College 8

What are the two main types of major bacterial pathogens?

• gram-negative bacteria

• gram-positive bacteria

How to attack bacteria

tegen te gaan door cell walls van bacteria te targetten

Beta-lactams

• largest class targeting bacterial cell wall

• Contain a beta-lactam ring → needed for their antibacterial activity (bactericidal)

• inhibit pencillin-binding proteins (PBPs) → these are needed for peptidoglycan cross-linking

What are the four different groups of beta-lactams

• penicillins

• cephalosporins

• carbapenems

• monobactams

How do beta-lactamase inhibitors bind?

they bind irreversibly to beta-lactamases

How do glycopeptides work?

• most common drug; vancomycin

• vancomycin binds to the peptidoglyxan precursor

• prevents transglycosylation and transpeptidation from inhibiting cell wall cross linking

Aminoglycosides

• bactericidal, inhibit bacterial protein synthesis

• bind reversibly (with high affinity) to the 16s ribosomal RNA on the 30S ribosome

What are the three phases of replication?

1. early events

   1. attachment

   2. penetration

   3. uncoating

2. Middle events

   1. viral messenger RNA synthesis

   2. Viral protein synthesis and processing

   3. viral genome replication

3. Late events

   1. viral assembly

   2. release

Antiviral therapy

• drugs need to target virus and not the host cell

• virus specific drugs → protease inhibitors

• ineffective → many cycles of viral replication occur during the incubation period (no symptoms)

• Some viruses become latent → CMV; impossible to treat when latent

• Drug-resistant viral mutants → ineffective/regimen change needed

Basis of HIV therapy

Antiretroviral therapy (ART)

ART initiation regardless of CD4 count → after entry to a cell, single-strand RNA is reverse transcribed into HIV DNA, which is then integrated into the host DNA → this fact makes the virus exceedingly difficult to eradicate with current therapies → HIV has a HIGH mutation rate

Combination of 3 medications – 1 pill

Monitoring therapy

• Viral loads

• CD4 cell count

What kind of virus is hepatitits C

Hepatitis C is an RNA virus and replicates via RNA-dependent RNA polymerase (NS5B)

What drug is used in hepatitis C and how does it work?

• Sofosbuvir is a nucleotide analogue prodrug → activated intracellularly (see acyclovir)

• Incorporates into viral RNA chain → chain termination → viral replication stops

• Human cells do not have RNAdependent RNA polymerase → highly selective (minimal toxicity)

What kind of inhibitor is Oseltamivir and for what disease does it work

neuraminidase inhibitor and oseltamivir for influenza

How does oseltamivir for influenza work?

• Inhibits viral neuraminidase enzyme on influenza surface

• Neuraminidase normally cleaves sialic acid → releases new virus particles from infected cell → allows viral particle spread

• Oseltamivir blocks neuraminidase → virus particles remain stuck to cell surface → cannot spread to new cells

• Reduces duration of illness by ~1 day if started within 48 hours of symptoms

Acyclovir in herpesviruses

• Prodrug must be activated in virus - infected cells only (selectivity)

• Step 1: Viral thymidine kinase phosphorylates acyclovir → acyclovir monophosphate

• Step 2: Cellular kinases → acyclovir triphosphate (active form)

• Acyclovir triphosphate: competitive inhibitor of viral DNA polymerase

• Also incorporated into viral DNA → chain termination → DNA synthesis stops

What are two types of antifungal drugs?

• echinocandins

• azoles

What is the MoA of echinocandins

• MoA: Inhibition of 1,3 - β -D glucan synthesis → a critical structural polysaccharide in the fungal cell wall

• β-1,3-glucan forms a scaffold-like mesh that maintains the integrity, rigidity, and shape of the fungal cell wall → progressive weakening of the cell wall, cell lysis, and fungal cell death

• Can cause hepatotoxicity

What is the MoA of azoles

MoA: inhibition of 14 -α sterol demethylase (needed for ergosterol synthesis)

Ergosterol is the primary sterol in the fungal cell membrane, maintains membrane integrity, and the function of proteins.

Azoles block the oxidative demethylation of lanosterol to ergosterol → disrupting membrane structure and function → increased membrane permeability, impaired nutrient transport, and inhibition of fungal growth

Where is insulin produced?

Insulin is a peptide hormone produced by B cells in the islets of Langerhans in the pancreas

Insulin release is stimulated by;

- ↑ Blood glucose (main stimulus, responds to both absolute level and rate of rise)

- Amino acids (arginine, leucine)

- Fatty acids

- Parasympathetic nervous system - Incretins — GLP-1 and GIP (gut hormones released after eating)

- Sulfonylurea drugs (pharmacological stimulus)

Insulin release is inhibited by;

• Sympathetic nervous system — adrenaline via α₂ receptors on β cells

• Somatostatin, galanin, amylin

Insulin release

• phase 1 (rapid) immediate release of pre-stored insulin granules

• phase 2 (slower) continued release + new insulin synthesis

• phase 1 response is lost early in type 2 diabetes

How does insulin decrease blood glucose?

• increasing glucose uptake into muscle and fat via Glut-4

• increasing glycogen synthesis

• decreasing gluconeogenesis

• decreasing glycogen breakdown

When and why is glucagon released?

Glucagon is released in response to low blood glucose levels, insulin lowers blood sugar, glucagon raises it

What does glucagon do?

It is a fuel-mobilising hormone (produced in the pancreas), stimulating gluconeogenesis (synthesizing new glucose from non-carbohydrate precursors like amino acids and fatty acids) and glycogenolysis (breaking down stored glycogen into glucose, which is released into the bloodstream), also lipolysis and proteolysis.

