Brett Lauring

Niacin Lipid Efficacy Is Independent of Both the Niacin Receptor GPR109A and Free Fatty Acid Suppression

GPR109A is not the target mediating niacin’s lipid efficacy and the free fatty acid hypothesis does not explain niacin’s mechanism of action. Breaking Free of the “FFA Hypothesis” Free fatty acids (FFAs) appear in the blood plasma after a meal. Niacin—a vitamin that helps to regulate lipid levels in the body—is given to patients to reduce the amount of FFAs. It also works to raise “good” cholesterol [high-density lipoprotein (HDL)] and lower both “bad” cholesterol [low-density lipoprotein (LDL)] and triglycerides. The “FFA hypothesis” suggests that niacin works to exert these beneficial lipid effects by limiting the amount of FFAs available to synthesize triglycerides. Lauring, Taggart, and colleagues now challenge this long-standing theory. In studies in mice and humans, the authors debunk the hypothesis, showing that the effect on HDL, LDL, and triglycerides is not directly linked to FFAs. To study the lipid-modifying effects of niacin (nicotinic acid), Lauring et al. used a genetic, humanized mouse model lacking the LDL receptor. In these animals, niacin increased HDL cholesterol levels, as expected. Lack of GPR109A in these animals blocked the anti-lipolytic effect of nicotinic acid on FFAs but had no effect on drug-related changes in plasma HDL and LDL cholesterol or triglyceride levels. Treatment of the mice with a GPR109A agonist, MK-1903, also caused an anti-lipolytic effect but did not affect levels of triglyceride or LDL and HDL cholesterol. Together, these in vivo preclinical studies suggest that niacin works to lower FFAs through GPR109A but has an independent mechanism of action on other lipids. The authors addressed the role of GPR109A in humans by testing the effects of MK-1903 and of another synthetic GPR109A agonist in clinical trials. Both agonists affected FFA lipolysis but had only minor effects on HDL cholesterol and triglyceride levels in patients, thus mirroring results seen in animals and showing that niacin works independently of GPR109A to modify dyslipidemia. The studies by Lauring et al. point to a new, yet-uncovered mechanism of action for niacin’s beneficial effects on lipids in the blood. Despite overturning the FFA hypothesis and potentially redirecting drug development away from GPR109A agonists, niacin could still be useful for treating other diseases in patients, including atherosclerosis and inflammation, where GPR109A plays a major role in cell signaling. Nicotinic acid (niacin) induces beneficial changes in serum lipoproteins and has been associated with beneficial cardiovascular effects. Niacin reduces low-density lipoprotein, increases high-density lipoprotein, and decreases triglycerides. It is well established that activation of the seven-transmembrane Gi-coupled receptor GPR109A on Langerhans cells results in release of prostaglandin D2, which mediates the well-known flushing side effect of niacin. Niacin activation of GPR109A on adipocytes also mediates the transient reduction of plasma free fatty acid (FFA) levels characteristic of niacin, which has been long hypothesized to be the mechanism underlying the changes in the serum lipid profile. We tested this “FFA hypothesis” and the hypothesis that niacin lipid efficacy is mediated via GPR109A by dosing mice lacking GPR109A with niacin and testing two novel, full GPR109A agonists, MK-1903 and SCH900271, in three human clinical trials. In mice, the absence of GPR109A had no effect on niacin’s lipid efficacy despite complete abrogation of the anti-lipolytic effect. Both MK-1903 and SCH900271 lowered FFAs acutely in humans; however, neither had the expected effects on serum lipids. Chronic FFA suppression was not sustainable via GPR109A agonism with niacin, MK-1903, or SCH900271. We conclude that the GPR109A receptor does not mediate niacin’s lipid efficacy, challenging the long-standing FFA hypothesis.

(1aR,5aR)1a,3,5,5a-Tetrahydro-1H-2,3-diaza-cyclopropa[a]pentalene-4-carboxylic acid (MK-1903): a potent GPR109a agonist that lowers free fatty acids in humans.

G-protein coupled receptor (GPCR) GPR109a is a molecular target for nicotinic acid and is expressed in adipocytes, spleen, and immune cells. Nicotinic acid has long been used for the treatment of dyslipidemia due to its capacity to positively affect serum lipids to a greater extent than other currently marketed drugs. We report a series of tricyclic pyrazole carboxylic acids that are potent and selective agonists of GPR109a. Compound R,R-19a (MK-1903) was advanced through preclinical studies, was well tolerated, and presented no apparent safety concerns. Compound R,R-19a was advanced into a phase 1 clinical trial and produced a robust decrease in plasma free fatty acids. On the basis of these results, R,R-19a was evaluated in a phase 2 study in humans. Because R,R-19a produced only a weak effect on serum lipids as compared with niacin, we conclude that the beneficial effects of niacin are most likely the result of an undefined GPR109a independent pathway.

Phase III, efficacy and safety study of ertugliflozin monotherapy in people with type 2 diabetes mellitus inadequately controlled with diet and exercise alone

To conduct a phase III study to evaluate the efficacy and safety of ertugliflozin monotherapy in people with type 2 diabetes.

