Vertical sleeve gastrectomy reduces hepatic steatosis while increasing serum bile acids in a weight-loss-independent manner

OBJECTIVE

Our objective was to investigate the role of bile acids in hepatic steatosis reduction after vertical sleeve gastrectomy (VSG).

DESIGN AND METHODS

High fat diet (HFD)-induced obese C57Bl/6 mice were randomized to VSG, Sham operation (Sham), Sham operation with pair feeding to VSG (Sham-PF), or nonsurgical controls (Naïve). All mice were on HFD until sacrifice. Mice were observed postsurgery and data for body weight, body composition, metabolic parameters, serum bile acid level and composition were collected. Further hepatic gene expression by mRNA-seq and RT-PCR analysis was assessed.

RESULTS

VSG and Sham-PF mice lost equal weight postsurgery while VSG mice had the lowest hepatic triglyceride content at sacrifice. The VSG mice had elevated serum bile acid levels that positively correlated with maximal weight loss. Serum bile composition in the VSG group had increased cholic and tauroursodeoxycholic acid. These bile acid composition changes in VSG mice explained observed downregulation of hepatic lipogenic and bile acid synthetic genes.

CONCLUSION

VSG in obese mice results in greater hepatic steatosis reduction than seen with caloric restriction alone. VSG surgery increases serum bile acids that correlate with weight lost postsurgery and changes serum bile composition that could explain suppression of hepatic genes responsible for lipogenesis.

Platelets promote liver regeneration in early period after hepatectomy in mice

BACKGROUND

Platelets contain several growth factors, including platelet-derived growth factor and hepatocyte growth factor.

MATERIALS AND METHODS

We examined the effects of platelet increment on liver regeneration after 70% hepatectomy. Hepatectomies were carried out in male BALB/c mice, and subsequently divided into three groups: (i) untreated mice, (ii) thrombocytotic mice induced with thrombopoietin, and (iii) thrombocytopenic mice induced with anti-platelet antibody. Growth kinetics in the liver were analyzed as a function of the liver/body weight ratio, the mitotic index, the proliferating cell nuclear antigen labeling index and Ki-67 labeling index. Activation of signal transduction pathways relating to cell proliferation were examined, including the STAT3, Akt, and ERK1/2 pathways. Platelet accumulation in the residual liver was quantified by immunohistochemistry and transmission electron microscopy.

RESULTS

In thrombocytotic and thrombocytopenic mice, liver/body weight ratios and Ki-67 labeling indices were significantly increased and significantly decreased, respectively, compared with untreated mice 48 hours post-hepatectomy. The Akt pathway was strongly activated, and platelet accumulation was significantly increased in thrombocytotic group 5 minutes post-hepatectomy compared with normal and thrombocytopenic groups. After hepatectomy platelets accumulated in the sinusoids of liver and promoted hepatocyte proliferation in early period after hepatectomy.

CONCLUSION

By increasing or decreasing the platelet, marked changes in liver regeneration can occur, due to differences in cellular signaling and mitosis.

A surgical model in male obese rats uncovers protective effects of bile acids post-bariatric surgery

Bariatric surgery elevates serum bile acids. Conjugated bile acid administration, such as tauroursodeoxycholic acid (TUDCA), improves insulin sensitivity, whereas short-circuiting bile acid circulation through ileal interposition surgery in rats raises TUDCA levels. We hypothesized that bariatric surgery outcomes could be recapitulated by short circuiting the normal enterohepatic bile circulation. We established a model wherein male obese rats underwent either bile diversion (BD) or Sham (SH) surgery. The BD group had a catheter inserted into the common bile duct and its distal end anchored into the middistal jejunum for 4-5 weeks. Glucose tolerance, insulin and glucagon-like peptide-1 (GLP-1) response, hepatic steatosis, and endoplasmic reticulum (ER) stress were measured. Rats post-BD lost significantly more weight than the SH rats. BD rats gained less fat mass after surgery. BD rats had improved glucose tolerance, increased higher postprandial glucagon-like peptide-1 response and serum bile acids but less liver steatosis. Serum bile acid levels including TUDCA concentrations were higher in BD compared to SH pair-fed rats. Fecal bile acid levels were not different. Liver ER stress (C/EBP homologous protein mRNA and pJNK protein) was decreased in BD rats. Bile acid gavage (TUDCA/ursodeoxycholic acid [UDCA]) in diet-induced obese rats, elevated serum TUDCA and concomitantly reduced hepatic steatosis and ER stress (C/EBP homologous protein mRNA). These data demonstrate the ability of alterations in bile acids to recapitulate important metabolic improvements seen after bariatric surgery. Further, our work establishes a model for focused study of bile acids in the context of bariatric surgery that may lead to the identification of therapeutics for metabolic disease.

