Release of markedly increased quantities of prostaglandin D2 in vivo in humans following the administration of nicotinic acid

Single-cell transcriptomics reveals aberrant skin-resident cell populations and identifies fibroblasts as a determinant in rosacea

Rosacea is a chronic inflammatory skin disorder, whose underlying cellular and molecular mechanisms remain obscure. Here, we generate a single-cell atlas of facial skin from female rosacea patients and healthy individuals. Among keratinocytes, a subpopulation characterized by IFNγ-mediated barrier function damage is found to be unique to rosacea lesions. Blocking IFNγ signaling alleviates rosacea-like phenotypes and skin barrier damage in mice. The papulopustular rosacea is featured by expansion of pro-inflammatory fibroblasts, Schwann, endothelial and macrophage/dendritic cells. The frequencies of type 1/17 and skin-resident memory T cells are increased, and vascular mural cells are characterized by activation of inflammatory pathways and impaired muscle contraction function in rosacea. Most importantly, fibroblasts are identified as the leading cell type producing pro-inflammatory and vasodilative signals in rosacea. Depletion of fibroblasts or knockdown of PTGDS, a gene specifically upregulated in fibroblasts, blocks rosacea development in mice. Our study provides a comprehensive understanding of the aberrant alterations of skin-resident cell populations and identifies fibroblasts as a key determinant in rosacea development.

Stimulation of the Hydroxycarboxylic Acid Receptor 2 With the Ketone Body 3-Hydroxybutyrate and Niacin in Patients With Chronic Heart Failure: Hemodynamic and Metabolic Effects

Background The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output (CO) in patients with heart failure through unknown mechanisms. 3-OHB activates the hydroxycarboxylic acid receptor 2 (HCA₂), which increases prostaglandins and suppresses circulating free fatty acids. We investigated whether the cardiovascular effects of 3-OHB involved HCA₂ activation and if the potent HCA₂-stimulator niacin may increase CO. Methods and Results Twelve patients with heart failure with reduced ejection fraction were included in a randomized crossover study and examined by right heart catheterization, echocardiography, and blood sampling on 2 separate days. On study day 1, patients received aspirin to block the HCA₂ downstream cyclooxygenase enzyme, followed by 3-OHB and placebo infusions in random order. We compared the results with those of a previous study in which patients received no aspirin. On study day 2, patients received niacin and placebo. The primary end point was CO. 3-OHB increased CO (2.3 L/min, P<0.01), stroke volume (19 mL, P<0.01), heart rate (10 bpm, P<0.01), and mixed venous saturation (5%, P<0.01) with preceding aspirin. 3-OHB did not change prostaglandin levels, neither in the ketone/placebo group receiving aspirin nor the previous study cohort. Aspirin did not block 3-OHB-induced changes in CO (P=0.43). 3-OHB decreased free fatty acids by 58% (P=0.01). Niacin increased prostaglandin D₂ levels by 330% (P<0.02) and reduced free fatty acids by 75% (P<0.01) but did not affect CO. Conclusions The acute increase in CO during 3-OHB infusion was not modified by aspirin, and niacin had no hemodynamic effects. These findings show that HCA₂ receptor-mediated effects were not involved in the hemodynamic response to 3-OHB. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04703361.

Glucocorticoid-induced thrombotic microangiopathy in paroxysmal nocturnal hemoglobinuria: A case report and review of literature

BACKGROUND

Thrombotic microangiopathy (TMA) is a group of disorders that converge on excessive platelet aggregation in the microvasculature, leading to consumptive thrombocytopenia, microangiopathic hemolysis and ischemic end-organ dysfunction. In predisposed patients, TMA can be triggered by many environmental factors. Glucocorticoids (GCs) can compromise the vascular endothelium. However, GC-associated TMA has rarely been reported, which may be due to the lack of awareness of clinicians. Given the high frequency of thrombocytopenia during GC treatment, particular attention should be given to this potentially fatal complication.

CASE SUMMARY

An elderly Chinese man had a 12-year history of aplastic anemia (AA) and a 3-year history of paroxysmal nocturnal hemoglobinuria (PNH). Three months earlier, methylprednisolone treatment was initiated at 8 mg/d and increased to 20 mg/d to alleviate complement-mediated hemolysis. Following GC treatment, his platelet counts and hemoglobin levels rapidly decreased. After admission to our hospital, the dose of methylprednisolone was increased to 60 mg/d in an attempt to enhance the suppressive effect. However, increasing the GC dose did not alleviate hemolysis, and his cytopenia worsened. Morphological evaluation of the marrow smears revealed increased cellularity with an increased percentage of erythroid progenitors without evident dysplasia. Cluster of differentiation (CD)55 and CD59 expression was significantly decreased on erythrocytes and granulocytes. In the following days, platelet transfusion was required due to severe thrombocytopenia. Observation of platelet transfusion refractoriness indicated that the exacerbated cytopenia may have been caused by the development of TMA due to GC treatment because the transfused platelet concentrates had no defects in glycosylphosphatidylinositol-anchored proteins. We examined blood smears and found a small number of schistocytes, dacryocytes, acanthocytes and target cells. Discontinuation of GC treatment resulted in rapidly increased platelet counts and steady increases in hemoglobin levels. The patient’s platelet counts and hemoglobin levels returned to the levels prior to GC treatment 4 weeks after GC discontinuation.

CONCLUSION

GCs can drive TMA episodes. When thrombocytopenia occurs during GC treatment, TMA should be considered, and GCs should be discontinued.

Nontryptase Urinary and Hematologic Biomarkers of Mast Cell Expansion and Mast Cell Activation: Status 2022

Quantitation of urinary metabolites of histamine, prostaglandin D₂, and leukotriene E₄ can fill the gap in our current efforts to improve diagnosis and management of symptomatic patients with systemic mastocytosis, and/or mast cell activation syndrome, In addition, patients symptomatic due to mast cell activation but who do not meet all the criteria for mast cell activation syndrome can have elevated baseline mediator metabolites. Serum tryptase levels have been the workhorse in diagnosing these disorders, but it has several drawbacks including the need to obtain acute and baseline samples, which require 2 visits to health care facilities and 2 venipunctures. Recently, increased baseline tryptase level has been reported in hereditary alpha tryptasemia, complicating diagnostic possibilities of an increased baseline tryptase level. Furthermore, no treatment can specifically be targeted at tryptase itself. In contrast, the finding of 1 or more elevated urinary levels of histamine, prostaglandin D₂, and/or leukotriene E₄ metabolites (1) greatly narrows diagnostic possibilities for causes of symptoms; (2) informs the practitioner what specific metabolic pathways are involved; and (3) targets the treatment in a specific, direct fashion. As a bonus, baseline spot/random urine samples can be obtained by the patients themselves and repeated at exactly the correct time when symptoms occur.

The efficacy and safety of niacin on hyperphosphatemia in ESRD patients undergoing hemodialysis: randomized controlled trial

Background

Hyperphosphatemia is a common complication of end-stage renal disease (ESRD) and particularly affects hemodialysis (HD) patients. Elevated serum phosphorus contributes to the development of secondary hyperparathyroidism, chronic kidney disease–mineral bone disorder (CKD-MBD), metastatic calcifications and calcific uremic arteriolopathy. There is a significant association between hyperphosphatemia and increased morbidity and mortality in ESRD patients including cardiovascular morbidity and mortality, and it is also associated with prolonged hospitalization of HD patients. This study aim to evaluate the serum phosphorus lowering effect of niacin in HD patients.

