BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to serum-based microRNAs and methods for differentiating patients suffering from Parkinson's disease, as well as assisting clinicians to determine treatment protocols for such patients.

2. Brief Description of the Background Art

Parkinson's Disease (PD) is a highly specific degeneration of dopamine-containing cells of the substantia nigra of the midbrain, causing a dopamine deficiency in the striatum. PD currently affects about 10 million people world-wide. Effective management of a patient with PD is possible in the first 5-7 years of treatment, after which time a series of often debilitating complications, together referred to as Late Motor Fluctuations (LMF) occur. It is believed that treatment with levodopa ((−)-L-α-amino-beta-(3,4-dihydroxybenzene) propanoic acid), or L-dopa, the most effective antiparkinson drug, may facilitate or even promote the appearance of LMF. Dopamine agonists are employed as a treatment alternative, but they do not offer the same degree of symptomatic relief to patients as L-dopa does.

Symptomatic therapies improve signs and symptoms without affecting the underlying disease state. Levodopa increases dopamine concentration in the striatum, especially when its peripheral metabolism is inhibited by a peripheral decarboxylase inhibitor (PDI). Levodopa/PDI therapy is widely used for symptomatic therapy for Parkinson's disease, such as combinations with levodopa, with carbidopa ((−)-L-α-hydrazino-α-methyl-beta-(3,4-dihydroxybenzene) propanoic acid monohydrate), levodopa and controlled release carbidopa, levodopa and benserazide, levodopa plus controlled release benserazide (2-Amino-3-hydroxy-propionic acid N′-(2,3,4-trihydroxy-benzyl)-hydrazide).

Catechol-O-methyltransferase (COMT) inhibitors enhance levodopa treatment as they inhibit levodopa's metabolism, enhancing its bioavailability and thereby making more of the drug available in the synaptic cleft for a longer period of time. Examples of COMT inhibitors include tolcapone (3,4-dihydroxy-4′-methyl-5-nitrobenzophenone) and entacapone ((E)-2-cyano-3-(3,4-dihydroxy-5-nitrophenyl)-N,N-diethyl-2-propenamide).

Dopamine agonists provide symptomatic benefit by directly stimulating post-synaptic striatal dopamine receptors. Examples include bromocriptine ((5α)-2-Bromo-12′-hydroxy-2′-(1-methylethyl)-5′-(2-methylpropyl)erg-otaman-3′,6′,18-trione), pergolide (8B-[(Methylthio)methyl]-6-propylergoline), ropinirole (4-[2-(Dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one), pramipexole ((S)-4,5,6,7-Tetrahydro-N6-propyl-2,6-benzothiazolediamine), lisuride (N′-[(8a)-9,10-didehydro-6-methylergolin-8-yl]-N,N-diethyl-urea), cabergoline ((8β)-N-[3-(Dimethylamino)propyl]-N-[(ethylamino)carbonyl]-6-(2-propenyl)ergoline-8-carboxamide), apomorphine ((6aR)-5,6,6a,7-Tetrahydro-6-methyl-4H-dibenzo[de,g]quinoline-10,11-diol), sumanirole (5-(methylamino)-5,6-dihydro-4H-imidazo {4,5,1-ij}quinolin-2(1H)-one), rotigotine ((−)(S)-5,6,7,8-tetrahydro-6-[propyl[2-(2-thienyl)ethyl]amino]-1-naphthol-), talipexole (5,6,7,8-Tetrahydro-6-(2-propenyl)-4H-thiazolo[4,5-d]azepin-2-amine), and dihydroergocriptine (ergotaman-3′,6′,18-trione,9,10-dihydro-12′-hydroxy-2′-methyl-5′-(phenylmethyl) (5′ cc)). Dopamine agonists are effective as monotherapy early in the course of Parkinson's disease and as an adjunct to levodopa in more advanced stages. Unlike levodopa, dopamine agonists directly stimulate post-synaptic dopamine receptors. They do not undergo oxidative metabolism and are not thought to accelerate the disease process.

Amantidine (1-Aminotricyclo (3,3,1,13,7) decane) is an antiviral agent that was discovered by chance to have anti-Parkinsonian activity. Its mechanism of action in PD has not been established, but is believed to work by increasing dopamine release. Patients who receive amantidine either as monotherapy or in combination with levodopa show improvement in akinesia, rigidity and tremor.