Platelets Strongly Induce Hepatocyte Proliferation with IGF-1 and HGF In Vitro

BACKGROUND

It is well known that platelets have a thrombotic effect. However, platelets play an important role not only in hemostasis but also in wound healing and tissue regeneration. Platelets have been reported to accumulate in the liver and promote liver regeneration after an extended hepatectomy, but the mechanism is unclear. The present study was designed to clarify the mechanism by which platelets have a direct proliferative effect on hepatocytes in vitro.

MATERIALS AND METHODS

Hepatocytes obtained from male BALB/c mice by collagenase digestion and immortalized hepatocytes (TLR2) were used. To elucidate the mechanism of the proliferative effect of platelets, DNA synthesis of hepatocytes was measured under various conditions and the related cellular signals were analyzed. Chromatographic analysis was also performed to clarify which elements of platelets have mitogenic activity.

RESULTS

DNA synthesis significantly increased in the hepatocytes cultured with platelets (P < 0.001). However, when the platelets and hepatocytes were separated, the platelets did not have a proliferative effect. Whole disrupted platelets, the supernatant fraction, and fresh isolated platelets had a similar proliferative effect, while the membrane fraction did not. After the addition of platelets, both Akt and extracellular signal-regulated kinases ERK1/2 were activated, but extracellular signal-regulated kinase STAT3 was not activated. Some mitogenic fractions were obtained from the platelet extracts by gel exclusion chromatography; the fractions were rich in hepatocyte growth factor and IGF-1.

CONCLUSIONS

Direct contact between platelets and hepatocytes was necessary for the proliferative effect. The direct contact initiated signal transduction involved in growth factor activation. Hepatocyte growth factor, vascular endothelial growth factor, and insulin-like growth factor-1, rather than platelet-derived growth factor, mainly contributed to hepatocyte proliferation.

Role of platelets on liver regeneration after 90% hepatectomy in mice

BACKGROUND/AIMS

Mortality after 90% partial hepatectomy in mice was associated with severe acute liver failure. Recently, we revealed that platelets have a strong promotional effect on hepatic regeneration. In the present study, we investigated the effect of thrombocytosis on liver regeneration after 90% hepatectomy in mice.

METHODS

For thrombocytosis induction PEG-rHuMGDF was injected 5 days before operation. Hepatectomy, sparing only the caudate lobe, was performed in normal and thrombocytotic BALB/c mice. Survival rate, platelet number, liver weight/body weight ratio, proliferating cell nuclear antigen, serum parameters, signal transduction and overexpressed genes were examined.

RESULTS

Platelet number was significantly higher in thrombocytotic group. All mice in normal group died within 30 h after hepatectomy. Survival rate in thrombocytotic group was 6/11 at 30 h and 3/11 one week after hepatectomy. Activation of Akt and STAT3 signaling pathways in thrombocytotic group was observed earlier and recognized to be stronger compared to normal group. Cell cycle, signaling pathways, metabolism and transport genes were significantly overexpressed in thrombocytotic group up to 24h after hepatectomy.

CONCLUSIONS

Under the thrombocytotic condition, liver regeneration occurred even in 90% hepatectomized mice. Platelets contribute to cell cycle progression and metabolic pathways in addition to preventing acute liver failure.

Activation of human liver sinusoidal endothelial cell by human platelets induces hepatocyte proliferation

BACKGROUND & AIMS

We previously reported that platelets promote hepatocyte proliferation. In this study, we focused on the role of platelets in liver sinusoidal endothelial cells (LSECs) in addition to their role in hepatocyte in liver regeneration.

METHODS

Immortalized human LSECs (TMNK-1) were used. The LSECs were co-cultured with human platelets, and the proliferation of LSECs and the excretion of growth factors and interleukin-6 (IL-6) were subsequently measured. The main factor from platelets which induced the excretion of IL-6 from LSECs was determined using inhibitors of each component contained in the platelets. The need for direct contact between platelets and LSECs was investigated using cell culture inserts. The proliferation of human primary hepatocytes was measured after the addition of the supernatant of LSECs cultured with or without platelets.