Results

There was a decrease in phosphate values during the first 3 months of the study in the niacin group, with a significant change in phosphate level at the third month (5.90 ± 0.52 vs. 6.42 ± 0.65 (mEq/l); P <  0.001) and at the sixth month (5.12 ± 0.41 vs. 5.76 ± 0.47 (mEq/l); P <  0.001) compared to the control group. It was noted that both groups had an insignificant difference regarding baseline parathormone (PTH), though the PTH showed a significantly lower level at the third month (192.39 ± 78.85 vs. 388.27 ± 263.10 pg/ml; P <  0.001) and at the sixth month (127.56 ± 90.87 vs. 249.85 ± 97.69 pg/ml; P <  0.001) in the niacin group.

Conclusion

Niacin caused a statistically significant decrease in levels of phosphate and PTH in dialysis patients.

Trial registration

Registered at ClinicalTrials.gov NCT03163576. Trial registration date: 22 May 2017. Date of first patient’s enrolment: 1 October 2018. Date of the ethical committee approval: 29 March 2017. Number of the ethical committee approval: 17100040.

Reduced Levels and Disrupted Biosynthesis Pathways of Plasma Free Fatty Acids in First-Episode Antipsychotic-Naïve Schizophrenia Patients

Membrane phospholipid deficits have been well-documented in schizophrenia (SZ) patients. Free fatty acids (FFAs) partially come from the hydrolysis of membrane phospholipids and serve as the circulating pool of body fatty acids. These FFAs are involved in many important biochemical reactions such as membrane regeneration, oxidation, and prostaglandin production which may have important implications in SZ pathology. Thus, we compared plasma FFA levels and profiles among healthy controls (HCs), affective psychosis (AP) patients, and first-episode antipsychotic-naïve schizophrenia (FEANS) patients. A significant reduction of total FFAs levels was observed in SZ patients. Specifically, significant reductions of 16:0, 18:2n6c, and 20:4n6 levels were detected in FEANS patients but not in APs when compared with levels in HCs. Also, disrupted metabolism of fatty acids especially in saturated and n-6 fatty acid families were observed by comparing correlations between precursor and product fatty acid levels within each fatty acid family. These findings may suggest an increased demand of membrane regeneration, a homeostatic imbalance of fatty acid biosynthesis pathway and a potential indication of increased beta oxidation. Collectively, these findings could help us better understand the lipid metabolism with regard to SZ pathophysiology.

Skin capillary extraction technique based on independent component analysis and Frangi filter using videomicroscopy

BACKGROUND

Videomicroscopy can be used to observe skin capillaries easily and non-invasively. In this study, we develop an algorithm that can handle skin regions by combining color component separation methods as pre-processing based on blood vessel extraction filtering.

MATERIALS AND METHODS

Images of skin on the inner upper arm were acquired using videomicroscopy. An algorithm using independent component analysis (ICA) and the Frangi filter was constructed, and capillary regions were extracted. The capillary blood vessel extraction images were compared with ground truth to verify accuracy. An evaluation of the physiological responses of skin exposed to carbon dioxide (CO₂ ) water, local heating, and methyl nicotinate was performed to test blood vessels with different mechanisms of action and layer depth.

RESULTS

Based on a comparison with ground truth images, a Dice coefficient of 0.82 was calculated. In examining physiological responses to stimuli on the skin, it was found that exposure to CO₂ for 2 minutes significantly increased the capillary area compared with the steady state.

CONCLUSION

An algorithm to extract capillaries from skin images using ICA and the Frangi filter method was proposed. Results suggest that this algorithm can quantitatively analyze physiological changes in capillaries on the skin surface.

Targeting immunometabolism as an anti-inflammatory strategy

The growing field of immunometabolism has taught us how metabolic cellular reactions and processes not only provide a means to generate ATP and biosynthetic precursors, but are also a way of controlling immunity and inflammation. Metabolic reprogramming of immune cells is essential for both inflammatory as well as anti-inflammatory responses. Four anti-inflammatory therapies, DMF, Metformin, Methotrexate and Rapamycin all work by affecting metabolism and/or regulating or mimicking endogenous metabolites with anti-inflammatory effects. Evidence is emerging for the targeting of specific metabolic events as a strategy to limit inflammation in different contexts. Here we discuss these recent developments and speculate on the prospect of targeting immunometabolism in the effort to develop novel anti-inflammatory therapeutics. As accumulating evidence for roles of an intricate and elaborate network of metabolic processes, including lipid, amino acid and nucleotide metabolism provides key focal points for developing new therapies, we here turn our attention to glycolysis and the TCA cycle to provide examples of how metabolic intermediates and enzymes can provide potential novel therapeutic targets.

Nicotinic acid transport into human liver involves organic anion transporter 2 (SLC22A7)

Nicotinic acid (NA) and nicotinamide (NAM) are biosynthetic precursors of nicotinamide adenine dinucleotide (NAD⁺) - a physiologically important coenzyme that maintains the redox state of cells. Mechanisms driving their entry into cells are not well understood. Here we evaluated the hepatic uptake mechanism(s) of NA and NAM using transporter-transfected cell systems and primary human hepatocytes. NA showed robust organic anion transporter (OAT)2-mediated transport with an uptake ratio (i.e., ratio of accumulation in transfect cells to wild-type cells) of 9.7 ± 0.3, and a Michaelis-Menten constant (K_m) of 13.5 ± 3.3 µM. However, no transport was apparent via other major hepatic uptake and renal secretory transporters, including OAT1/3/4, organic anion transporting polypeptide (OATP)1B1/1B3/2B1, sodium-taurocholate co-transporting polypeptide, organ cation transporter 1/2/3. OAT2-specific transport of NA was inhibited by ketoprofen and indomethacin (known OAT2 inhibitors) in a concentration-dependent manner. Similarly, NA uptake into primary human hepatocytes showed pH- and concentration-dependence and was subject to inhibition by specific OAT2 inhibitors. Unlike NA, NAM was not transported by the hepatic and renal solute carriers upon assessment in transfected cells, although its uptake into human hepatocytes was significantly inhibited by excess unlabelled NAM and a pan-SLC inhibitor (rifamycin SV 1 mM). In conclusion, these studies demonstrate, for the first time, a specific transport mechanism for NA uptake in the human liver and suggest that OAT2 (SLC22A7) has a critical role in its physiological and pharmacological functions.

Skin blood flow response to topically applied methyl nicotinate: Possible mechanisms

BACKGROUND

Methyl nicotinate (MN) induces a local cutaneous erythema in the skin and may be valuable as a local provocation in the assessment of microcirculation and skin viability. The mechanisms through which MN mediates its vascular effect are not fully known. The aim of this study was to characterize the vasodilatory effects of topically applied MN and to study the involvement of nitric oxide (NO), local sensory nerves, and prostaglandin-mediated pathways.

METHODS

MN was applied on the skin of healthy subjects in which NO-mediated (L-NMMA), nerve-mediated (lidocaine/prilocaine), and cyclooxygenase-mediated (NSAID) pathways were selectively inhibited. Microvascular responses in the skin were measured using laser speckle contrast imaging (LSCI).

RESULTS

NSAID reduced the MN-induced perfusion increase with 82% (P < .01), whereas lidocaine/prilocaine reduced it with 32% (P < .01). L-NMMA did not affect the microvascular response to MN.

CONCLUSION

The prostaglandin pathway and local sensory nerves are involved in the vasodilatory actions of MN in the skin.

