Microbiota-Gut-Brain Axis and Immunity

Liver Pathology Part III - MAFLD e-learning P1

• MAFLD (Metabolic Dysfunction Associated Fatty Liver Disease) is an e-learning part 1 of BMS 200, Week 1.
• The Canadian College of Naturopathic Medicine (CCNM) is the course provider.

Non-Alcoholic Fatty Liver Disease (NAFLD)

• NAFLD is steatosis in the absence of significant alcohol consumption; the most common cause of liver disease in the US.
• Estimated prevalence: up to 40% of the US population.
• Forms include:
  • Simple hepatic steatosis (steatosis complicated by inflammation)
  • Non-alcoholic steatohepatitis (NASH) – progression to cirrhosis in 10–20% of cases.
  • In those progressing to cirrhosis, the incidence of liver cancer can be as high as 1–2% per year
• Progression to NASH is uncommon.

Pathologic Findings of NAFLD

• Initially, hepatocyte ballooning, lobular inflammation, and steatosis (fat accumulation in hepatocytes) are observed.
• Progressive disease leads to increasing fibrosis, eventually causing cirrhosis.
• NAFLD is strongly associated with obesity and the metabolic syndrome.

Pathophysiology of NAFLD

• Two-hit model:
  • Hepatic fat accumulation
  • Increased oxidative stress – free radicals cause lipid peroxidation of the accumulated intracellular fat
• Obesity is associated with reduced intestinal barrier function and increased inflammation in the liver.
• Movement of microbes from the gut into the portal circulation may be a factor.

General Cirrhosis Pathogenesis

• Cirrhosis is defined as diffuse remodeling of the liver into parenchymal nodules surrounded by fibrous bands; with variable degrees of vascular shunting.
• Stellate cells become activated and differentiate to myofibroblasts, which are highly fibrogenic.
• This activation is triggered by inflammatory cytokines (e.g., TNF-alpha), toxins, and reactive oxygen species.
• Signals implicated include PDGF, TGF-beta, and IL-17.
• Deposition of extracellular matrix (ECM) in the space of Disse forms fibrous septae in regions of hepatocyte loss.

NAFLD - Dynamic Spectrum

• Demonstrates a dynamic spectrum progressing from healthy liver through steatosis, steatohepatitis (NASH), and cirrhosis, culminating in severe conditions such as cirrhosis and associated potentially life-threatening implications.
• Pictures labeled A, B, C, and D, exemplify healthy liver, fatty liver, steatohepatitis, and cirrhosis, respectively, with their features.

NAFLD - Clinical Features

• Typically asymptomatic until hepatic failure due to cirrhosis
• Clinical findings are often due to accompanying atherosclerotic disease/diabetes. Cardiovascular disease is a frequent cause of death.
• Fatigue and right-sided abdominal pain can occur in some cases.
• Increased risk of hepatocellular carcinoma (HCC).

NAFLD – Diagnosis

• Liver enzymes are often unreliable for diagnosis.
• Scoring systems (age, BMI, fasting glucose, AST, ALT) are helpful for assessing inflammation and fibrosis.
• Definitive diagnosis often requires imaging (e.g., ultrasound, CT) or biopsy. -

MAFLD vs NAFLD

• MAFLD is defined as metabolic dysfunction-associated fatty liver disease.
• Both MAFLD and NAFLD require a 5% level of hepatic steatosis.
• NAFLD diagnosis involves excluding other causes of liver disease as a negative criterion (e.g., significant alcohol use, hemochromatosis).
• MAFLD requires metabolic drivers of hepatic steatosis and inflammation, with examples including obesity, type 2 diabetes mellitus (T2DM), and a “metabolic dysfunction” composite score, with potentially serious long-term complications.

MAFLD and NAFLD Diagnostic Criteria

• Diagnostic criteria for MAFLD include 2 out of 7 metabolic risk factors (elevated waist circumference, blood pressure > 130/85, triglycerides > 1.7 mmol/L, lower HDL cholesterol, prediabetes, elevated HOMA insulin resistance score, or elevated C-reactive protein [CRP]).
• The criteria are compared to NAFLD, which does not require this many metabolic risk factors but includes presence of possible inflammation and potentially negative outcomes.

Why Diagnostic Differences Matter

• Clearer diagnoses can help distinguish patients who have non-alcoholic steatohepatitis (NASH) with a coexisting chronic viral hepatitis, making treatment more precise.
• More accurate diagnoses lead to improved identification of patients requiring aggressive and targeted management, particularly for those with worsened liver fibrosis.
• A MAFLD diagnosis carries a higher risk of subsequent conditions, such as diabetes, chronic kidney disease, and worsened lung function (especially after COVID infection).

