Organ selective toxicity

8 important questions on Organ selective toxicity

What is molecular homology?

A term that describes how a xenobiotic mimics, by its physicochemical properties.

What is an example of liver selective transcription factors?

HNF family: HNF1 can express Beta-fibrinogen, albumin, cypP450. phase II enzymes, HNF3 can express transthyretin.
HNF1alpha is abundantly expressed in liver and HNF1Beta in kidney.

What are the mechanisms behind DES induced developmental changes?

- Long-term changes in both men and female are due to the estrogenic effects mediated by interaction of DES with the estrogen receptor (ER).
- DES can methylate the DNA wherby DES is able to sensitize the target cells. like cells from the mullerian duct.
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Why can only DES induce embryotoxicity and not normal estrogen?

- Normal estrogen is shielded from the embryo by binding proteins.
- DES is an extremely potent ligand of the ER compared with estradiol.
-  maybe there are more factors involved like receptor conformational changes. Differential binding to response elements  on DNA, recruitment of coregulatory proteins and cross talk with signaling systems.
- Some of the effects of DES are caused by non-ER mechanisms

What are the mechanims behind the plasiticizer DEHP liver toxicity in rodents?

- These compounds are activators of peroxisome proliferator-activated receptor alpha (PPARalpha) (particularly abundant in the liver). Activation leads to decreases in rates of apoptosis, increases in cell proliferation, proliferation of peroxisomes in hepatocytes with induction of peroxisomal fatty acid beta-oxidation, increased production of oxidative stress and eventually development of hepatic tumors.
-   Most humans express mutated forms of PPARalpha (truncated) which are functionaly inactive.

Why are liver and kidneys so often involved in toxicity?

- both organs receive large amounts of blood (1,5 l/min in the liver)
- both organs have a large variety of metabolizing enzymes including p450
- both organs contain polarized cells. both cell types have excretory function. Such primary or secondary transport systems can highly upconcentrate xenobiotics or their metabolites in certain compartments.
- The liver also harbors high amounts of Kupffer cells that can induce immune mediated toxicity.

What is the role of CYP2E1 in the toxic respons of APAP?

it metabolizes APAP.

What are mechanisms underlying the cephalosporin nephrotoxicity?

- There is a concentrative uptake of the drug into proximal tubular cells in the kidney cortex.
- It is rapidly transported across the basolateral membrane via OAT1.
- cephalosporin has a low affinity for OAT4 at the apical membrane.
- result accumulation.
- Downstream consequences: redox cycling of the pyridine ring, acylation and inactivation of tubular cell proteins through spontaneous reactivity of the beta lactam ring and inhibition of the mitochondrial fatty acyl carnitine transport.
- inhibition of complex 4 in the mitochondria.
- Other xenobiotics have similar toxic mechanisms.

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