A novel mouse model for the study of the inhibitory effects of chronic ethanol exposure on direct bone formation

Six months of voluntary alcohol consumption in male cynomolgus macaques reduces intracortical bone porosity without altering mineralization or mechanical properties

Chronic heavy alcohol consumption is a risk factor for low trauma bone fracture. Using a non-human primate model of voluntary alcohol consumption, we investigated the effects of 6 months of ethanol intake on cortical bone in cynomolgus macaques (Macaca fascicularis). Young adult (6.4 ± 0.1 years old, mean ± SE) male cynomolgus macaques (n = 17) were subjected to a 4-month graded ethanol induction period, followed by voluntary self-administration of water or ethanol (4 % w/v) for 22 h/d, 7 d/wk. for 6 months. Control animals (n = 6) consumed an isocaloric maltose-dextrin solution. Tibial response was evaluated using densitometry, microcomputed tomography, histomorphometry, biomechanical testing, and Raman spectroscopy. Global bone response was evaluated using biochemical markers of bone turnover. Monkeys in the ethanol group consumed an average of 2.3 ± 0.2 g/kg/d ethanol resulting in a blood ethanol concentration of 90 ± 12 mg/dl in longitudinal samples taken 7 h after the daily session began. Ethanol consumption had no effect on tibia length, mass, density, mechanical properties, or mineralization (p > 0.642). However, compared to controls, ethanol intake resulted in a dose-dependent reduction in intracortical bone porosity (Spearman rank correlation = -0.770; p < 0.0001) and compared to baseline, a strong tendency (p = 0.058) for lower plasma CTX, a biochemical marker of global bone resorption. These findings are important because suppressed cortical bone remodeling can result in a decrease in bone quality. In conclusion, intracortical bone porosity was reduced to subnormal values 6 months following initiation of voluntary ethanol consumption but other measures of tibia architecture, mineralization, or mechanics were not altered.

Mouse models of type 1 diabetes and their use in skeletal research

PURPOSE OF REVIEW

In this review, we describe the three primary mouse models of insulin-deficiency diabetes that have been used to study the effects of type 1 diabetes (T1D) on skeletal outcomes. These models include streptozotocin (chemically)-induced diabetes, autoimmune-mediated diabetes (the nonobese diabetes mouse), and a mutation in the insulin gene (the Akita mouse). We then describe the skeletal findings and/or skeletal phenotypes that have been delineated using these models.

RECENT FINDINGS

Humans with T1D have decreased bone mineral density and an increased risk for fragility fracture. Mouse models of insulin-deficiency diabetes (hereafter denoted as T1D) in many ways recapitulate these skeletal deficits. Utilizing techniques of microcomputed tomography, bone histomorphometry, biomechanical testing and fracture modeling, bone biomarker analysis, and Raman spectroscopy, mouse models of T1D have demonstrated abnormalities in bone mineralization, bone microarchitecture, osteoblast function, abnormal bone turnover, and diminished biomechanical properties of bone.

SUMMARY

Mouse models have provided significant insights into the underlying mechanisms involved in the abnormalities of bone observed in T1D in humans. These translational models have provided targets and pathways that may be modifiable to prevent skeletal complications of T1D.

The biology of bone lengthening

Distraction osteogenesis biologically resembles fracture healing with distinctive characteristics notably in the distraction phase of osteogenesis. In the latency phase of bone lengthening, like in the inflammatory phase of fracture repair, interleukines are released and act with growth factors released from platelets in the local haematoma, leading to attraction, proliferation and differentiation of mesenchymal stem cells into osteoblasts and other differentiated mesenchymal cells. These in turn produce matrix, collagen fibers and growth factors. A callus containing cells, collagen fibers, osteoid and cartilage matrix is formed. Provided stable fixation, distraction will trigger intramembranous bone formation. As distraction proceeds, the distraction gap develops five distinctive zones with unmineralized bone in the middle, remodelling bone peripherally, and mineralizing bone in between. During consolidation, the high concentration of anabolic growth factors in the regenerate diminishes with time as remodelling takes over to form mature cortical and cancellous bone. Systemic disease, congenital bone deficiencies, medications and substance abuse can influence the quality and quantity of regenerate bone, usually in a negative way. The regenerate bone can be manipulated when needed by using injection of mesenchymal stem cells and platelets, growth factors (BMP-2 and -7), and systemic medications (bisphosphonates and parathyroid hormone). Growth factors and systemic anabolic and antiresorptive drugs are prescribed on special indications, while distraction osteogenesis is not an authorized indication. To some extent, however, these compounds can be used off-label. Use in children presents special problems since growth factors and specific anabolic medications may involve a risk of inducing cancer.

