Protective Effect of Carnosine on Excitable Structures of the Auditory Apparatus in Albino Rats with Acute Acoustic Trauma

The rat as a model for studying noise injury and otoprotection

A major challenge for those studying noise-induced injury pre-clinically is the selection of an animal model. Noise injury models are particularly relevant in an age when people are constantly bombarded by loud noise due to occupation and/or recreation. The rat has been widely used for noise-related morphological, physiological, biochemical, and molecular assessment. Noise exposure resulting in a temporary (TTS) or permanent threshold shift (PTS) yields trauma in peripheral and central auditory related pathways. While the precise nature of noise-related injuries continues to be delineated, both PTS and TTS (with or without hidden hearing loss) result in homeostatic changes implicated in conditions such as tinnitus and hyperacusis. Compared to mice, rats generally tolerate exposure to loud sounds reasonably well, often without exhibiting other physical non-inner ear related symptoms such as death, loss of consciousness, or seizures [Skradski, Clark, Jiang, White, Fu, and Ptacek (2001). Neuron 31, 537-544; Faingold (2002). Hear. Res. 168, 223-237; Firstova, Abaimov, Surina, Poletaeva, Fedotova, and Kovalev (2012). Bull Exp. Biol. Med. 154, 196-198; De Sarro, Russo, Citraro, and Meldrum (2017). Epilepsy Behav. 71, 165-173]. This ability of the rat to thrive following noise exposure permits study of long-term effects. Like the mouse, the rat also offers a well-characterized genome allowing genetic manipulations (i.e., knock-out, viral-based gene expression modulation, and optogenetics). Rat models of noise-related injury also provide valuable information for understanding mechanistic changes to identify therapeutic targets for treatment. This article provides a framework for selection of the rat as a model for noise injury studies.

The therapeutic effect of thymoquinone on acoustic trauma-induced hearing loss in rats

Thymoquinone has antioxidant properties. We hypothesized that thymoquinone may prevent or alleviate hearing loss induced by acoustic trauma. We aimed to study thymoquinone's effect on hearing function with distortion-product otoacoustic emissions and auditory brainstem response. Thirty adult Spraque Dawley rats were randomized into four groups following exposure to acoustic trauma for 4 h. Control group (n = 7) did not receive further treatment. Thymoquinone-20 (n = 8) and Thymoquinone-40 (n = 8) received 20 and 40 mg/kg of intraperitoneal thymoquinone, respectively. Corn-oil group (n = 7) received 1 ml of corn oil intraperitoneally. Hearing function of both ears was tested with distortion-product otoacoustic emission and auditory brainstem response before, and shortly after acoustic trauma, and 96 h following acoustic trauma. Post-trauma signal/noise ratios and wave V amplitude/latencies of all groups were significantly low compared with pre-trauma values, which indicate no preventive effect of thymoquinone. Rats in Thymoquinone-20 showed a significantly improved distortion-product otoacoustic emission and auditory brainstem response results at 4000 frequency and above in post-treatment tests (p < 0.05). Improvement in Thymoquinone-40 at the same frequencies was insignificantly inferior to Thymoquinone-20, yet superior to control and corn-oil groups (p < 0.05). We conclude that thymoquinone may not prevent acoustic trauma-induced hearing loss, however, at 20 mg/kg for 96 h, may repair the damage.

Management of cognitive determinants in senile dementia of Alzheimer's type: therapeutic potential of a novel polyherbal drug product

BACKGROUND AND OBJECTIVE

The enigmatic etiology of neurodegenerative diseases poses a challenge for the development of novel and efficient drugs. The objective of the present study was to evaluate the efficacy of a polyherbal (test) formulation on cognitive functions, inflammatory markers and oxidative stress in healthy elderly as well as senile dementia of Alzheimer's type (SDAT) patients.

METHOD

A randomized double-blind placebo- and active-controlled clinical trial was performed in healthy elderly subjects and SDAT patients with an age range of 60-75 years. The polyherbal test formulation along with a placebo was given to healthy elderly subjects while the SDAT patients received either the test formulation containing extracts of Bacopa monnieri (whole plant), Hippophae rhamnoides (leaves and fruits) and Dioscorea bulbifera (bulbils) at a dose of 500 mg or donepezil drug (Aricept) at a dose of 10 mg, twice daily, for a period of 12 months. After every three months, cognitive functions were assessed by determining the mini mental state examination (MMSE) score, digital symbol substitution (DSS; subtest of the Wechsler Adult Intelligence Scale-Revised), immediate and delayed word recall (digital memory apparatus-Medicaid systems, Chandigarh, India), attention span (Attention Span Apparatus-Medicaid systems, Chandigarh, India), functional activity questionnaire (FAQ) and depression (geriatric depression scale) scores. Further inflammatory markers and level of oxidative stress were analyzed using standard biochemical tests.

