Testicular toxicity and sperm quality following copper exposure in Wistar albino rats: ameliorative potentials of L-carnitine

Copper is a persistent toxic and bio-accumulative heavy metal of global concern. Continuous exposure of copper compounds of different origin is the most common form of copper poisoning and in turn adversely altering testis morphology and function and affecting sperm quality. L-carnitine has a vital role in the spermatogenesis, physiology of sperm, sperm production and quality. This study was designed to examine whether the detrimental effects of long-term copper consumption on sperm quality and testis function of Wistar albino rat could be prevented by L-carnitine therapy. The parameters included were sperm quality (concentration, viability, motility, and morphology), histopathology, serum aspartate aminotransferase (AST), serum alanine aminotransferase (ALT), serum urea, serum creatinine, serum testosterone and testis antioxidant enzyme levels (superoxide dismutase and glutathione-S-transferase), and biomarkers of oxidative stress (lipid peroxidation and expression of heat shock protein 70 in testis). Three-month-old male Wistar rats (n = 30) were divided into six groups as group 1 (G1, 0.9% saline control), group 2 (G2, CuSO4 200 mg/kg dissolved in 0.9% saline water), groups 3 and 4 (G3 and G4, L-carnitine 50 and 100 mg/kg dissolved in 0.9% saline water, respectively), and groups 5 and 6 (G5 and G6, CuSO₄ 200 mg/kg plus L-carnitine, 50 and 100 mg/kg dissolved in 0.9% saline water, respectively). Doses of copper (200 mg/kg) and L-carnitine (50 and 100 mg/kg) alone and in combinations along with untreated control were administered orally for 30 days. The following morphological, physiological, and biochemical alterations were observed due to chronic exposure of copper (200 mg/kg) to rats in comparison with the untreated control: (1) generation of oxidative stress through rise in testis lipid peroxidation (12.21 vs 3.5 nmol MDA equivalents/mg protein) and upregulation of heat shock protein (overexpression of HSP70 in testis), (2) liver and kidney dysfunction [elevation in serum ALT (81.65 vs 48.08 IU/L), AST (156.82 vs 88.25 IU/L), ALP (230.54 vs 148.16 IU/L), urea (12.65 vs 7.45 mmol/L), and creatinine (80.61 vs 48.25 μmol/L) levels], (3) significant decrease in body (99.64 vs 106.09 g) and organ weights (liver—3.48 vs 4.99 g; kidney—429.29 vs 474.78 mg; testes—0.58 vs 0.96 g), (4) imbalance in hormonal and antioxidant enzyme concentrations [significant decline in serum testosterone (0.778 vs 3.226 ng/mL), superoxide dismutase (3.07 vs 8.55 μmol/mg protein), and glutathione-S-transferase (59.28 vs 115.58 nmol/mg protein) levels], (5) severe alterations in the testis histomorphology [sloughed cells (90.65%, score 4 vs 15.65%, score 1), vacuolization (85.95%, score 4 vs 11.45%, score 1), cellular debris along with degenerative characteristics, accentuated germ cell depletion in the seminiferous epithelium, severe damage of spermatogonia and Sertoli cells (73.56%, score 3 vs 0%, score 1)], (6) suppression of spermatogenic process [hypospermatogenesis (low Jhonsen testicular biopsy score 4 vs 9.5), decrease in tubules size (283.75 vs 321.25 μm in diameter), and no. of germ cells (81.8 vs 148.7/100 tubules), Leydig cells (5.2 vs 36.65/100 tubules), and Sertoli cells (8.1 vs 13.5/100 tubules)], (7) sperm transit time was shorter in caput and cauda and ensued in incomplete spermatogenic process and formation of immature sperm leading to infertility, (8) sperm quality was affected significantly [decreased daily sperm production (13.21 vs 26.9 × 10⁶ sperms/mL), sperm count (96.12 vs 154.25 × 10⁶/g), sperm viability (26.88 vs 91.65%), and sperm motility (38.48 vs 64.36%)], and (9) increase of head (32.82 vs 2.01%) and tail (14.85 vs 0.14%) morphologic abnormalities and DNA fragmentation index (88.37 vs 11.11%). Oxidative stress and their related events appear to be a potential mechanism involved in copper testicular toxicity and L-carnitine supplementation significantly modulated the possible adverse effects of copper on seminiferous tubules damage, testes function, spermatogenesis, and sperm quality. It was validated that the use of L-carnitine at doses of 50 and 100 mg/kg protects against copper-induced testicular tissue damage and acts as a therapeutic agent for copper heavy metal toxicity.