What are type 1 and type 2 diabetes

• type 1 = an absolute deficiency of insulin

• type 2 = a relative deficiency of insulin associated with reduced sensitivity to its action (insulin resistance)

Mechanism of metformin - biguanides class

Activates AMPK (AMP-activated protein kinase) in the liver

→ ↓ hepatic gluconeogenesis → ↓ glucose output from liver

→ ↑ peripheral insulin sensitivity in muscle

→ ↑ GLUT-4 translocation → ↑ glucose uptake

How does a GLP-1 receptor agonist work?

• Mimic GLP-1 (incretin hormone released from gut after eating)

• Bind GLP-1 receptor → ↑ insulin secretion (glucose-dependent) → ↓ blood glucose/↓ glucagon → ↓ blood glucose, ↓ gastric emptying → ↓ appetite

• Glucose-dependent → low hypoglycaemia risk

• Significant weight loss, use in OBESITY (semaglutide)

What are the two types of thyroid hormones?

• T4 (thyroxine is the main secreted hormone

• T3 is the more active form (more potent) → T4 is converted to T3 in tissues

• Calcitonin controls plasma Ca2+ → involved in bone metabolism

What are the actions of T3 and T4

• stimulation of metabolism, causing increased oxygen consumption and increased metbolic rate

• regulation of growth and development

What do abnormalities of thyroid function include;

• hyperthyroidism → either diffuse toxic goitre or toxic nodular groitre

• hypothyroidism; in adults this cause myxoedema; in infants → gross restriction of growth and intellectual disability

• simple non-toxic goitre caused by dietary iodine deficiency, usually with normal thyroid function

Levothyroxine

• what is it used for

• which form

• how does it work

• levothyroxine = the synthetic form of thyroxine T4 and is the standard replacement therapy for hypothyroidism

• After PO admin: in peripheral tissues (liver, kidney, muscle) → deiodinase enzymes convert T4 → T3 (active form)

• T3 is 3 –5x more potent than T4

• T3 is lipid soluble → crosses cell membrane freely

• Binds to thyroid hormone receptors (THR) in the nucleus (nuclear receptor!)

• T3 -THR complex binds thyroid response elements (TREs) on DNA where activates or represses specific gene transcription

• → ↑ Production of proteins controlling metabolism, growth and development

Thionamides

• what is it used for

• which form

• how does it work

Antithyroid drugs (thionamides):

• Carbimazole, propylthiouracil (PTU)

• Inhibit thyroid peroxidase (TPO) → ↓ oxidation of iodide → ↓ iodination of thyroglobulin → ↓ T3/T4 synthesis

• PTU also blocks peripheral conversion of T4 → T3

Radioiodine

• what is it used for

• which form

• how does it work

• Radioactive iodine taken orally → concentrated in thyroid (thyroid naturally takes up iodine)

• Emits β radiation → destroys thyroid tissue → ↓ hormone production

• Often results in hypothyroidism → lifelong levothyroxine needed

What are the five female reproductive hormones

1. oestrogens → produced by ovaries → drive female development, uterine proliferation, bone maintenance

2. progesterone produced by corpus luteum; prepares uterus for implantation, maintains pregnancy

3. Follicle-stimulating hormone (produced by the anterioir pituitary gland) stimulates follicle development

4. Luteinising hormone (produced by the anterior pituitary gland) triggers ovulation + corpus luteum formation

5. Gonadotrophin-releasing hormone (produced in the hypothalamus) pulses stimulate FSH and LH release

OEstrogens and antioestrogens

• Oestrogen is a lipid-soluble steroid hormone → can passively diffuse across cell membrane and directly into the cytoplasm or nucleus

• Binds to receptors (ER) → gene transcription → synthesis of new proteins that mediate oestrogens physiological effects

• Such as proliferation of uterine and breast epithelium, bone maintenance, and cardiovascular protection.

• Slow onset (hours to days)

Antioestrogens are competitive antagonists or partial agonists.

Progestogens

• The mechanism of action: intracellular receptor (progesterone receptors PR-A or PR-B) → altered gene expression → progesterone physiological effects (relaxes smooth muscle, luteal phase, maintaining pregnancy etc..) Oestrogen stimulates synthesis of progesterone receptors, whereas progesterone inhibits synthesis of oestrogen receptors.

• Clinically: contraception, endometriosis,

• Combined with oestrogen for oestrogen replacement therapy in women with an intact uterus, to prevent endometrial hyperplasia and carcinoma.

Antiprogestogens

• Medical termination of pregnancy: mifepristone (partial agonist) combined with a PG (e.g. gemeprost).

• Emergency contraception (morning-after pill): ulipristal (selective progesterone receptor modulator), also used to reduce the size of uterine fibroids pre-operatively.

What are the six male reproductive hormones?

• Testosterone is produced by Leydig cells in testes; drives male development, spermatogenesis, muscle mass, libido

• DHT (dihydrotestosterone) is converted from testosterone by 5α-reductase; more potent; drives prostate growth and male pattern baldness

• FSH stimulates Sertoli cells → supports spermatogenesis

• LH stimulates Leydig cells → testosterone production

• GnRH hypothalamus → pulses → FSH + LH release

• Inhibin produced by Sertoli cells → negative feedback on FSH

Androgens

• The main endogenous hormone is testosterone; intramuscular depot injections of testosterone esters are used for replacement therapy.

• Mechanism of action is via intracellular receptors/altered gene expression.

• Clinical uses of androgens and anti-androgens Androgens (testosterone preparations) as hormone replacement in:

• male hypogonadism due to pituitary or testicular disease.

Anti-androgens

Anti-androgens (e.g. flutamide, cyproterone) are used as part of the treatment of prostatic cancer.

• 5α-Reductase inhibitors (e.g. finasteride) are used in benign prostatic hyperplasia