Under-reporting of Alcohol Ingestion

• Under-reporting of alcohol ingestion is a concern in NAFLD diagnoses, with up to 30% of individuals in some cohorts possibly consuming alcohol regularly at clinically significant quantities.
• Cultural stigma regarding alcohol consumption might influence under-reporting.

Is a MAFLD diagnosis "redundant"?

• The clinical relevance of a MAFLD diagnosis for the clinician vs. a diagnosis of NAFLD + metabolic syndrome or obesity/diabetes is debated.
• Several studies support that MAFLD is associated with worsening mortality compared to NAFLD, highlighting the potential implications of a MAFLD diagnosis over a less specific NAFLD diagnosis.

MAFLD - Additional Pathophysiology

• Obesity, insulin resistance, and fatty liver tend to cluster together because insulin resistance increases FFA, from adipocytes to triglycerides, storage in hepatocytes.
• Elevated levels of glucose and insulin can lead to hepatic triglyceride synthesis.
• Adiponectin, an adipokine released by visceral fat, increases glucose utilization and fatty acid oxidation, lowering levels with increased intra-abdominal fat.

MAFLD - Counteracting Pathophysiology

• Lifestyle modifications that promote weight loss are generally the best approach to treating MAFLD.
• Exercise and weight loss improve fibrosis and steatosis, particularly in those with obesity or type II diabetes.
• Some medication, for example, thiazolidinedione, are often used in tandem with lifestyle modifications and interventions support better insulin sensitivity, increasing adiponectin secretion.
• Incretin agonists can enhance insulin secretion and also promote weight loss.
• Supplements may provide some beneficial effects such as those shown to decrease oxidative stress in hepatocytes, lower steatosis, and decrease inflammation, potentially improving certain conditions of individuals with MAFLD and underlying conditions.

An Approach to Hepatic Investigations

• Blood tests (liver enzymes, liver function tests, etc.) and imaging are used for investigating liver health and pathology in e-learning P2 of BMS 200.

Laboratory Analysis of the Liver

• Compare and contrast various blood tests, including transaminases (ALT, AST), ALP, bilirubin, albumin, and PT/INR to assess the liver's etiology and extent of damage and associated pathologies.

General Patterns and Concepts

• Hepatocyte or biliary tree damage causes enzymes to leak into the bloodstream.

• Serum levels of liver enzymes (e.g., ALT, AST) can indicate damage but do not always reflect function.

• Serum parameters provide a more comprehensive functional assessment.

• Serum albumin, decreases with impaired hepatic function, indicative of hepatic function impairment.

• Bilirubin, excreted into the biliary tree, increases with damaged liver function or some hepatic dysfunction.

• Prothrombin time (PT) results reflected in PT/ INR show impaired function and less coagulation proteins.

General Patterns and Concepts (Hepatocellular vs Cholestatic)

• In cases where hepatocytes are damaged but biliary tree functions fine:
  • Elevated AST and ALT
  • Normal or mildly elevated ALP or GGT.
• In situations with biliary tree obstruction/inflammation:
  • Elevated ALP and GGT
  • Normal or elevated AST and ALT

Liver Enzymes - ALT

• ALT (alanine aminotransferase) is mainly found in the cytosol of hepatocytes.
• Small amounts are released into the bloodstream in healthy individuals.
• Significant elevations usually indicate hepatocyte damage.
• Normal levels typically range from 10 to 40 IU.
• Relatively specific for hepatocyte damage.

Liver Enzymes - AST

• AST (aspartate aminotransferase) is found in hepatocyte cytosol and mitochondria.
• Elevated levels are less specific for hepatocyte damage.
• Levels similar to ALT, 10–40 IU (normal range).
• In disrupted hepatocytes, its release is usually less than ALT.

Liver Enzymes – ALP

• ALP (alkaline phosphatase) is primarily present on the canalicular membrane of hepatocytes.
• Found also in bone (during growth) and placenta.
• Increased during pregnancy, childhood, and adolescence, or bone fracture/other bone changes.
• Released during biliary tree/gallbladder dysfunction.
• Normal level ranges from 35 to 100 IU.

Liver Enzymes – GGT & 5' Nucleotidase

• GGT (gamma-glutamyl transpeptidase) is associated with isolated elevations in the liver and more often in alcohol-use disorder.
• 5'-NT, hepatobiliary disease is more specific for increased levels.

Liver Function Tests – Bilirubin

• Two forms of bilirubin are measured: unconjugated (indirect) and conjugated (direct).
• Due to large hematomas, RBC disorders, and damage, unconjugated bilirubin might increase in the blood.
• Hepatocyte damage and some other conditions can cause an increase in conjugated bilirubin in the blood.

