Aristolochic acid (AA-I), a naturally occurring nitrophenanthrene carboxylic acid, commonly found in the plant family Aristolochiaceae, that are used in traditional Chinese medicine. Aristolochic acid exhibits nephrotoxic, carcinogenic, and mutagenic activities and can cause aristolochic acid nephropathy, and urothelial malignancies. The FDA has issued a strong warning to consumers to avoid herbs containing the chemical aristolochic acid. The mechanisms underlying AA-I toxicity in the kidneys are poorly understood. However, was found a protein α-actinin-4 that is inhibited by AA-I, resulting in kidney disease.

L-Gulonic acid, a diastereomer of d-gluconic acid is the one of a metabolite in the urinate cycle, is a substrate of L-Gulonate 3-dehydrogenase (GDH). This enzyme catalyzes the NAD(+)-linked dehydrogenation of L-gulonate into dehydro-L-gulonate. L-Gulonic acid is also a metabolite of the D-glucuronic acid pathway. It was suggested, that the measurement of a spectrum of urinary D-glucuronic acid metabolites might provide a more reliable index for assessment of the induction of hepatic xenobiotic-metabolizing enzyme activities in man than the determination of urinary D-glucaric acid alone.

Hordenine is a natural Phenethylamine compound that occurs in a number of different plants, but especially barley grass. It is structurally similar to the amino acid Tyramine. It antagonized D2-mediated beta-arrestin recruitment indicating functional selectivity. Hordenine inhibited melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins. Hordenine may be an effective inhibitor of hyperpigmentation. Hordenine is an indirectly acting adrenergic drug. It liberates norepinephrine from stores. In isolated organs and those structures with reduced epinephrine contents, the hordenine-effect is only very poor. Experiments in intact animals (rats, dogs) show that hordenine has a positive inotropic effect upon the heart, increases systolic and diastolic blood pressure, peripheral blood flow volume, inhibits gut movements but has no effect upon the psychomotorical behavior of mice. Hordenine is considered to be generally very safe and well-tolerated in healthy adults. Hordenine is a nootropic compound that works equally well for cognitive enhancement and athletic performance.

(1,1'-Biphenyl)-3,3',4,4'-tetramine (3,3'-Diaminobenzidine, DAB) is an organic benzidine derivative, that used as a precursor to polybenzimidazoles. As its water-soluble tetrahydrochloride, (1,1'-Biphenyl)-3,3',4,4'-tetramine has been used in immunohistochemical staining of nucleic acids and proteins. Diaminobenzidine is oxidized by hydrogen peroxide in the presence of hemoglobin to give a dark-brown color. This color change is used to detect fingerprints in blood. The solubility of (1,1'-Biphenyl)-3,3',4,4'-tetramin in water allows for adaptability compared to other detection solutions which use toxic solvents. In research, this reaction is used to stain cells that were prepared with hydrogen peroxidase enzyme, following common immunocytochemistry protocols. Relevant to Alzheimer's disease, Aβ protein amyloid plaques are targeted by a primary antibody, and subsequently by a secondary antibody, which is conjugated to a peroxidase enzyme. This will bind (1,1'-Biphenyl)-3,3',4,4'-tetramine as a substrate and oxidize it, producing an easily observable brown color. Plaques can then be quantified for further evaluation.

Guanosine 3′,5′-cyclic monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). Cyclic GMP is a cellular regulatory agent that acts as a second messenger. Its levels increase in response to a variety of signals (acetylcholine, insulin, oxytocin). cGMP is involved in the regulation of kinases G. cGMP binds to sites on the regulatory units of protein kinase G (PKG) and activates the catalytic units, enabling them to phosphorylate their substrates. cGMP is a common regulator of ion channel conductance, glycogenolysis, and cellular apoptosis. It also relaxes smooth muscle tissues. In blood vessels, relaxation of vascular smooth muscles lead to vasodilation and increased blood flow. cGMP is a secondary messenger in phototransduction in the eye. In the photoreceptors of the mammalian eye, the presence of light activates cGMP phosphodiesterase 5 (PDE5), which degrades cGMP. The sodium ion channels in photoreceptors are cGMP-gated, so degradation of cGMP causes sodium channels to close, which leads to the hyperpolarization of the photoreceptor's plasma membrane and ultimately to visual information being sent to the brain. Mutations in the cGMP phosphodiesterase cause defects in cGMP metabolism leading to retinal disease. Inhibition of cGMP degrading PDE5 by its selective inhibitor sildenafil induced migraine without aura in 10 of 12 migraine patients and in healthy subjects.

