patients in the nonoperative groups returned to their previous level of play compared with 85.7% of patients in the operative groups (P < .01). Study quality analysis revealed that the majority of the studies were inconsistent in reporting outcomes.

CONCLUSION

Meta-analysis revealed multiple trends that favor early surgical stabilization over nonoperative or delayed treatment. Patients after nonoperative and delayed treatment experienced more instability/pathological laxity and inability to return to previous activity levels than did patients treated with early surgical stabilization.

Approach to the pediatric supracondylar humeral fracture with neurovascular compromise

Supracondylar fractures of the humerus are exceedingly common in pediatric patients but may present treatment challenges when complicated by neurovascular compromise. Patients presenting with poor perfusion should be treated with urgent reduction because this is a limb-threatening emergency. If perfusion does not improve, or if a previously perfused extremity loses perfusion after reduction, arterial exploration is warranted. Controversy exists over whether to observe or explore a reduced, perfused, but pulseless extremity with a supracondylar fracture. Minimal management requires that these injuries be carefully monitored for 48 hours for loss of perfusion or the development of compartment syndrome. In general, nerve injuries accompanying supracondylar fractures of the humerus are neurapraxias and may be treated conservatively; however, nerve palsy with accompanying pulselessness warrants immediate exploration. Patients should be treated more urgently if excessive swelling, antecubital ecchymosis, skin puckering, an absent pulse, or fractures in the same limb are present. If a hand is not perfused or compartments are firm, emergent treatment should be considered.

Anti-PR3 immune responses induce segmental and necrotizing glomerulonephritis

Wegener's granulomatosis (WG) is a life-threatening autoimmune vasculitis that affects lungs, kidneys and other organs. A hallmark of WG is the presence of classic anti-neutrophil cytoplasmic antibodies (c-ANCA) against self-proteinase 3 (PR3). Little is known about the role of these antibodies and PR3-specific immune responses in disease development. In this study, we demonstrate that PR3-specific autoimmune responses are pathogenic in non-obese diabetic (NOD) mice with an impaired regulatory arm of the immune response. Immunization of autoimmunity prone NOD mice with rmPR3 (recombinant mouse PR3) in complete Freund's adjuvant (CFA) resulted in high levels of c-ANCA, without detectable disease development. However, when splenocytes from these immunized mice were transferred into immunodeficient NOD-severe combined immunodeficiency (SCID) mice, the recipient mice developed vasculitis and severe segmental and necrotizing glomerulonephritis. No disease developed in NOD-SCID mice that received splenocytes from the CFA-alone-immunized donors (controls), indicating that disease development depends upon PR3-specific immune responses. In contrast to the pathology observed in NOD-SCID mice, no disease was observed when splenocytes from rmPR3-immunized C57BL/6 mice were transferred into immunodeficient C57BL/6-RAG-1(-/-) mice, suggesting that complex and probably multi-genetic factors play a role in the regulation of disease development.

The clinical significance of malignant pleural effusions in patients with optimally debulked ovarian carcinoma

BACKGROUND

The objective of this study was to determine the impact of malignant pleural effusions on survival in patients with optimally debulked, advanced epithelial ovarian carcinoma.

METHODS

The authors conducted a retrospective review of all patients with advanced epithelial ovarian carcinoma who underwent optimal primary cytoreduction at their institution between January 1987 and August 2000. Survival rates were compared between patients with optimally debulked Stage IIIC epithelial ovarian carcinoma and patients with optimally debulked Stage IV epithelial ovarian carcinoma (according to the International Federation of Gynecology and Obstetrics [FIGO] staging system) based on cytology-proven malignant pleural effusions.

RESULTS

Ninety-nine patients were identified, and 97 of those patients were evaluable. The group with Stage IIIC disease included 76 patients, and the group with Stage IV disease included 21 patients. The median age at diagnosis was 55 years (range, 26-88 years). The majority of patients received platinum-based chemotherapy after undergoing optimal primary cytoreduction. Age, tumor grade and histology, and the percentage of patients with ascites were similar in the two groups. The median survival rate was 58 months for patients who had Stage IIIC disease and 30 months for patients who had Stage IV disease (P = 0.016).

CONCLUSIONS

Although both groups underwent optimal cytoreduction in the abdomen/pelvis and were treated in a similar fashion, the median survival rate of patients with malignant pleural effusions was significantly shorter than the survival of patients without effusions. Many factors that led to or were manifested by pleural effusions, such as undetected bulky residual intrathoracic disease, may have been the cause for this survival difference. In the patients with effusions, one or more of these contributing factors may have led to the observed decreased survival rate, warranting further investigation.

Ten-year experience with laparoscopy on a gynecologic oncology service: analysis of risk factors for complications and conversion to laparotomy

OBJECTIVE

The purpose of this study was to analyze our initial 10-year experience with laparoscopy and to determine risk factors for complications and conversions to laparotomy for technical difficulty.

STUDY DESIGN

We reviewed the charts of all laparoscopic procedures from January 1991 through December 2000 and divided the procedures into 4 levels on the basis of the degree of difficulty: level I, diagnostic; level II, procedures on the uterus and/or adnexa; level III, second look operations for malignancy; and level IV, lymphadenectomies/other complex procedures. Complications were graded from 1 (mild) to 5 (death). Standard univariate and multivariate analyses were performed.

RESULTS

We identified 1451 evaluable procedures. The number of complications was as follows: grades 1 to 5, 129 complications (9%); grades 3 to 5, 36 complications (2.5%). On multivariate analysis, older age ( P = .03), previous radiation ( P = .03), and malignancy ( P = .006) were associated with an increased risk of complications grades 3 to 5. Complication rates for grades 3 to 5 for patients with malignancy versus benign disease was 4% versus 1%, respectively. Technical difficulty led to conversion to laparotomy in 105 cases (7%). Previous abdominal surgery ( P < .001) significantly increased the rate of conversion to laparotomy; more complex, higher procedure levels were associated with a significant decrease in conversions ( P = .005).