Liver Function Tests – Albumin

• Albumin is a liver-synthesized protein maintaining oncotic pressure and transporting hydrophobic substances.
• Lower levels suggest impaired liver function
• Impaired hepatic function (e.g., long-term deficiency in production, protein malnutrition, loss from other organs, extracellular fluid accumulation due to overhydration) reduces albumin levels.
• Albumin has a long half-life (nearly 3 weeks); significant liver dysfunction must persist for some time before a drop in level is apparent.

Liver Function Tests – PT/INR

• PT/INR (prothrombin time/international normalized ratio) measures clotting time, a liver function test that is more acutely sensitive to liver damage.
• Higher values usually indicate impaired hepatic function due to deficient coagulation factors (liver dysfunction or reduced Vitamin K).
• INR values around 1.5 indicate a longer clotting time than normal.
• INR increases fairly quickly after liver synthetic capacity deterioration.
• Shorter half-life compared to albumin means it is a better test for acute liver function assessment.

Bringing It All Together – Liver Labs

• Review of various acute and chronic liver injury patterns (hepatocellular and cholestatic) based on abnormalities observed in blood tests and imaging.
• Liver test patterns in different disorders such as cirrhosis, hepatitis, and others are discussed.

Liver Imaging - FYI Review

• Simple forms of ultrasound are the best way to study the larger biliary ducts and gallbladder.
• MRI/CT is useful for studying masses, and MRI can provide details on liver fibrosis.
• MRCP is a specific form of MRI that provides detailed images of the biliary system.
• A liver biopsy is essential for evaluating and confirming a stage of fibrosis or cirrhosis when other tests do not provide a clear diagnostic picture or confirm an unclear diagnosis.

Liver Investigations in MAFLD - FYI

• Diagnosis of MAFLD is usually expensive, with the toughest part being to definitively and accurately diagnose steatosis larger than 5%.
• Elastography and ultrasound are well-used forms of assessment of liver steatosis.
• Liver biopsy is usually not required for diagnosis and assessment of steatosis and fibrosis.
• Blood tests (e.g., elevations of ALT (alanine transaminase)) are used to show changes of damage.

MAFLD Screening Tests (FYI)

• FIB-4 score calculation uses patient age, AST, ALT, and platelet count.
• NAFLD fibrosis score involves patient age, BMI, and insulin resistance/diabetes along with blood tests.

Etiology of Eating Disorders

• Anorexia nervosa and bulimia are complex disorders with many contributing factors, including psychological factors (OCD traits, cognitive rigidity, emotional sensitivity, impulsivity, history of developmental stressors, and interpersonal relationships), body dissatisfaction, and behavioral factors (dieting and athletics).
• Biological factors, including genetic effects and dysfunction in neurotransmitter systems (serotonin, dopamine, norepinephrine, opioid, and cholecystokinin), also play a role.

Complications of Eating Disorders

• All-cause mortality rates for individuals with eating disorders are 2–10 times higher than the general population, independently of weight.
• Complications include vitamin and mineral deficiencies, stunted growth, reduced gastric motility, and various consequences of malnutrition (e.g., bradycardia, hypotension, orthostasis, hypothermia, metabolic alkalosis, hypochloremia, increased bicarbonate, osteopenia, and myopathies).
• Purging behaviors can lead to complications, such as esophageal tears, intractable vomiting, hematemesis (vomiting blood/vomiting with blood), metabolic acidosis (from laxative abuse), hypokalemia, and cardiomyopathies.

Pathogenesis of Obesity, Part 1

• This segment introduces the factors involved in obesity's development.

Review from 150: Insulin Resistance & Obesity

• Obesity and a lack of exercise are the most important environmental risk factors for insulin resistance.
• Most cases of insulin resistance are multifactorial, influenced by both genetic and environmental factors.

Review from 150: Obesity FAQs

• Obese people often consume more calories compared to their lean counterparts, however this is not always the case.
• Research suggests that some obese people have impaired satiety and thus need more food intake to maintain their current weight.
• Obese individuals may have a decreased basal metabolic rate (BMR), burning fewer calories at rest.

Review from 150: Regulation of Body Weight and Appetite

• Satiety signals, such as leptin, GLP-1, CCK, PYY, and vagal afferents, regulate body weight and appetite in the hypothalamus.
• Hunger signals, such as ghrelin released by the stomach, stimulate eating behaviors.
• All these regulators act on specific hypothalamic nuclei to regulate food intake and energy expenditure.

