OBJECTIVETo describe the prevalence of biochemical B12 deficiency in adults with type 2 diabetes taking metformin compared with those not taking metformin and those without diabetes, and explore whether this relationship is modified by vitamin B12 supplements.RESEARCH DESIGN AND METHODSAnalysis of data on U.S. adults ≥50 years of age with (n = 1,621) or without type 2 diabetes (n = 6,867) from the National Health and Nutrition Examination Survey (NHANES), 1999–2006. Type 2 diabetes was defined as clinical diagnosis after age 30 without initiation of insulin therapy within 1 year. Those with diabetes were classified according to their current metformin use. Biochemical B12 deficiency was defined as serum B12 concentrations ≤148 pmol/L and borderline deficiency was defined as >148 to ≤221 pmol/L.RESULTSBiochemical B12 deficiency was present in 5.8% of those with diabetes using metformin compared with 2.4% of those not using metformin (P = 0.0026) and 3.3% of those without diabetes (P = 0.0002). Among those with diabetes, metformin use was associated with biochemical B12 deficiency (adjusted odds ratio 2.92; 95% CI 1.26–6.78). Consumption of any supplement containing B12 was not associated with a reduction in the prevalence of biochemical B12 deficiency among those with diabetes, whereas consumption of any supplement containing B12 was associated with a two-thirds reduction among those without diabetes.CONCLUSIONSMetformin therapy is associated with a higher prevalence of biochemical B12 deficiency. The amount of B12 recommended by the Institute of Medicine (IOM) (2.4 μg/day) and the amount available in general multivitamins (6 μg) may not be enough to correct this deficiency among those with diabetes.

BackgroundInsulin is a vital peptide hormone that is a central regulator of glucose homeostasis, and impairments in insulin signaling cause diabetes mellitus. In principle, it should be possible to enhance the activity of insulin by inhibiting its catabolism, which is mediated primarily by insulin-degrading enzyme (IDE), a structurally and evolutionarily distinctive zinc-metalloprotease. Despite interest in pharmacological inhibition of IDE as an attractive anti-diabetic approach dating to the 1950s, potent and selective inhibitors of IDE have not yet emerged.Methodology/Principal FindingsWe used a rational design approach based on analysis of combinatorial peptide mixtures and focused compound libraries to develop novel peptide hydroxamic acid inhibitors of IDE. The resulting compounds are ∼106 times more potent than existing inhibitors, non-toxic, and surprisingly selective for IDE vis-à-vis conventional zinc-metalloproteases. Crystallographic analysis of an IDE-inhibitor complex reveals a novel mode of inhibition based on stabilization of IDE's “closed,” inactive conformation. We show further that pharmacological inhibition of IDE potentiates insulin signaling by a mechanism involving reduced catabolism of internalized insulin.Conclusions/SignificanceThe inhibitors we describe are the first to potently and selectively inhibit IDE or indeed any member of this atypical zinc-metalloprotease superfamily. The distinctive structure of IDE's active site, and the mode of action of our inhibitors, suggests that it may be possible to develop inhibitors that cross-react minimally with conventional zinc-metalloproteases. Significantly, our results reveal that insulin signaling is normally regulated by IDE activity not only extracellularly but also within cells, supporting the longstanding view that IDE inhibitors could hold therapeutic value for the treatment of diabetes.

BACKGROUND: Approximately 70% of all suicides in patients aged >60 years are attributed to physical illness, with higher rates noted in patients with cancer. The purpose of the current study was to characterize suicide rates among patients with genitourinary cancers and identify factors associated with suicide in this specific cohort. METHODS: Patients with prostate, bladder, kidney, testis, and penile cancer were identified in the Surveillance, Epidemiology, and End Results database . Standardized mortality ratios (SMRs) and 95% confidence intervals (95% CIs) were calculated for each anatomic site. Multivariable logistic regression models generated odds ratios (ORs) for the identification of factors associated with suicide for each malignancy. RESULTS: There were 2268 suicides identified among 1,239,522 individuals with genitourinary malignancies observed for 7,307,377 person-years. The SMRs for patients with cancer were 1.37 for prostate cancer (95% CI, 0.99-1.86), 2.71 for bladder cancer (95% CI, 2.02-3.62), 1.86 for kidney cancer (95% CI, 1.32-2.62), 1.23 for testis cancer (95% CI, 0.88-1.73), and 0.95 for penile cancer (95% CI, 0.65-1.35). On multivariable analysis, male sex was found to be associated with odds of suicide among patients with bladder cancer (OR, 6.63) and kidney cancer (OR, 4.98). Increasing age was associated with suicide for patients with prostate, bladder, and testis cancer (OR range, 1.03-1.06). Distant disease was associated with suicide in patients with prostate, bladder, and kidney cancer (OR range,). Among patients with prostate, bladder, and kidney cancer, African American patients were less likely to commit suicide compared with white individuals (OR range, 0.26-0.46). CONCLUSIONS: Suicide in patients with genitourinary malignancies poses a public health dilemma, especially among men, the elderly, and those with aggressive disease. Clinicians should be aware of risk factors for suicide in these patients.