Laropiprant in Combination With Extended‐Release Niacin Does Not Alter Urine 11‐Dehydrothromboxane B2, a Marker of In Vivo Platelet Function, in Healthy, Hypercholesterolemic, and Diabetic Subjects

Laropiprant, an antagonist of the PGD2 receptor, DP1, is effective in reducing the flushing symptoms associated with extended‐release (ER) niacin and thereby improves the tolerability of niacin therapy for dyslipidemia. Because PGD2 has been reported to inhibit platelet aggregation in vitro, it has been speculated that antagonism of DP1 may enhance platelet reactivity. Three clinical studies evaluated the potential effect of laropiprant, with or without coadministration of ER niacin, on in vivo platelet function in healthy subjects and hypercholesterolemic or diabetic subjects by measuring urinary levels of 11‐dehydrothromboxane B2 (11‐dTxB2), a marker of in vivo platelet activation. Following 7 days of multiple‐dose administration, coadministration of laropiprant with ER niacin did not increase urinary 11‐dTxB2 levels compared to ER niacin alone in healthy, hypercholesterolemic, or diabetic subjects. In hypercholesterolemic and diabetic subjects, laropiprant did not increase urinary 11‐dTxB2 levels compared to placebo. These results demonstrate that laropiprant does not enhance in vivo platelet reactivity, either alone or in combination with niacin.

Efficacy and safety of the addition of ertugliflozin in patients with type 2 diabetes mellitus inadequately controlled with metformin and sitagliptin: The VERTIS SITA2 placebo-controlled randomized study

To assess ertugliflozin in patients with type 2 diabetes who are inadequately controlled by metformin and sitagliptin.

Ertugliflozin plus sitagliptin versus either individual agent over 52 weeks in patients with type 2 diabetes mellitus inadequately controlled with metformin: The VERTIS FACTORIAL randomized trial

To evaluate the efficacy and safety of ertugliflozin and sitagliptin co‐administration vs the individual agents in patients with type 2 diabetes who are inadequately controlled with metformin.

Effect of ertugliflozin on glucose control, body weight, blood pressure and bone density in type 2 diabetes mellitus inadequately controlled on metformin monotherapy (VERTIS MET)

We evaluated the efficacy and safety of ertugliflozin, an SGLT2 inhibitor, in type 2 diabetes mellitus (T2DM) inadequately controlled (HbA1c, 7.0%‐10.5%) with metformin monotherapy (≥1500 mg/d for ≥8 weeks).

Comment on: Butler et al. Marked Expansion of Exocrine and Endocrine Pancreas With Incretin Therapy in Humans With Increased Exocrine Pancreas Dysplasia and the Potential for Glucagon-Producing Neuroendocrine Tumors. Diabetes 2013;62:2595–2604

In the study by Butler et al. (1) in the July issue of Diabetes , we noted several issues in study design and data interpretation that substantially limit the ability to form conclusions from this small autopsy series. The study was designed with a nondiabetic control group ( n = 14) that was age-, sex-, and BMI-matched to a group of 20 subjects with diabetes, 8 of whom had received incretin-based therapy and 12 of whom had not. However, the authors conducted a series of comparisons between the two subsets of subjects with diabetes who were not matched and who differed in important ways that were not adjusted for with respect to key characteristics. …

Influence of renal and hepatic impairment on the pharmacokinetics of anacetrapib

Two open‐label, parallel‐group studies evaluated the influence of renal and hepatic insufficiency on the pharmacokinetics of a single‐dose anacetrapib 100 mg. Eligible participants included adult men and women with moderate hepatic impairment (assessed by Child–Pugh criteria) or severe renal impairment (CrCl <30 mL/min/1.73 m2). In both studies, patients were matched (race, age, sex, BMI) with healthy control subjects. Twenty‐four subjects were randomized in each study (12 with either moderate hepatic or severe renal impairment and 12 matched healthy controls). In the hepatic insufficiency study, the geometric mean ratio (GMR; mean value for the group with moderate hepatic insufficiency/mean value for the healthy controls) and 90% CIs for the area under the concentration–time curve from time zero to infinity (AUC0–∞) and the maximum concentration of drug in plasma (Cmax) were 1.16 (0.84, 1.60) and 1.02 (0.71, 1.49), respectively. In the renal insufficiency study, the GMRs (mean value for the group with severe renal insufficiency/mean value for the healthy controls) and 90% CIs for AUC0–∞ and Cmax were 1.14 (0.80, 1.63) and 1.31 (0.93, 1.83), respectively. Anacetrapib was generally well tolerated and there was no clinically meaningful effect of moderate hepatic or severe renal insufficiency on the pharmacokinetics of anacetrapib.

Single therapeutic and supratherapeutic doses of anacetrapib, a cholesteryl ester transfer protein inhibitor, do not prolong the QTcF interval in healthy volunteers

Anacetrapib is a cholesteryl ester transfer protein inhibitor in Phase III development. This double‐blind, double‐dummy, randomized, placebo‐ and active‐comparator‐controlled, 4‐period, balanced crossover study evaluated the effects of anacetrapib (100 mg and 800 mg) on QTcF interval in healthy subjects. QTcF measurements were made up to 24 h following administration of single doses of anacetrapib 100 or 800 mg, moxifloxacin 400 mg, or placebo in the fed state. The primary hypothesis was supported if the 90% CI for the least squares (LS) mean differences between anacetrapib 800 mg and placebo in QTcF interval change from baseline were entirely <10 msec at every post‐dose time point (1, 2, 2.5, 3, 4, 5, 6, 8, 12, and 24 h). The upper bounds of the 90% CIs for LS mean differences from placebo in changes from baseline in QTcF intervals for anacetrapib 100 and 800 mg were <5 msec at every time point. In conclusion, single doses of anacetrapib 100 and 800 mg do not prolong the QTcF interval to a clinically meaningful degree relative to placebo and are generally well tolerated in healthy subjects.