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HygY is a SPASM/twitch radical SAM enzyme hypothesized to catalyze the C2′-epimerization of galacamine during the biosynthesis of hygromycin B. This activity is confirmed via biochemical and structural analysis of the derivatized reaction products using chemically synthesized deuterated substrate, high-resolution mass spectrometry and 1H NMR. Electron paramagnetic resonance spectroscopy of the reduced enzyme is consistent with ligation of two [Fe4S4] clusters characteristic of the twitch radical SAM subgroup. HygY catalyzed epimerization proceeds with incorporation of a single solvent Hydron into the talamine product facilitated by the catalytic cysteine-183 residue. Mutation of this cysteine to alanine converts HygY from a C2′-epimerase to an C2′-dehydrogenase with comparable activity. The SPASM/twitch radical SAM enzymes often serve as anaerobic oxidases making the redox-neutral epimerases in this class rather interesting. The discovery of latent dehydrogenase activity in a twitch epimerase may therefore offer new insights into the mechanistic features that distinguish oxidative versus redox-neutral SPASM/twitch enzymes and lead to the evolution of new enzyme activities.

CRISPR-Cas systems provide bacteria and archaea with sequence-specific protection against invading mobile genetic elements. In the presence of divalent metal ions, Cas9 and Cas12a (formerly Cpf1) proteins target and cleave DNA that is complementary to a cognate guide RNA. The recognition of a protospacer adjacent motif (PAM) sequence in the target DNA by Cas9 and Cas12a is essential for cleavage. This RNA-guided DNA targeting is widely used for gene-editing methods. Here, we show that Francisella tularensis novicida(Fno) Cas12a, FnoCas9, and Streptococcus pyogenesCas9 (SpyCas9) cleave DNA without a guide RNA in the presence of Mn2+ions. Substrate requirements for the RNA-independent activity vary. FnoCas9 preferentially nicks double-stranded plasmid, SpyCas9 degrades single-stranded plasmid, and FnoCas12a cleaves both substrates. These observations suggest that the identities and levels of intracellular metals, along with the Cas9/Cas12a ortholog employed, could have significant impacts in genome editing applications.

Although percutaneous biopsies are considered to be the gold standard in diagnosing pancreas graft rejection, they are not performed routinely because of their association with severe complications. On the other hand, correct diagnosis of rejection is essential but may be difficult in cases of enteric drainage, particularly in patients with a pancreas transplant alone or a pancreas after kidney transplant.

Risk factors for delayed graft function (DGF) in pancreas transplantation (PTx) and its implications on graft survival are poorly defined.

The aim of our study was to examine whether an extensive surveillance protocol will promote early diagnosis and improved survival in patients with de novocancer following liver transplantation (LT). Of 779 consecutive LT recipients, 96 (12.3%) developed 105 malignancies. The cumulative risk for the development of de novocancer was 10%, 24%, 32% and 42% at 5, 10, 15 and 20 years after LT, respectively. The most frequent tumor types were skin (17%), lung (16%), oropharyngeal (11%) and prostate cancer (11%). The overall standard incidence ratio as compared to that of the general population was 1.9 (95% CI: 1.5–2.3). The median survival of patients with de novonon-skin cancers was 3.1 years after diagnosis. Only patients with skin cancers and solid tumors, diagnosed at early stages, showed an excellent outcome. After introducing an intensified surveillance protocol, the detection rate of de novocancers increased from 4.9% to 13% and more de novomalignancies were diagnosed in earlier stages. For non-skin cancers, the median tumor-related survival significantly improved from 1.2 to 3.3 years as well as the median overall survival post-LT. This study indicates that an extensive tumor surveillance program is highly recommendable in LT recipients.

