Alternatives to the Gold Standard: A Systematic Review of Profunda Artery Perforator and Lumbar Artery Perforator Flaps for Breast Reconstruction

INTRODUCTION

Breast reconstruction with the deep inferior epigastric perforator (DIEP) flap is the current gold-standard autologous option. The profunda artery perforator (PAP) and lumbar artery perforator (LAP) flaps have more recently been described as alternatives for patients who are not candidates for a DIEP flap. The aim of this study was to review the survival and complication rates of PAP and LAP flaps, using the DIEP flap as a benchmark.

METHODS

A literature search was conducted using PubMed, MEDLINE, Embase, BIOSIS, Web of Science, and Cochrane databases. Papers were screened by title and abstract, and full texts reviewed by three independent blinded reviewers. Quality was assessed using MINORS criteria.

RESULTS

Sixty-three studies were included, for a total of 745 PAP, 62 stacked PAP, 187 LAP, and 23,748 DIEP flap breast reconstructions. The PAP (98.3%) had comparable success rate to DIEP (98.4%), and the stacked PAP (88.7%) and LAP (92.5%) success rate was significantly lower (P < 0.0001). The PAP and LAP groups both had a low incidence of fat necrosis. However, the revision rate for the LAP group was 16.1% whereas the PAP group was 3.3%. Donor site wound dehiscence rate was 2.9 in the LAP group and 9.1% in the PAP group.

CONCLUSIONS

Profunda artery perforator and DIEP flaps demonstrate very high rates of overall survival. The LAP flap has a lower survival rate. This review highlights the survival and complication rates of these alternative flaps, which may help clinicians in guiding autologous reconstruction technique when a DIEP flap is unavailable.

Associations with Discharge to Post-Acute Care Facilities Among Patients Undergoing Open Reduction Internal Fixation of Distal Radius Fractures

Introduction: Distal radius fractures are a common injury of the hand and wrist that often require intensive rehabilitation. We sought to identify risk factors associated with discharge to a post-acute care facility following distal radius fracture repair. Methods: The 2011 to 2016 National Surgical Quality Improvement Program® (NSQIP) database was queried for all Current Procedural Terminology (CPT) codes that corresponded with open distal radius fracture repair. Patients with concomitant traumatic injuries were excluded. Patient demographics, comorbidities, perioperative factors, laboratory data, and surgical details were collected. Our primary outcome was to determine postoperative discharge destination: home versus a post-acute care facility, and to identify factors that predict discharge to post-acute care facility. Secondary outcomes included unplanned readmission, reoperation, and complications. Results: Between 2011 and 2016, a total of 12,001 patients underwent open distal radius fracture repair and had complete information for their discharge. Of these analyzed patients, 3.24% (n  =  389) were discharged to rehabilitation facilities. The following factors were identified on multivariate analysis to have an association with discharge to a post-acute care facility: 65 years or older, White race, underweight, using steroids preoperatively, American Society of Anesthesiologists (ASA) classification > 2, admitted from a nursing home or already hospitalized, anemic, undergoing bilateral surgery, wound classification other than clean, and complications prior to discharge. Conclusion: Factors identified by our study to have associations with discharge to post-acute care facilities following distal radius fracture repair can help in appropriate patient counseling and triage from the hospital to home versus a post-acute care facility.

Restoring Carboxylates on Highly Modified Alginates Improves Gelation, Tissue Retention and Systemic Capture

Alginate hydrogels are gaining traction for use in drug delivery, regenerative medicine, and as tissue engineered scaffolds due to their physiological gelation conditions, high tissue biocompatibility, and wide chemical versatility. Traditionally, alginate is decorated at the carboxyl group to carry drug payloads, peptides, or proteins. While low degrees of substitution do not cause noticeable mechanical changes, high degrees of substitution can cause significant losses to alginate properties including complete loss of calcium cross-linking. While most modifications used to decorate alginate deplete the carboxyl groups, we propose that alginate modifications that replenish the carboxyl groups could overcome the loss in gel integrity and mechanics. In this report, we demonstrate that restoring carboxyl groups during functionalization maintains calcium cross-links as well as hydrogel shear-thinning and self-healing properties. In addition, we demonstrate that alginate hydrogels modified to a high degree with azide modifications that restore the carboxyl groups have improved tissue retention at intramuscular injection sites and capture blood-circulating cyclooctynes better than alginate hydrogels modified with azide modifications that deplete the carboxyl groups. Taken together, alginate modifications that restore carboxyl groups could significantly improve alginate hydrogel mechanics for clinical applications. STATEMENT OF SIGNIFICANCE: Chemical modification of hydrogels provides a powerful tool to regulate cellular adhesion, immune response, and biocompatibility with local tissues. Alginate, due to its biocompatibility and easy chemical modification, is being explored for tissue engineering and drug delivery. Unfortunately, modifying alginate to a high degree of substitution consumes carboxyl group, which are necessary for ionic gelation, leading to poor hydrogel crosslinking. We introduce alginate modifications that restore the alginate's carboxyl groups. We demonstrate that modifications that reintroduce carboxyl groups restore gelation and improve gel mechanics and tissue retention. In addition to contributing to a basic science understanding of hydrogel properties, we anticipate our approach will be useful to create tissue engineered scaffolds and drug delivery platforms.

Hand and wrist injuries among collegiate athletes vary with athlete division

BACKGROUND

The rates, severity and consequences of hand and wrist injuries sustained by National Collegiate Athletic Association athletes are not well characterized. This study describes the epidemiology of hand and wrist injuries among collegiate athletes competing in different divisions.

METHODS

The National Collegiate Athletic Association Injury Surveillance Program (NCAA-ISP) was accessed from 2004 to 2015 for the following sports: baseball, basketball, football, ice hockey, lacrosse, soccer, wrestling, field hockey, gymnastics, softball and volleyball. The data were used to identify all hand and wrist injuries, the specific injury diagnosis, mean time loss of activity following injury, and need for surgery following injury. These were then stratified by gender. Descriptive statistics were performed to examine the association between sports, event type and division. Student's t test was used to calculate p-values for independent variables. Chi-Square test was used to calculate odds ratio. P < 0.05 was considered significant.

RESULTS

103,098 hand and wrist injuries were reported in in the studied NCAA sports from 2004 to 2015. Male athletes sustained 72,423 injuries (6.01/10,000 athlete exposure) and female athletes sustained 30,675 injuries (4.13/10,000 athlete exposure). Division I athletes sustained significantly more injuries compared to divisions II and III. Overall, 3.78% of hand and wrist injuries required surgical intervention. A significantly higher percentage of division I athletes (both male and female) underwent surgical intervention compared to divisions II and III. The mean time lost due to hand and wrist injury was 7.14 days for all athletes. Division I athletes missed the fewest days due to injury at 6.29 days though this was not significant.

CONCLUSIONS

Hand and wrist injuries are common among collegiate athletes. Division I athletes sustain higher rates of injuries and higher surgical intervention rates, while tending to miss fewer days due to injury. Improved characterization of divisional differences in hand and wrist injuries can assist injury management and prevention.

