Ciliary neurotrophic factor (CNTF) was originally described as a trophic factor for chick ciliary ganglion neurons in vitro, Science. 1979 Jun 29;204(4400):1434-6 but later cloned and sequenced and demonstrated to belong to the gp130 cytokine family along with interleukin-6, interleukin-11,Cardiotrophin-1 (CT-1), Oncostatin M (OSM), and Leptin. J Biol Chem. 1995 May 5;270(18):10915-22. Although mice lacking CNTF developed normally initially, they developed loss of motor neurons with ageing. Nature. 1993 Sep 2;365(6441):27-32. Mice deficient in the receptor for CNTF developed severe motor neuron defects with premature death due to lack of development of feeding behaviour. Cell. 1995 Oct 20;83(2):313-22. CNTF was thus evaluated as treatment for motor neuron disease (MND). CNTF administration in patients with MND demonstrated significant weight loss in patients, Ann Neurol. 1996 Feb;39(2):256-60 suggesting the possibility that CNTF may exert cytokine like effects producing cachexia. In the context of obesity, this negative energy balance promoting action of CNTF which is now recognised as a pluripotent neurocytokine seemed to hold promise.
CNTF actions and CNTF receptor
CNTF, a 200 amino acid peptide is expressed in glial cells in peripheral nerves and in the CNS. Pharm Acta Helv. 2000 Mar;74(2-3):265-72. CNTF synthesis in the CNS is increased in trauma, sepsis, and cancer, all of which are associated with anorexia. CNTF has been recognised to have a role in the differentiation and survival of neuronal cell types including sensory, sympathetic and motor neurons. CNTF also has non-neuronal effects including initiation of an acute phase response in the hepatocytes, as well as producing a myotrophic effect on denervated skeletal muscles.
Although CNTF is a cytokine, it does not have the undesirable side effects of other cachexia-producing cytokines. Thus while CNTF promotes weight loss at low doses, it does not induce muscle wasting or pro-inflammatory responses, nor does it produced conditioned taste aversion or corticosterone release as is seen with IL-1. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. CNTF exerts its actions through the CNTF-specific receptor (CNTFRα) that has homology to the interleukin-6Rα. Science. 1991 Jul 5;253(5015):59-63. Cell. 1994 Feb 11;76(3):493-504. CNTFRα has been described not only in neural tissue but also in skeletal muscle, adrenal gland, sciatic nerve, skin, kidney, testes, Cell. 1992 Jun 26;69(7):1121-32 serum and CSF. Binding of CNTF to the CNTFRα activates JAK/STAT pathways. J Neurosci. 2000 Jun 1;20(11):4081-90. Mice lacking CNTFRα tend to have severe motor neuron defects and die soon after birth as they fail to initiate feeding behaviour.
CNTF vs. Leptin- similarities
Leptin is an adipocyte-derived cytokine, found in circulation in proportion to fat mass. Many features suggest that CNTF and Leptin may stimulate common signalling pathways in the brain areas involved in feeding. CNTF receptors have characteristics similar to those of Leptin receptors with regard to their distribution in the hypothalamic nuclei which are involved in feeding. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. Both CNTF and Leptin produce suppression of food intake and weight loss in ob/ob mice which are Leptin deficient. Both CNTF and Leptin positively regulate the anorexigenic peptides (CART and MSH) while both of them negatively regulate the orexigenic peptides( NPY, AgRP, GABA) in the arcuate nucleus of the hypothalamus. Neurosci Lett. 1998 Jan 2;240(1):45-9. Intracerebroventricular administration of both CNTF and Leptin prevent the hypothalamic NPY expression induced by starvation.Endocrinology. 1998 Feb;139(2):466-73. Both CNTF and Leptin prevent the food deprivation induced reduction in LH secretion. This effect on LH secretion is mediated by suppression of NPY expression. Thus the NPY system may be a target of CNTF and Leptin. Of note, the weight reducing and anorectic actions of centrally administered CNTF is reversed by concomitant infusion of NPY. J Neuroendocrinol. 2000 Sep;12(9):827-32.