Nicotinic acid promotes sleep through prostaglandin synthesis in mice

Nicotinic acid has been used for decades for its antiatherogenic properties in humans. Its actions on lipid metabolism intersect with multiple sleep regulatory mechanisms, but its effects on sleep have never been documented. For the first time, we investigated the effects of acute systemic administration of nicotinic acid on sleep in mice. Intraperitoneal and oral gavage administration of nicotinic acid elicited robust increases in non-rapid-eye movement sleep (NREMS) and decreases in body temperature, energy expenditure and food intake. Preventing hypothermia did not affect its sleep-inducing actions suggesting that altered sleep is not secondary to decreased body temperature. Systemic administration of nicotinamide, a conversion product of nicotinic acid, did not affect sleep amounts and body temperature, indicating that it is not nicotinamide that underlies these actions. Systemic administration of monomethyl fumarate, another agonist of the nicotinic acid receptor GPR109A, fully recapitulated the somnogenic and thermoregulatory effects of nicotinic acid suggesting that they are mediated by the GPR109A receptor. The cyclooxygenase inhibitor indomethacin completely abolished the effects of nicotinic acid indicating that prostaglandins play a key role in mediating the sleep and thermoregulatory responses of nicotinic acid.

Association of Dietary Niacin Intake With Incident Hip Fracture, BMD, and Body Composition: The Cardiovascular Health Study

Interest in niacin has increased in the setting of reports suggesting that niacin plays a role in diseases of aging. No study to date has examined the association of dietary niacin intake with multiple skeletal health parameters including bone mineral density (BMD), hip fractures, and body composition, and none have included both African American and white men and women. Participants included 5187 men and women ≥65 years from the Cardiovascular Health Study (CHS). Mean daily dietary niacin intake was 32.6 mg, with quartiles 1 through 4 defined as 3.6 to 21.8 mg/day, 21.9 to 30.2 mg/day, 30.3 to 40.9 mg/day, and 41.0 to 102.4 mg/day, respectively. Risk of incident hip fracture per 10 mg increment of daily dietary niacin intake was estimated using proportional hazards models. During a median follow-up of 13 years, 725 participants had an incident hip fracture. In models adjusted for demographic and clinical characteristics and diet, dietary niacin intake was significantly associated with an increased risk of hip fractures (hazard ratio [HR] 1.12; 95% CI, 1.01 to 1.24) with spline models suggesting a U-shaped association. In post hoc analyses, both the lowest (HR 1.31; 95% CI, 1.04 to 1.66) and highest (HR 1.53; 95% CI, 1.20 to 1.95) quartiles of niacin intake were associated with an increased risk of incident hip fracture versus quartiles 2 and 3. There was a trend for a significant inverse association of dietary niacin intake with hip BMD (p = 0.06), but no significant association with total body BMD or any body composition measures. In this cohort of elderly, community-dwelling African American and white men and women, both high and low dietary niacin intakes were associated with a significantly increased risk of subsequent hip fracture, suggesting a possible U-shaped association. By comparison, dietary niacin may have an inverse linear association with hip BMD. © 2018 American Society for Bone and Mineral Research.

Niacin in the Central Nervous System: An Update of Biological Aspects and Clinical Applications

Niacin (also known as "vitamin B₃" or "vitamin PP") includes two vitamers (nicotinic acid and nicotinamide) giving rise to the coenzymatic forms nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). The two coenzymes are required for oxidative reactions crucial for energy production, but they are also substrates for enzymes involved in non-redox signaling pathways, thus regulating biological functions, including gene expression, cell cycle progression, DNA repair and cell death. In the central nervous system, vitamin B₃ has long been recognized as a key mediator of neuronal development and survival. Here, we will overview available literature data on the neuroprotective role of niacin and its derivatives, especially focusing especially on its involvement in neurodegenerative diseases (Alzheimer's, Parkinson's, and Huntington's diseases), as well as in other neuropathological conditions (ischemic and traumatic injuries, headache and psychiatric disorders).

Quantitative evaluation of retinal artery occlusion using optical coherence tomography angiography: A case report

RATIONALE

Retinal artery occlusion (RAO) results in painless, catastrophic vision loss in a period of seconds. Optical coherence tomography angiography (OCTA) can image retinal microcirculation, which is helpful to evaluate treatment response during the follow-up period. Using a single case with central RAO, we report its retinal perfusion changes before and after treatment using OCTA.

PATIENT CONCERNS

A 36-year-old Chinese man came to our clinic with a sudden, painless loss of vision (hand motion) in his left eye. A vasodilator (nicotinic acid) was used as the primary treatment. OCTA imaging and a visual field examination were performed to assess the retinal perfusion changes before and after treatment.

DIAGNOSIS

Retinal artery occlusion was considered.

INTERVENTIONS

This patient was treated with an inhaled oxygen-carbon dioxide mixture, nicotinic acid tablets (100 mg) taken orally twice a day, and intravenous infusion of nicotinic acid injections (60 mg) combined with 0.9% sodium chloride injections (100 ml) once a day for vasodilation.

OUTCOMES

After treatment and 9 months of follow-up, the vessel density of the left eye at the 9-month follow-up appointment was improved in all quadrants.

LESSONS

Retinal edema and retinal atrophy were observed at the RAO onset and several months later, respectively. However, macular perfusion gradually increased after treatment. The timely administration of a vasodilator and the presence of the cilioretinal artery play important roles in the prevention of profound vision loss.

Methylnicotinate stimulated prostaglandin synthesis in patients with schizophrenia: A preliminary investigation

Schizophrenia is a serious mental illness of unclear aetiology. The reduced ability of methylnicotinate to induce a topical vasodilatory response in patients with the disorder is well established. Methylnicotinate causes vasodilation via stimulating the release of prostaglandins (including prostaglandin D₂) in the skin which in turn leads to relaxation of vascular smooth muscle. To determine whether the abnormality is likely to be due to decreased prostaglandin production, or a decreased effect of prostaglandins upon the vessels, topical methylnicotinate was applied to the forearms of patients with schizophrenia or healthy controls, followed by rating of the resulting erythema. The concentration of prostaglandin D₂ and its metabolite 11β-prostaglandin F_2α in the blood draining the arm was also measured. Although erythema was reduced in the patient group, this was not correlated with plasma prostaglandin concentrations. This data suggests the abnormality underlying the reduced potency of methylnicotinate to produce vasodilation in the disorder occurs downstream of prostaglandin synthesis possibly within the vasculature itself.

A rapid UPLC-MS/MS assay for eicosanoids in human plasma: Application to evaluate niacin responsivity

A rapid and sensitive method using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed to simultaneously quantify hydroxyeicosatetraenoic (HETE), dihydroxyeicosatrienoic (DiHETrE), epoxyeicosatrienoic acid (EET), and prostaglandin metabolites of arachidonic acid in human plasma. Sample preparation consisted of solid phase extraction with Oasis HLB (30mg) cartridges for all metabolites. Separation of HETEs, EETs, and DiHETrEs was achieved on an Acquity UPLC BEH C18, 1.7µm (100×2.1mm) reversed-phase column (Waters Corp, Millford, MA) with negative electrospray ionization mass spectrometric detection. A second injection of the same extracted sample allowed for separation and assessment of prostaglandin metabolites under optimized UPLC-MS/MS conditions. Additionally, the endogenous levels of these metabolites in five different matrices were determined in order to select the optimal matrix for assay development. Human serum albumin was shown to have the least amount of endogenous metabolites, a recovery efficiency of 79-100% and a matrix effect of 71 - 100%. Linear calibration curves ranging from 0.416 to 66.67ng/ml were validated. Inter-assay and intra-assay variance was less than 15% at most concentrations. This method was successfully applied to quantify metabolite levels in plasma samples of healthy control subjects receiving niacin administration to evaluate the association between niacin administration and eicosanoid plasma level response.

Exacerbation of Aging-Associated and Instability-Induced Murine Osteoarthritis With Deletion of D Prostanoid Receptor 1, a Prostaglandin D2 Receptor

OBJECTIVE

D prostanoid receptor 1 (DP1), a receptor for prostaglandin D₂ , plays important roles in inflammation and cartilage metabolism. However, its role in the pathogenesis of osteoarthritis (OA) remains unknown. This study was undertaken to explore the roles of DP1 in the development of OA in murine models and to evaluate the efficacy of a DP1 selective agonist in the treatment of OA.