Other medications used in the treatment of Parkinson's disease include MAO-B inhibitors. Inhibition of L-dopa metabolism through inactivation of the monoamino oxidase type B (MAO-B) is an effective means of enhancing the efficacy of both endogenous residual dopamine and that exogenously derived from its precursor, L-dopa. Selegiline (methyl-(1-methyl-2-phenyl-ethyl)-prop-2-ynyl-amine) is a MAO-B inhibitor. There is evidence that treatment with selegiline may slow down disease progression in PD by blocking formation of free radicals derived from the oxidative metabolism of dopamine. Other examples of MAO B inhibitors include lazabemide (N-(2-Aminoethyl)-5-chloro-2-pyridinecarboxamide), rasagiline (N-propargyl-1-(R)aminoindan and caroxazone (2-oxo-2H-1,3-benzoxazine-3(4H)-acetamide).

It is imperative to diagnose individuals with PD at an early stage to increase the efficacy of therapeutic agents. However, there are neither any objective tests nor established biomarkers for diagnosing PD. Moreover, the heterogeneity, subtypes and progression of the disease make it difficult to develop specific therapeutic candidates.

MicroRNAs (“miRNAs) are a class of non-coding RNAs that play key roles in the regulation of gene expression. miRNAs act at the post-transcriptional level and fine-tune the expression of as much as 30% of all mammalian protein-encoding genes. Mature miRNAs are short, single-stranded RNA molecules approximately 22 nucleotides in length. miRNAs may be encoded by multiple loci, and may be organized in tandemly co-transcribed clusters. miRNA genes are transcribed by RNA polymerase II as large primary transcripts (pri-microRNA) that are processed by a protein complex containing the RNase III enzyme Drosha, DGCR8 and other cofactors, to form an approximately 70 nucleotide precursor microRNA (pre-miRNA). (Cathew R W, Cell, 2009; Kim V N, Nat Rev Mol Cel Biol, 2009; Siomi H, Mol Cel, 2010; Bartel D P, Cell, 2004; Lee Y, Nature 2003; Han J, Genes Dev, 2004.) Pre-miRNA is transported to the cytoplasm by Exportin-5 where it is processed by DICER, a second RNase III enzyme, together with TRBP, PACT and Ago2 in the RNA Induced Silencing Complex resulting in miRNA duplexes (Kim V N, Nat Rev Mol Cel Biol, 2009; Gregory R I, Nature 2004; MAcRae IJ, PNAS, 2008). The guide strands of miRNA duplexes separate and associate with Ago 2 for incorporation into a ribonuclear particle to form the RNA-induced silencing complex RISC that mediates gene silencing. The mechanisms of miRNA range from direct degradation or silencing of mRNA and repression of translation to post-transcriptional upregulations. (MacRae IJ, PNAS, 2008.)

The presence of miRNAs has been reported in body fluids including blood, cerebrospinal fluid (CSF), plasma, serum and saliva at detectable levels. The tissue-specificity of miRNAs suggests their vital and integral role in various physiological processes. The tissue-enrichment promises a new but less explored role as diagnostic biomarker and potential therapeutic target. Circulating miRNAs are understood to originate from passive leakage from damaged tissue as a result of cell lysis or apoptosis, active transport from cells via microvesicles, such as exosomes, or bound within RISC protein complexes (Etheridge et al, 2011). Exosome and osmotic pump-mediated delivery of small RNA molecules to the brain and CNS, respectively, provides a solution to overcoming the limitations of miRNA-based therapies (Alvarez-Erviti et al., 2011; Koval et al, 2013, Hum. Mol. Gen). miRNA has been demonstrated to be exceptionally stable and thus present as powerful candidates to be potential biomarkers (Chen et al, 2008; Grasso, 2014).

SUMMARY OF THE INVENTION

It is an object of the present invention to identify miRNAs relevant to patients suffering from Parkinson's disease.

It is another object of the present invention to provide methods for determining patients suffering from Parkinson's disease.

These objects and others are achieved by the present invention, which provides miRNA biomarkers that may be used singly, in pairs or in combination to determine patients suffering from Parkinson's disease.

