LKB1 Loss Correlates with STING Loss and, in Cooperation with β-Catenin Membranous Loss, Indicates Poor Prognosis in Patients with Operable Non-Small Cell Lung Cancer

To investigate the incidence and prognostically significant correlations and cooperations of LKB1 loss of expression in non-small cell lung cancer (NSCLC), surgical specimens from 188 metastatic and 60 non-metastatic operable stage I-IIIA NSCLC patients were analyzed to evaluate their expression of LKB1 and pAMPK proteins in relation to various processes. The investigated factors included antitumor immunity response regulators STING and PD-L1; pro-angiogenic, EMT and cell cycle targets, as well as metastasis-related (VEGFC, PDGFRα, PDGFRβ, p53, p16, Cyclin D1, ZEB1, CD24) targets; and cell adhesion (β-catenin) molecules. The protein expression levels were evaluated via immunohistochemistry; the RNA levels of LKB1 and NEDD9 were evaluated via PCR, while KRAS exon 2 and BRAFV600E mutations were evaluated by Sanger sequencing. Overall, loss of LKB1 protein expression was observed in 21% (51/248) patients and correlated significantly with histotype (p < 0.001), KRAS mutations (p < 0.001), KC status (concomitant KRAS mutation and p16 downregulation) (p < 0.001), STING loss (p < 0.001), and high CD24 expression (p < 0.001). STING loss also correlated significantly with loss of LKB1 expression in the metastatic setting both overall (p = 0.014) and in lung adenocarcinomas (LUACs) (p = 0.005). Additionally, LKB1 loss correlated significantly with a lack of or low β-catenin membranous expression exclusively in LUACs, both independently of the metastatic status (p = 0.019) and in the metastatic setting (p = 0.007). Patients with tumors yielding LKB1 loss and concomitant nonexistent or low β-catenin membrane expression experienced significantly inferior median overall survival of 20.50 vs. 52.99 months; p < 0.001 as well as significantly greater risk of death (HR: 3.32, 95% c.i.: 1.71-6.43; p <0.001). Our findings underscore the impact of the synergy of LKB1 with STING and β-catenin in NSCLC, in prognosis.

Optimization of Phloretin-loaded Nanospanlastics for Targeting of FAS/SREBP1c/AMPK/ OB-Rb Signaling Pathway in HFD-induced Obesity

OBJECTIVES

Obese patients are at increased risk for CVD, which is the main cause of premature death and has been a major cause of disability and ill health in recent years. PTN, a natural dihydrochalcone flavonoid, has a variety of pharmacological characteristics. This article aimed to prepare PTN-NSLs to evaluate their anti-obesity activity.

METHODS

Morphology, Particle size, zeta potential, UV-vis, entrapment efficiency, FT-IR spectra, and an in vitro release study of PTN-NSLs were described. PTN-NSLs were also tested for their anti-obesity properties in obese rats. The LD50 of PTN-NSLs was calculated, as was the 1/20 LD50 prepared for the treatment of obese rats. Also, the level of glycemic, oxidative stress and inflammatory biomarkers were estimated in the obese rat's model.

RESULTS

The synthesized PTN-NSLs were uniform, spherically shaped, and well dispersed with no aggregation noted, with a size range of 114.06 ± 8.35 nm. The measured zeta potential value of PTN-NSLs was -32.50.8 mv. Also, the UV spectra of PTN and PTN-NSLs have strong absorption at 225 and 285 nm. Also, the LD50 of PTN-NSLs was found to be 2750 mg/kg.b.w. Moreover, administrating obese rats with PTN-NSLs resulted in improved glycemic features as well as GSH, SOD, GPx, GR, IL10, TBARs, and IL-6 levels, as well as attenuated FAS, SREBP1c, AMPK, ACO, CPT1, and OB-Rb gene expression.

CONCLUSIONS

Administration of PTN-NSLs significantly attenuated the levels of glycemic, oxidative stress, and inflammatory biomarkers. The biochemical and PCR findings are aided by histological investigations. Also, the present findings imply that PTN-NSLs might be a promising pharmacological tool for the treatment of obesity-related diseases.