Review from 150: Controllers of Appetite

• Leptin, a hormone released by adipose tissue, regulates food intake and energy expenditure in the hypothalamus.
• Proopiomelanocortin (POMC) is a protein produced by the hypothalamus and converted to alpha-melanocyte-stimulating hormone (α-MSH).
• Agouti-related protein (AgRP) inhibits the effect of α-MSH.

Review from 150: Insulin Resistance and Visceral Fat

• Non-esterified fatty acids (NEFAs) increase insulin resistance.
• Adipokines modify the sensitivity of insulin receptors;
• Pro-inflammatory cytokines decreased insulin receptor sensitivity..

Visceral Obesity, Insulin Resistance, and Inflammation

• Visceral adipocytes recruit and activate macrophages.
• Proinflammatory cytokines (TNF-α, MCP-1) elevated due to increased production by CRP of the liver.
• The excess fatty acids activate DAMPs, which trigger the overproduction inflammatory cytokines in many cells leading to insulin resistance.

Review from 150: Chronic Inflammation and Obesity

• Systemic inflammatory effects of obesity;
• Excessive lipid buildup (ROS).
• Elevated concentrations of free fatty acids (FFAs) can bind to PAMP-R within adipocytes.
• Both conditions can trigger the production of IL-6 and TNF-α cytokines by the adipocyte and lead to insulin resistance.

Review from 150: Insulin Resistance and Visceral Fat

• Adipocytes produce adipokines, influencing insulin sensitivity.
• Circulating free fatty acids (FFAs) increase with obesity leading to increased insulin resistance;
• Beta-cells may compensate for insulin resistance initially, but eventually, these cells fail to keep up with demand, thus declining in insulin secretion, leading eventually to type 2 diabetes.

Obesity - Definitions

• Overweight and obesity are defined using BMI (body mass index), calculated as weight in kilograms divided by height in meters squared.
• Overweight (BMI ≥ 25 kg/m²).
• Obesity (BMI ≥ 30 kg/m²).
• Waist-to-hip ratio is another measure sometimes used for obesity assessment, which is calculated as waist circumference divided by hip circumference.

Obesity definitions - Energy Expenditure

• EE (energy expenditure) is the total amount of energy expended, measured in kcal/day.
• This includes basal metabolic rate (RMR), activity-related energy expenditure (AEE) – which include exercise activity thermogenesis (EAT), and non-exercise activity thermogenesis (NEAT).
• Diet-induced thermogenesis (DIT) is the increased metabolic rate following food intake (kcal/day).

Energy Expenditure Breakdown

• Exercise-related physical activity and spontaneous physical activity (fidgeting) are comparable with exercise-related activity thermogenesis (EAT) and non-exercise activity thermogenesis (NEAT), respectively;
• in most people, EAT is much less than NEAT.
• Training that amounts to 2 or more hours per week can increase EE by 1 to 2 percent points.

RMR

• RMR (resting metabolic rate) is the energy expenditure at rest.
• It is strongly associated with fat-free mass (FFM), that is proportional to the weight, age, sex, and time of day of an individual, as well as the degree of error in measuring.
• A 60 to 75% proportion of daily energy expenditure (EE) is often made up of RMR when individuals are sedentary.
• Intra-individual variation in RMR is approximately between 7.5-18%.

Components of Daily EE

• The graphic displays varying aspects of energy expenditure in lean and obese adults, including DIT, EAT, NEAT, and RMR.

RMR vs BMR

• RMR, resting metabolic rate, has less stringent conditions than BMR, basal metabolic rate.
• 80% of BMR variations are due to FFM variations.
• RMR values, which measure the baseline metabolic rate in a post-absorptive state, can vary by 10% from BMR values.

NEAT – Generalities

• NEAT (non-exercise activity thermogenesis) is the energy expenditure resulting from spontaneous physical activity or energy expenditure not specifically from exercise;
• It varies significantly between individuals and among populations based on occupation, leisure activities, molecular/genetic factors, and seasonal effects, which account for nearly 50% and even over 60% of all variation in daily energy expenditure among highly active individuals.

NEAT Impact of Diet and Exercise

• NEAT can be affected by overfeeding and underfeeding, however overfeeding doesn't substantially upregulate all of these aspects to a compensatory extent, although a minority do.
• A significant decrease in NEAT is associated with chronic underfeeding, which often also leads to FFM (Fat-Free Mass) loss.
• Exercise regimens coupled with underfeeding may not decrease NEAT to the same extent.