BackgroundHypocatabolism of the amyloid β-protein (Aβ) by insulin-degrading enzyme (IDE) is implicated in the pathogenesis of Alzheimer disease (AD), making pharmacological activation of IDE an attractive therapeutic strategy. However, it has not been established whether the proteolytic activity of IDE can be enhanced by drug-like compounds.Methodology/Principal FindingsBased on the finding that ATP and other nucleotide polyphosphates modulate IDE activity at physiological concentrations, we conducted parallel high-throughput screening campaigns in the absence or presence of ATP and identified two compounds—designated Ia1 and Ia2—that significantly stimulate IDE proteolytic activity. Both compounds were found to interfere with the crosslinking of a photoaffinity ATP analogue to IDE, suggesting that they interact with a bona fide ATP-binding domain within IDE. Unexpectedly, we observed highly synergistic activation effects when the activity of Ia1 or Ia2 was tested in the presence of ATP, a finding that has implications for the mechanisms underlying ATP-mediated activation of IDE. Notably, Ia1 and Ia2 activated the degradation of Aβ by ∼700% and ∼400%, respectively, albeit only when Aβ was presented in a mixture also containing shorter substrates.Conclusions/SignificanceThis study describes the first examples of synthetic small-molecule activators of IDE, showing that pharmacological activation of this important protease with drug-like compounds is achievable. These novel activators help to establish the putative ATP-binding domain as a key modulator of IDE proteolytic activity and offer new insights into the modulatory action of ATP. Several larger lessons abstracted from this screen will help inform the design of future screening campaigns and facilitate the eventual development of IDE activators with therapeutic utility.

Insulin-degrading enzyme (IDE) is a ubiquitous zinc-metalloprotease that hydrolyzes several pathophysiologically relevant peptides, including insulin and the amyloid ␤-protein (A␤). IDE is inhibited irreversibly by compounds that covalently modify cysteine residues, a mechanism that could be operative in the etiology of type 2 diabetes mellitus (DM2) or Alzheimer's disease (AD). However, despite prior investigation, the molecular basis underlying the sensitivity of IDE to thiol-alkylating agents has not been elucidated. To address this topic, we conducted a comprehensive mutational analysis of the 13 cysteine residues within IDE. Our analysis implicates C178, C812, and C819 as the principal residues conferring thiol sensitivity. The involvement of C812 and C819, residues quite distant from the catalytic zinc atom, provides functional evidence that the active site of IDE comprises two separate domains that are operational only in close apposition. Structural analysis and other evidence predict that alkylation of C812 and C819 disrupts substrate binding, whereas alkylation of C178 interferes with the apposition of active-site domains and subtly repositions zinc-binding residues. Unexpectedly, alkylation of C590 was found to activate hydrolysis of A␤ significantly, while having no effect on insulin, demonstrating that chemical modulation of IDE can be both bidirectional and highly substrate selective. Our findings resolve a long-standing riddle about the basic enzymology of IDE with important implications for the etiology of DM2 and AD. Moreover, this work uncovers key details about the mechanistic basis of the unusual substrate selectivity of IDE that may aid the development of pharmacological agents or IDE mutants with therapeutic value.Alzheimer's disease ͉ amyloid ␤-protein ͉ insulin ͉ type 2 diabetes mellitus

ObjectiveTo review the published literature on the efficacy of ketamine for the treatment of suicidal ideation (SI).MethodsThe PubMed and Cochrane databases were searched up to January 2015 for clinical trials and case reports describing therapeutic ketamine administration to patients presenting with SI/suicidality. Searches were also conducted for relevant background material regarding the pharmacological function of ketamine.ResultsNine publications (six studies and three case reports) met the search criteria for assessing SI after administration of subanesthetic ketamine. There were no studies examining the effect on suicide attempts or death by suicide. Each study demonstrated a rapid and clinically significant reduction in SI, with results similar to previously described data on ketamine and treatment-resistant depression. A total of 137 patients with SI have been reported in the literature as receiving therapeutic ketamine. Seven studies delivered a dose of 0.5 mg/kg intravenously over 40 min, while one study administered a 0.2 mg/kg intravenous bolus and another study administered a liquid suspension. The earliest significant results were seen after 40 min, and the longest results were observed up to 10 days postinfusion.ConclusionConsistent with clinical research on ketamine as a rapid and effective treatment for depression, ketamine has shown early preliminary evidence of a reduction in depressive symptoms, as well as reducing SI, with minimal short-term side effects. Additional studies are needed to further investigate its mechanism of action, long-term outcomes, and long-term adverse effects (including abuse) and benefits. In addition, ketamine could potentially be used as a prototype for further development of rapid-acting antisuicidal medication with a practical route of administration and the most favorable risk/benefit ratio.

Clinicians should be aware of risk factors for suicide in patients diagnosed with bladder cancer, particularly older, white, unmarried patients with distant disease, and/or those who have undergone radical cystectomy. A multidisciplinary team-based approach, including wound ostomy care trained nursing staff and mental health care providers, may be essential to provide care required to decrease suicide rates in this at-risk population.

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