At-risk alcohol use is a major contributor to the global health care burden and leads to preventable deaths and diseases including alcohol addiction, alcoholic liver disease, cardiovascular disease, diabetes, traumatic injuries, gastrointestinal diseases, cancers, and fetal alcohol syndrome. Excessive and frequent alcohol consumption has increasingly been linked to alcohol-associated tissue injury and pathophysiology, which have significant adverse effects on multiple organ systems. Extensive research in animal and in vitro models has elucidated the salient mechanisms involved in alcohol-induced tissue and organ injury. In some cases, these pathophysiological mechanisms are shared across organ systems. The major alcohol- and alcohol metabolite–mediated mechanisms include oxidative stress, inflammation and immunometabolic dysregulation, gut leak and dysbiosis, cell death, extracellular matrix remodeling, endoplasmic reticulum stress, mitochondrial dysfunction, and epigenomic modifications. These mechanisms are complex and interrelated, and determining the interplay among them will make it possible to identify how they synergistically or additively interact to cause alcohol-mediated multiorgan injury. In this article, we review the current understanding of pathophysiological mechanisms involved in alcohol-induced tissue injury.

Alcohol abuse; the most common and costly form of drug abuse, is a major contributing factor to many disease categories. The alcohol-attributable disease burden is closely related to the average volume of alcohol consumption, with dose-dependent relationships between amount and duration of alcohol consumption and the incidence of diabetes mellitus, hypertension, cardiovascular disease, stroke, and pneumonia. The frequent occurrence of alcohol use disorders in the adult population and the significant and widespread detrimental organ system effects highlight the importance of recognizing and further investigating the pathophysiological mechanisms underlying alcohol-induced tissue and organ injury.

Traumatic brain injury (TBI) is an increasingly frequent and poorly understood condition lacking effective therapeutic strategies. Inflammation and oxidative stress (OS) are critical components of injury, and targeted interventions to reduce their contribution to injury should improve neurobehavioral recovery and outcomes. Recent evidence reveals potential protective, yet short-lived, effects of the endocannabinoids (ECs), 2-arachidonoyl glycerol (2-AG) and N -arachidonoyl-ethanolamine (AEA), on neuroinflammatory and OS processes after TBI. The aim of this study was to determine whether EC degradation inhibition after TBI would improve neurobehavioral recovery by reducing inflammatory and oxidative damage. Adult male Sprague-Dawley rats underwent a 5-mm left lateral craniotomy, and TBI was induced by lateral fluid percussion. TBI produced apnea (17±5 sec) and a delayed righting reflex (479±21 sec). Thirty minutes post-TBI, rats were randomized to receive intraperitoneal injections of vehicle (alcohol, emulphor, and saline; 1:1:18) or a selective inhibitor of 2-AG (JZL184, 16 mg/kg) or AEA (URB597, 0.3 mg/kg) degradation. At 24 h post-TBI, animals showed significant neurological and -behavioral impairment as well as disruption of blood–brain barrier (BBB) integrity. Improved neurological and -behavioral function was observed in JZL184-treated animals. BBB integrity was protected in both JZL184- and URB597-treated animals. No significant differences in ipsilateral cortex messenger RNA expression of interleukin (IL)-1β, IL-6, chemokine (C-C motif) ligand 2, tumor necrosis factor alpha, cyclooxygenase 2 (COX2), or nicotinamide adenine dinucleotide phosphate oxidase (NOX2) and protein expression of COX2 or NOX2 were observed across experimental groups. Astrocyte and microglia activation was significantly increased post-TBI, and treatment with JZL184 or URB597 blocked activation of both cell types. These findings suggest that EC degradation inhibition post-TBI exerts neuroprotective effects. Whether repeated dosing would achieve greater protection remains to be examined.

