Advanced age is associated with an increased risk of vascular morbidity, attributable in part to impairments in new blood vessel formation. Mesenchymal stem cells (MSCs) have previously been shown to play an important role in neovascularization and deficiencies in these cells have been described in aged patients. Here we utilize single cell transcriptional analysis to determine the effect of aging on MSC population dynamics. We identify an age-related depletion of a subpopulation of MSCs characterized by a pro-vascular transcriptional profile. Supporting this finding, we demonstrate that aged MSCs are also significantly compromised in their ability to support vascular network formation in vitro and in vivo. Finally, aged MSCs are unable to rescue age-associated impairments in cutaneous wound healing. Taken together, these data suggest that age-related changes in MSC population dynamics result in impaired therapeutic potential of aged progenitor cells. These findings have critical implications for therapeutic cell source decisions (autologous versus allogeneic) and indicate the necessity of strategies to improve functionality of aged MSCs.

Background No consensus exists regarding the optimal strategy for perioperative thromboprophylaxis in high-risk microsurgical populations. We present our experience with lower extremity free tissue transfer (FTT) in thrombophilic patients and compare outcomes between non-stratified and risk-stratified anticoagulation protocols. Methods Between January 2013 and December 2017, 57 patients with documented thrombophilia underwent FTT for non-traumatic, lower extremity reconstruction by a single surgeon. Patients were divided into two cohorts based on the introduction of a novel, risk-stratified algorithm for perioperative anticoagulation in July 2015. Demographic data, chemoprophylaxis profiles, flap outcomes, and complications were retrospectively compared across time periods. Results Fifty-seven free flaps were performed in hypercoagulable patients treated with non-stratified (n = 27) or risk-stratified (n = 30) thromboprophylaxis. Patients in the risk-stratified cohort received intravenous heparin more often than non-stratified controls (73 vs. 15%, p < 0.001). Lower rates of total (3 vs. 19%, p = 0.06) and partial (10 vs. 37%, p = 0.025) flap loss were observed among risk-stratified patients, paralleling a significant reduction in the prevalence of postoperative thrombotic events (1.2 vs. 12.3%, p = 0.004). While therapeutic versus low-dose heparin infusion was associated with improved flap survival following intraoperative microvascular compromise (86 vs. 25%, p = 0.04), salvage rates in the setting of postoperative thrombosis remained 0%, regardless of protocol. On multivariate analysis, recipient-vessel calcification (odds ratio [OR]: 16.7, p = 0.02) and anastomotic revision (OR, 3.3; p = 0.04) were independently associated with total flap failure. Conclusion Selective therapeutic anticoagulation may improve microsurgical outcomes in high-risk patients with thrombophilia. Our findings highlight the importance of meticulous technique and recipient-vessel selection as critical determinants of flap success in this population.

One of the major intracellular barriers to non-viral gene delivery is efficient endosomal escape. The incorporation of histidine residues into polymeric constructs has been found to increase endosomal escape via the proton sponge effect. Statistical and diblock copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA), oligolysine, and oligohistidine were synthesized via reversible-addition fragmentation chain transfer (RAFT) polymerization, and tested for in vitro transfection efficiency, buffering ability, and polyplex uptake mechanism via the use of chemical endocytic inhibitors. Interestingly, histidine-containing statistical and diblock polymers exhibited increased buffer capacity in different endosomal pH ranges. Statistical copolymers transfected better than block copolymers that contained similar amounts of histidine. In addition, only the polymer containing the highest incorporation of oligohistidine residues led to increases in transfection efficiency over the HPMA-oligolysine base polymer. Thus, for these polymer architectures, high histidine incorporation may be required for efficient endosomal escape. Furthermore, uptake studies indicate that non-acidified caveolae-mediated endocytosis may be the primary route of transfection for these copolymers, suggesting that alternative approaches for increasing endosomal escape may be beneficial for enhancing transfection efficiency with these HPMA-oligolysine copolymers.

Optimal management requires a multimodal approach that centers around operative debridement and incorporates the use of adjunctive measures to facilitate the removal of infected tissue, biofilm, and/or senescent cells that impede the progression of normal wound healing.

Functional outcomes scores such as the LEFS demonstrate that patients can obtain an adequate level of functionality for independent community activity after free tissue transfer, although functional improvement diminishes with age.