FGF21 contributes to metabolic improvements elicited by combination therapy with exenatide and pioglitazone in patients with type 2 diabetes.

Fibroblast growth factor 21 (FGF21) is increased acutely by carbohydrate ingestion and is elevated in patients with type 2 diabetes (T2D). However, the physiological significance of increased FGF21 in humans remains largely unknown. We examined whether FGF21 contributed to the metabolic improvements observed following treatment of patients with T2D with either triple (metformin/pioglitazone/exenatide) or conventional (metformin/insulin/glipizide) therapy for 3 yr. Forty-six patients with T2D were randomized to receive either triple or conventional therapy to maintain HbA1c < 6.5%. A 2-h 75-g oral glucose tolerance test (OGTT) was performed at baseline and following 3 years of treatment to assess glucose tolerance, insulin sensitivity, and ß-cell function. Plasma total and bioactive FGF21 levels were quantitated before and during the OGTT at both visits. Patients in both treatment arms experienced significant improvements in glucose control, but insulin sensitivity and ß-cell function were markedly increased after triple therapy. At baseline, FGF21 levels were regulated acutely during the OGTT in both groups. After treatment, fasting total and bioactive FGF21 levels were significantly reduced in patients receiving triple therapy, but there was a relative increase in the proportion of bioactive FGF21 compared with that observed in conventionally treated subjects. Relative to baseline studies, triple therapy treatment also significantly modified FGF21 levels in response to a glucose load. These changes in circulating FGF21 were correlated with markers of improved glucose control and insulin sensitivity. Alterations in the plasma FGF21 profile may contribute to the beneficial metabolic effects of pioglitazone and exenatide in human patients with T2D.NEW & NOTEWORTHY In patients with T2D treated with a combination of metformin/pioglitazone/exenatide (triple therapy), we observed reduced total and bioactive plasma FGF21 levels and a relative increase in the proportion of circulating bioactive FGF21 compared with that in patients treated with metformin and sequential addition of glipizide and basal insulin glargine (conventional therapy). These data suggest that FGF21 may contribute, at least in part, to the glycemic benefits observed following combination therapy in patients with T2D.

GIPR agonism mediates weight-independent insulin sensitization by tirzepatide in obese mice.

Tirzepatide (LY3298176), a dual GIP and GLP-1 receptor (GLP-1R) agonist, delivered superior glycemic control and weight loss compared with GLP-1R agonism in patients with type 2 diabetes. However, the mechanism by which tirzepatide improves efficacy and how GIP receptor (GIPR) agonism contributes is not fully understood. Here, we show that tirzepatide is an effective insulin sensitizer, improving insulin sensitivity in obese mice to a greater extent than GLP-1R agonism. To determine whether GIPR agonism contributes, we compared the effect of tirzepatide in obese WT and Glp-1r-null mice. In the absence of GLP-1R-induced weight loss, tirzepatide improved insulin sensitivity by enhancing glucose disposal in white adipose tissue (WAT). In support of this, a long-acting GIPR agonist (LAGIPRA) was found to enhance insulin sensitivity by augmenting glucose disposal in WAT. Interestingly, the effect of tirzepatide and LAGIPRA on insulin sensitivity was associated with reduced branched-chain amino acids (BCAAs) and ketoacids in the circulation. Insulin sensitization was associated with upregulation of genes associated with the catabolism of glucose, lipid, and BCAAs in brown adipose tissue. Together, our studies show that tirzepatide improved insulin sensitivity in a weight-dependent and -independent manner. These results highlight how GIPR agonism contributes to the therapeutic profile of dual-receptor agonism, offering mechanistic insights into the clinical efficacy of tirzepatide.

Eccentric exercise increases circulating fibroblast activation protein α but not bioactive fibroblast growth factor 21 in healthy humans.

