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Title:  Target for treating athersclerosis, obesity and type II diabetes

United States Patent:  6,942,967

Issued:  September 13, 2005

Inventors:  Harosh; Itzik (Paris, FR)

Assignee:  Obe Therapy Biotechnology (Evry, FR)

Appl. No.:  607437

Filed:  June 29, 2000

Abstract

The invention concerns the use of the apobec-1 protein or associated proteins for treating atherosclerosis and obesity, type II diabetes (non-insulin-dependent), or other diseases, characterised in particular by hyperlipidemia and/or hyperglycemia, caused for example by a level of chylomicrons and/or VLDL in the plasma above normal. The invention also concerns the cloning of the gene(s) of Anderson disease as target for treating atheroscelerosis, obesity and type II diabetes (non-insulin-dependent), or other diseases characterised in particular by hyperlipidemia and/or hyperglycermia.

Description of the Invention

This invention relates to apobec-1 enzyme and the associated proteins which enable the production of the protein apoB48 in the intestine. The invention is especially applicable to a method for detecting inhibitors of apobec-1 and associated proteins, and to the use of the gene(s) for Anderson's disease as a target for a treatment for athersclerosis, obesity, type II diabetes (non-insulin dependent) or other diseases characterized in particular by a higher than normal level of chylomicrons and/or VLDL in the plasma (hyperlipidemia, such as hypercholesterolemia, hyperglyceridemia, etc) and/or by hyperglycemia.

The apoB gene codes for two proteins, apoB100 and apoB48. These two proteins are translated by the same messenger RNA, modified at a single nucleotide by a specialized enzyme, apobec-1 (apoB editing compound 1) and associated proteins. In the human digestive system, this enzyme is expressed in the intestine but not in the liver. In the intestine, it modifies codon 6666 of the apoB messenger RNA by creating a stop codon which results in the production of a polypeptide known as apoB48 (48% of messenger RNA translated). ApoB48 is essential for the formation of chylomicrons which act to absorb and transport cholesterol, triglycerides and other lipids originating in the intestine. In the liver, where the apobec-1 enzyme is not expressed, and where no modification of the apoB messenger RNA takes place, the protein produced is apoB100, belonging to the very low density lipoproteins (VLDL) and low density lipoproteins (LDL) families.

Currently, three human genetic diseases exist which affect the level of apoB expression, all with similar phenotypes: abetalipoproteinemia, hypobetalipoproteinemia and Anderson's disease, also known as chylomicron retention disease. Abetalipoproteinemia is due to a deficiency of MTP (microsomal transfer protein) while hypobetalipoproteinemia is due to multiple mutations of the apoB gene. In those two cases, neither VLDL nor chylomicrons can be detected in the plasma, respectively associated with the absence of apoB100 and apoB48.

In contrast, in Anderson's disease, only chylomicrons (apoB48) are lacking in the plasma, while VLDLs (apoB100) remain detectable.

In this invention, it is suggested:

bullet1. that the apobec-1 enzyme and its associated proteins are potential targets for the treatment of athersclerosis and obesity, and other diseases principally characterized by a higher than normal level of chylomicrons and/or VLDL in the plasma (hyperlipidemia, such as hypercholesterolemia, hypertriglyceridemia, etc) and/or by hyperglycemia;
bullet2. that the gene(s) responsible for Anderson's disease are potential targets for the treatment of athersclerosis and obesity, and other diseases principally characterized by a higher than normal level of chylomicrons and/or VLDL in the plasma (hyperlipidemia, such as hypercholesterolemia, hypertriglyceridemia, etc) and/or by hyperglycemia;
bullet3. that the apobec-1 gene or the genes coding for the associated proteins are candidate genes for Anderson's disease.


Human apoB protein is the principal apolipoprotein of triglyceride-rich lipoproteins (present in VLDL, LDL and chylomicrons). Its gene is expressed both in the intestine and in the liver. The liver produces a 4536 amino acid protein known as apoB100, while in the intestine, the same gene codes for a smaller protein containing 2152 amino acids, known as apoB48. This protein is identical to the N-terminal portion of apoB100. ApoB48 is the result of translation of apob messenger RNA (mRNA) modified post-transcriptionally by the apobec-1 enzyme (editing protein of apoB messenger RNA) at nucleotide 6666 (cytidine), which undergoes deamination to uridine. This modification of apoB messenger RNA creates a stop codon (UAA) (see FIG. 1 and Chan L (1995), Biochimie 75-78).

