Platelet-rich plasma (PRP) therapy is a recently developed technique that uses a concentrated portion of autologous blood to try to improve and accelerate the healing of various tissues. There is a considerable interest in using these PRP products for the treatment used in bone deficiency healing. Because PRP products are safe and easy to prepare and administer, there has been increased attention toward using PRP in numerous clinical settings. The benefits of PRP therapy appear to be promising, and many investigators are exploring the ways in which this therapy can be used in the clinical setting. At present, the molecular mechanisms of bone defect repair studies have focused on three aspects of the inflammatory cytokines, growth factors and angiogenic factors. The role of PRP works mainly through these three aspects of bone repair. The purpose of this paper is to review the current evidence on the mechanism of the effect of PRP in bone deficiency healing.

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Previous studies in our laboratory have shown that mixed lineage kinase 3 (MLK3) can be activated following global ischemia. In addition, other laboratories have reported that the activation of MLK3 may be linked to the accumulation of free radicals. However, the mechanism of MLK3 activation remains incompletely understood. We report here that MLK3, overexpressed in HEK293 cells, is S-nitrosylated (forming SNO-MLK3) via a reaction with S-nitrosoglutathione, an exogenous nitric oxide (NO) donor, at one critical cysteine residue (Cys-688). We further show that the S-nitrosylation of MLK3 contributes to its dimerization and activation. We also investigated whether the activation of MLK3 is associated with S-nitrosylation following rat brain ischemia/reperfusion. Our results show that the administration of 7-nitroindazole, an inhibitor of neuronal NO synthase (nNOS), or nNOS antisense oligodeoxynucleotides diminished the S-nitrosylation of MLK3 and inhibited its activation induced by cerebral ischemia/reperfusion. In contrast, 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (an inhibitor of inducible NO synthase) or nNOS missense oligodeoxynucleotides did not affect the S-nitrosylation of MLK3. In addition, treatment with sodium nitroprusside (an exogenous NO donor) and S-nitrosoglutathione or MK801, an antagonist of the N-methyl-D-aspartate receptor, also diminished the S-nitrosylation and activation of MLK3 induced by cerebral ischemia/reperfusion. The activation of MLK3 facilitated its downstream protein kinase kinase 4/7 (MKK4/7)-JNK signaling module and both nuclear and non-nuclear apoptosis pathways. These data suggest that the activation of MLK3 during the early stages of ischemia/reperfusion is modulated by S-nitrosylation and provides a potential new approach for stroke therapy whereby the post-translational modification machinery is targeted.As a free radical, NO is an endogenous cell signaling molecule involved in the regulation of many physiological and pathophysiological processes (1). NO and NO-related compounds exert both protective and cytotoxic effects, depending on the cellular context and the nature of the NO group. The multifaceted actions of the NO group can be classified into two categories, cGMP-dependent and cGMP-independent. The cGMP-dependent actions play critical roles in a variety of physiological processes, including NO-mediated vasodilation. In contrast, cGMP-independent, nitrosative protein modifications are postulated to be involved in both physiological and pathological responses (2).Endogenous NO is synthesized from L-arginine by NO synthase (NOS) and is associated with S-nitrosylation. S-Nitrosylation, the modification of the covalent attachment to the side chain of cysteine by an NO group, is considered as an important post-translational modification that has profound effects on protein function (3).

Our laboratory once reported that neuronal nitric oxide synthase (nNOS) S-nitrosylation was decreased in rat hippocampus during cerebral ischemia-reperfusion, but the underlying mechanism was unclear. In this study, we show that nNOS activity is dynamically regulated by S-nitrosylation. We found that overexpressed nNOS in HEK293 (human embryonic kidney) cells could be S-nitrosylated by exogenous NO donor GSNO and which is associated with the enzyme activity decrease. Cys331, one of the zinc-tetrathiolate cysteines, was identified as the key site of nNOS S-nitrosylation. In addition, we also found that nNOS is highly S-nitrosylated in resting rat hippocampal neurons and the enzyme undergos denitrosylation during the process of rat brain ischemia/reperfusion. Intrestingly, the process of nNOS denitrosylation is coupling with the decrease of nNOS phosphorylation at Ser847, a site associated with nNOS activation. Further more, we document that nNOS denitrosylation could be suppressed by pretreatment of neurons with MK801, an antagonist of NMDAR, GSNO, EGTA, BAPTA, W-7, an inhibitor of calmodulin as well as TrxR1 antisense oligonucleotide (AS-ODN) respectively. Taken together, our data demonstrate that the denitrosylation of nNOS induced by calcium ion influx is a NMDAR-dependent process during the early stage of ischemia/reperfusion, which is majorly mediated by thioredoxin-1 (Trx1) system. nNOS dephosphorylation may be induced by the enzyme denitrosylation, which suggest that S-nitrosylation/denitrosylation of nNOS may be an important mechanism in regulating the enzyme activity.

Objectives: To evaluate the therapeutic outcomes with Kalix II subtalar arthroereisis in sinus tarsi for juvenile flexible flatfoot.Methods: A retrospective analysis of the data of 20 juveniles with symptomatic flexible flatfoot (27 feet) who underwent the Kalix II implant procedure from January 2008 to September 2012 was performed. The pain during daily activities was assessed and followed up by use of a standard 10-point visual analog scale (VAS), and function was evaluated using the American Orthopaedic Foot and Ankle Society (AOFAS) ankle and hindfoot scoring system, and anteroposterior talar-first metatarsal angle, lateral talar-first metatarsal angle, calcaneal pitch angle, and talar declination angle at X-ray film were measured to assess the therapeutic outcomes. Patients were asked to grade the result of the procedure as excellent, good, fair, or poor at latest follow-up. The data was expressed as mean AE standard deviation (SD). A paired Student's t-test was used for comparisons of the preoperative and postoperative angular measurements for each foot, VAS scores, and AOFAS scores. In all tests, P < 0.05 was considered statistically significant.Results: The mean age of the patients was 12.1 years (range, 7-16 years), and 16 left feet and 11 right feet were involved. All patients finished the follow-up with a mean period of 28.1 months (range, 23-60 months). Eleven feet were treated with subtalar arthroereisis combined with reconstruction of the end point of the posterior tibialis tendon after dissection of the accessory scaphoid. The subtalar arthroereisis device displaced in 1 foot due to a fall from the inversion position 3 months after surgery, and was replaced by a new device after the failure of conservative treatment. The mean VAS score decreased from 5.6 AE 0.5 preoperatively to 1.2 AE 0.2 (P < 0.001), and the mean AOFAS hindfoot and ankle score improved from 71.1 AE 6.1 preoperatively to 88.1 AE 6.3 (P < 0.001). Differences between preoperative and postoperative measurements for each radiographic variable were statistically significant (P < 0.001).Comparison of radiographic measurements showed that the anteroposterior talar-first metatarsal (Meary) angle decreased by a mean of 12.8 AE 1.5 , the lateral talar-first metatarsal (Meary) angle decreased by a mean of 15.4 AE 1.3 , the calcaneal pitch angle increased by a mean of −2.1 AE 0.7 , and the talar declination angle decreased by a mean of 17.9 AE 2.8 . Overall, 12 patients rated the result as excellent, 6 as good, and 2 as fair. Conclusion:The application of Kalix II in subtalar arthroereisis combined with dissection of accessory scaphoid and reconstruction of posterior tibialis tendon is an effective therapy for flexible juvenile flatfoot.