Cardiac senescence is alleviated by the natural flavone acacetin via enhancing mitophagy

Cardiac senescence is associated with cardiomyopathy which is a degenerative disease in the aging process of the elderly. The present study investigates using multiple experimental approaches whether the natural flavone acacetin could attenuate myocardial senescence in C57/BL6 mice and H9C2 rat cardiac cells induced by D-galactose. We found that the impaired heart function in D-galactose-induced accelerated aging mice was improved by oral acacetin treatment in a dose-dependent manner. Acacetin significantly countered the increased serum advanced glycation end products, the myocardial telomere length shortening, the increased cellular senescence marker proteins p21 and p53, and the reduced mitophagy signaling proteins PINK1/Parkin and Sirt6 expression in aging mice. In H9C2 rat cardiac cells, acacetin alleviated cell senescence induced by D-galactose in a concentration-dependent manner. Acacetin decreased p21 and p53 expression, up-regulated PINK1/Parkin, LC3II/LC3I ratio, pLKB1, pAMPK and Sirt6, and reversed the depolarized mitochondrial membrane potential in aging cardiac cells. Mitophagy inhibition with 3-methyladenine or silencing Sirt6 abolished the protective effects of acacetin against cardiac senescence. Further analysis revealed that acacetin effect on Sirt6 was mediated by Sirt1 activation and increase of NAD+/NADH ratio. These results demonstrate that acacetin significantly inhibits in vivo and in vitro cardiac senescence induced by D-galactose via Sirt1-mediated activation of Sirt6/AMPK signaling pathway, thereby enhancing mitophagy and preserving mitochondrial function, which suggests that acacetin may be a drug candidate for treating cardiovascular disorders related to aging.

The anti-tumor agent, Dp44mT, promotes nuclear translocation of TFEB via inhibition of the AMPK-mTORC1 axis

Di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) and its analogues are potent anti-cancer agents through their ability to target lysosomes. Considering this, it was important to understand the mechanisms involved in the Dp44mT-mediated induction of autophagy and the role of 5'-adenosine monophosphate-activated protein kinase (AMPK) as a critical autophagic regulator. As such, this investigation examined AMPK's role in the regulation of the transcription factor EB (TFEB), which transcribes genes involved in autophagy and lysosome biosynthesis. For the first time, this study demonstrated that Dp44mT induces translocation of TFEB to the nucleus. Furthermore, Dp44mT-mediated nuclear translocation of TFEB was AMPK-dependent. Considering that: (1) the mammalian target of rapamycin complex 1 (mTORC1) plays an important role in the regulation of TFEB; and (2) that AMPK is a known regulator of mTORC1, this study also elucidated the mechanisms through which Dp44mT regulates nuclear translocation of TFEB via AMPK. Silencing AMPK led to increased mTOR phosphorylation, that activates mTORC1. Since Dp44mT inhibits mTORC1 in an AMPK-dependent manner through raptor phosphorylation, Dp44mT is demonstrated to regulate TFEB translocation through dual mechanisms: AMPK activation, which inhibits mTOR, and inhibition of mTORC1 via phosphorylation of raptor. Collectively, Dp44mT-mediated activation of AMPK plays a crucial role in lysosomal biogenesis and TFEB function. As Dp44mT potently chelates copper and iron that are crucial for tumor growth, these studies provide insight into the regulatory mechanisms involved in intracellular clearance and energy metabolism that occur upon alterations in metal ion homeostasis.

Determining the molecular landscape and impact on prognosis in HPV-associated head and neck cancer

BACKGROUND

Human papillomavirus (HPV) associated head and neck squamous cell carcinoma (HNSCC) has a better prognosis than HNSCC due to other risk factors. However, there is significant heterogeneity within HPV-associated HNSCC and 25% of these patients still do poorly despite receiving aggressive therapy. We currently have no good molecular tools to differentiate and exclude this "high-risk" sub-population and focus on "low-risk" patients for clinical trials. This has been a potential barrier to identifying successful de-escalation treatment strategies in HPV-associated HNSCC. We conducted an analysis of molecular markers with a well-known role in the pathogenesis of HPV-associated HNSCC and hypothesized that these markers could help independently predict recurrence and prognosis in these patients and therefore help identify at the molecular level "low-risk" patients suitable for de-escalation trials.

