Peter J. Rice

Differential High-Affinity Interaction of Dectin-1 with Natural or Synthetic Glucans Is Dependent upon Primary Structure and Is Influenced by Polymer Chain Length and Side-Chain Branching

Glucans are structurally diverse fungal biopolymers that stimulate innate immunity and are fungal pathogen-associated molecular patterns. Dectin-1 is a C-type lectin-like pattern recognition receptor that binds glucans and induces innate immune responses to fungal pathogens. We examined the effect of glucan structure on recognition and binding by murine recombinant Dectin-1 with a library of natural product and synthetic (1→3)-β/(1→6)-β-glucans as well as nonglucan polymers. Dectin-1 is highly specific for glucans with a pure (1→3)-β-linked backbone structure. Although Dectin-1 is highly specific for (1→3)-β-d-glucans, it does not recognize all glucans equally. Dectin-1 differentially interacted with (1→3)-β-d-glucans over a very wide range of binding affinities (2.6 mM–2.2 pM). One of the most striking observations that emerged from this study was the remarkable high-affinity interaction of Dectin-1 with certain glucans (2.2 pM). These data also demonstrated that synthetic glucan ligands interact with Dectin-1 and that binding affinity increased in synthetic glucans containing a single glucose side-chain branch. We also observed differential recognition of glucans derived from saprophytes and pathogens. We found that glucan derived from a saprophytic yeast was recognized with higher affinity than glucan derived from the pathogen Candida albicans. Structural analysis demonstrated that glucan backbone chain length and (1→6)-β side-chain branching strongly influenced Dectin-1 binding affinity. These data demonstrate: 1) the specificity of Dectin-1 for glucans; 2) that Dectin-1 differentiates between glucan ligands based on structural determinants; and 3) that Dectin-1 can recognize and interact with both natural product and synthetic glucan ligands.

Normal Human Fibroblasts Express Pattern Recognition Receptors for Fungal (1→3)-β-d-Glucans

ABSTRACT Fungal cell wall glucans nonspecifically stimulate various aspects of innate immunity. Glucans are thought to mediate their effects via interaction with membrane receptors on macrophages, neutrophils, and NK cells. There have been no reports of glucan receptors on nonimmune cells. We investigated the binding of a water-soluble glucan in primary cultures of normal human dermal fibroblasts (NHDF). Membranes from NHDF exhibited saturable binding with an apparent dissociation constant (KD) of 8.9 ± 1.9 μg of protein per ml and a maximum binding of 100 ± 8 resonance units. Competition studies demonstrated the presence of at least two glucan binding sites on NHDF. Glucan phosphate competed for all binding sites, with a KD of 5.6 μM (95% confidence interval [CI], 3.0 to 11 μM), while laminarin competed for 69% ± 6% of binding sites, with a KD of 3.7 μM (95% CI, 1.9 to 7.3 μM). Glucan (1 μg/ml) stimulated fibroblast NF-κB nuclear binding activity and interleukin 6 (IL-6) gene expression in a time-dependent manner. NF-κB was activated at 4, 8, and 12 h, while IL-6 mRNA levels were increased by 48% at 8 h. This is the first report of pattern recognition receptors for glucan on human fibroblasts and the first demonstration of glucan binding sites on cells other than leukocytes. It also provides the first evidence that glucans can directly modulate the functional activity of NHDF. These results provide new insights into the mechanisms by which the host recognizes and responds to fungal (1→3)-β-d-glucans and suggests that the response to glucans may not be confined to cells of the immune system.

Inhibiting efflux with novel non-ionic surfactants: Rational design based on vitamin E TPGS.

Tocopheryl Polyethylene Glycol Succinate 1000 (TPGS 1000) can inhibit P-glycoprotein (P-gp); TPGS 1000 was not originally designed to inhibit an efflux pump. Recent work from our laboratories demonstrated that TPGS activity has a rational PEG chain length dependency. In other recent work, inhibition mechanism was investigated and appears to be specific to the ATPase providing P-gp energy. Based on these observations, we commenced rational surface-active design. The current work summarizes new materials tested in a validated Caco-2 cell monolayer model; rhodamine 123 (10microM) was used as the P-gp substrate. These results demonstrate that one may logically construct non-ionic surfactants with enhanced propensity to inhibit in vitro efflux. One new surfactant based inhibitor, Tocopheryl Polypropylene Glycol Succinate 1000 (TPPG 1000), approached cyclosporine (CsA) in its in vitro efflux inhibitory potency. Subsequently, TPPG 1000 was tested for its ability to enhance the bioavailability of raloxifene - an established P-gp substrate -in fasted male rats. Animals dosed with raloxifene and TPPG 1000 experienced an increase in raloxifene oral bioavailability versus a control group which received no inhibitor. These preliminary results demonstrate that one may prepare TPGS analogs that possess enhanced inhibitory potency in vitro and in vivo.