Hand and Wrist Injuries Among Collegiate Athletes: The Role of Sex and Competition on Injury Rates and Severity

Background:

There is a high incidence of hand and wrist injuries in athletes participating in collegiate sports, but there is little information published characterizing them.

Purpose:

To characterize hand and wrist injuries in collegiate athletes using a large national database.

Study Design:

Descriptive epidemiology study.

Methods:

This retrospective cross-sectional analysis was designed using data from the National Collegiate Athletic Association (NCAA) Injury Surveillance Program database to identify hand and wrist injuries (exclusive of any radial or ulnar fractures) in male and female collegiate athletes participating in NCAA Division I, II, and III sports from 2004 to 2015. Descriptive analyses were performed on stratified data to examine the associations between these injuries and sport, event type, and sex.

Results:

Men’s ice hockey (8.25 per 10,000 athlete-exposures [AEs]) and women's ice hockey (8.21 per 10,000 AEs) had the highest rate of hand and wrist injuries in all exposures. In every sport except women’s gymnastics (P = .107), injuries were more commonly sustained during competition rather than during practice. Ligamentous injury to the phalynx was the most commonly sustained injury overall (1.416 per 10,000 AEs), and a metacarpal fracture was the most commonly sustained hand or wrist fracture (0.507 per 10,000 AEs). Injuries sustained during men’s wrestling (14.08 days) and women’s gymnastics (10.39 days) incurred the most time lost from sport. Surgery for hand and wrist injuries was most commonly required for men’s football (0.413 per 10,000 AEs) and women’s field hockey (0.404 per 10,000 AEs).

Conclusion:

Hand and wrist injuries were common among collegiate athletes. Male athletes experienced injuries with more frequency and severity. Injuries occurred more commonly during competition. While the majority of injuries were minor and did not require surgery, certain sports conferred a much higher risk of significant injuries requiring a surgical intervention.

Salvage of Threatened Cardiovascular Implantable Electronic Devices: Case Series and Review of Literature

BACKGROUND

The treatment of infected or exposed cardiac pacing and defibrillator devices is controversial. The conservative and widely accepted management calls for removal of the device and leads with immediate or delayed replacement of new components in a new site. Lead extraction carries a 2% major complication risk. In this article, we describe our experience with device salvage techniques and review the current literature.

METHODS

This is a retrospective case series of consecutive patients with infected, exposed, or at-risk implanted cardiac devices that were treated with aggressive surgical debridement, local pocket irrigation, and revision. A comprehensive review of the literature regarding device infection management was performed.

RESULTS

Ten patients with threatened devices were identified. Surgical revision with the aim to salvage the device was successful in 8 (80%) of 10 cases. Seventeen retrospective publications were reviewed. All indicate success with attempted salvage surgery, but heterogeneity of data limits formal meta-analysis and prevents management recommendations.

CONCLUSIONS

Cardiac pacing and defibrillator devices with low-grade infection or threatened exposure may be salvaged without explantation. Despite the lack of clear management guidelines or data, plastic surgeons may be asked to assist in the management of threatened cardiac devices. Further prospective trials are required to evaluate the safety, efficacy, and cost-effectiveness of attempted implant salvage.

Immediate Bilateral Breast Reconstruction Using Abdominally Based Flaps: An Analysis of the Nationwide Inpatient Sample Database

BACKGROUND

 Bilateral mastectomy rates are increasing in the United States. The abdomen is the most common harvest site for autologous reconstruction. Nationwide data were examined to determine differences in hospital charges, length of stay (LOS), and early postoperative complications following immediate bilateral pedicled transverse rectus abdominis myocutaneous (pTRAM), free TRAM (fTRAM), deep inferior epigastric perforator (DIEP), and superficial inferior epigastric artery (SIEA) perforator flaps and were compared with unilateral reconstruction.

METHODS

 Patients who underwent immediate bilateral breast reconstruction using a single method of abdominally based reconstruction were identified using the 2009 to 2014 Nationwide Inpatient Sample Database. Outcomes included total hospital charges, LOS, and immediate postoperative complications.

RESULTS

 We identified 13,348 cases of bilateral mastectomy with a single type of immediate bilateral autologous flap reconstruction. The majority were bilateral DIEP flaps. Mean total cost for bilateral pTRAM, fTRAM, DIEP, and SIEA flaps was US $21,886.80, US $28,839.40, US $30,051.30, and US $33,784.90, respectively (p < 0.0001). Mean LOS for bilateral pTRAM, fTRAM, DIEP, and SIEA was 4.3, 4.9, 4.5, and 5.4 days, respectively (p = 0.0002), and hematoma rates were 1.93, 2.61, 3.68, and 16.59%, respectively, (p = 0.0001), whereas return to the operating room for vascular anastomosis revision was 0, 1.63, 1.99, and 19.07%, respectively (p < 0.0001). Cost is less for unilateral pTRAM, fTRAM, and DIEP flaps (p < 0.0001). LOS is shorter for unilateral fTRAM versus bilateral (p < 0.0001). No differences were appreciated between unilateral and bilateral hematoma and reoperation rates for any reconstruction (p > 0.1).

CONCLUSION

 Immediate complication rates were higher in bilateral free flaps compared with bilateral pedicled flaps. pTRAM and fTRAM flap reconstructions are still performed frequently with acceptable immediate results without considering long-term morbidity, aesthetics, and abdominal muscle function. Bilateral SIEA free flaps were associated with significantly higher total cost, LOS, and complication rates compared with other groups. Complications were similar between unilateral and bilateral reconstruction procedures. While cost is significantly greater for bilateral procedures compared with unilateral pTRAM, fTRAM, and DIEP flaps, it is not doubled.

Predictors of complications following breast reduction surgery: A National Surgical Quality Improvement Program study of 16,812 cases

BACKGROUND

Breast reduction is one of the most common procedures performed by plastic surgeons. Despite good outcomes and high patient satisfaction, there are little national data on the predictors that lead to complications in this patient population. We accessed a national outcomes database to examine these factors.

METHODS

This is a retrospective study examining the National Surgical Quality Improvement Program database from 2006 to 2015. Patients who underwent primary breast reduction were identified. Patients who underwent any cancer-related procedures were excluded. We identified patient-related and procedure-related factors for analysis. Univariate and multivariate logistic regression analyses were used to identify independent predictors of complications.

RESULTS

In total, 16,812 individual cases were identified. The overall complication rate for the cohort was 6.2%, and the major complication rate was 3.0%. Diabetes, bleeding disorder, hypertension, obesity, smoking, steroid use, and prolonged operative time were associated with increased risk of complications (p < 0.05). Concurrent body contouring was a predictor of increased major complications; however, liposuction was not.

CONCLUSIONS

Common surgical risk factors are associated with complications in breast reduction surgery. Although liposuction is not an independent risk factor, concurrent body contouring is associated with increased complications. Surgeons should be aware of these associations when discussing breast reduction with patients.