Models of Energy Expenditure

• Independent model: changes in energy expenditure (EE) are independent of energy budgeted for behaviors (NEAT, EAT).
• Compensation model: increasing EE in one area (e.g., EAT) can lead to decreases in another area (e.g., RMR or NEAT)
• Evidence supports both models, but literature on weight loss indicates that some people respond to overfeeding by increasing NEAT, whereas others do not. This variation in response is noteworthy.

Exercise, Diet and Insulin Resistance

• Caloric restriction can make skeletal muscles more efficient.
• Molecular “switches” and decreased SNS activity contribute to less energy expenditure in the skeletal muscles in response to caloric restriction.
• Exercise causes translocation of GLUT-4 to the sarcolemma, improving glucose transport into active muscle and impacting insulin resistance.

Small Group Activity

• Students are assigned to research a specific scientific paper using provided details to answer questions related to the content of the paper.

How do we regulate energy intake?

• A homeostatic pathway is involved in regulating energy intake by increasing eating behavior when energy stores are low.
• Peripheral players like adipose tissue, stomach, intestines, special senses, pancreas, and liver release endocrine signals to modulate appetite and energy expenditure to maintain energy balance (homeostasis).
• Central players such as the vagus nerve, brainstem, nuclei of the hypothalamus, and cortical areas translate these peripheral signals and initiate signals to modulate energy intake and control eating behavior;
• Another pathway, called the hedonic pathway, is also vital in regulating and influencing food intake, especially in situations with no or little internal hunger cues, and is often influenced by external cues and hedoning.

Serotonin Signaling and the Homeostatic Pathway

• These serotonin-releasing neurons project to the arcuate nucleus, influencing MSH release and AGRP/NPY, critical signals in the homeostatic pathway.
• Serotonin signaling activation of MSH neurons and inhibition of AGRP/NPY neurons play important roles in regulating satiety and/or potentially causing dysregulated responses in appetite and eating behaviour.
• Lorcaserin acts as a 5-HT receptor agonist, stimulating weight loss in obese individuals, involving serotonin signaling changes.

How Do We Regulate Energy Intake? (Hedonic Model)

• Food intake is often driven by pleasure centers (reward pathways) in the brain, not solely by nutrient availability.
• The brain areas associated with reward, such as the lateral hypothalamus, ventral tegmental area (VTA), nucleus accumbens (NAc), amygdala, and the prefrontal/orbitofrontal cortex, integrate signals regarding pleasure/reward and initiate signals to modulate energy intake.
• The brain chemicals critical for these processes include dopamine and endogenous opioids, which are linked with positive feelings associated with eating certain food.
• Hedonic pathways may independently or otherwise influence intake in relation to homeostatic regulation, so regulation is likely a dual process.

Simple "CNS Portion" of the Hedonic Model

• The lateral hypothalamus projects to the ventral tegmental area (VTA).
• Dopamine release in the VTA diffuses to multiple brain areas and influences motivation and reward centers, specifically the nucleus accumbens (NAc) and amygdala.
• The prefrontal and orbitofrontal cortex and the VTA/NA project back to the hypothalamus, mediating the interplay between the hedonic and homeostatic pathways in overall energy intake regulation.

How Do We Regulate Energy Intake?

• The hedonic and homeostatic pathways regulate energy intake.
• The homeostatic pathway may be influenced by activity (or lack thereof) within the hedonic pathway in obesity, resulting in appetite and intake imbalances.
• The hypothalamus is the overall master regulator of the intake, balancing information from both hedonic and homeostatic pathways to drive eating behavior.

Energy Intake and Reward Deficiency

• The reward deficiency hypothesis suggests that lean individuals seem to have greater reward pathway activation than obese individuals, possibly due to “reward deprivation" in those who are not able to properly regulate intake or in the context of other conditions.
• This suggests that anticipation and experiencing pleasure from food intake are associated with energy intake.
• Food cues/palatable food stimuli elicit more activation in the obese corticolimbic system. Increased reward expectation may potentially lead to increased eating behavior.

The "Peripheral" Homeostatic Players

• Adipose tissue releases hormones like leptin, adiponectin, and resistin.
• The gastrointestinal tract (GI tract) releases hormones, including ghrelin, GLP-1, CCK, and PYY, which act on the hypothalamus to regulate appetite and energy intake/expenditure;
• The pancreas releases insulin and other hormones related to metabolism.

Interaction of Peripheral and Central Players in Homeostatic System

• The hypothalamus acts as the central regulator of homeostatic systems, receiving input from various peripheral players (hormones, etc.)
• A large amount of cross-talk and crossover happen with the cerebrospinal fluid (CSF).
• The vagus nerve plays an important role in conveying peripheral signals to the hypothalamus.