NEW FINDINGS: What is the central question of this study? The role of FGF21 as an exercise-induced myokine remains controversial. The aim of this study was to determine whether eccentric exercise would augment the release of FGF21 and/or its regulatory enzyme, fibroblast activation protein α (FAP), from skeletal muscle tissue into the systemic circulation of healthy human volunteers. What is the main finding and its importance? Eccentric exercise does not release total or bioactive FGF21 from human skeletal muscle. However, exercise releases its regulatory enzyme, FAP, from tissue(s) other than muscle, which might play a role in the inactivation of FGF21. ABSTRACT: The primary aim of the investigation was to determine whether eccentric exercise would augment the release of the myokine fibroblast growth factor 21 (FGF21) and/or its regulatory enzyme, fibroblast activation protein α (FAP), from skeletal muscle tissue into the systemic circulation of healthy human volunteers. Physically active young healthy male volunteers (age 25.0 ± 10.7 years; body mass index 23.1 ± 7.9 kg m-2 ) completed three sets of 25 repetitions (with 5 min rest in between) of single-leg maximal eccentric contractions using their non-dominant leg, whilst the dominant leg served as a control. Arterialized blood samples from a hand vein and deep venous blood samples from the common femoral vein of the exercised leg, along with blood flow of the superficial femoral artery using Doppler ultrasound, were obtained before and after each exercise bout and every 20 min during the 3 h recovery period. Muscle biopsy samples were taken at baseline, immediately and 3 and 48 h postexercise. The main findings showed that there was no significant increase in total or bioactive FGF21 secreted from skeletal muscle into the systemic circulation in response to exercise. Furthermore, skeletal muscle FGF21 protein content was unchanged in response to exercise. However, there was a significant increase in arterialized and venous FAP concentrations, with no apparent contribution to its release from the exercised leg. These findings raise the possibility that the elevated levels of FAP might play a role in the inactivation of FGF21 during exercise.

Rational design of a fibroblast growth factor 21-based clinical candidate, LY2405319.

Fibroblast growth factor 21 is a novel hormonal regulator with the potential to treat a broad variety of metabolic abnormalities, such as type 2 diabetes, obesity, hepatic steatosis, and cardiovascular disease. Human recombinant wild type FGF21 (FGF21) has been shown to ameliorate metabolic disorders in rodents and non-human primates. However, development of FGF21 as a drug is challenging and requires re-engineering of its amino acid sequence to improve protein expression and formulation stability. Here we report the design and characterization of a novel FGF21 variant, LY2405319. To enable the development of a potential drug product with a once-daily dosing profile, in a preserved, multi-use formulation, an additional disulfide bond was introduced in FGF21 through Leu118Cys and Ala134Cys mutations. FGF21 was further optimized by deleting the four N-terminal amino acids, His-Pro-Ile-Pro (HPIP), which was subject to proteolytic cleavage. In addition, to eliminate an O-linked glycosylation site in yeast a Ser167Ala mutation was introduced, thus allowing large-scale, homogenous protein production in Pichia pastoris. Altogether re-engineering of FGF21 led to significant improvements in its biopharmaceutical properties. The impact of these changes was assessed in a panel of in vitro and in vivo assays, which confirmed that biological properties of LY2405319 were essentially identical to FGF21. Specifically, subcutaneous administration of LY2405319 in ob/ob and diet-induced obese (DIO) mice over 7-14 days resulted in a 25-50% lowering of plasma glucose coupled with a 10-30% reduction in body weight. Thus, LY2405319 exhibited all the biopharmaceutical and biological properties required for initiation of a clinical program designed to test the hypothesis that administration of exogenous FGF21 would result in effects on disease-related metabolic parameters in humans.

The hypolipidemic natural product guggulsterone is a promiscuous steroid receptor ligand.

Guggulsterone (GS) is the active substance in guggulipid, an extract of the guggul tree, Commiphora mukul, used to treat a variety of disorders in humans, including dyslipidemia, obesity, and inflammation. The activity of GS has been suggested to be mediated by antagonism of the receptor for bile acids, the farnesoid X receptor (FXR). Here, we demonstrate that both stereoisomers of the plant sterol, (E)- and (Z)-GS, bind to the steroid receptors at a much higher affinity than to FXR. Both stereoisomers bind to the mineralocorticoid receptor (MR) with a Ki value of approximately 35 nM, which is greater than 100 times more potent than their affinity for FXR. Both (E)- and (Z)-GS also displayed high affinity for other steroid receptors, including the androgen (AR), glucocorticoid (GR), and progesterone receptors (PR) with Ki values ranging from 224 to 315 nM. In cell-based functional cotransfection assays, GSs behaved as antagonists of AR, GR, and MR, but as agonists of PR. Agonist activity was also demonstrated with estrogen receptor (ER) alpha; however, the potency was very low (EC50 > 5000 nM). In addition, GS displayed activity in functional assays in cell lines expressing endogenous AR, GR, ER, and PR. These data suggest that the variety of pharmacological effects exhibited by GS may be mediated by targeting several steroid receptors.