الفهرس 
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Abstract
Ginkgo biloba has been exist on earth since 200 million years and is considered as a “living fossil”. A standardized extract of Ginkgo biloba leaves EGb 761 is a popular dietary supplement - one of the most sold medicinal plants in the world - taken by the general public to enhance mental focus and by the elderly to delay onset of age-related loss of cognitive function. Ginkgo biloba extract has been therapeutically used for several decades to increase peripheral and cerebral blood flow as well as for the treatment of dementia. Substantial evidence indicates that EGb 761 has a blood properties enhancement and a neuroprotective effects. But, the actual modes of action exerted by the extract on the biological molecules are, unfortunately, poorly understood. In addition, there are no ultimate standards or guidelines regulating the exposure limits imposed by of EGb761.
The aim of this study is to investigate the effect of prolonged administration, up to 10 weeks, of EGb 761 on the RBC’s and on the mammalian retina. This is to reveal the actual mode of action exerted by EGb 761 on these different biological tissues. Also, to set guidelines that regulate the optimal duration of EGb administration for hematological purposes as well as for ophthalmic applications.
Two main groups were involved in this study: Fifty healthy mature Rex rabbits from the same colony weighing from 2:2.5 kg and fifteen healthy volunteer persons with age range 25 : 45 years divided as follows:
First group (50 Rex rabbits): were divided into two subgroups: normal group (n = 10) kept untreated and EGb 761-administrated group (n = 40) received orally through the stomach tube a dose of 40 mg/day for ten weeks.
Second group (15 volunteers): were also classified into 2 subgroups: normal group (n = 5) kept untreated and EGb 761 administered group (n = 10) received orally a dose of 120 mg/day for ten weeks. Each week, blood samples were collected from the groups and the rabbit retinal tissues were taken.
The conformational characteristics of the RBC’s and retina samples are presented and discussed by studying osmotic fragility properties, FTIR spectra and hematological properties for both subjects: human and rabbit.
Osmotic fragility test, RBCs FTIR spectroscopy and complete blood count (C.B.C.) were obtained as hematological analysis for blood samples in addition to FTIR spectroscopy for retinal tissue.
The experimental results show significant decrease in the osmotic fragility C50% - which is the NaCl concentration at which 50% of erythrocytes were hemolyzed - of the RBC’s membrane associated with an increase in the peak width in W-4 group in both rabbits group where (C50%=34.6±2.5%, W=3.9±0.8%) comparing with the normal (C50%=60.6±4.3%, W=10.5±1.8%) and human group where (C50%=28.9±1.8%, W=11.9±0.7%) comparing with the normal (C50%=53.1±3.1%, W= 8.7±1.6%). However, C.B.C. results show no significant changes in analyzed parameters in both groups.
In addition, FTIR spectroscopy results for RBCs show an increase in the detected band in the NH-OH region in the interval 4:8 weeks for the rabbit RBC’s and in the interval 4:5 weeks for human RBC’s due to a splitting in the bands in addition of detection of strNHasym mode. No significant changes detected in C-H region of RBC’s of both subjects. strCOC vibrational band has been detected in the finger print region of the RBC’s in the interval 2:5 weeks at average wavenumber u=1038±2 cm-1 and average bandwidth BW=31±10 cm-1 in rabbit and in the interval 2:8 weeks at average (u=1043±9, BW=40±8cm-1) in human. In addition to the detection of CHoop vibrational band only in W-4 in both subjects where it found at average (u=989±2, BW=43±3 cm-1) in rabbits group and at average (u=991±2, BW=20±2 cm-1) in human group. Amide I region shows maximum effect in the interval 4:5 weeks in both subjects where there was a significant decrease in a-helix content associated with an increase in b-turn content of the protein secondary structure of the RBC’s membrane on the area. There were no changes in the analyzed hematological parameters in both subjects. The FTIR results of the rabbit retina shows significant changes all over the administration period in NH-OH, finger print and amid I regions with a maximum effect in the interval 5:8 weeks which C-H region is unaffected by the administrations.
These results demonstrate that EGb 761 administration was associated with different beneficial effects in biological tissues where it increases RBC’s membrane resistance to osmotic lysis in hypotonic solution and increasing membrane elasticity after four weeks of administration. Also, it revel the actual made of action exerted by EGb 761 on mammalian RBC’s and retina by describing its effect in terms of molecule conformational changes ascribed by FTIR spectra. According to there results we suggest that the optimum administration period of EGb761 (40 mg/day for rabbit and 120 mg/day for adult human) for hematological applications ranges from 2 to 8 weeks with the maximum effect after 4 weeks of administration while the optimum administration period of EGb (40 mg/day) for ophthalmic applications that targeting the retina ranges from 5 to 8 weeks and that three weeks rest from EGb761 in enough to start a next administration period.