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Biomedical subjects

David Weinberg

Publications and source records attributed to David Weinberg.

9 recordsLinked to original sources
PubMed2006

Transgenic expression of beta-APP in fast-twitch skeletal muscle leads to calcium dyshomeostasis and IBM-like pathology.

Intracellular deposition of the beta-amyloid (Abeta) peptide is an increasingly recognized pathological hallmark associated with neurodegeneration and muscle wasting in Alzheimer's disease (AD) and inclusion body myositis (IBM), respectively. Previous reports have implicated dysregulation of beta-amyloid precursor protein (betaAPP) expression in IBM. Accumulation of full-length betaAPP, its various proteolytic derivatives including Abeta, and phospho-tau into vacuolated inclusions is an early pathogenic event. We previously reported on a statistical tendency favoring fast twitch fiber involvement in IBM, reminiscent of the tissue specific patterns of misfolded protein deposition seen in neurodegenerative diseases. To test this principle, we generated an animal model in which human wild-type (WT) betaAPP expression was limited to postnatal type II skeletal muscle. Hemizygous transgenic mice harboring increased levels of holo betaAPP751 and Abeta in skeletal muscle fibers became significantly weaker with age compared with nontransgenic littermates and exhibited typical myopathic features. A subpopulation of dissociated muscle fibers from transgenic mice exhibited a 2-fold increase in resting calcium and membrane depolarization compared with nontransgenic littermates. Taken together, these data indicate that overexpression of human betaAPP in fast twitch skeletal muscle of transgenic mice is sufficient for the development of some features characteristic of IBM, including abnormal tau histochemistry. The increase in resting calcium and depolarization are novel findings, suggesting both a mechanism for the weakness and an avenue for therapeutic intervention in IBM.

Amyloid beta-Protein Precursor↗
PubMed2006

A validated quantitative assay to detect occult micrometastases by reverse transcriptase-polymerase chain reaction of guanylyl cyclase C in patients with colorectal cancer.

PURPOSE: Guanylyl cyclase C (GCC), a receptor for bacterial diarrheagenic enterotoxins, may be a prognostic and predictive marker to detect occult micrometastases in patients undergoing staging for colorectal cancer. However, quantification of GCC expression in tissues by the quantitative reverse transcription-PCR (qRT-PCR) has not undergone analytic and clinicopathologic validation. EXPERIMENTAL DESIGN: A technique to quantify GCC mRNA in tissues employing RT-PCR was developed and validated employing external calibration standards of RNA complementary to GCC. RESULTS: GCC qRT-PCR exhibited reaction efficiencies >92%, coefficients of variations <5%, linearity >6 orders of magnitude, and a limit of quantification of >25 copies of GCC cRNA. This assay confirmed that GCC mRNA was overexpressed by colorectal tumors from 41 patients, which correlated with increased GCC protein quantified by immunohistochemistry. Analyses obtained with 164 lymph nodes from patients free of cancer and 15 nodes harboring metastases established a threshold for metastatic disease of approximately 200 GCC mRNA copies/mug total RNA, with a sensitivity of 93% and specificity of 97%. GCC mRNA above that threshold was detected in 76 of 367 (approximately 21%) nodes free of disease by histopathology from 6 of 23 (26%) patients, suggesting the presence of occult micrometastases. CONCLUSIONS: Quantifying GCC mRNA in tissues by RT-PCR employing external calibration standards is analytically robust and reproducible, with high clinicopathologic sensitivity and specificity. This validated assay is being applied to approximately 10,000 lymph nodes in a prospective trial to define the sensitivity of GCC qRT-PCR for staging patients with colorectal cancer.

Adult↗
PubMed2005

Guanylyl cyclase C is a marker of intestinal metaplasia, dysplasia, and adenocarcinoma of the gastrointestinal tract.