Alcohol: A Simple Nutrient with Complex Actions on Bone in the Adult Skeleton

BACKGROUND

Alcohol is an important nonessential component of diet, but the overall impact of drinking on bone health, especially at moderate levels, is not well understood. Bone health is important because fractures greatly reduce quality of life and are a major cause of morbidity and mortality in the elderly. Regular alcohol consumption is most common following skeletal maturity, emphasizing the importance of understanding the skeletal consequences of drinking in adults.

METHODS

This review focuses on describing the complex effects of alcohol on the adult skeleton. Studies assessing the effects of alcohol on bone in adult humans as well as skeletally mature animal models published since the year 2000 are emphasized.

RESULTS

Light to moderate alcohol consumption is generally reported to be beneficial, resulting in higher bone mineral density (BMD) and reduced age-related bone loss, whereas heavy alcohol consumption is generally associated with decreased BMD, impaired bone quality, and increased fracture risk. Bone remodeling is the principal mechanism for maintaining a healthy skeleton in adults and dysfunction in bone remodeling can lead to bone loss and/or decreased bone quality. Light to moderate alcohol may exert beneficial effects in older individuals by slowing the rate of bone remodeling, but the impact of light to moderate alcohol on bone remodeling in younger individuals is less certain. The specific effects of alcohol on bone remodeling in heavy drinkers are even less certain because the effects are often obscured by unhealthy lifestyle choices, alcohol-associated disease, and altered endocrine signaling.

CONCLUSIONS

Although there have been advances in understanding the complex actions of alcohol on bone, much remains to be determined. Limited evidence implicates age, skeletal site evaluated, duration, and pattern of drinking as important variables. Few studies systematically evaluating the impact of these factors have been conducted and should be made a priority for future research. In addition, studies performed in skeletally mature animals have potential to reveal mechanistic insights into the precise actions of alcohol and associated comorbidity factors on bone remodeling.

Increased 4-hydroxynonenal protein adducts in male GSTA4-4/PPAR-α double knockout mice enhance injury during early stages of alcoholic liver disease

To test the significance of lipid peroxidation in the development of alcoholic liver injury, an ethanol (EtOH) liquid diet was fed to male 129/SvJ mice (wild-type, WT) and glutathione S-transferase A4-4-null (GSTA4-/-) mice for 40 days. GSTA4-/- mice were crossed with peroxisome proliferator-activated receptor-α-null mice (PPAR-α-/-), and the effects of EtOH in the resulting double knockout (dKO) mice were compared with the other strains. EtOH increased lipid peroxidation in all except WT mice (P < 0.05). Increased steatosis and mRNA expression of the inflammatory markers CXCL2, tumor necrosis factor-α (TNF-α), and α-smooth muscle actin (α-SMA) were observed in EtOH GSTA4-/- compared with EtOH WT mice (P < 0.05). EtOH PPAR-α-/- mice had increased steatosis, serum alanine aminotransferase (ALT), and hepatic CD3+ T cell populations and elevated mRNA encoding CD14, CXCL2, TNF-α, IL-6, CD138, transforming growth factor-β, platelet-derived growth factor receptor-β (PDGFR-β), matrix metalloproteinase (MMP)-9, MMP-13, α-SMA, and collagen type 1 compared with EtOH WT mice. EtOH-fed dKO mice displayed elevation of periportal hepatic 4-hydroxynonenal adducts and serum antibodies against malondialdehyde adducts compared with EtOH feeding of GSTA4-/-, PPAR-α-/-, and WT mice (P < 0.05). ALT was higher in EtOH dKO mice compared with all other groups (P < 0.001). EtOH-fed dKO mice displayed elevated mRNAs for TNF-α and CD14, histological evidence of fibrosis, and increased PDGFR, MMP-9, and MMP-13 mRNAs compared with the EtOH GSTA4-/- or EtOH PPAR-α-/- genotype (P < 0.05). These findings demonstrate the central role lipid peroxidation plays in mediating progression of alcohol-induced necroinflammatory liver injury, stellate cell activation, matrix remodeling, and fibrosis.