Immediate Unilateral Breast Reconstruction using Abdominally Based Flaps: Analysis of 3,310 Cases

BACKGROUND

 The abdomen is the most common area from which tissue is harvested for autologous breast reconstruction. We sought to examine national data to determine the differences in total hospital charges, length of stay (LOS), and early postoperative complications following pedicled transverse rectus abdominis myocutaneous flap (pTRAM), free TRAM (fTRAM), deep-inferior epigastric perforator (DIEP), and superficial inferior epigastric artery perforator (SIEA) flaps.

METHODS

 The 2009-2013 Nationwide Inpatient Sample Database was used to identify patients who underwent a unilateral mastectomy and only one type of abdominally based autologous flap (pTRAM, fTRAM, DIEP, and SIEA) during the same hospital admission. Outcomes of interest included total charges, LOS, and complications including revision of vascular anastomosis and hematoma.

RESULTS

 A total of 3,310 cases were identified, corresponding to 15,991 abdominally based unilateral immediate breast reconstructions after standard weighting was applied; 5,079 (31.8%) were pTRAM flaps, 4,461 (27.9%) were fTRAM flaps, 6,206 (38.8%) were DIEP flaps, and 245 (1.5%) were SIEA flaps. The mean total charges for pTRAM, fTRAM, DIEP, and SIEA flaps were $17,765.5, $22,637.6, $25,814.6, and $26,605.2, respectively (p < 0.0001). The mean LOS for pTRAM, fTRAM, DIEP, and SIEA flaps were 96.5, 106.5, 106.7, and 108.9 hours, respectively (p = 0.002). The rates for return to the OR for the revision of a vascular anastomosis for pTRAM, fTRAM, DIEP, and SIEA were 0.0%, 1.72%, 2.66%, and 5.64%, respectively (p < 0.0001).

CONCLUSIONS

 There is variation in the total charges, LOS, and early complications between pTRAM, fTRAM, DIEP, and SIEA flap-based breast reconstruction. fTRAM, DIEP, and SIEA flaps incur higher hospital total charges, have longer lengths of stay, and experience more immediate complications compared with pTRAM. Well-designed prospective trials are required to better understand the findings from this study with the inclusion of other critical outcomes such as patient satisfaction, aesthetic results, and long-term outcomes such as abdominal wall morbidity.

Pancreatic transdifferentiation in porcine liver following lentiviral delivery of human furin-cleavable insulin

Type I diabetes mellitus (TID) results from the autoimmune destruction of the insulin-producing pancreatic β-cells. Gene therapy is one strategy being actively explored to cure TID by affording non-β-cells the ability to secrete insulin in response to physiologic stimuli. In previous studies, we used a novel surgical technique to express furin-cleavable human insulin (INS-FUR) in the livers of streptozotocin (STZ)-diabetic Wistar rats and nonobese diabetic (NOD) mice with the use of the HMD lentiviral vector. Normoglycemia was observed for 500 and 150 days, respectively (experimental end points). Additionally, some endocrine transdifferentiation of the liver, with storage of insulin in granules, and expression of some β-cell transcription factors (eg, Pdx1, Neurod1, Neurog3, Nkx2-2, Pax4) and pancreatic hormones in both studies. The aim of this study was to determine if this novel approach could induce liver to pancreatic transdifferentiation to reverse diabetes in pancreatectomized Westran pigs. Nine pigs were used in the study, however only one pig maintained normal fasting blood glucose levels for the period from 10 to 44 days (experimental end point). This animal was given 2.8 × 10(9) transducing units/kg of the lentiviral vector expressing INS-FUR. A normal intravenous glucose tolerance test was achieved at 30 days. Reverse-transcription polymerase chain reaction analysis of the liver tissue revealed expression of several β-cell transcription factors, including the key factors, Pdx-1 and Neurod1, pancreatic hormones, glucagon, and somatostatin; however, endogenous pig insulin was not expressed. Triple immunofluorescence showed extensive insulin expression, as was previously observed in our studies with rodents. Additionally, a small amount of glucagon and somatostatin protein expression was seen. Collectively, these data indicate that pancreatic transdifferentiation of the liver tissue had occurred. Our data suggest that this regimen may ultimately be used clinically to cure TID, however more work is required to replicate the successful reversal of diabetes in increased numbers of pigs.

Long-term correction of diabetes in rats after lentiviral hepatic insulin gene therapy

AIMS/HYPOTHESIS

Type 1 diabetes results from the autoimmune destruction of pancreatic beta cells. Exogenous insulin therapy cannot achieve precise physiological control of blood glucose concentrations, and debilitating complications develop. Lentiviral vectors are promising tools for liver-directed gene therapy. However, to date, transduction rates in vivo remain low in hepatocytes, without the induction of cell cycling. We investigated long-term transgene expression in quiescent hepatocytes in vitro and determined whether the lentiviral delivery of furin-cleavable insulin to the liver could reverse diabetes in rats.

MATERIALS AND METHODS

To improve transduction efficiency in vitro, we optimised hepatocyte isolation and maintenance protocols and, using an improved surgical delivery method, delivered furin-cleavable insulin alone or empty vector to the livers of streptozotocin-induced diabetic rats by means of a lentiviral vector. Rats were monitored for changes in body weight and blood glucose, and intravenous glucose tolerance tests were performed. Expression of insulin was determined by RT-PCR, immunohistochemistry and electron microscopy.

RESULTS

We achieved long-term transgene expression in quiescent hepatocytes in vitro (87 +/- 1.2% transduction efficiency), with up to 60 +/- 3.2% transduction in vivo. We normalised blood glucose for 500 days-a significantly longer period than previously reported-making this the first successful study using a lentiviral vector. This procedure resulted in the expression of genes encoding several beta cell transcription factors, some pancreatic endocrine transdifferentiation, hepatic insulin storage in granules, and restoration of glucose tolerance. Liver function tests remained normal. Importantly, pancreatic exocrine transdifferentiation did not occur.

CONCLUSIONS/INTERPRETATION

Our data suggest that this regimen may ultimately be employed for the treatment of type 1 diabetes.

