Dual effects of adenovirus-mediated thrombopoietin gene transfer on hepatic oval cell proliferation and platelet counts

Therapeutic implication of platelets in liver regeneration -hopes and hues

Mounting evidence highlights platelet involvement in liver regeneration via interaction with liver cells, growth factors release, and signaling contributions. Existing research suggests a compelling biological rationale for utilizing platelet biology, with the goal of improving liver function and accelerating its regenerative potential. Despite its expanding application in several clinical areas, the contribution of the platelet and its therapeutic implementation in liver regeneration so far has not yet fulfilled the initial high expectations. Areas covered: This review scrutinizes the progress, current updates, and discusses how recent understanding - particularly in the clinical implications of platelet-based therapy - may enable strategies to introduce and harness the therapeutic potential of the platelet during liver regeneration. Expert commentary: Several clinical and translational studies have facilitated a platform for the development of platelet-based therapy to enhance liver regeneration. While some of these therapies are effective to augment liver regeneration, the others have had some detrimental outcomes. The existing evidence represents a challenge for future projects that are focused on directly incorporating platelet-based therapies to induce liver regeneration.

Deficiency in thrombopoietin induction after liver surgery is associated with postoperative liver dysfunction

Background and Aims

Thrombopoietin (TPO) has been implicated in the process of liver regeneration and was found to correlate with hepatic function in patients with liver disease. With this investigation we aimed to determine if perioperative TPO levels were associated with postoperative outcome in patients undergoing liver resection.

Methods

Perioperative TPO was analyzed prior to liver resection as well as on the first and fifth postoperative day in 46 colorectal cancer patients with liver metastasis (mCRC) as well as 23 hepatocellular carcinoma patients (HCC). Serum markers of liver function within the first postoperative week were used to define liver dysfunction.

Results

While circulating TPO levels significantly increased one day after liver resection in patients without liver cirrhosis (mCRC) (P < 0.001), patients with underlying liver disease (HCC) failed to significantly induce TPO postoperatively. Accordingly, HCC patients had significantly lower TPO levels on POD1 and 5. Similarly, patients with major resections failed to increase circulating TPO levels. Perioperative dynamics of TPO were found to specifically predict liver dysfunction (AUC: 0.893, P < 0.001) after hepatectomy and remained an independent predictor upon multivariate analysis.

Conclusions

We here demonstrate that perioperative TPO dynamics are associated with postoperative LD. Postoperative TPO levels were found to be lowest in high-risk patients (HCC patients undergoing major resection) but showed an independent predictive value. Thus, a dampened TPO increase after liver resection reflects a poor capacity for hepatic recovery and may help to identify patients who require close monitoring or intervention for potential complications.

Gene therapy for liver regeneration: experimental studies and prospects for clinical trials

The liver is an exceptional organ, not only because of its unique anatomical and physiological characteristics, but also because of its unlimited regenerative capacity. Unfolding of the molecular mechanisms that govern liver regeneration has allowed researchers to exploit them to augment liver regeneration. Dramatic progress in the field, however, was made by the introduction of the powerful tool of gene therapy. Transfer of genetic materials, such as hepatocyte growth factor, using both viral and non-viral vectors has proved to be successful in augmenting liver regeneration in various animal models. For future clinical studies, ongoing research aims at eliminating toxicity of viral vectors and increasing transduction efficiency of non-viral vectors, which are the main drawbacks of these systems. Another goal of current research is to develop gene therapy that targets specific liver cells using receptors that are unique to and highly expressed by different liver cell types. The outcome of such investigations will, undoubtedly, pave the way for future successful clinical trials.

Thrombopoietin limits IL-6 release but fails to attenuate liver injury in two hepatic stress models

OBJECTIVE

Various pleiotropic substances have been suggested as candidates that directly reduce the severity of liver injury after hepatic ischemia/reperfusion (I/R) and upon acute liver failure (ALF). Herein, we studied whether thrombopoietin (TPO), the main regulator of megakaryopoiesis and thrombopoiesis, showed hepatoprotective effects and might mediate an antiapoptotic function in liver tissue under stress.

METHODS/RESULTS

In livers with ALF or undergoing warm hepatic I/R, injury was quantified by intravital fluorescence microscopy, chemical, and immunohistochemical analysis as well as western immunoblot. Induction of both ALF and I/R injury led to hepatocellular expression of c-mpl, the receptor of TPO. Exogenous application of recombinant TPO in a low (12.5 microg/kg) as well as a high (75 microg/kg) dose, however, did not ameliorate postischemic perfusion and leukocyte endothelial cell interaction, but slightly aggravated transaminase release upon I/R. Similarly, TPO was unable to dampen hepatic microcirculatory deteriorations after the induction of ALF, but caused an increase of leukocyte accumulation and transaminase activity when applied in high dose. Low dose of TPO did not influence the amount of hepatocellular apoptosis, whereas high-dose TPO slightly diminished the activation of caspase 3. Interestingly, exogenous TPO application completely reversed the stress-induced increase of plasma IL-6 levels, suggesting a negative feedback of TPO on IL-6 release.

CONCLUSION

Although the existence of the TPO-receptor on target liver cells TPO plays only a minor role in mediating hepatocyte apoptosis and does not provide protection against hepatic injury, contrasting the efficacy of the related hematopoietic growth factor erythropoietin.

Single administration of thrombopoietin prevents progression of liver fibrosis and promotes liver regeneration after partial hepatectomy in cirrhotic rats

OBJECTIVE

To evaluate the effect of thrombopoietin on liver regeneration after hepatectomy and antifibrosis under conditions of liver cirrhosis in rats.

SUMMARY BACKGROUND DATA

We revealed that platelets induced by thrombopoietin administration promote liver regeneration after hepatectomy in the normal liver.

METHODS

Seventy percent hepatectomy was carried out in rats, which were subsequently divided into 4 groups: (1) normal group without any treatment, (2) liver cirrhosis (LC) group, (3) combined thrombopoietin and liver cirrhosis (LC+TPO) group, and (4) combined thrombopoietin, antiplatelet serum and liver cirrhosis (LC+TPO+APS) group. Growth kinetics in the liver regeneration and growth factors were analyzed. Liver fibrotic area and activation of hepatic stellate cells were also investigated.

RESULTS

In LC group, liver regeneration was significantly delayed compared with normal group 24 hours after hepatectomy. On the other hand, liver regeneration of LC+TPO group increased significantly compared with LC group, to a level that was the same as that recorded in normal group. In LC group, liver fibrotic area before hepatectomy was significantly higher compared with the normal group. Liver fibrosis of LC+TPO group was significantly reduced compared with LC group. The antifibrotic and liver regeneration promoting effects of LC+TPO group were inhibited by antiplatelet serum in LC+TPO+APS group.

CONCLUSION

The administration of thrombopoietin reduces liver fibrosis and stimulates regeneration after hepatectomy through increment and accumulation of platelets in the cirrhotic liver. This could be a potentially useful treatment for liver cirrhosis.