Gastrointestinal (GI) tumors continue to be major causes of cancer-related mortality, in part, reflecting metastases that escape detection by histopathology. Moreover, although approximately 10% of carcinomas arise from unknown locations, these tumors frequently originate in the GI tract. Guanylyl cyclase C (GC-C) is a receptor selectively expressed by intestinal epithelial cells whose persistent expression by colorectal carcinomas and ectopic expression by adenocarcinomas of the upper GI tract suggest its use as a marker for GI malignancies. Here, expression of GC-C protein, identified by immunohistochemistry, was examined in tissues and tumors arising from the human GI tract. Guanylyl cyclase C protein was expressed by epithelial cells from the duodenum to the rectum, but not by those in normal esophagus and stomach. Expression was retained in tubular adenomas, inflammatory bowel disease, premalignant lesions, and in primary and metastatic adenocarcinomas from the colon, including metastases to lymph nodes and liver. Moreover, GC-C was ectopically expressed in all cases of dysplasia and adenocarcinomas arising from intestinal metaplasia in esophagus and stomach. Thus, GC-C appears to be an immunohistochemical marker for identifying adenocarcinomas of unknown origin, metastases in patients undergoing staging for GI adenocarcinomas, and intestinal metaplasia, dysplasia, and tumors arising therein in the upper GI tract.

Adenocarcinoma↗
PubMed2004

Nucleophilic aromatic substitution on aryl-amido ligands promoted by oxidizing osmium(IV) centers.

Addition of amine nucleophiles to acetonitrile solutions of the OsIV anilido complex TpOs(NHPh)Cl2 (1) [Tp = hydrotris(1-pyrazolyl)borate] gives products with derivatized anilido ligands, i.e., TpOs[NH-p-C6H4(N(CH2)5)]Cl2 (2) from piperidine and TpOs[NH-p-C6H4N(CH2)4]Cl2 (3) from pyrrolidine. These materials are formed in approximately 30% yield under anaerobic conditions, together with approximately 60% yields of the OsIII aniline complex TpOs(NH2Ph)Cl2 (5). Formation of the para-substituted materials 2 or 3 from 1 involves oxidative removal of two hydrogen atoms (two H+ and two e-). The oxidation can be accomplished by 1, forming 5, or by O2. Related reactions have been observed with other amines and with the 2-naphthylamido derivative, which gives an ortho-substituted product. Kinetic studies indicate an addition-elimination mechanism involving initial attack of the amine nucleophile on the anilido ligand. These are unusual examples of nucleophilic aromatic substitution of hydrogen. Ab initio calculations on 1 show that the LUMO has significant density at the ortho and para positions of the anilido ligand, resembling the LUMO of nitrobenzene. By analogy with nucleophilic aromatic substitution, 2 is quantitatively formed from piperidine and the p-chloroanilide TpOs(NH-p-C6H4Cl)Cl2 (7). Binding the anilide ligands to an oxidizing OsIV center thus causes a remarkable umpolung or inversion of chemical character from a typically electron-rich anilido to an electron-deficient aromatic functionality. This occurs because of the coupling of redox changes at the TpOsIV center with bond formation at the coordinated ligand.

Journal Article↗
PubMed2004

Impact of a physician-oriented intervention on follow-up in colorectal cancer screening.

BACKGROUND: Complete diagnostic evaluation or CDE (i.e., colonoscopy or combined flexible sigmoidoscopy plus barium enema X-ray) is often not performed for persons with an abnormal screening fecal occult blood test (FOBT+) result. METHOD: This study evaluated the impact of a reminder-feedback and educational outreach intervention on primary care practice CDE recommendation and performance rates. Four hundred seventy primary care physicians (PCPs) in 318 practices participated in the study. Patients were mailed an FOBT kit annually as part of a screening program. Practices were randomly assigned to a Control Group (N = 198) or an Intervention Group (N = 120). During an 18-month pre-randomization period and a 9-month post-randomization period, 2992 screening FOBT+ patients were identified. Intervention practices received the screening program and the intervention. Control practices received only the screening program. Study outcomes were baseline-adjusted CDE recommendation and performance rates. RESULTS: At baseline, about two-thirds of FOBT+ patients received a CDE recommendation, and about half had a CDE performed. At endpoint, CDE recommendation and performance rates were both significantly higher for the Intervention as compared to the Control practices (OR = 2.28; 95% CI: 1.37, 3.78, and OR = 1.63; 95% CI: 1.06, 2.50, respectively). CONCLUSIONS: The reminder-feedback plus educational outreach intervention significantly increased CDE recommendation and performance.

Colorectal Neoplasms↗
PubMed2003

Physician and patient factors associated with ordering a colon evaluation after a positive fecal occult blood test.

