Dose related effects of doxycycline on the glycation/lipoxydation-based structural and functional changes in thoracic aorta induced by restraint stress in rats

Doxycycline inhibits matrix metalloproteinase (MMP) enzymes. MMPs are effective enzymes that play role in some diseases and situations and cause degradation of certain proteins in extracellular matrix. On the other hand, doxycycline decreases systemic and vascular oxidative stress. Doxycycline also prevents non-enzymatic glycation of high blood glucose with proteins, lypoproteins and/or nucleic acids to result in a decrease in glycation end products (AGE; Advanced Glycation End-products). Carboxymethyl lysine (CML) is one of the common end products of AGE and Advanced Lipoperoxidation End-products (ALE) pathways. CML production is known to associate with diabetes, aging, hyperlipidemia, smoking, hypertension, inflammation and disease like Alzheimer. Doxycycline protects cell against stress and apoptosis. Stress hormones are hyperglycemic hormones. Hyperglysemia triggers oxidative stress. As all of the biochemical stresses, behavioral stress also leads to oxidant damage. Restrain stress causes oxidant damage as a result of dislipidemia, defect in carbonhydrate metabolism, decrease in nitric oxide (NO) production, atherosclerosis and imbalance in antioxidant state. It is expected from chronic stress to increases lipid peroxidation by increasing oxidative stress and to causes protein glycation via elevating blood glucose level to resuld in increased AGE and ALE levels. Thus doxycycline is expected to be protective against oxidative damage and protein glycation in rats exposed to restrain stress. This study was performed in 48 male Sprague Dawley rats to investigate whether behavioral stress results in the accumulation of AGE and ALE in the cardiovascular system by structurel and functional and also to examine that whether doxycycline exerts protective effects against this process. Mean body weights of the rats, blood glucose and HbA1c levels were evaluated. Isolated thoracic aort preperations were evaluated in the isolated organ bath system for endothelium - and smooth muscle - related functions. MMP activities were determined by gelatin zymography. As an indicator of oxidant/antioxidant status, glutation and malondialdehyde levels were determined. The presence of AGE/ALE, apoptosis and angiogenesis were evaluated by immunohistochemical staining. In order to determine effects of applications on the behaviour, Open Field and Elevated Plus Maze tests were used. Chronic stress caused body weight loss. Acute stress increased blood glucose levels. However HbA1c levels did not change. Chronic stress, caused not only endothelial damage on rat isolated thoracic aorta preparations but also lead to augmentation of the relaxant mechanism(s) in the smoot muscle. Doxycycline was found to be protective at 15 mg/kg/day dose against this effect but to cause stress-like effects at the dose of 30 mg/kg/day seen. Low dose doxycycline extented anti-oxidant but high dose doxycycline showed oxidant effects. Chronic stress increased proMMP-2 and MMP-9 activities. Both doses of doxycycline inhibited MMP-2 activity. By the help of behavioural findings, stress seemed to cause tendency to anxiety and doxycycline exented anxiolytic-like effects at 15 mg/kg/day dose. Key words: Doxycycline, restraint stress, aorta, carboxymethyl lysine, matrix metalloproteinase.