Effects of alcohol on brain oxygenation and brain hypoxia induced by intravenous heroin

Brain oxygen responses induced by opioids: focus on heroin, fentanyl, and their adulterants

Opioids are important tools for pain management, but abuse can result in serious health complications. Of these complications, respiratory depression that leads to brain hypoxia is the most dangerous, resulting in coma and death. Although all opioids at large doses induce brain hypoxia, danger is magnified with synthetic opioids such as fentanyl and structurally similar analogs. These drugs are highly potent, act rapidly, and are often not effectively treated by naloxone, the standard of care for opioid-induced respiratory depression. The goal of this review paper is to present and discuss brain oxygen responses induced by opioids, focusing on heroin and fentanyl. In contrast to studying drug-induced changes in respiratory activity, we used chronically implanted oxygen sensors coupled with high-speed amperometry to directly evaluate physiological and drug-induced fluctuations in brain oxygen levels in awake, freely moving rats. First, we provide an overview of brain oxygen responses to physiological stimuli and discuss the mechanisms regulating oxygen entry into brain tissue. Next, we present data on brain oxygen responses induced by heroin and fentanyl and review underlying mechanisms. These data allowed us to compare the effects of these drugs on brain oxygen in terms of their potency, time-dependent response pattern, and potentially lethal effect at high doses. Then, we present the interactive effects of opioids during polysubstance use (alcohol, ketamine, xylazine) on brain oxygenation. Finally, we consider factors that affect the therapeutic potential of naloxone, focusing on dosage, timing of drug delivery, and contamination of opioids by other neuroactive drugs. The latter issue is considered chiefly with respect to xylazine, which strongly potentiates the hypoxic effects of heroin and fentanyl. Although this work was done in rats, the data are human relevant and will aid in addressing the alarming rise in lethality associated with opioid misuse.

Endogenous Fructose Production and Metabolism Drive Metabolic Dysregulation and Liver Disease in Mice with Hereditary Fructose Intolerance

Excessive intake of sugar, and particularly fructose, is closely associated with the development and progression of metabolic syndrome in humans and animal models. However, genetic disorders in fructose metabolism have very different consequences. While the deficiency of fructokinase, the first enzyme involved in fructose metabolism, is benign and somewhat desirable, missense mutations in the second enzyme, aldolase B, causes a very dramatic and sometimes lethal condition known as hereditary fructose intolerance (HFI). To date, there is no cure for HFI, and treatment is limited to avoiding fructose and sugar. Because of this, for subjects with HFI, glucose is their sole source of carbohydrates in the diet. However, clinical symptoms still occur, suggesting that either low amounts of fructose are still being consumed or, alternatively, fructose is being produced endogenously in the body. Here, we demonstrate that as a consequence of consuming high glycemic foods, the polyol pathway, a metabolic route in which fructose is produced from glucose, is activated, triggering a deleterious mechanism whereby glucose, sorbitol and alcohol induce severe liver disease and growth retardation in aldolase B knockout mice. We show that generically and pharmacologically blocking this pathway significantly improves metabolic dysfunction and thriving and increases the tolerance of aldolase B knockout mice to dietary triggers of endogenous fructose production.

Co-use of Opioid Medications and Alcohol Prevention Study (COAPS)

While there is limited research in the field regarding the various dimensions of co-use of alcohol and opioid medication, particularly related to co-use and levels of severity, our research has shown 20% to 30% of community pharmacy patients receiving opioid pain medications are engaged in co-use. Co-use of alcohol and opioid medications is a significant risk factor for opioid-related overdose. Community pharmacy is a valuable yet underutilized resource and setting for addressing the US opioid epidemic, with an untapped potential for identification of and intervention for risks associated with co-use of alcohol and opioids. This commentary describing the "Co-use of Opioid Medications and Alcohol Prevention Study (COAPS)" offers an innovative and promising approach to mitigating serious risks associated with co-use of alcohol (risk and non-risk use) and opioids in community pharmacy. COAPS aim 1involves adapting an existing opioid misuse intervention to target co-use of alcohol and opioid mediations. COAPS aim 2 involves testing the adapted intervention within a small-scale pilot randomized controlled trial (N = 40) to examine feasibility, acceptability and preliminary efficacy of the intervention versus standard care. COAPS aim 3 involves conducting key informant interviews related to future implementation of larger scale studies or service delivery in community pharmacy settings.

The pattern of brain oxygen response induced by intravenous fentanyl limits the time window of therapeutic efficacy of naloxone

Opioids induce respiratory depression resulting in coma or even death during overdose. Naloxone, an opioid antagonist, is the gold standard reversal agent for opioid intoxication, but this treatment is often less successful for fentanyl. While low dosing is thought to be a factor limiting naloxone's efficacy, the timing between fentanyl exposure and initiation of naloxone treatment may be another important factor. Here, we used oxygen sensors coupled with amperometry to examine the pattern of oxygen responses in the brain and periphery induced by intravenous fentanyl in freely moving rats. At both doses (20 and 60 μg/kg), fentanyl induced a biphasic brain oxygen response-a rapid, strong, and relatively transient decrease (8-12 min) followed by a weaker and prolonged increase. In contrast, fentanyl induced stronger and more prolonged monophasic oxygen decreases in the periphery. When administered before fentanyl, intravenous naloxone (0.2 mg/kg) fully blocked the hypoxic effects of moderate-dose fentanyl in both the brain and periphery. However, when injected 10 min after fentanyl, when most of hypoxia had already ceased, naloxone had minimal effect on central and peripheral oxygen levels, but at a higher dose, it strongly attenuated hypoxic effects in the periphery with only a transient brain oxygen increase associated with behavioral awakening. Therefore, due to the rapid, strong but transient nature of fentanyl-induced brain hypoxia, the time window when naloxone can attenuate this effect is relatively short. This timing limitation is critical, making naloxone most effective when used quickly and less effective when used during the post-hypoxic comatose state after brain hypoxia has already ceased and harm for neural cells already done.

Basic metabolic and vascular effects of ketamine and its interaction with fentanyl

Ketamine is a short-acting general anesthetic with hallucinogenic, analgesic, and amnestic properties. In addition to its anesthetic use, ketamine is commonly abused in rave settings. While safe when used by medical professionals, uncontrolled recreational use of ketamine is dangerous, especially when mixed with other sedative drugs, including alcohol, benzodiazepines, and opioid drugs. Since synergistic antinociceptive interactions between opioids and ketamine were demonstrated in both preclinical and clinical studies, such an interaction could exist for the hypoxic effects of opioid drugs. Here, we focused on the basic physiological effects of ketamine as a recreational drug and its possible interactions with fentanyl-a highly potent opioid that induces strong respiratory depression and robust brain hypoxia. By using multi-site thermorecording in freely-moving rats, we showed that intravenous ketamine at a range of human relevant doses (3, 9, 27 mg/kg) dose-dependently increases locomotor activity and brain temperature, as assessed in the nucleus accumbens (NAc). By determining temperature differentials between the brain, temporal muscle, and skin, we showed that the brain hyperthermic effect of ketamine results from increased intracerebral heat production, an index of metabolic neural activation, and decreased heat loss due to peripheral vasoconstriction. By using oxygen sensors coupled with high-speed amperometry we showed that ketamine at the same doses increases NAc oxygen levels. Finally, co-administration of ketamine with intravenous fentanyl results in modest enhancement of fentanyl-induced brain hypoxia also enhancing the post-hypoxic oxygen increase. Therefore, in contrast to fentanyl, ketamine increases brain oxygenation but potentiates brain hypoxia induced by fentanyl.