RESULTS

The number of LSECs cocultured with platelets significantly increased. Excretion of IL-6 and vascular endothelial growth factor (VEGF) increased in LSECs with platelets. JTE-013, a specific antagonist for sphingosine 1-phosphate (S1P) 2 receptors, inhibited the excretion of IL-6 from LSECs after the addition of platelets. When the platelets and LSECs were separated by the cell culture insert, the excretion of IL-6 from LSECs was decreased. DNA synthesis was significantly increased in human primary hepatocytes cultured with the supernatant of LSECs with platelets.

CONCLUSIONS

Platelets promote LSEC proliferation and induce IL-6 and VEGF production. Direct contact between the platelets and LSECs and S1P, that are contained in platelets, were involved in the excretion of IL-6 from LSECs. IL-6 from LSECs induced proliferation of parenchymal hepatocytes.

Platelet dynamics in the early phase of postischemic liver in vivo

BACKGROUND

In liver surgery, ischemia/reperfusion injury occasionally leads to liver failure by activating Kupffer cells (KCs) and leukocytes. However, few reports have demonstrated a relationship between KCs and platelets in vivo. This study investigated the relationship between these cells using intravital microscopy.

MATERIALS AND METHODS

Male Wistar rats were divided into two groups: (1) KC+ group, receiving 1 mL saline; and (2) KC- group, intravenously injected with liposome-encapsulated dichloromethylene disphosphonate for elimination of KCs. At 48 h after administration, 20 min of total normothermic hepatic ischemia was induced. Rhodamine-6G-labeled platelets and sinusoidal alterations were monitored using intravital microscopy up to 120 min after reperfusion. P-selectin, accumulated leukocytes and morphological damage, and alanine aminotransferase were evaluated.

RESULTS

In the KC+ group, numbers of adherent platelets increased significantly within 30 min after reperfusion. Endothelial cells of sinusoids in which KCs were mainly located were destroyed and the sinusoids were significantly constricted after reperfusion. Conversely, in the KC- group, adherent platelets in sinusoids were suppressed, and sinusoidal perfusion, endothelial cell damage and serum alanine aminotransferase levels were significantly improved. P-selectin on sinusoidal endothelial cells was not observed up to 120 min after reperfusion in either group.

CONCLUSIONS

Adherent platelets appear to reflect activation of KCs and lead to leukocyte accumulation, resulting in sinusoidal perfusion disturbance and liver failure. Evaluation of adherent platelets in the microcirculation offers an important marker of hepatic injury.

The role of small heterodimer partner in nonalcoholic fatty liver disease improvement after sleeve gastrectomy in mice

OBJECTIVE

Bile acids (BA) are elevated after vertical sleeve gastrectomy (VSG) and farnesoid-X-receptor (FXR) is critical to the success of murine VSG. BA downregulate hepatic lipogenesis by activating the FXR-small heterodimer partner (SHP) pathway. The role of SHP in fatty liver disease improvement after VSG was tested.

METHODS

Wild type (WT), SHP liver transgenic (SHP-Tg), and SHP knockout (SHP-KO) high-fat diet (HFD) fed mice underwent either VSG or Sham surgery. Body weight, BA level and composition, steatosis, and BA metabolism gene expression were evaluated.

RESULTS

Obese WT mice post-VSG lost weight, reduced steatosis, decreased plasma alanine aminotransferase (ALT), had more BA absorptive ileal area, and elevated serum BA. Obese SHP-Tg mice post-VSG also lost weight and had decreased steatosis. SHP-KO mice were however resistant to steatosis despite weight gain on a HFD. Further SHP-KO mice that underwent VSG lost weight, but developed hepatic inflammation and had increased ALT.

CONCLUSIONS

VSG produces weight loss independent of SHP status. SHP ablation creates a proinflammatory phenotype which is exacerbated after VSG despite weight loss. These inflammatory alterations are possibly related to factors extrinsic to a direct manifestation of NASH.

Duodenal nutrient exclusion improves metabolic syndrome and stimulates villus hyperplasia

OBJECTIVE

Surgical interventions that prevent nutrient exposure to the duodenum are among the most successful treatments for obesity and diabetes. However, these interventions are highly invasive, irreversible and often carry significant risk. The duodenal-endoluminal sleeve (DES) is a flexible tube that acts as a barrier to nutrient-tissue interaction along the duodenum. We implanted this device in Zucker Diabetic Fatty (ZDF) rats to gain greater understanding of duodenal nutrient exclusion on glucose homeostasis.

