Lack of tolerance development with long-term administration of PEGylated cholecystokinin

Abstract

Cholecystokinin (CCK) is a short acting satiating peptide hormone produced in the proximal small intestine. Daily CCK injection in rats initially inhibits food intake, but after several days, food intake is no longer affected, suggesting development of tolerance. Previously, we covalently coupled CCK to a 10kDa polyethylene glycol (mPEG-OH) and showed that this conjugate, PEG-CCK(9), produced a significantly longer anorectic effect than unmodified CCK(9). The present study examined whether tolerance to the anorectic effect develops during long-term administration of PEG-CCK(9). For 14 consecutive days, male Wistar rats (n=12) received a daily i.p injection of 8microgkg(-1) of PEG-CCK(9) and a control group received a daily control injection of mPEG-OH. Body weight and food intake were monitored daily during the experiment. Effects on the pancreas were investigated. On each day, injection of PEG-CCK(9) induced an anorectic effect lasting 3-6h, but failed to significantly reduce daily total food intake compared to controls. The body weight gain of the PEG-CCK(9)-treated animals was not different from controls. The PEG-CCK(9)-treated group had a significantly higher pancreas weight, mainly due to hyperplasia. In conclusion, PEG-CCK(9) continued to have a daily suppressive effect on food intake when administered for 14 consecutive days, showing there was no development of tolerance.

Metabolic effects of activation of CCK receptor signaling pathways by twice-daily administration of the enzyme-resistant CCK-8 analog, (pGlu-Gln)-CCK-8, in normal mice

“…In agreement, circulating glucose and insulin were almost identical to saline-treated control mice, indicating lack of detrimental metabolic effects despite significantly lowered body weights. These observations accord with other studies using longer-acting CCK agonists, where the occurrence of adverse effects such as intestinal discomfort, tolerance, and conditioned taste aversion was atypical and dose related (Verbaeys et al 2008(Verbaeys et al , 2009a. The finding in one study of pancreatic hyperplasia and, in some cases, pancreatitis in rats treated with a long-acting PEGylated version of CCK-9 for 14 days (Verbaeys et al 2009a) was not replicated in previous investigations with (pGlu-Gln)-CCK-8, where amylase and lipase levels were actually reduced (Irwin et al 2012).…”

“…As such, numerous studies have shown notable therapeutic effectiveness of longer-acting CCK-based compounds (O'Harte et al 1998, Verbaeys et al 2007, 2008, 2009a. In particular, the recently characterized N-terminally modified, enzymatically stable CCK-8 analog, (pGlu-Gln)-CCK-8, causes sustained weight loss and improves both insulin resistance and glucose tolerance in mice with genetically and environmentally induced forms of obesity-diabetes (Irwin et al 2012).…”

Beneficial effects of the novel cholecystokinin agonist (pGlu-Gln)-CCK-8 in mouse models of obesity/diabetes

“…No evidence was found and ob/ob mice injected twice daily for 18 days with 25 nmol/kg (pGlu-Gln)-CCK-8 still displayed significant inhibitory effects on feeding when administered (pGlu-Gln)-CCK-8 following an 18-h fast. This observation contrasts with previous studies using native CCK-8 where tolerance appeared to develop quickly [34,35], but agrees with more recent work using a longer-acting PEGylated version of CCK-9 [11]. One potential reason for the lack of tolerance to (pGlu-Gln)-CCK-8 could be the induction of taste aversion.…”

“…Other possible barriers to the use of CCK-based peptides in the clinic include development of tolerance [11], induction of taste aversion [12] and induction of pancreatic inflammation [13]. Plasmamediated degradation of CCK is poorly understood and a number of enzymes have been postulated to be involved [14].…”

“…A more specific approach would therefore be to generate enzymatic-resistant analogues of CCK to extend the biological half-life of the peptide. Studies have already indicated that N-terminal modification or PEGylation of peptide hormones, including CCK, prevents enzymatic degradation and extends biological action [11,16].…”