Rosiglitazone disrupts endosteal bone formation during distraction osteogenesis by local adipocytic infiltration

Rosiglitazone (Rosi) is a drug in the thiazolidinedione class for treatment of type 2 diabetes mellitus (T2DM), which binds and activates PPARγ nuclear receptor in fat cells, sensitizing them to insulin. Despite proven antidiabetic efficacy, Rosi therapy may be associated with trabecular bone loss and an increased risk of fractures. To examine the potential side effects of Rosi treatment on bone formation, we delivered Rosi to mice using a combined model of distraction osteogenesis (DO) and type 2 diabetes mellitus (T2DM). DO provides a unique method to isolate the sequence of intramembranous bone formation, an important component of both fracture healing and bone homeostasis. Four groups of n=6 mice were used to compare the effects of Rosi on bone formation and cellular composition in both diabetic (Avy/a strain) and non-diabetic mice (a/a strain). New bone formation was examined by high resolution radiographs, micro-computed tomography, and histology. Precursor cells in the distraction gap were quantitated using immunohistochemical stains for proliferating cell nuclear antigen. Committed osteoblasts and adipocytes in the gap were identified and quantitated by immunostaining for osteocalcin and FABP4/aP2, respectively. The diabetic model developed obesity, hyperglycemia, hyperinsulinemia and insulin resistance, while the control littermates remained lean, normoglycemic and insulin sensitive. Rosi treatment decreased levels of non-fasted glucose and insulin and improved insulin sensitivity in the A(vy)/a mice, but had no effect in a/a mice, indicating antidiabetic efficacy of Rosi at the tested dose. Despite the diabetic, obese mice having twice the number of fat cells in their marrow than the non-diabetic mice, bone formation using DO was not adversely affected by the diabetes itself. However, Rosi treatment significantly diminished intramembranous endosteal bone formation, while increasing adipogenesis in and adjacent to the distraction gap up to 3.5- to 3.8-fold in both diabetic and non-diabetic models. This effect was independent of the anti-diabetic therapeutic response. These results raise the question of whether osteoblast precursors are inhibited in their development or actually converted to adipocytic phenotypes, possibly via marrow fat PPARγ nuclear receptor.

Vitamin D supplementation protects against bone loss associated with chronic alcohol administration in female mice

Chronic alcohol abuse results in decreased bone mineral density (BMD), which can lead to increased fracture risk. In contrast, low levels of alcohol have been associated with increased BMD in epidemiological studies. Alcohol's toxic skeletal effects have been suggested to involve impaired vitamin D/calcium homeostasis. Therefore, dietary vitamin D supplementation may be beneficial in reducing bone loss associated with chronic alcohol consumption. Six-week-old female C57BL/6J mice were pair-fed ethanol (EtOH)-containing liquid diets (10 or 36% total calories) for 78 days. EtOH exposure at 10% calories had no effects on any measured bone or serum parameter. EtOH consumption at 36% of calories reduced BMD and bone strength (P<0.05), decreased osteoblastogenesis, increased osteoclastogenesis, suppressed 1,25-hydroxyvitamin D3 [1,25(OH)2D3] serum concentrations (P<0.05), and increased apoptosis in bone cells compared with pair-fed controls. In a second study, female mice were pair-fed 30% EtOH diets with or without dietary supplementation with vitamin D3 (cholecalciferol; VitD) for 40 days. VitD supplementation in the EtOH diet protected against cortical bone loss, normalized alcohol-induced hypocalcaemia, and suppressed EtOH-induced expression of receptor of nuclear factor-κB ligand mRNA in bone. In vitro, pretreatment of 1,25(OH)2D3 in osteoblastic cells inhibited EtOH-induced apoptosis. In EtOH/VitD mice circulating 1,25(OH)2D3 was lower compared with mice receiving EtOH alone (P<0.05), suggesting increased sensitivity to feedback control of VitD metabolism in the kidney. These findings suggest dietary VitD supplementation may prevent skeletal toxicity in chronic drinkers by normalizing calcium homeostasis, preventing apoptosis, and suppressing EtOH-induced increases in bone resorption.