DESIGN

ZDF rats were randomised to four groups: Naive, sham ad libitum, sham pair-fed, and DES implanted. Food intake, body weight (BW) and body composition were measured for 28 days postoperatively. Glucose, lipid and bile acid metabolism were evaluated, as well as histological assessment of the upper intestine.

RESULTS

DES implantation induced a sustained decrease in BW throughout the study that was matched by pair-fed sham animals. Decreased BW resulted from loss of fat, but not lean mass. DES rats were also found to be more glucose tolerant than either ad libitum-fed or pair-fed sham controls, suggesting fat mass independent metabolic benefits. DES also reduced circulating triglyceride and glycerol levels while increasing circulating bile acids. Interestingly, DES stimulated a considerable increase in villus length throughout the upper intestine, which may contribute to metabolic improvements.

CONCLUSIONS

Our preclinical results validate DES as a promising therapeutic approach to diabetes and obesity, which offers reversibility, low risk, low invasiveness and triple benefits including fat mass loss, glucose and lipid metabolism improvement which mechanistically may involve increased villus growth in the upper gut.

MLK3 promotes metabolic dysfunction induced by saturated fatty acid-enriched diet

Saturated fatty acids activate the c-Jun NH₂-terminal kinase (JNK) pathway, resulting in chronic low-grade inflammation and the development of insulin resistance. Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that mediates JNK activation in response to saturated fatty acids in vitro; however, the exact mechanism for diet-induced JNK activation in vivo is not known. Here, we have used MLK3-deficient mice to examine the role of MLK3 in a saturated-fat diet model of obesity. MLK3-KO mice fed a high-fat diet enriched in medium-chain saturated fatty acids for 16 wk had decreased body fat compared with wild-type (WT) mice due to increased energy expenditure independently of food consumption and physical activity. Moreover, MLK3 deficiency attenuated palmitate-induced JNK activation and M1 polarization in bone marrow-derived macrophages in vitro, and obesity induced JNK activation, macrophage infiltration into adipose tissue, and expression of proinflammatory cytokines in vivo. In addition, loss of MLK3 improved insulin resistance and decreased hepatic steatosis. Together, these data demonstrate that MLK3 promotes saturated fatty acid-induced JNK activation in vivo and diet-induced metabolic dysfunction.

Maternal hepatic growth response to pregnancy in the mouse

Pregnancy is characterized by physiological adjustments in the maternal compartment. In this investigation, the influence of pregnancy on maternal liver was examined in CD-1 mice. Dramatic changes were observed in the size of the maternal liver during pregnancy. Livers doubled in weight from the non-pregnant state to day 18 of pregnancy. The pregnancy-induced hepatomegaly was a physiological event of liver growth confirmed by DNA content increase and detection of hepatocyte hyperplasia and hypertrophy. Growth of the liver was initiated following implantation and peaked at parturition. The expression and/or activities of key genes known to regulate liver regeneration, a phenomenon of liver growth compensatory to liver mass loss, were investigated. The results showed that pregnancy-dependent liver growth was associated with interleukin (IL)-6, tumor necrosis factor α, c-Jun and IL-1β, but independent of hepatocyte growth factor, fibroblast growth factor 1, tumor necrosis factor receptor 1, constitutive androstane receptor and pregnane X receptor. Furthermore, maternal liver growth was associated with the activation of hepatic signal transducer and activator of transcription 3, β-catenin and epidermal growth factor receptor, but pregnancy did not activate hepatic c-Met. The findings suggest that the molecular mechanisms regulating pregnancy-induced liver growth and injury-induced liver regeneration exhibit overlapping features but are not identical. In summary, the liver of the mouse adapts to the demands of pregnancy via a dramatic growth response driven by hepatocyte proliferation and size increase.

Bile Acid Signaling: Mechanism for Bariatric Surgery, Cure for NASH?