Cold ischemia time and preservation of organs are limited by I/R injury leading to primary nonfunction of the graft. In a rat heart transplant model, we compared cardioplegic St Thomas (ST) to histidine-tryptophan-ketoglutarate (HTK) and University of Wisconsin preservation solutions in terms of contractile function, and mitochondrial respiratory and enzymatic defects after prolonged cold ischemia and reperfusion. Contractile function was scored after transplantation and 24 h of reperfusion. Mitochondrial function was investigated by high-resolution respirometry of permeabilized myocardial fibers. Graft performance in terms of contractile function declined with the duration of cold storage. Recovery was significantly improved after 10 h of cold storage in HTK compared with ST (cardiac scores, 3.3 ± 0.5 and 1.8 ± 0.8, respectively). Tissue lactate dehydrogenase was better preserved in HTK than ST. Increase of tissue water content (edema) was less pronounced in HTK than ST (3.33 ± 0.14 and 3.73 ± 0.21 mg/mg dry weight, respectively). Similar cardiac scores (2.6 ± 0.9 and 2.9 ± 1.2, respectively) and mitochondrial respiratory parameters were obtained after preservation in HTK and University of Wisconsin. Decline in contractile function of individual grafts correlated well with loss of mitochondrial respiratory capacity, whereas citrate synthase activity remained largely preserved, indicating specific damage of respiratory complexes. Our data provide evidence for the superiority of preservation solutions versus a cardioplegic solution for prolonged cold storage of the heart. The correlation of graft performance and mitochondrial function indicates the potential of high-resolution respirometry for quantitative assessment of myocardial injury upon cold I/R, providing a basis for diagnostic approaches and evaluation of improved preservation solutions for heart transplantation.

Long-term survival after solid-organ transplantation is hampered by chronic changes in the arteries of the grafts, called chronic allograft vasculopathy (CAV). The lesions consist mainly of proliferating vascular smooth muscle cells that cause narrowing of the vessels; these lesions can develop within a few months. There is no effective treatment to prevent CAV. We previously noted that the pharmacological inhibition of p38 mitogen-activated protein kinase (MAPK) suppresses the proliferation of vascular smooth muscle cells. We hypothesized that in vivo inhibition of p38 MAPK in mice bearing allogeneic aortic allografts would prevent CAV. We here report that blockade of p38 MAPK, a signaling molecule involved in cell division, apoptosis, and cell death, markedly suppresses CAV. Given recent data indicating that inhibition of p38 MAPK is a promising approach for the treatment of autoimmune diseases plus our present findings, p38 MAPK blockade for CAV seems a reasonable approach to consider for clinical application.

Chronic rejection (CR) with graft vasculopathy is recognized as a major cause of graft loss over time. Sinomenine (SN) has anti-inflammatory, antirheumatic, and immunomodulatory effects. Previously, we demonstrated antimacrophage and anti-T cell effects of SN in acute rejection. In the current study, we investigated the effect of SN in a rat cardiac allograft model of CR.

Heart transplantation causes complex changes in the biological homeostasis of the graft. Current knowledge is restricted to a few genes and regulation of certain factors involved in ischemia-reperfusion (I/R) injury. Efficient strategies to prevent I/R injury, however, require a better understanding of its mechanisms. Using cDNA microarrays, we investigated gene expression profiles of murine cardiac isografts.

Although the value of duodenal histology as a means to diagnose acute rejection in pancreaticoduodenal allografts has been validated, it is not known how the duodenum responds to antirejection treatment in comparison with the pancreas.

Abstract: We have studied the accommodation (survival of an organ graft in the presence of anti‐graft antibodies and complement) of heterotopic Golden Syrian hamster heart xenografts transplanted to Lewis rat recipients. The rats were treated with cyclosporine A (15 mg/kg/day i.m.) for the duration of the experiment and for 11 days with cobra venom factor. This regimen resulted in long‐term xenograft survival in approximately 75% of cases. Analysis of endothelial cells (and smooth muscle cells) in long‐surviving grafts showed expression of “protective” genes: A20, Bcl‐xL, Bcl‐2, and hemoxygenase, which we define as genes that prevent endothelial cells from undergoing responses that might lead to graft rejection. Surviving xenografts were also associated with intragraft Th2 cytokine expression. Rejected grafts did not express the protective genes and had a Thl pattern of cytokine expression. These studies indicate a potential mechanism linking molecular and cellular responses to development of xenograft accommodation.

The use of anti-B-cell and T-cell immunosuppressive agents leads to only a few weeks' survival of mouse-to-rat cardiac xenografts.

Organ xenografts under certain circumstances survive in the presence of anti-graft antibodies and complement, a situation referred to as “accommodation.” We find that the endothelial cells (ECs) in hamster hearts that accommodate themselves in rats express genes, such as A20and bcl-2, that in vitroprotect ECs from apoptosis and prevent upregulation in those cells of proinflammatory genes such as cytokines, procoagulant and adhesion molecules. Hearts that are rejected do not express these genes. In addition, vessels of rejected hearts show florid transplant arteriosclerosis whereas those of accommodated hearts do not. Accommodated xenografts have an ongoing T helper cell type 2 (Th2) cytokine immune response, whereas the rejected grafts have a Th1 response. We propose a model for factors that contribute to the survival of xenografts and the avoidance of transplant arteriosclerosis.