Distraction osteogenesis in TNF receptor 1 deficient mice is protected from chronic ethanol exposure

Distraction osteogenesis (DO) is an orthopedic protocol, which induces direct new bone formation as a result of the stimulating effects of mechanical distraction. Chronic ethanol exposure has been demonstrated to inhibit bone formation in rodent models of DO. Further, it has been demonstrated that (1) tumor necrosis factor-α (TNF) blockers are protective against ethanol exposure and (2) recombinant mouse TNF (rmTNF) inhibits direct bone formation in ethanol naïve mice through TNF receptor 1 (TNFR1). These results suggest that the inhibitory effects are significantly mediated by TNF signaling. Therefore, we hypothesized that direct new bone formation in TNFR1 knockout (KO) mice would be protected from ethanol exposure. We used a unique model of mouse DO combined with liquid/chow diets to compare the effects of ethanol on both a strain of TNFR1 knockout (TNFR1 KO) mice and on mice of their C57BL/6 (B6) control strain. In the B6 study, and in concordance with previous work, both radiological and histological analyses of direct bone formation in the distraction gaps demonstrated significant osteoinhibition due to ethanol compared with chow- or pair-fed mice. In the TNFR1 KO study and in support of the hypothesis, both radiological and histological analyses of distraction gap bone formation demonstrated no significant differences between the ethanol, chow fed, or pair fed. We conclude that exogenous rmTNF and ethanol-induced endogenous TNF act to inhibit new bone formation during DO by signaling primarily through TNFR1.

Inhibin A enhances bone formation during distraction osteogenesis

Given the aging population and the increased incidence of fracture in the elderly population, the need exists for agents that can enhance bone healing, particularly in situations of delayed fracture healing and/or non-union. Our previous studies demonstrated that overexpression of the gonadal peptide, human inhibin A (hInhA), in transgenic mice enhances bone formation and strength via increased osteoblast activity. We tested the hypothesis that hInhA can also exert anabolic effects in a murine model of distraction osteogenesis (DO), using both transgenic hInhA overexpression and administration of normal physiological levels of hInhA in adult male Swiss-Webster mice. Tibial osteotomies and external ring fixation were performed, followed by a 3-day latency period, 14-day distraction, and sacrifice on day 18. Supraphysiological levels of hInhA in transgenic mice, but not normal physiological levels of hInhA, significantly increased endosteal bone formation and mineralized bone area in the distraction gap, as determined by radiographic and µCT analysis. Significantly, increased PCNA and osteocalcin expression in the primary matrix front suggested that hInhA increased osteoblast proliferation. This mechanism is consistent with the effects of other agents and pathologies that modulate bone formation during DO, and demonstrates the potential of hInhA to enhance bone repair and regeneration.

Alcohol induced epigenetic perturbations during the inflammatory stage of fracture healing

It is well recognized by orthopedic surgeons that fractures of alcoholics are more difficult to heal successfully and have a higher incidence of non-union, but the mechanism of alcohol's effect on fracture healing is unknown. In order to give direction for the study of the effects of alcohol on fracture healing, we propose to identify gene expression and microRNA changes during the early stages of fracture healing that might be attributable to alcohol consumption. As the inflammatory stage appears to be the most critical for successful fracture healing, this paper focuses on the events at day three following fracture or the stage of inflammation. Sprague-Dawley rats were placed on an ethanol-containing or pair-fed Lieber and DeCarli diet for four weeks prior to surgical fracture. Following insertion of a medullary pin, a closed mid-diaphyseal fracture was induced using a Bonnarens and Einhorn fracture device. At three days' post-fracture, the region of the fracture calluses was harvested from the right hind-limb. RNA was extracted and microarray analysis was conducted against the entire rat genome. There were 35 genes that demonstrated significant increased expression due to alcohol consumption and 20 that decreased due to alcohol. In addition, the expression of 20 microRNAs was increased and six decreased. In summary, while it is recognized that mRNA levels may or may not represent protein levels successfully produced by the cell, these studies reveal changes in gene expression that support the hypothesis that alcohol consumption affects events involved with inflammation. MicroRNAs are known to modulate mRNA and these findings were consistent with much of what was seen with mRNA microarray analysis, especially the involvement of smad4 which was demonstrated by mRNA microarray, microRNA and polymerase chain reaction.