Bariatric surgery is the most effective and durable treatment option for obesity today. More importantly, beyond weight loss, bariatric procedures have many advantageous metabolic effects including reversal of obesity-related liver disease--nonalcoholic steatohepatitis (NASH). NASH is an important comorbidity of obesity given that it is a precursor to the development of liver cirrhosis that may necessitate liver transplantation in the long run. Simultaneously, we and others have observed increased serum bile acids in humans and animals that undergo bariatric surgery. Specifically, our preclinical studies have included experimental procedures such as 'ileal transposition' or bile diversion and established procedures such as Roux-en-Y gastric bypass and the adjustable gastric band. Importantly, these effects are not simply the result of weight loss since our data show that the resolution of NASH and increase in serum bile acids are not seen in rodents that lose an equivalent amount of weight via food restriction. In particular, we have studied the role of altered bile acid signaling, in the potent impact of a bariatric procedure termed 'vertical sleeve gastrectomy' (VSG). In this review we focus on the mechanisms of NASH resolution and weight loss after VSG surgery. We highlight the fact that bariatric surgeries can be used as 'laboratories' to dissect the mechanisms by which these procedures work to improve obesity and fatty liver disease. We describe key bile acid signaling elements that may provide potential therapeutic targets for 'bariatric-mimetic technologies' that could produce benefits similar to bariatric surgery--but without the surgery!

Platelets prevent acute hepatitis induced by anti-fas antibody

BACKGROUND AND AIM

Platelets provide many functions in the body, especially to the liver. The purpose of this study is to investigate the effect of thrombocytosis with acute hepatitis induced by anti-Fas antibody and its mechanism.

METHODS

Acute hepatitis was induced by administration of anti-Fas antibody in normal and thrombocytotic C57BL6J mice. For thrombocytosis, thrombopoietin; PEG-rHuMGDF was injected 5 days before and just prior to administration of anti-Fas antibody. To investigate the mechanisms, hepatocyte cell line (AML12) and sinusoidal endothelial cell line (M1) were induced apoptosis by staurosporine. They were cultured with platelets or thrombopoietin. Examination items were as follows: platelet number, alanine aminotransferase (ALT), histological findings, TUNEL (TdT-mediated dUTP-biotin Nick End Labeling) staining, and the expression of proteins associated with apoptosis in vivo and in vitro.

RESULTS

Platelets were significantly increased in the thrombocytotic group (P < 0.01). Serum ALT levels were significantly reduced by thrombocytosis at 6, 24 and 72 h after the administration (P < 0.05). In histological findings, hemorrhagic necrosis was observed in the normal group, but not observed in the thrombocytotic group. TUNEL-positive hepatocytes were reduced and the expression of cleaved caspase-3 was significantly decreased in the thrombocytotic group. The phosphorylation of Akt, the increment of Bcl-xL and the decrease of cleaved caspase-3 were observed in AML12 cells cultured with platelets, but were not observed cultured with thrombopoietin. Platelets and thrombopoietin had no anti-apoptotic effect on M1 cells.

CONCLUSION

Increase of platelets has a preventative effect against acute hepatitis induced by the anti-Fas antibody. It is suggested that platelets have a direct protective effect against apoptosis of hepatocytes.

Freeze-dried platelets promote hepatocyte proliferation in mice

In recent years, platelets are reported to promote liver, as well as bone regeneration and dermal wound healing. Platelets are required not only for thrombocytopenia treating but also for regenerative therapy. Platelets cannot be stored beyond three days, therefore, shortage of fresh platelets sometimes occurs. To preserve platelets for a long duration without degrading growth factors, a freeze-dried technique is required. We report here that platelets can be preserved by freeze-drying, using a programmed freezing method to avoid intracellular ice crystal formation. Freeze-dried platelets kept their morphological countenance and response with the agonist of thrombin was well maintained. Freeze-dried platelets stored adenine nucleotides, PDGF, and IGF-1 the same as those of fresh platelets. Freeze dried platelets also preserved their proliferative effect on hepatocytes identical to that of fresh platelets. These results of our study suggest that freeze dried platelets will obviate the storage problem of fresh platelets.

Autonomic regulation of liver regeneration after partial hepatectomy in mice

BACKGROUND/AIMS

The autonomic vagus nerve is thought to play an essential role in liver regeneration since hepatic vagotomy delays hepatic DNA synthesis. However, how the parasympathetic vagus nerve is involved in liver regeneration remains obscure. Kupffer cells are located in liver sinusoids adjacent to hepatocytes and might regulate liver regeneration by releasing interleukin-6 (IL-6). The present study examines the role of the vagus nerve and how Kupffer cells are involved in parasympathetic nerve-mediated liver regeneration in mice.