Monocrotaline is an 11-membered macrocyclic pyrrolizidine alkaloid derived from the seeds of the Crotalaria spectabilis plant. Monocrotaline is activated to the reactive pyrrole metabolite dehydromonocrotaline in the liver, a reaction that is highly dependent on cytochrome P-450 (CYP3A4). Monocrotaline induces a syndrome characterized, among other manifestations, by pulmonary hypertension, pulmonary mononuclear vasculitis (acute necrotizing pulmonary arteritis in about one-third of the animals), and right ventricular hypertrophy. Monocrotaline is widely used to model pulmonary arterial hypertension in rodents. Monocrotaline aggregates on and activates the extracellular calcium-sensing receptor (CaSR) of pulmonary artery endothelial cells to trigger endothelial damage and, ultimately, induces pulmonary hypertension.

Thiazolyl Blue is a membrane-permeable yellow dye that is reduced by mitochondrial reductases in living cells to form the dark blue product. The net positive charge on Thiazolyl Blue appears to be the predominant factor involved in their cellular uptake via the plasma membrane potential. Thiazolyl Blue is used as a direct indicator of cytotoxicity (such as for screening cancer drugs), proliferation and apoptosis. Thiazolyl Blue is also an electron acceptor used for studying NADP-dependent dehydrogenases. Thiazolyl Blue reduction is associated not only with mitochondria, but also with the cytoplasm and with nonmitochondrial membranes including the endosome/lysosome compartment and the plasma membrane. Biological Applications: cell viability assay; microbial growth assays; DNA quantification assays; tissue viability assays; detecting enzymes; measuring membrane potential; treating Alzheimer’s disease, asthma, cancer. Because Thiazolyl Blue forms an insoluble formazan it has usually been applied in endpoint assays.

Cholesterol sulfate is quantitatively the most important known sterol sulfate in human plasma, where it is present in a concentration that overlaps that of the other abundant circulating steroid sulfate, dehydroepiandrosterone (DHEA) sulfate. Cholesterol sulfate is generated in the normal epidermis by cholesterol sulfotransferase but then is desulfated in the outer epidermis as part of a 'cholesterol sulfate cycle' that is a powerful regulator of epidermal metabolism and barrier function. It accumulates in the epidermis in the human genetic disorder X-linked ichthyosis. In XLI, cholesterol sulfate levels exceed 10% of total lipid mass (≈1% of total weight). Cholesterol sulfate is a component of cell membranes where it has a stabilizing role, e.g., protecting erythrocytes from osmotic lysis and regulating sperm capacitation. It is present in platelet membranes where it supports platelet adhesion. Cholesterol sulfate can regulate the activity of serine proteases, e.g., those involved in blood clotting, fibrinolysis, and epidermal cell adhesion. Because of its ability to regulate the activity of selective protein kinase C isoforms and modulate the specificity of phosphatidylinositol 3-kinase, cholesterol sulfate is involved in signal transduction.

Hordenine is a natural Phenethylamine compound that occurs in a number of different plants, but especially barley grass. It is structurally similar to the amino acid Tyramine. It antagonized D2-mediated beta-arrestin recruitment indicating functional selectivity. Hordenine inhibited melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins. Hordenine may be an effective inhibitor of hyperpigmentation. Hordenine is an indirectly acting adrenergic drug. It liberates norepinephrine from stores. In isolated organs and those structures with reduced epinephrine contents, the hordenine-effect is only very poor. Experiments in intact animals (rats, dogs) show that hordenine has a positive inotropic effect upon the heart, increases systolic and diastolic blood pressure, peripheral blood flow volume, inhibits gut movements but has no effect upon the psychomotorical behavior of mice. Hordenine is considered to be generally very safe and well-tolerated in healthy adults. Hordenine is a nootropic compound that works equally well for cognitive enhancement and athletic performance.