Effects of the rodenticide Vacor on cultured rat pancreatic beta cells

Enzymatic and Chemical Syntheses of Vacor Analogs of Nicotinamide Riboside, NMN and NAD

It has recently been demonstrated that the rat poison vacor interferes with mammalian NAD metabolism, because it acts as a nicotinamide analog and is converted by enzymes of the NAD salvage pathway. Thereby, vacor is transformed into the NAD analog vacor adenine dinucleotide (VAD), a molecule that causes cell toxicity. Therefore, vacor may potentially be exploited to kill cancer cells. In this study, we have developed efficient enzymatic and chemical procedures to produce vacor analogs of NAD and nicotinamide riboside (NR). VAD was readily generated by a base-exchange reaction, replacing the nicotinamide moiety of NAD by vacor, catalyzed by Aplysia californica ADP ribosyl cyclase. Additionally, we present the chemical synthesis of the nucleoside version of vacor, vacor riboside (VR). Similar to the physiological NAD precursor, NR, VR was converted to the corresponding mononucleotide (VMN) by nicotinamide riboside kinases (NRKs). This conversion is quantitative and very efficient. Consequently, phosphorylation of VR by NRKs represents a valuable alternative to produce the vacor analog of NMN, compared to its generation from vacor by nicotinamide phosphoribosyltransferase (NamPT).

Prioritizing Environmental Chemicals for Obesity and Diabetes Outcomes Research: A Screening Approach Using ToxCast™ High-Throughput Data

BACKGROUND

Diabetes and obesity are major threats to public health in the United States and abroad. Understanding the role that chemicals in our environment play in the development of these conditions is an emerging issue in environmental health, although identifying and prioritizing chemicals for testing beyond those already implicated in the literature is challenging. This review is intended to help researchers generate hypotheses about chemicals that may contribute to diabetes and to obesity-related health outcomes by summarizing relevant findings from the U.S. Environmental Protection Agency (EPA) ToxCast™ high-throughput screening (HTS) program.

OBJECTIVES

Our aim was to develop new hypotheses around environmental chemicals of potential interest for diabetes- or obesity-related outcomes using high-throughput screening data.

METHODS

We identified ToxCast™ assay targets relevant to several biological processes related to diabetes and obesity (insulin sensitivity in peripheral tissue, pancreatic islet and β cell function, adipocyte differentiation, and feeding behavior) and presented chemical screening data against those assay targets to identify chemicals of potential interest.

DISCUSSION

The results of this screening-level analysis suggest that the spectrum of environmental chemicals to consider in research related to diabetes and obesity is much broader than indicated by research papers and reviews published in the peer-reviewed literature. Testing hypotheses based on ToxCast™ data will also help assess the predictive utility of this HTS platform.

CONCLUSIONS

More research is required to put these screening-level analyses into context, but the information presented in this review should facilitate the development of new hypotheses.

CITATION

Auerbach S, Filer D, Reif D, Walker V, Holloway AC, Schlezinger J, Srinivasan S, Svoboda D, Judson R, Bucher JR, Thayer KA. 2016. Prioritizing environmental chemicals for obesity and diabetes outcomes research: a screening approach using ToxCast™ high-throughput data. Environ Health Perspect 124:1141-1154; http://dx.doi.org/10.1289/ehp.1510456.

Can exposure to environmental chemicals increase the risk of diabetes type 1 development?

Type 1 diabetes mellitus (T1DM) is an autoimmune disease, where destruction of beta-cells causes insulin deficiency. The incidence of T1DM has increased in the last decades and cannot entirely be explained by genetic predisposition. Several environmental factors are suggested to promote T1DM, like early childhood enteroviral infections and nutritional factors, but the evidence is inconclusive. Prenatal and early life exposure to environmental pollutants like phthalates, bisphenol A, perfluorinated compounds, PCBs, dioxins, toxicants, and air pollutants can have negative effects on the developing immune system, resulting in asthma-like symptoms and increased susceptibility to childhood infections. In this review the associations between environmental chemical exposure and T1DM development is summarized. Although information on environmental chemicals as possible triggers for T1DM is sparse, we conclude that it is plausible that environmental chemicals can contribute to T1DM development via impaired pancreatic beta-cell and immune-cell functions and immunomodulation. Several environmental factors and chemicals could act together to trigger T1DM development in genetically susceptible individuals, possibly via hormonal or epigenetic alterations. Further observational T1DM cohort studies and animal exposure experiments are encouraged.

The role of chemicals in the etiology of diabetes mellitus

Diabetes mellitus is a collection of diseases that culminate in defects in carbohydrate metabolism and result in inappropriate hyperglycemia. Most individuals with this disease can be categorized into 1 of 2 groups, depending upon their insulin requirements. Individuals who require insulin therapy to maintain life have been designated as having insulin-dependent diabetes mellitus (IDDM), while individuals who can live without insulin treatment have been classified as having noninsulin-dependent diabetes mellitus (NIDDM). The single most important pathological finding in IDDM is a substantial reduction in the number of insulin-secreting pancreatic beta cells. Compelling experimental and epidemiological evidence indicates that, at least in some forms of IDDM, environmental factors, such as chemical toxins, play an important role in the etiology of this disease. Chemical toxins can precipitate IDDM through a variety of mechanisms. They can poison beta cells directly and cause the destruction of a critical mass of beta cells; alternatively, they can trigger autoimmune processes directed against beta cells; or, finally, they can augment the diabetogenic properties of another agent, such as a virus, to hasten the onset of clinical manifestations. In NIDDM, impaired beta cell function appears to be the initial event observed at the onset of this syndrome. Functional defects similar to those seen in NIDDM can be produced in laboratory animals using a specific beta cell toxin. These animals develop permanent glucose intolerance and insulin resistance as a consequence of beta cell alteration. A variety of other chemicals also have been found to produce glucose intolerance; however, this condition is transient and is resolved when the chemical is removed.(ABSTRACT TRUNCATED AT 250 WORDS)