RESULTS

The trial was performed in 109 healthy subjects and 123 SDAT patients of whom 97 healthy subjects and 104 SDAT patients completed the study. Administration of the test formulation for a period of 12 months was effective in improving cognitive functions in the SDAT patients, when compared to the donepezil-treated group, as determined by the DSS (38.984 ± 3.016 vs 35.852 ± 4.906, P = 0.0001), word recall immediate (3.594 ± 1.003 vs 2.794 ± 0.593, P < 0.0001) and attention span (4.918 ± 1.239 vs 4.396 ± 0.913, P = 0.0208) scores. A significant improvement in the FAQ (11.873 ± 2.751 vs 9.801 ± 1.458, P < 0.0001) and depression (16.387 ± 2.116 vs 21.006 ± 2.778, P < 0.0001) scores was also observed, whereas no significant differences were observed in the MMSE and word recall delayed scores. The level of inflammation and oxidative stress was markedly reduced in the SDAT patients treated with the test formulation when compared to the donepezil-treated group indicating a likely mechanism of action of the test formulation (homocysteine 30.22 ± 3.87 vs 44.73 ± 7.11 nmol/L, P < 0.0001; C-reactive protein [CRP] 4.751 ± 1.149 vs 5.887 ± 1.049 mg/L, P < 0.0001; tumour necrosis factor alpha [TNF-α] 1139.45 ± 198.87 vs 1598.77 ± 298.52 pg/ml, P < 0.0001; superoxide dismutase [SOD] 1145.92 ± 228.75 vs 1296 ± 225.72 U/g Hb, P = 0.0013; glutathione peroxidase [GPx] 20.78 ± 3.14 vs 25.99 ± 4.11 U/g Hb, P < 0.0001; glutathione [GSH] 9.358 ± 2.139 vs 6.831 ± 1.139 U/g Hb, P < 0.0001; thiobarbituric acid reactive substances [TBARS] 131.62 ± 29.68 vs 176.40 ± 68.11 nmol/g Hb, P < 0.0001). Similarly, when healthy elderly subjects treated with the test formulation for 12 months were compared to the placebo group, a significant (P < 0.001) improvement in cognitive measures (MMSE, DSS, word recall delayed but not immediate, attention span, FAQ and depression scores) and a reduction in inflammation (reduction in homocysteine, CRP, IL-6 and TNF-α levels) and oxidative stress levels (reduction in SOD, GPx and TBARS and increase in GSH) was observed. This indicated a protective effect of the test formulation in managing cognitive decline associated with the ageing process.

CONCLUSION

The results of this study demonstrate the therapeutic potential of this novel polyherbal formulation for the management and treatment of SDAT.

Energy metabolism, proteotoxic stress and age-related dysfunction - protection by carnosine

This review will discuss the relationship between energy metabolism, protein dysfunction and the causation and modulation of age-related proteotoxicity and disease. It is proposed that excessive glycolysis, rather than aerobic (mitochondrial) activity, could be causal to proteotoxic stress and age-related pathology, due to the generation of endogenous glycating metabolites: the deleterious role of methylglyoxal (MG) is emphasized. It is suggested that TOR inhibition, exercise, fasting and increased mitochondrial activity suppress formation of MG (and other deleterious low molecular weight carbonyl compounds) which could control onset and progression of proteostatic dysfunction. Possible mechanisms by which the endogenous dipeptide, carnosine, which, by way of its putative aldehyde-scavenging activity, may control age-related proteotoxicity, cellular dysfunction and pathology, including cancer, are also considered. Whether carnosine could be regarded as a rapamycin mimic is briefly discussed.

Carnosine and its possible roles in nutrition and health

The dipeptide carnosine has been observed to exert antiaging activity at cellular and whole animal levels. This review discusses the possible mechanisms by which carnosine may exert antiaging action and considers whether the dipeptide could be beneficial to humans. Carnosine's possible biological activities include scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS), chelator of zinc and copper ions, and antiglycating and anticross-linking activities. Carnosine's ability to react with deleterious aldehydes such as malondialdehyde, methylglyoxal, hydroxynonenal, and acetaldehyde may also contribute to its protective functions. Physiologically carnosine may help to suppress some secondary complications of diabetes, and the deleterious consequences of ischemic-reperfusion injury, most likely due to antioxidation and carbonyl-scavenging functions. Other, and much more speculative, possible functions of carnosine considered include transglutaminase inhibition, stimulation of proteolysis mediated via effects on proteasome activity or induction of protease and stress-protein gene expression, upregulation of corticosteroid synthesis, stimulation of protein repair, and effects on ADP-ribose metabolism associated with sirtuin and poly-ADP-ribose polymerase (PARP) activities. Evidence for carnosine's possible protective action against secondary diabetic complications, neurodegeneration, cancer, and other age-related pathologies is briefly discussed.

NAC for noise: from the bench top to the clinic

Noise-induced hearing loss (NIHL) is an important etiology of deafness worldwide. Hearing conservation programs are in place and have reduced the prevalence of NIHL, but this disorder is still far too common. Occupational and recreational pursuits expose people to loud noise and ten million persons in the US have some degree of noise-induced hearing impairment. It is estimated that 50 million in the US and 600 million people worldwide are exposed to noise hazards occupationally. Noise deafness is still an important and frequent cause of battlefield injury in the US military. A mainstay of hearing conservation programs is personal mechanical hearing protection devices which are helpful but have inherent limitations. Research has shown that oxidative stress plays an important role in noise-induced cochlear injury resulting in the discovery that a number of antioxidant and cell death inhibiting compounds can ameliorate deafness associated with acoustic trauma. This article reviews one such compound, N-acetylcysteine (NAC), in terms of its efficacy in reducing hearing loss in a variety of animal models of acute acoustic trauma and hypothesizes what its therapeutic mechanisms of action might be based on the known actions of NAC. Early clinical trials with NAC are mentioned.

Pathomorphological peculiarities of damage to hair cells of the organ of corti in experimental sensorineural hearing loss

Pathomorphology of the organ of Corti was studied on models of acute and chronic sensorineural damage to the acoustic analyzer. Peculiarities of hair cell degeneration, necrosis, and apoptosis in the organ were studied by light and scanning electron microscopy. The type of pathomorphological substrate in abnormalities of the organ of Corti depends on the intensity of the destructive exposure, but not on the nature of otopathological factors.