Segue - Types of Fat

• White fat stores triglycerides and plays an important role as an endocrine organ.
• Brown fat steadily decreases with age; primarily found in infants. Its primary role is thermogenesis, energy balance, and "burning fat".
• Uncoupling protein in mitochondria is critical for "burning fat", allowing protons to leak across the membrane without ATP generation, releasing heat energy to regulate body temperature and energy expenditure.

Location/Characteristics of Different Types of Adipose Tissue

• White adipose tissue (WAT) is typically found beneath the skin (subcutaneous) as well as in other areas of the body, and typically associated with storage of energy in the form of triglycerides.
• Brown/brite adipose tissue plays a greater role in regulating energy expenditure via thermogenesis (energy to heat) through increased respiration rates and production of heat.
• Specific locations for these depots are associated with their respective function (e.g., visceral WAT is primarily associated with insulin resistance).

Homeostatic Pathway Mediators - Leptin

• Leptin is secreted by white adipocytes in response to insulin, its secretion declining as visceral fat and insulin resistance increase.
• It is an anorexigenic hormone that inhibits NPY/AGRP, increasing MSH secretion from the hypothalamic arcuate nuclei to promote satiety.
• Obese subjects have high leptin levels in the blood but often have resistance to the effects of this hormone..
• Congenital leptin deficiencies lead to obesity due to hyperphagia (overeating).

Homeostatic Pathway Mediators – Insulin

• Insulin is secreted by the pancreatic beta cells and is involved in regulating glucose levels and cellular uptake.
• Insulin receptors are present in the ventral striatum, with their presence linked to increased dopamine signaling.
• Increased hedonic pathway signaling can amplify homeostatic satiety signaling in the hypothalamus.

GI Hormones and Homeostatic Appetite Signaling

• Ghrelin, released by gastric cells during fasting, stimulates the hypothalamic hunger pathways (increased AGRP and NPY, inhibited MSH).
• Several other hormones (CCK, GLP-1, and PYY), released from the gastrointestinal tract (GI tract) slow gastric emptying and promote satiety through their effects on the vagus nerve;
• In individuals with a vagal transection (cut), the satiety effects of these GI hormones may be significantly less or absent.

BMS 150 Review

• Examines several aspects of digestion and metabolic regulation, specifically concerning specific locations and related hormones in the gastrointestinal tract (GI) and pancreatic systems, as a review for the course.

Cause and Effect in Regulation of Appetite

• Associations between elements of the homeostatic/hedonic pathway and obesity are not causal.
• High-calorie snacking may affect serotonin transporter activity, as shown in lean individuals, whereas bariatric surgery impacts striatal dopamine signaling.

Adipokines, Insulin Resistance, Obesity

• Adiponectin, a hormone produced mostly by white adipose tissue, is a part of the homeostatic pathway.
• Its levels tend to decrease with increased visceral fat and insulin resistance.
• However, adiponectin increases insulin sensitivity, potentially reducing the need for further insulin in the body to maintain function.

Summary of Obesity Complications

• Summarizes health complications of obesity that may be related to inflammation, such as dyslipidemia, fatty liver disease, T2DM, PCOS/hypogonadism, and impacts on skin, cardiovascular, respiratory, and GI systems.

DIRECT Trial in the UK

• A trial in the UK involving 306 individuals with T2DM undergoing a 3-month intensive, supervised weight loss program, with structured food reintroduction.

DIRECT Trial in the UK (results)

• The trial showed substantial weight loss and diabetes remission in the intervention group (compared to the control group), with sustained substantial weight loss, and a notable proportion achieving remission and maintaining these effects at 12-month post-intervention.
• Effects of the trial were very apparent in reducing plasma TG, liver fat and fasting glucose levels over time.

Impact of Insulin (and Insulin Resistance) - Endothelial Cells

• Insulin resistance negatively impacts vascular endothelial function;
• the release of mediators (affecting vasodilation/vasoconstriction);
• the recruitment and migration of leukocytes.
• Evidence connects insulin resistance to endothelial dysfunction, which likely contributes to hypertension and atherosclerosis.

Impact of Insulin (and Insulin Resistance) - Brain

• Components of the homeostatic and hedonic pathways can sense insulin and appetite-regulating hormones (e.g. serotonin).
• Insulin resistance in the brain can lead to issues with the brain vasculature and/or contribute to the development of or may exacerbate risk for dementia.
• Differences in the activation, function, and influence of hedonic\homeostatic pathways between men and women are also noted and could be of significant importance in clinical practice.