CNTF vs. Leptin- differences
Despite these similarities, there are salient differences between CNTF and Leptin. Although CNTF receptors have been described in the paraventricular nucleus, CNTF does not regulate CRH secretion at this site, while Leptin increases CRH mRNA expression here. Diabetes. 2000 Nov;49(11):1890-6. which is thought to be responsible for mediating Leptin's anorectic action. This study also demonstrated that while Leptin reverses the starvation induced rise in AgRP mRNA expression, CNTF does not. Thus despite some common pathways, there exists areas where the two cytokines act differently. Diet-induced obesity, the cause of common human obesity, is not responsive to Leptin administration even at supraphysiological levels, Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4279-81. but CNTF successfully normalises the obese phenotype in this setting. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. Activation of hypothalamic pathways downstream of leptin by CNTF might bypass the leptin resistance demonstrated in this model. Similar efficacy of CNTF over Leptin has also been demonstrated in the db/db and MC4r deficient mice Nat Genet. 1999 Jan;21(1):119-22
Mice lacking CNTFRα tend to have severe motor neuron defects and die soon after birth as they fail to initiate feeding behaviour. But CNTF deficiency is not associated with this deficiency of neuronal activity, suggesting that there may be other endogenous receptor ligands for this receptor. Humans lacking CNTF gene are not obese Nat Genet. 1994 May;7(1):79-84. suggesting that CNTF may not play a role in weight control in the normal physiological state.
AXOKINE - CNTF analogue
CNTF potency was found to be increased by an amino acid substitution. (glutamine at position 63 with an arginine) J Biol Chem. 1993 Sep 5;268(25):19000-3. Axokine, a re-engineered analog of CNTF was thus developed with up to 5 times greater potency than CNTF. The up-regulation of early growth response protein-1 gene in the area postrema, the subfornical organ, and in the ventral part of the third ventricle might account for the greater weight loss inducing potency of Axokine. Abstr Soc Neurosci 1999 25 1 Abs 165.7 Axokine treatment produces preferential loss of body fat. Axokine, binds to CNTF receptor alpha and activates JAK/STAT signalling pathway. Axokine actions on weight loss seem to be mediated through the medial arcuate nucleus. Abstr Soc Neurosci 2001 27 1 Abs 635.5 Axokine like CNTF is effective in producing weight loss in ob/ob mice as well as diet induced obese mice. Abstr Soc Neurosci 1998 24 1 abs 442.1 , the latter in contrast to leptin's ineffectiveness. The prominent stimulation of pATAT3 signalling in neurons in the medial arcuate nucleus in all strains of mice by axokine might account for this variance from leptin's actions, as leptin stimulates neurons in the medial arcuate nucleus only in ob/ob mice. Axokine produces reduction in food intake and weight along with improved glucose tolerance in the non-insulin dependent db/db mouse model. Axokine shows neuro-protective effects against hemorrhagic injury. J Neurol Sci. 2001 Nov 15;192(1-2):53-9
Axokine was evaluated in phase III trials involving 1467 subjects treated with subcutaneous injections of Axokine compared to 501 placebo treated subjects for one year. This study demonstrated that AXOKINE-treated patients lost 5% of their initial body weight compared to placebo-treated patients (25.1% vs. 17.6%, p<.001) . Regneron Pharmaceuticals data press release while more patients on AXOKINE treatment demonstrated weight loss amounting to at least 10% of their initial body weight (11.3% vs. 4.2%, p <.001). Development of antibodies in up to half of patients treated with AXOKINE seems to limit weight loss. Overcoming the immunogenicity of Axokine seems to be the next step to improve efficacy and durability of its effects.
CNTF actions and CNTF receptor
CNTF, a 200 amino acid peptide is expressed in glial cells in peripheral nerves and in the CNS. Pharm Acta Helv. 2000 Mar;74(2-3):265-72. CNTF synthesis in the CNS is increased in trauma, sepsis, and cancer, all of which are associated with anorexia. CNTF has been recognised to have a role in the differentiation and survival of neuronal cell types including sensory, sympathetic and motor neurons. CNTF also has non-neuronal effects including initiation of an acute phase response in the hepatocytes, as well as producing a myotrophic effect on denervated skeletal muscles.
Although CNTF is a cytokine, it does not have the undesirable side effects of other cachexia-producing cytokines. Thus while CNTF promotes weight loss at low doses, it does not induce muscle wasting or pro-inflammatory responses, nor does it produced conditioned taste aversion or corticosterone release as is seen with IL-1. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. CNTF exerts its actions through the CNTF-specific receptor (CNTFRα) that has homology to the interleukin-6Rα. Science. 1991 Jul 5;253(5015):59-63. Cell. 1994 Feb 11;76(3):493-504. CNTFRα has been described not only in neural tissue but also in skeletal muscle, adrenal gland, sciatic nerve, skin, kidney, testes, Cell. 1992 Jun 26;69(7):1121-32 serum and CSF. Binding of CNTF to the CNTFRα activates JAK/STAT pathways. J Neurosci. 2000 Jun 1;20(11):4081-90. Mice lacking CNTFRα tend to have severe motor neuron defects and die soon after birth as they fail to initiate feeding behaviour.
