Repositioning Linagliptin for the Mitigation of Cadmium-Induced Testicular Dysfunction in Rats: Targeting HMGB1/TLR4/NLRP3 Axis and Autophagy

Abstract

Cadmium, a ubiquitous environmental toxicant, disrupts testicular function and fertility. The dipeptidyl peptidase-4 inhibitor linagliptin has shown pronounced anti-inflammatory and anti-apoptotic features; however, its effects against cadmium-evoked testicular impairment have not been examined. Herein, the present study investigated targeting inflammation, apoptosis, and autophagy by linagliptin for potential modulation of cadmium-induced testicular dysfunction in rats. After 60 days of cadmium chloride administration (5 mg/kg/day, by gavage), testes, epididymis, and blood were collected for analysis. The present findings revealed that linagliptin improved the histopathological lesions, including spermatogenesis impairment and germ cell loss. Moreover, it improved sperm count/motility and serum testosterone. The favorable effects of linagliptin were mediated by curbing testicular inflammation seen by dampening of HMGB1/TLR4 pathway and associated lowering of nuclear NF-κBp65. In tandem, linagliptin suppressed the activation of NLRP3 inflammasome/caspase 1 axis with consequent lowering of the pro-inflammatory IL-1β and IL-18. Jointly, linagliptin attenuated testicular apoptotic responses seen by Bax downregulation, Bcl-2 upregulation, and suppressed caspase 3 activity. With respect to autophagy, linagliptin enhanced the testicular autophagy flux seen by lowered accumulation of p62 SQSTM1 alongside upregulation of Beclin 1. The observed autophagy stimulation was associated with elevated AMPK (Ser487) phosphorylation and lowered mTOR (Ser2448) phosphorylation, indicating AMPK/mTOR pathway activation. In conclusion, inhibition of testicular HMGB1/TLR4/NLRP3 pro-inflammatory axis and apoptosis alongside stimulation of autophagy were implicated in the favorable actions of linagliptin against cadmium-triggered testicular impairment.

Linagliptin, a DPP‐4 inhibitor, activates AMPK/FOXO3a and suppresses NFκB to mitigate the debilitating effects of diethylnitrosamine exposure in rat liver: Novel mechanistic insights

“…They ascribed stimulation of autophagic mechanisms to the documented activation of the AMPK/mTOR pathway. 33,61 Regarding the role of autophagy in carcinogenesis, interestingly, autophagy as previously stated, plays two contradicting tumor-suppressive or tumor-promoting roles depending mainly on the stage of neoplasm, tumor genetics, immune response, and nutritional factors. 62,63 During the early stages of oncogenesis, autophagy acts as a tumor suppressor via inhibiting aberrant cellular proliferation, invasion, and metastasis that could be attributed to the crucial role of autophagy in maintaining genomic stability, preventing intracellular aggregation of oncoproteins and elimination of defective organelles.…”

“…Moreover, the reported Beclin‐1 upregulation and diminished p62 accumulation in the current work coincide well with previous studies that demonstrated induction of autophagy following LNGTN treatment in in vivo animal models of neurodegeneration and testicular damage. They ascribed stimulation of autophagic mechanisms to the documented activation of the AMPK/mTOR pathway 33,61 …”

“…LNGTN demonstrated remarkable anti‐inflammatory 28 as well as anti‐oxidative properties in previous in vivo studies suggesting its beneficial role in modulating a range of health disorders including neurodegeneration, 29 colitis, 30 hepatic steatosis, and hepatic fibrosis 31 . In this respect, several molecular mechanisms were postulated to explain the observed effects including activation of 5′ AMP‐activated protein kinase (AMPK) axis 32 in addition to the previously reported autophagy induction through Beclin‐1‐dependent mechanisms 33 . However, LNGTN's ability to induce FOXO3a activation subsequent to AMPK activation has not been yet elucidated.…”

“…31 In this respect, several molecular mechanisms were postulated to explain the observed effects including activation of 5′ AMP-activated protein kinase (AMPK) axis 32 in addition to the previously reported autophagy induction through Beclin-1-dependent mechanisms. 33 However, LNGTN's ability to induce FOXO3a activation subsequent to AMPK activation has not been yet elucidated. This research question will illuminate the feasibility of repositioning LNGTN for cancer treatment potentially through activation of AMPK and FOXO3a cascades.…”

Development of sensitive spectrofluorometric approach based on formation of pyrrolidone derivative for determination of linagliptin through condensation reaction with ninhydrin and phenylacetaldehyde: Application to content uniformity and real plasma

“…LNG is used to treat other conditions as well, including polycystic ovary syndrome [2] and more recently, testicular dysfunction brought on by cadmium [3]. Negative effects of LNG include irritation of the nose and throat, while dangerous effects include pancreatitis, angioedema, and arthritic pain [3].…”