ODP300 c-MET expression in MEN1-associated neuroendocrine tumors

 

Multiple studies have shown that approximately 50-70% of patients with MEN1 die of causes directly related to MEN1 particularly gastroenteropancreatic (GEP) neuroendocrine tumors (NETs). While non-functional GEP-NETs are the most common in the general population, gastrinomas (40%) are the most common functional GEP-NETs in patients with MEN1. c-MET is a proto-oncogene that encodes for c-MET, a tyrosine kinase receptor which promotes tumor cell motility, proliferation, survival, invasion, and metastasis. Studies in patients with sporadic gastrinomas and pancreatic NETs (PNETs) have shown that c-MET expression correlates with decreased survival.

While c-MET inhibitors are currently in various stages of investigation for treatment of carcinoids and sporadic PNETs, data regarding their efficacy in patients with MEN1-related GEP NETs is lacking. The majority of trials in patients with GEP-NETs exclude or do not report the number of patients with MEN1. Importantly, somatic MEN1 mutations are observed in 20-40% of sporadic NETs (gastrinomas, PNETs, lung NETs, etc.) but correlation of cMET expression with the presence of somatic or germline MEN1 mutations has not been reported. We sought to investigate the expression of c-MET in tumor tissue from germline MEN1 patients with metastatic GEP-NETs.

Methods

We identified subjects with a germline positive MEN1 mutation and pathologically confirmed distant metastasis who had a follow-up visit between 2018-2020. Of these, we selected subjects with available tissue specimens (including either multiple organ sources or different tumor types). Where available, we identified specimens from multiple source or tumor types. Immunohistochemistry (IHC) to detect c-MET was performed with anti-MET (Cell Signaling) using the DAKO IHC kit (Agilent). IHC slides were imaged and observed to score the level of c-MET staining (-, 1+ to 5+). A score of 3+ or higher was considered consistent with overexpression. We investigated if age at initial GEP-NET presentation, tumor type, tissue source, tumor grade, total number of surgeries for GEP-NET, number of sites of distant metastasis and disease status from overall GEP-NET burden over the preceding 12 months (stable/progressive) predicted c-MET expression.

Results

Eight subjects with available tissue specimens were identified, of which six had tissue from multiple organs while five had tissue from multiple tumor types. Six subjects (75%) showed increased expression of c-MET in one or more tumor specimen(s). The frequency of c-MET overexpression varied with tumor types – carcinoids (n=2/2; 100%), gastrinomas (n=3/5; 60%) and non-functional tumors (n=3/6; 50%). c-MET expression also varied among different tumors in the same patient. Tumor tissue from liver (n=2/2), duodenum (n=3/4), stomach (n=1/1), ovary (n=1/1), pancreas (n= 1/5), and lymph nodes (n=1/3), all showed over-expression of c-MET. No clear predictors of c-MET overexpression emerged.

Conclusion

Our finding suggests a role for c-MET expression in personalizing therapy for patients with MEN1-related NETs with distant metastases.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m., Sunday, June 12, 2022 12:48 p.m. - 12:53 p.m.

LBSAT145 Localizing The "Difficult" Parathyroid Tumor

Background

The identification of parathyroid tumor(s) in patients with persistent/recurrent primary hyperparathyroidism (PHPT) is critical for a successful re-operative surgery. We describe our experience with invasive studies for parathyroid tumor localization and provide follow-up data regarding our experience with selective arterial hypocalcemic stimulation with central venous sampling (SAHSCVS).

Methods

We identified patients who underwent pre-operative invasive testing for localization of parathyroid tumor at our center. At our center, only PHPT patients with history of prior neck surgery without definitive findings on non-invasive testing (sestamibi, ultrasound, CT, MRI) proceed to invasive studies. The result of each invasive localization study (arteriogram, SAHSCVS and selective venous sampling (SVS)) was categorized as true-positive (TP), false-positive (FP) and false-negative (FN) based on biochemical outcome.

Results

Ninety-five patients with 98 tumors underwent invasive testing for parathyroid tumor localization. All but one had recurrent disease. Sixty-two patients (65%) had "apparently sporadic" PHPT, 19/95 (20%) had MEN1, three had parathyroid cancer (PC) and the remaining had other heritable forms of PHPT. Median age of index PHPT presentation was 47 [34-58] years. Of 87 tumors with available operative details, 66 (76%) were in the neck, 20 in the mediastinum (23%), and one in the forearm at site of prior autograft. Seventy-two (83%) showed hyperplasia or hypercellularity on histology. Median tumor size was 5 mm. Arteriogram, SAHSCVS and SVS accurately localized the tumor in 47/90 (52%), 54/90 (60%) and 49/61 (80%) tumors respectively. Positive Predictive Value of arteriogram, SAHSCVS and SVS was 47/50 (94%), 55/64 (86%) and 49/59 (83%) respectively. Both sensitivity and PPV showed no significant difference between patients with MEN1+PC vs. others. Among the 54 tumors accurately localized by SAHSCVS, SVS was performed in 29/54 with complete concordance. Twenty-seven tumors (30%) were missed (FN) on SAHSCVS, of these 14/25 (56%) were also missed on arteriogram. Nevertheless, 16/20 (80%) localized accurately on subsequent SVS. SAHSCVS was FP in localizing nine tumors - seven (78%) of these did not show a blush on arteriogram. All pre-operative localizing studies were unrevealing in 9/98 presentations (10%).

Conclusion

Patients with difficult to localize parathyroid tumors have clinical features suspicious for germline-predisposition forms of PHPT indicated by recurrent disease, hyperplastic glands, and age of index presentation. SAHSCVS can be a useful adjunct in patients who require invasive localization. 90% of these tumors are localized with combination of current non-invasive and invasive testing. AcknowledgementThis research is supported by the Intramural Research Program of NIDDK, NCI and NIH Clinical Center.

Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.

Liver-Specific Expression of Constitutively Active Gsα Leads to Hyperglycemia With Impaired Insulin Secretion

Liver-specific Expression of Constitutively Active G_sα Leads to Hyperglycemia With Impaired Insulin Secretion

The ubiquitously-expressed G protein G_sα couples hormone receptors to the stimulation of intracellular cAMP generation. We previously showed that mice with liver-specific G_sα deficiency (LGsKO) have improved glucose tolerance and enlarged pancreatic islets¹. In the present study, we have generated mice with liver-specific expression of a constitutively activated G_sα (LGsR201C) by breeding mice containing a Lox-STOP-Lox-G_sαR201C transgene within the Hipp11 locus with albumin-Cre mice. Male LGsR201C mice had normal survival but reduced body weight and increased liver weight. Compared to control littermates, LGsR201C mice had significantly increased hepatic cAMP levels and enhanced hyperglycemic response to glucagon, confirming the activation of liver G_sα/cAMP signaling in LGsR201C mice. As a consequence, LGsR201C mice showed elevated blood glucose levels during both fed and fasting states, as well as enhanced hepatic gluconeogenesis evidenced by pyruvate tolerance test. Serum levels of insulin, glucagon, free fatty acids and triglycerides were comparable between control and LGsR201C mice in the fed state. Results of glucose and insulin tolerance tests showed that LGsR201C mice had severe glucose intolerance with normal insulin sensitivity. Unlike control mice, when given a high dose of glucose (3mg/g ip.), LGsR201C mice had completely blunted first- and second-phase insulin secretory responses to glucose. Since LGsR201C mice exhibited normal pancreatic islet size and insulin content examined with immunohistochemistry, the impaired glucose tolerance in LGsR201C mice probably resulted from an impaired insulin secretion. Results of RNA-seq analysis revealed that an array of genes was oppositely regulated in the liver of LGsKO mice vs. LGsR201C mice. Thus, our data indicate possible organ-to-organ communication between liver and pancreatic β-cells that is regulated by liver G_sα signaling. 1.Chen M., et al., JCI 115:3217, 2005

A Blood-Based Polyamine Signature Associated With Disease Progression in Patients With Multiple Endocrine Neoplasia Type 1-Related Duodenopancreatic Neuroendocrine Tumors

Background: Multiple Endocrine Neoplasia Type 1 (MEN1) is a rare inherited autosomal dominant disease predisposing patients to endocrine tumors. MEN1 can be genetically diagnosed at an early age. Patients are prone to develop benign parathyroid tumors then multifocal duodenopancreatic neuroendocrine tumors (dpNETs), which have a penetrance of >80% by age 80. Although they can be identified at an early stage, preventive measures do not exist, and one fifth of patients develop distant metastases, which is the most significant cause of mortality. Currently, no biomarkers can reliably predict which patients with MEN1-related dpNETs are at high risk of developing metastatic disease. Polyamines are naturally occurring polycationic alkylamines that have been implicated to play functional roles in promoting neoplastic transformation and growth. We have previously demonstrated a plasma polyamine signature that associates with pancreatic cancer development and that also offers value for predicting future distant metastasis in patients with triple-negative breast cancer. We hypothesized that such a plasma polyamine signature may similarly associate with disease progression in subjects with MEN1-related dpNET.