A (1→3)-β-D-linked heptasaccharide is the unit ligand for glucan pattern recognition receptors on human monocytes

Glucans are fungal cell wall polysaccharides which stimulate innate immune responses. We determined the minimum unit ligand that would bind to glucan receptors on human U937 cells using laminarin-derived pentaose, hexaose, and heptaose glucan polymers. When U937 membranes were pretreated with the oligosaccharides and passed over a glucan surface, only the heptasaccharide inhibited the interaction of glucan with membrane receptors at a K(d) of 31 microM (95% CI 20-48 microM) and 100% inhibition. However, the glucan heptasaccharide did not stimulate U937 monocyte NFkappaB signaling, nor did it increase survival in a murine model of polymicrobial sepsis. Laminarin, a larger and more complex glucan polymer (M(w) = 7700 g/mol), only partially inhibited binding (61 +/- 4%) at a K(d) of 2.6 microM (99% CI 1.7-4.2 microM) with characteristics of a single binding site. These results indicate that a heptasaccharide is the smallest unit ligand recognized by macrophage glucan receptors. The data also indicate the presence of at least two glucan-binding sites on U937 cells and that the binding sites on human monocyte/macrophages can discriminate between glucan polymers. The heptasaccharide and laminarin were receptor antagonists, but they were not receptor agonists with respect to activation of NFkappaB-dependent signaling pathways or protection against experimental sepsis.

Developing Potent Human Uric Acid Transporter 1 (hURAT1) Inhibitors

The kidneys are a vital organ in the human body. They serve several purposes including homeostatic functions such as regulating extracellular fluid volume and maintaining acid-base and electrolyte balance and are essential regarding the excretion of metabolic waste. Furthermore, the kidneys play an important role in uric acid secretion/reabsorption. Abnormalities associated with kidney transporters have been associated with various diseases, such as gout. The current study utilized Xenopus oocytes expressing human uric acid transporter 1 (hURAT1; SLC22A12) as an in vitro method to investigate novel compounds and their ability to inhibit (14)C-uric acid uptake via hURAT1. We have prepared and tested a series of 2-ethyl-benzofuran compounds and probed the hURAT1 in vitro inhibitor structure-activity relationship. As compared to dimethoxy analogues, monophenols formed on the C ring showed the best in vitro inhibitory potential. Compounds with submicromolar (i.e., IC(50) < 1000 nM) inhibitors were prepared by brominating the corresponding phenols to produce compounds with potent uricosuric activity.

Pharmacokinetics of letrozole in male and female rats: influence of complexation with hydroxybutenyl-β-cyclodextrin

Cyclodextrins (CDs) are one of the most successful solutions to the problem of poor drug solubility. In this study, we examined the in‐vitro effects of three CDs on the solubility of letrozole, a breast cancer drug that is practically insoluble in water. The most promising, hydroxybutenyl‐β‐cyclodextrin (HBenβCD), was used for in‐vivo studies in male and female Sprague‐Dawley rats. Letrozole is a drug with dramatic gender‐based differences in pharmacokinetics. For example, the terminal half‐life (t1/2) of letrozole following intravenous administration in male rats was 11.5 ± 1.8 h (n = 3), while in female rats it was 42.3 ± 2.9 h (n = 3). HBenβCD increased the solubility and enhanced the dissolution rate of letrozole. Complexation of letrozole with HBenβCD improved oral absorption in male rats and maximized absorption in female rats. Regardless of gender, the presence of HBenβCD in the formulation increased the in‐vivo rate of absorption. When administered in a capsule formulation with letrozole, HBenβCD resulted in a higher Cmax (61% in male rats, 42% in female), shorter Tmax values (8.4 to 6.3 h in male, 16.4 h to 5.4 h in female) and increased absolute oral bioavailability (46 ± 2 vs 38 ± 3 in male, 101 ± 3 vs 95 ± 2 in female). Thus, solubility limits both rate and extent of letrozole absorption in male rats, but limits only the rate of absorption in female rats.