Estrogen deficiency decreases ischemic tolerance in the aged rat heart: roles of PKCδ, PKCε, Akt, and GSK3β

The mechanisms underlying the age-dependent reversal of female cardioprotection are poorly understood and complicated by findings that estrogen replacement is ineffective at reducing cardiovascular mortality in postmenopausal women. Although several protective signals have been identified in young animals, including PKC and Akt, how these signals are affected by age, estrogen deficiency, and ischemia-reperfusion (I/R) remains unknown. To determine the independent and combined effects of age and estrogen deficiency on I/R injury and downstream PKC-Akt signaling, adult and aged female F344 rats ( n = 12/age) with ovaries intact or ovariectomy (Ovx) were subjected to I/R using Langendorff perfusion (31-min global-ischemia). Changes in cytosolic (s), nuclear (n), mitochondrial (m) PKC (δ, ε) levels, and changes in total Akt and mGSK-3β phosphorylation after I/R were assessed by Western blot analysis. Senescence increased infarct size 50% in ovary-intact females ( P < 0.05), whereas no differences in LV functional recovery or estradiol levels were observed. Ovx reduced functional recovery to a greater extent in aged compared with adult rats ( P < 0.05). In aged (vs. adult), levels of m- and nPKC(-δ, -ε) were markedly decreased, whereas mGSK3β levels were increased ( P < 0.05). Ovx led to greater levels of sPKC(-δ, -ε) independent of age ( P < 0.05). I/R reduced p-Akt(Ser473) levels by 57% and increased mGSK-3β accumulation 1.77-fold ( P < 0.05) in aged, ovary-intact females. These data suggest, for the first time, that estrogen alone cannot protect the aged female myocardium from I/R damage and that age- and estrogen-dependent alterations in PKC, Akt, and GSK-3β signaling may contribute to loss of ischemic tolerance.

Dynamic myocardial contractile parameters from left ventricular pressure-volume measurements

A new dynamic model of left ventricular (LV) pressure-volume relationships in beating heart was developed by mathematically linking chamber pressure-volume dynamics with cardiac muscle force-length dynamics. The dynamic LV model accounted for >80% of the measured variation in pressure caused by small-amplitude volume perturbation in an otherwise isovolumically beating, isolated rat heart. The dynamic LV model produced good fits to pressure responses to volume perturbations, but there existed some systematic features in the residual errors of the fits. The issue was whether these residual errors would be damaging to an application where the dynamic LV model was used with LV pressure and volume measurements to estimate myocardial contractile parameters. Good agreement among myocardial parameters responsible for response magnitude was found between those derived by geometric transformations of parameters of the dynamic LV model estimated in beating heart and those found by direct measurement in constantly activated, isolated muscle fibers. Good agreement was also found among myocardial kinetic parameters estimated in each of the two preparations. Thus the small systematic residual errors from fitting the LV model to the dynamic pressure-volume measurements do not interfere with use of the dynamic LV model to estimate contractile parameters of myocardium. Dynamic contractile behavior of cardiac muscle can now be obtained from a beating heart by judicious application of the dynamic LV model to information-rich pressure and volume signals. This provides for the first time a bridge between the dynamics of cardiac muscle function and the dynamics of heart function and allows a beating heart to be used in studies where the relevance of myofilament contractile behavior to cardiovascular system function may be investigated.

Function of a genetically modified human liver cell line that stores, processes and secretes insulin

An alternative approach to the treatment of type I diabetes is the use of genetically altered neoplastic liver cells to synthesize, store and secrete insulin. To try and achieve this goal we modified a human liver cell line, HUH7, by transfecting it with human insulin cDNA under the control of the cytomegalovirus promoter. The HUH7-ins cells created were able to synthesize insulin in a similar manner to that which occurs in pancreatic beta cells. They secreted insulin in a regulated manner in response to glucose, calcium and theophylline, the dose-response curve for glucose being near-physiological. Perifusion studies showed that secretion was rapid and tightly controlled. Removal of calcium resulted in loss of glucose stimulation while addition of brefeldin A resulted in a 30% diminution of effect, indicating that constitutive release of insulin occurred to a small extent. Insulin was stored in granules within the cytoplasm. When transplanted into diabetic immunoincompetent mice, the cells synthesized, processed, stored and secreted diarginyl insulin in a rapid regulated manner in response to glucose. Constitutive release of insulin also occurred and was greater than regulated secretion. Blood glucose levels of the mice were normalized but ultimately became subnormal due to continued proliferation of cells. Examination of the HUH7-ins cells as well as the parent cell line for beta cell transcription factors showed the presence of NeuroD but not PDX-1. PC1 and PC2 were also present in both cell types. Thus, the parent HUH7 cell line possessed a number of endocrine pancreatic features that reflect the common endodermal ancestry of liver and pancreas, perhaps as a result of ontogenetic regression of the neoplastic liver cell from which the line was derived. Introduction of the insulin gene under the control of the CMV promoter induced changes in these cells to make them function to some extent like pancreatic beta cells. Our results support the view that neoplastic liver cells can be induced to become substitute pancreatic beta cells and become a therapy for the treatment of type I diabetes.

Susceptibility of insulin-secreting hepatocytes to the toxicity of pro-inflammatory cytokines

The liver has been suggested as a suitable target organ for reversing type I diabetes by gene therapy. Whilst gene delivery systems to the hepatocyte have yet to be optimized in vivo, whether insulin-secreting hepatocytes are resistant to the autoimmune process that kills pancreatic beta-cells has never been addressed. One of the mechanisms by which beta-cells are killed in type I diabetes is by the release of the cytokines interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) by immune cells. To test the effect of the cytokines on insulin-secreting hepatocytes in vitro we exposed the betacyte, also called the HEP G2ins/g cell which possesses cytokine receptors and can synthesize, store and secrete insulin in a regulated fashion to a glucose stimulus, to the above mentioned cytokines for 14 days. Viability of the HEP G2ins/g cells was similar to that of other liver cell lines/primary cells which were more resistant to the cytokines than the beta-cell line NIT-1. The cytokines had no adverse effect for the first six days on insulin secretion, content and mRNA levels of the HEP G2ins/g cells and insulin secretion in response to 1-h exposure to 20 mM glucose was enhanced 14-fold. Our results indicate that genetically engineered hepatocytes and primary liver cells are more resistant than pancreatic beta-cells to the adverse effects of cytokines offering hope that insulin secreting hepatocytes in vivo made by gene therapy are less likely to be destroyed by cytokines released during autoimmune destruction.

Guide RNAs of the recently isolated LEM125 strain of Leishmania tarentolae: an unexpected complexity

Guide RNAs (gRNAs) are encoded both in the maxicircle and minicircle components of the mitochondrial DNA of trypanosomatid protozoa. These RNAs mediate the precise insertion and deletion of U residues in transcripts of the maxicircle DNA. We showed previously that the old UC laboratory strain of Leishmania tarentolae apparently lost more than 40 minicircle-encoded gRNAs that are present in the recently isolated LEM125 strain (Thiemann et al., EMBO J, 1994, 13:5689-5700]. We have further analyzed the population of minicircle-encoded gRNAs in the LEM125 strain. Sau3AI and MspI minicircle libraries were constructed and screened for novel gRNAs by negative colony hybridization. This search yielded 20 minicircles encoding new gRNAs that covered most of the remaining gaps in the editing cascades of the ND8, ND9, G4, and G5 genes, and in addition, more than 30 minicircles containing either unassigned or undetectable gRNA genes. We also completely sequenced 34 of the 45 minicircle sequence classes encoding previously identified gRNAs. A total of 19 pairs of redundant gRNAs, which are gRNAs of different sequences covering the same editing blocks, were identified. The gRNAs in each redundant pair generally had different relative abundances and different extents of mismatches with edited sequences. Alignments of the minicircles encoding redundant gRNAs yielded 59 to 93% matching nucleotides, suggesting an origin from duplication of ancestral minicircles and subsequent genetic drift. We propose a functional explanation for the existence of redundant gRNAs in this strain.

