4. Discussions
GM is an effective aminoglycoside antibiotic widely prescribed for the treatment of infections, but its adverse effects associated with oxidative stress and kidney damage limit its long-term clinical use3. The beginning of renal failure and the increase of serum creatinine is usually slow. Serum creatinine and blood urea nitrogen characteristically increase 7-10 days after the start of aminoglycoside therapy 22. Especially in elderly individuals, a long time is required to treat GM-induced nephrotoxicity. Although most patients recover, the presence of certain risk factors may change the clinical picture or course. The recovery in kidney function may not completely improve in individuals with pre-existing chronic kidney disease 23. The side effects of GM are great importance to reduce for those reasons.
α-GST is an enzyme that has an important role in scavenging free radicals and reducing kidney damage. It was determined that α-GST level increased due to damage in the proximal tubules in the kidneys of rats in which GM was administered for 5 days 24. The urine biomarker such as IL-18, NGAL and KIM-1 is important for the early diagnosis of acute renal failure. Inflammatory cytokines (IL-1β, IL-6, IL-18 and TNF-α) and proteins that protect renal tubular cells such as NGAL and KIM-1 are released in the renal response by GM induced kidney damage 25. Although serum BUN and creatinine levels observed to be unchanged on the 4th day after GM (100 mg/kg) application, KIM-1 and NGAL levels increased 26. In case of exposure to antibiotics or environmental toxic substances, urinary RBP increases due to renal tubule dysfunction27. Resatorvid (5 mg/kg and 10 mg/kg doses) treatment has been reported to protect tissues against ischemia by inhibiting oxidative stress (MDA), TLR4 pathway and expression of IL-18, oxidative stress and apoptosis 9,10. ALA treatment (50 mg/kg) had a protective effect by preventing tubular damage with antioxidant effects in rabbits with GM-induced experimental nephrotoxicity28.
GST reduces the effectiveness of substances that cause renal toxicity due to it being conjugated with glutathione. ALA has high singlet oxygen binding capacity and prevents lipid peroxidation. Moreover, it accelerates tissue regeneration by reducing oxidative stress. It has been reported that ALA scavenges free oxygen radicals and increases SOD, CAT, GPx and GST activities in rats with experimental nephrotoxicity29. ALA by the antioxidant effects decreased KIM-1 expression on the 1st and 4th days in rats with colistin-induced nephrotoxicity however, the effect was not observed on day 7. In addition, serum creatinine level did not change in this period and it was emphasized that the KIM-1 parameter is a more sensitive marker than creatinine 15,30. In the current study, resatorvid treatment may have decreased the levels of IL-18, NGAL and KIM-1 in the urine by inhibiting the TLR4 pathway, reducing inflammation and kidney damage. This hypothesis is strengthened by the considerable decline in inflammation and nephropathological results in the histopathological examination. Alpha lipoic acid may have decreased oxidative stress with its antioxidant effect and decreased KIM-1 level by providing tissue regeneration.
It has been stated that biomarkers such as KIM-1 and NGAL released during tubular injury can be more accurate, earlier, real-time and proportional to injury than conventional markers 26. The administration of GM (100 mg/kg, intraperitoneal) for 7 days, increases statistically urinary creatinine and albumin levels, while creatinine clearance did not change 31. Glomerular filtration is impaired due to GM caused to damage in the proximal tubules, and creatinine clearance decrease and increase in urine protein levels 20,31. GM hasn’t caused to change in urine creatinine, microalbumin, and protein levels at 30 and 100 mg/kg in rats on day 4 however, it has increased their levels at only 100 mg/kg dose of GM on day 8. As a result of impaired glomerular filtration, urinary microalbumin, creatinine, and protein levels have increased and creatinine clearance partially decreased 26. Resatorvid inhibits inflammatory factors (IL-1β, IL-18, etc.) and the TLR4/NF-κB/NLRP3 signaling pathway in vivo. It also inhibits apoptosis and the TLR4/NF-κB pathway in podocytes in vitro 32. ALA (100 mg/kg, oral) treatment decreases oxidative stress and urine protein levels, increases antioxidant enzyme levels and creatinine clearance, and ultimately causes regeneration of kidneys in cisplatin-induced nephrotoxicity 13. In addition, ALA inhibits lipid peroxidation in kidney tissue by reacting with endogenous electrophilic molecules, free radicals and reactive drug metabolites, due to it has nucleophilic and antioxidant properties (Murugavel and Pari 2004). In the current research, no increase in serum creatinine levels suggests that nephrotoxicity is in the early stage however, microalbumin, creatinine, protein levels in the urine were statistically increased compared to the control group in GM group. However, GM treatment caused histopathologically moderate inflammation, tubular damage, and necrosis as reflected in other biomarkers. It shows that serum creatinine and urea levels do not increase in the early stages of nephrotoxicity, but it would be more significantly to use more specific markers such as KIM-1 and NGAL. Moreover, the results were confirmed by histopathological results. On the other hand, resatorvid treatment may have been suppressed inflammatory cytokines and TLR4/NF-κB/NLRP3 signaling pathway. ALA treatment may have been reduced oxidative stress by inducing antioxidant enzymes however, this effect limited for the regeneration of the glomerulus. Therefore, ALA treatment could be partially prevented the increased in urinary protein and creatine levels.
Free radicals formed inflammation, apoptosis and cytotoxicity in renal tissues via NF-κB and p38-MAPK after GM treatment 33. GM significantly increases the renal expression of TLR-4/p38MAPK, and NF-κB, and induces acute kidney injury 34. NRF2 expression is induced due to oxidative stress caused by GM, and apoptosis and acute renal failure develop by induction of caspase-3 expression 35,36. NR4A2 gene expression is increased in order to provide cell hemostasis in pathological conditions such as ischemia and some cancer types 37. ROS/NF-κB/NR4A2 signaling pathway is induced through increased oxidative stress, inflammation and free radicals and apoptosis occurs38. Resatorvid suppresses NF-κB and MAP kinase/AP-1 activity and the expression of some cytokines 39. ALA, a powerful thiol antioxidant, protects cells against oxidative stress and apoptosis by reducing lipid peroxidation and oxidative stress, inhibiting JNK and NF-κB signaling pathways 40. In addition, it protects renal tubular cells against nephrotoxicity by suppressing caspase-9 and caspase-3 41. In the current study, resatorvid therapy may have suppressed partially oxidative stress, free radicals and inflammation and apoptosis by inhibiting ROS/NF-κB/NR4A2 and TLR-4, and by suppressing caspase-3 expression. It may have ensured the survival of renal cells and minimized damage. ALA may have not been able to reduce inflammation sufficiently because it partially suppressed NF-kB expression. Accordingly, it may not have enough effect on IL-18, KIM-1, and NGAL parameters, which are more specific for nephrotoxicity. However, NRF and NR4A2 gene expressions may have been regulated by the antioxidant effects of ALA and increasing cellular antioxidant enzymes. Therefore, it may have reduced apoptosis and renal damage by inhibiting caspase-3 expression.