Pharmacogenetics-based population pharmacokinetic analysis of gabapentin in patients with chronic pain: Effect of OCT2 and OCTN1 gene polymorphisms

Genome-wide association reveals a locus in neuregulin 3 associated with gabapentin efficacy in women with chronic pelvic pain

Chronic pelvic pain (CPP) in women with no obvious pelvic pathology has few evidence-based treatment options. Our recent multicenter randomized controlled trial (GaPP2) in women with CPP and no obvious pelvic pathology showed that gabapentin did not relieve pain overall and was associated with more side effects than placebo. We conducted an exploratory genome-wide association study using eligible GaPP2 participants aiming to identify genetic variants associated with gabapentin response. One genome-wide significant association with gabapentin analgesic response was identified, rs4442490, an intron variant located in Neuregulin 3 (NRG3) (p = 2·11×10-8; OR = 18·82 (95% CI 4·86-72·83). Analysis of a large sample of UK Biobank participants demonstrated phenome-wide significant brain imaging features of rs4442490, particularly implicating the orbitofrontal cortex. NRG3 is expressed predominantly in central nervous system tissues and plays a critical role in nervous system development, maintenance, and repair, suggesting a neurobiologically plausible role in gabapentin efficacy and potential for personalized analgesic treatment.

Are age-related neurodegenerative diseases caused by a lack of the diet-derived compound ergothioneine?

We propose that the diet-derived compound ergothioneine (ET) is an important nutrient in the human body, especially for maintenance of normal brain function, and that low body ET levels predispose humans to significantly increased risks of neurodegenerative (cognitive impairment, dementia, Parkinson's disease) and possibly other age-related diseases (including frailty, cardiovascular disease, and eye disease). Hence, restoring ET levels in the body could assist in mitigating these risks, which are rapidly increasing due to ageing populations globally. Prevention of neurodegeneration is especially important, since by the time dementia is usually diagnosed damage to the brain is extensive and likely irreversible. ET and vitamin E from the diet may act in parallel or even synergistically to protect different parts of the brain; both may be "neuroprotective vitamins". The present article reviews the substantial scientific basis supporting these proposals about the role of ET.

Lack of impact of OCTN1 gene polymorphisms on clinical outcomes of gabapentinoids in Pakistani patients with neuropathic pain

Background and objective

Gabapentinoids are the first-line drugs for neuropathic pain. These drugs are the substrate of organic cation transporter (OCTN1) for renal excretion and absorption across the intestinal epithelium. Gabapentinoids exhibit wide interindividual variability in daily dosage and therapeutic efficacy which makes titration regimens prolonged for optimal efficacy. The present study aimed to investigate the possible influence of the single nucleotide polymorphism (SNP) of OCTN1 on therapeutic efficacy and safety of gabapentinoids in neuropathic pain patients of the Pakistani population.

Methods

Four hundred and twenty-six patients were enrolled in the study. All participants were genotyped for OCTN1 rs1050152 and rs3792876 by PCR-RFLP method and followed up for eight weeks. The therapeutic outcomes of gabapentinoids, reduction in pain score, inadequate or complete lack of response, adverse events (AEs) in responders and discontinuation of treatment on account of AEs were recorded for all patients.

Results

There was no significant association of genotypes and alleles of both SNPs on the clinical response of gabapentinoids (P ˃ 0.05). Similarly, significant differences were not found in the reduction of pain scores and AEs among different genotypes in the responders. The present study has reported the association of OCTN1 rs1050152 and rs3792876 polymorphisms with clinical outcomes of gabapentinoids for the first time in the real-world clinical setting.

Conclusion

Our results suggest a lack of influence of OCTN1 genetic variants in the determination of clinical response to gabapentinoids in patients with neuropathic pain in the Pakistani population. These findings signify the role of renal functions in predicting the interindividual variability to therapeutic responsiveness of gabapentinoids.

OCTN1: A Widely Studied but Still Enigmatic Organic Cation Transporter Linked to Human Pathology and Drug Interactions

The Novel Organic Cation Transporter, OCTN1, is the first member of the OCTN subfamily; it belongs to the wider Solute Carrier family SLC22, which counts many members including cation and anion organic transporters. The tertiary structure has not been resolved for any cation organic transporter. The functional role of OCNT1 is still not well assessed despite the many functional studies so far conducted. The lack of a definitive identification of OCTN1 function can be attributed to the different experimental systems and methodologies adopted for studying each of the proposed ligands. Apart from the contradictory data, the international scientific community agrees on a role of OCTN1 in protecting cells and tissues from oxidative and/or inflammatory damage. Moreover, the involvement of this transporter in drug interactions and delivery has been well clarified, even though the exact profile of the transported/interacting molecules is still somehow confusing. Therefore, OCTN1 continues to be a hot topic in terms of its functional role and structure. This review focuses on the most recent advances on OCTN1 in terms of functional aspects, physiological roles, substrate specificity, drug interactions, tissue expression, and relationships with pathology.