METHODS

The development of aging-associated OA and destabilization of the medial meniscus (DMM)-induced OA was compared between DP1-deficient (DP1^-/- ) and wild-type (WT) mice. The progression of OA was assessed by histology, immunohistochemistry, and micro-computed tomography. Cartilage explants from DP1^-/- and WT mice were treated with interleukin-1α (IL-1α) ex vivo, to evaluate proteoglycan degradation. The effect of intraperitoneal administration of the DP1 selective agonist BW245C on OA progression was evaluated in WT mice.

RESULTS

Compared to WT mice, DP1^-/- mice had exacerbated cartilage degradation in both models of OA, and this was associated with increased expression of matrix metalloproteinase 13 and ADAMTS-5. In addition, DP1^-/- mice demonstrated enhanced subchondral bone changes. Cartilage explants from DP1^-/- mice showed enhanced proteoglycan degradation following treatment with IL-1α. Intraperitoneal injection of BW245C attenuated the severity of DMM-induced cartilage degradation and bony changes in WT mice.

CONCLUSION

These findings indicate a critical role for DP1 signaling in OA pathogenesis. Modulation of the functions of DP1 may constitute a potential therapeutic target for the development of novel OA treatments.

The NAD+ precursor nicotinic acid improves genomic integrity in human peripheral blood mononuclear cells after X-irradiation

NAD⁺ is an essential cofactor for enzymes catalyzing redox-reactions as well as an electron carrier in energy metabolism. Aside from this, NAD⁺ consuming enzymes like poly(ADP-ribose) polymerases and sirtuins are important regulators involved in chromatin-restructuring processes during repair and epigenetics/transcriptional adaption. In order to replenish cellular NAD⁺ levels after cleavage, synthesis starts from precursors such as nicotinamide, nicotinamide riboside or nicotinic acid to match the need for this essential molecule. In the present study, we investigated the impact of supplementation with nicotinic acid on resting and proliferating human mononuclear blood cells with a focus on DNA damage and repair processes. We observed that nicotinic acid supplementation increased NAD⁺ levels as well as DNA repair efficiency and enhanced genomic stability evaluated by micronucleus test after x-ray treatment. Interestingly, resting cells displayed lower basal levels of DNA breaks compared to proliferating cells, but break-induction rates were identical. Despite similar levels of p53 protein upregulation after irradiation, higher NAD⁺ concentrations led to reduced acetylation of this protein, suggesting enhanced SIRT1 activity. Our data reveal that even in normal primary human cells cellular NAD⁺ levels may be limiting under conditions of genotoxic stress and that boosting the NAD⁺ system with nicotinic acid can improve genomic stability.

Measuring niacin-associated skin toxicity (NASTy) stigmata along with symptoms to aid development of niacin mimetics

Though cardioprotective, niacin monotherapy is limited by unpleasant cutaneous symptoms mimicking dermatitis: niacin-associated skin toxicity (NASTy). Niacin is prototypical of several emerging drugs suffering off-target rubefacient properties whereby agonizing the GPR109A receptor on cutaneous immune cells provokes vasodilation, prompting skin plethora and rubor, as well as dolor, tumor, and calor, and systemically, heat loss, frigor, chills, and rigors. Typically, NASTy effects are described by subjective patient-reported perception, at best semi-quantitative and bias-prone. Conversely, objective, quantitative, and unbiased methods measuring NASTy stigmata would facilitate research to abolish them, motivating development of several objective methods. In early drug development, such methods might better predict clinical tolerability in larger clinical trials. Measuring cutaneous stigmata may also aid investigations of vasospastic, ischemic, and inflammatory skin conditions. We present methods to measure NASTy physical stigmata to facilitate research into novel niacin mimetics/analogs, detailing characteristics of each technique following niacin, and how NASTy stigmata relate to symptom perception. We gave niacin orally and measured rubor by colorimetry and white-light spectroscopy, plethora by laser Doppler flowmetry, and calor/frigor by thermometry. Surprisingly, each stigma's abruptness predicted symptom perception, whereas peak intensity did not. These methods are adaptable to study other rubefacient drugs or dermatologic and vascular disorders.

Effect of PGD2 on middle meningeal artery and mRNA expression profile of L-PGD2 synthase and DP receptors in trigeminovascular system and other pain processing structures in rat brain

BACKGROUND

Prostaglandins (PGs), particularly prostaglandin D₂ (PGD₂), E₂ (PGE₂), and I₂ (PGI₂), are considered to play a role in migraine pain. In humans, infusion of PGD₂ causes lesser headache as compared to infusion of PGE₂ and PGI₂. Follow-up studies in rats have shown that infusion of PGE₂ and PGI₂ dilate the middle meningeal artery (MMA), and mRNA for PGE₂ and PGI₂ receptors is present in rat trigeminovascular system (TVS) and in the brain structures associated with pain. In the present study, we have characterized the dilatory effect of PGD₂ on rat MMA and studied the relative mRNA expression of PGD₂ receptors and lipocalin-type of PGD₂ synthase (L-PGDS).

METHOD

Rat closed-cranial window (CCW) model was used to study the effect of the DP₁ receptor antagonist, MK-0524, on PGD₂-induced vasodilation of middle meningeal artery. The qPCR technique was used for mRNA expression analysis.

RESULTS

PGD₂ infusion evoked a dose-dependent dilation of the rat MMA. The calculated mean pED₅₀ value was 5.23±0.10 and E_max was 103±18% (n=5). MK-0524 significantly (∼61%, p<0.05) blocked the PGD₂-induced dilation of MMA. mRNA for the DP₁, DP₂ and L-PGDS were expressed differentially in all tested tissues. DP₁ receptor mRNA was expressed maximally in trigeminal ganglion (TG) and in cervical dorsal root ganglion (DRG).

CONCLUSIONS

High expression of DP₁ mRNA in the TG and DRG suggest that PGD₂ might play a role in migraine pathophysiology. Activation of the DP₁ receptor in MMA was mainly responsible for vasodilation induced by PGD₂ infusion.

Effect of low dose nicotinic acid on hyperphosphatemia in patients with end stage renal disease

Hyperphosphatemia is a risk factor for ectopic calcification and coronary artery diseases in end stage renal diseases (ESRD). The aim of this study was to assess the effect of low-dose nicotinic acid on hyperphosphatemia in patients with ESRD. This randomized, double-blind clinical trial was done on 70 ESRD patients with serum phosphoure ≥5.5 mg/dl. Patients were randomly divided into two equal groups (n = 35) and the intervention group received niacin 25 mg/day as the initial dose. After 4 weeks, in patients who did not respond to treatment, niacin dose was increased up to 50 mg/dl. At the end of week 8, in case there was no treatment effect, the dose was raised to 100 mg/day. The appropriate response to treatment was defined as serum phosphorous level reductions <5.5 mg/dl. The age was 50.5 ± 14.3 years and duration of dialysis 5.1 ± 5.3 months. In the niacin group, mean phosphorus level decreased from 6.7 ± 0.84 mg/dl at the end of the 1(st) month to 5.8 ± 1.0 mg/dl at the end of the 2(nd) month and to 4.4 ± 1.4 mg/dl at the end of the 3(rd) month (P = 0.004). In the placebo group, mean phosphorus level increased from 6.5 ± 1.2 mg/dl to 7.2 ± 0.91 mg/dl at the end of the 3(rd) month (P = 0.006). In the niacin group, high density lipoprotein (HDL) increased significantly from 45.00 ± 14.9 to 47.2 ± 11.6 (P = 0.009). We conclude that niacin (100 mg/day) decreased phosphorus serum level and increased HDL serum level in patients on dialysis.