DM type 2 as a causative factor in AD

• Insulin resistance has been identified as a substantial component in the pathophysiology of Alzheimer's Disease; especially prominent in those with type 2 diabetes, where its prevalence is higher than in those without it.
• Insulin resistance may negatively impact synaptogenesis, neuronal physiology, and synaptic plasticity, potentially contributing to the development or progression of AD.
• Hyperglycemia, caused by insulin resistance, affects the blood-brain barrier's integrity, allowing proinflammatory markers and damaging or harmful substances to enter and cause tissue and neuronal damage.
• Increased circulating FFAs are also linked to an exacerbating effect on the risk of AD.

Impact of Insulin Resistance - Kidney

• Chronic kidney disease (CKD) arising from type 2 diabetes mellitus (T2DM) involves glomeruli sclerosis and reduced filtration function, resulting from various impacts to the kidneys.
• Increased risk of kidney infections (pyelonephritis).
• Hyaline arteriolosclerosis plays a major role in the progressive loss of kidney function.
• Increased angiotensin II ultimately exacerbates insulin resistance.

Impact of Insulin Resistance - Bone

• Bone metabolism is affected by insulin;
• Maintaining bone strength involves a balanced process of bone deposition (osteoblasts) and resorption (osteoclasts), both of which have insulin receptors.
• Individuals with T2DM may have good bone mineral density (BMD), which could be related to the resultant increased weight and stress on the skeleton.
• Conversely, lower BMD is a common finding in T1DM.

Impact of Insulin Resistance - Heart

• Insulin resistance in the heart results in various impacts and abnormalities including increased ER stress, mitochondrial dysfunction, increased ROS production, and impaired calcium balance during heart cycle components (systole and diastole), all relating to compromised function.
• Excessive angiotensin II induces further heart damage.
• Many individuals experiencing significant insulin resistance also develop cardiac hypertrophy and diastolic dysfunction (difficulty with filling), which is more prevalent after adjusting for other confounding factors.

Hyperglycemia - Overview

• Advanced glycation end products (AGEs) potentially lead to: a release of pro-inflammatory cytokines and growth factors from macrophages, ROS generation in endothelial cells, increased coagulant activity on endothelial cells, and an increase in smooth muscle cell proliferation.
• Further, AGEs cause significant cross-linking of matrix proteins, effectively reducing their vulnerability to cellular degradation.

Hyperglycemia - Impact on the Circulation

• AGEs heavily contribute to a significant decline in large arterial elasticity, making vessel walls stiffer.
• Trapping of LDL cholesterol in the AGE-linked matrix potentially contributes to the formation of atherosclerotic plaques and the narrowing of small arteries, and the resultant loss of vascular integrity.
• Hyperglycemia and increased AGE levels are associated with an elevated susceptibility to blood clotting and coagulation.

Diabetes - Small Vessel Disease

• Hyaline arteriolosclerosis, a vascular lesion, is more likely and seen in higher prevalence and severity in diabetic patients than those without it, especially when combined with hypertension.
• Thickening of the vessel walls (artery walls) causes the narrowing of arterioles' lumen.
• Diabetic microangiopathy affects capillaries in various tissues, increasing their permeability to plasma proteins, and is one of the mechanisms that underlie conditions like diabetic nephropathy, retinopathy, and neuropathy.

Diabetes - Neuropathy

• Diabetes can cause damage to both myelinated and unmyelinated nerve axons;
• This often includes an early loss of pain sensation, a somewhat unique characteristic among peripheral neuropathies.
• Vibration, proprioception, and fine touch can also be compromised.
• Diabetic neuropathy may severely impact autonomic nervous system functions, impacting blood pressure regulation (postural hypotension), as well as potentially affecting bladder/bowel/sexual/reproductive dysfunction regulation issues.

DM II - Clinical Features

• Type 2 diabetes (T2DM) often manifests subtly and insidiously and may remain undiagnosed.
• More than 80% of individuals with T2DM are obese.
• Diabetic ketoacidosis (DKA) is an uncommon complication of T2DM. Hyperosmotic non-ketotic crises (HONK) cases are more commonly observed in individuals with severe hyperglycemia;
• Symptoms may include gradual development of peripheral neuropathy, impaired wound healing, and vision problems including potential impairments in visual function like retinopathy;
• Early signs of resistance to insulin may include acanthosis nigricans.

Complications of Long-Term Hyperglycemia

• Long-term hyperglycemia significantly impacts diverse organ systems including the retina, circulatory system, heart (myocardial infarction), and kidneys.
  • Systemic inflammation may be exacerbated by long term hyperglycemia
• General symptoms of inflammation and heightened inflammatory states are very prevalent.