CONCLUSION

Both simple and complex laparoscopic procedures can be performed by a gynecologic oncology service with a low rate of complications and conversions to laparotomy. Older age, malignancy, previous radiation therapy, and previous abdominal surgery were identified as significant risk factors for complications and/or conversion and should be taken into account in patient selection, preoperative counseling, and surgical planning.

Improved optimal cytoreduction rates for stages IIIC and IV epithelial ovarian, fallopian tube, and primary peritoneal cancer: a change in surgical approach

OBJECTIVE

To determine the impact of the incorporation of extensive upper abdominal debulking procedures on the rates of optimal primary cytoreduction and complications in stages IIIC and IV epithelial ovarian, fallopian tube, and primary peritoneal carcinomas.

METHODS

Two groups of patients were identified for comparison. Group 1, the control group, consisted of 70 consecutive patients who underwent "standard" primary cytoreductive surgery before May 2000. Group 2, the study group, was composed of 70 consecutive patients who underwent surgery after January 2001, during which time, a more comprehensive debulking of upper abdominal disease was used, including diaphragm stripping/resection, splenectomy, distal pancreatectomy, liver resection, resection of porta hepatis tumor, and cholecystectomy.

RESULTS

The median age of the entire cohort was 60 years (range, 36-88 years). The majority had stage IIIC disease (86%) and serous histology (76%). Optimal cytoreduction (residual disease </=1 cm) rates were 50% for group 1 and 76% for group 2 (P < 0.01). Patients in group 2 were more likely to have undergone extensive procedure(s) (27% versus 3%; P < 0.001). Operative time and estimated blood loss were greater in group 2 than group 1 (264 versus 174 min, 880 versus 460 cc, respectively; P < 0.001 for both). Complication rates and length of hospitalization were not significantly different between the two groups.

CONCLUSION

The use of extensive upper abdominal surgical procedures significantly increased the rate of optimal primary cytoreduction. Although operative time and estimated blood loss were increased, the rate of major complications and length of hospitalization remained the same.

Disruption of redox homeostasis in tumor necrosis factor-induced apoptosis in a murine hepatocyte cell line

Tumor necrosis factor (TNF) is a mediator of the acute phase response in the liver and can initiate proliferation and cause cell death in hepatocytes. We investigated the mechanisms by which TNF causes apoptosis in hepatocytes focusing on the role of oxidative stress, antioxidant defenses, and mitochondrial damage. The studies were conducted in cultured AML12 cells, a line of differentiated murine hepatocytes. As is the case for hepatocytes in vivo, AML12 cells were not sensitive to cell death by TNF alone, but died by apoptosis when exposed to TNF and a small dose of actinomycin D (Act D). Morphological signs of apoptosis were not detected until 6 hours after the treatment and by 18 hours approximately 50% of the cells had died. Exposure of the cells to TNF+Act D did not block NFkappaB nuclear translocation, DNA binding, or its overall transactivation capacity. Induction of apoptosis was characterized by oxidative stress indicated by the loss of NAD(P)H and glutathione followed by mitochondrial damage that included loss of mitochondrial membrane potential, inner membrane structural damage, and mitochondrial condensation. These changes coincided with cytochrome C release and the activation of caspases-8, -9, and -3. TNF-induced apoptosis was dependent on glutathione levels. In cells with decreased levels of glutathione, TNF by itself in the absence of transcriptional blocking acted as an apoptotic agent. Conversely, the antioxidant alpha-lipoic acid, that protected against the loss of glutathione in cells exposed to TNF+Act D completely prevented mitochondrial damage, caspase activation, cytochrome C release, and apoptosis. The results demonstrate that apoptosis induced by TNF+Act D in AML12 cells involves oxidative injury and mitochondrial damage. As injury was regulated to a larger extent by the glutathione content of the cells, we suggest that the combination of TNF+Act D causes apoptosis because Act D blocks the transcription of genes required for antioxidant defenses.

Protection of acute myeloblastic leukemia cells against apoptotic cell death by high glutathione and gamma-glutamylcysteine synthetase levels during etoposide-induced oxidative stress

BACKGROUND

Etoposide mediates its cytotoxicity by inducing apoptosis. Thus, mechanisms which regulate apoptosis should also affect drug resistance. Oxidants and antioxidants have been shown to participate in the regulation of apoptosis. We were interested in studying whether responsiveness of acute myeloblastic leukemia (AML) cells to etoposide is mediated by oxidative stress and glutathione levels.

PATIENTS AND METHODS

Two subclones of the OCI/AML-2 cell line which are etoposide-sensitive (ES), and etoposide-resistant (ER), were established by the authors at the University of Oulu, and used as models. Assays for apoptosis included externalization of phosphatidylserine (as evidenced by annexin V binding), and caspase activation as indicated by cleavage of poly(ADP-ribose)polymerase (Western blotting). Peroxide formation was analyzed by flow cytometry. Glutathione and gamma-glutamylcysteine synthetase (gamma-GCS) levels were determined spectrophotometrically and by Western blotting, respectively.

RESULTS

Etoposide-induced apoptosis was evident 12 hours after treatment in the ES subclone, but was apparent in the ER subclone only after 24 hours. The basal glutathione and gamma-GCS levels were higher in the ER than the ES subclone. Etoposide increased peroxide formation in both subclones after 12-hour exposure. Significant depletion of glutathione was observed in the ES subclone during etoposide exposure, while glutathione levels were maintained in the ER subclone. In neither of the subclones was induction of gamma-GCS observed during 24-hour exposure to etoposide. Furthermore, the catalytic subunit of gamma-GCS was cleaved during apoptosis, concurrent with depletion of intracellular glutathione. When glutathione was depleted by treatment with buthionine sulfoximine, a direct inhibitor of gamma-GCS, the sensitivity to etoposide was increased, particularly in the ER subclone.