Prevalence and Specificity of the Abnormal Niacin Response: A Potential Endophenotype Marker in Schizophrenia

The skin flush response to niacin is abnormally blunted among a subset of patients with schizophrenia (SZ), preferentially associates with SZ compared to other mental illnesses, occurs frequently in nonpsychotic members of SZ-affected families, appears heritable, and shows evidence of genetic association. The niacin response abnormality (NRA) may prove to be a useful SZ endophenotype. Using a laser Doppler flowmeter, we undertook this study to estimate the prevalence of NRA in SZ (n = 70), bipolar disorder (BP, n = 59), and healthy control (HC, n = 87) groups, and to estimate its specificity for the illness. From the dose-response curves, we calculated the concentration of methylnicotinate required to elicit a half-maximal blood flow (MBF) response (EC50 value) and MBF value for each subject. The median log10EC50 of the SZ was above the third quartile of log10EC50 of either the HC or BP groups, whereas the MBF was significantly lower in the SZ than in the HC or BP groups. With a definition of NRA of having both EC50 above the ninetieth percentile of the control samples and MBF response below the sixtieth percentile for the control range, the NRA predicted SZ with 31% sensitivity and 97% specificity. Moreover, the NRA was not influenced by age, gender, race, and cigarette smoking. In summary, the NRA may define a SZ subtype with a clinically significant phospholipid signaling defect. Understanding its molecular origins may shed light on the pathophysiology of SZ and suggest new tools for its early diagnosis and treatment.

15d-Prostaglandin J2 induced reactive oxygen species-mediated apoptosis during experimental visceral leishmaniasis

15-Deoxy-delta (12,14)-prostaglandin J2 (15d-PgJ2) is a potent bioactive lipid mediator, known to possess several roles in cell regulation and differentiation along with antimicrobial efficacy against different bacterial and viral infections. In the present study, we investigated the therapeutic efficacy and mechanism of action of 15d-PgJ2 in vitro in Leishmania donovani promastigotes and infected J774 macrophages, and in vivo in Balb/c mice/golden hamster model of experimental visceral leishmaniasis. 15d-PgJ2 effectively killed L. donovani promastigotes and amastigotes in vitro with IC50 of 104.6 and 80.09 nM, respectively. At 2 mg/kg (mice) and 4 mg/kg (hamster) doses, 15d-PgJ2 decreased >90 % spleen and liver parasite burden. It significantly reduced interleukin (IL)-10 and transforming growth factor (TGF)-β synthesis in infected macrophages and splenocytes. 15d-PgJ2 induced reactive oxygen species (ROS)-dependent apoptosis of promastigotes by triggering phosphatidyl serine externalization, mitochondrial membrane damage and inducing caspase-like activity. In vitro drug interaction studies revealed an indifference to the synergistic association of 15d-PgJ2 with Miltefosine and Amphotericin-B (Amp-B). Moreover, when combined with sub-curative doses of Miltefosine and Amphotericin-B, 15d-PgJ2 resulted in >95 % parasite removal. Our results suggested that 15d-PgJ2 induces mitochondria-dependent apoptosis of L. donovani and is a good therapeutic candidate for adjunct therapy against experimental visceral leishmaniasis.

KEY MESSAGE

15d-PgJ2 effectively eliminated both promastigotes and amastigotes form of L. donovani. 15d-PgJ2 decreased parasite burden from infected mice and hamsters with reduced Th2 cytokines. 15d-PgJ2 induced ROS-mediated mitochondrial apoptosis of L. donovani promastigotes. 15d-PgJ2 is a good therapeutic candidate for adjunct therapy with Miltefosine and Amp-B.

Phylogenetic characterization of Clonorchis sinensis proteins homologous to the sigma-class glutathione transferase and their differential expression profiles

Glutathione transferase (GST) is one of the major antioxidant proteins with diverse supplemental activities including peroxidase, isomerase, and thiol transferase. GSTs are classified into multiple classes on the basis of their primary structures and substrate/inhibitor specificity. However, the evolutionary routes and physiological environments specific to each of the closely related bioactive enzymes remain elusive. The sigma-like GSTs exhibit amino acid conservation patterns similar to the prostaglandin D synthases (PGDSs). In this study, we analyzed the phylogenetic position of the GSTs of the biocarcinogenic liver fluke, Clonorchis sinensis. We also observed induction profile of the GSTs in association with the parasite's maturation and in response to exogenous oxidative stresses, with special attention to sigma-class GSTs and PGDSs. The C. sinensis genome encoded 12 GST protein species, which were separately assigned to cytosolic (two omega-, one zeta-, two mu-, and five sigma-class), mitochondrial (one kappa-class), and microsomal (one membrane-associated proteins in eicosanoid and glutathione metabolism-like protein) GST families. Multiple sigma GST (or PGDS) orthologs were also detected in Opisthorchis viverrini. Other trematode species possessed only a single sigma-like GST gene. A phylogenetic analysis demonstrated that one of the sigma GST lineages duplicated in the common ancestor of trematodes were specifically expanded in the opisthorchiids, but deleted in other trematodes. The induction profiles of these sigma GST genes along with the development and aging of C. sinensis, and against various exogenous chemical stimuli strongly suggest that the paralogous sigma GST genes might be undergone specialized evolution to cope with the diverse hostile biochemical environments within the mammalian hepatobiliary ductal system.

Central GPR109A Activation Mediates Glutamate-Dependent Pressor Response in Conscious Rats

G protein-coupled receptor 109A (GPR109A) activation by its ligand nicotinic acid (NA) in immune cells increases Ca(2+) levels, and Ca(2+) induces glutamate release and oxidative stress in central blood pressure (BP)-regulating nuclei, for example, the rostral ventrolateral medulla (RVLM), leading to sympathoexcitation. Despite NA's ability to reach the brain, the expression and function of its receptor GPR109A in the RVLM remain unknown. We hypothesized that NA activation of RVLM GPR109A causes Ca(2+)-dependent l-glutamate release and subsequently increases neuronal oxidative stress, sympathetic activity, and BP. To test this hypothesis, we adopted a multilevel approach, which included pharmacologic in vivo studies along with ex vivo and in vitro molecular studies in rat pheochromocytoma cell line (PC12) cells (which exhibit neuronal phenotype). We present the first evidence for GPR109A expression in the RVLM and in PC12 cells. Next, we showed that RVLM GPR109A activation (NA) caused pressor and bradycardic responses in conscious rats. The resemblance of these responses to those caused by intra-RVLM glutamate and their attenuation by NMDA receptor (NMDAR) blockade (2-amino-5-phosphonopentanoic acid) and enhancement by l-glutamate uptake inhibition (l-trans-pyrrolidine-2,4-dicarboxylic acid, PDC) supported our hypothesis. NA increased Ca(2+), glutamate, nitric oxide and reactive oxygen species (ROS) levels in PC12 cells and increased RVLM ROS levels. The inactive NA analog isonicotinic acid failed to replicate the cardiovascular and biochemical effects of NA. Further, GPR109A knockdown (siRNA) abrogated the biochemical effects of NA in PC12 cells. These novel findings yield new insight into the role of RVLM GPR109A in central BP control.

A randomized pilot study on the effect of niacin on pulmonary arterial pressure

Background

Niacin induces the release of vasodilating prostaglandins, for which receptors are present within the pulmonary arterial circulation. We hypothesized that immediate-release niacin would reduce right ventricular systolic pressure in patients with pulmonary hypertension in a randomized, double-blinded, single-dose provocation study.

Methods

We recruited inpatient subjects with a Doppler echocardiogram showing a peak tricuspid regurgitation (TR) jet velocity of 2.7 m/s or greater, and who were free of known pulmonary vascular disease. Subjects were randomized in a 1:2:2 ratio to receive a single dose of either placebo, niacin 100 mg or niacin 500 mg, respectively. TR jet velocities were measured immediately before, and 1 hour post dose, corresponding to peak niacin absorption and prostaglandin release. The primary endpoint was the change in mean TR jet velocity measured over ten successive cardiac cycles.

