The H-bonding network of acylguanidine complexes: combined intermolecular (2h)J(H,P) and (3h)J(N,P) scalar couplings provide an insight into the geometric arrangement.

The H-bonding networks of arginines and acylguanidines are crucial for many biological and pharmaceutical interactions. However, the effect of acylation of guanidines on the binding mode and the H-bond strengths has not yet been explored in solution. Therefore, the H-bonding network of a (15)N labeled acylguanidine derivative in a bisphosphonate arginine receptor is investigated. The direct NMR detection of 1D, 2D, and 3D correlations caused by (2h)J(H,P) and, for the first time in nonbiomacromolecules, (3h)J(N,P) couplings, allows for the geometric analysis of the H-bonding network and indicates an end-on binding mode with two different POH angles. The acylguanidine adopts the same binding mode as the corresponding guanidine but forms significantly stronger H-bonds. This may explain the success of acylguanidine ligands in medicinal chemistry applications.

Short-term cooling increases serum triglycerides and small high-density lipoprotein levels in humans.

BACKGROUND: Cold exposure and ß3-adrenergic receptor agonism, which both activate brown adipose tissue, markedly influence lipoprotein metabolism by enhancing lipoprotein lipase-mediated catabolism of triglyceride-rich lipoproteins and increasing plasma high-density lipoprotein (HDL) levels and functionality in mice. However, the effect of short-term cooling on human lipid and lipoprotein metabolism remained largely elusive. OBJECTIVE: The objective was to assess the effect of short-term cooling on the serum lipoprotein profile and HDL functionality in men. METHODS: Body mass index-matched young, lean men were exposed to a personalized cooling protocol for 2 hours. Before and after cooling, serum samples were collected for analysis of lipids and lipoprotein composition by 1H-nuclear magnetic resonance. Adenosine triphosphate-binding cassette A1 (ABCA1)-mediated cholesterol efflux capacity of HDL was measured using [3H]cholesterol-loaded ABCA1-transfected Chinese hamster ovary cells. RESULTS: Short-term cooling increased serum levels of free fatty acids, triglycerides, and cholesterol. Cooling increased the concentration of large very low-density lipoprotein (VLDL) particles accompanied by increased mean size of VLDL particles. In addition, cooling enhanced the concentration of small LDL and small HDL particles as well as the cholesterol levels within these particles. The increase in small HDL was accompanied by increased ABCA1-dependent cholesterol efflux in vitro. CONCLUSIONS: Our data show that short-term cooling increases the concentration of large VLDL particles and increases the generation of small LDL and HDL particles. We interpret that cooling increases VLDL production and turnover, which results in formation of surface remnants that form small HDL particles that attract cellular cholesterol.