Direct bone formation during distraction osteogenesis does not require TNFalpha receptors and elevated serum TNFalpha fails to inhibit bone formation in TNFR1 deficient mice

Distraction osteogenesis (DO) is a process which induces direct new bone formation as a result of mechanical distraction. Tumor necrosis factor-alpha (TNF) is a cytokine that can modulate osteoblastogenesis. The direct effects of TNF on direct bone formation in rodents are hypothetically mediated through TNF receptor 1 and/or 2 (TNFR1/2) signaling. We utilized a unique model of mouse DO to assess the effects of 1) TNFR homozygous null gene alterations on direct bone formation and 2) rmTNF on wild type (WT), TNFR1(-/-) (R1KO), and TNR2(-/-) (R2KO) mice. Radiological and histological analyses of direct bone formation in the distraction gaps demonstrated no significant differences between the WT, R1KO, R2KO, or TNFR1(-/-) and R2(-/-) (R1 and 2KO) mice. R1 and 2KO mice had elevated levels of serum TNF but demonstrated no inhibition of new bone formation. Systemic administration by osmotic pump of rmTNF during DO (10 microg/kg/day) resulted in significant inhibition of gap bone formation measures in WT and R2KO mice, but not in R1KO mice. We conclude that exogenous rmTNF and/or endogenous TNF act to inhibit new bone formation during DO by signaling primarily through TNFR1.

Drilled hole defects in mouse femur as models of intramembranous cortical and cancellous bone regeneration

In order to identify pertinent models of cortical and cancellous bone regeneration, we compared the kinetics and patterns of bone healing in mouse femur using two defect protocols. The first protocol consisted of a 0.9-mm-diameter through-and-through cortical hole drilled in the mid-diaphysis. The second protocol was a 0.9-mm-diameter, 1-mm-deep perforation in the distal epimetaphyseal region, which destroyed part of the growth plate and cancellous bone. Bone healing was analyzed by ex vivo micro-computerized X-ray tomography and histology. In the diaphysis, the cortical gap was bridged with woven bone within 2 weeks. This newly formed bone was rapidly remodeled into compact cortical bone, which showed characteristic parameters of intact cortex 4 weeks after surgery. In the epimetaphysis, bone formation was initiated at the deepest region of the defect and spread slowly toward the cortical gap. In this position, newly formed bone quickly adopted the characteristics of trabecular bone, whereas a thin compact wall was formed at its external border, which reached the density of intact cortical bone but failed to bridge the cortical gap even 13 weeks after surgery. This comparative study indicates that the diaphyseal defect is a model of cortical bone healing and that the epimetaphyseal defect is a model of cancellous bone repair. These models enable experimental genetics studies to investigate the cellular and molecular mechanisms of spontaneous cortical and cancellous bone repair and may be useful for pharmacological studies.

Alcohol exposure impairs myeloid dendritic cell function in rhesus macaques

BACKGROUND

Alcohol intoxication suppresses both the innate and adaptive immunities. Dendritic cells (DCs) are the major cell type bridging the innate and acquired immune responses. At the present time, the effects of alcohol on DC development in hematopoietic tissues and the functional activities of DCs are incompletely elucidated. This study investigated the impact of chronic alcohol exposure on the alteration of hematopoietic precursor cell and DC populations in the bone marrow and peripheral blood of rhesus macaques.

METHODS

Rhesus macaques were administered alcohol or isocaloric sucrose daily for a period of 3 months through surgically implanted gastric catheters. Peripheral blood mononuclear cells (PBMCs) and bone marrow cells (BMCs) were isolated for flow cytometric analysis after 3 months. Monocytes were cultured with human IL-4 (10 ng/ml) and GM-CSF (50 ng/ml) in the absence and presence of alcohol (50 mM). On day 6 of the culture, a cocktail of stimulants including IL-1beta (18 ng), IL-6 (1800 U), TNF-alpha (18 ng), and PGE(2) (1.8 microg) were added to the designated wells for transformation of immature dendritic cells (iDCs) to mature myeloid DCs. The cells were analyzed on day 8 by flow cytometry for expression of DC costimulatory molecule expression.

RESULTS

EtOH-treated animals had significantly lower numbers of myeloid DCs (lineage-HLA-DR+CD11c+CD123-) in both the PBMCs and BMCs compared to controls (5,654 +/- 1,273/10(6) vs. 2,353 +/- 660/10(6) PBMCs and 503 +/- 34 vs. 195 +/- 44/10(6) BMCs). Under culture conditions, the number of lineage-HLA-DR+CD83+ cells was low in control wells (0.38 +/- 0.08%). Alcohol inhibited the increase in the number of lineage-HLA-DR+CD83+ cells in iDC wells (2.30 +/- 0.79% vs. 5.73 +/- 1.40%). Alcohol also inhibited the increase in the number of lineage-HLA-DR+CD83+ cells in mature DC wells (1.23 +/- 0.15% vs. 4.13 +/- 0.62%).