Methods: As part of an international collaboration, we measured plasma polyamine levels using mass spectrometry from 14 MEN1 patients with distant metastatic dpNET (cases), 28 MEN1 patients with indolent dpNETs without distant metastases (control-1), and 14 MEN1 patients without dpNETs (control-2). Five circulating plasma polyamines were quantified in this initial test set. A combination rule was developed using logistic regression models. Findings were validated in an independent set of plasma from 6 cases and 22 controls (n=13 control-1 and n=9 control-2).

Results: Area under the Receiver Operating Characteristic Curve (AUC) of individual polyamines delineating cases from controls ranged from 0.50-0.75 in the test set. A polyamine signature consisting of 3 polyamines developed in the test set yielded an AUC of 0.84 (95% CI: 0.63-1.00) with 67% sensitivity at 95% specificity in the validation set for distinguishing cases from controls. The predictive performance of the polyamine signature for distinguishing cases from MEN1 patients with indolent dpNETS without distant metastasis or MEN1 patients without dpNETS in the validation set was 0.79 (95% CI: 0.53-1.00) and 0.91 (95% CI: 0.75-1.00) with respective resultant sensitivity at 95% specificity of 50% and 67%.

Conclusion: Our findings reveal a plasma polyamine signature associated with disease progression in subjects with MEN1-related dpNETs. This polyamine signature may provide a potential breakthrough for predicting progression and distant metastasis in MEN1 patients. Further prospective studies are warranted.

Distinct DNA Methylation Signatures in Neuroendocrine Tumors Specific for Primary Site and Inherited Predisposition

PURPOSE

To compare the deoxyribonucleic acid (DNA) methylation signature of neuroendocrine tumors (NETs) by primary tumor site and inherited predisposition syndromes von Hippel-Lindau disease (VHL) and multiple endocrine neoplasia type 1 (MEN1).

METHODS

Genome-wide DNA methylation (835 424 CpGs) of 96 NET samples. Principal components analysis (PCA) and unsupervised hierarchical clustering analyses were used to determine DNA methylome signatures.

RESULTS

Hypomethylated CpGs were significantly more common in VHL-related versus sporadic and MEN1-related NETs (P < .001 for both comparisons). Small-intestinal NETs (SINETs) had the most differentially methylated CpGs, either hyper- or hypomethylated, followed by duodenal NETs (DNETs) and pancreatic NETs (PNETs, P < .001 for all comparisons). There was complete separation of SINETs on PCA, and 3 NETs of unknown origin clustered with the SINET samples. Sporadic, VHL-related, and MEN1-related PNETs formed distinct groups on PCA, and VHL clustered separately, showing pronounced DNA hypomethylation, while sporadic and MEN1-related NETs clustered together. MEN1-related PNETs, DNETs, and gastric NETs each had a distinct DNA methylome signature, with complete separation by PCA and unsupervised clustering. Finally, we identified 12 hypermethylated CpGs in the 1A promoter of the APC (adenomatous polyposis coli) gene, with higher methylation levels in MEN1-related NETs versus VHL-related and sporadic NETs (P < .001 for both comparisons).

CONCLUSIONS

DNA CpG methylation profiles are unique in different primary NET types even when occurring in MEN1-related NETs. This tumor DNA methylome signature may be utilized for noninvasive molecular characterization of NETs, through DNA methylation profiling of biopsy samples or even circulating tumor DNA in the near future.

c-MET inhibition: novel treatment for sporadic and MEN1-associated GEP NETs

Gastroenteropancreatic neuroendocrine tumors (GEP NETs) comprise a heterogenous and diverse group of neoplasms arising from a common neuroendocrine cell origin. The majority of these tumors occur sporadically while ~20% manifest within the context of hereditary syndromes. Germline MEN1 mutations cause a syndrome with an increased susceptibility to multifocal primary GEP NETs. In addition, somatic MEN1 mutations also occur in these sporadic lesions. MEN1 alterations are the most frequent somatic mutation found in pancreatic neuroendocrine tumors. In this review, we explore the implication of the loss of the MEN1-encoded protein menin as a key pathogenic driver in subsets of GEP NETs with downstream consequences including upregulation of the oncogenic receptor c-MET (hepatocyte growth factor receptor). Furthermore, the review will summarize the data related to the clinical presentation, therapeutic standards, and outcomes of these tumors in both sporadic and germline MEN1 mutation-associated contexts. Finally, we present the data on c-MET expression in GEP NETs, clinical trials using c-MET inhibitors and provide an overview of the molecular mechanisms by which c-MET inhibition in these lesions represents a potential precision-medicine targeted approach.

SUN-128 Impaired Fasting Glucose Is Associated with Insulin Resistance in Patients with Germline Mutations in the Multiple Endocrine Neoplasia Type 1 (MEN1) Gene

BACKGROUND: Multiple endocrine neoplasia type 1 (MEN1) is an autosomal dominant syndrome characterized by hyperparathyroidism, pituitary adenomas, and gastro-entero-pancreatic neuroendocrine tumors. Patients with MEN1 mutations have impaired glucose homeostasis, but the role of insulin resistance and beta-cell function is unclear.

METHODS: Using a case-control study design, a retrospective analysis of germline mutation-positive MEN 1 patients (n=289) seen at our institution between 1991-2019 was performed. Patients with diabetes and/or insulinoma were excluded. Subjects were age, BMI, sex and race matched 1:1 to unrelated, healthy controls. Fasting glucose, insulin, c-peptide, calcium, PTH, 25-OH vitamin D, cholesterol, LDL, HDL and triglycerides (TG) were compared between two groups. Homeostasis model assessment (HOMA-IR) and HOMA-beta cell function (HOMA-b) were used as surrogate measures of insulin resistance and beta-cell function, respectively. Data is presented as mean ± SD.

RESULTS: MEN1 subjects (n=40; age 41±11 years; BMI 29.2±7.2 kg/m²) were matched to healthy controls (age 41±11 years; BMI 29.1±7.5 kg/m²). Only 3 MEN1 patients had no evidence of pancreatic neuroendocrine tumors. Impaired fasting glucose was more prevalent in MEN1 compared with controls (53% vs 10%, p<0.0001). HOMA-IR was positively associated with BMI, but not age, sex, calcium or vitamin D levels in either cohort. HOMA-IR adjusted for age, BMI, and sex was higher in patients with MEN1 compared with controls (4.01 vs. 2.44, adjusted ratio of means 1.54, 95% CI [1.14, 2.07], p=0.005). HOMA-b was not significantly different between the groups (177 vs. 129, adjusted ratio of means 1.17, 95% CI [0.86, 1.58], p=0.23). There were no significant differences in total cholesterol, LDL, HDL, and TG between the groups.

CONCLUSION: Lower insulin sensitivity, but not impaired beta cell function may contribute to the higher prevalence of impaired fasting glucose in MEN1 patients compared with controls. Mechanistic studies into the role of menin loss in glucose homeostasis are warranted.

SUN-116 The Role of 68Gallium DOTATATE PET/CT Versus 18F-FDOPA PET/CT in the Imaging of Neuroendocrine Neoplasms in Patients with Multiple Endocrine Neoplasia Type 1 (MEN1)

Background: Neuroendocrine neoplasms (NEN) are a heterogenous group of tumors. Patients with the multiple endocrine neoplasia type 1 (MEN1) syndrome often manifest with simultaneous functional and non-functional NEN in various endocrine glands. In MEN1, nuclear medicine plays an important role in the diagnostic work-up and localization of NEN. Little is known about the comparative efficacy of ⁶⁸Ga-Dotatate PET/CT (DOTA) versus ¹⁸F-FDOPA PET/CT (FDOPA) and both versus non-nuclear medicine imaging (CT and MRI) in the identification of primary and metastatic NEN.

Methods: This prospective MEN1 cohort study evaluated 15 germline MEN1 mutation-positive patients. Subjects were imaged using CT, MRI, DOTA and ¹⁸F-FDOPA. Radiological review with a multidisciplinary team was performed for each patient.

Results: One-hundred twenty-nine total lesions were identified using any of the four scans. DOTA sensitivity was 69% (89/129; 95% CI 61% to 76%) with a mean standardized uptake value (SUV) of 33.9 ± 30.1, FDOPA sensitivity was 18% (23/129; 95% CI 12% to 25%) with mean SUV of 12.1 ± 15.16. DOTA identified an additional 50 lesions not seen on CT (of which MRI detected 8 lesions with an average size 0.95 cm ± 0.48; 3 pancreatic, 2 duodenal, 2 liver, and 1 lymph node) and identified 55 lesions not seen on MRI (of which CT identified 13 with a mean size of 1.1 cm ± 0.45; 1 lung, 4 pancreatic, 2 duodenal, 1 liver, and 5 lymph nodes). Overall, CT detected 51.2% (66/129) of lesions (mean 0.61 cm ± 0.73; 95% CI 43% to 60%) and MRI detected 39.5% (51/129; 0.47 cm ± 0.71; 95% CI 32% to 48%), and there was no significant difference in the size of lesions detected (p=0.18). Analysis by organ NEN revealed equal sensitivity between FDOPA and DOTA for lung carcinoid, detecting 33% (4/12) of lesions, while CT detected 92% (11/12) of lesions. In the duodenum, DOTA identified 100% (11 /11) of lesions, while FDOPA had poor sensitivity (9%) in this location. Within the pancreas, DOTA has a sensitivity of 81% (31/38), while FDOPA had a sensitivity of 21% (8/38). CT localized 42% (16/38) of pancreatic lesions, of which MRI missed 6. Interestingly, DOTA missed 7 pancreatic lesions all approximately 1cm or larger, which is previously unrecognized (range 0.9 - 1.8cm). Twenty-three liver metastases were detected on anatomic imaging (CT identified 14, while MRI detected 15, with only 9 overlapping lesions). DOTA identified 60% (14/23) of lesions, of which 3 lesions were missed by CT and MRI. However, DOTA was more sensitive in the liver than FDOPA which only detected 2 lesions. FDOPA detected one lesion in the adrenal (0.9cm) that was not seen on DOTA.