Lowering of blood glucose to nondiabetic levels in a hyperglycemic pig by allografting of fetal pig isletlike cell clusters

BACKGROUND

Fetal pig isletlike cell clusters (ICCs) will differentiate when grafted into the thymus gland of outbred immunosuppressed nondiabetic pigs for up to 3 months. Whether these cells will survive for a similar period in a diabetic recipient and will mature with secretion of insulin to ameliorate the hyperglycemia is unknown.

METHODS

Between 40,000 and 125,000 ICCs (7,000 to 11,400 ICCs/kg) were injected into the thymus gland of five juvenile pigs immunosuppressed with cyclosporine and deoxyspergualin, and the animals were subsequently made diabetic by the injection of streptozotocin. Insulin was administered subcutaneously, with one pig dying from hypoglycemia. The animal with the least number of ICCs transplanted was killed 81 days later, and the graft was analyzed histologically. Blood glucose levels and porcine C-peptide in the remaining animals were monitored for a median of 101 days.

RESULTS

Histological analysis of the graft showed numerous epithelial cell clusters; the percentage of cells that contained insulin, glucagon, somatostatin, and pancreatic polypeptide were 61%, 64%, 25%, and 18%, respectively. Some cells contained more than one hormone. Porcine C-peptide was detected from 21 days after induction of diabetes but not before. In the pig receiving the most ICCs, blood glucose levels were lowered to nondiabetic levels 109 days after transplantation. Plasma C-peptide levels in response to glucagon in this pig steadily increased after grafting; peak levels were 0, 0.21, 0.45, and 0.52 ng/ml at 4, 21, 49, and 80 days after induction of diabetes compared to 0.09 ng/ml in control diabetic pigs. The secretion of C-peptide in response to oral and intravenous glucose and arginine also was greater than in untransplanted diabetic pigs, the pattern of secretion being consistent with developing fetal beta cells as the source of the C-peptide. Pancreatic insulin content was 0.1 mU/mg, 4% of that in nondiabetic pigs, and the number of beta cells per islet was 3 to 6 compared to 90 in nondiabetic controls.

CONCLUSIONS

ICCs will differentiate and function for up to 111 days when transplanted into outbred immunosuppressed pigs rendered diabetic. Blood glucose levels can be lowered to nondiabetic levels when sufficient numbers of ICCs are grafted.

In vitro dedifferentiation of fetal porcine pancreatic tissue prior to transplantation as islet-like cell clusters

The fetal porcine pancreas under experimental conditions can be transplanted in the form of explants or islet-like cell clusters (ICCs) to normalize blood glucose levels in diabetic recipients. ICCs are released from the collagenase-digested pancreas and require a 4- to 5-day culture period for their complete formation. In order to maximize insulin producing beta cell differentiation following transplantation, an understanding of ICC development is essential to utilize this alternative treatment for type 1 diabetes. In this study a role is proposed for exocrine cells in the generation of the multipotent pancreatic precursor cells during the culture period. Acinar cells undergo dedifferentiation during the initial stages of the culture period into multipotent pancreatic precursor cells, previously called protodifferentiated cells. The progressive loss of exocrine differentiation appears to involve rapid degranulation of zymogen granules by exocytosis and loss of the prominent secretory apparatus. These processes occur in parallel with a significant reduction in the expression of lipase in the period from day 0 to day 5 and simultaneously there is an increase in the epithelioid/ductal cell marker, cytokeratin 20. Using proliferating cell nuclear antigen, cell proliferation during the culture period does not appear to account for the increase in epithelioid/ductal cells. Further the rates of apoptosis and necrosis which were identified using the TUNEL technique and propidium iodide, respectively, do not appear to account for the reduction in exocrine cell numbers. Exocrine cell dedifferentiation appears to increase the pool of protodifferentiated cells which have the potential to develop into the insulin-producing beta-cell population following transplantation into the diabetic recipient

Distal renal tubular acidosis with severe hypokalaemia, probably caused by colonic H(+)-K(+)-ATPase deficiency

We describe a 21 month old male infant who presented with failure to thrive associated with severe hypokalaemia and metabolic acidosis, together with hypomagnesaemia. Evaluation revealed marked renal and probable faecal potassium wasting, distal renal tubular acidosis, mild urinary magnesium wasting, and a normal gastric pH (gastric H(+)-K(+)-ATPase). Hypokalaemic forms of metabolic acidosis, such as diabetic ketoacidosis and proximal renal tubular acidosis were ruled out from the clinical picture. The hypokalaemia of distal renal tubular acidosis usually improves with alkali therapy, but this was not observed: despite correction of acidosis with 5 mmol/kg potassium citrate per day, an additional 5 mmol/kg potassium chloride was required to bring serum potassium to 3.5 mmol/l. At 3 years of age potassium was provided in the absence of potential alkali and acidosis ensued; serum bicarbonate fell to 10 mmol/l. Although a specific genetic analysis is not yet possible, the abnormalities are consistent with a novel form of distal renal tubular acidosis. The pathophysiology probably does not stem from defects in the vacuolar H(+)-ATPase but more likely from deficient activity of the colonic isoform of H(+)-K(+)-ATPase that is resident in the medullary collecting duct and mediates potassium absorption and proton secretion.

Comparison of 0.25% S(-)-bupivacaine with 0.25% RS-bupivacaine for epidural analgesia in labour

We have compared the efficacy of 0.25% S(-)-bupivacaine with 0.25% RS-bupivacaine in providing epidural analgesia for labour in a randomized, multicentre, double-blind study. Analgesia was initiated with 10 ml of the study solution and maintained with 10-ml top-ups. We studied 137 women and treatments were found to be equivalent for onset, duration and quality of block. Median onset of pain relief was 12 min for both drugs and median duration was 49 (range 3-129) min and 51 (7-157) min for S(-)-bupivacaine and RS bupivacaine, respectively. The estimated treatment difference for duration of pain relief was -4 (90% CI -13, 6) min. Thirty patients failed to achieve pain relief after the first injection (20 patients after S(-)-bupivacaine and 10 after RS-bupivacaine; P = 0.039). However, median duration of pain relief from the first top-up was 82 (range 3-164) min for S(-)-bupivacaine and 76 (22-221) min for RS-bupivacaine. There were no significant differences in the quality of analgesia, as assessed by the investigators. There were no significant differences in the extent of sensory block, percentage of patients with motor block or incidence of adverse events.

Differentiation of fetal pig endocrine cells after allografting into the thymus gland

BACKGROUND

The thymus of large animals, such as the pig, is thought to be an appropriate site for transplanting adult islets, which contain numerous beta cells, for the purpose of reversing diabetes. Whether fetal islet-like cell clusters (ICCs), which contain few beta cells, will develop at this site, so that adequate amounts of insulin can be produced, is unknown.