CONCLUSIONS

The results underline the significance of glutathione biosynthesis in the responsiveness of AML cells to etoposide. The molecular mechanisms mediating glutathione depletion during etoposide exposure might include the cleavage of the catalytic subunit of gamma-GCS.

Human DU145 prostate cancer cells overexpressing mitogen-activated protein kinase phosphatase-1 are resistant to Fas ligand-induced mitochondrial perturbations and cellular apoptosis

Recent studies have suggested that MAP kinase phosphatase 1 (MKP-1) is overexpressed in prostate cancer. To evaluate the role of MKP-1 in regulating cell death and tumor growth in prostate cancer, MKP-1 was conditionally overexpressed in the human prostate cancer cell line DU145. Overexpression of MKP-1 in DU145 cells blocked activation of stress-activated protein kinase (SAPK/JNK). MKP-1 overexpression in DU-145 cells was also found to inhibit Fas ligand (FasL)-induced apoptosis, as well as block the activation of caspases by Fas engagement. In addition, MKP-1 blocked the activation of apoptosis by transfected MEKK-1 and ASK-1, presumably through its inhibition of the SAPK/JNK family of enzymes. MKP-1 blocked the ability of FasL to induce loss of mitochondrial transmembrane potential (delta Psi(m)), suggesting that MKP-1 acts upstream of mitochondrial pro-apoptotic events induced by FasL and that the SAPK/JNK pathway may form the signaling link between Fas receptor and mitochondrial dysfunction. Thus, MKP-1 overexpression in prostate cancer may play a role in promoting prostate carcinogenesis by inhibiting FasL-induced cell death.

Evaluation and management of dyslipoproteinemia in children

The major goal of the evaluation and management of DLP in children is to provide safe and effective therapy with lifestyle modification. There is a strong rationale for the initiation of DLP treatment in childhood to limit the earliest stages of atherosclerosis, to establish lifelong lifestyle changes in diet and activity, and to limit the acquisition of additional CVD risk factors such as smoking and obesity. The NCEP has recommended screening for children with a parent with total cholesterol of 240 mg/dL or greater or a parent or grandparent with onset of CVD before age 55 years. Clinical evaluation and management are based on an LDL-C level of 130 mg/dL or greater. This approach to screening has a low sensitivity to identify children with DLP. Initial therapy is with a step 1 diet followed by the step 2 diet if necessary. Medications are reserved for older children with LDL-C of 190 mg/dL or greater after diet therapy or 160 mg/dL or greater with other CVD risk factors.

Conditional expression of mitogen-activated protein kinase phosphatase-1, MKP-1, is cytoprotective against UV-induced apoptosis

UV irradiation induces apoptosis in U937 human leukemic cells that is accompanied by the activation of both the stress-activated protein kinase (SAPK) and p38 mitogen-activated protein kinase (MAPK) signal transduction pathways. The MAPK phosphatase, MKP-1, is capable of inactivating both SAPK and p38 MAPK in vivo. To determine whether MKP-1-mediated inhibition of SAPK and/or p38 MAPK activity provided cytoprotection against UV-induced apoptosis, a U937 cell line conditionally expressing MKP-1 from the human metallothionein IIa promoter was established. Conditional expression of MKP-1 was found to abolish UV-induced SAPK and p38 MAPK activity, and inhibit UV-induced apoptosis as judged by both morphological criteria and DNA fragmentation. MKP-1 was also found to inhibit other biochemical events associated with apoptosis, including activation of caspase-3 and the proteolytic cleavage of the caspase-3 substrate, poly(ADP ribose) polymerase. These findings demonstrate that MKP-1 acts at a site upstream of caspase activation within the apoptotic program. The cytoprotective properties of MKP-1 do not appear to be mediated by its ability to inhibit p38 MAPK because the p38 MAPK specific inhibitor SB203580 had no effect on UV-induced apoptosis in U937 cells. Furthermore, by titrating the level of MKP-1 expression it was found that MKP-1 inhibited UV-induced SAPK activity, DNA fragmentation, and caspase-3 activation in a similar dose-dependent manner. The dual-specificity phosphatase, PAC1, which does not inhibit UV-induced activation of SAPK, did not provide a similar cytoprotection against UV-induced apoptosis. These results are consistent with a model whereby MKP-1 provides cytoprotection against UV-induced apoptosis by inhibiting UV-induced SAPK activity.

Conditional expression of the mitogen-activated protein kinase (MAPK) phosphatase MKP-1 preferentially inhibits p38 MAPK and stress-activated protein kinase in U937 cells

Phorbol ester tumor promoters, such as phorbol 12-myristate 13-acetate (PMA), are potent activators of extracellular signal-regulated kinase 2 (ERK2), stress-activated protein kinase (SAPK), and p38 mitogen-activated protein kinase (MAPK) in U937 human leukemic cells. These kinases are regulated by the reversible dual phosphorylation of conserved threonine and tyrosine residues. The dual specificity protein phosphatase MAPK phosphatase-1 (MKP-1) has been shown to dephosphorylate and inactivate ERK2, SAPK, and p38 MAPK in transient transfection studies. Here we demonstrate that PMA treatment induces MKP-1 protein expression in U937 cells, which is detectable within 30 min with maximal levels attained after 4 h. This time course coincides with the rapid inactivation of PMA-induced SAPK activity, but not ERK2 phosphorylation, which remains elevated for up to 6 h. To examine directly the role of MKP-1 in the regulation of these protein kinases in vivo, we established a U937 cell line that conditionally expresses MKP-1 from the human metallothionein IIa promoter. Conditional expression of MKP-1 inhibited PMA-induced ERK2, SAPK, and p38 MAPK activity. By titrating the levels of MKP-1 expression from the human metallothionein IIa promoter, however, it was found that p38 MAPK and SAPK were much more sensitive to inhibition by MKP-1 than ERK2. This differential substrate specificity of MKP-1 can be functionally extended to nuclear transcriptional events in that PMA-induced c-Jun transcriptional activity was more sensitive to inhibition by MKP-1 than either Elk-1 or c-Myc. Conditional expression of MKP-1 also abolished the induction of endogenous MKP-1 protein expression in response to PMA treatment. This negative feedback regulatory mechanism is likely due to MKP-1-mediated inhibition of ERK2, as studies utilizing the MEK1/2 inhibitor PD98059 suggest that ERK2 activation is required for PMA-induced MKP-1 expression. These findings suggest that ERK2-mediated induction of MKP-1 may play an important role in preferentially attenuating signaling through the p38 MAPK and SAPK signal transduction pathways.