Results

The baseline mean estimated right ventricular systolic pressure (RVSP) for all 49 subjects (25 male) was 51.9 ± 12.1 mm Hg. The primary endpoint of mean change in TR jet velocity was 0.016 ± 0.065 m/s in the placebo group, compared to −0.017 ± 0.065 m/s with niacin 100 mg, and −0.063 ± 0.038 m/s with niacin 500 mg (P = 0.63). The change in maximum estimated RVSP across the three drug groups was 0.2 ± 1.6 mm Hg, −1.3 ± 1.8 mm Hg and −2.2 ± 1.2 mm Hg (P = 0.62). In exploratory pairwise analysis in the high-dose niacin group (500 mg), the reduction in mean RVSP was from 50.9 ± 9.4 mm Hg to 48.7 ± 10.0 mm Hg (P = 0.09).

Conclusions

A single dose of immediate-release niacin (100 mg or 500 mg) had no significant effect on RVSP 1 hour post administration. A nonsignificant dose-dependent trend for a modest reduction in RVSP, most notable in the 500 mg group, was noted.

(ISRCTN number 12353191, registered April 23, 2015).

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-015-1013-6) contains supplementary material, which is available to authorized users.

Urinary 11β-PGF2α and N-methyl histamine correlate with bone marrow biopsy findings in mast cell disorders

BACKGROUND

The utility of measuring histamine and prostaglandin metabolites in the urine of patients with mastocytosis has not been critically examined in a large series of patients. This study examined the relationship between the extent of increase in urinary excretion of 11β-prostaglandinF2α and N-methyl histamine, with serum tryptase, whole blood serotonin, and bone marrow findings including morphology, percentage involvement, and abnormal mast cell phenotype.

METHODS

This was a retrospective analysis of 90 patients who were continuously enrolled in the study for a period of 6 years (2008-2014). We recorded serum tryptase, whole blood serotonin, levels of urinary mast cell metabolites 11β-prostaglandinF2α and N-methyl histamine (NMH), and bone marrow findings.

RESULTS

Urinary mast cell metabolites 11β-prostaglandinF2α and N-methyl histamine correlated with levels of serum tryptase, mast cell burden in the bone marrow, the presence of mast cell aggregates, and atypical mast cells on bone marrow biopsy. Whole blood serotonin did not have a significant correlation with the serum tryptase or mast cell burden in the bone marrow. Urinary NMH was significantly different between c-kit D816V-positive and c-kit D816V-negative patients, while 11β-prostaglandinF2α was not. Urinary 11β-prostaglandinF2α 24-h excretion >3500 ng and NMH levels >400 μg/gm Cr corresponded with the high degree of bone marrow biopsies positive for atypical mast cells, the presence of aggregates, and c-kit mutation.

CONCLUSIONS

Easily obtained and quantified urinary metabolites of histamine (greater than twice the upper limit of normal) and prostaglandin D2 (>3.4 times the upper limit of normal) correlate well with bone marrow findings of mastocytosis.

Mechanistic Perspectives of Maslinic Acid in Targeting Inflammation

Chronic inflammation drives the development of various pathological diseases such as rheumatoid arthritis, atherosclerosis, multiple sclerosis, and cancer. The arachidonic acid pathway represents one of the major mechanisms for inflammation. Prostaglandins (PGs) are lipid products generated from arachidonic acid by the action of cyclooxygenase (COX) enzymes and their activity is blocked by nonsteroidal anti-inflammatory drugs (NSAIDS). The use of natural compounds in regulation of COX activity/prostaglandins production is receiving increasing attention. In Mediterranean diet, olive oil and table olives contain significant dietary sources of maslinic acid. Maslinic acid is arising as a safe and novel natural pentacyclic triterpene which has protective effects against chronic inflammatory diseases in various in vivo and in vitro experimental models. Understanding the anti-inflammatory mechanism of maslinic acid is crucial for its development as a potential dietary nutraceutical. This review focuses on the mechanistic action of maslinic acid in regulating the inflammation pathways through modulation of the arachidonic acid metabolism including the nuclear factor-kappa B (NF-κB)/COX-2 expression, upstream protein kinase signaling, and phospholipase A₂ enzyme activity. Further investigations may provide insight into the mechanism of maslinic acid in regulating the molecular targets and their associated pathways in response to specific inflammatory stimuli.

Nicotinic acid modulates intracellular calcium concentration and disassembles the cytoskeleton

Nicotinic acid (NA), a member of the vitamin B family, is well known for its functions in the treatment and prevention of atherosclerosis due to decreasing plasma levels of low-density lipoprotein cholesterol. In recent years, the major side effect of NA, cutaneous flushing, has also attracted extensive attention. However, the effects of NA in other aspects of physiology or cell biology have remained elusive. The present study provided evidence that high concentrations of NA were able to first reduce and later elevate intracellular [Ca²⁺] in the NIH3T3 cell line. The reduction of the intracellular Ca²⁺ concentration was achieved within the initial 10 sec, and was preceded by a gradual elevation of intracellular [Ca²⁺]. Notably, marked accumulation of opaque materials in the perinuclear region was observed in NIH3T3 cells treated with 70 mM NA. Further analysis revealed that treatment with 70 mM NA for 1 h disassembled the microtubule and F-actin cytoskeleton systems and resulted in β-tubulin degradation in an ubiquitin-proteasome-dependent manner. These data indicated that high concentrations of NA disrupted cytoskeleton structures, which may have contributed to minus end (nucleus region) to plus end (cell membrane region)-directed transport processes and resulted in the deposition of material in the perinuclear region. Artificially increasing [Ca²⁺] adding CaCl₂ to the culture media effected the disassembly of F-actin, while it had no apparent effect on microtubules. These results suggested that the disruption of the cytoskeleton systems was not entirely due to the NA-induced elevation of [Ca²⁺]. Finally, microinjection of NA into xenopus embryos blocked the transport of melanosomes to the peripheral cellular area. In conclusion, the present study indicated that NA disassembles F-actin and microtubule systems, thereby blocking cytoskeleton-dependent intracellular transport.

Non-obligatory role of prostaglandin D2 receptor subtype 1 in rosacea: laropiprant in comparison to a placebo did not alleviate the symptoms of erythematoelangiectaic rosacea

Erythematotelangiectatic rosacea shares facial flushing features with those seen after niacin. This study was performed to test the hypothesis whether prostaglandin D2 (PGD2) receptor subtype 1 antagonist (laropiprant) will improve the symptoms of rosacea. The purpose of this study was to evaluate the effect of laropiprant 100 mg administered once daily for 4 weeks on the signs and symptoms of erythematotelangiectatic rosacea. Subjects received laropiprant 100 mg once-daily (n = 30) or placebo (n = 30) for 4 weeks. The primary pharmacodynamics endpoint was change in Clinician's Erythema Assessment (CEA) score from baseline to week 4. The patient self-assessment (PSA) was a secondary endpoint. Laropiprant was generally well tolerated in this study for the primary endpoint of change in CEA score from Baseline to Week 4, the least-squares mean of change from baseline to visit 4/week 4 was -3.7 and -3.4 for placebo and laropiprant (100 mg), respectively. The least-squares mean difference (placebo minus laropiprant) with 90% confidence interval of change in CEA score from baseline to visit 4/week 4 was estimated as -0.3 (-1.6, 1.0). For the secondary endpoint, the least-squares mean difference (placebo minus laropiprant) with 90% confidence interval of change from baseline to visit 4/week 4 was estimated as -0.7 (-7.7, 6.4) for PSA total score, -4.5 (-14.2, 5.3) for PSA emotion score, -1.3 (-7.8, 5.3) for PSA symptoms score, and 3.6 (-4.3, 11.4) for PSA functioning score. Laropiprant administered once daily for 4 weeks was generally well tolerated in this population of subjects with rosacea. However, there were no clinically meaningful changes in the primary endpoint of CEA given that the response to laropiprant could not be differentiated from that to placebo. There was also no clinically meaningful change in the secondary endpoint, PSA. A DP1 antagonist is not likely to be effective in rosacea.