In humans and rats, the complementary DNA (cDNA) which codes for apobec-1 has recently been cloned and sequenced (Teng B et al (1993), Science, 1816-1819, Lau P P (1994), Proc. Natl. Acad. Sci. USA 8522-8526). In man, this gene is only expressed in the small intestine, the only location where apoB48 and chylomicrons are produced. In the human liver, no apoB48 production takes place, which is concomitant with the absence of observation of the apobec-1 enzyme in that organ. In contrast, in the rat, where apoB100 and apoB48 are produced in the liver and in the intestine, apobec-1 is expressed in both organs, suggesting an essential role for this protein in the production of apoB48 (Giannoni et al (1994) J. Biol. Chem., 5932-5936). Further, the same authors have demonstrated that transfection of HepG2 hepatic cells with an apobec-1 cDNA leads to a modification of endogenous apoB mRNA, and to secretion of apoB48 protein (Giannoni et al (1994) J. Biol. Chem., 5932-5936).

Finally, it has recently been demonstrated that transgenic mice which are knock-out for the apobec-1 gene lose apobec-1 activity and have no trace of apoB48 in the blood circulation (Hirano K I et al (1996), J. Biol. Chem. 7154-7159, Morrison J R et al (1996), Proc. Natl. Acad. Sci. USA, 9887-9890).

Three human diseases of genetic origin with a similar phenotype have been described: abetalipoproteinemia, hypobetalipoproteinemia and Anderson's disease, also known as chylomicron retention disease (Table 1 and Havel R J and Kane J B (1995), in "The metabolic and molecular basis of inherited disease"). The genetic cause of two of these diseases, abetalipoproteinemia and hypobetalipoproteinemia, has been elucidated. In the case of abetalipoproteinemia, a frameshift mutation has been described in the gene for the MTP (microsomal triglyceride transfer) protein which leads to a complete absence of this protein and its activity. As a result, this mutation prevents the formation and secretion of lipoproteins containing apoB and thus prevents the detection of apoB100 and apoB48 in the plasma of patients (Sharp D et al (1993), Nature, 65-69, Wetterau J R et al (1992), Science, 999-1001). Hypobetalipoproteinemia is a disease in which different mutations of the apoB gene have been described, leading to truncated apoB proteins of different sizes. At the present time, 25 different mutations (nonsense or frameshift) have been described as being at the origin of hypobetalipoproteinemia, resulting in a premature stop codon (Linton M F et al (1993), J. Lipid. Res., 521-541, Rosseneu M and Lauber C (1995), FASEB J., 768-776). The mechanisms by which these truncations of the apoB protein lead to hypobetalipoproteinemia are as yet unknown. In the case of abetalipoproteinemia and hypobetalipoproteinemia, the absence of chylomicron absorptions also leads to an absence of vitamin E absorption, creating severe neurological symptoms.

The third of these genetic diseases with similar phenotypes, chylomicron retention disease, first described by Anderson 36 years ago (Anderson C M et al (1961), Med. J. Aust., 617-621) is still an enigma. This disease is characterized by chronic diarrhoea, deficient fat absorption and a lack of energy. In certain cases, neurological symptoms due to an absence of vitamin E are observed, but these are less severe than in the case of abetalipoproteinemia and hypobetalipoproteinemia (Havel R J and Kane J B (1995) in "The metabolic and molecular basis of inherited disease"). These diseases appear to be inherited in a recessive autosomal manner. Finally, analysis of the plasma of patients shows a total absence of chylomicrons and apoB48 protein (Havel R J and Kane J B (1995) in "The metabolic and molecular basis of inherited disease").

Genetic linkage studies using RFLP (restriction fragment length polymorphism) have shown that the apoB gene is not involved in Anderson's disease (Pessah M et al (1991), J. Clin. Invest. 367-370, Stritch et al (1993), J. Pediatric Gastro. Nutrit., 257-264). In patients with Anderson's disease, MTP activity is normal, which suggests that a different gene is implicated in this disease (Linton M F et al (1993), J. Lipid Res., 521-541). These and other experiments thus suggest that the origin of Anderson's disease is not linked with secretion via MTP and that chylomicron retention involves a further mechanism (Wetterau J R (1992), Science, 999-1001).