Ligation of membrane IgM stimulates a novel c-Jun amino-terminal domain kinase activity in Daudi human B cells

Stress-activated protein kinases (SAPK; also known as JNK for c-Jun N-terminal kinase) phosphorylate Ser63 and Ser73 in the amino-terminus of the c-Jun protein and potentiate its transcriptional activity. We have analysed phosphorylation of GST fusion proteins containing the c-Jun N-terminal domain by lysates of Daudi human B lymphoblastoid cells stimulated with medium or anti-IgM. Crosslinking membrane IgM (mIgM) results in an increase in phosphorylation of GST-c-Jun (5-89) in an antibody dose-dependent manner. The kinase activity specifically phosphorylates the c-Jun N-terminal domain since it does not phosphorylate GST or GST-JunB. The activity preferentially phosphorylates the substrate that contains the sites for in vivo phosphorylation by SAPK/JNK and requires the delta domain of c-Jun, which is also required for SAPK/JNK activity. However, the c-Jun N-terminal kinase activity induced by mIgM ligation is not precipitatable with anti-SAPK/JNK antibodies. In addition, unlike SAPK/JNKs, the mIgM-dependent c-Jun N-terminal kinase activity is not detectable in assays for renaturable kinase activity (in-gel assay) or in assays that test activities that bind to c-Jun (solid-phase assay). The increased phosphorylation of c-Jun N-terminal domain in response to mIgM ligation is unlikely to be due to mIgM-activated ERKs as it was not suppressed by a selective MEK inhibitor. Thus, the mIgM-induced activity is distinct from the known SAPK/JNKs and may represent a novel mechanism for c-Jun phosphorylation in response to mIgM engagement in human B cells.

Constitutively active MAP kinase kinase (MEK1) stimulates SAP kinase and c-Jun transcriptional activity in U937 human leukemic cells

Treatment of U937 human leukemic cells with the phorbol ester PMA, activates both mitogen-activated protein kinase (MAPK) and stress-activated protein kinase (SAPK), stimulates c-Jun phosphorylation and transcriptional activity, and induces a macrophage-like differentiation of U937 cells. The involvement of the MAPK pathway in mediating both the early phosphorylation and transcriptional activation events and the chronic differentiation of U937 cells was examined utilizing constitutively active MAPK kinase (MEK1) mutants. Transient expression of an activated MEK1 construct in U937 cells was found to stimulate MAPK and SAPK activity, as well as enhancing AP1-, SRE- and c-Jun-mediated transcriptional activity. Transient transfection of MAPK phosphatase-1 (MKP-1), a protein phosphatase which preferentially dephosphorylates and inactivates MAPK, inhibited the functional effects of both PMA and the constitutively active MEK1 mutants. To determine whether specific activation of the MEK/MAPK pathway was sufficient to induce hematopoietic differentiation, U937 cell lines were established that conditionally expressed the activated MEK1 mutant under the control of the human IIa metallothionein promoter. The induction of constitutively active MEK1 protein expression resulted in an increase in MEK1 activity, c-Jun and AP-1 transcriptional activity and an inhibition of U937 cell growth. However, this growth inhibition was not accompanied by U937 cell differentiation. These results suggest that a cross-talk mechanism exists between the MAPK and SAPK signal transduction pathways in U937 cells and that PMA-mediated SAPK activation may involve the MAPK pathway. Furthermore, selective activation of the MEK/MAPK pathway utilizing a constitutively active MEK1 mutant, while growth inhibitory, was not sufficient to induce the macrophage-like differentiation of U937 cells.

Stress-activated protein kinases bind directly to the delta domain of c-Jun in resting cells: implications for repression of c-Jun function

The transactivating function of the c-Jun proto-oncogene component of the AP-1 transcription factor is acutely regulated by a wide variety of cellular signals via modulation of phosphorylation of two serines (63 and 73). The viral oncoprotein, v-Jun, while containing homologous serines, is not phosphorylated in cells. A novel family of stress-activated protein kinases (SAPKs), also termed Jun N-terminal domain kinases (JNKs), are responsible for mediating S63/73 phosphorylation in response to a variety of cellular stimuli including tumor necrosis factor-alpha, heat stress and u.v. light. The p54 alpha 1, alpha 2, p54 beta and p46 beta SAPKs are shown to bind directly to c-Jun but not to v-Jun, with an absolute requirement for c-Jun amino acids 31-47, a region deleted in v-Jun. Inactive SAPKs tightly bind c-Jun in resting cells and may be a manifestation of the 'delta' inhibitor, a previously described repressor of c-Jun function.

In vitro association between the Jun protein family and the general transcription factors, TBP and TFIIB

Transcriptional activator proteins interact with the general transcription factors TATA-binding protein (TBP), TFIIB and/or other TBP-associated factors (TAFs). Using affinity chromatography we demonstrate that members of the Jun family of transcriptional activators interact with both TBP and TFIIB in vitro. TBP binds to both the N-terminal activation domain and C-terminal bZIP regions of c-Jun, whereas TFIIB binds to only the c-Jun bZIP domain. This interaction requires the dimerization of the Jun protein. The ability of the N-terminal activation domains of c-Jun, JunB, JunD and v-Jun to interact with TBP in vitro correlates with their transcriptional activity in vivo. Domain mapping experiments indicate that c-Jun interacts with the conserved C-terminus of TBP. Studies using a set of TFIIB inframe deletion mutants demonstrate that C-terminal amino acids 178-201 and 238-316 play an important role in modulating the interaction between TFIIB and c-Jun. Although phosphorylation of the c-Jun N-terminal activation domain stimulates c-Jun transcriptional activity in vivo, it has no effect on the ability of c-Jun to interact with either TBP or TFIIB in vitro. These data suggest that the Jun family of activator proteins may activate transcription by interacting with the general transcription factors TBP and TFIIB.