METHODS

We performed surgical vagotomy of the hepatic branch and then partial hepatectomy (PH); some mice received acetylcholine (ACh) agonist/antagonist before PH. We then evaluated liver regeneration and signal transducer and activator of transcription-3 (STAT3) activation. We also investigated whether ACh stimulates IL-6 release from Kupffer cells.

RESULTS

Surgical vagotomy impaired liver regeneration. STAT3, which is activated by IL-6 after hepatectomy and plays a pivotal role in liver regeneration, was less activated in vagotomized mice after PH. Post-PH STAT3 activation was recovered by administering vagotomized mice with an ACh agonist. Furthermore, ACh stimulated IL-6 release in Kupffer cells in vitro.

CONCLUSION

The parasympathetic system (vagus nerve) contributes to liver regeneration after hepatectomy by stimulating IL-6 release from Kupffer cells followed by STAT3 activation in hepatocytes.

Metabolic comparison of one-anastomosis gastric bypass, single-anastomosis duodenal-switch, Roux-en-Y gastric bypass, and vertical sleeve gastrectomy in rat

BACKGROUND

One-anastomosis gastric bypass (OAGB) and single-anastomosis duodenal switch (SADS) have become increasingly popular weight loss strategies. However, data directly comparing the effectiveness of these procedures with Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (SG) are limited.

OBJECTIVES

To examine the metabolic outcomes of OAGB, SADS, RYGB, and SG in a controlled rodent model.

SETTING

Academic research laboratory, United States.

METHODS

Surgeries were performed in diet-induced obese Long-Evans rats, and metabolic outcomes were monitored before and for 15 weeks after surgery.

RESULTS

All bariatric procedures induced weight loss compared with sham that lasted throughout the course of the study. The highest percent fat loss occurred after OAGB and RYGB. All bariatric procedures had improved glucose dynamics associated with an increase in insulin (notably OAGB and SADS) and/or glucagon-like protein-1 secretion. Circulating cholesterol was reduced in OAGB, SG, and RYGB. OAGB and SG additionally decreased circulating triglycerides. Liver triglycerides were most profoundly reduced after OAGB and RYGB. Circulating iron levels were decreased in all surgical groups, associated with a decreased hematocrit value and increased reticulocyte count. The fecal microbiome communities of OAGB, SADS, and RYGB were significantly altered; however, SG exhibited no change in microbiome diversity or composition.

CONCLUSIONS

These data support the use of the rat for modeling bariatric surgical procedures and highlight the ability of the OAGB to meet or exceed the metabolic improvements of RYGB. These data point to the likelihood that each surgery accomplishes metabolic improvements through both overlapping and distinct mechanisms and warrants further research.

Assessment of the role of FGF15 in mediating the metabolic outcomes of murine Vertical Sleeve Gastrectomy (VSG)

Vertical sleeve gastrectomy (VSG) is the best current therapy for remission of obesity and its co-morbidities. It is understood to alter the enterohepatic circulation of bile acids in vivo. Fibroblast growth factor 19 (FGF19) in human and its murine orthologue Fgf15 plays a pivotal role in this bile acid driven enterohepatic signaling. The present study evaluated the metabolic outcomes of VSG in Fgf15 deficient mice. 6-8 weeks old male wildtype mice (WT) and Fgf15 deficient mice (KO) were fed a high fat diet (HFD) for 8 weeks. At 8th week of diet, both WT and KO mice were randomly distributed to VSG or sham surgery. Post-surgery, mice were observed for 8 weeks while fed a HFD and then euthanized to collect tissues for experimental analysis. Fgf15 deficient (KO) mice lost weight post VSG, but glucose tolerance in KO mice did not improve post VSG compared to WT mice. Enteroids derived from WT and KO mice proliferated with bile acid exposure in vitro. Post VSG both WT and KO mice had similarly altered bile acid enterohepatic flux, however Fgf15 deficient mice post VSG had increased hepatic accumulation of free and esterified cholesterol leading to lipotoxicity related ER stress, inflammasome activation, and increased Fgf21 expression. Intact Fgf15 mediated enterohepatic bile acid signaling, but not changes in bile acid flux, appear to be important for the metabolic improvements post-murine bariatric surgery. These novel data introduce a potential point of distinction between bile acids acting as ligands compared to their canonical downstream signaling pathways.