Chronic alcohol consumption perturbs the normal intestinal microbial communities (dysbiosis). To investigate the relationship between alcohol-mediated dysbiosis and pulmonary host defense we developed a fecal adoptive transfer model, which allows us to investigate the impact of alcohol-induced gut dysbiosis on host immune response to an infectious challenge at a distal organ, independent of prevailing alcohol use. Male C57BL/6 mice were treated with a cocktail of antibiotics (ampicillin, gentamicin, neomycin, vancomycin, and metronidazole) via daily gavage for two weeks. A separate group of animals was fed a chronic alcohol (or isocaloric dextrose pair-fed controls) liquid diet for 10 days. Microbiota-depleted mice were recolonized with intestinal microbiota from alcohol-fed or pair-fed (control) animals. Following recolonization groups of mice were sacrificed prior to and 48 hrs. post respiratory infection with Klebsiella pneumoniae. Klebsiella lung burden, lung immunology and inflammation, as well as intestinal immunology, inflammation, and barrier damage were examined. Results showed that alcohol-associated susceptibility to K. pneumoniae is, in part, mediated by gut dysbiosis, as alcohol-naïve animals recolonized with a microbiota isolated from alcohol-fed mice had an increased respiratory burden of K. pneumoniae compared to mice recolonized with a control microbiota. The increased susceptibility in alcohol-dysbiosis recolonized animals was associated with an increase in pulmonary inflammatory cytokines, and a decrease in the number of CD4+ and CD8+ T-cells in the lung following Klebsiella infection but an increase in T-cell counts in the intestinal tract following Klebsiella infection, suggesting intestinal T-cell sequestration as a factor in impaired lung host defense. Mice recolonized with an alcohol-dysbiotic microbiota also had increased intestinal damage as measured by increased levels of serum intestinal fatty acid binding protein. Collectively, these results suggest that alterations in the intestinal immune response as a consequence of alcohol-induced dysbiosis contribute to increased host susceptibility to Klebsiella pneumonia. Alcohol use disorders (AUD) are an established risk factor for bacterial pneumonia. Further, alcohol consumption perturbs the normal intestinal microbial communities. Intestinal microbiota dysbiosis has been linked to impaired pulmonary host defense, however the role of alcohol-associated intestinal dysbiosis on pulmonary host defense is unknown. Here, we used an innovative model system to examine the role of alcohol-mediated intestinal dysbiosis on pulmonary host defense against respiratory infection with Klebsiella pneumoniae, independent of direct alcohol toxicity. We found that alcohol-mediated dysbiosis significantly increases host susceptibility to K. pneumoniae infection, independent of prevailing alcohol consumption. Alcohol-dysbiosis was associated with an altered T-cell responses in both the lung and intestinal tract following Klebsiella infection. Alcohol-dysbiosis also lead to increased pulmonary inflammation, as well as intestinal inflammation and damage. Our study demonstrates that alcohol-mediated dysbiosis impacts host defense and contributes to the impaired host defense against pneumonia frequently seen in alcohol abusers, and thus shifts conventional understanding of mechanisms of host defense impacted by alcohol. Characterization of microbial populations and metabolic products that regulate the immune system during harmful alcohol use may reveal novel therapeutic targets, as well as host-specific microbial communities that may be central to alcohol-mediated alterations in host defense.

Δ ⁹ -Tetrahydrocannabinol (Δ ⁹ -THC), the primary psychoactive component in marijuana, is FDA approved to ameliorate AIDS-associated wasting. Because cannabinoid receptors are expressed on cells of the immune system, chronic Δ ⁹ -THC use may impact HIV disease progression. We examined the impact of chronic Δ ⁹ -THC administration (0.32 mg/kg im, 2 × daily), starting 28 days prior to inoculation with simian immunodeficiency virus (SIV _mac251 ; 100 TCID ₅₀ /ml, iv), on immune and metabolic indicators of disease during the initial 6 month asymptomatic phase of infection in rhesus macaques. SIV _mac251 inoculation resulted in measurable viral load, decreased lymphocyte CD4 ⁺ /CD8 ⁺ ratio, and increased CD8 ⁺ proliferation. Δ ⁹ -THC treatment of SIV-infected animals produced minor to no effects in these parameters. However, chronic Δ ⁹ -THC administration decreased early mortality from SIV infection ( p = 0.039), and this was associated with attenuation of plasma and CSF viral load and retention of body mass ( p = NS). In vitro , Δ ⁹ -THC (10 μm) decreased SIV (10 TCID ₅₀ ) viral replication in MT4-R5 cells. These results indicate that chronic Δ ⁹ -THC does not increase viral load or aggravate morbidity and may actually ameliorate SIV disease progression. We speculate that reduced levels of SIV, retention of body mass, and attenuation of inflammation are likely mechanisms for Δ ⁹ -THC-mediated modulation of disease progression that warrant further study.