METHODS

We analyzed 24 tumor specimens of patients with p16+ HNSCC who underwent definitive resection as primary treatment. Tissue microarray (TMA) was generated from the 24 pathology blocks and immunohistochemistry (IHC) was performed using highly specific antibodies for our chosen biomarkers (PI3K-PTEN, AKT pathway, mTOR, 4EBP1, S6, and pAMPK, ERCC-1). Transcriptome data was also obtained for 7 p16+ HNSCC patients from The Cancer Genome Atlas (TCGA). Data from the TMA and TCGA were analyzed for association of relapse-free survival (RFS) and overall survival (OS) with protein and gene expression of the chosen biomarkers.

RESULTS

Increased pAMPK protein activity by IHC and AMPK gene expression by TCGA gene expression data was correlated with improved RFS with a trend towards statistical significance.

CONCLUSIONS

This data suggests that increased pAMPK activity and expression may portend a better prognosis in HPV-associated HNSCC undergoing primary definitive resection. However, these findings require validation in larger studies.

Metformin Therapy Aggravates Neurodegenerative Processes in ApoE-/- Mice

Epidemiological studies suggest that individuals with diabetes mellitus are at greater risk of developing Alzheimer's disease. A well-known insulin-sensitizing drug and the most widely prescribed oral medication for diabetes is metformin. There is evidence that metformin acts in a neuroprotective manner via the AMPK/mTOR pathway by inhibiting the tau phosphorylation. In addition, it is known that metformin upregulates Fgf21, which in turn activates the AMPK/mTOR pathway and mediates neuroprotection. Thus, metformin-induced Fgf21 release may be involved in AMPK/mTOR activation. However, some studies reported that metformin causes cognition impairment. Due to the controversial data on the neuroprotective properties of metformin, we treated Apolipoprotein E deficient (ApoE- /-) mice, a mouse model of tauopathy, with metformin for 18 weeks. Metformin-treated mice revealed increased expression of lipogenic genes, i.e., lxrα and srebp1c. In line with this, metformin caused an increase in plasma triglyceride leading to enhanced gliosis as indicated by an increase of GFAP-positive cells. Although the systemic Fgf21 concentration was increased, metformin did not activate the FgfR1c/AMPK/mTOR pathway suggesting a Fgf21-resistant state. Further, metformin-treated mice showed increased tau phosphorylation and reduced numbers of NeuN-and PSD95-positive cells. Thus, metformin-associated lipogenesis as well as inflammation aggravated neurodegenerative processes in ApoE- /- mice. Consequently, this study supports previous observations showing that metformin causes impairment of cognition.

The protective effect of metformin in scopolamine-induced learning and memory impairment in rats

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease in the world. One of the most commonly prescribed oral antidiabetic drug, metformin, has been shown to have beneficial effects on restoring impaired cognitive function. In the present study, we investigated the effects of metformin on spatial memory in terms of alleviating scopolamine-induced learning and memory impairments in rats by using the Morris water maze (MWM) test and the modified elevated plus-maze (mEPM) test. Furthermore, we investigated the possible mechanisms of action of metformin in preventing cognitive dysfunction.

METHODS

Male Wistar rats received metformin (50, 100, or 200 mg/kg/day) via gavage feeding for three weeks. Scopolamine was administered intraperitoneally before the probe step of the MWM test or the acquisition session of the mEPM test.

RESULTS

The learning and memory impairment induced by scopolamine was reversed by metformin. In addition, metformin improved the level of phosphorylated AMP-activated protein kinase and cAMP responsive element binding protein. However, metformin pretreatment had no impact on inhibiting the scopolamine-induced changes in acetylcholine levels. Furthermore, metformin exerted its antioxidant effect by significantly reversing scopolamine-induced changes in malondialdehyde, total antioxidant status, and superoxide dismutase levels in the hippocampus.

CONCLUSION

Our results indicate that one of the most commonly used antidiabetic drug, metformin, has the potential to prevent the development of dementia and be a novel therapeutic drug for the amelioration of cognitive dysfunction in AD.