A Diet High in Fat and Fructose Induces Early Hepatic Mitochondrial Aging

ABSTRACT

To investigate the effect of high fructose diet on ultrastructure and content of hepatic mitochondria, we randomized 6-8 weeks old male C57Bl6/J mice to ad lib chow or high-fat-high-fructose (HF2) diet for 32 weeks. HF2-fed mice gained more weight, had higher plasma alanine aminotransferase, and fasting glucose levels and increased hepatic triglyceride content at all time points compared to chow-fed mice. HF2-fed mice had lower mitochondrial to nuclear DNA ratio compared to chow-fed mice. HF2-fed mice had lower average mitochondrial surface area and the number of mitochondria compared to chow-fed mice. HF2-fed mice had higher expression of the hepatic endoplasmic reticulum stress marker Chop, compared to chow-fed mice. A diet high in fat and fructose leads to enhanced hepatic mitochondrial aging, depletion, and dysfunction, which may be important determinants of nonalcoholic steatohepatitis pathogenesis.

Elevation and characteristics of Rab30 and S100a8/S100a9 expression in an early phase of liver regeneration in the mouse

Recent studies have revealed that cytokines, including TNFα and IL-6 play key roles in the priming phase of liver regeneration. However, further knowledge of molecular events in the priming phase is needed for more comprehensively understanding the initiation of liver regeneration. In the present study, we attempted to identify additional genes involved in an early phase (2-6 h post partial hepatectomy, PH). The expression of 71 genes was shown to be up-regulated more than 3-fold in the liver at 2 h and 6 h post PH, as compared to 0 h (normal livers) using microarray analysis. Among them, Rab30 and S100a8/S100a9, were identified as novel genes up-regulated over 20-fold at 2 h post PH as compared to normal liver, and were further examined by RT-qPCR to confirm microarray results. Rab30 showed no significant up-regulation in organs other than the liver, whereas S100a8/S100a9 showed significant up-regulation in other organs, such as the lung and spleen at 6 h post PH as compared to those of sham-operated mice, indicating the existence of a different up-regulation machinery between Rab30 and S100a8/S100a9. Their expression was further investigated in the liver at various developmental stages. Rab30 was shown to be expressed only in newborn liver, whereas S100a8/S100a9 was highly expressed in embryo stages, and exhibited the highest levels in newborn liver. These findings imply that Rab30 and S100a8/S100a9 are possibly involved in the functional switch from hematopoiesis support to metabolism in the newborn stage, but might play different roles in liver development. In conclusion, Rab30 and S100a8/S100a9 were indicated to play roles in the initiation of liver regeneration as well as possibly in the functional switch of the liver in the newborn stage.

Refinement of Perioperative Feeding in a Mouse Model of Vertical Sleeve Gastrectomy

Provision of liquid enteral nutrition (LEN) during the perioperative period is standard practice for rodents undergoing bariatric surgery, yet these diets are associated with several challenges, including coagulation of the liquid diet within the delivery system and decreased postoperative consumption. We investigated the use of a commercially available high-calorie dietary gel supplement (DG) as an alternative food source for mice during the perioperative period. C57BL/6J male mice were fed high-fat diet for 8 to 10 wk prior to surgery. The study groups were: vertical sleeve gastrectomy (VSG) +DG, VSG+LEN, sham surgery+DG, and sham+LEN. Food and water intakes, body weight, and body fat composition was monitored throughout the study. Mice that received DG lost significantly more weight preoperatively than those fed LEN. However, during the postoperative period, body weight, body fat composition, and water and caloric intake were similar among all experimental diet groups. Three mice in the VSG+LEN group were euthanized due to clinical illness during the course of the study. In summary, feeding a high-calorie DG to mice undergoing VSG surgery is a viable alternative to LEN, given that DG does not significantly affect the surgical model of weight loss or result in adverse clinical outcomes. We recommend additional metabolic characterization of DG supplementation to ensure that this novel diet does not confound specific research goals in the murine VSG model.