Conclusion: DOTA imaging proved to be superior to FDOPA, CT and MRI overall in detecting NENs in MEN1, specifically in the duodenum. Pancreatic NEN missed by DOTA may represent higher grade tumors and may benefit from ¹⁸FDG PET/CT imaging.

OR04-06 G Protein GSα in Muscle Is Essential for Survival During Cold Adaptation in the Absence of Thermogenesis of Brown Adipose Tissue

Adaptive thermogenesis is important for the control of body temperature (Tb) and maintenance of body weight, and it is primarily regulated by sympathetically-driven brown adipose tissue (BAT). Studies indicate that muscle is also involved in thermogenic regulation. G_sα couples to ligands and receptors, including β-adrenergic receptors, to increase intracellular cAMP. Our previous studies have showed that mice with adipose-specific G_sα deficiency had inactive BAT and impaired cold tolerance. To determine whether G_sα/cAMP signaling in skeletal muscle compensates for loss of BAT thermogenesis, we generated mice with G_sα deficiency in adipocyte tissue alone (AdipGsKO), in skeletal muscle alone (SkMGsKO) or in both (AdipSkMGsKO). Compared to control mice, AdipGsKO and SkMGsKO mice had normal body weight, while AdipSkMGsKO showed reduced body weight with normal food intake and energy expenditure. Both AdipGsKO and AdipSkMGsKO mice had elevated fasting glucose levels, but similar glucose tolerance to control or SkMGsKO mice. SkMGsKO mice displayed reduced insulin sensitivity. When acutely exposed to 6^oC for 3 hours, AdipGsKO and AdipSkMGsKO mice rapidly decreased their Tb, indicating that they are sensitive to acute cold exposure, consistent with their inactive BAT. To assess adaptation to chronic cold, mice were exposed to gradually declining ambient temperature from 22^oC to 6^oC with a daily decrease of 2^oC and were then kept at 6^oC for 5 days. As expected, both AdipGsKO and AdipSkMGsKO mice failed to stimulate BAT UCP1 by cold adaptation. Unexpectedly, AdipGsKO mice maintained normal Tb similar to control and SkMGsKO mice. However, AdipSkMGsKO mice started to rapidly drop their Tb when ambient temperature declined to 14^oC and 85% of SkMGsKO mice (11/13) died before the end of experiment. These results suggest that when there is a lack of BAT function, G_sα/cAMP signaling in muscle plays an essential role for mice to survive in response to chronic cold challenge.

SUN-124 Are Venous Thromboembolic Events Increased in MEN1 Patients?

Background: Multiple endocrine neoplasia type 1 (MEN1) is a rare inherited disorder in which patients develop multiple simultaneous hormone-secreting tumors. Most common tumors include: anterior pituitary adenomas (50%), multi-gland parathyroid adenomas (95%), and gastroenteropancreatic neuroendocrine tumors (40-80%). Only rare MEN1 associated glucagonomas (<1%), and ACTH-producing neuroendocrine tumors (<5%) are known to increase risk of hypercoagulability. It is unknown if patients with MEN1 syndrome have increased risk of venous thrombolytic events (VTE), defined as a deep-vein thrombosis and/or pulmonary embolism.

Methods: We queried a prospective natural history study of MEN1 patients who tested positive for germline MEN1 mutations (n=287) between 1991-2019 (54 patients on our current protocol were followed before 1991; the earliest was 1971). All lifetime events of VTE were included. Search terms included: DVT, thromb, embol, PE, pulmonary embolism, clot, hematology consult, anticoagulant, coumadin, lovenox, xarelto, warfarin, aspirin, rivaroxaban and apixaban. After initial screening, 10 patients were removed due to insufficient clinical data. Kaplan-Meier analysis was performed to compare age of death between the two cohorts. Results were expressed as mean ± standard deviation.

Results: Thirty-four subjects (mean 57.5 years-old, 17 women) were identified with any VTE, yielding a prevalence rate of 13.4%. The incidence of VTE corresponded to 264 events per 100,000 patient-years, which was ~2-fold higher than the estimated annual incidence rate in the general population (104-183/100,000 patient years).¹ Kaplan-Meier analysis revealed no significant difference in survival between the two groups (non-VTE cohort mean 81.1 years ± 2.23; VTE cohort mean 77.4 years ± 3.45; p = 0.96). Thirty-two events occurred during the surveillance period at our institution; 9 individuals had more than one VTE. At the time of VTE, 80% had hyperparathyroidism (mean PTH ± SD; 97.56 pg/mL ± 90.76), 21% had hyperprolactinemia (prolactin 25.7μg/L ± 43.41), 62.5% had hypergastrinemia (mean gastrin 1100.9 pg/mL ± 3127.8), and 84.6% had non-functional pancreatic neuroendocrine tumors. One patient was identified to have a Factor V Leiden mutation, 3 patients had lupus anti-coagulant. Eleven patients experienced events within a post-surgical period of 3 months.

Conclusions: Hypercoagulability in MEN1 has been previously unidentified. Our cohort data suggests a two-fold increase in the incidence of VTE as compared to the general population, with a high risk occurring within the perioperative period. Further mechanistic investigation and validation from other cohorts are needed to confirm the increased prevalence of VTE in this population.

¹Heit, John A., et al. Epidemiology of venous thromboembolism. Nat Rev Cardiol 2015 Aug;12(8): 464-474.

SUN-115 Distinct DNA Methylation Signature in Neuroendocrine Tumors of Different Primary Sites and Hereditary Predisposition

Objective

There is scant data of the genome-wide methylome alterations in neuroendocrine tumors (NET). Thus, the goal of this study was to compare the DNA methylation signature of NETs with respect to various primary sites and inherited genetic predisposition syndromes including von Hippel-Lindau (VHL) and multiple endocrine neoplasia type 1 (MEN1).

Methods

Genome-wide DNA methylation analysis of 96 NETs (primary and metastatic) was performed by using the Illumina Infinium EPIC Array. Principal component analysis (PCA) and unsupervised clustering analyses were performed to identify distinct methylome signatures. The methylation status of genetic drivers such as APC were assessed by primary site.

Results

A total of 835,424 CpGs methylation sites were quantified. Hypermethylated CpG sites were detected more frequently in sporadic vs. MEN1-related vs. VHL-related NETs, respectively (p < 0.001 for all comparisons), while hypomethylated CpGs sites were more common in VHL-related NETs vs. sporadic and MEN1-related NETs (p<0.001 for both comparisons).

Small-intestinal NETs (SINETs) had the most differences at CpGs with the highest number of hyper- and hypomethylated CpG sites, followed by duodenal NETs (DNETs) and pancreatic NETs (PNETs, p<0.001 for all comparisons). PCA showed distinct clustering of SINETs and three NETs of unknown primary. Sporadic, VHL-related and MEN1-related PNETs formed distinct groups on PCA. VHL-related NETs clustered separately showing pronounced CpG hypomethylation, while sporadic and MEN1-related NETs clustered together showing relative CpG hypermethylation. In a subgroup analysis, MEN1-related SINETs, DNETs and gastric NETs had distinct methylome signatures, respectively, with complete separation by PCA and unsupervised hierarchical clustering. Furthermore, we found CpG hypermethylation in the APC (adenomatous polyposis coli) gene, specifically in the 1A promoter, with higher methylation levels in gastric- and DNETs vs. SINETs, PNETs and NETs of unknown primary (p < 0.001 for all comparisons).

Conclusion

Various primary NET sites and genetically predisposed MEN1-related NETs have distinct DNA CpG methylation signatures. The methylome signatures identified in this study may be useful for non-invasive molecular characterization of NETs, through DNA methylation profiling of biopsy samples or circulating tumor DNA.

Role of G(s)α in central regulation of energy and glucose metabolism

GNAS is a complex imprinted locus with multiple oppositely imprinted gene products, including the G protein α-subunit Gsα that is expressed primarily from the maternal allele in some tissues and the Gsα isoform XLαs that is expressed only from the paternal allele. Maternal Gsα mutations in mice and in patients with Albright hereditary osteodystrophy lead to obesity, insulin resistance, and hyperlipidemia. Studies in mice show that these effects are primarily due to Gsα imprinting in the central nervous system and that Gsα deficiency in one or more regions of the central nervous system lead to reduced sympathetic nervous system and energy expenditure without affecting food intake. Loss of Gsα in the central nervous system appears to lead to these effects primarily through impairment of melanocortin signaling. Loss of XLαs in mice leads to opposite effects on energy and glucose metabolism.