Mechanistic evaluation of AMPK/SIRT1/FXR signaling axis, inflammation, and redox status in thioacetamide-induced liver cirrhosis: The role of Cichorium intybus linn (chicory)-supplemented diet

Liver cirrhosis is a scene profitable to the advance of hepatocellular carcinoma (HCC). The current work was engrossed to weigh the potential role of Cichorium intybus linn against thioacetamide (TAA)-induced liver cirrhosis and their probable underlying biochemical and molecular mechanisms. farnesoid-X-receptor (FXR) expression, proliferating cell nuclear antigen (PCNA) immunoreactivity, and activated AMP protein kinase (pAMPK), sirtuin-1 (SIRT1), and interleukin-6 (IL6) levels were estimated in hepatic tissue by real-time PCR, immunohistochemistry, and immunoassay, respectively. C. intybus linn supplementation caused a significant improvement in serum liver enzymes, albumin, bilirubin levels, tissues redox status and hepatic histological features in addition to decreased IL6 level, hydroxylproline content, and PCNA immunoreactivity. On contrary, increased pAMPK/SIRT1 levels and upregulated FXR gene expression were observed. C. intybus linn could feasibly protect against TAA-induced hepatic damage, fibrosis, and cirrhosis by relieving oxidative stress and by interruption of the inflammatory pathway via AMPK/SIRT1/FXR signaling. PRACTICAL APPLICATIONS: No specific therapies are available until now to target the underlying mechanisms for protection against liver diseases. Herbal protection is widely available and cheap with no side effect. Cichorium intybus linn, a natural supplement, is proved in this current work to have the potential of being hepatoprotectant, antioxidant, and anti-inflammatory agents, thus reducing the risk of hepatic cirrhosis.

CD24 Expression and B Cell Maturation Shows a Novel Link With Energy Metabolism: Potential Implications for Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

CD24 expression on pro-B cells plays a role in B cell selection and development in the bone marrow. We previously detected higher CD24 expression and frequency within IgD+ naïve and memory B cells in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) compared with age-matched healthy controls (HC). Here, we investigated the relationship between CD24 expression and B cell maturation. In vitro stimulation of isolated B cells in response to conventional agonists were used to follow the dynamics of CD24 positivity during proliferation and differentiation (or maturation). The relationship between CD24 expression to cycles of proliferation and metabolism in purified B cells from HC was also investigated using phospho-flow (phosphorylation of AMPK-pAMPK), 1proton nuclear magnetic resonance and Mitotracker Far-red (Mitochondrial mass-MM). In vitro, in the absence of stimulation, there was an increased percentage of CD24+ viable B cells in ME/CFS patients compared to HC (p < 0.05) following 5 days culture. Following stimulation with B cell agonists, percentage of CD24+B cells in both naïve and memory B cell populations decreased. P < 0.01). There was a negative relationship between percentage of CD24+B cells with MM (R² = 0.76; p < 0.01), which was subsequently lost over sequential cycles of proliferation. There was a significant correlation between CD24 expression on B cells and the usage of glucose and secretion of lactate in vitro. Short term ligation of the B cell receptor with anti-IgM antibody significantly reduced the viability of CD24+ memory B cells compared to those cross-linked by anti-IgD or anti-IgG antibody. A clear difference was found between naïve and memory B cells with respect to CD24 expression and pAMPK, most notably a strong positive association in IgD+IgM+ memory B cells. In vitro findings confirmed dysregulation of CD24-expressing B cells from ME/CFS patients previously suggested by immunophenotype studies of B cells from peripheral blood. CD24-negative B cells underwent productive proliferation whereas CD24+ B cells were either unresponsive or susceptible to cell death upon BCR-engagement alone. We suggest that CD24 expression may reflect variations in energy metabolism on different B cell subsets.

Long-term caloric restriction in ApoE-deficient mice results in neuroprotection via Fgf21-induced AMPK/mTOR pathway

Caloric restriction (CR) decelerates the aging process, extends lifespan and exerts neuroprotective effects in diverse species by so far unknown mechanisms. Based on known neuroprotective effects of fibroblastic growth factor 21 (Fgf21) we speculate that CR upregulates Fgf21, which phosphorylates neuronal AMP-activated protein kinase (AMPK), leading to a decrease of mammalian target of rapamycin (mTOR) signaling activity and an inhibition of tau-hyperphosphorylation. This in turn reduces the formation of neurofibrillary tangles, a neuropathological hallmark of Alzheimer's disease. ApoE-deficient mice (ApoE−/−), serving as a model of neurodegeneration, showed upon CR vs. ad libitum feeding increased Fgf21 levels in both, plasma and brain as well as higher phosphorylation of fibroblastic growth factor receptor 1c (Fgfr1c), extracellular signal-regulated kinases 1/2 (ERK1/2) and AMPK in brain, lower activity of mTOR and decreased Tau-phosphorylation. Finally, CR in ApoE−/− mice caused neuroprotection as indicated by a higher synaptic plasticity shown by immunohistochemical analysis with increased numbers of PSD95-positive neurons and a better cognitive performance as analyzed with Morris water maze test. These data provide substantial evidence that neuroprotection upon CR seems to be Fgf21-dependent. Further experiments are necessary to evaluate Fgf21 as a therapeutic tool to treat tauopathy for improvement of cognitive performance.