Phosphorylation of transcription factors

Many transcription factors are regulated by post-translational phosphorylation mechanisms. This chapter described several approaches that have been utilized to examine the phosphorylation of the c-Jun transcription factor. A combination of the techniques described in this chapter can be used to determine whether a transcription factor is phosphorylated in vivo, to analyze the sites of phosphorylation in vitro, and to permit the identification of putative protein kinases that may mediate this phosphorylation in vivo. Proteins labeled with 32P by either in vivo or in vitro techniques can be further analyzed by tryptic phosphopeptide mapping or phosphoamino acid analysis. These procedures have been described in detail elsewhere.

Multiple signal transduction pathways mediate c-Jun protein phosphorylation

A variety of protein kinases, including pp42 and pp54 mitogen-activated protein (MAP) kinases, p34cdc2, and a partially purified protein kinase from 4 beta-phorbol 12-myristate 13 alpha-acetate (PMA)-treated U937 cells have been shown to phosphorylate the NH2-terminal activation domain of c-Jun in vitro. To investigate the role of pp42 MAP kinase in mediating c-Jun phosphorylation in vivo, we have treated U937 monocytic leukemia cells with a variety of pharmacological agents, including PMA, cycloheximide, AIF4, and okadaic acid. Although all of these agents stimulated c-Jun phosphorylation, cycloheximide and okadaic acid had no effect on pp42 MAP kinase phosphorylation, suggesting that MAP kinase activation was not necessary for c-Jun phosphorylation in vivo. Because dominant-negative RasAsn17 has been shown to block the effects of PMA on pp42 MAP kinase phosphorylation, we assessed its effect on c-Jun phosphorylation by cotransfection with a truncated c-Jun construct (c-Jun234). We found that c-Jun234 was expressed only in the cytosol and was inducibly phosphorylated with kinetics similar to those of endogenous nuclear c-Jun. Furthermore, we found that RasAsn17 had no effect on PMA-induced phosphorylation of c-Jun234. Because Ha-Ras requires isoprenylation for membrane binding, we examined the effect of the isoprenylation inhibitors lovastatin and perillic acid on PMA-induced c-Jun phosphorylation. Pretreatment of U937 cells with these agents had no effect on PMA-induced c-Jun or pp42 MAP kinase phosphorylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-purification of mitogen-activated protein kinases with phorbol ester-induced c-Jun kinase activity in U937 leukaemic cells

Phorbol esters, such as phorbol myristate acetate (PMA), cause differentiation of U937 human monomyelocytic cells along the macrophage pathway. Within 15 min of PMA treatment DNA binding of the c-jun transcription factor is increased and is accompanied by rapid changes in the phosphate content of the c-jun protein. Phorbol esters stimulate phosphorylation of serines 63 and 73 located within the A1 transactivation domain of c-Jun that have previously been shown to positively regulate activity. A protein kinase activity is detectable in extracts of phorbol ester-treated U937 cells that specifically targets these two serines. Using novel assays, the protein kinase activity has been purified over 1000-fold. The major portion of protein kinase activity co-chromatographs over three columns with pp42/44 mitogen-activated protein kinases as judged by immunological methods. The significance of these results with respect to mitogen-induced transcription of AP-1-responsive genes is discussed.

Phorbol ester-induced amino-terminal phosphorylation of human JUN but not JUNB regulates transcriptional activation

Phorbol ester tumor promoters activate gene transcription by regulating both the synthesis and posttranslational modification of the activator protein 1 (AP-1) transcription factor, c-Jun and JunB are components of the mammalian AP-1 complex. Here we demonstrate that in U-937 human leukemic cells, phorbol esters stimulate the phosphorylation of the amino terminus of human c-Jun (JUN) but not human JunB (JUNB). Mutational analysis indicates that serine-63 and -73, which reside within the putative regulatory domain of JUN, are required for both constitutive and phorbol 12-myristate 13-acetate-inducible N-terminal JUN phosphorylation. To determine the functional role of this N-terminal phosphorylation, we prepared several chimeric proteins containing the N-terminal 84 amino acids (positions 5-89) of human JUN or murine JUNB fused to the yeast GAL4 DNA-binding domain. This region was found to be sufficient for the phorbol ester-inducible transcriptional activity of JUN, but not JUNB. This induction was abolished by the mutation of serine-63 and -73 to leucine residues. Thus, we propose that phorbol esters enhance the trans-activation potential of JUN, but not JUNB, by the phosphorylation of the N-terminal regulatory domain of JUN.

Phorbol esters stimulate the phosphorylation of c-Jun but not v-Jun: regulation by the N-terminal delta domain

c-Jun and its oncogenic counterpart v-Jun are completely conserved within the region from Ser-63 to Ser-73; these serines are sites for phorbol ester-inducible c-Jun phosphorylation. Using a U937 human leukemic cell line stably expressing v-Jun, we have demonstrated that phorbol esters stimulate the in vivo phosphorylation of c-Jun but not v-Jun. We developed an in vitro protein kinase assay to characterize the c-Jun protein kinase and to examine the determinants underlying this differential phosphorylation. Fusion proteins between glutathione S-transferase and the N terminus of c-Jun, v-Jun, or several c-Jun mutants were used as substrates. A c-Jun kinase activity was affinity-purified 5000-fold by using glutathione S-transferase-c-Jun-glutathione-Sepharose beads and was found to phosphorylate the N terminus of c-Jun but not v-Jun or c-Jun containing a 27-amino acid N-terminal deletion found in v-Jun. These effects were also observed in vivo as phorbol 12-myristate 13-acetate did not induce the phosphorylation of v-Jun or the c-Jun deletion mutant in U937 cell lines stably expressing these proteins. These findings indicate that the delta domain of c-Jun (amino acids 34-60), which is deleted in v-Jun, plays a critical role in regulating N-terminal c-Jun phosphorylation.

