Caralluma fimbriata extract activity involves the 5-HT2c receptor in PWS Snord116 deletion mouse model

Abstract

Introduction: In Prader-Willi syndrome (PWS), nonprotein coding small nucleolar (sno) RNAs are involved in the paternally deleted region of chromosome 15q11.2-q13, which is believed to cause the hyperphagic phenotype of PWS. Central to this is SnoRNA116. The supplement Caralluma fimbriata extract (CFE) has been shown to decrease appetite behavior in some individuals with PWS. We therefore investigated the mechanism underpinning the effect of CFE on food intake in the Snord116del mouse. Experiments utilized appetite stimulants which included a 5-hydroxytryptamine (5-HT) 2c receptor antagonist (SB242084), as the 5-HT2cR is implicated in central signaling of satiety.

Methods: After 9-week chronic CFE treatment (33 mg or 100 mg kg^-1 day^-1 ) or placebo, the 14-week-old Snord116del (SNO) and wild-type mice (n = 72) were rotated through intraperitoneal injections of (a) isotonic saline; (b) 400 mg/kg of 2-deoxyglucose (2DG) (glucose deprivation); (c) 100 mglkg beta-mercaptoacetate (MA), fatty acid signaling; and (d) SB242084 (a selective 5HT2cR antagonist), with 5 days between reagents. Assessments of food intake were from baseline to 4 hr, followed by immunohistochemistry of neural activity utilizing c-Fos, neuropeptide Y, and alpha-melanocyte-stimulating hormone within hypothalamic appetite pathways.

Results: Caralluma fimbriata extract administration decreased food intake more strongly in the SNO100CFE group with significantly stimulated food intake demonstrated during coadministration with SB242084. Though stimulatory deprivation was expected to stimulate food intake, 2DG and MA resulted in lower intake in the snord116del mice compared to the WT animals (p = <0.001). Immunohistochemical mapping of hypothalamic neural activity was consistent with the behavioral studies.

Conclusions: This study identifies a role for the 5-HT2cR in CFE-induced appetite suppression and significant stimulatory feeding disruptions in the snord116del mouse model.

Keywords: 5-HT2c receptor; Caralluma Fimbriata extract; Prader-Willi syndrome (PWS); appetite signaling; cactus supplement; snord116 deletion.

Figure 1

Appetite Stimulant Histograms. Figure 1 depicts the univariate between‐subject results for appetite signaling tests with SAL—saline control, mean and SD—standard deviation of food ingested in grams in comparison with the appetite signaling reagents 2DG—2‐deoxyglucose, MA—beta‐mercaptoacetate or the 5‐HT2c antagonist SB242804. The results present pairwise comparisons for food ingested over four hours, with significance set as Pillai's trace Sig value, p = ≤0.05, plus t tests between three chronic treatment groups saline versus appetite signaling. The animal models were the Snord116del (SNO) and wild‐type (WT) strains. All animals were ingesting a chronic treatment of either CFE—Caralluma fimbriata extract, at one of two doses 100 mg/kg/d or 33 mg/kg/d or PLAC—placebo of maltodextrin/cabbage leaf [SNO: n = 36; WT: n = 36: (100CFE/M: n = 6 and F: n = 6; 33CFE/M: n = 6 and F: n = 6; and PLAC/M: n = 6 and F: n = 6)]

Figure 2

Immunohistochemistry comparison of strain c‐Fos and NPY cell population. Colocalization of neuropeptide and activity: color image (purple) c‐Fos—Fos‐like early gene expression (green); NPY—neuropeptide Y and c‐Fos in brain slices from the ARC—arcuate nucleus of the hypothalamus in SNO (n = 5)—representative of Snord116del mice and in WT (n = 5)—wild‐type control, ingesting chronic treatment 100CFE—Caralluma fimbriata extract, at 100 mg/kg/d or PLAC—placebo 200 mg maltodextrin and 50 mg cabbage leaf, with food intake stimulant, signaling reagents, 2DG—2‐deoxyglucose, induced by i.p. injection (400 mg/kg, 10 mg =25 g mouse), in comparison with the control SAL—i.p. injection of isotonic saline

Figure 3

Immunohistochemistry comparison of strain c‐Fos and α‐MSH cell population. Colocalization of neuropeptide and activity: Color image (purple) c‐Fos—Fos‐like early gene expression (red); α‐MSH—alpha‐melanocyte‐stimulating hormone; and C‐Fos in brain slices from the ARC—arcuate nucleus of the hypothalamus in SNO (n = 5)—representative of Snord116del mice and in WT (n = 5)—wild‐type control, ingesting chronic treatment 100CFE—Caralluma fimbriata extract, at 100 mg/kg/d or PLAC—placebo 200 mg maltodextrin and 50 mg cabbage leaf, with food intake stimulant, signaling reagents, 2DG—2‐deoxyglucose, induced by i.p. injection (400 mg/kg, 10 mg =25 g mouse), in comparison with the control SAL—i.p. injection of isotonic saline