METHODS

Between 15,000 and 40,000 ICCs were injected into the thymus gland of six juvenile immunosuppressed pigs, and the animals were killed up to 30 days later. The graft was then examined histologically and comparisons made with untransplanted ICCs and those grafted into the omentum of immunosuppressed pigs.

RESULTS

At transplantation, the percentage of cells in the ICCs containing insulin, glucagon, somatostatin, or pancreatic polypeptide was 9+/-1%, 13+/-2%, 9+/-1%, and 3+/-1% respectively. Within 9-30 days of transplantation into the thymus, the percentage of all endocrine cells increased, insulin to 41+/-3%, glucagon to 43+/-6%, somatostatin to 26+/-4%, and pancreatic polypeptide to 9+/-3%. There was co-localization of more than one hormone in some cells. Omental grafts contained a similar percentage of insulin and glucagon-containing cells, but significantly fewer somatostatin and pancreatic polypeptide-containing cells.

CONCLUSIONS

Endocrine cells from the fetal pig pancreas will differentiate when transplanted into the thymus gland of the pig, making this a suitable site for grafting ICCs to test their ability to normalize blood glucose levels of diabetic recipients.

Gene therapy of diabetes: glucose-stimulated insulin secretion in a human hepatoma cell line (HEP G2ins/g)

In order to design a feasible somatic cell gene delivery system for the treatment of type I diabetes, a suitable cell type needs to be determined. We have previously shown that the stable transfection of the full-length insulin cDNA into the human liver cell line, (HEP G2ins) resulted in synthesis, storage and acute regulated release of insulin to analogues of cAMP, but not to the physiological stimulus glucose. In attempting to explain the lack of glucose responsiveness of the HEP G2ins cells we have stably transfected these cells with the human islet glucose transporter GLUT 2 (HEP, G2ins/g cells). The HEP G2ins/g cell clones exhibit glucose-stimulated insulin secretion and glucose potentiation of the secretory response to nonglucose secretagogues. While glucose responsiveness commenced at a lower concentration than normal islets, a secretion curve approaching normal physiological conditions was generated. Immunoelectron microscopy revealed the presence of insulin-containing granules, similar in size and appearance to those of the normal beta cell. These results demonstrate that while it is most likely that the HEP G2ins/g cell line predominantly secretes insulin via the constitutive pathway, significant acute regulated release was seen in response to glucose, and thus represents significant progress in the creation of a genetically engineered 'artificial beta cell' from a human hepatocyte cell line.

Effect of beta-cell toxins on genetically engineered insulin-secreting cells

The betacyte is a genetically engineered insulin-secreting liver cell line that is glucose responsive. Whether this cell is affected by specific beta-cell toxins is unknown. To explore this possibility we exposed these cells and those from the NIT-1 beta-cell line (positive controls) to the toxins streptozotocin (STZ, 2.5-20 mM), alloxan (ALL, 2.5-20 mM), and pentamidine (PENT, 10(-6)-1 mM). STZ and ALL were added for 1 h and pentamidine for 24 h. Insulin secretion from betacytes during a period of 5 h after removal of the toxin was inhibited only by pentamidine; all agents were inhibitory to NIT-1 cells. Glucose metabolism, as determined by a colorimetric MTT reduction assay, was adversely affected in betacytes by ALL (20 mM) and PENT (1 mM), and in NIT-1 cells by STZ (20 mM) as well as by ALL (2.5 mM) and PENT (1 mM). The magnitude of inhibition was less for the betacytes-58 v. 99%. Confluence of cells in culture wells and cell viability as assessed by the fluorochromes propidium iodide and acridine orange was reduced to a lesser extent for the betacytes than for the NIT-1 cells. The metabolic and microscopic effects of the toxins were unchanged in the betacyte from those in the liver cell line, HEP G2, from which the betacyte was engineered. These results of general resistance of the betacyte to beta-cell toxins with differing modes of action offer hope that this cell, or cells created in a similar manner from primary hepatocytes, may be at least partly resistant to the adverse effect of beta-cell toxins involved in autoimmune destruction of the pancreas. This increases the potential of the use of these cells for reversal of diabetes.

Native gel analysis of ribonucleoprotein complexes from a Leishmania tarentolae mitochondrial extract

Two polypeptides of 50 and 45 kDa were adenylated by incubation of a mitochondrial extract from Leishmania tarentolae with [alpha-32P]ATP. These proteins were components of a complex that sedimented at 20S in glycerol gradients and migrated as a single band of approximately 1800 kDa in a native gel. The facts that RNA ligase activity cosedimented at 20S and that the ATP-labeled p45 and p50 polypeptides were deadenylated upon incubation with a ligatable RNA substrate suggested that these proteins may represent charged intermediates of a mitochondrial RNA ligase. Hybridization of native gel blots with guide RNA (gRNA) probes showed the presence of gRNA in the previously identified T-IV complexes that sedimented in glycerol at 10S and contained terminal uridylyl transferase (TUTase) activity, and also in a previously unidentified class of heterodisperse complexes that sedimented throughout the gradient. gRNAs were not detected in the p45 + p50-containing 1800 kDa complex. The heterodisperse gRNA-containing complexes were sensitive to incubation at 27 degrees C and appear to represent complexes of T-IV subunits with mRNA. Polyclonal antiserum to a 70 kDa protein that purified with terminal uridylyl transferase activity was generated, and the antiserum was used to show that this p70 polypeptide was a component of both the T-IV and the heterodisperse gRNA-containing complexes. We propose that the p45 + p50-containing 1800 kDa complex and the p70 + gRNA-containing heterodisperse complexes interact in the editing process. Further characterization of these various complexes should increase our knowledge of the biochemical mechanisms involved in RNA editing.

Increased retinoic acid receptor gamma expression suppresses the malignant phenotype and alters the differentiation potential of human neuroblastoma cells

Human neuroblastoma (NB) tumor cell lines treated in vitro with the retinoid, all-trans-retinoic acid (aRA), form neurites and undergo growth arrest. Retinoids exert their diverse morphologic effects through a signalling pathway which involves the nuclear retinoid receptors. Defective retinoic acid receptor (RAR) function contributes to the malignant phenotype of several human and experimental tumors. Considerable evidence from gene disruption studies now suggests that one of the RARs, RAR gamma, may directly mediate some retinoid effects on embryonic and malignant cells. We, firstly, examined primary NB tumor tissue for a correlation between endogenous RAR gamma expression and clinical stage of the tumor and secondly, the effects of exogenous over-expression of the RAR gamma gene on a human NB tumor cell line. RAR gamma mRNA expression in 32 primary NB tumor tissue samples were significantly higher in clinically localised tumors compared with advanced or disseminated tumors. The human NB tumor cell line, BE(2)-C, was stably transfected with a mammalian expression vector (pREP4) over-expressing the human RAR gamma cDNA. Two selected clones over-expressing RAR gamma (BE/G1 and 2) exhibited a reduced growth rate compared to control cells. Tumorigenicity was inhibited for BE/G1 cells and there was a delayed onset to tumor formation for BE/G2 cells. aRA caused growth inhibition but not neuritic differentiation of the BE/G clones, while 9-cis-retinoic acid caused both growth arrest and neuritic differentiation. Taken together these results suggest that reduced endogenous RAR gamma expression may contribute to the malignant phenotype of human NB. In NB cells the retinoid signalling pathway for neuritic differentiation may be distinct from that causing growth inhibition.

