Passage Cyanide (CN − ) is a powerful, rapid toxin that binds to the cellular respiratory enzyme cytochrome c oxidase. The resulting enzyme-cyanide complex blocks the transfer of electrons to oxygen in the last step of the electron transport chain. This results in cytotoxic anoxia, causing asphyxiation at the cellular level.Exposure to cyanide can occur from dietary sources, medical treatments, industrial applications, smoke inhalation (structural fires), and intentional use (suicide). While dietary exposure from moderate consumption of naturally occurring plant compounds such as cyanogenic glycosides rarely results in acute adverse effects in humans, chronic effects have been observed from prolonged diets with significant levels of these compounds. In the developed world, risk of significant cyanide exposure is most likely to result from smoke inhalation during building fires or from industrial/occupational exposures.The impact of a given exposure depends on the amount (dose, duration), the chemical composition of the cyanide compound (HCN, NaCN, KCN), and the route of exposure (inhalation, absorption, ingestion). The ionic salts (NaCN, KCN) and free acid (HCN) forms of cyanide each have different acid-base properties that interact differently under the physiological conditions associated with each route of exposure.To better understand the toxicity of different forms of cyanide, animal models have been studied for comparison to known human exposure case studies. Table 1 presents a summary of selected animal toxicity studies that examine exposure via ingestion. The table provides the lethal dose to 50% of the population (LD 50 ) in milligrams of cyanide per kilogram of body weight (mg/kg).Table 1 Compilation of LD 50 Cyanide Values in Various Animal Species Based on animal models, one treatment developed for cyanide poisoning involves assisting the rhodanese enzyme in metabolizing CN − to SCN − via an intravenous solution of NaNO 2 and Na 2 S 2 O 3 . The Na 2 S 2 O 3 assists in the formation of a reactive S-SH (persulfide) bond in the enzyme on cysteine-247 (Reaction 1), which then reacts with the cyanide ion to form thiocyanate (Reaction 2). Adapted from: Hall AH, Isom GE, Rockwood GA. Toxicology of Cyanides and Cyanogens, Experimental, Applied and Clinical Aspects. John Wiley & Sons; 2015: 1-20; and Egekeze JO, Oehme FW. Cyanides and their toxicity: A literature review. Vet Q. 1980; 2(2): 104-114. -Based on the experimental data in Table 1, which cyanide compound(s) likely diffuse(s) most readily across the gastric lipid membrane?HCNNaCNKCN

Question

Quizplus · Accepted Answer

11ecba2d_11ca_a368_a3bf_1318470e1172_MD0008_00 The experimental results in Table 1 can be compared by examination of the LD₅₀ values. An LD₅₀ gives the concentration of a substance that is necessary to kill 50% of the group being tested. Comparing the experimental results for the same species shows that the solution containing the HCN form of cyanide gave the lowest LD₅₀ of the three forms of cyanide delivered. This indicates that HCN required the smallest dose to kill 50% of the rabbits and rats tested. The lower LD₅₀ for HCN suggests that this neutral molecule may diffuse more readily across the gastric lipid membrane than the charged ionic cyanide salts (Number I). Both NaCN and KCN show significantly higher values for LD₅₀ than HCN, suggesting that these may not as readily diffuse across the lipid membrane, allowing more opportunity for the metabolism to adjust and counteract a greater amount of the cyanide dose (Numbers II and III). Educational objective: An LD₅₀ value gives the concentration of a substance necessary to kill 50% of a group being tested. Therefore, a small LD₅₀ requires less of a compound for a lethal dose than a compound with a higher LD₅₀. These values can be used to evaluate the relative toxicity of various compounds and to infer differences in how the compounds are metabolized.

Passage Cyanide (CN−) Is a Powerful, Rapid Toxin That Binds to to the Cellular

Passage Cyanide (CN⁻) Is a Powerful, Rapid Toxin That Binds to to the Cellular