Antibodies to sclerostin or G-CSF receptor partially eliminate bone or marrow adipocyte loss, respectively, following vertical sleeve gastrectomy

Vertical sleeve gastrectomy (VSG), the most utilized bariatric procedure in clinical practice, greatly reduces body weight and improves a variety of metabolic disorders. However, one of its long-term complications is bone loss and increased risk of fracture. Elevated circulating sclerostin (SOST) and granulocyte-colony stimulating factor (G-CSF) concentrations have been considered as potential contributors to VSG-associated bone loss. To test these possibilities, we administrated antibodies to SOST or G-CSF receptor and investigated alterations to bone and marrow niche following VSG. Neutralizing either SOST or G-CSF receptor did not alter beneficial effects of VSG on adiposity and hepatic steatosis, and anti-SOST treatment provided a further improvement to glucose tolerance. SOST antibodies partially reduced trabecular and cortical bone loss following VSG by increasing bone formation, whereas G-CSF receptor antibodies had no effects on bone mass. The expansion in myeloid cellularity and reductions in bone marrow adiposity seen with VSG were partially eliminated by treatment with Anti-G-CSF receptor. Taken together, these experiments demonstrate that antibodies to SOST or G-CSF receptor may act through independent mechanisms to partially block effects of VSG on bone loss or marrow niche cells, respectively.

Intestinal extracellular vesicles are altered by vertical sleeve gastrectomy

Bariatric surgery is the most effective treatment for obesity and its comorbidities. However, our understanding of the molecular mechanisms behind its beneficial effects is limited. Extracellular vesicles (EVs) comprise an important mode of intercellular communication. They carry nucleic acids, hormones, and signaling molecules and regulate multiple processes. Our aim was to test the role of EVs in the effects of vertical sleeve gastrectomy (VSG) using a mouse model. Small intestinal EVs were obtained from the mice that underwent VSG or control surgery and were on chow or high-fat diet or diet-restricted, and then they were subjected to the proteomic analysis. Enteroid and bacterial cultures were treated with EVs to evaluate their survival effect. A mouse cohort received intraduodenal administration of EVs from VSG or Sham mice for 10 days. Body weight, glucose metabolism, and intestinal morphology were evaluated. EVs were enriched in the intestinal lumen and mucus of VSG compared with Sham mice. Protein composition of VSG and Sham-derived EVs was highly distinct. When introduced into culture, VSG EVs decreased survival of intestinal enteroids and, conversely, promoted proliferation of bacteria. Mice administered with EVs obtained from VSG and Sham groups did not show differences in body weight, food intake, or glucose metabolism. Intestinal morphology was altered, as VSG EVs caused reduction of ileal villi length and decreased epithelial proliferation in the jejunum and ileum. VSG causes remodeling of intestinal EVs, which results in unique protein composition. VSG-derived EVs exhibit cytotoxic effects on epithelial cells and reduce proliferation of intestinal progenitor cells in mice.NEW & NOTEWORTHY This is the first study that investigates the impact of bariatric surgery on protein composition of intestinal extracellular vesicles. Extracellular vesicle composition is greatly altered after vertical sleeve gastrectomy and may potentially modulate various signaling pathways. In our study, extracellular vesicles from vertical sleeve gastrectomy-treated mice promote bacterial proliferation but exhibit cytotoxic effect on epithelial cells and reduce proliferation of intestinal progenitor cells in mice.

The evolution of steatosis and fibrosis in mice on a MASH-inducing diet and the effects of housing temperature

Obesity induction in mice requires high-fat diet exposure. Although hepatic steatosis develops, progression to inflammation and fibrosis, as in humans, requires prolonged exposure and additional dietary factors. Immunosuppression at room temperature may slow this progression. We evaluated thermoneutrality's effect on metabolic dysfunction-associated steatohepatitis (MASH) development using a fibrosis-inducing MASH [Gubra-Amylin NASH (GAN)] diet. Mice were fed either a MASH or chow diet and housed at room temperature or thermoneutrality. MASH diet groups were euthanized monthly from 4 to 7 mo. Serum markers of hepatic function were analyzed, and liver histology assessed steatosis, inflammation, ballooning [nonalcoholic fatty liver disease activity score (NAS) score], and fibrosis via Picrosirius Red staining. MASH diet increased body weight, liver-to-body mass ratio, and hepatic fat, with no difference between housing conditions. Housing temperature had minimal effects on MASH. Serum markers and hepatic fibrosis were similar across groups. NAS score was lower at 4 mo in thermoneutral MASH mice but not by 7 mo. Thermoneutrality did not significantly impact MASH development. These findings, alongside existing literature, suggest thermoneutral housing does not consistently enhance MASH progression in GAN MASH-fed mice.NEW & NOTEWORTHY The development of MASH in mice-does housing temperature make a real difference?