Cognition and autonomic function in schizophrenia: inferior cognitive test performance in electrodermal and niacin skin flush non-responders

BACKGROUND

Patients with schizophrenia suffer from a broad range of cognitive disturbances. The impact in terms of functional outcome is significant. There are also several reports of disturbed autonomic regulation in the disease. The present study examined cognitive function as well as psychophysiological parameters in patients with schizophrenia and healthy controls.

METHODS

Twenty-five patients and 14 controls were investigated with electrodermal activity (EDA), an oral niacin skin flush test and a comprehensive neurocognitive test program including the Wechsler battery (WAIS-R), Fingertapping Test, Trail Making Test, Verbal Fluency, Benton Visual Retention Test, Wisconsin Card Sorting Test and Rey Auditory Verbal Learning Test.

RESULTS

The patients generally had inferior test results compared to controls. Further analysis revealed that the EDA non-responding patient group explained this variation with significant lower test results than controls. On executive tests, EDA non-responders also performed significantly worse than EDA responding patients. The small group of niacin non-responding patients exhibited an even lower overall test performance. Delayed niacin flush also correlated inversely with psychomotor function and IQ in the patients.

CONCLUSION

The findings support the hypothesis of a neurodevelopment disturbance affecting both autonomic function and higher cortical function in schizophrenia.

Mechanism of action of anti-hypercholesterolemia drugs and their resistance

Coronary artery disease is one of the leading causes of death worldwide. One of the significant causes of this disease is hypercholesterolemia which is the result of various genetic alterations that are associated with the accumulation of specific classes of lipoprotein particles in plasma. A number of drugs are used to treat hypercholesterolemia like statin, fibrate, bile acid sequestrants, niacin, ezetimibe, omega-3 fatty acids and natural extracts. It has been observed that these drugs show diverse response in different individuals. The present review explains the mechanism of action of these drugs as well as mechanism of its lesser effectiveness or resistance in some individuals. There are various identified genetic variations that are associated with diversity in the drugs response. Therefore, present study helps to understand the ethiology of drug mechanism and resistance developed against drugs used to treat hypercholesterolemia.

Tolerability and pharmacokinetics of delayed-release dimethyl fumarate administered with and without aspirin in healthy volunteers

BACKGROUND

Delayed-release dimethyl fumarate (DR-DMF) has cytoprotective and antiinflammatory properties and has recently been approved in the United States as an oral treatment for relapsing forms of multiple sclerosis. The most common adverse events associated with DR-DMF are flushing and gastrointestinal (GI) events, the incidences of which diminish over time.

OBJECTIVE

The purpose of this study was to evaluate the tolerability and pharmacokinetic (PK) profile of DR-DMF with or without concomitant acetylsalicylic acid (aspirin), a cyclooxygenase inhibitor.

METHODS

Healthy volunteers (N = 56) were randomized to receive different dosing regimens of DR-DMF or matching placebo with or without pretreatment with 325 mg aspirin for 4 days. Plasma levels of the active metabolite monomethyl fumarate were assessed on days 1 and 4. Flushing and GI events were assessed using patient-reported scales. Potential flushing mediators were explored.

RESULTS

DR-DMF showed a safety, tolerability, and PK profile consistent with previous clinical experience, with no evidence of accumulation. Pretreatment with aspirin had no effect on the primary PK parameters, AUC0-10h, or Cmax. Flushing severity, assessed by 2 subject-reported rating scales, was generally mild and was rated highest at the start of treatment. Pretreatment with aspirin reduced flushing incidence and intensity without affecting GI events or the PK profile of DR-DMF. In some DR-DMF-treated individuals, plasma concentrations of a prostaglandin D2 (PGD2) metabolite were increased.

CONCLUSIONS

In healthy volunteers, DR-DMF was well tolerated over 4 days of dosing, with a PK profile consistent with that previously reported and no evidence of accumulation. Aspirin pretreatment reduced the incidence and intensity of flushing without affecting GI events or the DR-DMF PK profile. Elevated levels of PGD2 in some DR-DMF-treated individuals suggest that flushing may be, at least in part, prostaglandin mediated. ClinicalTrials.gov identifier: ID: NCT01281111.

Niacin, an old drug with a new twist

Niacin (nicotinic acid) has been used for decades as a lipid-lowering drug. The clinical use of niacin to treat dyslipidemic conditions is limited by its side effects. Niacin, along with fibrates, are the only approved drugs which elevate high density lipoprotein cholesterol (HDLc) along with its effects on low density lipoprotein cholesterol (LDLc) and triglycerides. Whether niacin has a beneficial role in lowering cardiovascular risk on the background of well-controlled LDLc has not been established. In fact, it remains unclear whether niacin, either in the setting of well-controlled LDLc or in combination with other lipid-lowering agents, confers any therapeutic benefit and if so, by which mechanism. The results of recent trials reject the hypothesis that simply raising HDLc is cardioprotective. However, in the case of the clinical trials, structural limitations of trial design complicate their interpretation. This is also true of the most recent Heart Protection Study 2-Treatment of HDLc to Reduce the Incidence of Vascular Events (HPS2-THRIVE) trial in which niacin is combined with an antagonist of the D prostanoid (DP) receptor. Human genetic studies have also questioned the relationship between cardiovascular benefit and HDLc. It remains to be determined whether niacin may have clinical utility in particular subgroups, such as statin intolerant patients with hypercholesterolemia or those who cannot achieve a sufficient reduction in LDLc. It also is unclear whether a potentially beneficial effect of niacin is confounded by DP antagonism in HPS2-THRIVE.

Role of prostaglandin D2 and the autonomic nervous system in niacin-induced flushing

BACKGROUND

Although niacin often has beneficial effects on the lipoprotein profile, flushing is an untoward effect associated with its use. Aspirin can only reduce the flushing response by 30-40%. Thus, the aim of the present study was to investigate the mechanisms of niacin-induced flushing, with and without aspirin, in normal, healthy individuals.

METHODS

Niacin-induced flushing was evaluated in 30 healthy individuals after oral administration of 1000 mg niacin alone or with 325 mg aspirin. Neurological, autonomic nervous system, and skin blood flow measurements (using laser Doppler on the glabrous and hairy skin of each participant) were made at various times after drug administration. In addition, the systemic release of 9α,11β-prostaglandin (PG) F(2) was determined. Flushing symptoms of redness, warmth, tingling, itching, and intensity were recorded using the modified Flushing ASsessment Tool (FAST).

RESULTS

After aspirin, the mean flushing scores for all symptoms decreased significantly; however, 36-53% of participants still had some degree of symptoms, even though aspirin completely blocked 11β-PGF(2) synthesis. Maximum skin blood flow (MaxSkBF) in both the glabrous and hairy forearm increased significantly after niacin, but decreased significantly after aspirin only in hairy skin. Regression analysis showed that, in glabrous skin, both PGF(2) and parasympathetic activity were significant predictors of MaxSkBF after niacin, contributing 26% and 14%, respectively (total R(2) = 40%).

CONCLUSIONS

The present study indicates, for the first time, that the parasympathetic nervous system, in addition to PGD(2) , may play an important role in niacin-induced flushing. Changing the sympathetic/parasympathetic balance in favor of parasympathetic activation may be a good therapeutic target to reduce niacin-induced flushing.