OBJECTIVE: Successful colorectal cancer screening relies in part on physicians ordering a complete diagnostic evaluation of the colon (CDE) with colonoscopy or barium enema plus sigmoidoscopy after a positive screening fecal occult blood test (FOBT). DESIGN: We surveyed primary care physicians about colorectal cancer screening practices, beliefs, and intentions. At least 1 physician responded in 318 of 413 (77%) primary care practices that were affiliated with a managed care organization offering a mailed FOBT program for patients aged >/=50 years. Of these 318 practices, 212 (67%) had 602 FOBT+ patients from August through November 1998. We studied 184 (87%) of these 212 practices with 490 FOBT+ patients after excluding those judged ineligible for a CDE or without demographic data. Three months after notification of the FOBT+ result, physicians were asked on audit forms if they had ordered CDEs for study patients. Patient- and physician-predictors of ordering CDEs were identified using logistic regression. MEASUREMENTS AND MAIN RESULTS: A CDE was ordered for only 69.5% of 490 FOBT+ patients. After adjustment, women were less likely to have had CDE initiated than men (adjusted odds, 0.66; confidence interval, 0.44 to 0.97). Physician survey responses indicating intermediate or high intention to evaluate a FOBT+ patient with a CDE were associated with nearly 2-fold greater adjusted odds of actually initiating a CDE in this circumstance versus physicians with a low intention. CONCLUSIONS: Primary care physicians often fail to order CDE for FOBT+ patients. A CDE was less likely to be ordered for women and was influenced by physician's beliefs about CDEs.

Adult↗
PubMed2002

Structure-activity studies of the melanocortin peptides: discovery of potent and selective affinity antagonists for the hMC3 and hMC4 receptors.

We have designed and synthesized several novel cyclic SHU9119 analogues (Ac-Nle4-[Asp5-His6-DNal(2')7-Arg8-Trp9-Lys10]-NH2) modified in position 6 with nonconventional amino acids. SHU9119 is a high affinity nonselective antagonist at hMC3R and hMC4R with potent agonist activity at hMC1R and hMC5R. We measured the binding affinity and agonist potency of the novel analogues at cloned hMC3R, hMC4R, and hMC5R receptors and identified several selective, high affinity hMC3R and hMC4R antagonists. Compound 4 containing Che substitution in position 6 is a high affinity hMC4R antagonist (IC50 = 0.48 nM) with 100-fold selectivity over hMC3R antagonist. Analogue 7 with a Cpe substitution in position 6 is a high affinity hMC4R antagonist (IC50 = 0.51 nM) with a 200-fold selectivity vs the hMC3R. Interestingly, analogue 9 with an Acpc residue in position 6 is a high affinity hMC3R antagonist (IC50 = 2.5 nM) with 100-fold selectivity vs the hMC4R antagonist based on its binding affinities. This compound represents the first cyclic lactam antagonist with high selectivity for the hMC3R vs hMC4R. To understand the possible structural basis responsible for selectivity of these peptides at hMCR3 and hMCR4, we have carried out a molecular modeling study in order to examine the conformational properties of the cyclic peptides modified in position 6 with conformationally restricted amino acids.

Animals↗
PubMed2002

Design and synthesis of highly potent and selective melanotropin analogues of SHU9119 modified at position 6.

The melanocortin receptors are involved in several important physiological functions. The potent and enzymatically stable analogues MT-II (Ac-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-NH(2)) and SHU9119 (Ac-Nle-c[Asp-His-DNal(2')-Arg-Trp-Lys]-NH(2)) are important ligands of these receptors but are relatively nonselective. To differentiate between the physiological functions of these receptors, agonists, and antagonists with improved receptor selectivities are needed. We report here analogues of the well-characterized antagonist SHU9119 in which we replaced His(6) with conformationally constrained amino acids. By this structure-activity study we discovered two important compounds, PG-901 (Ac-Nle(4)-c[Asp(5)-Pro(6)-DNal(2')(7)-Arg(8)-Trp(9)-Lys(10)]-NH(2)) and PG-911 (Ac-Nle(4)-c[Asp(5)-Hyp(6)-DNal(2')(7)-Arg(8)-Trp(9)-Lys(10)]-NH(2)), characterized to be full agonists at the hMC5R (EC(50) = 0.072 nM and 0.031 nM, respectively), but full antagonists at the hMC3R and the hMC4R. We also demonstrated that the relative stereochemistry of the amino acid at the 6-position is critical for activity, and could play an important role in potency as well as in selectivity for the melanocortin receptors.

Amino Acid Substitution↗