CONCLUSIONS

Chronic EtOH decreases the bone marrow and circulating pools of myeloid DCs. Additionally, EtOH suppresses costimulatory molecule CD83 expression during DC transformation, which may attenuate the ability of DCs to initiate T-cell expansion.

Voluntary ethanol consumption in 22 inbred mouse strains

Inbred strains are genetically stable across time and laboratories, allowing scientists to accumulate a record of phenotypes, including physiological characteristics and behaviors. To date, the C57/C58 family of inbred mouse strains has been identified as having the highest innate ethanol consumption, but some lineages have rarely or never been surveyed. Thus, the purpose of the present experiment was to measure ethanol preference and intake in 22 inbred mouse strains, some of which have never been tested for ethanol consumption. Male and female mice (A/J, BALB/cByJ, BTBR+T(tf/tf), BUB/BnJ, C57BL/6J, C57BLKS/J, C58/J, CZECH/Ei, DBA/2J, FVB/NJ, I/LnJ, LP/J, MA/MyJ, NOD/LtJ, NON/LtJ, NZB/B1NJ, NZW/LacJ, PERA/Ei, RIIIS/J, SEA/GnJ, SM/J, and 129S1/SvlmJ) were individually housed and given unlimited access in a two-bottle choice procedure to one bottle containing tap water and a second containing increasing concentrations of ethanol (3%, 6%, 10%), 0.2% saccharin, and then increasing concentrations of ethanol (3%, 6%, 10%) plus 0.2% saccharin. Mice were given access to each novel solution for a total of 4 days, with a bottle side change every other day. Consistent with previous studies, C57BL/6J (B6) mice consumed an ethanol dose of >10g/kg/day whereas DBA/2J (D2) mice consumed <2g/kg/day. No strain voluntarily consumed greater doses of ethanol than B6 mice. Although the C58 and C57BLKS strains showed high ethanol consumption levels that were comparable to B6 mice, the BUB and BTBR strains exhibited low ethanol intakes similar to D2 mice. The addition of 0.2% saccharin to the ethanol solutions significantly increased ethanol intake by most strains and altered the strain distribution pattern. Strong positive correlations (rs> or =0.83) were determined between consumption of the unsweetened versus sweetened ethanol solutions. Consumption of saccharin alone was significantly positively correlated with the sweetened ethanol solutions (rs=0.62-0.81), but the correlation with unsweetened ethanol solutions was considerably lower (rs=0.37-0.45). These results add new strains to the strain mean database that will facilitate the identification of genetic relationships between voluntary ethanol consumption, saccharin preference, and other phenotypes.

Distraction osteogenesis: advancements in the last 10 years

Distraction is still evolving in the management of patients with orthopedic and craniomaxillofacial deformities. The relationship among latency, gap size, rate, rhythm, and duration of fixation is not totally understood for all of the individual patients and variations in their needs seen in a clinical practice. Numerous factors can influence the quality and quantity of bone seen with distraction, including the age and nutritional status of the patient and the type of distractor that is used.

Chronic ethanol exposure inhibits distraction osteogenesis in a mouse model: role of the TNF signaling axis

Tumor necrosis factor-alpha (TNF-alpha) is an inflammatory cytokine that modulates osteoblastogenesis. In addition, the demonstrated inhibitory effects of chronic ethanol exposure on direct bone formation in rats are hypothetically mediated by TNF-alpha signaling. The effects in mice are unreported. Therefore, we hypothesized that in mice (1) administration of a soluble TNF receptor 1 derivative (sTNF-R1) would protect direct bone formation during chronic ethanol exposure, and (2) administration of recombinant mouse TNF-alpha (rmTNF-alpha) to ethanol naïve mice would inhibit direct bone formation. We utilized a unique model of limb lengthening (distraction osteogenesis, DO) combined with liquid diets to measure chronic ethanol's effects on direct bone formation. Chronic ethanol exposure resulted in increased marrow TNF, IL-1, and CYP 2E1 RNA levels in ethanol-treated vs. control mice, while no significant weight differences were noted. Systemic administration of sTNF-R1 during DO (8.0 mg/kg/2 days) to chronic ethanol-exposed mice resulted in enhanced direct bone formation as measured radiologically and histologically. Systemic rmTNF-alpha (10 microg/kg/day) administration decreased direct bone formation measures, while no significant weight differences were noted. We conclude that chronic ethanol-associated inhibition of direct bone formation is mediated to a significant extent by the TNF signaling axis in a mouse model.