Control of insulin biosynthesis in the human fetal beta cell

The inability of the human fetal beta cell to secrete insulin in response to glucose has been exhaustively studied. In comparison, little attempt has been made to understand if the kinetics of insulin synthesis are as mature as those of an adult beta cell. Using a purified cell population in which 41% of the cells are beta cells, we generated a dose-response curve to glucose with half-maximal synthesis at 4.6 mM glucose, identical to that seen in adult islets. Unlike adult islets, however, in the absence of glucose, agents that raise cyclicAMP (cAMP) (theophylline and forskolin) generated dose-response curves similar to those obtained for glucose. cAMP levels in these cells were enhanced twofold in response to glucose and fourfold to theophylline. Inhibition of cAMP metabolism with 1 mM MDL 12,330A (RMI) reduced insulin synthesis stimulated by glucose and completely inhibited insulin synthesis stimulated by theophylline. Substances that block glucose transport (100 microM cytochalasin B) and protein synthesis (1 mM cycloheximide) also markedly reduced insulin biosynthesis. These results indicate that the regulation of insulin biosynthesis in the human fetal beta cell is cAMP dependent, although glucose transport is a limiting factor when glucose is used as the stimulus. Thus, the human fetal beta cell is relatively mature in its synthesis of insulin, unlike its immaturity in insulin release.

Functional expression of the human insulin gene in a human hepatoma cell line (HEP G2)

To develop a model somatic gene therapy system for diabetes, a human hepatoma cell line (HEP G2) was transfected with a mammalian expression vector carrying the full-length human insulin cDNA. More proinsulin than insulin was released daily by the stably transformed cell line (HEP G2ins). However, on acute stimulation with 5mM 8-Br-cAMP and 10mM theophylline the HEP G2ins cells released predominantly insulin into the medium. The cells did not secrete insulin in response to glucose. Examination of acid-ethanol extracts confirmed insulin was preferentially being stored. Immunohistochemical analysis of the cells also showed (pro)insulin was being stored. Electron microscopy revealed large membrane-bound vacuoles, containing electron-dense material, which were not seen in control cells. Glucokinase activity and albumin secretion of the transfectants were unaltered from the controls. Five-minute pulse-chase labelling of the HEP G2ins cells with 3H-leucine confirmed insulin synthesis in the presence of 20mM glucose and 5mM 8-Br-cAMP. A dose-response curve for insulin synthesis was also generated to increasing concentrations of glucose with a half Vmax of 4.9mM. Our results show that the introduction of insulin cDNA into a human hepatoma cell line results in synthesis, storage and acute regulated insulin release and lend credence to the possibility of engineering a liver cell to secrete insulin acutely in response to physiological stimuli.

In vitro RNA editing-like activity in a mitochondrial extract from Leishmania tarentolae

A mitochondrial extract from Leishmania tarentolae directs the incorporation of uridylate (U) residues within the pre-edited domain of synthetic cytochrome b (CYb) and NADH dehydrogenase subunit 7 mRNA. This has several characteristics of an in vitro RNA editing activity, but no direct evidence for involvement of guide RNAs was obtained. Inhibition by micrococcal nuclease suggests a requirement for some type of endogenous RNA. The limitation of internal U-incorporation to the pre-edited region in the CYb mRNA and the inhibition by deletion or substitution of both mRNA anchor sequences for CYb gRNA-I and -II could be consistent either with a gRNA-mediated process or a secondary structure-mediated process. A low level of incorporation of [alpha-32P]CTP occurs at the same sites as UTP. Internal U-incorporation activity is selectively inhibited by heterologous RNAs, suggesting an involvement of low affinity RNA-binding proteins which can be competed by the added RNA.

Characterization of two classes of ribonucleoprotein complexes possibly involved in RNA editing from Leishmania tarentolae mitochondria

The molecular mechanism of RNA editing in trypanosomatid mitochondria is an unsolved problem. We show that two classes of ribonucleoprotein complexes exist in a mitochondrial extract from Leishmania tarentolae and appear to be involved in RNA editing. The 'G' class of RNP complexes consists of 170-300 A particles which contain guide RNAs and proteins, show little terminal uridylyl transferase (TUTase) activity and exhibit an in vitro RNA editing-like activity. The 'T' class consists of approximately six RNP complexes, the endogenous RNA of which can be self-labeled with [alpha-32P]UTP. The most abundant T complex, T-IV, is visualized by electron microscopy as 80-140 A particles. This complex exhibits TUTase activity in the native gel and contains guide RNAs. Both G and T complexes are possibly involved with RNA editing in vivo. These results are a starting point for the analysis of the biochemistry of RNA editing.

A ribonuclease activity is activated by heparin or by digestion with proteinase K in mitochondrial extracts of Leishmania tarentolae

A ribonuclease activity in a 100,000 x g supernatant of a Triton lysate of a mitochondrial-kinetoplast fraction from Leishmania tarentolae is activated by incubation with heparin or by predigestion of the lysate with proteinase k or pronase. In vitro-transcribed pre-edited cytochrome b mRNA is cleaved at several sites. With time, complete degradation of the RNA occurs. All cleavages occurred within putative single-stranded regions of the RNA. No cleavage was observed with 9 S rRNA. The presence of a nonspecific nucleotide or nucleoside slows the rate of cleavage. The cleavage activity is inhibited by sodium dodecyl sulfate or phenol/chloroform extraction, is retained by a 10-kDa cutoff filter, and passes through a 30-kDa filter. Micrococcal nuclease inhibits the proteinase-induced activity but not the heparin-induced activity.

