Ketogenic diet enhances the effects of oxycodone in mice.

Opioids have been used to manage pain for thousands of years, but they have significant potential for abuse. Prescription opioids, like oxycodone, are associated with 32% of overdoses, that have reached a total of 75,673 deaths in 2021. A major challenge is maximizing their therapeutic potential while minimizing the negative side effects including opioid use disorder (OUD). The Ketogenic Diet (KD) has been reported to reduce pain and decrease the severity of alcohol use disorder, yet its effects on oxycodone responses remain unknown. KD mice displayed increased oxycodone-induced locomotor activity and enhanced antinociceptive effects of oxycodone, suggesting a dietary effect on opiate sensitivity. Male KD mice exposed to chronic oxycodone exhibited increased naloxone-induced jumps, suggesting a sex-specific effect of diet on opioid withdrawal. Consistent with this, male KD mice self-administered less oxycodone while female KD mice did not differ from controls. Finally, no effect of KD on motivation to obtain oxycodone was observed during a progressive ratio schedule. These data suggest sex-biased effects of KD on responses to opioids that should be considered and potentially leveraged in both clinical pain management and treatment of OUD.

The vitamin D metabolites 25(OH)D and 1,25(OH)2D are not related to either glucose metabolism or insulin action in obese women.

AIM: Vitamin D deficiency has been proposed to be involved in obesity-induced metabolic disease. However, data on the relationship between 25-hydroxycholecalciferol (25(OH)D) and insulin resistance have been inconsistent, and few studies have investigated the active vitamin D metabolite, 1,25-dihydroxycholecalciferol (1,25(OH)2D). This study aimed to determine the relationship between circulating levels of both 25(OH)D and 1,25(OH)2D and direct measures of glucose metabolism and insulin action in obese women. METHODS: Serum levels of 25(OH)D and 1,25(OH)2D, and glucose metabolism and tissue-specific insulin action, as assessed in the basal state and during a two-step euglycaemic-hyperinsulinaemic clamp study with [6,6-2H2]glucose infusion, were measured in 37 morbidly obese women (age: 43±10 years; body mass index: 44±6kg/m2). RESULTS: Sixteen subjects had circulating 25(OH)D levels<50nmol/L, consistent with vitamin D deficiency, and 21 had normal 25(OH)D levels. There were no differences in either baseline characteristics or parameters of glucose metabolism and insulin action between the groups. Serum 25(OH)D, but not 1,25(OH)2D, was negatively correlated with both body mass index (r=-0.42, P=0.01) and total body fat (r=-0.46, P<0.01). Neither 25(OH)D nor 1,25(OH)2D levels were related to any measured metabolic parameters, including fasting glucose, fasting insulin, basal endogenous glucose production, and hepatic, adipose-tissue and skeletal muscle insulin sensitivity. CONCLUSION: Obesity was associated with lower levels of circulating 25(OH)D, but not with the hormonally active metabolite 1,25(OH)2D. Neither 25(OH)D nor 1,25(OH)2D were related to glucose metabolism and tissue-specific insulin sensitivity in obese women, suggesting that vitamin D does not play a major role in obesity-related insulin resistance.

Dietary triglycerides act on mesolimbic structures to regulate the rewarding and motivational aspects of feeding.

Circulating triglycerides (TGs) normally increase after a meal but are altered in pathophysiological conditions, such as obesity. Although TG metabolism in the brain remains poorly understood, several brain structures express enzymes that process TG-enriched particles, including mesolimbic structures. For this reason, and because consumption of high-fat diet alters dopamine signaling, we tested the hypothesis that TG might directly target mesolimbic reward circuits to control reward-seeking behaviors. We found that the delivery of small amounts of TG to the brain through the carotid artery rapidly reduced both spontaneous and amphetamine-induced locomotion, abolished preference for palatable food and reduced the motivation to engage in food-seeking behavior. Conversely, targeted disruption of the TG-hydrolyzing enzyme lipoprotein lipase specifically in the nucleus accumbens increased palatable food preference and food-seeking behavior. Finally, prolonged TG perfusion resulted in a return to normal palatable food preference despite continued locomotor suppression, suggesting that adaptive mechanisms occur. These findings reveal new mechanisms by which dietary fat may alter mesolimbic circuit function and reward seeking.

The influence of leptin on the dopamine system and implications for ingestive behavior.

Food intake is regulated by many factors, including sensory information, metabolic hormones and the state of hunger. In modern humans, the drive to eat has proven to be incompatible with the excess food supply present in industrialized societies. A result of this imbalance is the dramatically increased rates of obesity during the last 20 years. The rise in obesity rates poses one of the most significant public health issues facing the United States and yet we do not understand the neural basis of ingestive behavior, and specifically, our motivation to eat. Understanding how the brain controls eating will lay the foundation for systematic dissection, understanding and treatment of obesity and related disorders. The lack of control over food intake bears resemblance to drug addiction, where loss of control over behavior leads to compulsive drug use. Work in laboratory animals has long suggested that there exist common neural substrates underlying both food and drug intake behaviors. Recent studies have shown direct leptin effects on dopamine neuron function and behavior. This provides a new mechanism by which peripheral hormones influence behavior and contribute to a more comprehensive model of neural control over food intake.

Efficient studies of long-distance Bmp5 gene regulation using bacterial artificial chromosomes.

The regulatory regions surrounding many genes may be large and difficult to study using standard transgenic approaches. Here we describe the use of bacterial artificial chromosome clones to rapidly survey hundreds of kilobases of DNA for potential regulatory sequences surrounding the mouse bone morphogenetic protein-5 (Bmp5) gene. Simple coinjection of large insert clones with lacZ reporter constructs recapitulates all of the sites of expression observed previously with numerous small constructs covering a large, complex regulatory region. The coinjection approach has made it possible to rapidly survey other regions of the Bmp5 gene for potential control elements, to confirm the location of several elements predicted from previous expression studies using regulatory mutations at the Bmp5 locus, to test whether Bmp5 control regions act similarly on endogenous and foreign promoters, and to show that Bmp5 control elements are capable of rescuing phenotypic effects of a Bmp5 deficiency. This rapid approach has identified new Bmp5 control regions responsible for controlling the development of specific anatomical structures in the vertebrate skeleton. A similar approach may be useful for studying complex control regions surrounding many other genes important in embryonic development and human disease.

An extensive 3' regulatory region controls expression of Bmp5 in specific anatomical structures of the mouse embryo.

Bone morphogenetic proteins (BMPs) are secreted signaling molecules that control important developmental events in many different organisms. Previous studies have shown that BMPs are expressed at the earliest stages of skeletal development, and are required for formation of specific skeletal features, strongly suggesting that they are endogenous signals used to control formation of skeletal tissue. Despite the importance of BMP signaling in normal development, very little is known about the mechanisms that control the synthesis and distribution of BMP signals in vertebrates. Here, we identify a large array of cis-acting control sequences that lay out expression of the mouse Bmp5 gene in specific skeletal structures and soft tissues. Some of these elements show striking specificity for particular anatomical features within the skeleton, rather than for cartilage and bone in general. These data suggest that the vertebrate skeleton is built from the sum of many independent domains of BMP expression, each of which may be controlled by separate regulatory elements driving expression at specific anatomical locations. Surprisingly, some of the regulatory sequences in the Bmp5 gene map over 270 kb from the Bmp5 promoter, making them among the most distant elements yet identified in studies of eukaryotic gene expression.