The role of GNAS and other imprinted genes in the development of obesity

Genomic imprinting is an epigenetic phenomenon affecting a small number of genes, which leads to differential expression from the two parental alleles. Imprinted genes are known to regulate fetal growth and a 'kinship' or 'parental conflict' model predicts that paternally and maternally expressed imprinted genes promote and inhibit fetal growth, respectively. In this review we examine the role of imprinted genes in postnatal growth and metabolism, with an emphasis on the GNAS/Gnas locus. GNAS is a complex imprinted locus with multiple oppositely imprinted gene products, including the G-protein alpha-subunit G(s)alpha that is expressed primarily from the maternal allele in some tissues and the G(s)alpha isoform XLalphas that is expressed only from the paternal allele. Maternal, but not paternal, G(s)alpha mutations lead to obesity in Albright hereditary osteodystrophy. Mouse studies show that this phenomenon is due to G(s)alpha imprinting in the central nervous system leading to a specific defect in the ability of central melanocortins to stimulate sympathetic nervous system activity and energy expenditure. In contrast mutation of paternally expressed XLalphas leads to opposite metabolic effects in mice. Although these findings conform to the 'kinship' model, the effects of other imprinted genes on body weight regulation do not conform to this model.

The role of tissue-specific imprinting as a source of phenotypic heterogeneity in human disease

Genomic imprinting is an epigenetic phenomenon affecting a small number of genes that leads to expression from only one parental allele. Several imprinted genes are important for neurologic development and function and several neurobehavioral disorders are caused by genetic defects involving imprinted genes. For some genes, the imprinting is tissue specific, leading to biallelic expression in some tissues and monoallelic expression in other tissues. Defects involving these genes may produce one restricted phenotype due to loss of expression of the gene product in tissues where the gene is imprinted and, in some instances, a second phenotype due to haploinsufficiency of the gene product in tissues where it is biallelically expressed.

Reoperation for hyperparathyroidism in multiple endocrine neoplasia type 1

BACKGROUND

Patients with multiple endocrine neoplasia type 1 and hyperparathyroidism often undergo multiple operations because of inadequate initial surgery, presence of supernumerary and ectopic glands, regrowth of remnant glands, or autograft hyperfunction. Management of this patient population is complex.

METHODS

From January 1975 to December 2000 we performed 94 reoperative parathyroidectomies consisting of 79 neck reexplorations, 12 autograft removals, and 3 median sternotomies in 75 patients. Data were gathered by retrospective chart review and follow-up telephone interviews.

RESULTS

Excluding autograft excision, reoperative surgery was successful (normocalcemia longer than 6 months) in 91%; autograft removal was successful in only 58%. With a median follow-up of 59 months, 64% of patients are currently free from hypercalcemia, and this outcome was not influenced by the total number of glands resected. The median time to recurrent hypercalcemia was 125 months. Thirty patients received an autograft after reoperation. The complication rate for all reoperations was 12%, including permanent recurrent laryngeal nerve injury in 2 patients (2.1%).

CONCLUSIONS

Reoperative parathyroidectomy in patients with multiple endocrine neoplasia type 1 was safe and successful in the majority of patients; however, recurrent hyperparathyroidism is likely to develop in most individuals beyond 10 years of follow-up. The total number of glands accounted for after reoperation is not associated with successful outcome.

Endocrine manifestations of stimulatory G protein alpha-subunit mutations and the role of genomic imprinting

The heterotrimeric G protein G(s) couples hormone receptors (as well as other receptors) to the effector enzyme adenylyl cyclase and is therefore required for hormone-stimulated intracellular cAMP generation. Receptors activate G(s) by promoting exchange of GTP for GDP on the G(s) alpha-subunit (G(s)alpha) while an intrinsic GTPase activity of G(s)alpha that hydrolyzes bound GTP to GDP leads to deactivation. Mutations of specific G(s)alpha residues (Arg(201) or Gln(227)) that are critical for the GTPase reaction lead to constitutive activation of G(s)-coupled signaling pathways, and such somatic mutations are found in endocrine tumors, fibrous dysplasia of bone, and the McCune-Albright syndrome. Conversely, heterozygous loss-of-function mutations may lead to Albright hereditary osteodystrophy (AHO), a disease characterized by short stature, obesity, brachydactyly, sc ossifications, and mental deficits. Similar mutations are also associated with progressive osseous heteroplasia. Interestingly, paternal transmission of GNAS1 mutations leads to the AHO phenotype alone (pseudopseudohypoparathyroidism), while maternal transmission leads to AHO plus resistance to several hormones (e.g., PTH, TSH) that activate G(s) in their target tissues (pseudohypoparathyroidism type IA). Studies in G(s)alpha knockout mice demonstrate that G(s)alpha is imprinted in a tissue-specific manner, being expressed primarily from the maternal allele in some tissues (e.g., renal proximal tubule, the major site of renal PTH action), while being biallelically expressed in most other tissues. Disrupting mutations in the maternal allele lead to loss of G(s)alpha expression in proximal tubules and therefore loss of PTH action in the kidney, while mutations in the paternal allele have little effect on G(s)alpha expression or PTH action. G(s)alpha has recently been shown to be also imprinted in human pituitary glands. The G(s)alpha gene GNAS1 (as well as its murine ortholog Gnas) has at least four alternative promoters and first exons, leading to the production of alternative gene products including G(s)alpha, XLalphas (a novel G(s)alpha isoform that is expressed only from the paternal allele), and NESP55 (a chromogranin-like protein that is expressed only from the maternal allele). A fourth alternative promoter and first exon (exon 1A) located approximately 2.5 kb upstream of the G(s)alpha promoter is normally methylated on the maternal allele and transcriptionally active on the paternal allele. In patients with isolated renal resistance to PTH (pseudohypoparathyroidism type IB), the exon 1A promoter region has a paternal-specific imprinting pattern on both alleles (unmethylated, transcriptionally active), suggesting that this region is critical for the tissue-specific imprinting of G(s)alpha. The GNAS1 imprinting defect in pseudohypoparathyroidism type IB is predicted to decrease G(s)alpha expression in renal proximal tubules. Studies in G(s)alpha knockout mice also demonstrate that this gene is critical in the regulation of lipid and glucose metabolism.

Increased insulin sensitivity in Gsalpha knockout mice

The stimulatory guanine nucleotide-binding protein (G(s)) is required for hormone-stimulated cAMP generation. Gnas, the gene encoding the G(s) alpha-subunit, is imprinted, and targeted disruption of this gene in mice leads to distinct phenotypes in heterozygotes depending on whether the maternal (m-/+) or paternal (+/p-) allele is mutated. Notably, m-/+ mice become obese, whereas +/p- mice are thinner than normal. In this study we show that despite these opposite changes in energy metabolism, both m-/+ and +/p- mice have greater sensitivity to insulin, with low to normal fasting glucose levels, low fasting insulin levels, improved glucose tolerance, and exaggerated hypoglycemic response to administered insulin. The combination of increased insulin sensitivity with obesity in m-/+ mice is unusual, because obesity is typically associated with insulin resistance. In skeletal muscles isolated from both m-/+ and +/p- mice, the basal rate of 2-deoxyglucose uptake was normal, whereas the rate of 2-deoxyglucose uptake in response to maximal insulin stimulation was significantly increased. The similar changes in muscle sensitivity to insulin in m-/+ and +/p- mice may reflect the fact that muscle G(s)alpha expression is reduced by approximately 50% in both groups of mice. GLUT4 expression is unaffected in muscles from +/p- mice. Increased responsiveness to insulin is therefore the result of altered insulin signaling and/or GLUT4 translocation. This is the first direct demonstration in a genetically altered in vivo model that G(s)-coupled pathways negatively regulate insulin signaling.

Evaluation of operative cholangiography in 2043 patients undergoing laparoscopic cholecystectomy: a case for the selective operative cholangiogram

BACKGROUND

There is still some controversy over whether to use laparoscopic operative cholangiograms routinely (RLOC) or selectively (SLOC). Due to their high cost as well as other issues, in March 1997 we converted from RLOC to SLOC. The purpose of this study was to validate that decision.

METHODS

The results of 2043 laparoscopic cholecystectomies (LC) were compiled and analyzed. The results of RLOC in 1556 patients undergoing LC from March 1990 through February 1997 were compared to the results of SLOC in 16 patients undergoing LC from March 1989 through February 1990 and 471 patients undergoing LC from March 1997 through December 1998. The literature was reviewed and data were compiled. Reasons that are typically given for operative cholangiograms (OC) were collected and scrutinized. Finally, cost surveys for RLOC and related procedures were obtained.