Soluble epoxide hydrolase null mice exhibit female and male differences in regulation of vascular homeostasis

Increased CYP epoxygenase activity and consequently up regulation of epoxyeicosatrienoic acids (EETs) levels provides protection against metabolic syndrome and cardiovascular diseases. Conversion of arachidonic acid epoxides to diols by soluble epoxide hydrolase (sEH) diminishes the beneficial cardiovascular properties of these epoxyeicosanoids. We therefore examined the possible biochemical consequences of sEH deletion on vascular responses in male and female mice. Through the use of the sEH KO mouse, we provide evidence of differences in the compensatory response in the balance between nitric oxide (NO), carbon monoxide (CO), EETs and the vasoconstrictor 20-HETE in male and female KO mice. Serum levels of adiponectin, TNFα, IL-1b and MCP1 and protein expression in vascular tissue of p-AMPK, p-AKT and p-eNOS were measured. Deletion of sEH caused a significant (p<0.05) decrease in body weight, and an increase in adiponectin, pAMPK and pAKT levels in female KO mice compared to male KO mice. Gene deletion resulted in a higher production of renal EETs in female KO compared to male KO mice and, concomitantly, we observed an increase in renal 20-HETEs levels and superoxide anion production only in male KO mice. sEH deletion increased p-AKT and p-eNOS protein expression but decreased p-AMPK levels in female KO mice. Increased levels of p-eNOS at Thr-495 were observed only in KO male mice. While p-eNOS at 1177 were not significantly different between male and female. Nitric oxide production was unaltered in male KO mice. These results provide evidence of gender differences in the preservation of vascular homeostasis in response to sEH deletion which involves regulation of phosphorylation of eNOS at the 495 site.

Estradiol regulates effects of hindbrain activator 5-aminoimidazole-4-carboxamide-riboside administration on hypothalamic adenosine 5'-monophosphate-activated protein kinase activity and metabolic neurotransmitter mRNA and protein expression

Hindbrain adenosine 5'-monophosphate-activated protein kinase (AMPK) activation alters hypothalamic neuronal genomic activity in an estradiol (E)-dependent manner. This study examines the premise that E regulates metabolic effector neuron reactivity to hindbrain AMPK. Paraventricular (PVH), arcuate (ARH), and ventromedial (VMH) nuclei were micropunched from brains of E- or oil (O)-implanted ovariectomized female rats that had been injected, into the fourth ventricle, with the AMPK activator 5-aminoimidazole-4-carboxamide-riboside (AICAR; A) or saline (S) and analyzed by quantitative polymerase chain reaction and Western blotting for neurotransmitter mRNA and protein expression. PVH corticotrophin-releasing hormone gene and protein profiles were decreased in O/A and E/A animals. ARH pro-opiomelanocortin (POMC) mRNA and protein were both elevated in O/A but were diminished or unchanged, respectively, in E/A animals; ARH neuropeptide Y (NPY) transcription was inhibited in O/A and E/A animals, but neuropeptide content was augmented in E/A only. VMH SF-1 mRNA and protein were reduced in O and E animals. AICAR did not alter AMPK protein in any structure but elevated PVH (↑E), did not alter ARH, and decreased VMH (↓O,↓E) pAMPK. Results demonstrate hypothalamic metabolic neurotransmitter and AMPK reactivity to hindbrain AMPK activation, including E-dependent adjustments in POMC and NPY transcription and protein expression. Dissimilar POMC (↑O vs. ↔E) and NPY (↓O vs. ↑E) neuropeptide responses to caudal fourth ventricle AICAR indicate E regulation of hindbrain AMPK signaling and/or target receptivity, implying that ARH-controlled metabolic responses may differ in the presence vs. absence of E. Evidence for variable changes in hypothalamic AMPK activity resulting from hindbrain sensor manipulation suggests that individual (or region-based groups of) AMPK-expressing neuron populations are uniquely impacted by hindbrain AMPK.