Acanthosis Nigricans

• Acanthosis nigricans is a dermatological condition described by hyperpigmentation and velvety patches often observed in skin folds like axillary regions or areas like the posterior cervical spine in high rates.

Insulin – The Skin and Hair

• Insulin can lead to several issues with hair thinning, loss of structural integrity/weakness, slowed growth, for poorly understood reasons.
• In the context of the skin, there are specific conditions that appear to be relevant to metabolic imbalances, such as acanthosis nigricans, usually associated with increased insulin or IGF-1 receptor signalling, and the increased prevalence of psoriasis in individuals exhibiting metabolic syndrome or obesity.

Bile Acids

• Bile acids (BAs) are synthesized from cholesterol in hepatocytes via classical and alternative pathways.
• Conjugated with glycine or taurine, BAs are secreted into bile and stored in the gallbladder.
• In the small intestine, the majority of BAs are reabsorbed via enterohepatic circulation and converted by microbial processes in the bowel to secondary BAs (e.g., deoxycholic and lithocholic acid).
• These secondary BAs can be reabsorbed by the colon.

Microbial Enzymes

• Bile salt hydrolases, hydroxysteroid dehydrogenases, and dehydroxylation of unconjugated BAs are the main microbial enzymes predominantly involved in BA metabolism.

Microbiome, Bile Acids, and Obesity

• Bile acids have multiple possible impacts on diverse metabolic functions, influencing lipid and carbohydrate metabolism, insulin sensitivity, inflammation, and the immune system.
• Gut microbiota heavily influences the composition of bile acids; the resulting effects (e.g. by increasing or decreasing the rate of lipoprotein lipase, reducing or increasing hepatic gluconeogenesis, or by affecting production of glucose or affecting thermogenesis) potentially impact obesity and associated complications (like reduced insulin sensitivity potentially).
• Gut microbial alterations are associated with increased intestinal permeability and systemic inflammation and may play a role in obesity-related disorders.
• Fecal transplantation may improve some metabolic syndrome features even if obesity persists, highlighting a possible major microbial influence.

Microbiota: Energy Harvesting/Lipogenesis

• Increased counts of Bacteroidetes bacteria are commonly seen in obese humans, possibly linked to a greater capacity for energy harvesting (e.g., carbohydrate metabolism or breakdown).
• Increased fermentation is commonly tied into a production of short-chain fatty acids (SCFAs), potentially influencing the rates of lipogenesis (fat synthesis).
• Mice deficient in SCFA receptors often display a leaner phenotype.

Pathogenesis of Diabetes, Part 2

• This segment focuses on the development and continuation of diabetes in the body.

The Twin Cycle Hypothesis and T2DM

• The twin cycle hypothesis describes two interconnected cycles, liver and pancreas, in the progression of T2DM, starting with early-onset insulin resistance and possibly related to positive energy balance. (leading to significant increased calorie intake).
• The hepatic cycle begins with pre-existing muscle insulin resistance and positive energy balance, leading to liver fat accumulation. Increased VLDL and islet triglycerides lead to resistance to insulin, decreased glucose production, and subsequent elevated plasma glucose levels.
• The pancreatic cycle involves a response to decreased insulin response, to ingested glucose, with continuous postprandial glucose elevation.

Background to the Twin Cycle Hypothesis

• T2DM development often follows early-onset insulin resistance, resulting in significant and often progressive dysregulation across multiple organ systems, like liver, muscle and pancreatic ones.
• Major contributors include excess caloric intake, often coupled with leptin resistance and potentially biopsychosocial factors that lead to significant imbalances in metabolic functioning.

The "First" Cycle - The Liver

• Early onset insulin resistance, often associated with sustained positive energy balance leading to excess caloric intake, frequently results in fat accumulation within the liver and adipose tissue (fatty liver and/or visceral fat accumulation).
• Circulating nutrients, such as glucose often remain in the bloodstream for longer periods, and the liver becomes less effective at converting these nutrients to stored triglycerides, due to widespread insulin resistance.
• Elevated fatty acids (FFAs) increase and require the liver to accommodate and dispose of these.
• The liver has essentially three options for handling elevated FFA levels from insulin resistance:
  • Burn FFAs via beta oxidation.
  • Storing them as fat, leading to hepatic steatosis (not optimal).
  • Exporting FFAs through VLDL production.
• VLDL characteristics and its role in circulation are presented in detail here.

The "First" Cycle - The Liver (Further details)

• The liver has 3 primary options for handling elevated FFA levels from insulin resistance:
  • Burn FFAs with beta oxidation.
  • Storing them as fat, leading to hepatic steatosis (not optimal).
  • Exporting FFAs and related lipids through VLDL production.
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