A role for protein kinase C in the supersensitivity of the rat vas deferens following chronic surgical denervation

Chronic surgical denervation of the rat vas deferens leads to an enhanced contractile response of the tissue to norepinephrine in vitro. Norepinephrine produces a higher rate of protein kinase C translocation to the particulate fraction of denervated tissues as compared with the paired, control vas deferens. Diacylglycerol generation in response to norepinephrine and contractile responses to phorbol diacetate were not altered by chronic denervation of the vas deferens. However, the contractile response to norepinephrine in these tissues was less susceptible to the inhibitory effects of the calcium channel blocker nifedipine. A potential role of protein kinase C in sensitizing the contractile apparatus to mobilized calcium in denervation supersensitivity is discussed.

Investigation of the Influence of Acetylsalicylic Acid on the Steady State of Long‐Term Therapy With Theophylline in Elderly Male Patients With Normal Renal Function

The risk inherent in the clinical control of patients with theophylline is widely recognized. Elderly patients may present an additional risk because of altered pharmacokinetics and the use of concomitant medication. Acetylsalicylic acid has been proposed for primary and secondary prevention of myocardial infarction and possible strokes. This investigation was undertaken to determine if concomitant administration of acetylsalicylic acid in elderly patients would alter steady‐state levels of theophylline. A population of smoking male patients older than 60 years of age under long‐term control of chronic obstructive pulmonary disease (COPD) with theophylline were evaluated for a baseline period of 3 days. Serum levels were measured at 6:00 am and 6:00 pm. An enteric‐coated acetylsalicylic acid preparation, 650 mg by mouth, was added to the daily slow‐release theophylline, 6:00 am hour dose regimen for 4 weeks. The serum levels of theophylline and salicylates were measured at 6:00 pm after dosing and at 6:00 am the following day, at weekly intervals for 4 weeks. Urine specimens collected before administration of medication at 6:00 am were analyzed for salicylates to further confirm dosage compliance. All volunteers continued to be clinically controlled throughout the treatment period, and no symptoms of either overdose or underdose of either medication occurred. Plateau or trough theophylline serum levels did not change significantly during the salicylate treatment period. Salicylate serum levels did show during treatment self‐induced metabolism. It is concluded that in elderly male patients, a daily concomitant therapeutic salicylate regimen does not alter steady‐state serum theophylline levels and therefore does not per se necessitate the assay of theophylline blood levels in elderly patients.

Potent human uric acid transporter 1 inhibitors: in vitro and in vivo metabolism and pharmacokinetic studies

Human uric acid transporter 1 (hURAT1; SLC22A12) is a very important urate anion exchanger. Elevated urate levels are known to play a pivotal role in cardiovascular diseases, chronic renal disease, diabetes, and hypertension. Therefore, the development of potent uric acid transport inhibitors may lead to novel therapeutic agents to combat these human diseases. The current study investigates small molecular weight compounds and their ability to inhibit 14C-urate uptake in oocytes expressing hURAT1. Using the most promising drug candidates generated from our structure–activity relationship findings, we subsequently conducted in vitro hepatic metabolism and pharmacokinetic (PK) studies in male Sprague-Dawley rats. Compounds were incubated with rat liver microsomes containing cofactors nicotinamide adenine dinucleotide phosphate and uridine 5′-diphosphoglucuronic acid. In vitro metabolism and PK samples were analyzed using liquid chromatography/mass spectrometry-mass spectrometry methods. Independently, six different inhibitors were orally (capsule dosing) or intravenously (orbital sinus) administered to fasting male Sprague-Dawley rats. Blood samples were collected and analyzed; these data were used to compare in vitro and in vivo metabolism and to compute noncompartmental model PK values. Mono-oxidation (Phase I) and glucuronidation (Phase II) pathways were observed in vitro and in vivo. The in vitro data were used to compute hepatic intrinsic clearance, and the in vivo data were used to compute peak blood concentration, time after administration to achieve peak blood concentration, area under the curve, and orally absorbed fraction. The experimental data provide additional insight into the hURAT1 inhibitor structure–activity relationship and in vitro–in vivo correlation. Furthermore, the results illustrate that one may successfully prepare potent inhibitors that exhibit moderate to good oral bioavailability.

Investigating idebenone and idebenone linoleate metabolism: in vitro pig ear and mouse melanocyte studies

Objective  The aim of this study was to investigate inherent in vitro permeability, metabolism, and cytotoxicity of idebenone – an active used to protect skin as an anti‐aging agent – and compare it to idebenone linoleate.