Induction of differentiation and c-jun expression in human leukemic cells by okadaic acid, an inhibitor of protein phosphatases

Okadaic acid, a protein phosphatase inhibitor, is a strong tumor promoter which activates protein phosphorylation. Because another activator of protein phosphorylation, phorbol esters, stimulates hematopoietic differentiation, we sought to determine whether okadaic acid could also induce the differentiation of the human leukemic cell line U937. Differentiation was assessed by measuring changes in the following: mRNA levels, cell growth, morphology, cell surface markers, and the ability to induce superoxide. We found that okadaic acid treatment of U937 cells induces immediate increases in total cellular levels of both c-jun and c-fos mRNAs. Nuclear run-on experiments demonstrate that initial increases are secondary to increases in transcription, whereas latter changes may be secondary to mRNA stabilization. Like phorbol esters, okadaic acid treatment also activates AP-1 enhancer activity and induces the phosphorylation of c-Jun protein. Approximately 6-12 hours after treatment with okadaic acid, mRNA levels of c-myc, p34cdc2, and p58GTA, two cell cycle regulated protein kinases, decrease. Okadaic acid inhibits the growth of U937 cells, induces changes in nuclear morphology, stimulates increases in Mac-1 and Leu 11 surface antigens, and induces these cells to produce superoxide. These changes, taken together, suggest that U937 cells have been induced by okadaic acid to differentiate towards a more mature cell type.

Protein kinase C-independent activation of c-jun and c-fos transcription by epidermal growth factor

Phorbol esters, epidermal growth factor (EGF) and serum induce the transient expression of the c-jun and c-fos proto-oncogenes in quiescent fibroblasts. While phorbol esters such as phorbol 12-myristate 13-acetate (PMA) are thought to induce the transcription of these genes by activating protein kinase C (PKC), the signal transduction pathway(s) mediating the effects of EGF and serum are still unclear. We have investigated whether PKC and/or calcium play a role in mediating EGF-stimulated c-jun and c-fos RNA and protein expression in quiescent NIH 3T3 fibroblasts. PMA, EGF or serum stimulated a rapid, transient increase in c-jun and c-fos expression and cJun protein synthesis in quiescent NIH 3T3 cells. Depletion of whole cell PKC activity by pretreatment with PMA abolished any subsequent response to PMA, but had no effect on the ability of EGF or serum to induce c-jun and c-fos RNA and cJun protein expression. Nuclear run-on analysis indicated that EGF-induced gene expression was due to an increase in the rate of transcription of c-jun and c-fos in both naive and PKC-depleted cells. The role of calcium in the EGF-induced expression of c-jun and c-fos was also investigated using an NIH 3T3 cell line (HER-14) overexpressing the wild type human EGF receptor. Removal of extracellular calcium by chelation with excess EGTA or use of the non-specific calcium channel blocker lanthanide, both of which abolish the EGF-induced calcium transient in HER-14 cells, had no effect on the PMA or EGF induced c-jun or c-fos response. These findings suggest that EGF induces c-jun and c-fos transcription and cJun protein synthesis in a manner independent of an increase in intracellular calcium or activation of PKC in quiescent NIH 3T3 cells.

Upstream regions of the c-jun promoter regulate phorbol ester-induced transcription in U937 leukemic cells

To understand the mechanism by which phorbol esters (PMA) stimulate c-jun transcription in human leukemic cell line U937, we have mutated specific enhancer sequences within the c-jun promoter. We find in the region of DNA from -132 to +170 containing Sp1, C-TF and AP-1 sequences that mutation of the AP-1 sequence alone is not sufficient to abrogate transcription, and mutation of the Sp1 sequence increases transcription 4-fold. Although mutation of the CTF site had no effect, CTF and AP-1 mutations together totally abrogate PMA-induced transcription. In comparison mutations of either of these sites alone or together in a construct containing -1639/+740 of the c-jun promoter had no effect on transcription. Because this data suggested the possibility of other upstream control regions, we sequenced the promoter from -142 to -1639. This sequence demonstrates a greater than 70% homology between human, and mouse c-jun promoters for the region from -142 to -441, and a second AP-1-like site in the -183 to -192 region. Mutation of this site did not influence transcription by PMA. By making constructs containing varying portions of the promoter, we have identified the region between -142 and -711 to be responsible for mediating PMA-induced c-jun transcription.

Regulation of calcium-activated potassium efflux by neurotensin and other agents in HT-29 cells

Neurotensin receptors have been shown previously to be coupled to polyphosphoinositide turnover and intracellular Ca2+ ([Ca2+]i) mobilization in HT-29 colonic epithelial cells (Bozou et al. Biochem. J. 264: 871, 1989; Turner et al. J. Pharmacol. Exp. Ther. 253: 1049, 1990). In this study, neurotensin was found to enhance dramatically the Ba2(+)- and tetraethylammonium chloride-sensitive K(+)-efflux rate (measured with 86Rb+) in the presence of ouabain and bumetanide, with basal efflux increasing 4.5 +/- 0.5-fold with 10 nM neurotensin. The K(+)-efflux rate, which was partially dependent on the extracellular Ca2+ concentration, was also increased by carbachol and ATP, two other [Ca2+]i-mobilizing agonists in HT-29 cells, as well as by the Ca2+ ionophores ionomycin and A23187, suggesting that the efflux was through Ca2(+)-activated K+ channels. Pretreatment of cells with neurotensin, carbachol, or ATP desensitized subsequent neurotensin-stimulated efflux by 82, 57, and 63%, respectively, confirming our previous results which indicated homologous and heterologous desensitization of the neurotensin receptor-signal transduction pathway. Pretreatment of cells with the protein kinase C activators phorbol 12-myristate 13-acetate (PMA) and mezerein did not affect [Ca2+]i mobilization or K+ efflux directly but desensitized neurotensin-stimulated efflux by greater than 80%. Pretreatment (2 h) with PMA also decreased K+ efflux in response to ionomycin by 59%, although ionomycin-induced [Ca2+]i mobilization was not inhibited. Downregulation of protein kinase C by overnight pretreatment with PMA resulted in recovery of ionomycin-stimulated efflux. These results suggest that agonist-stimulated Ca2(+)-activated K+ channels in HT-29 cells are regulated at multiple steps in the signal transduction pathway.