Influence of single nucleotide polymorphism of LAT1 on therapeutic response to gabapentinoids in Pakistani patients with neuropathic pain

Gabapentinoids are substrate of L-type amino acid transporter 1 (LAT1) for distribution across the blood-brain barrier. The present study aimed to evaluate the effect of LAT1 rs4240803 genetic polymorphism on the clinical efficacy and tolerability of gabapentinoids in Pakistani patients with neuropathic pain. Three-hundred and ninety-two patients were recruited, genotyped for SNP rs4240803, and followed up for eight weeks to evaluate the clinical response to gabapentinoids in terms of pain relief, inadequate response, and the emergence of adverse events. LAT1 rs4240803 GG, GA, and AA genotype frequency were 33.42%, 47.96% and 18.62%, respectively. Out of 392 patients, 323 responded to the treatment and 17.6% discontinued either due to insufficient response or intolerable adverse events (AEs). GA genotype was more frequent in non-responder group (P ˂ 0.001). Maximum pain responders (≥50%) in combination with the lowest incidence of AEs were observed in the GG group, whereas partial responders belonged to GA genotype and with the highest frequency of somnolence (83.6%) and dizziness (69.9%). Overall, 72.5% patients with GA genotype experienced AEs (P ˂ 0.001). In conclusion, clinical outcomes of gabapentinoids are influenced by LAT1 rs4240803 polymorphism and population pharmacogenetics should be considered to evaluate the maximum potential of gabapentinoids in the management of neuropathic pain.

Population pharmacokinetics of gabapentin in patients with neuropathic pain: Lack of effect of diabetes or glycaemic control

AIMS

Gabapentin (GBP) is widely used to treat neuropathic pain, including diabetic neuropathic pain. Our objective was to evaluate the role of diabetes and glycaemic control on GBP population pharmacokinetics.

METHODS

A clinical trial was conducted in patients with neuropathic pain (n = 29) due to type 2 diabetes (n = 19) or lumbar/cervical disc herniation (n = 10). All participants were treated with a single oral dose GBP. Blood was sampled up to 24 hours after GBP administration. Data were analysed with a population approach using the stochastic approximation expectation maximization algorithm. Weight, body mass index, sex, biomarkers of renal function and diabetes, and genotypes for the main genetic polymorphisms of SLC22A2 (rs316019) and SLC22A4 (rs1050152), the genes encoding the transporters for organic cations OCT2 and OCTN1, were tested as potential covariates.

RESULTS

GBP drug disposition was described by a 1-compartment model with lag-time, first-order absorption and linear elimination. The total clearance was dependent on estimated glomerular filtration rate. Population estimates (between-subject variability in percentage) for lag time, first-order absorption rate, apparent volume of distribution and total clearance were 0.316 h (10.6%), 1.12 h^-1 (10.7%), 140 L (7.7%) and 14.7 L/h (6.97%), respectively. No significant association was observed with hyperglycaemia, glycated haemoglobin, diabetes diagnosis, age, sex, weight, body mass index, SLC22A2 or SLC22A4 genotypes.

CONCLUSION

This population pharmacokinetics model accurately estimated GBP concentrations in patients with neuropathic pain, using estimated glomerular filtrationrate as a covariate for total clearance. The distribution and excretion processes of GBP were not affected by hyperglycaemia or diabetes.

Can Implementation of Genetics and Pharmacogenomics Improve Treatment of Chronic Low Back Pain?

Etiology of back pain is multifactorial and not completely understood, and for the majority of people who suffer from chronic low back pain (cLBP), the precise cause cannot be determined. We know that back pain is somewhat heritable, chronic pain more so than acute. The aim of this review is to compile the genes identified by numerous genetic association studies of chronic pain conditions, focusing on cLBP specifically. Higher-order neurologic processes involved in pain maintenance and generation may explain genetic contributions and functional predisposition to formation of cLBP that does not involve spine pathology. Several genes have been identified in genetic association studies of cLBP and roughly, these genes could be grouped into several categories, coding for: receptors, enzymes, cytokines and related molecules, and transcription factors. Treatment of cLBP should be multimodal. In this review, we discuss how an individual's genotype could affect their response to therapy, as well as how genetic polymorphisms in CYP450 and other enzymes are crucial for affecting the metabolic profile of drugs used for the treatment of cLBP. Implementation of gene-focused pharmacotherapy has the potential to deliver select, more efficacious drugs and avoid unnecessary, polypharmacy-related adverse events in many painful conditions, including cLBP.