Role of tumor necrosis factor-alpha and interferon-gamma as growth factors to the human fetal beta-cell

The effects of the cytokines tumor necrosis factor-alpha and interferon-gamma on the adult beta-cell have been well described: a reduction of insulin secretion and content and death of the cell. For this reason and because these cytokines may be released from activated lymphocytes and macrophages that infiltrate islets in insulin-dependent diabetes, they have been implicated in the pathophysiology of this form of diabetes. As to whether the human fetal beta-cell, which differs from the adult beta-cell in not releasing insulin in response to the nutrient glucose and not being adversely affected by the toxin streptozotocin, is similarly affected is unknown. To examine this question we cultured monolayers of a single cell suspension of human fetal pancreas in the presence or absence of 1000 U/mL of these cytokines for 7 days. Chronic insulin release was enhanced for the first 2 days of culture, but unchanged thereafter. Acute insulin release in response to the secretagogue theophylline (10 mM) was enhanced on day 7, but not earlier. There was an increase in the insulin content of the cells by the fourth day, probably due to an increase in the number of beta-cells present (45 +/- 5% vs. 22 +/- 3%). Microscopically, non-beta-cells also seemed to increase in number; there was an increase in both DNA and cell number by the seventh day. In contrast to these beneficial effects on the human fetal beta-cell, treatment of adult rat insulinoma cells, represented by RIN-m5F cells, resulted in inhibition of insulin secretion during the first day of culture and subsequent death of 86% of the cells by the sixth day of culture. It is hypothesized that the functional immaturity and lack of normal (adult) metabolic activity of the human fetal beta-cell somehow confers protection on these cells from the cytotoxic effects of tumor necrosis factor-alpha and interferon-gamma. Indeed, our findings suggest that these cytokines may be trophic for the developing beta-cell.

Characterization of endocrine-rich monolayers of human fetal pancreas that display reduced immunogenicity

Fibroblast-free insulin-secreting monolayers of human fetal pancreas (14-20 wk of gestation) were formed by plating isletlike cell clusters (ICCs) obtained from partially digested pancreases on plates coated with bovine corneal matrix. Human fetal pancreatic cells, freshly digested with collagen, displayed a 17-fold response to human peripheral blood lymphocytes (HPBLs) in mixed-lymphocyte culture. After 14 days in culture, monolayers derived from ICCs exhibited a smaller, twofold response to HPBLs. By comparison, in monolayers produced from single-cell suspensions, fibroblast overgrowth remained a problem. The endocrine component of the monolayers was 65 +/- 13 and 43 +/- 8%, respectively, with the number of beta-cells being 51 and 9%. Cells from both monolayers displayed increased insulin release when exposed to 10 mM theophylline, 10 mM Ca2+, and 0.6-1.3 microM 12-O-tetradecanoylphorbol-13-acetate but not to 20 mM glucose. Monolayers derived from ICCs synthesized DNA, proinsulin, and protein. This study showed that it is possible to establish an endocrine-rich monolayer of human fetal pancreas that has greatly reduced immunogenicity. The existence of residual activity to HPBLs suggests some additional form of immunosuppression is required to prevent rejection of this tissue when grafted into diabetic patients. Subculturing and cryopreservation may also be needed to achieve adequate numbers of beta-cells for clinical transplantation.

Chimeric gRNA-mRNA molecules with oligo(U) tails covalently linked at sites of RNA editing suggest that U addition occurs by transesterification

Chimeric RNA molecules were detected by polymerase chain reaction amplification of kinetoplast RNA using a 3' primer specific to mRNA and a 5' primer specific to guide RNA (gRNA), and directly by Northern analysis. Covalent linkage of the 3' oligo(U) tail of the gRNA to the mRNA occurs at editing sites. Chimeric molecules were isolated for NADH dehydrogenase subunit 7 and cytochrome oxidase subunits II and III. We propose that these molecules are intermediates in the editing process and that successive transesterifications result in the transfer of uridine residues from the gRNA 3' oligo(U) tail to an editing site, with the number of uridine residues determined by base pairing with adenine and guanine "guide" nucleotides in the gRNA.

Pig fetal pancreatic monolayers. A model of potential use in transplantation

Endocrine-rich monolayers of pig fetal pancreas that are free of fibroblasts have been established with the ultimate aim of providing guidelines for the culture of the human equivalent. The immunogenic potential of the monolayers--hence their capacity to be grafted--has also been analyzed. Fetuses ranging from 50 to 90 days were used, and, following digestion with collagenase (4 mg/ml, 15-20 min), the pancreatic suspension was plated onto tissue culture vessels containing RPMI 1640. The fetal calf serum concentration was kept low (5%) initially to inhibit fibroblast proliferation, but subsequently increased to 7%. Monolayers from a typical litter of 8-10 fetal pigs produced 6-8 x 10(8) viable epithelial cells by day 10 of culture, of which 75% were endocrine cells. This represents an 8-fold increase in a two-week period. The ratio of beta:alpha:delta:pancreatic polypeptide cells was 19:33:18:5. These monolayers synthesized both DNA, (pro)insulin and protein, and displayed increased insulin release when exposed to 10 mM theophylline, 10 mM Ca2+ and 1.3 microM 12-0-tetradecanoyl-phorbol-13-acetate. Static stimulation with 20 mM glucose however, did not elicit a response in insulin secretion. These cells displayed no reaction to allogeneic lymphocytes in a mixed lymphocyte culture, whereas freshly obtained porcine epithelial cells did. Methods may need to be found to increase the proportion of B cells in this enriched endocrine cell population. In general however, guidelines have been established that may be useful in developing a monolayer of human fetal pancreatic cells with the eventual aim of transplantation. The reduction in immunogenicity of the pig fetal pancreatic cells suggests that they too might be a potential source for transplantation.

The Leishmania kinetoplast-mitochondrion contains terminal uridylyltransferase and RNA ligase activities

Purified mitochondria of Leishmania tarentolae contain 3'-terminal uridylyltransferase and RNA ligase activities which can be solubilized by detergent lysis of the organelle. Run-off transcription of maxicircle and minicircle DNA also occurs in intact and Triton-lysed mitochondria, using [32P]GTP as the labeled precursor. Heparin inhibits the solubilized terminal uridylyltransferase activity but does not affect the labeling of endogenous RNAs in intact mitochondria with [32P]UTP. Clarification of the mitochondrial Triton lysate causes an increase in terminal uridylyltransferase activity with exogenous substrates. These two activities are candidates for involvement in a post-transcriptional RNA editing process of mitochondrial transcripts.

Kinetoplastid mitochondria contain functional tRNAs which are encoded in nuclear DNA and also contain small minicircle and maxicircle transcripts of unknown function

The mitochondrion of Leishmania tarentolae contains approximately 35-40 tRNAs many of which comigrate with cytoplasmic tRNAs. Both mitochondrial (KtRNA) and cytoplasmic (CtRNA) tRNAs are functional, as they could be acylated either by mitochondrial or cytoplasmic synthetase extracts. There are two methionyl tRNA species in the cytoplasmic and mitochondrial fractions, one of which is unique to each fraction, indicating that the KtRNA fraction is free of CtRNA contamination. Leucyl and glycyl tRNAs were identified by hybridization with a genomic clone from Trypanosoma brucei. KtRNA hybridizes with nuclear chromosomes, but not with minicircle or maxicircle DNA. KtRNA isolated by DEAE chromatography or agarose gel electrophoresis contains additional small RNAs which hybridize with both minicircle and maxicircle DNA. These transcripts do not migrate like tRNAs in acrylamide gels and their functions is unknown. We suggest that most if not all mitochondrial tRNAs in L. tarentolae are nuclear-encoded and imported into the mitochondrion.