RESULTS

Overall, laparoscopic operative cholangiogram (LOC) was attempted in 1661 patients and was successful in 1656 cases (99.7%). Bile duct stones (BDS) were evident in 166 patients. Laparoscopic bile duct exploration (LBDE) was attempted in all cases. None were referred for preoperative endoscopic retrograde cholangiopancreatography (ERCP). In the RLOC group, evidence of BDS was observed in 136 patients (9%). Forty-two were unsuspected (2.8%) and five were false positive (0.3%). In a collection of other RLOC studies, the average rate of unsuspected BDS was 2.9%, while the average rate of false positive cholangiograms was 1.6%. In the SLOC group, LOC was indicated in 139 of 487 patients (28.6%). None of the patients who did not have a LOC developed symptomatic residual BDS in < or = 11 years of follow-up. In a large collection of other SLOC studies, the rate of symptomatic residual BDS was 0.3%. A cost survey in February 1997 revealed that the average minimum global charge (MGC) for an OC was $1283.21; for a transcystic duct LBDE it was $1055.10, and for a transcholedochal LBDE it was $3263.61 [corrected]. The MGC for an ERCP with papillotomy was $4303.00. Thus, to avoid one patient with symptomatic residual BDS, 354 unnecessary procedures (333 RLOC, 18 LBDE, and three postoperative ERCP) costing $473,927.52 would be performed. There were no false negatives, bile duct injuries, or other complications attributable to RLOC or SLOC.

CONCLUSIONS

The increased morbidity and cost of RLOC to avoid symptomatic residual BDS is not justified. All other reasons given for RLOC are either flawed or indicate that the procedure can be safely employed selectively. SLOC is an effective method of verifying suspected BDS and is safer and less expensive than RLOC.

A GNAS1 imprinting defect in pseudohypoparathyroidism type IB

Pseudohypoparathyroidism type IB (PHPIB) is characterized by renal resistance to parathyroid hormone (PTH) and the absence of other endocrine or physical abnormalities. Familial PHPIB has been mapped to 20q13, near GNAS1, which encodes G(s)alpha, the G protein alpha-subunit required for receptor-stimulated cAMP generation. However, G(s)alpha function is normal in blood cells from PHPIB patients, ruling out mutations within the G(s)alpha coding region. In mice G(s)alpha is expressed only from the maternal allele in renal proximal tubules (the site of PTH action) but is biallelically expressed in most other tissues. Studies in patients with Albright hereditary osteodystrophy suggest a similar G(s)alpha imprinting pattern in humans. Here we identify a region upstream of the G(s)alpha promoter that is normally methylated on the maternal allele and unmethylated on the paternal allele, but that is unmethylated on both alleles in all 13 PHPIB patients studied. Within this region is an alternative promoter and first exon (exon 1A), generating transcripts that are normally expressed only from the paternal allele, but that are biallelically expressed in PHPIB patients. Therefore, PHPIB is associated with a paternal-specific imprinting pattern of the exon 1A region on both alleles, which may lead to decreased G(s)alpha expression in renal proximal tubules. We propose that loss of exon 1A imprinting is the cause of PHPIB.

Identification of a methylation imprint mark within the mouse Gnas locus

The imprinted mouse gene Gnas produces the G protein alpha-subunit G(S)alpha and several other gene products by using alternative promoters and first exons. G(S)alpha is maternally expressed in some tissues and biallelically expressed in most other tissues, while the gene products NESP55 and XLalphas are maternally and paternally expressed, respectively. We investigated the mechanisms of Gnas imprinting. The G(S)alpha promoter and first exon are not methylated on either allele. A further upstream region (approximately from positions -3400 to -939 relative to the G(S)alpha translational start site) is methylated only on the maternal allele in all adult somatic tissues and in early postimplantation development. Within this region lies a fourth promoter and first exon (exon 1A) that generates paternal-specific mRNAs of unknown function. Exon 1A and G(S)alpha mRNAs have similar expression patterns, making competition between their promoters unlikely. Differential methylation in this region is established during gametogenesis, being present in oocytes and absent in spermatozoa, and is maintained in preimplantation E3. 5d blastocysts. Therefore, this region is a methylation imprint mark. In contrast, differential methylation of the NESP55 and XLalphas promoter regions (Nesp and Gnasxl) is not established during gametogenesis. The methylation imprint mark that we identified may be important for the tissue-specific imprinting of G(S)alpha.

Variable imprinting of the heterotrimeric G protein G(s) alpha-subunit within different segments of the nephron

The heterotrimeric G protein G(s) is required for hormone-stimulated intracellular cAMP generation because it couples hormone receptors to the enzyme adenylyl cyclase. Hormones that activate G(s) in the kidney include parathyroid hormone, glucagon, calcitonin, and vasopressin. Recently, it has been demonstrated that the G(s)alpha gene is imprinted in a tissue-specific manner, leading to preferential expression of G(s)alpha from the maternal allele in some tissues. In the kidney, G(s)alpha is imprinted in the proximal tubule but not in more distal nephron segments, such as the thick ascending limb or collecting duct. This most likely explains why in both humans and mice heterozygous mutations in the maternal allele lead to parathyroid hormone resistance in the proximal tubule whereas mutations in the paternal allele do not. In contrast, heterozygous mutations have little effect on vasopressin action in the collecting ducts. In mice with heterozygous null G(s)alpha mutations (both those with mutations on the maternal or paternal allele), expression of the Na-K-2Cl cotransporter was decreased in the thick ascending limb, suggesting that its expression is regulated by cAMP. The G(s)alpha genes also generate alternative, oppositely imprinted transcripts encoding XLalphas, a G(s)alpha isoform with a long NH(2)-terminal extension, and NESP55, a chromogranin-like neurosecretory protein. The role, if any, of these proteins in renal physiology is unknown.

Paternal versus maternal transmission of a stimulatory G-protein alpha subunit knockout produces opposite effects on energy metabolism

Heterozygous disruption of Gnas, the gene encoding the stimulatory G-protein alpha subunit (G(s)alpha), leads to distinct phenotypes depending on whether the maternal (m-/+) or paternal (+/p-) allele is disrupted. G(s)alpha is imprinted, with the maternal allele preferentially expressed in adipose tissue. Hence, expression is decreased in m-/+ mice but normal in +/p- mice. M-/+ mice become obese, with increased lipid per cell in white and brown adipose tissue, whereas +/p- mice are thin, with decreased lipid in adipose tissue. These effects are not due to abnormalities in thyroid hormone status, food intake, or leptin secretion. +/p- mice are hypermetabolic at both ambient temperature (21 degrees C) and thermoneutrality (30 degrees C). In contrast, m-/+ mice are hypometabolic at ambient temperature and eumetabolic at thermoneutrality M-/+ and wild-type mice have similar dose-response curves for metabolic response to a beta(3)-adrenergic agonist, CL316243, indicating normal sensitivity of adipose tissue to sympathetic stimulation. Measurement of urinary catecholamines suggests that +/p- and m-/+ mice have increased and decreased activation of the sympathetic nervous system, respectively. This is to our knowledge the first animal model in which a single genetic defect leads to opposite effects on energy metabolism depending on parental inheritance. This probably results from deficiency of maternal- and paternal-specific Gnas gene products, respectively.

Comparison of insufflation vs. retractional technique for laparoscopic-assisted intervertebral fusion of the lumbar spine

Laparoscopic transperitoneal fusion of the L5-S1 spinal interspace has become a common procedure. Retroperitoneal retraction and laparoscopic instrumentation without insufflation also allows visualization of the upper lumbar spaces, but this procedure is much more difficult to accomplish. We review and compare our results using each of these techniques for the treatment of mechanical instability and chronic back pain. A total of 35 selected patients underwent intervertebral fusion between February 1996 and August 1998. Their mean age was 48 years. There were 22 female and 13 male patients. Standard CO2 insufflation was used in 10 patients with L5-S1 fusions. Retractional gasless technique was used in nine patients with fusions at L5-S1, 16 patients at L4-L5, one patient at L3-L4, three patients at L2-3, and one patient at L1-L2. Thus, we performed a total of 40 lumbar fusions in 35 patients. In the 19 patients with the gasless technique, a balloon dissector and retractor facilitated the retroperitoneal exposure. Seven of these 19 patients were converted to open procedures, most commonly due to lacerations of the peritoneal lining that prohibited visualization. None of the L5-S1 patients with insufflation were converted to open. Mean operative time in the insufflated patients was 152 min vs. 181 min for the retractional technique. There were seven complications in the transperitoneal group: one fusion device migration, one postoperative UTI, one intracerebral hemorrhage, one severe postoperative pancreatitis, and three iliac vein lacerations. There were 16 complications in the retroperitoneal group: one deep vein thromboses, one serosal bowel injury, one small tear in the spleen, one cage migration, one postoperative pulmonary atelectasis, one postoperative hydrocele, four postoperative ileus, and six peritoneal tears. The mean postoperative stay was three days for both groups. There were no deaths. The L5-S1 interspace is best approached transperitoneally for anterior fusion. Although the retroperitoneal retractional technique is much more difficult and has a longer and steeper learning curve, it does allow laparoscopic anterior fusion of the upper lumbar spine.

Balloon-tipped cannulas for use in laparoscopic diagnosis and treatment of acute upper GI bleeding

BACKGROUND

Percutaneous balloon-tipped laparoscopic cannulas designed for preperitoneal hernia repair can be readily used to treat gastric bleeding laparoscopically.

METHODS

Between 1995 and 1997, we successfully used balloon-tipped cannulas to visualize, biopsy, and suture acutely bleeding gastric lesions in five patients. These case histories are reviewed for this study.