A genome-wide quantitative linkage scan of niacin skin flush response in families with schizophrenia

Schizophrenia patients frequently display reduced niacin flush responses, and similar characteristics are also observed in their nonpsychotic relatives. This study aimed to identify loci influencing flush response to niacin in schizophrenia using genome-wide quantitative linkage scan. In a nationwide sample of families with at least 2 siblings affected with schizophrenia in each family, 115 families that had at least 2 affected siblings with information on the niacin skin test were subjected to quantitative trait loci linkage analysis, either involving affected individuals only or the whole family. Nonparametric linkage z (NPL-Z) scores were calculated for each of 386 microsatellite markers spaced at an average of 9-cM intervals. Niacin patches of 3 concentrations (0.001 M, 0.01, and 0.1 M) were applied to forearm skin, and the flush response was rated at 5, 10, and 15 minutes, respectively, with a 4-point scale. Determination of genome-wide empirical significance was implemented using 1000 simulated genome scans. One linkage peak attaining genome-wide significance was identified at chromosomal region 14q32.12 for 0.01 M concentration at 5 minutes (NPL-Z scores = 3.39, genome-wide empirical P = .03) in affected individuals, and the corresponding linkage signal remained strong (NPL-Z scores = 2.87) for the analyses of the whole family. This locus is distinct from the chromosomal region identified in the previous genome-wide scan for the diagnosis of schizophrenia, and the signal was higher than the peak linkage signal in that study. These findings indicate that there might be modifier or susceptibility-modifier genes at 14q32.12 for schizophrenia-related attenuation of flush response to niacin.

Nicotinic acid and DP1 blockade: studies in mouse models of atherosclerosis

The use of nicotinic acid to treat dyslipidemia is limited by induction of a "flushing" response, mediated in part by the interaction of prostaglandin D(2) (PGD(2)) with its G-protein coupled receptor, DP1 (Ptgdr). The impact of DP1 blockade (genetic or pharmacologic) was assessed in experimental murine models of atherosclerosis. In Ptgdr(-/-)ApoE(-/-) mice versus ApoE(-/-) mice, both fed a high-fat diet, aortic cholesterol content was modestly higher (1.3- to 1.5-fold, P < 0.05) in Ptgdr(-/-)ApoE(-/-) mice at 16 and 24 weeks of age, but not at 32 weeks. In multiple ApoE(-/-) mouse studies, a DP1-specific antagonist, L-655, generally had a neutral to beneficial effect on aortic lipids in the presence or absence of nicotinic acid treatment. In a separate study, a modest increase in some atherosclerotic measures was observed with L-655 treatment in Ldlr(-/-) mice fed a high-fat diet for 8 weeks; however, this effect was not sustained for 16 or 24 weeks. In the same study, treatment with nicotinic acid alone generally decreased plasma and/or aortic lipids, and addition of L-655 did not negate those beneficial effects. These studies demonstrate that inhibition of DP1, with or without nicotinic acid treatment, does not lead to consistent or sustained effects on plaque burden in mouse atherosclerotic models.

The effect of niacin on serum phosphorus levels in dialysis patients

Hyperphosphatemia is common in patients with end-stage renal disease. Recent studies have shown that niacinamide and niacin achieve clinically significant reductions in serum phosphate in patients undergoing dialysis. The aim of the present study was to evaluate the serum phosphorus lowering effect of niacin in long-term hemodialysis patients. In this 8-week randomized, double-blind clinical trial, 37 patients were assigned to niacin or placebo with titration from 400 to 1000 mg daily. A 2-week washout preceded the switch from niacin to placebo or vice versa. The mean dose of niacin at the end of the 8-week treatment period was 750±200 mg/day. Serum phosphorus decreased from 6.66±1.40 to 5.96±0.87 mg/dL (P = 0.006) in the niacin-treated group after 8-weeks. However, the main reduction occurred at the beginning of study and seems not to be related to the phosphate-lowering effect of drug. In spite of a sharp increase in phosphorus level between w6 and w8 in patients on placebo, phosphorus values in drug-treated group showed nearly steady trend, presumably due to the inhibitory effect of niacin on phosphate absorption from gut. Niacin also increased the high density lipoprotein (HDL) cholesterol (P = 0.018). Our study suggests that niacin should be considered as adjunctive therapy for patients with hyperphosphatemia despite management with phosphate binders. The modest increase in HDL values may be another beneficial effect of this treatment.

Laropiprant attenuates EP3 and TP prostanoid receptor-mediated thrombus formation

The use of the lipid lowering agent niacin is hampered by a frequent flush response which is largely mediated by prostaglandin (PG) D₂. Therefore, concomitant administration of the D-type prostanoid (DP) receptor antagonist laropiprant has been proposed to be a useful approach in preventing niacin-induced flush. However, antagonizing PGD₂, which is a potent inhibitor of platelet aggregation, might pose the risk of atherothrombotic events in cardiovascular disease. In fact, we found that in vitro treatment of platelets with laropiprant prevented the inhibitory effects of PGD₂ on platelet function, i.e. platelet aggregation, Ca²⁺ flux, P-selectin expression, activation of glycoprotein IIb/IIIa and thrombus formation. In contrast, laropiprant did not prevent the inhibitory effects of acetylsalicylic acid or niacin on thrombus formation. At higher concentrations, laropiprant by itself attenuated platelet activation induced by thromboxane (TP) and E-type prostanoid (EP)-3 receptor stimulation, as demonstrated in assays of platelet aggregation, Ca²⁺ flux, P-selectin expression, and activation of glycoprotein IIb/IIIa. Inhibition of platelet function exerted by EP4 or I-type prostanoid (IP) receptors was not affected by laropiprant. These in vitro data suggest that niacin/laropiprant for the treatment of dyslipidemias might have a beneficial profile with respect to platelet function and thrombotic events in vascular disease.

Attenuation of niacin-induced prostaglandin D(2) generation by omega-3 fatty acids in THP-1 macrophages and Langerhans dendritic cells

Niacin, also known as nicotinic acid, is an organic compound that has several cardio-beneficial effects. However, its use is limited due to the induction of a variable flushing response in most individuals. Flushing occurs from a niacin receptor mediated generation of prostaglandins from arachidonic acid metabolism. This study examined the ability of docosahexaenoic acid, eicosapentaenoic acid, and omega-3 polyunsaturated fatty acids (PUFAs), to attenuate niacin-induced prostaglandins in THP-1 macrophages. Niacin induced both PGD₂ and PGE₂ generation in a dose-dependent manner. Niacin also caused an increase in cytosolic calcium and activation of cytosolic phospholipase A₂. The increase in PGD₂ and PGE₂ was reduced by both docosahexaenoic acid and eicosapentaenoic acid, but not by oleic acid. Omega-3 PUFAs efficiently incorporated into cellular phospholipids at the expense of arachidonic acid, whereas oleic acid incorporated to a higher extent but had no effect on arachidonic acid levels. Omega-3 PUFAs also reduced surface expression of GPR109A, a human niacin receptor. Furthermore, omega-3 PUFAs also inhibited the niacin-induced increase in cytosolic calcium. Niacin and/or omega-3 PUFAs minimally affected cyclooxygenase-1 activity and had no effect on cyclooxygenase -2 activity. The effects of niacin on PGD₂ generation were further confirmed using Langerhans dendritic cells. Results of the present study indicate that omega-3 PUFAs reduced niacin-induced prostaglandins formation by diminishing the availability of their substrate, as well as reducing the surface expression of niacin receptors. In conclusion, this study suggests that the regular use of omega-3 PUFAs along with niacin can potentially reduce the niacin-induced flushing response in sensitive patients.