The management of proctitis in patients who have undergone very-high-dose conformal radiotherapy is extremely challenging. The fibrosis-necrosis, fistulae, and hemorrhage induced by pelvic overirradiation have an impact on morbidity. Augmenting tissue repair by the use of mesenchymal stem cells (MSCs) may be an important advance in treating radiation-induced toxicity. Using a preclinical pig model, we investigated the effect of autologous bone marrow-derived MSCs on high-dose radiation-induced proctitis. Irradiated pigs received repeated intravenous administrations of autologous bone marrow-derived MSCs. Immunostaining and real-time polymerase chain reaction analysis were used to assess the MSCs' effect on inflammation, extracellular matrix remodeling, and angiogenesis, in radiation-induced anorectal and colon damages. In humans, as in pigs, rectal overexposure induces mucosal damage (crypt depletion, macrophage infiltration, and fibrosis). In a pig model, repeated administrations of MSCs controlled systemic inflammation, reduced in situ both expression of inflammatory cytokines and macrophage recruitment, and augmented interleukin-10 expression in rectal mucosa. MSC injections limited radiation-induced fibrosis by reducing collagen deposition and expression of col1a2/col3a1 and transforming growth factor-β/connective tissue growth factor, and by modifying the matrix metalloproteinase/TIMP balance. In a pig model of proctitis, repeated injections of MSCs effectively reduced inflammation and fibrosis. This treatment represents a promising therapy for radiation-induced severe rectal damage.
Statins are drugs widely used in humans to treat hypercholesterolemia. Statins act by inhibiting cholesterol synthesis resulting in the activation of the transcription factor sterol-responsive element-binding protein-2 that controls the expression of genes involved in cholesterol homeostasis. Statin therapy also decreases plasma triglyceride and non-esterified fatty acid levels, but the mechanism behind this effect remains more elusive. Liver fatty acid-binding protein (L-FABP) plays a role in the influx of long-chain fatty acids into hepatocytes. Here we show that L-FABP is a target for statins. In rat hepatocytes, simvastatin treatment induced L-FABP mRNA levels in a dose-dependent manner. Moreover, L-FABP promoter activity was induced by statin treatment. Progressive 5 -deletion analysis revealed that the peroxisome proliferator-activated receptor (PPAR)-responsive element located at position ؊67/؊55 was responsible for the statin-mediated transactivation of the rat L-FABP promoter. Moreover, treatment with simvastatin and the PPAR␣ agonist Wy14,649 resulted in a synergistic induction of L-FABP expression (mRNA and protein) in rat Fao hepatoma cells. This effect was also observed in vivo in wild-type mice but not in PPAR␣-null animals demonstrating the direct implication of PPAR␣ in L-FABP regulation by statin treatment. Statin treatment resulted in a rise in PPAR␣ mRNA levels both in vitro and in vivo and activated the mouse PPAR␣ promoter in a reporter assay. Altogether, these data demonstrate that L-FABP expression is up-regulated by statins through a mechanism involving PPAR␣. Moreover, PPAR␣ might be a statin target gene. These effects might contribute to the triglyceride/non-esterified fatty acid-lowering properties of statins.Statins are competitive inhibitors of 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis. The resulting lower intracellular cholesterol concentration after statin treatment leads to a proteolytic activation of the transcription factor sterol responsive element-binding protein-2 (SREBP-2), 1 which up-regulates several genes controlling cholesterol homeostasis, including the LDL receptor (LDLr) (1). Induction of LDLr in the liver enhances clearance of circulating LDL resulting in decreased plasma LDL-cholesterol levels. Statins also increase, at least in part via a PPAR␣-dependent mechanism (2), the level of high density lipoproteins (3, 4). As a consequence, statins improve the blood cholesterol profile and markedly reduce cardiovascular mortality and morbidity in dyslipidemic patients (5-7). Statins also influence plasma TG and NEFA levels in rats and humans (4, 8 -11) through mechanisms not yet fully elucidated. Sustained hepatic clearance of TG-rich very low density lipoproteins by the LDLr (12), statin-dependent up-regulation of the lipoprotein lipase (LPL) gene, and down-regulation of the LPL inhibitor apolipoprotein C-III (13) may all contribute to the TG-lowering effect of statins. By contrast, it is not known if statins control th...
The small bowel is an important dose-limiting organ in abdominal radiotherapy because irradiation can cause acute enteritis that, in turn, leads to progressively reduced motility and finally, in a later phase, to fibrosis. Because these clinical symptoms may be caused by the early stage of an inflammatory process, we characterized the radiation-induced intestinal inflammation in rats. Abdominal gamma-irradiation (10-Gy) induced a cascade of inflammatory events characterized by an early (6 h after exposure) increase in IL-1beta, TNF-alpha, and IL-6 mRNA levels in the rat ileal muscularis layer. IL-8 [a cytokine-induced neutrophil chemoattractant (CINC)] mRNA appeared later (at 3 days). The expression of TGF-beta (a profibrotic cytokine) was higher in irradiated than control tissue at day 1, whereas IL-10 (an anti-inflammatory cytokine) expression vanished completely. Despite strong IL-1ra expression, the IL-1ra/IL-1beta ratio, which is an indicator of inflammatory balance, was -41% at day 1 in irradiated compared with control tissue. The nuclear transcription factors NF-kappaB and activator protein-1 (AP-1) govern transcription of these genes, directly or indirectly. Although expression of the subunits of NF-kappaB (p65, p50) and AP-1 (c-fos, c-jun) did not increase, irradiation caused a rapid and persistent translocation of p65 and p50. An imbalance between proinflammatory and anti-inflammatory mediators may contribute to perpetuating intestinal inflammation, thus making it chronic.
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