Screening, diagnosis, and management of dyslipoproteinemia in children

The authors provide an extensive and comprehensive review of dyslipoproteinemia in children. An effective program for CVD reduction in this population will include an accessible screening program to identify high-risk children, high-quality measurements of TC and LP-C, careful follow-up of screening results with multiple measurement to classify risk status and diagnose primary dyslipidemia, a key role for family and education, and consistent and long-term follow-up for diet and drug adherence, efficacy, and safety.

Vasoactive intestinal peptide stimulates active K+ transport and Na(+)-K(+)-Cl- cotransport in HT-29 cells

Regulation of active K+ influx and Na(+)-K(+)-Cl- cotransport activity in HT-29 cells by vasoactive intestinal peptide (VIP) was investigated. Both active K+ influx, defined as the ouabain-sensitive component, and Na(+)-K(+)-Cl- cotransport, defined as the ouabain-resistant bumetanide-sensitive component, of total K+ uptake were increased by VIP. VIP increased the maximum velocity (Vmax) values for both components with no change in apparent Michaelis constant (Km) values. Three lines of evidence support the role of adenosine 3',5'-cyclic monophosphate (cAMP) as a mediator of the VIP effects. 1) The rank order potencies of VIP and peptide histidineisoleucineamide (PHI) in binding and cAMP production (J. T. Turner, S. B. Jones, and D. B. Bylund, Peptides Fayetteville 7: 849, 1986) and K+ uptake were consistent; 2) alpha 2-adrenergic agonists inhibited both VIP-stimulated cAMP production (J. T. Turner, C. Ray-Prenger, and D. B. Bylund, Mol. Pharmacol. 28: 422, 1985) and K+ uptake; and 3) forskolin, but not dideoxyforskolin, mimicked the effects of VIP on K+ uptake. Because amiloride blocked the VIP-stimulated active K+ component, the VIP effects on active K+ influx may be secondary to a Na(+)-H+ antiporter-mediated increase in cellular Na+ content. Additional experiments indicated that pretreatment of cells with a protein kinase C activator, previously shown to decrease basal Na(+)-K(+)-Cl- cotransport activity and the apparent number of cotransporters in HT-29 cells (C. C. Franklin, J. T. Turner, and H. D. Kim, J. Biol. Chem. 264: 6667, 1989), did not change the magnitude of response of the remaining cotransporters after adenylate cyclase activation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of Na+/K+/Cl- cotransport and [3H]bumetanide binding site density by phorbol esters in HT29 cells

The involvement of protein kinase C in the regulation of Na+/K+/Cl- cotransport was investigated in cultured HT29 human colonic adenocarcinoma cells. We have demonstrated previously the presence of a Na+/K+/Cl- cotransport pathway in HT29 cells (Kim, H.D., Tsai, Y-S., Franklin, C.C., and Turner, J.T. (1989) Biochim. Biophys. Acta 946, 397-404). Treatment of cells with the phorbol esters phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDBu) caused an increase in membrane-associated protein kinase C activity that was accompanied by a concomitant decrease in cytosolic protein kinase C activity. PMA also produced a rapid transient increase in cotransport to 137% of control values by 5 min followed by a progressive decrease to 19% of control values by 2 h. To determine the underlying mechanism for the reduction in Na+/K+/Cl- cotransport, changes in cotransporter number and/or affinity were determined in radioligand binding studies using [3H]bumetanide. PMA and PDBu produced essentially identical time- and dose-dependent decreases in specific [3H]bumetanide binding that were similar to the observed decreases in cotransport. Analysis of saturation and competition binding data indicated that the decrease in binding was due to a lowered Bmax with no change in affinity. Both the decrease in binding and the changes in cotransport elicited by PMA were prevented by the protein kinase inhibitor H7. These findings suggest that phorbol esters cause a decrease in the number of cotransporters in HT29 cells, resulting in a reduction in Na+/K+/Cl- cotransport activity.

Characterization of Na+/K+/Cl- cotransport in cultured HT29 human colonic adenocarcinoma cells

A Na+/K+/Cl- cotransport pathway has been examined in the HT29 human colonic adenocarcinoma cell line using 86Rb as the K congener. Ouabain-resistant bumetanide-sensitive (OR-BS) K+ influx in attached HT29 cells was 17.9 +/- 0.9 nmol/min per mg protein at 25 degrees C. The identity of this pathway as a Na+/K+/Cl- cotransporter has been deduced from the following findings: (a) OR-BS K+ influx ceased if the external Cl- (Cl-o) was replaced by NO3- or the external Na+ (Na+o) by choline; (b) neither OR-BS 24Na+ nor 36Cl- influx was detectable in the absence of external K+ (K+o); and (c) concomitant measurements of 86Rb+, 22Na+, and 36Cl- influx indicated that the stoichiometry of the cotransport system approached a ratio of 1N+:1K+:2Cl-. In addition, OR-BS K+ influx was exquisitely sensitive to cellular ATP levels. Depletion of the normal ATP content of 35-40 nmol/mg protein to 10-15 nmol/mg protein, a concentration at which the ouabain-sensitive K+ influx was unaffected, completely abolished K+ cotransport. OR-BS K+ influx was slightly reduced by the divalent cations Ca2+, Ba2+, Mg2+ and Mn2+. Although changes in cell volume, whether shrinking or swelling, did not influence OR-BS K+ influx, ouabain-sensitive K+ influx was activated by cell swelling. As in T84 cells, we found that the OR-BS K+ influx in HT29 cells was stimulated by exogenous cyclic AMP analogues and by augmented cyclic AMP content in response to vasoactive intestinal peptide, forskolin, norepinephrine and forskolin or prostaglandin E1.

