Overview of genetic analysis of human opioid receptors

Association between Toll-like receptor 2 rs4696483 and rs1898830 polymorphisms and the risk of triple-negative breast cancer

PURPOSE

Breast cancer (BC) is heterogeneous in clinical manifestation, of which the triple-negative (TNBC) subtype is the most aggressive. This study examines the associations between Toll-Like Receptor (TLR)-2 polymorphisms and the susceptibility to BC and TNBC.

METHODS

Genotyping of TLR-2 rs1898830 and rs4696483 polymorphisms was done by real-time PCR in 488 women with BC (130 TNBC, 358 non-TNBC) and 476 cancer-free control women.

RESULTS

The minor allele frequency (MAF) of rs4696483 was significantly lower in BC cases compared to controls, and significantly lower frequencies of rs4696483 C/T and higher frequencies of rs1898830 G/G genotypes were seen in BC cases. Significantly higher MAF of rs4696483 and higher C/T and T/T rs4696483 genotypes frequencies were seen in TNBC than in non-TNBC cases. Considering the prevalent AC haplotype as a reference, 2-locus TLR-2 haplotype analysis did not identify any 2-locus TLR-2 haplotype associated with an altered risk of BC or TNBC. Positive associations of rs1898830 and rs4966483 were seen with the histological type in TNBC and negatively with distant metastasis and HR status in TNBC and non-TNBC rs1898830 carriers. In addition, rs4696483 was positively correlated with hormonotherapy and surgery in non-TNBC cases, while rs1898830 was negatively associated with hormonotherapy. Furthermore, rs1898830 was negatively and positively correlated with BMI in TNBC and TNBC cases, respectively, but positively with Ki-67 status.

CONCLUSIONS

Our study highlights the association between TLR-2 genetic polymorphisms and BC and TNBC susceptibility, suggesting these variants' diagnostic/prognostic capacity in BC patients and patient subgroups.

Interindividual variability in diabetic patients’ response to opium poppy: an overview of impressive factors

Diabetic patients always seek alternative treatments to lower their blood glucose level efficiently, because antidiabetic drugs produce adverse effects and many patients experience reduced response after a treatment period. Opium poppy ( Papaver somniferum) is frequently consumed by diabetic patients for reduction of blood glucose level. Scientific studies found controversial results in the investigation of the blood glucose-lowering effects of opium poppy. In this regard, we explored the antidiabetic effect of opium poppy more closely. The antidiabetic or antihyperglycemic effect of P. somniferum alkaloids were reviewed. Next, opioid receptors and their role in diabetes were explored. In the final part origins of interindividual variabilities in opioid receptors and metabolizing enzymes’ functions including genetic and epigenetic factors were reviewed.

Overview of Genetic Analysis of Human Opioid Receptors

The human μ-opioid receptor gene (OPRM1 ), due to its genetic and structural variation, has been a target of interest in several pharmacogenetic studies. The μ-opioid receptor (MOR ), encoded by OPRM1 , contributes to regulate the analgesic response to pain and also controls the rewarding effects of many drugs of abuse, including opioids, nicotine, and alcohol. Genetic polymorphisms of opioid receptors are candidates for the variability of clinical opioid effects. The non-synonymous polymorphism A118G of the OPRM1 has been repeatedly associated with the efficacy of treatments for pain and various types of dependence. Genetic analysis of human opioid receptors has evidenced the presence of numerous polymorphisms either in exonic or in intronic sequences as well as the presence of synonymous coding variants that may have important effects on transcription, mRNA stability, and splicing, thus affecting gene function despite not directly disrupting any specific residue. Genotyping of opioid receptors is still in its infancy and a relevant progress in this field can be achieved by using advanced gene sequencing techniques described in this review that allow researchers to obtain vast quantities of data on human genomes and transcriptomes in a brief period of time and with affordable costs.

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

Background

Genes involved in Tourette syndrome (TS) remain largely unknown. We aimed to identify genetic factors contributing to TS in a French cohort of 120 individuals using a combination of hypothesis-driven and exome-sequencing approaches.