RESULTS

Patients received an average of six units of blood preoperatively (range, 0-15). Operative time averaged 207 min (range, 149-270). At surgery, gastrotomies were made for cannula placement under laparoscopic visualization. Operative findings included: lesser curve gastric ulcer, Mallory-Weiss tear, prepyloric ulcer, duodenal ulcer, and angiosarcoma. Three patients had successful percutaneous suture of bleeding gastric lesions. One patient was converted to open surgery. One patient had local resection of an angiosarcoma.

CONCLUSION

The laparoscopic use of balloon-tipped cannulas allows the expeditious diagnosis and treatment of acute gastric hemorrhage.

Results of heterotopic parathyroid autotransplantation: a 13-year experience

BACKGROUND

The reported success of heterotopic parathyroid autotransplantation (HPA) in patients with primary hyperparathyroidism varies from 20% to 60%. The purpose of this study was to evaluate our results with HPA to help define its role in this patient group.

METHODS

Between July 1985 and June 1998, 44 patients underwent 51 HPA procedures at our institution. Twenty to 25 fragments of parathyroid tissue measuring 1 to 3 mm3 each were placed into the forearm musculature. HPA results were scored as nonfunctional (requiring calcium and vitamin D), partially functional (normocalcemia on calcium alone), fully functional (normocalcemia without supplementation), or hyperfunctional (hypercalcemia without supplementation).

RESULTS

Follow-up data were available for 39 patients who underwent 46 autografts (20 immediate and 26 cryopreserved). With a median follow-up of 35 months, 19 autografts (41%) were nonfunctional; 9 autografts (20%) were partially functional; 15 autografts (33%) were fully functional, and 3 autografts (7%) were hyperfunctional. Full function was observed in 35% of immediate and 31% of delayed autografts.

CONCLUSIONS

One third of parathyroid autografts develop full function, and an additional one fifth develop partial function. Recurrent hyperparathyroidism is uncommon. No benefit was observed from immediate versus delayed HPA, and the modest success rate of HPA suggests that improvements in technique are warranted.

Identification of two novel deletion mutations within the Gs alpha gene (GNAS1) in Albright hereditary osteodystrophy

Albright hereditary osteodystrophy (AHO) is a genetic disorder characterized by short stature, skeletal defects, and obesity. Within AHO kindreds, some affected family members have only the somatic features of AHO [pseudopseudohypoparathyroidism (PPHP)], whereas others have these features in association with resistance to multiple hormones that stimulate adenylyl cyclase within their target tissues [pseudohypoparathyroidism type Ia (PHP Ia)]. Affected members of most AHO kindreds (both those with PPHP and those with PHP Ia) have a partial deficiency of Gs alpha, the alpha-subunit of the G protein that couples receptors to adenylyl cyclase stimulation, and in a number of cases heterozygous loss of function mutations within the Gs alpha gene (GNAS1) have been identified. Using PCR with the attachment of a high melting domain (GC-clamp) and temperature gradient gel electrophoresis, two novel heterozygous frameshift mutations within GNAS1 were found in two AHO kindreds. In one kindred all affected members (both PHP Ia and PPHP) had a heterozygous 2-bp deletion in exon 8, whereas in the second kindred a heterozygous 2-bp deletion in exon 4 was identified in all affected members examined. In both cases the frameshift encoded a premature termination codon several codons downstream of the deletion. In the latter kindred affected members were previously shown to have decreased levels of GNAS1 messenger ribonucleic acid expression. These results further underscore the genetic heterogeneity of AHO and provides further evidence that PHP Ia and PPHP are two clinical presentations of a common genetic defect. Serial measurements of thyroid function in members of kindred 1 indicate that TSH resistance progresses with age and becomes more evident after the first year of life.

Decreased renal Na-K-2Cl cotransporter abundance in mice with heterozygous disruption of the G(s)alpha gene

Transport processes along the nephron are regulated in part by hormone stimulation of adenylyl cyclases mediated by the heterotrimeric G protein G(s). To assess the role of this pathway in the regulation of Na-K-2Cl cotransporter abundance in the renal thick ascending limb (TAL), we studied mice with heterozygous disruption of the Gnas gene, which codes for the alpha-subunit of G(s). Outer medullary G(s)alpha protein abundance (as assessed by semiquantitative immunoblotting) and glucagon-stimulated cAMP production were significantly reduced in the heterozygous G(s)alpha knockout mice (GSKO) relative to their wild-type (WT) littermates. Furthermore, Na-K-2Cl cotransporter protein abundance in the outer medulla was significantly reduced (band density, 48% of WT). In addition, GSKO mice had a significantly reduced (72% of WT) urinary osmolality in response to a single injection of 1-deamino-[8-D-arginine]vasopressin (DDAVP), a vasopressin analog. In contrast, outer medullary protein expression of the type 3 Na/H exchanger (NHE-3) or Tamm-Horsfall protein did not differ between the GSKO mice and their WT littermates. However, abundance of type VI adenylyl cyclase was markedly decreased in the outer medullas of GSKO mice, suggesting a novel feed-forward regulatory mechanism. We conclude that expression of the Na-K-2Cl cotransporter of the TAL is dependent on G(s)alpha-mediated hormone stimulation, most likely due to long-term changes in cellular cAMP levels.

Management of bile duct stones in 1572 patients undergoing laparoscopic cholecystectomy

Evidence of bile duct stones (BDSs) was identified on routine cholangiogram in 136 (8.7%) of 1572 patients undergoing laparoscopic cholecystectomy from March 1989 through March 1997. Forty-two (30.9%) were unsuspected. All patients with evidence of BDSs underwent laparoscopic bile duct exploration (LBDE). Initially, a standard choledochotomy with T-tube drainage as in the open approach was used. Later, transcystic duct exploration was added to the algorithm. The algorithm evolved into an ongoing treatment protocol study that was initiated in March 1992. Through March 1997, 100 patients underwent LBDE based on the protocol. The study is divided into two groups. Group A comprises the total 136 patients undergoing LBDE, including those in the protocol study. A subgroup, Group B, comprises only the 100 patients in the protocol study. In Group A, LBDE was successful in 114 patients (83.8%). Stones were missed in seven patients and left behind for spontaneous passage or later retrieval in six patients. Eleven patients (8.1%) were converted to open. There were 13 major complications (9.6%), including the seven missed stones and two deaths. In Group B, LBDE was successful in 94 per cent. Stones were missed in one patient and intentionally left behind in four patients. One patient was converted to open. There were seven major complications (7%), including one of the missed stones and one death. Using the protocol algorithm and the techniques described, BDSs can be effectively managed laparoscopically at the time of cholecystectomy in approximately 94 per cent of cases.

A mutation in the heterotrimeric stimulatory guanine nucleotide binding protein alpha-subunit with impaired receptor-mediated activation because of elevated GTPase activity

It has been reported that substitution of Arg258, a residue within the GTPase domain of the heterotrimeric guanine nucleotide binding protein (G protein) alpha-subunit (alphas), to alanine (alphas-R258A) results in decreased activation by receptor or aluminum fluoride (AlF4-) and increased basal GDP release. Arg258 interacts with Gln170 in the helical domain, and, presumably, loss of this interaction between the GTPase and helical domain leads to more rapid GDP release, resulting in decreased activation by AlF4- and increased thermolability. In this study, we mutate Gln170 to alanine (alphas-Q170A) and demonstrate that this mutant, like alphas-R258A, has decreased activation by AlF4-, increased thermolability (both reversed in the presence of excess guanine nucleotide), and an increased rate of GDP release. However, unlike alphas-R258A, alphas-Q170A does not have impaired receptor-mediated activation. Therefore, this interdomain interaction is critical to maintain normal guanine nucleotide binding (and hence normal activation by AlF4-) but is not important for receptor-mediated activation. In single turnover GTPase assays, the catalytic rate for GTP hydrolysis of alphas-R258A was 14-fold higher than normal whereas that of alphas-Q170A was unaffected. Examination of the alphas crystal structure suggests that Arg258, through interactions with Glu50, might constrain the position of Arg201, a residue critical for catalyzing the GTPase reaction. This is an example of a mutation in a heterotrimeric G protein that results in an increased intrinsic GTPase activity and provides another mechanism by which G protein mutations can impair signal transduction.

Mutagenesis of the conserved residue Glu259 of Gsalpha demonstrates the importance of interactions between switches 2 and 3 for activation

We previously reported that substitution of Arg258 within the switch 3 region of Gsalpha impaired activation and increased basal GDP release due to loss of an interaction between the helical and GTPase domains (Warner, D. R., Weng, G., Yu, S., Matalon, R., and Weinstein, L. S. (1998) J Biol. Chem. 273, 23976-23983). The adjacent residue (Glu259) is strictly conserved in G protein alpha-subunits and is predicted to be important in activation. To determine the importance of Glu259, this residue was mutated to Ala (Gsalpha-E259A), Gln (Gsalpha-E259Q), Asp (Gsalpha-E259D), or Val (Gsalpha-E259V), and the properties of in vitro translation products were examined. The Gsalpha-E259V was studied because this mutation was identified in a patient with Albright hereditary osteodystrophy. S49 cyc reconstitution assays demonstrated that Gsalpha-E259D stimulated adenylyl cyclase normally in the presence of GTPgammaS but was less efficient with isoproterenol or AlF4-. The other mutants had more severely impaired effector activation, particularly in response to AlF4-. In trypsin protection assays, GTPgammaS was a more effective activator than AlF4- for all mutants, with Gsalpha-E259D being the least severely impaired. For Gsalpha-E259D, the AlF4--induced activation defect was more pronounced at low Mg2+ concentrations. Gsalpha-E259D and Gsalpha-E259A purified from Escherichia coli had normal rates of GDP release (as assessed by the rate GTPgammaS binding). However, for both mutants, the ability of AlF4- to decrease the rate of GTPgammaS binding was impaired, suggesting that they bound AlF4- more poorly. GTPgammaS bound to purified Gsalpha-E259D irreversibly in the presence of 1 mM free Mg2+, but dissociated readily at micromolar concentrations. Sucrose density gradient analysis of in vitro translates demonstrated that all mutants except Gsalpha-E259V bind to beta gamma at 0 degreesC and were stable at higher temperatures. In the active conformation Glu259 interacts with conserved residues in the switch 2 region that are important in maintaining both the active state and AlF4- in the guanine nucleotide binding pocket. Although both Gsalpha Arg258 and Glu259 are critical for activation, the mechanisms by which these residues affect Gsalpha protein activation are distinct.