CNTF vs. Leptin- similarities
Leptin is an adipocyte-derived cytokine, found in circulation in proportion to fat mass. Many features suggest that CNTF and Leptin may stimulate common signalling pathways in the brain areas involved in feeding. CNTF receptors have characteristics similar to those of Leptin receptors with regard to their distribution in the hypothalamic nuclei which are involved in feeding. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. Both CNTF and Leptin produce suppression of food intake and weight loss in ob/ob mice which are Leptin deficient. Both CNTF and Leptin positively regulate the anorexigenic peptides (CART and MSH) while both of them negatively regulate the orexigenic peptides( NPY, AgRP, GABA) in the arcuate nucleus of the hypothalamus. Neurosci Lett. 1998 Jan 2;240(1):45-9. Intracerebroventricular administration of both CNTF and Leptin prevent the hypothalamic NPY expression induced by starvation.Endocrinology. 1998 Feb;139(2):466-73. Both CNTF and Leptin prevent the food deprivation induced reduction in LH secretion. This effect on LH secretion is mediated by suppression of NPY expression. Thus the NPY system may be a target of CNTF and Leptin. Of note, the weight reducing and anorectic actions of centrally administered CNTF is reversed by concomitant infusion of NPY. J Neuroendocrinol. 2000 Sep;12(9):827-32.
CNTF vs. Leptin- differences
Despite these similarities, there are salient differences between CNTF and Leptin. Although CNTF receptors have been described in the paraventricular nucleus, CNTF does not regulate CRH secretion at this site, while Leptin increases CRH mRNA expression here. Diabetes. 2000 Nov;49(11):1890-6. which is thought to be responsible for mediating Leptin's anorectic action. This study also demonstrated that while Leptin reverses the starvation induced rise in AgRP mRNA expression, CNTF does not. Thus despite some common pathways, there exists areas where the two cytokines act differently. Diet-induced obesity, the cause of common human obesity, is not responsive to Leptin administration even at supraphysiological levels, Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4279-81. but CNTF successfully normalises the obese phenotype in this setting. Proc Natl Acad Sci U S A. 2001 Apr 10;98(8):4652-7. Activation of hypothalamic pathways downstream of leptin by CNTF might bypass the leptin resistance demonstrated in this model. Similar efficacy of CNTF over Leptin has also been demonstrated in the db/db and MC4r deficient mice Nat Genet. 1999 Jan;21(1):119-22
Mice lacking CNTFRα tend to have severe motor neuron defects and die soon after birth as they fail to initiate feeding behaviour. But CNTF deficiency is not associated with this deficiency of neuronal activity, suggesting that there may be other endogenous receptor ligands for this receptor. Humans lacking CNTF gene are not obese Nat Genet. 1994 May;7(1):79-84. suggesting that CNTF may not play a role in weight control in the normal physiological state.
AXOKINE - CNTF analogue
CNTF potency was found to be increased by an amino acid substitution. (glutamine at position 63 with an arginine) J Biol Chem. 1993 Sep 5;268(25):19000-3. Axokine, a re-engineered analog of CNTF was thus developed with up to 5 times greater potency than CNTF. The up-regulation of early growth response protein-1 gene in the area postrema, the subfornical organ, and in the ventral part of the third ventricle might account for the greater weight loss inducing potency of Axokine. Abstr Soc Neurosci 1999 25 1 Abs 165.7 Axokine treatment produces preferential loss of body fat. Axokine, binds to CNTF receptor alpha and activates JAK/STAT signalling pathway. Axokine actions on weight loss seem to be mediated through the medial arcuate nucleus. Abstr Soc Neurosci 2001 27 1 Abs 635.5 Axokine like CNTF is effective in producing weight loss in ob/ob mice as well as diet induced obese mice. Abstr Soc Neurosci 1998 24 1 abs 442.1 , the latter in contrast to leptin's ineffectiveness. The prominent stimulation of pATAT3 signalling in neurons in the medial arcuate nucleus in all strains of mice by axokine might account for this variance from leptin's actions, as leptin stimulates neurons in the medial arcuate nucleus only in ob/ob mice. Axokine produces reduction in food intake and weight along with improved glucose tolerance in the non-insulin dependent db/db mouse model. Axokine shows neuro-protective effects against hemorrhagic injury. J Neurol Sci. 2001 Nov 15;192(1-2):53-9
Axokine was evaluated in phase III trials involving 1467 subjects treated with subcutaneous injections of Axokine compared to 501 placebo treated subjects for one year. This study demonstrated that AXOKINE-treated patients lost 5% of their initial body weight compared to placebo-treated patients (25.1% vs. 17.6%, p<.001) . Regneron Pharmaceuticals data press release while more patients on AXOKINE treatment demonstrated weight loss amounting to at least 10% of their initial body weight (11.3% vs. 4.2%, p <.001). Development of antibodies in up to half of patients treated with AXOKINE seems to limit weight loss. Overcoming the immunogenicity of Axokine seems to be the next step to improve efficacy and durability of its effects.