Vitamin D and type 2 diabetes mellitus.

WHAT IS KNOWN AND OBJECTIVE: The deleterious effect of vitamin D deficiency on bone health has long been known. More recent studies suggest a deleterious effect of low vitamin D (hypovitaminosis D) on general health. And specific studies propose an association between hypovitaminosis D and the aetiology and progression of type 2 diabetes (T2DM). Given a commonly assumed lack of toxicity of vitamin D, routine measurement of plasma vitamin D and supplementation is rapidly becoming accepted general practice. COMMENT: Authoritative practice guidelines have raised the level of vitamin D that is to be considered minimal for optimum health. This recommendation was based on a wealth of information and definitive evidence for skeletal benefits of vitamin D, but there was a lack of compelling evidence that hypovitaminosis D is causally related to extra-skeletal health outcomes such as diabetes. Hence, vitamin D supplementation for the purpose of achieving a level consistent with good health is evidence based, but measurement and supplementation for the purpose of preventing or treating T2DM is not. WHAT IS NEW AND CONCLUSION: Although the maintenance of adequate vitamin D levels is desirable for all patients, we conclude that routine measurement of vitamin D level in every patient or initiating high-dose supplementation for the purpose of preventing or treating T2DM is not evidence based.

The kidney as a new target for antidiabetic drugs: SGLT2 inhibitors.

WHAT IS KNOWN AND OBJECTIVE: A novel class of antidiabetic drugs - SGLT2 (Na(+) /glucose cotransporter type 2) inhibitors - target renal reabsorption of glucose and promote normal glucose levels, independent of insulin production or its action at receptors. We review this new mechanistic approach and the reported efficacy and safety of clinical testing of lead compounds. METHODS: Information was obtained from various bibliographic sources, including PubMed and others, on the basic science and the clinical trials of SGLT2 inhibitors. The information was then summarized and evaluated from the perspective of contribution to a fuller understanding of the potential and current status of the lead clinical candidates. RESULTS AND DISCUSSION: Diabetes mellitus is a spectrum of disorders that involves inadequate insulin function resulting in adverse health sequelae due to acute and chronic hyperglycaemia. Current antidiabetic pharmacotherapy primarily addresses either insulin production at the pancreatic ß-cells or insulin action at insulin receptors. These drugs have less than full clinical effectiveness and sometimes therapy-limiting adverse effects. The third major component of glucose balance, namely elimination, has not been a significant therapeutic target to date. SGLT2 inhibitors are a novel approach. WHAT IS NEW AND CONCLUSION: A sufficient number of clinical trials have been conducted on sufficiently chemically diverse SGLT2 inhibitors to reasonably conclude that they have efficacy (HbA1c reductions of 0·4-1%), and thus far, the majority of adverse effects have been mild and transitory or treatable, with the caveat of possible association with increased risk of breast cancer in women and bladder cancer in men.

Alternative conformations of a nucleic acid four-way junction.

A crystal structure of a 108 nucleotide RNA-DNA complex containing a four-way junction was solved at 3.1 A resolution. The structure of the junction differs substantially from the "stacked-X" conformation observed previously, due to a 135 degrees rotation of the branches. Comparison of the two conformers provides insight into the factors contributing to the flexibility of four-way junctions. The stacked-X conformation maximizes base-stacking but causes unfavorable repulsion between phosphate groups, whereas the 135 degrees -rotated "crossed" conformation minimizes electrostatic clashes at the expense of reduced base-stacking. Despite the large rotation of the branches, both junction structures exhibit an antiparallel arrangement of the continuous strands and opposite polarity of the crossover strands.

Crystal structure of an 82-nucleotide RNA-DNA complex formed by the 10-23 DNA enzyme.

The structure of a large nucleic acid complex formed by the 10-23 DNA enzyme bound to an RNA substrate was determined by X-ray diffraction at 3.0 A resolution. The 82-nucleotide complex contains two strands of DNA and two strands of RNA that form five double-helical domains. The spatial arrangement of these helices is maintained by two four-way junctions that exhibit extensive base-stacking interactions and sharp turns of the phosphodiester backbone stabilized by metal ions coordinated to nucleotides at these junctions. Although it is unlikely that the structure corresponds to the catalytically active conformation of the enzyme, it represents a novel nucleic acid fold with implications for the Holliday junction structure.

Crystallization of the 10-23 DNA enzyme using a combinatorial screen of paired oligonucleotides.

One of the most difficult steps in the X-ray crystallography of nucleic acids is obtaining crystals that diffract to high resolution. The choice of the nucleotide sequence has proven to be more important in producing high-quality crystals than the composition of the crystallization solution. This manuscript describes a systematic procedure for identifying the optimal sizes of a multi-stranded nucleic acid complex which provide high-quality crystals. This approach was used to crystallize the in vitro evolved 10-23 DNA enzyme complexed with its RNA substrate. In less than two months, 81 different enzyme-substrate complexes were generated by combinatorial mixing and annealing of complementary oligonucleotides which differed in length, resulting in duplexes of varying length, with or without nucleotide overhangs. Each of these complexes was screened against a standard set of 48 crystallization conditions and evaluated for crystal formation. The screen resulted in over 40 crystal forms, the best of which diffracted to 2.8 A resolution when exposed to a synchrotron X-ray source.