Identification and localization of G protein subunits in human spermatozoa

Antibodies to alpha and beta subunits of guanine nucleotide regulatory proteins (G proteins) were used to identify which G proteins are present in mature human spermatozoa and to determine their subcellular localization. Immunoblots of membranes from spermatozoa demonstrate the presence of Galphai2, Galphai3, Galphaq/11 and Gbeta35 and the absence of Galphai1, Galpha0, Galphas, Galpha12, Galpha13, Galpha16, Galpha and Gbeta36. Indirect immunofluorescence demonstrates the presence of Galphaq/11 in the acrosome, with the highest proportion in the equatorial segment. Galphai2 is present in the acrosome, midpiece and tailpiece and Galphai3 in the postnuclear cap, midpiece and tailpiece. The Gbeta35 subunit is found mostly in the midpiece, with marginal labelling of the head, tailpiece and the equatorial segment of the acrosome. The distinct pattern of distribution of G proteins suggests that they may couple to receptors or effectors which also have discrete regions of localization in spermatozoa. These highly localized signal transduction pathways may regulate discrete functions, such as activation of the acrosome reaction, fusion with the oocyte and motility.

A novel mutation in the switch 3 region of Gsalpha in a patient with Albright hereditary osteodystrophy impairs GDP binding and receptor activation

Albright hereditary osteodystrophy (AHO), a disorder characterized by skeletal abnormalities and obesity, is associated with heterozygous inactivating mutations in the gene for Gsalpha. A novel Gsalpha mutation encoding the substitution of tryptophan for a nonconserved arginine within the switch 3 region (Gsalpha R258W) was identified in an AHO patient. Although reverse transcription-polymerase chain reaction studies demonstrated that mRNA expression from wild type and mutant alleles was similar, Gsalpha expression in erythrocyte membranes from the affected patient was reduced by 50%. A Gsalpha R258W cDNA, as well as one with arginine replaced by alanine (Gsalpha R258A), was generated, and the biochemical properties of in vitro transcription/translation products were examined. When reconstituted with cyc- membranes, both mutant proteins were able to stimulate adenylyl cyclase normally in the presence of guanosine- 5'-O-(3-thiotriphosphate) (GTPgammaS) but had decreased ability in the presence of isoproterenol or AlF4- (a mixture of 10 microM AlCl3 and 10 mM NaF). The ability of each mutant to bind and be activated by GTPgammaS or AlF4- was assessed by trypsin protection assays. Both mutants were protected normally by GTPgammaS but showed reduced protection in the presence of AlF4-. The addition of excess GDP (2 mM) was able to rescue the ability of AlF4- to protect the mutants, suggesting that they might have reduced affinity for GDP. A Gsalpha R258A mutant purified from Escherichia coli had decreased affinity for GDP and an apparent rate of GDP release that was 10-fold greater than that of wild type Gsalpha. Sucrose density gradient analysis demonstrated that both Gsalpha R258W and Gsalpha R258A were thermolabile at higher temperatures and that denaturation of both mutants was prevented by the presence of 0.1 mM GTPgammaS or 2 mM GDP. The crystal structure of Gsalpha demonstrates that Arg258 interacts with a conserved residue in the helical domain (Gln170). Arg258 substitutions would be predicted to open the cleft between the GTPase and helical domains, allowing for increased GDP release in the inactive state, resulting in enhanced thermolability and reduced AlF4--induced adenylyl cyclase stimulation and trypsin protection, since activation by AlF4- requires bound GDP.

Variable and tissue-specific hormone resistance in heterotrimeric Gs protein alpha-subunit (Gsalpha) knockout mice is due to tissue-specific imprinting of the gsalpha gene

Albright hereditary osteodystrophy (AHO), an autosomal dominant disorder characterized by short stature, obesity, and skeletal defects, is associated with heterozygous inactivating mutations of GNAS1, the gene encoding the heterotrimeric G protein alpha-subunit (Gsalpha) that couples multiple receptors to the stimulation of adenylyl cyclase. It has remained unclear why only some AHO patients present with multihormone resistance and why AHO patients demonstrate resistance to some hormones [e.g., parathyroid hormone (PTH)] but not to others (e.g., vasopressin), even though all activate adenylyl cyclase. We generated mice with a null allele of the mouse homolog Gnas. Homozygous Gs deficiency is embryonically lethal. Heterozygotes with maternal (m-/+) and paternal (+/p-) inheritance of the Gnas null allele have distinct phenotypes, suggesting that Gnas is an imprinted gene. PTH resistance is present in m-/+, but not +/p-, mice. Gsalpha expression in the renal cortex (the site of PTH action) is markedly reduced in m-/+ but not in +/p- mice, demonstrating that the Gnas paternal allele is imprinted in this tissue. Gnas is also imprinted in brown and white adipose tissue. The maximal physiological response to vasopressin (urinary concentrating ability) is normal in both m-/+ and +/p- mice and Gnas is not imprinted in the renal inner medulla (the site of vasopressin action). Tissue-specific imprinting of Gnas is likely the mechanism for variable and tissue-specific hormone resistance in these mice and a similar mechanism might explain the variable phenotype in AHO.

A novel mutation adjacent to the switch III domain of G(S alpha) in a patient with pseudohypoparathyroidism

A novel G(S alpha) mutation encoding the substitution of arginine for serine 250 (G[S alpha] S250R) was identified in a patient with pseudohypoparathyroidism type Ia. Both G(S) activity and G(S alpha) expression were decreased by about 50% in erythrocyte membranes from the affected patient. The cDNA of this G(S alpha) mutant, as well as one in which the S250 residue is deleted (G[S alpha]-deltaS250), was generated, and the biochemical properties of the products of in vitro transcription/translation were examined. Both mutants had a sedimentation coefficient similar to that of wild type G(S alpha) (approximately 3.7S) when kept at 0 C after synthesis. However when maintained for 1-2 h at 30-37 C, both mutants aggregated to a material sedimenting at approximately 6.3S or greater (G[S alpha]-S250R to a greater extent than G(S alpha]-deltaS250), while wild type G(S alpha) sedimented at approximately 3.7S, suggesting that the mutants were thermolabile. Incubation in the presence of high doses of guanine nucleotide partially prevented heat denaturation of G(S alpha) deltaS250 but had no protective effect on G(S alpha-S250R. Sucrose density gradient centrifugation at 0 C in the presence and absence of beta gamma-dimers demonstrated that, in contrast to wild type G(S alpha) neither mutant could interact with beta gamma. Trypsin protection assays revealed no protection of G(S alpha)-S250R by GTPgammaS or AIF4- at any temperature. GTPgammaS conferred modest protection of G(S alpha)-deltaS250 (approximately 50% of wild-type G[S alpha]) at 30 C but none at 37 C, while AIF4- conferred slight protection at 20 C but none at 30 C or above. Consistent with this result, G(S alpha)-deltaS250 was able to stimulate adenylyl cyclase at 30 C when reconstituted with cyc- membranes in the presence of GTPgammaS but not in the presence of AIF4-. G(S alpha)-S250R showed no ability to stimulate adenylyl cyclase in the presence of either agent. Stable transfection of mutant and wild-type G(S alpha) into cyc- S49 lymphoma cells revealed that the majority of wild type G(S alpha) localized to membranes, while little or no membrane localization occurred for either mutant. Modeling of G(S alpha) based upon the crystal structure of G(t alpha) or G(i alpha) suggests that Ser250 interacts with several residues within and around the conserved NKXD motif, which directly interacts with the guanine ring of bound GDP or GTP. It is therefore possible that substitution or deletion of this residue may alter guanine nucleotide binding, which could lead to thermolability and impaired function.

Laparoscopic reconstruction of gastroesophageal anatomy for the treatment of reflux disease

This paper presents the technique and results of an operation that restores normal anatomical and physiological antireflux mechanisms for the treatment of gastroesophageal reflux disease (GERD). The Hill procedure was modified beginning in 1973, evolving into an operation that has been standard in our practice since 1987. Major changes included total fixation of the abdominal esophagus and elimination of phrenoesophageal bundle plication. We began performing the procedure laparoscopically in 1991 and simultaneously began a study to look at our results. This is the first report of the first 44 patients operated on from October 1991 through March 1994. There was one operative complication. Mean follow-up was 14 months. One patient was lost to follow-up and one patient died. There were no long-term side effects. A Visick grading scale was designed to categorize results. Forty graded satisfactory (95%) and two unsatisfactory.