Methods

We first sequenced exons of SLITRK1-6 and HDC in the TS cohort and subsequently sequenced the exome of 12 individuals harboring rare variants in these genes to find additional rare variants contributing to the disorder under the hypothesis of oligogenic inheritance. We further screened three candidate genes (OPRK1, PCDH10, and NTSR2) preferentially expressed in the basal ganglia, and three additional genes involved in neurotensin and opioid signaling (OPRM1, NTS, and NTSR1), and compared variant frequencies in TS patients and 788 matched control individuals. We also investigated the impact of altering the expression of Oprk1 in zebrafish.

Results

Thirteen ultrarare missense variants of SLITRK1-6 and HDC were identified in 12 patients. Exome sequencing in these patients revealed rare possibly deleterious variants in 3,041 genes, 54 of which were preferentially expressed in the basal ganglia. Comparison of variant frequencies altering selected candidate genes in TS and control individuals revealed an excess of potentially disrupting variants in OPRK1, encoding the opioid kappa receptor, in TS patients. Accordingly, we show that downregulation of the Oprk1 orthologue in zebrafish induces a hyperkinetic phenotype in early development.

Discussion

These results support a heterogeneous and complex genetic etiology of TS, possibly involving rare variants altering the opioid pathway in some individuals, which could represent a novel therapeutic target in this disorder.

Comparative study of hypoglycaemia induced by opioids. Is it a class effect?

Objective: Drug-induced hypoglycaemia has been described with the use of tramadol and methadone. The authors aimed to determine if drug-induced hypoglycaemia could be a class effect for opioids. Methods: The authors performed a disproportionality analysis in VigiBase®, the WHO global individual case safety report database with nine opioids (codeine, fentanyl, hydromorphone, methadone, morphine, oxycodone, tramadol, buprenorphine and nalbuphine) using the broad Standardised MedDRA Query for hypoglycaemia. The authors also carried out a descriptive study of opioid-induced hypoglycaemia in the French PharmacoVigilance DataBase (FPVDB) using the MedDRA Preferred Term 'hypoglycaemia'. Results: The global adjusted Reporting Odds Ratio (aROR) value for the 9 opioids was 1.53 (95% CI 1.52-1.54). The aROR ranged from 1.09 to 1.97 depending on the opioid, but all were statistically significant. A sex ratio of 0.74 was found for the reports of opioid-induced hypoglycaemia in Vigibase®. The authors also found 133 reports of hypoglycaemia in the FPVDB related to opioids. Among the reports, 55 were glycaemic imbalances in diabetics occurring shortly after the start of opioid treatment. Conclusion: This work highlighted a significant association between all opioids and hypoglycaemia, thereby indicating that opioid-induced hypoglycaemia is probably a class effect. Women and/or diabetics seem to be more at risk for developing opioid-induced hypoglycaemia.

Mu-Opioid receptor biased ligands: A safer and painless discovery of analgesics?

Biased activation of G-protein-coupled receptors (GPCRs) is shifting drug discovery efforts and appears promising for the development of safer drugs. The most effective analgesics to treat acute pain are agonists of the μ opioid receptor (μ-OR), a member of the GPCR superfamily. However, the analgesic use of opioid drugs, such as morphine, is hindered by adverse effects. Only a few μ-OR agonists have been reported to selectively activate the G_i over β-arrestin signaling pathway, resulting in lower gastrointestinal dysfunction and respiratory suppression. Here, we discuss the strategies that led to the development of biased μ-OR agonists, and potential areas for improvement, with an emphasis on structural aspects of the ligand-receptor recognition process.

Pharmacogenomics for personalized pain medicine

Pharmacogenomics aims to unravel the way that human genetic variation affects drug efficacy and toxicity. Genome-wide association studies and candidate gene findings suggest that genetic approaches may help choose the most appropriate drug and dosage while preventing adverse drug reactions (ADRs). Pain is an unpleasant feeling that usually results from tissue damage. The management of different types of pain (acute, chronic, inflammatory, neuropathic, or cancer) is challenging. Currently, drug intervention is the first-line therapy for resolving pain. However, differences in drug efficacy between individuals are common with pain medications. Moreover, some patients experience ADRs after being treated with specific pain drugs. This review discusses the use of drugs for pain management in the context of the recent pharmacogenomic studies on ADRs and drug efficacy.