The impacts of commonly used medications on the trans-sulphuration pathway

Abstract

Worldwide life expectancy is predicted to increase, which can lead to an increased reliance on medications to manage multimorbidity. Self-medication and cost of living crisis has increased this pattern. The trend towards increased medication use can increase the possibility of having a larger population at risk of micronutrient deficiencies / inadequacy in users. Despite the widespread use of medications, studies on drug-nutrient interactions remain limited. This is particularly concerning for critical metabolic processes like the trans-sulphuration pathway (TSP) that depend on vitamin B6 for its flux. This work employed a multi-faceted approach aimed at providing crucial insights into how commonly prescribed drugs influence the TSP. We conducted a scoping review to assess current evidence on the impacts of medications on TSP metabolites in humans using paracetamol (APAP) as a model therapeutic. Eight out of 13 studies showed that, despite a lack of risk factors for dysregulate glutathione (GSH) homeostasis among participants in this review, significant reduction in GSH upon short-term use (≤ 4 days) of APAP treatment was reported. No definitive conclusion could be made regarding other TSP metabolites assessed due to lack of human studies. While we acknowledge these metabolic targets are largely identified as GSH related due to the known detoxification pathway for APAP. This review raised a gap of knowledge which would be interesting to investigate; i) advancing age coupled with malnutrition with low protein intakes and other specific dietary patterns with low SAAs (such as vegetarian) are reported in animal models as risk factors for APAP-induced GSH depletion leading to toxicity; whether or not this phenomena and other health consequences viz. sarcopenia would mirror such studies in humans needs further investigation, and ii) previous in vitro work showed that GSH depletion can lead to H2S production reduction, we hence raise a hypothesis that APAP-associated cardiovascular risk may be mediated through reduced H2S production resulting from GSH depletion. Secondary, reductions in dietary vitamin B6 and pyridoxal 5′-phosphate (PLP) levels could affect the flux of TSP and are associated with increased relative risk of age- related diseases. In regards to this, we carried out a secondary analysis using the National Diet and Nutrition Survey Rolling Programme (NDNS) to assess dietary intake of vitamin B6 and plasma PLP among the UK population (aged ≥ 19 years) and to investigate the impact of common medications on vitamin B6 status. Results showed that median dietary vitamin B6 intake of UK population met the reference nutrient intake (RNI) reaching 1.7 mg day-1 and the median plasma PLP in the entire population was 42.8 nmol L-1 and were higher than the threshold for vitamin B6 deficiency. However, data showed that both plasma PLP concentrations and dietary vitamin B6 intake tend to decline with age (P < 0.001). The NDNS data set included twelve reported therapeutic drugs. Of these, only antidepressant was associated with low dietary vitamin B6 (P = 0.007, R2 = 0.15). Seven drug classes were associated with plasma PLP concentrations reduction namely lipid-lowering drugs, analgesics, antibacterials, antidiabetics, antidepressants, Ca2+ blocker and prescribed asthma. Further, we validated and developed a human hepatoma HepG2 model to assess the cytotoxicity profile of two drugs, APAP and sulphasalazine (SSZ). Results showed that both APAP and SSZ exhibit cytotoxicity in HepG2 cells. Mechanistic findings showed possible mechanisms of cytotoxicity i) inducing early oxidative markers; ROS formation, lipid peroxidation and mitochondria depolarisation (P < 0.01, for both drugs) and ii) inducing later markers of apoptotic cascade; DNA damage, LDH leakage and PARP cleavage. Both drugs are partially caspase-dependent, however, caspase-3 plays a more prominent role in the apoptotic cascade induced by SSZ. Both drugs significantly reduce intracellular GSH levels in a concentration-dependent manner at 24 hours (P < 0.001, for both drugs). Interestingly, APAP at low concentrations (≤1 mM) significantly reduced cellular GSH levels without immediate cell death. However, this GSH depletion increased cell vulnerability to additional oxidative stress i.e. DNA damage. In the second set of our in vitro studies, we assessed the impact of APAP and SSZ on hydrogen sulphide (H2S) and it key enzymes (CBS and CSE), alongside polysulphide (H2Sn) levels. We showed that APAP could indirectly affect H2S production in HepG2 cells by significantly reduce the expressions of CBS (P < 0.01) and CSE (P = 0.023), however, no significant direct reduction in H2S was noticed upon short time APAP exposure (up to 4 hours). SSZ showed interesting findings as CSE expression was significantly elevated when cells were treated for 24 hours with low concentrations (0.12 mM and 0.25 mM; (P = 0.034, P = 0.049), respectively). At higher concentrations, CSE expression started to decrease, though not statistically significantly. A concentration-dependent reduction in CBS expression, however, not statistically significant, was noticed when cells treated with SSZ. In this chapter, we also assess the impact of H2S and H2Sn donors (NaHS and Na2S2, respectively) on APAP- and SSZ- induced oxidative stress markers. Our results showed both NaHS and Na2S2 had protection effects as shown by reduction in ROS formation, lipid peroxidation, mitochondria depolarisation, LDH leakage, DNA damage, cleaved PARP as well as preserving GSH levels. But also, both donors can act as direct scavengers as both NaHS and Na2S2 exhibit antioxidant properties, detected by the ABTS and copper reduction assays. In conclusion, multi-faceted investigation provides evidence for medication-induced dysregulation of the TSP metabolites, enzymes and vitamin B6 cofactor. However, further work is needed to measure TSP metabolites in humans using medications such as Tau and H2S and whether or not their reductions contributed to some side effects of drugs. A causal link between medication use, vitamin B6 inadequacy and changes in TSP metabolites in humans, an interesting area to be explored in the future.