Pseudohypoparathyroidism type Ib is not caused by mutations in the coding exons of the human parathyroid hormone (PTH)/PTH-related peptide receptor gene

Pseudohypoparathyroidism type Ib (PHP-Ib) is thought to be caused by a PTH/PTH-related peptide (PTHrP) receptor defect. To search for receptor mutations in genomic DNA from 17 PHP-Ib patients, three recently isolated human genomic DNA clones were further characterized by restriction enzyme mapping and nucleotide sequencing across intron/exon borders. Regions including all 14 coding exons and their splice junctions were amplified by polymerase chain reaction, and the products were analyzed by either temperature gradient gel electrophoresis or direct nucleotide sequencing. Silent polymorphisms were identified in exons G (1 of 17), M4 (1 of 17), and M7 (15 of 17). Two base changes were found in introns, 1 at the splice-donor site of the intron between exons E2 and E3 (1 of 17) and the other between exons G and M1 (2 of 17). Total ribonucleic acid from COS-7 cells expressing minigenes with or without the base change between exons E2 and E3 showed no difference by either Northern blot analysis or reverse transcriptase-polymerase chain reaction. Radioligand binding was indistinguishable for both transiently expressed constructs. A missense mutation (E546 to K546) in the receptor's cytoplasmic tail (3 of 17) was also found in 1 of 60 healthy individuals, and PTH/PTHrP receptors with this mutation were functionally indistinguishable from wild-type receptors. PHP-Ib thus appears to be rarely, if ever, caused by mutations in the coding exons of the PTH/PTHrP receptor gene.

Inhibition of adenylate cyclase activity by galanin in rat insulinoma cells is mediated by the G-protein Gi3

Galanin inhibits adenylate cyclase activity and insulin secretion and modulates ion channels in pancreatic beta-cells through pertussis-toxin-sensitive G-protein(s). Antibodies directed against the C-terminal region of specific G-protein alpha-subunits were used to determine which G-protein(s) couple galanin receptors to inhibition of adenylate cyclase in the rat insulinoma cell line RINm5F. Preincubation of membranes with EC antibody (anti-alpha i3) decreased the inhibition of forskolin-stimulated adenylate cyclase activity by galanin (100 nM) by 45% compared with control IgG (P < 0.05) whereas preincubation with AS (anti-alpha i1, alpha i2) or GO (anti-alpha o) antibodies had no significant effect. To confirm these results, RINm5F cells were exposed intermittently over a 4-day period to phosphorothioate oligodeoxynucleotides that were either sense or antisense to alpha i1, alpha i2, alpha i3 or alpha o. Oligodeoxynucleotides antisense to alpha i2, alpha i3 and alpha o specifically decreased the levels of the targeted alpha-subunit in membranes. alpha i1 was undetectable in these cells. Inhibition of adenylate cyclase activity by galanin was largely abolished in membranes from cells exposed to the oligodeoxynucleotide antisense to alpha i3, whereas all other oligodeoxynucleotides had no significant effect on this pathway. Indirect immunofluorescence and immunoblotting of specific membrane fractions with EC antibody show significant localization of alpha i3 to intracellular membrane compartments. These results suggest that Gi3 is the G protein that couples galanin receptors to inhibition of adenylate cyclase activity in RINm5F cells.

An activating Gs alpha mutation is present in fibrous dysplasia of bone in the McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a sporadic disease characterized by polyostotic fibrous dysplasia, café-au-lait spots, and multiple endocrinopathies. The etiology of fibrous dysplasia is unknown. Activating mutations of codon 201 in the gene encoding the alpha-subunit of Gs, the G-protein that stimulates adenylyl cyclase, have been found in all affected MAS tissues that have been studied. Initial attempts to amplify DNA from decalcified paraffin-embedded bone specimens from MAS patients were unsuccessful. Therefore, we analyzed DNA from frozen surgical bone specimens from five MAS patients using polymerase chain reaction and allele-specific oligonucleotide hybridization. Most of the cells in four specimens of dysplastic bone contained a heterozygous mutation encoding substitution of Arg201 of Gs alpha with His, but the mutation was barely detectable in peripheral blood specimens from the patients. Only a small amount of mutant allele was detected in a specimen of normal cortical bone from the fifth patient, although this patient had a high proportion of mutation in other, affected tissues. The mosaic distribution of mutant alleles is consistent with an embryological somatic cell mutation of the Gs alpha gene in MAS. The presence of an activating mutation of Gs alpha in osteoblastic progenitor cells may cause them to exhibit increased proliferation and abnormal differentiation, thereby producing the lesions of fibrous dysplasia.

G protein mutations in human disease

The heterotrimeric G proteins couple cell-surface receptors for extracellular signals to intracellular effectors that generate second messengers. Abnormal G protein signalling, resulting from posttranslational modifications by bacterial toxins, altered gene expression, or gene mutations, may lead to diverse biological consequences. Mutations within G protein alpha subunit genes that lead to either constitutive activation or loss of function have been identified. Such G protein mutations play a role in the pathogenesis of several human diseases, including sporadic endocrine tumors, McCune-Albright syndrome, and Albright hereditary osteodystrophy.

Severe endocrine and nonendocrine manifestations of the McCune-Albright syndrome associated with activating mutations of stimulatory G protein GS

McCune-Albright syndrome (MCAS) is a sporadic disease classically including polyostotic fibrous dysplasia, café au lait spots, sexual precocity, and other hyperfunctional endocrinopathies. An activating missense mutation in the gene for the alpha subunit of GS, the G protein that stimulates cyclic adenosine monophosphate formation, has been reported to be present in these patients. The mutation is found in variable abundance in different affected endocrine and nonendocrine tissues, consistent with the mosaic distribution of abnormal cells generated by a somatic cell mutation early in embryogenesis. We describe three patients with MCAS who had profound endocrine and nonendocrine disease and who died in childhood. Two of the patients were severely ill neonates whose complex symptoms did not immediately suggest MCAS. A mutation of residue Arg201 of GS alpha was found in affected tissues from all three children. A review of the literature and unpublished case histories emphasizes the existence of other patients with severe and unusual clinical manifestations. We conclude that the manifestations of MCAS are more extensive than is generally appreciated, and may include hepatobiliary disease, cardiac disease, other nonendocrine abnormalities, and sudden or premature death.

Linear gastrectomy: an endoscopic staple-assisted anterior highly selective vagotomy combined with posterior truncal vagotomy for treatment of peptic ulcer disease

A technique of anterior highly selective vagotomy is described that uses an endoscopic stapling device to facilitate and speed the procedure. Further study is necessary to ascertain the long-term recurrence rate for this new procedure, but it shows great promise as a simplified procedure for laparoscopic application in peptic ulcer disease.

A heterozygous 4-bp deletion mutation in the Gs alpha gene (GNAS1) in a patient with Albright hereditary osteodystrophy

Several heterozygous mutations within the gene encoding the alpha-subunit of Gs (GNAS1), the G protein that stimulates adenylyl cyclase, have been previously identified in patients with Albright hereditary osteodystrophy (AHO). We have now identified a fourth GNAS1 mutation from an AHO patient. Amplification by the polymerase chain reaction (PCR) of a genomic fragment encompassing GNAS1 exons 7 and 8 from one patient resulted in a product with aberrant migration on nondenaturing polyacrylamide and agarose gels. Direct DNA sequencing identified a 4-bp deletion in one allele of exon 7 encoding a frameshift with a premature stop codon. Analysis of lymphocyte RNA by reverse transcription-PCR and direct sequencing showed that the GNAS1 allele bearing the mutation is not expressed as mRNA. Consistent with this, Northern analysis revealed an approximate 50% deficiency in steady-state levels of GNAS1 mRNA. These findings further illustrate the heterogeneity of GNAS1 gene defects in AHO.

Studies in a kindred with parathyroid carcinoma

We report a family with primary hyperparathyroidism in four patients in two generations with apparent autosomal dominant transmission. A fifth member was probably affected. Two cases had definite parathyroid carcinoma (PC), and two had parathyroid adenoma with atypical features that could represent an early stage of cancer. In each of our patients, one parathyroid gland was abnormal. Five other parathyroid glands (in two patients) were normal in histology and size. There was no evidence of neoplasia in other tissues. Constitutional karyotypes were normal in all four patients. We identified three chromosomal abnormalities (a reciprocal translocation between chromosomes 3 and 4, trisomy 7, and a pericentric inversion in chromosome 9) in cultured PC tissue from one patient. These chromosomal changes are of unclear significance. Analyses on tumor DNA from one case of PC and one of atypical adenoma showed no evidence of ras gene mutations, PTH gene rearrangement, or allelic loss from chromosome 11q13 (locus of the gene for multiple endocrine neoplasia type 1). This family shows susceptibility to cancer without antecedent hyperplasia in all parathyroids. It could help identify a novel tumor susceptibility gene.