Hindbrain medulla catecholamine cell group involvement in lactate-sensitive hypoglycemia-associated patterns of hypothalamic norepinephrine and epinephrine activity

Cell-type compartmentation of glucose metabolism in the brain involves trafficking of the oxidizable glycolytic end product, l-lactate, by astrocytes to fuel neuronal mitochondrial aerobic respiration. Lactate availability within the hindbrain medulla is a monitored function that regulates systemic glucostasis as insulin-induced hypoglycemia (IIH) is exacerbated by lactate repletion of that brain region. A2 noradrenergic neurons are a plausible source of lactoprivic input to the neural gluco-regulatory circuit as caudal fourth ventricular (CV4) lactate infusion normalizes IIH-associated activation, e.g. phosphorylation of the high-sensitivity energy sensor, adenosine 5'-monophosphate-activated protein kinase (AMPK), in these cells. Here, we investigated the hypothesis that A2 neurons are unique among medullary catecholamine cells in directly screening lactate-derived energy. Adult male rats were injected with insulin or vehicle following initiation of continuous l-lactate infusion into the CV4. Two hours after injections, A1, C1, A2, and C2 neurons were collected by laser-microdissection for Western blot analysis of AMPKα1/2 and phosphoAMPKα1/2 proteins. Results show that AMPK is expressed in each cell group, but only a subset, e.g. A1, C1, and A2 neurons, exhibit increased sensor activity in response to IIH. Moreover, hindbrain lactate repletion reversed hypoglycemic augmentation of pAMPKα1/2 content in A2 and C1 but not A1 cells, and normalized hypothalamic norepinephrine and epinephrine content in a site-specific manner. The present evidence for discriminative reactivity of AMPK-expressing medullary catecholamine neurons to the screened energy substrate lactate implies that that lactoprivation is selectively signaled to the hypothalamus by A2 noradrenergic and C1 adrenergic cells.

Amelioration of palmitate-induced insulin resistance in C₂C₁₂ muscle cells by rooibos (Aspalathus linearis)

Increased levels of free fatty acids (FFAs), specifically saturated free fatty acids such as palmitate are associated with insulin resistance of muscle, fat and liver. Skeletal muscle, responsible for up to 80% of the glucose disposal from the peripheral circulation, is particularly vulnerable to increased levels of saturated FFAs. Rooibos (Aspalathus linearis) and its unique dihydrochalcone C-glucoside, aspalathin, shown to reduce hyperglycemia in diabetic rats, could play a role in preventing or ameliorating the development of insulin resistance. This study aims to establish whether rooibos can ameliorate experimentally-induced insulin-resistance in C₂C₁₂ skeletal muscle cells. Palmitate-induced insulin resistant C₂C₁₂ cells were treated with an aspalathin-enriched green (unfermented) rooibos extract (GRE), previously shown for its blood glucose lowering effect in vitro and in vivo or an aqueous extract of fermented rooibos (FRE). Glucose uptake and mitochondrial activity were measured using 2-deoxy-[³H]-D-glucose, MTT and ATP assays, respectively. Expression of proteins relevant to glucose metabolism was analysed by Western blot. GRE contained higher levels of all compounds, except the enolic phenylpyruvic acid-2-O-glucoside and luteolin-7-O-glucoside. Both rooibos extracts increased glucose uptake, mitochondrial activity and ATP production. Compared to FRE, GRE was more effective at increasing glucose uptake and ATP production. At a mechanistic level both extracts down-regulated PKC θ activation, which is associated with palmitate-induced insulin resistance. Furthermore, the extracts increased activation of key regulatory proteins (AKT and AMPK) involved in insulin-dependent and non-insulin regulated signalling pathways. Protein levels of the glucose transporter (GLUT4) involved in glucose transport via these two pathways were also increased. This in vitro study therefore confirms that rooibos can ameliorate palmitate-induced insulin resistance in C₂C₁₂ skeletal muscle cells. Inhibition of PKC θ activation and increased activation of AMPK and AKT offer a plausible mechanistic explanation for this ameliorative effect.