Effect of High Positive Acceleration (+Gz) Environment on Dental Implant Osseointegration:A Preliminary Animal Study

OBJECTIVE

To observe the effect of high positive acceleration (+Gz) environment on dental implant osseointegration in a rabbit model and to investigate its mechanism.

METHODS

Forty-eight New Zealand white rabbits were randomly divided into 6 groups. The rabbit's mandibular incisors were extracted and 1 implant was placed in each socket immediately. After 1 week of rest, the rabbits were exposed to a high +Gz environment, 3 times a week. The rabbits were sacrificed at 3 weeks (2 weeks +Gz exposure), 5 weeks (4 weeks +Gz exposure), and 12 weeks (4 weeks +Gz exposure and 7 weeks normal environment) after surgery, respectively. Specimens were harvested for micro-CT scanning, histological analysis, and real-time polymerase chain reaction examination.

RESULTS

Compared with those in the control group, the mRNA expression levels of bone morphogenetic protein-2 (BMP-2), osteopontin (OPN), and transforming growth factor-β1 (TGF-β1) were significantly lower (P < 0.05), while the mRNA expression level of receptor activator of nuclear factor κB ligand (RANKL) and the RANKL/osteoprotegerin (OPG) ratio were significantly higher (P < 0.05) at 3 weeks; values of bone volume fraction, trabecular number, bone-implant contact (BIC), and TGF-β1 and OPG mRNA expression levels were significantly lower (P < 0.05), and the value of trabecular separation, RANKL mRNA expression level and RANKL/OPG ratio were significantly higher (P < 0.05) at 5 weeks; and the value of BIC was still significantly lower (P < 0.05) at 12 weeks in the experimental group.

CONCLUSION

Early exposure to the high +Gz environment after implant surgery might have an adverse effect on osseointegration, and its mechanism could be related to the inhibition of osteoblast activity and promotion of osteoclast activity.

Effects of positive acceleration (+Gz stress) on liver enzymes, energy metabolism, and liver histology in rats

BACKGROUND

Exposure to high sustained +Gz (head-to-foot inertial load) is known to have harmful effects on pilots’ body in flight. Although clinical data have shown that liver dysfunction occurs in pilots, the precise cause has not been well defined.

AIM

To investigate rat liver function changes in response to repeated +Gz exposure.

METHODS

Ninety male Wistar rats were randomly divided into a blank control group (BC group, n = 30), a +6 Gz/5 min stress group (6GS group, n = 30), and a +10 Gz/5min stress group (10GS group, n = 30). The 6GS and 10GS groups were exposed to +6 Gz and +10 Gz, respectively, in an animal centrifuge. The onset rate of +Gz was 0.5 G/s. The sustained time at peak +Gz was 5 min for each exposure (for 5 exposures, and 5-min intervals between exposures for a total exposure and non-exposure time of 50 min). We assessed liver injury by measuring the portal venous flow volume, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), liver tissue malondialdehyde (MDA), Na⁺-K⁺-ATPase, and changes in liver histology. These parameters were recorded at 0 h, 6 h, and 24 h after repeated +Gz exposures.

RESULTS

After repeated +Gz exposures in the 6GS and the 10GS groups, the velocity and flow signal in the portal vein (PV) were significantly decreased as compared to the BC group at 0 h after exposure. Meanwhile, we found that the PV diameter did not change significantly. However, rats in the 6GS group had a much higher portal venous flow volume than the 10GS group at 0 h after exposure. The 6GS group had significantly lower ALT, AST, and MDA values than the 10GS group 0 h and 6 h post exposure. The Na⁺-K⁺-ATPase activity in the 6GS group was significantly higher than that in the 10GS group 0 h and 6 h post exposure. Hepatocyte injury, determined pathologically, was significantly lower in the 6GS group than in the 10GS group.

CONCLUSION

Repeated +Gz exposures transiently cause hepatocyte injury and affect liver metabolism and morphological structure.