The present invention proposes that the gene for the apobec-1 protein is a candidate for Anderson's disease for the following reasons:
 
bullet1. apobec-1 is exclusively expressed in the intestine;
bullet2. apoB48 and chylomicrons are absent in the plasma of patients with Anderson's disease, while VLDL containing apoB100 are present. This constitutes the principal phenotype of patients with Anderson's disease;
bullet3. mice which are knock-out for the apobec-1 gene lose apobec-1 activity and the mRNA modification which ordinarily leads to the apoB48 protein, leading to the absence of this protein in the plasma (Hirano K I et al (1996) J. Biol. Chem. 7154-7159, Morrison J R et al (1996), Proc. Natl. Acad. Sci. USA 9887-9890);
bullet4. the apobec-1 activity of obese Zucker rats is 42% higher than that of non obese control rats, with the result that the level of chylomicrons and apoB48 in the blood is 4.7 times higher than that of the control rats (Phung T L et al (1996), Metabolism, 1056-1058);
bullet5. it has also been proposed that Anderson's disease is due to a modification in other genes involved in the protein secretion or glycosylation route (Levy E et al (1987), J. Lipid. Res., 1263-1274). Their results clearly show that one patient with Anderson's disease out of the three patients studied had a high level of apoB100 and relatively little apoB48. Using a more sensitive detection system, radioactive labelling followed by a SDS-PAGE analysis, for example, a visible amount of apoB100 was detected in the other two patients. The probable presence of apoB48 among the other visible bands of proteins which are smaller than apoB100 could be explained by degradation of apoB100.

Finally, it has been demonstrated that a mutation in the anchoring sequence around the apoB mRNA deamination site (site 6666) can cause a reduction or even a loss in editing of this site (Shah R R et al (1991), J. Biol. Chem., 16301-16304). It is thus not excluded that Anderson's disease is a particular case of hypobetalipoproteinemia wherein certain mutations of the apoB100 gene uniquely affect the formation and secretion of chylomicrons, while the formation and secretion of VLDL are not affected.

Thus the present invention suggests that a mutation or other modification of the anchoring sequence around the apoB mRNA deamination site may be at the origin of Anderson's disease.

In order to test the hypothesis that the apoB gene is a candidate for Anderson's disease, the present invention proposes to use RT-PCR (reverse transcriptase polymerase chain reaction) to sequence the apoB mRNA of intestinal biopsies of patients suffering from Anderson's disease, around the anchoring sequence surrounding site 6666, and to study the degree of deamination (C→U conversion) of this site. If no modification or mutation of the anchoring sequence surrounding the deamination site is observed, this will be highly indicative that the origin of Anderson's disease is due to apobec-1 or the associated proteins.

To test the hypothesis that the apobec-1 protein gene is at the origin of Anderson's disease, the present invention proposes to re-clone and sequence the apobec-1 gene in the patients. To test the hypothesis that the gene for the ABBP-1 gene (apobec-1 binding protein), the only protein associated with apobec-1 which has been cloned at present (Lau P P et al (1997), J. Biol. Chem., 1452-1455), is at the origin of Anderson's disease, the present invention proposes to re-clone and sequence the ABBP-1 gene in patients, to detect any differences with the normal genotype. In the case where other proteins associated with apobec-1 should be cloned, the present invention proposes to adopt the same technique to test the hypothesis that those are at the origin of Anderson's disease.

In the case where Anderson's disease is not due to modification of the apoB sequence, nor to modification of the apobec-1 protein and its associated proteins which are known and cloned, the present invention proposes to clone the responsible gene(s) by a subtractive hybridization technique as described in Example 1 (Kaneko-Ishino T (1995), Nature. Genet., 52-59) or a cloning technique by detecting point mutations using mutS protein as described in Example 2.

This invention also concerns apobec-1 inhibitor molecules or associated proteins for therapeutic use in the case of atherosclerosis or obesity, and other diseases characterized by a higher than normal level of chylomicrons and/or VLDL in the plasma (hyperlipidemia, such as hypercholesterolemia, hypertriglyceridemia, etc) and/or by hyperglycemia, obtained using a technique for detecting deamination of a cytidine in an RNA (French patent application 97 04388) as described in Example 3. The deaminated cytidine studied here is the cytidine in position 6666 of the apoB mRNA, the RNA sequence used as a substrate containing the apobec-1 anchoring zone or associated proteins is as described in the literature (Shah R R et al (1991), J. Biol. Chem., 16301-16304, Davies M S et al (1989), J. Biol. Chem., 13395-13398), and the protein extracts used can originate from the rat liver or from other sources. The sequence used as a primer in carrying out the technique contains a number of complementary nucleotides of the 3′ sequence of site 6666 of the apoB mRNA sufficient for correct hybridization (14 nucleotides or more).