Insulin regulation of glucose metabolism in HT29 colonic adenocarcinoma cells: activation of glycolysis without augmentation of glucose transport

The effects of insulin on glucose transport and metabolism were examined in cultured HT29 human colonic adenocarcinoma cells. The presence of glucose transporters was verified by D-glucose displaceable [3H]cytochalasin B binding. The Kd and Bmax values from cytochalasin B binding studies were 190 +/- 30 nM and 8.4 +/- 1.4 pmol/mg protein, respectively. Glucose transport determined with 3-O-methylglucose showed saturable kinetics with a Km of 5.8 +/- 0.4 mM and a Vmax of 0.047 +/- 0.003 mumol/mg protein per min at 25 degrees C. Moreover, in HT29 cells, two classes of insulin binding sites were detected in radioligand binding experiments. Although insulin failed to stimulate glucose transport, it was found to activate glycolysis in HT29 cells. Glucose consumption increased from 0.33 +/- 0.03 mumol/mg protein per h to 0.49 +/- 0.05 mumol/mg protein per h and lactate production was augmented from 0.67 +/- 0.04 mumol/mg protein per h to 0.87 +/- 0.06 mumol/mg protein per h in response to 10(-7) to 10(-5) M insulin. Insulin also enhanced mannose metabolism. Apart from these two hexoses, HT29 cells exhibited a surprisingly narrow substrate specificity. With the possible exception of glyceraldehyde, little lactate was produced from alternative substrates, including adenosine, inosine, ribose, deoxyribose, dihydroxyacetone, galactose and fructose either with or without insulin. Despite its limited utilization by the glycolytic pathway, adenosine was readily salvaged for de novo synthesis of adenine nucleotides. These findings suggest that insulin directly influences substrate utilization through the glycolytic pathway in HT29 cells without activating the glucose transport pathway.

Activation of phospholipase C in platelets by platelet activating factor and thrombin causes hydrolysis of a common pool of phosphatidylinositol 4,5-bisphosphate

Despite their physicochemical and mechanistic differences platelet activating factor (or acetylglycerylether phosphorylcholine; AGEPC) and thrombin, both platelet stimulatory agents, induce phosphoinositide turnover in platelets. We therefore investigated the stimulation of the phosphoinositide phosphodiesterase by these agents and questioned whether they evoked hydrolysis of the same or different pools of phosphoinositides. [3H]Inositol-labelled rabbit platelets were challenged with thrombin and/or AGEPC under a variety of protocols, and the phospholipase C mediated production of radioactive inositol monophosphate (IP); inositol bisphosphate (IP2) and inositol trisphosphate (IP3) was used as the parameter. AGEPC (1 X 10(-9) M) caused a transient maximum (5 to 6-fold) increase in [3H]IP3 at 5 s followed by a decrease. Thrombin (2 U/ml) elicited an increase in [3H]IP3 at a much slower rate than AGEPC; 2 fold at 5 s, 5 fold at 30 s and a maximum 6 to 8-fold at 2-5 min. Compared to AGEPC, thrombin stimulated generation of [3H]IP2 and [3H]IP were severalfold higher. When thrombin and AGEPC were added together to platelets there was no evidence for an additive increase in inositol polyphosphate levels except at earlier time points where increases were submaximal. When AGEPC was added at various time intervals after thrombin pretreatment, no additional increases in [3H]IP3 were observed over that maximally seen with thrombin or AGEPC alone. In another set of experiments, submaximal increases (about 1/4 and 1/2 of maximum) in [3H]IP3 were achieved by using selected concentrations of thrombin (0.1 U and 0.3 U, respectively) and then AGEPC (1 X 10(-9) M) was added for 5 s. Once again the increase in [3H]IP3 was close to the maximal level seen with thrombin or AGEPC individually. It is concluded that thrombin and AGEPC differentially activated phosphoinositide phosphodiesterase (phospholipase C) in rabbit platelets and that the stimulation of the phospholipase C by these two stimuli causes IP3 production via hydrolysis of a common pool of phosphatidylinositol 4,5-bisphosphate.

Gastrointestinal adenovirus: an important cause of morbidity in patients with necrotizing enterocolitis and gastrointestinal surgery

Adenoviruses have recently been recognized as etiologic agents of enteric disease in hospitalized infants and young children. Patients who have undergone surgical procedures related to the complications of neonatal necrotizing enterocolitis constitute a population of infants who are often hospitalized for extended periods of time. We studied the incidence of enteric adenovirus infections in infants with necrotizing enterocolitis who had undergone intestinal surgery resulting in colostomies or ileostomies. These studies revealed that 31.7% of the hospital admissions in such patients were complicated by symptomatic infection with enteric adenoviruses. The rate of adenovirus infection in this population was significantly higher than the rate of such infections encountered in infants undergoing ostomy procedures for other conditions and in age-matched hospitalized infants without prior gastrointestinal surgery. The infections with enteric adenovirus were generally accompanied by an increase in intestinal output which was temporally associated with the excretion of adenovirus in the intestinal fluid. In addition infections with enteric adenoviruses in the infants with necrotizing enterocolitis and ostomies were associated with a marked increase in length of hospitalization as compared to uninfected infants with similar underlying gastrointestinal pathology. Epidemiologic analysis revealed that many of the cases of enteric adenovirus infection in the study population occurred during seasons in which enteric adenovirus infections were prevalent in the hospital population. These studies demonstrate that enteric adenovirus infections are major causes of morbidity in hospitalized patients who have of morbidity in hospitalized patients who have undergone ileostomy or colostomy procedures for necrotizing enterocolitis and that the prevention of enteric adenovirus infections might result in a significant improvement in the hospital care of infants with these conditions.