Metabolomics reveals positive acceleration(+Gz)-induced metabolic perturbations and the protective effect of Ginkgo biloba extract in a rat model based on ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

Positive acceleration (+Gz) in the head-to-foot direction generated by modern high-performance fighter jets during flight maneuvers is characterized by high G values and a rapid rate of acceleration, and is often long in duration and a repeated occurrence. The acceleration overload far exceeds the pilot's physiological tolerance limits and causes considerable strain on several organ systems. Despite the importance of monitoring pathophysiological alterations related to +Gz exposure, we lack a complete explanation of the pathophysiology of +Gz exposure. Ginkgo biloba extract (GBE) is a classic traditional Chinese medicine (TCM) that might exert a protective effect against +Gz exposure. However, its mechanism remains unclear. Here, a metabolomics approach based on ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOFMS) was used to characterize +Gz-induced metabolic fluctuations in a rat model and to evaluate the protective effect of GBE. Using partial least-squares discriminant analysis for the classification and selection of biomarkers, eighteen serum metabolites related to +Gz exposure were identified, and were found to primarily involve the fatty acid β-oxidation pathway, glycerophospholipid metabolism, phospholipid metabolism, bile acid metabolism, purine metabolism and lysine metabolism. Taking these potential biomarkers as screening indexes, we found that GBE could reverse the pathological process of +Gz exposure by partially regulating the perturbed fatty acid β-oxidation pathway, glycerophospholipid metabolism, purine metabolism and lysine metabolism. This indicates that UHPLC-Q-TOFMS-based metabolomics provides a powerful tool to reveal serum metabolic fluctuations in response to +Gz exposure and to study the mechanism underlying TCM.

Effect of positive acceleration exposure on gut barrier in rats

With the development of modern high-performance fighter aircrafts, the requirement of acceleration is growing faster and higher, which is far beyond the tolerance of the pilots. In the process of flight, exposure to positive acceleration ( + Gz) is the most important threat to the tissues and organs of pilots. As we all know, the intestinal barrier is one of the significant barriers to prevent the endogenous pathogenic microorganisms and their toxins. This article reviews the impact of + Gz exposure on the gut barrier with regards to the establishment of + Gz models, the detection of related parameters of the gut barrier, and the damage of + Gz to the intestine, with an aim to improve the basic research of the gastrointestinal system in aviation medicine, and the pilot's health and flight safety.

Levels of MDA and SOD in acute gastric mucosal injury in rats exposed to positive acceleration

AIM: To determine the levels of malondialdehyde (MDA) and superoxide dismutase (SOD) in acute gastric mucosal injury in rats exposed to positive acceleration (+Gz), observe the impact of +Gz exposure on gastric mucosal injury, and clarify the role of oxygen free radicals in this process.

METHODS: Thirty male SD rats were randomly divided into three groups: A (ethanol), B (ethanol with +5Gz exposure), and C (ethanol with +10Gz exposure). All rats were intragastrically given ethanol (0.4 mL/100 mg) after 24 h of fasting and water deprivation for 12 h. One hour after ethanol administration, group A did not undergo +Gz, while groups B and C were continuously exposed to +5Gz and +10Gz for 3 minutes, respectively. Immediately after +Gz exposure, gastric tissue samples were taken to observe gastric mucosal injury by light microscopy. The indexes of gastric mucosal injury were calculated, and the contents of MDA and SOD in the gastric mucosa were determined by ELISA.

RESULTS: Gastric mucosal injury was observed in all the groups, and gastric mucosal injury was most severe in group C, followed by groups B and A. Group A had mildest gastric mucosal injury. Group B showed visible gastric mucosal congestion, edema and scattered bleeding spots, and light microscopy revealed acute inflammatory cell infiltration. The indexes of gastric mucosal injury were significantly higher in group B than in group A (naked eye: 23.654 ± 9.678 vs 11.410 ± 3.742; light microscopy: 5.000 ± 1.054 vs 3.800 ± 1.399; both P < 0.05). Group C had heaviest gastric mucosal injury. Diffuse gastric mucosal congestion, edema, erosion and many bleeding spots were visible, and light microscopy revealed disorderly arranged gland structure, interstitial congestion, erosion, and acute inflammatory cell infiltration. The indexes of gastric mucosal injury were significantly higher in group C than in groups A and B (naked eye: 49.080 ± 10.254, light microscopy: 9.400 ± 2.011; all P < 0.05). Compared with group A, the content of MDA in the gastric mucosa did not rise significantly in group B (0.255 ± 0.074 vs 0.235 ± 0.044, P > 0.05); however, MDA content in group C (0.376 ± 0.084) was significantly higher than those in groups A and B (both P < 0.05). The content of SOD in the gastric mucosa was significantly lower in group C than in groups A and B (8.852 ± 1.001 vs 10.000 ± 1.067, 10.694 ± 0.965, P < 0.05), although no significant difference was observed between the latter two groups (P > 0.05).

CONCLUSION: +Gz exposure aggravates acute gastric mucosal injury in rats possibly by altering the contents of MDA and SOD in gastric tissue.