Thus the present invention concerns the use of the gene for the apobec-1 enzyme or the gene for the ABBP-1 protein or that of a protein associated with the apobec-1 enzyme, or a gene involved in Anderson's disease, for research and to producing therapeutic agents or molecules inhibiting expression of one or more of these genes or the activity of enzymes or proteins expressed by these genes.

The present invention also concerns the use of therapeutic agents or molecules discovered and produced in accordance with the preceding claim for the prevention, stabilisation or treatment of atherosclerosis, obesity, type II diabetes (non-insulin dependent), or other diseases characterized by hyperlipidemia, such as hypercholesterolemia, hypertriglyceridemia, etc., and/or by hyperglycemia due, for example, to a higher than normal level of chylomicrons and/or VLDL in the plasma.

The present invention also concerns any therapeutic agent or molecule enabling inhibition of the activity of these enzymes or proteins, or inhibiting expression of these genes.

This invention especially concerns the use of anti-sense nucleic acid molecules which can reduce the quantity of apobec-1 or associated proteins, or the quantity of proteins expressed by the gene(s) for Anderson's disease or any gene involved in the formation, stabilization, secretion, glycosilation or transport of chylomicrons and/or VLDL (Uhlmann E and Peyman A (1990), Chem. Rev., 543-584). Such anti-sense molecules can bind covalently or otherwise to the DNA or RNA of apobec-1 or associated proteins, or to the DNA or RNA of the gene or genes responsible for Anderson's disease or any gene involved in the formation, stabilization, secretion, glycosilation or transport of chylomicrons and/or VLDL. As an example, such an anti-sense molecule linkage can cleave or facilitate cleavage of the DNA or RNA of apobec-1 or associated proteins, or of the gene(s) responsible for Anderson's disease or any gene involved in the formation, stabilization, secretion, glycosilation or transport of chylomicrons and/or VLDL. Such an anti-sense molecule can also increase degradation of the corresponding nuclear or cytoplasmic mRNA, or inhibit its translation, fixing of transcription factors or pre-messenger RNA, or, for example, by inhibiting splicing of pre-messenger RNA. The totality of these modes of anti-sense molecule action have the effect of reducing expression of the apobec-1 gene, or the associated proteins, or of the gene(s) responsible for Anderson's disease or any gene involved in the formation, stabilization, secretion, glycosilation or transport of chylomicrons and/or VLDL, resulting in an important treatment for obesity, type II diabetes (non-insulin dependent) or atherosclerosis, for example.

Non limiting examples of potential targets for such anti-sense molecules which can be cited are sequences of the apobec-1 gene or associated proteins, or the gene(s) responsible for Anderson's disease or any gene involved in the formation, stabilization, secretion, glycosilation or transport of chylomicrons and/or VLDL, but also the 3′ and 5′ sequences of these genes which could be the control regions for these genes.

The present invention thus also concerns single stranded (DNA or RNA) anti-sense nucleic acid molecules containing at least 12 nucleotides acting on the gene or its RNA, or on a region regulating expression of the gene to inhibit expression of the gene for the apobec-1 enzyme, or of the gene for the ABBP-1 protein, or that of a protein associated with the apobec-1 enzyme, or again a gene involved in Anderson's disease or the activity of the enzymes or proteins expressed by these genes.

 

Claim 1 of 10 Claims

1. A method of identifying a drug candidate for the treatment of obesity or other diseases characterized by hyperlipidemia or type II diabetes (non insulin dependent), comprising:

a) incubating a synthetic RNA sequence comprising the anchoring sequence of apobec-1 with a test inhibitor and an apobec-1 enzyme;

b) adding a complementary primer of 3′ sequence of the synthetic sequence under hybridizing conditions;

c) adding reverse transcriptase and a radiolabelled nucleotide; and

d) detecting whether the inhibitor inhibits the apobec-1 enzyme by detecting the absence of deamination of the anchoring sequence, wherein inhibition of the apobec-1 enzyme is indicative that said test inhibitor is a drug candidate for the treatment of obesity or other diseases characterized by hyperlipidemia or type II diabetes (non insulin dependent).

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